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What is latex? | YICHANG

latex

Introduction

Latex, the general term for colloidal emulsion formed by polymer particles dispersed in water. Usually, the water dispersion system of rubber particles is called latex; the water dispersion system of resin particles is called emulsion. It can be directly used as surface coating, film, and adhesive, etc. After processing, it can be made into raw rubber and latex products (such as sponges, gloves, balloons, condoms, medical hoses, etc.), which are widely used in daily life. It can be divided into three categories: natural latex, synthetic latex, and artificial latex.


Classification

Natural rubber latex

The rubber tapped from the rubber tree (see natural rubber) is milky white, with a solid content of 30% to 40%, and the average rubber particle size is 1.06μm. Fresh natural rubber latex contains 27%~41.3% (mass) of rubber component, 44%~70% water, 0.2%~4.5% protein, 2%~5% natural resin, 0.36%~4.2% sugar, 0.4% ash . To prevent natural rubber latex from coagulating due to the action of microorganisms and enzymes, ammonia and other stabilizers are often added. To facilitate transportation and processing, natural rubber latex is concentrated to a solids content of more than 60% by centrifugation or evaporation, which is called concentrated latex. Natural rubber latex is mainly used in sponge products, extruded products, and impregnated products.

Synthetic latex

Generally, synthetic latex (such as polybutadiene latex, styrene-butadiene latex, etc.) with a solid content of 20%-30% can be prepared by emulsion polymerization. To achieve a solid content of 40% to 70%, the rubber particles are firstly agglomerated into larger particles. That is, in the industry, measures such as adjusting the polymerization formula, adding agglomerating agents, stirring, pressurizing, and freezing are mainly adopted, and then used with Natural rubber latex is concentrated similarly. Synthetic latex is mainly used in industrial sectors such as carpets, papermaking, textiles, printing, coatings, and adhesives.

Artificial latex

Non-emulsion polymerized rubber latex. It is made by adding water and surfactant to the glue liquid (such as isoprene rubber) produced by solution polymerization, dispersing rubber particles in water, and then evaporating the solvent. If the rubber cannot be fully dissolved in the solvent, the raw rubber or rubber can also be continuously kneaded in the presence of an emulsifier-containing water phase until a stable aqueous rubber dispersion is formed. The use of artificial latex is similar to that of synthetic latex.


Production of latex products

Overview

Since latex products were directly made from natural rubber latex in the 1820s, the production of latex products has developed into an important part of the rubber industry. In the 1980s, the world's rubber latex consumption accounted for about 10% of the total rubber consumption.
The production process of latex products is completely different from the processing of dry rubber. It does not require huge heavy machinery and numerous procedures. The compounding agents are all added to the latex in the form of water dispersion to make the batching latex and then gelled under the action of the coagulant. The wet gel is leached, dried, and vulcanized to obtain a product. The production methods of latex products mainly include the dipping method, foaming method, injection molding method, an extrusion method. In addition, there are electro-precipitation methods and microporous mold casting methods, but they are not widely used. The production of latex products can realize batching mechanization, feeding pipeline, process continuity, and detection automation.

Dipping method

The product model (usually made of ceramic, glass, or metal) is first immersed in a coagulant liquid (usually a divalent metal salt), and then immersed in the batching latex. The latex is gelled by the coagulant on the surface of the product model. The wet gel is dehydrated, leached, dried, and vulcanized to obtain a finished product. This method is used to make latex products with simple shapes, such as Latex Gloves, balloons, and hoses. If it is necessary to manufacture thin-walled products (such as condoms), the product model is directly impregnated with latex without impregnating coagulant.

Foaming method

It is a method of producing latex sponge products. The ingredient latex is foamed to form a latex foam, then injected into the model, and then gelled, vulcanized, demolded, washed, and dried.

Injection molding

The latex containing the gelling agent or the heat sensitizer is poured into the hot mold, the latex is gelled when heated, and the semi-finished product is demolded, which is washed, dried, and vulcanized to obtain the product. This method is used to produce thick-walled and more complex shapes.

Extrusion method

The method used to produce rubber filaments and long hoses is to extrude the latex containing the heat sensitizer through a hot mold. The latex gels when heated. This method is used to prepare hoses. If the ingredient latex is sprayed directly into the acid through the extrusion nozzle, the latex can be coagulated by the acid to form a rubber thread.

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