JP2003300224A - Method for changing color of resin in injection molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for changing a color of a resin which can decrease generation of a defective owing to a color mixture in changing the color in an injection molding using a single spindle injection molding machine. <P>SOLUTION: A change is carried out from a former color resin 18 before changing the color to a latter color resin 20 after changing the color at a specific timing in the process of measuring with a screw 14. A skin layer 18a of a molded article just after an article of good quality molded only by the former color resin 18 is formed of a sufficient quantity of the former color resin 18 to completely cover a core layer 22a formed of a mixed color resin 22 comprising the former color resin 18 and the latter color resin 20, and a molded article formed of the former color resin 18 and the mixed color resin 22 is turned into an article with an acceptable appearance. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin color changing method in injection molding, and more particularly to an improvement in a resin color changing method capable of reducing the occurrence of defective molding due to color mixture during color changing.

[0002]

2. Description of the Related Art Conventionally, resin molded products have been used for many parts of industrial products. For resin molded products, if a mold is created in the desired shape, the mold is set in the injection molding machine, and if the prescribed injection conditions are maintained, resin molded products of constant quality can be continuously manufactured. You can Further, in the case of resin molding, it is possible to change the color of the molded product by changing the resin used, and it is possible to easily cope with products of different colors.

By the way, when it is desired to manufacture molded products of different colors, a desired molded product can be manufactured freely by preparing an injection molding machine and a mold for each color. The manufacturing cost of the mold is not cheap, and it is not realistic to prepare for each color of the same product.
Therefore, usually, the same injection molding machine or mold is used to change the color of the resin to be injected, so as to deal with different color products.

FIG. 3 shows a conventional injection molding procedure. It should be noted that FIG. 3 and FIG. 4 described later show only the mold 10 and the barrel 12 of the injection molding machine for injecting the resin into the mold 10 for simplification of the drawing. There are various types of resin injection, but as an example, FIG. 3 shows a barrel 12 of a single-screw type injection molding machine.

As shown in FIG. 3, in the case of single-screw type injection, a rotatable screw 14 having spiral wings fixed around the shaft is arranged inside the barrel, and the screw 14 rotates. While retreating (moving to the right in the drawing), the resin for one shot required for molding one molded product is weighed and sequentially moved to the tip side (left side in the drawing) of the barrel 12. Then, when the measurement of a predetermined amount is completed, the screw 14 is non-rotated to advance the inside of the barrel 12 toward the tip (left side) by one shot (retracted amount) and the measured resin (moved to the tip side of the barrel 12). The resin thus obtained is extruded and injected into the mold 10.

In the case of the injection molding machine shown in FIG. 3, the color of the resin is, for example, a white base resin constantly supplied into the barrel 12 and a predetermined amount of pelletized master batch (pigment) added from a hopper 16. Then, the resin is agitated while being measured by the screw 14 to be mixed and toned in the barrel 12 to obtain a desired resin color.

Since the resin is usually measured for each molded product, that is, for each molding shot, after the measurement of the previous color resin 18 before the color change is completed, the master batch is changed and the color is changed. The post-color resin 20 is weighed. When the color of the resin is changed, the front color resin 18 remains on the inner wall portion of the barrel 12 or the like. Therefore, the resin immediately after the masterbatch is changed is the front color resin 18 and the rear color resin 20.
And the mixed color resin 22 is mixed. That is, in FIG. 4, when the black master batch is used up to the nth measurement and the red masterbatch is used for color change from the (n + 1) th measurement, for example, the (n + 1) th measurement and the (n + 2) th measurement are performed. At the second measurement, the (n + 3) th measurement, and the like, the color of the resin is the mixed-color resin 22 in which black and red are mixed. Then, when the weighing is performed a plurality of times, the proportion of the red post-color resin 20 increases, and the black pre-color resin 18 remaining in the barrel 12 disappears, the resin in the barrel 12 becomes, for example,
The regular red post-color resin 20 is changed from the (n + 4) th measurement.

Returning to FIG. 3, in FIGS. 3 (a) to 3 (e),
The ejection operation after color change is shown. As previously mentioned,
As shown in FIG. 3A, the mixed color resin 22 exists after the previous color resin 18 by changing the master batch to be input for color change. When the resin is injected in this state, first, as shown in FIG.
The remaining part (the product to be molded one before is completely colored with the previous resin 1
The pre-colored resin 18 is left in a predetermined amount at the time of the next injection so as to mold only 8) is injected into the mold 10. The injected front color resin 18 is cooled by the mold 10 to form the skin layer 18a, and the succeeding color mixture resin 22 is formed.
Are sequentially injected into the skin layer 18a to form the core layer 22a.

When the mixed color resin 22 is further injected, as shown in FIG.
As shown in (c) and FIG. 3 (d), the increased color mixture resin 2
2 penetrates the skin layer 18a and leaks to the outside of the skin layer 18a, and finally, as shown in FIG.
Becomes a defective product that appears on the surface of the molded product. Thereafter, defective products are molded until the mixed color resin 22 inside the barrel 12 is used up. That is, in the example of FIG.
After the color change, four defective products will be produced until good products are manufactured.

[0010]

In the case of a single-screw type injection molding machine, color mixing of resins is inevitable during color change. That is,
Occurrence of defective products due to mixed color resin is inevitable. But,
There is a demand to reduce the number of defective products generated as much as possible.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a resin color changing method capable of reducing the occurrence of defects due to color mixing at the time of color changing.

[0012]

In order to achieve the above-mentioned object, the present invention measures the amount of resin required for one shot for molding one molded article, and sequentially measures the measured resin. A method of changing the color of a resin during continuous injection molding using a single-screw injection molding machine for producing a molded product by extruding into a molded product, at a predetermined timing in the middle of the measurement, the pre-color resin before the color change. The core layer is formed by the preceding color resin and is completely covered by the skin layer, in which the skin layer of the molded product immediately after the non-defective product is formed by only changing the color to the post-color resin after the color change. Is formed of a mixed color resin of the front color and the rear color.

According to this structure, by changing the color during the measurement, it is possible to secure a sufficient amount of the pre-color resin forming the skin layer. As a result, the mixed color resin injected into the core layer later does not break through the skin layer and come out to the surface, the surface is covered with the preceding color resin, and the mixed color resin is present in the interior, which causes problems in practical use. It becomes possible to make a non-defective product, and it is possible to make a molded product composed of a previous color resin and a mixed color resin, which has been conventionally regarded as a defective product, into a good product. As a result, the number of defectives can be reduced.

In order to achieve the above-mentioned object, in the present invention, in the above-mentioned constitution, switching from the front color resin to the rear color resin is performed by changing the amount of the front color resin with respect to the amount of resin for one shot. Is performed at a timing of occupying at least 60% or more.

According to this structure, since the skin layer is made up of 60% or more of the front color resin, it is possible to surely cover the core layer which is the color mixture resin, and the front color resin and the color mixture resin are formed. The molded product to be processed can be surely made to be a good product.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention (hereinafter referred to as an embodiment) will be described below with reference to the drawings.

FIG. 1 is an explanatory view for explaining the resin color changing method in the present embodiment in association with the measurement of resin and injection into a mold. The mold 1 used in this embodiment
The structure of the barrel 12 of the injection molding machine for injecting the resin into the mold 0 and the mold 10 is the same as the conventional one shown in FIGS. In FIG. 1, the injection molding machine itself is omitted for simplification of the drawing, and only the barrel 12 is shown. Also, in this embodiment, a single screw type injection molding machine will be used for description.

As shown in FIG. 3, in the case of single-screw type injection, a rotatable screw 14 having spiral wings fixed around the shaft is arranged inside the barrel, and the screw 14 rotates. While retreating (moving to the right in the figure), the resin for one shot required for molding one molded product is measured and sequentially moved to the tip side of the barrel 12 (left side in the figure). . Then, when the measurement of a predetermined amount is completed, the screw 14 is rotated without rotation.
The resin (resin moved to the tip side of the barrel 12) measured by advancing the inside toward the tip (left side) by one shot (backward) is extruded and injected into the mold 10.

The measurement of resin will be specifically described. Since the resin is measured while the resin previously injected is present in the mold 10, the resin in the barrel 12 is prevented from entering at the entrance portion to the mold 10. Therefore, as the screw 14 rotates, the blades of the screw 14 sequentially push out the resin toward the front of the screw 14. However, as described above, the former molded product (resin) still exists inside the mold 10. Therefore, the resin is prevented from entering the mold 10, and the screw 14 is pushed backward (on the right side in the drawing) in accordance with the amount of the resin pushed out. Therefore, screw 1
By rotating the screw 4 a predetermined number of times (for one shot for molding one molded product), one shot of resin is prepared ahead of the screw 14. After that, the mold 10 is opened, the molded product made of the previously injected resin is discharged, and the mold 10 is closed, and at the same time, the entire screw 14 is advanced to the tip side of the barrel 12 (the left side in the figure). To 1
Resin injection for shots can be performed.

The color of the resin is also the same as the conventional one. For example, a predetermined amount of pelletized master batch (pigment) is added from a hopper 16 to a white base resin which is constantly supplied into the barrel 12, The resin is mixed in the barrel 12 by stirring while being measured with the screw 14, and toning is performed to obtain a desired resin color.

The characteristic feature of this embodiment is that the color change from the pre-color resin before the color change to the post-color resin after the color change is performed during the measurement of one shot of the resin.

That is, as shown in FIG. 1, after the master batch is changed for the nth measurement, the (n + 1) th measurement is started, and when the predetermined amount of the front color resin 18 is measured, the rear color resin 20 is changed. Are switching. The switching to the post-color resin 20 is performed by mixing the pre-color resin 18 and the pre-color resin 18 and the post-color resin 20 which are formed immediately after the non-defective product (injection n-th shot) molded only from the pre-color resin 18. The skin layer of the molded product formed of the mixed resin 22 is sufficiently formed only by the pre-colored resin 18, and the mixed color resin 22 serving as the core layer injected into the inside of the skin layer does not push through the skin layer and come out. This is the timing when the front color resin 18 can be secured.

Preferably, the measurement corresponding to the injection (n + 1) th time is started, and the color change timing is delayed until the amount of the resin 18 for the previous color occupies at least 60% or more of the amount of resin for one shot. Is desirable.

As described above, the pre-color resin 18 and the pre-color resin when the color change from the pre-color resin 18 before the color change to the post-color resin 20 after the color change is performed during the measurement of one shot of the resin. FIG. 2 shows a molding process of a molded product formed of the mixed resin 22 in which 18 and the post-color resin 20 are mixed.

FIG. 2A shows a state immediately after performing the next shot after performing the one-shot injection from the state shown in FIG. 1 and molding the molded product with only the resin 18 of the previous color. At this point, the injected resin for one shot is the previous color resin 1.
8 is, for example, 60%, and the mixed color resin 22 by mixing the front color resin 18 and the rear color resin 20 is 40%.

In FIG. 2B, the screw 14 is used for the mold 10.
The state in which the injection operation is started by advancing to the side is shown.
In FIG. 2C, the injection operation further progresses, and the skin layer 18 a
The state is shown in which the entire amount of the pre-colored resin 18 forming the is extruded into the mold 10. As described above, the skin layer 18a made of the previous color resin 18 is formed to such an extent that the color mixture resin 22 to be injected into the interior later does not break through the already formed skin layer 18a.

Further, as the injection injection of the resin progresses, as shown in FIG.
As shown in (d), the pre-color resin 18 and the post-color resin 20 are contained in the skin layer 18a formed of a sufficient amount of the pre-color resin 18.
Mixed with the mixed color resin 22 enters the core layer 22a.
To form. In FIG. 2E, the injection of the mixed color resin 22 further progresses, and the resin for one shot is completely injected into the mold 10, and the core layer 22a is completely formed in the skin layer 18a. The injection is completed.

As described above, the skin layer 18 is made of a sufficient amount of the pre-colored resin 18 so as not to leak the mixed color resin 22 to the outside.
a and the core layer 22a is completely sandwiched to form a sandwich structure.
Is produced on the surface of the molded article, and a molded article which is functionally good is manufactured.

In this way, as shown in FIG. 1, the molded product having the mixed color resin 22 in the core layer 22a is, as shown in FIG. Molded as a good eye product. Then, the injection (n + 2) shot and the injection (n + 3) shot molded products are molded as defective products of only the completely mixed resin 22, and the injection (n + 4) shot molded product is mixed with the resin mixture on the skin layer. 22 is molded as a defective product having the post-color resin 20 in the core layer.

As is apparent from a comparison between FIG. 1 using the color changing method according to the present embodiment and FIG. 4 using the conventional color changing method, a molded product which has been a defective product in the past is regarded as a good product. It becomes possible to improve the production efficiency. The amount of color-mixed resin generated when changing colors is
Although the number of defective products that change due to conditions such as the amount of the pre-colored resin 18 remaining in the barrel 12 after the color change and the viscosity of the resin to be used changes, in the case of color change molding under the same conditions, As described above, the number of defective products can be surely reduced.

The color change timing can be easily adjusted by adjusting the timing of charging the master batch, that is, the timing of switching the valve connecting the hopper 16 and the barrel 12. In this case, it is desirable to prepare the hopper 16 for each color and appropriately control the connection state to the barrel 12 by the switching valve.

[0032]

According to the present invention, by changing the color during measurement, it is possible to secure a sufficient amount of the pre-color resin forming the skin layer. As a result, the mixed color resin injected into the core layer later does not break through the skin layer and come out to the surface, the surface is covered with the preceding color resin, and the mixed color resin is present in the interior, which causes problems in practical use. It is possible to regard it as a non-defective product, and it is possible to make a molded product composed of a previous color resin and a mixed color resin, which has been conventionally regarded as a defective product, into a good product. As a result, the number of defectives can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a resin color changing method in injection molding according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a molding process of a molded product formed of the pre-color resin and the mixed resin when the resin color changing method in the injection molding according to the embodiment of the present invention is used.

FIG. 3 is an explanatory diagram illustrating a molding process of a molded product formed of a previous color resin and a mixed resin when a conventional resin color changing method in injection molding is used.

FIG. 4 is an explanatory diagram illustrating a resin color changing method in conventional injection molding.

[Explanation of symbols]

10 molds, 12 barrels, 14 screws, 16
Hopper, 18 front color resin, 18a skin layer, 20 post color resin, 22 mixed color resin, 22a core layer.

Claims (2)

[Claims] 1. Continuous injection using a single-screw injection molding machine for measuring the amount of resin required for one shot for molding one molded product and extruding the measured resin sequentially into a molding die to manufacture the molded product. A color changing method of changing the color of a resin during molding, wherein at a predetermined timing during the measurement, the resin is changed from a pre-color resin before color change to a post-color resin after color change, and is molded only by the front color. The molded product has a skin layer immediately after the non-defective product formed of the preceding color resin, and a core layer completely covered with the skin layer is formed of a mixed color resin of the preceding and succeeding colors. How to change the color of resin. 2. The method according to claim 1, wherein the switching from the front color resin to the rear color resin is carried out when the amount of the front color resin is at least 60% with respect to the resin amount for one shot.
A resin color changing method, which is performed at the above occupying timing.