KR20250092721A - In-mold coating mold and method for simultaneous injection molding and surface coating - Google Patents

Abstract

The present invention relates to an in-mold coating mold and an in-mold coating method for simultaneous implementation of injection molding and surface coating.
The present invention relates to an in-mold coating mold having two cavities and one core capable of simultaneously performing injection molding and surface coating, wherein a thermoplastic resin is injection-molded, and a liquid-state curable coating agent is injected between the substrate and the mold before the molded product is taken out of the mold, thereby forming a coating layer, thereby enabling simultaneous performance of injection molding and surface coating, thereby enabling a high production speed since a large quantity of products can be coated with uniform quality in a short lead time, and since the coating thickness can be controlled, the defect rate is low, and since the transferability of the mold surface is excellent, fine shapes can be reproduced, and there is the effect of making invisible defects that appear on the appearance of injection-molded products, such as weld lines or sink marks on the substrate, and since a coating film is formed by a curing reaction, no volatile organic compounds (VOCs) are emitted during or after the molding process, which reduces the burden on the environment, and since the coating material is all attached to the product as a coating film, the generation of waste is also reduced.

Description

In-mold coating mold and method for simultaneous injection molding and surface coating

The present invention relates to an in-mold coating mold and an in-mold coating method for simultaneously implementing injection molding and surface coating, and more particularly, to an in-mold coating mold having two cavities and one core capable of simultaneously implementing injection molding and surface coating, wherein a thermoplastic resin is injection-molded, and before taking the molded product out of the mold, a liquid-state curable coating agent is injected between the substrate and the mold and cured within the mold to form a coating layer, thereby enabling simultaneous implementation of injection molding and surface coating, and a method therefor.

Plastics are utilized as core materials in most products leading domestic and international industries because they are advantageous for mass production at low cost, are lightweight, and can implement various physical properties. Among them, most molded products are produced by injection molding. In particular, with the trend toward high-end and multi-functional plastic products, the importance of coating on the surface of plastics is increasing in order to go beyond the product design centered on appearance, such as high gloss and various color implementation, to high sensitivity including texture and touch, and implement various functions, such as electromagnetic wave blocking, scratch resistance, chemical resistance, and weather resistance, not only for automobiles, mobile phones, and home appliances, but also for ships, aircraft, and interior and exterior building materials.

However, in order to protect the surface of injection molded products and improve the appearance quality, gloss, scratch resistance, durability, and weather resistance, a separate process is required after the molding of the parent product is completed. Surface treatment technologies such as plating, painting, deposition, and printing, which are commonly used post-processes, are not only greatly affected by the surface condition of the injection molded material and the manufacturing environment, but also increase the production cost and lead time, and there are always problems such as environmental problems due to hazardous substances and uneven coating thickness.

To reduce these problems, technologies such as in-mold decoration (IMD), in-mold labeling (IML), and film insert molding (FIM) have been introduced for a relatively long time, which integrate the injection molding and skin material by placing the skin material molded into the desired shape in advance during the injection molding process inside the mold. Although this reduces the number of process steps compared to post-processing, it also has the disadvantage of requiring separate processing of the skin material and being unable to reduce the coating thickness.

As a prior art requiring preparation of a skin material as described above, there may be mentioned "Method for manufacturing a panel by inserting and molding a film and a mold used in manufacturing the same" described in the following patent document (1). The invention of the above patent document (1) inserts a film (F) into a parting line (PL) formed by an upper mold (100) fixed to an upper platen of an injection molding machine and a lower mold (200) fixed to a lower platen, and a resin introduced through a nozzle and a sprue bush (110) of the injection molding machine is injected into the cavity space of the upper and lower cores accommodated in the upper and lower plates, and is taken out after a cooling process, thereby forming a panel. Unlike the present invention which can simultaneously implement injection molding and surface coating, there is an inconvenience in that the film must be prepared in advance.

Korean Patent Registration No. 10-0420631

Accordingly, the present invention is intended to solve the problems of the above-described prior art, and provides an in-mold coating mold and an in-mold coating method that enable injection molding and surface coating to be implemented simultaneously by injection-molding a thermoplastic resin, and injecting a liquid-state curable coating agent between a substrate and a mold and curing it within the mold before taking the molded product out of the mold.

In order to achieve the technical task described above, the in-mold coating mold for simultaneous injection molding and surface coating of the present invention comprises: a movable mold having a movable core in which a substrate is molded and a hardening coating material injection channel; a sliding plate having a substrate cavity and a coating cavity formed on a surface opposite to the movable mold so that the substrate cavity and the coating cavity can be selected and molded; and a fixed mold having a thermoplastic resin injection channel; a thermoplastic resin is injected into the substrate cavity through the thermoplastic resin injection channel and cooled; after the substrate of the thermoplastic resin is solidified, the fixed mold is separated from the movable mold; the fixed mold is slid using the sliding plate so that the fixed mold and the coating cavity face each other, and the movable mold to which the substrate is attached is closed, and the coating material is applied to the surface of the substrate and the coating material through the hardening coating material injection channel. It is characterized by being configured to form a coating layer on the substrate by injecting the coating material into the space between the cavities and curing it inside the mold.

In addition, the fixed-side mold is characterized in that a cooling channel is formed in the upper plate.

In addition, the fixed-side mold is characterized in that two pressure sensors are mounted in the curable coating material injection path portion.

In addition, the above-mentioned device is characterized in that a sealing edge is formed on each of the upper surface and both sides to prevent leakage of the coating material.

In addition, the movable side mold is characterized in that a core mold is installed.

In addition, it is characterized in that the mixing head is assembled at an angle of 3 to 7° with respect to the movable mold.

In addition, the injection path for the cured coating material is characterized by having a depth in the range of 04 to 10 mm.

In addition, the in-mold coating method for simultaneous injection molding and surface coating of the present invention comprises: a movable mold having a movable core in which a substrate is molded and a curable coating material injection path; and a sliding member formed on a surface facing the movable mold so that the substrate cavity and the coating cavity can be selected and molded.

A method for in-mold coating using an in-mold coating mold including a fixed mold having a plate and a thermoplastic resin injection channel, the method comprising: a cooling process of injecting resin into a substrate cavity through the thermoplastic resin injection channel and cooling it; a coating cavity moving process of separating the fixed mold from the movable mold after the thermoplastic resin substrate is solidified, slidingly moving the fixed mold, and closing the movable mold to which the substrate is attached; and a coating process of injecting a coating material into the space between the substrate surface and the fixed cavity through a curable coating material injection channel and curing the coating material inside the mold to form a coating layer on the substrate.

In addition, the curable coating material is composed of a polyol as a main agent and an isocyanate as a curing agent as a polyurethane, and is characterized in that the mixing ratio of the main agent and the curing agent is 100:130 to 100:180 in order to maintain the coating surface hardness at Shore A 80 or higher.

In addition, the present invention is characterized by further including a sealing edge forming process for forming a sealing edge on each of the upper surface and both sides of the above-described substrate to prevent leakage of the coating material.

In addition, the depth of the injection path for the cured coating material is characterized by being in the range of 04 to 10 mm.

The present invention having the above-described configuration enables a high production speed because a large quantity of products can be coated with uniform quality in a short lead time, and the coating thickness can be controlled so that the defect rate is low, and the transferability of the mold surface is excellent so that a fine shape can be reproduced, and provides the effect of making defects that appear on the appearance of an injection-molded product, such as weld lines or sink marks on a substrate, invisible.

In addition, since the present invention forms a coating film by a curing reaction, no volatile organic compounds (VOCs) are emitted during the molding process or thereafter, thereby reducing the environmental burden. In addition, since the coating material is attached to the product as a coating film, the generation of waste is also reduced.

Fig. 1 is a cross-sectional view showing a mold structure for injection molding of a substrate according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a mold structure for in-mold coating a substrate surface according to an embodiment of the present invention.
Figure 3 is a drawing showing two pressure sensors installed in the injection path of the curable coating material.
Figure 4 is a cross-sectional view showing the substrate and coating layer.
Figure 5 is a cross-sectional view showing the design variables of a curable coating material injection path, which is a coating material injection path.
Figure 6 is a drawing showing the shape of the flow front of a curable coating material according to the depth of the euro.
Figure 7 is a graph showing the injection pressure at the inlet required according to the change in depth of the euro.
Figure 8 is a drawing showing the shape of the flow front when the depth of the injection path is fixed at 0.6 mm and the width is changed.
Figure 9 is a drawing showing the change in injection pressure when the depth of the injection path is fixed at 0.6 mm and the width is changed.
Fig. 10 is a cross-sectional view showing the coating material injection path and the mold cavity block in section A-A' illustrated in Fig. 2.
Fig. 11 is a cross-sectional view showing section B-B' shown in Fig. 2.
Fig. 12 is a photograph showing (a) a fixed-side mold and (b) a movable-side mold as an in-mold coating mold of the present invention.
Figure 13 is a graph showing the nozzle pressure value measured at the nozzle of the mixing head according to the change in the total discharge flow rate.
Figure 14 is a drawing showing the flow pattern through a coating material non-forming experiment and the flow pattern result of a flow analysis with or without a sealing edge.
Figure 15 is a photograph showing a sample taken 15 seconds after coating material injection to determine the progress behavior of the coating material.
Figure 16 is a graph showing the amount of bubbles measured when the amount of coating material injected was changed while the discharge flow rates of polyol and isocyanate were fixed.
Figure 17 is a graph showing the total sum of bubble diameters generated on the surface according to the amount of coating material injected.
Figure 18 is a graph showing the results of measuring bubble size according to the total discharge flow rate while fixing the coating material injection amount.
Figure 19 is a photograph showing the change in surface appearance according to the discharge flow rate.
Figure 20 is a drawing showing the mixing head assembled on the movable side core mold.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings showing embodiments of the present invention.

In describing the present invention below, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

FIG. 1 is a cross-sectional view showing a mold structure for injection molding of a substrate, and FIG. 2 is a cross-sectional view showing a mold structure for in-mold coating a surface of a substrate. As shown in FIGS. 1 and 2, an in-mold coating mold (10) according to the present invention comprises a movable-side mold (200) having a movable-side core (160) in which a substrate (150) is molded and a hardened coating material injection path (145), a sliding plate (180) in which a substrate cavity (130) and a coating cavity (140) are formed on a surface facing the movable-side mold (200) and which slides, and a fixed-side mold (100) having a thermoplastic resin injection path (112), so that a thermoplastic resin is injected into the substrate cavity (130) through the thermoplastic resin injection path (112) and cooled, and the substrate (150) of the thermoplastic resin is After solidification, the fixed-side mold (100) is separated from the movable-side mold (200), the fixed-side mold (100) is slid using the sliding plate (180), so that the fixed-side mold (100) and the coating cavity (140) are faced each other, the movable-side mold (200) to which the substrate (150) is attached is closed, and the coating material is injected into the space between the substrate surface and the coating cavity (140) through the hardening coating material injection path (145), thereby hardening the coating material inside the mold to form a coating layer (135) on the substrate (150), thereby forming the substrate (150) and the coating layer (135) as one unit, so that injection molding and surface coating can be performed simultaneously.

In the fixed-side mold (100) above, a cooling channel (102) is formed in the upper plate (110), a cavity mold for substrate (130) and a cavity mold for coating (140) are attached to a sliding plate (180), and a hydraulic cylinder (170) is mounted for operating the sliding plate (180).

In addition, two pressure sensors (240) are mounted on the hardening coating material injection path (145) of the fixed-side mold (100) to measure the pressure inside the cavity due to the flow of the hardening coating material.

The substrate (150) molded by the mold described above is provided with sealing edges (120) molded on both sides of the upper surface and on both sides, which is to prevent leakage from occurring at the parting surface when the polyurethane coating material has a very low viscosity of 1/10,000 to 1/100,00 times that of a thermoplastic resin and is injected between the injection surface and the mold.

A core mold (160) is installed in the above movable mold (200).

In addition, as shown in Fig. 20, the mixing head (250), which is a curable coating material injector, is preferably assembled at an angle of 3 to 7° with respect to the movable side mold (200). Since the mixing head (250) for mixing two-component polyurethane is not a device mounted inside the injection molding machine, it must be attached inside the mold, and the mixing head (250) is assembled at an angle with respect to the movable side core mold (160) as described above so that the coating cavity (140) and the mixing head (250) can be completely in close contact.

The depth of the above-mentioned hardened coating material injection path (145) is in the range of 04 to 10 mm.

Next, the in-mold coating method including the injection molding process and the coating process of the present invention is an in-mold coating method using an in-mold coating mold (10) including a movable side mold (200) provided with a movable side core (160) in which a substrate (150) is molded and a hardening coating material injection channel (145), a sliding plate (180) in which a substrate cavity (130) and a coating cavity (140) are formed on a surface facing the movable side mold (200) and slide, and a fixed side mold (100) provided with a thermoplastic resin injection channel (112), the method comprising: a cooling process in which resin is injected into the substrate cavity (130) through the thermoplastic resin injection channel (112) and cooled; after the thermoplastic resin substrate (150) is solidified, the fixed side mold (100) is separated from the movable side mold (200); The process of moving the coating cavity (140) by sliding the fixed side mold (100) and closing the movable side mold (200) to which the substrate (150) is attached.

It consists of a process of injecting a coating material into the space between the surface of a substrate (150) and a fixed-side cavity through a hardening coating material injection path (145) and hardening the coating material inside a mold to form a coating layer (135) on the substrate (150).

In other words, the mold is opened while the first-injected substrate (150) is attached to the core (160) installed on the movable side, and the hydraulic cylinder (170) is operated to move the sliding plate (180) installed on the fixed side to combine the coating cavity (140) and the movable-side core mold (200) to which the substrate (150) is attached. Thereafter, a curable coating material is injected through the mixing head (250) installed on the lower part of the movable-side core mold (200) to coat the surface of the substrate.

The above-described in-mold coating method further includes a sealing edge forming process of forming a sealing edge (120) on both sides of the upper surface and both sides of the substrate (150) during the process of injecting the curable coating material.

In addition, the in-mold coating method is characterized in that the depth of the curable coating material injection path (145) is in the range of 04 to 10 mm.

The curable coating material used in the above coating process is composed of a subject and a curing agent, and in order to maintain the coating surface hardness at Shore A 80 or higher, it is preferable that the mixing ratio of the subject and the curing agent is 100:130 to 100:180.

The above-mentioned curable coating material preferably uses polyurethane, and since polyurethane has a very high viscosity when the temperature is low, the fluidity is not good and mixing is not done properly, and on the contrary, when the temperature is too high, molding becomes difficult due to curing. Therefore, a mixing head (250), which is equipment that evenly mixes the main agent and the curing agent at a certain ratio, is required in in-mold coating, because this can affect chemical reactions and physical properties and minimize bubble generation.

In addition, in order to remove air bubbles generated during the coating material mixing process, an overflow (115) area is installed at the top where the coating material is filled the latest. The overflow (115) controls the flow direction of the coating material and removes air bubbles.

The coating material passing through the coating material injection port connected to the discharge portion of the mixing head (250) must satisfy sequential and uniform flow, and it is important to design the flow path so that the coating material can flow over the surface of the injection material and push out air bubbles within the product surface to the overflow (115) area.

The above subject matter preferably uses polyol, and the above curing agent preferably uses isocyanate, but is not limited thereto.

In addition, since the polyurethane coating process is sensitive to maintaining an appropriate temperature, it is preferable that the heating channel in the fixed-side cavity (100) where the coating material comes into contact be installed closer to the product section than the heating channel in the movable-side core (200).

According to the in-mold coating mold (10) and the in-mold coating method according to the present invention described in detail above, a high production speed can be obtained because a large quantity of products can be coated with uniform quality in a short lead time, and the coating thickness can be controlled so that the defect rate is low, and the transferability of the mold surface is excellent so that a fine shape can be reproduced.

In addition, it makes it possible to hide defects that appear on the appearance of injection-molded products, such as weld lines or sink marks, and because it forms a coating film through a curing reaction, no volatile organic compounds (VOCs) are emitted during or after the molding process, which reduces the environmental burden. In addition, because the coating material is attached to the product as a coating film, it also has the effect of reducing the generation of waste.

Below, the present invention is described in detail based on examples. The presented examples are illustrative and are not intended to limit the scope of the present invention.

<Example 1> Mold design and manufacturing

The applicable model is a square plate measuring 70 mm x 70 mm, with a substrate (150) thickness of 14 mm and a coating layer (135) thickness of 02 mm.

Fig. 1 shows a mold structure for injection molding of a substrate, in which a cavity mold (130, 140) is installed on the fixed side and a core mold (160) is installed on the movable side. In addition, Fig. 2 shows a mold structure for in-mold coating the surface of a substrate, in which a substrate (150) is installed on the movable side.

While attached to the core (160) installed on the fixed side, the hydraulic cylinder (170) is operated to move the sliding plate (180) installed on the fixed side and combine the coating cavity (140) with the core (160). Then, the coating material is injected through the mixing head (250) and the coating layer (135) is formed on the surface of the substrate.

Figure 3 shows two pressure sensors (240) installed in the curable coating material injection path (145) to measure the pressure inside the cavity due to the flow of the curable coating material.

Fig. 4 is a cross-sectional view showing a substrate (150) and a coating layer (135), showing a thermoplastic resin substrate (150), a coating material injection path (145), and an overflow (115) region. In order to perform injection molding of the substrate, a direct gate (125) having a length of 110 mm was installed on the right side so as not to impede the flow of the coating material, and an overflow (115) region was installed at the top where the coating material is filled the latest to remove air bubbles.

The coating material injection path (145) was designed so that the coating material passing through the injection port to which the mixing head (250) is connected flows on the surface of the substrate while satisfying uniform flow, and the coating material flow analysis was performed using Sigmasoft while changing the depth (D) and width (W) of the coating material injection path (145) shown in Fig. 5. At this time, the viscosity of the coating material was 119 mPas and the flow rate was 377 g/s.

Fig. 6 shows the shape of the coating material flow front according to the depth of the flow path. When the flow path depth is small, the flow in the center is faster than that in the side, and when the depth is 0.6 mm or more, the flow in the center is rather slower. When the flow front of the coating material is not uniform, a problem may occur where bubbles cannot escape in the overflow (115) direction and become trapped in a specific area.

Figure 7 shows the injection pressure at the inlet according to the change in the flow depth. It was found that the injection pressure decreases rapidly as the flow depth increases, and that there is almost no pressure change when the flow depth is 0.6 mm or more.

Fig. 8 is a drawing showing the shape of the flow front while the depth of the injection channel is fixed at 0.6 mm and the width is changed, and Fig. 9 is a graph showing the result of the change in injection pressure while the depth of the injection channel is fixed at 0.6 mm and the width is changed. It was found that the width of the injection channel had little effect on the shape of the flow front, and that the injection pressure decreased as the width of the channel increased.

FIG. 10 shows the coating material injection channel (145) and the mold cavity block in the cross-section A-A?? illustrated in FIG. 4, and the injection channel with a depth of 06 mm and a width of 5 mm was designed by reflecting the flow analysis results. In addition, a sealing edge (120) with a base of 08 mm and a height of 05 mm was formed on the surface of the substrate to prevent the coating material from leaving the surface of the substrate while flowing along the injection channel. In addition, as in FIG. 11 illustrating the cross-section B-B?? illustrated in FIG. 4, a sealing edge (120) with a size of 02 mm was formed on the edge surface of the substrate to prevent leakage of the coating material at the parting surface. When the first injection molding is completed and the core mold (160) to which the substrate (150) is attached is combined with the coating cavity mold (140), the sealing edge (120) formed on the substrate (150) is deformed and designed to completely block any leakage of the coating material that may occur during the coating material injection process.

When the depth of the injection channel for the curable coating material was in the range of 0.4 to 10 mm, the shape of the flow front was most uniform and the coating quality was the best.

Fig. 12 shows a manufactured in-mold coating mold (10). It can be seen that a cavity mold for substrate (130) and a cavity mold for coating (140) are each attached to a sliding plate (180) installed on the fixed side, and a core mold (160) is installed on the movable side.

<Example 2> Injection molding and in-mold coating experiment

For the injection molding of the substrate, ABS resin (HF-380) produced by LG Chemical was used, which is a raw material produced by Votteler of Germany for the polyurethane coating. The main agent polyol (Polyol, Puriflow PU993) and the curing agent isocyanate (Isocyanate, Puriflow PU955) were used, and the mixing ratio of the main agent and the curing agent was 100:130. Since the viscosity of the main agent and the curing agent greatly decreases as the temperature increases, the temperature of the raw materials and the temperature of the coating cavity mold (140) were both kept constant at 80℃ in order to improve uniform mixing and fluidity. At this time, the viscosity of the polyol and the isocyanate were 120 mPas and 60 mPas, and the densities were 1,128 kg/cm3 and 1,180 kg/cm3, respectively.

For injection molding and in-mold coating experiments, a 160-ton injection molding machine (KM 160/750CX) and a two-component polyurethane supply device (RimStar Nano 4-4) manufactured by Krauss Maffei of Germany were used.

For the injection molding of the substrate, the process conditions of injection temperature 230 ℃, injection cavity mold temperature 50 ℃, injection speed 30 mm/sec, holding pressure size 70 MPa, and holding pressure holding time 11 sec were used. For the in-mold coating experiment, the polyol discharge flow rate was set in the range of 15 to 18 g/sec, the isocyanate discharge flow rate was set in the range of 20 to 23 g/sec, and the total discharge weight was varied between 20 and 35 g.

4. Experimental Results

4.1 Nozzle pressure

When a raw material having a viscosity [mPas] and density [kg/cm3] passes through a nozzle having a diameter [mm] at a mass flow rate [g/sec] inside a mixing head (250), the velocity of the raw material in the nozzle section is as shown in Equation (1).

(1)

Additionally, the pressure generated while passing through the nozzle is as shown in Equation (2).

(2)

In equation (2), ξ represents the resistance coefficient, which can be assumed as equation (3).

(3)

Here, Re is the Reynolds number, It is the same as .

In order to inject polyol and isocyanate into the mixing head (250), nozzles having diameters of 012 mm and 013 mm, respectively, were used. Using equation (2), the pressures generated when the polyol and isocyanate each pass through the nozzle according to the change in the total discharge flow rate were calculated, and the results were compared with the results measured by the pressure sensor installed in the nozzle of the mixing head (250) through an experiment under the same conditions. As shown in Fig. 13, the nozzle pressure is almost linearly proportional to the discharge flow rate, and it can be seen that the calculated and measured pressure values are in relatively good agreement. However, it was found that the difference between the measured and calculated values increased as the discharge flow rate decreased. This is because the mixing head (250) used in the experiment was designed to be used in the range of 5 to 50 g/sec, and therefore, when the set flow rate value is small, a difference occurs between the actual discharged flow rate and the measured pressure.

4.2 Flow Patterns

Flow analysis was performed for cases where the discharge flow rates of polyol and isocyanate were 16 g/sec and 21 g/sec, respectively, and the flow patterns were compared through a coating material non-molding experiment under the same conditions. As shown in Fig. 14, the predicted flow pattern was found to be in good agreement with the experiment.

Meanwhile, in the injection molding of thermoplastic resins, it is known that the late injected resin spreads from the flow front toward the solidified layer due to the fountain flow phenomenon and is located farther away from the inlet. In order to understand the progression behavior of the coating material, a specimen was taken out before curing occurred in all parts after the injection of the coating material was completed. Fig. 15 shows a test piece taken out 15 seconds after 32 g of the coating material was injected, indicating that the inner part was already cured, while the inlet side was hardly cured. The cured part indicates that the coating material was injected early and that the time for curing was sufficient, while the uncured part is because the coating material was injected late and that the curing time was insufficient. Therefore, unlike the injection molding of thermoplastic resins, it was found that the raw material injected early was located farther away from the inlet in the coating material flow. It was found that the coating material has a very low viscosity compared to thermoplastic resin, and because the temperature of the raw material and the mold are the same, a solidified layer is not formed on the wall surface, and thus the fountain flow phenomenon does not occur.

4.3 Bubbles

The coating material generates numerous bubbles during the mixing and flowing process, and it is important to allow these bubbles to escape to the overflow (115) area. The effect of the coating material injection amount on the bubbles generated on the product surface was examined, and a tool microscope (Sometech STV-C-2010) was used to measure the bubbles. Fig. 16 shows the bubbles measured when the injection amounts of the coating material were 20 g and 25 g, while the discharge flow rates of the polyol and isocyanate were fixed at 16 g/sec and 21 g/sec, respectively, enlarged five times. In addition, Fig. 17 shows the total diameter of the bubbles generated on the surface according to the injection amount, and it was found that the bubble size decreased as the injection amount increased. This is because the bubbles formed on the product surface are pushed out to the overflow (115) area as the injection amount increases.

Figure 18 shows the results of measuring bubble size according to the total discharge flow rate when the coating material injection amount is fixed at 30 g. As the discharge flow rate increases, the bubble size increases. The reason for this is that the faster the discharge flow rate, the more bubbles are generated and they cannot escape to the overflow (115) area.

4.4 Mixing characteristics

In the mixing head (250), polyol and isocyanate are mixed by collision as they are sprayed through the nozzle, respectively. In order to examine the effect of the discharge flow rate on the mixing characteristics, a coating experiment was performed while changing the total discharge flow rate, and the surface appearance was observed. Fig. 19 shows the change in the surface appearance according to the discharge flow rate. When the flow rate is small, it can be seen that the surface is not smooth due to uneven mixing of the main agent and the curing agent. As the flow rate increases, the surface condition becomes smoother, and it can be seen that complete mixing is achieved at a discharge flow rate of 41 g/sec. As shown in Fig. 14, a discharge flow rate of 41 g/sec matches the condition in which the polyol and isocyanate collide with each other at nozzle pressures of 187 bar and 197 bar, respectively. Therefore, it can be seen that the discharge flow rate is an important process condition for uniform mixing of the main agent and the curing agent in the mixing head (250). However, in general, due to the control performance limitations of the injection device, it is not possible to quickly set the discharge flow rate above a certain value, and in this case, it will be necessary to change the nozzle diameter to form a high pressure of at least 180 bar.

FIG. 20 is a drawing showing a state in which a mixing head (250) is assembled at an angle of 3 to 7° with respect to a movable core mold (160) so that the coating cavity (140) and the mixing head (250) can be completely sealed. Since the mixing head (250) is for mixing two-component polyurethane and is not equipment mounted inside an injection molding machine, it must be attached inside the mold (10).

5. Conclusion

An in-mold coating mold (10) having two cavities and one core was developed, and the following conclusions were derived through injection molding and coating experiments using two-component polyurethane.

(1) The nozzle pressure was almost linearly proportional to the discharge flow rate, and the pressure calculation results considering the resistance coefficient were in relatively good agreement with the measured results.

(2) The flow pattern of the coating material predicted by the analysis was in good agreement with the results of the non-molding experiment, and it was confirmed that the first injected coating material was located far from the inlet. From this, it was found that the fountain flow phenomenon did not occur in the coating material flow, and that the slip boundary condition on the mold wall should be used in the flow analysis.

(3) As the injection amount increased, the bubble size decreased, and as the discharge flow rate increased, bubble generation increased and the bubble size increased.

(4) As the flow rate decreased, an uneven surface appeared due to uneven mixing of the subject and the hardener. A nozzle pressure of 180 bar or more was required for uniform mixing, and it was found that it was necessary to change the nozzle diameter as well as the discharge flow rate for this purpose.

10: In-mold coating mold 100: Fixed side mold
102: Cooling channel 110: Top plate
112: Thermoplastic resin injection path 115: Overflow
120: Sealing Edge 125: Gate
130: Cavity for substrate 135: Coating layer
140: Cavity for coating 145: Injection path for curable coating material
150: Base 160: Core
170: Hydraulic cylinder 180: Sliding plate
200: Movable side mold 210: Lower plate
220: Eject 230: Eject Plate
240: Pressure sensor 250: Mixing head

Claims (1)

The method comprises: a movable mold having a movable core in which a substrate is formed and a curable coating material injection channel; a sliding plate having a substrate cavity and a coating cavity formed on a surface opposite to the movable mold so that the substrate cavity and the coating cavity can be selected and molded; and a fixed mold having a thermoplastic resin injection channel; wherein a thermoplastic resin is injected into the substrate cavity through the thermoplastic resin injection channel and cooled, and after the substrate of the thermoplastic resin is solidified, the fixed mold is separated from the movable mold, the fixed mold is slid using the sliding plate so that the fixed mold and the coating cavity face each other, and after the movable mold to which the substrate is attached is closed, a coating material is injected into the space between the substrate surface and the coating cavity through the curable coating material injection channel so that the coating material is cured within the mold to form a coating layer on the substrate, and the substrate is configured to have both sides of the upper surface and the An in-mold coating mold for simultaneous injection molding and surface coating, characterized in that a sealing edge is formed on each side to prevent leakage of the coating material.