JPS5840985B2 - Cross-linked high foam - Google Patents

Description

Detailed Description of the Invention The present invention is characterized in that the main components are polyethylene and a polyolefin thermoplastic elastomer, and 5 to 40 parts of crystalline low molecular weight polypropylene is added to 100 parts of this mixed resin. Regarding crosslinked highly foamed materials, the purpose is to propose a crosslinked highly foamed material that is particularly flexible, has excellent heat insulation properties, and has improved high temperature heat resistance, especially dimensional stability at high temperatures. .

Cross-linked highly foamed materials made of low-density polyethylene are widely used as heat insulating materials because they are closed cells, have low thermal conductivity, low water absorption, and are relatively inexpensive.

In addition, polyethylene cross-linked high foam has characteristics that are not found in polystyrene foam insulation materials such as flexibility and rigid urethane foam insulation materials, so it can be used as a heat insulation material for preventing freezing of water pipes, and as a cold insulation material for electric refrigerators and air conditioners. insulation material,
It is valued as a pie-fu insulation material for various centrifugal heating high-temperature media, and has recently come to be used in large quantities.

However, even with these excellent properties, cross-linked polyethylene foam can only be used at a temperature of 100°C.
Considering long-term durability, the limit is 800C to 90C.

However, recently, as seen in heat pump type near conditioners that use Freon as a heat medium,
Insulating materials that can withstand temperatures of 110'C to 130C are now required.

The present inventors focused on the good properties of conventional polyethylene crosslinked highly foamed materials, and as a result of intensive research in order to obtain a crosslinked highly foamed material that is further heat resistant at high temperatures without losing its properties,
We have arrived at the present invention.

The main components of the present invention are polyethylene and polyolefin thermoplastic elastomer, and 5 parts per 100 parts of this mixed resin.
The present invention relates to a crosslinked highly foamed material with improved dimensional stability at high temperatures, characterized in that ~40 parts of crystalline low molecular weight polypropylene is added.

The crosslinked highly foamed material of the present invention has a specific gravity of 0.02 to 0.1.
0, foaming ratio 10 to 50 times If the residue extracted for 16 hours in boiling xylene is defined as the gel fraction, the value is 30 to 7.
0% foam.

If the specific gravity of the foam exceeds the above value, the price of the foam per unit volume increases, making it uneconomical, and the thermal conductivity increases as the specific gravity increases, making it undesirable as a heat insulating material.

If the specific gravity is lower than the above value, the mechanical properties of the foam will be poor, and the foam may break, bubble, or break (soak) during processing or construction, which is not preferable.

On the other hand, the gel fraction defined above is 30% in terms of the heat resistance of the foam and the provision of cell stability during foam production.
determined to be ~70%.

The polyethylene used in the present invention refers to polyethylene produced by a low-medium-high-pressure method, and preferably high-pressure polyethylene with a specific gravity of 0.93 or less can be used best.

The fluidity of polyethylene is an important factor that affects foam moldability.

The polyethylene of the present invention has a flow index (MI JIS
K6760, ), 1 to 5 are appropriate.

If the MI of polyethylene becomes low and the viscosity at the time of melting increases more than necessary, free foaming expansion will be adversely affected, while the MI
If the temperature is too high, the cells during foaming will not be stable, and the resulting foam will have insufficient cell strength and will not buckle or lose its recovery properties after deformation, and will not lose its properties as a foam. ``Exhibits rubber elasticity at room temperature,
Defined as "a material that plasticizes, flows, and is moldable at high temperatures."

The present invention is characterized in that a polyolefin thermoplastic elastomer is used in combination with polyethylene.

What is the polyolefin thermoplastic elastomer mentioned here?
Ethylene-propylene copolymer rubber, or ethylene-propylene-non-covalent diene copolymer rubber is used as the rubber phase, and highly crystalline polypropylene is used as the freezing phase. An elastomer with a crosslinked structure.

The degree of partial crosslinking is generally 5 to 50 yen, based on the amount insoluble in boiling xylene.

Such polyolefin thermoplastic elastomers are commercially available and can be used.

Polyolefin thermoplastic elastomers are completely different from conventional ethylene-propylene copolymer rubbers or ethylene-propylene non-co-yielded diene copolymer rubbers in that they do not have a highly crystalline frozen phase inside them. However, the purpose of the present invention can be achieved even if a rubber such as ethylene-propylene copolymer rubber or ethylene-propylene non-copyrene diene copolymer rubber is used instead of the polyolefin thermoplastic elastomer. I can't.

Furthermore, since the rubber phase of a thermoplastic elastomer is originally frozen by the crystalline phase at room temperature, it is not newly crosslinked during molding, unlike other rubbers.

In the present invention, polyethylene and polyolefin thermoplastic elastomer are co-crosslinked by a new method of mixing polyolefin thermoplastic elastomer with polyethylene and crosslinking both at the same time to form a continuous phase, and the polypropylene frozen phase of the thermoplastic elastomer The idea is to make it responsible for high-temperature heat resistance.

In the present invention, the purpose of using polyethylene as another component is, of course, to maintain the good properties of the cross-linked polyethylene foam described above, but the polyolefin thermoplastic elastomer alone is not suitable for foaming. Since the viscosity at high temperatures is extremely high, it is not possible to freely foam and expand, making it difficult to obtain a good foam.As an improvement measure, polyethylene is added as one component.

That is, in the present invention, mixing polyethylene and thermoplastic elastomer is inevitable in order to obtain a crosslinked highly foamed material with good heat resistance.

and 90 to 40 parts of polyethylene, preferably 80 to 40 parts
It has been found that by mixing 10 to 60 parts, preferably 20 to 50 parts, of a polyolefin thermoplastic elastomer to 50 parts, a highly foamed product having satisfactory foamability and heat resistance can be obtained.

However, although the crosslinked highly foamed material obtained in this way has sufficient heat resistance when used as a heat insulating cover for piping passing through a high temperature medium of, for example, 120 to 130 °C, it In tests conducted in an unrestrained state, the dimensional shrinkage rate was somewhat large.

5 In other words, the present invention provides a highly crosslinked foam with low dimensional shrinkage and excellent heat resistance, and it has been discovered that crystalline low molecular weight polypropylene is unique in providing this effect. be.

The crystalline low molecular weight polypropylene of the present invention can be produced by thermal decomposition of high molecular weight polypropylene or direct polymerization of propylene.

Alternatively, by-products produced during the production of high molecular weight polypropylene can also be used.

This material has a high melting point almost as high as high molecular weight polypropylene, but has a low melt viscosity and is highly compatible with various plastics.

It is generally a white powder.

In the present invention, crystalline low molecular weight polypropylene having a molecular weight of 2000 to 5000 and a melting point of 140 to 160° C. can be suitably used.

The effect of adding crystalline low molecular weight polypropylene in the present invention is to very effectively improve the dimensional stability of the crosslinked highly foamed material in a high temperature atmosphere, as will be clear from the examples described below.

The mechanism by which such an effect is obtained is not necessarily clear, but can be considered as follows.

That is, in a general method for producing a crosslinked highly foamed material, the crosslinking of the resin usually precedes foaming, or the crosslinking and foaming proceed simultaneously, as described below.

Therefore, in the actual foaming process, the strain caused by the expansion and stretching of the crosslinked cell membrane is strongly memorized as residual strain even after cooling and solidification, so when the foam is placed in a high temperature atmosphere again, the residual strain cannot be recovered. This will result in a large contraction.

However, crystalline low molecular weight polypropylene has a characteristic of low crosslinkability, and therefore, when melted at high temperatures during foaming, it has the effect of appropriately reducing the viscosity of the expanding resin system and easing strain.

Further, the low molecular weight polypropylene used in the present invention is highly crystalline, has a high melting point, and is difficult to soften, so it goes without saying that it contributes to improving the heat-resistant dimensional stability of the foam.

Therefore, even if a so-called amorphous polypropylene with a low melting point is used, the remarkable effects of the crystalline polypropylene of the present invention cannot be achieved.

The amount of low molecular weight crystalline polypropylene added in the present invention is suitably 5 to 40 parts per 100 parts of polyethylene and polyolefin thermoplastic elastomer mixed resin.

-Addition of more than this is not preferable because not only can no increase in effectiveness be expected, but the foam tends to collapse and the compression recovery properties tend to deteriorate.

On the other hand, if the amount is added below the above range, no significant effect can be expected.

The method for producing the crosslinked highly foamed body of the present invention will be described.

By mixing polyethylene and polyolefin thermoplastic elastomer with crystalline low molecular weight polypropylene, a thermally decomposable blowing agent, and a crosslinking agent that generates radicals when heated,
Formed into a molded product at a temperature that does not decompose the crosslinking agent and foaming agent,
Next, this foamable molded product is transferred to a high temperature atmosphere to decompose the crosslinking agent and the foaming agent, thereby producing a highly crosslinked foamed product.

In other methods, the foamable molded product that does not contain a crosslinking agent is irradiated with ionizing radiation such as β rays, R rays, α rays, neutron rays, and X rays to introduce a crosslinked structure and then exposed to a high temperature atmosphere. You can also foam underneath.

Furthermore, a vinyl silane such as vinyl trimexysilane is kneaded into the polyethylene-polyolefin thermoplastic elastomer mixed resin of the present invention together with a crosslinking agent to make it into a kraft, converting it into a crosslinkable resin, and then mixing with a blowing agent to form a molded product. .

Thereafter, a crosslinked structure can be introduced by a siloxane condensation reaction, and foaming can be performed in a high temperature atmosphere.

Examples of the above-mentioned crosslinking agents used in the production of the present foam include di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α, α
'-Bis(t-butylperoxy)P-diisopropylbenzene, 2,5-dimethyl-25-di(1-butylperoxy)hexane, t-butylperoxyisopropylbenzene, 1.3-bis(1-butyl Peroxyisopropylbenzene and the like.

However, dicumyl peroxide is generally used in an amount of 0.1 to 1.0 parts by weight per 100 parts by weight of the mixed resin.

Further, the above-mentioned blowing agent is a compound that is decomposed and gasified by heating, and specifically, for example, azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, 4.4
-Oxybis(benzenesulfonyl hydrazide) and the like, which can be used alone or in combination.

Further, a small amount of polybutadiene, SBR, chlorinated polyethylene, chlorosulfonated polyethylene, etc. can be added to the polyethylene-polyolefin thermoplastic elastomer mixed resin as a modifier.

Furthermore, a lubricant, an antioxidant, an ultraviolet absorber, a coloring agent, etc. can be added as necessary.

Examples 1 to 8 and Comparative Example 1 Low density polyethylene 70 with specific gravity 0.924 and MI 3.5
Part and polyolefin thermoplastic elastomer (TPE53
8. Manufactured by Sumitomo Chemical ■, EPDM/PP type crosslinking degree 30.1φ
) was extruded using an extruder having a 65φ, L'/D-26, full-flight screw at a resin temperature of 160°C to obtain a pellet-shaped mixed resin.

5, to 100 parts of this mixed resin, 15 parts of azodicarbonamide, 0.8 parts of dicumyl peroxide, 0.3 parts of phenolic antioxidant, and crystalline low molecular weight polypropylene (Viscol 550 P, Sanyo Ka Made by a certain industrial company, specific gravity 0.89, melting point 150°C, molecular weight 4000
) was added thereto, thoroughly kneaded in an 8' mill at a surface temperature of 120°C, and then press-molded at the same temperature into a 3-inch thick sheet to obtain a foamable molded product.

Next, this sheet was foamed in a dryer at 230°C, and the resulting foamed sample was left unrestrained in a gear open at 130°C for 40 hours, and the length shrinkage rate was measured.

The results are shown in Table 1 and the figure (curve (a)).

It is clearly seen that the addition of crystalline low molecular weight polypropylene reduces the length shrinkage within the open, ie the dimensional stability of the foam at high temperatures is greatly improved.

Examples 9 to 14 and Comparative Example 2 Low density polyethylene 60 with specific gravity 0.924 and MI 3.5
and polyolefin thermoplastic elastomer (TPE16)
00. Manufactured by Sumitomo Chemical ■, EPDM/PP system, degree of crosslinking 42
．． Example 1 Mixed resin pellets consisting of 40 parts (0%)
Created in the same way.

Next, to 100 parts of this mixed resin, 15 parts of azodicarbonamide, 0.8 parts of dicumyl peroxide, 0.3 parts of phenolic antioxidant, and crystalline low molecular weight polypropylene (Viscol TS-200゜ manufactured by Sanyo Chemical Industries, Ltd.) were added. , specific gravity 0.89, melting point 140°C, molecular weight 2000) 5
~40 parts were added, thoroughly kneaded with an 8'' roll with a surface temperature of 120°C, and then press-molded at the same temperature into a 3-inch thick sheet to obtain a foam molded product.

Next, this sheet was foamed in a dryer at 230'C, and the resulting foamed sample was left unrestrained in a gear open at 130'C for 40 hours, and the length shrinkage rate was measured.

The results are shown in Table 1 and the figure (curve (b)).

Comparative Examples 3 to 4 Instead of crystalline low molecular weight polypropylene, low molecular weight polypropylene that is liquid at room temperature (Demopol C-201 manufactured by Amoco Chemical, specific gravity 0.84 to 0.86, molecular weight 550 to
Foaming was carried out in exactly the same manner as in Example 1 except that 600, ) was added, and the foamed samples obtained were subjected to the same tests.

The results are shown in Table 1 and the figure (curve (C)).

Additives have some effect on improving heat-resistant dimensional stability, but the effect is far less than that of crystalline low molecular weight polypropylene.

Moreover, the surface of this foam was slightly sticky and the product value was reduced.

Example 15 and Comparative Example 5 Low density polyethylene 50 with specific gravity 0.924 and MI 3.5
and polyolefin thermoplastic elastomer (TPE1
600, manufactured by Sumitomo Chemical ■, EPPM/PP system, degree of crosslinking 42
．． A mixed resin pellet consisting of 50 parts of 0φ) was prepared in the same manner as in Example 1, and the same crystalline low molecular weight polypropylene as in Example 1 was added to form a foam, which was subjected to a heat resistance test.

The results are shown in Table 1. As is clear from the examples, it can be seen that the addition of crystalline low molecular weight polypropylene greatly improves the heating dimensional stability of the foam of the present invention.

[Brief explanation of the drawing]

The drawing is a graph showing the relationship between the amount of low molecular weight polypropylene added and the length shrinkage rate of the foam upon heating, and curve a
correspond to Examples 1 to 8 of the text, and the curves are the same <Example 9
Corresponds to ~14. Curve C corresponds to Comparative Examples 3 and 4.

Claims (1)

[Claims] 1 The main components are polyethylene and polyolefin thermoplastic elastomer, and 5 to 4 parts per 100 parts of this mixed resin.
A crosslinked highly foamed material with improved dimensional stability at high temperatures, characterized in that 0 parts of crystalline low molecular weight polypropylene is added. 2. The crosslinked highly foamed material according to claim 1, wherein the mixed resin comprises 90 to 40 parts (by weight) of polyethylene and 10 to 60 parts (by weight) of a polyolefin thermoplastic elastomer. 3. The polyolefin thermoplastic elastomer is made of an ethylene-propylene copolymer rubber or a mixture of an ethylene-propylene non-co-linked diene copolymer rubber and polypropylene, which are partially cross-linked with each other. The crosslinked highly foamed material according to item 1 or 2. 4. The crosslinking according to any one of claims 1 to 3, wherein the specific gravity is 0.02 to 0.10, and the degree of crosslinking as shown by the residue after 16 hours of extraction in boiling xylene is 30 to 70%. High foam.