JPS62130831A - Manufacture of in-mold expansion-molded body of polyolefin-based resin - Google Patents

Abstract

PURPOSE:To obtain an in-mold expansion-molded body of polyolefin-based resin which is excellent with no application of special curing after molding by a method wherein prefoamed particles of polyolefin-based resin containing inorganic gas, the pressure of which is substantially equal to the atmospheric pressure, is loaded in a mold and, after that, the mold is evacuated and the prefoamed particles are heated for expansion molding. CONSTITUTION:After prefoamed particles containing inorganic gas, the pressure of which is substantially equal to the atmospheric pressure, are loaded in a mold, the mold is evacuated. The pressure in the evacuated mold depends on the expansion ratio of the prefoamed particle and normally and is preferably below 710mmHg. After the evacuation of the mold, the expansion molding is done by heating. Normally, the steam having a pressure of 2-5kg/cm<2> by gage is used for heating the prefoamed particles. A molded body, which is obtained by expanding the prefoamed particles in the mold under heat, is removed from the mold after being cooled down to a temperature at which the releasing is done easily. The degree of cooling can be known by the surface pressure of the foam. In case of ethylene propylene random copolymer, for example, the molded body is preferably removed from the mold in the state that the surface pressure lies within the order of 1-0.5kg/cm<2> by gage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a polyolefin resin in-mold foam molding.

[Conventional technology]

The in-mold foam molding method, in which pre-expanded thermoplastic resin particles are filled into a mold and heated and foamed to form a molded product, is generally used as a method for manufacturing foam products, and is conventionally used as an in-mold foam molding method. (1) A method in which pre-expanded particles are pressurized with an inorganic gas, the inorganic gas is injected into each particle to impart foaming ability, and then the particles are filled into a mold and heated and foamed.
Japanese Patent Publication No. 52-22951, Japanese Patent Publication No. 49-128065
No.), ■ A method of compressing pre-expanded particles, filling them into a mold and heating and foaming them (Special Publication No. 53-33996), ■
Pre-expanded particles with an internal pressure almost equal to atmospheric pressure are placed in a mold for molding.
A method is known in which the molded product is filled into a mold, heated and foamed, and then the resulting molded product is cured at a predetermined temperature (Japanese Patent Publication No. 55-7816, Japanese Patent Application Laid-Open No. 60-166442).

[Problem that the invention seeks to solve]

However, in method (2), the time that the inorganic gas injected into the pre-expanded particles is retained within the particles is relatively short, so it is necessary to mold the particles in a short period of time after pressurizing and applying internal pressure. In addition, method (2) imparts foaming ability to the pre-expanded particles by compressing the pre-expanded particles, and requires equipment for compressing and filling the pre-expanded particles. Furthermore, it is necessary to link the compression filling equipment and the molding machine, which poses a problem of complicating the equipment. On the other hand, if the pre-expanded particles are not pressurized and the pre-expanded particles are molded at an internal pressure that is almost equal to atmospheric pressure as in method (2), the molding will have many voids due to the poor secondary foaming ability of the pre-expanded particles. However, if methods such as lengthening the heating time or increasing the pressure of the steam for hot molding are adopted to solve these drawbacks, the molded product taken out of the mold into the room temperature atmosphere will be It expands once and then rapidly shrinks and contracts. For this reason, in method (2), it is necessary to cure the molded product at a predetermined temperature after completion, which requires complicated temperature control for one hour during curing, requires a long molding cycle, and provides efficient molding. The problem was that it could not be done.

[Means for solving problems]

This is the result of intensive research by the inventors in view of the above points.

An excellent polyolefin resin mold that can be pressurized with inorganic gas to apply internal pressure to polyolefin resin pre-expanded particles, or can be compressed and molded without applying internal pressure, and can be specially cured after molding. The present invention was completed by discovering a method by which an internally foamed molded product can be obtained.

That is, 1. The method for producing an in-mold polyolefin resin foam molded article of the present invention is to fill a mold with pre-expanded polyolefin resin particles containing an inorganic gas at a pressure substantially equal to atmospheric pressure, and then fill the inside of the mold with This is a method of foam molding by reducing the pressure, then heating the pre-foamed particles in the mold with a knife.

The polyolefin resin pre-expanded particles used in the present invention include polyethylene pre-expanded particles, polypropylene pre-expanded particles, and ethylene-propylene block copolymers whose base resin is low-density polyethylene, linear low-density polyethylene, high-density polyethylene, etc. Examples include pre-expanded particles, pre-expanded ethylene-propylene random copolymer particles, and among them, non-crosslinked ethylene-propylene random copolymer pre-expanded particles are preferred. In the case of pre-expanded particles made of resin such as thermally crosslinked polyglopylene pre-expanded particles and non-crosslinked ethylene-propylene random copolymer pre-expanded particles, the 080 curve obtained by differential scanning calorimetry of the pre-expanded particles.

It has a crystal structure in which a high-temperature heater appears on the high-temperature side of the characteristic peak specific to the base resin, and has a bulk density of 0.04. lit/d
For the above, the melting energy of the high temperature peak is 8 to 12
J/fj, and bulk density of 0.04 J/cII.For non-droplets, pre-expanded particles having a high temperature peak melting energy of 8 J/l/or more are preferred.

The above 080 curve is the 080 curve obtained when pre-expanded particles 1 to 3 mfi are heated to 220°C at a heating rate of 10°C/min using a differential scanning calorimeter. The first 080 curve is the 080 curve obtained when the temperature is increased at a rate of 10°C/min from 220°C to 40°C at a rate of 10°C/min.
The temperature is lowered to around ℃, and then the temperature is increased again to 220℃ at a heating rate of 10℃/min.
The second 080 curve obtained when the temperature is raised to ℃
80 curves, and from these 080 curves, the characteristic peak and
High temperature peaks can be determined.

That is, the above-mentioned characteristic peak is an endothermic peak unique to the polypropylene resin constituting the expanded particles.

This is thought to be due to the so-called endotherm during melting of the polypropylene resin. Usually the characteristic peak is the first 0
It appears in both the 80 curve and the second 080 curve, and the temperature at the top of the peak may be slightly different between the first and second runs, but the difference is less than 5°C, usually less than 2°C.

On the other hand, the high temperature peak is an endothermic peak that appears on the high temperature side of the above-mentioned characteristic peak in the first 080 curve. The melting energy of the high temperature peak is the melting energy of the endothermic peak that appears on the high temperature side of the intrinsic peak.

The pre-expanded particles used in the present invention are produced by a method in which expandable resin particles containing a blowing agent are foamed under pressure in a pressure-resistant container, and after melt-kneading the resin and the blowing agent in an extruder.
A method of extrusion foaming to form a foamed strand and cutting it. After dispersing resin particles and a foaming agent in a dispersion medium in a pressure-resistant container and heating under pressure to impregnate the resin particles with one foaming agent.

It can be obtained by a method such as releasing it under atmospheric pressure and foaming it.

The pre-expanded particles used in the present invention contain an inorganic gas at a pressure substantially equal to atmospheric pressure, and the pressure of the fused gas within the particles that is substantially equal to atmospheric pressure is 0.8 to 1.
The pressure is about 1 kliJ/-. Usually, the obtained pre-expanded particles are left under atmospheric pressure at room temperature or dried with hot air to replace the gas in the pre-expanded particles containing the blowing agent with inorganic gas, and then molded into nine particles. The particles are subjected to molding without any pretreatment of applying internal pressure.

In the present invention, pre-expanded particles containing an inorganic gas at a pressure substantially equal to the atmospheric pressure are used in the mold internal force method for molding.
y ==='2 There are several methods to use, such as flowing steam with the drain outlet of the growth mold open and reducing the pressure by the flow of steam, among others, the method using vacuum stop = ugly. However, the degree of vacuum can be further increased, and the present invention can be made more effective. The pressure inside the mold when the pressure is reduced varies depending on the expansion ratio of the pre-expanded particles, but it is usually 710 m+11 (g or less, particularly preferably 6601 mHg or less).

The pre-expanded particles filled in the mold are heated and foam-molded after the inside of the mold is reduced in pressure.

Heating of pre-expanded particles usually requires 2-skg/c++1 (G
) steam is used.

The molded product obtained by heating and foaming the pre-expanded particles in a mold is cooled until it can be easily released from the mold, and then the molded product is removed from the mold. Generally, if this cooling is insufficient, when the molded product is taken out from the mold, the molded product expands too much and is likely to cause cracks on the surface. The degree to which the molded product has been cooled to the extent that it can be removed from the mold can be determined by the surface pressure of the foam. For example, in the case of ethylene-propylene random copolymer, the surface pressure is 1 to 0.5'Q/Cd
It is preferable to take it out from the mold at about (G) level. As a cooling method, in addition to normal water cooling, cooling by vacuum drying may be used. Cooling by vacuum drying increases the surface hardness of the molded product, improves mold release, and improves the quality of the molded product. There is no need to dry the molded body.

The molded body is usually removed from the mold.

The temperature is generally 50 to 110°C, but in order to dry in a short time, the temperature should be 60°C or higher, especially 70°C.
The temperature is preferably 0°C or higher.

In the method of the present invention, pre-expanded particles are used either after being pressurized with an inorganic gas or without being compressed. Expanded particles can also be applied to the method of the invention.

〔Example〕

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

Examples 1-6. Comparative Examples 1 to 3 Pre-expanded particles shown in Table 1 using a non-crosslinked ethylene-propylene random copolymer (melting point 145°C, ethylene content λ6 wt%) as a base resin were mixed with 3001 tlX 30
011 . After heating and foaming, density is 0.04! For those using pre-expanded particles of l/- or more, the surface pressure of the molded product is o, s kg/cj (G
) and then take it out, and the density is 0.045.
．． In the case of using pre-expanded particles of less than i7/ad, the molded body was cooled with water until the surface pressure reached 0.5 kg/m (G) and then taken out. In Examples 5 and 6, after water cooling was performed for 5 seconds, vacuum drying cooling was performed for 10 seconds, and then allowed to cool until a predetermined surface pressure was reached.

Table 1 shows the properties of the molded body after drying the molded body at 80° C. for 6 hours. Note that the molded product obtained in Example 5.6 had a temperature of K when taken out from the mold.

Since no adhering water was observed on the surface of the finished body, the properties were measured without drying.

*l Particulate inorganic gas pressure was determined using the following formula.

Particulate inorganic gas pressure (y/d) (a-b)Xo, 082X(273+t)Xl, 033
2 air molecules × volume of air bubbles in particles C6) where a is the weight (g) of the pre-expanded particles in a 20°C atmosphere at the time of molding, and b is the weight (g) of the pre-expanded particles in a 20°C atmosphere after curing for one week. Weight (g), O, Q8
2 is a gas constant, t is room temperature (20° C. in this example), and air molecular weight is 28.8.

1.0332 is the coefficient for converting atmospheric pressure to kg/-, and is 9
The intraparticle air bubble volume is a value that was determined separately.

The true volume (J) of the pre-expanded particles was determined by immersing the pre-expanded particles in water in a measuring cylinder.

*2 After drying and leaving at room temperature for 24 hours, measure the dimensions of the finished product and determine the shrinkage rate with respect to the surface direction dimension of the mold, and the shrinkage rate is less than 3%. −−・−−−−−−1−−
---・-・-03% or more and less than 5%---m----・-
−−−m−−・−・−△5% or more−, −−−−−=−−
------------ It was determined as X.

*3 After drying and leaving it at room temperature for 24 hours, measure the thickness of the center of the molded body, calculate the shrinkage rate relative to the thickness of the gold, and find that the shrinkage rate is less than 3%.・−111−−−−−・−0
3% or more and less than 5%・----1111--・-1--
−−△5% or more−−−−−−−・−−−−−=−−−
-----= Determined as X.

*4 The foam molded body was tensile broken using Tensilon.

The interparticle fracture and material fracture rate of the cross section were determined.

Material destruction of 70% or more---------111------
−−○Material destruction less than 70% 40% or more−−−△Material destruction less than 40%−・−−−−−−−−−=−−−−−−x※
5 Observe the surface of the molded product.

Surface smoothness ------------
1--------・---111--There are some voids on the surface 111----------111--
△Many voids on the surface−・−1−−−−−・−・−・−
-------x was determined.

〔Effect of the invention〕

As explained above, according to the method of the present invention, it is not necessary to compress the pre-expanded particles to impart foaming ability, since the inorganic scum is press-injected into the pre-expanded particles. Excellent foam molded articles can be produced using pre-expanded particles containing gas, and even pre-expanded particles immediately after production can be molded immediately without curing such as pressure treatment. Moreover, in the method of the present invention, a foam molded product obtained by molding using pre-expanded particles containing an inorganic gas at a pressure substantially equal to atmospheric pressure is cooled in the same way as in normal molding without special curing. Since it can be taken out from the mold, the molding cycle can be shortened, and excellent foam molded products can be efficiently produced.

Patent Applicant: Japan Nutele No Paper Co., Ltd. Agent Patent Attorney: Hosoi Otete 3 da εneyu-marin (Voluntary) December 10, 1985 Commissioner of the Japan Patent Office Michibe Uga 2, Name of the invention i! of polyolefin resin in-mold foam moldings! ! Manufacturing method 3, )Relationship with the case of a person who commits di-correction Patent applicant address: 2-1-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Name: Shinyo Uchiyama 4, representative of Nippon Styrene Paper Co., Ltd., agent: 101 Address: Chiyoda, Tokyo 2-7, Kanda Sakuma-cho, Ward, Voluntary Amendment 6, Detailed Description of the Invention column 7 in the Specification Subject to Amendment, Contents of the Amendment (1) Page 12 of the Specification, Lines 2-3, 2 “Particle Inorganic Gas Pressure ( kg/ci), [intraparticle gas pressure (kg/cd) or less]
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Claims (3)

[Claims] (1) After filling a mold with polyolefin resin pre-expanded particles containing an inorganic gas at a pressure substantially equal to atmospheric pressure, the pressure inside the mold is reduced, and then the pre-expanded particles in the mold are heated and foamed. A method for producing a polyolefin resin in-mold foam molded product, which comprises molding. (2) A method for producing a polyolefin resin in-mold foam molded article according to claim 1, wherein the pressure inside the mold is set to 710 mmHg or less. (3) The method for producing a polyolefin resin in-mold foam molded article according to claim 1 or 2, wherein the polyolefin resin is a non-crosslinked ethylene-propylene random copolymer.