JPH0631726A - Manufacture of foamable thermoplastic resin particles - Google Patents

Abstract

PURPOSE:To obtain foamable thermoplastic resin particles of small and high sphericity by an underwater cutting system, a hot cutting system. CONSTITUTION:Dies 2 heat insulated at surfaces are mounted at ends of extruders 1A, 1B. A rotary cutter 4 is disposed in a noncontact state with the die 2 (heat insulator). Melted resin containing foaming agent is extruded from a nozzle of the die 2 into coolant, cut by, the cutter, discharged together with the circulated coolant from a cut part to manufacture foamable resin particles. The particles having a small diameter of 0.8-2.0mm can be manufactured by using the heat insulated die 2, and the edge of the cutter is not brought into contact with the die 2 (heat insulator), thereby preventing damages of the edge of the cutter and the die 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing expandable thermoplastic resin particles used as a molding material.

[0002]

2. Description of the Related Art Conventionally, a method has been used in which a thermoplastic resin such as polystyrene is extruded in an unexpanded state while injecting and mixing a foaming agent with an extruder and then cut to obtain expandable thermoplastic resin particles. In this case, the expandable thermoplastic resin particles are
In order to improve the homogeneity of the molded product, it is preferable that the molded product has a diameter as small as possible and high sphericity.

However, according to the widely-used strand-cut method, the particle shape is columnar,
Also, when trying to produce small-diameter particles, the strands are disturbed,
Distortion of the particle shape due to fusion is significant, and the particle size is practically about 2 m.
It was extremely difficult to produce expandable thermoplastic resin particles of m or less.

Therefore, a method for producing expandable thermoplastic resin particles by an underwater cutting method or a hot cutting method, which is capable of producing spherical particles having a uniform shape and particle size, has been attempted.

[0005]

However, in these methods, since the cooling water is brought into direct contact with the outer surface of the die to flow the cooling water, the temperature of the molten resin in the nozzle is rapidly lowered and solidified, and the nozzle Clogging easily occurs.

To prevent this, the temperature of the die and the cooling water may be raised, but the temperature of the molten resin also rises accordingly, so that the resin particles are slightly foamed to form flat or columnar resin particles. . In addition, because the molten resin is not sufficiently cooled at the outlet of the die and foams, or the resin discharged from the nozzle is soft, the cutting by the rotary cutter is not good, and resin particles having a whisker-like protrusion, flattened It becomes the resin particles of the shape. Moreover, even if the blade of the rotary cutter is brought into contact with the die outlet end, even the cutting cannot be performed, and the die or rotary cutter
However, there was a problem that the blade was easily damaged. When molding is performed using such resin particles, there is a problem in that resin particles are easily fused with each other and the molding efficiency is reduced.

There is also a method for producing expandable thermoplastic resin particles in which raw material resin particles obtained by suspension polymerization are impregnated with a foaming agent, but the expandable resin particles obtained by this method have a high sphericity. However, there was a problem that the variation in particle size was so great that a large amount of particles could not be used for molding.

The present invention has been made in view of the above conventional problems, and solves the above problems in the case of producing expandable resin particles by an underwater cutting method or a hot cutting method, and has a smaller diameter than ever before. An object of the present invention is to provide a method for producing expandable thermoplastic resin particles capable of accurately producing resin particles having a high sphericity.

[0009]

In order to solve the above-mentioned problems, the present invention provides a method for producing expandable thermoplastic resin particles in which a foaming agent-containing molten resin extruded from a die is cut into resin particles by a rotary cutter. In the above method, a die having a heat-insulated surface is used, and the rotary cutter is arranged in a non-contact state with the die surface.

The present invention has been made as a result of diligent research on the factors affecting the particle shape when the nozzle has a small diameter for the production of small-diameter spherical resin particles. That is,
By using a die having a heat-insulated surface, it is possible to prevent the temperature of the molten resin in the nozzle from decreasing and prevent the molten resin from solidifying. As a result, it is not necessary to raise the temperature of the die and the cooling water in particular, so that the temperature of the molten resin does not rise above a predetermined value, and there is no risk of foaming the resin particles.
Further, the molten resin flows efficiently to the die outlet, and after that, it is rapidly cooled by the cooling water at the die outlet and solidified, so that the rotary cutter can be cut in a non-contact state with the die surface. The resin can be cut well, and spherical resin particles having no small-sized whisker-like protrusions can be produced.

The production method of the present invention is widely applicable to the production of various expandable thermoplastic resin particles such as expandable polyethylene resin particles, expandable polypropylene resin particles, expandable polystyrene resin particles, etc. Is optimal when the expandable polystyrene resin particles are manufactured as spherical resin particles having a particle diameter of 0.8 to 2.0 mm. As the foaming agent, a volatile physical foaming agent such as propane, butane or pentane is used.

As an extruder used for carrying out the production method of the present invention, a conventional extruder can be used as it is, but the step of mixing the raw material resin and the foaming agent at a high temperature and the melt containing the foaming agent. It is preferable to use a two-stage tandem type extruder in which the step of extruding the resin at a lower temperature than the previous step is performed by a separate extruder, because the production efficiency is further improved.

As a material of the heat insulating material used to heat the die surface, the thermal conductivity is 1.0 (kcal / m · hr).
Materials such as synthetic resins, ceramics, and metals having a temperature of ℃) or less are suitable. Also, the heat insulating material has a wall thickness of 0.1 to 1.0 mm,
It is attached on the entire surface of the die or around the nozzle, and the molten resin is discharged from the die outlet after passing through this heat insulating material attaching portion.

The manufacturing method of the present invention is carried out by using the above-mentioned materials, devices, members, etc., and the thermoplastic resin and the foaming agent are mixed in the extruder, and then the die nozzle equipped with the heat insulating material is used. The molten resin is extruded and rapidly cooled, and the resin which has started to solidify is cut by a rotary cutter placed in a non-contact state on the die surface.

[0015]

EXAMPLES Next, the present invention will be described in more detail by comparing Examples with Comparative Examples.

(Embodiment 1) As shown in FIG. 1, a two-stage tandem type extruder having 65 mmφ extruders 1A and 1B as the first and second stages is used, and a second 65 mmφ extruder is used. Thermal conductivity of 0.1 (kcal /
(m · hr · ° C.) A die 2 heat-insulated with a heat insulating material 3 made of a polyether ether ketone resin was mounted, and a rotary cutter 4 was placed at the die exit end in a non-contact state. 65m on the first stage
Pentane was injected into the expandable polystyrene resin melted by the mφ extruder 1A and mixed at 210 ° C., and the second stage 65 m
The molten resin containing the foaming agent is extruded into cooling water from a die nozzle as a strand having a diameter of 0.8 mm in an mφ extruder 1B at 130 ° C., cut by a blade of a cutter-4 rotating at the die exit end, and circulated. The expandable resin particles 7 were manufactured by discharging together with the cooling water 6 from the cutting portion.

(Comparative Examples 1 and 2) Expandable resin particles were prepared by using the same materials, devices, members, etc. as in Example 1 except that a die not heat-insulated was attached to the tip of the second stage 65 mmφ extruder. Was manufactured.

(Embodiment 2) 30 mmφ as shown in FIG.
The surface of the extruder tip 1C has a thermal conductivity of 0.1 (kca).
A die 2 heat-insulated with a heat insulating material 3 of a polyether ether ketone resin of 1 / m · hr · ° C.) was mounted, and a rotary cutter-4 was placed in a non-contact state at the die exit end. Pentane is injected into the molten expandable polystyrene resin and mixed, the molten resin containing the foaming agent is extruded into the cooling water from the nozzle 5 of the die 2, cut by the blade of the rotating cutter-4 at the exit end of the die 2, and circulated. The expandable resin particles 7 were manufactured by discharging the foamable resin particles 7 together with the cooling water 6 to be discharged from the cutting portion.

(Comparative Examples 3, 4 and 5) Expandable resin particles were produced using the same materials, devices, members and the like as in Example 2 except that a die which was not thermally insulated was mounted.

Comparative Example 6 Expandable resin particles were produced using the same materials, devices, members, etc. as in Example 2 except that the rotary cutter was placed in contact with the die exit end.

Table 1 shows the shapes and particle sizes of the expandable polystyrene resin particles obtained in the above Examples and Comparative Examples.

[0022]

[Table 1]

From the above results, according to the production method of the present invention, a foamable resin having a small particle size of 0.8 to 2.0 mm and a high sphericity, which has been difficult to produce by the conventionally known method. It was confirmed that particles could be produced.

[0024]

EFFECT OF THE INVENTION According to the method for producing expandable thermoplastic resin particles of the present invention, the particle diameter of 0.8 to 2.0 m, which has been difficult in the prior art.
The expandable thermoplastic resin particles having a small diameter of m and a high sphericity can be accurately manufactured, and the manufacturing efficiency can be significantly improved.

Further, since the resin is cut by the rotary cutter blade which is disposed in a non-contact state with the die (heat insulating material) outlet end, damage to the die and the rotary cutter blade can be prevented.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of one embodiment of an extruder and die used in the present invention.

FIG. 2 is a cross-sectional view of another embodiment of the extruder and die used in the present invention.

[Explanation of symbols]

 1A, 1B, 1C Extruder 2 Die 3 Heat insulating material 4 Rotating cutter 5 Nozzle

Claims (1)

[Claims] 1. A method for producing expandable thermoplastic resin particles, wherein a foaming agent-containing molten resin extruded from a die is cut by a rotary cutter into resin particles, and a die having a heat-insulated surface is used, and a die surface is used. A method for producing expandable thermoplastic resin particles, which comprises arranging a rotary cutter in a non-contact state.