JPS5876227A - Manufacture of polypropylene resin foamed and molded body - Google Patents

Abstract

PURPOSE:To improve the dimensional stability, cushioning property, etc. of a molded body, by heating a polypropylene resin prefoamed particles to a temperature >= its heat distortion temperature, filling a mold, which can be closed, but not be tightly closed, with the prefoamed particles, and heating the prefoamed particles to allow them to foam. CONSTITUTION:The prefoamed particles are produced by incorporating 5- 40pts.wt. volatile foaming agent such as aliphatic hydrocabons, cycloaliphatic hydrocarbons, halogenated hydrocarbons, etc. into 100pts.wt. polypropylene polymer particles. After the prefoamed particles are heated to a temperatue >= its heat distortion temperature, the mold which can be closed, but not be tightly closed, is filled with the prefoamed particles, and the prefoamed particles are heated and allowed to foam to obtain a polypropyrene resin foamed and molded body. The molded body can be used as a packaging material, a container for food, a floating material, and in particular if it is used as a packaging material or cushioning material that will be used at high temperatures, it exhibits the remarkable effects.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polypropylene resin foam molding, and more particularly to a polypropylene resin foam molding having good dimensional stability.

The present applicant has successfully developed a bead molding method using pre-expanded particles in the production of pre-foamed polypropylene resin articles, and has already proposed the pre-foaming method (Japanese Patent Publication No. 56-1344). issue). This pre-foaming method involves dispersing polymer particles containing a volatile blowing agent in a closed container, maintaining the pressure inside the container at the vapor pressure of the blowing agent or higher, and increasing the softening temperature of the polymer. After heating to the above extent, one end below the water surface in the container is opened and the polymer particles and water are simultaneously discharged into an atmosphere having a lower pressure than the inside of the container, thereby obtaining pre-expanded particles. The pre-expanded particles obtained by this method are revolutionary and have excellent properties of high foaming, and the foam molded products obtained using these pre-expanded particles have excellent properties, but the mold There is still room for improvement in terms of dimensional stability due to shrinkage during internal molding, dimensional stability when used as a packaging material or cushioning material, especially when used at high temperatures, cushioning properties, etc.

The purpose of the present invention is to provide a method for producing a polypropylene resin foam molded product that is a further improvement over the above-mentioned conventional technology. We have succeeded in developing a method for producing a polypropylene resin foam molding with excellent stability and cushioning properties, and have completed the present invention.

That is, the present invention involves heating pre-expanded particles of l-propylene resin to a temperature higher than the heat distortion temperature of the particles, then filling the particles into a mold that can be closed but cannot be sealed, and heating and foaming the particles. The gist of the present invention is a method for producing a polypropylene resin foam molded article, which is characterized by the following.

Examples of the material for the pre-expanded bopperpyrene resin particles used in the present invention include propylene homopolymer, ethylene-butypyrene random copolymer, ethylene-purpyrene block copolymer, etc., and these may be crosslinked. Although it is not necessary, a non-crosslinked one is particularly useful. Among the above-mentioned polymers, ethylene-propylene random copolymers are preferred, and copolymers with an ethylene component of 0.5 to 10% by weight are particularly preferred.

The polypropylene resin pre-expanded particles used in the present invention can be produced, for example, by the following pre-expanding method. In other words, there is a step in which a volatile blowing agent is added to the polymer particles, a step in which the polymer particles are dispersed in a dispersion medium in a closed container and heated to a predetermined temperature, and one end of the container is opened to allow the particles and the dispersion medium to be mixed together. It can be produced by a pre-foaming method comprising a step of simultaneously releasing the foam into an atmosphere at a lower pressure than in the container.

Volatile blowing agents used in this method include, for example, aliphatic hydrocarbons such as butane, butane, pentane, hexane, heptane, etc., and cyclic aliphatic hydrocarbons such as cyclobutane, cyclopentane, etc. and triclosia 0 romethane, dichlorosifu 0 rimethane, dichlorotetra 70p ethane, methyl chloride, ethyl chloride,
Halogenated hydrocarbons such as methylene chloride are used. The amount of the blowing agent added is not particularly limited, but it is usually 5 to 40 parts by weight per 100 parts by weight of the polymer particles. There is no particular limitation on the timing of incorporating the volatile blowing agent into the polymer particles.

Therefore, the foaming agent may be contained in the polymer particles in advance, and the polymer particles containing the foaming agent may be placed in a closed container and dispersed in a dispersion medium in the closed container, or the polymer particles and the foamed The blowing agent may be incorporated into the polymer particles while the agent is placed in a closed container and dispersed in a dispersion medium within the closed container. Further, during the process of heating the particles to a predetermined temperature in a closed container, or after heating, a blowing agent may be placed in a closed container to disperse the particles and the blowing agent, and the blowing agent may be contained in the particles. . Note that the temperature at which the blowing agent is incorporated into the particles is also arbitrary and is not particularly limited.

In this method, the polymer particles and the volatile blowing agent are separated or the volatile blowing agent is added to the polymer particles and then dispersed in a dispersion medium. Aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, etc. can be used.

The amount of this dispersant added is usually 0.01 to 10 parts by weight per 100 parts by weight of the polymer particles. Further, the dispersion medium may be any solvent that does not dissolve the polymer particles, and examples thereof include one of water, ethylene glycol, glycerin, methanol, ethanol, etc., or a mixture of two or more thereof, but usually Water is preferred.

In this method, one end of the container is opened and the polymer particles and dispersion medium are simultaneously released into an atmosphere at a lower pressure than the inside of the container.
The pressure inside the container at this time may be either higher than or lower than the vapor pressure of the volatile blowing agent, and the atmosphere to be released is normally selected to be an atmosphere at normal pressure.

The pre-expanded particles obtained in this way vary depending on the temperature, pressure, amount of blowing agent, etc. during foaming, but are usually 3 to 6
An appearance of 0x has a foaming magnification.

In the present invention, the pre-expanded particles are heated above the heat distortion temperature of the particles. When the heating temperature is lower than the heat distortion temperature, shrinkage of the pre-expanded particles does not occur and it is difficult to obtain dimensional stability of the foamed molded product. The pre-expanded particles are shrunk by the heating described above. The degree of this shrinkage is not particularly limited, but considering the effect of dimensional stability, uniformity of shrinkage, etc., it is
35≦Shrinkage is preferred. Although the heating step can be carried out after the pressurized heat tiJ described later, it is preferable to carry out it before the pressurized ripening. Also, if it is carried out immediately after the completion of pre-foaming, residual heat will remain in the pre-foamed particles, and the heating amount and heating time will be reduced. This is preferable because it requires less. As a heating method, for example, a method can be used in which pre-expanded particles are stored in a mesh tank and heated by blowing hot air onto them. In the present invention, the heating temperature is higher than the thermal deformation temperature of the pre-expanded particles;
50°C is preferred. Incidentally, the heat distortion temperature of each polymer used in the present invention is preferably in the range of 90 to 130°C, and examples thereof are shown below.

Base material Heat distortion temperature (°C) (ethylene component = 4% by weight) Propylene homopolymer 117 After heating, the pre-expanded particles are usually aged under pressure. This pressure aging is usually carried out for 3 to 72 hours using an inorganic gas or a mixed gas of an inorganic gas and a volatile blowing agent at a temperature of 0.3 to 8 Y/- for 3 to 72 hours. 5kg/-
Width), preferably 3 mm/-C) or less internal pressure is applied. Air, nitrogen, argon, helium, etc. are used as the inorganic gas.

In the present invention, the pre-expanded particles treated as described above are filled into a mold that can close the particles but cannot be sealed, for example, a mold having small holes in the mold surface through which a heating medium such as water vapor can pass. For example, by heating and expanding using water vapor of 2 to 5 Y/-(G), a foam molded product according to the shape can be obtained.

The polypropylene resin foam R& mold body obtained by the present invention can be used, for example, in packaging materials, cushioning materials, vehicle parts, construction materials,
It can be used for heat insulating materials, food containers, flotation materials, etc., and is particularly preferable when used as packaging materials and cushioning materials used at high temperatures because it has a remarkable effect.

As explained above, according to the present invention, the pre-expanded particles are heat-treated at a temperature higher than the heat distortion temperature of the particles to shrink them before the I& mold, and the bubbles are stabilized, thereby improving moldability and dimensional stability. A foamed molded product can be obtained which has excellent physical properties such as high tensile strength, tensile elongation, tear strength, and flexibility, and low compression set.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Examples 1 to 4, Comparative Examples 1 to 6 Thermal deformation temperature was 96″9 (melting point 15
0°C), 100 m of ethylene-propylene random copolymer with ethylene component a, s wt %, 23 kl of dichlorodifluoromethane, 20 μ particle size aluminum oxide o, 5 kI
I, 300'kII of water was stored in a sealed container, and while stirring,
After raising the temperature to 139°C and holding it for 05 hours, one end of the container was opened while maintaining the pressure inside the container at 30 kg 10 n), and the resin particles and water were released into the atmosphere at the same time, resulting in an apparent foaming ratio of 35. twice as many pre-expanded particles were obtained. The pre-expanded particles were stored in a mesh tank and heat-treated by blowing hot air at the temperatures shown in Table 1 to obtain particles having the shrinkage ratio and expansion ratio shown in Table 1.

In addition, pre-expanded particles having different expansion ratios shown in No. 1 Mugi were obtained by the same method as the above-mentioned pre-foaming method except that the amount of blowing agent was changed (without heat treatment).

Each of the above pre-expanded particles was heated at 30°C and 2.5ky/cj (G
) After 50 hours of pressure aging in air, the length is 1000 m.
.

Filling a mold with a width of 600m and a thickness of 60H, 2.5
#/dG) was heated and foamed with water vapor to obtain a foamed molded product. The obtained foam molded product was subjected to a begging test.

The results are shown in Table 1.

*1. Mine 2. *3. *4. *5- The shrinkage rate, tear strength, and compression set of the molded body were determined according to JIS K 6767, and the tensile strength and tensile elongation were determined according to JIS K 6767.

*6- Flexibility was evaluated according to NDS Z 0503 and divided into the following three stages.

〇 - Not formed. 8 - Some cracks and fissures occurred between particles.

〇-Smooth finish with almost no unevenness on the surface △Partially uneven × - full surface unevenness

Claims (1)

[Claims] A polypropylene resin foam molded product characterized by heating pre-expanded polypropylene resin particles to a temperature equal to or higher than the heat deformation temperature of the particles, and then filling the particles into a mold that can be closed but not sealed, and then heated and foamed. manufacturing method.