JPH0444823A - Smc in-mold coat molding - Google Patents

Abstract

PURPOSE:To obtain an FRP base material having a coating layer with a uniform thickness and no possibility of peeling without deforming and destroying an SMC molding by detecting a change in SMC resin pressure and casting a coating agent when the degree of curing of the SMC molding becomes optimum. CONSTITUTION:A pressure sensor 1 is provided on the bottom force 3 and casting of a coating agent 12 and adjustment of molding pressure are automatically performed based on its detecting signal. An electric signal of the detected pressure of the pressure sensor 1 is transferred from an amplifier 4a of a controlling apparatus 4 to a molding pressure-setting and comparing device 4b. When the width of change in a resin pressure of an SMC molding 13 for 1sec in a mold becomes smaller than 0.3kg/cm<2> cone sec or later after the molding pressure is controlled, the controlling apparatus 4 opens an solenoid valve 6 of a hydrauric pump 9 to actuate a cylinder for feeding a coating agent. Working condition of the cylinder 8 for feeding is adjusted in advance by means of a throttle valve 10. The coating agent 12 is thereby fed in the mold through a feeding head 7 for the coating agent at the optimum time. The SMC molding 13 which has not completely cured yet is however cured in such a level that it is not deformed or destroyed by high pressure feeding of the coating agent and it is completely cured during the curing time of the coating agent.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an SMC in-mold coat molding method for producing an FRP base material that can be used for automobile outer panel parts and the like.

(Prior art) SMC (Sheet Molding Comp) is a sheet-shaped molding material made by mixing and aging a thermosetting resin with reinforcing fibers, fillers, catalysts, thickeners, low-shrinkage agents, etc.
.

-und) is heated and pressed in a mold to harden the molding blade (2) method, which is known as the SMC compression molding method. FRP (Fiber Re1n) obtained by SMC compression molding method
Fine pinholes are likely to occur on the surface of a for-ced plastic base material. This is because SMC is manufactured in such a way that the air trapped in it cannot be completely removed.When baking or painting an FRP base material that has pinholes on its surface, the air inside the pinholes will expand and come out. Therefore, there is a problem that pinholes appear in the coating film.

The SMC in-mold coat molding method is known as a method for eliminating pinholes from an FRP base material made by the SMC compression molding method. These can be roughly divided into: ■In-mold coat method (IMC method) ■High pressure in-mold coat method? (HPI
MC method), ■IMC method is as shown in Fig. 6 (a), after compression molding the SMC molded body 13 with upper mold 2 and lower mold 3,
As shown in Figure (B), raise the upper mold 2 by about 0.5 to 1 mm to create a gap 15, and fill the gap 15 with Figure 6 (C).
As shown in Figure 1, the coating agent 12 is filled and then pressurized again to harden it (see Japanese Patent Publication No. 55-9291). This is a method in which a coating agent is injected under high pressure while the material is being molded (see JP-A-61-273921). Therefore, in the IMC method and the HPIMC method, molding pressure cover turns as shown in FIGS. 5(a) and 5(b) are adopted, respectively. In any case, the injected coating agent covers the surface of the SMC molded body and becomes a hardened coating layer.

The advantages of the SMC in-mold coat molding method include that pinholes on the surface of the FRP base material are hidden, and that the surface smoothness of the base material is improved.

(Problems to be Solved by the Invention) In the SMC in-mold coat molding method, the injection timing of the coating agent is very important, especially in terms of its influence on the surface smoothness of the FRP base material. As can be seen from Figure 4, which shows the range in which the coating agent can be injected (molding pressure and time conditions) in the SMC in-mold coat molding method, if the coating agent is injected too early, the coating agent will harden. A situation may occur in which the coating agent penetrates an insufficient SMC molded body, and conversely, if the coating agent is injected too late, the SMC molded body is cured too much, resulting in poor adhesion of the coating agent to the molded body.

Particularly in the case of HPIMC, since the SMC molded body serving as the base material is compressed and the coating agent is fluidized and filled into the mold, the surface smoothness of the FRP base material is greatly influenced by the injection timing of the coating agent. In addition, if you try to lower the molding pressure and speed up the injection timing to widen the range of possible injection times,
There is a problem in that "sink marks" occur on the ribs and bosses of the FRP base material.

As described above, the timing of injection of the coating agent is very important, but the optimal timing of injection of the coating agent, including the molding quality, differs depending on the SMC material and is not clear. Therefore, coating agents have conventionally been injected within a time period determined based on empirical rules. As a result, the timing of injecting the coating agent is often incorrect.
There is a problem in that it is not possible to completely avoid the occurrence of defective molded products.6 The present invention was made for the purpose of solving the above problem, and the problems to be solved are the improvement of surface smoothness and rib and boss parts. To provide an SMC in-mold coat molding method in which a coating agent is injected at an optimal timing so as to obtain an FRP base material of the best constant quality including shrinkage.

(Means for Solving the Problems) The SMC in-mold coat molding method of the present invention involves injecting a coating agent into the mold during the process of heat-compressing SMC in a mold and curing the molded product to coat the FRP base. When manufacturing materials, we measure the SMC resin pressure from molding to curing,
It is characterized in that the coating agent is injected when the resin pressure stops decreasing.

The injection timing of the coating agent is usually the point when the SMC resin pressure during molding is at its lowest, but it depends on the type of SMC in terms of material, the shape of the FRP base material to be obtained, the injection speed of the coating agent, etc. It may be a little more or less.

To measure the SMC resin pressure, it is sufficient to install a pressure sensor on the mold with the pressure-receiving part in contact with the SMC. It is better to install a pressure sensor on the mold surface of the lower mold.Also, considering that when SMC is normally pressurized and flows from the center of the cavity to the corners, it is difficult to accurately measure the pressure at all times. Preferably, the pressure sensor is provided in the center of the mold.

It is preferable that the pressure sensor be durable enough to not break down even after repeated use in molding, have a pressure-receiving part that hardly deforms due to pressure or have no moving parts, and have quick response. Examples of such pressure sensors include force balance pressure sensors, piezoelectric pressure sensors, and the like. The method of the present invention also includes a method in which a pressure gauge of a type read by a mechanical indicator is used as a pressure sensor and the coating agent is injected by visual judgment. However, it is preferable to completely automate the SMC in-mold coat molding, including the injection of the coating agent, by converting the pressure received by the pressure sensor into an electrical signal and sending it to the control device.

In the present invention, molding is performed using a known SMC, but it is not possible to use SMC that does not contain a low-shrinkage agent (rubber, saturated polyester, polyvinyl acetate, etc.), which is usually added as an essential component to SMC. .

Coating agents for IMC include conventionally used coating agents, such as fillers (carbon, calcium carbonate, talc, etc.) and polymerization initiators (t-butyl-
A two-component coating agent made of unsaturated polyester and polyurethane to which a cross-linking agent (such as styrene, etc.) is added, or a one-component coating agent based on epoxy or polyurethane can be used.

(Function) The matrix resin of SMC contracts as it hardens. On the other hand, the shrinkage reducing agent added to suppress the shrinkage of SMC expands. Therefore, the SMC inside the mold
There will be a minimum value for the resin pressure.

Before the SMC resin pressure reaches its minimum value, the SMC molded body is unstable, so the coating agent injected into the mold
It invades the SMC molded body and does not form a uniform coating layer over the entire surface of the molded body.

On the other hand, after the time when the SMC resin pressure reaches its minimum value, S
Since the curing of the MC molded body has progressed considerably, the adhesion of the coating layer to the base material weakens (the coating layer easily peels off from the base material).
At the same time, since the time for curing the SMC and the coating agent to proceed at the same time becomes shorter, the overall SMC in-mold coat molding time becomes longer.

Therefore, if the coating agent is injected based on the detection when the SMC resin pressure stops decreasing, the coating agent will be injected at the optimal timing to avoid the above molding defects, and high-quality FRP can be produced in a short time. A base material will be obtained.

(Example) Hereinafter, an example of the method of the present invention will be described with reference to the drawings.

In this embodiment, as shown in FIG. 3, a molding machine is used in which a pressure sensor 1 is provided on the lower mold 3, and the injection of the coating agent 12 and the molding pressure adjustment are automatically performed based on the detection signal. .

First, with the upper die 2 open, an SMC cut to an appropriate size is placed on the lower die 3. The SMC used here includes 260 parts of unsaturated polyester (polypropylene glycol fumarate), 245 parts of styrene (crosslinking agent), 105 parts of polymethyl methacrylate (low shrinkage agent), 1050 parts of calcium carbonate (filler), and t-butyl. - 7 parts perbenzoate (polymerization initiator), zinc stearate (thickener)
35 parts, magnesium hydroxide (thickener), 31 parts, and glass fiber (reinforcing fiber), 783 parts. After placing the SMC, the upper mold 2 is lowered by adjusting the proportional 1tFiFi type relief valve 5 between the hydraulic pump 9 and the molding machine pressurizing cylinder 11 with the control device 4, and the mold is closed.
SMC is compression molded at a molding pressure of kg/cm2 and a mold temperature of 145°C.

During molding, the SMC resin pressure within the mold increases once, as shown by solid lines A to broken HaB in FIG. 1, but then decreases and then becomes constant. The range in which the coating agent can be injected in terms of time is the point at which the SMC resin pressure reaches its peak, TIMc (min
) to the point when the resin pressure becomes constant T + Me (maxl), but as shown in Figure 2, the optimum injection timing of the coating agent to improve the surface smoothness of the FRP base material is S
Time when MC resin pressure stops decreasing TlMCfbest)
It has been confirmed in advance that

In this embodiment, the electric signal of the detected pressure of the pressure sensor l (see Fig. 3) is transmitted from the amplifier 4a of the control device 4 to the molding pressure setting and
The signal is sent to comparator 4b. The control device 4 controls the injection sill 8 of the coating agent at the time when the variation width of the resin pressure of the SMC molded body 13 in the mold becomes smaller than 0.3 kg/cm2 after 1 second after controlling the molding pressure. Open the 1itM'i valve 6 of the hydraulic pump 9 to operate it. injection shilling 8
The operation condition is adjusted in advance by the throttle valve 10, so that the coating agent 12 is injected into the mold through the coating agent injection head 7 provided on the upper mold 2 at the optimum time.

The coating agent 12 injected here is an isocyanate solution (
220 parts of diphenylmethane-4,4-diisocyanate, 130 parts of polypropylene butylene adipate, t-
butyl-barbenzoate (90 parts) and polyester liquid (
It is a two-part type coating agent consisting of 210 parts of hydroxy-terminated polypropylene fumarate, 90 parts of styrene, 85 parts of a propylene oxide adduct of pentaerythritol, 167 parts of talc, and small amounts of each of a stabilizer, a mold release agent, and a coloring agent.

When the coating agent 12 is injected, the molding pressure is kept low by the control device 4, and the coating agent 12 is
Injected instantly at more than double the pressure.

The uncured SMC molded body 13 is cured to the extent that it will not be deformed or damaged by high-pressure injection of the coating agent, and is completely cured within the curing time of the coating agent (about 60 seconds at about 1.50° C.). When mold 2 is opened, an FRP base material having a uniform coating layer on the surface and free from defects such as pinholes and sink marks is obtained. Even if this FRP base material is baked and painted, no pinholes will occur in the paint film.

(Effect of the invention) According to the SMC in-mold coat molding method of the present invention,
The change in SMC resin pressure is detected and the coating agent is injected when the degree of curing of the SMC molded body is optimal.
It is possible to obtain an FRP base material having a uniform thickness and a coating layer without fear of peeling, without deforming or damaging the C molded body.

Further, since the coating agent can be injected while correcting the variation in the timing when the coating agent can be injected due to the difference in the curing speed of each SMC production lot, an FRP base material of constant quality can always be obtained. This effect is further enhanced by controlling the coating agent injection machine and the molding machine in conjunction with each other, especially while detecting the SMC resin pressure.

In this way, since the FRP base material can be provided without problems in quality control, it can be applied to, for example, outer panel parts for automobiles where surface quality is important, and can contribute to reducing the weight of automobiles.

Moreover, while maintaining the good surface quality of the FRP base material,
Since the coating agent can be injected at the shortest timing to shorten the molding cycle, productivity can be increased.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the change pattern of SMC resin pressure during molding and the injection timing of the coating agent according to one example, and Figure 2 is an illustration of the injection timing of the coating agent and the surface smoothness of the molded product (FRP base material). Figure 3 is a schematic diagram showing the molding machine used in one example, Figure 4 is an explanatory diagram showing the range (conditions) in which the coating agent can be injected, Figure 5 +a) and fb ) are diagrams showing molding pressure cover turns in the IMC method and HPIMC method, respectively, and FIGS. 6(a) to 6(c) are explanatory diagrams of the conventional SMC in-molt coat molding method. In the figure, 1...pressure sensor, 2...upper mold, 3...
Lower mold, 4... Control device, 8... Coating agent injection cylinder, 9... Molding machine pressurizing cylinder, 13... SMC molded body 6 12... Coating agent,

Claims (1)

[Claims] When manufacturing a coated FRP base material by injecting a coating agent into the mold during the process of heating and compressing SMC in a mold and curing the molded object, the SMC resin pressure during the period from molding to curing is measured, An SMC in-mold coat molding method characterized in that a coating agent is injected when the resin pressure stops decreasing.