Rubber can be divided into unvulcanized rubber (hereinafter referred to as rubber compound) and vulcanized rubber (hereinafter referred to as products), and rubber frosting includes frosting on the surface of rubber compound and frosting on the surface of products. Frosting is a phenomenon that liquid or solid compounding agent migrates from the inside of rubber to the surface of rubber. When the compounding agent in rubber precipitates, frost spraying is formed.
II. Orms of Blooming
To sum up, the forms of rubber frosting can be roughly divided into three types. That is, powder spraying, wax spraying and oil spraying (also known as exudation).
Powder spraying is that powder additives such as vulcanizing agent, accelerator, activator, antioxidant and filler are precipitated on the rubber surface to form a layer of powder.
Wax spraying is that wax, such as paraffin wax and ceresin, precipitates on the rubber surface to form a wax film.
Oil spraying is that liquid additives such as softener, tackifier, lubricant and plasticizer are precipitated on the rubber surface to form a layer of oil.
III. Causes of Blooming
In practice, the form of frosting on rubber surface sometimes appears in one form, but sometimes it appears in two or three forms at the same time. Improper formula design:
Saturated spraying: it is common in sulfur, accelerant, activator, antioxidant, etc.
Migration outgassing: it is common in processing AIDS, migration antioxidants, antistatic agents, etc.
Generation of spray: it is commonly used in sulfur vulcanization system to promote the combination of reaction products.
Reaction retention: common in organic peroxide curing system with excessive low molecular weight substances.
Stress ejection: common in inorganic fillers, such as calcium carbonate. Improper process operation and uneven mixing lead to poor grading, which partially exceeds saturation.
The refining temperature is too high, so that the cooperating agent local excess, weighing inaccuracy (more weighing, less weighing, omission, wrong weighing).
Vulcanization temperature is too high, polymer degradation caused by frost.Under-sulfur frosting caused by incomplete reaction due to too low vulcanization temperature.
Vulcanization temperature is too low, resulting in incomplete reaction and the occurrence of undersulfurization.
Insufficient vulcanization time, resulting in under-sulfur spraying
Improper operation of spraying mold release agent or mold washing water, resulting in the phenomenon of white rubber surface.
IV. Treatment Methods for Frosting
1. Formula design:
When designing the formula, control the dosage, and control the dosage of the accelerator which is easy to spray frost to reduce the saturation spray.
When that material is selecte, the possibility of reaction between auxiliaries is reduce.
Processing AIDS are frosted due to migration, and the dosage of formula design should not be too large. The general dosage of processing AIDS is: 1.5-2.0 parts, and there will be no frost spraying.
When mixing rubber, pay attention to control the temperature, and the mixing temperature should not be too high.
Ensure the mixing uniformity of additives: thin pass several times or use processing additives (improve the dispersion of fillers).
Vulcanization process: It is best to choose "low temperature and long time vulcanization".
3.The choice of rubber oil
Select rubber oil with large molecular weight, wide molecular weight distribution and good compatibility with rubber.
Choose the right softener for different rubbers. EPDM: paraffin oil and naphthenic oil are better; NBR: It is better to choose synthetic ester softener, and the one with large weight is better than the one with small molecular weight.
4. Use anti-frost agent
Because the proportion of additives was not adjusted during the formulation design, the product was frosted after being stored for a period of time.
Use gasoline to clean the surface, and then apply a layer of frosting treatment agent. Time-consuming, laborious and costly.
In the formulation design, the use of anti-frost agent has a good effect. The dosage is 1-1.5% of the rubber compound.
5. Anti-frost agent LR-638
Product appearance: white or light yellow granules
Effective content: 99.8%
Density: 2.2
Use:
1. LR-638 has obvious anti-frost effect when used in diene rubber (natural rubber, SBR, BR, NBR, EPDM, etc.).
2. LR-638 has a strong decomposition power and inhibition effect on the phenomenon of white frost caused by excessive addition of some accelerators and fillers or temperature change.
3. LR-638 has obvious reinforcing effect on rubber (the reinforcing effect is second only to silica).
4. The anti-frost ability of LR-638 is beyond the reach of general defrosting agents, and the anti-frost effect is extensive.
Consumption:
1-1.5% of the total mass of the rubber compound (increase or decrease depending on the degree of frost spitting when frost prevention is the purpose).
