JPS629915A - Molding method for plastics - Google Patents

Abstract

PURPOSE:To enable to mold a product whose material composition is uniform and preventing two kinds of pellets from separating, by a method wherein the low chargeable and/or high-density pellet containing an additive is made into a particle diameter smaller than the other pellet. CONSTITUTION:A capacity of a pellet 3 containing an additive is made small to such an extent of about 70% to a pellet 2 containing no additive. These two kinds of the pellets are made to mixed with each other at the ratio of 50 of the pellet 2 to 1 of the pellet 3 and fed to a molding machine by making the mixture transfer within a pipe with air. As for the ratio between a particle diameter of the pellet 2 and that of the pellet 3, through the optimum value is decided according to difference values of specific gravity and chargeable properties and terms of transfer, when a capacity ratio is more than 1.5 the titled method becomes effective, which is good to be 2-8 favorably. With this construction, two kinds of the pellets are prevented from separating by changing only the sizes of the pellets and a homogeneous product is obtained in plastic molding.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to improvements in plastic molding methods, in particular:
This invention relates to an improvement in a molding method called the masterbatch method, which uses a mixture of two types of plastic pellets.

BACKGROUND OF THE INVENTION Conventionally, this type of molding method was as shown in FIG. In Figure 2, 1 is a stainless steel vibrator, and inside it are plastic pellets 2 (shown in white) such as polystyrene 2 ＼-7 (ps) or ABS, and plastic pellets 2 made of the same material. Pellet 3 with added concentration of antistatic agent, coloring agent, mold release agent, etc.
(shown in black) is being transported by air currents in the directions of arrows A and B.

Pellet 1 and Pellet 2U: As shown in FIG. 3, they are often approximately cylindrical, approximately elliptical, or cylindrical in shape, but polyacetal and the like may also be approximately spherical. In either case, pellets 1 and 2 generally have the same shape and the same size (particle size).

Pellets 1 and 2 are prepared separately and are uniformly stirred and mixed in a tumbler at a ratio of several tens of parts, and then supplied to a molding machine through a pipe 1 shown in FIG.

As described above, pellet 3 contains a high concentration of additives, so it has a higher specific gravity than pellet 2, and when it contains an antistatic agent, it has significantly lower chargeability than pellet 2. That is, the surface resistivity of pellet 2, which does not contain an antistatic agent, is 10153 to 16Ω, while pellet 3 has a surface resistivity of 1012Ω.
It is as follows.

Problems to be Solved by the Invention In the conventional method, since the chargeability and specific gravity of the two types of pellets are different, the two types of pellets are separated by gravity, centrifugal force, and electrostatic force when they are transferred through a pipe. When the pellets separate and reach the part of the screw that performs heating and finishing in the molding machine, the mixing ratio fluctuates, making it difficult to mold products with uneven material compositions.

The present invention aims to solve these problems and provide a method in which separation is less likely to occur during transport.

In order to solve this problem, the present inventor previously proposed that the apparent specific gravity of pellets with a high specific gravity be made into irregular shapes such as an irregular cross section, but this method is effective against separation due to differences in chargeability. This has the opposite effect because the area of contact with other materials is small, and the extruder for producing pellets becomes somewhat complicated.

The present inventor conducted various studies focusing on the effect of pellet size from the behavior of large and small chips when machining plastics.

Regarding the influence of gravity, when two types of particles with different particle sizes are mixed, and when multiple small particles are placed in a space with the same shape and volume as a space occupied by one large particle, Since there are gaps between the particles and the specific gravity of the entire space is smaller than the specific gravity of the small particles themselves, it is concluded that the smaller the particle size of the high specific gravity pellets, the better.

Next, regarding centrifugal force, it is a problem of air resistance when the pellet is directed outward by centrifugal force across the air flow at the bend in the pipe, so objects with the same specific gravity and shape are suspended in the air. Due to the fact that the smaller the pellet falls, the smaller the falling speed, the smaller the particle size of the high specific gravity pellet, the better.

Regarding static electricity, since the surface area and volume have a square and cube relationship with the particle size, the smaller the particle size, the more likely it is that electrostatic adhesion will occur.

Therefore, pellets containing a large amount of antistatic agent and having low electrostatic properties should be made to have a small particle size.

Means to solve the problem In this way, even against the two forces considered to be responsible for the separation of the two types of pellets: gravity, centrifugal force, and electrostatic force,
Low charge and/or high specific gravity pellets containing additives,
It has a smaller particle size than other pellets.

Effect With this configuration, pellets containing a high concentration of additives and having a low chargeability and/or high specific gravity have a small particle size that makes them similar to other pellets in terms of gravity, centrifugal force, and electrostatic forces. as a result of which they are transported without significant separation.

Embodiment FIG. 1 is a perspective view of a plastic pellet according to an embodiment of the present invention, in which the volume of the pellet 3 containing an additive is reduced to about 70 times that of the pellet 2 containing no additive. . 50 pellets of 2 types of pellets,
Pellets 3 are mixed at a ratio of 10, transported through a pipe by air, and supplied to a molding machine.

In this example, the pellet 3 has a small cross-sectional area and a small length, but only one of them may be changed.

The optimum value for the particle size ratio of pellets 2 and 3 is determined by the value of the difference between specific gravity and chargeability and the transport conditions, but an effect will be seen if the volume ratio is 1.5 or more, and preferably 2. ~8 is good.

Effects of the Invention As described above, according to the present invention, separation of two types of pellets can be prevented simply by changing the size of the pellets, and a homogeneous product can be obtained especially in masterbatch type plastic molding.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a pellet used in a molding method according to an embodiment of the present invention, FIG. 2 is a sectional view showing a part of a conventional plastic molding method, and FIG. 3 is a perspective view of a conventional pellet. be. 2...Pellet, 3...Pellet. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure? (3)

Claims (1)

[Claims] Mixing and heating pellets of a first plastic having a high chargeability and/or a small specific gravity and large particles and pellets of a second plastic having a low chargeability and/or a small specific gravity and a small particle. A plastic molding method characterized by plasticization.