JPS6362372B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ethylene polymer or an ethylene polymer having a rigid low-density or non-foam core inside and a surface layer covered with a high-density foam with a highly elastic skin. The present invention relates to a method for producing a crosslinked foam of a copolymer. An integrally molded foam product having an internal core as described above and a method for manufacturing the same have not been known in the past. Such molded articles can be used in a variety of interesting applications, as described below. The present inventors have arrived at the present invention as a result of researching various methods for manufacturing foam molded products as described above. That is, in the present invention, a foamable compound containing an ethylene polymer or copolymer, a blowing agent, and a crosslinking agent whose decomposition temperature is lower than that of the blowing agent is filled into a first mold, heated under pressure for a certain period of time, and blended. The decomposition rate of the foaming agent used is 50% or less,
and a first step of producing a crosslinked intermediate product; loading the intermediate product into a second mold and heating it through the mold at a temperature equal to or higher than the decomposition temperature of the blowing agent for a predetermined time; A rigid molded product characterized by a second step in which the inner layer of the molded product is made to have a foaming ratio lower than that of the surface layer or to a non-foamed state by selecting the time, and the molded product is removed from the mold after cooling. This is a method for producing a crosslinked foam molded product having a core. According to the method of the present invention, an ethylene polymer or copolymer having a rigid low-density or non-foam core inside and covered with a high-density foam with a highly elastic skin on the surface layer. crosslinked foam can be easily produced. The ethylene polymer or copolymer referred to in the present invention refers to low-density polyethylene, ethylene-vinyl acetate copolymer containing ethylene as a main component, ethylene-acrylic acid ester copolymer, ethylene-propylene copolymer, and ethylene-vinyl acetate copolymer. These include butene copolymers, ethylene-4-methylpentene copolymers, etc., and also include modified resins such as partially chlorinated polyethylene and ionomers. The blowing agents used in the present invention include azodicarbonamide, N,N'-dinitrosopentamethylenetetramine, and the like. The amount of foaming agent to be used is appropriately determined depending on the expansion ratio of the intended product, but is generally about 2 to 25 parts per 100 parts of resin. Now the foaming ratio is 3 to 25
You can get about twice as much product. These blowing agents can be used in combination with a blowing aid to adjust their decomposition temperature. Examples of the foaming aid include urea compounds, organic acid salt compounds such as zinc stearate, and inorganic compounds such as basic zinc carbonate. The crosslinking agents used in the present invention include dicumyl peroxide, α,α′-bis(tert-butylperoxy)diisopropylbenzene, 1,
1'-bis(tert-butylperoxy)-
3,5,5-trimethylcyclohexane and the like. The amount of crosslinking agent used is 0.5 to 5 parts per 100 parts of resin.
The appropriate amount is preferably about 0.5 to 3 parts. In the present invention, it is desirable to select a crosslinking agent that has a lower decomposition temperature than the blowing agent. In the method of the present invention, first, an ethylene polymer or copolymer is blended with a blowing agent and a crosslinking agent and kneaded, and a compound having a desired shape is formed by a conventional method. At this time, if necessary, add metal,
It can also be insert molded with materials such as wood or other plastics. The compound is then placed in a hermetically sealed mold and heated for a certain period of time to suppress decomposition of the blowing agent and carry out a crosslinking reaction. In this way, in the first step, a crosslinked intermediate product is produced in which the decomposition rate of the blowing agent is 50% or less, preferably 15% or less. If the decomposition rate of the blowing agent exceeds 50%, it will be difficult to form a core with good rigidity in the second step. The intermediate product must be crosslinked. The degree of crosslinking can be selected from a wide range from low to high. The limit for low-grade products is the heating temperature in the first step that allows the product to be removed from the mold without being significantly deformed. Expressing the range of crosslinking degree in terms of gel fraction, for example, 1 to 95% by weight (the amount charged when a 0.3 g sample is placed in a 200 mesh wire mesh basket and immersed in 100 c.c. of xylene at 80°C for 6 hours) percentage of sample remaining in the basket). Parts made of metal, wood, other plastics, etc. can be inserted into the intermediate product after the first step, if necessary. The intermediate product taken out from the mold in the first step is then heated through the mold under normal pressure or a pressure close to it in a mold of a desired size that can be closed but not airtight. By selecting the time and time, the inner layer of the molded product is made to have very low foaming or non-foaming, preferably with a foaming ratio of 2 times or less, and the surface layer is made to have a higher foaming ratio, and after cooling, it is taken out of the mold. In the second step, the intermediate product is heated through the surrounding mold, so that the surface layer of the intermediate product reaches the decomposition temperature of the blowing agent first, and the inner layer lags behind. Therefore, if the foaming agent in the surface layer decomposes and is cooled before the foaming agent in the inner layer decomposes, a structure with a rigid core inside and a skin with high elasticity in the surface layer can be created. A molded article made of a high-magnification foam is obtained. According to the method of the present invention, any shape can be molded as long as it has a certain degree of thickness. The thickness of the molded product should preferably be approximately 2 cm or more at its maximum thickness. Since the product with an insert obtained by the method of the present invention has an internally rigid core, the insert can be firmly bonded to the ethylene polymer or copolymer foam that is the main body of the product. . An ethylene polymer or copolymer obtained by the method of the present invention, which is made of a high-density foam with a skin having a rigid, low-density or non-foamed core and a highly elastic surface layer. Applications of the combined cross-linked foam include baseball substitutes, softball substitutes, surfboards, footwear soles, core materials or insoles for footwear, floats for the fishing industry, safety pillows for automobiles, etc. . The present invention will be explained below with reference to Examples, but the present invention is not limited thereto. Example 1 A compound was prepared by kneading the ingredients shown in Table 1 using an open roll at 70 to 80°C. Compounds of approximately the same size were placed in a 60 mmφ spherical mold and heated at 145 to 150°C for 15 minutes to obtain an intermediate product. Next, this intermediate product was placed in a spherical mold with a diameter of 72 mm engraved with a ball design, and heated to 200°C.
After heating for 18 minutes, the product was cooled and taken out. Cut the obtained product (ball) into two,
When you look at the cross section, you can see that there is a skin on the surface of the ball, and the surface layer about 10mm from that is made of foam with moderate elasticity, and the core deeper than that is made of extremely low-magnification foam, with moderate elasticity. It gives a sense of weight. Note that there is an intermediate foam layer with a width of about 3 mm between the surface layer and the core. Table 2 shows the results of measuring the hardness of the surface layer and core. Example 2 A compound made by kneading the same ingredients and under the same conditions as in Example 1 was put into a 66 mmφ spherical mold, and the compound was made into a mold with approximately the same size as 145 to 150 mm.
℃ for 15 minutes to obtain an intermediate product. Next, this intermediate product was placed in a spherical mold with a diameter of 72 mm engraved with a ball design, and heated to 200°C.
After heating for 18 minutes, the product was cooled and taken out. The obtained product (ball) was cut into two halves in the same manner as in Example 1, and when viewed in cross section, it had the same structure as in Example 1. The surface of the ball has a skin, then about 4
The surface layer of the mm is made of a moderately elastic foam, the core is made of extremely low-magnification foam, and there is an intermediate foam layer with a width of about 2 mm between the surface layer and the core. Table 2 shows the results of measuring the hardness of the surface layer and core. This ball is similar to regular hardball baseballs in terms of weight, rebound, and other properties, and has superior durability and water resistance compared to regular baseballs, making it useful as a practice ball. Table 1 Formula resin (parts by weight) EVA 100 EPT 20 Foaming agent Azodicarbonamide 2.05 Crosslinking agent Dicumyl peroxide 1.0 Lubricant Stearic acid 1.0 Filler Calcium carbonate 10.0 Pigment Titanium white 4.0 (Note) EVA: Ethylene - Vinyl acetate copolymer, vinyl acetate content 10% by weight, trade name Evatate D3010 manufactured by Sumitomo Chemical Co., Ltd. EPT: ethylene-propylene terpolymer,
Product name Esplen 501A Sumitomo Chemical Co., Ltd.
Manufactured by Azodicarbonamide system: Product name Vinifol
DW-6, manufactured by Eiwa Kasei Kogyo Co., Ltd. [Table]

Claims (1)

[Claims] 1 Fill a first mold with a foamable compound containing an ethylene polymer or copolymer, a blowing agent, and a crosslinking agent whose decomposition temperature is lower than that of the blowing agent, and heat under pressure for a certain period of time to decompose the blended blowing agent. a first step of producing a crosslinked intermediate product with a crosslinking rate of 50% or less, and loading the intermediate product into a second mold and passing it through the mold at a temperature above the decomposition temperature of the blowing agent for a predetermined time The second step consists of heating, and by selecting the heating temperature and time, the inner layer of the molded product is made to have a foaming ratio lower than that of the surface layer or to a non-foamed state, and after cooling, it is removed from the mold. A method for producing a cross-linked foam molded product having a rigid core, characterized by: