JPS633735B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to elastic modification of foam, and in particular to improving the elasticity of ethylene-vinyl acetate copolymer (hereinafter referred to as EVA). Traditionally
EVA foam was known. However, all of the conventionally known EVA foams are high-density, low-foam foams. That is, the density is 0.2 to 0.4, and the expansion ratio is
Limited to a range of 2.5 to 5. This is the conventional
This was because it was impossible to manufacture products with higher foaming and lower density using the EVA foam manufacturing method. Therefore, despite the fact that EVA foam has excellent abrasion resistance and elastic properties, it is actually used only in very limited applications such as sandals and shoe soles. Therefore, the inventors have been working for some time to solve the problem of lowering the density and increasing foaming of EVA foam. As a result, we achieved this goal and have already applied for a patent application in 1984.
We proposed a technology related to this as No. 65843. However, the inventors continued their research on this subject even after that. As a result, we have further developed a new method completely different in concept from the above proposal.
We have developed an elastic modification method suitable for lowering the density and increasing foaming of EVA foam. If this new method is used in conjunction with the method already proposed by the inventors, it will be possible to create an unprecedented EVA foam with low foaming, high density, and significantly improved elasticity with internal voids. I have confirmed that I can get it. That is, this invention involves adding and mixing raw materials each containing an ethylene-vinyl acetate copolymer, a blowing agent, and a crosslinking agent as essential components in a mold, and inserting a plurality of rod-shaped members for forming voids at both ends of the mold. The foam raw material embedded through the mold is filled, the mold is then tightly closed with a cover, and then heated to form a foam, the foam is pressurized within the mold, and then The method is characterized in that the cover of the mold is then opened, the foam is removed from the mold all at once, and the void-forming rod-shaped member embedded in the foamed material is removed from the resulting foam.
The present invention will be explained below using an example in which the present invention is applied to the production of EVA low-density foam.

The main raw material ethylene-vinyl acetate copolymer used in this invention can be of any compound, but usually 100% of ethylene is mixed with vinyl acetate.
10 to 40 are used. A blowing agent, a crosslinking agent, and others are added to such a copolymer, and the mixture is thoroughly kneaded using, for example, a roll to form a sheet. The blowing agent used here is the same as that used in conventional EVA foams. Examples include azodicarbonamide, dinitrosopentamethylenetetramine, P-toluenesulfonylhydrazine, azobisisobutyronitrile, diazoaminoazobenzene, and toluenesulfonyl semicarbazide. These blowing agents are used in an amount of 20 to 80 parts by weight, preferably 20 to 50 parts by weight, per 100 parts by weight of EVA to obtain a low density foam. If the amount is less than 20 parts by weight, a low-density foam cannot be obtained, and if it exceeds 80 parts by weight, rapid foaming will occur, making it impossible to produce a stable foam.

In addition, especially when a low-density foam is not used, the amount of the blowing agent used here may be 5 to 15 parts by weight. In addition to the blowing agent, a crosslinking agent is added. Examples of the crosslinking agent here include dicumyl peroxide,
2,5-dimethyl-2,5 di(tert-butyl) peroxide, 1,3 bis(tert-butyl peroxy-isopropyl) benzene, m-
These are organic peroxides such as octadecyl azide formate and tertiary ligyl peroxycumene. The amount added is also related to the amount of blowing agent used,
The amount is 1 to 5 parts by weight, preferably 1 to 2 parts by weight, per 100 parts by weight of EVA. If the amount is less than 1.0 parts by weight, sufficient crosslinking will not occur, and the balance with the foaming agent exceeding 5 parts by weight will be lost, resulting in unstable foaming. Other additives include urea, amines, colorants, and fillers as foaming aids. After the above mixed raw materials are sufficiently kneaded, they are formed into a sheet, cut into a predetermined shape, and filled into a mold together with a large number of rod-shaped members for forming voids. That is, when this sheet-shaped foaming raw material is filled into a mold, a plurality of rod-shaped members for forming voids are embedded therein so as to penetrate to both ends of the raw material body. Specifically, a plurality of foamed raw material sheets are constructed, and the plurality of rod-shaped members are buried in the middle of the sheets in parallel or intersecting, and further in one or more stages in an arbitrary arrangement. . The gap-forming rod member used here may be made of aluminum, steel, stainless steel, or any other metal material, or a thermosetting resin material such as melamine resin or phenol resin, and may have a circular, oval, square, or other arbitrary shape in cross section. . The thickness is not particularly limited either. However, the length needs to be such that it reaches from one end surface of the foamed raw material to be filled into the mold to the other end surface.
The mold used here may be of any shape, but it is preferable to have a wide opening at the top because the product will fly out of the mold all at once when the foamed molded product is demolded.
The foaming raw material is filled into the mold, or slightly pressed, and then the mold is covered and firmly fixed. The method of fixing the cover can be arbitrary, but a convenient method for opening and closing the mold cover freely and for firmly closing the mold is to use a press machine.
In this method, a mold cover is attached to the tip of the mold, and the mold is opened and closed using this. After the mold is closed with a lid, it is immediately heated and foamed. The heating temperature is determined by the decomposition temperature of the blowing agent used, but approximately
The temperature is around 160-170℃. Next, once the foaming has been sufficiently completed, this is allowed to cool once. The cooling temperature here is the raw material used, i.e.
It is determined by the content of vinyl acetate in EVA, the type and amount of blowing agent used, the type and amount of crosslinking agent used, etc. Although it cannot be set uniformly, it is generally 50% higher than the temperature during heat foaming.
The temperature should be 60-110℃, which is about ~80℃ lower. This cooling is
Forced cooling is performed by, for example, sending cooling water to the jacket of the mold. It is thought that this cooling reduces the internal pressure of the mold filled with the EVA foam made by heating and foaming. This is presumed to be because the vapor pressure generated during foaming of EVA is reduced by the temporary temperature drop. After this state, the mold is opened, and as a result, the EVA foam is woven into a fiber shape so as to be ejected from the inside of the mold. The volume of the instant foam is expanded 15 to 50 times.

At this time, since there is a metal or other non-expandable rod-shaped member for forming voids inside the foam raw material, all but this member is foamed outward. As a result, a large gap is formed at the outer periphery of each rod-shaped member. The foam is then demolded, and all of the rod-shaped members described above are extracted from the foam.

The EVA foam obtained in this way has a large number of cavities inside, so its elastic properties are greatly improved, and this has been applied to low-density, highly foamed EVA foam. The foam is lightweight and has very unique physical properties. In addition,
In the above explanation, a low-density, high-foaming EVA foam was explained. However, if the foaming agent is 5 to 15 parts by weight and the crosslinking agent is 0.5 to 1.0 parts by weight to 100 parts by weight of EVA, a high-density, low-foaming product can be obtained. is obtained. However, in this case, the step of cooling the foam prior to demolding becomes unnecessary. The resulting product also has a cavity inside, and its elastic properties are greatly improved as described above. These EVA foams, like other foams, can be widely used in automobiles, furniture, and other fine cushions.

Example 1 EVA (VA content 14%) 100 parts by weight Dicumyl peroxide 1.5 〃 Azodicarbonamide 20 〃 Calcium carbonate 15.0 〃 Of the above raw materials, EVA, dicumyl peroxide, and calcium carbonate were mixed in advance, and this was mixed. The mixture was kneaded for 5 minutes using rolls with a surface temperature of 90° C., azodicarbonamide was added thereto, and the mixture was kneaded again for 4 minutes to form a sheet with a thickness of 2 mm. This was cut to the same size as the mold, and two pieces were first put into a mold with a depth of 8 mm, an inner shape of 30 cm vertically and horizontally, and a wide top opening with an opening of 45 degrees. Next, 10 stainless steel round rods with a diameter of 2 mm and a length of 30 cm were arranged at equal intervals on top of this, and then two raw material sheets similar to those above were placed on top of this, and a single plate cover was placed on top of this. . This mold is pressed from above and below using a press machine.
It was pressed at a pressure of 150 kg/cm ² , heated steam was put into the jacket of the press, and the mold side temperature was heated to 170° C. and held for 15 minutes. Thereafter, the heated steam from the press was removed, water was added thereto, and the mold was held for 5 minutes, resulting in a mold temperature of 80°C. Thereafter, when the press was opened, the bubbles flew upward from the mold all at once. Next, all 10 stainless steel round rods that had been placed in the bubble were removed. The density of this foam was 0.035, and the diameter of the cavity after removing the round rod was 8 mm. Moreover, the external shape was exactly the same as the internal shape, and no cracking or explosion occurred. In addition, when the rebound elasticity of this foam was measured according to JISK6401, the average
55%, and the tensile strength was 6.5 Kg/cm ² . Furthermore, the strength of the hips and the feeling of hitting the bottom were extremely good. It also had excellent abrasion resistance and water absorption resistance.

Example 2 The same procedure as in Example 1 was carried out except that the blending ratio was changed as follows. The round rod used was a stainless steel round rod with a diameter of 3 mm.

EVA (VA content 14%) 100 parts by weight Dicumyl peroxide 1.5 〃 Azodicarbonamide 25 parts by weight Calcium carbonate 20 〃 However, the heating temperature was 160°C, which was 10°C lower than in Example 1.
℃, and after foaming, add water to the mold jacket and
When held for a minute, the temperature on the mold side reached 75°C. Thereafter, the same operations as in Example 1 were performed, and the product was taken out from the mold. The density of this bubble is
0.029, and the cavity after removing the round bar was 12 mm. The appearance was similar to that of Example 1.

Example 3 The same procedure as in Example 2 was carried out except that the blending ratio was changed as follows. The round rod used was made of phenolic resin and had a diameter of 2 mm.

EVA (VA content 16%) 100 parts by weight 1,3-bis(tert-butylperoxy-isopropyl)benzene 2.2 parts by weight Azodicarbonamide 30 〃 Zinc oxide 15 〃 However, the cooling holding time is 10 minutes, and the mold is The temperature was 70℃.

The result is a foam with a density of 0.025 and a cavity size of 10.
It was warm in mm.

Example 4 The same procedure as in Example 1 was conducted except for the cooling step and changing the blending ratio as shown below. The round rod used was made of stainless steel and had a diameter of 2 mm.

EVA (VA content 14%) 100 parts by weight 1,3-bis(tert-butylperoxy-isopropyl)benzene 0.7 parts by weight Azodicarbonamide 7.0 〃 Calcium carbonate 20 〃 However, at a heating temperature of 175℃ and a pressure of 150Kg/cm ² It was heated and foamed for 12 minutes. The specific gravity of the product obtained was 0.1 and the cavity had a diameter of 5 mm.

Claims (1)

[Claims] 1 Add and mix the raw materials whose essential components are ethylene-vinyl acetate copolymer, foaming agent, and crosslinking agent in the mold, and insert multiple rod-shaped members for forming voids into the mold by penetrating them to both ends. After that, the mold is tightly closed with a cover, and then heated to form a foam to pressurize the foam in the mold. An elastically modified foam characterized in that the cover is opened, the foam is demolded all at once, and a rod-like member for forming voids buried in the foam material is removed from the resulting foam. Manufacturing method.