JP7808064B2 - Transfer paper - Google Patents

Description

The present invention relates to transfer paper used to transfer a pattern in a transfer printing method using textile ink to form a pattern on a substrate such as a textile material. In particular, the present invention relates to transfer paper suitable for transfer printing methods using dye-sublimation textile ink.

A known example of such transfer paper is an inkjet recording medium for sublimation ink transfer, which comprises an ink-receiving layer containing at least a pigment and an adhesive on a support, and which contains silicone spherical powder in the ink-receiving layer (see, for example, Patent Document 1).
The inkjet recording medium for sublimation ink transfer described in Patent Document 1 prevents sticking between the recording medium and the print medium due to heat fusion that occurs during transfer.
Further, as an example of a recording medium, a recording medium is known in which an ink receiving layer containing inorganic fine particles and a binder is provided on a substrate, some of the inorganic fine particles protrude from the binder layer of the ink receiving layer, and the inorganic fine particles are contained in an amount of 0.05 parts to 3 parts per 100 parts of the solid content of the binder (see, for example, Patent Document 2).
The recording medium described in Patent Document 2 is excellent in image characteristics, anti-blocking properties, transportability in various printers, and continuous paper feed properties.

Japanese Patent Application Laid-Open No. 2006-256018 Japanese Patent Application Publication No. 07-304249

The transfer printing method involves two steps: printing a design onto transfer paper to obtain transfer paper, and then bringing the printed side of the transfer paper face-to-face with the substrate to be printed and bringing them into close contact. The contacting step may involve heating or applying heat and pressure, as necessary. Examples of the contacting step include using a press, heated roll, or heated drum to bring the transfer paper and the substrate into close contact with each other, and then applying heat or heat and pressure. In particular, in the transfer printing industry, in order to increase productivity, a method is often adopted in which the transfer paper and the substrate are transported in close contact with each other, while being sandwiched between heated rolls or heated drums.

In the above-described conveyance, while this is not a problem when the conveyance path is straight, when the conveyance path is curved, particularly when it has a U-shaped curve that reverses the conveyance direction, the trailing edge of the closely-contacted transfer paper and printed material may flutter or bounce as it passes between the conveyance rolls, i.e., "trailing edge turbulence." This phenomenon adversely affects the image formed on the printed material at and near the trailing edge. Conventionally, for example, clear trailing edge turbulence occurred about once out of about 25 transfer printing runs, necessitating quality checks in subsequent processes, and thus posing a problem in terms of stable production.
SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a transfer paper sheet that is less prone to rear end upset than conventional transfer paper sheets.

The inventors have conducted extensive research to solve the above problems. As a result, the object of the present invention has been achieved as follows:

[1] Transfer paper for use in transfer printing, comprising base paper and one or more coating layers on at least one side of the base paper, wherein the outermost coating layer, which is the coating layer located outermost relative to the base paper, contains a white inorganic pigment and a binder, and wherein the white inorganic pigment contains at least one type whose volume-based average particle size (diameter, unit μm) is 110% to 200% of the average layer thickness (unit μm) of the outermost coating layer, and wherein the static friction coefficient measured on the side having the outermost coating layer is 0.8 or less and the dynamic friction coefficient is 0.6 or less.

The present invention makes it possible to provide transfer paper in a transfer printing method in which the transfer paper, on which a pattern to be transferred is printed, and the printed material are in close contact with each other, and in which the rear end of the closely contacted material is less likely to move uncontrollably during transport than in conventional methods.

The present invention will be described in detail below.
In this specification, "transfer paper" refers to a blank sheet of paper before a design to be transferred is printed on it. "Transfer paper" refers to a sheet of paper on which a design to be transferred has been printed.

The transfer paper comprises a base paper and one or more coating layers on at least one side of the base paper.
The base paper may be made from chemical pulp such as LBKP (Leaf Bleached Kraft Pulp) or NBKP (Needle Bleached Kraft Pulp), mechanical pulp such as GP (Groundwood Pulp), PGW (Pressure Groundwood pulp), RMP (Refiner Mechanical Pulp), TMP (ThermoMechanical Pulp), CTMP (ChemiThermoMechanical Pulp), CMP (ChemiMechanical Pulp), or CGP (ChemiGroundwood Pulp), or DIP (Deinked Pulp). The paper is obtained by making a paper stock containing a slurry of one or more pulps selected from recycled paper pulp such as recycled pulp (e.g., recycled pulp), calcium carbonate, talc, clay, various kaolins, and other fillers, as well as additives such as binders, sizing agents, fixing agents, retention agents, cationizing agents, paper strength agents, pigment dispersants, thickeners, flow improvers, antifoaming agents, foam suppressors, release agents, foaming agents, penetrating agents, coloring dyes, coloring pigments, fluorescent brighteners, ultraviolet absorbers, antioxidants, preservatives, mildew inhibitors, and water-resistant agents, as needed. The base paper also includes wood-free paper obtained by calendering the paper, or by surface-sizing or surface-treating the paper with starch, styrene-acrylic resin, or the like. The base paper also includes wood-free paper obtained by calendering the surface-sizing or surface-treating the paper.

In some embodiments, the paper has a density of 0.75 g/cm ^or more and 0.85 g/cm or ^less as determined in accordance with ISO 534:2011 "Paper and board - Determination of thickness, density and specific volume." The reason for this is that this improves adhesion between the transfer paper and the printed material.

Papermaking is carried out by adjusting the paper stock to an acidic, neutral or alkaline state and using a paper machine conventionally known in the papermaking field, such as a Fourdrinier paper machine, a twin-wire paper machine, a combination paper machine, a cylinder paper machine, or a Yankee paper machine.
The calendering is carried out using a calendering device conventionally known in the papermaking field, such as a machine calender, a soft nip calender, a super calender, a multi-stage calender, or a multi-nip calender.

In some embodiments, the pulp contains 80% by mass or more of LBKP and NBKP in total, 75% by mass or more and 95% by mass or less of LBKP with a freeness in the range of 380 ml to 480 ml, and 5% by mass or more and 25% by mass or less of NBKP with a freeness in the range of 400 ml to 480 ml, based on the pulp of the base paper. The reason for this is that this improves adhesion between the transfer paper and the printed material.
The freeness is the CSF freeness determined in accordance with ISO 5267-2:2001 "Pulps - Determination of drainability - Part 2 Canadian Standard freeness method."

Among the coating layers, the coating layer located outermost relative to the base paper is referred to as the outermost coating layer. When there is only one coating layer, that coating layer becomes the outermost coating layer. The outermost coating layer contains at least a white inorganic pigment and a binder. When there are two or more coating layers, the coating layer located between the base paper and the outermost coating layer is a coating layer conventionally known in the field of coated paper, and there are no particular restrictions on the presence, type, and quantity of a white inorganic pigment, the presence, type, and quantity of a binder, or the presence and quantity of other conventionally known additives.
In some embodiments, the transfer paper has one coating layer. This is because the manufacturing cost of the transfer paper is advantageous. In some embodiments, the transfer paper has two coating layers, including the outermost coating layer. This is because migration of the printing ink from the transfer paper to the printing substrate, rather than to the opposite direction, can be suppressed in a contact state during transfer printing.

In some embodiments, when the coating layer consists of two layers including the outermost coating layer, the coating layer located between the base paper and the outermost coating layer contains a white inorganic pigment and a binder, because this can further suppress the migration of the printing ink in the opposite direction as described above.
The white inorganic pigment is one that has been conventionally known in the field of coated paper. Examples of the white inorganic pigment include various kaolins such as kaolin, delaminated kaolin, calcined kaolin, and engineered kaolin, heavy calcium carbonate, light calcium carbonate, talc, satin white, lithopone, titanium oxide, zinc oxide, amorphous silica, colloidal silica, alumina, aluminum hydroxide, zinc oxide, activated clay, and diatomaceous earth. The binder is one that has been conventionally known in the field of coated paper. Examples of binders include starches such as starch, modified starch, and modified starch, celluloses such as carboxymethyl cellulose and hydroxyethyl cellulose, naturally occurring resins or derivatives thereof such as casein, gelatin, soy protein, pullulan, gum arabic, Karaya gum, and albumin, polyvinyl alcohols such as polyvinyl alcohols of various degrees of saponification or polymerization and various modified polyvinyl alcohols, polypropylene glycol, polyethylene glycol, copolymer resins such as maleic anhydride resins, acrylic acid resins, methacrylic acid resins, acrylate resins, methacrylate resins, acrylate-butadiene copolymers, styrene-butadiene copolymers, and ethylene-vinyl acetate copolymers, as well as functional group-modified resins obtained by introducing functional groups such as carboxy groups into these copolymer resins, thermosetting resins such as melamine resins and urea resins, polyurethane resins, unsaturated polyester resins, polyvinyl butyral, and alkyd resins. The coating layer located between the base paper and the outermost coating layer can contain various additives conventionally known in the field of coated paper, as needed. Examples of the additives include organic pigments, dispersants, surfactants, fixing agents, thickeners, flow improvers, antifoaming agents, release agents, foaming agents, penetrating agents, colorants, printability improvers, fluorescent brighteners, ultraviolet absorbers, antioxidants, preservatives, mildew inhibitors, cationic resins such as modified polyamines and modified polyamides, and the like.

In some embodiments, the transfer paper has two coating layers including an outermost coating layer, and the coating layer located between the base paper and the outermost coating layer contains a white inorganic pigment and a binder, and the white inorganic pigment contains at least one selected from various kaolins and heavy calcium carbonate. The reason for this is that the migration of the textile printing ink in the opposite direction can be further suppressed, and the solvent contained in the textile printing ink is easily vaporized and permeable when heated in a contact state during transfer printing.
In some embodiments, the coating layer has two layers including the outermost coating layer, and the coating layer located between the base paper and the outermost coating layer contains a white inorganic pigment and a binder, and the binder contains at least one selected from starches and at least one selected from polyvinyl alcohols. The reason for this is that the migration of the printing ink in the opposite direction can be further suppressed, and the solvent contained in the printing ink is easily vaporized and permeable when heated in a contact state during transfer printing.
In at least one embodiment, the coating layer has two layers including the outermost coating layer, and the coating layer located between the base paper and the outermost coating layer contains a white inorganic pigment and a binder, the white inorganic pigment containing at least one selected from various kaolins and heavy calcium carbonate, and the binder containing at least one selected from starches and at least one selected from polyvinyl alcohols. The reason for this is that the migration of the textile ink in the opposite direction can be further suppressed, and when heated in a contact state during transfer printing, the solvent contained in the textile ink evaporates and becomes more easily permeable.

In some embodiments, the transfer paper has coating layers, including the outermost coating layer of the present invention, on only one side of the base paper. This is because this reduces the manufacturing cost of the transfer paper. In some embodiments, the transfer paper has coating layers, including the outermost coating layer of the present invention, on both sides of the base paper. This is because the transfer paper can be used regardless of whether it is on the front or back side. In some embodiments, when the outermost coating layer of the present invention is on only one side of the base paper (referred to as the "front side" for convenience), the transfer paper has a conventionally known backcoat layer on the back side of the base paper for purposes such as preventing paper curling and preventing print ink from showing through.

In some embodiments, the transfer paper has the outermost coating layer of the present invention on only one side of the base paper, and a conventionally known backcoat layer on the back side of the base paper, the backcoat layer containing a white inorganic pigment and a binder, and the white inorganic pigment containing at least one selected from various kaolins and heavy calcium carbonate, because this can further suppress rear end upset.
In some embodiments, the transfer paper has the outermost coating layer of the present invention on only one side of the base paper, and has a conventionally known backcoat layer on the back side of the base paper, the backcoat layer containing a white inorganic pigment and a binder, and the binder contains at least one kind selected from starches and at least one kind selected from polyvinyl alcohols, because this can further suppress rear end upset.
In at least one embodiment, the transfer paper has the outermost coating layer according to the present invention on only one side of the base paper, and a conventional backcoat layer on the back side of the base paper, the white inorganic pigment containing at least one selected from various kaolins and heavy calcium carbonate, and the binder containing at least one selected from starches and at least one selected from polyvinyl alcohols, because this can further suppress rear end upset.

In some embodiments, the transfer paper has one coating layer, including the outermost coating layer of the present invention, on only one side of the base paper, and a backcoat layer on the back side of the base paper.
In at least one embodiment, the transfer paper has one coating layer, including the outermost coating layer according to the present invention, on only one side of the base paper, and a backcoat layer on the back side of the base paper, the backcoat layer containing a white inorganic pigment and a binder, the white inorganic pigment containing at least one selected from various kaolins and heavy calcium carbonate, and the binder containing at least one selected from starches and at least one selected from polyvinyl alcohols.

In some embodiments, the transfer paper has two coating layers, including an outermost coating layer, on only one side of the base paper, and the coating layer located between the base paper and the outermost coating layer contains a white inorganic pigment and a binder, the white inorganic pigment containing at least one selected from various kaolins and heavy calcium carbonate, and the binder containing at least one selected from starches and at least one selected from polyvinyl alcohols, and has a backcoat layer on the back side of the base paper.
In at least one embodiment, the transfer paper has two coating layers, including an outermost coating layer, on only one side of the base paper, and the coating layer located between the base paper and the outermost coating layer contains a white inorganic pigment and a binder, the white inorganic pigment including at least one selected from various kaolins and heavy calcium carbonate, and the binder including at least one selected from starches and at least one selected from polyvinyl alcohols, and has a backcoat layer on the back side of the base paper, the backcoat layer containing a white inorganic pigment and a binder, the white inorganic pigment including at least one selected from various kaolins and heavy calcium carbonate, and the binder including at least one selected from starches and at least one selected from polyvinyl alcohols.

Coating layers, including the outermost coating layer, can be obtained by applying and drying a coating solution to the base paper or coating layer using conventional coating and drying equipment. After applying and drying the coating solution, the coating layer can be subjected to a calendaring process.

Examples of conventionally known coating devices include a size press, a gate roll coater, a film transfer coater, a blade coater, a rod coater, an air knife coater, a gravure coater, a bar coater, an E-bar coater, and a curtain coater.
Examples of conventionally known drying devices include various drying devices such as hot air dryers such as linear tunnel dryers, arch dryers, air loop dryers, and sine curve air float dryers, infrared heating dryers, and dryers that utilize microwaves, etc.

In some embodiments, the coating weight of the coating layers is from 8 g/ ^m2 to 25 g/ ^m2 in dry solids content per side of the base paper. The above range refers to the total coating weight of the coating layers, including the outermost coating layer, per side of the base paper. In at least one embodiment, when there are two or more coating layers including the outermost coating layer, the total coating weight of the coating layers, including the outermost coating layer, is from 8 g/ ^m2 to 25 g/ ^m2 in dry solids content per side of the base paper, and the coating weight of the outermost coating layer is from 5 g/ ^m2 to 22 g/ ^m2 in dry solids content per side of the base paper.
The reason for this is that the adhesion between the transfer paper and the printing material is improved.

The outermost coating layer contains a white inorganic pigment and a binder. The white inorganic pigment is one that is conventionally known in the field of coated paper. Examples of white inorganic pigments include various kaolins, such as kaolin, delaminated kaolin, calcined kaolin, and engineered kaolin, heavy calcium carbonate, light calcium carbonate, talc, satin white, lithopone, titanium oxide, zinc oxide, amorphous silica, colloidal silica, alumina, aluminum hydroxide, zinc oxide, activated clay, and diatomaceous earth. The binder is one that is conventionally known in the field of coated paper. Examples of binders include starches such as starch, modified starch, and modified starch, celluloses such as carboxymethyl cellulose and hydroxyethyl cellulose, naturally occurring resins or derivatives thereof such as casein, gelatin, soy protein, pullulan, gum arabic, Karaya gum, and albumin, polyvinyl alcohols such as polyvinyl alcohols of various degrees of saponification or polymerization and various modified polyvinyl alcohols, copolymer resins such as polypropylene glycol, polyethylene glycol, maleic anhydride resin, acrylic acid resin, methacrylic acid resin, acrylate resin, methacrylate resin, acrylate-butadiene copolymer, styrene-butadiene copolymer, and ethylene-vinyl acetate copolymer, as well as functional group-modified resins obtained by introducing functional groups such as carboxy groups into these copolymer resins, thermosetting resins such as melamine resin and urea resin, polyurethane resin, unsaturated polyester resin, polyvinyl butyral, and alkyd resin. The outermost coating layer may contain various additives conventionally known in the field of coated paper, as needed. Examples of additives include organic pigments, dispersants, surfactants, fixing agents, thickeners, flow improvers, antifoaming agents, release agents, foaming agents, penetrating agents, colorants, printability improvers, fluorescent brighteners, ultraviolet absorbers, antioxidants, preservatives, mildew inhibitors, cationic resins such as modified polyamines and modified polyamides, and the like.

The outermost coating layer contains at least one white inorganic pigment having a volume-based average particle size (diameter, unit μm) of 110% to 200% of the average layer thickness (unit μm) of the outermost coating layer. By satisfying the above-mentioned relationship between the average particle size of the white inorganic pigment and the average layer thickness of the outermost coating layer, the transfer paper can suppress trailing-end running-up to a greater extent than in the past due to a synergistic effect with the friction coefficient described below. If the above-mentioned relationship is not satisfied, trailing-end running-up cannot be suppressed to a greater extent than in the past. In some embodiments, the outermost coating layer contains at least one white inorganic pigment having a volume-based average particle size (diameter, unit μm) of 110% to 200% of the average layer thickness (unit μm) of the outermost coating layer, and the amount of the white inorganic pigment having a volume-based average particle size that is 110% to 200% of the average layer thickness (unit μm) of the outermost coating layer is 5 to 25 parts by mass per 100 parts by mass of the white inorganic pigment in the outermost coating layer. The reason for this is that rear end movement can be further suppressed.
The volume-based average particle size of the white inorganic pigment can be determined from a volume-based particle size distribution curve. The volume-based average particle size of the white inorganic pigment refers to the average particle size of a single particle when the white inorganic pigment is a single particle, or the average particle size of an aggregate when the white inorganic pigment forms aggregate particles. The volume-based average particle size can be determined, for example, from a volume-based particle size distribution curve obtained by measurement using a particle size distribution measuring device based on a laser diffraction/scattering method. An example of the particle size distribution measuring device is Nikkiso Co., Ltd.'s Microtrac MT3000II.

There are no particular limitations on the method for measuring the average layer thickness of the outermost coating layer. For example, the average layer thickness of the outermost coating layer can be obtained by taking an image of the cross section of a paper cut using a microtome and then measuring it from the resulting image using an electron microscope. The average layer thickness of the outermost coating layer is the average value measured at any 10 or more points on the outermost coating layer that can be seen in the resulting image.

In some embodiments, the outermost coating layer has an average layer thickness of 4 μm to 18 μm. In at least one embodiment, the outermost coating layer has an average layer thickness of 8 μm to 14 μm. In some embodiments, the outermost coating layer contains at least one white inorganic pigment whose volume-based average particle diameter (diameter, unit μm) is 110% to 200% of the average layer thickness (unit μm) of the outermost coating layer, and the average layer thickness of the outermost coating layer is 4 μm to 18 μm. In at least one embodiment, the outermost coating layer contains at least one white inorganic pigment whose volume-based average particle diameter (diameter, unit μm) is 110% to 200% of the average layer thickness (unit μm) of the outermost coating layer, and the average layer thickness of the outermost coating layer is 8 μm to 14 μm. The reason for this is that rear-end runaway can be further suppressed.
The average thickness of the outermost coating layer can be adjusted by the concentration of the resin component in the coating solution, the coating amount, drying conditions, and whether or not calendering is performed and the treatment conditions.

In some embodiments, the white inorganic pigment in the outermost coating layer comprises at least one selected from various kaolins and one or more selected from the group consisting of heavy calcium carbonate and talc. In some embodiments, the mass ratio of the total amount of species selected from various kaolins (various kaolin amounts) to the total amount of species selected from the group consisting of heavy calcium carbonate and talc (heavy calcium carbonate and talc amounts) contained in the outermost coating layer is various kaolin amounts:heavy calcium carbonate and talc amounts = 70:30 to 97:3. In some embodiments, the total content of the species selected from various kaolins and the species selected from the group consisting of heavy calcium carbonate and talc accounts for 90 mass% or more of the total amount of the white inorganic pigment in the outermost coating layer. In at least one embodiment, the white inorganic pigment of the outermost coating layer comprises at least one selected from various kaolins and one or more selected from the group consisting of heavy calcium carbonate and talc, the mass ratio of the total amount of species selected from the various kaolins (amount of various kaolins) to the total amount of species selected from the group consisting of heavy calcium carbonate and talc (amount of heavy calcium carbonate and talc) contained in the outermost coating layer being various kaolins:heavy calcium carbonate and talc = 70:30 to 97:3, and the content of the species selected from the various kaolins and the species selected from the group consisting of heavy calcium carbonate and talc is 90 mass% or more of the total amount of the white inorganic pigment contained in the outermost coating layer.
The reason for this is that rear end movement can be further suppressed.

In some embodiments, the outermost coating layer contains a white inorganic pigment comprising at least one selected from various kaolins and one or more selected from the group consisting of heavy calcium carbonate and talc, and the white inorganic pigment having a volume-based average particle size of 110% or more and 200% or less of the average layer thickness of the outermost coating layer is heavy calcium carbonate and/or talc.
In some embodiments, the outermost coating layer contains a white inorganic pigment that is selected from the group consisting of calcined kaolin, ground calcium carbonate, and talc. In at least one embodiment, the outermost coating layer contains a white inorganic pigment that is selected from the group consisting of calcined kaolin, ground calcium carbonate, and talc, and the white inorganic pigment that has a volume-based average particle size that is 110% to 200% of the average layer thickness of the outermost coating layer is ground calcium carbonate and/or talc.
The reason for this is that rear end movement can be further suppressed.

In some embodiments, the binder of the outermost coating layer comprises carboxymethyl cellulose and at least one selected from polyvinyl alcohols. In some embodiments, the binder of the outermost coating layer comprises carboxymethyl cellulose and at least one selected from polyvinyl alcohols, and the mass ratio of the amount of carboxymethyl cellulose to the total amount of polyvinyl alcohols contained in the outermost coating layer (amount of carboxymethyl cellulose:total amount of polyvinyl alcohols) is 35:65 to 55:45. In some embodiments, the binder of the outermost coating layer comprises carboxymethyl cellulose and at least one selected from polyvinyl alcohols, and the total amount of carboxymethyl cellulose and polyvinyl alcohols accounts for 90 mass% or more of the total amount of binders contained in the outermost coating layer. In at least one embodiment, the outermost coating layer contains a binder comprising carboxymethyl cellulose and at least one selected from polyvinyl alcohols, the mass ratio of the amount of carboxymethyl cellulose to the total amount of polyvinyl alcohols contained in the outermost coating layer is 35:65 to 55:45 (amount of carboxymethyl cellulose:total amount of polyvinyl alcohols), and the total amount of carboxymethyl cellulose and polyvinyl alcohols accounts for 90 mass% or more of the total amount of binders contained in the outermost coating layer.
The reason for this is that the trailing end runaway can be further suppressed by a synergistic effect with the white inorganic pigment.

In some embodiments, the outermost coating layer contains a white inorganic pigment that is one or more selected from the group consisting of calcined kaolin, heavy calcium carbonate, and talc, and a binder that is carboxymethyl cellulose and at least one selected from polyvinyl alcohols. In at least one embodiment, the outermost coating layer contains a white inorganic pigment that is one or more selected from the group consisting of calcined kaolin, heavy calcium carbonate, and talc, and the white inorganic pigment having a volume-based average particle size that is 110% to 200% of the average layer thickness of the outermost coating layer is heavy calcium carbonate and/or talc, and the binder of the outermost coating layer contains carboxymethyl cellulose and at least one selected from polyvinyl alcohols.
The reason for this is that rear end movement can be further suppressed.

Carboxymethylcellulose is a type of cellulose ether and is a conventionally known compound. It includes alkali metal salts. For example, carboxymethylcellulose can be obtained by reacting pulp with sodium monochloroacetate and sodium hydroxide (direct method). In addition to the direct method, it can also be obtained by the alkali method and the solvent method. Carboxymethylcellulose can be produced with various molecular weights or degrees of polymerization depending on the properties of the pulp used and the production method. Generally, carboxymethylcellulose is industrially produced and sold as alkali metal salts of carboxymethylcellulose. Most carboxymethylcellulose is sodium carboxymethylcellulose or potassium carboxymethylcellulose. Conventionally, the sodium and potassium are often omitted. In some embodiments, the carboxymethylcellulose is sodium carboxymethylcellulose. This is because sodium carboxymethylcellulose is readily available commercially.

Polyvinyl alcohols are a general term that includes both standard polyvinyl alcohol and various modified polyvinyl alcohols. Polyvinyl alcohols include conventionally known polyvinyl alcohols with various degrees of saponification and polymerization, as well as various modified polyvinyl alcohols. Examples of modified polyvinyl alcohols include polyvinyl alcohols into which various functional groups, such as silyl groups, carboxy groups, amino groups, and acetoacetyl groups, have been introduced, as well as polyvinyl alcohols into which other monomers, such as ethylene, have been introduced randomly, graft-wise, or in blocks.

The outermost coating layer can contain various auxiliaries conventionally known in transfer printing methods. These auxiliaries are added to optimize various physical properties of the coating layer coating liquid or to improve the dyeability of colorants contained in dye-sublimation inks and other printing inks. Examples of auxiliaries include humectants, wetting agents, pH adjusters, alkali agents, mordants, dye-deepening agents, degassing agents, and reduction inhibitors.

The transfer paper has a static friction coefficient of 0.8 or less and a dynamic friction coefficient of 0.6 or less, measured on the side having the outermost coating layer. The friction coefficients are determined in accordance with ISO 15359:1999, "Paper and board - Determination of the static and kinetic coefficients of friction - Horizontal plane method." By satisfying the above-mentioned range of friction coefficients, the transfer paper can suppress trailing edge upset to a greater extent than conventional levels due to the synergistic effect of the above-mentioned relationship between the average particle size of the white inorganic pigment in the outermost coating layer and the average layer thickness of the outermost coating layer. If the friction coefficient does not satisfy the above-mentioned range, trailing edge upset cannot be suppressed to a greater extent than conventional levels.

The coefficient of friction can be controlled, for example, in terms of the smoothness of the outermost coating layer, the coating weight of the outermost coating layer, the type, content, and average particle size of the white inorganic pigment contained in the outermost coating layer, the coating layer components, and density. Increasing the coating weight of the outermost coating layer increases the coefficient of friction. Increasing the smoothness and density decreases the coefficient of friction. Increasing the hydrophilicity of the outermost coating layer increases the coefficient of friction. The coefficient of friction decreases when the outermost coating layer contains a lubricant and surfactant. Increasing the resin content of the outermost coating layer increases the coefficient of friction. The density of the outermost coating layer can be controlled to some extent by the application and drying conditions of the coating layer coating liquid. For example, the density of the outermost coating layer tends to increase when a contact coating device is used and the drying speed is slowed.

The transfer paper can be obtained by printing a design on the surface of the transfer paper having the outermost coating layer using any of various conventionally known printing methods using dye-sublimation ink or other textile ink.
The various printing methods for printing a design on transfer paper are conventionally known printing methods and are not particularly limited. Examples of printing methods include gravure printing, inkjet printing, electrophotographic printing, and screen printing. In at least one embodiment, the printing method for printing a design on transfer paper is inkjet printing. This is because it allows high-resolution printing from digital data.

The transfer printing method is a method comprising the steps of printing a design on transfer paper to obtain transfer paper, and bringing the surface of the transfer paper with the design printed thereon into close contact with the substrate to be printed. The contacting step includes heating or heating and pressurizing as necessary. The heating and heating and pressurizing conditions in the contacting step are those conventionally known for transfer printing methods. The contacting step can be exemplified by a method in which the transfer paper is brought into close contact with the substrate to be printed using a press, a heated roll, a heated drum, or the like, and then heating or heating and pressurizing.
In at least one embodiment, the printing ink used in the transfer printing process is a dye sublimation ink.

The substrate is a fibrous material and is not particularly limited. The fibrous material may be either a natural or synthetic fibrous material. Examples of natural fibrous materials include cellulosic fibrous materials such as cotton, linen, lyocell, rayon, and acetate, and protein-based fibrous materials such as silk, wool, and animal hair. Examples of synthetic fibrous materials include polyamide fiber (nylon), vinylon, polyester, and polyacrylic. In at least one embodiment, when sublimation printing ink is used, the fibrous material is polyester. If necessary, the substrate may be pretreated with an agent that is effective in promoting dyeing.

The present invention will be described in more detail below with reference to the following examples. However, the present invention is not limited to these examples. Here, "parts by mass" and "% by mass" represent the dry solid content and the actual component amount, respectively. The amount of coating layer applied represents the dry solid content.

(base paper)
A total of 1,000 parts by mass of 870 parts by mass of LBKP (CSF freeness 430 ml) and 130 parts by mass of NBKP (CSF freeness 450 ml), the freeness of which had been adjusted by beating, was dispersed in water to form a pulp slurry. 25 parts by mass of talc as a filler, 50 parts by mass of light calcium carbonate, 10 parts by mass of cationized starch, 9 parts by mass of aluminum sulfate, and 0.7 parts by mass of an alkyl ketene dimer sizing agent were added to the pulp slurry, and the mixture was made into paper on a Fourdrinier paper machine. The resulting paper was subjected to a machine calendering process to obtain a calendered paper. The density of the paper obtained was 0.81 g/ ^cm3 . Oxidized starch was applied to both sides of the calendered paper using a size press to a coating amount of 1 g/ ^m2 per side, to produce a base paper.

(Coating liquid for outermost coating layer)
The coating layer coating solution was prepared as follows.
White inorganic pigment (type and parts by mass are shown in the table) Carboxymethyl cellulose 7.5 parts by mass Polyvinyl alcohol 10.5 parts by mass Surfactant (nonionic type) as needed Modified polyamide resin 1 part by mass The above ingredients were blended, mixed and dispersed in water, and adjusted to a concentration of 12% by mass.

(Coating liquid for coating layer provided between base paper and outermost coating layer)
The coating layer coating solution was prepared as follows.
Kaolin 80 parts by mass Heavy calcium carbonate 20 parts by mass Starch (phosphated starch) 40 parts by mass Polyvinyl alcohol (saponification degree 98%, average polymerization degree 300) 10 parts by mass Surfactant (nonionic type) 0.1 parts by mass The above ingredients were blended, mixed and dispersed in water, and adjusted to a concentration of 12% by mass.

(Coating liquid for backcoat layer)
The coating layer coating solution was prepared as follows.
Kaolin 80 parts by mass Heavy calcium carbonate 20 parts by mass Starch (phosphated starch) 40 parts by mass Polyvinyl alcohol (saponification degree 98%, average polymerization degree 300) 10 parts by mass Surfactant (nonionic type) 0.1 parts by mass The above ingredients were blended, mixed and dispersed in water, and adjusted to a concentration of 12% by mass.

The white inorganic pigments used in the outermost coating layer are as follows:
Kao A: Kaolin (average particle size 1.8 μm)
Kao B: Calcined kaolin (average particle size 1.4 μm)
Talc: Talc (average particle size 13.7 μm)
Heavy calcium carbonate A: Heavy calcium carbonate (average particle size 9.0 μm)
Heavy calcium carbonate B: Heavy calcium carbonate (average particle size 10.8 μm)
Heavy calcium carbonate: heavy calcium carbonate (average particle size 15.4 μm)
Heavy calcium carbonate D: Heavy calcium carbonate (average particle size 19.3 μm)
Heavy calcium carbonate E: Heavy calcium carbonate (average particle size 21.3 μm)
Silica: amorphous silica (average particle size 12.8 μm)

(average particle size of white pigment)
The average particle diameter of these white inorganic pigments was calculated from a volume-based particle size distribution curve obtained from measurements using a particle size distribution measuring device based on a laser diffraction/scattering method, Nikkiso Co., Ltd.'s Microtrac MT3000II.

(Transfer paper - 1 layer type)
The transfer paper was prepared according to the following procedure.
The coating solution for the outermost coating layer was applied to one side of the base paper (referred to as the "front side" for convenience) using an air knife coater and dried using a hot air dryer. After drying, the front side was subjected to either no calendaring or light calendaring. The coating amount, drying conditions, and calendaring were adjusted so that the outermost coating layer would have a predetermined thickness. Next, the coating solution for the backcoat layer was applied to the back side of the base paper using a blade coater and dried using a hot air dryer. The coating amount was intended to be in the range of 4 to 6 g/ ^m2 . As a result, transfer paper having an outermost coating layer and a backcoat layer on the base paper was obtained.

(Transfer paper - 2-layer type)
The transfer paper was prepared according to the following procedure.
The coating solution for the primer layer was applied to one side of the base paper (referred to as the "front side" for convenience) using a blade coater and dried in a hot air dryer. The coating amount was in the range of 4 to 6 g/ ^m² . Next, the coating solution for the outermost coating layer was applied to the front side using an air knife coater and dried in a hot air dryer. After drying, the front side was subjected to no or only light calendaring. The coating amount, drying conditions, and calendaring were adjusted so that the outermost coating layer would have a predetermined thickness. Finally, the coating solution for the backcoat layer was applied to the back side of the base paper using a blade coater and dried in a hot air dryer. The coating amount was in the range of 4 to 6 g/ ^m² . This resulted in a transfer paper having a primer layer, an outermost coating layer, and a backcoat layer on the base paper.

(Layer thickness of outermost coating layer)
The average thickness of the outermost coating layer was measured from an image obtained by photographing the cross section of the transfer paper cut using a microtome with an electron microscope. Measurements were taken at 10 random locations on the image. The average film thickness of the outermost coating layer was calculated as the average of the 10 locations. The thicknesses of the outermost coating layer are shown in Table 1.

(coefficient of friction)
The static and dynamic friction coefficients of the resulting transfer paper, measured on the side having the outermost coating layer, were measured in accordance with ISO 15359: 1999. The measuring device used was a Tensilon 1210 manufactured by A&D Co., Ltd. The values of the friction coefficients are shown in Table 1.

(Transfer paper)
On the side of the resulting transfer paper having the outermost coating layer, an evaluation pattern consisting of each ink single color of sublimation textile ink (cyan, magenta, yellow, black), as well as green, which is a mixture of yellow and cyan, red, which is a mixture of yellow and magenta, blue, which is a mixture of cyan and magenta, and black, which is a mixture of yellow, cyan, and magenta, was printed using an inkjet printer (Mimaki Engineering Co., Ltd., JV2-130II) using sublimation textile printing ink, to obtain transfer paper.

(Transfer printing)
White polyester cloth was used as the printing substrate. The coated side of 3 m of transfer paper was placed face-to-face with 3 m of white polyester cloth, and the resulting bonded object was then tightly attached. The bonded object was sandwiched and transported between two paired rolls, each driven with a U-shaped curve in the transport path, such as that shown in Figure 3 of JP-A-2015-16978. The paired rolls, each approximately 30 cm in diameter and located in the middle of the U-shaped curve, consisted of a heated metal roll on the inside and a rubber roll on the outside. The transfer paper was oriented in contact with the metal roll, and the paired rolls heated and pressurized the transfer paper and the white polyester cloth. The temperature of the metal roll was 200°C, and the transfer paper was transported while in contact with the outer periphery of the metal roll, and the contact time between the metal roll and the bonded object was 35 seconds.

(Evaluation of rear end movement)
In carrying out the above transfer printing, the trailing edge of the adhered article was visually observed passing between the transport rolls that heat and pressurize the U-shaped portion in the transport path. The textile transfer was carried out 25 times. From the observation results, the "trailing edge unrest" was evaluated according to the following criteria. In the present invention, if the transfer paper was rated A, B, or C, it was considered that the trailing edge unrest was suppressed compared to conventional transfer paper.
A: In practice, almost no rear end roughness was observed, and the result was extremely good.
B: Slight rear end irregularity observed in 1 out of 25 times, but good.
C: Slight rear end roughness was observed in more than 1 and 3 times out of 25 times, but generally good.
D: Slight rear end roughness is observed in more than 3 out of 25 times.
Or, clear rear end irregularity was observed in more than one out of 25 times, which posed problems in terms of stable production.

The evaluation results are shown in Table 1.

The evaluation results in Table 1 show that the transfer papers of Examples 1 to 8, which correspond to the present invention, are able to suppress rear-end fluctuation more effectively than conventional methods when used in transfer printing. On the other hand, the transfer papers of Comparative Examples 1 to 4, which do not satisfy the configuration of the present invention, are unable to suppress rear-end fluctuation more effectively than conventional methods when used in transfer printing.

Claims (2)

1. A transfer paper for use in a transfer printing method, comprising a base paper and one or more coating layers on at least one side of the base paper, wherein an outermost coating layer, which is the coating layer located outermost relative to the base paper, contains a white inorganic pigment and a binder, wherein the white inorganic pigment in the outermost coating layer comprises at least one selected from various kaolins and one or more selected from the group consisting of heavy calcium carbonate and talc, and wherein the white inorganic pigment contains at least one type whose volume-based average particle size (diameter, unit μm) is 110% or more and 200% or less of the average layer thickness (unit μm) of the outermost coating layer, and wherein the static friction coefficient measured on the side having the outermost coating layer is 0.8 or less and the dynamic friction coefficient is 0.6 or less. 2. The transfer paper used in the transfer printing method according to claim 1, wherein the total content of the species selected from various kaolins and the species selected from the group consisting of heavy calcium carbonate and talc is 90% by mass or more of the total amount of white inorganic pigments contained in the outermost coating layer.