JP4418420B2 - Thermal transfer image receiving sheet - Google Patents

Description

  The present invention relates to a thermal transfer image receiving sheet, and more particularly to a thermal transfer image receiving sheet having improved durability and capable of obtaining a sufficient print density.

  A thermal transfer recording system is widely used as a simple and clear recording system. This recording method forms an image by thermally transferring an image from the colored transfer layer to the surface of the thermal transfer image-receiving sheet by applying thermal energy from a thermal head or the like from the back of the thermal transfer sheet having the colored transfer layer on the substrate. It is. This transfer system is roughly classified into a sublimation transfer type and a heat melting type depending on the structure of the colored transfer layer.

  Further, since the thermal transfer recording method can form full-color images, its application is expanding as a full-color hard copy system for analog images such as digital images and video typified by computer graphics, DVDROM and others. For example, an output of a design such as CAD, an output of a medical measuring instrument such as a CT scan, an output of a face photo to an identification card (ID card), a credit card, or the like.

By the way, generally, when an image is formed by a sublimation transfer type thermal transfer sheet, durability such as weather resistance, scratch resistance, chemical resistance and the like is inferior to that of a normal printing ink. For this reason, various studies have been made on the binder resin of the receiving layer for the purpose of improving durability (for example, Patent Document 1).
JP 2003-154664 A

  However, even if a receiving layer capable of improving durability such as weather resistance, scratch resistance, and chemical resistance is obtained, such a receiving layer has a problem that the printing density is inferior. For this reason, there has been a demand for a thermal transfer image-receiving sheet that is excellent in durability and can obtain a sufficient printing density.

  As a result of intensive studies to solve the above problems, the present inventors have improved durability such as weather resistance, scratch resistance, chemical resistance, etc. by using a specific resin as a resin for forming the receiving layer. And it discovered that sufficient print density was obtained, and came to complete this invention.

  That is, the thermal transfer image-receiving sheet of the present invention is provided with a receiving layer on a substrate, and the receiving layer is a (meth) acrylate modified product of an acrylic polymer containing at least a repeating unit derived from glycidyl (meth) acrylate. And an epoxy resin. In the present invention, a (meth) acrylate modified product having an acrylic polymer that can be polymerized as a basic skeleton rather than a compound having a thermosetting resin as a basic skeleton is used as the crosslinkable compound.

The cross-linking of the (meth) acrylate-modified product in the present invention will be described taking the case of methacrylate as an example. As shown in the following reaction formula, side chains derived from glycidyl (meth) acrylate contained in an acrylic polymer (1 ) And methacrylate (2) are bonded to each other by the reaction between the glycidyl group at the end of the side chain (1) and the hydroxyl group in methacrylate (2). And the C = C group at the end of the side chain (3) of the (meth) acrylate modified product of the acrylic polymer synthesized by this bond is, for example, a photopolymerization initiator excited by light irradiation or the other side chain ( This (meth) acrylate modified product is crosslinked by polymerization reaction with the terminal C═C group of 3).

  In the present invention, the epoxy resin is preferably a bisphenol type epoxy resin. Furthermore, the ratio of the epoxy resin is preferably in the range of 95/5 to 60/40, expressed as a weight ratio A / E between the (meth) acrylate modified product A of the acrylic polymer and the epoxy resin E. When the ratio of the epoxy resin E is less than this range, there is a possibility that the effect of improving the dyeing property of the receiving layer and obtaining the color density cannot be sufficiently obtained by using the epoxy resin together. In addition, when the ratio of the (meth) acrylate modified product A is smaller than the above range, the tape-like thermal transfer image-receiving sheet is attached to a substrate that contacts the receiving layer when stored in a roll-like state. It is easy to cause so-called blocking. Furthermore, the scratch resistance, solvent resistance, and weather resistance of the receptor layer after crosslinking may be reduced, or the transparency may be reduced.

  In the present invention, a (meth) acrylate modified product having an acrylic polymer as a basic skeleton, which can be polymerized more than a compound having a thermosetting resin as a basic skeleton, is used as a crosslinkable compound. Therefore, blocking can be prevented by adjusting the molecular weight of the acrylic polymer as the basic skeleton.

  In the modified (meth) acrylate, the glycidyl group part of this repeating unit is bonded by changing the proportion of the repeating unit derived from glycidyl (meth) acrylate contained in the acrylic polymer that is the basic skeleton. The number of (meth) acrylate-modified products as the crosslinkable functional group can be arbitrarily changed. Therefore, it is possible to freely design the crosslink density of the receptor layer after crosslinking and the characteristics such as scratch resistance, chemical resistance and weather resistance of the receptor layer. Moreover, since the acrylic polymer, which is the basic skeleton of the (meth) acrylate modified product, has the highest level of transparency among ordinary resins, it is possible to improve the transparency of the receiving layer.

  The receiving layer in the present invention uses an epoxy resin in combination. The epoxy resin reacts with the hydroxyl group contained in the side chain (3) of the (meth) acrylate modified product by the heat generated by the light irradiation when the (meth) acrylate modified product is crosslinked by light irradiation, and is taken into the crosslinked product. Therefore, a stronger film can be formed by crosslinking the transferred receiving layer by light irradiation.

  In addition, as described above, each component of the (meth) acrylate modified product, the epoxy resin, and the photopolymerization initiator undergoes a cross-linking reaction to form a cross-linked product having a three-dimensional network structure and a large molecular weight. Therefore, the scratch resistance, solvent resistance, and weather resistance of the receptor layer after crosslinking can be improved. In addition, by changing the proportion of the epoxy resin, it is possible to adjust the sensitivity at the time of transfer of the receptor layer, adjust the adhesive strength of the receptor layer after transfer, and the crosslinking density of the receptor layer after crosslinking, It is also possible to freely design properties such as scratch resistance, solvent resistance, and weather resistance.

  When a bisphenol type epoxy resin is used as the epoxy resin, the bisphenol type epoxy resin contains a hydroxyl group in the molecule, and a stronger film can be formed by crosslinking the receptor layer.

  The thermal transfer image-receiving sheet of the present invention is provided with a receiving layer on a substrate, and the receiving layer is a (meth) acrylate modified product of an acrylic polymer containing at least a repeating unit derived from glycidyl (meth) acrylate, It consists of an epoxy resin.

  Among them, the acrylic polymer which is the basic skeleton of the (meth) acrylate modified product is composed only of glycidyl (meth) acrylate, that is, glycidyl acrylate homopolymer, glycidyl methacrylate homopolymer, glycidyl acrylate and glycidyl methacrylate copolymer. In addition, copolymers of glycidyl (meth) acrylate and other monomers can also be used.

  Other monomers that can form copolymers with glycidyl (meth) acrylate include, for example, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-butyl acrylate, cyclohexyl acrylate, 1 carbon number of alkyl groups such as octyl acrylate, dodecyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-propyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-butyl methacrylate, cyclohexyl methacrylate, octyl methacrylate, dodecyl methacrylate, etc. ~ 18 alkyl (meth) acrylate monomers , Styrene, one or more kinds of styrene-based monomers such as α- methyl styrene.

  When the acrylic polymer is a copolymer of glycidyl (meth) acrylate and another monomer, the content of glycidyl (meth) acrylate in the copolymer is preferably 50% by weight or more, particularly preferably 60% by weight or more. If the content ratio is less than this range, the number of (meth) acrylates as photocrosslinkable functional groups bonded to the glycidyl group portion of the copolymer is too small, and the crosslinking density of the receiving layer after crosslinking becomes insufficient. The scratch resistance, solvent resistance, and weather resistance of the receiving layer may be reduced.

  In addition, since an acrylic polymer may be formed only with glycidyl (meth) acrylate as demonstrated previously, the upper limit of the content rate is not limited to 100 weight%. However, in order to demonstrate the effect of freely designing the crosslink density of the receptor layer after crosslinking by copolymerizing with other monomers and the characteristics such as scratch resistance, solvent resistance, weather resistance, etc. The content ratio of glycidyl (meth) acrylate is preferably 95% by weight or less.

  As a polymer containing only glycidyl (meth) acrylate, the content ratio is set to 100% by weight, or other monomers are copolymerized to adjust the content ratio of glycidyl (meth) acrylate within a range of 50% by weight or more. Thus, the crosslink density of the receiving layer after cross-linking and the characteristics such as scratch resistance, solvent resistance, weather resistance, and the like can be freely designed. In the present invention, the (meth) acrylate modified product of an acrylic polymer used as a photocrosslinkable compound has a structure in which (meth) acrylate is bonded to the glycidyl group portion of the acrylic polymer. Specifically, in addition to a compound in which an acrylate is bonded to a plurality of glycidyl groups in one acrylic polymer, a compound in which a methacrylate is bonded, or a compound in which an acrylate and a methacrylate are mixed and bonded. .

  The acrylic polymer (meth) acrylate-modified product preferably has a glass transition temperature of 40 to 80 ° C, particularly 40 to 70 ° C. If the glass transition temperature is less than this range, the receptor layer tends to melt and soften even below the transfer temperature, and may be easily blocked due to, for example, a thermal history during storage. On the other hand, when the glass transition temperature exceeds this range, the print density during printing may be reduced.

  In addition, in order to adjust the glass transition temperature of the (meth) acrylate modified product of acrylic polymer, there are the following methods, and any one may be adopted. (1) The type of glycidyl (meth) acrylate constituting the acrylic polymer is changed. (2) When two types of glycidyl (meth) acrylate are copolymerized, the ratio is changed. (3) When other monomers are copolymerized, the type is changed or the ratio is changed. (4) The type of (meth) acrylate to be bonded to the glycidyl group is changed. (5) When two (meth) acrylates are mixed and bonded, the ratio is changed.

  As the (meth) acrylate modified product of the acrylic polymer, one of these various compounds may be used alone, or two or more thereof may be used in combination.

  The epoxy resin can generate an adhesive force to the transferred material in the receiving layer at the time of transfer, and can react with the (meth) acrylate modified product of the acrylic polymer by heat by light irradiation to form a crosslinked product. Any of various epoxy resins can be used, and a bisphenol type epoxy resin is particularly preferable. Since a bisphenol type epoxy resin contains a hydroxyl group in the molecule, it is possible to improve durability such as scratch resistance, solvent resistance, and weather resistance by crosslinking.

  It is preferable to use an epoxy resin having a number average molecular weight of 1,000 to 3,000, particularly 1,000 to 2,000. The receiving layer containing an epoxy resin having a number average molecular weight less than this range tends to easily generate an adhesive force even at a predetermined transfer temperature or lower. Therefore, for example, the receiving layer may be easily blocked due to a thermal history during storage. On the other hand, a receiving layer containing an epoxy resin having a number average molecular weight exceeding the above range may not be able to obtain a desired printing density during printing.

  In addition, it is preferable to use an epoxy resin having an epoxy resin equivalent of 1,500 g / eq or less, particularly 600 to 1,000 g / eq. Epoxy resins with epoxy equivalents exceeding this range have reduced reactivity with (meth) acrylate modified products of acrylic polymers and cannot form strong cross-linked products when irradiated with light, and the scratch resistance and solvent resistance of the receiving layer. Property and weather resistance may be reduced.

  Specific examples of the bisphenol-type epoxy resin that satisfies the above-mentioned conditions are not limited to these, but, for example, all of the Epicoat (registered trademark) series manufactured by Japan Epoxy Resin Co., Ltd. are bisphenol A-type epoxy resins. Epicoat 1002 (epoxy equivalent 600-700 g / eq, softening point: 78 ° C., number average molecular weight: about 1,060), Epicoat 1003 (epoxy equivalent 670-770 g / eq, softening point: 89 ° C., number average molecular weight: about 1 , 200), Epicoat 1055 (epoxy equivalent 800-900 g / eq, softening point: 93 ° C., number average molecular weight: about 1,350), Epicoat 1004 (epoxy equivalent 875-975 g / eq, softening point: 97 ° C., number average) Molecular weight: about 1,600), Epicoat 1004AF (epoxy equivalent 875- 75 g / eq, softening point: 97 ° C., a number average molecular weight: about 1,600), and the like.

  The receiving layer comprises a modified (meth) acrylate of an acrylic polymer A and an epoxy resin E at a weight ratio A / E = 95 / 5-60 / 40, particularly A / E = 90 / 10-70 / 30. It is preferable to include. If the weight ratio A / E is within this range, the blocking of the receptor layer is prevented and the effect of improving the scratch resistance, solvent resistance, weather resistance, heat resistance and transparency of the receptor layer after crosslinking is maintained. can do. In addition, a desired print density can be obtained during printing.

  As the photopolymerization initiator, any of various compounds capable of photopolymerizing an acrylic polymer (meth) acrylate-modified product by irradiation with ultraviolet light or the like and taking in an epoxy resin to form a crosslinked product can be used. For example, biacetylacetophenone, benzophenone, 4,4-bis (diethylamine) benzophenone, phenanthraquinone, azobisisobutylnitrile, Michler's ketone, benzylbenzoin, benzoin isobutyl ether, benzyldimethyl ketal, tetramethylthiuram sulfide, benzoyl peroxide , Di-tert-butyl peroxide, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1- (4-isopropylphenyl- - hydroxy-2-methylpropan-1-one, 2-chloro thioxanthone, methyl benzoyl Four mate like.

  The photopolymerization initiator is preferably contained in the receiving layer at a ratio of 1 to 10 parts by weight with respect to 100 parts by weight of the total amount of the (meth) acrylate modified product of the acrylic polymer and the epoxy resin.

  In the image formation, a release agent can be added to the receiving layer in order to prevent fusion between the sublimation transfer sheet having a colored layer and the receiving layer of the thermal transfer image receiving sheet. Examples of the release agent include silicone oil, fluorine-based surfactant, phosphate ester-based surfactant, and various waxes. You may use a mold release agent individually by 1 type or in combination of 2 or more types. Further, these release agents may not be added to the receiving layer but may be separately applied on the receiving layer.

  In addition to the above components, the receiving layer further includes a colorant for coloring the receiving layer, a dispersant for dispersing the pigment, a sensitizer, an ultraviolet absorber, a leveling agent, a viscoelasticity modifier, etc. These additives can be contained in any proportion.

  The thermal transfer image-receiving sheet of the present invention is produced by applying a coating liquid containing each of the above components and a solvent to one side of a substrate and drying it to form a receiving layer.

  As the substrate, various conventionally known materials, for example, various films such as polyester film, polypropylene film, aramid film, polycarbonate film, and materials having heat resistance such as fine paper, art paper, coated paper, cast coated paper, etc. Can be used. Further, a composite material in which a foam film and a non-foam film are provided on one side or both sides of the core material using these as a core material may be used.

  The substrate preferably has a thickness of 3 to 100 μm from the viewpoint of transportability in a thermal transfer printer.

On the surface of the base material on which the receiving layer is formed, a layer having a release property or conductivity such as a wax as a main component may be formed, and the receiving layer may be provided on the release layer. Good. Further, an intermediate layer may be provided on the receiving layer side. Furthermore, the surface of the substrate opposite to the surface on which the receiving layer is formed is composed of a silicone resin, a fluororesin, a nitrocellulose resin, a silicone-modified urethane resin, and a silicone-modified acrylic resin, and a lubricant is dispersed as necessary. A heat resistant protective layer may be formed.
(Preparation of thermal transfer image receiving sheet)

[Example 1]
17 parts by weight of a methacrylate-modified copolymer of glycidyl methacrylate and methyl methacrylate as a (meth) acrylate-modified product of acrylic polymer (GMM / MMA-MAA, glycidyl methacrylate content: 90% by weight, glass transition temperature: 46 ° C.) As a photopolymerization initiator, 3 parts by weight of a bisphenol A type epoxy resin (Epicoat 1003 manufactured by Japan Epoxy Resin Co., Ltd., epoxy equivalent: 670 to 770 g / eq, softening point 89 ° C., number average molecular weight: about 1,200) 1 part by weight of 1-hydroxycyclohexyl phenyl ketone (Irgacure (registered trademark) 184 manufactured by Ciba Specialty Chemicals) and 79 parts by weight of methyl ethyl ketone were mixed and adjusted to prepare a coating solution for the receiving layer.

As a base material, a non-stretched polypropylene film (Toyobo Co., Ltd. pyrene film-CTP1128, thickness 30 μm) is coated on a 165 μm thick A-2 coat made by Mitsubishi Paper Industries Co., Ltd. Used in an amount of 5 g / m ² and laminated by dry lamination.

Further, a coating liquid having the above composition was applied onto the unstretched polyester film and dried, and a receiving layer was formed so as to be 5.0 g / cm ² after drying. The weight ratio A / E between the (meth) acrylate modified product A of the acrylic polymer and the epoxy resin E in the receiving layer was 85/15.

[Example 2]
Example except that the same amount of methacrylate modified glycidyl methacrylate homopolymer (GMA-MAA, glass transition temperature: 41 ° C.) was used as the (meth) acrylate modified acryl polymer instead of GMA / MMA-MAA In the same manner as in Example 1, a thermal transfer image receiving sheet was prepared.

[Examples 3 to 7]
As the epoxy resin, in place of Epicoat 1003, a thermal transfer image-receiving sheet was prepared in the same manner as in Example 1 except that the same amount of each of the bisphenol A type epoxy resins described below manufactured by Japan Epoxy Resin Co., Ltd. was used. did.
Example 3: Epicoat 1001 (epoxy equivalent: 450-500 g / eq, softening point: 64 ° C., number average molecular weight: about 900)
Example 4: Epicoat 1002 (epoxy equivalent: 600-700 g / eq, softening point: 78 ° C., number average molecular weight: about 1,060)
Example 5: Epicoat 1004 (epoxy equivalent: 875-975 g / eq, softening point: 97 ° C., number average molecular weight: about 1,600)
Example 6: Epicoat 1007 (epoxy equivalent: 1,750 to 2,200 g / eq, softening point: 128 ° C., number average molecular weight: about 2,900)
Example 7: Epicoat 1009 (epoxy equivalent: 2,400-3,300 g / eq, softening point: none, number average molecular weight: about 3,750)

[Example 8]
A thermal transfer image-receiving sheet was produced in the same manner as in Example 1 except that the same amount of cresol novolac type epoxy resin (Araldite (registered trademark) ECN-1280 manufactured by Bantico) was used instead of Epicoat 1003 as the epoxy resin.

[Examples 9 to 12]
A thermal transfer image-receiving sheet was produced in the same manner as in Example 1 except that the amounts used of GMA / MMA-MAA and Epicoat 1003 and the weight ratio A / E between the two were set to the values shown in Table 1, respectively.

[Comparative Example 1]
A thermal transfer image-receiving sheet was prepared in the same manner as in Example 1 except that the same amount of a cresol novolac polyglycidyl ether methacrylate compound (CNEPX-MAA, glass transition temperature: 40 ° C.) was used as an epoxy acrylate instead of GMA / MMA-MAA. Produced.

[Comparative Example 2]
A thermal transfer image receiving sheet was prepared in the same manner as in Example 1 except that 20 parts by weight of GMA / MMA-MAA was used and Epicoat 1003 was not used.

[Comparative Examples 3 to 4]
A thermal transfer image-receiving sheet was prepared in the same manner as in Example 1 except that the amounts used of GMA / MMA-MAA and Epicoat 1003 and the weight ratio A / E between the two were set to the values shown in Table 2, respectively.

(Abrasion resistance test)
The thermal transfer image-receiving sheets prepared in Examples 1 to 12 and Comparative Examples 1 and 2 were cut into 100 × 140 mm, and a sublimation thermal transfer ribbon for the printer was set in a sublimation thermal transfer printer CVP-G7 manufactured by Sony Corporation. A face photograph was printed on the receiving layer surface of each thermal transfer image receiving sheet.

Next, using an ultraviolet irradiation device (LH-6 manufactured by Fusion Ubui Systems Japan), the sample was evaluated by irradiation with ultraviolet rays so as to obtain an integrated light amount of 1,500 mj / cm ² to obtain a sample for evaluation.

The receiving layer surface of the obtained sample was rubbed 100 times under a condition of a pressure of 450 g / cm ² using a clock meter type friction tester equipped with a non-woven fabric (Bemcot M-1 manufactured by Asahi Kasei Co., Ltd.) as a friction element. The scratch resistance was evaluated according to the following criteria. The obtained results are shown in Tables 3, 4 and 5.
○: No change was observed in the image. Very good scratch resistance.
Δ: A level where the receiving layer was slightly removed but was practical. Good scratch resistance.
X: The image disappeared. Poor scratch resistance.

(Solvent resistance test)
A sample similar to the sample for evaluation used in the scratch resistance test was prepared, and a non-woven fabric (Bemcot M-1 manufactured by Asahi Kasei Co., Ltd.) impregnated with acetone or dimethyl sulfoxide (DMSO) was attached as a friction element. Using a meter-type friction tester, rubbing was performed 100 times under the condition of a pressure of 450 g / cm ² and the solvent resistance was evaluated according to the following criteria. The obtained results are shown in Tables 3, 4 and 5.
○: No change was observed in the image. Very good solvent resistance.
Δ: A level where the receiving layer was slightly removed but was practical. Good solvent resistance.
X: The image disappeared. Poor solvent resistance.

(Print density)
The thermal transfer image-receiving sheets prepared in Examples 1 to 12 and Comparative Examples 1 and 2 were cut into 100 × 140 mm, and a sublimation thermal transfer ribbon for the printer was set in a sublimation thermal transfer printer CVP-G7 manufactured by Sony Corporation. Then, gradation printing of 32 gradations was performed on the image receiving sheet, and the printing density of the high density gradation part (32 gradation part) was measured with a Macbeth densitometer (Macbeth RD914). The evaluation criteria are as follows, and the measurement results are shown in Table 3, Table 4, and Table 5.
○: 2.2 or more.
(Triangle | delta): Less than 2.0-2.2.
X: Less than 2.0.
-: Blocking occurs during printing and evaluation is impossible.

Claims (3)

  In the thermal transfer image-receiving sheet having a receiving layer provided on a base material, the receiving layer comprises at least a (meth) acrylate modified product of an acrylic polymer containing a repeating unit derived from glycidyl (meth) acrylate, and an epoxy resin A thermal transfer image-receiving sheet.   2. The thermal transfer image receiving sheet according to claim 1, wherein the epoxy resin is a bisphenol type epoxy resin. The thermal transfer image-receiving sheet according to claim 1 or 2, wherein the weight ratio of the acrylic polymer (meth) acrylate modified product A and the epoxy resin E is A / E = 95/5 to 60/40.