JPS60151030A - Manufacturing method of polyolefin resin foamed molding unit - Google Patents

Abstract

PURPOSE:To obtain a foamed polyolefin resin molding unit which produces extremely less pinhole and irregular surface by filling polyolefin resin preliminary foamed particles in a mold, heating and foaming, fusion-bonding among the particles as the foamed molding unit, applying an internal pressure larger than the atmospheric pressure to the molding unit and then heatng to foam in the molds of substantially the same shape and size. CONSTITUTION:The primary foaming step of filling preliminary foamed polyolefin resin particles in a mold, heatig, foaming of fusion-bond among the particles to obtain the foamable molding unit, and the secondary foaming step of pressuring the molding unit obtained in the primary foaming step to apply an internal pressure larger than the atmospheric pressure and then heating to foam the molding unit in the molds of substantially the same shape and size are provided. Thus, the disadvantages of the foamed polyolefin resin molding unit which feasibly occurs in the irregularity of the thickness due to the pinhole or irregular surface are eliminated, thereby manufacturing the foamed polyolefin resin molding unit having preferable physical properties.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyolefin resin foam molded article.

In recent years, foamed R& mold bodies made by heating and foaming pre-expanded polystyrene resin particles in a mold have been widely used in the fields of containers, packaging materials, insulation materials, etc.; Due to the nature of polystyrene resin, it has the disadvantage of being brittle and is easily damaged by external stress, so when used as a hot water container in particular, there are problems such as easy burn accidents. Furthermore, when used as food containers, polystyrene resins have poor oil resistance, which limits the types of foods that can be packaged, and because they have high water vapor permeability, the packaged foods tend to deteriorate due to moisture absorption. It had

On the other hand, a polyolefin resin foam molded product obtained by molding in a mold using pre-expanded particles having a polyolefin resin as a base resin can overcome the drawbacks of the polystyrene resin foam molded product described above. Pre-expanded resin particles are inferior to pre-expanded polystyrene-based resin particles in secondary foaming ability (expansion ability of pre-expanded particles), so each pre-expanded particle is difficult to sufficiently expand when molded in a mold. However, there have been problems such as pinholes occurring between the pre-expanded particles due to poor fusion between the pre-expanded particles, and unevenness on the surface of the foam resulting in non-uniform wall thickness.

The present invention has been made in view of these points, and an object of the present invention is to provide a method for producing a polyolefin resin foam molded product that can produce a polyolefin resin foam molded product with extremely few occurrences of pinholes and surface irregularities. shall be.

That is, in the present invention, pre-expanded polyolefin resin particles are filled into a mold, heated and foamed, the particles are fused together to obtain a foamed molded product, and then an internal pressure higher than atmospheric pressure is applied to the foamed molded product. After that, the present invention provides a method for producing a polyolefin resin foam molded article, which is characterized in that the foamed molded article is heated and foamed in a mold having substantially the same shape and size as the foam molded article.

The method for producing a polyolefin resin foam molded article of the present invention includes a primary foaming step of filling pre-expanded polyolefin resin particles into a molding mold and heating and foaming them to fuse the particles to each other to obtain a foam molded article; - After applying pressure to the foamed molded product obtained in the secondary foaming step to apply an internal pressure higher than atmospheric pressure, the foamed molded product is heated and foamed in a mold having approximately the same shape and size as the foamed molded product. It consists of a foaming process. - The polyolefin resin pre-expanded particles used in the subsequent foaming process have a polyolefin resin such as polyethylene resin or polypropylene resin as a base resin, and these base resins may be either crosslinked or non-crosslinked. In particular, thermally crosslinked ribropylene resins are preferred. The above polypropylene resin is JIS K 6758-1981.
For example, propylene homopolymer, ethylene-tetrapyrene-butyl copolymer,
Examples include ethylene-propylene random copolymers, and so-called polymer blend products in which these polymers are blended with elastomers and 1-olefin polymers. Examples of elastomers used for blending include polyisobutylene and ethylene propylene rubber, and examples of 1-olefin polymers include polyethylene. Examples of blend products include two-type blend products such as propylene homopolymer/polyisobutylene and propylene cogelimer/polyethylene, and three-type blend products such as propylene homopolymer/ethylene propylene rubber/polyethylene.

Among these, ethylene-propylene random copolymers are preferred, and ethylene-propylene random copolymers containing 90 to 98% of propylene components are particularly preferred.

The pre-expanded particles having the above-mentioned polyolefin resin as a base resin used in the present invention are prepared by, for example, adding 1 olefin resin particles to 100 parts by weight of the resin particles in a closed container, and adding 100 parts by weight of a dispersion medium such as water to 100 parts by weight of the resin particles. ~400 parts by weight, Zikp
5 to 30 parts by weight of a blowing agent such as rhodifluoromethane and, if necessary, 0.1 to 0.1 to 30 parts of a dispersing agent such as finely divided aluminum oxide.
After impregnating the resin particles with the foaming agent by heating with stirring to a temperature around the temperature at which the resin particles soften with 3 parts by weight, one end of the container is opened and the resin particles and dispersion medium are placed in a lower pressure atmosphere than the inside of the container. It can be obtained by a method such as releasing the resin particles downward and foaming the resin particles. The pre-expanded particles obtained in this way are pressurized with an inorganic gas such as air, nitrogen, or argon, or a mixed gas of an inorganic gas and a volatile blowing agent, and are usually
．． 5 to 10kII/ctI(G), preferably 1.5 to
After applying an internal pressure of 7 kliJ/d (G), it is filled into a mold.

In the primary foaming step of the present invention, pre-expanded particles filled in a mold are heated and foamed to obtain a foamed molded product.
Water vapor, heating gas, a heater, etc. are used to heat the pre-expanded particles, and usually water vapor of 2 to 6 kII/cIIi (G) is used.

In the present invention, an internal pressure higher than atmospheric pressure is applied to the foamed molded product obtained in the primary foaming step, and this internal pressure is applied by heating the foamed molded product with an inorganic gas or a mixed gas of an inorganic gas and a volatile blowing agent. It is done by pressure treatment,
The internal pressure applied to the foam molded product is 0.5 to xokg/d (
G) is preferred. If the internal pressure of the foam molded product is below atmospheric pressure, the pinholes and surface irregularities of the foam molded product obtained in the primary foaming process will appear almost as they are in the foam molded product finally obtained through the secondary foaming process, and the product will be good. It is not possible to obtain a foam molded product.

Examples of the inorganic gas used in the pressure treatment include air, nitrogen, carbon dioxide, argon, helium, etc., but air is usually preferred. Examples of volatile blowing agents include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane; trichlorofluoromethane;
Examples include halogenated hydrocarbons such as dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride.

The foamed molded product to which the internal pressure has been applied is heated and foamed in a mold having approximately the same shape and size as the molded product, but the heating of the foamed molded product is performed using the same heating method as in the soft foaming step. method is adopted.

The mold for storing the foamed molded product may be the mold used in the soft foaming step, or another mold may be used. When using another mold, the size of the mold may be slightly larger than the size of the foam molded product obtained in the primary foaming process, but - the foam molded product obtained in the soft foaming process The foaming ratio of the foam molded product obtained in the secondary foaming process is 1
．． The size is preferably about 5 times or less. In addition, a mold that can change the volume inside the mold is used, and the foam molded product obtained in the primary foaming process is housed in the mold and heated to foam and increase the volume inside the mold. Foam molding may also be carried out; conversely, the internal volume of the mold is reduced and the foam molded product is compressed, and the foaming ratio of the foam molded product obtained in the secondary foaming process is - - the foam molding obtained in the soft foaming process. Foam molding may be performed so that the foaming ratio is about 0.30 to 0.99 times the foaming ratio of the body. When foam molding is performed by compressing the foam molded product obtained in the primary foaming step in the secondary foaming step, the finally obtained foam molded product has stronger fusion properties between the pre-expanded particles, A foamed molded product with higher strength can be obtained.

In the present invention, not only the foamed molded product obtained in the primary foaming step is immediately heated and foamed in the secondary foaming step, but also - the soft foaming step and the secondary foaming step are each carried out separately and consecutively. Therefore, by applying internal pressure higher than atmospheric pressure and heating and foaming in the secondary foaming process, foam molded products manufactured and stored using conventional methods can be made into good quality products with extremely few pinholes and surface irregularities. It can be made into a foam molded product.

Although the manufacturing method of the present invention can be applied to any shape or size of olefin resin foam molded products, it is particularly suitable as a manufacturing method of thin-walled foam molded products such as containers.

As explained above, according to the present invention, although it has superior strength and physical properties such as oil resistance and water vapor permeability compared to polystyrene resin foam moldings, it does not cause pinholes or surface irregularities. We have improved the drawbacks of polyolefin resin foam molded products, which tend to cause variations in wall thickness due to the occurrence of
It has the effect of producing a polyolefin resin foam molded product having good physical properties.

The present invention will be explained in more detail below by giving Examples and Comparative Examples.

Examples 1-5. Comparative Examples 1-2 A spherical ethylene-propylene random copolymer (ethylene component: 3.5
Weight%) 100 parts by weight of particles, 300 parts by weight of water, 20 parts by weight of diktetralodiphtetramethane, 0 parts by weight of finely divided aluminum oxide
．． After heating 3 parts by weight with stirring and maintaining it at the foaming temperature shown in Table 1, one end of the container was opened while maintaining the internal pressure of the container at 30 to 9/- (G) at the same temperature with nitrogen gas, The resin particles and water were simultaneously released under atmospheric pressure to foam the resin particles to obtain pre-expanded particles having the expansion ratio shown in Table 1. These pre-expanded particles are pressurized with air and
After applying an internal pressure of kg/l:nl (o), it was filled into a mold for molding a cup and heated with steam of 5 kg/cd (G), and the inner diameter of the opening having the wall thickness shown in Table 1 was obtained. 8
A container with an inner diameter of 64 m and a depth of 100 m at the bottom was obtained. Table 1 shows the results of observing the number of pinholes and surface condition of the container obtained in this soft foaming process. Next, this container was pressurized with the gas shown in Table 1 to give the internal pressure (absolute pressure: kg15!・αbs) shown in the same table. It was left for 48 hours.The internal pressure at that time was 10 k&/ca・αh3
Met. ), - It was stored in the cup molding mold used in the soft foaming process, and heated for 10 seconds with 5 kg/cfIl (G) steam. Table 1 also shows the results of observing the number of pinholes and surface condition of the container obtained after the completion of the secondary foaming step.

*1 The container was turned upside down and submerged 30 cm below the water surface, and the number of locations where air bubbles were generated from the surface of the container was measured.

East 2 Observe the surface of the container and find that the surface is smooth and has very small irregularities.
0 Poor surface smoothness and large unevenness ・・・・・・・・・
It was determined as ×.

Claims (1)

[Claims] Pre-expanded polyolefin resin particles are filled into a mold and heated to foam, the particles are fused together to obtain a foamed molded product, and then an internal pressure greater than atmospheric pressure is applied to the foamed molded product, followed by foaming. The molded body has approximately the same shape as the foamed molded body,
A method for producing a poly first/fin type resin foam molded product, which comprises heating and foaming the product in a hollow having a certain size.