JPH0740366A - In-mold coating method for plastics - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain accurate in-mold pressure data at the time of actual molding by multistage pressure control, eliminating the influence caused by switching of molding pressure. [Structure] A pressure sensor 4 is installed in a lower mold of a molding die, a pressure-imparting member 5 is arranged in a portion of an upper mold facing the pressure sensor, and a molding pressure is applied to the pressure-imparting member 5. Is changed in multiple stages to perform molding, the change in the mold pressure during the molding process is read by the pressure sensor, and the switching timing of the molding pressure and the injection timing of the paint are set based on this data. When switching the molding pressure in multiple stages,
Although the pressure inside the mold changes abruptly due to a slight movement of the upper mold, since the pressure-applying member that applies a constant pressure is arranged at the portion facing the pressure sensor, the read data of the pressure sensor Is not affected by the switching of the molding pressure, and the curing characteristic data of the plastic material can be accurately obtained during actual molding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for obtaining in-mold pressure data for setting a molding pressure switching timing and a paint injection timing in a plastic in-mold coating method.

[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 compression molded. The molded product obtained by
Sinks and pinholes occur. There is an in-mold coating method (hereinafter referred to as IMC) as one of countermeasures against pinholes generated on the surface of an SMC molded product. This IMC is
The present applicant has previously filed a patent application regarding the invention of the plastic in-mold coating method (Patent Application No. 1-181778, Japanese Patent Application Laid-Open No. 3-47719), which is a method of coating simultaneously with molding of plastic. .

At present, the IMC is being developed toward the high pressure injection process (hereinafter referred to as HPIP). In this HPIP, the SMC material is placed in the lower mold of a temperature-controlled mold, the upper mold is closed, and pressure is applied to cure it for a specified time. Next, the paint is injected at a high pressure into the mold that is still closed with the pressure slightly lowered, and then the pressure is increased again after stopping the injection of the paint, and the paint is cured by holding it for a predetermined time in this state. Is.

Also, for products having ribs and bosses that are liable to sink, the development of a multi-stage pressure control press that changes the molding pressure makes it possible to reduce the amount of sink marks on the upper surfaces of the ribs and bosses. SMC molding has come to be performed. Therefore, SMC molding that incorporates HPIP injection technology and multi-stage pressure control molding technology
Although the molding cost can be reduced and the surface quality can be improved, it is important to set the timing of changing the molding pressure and the timing of the IMC in order to put this technology into practical use.

FIG. 7 shows changes in the pressure inside the mold when the molding pressure applied by the press is constant. In the figure, the broken line indicates the constant molding pressure applied by the press,
The actual pressure in the mold changes over time as shown by the solid line. That is, the pressure curve in the mold at the time of actual molding starts to rise from the point a due to heat generation and expansion accompanying the curing of the SMC material, reaches a peak at the point b, and then descends during the curing shrinkage process to reach the point c. It gradually rises again and the curing is completed.

Regarding the setting of the paint injection timing in the IMC, a method of obtaining from the pressure curve in the mold at the time of actual molding shown by the solid line in FIG. 7 is disclosed (Japanese Patent Laid-Open Nos. 3-47719 and 4-44823). The range where the heat generation / expansion peak b point of the SMC material shown by the alternate long and short dash line in FIG. Then, the paint injection timing is set by setting a time or a threshold pressure so as to be linked with the press.

The timing of changing the molding pressure using the multi-stage pressure control press can also be obtained from the pressure curve of FIG. In other words, when molding products with ribs or bosses that are susceptible to sink marks, the amount of sink marks on the top surface of the ribs or bosses can be effectively reduced by lowering the pressure of the press machine before reaching point a where the SMC material begins to generate heat and expand. It is clear from the experimental results that it can be reduced to.

Therefore, in the molding of products having ribs and bosses, as a measure to prevent sink marks, before the injection of IMC paint,
It is necessary to reduce the molding pressure over several stages. FIG. 8 shows an example of control of press pressure. Before the SMC material flows in the mold and starts to generate heat and expand, the pressure of the press machine is set to the initial value P.
From 1 to P2, further down to P3 before reaching the peak of heat generation / expansion, and in this state IM as indicated by arrow I
Inject C paint. After injecting IMC paint, press pressure P
4 and then in the curing shrinkage process, the coating is cured by lowering it in multiple stages like P5 and P6.

[0009]

When the pressure of the multi-stage pressure control press is switched, it is inevitable that the upper die slightly rises due to the structure of the machine. Therefore, the pressure curve in the die during actual molding is inevitable. Changes abruptly each time the pressing force is switched. FIG. 9 shows the relationship between the pressing force and the pressure curve in the mold during actual molding. In the figure, the broken line shows the pressing force, and the solid line shows the pressure curve in the mold during actual molding. Therefore, the curing characteristics of the SMC material as shown in FIG. 7 cannot be grasped, and the IMC timing cannot be set.

Under the present circumstances, the pressure curve in the mold is obtained with the pressing force kept constant, and the switching timing of the pressing force and the injection timing of the IMC are set based on this curve. Since the curing characteristics change depending on the storage period and the use period (summer and winter), the pressure curve in the mold must be calculated as the constant pressing force each time, which complicates management during mass production and lowers productivity. It will be. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, eliminate the influence of switching of molding pressure in SMC molding by multi-stage pressure control, and obtain accurate in-mold pressure data during actual molding by multi-stage pressure control.

[0011]

According to the present invention, when the peak pressure due to the exothermic expansion of the plastic material in the mold is exceeded, the molding pressure is released, the paint is injected into the mold at high pressure, and then the molding is performed. Increase the pressure of to make the injected paint flow into the mold,
A method of curing the paint after that, in which a pressure sensor is installed in one of the split-type molding dies, and a pressure-imparting member is disposed in a portion of the other mold facing the pressure sensor, Molding is performed by switching the molding pressure in multiple stages while pressure is applied to the member, the change in the mold pressure in the molding process is read by the pressure sensor, and the molding pressure switching timing and the paint injection timing based on the data. Is an in-mold coating method for plastics.

[0012]

When the molding pressure is switched in multiple stages, the pressure inside the mold changes abruptly due to a slight movement of one mold, but the pressure-applying member that applies a constant pressure to the part facing the pressure sensor Since it is provided, the reading data of the pressure sensor is not affected by the switching of the molding pressure, and the curing characteristic data of the plastic material can be accurately obtained during the actual molding.

[0013]

Embodiments of the present invention will be described with reference to the drawings.
1A and 1B are sectional views showing a molding die used in the method of the present invention. FIG. 1A shows a state before molding and FIG. 1B shows a state at the time of molding. A cavity 3 is formed between the upper mold 1 and the lower mold 2, a pressure sensor 4 is installed on the lower mold 2, and a pressure-applying member that can be hydraulically lowered to a portion of the upper mold 1 facing the pressure sensor 4. Install 5. This pressure-imparting member 5 introduces pressure oil from a hydraulic pump into a hydraulic cylinder with a hose 9 and is pushed down by a piston 6 to apply a predetermined pressure. Reference numeral 7 is a stopper, and 8 is an adjusting screw thereof.

The pressure-imparting member 5 is formed to be larger than the outer circumference of the tip portion, which is the pressure sensing portion of the pressure sensor 4, and its outer peripheral shape is arbitrary, but it is preferable to make it a cylindrical shape. Further, as shown in FIG.
a is formed, and the height h of this protrusion is made equal to the thickness of the molded product so that the flow of the SMC material is not hindered when the pressure-imparting member 5 is pushed down into the cavity 3 during molding.
As shown in the bottom view of FIG. 6, three protrusions 5b may be formed as the protrusions on the tip of the pressure-imparting member 5.

The location of the pressure sensor 4 in the mold will be described with reference to FIGS. 2 and 3. For example, in the case of molding a front panel of an automobile, the molded product of the front panel 10 has a portion for bonding another component to the molded front panel as shown by a chain line 11 in FIG. 2 and a tab necessary for molding. Formed outside the product. The pressure sensors 4a, 4 are provided on a product portion that does not require such an appearance and a molding portion that is removed by post-processing.
Install b. FIG. 3 is a cross-sectional view of a mold for molding a portion along the line XX of FIG.
Or install 4b. Although not shown in FIG. 3,
In the present invention, the pressure-increasing member is provided in the upper die portion facing the pressure sensor.

Next, a method of obtaining pressure data in the mold during actual molding will be described with reference to FIG. As shown in FIG. 1A, the position of the stopper 7 is adjusted by the adjusting screw 8 and the tip of the protrusion 5a of the pressure-imparting member 5 is placed in alignment with the inner surface of the upper mold 1. 1
The mold whose temperature is controlled at 40 to 155 ° C. is opened, the SMC material W is charged in the cavity 3 of the lower mold 2 in an amount according to the product thickness, the upper mold 1 is closed, and the initial molding pressure is 80 to 100 Kg.
Pressurize at / cm ² . Immediately after this pressurization, a pressure higher than the initial molding pressure is applied to the pressure-applying member 5 of the upper mold 1. This timing is controlled by a time setting or a signal from the press machine.

Since a pressure higher than the initial molding pressure is applied to the pressure-imparting member 5, the tips of the protrusions 5a of the pressure-imparting member 5 are in contact with the lower mold 2 or the SMC material W has a thin layer as shown in FIG. 1B. Descend in the mold until Next, as shown in FIG. 8, molding is performed at a preset switching of molding pressure and injection timing of IMC. The hydraulic pressure applied to the pressurizing member 5 is IMC.
After pouring, pull out at time setting or signal from press machine.

The pressure sensor 4 in the above actual molding process
Read the output of. This read data serves as pressure data between the pressure-imparting member 5 and the pressure sensor 4, and is not affected by the switching of the molding pressure of the press machine. By immediately feeding back the data, the read data can be adjusted according to the curing characteristics of the SMC material. Pressing force switching timing and IMC
Change the injection timing setting value of.

Next, another method for obtaining the pressure data in the mold will be described with reference to FIG. As shown in FIG. 4A, the adjustment screw 8
Adjust the position of the stopper 7 with the
The tip of the mold is clamped and lowered to a position where it comes into contact with the lower mold 2 in advance. In the same manner as described in FIG. 1, the temperature-controlled mold is opened, the lower mold 2 is charged with the SMC material, and the upper mold 1
Is closed and pressure is applied at an initial molding pressure of 80 to 100 Kg / cm ² , the tips of the protrusions 5a of the pressure-imparting member 5 penetrate the SMC material W and come into contact with the lower mold 2, as shown in FIG. 4B. Immediately after this pressurization, a pressure lower than the initial molding pressure is applied to the pressure-applying member 5 of the upper mold 1. The control of this timing, the subsequent molding, the reading of the pressure data, etc. are the same as those described in FIG.

[0020]

According to the present invention, since the in-mold pressure data based on the curing characteristics of the SMC material can be obtained without being affected by the switching of the molding pressure at the time of actual molding, the timing of switching the pressing force depending on the curing characteristics of the SMC material. It is possible to change the injection timing setting values of IMC and IMC, and it is possible to prevent molding defects due to variations in the curing characteristics of SMC materials.
MC molded products can be manufactured efficiently.

[Brief description of drawings]

FIG. 1 is a sectional view of a mold for explaining an embodiment of the present invention.

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

3 is a cross-sectional view of a mold for molding the XX line portion of FIG.

FIG. 4 is an explanatory view of another embodiment of the present invention.

FIG. 5 is a front view and a bottom view of the pressure-applying member.

FIG. 6 is a bottom view of another pressure-applying member.

FIG. 7 is a view showing a change in pressure inside the mold when the molding pressure is constant.

FIG. 8 is a diagram showing an example of control of press pressure.

FIG. 9 is a diagram showing a relationship between press pressure and pressure in a mold.

[Explanation of symbols]

1 Upper mold 2 Lower mold 3 Cavity 4 Pressure sensor 5 Pressure-imparting member 6 Piston 7 Stopper
8 adjustment screws

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B29L 9:00

Claims (1)

[Claims] 1. A coating material in which the molding pressure is released when the peak pressure due to the exothermic expansion of the plastic material in the mold is exceeded, the coating material is injected into the mold at a high pressure, and then the molding pressure is increased. A pressure sensor is installed in one of the split-type molding dies, and a pressure-imparting member is provided in the other mold portion facing the pressure sensor. The pressure is applied to the pressure-applying member, and the molding pressure is switched in multiple stages to perform molding, the change in the mold pressure during the molding process is read by the pressure sensor, and the molding pressure is changed based on the data. A plastic in-mold coating method characterized by setting a switching timing and a paint injection timing.