JP5021974B2 - Laminated film - Google Patents

Description

  The present invention relates to a laminated film, and more particularly to a laminated film having a high reflectance.

  In a liquid crystal display, a backlight system in which light is applied from the side or the back of the display has been adopted. A reflective film is installed on the back as viewed from the display surface in both the side and back side. This reflective film is required to have high light reflectivity, high diffusibility, and film flatness (hereinafter sometimes referred to as flatness). This requirement becomes stronger as the liquid crystal screen size increases.

Conventionally, a plastic film has been used as a substrate for a reflector, but in the prior art, the layer responsible for reflection was a reflective layer arranged in the middle.
In general, a cold cathode tube is used as a light applied from the side or the back. Since ultraviolet rays are generated from this cold cathode tube, when the usage time of the liquid crystal display is extended, the film used as the reflector is deteriorated by the ultraviolet rays, and the reflectance is lowered, that is, the brightness of the screen is lowered.

  In recent years, there has been a strong demand for larger screens and higher brightness of liquid crystal displays, which increases the amount of heat emitted from the light source, and demands for flatness such as suppressing film deformation due to heat and less distortion of the film. Is getting stronger. On the other hand, in order to increase the brightness, a film containing more voids has been studied.

JP 63-62104 A Japanese Patent Publication No. 8-16175 JP 2004-50479 A JP 2004-330727 A JP 2005-125700 A

  However, conventional films are insufficient in resistance to ultraviolet rays and heat, and the film itself is easily deformed greatly due to crushing or deformation of voids in the film, resulting in insufficient flatness. It was.

  An object of the present invention is to solve the problems of the prior art, has practically sufficient visible light region reflection performance, can be stably formed, and deterioration (yellowing) due to ultraviolet rays is suppressed. An object of the present invention is to provide a laminated film that can be suitably used as a reflector substrate of a liquid crystal display that is less deformed by heat and has excellent flatness.

That is, the present invention is a laminated film comprising a reflective layer A having a void volume ratio of 30 to 80% and a support layer B in contact with the void volume ratio of 0 to 25%, and the laminated film is at 85 ° C. for 30 minutes. The heat shrinkage rate of each of the two directions perpendicular to each other is 0.5% or less, the reflection layer A is formed on at least one surface layer of the laminated film, and the reflectance when measured from the reflection layer A side is 90% or more In addition, the laminated film is characterized in that the knurling is provided with a knurling of 5 to 50 μm.

  According to the present invention, practically sufficient visible light region reflection performance can be obtained, a stable film can be formed, deterioration due to ultraviolet rays (yellowing) is suppressed, deformation due to heat is small, and flatness is excellent. In addition, it is possible to provide a laminated film that can be suitably used as a reflector substrate for liquid crystal displays.

Hereinafter, the present invention will be described in detail.
The laminated film of the present invention comprises a reflective layer A and a support layer B that contacts and supports the reflective layer A.

[Reflection layer A]
The reflective layer A is a layer having a void volume ratio of 30 to 80%, and this layer is composed of a thermoplastic resin composition. The void volume ratio is generated when, for example, the interface between the incompatible resin or the inorganic particles and the thermoplastic resin contained in the thermoplastic resin composition is reduced, and a void is generated when the interface is stretched. .

[Thermoplastic resin]
As the thermoplastic resin, polyester is preferably used.
As the polyester, for example, known polyesters such as polyethylene terephthalate and polyethylene naphthalate can be used. From the viewpoint of obtaining high heat resistance, a copolymerized polyethylene terephthalate containing a naphthalenedicarboxylic acid component as a copolymer component in an amount of 3 to 20 mol%, more preferably 4 to 18 mol%, particularly preferably 8 to 15 mol% is preferable. If the naphthalenedicarboxylic acid component is less than 3 mol%, the film-forming property may not be secured, which is not preferable. If it exceeds 20 mol%, the heat resistance and the film-forming property may be deteriorated.

  As the polyester, it is preferable to use a polyester that does not substantially contain antimony. “Substantially not contained” means that the concentration of antimony in the polyester is 20 ppm or less, preferably 15 ppm or less, more preferably 10 ppm or less. When polyester containing antimony is used at a low level, black streaks may be generated on the film, which is not preferable because the film appearance is remarkably impaired.

  In order to obtain a polyester substantially free of antimony, the polyester may be polymerized using a catalyst other than the antimony compound. As a catalyst used at this time, it is preferable to use any one of a manganese (Mn) compound, a titanium (Ti) compound, and a germanium (Ge) compound. As the titanium compound, for example, titanium tetrabutoxide and titanium acetate can be used. Examples of the germanium compound include amorphous germanium oxide, fine crystalline germanium oxide, a solution in which germanium oxide is dissolved in glycol in the presence of an alkali metal, an alkaline earth metal, or a compound thereof, and germanium oxide is dissolved in water. A solution can be used.

[Incompatible resin]
When a polyester and a polyester and an incompatible resin are used in combination as the thermoplastic resin composition, examples of the incompatible resin include polyolefin and polystyrene. Specifically, for example, poly-3-methylbutene-1, poly- 4-methylpentene-1, polyethylene, polypropylene, polyvinyl-t-butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polyfluorostyrene, cellulose acetate cellulose propionate, polychloro Trifluoroethylene can be used, and particularly preferably polypropylene and polymethylpentene are used. Since these polypropylenes and polymethylpentenes are highly transparent, they are optimal because they can suppress light absorption and improve reflectance.

  When using incompatible resin, it is 5-40 weight% per 100 weight% of polyester compositions of the reflection layer A, Preferably it is 8-30 weight%, Most preferably, it is used 10-25 weight%. When the content exceeds 40% by weight in the reflective layer A, the film is very apt to break and the productivity is inferior. On the other hand, if the content as a void-generating substance is less than 5% by weight, sufficient void formation is not achieved, and the resulting film has low reflectivity or inferior resistance to ultraviolet rays. .

[Inorganic particles]
When polyester and inorganic particles are used in combination as the thermoplastic resin composition, the inorganic particles have an average particle size of 0.3 to 5.0 μm, preferably 0.4 to 4.0 μm, more preferably 0.5 to Inorganic particles of 3.0 μm are used. If the average particle size is less than 0.3 μm, aggregation is likely to occur, and if it exceeds 5.0 μm, on the other hand, it may lead to film breakage. Inorganic particles are used in an amount of, for example, 31 to 60% by weight, preferably 35 to 55% by weight, and more preferably 37 to 50% by weight per 100% by weight of the polyester composition of the reflective layer A. If it is less than 31% by weight, the reflectance is lowered, and deterioration due to ultraviolet rays becomes severe. On the other hand, if it exceeds 60% by weight, the film is easily broken, which is not preferable.

  As the inorganic particles, it is preferable to use a white pigment from the viewpoint of obtaining high reflection performance. As the white pigment, for example, titanium oxide, barium sulfate, calcium carbonate, silicon dioxide particles, preferably barium sulfate particles are used. The barium sulfate particles may be either plate-like or spherical. Particularly good reflectance can be obtained by using particles of barium sulfate.

  When titanium oxide particles are used as the inorganic particles, rutile titanium oxide particles are preferably used. When the rutile type titanium oxide particles are used, the yellowing after the light is irradiated to the polyester film for a long time is less than that when the anatase type titanium oxide particles are used, and the change of the color difference can be suppressed. When the rutile-type titanium oxide particles are surface-treated with a fatty acid such as stearic acid and / or a derivative thereof, the dispersibility can be improved, and a film with particularly high gloss can be obtained. More preferable.

  In addition, when using the particle | grains of a rutile type titanium oxide, it is preferable to perform a particle size adjustment and coarse particle removal using a refinement | purification process, before adding to polyester. As industrial means of the purification process, for example, a jet mill or a ball mill can be applied as a pulverizing means, and as a classification means, for example, dry or wet centrifugation can be applied. These means may be purified stepwise by combining two or more.

As a method of incorporating the inorganic particles into the polyester, it is preferable to take any of the following methods.
(A) A method of adding before transesterification or esterification reaction at the time of polyester synthesis or adding before the start of polycondensation reaction.
(A) A method of adding to polyester and melt-kneading.
(C) A method of producing master pellets to which a large amount of inert particles are added in the method (a) or (b) above, and kneading these with a polyester not containing an additive to contain a predetermined amount of additive.
(D) A method of using the master pellet of (c) as it is.

In addition, when using the method added at the time of the polyester synthesis | combination of said (a), it is preferable to add to a reaction system as a slurry disperse | distributed to glycol in the titanium oxide particle.
In particular, it is preferable to take the above method (c) or (d).

  In the present invention, it is preferable to filter the molten polymer by using a nonwoven fabric type filter having an average opening of 10 to 100 μm, preferably an average opening of 20 to 50 μm made of a stainless steel fine wire having a wire diameter of 15 μm or less as a filter during film formation. . By performing this filtration, it is possible to obtain a film with few coarse foreign matters by suppressing aggregation of particles that are generally agglomerated and become coarse agglomerated particles.

[Support layer B]
For the support layer B, a thermoplastic resin can be used. When a polyester composition is used for the reflective layer A, it is preferable to use a polyester for the support layer B from the viewpoint of increasing the adhesion to the reflective layer A. The polyester of the support layer B may be the same polyester as that used for the reflective layer A, or may be a different polyester. The polyester composition of the support layer B preferably contains inorganic particles, preferably 0.1 to 25% by weight, more preferably 1 to 20% by weight, and particularly preferably 2 to 15% by weight. When the content is less than 0.1% by weight, sufficient slipperiness cannot be obtained, which is not preferable. When the content exceeds 25% by weight, the strength as the support layer B that supports the reflective layer A cannot be maintained, and the film This is not preferable because it may lead to breakage.

  The average particle diameter of the inorganic particles is preferably 0.1 to 5.0 μm, preferably 0.3 to 4 μm, and more preferably 0.5 to 4 μm. If the average particle size is less than 0.1 μm, the particles are likely to aggregate. On the other hand, if the average particle size exceeds 5.0 μm, coarse protrusions are formed, leading to film breakage.

[Knurling]
Knurling of the laminated film of the present invention can be imparted in the production process or processing process of the laminated film. When this knurling is provided, when the laminated film is wound and stored as a roll, or when the laminated films that have been cut are stacked and stored, the deterioration of the flatness of the laminated film is suppressed and good flatness is maintained. be able to. In particular, the effect of suppressing deformation of a laminate film that is easily deformed, such as a laminate film containing many voids (voids) in the film and a laminate film using a copolymerized polyester for the purpose of improving stretchability, is great.

  In order to impart knurling to the laminated film, for example, a method in which a roll surface made of metal or the like is subjected to uneven processing is pressed against the laminated film to form a valley on the laminated film surface. When the concavo-convex processing is performed, the laminated film and the roll surface may be at room temperature, or may be at a temperature not lower than the glass transition point (Tg) and not higher than the melting point (Tm) of the polymer constituting the laminated film. Adjustment is made so that the difference between peaks and valleys formed on the laminated film is 5 to 50 μm, preferably 7 to 40 μm, and more preferably 9 to 30 μm. If the difference between the valleys and valleys is less than 5 μm, the effect of floating the film is very small, and deterioration of the flatness of the laminated film cannot be suppressed. On the other hand, when it exceeds 50 μm, the handling property of the laminated film may be deteriorated.

  The position for imparting knurling is preferably within 100 mm, more preferably within 80 mm from the end of the laminated film from the viewpoint of maintaining high production efficiency. The application of knurling is effective for stacking and storing laminated films, but there is no factor that causes deformation at the stage of using one sheet at a time. It can be used as a laminated film without any.

[Additive]
You may mix | blend a fluorescent whitening agent with the laminated | multilayer film of this invention. When the fluorescent whitening agent is blended, the concentration of the reflective layer A with respect to the polyester composition or the polyester of the support layer B is, for example, in the range of 0.005 to 0.2% by weight, preferably 0.01 to 0.1% by weight. It is good to mix with. If it is less than 0.005% by weight, the reflectance in the wavelength region near 350 nm is not sufficient, so it is not preferable to add it. If it exceeds 0.2% by weight, a characteristic color of the fluorescent whitening agent appears. Therefore, it is not preferable.
As the fluorescent brightening agent, for example, OB-1 (manufactured by Eastman), Uvitex-MD (manufactured by Ciba Geigy), or JP-Conc (manufactured by Nippon Chemical Industry Co., Ltd.) can be used.

The thickness ratio of the reflective layer A is preferably 40 to 90, more preferably 50 to 85 with respect to the total thickness 100 of the reflective layer A and the support layer B of the laminated film. If it is less than 40, the reflectance may be inferior, which is not preferable, and if it exceeds 90, it is not preferable from the viewpoint of stretchability.
The white reflective film of the present invention may be a laminate in which other layers are further laminated in order to impart other functions to one side or both sides. Examples of other layers herein include a transparent polyester resin layer, a metal thin film, a hard coat layer, and an ink receiving layer.

[Production method]
Hereinafter, as an example of a method for producing the laminated film of the present invention, a method for producing a laminated film made of polyester having the structure of the reflective layer A / support layer B will be described. The stretching may be a sequential biaxial stretching method or a simultaneous biaxial stretching method, but here, a manufacturing method by the sequential biaxial stretching method will be described.

  First, a laminated unstretched sheet is produced by simultaneous multilayer extrusion using a feed block of polyester melted from a die. That is, the polyester melt composing the reflective layer A and the polyester melt composing the support layer B are laminated so as to be the reflective layer A / support layer B using a feed block, and are spread on a die and extruded. To obtain a laminated unstretched sheet. At this time, the polymer laminated by the feed block maintains the laminated form.

  The laminated unstretched sheet extruded from the die is cooled and solidified by a casting drum to form a laminated unstretched film. This laminated unstretched film is heated by roll heating, infrared heating or the like and stretched in the longitudinal direction to obtain a longitudinally stretched film. This stretching is preferably performed by utilizing the difference in peripheral speed between two or more rolls. The stretching temperature is preferably a temperature equal to or higher than the glass transition point (Tg) of the polyester, and more preferably a temperature higher by Tg to 70 ° C. The draw ratio is preferably 2.2 to 4.0 times, more preferably 2.3 to 3.9 times in the machine direction, although it depends on the required characteristics of the application. If it is less than 2.2 times, the thickness unevenness of the film is deteriorated and a good film cannot be obtained, and if it exceeds 4.0 times, breakage tends to occur during film formation, which is not preferable.

  Subsequently, the film after longitudinal stretching is subjected to lateral stretching, heat setting, and thermal relaxation in order to form a biaxially oriented film. These processes are performed while the film is running. The transverse stretching process starts from a temperature higher than the glass transition point (Tg) of the polyester. And it is performed while raising the temperature to (5 to 70) ° C. higher than Tg. Although the temperature rise in the transverse stretching process may be continuous or stepwise (sequential), the temperature is usually raised sequentially. For example, the transverse stretching zone of the tenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium having a predetermined temperature for each zone. The transverse stretching ratio is preferably 2.5 to 4.5 times, more preferably 2.8 to 3.9 times, although it depends on the required characteristics of this application. If it is less than 2.5 times, the thickness unevenness of the film is deteriorated and a good film cannot be obtained, and if it exceeds 4.5 times, breakage tends to occur during film formation.

  The film after transverse stretching is preferably heat treated at a constant width or a width reduction of 10% or less at a temperature (Tm-20 to 100) while holding both ends to reduce the thermal shrinkage. When the heat treatment is performed at a temperature higher than this, the flatness of the laminated film is deteriorated and the thickness unevenness is increased, which is not preferable. On the other hand, if the heat treatment temperature is lower than (Tm-80) ° C., the thermal shrinkage rate may increase. Moreover, in order to adjust the heat shrinkage in the region of (Tm-20 to 100) ° C. or lower in the process of returning the film temperature to room temperature after heat setting, both ends of the laminated film being gripped are cut off in the longitudinal direction of the film. The take-up speed can be adjusted and relaxed in the vertical direction. As a means for relaxing, the speed of the roll group on the tenter exit side is adjusted. As the rate of relaxation, the speed of the roll group is reduced with respect to the film line speed of the tenter, preferably 0.1 to 1.5%, more preferably 0.2 to 1.2%, particularly preferably 0.3. A rate reduction of ˜1.0% is performed to relax the film (this value is referred to as “relaxation rate”) and adjust the rate of heat shrinkage in the machine direction by controlling the relaxation rate. Further, the width of the film in the horizontal direction can be reduced in the process until both ends are cut off, so that a film having a desired heat shrinkage rate can be obtained.

  The thickness of the laminated film after biaxial stretching is preferably 25 to 350 μm, more preferably 40 to 320 μm, and particularly preferably 50 to 300 μm. If the thickness is less than 25 μm, the reflectance decreases, which is not preferable. If the thickness exceeds 350 μm, the increase in reflectance cannot be expected even if the thickness is further increased.

  The laminated film of the present invention thus obtained can have a flatness of 3 mm or less and a hue change dE * due to ultraviolet rays of 10 or less. Further, the heat shrinkage rate at 85 ° C. can be 0.5% or less, more preferably 0.4% or less, and particularly preferably 0.3% or less in two orthogonal directions. The reflectance of at least one of the surfaces can be 90% or more, more preferably 93% or more, particularly preferably 96% or more in terms of the average reflectance at a wavelength of 400 to 700 nm. An average reflectance of less than 90% is not preferable because sufficient screen brightness cannot be obtained.

Hereinafter, the present invention will be described in detail by way of examples. Each characteristic value was measured by the following method.
(1) Film thickness A film sample was measured for 10-point thickness with an electric micrometer (K-402B manufactured by Anritsu), and the average value was taken as the thickness of the film.

(2) Thickness of each layer A sample was cut into a triangle, fixed in an embedded capsule, and then embedded in an epoxy resin. And after making the cross section parallel to the vertical direction into a thin film slice with a microtome (ULTRACUT-S), the embedded sample was observed and photographed using an optical microscope, and the thickness ratio of each layer was measured from the photograph. The thickness of each layer was calculated from the thickness.

(3) Reflectance An integrating sphere is attached to a spectrophotometer (Shimadzu Corporation UV-3101PC), and the reflectance when BaSO ₄ white plate is 100% is measured over 400 to 700 nm. From the obtained chart, the interval is 2 nm. The reflectance was read. When the film was composed of two layers of reflective layer A / support layer B, the measurement was performed from the reflective layer A side.

(4) Stretchability The film was stretched 2.5 to 3.4 times in the longitudinal direction and 3.5 to 3.7 times in the transverse direction to form a film, and it was observed whether it could be stably formed. Evaluation was made according to the following criteria.
○: Stable film formation over 1 hour ×: Cutting occurs within 1 hour and stable film formation is not possible

(5) Thermal shrinkage rate The film was held in an oven set at 85 ° C. for 30 minutes in an unstrained state, the distance between the gauge points before and after the heat treatment was measured, and the thermal shrinkage rate (85 ° C. thermal shrinkage rate) according to the following formula: ) Was calculated.
Thermal contraction rate (%) = ((L ₀ −L) / L ₀ ) × 100
L ₀ : Distance between gauge points before heat treatment L: Distance between gauge points after heat treatment

(6) Glass transition point (Tg), melting point (Tm)
Using a differential scanning calorimeter (TA Instruments 2100 DSC), the measurement was performed at a heating rate of 20 m / min.

(7) Deterioration by ultraviolet rays (evaluation of light resistance)
With a xenon lamp irradiation (SUNTEST CPS +), the color change before and after the panel temperature was 60 ° C. and the irradiation time was 300 hours. When the film was composed of two layers of reflective layer A / support layer B, the measurement was performed by irradiating from the reflective layer A side.
Measure the initial film hue (L1 *, a1 *, b1 *) and the film hue after irradiation (L2 *, a2 *, b2 *) with a color difference meter (Nippon Denka SZS-Σ90 COLOR MEASURING SYSTEM). The following criteria were used to evaluate the hue change dE * represented by the following formula.
dE * = {(L1 * -L2 *) 2 + (a1 * -a2 *) 2 + (b1 * -b2 *) 2} 1/2
○: dE * ≦ 10
Δ: 10 <dE * ≦ 15
×: 15 <dE *

(8) Flatness (Evaluation of flatness)
Cut the film into 30 cm squares and place on a flat plate. Remove curl curl from samples taken from film rolls. The amount of lift (mm) from the flat plate of the film was measured.

(9) Void volume ratio After isolating only the reflective layer A, after obtaining the density with an Anton Paar vibration digital density meter DMA4500, the film of the reflective layer A is melted to obtain the density, and the following formula Calculated.
Void volume ratio (%) = 100-100 × (density before melting) / (density after melting)

(10) Knurling height Using a profile micrometer VF-7500 manufactured by Keyence Corporation, the difference between the peaks and valleys was measured, and an average value of five irregularities was used.

[Example 1]
132 parts by weight of dimethyl terephthalate, 23 parts by weight of dimethyl 2,6-naphthalenedicarboxylate (12 mol% based on the acid component of the polyester), 96 parts by weight of ethylene glycol, 3.0 parts by weight of diethylene glycol, 0.05 weight of manganese acetate And 0.012 parts by weight of lithium acetate were charged into a rectification column and a flask equipped with a distillation condenser, and heated to 150 to 235 ° C. with stirring to distill methanol to conduct a transesterification reaction. After the methanol was distilled off, 0.03 part by weight of trimethyl phosphate and 0.04 part by weight of germanium dioxide were added, and the reaction product was transferred to the reactor. Subsequently, while stirring, the pressure in the reactor was gradually reduced to 0.5 mmHg and the temperature was raised to 290 ° C. to carry out a polycondensation reaction. This polyester resin was used for the reflective layer A and the support layer B, and inert particles shown in Table 1 were added. Supplying to two extruders each heated to 285 ° C., using a two-layer feed block apparatus in which the reflection layer A polymer and the support layer B polymer are A / B in the reflection layer A and the support layer B. The sheet was merged and formed into a sheet from a die while maintaining the laminated state. Further, an unstretched film obtained by cooling and solidifying the sheet with a cooling drum having a surface temperature of 25 ° C. was heated at the described temperature, stretched in the longitudinal direction (longitudinal direction), and cooled by a roll group at 25 ° C. Subsequently, the film was stretched in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 120 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, the film is heat-set in the tenter at the temperature shown in Table 2, and is subjected to longitudinal relaxation and lateral width insertion under the conditions shown in Table 2, cooled to room temperature, and heated with a knurling roll heated to 160 ° C. A knurling shown in Table 2 is applied at a position 20 mm from the end, and rolled into a 6-inch diameter tube at a tension of 250 N / m and a contact pressure of 250 N / m at a speed of 200 m / min. Got a roll. The knurling Yamatani difference was adjusted by the contact pressure of the knurling roll. Table 2 shows the evaluation results of the films collected from the obtained film rolls.

[Examples 2 to 12, Comparative Example 11 ]
The addition amount shown in Table 1, inorganic particles, and the acid component amount of polyester were changed, and a laminated film composed of the reflective layer A / support layer B was produced and evaluated under the film forming conditions shown in Table 2.

[Comparative Examples 1 to 10]
Except for changing the conditions as described in Tables 1 and 2, a laminated film of a reflective layer A / support layer B or a single layer film was prepared and evaluated in the same manner as in Example 1. In some comparative examples, samples could not be collected due to film breakage during film formation.

  The laminated film of the present invention has a high reflectance of light and suppresses deterioration against ultraviolet rays, and is used for various reflectors, especially a reflector for a liquid crystal display, a back sheet for a solar cell, and a reflector for an internally illuminated signboard. It can be used optimally. In addition, when using as a reflecting plate, it is preferable to use a surface with a high void rate as a reflecting surface.

  Other uses include paper substitution, ie cards, labels, stickers, home delivery slips, video printer paper, inkjets, barcode printer paper, posters, maps, dust-free paper, display boards, white boards, thermal transfer, offset It can also be used as a substrate for receiving sheets used for various printing records such as printing, telephone cards and IC cards.

Claims (2)

A laminated film comprising a reflective layer A having a void volume ratio of 30 to 80% and a support layer B in contact with the void volume ratio of 0 to 25%, and the laminated film has a heat shrinkage rate of 85 ° C. for 30 minutes. The two orthogonal directions are 0.5% or less, the reflection layer A is formed on at least one surface layer of the laminated film, and the reflectance when measured from the reflection layer A side is 90% or more. A laminated film comprising a knurling having a difference of 5 to 50 μm.   The roll of the laminated film of Claim 1.