JP2007172674A - Receiving layer forming method and coated object - Google Patents

Abstract

An object of the present invention is to make the thickness of a receiving layer more uniform to improve the yield and improve the appearance.
SOLUTION: First concave grooves 5A and 5E and first convex portions 5B and 5F are formed in inner and outer boundary regions 5a and 5b of a printing surface 5 of a ring-shaped substrate 1A, and second concave grooves are formed on the outer sides thereof. 5C, 5G and second convex portions 5D, 5H are formed. A water-based coating liquid is applied to a region surrounded by the first convex portions 5B and 5F with a nozzle composed of a plurality of nozzle portions. The nozzle coats the aqueous coating liquid up to a region projected by a distance x outside the first protrusions 5B and 5F in order to compensate for the insufficient amount of coating in the boundary region. A coating film 6A for forming a receiving layer is formed inside the first convex portions 5B and 5F. A part of the aqueous coating liquid flows over the first convex portions 5B and 5F, but dams up and accumulates at the second concave grooves and the second convex portions. Since the film thickness in the first concave grooves 5A and 5E is equal to or greater than the film thickness in the central region 5c, the coating film 6A can suppress sink marks and flow during drying.
[Selection] Figure 7

Description

  The present invention relates to a receiving layer forming method for forming a receiving layer such as ink on the surface of an object to be coated, and an object to be coated on which a receiving layer is formed. In particular, the present invention relates to a receiving layer forming method for forming a coating film as a receiving layer by applying a coating film on a surface of a flat coated object that does not absorb a coating solution, and then drying the coating film, and the coating object.

2. Description of the Related Art Conventionally, a uniform functional coating film is formed by applying a coating solution to a certain region and drying it on a non-solvent-absorbing flat plate-like article such as a plastic sheet or substrate. In particular, the formation of a coating film for an ink receiving layer formed by coating a coating solution on the surface of an OHP sheet or optical disk is a means for printing on a non-ink-absorbing coated material, and various receiving layer configurations and methods for forming the receiving layer. Has been reported. Particularly in the optical disc field, it is desired to improve the quality of printed images and reduce the total cost by improving the receiving layer.
Conventionally, ROM (Read Only Memory) type CDs and DVDs in which information (contents) is recorded in advance are known as optical disks. Among these optical disks, for example, a DVD has a configuration in which an information recording layer is formed on one surface of a PC (polycarbonate) disk substrate, and another disk substrate is bonded to the other surface via an adhesive layer. Yes. Alternatively, it may have a structure having two information recording layers in which another information recording layer is further provided on the surface of another disk substrate in contact with the adhesive layer. A label is attached to the other surface facing the information recording layer or the adhesive layer across the bonded disc substrate, and various information such as photographs, pictures, titles, and the like regarding the DVD or the like is printed.
Conventionally, as a label, for example, paper on which information is recorded by offset printing or the like is attached on a disk substrate, or offset printing or screen printing is directly performed on a disk substrate. Labels such as paper by offset printing are printed in large quantities and affixed to a disk, or are employed in various disks such as DVDs that are mass-produced together with printing methods such as direct offset printing and screen printing.

By the way, in recent years, demand for high-mix low-volume production of hundreds to thousands of optical disks such as DVDs is increasing. Recording information on such a small amount of a label such as a DVD by offset printing as described above is not suitable because it requires pre-processing such as editing, plate making, color matching, and so on, and the cost is extremely high. In the case of such a low-volume optical disc, on-demand printing or digital printing, in which a digital image processed by a personal computer or the like is directly printed on a receiving layer on the surface of the optical disc by inkjet printing or the like without performing editing, plate making, color matching, etc. Printing was in progress.
When performing on-demand printing or digital printing, the superiority or inferiority of ink-jet printed images depends on the quality performance of the receiving layer, and if a high-performance receiving layer is used, it is possible to obtain a clear image at the same level as the photographic image quality. It has become.

In addition to the ROM type described above, the optical disc includes a recording type that allows a user to record information freely. Further, an R type that can be recorded only once, an RW type that can be recorded repeatedly, a RAM type, and the like. It has been known. Many of these recordable optical discs are on the market in which a receiving layer that absorbs ink jet is provided on the surface to which a printed label has been attached. These optical discs are also called “printable discs”, and allow users to print free images using inexpensive inkjet printers that are generally commercially available.
For example, in a recording disk on which a receiving layer described in Patent Document 1 is formed, a coating ink containing UV curable monomer or UV curable oligomer and polyvinyl alcohol which is a water-soluble / hydrophilic resin is applied to the surface of the optical disk. The receiving layer is formed by UV curing.

On the other hand, the one described in Patent Document 2 or 3 below employs an inorganic porous ink receiving layer coated with a coating liquid mainly composed of an aqueous alumina sol as a receiving layer used as a label of an optical disk such as a CD or DVD. Has been. When ink-jet printer printing is performed on a receiving layer obtained with an aqueous coating liquid mainly composed of a pigment and a binder (hereinafter, simply referred to as an aqueous coating liquid), the formed coating film becomes a porous ink receiving layer, as in photographic image quality. It is known that a clear image can be obtained.
When using a porous ink receiving layer with an aqueous coating solution containing such an aqueous alumina sol as an optical disk label, various coating devices such as a die coater, slide coater, curtain coater, spin coater, etc. can be used. A coating liquid is formed on the disk substrate to form a liquid coating film. Then, the liquid coating film is naturally dried or warm air dried.
In addition, in the optical disc described in Patent Document 4 and the method for forming a receiving layer thereof, a coating layer formed by applying a coating liquid mainly composed of an aqueous alumina sol having a low solid content ratio and a low viscosity to the surface of the optical disc. The structure which forms and encloses a ditch | groove, a ditch | groove, and a convex part in the boundary of an inner peripheral side and an outer peripheral side is employ | adopted. As a result, the coating area is determined for the coating film after the coating liquid is applied, and the film thickness of the inner peripheral boundary area and the outer peripheral boundary area is ensured to be equal to that of the central area. The film thickness after drying is made more uniform.
JP-A-9-245380 JP-A-2-276670 JP 2001-301323 A Japanese Patent Laid-Open No. 2004-355781

However, in the case of the above-mentioned Patent Document 1, the receiving layer formed of the UV curable resin does not have sufficient ink receiving ability, and bleeding tends to occur during printing by an ink jet printer or the like. Therefore, the resolution of the printed image on the receiving layer is low, and there is a disadvantage that a clear image cannot be obtained particularly when printing a photographic image or the like. Further, in the vicinity of the boundary of the coating region of the receiving layer coating solution, the film thickness becomes thin, so that the receiving capability of the receiving layer is likely to decrease. In that respect, the porous ink receiving layers described in Patent Documents 2 and 3 have high ink receiving ability, and a clear image similar to photographic image quality can be obtained.
However, the acceptability in the vicinity of the boundary of the coating region of the receiving layer coating solution as described below is rather lowered because the solid content ratio of the receiving layer coating solution is small. That is, since the aqueous coating liquid for forming the porous ink receiving layer described in Patent Documents 2 and 3 has a solid content ratio of about 20% at the time of coating, the coating film is smoothly applied to the disk surface. There is a drawback that it is difficult to form. For example, when an aqueous coating solution is applied in a substantially ring shape on the hydrophobic surface of an optical disk substrate, the inner peripheral side and the outer peripheral side boundary region are curved in a substantially arc shape due to surface tension with respect to the central region of the coating film. However, the amount of the coating solution at the curved portion becomes insufficient.
Then, when the coating film is dried, the drying of the inner peripheral side and outer peripheral side boundary region surfaces proceeds first, and a phenomenon occurs in which the internal coating liquid flows toward the central region. Therefore, the film thickness of the inner and outer peripheral side boundary regions becomes smaller than the central region, and the film thickness gradually increases from the inner and outer peripheral side boundary regions toward the central region, so that a uniform film thickness cannot be obtained. There were drawbacks. In this case, since the ink receiving ability in the inner peripheral side and outer peripheral side regions having a relatively small film thickness is reduced, the ink applied by the ink jet printer or the like overflows and bleeds in the inner peripheral side and outer peripheral side regions. And disadvantageous in that a clear printed image cannot be obtained.

On the other hand, in the case of Patent Document 4, the boundary portion of the application region is formed by the concave grooves and the convex portions, so that the application from the inner and outer peripheral side boundary regions, which is the disadvantage of Patent Documents 2 and 3 described above, to the central region. Although the flow and surface tension of the liquid can be suppressed, it has been found that there are the following disadvantages even in this case.
That is, when the coating liquid is applied to the optical disk surface, the edge of the nozzle is located in the concave groove, so that the coating liquid is not sufficiently filled near the boundary of the concave groove, or the coating liquid has a predetermined height relative to the convex part. There was often a drawback that it was not uniformly applied. If the coating solution is not sufficiently filled in the concave groove, bubbles are mixed in, resulting in defects such as bubbles rising during heating and drying and leaving a rupture mark on the surface of the receiving layer. In addition, the edge of the coating film becomes a convex curved surface shape due to surface tension at the inner and outer peripheral boundary portions, but it is not uniformly applied due to insufficient supply, and if the bulge of the convex curved surface at the coating film edge becomes small, Sink marks and fluid flow of the coating liquid occur in the boundary region of the receiving layer, resulting in a disadvantage that the film thickness is locally thin and poorly organized and detracts from aesthetics. When such a film thickness non-uniformity occurs, the receiving ability of the receiving layer changes depending on the position of the disk substrate, so that a portion of the image formed on the receiving layer is blotted or overflowed, resulting in a fine image. Will be damaged.
Therefore, if it is attempted to apply the coating liquid so that insufficient supply of the coating liquid does not occur to the concave grooves and the convex portions on the inner and outer peripheral side boundary portions, a nozzle is arranged to the very edge of the boundary portion and sufficient coating liquid is applied to the end portions. Since it is necessary to apply, a part of the coating liquid protrudes from the groove and the convex portion, flows to the outer surface, spreads, and dries, so that the appearance is lost again.

  In view of such circumstances, the present invention provides a method for forming a receiving layer that can form a receiving layer more uniformly to give a good receiving performance to the entire receiving layer, improve yield, and have a good aesthetic appearance. An object is to provide an object to be coated.

The receiving layer forming method according to the present invention is a receiving layer forming method in which a coating liquid is applied to the surface of an object to be coated to form a coating film, and the coating film is dried to form a receiving layer. In addition to providing a groove and a convex in the boundary portion of the region where the receiving layer is formed in the direction toward the outer side of the receiving layer, at least one of the other groove and the other convex is formed on the outer side. It is characterized by.
According to the present invention, the coating liquid can be sufficiently applied to the region where the receiving layer partitioned by the concave grooves and the convex portions on the surface of the coating object is formed, and the bulge of the convex curved surface due to the surface tension at the end of the coating film is large. Since the film thickness in the concave groove is equal to or greater than the film thickness in the central area, it is possible to suppress the flow of sink marks and coating liquid in the boundary area of the coating film during subsequent drying, and the film thickness is flat and almost uniform throughout. As a result, it is possible to form a receiving layer with a beautiful boundary. In addition, even when a part of the coating liquid applied near the convex portion of the boundary portion flows to the outside beyond the convex portion in order to prevent sink marks or flow during application, other concave grooves formed on the outside or The coating liquid that has been dammed up and collected by other convex portions and leaked from the convex portions does not spread irregularly. Thus, when the coating film is dried by providing at least one of the concave groove and the convex part, and the other concave groove and the other convex part at the boundary part, the film thickness of the coating film at the boundary part is sufficiently secured. Therefore, it is possible to prevent the flow and form a flat and almost uniform film thickness as a whole, improving the quality of the receiving layer and improving the yield.

In addition, the coated object according to the present invention is a coated object in which a coating liquid is applied to the surface of the coated object to form a coating film, and the coating film is dried to form a receiving layer. A concave groove and a convex portion are provided in the boundary portion of the region where the receiving layer is formed toward the outer side of the receiving layer, and at least one of another concave groove and another convex portion is further formed on the outer side, and the convex portion is formed. A receiving layer is formed in a region surrounded by the portion.
According to the present invention, the receiving layer formed by drying the coating film applied on the surface of the object to be coated is formed in a flat and substantially uniform film thickness on the whole with the concave grooves and convex portions, and beyond the convex portions. The coating liquid that has flowed out is dammed up by other concave grooves or / and other convex portions formed on the outside thereof and dried and solidified to form a receiving layer having a clean boundary region and a good appearance. In addition, these other grooves or / and other protrusions and the coating solution contained therein do not stand out visually after drying and do not impair the appearance.
In the present invention, the outer side refers to the direction away from the receiving layer with respect to the receiving layer, and the inner side refers to the inner direction of the receiving layer.

  As described above, according to the receiving layer forming method and the object to be coated of the present invention, the surface of the object to be coated is affected by sink marks and the flow of the coating liquid during drying within the range of the region partitioned by the concave grooves and the protrusions. In addition, a flat and almost uniform film thickness of the boundary region can be formed, and the coating liquid exceeding the convex portion can be stored in other concave grooves or / and other convex portions. A coating film is regularly formed without unnecessarily spreading, and a boundary region having a beautiful appearance can be formed. Therefore, the yield of the coated object is improved.

The receiving layer forming method and the object to be coated according to the present invention are preferably formed by forming other concave grooves and other convex portions on the outside of the convex portion, and the inner peripheral side of the convex portion with respect to the coating film when the coating liquid is applied. If the coating liquid is discharged sufficiently and sufficiently until it flows to the outside of the convex part to prevent sink marks due to insufficient coating liquid in the boundary area, some of the coating liquid flows over the convex part. In addition, it is dammed and accommodated by other convex portions and dried, for example, in a line shape or a belt shape. Moreover, these grooves and protrusions and the coating films in the other grooves and other protrusions do not stand out visually after drying and do not impair the appearance.
It is preferable that the height of the convex portion is equal to or higher than the height of the other convex portion.
Since the other convex part retains a part of the coating liquid leaking outside the convex part forming the receiving layer, the height may be lower than that of the inner convex part.
Further, the concave groove is preferably formed by being depressed in a direction substantially perpendicular to the surface of the object to be coated at the boundary of the convex portion located in the outer direction, and the depth of the boundary with the convex portion of the concave groove. Since the thickness can be ensured, it is possible to reliably prevent sinking or flow of the coating liquid toward the central region during drying.

The object to be coated is formed in a disc shape, and at least one of the concave groove and the convex portion and the other concave groove and the other convex portion may be provided on the inner peripheral side and the outer peripheral side, respectively. In particular, the object to be coated is preferably an optical disk. Images can be printed directly with ink or the like using the receiving layer of the optical disk as a label, for example.
In the receiving layer forming method according to the present invention, the receiving layer coating solution is particularly suitable when an aqueous coating solution whose solid content ratio is small and takes a long time to dry and is likely to cause sink due to movement of the coating solution during drying. It is.
The aqueous receiving layer coating liquid is an aqueous coating liquid that contains a pigment and a binder and forms a porous ink receiving layer, and the pigment may be any of alumina, silica, and silica-alumina composite particles. . Alternatively, it may be a water-based coating liquid that contains a water-soluble polymer and forms a swollen ink receiving layer.
Since the ink is received by the receiving layer formed on the entire surface with a substantially uniform film thickness, the ink does not overflow and ooze out to the outside, and in any case, a clear printed image that does not bleed is obtained.
In addition, the receiving layer formed by drying the coating film made of the aqueous coating liquid has a high ink receiving ability and forms a good print image, while the aqueous coating liquid is an aqueous paint and has a solid content ratio of 25% by mass or less. Preferably, it is often used as a coating solution having a low solid content ratio of 20% by mass or less, and the viscosity is as low as about 20 to 100 mPa · s. For this reason, the time required for drying is relatively long, and the coating film forming method of the present invention can be effectively applied to various problems caused by drying, such as a reduction in film thickness in the boundary region after coating. .

Further, the aqueous coating solution used in the present invention contains a pigment and a binder in water or a solvent containing water as a main component as described above, or contains a hydrophilic polymer. The hydrophilic polymer means a polymer substance that has a hydrophilic sensitive group in the molecule and is dissolved in water, self-emulsified, or dispersed by the addition of an emulsifier. A water-soluble polymer may be used as the hydrophilic polymer.
The materials of the pigment, binder and hydrophilic polymer are not particularly limited, and known inorganic pigments, organic pigments, known binders for coating liquids, and hydrophilic polymers can be widely used. Further, when the pigment is an inorganic pigment and the binder is a water-soluble resin, the effect of the present invention is exhibited very well.
A porous ink-receiving layer is obtained from an aqueous coating liquid containing a pigment and a binder, and a swelling ink-receiving layer is obtained from an aqueous coating liquid containing a hydrophilic polymer. In the swelling type ink receiving layer, the receiving layer itself absorbs the ink, and expands or dissolves itself to adsorb the ink in the receiving layer. Among these, a porous ink receiving layer that allows ink to be received in the voids between the pigment fine particles is preferable.
The receiving layer formed from such an aqueous coating solution has a high ink receiving ability and forms a good printed image, while the aqueous coating solution is an aqueous coating and has a low solid content ratio of 25% by mass or less. Often used as a paint. For this reason, the receiving layer formation method of this invention can be used suitably.

This porous ink receiving layer is mainly composed of a pigment and a binder, and not only alumina but also silica, boehmite, synthetic fine particle silica, synthetic fine particle alumina silicate, vapor phase synthetic silica, silica alumina composite particles, zeolite , Montmorillonite group mineral, beidellite group mineral, saponite group mineral, hectorite group mineral, stevensite group mineral, hydrotalcite group mineral, smectite group mineral, bentonite group mineral, calcium carbonate, magnesium carbonate, calcium sulfate, barium sulfate, oxidation Examples include titanium, zinc oxide, zinc carbonate, aluminum silicate, calcium silicate, magnesium silicate, kaolin, talc, alumina hydrate, plastic pigment, urea resin pigment, cellulose particles, and starch particles. Na, silica-alumina composite particles, boehmite, gas phase synthetic silica is preferred. Of these, boehmite (Al ₂ O ₃ · nH ₂ O, n = 1 to 1.5) is particularly preferable from the viewpoint of ink absorbability and fixability.
More preferably, the average pore radius of the porous ink receiving layer is ³ to 25 nm, particularly 5 to 15 nm is suitable, and the pore volume is preferably 0.3 to 2.0 cm ³ / g. It is particularly preferably 0.5 to 1.5 cm ³ / g.

  Examples of binders include starch, modified products thereof, polyvinyl alcohol or modified products thereof, styrene / butadiene rubber latex, nitrile / butadiene rubber latex, hydroxycellulose, hydroxymethylcellulose, polyvinylpyrrolidone, polyacrylic acid, and polyacrylamide. A water-soluble resin such as a polymer, an alcohol-soluble polymer, or a mixture of these polymers can be used. In particular, in this embodiment, it is preferable to use polyvinyl alcohol or a modified product thereof because ink absorbency and water resistance are required. The binder is preferably contained in an amount of 1 to 100 parts by weight, particularly 3 to 50 parts by weight, based on 100 parts by weight of the pigment.

On the other hand, as the hydrophilic polymer used for obtaining the swelling type ink receiving layer, urethane resin or a modified product thereof, fully saponified or partially saponified polyvinyl alcohol, modified polyvinyl alcohol, ethylene vinyl alcohol, polyvinyl pyrrolidone, polyalkylene oxide, Water-soluble synthetic polymers such as polyacrylamide or derivatives thereof, gelatin, modified gelatin, starch, modified starch, casein, soybean casein, modified soybean casein or modified products thereof, or derivatives thereof, methylcellulose, ethylcellulose, carboxymethylcellulose , Water-soluble natural polymers such as cellulose derivatives such as hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and nitrocellulose Of these, urethane resins or modified products thereof, polyvinyl alcohol or derivatives thereof, polyvinyl pyrrolidone or derivatives thereof, polyacrylamide, cellulose derivatives, gelatin or derivatives thereof are particularly preferable.
In the present invention, the modified urethane resin means a water-based urethane resin and introduces a hydrophilic group into the main chain of the urethane skeleton so that it can be stably dispersed in water, or self-emulsification, or An aqueous dispersion of urethane resin obtained by dispersing with an external emulsifier is shown. The modified urethane resin is particularly preferably a self-emulsifying type obtained from a polycarbonate-based polyol or a polyester-based polyol and an aliphatic isocyanate.
These hydrophilic polymers are used alone or in the form of a mixture of two or more.

In the case of the swelling type ink receiving layer, in addition to the above-described hydrophilic polymer, if necessary, the pigment can be contained in an amount of 0.05 to 10% by weight based on the hydrophilic water-soluble polymer. In addition, as a pigment, the same thing as a porous type can be used.
In the ink receiving layer, as other additives, a curing agent, a leveling agent, an antifoaming agent, a thickening agent, a fluorescent whitening agent, a coloring dye, a coloring pigment, and the like can be used as necessary. . In particular, in the case of a porous layer, the curing agent has a great influence on the formation process, and by coating gel defects such as cracks caused by distortion due to volume shrinkage due to moisture evaporation in the drying process of the aqueous coating liquid, There is an inhibitory effect. When polyvinyl alcohol is used as the binder, boric acid or borate is effective.
In this embodiment, the coating thickness of the ink receiving layer provided on the disk substrate is selected depending on the ink absorptivity, the strength of the coating layer, the application, etc., but preferably 2 to 80 μm is employed. If this coating thickness is less than 2 μm, the effect as an ink receiving layer is hardly exhibited, whereas if it exceeds 80 μm, it is not preferable because transparency or strength may be reduced or fine cracks may occur on the surface. . In particular, the coating thickness of the ink receiving layer is suitably 10 to 50 μm, and more preferably 30 to 40 μm. Dry coating is preferably 2~80g / ^{m 2} when the weight of the film, more preferably ^{20~70g / m 2, 30~50g / m} 2 is most preferred. The coating thickness of the coating solution can be about 4 to 8 times the dry thickness, for example, corresponding to the solid content concentration of the coating solution, and can be 10 to 400 g / m ² in terms of the weight of the coating solution.
Further, by forming a layer containing a white pigment in advance using a white ink on a disk substrate and forming a receiving layer on the layer, it is possible to improve the color of the image by the ink jet recording method.

In the receiving layer forming method of the present invention, an absorbent member can be used without any particular limitation as the material of the object on which the concave grooves and the convex portions are formed. When the object to be coated is an optical disk substrate, a material generally used for an optical disk substrate can be widely used, and polycarbonate is particularly preferable.
There are no particular limitations on the shape of the concave grooves and convex portions, and various cross-sectional shapes can be used. V-shaped, U-shaped, rectangular, inverted trapezoidal, etc. can be used for concave grooves, and inverted V-shaped, inverted U-shaped, rectangular, trapezoidal, etc. for convex portions. Can do. The concave groove has a V-shaped or inverted trapezoidal cross-sectional shape because of ease of production, shape stability against external force, and ease of filling with a coating solution. Alternatively, those having a trapezoidal cross-sectional shape are preferable.
The depth of the groove is to prevent an increase in the drying speed due to a decrease in the coating film thickness at the edge of the coating region.
It is preferable to have a depth (film thickness) equivalent to the coating film thickness in the central region at the deepest portion of the groove. The width of the upper end of the opening of the concave groove is preferably equal to or greater than the depth of the concave groove in consideration of ease of filling the concave groove with the coating liquid.
As for the height of the convex portion, even if the height of the convex portion is lower than the coating film thickness, the coating liquid is blocked by the surface tension of the coating liquid in contact with the inner wall of the convex portion. For this reason, the height of a convex part does not necessarily need to be higher than the height corresponding to a coating film thickness, and should just be high enough to determine the boundary area | region which dams a coating liquid. The convex portion having a height exceeding the height corresponding to the coating film thickness is excellent in terms of completely blocking the coating liquid, but forms a protrusion near the boundary of the coating area of the coating object, It is easy to impair the smoothness of the surface of the object. Furthermore, if a convex part that is too high is formed in the boundary region, there is a possibility that, for example, a part of the coating apparatus such as an application nozzle contacts the convex part and smooth application is not performed. The distance between the first groove and the first protrusion formed in this way and the other groove and other protrusion formed on the outer side of the groove is the amount of coating liquid to be filled and the appearance. However, when the receiving layer is formed on the optical disk substrate, the film thickness is 50 to 50 μm when the coating thickness for the receiving layer coating of 100 to 200 μm is taken into consideration. 700 μm is preferable, and 100 to 500 μm is more preferable.
For example, when a coating method that uses dropping of the coating liquid from the nozzle row to discharge the coating liquid is used as a coating apparatus, the nozzle may be brought as close to the coated surface (surface) of the coated object as possible in order to increase the coating accuracy. preferable. In addition, when the smoother is placed at a position where the distance from the object to be coated is shorter than the position corresponding to the coating film surface formed with the coating liquid, and the coating surface is smoothed together with the coating liquid, In the application boundary region, the height of the convex portion needs to be smaller than the height corresponding to the coating film thickness so that the smoother and the convex portion do not contact each other. In such a case, the convex part is preferably 50 to 80% of the film thickness of the coating solution. 60 to 75% is more preferable. For example, when a receiving layer is formed by applying a 150 μm receiving layer coating solution on an optical disk substrate, the receiving layer can be formed to a height of 75 to 120 μm.
The groove formed in this way and the other groove formed further outside the protrusion can be made shallower than the first groove, and the other protrusion can be the first groove. It is necessary to set the height below the convex part so that the application of the end of the application region is performed smoothly.
The method for forming the grooves and protrusions in the application boundary region of the object to be coated is not particularly limited, and any cutting method or molding method suitable for the material of the object to be coated, the size and shape of the grooves, or the protrusions. Etc. can be formed.

For example, in order to form the concave groove and the convex portion on the disk substrate, while rotating the molded disk substrate, from above the concave groove forming position, apply a cutting blade whose tip is formed into the shape of the concave groove, This can be done by cutting or deforming the disk substrate. The resin in the groove is pushed up to both ends of the groove by the cutting blade to form convex portions at both ends, but the inner peripheral wall of the concave groove is formed perpendicular to the disk substrate surface, and the outer peripheral wall is By forming a substantially V-shaped cross section having a specific inclination, the resin in the concave groove is pushed up to the outer peripheral side of the disk substrate surface along the inclination of the outer wall, so that the convex portion is formed only on the outer side of the concave groove. Can be formed.
In addition, by forming a disk substrate mold and producing a disk substrate so that a concave groove and a convex portion can be formed at the same time in the molding process when molding the disk substrate, a precise concave groove or A disk substrate having projections in advance can be prepared.

Thus, the receiving layer coating is applied to the coating region having at least one of the concave groove and the convex portion formed on the boundary of the coating region of the object to be coated and the other concave groove or the other convex portion formed on the outer side. In order to form a receiving layer with a uniform film thickness by liquid, especially when the solid content ratio of the coating liquid is low and the viscosity is low, a coating film is formed on the surface to be coated by dropping the coating liquid from the nozzle. Preferably formed. In order to achieve the coating efficiency and the uniformity of the coating film thickness over a wide range, it is preferable to drop the coating solution from the nozzle row. In the present invention, the first concave groove formed in the boundary portion of the coating region is sufficiently filled with the coating liquid, touches the inside of the first convex portion, and rises beyond the height of the top portion of the convex portion. It is preferable that the coating solution is sufficiently filled.
For application to the boundary portion of the application region, it is preferable to drop the application liquid by disposing the nozzle so that it is positioned outside the top of the convex portion facing the discharge port at the end. Since the coating liquid dripped from the nozzle gathers at the center of the discharge port due to surface tension during the dripping, by applying the coating while maintaining such a positional relationship between the discharge port and the top, the inside of the concave groove or convex portion A sufficient coating liquid can be reliably supplied to the region corresponding to the above.
Further, the coating liquid is applied so that the coating liquid from the discharge port flows outside the convex portion and between the convex portion and another concave groove or other convex portion formed outside the convex portion. It is preferable because a more sufficient coating solution is supplied to the region corresponding to the groove and the inside of the convex portion. Further, by supplying the coating liquid further between the convex portion and another concave groove or other convex portion formed outside the convex portion, the first convex portion is completely covered with the coating liquid. Since the coating solution is sufficiently supplied up to this point, a sufficient coating solution is preferably supplied to the boundary portion of the coating region. Thus, when making a discharge port protrude outside from the top part of a corresponding convex part, 0.1-0.5 mm is preferable as the distance made to protrude, and 0.2-0.4 mm is still more preferable.
The coating film made of the coating solution for the receiving layer on the coated material thus coated is dried by heating to form a receiving layer. In drying, the drying method and drying conditions can be selected appropriately according to the material of the object to be coated, the film thickness of the coating film, etc., but take sufficient time to prevent the coating film surface from being suddenly heated. It is preferable to perform drying. The heating is preferably performed so that the heat is transmitted from the coated object side toward the coating film.

An embodiment of the present invention will be described with reference to FIGS. 1 to 7, taking a receiving layer on an optical disk as an example.
FIG. 1 is a partial longitudinal sectional view of an optical disk according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view of concave grooves and convex portions at the outer peripheral side boundary portion of the substrate shown in FIG. FIG. 4 and FIG. 5 are diagrams showing the discharge ports of the nozzles in the application unit, FIG. 6 is a partially enlarged view showing the positional relationship between the nozzles and the inner and outer peripheral side boundaries of the substrate, and FIG. It is a fragmentary longitudinal cross-section which shows the receiving layer formation process to a board | substrate.
An optical disk 1 as an optical information medium according to the present embodiment is, for example, a normal digital video disk (DVD), a compact disk, or the like. As shown in FIG. 1, a ring-shaped disk substrate 2 made of, for example, a polycarbonate substrate (PC substrate). An information recording layer 3 is formed on one surface 2a, and this information recording layer 3 is formed by coating a reflective film made of a metal thin film on the surface of irregularities of about 0.1 μm formed by a stamper or the like. .
Then, another disk substrate 4 is bonded to the surface of the information recording layer 3 via an adhesive layer. Reproduction light is irradiated from the other surface 2 b side of the disk substrate 2, and reading is performed by reflected light from the information recording layer 3. Porous ink obtained by drying a thin film made of an aqueous coating solution on the surface of the optical disc 1 opposite to the surface 2b on the information reading side, that is, on the printing surface 5 opposite to the adhesive layer of the disc substrate 4. A receiving layer 6 (receiving layer) is provided. The printing surface 5 of the disk substrate 4 is a hydrophobic surface.
Here, the aqueous coating liquid is an aqueous coating liquid that forms a receiving layer after drying. In this embodiment, an aqueous coating liquid for forming a porous ink receiving layer containing a pigment and a binder is used, and an aqueous coating liquid is used. This was carried out using a water-based coating liquid for forming a swelling ink-receiving layer containing a conductive polymer. The swelling type ink receiving layer is mainly composed of a water-soluble polymer, and the receiving layer 6 itself absorbs ink and swells or dissolves itself to adsorb the ink in the receiving layer 6. is there.

In FIG. 1, an information recording layer 3 on a disk substrate 2 and a disk substrate 4 laminated with an adhesive layer 3a are used as an optical disk 1 (for example, DVD), and a receiving layer is provided on a printing surface 5 of the disk substrate 4. The first concave groove 5A, the first convex part 5B, the second concave groove 5C, and the second convex part 5D, which are substantially ring-shaped, are concentrically directed radially inward in the inner peripheral side boundary part 5a of the region forming the groove 6. Are formed sequentially. Similarly, a substantially ring-shaped first concave groove 5E, first convex part 5F, second concave groove 5G, and second convex part 5H are concentrically arranged on the outer peripheral side boundary part 5b of the area where the receiving layer 6 of the printing surface 5 is formed. Are formed sequentially toward the outside in the radial direction.
Here, in the printing surface 5, an area including the first concave groove 5 </ b> A, the first convex part 5 </ b> B, the second concave groove 5 </ b> C, and the second convex part 5 </ b> D is defined as the inner peripheral boundary part 5 a, the first concave groove 5 </ b> E, and the first. A region including the convex portion 5F, the second concave groove 5G, and the second convex portion 5H is defined as an outer peripheral side boundary portion 5b, and a ring-shaped flat surface surrounded by the boundary portions 5a and 5b is defined as a central application portion 5c. Similarly, for the receiving layer 6, the first concave groove 5A and the first convex portion 5B are the inner peripheral boundary region 6a, the first concave groove 5E and the first convex portion 5F are the outer peripheral boundary region 6b, and both boundaries. A ring-shaped portion surrounded by the regions 6a and 6b is defined as a central region 6c.
The first concave grooves 5A and 5E and the second concave grooves 5C and 5G have a substantially V-shaped cross-sectional shape as shown in the longitudinal sectional view of FIG. Similarly, the first convex portions 5B and 5F and the second convex portions 5D and 5H have a substantially inverted V-shaped cross-sectional shape. The inner peripheral side boundary region 6a and the outer peripheral side boundary region 6b of the receiving layer 6 are partitioned by the first concave groove 5A and the first convex portion 5B, the first concave groove 5E and the first convex portion 5F, respectively. The second concave groove 5C and the second convex part 5D, the second concave groove 5G and the second convex part 5H provided on the radially inner side and the outer side exceed the first convex parts 5B and 5F when the aqueous coating liquid is applied. This is for blocking the flowing aqueous coating solution.

Therefore, the first convex portions 5B and 5F are formed at a height equal to or higher than that of the second convex portions 5D and 5H in order to partition the applied aqueous coating solution as the receiving layer 6. Further, the first concave grooves 5A and 5E are formed deeper than the second concave grooves 5C and 5G in order to suppress the flow of the aqueous coating liquid from the boundary portions 5a and 5b to the central coating portion 5c in the drying step of the aqueous coating liquid. ing. That is, when the aqueous coating liquid is applied in a ring shape on the printing surface 5, the film thickness of the portion of the first concave groove 5A, 5E of the aqueous coating liquid that forms the convex curved surface of the coating film 6A is the central coating part 5c. The depth is set so as to be equal to or greater than the film thickness.
The depth of the second concave grooves 5C and 5G is only to dam the aqueous coating liquid flowing beyond the first convex parts 5B and 5F in relation to the second convex parts 5D and 5H. It may be shallower than 5E.
5A, 1st convex part 5B, 2nd concave groove 5C, 2nd convex part 5D and 1st convex groove 5E of the outer peripheral side, 1st convex part 5F, 2nd concave groove 5G The two convex portions 5H have a substantially line-symmetric shape in the longitudinal sectional view shown in FIG. 1, but may not be line-symmetric.

The radial width W and depth D of the openings of the concave grooves 5A, 5E, 5C, and 5G are appropriately set depending on the application and size. In the optical disc 1, the first concave grooves 5A and 5E have, for example, a width W1. The depth D1 is set to about 150 μm, and the second concave grooves 5C and 5G are set to have a width W2 of about 300 μm and a depth D2 of about 100 μm.
When the width W1 is less than about 200 μm, it is not possible to sufficiently flow into the groove when applying the aqueous coating liquid, and when air enters the grooves 5A and 5E, it is enclosed inside without being escaped upward. End up. And if it heats at the time of drying, the inside air expand | swells and bursts, and the malfunction that the burst trace remains on the surface of the receiving layer 6 arises. For this reason, the width W needs to be large enough for the coating liquid to sufficiently flow into the concave grooves 5A and 5E and for the mixed bubbles to escape to the outside.
Regarding the depth D1, the water-based coating liquid has a water ratio of about 80% with respect to the water-based coating liquid as will be described later, while the receiving layer 6 needs a film thickness after drying of, for example, about 30 μm for ink reception. Therefore, the aqueous coating solution needs to be applied to the printing surface 5 with a film thickness of about 150 μm. In the first concave grooves 5A and 5E, the aqueous coating liquid swells and curves in a substantially arc shape due to surface tension, and the film thickness decreases to contact the first convex portions 5B and 5F. As shown by a two-dot chain line in FIG. 2, a substantially vertical shape having a depth D1 having a minimum film thickness of 150 μm at the boundary between the first convex portions 5B and 5F is preferable. However, as illustrated by a solid line in FIG. 2, a substantially V-shaped cross-sectional shape having a depth D1 at which the film thickness of a part of the aqueous coating liquid in the first concave grooves 5A and 5E is 150 μm or more may be used.
The receiving layer 6 formed on the printing surface 5 has a substantially uniform film thickness over the entire surface. However, in the inner peripheral side boundary region 6a and the outer peripheral side boundary region 6b, the first concave grooves 5A and 5E are formed. Therefore, the film thickness becomes thicker. In most of the first concave grooves 5A and 5E, the film thickness is almost equal to or greater than the central area 6c (inner area surrounded by the first concave grooves 5A and 5E).

Therefore, according to the optical disc 1 according to the present embodiment, when ink is applied to the receiving layer 6 with an ink jet printer or the like, a clear printed image can be obtained over the entire coating region. In particular, in the case of a porous ink receiving layer, the ink is received by the pores in the receiving layer 6 that is flat and has a substantially uniform film thickness over the entire surface, so that each hole overflows and oozes out to the outside. And a clear printed image can be obtained.
In addition, also in the inner peripheral side and outer peripheral side boundary regions 6a and 6b of the receiving layer 6, in almost all the regions in the first concave grooves 5A and 5E, a film thickness almost equal to or larger than the other regions can be secured, so that it is clear. A printed image is obtained, but the inner and outer boundary regions 6a and 6b are formed to have a film thickness larger than that of the central region 6c and relatively small because of the cross-sectional shape of the first concave grooves 5A and 5E. Therefore, it is more preferable that printing on the receiving layer 6 is performed in the central region 6c excluding the inner peripheral side and the outer peripheral side boundary regions 6a and 6b.

Next, the coating film forming apparatus 10 used for the receiving layer forming method of the optical disc 1 will be described with reference to FIGS.
In FIG. 3, the coating film forming apparatus 10 includes a coating unit 11 that coats the aqueous coating solution S on the printing surface 5, and a drying unit (not shown) that dries the coating film 6 </ b> A formed by coating the aqueous coating solution S. And is roughly composed.
Here, as the aqueous coating solution S, for example, the following prescription is used. Receiving layer prescriptions 1 to 3 are prescriptions relating to the coating liquid for the porous ink receiving layer, and receiving layer prescription 4 is a prescription relating to the coating liquid for the swelling type ink receiving layer.

Receiving layer prescription 1
Alumina sol (solid content concentration 20%): 100 parts by mass Polyvinyl alcohol (Kuraray Co., Ltd., trade name PVA-124, solid content concentration 7%): 28.6 parts by mass Boric acid (solid content concentration 4%): 5 parts by mass (Method for producing alumina sol)
The alumina sol is prepared by adding a sodium aluminate solution to a solution composed of polyaluminum chloride heated to 95 ° C. and water, washing the aged slurry with ion-exchanged water, raising the temperature to 95 ° C. again, and adding acetic acid. It is obtained by glue and concentration, followed by sonication.
Receiving layer prescription 2
Silica alumina composite sol (solid content concentration 20%): 100 parts by weight Polyvinyl alcohol (Kuraray Co., Ltd., trade name PVA-140H, solid content concentration 7%): 57.2 parts by weight Boric acid (solid content concentration 4%): 5 parts by mass (silica alumina composite sol production method)
To the silica-alumina composite sol, 5 mol / L hydrochloric acid was gradually added to No. 3 sodium silicate solution and water while stirring. Thereafter, the mixture was heated to 80 ° C. and aged to obtain a silica hydrogel. This silica hydrogel was pulverized by a colloid mill and ultrasonic dispersion treatment. The pulverized silica hydrogel was heated to 80 ° C., and an aqueous polyaluminum chloride solution was gradually added. 5 mol / L sodium hydroxide was added to the reaction solution at room temperature, and the pH of the reaction solution was adjusted to 7.7, followed by ultrafiltration, and the filtrate was purified until the conductivity was 20 μS / cm or less. . Next, 10% amidosulfuric acid aqueous solution was added to the purified solution to adjust the pH to 4.0. After heating and concentrating under reduced pressure and cooling, 10% amidosulfuric acid aqueous solution was added again to adjust the pH to 4.0 to obtain a silica-alumina composite sol.
Receiving layer prescription 3
Silica dispersion (solid content concentration 14%): 100 parts by mass Polyvinyl alcohol (Kuraray Co., Ltd., trade name PVA-420, solid content concentration 7%): 50 parts by mass (Method for producing silica dispersion)
Vapor phase silica fine particles (Aerosil 300 manufactured by Nippon Aerosil Co., Ltd.) and water are mixed for 30 minutes at 10,000 rpm using a high-speed rotating colloid mill (Cleamix manufactured by M Technique Co., Ltd.). A silica dispersion was obtained.
Receiving layer prescription 4
Methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., Metrics SM15): 100 parts by mass Amorphous silica (manufactured by Fuji Silysia Chemical Co., Ltd., Silicia 370): 0.03 parts by mass Were mixed and stirred to obtain an aqueous coating solution.

In the coating film forming apparatus 10, the coating unit 11 includes a rotary table 12 on which the substrate 1A is placed coaxially with the rotation axis O, and the rotation speed of the rotary table 12 is controlled by control means (not shown). Discharge means 14 for discharging the aqueous coating solution S in the radial direction about the rotation axis O is disposed on the turntable 12.
The discharge means 14 is composed of a single supply system 15 (supply source) and a nozzle unit 16 including nozzles 16a, 16b,... 16h branched from the supply system 15 into a plurality of nozzles. The discharge and stop of the aqueous coating liquid S from the nozzles 16a to 16h are controlled by opening and closing a valve (not shown) provided in the region of the section 15. Each nozzle 16a-16h consists of a microdispenser nozzle, for example, is arranged along with the radial direction of the board | substrate 1A, for example, is linearly arranged over the formation width of the printing surface 5. For example, as shown in FIG.

Moreover, each of the nozzles 16a to 16h has a circular or polygonal discharge port as shown in FIG. 4, and the innermost peripheral nozzle 16a located on the innermost peripheral side in the arrangement direction has a minimum discharge port area. .., And the plurality of nozzles 16b, 16c,... Gradually increase in area of the discharge port, and the outermost peripheral nozzle 16h is set to have the largest area of the discharge port.
Therefore, the discharge amount per unit time is gradually increased from the innermost peripheral nozzle 16a toward the outermost peripheral nozzle 16h, and the application liquid discharge amount of each nozzle 16a to 16h per unit area is set to be constant. Has been. This is because the nozzles 16a to 16h arranged in the radial direction with respect to the substrate 1A relatively rotate at the same angular velocity, and the coating amount per unit area on the printing surface 5 of the substrate 1A by the nozzles 16a to 16h. The discharge amount per unit time of each of the nozzles 16a to 16h is set so as to be uniform.
As a modification, as shown in FIG. 5, the nozzles 16 a to 16 h may be arranged in a zigzag pattern that is alternately shifted in a direction substantially orthogonal to the arrangement direction.

Next, a method for forming the receiving layer 6 according to the present embodiment will be described with reference to FIGS.
First, a substrate 1A in which another disk substrate 4 is laminated on one side of a disk substrate 2 shown in FIG. 7A via an information recording layer 3 and an adhesive layer 3a is placed on the rotary table 12 coaxially. As shown in FIG. 3, the ring-shaped printing surface 5 shifted from the rotation axis O of the substrate 1 </ b> A is opposed to the discharge means 14 of the coating film forming apparatus 10. The nozzles 16 a to 16 h of the ejection unit 14 are arranged in the radial direction of the printing surface 5 with the ejection unit 14 approaching the printing surface 5.
In this state, the positional relationship between the nozzle portion 16 of the discharge means 14 and the first concave grooves 5A and 5E and the first convex portions 5B and 5F of the ring-shaped printing surface 5 when applying the aqueous coating liquid S is shown in FIG. And FIG. 6 demonstrates. The nozzle portions 16 are arranged in the radial direction of the substrate 1A, and the innermost peripheral nozzle 16a is disposed on the innermost side and the outermost peripheral nozzle 16h is disposed on the outermost side.
In addition, as shown in FIG. 6, the nozzle portion 16 faces the first convex portions 5B and 5F with a slight distance L so as to prevent interference. The distance L is, for example, about 30 to 40 μm. The nozzle portion 16 is provided at a position closer to the substrate 1A side by about 20 to 30 mm than the thickness of the coating film of the aqueous coating solution S. Further, the innermost peripheral nozzle 16a protrudes toward the second concave groove 5C by a distance x with respect to the top of the first convex portion 5B facing the discharge port, and the outermost peripheral nozzle 16h is the first convex portion 5F facing the discharge port. Is disposed so as to project toward the second concave groove 5G side by a distance x with respect to the top of the first groove. The distance x is, for example, 0.1 mm.

Then, the rotary table 12 is rotated around the rotation axis O at a constant low speed, and at the same time, the valve of the supply system 15 of the discharge means 14 is opened to supply the aqueous coating liquid S to the nozzles 16a to 16h under the same pressure. Each is supplied and continuously discharged onto the printing surface 5. The discharge amount per unit time of the coating liquid S discharged from the nozzles 16a to 16h is the smallest at the innermost peripheral nozzle 16a and gradually increases toward the outer peripheral nozzles 16b, 16c... 16h, but the nozzles 16a to 16h. Therefore, the coating amount per unit area on the printing surface 5 is set almost uniformly.
Moreover, the water-based coating liquid S discharged from the nozzles 16a to 16h is a necessary amount in a state where the nozzles 16a to 16h partially overlap each other in the relative movement direction (circumferential direction) and the arrangement direction (radial direction). Only at the discharge position, for example, it is continuously applied in the form of droplets or peaks. In this case, since the water-based coating liquid S has a water ratio of about 80% with respect to the solid content, the water-based coating liquid S discharged simultaneously from the nozzles 16a to 16h onto the printing surface 5 has high fluidity and mutual affinity. Therefore, the leveling action works quickly and the entire surface is flattened with the same thickness. Such application of the aqueous coating solution S and leveling action occur not only in the arrangement direction of the nozzles 16a to 16h but also in the relative movement direction of the nozzles 16a to 16h.

Here, since each discharge port of the innermost peripheral nozzle 16a and the outermost peripheral nozzle 16h protrudes outward by a distance x from the top of the first convex portions 5B and 5F, the innermost peripheral nozzle 16a and the outermost outer periphery of the nozzle portion 16 The aqueous coating solution S discharged from the nozzle 16h is sufficiently filled in the first concave groove 5A and the first concave groove 5E of the printing surface 5, respectively, so that the upper surface is convex by surface tension so as not to cause sink marks or flow during drying. It swells and rises greatly in a curved surface (see FIG. 7B). In addition, a part of the aqueous coating liquid S is stored in the second concave grooves 5C and 5G beyond the first convex portions 5B and 5F.
In this case, the water-based coating liquid S that flows down into the second concave grooves 5C and 5G is small, and since the second convex portions 5D and 5H are provided, they do not flow out to the outside.
Since the substrate 1A rotates at a low speed together with the turntable 12, the aqueous coating solution S applied to the printing surface 5 does not spread outward in the radial direction by the centrifugal force of the rotating substrate 1A. . Each coating liquid S ejected by the nozzles 16a to 16h is held at the ejection position on the printing surface 5, and is leveled by high fluidity to make the coating film uniform.
In addition, since the discharge ports of the nozzles 16a to 16h are located slightly below the surface of the film thickness t (for example, t = 150 μm) of the aqueous coating solution S on the printing surface 5, the nozzles 16a to 16h are caused by relative rotation of the substrate 1A. Is flattened by relative sliding so as to rub the coated film 6A.

Accordingly, as the nozzles 16a to 16h rotate relative to the printing surface 5 by one rotation, the coating film 6A of the aqueous coating liquid S discharged on the printing surface 5 becomes the first as shown in FIG. The inner regions of the one groove 5A, 5E are leveled and flattened to have a predetermined film thickness t (for example, t = 150 μm), and the first groove 5A, 5E has a film thickness portion larger than the film thickness t. It curves into a convex curved surface shape due to surface tension and comes into contact with the tops of the first convex portions 5B and 5F.
In addition, a part of the aqueous coating solution S that flows over the first convex portions 5B and 5F is stored in the second concave grooves 5C and 5G and the second convex portions 5D and 5H, and therefore flows irregularly on the printing surface 5. Will not spread. Therefore, the inner peripheral side and the outer peripheral side boundary portion form a regular and clean circumferential boundary line by the first convex portions 5B and 5F and the second concave grooves 5C and 5G or the second convex portions 5D and 5H.

In this way, the coating process is completed, and the substrate 1A on which the coating film 6A shown in FIG. 7B is formed is sent to the drying process.
In the drying process, the substrate 1A is left in the outside air to be naturally dried. Alternatively, a heating means using steam, infrared rays, or the like may be disposed on the other surface 2b of the disk substrate 2 of the substrate 1A so that the entire surface 2b is heated and the coating film 6A is dried through the substrate 1A.
In the heating step, the coating film 6A having a ring shape on the printing surface 5 of the substrate 1A is concave when the aqueous coating liquid S in the concave grooves 5A and 5E is included in the inner peripheral side and outer peripheral side boundary regions 6a and 6b. Since the film thickness is equal to or greater than that of the central region 6c surrounded by the grooves 5A and 5E, the drying speed is suppressed. Further, since the aqueous coating liquid S in the concave grooves 5A and 5E is partitioned on one side by the first convex portions 5B and 5F, even if it partially flows in the direction of the central region 6c, it is suppressed to a small extent. Drying in the boundary regions 6a and 6b does not proceed beyond the central region 6c, and drying proceeds almost simultaneously throughout.

Since the aqueous coating solution S has a solid content of about 20%, the film thickness of the coating film 6A decreases during the drying process, but the flow of the aqueous coating solution S from the inner and outer boundary regions 6a and 6b Therefore, the film is dried in a state where the film thickness distribution at the time of coating is substantially maintained. When drying is completed in this way, the thickness of the coating film 6A is reduced to about one fifth as shown in FIG. 7C, and the receiving layer 6 is formed.
The obtained receiving layer 6 has a uniform and flat film thickness (for example, about 30 μm) almost entirely including not only the central region 6c but also the inner and outer boundary regions 6a and 6b. The first convex portions 5B and 5F of the inner peripheral side and outer peripheral side boundary regions 6a and 6b have a film thickness larger than that of the central region 6c, and the film thickness is reduced only in the vicinity of the end portion in relation to the surface tension.
While the central region 6c of the receiving layer 6 surrounded by the first concave grooves 5A and 5E is located on the printing surface 5, the thickness of the receiving layer 6 in the concave grooves 5A and 5E is the central region 6c. On the other hand, it becomes large and is formed in a substantially flat shape.
When the receiving layer 6 on the printing surface 5 of the substrate 1A thus obtained is printed by an ink jet printer or the like, not only the central region 6c but also the first concave grooves 5A and 5E of the receiving layer 6 are inside. The peripheral side and outer peripheral side boundary regions 6a and 6b also have a sufficient film thickness, and a clear printed image can be obtained.

The porous ink receiving layer 6 according to the present embodiment is preferably a so-called porous void absorption type receiving layer in which ink is received in the voids between the pigment fine particles because the drying time of the ink is short.
This void absorption type receiving layer mainly comprises a pigment and a binder, and not only alumina but also silica, boehmite, synthetic fine particle silica, synthetic fine particle alumina silicate, vapor phase synthetic silica, silica alumina composite particle, zeolite , Montmorillonite group mineral, beidellite group mineral, saponite group mineral, hectorite group mineral, stevensite group mineral, hydrotalcite group mineral, smectite group mineral, bentonite group mineral, calcium carbonate, magnesium carbonate, calcium sulfate, barium sulfate, oxidation Titanium, titanium, zinc oxide, zinc carbonate, aluminum silicate, calcium silicate, magnesium silicate, kaolin, talc, alumina hydrate, plastic pigment, urea resin pigment, cellulose particles, starch particles, etc., among others, silica Alumina, silica-alumina composite particles are preferred. Of these, boehmite (Al2O3 · nH2O, n = 1 to 1.5) is particularly preferable from the viewpoint of ink absorbability, fixability, and transparency.

More preferably, the average pore radius of the porous ink receiving layer 6 is 3 to 25 nm, particularly 5 to 15 nm is suitable, and the pore volume is preferably 0.3 to 2.0 cm 3 / g, Is preferably 0.5 to 1.5 cm 3 / g.
Examples of binders include starch, modified products thereof, polyvinyl alcohol or modified products thereof, styrene / butadiene rubber latex, nitrile / butadiene rubber latex, hydroxycellulose, hydroxymethylcellulose, polyvinylpyrrolidone, polyacrylic acid, polyacrylamide, and other water-soluble polymers. An alcohol-soluble polymer or a mixture of these polymers can be used. In particular, in this embodiment, it is necessary to use good ink absorbability and water resistance, and therefore it is preferable to use polyvinyl alcohol or a modified product thereof. The binder is preferably contained in an amount of 1 to 100 parts by weight, particularly 3 to 50 parts by weight, based on 100 parts by weight of the pigment in the porous ink receiving layer 6.
On the other hand, as the water-soluble polymer used for obtaining the swelling type ink receiving layer, fully saponified or partially saponified polyvinyl alcohol, modified polyvinyl alcohol, ethylene vinyl alcohol, polyvinyl pyrrolidone, polyalkylene oxide, polyacrylamide, or derivatives thereof. Water-soluble synthetic polymers such as gelatin, modified gelatin, starch, modified starch, casein, soybean casein, modified soybean casein or modified products thereof, or derivatives thereof, methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose Water-soluble natural polymers such as cellulose derivatives such as hydroxypropylmethylcellulose and nitrocellulose. Of these, polyvinyl alcohol or derivatives thereof, polyvinyl pyrrolidone or derivatives thereof, polyacrylamide, cellulose derivatives, gelatin or derivatives thereof are particularly preferable. Each of these water-soluble polymers is used alone or in the form of a mixture of two or more.
In the case of the swelling type ink receiving layer, in addition to the water-soluble polymer described above, a pigment can be contained in an amount of 0.05 to 100% by weight based on the water-soluble polymer, if necessary. The pigment content is more preferably 0.05 to 50% by weight. In addition, as a pigment, the same thing as a porous type can be used.
For the ink receiving layer, as other additives, a curing agent, a leveling agent, an antifoaming agent, a thickening agent, a fluorescent whitening agent, a coloring dye, a coloring pigment, etc. may be used as necessary. Can do. In particular, the curing agent has a large influence in the porous layer formation process, and suppresses coating film defects such as cracks resulting from distortion due to volume shrinkage due to moisture evaporation in the drying process of the aqueous coating liquid S by early gelation. effective. When polyvinyl alcohol is used as the binder, boric acid or borate is effective.
In this embodiment, the film thickness of the porous ink receiving layer 6 provided on the printing surface 5 of the substrate 1A is selected depending on the ink absorptivity, the strength of the coating layer, the application, etc. Adopted. The film thickness is preferably in the range of 5 to 80 μm. When the film thickness is less than 5 μm, the effect as the porous ink receiving layer 6 is hardly exhibited, whereas when it exceeds 80 μm, the film is transparent. Further, it is not preferable because the strength may decrease or the surface may have fine cracks. Especially, it is suitable that the film thickness of the receiving layer 6 is 10-50 micrometers.

As described above, according to the receiving layer forming method of the substrate 1A and the optical disc 1 according to the present embodiment, the first concave grooves 5A, 5E and the first grooves 5A, 5E provided in the inner peripheral side and outer peripheral side boundary portions 5a, 5b of the receiving layer forming region. The application area | region of the aqueous coating liquid S can be prescribed | regulated by the one convex part 5B and 5F. In addition, by discharging the aqueous coating solution S beyond the first convex portions 5B and 5F by the nozzle portion 16, at the boundary portions 5a and 5b partitioned by the first concave grooves 5A and 5E and the first convex portions 5B and 5F. Since the coating film 6A does not sink when dried, the film thickness is flat and uniform over almost the entire area including the central region 6c of the printing surface 5 surrounded by the first concave grooves 5A and 5E and the first convex portions 5B and 5F. The receiving layer 6 can be formed in a well-balanced manner, and the yield can be improved. Therefore, when ink-jet printing or the like is performed on the receiving layer 6, a clear and distortion-free image is obtained as a whole in the central region 6c and the inner and outer peripheral side boundary regions 6a and 6b of the receiving layer 6.
Further, since the aqueous coating liquid S flowing outside the first convex portions 5B and 5F is blocked by the second concave grooves 5C and 5G and the second convex portions 5D and 5H, the boundary line of the receiving layer 6 is on the printing surface 5. It is formed with a regular and clean continuous line without being irregularly formed.

Next, a modification of the discharge means 14 of the coating film forming apparatus 10 according to the first embodiment will be described with reference to FIG.
In FIG. 8, the substrate 1 </ b> A of the optical disk 1 is placed in a stationary state on a turntable 12 (not shown). The discharge means 20 that discharges the aqueous coating solution S includes a supply system unit 15 that is a single coating agent supply source, and a nozzle unit 21 having a plurality of nozzles 21 a branched from the supply system unit 15. . The plurality of nozzles 21a are arranged to face the receiving layer forming region of the printing surface 5 of the substrate 1A. The nozzle unit 21 is also held stationary, and the aqueous coating liquid S is discharged from each nozzle 21a.
In this example, since the region where the receiving layer 6 is to be formed is formed in a ring shape, the nozzle portion 21 also has a number of nozzles 21a arranged in a ring shape in the radial direction and the circumferential direction in a substantially honeycomb shape. Is formed. Moreover, the discharge ports of the individual nozzles 21a have the same area, but may have different areas. In addition, the plurality of nozzles 21a on the innermost and outermost circumferences are positions where the respective outlets protrude outward from the first convex portions 5B and 5F by a distance x in the same manner as the nozzle portion 16 of the first embodiment shown in FIG. Is arranged.
Therefore, in order to apply the aqueous coating liquid S to the printing surface 5 using such a discharge means 20, the same amount of the aqueous coating liquid S is discharged from the plurality of nozzles 21 a of the nozzle portion 21 and each of the aqueous surface coating liquids S on the printing surface 5. An amount of liquid droplets that partially overlap each other is discharged.
In particular, according to the discharge means 20, the substrate 1A and the nozzle portion 21 discharge the aqueous coating liquid S in a stationary state, so that the coating operation can be performed in a shorter time and the leveling process can be more naturally dried. There is an advantage that it can be done before.

Next, other embodiments of the present invention will be described. The same or similar members and parts as those of the above-described embodiments will be described using the same reference numerals.
FIG. 9 is a partial vertical cross-sectional view of the concave grooves and convex portions formed in the boundary portion of the printing surface 5 of the substrate 1A according to the second embodiment. In the second embodiment, as in the first embodiment, the inner peripheral side boundary portion 5a and the outer peripheral side boundary portion 5b of the printing surface 5 are substantially line symmetrical and have the same configuration. The boundary portion 5b will be described as a representative.
In the drawing, the outer peripheral side boundary portion 5b of the printing surface 5 has the same configuration as the first embodiment with respect to the first concave groove 5E, the first convex portion 5F, and the second convex portion 5H, and the second concave groove 5G. Is not formed. Between the first convex portion 5F and the second convex portion 5H, a flat surface 5i included in the printing surface 5 flush with the central region 6c is formed.
In the present embodiment, the aqueous coating liquid S discharged beyond the first convex portion 5F is relatively small and is stored on the flat surface 5i between the first convex portion 5F and the second convex portion 5H.
Also in this embodiment, the same effects as in the first embodiment can be obtained.

FIG. 10 is a partial vertical cross-sectional view of the grooves and protrusions formed on the printing surface 5 of the substrate 1A according to the third embodiment. In the third embodiment, as in the first embodiment, the inner peripheral side boundary portion 5a and the outer peripheral side boundary portion 5b of the printing surface 5 are substantially line symmetric and have the same configuration. The boundary portion 5b will be described as a representative.
In the drawing, the outer peripheral side boundary portion 5b of the printing surface 5 has the same configuration as the first embodiment with respect to the first concave groove 5E, the first convex portion 5F, and the second concave groove 5G, and the second convex portion 5H. Is not formed.
In the present embodiment, since the aqueous coating liquid S discharged beyond the first convex portion 5F is relatively small, it flows into the second concave groove 5G and is dammed up and stored.
Also in this embodiment, the same effects as in the first embodiment can be obtained.

In the first to third embodiments described above, the bottom and top of the first concave grooves 5A and 5E, the second concave grooves 5C and 5G, the first convex portions 5B and 5F, and the second convex portions 5D and 5H are sharp. However, if this configuration is adopted, it is possible to prevent the air-borne coating liquid S from being easily filled into the concave groove and to prevent bubbles from being mixed. The cross-sectional shapes of the first concave grooves 5A and 5E, the second concave grooves 5C and 5G, the first convex portions 5B and 5F, and the second convex portions 5D and 5H are not limited to a substantially triangular shape, and any shape can be adopted.
In the first embodiment, the first and second grooves 5A and 5E and the first protrusions 5B and 5F and the second grooves 5C and 5G and the second protrusion 5D are formed at the inner and outer peripheral side boundaries 5a and 5b of the printing surface 5. Although it is composed of two sets of concave grooves and protrusions made of 5H, it may be composed of three or more sets. Or you may abbreviate | omit one of 2nd ditch | groove 5C, 5G and 2nd convex part 5D, 5H like a 2nd, 3rd Example. In short, the first concave grooves 5A, 5E and the first convex parts 5B, 5F are formed as the innermost concave grooves and convex portions, and other concave grooves are formed in the outer direction (inner peripheral side and outer peripheral side in the optical disc 1). And other convex portions (second concave grooves 5C, 5G and second convex portions 5D, 5H) may be provided to dam the coating liquid.
Further, in the case where any one of the other groove and the other convex portion is formed on the inner peripheral side and the outer peripheral side boundary portions 5a and 5b on the printing surface 5 of the substrate 1A, it is not necessary to have the same kind of configuration, and one boundary portion. Other convex grooves may be formed on the other boundary portion.
The present invention can be applied not only to compact discs such as optical discs but also to various coated objects including other disks, and can be applied to a receiving layer forming method and a coated object in which a coating film is applied and dried.

1 is a cross-sectional view of a main part of an optical disc according to a first embodiment of the present invention. FIG. 2 is an enlarged partial cross-sectional view illustrating an outer peripheral side boundary portion of a printing surface in a base portion of the optical disc illustrated in FIG. 1. It is a principal part perspective view which shows the application part of a receiving layer forming apparatus. It is a figure which shows the discharge outlet of each nozzle in an application means. It is a figure which shows the discharge outlet by the modification of each nozzle shown in FIG. It is the elements on larger scale which show the positional relationship of the nozzle and the printing surface of a board | substrate. It is a partial longitudinal cross-sectional view which shows the receiving layer formation process to a board | substrate, (a) is a figure which shows the board | substrate before apply | coating an aqueous coating liquid, (b) is a figure of the state which apply | coated the aqueous coating liquid, (c). FIG. 4 is a view of a substrate including a receiving layer after drying. It is the perspective view seen from the lower part which shows the application means and board | substrate by a modification. It is an enlarged partial sectional view similar to the substrate shown in FIG. 2 showing a second embodiment of the outer peripheral side boundary portion of the printing surface. It is an expanded partial sectional view similar to the board | substrate shown in FIG. 2 which shows the 3rd Example of the outer peripheral side boundary part of a printing surface.

Explanation of symbols

1 Optical disk (to be coated)
1A substrate (object to be coated)
2 Disc substrate 3 Information recording layer 3a Adhesive layer 4 Disc substrate (to be coated)
5 Printing surface (surface to be coated: surface of the material to be coated)
5A, 5E First concave groove (concave groove)
5B, 5F First convex part (convex part)
5C, 5G Second groove (other grooves)
5D, 5H Second convex part (other convex part)
5a Inner peripheral side boundary part 5b Outer peripheral side boundary part 5c Central application part 5i Flat part 6 Receiving layer 6a Inner peripheral side boundary area 6b Outer peripheral side boundary area 6c Central area 10 Receiving layer forming apparatus 11 Application part 16, 20 Nozzle part (application) means)
16a-16h, 20a-16h Nozzle S Aqueous coating solution (coating solution)
6A coating film

Claims (16)

In a receiving layer forming method of applying a coating liquid on the surface of an object to be coated to form a coating film, and drying the coating film to form a receiving layer,
In the surface of the coated object, a groove and a convex are provided in the boundary portion of the region where the receiving layer is formed toward the outer side of the receiving layer, and another groove and another convex are formed on the outer side. A method for forming a receiving layer, wherein at least one of them is formed.   The receiving layer forming method according to claim 1, wherein another concave groove and another convex portion are formed outside the convex portion.   The receiving layer forming method according to claim 2, wherein a height of the convex portion is equal to or higher than a height of the other convex portion.   The acceptance according to any one of claims 1 to 3, wherein the concave groove is formed to be depressed in a substantially vertical direction with respect to a surface of the object to be coated at a boundary with the convex portion located in an outer side direction thereof. Layer formation method.   The coated object is formed in a disc shape, and at least one of the concave groove and the convex portion and the other concave groove and the other convex portion is provided on the inner peripheral side and the outer peripheral side, respectively. The receiving layer formation method in any one of Claims 1 thru | or 4.   The receiving layer forming method according to claim 1, wherein the object to be coated is an optical disk.   The receiving layer forming method according to claim 1, wherein the coating solution is a water-based coating solution that contains a pigment and a binder and forms a porous ink receiving layer.   The receiving layer forming method according to claim 7, wherein the pigment is any one of alumina, silica, and silica-alumina composite particles.   The receiving layer forming method according to claim 1, wherein the coating solution is a water-based coating solution that contains a water-soluble polymer and forms a swollen ink receiving layer. In a coated object in which a coating liquid is applied to the surface of the coated object to form a coating film, and the coated film is dried to form a receiving layer.
In the surface of the coated object, a groove and a convex are provided in the boundary portion of the region where the receiving layer is formed toward the outer side of the receiving layer, and another groove and another convex are formed on the outer side. At least one of them,
An object to be coated, in which a receiving layer is formed in a region surrounded by the convex portions.   The article to be coated according to claim 10, wherein the other groove and the other protrusion are formed in the outer direction of the groove and the protrusion.   The article to be coated according to claim 11, wherein a height of the convex portion is equal to or higher than a height of the other convex portion.   13. The coated object is an optical disk, and the concave grooves and convex portions and at least one of the other concave grooves and other convex portions are provided on the inner peripheral side and the outer peripheral side, respectively. An article to be coated according to any one of the above.   The article to be coated according to claim 10, wherein the coating liquid is a water-based coating liquid that contains a pigment and a binder and forms a porous ink receiving layer.   The article to be coated according to claim 14, wherein the pigment is any one of alumina, silica, and silica-alumina composite particles. 14. The article to be coated according to claim 10, wherein the coating liquid is a water-based coating liquid that contains a water-soluble polymer and forms a swelling type ink receiving layer.

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