JPH06328504A - Method for in-mold coating - Google Patents

Abstract

PURPOSE:To prevent separation of resin and pigment in the composition of a coating agent and generation of color nonuniformity and a stria by pouring the coating agent to the boundary of both the internal surface of a forming mold and the molding of synthetic resin through a necessary pouring velocity pattern and multistage variable velocity. CONSTITUTION:The plasticized synthetic resin material is injected into a cavity 5 from an injection cylinder 6. An injector 11 actuates its shut off-pin 11A and the pouring port thereof is opened in a stage wherein synthetic resin material has been properly cured in a mold. While an opening is formed between the inner wall of the cavity 5 and the surface for molding synthetic resin by the pouring pressure of the coating agent, the coating agent is filled in the opening. In the case, the coating agent is poured e.g. at, a pouring velocity of three stages by controlling the actuation velocity of a plunger-regulator 12A. The proper injection velocity is set according to the conditions of the size and the shape of the cavity. Thereby high-quality in-mold coating is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is mainly applied to molding of synthetic resin such as compression molding, injection molding and injection compression molding.
The present invention relates to an in-mold coating method for coating the surface of a synthetic resin molded article with a coating agent in the molding die.

[0002]

2. Description of the Related Art Generally, in-mold coating methods are
It is widely used for molding thermosetting synthetic resins. Especially in the automobile industry, where the quality of appearance is highly demanded, the "SM
When adopting glass fiber reinforced plastics, which has an unsaturated polyester resin as a matrix, called “C”,
The in-mold coating method is used for the purpose of improving quality and shortening the coating process.

[0003] As such a method for coating in a mold, there is Japanese Patent No. 1020816 "Molding Method for Composite Polymer Article". This method is one of the methods, in which one of the molding dies is separated from the surface of a synthetic resin molded article. Then, after providing a gap between the surface of the molding die and the synthetic resin molded product, the coating material is injected and the molding pressure is applied again. In this method, steps such as a step of providing a gap and a step of applying a molding pressure again are added, so that the molding cycle is delayed as a whole. Further, when the molding die is opened in order to coat the coating agent, the so-called burrs of the synthetic resin formed in the so-called shear edge portion around the die are damaged during opening and closing, and the sealing performance becomes uncertain, The coating material leaks. Due to this leak, the injection of the coating agent on the planned coating surface was insufficient,
This causes defective products. Further, as described above, the method of supporting and opening the molding die due to the injection of the coating material makes it impossible to adopt the structure of the slide or the secondary core, which imposes restrictions on the design of the molded product.

In order to solve these problems, already,
Japanese Patent Publication No. 4-33252 proposes a "substrate forming and coating method". In addition, as a coating agent injecting device of this method, the "in-mold process" manufactured by Morell Inc. in the United States is already known. Here, at the same time as molding of synthetic resin, a synthetic resin molded product is produced in the mold. In-mold coating is carried out on.

[0005]

In this method, the drawbacks of the above-described mold opening type coating material injection method are improved, but the coating material is applied with a considerable pressure, and the surface of the mold and the surface of the molded product are prevented. Since it is injected and flows while creating a gap between the coating material and the coating material, the shearing force acting on the coating material at this time tends to cause defects such as separation of the resin and pigment components in the coating material composition, color unevenness, and streaks. . In particular, it has been confirmed that this defect is likely to occur at the flow end.

[0006]

SUMMARY OF THE INVENTION The present invention has been made based on the above circumstances, and at the time of molding synthetic resin such as compression molding, injection molding, injection compression molding, at the same time as molding the synthetic resin, a molded article When coating the surface with a coating agent, an in-mold coating method that ensures high quality by avoiding the separation of resin and pigment components in the coating composition, color unevenness, streaks, etc. It is the one we are trying to provide.

[0007]

In the present invention, attention is paid to the fact that the state of the coating material on the surface of the synthetic resin molded article changes depending on the injection speed of the coating material from the initial stage to the end thereof. In order to coat the surface of the molded product with the coating agent, in the mold for synthetic resin molding, after the synthetic resin molding, the surface of the synthetic resin withstands the injection and flow pressure against the coating agent. At the time of proper curing or solidification to be obtained, while holding the molding die as it is, the coating agent is injected into the boundary between the inner surface of the molding die and the synthetic resin molded article, and the synthetic resin is used in the coating agent. In an in-mold coating method having a step of coating the surface of a molded article and a step of curing the coating agent, in the step of injecting the coating agent, performing injection at a multistage variable speed with a required injection speed pattern. Is characterized by.

[0008]

By this, when filling the coating agent into the mold after molding the resin, the coating agent is coated on the surface of the synthetic resin molded article while maintaining an appropriate injection speed according to the shape and size of the cavity. To do.

[0009]

EXAMPLES An example of the structure of an injection molding machine for carrying out the in-mold coating method of the present invention and an example of its molding die will be described below.
A specific description will be given with reference to the drawings. In the figure, reference numerals 1 and 2 denote left and right (may be upper and lower) embossing members (press rams) of the molding machine, which are provided with molding die members 3 and 4, which face each other. In this embodiment, the die pressing member 1 is fixed and the die pressing member 2 is moved forward and backward. And both mold members 3
A cavity 5 having a required shape is formed at the fitting points of 4 and 4 by an injection molding method (or a compression molding method, an injection compression molding method, etc.), and a molten or softened synthetic resin is filled therein. It then hardens. When the molten synthetic resin is filled, the cavity 5 includes a nozzle 7 and a spool 8 from an injection cylinder 6 having a screw.
The molten synthetic resin can be injected through the. In the figure, reference numeral 9 is an ejector pin at the time of mold release.

On the other hand, as means for injecting the coating material in the embodiment shown in FIG. 1, an injector 11 having a shut-off pin 11A and a coating material measuring cylinder 12 for supplying a predetermined amount of the coating material to the injector 11. , And a supply pump 14 for supplying the coating material from its reservoir 13 to the metering cylinder 12. The measuring cylinder 12 is provided with a plunger regulator 12A for injecting the coating material.

The plunger / regulator 1 is used.
2A requires an operating pressure that considerably exceeds the pressure in the cavity 5 immediately before injection, and for example, in this embodiment, 5A.
It is desirable to drive at an operating pressure of about 00 kgf / cm ² .

In molding, first, the mold pressing member 2 is operated to close the molds (molding mold members 3 and 4) and apply mold clamping pressure. This mold clamping pressure needs to be able to withstand the injection pressure of the synthetic resin material. In the process,
The supply pump 14 is activated to supply the metering cylinder 12 with the required amount of coating material. At this time, the working pressure of the plunger regulator 12A is released, and the coating pressure is filled in the measuring cylinder 12 by the working pressure of the supply pump 14.

Next, the plasticized synthetic resin material is injected from the injection cylinder 6 into the cavity 5 through the nozzle 7. At the stage where the synthetic resin material is properly hardened (hardened enough to withstand injection of coating material and flow pressure) or solidified in the mold, the injector 11 operates its shut-off pin 11A to open its injection port. The coating material is filled into the gap while opening the gap between the inner wall of the cavity 5 and the surface of the synthetic resin molded product by the injection pressure of the coating material. In this way, in-mold coating of the surface of the molded article is achieved.

In this case, according to the present invention, the operating speed of the plunger / regulator 12A is controlled by an appropriate control system, so that the coating material is injected at three injection speeds as shown in FIG. 2, for example. is there. This proper injection rate is set under conditions such as the size and shape of the cavity 5. For example, when the injection speed in the initial stage 〓 is 1, it is preferable to set the injection speed in the intermediate stage 〓 to about 1.5 to 6 and the injection speed in the final stage 〓 to about 0.1 to 1. Also, taking into consideration the gelation rate of coating materials such as paints, the total injection time is within 15 seconds, preferably 1
0 second or less is suitable from the viewpoint of maintaining high quality of the coating. The setting of the absolute value of the coating material injection speed is selected depending on the pressure (pressing pressure) applied to the mold during the coating material injection, the degree of curing of the molded product itself, the material, and the like.

FIG. 3 shows an example of a control hydraulic circuit for controlling the plunger regulator 12A and the shut-off pin 11A as a coating material injection means. Here, the hydraulic pump 16 is the pressure regulating valve 1.
7 through solenoid valve 20 and injector 1
The first chamber 111 and the second chamber of the first hydraulic control cylinder 11B
It is connected to the chamber 112. In addition, the hydraulic pump 16
Is connected to the first chamber 121 and the second chamber 122 of the hydraulic cylinder 12B of the regulator 12A via the pressure adjusting valve 21 and the solenoid valve 24.

A position sensor 25 for detecting the operation of the plunger rod 12C is provided corresponding to the regulator 12A.
The detection signal of is supplied to the program controller 28 via the amplifier 27. As a result, a control signal is sent from the program controller 28 to the electromagnetic float control valve 23 via the amplifier 26, whereby the injection speed of the coating material into the cavity 5 is controlled and adjusted.

The hydraulic circuit has a pressure adjusting valve 2 for adjusting the delivery pressure of the hydraulic pump 16.
9 is equipped. Further, in the figure, reference numerals 18 and 22
Is a pressure gauge, and 19 is a check valve.

However, the hydraulic circuit is controlled by the drive control of the solenoid valves 20 and 24 and the command of the program controller 28, and the multi-stage injection speed control of the coating agent as illustrated in FIG. 2 is performed. Is done.

FIG. 4 and FIG. 5 show the above control system,
1 shows an embodiment for performing a small amount of coating material injection into the cavity 5 with high accuracy. Here, in the above-described embodiment, the measuring cylinder 12 is omitted, and the position sensor 31 is directly provided corresponding to the injector 11, and the injection speed is controlled by the information from this position sensor 31. . That is, after the plasticized synthetic resin material is injected from the injection cylinder 6 into the cavity 5 through the nozzle 7, the synthetic resin material is appropriately charged in the mold (injection of the coating agent, flow pressure). At the stage of hardening (or solidifying to an extent), the injector 11 operates its shut-off pin 11A to open its injection port and receive the required amount of coating agent in its supply cylinder portion 11C. Then, when it is confirmed by the position sensor 31 that the predetermined amount of the coating agent is received, the hydraulic pressure supply control to the hydraulic control cylinder 11B of the injector 11 is performed, and the shut-off pin 11A is operated to perform the coating. The agent is injected into the cavity 5. Then, by the injection pressure at this time, a gap is created between the inner wall of the cavity 5 and the surface of the synthetic resin molded product, and the gap is filled with the coating agent.

In each of the above-mentioned embodiments, what is important is to control the injection rate of the coating material in multiple stages, which is effective for separating the resin and pigment components in the composition of the coating material, color unevenness, streaks and the like. It is a condition for avoiding the occurrence and ensuring high quality. This point will be specifically described in the following embodiments.

[Embodiment-1] (Compression molding method) A mold having a cavity for obtaining an oval-shaped synthetic resin molded product, such as a plate having a length of 450 mm, a width of 300 mm, and a depth of 40 mm. When performing in-mold coating on the mold, the mold temperature is set to 155 ° C. for the upper mold 3 and 14 for the lower mold 4.
Setting to 5 ° C., first, thermosetting glass fiber reinforced plastics (so-called SMC) having an unsaturated polyester resin as a matrix is set in a mold, and a molding pressure is set to 80.
Molding was performed under the conditions of kgf / cm ² and molding time of 60 seconds.

Next, the molding pressure (pressure in the cavity)
Was reduced to 20 kgf / cm ² , and then 12 cm ³ of an in-mold coating agent (see Table 1) containing urethane acrylate oligomer and epoxy acrylate oligomer as main components was injected. The injection speed control at this time was 6.8 from the initial 3 cm ³ .
cm ³ / sec, then the next 6 cm ³ to 13.6 cm
³ / sec, the remaining 3 cm ³ is 2.7 cm ³ / sec
The procedure was divided into 3 steps. At this time, the time required for the injection is about 2 seconds. And, 60kg again after the injection is completed
Pressurized to f / cm ² and held for 80 seconds. In this way, the results of molding and coating in the mold are good,
Separation of the pigment component, color unevenness, streaks, etc. did not occur.

[0023]

[Table 1] Incidentally, under the same conditions as in the above embodiment, when the injection speed of the coating agent was set to 13.6 cm ³ / sec in the entire injection process (Comparative Example), the surface of the coating layer of the molded synthetic resin molded article On the other hand, separation of pigment component, color unevenness, streaks and the like were recognized. This is, as already experienced by the inventor, during the injection of the coating (especially in the final stage),
This is because the shearing force acting on the coating agent has exceeded the limit at which separation of the pigment component occurs and has an effect.

[Embodiment-2] (Compression molding method) A mold having a cavity of 1,000 mm in length and 1,400 mm in width and having a cavity for obtaining a flat-shaped synthetic resin molded product. In carrying out the above, the mold temperature is set to 150 ° C. for the upper mold 3 and 140 ° C. for the lower mold 4, and first, thermosetting glass fiber reinforced plastics (so-called, SM
C) is set in the mold and the molding pressure is 100 kgf / c
Molding was performed under the conditions of m ² and molding time of 60 seconds.

Next, the molding pressure (pressure in the cavity)
Was depressurized to 10 kgf / cm ² , then the in-mold coating agent A (see Table 2) containing urethane acrylate oligomer and epoxy acrylate oligomer as main components was received in the measuring cylinder 12 (377 cm ³ can be measured), and 210 cm ³ was measured. did. The measuring stroke of the measuring cylinder 12 at this time is 85 mm. Then, the injection speed control to the cavity 5 is 8 mm / se for the initial measurement stroke of 12 mm.
c, the next measuring stroke 73mm is 20mm /
sec, the remaining weighing stroke is 4 mm / sec,
The procedure was divided into 3 steps. At this time, the time required for the injection is about 7.6 seconds. And, 60kg again after the injection is completed
It was pressurized to f / cm ² and held for 80 seconds to cure (or solidify). In this way, the result of molding and coating in the mold was good, and separation of the pigment component, color unevenness, streaks and the like did not occur.

[0026]

[Table 2] [Embodiment 3] (Injection molding method) A mold having a cavity of 200 mm in length and 100 mm in width for obtaining a pen-shaped synthetic resin molded product, and when performing in-mold coating on the molded product, The mold temperature is set to 130 ° C. for the mold member 3 and 135 ° C. for the mold member 4,
First, fill the injection cylinder 6 with polyamide resin,
It was heated and melted at 250 to 280 ° C., injected into a mold clamped at a mold clamping pressure of 300 tons for about 4 seconds, and cooled for 20 seconds.

Next, after the mold clamping pressure was reduced to 5 tons, the in-mold coating agent B containing urethane acrylate oligomer and epoxy acrylate oligomer as main components (Table 2)
5 cm ³ was received by the measuring cylinder 12 (capable of measuring 20 cm ³ ). The measuring stroke of the measuring cylinder 12 at this time is 37 mm. Then, the injection speed control into the cavity 5 is performed such that the initial measuring stroke 10 mm is 5 mm / sec and the next measuring stroke 30 mm is 10 mm.
mm / sec, remaining measurement stroke is 3 mm / se
In step c, the procedure was divided into 3 steps. At this time, the time required for injection is about 6.3 seconds. Then, once the injection is completed,
It was pressurized to 0 ton and held for 60 seconds to cure. In this way, the result of molding and coating in the mold was good, and separation of the pigment component, color unevenness, streaks and the like did not occur.

As will be understood from the above embodiments, in the present invention, the control of the injection rate divided into multiple stages corresponds to the conditions such as the size and shape of the cavity.
Of course, it can be set appropriately.

[0029]

The present invention has been described in detail above. In order to coat the surface of a synthetic resin molded article with a coating agent, the synthetic resin molding is performed in the mold for synthetic resin molding, and When the surface of the resin is properly cured or solidified to withstand the pouring / flowing pressure of the coating material, the molding die inner surface and the synthetic resin molded article are held while the molding die is kept as it is. Injecting the coating agent at the boundary with, and coating the surface of the synthetic resin molded article with the coating agent,
In the in-mold coating method including the step of curing the coating agent, in the step of injecting the coating agent, injection is performed at a variable injection rate in multiple steps at a required injection rate pattern. When filling the agent, it is possible to coat the surface of the synthetic resin molded article with the coating agent while maintaining an appropriate injection rate according to the shape and size of the cavity, without delaying the molding cycle, and In-mold coating can be realized with high quality without imposing design restrictions on the structure of the molding die.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a molding die for realizing the method of the present invention.

FIG. 2 is a graph showing coating agent injection rate control in the above example.

FIG. 3 is a circuit diagram showing a hydraulic pressure control circuit for controlling the coating agent injection speed.

FIG. 4 is a schematic view showing another embodiment of the present invention.

FIG. 5 is a schematic diagram showing a state immediately before injection of a coating agent.

[Explanation of symbols]

 1, 2 Mold pressing member 3, 4 Mold member 5 Cavity 6 Injection cylinder 7 Nozzle 8 Spool 9 Ejector 11 Injector 12 Measuring cylinder 12A Plunger regulator 13 Storage section 14 Supply pump 16 Hydraulic pump 17, 21, 29 Pressure adjusting valve 20 , 24 Solenoid valve 23 Electromagnetic flow control valve 25 Position sensor

Claims (2)

[Claims] 1. In order to coat the surface of a synthetic resin molded article with a coating agent, the surface of the synthetic resin is molded into a molding die for molding the synthetic resin, and the surface of the synthetic resin is coated against the coating agent.
At the time of proper curing or solidification that can withstand the pouring / flowing pressure, while maintaining the molding die as it is, the coating agent is injected at the boundary between the inner surface of the molding die and the synthetic resin molded article, An in-mold coating method comprising a step of coating the surface of the synthetic resin molded product with a coating agent and a step of curing the coating agent, wherein a multi-step variable with a required injection speed pattern in the injection step of the coating agent. An in-mold coating method, characterized in that the injection is carried out at a rate. 2. The in-mold coating method according to claim 1, wherein the synthetic resin is a thermoplastic resin.