JP2023082441A - thermal transfer image receiving sheet - Google Patents

Abstract

To provide a thermal transfer image receiving sheet capable of achieving both excellent image quality, and sufficient rigidity even with a thin thickness.SOLUTION: A thermal transfer image receiving sheet 10 which includes an ink image receiving layer 11 and a film base material 12 is such that: the film base material 12 has voids; average porosity (A) in a half region 12a in a thickness direction at the image receiving layer 11 side of the film base material 12 is 26-45%; average porosity (B) in a half region 12b in the thickness direction at an opposite side to the image receiving layer 11 of the film base material 12 is 18-40%; a ratio A/B of the average porosities is 1.05/1-2.2/1; the film base material 12 has a skin layer 12c without voids at least at the ink image receiving layer 11 side; a thickness of the skin layer 12c is 0.5-20 μm; and a total thickness of the entire thermal transfer image receiving sheet 10 is 140-280 μm.SELECTED DRAWING: Figure 1

Description

The present invention relates to a thermal transfer image receiving sheet.

In a conventional thermal transfer image-receiving sheet, it is known that high-quality printing can be achieved by imparting heat insulating properties and cushioning properties to the base material under the ink image-receiving layer.

For example, in Patent Document 1, a foamed PP film having a porosity of 20 to 60% having closed cells or a foamed PET film having a porosity of 20 to 80% having closed cells is provided between the substrate and the ink image-receiving layer. is proposed.

Further, in Patent Document 2, the surface of the sheet-like substrate on which the image receiving layer is formed is formed of a biaxially stretched film having a void structure, and has a Bekk smoothness of 1000 seconds or more and 50% or less. is proposed to have a gloss of

JP-A-3-221490 JP-A-5-16539

If the base film has voids, the insulation and cushioning properties are enhanced, and high-quality printing can be realized, but the rigidity of the film is reduced. As a result, for example, when an image is viewed by gripping the edge of the sheet with fingers, the sheet cannot stand on its own and tends to bend.

In order to compensate for the lack of rigidity of the film, it is conceivable to increase the thickness of the film having voids or to laminate paper or film. However, the lower the stiffness of the film, the greater the thickness required to compensate for the lack of stiffness. As a result of the increased total sheet thickness, the number of sheets that can be stored in the printer's paper feed tray decreases. Difficulties such as being bulky arise when doing so.

An object of the present invention is to provide a thermal transfer image-receiving sheet capable of achieving both excellent image quality and sufficient rigidity despite being thin.

A first aspect of the present invention is a thermal transfer image-receiving sheet comprising an ink image-receiving layer and a film substrate, wherein the film substrate has voids, and the thickness direction of the ink image-receiving layer side of the film substrate is The average porosity (A) in the half region is 26 to 45%, and the average porosity (B ) is 18 to 40%, and the average porosity A/B ratio is 1.05/1 to 2.2/1, and the film substrate has at least the ink image-receiving layer side of the voids. The thermal transfer image-receiving sheet is characterized in that it has a skin layer with no skin layer, the skin layer has a thickness of 0.5 to 20 μm, and the total thickness of the thermal transfer image-receiving sheet as a whole is 140 to 280 μm.

A second aspect of the present invention is characterized in that, in the first aspect, the film substrate is polyester.
A third aspect of the present invention is characterized in that, in the first or second aspect, the film substrate further has a void-free skin layer on the side opposite to the ink image-receiving layer.

In a fourth aspect of the present invention, in any one of the first to third aspects, the thermal transfer image-receiving sheet is provided on the opposite side of the film substrate from the ink image-receiving layer via an adhesive layer from the film. It is characterized by further having a back layer.
According to a fifth aspect of the present invention, in the fourth aspect, the adhesive layer is a polyurethane adhesive.
A sixth aspect of the present invention is characterized in that the back layer is polyester in the fourth or fifth aspect.

According to the present invention, it is possible to provide a thermal transfer image-receiving sheet capable of achieving both excellent image quality and sufficient rigidity despite being thin.

1 is a schematic cross-sectional view of a thermal transfer image-receiving sheet; FIG.

The present invention will be described below based on preferred embodiments. FIG. 1 shows an outline of a thermal transfer image-receiving sheet 10 of an embodiment. The thermal transfer image-receiving sheet 10 includes an ink image-receiving layer 11 and a film substrate 12 . In addition, in FIG. 1, the dimensional ratios and the like of the constituent elements are not necessarily the same as the actual ones.

The thermal transfer image receiving sheet 10 is a sheet on which an image is formed by, for example, a thermal sublimation transfer method. In the thermal sublimation transfer method, a sublimation dye layer is formed on a thermal transfer sheet (not shown) using a sublimation dye as a coloring material and using a heating device such as a thermal head whose heat generation is controlled according to image information. The dye inside is transferred to the thermal transfer image receiving sheet 10 to form an image.

As the thermal transfer sheet (ink ribbon), for example, three colors of yellow (Y), magenta (M), and cyan (C), or four colors of sublimation dyes obtained by adding black (K) to these three colors are applied on the film. A thermal transfer sheet having a sublimable dye layer of each color coated on the surface is used. The density gradation of each color is controlled by controlling the heating energy of the thermal head. A full-color image is formed by sequentially and repeatedly transferring the dyes of each color onto the thermal transfer sheet. The number and types of colors of the thermal transfer sheet can be appropriately designed and changed.

<Ink image receiving layer>
The ink image-receiving layer 11 is, for example, a layer for receiving dyes from a thermal transfer sheet to form an image. The ink image-receiving layer 11 preferably contains a resin material such as a binder resin for dyeing. If necessary, the ink image-receiving layer 11 may contain additives such as release agents.

Examples of the binder resin include polyolefin resins such as polyethylene and polypropylene; polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylate, vinyl chloride-vinylidene chloride copolymer resin, vinyl chloride-vinyl acetate copolymer resin, vinyl resins such as vinyl chloride-acrylate copolymer resins; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polystyrene resins such as polystyrene and copolymers of styrene and other olefins; polyamide resins; Resins; copolymers of olefins such as ethylene and propylene with other vinyl monomers; ionomers; cellulose derivatives and the like. One type of binder resin may be used alone, or two or more types may be used in combination. The content of the binder resin is preferably 90% by mass or more with respect to the total mass of the ink image-receiving layer 11, and may be 100% by mass.

Examples of release agents include silicone oil, phosphate ester plasticizers, fluorine compounds, and the like. The silicone oil may be straight silicone oil or modified silicone oil. The content of the releasing agent is preferably 0.01 to 20 parts by mass with respect to 100 parts by mass of the binder resin.

Other additives that the ink image-receiving layer 11 may contain as necessary include, for example, one or more of fluorescent whitening agents, pigments, dyes, antistatic agents, and the like. The basis weight of the ink image-receiving layer 11 may be, for example, 0.5 to 6.0 g/m ² in terms of solid content.

The method for forming the ink image-receiving layer 11 is not particularly limited. can be formed by coating on the surface of the support and drying. Examples of liquid media include water and organic solvents.

A coating method for forming the ink image-receiving layer 11 can be performed by a known coating method. For example, known coating equipment such as bar coater, wire bar coater, micro gravure coater, gravure coater, comma coater, blade coater, air knife coater, gate roll coater, curtain coater, spray coater and die coater can be used. can. A drying process after coating can be performed using a known drying method such as a roll support method or a floating method.

<Film substrate>
The film substrate 12 is a substrate using a film having voids inside, and can support the ink image receiving layer 11 . The film substrate 12 may be a single layer or multiple layers. As the film substrate 12, a resin film in which voids are formed inside a matrix resin may be used. As the matrix resin, thermoplastic resins such as polyester-based resins, polyolefin resins, vinyl-based resins, polystyrene-based resins, and the like are preferable.

The matrix resin of the film substrate 12 may be the same type of resin as the binder resin of the ink image-receiving layer 11, or may be a different resin. Specific examples of suitable matrix resins include polypropylene (PP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and the like.

As the matrix resin, a polyester-based resin is preferable in that it has a high Young's modulus, excellent rigidity, excellent heat resistance and versatility, and has a chemical structure in which an aromatic carboxylic acid component and an aliphatic polyol component are condensed. family polyesters are more preferred. The aromatic carboxylic acid component includes one or more of terephthalic acid, isophthalic acid, naphthalic acid, biphenyldicarboxylic acid, and the like. The aliphatic polyol component includes one or more of ethylene glycol, trimethylene glycol, butylene glycol, 1,6-hexanediol, cyclohexanedimethanol, and the like.

The method for manufacturing the film substrate 12 is not particularly limited, and can be appropriately selected from known methods. Film forming methods include cast molding, calendar molding, roll molding, and inflation molding.

In cast molding, for example, a single-layer or multi-layer T-die, I-die, or the like connected to a screw extruder may be used to extrude the molten resin into a sheet. In inflation molding, for example, a single-layer or multi-layer inflation die may be used to extrude a molten resin into a tubular shape. When forming a film, for example, a method of forming a mixture of a thermoplastic resin and an organic solvent or oil into a film by cast molding, calendering or the like, and then removing the solvent or oil may be used. The solvent may be removed after forming the film from the thermoplastic resin solution.

A method of forming voids in the film substrate 12 is not particularly limited, but a method of adding an incompatible material to the matrix resin and forming voids around the incompatible material is preferable. Incompatible materials include incompatible polymers, fillers (particles), and the like. Compared to the method of adding a substance that generates gas by thermal decomposition to the resin, the voids formed around the incompatible material are less likely to expand in the thickness direction, and the voids are more likely to be distributed. Further, according to the method of stretching the matrix resin containing the incompatible material, it is easy to form the skin layers 12c and 12d on at least one surface of the film substrate 12 in the thickness direction.

When the incompatible polymer is added to the matrix resin, the incompatible polymer becomes fine particles by dispersing the incompatible polymer in the matrix resin by melt-kneading. For example, when a polyester-based resin is used as the matrix resin, one or two of polystyrene-based resins, polyolefin-based resins, polyacrylic-based resins, polycarbonate resins, polysulfone-based resins, and cellulose-based resins are used as incompatible polymers with polyester. The above are mentioned. Polyolefin resins such as polystyrene resins, polymethylpentene, and polypropylene are particularly preferred.

When a filler (particles) is added to the matrix resin, it may be an inorganic filler or an organic filler. Examples of inorganic fillers include calcium carbonate, silica, alumina, titanium oxide, zinc oxide, barium sulfate, zeolite, and aluminum hydroxide. Examples of organic fillers include polymethyl acrylate, styrene resins, and phenol resins. Calcium carbonate is particularly preferred. Various surface treatments can be applied to the surface of the filler. One type of filler may be used alone, or two or more types of fillers may be used in combination.

When polyester such as PET is used as the matrix resin, a method of adding an incompatible polymer and melt-kneading is preferred. When polyolefin such as PP is used as the matrix resin, it is preferable to add an inorganic or organic filler as a foaming agent. The porosity control method can be adjusted by the compounding ratio of the matrix resin and the immiscible material, the particle size of the immiscible material, the stretching temperature of the film, and the like.

The film substrate 12 used in the embodiment has an average porosity (A) of 26 to 45% in the region 12a, which is half the thickness direction of the film substrate 12 on the ink image receiving layer 11 side. 12 has an average porosity (B) of 18 to 40% in a half-thickness region 12b on the opposite side of the ink image-receiving layer 11, and the ratio of the average porosity A/B is 1.05. /1 to 2.2/1.

In the following description, the half-thickness region 12a on the side of the ink image-receiving layer 11 is called the image-receiving-side region 12a, and the half-thickness region 12b on the opposite side is called the opposite side region 12b. Sometimes. The average porosity A is greater than the average porosity B because the ratio of the average porosity A of the image-receiving side area 12a to the average porosity B of the opposite side area 12b is greater than 1.

The average porosity (A) of the area 12a on the image receiving side is preferably 26 to 45%, more preferably 31 to 40%. When the average porosity (A) is at least the above lower limit, the heat insulating properties of the voids are effectively exhibited, making it easier to obtain an image with clear color development. When the average porosity (A) is equal to or less than the upper limit, the interlayer strength of the film substrate 12 is sufficiently increased, delamination is suppressed, and rigidity is increased.

The average porosity (B) of the region 12b on the opposite side is preferably 18-40%, more preferably 24-34%. When the average porosity (B) is at least the lower limit, the heat insulating properties of the voids are effectively exhibited, making it easier to obtain an image with clear color development. When the average porosity (B) is equal to or less than the upper limit, the rigidity of the film substrate 12 is increased, and the rigidity of the thermal transfer image-receiving sheet 10 as a whole is also increased. In addition, the interlayer strength of the film substrate 12 is sufficiently increased, and the occurrence of delamination can be suppressed.

The average porosity A/B ratio is preferably 1.05/1 to 2.2/1, more preferably 1.1/1 to 1.67/1. When the ratio of A/B of the average porosity is equal to or higher than the lower limit, the heat insulating properties of the voids are effectively exhibited, making it easier to obtain an image with clear color development. Further, the rigidity of the film substrate 12 is increased, and the rigidity of the thermal transfer image receiving sheet 10 as a whole is also increased. When the ratio of A/B of the average porosity is equal to or less than the upper limit, the interlayer strength of the film substrate 12 is sufficiently increased, and the occurrence of delamination can be suppressed. Further, the rigidity of the film substrate 12 is sufficient, and the rigidity of the thermal transfer image receiving sheet 10 as a whole is also sufficient.

The porosity can be measured as follows. First, a cross section in the thickness direction of the film substrate 12 is photographed with an electron microscope. Next, the obtained image is binarized using image processing software. For the binarized image, the area ratio of void portions to a predetermined area of the film substrate 12 is calculated. The average porosity can be obtained by calculating the area ratio of the void portions at any two or more locations from the same sample of the film substrate 12 and calculating the average value.

The film substrate 12 preferably has a void-free skin layer 12c at least on the ink image-receiving layer 11 side. In the following description, the skin layer 12c on the ink image receiving layer 11 side may be referred to as the image receiving side skin layer 12c. The image-receiving-side skin layer 12c is a region of the film substrate 12 on the side of the ink image-receiving layer 11 in the thickness direction that has substantially no voids. The image-receiving side skin layer 12 c can be continuously formed from the same resin material as the matrix resin of the film substrate 12 . The void-containing layer 12e of the film substrate 12 is a region other than the skin layers 12c and 12d. The skin layer 12d on the side opposite to the ink image receiving layer 11 will be described later.

The thickness of the image-receiving side skin layer 12c is preferably 0.5 to 20 μm, more preferably 1 to 10 μm. When the thickness of the image-receiving side skin layer 12c is at least the above lower limit, voids in the film substrate 12 are less likely to be exposed to the surface, and smoothness is less likely to be impaired, so unevenness in density and blurring of images are less likely to occur. . When the thickness of the image-receiving side skin layer 12c is equal to or less than the above upper limit, the distance from the thermal head of the sublimation printer to the layer having voids of the film base material 12 is sufficiently close, and heat insulation is exhibited more effectively. This makes it easier to obtain an image with vivid colors.

When the image-receiving side skin layer 12c is said to have substantially no voids, it means that the void ratio is less than 1%, for example. A binarized image is created in the same manner as the porosity measurement method, and the void ratio is measured between the boundary line parallel to the surface of the film substrate 12 on the ink image receiving layer 11 side. When the area is set, if the porosity is less than 1%, the area to be measured is determined to be the image-receiving side skin layer 12c. The thickness of the image-receiving side skin layer 12c is obtained as the distance between the surface on the side of the ink image-receiving layer 11 and the boundary line of the measurement target area. At this time, the boundary line of the measurement target area is the boundary line between the image-receiving side skin layer 12c and the void-containing layer 12e.

The total thickness of the entire thermal transfer image-receiving sheet 10 is preferably 140-280 μm, more preferably 180-240 μm. When the total thickness of the thermal transfer image-receiving sheet 10 is at least the lower limit value, it is easy to ensure sufficient rigidity of the thermal transfer image-receiving sheet 10 as a whole. When the total thickness of the entire thermal transfer image receiving sheet 10 is equal to or less than the upper limit value, the number of thermal transfer image receiving sheets 10 that can be set in the paper feed cassette is substantially the same as or more than the conventional one, and the frequency of paper feeding is not troublesome, and handling (handling) is possible. ) becomes easier.

The total thickness of the entire thermal transfer image-receiving sheet 10 may be measured using a measuring instrument at room temperature (5 to 35° C.), for example. The total thickness of the entire thermal transfer image-receiving sheet 10 may be the total thickness of each layer included in the thermal transfer image-receiving sheet 10 . For example, when the thermal transfer image-receiving sheet 10 has the back layer 14 , it may be the total thickness from the ink image-receiving layer 11 to the back layer 14 . When the thermal transfer image-receiving sheet 10 does not have the back layer 14, the total thickness of the ink image-receiving layer 11 and the film substrate 12 may be used.

The film substrate 12 may further have a void-free skin layer 12 d on the side opposite to the ink image-receiving layer 11 . In the following description, the skin layer 12d on the side opposite to the ink image receiving layer 11 may be referred to as the opposite side skin layer 12d. The opposite-side skin layer 12d is a region of the film substrate 12 on the side opposite to the ink image-receiving layer 11 in the thickness direction and having substantially no voids. The opposite side skin layer 12 d can be continuously formed from the same resin material as the matrix resin of the film substrate 12 .

The thickness of the opposite side skin layer 12d is preferably 0.5-20 μm, more preferably 1-10 μm. When the thickness of the opposite side skin layer 12d is equal to or greater than the above lower limit, voids in the film substrate 12 are less likely to be exposed to the surface, and smoothness is less likely to be impaired. When the thickness of the opposite-side skin layer 12d is equal to or less than the upper limit, sufficient smoothness necessary for laminating the adhesive layer 13 can be obtained.

When the opposite skin layer 12d is said to have substantially no porosity, it means that the porosity is less than 1%, for example. The thickness of the opposite side skin layer 12d can be measured in the same manner as the thickness of the image receiving side skin layer 12c except that the opposite side skin layer 12d is a region including the surface opposite to the ink image receiving layer 11. can. At this time, the boundary line of the measurement target area is the boundary line between the opposite side skin layer 12d and the void-containing layer 12e. When the film substrate 12 does not have the opposite side skin layer 12d, the void-containing layer 12e may be exposed on the side opposite to the ink image receiving layer 11. FIG.

The method of forming the film substrate 12 having different porosities in the thickness direction is not particularly limited, and any appropriate method can be adopted. The film substrate 12 having different distributions of porosity may be formed from a single resin layer. The film substrate 12 may be formed from two or more resin layers having different porosities.

In order to form a distribution of different porosities in the thickness direction of the single-layer film substrate 12, a matrix resin to which an incompatible material such as an incompatible polymer and a foaming agent is added is kneaded and melted, followed by extrusion molding. Afterwards, the stretching step may be carried out in a state having a temperature distribution in the thickness direction. The film material is cooled by passing the extruded resin film through a raw material cooling device. For example, when one side of the extruded film material is cooled by contacting the cooling roll, the thickness direction of the film can be adjusted by adjusting the outer circumference of the cooling roll and the method of passing the paper through the cooling roll (holding angle). temperature gradient can be created. In this way, by performing the step of stretching in a state where there is a temperature gradient in the thickness direction, it is possible to adjust the porosity to be different in the thickness direction.

When the film substrate 12 is formed from two or more resin layers with different porosities, for example, by adjusting the addition amount of the incompatible material such as the incompatible polymer and foaming agent, the subsequent processing conditions, etc. , the porosity can be adjusted layer by layer. Also when forming the film substrate 12 from two or more resin layers, the step of stretching may be performed in a state where there is a temperature gradient in the thickness direction. When two or more resin layers contain the same kind of matrix resin, it is possible to laminate with less occurrence of delamination, which is preferable. For example, two or more layers may be simultaneously molded and laminated using a multi-layer T die for co-extrusion, an inflation die, or the like.

The area 12a on the image receiving side and the area 12b on the opposite side may be formed from the same resin layer. The image-receiving side area 12a and the opposite side area 12b may be formed from resin layers having different porosities and integrated. At least one of the skin layers 12c and 12d may be formed from the same resin layer as the void containing layer 12e. The skin layers 12c and 12d and the void containing layer 12e may be formed from different resin layers and integrated. The region 12a on the image receiving side and the region 12b on the opposite side of the void containing layer 12e may be the same resin layer or different resin layers.

The distribution of voids in the void-containing layer 12e is not particularly limited as long as the above upper limit is satisfied. The voids may be distributed substantially uniformly from the ink image receiving layer 11 side to the opposite side. The porosity may change in a gradient manner, or may change in a stepwise manner. Regions of the void-containing layer 12e adjacent to the skin layers 12c and 12d have a higher porosity than the skin layers 12c and 12d (for example, 1% or more). At positions away from the skin layers 12c and 12d, the void-containing layer 12e may partially include regions having substantially no voids.

The obtained film substrate 12 is preferably stretched and oriented at least uniaxially, preferably biaxially, under known conditions by roll stretching, tenter stretching, inflation stretching, or the like, and then heat-treated.

<Other Configurations of Thermal Transfer Image Receiving Sheet>
The thermal transfer image-receiving sheet 10 of the embodiment should include at least the ink image-receiving layer 11 and the film substrate 12 . The thermal transfer image receiving sheet 10 may further have a back layer 14 made of a film on the opposite side of the film substrate 12 to the ink image receiving layer 11 with an adhesive layer 13 interposed therebetween.

The adhesive layer 13 is a layer that bonds the film substrate 12 and the back layer 14 together. The adhesive layer 13 is not particularly limited, and can be formed using various known adhesives. Examples of adhesives include polyurethane resins, polyolefin resins such as α-olefin-maleic anhydride copolymer resins, polyester resins, acrylic resins, epoxy resins, urea resins, melamine resins, and phenol resins. , vinyl acetate-based resins, cyanoacrylate-based resins, and the like. The adhesive layer 13 is preferably made of a polyurethane-based resin because it has excellent suitability for dry lamination and can be adhered with a small coating amount.

The adhesive layer 13 may be made of the adhesive (resin) described above as a main agent, and may be cured by adding a curing agent. The curing agent can be appropriately selected depending on the main agent, and for example, isocyanate compounds, aliphatic amines, cycloaliphatic amines, aromatic amines, acid anhydrides and the like can also be used.

Formation of the adhesive layer 13 can be performed by a known coating method. For example, known coating equipment such as bar coater, wire bar coater, micro gravure coater, gravure coater, comma coater, blade coater, air knife coater, gate roll coater, curtain coater, spray coater and die coater can be used. can. A drying process after coating can be performed using a known drying method such as a roll support method or a floating method.

A resin film may be used for the back layer 14 . As the resin film, films of thermoplastic resins such as polyester and polyolefin are preferable. Specific examples of resins suitable for the material of the back layer 14 include polypropylene (PP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and the like. The resin of the back layer 14 may be the same as or similar to the matrix resin of the film substrate 12 .

The back layer 14 may be a resin film having substantially no voids. When the back layer 14 is said to be substantially free of voids, it means that the porosity is less than 1%, for example. Back layer 14 may be transparent or may be colored. The back layer 14 may or may not contain an antistatic agent.

In the thermal transfer image-receiving sheet 10 of the embodiment, in the film base material 12 on the ink image-receiving layer 11 side, by increasing the porosity on the ink image-receiving layer 11 side, heat insulating properties and cushioning properties are imparted, and excellent image quality is obtained. can be done. In addition, by reducing the porosity of the film substrate 12 on the side opposite to the ink image receiving layer 11 and by providing the skin layers 12c and 12d without voids on the ink image receiving layer 11 side or both sides, sufficient rigidity is achieved even if the thickness is thin. can provide the thermal transfer image-receiving sheet 10 having

The thermal transfer image-receiving sheet 10 of the embodiment may further include layers other than those described above, if necessary. For example, an adhesive layer, an adhesive layer, a release layer, a back printing layer, an antistatic layer, a cover layer, a matte layer (mat layer), an anti-slip layer, an easy-adhesion layer, or a film may be added to the back surface of the thermal transfer image-receiving sheet 10. A base material such as paper may be a single layer or a laminate of two or more layers in any combination. The antistatic layer (not shown) can be formed, for example, by applying a paint containing an antistatic agent. The antistatic layer may contain a resin material such as a binder resin.

Also, a release sheet may be laminated on the back surface of the thermal transfer image receiving sheet 10 . For example, at least an adhesive layer may be laminated on the surface of the back layer 14 opposite to the adhesive layer 13, and a release sheet may be attached. When the film substrate 12 is the first substrate and the back layer 14 is the second substrate, the release sheet may have a third substrate. At least an adhesive layer may be laminated on the surface of the film substrate 12 opposite to the ink image-receiving layer 11, and a release sheet may be attached. More specifically, for example, an easy-adhesive layer and an adhesive layer are laminated in this order on the back surface of the thermal transfer image-receiving sheet 10 to form an adhesive sheet (seal). ), an easy-adhesive layer, a back printing layer, and an antistatic layer may be attached in this order, and may be peelable at the boundary between the adhesive layer and the release layer.

The total thickness of the thermal transfer image receiving sheet 10 having a release sheet includes the thickness of the release sheet. The release base material is the base material of the release sheet. A release layer may be laminated to one side of the release substrate, and optionally other layers may be laminated to the opposite side. The material of the release substrate is not particularly limited, but a resin film having voids, a resin film having no voids, paper, or the like can be used.

The thermal transfer image-receiving sheet 10 of the embodiment can be used for producing prints. A printed matter can be produced by forming an image on the ink image-receiving layer 11 . An image protection layer may be provided over the image, if desired. The image protection layer can be formed, for example, from a transparent or translucent resin coat, laminate, or the like. The printed matter may be, for example, cards, games, or the like.

The thermal transfer image-receiving sheet 10 of the embodiment or a print produced using the sheet may further have a design on the back side. For example, the back surface of the thermal transfer image-receiving sheet 10 may be provided with a back printing layer, a cover layer, and the like. The back printed layer (not shown) is a printed layer formed by, for example, a known printing method. The cover layer (not shown) can be formed of a transparent or translucent resin coat, laminate, or the like in order to protect the back printing layer, for example.

Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. Modifications include additions, substitutions, omissions, and other changes of components in each embodiment.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

<Preparation of film substrate>
Polyethylene terephthalate (PET) or polypropylene (PP) was used to prepare a single-layer or multi-layer film substrate having voids. When the material was PET, an incompatible polymer was added to PET, melt-kneaded and dispersed, and then the film was stretched to form voids having a distribution in the thickness direction. When the material was PP, a filler such as calcium carbonate was added to PP, melt-kneaded and dispersed, and then the film was stretched to form voids having a distribution in the thickness direction.

<Preparation of Thermal Transfer Image Receiving Sheet>
An ink image-receiving layer-forming paint was applied to one side of the film substrate to form an ink image-receiving layer. In Example 12, the back layer was omitted, but in other thermal transfer image-receiving sheets, an adhesive was applied to the surface of the film substrate opposite to the ink image-receiving layer, and then a void-free resin film was laminated. . A urethane adhesive or an acrylic adhesive was used as the adhesive. PET or PP was used for the resin film having no voids in the back layer.

<Measurement of average porosity>
The thermal transfer image-receiving sheet was cut in the thickness direction, and the cut surface including the film substrate was photographed at a magnification of 2000 using a scanning electron microscope (manufactured by JEOL Ltd., JSM-6460LV). Next, using image processing software (manufactured by Mitani Shoji Co., Ltd., product name: WinROOF), the image obtained by the photographing was binarized. For the binarized image, the area ratio of void portions in the image was calculated.

A half area in the thickness direction on the side of the ink image-receiving layer and a half area in the thickness direction on the side opposite to the ink image-receiving layer are separated, and the average porosity of the area on the side of the ink image-receiving layer is calculated. The "average porosity A on the image-receiving side" and the average porosity of the area opposite to the ink image-receiving layer were "average porosity B on the opposite side". The ratio of the two was calculated to obtain the "ratio of A/B".

<Measurement of skin layer thickness>
For the binarized image obtained by measuring the average porosity, the thickness of the area of the film substrate that is in contact with the ink image-receiving layer and has a porosity of less than 1% is calculated as the "image-receiving side skin layer thickness. thickness. Similarly, the thickness of the region of the film substrate that is in contact with the surface opposite to the ink image-receiving layer (adhesive layer, if any) and has a porosity of less than 1% is calculated. thickness of the skin layer".

<Evaluation of image quality>
The thermal transfer image-receiving sheet was cut into a width (short side) of 100 mm and a length (long side) of 177 mm to obtain an evaluation sheet. The evaluation sheet was set in a sublimation-type thermal transfer printer (SELPHY CP1300 manufactured by Canon Inc.), and a portrait image and a landscape image were printed. The image on the evaluation sheet after printing was visually confirmed, and the image quality was determined according to the following criteria.

⊚: The level was completely free of unevenness in density, fading, and unclear portions of color development.
◯: Unevenness in density, faintness, or unclear color development could not be observed unless carefully observed.
Δ: Unevenness in density, faintness, or indistinct portions of color development were conspicuous, and the image quality was impaired.
x: Obvious shading unevenness, faintness, or unclear portions of color development were observed, and the image quality was significantly impaired.

<Rigidity evaluation>
Is the image easy to see when holding the thermal transfer image-receiving sheet used for image quality evaluation horizontally, with the short side (100 mm) vertical and the long side (177 mm) horizontal, with the lower right corner sandwiched between the thumb and forefinger? , and the degree of curvature of the thermal transfer image-receiving sheet was visually confirmed and evaluated according to the following criteria.

⊚: Almost no bending due to its own weight was observed, and the image was at a level at which it was easy to see.
◯: Slight curvature due to its own weight was observed, but it was at a level that did not hinder viewing of the image.
Δ: Curvature due to its own weight was observed, and the image was at a level where it was difficult to see.
x: Remarkably curved due to its own weight, and the image was at a level where it was extremely difficult to see.

<Evaluation of handling>
The complexity of paper feeding due to a change in the number of thermal transfer image-receiving sheets that can be set in the paper feed cassette at one time was evaluated according to the following criteria. A thermal transfer image-receiving sheet having a thickness of 210 μm was used as a conventional evaluation sheet.

(double-circle): The frequency of sheet feeding was reduced, and the complexity was reduced.
◯: Paper feeding frequency is the same as in the conventional case.
Δ: The paper feed frequency increased compared to the conventional method, and the paper became somewhat complicated.
x: The frequency of paper feeding was greatly increased compared with the conventional method, and the paper became extremely complicated.

<Evaluation of interlayer strength>
Polyester adhesive tape (manufactured by Nitto Denko Corporation, No. 31B 75 high, thickness 25 μm, width 25 mm) was adhered to a length of 50 mm on the surface of the thermal transfer image-receiving sheet facing the ink image-receiving layer. The attached adhesive tape was quickly peeled off at an angle of 90° in the vertical direction with respect to the side surface (peeling operation). The peeling operation was repeated up to 10 times at the same position on the surface of the ink image-receiving layer, and evaluation was made according to the following criteria.

A: No delamination was observed after 10 peeling operations, and the interlayer strength was at a sufficient level.
◯: Delamination was observed by the 10th peeling operation, but the interlayer strength level was such that there was little possibility of impeding practical use.
Δ: Delamination was observed by the third peeling operation, and the level of interlaminar strength was such that there is a possibility of hindering practical use.
x: Delamination was observed at the first peeling operation, and the interlayer strength level was such that it could not withstand actual use.

<Comprehensive Evaluation Criteria>
A comprehensive evaluation was obtained from the evaluation results of the four items of image quality, rigidity, handling, and interlaminar strength.
(double-circle): When evaluation of all four items is (double-circle) or (circle).
◯: Evaluation of 4 items does not include x, includes △, and the rest is only ⊙ or ◯.
×: When even one × is included in the evaluation of the four items.

The above results are shown in Tables 1-4.

The thermal transfer image-receiving sheets of Examples 1 to 19 were excellent in image quality, rigidity and handling, and were excellent in interlayer strength.

The thermal transfer image-receiving sheet of Comparative Example 1 having a small total thickness was inferior in stiffness.
The thermal transfer image-receiving sheet of Comparative Example 2, in which the thickness of the image-receiving side skin layer is thin, was inferior in image quality.
The thermal transfer image-receiving sheet of Comparative Example 3, in which the average void ratio B on the opposite side was small and the ratio of A/B was large, was inferior in image quality.
The thermal transfer image-receiving sheet of Comparative Example 4, in which the average void ratio A and the ratio of A/B on the image-receiving side were small, was inferior in image quality.

The thermal transfer image-receiving sheet of Comparative Example 5, which had a large average void ratio A on the image-receiving side, was inferior in interlayer strength.
The thermal transfer image-receiving sheet of Comparative Example 6, which had a large average void ratio B on the opposite side and a small A/B ratio, was inferior in stiffness.
The thermal transfer image-receiving sheet of Comparative Example 7, in which the average void ratios A and A/B on the image-receiving side were large, was inferior in interlayer strength.
The thermal transfer image-receiving sheet of Comparative Example 8 having a thick image-receiving side skin layer was inferior in image quality.
The thermal transfer image-receiving sheet of Comparative Example 9 having a large total thickness was inferior in handling.

10 Thermal transfer image receiving sheet 11 Ink image receiving layer 12 Film substrate 12a Image receiving side area 12b Opposite side area 12c Image receiving side skin layer 12d Opposite side skin layer 12e Contains voids Layer, 13...adhesive layer, 14...back layer.

Claims (6)

A thermal transfer image-receiving sheet comprising an ink image-receiving layer and a film substrate,
The film substrate has voids, and an average void ratio (A) in a half thickness direction region of the film substrate on the ink image-receiving layer side is 26 to 45%. The average porosity (B) in the 1/2 region in the thickness direction opposite to the ink image-receiving layer is 18 to 40%, and the ratio of the average porosity A/B is 1.05/1. ~2.2/1;
The film substrate has a void-free skin layer at least on the ink image-receiving layer side, and the skin layer has a thickness of 0.5 to 20 μm,
A thermal transfer image-receiving sheet, wherein the total thickness of the entire thermal transfer image-receiving sheet is 140 to 280 μm. 2. The thermal transfer image-receiving sheet according to claim 1, wherein said film substrate is polyester. 3. The thermal transfer image-receiving sheet according to claim 1, wherein the film substrate further has a void-free skin layer on the side opposite to the ink image-receiving layer. 4. The thermal transfer image-receiving sheet according to any one of claims 1 to 3, further comprising a back layer made of a film on the opposite side of the film substrate to the ink image-receiving layer via an adhesive layer. The thermal transfer image-receiving sheet described in . 5. The thermal transfer image-receiving sheet according to claim 4, wherein the adhesive layer is a polyurethane adhesive. 6. The thermal transfer image-receiving sheet according to claim 4, wherein said back layer is made of polyester.

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