JPH0686074B2 - In-mold coating method for plastics - Google Patents

Description

TECHNICAL FIELD The present invention relates to an in-mold coating method effective as a countermeasure against pinholes and sink marks, which are problems for plastic molded products, particularly sheet molded compound compression molded products.

[Conventional technology]

Sheet molding compound (hereinafter referred to as SMC)
On the surface of the molded product obtained by compression molding, fine holes called pinholes and defects such as sink marks generated on the back surface of ribs and bosses occur. The in-mold coating method (hereinafter referred to as IMC) is one of the countermeasures against these pinholes and sink marks.

IMC is a method of painting at the same time as molding of plastic.
There are the following two methods for injecting the MC material paint into the mold.

Conventionally, the SMC material is placed on the lower mold of the temperature-controlled mold and the upper mold is closed, and as shown in FIG.
Hold T ₁ to cure the SMC material, open the mold a few millimeters and inject the paint into the mold as indicated by arrow I, then close the mold and hold T _{3 for} a specified time to cure the paint The mold is opened and the molded product is taken out.

Since this conventional IMC has to open the mold in the middle of molding, there are problems that foreign matter is mixed into the mold and the molding cycle time becomes long.

Currently, technological development is progressing toward high pressure injection process (hereinafter referred to as HPIP).

In this HPIP method, as shown in FIG. 7, the SMC material is placed in the lower mold of a mold whose temperature is controlled at 140 to 150 ° C., the upper mold is closed and pressure P ₁ is applied to cure it for a specified time T ₁ . . Then, by injecting coating material to 300 kg / cm ² about the high pressure in the left mold closed as shown by an arrow I in a state where a P ₂ was lowered a little pressure, coating after T _IM time indicated by the arrow E Is stopped, then the pressure is raised to P ₃ and held for T ₃ hours to cure the paint.

[Problems to be Solved by the Invention]

In the HPIP method, the paint is injected into the high-pressure mold without opening the mold.Therefore, in the case of parts with a large surface area, air can be trapped inside the mold, and the unpainted part of the paint called IMC short or IMC material. The flow trace of occurs. Fig. 9 (A) shows a molded article 1 of an automobile bonnet. An IMC short 10 is generated at a portion far from the tab 2 of the paint injection port, and an IMC flow trace 11 called a flow mark is generated. There is.

As a measure against this, as shown by T ₂ in FIG. 8, the molding pressure is increased for a few seconds after the paint is injected to cause the paint to flow into the mold,
A means to prevent the occurrence of a short circuit is adopted, but as shown in Fig. 9 (B), the IMC short circuit 10 can be made smaller, but the IMC short circuit cannot be completely eliminated and is stable. A molded product of the specified quality cannot be obtained. Further, since it is necessary to use a press capable of multistage pressure control, equipment investment becomes high.

Further, in the HPIP method, since the IMC material is injected at a high pressure into the mold in a state where the molding pressure is applied without opening the mold, if the injection timing of IMC is incorrect, as shown in FIG. 10 (A), Not only IMC shorts 10 occur on the surface of the bonnet 1, but I
The MC material passes through the uncured SMC layer and goes to the back surface. As shown in FIG. 10 (B), IMC is formed on a part of the back surface of the bonnet 1.
Due to the formation of the material layer 12 and the heat and expansion of the SMC,
Almost no MC is injected into the mold, and as shown in FIG. 11, the coating film 13 is formed only on the tab 2 of the injection port and its vicinity.

The timing of IMC injection in the HPIP method is determined by repeating the molding test and setting the conditions, but even with the same brand of SMC material, there are variations in the curing characteristics between production lots, and the molding conditions The setting becomes complicated.

An object of the present invention is to provide an in-mold coating method that solves the above-mentioned problems, optimizes the timing of IMC injection in the HPIP method, completely eliminates IMC short-circuiting, and excellently molds the surface quality of a molded product. It is a thing.

[Means and Actions for Solving the Problems] The present invention is to perform compression molding of a plastic using a mold provided with a pressure sensor in the shape part of a molded article, and the pressure sensor generates heat in the compression molding step of the plastic. When the predetermined pressure drop is detected after the peak pressure due to expansion, the molding pressure is released, the paint is injected at high pressure into the vacuum degassed mold while it is closed, and then the molding pressure is increased to remove the injected paint. This is a plastic in-mold coating method in which a paint is allowed to flow and then the paint is cured.

When the mold is closed and the plastic is compression-molded, the plastic exothermically expands and the pressure in the mold rises, and when the peak of the exothermic expansion of the plastic passes and the curing shrinkage stage is reached, the pressure drops. The pressure sensor detects changes in the pressure inside the mold, and the mold pressure is released based on this detected value.
Since the paint is injected at high pressure into the mold that is still closed after the mold is degassed in vacuum, the paint flows smoothly on the surface of the molded product, and then the molding pressure is raised. Since the fluid flows sufficiently in the mold to cover the surface of the plastic molded product and the coating material is cured in this state, no coating defects due to air pockets or the like occur.

〔Example〕

 Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a case where the present invention is applied to the molding of an automobile bonnet, FIG. 1 is a sectional view showing a molding die, and XX of a molded product 1 shown in a plan view in FIG. The sectional view by a line is shown.

The molded product 1 is provided with a tab 2 serving as a paint injection port.
As shown in FIG. 1, the mold for molding the molded product 1 with the tab 2 has a cavity having a shape corresponding to the molded body formed between the lower mold 3 and the upper mold 4 of the split mold. 4, a paint inlet 5 is provided at a portion corresponding to the tab 2, and a nipple 6 connected to a vacuum pump is provided on the opposite side thereof, and a temperature adjusting circuit 7 is provided at the lower mold 3 and the upper mold 4. A sealing material 8 is disposed on the joint surface between the lower mold 3 and the upper mold 4, and a pressure sensor 9 is provided on the lower mold 3 at a position close to the injection port tab 2.

Next, a molding method using the mold shown in FIG. 1 will be described with reference to FIGS. 3 to 5.

As shown in Fig. 4, the SMC material in which the sheet S ₂ of 200 × 1100 mm for adjusting the charge amount is placed between the two sheets S ₁ of 600 × 1100 mm and superposed, the temperature is adjusted to 140 to 150 ° C. Placed on the lower mold 3 of the mold and closed the upper mold 4, 70-80kg / cm ²
The molding pressure of _{1 is} maintained for a specified time T ₁ as shown in FIG.
This T ₁ time is the time when the SMC material in the mold passes the peak of exothermic expansion and enters the curing shrinkage stage, as described later.

Next, the pressure of the press is released, and the inside of the mold held in the closed state without applying the molding pressure is vacuum deaerated as shown by an arrow V. Next, as shown by the arrow I, IMC paint is injected from the injection port 5 at the position of the tab 2 at a high pressure of about 300 kg / cm ² , and the molding pressure is increased to 70-80 kg / cm ² again after the paint is injected. , T Hold in this state for ₃ hours to cure the paint.

The setting of the above T ₁ time is determined as follows. Fifth
The figure shows the resin pressure monitor measurement diagram. The SMC enclosed in the mold.
The material exothermically expands and the pressure rises as indicated by the arrow, reaches the peak pressure after t ₁ hours, then enters the contraction stage as indicated by the arrow, and the forming pressure drops. This change in pressure is measured by the pressure sensor 9 installed in the lower mold 3. The threshold pressure is set in advance on this pressure curve.

During the molding of SMC, the value detected by the pressure sensor 9 exceeds the threshold pressure, and when the peak pressure is reached, a signal is sent to the vacuum degassing device at time t ₁ to degas the mold as shown by V in FIG. To start. Next, at time t ₂ when the pressure sensor 9 detects the threshold pressure, a signal is sent to the press side to release the molding pressure and the mold is kept closed. Inject the IMC material into the mold at high pressure as shown in.

In this way, the molding pressure is released, the mold is evacuated with the mold closed, and when the paint is injected, the SMC material in the mold is in the shrinking stage, so no air can be trapped and the paint is It flows well on the surface of SMC and does not cause IMC short circuit.
Further, the paint injected into the mold further flows on the surface of the cured SMC due to the subsequent increase in molding pressure, and a good coating can be stably obtained.

Next, a comparative example with the example of the present invention is shown, the filling properties of IMC,
The table below shows a comparison of the occurrence of air pockets and flow marks.

(Comparative Example 1) Lower mold 3 of a mold whose SMC material was temperature-controlled at 140 to 150 ° C.
Then, the upper mold 4 is closed and the molding pressure of 70 to 80 kg / cm ² is maintained for a specified time (50 seconds) to cure. Next, the molding pressure is 20
reduced to kg / cm ² of maintaining this state, injecting IMC material at a high pressure of 300 kg / cm ^2, injection after completion 70~80kg / cm ² in forming pressure was raised to the specified time (90 seconds) and held To cure.

As the SMC material, a sheet S 2 of 600 × 1100 mm used in the example and a sheet S ₂ of 200 × 1100 mm for adjusting the charge amount were put between the sheets S ₁ and stacked.

(Comparative Example 2) The same as Comparative Example 1 except that an SMC material obtained by stacking three sheets of 600 x 1100 mm was used.

(Comparative Example 3) The same as Comparative Example 1 except that vacuum degassing was performed at the time of IMC injection.

(Comparative Example 4) After IMC injection, the molding pressure was 50 kg / cm ² , 40 kg / cm ² and 20 kg / cm.
Same as Comparative Example 1 except that IMC was cured by changing to ² .

(Comparative Example 5) The same as Comparative Example 4 except that vacuum degassing was performed at the time of IMC injection.

(Comparative Example 6) Comparative Example 1 except that the curing time (T ₁ ) of the SMC material was set to 40 seconds.
Same as

(Comparative Example 7) Comparative Example 1 except that the curing time (T ₁ ) of the SMC material was set to 30 seconds.
Same as

The materials used for the test are as follows.

SMC material: Asahi Fiber Glass Co., Ltd. Glass Rono 1
800 Class A SMC material IMC material: Paurain glass clad B30-EX ₂ manufactured by Dainippon Paint Co., Ltd. (Effect of the invention) The present invention has a feature of the HPIP method of injecting IMC material at high pressure without opening the mold at the time of injecting the IMC material, when in-mold coating is performed using a die together with molding of plastic. While making the best use of it, the timing of IMC material injection is optimized, the defect of HPIP method is corrected by a simple method to completely eliminate the IMC short circuit, and there is an effect that a good painted surface can be stably obtained on the surface of the molded product.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a mold when the present invention is applied to the molding of an automobile bonnet, showing a cross section taken along line XX of FIG. 2, FIG. 2 is a plan view of a molded product, and FIG. FIG. 4 is a perspective view of a molding material of the present invention, FIG. 4 is a perspective view of a molding material, FIG. 5 is a measurement diagram for determining the time of paint injection according to the present invention, and FIGS. 6 to 8 are all conventional molding processes. FIGS. 9 to 11 are views showing the steps, all of which show defects in the coating of the molded product, and FIG. 10 (B) shows the back surface and the other surfaces are the front surface. 1: Molded product, 2: Paint inlet tab 3: Lower mold, 4: Upper mold 5: Paint filler, 6: Nipple 7: Temperature control circuit, 8: Seal material 9: Pressure sensor

Claims (1)

[Claims] 1. A plastic mold is compression-molded by using a mold provided with a pressure sensor in the shape part of a molded product, and the pressure sensor passes a peak pressure due to exothermic expansion in the compression molding process of the plastic, and a predetermined pressure drop occurs. When the pressure is detected, the molding pressure is released, the paint is injected at high pressure into the vacuum degassed mold, then the molding pressure is increased to cause the injected paint to flow into the mold, and then the paint is cured. A plastic in-mold coating method characterized by the following.