Vinyl chloride-based resin paste for synthetic leather

Abstract

Provided is a vinyl chloride paste for synthetic leather, capable of forming synthetic leather with excellent flexibility and texture.　This vinyl chloride-based resin paste for synthetic leather is a vinyl chloride-vinyl acetate copolymer paste containing 3%-15% by weight of a vinyl acetate residue unit and having an average polymerization degree of 900-2,200. This synthetic leather preferably comprises the vinyl chloride-based resin paste for synthetic leather as a constituent material of a skin layer and / or a foamed layer.

Description

PVC resin paste for synthetic leather

[0001] The present invention relates to a paste vinyl chloride resin having properties suitable for use in synthetic leather, and in particular to a paste vinyl chloride resin that has a specific amount of vinyl acetate residue units and an average degree of polymerization, thereby enabling the provision of synthetic leather with excellent flexibility and feel, and to synthetic leather containing the same.

[0002] Paste vinyl chloride resin (hereinafter sometimes abbreviated as "paste PVC") is generally kneaded with a plasticizer, a filler, a stabilizer or other compounding agents to prepare a paste vinyl chloride sol (hereinafter sometimes abbreviated as "paste PVC sol"). The paste PVC sol is then used in a variety of molded products such as wallpaper, carpet tiles and gloves by a variety of molding methods.

[0003] Furthermore, synthetic leather made from vinyl chloride resin, which has high mechanical strength and excellent abrasion resistance, chemical resistance, and oil resistance, has been proposed for use in a wide range of fields, including automobile interiors, furniture, bags, footwear, clothing, and stationery (see, for example, Patent Document 1). While the flexibility of such synthetic leather can be improved by adding a plasticizer, there have been cases where issues have arisen that affect the feel of the leather, such as stickiness due to the plasticizer's influence, along with the imparted flexibility, depending on the amount added. Therefore, a method using a specific plasticizer has been proposed (see, for example, Patent Document 2).

[0004] Japanese Unexamined Patent Publication No. 6-116875 Japanese Unexamined Patent Application No. 6-2281

[0005] However, the proposals in Patent Documents 1 and 2 only propose synthetic leather and its composition, but do not consider paste PVC for use in synthetic leather, and the effects of only considering the plasticizer are limited. Therefore, the present invention aims to provide paste PVC suitable for synthetic leather, which enables the provision of synthetic leather with excellent flexibility and feel, and synthetic leather made therefrom.

[0006] As a result of extensive research into the above-mentioned problems, the present inventors have found that a paste vinyl chloride-vinyl acetate copolymer containing a specific amount of vinyl acetate residue units and having a specific average degree of polymerization is a paste vinyl chloride suitable for use in synthetic leather that is excellent in flexibility and feel, and have thereby completed the present invention.

[0007] That is, the present invention resides in the following [1] to [8]. [1] A paste vinyl chloride resin for synthetic leather, characterized by being a paste vinyl chloride-vinyl acetate copolymer containing 3 to 15% by weight of vinyl acetate residue units and having an average degree of polymerization of 900 to 2,200. [2] The paste vinyl chloride resin for synthetic leather according to [1], characterized in that the distribution of the vinyl acetate residue unit content shows a continuous distribution with one maximum and a mode of 1 to 30% by weight, and the particle size showing the maximum peak of the cumulative weight frequency in the primary particle size is 0.1 to 5 μm. [3] Synthetic leather, characterized by containing a paste vinyl chloride-vinyl acetate copolymer containing 3 to 15% by weight of vinyl acetate residue units and having an average degree of polymerization of 900 to 2,200. [4] The synthetic leather according to [3], which is composed of at least a surface layer, a foam layer, and a base fabric, wherein the surface layer and / or foam layer contains a paste vinyl chloride-vinyl acetate copolymer having 3 to 15% by weight of vinyl acetate residue units and an average degree of polymerization of 900 to 2,200. [5] The synthetic leather according to [4], wherein the surface layer contains 40 to 100 parts by weight of a plasticizer per 100 parts by weight of a paste vinyl chloride-vinyl acetate copolymer having 3 to 15% by weight of vinyl acetate residue units and an average degree of polymerization of 900 to 2,200.

[0008] [6] The synthetic leather according to [4] or [5], characterized in that the foamed layer contains 50 to 150 parts by weight of a plasticizer per 100 parts by weight of a paste vinyl chloride-vinyl acetate copolymer having 3 to 15% by weight of vinyl acetate residue units and an average degree of polymerization of 900 to 2,200. [7] The synthetic leather according to [5] or [6], characterized in that the plasticizer is at least one plasticizer selected from the group consisting of diisononyl phthalate, bis(2-ethylhexyl) terephthalate, diisodecyl phthalate, dibutyl phthalate, (2-ethylhexyl) adipate, diisononyl adipate, tri(2-ethylhexyl) trimellitate, and triisodecyl trimellitate. [8] A method for producing synthetic leather by laminating a surface layer, a foam layer, and a base fabric, wherein the surface layer and the foam layer are formed by paste processing, and the paste vinyl sol for the surface layer and / or the paste vinyl sol for the foam layer contains a paste vinyl chloride-vinyl acetate copolymer having 3 to 15% by weight of vinyl acetate residue units and an average degree of polymerization of 900 to 2,200, and a plasticizer.

[0009] The synthetic leather containing the paste PVC of the present invention has excellent flexibility and feel, and is therefore expected to be used in a wide range of fields, including automobile interiors, furniture, bags, footwear, clothing, and stationery.

[0010] The present invention is described in detail below. The paste vinyl chloride copolymer for synthetic leather of the present invention is a paste vinyl chloride-vinyl acetate copolymer containing 3 to 15 wt% vinyl acetate residue units and having an average degree of polymerization of 900 to 2,200. The paste vinyl chloride-vinyl acetate copolymer has a vinyl acetate residue unit content of 3 to 15 wt% (i.e., the vinyl acetate residue unit content is equivalent to 3 to 15 parts by weight per 100 parts by weight of the vinyl chloride-vinyl acetate copolymer). Since this provides excellent flexibility for synthetic leather, it is preferable that the vinyl acetate residue unit content be 7 to 12 wt% (i.e., the vinyl acetate residue unit content is equivalent to 7 to 12 parts by weight per 100 parts by weight of the vinyl chloride-vinyl acetate copolymer). Here, if the vinyl acetate residue unit content is less than 3 wt%, the resulting synthetic leather will have poor flexibility. On the other hand, if the vinyl acetate residue unit content is more than 15 wt%, the viscosity of the paste vinyl chloride copolymer will change significantly over time when processed into synthetic leather, resulting in poor processability.

[0011] Furthermore, the vinyl chloride-vinyl acetate copolymer paste has an average degree of polymerization of 900 to 2,200, and preferably an average degree of polymerization of 1,000 to 2,000, since this makes it possible to provide an excellent synthetic leather. If the average degree of polymerization is less than 900, the mechanical strength of the synthetic leather produced will be poor. On the other hand, if the average degree of polymerization is greater than 2,200, the processability of the synthetic leather produced will be poor. The average degree of polymerization can be determined, for example, by a method conforming to JIS-K6721.

[0012] The vinyl chloride-vinyl acetate copolymer for synthetic leather of the present invention exhibits excellent viscosity with minimal change over time when made into a vinyl chloride sol, resulting in synthetic leather with excellent mechanical strength. Therefore, the vinyl acetate residue unit content distribution is preferably a continuous distribution with a single maximum and a mode of 1 to 30% by weight. Measurement of the vinyl acetate residue unit content distribution can be performed, for example, by measuring the concentration of components separated into vinyl acetate residue units by 2D-HPLC or liquid chromatography gradient elution using an evaporative light scattering detector to determine the vinyl acetate residue unit content distribution. A continuous distribution with a mode of vinyl acetate residue unit content in the range of 1 to 30% by weight and a single maximum indicates the compositional distribution of vinyl acetate residue units in the vinyl acetate-vinyl chloride copolymer, as well as the uniformity of the compositional distribution. The narrower the distribution range of the vinyl acetate residue unit content, the fewer the number of maximums, and the stronger the distribution.

[0013] The synthetic leather paste PVC of the present invention is a paste PVC, and therefore is composed of aggregates of primary particles of vinyl chloride-vinyl acetate copolymer. The primary particle diameter, which indicates the maximum peak in cumulative weight frequency, is preferably 0.1 to 5 μm, particularly 0.5 to 3.0 μm, and even more preferably 1.0 to 2.0 μm, since this paste PVC exhibits minimal change in viscosity over time when made into a paste PVC sol and is suitable for synthetic leathers with excellent processability. The vinyl chloride-vinyl acetate copolymer paste constituting the synthetic leather paste PVC of the present invention may be any vinyl chloride-vinyl acetate copolymer generally known to be suitable for paste processing, such as a vinyl chloride-vinyl acetate copolymer paste obtained by polymerizing vinyl chloride monomer and vinyl acetate monomer by emulsion polymerization, microsuspension polymerization, seed emulsion polymerization, seed microsuspension polymerization, or the like. It may also be a commercially available product.

[0014] The PVC paste for synthetic leather of the present invention makes it possible to provide synthetic leather with excellent flexibility and feel. Examples of such synthetic leather include synthetic leathers consisting of at least a surface layer, a foam layer, and a base fabric. Among these, a laminated structure with a base fabric as the substrate, a foam layer in the middle, and a surface layer on the outer surface is preferred, as it results in synthetic leather with excellent feel and design. The PVC paste for synthetic leather of the present invention can be used as a constituent material for the surface layer and / or the foam layer.

[0015] When the vinyl chloride paste for synthetic leather of the present invention is used for a surface layer, it is preferable to contain 40 to 100 parts by weight, more preferably 50 to 90 parts by weight, and even more preferably 50 to 80 parts by weight of a plasticizer per 100 parts by weight of vinyl chloride-vinyl acetate copolymer, in order to obtain particularly excellent flexibility and to prevent quality and hygiene problems such as bleed-out. The plasticizer used in this case may be any plasticizer generally known for use in vinyl chloride resins, and among these, at least one plasticizer selected from the group consisting of diisononyl phthalate, bis(2-ethylhexyl) terephthalate, diisodecyl phthalate, dibutyl phthalate, (2-ethylhexyl) adipate, diisononyl adipate, tri(2-ethylhexyl) trimellitate, and triisodecyl trimellitate is preferred, as this will result in synthetic leather with an excellent balance of flexibility, permanent elongation, and mechanical strength, and diisononyl phthalate (hereinafter sometimes referred to as DINP) is preferred, as this will result in synthetic leather with extremely excellent flexibility.

[0016] When forming the surface layer, other additives such as pigments, diluents, inorganic fillers, heat stabilizers, viscosity modifiers, colorants, flame retardants, etc. Examples of inorganic fillers that can be used include calcium carbonate such as precipitated calcium carbonate, heavy calcium carbonate, and ultrafine calcium carbonate, magnesium carbonate, silicates such as silica, talc, diatomaceous earth, clay, and mica, aluminum hydroxide, and alumina. Examples of the heat stabilizer include metal soaps such as magnesium stearate, aluminum stearate, calcium stearate, barium stearate, zinc stearate, calcium laurate, barium laurate, and zinc laurate, metal salts of phenol or naphthol such as sodium, zinc, and barium, organotin compounds such as dibutyltin dilaurate and dibutyltin dimaleate, and phosphite esters such as diethyl phosphite, dibutyl phosphite, dioctyl phosphite, diphenyl isodecyl phosphite, tricresyl phosphite, triphenyl phosphite, tris(nonylphenyl)phosphite, and triisooctyl phosphite. Examples of the viscosity modifier and diluent include solvents such as xylene, solvent naphtha, mineral spirits, diisobutyl ketone, and butyl acetate, as well as appropriate surfactants. Examples of the flame retardant include antimony trioxide, red phosphorus, zinc borate, organic bromides, and chlorinated paraffins. Examples of the colorant include aniline blue, phthalocyanine green, chrome yellow, titanium oxide, and carbon black.

[0017] To enhance the design and texture of the surface layer, various patterns such as lattice, check, grain, diamond, heart, clover, spade, cow, lizard, snake, crocodile, tiger, and leopard patterns may be applied to the surface layer. Furthermore, the surface layer may be surface-treated with enamel, glitter, or a glossing agent. When the synthetic leather PVC paste of the present invention is used for a foam layer, it preferably contains 50 to 150 parts by weight, more preferably 70 to 130 parts by weight, and even more preferably 90 to 110 parts by weight, of a plasticizer per 100 parts by weight of the vinyl chloride-vinyl acetate copolymer paste, in order to achieve particularly excellent flexibility and to prevent quality and hygiene problems such as bleedout. Examples of the plasticizer used in this case include those listed above.

[0018] Furthermore, when the vinyl chloride paste for synthetic leather of the present invention is used for a foam layer, it is preferable to use 2 to 7 parts by weight of a foaming agent per 100 parts by weight of the vinyl chloride-vinyl acetate copolymer paste, particularly 3 to 6 parts by weight, and even more preferably 4 to 6 parts by weight. The foaming agent may be any of those commonly known as foaming agents for vinyl chloride resins, such as azodicarbonamide, azobisisobutyronitrile, benzenesulfonylhydrazide, p-toluenesulfonylhydrazide, p,p'-oxybis(benzenesulfonylhydrazide), dinitrosopentanemethylenetetramine, N,N'-dinitroso-N,N'-dimethylterephthalamide, and trihydrazinotriamine. These foaming agents may be used alone or in combination of two or more.

[0019] Furthermore, when forming a foamed layer, the above-mentioned other pigments, diluents, inorganic fillers, heat stabilizers, viscosity modifiers, colorants, flame retardants, etc. can be blended. The foamed layer may be either a closed-cell foamed layer or an open-cell foamed layer, and among these, a closed-cell foamed layer with uniform cells is preferred, as this will result in a synthetic leather with an excellent balance between tactile feel and durability. The foamed layer preferably has an expansion ratio of 2 to 10 times, and more preferably 3 to 7 times.

[0020] The base fabric (sometimes referred to as fabric) supports the foam layer and further the surface layer, and any fabric (base fabric) commonly used for synthetic leather or artificial leather can be used, including knitted fabric, woven fabric, nonwoven fabric, etc. Furthermore, examples of knitted fabric, woven fabric, nonwoven fabric, etc. include those made of a single fiber selected from synthetic fibers such as polyester, polyamide, polyacrylonitrile, nylon, etc.; natural fibers such as cotton, hemp, etc.; regenerated fibers such as rayon, acetate, etc.; and the like, or blends of these fibers.

[0021] The method for producing synthetic leather in the present invention may be any method that can produce synthetic leather consisting of at least a surface layer, a foam layer, and a base fabric. Examples of such methods include a method in which the surface layer, foam layer, and base fabric are each bonded together using an adhesive, thermocompression bonding, or the like, or a method that takes advantage of the properties of paste PVC by preparing a paste PVC sol for the surface layer and a paste PVC sol for the foam layer, laminating these together, then laminating the base fabric on top, and heating to resinify and foam the resulting material.

[0022] The paste vinyl vinyl sol for the skin layer and the paste vinyl vinyl sol for the foam layer can be prepared by uniformly mixing the paste vinyl vinyl, plasticizer, and, if necessary, the foaming agent and other additives using, for example, a planetary mixer, kneader, three-roll mill, Hobart mixer, butterfly mixer, dissolver, mortar and pestle mixer, ribbon blender, Henschel mixer, etc. Shaping can be performed by, for example, spreading the mixture onto release paper using a doctor knife, reverse roll, natural roll, floating knife, air knife, curtain flow, etc., or by spraying it onto release paper. The synthetic leather of the present invention has excellent flexibility and tactile feel and can be used in a wide range of applications, including automotive interiors such as seats, dashboards, instrument panels, door panels, roof panels, and console boxes, furniture such as sofas, dressers, and cupboards, bags and pouches such as business bags, pouches, and handbags, footwear such as shoes and sandals, clothing such as jackets, coats, and jumpers, and stationery.

[0023] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples. Evaluation and measurement methods in the examples are described below.

[0024] <Evaluation of Flexibility> The flexibility of the synthetic leathers obtained in the Examples and Comparative Examples was evaluated based on the feel of a number of randomly selected people. ◯: The synthetic leather felt soft when held. ×: The synthetic leather felt hard when held.

[0025] <Average Degree of Polymerization> Calculated in accordance with JIS-K6721.

[0026] <Average Content of Vinyl Acetate Residue Units> The average content (wt%) of vinyl acetate residue units contained in a vinyl chloride-vinyl acetate copolymer paste (sometimes referred to as VAc content) was calculated from the spectrum of a measurement sample obtained by mixing 100 mg of vinyl chloride-vinyl acetate copolymer paste particles with 10 mg of potassium bromide, grinding and molding the mixture, using an infrared spectrophotometer (manufactured by Shimadzu Corporation, (trade name) FTIR-8100A), using the following formula: VAc content = (3.73 × B / A + 0.024) × 1.04 A: 1430 cm －１ Abs. value of the absorption peak top due to the C-H in-plane bending angle around 1740 cm －１ Abs. value of the absorption peak top due to C=O stretching near

[0027] <Measurement of distribution of vinyl acetate residue unit content> The distribution of vinyl acetate residue unit content was measured by 2D-HPLC (two-dimensional HPLC). Apparatus: Agilent 1290 Infinity II series (manufactured by Agilent Technologies). Detector: Evaporative light scattering detector (ELSD) G4260B (manufactured by Agilent Technologies). First dimension (GPEC) column: TSKgel ODS-80Ts (manufactured by Tosoh Corporation). Column temperature: 40°C. Mobile phase: Solution A: 50% MeOH aqueous solution, Solution B: tetrahydrofuran, Flow rate: 0.6 ml / min, Concentration: 1.0 mg / ml, Injection volume: 20 μl. Second dimension (GPC) column: TSKgel SuperAWM-H (manufactured by Tosoh Corporation). Column temperature: 40° C. Eluent: tetrahydrofuran Flow rate: 0.6 ml / min Loop volume: 40 μl

[0028] <Particle Size Distribution> The synthetic leather paste vinyl chloride was dispersed in water, ultrasonically dispersed, and the particle size distribution was measured using a disc centrifugal particle size distribution measuring device (Nippon Rufuto Co., Ltd., (trade name) DC24000UHR).

[0029] Synthesis Example 1 1m ３ A stainless steel autoclave was charged with 360 kg of deionized water, 300 kg of vinyl chloride monomer, 5.7 kg of lauroyl peroxide, and 30 kg of a 15 wt % aqueous solution of sodium dodecylbenzenesulfonate, and the mixture was circulated using a homogenizer for 3 hours to homogenize it. Then, the temperature of the reaction system was raised to 45° C. to initiate polymerization. After the pressure in the polymerization system was reduced, the unreacted vinyl chloride monomer was recovered, yielding a vinyl chloride resin seed latex (a) having a solid content of 35 wt %, an average particle size of 0.55 μm, and containing 2 wt % lauroyl peroxide relative to the vinyl chloride resin.

[0030] Synthesis Example 2 1m ３A stainless steel autoclave was charged with 400 kg of deionized water, 300 kg of vinyl chloride monomer, 81 g of potassium persulfate, and 10 kg of a 16 wt % aqueous potassium laurate solution, and the temperature of the reaction system was raised to 54°C to initiate polymerization. From the start of polymerization to the end of polymerization, 0.7 parts by weight of a 15 wt % aqueous sodium dodecylbenzenesulfonate solution relative to the vinyl chloride monomer was continuously added. After the pressure in the polymerization system was reduced, unreacted vinyl chloride monomer was recovered to obtain a vinyl chloride resin seed latex (b) having a solids content of 40 wt % and an average particle size of 0.15 μm.

[0031] Example 1: A 2.5-liter autoclave was charged with 610 g of deionized water, 493 g of vinyl chloride monomer (62 wt % based on the total amount of the mixed monomers) and 96 g of vinyl acetate monomer (12 wt % based on the total amount of the mixed monomers) as first-stage monomer feeds, 9 g of a 5% aqueous solution of sodium lauryl sulfate, 85 g of the seed latex (a) having an average particle size of 0.55 μm obtained in Synthesis Example 1, and 4 g of a 0.1% aqueous solution of copper sulfate. The temperature of the reaction mixture was then raised to 35° C. to initiate first-stage polymerization, and a 0.05 wt % aqueous solution of ascorbic acid was continuously added throughout the entire polymerization period so as to maintain the polymerization temperature. When the polymerization conversion rate reached 50%, 140 g of vinyl chloride monomer (17 wt % based on the total amount of the mixed monomers) was charged as the second-stage monomer feed into the 2.5-liter autoclave, and the second-stage polymerization was continued at a polymerization temperature of 35° C. Furthermore, when the polymerization conversion rate relative to the total of the first-stage and second-stage monomer charges reached 80%, 70 g of vinyl chloride monomer (9 wt % relative to the total amount of the mixed monomer charges) was charged as the third-stage monomer charge into a 2.5-liter autoclave, and the third-stage polymerization was continued at a polymerization temperature of 35°C. The polymerization was terminated when the polymerization conversion rate relative to the total amount of the mixed monomers reached 90%. From the start of the polymerization to the end of the polymerization, 0.7 parts by weight of a 5 wt % aqueous solution of sodium lauryl sulfate and 0.1 parts by weight of an aqueous solution of a nonylpropenylphenol ethylene oxide 10 mol adduct sulfate ester ammonium salt (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.: AQUALON BC-1025 (trade name)) were continuously added relative to the vinyl chloride monomer to obtain a vinyl chloride-vinyl acetate copolymer latex. 1 kg of the obtained vinyl chloride-vinyl acetate copolymer latex was spray-dried using a rotary disk spray dryer at a hot air temperature of 160°C and an outlet temperature of 60°C to obtain a paste vinyl chloride-vinyl acetate copolymer, namely, a paste PVC for synthetic leather. The obtained paste PVC for synthetic leather had a vinyl acetate residue unit content of 9.0 wt% and a degree of polymerization of 1,900. The results of measuring the distribution of the vinyl acetate residue unit content and the particle size distribution are shown in Table 1.

[0032] Example 2: Into a 2.5-liter autoclave were charged 610 g of deionized water, 501 g of vinyl chloride monomer (62 wt % based on the total amount of the mixed monomers) and 82 g of vinyl acetate monomer (10 wt % based on the total amount of the mixed monomers) as first-stage monomer feeds, 9 g of a 5% aqueous solution of sodium lauryl sulfate, 85 g of the seed latex (a) having an average particle size of 0.55 μm obtained in Synthesis Example 1, and 4 g of a 0.1% aqueous solution of copper sulfate. The temperature of the reaction mixture was then raised to 40° C. to initiate first-stage polymerization, and a 0.05 wt % aqueous solution of ascorbic acid was continuously added throughout the entire polymerization period to maintain the polymerization temperature. When the polymerization conversion rate reached 73%, 140 g of vinyl chloride monomer (17 wt % based on the total amount of the mixed monomers) was charged as the second-stage monomer feed into the 2.5-liter autoclave, and the second-stage polymerization was continued at a polymerization temperature of 35° C. Furthermore, when the polymerization conversion rate relative to the total of the first-stage and second-stage monomer charges reached 82%, 70 g of vinyl chloride monomer (9 wt % relative to the total amount of the mixed monomer charges) was charged as the third-stage monomer charge into a 2.5-liter autoclave, and the third-stage polymerization was continued at a polymerization temperature of 35°C. The polymerization was terminated when the polymerization conversion rate relative to the total amount of the mixed monomers reached 90%. From the start of the polymerization to the end of the polymerization, 0.7 parts by weight of a 5 wt % aqueous solution of sodium lauryl sulfate and 0.1 parts by weight of an aqueous solution of a nonylpropenylphenol ethylene oxide 10 mol adduct sulfate ester ammonium salt (manufactured by Dai-ichi Kogyo Seiyaku: (trade name) AQUALON BC-1025) relative to the vinyl chloride monomer were continuously added to obtain a vinyl chloride-vinyl acetate copolymer latex. 1 kg of the obtained vinyl chloride-vinyl acetate copolymer latex was spray-dried using a rotary disk spray dryer at a hot air temperature of 160°C and an outlet temperature of 60°C to obtain a paste vinyl chloride-vinyl acetate copolymer, namely, a paste PVC for synthetic leather. The obtained paste PVC for synthetic leather had a vinyl acetate residue unit content of 6.6 wt% and a degree of polymerization of 1,810. The results of measuring the distribution of the vinyl acetate residue unit content and the particle size distribution are shown in Table 1.

[0033] Example 3: A 2.5-liter autoclave was charged with 610 g of deionized water, 225 g of vinyl chloride monomer (26 wt % based on the total amount of the mixed monomers) and 51 g of vinyl acetate monomer (6 wt % based on the total amount of the mixed monomers) as first-stage monomer feeds, 9 g of a 5% aqueous solution of sodium dodecylbenzenesulfonate, 90 g of the seed latex (a) having an average particle size of 0.55 μm obtained in Synthesis Example 1, and 4 g of a 0.1% aqueous solution of copper sulfate. The temperature of the reaction mixture was then raised to 47° C. to initiate first-stage polymerization, and a 0.05 wt % aqueous solution of ascorbic acid was continuously added throughout the entire polymerization period to maintain the polymerization temperature. When the polymerization conversion rate reached 85%, 250 g of vinyl chloride monomer (29 wt % based on the total amount of the mixed monomers) was charged as a second-stage monomer feed into the 2.5-liter autoclave, and the second-stage polymerization was continued at a polymerization temperature of 44° C. Furthermore, when the polymerization conversion rate relative to the total of the first-stage and second-stage monomers was 89%, 331 g of vinyl chloride monomer (39 wt % relative to the total amount of mixed monomers) was charged into a 2.5-liter autoclave as the third-stage monomer. The third-stage polymerization was continued at a polymerization temperature of 40°C, and terminated when the polymerization conversion rate relative to the total amount of mixed monomers reached 90%. From the start of polymerization to the end of polymerization, 0.7 parts by weight of a 5 wt % aqueous solution of sodium dodecylbenzenesulfonate relative to the vinyl chloride monomer was continuously added, yielding a vinyl chloride-vinyl acetate copolymer latex. One kg of the resulting vinyl chloride-vinyl acetate copolymer latex was spray-dried using a rotary disk spray dryer at a hot air temperature of 160°C and an outlet temperature of 60°C to yield a vinyl chloride-vinyl acetate copolymer paste PVC for synthetic leather. The resulting paste PVC for synthetic leather had a vinyl acetate residue unit content of 4.8 wt % and a degree of polymerization of 1,650. The results of the measurement of the distribution of the vinyl acetate residue unit content and the particle size distribution are shown in Table 1.

[0034] Example 4: A 2.5-liter autoclave was charged with 610 g of deionized water, 227 g of vinyl chloride monomer (28 wt % based on the total amount of the mixed monomers) and 41 g of vinyl acetate monomer (5 wt % based on the total amount of the mixed monomers) as first-stage monomer feeds, 9 g of a 5% aqueous solution of sodium dodecylbenzenesulfonate, 90 g of the seed latex (a) having an average particle size of 0.55 μm obtained in Synthesis Example 1, and 4 g of a 0.1% aqueous solution of copper sulfate. The temperature of the reaction mixture was then raised to 58° C. to initiate first-stage polymerization, and a 0.05 wt % aqueous solution of ascorbic acid was continuously added throughout the entire polymerization period to maintain the polymerization temperature. When the polymerization conversion rate reached 86%, 227 g of vinyl chloride monomer (28 wt % based on the total amount of the mixed monomers) as the second-stage monomer feed was charged into the 2.5-liter autoclave, and the second-stage polymerization was continued at a polymerization temperature of 55° C. Furthermore, when the polymerization conversion rate relative to the total amount of the first-stage and second-stage monomers was 90%, 300 g of vinyl chloride monomer (38 wt % relative to the total amount of mixed monomers) was charged into a 2.5-liter autoclave as the third-stage monomer. The third-stage polymerization was continued at a polymerization temperature of 51°C, and terminated when the polymerization conversion rate relative to the total amount of mixed monomers was 90%. From the start of polymerization to the end of polymerization, 0.7 parts by weight of a 5 wt % aqueous solution of sodium dodecylbenzenesulfonate relative to the vinyl chloride monomer was continuously added to obtain a vinyl chloride-vinyl acetate copolymer latex. One kg of the resulting vinyl chloride-vinyl acetate copolymer latex was spray-dried using a rotary disk spray dryer at a hot air temperature of 115°C and an outlet temperature of 55°C to obtain a vinyl chloride-vinyl acetate copolymer paste PVC for synthetic leather. The resulting paste PVC for synthetic leather had a vinyl acetate residue unit content of 4.0 wt % and a degree of polymerization of 1,020. The results of the measurement of the distribution of the vinyl acetate residue unit content and the particle size distribution are shown in Table 1.

[0035] Synthesis Example 3: A 2.5-liter autoclave was charged with 610 g of deionized water, 420 g of vinyl chloride monomer (60 wt % based on the total amount of the mixed monomers) as the first-stage monomer charge, 8 g of a 5% aqueous solution of sodium lauryl sulfate, 85 g of the seed latex (a) having an average particle size of 0.55 μm obtained in Synthesis Example 1, and 4 g of a 0.1% aqueous solution of copper sulfate. The temperature of the reaction mixture was then raised to 49° C. to initiate first-stage polymerization, and a 0.05 wt % aqueous solution of ascorbic acid was continuously added throughout the entire polymerization time so as to maintain the polymerization temperature. When the polymerization conversion rate reached 88%, 280 g of vinyl chloride monomer (40 wt % based on the total amount of the mixed monomers) was charged as the second-stage monomer charge into the 2.5-liter autoclave. The second-stage polymerization was continued at a polymerization temperature of 45° C. and terminated when the polymerization conversion rate based on the total amount of the mixed monomers reached 90%. From the start of polymerization to the end of polymerization, 0.7 parts by weight of a 5 wt% aqueous solution of sodium lauryl sulfate relative to the vinyl chloride monomer was continuously added to obtain a vinyl chloride polymer latex. 1 kg of the obtained vinyl chloride polymer latex was spray-dried using a rotating disk spray dryer at a hot air temperature of 160°C and an outlet temperature of 60°C to obtain a vinyl chloride polymer paste. The degree of polymerization of the obtained vinyl chloride polymer paste was 1,660.

[0036] Synthesis Example 4 A 2.5 L stainless steel autoclave was charged with 610 g of deionized water, 800 g of vinyl chloride monomer, 10 g of a 5 wt % aqueous solution of sodium sulfosuccinate, 4 parts by weight of seed latex (a) having an average particle size of 0.55 μm obtained in Synthesis Example 1 per 100 parts by weight of vinyl chloride monomer, and 1 part by weight of seed latex (b) having an average particle size of 0.15 μm per 100 parts by weight of vinyl chloride monomer, and the temperature of the reaction mixture was raised to 42° C. to initiate polymerization. From the start of polymerization to the end of polymerization, 0.5 parts by weight of a 5 wt % aqueous solution of sodium sulfosuccinate per vinyl chloride monomer was continuously added. The polymerization was terminated when the polymerization pressure dropped to 0.30 MPa from the saturated vapor pressure of vinyl chloride monomer at 42° C., and unreacted vinyl chloride monomer was recovered to obtain a vinyl chloride polymer latex. 1 kg of the obtained vinyl chloride polymer latex was spray-dried using a rotary disk type spray dryer at a hot air temperature of 160°C and an outlet temperature of 60°C to obtain a vinyl chloride polymer paste. The degree of polymerization of the obtained vinyl chloride polymer paste was 2,120.

[0037] Synthesis Example 5: A 2.5 L stainless steel autoclave was charged with 610 g of deionized water, 730 g of vinyl chloride monomer, 15 g of a 5 wt % aqueous solution of sodium dodecylbenzenesulfonate, 4 parts by weight of seed latex (a) having an average particle size of 0.55 μm obtained in Synthesis Example 1 per 100 parts by weight of vinyl chloride monomer, and 5 parts by weight of seed latex (b) having an average particle size of 0.15 μm per 100 parts by weight of vinyl chloride monomer, and the temperature of the reaction mixture was raised to 54° C. to initiate polymerization. From the start of polymerization to the end of polymerization, 0.7 parts by weight of a 5 wt % aqueous solution of sodium lauryl sulfate per vinyl chloride monomer was continuously added. The polymerization was terminated when the polymerization pressure dropped to 0.35 MPa from the saturated vapor pressure of vinyl chloride monomer at 54° C., and unreacted vinyl chloride monomer was recovered to obtain a vinyl chloride polymer latex.

[0038] One kilogram of the resulting vinyl chloride polymer latex was spray-dried using a rotary disk spray dryer at a hot air temperature of 160°C and an outlet temperature of 60°C to obtain a vinyl chloride polymer paste. The resulting vinyl chloride polymer paste did not contain sodium lauryl sulfate or ammonium salt of a nonylpropenylphenol-ethylene oxide 10-mol adduct sulfate. The degree of polymerization was 1,120. The results of measuring the distribution of vinyl acetate residue unit content and particle size distribution are shown in Table 1.

[0039]

[0040] Example 5 To 100 parts by weight of the synthetic leather paste PVC obtained in Example 1, 60 parts by weight of DINP (manufactured by J-Plus Co., Ltd.) as a plasticizer and 3 parts by weight of a calcium-zinc composite heat stabilizer (manufactured by ADEKA Corporation, (grade name) SC-320) were added, and the mixture was kneaded using a dissolver to prepare a paste PVC sol for a surface layer. To 100 parts by weight of the PVC paste obtained in Synthesis Example 5, 100 parts by weight of DINP (manufactured by J-Plus Co., Ltd.) as a plasticizer, 50 parts by weight of calcium carbonate ((trade name) NN#500, manufactured by Nitto Funka Kogyo Co., Ltd.), 4 parts by weight of titanium oxide (Teika Corporation, trade name JR600A) as a pigment, 5 parts by weight of a foaming agent (Otsuka Chemical Co., Ltd., trade name AZ Ultra 1050), and 1.6 parts by weight of a stabilizer (Asahi Denka Co., Ltd., (trade name) FL103N) were added, and the mixture was kneaded using a dissolver to prepare a paste PVC sol for a foam layer. The paste vinyl sol for the surface layer was coated to a thickness of 0.2 mm onto release paper that had been preheated at 180°C for 5 seconds, and then heated at 180°C for 10 seconds to obtain raw fabric 1. The paste vinyl sol for the foam layer was then coated to a thickness of 0.2 mm onto raw fabric 1, which was then heated at 200°C for 6 seconds to obtain raw fabric 2. A knitted fabric was then attached to the foam layer surface as a base fabric, and the resulting material was heated at 200°C for 90 seconds to cause gelation (resinification) and foaming. The release paper was then peeled off to obtain a synthetic leather having a closed-cell foam layer as the foam layer. The evaluation results of the resulting synthetic leather are shown in Table 2. The resulting synthetic leather was flexible and had an excellent feel.

[0041] Examples 6 to 8 Synthetic leathers having closed-cell foam layers were obtained and evaluated in the same manner as in Example 5, except that the synthetic leather paste vinyl chloride sols obtained in Examples 2, 3, and 4 were used as the surface layer paste vinyl chloride sols instead of the synthetic leather paste vinyl chloride sol obtained in Example 1. The evaluation results are shown in Table 2. The synthetic leathers obtained were flexible and had an excellent feel.

[0042] Example 9 Synthetic leather having a closed-cell foam layer was obtained and evaluated in the same manner as in Example 5, except that the synthetic leather paste vinyl chloride sol obtained in Example 1 was used as the foam layer paste vinyl chloride sol instead of the paste vinyl chloride obtained in Synthesis Example 5. The evaluation results are shown in Table 2. The synthetic leather obtained was flexible and had an excellent feel.

[0043] Example 10: Synthetic leather was obtained in the same manner as in Example 5, except that the amount of plasticizer in the vinyl chloride sol paste for the surface layer was changed to 80 parts by weight, and the synthetic leather was evaluated. The evaluation results are shown in Table 2. The synthetic leather obtained was flexible and had an excellent feel.

[0044] Example 11 Synthetic leather was obtained in the same manner as in Example 5, except that the amount of plasticizer in the vinyl chloride sol paste for the foam layer was changed to 120 parts by weight, and the synthetic leather was evaluated. The evaluation results are shown in Table 2. The obtained synthetic leather was flexible and had an excellent feel.

[0045]

[0046] Comparative Examples 1 and 2 Synthetic leathers were obtained and evaluated in the same manner as in Example 5, except that the vinyl chloride polymer pastes obtained in Synthesis Examples 3 and 4 were used in the sol for the surface layer instead of the vinyl chloride paste for synthetic leather obtained in Example 1. The evaluation results are shown in Table 3. The obtained synthetic leathers had poor flexibility and a poor feel.

[0047] Comparative Example 3 Synthetic leather was obtained in the same manner as in Example 5, except that the vinyl chloride polymer paste obtained in Synthesis Example 3 was used in the sol for the surface layer instead of the vinyl chloride paste for synthetic leather obtained in Example 1, and the amount of plasticizer in the sol for the surface layer was changed to 80 parts by weight, and then evaluated. The evaluation results are shown in Table 3. The obtained synthetic leather had poor flexibility and a poor feel.

[0048] Comparative Example 4 Synthetic leather was obtained in the same manner as in Example 5, except that the vinyl chloride polymer paste obtained in Synthesis Example 3 was used for the sol for the surface layer instead of the vinyl chloride paste for synthetic leather obtained in Example 1, the amount of plasticizer in the sol for the surface layer was changed to 80 parts by weight, and the amount of plasticizer in the sol for the foam layer was changed to 120 parts by weight, and then evaluated. The evaluation results are shown in Table 3. The obtained synthetic leather had poor flexibility and a poor feel.

[0049]

[0050] The claims, specifications and abstracts of Japanese Patent Application No. 2023-105601 filed on June 28, 2023 and Japanese Patent Application No. 2024-058761 filed on April 1, 2024 are all cited herein and incorporated as the disclosure of the specification of the present invention.

[0051] The PVC paste for synthetic leather of the present invention can provide synthetic leather having excellent flexibility and feel, and this synthetic leather can be used in various industrial applications, and its industrial value is extremely high.

Claims

1. A paste vinyl chloride resin for synthetic leather, which is a paste vinyl chloride-vinyl acetate copolymer containing 3-15% by weight of vinyl acetate residue units and having an average degree of polymerization of 900-2,200.

2. The vinyl chloride resin paste for synthetic leather according to claim 1, characterized in that the distribution of vinyl acetate residue unit content shows a continuous distribution with one maximum value and a mode value of 1 to 30 weight %, and the particle size showing the maximum peak of cumulative weight frequency in the primary particle size is 0.1 to 5 μm.

3. Synthetic leather characterized in that it contains a paste vinyl chloride-vinyl acetate copolymer containing 3-15% by weight of vinyl acetate residue units and having an average degree of polymerization of 900-2,200.

4. Synthetic leather according to claim 3, which is composed of at least a skin layer, a foam layer, and a base fabric, and wherein the skin layer and / or the foam layer contains a paste vinyl chloride-vinyl acetate copolymer containing 3-15% by weight of vinyl acetate residue units and having an average degree of polymerization of 900-2,200.

5. The synthetic leather according to claim 4, characterized in that the skin layer contains 3 to 15% by weight of vinyl acetate residue units and 40 to 100 parts by weight of a plasticizer for 100 parts by weight of a paste vinyl chloride-vinyl acetate copolymer having an average degree of polymerization of 900 to 2,200.

6. The synthetic leather according to claim 4, characterized in that the foam layer contains 50 to 150 parts by weight of a plasticizer for 100 parts by weight of a vinyl chloride-vinyl acetate copolymer paste having 3 to 15% by weight of vinyl acetate residue units and an average degree of polymerization of 900 to 2,200.

7. Synthetic leather according to claim 5 or 6, characterized in that the plasticizer is at least one selected from the group consisting of diisononyl phthalate, bis(2-ethylhexyl) terephthalate, diisodecyl phthalate, dibutyl phthalate, (2-ethylhexyl) adipate, diisononyl adipate, tri(2-ethylhexyl) trimellitate, and triisodecyl trimellitate.

8. A method for producing synthetic leather comprising laminating a surface layer, a foam layer and a base fabric, the surface layer and the foam layer being formed by paste processing, the paste vinyl chloride sol for the surface layer and / or the paste vinyl chloride sol for the foam layer containing 3 to 15% by weight of vinyl acetate residue units and a paste vinyl chloride-vinyl acetate copolymer having an average degree of polymerization of 900 to 2200, and a plasticizer.

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