JPWO2008114319A1 - Leather modifier - Google Patents

Abstract

The present invention provides a leather modifier useful for producing a high-strength leather and a method for producing a modified leather using the same. The present invention relates to a leather modifying agent comprising a hard protein degradation product or fine powder as an active ingredient.

Description

  The present invention relates to a leather modifier and a method for producing a modified leather using the same.

  Natural leather of animals such as cattle, pigs, deer, sheep, horses and goats has been used for footwear, clothing, etc. since prehistoric times. At present, in daily life, footwear such as shoes, bags, handbags, clothing, gloves, belts, and other furniture, chairs, interior, car seats, and other sports equipment, as well as harnesses, drums, and handicrafts. Widely used, it is an important material for daily necessities.

  The production of natural leather can be roughly divided into four steps: 1) preparatory work, 2) tanning step, 3) re-tanning / dyeing / greasing step, and 4) finishing step. In the preparatory work, blood, dirt, salt, meat pieces, fat, etc. adhering to the raw skin are removed, the skin is swollen with lime and sulfide, collagen fibers are loosened and hair is decomposed and removed. In the tanning process, collagen, which is a skin protein, is chemically fixed and stabilized using metal tanning agents such as chromium, aluminum, zirconium, etc., plant tannin, aldehyde, etc., making it less susceptible to spoilage. This is a process for imparting excellent properties such as heat resistance, flexibility and breathability to leather. In the retanning / dyeing / greasing process, the leather is given characteristics according to the application, dyed to the desired color, and the leather is given characteristics such as flexibility and fullness by the greasing agent. The purpose of the finishing process is to comprehensively provide the properties necessary for the final leather product. For example, the leather silver surface is coated for the purpose of adjusting color tone, improving smoothness, improving touch, imparting resistance to water, light and chemicals, and imparting water repellency.

  However, there is a problem that physical properties such as strength, texture, and dyeability are not constant due to the type and method of tanning, the type of raw material skin, individual differences, site differences, scratches, and the like. In particular, regarding the strength, it is universally required to make the parts and individual differences as small and uniform as possible, and at the same time, increase them further. Furthermore, leather has more or less differences in tissue structure depending on the part derived from the living body, and there are scratches, and uniform dyeing is difficult, but improvement in leveling and dyeing fastness are required.

For improving the strength of leather, the use of greasing agents, retanning agents, and resin agents has been studied for a long time. For example, greasing agents are mainly composed of cationic aliphatic sulfochloride and quaternized fatty acids. Triethanolamine ester salts (see Patent Document 1), sulfates of fatty acid alcohol, triglyceride sulfonates, etc., anionic, aldehyde compounds such as glutaraldehyde and oxazolidine as tanning agents, acrylic resins, etc., polyurethane as a finishing agent (See Patent Document 2) and the like have been reported, but sufficient effects have not been obtained.
In recent years, environmental issues have become an unavoidable issue even in the leather industry due to heightened environmental awareness, disclosure of safety information to consumers, and the necessity of acquiring eco-labels for international transactions. There is a need for environmentally friendly drugs.

On the other hand, protein hydrolysates such as collagen and keratin are applied to foods such as ham and sausage, health foods, hair care products such as shampoos and rinses, and cosmetics. In the past, gelatin and glue have been used to give gloss in the leather finishing process (Non-Patent Documents 1 and 2).
However, it is not known at all that collagen hydrolyzate is used for leather production.
Matsui Shigetake, “Leather Finishing and Finishing Technology”, Leather Technology, Vol. 28, No. 1, 1-8 (1987) Koichi Hirao, “Leather Finishing Agent”, Leather Technology, Vol. 21, No. 2, 30-37 (1980) JP 9-512844 A JP-A-6-340900

  An object of the present invention is to provide a leather modifier useful for producing a high-strength leather and a method for producing a modified leather using the same.

  In view of such circumstances, the present inventors have a strong affinity for the hydrolyzate or fine powder of hard protein such as collagen and keratin with the collagen fibers of the leather, and by using these during the leather production, the strength is increased. It has been found that leather with high and excellent physical properties can be produced.

  That is, the present invention relates to a leather modifier containing a hard protein degradation product or fine powder as an active ingredient.

  The present invention also relates to a method for producing a modified leather, which comprises a step of treating with a hard protein degradation product or fine powder in the production of natural leather.

  The present invention also relates to a modified leather produced by the above method.

  According to the present invention, there is provided a leather modifier that improves the physical properties of natural leather. That is, according to the present invention, it is possible to produce leather having uniform physical characteristics, including improvement of leather strength, improvement of thickness, effect of repairing scratches, improvement of leveling or dyeing fastness. Become. Further, since the amount of collagen in the leather increases, moisture absorption and release properties are imparted, and the functionality such as the texture is improved, so that it is possible to produce a leather having more excellent comfort. Therefore, the modified leather of the present invention is used for automobiles such as car seats, steering covers and dashboard covering materials, for sports such as golf, baseball, skis and other gloves, baseball gloves, motorcycle racing suits, and belts. It can be widely used for clothing such as leather clothing and clothing gloves, shoes, bags, bags and the like.

  “Modification” in the leather modifier of the present invention means to improve and uniform the physical properties of natural leather. Specifically, at least improve the leather strength, preferably further improve the thickness, repair the wound, improve the leveling or dyeing fastness, improve the texture, impart moisture absorption and release, etc. Say.

  Examples of the hard protein in the present invention include fibrous proteins such as collagen, keratin, elastin, fibroin, sericin, and cuticle, and these may be used alone or in combination. From the viewpoint of improving the strength of leather, collagen, keratin or elastin is preferable, and collagen and keratin are particularly preferable.

  As a hard protein degradation product, a part of chemical bonds existing in the hard protein is hydrolyzed with acid, alkali, enzyme, etc., and the protein is reduced in molecular weight (for example, in the case of a collagen degradation product, the molecular weight is 1,000). To 100,000, preferably 2,000 to 10,000). Examples of the fine powder include finely pulverized products obtained by finely pulverizing the hard protein so that the particle diameter is 50 μm or less, preferably 25 μm or less.

Such a hard protein decomposition product or fine powder is extracted from the hard protein-containing raw material, or is hydrolyzed with an acid, alkali, enzyme, or the like as it is, or is pulverized into fine particles by a grinder or the like. Can be obtained.
Examples of hard protein-containing raw materials include, for collagen, cattle, pigs, sheep, goats, horses, chickens, fish dermis and bones, fish scales, etc., and for keratin, waterfowl, chicken feathers, wool, pig hair, cow hair, etc. As for elastin, the dermis of cattle, pigs, sheep, goats, horses, chickens, ligaments, tendons, blood vessel walls and the like can be mentioned.

For example, when preparing a collagen degradation product or fine powder, the collagen-containing raw material is treated with acid or alkali to remove impurities, and then heated with hot water to extract gelatin, which is then subjected to hydrolysis, etc. It is preferable to attach. The alkali used here is preferably lime, and the acid is preferably an inorganic acid such as hydrochloric acid or sulfuric acid. The treatment time generally requires several hours to several days for acid treatment and 2-3 months for lime treatment.
In addition, when preparing a keratin degradation product or fine powder, the raw material containing keratin may be subjected to decomposition or pulverization treatment as it is, but it may be subjected to a low concentration alkali (for example, 0.5 M sodium hydroxide solution). It is preferable to subject it to hydrolysis after immersion to remove impurities.

  The hydrolysis treatment with acid or alkali to obtain a hard protein degradation product is carried out by using a hard protein-containing raw material as water and / or methanol, ethanol, propanol, butanol, propylene glycol, 1,3-butylene glycol or the like. It is carried out by dissolving in a mixture of seeds or more, preferably water and / or ethanol, and adding an acid or alkali such as sulfuric acid, hydrochloric acid, acetic acid or phosphoric acid.

  Examples of the alkali include those usually used for hydrolysis of proteins and peptides, for example, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide, ammonia and the like. And may be appropriately selected depending on the properties of the target protein raw material. The alkaline solution is preferably an alkaline aqueous solution, but a mixed solvent of alcohol and water may be used.

  The concentration of the acid or alkali in the solution may be appropriately selected according to conditions suitable for the target protein raw material. However, when an acid is used, it is usually preferably 0.1 to 0.8 mol / L. Usually, it is preferably 0.2 to 0.5 mol / L.

  The hydrolysis treatment is performed by shaking or stirring the protein raw material in the acid or alkali solution. The reaction is preferably carried out usually in the range of 20 to 120 ° C. for 0.1 to 72 hours.

In the hydrolysis by an enzyme, a protein is usually made into a 0.1 to 40% by weight solution, and the enzyme is allowed to act in the working pH range and working temperature range of the enzyme used.
As an enzyme used for hydrolysis, any enzyme capable of degrading hard proteins such as collagen, keratin, and elastin may be used, and any of neutral protease, alkaline protease, and acidic protease may be used. Any of these may be used. Specific examples include pepsin, papain, bromelain, ficin and the like.

  The hard protein hydrolyzate thus obtained is, for example, neutralized, filtered, desalted (ultrafiltration, ion exchange, dialysis membrane, electrodialysis, electrodialysis, gel filtration, etc.), if necessary. Separation / purification treatment can be performed using centrifugation or the like, and it is also possible to remove water to concentrate or powder.

  The pulverization to obtain a hard protein fine powder is not particularly limited as long as the particle size can be atomized to 50 μm or less, preferably 25 μm or less. For example, a millstone, ball mill, jet mill, freeze pulverization And the like.

  In addition, a commercial item may be used for the decomposition product or fine powder of the said hard protein. For example, as collagen degradation products, PA-10, PA-100, PRA (Nippi Co., Ltd.), collagen peptide GCP-1000, collagen peptide 700F, collagen peptide 800F, super collagen peptide SCP-5000 (above, Nitta) Gelatin Co., Ltd.) can be used.

The hard protein degradation product or fine powder thus obtained adheres to the collagen fibers in the leather, improves the strength of the leather, improves the thickness, and exhibits a wound repair effect (see Examples below).
Therefore, a preparation comprising a hard protein degradation product or fine powder as an active ingredient is useful as a leather modifier, and a method for producing leather including a step of treating leather with this is a method for obtaining a modified leather. Useful.
The leather means natural leather of animals such as cattle, pigs, deer, sheep, horses, goats, etc., but has collagen fibers, and the decomposition product or fine powder of the hard protein of the present invention adheres to this leather. The animal species is not limited as long as the effects of the invention can be exhibited.

The dosage form of the leather modifier of the present invention is not particularly limited, but is preferably in a liquid or powder form.
The liquid preparation can be prepared by dissolving the hard protein degradation product or fine powder of the present invention in a solvent so as to have a desired protein-containing concentration. As a solvent used here, 1 type, or 2 or more types of mixtures, such as water and / or methanol, ethanol, propanol, a butanol, propylene glycol, 1, 3- butylene glycol, are mentioned.
Such preparations include neutral salts such as sodium sulfate and sulfites, organic acids such as ascorbic acid, citric acid and lactic acid, paraoxybenzoates, preservatives such as phenoxyethanol, alcohol sulfates, polyoxyethylene alkyl ethers, Various surfactants such as sulfosuccinate can be appropriately blended.

  The powdered preparation is prepared by spray-drying the above liquid preparation, or the hard protein degradation product or fine powder is directly mixed with so-called auxiliaries such as talc, zinc oxide, silica, titanium oxide as necessary. Can be prepared.

  The blending amount of the hard protein degradation product or fine powder in the leather modifier of the present invention may contain an effective amount capable of exhibiting the effects of the present invention, but is preferably 1 to 50% by weight, particularly 5 to 30%. Weight percent is particularly preferred.

The leather treatment using the protein degradation product or fine powder of the present invention can be performed in any step of leather production.
The treatment may be carried out by mixing or dissolving the hard protein degradation product or fine powder of the present invention in a solvent such as water or alcohol or various auxiliary agents and directly acting on the leather, or the above-mentioned hard protein degradation product or fine powder. A leather modifier containing powder may be allowed to act.
For example, when using a hard protein degradation product, it is treated for a certain period of time in a water bath using a drum and penetrates into collagen fibers in the leather, and if necessary, a water-soluble metal salt such as basic chromium sulfate. Further, it is only necessary to polymerize in leather by treatment with an aldehyde compound such as glutaraldehyde, a cross-linking agent such as polyethyleneimine or a cationic polyamine resin to further strengthen the bond. Moreover, when using hard protein fine powder, it can carry out by mixing the said fine powder with chemical | medical agents, such as a binder and fats and oils, and making it adhere to the collagen fiber in leather using this.

  In the leather manufacturing process, the timing of applying the treatment with the protein degradation product or fine powder is not particularly limited. 1) At the time of the pickling process before tanning, 2) At the time of the retanning process, 3) It is also possible in the neutralization process, 4) the dyeing process, 5) the greasing process, 6) the final water treatment process, and 7) the finishing process (spray, roll coater, etc.). In any case, it is effective to use the crosslinking agent in accordance with the purpose.

1) When performing in the soaking (pickling) process before tanning Soaking is usually performed after the preparation work is finished by putting the raw material skin into a water bath at about 20 ° C. and adding sodium chloride for several tens of minutes. Thereafter, 1 to 2% sulfuric acid is added alone or in combination with 0.5 to 1% formic acid, and the mixture is treated for several hours.
In this step, the leather modifier of the present invention can be added, for example, following sodium chloride treatment, and treatment may be performed for 30 to 60 minutes.

2) When performing in the retanning step Retanning is usually performed by putting the raw material skin into a water bath at about 30 ° C., and then using an organic acid or a cationic retanning agent (for example, basic chromium sulfate, basic aluminum sulfate, etc.) Is added. In this step, an electrolyte-stable drug (for example, a fatty acid phosphate ester compound, triglyceride sulfitized oil) or the like can be added in combination for the purpose of imparting flexibility and dispersing the drug.
In this step, the leather modifier of the present invention can be added, for example, after the organic acid treatment (before the tanning agent addition), and the treatment may be performed for 30 to 60 minutes.

3) When performing in the neutralization step Neutralization is usually carried out after cationic retanning, after the raw leather is washed in a water bath at about 35 ° C., and then put into a new water bath. Baking soda, sodium formate, synthetic tannin for neutralization) is added, treated for 30 to 90 minutes, and the pH is adjusted.
In this step, the leather modifier of the present invention can be added simultaneously with the addition of the neutralizing agent, for example.

4) When performing in the dyeing process Dyeing is usually performed by putting the raw leather into a water bath at about 40 ° C. and then treating with a dye-penetrating agent (for example, 0.5 to 1% ammonia water), and then uniformizing the dyeing. After treatment with a chemical (for example, 1 to 3% phenolsulfonic acid condensate), a predetermined amount of an acidic dye having a desired color is added.
In this step, the leather modifier of the present invention can be added, for example, following the treatment with the dyeing and homogenizing agent, and the treatment may be performed for about 30 minutes.

5) When performing in the greasing process When greasing is usually performed in the dyeing process bath, a predetermined greasing agent according to the purpose of the product leather to be manufactured is added to the dyeing bath, and then formic acid is added. It is done by throwing in.
In this step, the leather modifier of the present invention may be added simultaneously with the addition of a greasing agent, for example.

6) When performing in the final water treatment process The final water treatment is performed when special processing such as waterproofing is performed. Usually, the raw leather is put in a water bath at about 45 ° C. immediately before that, that is, after the greasing process. Then, a waterproofing agent (for example, 2 to 5% alkyl phosphate ester), formic acid, a metal salt (for example, basic chromium sulfate, etc.), and optionally a fatty acid metal compound (for example, aluminum stearate) are added for treatment. And finally by washing with a water bath.
In this step, the leather modifier of the present invention can be added, for example, before the waterproofing agent is added, and the treatment may be performed for about 30 minutes.

7) When performing during the finishing process The finishing process is roughly divided into (i) a wound coat for the purpose of repairing wounds and uniform drug absorption, (ii) an intermediate coat for the purpose of film formation and coloring, (iii) a touch imparting, surface Each work has a protective top coat. There are two types of solvents for finishing chemicals, using water and a mixed solvent mainly composed of methylcellulose and butylcellulose, and the aqueous solvent system has become mainstream due to problems such as working environment.

(I) The seal coat is sprayed with a chemical solution in which a plasticizer mainly composed of paraffin wax, a resin binder mainly composed of acrylic, urethane, etc., a film reinforcing aid mainly composed of milk casein, and water are mixed, or Applying to the surface with a roller coater, brush, etc., drying at room temperature or hot air, and then applying pressure to the painted surface while heating with an ironing machine such as a roll iron or hydraulic press to form a film and smooth the surface It is.
In this step, the leather modifier of the present invention is mixed with a crosslinking agent and water, applied, dried, ironed, or the leather modifying preparation alone or together with the crosslinking agent, for example, prior to the sealing coat. It can be used by mixing with pharmaceuticals.

(Ii) The intermediate coat is coated with a chemical solution containing a plasticizer based on paraffin wax, a resin binder based on acrylic, urethane, etc., an organic or inorganic pigment, and a film reinforcing aid based on milk casein. And drying and ironing.
In this step, the leather modifier of the present invention can be added, for example, alone or together with a crosslinking agent to the intermediate coating mixed agent.

(Iii) The top coat is a mixture of a touch agent mainly composed of silicon or the like, a lacquer emulsion mainly composed of cellulose acetate, a plasticizer mainly composed of paraffin wax, a film reinforcing aid mainly composed of milk casein, and water. In this process, a chemical solution is applied, dried, and ironed.
In this step, the leather modifier of the present invention can be added, for example, alone or together with a cross-linking agent to the top coat mixed medicine.

PRA (average molecular weight 5,000) manufactured by Nippi Co., Ltd. was dissolved in water as a collagen degradation product to prepare a 10% hydrolyzed collagen solution, which was used in Examples 1 and 3 below.
The keratin hydrolyzate was prepared as follows.
That is, after adding 0.5M sodium hydroxide solution to pork hair and soaking at room temperature for 12-24 hours, discard the sodium hydroxide solution and add 10 to 20 times the amount of water, and keep it at 70 ° C. Stir for 6 hours to solubilize. The extraction residue was centrifuged or filtered through a filter, the filtrate was neutralized with hydrochloric acid, desalted by ultrafiltration, and freeze-dried to obtain a keratin hydrolyzate. The obtained keratin degradation product was dissolved in water to prepare a 10% hydrolyzed keratin solution, which was used in Example 2 below.

Example 1 Treatment of Leather with Collagen Hydrolyzate Spanish sheep wet blue treated in a conventional manner was placed in a drum, washed with 300 parts by weight of water with respect to 100 parts by weight of wet blue, 200 parts by weight of water, Neutralization was performed by adding 2% sodium hydrogen carbonate and rotating for 60 minutes. Further, it was washed with water (500 parts by weight). To this, 10% hydrolyzed collagen solution was added and rotated at 50 ° C. for 30 minutes. Subsequently, an emulsified greasing agent (10 parts by weight) was added, and greasing was performed at 50 ° C. for 60 minutes. An organic acid such as formic acid was added and subjected to a rotation fixing treatment for 30 minutes, followed by hanging, drying a glass, seasoning, vibrating, and netting.

  The obtained leather was tested based on the JIS K 6550 leather test method, using as a control the leather treated in the same manner without adding only the hydrolyzed collagen solution. The results are shown in Table 1.

  As shown in Table 1, an effect of increasing the strength by about 2.1 times in the tensile cutting load was obtained. In addition, an increase in strength of about 17% was observed even in the tear and cut load.

Example 2 Treatment of Leather with Keratin Hydrolyzate Spanish sheep wet blue treated in a conventional manner was placed in a drum, washed with 300 parts by weight of water with respect to 100 parts by weight of wet blue, 200 parts by weight of water, Neutralization was performed by adding 2% sodium hydrogen carbonate and rotating for 60 minutes. Further, it was washed with water (500 parts by weight). To this, 10% keratin hydrolysis solution was added and rotated at 50 ° C. for 30 minutes. Subsequently, 10% of the emulsified greasing agent was added, and greasing was performed at 50 ° C. for 60 minutes. An organic acid such as formic acid was added and subjected to a rotation fixing treatment for 30 minutes, followed by hanging, drying the glass, adding a flavor, vibrating, and netting.
Table 2 shows the results of testing the obtained leather based on the JIS K 6550 leather test method using, as a control, leather treated in the same manner without adding only the keratin hydrolysis solution.

  As shown in Table 2, a strength increase effect of about 1.7 times was obtained in the tensile cutting load. In addition, an increase in strength of about 10% was observed even in the tearing and cutting load.

Example 3
A sample obtained by shaving the surface of a commercially available bovine leather with sandpaper was used as a sample, and a 10% hydrolyzed collagen solution was applied to the sample and dried sufficiently, followed by ironing. The leather thickness before and after treatment was measured. The results are shown in Table 3.

  It was recognized that the hydrolyzed collagen solution was selectively adsorbed on the damaged site and had a great sealing effect.

Example 4
A pig wet blue treated by a conventional method was put in a drum, washed with 300% water with respect to the weight of the wet blue, 200% water and 2% sodium hydrogen carbonate were added, and the mixture was rotated for 60 minutes for neutralization. Further, it was washed with 500% water. A 10% collagen hydrolysis solution was added thereto, and the mixture was rotated at 50 ° C. for 30 minutes. Subsequently, 10% of the emulsified greasing agent was added and greasing was performed at 50 ° C. for 60 minutes. An organic acid such as formic acid was added and subjected to a rotation fixing treatment for 30 minutes, followed by hanging, drying the glass, adding a flavor, vibrating, and netting.
The same treatment was performed on beef wet blue.

  For the obtained pig leather and cow leather, the results of testing based on the JIS K 6550 leather test method using leather treated in the same manner without adding only the collagen hydrolysis solution as the control are shown in Table 4 (pig leather) and Table 5 (respectively). Cowhide). The tensile cutting load was about 1.5 times higher for pigs and 1.3 times higher for cattle. Also, in terms of tearing and cutting load, an increase in strength of about 6% for pigs and about 60% for cows was observed.

Example 5
After degreasing and neutralizing Ethiopian sheep pickle skin that had been treated by a conventional method, 60% water, 6% sodium chloride, and 1% formic acid were added and re-pickling was performed. After adding 50% water, 6% sodium chloride, and 5% collagen hydrolyzate solution and rotating for 60 minutes, 6% chromium glaze was added and rotated for 120 minutes to perform chromium plating. After raising the basicity with sodium hydrogen carbonate, the mixture was further rotated for 180 minutes and allowed to stand until the next morning to obtain wet blue. After washing with 300% water with respect to the wet blue weight, neutralization was performed by adding 200% water and 2% sodium hydrogen carbonate and rotating for 60 minutes. Further, it was washed with 500% water. Subsequently, 10% of the emulsified greasing agent was added and greasing was performed at 50 ° C. for 60 minutes. An organic acid such as formic acid was added and subjected to a rotation fixing treatment for 30 minutes, followed by hanging, drying the glass, adding a flavor, vibrating, and netting.

Table 6 shows the results of testing the obtained leather based on the JIS K 6550 leather test method using, as a control, leather treated in the same manner without adding only the collagen hydrolysis solution.
In particular, the solidity of the leather increased, and it was possible to produce leather having various textures depending on the concentration of the collagen hydrolyzate added. Leather wrinkles have also been improved. An increase of 10% in thickness, an increase of about 1.6 times in tensile cutting load, and an increase of about 1.7 times in tear cutting load were observed.

Example 6
Rotate Spanish sheep crust leather with 400% water, 1% ammonia (1:10 solution) for 60 minutes, then add 8% collagen hydrolyzate solution, then add 200% water and rotate for 60 minutes. I let you. An organic acid such as formic acid was added and the mixture was rotated for 15 minutes, then hung, dried, dried, seasoned, vibrated, and netted.

  Table 7 shows the results of testing the obtained leather based on the JIS K 6550 leather test method using, as a control, leather treated in the same manner without adding only the collagen hydrolysis solution. In particular, the solidity of the leather increased, and it was possible to produce leather having various textures depending on the collagen addition concentration. Leather wrinkles have also been improved. A strength increase of about 10% was observed in the tensile cutting load and the tear cutting load.

Example 7
The dyed / greased leather was mixed at a ratio of 911 g of water with respect to 9 g of collagen hydrolyzate, followed by spray coating and drying.

  When the surface of the obtained leather was evaluated, as shown in Table 8, a leather excellent in surface smoothness and appearance uniformity was obtained, and a small scratch repair effect was recognized.

Claims (5)

  A leather modifier comprising a hard protein degradation product or fine powder as an active ingredient.   The leather modifier according to claim 1, wherein the hard protein is one or more selected from collagen, keratin and elastin.   A method for producing a modified leather, which comprises a step of treating with a hard protein degradation product or fine powder in the production of natural leather.   The method according to claim 3, wherein the hard protein is one or more selected from collagen, keratin and elastin.   A modified leather produced by the method according to claim 3 or 4.