JPS59133233A - Production of pre-expanded particle of polypropylene resin - Google Patents

Abstract

PURPOSE:To obtain pre-expanded particles having a heightened expansion ratio and a large cell diameter and being capable of forming a foam of a good dimensional accuracy and strong nerve, by heating, with steam, pre-expanded PP resin particles having a specified relationship between the expansion ratio and the number of cells. CONSTITUTION:Pre-expanded particles having an expansion ratio which is higher than the initial expansion ratio are produced by expanding, by heating with steam, pre-expanded PP resin particles having a relationship: 2<E<1/2>Xn<1/245, wherein E is an expansion ratio and n is the number of cells per mm.<2>-cross-sectional area. According to this process, it is possible to produce easily pre-expanded PP resin particles which have a high content of closed cell even at a high expansion ratio of, say, about 50-150, and can be used in molding. It is possible to obtain a molding of a strong nerve and a good dimensional accuracy and good moldability in both cases of low and high expansion.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing pre-expanded polypropylene resin particles, and more particularly to a method for producing pre-expanded polypropylene resin particles having good moldability.

Conventionally, foamed polystyrene and foamed polyethylene have been mainly used for various purposes such as cushioning materials and packaging materials.

Along with these foams, polypropylene resin foam moldings have been used, and the applicant has already filed an application for a method for obtaining pre-expanded particles used in a polypropylene resin bead molding method (Kokusho 56-1344). issue). According to this method, it was considered very difficult to form two foams. Although this is an epoch-making method that allows relatively highly foamed pre-expanded particles to be easily obtained from polypropylene shoulder fat particles, it also has the following problems, and there is still room for improvement. It is something that exists. Namely.

fl) Although relatively high foaming can be obtained, 2
The limit is about 5 times, and even if you try to obtain a product with a magnification higher than this, the closed cell ratio will decrease and it will not be possible to use it for molding.

(2) The cells of the obtained pre-expanded particles tend to be as small as 4, and even if it is attempted to obtain a molded article using such pre-expanded particles, it is difficult to obtain a strong foam with good dimensional accuracy.

The present invention aims to overcome the problems of the prior art described above. That is, one of the objects of the present invention is to provide a method for easily producing pre-expanded polypropylene resin particles that have a high closed cell ratio and can be molded even when the expansion ratio is high, for example, 50 to 150 times. It is to be. Another object of the present invention is to easily produce pre-expanded polypropylene resin particles that have good moldability regardless of whether they are low-foamed or highly foamed, and are strong and can yield molded bodies with good two-dimensional accuracy. The object of the present invention is to provide a method for manufacturing the same.

As a result of intensive research by the present inventors in order to achieve the above object, 1
By heating pre-expanded polypropylene resin particles with a specific relationship between the expansion ratio and the number of cells with steam, the expansion ratio is improved and pre-expanded particles with a larger cell diameter (smaller number of cells) can be obtained. It was discovered that such pre-expanded particles have excellent moldability, and that the foamed molded product obtained using the same has good two-dimensional accuracy and is strong.

The present invention has now been completed.

In other words, in the present invention, pre-expanded polypropylene resin particles satisfying the relationship of the quadratic formula: 2<E" Heat and foam.

The gist of this invention is a method for producing pre-expanded polypropylene resin particles, which is characterized by obtaining pre-expanded particles having an expansion ratio greater than the original expansion ratio E.

Examples of the polypropylene resin used in the present invention include propylene homopolymers, ethylene-propylene random copolymers, ethylene-globylene block copolymers, mixtures thereof, and ethylene-propylene random copolymers. is particularly preferred.

In the present invention, the polypropylene resin pre-expanded particles used for foaming are expressed by the linear formula: 2 x 1/3 1/2 where the expansion ratio is E and the number of bubbles per cross section is n.
E Xn is a pre-expanded particle that satisfies <45. If E1/3 1/2 is less than 2, heat it
n The bubbles of the pre-expanded particles obtained by foaming become too coarse,
It is difficult to obtain a foam molded product with good physical properties l/a
When s/x is 45 or more (in such cases, E
In the case of Xn, the expansion ratio E is extremely high, the number of bubbles n is extremely large, or both are the case. In Y, even if such pre-expanded particles are heated and foamed, they tend to shrink, resulting in extremely poor foaming efficiency, and if they are forced to foam, the closed cell ratio will decrease. Even if two-foam molding is performed using the pre-expanded particles obtained in this manner, the resulting foamed molded product has poor dimensional accuracy and does not have satisfactory physical properties.

In the present invention, the first pre-expanded particles as a starting material to be subjected to heat foaming can be obtained, for example, by the following method. That is, polypropylene resin particles, a volatile blowing agent, and a dispersion medium are placed in a closed container, and heated to a temperature higher than the temperature at which the resin particles soften to incorporate the volatile blowing agent into the resin particles. This can be obtained by opening the container and simultaneously releasing the resin particles and the dispersion medium into an atmosphere having a lower pressure than the inside of the container.

In the present invention, it is not particularly necessary to actively impart foaming ability to the pre-expanded particles. but.

If the original pre-expanded particles are expanded to 1.4 times or more, or if the original expanded particles are 10 times or less, it is not possible to obtain highly expanded particles with a single foaming operation, so it is necessary to add foaming ability. preferable.

The foaming ability is imparted to the pre-expanded particles by containing an inorganic gas, a volatile foaming agent, or a mixed gas of an inorganic gas and a volatile foaming agent. 1.5~1oky/d(G
) is applied. Examples of the inorganic gas include air, nitrogen, argon, helium, etc., but air is usually used. Examples of volatile blowing agents include aliphatic hydrocarbons such as propane, butane, pentane, and hexano; cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane; trichlorofluoromethane; Halogenated hydrocarbons such as lomethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, etc. can be used.

In the present invention, the polypropylene resin pre-expanded particles are heated with steam. This heating method.

For example, this is carried out by placing the pre-expanded particles in a container and introducing steam directly into the container while stirring. As the above-mentioned steam, 2, for example, 0.5 to 3&/d (G) steam is usually used, and the heating time is usually within 2 minutes, preferably within 1 minute. By using steam in this manner, heating can be performed in a shorter time than in the case of hot air, and highly expanded particles can be obtained, resulting in improved productivity.

1/s 1/2 In the present invention, polypropylene resin particles having the relationship of the quadratic formula: 2(E ,
The operation of heating and foaming the pre-expanded particles with steam and foaming them twice may be repeated. Such operations may be repeated any number of times as long as the polypropylene resin pre-expanded particles to be subjected to heat foaming satisfy the above relationship.

In the present invention, 1 expansion ratio E means the true expansion ratio. The true expansion ratio is the reciprocal of the density of the pre-expanded particles divided by the resin density of the base resin. Here, the density of the pre-expanded particles can be measured, for example, as follows. First, a predetermined amount of pre-expanded particles with a known weight is placed in a predetermined amount of water previously placed in a graduated cylinder, and the total volume is then measured.

Next, the volume of the pre-expanded particles can be determined by subtracting the original volume of water from the total volume, and dividing the weight by the volume.

The pre-expanded particles obtained by the present invention usually have an expansion ratio of 115 times or more than that of the original pre-expanded particles.
It has a foaming ratio of 100 times, preferably 10 to 60 times,
It also has a bubble count of 01 to 200/i+m2.

The pre-expanded polypropylene resin particles obtained according to the present invention are used for producing foam molded articles. First, the pre-expanded particles are aged at room temperature and pressure for a predetermined time, and then, if necessary, aged at a predetermined pressure for a predetermined time using an inorganic gas such as nitrogen or air, or a mixed gas with a volatile blowing agent. Next, the pre-expanded particles are filled into a mold having, for example, small holes on the mold surface through which a heating medium such as water vapor can pass, and the pre-expanded particles are packed at a rate of, for example, 2 to 2 s kg/2.
By heating and foaming with water vapor of 1(G), a foam molded product according to the shape can be obtained.

The polypropylene resin foam molded product mentioned above can be used, for example, as a packaging material, a cushioning material, a heat insulating material, a heat insulating material, and a construction material.

It can be used for vehicle parts, flotation material 1 food containers, etc.

As explained above, according to the present invention, it is possible to obtain pre-expanded polypropylene resin particles with even higher foaming, and the foamed molded article obtained using the pre-expanded particles has good moldability, I have a strong back.

It also has excellent properties such as good dimensional accuracy.

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

Pre-expanded particles of Robylene random copolymer (melting point 145° C.) were placed in a container and heated directly with steam having a pressure shown in Table 1 while stirring. An internal pressure of z, skg/-J (absolute pressure) was applied to the obtained pre-expanded particles using air. The pre-expanded particles are then filled into a mold, 3.2
kg/cd CG) was heated and foamed with water vapor to obtain a foamed molded product. The dimensional accuracy and fusion properties of the obtained foam molded product were measured. The results are shown in Table 1.

*1 - Dimensional accuracy was determined as follows based on the shrinkage rate of the foam molded product.

Less than 1 to 2% 0 Less than 2 to 4% Δ 4% or more
The specimen was pulled at a speed of 100 mL to break, and the shape of the cross section was evaluated as follows.

Material destruction ○ Material destruction and interparticle cutting mixture △ Interparticle cutting No. 3. Relationship with the case of the person making the amendment Patent applicant address: 2-1-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Name (
Name) Japan Styrene Paper Co., Ltd. Representative Director
Kazuyoshi No 4, attorney 101-5, date of amendment order voluntary amendment 8, contents of amendment attached.

(1) F! Book A, page 6, line 7, ``騨/eJ(G)J
is corrected as [騨/d・abJ.

(2>"Usually within 2 minutes, preferably within 1 minute." in lines 3 and 4 of page 7 of the same page is corrected to "Usually within 1 minute, preferably within 30 seconds."

(3) In Table 1 on page 11, in the section of internal pressure of pre-expanded particles before treatment, the value of a of Example 1 [2, 2j is l''
2.5 J, and the value of C in Example 1 is "1.2 J".
1. Correct it as s J.

(4) The unit for steam pressure in the same table is “(K2/c11・q
)” is corrected as r(KP/eJ”asu”).

that's all

Claims (1)

[Claims] When the expansion ratio is E and the number of cells per cross-section is n, the polypropylene resin pre-expanded particles having the relationship of: 2(E"" X n""<45) are heated with steam. A method for producing pre-expanded polypropylene resin particles, which comprises foaming the particles to obtain pre-expanded particles having a larger expansion ratio than the original expansion ratio E.