The stabilizer used to stabilize hard and soft PVC films is generally used in an amount of 0.5%~3% of the amount of PVC. Due to the small amount, if used properly, the stabilizer has little effect on the performance (mainly physical properties) of the film. But stabilizers can affect light stability and sometimes color, water properties, transparency of transparent films, and softening point of hard films. It is also worth noting whether there is a physiological effect on the rigid packaging film.
Although the amount of stabilizer is small, it is indeed an extremely important and one of the most expensive components in the formulation for film production. Whether all the additives in polyvinyl chloride can ensure that they can meet the required requirements and can produce a film of good quality (first of all, the color is normal) when manufacturing the film, the key lies in the selection of the stabilizer and whether the ratio and dosage are correct. The stabilizers commonly used in the production of polyvinyl chloride films are introduced below. According to their functions, they can be divided into stabilizers, ultraviolet absorbers, antioxidants, etc.
1. Stabilizer
(1) Lead compounds Lead compounds include lead salts of sulfuric acid, carbonic acid, phosphoric acid, phthalic acid, and stearic acid. Lead stabilizer is the earliest variety used to stabilize polyvinyl chloride, and its thermal stabilization effect is very good, and some lead salts also have a good light stabilization effect. Clear and transparent films cannot be obtained with this stabilizer, and in the presence of hydrogen sulfide, the film will appear dark brown. For the above reasons, it cannot be used in all films.
(2) Barium soap and cadmium soap Barium and cadmium (also calcium) organic acid soaps (such as stearic acid soaps, lauric acid soaps) can often be used alone or mixed with other stabilizers as polyvinyl chloride films (especially soft polyvinyl chloride film) heat and light stabilizer. The application of barium and cadmium soaps can solve many manufacturing and application technical problems.
If the ratio is appropriate, in addition to the thermal stabilization effect, it will also produce a satisfactory light stabilization effect.
The chelating agent can form complexes with the metal chlorides produced and thereby prevent them from having a deleterious effect. At present, the commonly used admixtures are phenyl diisooctyl phosphite and triphenyl phosphite. At present, the application of liquid barium-cadmium is being expanded, and a large amount of compounding agent benzenediisooctyl phosphite and a small amount of bisphenol A and pentaerythritol are added to the liquid barium-cadmium. The stabilizer system composed of chelating agent and liquid stabilizer is often used in soft films to achieve good results.
It is well known that the compounds of barium and cadmium are not non-toxic. Calcium and zinc compounds can be used to obtain a physiologically unaffected stabilization effect.
(3) Tin compounds Dihydrocarbyl tin esters of marmic acid and lauric acid and dihydrocarbyl tin mercaptans are the most expensive, but they are also the best stabilizers for hard or soft PVC plastics. It can ensure that the transparent film has the best transparency and good thermal stabilization effect, and is mainly used for the production of suspension method PVC soft and hard transparent film. Long-chain alkyl tin compounds play a stabilizing role and at the same time ensure that the rigid film used for packaging is completely non-toxic.
(4) When the amount of pure organic stabilizer added is very small (less than 1%), the soft and hard film made of pure organic dispositionable polyvinyl chloride resin has excellent thermal stability, but it cannot be used as a light stabilizer. agent use. Diphenylthiourea, phenylindole and aminocrotonic acid are pure organic stabilizers.
(5) Epoxy compounds Epoxy compounds play both a stabilizing and plasticizing role. Hydrogen chloride can be absorbed, and the residue is well soluble with polyvinyl chloride. In PVC soft film, the maximum amount of epoxy plasticizer can reach about 20% of the total amount of plasticizer. In addition to good thermal stabilization effect, it also has good light stabilization effect, so it is often added to the film used in the open air.
2. UV Absorber
Ultraviolet absorber is a kind of stabilizer that acts as a light stabilizer, and produces a stabilizing effect by absorbing and converting the destructive ultraviolet part of sunlight. Ultraviolet absorbers are sometimes added to the film of packaging food to inhibit the effect of external light on the packaged items.
Under normal circumstances, if the UV absorber is not added to the film, when it is used outdoors, it will become brittle in two months. The service life of the film can also reach more than one year.
It is necessary to add UV absorbers to agricultural films. Tests have shown that when the amount of UV absorber is 0.2 parts, the exposure time of the film can be extended from three months to about one year (depending on the formula design of Guxiu). Commonly used UV absorbers are benzophenones, benzotriazoles, triazines, and salicylates.
There is only a narrow range of light waves in sunlight that can degrade PVC, and the most harmful is the light wave with a wavelength of 310 nanometers, which is the central band of ultraviolet light.
It has been proved in practice that under the condition of dosage of 0.3 parts, the absorption effect of triazine ultraviolet absorber is far better than that of UV-9, which can be clearly seen from the spectroscopic curve of the film in the ultraviolet region.
Among the several commonly used UV absorbers introduced, UV-531, UV-9, UV-P, TBS, RMB, etc. have relatively significant light stabilization effects, and generally can make the film withstand outdoor exposure for about fifteen months. The light stabilization effect of triazine is more prominent. Triazine, UV-531, UV-9, UV-P, UV-0 have strong absorption of light waves with wavelengths of 290-340 nm, and the transmittance is below 15%. The weather resistance of BAD is excellent, the elongation of the film is still 80% after 19 months of exposure, and no spots are produced after 20 months of exposure. To sum up, UV absorbers have the best effect, including substances that can be converted into substances that can absorb UV rays under the action of light. H.P.T and phenyl salicylate have very weak ability to absorb ultraviolet rays, and have poor light resistance and stability, but they still have a certain light resistance effect, and they will cause spots after one year of exposure. The ability of TBS and RMB to absorb ultraviolet rays is also weak, but the weather resistance is very good, and spots appear only after 15 months of exposure. To.
3. Antioxidants
Plasticizers are easily oxidized when heated and in contact with air. After the plasticizer is oxidized, not only the molecular weight is reduced, the volatilization loss is increased, but also the acid value is increased, which not only affects the plasticizing efficiency of the resin, but also affects the plastic aging and electrical insulation properties.
Commonly used antioxidants are bisphenol A and I, 1,3-tris (2-methyl-4-carboxyl-5-tert-butylphenyl) butane (trade name Topanol CA), from phthalic acid two In terms of the acid value change and heat loss of octyl ester, the antioxidant Topanol CA has a better effect on preventing the oxidation of the plasticizer dioctyl phthalate. In order to prevent oxidative degradation during long-term use in agricultural films, antioxidants, such as bisphenol A, should also be added.
The ratio of the stabilizer must be selected correctly, and the application range, production conditions and secondary processing methods of the film should be considered, and the types of PVC, plasticizers, pigments, fillers, etc. used should also be considered; also consider The influence of moisture, whether the addition will have an impact on odor and other factors.