Application Of Organo Fluorine Compounds In Leather Industry

The application of organic fluorine in leather finishing agent has been reported. It is used for the synthesis of multifunctional finishing agents, that is, the grafting of organic fluorine in molecules, so that the finishing agent has special functions, such as weathering, waterproof, oil proofing, antifouling and flame retardancy.

The pure acrylic resin has the disadvantages of thermal viscosity, crispness and poor weather resistance, so fluorinated monomers are often used in the modification of acrylic resin.

Organic fluorine and acrylate copolymer modified finishing agent has good hydrophobicity, weatherability, oil repellency and antifouling. It gives leather soft and smooth handle and is a good material for leather top coating.

However, some studies have shown that fluorine-containing monomers should account for about 70% of the comonomers in order to make the copolymers have good antifouling properties.

At present, the price of fluorinated monomer is high, so it has not been widely used.

In order to solve this problem, many experts have studied that the structure of fluoroalkyl and the structure of hydrocarbon part in perfluorinated monomer will affect its waterproofing and antifouling properties. Therefore, alkyl amine perfluoroacrylate with branched chain structure is developed, and its dosage is between 1% and 10%, so that it can obtain good waterproof and antifouling properties.

Jong et al. Introduced the concept of latex particle design, and synthesized fluorinated acrylic resin emulsion with core shell structure and fluorinated monomer as shell.

As long as a small amount of fluorinated monomer is added, the surface tension of the polymer can be reduced a lot, giving the coating excellent waterproof, oilproof and antifouling properties.

In addition, there are many reports on the application of organo fluorine compounds in waterborne polyurethane (PU) modification.

Waterborne PU has many advantages, but the coating is easy to absorb moisture, wet resistance, poor adhesion and gloss.

For this reason, a series of studies have been carried out abroad, such as adding fluorinated water repellent in the PU formula, or spraying a waterproof layer after finishing, so as to improve water resistance.

The introduction of silicon and fluorine modified PU on the main chain can combine the advantages of the two to improve the water resistance, antifouling, touch and smoothness of PU.

West Germany patent also reported the synthesis of fluorinated PU emulsion, using fluorinated surfactants, so that PU dispersed in water, excellent water resistance and oil resistance.

Dirschl and others reported 5% to 25% perfluoroalkyl two carboxylate polymers, 5% to 25% perfluoroalkyl polyurethane, 3% to 20% (methyl) acrylic acid copolymers and 3% to 15% NCO groups. The water dispersible waterproofing and oil repellent coating was synthesized by the multifunctional polyisocyanate terminated by the sealing agent. It has good storage stability and good waterproof and oil repellency. It is a new type of multifunctional finishing agent with the advantages of acrylic acid and polyurethane finishing agent.

In this regard, domestic research is relatively small, and started relatively late, such as fluorinated polyurethane top coating agent developed by Chengdu silicone Research Center, not only has good waterproof performance, but also has antifouling and oil repellency.

Wang Zema and others have synthesized fluorocarbamate finishing agent, sprayed on suede garment leather, and its oil resistance is up to 3~5 grade (AATCCTestMethod118-1997HydrocarbonResistanceTest oil resistance test method is used).

Meng Xiangchun and others have synthesized fluorinated acrylate copolymers. It is considered that the length and stacking state of perfluorocarbon chains are the key to determining water resistance and oil repellency. Fluorine-containing monomer accounts for 40% to 60% of the total number of monomers.

This copolymer can be dissolved in common solvents, and has little harm to environment and operators. It can be directly sprayed on leather surface, and can be quickly and lightly used. It can endow leather with durable waterproof and oil repellency. It is an ideal high-grade leather finishing material.

2 retanning agent

Fluorinated retanning agent is a new product developed after 1980s.

A European patent has been reported that the copolymer of maleic anhydride, long chain olefin and fluorinated olefin can be used in leather retanning, and the water repellency of leather can be improved obviously.

Bildhauer et al. Used copolymers of 20% to 40% maleic anhydride, 50% to 79% long chain olefin and 1% to 10% C6 to C12 perfluorinated terminated olefin, which were synthesized by bulk polymerization, with a weight average molecular weight of 500~20000 (determined by gel permeation chromatography).

The initiator uses two isopropyl peroxy two carbonate (IPP), peroxide benzoate, azo two isobutyl (AIBN) and so on, and its dosage is generally 0 2% to 10% of monomer quality.

In addition, redox initiators such as two phenyl ethyl ketone, dimethylaniline, ascorbic acid and heavy metal (copper, cobalt, iron, etc.) can also be used to reduce the polymerization temperature.

The copolymer has stable properties and long storage life. It is especially suitable for retanning of chrome tanned leather. It can give leather good softness, and the copolymer system does not contain emulsifiers, and is convenient to use.

The fluorinated retanning agent has promoted the development of leather industry to a large extent, but it is anionic and the problem of color fading still exists.

In the patent of Coppens, the amphoteric retanning agent is synthesized from perfluoroalkyl olefin monomer. The leather treated with it has good water resistance, oil resistance, fullness and softness, and overcomes the problem of color fading of anionic retanning agent.

This amphoteric copolymer can be polymerized with 1% to 10% fluorinated olefin, 5% to 60% unsaturated carboxyl olefin (mainly acrylic acid and methacrylic acid) and alkyl ester of more than 20% acrylic acid long chain (C8 to C40).

In the synthesis, we should pay attention to the ratio of the three. When the carboxyl content increases, the water solubility of the copolymer will increase, and the water resistance of the leather will be reduced. Otherwise, when the content of the carboxyl group is reduced, the copolymer can not penetrate into the leather fiber sufficiently, and can better adhere to it.

Therefore, we must strictly control the content of carboxyl groups in copolymers, so that they can produce certain crosslinking with leather after pre tanning, without affecting their water resistance.

In addition, other monomers or oligomers can be introduced into the copolymer in order to improve the properties of leather.

For example, in order to increase the softness of leather, short chain (methyl) butyl acrylate or monomers containing siloxane groups can be added.

In the same period, the retanning agent containing fluorosilicone has also been developed, such as the synthesis of perfluoroalkyl olefin, long chain alpha olefin and organic polysiloxane three way copolymer by emulsion polymerization.

The copolymer can also make the leather well resistant to water and oil.

Anvers et al. Used fluorinated alkyl alcohols (mercaptan, amine) and two carboxylic anhydride to replace polyalkylsiloxane to make fluorinated alkyl and carboxyl terminal fluorinated retanning agents. When retanning, spray or impregnation method is used to coat the treatment liquid on the leather surface, which is used for suede leather treatment.

In leather processing, the alkyl group in fluorosilicone and the active base (COOH - NH - OH) in leather collagen fiber are combined.

In addition, alkoxy groups can also be combined with hydrogen bonds of collagen fibers to form a crosslinking network, so as to form an organic compound network layer on the surface of leather fibers, so as to achieve the purpose of waterproofing and oil prevention.

This kind of retanning agent is also an organic fluorine prominent oil proof property and organosilicon compound outstanding waterproofing property. It has good properties of fluorine and silicon, and domestic research in this field is still blank.

3 waterproof and antifouling agents

Organic fluorine waterproofing agents are usually fluorinated compounds or polymers. Because of its low critical surface tension and directional alignment of leather fibers, the surface tension of leather can be reduced to about 20mN/m, much lower than the surface tension of water and oil.

As early as 1950s, the research and development of organic fluorine waterproofing and oil proofing agents began in foreign countries.

In 1953, 3M's Cracck first reported the application of organo fluorine compounds in water proofing and oil proofing of textile materials such as textiles, leather, paper and so on. We successfully developed an organic fluorine water proofing and anti oil treatment agent based on chromium perfluorochromic acid, and developed an organic fluorine treating agent called Scotchgard Series in 1956.

After 1970s, people began to study the polymers containing fluoroalkyl acrylic acid, and further studied the action mechanism of organic fluoropolymers. Through a series of studies on the surface characteristics of organic fluorine compounds, it was found that the increase of fluorine content in molecular structure would cause the surface tension of polymers to decrease. The surface tension of polyacrylic Fluoroalkane with perfluoroalkyl side chain was the lowest, that is, it had excellent hydrophobic and oil-free properties.

The representative products of perfluoroalkyl acrylic copolymer are FC-905 and FC-326 of Union Carbine Co, Scotchban of ZonylRP of American 3M and Scotchban of DuPont company.

Since 1980s, due to the requirements of environmental protection, people have developed water-soluble waterproofing and oil repellent agents for emulsion polymerization of fluorinated acrylic acid and non fluorinated alkane acrylic acid. These products have developed water-soluble fluorinated polyurethane waterproofing and oil repellent for German Hoechst company.

Later, the 3M company made a leather waterproof and oil resistant agent containing fluorocarbon condensates from hydroxymethylated amine or alkoxylated derivatives, containing at least 6 carbon atoms of alcohols, amine or fatty acids and vinyl monomers containing perfluorocarbon chains.

Daikin, Japan, has applied for a patent of water dispersible fluorocarbon leather waterproof and oil resistant agent with friction resistance. It is a copolymer of vinyl monomers and non fluorinated monomers containing perfluorocarbon chains.

Since twenty-first Century, foreign studies in this field have been further developed.

Soft waterproof and oil resistant agents, such as organosiloxane, fluorinated compounds and organosilicon containing amino groups, are reported by Omura et al.

This polymer has the advantages of fluorine and silicon. Compared with other polymers, it can not only give the leather surface good water resistance, oil resistance and softness, but also will not change the surface texture of leather.

In addition, fluorine containing waterproofing and antifouling agents are widely used in leather industry, but there are still some problems, such as washability and durability of leather.

Many experts have great interest in this problem, such as the introduction of three hydroxymethyl melamine, multifunctional isocyanate, N- hydroxymethylpropamide, 2- hydroxyethyl (methyl) acrylate and other monomers, but their durability has not been improved, especially washing resistance is very poor.

Some people tried to use polyphenols or sulfonated phenolic resin to treat leather, and then treated with fluorine-containing waterproofing and antifouling agents. Although this method improved the durability of leather, the washability was not ideal, and the surface of the leather was rough, and it was not resistant to dirt.

In order to solve this problem, Oharu et al. Based on the molecular structure, it is considered that the functional groups of the crosslinking agent are very close to the main chain of the polymer, and the perfluoroalkyl can not fully participate in the cross-linking reaction due to steric hindrance, so its performance is affected.

Therefore, water dispersible waterproofing and antifouling agents are synthesized from perfluoroalkyl acrylate, unsaturated chain monomer containing long chain hydrocarbon and crosslinking agent isocyanate.

This copolymer can be used to treat leather. It can make leather waterproof and antifouling. The washing resistance has been greatly improved. No emulsion, solvent and complexing fluorine containing leather antifouling agent has been studied in China. Its main components are fluoroalkyl acrylic acid, fluorosilicone and fluorine substituted organic acids.

For example, Li Huifang and others synthesized fluorinated monomers with perfluorooctanoic acid and perfluorooctane sulfonic acid, and then synthesized water-borne and oil repellent agents containing fluorinated acrylic acid through solution polymerization and emulsion polymerization with non fluorinated monomers and acrylic acid.

4 waterproofing fatliquoring agent

Organic fluorine compounds are the most effective leather waterproof materials. The leather treated by fluorine compounds is coated with oil film around the leather fibers or fluorocarbon resin thin layer on the surface of the leather fibers, so that the leather is waterproof, oil resistant and antifouling.

At present, the medium chain long perfluoroalkyl phosphate has been used in foreign countries, and waterproof and antifouling treatment for leather and garment leather.

Organic fluorine materials are very effective in waterproof, antifouling and lubrication of leather fibers, but their synthesis is difficult, pollute and high cost.

5 conclusions and Prospects

Organic fluoropolymer is an environmentally friendly product. Polymer has excellent weatherability, chemical stability, waterproof and oil repellency. It has shown great advantages in leather materials.

In order to meet the needs of the leather market and clean production and environmental protection requirements, the research direction and development trend of leather chemicals in the future are:

(1) green environment-friendly new tanning agents, such as modified plants.