Reasons for Rubber Frost
Analysis of the Main Causes of Rubber Whitening (Frost Spraying)
1. Summary of Frost Spraying
Rubber is divided into unvulcanized rubber (hereinafter referred to as rubber compound) and vulcanized rubber (hereinafter referred to as products). Rubber frosting includes rubber surface frosting and product surface frosting. Blooming is a phenomenon in which liquid or solid admixtures migrate from the interior of rubber to the surface of rubber. It can be seen that the precipitation of the rubber internal compounding agent forms frost spraying. Generally speaking, there are three types of rubber frost. That is, powder spraying, wax spraying and oil spraying (also known as exudation).
Powder spraying is a kind of powder compounding agent, such as vulcanizer, accelerator, activator, antioxidant and filler, which precipitates on the rubber surface and forms a layer of powder.
Wax spraying is a wax-like substance, such as paraffin and ground wax, which precipitates on the surface of rubber and forms a wax film.
Oil injection is a liquid mixture of softener, tackifier, lubricant and plasticizer which precipitates on the rubber surface and forms a layer of oily substance. In practice, the form of rubber surface frost sometimes appears in one form, sometimes in two or three forms at the same time.
(1) Inappropriate formulation design:
Saturated ejection: common in sulfur, accelerants, active agents, antioxidants
Migration ejection: common in processing aids, migratory antioxidants. antistatic agents
Formation Ejection: Accelerator and Reaction Products Commonly Used in Sulphur Sulphur Sulphur Sulphur Sulphur Sulphur Sulphur Sulphur System
Reaction Retention: Excess Low Molecular Matter Commonly seen in Organic Peroxide Sulfuration Systems
Stress ejection: common in inorganic fillers: such as calcium carbonate
(2) improper process operation
Non-uniform mixing results in poor dispersion and local excess of saturation.
Excessive temperature of rubber mixing causes local excess of mixing agent
Weighing is inaccurate (more, less, omitted, misnamed)
High vulcanization temperature, polymer degradation and frost spraying
Sulfur-deficient frost spraying due to incomplete reaction due to low sulfidation temperature
Sulfur-deficient frost spraying due to insufficient sulfurization time
Improper operation of spraying release agent or washing water resulted in whitening of rubber surface
(3) Quality fluctuation of raw materials
Because of the difference of material, preparation method, process and batch of raw materials, the synthetic process of raw rubber: polymerization temperature, catalyst, synthetic monomer and so on, causes the difference of solubility. Purity, moisture, ash content, pH value, physical properties and so on change.
(4) Poor storage conditions
Temperature: The solubility of the mixture in rubber generally increases and decreases with the increase of temperature.
Time (Pressure Humidity): Pressure, humidity of surrounding air and time during rubber storage also have an effect on the solubility of the formulation, but generally have little effect [6]. However, if the pressure is high, the compounding agent in the rubber will form nucleus and precipitate out of the rubber surface to form frost spraying; if the humidity of the air is too high, the effect of the compounding agent with large polarity on the raw rubber (non-polarity) will be weakened, and the solubility of the compounding agent will decrease, which will lead to frost spraying; the longer the storage time, the rubber surface will be sprayed. The more obvious the frost is, because the temperature and humidity of the air in the storage environment vary with the season, and the difference is large, it is easy to cause the change of the solubility of the mixture, which leads to the frost spraying.
(5) Rubber aging
The aging of rubber mostly results in the destruction of the complete and balanced network structure of vulcanizate, which also destroys the chemical or physical combination between various compounding agents, raw rubber molecules and compounding agents in the rubber system, and reduces the solubility of compounding agents in the rubber system. Therefore, the compounding agents that are partially supersaturated will dissociate from the rubber and form a frost spray.
Frost spraying refers to the phenomenon that sulfur, SA, waxes, accelerators, antioxidants and fillers are used to restrain and precipitate the surface from the inside of the compound. After the surface of the rubber products without frost is oxidized by sunlight, the surface has obvious changes, such as brass color, which is called Rainbow frost.

It has been pointed out in rubber technology that frost spraying is mainly caused by the phenomena that the dosage of compounding agent exceeds the solubility in rubber or vulcanizate, from metastable state to steady state. Frost spraying is harmful to the performance of rubber compound. If the self-stickiness decreases, the appearance of vulcanizate is not good enough to become unqualified products, and the antioxidant. Especially the antioxidant of ozone aging, hoping to restrain the surface. But there is no need to spray frost, wax needs to restrain the surface frost to form a protective film, which plays a physical protective role. In addition, for products whose surface requires extinction, it is necessary to control the appropriate spraying of some complexes, destroy the oxide film on the surface with the frost spray, and achieve extinction effect.