JPH0263051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The disclosed technology belongs to the technical field of a method for changing the color of an added colorant when producing a colored resin product using an injection molding machine.

<Summary of the gist> Accordingly, the present invention provides a method in which a colorless raw material resin and a liquid color of a predetermined color are simultaneously supplied into the cylinder of an injection molding machine through the previous injection process, and the raw material resin and liquid color are transferred through a screw plunger. After kneading the product through a molding machine and injecting it into the cavity and molding a predetermined number of products, the color changing process is repeated a predetermined number of times, and then other products of different colors are made by the next injection process using the same molding machine. This invention relates to a color changing method for an injection molding machine that performs molding, and in particular, in the color changing process, a screw plunger is continuously rotated with a large back pressure applied to inject raw resin, and then the screw plunger is continuously rotated with a large back pressure applied, and then the screw plunger is The screw plunger is slid back inside the cylinder with its rotation stopped, and then the screw plunger is kept in the retreated position and continuously rotated with a large back pressure applied to inject the raw resin. After these steps are completed, the above-mentioned This invention relates to a color changing method for an injection molding machine in which the screw plunger is returned to its original forward position.

<Prior art> In general, injection molding is a molding technology in which the molding material is melted and fluidized by heating, then injected into a cavity with a screw plunger, and processed to solidify by cooling. It is effective in molding resin products and is widely used in various industries due to its high mass productivity.

The above-mentioned injection molded resin molded products are often used for automobile interior parts and the like, and these parts are generally colored in various ways to improve the richness of their design.

When producing large quantities of colorful resin molded products, colored pellets are generally used.
When changing the color, the color of the injection molding can be quickly changed by simply changing the raw material of the colored pellets.

However, when using the raw material for the seed colored pellets, there is a problem that there is no flexibility in changing the color because the color has already been determined, and furthermore, the raw material must be colored to a constant color in the coloring process. Generally, the disadvantage was that raw material costs were high.

On the other hand, in order to have flexibility in changing colors, reduce costs, and maintain flexibility in the design of resin products, pellet-shaped resin raw materials are made into so-called colorless pellets that are colorless or nearly colorless. An injection molding technique has been developed and widely used in which the raw material is supplied to the hopper of an injection molding machine, a liquid color of a desired shade is added at the same time, the two are kneaded, and then extruded.

That is, as shown in FIG. 8, in this technique, a colorless pellet raw material 3 is supplied to a hopper 2 of an injection molding machine 1, and at the same time a liquid color of a predetermined color is injected and added from a tank 4 via a pump 5. In parallel with the operation, the screw plunger 6 is rotated at high speed and retreated to a predetermined position in the cylinder 7, and the raw material 3 and the added liquid color are mixed, kneaded, plasticized, and weighed at the same time, and then the screw plunger 6 is Injection molding is performed by moving the plunger 6 forward and extruding the plasticized raw material 3 into a cavity (not shown).

In addition, when changing the color in injection molding with the addition of the liquid color mentioned above, unlike the case of the colored pellets mentioned above, if the color residue from the previous stage is not cleaned and the color is not changed, a so-called color residue phenomenon will occur. After the color change process, such as temporarily stopping the injection of liquid color into the raw material and performing a so-called free shot on the raw material resin 3 for cleaning, or performing cleaning by performing a free shot while switching to the next liquid color, the next step may be performed. Injection molding was carried out by injecting the liquid color of the stage.

<Problems to be Solved by the Invention> However, when the above-mentioned conventional color changing method is adopted, since the nozzle 8 is always open during free shot, each of the nozzle 8, cylinder 7, and screw plunger 6 There is a disadvantage that the internal pressure due to the resin material 3 applied to the surface is reduced and the cleaning effect is reduced, and as a result, the number of free shots has to be increased, resulting in material loss and an increase in color change time. There was also the disadvantage of being invited.

Currently, to deal with this, as shown in Figure 9,
A large back pressure is applied to the screw plunger 6, and the screw plunger 6 is fixed to the front end of the cylinder 7 and rotated continuously to produce uncolored resin raw material or colored resin raw material to which the next stage liquid color has been added. There is also a method of extruding at high pressure and cleaning the remaining liquid color on the inner surface of the nozzle 8, the inner surface of the cylinder 7, the screw groove of the screw plunger 6, etc. by high-speed resin flow action. It has been devised and implemented.

However, this method has the disadvantage that when the resin raw material flows through the groove of the screw plunger 6, the resin raw material is biased toward the rear wall side of the screw groove of the screw plunger 6, resulting in uneven removal of the adhered liquid color. Moreover, as a result, there was a problem in that defective products with mixed colors were sometimes molded during the next stage of injection molding.

The purpose of the present invention is to solve the problems of the color changing method of an injection molding machine based on the above-mentioned prior art, and to solve the problem when injection molding of different colors is performed continuously by the same injection molding machine. By quickly and reliably removing the liquid color used in the previous injection molding process, reducing the loss of raw materials and shortening the color change time, it is beneficial to the fields where resin molding technology is used in various industries. The purpose of this invention is to provide an excellent method for changing the color of an injection molding machine.

<Means/effects for solving the problems> In order to solve the above-mentioned problems, the structure of the present invention, which is summarized in the above-mentioned claims, is to provide a cylinder containing a raw material resin to which a liquid color of a predetermined color is added. After the injection molding is completed, the screw plunger is continuously rotated with a high back pressure using an advance device to extrude the raw material resin. Remove the large amount of colored resin remaining in the cylinder from the previous injection molding process.
Next, with the rotation of the screw plunger stopped, slide it back inside the cylinder to remove the liquid color from the previous injection molding process. The raw material resin remaining between the screw parts is slid onto the rear wall surface, and then the screw plunger is kept in the retreated position and continuously rotated with high back pressure to extrude and discharge the raw material resin, and the raw material resin that has been slid is supplied. The liquid color on the rear wall of the screw is wiped off together with the raw material resin, and then the screw plunger is returned to the predetermined position to complete the color change process. After repeating this color change process a set number of times, the liquid color on the rear wall of the screw is removed. This is a technical measure that allows products of different colors to be injection molded in a process similar to injection molding.

<Example> Next, an example of the present invention will be described below based on FIGS. 1 to 7. In addition, the 8th and 9th
Components having the same features as those in the drawings will be described using the same reference numerals.

In the embodiment shown in FIG. 1, 1' is an injection molding machine which uses colorless pellets as raw material and injects liquid color into them to mold colored resin products of a predetermined color.

The injection molding machine 1' has a supply hopper 2 at the base thereof,
An injection pipe connected to the liquid color supply tank 4 via a pump 5 faces out, and a mixing nozzle 8' is provided at the tip of the cylinder 7, and a screw plunger 6 installed inside the cylinder 7 is connected to the liquid color supply tank 4 through a pump 5. A back pressure applying device 12 such as a hydraulic cylinder is linked to the base end.

The configuration is substantially the same as the conventional injection molding machine 1 shown in FIG.

The back pressure applying device 12 and the pump 5 are electrically connected to a control device (not shown) and are operated according to a predetermined program.

When injection molding a predetermined colored resin molded product using the injection molding machine 1', first, the colorless pellet raw material 3 is supplied to the hopper 2 in the same manner as in the conventional method, and at the same time, the liquid color supply tank is A liquid color of a predetermined color is supplied from 4 to the base of the hopper 2 by a pump 5 and mixed with the raw material 3.Furthermore, in parallel with these operations, a screw plunger 6 installed in a cylinder 7 is rotated in a predetermined cycle. After retreating, the raw material 3 is measured.

Furthermore, after this metering operation, the screw plunger 6 is moved forward again to extrude the plasticized raw material 3 through the mixing nozzle 8' at the tip of the casing 7, and is supplied to a mold (not shown) for predetermined injection molding. is being carried out.

In this case, the back pressure application device 12 that moves the screw plunger 6 forward and backward, and the pump 5 that adjusts the supply amount of liquid collar are operated via the above-mentioned control device.

As shown in FIG. 5, the mixing nozzle 8' is formed in a portion of the casing 7 beyond the tip barrel 9 in a plurality of axially reciprocating stages whose communication ports slightly overlap each other in the radial direction. Extrusion holes 13, 13, 13' are formed, and in each extrusion hole 13, 13', a plurality of conduit mixing blades 14, 1 as a non-stirring mixing jig intersect with each other.
4, 14', . . . are arranged inside the extrusion process in which color-mixing materials are extruded as shown by the arrows, so that color-mixing is promoted in a geometrical progression and mixing with a high concealment rate is achieved.

Therefore, when the injection molding of a predetermined color of the previous stage is completed, the next stage of injection molding of a different color is performed continuously,
It requires a color change process, but this process
As a first step, as shown in FIG. 2, without repeatedly advancing and retracting the screw plunger 6 for metered extrusion, a large back pressure is applied by the back pressure applying device 12, and the screw plunger The yarn 6 is continuously rotated with the barrel metering part 9 at the tip thereof being made the narrowest, and then liquid color of a predetermined shade is hopped from the tank 4 in an amount that is increased by a set amount from the amount used in the normal injection molding process. The colorless pellet raw material 3 in 2 is supplied and stirred.

In this case, since the back pressure of the screw plunger 6 is large, the colored material is removed from the gap in the measuring section 9 by the large extrusion pressure of the continuously rotating screw plunger 6 together with the residual colored material in the previous stage. It is extruded through the mixing nozzle 8'.

Furthermore, since the material extruded from the mixing nozzle 8' has an increased amount of liquid color, the color is not diluted, and the material is kneaded and extruded into a material with a uniform hue similar to that obtained in the injection molding process.

After repeating the operation in the first stage above for a predetermined time,
In the second step, as shown in Fig. 3, the rotation of the screw plunger 6 and the supply of the raw material 3 and liquid color are both stopped, and in this state, the screw plunger 6 is slid back by the set stroke. Thereafter, the screw plunger 6 is kept in the retracted position and continuously rotated with increased back pressure, and at the same time, the colorless pellet raw material 3 and the increased amount of liquid color are supplied to the hopper 2.

In the screw groove 15 of the screw plunger 6, in the first stage, the colored material remains in front of the screw wall, as shown in FIG.
Also, when the screw plunger 6 is continuously rotated, the material flows past the front of the screw wall, and the liquid collar of the previous stage is still attached to the rear of the screw wall, but in the second stage mentioned above, it is not rotated. As the slide retreats, the colored material moves to the rear of the screw wall as shown in FIG.
It comes into contact with the residual liquid color from the previous stage adhering to the rear of the screw wall, and the residual liquid color is almost completely wiped off by the subsequent supply of raw materials.

After the material has been continuously extruded for a predetermined period of time, the screw plunger 6 is moved forward in a rotating state to discharge the color-mixed material, thereby completing one cycle of the color change process.

Incidentally, the rotational movement of the screw plunger 6, the adjustment of the forward and backward movements, and the adjustment of the amount of liquid color supplied are performed according to a program of a control device (not shown), as in the previous stage injection molding.

Furthermore, the above-mentioned color change process is repeated a predetermined number of times, and then the next stage of injection molding with a different hue is performed in the same process as the previous stage injection molding. is almost completely removed and the amount of liquid color contained in the next stage is kept uniform, so color mixing is eliminated and the hiding rate is improved.

It goes without saying that the embodiments of this invention are not limited to the above-mentioned embodiments. For example, the mixing nozzle attached to the tip of the injection molding machine may be attached only when changing colors, and may be changed as appropriate so as not to be used during injection molding. Various aspects can be adopted, such as providing a switching valve.

Also, according to the experiment in accordance with the above example, the material loss of 30 kg can be reduced by 30% to about 20 kg,
This is a great addition to cost reduction, and the color change time, which used to be 20 minutes, has been reduced by 50%, which is approximately
It was possible to reduce the time to 10 minutes, significantly improving work efficiency.

In addition, the conventional 2 to 10 shots required to avoid color mixing defects at the start of injection molding immediately after a liquid color change can be reduced to 0, reducing costs and promoting work efficiency. I was able to do it.

In addition, since the color change is an automatic system, the operator can perform other work during the color change, improving the efficiency of related work and reducing the number of man-hours accordingly.

<Effects of the Invention> As described above, according to the present invention, basically, when injection molding of different colors is performed continuously using the same injection molding machine, the liquid color used in the previous injection molding can be quickly and It has the excellent effect of reliably removing the liquid color, reducing the loss of raw materials used, improving production efficiency, and shortening the time required to change the color of the liquid color, thereby improving production efficiency.

That is, after injection molding of a predetermined color is completed in the first step, when injection molding of a different color is performed in the next step,
The screw plunger is continuously rotated at the forward position with a large back pressure to extrude and discharge the raw material resin at high speed to remove a large amount of colored resin remaining in the cylinder from the previous stage injection molding. With the rotation of the U-Plunger stopped, slide the inside of the cylinder backwards to remove the raw resin remaining between the screws on the rear wall of the screw part of the Screw-Plunger, where liquid color is attached and cannot be removed in the above process. Slide and move the
After that, the screw plunger is kept in the retracted position and continuously rotated with high back pressure to extrude and discharge the raw resin, and the raw resin that has been slid away wipes away the liquid collar on the rear wall of the screw. An excellent effect is achieved in that the liquid color from the previous stage that has adhered to the screw groove of the screw plunger, etc., which could not be removed, can be dispersed and removed reliably and extremely efficiently by the wiping action of the raw resin.

Further, since cleaning can be performed more reliably when changing colors, an excellent effect can be achieved in that defective products due to color mixing in the next stage injection molding can be extremely reduced.

[Brief explanation of drawings]

Fig. 1 is a schematic partial cross-sectional side view of the structure of an injection molding machine used in the present invention, Figs. 2 to 4 are partial cross-sectional side views of an injection molding machine according to an embodiment of the present invention, and Fig. 5 is a schematic cross-sectional view of a mixing nozzle. Figures 6 and 7 are enlarged partial side views of the screw plunger, and Figures 8 and 9.
The figure is a partially sectional side view of an injection molding machine used in a conventional color change method. 7...Cylinder, 6...Screw plunger, 1'...Injection molding machine.

Claims (1)

[Claims] 1 Raw material resin and liquid color of a predetermined color are simultaneously fed into a cylinder, the first stage injection molding is performed via a screw plunger, the color changing process is repeated a predetermined number of times, and then a different liquid color is added to the next stage injection molding. In a color changing method for an injection molding machine that performs injection molding, the above color changing process is carried out by continuously rotating the screw plunger at the forward position with high back pressure to extrude the raw resin, and then rotating the screw plunger. The screw plunger is stopped and the inside of the cylinder is slid back, and then the screw plunger is kept in the retreat position and the back pressure is increased to extrude the raw material resin in continuous rotation, and finally the screw plunger is returned to the forward position. A method for changing the color of an injection molding machine.