JP7788813B2 - leather - Google Patents

Description

The present invention relates to leather that suppresses static electricity generation and has a deep color.

Leather is used as a luxurious material for applications such as vehicle interiors, building interiors, furniture, bags, and shoes. Synthetic leathers that offer a luxurious feel comparable to natural leather have also been developed, and their uses are expanding.

Leather that is less susceptible to static electricity is particularly desirable for applications such as sheet materials that frequently come into contact with the human body, and numerous proposals have been made for antistatic treatment of leather. For example, Patent Document 1 discloses a conductive synthetic leather having a conductive skin layer and a conductive fiber substrate, in which the surface resistance of the skin layer is 1.0× ¹⁰ Ω to 1.0× ¹⁰ Ω, the surface resistance of the fiber substrate is lower than the surface resistance of the skin layer, and the resistance to ground is 1.0× ¹⁰ Ω to 1.0× ¹⁰ Ω. Examples of conductive agents for imparting conductivity to the skin layer include carbon-based conductive materials such as carbon black, metal-based conductive materials such as zinc oxide, indium tin oxide (ITO), or antimony tin oxide, and surfactants.

Japanese Patent Application Laid-Open No. 2020-50998

The conductive synthetic leather described in Patent Document 1 produces synthetic leather with excellent antistatic properties, but the surface of leather containing particulate conductive agents in the skin layer is pale and unable to express the deep, wet-looking color. It also has the drawback of making the unevenness of the leather surface less noticeable. As a result, the surface is unattractive and has a cheap appearance.

The leather of the present invention is characterized in that an antistatic layer and an antireflection layer are laminated in this order on the surface of natural leather or synthetic leather, the antistatic layer being made of a resin and conductive particles, and the antireflection layer being made of a resin and low-refractive-index particles having a refractive index of 1.2 to 1.45 .

The antistatic layer preferably comprises a resin and conductive particles with a refractive index of 1.6 to 2.1. The thickness of the antistatic layer preferably ranges from 50 nm to 1 μm.

The present invention makes it possible to provide leather that has excellent surface conductivity, a deep color, a distinct grain, and a luxurious feel.

1 is a schematic diagram showing the cross-sectional structure of the leather (based on natural leather) of the present invention. 1 is a schematic diagram showing the cross-sectional structure of the leather (synthetic leather base) of the present invention.

The leather of the present invention uses natural leather or synthetic leather as its base. The natural leather used in the present invention is not fur, but leather that has been dehaired and tanned as necessary. There are no limitations on the type of rawhide or tanning method. Examples include rawhide from mammals such as cattle, pigs, horses, goats, sheep, and deer; birds such as ostriches; and reptiles such as sea turtles, monitor lizards, pythons, and crocodiles. Tanning methods include the typical chrome tanning and tannin tanning, as well as methods using mineral tanning agents such as aluminum tanning, zirconium tanning, titanium tanning, and ferric salt tanning; methods using organic tanning agents such as aldehyde tanning; tanning using synthetic tanning agents such as naphthalene-based synthetic tanning agents, phenol-based synthetic tanning agents, and resin tanning agents; and oil tanning, typified by chamois leather.

The natural leather used in the present invention undergoes the preparatory processes of soaking, lining, unhairing and liming, splitting, descaling, reliming, and deliming and bating, followed by a tanning process to impart flexibility and heat resistance to the leather. Further processes such as dyeing and greasing may be performed. A resin skin layer made of acrylic resin, urethane resin, epoxy resin, etc. may also be laminated on the surface of the natural leather.

On the other hand, the synthetic leather of the present invention may be composed of a fabric substrate made of fibers and a resin skin layer formed on the surface thereof. The fabric substrate may be a woven fabric, knitted fabric, nonwoven fabric, or the like. Examples of fiber materials that make up the fabric substrate include natural fibers such as cotton, linen, and wool; synthetic fibers such as polyamide, polyester, and polyacrylonitrile; semi-synthetic fibers such as acetate; and regenerated fibers such as rayon. The fabric substrate may be subjected to processes such as scouring and dyeing under general conditions.

The main component constituting the resin skin layer is a synthetic resin, such as acrylic resin, urethane resin, or epoxy resin. Among these, urethane resin is preferred for its durability and texture. The resin skin layer may also contain other components such as pigments, dyes, and additives such as silicone.

There are no particular restrictions on the thickness of the resin skin layer, but it is preferably between 20 and 50 μm. A resin skin layer thickness in the range of 20 to 50 μm allows for the formation of a uniform resin film without impairing flexibility.

One method for laminating the resin skin layer on one surface of the fabric substrate is to attach the resin skin layer formed on the surface of release paper or the like via an adhesive layer. Another method is to apply a resin composition that will become the resin skin layer upon drying and solidification to one surface of the fabric substrate, followed by drying and solidification.

Examples of materials that can be used to form the adhesive layer include acrylic resin, urethane resin, and epoxy resin. Among these, urethane resin is preferred because it provides durability and a luxurious texture.

The urethane resin component that makes up the resin skin layer is generally called polyurethane resin or polyurethane urea resin, and examples include those obtained by reacting polyalkylene ether glycols, hydroxyl-terminated polyester polyols, poly-ε-caprolactone polyols, polycarbonate polyols, etc., each having a molecular weight of 400 to 4,000, alone or in combination, with organic diisocyanates. If necessary, these can be chain-extended with a compound containing two active hydrogens (chain extender).

Examples of the polyalkylene ether glycol include polytetramethylene ether glycol, polypropylene glycol, polyethylene glycol, glycerin propylene oxide adduct, polyether polyols with ethylene oxide added to the terminals, and vinyl monomer-grafted polyether polyols.

Examples of the polyester polyol include those obtained by reacting alkylene glycols such as ethylene glycol, butylene glycol, hexylene glycol, diethylene glycol, dipropylene glycol, and neopentyl glycol with carboxylic acids such as succinic acid, glutaric acid, adipic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid, and trimellitic acid so that the terminal groups are hydroxyl acids.

Examples of the polycarbonate polyol include polyethylene carbonate diol, polytetramethylene carbonate diol, and polyhexamethylene carbonate diol.

Examples of the organic diisocyanate include aromatic isocyanates such as 2,4- or 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, and xylylene diisocyanate; and aliphatic isocyanates such as 1,6-hexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 3-isocyanatomethyl-3,5,5'-trimethylcyclohexyl isocyanate, and 2,6-diisocyanatomethyl caproate. These may be used alone or in combination of two or more.

The chain extender may be hydrazine, ethylenediamine, tetramethylenediamine, water, piperazine, isophoronediamine, ethylene glycol, butylene glycol, hexylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, or glycols and diamines that can improve hydrophilicity, such as dimethylolpropionic acid and ethylene oxide adducts of aminoethanesulfonic acid, and may be used alone or in combination.

Acrylic resins are resins composed of polyfunctional acrylic monomers, polyfunctional acrylic oligomers, or both.

Examples of polyfunctional acrylic monomers include polyol polyacrylates such as ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; epoxy acrylates such as bisphenol A diglycidyl ether di(meth)acrylate and hexanediol diglycidyl ether di(meth)acrylate; and urethane acrylates obtained by reacting polyisocyanate with hydroxyl group-containing acrylates such as hydroxyethyl (meth)acrylate.

The polyfunctional acrylic oligomers used in the acrylic component are common oligomers such as polyester acrylate, epoxy acrylate, urethane acrylate, and polyol acrylate, and among these oligomers, the main skeleton is either linear (zero branching points) or has one branching point on the main skeleton.

In the leather of the present invention, an antistatic layer is laminated on the surface of the natural leather or synthetic leather. The antistatic layer is made of resin and conductive particles. The conductive particles preferably have a refractive index of 1.6 to 2.1. When the refractive index of the conductive particles is within this range, the effect of making the leather grain more pronounced is achieved. Examples of such conductive particles include ITO (indium tin oxide), ATO (antimony-doped tin oxide), FTO (fluorine-doped tin oxide), GZO (gallium-doped zinc oxide), AZO (aluminum-doped zinc oxide), carbon, carbon nanofibers, etc.

The primary particle diameter of the conductive particles is preferably 10 nm to 100 nm. A primary particle diameter within this range provides the effects of imparting antistatic properties and clarifying the leather grain.

Examples of resins that can be used to form the antistatic layer include urethane resins, acrylic resins, and epoxy resins. Among these, urethane resins and acrylic resins are preferred because they provide durability and a luxurious texture.

Examples of urethane resins include those obtained by reacting polyester diols, polyether diols, polycarbonate polyols, etc., alone or in combination, with polyisocyanate. If necessary, these can be chain-extended with a compound containing two active hydrogens (chain extender). Examples of acrylic resins include polyester acrylates, epoxy acrylates, urethane acrylates, and polyol acrylates.

The thickness of the antistatic layer is preferably between 50 nm and 1 μm. A thickness within this range of the antistatic layer provides antistatic properties and makes the leather grain more pronounced.

The content of the conductive particles contained in the antistatic layer is preferably 30 to 90 mass % in terms of solid content.

Methods for forming the antistatic layer on the surface of the natural leather or synthetic leather include spraying, slit coating, screen printing, and inkjet printing. Among these, inkjet printing is preferred because it allows for pattern printing in any shape and allows for thin film coating.

The leather of the present invention further comprises an antireflection layer laminated on the surface of the antistatic layer. The antireflection layer is composed of a resin and low-refractive-index particles with a refractive index of 1.2 to 1.45. The "low" in low-refractive-index particles here refers to particles with a refractive index lower than that of the conductive particles. When the refractive index of the low-refractive-index particles is within this range, it becomes possible to express deep colors. Examples of such low-refractive-index particles include inorganic particles such as SiO ₂ (refractive index 1.40) and hollow silica (refractive index 1.25), and organic particles such as PTFE (polytetrafluoroethylene, refractive index 1.30).

The primary particle diameter of the low refractive index particles is preferably 10 nm to 300 nm. A primary particle diameter within this range provides the effect of achieving deep color due to anti-reflection.

Examples of resins that make up the anti-reflection layer include acrylic resins and urethane resins. Among these, acrylic resins and urethane resins are preferred because they provide durability and a luxurious texture.

Examples of urethane resins include those obtained by reacting polyester diols, polyether diols, polycarbonate polyols, etc., alone or in combination, with polyisocyanate. If necessary, these can be chain-extended with a compound containing two active hydrogens (chain extender). Examples of acrylic resins include polyester acrylates, epoxy acrylates, urethane acrylates, and polyol acrylates.

The thickness of the antireflection layer is preferably 50 nm to 1 μm. If the thickness of the antireflection layer is within this range, the effect of deep color due to low reflection can be obtained, and at the same time, the surface resistance of the obtained leather can be set to 1.0 × 10 ⁶ to 1.0 × 10 ¹¹ Ω/□. If the thickness of the antireflection layer is less than 50 nm, a deep color cannot be expressed. If the thickness of the antireflection layer exceeds 1 μm, the surface resistance of the obtained leather becomes too high and surface conductivity cannot be obtained. As a result, it becomes difficult to obtain the antistatic effect.

Methods for forming the antireflection layer on the surface of the antistatic layer include spraying, slit coating, screen printing, and inkjet printing. The antireflection layer may be formed over the entire surface, or may be formed as a pattern or design on a portion of the surface. Furthermore, multiple antireflection layers with different apparent refractive indices may be arranged and formed side by side or stacked. By changing the type and content of low refractive index particles contained, antireflection layers with different apparent refractive indices can be formed. Inkjet printing is a suitable method for forming antireflection layers in such free shapes.

The present invention will be explained in more detail below using examples. However, the present invention is not limited to these examples, and modifications may be made within the scope of the above and below-described aims, and all such modifications are within the technical scope of the present invention.

[Surface resistance value]
The surface resistance (Ω/□) of the leathers obtained in the examples and comparative examples was measured using a high resistivity meter Hiresta-UP (manufactured by Nitto Seiko Analytech Co., Ltd.).
[Color difference (ΔL ^* )]
The surface of the fibrous composite, i.e., the surface of the resin skin layer, was measured using an integrating sphere spectrophotometer Color-i5 (manufactured by X-Rite). Next, the surface of the leather obtained in the Examples and Comparative Examples was measured. The leather surface corresponds to the surface of the antireflection layer in the Examples and the surface of the antistatic layer in the Comparative Examples. _D65 was used as the light source. The color difference ΔL ^* was calculated by subtracting the lightness of the fibrous composite surface from the lightness of the leather surface. If the color difference ΔL ^* is a negative value, it can be determined that a dark color effect has been achieved.
[Effect of clarifying the grain]
The clarity of the grain was evaluated by visual inspection. A grain (uneven design) that replicates the embossed pattern of the release paper is formed on the surface of the fibrous composite material, i.e., the surface of the resin skin layer. The grain on the leather surface obtained in the examples and comparative examples was evaluated visually, with a ◎ indicating that the grain on the leather surface was more clearly visible than the grain on the resin skin layer surface, a ◯ indicating that there was no change in the grain, and an × indicating that the grain was weakly visible.

[Production Example 1: Polyurethane resin composition a]
To 100 parts by mass of a polycarbonate-based polyurethane resin (CRISBON NY-328; manufactured by DIC Corporation), 25 parts by mass of dimethylformamide and 25 parts by mass of methyl ethyl ketone were added, and 15 parts by mass of perylene black pigment (Lumogen Black FK4280; manufactured by BASF) was further added to prepare a polyurethane resin composition a.

[Production Example 2: Polyurethane resin composition b (adhesive polyurethane resin composition)]
A polyurethane resin composition b was prepared by adding 40 parts by mass of dimethylformamide to 100 parts by mass of a polycarbonate-based polyurethane resin (TA-205; manufactured by DIC Corporation).

Polyurethane resin composition a was applied to release paper (PXD R-86; manufactured by Lintec Corporation) so that the film would have a dry thickness of 40 μm, and then dried in a dryer at 100°C for 2 minutes to form urethane resin layer A, which would serve as the resin skin layer. The refractive index of this urethane resin layer A was 1.59.

Next, polyurethane resin composition b (adhesive polyurethane resin composition) was applied to urethane resin layer A so that the film thickness after drying would be 80 μm, and the mixture was dried in a dryer at 100°C for 1 minute to form urethane resin layer B (adhesive layer), producing a urethane resin laminated release material having a two-layer urethane resin layer structure.

Next, the urethane resin layer B side of the urethane resin laminated release material was attached to one side of the polyester tricot knit fabric base layer, and the material was pressed together at 392.3 kPa for 4 seconds. After that, the release paper was peeled off, producing a fibrous composite material in which a resin skin layer (urethane resin layer A) was laminated to the base layer via an adhesive layer (urethane resin layer B).

[Example 1]
A polyurethane resin liquid for an antistatic layer prepared according to the following formulation 1 was coated on the surface of the resin skin layer of the above-mentioned fibrous composite material using a bar coater (wet: 4 μm), and then dried at 100° C. for 60 minutes to form an antistatic layer with a thickness of 250 nm. Next, a polyurethane resin liquid for an antireflective layer prepared according to the following formulation 2 was coated on the antistatic layer using a bar coater (wet: 6 μm), and then dried at 100° C. for 60 minutes to form an antireflective layer with a thickness of 120 nm, thereby obtaining the leather of the present invention.

Formulation 1 (Polyurethane resin solution for antistatic layer)
Polycarbonate diol (Benebiol NL2030DB, manufactured by Mitsubishi Chemical Corporation, solid content 100% by mass): 1 part by mass Polyisocyanate (Coronate 2770, manufactured by Tosoh Corporation, solid content 100% by mass): 0.23 parts by mass Thermal base generator (U-CAT1102, manufactured by San Nopco Ltd.): 0.01 parts by mass ATO dispersion (EA-D, manufactured by Dai Nippon Paint Co., Ltd., solid content 40% by mass): 12.4 parts by mass Dipropylene glycol monomethyl ether: 110.4 parts by mass

Formulation 2 (Polyurethane resin liquid for anti-reflection layer)
Polycarbonate diol (Benebiol NL2030DB, manufactured by Mitsubishi Chemical Corporation, solid content 100% by mass): 2 parts by mass; Polyisocyanate (Coronate 2770, manufactured by Tosoh Corporation, solid content 100% by mass): 0.5 parts by mass; Thermal base generator (U-CAT1102, manufactured by San Nopco Ltd.): 0.01 parts by mass; Hollow silica dispersion (Sururia, manufactured by JGC Catalysts and Chemicals Co., Ltd., solid content 25% by mass): 2.5 parts by mass; Dipropylene glycol monomethyl ether: 95 parts by mass

The conductive particles (ATO) contained in the antistatic layer have a refractive index of 2.00, a primary particle diameter of 30 to 40 nm, and the content of ATO particles is approximately 80 mass %. The low refractive index particles contained in the antireflection layer are hollow silica particles with a refractive index of 1.25 and a primary particle diameter of 50 nm. The surface resistance of the obtained leather was 7.3 x 10 ⁸ Ω/□. The color difference was -2.4, and it was confirmed that the grain was clearly defined.

[Example 2]
Leather of the present invention was obtained in the same manner as in Example 1, except that a polyurethane resin solution for an antistatic layer prepared according to the following formulation 3 was used instead of formulation 1.

Formulation 3 (Polyurethane resin solution for antistatic layer)
Polycarbonate diol (Benebiol NL2030DB, manufactured by Mitsubishi Chemical Corporation, solid content 100% by mass): 1 part by mass Polyisocyanate (Coronate 2770, manufactured by Tosoh Corporation, solid content 100% by mass): 0.23 parts by mass Thermal base generator (U-CAT1102, manufactured by San Nopco Ltd.): 0.01 parts by mass AZO dispersion (product name "9407 ZO", manufactured by Tokushiki Corporation, solid content 30% by mass): 16.4 parts by mass Dipropylene glycol monomethyl ether: 106.8 parts by mass

The conductive particles contained in the antistatic layer were AZO particles with a refractive index of 1.80 and a primary particle diameter of 20 to 40 nm. The content of AZO particles was approximately 80% by mass. The surface resistance of the obtained leather was 5.6 x 10 ⁹ Ω/□. The color difference was -2.8, and it was confirmed that the grain was clearly defined.

[Example 3]
Leather of the present invention was obtained in the same manner as in Example 1, except that instead of Formulation 1, a polyurethane resin solution for an antistatic layer prepared according to the following Formulation 4 was used and coated with a bar coater (wet: 8 μm) to form an antistatic layer with a thickness of 720 nm.

Formulation 4 (Polyurethane resin solution for antistatic layer)
Polycarbonate diol (Benebiol NL2030DB, manufactured by Mitsubishi Chemical Corporation, solid content 100% by mass): 4 parts by mass; Polyisocyanate (Coronate 2770, manufactured by Tosoh Corporation, solid content 100% by mass): 1 part by mass; Thermal base generator (U-CAT1102, manufactured by San Nopco Ltd.): 0.01 parts by mass; ATO dispersion (trade name EA-D, manufactured by Dai Nippon Paint Co., Ltd., solid content 40% by mass): 12.4 parts by mass; Dipropylene glycol monomethyl ether: 110.4 parts by mass

The conductive particles contained in the antistatic layer were ATO with a refractive index of 2.00 and a primary particle diameter of 30 to 40 nm. The content of ATO particles was approximately 50% by mass. The low refractive index particles contained in the antireflection layer were hollow silica with a refractive index of 1.25 and a primary particle diameter of 50 nm. The surface resistance of the obtained leather was 8.3 x 10 ¹⁰ Ω/□. The color difference was -1.2, and it was confirmed that the grain was clearly defined.

[Example 4]
Leather of the present invention was obtained in the same manner as in Example 1, except that a polyurethane resin solution for an antireflection layer prepared according to the following formulation 5, instead of formulation 2, was coated using a bar coater (wet: 8 μm) to form an antireflection layer with a thickness of 500 nm.

Formulation 5 (Polyurethane resin liquid for anti-reflection layer)
Polycarbonate diol (Benebiol NL2030DB, manufactured by Mitsubishi Chemical Corporation, solid content 100% by mass): 4 parts by mass; Polyisocyanate (Coronate 2770, manufactured by Tosoh Corporation, solid content 100% by mass): 1 part by mass; Thermal base generator (U-CAT1102, manufactured by San Nopco Ltd.): 0.01 parts by mass; Hollow silica dispersion (Sururia, manufactured by JGC Catalysts and Chemicals Co., Ltd., solid content 25% by mass): 5 parts by mass; Dipropylene glycol monomethyl ether: 90 parts by mass

The surface resistance of the obtained leather was 2.4×10 ¹⁰ Ω/□, and the color difference was −3.4, confirming that the grain was clearly defined.

[Example 5]
Leather of the present invention was obtained in the same manner as in Example 1, except that instead of Formulation 2, a polyurethane resin liquid for an antireflection layer prepared according to Formulation 6 below was applied using a bar coater (wet: 4 μm), and then dried at 130° C. for 2 minutes to form an antireflection layer with a thickness of 250 nm.

Formulation 6 (Polyurethane resin liquid for anti-reflection layer)
Polycarbonate-based polyurethane resin (RU-40-350, manufactured by Stahl Japan Co., Ltd., solid content 40% by mass): 113 parts by mass Smoothing agent (HM-183, manufactured by Stahl Japan Co., Ltd., solid content 30% by mass): 3 parts by mass Crosslinking agent (XR-78-017, manufactured by Stahl Japan Co., Ltd., solid content 50% by mass): 1 part by mass PTFE water dispersion (D-210C, manufactured by Daikin Industries, Ltd., solid content 60% by mass): 26 parts by mass Water: 857 parts by mass

The low refractive index particles contained in the anti-reflection layer were PTFE with a refractive index of 1.30 and a primary particle diameter of 200 nm. The surface resistance of the obtained leather was 4.1 x 10 ⁹ Ω/□. The color difference was -1.8, and it was confirmed that the grain was clearly defined.

[Comparative Example 1]
Leather having only a 250 nm thick antistatic layer laminated thereon was obtained in the same manner as in Example 1, except that no antireflection layer was formed. The surface resistance of the obtained leather was 6.5 × ¹⁰ Ω/□. Although the grain was clearly defined, the color difference was +3.4, indicating that the color was not deep and a deep color could not be expressed.

11, 21: Leather 2: Natural leather 3: Resin surface layer 4: Antistatic layer 5: Anti-reflection layer 6: Fabric substrate 7: Adhesive layer 8: Synthetic leather

Claims (5)

An antistatic layer and an anti-reflective layer are laminated in this order on the surface of natural leather or synthetic leather.
The leather is characterized in that the antistatic layer is made of a resin and conductive particles, and the antireflection layer is made of a resin and low refractive index particles having a refractive index of 1.2 to 1.45 . Leather according to claim 1, characterized in that the antistatic layer is made of resin and conductive particles with a refractive index of 1.6 to 2.1. Leather according to claim 1 or 2, characterized in that the antistatic layer has a thickness of 50 nm to 1 μm. 4. The leather according to claim 1 , wherein the anti-reflection layer has a thickness of 50 nm to 1 μm. 5. The leather according to claim 1 , wherein the surface resistance of the antireflection layer is 1.0×10 ⁶ to 1.0×10 ¹¹ Ω/□.