JP3094508B2 - Plastic inmold coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for in-mold coating of plastics, and more particularly to a method for in-mold coating bulk molded compound moldings.

[0002]

2. Description of the Related Art In recent years, a sheet molding compound (hereinafter referred to as SMC), which is a typical molded product of FRP (glass fiber reinforced resin) which has come into practical use as an outer panel of an automobile, is compressed. In the molded product obtained by molding,
Sink marks and pinholes occur. One of the measures against pinholes generated on the surface of the SMC molded product is an in-mold coating method (hereinafter referred to as IMC). This IMC is
The present applicant has previously applied for patents on the invention of the plastic in-mold coating method (Japanese Patent Application Nos. 1-81047, 2-258319 and 1). 181778,
JP-A-3-47719)).

[0003] IMC is a method of coating simultaneously with molding of plastics. There are two methods for injecting a paint as an IMC material into a mold. Conventionally, the SMC material is placed on the lower mold of a temperature-controlled mold, the upper mold is closed, the molding pressure is increased, and the SMC material is cured by holding for a specified time, the mold is opened several millimeters, and the paint is placed in the mold. Then, the mold is closed and held for a specified time, and after the coating material is cured, the mold is opened and the molded product is taken out. This conventional IMC
However, since the mold must be opened in the middle of molding, there is a problem that foreign matter is mixed in the mold and a molding cycle time is increased.

At present, technical development is progressing toward a high pressure injection process (hereinafter referred to as HPIP). In this HPIP, an SMC material is placed in a lower mold of a mold whose temperature is controlled at 140 to 150 ° C., the upper mold is closed, pressure is applied, and curing is performed for a predetermined time. Next, the paint is injected into the closed mold at a high pressure of about 300 kg / cm2 while the pressure is slightly lowered, and after the injection of the paint is stopped, the pressure is increased and the paint is cured by holding for a predetermined time. Things.

A material similar to the SMC material is a bulk molding compound (hereinafter referred to as BMC). This BMC is a molding material obtained by mixing or impregnating an unsaturated polyester resin in which a hardening agent and a condensing agent are blended into a chopped strand of glass fiber, and then gelling the mixed resin. Mainly, transfer molding, injection molding, injection molding is performed. It is formed by a method such as compression molding. With these molding methods of BMC, it has not been possible to improve the surface quality of molded articles by IMC and HPIP. The reason is as follows.

For example, as shown in FIG.
When a bonnet for an automobile is formed by injecting a BMC material from the sprue 5 into the mold using the sprue 4, the parting surface 18 which is the contact surface of the molding die is a flat contact. When the IMC and HPIP paints are injected at a high pressure from the paint inlet 6, the parting surface 18 from the mold cavity is removed.
Paint flows out through the surface of the molded article 1,
As shown in FIG. 5, an unpainted portion 12 called an IMC short
Can be done. On the other hand, in the case of parts having a large surface area, such as a bonnet, an air pocket is formed in the mold, and an IMC short 13 is generated as shown in FIG.

Further, in the HPIP, since the paint is injected at a high pressure without opening the mold, not only an IMC short occurs, but if the injection timing is incorrect, the paint is uncured BM.
The material C may pass through the material C to the back side of the product, or the coating film 14 may be formed only near the tab 2 of the product as shown in FIG.

[0008]

As described above, the BMC
Surface quality defects such as sink marks and pinholes that occurred in molded products that were injection-molded using a conventional method had to be corrected manually by hand after molding. Problems remain in the surface quality of the product.

The present invention solves the above-mentioned problems and provides an in-mold coating method which eliminates the IMC short in molding using BMC, and forms the molded product with good surface quality and efficiently. The purpose is to:

[0010]

SUMMARY OF THE INVENTION According to the present invention, a pressure sensor is provided near a plastic injection port of a mold having a cutout formed on the periphery of a shape of a molded article, and plastic is injected into the mold. When molding, the pressure is released when the pressure sensor detects a predetermined pressure drop after passing a peak pressure due to the heat expansion of the plastic in the mold, and the paint is applied to the vacuum degassed mold at a high pressure. This is a plastic in-mold coating method in which the injected paint is then increased in molding pressure to flow the injected paint into the mold, and then the paint is cured.

[0011]

When a paint is injected into a mold at a high pressure, a pressure sensor is used.
The reaction state of the molded product in the mold is detected and the timing is determined, and the inside of the mold is vacuum degassed in advance.Therefore, the paint injected at high pressure into the mold will flow out to the outside by cutting the mold. Stopped and the paint poured into the mold completely covers the surface of the molded article, and no IMC short occurs.

[0012]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a molding die for a hood of an automobile;
FIG. 2 is a plan view showing a molded product, and FIG. 3 is an enlarged sectional view of a part of a mold. The molded article 1 has a tab 2 serving as a paint inlet.
To form As shown in FIG. 1, the mold for molding the molded article 1 with the tab 2 forms a cavity between the fixed mold 3 and the upper mold 4 having a shape corresponding to the molded article. Is provided with a sprue 5 for injecting BMC, and a tab 2 of the upper die 4 is provided.
3. A paint inlet 6 is provided at a position corresponding to the above, and the contact surface between the fixed die 3 and the upper die 4 is formed by a cut-off 7 and a flat parting surface 8 as shown in FIG. I do. 7
A passage leading to a vacuum deaeration port 10 connected to a vacuum pump is provided between the air conditioner and the parting surface 8, and a seal material 11 is provided therearound. A pressure sensor 9 is disposed near the sprue 5 of the fixed mold 3.

Next, the BMC I using the mold shown in FIG.
The outline of MC will be described. When the upper mold 4 is set on the fixed mold 3, the cavities around the mold are sealed with the cutouts 7,
The clamping pressure is received on the flat parting surface 8 around it. 10 ~ 150K for mold controlled to 140 ~ 170 ℃
BMC is injected from the sprue 5 into the cavity at a pressure of g / cm2. BMC in this state for 0.5 to 3 minutes
Allow the material to cure. After the BMC material is cured, the air in the mold is discharged from the vacuum deaeration port 10, and then the IMC paint is injected at a high pressure from the paint inlet 6, and the paint is cured by keeping the state for a specified time. . Since the inside of the mold is evacuated with the mold closed before the paint is injected, air cannot be trapped in the mold when the paint is injected. Flushing is prevented. The molded product taken out of the mold has a 70 to 100 µm thick IMC coating film firmly adhered to the surface of the BMC molded product, and the pinhole generated on the surface of the molded product by the BMC is filled with IMC paint. The surface becomes smooth.

Next, IMC of BMC will be described in detail.
BMC is injected from the sprue 5 into the cavity at a temperature adjusted to 140 to 170 ° C., and a molding pressure of 100 to 200 kg / cm 2 is maintained for a specified time T1 as shown in FIG. The T1 time is, as will be described later, the time when the BMC material in the mold passes through the peak of exothermic expansion and enters the curing and shrinking stage. Next, the pressure of the press is released, and the inside of the mold, which is kept closed without applying the molding pressure, is vacuum-evacuated as shown by an arrow V. Next, as shown by the arrow I, the IMC paint is injected at a high pressure of about 300 kg / cm 2 from the injection port located at the position of the paint injection tab, and after the paint is injected, the molding pressure is increased to 100 to 200 kg / cm 2 again.
This state is maintained for T3 hours to cure the paint.

The setting of the T1 time is determined as follows. FIG. 9 is a resin pressure monitor measurement diagram, in which the BMC material sealed in the mold expands due to heat generation and the pressure rises as shown by the arrow. As shown, the contraction phase is entered and the pressure in the mold drops. This change in pressure is measured by a pressure sensor 9 installed on the fixed mold 3. A threshold pressure is set in advance on this pressure curve. At the time t1 when the detection value of the pressure sensor 9 becomes equal to or higher than the threshold pressure at the time of forming the BMC and the peak pressure is reached, a signal is sent to the vacuum deaerator, and as shown by V in FIG. Start degassing. Next, at time t2 when the pressure sensor detects the threshold pressure, a signal is sent to the press side to release the molding pressure, the mold is kept closed, and then the signal from the press side is used as the signal I in FIG. The IMC material is injected at high pressure into the mold as shown.

As described above, when the molding pressure is released, the inside of the mold is evacuated while the mold is closed, and the paint is injected, the BMC material in the mold has entered the shrinking stage, so that air cannot be trapped. The paint flows well on the surface of the BMC, and no IMC short occurs. Also, the paint injected into the mold,
Due to the subsequent increase in molding pressure, it further flows to the surface of the cured BMC, and a good coating is stably obtained.

The location of the pressure sensor 9 is preferably near the sprue 5, which is an inlet for BMC material. This is because the reaction of the last material injected into the mold is the slowest, so that it is appropriate to set the injection timing of the IMC paint at that position. If shown at 9 'in FIG.
When the pressure sensor is installed at a position distant from the sprue 5 and the injection timing of the IMC paint is set based on the data, the BMC material near the sprue is uncured.
The paint wraps around the back side, and a good IMC coating film cannot be formed on the surface.

[0018]

According to the present invention, IMC is applied to the surface of a BMC molded product.
A molded article having good surface quality can be efficiently produced without generating a short.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mold used in the method of the present invention.

FIG. 2 is a plan view of a molded product.

FIG. 3 is a partially enlarged sectional view of FIG. 1;

FIG. 4 is a cross-sectional view of a conventional injection mold.

FIG. 5 is a view showing a conventional coating defect.

FIG. 6 is a view showing a conventional coating defect.

FIG. 7 is a view showing a conventional coating defect.

FIG. 8 is a view showing a molding step of the present invention.

FIG. 9 is a measurement diagram for determining paint injection according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molded product 3 Fixed mold 4 Upper mold 5 Sprue 6 Paint injection port 7 Cut-off 8 Parting surface 9 Pressure sensor 10 Vacuum deaeration port

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-47719 (JP, A) JP-A-1-229605 (JP, A) JP-A-62-126918 (JP, A) 75013 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 43/00-43/58 B29C 45/00-45/84

Claims (1)

(57) [Claims] 1. A pressure sensor is provided near a plastic injection port of a mold having a cutout formed on a peripheral edge of a shape of a molded product, and the pressure sensor is used when molding is performed by injecting plastic into the mold. When a predetermined pressure drop is detected after passing the peak pressure due to the exothermic expansion of the plastic in the mold, the molding pressure is released, and the paint is injected at a high pressure into the vacuum-degassed mold, and then the molding pressure is reduced. An in-mold coating method for plastics, characterized in that the raised and poured paint is allowed to flow into a mold, and then the paint is cured.