JPS5824259B2 - Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a thermoplastic resin foam having uniform and fine cells, and more specifically, the present invention relates to a method for producing a thermoplastic resin foam having uniform and fine cells, and more specifically, the cell size is made to have an average cell diameter of 0. The aim is to obtain a foam made of cells with less variation in the power of 4W or less.

Conventionally, there are several methods for obtaining thermoplastic resin foams. For example, a chemical blowing agent and an organic peroxide having a lower decomposition temperature than the blowing agent are mixed with the resin, and the organic peroxide is decomposed and crosslinked. A method of forming bonds and then decomposing the blowing agent to obtain a foam, or adding and kneading a resin blowing agent, molding it, irradiating it with electron beams to form a crosslinking bond, and heating it to remove the blowing agent. There is a method of obtaining a foam by decomposing it.

However, in the former method, if crosslinking and foaming are performed in a single heating step, a foam can be obtained continuously;
In that case, the bubbles are coarse and the effective utilization rate of the blowing agent is low.Also, if crosslinking and foaming are performed in a two-stage heating process, the bubbles become finer because the crosslinking is completed and foaming is performed, but the foaming agent is The crosslinking process must be carried out under pressure in order to prevent the initial decomposition gas or the decomposition gas from the crosslinking agent from forming bubbles, which is inefficient.

In addition, in the latter method, a foam having relatively fine cells can be obtained, but if foaming is performed immediately after irradiation, the cells have a drawback that the diameter of the cells becomes coarse.

In order to improve the drawbacks of the present invention, we conducted extensive research on a method for producing foams with uniform fine cells in a continuous cross-linking and foaming process that does not require manual labor. The present invention was based on the discovery that there is a close relationship between the amount of gas dissolved in the foam and the cell diameter of the foam.

That is, the present invention provides a method for producing a foam by heating a foamable composition in which a thermoplastic resin is mixed with a pyrolyzable blowing agent. The amount of gas per 1g of foaming composition is 0.06CG
This is done until the following is achieved.

Although it is not clear why a foam having fine cells is obtained by performing the degassing process in the present invention, if a gas component is present in the foaming composition, the gas is released from the foaming agent generated during the foaming process. Together with decomposed gas, nuclear bubbles are formed at the very early stage of foaming.

In this way, in a foaming process where a small number of core bubbles are formed at the beginning of foaming, it is assumed that the decomposed gas of the blowing agent thereafter concentrates on the core bubbles, resulting in the formation of coarse bubbles. .

In the present invention, degassing refers to removing any gas components or volatile low-boiling liquid components contained in the composition during or after molding the foam.

It is something that is removed from a substance, and by reducing the amount of gas it contains as much as possible, it is possible to make the bubbles finer.

The amount of gas contained in the molded article before heating and foaming is determined by the following measuring method: 0.060 cc or less per 1 gram of foamable composition, preferably 0.055 cc or less, and more preferably 0. The temperature is removed until the temperature reaches 0.0450C or less.If the temperature exceeds 0.06CC, the bubble diameter becomes coarse and the physical properties, that is, the heat insulation properties and texture are poor.

That is, to measure the amount of gas, the inside of the container with a glass tube for introducing the gas is sufficiently evacuated, and the foamed composition is heated to 80%
Almost complete desorption is performed under vacuum while heating to ~100°C for 30 minutes, and this is introduced into a constant volume system using a diffusion pump.

Note that the pressure inside the container can be monitored using, for example, a MacLeod vacuum gauge.

The amount of gas under standard conditions can be determined from the degree of vacuum (gas pressure) and its volume.

Further, any method may be used to remove the gas component or low-boiling liquid component from the foamed composition of the present invention, but it is usually a method of keeping the foamed composition molded product in a reduced pressure zone or a method of removing the gas component or low-boiling point liquid component from the foamed composition. This is done by keeping the temperature within the heating zone.

For the method using a reduced pressure zone, the molded body is 5007 ta
Hg or less, preferably 300 MHg or less, and in the case of heating methods, the higher the temperature is, the better, as it promotes the diffusion of gas components, etc., and it is usually desirable to keep the molded body at least 10°C higher than the softening temperature of the resin. .

However, it is necessary to maintain the temperature below the decomposition temperature of the crosslinking agent and blowing agent, for example, when producing low density polyethylene foam, it is preferably 90 to 150 degrees Celsius, preferably 100 to 13 degrees Celsius.
It is heated to 0°C.

In addition, the heating time varies depending on the resin used, the gas components contained, the heating temperature, the thickness of the molded sheet, etc.
It is generally desirable to carry out the heating for 2 to 30 minutes, particularly for 5 to 20 minutes.

Processing time can be shortened by using the above-mentioned method using a reduced pressure zone and method using a heating zone in combination.

Regarding the point of degassing, the thermoplastic resin is mixed with a blowing agent or a blowing agent and a crosslinking agent, and after being formed into a sheet using an extruder, the degassing process is performed continuously without cooling, and immediately the continuous foaming process is performed. By doing this, the processing time for degassing is shortened, and the foamed material with extremely fine bubbles can be processed efficiently.

Thermoplastic resins in the present invention include, for example, olefinic polymers such as high-density and low-density polyethylene, polypropylene, and polybutene-1, ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-vinyl acetate copolymers, Olefin copolymers such as ethylene-acrylic acid copolymer and ethylene-acrylic ester copolymer, polyvinyl chloride, polyvinyl polymer such as vinyl chloride-vinyl acetate copolymer, polyacrylic acid, polymethacrylic acid etc.

The thermally decomposable blowing agent used in the present invention must have a decomposition temperature higher than the softening point of the resin, such as azocabonamide, dinitropentamethylenetetramine, PP'
These include oxyvinylhydrazide, benzenesulfonyl hydrazide, azobisisobutyronitrile, and paratoluenesulfonyl semicarbazide.

In addition, the crosslinking agent in the present invention includes ditertiary butyl peroxide, 1,3bis(tertiarybutylperoxyisopropyl)benzene, 2,5dimethyl 2-5di(tertiarybutylperoxy)hexane, and dicumylperoxide. These include organic peroxides such as I-9 nonanubisulfonazide, azide compounds such as octachlorocyclopentene, and organic chlorides such as octachlorocyclopentene, which are decomposed by heating to form crosslinks in the resin.

Furthermore, along with the above crosslinking agents, triallyl cyanurate, triallyl isocyanurate, trimethylolpropane,
The use of gas trapping agents such as trimethacrylate can significantly reduce decomposition gases generated from crosslinking agents.

Generally, when a foamed composition is obtained and when it is molded, the crosslinking agent decomposes to a very small extent and gas is generated.

However, if the gas trapping agent is mixed in, the decomposition gas from the crosslinking agent will be captured, and the amount of residual gas will be reduced accordingly.

Therefore, if a degassing step is performed before crosslinking, the foamed composition will become gas-free in a shorter time.

During crosslinking, a similar effect of the gas trapping agent creates a completely gas-free state, and foaming begins in a state where there are no more nuclear bubbles, so it is possible to create a foam made of ultrafine bubbles.

In addition, the kneading step in the present invention involves kneading a foaming agent into the resin in the case of radiation crosslinking, and kneading the foaming agent and the chemical crosslinking agent into the resin in the case of chemical crosslinking.
The foaming agent and the crosslinking agent must not be decomposed in any case.

Further, the molding step in the present invention means molding into a plate shape, sheet shape, granule shape, etc. using an extruder or press molding, and even in this case, it is necessary that the blowing agent and the crosslinking agent are not decomposed.

In the present invention, heating is performed to a temperature higher than the decomposition temperature of the blowing agent in order to foam the degassed foam composition.

The heating means may be an infrared heater, a hot air heating furnace, a salt bath, or other methods.

In the present invention, a flame retardant, a crosslinking accelerator, a foaming aid, etc. may be appropriately added to the foamable composition.

Next, the present invention will be described with reference to Examples (all parts hereinafter indicate parts by weight).

Example 1 Low density polyethylene 100 with melt index 1.0
．． 0 parts and 100 parts of azosica-bonamide as a blowing agent,
and 1.0 part of dicumyl peroxide as a crosslinking agent were added, and the mixture was extruded into a sheet having a thickness of 2 cm using an extruder.

The gas content in the sheet thus obtained was determined to be 0.088σ in 1 g of the sheet as measured by the measuring method described above.

Cut this sheet into 3cm squares, put them in a vacuum desiccator, and use a rotary pump to remove 10011#. After processing for 5 hours in Hg vacuum, this sample 1. ! The gas content in i' was 0.041 CC.

When this was heated and foamed in a metal bath at 200° C., a foam having uniform fine cells (0.4M) was obtained.

For comparison, a small piece of the same size from the above sheet (gas content 6.088cc in 1g of sheet) was heated and foamed in a metal bath at 200°C, resulting in coarse bubbles (0.65M). In addition, a foam was obtained which was somewhat lacking in uniformity.

Example 2 Low density polyethylene 100 with melt index 1.0
．． To 0 parts, 10.0 parts of azosicabonamide as a blowing agent, 0.7 parts of dicumyl peroxide as a crosslinking agent, and 0.2 parts of triallyl cyanuride as a gas trapping agent were added, and mixed on a roll. Kneaded thickness 3m, 23
．． 5CrrLx 13. It was press-molded into an Ocm sheet.

This sheet (gas content in 1 g of sheet 0.085 (f
) was cut into 3 square pieces and heat treated at 120℃ for 20 minutes in a constant temperature bath.The gas content in 1g of this specimen was 0.
．． It was 035CC.

When this was heated and foamed in a metal bath at 200° C., a foam having uniform fine cells (0.207 parts gl) was obtained.

Example 3 Low density polyethylene 100 with tart index 1.0
．． 15.0 parts of azosicabonamide as a foaming agent, 0.6 parts of dicumyl peroxide as a crosslinking agent, and 0.39 parts of triallyl cyanuride as a gas trapping agent were added to 0 parts, and the mixture was thickened using an extruder. It was extruded into a two-dimensional sheet.

This sheet (gas content in 1g of sheet is 0.090CC)
,,) are continuously passed through a hot air oven at 120°C,
When heat treatment for degassing was performed for about 10 minutes, the gas content in the sea hIF was 3 cc.

Immediately after this heat treatment, this was heated and foamed in a foaming furnace at 220°C to obtain a foam having uniform fine cells (0.33 m).

Example 4 Low density polyethylene 100 with tart index 2.0
．． Add 10.0 parts of Azocicabonamide as a foaming agent to 0 parts, and use an extruder to achieve a thickness of 17#! extruded into a sheet.

This sheet is immediately placed in the air using a linear accelerator for 6
Immediately after the Mrad irradiation, heat treatment was performed at 120°C for 6 minutes (under standard conditions, the amount of gas per 1 g of the foaming composition was 0.
04CC), a foaming furnace with a conveyor (temperature 2
The density was 0.052 when foamed in 40℃).
．． A foam consisting of uniform cells as small as 9/7 and having an average cell diameter of 0.43M was obtained.

The gas content in 1g of the sheet after the above heat treatment is 0.052
It was CC.

When the above-mentioned radiation-irradiated sheet (gas content in 1 g of sheet 0.094 CC) was heated and foamed without heat treatment, the density was as small as 0.050 g/Crfl, but the average cell diameter was 0.6 M, which was quite large. A large foam was obtained.

As detailed above, the method of the present invention has remarkable effects such as obtaining a foam having a uniform and fine foam diameter through simple operations.

Claims (1)

[Claims] 1. In a method of manufacturing a foam by heating a foamable composition in which a thermoplastic resin is mixed with a pyrolytic foaming agent, degassing is performed during or after molding the composition, prior to heating and foaming treatment. A method for producing a thermoplastic resin foam, characterized in that the process is carried out until the amount of gas per gram of the composition becomes 0.06 CC or less.