Why use anti-fogging agent?
Transparent plastic film, sheet or sheet, in a humid environment, when the humidity reaches below the dew point, it will condense a layer of fine water droplets on the surface, causing the surface to be fogged and fogged, hindering the transmission of light waves, for example, using film packaging products. At the same time, the contents are also invisible due to fogging, and the generated mist droplets are liable to cause damage to the contents.
Therefore, in order to improve the service life of the product, it is necessary to add a certain amount of anti-fogging agent.
What is a plastic antifogging agent?
Anti-fogging agents are some surfactants with hydrophilic groups, which can be oriented on the surface of plastics. The hydrophobic groups are inward and the hydrophilic groups are outwards, so that water can easily wet the plastic surface, and the condensed fine water droplets can rapidly diffuse to form extremely thin. The water layer or large water droplets flow down the film. In this way, the atomization caused by the light scattering of the small water droplets can be avoided, and the condensed water droplets can be prevented from falling onto the packaged object, thereby damaging the packaged object.
The chemical composition of the antifogging agent is mainly a partial esterified product of a fatty acid and a polyhydric alcohol. Commonly used polyols are glycerin, sorbitol and anhydrides thereof. Commonly used fatty acids are saturated or unsaturated acids of C11 and C12, and fatty acids having 24 or more carbon atoms can also be used. In general, esters of medium-chain fatty acids have good initial anti-fog effects; long-chain fatty acids have good long-lasting anti-fog effects. In fact, antifogging agents are often mixed esters of various acids. Many fatty acid esters of polyhydric alcohols lack hydrophilicity. By adding ethylene oxide, hydrophilicity can be improved, initial antifogging properties and low temperature antifogging can be increased. Sex.
Classification of antifogging agents
The type of plastic anti-fogging agent can be divided into two types: internal type and external type according to the manner in which the anti-fogging agent is added to the plastic.
Internal anti-fogging agent: It is added to the resin during the compounding, which is characterized by low loss and long-lasting performance, but it is difficult to obtain good anti-fog property for polymers with high crystallinity (for example, PET, PS, etc.);
External anti-fogging agent: It is applied to the surface of plastic film after being dissolved in organic solvent or water. It is easy to use and low in cost, but has poor durability and is easy to be washed away or wiped off. Only anti-fogging agent is ineffective. Use when occasions or when durability is not required.
Anti-fogging agent performance requirements
The effectiveness of antifogging agents can be divided into four types: initial anti-fog, long-lasting anti-fog, low-temperature anti-fog and high-temperature anti-fog. An anti-fog property is difficult to have four effects, and it is often selected according to the requirements of the anti-fog effect of the film.
Antifogging agents should have the following properties:
1. High anti-fog performance, rapid effect and good durability;
2. It has good thermal stability, is not easily decomposed by heat, and the decomposition product does not cause degradation of the polymer;
3, good compatibility with other additives, does not hinder the function of other additives;
4, does not affect the film's transparency, electrical properties, adhesion, pollution resistance and other functions.
Characteristics and applications of several common anti-fogging agents
1. Glycerol monooleate, white wax, can be used as an anti-fogging agent. It has good initial anti-fog property and low temperature anti-fog property. It is suitable for food packaging film. The general dosage in polyethylene is 1 to 1.5 parts, and 0.5 to 1 part in polyolefin.
2, sorbitan monopalmitate, yellow granules, is an internal anti-fog agent, effective and long-lasting effect, the amount of use in polyvinyl chloride is 1 ~ 1.7 parts.
3, sorbitan monostearate is also an internal anti-fogging agent, it is a yellow granular solid, melting point of about 60 ° C, long-lasting effect, commonly used in agricultural film, can also be used as food packaging materials, it is in the poly The amount used in the vinyl chloride is generally 1.5 to 1.8 parts, and in the polyvinyl acetate is 0.7 to 1 part.
4. Polyethylene oxide glycerin monostearate is also an internal anti-fogging agent, which is very effective and has good initial and low temperature anti-fog properties. It is a light yellow liquid with antistatic properties and is suitable for food packaging films. It is generally used in an amount of from 1 to 1.5 parts in the polyvinyl chloride and from 0.5 to 1 part in the polyolefin.
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