JP3867611B2 - Resin color changing method in injection molding - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a resin color change method in injection molding, and more particularly to an improvement in resin color change method that can reduce the occurrence of defective molding due to color mixing during color change.
[0002]
[Prior art]
Conventionally, resin molded products have been used for many parts of industrial products. Resin molded products can be manufactured continuously as long as a mold is formed in a desired shape, the mold is set in an injection molding machine, and the prescribed injection conditions are maintained. Can do. In the case of resin molding, it is possible to change the color of a molded product by changing the resin used, and it is possible to easily cope with products of different colors.
[0003]
By the way, if you want to manufacture molded products of different colors, you can freely manufacture the desired molded products by preparing injection molding machines and dies for each color. Production costs are not cheap and it is not realistic to prepare for each color of the same product. For this reason, usually, the same injection molding machine or mold is used, and the color of the resin to be injected is changed to cope with different color products.
[0004]
FIG. 3 shows a conventional injection molding procedure. 3 and FIG. 4 described later show only the mold 10 and the barrel 12 of the injection molding machine that injects and injects 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 injection molding machine.
[0005]
As shown in FIG. 3, in the case of single-screw injection, a rotatable screw 14 having a wing fixed helically around the shaft is disposed inside the barrel, and the screw 14 moves backward while rotating ( By moving in the right direction in the figure), the resin for one shot necessary for molding one molded product is weighed and sequentially moved to the tip side (left side in the figure) of the barrel 12. When a predetermined amount of metering is completed, the metered resin is moved by moving the inside of the barrel 12 forward by one shot (retracted) toward the tip (left side) without rotating the screw 14 (moves toward the tip of the barrel 12). Resin) is extruded into the mold 10 and injected.
[0006]
In the case of the injection molding machine of FIG. 3, the resin color is, for example, by adding a predetermined amount of a pellet-shaped masterbatch (pigment) from the hopper 16 to the white base resin that is constantly supplied into the barrel 12, The mixture is mixed in the barrel 12 and toned to obtain a desired resin color.
[0007]
Normally, resin weighing is performed for each molded product, that is, for each shot of molding. Therefore, after the weighing for the previous color resin 18 before color change is completed, the master batch is changed, and the after color after color change. Weighing the resin 20 is performed. When the color of the resin is changed, the front color resin 18 remains on the inner wall of the barrel 12 and the like, and the resin immediately after the master batch change is mixed with the front color resin 18 and the rear color resin 20. The mixed color resin 22 is obtained. That is, in FIG. 4, when the black master batch is used up to the n-th measurement and the red master batch is used for color change from the measurement (n + 1), for example, the measurement (n + 1) -th, measurement (n + 2) In the first time, the measurement (n + 3) time, etc., the color of the resin is the mixed color resin 22 in which black and red are mixed. When weighing is performed a plurality of times, the proportion of the red after-color resin 20 increases and the black front-color resin 18 remaining in the barrel 12 disappears, the resin in the barrel 12 is, for example, metered ( From the (n + 4) th time, the color changes to the regular red aftercolor resin 20.
[0008]
Returning to FIG. 3, FIGS. 3A to 3E show the injection operation after color change. As described above, by changing the master batch to be input for color change, the mixed color resin 22 exists after the front color resin 18 as shown in FIG. When the resin is injected in this state, as shown in FIG. 3B, first, the remaining portion of the front color resin 18 (the product to be molded one before is completely molded with only the front color resin 18). A predetermined amount of the front color resin 18 remains at the time of the next injection) and 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 subsequent mixed color resin 22 is sequentially injected into the skin layer 18a to form the core layer 22a.
[0009]
When the mixed color resin 22 is further injected, as shown in FIGS. 3C and 3D, the increased mixed color resin 22 penetrates the skin layer 18a and leaks to the outside of the skin layer 18a. As shown in (e), the color mixing resin 22 becomes a defective product appearing on the surface of the molded product. Thereafter, defective products are molded until the mixed color resin 22 in the barrel 12 is used up. That is, in the example of FIG. 4, four defective products are produced until a good product is manufactured after the color change.
[0010]
[Problems to be solved by the invention]
In the case of a single-shaft injection molding machine, resin color mixing is unavoidable when changing colors. That is, the occurrence of defective products due to the color mixture resin is inevitable. However, there is a desire to reduce the number of defective products as much as possible.
[0011]
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 that can reduce the occurrence of defects due to color mixing during color changing.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention measures the amount of resin required for one shot of molding one molded article, and sequentially extrudes the measured resin into a molding die to produce a molded article. A color changing method for changing the color of a resin during continuous injection molding using a shaft type injection molding machine, from a previous color resin before color change to a subsequent color resin after color change at a predetermined timing during the measurement. The skin layer of the molded product immediately after the non-defective product which is molded only with the previous color is formed with the front color resin, and the core layer completely covered with the skin layer is a color mixture of the front color and the rear color It is formed by resin.
[0013]
According to this configuration, it is possible to secure a sufficient amount of the previous color resin for forming the skin layer by changing the color during measurement. As a result, the mixed color resin that is injected into the core layer later does not break through the skin layer and come out on the surface, the surface is covered with the previous color resin, and the mixed color resin is present in the interior, and there is a practical problem. It is possible to make a non-defective product, and it is possible to make a molded product composed of a front color resin and a mixed color resin, which has been regarded as a defective product, a non-defective product. As a result, the number of defects can be reduced.
[0014]
In order to achieve the above object, according to the present invention, in the above configuration, the amount of the front color resin is at least 60 with respect to the amount of resin for one shot. It is characterized in that it is performed at a timing that occupies at least%.
[0015]
According to this configuration, since the skin layer is composed of 60% or more of the front color resin, it is possible to reliably cover the core layer that is the color mixture resin, and the molding composed of the front color resin and the color mixture resin. The product can be reliably made good.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[0017]
FIG. 1 is an explanatory diagram illustrating a resin color changing method according to the present embodiment in association with resin weighing and injection into a mold. The structure of the mold 10 used in this embodiment and the barrel 12 of the injection molding machine for injecting and injecting resin into the mold 10 are the same as the conventional ones shown in FIGS. 1, the illustration of the injection molding machine itself is omitted for the sake of simplification, and only the barrel 12 is shown. Also in this embodiment, description will be made using a single screw injection molding machine.
[0018]
As shown in FIG. 3, in the case of single-screw injection, a rotatable screw 14 having a wing fixed spirally around the shaft is disposed inside the barrel, and the screw 14 rotates backward while rotating. By moving (moving in the right direction in the figure), one shot of resin necessary for molding one molded product is weighed and sequentially moved to the tip side (left side in the figure) of the barrel 12. When a predetermined amount of metering is completed, the metered resin is moved by moving the inside of the barrel 12 forward by one shot (retracted) toward the tip (left side) without rotating the screw 14 (moves toward the tip of the barrel 12). Resin) is extruded into the mold 10 and injected.
[0019]
Specific measurement of resin will be described. Since the resin is measured while the previously injected resin is present in the mold 10, the resin in the barrel 12 is prevented from entering at the entrance to the mold 10. Therefore, when the screw 14 is rotated, the resin is sequentially pushed forward by the blades of the screw 14, but as described above, the previous molded product (resin) still exists in the mold 10. Thus, the resin is prevented from entering the mold 10 and the screw 14 is pushed backward (right side in the figure) according to the amount of resin extruded. Therefore, the resin for one shot is prepared at the tip of the screw 14 by rotating the screw 14 a predetermined number of times (one shot for molding one molded product). Thereafter, the mold 10 is opened, the molded product made of the previously injected resin is discharged, the mold 10 is closed, and at the same time, the entire screw 14 is moved forward to the tip end side (left side in the figure) of the mold 10. It is possible to inject resin for one shot.
[0020]
The resin color is the same as the conventional one. For example, a predetermined amount of a pellet-like masterbatch (pigment) is added from a hopper 16 to a white base resin that is constantly supplied into the barrel 12, and the resin is screwed. The mixture is mixed in the barrel 12 and toned to obtain a desired resin color.
[0021]
A characteristic matter of this embodiment is that, during the measurement of one shot of resin, color change is performed from the previous color resin before color change to the rear color resin after color change.
[0022]
That is, as shown in FIG. 1, after changing the master batch, after the measurement nth time, the measurement (n + 1) th time is started, and when the measurement of the front color resin 18 is completed by a predetermined amount, the master batch is switched to the rear color resin 20. . The switching to the rear color resin 20 is performed by mixing the front color resin 18 and the front color resin 18 and the rear color resin 20 formed immediately after the non-defective product (the injection n-th shot) formed only by the front color resin 18. The skin layer of the molded product formed of the mixed resin 22 is sufficiently formed only by the front color resin 18, and the mixed color resin 22 that becomes the core layer injected into the skin layer does not break through the skin layer and come out. Is the timing at which the front color resin 18 can be secured.
[0023]
Preferably, the measurement corresponding to the injection (n + 1) th time is started, and it is desirable to delay the color change timing until the timing when the amount of the front color resin 18 occupies at least 60% or more with respect to the resin amount for one shot.
[0024]
In this way, during the weighing of one shot of the resin, the front color resin 18 and the front color resin 18 and the rear color when the color change is performed from the front color resin 18 before the color change to the rear color resin 20 after the color change. FIG. 2 shows a molding process of a molded product formed of the mixed resin 22 mixed with the color resin 20.
[0025]
FIG. 2A shows a state immediately after the next shot is performed after one shot injection is performed from the state shown in FIG. At this time, the resin for one shot to be injected is composed of, for example, 60% of the front color resin 18 and 40% of the color mixture resin 22 obtained by mixing the front color resin 18 and the rear color resin 20.
[0026]
FIG. 2B shows a state in which the screw 14 has advanced to the mold 10 side and the injection operation has started. FIG. 2C shows a state where the injection operation has further progressed and the entire amount of the front color resin 18 forming the skin layer 18 a has been pushed out to the mold 10. As described above, the skin layer 18a made of the front color resin 18 is formed to such an extent that the mixed color resin 22 to be injected into the interior does not break through the skin layer 18a already formed.
[0027]
Further, as the injection of the resin proceeds, as shown in FIG. 2D, the front color resin 18 and the rear color resin 20 are mixed in the skin layer 18a formed of a sufficient amount of the front color resin 18. The configured color mixing resin 22 enters to form the core layer 22a. In FIG. 2 (e), the mixed color resin 22 is further injected, and one shot of the resin is completely injected into the mold 10, and the core layer 22a is completely formed in the skin layer 18a. The state where the injection for is completed is shown.
[0028]
As described above, the skin layer 18a is formed with a sufficient amount of the front color resin 18 so as not to leak the color mixing resin 22 to the outside, and the sandwich structure in which the core layer 22a is completely sandwiched is formed. The resin 22 does not appear on the surface of the molded product, and a molded product that is functionally good is manufactured.
[0029]
As shown in FIG. 1, the molded product having the color mixture resin 22 in the core layer 22 a as described above is a good product of the injection (n + 1) shot after the good product of the injection n shot formed by only the front color resin 18. As molded. Thereafter, the molded product of the injection (n + 2) shot and the injection (n + 3) shot is molded as a defective product of only the complete color mixing resin 22, and the molded product of the injection (n + 4) shot is mixed resin in the skin layer. 22 is molded as a defective product having the rear color resin 20 in the core layer.
[0030]
As apparent from comparing FIG. 1 using the color changing method according to the present embodiment with FIG. 4 using the conventional color changing method, it is possible to make a molded product that has been a defective product as a non-defective product. Thus, the production efficiency can be improved. Note that the amount of the color mixing resin generated when the color change is performed varies depending on conditions such as the amount of the front color resin 18 remaining in the barrel 12 after the color change and the viscosity of the resin used, and the number of defective products generated is However, in the case of color change molding under the same conditions, the number of defective products can be surely reduced as described above.
[0031]
It should be noted that the color change timing can be easily adjusted by adjusting the timing at which the master batch is charged, that is, the timing at which the valve connecting the hopper 16 and the barrel 12 is switched. In this case, it is desirable to prepare a hopper 16 for each color and to control the connection state to the barrel 12 as appropriate by a switching valve.
[0032]
【The invention's effect】
According to the present invention, it is possible to secure a sufficient amount of the previous color resin for forming the skin layer by changing the color during measurement. As a result, the mixed color resin injected into the core layer later does not break through the skin layer and come out on the surface, the surface is covered with the previous color resin, and the mixed color resin exists in the inside, and there is a practical problem. It can be regarded as a non-defective product, and a molded product composed of a front color resin and a mixed color resin, which has been conventionally regarded as a defective product, can be made a non-defective product. As a result, the number of defects can be reduced.
[Brief description of the drawings]
FIG. 1 is an explanatory view illustrating a resin color changing method in injection molding according to an embodiment of the present invention.
FIG. 2 is an explanatory view illustrating a molding process of a molded product formed of a front color resin and a mixed resin when using a resin color changing method in injection molding according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram for explaining a molding process of a molded product formed of a front color resin and a mixed resin when a resin color changing method in conventional injection molding is used.
FIG. 4 is an explanatory view for explaining a resin color changing method in conventional injection molding.
[Explanation of symbols]
10 mold, 12 barrel, 14 screw, 16 hopper, 18 front color resin, 18a skin layer, 20 rear color resin, 22 mixed color resin, 22a core layer.

Claims (2)

The amount of resin required for one shot of molding a molded product is measured, and the resin is measured during continuous injection molding using a single-shaft injection molding machine that manufactures the molded product by sequentially extruding the measured resin into a mold. A color changing method for changing colors,
At a predetermined timing during the measurement, the front color resin before color change is switched to the rear color resin after color change, and the skin layer of the molded product immediately after the non-defective product molded only with the front color is the front color resin. A resin color changing method, characterized in that the core layer that is formed by the step and is completely covered with the skin layer is formed of the mixed resin of the front color and the rear color. The method of claim 1, wherein
Switching from the front color resin to the rear color resin is performed at a timing when the amount of the front color resin occupies at least 60% or more of the resin amount for one shot.

Images