JPH0292377A - Resin ball having countless independent small bubble in sphere, and manufacture of its resin ball - Google Patents

Abstract

PURPOSE:To obtain a resin ball without uneven thickness, an eccentric load, and disturbance by generating countless independent small bubbles in a sphere at the time of injection molding. CONSTITUTION:The blowing agent of a proper quantity according to plasticized molding raw-material resin is mixed with the resin, and the resin is fed with fixed automatic weighing and the injection of high pressure at a low speed is started. At a time point when molding material in a plasticized fluid state reaches a gate 9, the injection of the high pressure at the low speed is automatically lowered to come to low pressure, and when the molding material is sufficiently fed to a cavity 10 for starting the filling of the cavity 10 through the gate 9 at a speed higher than an injecting speed, then the filling is completed. Compression pressure is retained in the state of low pressure and slow cooling is performed after the gate 9 is sealed, and moldings are taken out after opening molds, and when the moldings are cast in a water tank quickly and is quickly cooled, then resin balls 1, 1' with independent small bubbles 2 distributed uniformly in spheres can be molded.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a resin sphere that has countless small closed cells inside the sphere, is free from eccentric loads, and is free from external disturbances such as sink marks, voids, and distortions, and the resin sphere. It concerns the manufacture of balls.

"Conventional technology" By the conventional injection molding method, the thick-walled, solid resin spheres with large diameters are molded with irregularly large and irregular shapes inside the spheres during injection molding.
Small cavities occur and they are unevenly distributed, and the direction of the resultant force of the load does not pass through the center of gravity of the sphere, resulting in load eccentricity, which is a problem as a material for polishing to obtain a resin sphere with little error in sphericity. was there.

``Problem to be solved by the invention'' Suppressing the generation of air bubbles that are the cause of uneven thickness that occurs inside resin spheres due to conventional injection molding, eliminating uneven distribution of wall thickness and eliminating the cause of eccentric load. do. By eliminating disturbances such as sink marks, voids, distortions, etc., and averaging the radius of the sphere, a resin sphere is created that does not cause eccentric movement due to eccentric loads.

It is an object of the present invention to provide a method for manufacturing resin balls made of spherical material, which is suitable for precision polishing without causing eccentric loading as described above.

"Means for Solving the Problem" In order to achieve the above objective, countless small closed cells are generated inside the sphere during injection molding, and by averaging the distribution of the small cells, uneven distribution of wall thickness is eliminated, and eccentric loads are completely eliminated. be equal to

Low pressure molding eliminates disturbances.

In order to ensure the generation of small closed cells inside the sphere, an appropriate amount of blowing agent corresponding to the raw material resin is mixed in when plasticizing and kneading the molding material.

Injection starts at high pressure and low speed, and at the stage of filling the cavity, the pressure is lowered to a low speed and the injection speed is increased to fill the cavity.
After compressing and holding pressure, the mold is opened after the gate is sealed, and the molded product is taken out and rapidly cooled in a water tank.

``Function'' In injection molding, after high-pressure, low-speed injection, the secondary pressure is lowered and the injection speed is increased to perform filling using so-called low-pressure molding. To obtain a molded product in which an uncured part with low internal stress remains inside.

Apart from the above process, at the start of injection, a process beyond the molding material is carried out to remove the molded product after opening the mold in the filling path. The surface is solidified, and the unhardened inner insufficient portion attracted by the solidified surface portion is generated into numerous closed small bubbles at the outer periphery.The present invention will be described in detail below with reference to the drawings.

A solid powder or granular molding material corresponding to the product is prepared, and the material is introduced into the material input hopper 5 and shaped into the required spherical cavity 10 in the screw heating cylinder 6 at a uniform temperature. Thoroughly plasticize and knead to the optimum fluidity state.

An appropriate amount of foaming agent corresponding to the plasticized molding material raw material resin is mixed and automatically weighed to a certain level, and then high-pressure and low-speed injection is started.

When the plasticized and fluidized molding material reaches the gate 9, the high-pressure, low-speed injection is automatically lowered to a low pressure, and the injection speed is increased to start filling the cavity 10 from the gate 9. When the molding material is sufficiently supplied to the cavity 10, filling is completed.

After compressing and holding the pressure at a low pressure and sealing the gate 9, the molded product is slowly cooled. After the mold is opened, the molded product is taken out and immediately placed in a water tank to rapidly cool it. A resin sphere 1.1' in which the air bubbles 2 are evenly distributed can be molded.

"Effects of the Invention" Since the outer circumferential surface was free from disturbance, a resin sphere with an even radius at the center of the sphere without eccentric movement was obtained.

Therefore, it is a resin sphere that is ideal for precision polishing using a material method that does not have errors in sphere sphericity.

In order to obtain the above-mentioned molded product, a blowing agent was mixed into the molding material, injection was started at high pressure and low speed, and the secondary pressure was lowered and the injection speed was increased to ensure reliable molding by low-pressure molding.

[Brief explanation of the drawing]

Fig. 1 is a resin ball of the present invention made of acrylic resin as a raw material, and is a normal projection view in which countless small independent bubbles can be seen from the outside. FIG. 2 In the full cross-sectional perspective view of FIG. 1, small closed cells form a group on average. FIG. 3 is a full cross-sectional perspective view of a resin sphere made of an opaque resin other than acrylic resin according to the present invention; small bubbles cannot be seen from the outside. FIG. 4 is a full cross-sectional perspective view of a resin sphere with large bubbles produced by a conventional molding method. FIG. 2 is an explanatory diagram of the resin ball manufacturing method of the present invention. Acrylic resin ball 7... Screw opaque resin ball 8... Spool closed small bubble group 9...
Gate molten resin zone 10... Cavity large bubbles
11... Injection ramhoch 12... Injection cylinder Heating cylinder Fig. 5 1... 1'... 2... 3... 4... 5...・ 6...

Claims (3)

[Claims] (1) A resin sphere with countless small closed cells inside the sphere. (2) The method for producing resin spheres according to item 1. (3) The method for producing resin spheres according to item 2, in which a blowing agent is mixed.