JP3095837B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved injection molding method for molding a colored molded product by injecting a molten molding material by mixing and kneading a colorant into resin pellets. .

[0002]

2. Description of the Related Art Conventionally, as shown in the prior art in Japanese Patent Application Laid-Open No. 61-32727, for example, resin pellets are supplied from a hopper into a heating cylinder and kneaded by rotating a screw. In an injection molding device configured to melt and inject a predetermined amount of molten resin into a mold when a predetermined amount of the molten resin is measured, a colorant is mixed into the resin pellet to form a colored molded product. Known to do so. Then, in order to produce a molded product without color spots by the injection molding apparatus, an appropriate amount of colorant is mixed into the entire area of the resin pellets supplied into the heating cylinder, thereby uniformly dispersing the colorant in the molten resin. Control is performed so as to be dispersed.

[0003]

In order to mix an appropriate amount of colorant into the entire area of the resin pellets supplied into the heating cylinder as described above, the time required to supply the resin pellets into the heating cylinder is reduced. And, it is necessary to control so that the mixing time of the colorant is exactly the same, but the supply time of the resin pellets varies according to the time required to melt the resin pellets in the heating cylinder, Accordingly, there is a problem that it is difficult to make the mixing time of the coloring agent equal.

That is, the melting time of the resin pellets varies depending on various factors such as the ambient temperature, the temperature of the heating cylinder, and the viscosity of the molding material. In this method, the mixing time of the colorant is set based on the average value of the pellet supply time, and a deviation from the actual pellet supply time cannot be avoided. For this reason, when the mixing time of the coloring agent is shorter than the actual pellet supply time, there is a portion where the coloring material is not mixed in the resin pellet supply region, thereby causing color unevenness due to the density of the coloring agent. Occur. Conversely, if the mixing time of the coloring agent is longer than the above-mentioned pellet supply time, mixing of the coloring agent is stopped halfway, so that there is a problem that the mixing amount of the coloring agent is insufficient.

The state of change in the pellet supply time is empirically determined according to the seasonal change and the time change from the start of the work, and is graphed. Based on this graph, the control according to the season and the work time is performed. It is also conceivable to reduce the difference between the actual pellet supply time and the mixing time of the colorant by performing the above, but also in this case, the weather change in each season and the daily work time The appropriate control according to the change of the pellet supply time caused by the color change operation of the colorant cannot be performed, and thus the mixing time of the colorant cannot accurately correspond to the pellet supply time. There is.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. Injection molding capable of producing a molded product without color spots by accurately adjusting the mixing time of the colorant to the pellet supply time. It is intended to provide a way.

[0007]

According to the present invention, a resin pellet is supplied to a heating cylinder, a coloring agent is mixed into the resin pellet, and the resin is kneaded and melted by a screw. In the injection molding method of molding a colored molded article by injecting the resin, the supply time of the resin pellet is detected by a detection unit, and the current pellet supply time detected by the detection unit and the previous pellet supply time are stored. After calculating the change rate of the pellet supply time based on the value, the calculation result, and predicting the next pellet supply time according to the current pellet supply time and the colorant based on the predicted value Is set, and the mixing means of the colorant is controlled according to the mixing time.

[0008]

According to the present invention having the above-described structure, the colorant mixing means is controlled in accordance with the changing state of the pellet supply time which changes every moment from the start of operation, and the mixing time and mixing speed of the colorant are appropriately set. Thus, an appropriate amount of the coloring agent can be evenly mixed into the resin pellets supplied into the heating cylinder.

[0009]

FIG. 1 shows an example of an injection molding apparatus used to carry out an injection molding method according to the present invention. The injection molding apparatus includes a heating cylinder 2 having a screw 1 provided therein, a charge hopper 3 for supplying resin pellets into the heating cylinder 2, and a resin supplied from the charge hopper 3 into the heating cylinder 2. A colorant mixing means 4 for mixing a colorant into the pellets;

In the injection molding apparatus, the resin pellets contained in the charge hopper 3 are sequentially introduced into the heating cylinder 2 in accordance with the rotation of the screw 1, and the resin pellets are kneaded and melted and transferred to the front. When the screw 1 is gradually retracted by the pressure of the molten resin transferred to the front of the heating cylinder 2 and reaches a predetermined position, the screw 1 is advanced by a hydraulic cylinder (not shown) so that a predetermined amount of molten resin Is injected into the mold K.
That is, the injection molding apparatus measures the amount of the molten resin according to the retreat distance of the screw 1, and when it is confirmed that the amount of the molten resin has reached the preset injection amount, the screw 1 is advanced. The resin material is injected into the mold K to form an injection molded product having a predetermined shape.

The colorant mixing means 4 includes a weighing hopper 5 for storing a colorant supplied from a tank (not shown),
While weighing the colorant stored in the weighing hopper 5,
It has a metering section 7 leading to the discharge section 6 and a supply line 8 for carrying the colorant led out of the metering section 7 to the pellet supply section of the charge hopper 3 by air. The metering unit 7 includes a screw feed shaft 9 and a drive motor 10 that drives the screw feed shaft 9 to rotate. Control output from a control unit 11 that sets the operation time and rotation speed of the screw feed shaft 9 is provided. By controlling the operation state of the drive motor 10 according to the signal, the speed and amount of the colorant to be drawn out from the weighing hopper 3 to the supply line 8 are controlled.

As shown in FIG. 2, the control section 11 supplies the predicted pellet supply time at the start of operation from a table in which various values are set according to the season and the like. Reading means 12 for reading a predicted time value; detecting means 13 for detecting the operation time of the screw 1, that is, the supplying time of the resin pellets; and storing means 14 for storing the pellet supplying time detected by the detecting means 13. And the detection means 13 and the storage means 14
And a mixing amount setting means 16 for setting the mixing amount of the colorant according to the molded product.

The reading means 12 and the detecting means 13
And the output signal of the change rate calculating means 15
1, the operation time setting means 17 predicts the next pellet supply time and sets the corresponding operation time of the screw feed shaft 9. When the output signals of the mixing amount setting means 16 and the operation time setting means 17 are input to the rotation speed calculation means 18 provided in the control unit 11, the rotation speed calculation means 18 And the rotation speed of the screw feed shaft 9 which is adapted to the amount of the coloring agent to be mixed into the unit per unit time is set.

The control operation executed by the control unit 11 will be described with reference to the flowchart shown in FIG.
When the control operation starts, first, it is determined whether or not the present time is the start of operation according to the operation state of the injection molding apparatus (step S1). As a result of this determination, when it is confirmed that the present time is at the start of operation, the operating time setting means 17 performs the operation based on the predicted value of the pellet supply time at the start of operation corresponding to the current season read by the reading means 12. The operation time of the screw feed shaft 9 corresponding to the predicted value is set (step S2).

Further, based on the operation time of the screw feed shaft 9 set by the operation time setting means 17 and the mixing amount of the colorant set by the mixing amount setting means 16, The rotation speed of the screw feed shaft 9 is set (step S3). Then, a control signal for controlling the operation time and the rotation speed of the screw feed shaft 9 is output from the operation time setting means 17 and the rotation speed calculation means 18 to the drive motor 10 of the colorant mixing means 4 (step S4). As a result, the state of mixing of the colorant at the start of operation is controlled based on the predicted value of the pellet supply time.

If the result of the determination in step S1 is NO, and it is confirmed that the injection molding apparatus is already in operation, the current pellet supply time detected by the detection means 13 and the storage means 14 The change rate calculating means 15 calculates the change rate of the pellet supply time based on the previous pellet supply time read from (step S5). Next, based on the change rate of the pellet supply time and the detected value of the current pellet supply time, the operating time setting means 17 predicts the next pellet supply time, and the colorant mixing means corresponding to the predicted time. 4 (Step S)
6). For example, when it is confirmed that the pellet supply time is increasing in step S5, the next pellet supply time is predicted by adding this increase to the detected value of the current pellet supply time, The operation time of the screw feed shaft 9 is set according to the estimated time.

Next, the operation time of the screw feed shaft 9 will be described.
Based on the amount of the coloring agent mixed, the rotation speed calculating means 18
After calculating the rotation speed of the screw feed shaft 9 at step S7, the process proceeds to step S4. As a result, the state of mixing of the colorant after the start of the injection molding apparatus is controlled based on the predicted value of the pellet supply time.

As described above, the change rate of the supply time of the resin pellets, which changes every moment from the start of operation, is calculated by the calculating means 15, and the next pellet supply time is predicted in accordance with the calculation result. Thus, the colorant mixing means 4 is controlled to control the mixing of the colorant suitable for the actual operating state of the injection molding apparatus.

That is, as shown in FIG. 4, when the predicted value A1 of the pellet supply time at the start of operation and the detected value B1 of the actual pellet supply time are different, the detected value B1 is determined based on the detected value B1. By setting the predicted value A2 of the second pellet supply time, control is performed to eliminate the difference. From the third time onward, the previous detection value B
Since the next predicted value An + 1 is set based on the difference between n-1 and the current detection value Bn, appropriate prediction control according to the change state of the pellet supply time is executed, and the predicted value It is possible to effectively prevent a situation in which the actual pellet supply time deviates significantly.

Therefore, the supply time of the resin pellets and the mixing time of the colorant can be made to coincide with considerable accuracy, and the charge hopper can be mixed based on the mixing time of the colorant and the required mixing amount. Since the amount of the colorant to be discharged to the pellet supply unit 3 per unit time can be accurately calculated, the drive motor 10 is appropriately controlled accordingly, and the charge hopper 3 An appropriate amount of colorant can be uniformly supplied between the start of supply of resin pellets and the end of supply of resin pellets, and this can be uniformly dispersed in the molten resin.

In the above embodiment, the case where a single colorant is mixed in the resin pellets has been described. However, a plurality of colorant tanks containing colorants of various colors are provided. The present invention can also be applied to an injection molding apparatus configured to perform color change by switching a connection path with the weighing hopper 5 or the like. In the case of performing the color change, it may be determined that the work has ended when the injection molding apparatus is stopped, and the control may be started from step S1 after the color change. It may be configured that it is determined that the molding apparatus is in the halt state, and the control is restarted from step S5 after the color change.

Note that the previous detection value output from the storage means 14 is not necessarily limited to the immediately preceding detection value, and may be a predetermined number of previous detection values, or a value obtained by averaging several detection values. May be used.

[0023]

As described above, according to the present invention, the change rate of the supply time of the resin pellet is calculated by the calculating means,
In order to predict the next pellet supply time according to the calculation result and to control the colorant mixing means according to the predicted value, the colorant mixed into the resin pellets by the mixing means The mixing time and mixing speed can be appropriately adapted to the pellet supply time that changes every moment from the start of operation.

Accordingly, it is possible to prevent the mixing time of the colorant from being shorter than the actual pellet supply time, thereby preventing a portion in which the colorant is not mixed into the resin pellet supply area from being generated. Occurrence can be prevented.
In addition, the mixing time of the colorant is longer than the pellet supply time, thereby preventing the occurrence of a situation in which the mixing of the coloring agent is stopped halfway, and effectively preventing the occurrence of insufficient mixing of the coloring agent due to this. There is an advantage that it can be prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of an injection molding apparatus used for carrying out an injection molding method according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a control unit of the injection molding apparatus.

FIG. 3 is a flowchart showing a control operation of the control unit.

FIG. 4 is a graph showing a change state of a pellet supply time and a change state of an expected value of a pellet supply time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Screw 2 Heating cylinder 13 Detecting means 14 Storage means 15 Change rate calculating means 16 Mixing amount setting means 17 Operating time setting means 18 Rotation speed calculating means K Mold

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-251420 (JP, A) JP-A-3-264319 (JP, A) JP-A-3-199021 (JP, A) JP-A-53- 147757 (JP, A) JP-A-52-8068 (JP, A) JP-A-3-256705 (JP, A) JP-A-61-32727 (JP, A) JP-A-62-85406 (JP, U) Hira 4-26714 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (1)

(57) [Claims] 1. A colored molded article is supplied by supplying resin pellets to a heating cylinder, mixing a coloring agent into the resin pellets, kneading them with a screw and melting them, and injecting them into a mold. In the injection molding method of molding, the supply time of the resin pellets is detected by a detection unit, and the pellet supply time based on the current pellet supply time detected by the detection unit and the stored value of the previous pellet supply time. After calculating the rate of change, the calculation result and the next pellet supply time are predicted according to the present pellet supply time, and the mixing time of the coloring agent is set based on the predicted value. An injection molding method, characterized in that the mixing means of the colorant is controlled according to the mixing time.