Leather-like material and method for manufacturing the same

Abstract

This invention provides a leather-like material using casein and a method for producing the same. [Solution] The leather-like material is manufactured by the following steps: preparing a mixture containing casein, water, and a thickener; making the mixture alkaline and performing a first stirring; heating the mixture after the first stirring and performing a second stirring until the mixture becomes neutral; cooling the mixture after the second stirring and controlling the viscosity of the resulting material solution to a specified viscosity before drying; and placing the material solution with the specified viscosity before drying into a mold and drying it. The leather-like material is a substitute leather made using casein.

Description

[[Technical Field]]

[0001] The present invention relates to a leather-like material using casein and a method for producing the same. [[Background Art]]

[0002] In recent years, the dairy industry has faced the serious problem of excess inventory of skimmed milk powder. From raw milk, fat and skimmed milk powder are produced at a production ratio of 1:2. Of these, while there is high demand for fat for processing into butter and the like, although skimmed milk powder is processed into powdered milk and the like, demand is low and it tends to be surplus.

[0003] However, if the consumption of skimmed milk powder does not progress, the production of raw milk has no choice but to be reduced. Furthermore, when the production of raw milk decreases, domestic butter production also decreases, and to compensate for this, foreign butter is imported, which may threaten the market for domestic butter. In order to prevent such a vicious cycle and stabilize the management of dairy farmers, an expansion in the consumption of skimmed milk powder is strongly desired.

[0004] As one mode of utilizing skimmed milk powder in applications other than food, casein plastic, which uses casein, a protein extracted from skimmed milk powder, as a plastic material, is known. However, casein plastic has not spread widely because its production cost is higher than that of petroleum-derived plastics. For this reason, it is difficult to expand the consumption of skimmed milk powder in this mode.

[0005] As one mode of utilizing casein, it is also known to use casein as a coating for leather to impart gloss and durability (casein finishing). In Patent Document 1, casein is added to a leather material containing synthetic resin as a main component for the purpose of improving texture. In Patent Document 2, casein particles are added to a resin coating layer on leather for the purpose of improving air permeability. [[Prior Art Documents]] [[Patent Documents]]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 06-016952

[0007] [Patent Document 2] Japanese Patent Publication No. 2012-117154 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, until now, no leather material has been made from casein itself. Therefore, if a leather-like material can be created using casein, casein can be used in the apparel industry, leading to an increase in the consumption of skim milk powder for non-food purposes. In addition, a leather-like material made from casein would be a new ethical material that is biodegradable, environmentally friendly, does not involve the killing of animals, and reduces dairy waste.

[0009] This invention has been made in view of these circumstances, and aims to provide a leather-like material using casein and a method for producing the same. [Means for solving the problem]

[0010] To solve the above problems, a method for producing a leather-like material according to a first aspect of the present invention comprises the steps of: preparing a mixed solution containing casein, water, and a thickener; making the mixed solution alkaline and performing a first stirring; heating the mixed solution after the first stirring and performing a second stirring until the mixed solution becomes neutral; cooling the mixed solution after the second stirring and controlling the viscosity of the resulting material solution to a specified viscosity before drying; and placing the material solution with the specified viscosity before drying into a mold and drying it.

[0011] In the second embodiment of the method for manufacturing a leather-like material, in the first embodiment, it is also preferable that the specified viscosity before drying be 650 mPa·s or more and 5900 mPa·s or less. Furthermore, it is also preferable that the specified viscosity before drying be 1000 mPa·s or more and 5550 mPa·s or less. Furthermore, it is also preferable that the specified viscosity before drying be 1050 mPa·s or more and 3780 mPa·s or less.

[0012] In the third embodiment of the method for producing a leather-like material, in the first or second embodiment, the mixture is preferably prepared with 100 to 140 parts by weight of the thickener and 450 to 650 parts by weight of water per 100 parts by weight of casein. Alternatively, the mixture is preferably prepared with 110 to 122 parts by weight of the thickener and 610 to 640 parts by weight of water per 100 parts by weight of casein.

[0013] In addition, in any of the first to third embodiments, it is preferable to add ammonia water to the first stirring. Also, in any of the first to third embodiments, it is preferable to add pigment to the mixture after the second stirring. Furthermore, in any of the first to third embodiments, it is preferable to place the material solution in the mold, allow it to dry for a primary period, then cover it with a texture mold and allow it to dry for a secondary period.

[0014] To solve the above problems, a leather-like material according to a fourth aspect of the present invention comprises a base material having voids, and a casein material in which a material solution obtained by turning a mixed solution containing casein, water, and a thickener from alkaline to neutral has permeated the base material and solidified.

[0015] In the fourth embodiment, it is also preferable that the thickness of the leather-like material is 0.9 to 2.0 mm. Furthermore, in the fourth embodiment, the leather-like material is a sample with a width of approximately 6 mm and a gripping distance of 80 mm and a tensile speed of 100 tensiles per minute, and the stress is 6.9 N / mm². 2 It is also preferable that the above conditions are met. Furthermore, in a fourth embodiment, the leather-like material, in a sample with a thickness of approximately 6 mm, under conditions of a gripping distance of 80 mm and a tensile speed of 100 tensiles / min, exhibits a stress of 8.2 N / mm². 2It is also preferable that it is as described above. [Effects of the Invention]

[0016] According to the present invention, a leather-like material using casein and a method for producing the same can be provided. [Brief Description of the Drawings]

[0017] [Figure 1] It is an external appearance photograph of the example. [Figure 2] It is an external appearance photograph of the comparative example. [Figure 3] It is a cross-sectional photograph of the example. [Figure 4] It is a cross-sectional photograph of the comparative example. [Figure 5] It is a photograph of a product example. [Mode for Carrying Out the Invention]

[0018] Next, preferred embodiments of the present invention will be described with reference to the drawings. In the present invention, unless otherwise specified, the descriptions of "from ◯◯ to ××" representing numerical ranges mean numerical ranges including the lower limit and the upper limit which are the endpoints.

[0019] The leather-like material of the present invention is produced using casein, which is a protein extracted from skim milk powder. Hereinafter, the leather-like material of the present invention and the method for producing the same will be described.

[0020] The leather-like material of the present invention is obtained by solidifying a "material solution" obtained by neutralizing an alkaline "mixed solution" containing casein powder, water, and a thickener.

[0021] • Casein A method for extracting casein has already been established. Casein can be precipitated by adjusting the pH of skim milk to 4.6, separating it from the whey. For example, a solution of skim milk powder dissolved in water is precipitated with acid (or it can be further dissolved with alkali and precipitated again with acid), the precipitated mass is strained out, and the remaining acid and lactose are washed off with water and dehydrated with ethanol or the like to obtain dry powdered casein.

[0022] ·water While tap water can be used in the mixture, from a quality control standpoint, it is preferable to use purified water such as distilled water or deionized water.

[0023] • Thickening agent The thickening agent used in the mixture should provide a suitable viscosity, not react with alkaline solutions, not deteriorate when stirred at temperatures below 100°C, and have minimal impact on the human body. Glycerin and sorbitol aqueous solutions are suitable thickening agents for use in this invention, and their actual usability has been confirmed. In particular, glycerin is one of the preferred embodiments because it satisfies the above characteristics, is easily soluble in water, and has no toxicity or volatility. Other thickening polysaccharide solutions and cellulose-based solutions having the above characteristics may also be usable.

[0024] ·Composition The preferred composition of the mixed solution is 100 to 140 parts by weight of thickener and 450 to 650 parts by weight of water per 100 parts by weight of casein. More preferably, the composition is 110 to 122 parts by weight of thickener and 610 to 640 parts by weight of water per 100 parts by weight of casein.

[0025] If the amount of thickener is less than 100 parts by weight per 100 parts by weight of casein, the viscosity of the mixture is low, and the material solution described later does not reach the specified viscosity before drying, as described later. If the amount of thickener exceeds 140 parts by weight, the viscosity of the mixture is high, and the material solution described later does not fall within the specified viscosity before drying, as described later. If the amount of water is less than 450 parts by weight per 100 parts by weight of casein, there is a tendency for undissolved casein to remain in the mixture. If the amount of water exceeds 650 parts by weight, the viscosity of the mixture is low, and the material solution described later does not reach the specified viscosity before drying, as described later. In addition, the drying time tends to be prolonged in the drying process described later. If the amount of thickener is 110 to 122 parts by weight and water is 610 to 640 parts by weight per 100 parts by weight of casein, good results are obtained in the evaluation of "texture" and "rigidity" described later.

[0026] • Additives The mixture may contain preservatives, antibacterial agents, deodorants, penetrating agents, defoaming agents, lubricants, oil repellents, and stabilizers, to the extent that they do not impair the effects of the present invention.

[0027] ·Manufacturing method Step 1: First, prepare a mixture of casein powder, water, and a thickener according to the above-described formulation. It is preferable to leave the mixture for about half a day to allow the casein to hydrate. It is also preferable to seal it and store it in the refrigerator to prevent the growth of unwanted bacteria.

[0028] Step 2: Next, make the mixture alkaline and perform the first stirring. It is preferable to add an alkaline solution to the mixture. For example, add 6.4 to 12.3 parts by weight of the alkaline solution per 100 parts by weight of the mixture. To obtain a uniform reaction, add the alkaline solution in several stages. For the first stirring, a stirrer may be used or the mixture may be mixed manually. After the first stirring, confirm that the mixture is alkaline (preferably pH 9 to 10).

[0029] Here, we confirmed that aqueous ammonia and aqueous sodium hydroxide are suitable and actually usable as alkaline solutions to be added to the mixture in step 2. In particular, aqueous ammonia is one of the preferred embodiments because it is easily soluble in water, volatilizes during heating in step 3 (described later), and leaves no toxic residue. Aqueous potassium hydroxide may also be usable.

[0030] Step 3: Next, heat the mixture to advance the reaction and stir it a second time until the mixture becomes neutral. The mixture is gradually heated and maintained at approximately 80°C. For example, fill a water bath with room temperature water or oil and maintain it at approximately 90°C, then place the container with the mixture in the water bath to maintain the temperature of the mixture at approximately 80°C. Once the temperature of the mixture reaches approximately 80°C, stir it with a stirrer. Continue stirring the mixture a second time until it becomes neutral (pH 7±1). Once the mixture is neutral, remove it from the water bath. At this point, if ammonia water was used in Step 2, the ammonia will evaporate. If another alkaline solution was used in Step 2, neutralize it by adding a less toxic acidic solution such as citric acid or acetic acid.

[0031] Step 4: Next, the mixture after the second stirring is cooled to obtain the “raw material solution”. After the second stirring in Step 3, the mixture is cooled to approximately 35°C (±10°C). In this specification, the mixture in this state, i.e., the mixture after the second stirring and cooling, is referred to as the “raw material solution”.

[0032] During the cooling process, any bubbles that appear on the surface of the mixture should be removed by scooping or other means. It is also preferable to place the mixture in a vacuum chamber to promote defoaming.

[0033] At this point, the material solution, having completed step 4, moves on to drying in step 5. However, the viscosity of the material solution before moving on to this drying step is controlled to reach the "specified viscosity before drying" as shown below. The specified viscosity before drying affects the evaluation of the texture and / or stiffness of the leather-like material. (i) The specified viscosity before drying shall be between 650 mPa·s and 5900 mPa·s. By keeping it within this range, the evaluation of "not being able to be called leather" described later can be avoided. (ii) The specified viscosity before drying shall be between 1000 mPa·s and 5550 mPa·s. By keeping it within this range, the evaluation of "can be called leather" as described later can be obtained. (iii) The specified viscosity before drying shall be between 1050 mPa·s and 3780 mPa·s. By keeping it within this range, the evaluation of "equivalent to leather" described later can be obtained. Therefore, it is important to check (control) the specified viscosity of the material solution before proceeding to drying in step 5.

[0034] Step 5: Next, pour the material solution into the mold and let it dry. Set the base material in the mold, and pour the material solution onto the base material.

[0035] The base material that can be used in this invention is selected from the viewpoint of bonding with the material solution, and is thin with uniformly distributed voids throughout the material. For example, nonwoven fabrics, woven fabrics, and knitted fabrics are suitable and have been confirmed to be usable in practice. In particular, nonwoven fabrics are commercially available in thin form, and the voids created by the entanglement of fibers are maintained at a constant density, and the material solution penetrates into these voids, making it one of the preferred embodiments as an inexpensive material that satisfies the above characteristics. In addition, porous structures such as urethane foam, polyethylene foam, rubber, silicone, and synthetic resin cloth may also be usable because they possess the above characteristics.

[0036] The material solution poured into the mold can be air-dried, but it is preferable to dry it in a drying apparatus with forced convection at a temperature of 25-35°C inside the chamber. In the drying apparatus, the material solution will solidify after a drying time of 24-72 hours, depending on the desired thickness. When the material solution that has penetrated the base material solidifies (solidified casein material is formed on the base material), the leather-like material of the present invention is obtained.

[0037] Leather-like materials are manufactured to have a thickness equivalent to genuine leather. Just as the thickness of genuine leather is selected according to its intended use, the thickness of leather-like materials may also be adjusted according to its intended use. A thickness of 0.9 to 2.0 mm, commonly used for clothing, bags, wallets, and small accessories, is one preferred embodiment.

[0038] While leather-like materials can be made solely from casein, including a base material provides durability and flexibility (bendability) similar to genuine leather.

[0039] • Addition of pigments Casein material has a pale yellow (cream-colored) hue. When coloring leather-like materials, it is preferable to add the pigment after step 3 and before step 4. The pigment can be used in either powder or liquid form, but if using powder, it is preferable to dissolve it in water or a small amount of material solution before adding it.

[0040] Embossed When the material solution solidifies as is, it will have a surface similar to calf leather. To give the leather-like material a leather-like pattern or texture, it is preferable to emboss it during the drying process in step 5. For the leather-like texture mold, a resin plate or metal plate with animal skin (grain) or geometric patterns can be used.

[0041] As an example, in step 5, the base material is set in the mold, and the material solution with the specified viscosity before drying is poured onto the base material. Then, primary drying is performed in a drying apparatus for approximately half of the total drying time. That is, if the total drying time is 24 hours, the primary drying time is approximately 12 hours, and if the total drying time is 72 hours, the primary drying time is approximately 36 hours. However, this primary drying time is a guideline and may be changed while observing the condition.

[0042] After the initial drying, the textured mold coated with silicone spray is placed on top, and then a weight is placed on top. Then, it is returned to the drying apparatus for secondary drying until the total drying time has elapsed. [Examples]

[0043] The present invention will be described below with reference to examples. However, the present invention is not limited to the examples shown below.

[0044] (Preparation of Examples 1-8 and Comparative Examples 1-10)

[0045] Step 1: The mixture was prepared using casein powder, deionized water, and glycerin (a product of Fujifilm Wako Pure Chemical Industries, Ltd.). The casein powder was obtained by precipitating a solution of skim milk powder dissolved in water with acid, then dissolving it with alkali and precipitating it again with acid, filtering out the precipitated mass, washing away the remaining acid and lactose with water, and dehydrating with ethanol or the like. The composition of each mixture is shown in Table 1. The mixture was sealed and stored in a refrigerator at 4°C for half a day. Step 2: Ammonia water was added to each mixture, and a first stirring was performed using a stirrer (EYELA, MAZELA Z) at a rotation speed of 100 rpm. Step 3: Each mixture was placed in a water bath and maintained at approximately 80°C, and a second stirring was performed using the stirrer described above at a rotation speed of 400-600 rpm. Step 4: Each mixture was removed from the water bath and cooled to obtain each material solution. The viscosity of each material solution before drying is shown in Table 1. Viscosity was measured using a tuning fork vibrating viscometer (SV-A / H, manufactured by A&D Company, Limited). Step 5: A nonwoven fabric with a thickness of 0.62-0.74 mm was laid in a mold tray, and each material solution was poured in. Primary drying was performed at approximately 25°C for 5-6 hours using a drying device (KWASYO Co., Ltd. stainless steel food dryer), after which a textured mold was placed on top for secondary drying to obtain each material.

[0046] Appearance evaluations were conducted for Examples 1-8 and Comparative Examples 1-10. Appearance evaluations were based on the evaluator's visual assessment of whether the surface texture resembled leather. The evaluations are shown in Table 2.

[0047] The quality of texture transfer was evaluated for Examples 1-8 and Comparative Examples 1-10. Texture transfer was evaluated based on whether the texture was transferred clearly and uniformly. The evaluation is shown in Table 2.

[0048] For Examples 1-8 and Comparative Examples 1-10, we checked whether the materials recovered from bending. Recovery was evaluated by having evaluators manually bend each material and determine whether it recovered to roughly its original shape without significant creases or permanent deformation. The evaluations are shown in Table 2.

[0049] Tensile tests were performed on Examples 3-8 and Comparative Examples 4-9. A small benchtop testing machine (Shimadzu Corporation EZ-SX 500N) was used for the tensile tests. The thickness of each material was confirmed to be within the specified range (0.9-2.0 mm), and samples approximately 6 mm wide were used. The tests were conducted with a gripping distance of 80 mm and a tensile speed of 100 N / min. Table 1 shows the thickness and tensile stress (hardness stress) of each material. The tensile test results for eight genuine leather samples, conducted under the same conditions, showed a distribution of tensile stress (hardness stress) ranging from 9.8 to 23.3 N / mm². 2 Based on the fact that it was located at 9.8 N / mm 2 The closer it was to the ideal, the better it was judged to be.

[0050] [Table 1]

[0051] (evaluation) Each leather-like material obtained was evaluated on two axes: "texture" and "rigidity." "Texture" was evaluated using the two items described above: appearance evaluation and grain transfer. "Rigidity" was evaluated using the two items described above: resilience evaluation and tensile testing. The following criteria were used to evaluate whether each material was "equivalent to leather," "can be called leather," or "cannot be called leather." The evaluation results are shown in Table 2. Equivalent to leather: Something that satisfies both "texture" and "rigidity". Leather can be defined as something that satisfies either "texture" or "rigidity". Not really leather: Something that doesn't meet the requirements for either "texture" or "rigidity."

[0052] [Table 2]

[0053] Examples 1-5 satisfied both the "texture" and "rigidity" criteria and were equivalent to leather. Examples 6 and 7 satisfied the two criteria of "rigidity" and could therefore be considered leather. Example 8 satisfied the two criteria of "texture" and could therefore be considered leather.

[0054] Comparative Examples 1-3 did not reach the specified viscosity before drying and failed to retain their shape when poured into the mold. They also took a long time to dry. Comparative Examples 4-5 and 9-10 did not reach the specified viscosity before drying and did not spread uniformly when poured into the mold, resulting in unevenness (irregularities) on the material surface. Furthermore, Comparative Examples 4-8 and 10 did not successfully transfer the texture. Comparative Examples 6-8 reached the specified viscosity before drying and met the evaluation criteria for resilience among the "rigidity" aspects, but their tensile test values ​​were low.

[0055] Figure 1 shows an external photograph of Example 4, and Figure 2 shows an external photograph of Comparative Example 5. In Example 4, the grain transfer is clear and uniform, and the appearance has a leather-like luster and sheen. On the other hand, in Comparative Example 5, there is unevenness on the material surface, and the grain transfer is not successful.

[0056] Figure 3 is a cross-sectional image (SEM image) of Example 4, and Figure 4 is a cross-sectional image (SEM image) of Comparative Example 5. In Example 4, the material solution penetrated well into the gaps of the nonwoven fabric. Therefore, it showed good strength in the tensile test. On the other hand, in Comparative Example 5, the material solution sank to the bottom of the nonwoven fabric, and the material solution did not penetrate well into the gaps of the nonwoven fabric. Therefore, the tensile test value was low, and the durability characteristic of leather was not obtained. From the tensile test results of Examples 3 to 8 and Comparative Examples 4 to 9, the hardness stress under these conditions was 6.9 N / mm 2If the above conditions are met, the evaluation of "not being leather" will be avoided, and the hardness stress under these conditions is 8.2 N / mm 2 If the above conditions are met, it will receive a rating of "equivalent to leather" or "can be called leather."

[0057] In summary, the leather-like material according to the present invention will create new uses for casein. According to the method for producing the leather-like material according to the present invention, approximately 1 m³ can be produced from 1 kg of skim milk powder. 2 Because it is possible to manufacture leather-like materials, it can contribute to increasing the consumption of skim milk powder. Furthermore, the leather-like material according to the present invention is biodegradable, environmentally friendly, does not involve the killing of animals, and is an ethical material that reduces dairy waste. In recent years, vegan leather made from cacti, pineapples, etc. has attracted attention as an alternative leather, and the leather-like material according to the present invention can become a high value-added material that will be accepted in such a sustainable market. Figure 5 is a photograph of an example product (keychain) made from the leather-like material according to the present invention.

[0058] While preferred embodiments and variations of the present invention have been described above, these can be modified and combined based on the knowledge of those skilled in the art, and such forms are also included within the scope of the present invention.

Claims

[Claim 1] A step of preparing a mixed solution of 100 parts by weight of casein, 110 to 122 parts by weight of glycerin, and 624 parts by weight of water, The process involves making the mixture alkaline and performing a first stirring, The process involves heating the mixture after the first stirring and performing a second stirring until the mixture becomes neutral, A step of controlling the viscosity of the material solution obtained by cooling the mixture after the second stirring to a specified viscosity before drying of 1050 mPa·s or more and 3780 mPa·s or less, The process involves pouring the material solution having a specified viscosity before drying into a mold and drying it, A method for manufacturing a leather-like material, characterized by having the following characteristics.

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