Coating agent introduction

First, the introduction of coating agent

There are many classification methods for coating rubber. According to the chemical structure, there are mainly:

1. Polyacrylates (PA); 2. Polyurethanes (PU); 3. Polyvinyl chlorides (PVC); 4. Silicones; 5. Synthetic rubbers (such as polychloroprene).

In addition, there are also polytetrafluoroethylene, polyamide, polyester, polyethylene, polypropylene and proteins. At present, the main applications are polyacrylates and polyurethanes.

According to the medium used in the use, it is divided into two types: solvent type and water type.

The oil-based coating gel is prepared by dissolving acrylic acid or polyurethane in an oil solvent (toluene, DMF, methyl ethyl ketone, etc.) as a solvent. The advantage is that the film forming property is good, the fastness is good, and the PU can be attached with hot air glue, which is a coating glue which is generally used at present. The disadvantage is that due to the use of oily solvents, there is a lack of environmental protection, especially now that oil prices have risen, resulting in soaring oil-based solvents. Most of the coating glues use too much oily solvents because of the high cost. Environmental protection is not up to standard, and with the further improvement of environmental standards in various countries, the environmental protection requirements for coated rubber are getting higher and higher.

The water-based coating glue is obtained by emulsification of acrylic or polyurethane resin through a special emulsification device using water as a solvent. Its biggest advantages are: variety, environmental protection, low price, many coatings are now made of water-soluble glue, such as: general water-soluble PA, water-soluble PU and film glue, oily waxy, scratching paste And other functional pulp. Water solubility is the direction of coating in the future due to its functionality, environmental friendliness and low price. The disadvantages are poor film formation, poor washing fastness, and PU can not be attached to hot air glue.

According to the coating process and baking conditions, there are dry coating glue and wet coating glue, low temperature cross-linking coating glue and high temperature cross-linking coating glue. Dry and low temperature cross-linked coatings are the development trend of coated fabrics in the future due to their simple coating process, low baking temperature and energy saving.

Polyacrylate coating adhesive (Polyacrylate referred to as PA) acrylic

Performance: good sunlight and weather fastness, not easy to yellow; good transparency and compatibility, good for producing colored coated products; good washability; strong adhesion; lower cost. Poor elasticity, easy to wrinkle; poor surface finish; difficult to adjust the feel.

Polyurethane coating adhesive (Polyurethane referred to as PU)

Polyurethane is a polyurethane compound and is a polymer compound containing a -NHCOO unit in a molecular structure. The unit is formed by reacting an isocyanate group with a hydroxyl group. Polyurethane coatings are the main category of development today, and their advantages are:

The coating is soft and elastic; the coating is strong and can be used for very thin coatings; the coating is porous, has moisture permeability and aeration properties; abrasion resistance, moisture resistance and dry cleaning resistance.

The disadvantage is that:

Higher cost; poor weather resistance; hydrolysis in water, heat and alkali.

PU coating agent classification

The PU coating agent is classified into a polyester type polyurethane, a polyether type polyurethane, an aromatic isocyanate type polyurethane, and an aliphatic isocyanate type polyurethane.

According to the medium used in the use, it is divided into solvent and water.

 Solvent-based PU coating adhesive

Solvent-based PU has good tensile strength and water resistance, but is highly toxic and easy to burn. In terms of components, it is also divided into two-group classification and single-group classification. The two-component product consists of a prepolymer and a cross-linking agent, which is a hydroxyl-terminated prepolymer formed by reacting an isocyanate with an oligomeric polyol. The crosslinking agent is a compound containing a plurality of (three or more) isocyanate groups. Most of the solvent-based PU coating gels use DMF, or a mixture of toluene and isopropanol as a solvent. In order to achieve the effect of waterproofing and moisture permeable, the solvent-based coating finishing agent generally processes the fabric by a wet coating process.

Water-based PU coating adhesive

The water system is divided into two types: water-soluble and water-dispersible. The water-based PU is used for fabric coating finishing, has a large amount of surface, and has good waterproofness. Waterborne PU coatings are commonly used in dry coatings. In order to improve the water resistance, softness and durability of the coated products, the front and back waterproofing should be carried out.

From the perspective of waterproof coating, PVC is waterproof, but it will be hard and brittle in winter, easy to produce creases or breaks, and the weight is larger than PU coating. The PU coating not only overcomes the defects of the PU, but also is very waterproof. The silicone coating is similar to PU, but has better ductility and can achieve multiple PU coatings with a small applied thickness.