KR102182425B1 - Mixing head for in-mold coating based on two-component polyurethane with a high difference in mixing ratio - Google Patents

Abstract

The present invention relates to a mixing head for use in an in-mold coating process for carrying out surface coating in a mold by using polyurethane. Particularly, the mixing head is for mixing a two-part polyurethane having a high difference in mixing ratio homogeneously in an in-mold coating process, and includes: a cleaning cylinder; a cleaning piston which has a piston head portion operated in the cleaning cylinder and a piston pin connected to the piston head portion and operated in a mixing hole; a mixing block having the mixing hole at the center thereof and including three material distributers formed outwardly and radially; and an introduction nozzle provided in each of the material distributers, and connected to the mixing hole at the end thereof for spraying a main ingredient or curing agent toward the mixing hole. When the main ingredient and the curing agent show a high difference in mixing ratio, the mixing head provided with three nozzles accomplishes homogeneous mixing of the main ingredient with the curing agent under a low nozzle pressure.

Description

Mixing head for in-mold coating applied with two-component polyurethane with a large difference in mixing ratio {MIXING HEAD FOR IN-MOLD COATING BASED ON TWO-COMPONENT POLYURETHANE WITH A HIGH DIFFERENCE IN MIXING RATIO}

The present invention relates to a mixing head used in an in-mold coating process to implement surface coating in a mold using polyurethane, and more particularly, to uniformly prepare a two-component polyurethane having a large difference in mixing ratio in the in-mold coating process. It relates to a mixing head for mixing.

Thermoplastic injection molding products are used in a wide variety of fields such as automobiles, home appliances, and displays. However, in many molded products, a separate coating process is required to increase durability and weather resistance or to improve paint adhesion.

In this process, various problems arise such as environmental pollution due to the use of volatile solvents, non-uniform coating thickness, and increase in manufacturing cost due to post-processing. In-mold coating is a new coating method in which a thermoplastic resin is injection-molded, and then a liquid curable coating material is injected into the mold, and a pressure of several MPa is maintained to cure it in a compressed state.

The material used in in-mold coating does not contain volatile organic solvents and is eco-friendly because it does not emit any organic compounds during the process, and it is advantageous for thick coating because the injected coating material adheres to the surfaces of both molded products. It has the advantage of getting

The transferability of the mold surface is excellent so that a fine shape can be reproduced, and when a glass fiber reinforced resin is applied, a surface condition similar to that of a resin molded article without fibers can be realized. In addition, it is possible to prevent molding defects such as weld lines and sink marks from appearing on the coating surface. In recent years, in order to realize high gloss and scratch resistance on the surface of a thermoplastic substrate, in-mold coating technology applied with polyurethane is being applied in advanced automobile fields in Europe. Polyurethane has very good transparency, gloss, durability, and resilience, and has a great advantage that mass production is possible.

Polyurethane has a very high viscosity when the temperature is low, so it has poor fluidity and is not properly mixed. On the contrary, when the temperature is too high, molding becomes difficult due to hardening. Therefore, in order to facilitate the mixing of the main material and the hardener and the discharging of the mixed raw material, it is necessary to keep the temperature of each tank and the moving pipeline constant, and the mixed material remaining in the mixing head after discharging into the mold is completed. Raw materials must be completely removed.

Referring to Figures 1a and 1b, looking at the manufacturing mixing and injection process of a general polyurethane, a liquid polyol is accommodated in one tank, and a liquid isocyanate is accommodated in another tank. When the feed pump connected to the (polyol) storage tank and the isocyanate storage tank is operated, the polyol stock solution and the isocyanate solution are transferred to the mixing head through each supply pipe.

In general, the mixing head has an L-shaped structure, and the existing mixing head consists of two nozzles. The polyol and isocyanate solution transferred to the mixing head collide with each other in the mixing head to generate turbulent flow, are mixed with each other by kinetic energy, and injected into the mold having a predetermined shape for primary injection molding. The surface of the substrate is coated in the mold.

The viscosity of the raw material used varies according to the surface characteristics required by the applied product, and the mixing ratio of polyol and isocyanate is greatly different. In particular, as in the case of hard coating, the higher the hardness is required, the higher the mixing ratio of isocyanate is compared to polyol. At this time, the mixing head having two nozzles has a problem in that it is difficult to uniformly mix polyol and isocyanate, and a high nozzle pressure must be generated for mixing.

As described above, as a prior art for achieving uniform mixing of polyol and isocyanate, the “mixing head with improved mixing ability and its discharging device” described in Patent Document (1) below may be mentioned. have. The invention of the patent document (1) is installed in a state in which the central axis of the through flow path can coincide with the central axis of the discharge flow path, and a controller to control the actuator is installed, and the controller is installed before the cleaning piston moves forward. By rotating the rotating body, the central axis of the through flow path is matched with the center axis of the discharge flow path. In the mixing head, a separate rotating body, a driver and a controller for driving it must be separately installed, and there is a disadvantage that an additional rotating space is required.

Korean Patent Registration No. 10-1353564

Therefore, the present invention was conceived to solve the conventional problems as described above, and according to an embodiment of the present invention, the mixing ratio of isocyanate compared to polyol, as in the case of hard coating requiring high hardness It is an object of the present invention to provide a mixing head structure capable of uniformly mixing polyol and isocyanate at low nozzle pressure when this is very large.

Meanwhile, the technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems that are not mentioned are clearly to those of ordinary skill in the technical field to which the present invention belongs from the following description. It will be understandable.

An object of the present invention is a mixing head for uniformly mixing a two-component polyurethane having a large difference in mixing ratio in an in-mold coating process, comprising: a cleaning cylinder; A cleaning piston having a piston head driven in the cleaning cylinder and a piston pin connected to the piston head and driven in a mixing hole; A mixing block having the mixing hole formed in the center and having three raw material distributors radially outward; And an inlet nozzle provided in each of the raw material distributors and having an end connected to the mixing hole to inject a main material or a curing agent toward the mixing hole; including, when the mixing ratio difference between the main material and the curing agent is large, three nozzles are provided. Thus, it can be achieved as a mixing head for in-mold coating applied with a two-component polyurethane having a large difference in mixing ratio, characterized by uniformly mixing the main material and the curing agent at a low nozzle pressure.

And the subject is polyol, the curing agent is isocyanate, the seal plate is installed between the cleaning cylinder and the cleaning piston to prevent leakage of liquid; may further include a.

In addition, a circulation channel is formed in the longitudinal direction on one side of the outer surface of the piston pin, and discharge holes are formed in each of the raw material distributors. When the raw material is not discharged, the raw material introduced through the inlet nozzle passes through the circulation channel and passes through the discharge hole. It may be characterized by being circulated through.

And when the ratio of polyol and isocyanate is 100:200, the polyol supplied through the input unit is injected into the mixing hole through one specific inlet nozzle, and the isocyanate is injected into the mixing hole through two inlet nozzles other than the specific inlet nozzle. Thus, it may be characterized in that the raw materials injected from the three inlet nozzles collide with each other at the center of the mixing hole and are mixed.

According to the mixing head having three nozzles according to the embodiment of the present invention, the advantage of being able to uniformly mix polyol and isocyanate when the mixing ratio difference between polyol and isocyanate is large. Have.

In addition, according to the mixing head having three nozzles according to the embodiment of the present invention, since polyol and isocyanate can be uniformly mixed at a low nozzle pressure of 100 bar or less, coating from the storage tank to the mixing head There is an advantage of reducing cost because a device for supplying materials can be built for low pressure.

On the other hand, the effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those of ordinary skill in the art from the following description. I will be able to.

The following drawings attached to the present specification illustrate a preferred embodiment of the present invention, and serve to further understand the technical idea of the present invention together with the detailed description of the present invention, so the present invention is limited to the matters described in such drawings. It is limited and should not be interpreted.
1A is a view showing a two-component polyurethane supply system,
1B is a view showing an operation step of the mixing head shown in FIG. 1A;
Figure 2 is a mixing head model in the case of having two nozzles (a) and three nozzles (b),
3 is a view showing the main design parameters of the mixing head,
4 is a graph of the mixing ratio of the polyol at the nozzle pressure and the outlet according to the nozzle diameter change,
5 is a polyol mixing ratio distribution (a) at the outlet for two nozzles each having a nozzle diameter of 0.17 mm and 0.21 mm, and a polyol at the outlet for three nozzles having both nozzle diameters of 0.17 mm. A diagram showing the mixing ratio distribution (b) of,
6 is a view showing the velocity vector (a) of polyol and isocyanate at the outlet when having two nozzles and the velocity vector (b) of polyol and isocyanate at the outlet when having three nozzles;
7 is a longitudinal cross-sectional view of a mixing head having three nozzles according to an embodiment of the present invention;
8 is a perspective view of a mixing head having three nozzles according to an embodiment of the present invention,
9 is a cross-sectional view illustrating an area (length perpendicular direction) in which three nozzles are mounted in a mixing head according to an embodiment of the present invention.

The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments related to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed contents may be thorough and complete, and the spirit of the present invention may be sufficiently conveyed to those skilled in the art.

In the present specification, when a component is referred to as being on another component, it means that it may be formed directly on the other component or that a third component may be interposed between them. In addition, in the drawings, the thickness of the components is exaggerated for effective description of the technical content.

Embodiments described herein will be described with reference to cross-sectional views and/or plan views, which are ideal exemplary views of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for effective description of technical content. Accordingly, the shape of the exemplary diagram may be modified by manufacturing technology and/or tolerance. Accordingly, embodiments of the present invention are not limited to the specific form shown, but also include a change in form generated according to the manufacturing process. For example, an area shown at a right angle may be rounded or may have a shape having a predetermined curvature. Accordingly, the regions illustrated in the drawings have properties, and the shapes of the regions illustrated in the drawings are intended to illustrate a specific shape of a device region and are not intended to limit the scope of the invention. In various embodiments of the present specification, terms such as first and second are used to describe various elements, but these elements should not be limited by these terms. These terms are only used to distinguish one component from another component. The embodiments described and illustrated herein also include complementary embodiments thereof.

The terms used in the present specification are for describing exemplary embodiments and are not intended to limit the present invention. In this specification, the singular form also includes the plural form unless specifically stated in the phrase. As used in the specification, "comprises" and/or "comprising" does not exclude the presence or addition of one or more other elements.

In describing the specific embodiments below, a number of specific contents have been prepared to explain the invention in more detail and to aid understanding. However, readers who have knowledge in this field to the extent that they can understand the present invention can recognize that it can be used without these various specific contents. In some cases, it is mentioned in advance that parts that are commonly known in describing the invention and are not largely related to the invention are not described in order to prevent confusion without any reason in describing the invention.

As shown in FIG. 1A, in a general polyurethane manufacturing and mixing process, a liquid polyol is accommodated in one tank, and a liquid isocyanate is accommodated in another tank, and the polyol ( When the feed pump connected between the polyol) storage tank and the isocyanate storage tank is operated, the polyol stock solution and the isocyanate solution are transferred to the dynamic mixing head through each supply pipe.

1B shows the operating state of the L-shaped mixing head. When the coating agent is not discharged, both the cleaning piston and the mixing chamber piston are in the advanced state as shown in (a). Polyol as the main material and isocyanate as the hardener are circulated back to the tank through the feed pump and the high pressure pump from the stock solution storage tank, passing through the nozzle of the mixing head through the pipeline.

In particular, each raw material passes through the recirculation groove in the plunger of the mixing chamber piston, so that a high pressure of about 180 bar can be formed. When receiving the coating agent discharge signal, the cleaning piston moves backward as shown in (b) of Fig. 1b, and then the mixing chamber piston moves backward as shown in Fig. (c), and each nozzle is opened, and the main material and hardener enter the mixing chamber through the nozzle. They are sprayed and collide with each other. At this time, the raw materials mixed with each other by the collision energy are injected into the mold through the outlet. Thereafter, the mixing chamber piston moves forward and seals the nozzles of the main material and the hardener so that the raw material is not discharged anymore, and the cleaning piston moves forward and pushes out the raw material remaining in the discharge part.

In the embodiment of the present invention, a mixing head having 3 nozzles was applied, and flow analysis was applied to analyze the mixing characteristics of polyol and isocyanate.

ANSYS-CFX was used for flow analysis, and the k-ε turbulence model was applied.

FIG. 2 shows analysis models for the case where the number of nozzles is two (a) and three cases (b), respectively. The viscosity of the subject and curing agent applied to the analysis was the same as 230 mPa·s, and the mixing ratio of polyol and isocyanate was set to 100:200 required for hard coating.

3 shows the main design parameters of the mixing head. As shown in FIG. 3, the diameter of the mixing chamber (DM) and the diameter of the cleaning cylinder (DC) are 3.5 mm and 5 mm, respectively, and the length of the mixing chamber (LM) and the length of the cleaning cylinder (LC) are 8.5 mm, respectively. And 11mm, and an analysis model was constructed.

4 is a result of predicting the nozzle pressure and the mixing ratio at the outlet according to the nozzle diameter change. In the case of two or three nozzles, as the nozzle diameter increases, the nozzle pressure decreases almost linearly, and it can be seen that when the nozzle diameter is 0.15mm or more, the nozzle pressure decreases to 170bar or less.

On the other hand, it can be seen that the volume ratio occupied by the polyol at the exit cross-section varies greatly depending on the number of nozzles. In the case of two nozzles, as the nozzle diameter increases, the volume ratio of the polyol is larger than 0.5, indicating that the mixing is becoming non-uniform. However, in the case of three nozzles, it can be seen that the polyol volume ratio is maintained at almost 0.5 depending on the nozzle diameter.

5 is a polyol mixing ratio distribution (a) at the outlet for two nozzles each having a nozzle diameter of 0.17 mm and 0.21 mm, and a polyol at the outlet for three nozzles having both nozzle diameters of 0.17 mm. The mixing ratio distribution (b) of is shown. As shown in FIG. 5, when there are three nozzles, it can be seen that uniform mixing can be implemented even at a low pressure of 0.17 mm in diameter and 100 bar or less of nozzle pressure.

FIG. 6 shows the velocity vectors (a) of polyol and isocyanate at the outlet when having two nozzles and the velocity vectors (b) of polyol and isocyanate at the outlet when having three nozzles. As shown in FIG. 6, when there are two nozzles, the collision position between the main material and the hardener is eccentric, and the mixing becomes uneven when the nozzle pressure is low. On the other hand, in the case of three nozzles, it can be seen that uniform mixing can be achieved even at low nozzle pressure because the main material and the hardener collide in the center.

In summary, in the case of two nozzles, the mixing becomes uneven as the nozzle diameter increases, but in the case of three nozzles, the nozzle diameter is large, and even when the nozzle pressure is less than 100 bar, uniform mixing can be implemented.

Hereinafter, a configuration of a mixing head for in-mold coating applied with a two-component polyurethane having a large difference in mixing ratio according to an embodiment of the present invention will be described. 7 is a longitudinal cross-sectional view of a mixing head having three nozzles according to an embodiment of the present invention.

7, the mixing head according to the embodiment of the present invention is composed of a mixing block (1), a cleaning cylinder (3), a cleaning piston (4), a cleaning cylinder (3) and the cleaning piston (4) ), it can be seen that it is configured to prevent leakage of liquid by installing the seal plate 2 between them. In addition, it may be configured to include a dummy sensor 5 and a guide pin 6.

When the nozzle 7 is installed at the location of the cleaning piston 4 and the material is not discharged, the material continuously circulates through the groove-shaped circulation channel 9. The nozzle 7 is installed in the raw material distributor 8.

The mixing head for in-mold coating applied with a two-component polyurethane having a large difference in mixing ratio according to an embodiment of the present invention is connected to a cleaning cylinder 3, a piston head driven in the cleaning cylinder 3, and a piston head. A cleaning piston (4) having a piston pin driven in the mixing hole, a mixing hole formed in the center, and a mixing block (1) having three raw material distributors (8) radially outward, and a raw material distributor (8) Including an inlet nozzle (7) provided in each of the ends and connected to the mixing hole to spray the main material or the curing agent toward the mixing hole; including, when the mixing ratio difference between the main material and the curing agent is large, three nozzles are provided to lower the nozzle pressure It is characterized by uniformly mixing the main material and the hardener.

The subject according to an embodiment of the present invention is a polyol, and the curing agent may be composed of isocyanate.

Further, it may be configured to include a seal plate 2 installed between the cleaning cylinder 3 and the cleaning piston 4 to prevent leakage of liquid.

In addition, a circulation channel 9 is formed in the longitudinal direction on one side of the outer surface of the piston pin, and discharge holes are formed in each of the raw material distributors. When the raw material is not discharged, the raw material introduced through the inlet nozzle 7 is the circulation channel 9 ) And is configured to circulate through the discharge hole.

8 is a perspective view of a mixing head having three nozzles according to an embodiment of the present invention. It can be seen that the mixing head having three nozzles 7 is assembled together with the mixing block 1, the cleaning cylinder 3, the cleaning piston 4, and the raw material distributor 8.

9 is a cross-sectional view of a region in which three nozzles are mounted in a mixing head according to an embodiment of the present invention. When the ratio of polyol and isocyanate is 100:200, the polyol supplied through the input unit 10 is sprayed through one nozzle 7 and the isocyanate is sprayed through two nozzles 7. Eventually, the raw materials sprayed from the three nozzles collide with each other at the center and are mixed.

In addition, the above-described apparatus and method are not limitedly applicable to the configuration and method of the above-described embodiments, but all or part of each of the embodiments may be selectively combined so that various modifications can be made to the embodiments. It can also be configured.

1: mixing block
2: thread plate
3: cleaning cylinder
4: cleaning piston
5: dummy sensor
6: guide pin
7: nozzle
8: raw material distributor
9: circulation channel
10: input

Claims (4)

As a mixing head for uniformly mixing two-component polyurethane with a large difference in mixing ratio in the in-mold coating process,
Cleaning cylinder;
A cleaning piston having a piston head driven in the cleaning cylinder and a piston pin connected to the piston head and driven in a mixing hole;
A mixing block having the mixing hole formed in the center and having three raw material distributors radially outward; And
An inlet nozzle provided in each of the raw material distributors and having an end connected to the mixing hole to inject a main material or a curing agent toward the mixing hole;
Including; a seal plate installed between the cleaning cylinder and the cleaning piston to prevent leakage of liquid
When the difference in the mixing ratio between the main material and the curing agent is large, three nozzles are provided to uniformly mix the main material and the curing agent at low nozzle pressure, the main material is polyol, and the curing agent is isocyanate,
A circulation channel is formed in the longitudinal direction on one side of the outer surface of the piston pin, and a discharge hole is formed in each of the raw material distributors. When raw material is not discharged, the raw material introduced through the inlet nozzle passes through the circulation channel through the discharge hole. Cycle,
When the ratio of polyol and isocyanate is 100:200, the polyol supplied through the input unit is injected into the mixing hole through one specific inlet nozzle, and the isocyanate is injected into the mixing hole through two inlet nozzles other than the specific inlet nozzle. , Mixing head for in-mold coating applied with two-component polyurethane having a large difference in mixing ratio, characterized in that each raw material sprayed from the three inlet nozzles collides with each other at the center of the mixing hole.



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