Sheet for inkjet printing

Abstract

Provided is a sheet for inkjet printing, wherein an ink-receiving layer is in direct contact with one surface of a substrate layer or with an easy-adhesion layer formed on one surface of the substrate layer, the other surface of the substrate layer has, in this order, an adhesive layer and a release liner in a laminated structure. The release liner has a silicone-based release agent layer on the contact surface contacting the adhesive layer. The ink-receiving layer is a cured layer of a composition for forming the ink-receiving layer, contains an energy ray-curable compound (A), a silicone-based leveling agent (B), and a filler (C). The energy ray-curable compound (A) is an ester of a polyol compound and (meth)acrylic acid. The water contact angle of the ink-receiving layer is 80° or less, and the difference in refractive index [(X)-(Y)] between the refractive index (X) of the ink-receiving layer and the refractive index (Y) of the layer directly in contact with the ink-receiving layer is greater than -0.03.

Description

Inkjet printing sheets

[0001] The present invention relates to a sheet for inkjet printing.

[0002] Inkjet recording is a method of recording by ejecting ink droplets and depositing the ink onto an inkjet printing medium to form dots. Inkjet recording is rapidly gaining popularity due to its advantages, such as the ease with which high-quality full-color images can be obtained, its ease of high speed, and its low running costs. Furthermore, with the spread of inkjet recording, various inkjet printing media have also been proposed. For example, an inkjet printing sheet has been proposed that has a layered structure including, in this order, an ink-receiving layer, a substrate layer, an adhesive layer, and a release liner, and that can be attached to glass or the like to be used as indoor or outdoor decoration.

[0003] In this specification, the term "ink receiving layer" refers to a layer to which ink for inkjet printing is applied and which has the function of fixing the printed portion of the applied ink for inkjet printing.

[0004] In recent years, various ink-receiving layers have been proposed, including, for example, an ink-receiving layer containing a vinyl chloride-vinyl acetate copolymer (see Patent Document 1, etc.) and an ink-receiving layer containing polyvinyl butyral (see Patent Document 2, etc.).

[0005] JP 2019-172877 A JP 2007-130776 A

[0006] The present inventors encountered the problem of print unevenness during research and development on ink-receiving layers. Specifically, when ink droplets are ejected onto an ink-receiving layer using an inkjet recording method to form dots, the dots do not properly interfere with each other (do not coalesce) in some areas of the ink-receiving layer, resulting in uneven interference between the dots within the ink-receiving layer, making the print in those areas lighter than normal. When the entire printed area formed on the ink-receiving layer was observed, print unevenness could be visually recognized. After extensive research to solve this problem, the present inventors discovered that attempts to eliminate the print unevenness resulted in a decrease in print density throughout the entire printed area formed on the ink-receiving layer. Thus, it was difficult to simultaneously suppress print unevenness and ensure print density in the ink-receiving layer.

[0007] Furthermore, in the course of further research and development into ink-receiving layers, the present inventors also encountered the problem that optical interference patterns may appear in the ink-receiving layer itself before printing. Inkjet printing sheets are often used by attaching them to a transparent plate such as glass. Therefore, transparency is required in the unprinted areas of inkjet printing sheets. Therefore, if such optical interference patterns appear in the ink-receiving layer, there is a concern that transparency may be impaired, and therefore improvement in this regard is necessary.

[0008] The present invention has been made in consideration of such problems, and its object is to provide an inkjet printing sheet that can suppress variations in interference between dots within the ink-receiving layer surface, thereby suppressing printing unevenness, while ensuring sufficient print density, and also suppressing optical interference patterns in the ink-receiving layer itself before printing.

[0009] As a result of extensive research into solving the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by (1) making the ink-receiving layer a cured layer of a composition for forming an ink-receiving layer that contains a specific energy ray-curable compound, a silicone-based leveling agent, and a filler, (2) making the water contact angle of the ink-receiving layer 80° or less, and (3) adjusting the difference in refractive index between the ink-receiving layer and the layer that is in direct contact with the ink-receiving layer to be within a specific range.

[0010] That is, the present invention relates to the following items [1] to [7]: [1] A sheet for inkjet printing, wherein the sheet has a laminated structure in which an ink-receiving layer is in direct contact with one surface of a base layer or an easy-adhesion layer formed on one surface of the base layer, and has a pressure-sensitive adhesive layer and a release liner, in this order, on the other surface of the base layer, the release liner has a silicone-based release agent layer on the surface that comes into contact with the pressure-sensitive adhesive layer, the ink-receiving layer is a cured layer of a composition for forming an ink-receiving layer, the cured layer containing an energy ray-curable compound (A), a silicone-based leveling agent (B), and a filler (C), the energy ray-curable compound (A) is an ester of a polyol compound and (meth)acrylic acid, the ink-receiving layer has a water contact angle of 80° or less, and the difference [(X) - (Y)] between the refractive index (X) of the ink-receiving layer and the refractive index (Y) of a layer that is in direct contact with the ink-receiving layer is greater than -0.03. [2] The inkjet printing sheet according to [1] above, wherein the layer in direct contact with the ink-receiving layer is formed from a polyurethane resin or polyethylene terephthalate. [3] The inkjet printing sheet according to [2] above, wherein the filler (C) is one or more selected from the group consisting of alumina particles and zirconia particles. [4] The inkjet printing sheet according to any one of [1] to [3] above, wherein the inkjet printing sheet is in the form of a rolled body or a wound body wound around a core material. [5] A method of use, comprising using the inkjet printing sheet according to any one of [1] to [4] above to form a printed section on the ink-receiving layer of the inkjet printing sheet according to any one of [1] to [4] above, using an inkjet printing ink. [6] A method for producing a printed matter, comprising a step of forming a printed section on the ink-receiving layer of the inkjet printing sheet according to any one of [1] to [4] above, using an inkjet printing ink. [7] A printed matter having a printed section printed with an inkjet printing ink on the ink-receiving layer of the inkjet printing sheet according to any one of [1] to [4] above.

[0011] According to the present invention, it is possible to provide an inkjet printing sheet that can suppress variations in interference between dots within the ink-receiving layer surface, thereby suppressing printing unevenness, while still ensuring sufficient print density, and also suppressing optical interference patterns in the ink-receiving layer itself before printing.

[0012] Fig. 1 is a schematic cross-sectional view showing an example of an inkjet printing sheet according to one embodiment of the present invention. Fig. 2 is a schematic cross-sectional view showing another example of an inkjet printing sheet according to one embodiment of the present invention. Fig. 3 is a schematic cross-sectional view showing the stacked state of two inkjet printing sheets in the pretreatment carried out before evaluations (2) and (3) in the examples. Fig. 4 is a drawing-substitute photograph showing an example of an optical interference pattern that occurs in the ink-receiving layer itself before printing (Evaluation 1 of Evaluation (5) in the examples).

[0013] As used herein, the term "active ingredient (solid content)" refers to the components contained in the target composition, excluding diluting solvents such as water and organic solvents. In this specification, (meth)acrylate refers to both methacrylate and acrylate, and the same applies to other similar terms. For example, (meth)acrylic acid refers to both methacrylic acid and acrylic acid, and (meth)acryloyl group refers to both methacryloyl and acryloyl groups. In this specification, the lower and upper limits of preferred numerical ranges (e.g., ranges of content, etc.) described in stages can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferred upper limit (60)" to form "10 to 60." In this specification, the numerical values ​​in the examples are values ​​that can be used as upper or lower limits.

[0014] [Embodiments of the Inkjet Printing Sheet of the Present Invention] The inkjet printing sheet of the present invention has a laminated structure in which an ink-receiving layer is in direct contact with one surface of a base layer or an easy-adhesion layer formed on one surface of the base layer, and a pressure-sensitive adhesive layer and a release liner are provided, in this order, on the other surface of the base layer. The release liner has a silicone-based release agent layer on the surface that contacts the pressure-sensitive adhesive layer. The ink-receiving layer is a cured layer of an ink-receiving layer-forming composition containing an energy ray-curable compound (A), a silicone-based leveling agent (B), and a filler (C). The energy ray-curable compound (A) is an ester of a polyol compound and (meth)acrylic acid. The water contact angle of the ink-receiving layer is 80° or less. The difference [(X) - (Y)] between the refractive index (X) of the ink-receiving layer and the refractive index (Y) of the layer directly in contact with the ink-receiving layer is greater than -0.03.

[0015] The present inventors first conducted extensive research into how to ensure sufficient print density while suppressing print unevenness by suppressing variations in interference between dots within the ink-receiving layer surface. As a result, they discovered that incorporating a silicone-based leveling agent into the ink-receiving layer can suppress variations in interference between dots within the ink-receiving layer surface and thereby suppress print unevenness. However, they found that suppressing print unevenness by incorporating a silicone-based leveling agent into the ink-receiving layer reduces the print density of the entire printed area formed on the ink-receiving layer. To address this issue, the present inventors conducted further extensive research. As a result, they discovered that by forming the ink-receiving layer as a cured layer of an ink-receiving layer-forming composition containing the specific energy ray-curable compound (A) and silicone-based leveling agent (B) and adjusting the water contact angle of the ink-receiving layer to 80° or less, it is possible to ensure sufficient print density while suppressing print unevenness.

[0016] Although the mechanism by which the above-described effect is achieved is unclear, it is speculated as follows. Specifically, by forming an inkjet printing sheet having the above-described laminated structure into a rolled body or a wound body wrapped around a core, minute amounts of silicone components migrate to the surface of the ink-receiving layer when the ink-receiving layer comes into contact with the back surface of the release liner. As a result, the surface free energy of the ink-receiving layer is partially reduced. In areas where the surface free energy is partially reduced, the wettability of dots to the ink-receiving layer is reduced compared to areas where the surface free energy is not reduced, resulting in less interference between dots than usual. This phenomenon inhibits the proper interference between dots that should occur, resulting in a pale printed area. It is speculated that the pale printed area in areas where the surface energy is reduced and the standard dark printed area in areas where the surface free energy is not reduced result in visible print unevenness. Furthermore, the print unevenness is suppressed by suppressing the variation in interference between dots within the ink-receiving layer surface by incorporating a silicone-based leveling agent into the ink-receiving layer. The effect of suppressing print unevenness is presumably achieved by incorporating a silicone-based leveling agent into the ink-receiving layer, which prevents regions with an excessive silicone component from being mixed with regions with no silicone component at all within the ink-receiving layer surface. In other words, the print unevenness suppression effect is presumably achieved by homogenizing the surface free energy within the ink-receiving layer surface. On the other hand, incorporating a silicone-based leveling agent into the ink-receiving layer reduces the wettability of the entire ink-receiving layer, making it difficult for dots to wet and spread across the entire ink-receiving layer. As a result, the print density of the entire printed area formed on the ink-receiving layer decreases. Therefore, the ink-receiving layer is formed as a cured layer of a composition for forming an ink-receiving layer containing the specific energy ray-curable compound (A) and silicone-based leveling agent (B), and the water contact angle of the ink-receiving layer is adjusted to 80° or less, thereby improving the wettability of the entire ink-receiving layer, making it easier for the dots to wet and spread, ensuring sufficient print density while also fully suppressing print unevenness.

[0017] Next, the inventors conducted extensive research into suppressing optical interference patterns in the ink-receiving layer itself before printing. As a result, they discovered that by further blending a filler (C) into the ink-receiving layer and adjusting the difference between the refractive index (X) of the ink-receiving layer and the refractive index (Y) of the layer in direct contact with the ink-receiving layer [(X) - (Y)]] to be greater than -0.03, it is possible to suppress optical interference patterns in the ink-receiving layer itself before printing. Note that "optical interference patterns" can also be expressed as "interference fringes." Transparency is required in the unprinted areas of inkjet printing sheets. If "interference fringes" occur in the ink-receiving layer, rainbow-colored fringes become more visible, impairing the transparency of the unprinted areas of the inkjet printing sheet. According to the present invention, such "interference fringes" can be effectively suppressed.

[0018] Although the mechanism by which the above effect is achieved is not clear, it is presumed that this is due to an appropriate balance of optical properties between the ink-receiving layer and the layer in direct contact with the ink-receiving layer.

[0019] Hereinafter, the inkjet printing sheet of the present invention will be described in detail, including the configuration of the inkjet printing sheet, the ink-receiving layer, the base layer, the pressure-sensitive adhesive layer, and the release liner that constitute the inkjet printing sheet, the method for producing the inkjet printing sheet, and uses of the inkjet printing sheet.

[0020] [Configuration of Inkjet Printing Sheet] The inkjet printing sheet of the present invention has a laminated structure in which an ink-receiving layer is in direct contact with one surface of a substrate layer or an easy-adhesion layer formed on one surface of the substrate layer, and a pressure-sensitive adhesive layer and a release liner are provided, in this order, on the other surface of the substrate layer. Figure 1 shows a schematic cross-sectional view of one embodiment of the inkjet printing sheet of the present invention. The inkjet printing sheet 1 shown in Figure 1 has a laminated structure in which an ink-receiving layer 2, a substrate layer 3, a pressure-sensitive adhesive layer 4, and a release liner 5 are provided, in this order. The release liner 5 has a silicone-based release agent layer 5a and a support 5b, with the silicone-based release agent layer 5a in contact with the pressure-sensitive adhesive layer 4. In the inkjet printing sheet 1 shown in Figure 1, the ink-receiving layer 2, substrate layer 3, pressure-sensitive adhesive layer 4, and release liner 5 are directly laminated together without any intervening layers. Therefore, the inkjet printing sheet 1 shown in Figure 1 is composed only of the ink-receiving layer 2, substrate layer 3, pressure-sensitive adhesive layer 4, and release liner 5. In this case, the layer in direct contact with the ink-receiving layer 2 is the substrate layer 3. The substrate layer 3 is preferably formed from polyethylene terephthalate. However, the inkjet printing sheet 1 is not necessarily limited to this configuration. For example, as in the inkjet printing sheet 1a shown in FIG. 2, an easy-adhesion layer 3a may be provided on one side of the substrate layer 3, and the easy-adhesion layer 3a may be interposed between the ink-receiving layer 2 and the substrate layer 3. In this case, the layer in direct contact with the ink-receiving layer 2 is the easy-adhesion layer 3a. The easy-adhesion layer 3a is preferably formed from a polyurethane-based resin or polyethylene terephthalate, and more preferably from a polyurethane-based resin. The easy-adhesion layer is provided to improve the adhesion between the substrate layer and the ink-receiving layer. The thickness of the easy-adhesion layer is preferably 30 nm to 300 nm, more preferably 40 nm to 200 nm, and even more preferably 50 nm to 100 nm. Furthermore, another layer may be provided between the substrate layer 3 and the pressure-sensitive adhesive layer 4, as needed. Furthermore, the silicone-based release agent layer 5a and the support 5b may be laminated directly as shown in Figures 1 and 2, but if necessary, another layer may be provided between the silicone-based release agent layer 5a and the support 5b.The other layer may be, for example, a filling layer.

[0021] <Ink-Receiving Layer> In the inkjet printing sheet of the present invention, the ink-receiving layer is a cured layer of an ink-receiving-layer-forming composition containing an energy ray-curable compound (A), a silicone-based leveling agent (B), and a filler (C), and has a water contact angle of 80° or less, and the difference [(X) - (Y)] between the refractive index (X) of the ink-receiving layer and the refractive index (Y) of the layer in direct contact with the ink-receiving layer is greater than -0.03. This configuration makes it possible to ensure sufficient print density while suppressing variations in interference between dots within the ink-receiving layer surface and thereby suppressing print unevenness. Furthermore, it also makes it possible to suppress optical interference patterns in the ink-receiving layer itself before printing.

[0022] (Water contact angle of ink-receiving layer) In the present invention, the water contact angle of the ink-receiving layer must be 80° or less. If the water contact angle of the ink-receiving layer is 81° or more, the wettability of the ink-receiving layer cannot be sufficiently ensured, making it difficult for the dots to wet and spread, resulting in a decrease in print density. From the viewpoint of making it easier to ensure a sufficient print density, the water contact angle of the ink-receiving layer is preferably 79° or less, and more preferably 78° or less. There is no particular restriction on the lower limit of the water contact angle of the ink-receiving layer, but taking into consideration the configuration of the ink-receiving layer, it is usually 58° or more, for example.

[0023] In this specification, the water contact angle of the ink-receiving layer refers to a value measured by the method described in the Examples below. The portion of the ink-receiving layer where the water contact angle is measured is the portion where the ink for inkjet printing is applied.

[0024] The water contact angle of the ink-receiving layer can be adjusted by adjusting the type and content of the energy ray-curable compound (A) and the silicone-based leveling agent (B) contained in the composition for forming the ink-receiving layer.

[0025] (Refractive Index Difference [(X) - (Y)]) In the present invention, the difference [(X) - (Y)] between the refractive index (X) of the ink-receiving layer and the refractive index (Y) of the layer in direct contact with the ink-receiving layer must be greater than -0.03. If the refractive index difference [(X) - (Y)] is -0.03 or less, optical interference patterns in the ink-receiving layer itself before printing are likely to occur. Here, from the viewpoint of easily suppressing optical interference patterns in the ink-receiving layer itself before printing, the refractive index difference [(X) - (Y)] is preferably -0.02 or more, more preferably 0.00 or more, even more preferably more than 0.00 (i.e., the refractive index (X) is greater than the refractive index (Y)), still more preferably 0.02 or more, and even more preferably 0.04 or more.

[0026] In this specification, the refractive index (X) of the ink-receiving layer is a value measured using an Abbe refractometer at a wavelength of 589 nm. The refractive index (Y) of a layer in direct contact with the ink-receiving layer is a value measured using an Abbe refractometer at a wavelength of 589 nm when the thickness of the layer is on the order of μm. Furthermore, when the thickness of the layer is on the order of nm, the value is a value measured using a spectroscopic ellipsometer at a wavelength of 589 nm. However, as described in the examples below, the refractive index (X) may be calculated from the known refractive index (literature values) of each component constituting the ink-receiving layer. Furthermore, a known refractive index (literature value) may also be used for the refractive index (Y).

[0027] The refractive index (X) of the ink-receiving layer can be adjusted by adjusting the types and contents of the energy ray-curable compound (A) and filler (C) contained in the composition for forming the ink-receiving layer (particularly by adjusting the type and content of the filler (C)). Therefore, the refractive index difference [(X)-(Y)] can be adjusted by adjusting the refractive index (X) of the ink-receiving layer in accordance with the refractive index (Y) of the layer in direct contact with the ink-receiving layer.

[0028] As an example of a preferred value of the refractive index (X) of the ink-receiving layer, when the refractive index (Y) of the layer in direct contact with the ink-receiving layer is 1.55, the refractive index (X) is preferably greater than 1.52, more preferably 1.53 or more, even more preferably 1.55 or more, still more preferably 1.57 or more, and even more preferably 1.59 or more.

[0029] Hereinafter, the energy ray-curable compound (A), the silicone-based leveling agent (B), the filler (C), and the like will be described in detail, taking into consideration the method for adjusting the water contact angle of the ink-receiving layer and the method for adjusting the refractive index (X) of the ink-receiving layer.

[0030] (Energy ray-curable compound (A)) In the present invention, the composition for forming the ink-receiving layer contains an energy ray-curable compound (A). If the composition for forming the ink-receiving layer does not contain the energy ray-curable compound (A), it becomes difficult to adjust the water contact angle of the ink-receiving layer to 80° or less, and it becomes difficult to ensure sufficient print density. In addition, it becomes easy to increase the surface hardness of the ink-receiving layer, and it becomes easy to suppress scratches during application or use. Here, "energy ray-curable compound" means a compound that is cured (polymerized) by irradiation with energy rays. Therefore, the ink-receiving layer contains a polymer (resin) derived from the energy ray-curable compound (A). In addition, "energy rays" means electromagnetic waves or charged particle beams that have an energy quantum, and examples of such rays include ultraviolet rays and electron beams, with ultraviolet rays being preferred.

[0031] In the present invention, the energy ray-curable compound (A) is an ester of a polyol compound and (meth)acrylic acid. If the energy ray-curable compound (A) is a compound other than the ester of a polyol compound and (meth)acrylic acid, it becomes difficult to adjust the water contact angle of the ink-receiving layer to 80° or less, and it becomes difficult to ensure sufficient print density. The energy ray-curable compound (A) may be used alone or in combination of two or more.

[0032] The energy ray-curable compound (A) may be a polymerizable compound having one or more (meth)acryloyl groups in one molecule. From the viewpoint of further improving the effects of the present invention, the energy ray-curable compound (A) preferably has two or more (meth)acryloyl groups in one molecule, and more preferably has 2 to 6 (meth)acryloyl groups in one molecule.

[0033] The polyol compound constituting the energy ray-curable compound (A) is preferably a dihydric to decahydric polyol, more preferably a trihydric to hexahydric polyol. The polyol compound may also be an alkylene oxide-modified product. Therefore, alkylene oxide-modified products of dihydric to decahydric polyols, and more preferably alkylene oxide-modified products of trihydric to hexahydric polyols, are also examples of polyol compounds. The alkylene group constituting the alkylene oxide-modified product preferably has 2 to 4 carbon atoms, more preferably 2 to 3 carbon atoms, and even more preferably 2 carbon atoms.

[0034] Specific examples of preferred polyol compounds include polyols such as trimethylolethane, trimethylolpropane, trimethylolbutane, ditrimethylolpropane, tritrimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, polyglycerin (a glycerin polymer, preferably a dimer to decamer of glycerin, more preferably a dimer to hexamer of glycerin, and even more preferably a trimer to pentamer of glycerin), 1,3,5-pentanetriol, sorbitol, adonitol, arabitol, xylitol, and mannitol; and alkylene oxide modified products (preferably ethylene oxide modified products) of these polyols.

[0035] From the viewpoint of making it easier to adjust the water contact angle of the ink-receiving layer to 80° or less and to make it easier to appropriately adjust the refractive index difference [(X)-(Y)] (particularly, from the viewpoint of making it easier to appropriately adjust the refractive index difference between the ink-receiving layer and a layer formed of polyethylene terephthalate, which is commonly used as a base layer or an easy-adhesion layer), the energy ray-curable compound (A) preferably satisfies one or more of the following requirements (α1) to (α3), more preferably satisfies two or more of them, and even more preferably satisfies (α2) and (α3). Requirement (α1): The ester is a partial ester. Requirement (α2): The polyol compound constituting the ester is an alkylene oxide modified product, with the proviso that the alkylene group constituting the alkylene oxide modified product has 2 to 4 carbon atoms. Requirement (α3): The polyol compound constituting the ester has a glycerin skeleton.

[0036] Esters of polyol compounds and (meth)acrylic acid that satisfy the above requirement (α1) tend to have a high hydroxyl value and high hydrophilicity, making it easy to adjust the water contact angle of the ink-receiving layer to 80° or less. From the viewpoint of further enhancing hydrophilicity and making it easier to adjust the water contact angle of the ink-receiving layer to 80° or less, the partial esters of polyol compounds and (meth)acrylic acid preferably have a hydroxyl value of 50 mgKOH / g or more, more preferably 70 mgKOH / g or more, and even more preferably 80 mgKOH / g or more. In this specification, the hydroxyl value refers to a value measured in accordance with JIS K0070:1992.

[0037] Esters of polyol compounds and (meth)acrylic acid that satisfy the above requirement (α2) tend to be highly hydrophilic, making it easy to adjust the water contact angle of the ink-receiving layer to 80° or less. The ester that satisfies the above requirement (α2) may be a complete ester or a partial ester. When the ester that satisfies the above requirement (α2) is a partial ester, it also satisfies the above requirement (α1). The alkylene group constituting the alkylene oxide modified product preferably has 2 to 4 carbon atoms, more preferably 2 to 3 carbon atoms, and even more preferably 2 carbon atoms. The number of alkylene oxides (molar number) in one molecule is not limited, but is preferably 4.0 or more, more preferably 5 or more, and even more preferably 6 or more, from the viewpoint of increasing the hydrophilicity of the ester of polyol compounds and (meth)acrylic acid and making it easy to adjust the water contact angle of the ink-receiving layer to 80° or less.

[0038] Esters of polyol compounds and (meth)acrylic acid that satisfy the above requirement (α3) tend to be highly hydrophilic, making it easy to adjust the water contact angle of the ink-receiving layer to 80° or less. The ester that satisfies the above requirement (α3) may be a complete ester or a partial ester. When the ester that satisfies the above requirement (α3) is a partial ester, it also satisfies the above requirement (X1). The polyol compound having a glycerin skeleton refers to glycerin or polyglycerin. As mentioned above, polyglycerin refers to a glycerin polymer, and is preferably a dimer to decamer of glycerin, more preferably a dimer to hexamer of glycerin, even more preferably a trimer to pentamer of glycerin, and even more preferably a tetramer of glycerin.

[0039] In one embodiment of the present invention, the content of the energy ray-curable compound (A) is appropriately adjusted so that the water contact angle of the ink-receiving layer can be adjusted to 80° or less. Increasing the content of the energy ray-curable compound (A) in the composition for forming an ink-receiving layer reduces the water contact angle of the ink-receiving layer. Conversely, decreasing the content of the energy ray-curable compound (A) in the composition for forming an ink-receiving layer increases the water contact angle of the ink-receiving layer. In light of this tendency, the content of the energy ray-curable compound (A) is adjusted from the viewpoint of balancing with the amount of the silicone-based leveling agent (B) to be blended so that the water contact angle of the ink-receiving layer can be adjusted to 80° or less.

[0040] (Silicone-based leveling agent (B)) In the present invention, the composition for forming the ink-receiving layer and the ink-receiving layer contain a silicone-based leveling agent (B). If the composition for forming the ink-receiving layer and the ink-receiving layer do not contain the silicone-based leveling agent (B), it will be impossible to suppress print unevenness. The silicone-based leveling agent (B) is presumed to have the effect of suppressing partial surface free energy disturbances on the surface of the ink-receiving layer caused by silicone components migrating from the back surface of the release liner to the ink-receiving layer, homogenizing the surface free energy within the ink-receiving layer surface, and suppressing variations in interference between dots within the ink-receiving layer surface. It is believed that this effect suppresses print unevenness.

[0041] The silicone leveling agent (B) is a compound having a siloxane skeleton, and specifically includes one or more compounds selected from compounds having a siloxane skeleton and an organic functional group, compounds having a siloxane skeleton and an organic modified group, etc. The organic modified group refers to a group in which a part of the organic functional group is substituted with another group. Specific examples of the silicone leveling agent (B) include polyether-modified silicone oils (manufactured by Dow-Toray Industries, Inc.) such as DOWSIL (registered trademark) BY16-036 Fluid, DOWSIL SH28 Paint Additive, DOWSIL SF8428 Fluid, DOWSIL 501W Additive, DOWSIL L-7001 Fluid, DOWSIL FZ-2104 Fluid, DOWSIL L-7002 Fluid, and DOWSIL SF8427 Fluid; DOWSIL (registered trademark) SF8416 Fluid, DOWSIL BY16-846 Fluid, DOWSIL SH203 Fluid, and DOWSIL 56 Alkyl-modified silicone oils such as Additive (manufactured by Dow-Toray Industries, Inc.); carboxyl-modified silicone oils such as DOWSIL (registered trademark) BY-16-880 and BY16-750 Fluid (manufactured by Dow-Toray Industries, Inc.); amino-modified silicone oils such as XIAMETER (registered trademark) OFX-8417 Fluid, DOWSIL (registered trademark) BY-16-849 Fluid, DOWSIL (registered trademark) FZ-3785 Fluid, DOWSIL (registered trademark) 16-872 Fluid, and DOWSIL (registered trademark) 16-853U Fluid (manufactured by Dow-Toray Industries, Inc.); DOWSIL (registered trademark) SF8413 Fluid, DOWSIL SF8411 Fluid, DOWSIL BY16-839 Fluid, and DOWSIL (registered trademark) SF8412 Fluid. Examples of the silicone leveling agent (B) include epoxy-modified silicone oils (manufactured by Dow-Toray Industries, Inc.), such as FZ-3736 Fluid, SF8421 EG Fluid, BY16-870 Fluid, BY16-876 Fluid, BY16-869 Fluid, and BY16-760 Fluid. Among these, polyether-modified silicone oils are more preferred. The silicone leveling agent (B) may be used alone or in combination of two or more.

[0042] In one embodiment of the present invention, the content of the silicone-based leveling agent (B) in the ink-receiving layer-forming composition is appropriately adjusted so as to suppress printing unevenness and adjust the water contact angle of the ink-receiving layer to 80° or less. Increasing the content of the silicone-based leveling agent (B) in the ink-receiving layer-forming composition increases the water contact angle of the ink-receiving layer. Conversely, decreasing the content of the silicone-based leveling agent (B) in the ink-receiving layer-forming composition decreases the water contact angle of the ink-receiving layer. Taking this tendency into consideration, the content of the silicone-based leveling agent (B) is adjusted so as to adjust the water contact angle of the ink-receiving layer to 80° or less, from the viewpoint of balancing with the effect of the energy ray-curable compound (A) in improving the hydrophilicity of the ink-receiving layer. For example, the content of the silicone-based leveling agent (B) is preferably 0.01 to 0.06 parts by mass, more preferably 0.02 to 0.05 parts by mass, per 100 parts by mass of the energy ray-curable compound (A). In addition, the ink receiving layer 1 m ２ An example of the content of the silicone-based leveling agent (B) per unit area is preferably 0.12 mg / m ２ ~1.0 mg / m ２ , more preferably 0.27 mg / m ２ ~0.75 mg / m ２ is.

[0043] (Filler (C)) The ink-receiving layer-forming composition and ink-receiving layer of the present invention contain a filler (C). By including the ink-receiving layer-forming composition and ink-receiving layer with the filler (C), the refractive index (X) of the ink-receiving layer can be appropriately adjusted, thereby suppressing optical interference patterns in the ink-receiving layer itself before printing. This can also have the secondary effect of improving the slipperiness of the ink-receiving layer surface, thereby facilitating improved transportability of the inkjet printing sheet. "Improved transportability" refers to improved slipperiness between inkjet printing sheets and between the inkjet printing sheet and the device (roller or cylinder). This allows for smooth winding and unwinding of the inkjet printing sheet, and helps to prevent wrinkles, scratches, misalignment of the printing position, and other problems from occurring in the sheet.

[0044] The filler (C) is not particularly limited as long as it can appropriately adjust the refractive index (X) of the ink-receiving layer and thereby appropriately adjust the refractive index difference [(X)-(Y)], but is preferably one or more selected from the group consisting of alumina and zirconia. Alumina and zirconia have high refractive indices themselves, making it easy to adjust the refractive index difference with polyethylene terephthalate, which is commonly used for the base layer and the easy-adhesion layer, within the above range. Therefore, the filler (C) is preferably one or more selected from the group consisting of alumina particles and zirconia particles.

[0045] The particle size of the filler (C) is preferably 10 nm to less than 1 μm, more preferably 10 nm to 500 nm, even more preferably 10 nm to 200 nm, and even more preferably 10 nm to 100 nm. When the particle size of the filler (C) is within the above range, the refractive index (X) of the ink-receiving layer can be appropriately adjusted, making it easier to appropriately adjust the refractive index difference [(X) - (Y)]. Furthermore, the effect of improving the slipperiness of the ink-receiving layer surface and facilitating improved transportability of the inkjet printing sheet is easily obtained, and the transparency of the ink-receiving layer is less likely to be impaired. The particle size of the filler (C) is the average particle size converted from the specific surface area by the BET method.

[0046] The filler (C) may be in the form of a dry powder, but from the viewpoint of dispersion stability, it is preferable to use a colloidal solution obtained by dispersing the filler in an organic solvent.

[0047] The filler (C) may be used alone or in combination of two or more.

[0048] In one embodiment of the present invention, the content of the filler (C) in the composition for forming an ink-receiving layer is not particularly limited, but from the viewpoint of appropriately adjusting the refractive index (X) of the ink-receiving layer to make it easier to appropriately adjust the refractive index difference [(X)-(Y)], improving the slipperiness of the surface of the ink-receiving layer to make it easier to improve the transportability of the inkjet printing sheet, and making it difficult to impair the transparency of the ink-receiving layer, the content is preferably 4 parts by mass to 200 parts by mass, more preferably 10 to 150 parts by mass, even more preferably 20 to 100 parts by mass, and still more preferably 40 to 100 parts by mass, relative to 100 parts by mass of the energy ray-curable compound (A).

[0049] (Photopolymerization initiator (D)) In one aspect of the present invention, the composition for forming the ink-receiving layer and the ink-receiving layer preferably contain a photopolymerization initiator (D). When the composition for forming the ink-receiving layer contains the photopolymerization initiator (D) together with the energy ray-curable compound (A), it is possible to facilitate the progress of energy ray curing by ultraviolet rays or the like. As the photopolymerization initiator (D), any general compound having the function of facilitating the progress of energy ray curing by ultraviolet rays or the like can be used without any particular limitation. Examples of such compounds include 1-hydroxycyclohexyl phenyl ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl diphenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, benzyl, dibenzyl, diacetyl, β-chloroanthraquinone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,4,6-trimethylzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methylpropan-1-one, etc. The photopolymerization initiator (D) may be used alone or in combination of two or more.

[0050] In one embodiment of the present invention, the content of the photopolymerization initiator (D) in the composition for forming an ink-receiving layer is not particularly limited, but is preferably 0.1 to 10 parts by mass relative to 100 parts by mass of the energy ray-curable compound (A).

[0051] (Other Additives) In one embodiment of the present invention, the composition for forming the ink-receiving layer may or may not contain other components other than the energy ray-curable compound (A), the silicone-based leveling agent (B), the filler (C), and the photopolymerization initiator (D), as long as the water contact angle of the ink-receiving layer can be adjusted to 80° or less. For example, the composition for forming the ink-receiving layer may or may not contain an energy ray-curable compound (A') other than the energy ray-curable compound (A), as long as the water contact angle of the ink-receiving layer can be adjusted to 80° or less.

[0052] <Substrate Layer> The inkjet printing sheet of the present invention has a substrate layer. The substrate layer supports the inkjet printing sheet and also functions as a support for supporting the printing area formed on the ink-receiving layer.

[0053] The substrate layer is not particularly limited, but is preferably a resin sheet. The resin substrate layer improves the rigidity and flexibility of the inkjet printing sheet, improving the ease of handling of the inkjet printing sheet. This is also advantageous from the viewpoint of reducing the production cost and weight of the inkjet printing sheet.

[0054] Examples of resins constituting the resin sheet include polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyolefin resins such as polyethylene and polypropylene; polystyrene; acrylonitrile-butadiene-styrene copolymers; cellulose triacetate; polycarbonate; urethane resins such as polyurethane and acrylic-modified polyurethane; polymethylpentene; polysulfone; polyether ether ketone; polyethersulfone; polyphenylene sulfide; polyimide-based resins such as polyetherimide and polyimide; polyamide-based resins; acrylic resins; and fluorine-based resins. Among these, from the viewpoint of easily adjusting the difference [(X) - (Y)] between the refractive index (X) of the ink-receiving layer and the refractive index (Y) of the layer in direct contact with the ink-receiving layer to fall within the above-mentioned range and from the viewpoint of easily improving adhesion to the ink-receiving layer, polyester-based resins and polyolefin-based resins are preferred, polyester-based resins are more preferred, and resins with a refractive index of 1.55 to 1.60 are even more preferred. A preferred example of such a resin is polyethylene terephthalate.

[0055] The resin sheet may be composed of only one type of resin, or may be composed of two or more types of resin. When the resin sheet is composed of two or more types of resin, it is preferably a multi-layered structure. Furthermore, the uppermost layer of the multi-layered structure (the layer in contact with the ink-receiving layer) is preferably a polyester-based resin, more preferably polyethylene terephthalate, from the viewpoints of easily adjusting the difference [(X) - (Y)] between the refractive index (X) of the ink-receiving layer and the refractive index (Y) of the layer in direct contact with the ink-receiving layer within the above-mentioned range, and easily improving adhesion to the ink-receiving layer. For example, from the above viewpoints, the aforementioned easy-adhesion layer is preferably a polyester-based resin, more preferably a resin with a refractive index of 1.55 to 1.60. A preferred example of such a resin is polyethylene terephthalate. Furthermore, the resin sheet may be unstretched or may be stretched uniaxially or biaxially, e.g., longitudinally or transversely.

[0056] In addition, the resin sheet may contain, together with these resins, additives for the base layer such as a surface conditioner, a plasticizer, an ultraviolet absorber, a light stabilizer, and a colorant. The content of the additives for the base layer is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, based on the total amount of the base layer.

[0057] The thickness of the substrate layer is not particularly limited, but is preferably 15 μm to 300 μm, and more preferably 30 μm to 200 μm.

[0058] <Adhesive Layer> The inkjet printing sheet of the present invention has an adhesive layer. By having an adhesive layer, the inkjet printing sheet of the present invention can be suitably used as an adhesive sheet.

[0059] The adhesive constituting the adhesive layer is not particularly limited, and examples thereof include acrylic adhesives, urethane adhesives, and the like. When the inkjet printing sheet is used for applications such as window displays, the adhesive layer may be formed from an acrylic adhesive from the viewpoint of weather resistance, etc. Furthermore, when removability from the adherend is required, the adhesive layer may be formed from a urethane adhesive. The adhesive layer may contain other components such as ultraviolet absorbers, tackifiers, antioxidants, light stabilizers, softeners, silane coupling agents, and fillers, as necessary. These may be used alone or in combination of two or more.

[0060] The thickness of the adhesive layer is not particularly limited, but from the viewpoint of improving the handleability when using the inkjet printing sheet as an adhesive sheet, it is preferably 5 μm to 100 μm, more preferably 10 μm to 70 μm, and even more preferably 15 μm to 50 μm.

[0061] <Release Liner> The inkjet printing sheet of the present invention has a release liner. By covering the adhesive surface of the pressure-sensitive adhesive layer of the inkjet printing sheet of the present invention with a release liner, the adhesive surface of the pressure-sensitive adhesive layer can be suitably protected during transportation and storage of the inkjet printing sheet.

[0062] In the inkjet printing sheet of the present invention, the release liner has a silicone-based release agent layer. When the release liner is rolled or wound, a very small amount of silicone components may migrate to the back surface of the release liner. Therefore, when the inkjet printing sheet having the above-described laminated structure is rolled or wound, the very small amount of silicone components present on the back surface of the release liner may migrate to the ink-receiving layer. The silicone components that migrate from the back surface of the release liner to the ink-receiving layer cause localized surface free energy disturbances on the surface of the ink-receiving layer. As a result, interference between dots within the ink-receiving layer varies, resulting in print unevenness. However, according to the present invention, by incorporating a silicone-based leveling agent (B) into the ink-receiving layer-forming composition and the ink-receiving layer, the localized surface free energy disturbances on the surface of the ink-receiving layer are suppressed, the surface free energy of the ink-receiving layer is homogenized, and the variation in interference between dots within the ink-receiving layer is suppressed, thereby suppressing print unevenness. Furthermore, by making the water contact angle of the ink-receiving layer 80° or less, the decrease in print density that occurs when the silicone-based leveling agent (B) is blended can be suppressed, and sufficient print density can be ensured.

[0063] As the silicone-based release agent layer that constitutes the release liner, any material that is generally used for release liners can be used without any particular limitation.

[0064] The support constituting the release liner may be a sheet substrate or a paper substrate commonly used for release liners. Examples of the sheet substrate include polyester resins such as polyethylene terephthalate, and polyolefin resins such as polyethylene resins and polypropylene resins. Examples of the paper substrate include papers such as fine paper, kraft paper, and glassine paper.

[0065] The thickness of the release liner is not particularly limited, but is preferably 10 μm to 150 μm, more preferably 20 μm to 130 μm, and even more preferably 30 μm to 120 μm.

[0066] [Method for producing inkjet printing sheet] The method for producing the inkjet printing sheet of the present invention is not particularly limited, and may be appropriately selected depending on the configuration of the inkjet printing sheet.

[0067] A preferred method for forming the ink-receiving layer involves applying an ink-receiving layer-forming composition containing an energy ray-curable compound (A), a silicone-based leveling agent (B), and a filler (C) to one side of the base layer or to the surface of an easy-adhesion layer formed on one side of the base layer to form a coating film, and then drying and curing the coating film. As described above, the ink-receiving layer-forming composition preferably further contains a photopolymerization initiator (D). In order to improve the workability of application to the base layer, the ink-receiving layer-forming composition is preferably further diluted with a dilution solvent to form a solution.

[0068] Examples of dilution solvents include organic solvents such as methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexane, n-hexane, toluene, xylene, n-propanol, and isopropanol. The concentration of the active ingredients (solid content) in the solution of the composition for forming the ink-receiving layer is preferably 10 to 50% by mass.

[0069] Examples of methods for applying the solution of the composition for forming the ink-receiving layer include bar coating, gravure coating, roll coating, knife coating, and die coating.

[0070] The heating conditions for drying the coating film are, for example, a drying temperature of 60° C. to 120° C. and a drying time of 30 seconds to 3 minutes.

[0071] After drying the coating film, the coating film is irradiated with energy rays (preferably ultraviolet rays) to cure (polymerize) the energy ray-curable compound (A). When ultraviolet rays are used as the energy rays, the irradiation conditions of the ultraviolet rays are an integrated irradiation amount (integrated light amount) of 5 to 1200 mJ / cm. 2 is preferred, and 30 to 500 mJ / cm 2 The ultraviolet light can be irradiated using, for example, a high-pressure mercury lamp, an electrodeless lamp, a xenon lamp, an LED, or the like as an ultraviolet light source.

[0072] The pressure-sensitive adhesive layer of the inkjet printing sheet of one embodiment of the present invention is formed on the other side of the base layer, on which the ink-receiving layer is not formed. The pressure-sensitive adhesive layer is formed, for example, by applying a composition for forming a pressure-sensitive adhesive layer (pressure-sensitive adhesive layer-forming composition) to the other side of the base layer, and a release liner is laminated on the pressure-sensitive adhesive layer. Alternatively, the pressure-sensitive adhesive layer may be formed by applying the pressure-sensitive adhesive layer-forming composition to the release surface of the release liner (the surface of the silicone-based release agent layer), and this may then be laminated to the other side of the base layer. The method for applying the pressure-sensitive adhesive layer-forming composition is the same as the method for applying the ink-receiving layer-forming composition described above.

[0073] [Ink for Inkjet Printing] The inkjet printing sheet of the present invention is effective in ensuring sufficient print density while suppressing print unevenness in inkjet printing using ultraviolet-curable ink or latex ink, which does not or is unlikely to penetrate into the ink-receiving layer, and is particularly effective in ensuring sufficient print density while suppressing print unevenness in inkjet printing using ultraviolet-curable ink.

[0074] <UV-curable ink> The UV-curable ink is an ink that does not substantially contain an organic solvent and is cured by irradiation with UV light. The UV-curable ink contains a photopolymerizable monomer, a colorant that is a pigment or dye, and a photopolymerization initiator that starts a polymerization reaction. In one aspect of the present invention, from the viewpoint of further improving the adhesion between the ink-receiving layer and the printed portion, it is preferable that the UV-curable ink contains an acrylic monomer.

[0075] (Photopolymerizable Monomer) Examples of photopolymerizable monomers include monofunctional acrylates, difunctional acrylates, polyfunctional acrylates, and mixtures thereof. It should be noted that the photopolymerizable monomer may be an acrylic monomer formed by combining one or more of these acrylates. Examples of monofunctional acrylates include hydroxypropyl acrylate, tetrahydrofurfuryl acrylate, phenol EO-modified (n=2) acrylate, 2-ethylhexyl EO-modified (n=2) acrylate, 2-hydroxy-3-phenoxypropyl acrylate, isobornyl acrylate, and acryloylmorpholine. Examples of bifunctional acrylates include hexanediol diacrylate, neopentyl glycol diacrylate, tripropylene glycol diacrylate, neopentyl glycol hydroxypivalate diacrylate, and bisphenol A EO-modified (n=4) diacrylate. Examples of polyfunctional acrylates include trimethylolpropane triacrylate, pentaerythritol triacrylate, trimethylolpropane PO-modified (n=3) triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate.

[0076] (Colorant) The ultraviolet curable ink usually contains a colorant, which may be any of various dyes, pigments, etc.

[0077] (Photopolymerization initiator) A photopolymerization initiator generally initiates a polymerization reaction by irradiation with ultraviolet light. As such a photopolymerization initiator, for example, a photopolymerization initiator that is a single agent or a mixture of multiple agents may be used, or a combination of a photopolymerization initiator and a photosensitizer may be used. For example, a combination of multiple photopolymerization initiators with different excitation wavelengths, or a combination to which a photosensitizer has been added, may be used.

[0078] (Other Components) As other components, for example, various conventionally known components such as dispersants, stabilizers, surfactants, etc. may be further blended as necessary.

[0079] <Latex Ink> Latex ink contains a liquid dispersion medium and a dispersoid composed of a material containing at least a resin, which is dispersed (emulsified and / or suspended) in the dispersion medium.

[0080] (Resin) The resin contained in the latex ink is not particularly limited, but examples thereof include vinyl resins, acrylic resins, styrene resins, alkyd resins, polyester resins, polyurethane resins, epoxy resins, phenoxy resins, polyolefin resins, and modified resins thereof (for example, modified resins modified to be water-soluble), and one or more types selected from these may be used in combination.

[0081] (Dispersion Medium) The latex ink contains water as a dispersion medium.

[0082] (Colorant) Latex ink usually contains a colorant, which may be any of various dyes, pigments, etc.

[0083] (Other Components) The latex ink may contain components other than those described above (other components), such as dispersants, antifungals, antirust agents, pH adjusters, surfactants, plasticizers, UV absorbers, and light stabilizers.

[0084] [Method of forming printed portion] The printed portion using inkjet printing ink is formed by applying the inkjet printing ink onto the ink-receiving layer of the inkjet printing sheet by an inkjet method. Examples of inkjet methods include a piezo method and a thermal jet method. When applying an ultraviolet-curable ink as inkjet printing ink, the amount of ultraviolet light irradiated onto the ultraviolet-curable ink is not particularly limited, but is preferably 40 J / m 2 ~400 J / m 2The heating temperature of the latex ink when applying the latex ink as the inkjet printing ink is not particularly limited, but is preferably 40°C to 90°C. By the above method, a printed matter having a printed portion on the ink-receiving layer of the inkjet printing sheet in which print unevenness caused by the inkjet printing ink is suppressed while ensuring sufficient print density can be obtained. Note that the inkjet printing sheet of the present invention can suppress print unevenness even in inkjet printing using a reduced amount of ink. Specifically, even when the total ink amount is 10% to 70% (preferably 10% to 50%, more preferably 15% to 40%), it is possible to form a printed portion in which print unevenness is suppressed while ensuring sufficient print density.

[0085] [Uses of Inkjet Printing Sheet] The inkjet printing sheet of the present invention is used for printing using inkjet printing ink. Therefore, according to the present invention, there is provided a method of use in which the inkjet printing sheet is used to form a printed section on the ink-receiving layer of the inkjet printing sheet using inkjet printing ink. The present invention also provides a method for producing a printed matter, which includes a step of forming a printed section on the ink-receiving layer of the inkjet printing sheet using inkjet printing ink. Furthermore, according to the present invention, there is provided a printed matter having a printed section printed with inkjet printing ink on the ink-receiving layer of the inkjet printing sheet.

[0086] Inkjet printing using ultraviolet-curable ink and latex ink is employed in the method of use, method of producing a printed matter, and printed matter of one embodiment of the present invention. The method of use, method of producing a printed matter, and printed matter of the present invention use the inkjet printing sheet of the present invention, and therefore, even in inkjet printing using ultraviolet-curable ink and latex ink, which do not or are unlikely to penetrate into the ink-receiving layer, it is possible to form a printed portion that ensures sufficient print density while suppressing print unevenness. Among ultraviolet-curable inks and latex inks, ultraviolet-curable inks are particularly suitable for use.

[0087] Furthermore, in the method of use, method of producing a printed matter, and printed matter of one embodiment of the present invention, the total amount of ink used in inkjet printing is not particularly limited, but the effects of the present invention are particularly likely to be achieved when the total amount of ink is preferably 10% to 70%, more preferably 10% to 50%, and even more preferably 15% to 40%. According to the method of use, method of producing a printed matter, and printed matter of one embodiment of the present invention, even with the above ink amount, sufficient print density is ensured while suppressing print unevenness. Therefore, this is particularly useful when printing with shades or gradations.

[0088] The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0089] [Examples 1 to 8, Comparative Examples 1 to 4] Inkjet printing sheets of Examples 1 to 8 and Comparative Examples 1 to 4 were prepared by the following procedure.

[0090] <Preparation of composition for forming ink-receiving layer> A composition for forming an ink-receiving layer was prepared having the formulation shown in Table 1. Details of the raw materials used in preparing the composition for forming the ink-receiving layer are shown below.

[0091] (Energy ray-curable compounds (A)) "Compound 1": ethylene oxide-modified hexafunctional polyglycerin acrylate (the polyol compound is an ethylene oxide-modified product of polyglycerin (a tetramer of glycerin), and is a complete ester having six acryloyl groups. The number of moles of ethylene oxide is 6.) "Compound 2": dipentaerythritol hexaacrylate (the polyol compound is dipentaerythritol, and is a complete ester having six acryloyl groups. The hydroxyl value is 10 mgKOH / g.)

[0092] (Silicone leveling agent (B)) Polyether-modified silicone oil

[0093] (Filler (C)) Zirconia particles: zirconia sol (particle diameter 30 to 50 nm) Alumina particles: alumina sol (particle diameter 120 to 150 nm)

[0094] (Filler (C')) Silica particles: organosilica sol (particle diameter 70 to 100 nm)

[0095] (Photopolymerization initiator (D)) 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methylpropan-1-one

[0096] Each composition for forming an ink-receiving layer having the composition shown in Table 1 (amounts of active ingredients converted into active ingredients) was diluted with a dilution solvent (ethyl acetate) to prepare a coating liquid with an active ingredient concentration of 30% by mass, and used to prepare a sheet for inkjet printing.

[0097] (Preparation of inkjet printing sheet) The ink-receiving layer-forming composition thus prepared was applied to the surface of a polyethylene terephthalate substrate layer (substrate layer thickness: 50 μm, substrate layer thickness: 55 nm to 60 nm) on one side of which a polyurethane adhesive layer was formed, on the adhesive layer side, using a bar coater so that the film thickness after drying would be 1.8 μm (coating amount: 2.5 g / m ２ Next, the solvent contained in the ink-receiving layer-forming composition applied to the base layer was removed by heating at 70°C for 1 minute using a hot air dryer, and then ultraviolet light having a peak wavelength of 365 nm was applied at an integrated light intensity of 90 mJ / cm２ The ink-receiving layer was formed by irradiating the substrate with light. Next, a release liner (50 μm thick) was prepared, with a silicone-based release agent layer provided on one side of a polyethylene terephthalate sheet. An acrylic pressure-sensitive adhesive was applied to the silicone-based release agent layer side so that the dried film thickness would be 20 μm. The coating was then heated at 90°C for 1 minute using a hot air dryer to remove the solvent contained in the coating liquid, forming an acrylic pressure-sensitive adhesive layer. The acrylic pressure-sensitive adhesive layer formed on the release liner was then bonded to the surface of the substrate layer opposite the ink-receiving layer, yielding a sheet for inkjet printing. The thickness of each layer, when measured on the order of μm, was measured using a constant-pressure thickness meter (model number: "PG-02J" manufactured by Teclock Corporation, standard specifications: JIS K6783:1994, JIS Z1702:1994, JIS Z1709:1995). When measured on the order of nm, the thickness was measured using a spectroscopic ellipsometer SE-2000 (manufactured by Nippon Semilab Co., Ltd.).

[0098] <Evaluation> The evaluations described in (1) to (6) below were carried out. When carrying out the evaluations (2) and (3) below, the pretreatment described below was carried out, assuming that the ink-receiving layer would come into contact with the back surface of the release liner due to the ink-jet printing sheet being rolled up. That is, two identical ink-jet printing sheets were prepared, and as shown in Figure 3, they were stacked so that the surface of the ink-receiving layer 2x of one ink-jet printing sheet 1x came into contact with the back surface of the release liner 5y of the other ink-jet printing sheet 1y, and the sheets were subjected to a pressure of 20 kg / cm in an environment at a temperature of 70°C. ２ The mixture was left standing for 12 hours under a pressure of 1.0 MPa.

[0099] (1) Measurement of Water Contact Angle of Ink-Receiving Layer The water contact angle of the ink-receiving layer (the portion of the ink-receiving layer to which the ink for inkjet printing is applied) of the inkjet printing sheets of Examples 5 and 8 and Comparative Examples 1 to 4 was measured using an automatic contact angle meter DSA100S (manufactured by KRUSS). The measurement was performed in an atmosphere of 23°C and 50% RH, with 2 μL of water being dropped and the static contact angle calculated by the θ / 2 method. The water contact angles of the ink-receiving layers of Examples 1 to 4 were estimated from the water contact angles of the ink-receiving layers of Comparative Example 1 and Example 5, and the water contact angles of the ink-receiving layers of Examples 6 and 7 were estimated from the water contact angles of the ink-receiving layers of Comparative Example 1 and Example 8.

[0100] (2) Evaluation of Printing Unevenness Printed portions were formed on the surface of the ink-receiving layer of each of the inkjet printing sheets of Examples 1 to 8 and Comparative Examples 1 to 4 by inkjet printing using an inkjet printer (UCJV300, manufactured by Mimaki Engineering Co., Ltd.) using ultraviolet-curable ink (LUS-170, manufactured by Mimaki Engineering Co., Ltd.) with 5% each of CMYK and a total ink amount of 20% by ink jet method. After printing was completed, the entire printed surface was visually observed and evaluated according to the following criteria: A: No printing unevenness was observed on the entire printed surface. B: Slight printing unevenness was observed on part of the printed surface, but this did not pose a major problem in terms of print quality. C: Light and dark shading was noticeable on the entire printed surface, and printing unevenness was significant.

[0101] (3) Evaluation of Print Density A print was formed on the surface of the ink-receiving layer of each of the inkjet printing sheets of Examples 1 to 8 and Comparative Examples 1 to 4 by printing with an inkjet printer (UCJV300, manufactured by Mimaki Engineering Co., Ltd.) using ultraviolet-curable ink (LUS-170, manufactured by Mimaki Engineering Co., Ltd.) in an ink volume of 20% with ink color Y by the inkjet method. After printing was completed, the entire printed surface was visually observed and evaluated according to the following criteria: A: Sufficient print density was observed. B: The print density was slightly low, but there was no major problem in terms of print quality. C: The print density was low.

[0102] (4) Refractive Index Difference [(X) - (Y)] The refractive index (X) of the ink-receiving layer of each of the inkjet printing sheets of Examples 1 to 8 and Comparative Example 2 was calculated using the following formula (1): Refractive Index (X) = (Rc x A + Rf x C) / (A + C) (1) In the formula (1), Rc is the measured refractive index of the ink-receiving layer excluding the filler (the refractive index of the ink-receiving layer of Comparative Example 1). Rf is the refractive index of the filler. A is the content ratio of the energy ray-curable compound (A), which was set to 1 in this example. C is the content ratio of the filler (C) when the content of the energy ray-curable compound (A) is set to 1. For example, in Example 1, A = 1 and C = 0.04. The contents of the silicone-based leveling agent (B) and the photopolymerization initiator (D) were so small that they had little effect on the calculation results, and therefore were excluded when calculating the refractive index (X). The refractive index of the ink-receiving layer of Comparative Example 1 was measured using an Abbe refractometer (manufactured by ATAGO, product name "Multi-wavelength Abbe refractometer DR-M2", measurement wavelength: 589 nm). The refractive index of the ink-receiving layer of Comparative Example 1 was measured using a sample in which the thickness of the ink-receiving layer of the inkjet printing sheet of Comparative Example 1 was changed to 20 μm and no release liner was provided. The refractive index of the filler was the refractive index at a wavelength of 589 nm listed in the refractive index table on the official FILMETRICS website. The refractive indexes of each filler are as follows: Organosilica sol: 1.46 Zirconia sol: 2.22 Alumina sol: 1.77 The refractive index of the easy-adhesion layer (polyurethane) was 1.55. The refractive index of the easy-adhesion layer (polyurethane) was measured using a polyethylene terephthalate substrate layer on which a polyurethane easy-adhesion layer was formed, which was used in the production of an inkjet printing sheet, at a measurement wavelength of 589 nm using a spectroscopic ellipsometer SE-2000 (manufactured by Nippon Semilab Co., Ltd.).

[0103] (5) Optical interference patterns The inkjet printing sheets of Examples 1 to 8 and Comparative Examples 1 and 2 were placed under a three-band fluorescent lamp, and the surface of the ink-receiving layer was visually observed and evaluated according to the following criteria. Figure 4 shows a photograph of Evaluation 1 as a substitute for a drawing. 5: No interference pattern or barely visible interference pattern. 4: Slightly visible, slightly small interference pattern. 3: Easily visible, slightly small interference pattern. 2: Easily visible, slightly large interference pattern. 1: Easily visible, large interference pattern. In these examples, a rating of 4 or higher was considered acceptable.

[0104] (6) Slipperiness Two inkjet printing sheets were prepared for each of Examples 1 to 8 and Comparative Examples 1 and 2, and the surfaces coated with the ink-receiving layers were placed together and subjected to a sensory evaluation of slipperiness. The evaluation criteria were as follows. The higher the evaluation value, the better and more preferable the slipperiness. 5: No resistance at all, slides easily. 4: There is slight resistance, but slides easily. 3: There is resistance, but slides if strong force is applied. 2: There is strong resistance, and slides slightly if strong force is applied. 1: The surfaces are in close contact with each other and do not slide at all.

[0105] The evaluation results are shown in Table 1.

[0106]

[0107] The results shown in Table 1 reveal the following. The results shown in Examples 1 to 8 reveal that when the water contact angle of the ink-receiving layer, which is a cured layer of the ink-receiving layer-forming composition containing the energy ray-curable compound (A), the silicone-based leveling agent (B), and the filler (C), is 80° or less, it is possible to ensure sufficient print density while suppressing print unevenness. Furthermore, it is also clear that when the refractive index difference [(X) - (Y)] is greater than -0.03, it is possible to suppress optical interference patterns in the ink-receiving layer itself before printing. In contrast, as shown in Comparative Examples 1 and 2, when the refractive index difference [(X) - (Y)] is -0.03 or less, it is not possible to suppress the occurrence of optical interference patterns in the ink-receiving layer itself before printing. Furthermore, as shown in Comparative Example 3, it is clear that an ink-receiving layer formed from an ink-receiving layer-forming composition that does not contain the silicone-based leveling agent (B) can ensure sufficient print density but cannot suppress print unevenness. Furthermore, as shown in Comparative Example 4, when the water contact angle of the ink receiving layer is 81°, it is possible to suppress print unevenness, but it is not possible to ensure sufficient print density.

[0108] 1, 1a, 1x, 1y Inkjet printing sheet 2, 2x, 2y Ink receiving layer 3, 3x, 3y Base material layer 3a Easy adhesion layer 4, 4x, 4y Pressure sensitive adhesive layer 5, 5x, 5y Release liner 5a, 5ax, 5ay Silicone release agent layer 5b, 5bx, 5by Support

Claims

1. The laminated structure has an ink receiving layer in direct contact with one surface of the substrate layer or with an easy-adhesion layer formed on one surface of the substrate layer, and an adhesive layer and a release liner provided in this order on the other surface of the substrate layer. The release liner has a silicone-based release agent layer on the contact surface with the adhesive layer. The ink receiving layer is a cured layer of an ink receiving layer forming composition containing an energy ray curable compound (A), a silicone-based leveling agent (B), and a filler (C). The energy ray curable compound (A) is an ester of a polyol compound and (meth)acrylic acid, The water contact angle of the ink receiving layer is 80° or less. An inkjet printing sheet in which the difference between the refractive index (X) of the ink receiving layer and the refractive index (Y) of the layer in direct contact with the ink receiving layer [(X) - (Y)] is greater than -0.

03.

2. The inkjet printing sheet according to claim 1, wherein the layer that is in direct contact with the ink receiving layer is made of a polyurethane resin or polyethylene terephthalate.

3. The inkjet printing sheet according to claim 1 or 2, wherein the filler (C) is one or more selected from the group consisting of alumina particles and zirconia particles.

4. The inkjet printing sheet according to claim 1 or 2, which is a wound body wound in a roll shape or a wound body wound around a core material.

5. A method of using an inkjet printing sheet according to claim 1 or 2, for the purpose of forming a printed area on the ink receiving layer of the inkjet printing sheet using inkjet printing ink.

6. A method for manufacturing a printed material, comprising the step of forming a printed portion on the ink receiving layer of an inkjet printing sheet according to claim 1 or 2 using inkjet printing ink.

7. A printed material having a printed portion on the ink receiving layer of an inkjet printing sheet according to claim 1 or 2, printed with inkjet printing ink.