JPS59174326A - Manufacture of foamed molding of polypropylene type resin - Google Patents

Abstract

PURPOSE:To obtain a foamed molding that is uniform and good in dimensional accuracy, appearance and moldability, by molding prefoamed particles under a condition wherein the relationship between the expansion ratio of the prefoamed particles, the internal pressure and the expansion ratio of the foamed molding is specified. CONSTITUTION:In a method of producing a polypropylene type resin foamed molding wherein a force is filled with prefoamed particles of a polypropylene type resin followed by heating to expand the particles, the molding is effected under a condition wherein the following formula: 0.5+E/100<ep/E wherein (e) represents the expansion ratio of the prefoamed particles, (p) represents the internal pressure that will be applied to the prefoamed particles, and E represents the expansion ratio of the foamed and molded body, is satisfied.

Description

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

Polypropylene resin foam moldings have recently begun to attract particular attention due to their excellent properties.For example, they are used in packaging of various goods, cushioning materials during transportation, cushioning materials such as mats and backings, building materials, refrigerators, ships, automobiles, etc. Used in insulation materials, decorative items, toys, etc.

However, there is a drawback that the dimensional accuracy, appearance, moldability, etc. of the foamed molded product are not constant, making it difficult to obtain a uniform product.

The purpose of the present invention is to provide a method for producing a polypropylene resin foam molded product that eliminates the drawbacks of the above-mentioned conventional techniques. We have discovered that a uniform foam molded product with good dimensional accuracy, appearance, and moldability can be obtained by molding under conditions that specify the relationship between the expansion ratio of the foam particles, the internal pressure, and the expansion ratio of the foam molded product. We have succeeded in developing a manufacturing method and completed the present invention.

That is, the present invention provides a method for producing a polypropylene resin foam molded article in which pre-expanded polypropylene resin particles are filled into a molding mold, heated and foamed, and the expansion ratio of the pre-expanded particles is e, and the pre-expanded particles are heated and foamed. A polypropylene resin characterized in that it is molded under conditions that satisfy the following formula: o, s + 100 < e p/E, where p is the applied internal pressure and E is the expansion ratio of the foamed product. The gist of this paper is a method for producing a foam molded product.

In the present invention, examples of the material for the pre-expanded polypropylene resin particles include propylene homopolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, etc., but in particular, the ethylene content is 0.5 to 7.0% by weight ethylene-propylene random copolymer is preferred.

In the present invention, pre-expanded particles are filled into a mold and heated and foamed. In this case, the expansion ratio of the pre-expanded particles is e, and the internal pressure applied to the particles is p (kll/cd
It is necessary to carry out the process under conditions that satisfy the following formula: o,s+-'200<ep/E, where E is the foaming ratio of the resulting foamed molded product (absolute pressure). If ep/E is less than 0.5+Ibetsu, a molded product with excellent dimensional stability, appearance, and excellent appearance cannot be obtained, and the object of the present invention cannot be achieved. ``The preferable noise is 4.5 or less, and if this value is exceeded, the time required for cooling during molding will be long, and the raw material will be 1.10 <
E<70.

In the present invention, the expansion ratio e of the pre-expanded particles and the expansion ratio E of the foamed molded product are defined as the expansion ratio e of the pre-expanded particles and the expansion ratio E of the foamed molded article for pre-expanded particles cured for 48 hours or more under atmospheric pressure at 20° C. after pre-foaming and after molding.
After curing for more than 24 hours at 0'C, 5 at 20C under atmospheric pressure.
The foamed molded products that had been left for more than an hour were each submerged in a container filled with water, the 8 volume of water removed was measured, and the value was calculated from the following formula.

e (E) = ρX V/W (In the above formula, p is the density of polypropylene resin (f!/C
1? >, ■ is the volume of excluded water <cv? > and W indicate the weight <g> of the pre-expanded particles or the foamed molded product, respectively. ) The internal pressure p of the pre-expanded particles is given by air, for example, and this internal pressure p (glare/i absolute pressure) is equal to the volume V(i),
The air contained in the particles of weight W (l) is degassed under vacuum, and the gas pressure in the standard state is determined from the weight loss, p. Here, the weight of the particles after degassing is Wo (1, bubble volume vo = (v-WO/
, 11)) (i), p□x (w-Wo)/(ρV
-WO).

Adjustment of the numerical value of the above formula 20.5 + square oo <ep/E is,
Adjustment can be made not only by changing the internal pressure, but also by using a movable mold or changing the filling rate of pre-expanded particles depending on the foaming pressure during molding.

As the molding mold used in the present invention, for example, a normal mold having small holes in the mold surface through which a heating medium passes can be used. /cd(,
G) water vapor can be used.

In addition, the polypropylene resin pre-expanded particles used in the present invention are, for example, resin particles, a volatile blowing agent,
Add the dispersion medium, raise the temperature to a predetermined temperature with stirring, open one end of the container while maintaining the pressure inside the container at a pressure above or below the vapor pressure of the volatile blowing agent, and place the resin particles and dispersion medium into the container at the same time. It can be obtained by discharging into a lower pressure atmosphere. The above-mentioned pre-expanded particles are usually used having a particle size of 3 to 15 m, and those having a cell size of 0.1 to L5 m.

The polypropylene resin foam molded product obtained by the present invention can be suitably used for, for example, packaging materials, cushioning materials, heat insulating materials, vehicle components, construction materials, food containers, toys, and the like.

As explained above, according to the present invention, when filling a molding mold with pre-expanded polypropylene resin particles, heating and foaming them to obtain a foamed body, the expansion ratio and internal pressure of the ζ pre-expanded particles are determined. By specifying the relationship between the foaming ratio and the foaming ratio of the foamed molded product, it is possible to obtain a foamed molded product with excellent dimensional accuracy, appearance, moldability, etc.

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

Examples 1 to 15 and Comparative Examples 1 to 10 Polyethylene component 3.0%, melt index 7.517
100 parts of 710-minute ethylene-propylene random copolymer particles, 25 to 45 parts by weight of dichloromethane, 0.5 parts by weight of finely divided aluminum oxide, and 300 parts by weight of water were placed in an autoclave, and the temperature was raised to 130 to 150°C. After warming, one end of the container was opened and the copolymer particles and water were simultaneously discharged into the atmosphere to obtain pre-expanded particles with an expansion ratio e of 7 to 30 times.

The obtained pre-expanded particles were subjected to an internal pressure p (kl?/) shown in Table 1.
,, After applying i) with air, the length is 300 m and the width is 3.
00, filled into a mold with a thickness of 30 mm, 3.2 yen/
The mixture was heated and foamed with water vapor in step d to obtain a foamed molded product according to the shape. The foaming ratio E, dimensional accuracy, appearance, and moldability of the obtained foamed molded product were measured.

Note that the calculation results for ep/E and 0.5+1 block are also shown in Table 1.

*1 - Dimensional accuracy is measured at 70℃ when the foam molded body is removed from the mold.
Leave to cure for 24 hours at a temperature of
The following judgments were made based on the rate of change in dimensions of the mold after standing for a period of time.

Less than 3.0 inches ○, 3.0 or more

Slightly uneven and smooth ○ Significant unevenness and cracks × *3-Moldability was judged as follows.

Molded according to the mold ○ Dog size, small size, and distortion compared to the mold ×

Claims (1)

[Claims] In a method for producing a polypropylene resin foam molded product, in which pre-expanded polypropylene resin particles are filled into a molding mold and heated and foamed, the expansion ratio e of the pre-expanded particles,
When p is the internal pressure applied to the pre-expanded particles and E is the expansion ratio of the foamed molded product, the following formula: o-s + T
o o < e A method for producing a polypropylene resin foam molded product, characterized by molding under conditions that satisfy P/E.