JP4666355B2 - Method for producing crosslinked polyolefin open cell foam - Google Patents

Description

  The present invention relates to a method for producing a crosslinked polyolefin open-cell foam formed into a desired product shape.

  Cross-linked polyolefin foams are used in various applications by taking advantage of their excellent cushioning properties, cushioning properties, and compression deformation recovery properties. The crosslinked polyolefin foam includes a closed cell type and an open cell type. In some applications, there is a need for a crosslinked polyolefin foam having a three-dimensional shape different from a simple flat plate or block shape.

  Regarding the demand for the three-dimensional shape of the cross-linked polyolefin closed cell foam, the cross-linked polyolefin closed cell foam is placed in a shaping mold and heat-softened to adhere closely to the mold surface and then shaped into a mold surface shape, and then cooled. The shape of the crosslinked polyolefin closed-cell foam is fixed.

  On the other hand, the demand for a three-dimensional shape for the crosslinked polyolefin open-cell foam is the same as that for shaping the crosslinked polyolefin closed-cell foam into a three-dimensional shape. When trying to shape by close contact with the mold surface by storing in a mold and softening by heating, the crosslinked polyolefin open-cell foam is greatly shrunk in a short time by heating, and can adhere to the mold surface of the shaping mold. Loss of good shape becomes impossible. The reason for this is that the cross-linked polyolefin open-cell foam is made of open cells and communicates with the outside, so that heated air quickly enters the cross-linked polyolefin open-cell foam to dissolve the cell skeleton. This is thought to be due to the fact that the space formed by the bubble skeleton disappears.

  Also, in order to prevent shrinkage during heating of the crosslinked polyolefin open cell foam, it is possible to reduce the amount of heat applied to the foam by lowering the heating temperature or shortening the heating time. Due to insufficient heating, the foam is not sufficiently softened and is not deformed along the mold surface, and the mold surface shape cannot be shaped well.

JP 2002-36338 A Japanese Patent Laid-Open No. 7-119311

  This invention is made | formed in view of the said point, Comprising: It aims at provision of the manufacturing method of the crosslinked polyolefin open cell foam which consists of desired three-dimensional shapes.

  In the present invention, the cross-linked polyolefin closed-cell foam is accommodated in a shaping mold and softened by heating, so that it is brought into close contact with the mold surface of the shaping mold and shaped into a mold surface, and then cooled to Cross-linked polyolefin open cell by fixing the shape of the cross-linked polyolefin closed-cell foam and compressing the cross-linked polyolefin closed-cell foam after shaping to break the cell wall of the cross-linked polyolefin closed-cell foam The present invention relates to a method for producing a cross-linked polyolefin open-cell foam, characterized by performing a communication step of forming a foam.

  According to the first aspect of the present invention, prior to the communicating step, the cross-linked polyolefin closed cell foam is accommodated in the shaping mold and heat-softened so as to be in close contact with the mold surface of the shaping mold. The forming process is performed. For this reason, the heat at the time of shaping is prevented from entering the cross-linked polyolefin closed-cell foam by the closed cells of the cross-linked polyolefin closed-cell foam, and the cell structure is prevented from being dissolved by heat at the time of shaping. Shrinkage of the foam is prevented. From this, the cross-linked polyolefin closed-cell foam in the heat-softened state can be well shaped and adhered efficiently to the mold surface. Furthermore, since the cross-linked polyolefin open-cell foam in which the cell walls have been destroyed by compression in the communication process has good compression recovery, it can be restored well when the compression is released, and the shape formed in the shaping process is There is no risk of damage.

  Embodiments of the present invention will be described below. In the method for producing a crosslinked polyolefin open-cell foam in the present invention, a shaping step and a communication step are performed on the foamed crosslinked polyolefin closed-cell foam.

  The crosslinked polyolefin closed cell foam is obtained by foaming a kneaded product obtained by kneading a compound containing at least a polyolefin resin, a crosslinking agent, a foaming agent and further containing an appropriate auxiliary agent in the kneading step. It consists of things.

  The polyolefin resin used in the present invention is not particularly limited, and ethylene vinyl acetate copolymer (EVA), low density polyethylene (LDPE), high density polyethylene (HDPE), ethylene-propylene copolymer, ethylene- Butene copolymers, copolymers of ethylene and methyl, ethyl, propyl or butyl acrylates, or chlorinated products thereof, or a mixture thereof, and also a mixture of them with isotactic polypropylene or atactic polypropylene. Etc.

  As the cross-linking agent, conventionally known cross-linking agents used for foaming cross-linked polyolefin closed-cell foams are used. Examples thereof include organic peroxides such as dicumyl peroxide, 2,5-dimethyl-2,5-bis-tertiary butyl peroxyhexane, 1,3-bis-tertiary peroxy-isopropylbenzene, and the like. . The amount of the crosslinking agent is usually 0.50 to 1.3 parts by weight with respect to 100 parts by weight of the polyolefin resin.

  As a foaming agent, what decomposes | disassembles by heating and generate | occur | produces gas is used, and it does not restrict | limit in particular. For example, azodicarbonamide, 2,2'-azobisisobutyronitrile, diazoaminobenzene, benzenesulfonyl hydrazide, benzene-1,3-sulfonyl hydrazide, diphenyl oxide-4,4'-disulfonyl hydrazide, 4,4 ' -Oxybisbenzenesulfonyl hydrazide, paratoluenesulfonyl hydrazide, N, N'-dinitrosopentamethylenetetramine, N, N'-dinitroso-N, N'-dimethylphthalamide, terephthalazide, pt-butylbenzazide, One or more of sodium bicarbonate, ammonium bicarbonate and the like are used. In particular, azodicarbonamide and 4,4′-oxybisbenzenesulfonyl hydrazide are preferable. The addition amount is usually 2 to 30 parts by weight with respect to 100 parts by weight of the polyolefin resin.

  Examples of compounding agents that are added as appropriate include foaming aids and additives. Examples of the foaming aid include compounds containing urea as a main component, metal oxides such as zinc oxide and lead oxide, lower or higher fatty acids, and metal salts of lower or higher fatty acids. Examples of the additive include a lubricant and a pigment.

  In the kneading step, the polyolefin resin, the crosslinking agent, the foaming agent and the like are kneaded with a kneader or a roll to obtain a kneaded product.

  In the foaming step, the kneaded product is foamed according to a two-stage foaming method used for producing a known crosslinked polyolefin closed-cell foam. In the two-stage foaming method, first, the kneaded product is filled into a hermetic primary foaming mold, heated under pressure and then decompressed to perform primary foaming to form a primary foam. Next, the said primary foam is accommodated in a secondary foaming mold, it heats at a normal pressure, is subjected to secondary foaming, and is then cooled to obtain a crosslinked polyolefin closed cell foam. The expansion ratio is appropriately determined according to the intended use, but generally 10 to 60 times is preferable.

  In the shaping step, the cross-linked polyolefin closed-cell foam is placed in a shaping mold and heat-softened so that it is brought into close contact with the shaping surface of the shaping mold and shaped into a mold surface shape, and then cooled. The shape of the crosslinked polyolefin closed cell foam is fixed. The shaping mold has a mold surface having a shape corresponding to the outer shape of the target product, and can be heated. Further, the shaped mold is divided into a lower mold and an upper mold, and the space between the lower mold and the upper mold is narrowed to press (compress) the crosslinked polyolefin closed cell foam in the shaped mold. Thus, the cross-linked polyolefin closed-cell foam may be securely brought into close contact with the mold surface of the shaping mold and shaped more accurately. The method for heating and pressing the shaping mold is not particularly limited. For example, a shaping die may be disposed between the heating plates of the heating press apparatus so that both heating and pressing can be performed efficiently. Generally, the crosslinked polyolefin closed cell foam is pressed so as to be 50 to 90% of the thickness before compression.

  The cross-linked polyolefin closed-cell foam accommodated in the shaping mold was previously made to correspond to the dimension and shape corresponding to the mold surface of the shaping mold by punching or cutting, that is, the desired shaping shape. Dimensioned and shaped. Furthermore, the crosslinked polyolefin closed-cell foam accommodated in the shaping mold is shaped so as to have a required amount larger than the intended shaping shape, and the shaped polyolefin is formed using the elastic deformation of the crosslinked polyolefin closed-cell foam. It is preferable that only the heating or the heating and pressing be performed in the state of being accommodated in the mold. In this way, the cross-linked polyolefin closed-cell foam can be more accurately shaped by more closely contacting the mold surface of the shaping mold.

  The heating condition in the shaping step is a temperature at which the cross-linked polyolefin closed cell foam is softened or the surface is partially melted, and varies depending on the type of the cross-linked polyolefin closed cell foam. ° C, preferably in the range of 100 to 150 ° C. The heating time varies depending on the kind of the crosslinked polyolefin closed-cell foam, the heating temperature, the intended shaping shape, etc., but is usually 30 seconds to 20 minutes, preferably about 2 minutes to 10 minutes. The cooling in the shaping step is performed by lowering the temperature of the shaping mold in a state where the crosslinked polyolefin closed cell foam is accommodated in the shaping mold.

  In the communicating step, the crosslinked polyolefin closed cell foam after shaping is compressed to break the cell walls of the crosslinked polyolefin closed cell foam to form a crosslinked polyolefin open cell foam. The degree of compression of the crosslinked polyolefin closed-cell foam after shaping is not particularly limited as long as it can destroy the cell walls of the crosslinked polyolefin closed-cell foam. Generally, it presses so that it may become 1 / 2-1 / 20 with respect to the original thickness before compression. The compression method is not particularly limited, and for example, a method may be employed in which a crosslinked polyolefin closed-cell foam after shaping is sandwiched between flat plates and compressed or passed through a biaxial roll.

  Ethylene vinyl acetate copolymer (product number: EVAFLEX P-1403, manufactured by Mitsui DuPont Polychemical Co., Ltd.) as a polyolefin resin, azodicarbonamide (product number: VINYHALL AC # 3, Eiwa Chemical Co., Ltd.) as a foaming agent 19 parts by weight), 0.8 parts by weight of dicumyl peroxide as a crosslinking agent, 0.3 parts by weight of zinc stearate as a foaming aid, and 20 parts by weight of calcium bicarbonate as an additive. A kneader and an 8 inch roll are kneaded in this order to obtain a kneaded product. This kneaded product is sealed in a primary foaming mold having a storage space of 30 mm in depth, 170 mm in width and 170 mm in length, and heated under pressure for 40 minutes. After that, primary foaming was performed by depressurizing to obtain a primary foam. Next, the primary foam is accommodated in a secondary foaming mold having a housing space having a depth of 100 mm, a width of 500 mm, and a length of 500 mm, and subjected to secondary foaming by heating at 160 ° C. for 100 minutes under normal pressure, followed by cooling. Thus, a block-like crosslinked polyolefin closed cell foam was obtained.

  The crosslinked polyolefin closed cell foam was cut into a thickness of 25 mm and punched into a cyclic crosslinked polyolefin closed cell foam 11 as shown in FIG. 1 with a punching die having an inner diameter of 130 mm and an outer diameter of 180 mm. Thereafter, the crosslinked polyolefin closed cell foam 11 is accommodated in the lower mold 21 of the shaping mold 20 having the mold surface 22 having the depth d1 of 20 mm, the center diameter d2 of 125 mm, and the inner peripheral diameter d3 of 175 mm. As shown in FIG. 2, the lower mold 21 and the upper mold 23 of the shaping mold 20 were closed with a heating press device 30. At this time, the interval between the lower mold 21 and the upper mold 23 of the shaping mold 20 was set so that the crosslinked polyolefin closed-cell foam 11 in the shaping mold 20 had a thickness of 20 mm. In that state, 0.5 MPa steam was introduced into the hot platen 31 of the hot press apparatus 30 to heat the shaping mold 20 and the crosslinked polyolefin closed-cell foam 11 for 2 minutes. Thereby, the cross-linked polyolefin closed-cell foam 11 was softened by heating and was brought into close contact with the mold surface of the shaping mold 20 and shaped into a mold surface shape. Thereafter, the introduction of steam into the hot platen 31 was stopped, cooling water was introduced to cool the crosslinked polyolefin closed cell foam 12 after shaping, and it was taken out from the shaping mold 20. Next, as shown in FIG. 3, the crosslinked polyolefin closed-cell foam 12 after shaping is compressed to a thickness of 1/5 through constant-speed biaxial rolls 41 and 41 whose roll interval is adjusted to 4 mm, By performing this compression twice, the cell wall of the crosslinked polyolefin closed cell foam 12 was broken and connected to obtain a crosslinked polyolefin open cell foam. The obtained crosslinked polyolefin open-cell foam was finished according to the mold surface of the shaping mold. In this embodiment, the molded product is shaped so as to be rounded on one side, and the obtained molded product is suitable for a buffer member such as a sealing material or a pad material.

  For comparison, a cross-linked polyolefin closed-cell foam was used instead of the cross-linked polyolefin closed-cell foam, and the molding process was performed using a shaping mold in the same manner as in the case of the cross-linked polyolefin closed-cell foam. The cross-linked polyolefin open-cell foam taken out of the mold was greatly shrunk and did not become a product.

It is a schematic sectional drawing which shows the crosslinked polyolefin closed-cell foam before shaping, a shaping die, etc. in one Embodiment of this invention. It is a schematic sectional drawing which shows the time of a shaping process in the same embodiment. It is a schematic sectional drawing which shows a communication process in the same embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Crosslinked polyolefin closed cell foam before shaping 12 Crosslinked polyolefin closed cell foam after shaping 20 Molding die 30 Hot press device 41 Constant speed biaxial roll

Claims (1)

The crosslinked polyolefin closed cell foam is housed in a shaping mold and softened by heating, so that it is brought into close contact with the mold surface of the shaping mold and shaped into a mold surface shape, and then cooled to form the crosslinked polyolefin closed cell foam. A shaping process to fix the shape of the foam;
Communicating step to form a crosslinked polyolefin open-cell foam by compressing the crosslinked polyolefin closed-cell foam after shaping and destroying the cell wall of the crosslinked polyolefin closed-cell foam,
A method for producing a cross-linked polyolefin open-cell foam, characterized in that

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