Update:In order to adjust the viscosity of the polyurethane adhesive to facilitate the process operation, a solvent is often us...
In order to adjust the viscosity of the
polyurethane adhesive to facilitate the process operation, a solvent is often used in the preparation and use of the polyurethane adhesive. Through the dilution of the solvent, the adhesive can be better coated on the composite film. Most of the current polyurethane adhesives for food packaging use ethyl acetate as a diluent, and alcohol-soluble polyurethane adhesives can use ethanol as a diluent. Compared with ethyl acetate, ethanol has the following advantages:
1. Toxicity
As an adhesive used for food packaging, the composite film to which it is bonded is in direct contact with food. In order to be responsible for the health and safety of consumers' bodies, not only the substrate film used for packaging must be odorless, odorless and non-toxic, but the adhesive used must also have the same properties.
LD50, which measures the toxicity of a solvent, is an index to roughly identify the magnitude of acute toxicity. It refers to the lowest dose required to poison half of a group of tested animals, and its unit is mg/kg (body weight). The larger the value, the lower the toxicity. The LD50 of ethyl acetate (rat, oral) is 5620 mg/kg, while the LD50 of ethanol (rat, oral) is 10810 mg/kg, which shows that ethanol has lower toxicity than ethyl acetate.
In addition, ethyl acetate has a strong and irritating odor, which has a great impact on the mucous membranes and can cause keratitis; ethyl acetate sticks to the skin and can cause epidermis dehydration and whitening. These hazards will not occur when alcohol-soluble polyurethane adhesives are used, so when using alcohol-soluble polyurethane adhesives to laminate films, the working environment can be optimized and the degree of poisoning of operators can be reduced.
2. remaining solvent
This is a major disadvantage of solvent-based adhesives, and a large amount of solvent used to dilute the glue needs to be removed by drying tunnels. The boiling points of ethanol and ethyl acetate are close, but because the polarity of ethyl acetate is greater than that of ethanol, it is difficult to volatilize. Under normal circumstances, ethyl acetate will cause larger solvent residues.
3. Compatible with alcohol solvent ink
At present, the printing industry has begun to transition from the solvent used in ink to benzene series such as toluene to alcohol such as ethanol and isopropanol. Alcohol-soluble polyurethane adhesives use ethanol as a solvent, which has good compatibility with alcohol-soluble inks and excellent adhesion properties. Ethyl acetate has an erosive effect on some printing inks, which will cause ink smearing, which often occurs in surface printing inks.
4. Economical
As we all know, ethanol is a raw material for the manufacture of ethyl acetate. The market price of ethanol is about 4,000 yuan/ton, while the market price of ethyl acetate is about 7,000 yuan/ton. There is a big difference between the two. In addition, the alcohol-soluble polyurethane adhesive can be cured at room temperature, saving the civil construction and heating energy costs of the curing room. Considering the above factors, alcohol-soluble polyurethane adhesive is a good product more suitable for compound manufacturers.
Development of Alcohol Solvent Polyurethane Adhesives
At present, with the vigorous development of the economy and the continuous improvement of the quality of life of the people in my country, the environmental protection of composite film packaging products has been paid more and more attention. The market needs more environmentally friendly composite adhesives, and alcohol-soluble polyurethane adhesives are environmentally friendly products that meet this demand.
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