JPH04201528A - Method for setting paint injection timing to cavity in injection molding - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for setting the timing of paint injection into a cavity in injection molding.

(Prior Art) Conventionally, in injection molding, there has been provided a method of injecting paint into a cavity at a predetermined timing to apply a coating film to a molded product, a so-called decorative molding method.

(Problem B to be solved by the invention) In this decorative molding method, the timing of injecting the paint into the mold is important. For example, if the timing of injecting the paint is too early, the thickness of the molded product in the cavity may increase. A problem occurs in which the paint enters the inside of the mold, and conversely, if the timing of paint injection is too late, the paint will not flow through the gap between the cavity surface and the surface of the molded product, making injection difficult.

Conventionally, this injection timing is set by trial and error by performing several test shots at the start of molding, which takes time and reduces molding efficiency. Furthermore, even after setting the injection timing as in the conventional method, there is a problem in that it is not possible to determine whether the injection timing is optimal.

Furthermore, there is no way to check whether the coating film has been applied to the molded product until after the mold is opened, making it impossible to promptly deal with problems.

(Means for Solving the Problems) A method for setting the timing of paint injection into a cavity in injection molding of the present invention is a method for setting the timing of paint injection into a cavity in injection molding, and when applying a coating film to a molded product. The method includes transmitting ultrasonic waves into the cavity using an ultrasonic probe provided in a part of the mold, and transmitting reflected waves of the ultrasonic waves reflected from the cavity side. A sound speed value is calculated based on the received reflected waves, and when this sound speed value reaches a preset sound speed value, paint is injected into the cavity.

(Function) During injection molding, by calculating the sound velocity value of the molded product inside the cavity, the solidification state of the molded product can be grasped, and the paint can be applied when the molded product has solidified enough to withstand the injection pressure of the paint. Inject and apply a coating to the molded product.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a part of an injection molding apparatus for carrying out a method of setting timing for injecting paint into a cavity in injection molding according to the present invention.

In FIG. 1, numeral 2 denotes a mold placed opposite to the tip of an injection nozzle 1 of an injection molding machine. The mold 2 is composed of a pair of divided fixed molds 3 and a movable mold 5, and the movable mold 5 on the side of the injection nozzle 1 is provided so as to be able to reciprocate in the direction of arrow A in the figure. This reciprocating movement opens and closes the mold 2.

6 is a cavity formed facing the dividing surface between the fixed mold 3 and the movable mold 5.

Reference numeral 7 denotes a paint injection machine, and this paint injection machine 7 injects paint onto the surface of the molded product in the cavity 6 at a predetermined timing using a paint injection control unit 15, which will be described later, to form a coating film on the molded product. It is something that is given.

Further, the fixed mold 3 is equipped with an ultrasonic flaw detector 10 shown in FIG.
An ultrasonic probe 11 connected to is provided.

The ultrasonic probe 11 emits 5 MHz ultrasonic waves toward the cavity 6 using the ultrasonic flaw detector 10 at a rate of, for example, 100 per second.
Call 0 times (this number of calls can be changed arbitrarily). The emitted ultrasonic waves are reflected by the cavity 6, received by the ultrasonic probe 11 as reflected waves (echo waves), and inputted into the ultrasonic flaw detector 10. Ultrasonic flaw detector 1
At 0, the sound velocity value is calculated based on the reflected wave. In other words,
The sound velocity value of the resin filled in the cavity 6 is calculated.

Here, the sound velocity value calculated by the ultrasonic flaw detector 10 changes depending on the change in the resin temperature of the molten resin. This is because when the resin temperature rises, the density of the molten resin decreases, which causes the sound velocity value to become smaller (slower), and conversely, when the resin temperature becomes lower, the density of the molten resin increases, which causes the sound velocity value to become larger (faster). In other words, the solidification state of the resin (the elasticity of the resin changes as the solidification state changes) can be determined from the sound velocity value.

As shown in FIG. 2, the ultrasonic flaw detector 10 is connected to a comparator 12 into which the sound velocity value calculated by the ultrasonic flaw detector 10 is input. The comparator 12 compares the calculated sound speed value with a preset sound speed value. This set sound velocity value is determined based on a preliminary measurement of the sound velocity value of the molded product (resin) in the case where a good coating film is applied to the molded product in the cavity 6. That is, when injecting the paint, the sound velocity value when the molded product solidifies to the point where it can withstand the injection pressure of the paint is measured, and this value is set as the set sound velocity value. For example, point A shown in FIG. 3 becomes the set sound velocity value.

Further, the comparator 12 is connected to a signal generator 13 that outputs a signal when the comparison result of the comparator 12, that is, the sound speed value reaches a set sound speed value. Based on this signal, the signal generator 13 outputs an injection start signal to the paint injection control section 15. Then, the paint injection control section 15 receives the injection start signal from the signal generator 13 and starts the injection of paint into the cavity 6 by the paint injection machine 7.

Next, a method of setting timing for injecting paint into a cavity using the injection molding apparatus configured as described above will be described.

First, the cavity 6 is filled with molten resin injected from the injection nozzle 1 of the injection molding machine. In conjunction with this, the ultrasonic flaw detector IO emits 5 MHz ultrasonic waves from the ultrasonic probe 11 toward the cavity 6 1000 times per second.

FIG. 4 shows the reflected waves of the ultrasound received by the ultrasound probe 11 after transmitting the ultrasound from the ultrasound probe 11 as described above.

In FIG. 4, 20 is a transmitted wave, 21 is an ultrasonic probe 1
The reflected wave 22 is reflected from the surface 6a of the molded product on the side 1 (see Figure 5), and the reflected wave 22 passes through the resin in the cavity 6 and reaches the inner surface 6b of the injection nozzle of the cavity 6 (see Figure 5). The reflected wave 23 indicates that the reflected wave 21 is the ultrasonic probe 1
This is a secondary reflected wave of the reflected wave 21 that was reflected at 1 and then reflected again at the surface 6a of the molded product.

In addition, in the ultrasonic probe 11, the reflected wave 22 is reflected by the ultrasonic probe 11 after the secondary reflected wave 23, and the reflected wave 22 is reflected again by the inner surface 6b of the cavity 6. While the waves are received, third-order and fourth-order reflected waves obtained by reflecting these second-order reflected waves again are also received, but they will not be specifically mentioned here.

Then, in the ultrasonic flaw detector IO, the resin is detected based on the time t from when the reflected wave 21 is received by the ultrasonic probe 11 until the reflected wave 22 is received (this time t is the resin passing time). The sound velocity value of is calculated and outputted to the comparator 12. The comparator 12 compares this sound speed value with a preset sound speed value, and outputs a signal to the signal generator 13 when the sound speed value reaches the set sound speed value. The signal generator 13 outputs an injection start signal to the paint injection control section 15 based on this signal,
In response to this injection start signal, the paint injection control section 15 causes the paint injection machine 7 to start injecting the paint into the cavity 6.

As a result, the inner surface 6a of the cavity 6 and the molded product (resin)
The paint is injected at the optimal injection timing between the molded parts and a good coating film on the surface of the molded product.

FIG. 6 shows reflected waves of ultrasonic waves received by the ultrasonic probe 11 when a coating film is applied to the surface of a molded article as described above.

In FIG. 6, 30 is a transmitted wave, 31 is a reflected wave reflected by the coating layer surface 6C on the ultrasonic probe 11 side as shown in FIG. 7, and 32 is a surface 6a of the molded product (7th The reflected wave 33 passes through the molded product (resin) in the cavity 6 and passes through the inner surface 6 of the cavity 6 on the injection nozzle 1 side.
The reflected wave reflected by b (see Figure 7), 35 is the reflected wave 3
1 is a secondary reflected wave of the reflected wave 31 reflected by the ultrasonic probe 11 and reflected again by the coating layer surface 6C.

In addition, in the ultrasonic probe 11, after the secondary reflected wave 35, the reflected wave 32 is reflected by the ultrasonic probe 11, and the reflected wave 32 is reflected again by the surface 6a of the molded product. While the wave is received, a secondary reflected wave of the reflected wave 33 is received,
Furthermore, third-order and fourth-order reflected waves obtained by reflecting these second-order reflected waves again are received, but they will not be specifically mentioned here.

Therefore, by looking at the reflected waves received by the ultrasonic probe 11, especially the reflected waves 32 and 33, it is possible to confirm whether or not a coating film has been applied to the molded product with the mold 2 closed. can.

Therefore, when a box-shaped molded product is molded from polycarbonate resin using the method of the present invention described above, if the initial molding conditions are adjusted and then the paint is injected and molded, the molded product will be coated well from the first shot. Goods were obtained. In contrast, when a similar molded product was molded using the conventional method, it took 25 shots to produce a good product through trial and error even after adjusting the initial molding conditions.

(Effects of the Invention) As described above, according to the method of the present invention, an ultrasonic probe provided in a part of the mold emits ultrasonic waves into the cavity, and Receiving the reflected wave of the ultrasonic wave reflected by the side, calculating a sound speed value based on the received reflected wave, and injecting paint into the cavity when this sound speed value reaches a preset sound speed value. With this, it is possible to easily set the paint injection timing that allows a coating film to be applied to a molded product in a good condition, and it is possible to improve molding efficiency and yield.

Furthermore, it is possible to check whether the coating film has been applied to the molded product while the mold is closed, and troubles can be promptly dealt with.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a part of an injection molding apparatus that implements the method for setting the timing of paint injection into a cavity in injection molding according to the present invention, and FIG. 2 is a block diagram showing a control system.
Figure 3 shows the relationship between time and the sound velocity value of the resin in the cavity during injection molding, and Figure 4 shows the reflected waves received by the ultrasonic probe when the cavity was filled with resin. Figure 5 is a schematic explanatory diagram showing the ultrasonic probe and the inside of the cavity to explain Figure 4. Figure 6 is a diagram showing the state of the molded product after injecting paint into the cavity. Figure 7 is a diagram showing the state of reflected waves received by the ultrasonic probe when a coating film is applied to the ultrasonic probe, and Fig. 7 is a schematic diagram showing the ultrasonic probe and the inside of the cavity to explain Fig. 6. FIG. 2...Mold 6...Cavity 11...Ultrasonic probe patent applicant Sekisui Chemical Co., Ltd. Representative Hiroshi 1) Kaoruyoshi 1 and 2nd L! 4

Claims (1)

[Claims] 1) A method for setting the injection timing of paint when injecting paint into a cavity and applying a coating film to a molded product in injection molding, the method comprising: Using an ultrasonic probe, transmitting an ultrasonic wave into the cavity, receiving a reflected wave of the ultrasonic wave reflected from the cavity side, and calculating a sound velocity value based on the received reflected wave,
A method for setting timing for injecting paint into a cavity in injection molding, characterized in that the paint is injected into the cavity when the sound speed value reaches a preset sound speed value.