JPS5812320B2 - Jiyuuhihou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a peeling method using seawater magnesia clinker as a chromium salt and a pH adjusting agent.

Generally, when animal skin is rubbed using a rubbing solution containing chromium salts, as the chromium salts are adsorbed to the skin, acid is released into the solution, and the pH of the solution is adjusted to the optimum level necessary for the rubbing operation. Therefore, it is necessary to use some kind of acid binder during the rubbing process to keep the pH of the liquid around a certain appropriate value.

Adjusting the pH of this massaging solution is extremely important when performing skin massaging; if the pH value is too low, the adsorption of chromium salts to the skin will be insufficient, resulting in insufficient massaging effect, and on the other hand, the pH value If it is too high, there is a danger that permanent chromium hydroxide precipitation will occur, making it impossible to obtain high-quality leather.

Conventionally, an acid binder (alkaline agent) such as soda carbonate or bicarbonate of soda was added to the rubbing solution during the rubbing process to adjust the pH.
A method in which chromium salt is added in several stages, or a method in which an acid binder made of a mineral double salt such as dolomite or limestone is added to the chromium salt in advance (Japanese Patent Publication No. 39-23852)
is being carried out.

However, methods using water-soluble alkali salts such as soda carbonate or bicarbonate have the disadvantage that calculated amounts of the acid binder must be carefully added at each step during the long rolling process. In the method of adding mineral double salts such as reeds, dolomite, or limestone to the chromium salt in advance, a large amount of carbon dioxide gas is often generated when adding it to the water in the drum to adjust the mixing solution. Disadvantages include overflow of the milling solution and undissolved chromium salts from the drum, or the danger of operating the drum in a closed condition, and as a result of the neutralization reaction.
The drawback is that bulky gypsum hydrate precipitates, which are deposited on the surface of the leather and rubbed, causing uneven spots and impairing the appearance and quality of the final leather. be.

The present inventors conducted various studies to eliminate the drawbacks of the conventional i-binder added to the mixing solution, and as a result, discovered that seawater magnesia clinker is an excellent acid binder, and completed the present invention. This is what I did.

That is, the present invention is a chromium salt rubbing method characterized in that it is carried out in the presence of seawater magnesia clinker as a pH adjusting agent.

The seawater magnesia clinker used in the present invention is a fired product of magnesium hydroxide and magnesium carbonate separated and collected from seawater, and has magnesium oxide as its main component.

Such seawater magnesia clinker is usually used in powder form, but its reactivity with the free acid in the mixing solution can be adjusted by adjusting the particle size, firing conditions, etc.

The amount of seawater magnesia clinker used is Mg0 per 100 parts of chromium (calculated as Cr203) used for rubbing skin.
The amount is about 5 to 30 parts, and sufficient effects can be obtained with the above amount, but there is no harm in using more than the above amount.

In carrying out the present invention, it is necessary to temporarily maintain the pH range of the rubbing solution within the preferred range described below, especially in cases where solubility is poor at low temperatures such as in winter, or in consideration of operability due to differences in skin types. In addition to the above-mentioned seawater magnesia clinker, known acid binders such as soda carbonate, sodium bicarbonate, and sodium sulfite can also be used in combination, and even in this case, the amount of seawater magnesia clinker used is the same as in the case of using it alone. 100 parts of chromium inside (Cr203 equivalent)
As mentioned above, it is desirable that the amount is at least 5 parts in terms of MgO.

The chromium salt used in the rubbing process can be either a conventional chromium salt for leather tanning or a so-called chromium rubbing agent, such as chromium sulfate, basic chromium sulfate, masked chromium salt, hexavalent chromium salt, etc. Examples include reaction products of chromium compounds and reducing agents.

Its shape may be either powder or liquid.

The seawater magnesia clinker used in the present invention slowly reacts with the acid liberated during the rubbing process over several hours, and during this period the pH of the rubbing solution is maintained in a suitable range of 2.5 to 3.9 for a long period of time.

Therefore, the amount of seawater magnesia clinker required to maintain the required pH can be added to the massaging solution from the beginning of the massaging process, eliminating the need to add it in stages like when using alkali carbonate, and permanently. No significant chromium hydroxide precipitation occurs.

In the present invention, the reaction between the free acid and the seawater magnesia clinker is typically carried out as shown in the following formula (1), and therefore, H2S040Mgo=MgSO4+H20...
(1) Only water-soluble magnesium sulfate is produced as a result of the reaction, without the generation of harmful gases or the formation of insoluble residues. Therefore, according to the present invention, workability is good and the rubbing effect is homogeneous, resulting in a silver surface. You can obtain high quality leather with no uneven color.

Furthermore, according to the present invention, since the seawater magnesia clinker has a relatively small molecular weight, it binds a large amount of free acid per unit weight. Another advantage is that relatively small amounts can be used to achieve the purpose of pH adjustment.

Further, according to the present invention, the reactivity with the free acid can be adjusted as desired depending on the type and thickness of the skin, the temperature of the liquid, and other rubbing conditions.

The present invention will be specifically explained below with reference to Examples.

In the examples, % and % are parts by weight and % by weight, respectively.

Example 22.8% Cr203, 24.0% S03 and 3
100 parts of powdered basic chromium sulfate containing 1.9% Na2SO4 are uniformly mixed with 6.1 parts of ground seawater magnesia clinker.

100 parts of the pickled raw cowhide are then rotated in a drum for 8 hours with 10 parts of the above mixture and 100 parts of water.

The temperature of the liquid in the drum is 20C at the beginning and 38C at the end.

During this time, no foaming or new insoluble residue was observed due to gas generation, and workability was good.

The leather thus obtained has a uniform and sufficient rolling effect, so it does not shrink in boiling water and has a uniform appearance.

Claims (1)

[Claims] 1. A chromium salt rubbing method characterized in that it is carried out in the presence of seawater magnesia clinker as a pH adjuster.