Preparation method of high-grade cowhide leather with high bending resistance

Abstract

The present application relates to the technical field of leather production, and provides a preparation method of high-grade and flexible cowhide leather, which solves the problems of slight poor flexibility, obvious wrinkles, low quality and grade of the leather produced by the existing leather production process; the method comprises the following steps: (1) pre-treatment; (2) bottom sealing; (3) bottom coating; (4) middle coating; and (5) top coating, so as to obtain the high-grade and flexible cowhide leather product.

Description

Technical Field

[0001] This invention relates to the field of leather production technology, and in particular to a method for preparing high-grade cowhide that is resistant to bending. Background Technology

[0002] The leather industry is one of the important sectors within my country's light industry, boasting a long history and holding a pivotal position in the national economy. Currently, my country has become a global leather production base. With rising living standards, consumers' consumption concepts and behaviors are changing. The pursuit of leather products that are soft to the touch, have a full and fine grain, good elasticity, comfortable feel, and aesthetically pleasing qualities has become a trend, especially high-quality, high-end full-grain leather products, which are highly favored by consumers.

[0003] Leather finishing is the final step in tanning, playing a decisive role in the quality, grade, and use value of the finished leather. Finishing raw leather improves its durability and breathability, gives it a glossy and attractive surface, and enhances its hygienic properties, significantly improving its quality and grade, and increasing its variety and commercial value. In recent years, with the enrichment and improvement of leather chemical materials and the innovation of leather-making technology, leather products have seen tremendous improvements in color variety and physical properties.

[0004] Application number 202010001045.6, publication number CN111057804B, this Chinese invention patent application discloses a method for making patterned leather, leather, and leather products. The effect paste includes 100-150 parts of liquid sodium silicate, 10-50 parts of water, 10-20 parts of leveling agent, and 10-20 parts of plasticizer. It has good adhesion, film-forming properties, and uniform flowability, and can form a uniform effect paste layer on the leather grain surface. The prepared patterned leather has a complete and clear grain surface, solving the problems of single grain pattern and uncontrollable pattern shape and distribution in the prior art. However, the finished leather has slightly poor flexural resistance, and obvious wrinkles easily form on the surface during use, affecting the quality of the leather.

[0005] Application number 201611029176.5, publication number CN106480241B, this Chinese invention patent application discloses a production process for ultra-waterproof leather. The process involves sequentially treating a split leather substrate with rehydration, retanning, neutralization, filling, dyeing, fatliquoring, fixing, and then laminating an epidermal layer and a resin layer. This process not only includes multiple waterproofing steps but also laminates a breathable epidermal layer and a fat layer onto the surface of the split leather substrate. This ensures both the leather's texture and its physical strength, resulting in leather with superior waterproof and breathable properties without compromising its texture. However, the finished leather has a less desirable feel, slightly lower flexural strength, and noticeable wrinkles, affecting its perceived quality. Summary of the Invention

[0006] Therefore, in view of the above problems, the present invention provides a method for preparing high-grade cowhide that is resistant to bending, which solves the problems that leather produced by existing leather-making processes has slightly poor bending resistance, obvious wrinkles on the surface, and low quality and grade of finished leather.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing high-grade, flexurally resistant cowhide, characterized by comprising the following steps:

[0009] S1. Pre-treatment: Take the raw leather and perform a sanding treatment. Then use a scraper to fully apply the repair paste to the sanded area to fill in the sunken damaged areas.

[0010] S2, Sealing the bottom: Spray the sealing paste onto the flesh side of the raw leather, bake it dry, and then iron it flat;

[0011] S3, Primer: Dissolve pigment paste and anionic composite resin in water to obtain primer slurry, turn on the sprayer and spray, and after drying, repeat the above primer once.

[0012] S4, Intermediate Coat: Spray with intermediate coat slurry and bake dry. Repeat the above intermediate coat once.

[0013] S5. Topcoat: After spraying, drying and ironing the oil and wax layer, repeat once. Then polish and iron. Next, spray, dry and iron the top gloss water layer, repeat once. Then soften by tumbling, vibrating and vacuuming. Finally, spray, dry and iron the hand feel layer.

[0014] Furthermore, the leather is characterized in that: the raw leather is grade A black cowhide with a thickness of 1.0 to 1.2 mm, the main tanning process is full chrome tanning, the raw leather is firm, full and fleshy, durable, and has an extensibility of 25 to 30%.

[0015] Furthermore, in step S1, the leather sanding is performed by using a manual sander, selecting 320# sandpaper, and sanding large damaged areas such as rotten surfaces, scratches, old lines, and healed wounds, sanding away 1 / 5 to 1 / 4 of the grain layer from the large damaged areas.

[0016] Furthermore, in step S1, the repair paste includes: nonionic wax emulsion, full-grain polishing repair paste, pigment paste, softening oil, and water.

[0017] Furthermore, in step S2, the sealing slurry comprises: cationic polyurethane resin, cationic casein, cationic wax emulsion, and water.

[0018] Furthermore, in step S3, the primer slurry includes: a shaping composite resin, an anionic composite resin, an adhesive resin, a self-crosslinking acrylic resin, an ultrafine white pigment paste, a matting filler, a release wax, and water.

[0019] Furthermore, in step S4, the intermediate coating slurry comprises: cationic polyurethane resin, cationic casein, cationic wax emulsion, and water.

[0020] Furthermore, in step S5, the oil and wax layer slurry includes: nonionic polyurethane resin, cationic high-gloss ester, nonionic wax emulsion, penetrant, and water.

[0021] Furthermore, in step S5, the top-gloss water layer slurry includes: nonionic high-gloss oil wax, cationic high-gloss casein, nitrocellulose varnish, nonionic polishing wax, and water.

[0022] Furthermore, in step S5, the tactile layer slurry includes: an oily tactile agent, a smoothing tactile agent, and water.

[0023] Furthermore, in step S5, the polishing is performed using a through-felt roller polishing machine with a linear speed of 25-30 m / min, a rotation speed of 1200-1800 r / min, and an operating gap of 0.6-1.0 mm.

[0024] Furthermore, in step S5, the softening process involves: using an octagonal stainless steel drum to soften the leather at a temperature of 25-30°C and a humidity of 20-30% for 1-2 hours, and then checking the softness. The softness of the leather in the head and neck area is 4.9-5.2, and the softness of the leather in the abdomen and buttocks area is 5.3-5.6.

[0025] Furthermore, in step S5, the vibration softening is performed using a through-type vibration softener at a speed of 10-15 m / min.

[0026] Furthermore, in step S5, the dry vacuum is achieved by using a vacuum machine to perform a dry vacuum at a temperature of 60–90°C for 10–20 seconds.

[0027] Furthermore, the slurry preparation process is as follows: weigh each raw material component separately, stir thoroughly with a stirring rod to ensure uniform mixing of all materials, and then filter using a 200-mesh filter screen.

[0028] Furthermore, the spraying process involves using a spraying machine to lightly spray the slurry onto the meat surface under parameters of air pressure of 1.4–1.8 MPa, spray volume of 2–4 g / sq.ft, and belt speed of 10–15 m / min, and then placing it in an oven to dry at a temperature of 60–90°C.

[0029] Furthermore, the ironing is performed using a pass-through ironing machine at a temperature of 100–120°C, a pressure of 30–40 kg, and a speed of 5–8 m / min.

[0030] Furthermore, the dosage of each raw material component of the repair ointment is as follows: 80-120g of nonionic wax emulsion, 20-40g of full-grain polishing repair ointment, 10-20g of pigment paste, 10-20g of softening oil, and 100-200g of water.

[0031] Furthermore, the amounts of each raw material component in the sealing slurry are as follows: 80-120g of cationic polyurethane resin, 80-120g of cationic casein, 80-120g of cationic wax emulsion, and 240-360g of water.

[0032] Furthermore, in step S3, the amounts of each raw material component of the primer slurry are as follows: 80-120g of shaping composite resin, 100-200g of anionic composite resin, 30-60g of bonding resin, 30-60g of self-crosslinking acrylic resin, 80-120g of ultrafine white pigment paste, 30-60g of matting filler, 80-120g of release wax, and 150-300g of water.

[0033] Furthermore, in step S4, the amounts of each raw material component of the intermediate coating slurry are as follows: 80-120g of cationic polyurethane resin, 80-120g of cationic casein, 80-120g of cationic wax emulsion, and 200-400g of water.

[0034] Furthermore, in step S5, the amounts of each raw material component of the oil and wax layer slurry are as follows: 80-120g of nonionic polyurethane resin, 40-80g of cationic high-gloss casein, 80-120g of nonionic wax emulsion, 30-60g of penetrant, and 200-400g of water.

[0035] Furthermore, in step S5, the amount of each raw material component of the top-gloss water layer slurry is as follows: 80-120g of nonionic high-gloss wax, 40-80g of cationic high-gloss casein, 10-30g of nitrocellulose varnish, 30-60g of nonionic polishing wax, and 100-300g of water.

[0036] Furthermore, in step S5, the amount of each raw material component of the tactile layer slurry is as follows: 10-20g of oily tactile agent, 8-15g of smooth tactile agent, and 80-160g of water.

[0037] By adopting the aforementioned technical solution, the beneficial effects of the present invention are as follows:

[0038] 1. To solve the problem that leather produced by existing tanning processes has slightly poor flexural strength, obvious wrinkles, and low quality and grade during use.

[0039] 2. This invention employs a base coat, intermediate coat, and top coat process to treat the raw hide, thereby achieving better flexural resistance in the finished leather. The principle is as follows: common factors affecting the flexural resistance of finished leather include coating adhesion, the ratio of pigment paste and filler to resin in the coating, coating thickness, and process control. The cationic casein added to the sealing slurry is a type of cationic natural protein material. It combines with the anionic active groups such as carboxyl groups contained in the anionic resin of the base coat slurry, exhibiting good adhesion and film-forming properties. The addition of resins such as polyurethane to the coating formulation results in a continuous, soft film with excellent fullness and a natural appearance and feel. The formed coating has strong adhesion, good flexibility and extensibility, effectively improving the flexural resistance of the finished leather. In terms of process, the leather spraying uses high-pressure airless spraying. A high-pressure pump applies pressure to the coating, which is then sprayed at high speed from the small orifice of the spray gun. The coating is atomized by intense impact with air and sprayed onto the leather surface, resulting in a uniform, smooth, and even coating with good decorative appearance. Detailed Implementation

[0040] Example 1

[0041] A method for preparing high-grade, flexurally resistant cowhide includes the following steps:

[0042] (1) Pretreatment: Take the raw leather and perform sanding treatment. Then use a scraper to fully scrape the repair paste onto the sanded area to fill in the sunken damaged area.

[0043] (1-1) The raw leather is Grade A black cowhide with a thickness of 1.2mm. The main tanning process is full chrome tanning. The raw leather is firm, full and fleshy, durable and has an elongation of 25%.

[0044] (1-2) The leather sanding process is as follows: use a manual sander to sand the leather, select 320# sandpaper, and sand the large damaged areas such as rotten surfaces, scratches, old lines, and healed wounds, and sand away 1 / 5 to 1 / 4 of the grain layer of the large damaged areas.

[0045] (1-3) The repair paste includes: nonionic wax emulsion, full-grain polishing repair paste, pigment paste, softening oil, and water;

[0046] (1-4) The dosage of each raw material component of the repair ointment is as follows: 100g of nonionic wax emulsion, 30g of full-grain polishing repair ointment, 15g of pigment paste, 15g of softening oil, and 150g of water.

[0047] (2) Sealing the bottom: Using a spraying machine, under the parameters of air pressure of 1.5MPa, spray volume of 3g / sq.ft and belt speed of 12m / min, the sealing paste is sprayed onto the flesh side of the raw leather, and then placed in an oven to dry at a temperature of 70℃. Then, a pass-through ironing machine is used to sprue the leather at a temperature of 120℃, a pressure of 30kg and a speed of 5m / min.

[0048] (2-1) The sealing slurry comprises: cationic polyurethane resin, cationic casein, cationic wax emulsion, and water;

[0049] (2-2) The amount of each raw material component of the sealing slurry is as follows: 100g of cationic polyurethane resin, 100g of cationic casein, 100g of cationic wax emulsion, and 300g of water.

[0050] (2-3) The slurry preparation method is as follows: weigh each raw material component separately, stir thoroughly with a stirring rod to make the various materials evenly mixed, and filter it with a 200-mesh filter after preparation.

[0051] (3) Primer: Using a spraying machine, under the parameters of air pressure of 1.5MPa, spray volume of 3g / sq.ft and belt speed of 12m / min, the primer is sprayed onto the flesh side of the raw leather, and then placed in an oven to dry at 70℃. After drying, the primer is repeated once.

[0052] (3-1) The primer slurry includes: a shaping composite resin, an anionic composite resin, an adhesive resin, a self-crosslinking acrylic resin, an ultrafine white pigment paste, a matting filler, a release wax, and water;

[0053] (3-2) The amount of each raw material component of the primer slurry is as follows: 100g of shaping composite resin, 150g of anionic composite resin, 50g of adhesive resin, 50g of self-crosslinking acrylic resin, 100g of ultrafine white pigment paste, 50g of matting filler, 100g of release wax, and 200g of water.

[0054] (3-3) The slurry preparation method is as follows: weigh each raw material component separately, stir thoroughly with a stirring rod to make the various materials evenly mixed, and filter it with a 200-mesh filter after preparation.

[0055] (4) Intermediate coating: Using a spraying machine, under the parameters of air pressure of 1.5MPa, spray volume of 3g / sq.ft and belt speed of 12m / min, the intermediate coating slurry is sprayed onto the flesh side of the raw leather, and then placed in an oven to dry at a temperature of 70℃. After drying, the above intermediate coating is repeated once.

[0056] (4-1) The intermediate coating slurry is composed of: cationic polyurethane resin, cationic casein, cationic wax emulsion, and water;

[0057] (4-2) The amount of each raw material component of the intermediate coating slurry is as follows: 100g of cationic polyurethane resin, 100g of cationic casein, 100g of cationic wax emulsion, and 300g of water.

[0058] (4-3) The slurry preparation method is as follows: weigh each raw material component separately, stir thoroughly with a stirring rod to make the various materials evenly mixed, and filter it with a 200-mesh filter after preparation.

[0059] (5) Top coat: After spraying, drying and ironing the oil wax layer, repeat once, then polish and iron, then spray, dry and iron the top gloss water layer, repeat once, then tumble to soften, vibrate to soften, and dry vacuum, and finally spray, dry and iron the hand feel layer.

[0060] (5-1) The oil and wax layer slurry includes: nonionic polyurethane resin, cationic high gloss ester, nonionic wax emulsion, penetrant, and water;

[0061] (5-2) The amount of each raw material component of the oil and wax layer slurry is as follows: 100g of nonionic polyurethane resin, 60g of cationic high-gloss casein, 100g of nonionic wax emulsion, 40g of penetrant, and 300g of water.

[0062] (5-3) The top-gloss water layer slurry includes: nonionic high-gloss oil wax, cationic high-gloss casein, nitrocellulose varnish, nonionic polishing wax, and water;

[0063] (5-4) The amount of each raw material component of the top-gloss water layer slurry is as follows: 100g of nonionic high-gloss oil wax, 50g of cationic high-gloss casein, 20g of nitrocellulose varnish, 50g of nonionic polishing wax, and 200g of water.

[0064] (5-5) The hand-feeling slurry includes: an oily hand-feeling agent, a smooth hand-feeling agent, and water;

[0065] (5-6) The amount of each raw material component of the tactile layer slurry is as follows: 15g of greasy tactile agent, 10g of smooth tactile agent, and 100g of water.

[0066] (5-7) The polishing is performed using a through-felt roller polishing machine with a linear speed of 28m / min, a rotation speed of 1500r / min, and an operating gap of 0.8mm.

[0067] (5-8) The softening process is as follows: the leather is softened by tumbling with an octagonal stainless steel drum at a temperature of 25°C and a humidity of 25% for 2 hours. The softness is then checked. The softness of the leather in the head and neck area is 5, and the softness of the leather in the abdomen and buttocks area is 5.4.

[0068] (5-9) The vibration softening is performed by using a through-type vibration softener at a speed of 12m / min;

[0069] (5-10) The dry vacuum is: dry vacuum is performed using a vacuum machine at a temperature of 80°C for 15 seconds;

[0070] (5-11) The slurry preparation process is as follows: weigh each raw material component separately, stir thoroughly with a stirring rod to make the various materials evenly mixed, and filter with a 200-mesh filter after preparation.

[0071] Comparative Example 1

[0072] The difference from Example 1 is that the leather slurry of this application is not used in the base coat, intermediate coat, and top coat processes; instead, commercially available slurries are used, the raw material composition of which includes: 100-150 parts of liquid sodium silicate, 10-50 parts of water, 10-20 parts of leveling agent, and 10-20 parts of plasticizer. Other technical solutions are the same as in Example 1.

[0073] The performance test results of the product of Example 1 and the product of Comparative Example 1 are shown in the table below.

[0074] Table 1

[0075]

[0076] Peel strength performance: Refer to the peel strength test method in ASTM / D751-2006 "Standard Test Methods for Coated Fabrics".

[0077] Wear resistance: The test standard is GB / T3903.16-2008.

[0078] Bending resistance: The test standard is QB / T2714-2005. After counting to the specified number of times, observe the changes in the folded part with a magnifying glass.

[0079] Yellowing resistance: The yellowing resistance of the raw leather was tested using a yellowing resistance test chamber (GT-7035-UA). The test standard was HG / T3689-2001. The difference between the test piece and the original test piece was observed in a standard light source box, and the grade was judged using the GB / T250-2008 color card, accurate to 0.5 grade.

[0080] As can be seen from the table above, the leather products produced by the flexural leather production method described in this invention have improved flexural resistance due to the multiple coatings applied and the layered protection. The leather can withstand 156,000 flexes at room temperature and 89,000 flexes at low temperature. Furthermore, the leather has excellent crack resistance, with no cracks after 96,000 flexes, indicating that it is not prone to creases during wear and use.

[0081] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A method for preparing high-grade, flexurally resistant cow leather, characterized in that, Includes the following steps: S1. Pre-treatment: Take the raw leather and perform sanding treatment. Then use a scraper to fully apply the repair paste to the sanded area to fill in the sunken damaged areas. S2, Sealing the bottom: Spray the sealing paste onto the flesh side of the raw leather, bake it dry, and then iron it flat; S3, Primer: Dissolve pigment paste and anionic composite resin in water to obtain primer slurry, turn on the sprayer and spray, and after drying, repeat the above primer once. S4, Intermediate Coat: Spray with intermediate coat slurry and bake dry. Repeat the above intermediate coat once. S5. Topcoat: After spraying, drying and ironing the oil and wax layer, repeat once. Then polish and iron. Next, spray, dry and iron the top gloss water layer, repeat once. Then soften by tumbling, vibrating and vacuuming. Finally, spray, dry and iron the hand feel layer. In step S1, the repair ointment comprises the following raw materials in parts by weight: 80-120 parts of nonionic wax emulsion, 20-40 parts of full-grain polishing repair ointment, 10-20 parts of pigment paste, 10-20 parts of softening oil, and 100-200 parts of water. In step S2, the sealing slurry comprises the following raw materials in parts by weight: 80-120 parts of cationic polyurethane resin, 80-120 parts of cationic casein, 80-120 parts of cationic wax emulsion, and 240-360 parts of water. In step S3, the primer slurry comprises the following raw materials in parts by weight: 80-120 parts of shaping composite resin, 100-200 parts of anionic composite resin, 30-60 parts of bonding resin, 30-60 parts of self-crosslinking acrylic resin, 80-120 parts of ultrafine white pigment paste, 30-60 parts of matting filler, 80-120 parts of release wax, and 150-300 parts of water. In step S4, the intermediate coating slurry comprises the following raw materials in parts by weight: 80-120 parts of cationic polyurethane resin, 80-120 parts of cationic casein, 80-120 parts of cationic wax emulsion, and 200-400 parts of water. In step S5, the oil and wax layer slurry comprises the following raw materials in parts by weight: 80-120 parts of nonionic polyurethane resin, 40-80 parts of cationic high-gloss casein, 80-120 parts of nonionic wax emulsion, 30-60 parts of penetrant, and 200-400 parts of water; the top-gloss water layer slurry comprises the following raw materials in parts by weight: 80-120 parts of nonionic high-gloss oil wax, 40-80 parts of cationic high-gloss casein, 10-30 parts of nitrocellulose varnish, 30-60 parts of nonionic polishing wax, and 100-300 parts of water; the hand-feel layer slurry comprises the following raw materials in parts by weight: 10-20 parts of oily hand-feel agent, 8-15 parts of smooth hand-feel agent, and 80-160 parts of water. In step S5, the polishing is performed using a through-felt roller polishing machine with a linear speed of 25-30 m / min, a rotation speed of 1200-1800 r / min, and an operating gap of 0.6-1.0 mm. The softening process involves using an octagonal stainless steel drum to soften the leather at a temperature of 25-30°C and a humidity of 20-30% for 1-2 hours. The softness is then checked, with the leather on the head and neck area having a softness of 4.9-5.2 and the leather on the abdomen and buttocks area having a softness of 5.3-5.

6. The vibration softening is performed using a through-type vibration softening machine at a speed of 10~15m / min; The dry vacuum is achieved by using a vacuum machine to create a dry vacuum at a temperature of 60~90℃ for 10~20 seconds.

2. The method for preparing a flexurally resistant high-grade cowhide according to claim 1, characterized in that: The raw leather is grade A black cowhide, with a thickness of 1.0~1.2mm and an elongation of 25~30%.

3. The method for preparing a flexurally resistant high-grade cowhide according to claim 1, characterized in that, In step S1, the leather sanding is performed by using a manual sander, selecting 320# sandpaper, sanding the large damaged areas, and removing 1 / 5 to 1 / 4 of the grain layer from the large damaged areas.

4. The method for preparing a flexurally resistant high-grade cowhide according to claim 1, characterized in that, The slurry preparation process is as follows: weigh each raw material component separately, stir thoroughly with a stirring rod to ensure uniform mixing of all materials, and then filter it using a 200-mesh filter screen. The spraying process involves using a spraying machine to lightly spray the slurry onto the meat surface under parameters of air pressure of 1.4~1.8MPa, spray volume of 2~4g / sq.ft, and belt speed of 10~15m / min, and then placing it in an oven to dry at a temperature of 60~90℃. The ironing is performed using a pass-through ironing machine at a temperature of 100~120℃, a pressure of 30~40kg, and a speed of 5~8m / min.

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