JPH0662999B2 - A method for producing chrome leather that has a smooth silver surface and is strong and supple - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing chrome leather with a fine grained silver surface. Specifically, by applying chrome tanning that utilizes the characteristics of chrome (V) or chrome (IV) to the bare skin in an alkaline state, the silver surface has a smooth texture that cannot be obtained with conventional chrome tanning. For more details on the chrome tanning method for obtaining a supple, supple and finely grained chrome leather, see more details on alkaline chrome (VI)
Reduction of chromium (VI) ion, which appears by immersing a bare skin that has been soaked in an acid salt solution, fully penetrated into the solution, and acclimated to the alkalinity of the solution, into a weakly acidic or alkaline reducing solution Manufactures chrome leather with a fine, grainy, supple, and supple texture of silver surface, which cannot be obtained by the conventional chrome tanning (one-bath method), which is characterized by utilizing the chrome tanning action in parallel with the reaction. On how to do.

Furthermore, the present invention relates to a method for chrome tanning bare skin under weakly alkaline conditions, or untanned artificial skin made of collagen protein under the same conditions as described above, surgical sutures or artificial organs. More specifically, the above-mentioned article is dipped in a weakly alkaline chromium (VI) salt solution to allow the liquid to sufficiently penetrate into the tissue, and the untanned artificial skin made of bare skin or collagen that has been soaked in the liquid. , Surgical sutures, chrome tanning of articles made of bare skin or collagen by immersing artificial organs in a weakly alkaline reducing solution.

At present, the chrome tanning method applied to bare skin and other articles made of collagen is mainly the "one-bath chrome tanning method". This method has been practiced for the past 100 years, and basic chromium (III) salt (mainly sulfate) is used as a chrome tanning agent, and the bare skin is placed in an aqueous solution (chrome tanning solution) of an appropriate concentration. While soaking, the solution is chrome tanned slowly over a narrow acidic range of pH 2.5 to 3.8.

Before the one-bath method, the two-bath method chrome tanning was performed. This is done by immersing bare skin in an acid solution of dichromic acid (dichromic acid), soaking it in the skin, and then thiosulfate-hydrochloric acid. It was soaked in the solution and tanned with chromium (III) produced by the reduction, but the reaction liquid was all acidic. As described above, all the conventional chrome tanning is performed in the acidic bath liquid.

Chromium (III) in the chrome tanning agent easily forms turbidity and precipitates like chromium (III) hydroxide at pH 4 or above. This phenomenon may lead to a marked decrease in the efficiency of chrome tanning and deterioration of the product. Therefore, in the conventional chrome tanning, a pickling treatment is always performed immediately before that in order to make the bare skin acidic.

JH Highbeger is
GLCA 31, 345 (1936) reported that the degree of swelling of a few pieces of steerhide dipped in aqueous solutions having different pHs was minimized in the pH value range of 7-10 of the dipping solution. It is considered that the results of this experiment show that the collagen tissue of the naked skin becomes the densest in the range of pH 7-10. Therefore, it is considered that the silver surface tissue composed of collagen is also most dense under the same conditions. That is, the organization of the leather itself becomes dense, and as a result, the waist becomes strong and supple. For the purpose of actually investigating this, the same experiment as in the above-mentioned literature was conducted on a bare skin piece cut from the same steer half-cut, and the silver surface of the sample immersed in an alkaline aqueous solution (containing 5% sodium chloride) was medium. It was confirmed that the sample soaked in a neutral or acidic solution (containing 5% sodium chloride) had a more velvety texture and a firmer and more supple texture. However, it was recognized that the silver surface had such a fine texture when the pH of the immersion liquid was 9 or more, and it was not clearly observed at pH 7 to 8.5. This means that the minimum swelling degree of collagen protein in the above literature is
Suggests that there is a considerable gap between and.

To apply chrome tanning to the bare skin in the alkaline state,
The conventional chrome tanning method is not suitable. One of the reasons is that chromium (III) ion is a typical substitutional and inactive metal ion, and therefore the coordination rate with free amino groups and carboxyl ions in collagen fiber tissue of naked skin is remarkably low. That is. Another reason is that chromium (III) ions easily form turbidity or precipitates like chromium (III) hydroxide, which is hardly soluble in water, in a solution having a pH of 4 or more. These significantly reduce the tanning effect of bare skin.

In order to search for a chrome tanning method suitable for bare skin in an alkaline state, various considerations and experiments were tried. As a result, they have found that a chromium tanning method using chromium (V) ions or chromium (IV) ions instead of chromium (III) is effective.

The object of the present invention is a method for producing chrome leather with a fine silver surface by subjecting bare leather in an alkaline state to chrome tanning using chromium (V) ions and / or chromium (IV) ions. Is to provide.

That is, the present invention comprises a steer, a kip, a calf or a bark of a beast other than a cow (hereinafter referred to as A) containing an alkaline chromium (VI) salt having a pH of 8.6 or more and, if necessary, a masking agent. The solution is soaked in a solution (hereinafter referred to as “B”) to sufficiently infiltrate the chromium (VI) acid salt solution into the skin and then taken out, and the pH is 3.5 to 10.5, and a reducing agent containing a masking agent as necessary. It is a method for producing chrome leather having a fine silver surface and fine grain, which is characterized by immersing in a solution (hereinafter referred to as C).

If the pH of the solution B is 8.6 or more, the chromium (V
I) The oxidative effect of acids is not significant and does not impair bare skin and articles of collagen composition. Also, the texture of the silver surface can be maintained in a fine state. However, when the pH of the solution B is 11 or more, the naked skin and the article having the collagen composition swell and are further hydrolyzed, so that the pH of the solution B is preferably 9.6 to 11.

In addition, artificial skin in an untanned state produced by regenerating solubilized collagen, surgical sutures, artificial organs, etc. also swell easily when immersed in a solution having a pH of 4 or less, causing sticking, and further. It dissolves, so it is roomy aldehyde,
It is necessary to pre-tanning with glutaraldehyde. Therefore, there has been a demand for a chrome tanning method in a neutral or alkaline liquid state.

The present invention can also solve this problem. That is, the present invention is a solution containing an alkaline chrome (VI) salt having a pH of 8.6 or more for artificial skin in an untanned state produced by regenerating solubilized collagen, surgical suture or other artificial organs ( The product is soaked in a masking agent (if necessary) so that the chromium (VI) acid salt solution is sufficiently permeated into the inside of the article, and then taken out, and a reducing solution having a pH of 3.5 to 10.5 (a masking agent is added if necessary). Method).

Further, the present invention provides that the leather tanned by the above-mentioned method of the present invention, or the article treated by the above-mentioned method of the present invention is further re-tanned by conventional chrome tanning or other tanning. Can be done That is, the chrome leather thus pretanned by the method of the present invention is further subjected to conventional chrome tanning, tannin tanning, alumina tanning, synthetic tannin tanning, and zirconium tanning throat, even when the chrome tanning is performed by the method of the present invention. While maintaining the finely grained silver surface seen in leather, the texture of the leather itself can be made strong and supple. Therefore, the present invention provides that the leather tanned by the method of the present invention described above, or the article tanned by the method of the present invention, is re-tanned by conventional chrome tanning or other tanning. Provide a way to do it.

In the natural world, chromium (II
Only I) and chromium (VI) ion are stable. All other chromium (II), chromium (IV) and chromium (V) ions are generally unstable and tend to be easily oxidized or reduced to change to chromium (III) or chromium (VI) ion. There is. Since it is almost impossible to take out chromium (V) or chromium (IV) as crystals of their salts and to store them as a solution without changing them for a long time, these chromium (V) and chrome (IV) for tanning of the present invention can be used. It is not possible to prepare a stable solution of chromium metal ions.

Further, chromium (VI) in an acidic solution [in an acidic solution, chromium (VI) acid is mainly dichromic (VI) acid. ] The fact that chromium (IV) and chromium (V) ions are generated during the reduction process of ions means that K. Jabltswinski (K. Jablins
czinski), Zite Schrift Anorga Chemie (Z.anorg, Chem.), 60, 38-49 (1908) and others, showing that chromium (VI) ion in weakly acidic, especially alkaline solutions No literature is found on the formation of these chromium metal ions on reduction. However, under the conditions applicable to the reduction of the chromium (VI) ion of the present invention, these chromium (V), chromium (IV)
It is inferred from the following description that ions will be generated.

The reduction reaction of chromium (VI) to chromium (III) involves transfer of three electrons as a whole. The reducing agent to chromium (VI) used in the present invention, on the other hand (SO ₃ ^{2 -,
_{S 2 O 3 2 -, S}} 2 O 4 2 -) is one or two mobile number of electrons participates in reducing both (Latimer (Latime
r); Oxidation Potentials, 2nd edition, (195
2), Prentice Hall], not three. From the standpoint of reaction kinetics, it is considered that chromium (VI) does not directly generate chromium (III), but that chromium (V) or chromium (IV) is used as an intermediate product. .

Chrome leather refers to the state in which chromium (III) and the skin are bound together, so even in chrome tanning that uses chromium (V) or chromium (IV), these chromium metal ions bound to the bare skin are ultimately Must be reduced to chromium (III).
If this point is taken into consideration, it is presumed that the method of utilizing the chromium metal ion generated in the process of reducing the chromium (VI) ion to chromium (III) is rational. I tried to set tanning conditions. Among the specific experimental items, the most important and technically difficult points are: a) short-lived chromium (V) or chromium (IV) produced by reduction of chromium (VI) ion, and naked Efficient binding between amino groups and carboxyl ions of the collagen fibers of the skin, and (2) suppressing the formation of the colloid (III) hydroxide-like precipitate, which is a by-product of the reaction.

Chromium (V) ion or Chromium (IV) in b)
The heterogeneous reaction between the ions and the functional groups of the naked skin is a heterogeneous reaction between the liquid phase and the solid phase and the short life of their chromium metal ions reduces the yield of the reaction. It becomes a factor. However, the property that chromium (V) and chromium (IV) have a substitution activity accelerates coordination with amino groups and carboxyl ions of collagen fibers. It is considered to be effective in improving the efficiency of the coordination reaction between groups.

Regarding (b), some of the chromium (V) or chromium (IV) ions generated in the reducing solution C are reduced to chromium (III) without forming a coordinate bond with the skin functional group, When the pH of the reducing solution C is 4 or more and the solution does not contain a substance that binds to chromium metal ions,
They become cloudy or precipitate as chromium (III) hydroxide. In order to suppress this, it is necessary to add an appropriate masking agent to the chromium (VI) acid solution B or the reducing solution C or both solutions.

Examples of the masking agent include phosphate or other inorganic salts, or organic carboxylic acid such as formic acid. This masking agent is 0.5 to 3% in solution B
In solution C, 1.0 to 4.5% of the weight of bare bare skin using organic carboxylic acid is used. However, in solutions B and C, ammonia is used as the free ammonia concentration.
When the content is 0.7% or more, it is not always necessary to add a masking agent to both solutions.

Most preferably, the water-soluble chromium (III) complex formed by the coordination of this masking agent slowly undergoes a substitution reaction with the functional groups of the skin. Alternatively, it may flow away without causing a substitution reaction.

That is, when the reducing solution C is not ammonia-alkaline, an inorganic acid salt such as phosphate or an organic carboxylic acid such as formic acid is added to the chromium (VI) acid salt solution B as a masking agent. % Or less, turbidity or precipitation like chromium (III) hydroxide is likely to occur in the reducing solution C. On the other hand, when the content is 3% or more, the amount of chromium bound to bare skin or an article having a collagen composition decreases, and in the case of phosphate, chromium leather becomes greenish. The same applies to the amount of the masking agent used in the solution C being 1.0 to 4.5% of the weight of the bare skin in the wet state or the article of the collagen composition.

However, when free ammonia is present in solutions B and C in an amount of 0.7% or more as ammonia, chromium (III) that does not bind to bare skin or an article of collagen composition is dissolved as an ammine complex of chromium (III). Therefore, in the reducing solution C, turbidity like chromium (III) hydroxide and precipitation do not occur. Therefore, no masking agent is required.

Regarding the chromium (VI) acid ion concentration in solution B,
Depending on the amount of chromium bound in the chrome leather or the article of chrome-tanned collagen composition, CrO ₄ ^{2 in} solution B
^{It is determined by the} ion concentration and the weight ratio of CrO ₄ ^{2 −} to the article of wet bare skin or untanned collagen composition used. Therefore, CrO ₄ ^{2 -} ion concentration the amount of chromium bonded becomes small at 2.2% or less, tanning efficiency decreases. CrO
₄ ^{2 -} concentration is 6.5% or more occurs tends chromium dissolved in the solution without binding to collagen (III) is increased.

Examples of the reducing agent used in the reducing solution C include dithionite. And, if necessary, a sulfite salt, a hydrogen sulfite salt, a thiosulfate salt or the like can be used in combination therewith. The necessary amount of the reducing agent added to the reducing solution C efficiently reduces the chromium (VI) ion contained in the article of bare skin or collagen composition, and binds chromium (III) to collagen. The purpose was to keep the amount within the required range and to reduce the amount of unbound chromium (III) as much as possible. Furthermore, the fact that the pH of the reducing solution C is 3.5 to 10.5 takes into consideration the temperature, time, etc. of the chrome tanning condition caused by the reduction of the chromium (VI) salt contained in the article of bare skin and collagen composition. Is defined as the required pH range when
Above pH 10.5, reduction with dithionite, sulfite and thiosulfate does not occur easily and quickly. Also pH
When it is 3.5 or less, the fineness of the silver surface of the obtained chrome leather tends to be lost.

In the chrome tanning of the present invention, there are two cases, that is, a case where a masking agent is not required as in Example 1 below and a case where it is required as in Example 2.

Example 1 540 kg of bare skin (40 pieces of half cut) prepared by preliminarily performing deliming and baking on steered hide is treated with 1000 L of ammonia-alkali 3.3% ammonium chromium (VI) acid solution.
Rotate for about 10 hours in a drum together with (pH 9.6) to allow the chromic (VI) acid solution to fully penetrate into the skin, and after removing the chromic (VI) acid solution, 4.5% sodium dithionite ammonia Alkaline solution 500 L (pH 9.
Inject 5) and rotate for 60 minutes. At this time, 5 and 15 minutes after injecting the liquid, divided into two
Add 70 L of 28% sodium dithionite solution. The pH at this time is about 9.2. After that, heat it to 40 ℃ and keep it at the same temperature for about 3 hours. The leather is soaked in 1000 L of water at room temperature and rotated for about 10 minutes every hour for 3 hours, and then left overnight to wash away unbound chromium (III) and salts.

Visual observation with a naked eye and a magnifying glass shows that the appearance of the chrome leather according to this formulation is light reddish purple, and the texture of the silver surface is more detailed than the chrome leather obtained by the conventional chrome tanning from the same raw leather, It was recognized that the leather itself was strong and supple and had fine grain.

Chromium leather analysis results: Cr ₂ O ₃ content 1.8-2.2% Ts (heat shrinkage temperature) 85-90 ℃ Even when using bare leather that has undergone preparatory work such as deliming, baking and pickling as steer raw leather. Similar results were obtained.

Example 2 480 kg of raw steared leather (33 pieces of half cut) which had undergone the preparatory process described in Example 1 was treated with 3.0% ammonium chromium (VI) ate, 1.0%.
Put it in a drum together with 950 L (pH 9.5) of ammoniacal alkaline solution of trisodium phosphate dodecahydrate and leave it overnight while rotating occasionally. Drain the liquid from the drum, 7.2%
Inject 500 L of a solution containing sodium bisulfite and 2.5% sodium dithionite (pH 5 to 6) and rotate. Five minutes after the injection of the liquid, 3.5% of formic acid in the bare skin is added. After 10 minutes, 35% sulfuric acid, which is 1.9% of the amount of bare skin, is added. The pH at this time is 4. Rotate continuously for 60 minutes from the time of injection of reducing solution. Then raise the temperature to 40 ° C at 20 minute intervals
Keep the same temperature for 3 hours while rotating for 10 minutes. The pH of the liquid in this case is approximately 4. The chrome leather is left for two days at room temperature in a reducing solution and occasionally rotated to promote the oarization. Remove the liquid, add 900 L of water and rotate to wash, replace water until the smell of sulfite disappears, and wash. The obtained chrome leather had a more smooth silver surface and was more supple and supple than the one obtained by treating the raw material of the same raw material by the conventional method.

Analysis value of chrome leather: Cr ₂ O ₃ content 2.8 to 3.4% Ts (heat shrink temperature) 98 to 105 ° C.

Example 3 54 g of an untanned surgical suture prepared by regenerating a solubilized collagen solution (in a wet state in which free water was wiped off with a blotter) was used as an ammoniacal solution of 3.6% ammonium chromium (VI) ate. Soak it in 100 ml (pH 9.6) and allow it to fully adapt to the liquid. Remove the thread from the liquid, and use 60% ammonia-alkaline reducing solution of 4.5% sodium dithionite.
Soak in (pH9.5) and stir well for 60 minutes. In this case, 1.5 minutes each of solid sodium dithionite powder is added 10 minutes and 20 minutes after the immersion in the reducing solution. Thereafter, the mixture is heated to 40 ° C. and kept at the same temperature while stirring for about 2 hours, and then left for 2 hours, and then unbound chromium (III) and salts are washed away with water. The resulting chrome-tanned surgical suture has a reddish purple appearance and no sticking. (Agglutination is often observed in the conventional method.) Cr ₂ O ₃ content 2.0% Example 4 5% of 62 Kg bare steered skin (wet state, 5 half-cuts) after completion of preparatory work up to pickling Soak in 150 L of ammonia buffer containing ammonia and 2% ammonium chloride and let stand overnight. Then, it is rotated for about 3 hours in a drum together with 100 L of ammonium-alkali 3.3% ammonium chromate (VI) (pH 9.4) so that the chromium (VI) acid salt solution is thoroughly penetrated inside the skin. After the chromium (VI) salt solution has been drawn off, 55 L (pH 9) of 4.5% sodium dithionite in ammoniacal alkaline solution is injected and the mixture is rotated for 60 minutes. In this case, 5 and 15 minutes after the completion of the injection, 7 L of 28% sodium dithionite solution is added. After that, heat to 40 ° C and rotate occasionally while maintaining the same temperature for about 3 hours. The leather is soaked in 120 L of water at room temperature and rotated for about 10 minutes every hour for 3 hours, and then unbound chromium (III) and salts are washed away.

The chrome leather that had been subjected to the front tanning was immersed in 31 L of water at 30 ° C., a formic acid solution (a solution in which 250 g of 100% formic acid was dissolved in 3.1 L of water) was added, and the mixture was rotated for 10 minutes (pH 2.8). Add 5.1 Kg of bare chrome containing 17.2% Cr and rotate for 60 minutes. Next, a solution prepared by dissolving 1.0 kg of sodium hydrogen carbonate in 12 L of water was added to the above tanning solution in the following manner. First add 1/3 volume and rotate for 20 minutes (pH of tanning solution
3.1), then add 1/3 volume and rotate for 20 minutes (tanning solution pH 3.
4) Add the final 1/3 volume and spin for 40 minutes (tanning solution pH
3.7). 31 L of water was added, the temperature was raised to 40 ° C., stirring was continued for 3 hours, and the mixture was left standing overnight. The leather is taken out of the immersion liquid and left to stand for 3 to 5 hours in the liquid-containing state so as not to dry.
Then, it was immersed in 120 L of water (200% of the bare leather) to wash out unbound chromium (III) ions and other salts contained in the leather. The silver surface of the obtained leather had a smoother silver surface and was supple and supple, as compared with the chrome leather obtained from the same bare leather only by the conventional method. This suggests that the front tanning determines the state of the silver surface and the suppleness of the leather.

Analysis Results Cr ₂ O ₃ content rate 3.6% Ts (heat shrinkage temperature) 110 ° C. Above, specific examples of the present invention are shown, but it is clear that the present invention is not limited to these, and It is also obvious that various improvements can be made without departing from the scope and spirit of the invention, and these all fall within the scope of the invention.

Claims (8)

[Claims] 1. A steer, a kip, a calf or a bark of an animal other than a cow is soaked in a solution containing an alkaline chromium (VI) salt having a pH of 8.6 to 11 and optionally a masking agent. A silver surface texture characterized by immersing a solution of chromium (VI) in the inside of the skin, taking it out, and immersing it in a reducing solution having a pH of 3.5 to 10.5 and optionally a masking agent. A method for producing fine, finely grained chrome leather. 2. The naked skin is mainly a naked skin that has been prepared in an alkaline or neutral solution until deliming or baking, or a naked skin that has been pickled, and further an aqueous ammonia or other alkaline solution. The method according to claim 1, which means a bare skin immersed in an aqueous solution. 3. A chromium (VI) salt solution has a pH of 8.6.
To 11 by weight, and chromium (VI) ion concentration in the liquid CrO ₄ ^{2 -} is 2.2 to 6.5% as a whole CrO
₄ ^{2 -} 3 with respect to the weight of the pelts wet weight is used
The method of claim 1 which is meant to be in the range of -15%. 4. The reducing agent used in the reducing solution is a reducing agent mainly containing dithionite, and a sulfite, hydrogen sulfite, thiosulfate or the like used in combination therewith as required. The method according to Item 1. 5. When the reducing solution is not ammonia-alkaline, a phosphate (or other inorganic salt) or an organic carboxylic acid such as formic acid is added as a masking agent to the chromium (VI) salt solution at a concentration of 0.5 to 3.0. %, And an organic carboxylic acid such as formic acid is added to the reducing solution in an amount of 1.0 to 4.5% of the weight of the bare bark used. 6. A solution containing an alkaline chromium (VI) salt having a pH value of 8.6 to 11 and a reducing solution having a pH value of 3.5 to 10.5, which contains 0.7% or more of ammonia as a free ammonia concentration, The method according to claim 1, wherein a masking agent is not necessarily added to the both liquids. 7. Application of the chrome tanning according to claim 1 to an untanned artificial skin produced by regenerating solubilized collagen, a surgical suture or other artificial organs. 8. Leather tanned by the method according to claim 1, or untanned artificial skin produced by regenerating solubilized collagen, surgical sutures or other artificial organs. Retanning by chrome tanning or other tanning.