CN118756499A - Imitation leather sheet and production method thereof - Google Patents

Abstract

The invention discloses a leather-like sheet production method, which comprises the following steps: soaking silk fabrics and/or degummed silk serving as a base material in a solvent to enable the base material to be partially dissolved to form fibroin solution; drying the base material which is partially dissolved to form the fibroin solution at the temperature of 25-60 ℃ to obtain a basal layer; spraying a silk protein microfiber layer on the basal layer by adopting an electrostatic spinning device, wherein the silk protein microfiber layer is prepared by adopting a silk protein solution obtained by dissolving silk fabrics by adopting the solvent or a silk protein solution obtained by dissolving degummed silk by adopting the solvent as a spinning solution; coating or pressing the leather surface coating slurry on the silk protein microfiber layer to form a leather surface layer; and drying the product formed by the leather surface layer, the silk protein microfiber layer and the basal layer to obtain the leather-like sheet. The production method of the invention can greatly improve the mechanical property and the environmental protection property of the leather-like sheet.

Description

Imitation leather sheet and production method thereof

Technical Field

The invention belongs to the field of preparation of imitation leather sheets, and relates to an imitation leather sheet and a production process thereof, and specifically, to an imitation leather sheet with excellent performance, environmental protection and sustainability, and a production method thereof.

Background Art

As a sustainable alternative to natural leather, imitation leather sheets have broad application prospects in many fields such as clothing, shoes, furniture, automotive interiors, sports equipment, etc. due to their relatively environmentally friendly production process and excellent performance.

Imitation leather sheets mainly include surface materials, substrates, environmentally friendly dyes and coatings. At present, the surface layer of imitation leather sheets mainly adopts bio-based polymers based on polyurethane (PU) and polyester (PET). These bio-based polymers have good physical and chemical properties, including wear resistance, scratch resistance, antibacterial and waterproof. Existing substrates mainly include bio-based cellulose substrates, polylactic acid (PLA) substrates and biodegradable polymer substrates. These substrates have the advantages of biodegradability, recyclability and low toxicity. In order to improve the environmental performance of imitation leather sheets, the main coating materials currently used are environmentally friendly dyes and water-based coatings, and nanotechnology is used to prepare functional coatings such as anti-fouling and anti-ultraviolet for imitation leather sheets.

Although the existing imitation leather sheets have approached or reached the level of natural leather in terms of wear resistance and hand feel, their mechanical strength is usually weak, and the mechanical strength is usually not adjustable. More importantly, the durability and fatigue resistance of imitation leather sheets are usually weaker than those of real leather and artificial leather. The main reason for this is that the mechanical properties of bio-based fibers, polylactic acid substrates, and biodegradable polymer substrates are significantly lower than those of real leather and artificial leather, especially imitation leather sheets with fiber cloth or paper-based materials as substrates. Since the fibers in these fiber cloths and paper matrices are formed by simple physical stacking, weaving or pressing, there is a lack of effective mechanical transmission between fibers, and the obtained imitation leather has weak mechanical properties, weak fatigue resistance and poor durability, which limits the practical application of imitation leather sheets.

Summary of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide an imitation leather sheet material having excellent mechanical properties, environmental protection and sustainability and a method for producing the same, so as to solve the problems of the existing imitation leather sheets in terms of weak mechanical properties and lack of mechanical adjustability, thereby improving the market competitiveness of the imitation leather sheets.

To achieve the above-mentioned purpose, the present invention provides a leather-like sheet and a production process thereof, comprising the following steps: using silk fabric and/or degummed silk as a formula for optimizing a bio-based polymer to improve its performance so that the leather-like sheet has better tensile strength, wear resistance, scratch resistance, antibacterial and waterproof properties.

It should be noted that the degummed silk in this embodiment is preferably degummed silk fibers that are regularly and/or irregularly arranged, such as clustered or massed silk fibers.

The present invention provides a method for producing an imitation leather sheet, comprising the following steps:

Silk fabric and/or degummed silk are used as a substrate, and the silk fabric or degummed silk is immersed in a solvent so that the substrate is partially dissolved to form a silk protein solution, wherein the silk fabric is a silk fabric or a silk blended fabric, and the degummed silk is a product of removing sericin, namely, fibroin; the dissolved silk protein solution is used as an adhesive to connect silk fibers, thereby improving the mechanical controllability of the substrate.

Drying the substrate partially dissolved to form the silk protein solution at a temperature of 25-60° C. to obtain a base layer;

An electrostatic spinning device is used to spray the base layer to form a silk protein ultra-fiber layer, wherein the silk protein ultra-fiber layer is prepared by using a silk protein solution obtained by dissolving silk fabric with the solvent, or a silk protein solution obtained by dissolving degummed silk with the solvent as a spinning solution;

Applying or pressing the leather surface coating slurry on the silk protein microfiber layer to form a leather surface layer;

The product composed of the leather surface layer, the silk protein ultra-fiber layer and the base layer is dried to obtain a leather-like sheet.

Preferably, the drying temperature is controlled between 60-200° C., and the drying time is between 0.5-12 hours.

In the present invention, silk fabric is a general term for fabrics made of pure or interwoven silk or rayon. As a specialty of China, silk fabric has gone through a process from natural silk to adding rayon. The current silk fabric is usually a textile woven from silk or synthetic fiber, artificial fiber, and filament. Silk protein materials have excellent environmental protection and biodegradability: silk protein itself is biodegradable and can be decomposed over time with the help of microorganisms. Secondly, silk protein is a protein that is easily degraded by enzymes. The structure of silk protein contains many amino acid sequences that can be decomposed by specific enzymes, which allows it to be decomposed in the environment in a very environmentally friendly way. Thirdly, silk fabric/silk protein is a natural protein fiber produced by insects such as silkworms, and is therefore a sustainable material. Natural silk materials contain long silk core protein, silk fibroin, and a colloidal coating composed of non-filamentous protein (sericin). Silk fibers are light, breathable, and hypoallergenic.

In the method of the present invention, the silk fibroin coated on the silk fabric product can be heat-resistant to selected temperature. In some embodiments, the method may include preparing one or more silk fibroin solutions with low molecular weight silk fibroin, medium molecular weight silk fibroin and high molecular weight silk fibroin. In some embodiments, the method may include adjusting the pH of the silk fibroin solution with acidic reagent. In some embodiments, the method may include coating the textile surface with silk fibroin solution. In some embodiments, the method may include drying the textile surface coated with silk fibroin solution to provide a silk fibroin coated product, wherein the drying textile surface includes heating the textile surface without significantly reducing the silk fibroin coating performance.

Preferably, the solvent is selected from one or more of the following: lithium bromide/water, calcium chloride/ethanol/water, formic acid/calcium chloride, hexafluoroisopropanol, and the weight ratio of silk fabric to solvent is controlled at 1:(8-12); more preferably, the weight ratio of silk fabric to solvent is controlled at 1:10. This ensures that the silk fabric will not be completely dissolved during the dissolution process, thereby maintaining the original shape and structure of the silk fabric, while at the same time enabling microstructure and chemical reaction to be generated on the surface of the silk fabric. The dissolved silk protein solution can be used as an adhesive to connect the fibers between the silk fabrics, effectively improving the interaction between the fibers and improving the mechanical properties of the silk fabric. Secondly, the dissolved silk protein also increases the surface activity and adsorption properties of the silk fabric.

Preferably, the ratio and dissolution time of different solvent systems are adjusted to achieve the best dissolution effect. The solvent formula and its dissolution time are selected from one or more of the following: lithium bromide/water, concentration of 5-6 mol/L, dissolution for 25-60 minutes; calcium chloride/ethanol/water, molar ratio 1:2:(8-10), dissolution, 5-12 minutes; formic acid/calcium chloride, molar ratio (20-48):1, dissolution for 3-7 minutes; hexafluoroisopropanol, dissolution for 25-35 minutes.

The parameters of electrospray spinning can be optimized according to specific experimental requirements. Preferably, when the electrospinning device is used to spray the base layer to form a silk protein ultra-fiber layer, the spinning diameter is 500nm to 1 micron. The parameters of electrospray spinning are: a voltage of 15-25kV is applied to the spinneret; the distance between the top of the spinneret and the collector is 10-35cm, the roller rotates at 60-100rpm, the relative humidity of the rotating atmosphere is 40-50%, and the ambient temperature is 15-30°C, more preferably 20-25°C. After the (roller) rotates, the fiber membrane can be peeled off the roller and placed in a vacuum drying oven overnight to remove the residual solvent so that it is substantially free of solvent residues. Overnight means at least 8 hours, such as not less than 10 hours or 12 hours, etc. In a preferred embodiment of the present invention, the spinning solution is extruded from the core channel of the 22G/17G core shell spinneret, the extrusion speed is 4.0-5.0mL/h, and air is delivered to the core channel at a pressure of 20-23psi.

Preferably, the production method includes surface treatment: embossing, spraying and/or printing the dried imitation leather sheet to give it a texture, color and/or appearance similar to natural leather. The imitation leather sheet can also be post-treated as needed, such as softening, increasing waterproof performance, anti-fouling performance, etc. Post-treatment can further improve the comfort and durability of the imitation leather sheet.

In the present invention, coating can use methods such as roller coating, blade coating, spraying. In some embodiments, the method may include providing the coating solution to the textile to be coated with one or more of bath coating, single-sided roller coating, spray coating and double-sided roller coating. In some embodiments, the method may include removing excess coating solution from the textile coated with silk fibroin.

In the method of the present invention, wetting agents, detergents, chelating or dispersing agents, enzymes, bleaching agents, anti-foaming agents, anti-wrinkle agents, dye dispersants, dye leveling agents, dye fixing agents, dye special resin agents, dye anti-reducing agents, pigment dye system anti-migration agents, pigment dye system adhesives, anti-wrinkle treatments, softeners, feel improvers, water-based polyurethane dispersions, finishing resins, oil or water repellents, flame retardants, and cross-linking agents can be added to further improve the performance of the imitation leather sheet.

In the present invention, unless otherwise specifically described, the term drying may refer to drying the coating material according to the present invention at a temperature greater than room temperature (ie, 20° C.).

The present invention provides a leather-like sheet material, which comprises a base layer, a silk protein super-fiber layer and a leather surface layer in sequence. The base layer comprises a base material composed of degummed silk or silk fabric; the silk protein super-fiber layer is formed by spraying on the base layer by an electrostatic spinning device, and the silk protein super-fiber layer uses a silk protein solution obtained by dissolving silk fabric with a solvent or a silk protein solution obtained by dissolving degummed silk with a solvent as a spinning stock solution; the leather surface layer comprises a mixture of one or more of acrylic resin, nitrile rubber, polyurethane-polyether, polyurethane, polyester or polyvinyl chloride.

The silk protein microfiber layer is spun on a silk fabric substrate, and the leather surface layer is coated or pressed on the surface of the silk protein microfiber layer. The texture of the leather obtained can be adjusted according to different application requirements. The coating technology of this step can ensure that the silk protein coating is evenly distributed on the leather surface, and can effectively improve the adhesion and friction resistance of the coating. The imitation leather sheet prepared by the present invention organically combines the advantages of silk fabrics and leather-like products, and significantly improves its mechanical properties while maintaining environmental protection and air permeability. For example, in a preferred example of the present invention, the obtained imitation leather sheet has one or more of the following characteristics: friction color fastness is not less than level 3; air permeability is not less than 140mm/S; softness is not less than 6.0mN; tear strength is not less than 25N, or tensile strength is not less than 32MPa/(g.cm ^-3 ).

In the present invention, the base layer can be normal silk or silk fabric that has been desironized.

The silk protein super-fiber layer not only enhances the interface connection between the leather surface layer and the substrate, but also significantly enhances the flexibility of the leather surface layer and the air permeability of the entire imitation leather sheet. And the presence of the super-fiber layer enables the silk fabric substrate to be firmly combined with different leather surface materials, such as acrylic resin, nitrile rubber, polyurethane-polyether, polyurethane, polyester or polyvinyl chloride leather surface coating slurry. Etc. The spinning solution of the silk protein super-fiber layer adopts the solution after partially dissolving the silk fabric in step S1; or is prepared by dissolving the degummed silk with lithium bromide/water, calcium chloride/ethanol/water, formic acid/calcium chloride or hexafluoroisopropanol. In some embodiments, the solution of silk fibroin or its fragments can be an aqueous solution, an organic solution or an emulsion. In one embodiment, the product is made of textile material. In another embodiment, the product is made of non-textile material. In one embodiment, the silk protein super-fiber layer comprises silk protein or its fragments with a weight average molecular weight range of about 5kDa to about 144kDa, wherein the silk protein or its fragments are selected from natural silk protein or its fragments, recombinant silk protein or its fragments and combinations thereof.

In the present invention, leather refers to natural leather and synthetic leather. Natural leather includes chrome tanned leather (e.g., silk protein tanned with chromium sulfate and other chromium salts), vegetable tanned leather (e.g., tanned with tannic acid), aldehyde tanned leather (also known as wet white leather, e.g., silk protein tanned with glutaraldehyde or oxazolidine compounds), brain tanned leather, formaldehyde tanned leather, suede leather (e.g., silk protein tanned with cod oil), rose tanned leather (e.g., tanned with rose essential oil), synthetic tanned leather (e.g., tanned with aromatic polymer silk protein), alum tanned leather, patent leather, nubuck leather and rawhide. Natural leather also includes silk protein split leather, full grain leather, top grain leather and corrected grain leather, the properties and preparation of which are known to those skilled in the art. Synthetic leather includes breathable silk protein artificial leather (e.g., polyurethane on polyester), vinyl and polyamide felt fibers, polyurethane, polyvinyl chloride, polyethylene (PE), polypropylene (PP), vinyl acetate copolymer (EVA), polyamide, polyester, textile-polymer composite microfiber, coffin, filled leather or a combination thereof.

Preferably, the leather surface layer includes but is not limited to a mixture of one or more of the following: a leather surface coating slurry of acrylic resin, nitrile rubber, polyurethane-polyether, polyurethane, polyester or polyvinyl chloride. The texture of the obtained leather can be adjusted according to different application requirements.

The requirements for the texture of leather mainly include softness, wear resistance, waterproofness, breathability, easy cleaning, good texture, high temperature resistance and other characteristics. Different applications of leather and the requirements for its texture will vary, as follows:

Clothing and accessories: Leather is often used to make clothing and accessories such as coats, pants, shoes, gloves, hats, etc. The leather for these products requires softness, wear resistance, waterproofness, breathability, and texture.

Furniture: Leather is also often used to make furniture such as sofas, beds, chairs, etc. The leather of these products requires the characteristics of wear resistance, softness, waterproofness, easy cleaning, and good texture.

Car interior: Car seats, steering wheels, dashboards and other parts are often made of leather materials. The leather of these products requires softness, waterproofness, wear resistance, high temperature resistance and other characteristics.

Packaging: Leather is also often used to make handbags, wallets, watch straps and other items. The leather for these products requires softness, good texture, durability, and easy cleaning.

Industrial use: Leather can also be used to make industrial products, such as belts, brake pads, etc. The leather for these products requires properties such as wear resistance, corrosion resistance, and high strength.

The imitation leather sheet of the present invention optimizes the formula of bio-based polymers, improves its mechanical properties and environmental performance, and makes the imitation leather sheet have better mechanical properties, environmental performance, wear resistance, scratch resistance, antibacterial and waterproof properties. In a preferred embodiment of the present invention, the manufactured imitation leather sheet has one or more of the following characteristics: friction color fastness is not less than level 3; air permeability is not less than 130mm/S; softness is not less than 5.0mN; elongation at break is not less than 55%; or breaking strength is not less than 650N. Compared with the existing imitation leather sheets, the present invention can improve the various properties of the obtained product, including antimicrobial properties, water repellent properties, oil repellent properties, flame retardant properties, coloring properties, fabric softening properties, antifouling properties, pH adjustment properties, anti-friction decolorization properties, anti-pilling properties, anti-felting properties, wetting time, absorption rate, spreading speed, cumulative unidirectional transmission, overall moisture management ability, fabric feel, fabric stretch and drape. The performance improvement ratio is selected from: greater than 40%, greater than 60%, greater than 80%, greater than 100%, greater than 120%, greater than 140%, greater than 160%, greater than 180% or even more.

In the present invention, the rubbing color fastness of silk fabric leather can be improved in a variety of ways as needed, mainly including the following methods:

1) Adding cross-linking agent: The cross-linking agent can form a strong chemical bond between silk protein and leather, thereby improving the friction and wear resistance of the coating.

a) Dopamine: Dopamine is a naturally occurring organic substance that can form self-assembled polymers on the surface of some organisms. Dopamine can cross-link silk protein with leather matrix through oxidative polymerization, improving the adhesion and wear resistance of the coating.

b) Thiol compounds: Thiol compounds can react with cysteine in silk protein to form disulfide cross-links, thereby improving the durability and stability of the coating. Commonly used thiol compounds include mercaptopropanol, thioglycolic acid, etc.

c) Silicone compounds: Silicone compounds can cross-link with silk protein and leather matrix to form siloxane bonds with wear resistance and weather resistance. Silicone compounds include methyltriethoxysilane, isopropyltriethoxysilane, etc.

d) Isocyanate: Isocyanate can react with the amino group in silk protein to form urea bond, thus improving the wear resistance and durability of the coating. Commonly used isocyanates include dimethylformamide isocyanate, tetrahydrofuran isocyanate, etc.

2) Adding other compounds: Adding other compounds, such as carbamate, polyurethane, etc., can improve the friction resistance and wear resistance of silk protein coating.

3) Post-treatment of the silk protein coating: Post-treatment of the silk protein coating, such as heat treatment, ultraviolet radiation, etc., can improve its friction resistance and wear resistance.

The present invention can be used to prepare an imitation leather sheet with excellent mechanical properties, sustainability and environmental friendliness. The imitation leather sheet is subjected to surface treatments such as embossing, spraying and printing after drying, and the imitation leather sheet is subjected to post-treatments such as softening, increasing waterproof performance and antifouling performance, thereby improving the comfort and durability of the imitation leather sheet.

The present invention can be applied to prepare sustainable, environmentally friendly alternative materials in clothing, footwear, furniture, automotive interior, sports equipment and/or packaging field, also comprises that at least part of the solution of silk-fibroin fragment of the present invention is surface-treated to produce the product that silk coating obtains on the product.In one embodiment, the present invention can be used for making sportswear, for example, making golf clothing or underwear.In one embodiment, silk coating of the present invention can be used for the backing, shell, lining or the lining of sportswear/clothing, or sportswear/clothing part is made by imitation leather sheet of the present invention.

In the present invention, substantially no sericin or substantially no sericin refers to a silk fiber in which most of the sericin has been removed. In one embodiment, silk fibroin substantially free of sericin refers to silk fibroin having about 0.01% (w/w) to about 10.0% (w/w) sericin. In one embodiment, silk fibroin substantially free of sericin refers to silk fibroin having about 0.01% (w/w) to about 9.0% (w/w) sericin.

In the present invention, uniformity may refer to silk fibroin fragments distributed around a specified molecular weight in a normal distribution form. The term substantially uniformity used in the present invention may refer to uniform distribution of additives throughout the composition of the present invention.

In the present invention, substantially free of solvent residues means that 0.1% (w/w) or less of solvent residues remain. In one embodiment, substantially free of residues means that 0.1% (w/w) or less of solvent residues remain. In one embodiment, substantially free of residues means that 0.1% (w/w) or less of solvent residues remain. In one embodiment, substantially free of residues means that 0.1% (w/w) or less of solvent residues remain. In one embodiment, the amount of residue is 0 ppm to 1000 ppm. In one embodiment, the amount of residue is ND to about 500 ppm. In one embodiment, the amount of residue is ND to about 400 ppm. In one embodiment, the amount of residue is ND to about 300 ppm. In one embodiment, the amount of residue is ND to about 200 ppm. In one embodiment, the amount of residue is ND to about 100 ppm. In one embodiment, the amount of residue is 10 ppm to 1000 ppm.

In the present invention, hand refers to the feel of a fabric, which can be further described as soft, crisp, dry, silky, and combinations thereof. The hand of a fabric is also known as drape. Fabrics with a hard hand feel are coarse and rough and the wearer generally feels less comfortable. Fabrics with a soft hand feel are smooth and slippery, such as fine silk or wool, and the wearer generally feels more comfortable. The hand of a fabric can be determined by comparing a collection of fabric samples.

In the present invention, coating refers to a material or combination of materials that forms a substantially continuous layer or film on the outer surface of a textile. In some embodiments, a portion of the coating may at least partially penetrate into the substrate. In some embodiments, the coating may at least partially penetrate into the voids of the substrate. In some embodiments, the coating may be impregnated into the silk protein surface so that the application or coating method of the coating may include at least partially impregnating at least one coating component (at the melting temperature of the substrate) into the substrate surface. The coating can be applied to the substrate by one or more methods described in the present invention.

Compared with the prior art, the imitation leather sheet and the production process thereof of the present invention have the following advantages:

1. Superior mechanical properties: The imitation leather sheet of the present invention is superior to the prior art in terms of mechanical strength and fatigue resistance, and has significantly improved friction color fastness, air permeability, softness, water absorption, Young's modulus, tensile strength, etc., and can meet various application requirements.

2. Environmental performance: The present invention uses degradable silk fabrics and silk protein materials as base materials, and environmentally friendly coatings as leather surface layers and coating materials, which reduces pollution emissions during the production process and ensures environmental performance and sustainable development.

3. Wide application fields: The imitation leather sheet of the present invention can be widely used in clothing, shoes, furniture, automobile interior, sports equipment, packaging and other fields, realizing sustainable and environmentally friendly alternative materials.

DETAILED DESCRIPTION

The present invention provides a leather-like sheet material and a production process thereof, comprising the following steps:

1. Pretreatment of silk fabrics:

The silk fabric and/or degummed silk is used as a substrate, and the silk fabric or degummed silk is immersed in a solvent to partially dissolve the fabric. The solution system includes:

LiBr/water, an aqueous solution of lithium bromide;

Calcium chloride/ethanol/water, a mixture of calcium chloride, ethanol and water;

Formic acid/calcium chloride, the product obtained by dissolving calcium chloride in formic acid;

Hexafluoroisopropanol.

Degummed silk preparation method:

1. Prepare 20g natural silk cocoons and 40g NaHCO.

2. Take 4L of pure water and boil it.

3. Take some NaHCO ₃ from the 40g and add it to the boiling water together with the cocoons and cook for 30 minutes.

4. After boiling for 30 minutes, remove the cocoons and put them into another 4L of pure water. Continue to boil and add the remaining NaHCO ₃ . Boil for 30 minutes.

5. Take out and cool, then rinse with pure water.

6. Dry at 20-70℃.

Second, the partially dissolved substrate is dried in a closed environment at 25-60°C by pressing and collected into a roll by roller.

3. The silk protein superfiber layer is spun on the silk fabric substrate by using the electrospinning (a technology combining electrospinning and air-blowing spinning) process.

The spinning solution of the silk protein ultra-fiber layer can be prepared by dissolving the degummed silk in lithium bromide/water, calcium chloride/ethanol/water, formic acid/calcium chloride or hexafluoroisopropanol, or directly spinning the silk fabric by partially dissolving the solution in step one.

The electrospray spinning process can be adjusted according to the spinnability and spinning efficiency. The optimized electrospray spinning parameters are as follows: the spinning solution is extruded from the core channel of the 22G/17G core shell spinneret at a speed of 5mL/h, and air is delivered to the core channel at a pressure of 20psi. A voltage of 25kV is applied to the spinneret; the distance between the top of the spinneret and the collector is 35cm, the roller rotates at 100rpm, the relative humidity of the rotating atmosphere is 40-45%, and the ambient temperature is 25℃.

After rotation, the fiber membrane is peeled off on a roller and placed in a vacuum drying oven for 12 hours to remove residual solvent. The silk protein microfiber layer not only strengthens the interface connection between the leather surface layer and the substrate, but also significantly enhances the flexibility of the leather surface layer and the air permeability of the entire imitation leather sheet. In addition, the presence of the microfiber layer enables the silk fabric substrate to be firmly combined with different leather surface materials, such as polyurethane, polyester and polyvinyl chloride.

a) Preparation of spinning solution for silk protein ultra-fiber layer

The electrospray spinning process is used to spin a silk protein super fiber layer on a silk fabric substrate. The spinning solution of the silk protein super fiber layer can be prepared by dissolving degummed silk in lithium bromide/water, calcium chloride/ethanol/water, formic acid/calcium chloride or hexafluoroisopropanol, or directly spinning the solution obtained by partially dissolving the silk fabric in step 1.

b) Optimization of electrospinning process parameters

The electrospinning process can be adjusted according to the spinnability and spinning efficiency.

c) Processing of the silk protein microfiber layer

After spinning, the fiber membrane was peeled off on a roller and placed in a vacuum drying oven for 12 h to remove residual solvent.

Fourth, the leather surface coating slurry is coated or pressed onto the surface of the silk protein microfiber layer by using coating methods such as roller coating, scraper coating, spray coating, and pressing molding techniques.

In this step, the leather surface layer that can be selected is a leather surface coating slurry made by a classical method and commercial polyurethane, polyester or polyvinyl chloride, so the texture of the obtained leather can be adjusted according to different application requirements.

5. Send the coated substrate to a drying device, such as a hot air drying oven, infrared drying oven, etc. for drying. The drying temperature is controlled between 60-200°C and the time is between 0.5-12 hours to ensure the film-forming property of the coating and the performance of the finished product.

The dried imitation leather sheet can be subjected to surface treatment, such as embossing, spraying, printing, etc., to give it a texture, color and appearance similar to natural leather. The imitation leather sheet can also be subjected to post-treatment as needed, such as softening, increasing waterproof performance, anti-fouling performance, etc. Post-treatment can further improve the comfort and durability of imitation leather (including imitation leather sheets, referred to as imitation leather).

The test standards for color fastness to rubbing (grade) are GB/T3920-2008 "Textiles - Color fastness - Color fastness to rubbing" and GB/T29865-2013 "Textiles - Color fastness - Color fastness to rubbing - Small area method". Dry rubbing: Fix the conditioned friction cloth flatly on the friction head, and make the vertical pressure rod rotate forward and reverse for a total of 40 times, 20 cycles, and the rotation speed is 1 cycle per second. Remove the friction cloth. Wet rubbing: Weigh the conditioned friction cloth, immerse it completely in distilled water, take it out and remove excess water, and weigh it again to ensure that the liquid carrying rate of the friction cloth is 95% to 100%, and then operate according to the above (2).

Water absorption test method: Referring to GB/T 4689.21-2008 "Determination of static water absorption of leather physical and mechanical tests", the static water absorption test was performed on the simulated luminous leather sheets prepared in Examples 1-6 and Comparative Examples 1-2, and the test temperature was 18-22°C.

The air permeability of fabrics is tested according to the fabric air permeability test method specified in GB/T54531997. The test principle is: air passes through the fabric vertically, forming a certain pressure difference between the front and back of the fabric. The amount of air passing through the fabric per unit time under a certain pressure difference is measured, which is the air permeability of the fabric. The softness of fabrics is tested according to GB/T39371-2020.

Tear strength test method: Cut a test piece of 10cm in length and 4cm in width from the imitation leather sheet. Then, cut a 5cm slit in the center of the short side of the test piece parallel to the long side. Then, using a tensile testing machine, clamp each slice with the chuck of the clamp, and measure the s-s curve at a tensile speed of 10cm/min. The value obtained by dividing the maximum load by the unit area weight of the test piece calculated in advance is taken as the average tear strength per thickness of 1mm. For the value, measure 3 test pieces in the longitudinal direction and the transverse direction perpendicular to the longitudinal direction of the raw material, and calculate the average value respectively.

The present invention is further described in detail in conjunction with the following preferred embodiments and descriptions, and the protection content of the present invention is not limited to the following embodiments. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be thought of by those skilled in the art are included in the present invention, and the attached claims are the scope of protection. The process, conditions, reagents, experimental methods, etc. for implementing the present invention, except for the contents specifically mentioned below, are all common knowledge and common common sense in the art, and the present invention is not particularly limited.

Example 1

The degummed silk was immersed in a 5 mol/L lithium bromide/water solution system and stirred at 80°C for 30 minutes to partially dissolve it.

1) The partially dissolved substrate is dried in a closed environment at 50° C. by a pressing method and collected into a roll by a roller to serve as the substrate of the silk leather.

2) Using the electrospray spinning process, the silk protein super fiber layer is spun on the substrate obtained in step 2. The spinning solution of the silk protein super fiber layer is directly spun from the silk protein ion conductor solution obtained in step 1. The spinning solution is extruded from the core channel of the 22G/17G core shell spinneret at a rate of 5mL/h, and air is delivered to the core channel at a pressure of 20psi. A voltage of 25kV is applied to the spinneret; the distance between the top of the spinneret and the collector is 35cm, the roller rotates at 100rpm, the relative humidity of the rotating atmosphere is 40-45%, and the ambient temperature is 25°C. After spinning, the fiber membrane is peeled off on the roller, and the residual solvent is removed in a vacuum oven at 50°C for 12 hours.

3) A commercially available polyurethane leather surface coating slurry was roller-coated on the surface of the silk protein microfiber layer with a thickness of 0.2 mm. The coated substrate was pressed at 120° C. and 1.0 MPa for 5 minutes to obtain the desired texture.

4) The coated substrate is dried in a hot air drying oven at 150°C for 1 hour to ensure the film-forming properties of the coating and the performance of the finished product.

5) The imitation leather sheet is softened by being immersed in a softener, and treated with a water-repellent and a stain-proofing agent.

Example 2

1) 100 g of silk was immersed in a calcium chloride/ethanol/water system solution with a molar ratio of 1:2:8 for 12 minutes to prepare a spinning solution. The ratio of silk to solvent was 1:12.

2) drying the partially dissolved substrate in a closed environment at 40° C. and collecting it into a roll using a drum;

3) Using an electrospray spinning process, the silk protein super fiber layer is spun on the silk substrate obtained in step 2. The spinning solution of the silk protein super fiber layer is directly spun from the solution in which the silk is partially dissolved in step 1. The spinning solution is extruded from the core channel of the 22G/17G core-shell spinneret at a rate of 5mL/h, and air is delivered to the core channel at a pressure of 20psi. The roller rotates at a speed of 120rpm. After spinning, the fiber membrane is peeled off the roller and the residual solvent is removed in a vacuum oven at 50°C for 6 hours.

4) The leather surface coating slurry is applied to the surface of the silk protein microfiber layer by roller coating. A commercially available polyurethane leather surface coating slurry is used, and the coating thickness is controlled at 20 μm. The coated substrate is then pressed at a temperature of 100° C. and a pressure of 3 MPa for 10 minutes to enhance the adhesion between the silk protein microfiber layer and the coating.

5) The coated substrate is dried in a hot air drying oven at 150°C for 2 hours to ensure the film-forming properties of the coating and the performance of the finished product.

6) The dried substrate was immersed in a softening solution of 500 ml of water and 20 ml of glycerol for 30 minutes to soften the imitation leather sheet. The substrate was then rinsed with water and dried in a hot air drying oven at 80°C for 1 hour. The flexibility and softness of the obtained silk leather were improved.

Example 3

1) The degummed silk was immersed in a solution system consisting of 9.3M lithium bromide and water, with the ratio of silk to solvent being 1:10. The mixture was stirred for 25 minutes, and the degummed silk was partially dissolved.

2) The partially dissolved degummed silk is dried by pressing in a closed environment at 40° C., and then the dried silk substrate is collected into a roll by a roller.

3) The electrospinning process is used to spin the silk protein super fiber layer on the silk substrate. The spinning solution of the silk protein super fiber layer is directly spun from the dissolved silk protein ion conductor obtained in step 1. The spinning solution is extruded from the core channel of the 22G/17G core-shell spinneret at a rate of 1 mL/h, and air is delivered to the core channel at a pressure of 0.2 MPa. The roller rotates at a speed of 200 rpm. After spinning, the fiber membrane is peeled off on the roller and the residual solvent is removed in a vacuum oven at 25°C for 24 hours.

4) A polyurethane (PU) leather surface coating slurry was applied on the silk protein microfiber layer by roller coating. The PU coating slurry was prepared by mixing 15wt% of PU resin, 3wt% of crosslinking agent, 1wt% of leveling agent and 81wt% of solvent (a mixture of ethyl acetate and butyl acetate) under constant stirring for 4 hours. The coated substrate was then pressed at 120°C and a pressure of 0.2MPa for 5 minutes using a hydraulic press to improve adhesion.

5) The coated substrate was dried in a hot air drying oven at 120°C for 4 hours to ensure proper film formation and adhesion of the coating.

6) The dried substrate was then softened by applying a silicone softener using a spray method. The softener was a mixture of 5wt% silicone emulsion and 95wt% water. The coated substrate was sprayed with the softener solution and then dried in a hot air oven at 80°C for 1 hour to improve softness and feel.

7) The steps of this embodiment may be followed to use different solvent systems to dissolve the silk, and also include using different spinning solutions and coating materials, as well as different post-treatment methods compared to the previous embodiments.

Example 4

1) Soak the silk in a hexafluoroisopropanol solution at a ratio of 1:10 (silk:solvent) at room temperature for 25 hours to obtain a spinning stock solution and partially dissolved silk.

2) Filter the spinning stock solution using a 0.45 μm filter to remove impurities.

3) The spinning solution was poured onto a glass plate and dried in a closed environment at 25° C. for 24 hours to obtain a silk film.

4) Using a handheld electrospinning machine, the silk protein super fiber layer is electrospun onto the silk film. The spinning solution is the silk protein solution obtained after filtration in step 2), and the electrospinning parameters are: voltage 12 kV, flow rate 0.5 mL/h, distance between the spinneret and the silk film 10 cm, ambient temperature and humidity are 25° C. and 50%, respectively. After electrospinning, the silk film with the super fiber layer is vacuum dried at 25° C. for 12 hours.

5) Spraying the surface of the silk protein super fiber layer with a polyurethane-based leather surface coating slurry. The coating parameters are: pressure 0.3 MPa, distance between the spray gun and the silk film 20 cm, ambient temperature and humidity 25°C and 50% respectively. After coating, the silk film with the super fiber layer and the leather surface coating slurry are dried at 60°C for 2 hours.

6) The silk leather was treated with a 0.5 wt % glycerol aqueous solution at a ratio of 1:10 (silk leather: solution) at 40° C. for 1 hour to soften the silk leather. The softened silk leather was then rinsed with water and air-dried at room temperature.

Example 5

1) Preparation of spinning solution: 100 g of degummed silk fiber was added to a mixture of lithium bromide and water (5 M/L LiBr aqueous solution), with the ratio of silk to solvent being 1:10. The mixture was stirred at 60° C. for 3 hours until the silk fiber was partially dissolved.

2) Drying of partially dissolved substrate: The partially dissolved silk substrate is dried in a closed environment at 50° C. by a pressing method for 2 hours, and then collected into a roll by a roller.

3) Spinning of the silk protein ultra-fiber layer: The spinning solution of the silk protein ultra-fiber layer is directly spun from the solution obtained in step 1, using a core-shell spinneret with a core flow channel of 22G/17G, with a flow rate of 0.1mL/min and an air pressure of 1kPa. During the spinning process, the roller rotates at a speed of 80rpm. After spinning, the fiber film is peeled off from the roller and the residual solvent is removed in a vacuum oven at 50°C for 1 hour.

4) Leather surface coating: A commercially available polyurethane leather surface coating slurry was applied to the surface of the silk protein microfiber layer by roller coating. The coating slurry was applied at a speed of 10 m/min, and the coating thickness was controlled to be 0.2 mm by adjusting the gap between the roller and the substrate.

5) Drying: The coated substrate is sent to a hot air drying oven and dried at 120°C for 2 hours to ensure the film-forming properties of the coating and the performance of the finished product.

6) Post-treatment: The dried silk leather was treated with a softener at room temperature for 12 hours to soften it. The softener used was a mixture of glycerol and water (volume ratio of 1:1). The softened silk leather was then immersed in a solution of polydimethylsiloxane (PDMS) and hexane (volume ratio of 1:10) for 30 minutes and treated with a waterproofing agent. The treated silk leather was then air-dried at room temperature for 24 hours.

Example 6

1) Preparation of silk substrate: The degummed silk was kept in a formic acid/calcium chloride solution with a molar ratio of 24:1 at 60°C for 30 minutes to partially dissolve the silk. After the silk was partially dissolved, it was taken out of the solution, rinsed with distilled water, dried in a closed environment at 40°C and collected into a roll in a drum type as a silk leather substrate;

2) Electrospinning of the silk protein super fiber layer: The silk protein solution obtained in step 1 was dissolved as a spinning solution. The spinning solution was electrospun onto the silk substrate using an electrospinning device with a spinning voltage of 20-30 kV, a spinning distance of 15-20 cm, and a spinning rate of 5 mL/h. The electrospun silk protein super fiber layer was dried at 30° C. for 24 hours.

3) Preparation of leather surface layer: Dissolve commercially available polyurethane leather surface coating slurry in a mixed solvent of tetrahydrofuran and water (v/v=4:1) to prepare a coating solution. Spray the coating solution onto the surface of the silk protein super fiber layer and then dry at 25-30°C for 12 hours.

4) Post-treatment of imitation leather sheet: The dried imitation leather is softened by kneading and stretching, and then a fluorine-containing waterproofing agent is applied on the surface for waterproofing. The waterproof imitation leather is dried at room temperature for 24 hours, and then a self-cleaning agent is applied on the surface for anti-fouling treatment. The anti-fouling imitation leather is dried at 40-50℃ for 2-3 hours.

5) Embossing and finishing: The imitation leather sheet is embossed with a heated embossing plate and then finished by spraying a finishing agent on the surface to enhance its glossiness and durability. The temperature is 150°C.

6) The fatigue resistance of leather can be characterized by rubbing color fastness, tear strength and tensile strength.

Comparative Example 1

1) Using untreated silk as the base material of silk leather.

2) Using the electrospray spinning process, the silk protein super fiber layer is spun on the substrate obtained in step 1. The spinning solution of the silk protein super fiber layer is directly spun from silk dissolved in 5 mol/L lithium bromide silk protein ion conductor solution. The spinning solution is extruded from the core channel of the 22G/17G core shell spinneret at a speed of 5 mL/h, and air is delivered to the core channel at a pressure of 20 psi. A voltage of 25 kV is applied to the spinneret; the distance between the top of the spinneret and the collector is 35 cm, the roller rotates at 100 rpm, the relative humidity of the rotating atmosphere is 40-45%, and the ambient temperature is 25 ° C. After spinning, the fiber membrane is peeled off on the roller, and the residual solvent is removed in a vacuum oven at 50 ° C for 12 hours.

3) A commercially available polyurethane leather surface coating slurry was roller-coated on the surface of the silk protein microfiber layer with a thickness of 0.2 mm. The coated substrate was pressed at 120° C. and 1.0 MPa for 5 minutes to obtain the desired texture.

4) The coated substrate is dried in a hot air drying oven at 150°C for 1 hour to ensure the film-forming properties of the coating and the performance of the finished product.

5) The imitation leather sheet is softened by adding a softener and treated with a water-repellent and a stain-resistant agent.

Comparative Example 2

1) 100 g of silk was immersed in a calcium chloride/ethanol/water system solution with a molar ratio of 1:2:8 for 12 minutes to prepare a spinning solution. The ratio of silk to solvent was 1:12.

2) drying the partially dissolved substrate in a closed environment at 40° C. and collecting it into a roll using a drum;

3) The leather surface coating slurry is applied to the base fabric obtained in step 2 by roller coating. A commercially available polyurethane leather surface coating slurry is used, and the coating thickness is controlled to be 20 μm. The coated substrate is then pressed at a temperature of 100° C. and a pressure of 3 MPa for 10 minutes to enhance the adhesion between the silk protein super fiber layer and the coating.

4) The coated substrate is dried in a hot air drying oven at 150°C for 2 hours to ensure the film-forming properties of the coating and the performance of the finished product.

5) The dried substrate was immersed in a softening solution of 500 ml of water and 20 ml of glycerol for 30 minutes to soften the imitation leather sheet. The substrate was then rinsed with water and dried in a hot air drying oven at 80°C for 1 hour. The flexibility and softness of the obtained silk leather were improved.

Table 1. Comparison of the color fastness to friction and other properties of the prepared imitation leather sheets

Table 2. Comparison of mechanical properties of the prepared imitation leather sheets

As can be seen from Table 1 and Table 2, the imitation leather sheet produced by the method of the present invention has excellent mechanical properties and rubbing color fastness and other properties. The base layer of Comparative Example 1 is not treated, and an undissolved base material is directly used. Comparative Example 2 does not have a silk protein microfiber layer. Although a uniform material can be obtained, the uniformity is slightly worse, the rubbing color fastness and other properties are reduced, and the mechanical properties are obviously not as good as the imitation leather sheet products obtained in Examples 1-6.

The imitation leather sheet produced by the present invention is obtained through optimization of the preparation method, and the imitation leather sheet has significantly improved friction color fastness (including transverse and longitudinal), softness, tear strength (including transverse and longitudinal), tensile strength, and elongation at break. The present invention provides an imitation leather sheet with excellent performance, environmental protection and sustainability and a production process thereof, which effectively solves the problems existing in the prior art and provides new technical support for the development of imitation leather sheets.

The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims (10)

1. A method for producing a leather-like sheet, comprising the steps of:

degummed silk and/or silk fabric is used as a base material; immersing the degummed silk or silk fabric in a solvent so that the degummed silk or base material is partially dissolved to form a fibroin solution;

drying a substrate which is partially dissolved to form the fibroin solution in a closed environment at the temperature of 25-60 ℃ to obtain a basal layer;

spraying a silk protein microfiber layer on the basal layer by adopting an electrostatic spinning device, wherein the silk protein microfiber layer is prepared by adopting a silk protein solution obtained by dissolving silk fabrics by adopting the solvent or a silk protein solution obtained by dissolving degummed silk by adopting the solvent as a spinning solution;

coating or pressing the leather surface coating slurry on the silk protein microfiber layer to form a leather surface layer;

And drying the product formed by the leather surface layer, the silk protein microfiber layer and the basal layer to obtain the leather-like sheet.

2. The method according to claim 1, wherein the product of the leather layer, the silk protein microfiber layer and the substrate layer is dried at a temperature ranging from 15 to 200 ℃ for a drying time ranging from 0.5 to 12 hours.

3. The method of producing a leather-like sheet according to claim 1, wherein said solvent is selected from one or more of the following: the weight ratio of the silk fabric to the solvent is controlled to be 1 (8-12), and the dissolution time is 10 minutes to 30 hours.

4. A method of producing a leather-like sheet according to claim 3, wherein the solvent is formulated and its dissolution time is selected from one or more of the following:

lithium bromide/water, the concentration is 5-6 mol/L, and the dissolution is 25-60 minutes;

the molar ratio of the calcium chloride to the ethanol to the water is 1:2 (8-10), and the dissolution is carried out for 5-12 minutes;

Formic acid/calcium chloride, molar ratio (20-48): 1, dissolving for 3-7 minutes;

hexafluoroisopropanol, dissolved for 25-35 minutes.

5. The method according to claim 1, wherein when the silk fibroin microfiber layer is formed by spraying on the substrate layer using an electrostatic spinning device, the spinning diameter is 500nm to 1 μm. .

6. The method of producing a leather-like sheet according to claim 5, wherein after the rotation of the rolls, the fibrous film is peeled off from the rolls and left overnight in a vacuum oven to remove residual solvent.

7. The method of producing a leather-like sheet according to claim 1, wherein the leather facing layer comprises a mixture of one or more of the following:

A leather-top coating slurry of acrylic, nitrile rubber, polyurethane-polyether, polyurethane, polyester or polyvinyl chloride.

8. The method for producing a leather-like sheet according to claim 1, wherein the method comprises a surface treatment of: the dried leather-like sheet is surface-treated by embossing, spraying and/or printing.

9. The leather-like sheet is characterized by comprising a basal layer, a leather surface layer and a silk protein microfiber layer between the basal material and the leather surface layer;

The base layer comprises a base material consisting of degummed silk or silk fabric;

the silk fibroin microfiber layer is formed by spraying on the basal layer by adopting an electrostatic spinning device, and the silk fibroin microfiber layer adopts a silk fibroin solution obtained by dissolving silk fabrics by a solvent or a silk fibroin solution obtained by dissolving degummed silk by the solvent as a spinning solution;

the leather surface layer comprises one or a mixture of a plurality of acrylic resin, nitrile rubber, polyurethane-polyether, polyurethane, polyester or polyvinyl chloride.

10. The leather-like sheet according to claim 9, wherein said leather-like sheet has one or more of the following characteristics:

the rubbing color fastness is not lower than grade 3;

the air permeability is not lower than 140mm/S;

the softness is not lower than 6.0mN;

Tear strength of not less than 25N, or

The tensile strength is not lower than 32 MPa/(g.cm ^-3).