JPS5855228A - Manufacture of polyethylene foam - Google Patents

Abstract

PURPOSE:To obtain a foam with an extremely small shrinkage and excellent mechanical characteristics by a method wherein material is thermally pressurized in a mold to generate a decomposed gas and then, allowed to foam leaving the mold after cooled under a specific condition. CONSTITUTION:A mixture of a polyethylene resin A, a foaming agent B (e.g. azodicarbonamide) as additive and a cross-linking agent C (e.g. dicumylic peroxide) which is added thereto as required fills a mold and then, is thermally pressurized at a temperature exceeding the decomposition temperature of the component B (normally 155-180 deg.C) to generate a decomposed gas, which is contained in the mixture. Then, the mold filled with the mixture suppressing the foaming is cooled down by 25-90 deg.C below the decomposition temperature of the component B (normally 90-130 deg.C) and the mixture is allowed to foam leaving the mold to obtain the intended foam.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the method of manufacturing polyethylene foam.

Conventional I polyethylene foam t-K is produced by filling the whole room with a mixture of I polyethylene and adding a blowing agent and, if necessary, a crosslinking agent, and heating and pressurizing it to a temperature above the decomposition temperature of the foaming agent by steam. A foam is obtained by filling the skeleton crystal hydrate into an extruder and extruding it at a temperature higher than the decomposition temperature of the cough foaming agent.

Note that when a crosslinking agent is added, the crosslinking agent (like the foaming agent) decomposes first to crosslink 4-riederene.

However, when such a method is used, the shrinkage rate is large, and it is difficult for the polyethylene foam to maintain a predetermined shape when deposited from the mold. Although it is not possible to determine the reason for this, it is assumed that polyethylene foam is not composed of closed cells and is formed while the bonds between molecules are unstable. In addition, since the foaming agent is heated to a temperature higher than the decomposition temperature of the foaming agent and foamed in a good state, the mechanical properties, especially tensile strength and tear strength, are inferior.

The present invention has an extremely small shrinkage rate and excellent mechanical performance. We have discovered a method of manufacturing je IJ ethylene foam. That is, in the method of the present invention, a foaming agent and, if necessary, a crosslinking agent are added to the 4-lyethylene resin.

A mixture to which a crosslinking aid has been added is filled into a t-deaf, and heated and pressurized to a temperature higher than the decomposition temperature of the blowing agent to generate decomposition gas,
The gas is contained in a mild substance and cooled in a state in which foaming is suppressed, and the gas is detuned at a temperature H that is 25 to 90°C lower than the decomposition temperature, and foaming occurs. It is.

The method of the present invention does not foam the polyethylene resin at a high temperature, such as above the decomposition temperature of the foaming agent, but only suppresses one foaming in this state. That is, the foaming agent is sufficiently decomposed to generate a sufficient amount of foaming gas, and this gas is incorporated into the ethylene resin and rises to cool the ethylene resin, causing it to transition from a softened state to a hardened state. The gas is used to foam the polyethylene resin all at once in a temperature range of . In this case, if a crosslinking agent is mixed in the mixture, the tetraethylene resin is first crosslinked with the crosslinking agent and then foamed to form a foam.

The polyethylene foam produced in this way has an extremely small shrinkage rate even when left unused, and can be used to produce products with good dimensional accuracy. The reason for this is thought to be that stable intermolecular bonds are formed. Furthermore, since the polyethylene resin is foamed in its cured state, the resulting foam is necessarily hard and has excellent mechanical properties.

In the method of the present invention, the temperature at which the /'J ethylene resin mixture is demolded is limited to a temperature that falls within the range of 25°C to 90°C, which is the decomposition temperature of the blowing agent. In this case, the performance of the resulting foam, such as shrinkage rate and mechanical properties, cannot be improved, and furthermore, the foam scatters, making it impossible to obtain a foam with a satisfactory shape.

Furthermore, if the resin is exposed to a temperature lower than 90° C., the ethylene resin will rise and become a solid solution, making it impossible to foam sufficiently.

In the method of the present invention, the temperature above the decomposition temperature of the blowing agent is usually 155° to 180°C, and the demolding temperature is usually 90'' to 130°C. The heating time is approximately 10-15 minutes.

In addition, in the present invention, the blowing agent is not particularly limited, and for example, Azoshika Ganryokendo is used, and the amount added is 2 to 2 times the amount of polyethylene resin.
It is about 0 weight.

Further, as the crosslinking agent, for example, dicumyl/arm oxide is used, and the amount thereof added is 2 to 5 degrees SS by weight.

Next, examples of the present invention will be described.

Example 1 For 100 parts by weight of 4-re-engineered tyrene resin, 20 parts by weight of Azosikaganad, 5 parts by weight of zinc stearate, 3.0 parts by weight of dicumyl oxide, 111 L, 30 parts by weight of calcium carbonate.
Parts by weight, 10 parts by weight of naphthenic oil were added, kneaded with a roll to form a sheet, and this was filled into a metal container at 95 mm.
It was heated and pressurized in a heat press at 60° C. for 100 minutes. Thereafter, the mold was cooled with water for 50 seconds to 110° C. and demolded, yielding a polyethylene foam having a specific gravity of 0.045.

Example 2 Azoshika added 20 parts by weight of Noamide, 3.0 parts by weight of stearin@saliva lead, and 3.0 parts by weight of Noraside to 100 parts by weight of 4-reproduced tyrene resin, and kneaded with a roll. This was formed into a sheet, filled into a mold with 95% of the metal, and heated and pressed for 15 minutes using a hot press at 166°C.
The mixture was cooled with water and cooled to 110° C. and demolded to obtain a polyethylene foam having a specific gravity of 0.035.

Therefore, the product of the present invention and the conventional polyethylene foam (specific gravity 0
．． The results of measuring the physical properties of 042) were 17g1
As shown in the table.

As detailed in Table 1, the method of the present invention has a remarkable effect in producing a polyethylene foam with extremely low shrinkage and excellent mechanical performance.

Claims (1)

[Claims] 4! A mixture of JX fv resin and a blowing agent and a crosslinking agent added thereto as necessary is filled into a disk, heated and pressurized to a temperature higher than the decomposition temperature of the blowing agent to generate a decomposed gas, and the gas t- Polyethylene foaming characterized by incorporating it into a mixture to suppress foaming, cooling it in a good state, demolding at a falling temperature range of 25" to 90°C or less, and foaming. Body manufacturing method/