JPH03247633A - Volatile foaming agent for expansion of thermoplastic resin - Google Patents

Abstract

PURPOSE:To obtain the subject volatile foaming agent consisting of a chlorotetrafluoroethane, capable of providing an expanded material free from post-shrinkage or post-expansion after production, having a low danger of destruction of ozone layer and suitable for production of a thermoplastic resin expanded material. CONSTITUTION:A volatile foaming agent consisting of a chlorotetrafluoroethane (e.g. 1-chloro-1,2,2,2-tetrafluoroethane). Expansion is carried out by blending the above-mentioned foaming agent with a thermoplastic resin such as polyethylene or polypropylene.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention [Field of Industrial Application] The present invention relates to a volatile blowing agent for producing thermoplastic resin foams such as polyethylene, polypropylene, and polybutylene.

[Prior Art] Conventionally, in the foaming of thermoplastic resins, particularly in the foaming of polyolefins such as polyethylene, there has been a problem that the foam shrinks immediately after extrusion foaming.

This is due to the difference in the permeation speed of the blowing agent and air to the resin used, and the blowing agent quickly forms (cells).
This is because air enters the cell slowly, even though it passes from the inside to the outside world. Therefore, there was a problem in that aging had to be carried out for a long time in order to recover the diameter of the extruded foam.

Freon 114 has been used as a volatile foaming agent because its permeation rate is relatively close to that of air, but this problem has not been completely solved.

In addition, CFCs (chlorofluorocarbons), including the above-mentioned Freon 114, are extremely stable in the atmosphere and reach the ozone layer above the atmosphere without being decomposed, where they are decomposed by the action of ultraviolet rays, and the decomposed products destroy the ozone layer. There are also concerns about concerns, so instead of these CFCs,
A blowing agent that is less likely to cause ozone layer depletion is desired.

[Problems to be Solved by the Invention] The present invention is characterized in that when a thermoplastic resin foam is manufactured using a volatile blowing agent, almost no contraction or expansion occurs, and the foam decomposes before reaching the ozone layer. The purpose of the present invention is to provide a foaming agent that is less likely to break.

Configuration of the Invention [Means for Solving the Problems] The volatile foaming agent for foaming thermoplastic resin according to the present invention is composed of chlorotetrafluoroethane.

A typical example of chlorotetrafluoroethane is 1-chloro-1,2,2,2-tetrafluoroethane (hereinafter abbreviated as Freon 124).

In particular, Freon 124 has a much lower permeability to polyolefins than blowing agents conventionally used for foaming polyolefins, such as propane, butane, pentane, Freon 11, Freon 12, Freon 114, etc. It was found that the transmittance was almost the same as the transmittance.

Thermoplastic resins that can be used with the blowing agent of the present invention include polyolefins, that is, homopolymers of olefins such as ethylene, propylene, and butene, or copolymers thereof, or other vinyl monomers mainly composed of these olefins. copolymers with polymers, or mixtures of these polymers. Also, polystyrene and polystyrene mixtures can be similarly used.

The foaming method does not require any modification of conventional thermoplastic resin foaming means.

For example, a polyolefin and a nucleating agent are thoroughly mixed, and this is fed from an extruder hopper into a heated extruder,
A foam is obtained by melt-blending a polyolefin, pressurizing the volatile blowing agent of the present invention, and extruding it into the atmosphere through a temperature-controlled die.

The foam can be extruded into a sheet, rod, or any other desired shape. Further, the nucleating agent used at this time may be any conventionally used nucleating agent such as inorganic fine powder or decomposable foaming agent.

[Function] The foam extruded by the foaming agent of the present invention hardly shrinks or expands immediately after extrusion. Therefore, aging of the foam is almost unnecessary, and the time and effort required for unwinding the wound foam can be simplified.

[Test example] Non-crosslinked low density polyethylene film (film thickness 50
Dr, Lyssy gas permeability for μ)
Measured using a water vapor permeability measuring device. Table 1 shows the average value of the results of measuring each gas twice and the magnification when the air permeability is set to 1.0.

As shown in Table 1, the permeability of Freon 124 is almost the same as that of air.

[Example 1] Non-crosslinked low density polyethylene (MI value 7.2, density 0.
917 g/cm", melting point 106°C) to 100 parts by weight,
Add 0.3 parts by weight of talc as a nucleating agent and mix in a blender (after mixing, the mixture was fed from the extruder hopper. The mixture was heated and melted in the supplied extruder, and moved forward in the extruder by a screw. At this time, 120 kg/cm of Freon 124 was added from the middle part of the extruder.
This molten resin mixed with a foaming agent was extruded through a nozzle at the tip of the extruder whose temperature was controlled at 110°C to a thickness of 2 mm. A sheet-like foam was obtained.

This foam had a foaming ratio of about 30 times, the cells were uniform and fine, and when cut into a 10100 mm x 100 square, there was almost no change in the size from the size immediately after foaming.

C Comparative Example 1] Freon 114 was used instead of Freon 124 used in the example.
The foam was obtained using The conditions of use, equipment used, extrusion conditions, etc. were all the same as in the examples. Shrinkage and expansion were observed from the size immediately after foaming.

Table 2 shows the observation results of the foams produced in Example 1 and Comparative Example 1.

Table 2 Note: All foams were sized and stored at 24°C.

Freon 124 has better dimensional stability of the foam than Freon 114.

C. Effects of the Invention By using the blowing agent of the present invention, it is possible to produce thermoplastic resin foams that undergo almost no shrinkage or expansion after production. Therefore, there is no need for a foam aging process, and the time and effort required for storing the foam in a storage for aging and unwinding the rolled sheet can be simplified.

Further, since chlorotetrafluoroethane in the present invention is a compound containing a hydrogen atom, it is estimated that it decomposes before reaching the ozone layer, and is considered to have little risk of ozone destruction.

Claims (1)

[Claims] 1. A volatile foaming agent for foaming thermoplastic resins comprising chlorotetrafluoroethane. 2 Chlorotetrafluoroethane is 1-chloro-1,2
, 2,2-tetrafluoroethane. The volatile foaming agent for thermoplastic resin foaming according to claim 1, which is 2,2-tetrafluoroethane.