Leather fatting and application of fatting agent

Grease is an important process in leather processing, it can give the finished leather with soft, plump, elastic and other good hand feel and greatly improve its physical properties. Leather fat additive is generally composed of emulsifier, neutral oil and fat additive. The neutral oil in the fat material is emulsified by the emulsifier and brought into the finished leather. The ratio of the sexual fat (or modified fat) to the emulsifier and the type of active group have considerable influence on the efficiency of the fat.

There are a variety of classification methods of leather fat agent, but generally can be divided into two categories, one is synthetic fat agent, the other is compound, functional type fat agent, but from the product composition and function point of view, in recent years, fat agent more toward compound, functional type development.

1, synthetic fat agent

The main sources of raw materials for synthetic fat additives are petroleum and petrochemicals. The former is paraffin, mineral oil, the latter is fatty acids, fatty acid esters, fatty amides and fatty alcohols. Synthesis methods include: sulfonation, sulfation, chlorination, sulfonic chloride, aliphatic amide, etc., the product has a good bond to leather, light resistance and mercerization performance.

2, compound, functional fat agent

2.1 Combined fat filler

After the 1980s, there has been a boom in the development of binding type fatening agent in China. The so-called binding type fatening agent has a variety of active bases that can permanently bind with leather collagen or chromium ions on leather, thereby reducing the loss of oil in leather. The binding type of fatting agent is generally obtained by introducing sufficient active groups in the oil molecules that can bind to leather, by the reaction of the oil and alkyl alcohol amine, and then introducing carboxyl and sulfonic acid groups. Dry cleaning resistant fat additives are mainly based on the high activity of alkyl alcohol amides. In China, Liu Yisheng et al. first used the method of amidation and esterification of rapeseed oil to produce hydroxyethyl fatty amide succinate sulfonate-type binding fat agent. After fat addition, the leather has good fullness, clean leather surface, good wax, good mercerization and strong binding force. Then, according to this synthesis method, the products of RCF binding type fat filler and CM-1 binding type fat filler were synthesized by using castor oil, cottonseed oil and other raw materials, which met the domestic demand for binding type fat filler. However, as far as the application of the most common SCF grease agent is concerned, the defects of poor emulsification, low electrolyte resistance and poor penetration also affect its performance. To solve the above problems, Li Ming adopted the method of fatty acid methyl ester amidation and introduction of carboxyl group, sulfonation and introduction of sulfonic acid group to prepare TCF binding compound fatening agent. The fatening effect is outstanding, the product emulsification is good, the permeability is strong, the absorption and binding of leather is fast, and the leather is plump and oily.

3 Phospholipid fatty agent

Phospholipid fat additives are generally divided into two kinds: one is directly compounded with natural phospholipids into fat additives, such as Lyu Xuyong, etc., with sulfated castor oil, Pingjia and soybean phospholipid compound preparation of fat additives, which is characterized by good filling to make the skin significantly thicker. Shen Yding et al. used soybean phospholipid, mineral oil, modified mineral oil, high carbon alcohol and soybean alkyl amide to prepare a multifunctional phosphoric acid fatting agent, which made the leather waxy, soft and waterproof. In addition, other domestic units have also synthesized a variety of phospholipid fat additives by means of compounding.

The other is to phospholipify the oil (mainly castor oil), and then combine with phospholipids and other auxiliaries to make a phosphate ester fat agent. For example, Zheng Tao uses castor oil and methanol for transesterification, and uses phosphoric acid as phosphorylation agent to synthesize phosphate-based products and other products for leather fatening, and its oil lubricity and fullness are ideal. Phosphorous pentoxide has also been used for lipid phosphorylation modification in China, but there are some problems in controlling the reaction. The product tends to be mainly alkyl phosphate based on synthetic single ester. This structure is used to treat leather fat, and its softness, elasticity and water resistance are more guaranteed.

4 Containing silicone grease agent

Silicone monomer is introduced into the grease agent mainly because of its good lubricity and water resistance. According to reports, the static water absorption of the silicone waterproof leather is reduced from 105% without treatment to 10-30% after treatment, and the dynamic flexure can reach more than 10,000 times, and the finished leather shows good performance. Wang Baohe et al modified vegetable oil and hydroxy-terminated polysiloxane for grafting and then sulfated treatment, leather after this grease has a strong: "silicon". Zhang Zhongcheng grafted dimethyldichlorosilane with modified soybean oil so that silicone would not migrate in leather fatening due to its polarity. The product is applied to suede leather, soft leather and other obvious effect, the leather is soft, smooth, mercerizing and has a certain waterproof.

5 Electrolyte resistant grease agent

The electrolyte resistance of the fat emulsion is based on the requirements of the step fat of leather. In the practice of acid soaking and chrome tanning, the fat emulsion needs to have sufficient acid resistance and electrolyte resistance stability. Cationic or positive/non-ionic fatening agent made of cetyl trimethyl ammonium chloride, motor oil, petroleum and nonylphenol polyoxyethylene ether is the earliest fatening agent used in acid leaching and chrome tanning stage in China. This kind of fatting agent embodies the characteristics of acid resistance and chromium tanning liquor resistance in use. However, due to the single function, there are also some problems, such as poor absorption, and the use of other fat-adding and retanning materials in the same bath. In view of the above problems, in recent years, all units have given priority to the development of fat additives, and the products produced have their own characteristics.

First of all, the raw materials are directly synthesized. For example, Li Ming used stearic acid and amino alcohol to synthesize weak cationic emulsifier in the development of acid-resistant multi-functional fat agent, and then combined with non-ionic surfactants-polyolefin-chloroalkanes, etc. The product has a wide PH range, good fullness and elasticity of leather after fat, and smooth suffon. Guan et al. selected long chain unsaturated fatty acids or their derivatives to be esterified with polyethylene glycol and then sulfited to make the product have excellent properties. Qing Ning et al. 's NAF fatening agent, which was synthesized by ethoxylation, phosphorylation and sulfite of animal and vegetable oil polyethylene glycol, has excellent acid and electrolyte resistance. After fatening of leather, it is soft, plump, mercerized and elastic. Because of the wide range of adaptation, outstanding characteristics, multi-function is also the current research aspects of fat additives.

6 Compound, multi-performance fat agent

It is a direction to develop fatening agent to compound and multi-performance. From the development of tannery industry to the demand for fat agent, fat agent needs more and better performance. Traditionally, it is difficult to meet the requirements of leather upgrading with single animal and vegetable oil fatening agent. Compound fatting agent has been recognized in China, and some products have been developed and produced successively. Such as OES compound fat agent, S-4 fat agent, SQ-1 compound fat agent and so on. The composition of raw materials mainly uses more than four kinds of fat-adding components, basically all kinds of animal, vegetable oil, synthetic ester and its sulfation, sulfonation, sulfite, mineral oil and chlorination, oxidation, ethoxylation, sulfonyl chloride, lanolin and its derivatives, plus change the ionicity of the fat agent or increase the emulsification, permeability of surfactants and other additives. The synthetic fat additive and electrolyte resistant fat additive mentioned earlier in this paper are also the combination of multiple components. SG series of Chen Mingyue leather fat agent used more than 15 components, the series of products outstanding fat performance.