JP3163588B2 - Method for producing open-cell foam - Google Patents

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.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a cross-linked polyolefin open cell, a foaming agent and a cross-linking agent in a foamable cross-linkable composition are partially decomposed in a closed mold, and a foaming agent remaining under normal pressure is obtained. And a crosslinking agent are decomposed to obtain closed cells, and then the obtained closed cells are compressed to break closed cells (Japanese Patent Publication No. 59-23545 and Japanese Patent Application Laid-Open No. 56-146732). reference). However, in such a method, the foaming agent and the cross-linking agent are decomposed by heating in a pressurized closed mold, and a cross-linking reaction has occurred, but no bubbles have been formed. It will be foaming for the first time. That is, a method of first causing a cross-linking reaction and then performing foaming is adopted. Since so-called pre-crosslinking is performed in the production stage of the closed cell, the foam film becomes tough. Therefore, it was difficult to make closed cells open, and it was not possible to obtain a foam having an open cell ratio of 100% or close to 100%.

In order to solve the above problem, the present applicant heat-shapes a foamable crosslinkable composition into a desired shape and then heats it under normal pressure to simultaneously decompose the crosslinker and the foaming agent. A method was developed to generate bubbles and then to apply mechanical deformation to make the bubbles open (Japanese Patent Publication No. 62-1929).
No. 4, JP-B 1-44499).

[0004]

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

[0005] Accordingly, an object of the present invention is to solve the above-mentioned conventional disadvantages, to have 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 having excellent rubber elasticity.

[0006]

According to the present invention, a foaming agent and a crosslinking agent are added and kneaded to a styrene-based thermoplastic elastomer to achieve the above object, and the resulting foamable crosslinkable composition is not airtight. There is provided a method for producing an open-cell body, characterized in that the cell is heated and foamed in a mold to form a cell, and then the cell is subjected to mechanical deformation to make the cell open.
In the method of the present invention, it is preferable to add 1 to 80 parts by weight of a polyethylene resin to 99 to 20 parts by weight of a styrene-based thermoplastic elastomer in order to improve moldability. Further, when 30 to 70 parts by weight of the polyethylene resin is added to 70 to 30 parts by weight of the styrene-based thermoplastic elastomer, the moldability is further improved.

[0007]

According to the method of the present invention, a styrenic thermoplastic elastomer is used as a base resin as described above. Styrene-based thermoplastic elastomers are
It is roughly classified into SBS (styrene-butadiene-styrene block copolymer) type and SEBS (styrene-ethylene-butylene-styrene block copolymer) type. 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)
Polystyrene is dispersed as islands in the sea of (butylene). At room temperature, the polystyrene portion constrains the butadiene (or ethylene / butylene) portion. However, at high temperatures (molding), the polystyrene melts and exhibits thermoplasticity, so that it can be easily molded in the same manner as a thermoplastic resin. Further, since the styrene-based thermoplastic elastomer has elasticity and viscosity like rubber, the obtained foam has a special cell structure, does not easily pass water, and is excellent in water stoppage.

The method for obtaining the open-cell body of the present invention includes:
A foaming agent and a crosslinking agent are added and kneaded to the base resin, and the resulting foamable crosslinkable composition is foamed by heating to form a foam,
Next, a conventionally known method can be applied as long as it is a method of making the bubbles open by applying mechanical deformation, and is not particularly limited.
Among such methods, as described in JP-B-62-19294 and JP-B-1-44499, after heat-shaping a foamable crosslinkable composition into a desired shape, non-airtight gold is used. Heating under normal pressure in the mold to simultaneously decompose the crosslinking agent and the foaming agent to form a foam,
The effect of the present invention is particularly remarkable in a method in which bubbles are communicated by applying mechanical deformation.

Hereinafter, a preferred embodiment of the method for producing an open-cell body according to the present invention will be specifically described. First, a styrene-based thermoplastic elastomer is used as a base resin. The styrene-based thermoplastic elastomer is a styrene-based thermoplastic resin represented by the general formula: A- (BA) _n ,
(Here, A is styrene, B is butadiene, and n is an integer of 1 to 5.) It is preferable to use as a main component a hydrogenated derivative of a block copolymer represented by the following formula: A softening agent, a filler, and the like are appropriately added (for example, trade name “Lavalon” manufactured by Mitsubishi Yuka Co., Ltd.). The hydrogenated derivative is a product obtained by highly hydrogenating the butadiene portion of a styrene-butadiene-styrene block copolymer, thereby saturating a double bond portion of a main chain and a side chain. 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 about 20 parts by weight. Particularly preferably, the composition 70
To 30 to 70 parts by weight of the polyethylene resin is added 30 to 70 parts by weight of the polyethylene resin. A foaming agent, a crosslinking agent, and, if necessary, a foaming aid, a filler, a pigment, etc. are added to the above-described base resin or a mixture of the base resin and the polyethylene-based resin, and a mixing roll heated by heating is added. The mixture is kneaded with a pressure kneader, a Banbury mixer, an extruder or the like. Charge the foamable crosslinkable composition obtained by kneading as described above in a mold,
Depending on the type of resin and crosslinking agent under pressure with a press, 11
Heat shaping is performed at 5 ° C to 165 ° C, preferably at 120 ° C to 150 ° C. In this heating shaping step, shaping while maintaining the foamable crosslinkable composition preferably in a state where the gel fraction is zero can be performed by an open cell ratio of 100% or 100%.
This is the condition for obtaining an open cell close to Here, the gel fraction is a weight ratio of a sample before extraction and a sample after extraction measured by placing a sample in a 200-mesh wire net and performing extraction with a Soxhlet extractor under reflux of a solvent of trichloroethylene for 24 hours. In this heating shaping step, a very small amount of the foaming agent undergoes initial decomposition, and when the shaped composition is taken out of the mold, it can expand to about twice, but this is far from the concept of foaming, There is no problem for the present invention.

The shaped composition obtained as described above is then heated under normal pressure to simultaneously decompose the crosslinking agent and the foaming agent. The foaming / crosslinking step is performed, for example, by placing the shaped composition in a non-hermetic, i.e., unsealed mold having a desired cross-sectional shape and dimensions, and heating the metal plate of the mold from the outside. The composition is heated indirectly. As a method of indirectly heating, for example, there is a method in which a heater is closely attached to an outer surface of a metal plate, or a method in which a heating medium flow path is provided in a metal plate, and heating is performed by steam, heating oil, or the like in a jacket system. . Alternatively, the intermediate foam is placed in a mold that is not airtight and can be opened and closed, and one or more kinds of salts such as sodium nitrate, potassium nitrate, and potassium nitrite are melted in a metal bath or an oil bath using a rose alloy, a 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 extensible (or expandable) iron plate or the like. Alternatively, heating may be performed using high frequency. According to the above-mentioned 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 minute.
00 to 200 minutes. In this way, a foam having a foam film that can be easily broken by applying mechanical deformation and having a degree of crosslinking (up to a gel fraction of about 90%) similar to that of a conventional foam can be obtained. .

The foam obtained as described above (a so-called closed cell) is then subjected to compressive deformation by, for example, a constant-speed double roll or the like, whereby the bubble film is broken, and the bubbles are made open to open cells. The body is obtained. A countless small needles are provided on the surface of the constant velocity double roll, or a roll provided with countless needles before and / or after the constant velocity double roll is arranged, and countless small holes are formed on the surface of the foam. By opening the opening, communication of air bubbles can be promoted. According to this method, an open-cell body having an open-cell ratio of 100% or close to 100% is obtained based on the Remington Parser method.

The polyethylene resin used in the present invention is, for example, a commercially available polyethylene resin produced by a high, medium or low pressure method, or a copolymer with vinyl acetate or the like. Examples of the blowing agent used in the present invention include various chemical blowing agents such as azo compounds such as azodicarbonamide and barium azodicarboxylate: nitroso compounds such as dinitrosopentamethylenetetramine and trinitrosotrimethyltriamine; and hydrazide compounds. P, p '
-Oxybisbenzenesulfonylhydrazide and the like; sulfonylsemicarbazide-based compounds such as p, p'-oxybisbenzenesulfonylsemicardide and toluenesulfonylsemicarbazide can be suitably used, but not limited thereto. .

The cross-linking agent used in the present invention has a decomposition temperature higher than the flow start temperature of the resin to be used, and is decomposed by heating to generate free radicals to form intermolecular or intramolecular molecules. Organic peroxides which are radical generators that cause cross-linking, such as dicumyl peroxide, 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5 -T-butyl peroxyhexane,
2,5-Dimethyl-2,5-di-tert-butylperoxyhexine, α, α-di-tert-butylperoxydiisopropylbenzene, tert-butyl peroxyketone, tert-butylperoxybenzoate, etc., used at that time The optimum organic peroxide must be selected according to the type of resin to be 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 significantly affect cross-linking, for example, zinc oxide, titanium oxide, oxide, etc. Requires metal oxides such as calcium, magnesium oxide and silicon oxide, carbonates such as magnesium carbonate and calcium carbonate, or fibrous materials such as pulp, or various dyes, pigments, fluorescent materials, and other common rubber compounding agents. It can be added according to.

[0015]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples. Example 1 Styrene-based thermoplastic elastomer (trade name: Lavalon S)
J4400N, manufactured by Mitsubishi Yuka Co., Ltd.) 100 parts by weight, azodicarbonamide 17 parts by weight, zinc white 0.03 parts by weight,
A composition comprising 0.01 part by weight of zinc stearate, 0.01 part by weight of urea, and 0.8 part by weight of dicumyl peroxide was kneaded with a mixing roll at 110 ° C., and 135 ° C.
(160x160x37m)
m) was filled with the above kneaded material, and heated under pressure at the above temperature for 50 minutes to shape the composition. Next, the composition was placed in a non-hermetic open / close mold (500 × 500 × 100 mm) already heated to 170 ° C., heated with steam at 170 ° C. for 140 minutes by a jacket method, taken out after cooling, and a foam was obtained. . The obtained foam was passed four times between two constant-velocity rolls set at a roll interval of 20 mm to break bubbles, thereby making the bubbles open. The size of the obtained foam with skin after communication is 500 × 500 × 100.
mm, the apparent density was 0.027 g / cm ³ , the open cell ratio was 100%, and the internal air bubbles were uniform. JI
The compression set of the obtained open-cell foam was measured in accordance with S K 6767 (50%, compression at 70 ° C. for 22 hours, 2
(A) left at 0 ° C. for 1 hour and (b) left for 24 hours). As a result, it was found that (a) was 34% and (b) was 35%, indicating high heat resistance.

Example 2 70 parts by weight of a styrene-based thermoplastic elastomer (described above) and low-density polyethylene (trade name: Yucalon YF-30, M
Example 1 except that 30 parts by weight of FR 1.0 and a density of 0.920 g / cm ³ manufactured by Mitsubishi Yuka Co., Ltd.) were mixed, and 0.7 part by weight of dicumyl peroxide was added to 100 parts by weight of the mixed resin. Under the same blending conditions and the same foaming conditions and communication conditions, open-celled bodies were obtained. The size of the resulting open cell,
Apparent density and open cell rate are the same as in Example 1,
As a result of measuring the compression set by the same method as in Example 1,
(A) 35% and (b) 36%, indicating high heat resistance.

Example 3 50 parts by weight of a styrene-based thermoplastic elastomer (supra) and 50 parts by weight of a low-density polyethylene (supra) were mixed, and 100 parts by weight of the mixed resin was mixed with 0.1 part of dicumyl peroxide.
Except for the addition of 6 parts by weight, an open-cell body was obtained under the same composition as in Example 1, under the same foaming conditions and communication conditions. The size, apparent density, and open cell ratio of the obtained open-cell foam were the same as those in Example 1. As a result of measuring the compression set by the same method as in Example 1, (a) 36%, (b) 37 %
It turned out that heat resistance was high. Example 4 30 parts by weight of a styrene-based thermoplastic elastomer (described above) and 70 parts by weight of a low-density polyethylene (described above) were mixed, and 100 parts by weight of the mixed resin was added with 0.1 part of dicumyl peroxide.
Except for adding 5 parts by weight, an open-celled body was obtained under the same composition as in Example 1, and under the same foaming conditions and communication conditions. The size, apparent density, and open cell rate of the obtained open-cell foam were the same as those in Example 1. As a result of measuring the compression set by the same method as in Example 1, (a) 37% and (b) 38 %
It turned out that heat resistance was high.

COMPARATIVE EXAMPLE 1 10 parts by weight of a styrene-based thermoplastic elastomer (described above) and 90 parts by weight of a low-density polyethylene (described above) were mixed, and 100 parts by weight of the mixed resin was mixed with 0.1 part of dicumyl peroxide.
Except for the addition of 45 parts by weight, an open-cell body was obtained under the same composition as in Example 1, under the same foaming conditions and communication conditions. The size, apparent density and open cell rate of the obtained open cell,
It 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% and (b) 43%, the heat resistance was low, and the thickness was recovered by hot pressing. Did not. Comparative Example 2 Ethylene-vinyl acetate copolymer (trade name Evaflex P1403, vinyl acetate content 14% by weight, DuPont
Except that 0.6 parts by weight of dicumyl peroxide was added to 100 parts by weight of Mitsui Polychemicals Co., Ltd., the same formulation as in Example 1 was prepared.
An open cell 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 rate of the obtained open-cell foam were the same as those in Example 1. As a result of measuring the compression set by the same method as in Example 1, (a) 4
3%, (b) 43%, heat resistance was low, and the thickness did not recover due to hot pressing.

[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-cell body has higher heat resistance than the open-cell body based on the ethylene-vinyl acetate copolymer or the low-density polyethylene, and It has the same elasticity as an open cell of ethylene-vinyl acetate copolymer, and is suitable as a packing material, a sealing material, and a heat insulating material for air conditioners and automobiles. Further, by adding a polyethylene resin to the styrene-based thermoplastic elastomer, the moldability and workability in the foaming step are improved, and an open cell having uniform properties and excellent physical properties can be obtained by a simple operation. Further, as a styrene-based thermoplastic elastomer, a compound represented by 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 a hydrogenated derivative of a block copolymer represented by the formula: Therefore, it is possible to obtain an open cell having particularly excellent heat resistance and weather resistance.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C08L 25:00 53:02

Claims (4)

(57) [Claims] 1. A foaming agent and a crosslinking agent are added and kneaded to a styrene-based thermoplastic elastomer, and the resulting foamable crosslinkable composition is heated and foamed in a non-hermetic mold to form a foam. A method for producing an open-cell body, characterized in that cells are made open by deformation. 2. A styrenic thermoplastic elastomer 99 or more.
2. The method according to claim 1, wherein 1 to 80 parts by weight of the polyethylene resin is added to 20 parts by weight. 3. A styrenic thermoplastic elastomer 70 to
The method according to claim 1, wherein 30 parts by weight and 30 to 70 parts by weight of a polyethylene resin are added. 4. A styrene-based thermoplastic elastomer represented by the general formula: A- (BA) _n , wherein A is styrene and B is
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 the formula: