Engineering paper for synthetic leather

Abstract

To provide a process paper for synthetic leather, which prevents defect in detachability from a peeling agent layer from occurring and prevents yellow discoloration from occurring on a surface of the peeling agent layer.SOLUTION: A process paper for synthetic leather 100 has a base material 10 and a peeling agent layer 30 that is disposed on the base material 10 and contains a binder resin and a peeling agent. The binder resin contains (A) component described below and (B) component described below. The peeling agent contains silicone-based peeling agent and satisfies (i) described below. (A) component: polyvinyl alcohol. (B) component: at least one type selected from a group consisting of styrene butadiene latex and methyl methacrylate butadiene latex. (i): ratio of solid content of the (A) component to the (B) component ((A) component / (B) component) is 20 / 80 or more and 80 / 20 or less in terms of mass.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a casting paper for synthetic leather. [Background technology]

[0002] Synthetic leather is produced using synthetic leather casting paper. Examples of methods for producing synthetic leather include the following: First, a coating liquid containing a synthetic resin such as a urethane resin or a vinyl chloride resin as a main component is applied onto the release agent layer of the synthetic leather casting paper, and the applied coating liquid is dried to form a resin layer. If necessary, a base fabric is further laminated onto the resin layer via an adhesive to form a laminate with the synthetic leather. Finally, the synthetic leather is produced by peeling the synthetic leather casting paper from the resin layer of the laminate. The synthetic leather casting paper has, for example, a substrate and a release agent layer.

[0003] For example, Patent Document 1 discloses a release material used in the production of synthetic leather, etc. The release material disclosed in Patent Document 1 is obtained by coating a release agent composition on the surface of a substrate. The release agent composition contains (A) an alkyd resin, (B) an amino resin, (C) a silicone resin containing a functional group reactive with the alkyd resin and / or the amino resin, and (D) 0.05 to 10 parts by mass of a cationic surfactant per 100 parts by mass of the total amount of component (A), component (B), and component (C). The release agent composition disclosed in Patent Document 1 also uses a solution of paratoluenesulfonic acid in methanol.

[0004] Patent Document 2 discloses cast-coated paper that serves as a substrate for process paper that is repeatedly used in the manufacture of synthetic leather, etc. The cast-coated paper for process paper substrate disclosed in Patent Document 2 has an underlayer and a cast layer, in that order, formed on at least one side of base paper. The underlayer is composed of 100 parts by weight of inorganic pigment and 1 to 50 parts by weight of organic pigment, while the cast layer does not contain any organic pigment. The cast-coated paper for process paper substrate disclosed in Patent Document 2 has a release layer (release agent layer) formed by applying a release agent to the surface of the cast layer. The release agent (release agent composition) for the release layer can be an alkyd-based resin, a silicone-based resin, a polyethylene-based resin, a polypropylene resin, an acrylic resin, or the like. Furthermore, a solution of paratoluenesulfonic acid in methanol is used as the release agent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-047476 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-163007 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, in consideration of environmental impact, etc., there has been a demand for synthetic leather casting papers that do not use, for example, organic solvents in the release agent composition for forming the release agent layer. For example, the casting papers used for producing synthetic leather disclosed in Patent Document 1 and Patent Document 2 use organic solvents in the release agent layer, and improvements have been required in terms of environmental impact. For this reason, there has been a demand for synthetic leather casting papers that form a release agent layer using a release agent composition that contains an aqueous resin as a main component as a binder resin and does not contain an organic solvent.

[0007] When synthetic leather casting paper having a release agent layer formed from a release agent composition containing an aqueous resin as the main binder resin component is used to produce synthetic leather having a resin layer containing a vinyl chloride resin as the main component, yellowing may occur on the surface of the release agent layer in the portion where the vinyl chloride resin-based resin layer is formed. When yellowing occurs on the surface of the release agent layer, the release agent layer appears to have deteriorated, even though there is no problem with the release performance of the release agent layer. For this reason, further improvement in synthetic leather casting paper against yellowing of the surface of the release agent layer has been desired.

[0008] An object of the present invention is to provide a casting paper for synthetic leather that, when used in the manufacture of synthetic leather having a resin layer containing a vinyl chloride resin as a main component, prevents problems with release from the release agent layer and prevents yellowing of the surface of the release agent layer when a resin layer containing a vinyl chloride resin as a main component is formed on the surface of the release agent layer. [Means for solving the problem]

[0009] According to one aspect of the present invention, there is provided a casting paper for synthetic leather, comprising a substrate and a release agent layer provided on the substrate and containing a binder resin and a release agent, wherein the binder resin contains the following component (A) and the following component (B), the release agent contains a silicone-based release agent, and the casting paper satisfies the following (i): (A) Component: Polyvinyl alcohol Component (B): At least one selected from the group consisting of styrene-butadiene latex and methyl methacrylate-butadiene latex (i): The solid content ratio of the component (A) to the component (B) (component (A) / component (B)) is 20 / 80 or more and 80 / 20 or less in terms of mass.

[0010] According to one aspect of the present invention, there is provided a casting paper for synthetic leather, comprising a substrate and a release agent layer provided on the substrate and containing a binder resin and a release agent, wherein the binder resin contains the following component (A) and the following component (B), the release agent contains a silicone-based release agent, and the casting paper satisfies the following (ii) and the following (iii): (A) Component: Polyvinyl alcohol Component (B): At least one selected from the group consisting of styrene-butadiene latex and methyl methacrylate-butadiene latex (ii): A vinyl chloride resin composition is applied to the surface of the release agent layer, and the vinyl chloride resin layer is formed by drying at a temperature of 200°C for 2 minutes, and then peeled from the release agent layer. The application of the vinyl chloride resin composition, the formation of the vinyl chloride resin layer, and the peeling from the release agent layer are counted as a single operation, and the difference ΔYI(1) between the yellowing index YI-1 of the surface of the release agent layer after the single operation and the yellowing index YI-0 before the vinyl chloride resin composition was applied is 10 or less. (iii): When a scratch test is performed on the surface of the release agent layer before the vinyl chloride resin composition is applied, the critical peel load value at which the release agent layer peels off, as measured by the scratch test, is 5 mN or more.

[0011] In the casting paper for synthetic leather according to one embodiment of the present invention, it is preferable that the following (iv) be further satisfied: (iv): A vinyl chloride resin composition is applied to the surface of the release agent layer, and the vinyl chloride resin layer is formed by drying at a temperature of 200°C for 2 minutes, and then peeled from the release agent layer. The application of the vinyl chloride resin composition, the formation of the vinyl chloride resin layer, and the peeling from the release agent layer are counted as one operation, and the difference ΔYI(3) between the yellowing index YI-3 of the surface of the release agent layer after repeating the one operation three times and the yellowing index YI-0 before the application of the vinyl chloride resin composition is 25 or less. [Effects of the Invention]

[0012] According to one aspect of the present invention, when the synthetic leather casting paper is used in the production of synthetic leather having a resin layer containing a vinyl chloride resin as a main component, when a resin layer containing a vinyl chloride resin as a main component is formed on the surface of the release agent layer, it is possible to provide a synthetic leather casting paper that suppresses problems with release from the release agent layer and also suppresses yellowing of the surface of the release agent layer. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view schematically illustrating a casting paper for synthetic leather according to one embodiment of the present invention. [Figure 2] 1 is a cross-sectional view schematically illustrating a casting paper for synthetic leather according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] A preferred embodiment of a casting paper for synthetic leather, which is an example of the present invention, will be described below.

[0015] First Embodiment The synthetic leather casting paper according to the first embodiment comprises a substrate and a release agent layer provided on the substrate and containing a binder resin and a release agent, the binder resin containing the following component (A) and the following component (B), and the release agent containing a silicone-based release agent. The synthetic leather casting paper according to this embodiment satisfies the following (i): (A) Component: Polyvinyl alcohol Component (B): At least one selected from the group consisting of styrene-butadiene latex and methyl methacrylate-butadiene latex (i): The solid content ratio of the component (A) to the component (B) (component (A) / component (B)) is 20 / 80 or more and 80 / 20 or less in terms of mass.

[0016] When a synthetic leather casting paper having a release agent layer made of a binder resin containing an aqueous resin as its main component uses only a resin with low acid resistance, such as polyvinyl alcohol (hereinafter sometimes referred to as "PVA"), for example, in the production of synthetic leather having a resin layer containing a vinyl chloride resin as its main component (hereinafter sometimes referred to as a vinyl chloride resin layer), yellowing is likely to occur on the surface of the release agent layer of the synthetic leather casting paper. This phenomenon is thought to be due to the following: When a vinyl chloride resin layer is formed on the surface of the release agent layer of the synthetic leather casting paper, the film-forming temperature of the vinyl chloride resin layer is high (e.g., 200°C or higher), and hydrochloric acid and other products are generated as thermal decomposition products of the vinyl chloride resin. It is thought that hydrochloric acid generated as a thermal decomposition product of the vinyl chloride resin may chemically react with functional groups contained in the PVA and components contained in the vinyl chloride resin composition. It is thought that this chemical reaction causes the yellowing of the surface of the release agent layer of the synthetic leather casting paper.

[0017] In contrast, the synthetic leather casting paper according to this embodiment contains, as the binder resin in the release agent layer, at least one selected from the group consisting of styrene-butadiene latex (hereinafter sometimes referred to as "SBR") and methyl methacrylate-butadiene latex (hereinafter sometimes referred to as "MBR"), and PVA. Because SBR and MBR have higher acid resistance than PVA, it is believed that yellowing of the surface of the release agent layer after film formation of the vinyl chloride-based resin layer is suppressed. Furthermore, even though the synthetic leather casting paper according to this embodiment contains both PVA and at least one selected from the group consisting of SBR and MBR as the binder resin in the release agent layer, adverse effects on the releasability of the vinyl chloride-based resin layer after film formation are suppressed.

[0018] Therefore, by having the above-mentioned configuration, the synthetic leather casting paper according to this embodiment is thought to be able to suppress problems with releasability when peeling the vinyl chloride resin layer from the release agent layer during production of the vinyl chloride resin layer, and to suppress yellowing of the surface of the release agent layer.

[0019] In this specification, the term "aqueous resin" refers to a resin that can be dispersed in water or dissolved in water. The term "aqueous resin" includes not only water-soluble resins but also resins that can be dispersed in water, such as emulsion-type and dispersion-type resins. In this specification, the term "major component" refers to the component that is contained in the target object in the largest amount. For example, the term "major component" refers to a component that is contained in the target object in an amount of 50% by mass or more (up to 100% by mass). In this specification, vinyl chloride resin is a resin having a repeating unit represented by —CH 2 —CHCl—, and refers to a vinyl chloride homopolymer and a vinyl chloride copolymer. In this specification, the term "vinyl chloride resin layer" refers to a resin layer formed from a vinyl chloride resin composition. Also, in this specification, the term "vinyl chloride resin composition" refers to a resin composition containing a vinyl chloride resin as a main component and including a liquefied product obtained by dispersing the vinyl chloride resin in a plasticizer.

[0020] The synthetic leather casting paper according to this embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically illustrating an example of the synthetic leather casting paper according to this embodiment. As shown in FIG. 1, the synthetic leather casting paper 100 comprises a substrate 10 and a release agent layer 30. The synthetic leather casting paper 100 has the release agent layer 30 provided directly on the surface 10S of the substrate 10. The release agent layer 30 contains a binder resin, and includes PVA as component (A) and at least one selected from the group consisting of styrene-butadiene latex and methyl methacrylate-butadiene latex as component (B).

[0021] The binder resin contained in the release agent layer 30 has a PVA content of 20 to 80 parts by mass as component (A) and a content of at least one selected from the group consisting of styrene-butadiene latex and methyl methacrylate-butadiene latex as component (B) of 20 to 80 parts by mass, where the total of components (A) and (B) is taken as 100 parts by mass. In other words, the synthetic leather casting paper 100 satisfies the above condition (i).

[0022] Even when a vinyl chloride resin layer is formed on the surface 30S of the release agent layer 30, the synthetic leather casting paper 100 prevents problems with releasability when the vinyl chloride resin layer is peeled from the release agent layer 30. Furthermore, even when a vinyl chloride resin layer is formed on the surface 30S of the release agent layer 30, the synthetic leather casting paper 100 prevents yellowing of the surface 30S of the release agent layer 30.

[0023] An example of the casting paper for synthetic leather according to this embodiment has been described above with reference to Fig. 1, but the casting paper for synthetic leather according to this embodiment is not limited to this. The casting paper for synthetic leather according to this embodiment can take various forms as long as it satisfies the above-mentioned (i).

[0024] For example, in the casting paper for synthetic leather, the substrate and the release agent layer may be in direct contact with each other. Furthermore, the casting paper for synthetic leather may have an intermediate layer between the substrate and the release agent layer. Examples of the intermediate layer include an adhesive layer. Furthermore, for example, the release agent layer may or may not contain a filler. Furthermore, regardless of whether the release agent layer contains a filler or not, the surface of the release agent layer may be a smooth surface with small irregularities, or may be a surface with an irregular shape with larger irregularities than a smooth surface.

[0025] Next, the materials constituting each layer will be described.

[0026] [1] Base material The substrate of the casting paper for synthetic leather is not particularly limited as long as it can support the release agent layer described below.

[0027] Examples of the substrate include a paper substrate and a resin film. The substrate may be, for example, a laminated paper comprising a paper substrate and a laminate layer. The laminate layer is formed by laminating a thermoplastic resin onto the paper substrate. Examples of the thermoplastic resin in the laminate layer include polyolefin resins, and examples of the polyolefin resin include polyethylene. Examples of paper substrates include fine paper, medium-quality paper, glassine paper, art paper, clay-coated paper, and cast-coated paper.

[0028] Examples of resin films include polyester films and polyolefin films. Examples of polyester films include polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate. Examples of polyolefin films include polyethylene, polypropylene, and polymethylpentene. The resin film may be a single layer, or may be a multilayer film made up of two or more layers of the same or different resin films.

[0029] Among these substrates, the substrate is preferably a paper substrate from the viewpoints of strength and easy availability.

[0030] The substrate is preferably a coated paper having a pigment coating layer, such as art paper, clay-coated paper, or cast-coated paper. The release agent layer is preferably provided on the pigment coating layer of the coated paper. Providing a pigment coating layer on the paper substrate improves the sealing effect when the release agent layer is provided. In this specification, coated paper refers to a paper substrate comprising a base paper primarily composed of pulp fibers and a pigment coating layer provided on the base paper. The pigment coating layer may have a single-layer structure or a multi-layer structure. The pigment coating layer is a coating layer containing, for example, 2 to 50 parts by mass of an adhesive, such as an aqueous resin, per 100 parts by mass of one or more pigments, such as calcium carbonate, kaolin, clay, talc, satin white, titanium oxide, and plastic pigments. In the casting paper for synthetic leather according to the present invention, when a paper substrate is used as the substrate, the release agent layer in the present invention is provided on the paper substrate, and therefore the pigment coating layer is to be distinguished from the release agent layer in the present invention.

[0031] The thickness of the substrate is not particularly limited, and is preferably, for example, 5 μm or more, more preferably 10 μm or more, and is preferably, for example, 300 μm or less, more preferably 200 μm or less.

[0032] When the substrate is coated paper, the thickness of the base paper is preferably 50 μm or more, more preferably 100 μm or more. The thickness of the base paper is preferably 250 μm or less, more preferably 200 μm or less. The thickness of the pigment coating layer is preferably 5 μm or more, more preferably 10 μm or more. The thickness of the pigment coating layer is preferably 40 μm or less, more preferably 30 μm or less.

[0033] [2] Release layer The release agent layer is formed from a release agent composition. The release agent composition includes a binder resin and a release agent. The release agent composition may or may not further include a filler.

[0034] (binder resin) The binder resin contains component (A) and component (B). Component (A) is PVA (polyvinyl alcohol), and component (B) is at least one selected from the group consisting of SBR (styrene-butadiene latex) and MBR (methyl methacrylate-butadiene latex).

[0035] By including PVA (polyvinyl alcohol) as component (A), the binder resin is likely to maintain its releasability even when repeatedly used in the production of synthetic leather. Furthermore, by including at least one of SBR and MBR as component (B), the binder resin is likely to suppress yellowing of the release agent layer after the vinyl chloride resin layer is formed. As component (B), SBR or MBR may be used alone, or SBR and MBR may be used in combination.

[0036] [PVA] The type of PVA is not particularly limited. PVA is obtained by saponifying polyvinyl acetate. The degree of saponification of PVA is expressed as a percentage of the number of hydroxyl groups relative to the total number of acetate groups and hydroxyl groups in PVA. The degree of saponification and degree of polymerization of PVA are not particularly limited. The degree of saponification of PVA may be 87% or more, or 98% or more. The degree of saponification of PVA may be 100% or less, or 99% or less. The degree of polymerization of PVA may be 500 or more, or 1700 or more. The degree of polymerization of PVA may be 2400 or less, or 600 or less. Among these, from the viewpoint of the sealing effect of the release agent, it is preferable that the PVA has a degree of saponification of 98% or more and a degree of polymerization of 500 or more. One type of PVA may be used alone, or two or more types may be used in combination.

[0037] [SBR] SBR is a copolymer latex obtained by copolymerizing at least a styrene monomer and a butadiene monomer. SBR can be obtained by emulsion polymerization of a monomer composition containing, for example, a styrene monomer such as styrene, α-methylstyrene, or monochlorostyrene, and a butadiene monomer such as 1,3-butadiene, 2-methyl-1,3-butadiene, or 2,3-dimethyl-1,3-butadiene. The glass transition temperature (Tg) of SBR is preferably −30° C. or higher and 30° C. or lower.

[0038] [MBR] MBR is a copolymer latex obtained by copolymerizing at least a methyl methacrylate monomer and a butadiene monomer. MBR can be obtained, for example, by emulsion polymerization of a monomer composition containing a methyl methacrylate monomer and a butadiene monomer such as 1,3-butadiene, 2-methyl-1,3-butadiene, or 2,3-dimethyl-1,3-butadiene. The glass transition temperature (Tg) of MBR is preferably −30° C. or higher and 30° C. or lower.

[0039] In this embodiment, the ratio of the (A) component to the (B) component contained in the release agent layer is, in mass terms, a solids ratio of the (A) component to the (B) component ((A) component / (B) component), of 20 / 80 or more and 80 / 20 or less. When the solids ratio of the (A) component to the (B) component is 20 / 80 or more and 80 / 20 or less, yellowing on the surface of the release agent layer after the vinyl chloride resin layer is formed is suppressed, strength sufficient to withstand repeated use of the casting paper for synthetic leather is obtained, and the film-forming properties of the release agent layer are easily ensured. From the viewpoints of more easily suppressing yellowing on the surface of the release agent layer, more easily obtaining strength sufficient to withstand repeated use of the casting paper for synthetic leather, and more easily ensuring the film-forming properties of the release agent layer, the solids ratio of the (A) component to the (B) component is preferably 25 / 75 or more and 75 / 25 or less, and more preferably 30 / 70 or more and 70 / 30 or less.

[0040] When the solid content ratio of the (A) component to the (B) component is 20 / 80 or more, the film-forming properties of the release agent layer are easily ensured, and yellowing of the surface of the release agent layer after the vinyl chloride resin layer is formed is easily suppressed. When the solid content ratio of the (A) component to the (B) component is 80 / 20 or less, yellowing of the surface of the release agent layer after the vinyl chloride resin layer is formed is suppressed, and deterioration of the release properties is more easily suppressed even with repeated use. Furthermore, when the solid content ratio of the (A) component to the (B) component is 80 / 20 or less, scratches on the surface of the release agent layer are easily suppressed. From the viewpoint of suppressing scratches on the surface of the release agent layer, it is preferable to satisfy the condition (iii) described in the second embodiment.

[0041] [Removal Agent] The release agent used is a silicone-based release agent. The silicone-based release agent is preferably an emulsion-type silicone-based release agent (emulsion silicone). The emulsion-type silicone-based release agent is compatible with water at any ratio, and is therefore suitable from the viewpoints of compatibility with the binder resin contained in the release agent composition and environmental friendliness. The emulsion-type silicone-based release agent can be obtained, for example, by emulsifying silicone oil with various emulsifiers.

[0042] From the viewpoint of achieving good release of the resin layer in the synthetic leather, the ratio of the binder resin to the release agent contained in the release agent layer is preferably 50 / 50 or more and 95 / 5 or less, in terms of the solid content ratio of the binder resin to the release agent (binder resin / release agent), in mass terms, preferably 60 / 40 or more and 93 / 7 or less, and more preferably 70 / 30 or more and 90 / 10 or less.

[0043] [Filler] Fillers are components that are used as needed. Fillers can be used, for example, to impart desired surface properties (e.g., gloss or matte) to the surface of the release agent layer. Examples of filler materials include inorganic particles such as silica particles, alumina particles, titanium oxide particles, zinc oxide particles, calcium carbonate particles, magnesium hydroxide particles, aluminum hydroxide particles, kaolin particles, talc particles, and clay particles; and organic particles such as urea resin, starch particles, and cellulose acetate. The shape of the filler is not particularly limited and may be spherical or amorphous. The material and shape of the filler may be selected depending on the releasability, appearance, and functionality of the synthetic leather formed on the release agent layer, as well as the surface properties of the release agent layer.

[0044] The average particle size of the filler is the median particle size (D50) of particle sizes as viewed from the fine particle side at 50% cumulative volume. The average particle size (D50) can be measured using a laser diffraction particle size distribution analyzer, with the release agent composition containing the filler as the measurement target. The average particle size (D50) of the filler is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. The average particle size (D50) of the filler is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less. The average particle size (D50) of the filler may be selected depending on the properties, such as releasability, of the synthetic leather formed on the release agent layer.

[0045] When a filler is contained in the release agent composition for forming the release agent layer, the content of the filler in the release agent composition is not particularly limited. When the synthetic leather casting paper is used to produce a matte synthetic leather, from the viewpoint of forming irregularities on the surface of the release agent layer of the synthetic leather casting paper, the content of the filler in the release agent composition is, for example, preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, relative to 100 parts by mass of the binder resin, in terms of solid content ratio. From the same viewpoint, the content of the filler in the release agent composition is, for example, preferably 200 parts by mass or less, more preferably 180 parts by mass or less, and even more preferably 150 parts by mass or less, relative to 100 parts by mass of the binder resin. The content of the filler may be selected depending on the desired degree of irregularity on the release agent layer surface and the properties such as the releasability of the synthetic leather formed on the release agent layer. The filler is a component that is used as needed, and therefore the content of the filler contained in the release agent layer is preferably 0 to 200 parts by mass relative to 100 parts by mass of the binder resin.

[0046] The release agent composition is preferably used in the form of a dispersion liquid using water as a dispersion medium. The release agent composition may further contain additives in addition to the binder resin, the release agent, and the filler used as needed. Examples of the additives include a curing agent, a crosslinking agent, a reaction initiator, and a catalyst.

[0047] From the viewpoints of coatability and drying property, the solid content concentration of the release agent composition solution is preferably 5% by mass or more, more preferably 10% by mass or more, and from the same viewpoints, the solid content concentration of the release agent composition solution is preferably 50% by mass or less, more preferably 40% by mass or less.

[0048] The lower limit of the thickness of the release agent layer is not particularly limited and may be, for example, 3 μm or more. The upper limit of the thickness of the release agent layer is not particularly limited and may be 12 μm or less, 10 μm or less, or 8 μm or less.

[0049] [Manufacturing method for casting paper for synthetic leather] The method for producing the casting paper for synthetic leather is not particularly limited. A method for producing casting paper for synthetic leather includes, for example, a step of preparing a release agent composition and a step of applying the release agent composition to a substrate to form a coating film. Specifically, the following method can be mentioned. First, a release agent composition for forming the release agent layer is prepared, and then the release agent composition is applied to a substrate and heated to form a coating film, thereby providing the release agent layer on the substrate. Examples of methods for applying the release agent composition include spin coating, spray coating, bar coating, knife coating, roll coating, roll knife coating, blade coating, die coating, gravure coating, and air knife coating.

[0050] In the synthetic leather casting paper according to this embodiment, after a vinyl chloride resin layer is formed on the surface of the release agent layer, the yellowing index (YI value) of the surface of the release agent layer in the area where the vinyl chloride resin layer is formed is preferably small. For example, the yellowing index of the surface of the release agent layer before forming the vinyl chloride resin layer and after forming the vinyl chloride resin layer by applying a vinyl chloride resin composition to the surface of the release agent layer and drying at 200°C for 2 minutes is preferably in the same range as the range described below for "yellowing index (YI value)" in the second embodiment. The yellowing index (YI value) can be measured by the method described below in the second embodiment. Furthermore, for example, the difference in yellowing degree of the surface of the release agent layer before forming a vinyl chloride resin layer on the surface of the release agent layer and after forming a vinyl chloride resin layer by applying a vinyl chloride resin composition to the surface of the release agent layer and drying it for 2 minutes at 200° C. is preferably in the same range as the range described below for "difference in yellowing degree (ΔYI)" in the second embodiment. That is, the difference in yellowing degree preferably satisfies the condition (ii) described below in the second embodiment, and more preferably satisfies both the condition (ii) and the condition (iv) described below.

[0051] The release agent layer of the synthetic leather casting paper according to this embodiment preferably has a peel strength from the resin layer of the synthetic leather (i.e., a resin layer containing a vinyl chloride resin as a main component) of 30 mN / 30 mm or more and 3,000 mN / 30 mm or less, more preferably 50 mN / 30 mm or more and 2,000 mN / 30 mm or less, even more preferably 60 mN / 30 mm or more and 1,000 mN / 30 mm or less, even more preferably 70 mN / 30 mm or more and 500 mN / 30 mm or less, and even more preferably 90 mN / 30 mm or more and 200 mN / 30 mm or less.

[0052] The peel strength can be measured, for example, as follows. A vinyl chloride resin composition is applied to the surface of the release agent layer of synthetic leather casting paper so that the film thickness after drying is 250 μm, and then heated at 200°C for 2 minutes to form a vinyl chloride resin layer. The film is then left to stand in a thermostatic chamber at 23°C and a relative humidity of 50%RH for 30 minutes and cut into a 30 mm wide specimen. Using a tensile tester (Tensilon manufactured by A&D Co., Ltd.), the vinyl chloride resin layer is pulled at an angle of 180° from the synthetic leather casting paper at a peeling rate of 1000 mm / min, and the peel strength is measured. The vinyl chloride resin composition used to measure the peel strength may be a vinyl chloride resin composition containing 100 parts by mass of vinyl chloride resin powder (ZEST P22, manufactured by Shin-Dai-ichi Vinyl Corporation), 60 parts by mass of bis-2-ethylhexyl phthalate (manufactured by Sankyo Chemical Co., Ltd.), and 3 parts by mass of black pigment (Vinyl Toner Color 6740, Black, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.). As described above, the operation of forming the vinyl chloride resin layer and peeling in a 180° direction at a peel speed of 1000 mm / min is counted as one cycle. The peel strength after the above-mentioned single cycle (after one use) and the peel strength after repeating the above-mentioned single cycle three times (after three uses) preferably fall within the range of 30 mN / 30 mm or more and 3000 mN / 30 mm or less.

[0053] When the peeling strength of the release agent layer relative to the resin layer of the synthetic leather is equal to or greater than the above-mentioned lower limit, the resin layer of the synthetic leather can be prevented from accidentally peeling off from the release agent layer.When the peeling strength of the release agent layer relative to the resin layer of the synthetic leather is equal to or less than the above-mentioned upper limit, the casting paper for synthetic leather can be stably peeled off from the synthetic leather even after repeated use of the casting paper for synthetic leather.

[0054] Second Embodiment The synthetic leather casting paper according to the second embodiment comprises a substrate and a release agent layer provided on the substrate and containing a binder resin and a release agent, the binder resin containing the following component (A) and the following component (B), and the release agent containing a silicone-based release agent. The synthetic leather casting paper according to this embodiment satisfies the following (ii) and also satisfies the following (iii): (A) Component: Polyvinyl alcohol Component (B): At least one selected from the group consisting of styrene-butadiene latex and methyl methacrylate-butadiene latex (ii): A vinyl chloride resin composition is applied to the surface of the release agent layer, and the vinyl chloride resin layer is formed by drying at a temperature of 200°C for 2 minutes, and then peeled from the release agent layer. The application of the vinyl chloride resin composition, the formation of the vinyl chloride resin layer, and the peeling from the release agent layer are counted as a single operation, and the difference ΔYI(1) between the yellowing index YI-1 of the surface of the release agent layer after the single operation and the yellowing index YI-0 before the vinyl chloride resin composition was applied is 10 or less. (iii): When a scratch test is performed on the surface of the release agent layer before the vinyl chloride resin composition is applied, the critical peel load value at which the release agent layer peels off, as measured by the scratch test, is 5 mN or more.

[0055] In the casting paper for synthetic leather according to this embodiment, from the viewpoint of further suppressing yellowing on the surface of the release agent layer, it is preferable that the surface of the release agent layer further satisfies the following condition (iv).

[0056] (iv): A vinyl chloride resin composition is applied to the surface of the release agent layer, and the vinyl chloride resin layer is formed by drying at a temperature of 200°C for 2 minutes, and then peeled from the release agent layer. The application of the vinyl chloride resin composition, the formation of the vinyl chloride resin layer, and the peeling from the release agent layer are counted as one operation, and the difference ΔYI(3) between the yellowing index YI-3 of the surface of the release agent layer after repeating the one operation three times and the yellowing index YI-0 before the application of the vinyl chloride resin composition is 25 or less.

[0057] The application of the vinyl chloride resin composition, the formation of the vinyl chloride resin layer, and the peeling off of the release agent layer are counted as one operation, and the completion of this one operation corresponds to the completion of one use of the synthetic leather casting paper. Repeating this one operation three times corresponds to the completion of three uses of the synthetic leather casting paper.

[0058] The synthetic leather casting paper according to this embodiment will be described with reference to Figure 2. The synthetic leather casting paper 120 according to the second embodiment comprises a substrate 10 and a release agent layer 32, with the release agent layer 32 provided directly on the surface 10S of the substrate 10. The release agent layer 32 contains PVA as component (A) and at least one selected from the group consisting of styrene-butadiene latex and methyl methacrylate-butadiene latex as component (B).

[0059] The synthetic leather casting paper 120 suppresses problems with releasability when peeling the vinyl chloride resin layer from the release agent layer 32, even when a vinyl chloride resin layer is formed on the surface 32S of the release agent layer 32. Furthermore, the synthetic leather casting paper 120 reduces changes in the yellowing index (YI value) of the surface 32S of the release agent layer 32 in the area where the vinyl chloride resin layer is formed, even when a vinyl chloride resin layer is formed. In other words, the synthetic leather casting paper 120 has a surface 32S of the release agent layer 32 that satisfies both of the conditions (ii) and (iii). Furthermore, it is preferable that the synthetic leather casting paper 120 has a surface 32S of the release agent layer 32 that satisfies all of the conditions (ii), (iii), and (iv).

[0060] In the synthetic leather casting paper 120 according to the second embodiment, the specific material of the substrate 10 can be the same as the material described in the first embodiment. Also, in the synthetic leather casting paper 120 according to the second embodiment, the specific material of the release agent layer 32 can be the same as the material described in the first embodiment. The composition of the release agent layer 32 may be the same as the composition of the release agent layer 30 in the synthetic leather casting paper 100 according to the first embodiment, or it may be a different composition.

[0061] An example of the casting paper for synthetic leather according to this embodiment has been described above with reference to Fig. 2, but the casting paper for synthetic leather according to this embodiment is not limited to this. As with the casting paper for synthetic leather according to the first embodiment, the casting paper for synthetic leather according to this embodiment can take various forms as long as it satisfies the above-mentioned (ii) and (iii).

[0062] There are no particular limitations on the means by which the surface of the release agent layer of the synthetic leather casting paper according to this embodiment satisfies both of the above-mentioned conditions (ii) and (iii), or all of the above-mentioned conditions (ii), (iii), and (iv). One example of a means for satisfying both of the above-mentioned conditions (ii) and (iii), or all of the above-mentioned conditions (ii), (iii), and (iv), is to adjust the composition of the release agent composition used to form the release agent layer. Specifically, it is preferable to adjust the ratio of the (A) component and the (B) component contained as the binder resin of the release agent layer. The ratio of the (A) component to the (B) component is preferably such that, when the total of the (A) component and the (B) component is taken as 100 parts by mass, the content of PVA as the (A) component is 20 parts by mass or more and 80 parts by mass or less, and the content of at least one selected from the group consisting of SBR and MBR as the (B) component is 20 parts by mass or more and 80 parts by mass or less. By adjusting the ratio of component (A) to component (B) within this range, the above conditions (ii) and (iii) are more easily satisfied, and further, the above conditions (ii), (iii), and (iv) are more easily satisfied.

[0063] From the viewpoints of suppressing defects in releasability from the release agent layer when the vinyl chloride resin layer is formed and suppressing yellowing of the surface of the release agent layer, the ratio of the solids content of the component (A) to the component (B) (component (A) / component (B)) is preferably 20 / 80 or more and 80 / 20 or less, more preferably 25 / 75 or more and 75 / 25 or less, and even more preferably 30 / 70 or more and 70 / 30 or less, by mass.

[0064] (Yellowing index (YI value)) The yellowing index is measured in accordance with JIS K7373:2006. For example, the yellowing index is measured using a spectrophotometer with standard illuminant D in accordance with JIS K7373:2006. 65 It can be measured by the reflection method using the XYZ color system.

[0065] In this embodiment, the yellowing degree may be measured before and after forming a vinyl chloride resin layer on the surface of the release agent layer of the casting paper for synthetic leather. The timing for measuring the yellowing degree of the surface of the release agent layer of the casting paper for synthetic leather before and after forming the vinyl chloride resin layer may be, for example, the timing described below. For example, the vinyl chloride resin layer may be formed by applying a vinyl chloride resin composition to the surface of the release agent layer of the casting paper for synthetic leather and drying it at 200°C for 2 minutes.

[0066] Yellowing index before use (YI-0): Yellowing index before use in forming a vinyl chloride resin layer. Yellowing after one use (YI-1): After a vinyl chloride resin layer was formed on the surface of the release agent layer of the synthetic leather casting paper and then peeled off once. Yellowing after three uses (YI-3): The process of forming a vinyl chloride resin layer on the surface of the release agent layer of synthetic leather processing paper and then peeling it off is counted as one operation, and this process is repeated three times.

[0067] The yellowing index (YI-0) before use is preferably 1.5 or less, more preferably 1.4 or less, and even more preferably 1.3 or less. The lower limit of the yellowing index (YI-0) before use is not particularly limited, and may be, for example, 1 or more.

[0068] When a vinyl chloride resin composition is applied to the surface of the release agent layer of a synthetic leather casting paper and dried at 200°C for 2 minutes to form a vinyl chloride resin layer, the yellowing index (YI-1) after a single use is preferably 10 or less, more preferably less than 10, even more preferably 8 or less, and even more preferably 6 or less. The lower limit of the yellowing index (YI-1) after one use is not particularly limited, and may be, for example, 3 or more.

[0069] When a vinyl chloride resin composition is applied to the surface of the release agent layer of a synthetic leather casting paper and dried at 200°C for 2 minutes to form a vinyl chloride resin layer, the yellowing index (YI-3) after three uses is preferably 25 or less, more preferably less than 25, even more preferably 24 or less, and even more preferably 23 or less. The lower limit of the yellowing index after three uses (YI-3) is not particularly limited, and may be, for example, 10 or more.

[0070] (Difference in yellowing index (ΔYI)) The difference in yellowing degree (ΔYI) after one use is calculated by subtracting the above yellowing degree (YI-0) from the above yellowing degree (YI-1), to obtain ΔYI(1).Furthermore, the difference in yellowing degree (ΔYI) after three uses is calculated by subtracting the above yellowing degree (YI-0) from the above yellowing degree (YI-3), to obtain ΔYI(3).

[0071] In this embodiment, ΔYI(1) is equal to or less than 10. ΔYI(1) is preferably equal to or less than 8, more preferably equal to or less than 6, and even more preferably equal to or less than 5. The lower limit of ΔYI(1) is not particularly limited, and may be, for example, 0 or greater, or 1 or greater.

[0072] ΔYI(3) is preferably 25 or less, more preferably 24 or less, and even more preferably 23 or less. The lower limit of ΔYI(3) is not particularly limited, and may be, for example, 5 or more, or 8 or more.

[0073] (Critical peel load value) The critical peel load value is measured by a scratch test on the surface of the release agent layer (i.e., the release agent layer of unused synthetic leather casting paper) before the vinyl chloride resin composition is applied, and the critical peel load value at which the release agent layer of unused synthetic leather casting paper peels off is preferably 5 mN or more, more preferably 6 mN or more, even more preferably 8 mN or more, and even more preferably 10 mN or more. The upper limit of the critical peel load value is not particularly limited, and may be, for example, 30 mN or less.

[0074] The critical peel load value measured by the scratch test is an index for evaluating the scratch resistance of the release agent layer surface. If the critical peel load value is 5 mN or more, scratches on the release agent layer surface are likely to be suppressed even when the synthetic leather casting paper is used repeatedly. Furthermore, deterioration of the release property is likely to be suppressed even when the synthetic leather casting paper is used repeatedly.

[0075] The scratch test is performed using a scratch tester, in which an indenter needle is slightly vibrated in a horizontal direction perpendicular to the scratch direction, and the indenter needle is pressed against the surface of the release agent layer of the synthetic leather casting paper, scratching the surface while increasing the load applied to the indenter needle. The critical peel load value is calculated as the load value applied to the indenter needle when peeling occurs in the release agent layer of the synthetic leather casting paper. The scratch test can be performed under measurement conditions set to, for example, a scratch speed of 25 μm / s, an indenter needle stylus diameter of 5 μm, an indenter needle spring constant of 100 g / mm, and an excitation amplitude of 100 μm.

[0076] The synthetic leather casting paper according to this embodiment preferably has a peel strength from the resin layer of the synthetic leather (i.e., the resin layer containing a vinyl chloride resin as a main component) in the same range as the peel strength described in the first embodiment. A peel strength in the same range as the first embodiment can prevent the resin layer of the synthetic leather from accidentally peeling off from the release agent layer, and the synthetic leather casting paper can be stably peeled off from the synthetic leather even after repeated use. The method for measuring the peel strength is the same as the method for measuring the peel strength described in the first embodiment.

[0077] (How to use synthetic leather casting paper) When synthetic leather contains a resin containing a vinyl chloride resin as a primary component, the synthetic leather casting paper according to the first and second embodiments is used in the production of synthetic leather, for example, as follows. First, a vinyl chloride resin composition for forming synthetic leather, containing a vinyl chloride resin as a primary component, is applied to the surface of the release agent layer of the synthetic leather casting paper. The vinyl chloride resin composition preferably contains, for example, a liquefied product obtained by dispersing 100 parts by mass of vinyl chloride resin in 40 to 100 parts by mass of a plasticizer (e.g., a phthalate ester plasticizer, a fatty acid ester plasticizer, etc.) in terms of non-volatile content, and various additives such as antioxidants, stabilizers, fillers, and pigments, as needed. After the vinyl chloride resin composition is applied, it is heated and dried at a predetermined temperature (e.g., 200°C or higher) for a predetermined time (e.g., 2 minutes or longer) to form a vinyl chloride resin layer on the surface of the release agent layer of the synthetic leather casting paper. After forming the vinyl chloride resin layer, a base fabric is attached via an adhesive. After lamination, the vinyl chloride resin layer is aged. Finally, the vinyl chloride resin layer and the base fabric are peeled off from the interface with the release agent layer of the synthetic leather casting paper. This procedure allows synthetic leather to be produced.

[0078] The present invention is not limited to the above-described embodiment, and may include modifications and improvements within the scope of achieving the object of the present invention. [Example]

[0079] Examples will be described below, but the present invention is not limited to these examples in any way.

[0080] The following raw materials were prepared as raw materials for producing the casting paper for synthetic leather of each Example and Comparative Example.

[0081] (binder resin) "Component (A)": PVA (Kuraray Poval 22-98, manufactured by Kuraray Co., Ltd.)

[0082] "(B) Component": SBR-1 (styrene-butadiene latex, SN-309R, manufactured by Nippon A&L Co., Ltd., glass transition temperature 0°C) SBR-2 (styrene-butadiene latex, SR-102, manufactured by Nippon A&L Co., Ltd., glass transition temperature 21°C) SBR-3 (styrene-butadiene latex, Lackstar 3290N, manufactured by DIC Corporation, glass transition temperature -20°C) MBR (methyl methacrylate butadiene latex, MR-171, manufactured by Nippon A&L Co., Ltd., glass transition temperature -20°C)

[0083] "others": Starch: Oji Ace C (oxidized starch, manufactured by Oji Cornstarch Co., Ltd.)

[0084] (Removal agent) Em Silicone: Emulsion Silicone KM-3951 (Shin-Etsu Chemical Co., Ltd.)

[0085] (base material) Clay-coated paper: Silver Diamond SE (UT) W165G (Nippon Paper Industries Co., Ltd.)

[0086] Example 1 PVA as component (A) and SBR-1 as component (B) were blended at a mass solids ratio of 70 / 30 (=PVA / SBR-1) to form a binder resin. The PVA was dissolved in water and mixed with SBR-1. Emulsion silicone (KM-3951, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as a release agent, and the emulsion silicone and binder resin were added at a mass solids ratio of 80 / 20 (=binder resin / emulsion silicone). The release agent composition coating liquid was then diluted with water to a solids concentration of 15% by mass to prepare a release agent composition coating liquid. The release agent composition coating liquid was applied to the pigment coating layer (clay-coated surface) of clay-coated paper using a Mayer bar to a film thickness of 5 μm after drying. After coating, the coating was dried at 160°C for 1 minute to produce casting paper for synthetic leather. The ratio of component (A) to component (B) is the ratio when the binder resin is 100 parts by mass, and the ratio of emulsion silicone to binder resin is the ratio when the total of emulsion silicone and binder resin is 100 parts by mass.

[0087] <Examples 2 and 3> A casting paper for synthetic leather was prepared in the same manner as in Example 1, except that the solid content ratio of component (A) to component (B) converted into mass was changed according to Table 1.

[0088] <Examples 4 to 6> Casting paper for synthetic leather was prepared in the same manner as in Example 1, except that the type of component (B) was changed according to Table 1.

[0089] <Comparative Example 1> A casting paper for synthetic leather was prepared in the same manner as in Example 1, except that component (B) was not used.

[0090] <Comparative Example 2> A casting paper for synthetic leather was prepared in the same manner as in Example 1, except that the solid content ratio of component (A) to component (B) converted into mass was changed according to Table 1.

[0091] <Comparative Example 3> A casting paper for synthetic leather was prepared in the same manner as in Example 1, except that starch was used instead of component (B).

[0092] <Comparative Example 4> A casting paper for synthetic leather was prepared in the same manner as in Example 1, except that the solid content ratio of component (A) to component (B) converted into mass was changed according to Table 1.

[0093] [Method for forming vinyl chloride resin layer] The vinyl chloride resin composition for evaluation, a paste for forming a vinyl chloride resin layer, was applied to the surface of the release agent layer of the casting paper for synthetic leather obtained in each Example and Comparative Example so that the film thickness after drying would be 250 μm. After coating, the coating layer was dried by heating at 200° C. for 2 minutes to form a vinyl chloride resin layer. Using the above procedure, a vinyl chloride resin layer was formed on the release agent layer of the synthetic leather casting paper, and the yellowing, releasability, and scratch resistance of the surface of the release agent layer were evaluated as described below. The results are shown in Table 2.

[0094] The composition of the paste for forming the vinyl chloride resin layer is as follows: Vinyl chloride resin powder (ZEST P22, manufactured by Shin-Daiichi Vinyl Corporation): 100 parts by mass Bis-2-ethylhexyl phthalate (manufactured by Sankyo Chemical Co., Ltd.): 60 parts by mass Black pigment (Vinyl Toner Color 6740, Black, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.): 3 parts by weight

[0095] (Yellowing index (YI value)) The yellowing index (YI value) of the surface of the release agent layer of the synthetic leather casting paper obtained in each Example and Comparative Example was measured using a spectrophotometer (SE6000, manufactured by Nippon Denshoku Industries Co., Ltd.). The yellowing index was measured using Standard Illuminant D in accordance with JIS K7373:2006. 65 The XYZ color system was used and the measurement was made by the reflection method. The yellowing degree was measured for the following three types. (YI-0): Before forming a vinyl chloride resin layer on the surface of the release agent layer of the synthetic leather casting paper (before use). (YI-1): After a vinyl chloride resin layer was formed on the surface of the release agent layer of the synthetic leather casting paper and then peeled off once (single use). (YI-3): The process of forming a vinyl chloride resin layer on the surface of the release agent layer of synthetic leather casting paper and then peeling it off was counted as one operation, and this operation was repeated three times (three uses).

[0096] (Difference in yellowing (ΔYI value)) ΔYI(1) was calculated by subtracting the YI value of the surface of the release agent layer of the synthetic leather casting paper before use from the YI value of the surface of the release agent layer of the synthetic leather casting paper after one use. Also, ΔYI(3) was calculated by subtracting the YI value of the surface of the release agent layer of the synthetic leather casting paper before use from the YI value of the surface of the release agent layer of the synthetic leather casting paper after three uses.

[0097] (peelability) The process of forming a vinyl chloride resin layer on the surface of the release agent layer of the synthetic leather casting paper and peeling it off was repeated three times, and a sensory evaluation was conducted on the peelability on the third peel. When peeled, if the vinyl chloride resin layer and the synthetic leather casting paper could be peeled off without any problems at the interface, it was given an "A", and if the synthetic leather casting paper was damaged or if peeling did not occur at the interface, it was given an "F".

[0098] (Scratch resistance of release agent layer (critical peel load)) The scratch resistance of the surface of the release agent layer of unused synthetic leather casting paper was evaluated. The scratch resistance of the release agent layer was evaluated using a scratch tester (CSR-2000, manufactured by Rhesca Co., Ltd.) by slightly vibrating an indenter needle in the horizontal direction perpendicular to the scratch direction, pressing the indenter needle against the surface of the release agent layer of the synthetic leather casting paper, and increasing the load pressing the indenter needle while scratching the surface of the release agent layer. When peeling occurred in the release agent layer of the synthetic leather casting paper, the load value applied to the indenter needle was calculated as the critical peel load value. The measurement conditions were as follows:

[0099] Test conditions Scratch speed: 25 μm / s Indenter stylus diameter: 5 μm Indenter needle spring constant: 100g / mm Excitation amplitude: 100μm

[0100] [Table 1]

[0101] [Table 2]

[0102] In each of the Examples, even when the casting paper for synthetic leather is repeatedly used, there is no problem in the sensory evaluation of the releasability when peeling off the resin layer containing a vinyl chloride resin as a main component from the release agent layer, and there is little change in the yellowing degree before and after forming the resin layer containing a vinyl chloride resin as a main component on the surface of the release agent layer, compared to Comparative Examples 1 to 3. It is also clear that each of the Examples has superior scratch resistance compared to Comparative Example 4. From the above, it can be seen that the synthetic leather casting paper obtained in each example can suppress yellowing of the surface of the release agent layer while suppressing problems with releasability when peeling the resin layer from the release agent layer when producing a resin layer containing vinyl chloride resin as the main component. [Explanation of symbols]

[0103] 10...substrate, 10S...surface (surface of substrate), 30, 32...release agent layer, 30S, 32S...surface (surface of release agent layer), 100, 120...processing paper for synthetic leather.

Claims

1. A substrate; a release agent layer provided on the substrate and containing a binder resin and a release agent; Equipped with The binder resin contains the following component (A) and the following component (B): the release agent comprises a silicone-based release agent; Satisfies the following (i): Process paper for synthetic leather. Component (A): Polyvinyl alcohol Component (B): At least one selected from the group consisting of styrene-butadiene latex and methyl methacrylate-butadiene latex (i): The solid content ratio of the component (A) to the component (B) (component (A) / component (B)) is 20 / 80 or more and 80 / 20 or less in terms of mass.

2. A substrate; a release agent layer provided on the substrate and containing a binder resin and a release agent; Equipped with The binder resin contains the following component (A) and the following component (B): the release agent comprises a silicone-based release agent; The following (ii) is satisfied and the following (iii) is satisfied: Process paper for synthetic leather. Component (A): Polyvinyl alcohol Component (B): At least one selected from the group consisting of styrene-butadiene latex and methyl methacrylate-butadiene latex (ii) A vinyl chloride resin composition is applied to the surface of the release agent layer, and the vinyl chloride resin layer is formed by drying at a temperature of 200°C for 2 minutes, and then peeled from the release agent layer, the process consisting of applying the vinyl chloride resin composition, forming the vinyl chloride resin layer, and peeling it from the release agent layer being counted as a single operation, and the difference ΔYI(1) between the yellowing index YI-1 of the surface of the release agent layer after the single operation and the yellowing index YI-0 before the vinyl chloride resin composition was applied is 10 or less. (iii): When the surface of the release agent layer before the application of the vinyl chloride resin composition is subjected to a scratch test, the critical peel load value at which the release agent layer peels off, as measured by the scratch test, is 5 mN or more.

3. The synthetic leather casting paper according to claim 2, Furthermore, the following (iv) is satisfied: Process paper for synthetic leather. (iv): A vinyl chloride resin composition is applied to the surface of the release agent layer, and the vinyl chloride resin layer is dried at a temperature of 200°C for 2 minutes to form a film, and then the vinyl chloride resin layer is peeled from the release agent layer, the process consisting of applying the vinyl chloride resin composition, forming the vinyl chloride resin layer, and peeling it from the release agent layer being counted as one operation, and the difference ΔYI(3) between the yellowing index YI-3 of the surface of the release agent layer after repeating the one operation three times and the yellowing index YI-0 before applying the vinyl chloride resin composition is 25 or less.

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