JP7057236B2 - Ink composition for laser marking, ink layer for laser marking, laminate, laser marking method - Google Patents

Description

The present invention relates to an ink composition for laser marking, an ink layer for laser marking, a laminate, and a laser marking method.

Various packaging materials such as beverage cans, beverage containers, food containers, and pharmaceutical packaging are printed or marked with variable traceability information such as production lot number, production date, expiration date of contents, and expiration date. Needed. As a marking method, it is known that the laser marking method is more effective in establishing traceability by preventing tampering because there is no peeling or erasure of printing or marking as compared with the hot stamping method and the inkjet method.

As an ink composition that can be used in the laser marking method, a laser marking ink composition containing a laser light absorber having an absorption band in a wavelength range such as YVO ₄ laser light (1064 nm) is disclosed (Patent Documents 1 to 1). 4).

Japanese Unexamined Patent Publication No. 2010-47681 Japanese Unexamined Patent Publication No. 2009-137261 Japanese Unexamined Patent Publication No. 2009-83185 Japanese Unexamined Patent Publication No. 2007-55110

On the other hand, UV laser light (355 nm) having a wavelength range (ultraviolet region) shorter than the wavelength range such as YVO ₄ laser light (1064 nm) as described above has less thermal stress due to laser light irradiation. It is expected as a next-generation laser marking type laser beam.

The laser marking ink composition disclosed in the above patent document has a certain laser printability (visibility) by irradiation with _YVO4 laser light or the like, but is a laser marking type laser marking ink using UV laser light. The composition had insufficient laser printability (visibility).

Further, the laser marking ink composition is required to have blocking resistance so that the printed surface (ink layer) and the non-printed surface of the ink composition do not adhere (block) in consideration of the productivity of the printed matter. .. In addition, the ink composition for laser marking has adhesiveness to the support film on the printed surface (ink layer), and the resin film is bonded to the printed surface (ink layer) via an adhesive or the like. An ink composition having laminating strength in a laminating processing method (also referred to as a dry laminating processing method) is eagerly desired.

As described above, the current situation is that an ink composition for laser marking having sufficient laser printability (visibility), blocking resistance, adhesiveness, and laminating strength has not yet been found.

The present invention has been made in view of the above circumstances, and provides an ink composition for laser marking having sufficient laser printability (visibility), blocking resistance, adhesiveness, and laminating strength. The purpose.

That is, the present invention contains a binder resin, a white pigment, and an organic solvent, the binder resin contains a polyurethane resin and a cellulose derivative, and the cellulose derivative is a lower acyl group substituted cellulose derivative and / or a lower alkyl substituted. The white pigment is a cellulose derivative, and relates to an ink composition for laser marking, characterized in that the white pigment is titanium oxide having an average particle size of 0.26 μm or less.

Further, in the laser marking ink composition of the present invention, the white pigment is preferably titanium oxide having an average particle size of 0.22 μm or more.

The present invention also relates to a laser marking ink layer, which is formed from the laser marking ink composition.

The present invention also relates to a laminate characterized in that a support film is provided on one side of the laser marking ink layer and a base material is provided on the other side of the ink layer.

The present invention also relates to a laser marking method comprising irradiating the laminated body with a laser beam.

The details of the action mechanism of the effect in the laser marking ink composition of the present invention are unknown, but it is presumed as follows. However, the present invention does not have to be construed as being limited to this mechanism of action.

The ink composition for laser marking of the present invention contains a binder resin, a white pigment, and an organic solvent, the binder resin contains a polyurethane resin and a cellulose derivative, and the cellulose derivative is a lower acyl group substituted cellulose derivative and /. Alternatively, it is a lower alkyl-substituted cellulose derivative, and the white pigment is titanium oxide having an average particle size of 0.26 μm or less. The smaller the average particle size of the titanium oxide, the larger the specific surface area. Therefore, the titanium oxide efficiently absorbs laser light having a short wavelength region (ultraviolet region) such as UV laser light (355 nm) and is contained in the ink layer. Since the binder resin around titanium oxide can be carbonized to develop color (discoloration), it is presumed that the laser marking ink composition of the present invention is excellent in laser printability (visibility). Further, in the laser marking ink composition of the present invention, the titanium oxide is blended with a binder resin containing a polyurethane resin and a cellulose derivative (lower acyl group substituted cellulose derivative and / or lower alkyl substituted cellulose derivative). , Has a good balance of blocking resistance, adhesiveness, and laminate strength.

Further, the present invention has good doctor cutting property when the laser marking ink composition is applied to a printing method such as gravure printing because the average particle size of the titanium oxide is 0.22 μm or more.

The ink composition for laser marking of the present invention contains a binder resin, a white pigment, and an organic solvent.

<Binder resin>
The binder resin of the present invention contains a polyurethane resin and a cellulose derivative, and the cellulose derivative is a lower acyl group substituted cellulose derivative and / or a lower alkyl substituted cellulose derivative.

The polyurethane resin is a resin having two or more urethane bonds in the molecule and can be used without particular limitation, and is obtained by reacting with, for example, a diisocyanate compound, a diol compound, a chain extender, and a reaction terminator (a reaction terminator). Examples thereof include polyurethane resin (obtained by reacting a chain extender and a reaction terminator with a urethane prepolymer obtained by reacting a diisocyanate compound and a diol compound). At least one type of polyurethane resin may be used, and two or more types may be used in combination.

Examples of the diisocyanate compound include aliphatic diisocyanate compounds such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; alicyclic diisocyanate compounds such as isophorone diisocyanate and hydrogenated xylylene diisocyanate; xylylene diisocyanate and α. , Α, α', α'-Aromatic aliphatic diisocyanate compounds such as tetramethylxylylene diisocyanate; Examples thereof include aromatic diisocyanate compounds such as toluylene diisocyanate and diphenylmethane diisocyanate. Among these, alicyclic or aromatic aliphatic diisocyanate compounds are preferable, and isophorone diisocyanate, α, α, α', are particularly preferable from the viewpoint that the reaction is easily controlled and the obtained polyurethane resin has a good balance of performance. α'-Tetramethylxylylene diisocyanate is preferred. At least one of the diisocyanate compounds may be used, and two or more of them may be used in combination.

Examples of the diol compound include polymer diols such as polyester diol compounds, polyether diol compounds, polycarbonate compounds, and polybutadiene glycol compounds. At least one type of diol compound may be used, and two or more types may be used in combination.

The number average molecular weight of the diol compound is preferably 400 or more, more preferably 1,000 or more, from the viewpoint of obtaining an ink layer for laser marking having good film characteristics. The number average molecular weight of the diol compound is preferably 10,000 or less, more preferably 6,000 or less, from the viewpoint of enhancing the reactivity with the diisocyanate compound.

Examples of the polyester diol compound include low molecular weight diol components (linear glycols such as ethylene glycol, 1,3-propanediol and 1,4-butanediol; 1,2-propanediol, neopentyl glycol and 3). -Branched glycols such as methyl-1,5-pentanediol and 2,4-diethyl-1,5-pentanediol; ether-based diols such as diethylene glycol and triethylene glycol) and dicarboxylic acid components (succinic acid and adipine). Examples thereof include those obtained by reacting saturated and unsaturated aliphatic dicarboxylic acids such as acid and maleic acid; aromatic dicarboxylic acids such as phthalic acid).

Examples of the polyether diol compound include a polyester diol compound obtained by ring-opening a cyclic ester compound (lactone, etc.), or a diol compound ((poly) alkylene glycol compound, bisphenol, etc.) and oxyalkylene (ethylene oxide, Examples thereof include a polyether diol compound obtained by double-adding (such as propylene oxide) and tetrahydrofuran.

The diol compound is preferably a polyester diol or a polyether diol from the viewpoint of various physical characteristics of the ink.

As the chain extender, a compound having two or more functional groups (amino group, hydroxyl group, etc.) capable of reacting with an isocyanate group in the molecule can be used. Examples of the compound containing two or more amino groups in the molecule include diamines having two primary amino groups (ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, hexamethylenediamine, isophoronediamine, etc.). ) Diamines having one primary amino group and one secondary amino group (2-ethylaminoethylamine, etc.)) Polyamines having two primary amino groups and one or more secondary amino groups (diethylenetriamine, triethylene) (Tetramine, etc.) and the like. Examples of the hydroxyl group-containing compound containing two or more hydroxyl groups in the molecule include low-molecular-weight diols (ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, etc.). Further, as a compound having two amino groups and one hydroxyl group in the molecule, for example, 1 mol of ethylene oxide is added to the above-mentioned diamines having two primary amino groups such as aminoethylethanolamine and aminopropylethanolamine. Things and the like can be mentioned. At least one type of chain extender may be used, and two or more types may be used in combination.

As the chain extender, a compound having three or more functional groups such as an amino group and a hydroxyl group can be used from the viewpoint of introducing a functional group such as a hydroxyl group or an amino group into the molecule of the polyurethane resin. Examples of the compound having three or more functional groups such as an amino group and a hydroxyl group include glycerin and aminoethylethanolamine.

As the reaction terminator, a compound having at least one functional group (amino group, hydroxyl group, etc.) capable of reacting with an isocyanate group in the molecule can be used, and specifically, monoalcohols (methanol, ethanol, etc.), Examples thereof include monoamines (n-butylamine, di-n-butylamine, etc.) and alkanolamines (monoethanolamine, ethylethanolamine, diethanolamine) having one amino group and one hydroxyl group in the molecule. Further, as the reaction terminator, the compound mentioned as the chain extender can also be used. The reaction terminator has been exemplified as an alkanolamine having one amino group and one hydroxyl group in the molecule and the chain extender from the viewpoint of introducing a functional group such as a hydroxyl group or an amino group into the molecule of the polyurethane resin. Diamines having two primary amino groups and low molecular weight diols can be used. At least one type of the reaction terminator may be used, and two or more types may be used in combination.

In the production of the urethane prepolymer obtained by reacting the diisocyanate compound with the diol compound, the equivalent ratio of NCO of the diisocyanate compound to OH of the diol compound (the equivalent of NCO of the diisocyanate compound / the equivalent of OH of the diol compound) is 1. The reaction is preferably 3 to 3, and more preferably 1.5 to 2.

The chain extender is preferably reacted with the remaining isocyanate group of the prepolymer in the range of about 0.5 to 0.95 equivalent. Further, it is preferable that the reaction terminator is reacted at a ratio of about 2 mol with 1 mol of the polyurethane resin after chain extension.

The weight average molecular weight of the polyurethane resin is preferably 5,000 to 50,000, more preferably 10,000 to 30,000. The weight average molecular weight of the present invention can be measured by a gel permeation chromatography (GPC) method. As an example, using Water2690 (manufactured by Waters) as a GPC device, PLgel 5μ as a column, and MIXED-D (manufactured by Polymer Laboratories) as a developing solvent, tetrahydrofuran, column temperature 25 ° C., flow velocity 1 ml / min, RI. Chromatography can be performed under the conditions of a detector, a sample injection concentration of 10 mg / ml, and an injection amount of 100 microliters, and the weight average molecular weight in terms of polystyrene can be obtained.

The polyurethane resin is preferably a polyurethane resin having a functional group such as a hydroxyl group or an amino group. As a method for obtaining a polyurethane resin having such a functional group, a method using the above-mentioned compound having three or more functional groups such as an amino group and a hydroxyl group as a chain extender, and the above-mentioned chain extender and the reaction terminator are used. A known method such as a method of reacting the diisocyanate compound at a molar ratio of less than 1.0 times that of the diol compound can be adopted without using the compound. When the polyurethane resin has an amino group, the amine value is preferably in the range of 0.1 to 10 mgKOH / g. The amine value means an amine value per 1 g of solid content, and a potentiometric titration method (for example, COMTITE (AUTO TITTOR COM-900, BURET B-900, TISTATIONK-900), Hiranuma) using a 0.1 N hydrochloric acid aqueous solution is used. After measurement by Sangyo Co., Ltd.), it can be measured by converting it to the equivalent of potassium hydroxide.

The cellulose derivative is a lower acyl group substituted cellulose derivative and / or a lower alkyl substituted cellulose derivative. Examples of the lower acyl group substituted cellulose derivative include cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate. Examples of the lower alkyl-substituted cellulose derivative include methyl cellulose and ethyl cellulose. At least one of the cellulose derivatives may be used, and two or more of them may be used in combination.

The weight average molecular weight of the cellulose derivative is preferably 10,000 to 500,000, more preferably 10,000 to 300,000.

In the binder resin, the mass ratio of the polyurethane resin to the cellulose derivative (polyurethane resin / cellulose derivative) is preferably 60/40 or more, preferably 75/25, from the viewpoint of improving the adhesiveness to the support film. The above is more preferable, 80/20 or more is further preferable, and 95/5 or less is preferable from the viewpoint of improving the laminating strength.

The total ratio of the polyurethane resin and the cellulose derivative in the binder resin is
It is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and further preferably 98% by mass or more.

As the binder resin, other resins other than the polyurethane resin and the cellulose derivative may be used as long as the performance of the ink composition is not deteriorated. Examples of the other resin include polyamide resins, vinyl chloride / vinyl acetate copolymers, (meth) acrylic copolymers, butyral resins and the like.

<White pigment>
The white pigment of the present invention is titanium oxide having an average particle size of 0.26 μm or less.

The titanium oxide preferably has an average particle size of 0.25 μm or less from the viewpoint of improving laser printability (visibility). Further, the titanium oxide preferably has an average particle diameter of 0.22 μm or more, and more preferably 0.23 μm or more, from the viewpoint of improving the doctor's breakability. The average particle size can be obtained by a method of statistically processing an image taken by a transmission electron microscope. As the method, for example, the method disclosed in JP-A-2003-26856, JP-A-2006-341628 and the like may be adopted. Further, the titanium oxide may be an anatase type, a rutile type, or a titanium sol. At least one type of titanium oxide may be used, and two or more types may be used in combination.

The titanium oxide may be titanium oxide coated with an inorganic compound from the viewpoint of improving the dispersibility in the laser marking ink composition. Examples of the inorganic compound include oxides of metals such as aluminum, silicic acid, zirconium, zinc, tin, antimony, and cerium, or hydroxides. Among these, oxides of aluminum, silicic acid, zirconium, zinc or hydrous oxides are suitable. Specifically, examples of the metal oxide or hydrous oxide include sodium aluminate, aluminum sulfate, aluminum chloride, sodium silicate, hydrous silicic acid, zirconium sulfate, zirconium chloride, zinc sulfate, zinc chloride, and tin sulfate. , Tin chloride, antimony chloride, cerium chloride, cerium sulfate and the like.

As a method for coating the titanium oxide with the inorganic compound, a known method can be applied. For example, the metal oxide or the hydrous oxide is added to the titanium oxide slurry and stirred to adjust the pH and the like. The method can be mentioned. As the method, for example, the methods disclosed in JP-A-55-10428, JP-A-55-154317, JP-A-4-81470, and the like may be adopted.

When titanium oxide coated with the inorganic compound is used as the titanium oxide, the proportion of titanium oxide (TiO ₂ ) in the titanium oxide coated with the inorganic compound is preferably 90% by mass or more. It is more preferably 93% by mass or more, and further preferably 95% by mass or more. Examples of such commercially available titanium oxide products include trade names "JR-403", "JR-405", "JR-600A", and "JR-605" (all manufactured by TAYCA CORPORATION). The ratio of titanium oxide (TiO ₂ ) in the titanium oxide coated with the inorganic compound is usually such that the metal contained in the inorganic compound is mixed with the metal oxide (for example, Al ₂ O ₃ , SiO ₂ , ZrO). Calculated from the ratio of the mass converted to ( ₂ , etc.) and the total mass of TiO ₂ in the titanium oxide particles (Japanese Patent Laid-Open No. 55-10428, JP-A-11-171541, JP-A-2008-069193). See publications, etc.).

<Organic solvent>
The organic solvent of the present invention can be used without particular limitation as long as it dissolves or disperses the above components. Examples of the organic solvent include alcohol-based organic solvents such as methanol, ethanol, n-propanol, isopropanol and butanol; ketone-based organic solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; methyl acetate, ethyl acetate, propyl acetate and acetic acid. Ester-based organic solvents such as butyl; aliphatic hydrocarbon-based organic solvents such as n-hexane, n-heptane, and n-octane; alicyclic hydrocarbon-based solvents such as cyclohexane, methylcyclohexane, ethylcyclohexane, cycloheptane, and cyclooctane. Organic solvent; Examples thereof include aromatic hydrocarbon-based organic solvents such as toluene and xylene. At least one type of the organic solvent may be used, and two or more types may be used in combination in consideration of the solubility and drying property of the binder resin.

As the organic solvent, the alcohol-based organic solvent and / or the ester-based organic solvent shall be used from the viewpoint of applying the laser marking ink composition of the present invention to the flexographic printing ink composition or the gravure printing ink composition. Is preferable. In this case, the proportion of the alcohol-based organic solvent and / or the ester-based organic solvent in the organic solvent is preferably 90% by mass or more, and more preferably 95% by mass or more.

Hereinafter, the ratio of each component contained in the laser marking ink composition of the present invention will be described.

In the solid content (non-emission component) in the laser marking ink composition of the present invention, the proportion of the binder resin is preferably 10% by mass or more, preferably 10% by mass or more, from the viewpoint of the film strength of the ink layer and the coating suitability. It is more preferably mass% or more, preferably 40 mass% or less, and more preferably 30 mass% or less.

In the solid content (non-emission component) in the laser marking ink composition of the present invention, the proportion of the white pigment is 60% by mass or more from the viewpoint of enhancing the hiding power of the ink layer and improving the laser printability. Is more preferable, 70% by mass or more is more preferable, and 90% by mass or less is preferable, and 85% by mass or less is more preferable.

The ratio of the solvent is preferably 30 to 80% by mass, more preferably 40 to 70% by mass in the laser marking ink composition.

The ink composition for laser marking of the present invention includes metal chelate cross-linking agents such as titanium chelate and zirconium chelate; waxes such as polyolefin wax and paraffin wax; saturated fatty acid amides and unsaturated fatty acids, as long as the performance of the ink composition is not deteriorated. Fatty acid amides such as fatty acid amides and modified fatty acid amides; hard resins such as dimer acid-based resins, rosin-based resins, maleic acid-based resins, petroleum resins, terpene resins, ketone resins, dammer resins, copal resins, chlorinated polypropylene, and polypropylene oxides. A leveling agent, a surfactant, a plasticizer and the like can be arbitrarily added.

<Preparation method of ink composition for laser marking>
The method for preparing the ink composition for laser marking of the present invention is not particularly limited, and for example, the above components are added in order or at the same time to a bead mill, a ball mill, a sand mill, an attritor, a roll mill, a pearl mill, and a high speed. It can be prepared by mixing with a stirrer, a paint conditioner, or the like.

<Laser marking ink layer>
The laser marking ink layer of the present invention is formed from the laser marking ink composition. Specifically, it is an ink layer (printing film) obtained by applying (printing) the laser marking ink composition on a support film (or a substrate described later) described later and drying the ink composition. As the printing method, offset printing, sheet-fed printing, digital printing (inkprint method, toner method), flexographic printing, and gravure printing can be used, and flexographic printing and gravure printing are preferable. The drying may be provided with a step of evaporating the solvent with hot air or the like. As the printing conditions by the printing machine, conventionally known conditions can be appropriately adopted.

The thickness of the laser marking ink layer is usually preferably 0.1 to 20 μm, more preferably 0.2 to 15 μm.

<Laminated body>
In the laminate of the present invention, a support film is provided on one side of the laser marking ink layer, and a base material is provided on the other side of the ink layer.

As the support film, any plastic film can be used without limitation. Examples of the plastic film include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polycycloolefins, polyacetates, polyethersulfones, polycarbonates, polyamides, polyimides, (meth) acrylic polymers, polyvinyl chlorides, and polyvinylidene chlorides. Plastic films such as polystyrene, polyvinyl alcohol, polyarylate, polyphenylene sulfide, cellulose-based polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, and polyolefins such as polyethylene, polypropylene, and ethylene / propylene copolymers. Can be mentioned.

The surface of the support film may be surface-treated by corona treatment, plasma treatment, or the like from the viewpoint of improving printability (wetting property and adhesiveness) of the laser marking ink composition, and a gas barrier. From the viewpoint of improving the properties and the like, a transparent vapor-deposited layer of an inorganic oxide or the like may be laminated.

The base material may be metal, paper, or plastic. Examples of the metal include a metal thin film such as aluminum foil, and examples of the paper include art paper, woodfree paper, Japanese paper, synthetic paper and the like. Examples of the plastic include the plastic film and the like.

Further, the base material is preferably a material capable of forming a sealant layer that can be laminated, from the viewpoint that the laminate of the present invention can be used as a packaging container. As a method for forming the sealant layer, for example, 1) an anchor coating agent (for example, titanium-based, urethane-based, imine-based, polybutadiene, etc.) is applied to the ink layer (printing surface) on the support film, if necessary. Extruded laminating process in which a hot-melt polymer (for example, low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, etc.) is laminated in a thin film, and adhered to the ink layer (printing surface) on the support film. Examples thereof include a dry laminating process in which an unstretched plastic film (for example, unstretched polyethylene film, unstretched polypropylene film, etc.) is laminated after applying an agent (for example, urethane-based, isocyanate-based, etc.).

Further, a functional layer having various functions may be provided between the ink layer and the base material. Examples of the functional layer include aluminum foil, aluminum-deposited polyester film, inorganic oxide-deposited polyester film, and specially modified ethylene vinyl alcohol film for the purpose of improving the gas barrier property of the laminated body. Further, as the functional layer, for example, a stretched nylon film or the like is mentioned for the purpose of improving the strength reinforcement of the laminated body, and further, for the purpose of further improving the functions of both of the above, for example, a nylon-based metaxylylenediamine. Examples include resin films.

<Laser marking method>
The laser marking method of the present invention is a method of irradiating the laminated body with a laser beam. Examples of the laser light include carbon dioxide laser light (10600 nm), YVO ₄ laser light (1064 nm), UV laser light (355 nm), and among these, short wavelength regions such as UV laser light (355 nm). A laser beam having an ultraviolet region) is preferable.

Irradiation of the laser beam is usually performed from the support film side. However, when the base material transmits the laser light, the irradiation of the laser light may be performed from the base material side. Further, the irradiation conditions of the laser beam may be appropriately set in consideration of the printing quality such as the equipment to be used and the printability of the printed matter.

Hereinafter, the present invention will be described with reference to Examples and the like, but the present invention is not limited thereto.

<Manufacturing example 1>
<Manufacturing of polyurethane resin varnish>
In a four-necked flask equipped with a stirrer, a cooling tube and a nitrogen gas introduction tube, 100 parts by mass of poly (3-methyl-1,5-pentylene adipate) diol having a number average molecular weight of 1,000 and 44.4 parts of isophorone diisocyanate. A mass portion was charged and reacted at 100 to 105 ° C. for 6 hours while introducing nitrogen gas. After allowing to cool to near room temperature, 379.4 parts by mass of ethyl acetate and 94.9 parts by mass of isopropyl alcohol were added, and then 7.1 parts by mass of isophoronediamine and 4.2 parts by mass of aminoethylethanolamine were added to carry out a chain extension reaction. Then, 2.4 parts by mass of ethylenediamine was further added to terminate the reaction to obtain a polyurethane resin varnish (solid content: 25% by mass, weight average molecular weight of polyurethane resin about 12,000, amine value 9.3 mgKOH / g). rice field.

<Manufacturing example 2>
<Manufacturing of varnish of lower acyl group substituted cellulose derivative>
25 parts by mass of cellulose acetate propionate (trade name "CAP-482-0.5", manufactured by Eastman Chemical Company) is dissolved in a mixed organic solvent consisting of 56 parts by mass of ethyl acetate and 19 parts by mass of isopropyl alcohol to be solid. A varnish of a lower acyl group substituted cellulose derivative having a content of 25% by mass was obtained.

<Comparative manufacturing example 1>
<Manufacturing of vinyl chloride / vinyl acetate copolymer varnish>
Vinyl Chloride Vinyl Acetate Copolymer (trade name "Solvine TA5R", manufactured by Nissin Chemical Industry Co., Ltd.) is dissolved in a mixed organic solvent consisting of 56 parts by mass of ethyl acetate and 19 parts by mass of isopropyl alcohol to have a solid content of 25. A varnish of a mass% vinyl chloride / vinyl acetate copolymer was obtained.

<Comparative manufacturing example 2>
<Manufacturing of (meth) acrylic copolymer varnish>
25 parts by mass of a (meth) acrylic copolymer (trade name "Dianal BR-87", manufactured by Mitsubishi Chemical Co., Ltd.) is dissolved in a mixed organic solvent consisting of 56 parts by mass of ethyl acetate and 19 parts by mass of isopropyl alcohol to be solid. A varnish of a (meth) acrylic copolymer having a mass of 25% by mass was obtained.

<Comparative manufacturing example 3>
<Manufacturing of nitrocellulose (nitrated cotton) varnish>
35.7 parts by mass of nitrocellulose (trade name "SS1 / 8S", manufactured by KOREA CNC, solid content 70% by mass) is dissolved in a mixed solvent consisting of 60 parts by mass of ethyl acetate and 4.3 parts by mass of isopropyl alcohol. A nitrocellulose varnish having a solid content of 25% by mass was obtained.

<Examples 1 to 3 and Comparative Examples 1 to 6>
<Preparation of ink composition for laser marking>
Each material was kneaded with a paint conditioner according to the formulation shown in Table 1 to prepare ink compositions for laser marking of Examples 1 to 3 and Comparative Examples 1 to 6. The numerical values shown in Table 1 are parts by mass.

<Creation of a laminate (printed matter) for evaluation of laser printability and evaluation of laminate strength>
The laser marking ink compositions of Examples 1 to 3 and Comparative Examples 1 to 6 obtained above were applied to a polypropylene film (trade name "P-2161", manufactured by Toyobo Co., Ltd.) and a bar coater (wire diameter 0). .10 mm) was applied, dried with a dryer, and then held at 60 ° C. for 12 hours to form an ink layer (thickness: about 1 μm). On the obtained ink layer, a polyether adhesive composition (trade name "A-969V", manufactured by Mitsui Chemicals Polyurethane Co., Ltd.) / curing agent (trade name "A-5", manufactured by Mitsui Chemicals Polyurethane Co., Ltd.) = After laminating a sealant film (trade name "P-1128 # 25", manufactured by Toyobo Co., Ltd.) via 3/1 (mass ratio), the sealant film was held at 40 ° C. for 48 hours to evaluate laser printability. A laminate (printed matter) for evaluation of the laminate strength was obtained.

<Creation of printed matter for evaluation of blocking resistance and adhesiveness>
The laser marking ink compositions of Examples 1 to 3 and Comparative Examples 1 to 6 obtained above were applied to a polypropylene film (trade name "P-2161", manufactured by Toyobo Co., Ltd.) and a bar coater (wire diameter 0). .10 mm) was applied, dried with a dryer, and then held at 60 ° C. for 12 hours to form an ink layer (thickness: about 1 μm) to obtain a printed matter.

The following evaluations were made on the laser marking ink composition or the laminate (printed matter) obtained in the above Examples and Comparative Examples. The evaluation results are shown in Table 1.

<Evaluation of laser printability (visibility)>
Using the UV laser marker MD-U1000C manufactured by Keyence, laser light is irradiated from the polypropylene film side of the laminate (printed matter) for evaluation of laser printability obtained above to print (printing condition: laser power). 20%, pulse period 40 kHz, scan speed 5,000 mm / min, number of prints once), and laser printability (visibility) were evaluated in the following three stages.
A: Easy to see the printed part B: Not clear, but the printed part can be confirmed C: Difficult to see visually

<Evaluation of blocking resistance>
For the evaluation of blocking resistance, the printed surface and the non-printed surface of the printed matter for evaluation of blocking resistance obtained above are combined, squeezed with a vise, left at 40 ° C. for 12 hours, and then peeled off by hand to form a printing film. The degree of peeling and the strength of peeling resistance were evaluated in the following three stages.
A: There is no peeling of the printed film and no peeling resistance is felt. B: There is no peeling of the printed film, but peeling resistance is felt. C: There is peeling of the printed film and peeling resistance is strongly felt.

<Evaluation of adhesiveness>
The evaluation of adhesiveness is based on the degree to which the printed matter peels off from the film when the cellophane tape is attached to the ink layer (printed matter) in the printed matter for evaluation of adhesiveness obtained above and rapidly peeled off. It was evaluated in the following three stages.
A: No peeling of the print film from the film B: There is peeling of the print film from the film, but the peeling area is less than 30% C: There is peeling of the printing film from the film, and the peeling area is 30% or more. Is

<Evaluation of laminate strength>
The evaluation of the laminate strength was carried out by evaluating the peel strength at a peeling speed of 300 mm / min in the following three stages in the laminate (printed matter) for evaluating the laminate strength obtained above.
A: Strength is 200 g / 15 mm or more B: Strength is 100 g / 15 mm or more and less than 200 g / 15 mm C: Strength is less than 100 g / 15 mm

<Evaluation of doctor cutability>
For the evaluation of the doctor's breakability, the laser marking ink compositions according to Examples 1 to 3 and Comparative Examples 1 to 6 obtained above were printed on a gravure printing machine (Toshiba 5-color machine) at a printing speed of 100 m. The state of the printed surface at / min was evaluated in the following three stages.
A: Plate fog, betasuji, two-to-two stains (linear stains), etc. do not occur and are at a level that can be actually used. Possible level C: Plate fog, betasji, two-to-two stains (linear stains), etc. occur a lot and are not at the actual usable level

In Table 1,
The polyurethane resin is the polyurethane resin varnish of Production Example 1;
The lower acyl group substituted cellulose derivative is the varnish of the lower acyl group substituted cellulose derivative of Production Example 2.
The vinyl chloride / vinyl acetate copolymer is a varnish of the vinyl chloride / vinyl acetate copolymer of Comparative Production Example 1.
The (meth) acrylic copolymer is a varnish of the (meth) acrylic copolymer of Comparative Production Example 2.
Nitrocellulose is a varnish of nitrocellulose of Comparative Production Example 3;
Titanium oxide (average particle size is 0.25 μm) is rutile-type titanium oxide (trade name “JR-600A”, manufactured by TAYCA);
Titanium oxide (average particle size 0.23 μm) is rutile-type titanium oxide;
Titanium oxide (average particle size 0.21 μm) is rutile-type titanium oxide (trade name “JR-405”, manufactured by TAYCA);
Titanium oxide (average particle size is 0.27 μm) is rutile-type titanium oxide (trade name “JR-600E”, manufactured by TAYCA);
Titanium oxide (average particle size is 0.30 μm) is rutile-type titanium oxide (trade name “JR-301”, manufactured by TAYCA);
The organic solvent is a mixed solvent of ethyl acetate / isopropyl alcohol (mass ratio: 4/1);

In the above four evaluations excluding the doctor's breakability evaluation, it was judged that the ink composition having one or more evaluations of B is unsuitable for actual use.

Claims (7)

Contains binder resin, white pigments, and organic solvents
The binder resin contains a polyurethane resin and a cellulose derivative, and contains
The cellulose derivative is a lower acyl group substituted cellulose derivative and / or a lower alkyl substituted cellulose derivative.
The white pigment is an ink composition for laser marking, which is titanium oxide having an average particle size of 0.26 μm or less. The ink composition for laser marking according to claim 1, wherein the white pigment is titanium oxide having an average particle size of 0.22 μm or more. The ink composition for laser marking according to claim 1 or 2, wherein the mass ratio of the polyurethane resin to the cellulose derivative (polyurethane resin / cellulose derivative) is 60/40 to 95/5. The laser marking ink composition according to any one of claims 1 to 3 , wherein the ink composition is a gravure printing ink composition or a flexographic printing ink composition. An ink layer for laser marking, which is formed from the ink composition for laser marking according to any one of claims 1 to 4 . A laminate characterized in that a support film is provided on one side of the laser marking ink layer according to claim 5 , and a base material is provided on the other side of the ink layer. A laser marking method comprising irradiating the laminate according to claim 6 with a laser beam.