JPH0227928B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for pre-foaming thermoplastic resin particles. More specifically, the present invention relates to a method and apparatus for pre-foaming thermoplastic resin particles containing a volatile blowing agent dispersed in water under pressure and heat by releasing pressure.

Conventionally, there is no known method of dispersing thermoplastic resin particles and a volatile foaming agent in water in a pressure-resistant container such as an autoclave, creating a state suitable for foaming under high temperature and high pressure conditions, and then releasing the mixture into a low pressure area. This is described in, for example, West German Publication No. 2107683 and Japanese Patent Publication No. 1344/1983. However, according to these methods, foaming is suppressed under high temperature and high pressure, and thermoplastic resin particles in a plastic state are released into a low pressure region. Released at high velocity. For this reason, these methods have the advantage that the process up to pre-foaming is simple and that pre-foamed particles foamed to an extremely high ratio can be obtained, but on the other hand, blocking may occur due to fusion of particles after pressure is released. There were practical difficulties in the discharge and recovery process, such as the need for extremely large discharge containers.

In order to improve these problems, in the conventional method, a mixture of water and particles is discharged into a discharge pipe maintained at a low pressure, and water is further introduced into the discharge pipe to collect the foamed particles while cooling. It has been proposed to discharge the substance into a container having the necessary and sufficient free space and maintained at atmospheric pressure, but these have not yet solved the above-mentioned problems.

The present inventors have arrived at the present invention as a result of intensive research in view of these problems.According to the present invention, not only the problems in the conventional process can be solved, but also extremely practical. Pre-expanded particles of thermoplastic resin having excellent properties can be obtained.

That is, the present invention disperses thermoplastic resin particles containing a volatile blowing agent in water in a pressure-resistant container,
After heating the thermoplastic resin particles to a temperature higher than the softening temperature under pressure higher than the vapor pressure of the volatile blowing agent, the mixture of the particles and water is discharged into a low pressure region. The present invention provides a method and apparatus for pre-foaming thermoplastic resin particles, characterized in that the particles are discharged into water maintained at a pressure lower than the pressure in the pressure-resistant container, and recovered after increasing their buoyancy in the water.

The type of thermoplastic resin particles used in the present invention is not particularly limited, as long as it is a thermoplastic resin that can contain a volatile foaming agent and becomes a viscoelastic state suitable for foaming when heated. For example, polystyrene, high impact polystyrene, poly-
Polystyrene polymers such as α-methylstyrene, styrene-maleic anhydride copolymer, polyphenylene oxide-polystyrene blend or graft polymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene terpolymer, styrene-butadiene copolymer; low-density polyethylene , medium density polyethylene, high density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, and other polyolefin polymers; polyvinyl chloride polymer and polymethyl methacrylate polymer, etc. These polymers may be used alone or in combination of two or more. The polyolefin polymer may be crosslinked with peroxide or radiation, but it can also be used without crosslinking. For these thermoplastic resins, resin particles obtained by suspension polymerization or resin particles formed into extrusion pellets are used in the present invention, but there are no particular restrictions on the size of the particles. Normal sphere volume equivalent diameters are 0.25 to 10.0 mm, and 0.5 to 6.0 mm.
mm is suitably used for in-mold molding.

Volatile blowing agents used in the present invention include hydrocarbons or halogenated hydrocarbons with a boiling point of -50 to 120°C, such as propane, butane, pentane, hexane, heptane, cyclopentane, cyclohexane, monochloromethane, dichloromethane, Monochloroethane, trichloromonofluoromethane,
Examples include dichlorodifluoromethane, dichloromonofluoromethane, trichlorotrifluoromethane, dichlorotetrafluoroethane, and these may be used alone or in combination of two or more.

In the present invention, when dispersing thermoplastic resin particles in water, it is desirable to use a small amount of a dispersant to prevent the thermoplastic resin particles from fusing together during heating. Dispersants include water-soluble polymers such as polyvinyl alcohol, methylcellulose, and N-polyvinylpyrrolidone, inorganic substances that are poorly soluble in water such as calcium phosphate, magnesium pyrophosphate, and zinc carbonate, or these inorganic substances and a small amount of sodium dodecylbenzenesulfonate. , anionic surfactants such as sodium α-olefin sulfonate are used.

The heating temperature in the method of the present invention is suitably above the softening temperature of the thermoplastic resin in a state containing a blowing agent and usually below the softening temperature +50°C. The heating temperature is appropriately adjusted within the above range depending on the type of resin and the type and amount of the blowing agent, etc., and pre-expanded particles with a desired expansion ratio can be obtained by setting the amount of blowing agent used and the heating temperature. .

In the method of the present invention, the pressure within the pressure vessel is maintained below the vapor pressure of the volatile blowing agent used when the particles are discharged into water maintained at low pressure.
The vapor pressure of the volatile blowing agent referred to here is the vapor pressure in a system in which thermoplastic resin particles are impregnated with the blowing agent under heated and pressurized conditions. In order to maintain the pressure above the vapor pressure of the agent, the pressure may be increased by introducing a volatile blowing agent (liquid or gaseous) and/or an inert gas such as _N2 .

The mixture in the pressure vessel is then continuously or intermittently discharged into the water through one or more discharge openings communicating with the lower part of the vessel via a discharge valve while maintaining the temperature and pressure as described above. be done. The discharge opening is located below the water surface of a pre-foaming device having a water tank, and the discharged and foamed thermoplastic resin particles increase in buoyancy and accumulate on the water tank surface;
Usually, the overflow is continuously or intermittently collected outside the prefoaming device. In addition, the discharge opening can be adjusted to 0.2 to 300 mm by using an orifice, etc.
mm ² , preferably 0.8 to 120 mm ² (this is approximately πd ² /4 to approximately πd 2 / ² , calculated with d being the spherical diameter of the expandable thermoplastic resin particles). ).
Also, the pressure in the water to be released may be lower than the pressure in the pressure container at the time of release, but if the water is released in a system that communicates with the atmosphere, the pressure is generally atmospheric pressure plus water pressure. It is.

With this method, particles ejected at high speed are rapidly decelerated as they foam in water, and then rise through the water due to buoyancy and are cooled. Therefore, according to this method, compared to the method of releasing into the atmosphere, the equipment is extremely compact, the cooling effect is large, blocking etc. can be effectively prevented, and the foam particles are continuously or intermittently dispersed in the system. It is advantageous to be able to collect it outside.

Furthermore, in the method of the present invention, it is preferable to recover the blowing agent emitted from the expanded particles when the particles are released under pressure, or the blowing agent present in the gas phase of the pressure-resistant container. devices based on, e.g.
The blowing agent can be easily separated from the foamed particles and recovered by using the apparatus shown in the figure or FIG. 2.

In addition, in the present invention, when using the above-mentioned dispersant, in the conventional method, the dispersant adheres to the surface of the pre-expanded particles, and when performing in-mold molding using the pre-expanded particles, It may inhibit the fusion of particles. However, according to the method of the present invention, the dispersant adhering to the pre-expanded particles is washed away when the pre-expanded particles are buoyantly raised in water, so that the fusion properties between the particles are improved.

Further, according to the present invention, there is no noise that is generated when the gas is discharged into atmospheric pressure, which greatly contributes to noise prevention and safe operation.

In addition to the above-mentioned process advantages, surprisingly, according to the method of the present invention, by selecting conditions such as the temperature and pressure in the pressure container and the water depth and temperature in the pre-foaming device, It has been found that it is possible to achieve spheroidization of foamed particles, and it is possible to provide an extremely advantageous method from the viewpoint of improving the moldability and physical properties of foamed particles.

Next, a device according to the present invention will be explained based on an example shown in the drawings.

In FIG. 1, the thermoplastic resin particles containing a volatile blowing agent are pressurized and heated in a pressure-resistant container 1.
It is released through the discharge pipe 2, discharge valve 3, and orifice 4 into the storage water 7 in the pre-foaming device 5, expands rapidly, rises in the storage water due to buoyancy, and is cooled.
It is collected from the outlet 6 by overflow from above the water surface. Furthermore, by introducing water into the apparatus through the water pipe 9 or the like, it is possible to generate a water flow in the stored water to impart fluidity to the particles and to adjust the temperature of the stored water. In this case, the particles may be collected together with the water through the outlet 6 by overflow, or the water may be discharged through a separate outlet 11. Further, when a volatile foaming agent is introduced into the pressure container 1 and released while being pressurized, the foaming agent is passed through the water storage 7 to the pre-foaming device 5.
It is collected in the inner upper space and recovered via the exhaust line 8.

In order to facilitate the recovery of the foaming agent, the particles and the gaseous foaming agent may be separated from each other by a mesh net 10 that does not allow the foam particles to pass through, using a device such as that shown in FIG. 2, and then recovered. I can do it.

The present invention will be further explained below with reference to Examples, but the present invention is not limited thereto.

Example 1 In an autoclave with an internal volume of 3.5 mm, 100 non-crosslinked polymer particles (spherical volume equivalent diameter of about 2 mm) of ethylene-propylene Mandom copolymer [Sumitomo Noblen, manufactured by Sumitomo Chemical Co., Ltd., WF-816C, MI = 7] were placed. Parts by weight (700g) and dichlorodifluoromethane 40
parts by weight, further 0.5 parts by weight of tertiary calcium phosphate,
Disperse 0.025 parts by weight of sodium dodecylbenzenesulfonate in 300 parts by weight of water and heat to 136°C while stirring.
The temperature rose to . Next, dichlorodifluoromethane was introduced into the autoclave and the internal pressure was increased to 22Kg/cm ²
While holding the autoclave at the same temperature, open the discharge valve (1 inch diameter) connected to the bottom of the autoclave and release the particles and water through an orifice with one opening with a cross-sectional area of approximately 7.07 mm ² (3 mm diameter) installed after the discharge valve. The mixture containing
It was released from a distance of 10 cm. The internal temperature inside the autoclave during discharge was maintained at 136°C, and the temperature of the water stored in the prefoaming device was 32°C. During release, the particles did not cause any blocking. When the particles floating in water and overflowing were collected, pre-expanded particles having a glossy surface and having a spherical shape were obtained. When the foaming ratio was measured, it was 10.3 times.

Example 2 The pressure inside the autoclave was set to 27 Kg/ ^cm2 , dichlorodifluoromethane was set to 50 parts by weight, water was introduced, and during the particle discharge operation, a water flow was created in the water storage, and the particles were discharged from 15 cm below the water surface. Except that I did
It was carried out under the same conditions as in Example 1. During release, the particles do not undergo any blocking, and the resulting particles are
Although it did not reach spherical shape, particles with rounded corners were obtained. When the foaming ratio was measured, it was 28 times.

[Brief explanation of drawings]

FIGS. 1 and 2 are explanatory cross-sectional views showing examples of the apparatus of the present invention. 1... Pressure-resistant container, 2... Discharge pipe, 3... Discharge valve, 4... Orifice, 5... Pre-foaming device,
6...Discharge port, 7...Water storage, 8...Exhaust line,
9...Water pipe, 10...Net, 11...Drain pipe.

Claims (1)

[Scope of Claims] 1. Thermoplastic resin particles containing a volatile blowing agent are dispersed in water in a pressure-resistant container, and the thermoplastic resin particles are softened under pressure equal to or higher than the vapor pressure of the volatile blowing agent. After heating above the temperature, the mixture of particles and water is released into a low-pressure area, and the mixture of particles and water is released into water maintained at a pressure lower than the pressure in the pressure container, and the water is buoyant. A method for pre-foaming thermoplastic resin particles, which comprises raising and then recovering the particles. 2. In a pressure-resistant container, thermoplastic resin particles containing a volatile blowing agent are dispersed in water, and heated to a temperature higher than the softening point of the thermoplastic resin particles under pressure higher than the vapor pressure of the volatile blowing agent. , an apparatus for pre-foaming thermoplastic resin particles by discharging the mixture of particles and water into a low pressure area, a discharge pipe connected to the lower part of the pressure-resistant container and a discharge valve connected to one end of the discharge pipe; The opening is connected to a lower part of the foaming tank comprising a water storage part and a space, so that the mixture of particles and water can be discharged into the water storage part of the foaming tank, and further float up in the water in the foaming tank. A pre-foaming device for thermoplastic resin particles having a structure in which a discharge port for discharging pre-foamed particles to the outside of the tank and an exhaust line for recovering a foaming agent from a space are provided at the top of the foaming tank.