JPS625053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a foam molded product by foaming a synthetic resin in a mold and molding the same at the same time.

The method for producing in-mold foam molded products such as polystyrene synthetic resins and polyolefin synthetic resins involves impregnating granulated raw material resin with a foaming agent and foaming it.
Conventionally, a method has been commonly used in which the obtained granular foam (pre-expanded particles) is heated in a mold to re-foam and the expanded particles are fused together to form a molded article. However, this method has disadvantages in that the foaming of the resin particles is carried out in two stages, resulting in a large number of steps and a large amount of energy consumption. Furthermore, when a polyolefin resin is used as a raw material, the blowing agent tends to dissipate from the resin particles and pre-expanded particles, making it extremely difficult to obtain a foam molded product with a high magnification. Another known method is to inject a molten synthetic resin mixed with a foaming agent into a mold, foam it, and mold it at the same time, but this method not only does not produce a highly foamed molded product, but also significantly slows down the molding speed. It had the drawback of being slow.

On the other hand, according to the present invention, a highly foamed molded product can be manufactured with high efficiency regardless of the type of raw material resin.

A feature of the method for manufacturing a foam molded product according to the present invention is that a slurry-like mixture consisting of thermoplastic synthetic resin particles containing a blowing agent and a dispersion medium that does not dissolve the resin particles is heated at a temperature at which the resin particles neither fuse nor foam. The dispersion medium is heated to a temperature above the heat distortion temperature of the resin particles in a range and under pressure, and then the dispersion medium is discharged to a system at low pressure, which does not allow the uncured resin foam to pass through, but allows the dispersion medium to pass through. Instant foaming of resin particles by injection into a mold with holes,
After cooling, the foamed resin particles are fused together and the dispersion medium (including some foaming agents) escapes from the mold.
The purpose is to remove the foamed product from the mold.

The above slurry-like mixture is obtained by heating a mixture of thermoplastic synthetic resin particles, a dispersion medium, and a low-boiling organic compound blowing agent under pressure, and then absorbing the blowing agent into the synthetic resin particles (taken out from the processing equipment or cooled). In this case, even the blowing agent impregnation step is integrated with the foaming/molding step, thereby achieving further rationalization of the manufacturing process.

The method for producing a foam molded product according to the present invention will be described in detail below.

The raw thermoplastic synthetic resins include polystyrene resins (e.g. polystyrene, high impact polystyrene, styrene acrylonitrile copolymer),
Polyolefin resins (e.g. polyethylene, polypropylene, ethylene/propylene copolymers or crosslinked products thereof), polyamides (e.g. nylon 12), copolymerized polyesters (e.g. polyethylene terephthalate/isophthalate, polybutylene terephthalate/polytetramethylene glycol) It is possible to use a wide range of resins, such as block copolymers), which are conventionally used in the production of foamed molded products, as well as resins that have hitherto been difficult to form into high-density foamed products. These resins usually have an average diameter of 0.5 to 10 mm, preferably 1 to 10 mm.
It is desirable to contain the blowing agent in the form of particles of about 5 mm.

As blowing agents, conventionally used low boiling point organic compounds, chemical blowing agents, inorganic gases, etc.
It can be selected and used as appropriate depending on the type of raw material resin, but particularly preferred are those based on low boiling point organic compounds, that is, those with a boiling point of - - which can penetrate into resin particles without chemically altering the raw material resin. Organic compounds at about 50℃ to 110℃, such as aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane, cycloaliphatic hydrocarbons such as cyclobutane, cyclopentane, and cyclohexane, trichlorofluoromethane, dichlorofluoromethane, and dichloro These include halogenated hydrocarbons such as difluoromethane, dicrotetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride.

Any method can be used to incorporate the foaming agent into the resin particles. For example, the following method is used.

a After mixing a low boiling point organic compound blowing agent with resin particles or a suspension of the same in a dispersion medium consisting of an inert liquid such as water, and heating the resin particles under pressure to absorb the blowing agent into the resin particles. , cool, and separate the resin particles.

b. A foaming agent is mixed with a resin in a melt extrusion device, and then extruded as fibers, rapidly cooled, and then shredded to obtain resin particles containing a foaming agent.

c Resin particles are brought into contact with a liquid blowing agent for a long time at low temperature and normal pressure.

However, as mentioned above, when a mixture of resin particles, a dispersion medium, and a low-boiling point organic compound blowing agent is heated under pressure to absorb the blowing agent into the synthetic resin particles, and the mixture is used as a foam molding material as it is, Needless to say, there is no room for adopting other blowing agent-containing resin particle preparation methods.

The dispersion medium in which the synthetic resin particles containing the blowing agent are dispersed must be one that does not dissolve the resin even under heating and, of course, does not change its quality.
It is preferable that the boiling point is 200°C or less; if the boiling point is too high, it will be difficult to separate it from the molded product by drying. Water is an excellent dispersion medium that can be used for almost all resins, but in the case of polystyrene and polyolefin, water-washable solvents such as ethylene glycol and glycerin can also be used.

The weight ratio of the dispersion medium to the resin particles is approximately 1.5 to 5.
Double amounts are used so that both forms a uniform slurry that is easy to transfer quantitatively.

This slurry contains fine inorganic powders (e.g. aluminum oxide, titanium oxide, magnesium carbonate, zinc carbonate, carbonate calcium, basic zinc carbonate, etc.),
A small amount of polyvinyl alcohol, carboxymethyl cellulose, etc. may be added.

The slurry of resin particles obtained as described above is heated to a temperature higher than the heat deformation temperature of the resin particles (ASTM-O-648, load 4.6 kg/cm ² ) while stirring in a closed container. Heat to such an extent that the particles do not fuse together. In order to prevent foaming of the resin particles due to gasification of the foaming agent, the container is kept in a closed state, and if necessary, it is pressurized to a pressure higher than the vapor pressure. Once the whole is uniformly heated to the target temperature, move on to the next foam molding process as soon as possible.

As a molding mold, one having a dispersion medium discharge hole as described above is used. The shape of the dispersion medium discharge hole is arbitrary, but it is usually a small hole with a diameter of about 0.1 to 2.0 mm or a slit with a width of about 0.1 to 2.0 mm.
Seventh of the number is provided to maintain the inside of the mold at a low pressure that allows the resin particles to foam during foam molding. The "low-pressure system" in which the mold space is communicated through the dispersion medium discharge hole may be the atmosphere at normal pressure, but if necessary, it may be a closed system with a pressure slightly lower or higher than atmospheric pressure.

When a certain amount of the heated and pressurized resin particle slurry is injected into the above-mentioned mold using a plunger, screw, etc., the resin particles foam as the foaming agent vaporizes (the structure of the injection mechanism (Depending on the mold, foaming may start immediately before the resin particles enter the mold.) The foamed resin particles are fused together in the mold and molded into the mold. During this time, the dispersion medium is discharged out of the mold from the dispersion medium discharge hole while being partially vaporized depending on its type and molding conditions. Along with the dispersion medium, a portion of the blowing agent, dispersant, etc. contained in the dispersion medium is also discharged out of the mold. Note that during the above-mentioned in-mold foam molding, heat may be supplied using steam or the like to promote foaming and fusion.

Thereafter, the mold is cooled with water or the like, and the foam is preferably cooled to a temperature 20° C. or more lower than the melting point of the resin, sufficiently solidified, and then taken out of the mold.

The foam molding process in the present invention is a continuous process in which the heated and pressurized resin particle slurry is injected into a space with a rectangular cross section formed by a pair of belts and side walls that move in the same direction at a constant interval. It may also be formed into a foamed sheet.

As described above, according to the present invention, a foam molded product can be obtained all at once without going through the step of pre-foaming the expandable resin particles, and in particular, the resin particles,
In the case of a method in which a mixture of a dispersion medium and a blowing agent is heated under pressure to absorb the blowing agent into resin particles and then foam-molded as is, the manufacturing process is linked to the manufacturing process of the resin particles containing the blowing agent. Since it is a method, production efficiency is greatly improved compared to the conventional conventional method, as well as energy consumption is significantly reduced, equipment and auxiliary equipment are simplified, and labor costs are also reduced. In addition, as mentioned above, even in the case of polyolefin resin, which was difficult to perform high-magnification foam molding in the past, because there is no chance for the foaming agent to dissipate, foam molding can be easily performed in the same way as in the case of polystyrene resin. It can be performed.

The present invention will be explained below with reference to Examples. Note that the tensile strength and elongation shown in the examples are values measured according to JIS K6767.

Example 1 Ethylene-propylene random copolymer with an ethylene content of 3.5% by weight (MeltInx)
1.2, heat deformation temperature: 106°C) with an average weight of 5 mg per particle, 100 parts by weight of these particles, 250 parts by weight of water (dispersion medium), and 20 parts by weight of dichlorodifluoromethane (blowing agent) in a closed container. The mixture was heated under stirring to gradually raise the temperature, held at 140°C for 30 minutes, and then raised to 145°C. After that, the outlet valve at the bottom of the container is opened, and the slurry mixture in the container is pushed out into the pipe leading to the mold using the internal pressure of the container, and a plunger-type metering transfer means provided in the middle of the pipe is used to The calculated amount of slurry necessary to obtain a foam molded product with an expansion ratio of 35 times was injected into the mold. The mold used has a closed space of 6 cm x 30 cm x 30 cm, and a width that allows communication between the closed space and the atmosphere around the mold.
It has 150 slits of 0.2 mm and 10 mm in length, and can be water cooled.

One minute after injection, the mold was cooled by running water at 50°C, and then the foam molded product was taken out of the mold and dried at 65°C. The resulting foamed molded product had good physical properties, with the boundaries between the foamed particles not being noticeable, well fused, and a smooth surface with a tensile strength of 5.8 Kg/cm ² and a tensile elongation of 35%. It was hot.

For comparison, the slurry for molding in the above example was discharged into the atmosphere and dried to obtain pre-expanded particles with a bulk expansion ratio of 39 times, and after pressurizing with air at 2 kg/cm ² (G), Using a mold of the same size as that used in the example, molding was performed by steam heating at 140°C to produce a molded product with an expansion ratio of 35 times. In the molded product obtained, it was observed with the naked eye that the fusion between the expanded particles was incomplete, and the surface was significantly uneven.
The tensile strength was 3.2 Kg/cm ² and the tensile elongation was 20%.

Example 2 Polyethylene/polystyrene mixed particles (average diameter 4 mm, heat distortion temperature 90°C) are produced by absorbing styrene monomer into polyethylene particles and then polymerizing them, so that the amount of styrene polymer is 45% of the total weight of the particles.
30 parts by weight of a blowing agent (dichlorodifluoromethane) was added to 100 parts by weight of the obtained mixture, and after stirring at 50°C for 10 hours, the mixture was cooled and the unabsorbed blowing agent was separated. The blowing agent absorbed was 17 parts by weight.

100 parts by weight of the obtained blowing agent-containing resin particles, 200 parts by weight of water
Parts by weight and 0.5 parts by weight of aluminum oxide fine particles were charged into a closed container, and the temperature was raised to 115°C at a rate of 10°C/min while stirring. The obtained heated and pressurized slurry mixture was molded into a foam molded product with a foaming ratio of 24 times in the same manner as in Example 1. The obtained molded product had good fusion between expanded particles and surface smoothness, and had a tensile strength of 2.9 Kg/cm ² and a tensile elongation of 18%.

For comparison, the resin particles after the blowing agent absorption treatment were pre-foamed to a bulk expansion ratio of 26 times by heating them with steam to 110°C, and then secondary foam molding was performed by heating with steam at 1.3 kg/cm ² using a conventional method. A molded product with a foaming ratio of 24 times was produced. In this molded product, the boundaries between the expanded particles due to poor fusion were noticeable, and the surface had large irregularities. The tensile strength was 2.2Kg and the tensile elongation was 12%.

Claims (1)

[Claims] 1. A slurry-like mixture consisting of thermoplastic synthetic resin particles containing a blowing agent and a dispersion medium that does not dissolve the resin particles is heated in a temperature range and under pressure that neither fuses nor foams the resin particles. Inside the mold, which is heated to a temperature higher than the thermal deformation temperature of the resin particles, has a dispersion medium discharge hole that does not allow the uncured resin foam to pass through, but allows the dispersion medium to pass through, and is connected to a low-pressure system. The heated slurry mixture is injected into the mold to cause foaming of the resin particles, fusion of the foamed resin particles, and escape of the dispersion medium from the mold, and after cooling, the foam molded product is taken out of the mold. A method for producing synthetic resin foam molded products. 2 A slurry-like mixture consisting of thermoplastic synthetic resin particles, a dispersion medium that does not dissolve the resin particles, and a low-boiling organic compound blowing agent is heated under pressure to cause the synthetic resin particles to absorb the blowing agent, and the above-mentioned mixture after treatment is heated. is heated above the heat deformation temperature of the resin particles in a temperature range where neither fusion nor foaming occurs and under pressure, the uncured resin foam is not allowed to pass through, but the dispersion medium is allowed to pass through. In addition, the resin particles are injected into a mold having a dispersion medium discharge hole communicating with a low-pressure system to cause foaming of the resin particles, fusion of the foamed resin particles, and escape of the dispersion medium from the mold, and after cooling, A method for producing a synthetic resin foam molded product, which comprises removing the foam molded product from a mold.