JPS6026416B2 - foamable composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a foamable composition having uniform closed cells, excellent heat resistance, and a high expansion ratio.

In general, polyethylene cross-linked foam has the properties of polyethylene itself, and at the same time provides heat insulation, sound absorption, shock absorption, and a lightweight and flexible feel. Anti-dew agents, sound absorbing materials,
Recently, it has been widely used as packaging materials for articles, cushioning materials for packaging, sealing materials, surface protection materials, buoyancy materials, etc.

However, most of the conventional cross-linked polyethylene foams are related to low-density polyethylene, but the low-density polyethylene cross-linked foam has a low compression hardness, and the cell structure collapses at temperatures below 10 mm. The disadvantage was that the operating temperature was low and the heat resistance was poor.

For this reason, various methods have been attempted in which high-density polyethylene is used instead of low-density polyethylene in order to improve these drawbacks.

For example, examples of crosslinked foaming compositions intended for heat resistance include the following. A method of adding a cross-linking aid and a thermally decomposable foaming agent to a polyolefin resin whose temperature is 13°C and foaming it in hot air (Hakama Sekisho No. 51-45176) ) has been proposed. However, with foamable compositions intended for heat resistance, the crosslinking reaction and foaming reaction are carried out simultaneously and in parallel at normal pressure, so the speed of crosslinking and the final degree of crosslinking become a problem. Since it is necessary to use an organic peroxide with a decomposition temperature of 17?0 or higher, the crosslinking rate is slow, and the addition of a crosslinking agent is an essential condition for increasing the weaving speed.

In other words, there is a problem that if a crosslinking aid is not added, the crosslinking speed is too slow and a foam cannot be obtained. Also,
Pyrolytic foaming agents are used as blowing agents, but pyrolytic foaming agents have problems such as difficulty in uniformly dispersing them into polyolefins, and residual decomposition sludge remaining in the foam, resulting in coloring. There is. The present invention was developed in view of the above-mentioned circumstances, and was created by discovering a novel foaming composition that has not been studied in the past. That is, the present invention provides a foamable composition comprising a crosslinked resin of high density polyethylene mixed with a low molecular weight substance having compatibility with high density polyethylene, and a volatile foaming agent which is normally gaseous; The present invention relates to a blowing agent composition comprising a crosslinked resin in which a low molecular weight substance having compatibility with the resin and low density polyethylene is blended, and a volatile blowing agent which is normally gaseous. Various foamable compositions of high-density polyethylene have been studied in an attempt to obtain the desired foam, but it has been difficult to obtain a foam with a high expansion ratio.

However, surprisingly, a foam with a high expansion ratio was obtained using a crosslinked resin made by blending polyethylene wax, a low molecular weight substance, with high density polyethylene. Even more surprisingly, the cell diameter of the foam made from a cross-linked resin made by blending high-density polyethylene with polyethylene wax was still not satisfactory, so when a cross-linked resin made by blending low-density polyethylene was further foamed, the cells were found to be small. It was found that a foam with a uniform diameter could be obtained. The effect of the present invention is that the polyethylene wax, which is a low molecular weight substance used in the present invention, has the effect of enlarging cell fleas, that is, acts as a foaming nucleating agent.

In addition, the low density polyethylene used in the present invention has the effect of making the cells uniform, that is, it has the effect of controlling the cells. Further, as a result of various studies, it has been found that low molecular weight substances used in the present invention are effective if they are compatible with high density polyethylene including polyethylene wax, and low molecular weight substances that are incompatible with high density polyethylene (e.g. polyethylene wax) are effective. chin wax, etc.) were found to be unsuitable for the purposes of the present invention.

For example, not only is it difficult to uniformly knead polystyrene wax with high-density polyethylene, but when the foamability of the resin composition was investigated, only foams with a low expansion ratio were obtained. Conventionally, there are the following foamable compositions containing a cell regulator.

A foamed product has been proposed in which an organic peroxide and a pyrolyzable foaming agent are uniformly blended, and a foaming agent is added to a polyolefin molded product and foamed by heating. However, the above composition uses a low molecular weight saturated dicarboxylic acid ester or dicarboxylic acid ester mixture and a polymeric saturated dicarboxylic acid ester or dicarboxylic acid ester mixture as a foam regulator; must be newly manufactured, and is a special product. Furthermore, these cell regulators are not only incompatible with polyolefins, but also have the effect of reducing cell diameters, and therefore exhibit effects completely different from those of the present invention. In the present invention, the blending amount of the low molecular weight substance that is compatible with the high density polyethylene and the resin is 80 to 6% by weight of the high density polyethylene.
and 20 to 4% by weight of the low molecular weight substance.

Further, when low density polyethylene is added to the above composition, the blending amount is 75 to 4% by weight of high density polyethylene, 20 to 5% by weight of low molecular weight substance, and 5 to 5% by weight of low density polyethylene.
It may be 5% by weight. In a three-component system, if the amount of high-density polyethylene in the resin modifier exceeds 75% by weight, a foam with a high expansion ratio cannot be obtained.
This is because if the amount is less than 2% by weight, the effect of improving the compression hardness and heat resistance of the foam will be significantly reduced, and the properties of high-density polyethylene cannot be effectively utilized.

In addition, if the blending amount of the low molecular weight substance in the resin composition exceeds 2% by weight, the cell diameter of the foam will become too coarse, making it impossible to obtain a foam with uniform cells, and the blending amount will be reduced to 5% by weight. If it is less than this, the effect as a foaming nucleating agent will not be obtained and a foam with a high expansion ratio will not be obtained. Furthermore, the amount of low-density polyethylene is limited to the amount of oligomer that is compatible with the high-density polyethylene and the resin, and is 5 to 55%.
This is because if the content exceeds the range of weight %, the properties of high-density polyethylene may not be exhibited or the effect of adjusting the cell diameter may not be obtained. The high-density polyethylene used in the present invention is manufactured by, for example, a medium-pressure method or a low-pressure method and has a density of 0. It is polyethylene with a rating of 1/cc or higher.

Density is 0. Polyethylene of less than 1/cc has low compression hardness and low heat resistance, and therefore only foams with lower quality can be obtained. Specifically, the low molecular weight substances that are compatible with high density polyethylene used in the present invention include low molecular weight polybutene, polyethylene wax, carnauba wax, paraffin wax, montan wax, etc.
In particular, those having an average molecular weight of 300 to 5,000 have excellent effects as foaming nucleating agents.

The low-density polyethylene used in the present invention is manufactured by a high-pressure method and has a density of 0.91 to 0.93/c.
It is also possible to use copolymers based on ethylene, or copolymers based on ethylene.

The resin of the present invention may be crosslinked by any of the following methods: kneading an organic peroxide and thermally crosslinking the resin, or irradiating it with irradiation with radiation or radiation. The normally gaseous bright blowing agent used in the present invention is selected from aliphatic hydrocarbons such as butane and propane, and halogenated hydrocarbons such as dichlorofluoromethane, dichloromonofluoromethane, and dichlorotetrafluoroethane. It can be a single item or a mixture. Among these, dichlorodifluoromethane is effective because of its excellent compatibility with resins. The method of incorporating a foaming agent into the crosslinked resin is carried out by a conventionally known method.
For example, there is a direct immersion method in which a crosslinked resin and a foaming agent are brought into contact under optimal conditions (pressure/temperature/time). Examples of the present invention will be described below.

Example-1 High-density polyethylene (density 0.95/cc, MII.
0/1 minute) and polyethylene wax (average molecular weight 1 minute) and polyethylene wax (average molecular weight 1
500) in the amounts shown in Table 1 (composition numbers 1 and 2), and 100 parts by weight of 2,5 dimethyl 2,5 di(t-butylperoxy)hexane was added to 100 parts by weight of the resin. 0.5 parts by weight was added and kneaded at 135mm using an extruder with a diameter of 2mm and 0, to make an end-crosslinked strand with a diameter of 3mm, and then 18mm.
Crosslinked strands with a degree of crosslinking of 60% were formed by immersion in a silicone oil bath heated to 0 qo for 15 minutes, cut into lengths of 3 to form crosslinked particles, and then the crosslinked particles and dichlorodifluoromethane were heated under pressure. The particles were placed in a container and directly impregnated at a temperature of 90°C and a pressure of 28kg/m2 for 2 hours, and then cooled to normal pressure and room temperature to obtain expandable particles impregnated with a blowing agent of 18% and pine%, respectively.

The composition numbers of these were set as 1 and 2. Example-2 High-density polyethylene (density 0.95 / enemy, skin 1.0)
and polyethylene wax (average molecular weight 1500) and low-density polyethylene (density 0.92/2, skin 3.5/1
0 minutes) in the amounts shown in Table 1 (composition numbers 3 to 5) to produce crosslinked particles under the same conditions as Example 1, and dichloromethane with the crosslinked particles.

Difluoromethane was placed in a pressure-resistant container and impregnated directly at a temperature of 90qo and a pressure of 28k9/base for 2 hours, and blowing agents were added to each
Expandable particles impregnated with 2%, 24% and 30% were obtained. Example 3 The resin composition of Example 2 was used, but polybutene (average molecular weight 500) was used instead of polyethylene wax.
They were mixed in the blending amount of composition number 6 in the table, and then crosslinked particles were produced under the same conditions as in Example-1, and further impregnated with a foaming agent under the same conditions as in Example-2 to obtain expandable particles.

Comparative Example-1 A case in which only the high-density polyethylene used in Example 1 was used, a case in which only the low-density polyethylene used in Example-2 was used, and a case in which high-density polyethylene and low-density polyethylene were used at 1, 1 In each case, crosslinked particles were produced under the same conditions as in Example 1, and a blowing agent was further mixed in to obtain expandable particles.

The composition numbers were set to 7, 8, and 9, respectively. Comparative Example-2 Same blending amount as Example-3 except that polystyrene wax (average molecular weight 1400) which is not compatible with high-density polyethylene was used instead of polybutene in the resin composition used in Example-3. Crosslinked particles were prepared under the same conditions as in Example 1, and further impregnated with a foaming agent to obtain expandable particles.

This composition number was set to 10. Experiment-■ 180q of the expandable particles obtained in the above Examples and Comparative Examples
Silicone heated to C. The particles were heated in an oil bath to produce foamed particles, and the foamability was evaluated based on the foaming ratio and foaming condition using the following scale.

The results are shown in Table 1. Note that the expansion ratio was determined by the following method. The apparent density was determined by dividing the weight (weight) of the foam by its volume (base), and the reciprocal of the apparent density was taken as the foaming ratio. ◎: Uniform bubbles with a foaming ratio of 1 or higher.

○: Non-uniform bubbles with a foaming ratio of 1" or more.

×: Foaming ratio is 1 pm or less. Experiment-■ The foamed particles obtained in Experiment-■ were left for 5 hours in a constant temperature bath heated to 12,000 ℃ for heat treatment, and the expansion ratio was measured. From the difference in expansion ratio before and after the heat treatment, the following results were obtained. Heat resistance was evaluated using a scale.

The results are shown in Table 1. ◎: Difference in foaming ratio is 10%
Below: ×: The difference in expansion ratio is 50% or more.As is clear from the results, either a low molecular weight substance that is compatible with the resin is blended with high density polyethylene, or low density polyethylene is further blended with the above resin. By heating the foamable composition obtained by impregnating the crosslinked resin with a volatile foaming agent, a highly foamed foam having the heat resistance and other properties of high-density polyethylene is produced. You can see what you can get.

The present invention provides a novel foamable composition, and its industrial value is extremely large. Table 1 (Note) HOPE: High density polyethylene LDPE: Low density polyethylene Type of low molecular weight substance: A: Polyethylene wax B - Polybutene C - Polystyrene wax

Claims (1)

[Claims] 1 80 to 60% by weight of high density polyethylene, polybutene with an average molecular weight in the range of 300 to 5000, polyethylene wax, carnauba wax, paraffin wax,
A foaming composition comprising a crosslinked resin obtained by blending and crosslinking 20 to 40% by weight of one or more mixtures of two or more selected from Montan waxes, and a volatile foaming agent that is normally gaseous. . 2 High-density polyethylene 75 to 40% by weight and one or more mixtures selected from polybutene, polyethylene wax, carnauba wax, paraffin wax, and montan wax with an average molecular weight in the range of 300 to 5000 20 A foamable composition comprising a crosslinked resin obtained by blending and crosslinking ~5% by weight and 5% to 55% by weight of low density polyethylene, and a volatile foaming agent that is normally gaseous.