JPH061872A - Production of open-cell foam - Google Patents

Abstract

PURPOSE:To obtain an open-cell foam having improved heat resistance and rubber elasticity by using a styrene-based thermoplastic elastomer as a base material of the foam. CONSTITUTION:A styrene-based thermoplastic elastomer mainly comprising a hydrogenation product of a block copolymer represented by the general formula: A-(B-A)n wherein A is a styrene block; B is a butadiene block; and n is an integer of 1-5 is mixed with a polyethylene resin and then with a blowing agent and a crosslinker. The resulting foamable and crosslinkable compsn. is thermally foamed in a metal mold loosely sealed to give a foam, which is then deformed mechanically to give an open-cell foam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an open cell body.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a crosslinked polyolefin open-celled body, a foaming agent which partially decomposes a foaming agent and a crosslinking agent in a foamable crosslinkable composition in a closed mold and remains under normal pressure. A method has been proposed in which the cross-linking agent is decomposed to obtain a closed cell body, and then the obtained closed cell body is compressed to break the closed cell body (JP-B-59-23545 and JP-A-56-146732). reference). However, in such a method, the foaming agent and the cross-linking agent are decomposed by heating in a closed mold under pressure, and although the cross-linking reaction occurs, the formation of bubbles is not performed, and at the time of depressurization. It will foam for the first time. That is, a method of first causing a crosslinking reaction and then performing foaming is adopted, and so-called pre-crosslinking is performed in the manufacturing stage of the closed cell body, so that the cell membrane becomes tough. Therefore, it is difficult to connect the closed cells to each other, and it is impossible to obtain a foam body having an open cell ratio of 100% or close to 100%.

In order to solve the above-mentioned problems, the applicant of the present invention heats and shapes the expandable crosslinkable composition into a desired shape and then heats it under normal pressure to decompose the crosslinker and the foaming agent simultaneously in a progressive manner. To generate bubbles, and then mechanically deform the bubbles to make them communicate with each other (Japanese Patent Publication No. Sho 62-1929).
No. 4, Japanese Patent Publication No. 1-44499).

[0004]

According to the method of the present applicant described above, it is possible to obtain an open cell body having an open cell rate of 100% or close to 100%. However,
This method discloses a method for producing an open cell based on low density polyethylene or an ethylene-vinyl acetate copolymer, and an open cell based on polyethylene or an ethylene-vinyl acetate copolymer. Has a limited heat-resistant temperature, so its use was limited. On the other hand, when this method is applied to polypropylene, the heat resistance is improved, but the rubber elasticity is poor, and it cannot be used for applications such as packing materials and sealing materials.

Therefore, an object of the present invention is to solve the above-mentioned conventional drawbacks, have a higher heat resistance than an open cell body based on an ethylene-vinyl acetate copolymer or low density polyethylene, and An object of the present invention is to provide a method for producing an open cell body having excellent rubber elasticity.

[0006]

According to the present invention, in order to achieve the above object, a foaming agent and a crosslinking agent are added and kneaded to a styrene thermoplastic elastomer, and the resulting foamable crosslinking composition is not airtight. Provided is a method for producing an open-cell body, which comprises foaming by heat-foaming in a mold to form a cell, and then mechanically deforming the cell to make the cells communicate with each other.
In the method of the present invention, in order to improve moldability, it is preferable to add 1 to 80 parts by weight of a polyethylene resin to 99 to 20 parts by weight of the styrene thermoplastic elastomer. Further, by adding 30 to 70 parts by weight of the polyethylene resin to 70 to 30 parts by weight of the styrene thermoplastic elastomer, the moldability is further improved.

[0007]

According to the method of the present invention, as described above, the styrene-based thermoplastic elastomer is used as the resin for the base material. Styrenic thermoplastic elastomer is
It is roughly classified into SBS (styrene-butadiene-styrene block copolymer) system and SEBS (styrene-ethylene-butylene-styrene block copolymer) system. The structure of the styrene-based thermoplastic elastomer is such that the polystyrene portion and the polybutadiene (or ethylene / butylene) portion are incompatible with each other, and the polybutadiene (or ethylene / butylene)
Butylene) has polystyrene dispersed as islands in the sea. At room temperature, this polystyrene part restrains the butadiene (or ethylene / butylene) part, but at high temperature (molding process), polystyrene melts and exhibits thermoplasticity, so that it can be molded as easily as a thermoplastic resin. Further, since the styrene-based thermoplastic elastomer has elasticity and viscosity similar to rubber, the obtained foam has a special cell structure, does not easily pass water, and is excellent in waterproofness.

As a method for obtaining the open-cell body of the present invention,
A base material resin is kneaded with a foaming agent and a cross-linking agent, and the foamable cross-linkable composition obtained is heat-foamed to form a foam,
A conventionally known method can be applied as long as it is a method of making mechanical communication to make bubbles communicate with each other and is not particularly limited.
Among such methods, as described in Japanese Patent Publication No. 62-19294 and Japanese Patent Publication No. 1-44499, the foamable crosslinkable composition is heat-molded into a desired shape, and then is not hermetically sealed. By heating in a mold under normal pressure, the crosslinking agent and the foaming agent are simultaneously decomposed to form a foam body,
Then, the effect of the present invention is particularly remarkable in the method in which the bubbles are communicated by applying mechanical deformation.

A preferred embodiment of the method for producing an open-cell body according to the present invention will be specifically described below. First, a styrene-based thermoplastic elastomer is used as the base resin. The styrene-based thermoplastic elastomer is a styrene-based thermoplastic resin represented by the general formula: A- (BA) _n ,
(Wherein A is styrene, B is butadiene, and n is an integer of 1 to 5), and those containing a hydrogenated derivative of a block copolymer as a main component are preferable, and polyolefin resins such as polypropylene and various types. A softener, a filler and the like are appropriately added (for example, trade name "Lavalon" manufactured by Mitsubishi Petrochemical Co., Ltd.). The hydrogenated derivative is obtained by highly hydrogenating the butadiene portion of the styrene-butadiene-styrene block copolymer to saturate the double bond portions of the main chain and side chains, and therefore has high weather resistance and heat resistance. Especially excellent. In order to improve moldability, the composition 99
It is preferable to add 1 to 80 parts by weight of the polyethylene resin to 20 to 20 parts by weight. Particularly preferably, the composition 70
30 to 70 parts by weight of a polyethylene resin is added to 30 to 30 parts by weight. A foaming agent, a cross-linking agent, and a foaming auxiliary agent if necessary, a filler, a pigment, etc., to the mixture of the base material resin or the base material resin and the polyethylene-based resin as described above, and the mixing roll heated to this, Knead with a pressure type kneader, Banbury mixer, extruder or the like. Charge the foamable crosslinkable composition obtained by kneading as described above into a mold,
Depending on the type of resin and crosslinker under pressure in a press, 11
Heat shaping is performed at 5 ° C to 165 ° C, preferably 120 ° C to 150 ° C. In this heat shaping step, it is preferable that the foamable crosslinkable composition is shaped while maintaining the gel fraction at zero, and the open cell ratio is 100% or 100%.
This is a condition for obtaining an open cell body close to. Here, the gel fraction is the weight ratio of the sample before extraction and the sample after extraction measured by putting the sample in a wire mesh of 200 mesh and performing extraction for 24 hours under reflux of the solvent trichlorethylene with a Soxhlet extractor. In this heat shaping step, a very small amount of the foaming agent causes initial decomposition, and when the shaped composition is taken out of the mold, it can expand up to about twice, but this is far from the concept of foaming. There is no problem for the present invention.

The shaped composition thus obtained is then heated under normal pressure to simultaneously decompose the crosslinking agent and the foaming agent. This foaming / crosslinking step is carried out, for example, by placing the shaped composition in a mold that is not airtight, that is, has a desired cross-sectional shape and dimensions, that is, is not sealed, and heats the metal plate of the mold from the outside. The composition is allowed to heat indirectly. As a method of indirectly heating, for example, there is a method in which a heater is brought into close contact with the outer surface of a metal plate for heating, or a heat medium flow path is provided in the metal plate and heating is performed with steam, heating oil, etc. in a jacket method. . Alternatively, the intermediate foam is placed in a non-airtight open-close mold, and one or more salts of sodium nitrate, potassium nitrate, potassium nitrite, etc. are melted in a metal bath or oil bath using a rose alloy, wood alloy, or the like. It is heated directly in a salt bath using salt, in a nitrogen stream, or in a state covered with an expandable (or expandable) iron plate or the like. Alternatively, heating may be performed using high frequency. By the above method, after heating for a predetermined time, it is cooled to obtain a foam. The heating temperature is set in the range of 140 ° C to 210 ° C, preferably 150 ° C to 180 ° C, depending on the type of polyolefin used. The heating time is preferably 30 to 300 minutes, more preferably 1
It is from 00 to 200 minutes. In this way, a foam having a foam film that can be easily broken by applying mechanical deformation and having the same degree of crosslinking (up to about 90% gel fraction) as that of the conventional foam is obtained. .

The foamed body (so-called closed-celled body) obtained as described above is then subjected to compressive deformation by, for example, a constant-velocity two-roll roll, whereby the foamed film is destroyed, and the bubbles are made continuous to form continuous cells. The body is obtained. Innumerable small needles are provided on the surface of the constant velocity two rolls, or rolls provided with innumerable needles before and / or after the constant velocity two rolls are arranged, and innumerable small holes are formed on the surface of the foam. By opening the opening, communication of bubbles can be promoted. By this method, an open cell body having an open cell rate measured based on the Remington Pariser method is 100% or close to 100% is obtained.

The polyethylene resin used in the present invention is, for example, a commercially available polyethylene produced by a high, medium or low pressure method, or a copolymer with vinyl acetate or the like. As the foaming agent used in the present invention, various chemical foaming agents, for example, azo compounds such as azodicarbonamide, barium azodicarboxylate, etc .: Nitroso compounds such as dinitrosopentamethylenetetramine, trinitrosotrimethyltriamine, etc .; Hydrazide compounds P, p '
-Oxybisbenzenesulfonyl hydrazide and the like; sulfonyl semicarbazide compounds such as p, p'-oxybisbenzenesulfonyl semicarbazide and toluenesulfonyl semicarbazide can be preferably used, but are not limited thereto. .

The cross-linking agent used in the present invention has a decomposition temperature higher than the flow initiation temperature of the resin used and is decomposed by heating to generate free radicals to generate intermolecular or intramolecular formation thereof. Organic peroxides that are radical generators that cause cross-linking, such as dicumyl peroxide, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5 -Di-t-butylperoxyhexane,
There are 2,5-dimethyl-2,5-ditertiary butyl peroxyhexyne, α, α-ditertiary butyl peroxydiisopropylbenzene, tertiary butyl peroxyketone, tertiary butyl peroxybenzoate, etc. The optimum organic peroxide must be selected according to the type of resin used.

In the present invention, for the purpose of improving the physical properties of the composition to be used or lowering the price, a compounding agent (filler) which does not exert a significant adverse effect on cross-linking, such as zinc oxide, titanium oxide, or oxidation. Metal oxides such as calcium, magnesium oxide and silicon oxide, carbonates such as magnesium carbonate and calcium carbonate, fiber materials such as pulp, various dyes, pigments and fluorescent materials, and other commonly used rubber compounding agents are required. Can be added according to

[0015]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples. Example 1 Styrenic thermoplastic elastomer (trade name: Lavalon S
J4400N, manufactured by Mitsubishi Petrochemical Co., Ltd.) 100 parts by weight, azodicarbonamide 17 parts by weight, zinc white 0.03 parts by weight,
A composition comprising 0.01 parts by weight of zinc stearate, 0.01 parts by weight of urea, and 0.8 parts by weight of dicumyl peroxide was kneaded with a mixing roll at 110 ° C., and 135 ° C.
The mold in the press (160x160x37m)
m) was filled with the above kneaded product and heated at the above temperature for 50 minutes under pressure to shape the composition. Next, the composition was placed in a non-airtight open-close mold (500 x 500 x 100 mm) that had already been heated to 170 ° C, heated by steam at 170 ° C for 140 minutes by a jacket type, taken out after cooling, and a foam was obtained. . The obtained foam was passed between two constant-velocity two-rolls set at a roll interval of 20 mm four times to break the bubbles, thereby making the bubbles continuous. The size of the obtained foam with skin after communication is 500x500x100.
mm, the apparent density was 0.027 g / cm ³ , the open cell ratio was 100%, and the cells inside were uniform. JI
In accordance with SK 6767, the compression set of the obtained open-cell body was measured (50%, compressed at 70 ° C. for 22 hours, and
As a result of (a) left for 1 hour and (b) left for 24 hours at 0 ° C., the results were (a) 34% and (b) 35%, showing high heat resistance.

Example 2 70 parts by weight of styrene thermoplastic elastomer (described above) and low density polyethylene (trade name: Yucaron YF-30, M
Example 1 except that 30 parts by weight of FR 1.0, density 0.920 g / cm ³ manufactured by Mitsubishi Petrochemical Co., Ltd.) were mixed, and 0.7 parts by weight of dicumyl peroxide was added to 100 parts by weight of the mixed resin. An open-cell body was obtained under the same composition, the same foaming conditions and the same communication conditions. The size of the obtained open cells,
The apparent density and the open cell ratio are the same as in Example 1,
As a result of measuring the compression set by the same method as in Example 1,
(A) was 35% and (b) was 36%, showing that the heat resistance was high.

Example 3 50 parts by weight of a styrene-based thermoplastic elastomer (described above) and 50 parts by weight of low-density polyethylene (described above) were mixed, and 100 parts by weight of the mixed resin was mixed with dicumyl peroxide of 0.
An open-cell body was obtained under the same composition, the same foaming conditions, and the same communication conditions as in Example 1 except that 6 parts by weight was added. The size, apparent density, and open cell ratio of the obtained open-cell body were the same as in Example 1, and the compression set was measured by the same method as in Example 1, resulting in (a) 36% and (b) 37. %,
It turned out that it has high heat resistance. Example 4 30 parts by weight of a styrene-based thermoplastic elastomer (described above) and 70 parts by weight of low density polyethylene (described above) were mixed, and 100 parts by weight of the mixed resin was mixed with dicumyl peroxide in an amount of 0.
An open-cell body was obtained under the same composition, the same foaming conditions, and the same communication conditions as in Example 1 except that 5 parts by weight was added. The size, apparent density and open cell ratio of the obtained open-cell body were the same as in Example 1, and the compression set was measured by the same method as in Example 1, and as a result, (a) 37%, (b) 38 %,
It turned out that it has high heat resistance.

Comparative Example 1 10 parts by weight of a styrene-based thermoplastic elastomer (previously described) and 90 parts by weight of low density polyethylene (previously described) were mixed, and 100 parts by weight of the mixed resin was mixed with dicumyl peroxide in an amount of 0.
An open-cell body was obtained under the same composition, the same foaming conditions and communicating conditions as in Example 1 except that 45 parts by weight was added. The size, apparent density and open cell ratio of the obtained open cell body are
The compression set was the same as in Example 1, and the compression set was measured by the same method as in Example 1. As a result, (a) 43%, (b) 43%, the heat resistance was low, and the thickness was restored by thermocompression molding. I didn't. Comparative Example 2 Ethylene-vinyl acetate copolymer (trade name: Evaflex P1403, vinyl acetate content 14% by weight, DuPont-
(Mitsui Polychemical Co., Ltd.) except that 0.6 part by weight of dicumyl peroxide was added to 100 parts by weight, the same formulation as in Example 1 was prepared, and the temperature of the mixing roll was 90.
An open-cell body was obtained under the same foaming and communicating conditions as in Example 1 except that the temperature was changed to ° C. The size, apparent density, and open cell ratio of the obtained open-cell body were the same as in Example 1, and the compression set was measured by the same method as in Example 1, and as a result, (a) 4
3% and (b) 43%, the heat resistance was low, and the thickness was not recovered by thermocompression molding.

[0019]

As described above, according to the method of the present invention,
Since the styrene-based thermoplastic elastomer is used as the base resin, the obtained open cells have excellent heat resistance than the open cells having an ethylene-vinyl acetate copolymer or low density polyethylene as a base material, and It has elasticity equivalent to that of an open cell of ethylene-vinyl acetate copolymer, and is suitable as a packing material for air conditioners, automobiles, sealing materials, and heat insulating materials. Further, by adding a polyethylene resin to the styrene thermoplastic elastomer, the moldability and processability in the foaming step are improved, and it is possible to obtain an open cell body having uniform physical properties and excellent by simple work. Further, as the styrene-based thermoplastic elastomer, the general formula, A- (B
-A) _n , (wherein A is styrene, B is butadiene, and n is an integer of 1 to 5), by using the hydrogenated derivative of the block copolymer, there is no double bond. Therefore, it is possible to obtain an open cell body having particularly excellent heat resistance and weather resistance.

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Claims (4)

[Claims] 1. A foaming agent and a cross-linking agent are added to and kneaded with a styrene-based thermoplastic elastomer, and the foamable cross-linkable composition obtained is heat-foamed in a mold that is not airtight to form a foam, and then mechanically. A method for producing an open-cell body, characterized in that deformation is applied to make the cells communicate with each other. 2. A styrene-based thermoplastic elastomer 99 to
The production method according to claim 1, wherein 1 to 80 parts by weight of a polyethylene resin is added to 20 parts by weight. 3. A styrene-based thermoplastic elastomer 70 to
The manufacturing method according to claim 1, wherein 30 parts by weight and 30 to 70 parts by weight of a polyethylene resin are added. 4. The styrenic thermoplastic elastomer has the general formula A- (BA) _n , where A is styrene and B.
Is butadiene, and n is an integer of 1 to 5. 4. The method according to claim 1, 2 or 3, which comprises a hydrogenated derivative of a block copolymer represented by