JPS5968215A - Manufacture of polyolefin resin molded body foamed in mold - Google Patents

Abstract

PURPOSE:To make the moldability, appearance and fusability better, by mixing two or more different polyolefin resin pre-expanded particles that differ only in the melting point, filling a mold with the mixture, and heating it to be foamed and to be molded. CONSTITUTION:Pre-expanded particles are prepared for example by incorporating a volatile foaming agent into polyolefin resin particles of for example polyethylenes such as a low-density polyethylene, a linear low-density polyethylene, a high-density polyethylene, a polypropylene single polymer, etc. within closed container. As the volatile foaming agent can be employed propane, butane, cyclobutane, trichloromethane, etc. Then the thus prepared two or more different polyolfin resin pre-expanded particles that are different in the melting point are mixed, and charged into a mold, and the mixture is heated to be foamed to produce a foamed and molded item. The difference of the melting points of the different pre-expanded particles is generally 2-35 deg.C, preferably, 3-20 deg.C.

Description

[Detailed description of the invention] Regarding the method.

Conventionally, synthetic resin foam moldings, such as polystyrene foam moldings and polyethylene foam moldings, have been used as packaging materials, cushioning materials,
It is used in many ways such as flotation materials.

These foam molded bodies are manufactured by an extrusion maturation method or a so-called bead molding method using pre-expanded particles. When obtaining a foam molded product using the bead molding method, pre-expanded particles are produced from the same resin, and the pre-expanded particles are used to produce a foam molded product, but if the particles are not in an appropriate softened state. It is necessary to control the molding temperature since the appearance, fusion properties, etc. of the resulting foam molded product are impaired. However, polyolefin resins have a very narrow range of suitable molding temperatures, and the conditions must be set strictly, so there is still room for improvement in terms of moldability.

The present inventors mixed and filled the above ingredients into a mold, then heated and foamed them, thereby producing a foam molded product with good moldability, appearance, and fusion properties under a wide range of temperature conditions. The present inventors have discovered that the following can be obtained and succeeded in developing a method for producing the same, thereby completing the present invention.

That is, the present invention uses pre-expanded polyolefin resin particles of the same type having different melting points of 29 or more as a mold.

In the present invention, the material of the polyolefin resin pre-expanded particles is, for example, low density polyethylene (hereinafter referred to as LDP).
It is abbreviated as E. ), linear low-density polyethylene (hereinafter referred to as L
It is abbreviated as LDPE. ), high-density polyethylene (hereinafter referred to as
Polyethylene such as HDPE (0), polypropylene homopolymer, polypropylene resin such as ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-α-olefin copolymer, propylene-α- Examples include olefin copolymers, ethylene-butadiene copolymers, polybutenes, and the like. The above polyolefin resin may be either crosslinked or non-crosslinked.

The pre-expanded polyolefin resin particles used in the present invention can be produced, for example, by the following pre-expanding method. That is, a step of incorporating a volatile blowing agent into polyolefin resin particles in a closed container, a step of dispersing the resin particles in a dispersion medium and heating them to a predetermined temperature, and a step of opening one end of the container and performing the above-mentioned steps. It can be produced by a pre-foaming method comprising a step of simultaneously releasing the particles and the dispersion medium into an atmosphere at a lower pressure than in the container.

Volatile blowing agents used in the above method include aliphatic hydrocarbons such as haflopane, 'butane, pentane, hexano, heptane, etc., cyclic aliphatic hydrocarbons such as cyclobutane, cyclopentane, etc. Also used are halogenated hydrocarbons such as trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methylfluorochloride, ethyl chloride, and methylene chloride. The amount of the blowing agent added is usually 5 to 40 parts by weight per 100 parts by weight of the resin particles.

In the above method, the resin particles and the volatile blowing agent are separated separately or the volatile blowing agent is contained in the resin particles and dispersed in the atmospheric dispersion medium. Titanium, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, etc. can be used. The amount of the dispersant added is 0.01 to 10 parts by weight per 100 parts by weight of the resin particles. The dispersion medium may be any solvent that does not dissolve the resin particles, and examples include water, ethylene glycol, glycerin, methanol, ethanol, etc., or a mixture of two or more thereof, but water is usually used. preferable.

In addition, in the above method, one end of the container is opened and the resin particles and dispersion medium are simultaneously released into an atmosphere with a lower pressure than the inside of the container. At this time, the temperature inside the container is preferably 90 to 170°C, and the pressure is set to evaporate. The pressure may be higher than or lower than the vapor pressure of the foaming agent, and the atmosphere to be discharged is normally selected to be at normal pressure.

The polyolefin resin pre-expanded particles thus obtained usually have an apparent expansion ratio of 5 to 50 times, although this varies depending on the amount of volatile blowing agent, temperature, pressure, etc. Further, it is also possible to obtain pre-expanded particles having an apparent expansion ratio of 20 to 150 times by applying internal pressure to the obtained pre-expanded particles using a volatile blowing agent or an inorganic gas as described below and then heating them.

The obtained pre-expanded particles are aged under normal temperature and pressure, if necessary, with a mixed gas with a volatile foaming agent to impart internal pressure to the inside of the particles. As the inorganic gas, for example, air, nitrogen, argon, helium, etc. are used.

In the present invention, the polyolefin resin pre-expanded particles are mixed with particles having different melting points, and the difference in melting point is usually 2 to 35.
℃, preferably 3 to 20℃, more preferably 5 to 15℃. It is also necessary to mix particles of the same type, for example, polyethylene resin-polyethylene resin, polypropylene resin-polypropylene resin. In the case of different types of resins, it is difficult to obtain a foam molded product with good fusion bonding due to affinity problems between the resins.

When mixing and filling the above pre-expanded particles into a mold, the mixing ratio A to B of particles A with a high melting point and particles B with a low melting point is not particularly limited, but is preferably in the range of 1:5 to 5:1. preferable. In addition, it is preferable that the pre-expanded particles be mixed and filled in a dispersed state without particles having the same melting point being aggregated.

An example of the melting point of the pre-expanded particles is as follows.

Base material resin melting point (OLDPK 98~110 LLDP g 115~130HDPE
130-138 Moreover, three or more types of pre-expanded particles can be mixed, and in this case, there is an effect that particles having a larger difference in melting point can also be molded.

In the present invention, as the mold for molding, an ordinary mold having small holes on the mold surface through which a heating medium passes can be used, and the heating medium is 0.8 to 5. Oq/ca (G)
water vapor can be used. As a result, the pre-expanded particles are heated and foamed to produce a foam molded product that can be used, for example, in packaging materials, cushioning materials, heat insulating materials, insulation materials, building materials, vehicle components, etc.
It can be used for flotation materials, food containers, etc.

As explained above, according to the present invention, two or more types of polyolefin resin pre-expanded particles of the same type with different melting points are mixed and filled into a mold, heated and foamed, so that moldability is good. The foamed molded product obtained also has good appearance, fusion properties, etc.

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

In Preparation Example A-, 100 parts by weight of base resin particles having the melting point shown in Table 1,
Volatile blowing agents, dispersants, and dispersion media of the types and amounts shown in Table 1 were placed in an autoclave, and the
The autoclave was heated to a temperature of 165°C, one end of the autoclave was opened, and the resin particles and water were simultaneously discharged into the atmosphere to obtain pre-expanded particles having the expansion ratio shown in Table 1.

Examples 1 to 9 and Comparative Examples 1 to 11 After leaving the pre-expanded particles (A-K) obtained in the Preparation Example at room temperature and normal pressure for 48 hours, the particles were heated with air (18K).
After applying an internal pressure of P/c4 (G), particles of the same kind with different melting points as shown in Table 2 are mixed and filled into a mold with a length of 300 mm, a width of 300 mw, and a thickness of 30+ g. 4KP
/JG) was heated and foamed with water vapor, and the foam moldability, appearance, and fusion properties were measured. The results are shown in Table 2.

Table 2 *1 - Moldability was determined as follows based on the range of moldable vapor pressure.

0,4 KP/c or more 00.2~0.4
KP/c4%J ”0,2 Ky/cA
Less than × *2 - Appearance was determined as follows based on the surface condition of the molded product.

Smooth ○ Some unevenness
△ Significant unevenness × *3 - Fusion adhesion was determined as follows based on the state of the foamed molded product when it was folded.

Fused 　　　　　○ Partially cracked △

Claims (1)

[Claims] A method for producing two or more polyolefin foam molded products of the same type having different melting points.