Polyurethane (PU) synthetic leather, with its outstanding performance of wear resistance, strength and toughness, solvent resistance, oil resistance, high cutting rate, etc. is widely used in sports and casual shoes, leather shoes, leather clothes, luggage, sofa (furniture), belts, ticket holders, stationery, car interiors, etc. It is an ideal substitute for natural leather.

However, the surface of ordinary polyurethane synthetic leather becomes moldy and cracked soon after the finished product is made, so that it is unusable and loses its value. The main reason is that the PU material contains nutrients necessary for bacteria and mold. Under the right temperature and humidity conditions, microorganisms (bacteria and mold) will multiply on PU synthetic leather. Then, the mold secretions cause biodegradation of polyurethane, resulting in mold spots and cracks on the fiber surface, shortening the service life of synthetic leather and leather.

In order to prevent PU synthetic leather being moldy, the effective way is to treated polyurethane (PU) materials with anti-mold or anti-bacterial function.

The core technology of antimicrobial synthetic leather (PU) is to choose the suitable antimicrobial anti-mildew agent and load the antimicrobial additives to the synthetic leather.

Applicable antimicrobial and anti-mildew agents

The currently applied antimicrobial agents include inorganic metal compounds, organic synthetic compounds, and natural organic extracts.

inorganic metal compounds antimicrobial agent

Example: silver-carried zeolite, silver silicate, silver zirconium phosphate, nano zinc oxide, etc.,

This class of compounds is the fastest growing antimicrobial materials. They have the advantages of long-lasting, no drug-resistant and outstanding heat resistance (600-1000 ℃ or more) so that they are widely used in the field of plastics, chemical fibers, ceramics and other materials.

organic synthetic compounds antimicrobial agent

Example: quaternary amines, biguanides, alcohols, phenols, organometallics, pyridines, imidazoles, thiophenes, etc.,

This class of antimicrobial agents has a good inhibition effect for fungi and molds but the disadvantage is the poor heat resistance stability. Besides, the agents are easy to produce drug resistance and has poor long-term effectiveness.

natural organic antimicrobial agent

Example:  chitosan

This type of antimicrobial agent is safe but poorin heat resistance. The antimicrobial efficiency is low and its large-scale commercialization is still waiting for time.

How to load the antimicrobial agent to the PU leather

The successful application of antimicrobial agents in various materials depends on whether they can be uniformly dispersed, firmly combined, stable kept in the material. Therefore, the application of antimicrobial technology is largely based on solving the problem of dissolution, dispersion and stability of antimicrobial agents in the base resin, which is a set of specialized technology and requires a targeted “tailor-made” solution.

To prepare antimicrobial anti-mildew PU leather, the dispersibility, acid and alkali resistance and antimicrobial function decrease of antimicrobial agent should be put into important consideration. Generally, inorganic antimicrobial agents with high chemical stability and good dispersion of ultra-fine particles should be selected and supplemented with good dispersion means. The production technology of antimicrobial polyurethane is complicated, and the solution is to be determined after analyzing the application, equipment conditions, and product usage characteristics.

(1) Direct addition method

The production of polyurethane leather includes transfer coating method and wet synthetic method. The so-called direct addition method is to add the antimicrobial agent in one part of the production process of PU leather, so that the antimicrobial agent is firmly loaded into the synthetic leather material.

• In the polyurethane synthetic leather produced by transfer coating method, firstly, the antimicrobial agent is added to the polyurethane slurry in a certain proportion with suitable dispersion technology. Then the slurry is pre-coated on the transfer paper to make polyurethane film, then this film is bonded to the fabric, and the polyurethane film is transferred to the fabric. Finally, the transfer paper is removed to reveal the surface of the polyurethane fabric, so that the production of antimicrobial polyurethane synthetic leather material can be completed.

•  In the polyurethane wet synthesis leather, firstly adding the antimicrobial agent in a certain proportion to the solvent-based one-component polyurethane containing the solvent dimethylformamide (DMF) and other necessary additives and coloring agents.

Then apply the coating slurry to the surface of a certain fabric, and when the fabric with the coating slurry applied enters the solidification bath (water bath), its surface layer first comes into contact with water, in which the DMF immediately diffuses into the water phase, and the concentration decrease. As a result, the concentration of DMF inside the coating is reduced, so that the internal DMF gradually diffuses to the water bath, and the water in the solidification bath also gradually diffuses to the coating layer.

Polyurethane is insoluble in water and has strong coagulation force, so the wet coating method is to use the above characteristics to form a thin film, which is rapidly solidified into a sponge-like film with continuous through micro-pores, and the antimicrobial agent is implanted into the synthetic leather material through this process.

(2) Finishing method

The antimicrobial finishing process of synthetic leather is the method to obtain the antimicrobial function on the finished polyurethane synthetic leather through the surface finishing process, such as dissolving or dispersing the antimicrobial agent into the special liquid system with high fastness to the polyurethane synthetic leather to make the antimicrobial finishing solution, and then applying the finishing solution to the surface of the synthetic leather material or products through surface painting, spraying, impregnating or dipping and rolling, etc. Finally, the antimicrobial finishing process is completed through drying and shaping, etc. The finishing process of antimicrobial finishing is completed.

Compared with the direct addition method, the finishing process is simpler and easier to operate, and it is also possible to carry out antimicrobial finishing on some finished products, but the durability and wear fastness of the antimicrobial components cannot be guaranteed. In practice, it is more ideal to use the direct addition method to implant the antimicrobial component directly into the polyurethane synthetic leather material during the processing and molding process, so that the antimicrobial component in the synthetic leather material can be released continuously and the antimicrobial efficacy will not be greatly damaged due to local slight wear on the surface.

Langyi New Materials has more than 10 years of research, development and application experience in the field of inorganic metal antimicrobial agents. The silver ion antimicrobial agent independently developed and produced by Langyi has been successfully applied to PU leather. This antibacterial PU leather has good antibacterial and anti-mildew properties. Its service life is greatly extended than ordinary PU leather. If you need to consult more related questions or test samples, please contact us.