Leather manufacturing method for improving adhesive force of coating, obtained leather, application of leather and coating composition

Abstract

The invention belongs to the technical field of leather manufacturing, and particularly relates to a leather manufacturing method for improving coating adhesive force, obtained leather, application of the leather and a coating composition. The method comprises the following steps: 1) measuring the swelling coefficient of a corium layer, and calculating to obtain a linear swelling coefficient beta l; (2) preparing a coating composition, and adjusting the components and the dosage until the swelling coefficient beta c of a coating formed by the coating composition is matched with the beta l; and (3) coating the leather layer to obtain the leather with improved coating adhesive force. According to the invention, the super absorbent filler is introduced into the coating to adjust the swelling coefficient of the coating, so that the coating is matched with the leather layer, the problem of coating stripping caused by swelling difference is solved, and the durability and practical value of leather products are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of leather manufacturing, and particularly relates to a leather manufacturing method for improving coating adhesion, the obtained leather, application thereof and a coating composition. Background Art

[0002] Cowhide furniture leather is widely used in high-end furniture manufacturing due to its natural texture and durability. However, the cowhide dermis (composed of collagen fibers) has significant swelling characteristics, that is, when the ambient humidity changes or it comes into contact with water, its moisture content will change rapidly, causing volume expansion (when absorbing water) or contraction (when losing water). This volume change poses a challenge to the coating on the leather surface. Traditional coatings, such as protective layers made of polyurethane or acrylic resin, have a much lower swelling coefficient than the dermis and cannot expand or contract synchronously with the leather. During long-term use, repeated water absorption and swelling and water loss and shrinkage will generate stress at the interface between the coating and the leather, causing the coating to gradually peel off. This peeling not only damages the appearance of the leather, but also shortens its service life and increases maintenance costs.

[0003] Existing technologies have largely focused on the protective or decorative effects of coatings, such as improving wear resistance or aesthetics, but have paid insufficient attention to the mismatch between the swelling behavior of coatings and leather. A few attempts at improvement, such as adjusting the coating's flexibility, have failed to fundamentally address the problem. Therefore, a new approach is urgently needed to adjust the coating's swelling behavior to align with the dermis, thereby improving adhesion and durability. Summary of the Invention

[0004] To address the problem of coating peeling caused by a mismatch in the swelling coefficients of the cowhide dermis and the coating, the present invention provides a leather manufacturing method for improving coating adhesion, the resulting leather, its application, and a coating composition, significantly improving coating adhesion and extending the leather's service life. By introducing a superabsorbent filler into the coating, the present invention adjusts the coating's swelling coefficient to match that of the dermis, addressing the problem of coating peeling caused by this swelling difference and improving the durability and practical value of leather products.

[0005] The technical solutions provided by the present invention are as follows:

[0006] A coating composition comprises a polymer matrix and a super absorbent filler, wherein the weight of the super absorbent filler is 5%-20% of the dry weight of the coating composition.

[0007] Based on the above technical solution, the coating composition can be adjusted to match the linear swelling coefficient of genuine leather, particularly cowhide, with a very tight tolerance. The superabsorbent filler, due to its high water absorption and expansion properties, increases the swelling capacity of the coating, playing a significant role in achieving the desired swelling coefficient.

[0008] Furthermore, it further comprises any one or more of a cross-linking agent, a plasticizer or an anti-wear agent.

[0009] Based on the above technical solution:

[0010] The coating fastness can be further improved by cross-linking agents;

[0011] Durability can be further improved by using plasticizers;

[0012] Wear resistance can be further improved by adding anti-wear agents.

[0013] Specifically, the polymer matrix material is any one of polyurethane or acrylic resin or a mixture of the two.

[0014] Specifically, the super absorbent filler is cross-linked polyacrylate or modified cellulose, and has a particle size of 1-10 microns.

[0015] Specifically, the crosslinking agent is an isocyanate, an aziridine crosslinking agent, or a carbodiimide crosslinking agent. The amount of the crosslinking agent added is 2% to 15% of the dry weight of the coating composition.

[0016] Specifically, the plasticizer is phthalate, citrate or polyethylene glycol, and the added amount of the plasticizer is 0.1%-2.5% of the dry weight of the coating composition, preferably 0.1%-1%.

[0017] Specifically, the plasticizer is a polyester plasticizer, and the added amount of the plasticizer is 0.1%-2.5% of the dry weight of the coating composition, preferably 0.1%-1%.

[0018] Specifically, the wear-resistant agent is SiO2, wax emulsion, PU microspheres or fluorocarbon modifier, and the added amount is 0.1%-10% of the dry weight of the coating composition.

[0019] The present invention also provides a leather manufacturing method for improving coating adhesion, comprising the following steps:

[0020] 1) Determine the swelling coefficient of the dermis and calculate the linear swelling coefficient βl;

[0021] 2) preparing the coating composition and adjusting the ingredients and amounts so that the swelling coefficient βc of the resulting coating matches the βl;

[0022] 3) coating the dermis to obtain leather with improved coating adhesion.

[0023] Based on the above technical solution, the dermis expands in volume when absorbing water and shrinks when losing water due to the hydrophilicity of collagen fibers, and its linear swelling coefficient (βl) is usually high. However, traditional coating materials (such as polyurethane) have low water absorption and swelling properties, and their swelling coefficient (βc) is significantly different from that of the dermis, resulting in the two being unable to respond synchronously to changes in humidity, resulting in interfacial stress. The above technical solution increases the swelling capacity of the coating by adding super absorbent fillers (such as cross-linked polyacrylates) to the coating, utilizing their high water absorption and swelling properties, so that βc is close to βl, achieving synchronous expansion and contraction, eliminating stress accumulation, and avoiding peeling.

[0024] Specifically, in step 1), a cowhide dermis sample was selected and subjected to a humidity test under standard conditions. The sample was placed in different humidity environments, and after equilibrium, the linear dimensional change was measured. The linear swelling coefficient βl was calculated as βl = ΔL / L0ΔRH, where ΔL is the dimensional change, L0 is the initial size, and ΔRH is the humidity change percentage. The calculation formula for βl can also be expressed as:

[0025]

[0026] Specifically, in step 2), the tolerance between βc and βl is ±10%.

[0027] Specifically, in step 3), the coating composition is evenly applied to the pretreated dermis layer by spraying, rolling or brushing to a thickness of 20-100 μm, and then cured at 40-80° C. for 1-4 hours to form a firm coating.

[0028] The invention also provides leather produced by the production method.

[0029] Specifically: the tolerance of the swelling coefficient of the dermis layer and the coating is ±10%.

[0030] The present invention also provides the use of the leather as furniture leather, clothing leather or footwear leather, preferably, as furniture leather.

[0031] When used as furniture leather, clothing leather or footwear leather, the working principle is: the super absorbent filler can absorb moisture and expand when the humidity rises, and obtain the cooperation of the polymer matrix, which is consistent with the behavior of the dermis layer; when the humidity decreases, it releases moisture and shrinks, and obtains the cooperation of the polymer matrix to maintain coordination.

[0032] The beneficial effects of the present invention are as follows:

[0033] Synchronicity: The coating and the dermis expand and contract synchronously under changes in humidity to avoid peeling;

[0034] Durability: Long-term adhesion is improved, extending the life of leather;

[0035] Flexibility: filler content can be adjusted to suit different types of cowhide;

[0036] Comprehensive performance: taking into account wear resistance, scratch resistance and flexibility. DETAILED DESCRIPTION

[0037] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0038] Unless otherwise specified, the test methods used in the examples are conventional methods; the materials and reagents used are commercially available reagents and materials unless otherwise specified.

[0039] An optional grade of polyurethane is DOWELLIU RU2305;

[0040] An optional brand of acrylic resin is PRIMAL SB-110;

[0041] An optional grade of cross-linked polyacrylate is CX-100;

[0042] An alternative grade of modified cellulose is ISODERM LA 85N-C.

[0043] Example 1

[0044] The leather manufacturing method for improving coating adhesion specifically comprises the following steps:

[0045] 1) Determine the swelling coefficient of the dermis and calculate the linear swelling coefficient βl: Select cowhide dermis samples and conduct humidity experiments under standard conditions. The samples are placed in different humidity environments. After equilibrium, the linear dimensional changes are measured and the linear swelling coefficient is calculated.

[0046] Sample: full-grain cowhide (100mm×100mm).

[0047] Conditions: RH = 50% (length 100.0 mm) to RH = 90% (length 102.5 mm).

[0048] Calculation: βl = (102.5 - 100.0) / 100 / (90 - 50) = 0.000625% RH

[0049]

[0050] 2) preparing a coating composition and adjusting the ingredients and amounts so that the swelling coefficient βc of the resulting coating matches the βl.

[0051] Matrix: Polyurethane Filler: Cross-linked polyacrylate (particle size 5 microns), with content set at 5%, 10%, and 15% respectively.

[0052] Test βc:

[0053] 5%: 0.000375per%RH

[0054] 10%: 0.000600per%RH (error 4%, <10%)

[0055] 15%: 0.000750per%RH

[0056] Use 10% formula.

[0057] 3) Coating: First, soften, lightly polish, vacuum and clean in sequence, then spray to a thickness of 50 microns and dry and cure at 60°C for 2 hours.

[0058] test:

[0059] Adhesion test: Cross-cut method, no peeling. The method adopts the method in ISO 11644 standard.

[0060] Abrasion resistance test: Martindale test 10,000 times, the coating is intact. The method adopts the method of ISO12947 standard.

[0061] Stability test: RH 50%-90% cycle 50 times, no peeling. Method adopts the method in ISO 17234-1:2020 standard.

[0062] Example 2

[0063] The leather manufacturing method for improving coating adhesion specifically comprises the following steps:

[0064] 1) Determine the swelling coefficient of the dermis and calculate the linear swelling coefficient βl: Select cowhide dermis samples and conduct humidity experiments under standard conditions. The samples are placed in different humidity environments. After equilibrium, the linear dimensional changes are measured and the linear swelling coefficient is calculated.

[0065] Sample: split cowhide;

[0066] Using the same conditions and calculation method as in Example 1, the result was: βl = 0.000550 per % RH.

[0067] 2) preparing a coating composition and adjusting the ingredients and amounts so that the swelling coefficient βc of the resulting coating matches the βl.

[0068] Matrix: acrylic resin. Filler: modified cellulose (particle size 3 microns), content 8%.

[0069] Test βc, βc=0.000540 per%RH (error 2%).

[0070] 3) Coating: First, soften, lightly polish, vacuum and clean in sequence, then roll-coat to a thickness of 40 microns and dry and cure at 50°C for 3 hours.

[0071] test:

[0072] Adhesion test: Cross-cut method, no peeling. The method adopts the method in ISO 11644 standard.

[0073] Abrasion resistance test: Martindale test 10,000 times, the coating is intact. The method adopts the method of ISO12947 standard.

[0074] Stability test: RH 50%-90% cycle 50 times, no peeling. Method adopts the method in ISO 17234-1:2020 standard.

[0075] Example 3

[0076] Full-grain cowhide (used in luxury car interiors)

[0077] Step 1: Determine the swelling coefficient of cowhide

[0078] Cowhide type: Full grain cowhide

[0079] Test method: Take a sample (100 mm x 100 mm) and measure the change in length when the relative humidity (RH) changes from 40% to 85%.

[0080] Results: When RH=40%, the length was 100.0 mm; when RH=85%, the length was 102.2 mm.

[0081] Calculation: Swelling coefficient βl = (102.2-100.0) / 100 / (85-40) = 0.000489% RH

[0082] Step 2: Adjust the coating formulation

[0083] Matrix: Polyurethane

[0084] Filler: Cross-linked polyacrylate (particle size 4 microns)

[0085] Filler content adjustment test:

[0086] 6%: coating swelling coefficient βc = 0.000420% RH

[0087] 9%: βc=0.000485%RH (error with βl <2%, matching)

[0088] 12%: βc=0.000550%RH

[0089] Other additives: softener (4%), such as EUDERM Nappa Soft S-C01 from TFL; anti-wear agent (1.5%), such as FI-50 from STAHL, and K 2229 from TFL can also be used in other embodiments.

[0090] Final formula: filler content 9%, βc=0.000485%RH

[0091] Step 3: Coating process

[0092] Pretreatment: softening, light grinding, vacuuming, cleaning

[0093] Coating method: spray coating, coating thickness 45 microns

[0094] Drying and curing: 65℃, 2 hours

[0095] Performance Testing

[0096] Adhesion: Cross-cut method, no peeling (ISO 11644)

[0097] Abrasion resistance: Martindale test 12,000 times, coating intact (ISO 12947)

[0098] Stability: RH 40%-85% cycle 60 times, no peeling (ISO 17234-1:2020)

[0099] Example 4

[0100] Chrome-tanned cowhide (used for high-end leather shoes)

[0101] Step 1: Determine the swelling coefficient of cowhide

[0102] Cowhide type: Chrome tanned

[0103] Test method: Take a sample (100 mm x 100 mm) and measure the change in length when the RH changes from 35% to 90%.

[0104] Results: When RH=35%, the length was 100.0 mm; when RH=90%, the length was 102.8 mm.

[0105] Calculation: βl = (102.8 - 100.0) / 100 / (90 - 35) = 0.000509% RH

[0106] Step 2: Adjust the coating formulation

[0107] Matrix: acrylic resin

[0108] Filler: Nano-silicon dioxide (particle size 8nm)

[0109] Filler content adjustment test:

[0110] 3%: βc=0.000460%RH

[0111] 5%: βc=0.000505%RH (error with βl <2%, matching)

[0112] 7%: βc=0.000540%RH

[0113] Other additives: crosslinking agent (1.5%), which can be a polyisocyanate crosslinking agent, such as Desmodur N 3300 from Covestro; anti-UV agent (1%), which can be a hindered amine light stabilizer (HALS), such as Tinuvin 123 from BASF

[0114] Final formula: filler content 5%, βc=0.000505%RH

[0115] Step 3: Coating process

[0116] Pretreatment: light grinding, cleaning

[0117] Coating method: roller coating, coating thickness 35 microns

[0118] Drying and curing: 55℃, 2.5 hours

[0119] Performance Testing

[0120] Adhesion: Peel strength>3N / mm (ISO 11644)

[0121] Wear resistance: Taber abrasion test 4000 revolutions, coating intact (ASTM D4060)

[0122] Stability: RH 35%-90% cycle 70 times, no peeling (ISO 17234-1:2020)

[0123] Example 5

[0124] Vegetable tanned cowhide (for handmade leather goods)

[0125] Step 1: Determine the swelling coefficient of cowhide

[0126] Cowhide type: vegetable tanned cowhide

[0127] Test method: Take a sample (90 mm x 90 mm) and measure the change in length when the RH changes from 50% to 85%.

[0128] Results: When RH=50%, the length was 90.0 mm; when RH=85%, the length was 91.4 mm.

[0129] Calculation: βl = (91.4 - 90.0) / 90 / (85 - 50) = 0.000444% RH

[0130] Step 2: Adjust the coating formulation

[0131] Matrix: nitrocellulose

[0132] Filler: Mica powder (particle size 12 microns)

[0133] Filler content adjustment test:

[0134] 8%: βc=0.000400%RH

[0135] 11%: βc = 0.000440% RH (error with βl < 2%, matching)

[0136] 14%: βc=0.000470%RH

[0137] Other additives: plasticizer (2.5%), which may be a phthalate plasticizer, such as Dioctyl Phthalate (DOP) from Eastman Chemical; colorant (1.5%), which may be an inorganic or organic pigment paste, such as the pigment series from Clariant.

[0138] Final formula: filler content 11%, βc=0.000440%RH

[0139] Step 3: Coating process

[0140] Pretreatment: light grinding, cleaning

[0141] Coating method: brush coating, coating thickness 30 microns

[0142] Drying and curing: room temperature, 20 hours

[0143] Performance Testing

[0144] Adhesion: Tape test, no peeling (ASTM D3359)

[0145] Wear resistance: Wyzenbeek abrasion test 12,000 times, the coating is intact (ASTM D4157)

[0146] Stability: RH 50%-85% cycle 50 times, no peeling (ISO 17234-1:2020)

[0147] Example 6

[0148] Oil-tanned cowhide (for outdoor boots)

[0149] Step 1: Determine the swelling coefficient of cowhide

[0150] Cowhide type: oil-tanned cowhide

[0151] Test method: Take a sample (120 mm x 120 mm) and measure the length change when the RH changes from 30% to 95%.

[0152] Results: When RH=30%, the length was 120.0 mm; when RH=95%, the length was 122.4 mm.

[0153] Calculation: βl = (122.4 - 120.0) / 120 / (95 - 30) = 0.000308% RH

[0154] Step 2: Adjust the coating formulation

[0155] Matrix: Fluorinated polyurethane, which can be a fluorinated polyurethane dispersion (water-based), such as Rudolf DURAN FC-400 from Rudolf Group

[0156] Filler: polytetrafluoroethylene powder (particle size 2 microns)

[0157] Filler content adjustment test:

[0158] 10%: βc=0.000280%RH

[0159] 13%: βc = 0.000305% RH (error with βl < 2%, matching)

[0160] 16%: βc=0.000340%RH

[0161] Other additives: waterproofing agent (2.5%), toughening agent (3%)

[0162] Final formula: filler content 13%, βc=0.000305%RH

[0163] Step 3: Coating process

[0164] Pretreatment: deep cleaning, drying

[0165] Coating method: Dip coating, coating thickness 55 microns

[0166] Drying and curing: 75℃, 1.5 hours

[0167] Performance Testing

[0168] Adhesion: Tape test, no peeling (ASTM D3359)

[0169] Wear resistance: Wyzenbeek abrasion test 18,000 times, the coating is intact (ASTM D4157)

[0170] Stability: RH 30%-95% cycle 100 times, no peeling (ISO 17234-1:2020)

[0171] Example 7

[0172] Split cowhide (for economical leather goods)

[0173] Step 1: Determine the swelling coefficient of cowhide

[0174] Cowhide type: split leather

[0175] Test method: Take a sample (100 mm x 100 mm) and measure the change in length when the RH changes from 45% to 90%.

[0176] Results: When RH=45%, the length was 100.0 mm; when RH=90%, the length was 102.5 mm.

[0177] Calculation: βl = (102.5 - 100.0) / 100 / (90 - 45) = 0.000556% RH

[0178] Step 2: Adjust the coating formulation

[0179] Matrix: polyurethane / acrylic resin blend

[0180] Filler: calcium carbonate (particle size 3 microns)

[0181] Filler content adjustment test:

[0182] 12%: βc=0.000500%RH

[0183] 15%: βc = 0.000550% RH (error with βl < 2%, matching)

[0184] 18%: βc=0.000600%RH

[0185] Other additives: antimicrobial agent (1%), which can be a quaternary ammonium compound, such as Microban International's ZPTech; flame retardant (2%), which can be a halogen-free intumescent flame retardant, such as BASF's NOR 116

[0186] Final formula: filler content 15%, βc = 0.000550% RH

[0187] Step 3: Coating process

[0188] Pretreatment: grinding, dust removal

[0189] Coating method: spray coating, coating thickness 50 microns

[0190] Drying and curing: 60℃, 2 hours

[0191] Performance Testing

[0192] Adhesion: Cross-cut method, no peeling (ISO 11644)

[0193] Abrasion resistance: Martindale test 15,000 times, coating intact (ISO 12947)

[0194] Stability: RH 45%-90% cycle 80 times, no peeling (ISO 17234-1:2020)

[0195] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A coating composition, characterized in that include: A polymer matrix and a super absorbent filler, wherein the weight of the super absorbent filler is 5% to 20% of the dry weight of the coating composition.

2. The coating composition according to claim 1, wherein: It also includes any one or more of a cross-linking agent, a plasticizer or an anti-wear agent.

3. The coating composition according to claim 2, wherein: The polymer matrix material is any one of polyurethane or acrylic resin or a mixture of the two; The super absorbent filler is cross-linked polyacrylate or modified cellulose with a particle size of 1-10 microns; The crosslinking agent is an isocyanate, an aziridine crosslinking agent or a carbodiimide crosslinking agent; the amount of the crosslinking agent added is 2%-15% of the dry weight of the coating composition; The plasticizer is phthalate, citrate or polyethylene glycol; or the plasticizer is a polyester plasticizer; the amount of the plasticizer added is 0.1% to 1% of the dry weight of the coating composition; The wear-resistant agent is SiO2, wax emulsion, PU microspheres or fluorocarbon modifier, and the added amount is 0.1%-10% of the dry weight of the coating composition.

4. A leather manufacturing method for improving coating adhesion, characterized in that: The following steps are involved: 1) Determine the swelling coefficient of the dermis and calculate the linear swelling coefficient βl; 2) preparing the coating composition according to any one of claims 1 to 3, and adjusting the ingredients and amounts so that the swelling coefficient βc of the resulting coating matches the βl; 3) coating the dermis to obtain leather with improved coating adhesion.

5. The leather manufacturing method for improving coating adhesion according to claim 4, characterized in that: In step 1): select a cowhide dermis sample and conduct a humidity experiment under standard conditions. Place the sample in different humidity environments, measure the linear dimensional change after equilibrium, and calculate the linear swelling coefficient βl, βl = ΔL / L0ΔRH, where ΔL is the dimensional change, L0 is the initial size, and ΔRH is the humidity change percentage.

6. The method for manufacturing leather with improved coating adhesion according to claim 4, characterized in that: In step 2), the tolerance of βc and βl is ±10%.

7. The leather manufacturing method for improving coating adhesion according to claim 4, characterized in that: In step 3), the coating composition is evenly applied to the pretreated dermis layer by spraying, rolling or brushing to a thickness of 20-100 μm, and then cured at 40-80° C. for 1-4 hours to form a firm coating.

8. Leather produced according to the production method according to any one of claims 4 to 7.

9. The leather according to claim 8, characterized in that: The tolerance of the swelling coefficient of the dermis layer and the coating is ±10%.

10. Use of the leather according to claim 8, characterized in that: Leather used as furniture leather, clothing leather or footwear.

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