Find the formula of water-based glue.

Natural rubber, vinyl resin, acrylate (emulsion polymerization), animal glue, starch glue, etc.

This adhesive is made of materials that can be dispersed or dissolved in water, some of which are the base materials of solvent-based adhesives and the main materials of liquid adhesives, as shown in Table 1.

Table 1 Main polymer specially used as water-based adhesive.

Starch and dextrin? Casein?

Trees? Glue? Sodium carboxymethyl cellulose?

Animal glue lignin?

Protein polyvinyl alcohol?

Sodium silicate?

Water-based adhesives are cheaper than the same solvent-based adhesives, and even cheap organic solvents are more expensive than water. The flammable and toxic problems of organic solvents can be eliminated by using water. However, in most cases, water-based glue must be antifreeze during storage and transportation, because it may cause permanent damage to the container or glue.

Because the government has formulated laws and regulations on the use of organic solvents, solvent-based adhesives are undoubtedly not allowed to be used in the future. The most likely products to be replaced are hot melt adhesive, 100% reactive adhesive and water-based adhesive. It is predicted that solvent-based adhesives will be almost abandoned after 2000.

Two common water-based adhesives are solutions and emulsions. The solution is made of materials that are only soluble in water or alkaline water. Water-soluble substances include animal glue, starch, dextrin, hemoglobin, methyl cellulose and polyvinyl alcohol. Substances soluble in alkaline water include casein, rosin, shellac, vinyl acetate or carboxyl-containing acrylate polymer, and carboxymethyl cellulose.

Emulsion (composite emulsion) is a stable dispersion of polymer materials mainly in water medium. Emulsion is a stable dispersion of two or more immiscible liquids suspended by a small amount of emulsifier. In the adhesive industry, the terms emulsion and latex are sometimes used interchangeably. There are three types of latex: natural latex, synthetic latex and artificial latex. Natural latex mainly comes from rubber trees. Synthetic latex is an aqueous emulsion of polymer obtained by emulsion polymerization. These polymers include polychloroprene, polybutadiene-styrene, polybutadiene-acrylonitrile, polyvinyl acetate, polyacrylate, polymethacrylate, polyvinyl chloride, polystyrene and polyvinylidene chloride. Artificial latex is a dispersion of solid polymers, including reclaimed rubber, butyl rubber, rosin, rosin derivatives, asphalt, coal tar and a large number of resin dispersions synthesized from coal and petroleum.

Emulsion adhesive is more likely to replace solvent adhesive than solution adhesive. Most emulsion adhesives are produced from polymers that are not used in adhesives, so complex formulations are needed to make adhesives have appropriate uses and properties. The construction methods of emulsion adhesive include brush coating, spray coating, roller coating, missing coating, sagging and scraping coating. The bonding method of emulsion adhesive is similar to that of solvent adhesive, and the specific method is as follows:

(1) Wet bonding can only be used if at least one adherend is porous. Usually the glue is coated on only one side, and it will stick when it is still wet or sticky.

(2) Open-air bonding This method is to coat the adhesive on both sides, and then let it stand in the open air until the adhesive still has a proper viscosity. When this method is used, at least one adherend should be porous.

(3) Contact Bonding This method is also gluing on both sides, which makes the adhesive dry and touchable, and presses the two sides together in a certain period of time, and immediately obtains the bonding strength close to the limit. This method is used for two kinds of non-porous adherends, and neoprene latex is usually bonded in this way.

(4) Solvent activation This method is to coat the adhesive on the surface of the part and let it dry. When bonding, wipe the parts with solvent or put the parts on a washer soaked with solvent to activate the adhesive and press the surfaces of the bonded parts together. This method is only applicable to small-sized parts.

(5) Heating activation This method is to coat one or two bonded surfaces with a layer of thermoplastic adhesive and dry it. When bonding, the parts are heated until the adhesive layer softens and becomes sticky, then bonded under pressure while it is hot, and firmly bonded after cooling. This method is suitable for non-porous heat-resistant materials and can also be used for continuous production lines. The adhesive is coated on the film or sheet in liquid form, heated and forced to dry to remove water, and then laminated on the other side while it is hot, usually at 12 1- 177℃.

The solid content of emulsion adhesive is 40-50%, while the solid content of solvent adhesive is about 20-30%. The main disadvantage of emulsion adhesive is that it takes a long drying time to increase viscosity and build strength. On the other hand, emulsion adhesive has good brushing performance, and the pump pressure required for spraying is smaller than that of solvent adhesive. The adhesive can be washed with water before drying. Generally speaking, the current technological level of emulsion adhesives is far behind that of solvent-based adhesives. The application of water-based adhesives such as natural latex, elastic adhesives (natural rubber), polyvinyl acetate, neoprene and styrene-butadiene rubber (SBR) was briefly introduced in the previous section.