JPH05301218A - Production of thermoplastic resin particle - Google Patents

Abstract

PURPOSE:To obtain a method for producing thermoplastic resin particles having a small diameter and a high sphericality by an under-water cutting system or a hot cutting system. CONSTITUTION:A die 2 with a heat insulating surface is loaded on the top end of an extruder 1. A rotating cutter is disposed on the die 2 (a heat insulating material) in a contact or non-contact state. A melt resin is extruded into cooling water from a nozzle 5 of the die 2. By cutting the resin by a rotating cutter blade 4, spherical resin particles are produced. The use of the heat insulating die 2 realizes the production of spherical particles having a particle diameter as small as 0.8-2.0mm and a high sphericality. With the cutter blade 4 in non- contact with the die 2 (a heat insulating material), the damages of the cutter blade 4 and the die 2 are also prevented.

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 thermoplastic resin particles (pellets) used as a molding material.

[0002]

2. Description of the Related Art In the case of producing expanded resin particles by impregnating thermoplastic resin particles (pellets) with a foaming agent, it is preferable that the raw material pellets have a diameter as small as possible and a high sphericity.

However, according to the widely-used strand cutting method, the pellet shape is columnar, and when trying to manufacture a small-diameter pellet, the strand shape is disturbed and the pellet shape is significantly disturbed due to fusion, and the pellet size is substantially reduced. It was extremely difficult to produce pellets with a diameter of about 2 mm or less.

Under the circumstances, attempts have been made to produce pellets by an underwater cutting method or a hot cutting method capable of producing spherical pellets having a uniform shape and particle size.

[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 Clogging easily occurs.

In order to prevent this, the temperature of the die and the cooling water is increased, but on the contrary, the molten resin is insufficiently cooled at the die outlet, and the resin discharged from the nozzle is soft. Therefore, even if the blade of the rotary cutter does not come into contact with the exit end of the die, it cannot be cut, and the blade of the die and the rotary cutter is easily damaged. The pellets will have a flat shape. Then, when the pellets are molded using such pellets, there is a problem that the pellets are easily fused with each other and the molding efficiency is lowered.

The present invention has been made in view of the above problems, and solves the above problems in the case of producing resin particles (pellets) by an underwater cutting method or a hot cutting method, and has a small diameter and a true diameter. It is intended to provide a method for producing thermoplastic resin particles capable of producing resin particles (pellets) having high sphericity.

[0008]

In order to solve the above-mentioned problems, the present invention relates to an underwater cutting method, a hot cutting method, that is, a method in which a melt of a thermoplastic resin is cooled in water by a nozzle of a die attached to the tip of an extruder. It employs a method of extruding into cooling air, cutting with a rotary cutter and granulating, and is characterized in that a die whose surface is heat-insulated is used in particular.

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 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, the molten resin efficiently reaches the die outlet and is rapidly cooled by the cooling water at the die outlet to be solidified, and the cutting by the cutter blade becomes good,
It becomes possible to manufacture spherical particles having no small-sized beard-like protrusions.

The production method of the present invention can be widely applied to the production of various thermoplastic resin particles. In particular, polyethylene-based resin, polypropylene-based resin, polystyrene-based resin or the like is used as a raw material, and the particle size is 0.8 to 2.0 mm. It is most suitable for the production of spherical resin particles.

It has been found that the manufacturing method of the present invention also has the effect of increasing the discharge capacity of the extruder.

The material of the heat insulating material used to insulate the surface of the die has a thermal conductivity of 1.0 (kcal / m · h).
Materials such as synthetic resins, ceramics, and metals having a temperature of r.degree. C. or less are preferable. The heat insulating material has a wall thickness of 0.1 to 1.0 mm and is attached on the entire surface of the die or around the nozzle so that the molten resin is discharged from the die outlet after passing through the heat insulating material attaching portion.

[0013]

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

(Examples 1 to 12) The surface of the 30 mmφ extruder had a thermal conductivity of 0.1 (kcal / m · hr ·).
A die insulated with a polyetheretherketone resin (° C.) Was attached. Under predetermined conditions, polystyrene, polyethylene, polypropylene melt is extruded from the die nozzle into cooling water and cut with a cutter blade that rotates in contact with or not in contact with the die (heat insulating material) outlet end to produce resin particles. did. Table 1 shows the shape and particle size of the resin particles produced.

[0015]

[Table 1]

(Comparative Examples 1 to 6) A die whose surface was not heat-insulated was attached to the tip of the 30 mmφ extruder. Under predetermined conditions, a melt of polystyrene, polyethylene, and polypropylene was extruded from the nozzle of this die into cooling water, and cut with a cutter blade that rotates in contact with the exit end of the die to produce resin particles. Table 2 shows the shapes and particle sizes of the resin particles produced.

[0017]

[Table 2]

According to the manufacturing method of the present invention, as is clear from the examples, the particle diameter of 0.8 to 2.0 m, which was difficult in the prior art, was obtained.
Spherical particles having a small diameter of m and high sphericity can be produced, and the granulating ability is increased. Further, good cutting can be performed without bringing the blade of the rotary cutter into contact with the exit end of the die (heat insulating material), and particles having a uniform shape and particle size can be produced.

[0019]

According to the method for producing thermoplastic resin particles of the present invention, it is possible to produce spherical particles having a small diameter of 0.8 to 2.0 mm and a high sphericity, which has been difficult so far. The granulating ability can be increased.

Further, the blade of the rotary cutter is a die (heat insulating material).
Since it is possible to granulate even in the non-contact state with the outlet end, damage to the die and the blade of the rotary cutter can be prevented.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of one example of an extrusion die used in the present invention.

[Explanation of symbols]

 1 Extruder 2 Die 3 Insulation 4 Rotating Cutter Blade 5 Nozzle

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinari Ito 1000 Kawajiri-cho, Yokkaichi-shi, Mie Mitsubishi Yuka Birdishe Co., Ltd.

Claims (1)

[Claims] 1. A method of producing thermoplastic resin particles, wherein molten resin extruded from a die is cut by a rotary cutter to form resin particles, and a die having a heat-insulated surface is used. Production method.