JPS59172532A - Pre-expansion of polyolefin resin particle - Google Patents

Abstract

PURPOSE:To obtain uniform pre-expanded particles, by dispersing polyolefin resin particles containing a volatile blowing agent in water with the aid of a dispersant and a surfactant in a pressure vessel equipped with a special H- shaped paddle, applying heat and pressure to the mixture and releasing the pressure. CONSTITUTION:An H-shaped paddle is secured to an agitator shaft so that it may slant toward the direction of agitation at an angle of 5-45 deg. with the vertical plane for the paddle. The special H-shaped paddle thus obtained is attached to a pressure vessel 1. In this vessel 1, polyolefin resin particles (e.g., polyethylene or polypropylene particles) containing a volatile blowing agent (e.g., propane) is dispersed in water with the aid of a dispersant (e.g., calcium tertiary phosphate) and a surfactant (e.g., sodium dodecylbenzenesulfonate). This dispersion is heated to the softening temperature of the resin particles or above and pressurized to the vapor pressure of the blowing agent or above and then discharged into a low-pressure zone to pre-expand the resin particles.

Description

Detailed Description of the Invention The present invention is a method for pre-foaming polyolefin resin particles containing a volatile blowing agent dispersed in water under high temperature and high pressure by releasing the pressure, which makes the dispersion state extremely stable. This relates to a stirring method.

Conventionally, polyolefin resin particles and a volatile foaming agent are dispersed in water in a pressure-resistant container such as an autoclave, brought to a high temperature and high pressure state, and then released into a low pressure area to pre-foam the polyolefin resin. The method is well known and is described, for example, in West German Published Patent Application No. 21076133, Japanese Patent Publication No. 56-1344, and the like.

In the above method, there is a description of dispersing polyolefin resin particles and a volatile blowing agent in water by stirring, but ordinary stirring methods using H-type stirring blades, propellers, blue margins, etc. However, it was observed that the polyolefin resin particles coagulated and fused together in the pressure container before being discharged into a low pressure region, resulting in poor dispersibility.

The reason for this is that polyolefin resin particles generally have a density smaller than 1'f/cA and tend to float in water, so normal stirring cannot uniformly spread the polyolefin resin particles throughout the water in the pressure container. It may be difficult to disperse. To investigate this, we conducted an experiment using an H-type stirring blade and varied the stirring speed, and found that increasing the stirring speed slightly improved the agglomeration and fusion of polyolefin resin particles, but it did not completely solve the problem. There wasn't. Alternatively, in order to prevent the heated polyolefin resin particles from fusing together, calcium carbonate, *basic zinc carbonate,
Basic magnesium carbonate, calcium pyrophosphate, tertiary
It is known to add fine powder of an inorganic compound such as calcium phosphate. However, even if these are added, if the amount used is small, the effect of preventing fusion is small, and in order to completely prevent fusion, it is necessary to use a large amount of dispersant. Moreover,
The pre-expanded particles obtained in this way are then filled into a mold and heated with steam etc. to form a foam molded product according to the mold, but since a large amount of dispersant is deposited on the surface of the pre-expanded particles. ,
There was a problem in that the adhesiveness of the expanded particles to each other was poor, reducing the commercial value. Therefore, the present inventors conducted intensive research to solve the problems of the above-mentioned prior art, and as a result, they arrived at the present invention.

That is, in the present invention, polyolefin resin particles containing a volatile blowing agent are dispersed in water in a pressure-resistant container, heated to a temperature higher than the softening temperature of the particles, and under a pressure higher than the vapor pressure of the blowing agent. , a pre-foaming method for polyolefin resin particles in which a mixture of the particles and water is discharged into a low-pressure region.Dispersion of the particles in water uses a dispersant and a surfactant, and an H-type stirring blade is used to disperse the particles in water. The gist of this invention is a method for pre-foaming polyolefin resin particles, which is characterized by stirring with a special H-shaped stirring blade that is inclined from the vertical surface of the stirring blade in the direction of stirring.

According to the method of the present invention, homogeneous pre-expanded particles without any fusion of polyolefin resin particles in a pressure container can be obtained by using only a small amount of dispersant.

The polyolefin resin used in the present invention includes low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-vinyl acetate copolymer. etc. are preferred, and ethylene-ethyl acrylate copolymer, polybutene-1, ethylene-acrylic acid metal salt type copolymer (ionomer), poly-4-methylpentene-1, etc. can also be used. These resins can be used alone or in a blend of two or more, or a mixture of these resins and a filler. Furthermore, those obtained by crosslinking the above-mentioned polyolefin resins with organic peroxides, radiation, etc. can also be used.

The particle diameter of the polyolefin resin particles in the present invention is
There is no limit to the fort, usually the particle size is 0.25-10.0
7 Im, more preferably 0.5 to 6, Q mrr
It is suitable for use in in-mold foam molding.

The volatile blowing agent used in the present invention has a boiling point of
0-120°C hydrocarbon or halogenated hydrocarbon,
For example, propane, butane, pentane/hexane, heptane, cyclopenkune, cyclohexane, monochloromethane, dichloromethane, monochloroethane, trichloromonofluoromethane.

Examples include dichlorodifluoromethane, dichloromonofluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, and the like. These may be used alone or in combination of two or more.

In the present invention, polyrefin resin particles are dispersed in water using a small amount of dispersant in a pressure-resistant container equipped with a stirrer.

The stirrer will be explained with reference to the drawings. In FIG. 1, 1 is a pressure-resistant container, 2 is a stirring device, and 3 is a special H-type stirring blade in which the H-type stirring blade is inclined from the vertical surface of the stirring blade toward the stirring direction. Second
The figure shows the normal I-I full stirring blade, and Figure 3 shows the special H of the present invention.
This is an enlarged view of the type stirring blade. The width, wall thickness, and number of stirring blades of the special H-type stirring blade of the present invention are not particularly limited, but the width is approximately 10% of the inner diameter of the pressure vessel, and the wall thickness is determined to be strong enough to withstand the load during stirring. It is usually sufficient if the number of stirring blades is two. There are no particular restrictions on the material as long as it is durable, but stainless steel is preferred from the viewpoint of corrosion resistance. The angle of inclination of the special H-shaped stirrer of the present invention from the vertical plane can be selected within the range of 5° to 45°. If the angle is less than 5°, it is almost the same as a normal H-type stirring blade, and if it exceeds 45°, the stirring power is lost, so that the dispersion stabilizing effect of the present invention cannot be obtained in either case. A preferred angular range is 5° to 30°, and a more preferred angular range is 5° to 20°.

The reason why the polyolefin resin particles are dispersed extremely uniformly when the special H-type stirring blade of the present invention is used, and no agglomeration and fusion of the particles occurs is that the polyolefin resin particles dispersed in water have a density of f/cA, the polyolefin particles tend to float on the water surface, but because the H-shaped stirring blades are tilted toward the stirring direction, a force that tries to transport the water and polyolefin particles to the bottom of the pressure container acts. This is thought to be due to the fact that the buoyancy of the particles is suppressed and the particles in the water are dispersed extremely uniformly within the pressure container without being unevenly distributed.

Dispersants used in the present invention include basic magnesium carbonate, basic zinc carbonate, calcium pyrophosphate,
Examples include tertiary calcium phosphate and calcium carbonate. In some cases, these inorganic substances may be used in combination with a small amount of a surfactant, such as an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium α-olefinsulfonate, and sodium n-paraffinsulfonate. The amount of the dispersant used is 0.05 to 1.0 parts by weight, preferably 0.1 to 0 parts by weight, per 10 parts by weight of the polyolefin resin.
．． 7 is the vertical part. The amount of surfactant to be used is 0.001 to 0.00 parts by weight per 100 parts by weight of the polyolefin resin.
1 part by weight, preferably 0.001 to 0.05 part by weight. Dispersants and surfactants suitable for the present invention are tertiary calcium phosphate and sodium dodecylbenzenesulfonate, or tertiary calcium phosphate and sodium n-paraffinsulfonate.

The heating temperature in the present invention is higher than the softening temperature of the polyolefin resin in a state containing a blowing agent, and is usually in the range of the softening temperature to the softening temperature +50°C. The softening temperature is appropriately adjusted within the above range depending on the type of resin and the type and amount of the blowing agent. For example, in the combination of low density polyethylene and dichlorodifluoromethane, 90 to 14
110-160° for the combination of 0°C1 ethylene-propylene random copolymer and dichlorodifluoromethane
Foaming is possible within the range of C, and pre-expanded particles with a desired expansion ratio can be obtained by adjusting the amount of blowing agent used and the heating temperature. If the heating temperature is below the softening temperature of the polyolefin resin containing a blowing agent, it is difficult to foam, and if the heating temperature exceeds the softening temperature +50°C, the melt viscosity of the resin becomes too low. - (Even with type stirring blades, it is not possible to prevent particles from fusing together in a pressure-resistant container.

In the method of the present invention, the pressure within the pressure vessel when water and particles are discharged into the low pressure region is maintained at a level higher than the vapor pressure of the volatile blowing agent used. The vapor pressure of the volatile blowing agent referred to here is the vapor pressure in a system in which polyolefin resin particles are impregnated with Genasahi agent under heated and pressurized conditions. To maintain the vapor pressure above the blowing agent, volatile blowing agent (liquid or gaseous) and/or N
What is necessary is to introduce an inert gas such as No. 2 and pressurize it.

The polyolefin resin particles are discharged into a low pressure region, usually atmospheric pressure, from one end of the bottom of the pressure container that has a suitable opening that can be opened and closed.

In this way, closed-cell pre-expanded particles having an expansion ratio of 5 to 90 times and having uniform fine cells in which there is no fusion between the particles are obtained. The result obtained in this way is if
ff After curing and ripening, the foamed particles are further pressure-ripened and filled into a mold that can be closed but cannot be sealed, and the particles are fused together using a heating method such as steam, and foam molded into the desired mold shape. It can be used as a body.

As described above, according to the method for producing pre-expanded polyolefin resin particles of the present invention, it is possible to obtain pre-expanded particles without fusion of particles before and after pre-foaming by using a special H-type stirring blade, and in addition, inorganic Since the amount of system dispersant used is extremely small, the molded article obtained using the pre-expanded particles has the advantage that the fusion between the particles is extremely excellent and the amount of steam used is also small.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. All parts are by weight.

Example 1 800 parts of pure water and ethylene-propylene random copolymer particles (ethylene-containing Amount: 4.5% by weight, particle size: about 2 questions, Ml: 9) 100 parts, and tertiary calcium phosphate (manufactured by Taihei Kagaku Co., Ltd., 2 particle size: 0.5-2μ) as a dispersant: 0.5
Add 0.025 parts of sodium dodecylbenzenesulfonate (Neoperex No. 25 manufactured by Kao Soap) and add 55 parts of dichlorodifluoromethane while stirring i'+:j.
After straining, the mixture was heated to 136°C. Next, in order to evaluate the stability of the dispersion, the internal pressure of the autoclave was reduced to 30/c with nitrogen after being left at this temperature for 3 hours.
g/c2! Do not keep the autoclave in the lower chamber,
Pre-foaming was performed by opening the lube and releasing the mixture of resin particles and water to atmospheric pressure. The obtained pre-expanded particles had no fusion between particles, were substantially composed of uniform fine closed cells, and had an expansion ratio of 40 times.

Comparative Example 1 An experiment was conducted in the same manner as in Example 1, except that stirring was performed using a normal H-type stirring blade with no inclination angle. However, after heating the autoclave to 136° C., the resin particles in the autoclave fused together in about 80 minutes, making stirring impossible and making it impossible to perform preliminary foaming.

Examples 2-5. Comparative Example 2 Pre-foaming was carried out in the same manner as in Example 1 except that the angle was changed to 45°. The results are shown in Table-1.

Table 1 ［ `` fire `` * 1 40 minutes after holding, the resin particles fuse and form a lump. Furthermore, if the inclination angle is 50°, there is almost no stirring force and the particles fuse, making it impossible to carry out the process. Met.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a pressure-resistant container for pre-foaming used in the method of the present invention. FIG. 2 shows a normal H-type stirring blade, and FIG. 3 shows a special H-type stirring blade of the present invention, where A is a front view and B is a side view. In the figures, A is a front view and B is a side view. 1 is the pressure-resistant container main body, 2 is a stirring device equipped with a special H-type stirring blade, 3 is a special ■ (type stirring blade), 4 is for heating, 2 is a jacket, 5 is polyolefin resin particles, 6 is a discharge valve. Patent Representative Makoto Asano, Patent Attorney, Kanebuchi Chemical Industry Co., Ltd.

Claims (7)

[Claims] (1) In a pressure-resistant container, polyolefin resin particles containing a volatile foaming agent are dispersed in water, heated to a temperature higher than the softening temperature of the resin particles, and under pressure higher than the vapor pressure of the foaming agent. , a pre-foaming method for polyolefin resin particles in which a mixture of the particles and water is discharged into a low pressure region, in which the particles are dispersed in water using a dispersant and a surfactant, and an H-type stirring blade is used to stir the particles. Special H tilted from the vertical plane of the blade toward the stirring direction
A method for pre-foaming polyolefin resin particles characterized by stirring with a molded stirring blade. (2) The method for pre-foaming polyolefin resin particles according to claim 1, which comprises stirring with a special H-type stirring blade tilted in the stirring direction at an angle of 5° to 45°. (3) The method for pre-foaming polyolefin resin particles according to claim 1, wherein stirring is carried out using a special H-shaped stirring blade tilted in the stirring direction at an angle of 5° to 30°. (4) The method for pre-foaming polyolefin resin particles according to claim 1, wherein stirring is carried out using a special H-type stirring blade tilted at an angle of 5° to 20° in the stirring direction. (5) The dispersant is tertiary calcium phosphate, and the amount used is 0.05 to 1.0 parts by weight per 100 parts by weight of the polyolefin resin particles. Pre-foaming method. (6) A patent claim in which the surfactant is dodecylbenzene sulfonate or sodium n-paraffin sulfonate, and the amount used is 0.001 to 0.05 parts by weight per 100 parts by weight of the polyolefin resin particles. range 1
A method for pre-foaming polyolefin resin particles as described in 1. (7) The polyolefin resin is selected from the group consisting of low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer, and ethylene-vinyl acetate copolymer. The method for pre-foaming polyolefin resin particles according to claim 1, wherein the polyolefin resin particles are one or more mixed resins.