JP5271589B2 - Method for producing polyolefin foam hot-press molded product - Google Patents

Description

    The present invention relates to a method for producing a hot-press molded product of a foam.

    A conventionally known hot-press molded product of foam is formed in the same shape as the inner shape of the mold by placing the foam in a heated mold and heating it under pressure (Japanese Patent Application Laid-Open No. 2007-245601). Publication).

In addition, a method for obtaining a molded product by foaming foamed particles in a mold (Japanese Patent Laid-Open No. 8-92407) and (Japanese Patent Laid-Open No. 2003-226775) are known.
JP 2007-245601 A JP-A-8-92407 JP 2003-226775 A

However,
Since a foam having a size larger than that of the mold was put into the mold and pressed, color unevenness occurred depending on the occurrence of burrs on the mating surfaces of the mold and the degree of heat circulation.

, Since foamed particles were put in a mold and foamed, no burr was produced, but a line in which the foamed particles were fused was formed into a molded product, and a molded product with a clean appearance could not be obtained.

    The inventors of the present invention have developed a method for producing a molded article that eliminates the drawbacks of the conventional method for producing a molded article and has no appearance of burrs and has a beautiful appearance.

A foaming agent and a crosslinking agent are added and kneaded to the polyolefin resin, and the resulting crosslinkable foamable composition is filled into a closed mold A, heated under pressure, shaped and taken out, and then put into a closed mold B under pressure. After heating, the foaming agent and the crosslinking agent are decomposed and cooled to obtain a foam smaller than the molded product, and the foam obtained is put into a mold C and heated to form under pressure. Product manufacturing method.
In the present invention, the volume of the mold A is preferably 1 to 5% smaller than the volume of the mold B, and the dimension of the mold C is 1.5 to 2.5 times the dimension length and width of the mold B. It is preferable that When the volume of the mold A is larger than 5% of the volume of the mold B, charging is insufficient in the mold B, and when the volume is smaller than 1%, the burrs leak in the mold B. When the dimension of the mold C is less than 1.5 times the dimension of the mold B, burrs are generated in the molded product, and when it exceeds 2.5, only a molded product inferior in hardness and strength can be obtained.

  According to the method of the present invention, since a foam larger than the mold is not put into the mold and molded, no burr is generated on the mating surface of the mold.

In addition, since the foamed particles are not put into a mold and foamed, a molded product having a clean appearance can be obtained.

    Resins that can be used in the present invention are thermoplastic resins, for example, low, medium, high, linear polyethylene, ethylene-vinyl acetate copolymers, polyolefin resins such as polypropylene, vinyl chloride resins, polystyrene, elastomers, etc. Mention may be made of rubbers such as ethylene propylene diene copolymer rubber (EPDM).

The foaming agent referred to in the present invention is a chemical foaming agent having a decomposition temperature equal to or higher than the melting temperature of the resin used. For example, azo compounds such as azodicarbonamide and barium azodicarboxylate; nitroso compounds such as dinitrosopenta Methylenetetramine, trinitrotrimethyltriamine, etc .; p, p′-oxybisbenzenesulfonyl hydrazide, etc. of hydrazide compounds; p, p′-oxybisbenzenesulfonyl semicarbazide, toluenesulfonyl semicarbazide of sulfonyl semicarbazide compounds, etc. There are Jid etc.

The cross-linking agent as used in the present invention has a decomposition temperature that is at least equal to or higher than the resin flow start temperature in the resin to be used, decomposes by heating, generates free radicals, and crosslinks between or within the molecules. Organic peroxides that are radical generators that form bonds, such as dicumyl peroxide, 1,1-ditertiary butyl peroxide, 1,1-ditertiary butyl peroxy-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-ditertiary butyl peroxyhexane, 2,5-dimethyl-2,5-ditertiary butyl peroxyhexyne, α, α-ditertiary butyl peroxyisopropylbenzene, tertiary butyl peroxy Such as ketones and tertiary butyl peroxybenzoate However, the optimum organic peroxide must be selected depending on the resin used at that time.

In the present invention, a foaming aid can be added depending on the type of foaming agent. Examples of the foaming aid include compounds mainly composed of urea, metal oxides such as zinc oxide and lead oxide, compounds mainly composed of salicylic acid and stearic acid, that is, higher fatty acids or higher fatty acid metal compounds.

    In the present invention, for the purpose of improving the physical properties of the composition to be used or reducing the price, a compounding agent (filler) that does not significantly adversely affect the cross-linking, such as zinc oxide, titanium oxide, calcium oxide, magnesium oxide, oxidation Metal oxides such as silicon, carbonates such as magnesium carbonate and calcium carbonate, fiber materials such as pulp, various dyes, pigments, fluorescent materials, and other conventional rubber compounding agents can be added as necessary. .

    As the material of the mold used in the present invention, a metal such as iron or aluminum can be used. However, since a very high press pressure is applied to the mold B, it is better to use an iron mold.

    Next, the manufacturing method of the hot-press molded product of this invention is demonstrated.

    The method for producing a foam hot-press molded product of the present invention can be foamed and molded by a conventionally known method and appropriate conditions depending on the foaming temperature, crosslinking initiation temperature, etc. with the used foaming agent or organic peroxide. it can. Particularly preferred methods and conditions are described below.

A well-known foaming agent, foaming assistant, and organic peroxide are added to 100 parts by weight of the resin component, and this is kneaded by a mixing roll, a pressure kneader, an extruder, or the like. Next, the obtained expandable resin composition is put into a mold A during pressing and heated at 90 to 110 ° C. at a pressure of 20 kg / cm ² or more for a certain time. Next, the composition is put in a mold B, heated at 140 to 170 ° C. at a pressure of 130 kg / cm ² or more for a predetermined time to decompose the foaming agent and the crosslinking agent, and then cooled to take out the foam. When the taken-out foam is put into the mold C and heated at 110 to 120 ° C. at a pressure of 20 kg / cm ² or more for a predetermined time, the foam swells and fills the inside of the mold C. Cool after filling and remove the molded product.

Linear low-density polyethylene (trade name: affinity EG8200, density 0.870 g / cm ³ , melt index 5.0 g / 10 min, manufactured by Dow Chemical Japan), 100 parts by weight, azodicarbonamide 4.5 parts by weight, dicumyl A composition comprising 0.8 parts by weight of peroxide and 30 parts by weight of calcium carbonate was placed in a mold A, heated at 40 kg / cm ² at 100 ° C. for 10 minutes, and then taken out. The taken-out compound was put into the metal mold B, heated under pressure at 150 kg / cm ² and 160 ° C. for 60 minutes, and then cooled to obtain a foam.
Next, the foam was put into a mold C, heated under pressure at 40 kg / cm ² and 120 ° C. for 20 minutes, and then cooled to obtain a hot-pressure molded product.

  The mold A was 2% smaller than the volume of the mold B, and the mold C was twice as long as the dimension B of the mold B.

The obtained hot-pressed molded product was a molded product with a beautiful appearance that did not require burr cutting.
Comparative Example 1

  With the same composition as in Example 1, the process of putting in the mold A was omitted, and only the processes of the molds B and C were performed to obtain a hot-press molded product.

The obtained hot-press molded product was a molded product in which a crack occurred on the mating surface of the mold.
Comparative Example 2

In the same composition as in Example 1, the processes of molds A and B were performed, and the molds C and B were taken out without being cooled and put in the mold C. I could not prepare.
Comparative Example 3

    Except that the volume of the mold A was 0.5% smaller than the volume of the mold B, the same process as in Example 1 was performed to obtain a hot-press molded product.

The obtained hot-press molded product was a molded product in which burrs occurred on the mating surface of the mold.
Comparative Example 4

Except that the volume of the mold A was 6% smaller than the volume of the mold B, the same process as in Example 1 was performed, but the mold C was not filled and a clean hot-press molded product was not obtained.
Comparative Example 5

    Except that the dimension of the mold C was 1.3 times the vertical and horizontal thicknesses of the mold B, the same process as in Example 1 was performed to obtain a hot-press molded product.

The obtained hot-press molded product was a molded product in which burrs occurred on the mating surface of the mold.
Comparative Example 6

    Except that the dimension of the mold C is 2.8 times the vertical and horizontal thicknesses of the mold B, the same process as in Example 1 was performed, but only a hot-press molded product with poor hardness and strength was obtained. It was.

As described above, according to the method of the present invention, a hot-press molded product having no appearance of burrs and having a beautiful appearance can be obtained. The hot-press molded product produced by the method of the present invention can be applied to uses of molded products that require flexibility and elasticity, as well as general merchandise and welfare relationships.

Claims (1)

A foaming agent and a crosslinking agent are added and kneaded to the olefin resin, and the resulting crosslinkable foamable composition is filled into a sealed mold A whose volume is 1 to 5% smaller than that of the mold B , and heated and shaped under pressure. extraction, and then foamed by heating to put under pressure in a closed mold B agent, it cooled after decomposing a crosslinking agent to obtain a small foam than moldings, resulting foam dimensions aspect thickness of the mold B A method for producing a foam hot-pressure molded article, which is put in a mold C 1.5 to 2.5 times larger than the above and heated and molded under pressure.