JPH0316968B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing spherical polypropylene resin particles. BACKGROUND ART Foam molded articles have conventionally been produced using polystyrene or crosslinked polyethylene as a material, for example, by a bead molding method using pre-expanded particles. On the other hand, since polypropylene resin has excellent mechanical strength, heat resistance, chemical resistance, oil resistance, etc., the applicant has conducted research on the development of foam molded products using polypropylene resin, and has found a method for obtaining pre-expanded particles. We have successfully developed a method to obtain a foamed molded product using the pre-expanded particles, and have already proposed it. However, spherical resin particles can be obtained for polystyrene by a suspension polymerization method and for polyethylene by a crosslinking process, and the pre-expanded particles obtained using these resin particles are spherical, whereas in the case of polypropylene resins. Although pre-expanded particles can be obtained using non-crosslinked resin particles, it is difficult to obtain uniform spherical pre-expanded particles, and the pre-expanded particles cannot be efficiently filled into a mold. However, the problem was that it was difficult to obtain a uniform foamed molded product. As a result of intensive research aimed at establishing a method for producing spherical polypropylene resin particles, the present inventors discovered that polypropylene resin particles were treated with a dispersant containing one or more of basic magnesium carbonate, talc, and aluminum oxide. They found that good spherical polypropylene resin particles could be obtained by dispersing them in a dispersion medium and heating them, and filed an application (Japanese Patent Application No. 51765/1982). Magnesium carbonate, talc, aluminum oxide, aluminum hydroxide 1
The surprising fact that when a dispersant or a dispersant consisting of two or more species is used, not only can the dispersant be used repeatedly without deteriorating its dispersing effect, but its effectiveness as a dispersant further improves with repeated use. This discovery led to the completion of the present invention. That is, in the present invention, polypropylene resin particles are dispersed in a dispersion medium in a heating tank together with a dispersant consisting of one or more of basic magnesium carbonate, talc, aluminum oxide, and aluminum hydroxide, and the resin particles are dispersed under stirring. A step of spheroidizing the resin particles by heating to a temperature higher than the melting point of the particles +10°C, a step of separating the spheroidized resin particles from a dispersion medium and a dispersant, and dispersion of the spheroidized resin particles in the separated dispersion medium. The gist of the present invention is a method for producing spherical polypropylene resin particles, characterized in that the steps of separating the agent from the dispersion medium or recovering the agent without separating it and supplying it to the heating tank are continuously repeated. In the present invention, examples of the material of the polypropylene resin particles include propylene homopolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, etc., and these can be used alone or in combination. However, ethylene-propylene random copolymer is particularly preferred. In addition, the polypropylene resin particles can be pelletized by an extruder or pulverized by a pulverizer, and may have any shape, but the weight of the resin particles is 6 mg/piece or less. , preferably 5 mg/piece or less. In the present invention, the dispersant that can be used is one of basic magnesium carbonate, talc, aluminum oxide, and aluminum hydroxide, or a mixture of two or more thereof. This dispersant is 0.4 parts by weight per 100 parts by weight of polypropylene resin particles.
Use at least part by weight. If the amount of the dispersant added is less than 0.4 parts by weight, the spherical formation of resin particles by reusing the dispersant, which is the object of the present invention, cannot be expected. Further, even if a dispersant other than those mentioned above, such as basic zinc carbonate, calcium phosphate, calcium carbonate, etc., is used, no effect of spheroidization or reuse of the dispersant can be expected. However, these dispersants may also be added to the extent that they do not impede the effects of the present invention. In the present invention, the above-mentioned dispersant is recovered and reused, but at this time, if necessary, the loss of dispersant due to recovery can be compensated for by appropriately adding unused dispersant. Examples of the dispersion medium in which the resin particles are dispersed in the present invention include water, ethylene glycol, glycerin, methanol, ethanol, etc., or a mixture of two or more thereof, but water is usually preferred. The amount of the dispersion medium used is usually 100 parts by weight or more per 100 parts by weight of the resin particles. The above-mentioned resin particles dispersed in a dispersion medium together with a dispersant are heated to a temperature of at least 10° C. above the melting point of the resin particles, preferably at a temperature from above +12° C. to the melting point plus 50° C. If the heating temperature is lower than the melting point +10° C., it is difficult to make the resin particles spherical, and the object of the present invention cannot be achieved. Further, it is preferable to maintain the heating temperature for 15 minutes or more after reaching the desired temperature. In the present invention, the melting point of the resin particles was measured by differential scanning calorimetry (DSC). In this measurement method, the sample is set at 10°C/10°C in a nitrogen atmosphere.
Raise the temperature to 200℃ at a rate of 10℃/min, then increase the temperature to 200℃ at a rate of 10℃/min.
The apex of the melting peak when the temperature was lowered to 50°C and then raised again at 10°C/min was taken as the melting point, and if there were multiple peaks, the average temperature was taken as the melting point. An embodiment of the method of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a raw resin tank, 2 is a heating layer, and the resin particles, which are heated in the heating layer 2 and made spherical, are separated from the dispersion medium and the dispersant in a centrifugal separation tank 3. The separated dispersion medium and dispersant are collected in the collection tank 4. At this time, if necessary, the dispersant and the dispersion medium can be further separated by an appropriate means and only the dispersant can be recovered, but when producing spherical particles continuously, the dispersion medium can be used together with the dispersant. By collecting and reusing the dispersion medium, it is possible to save consumption of the dispersion medium and also to reuse the thermal energy held by the dispersion medium, so that the amount of thermal energy supplied to the heating layer 2 can be saved. In the recovery tank 4, unused dispersant is supplied from the dispersant tank 5 as necessary to compensate for the loss of dispersant, and the dispersant content in the dispersant is adjusted and the heating layer 2
In the heating layer 2, the resin particles supplied from the raw resin tank 1 are again dispersed, and the resin particles are spheroidized. The spherical polypropylene resin particles obtained by the present invention can be effectively used, for example, in the production of pre-expanded particles of the resin. The method for producing pre-expanded particles includes, for example, placing resin particles, a volatile blowing agent, and a dispersion medium in a closed container, raising the temperature to a predetermined temperature while stirring, and raising the pressure inside the container to a level higher than the vapor pressure of the volatile blowing agent. Alternatively, it may be carried out by opening one end of the container while maintaining the pressure below, and simultaneously releasing the resin particles and dispersion medium from the inside of the container into a low-pressure atmosphere.
The pre-expanded particles thus obtained have less variation in particle shape and also less variation in cell diameter (number of cells). Furthermore, when producing pre-expanded particles, a dispersant is usually used and the dispersant adhering to the pre-expanded particles is washed and removed, but if the resin particles obtained by the present invention are used, the pre-expanded particles It is not necessary to wash the resin particles, and the amount of resin particles remaining in the closed container during the production of pre-expanded particles is also very small. In addition, a foamed molded article can be obtained using the pre-expanded particles obtained as described above, and since the shape of the pre-expanded particles is uniform, it can be efficiently filled into a mold for molding, and variations in cell diameter can be avoided. Since the amount is small, a foamed molded article having uniform and excellent physical properties can be obtained. As explained above, according to the present invention, resin particles are dispersed in a dispersion medium using a dispersant consisting of one or more of basic magnesium carbonate, talc, aluminum oxide, and aluminum hydroxide. Spherical resin particles can be obtained by heating the resin particles to a temperature higher than the melting point +10°C, and when these spherical resin particles are used, for example, to produce pre-expanded particles, the pre-expanded particles are uniform in shape, cell diameter, etc. It has the advantage that foamed particles can be obtained, and the foamed molded product obtained using the pre-expanded particles has excellent physical properties. Furthermore, according to the present invention, the dispersant or the dispersant and the dispersion medium can be recovered and used repeatedly without deteriorating the dispersion effect.
It can contribute to saving consumption of dispersant or dispersant and dispersion medium, and also saves thermal energy.Furthermore, repeated use of the dispersant will not reduce the dispersion effect, but will further improve the dispersion effect. This has the effect of Hereinafter, the present invention will be explained in more detail by giving specific examples. Examples 1 to 2, Comparative Examples 1 to 2 The polypropylene resin particles, dispersant, and water shown in Table 1 were placed in the autoclave of 5, heated to the temperature shown in the same table, held for 1 hour, and then centrifuged. The resin particles were separated, and the dispersion medium and dispersant were recovered. Next, using the recovered dispersion medium and dispersant, and adding a new dispersant in the amount shown in Table 2 as necessary, the same heat treatment as the first time was repeated four times. Table 2 shows the results of observing the shape of the resin particles obtained by each of the five heat treatments. Comparative Example 3 Heat treatment was performed five times in total under the same conditions as in Example 1, except that a new dispersion medium and dispersant were used each time without recovering the dispersion medium and dispersant. The shapes of the obtained resin particles are also shown in Table 2. Table 3 also shows the total amount of dispersant and dispersion medium used in the five heat treatments, and the total amount of steam used for heating the autoclave, together with Examples 1 and 2. The shapes of the resin particles obtained in the above Examples and Comparative Examples are: Very good spherical shape...◎ Very good spherical shape...〇 Some are slightly spherical, but most are amorphous.
...△ Partial fusion occurred and amorphous shape ... It was judged as ×.

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【table】 [Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is a schematic process diagram of the method of the present invention. 2...Heating layer, 3...Centrifugal separation tank, 4...Recovery tank.

Claims (1)

[Claims] 1. Polypropylene resin particles are dispersed in a dispersion medium in a heating tank together with a dispersant consisting of one or more of basic magnesium carbonate, talc, aluminum oxide, and aluminum hydroxide, and the melting point of the resin particles is adjusted while stirring. A step of heating the resin particles to a temperature of +10°C or higher to make them spheroidal, a step of separating the spheroidized resin particles from a dispersion medium and a dispersant, and a step of dispersing the dispersant in the dispersion medium from which the spheroidized resin particles have been separated. A method for producing spherical polypropylene resin particles, characterized in that the steps of separating from the medium or recovering without separating and supplying to the heating tank are continuously repeated.