JP4120088B2 - RIM polyurethane molding method and polyurethane molded article - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for RIM molding (reaction injection molding) of a molded product having a shell-like surface portion with a polyurethane material, and the molded product.
[0002]
[Prior art and problems to be solved by the invention]
(1-1) The applicant of the present application previously proposed a RIM polyurethane two-color molding method as described below (JP-A-6-143340).
(1) Depressurize the mold cavity.
(2) The surface polyurethane material is injected from the gate into the cavity under reduced pressure. The injected polyurethane material for the surface portion foams under reduced pressure and flows in the cavity, and the bubbles are broken and adhere to the cavity surface almost in the form of a thin film, forming a dense surface portion with almost no bubbles. The
(3) An internal polyurethane material is injected into the cavity under reduced pressure from the gate. The injected internal polyurethane material flows and fills the cavities and reacts and cures to form the interior of the two-color molded product.
[0003]
By this two-color molding method, a two-color molded product having a surface portion and an inside can be easily molded by RIM polyurethane, but the surface portion polyurethane material adhered to the cavity surface in the above step (2) When the polyurethane material for internal use in the above step (3) is injected while the fluid is still fluid, the polyurethane material for the surface portion adhering to the portion near the gate on the cavity surface is caused by the polyurethane material for internal use. As a result, the surface part of the same part is thinned, and there is a problem that the inside can be seen through this, or the property of the same part is deteriorated.
[0004]
(1-2) In blow molding, a parison having a constant wall thickness is generally extruded, and the parison is expanded in a mold to obtain a predetermined molded product shape. However, when blow-molding a molded product with a different external shape depending on the part, since the bulge of the parison and the change in the wall thickness differ depending on the part, the thickness of the final molded product also varies depending on the part. The uneven thickness may be a problem. 11A shows an example in which the thickness of the portion 101 having a small outer shape (65 mm) is 4 mm and the thickness of the portion 102 having a large outer shape (90 mm) is 2.5 mm. .
[0005]
Currently, this problem is dealt with by increasing the thickness of the parison corresponding to the large outer portion, but there are restrictions due to the shape and dimensions of the molded product and the parison extrusion die. When the difference from the large portion is very large, or when the inner diameter of the parison corresponding to the small outer portion is small, it is very difficult to make the wall thickness substantially uniform. In the case of the latter, in the example shown in FIG. 11B, when the outer shape of the parison 104 extruded from the parison extruder 103 is A and the wall thickness of the parison 104 corresponding to the small portion of the outer shape is B, the outer shape The wall thickness of the parison 104 corresponding to the large portion of the area needs to be larger than B, but the upper limit is A / 2, and when the wall thickness larger than A / 2 is required, the parison cannot be formed. Therefore, naturally it is impossible to make the thickness of the molded product uniform.
[0006]
(1-3) When forming a skin by rotating a mold by slush molding, the molding equipment needs to have a mold rotation mechanism, so the equipment is enlarged, the area of exclusive use is increased, a protective cover is installed, etc. There were various problems such as a decrease in workability, an increase in cycle time, an increase in equipment and maintenance costs, and an increase in the cost of molded products.
[0007]
(2) Generally, when a foamed molded product is molded by RIM polyurethane molding with foaming, the foamed molded product becomes a rebound elastic body due to the presence of substantially uniform and fine bubbles (diameter of 10 μm to several mm). The main feeling is that it will be restored immediately when it is pushed in and then released. For example, in the case of a polyurethane coating of a steering wheel for an automobile, the elasticity is adjusted to an appropriate tone desired by an average user.
[0008]
However, depending on the use of the foam molded article, a new tactile sensation other than the elasticity may be required, and the conventional RIM polyurethane foam molding method and polyurethane foam molded article cannot provide such a new tactile sensation. .
[0009]
(3) According to the RIM polyurethane two-color molding method described in the above section (1-1) (Japanese Patent Laid-Open No. 6-143340), the internal polyurethane material has a composition that does not easily foam or a composition that easily foams. Thus, it is possible to change the internal foaming rate in a wide range. However, in that case, it is necessary to prepare the polyurethane material for the surface portion and the polyurethane material for the interior having different compositions separately, and complicated and expensive equipment such as a four to six component mixing head is also required. Further, as described above, there is also a problem that the surface portion near the gate is thinned.
On the other hand, in the conventional method of forming a foam-free surface portion and a foamed interior by RIM polyurethane molding using a single composition polyurethane material, a uniform thickness and a high specific gravity of 0.3 or less It was not possible to obtain a foamed molded product combined with the foamed interior.
[0010]
Therefore, the first object of the present invention is to solve the problems described in the above items (1-1) to (1-3), and to provide a molded product having a shell-like surface portion having a substantially uniform thickness. The purpose is to form the product at a low cost with simple and small equipment, without almost any restrictions due to the shape and dimensions of the molded product.
The second object of the present invention is to solve the problem described in the above item (2), and has a shell-like surface portion having a substantially uniform wall thickness, and a new tactile sensation other than a feeling of elasticity, specifically, The object is to obtain a molded product having a soft texture that slowly restores when pressed and released.
The third object of the present invention is to solve the problem described in the above item (3), and by using a polyurethane material having a single composition, a surface portion having a substantially uniform wall thickness and a high foaming with a specific gravity of 0.3 or less. The object is to obtain a foam molded product combined with the interior.
[0011]
[Means for Solving the Problems]
[0012]
In order to achieve the first object, the following means [1-1] and reference means [1-2] were employed.
[1-1] Depressurizing the mold cavity;
Injecting the surface portion polyurethane material into the cavity under reduced pressure, foaming the surface portion polyurethane material and flowing into the cavity;
Releasing the vacuum of the cavity and releasing it to atmospheric pressure before the surface polyurethane material starts to cure, defoaming the surface polyurethane material by shrinkage of the foam, and attaching to the cavity surface;
Curing the surface portion polyurethane material to form a shell-shaped surface portion.
[0013]
After forming the surface portion, it is possible to include a step of injecting an internal material into the cavity and forming the inside inside the surface portion.
[0014]
[1-2] A polyurethane molded article having a shell-like surface portion formed by foaming the surface portion polyurethane material once under reduced pressure and then defoaming by releasing to the atmospheric pressure by releasing the reduced pressure.
[0015]
As an aspect inside a surface part, the aspect which is hollow and the aspect provided with the inside formed with the polyurethane material for an inside can be illustrated.
[0016]
In order to achieve the second object, the following means [2-1] and [2-2] were adopted.
[2-1] Depressurizing the mold cavity;
Injecting polyurethane material into the cavity under reduced pressure, foaming the polyurethane material and flowing into the cavity;
In the course of curing from the start of the polyurethane material to completion, the vacuum of the cavity is released or relaxed, and a part of the polyurethane material is defoamed by shrinkage of the foam to adhere to the cavity surface. Making the remainder of the material continuous in a string or band form with respect to the part; and
Forming a shell-shaped surface portion by completing the partial curing, and forming a bridge portion inside the surface portion by completing the curing of the remaining portion.
[0017]
[2-2] The polyurethane material is once foamed under reduced pressure and then defoamed by release or relaxation of the reduced pressure. The shell-like surface portion is connected to the inside of the surface portion in a string or band shape. Polyurethane molded product with a bridge.
[0018]
In order to achieve the third object, the following reference means [3-1] and [3-2] were employed.
[3-1] A step of cooling the mold to a temperature at which reaction hardening of the polyurethane material is delayed and depressurizing the cavity of the mold;
Polyurethane material is injected into the cavity under cooling and reduced pressure, the polyurethane material is foamed to flow through the cavity, a part of the polyurethane material is defoamed due to excessive expansion of bubbles, and adhered to the cavity surface, Delaying the polyurethane reaction by letting the mold under cooling take heat and making the remainder of the polyurethane material highly foamed;
Curing the part to form a shell-shaped surface portion, and curing the remaining portion to form a sponge-like interior having a specific gravity of 0.3 or less inside the surface portion.
[0019]
[3-2] Specific surface density formed by the same polyurethane material on the inner side of the shell-shaped surface portion formed by foaming the polyurethane material once under reduced pressure and then defoaming by excessive expansion of the foam A polyurethane molded product having a sponge-like interior of 0.3 or less.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention embodied in RIM polyurethane molding of a steering wheel polyurethane coating will be described below with reference to FIGS.
First, as shown in FIGS. 1 to 6, the molding apparatus used in the present embodiment is composed of a molding die 1, a vacuum box 11, a material injection mechanism 21, and the like, which will be described in detail in order. .
[0021]
The molding die 1 is divided into an upper die 2 and a lower die 3. On the mold dividing surfaces 2a and 3a of the upper mold 2 and the lower mold 3, a cavity surface 5 that forms a ring-shaped cavity 4 when the mold is closed and a gate 6 to the cavity 4 are formed. A vent hole 7 is formed at the final filling position of the polyurethane material in the upper mold 2.
[0022]
Next, the vacuum box 11 is divided into an upper box 12 and a lower box 13. The upper mold 2 is attached to the upper box 12, and the lower mold 3 is attached to the lower box 13. The upper box 12 and the lower box 13 are attached to a mold clamping device (not shown). In this embodiment, the upper box 12 and the lower box 13 are opened and closed, and the upper mold 2 and the lower mold 3 are moved by raising and lowering the lower box 13. Opening and closing is performed at the same time. An O-ring 14 is attached to the groove formed on the dividing surface of the upper box 12, and when the vacuum box 11 is closed, the O-ring 14 comes into contact with the dividing surface of the lower box 13 and the upper box 12, the lower box 13, Seal between.
[0023]
A suction plug 15 is attached to the lower box 13, and a vacuum pump 18 is connected to the suction plug 15 via a suction hose 16 and a valve 17. The lower box 13 is provided with a see-through window 19 through which the vicinity of the vent hole 7 can be viewed from the outside of the vacuum box 11 so as to keep airtightness.
[0024]
The material injection mechanism 21 includes a three-component mixing head 22 as shown in FIG. 5, and can mix a polyol component and an isocyanate component as main components with a third component as a secondary component. The three-component mixing head 22 includes a cylinder 23 and a body 24 attached to the tip of the cylinder 23. The body 24 has a thin injection nozzle 25 at the tip.
[0025]
A through hole 26 is formed in the center of the body 24, and a spool 28 attached to a piston (not shown) of the cylinder 23 is slidably inserted into the through hole 26. A pair of long grooves 29 extending in the longitudinal direction are provided at positions opposite to the outer periphery of the spool 28 by 180 degrees. As the piston 27 reciprocates, the spool 28 slides between a forward position indicated by a two-dot chain line in FIG. 5 and a backward position indicated by a solid line, and the tip of the retracted spool 28 serves as a mixing chamber 30 for each component described later.
[0026]
In the left and right interiors of the body 24, a nozzle body 31 for a polyol component and a nozzle body 32 for an isocyanate component having a cylindrical shape are provided opposite to each other. Each nozzle body 31, 32 is formed with a tapered orifice 35 that opens into the mixing chamber 30 or the long groove 29. A holder (not shown) that holds the nozzle bodies 31 and 32 is mounted on the outer surface of the body 24, and the tip of the needle 37 inserted through the holder 24 adjusts the opening degree of the orifice 35. Also, a reflux hole 38 for polyol component and a reflux hole 39 for isocyanate component are formed adjacent to the nozzle bodies 31 and 32 of the body 24, both of which are open to the long groove 29.
[0027]
A polyol component tank 41b and a pump 41c are connected to the nozzle body 31 and the reflux hole 38 by a hose 41a, and the polyol component circulation of the tank 41b → the pump 41c → the nozzle body 31 → the long groove 29 → the reflux hole 38 → the tank 41b. A road is formed. The isocyanate component tank 42b and the pump 42c are also connected to the nozzle body 32 and the reflux hole 39 by the hose 42a, and the isocyanate component circulation of the tank 42b → the pump 42c → the nozzle body 32 → the long groove 29 → the reflux hole 39 → the tank 42b. A road is formed.
[0028]
A third component sub-ejection hole 52 is provided at the center of the spool 28. The front end of the sub-ejection hole 52 opens to the front end surface of the spool 28, and the rear end opens to the outer periphery of the middle portion of the spool 28. In the rear portion of the body 24, an introduction hole 53 that communicates with the rear end opening of the auxiliary discharge hole 52 only when the spool 28 is retracted is formed. A third component tank 43b is connected to the introduction hole 53 via a hose 43a through a flow rate adjusting device 43d and a valve 43c, and the inside of the tank 43b is constantly pressurized by an air pressurizing device 43e. The valve 43c may be provided at any location from the tank 43b to the body 24, and may be provided between the tank 43b and the air pressurizing device 43e. The driving method of the valve 43c is not limited, and may be, for example, an air type or an electric type. The valve 43c is controlled to be opened and closed by a dedicated timer, a sequence internal timer, or the like. The coloring material as the third component is obtained by dispersing a pigment in a polyol component.
[0029]
The injection nozzle 25 of the three-component mixing head 22 is connected to the gate 6 of the lower mold 3 through a through hole 40 formed in the lower box 13. The three-component mixing head 22 and the through hole 40 are sealed by a plurality of O-rings 50.
[0030]
The material injection mechanism 21 is also provided with a six-component mixing head 20 as shown in FIG. 6 and can be used in place of the three-component mixing head 22. The six-component mixing head 20 is formed by connecting two of the three-component mixing heads 22 to a central injection mechanism 55. The upper three-component mixing head 22 in the figure creates a surface portion polyurethane material U1 which is a high-performance material (for example, a non-yellowing material with excellent light resistance). A coloring material formed by adding a urethane reaction promoting catalyst is used. The lower three-component mixing head 22 in the figure creates a normal grade material (for example, a yellowing material) internal polyurethane material U2 and a gate vicinity polyurethane material U3. The catalyst is added. The injection mechanism 55 includes a body 56 that couples the two injection nozzles 25, and the tip of the body 56 is a thin injection nozzle 57. A through hole 58 in which two injection nozzles 25 are opened is formed at the center of the body 56, and a spool 60 attached to a piston (not shown) of a cylinder 59 is slidably inserted into the through hole 58. Yes.
[0031]
Now, the RIM polyurethane molding method for polyurethane coating of the first to third embodiments performed using the molding apparatus will be described in the order of steps. FIG. 7 is a time chart showing the injection timing of the polyurethane material, the cured state of the material, and the change in pressure of the cavity in the molding.
[0032]
(1) The upper mold 2 and the lower mold 3 of the mold 1 are opened, and a release agent is applied to the cavity surface 5. The temperature of the upper mold 2 and the lower mold 3 is set to 50 to 70 ° C. by flowing a heat medium having a predetermined temperature through a temperature control tube (not shown) provided therein.
(2) After setting the core metal 46 of the steering wheel 45 to the lower mold 3, the upper mold 2 and the lower mold 3 are closed to form the cavity 4, and at the same time, the upper box 12 and the lower box 13 are closed. The vacuum box 11 is sealed.
(3) The inside of the vacuum box 11 is depressurized to an appropriate degree of vacuum by the vacuum pump 18 to make the cavity 4 from the vent hole 7 into a depressurized atmosphere. The appropriate degree of vacuum varies depending on the composition of the polyurethane material, the dimensions of the molded product, and the like, and is not particularly limited, but is 10 Torr in the present embodiment.
[0033]
(4) Surface portion material injection step: The surface portion polyurethane material U1 is prepared by the six-component mixing head 20 of FIG. In this embodiment, a foaming agent is not substantially added to the surface portion polyurethane material U1.
[0034]
As shown in FIG. 1, the surface portion polyurethane material U1 is injected into the cavity 4 from the injection nozzle 25 while the cavity 4 is continuously decompressed (the degree of vacuum is 10 Torr). As shown in FIG. 7, assuming that the start of injection is the starting point (0 seconds), the completion of the injection is 1.2 seconds, and the injection amount is smaller than the internal volume of the cavity 4. However, the injected polyurethane material U1 for the surface portion has a cavity as the natural occlusion gas in the material (and the foaming agent in the case of adding a foaming agent) rapidly foams due to bumping due to pressure drop. It flows in almost the whole area of 4. Further, the injected polyurethane material U1 for the surface portion starts to be cured by polyurethane reaction after the elapse of 2.2 seconds, and is completed when about 60 seconds elapse. And 1st-3rd embodiment differs as follows regarding the atmospheric pressure operation of the cavity 4 after this injection completion.
[0035]
(1) First embodiment: As shown in (1) in FIG. 7, when the surface portion polyurethane material U1 starts to harden for 1.3 seconds, the decompression of the cavity 4 is released to the atmospheric pressure. The release to the atmospheric pressure is completed when 2.1 seconds have elapsed. Then, as shown in FIG. 8 (a), the surface portion polyurethane material U1 before the start of curing is almost completely defoamed due to the shrinkage caused by the atmospheric pressure due to the pressure drop. 5 and the metal core 46 adhere to the film.
[0036]
(2) Second embodiment: As shown in (2) in FIG. 7, the cavity 4 is decompressed when 2.4 seconds elapse from the start to the completion of the curing of the surface portion polyurethane material U1. Is released, and release to atmospheric pressure is started, and release to atmospheric pressure is completed when 3.2 seconds have elapsed. Then, as shown in FIG. 9 (a), a part of the polyurethane material U1 for the surface portion in the middle of curing adheres to the cavity surface 5 because the foam generated by the pressure drop disappears due to contraction due to the atmospheric pressure. To do. Further, the remaining portion of the material U1 is connected to the part in a string form (rarely a band).
[0037]
(3) Third embodiment: As shown in (3) of FIG. 7, the pressure reduction of the cavity 4 occurs when 3.3 seconds elapse from the time when the surface polyurethane material U1 is cured until the completion. Is released, and release to atmospheric pressure is started, and release to atmospheric pressure is completed when 4.1 seconds have elapsed. Then, as shown in FIG. 9 (b), a part of the polyurethane material U1 for the surface portion in the middle of curing adheres to the cavity surface 5 because the foam generated by the pressure drop disappears due to contraction due to the atmospheric pressure. To do. Further, the remaining part of the material U1 is connected to the part in a band shape (rarely a thread shape).
[0038]
(5) Curing step; This step is performed for a short time in the first embodiment, and for a long time in the second and third embodiments.
That is, in the first embodiment, from the start of the injection of the surface portion polyurethane material U1 until, for example, 10 seconds elapses, the state after the injection is left as it is, and the curing of the material proceeds.
Further, in the second and third embodiments, the state after the injection is left for about 60 seconds from the start of the injection of the surface portion polyurethane material U1 to complete the curing of the material. As a result, as shown in FIGS. 9A and 9B, a part attached to the cavity surface 5 in the previous step is cured as a surface portion 48 of the polyurethane coating 47, and a thread or The remaining portion connected in a band shape is cured as a bridge portion 51 of the polyurethane coating 47.
[0039]
(6) Internal material injection step; this step is performed only in the first embodiment, and is not performed in the second and third embodiments. The internal polyurethane material U2 is prepared by the six-component mixing head 20 shown in FIG. In this embodiment, water as a foaming agent is also added to the internal polyurethane material U2. As shown in FIG. 2, the internal polyurethane material U2 is injected from the injection nozzle 25 into the cavity 4 under atmospheric pressure. The injected internal polyurethane material U2 is foamed by the generation of CO2 bubbles due to the reaction between isocyanate and water as a foaming agent to form a highly foamed interior 49 as shown in FIG. 8 (b).
When the cavity 4 is filled with all the materials U1 and U2 by the above injection, the flow front end portion of the internal polyurethane material U2 is blown out from the vent hole 7 to be hardened, and the blowout portion 9 is formed.
[0040]
(7) Waiting for all the materials U1 and U2 to be cured, as shown in FIG. 3, the upper mold 2 and the lower mold 3 are opened, and at the same time, the upper box 12 and the lower box 13 are opened. As shown in FIG. 4, the steering wheel 45 with the polyurethane coating 47 is taken out. In FIG. 4, the steering wheel 45 is shown enlarged with respect to the lower mold 3.
[0041]
Next, a reference example is demonstrated by showing the difference with said 1st-3rd embodiment.
a: In the step (1), the temperatures of the upper mold 2 and the lower mold 3 are set to 10 to 30 ° C., which is a temperature at which the reaction hardening of the polyurethane material U1 is delayed.
b: Steps (2) and (3) are the same.
c: In the step (4), the single-component polyurethane material U1 is prepared by the three-component mixing head 22 shown in FIG. In this reference example , water as a foaming agent is added to this polyurethane material U1. Further, even after the injection of the material, as shown by a circle 4 in FIG. 8, the pressure reduction of the cavity 4 is continued and the atmospheric pressure is maintained at 10 Torr. Then, as shown in FIG. 10, a part of the foamed and fluidized surface portion polyurethane material U1 is broken (defoamed) and adhered to almost the entire cavity surface 5 in the form of a film. A surface portion 48 of the coating 47 is formed. At this time, in this reference example , the temperature of the upper mold 2 and the lower mold 3 is set to 10 to 30 ° C., which is a temperature at which the reaction hardening of the polyurethane material U1 is delayed. Is easily broken, and the surface portion 48 having a certain thickness or more is easily formed. Further, in the remainder of the polyurethane material U1, the generation of CO ₂ bubbles due to the reaction between isocyanate and water as a foaming agent and the expansion of the CO ₂ bubbles under reduced pressure result in a highly foamed interior having a specific gravity of 0.3 or less. 49 is formed.
d: Step (5) is the same as in the second and third embodiments.
e: Step (6) is not performed.
f: Step (7) is the same.
[0042]
And according to 1st embodiment, the problem demonstrated by the paragraph (1-1)-(1-3) of the prior art was solved, and the polyurethane provided with the shell-shaped surface part 48 with a substantially uniform thickness. The coating 47 can be molded at low cost with a simple and small equipment without being substantially restricted by the shape and dimensions of the molded product. In addition, since the thickness of the surface portion 48 is substantially uniform, there is a possibility that the mold coating step required in the conventional polyurethane coating can be omitted.
In addition, according to the second and third embodiments, the problem described in the section (2) of the prior art is solved, the shell-like surface portion 48 having a substantially uniform thickness is provided, and the presence of the bridge portion 51 is provided. Thus, it is possible to obtain a polyurethane coating 47 having a new tactile feeling other than a feeling of elasticity, specifically, a soft texture that slowly restores when pressed and released.
Further, according to the reference example , the problem described in the section (3) of the prior art is solved, and the surface portion 48 having a substantially uniform thickness and the high foaming having a specific gravity of 0.3 or less are obtained by a single composition polyurethane material. The polyurethane coating 47 combined with the interior 49 can be obtained.
[0043]
In addition, this invention is not limited to the structure of the said embodiment, For example, as follows, it can also be changed and embodied suitably in the range which does not deviate from the meaning of invention.
(1) In the first embodiment, by not performing the internal material injection step, it is possible to obtain a hollow molded article (state of FIG. 8A) consisting only of the surface portion 48.
(2) In addition to the polyurethane coating on the steering wheel, for example, it can be applied to RIM polyurethane molding of various molded products such as a steering wheel pad, a lid of a console box or a glove box, an armrest, and an air spoiler.
[0044]
【The invention's effect】
As described in detail above, according to the invention described in claim 1 or 2 , a molded product having a shell-shaped surface portion with a substantially uniform thickness is not substantially restricted by the shape and dimensions of the molded product. It can be molded at low cost with simple and small equipment.
According to the invention described in claim 3 or 4 , the shell-shaped surface portion having a substantially uniform wall thickness is provided, and a new tactile feeling other than a feeling of elasticity, specifically, when it is pushed and released, it is slowly restored. A molded product having a soft texture can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a process of forming a surface portion of a polyurethane coating of a steering wheel in an embodiment embodying the present invention.
FIG. 2 is a cross-sectional view of a process for forming the interior.
FIG. 3 is a sectional view of the same demolding process.
FIG. 4 is a plan view of the same demolding process.
FIG. 5 is a cross-sectional view of a three-component mixing head used for the molding.
FIG. 6 is a cross-sectional view of a six-component mixing head used for the molding.
FIG. 7 is a timing chart showing the material injection timing and the like in the molding.
FIG. 8A is a perspective view of a surface portion formed according to the first embodiment, and FIG. 8B is a perspective view of a polyurethane coating formed according to the first embodiment.
FIG. 9A is a perspective view of a polyurethane coating formed by the second embodiment, and FIG. 9B is a perspective view of a polyurethane coating formed by the third embodiment.
FIG. 10 is a perspective view of a polyurethane coating formed according to a reference example .
FIG. 11 is a cross-sectional view showing a problem of conventional blow molding.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Molding die 2 Upper mold 3 Lower mold 4 Cavity 5 Cavity surface 11 Vacuum box 12 Upper box 13 Lower box 18 Vacuum pump 21 Material injection mechanism 45 Steering wheel 47 Polyurethane coating 48 Surface portion 49 Interior 51 Bridge portion U1 For surface portion Polyurethane material U2 Internal polyurethane material

Claims (4)

Depressurizing the mold cavity;
Injecting the surface portion polyurethane material into the cavity under reduced pressure, foaming the surface portion polyurethane material and flowing into the cavity;
Releasing the vacuum of the cavity and releasing it to atmospheric pressure before the surface polyurethane material starts to cure, defoaming the surface polyurethane material by shrinkage of the foam, and attaching to the cavity surface;
Curing the surface portion polyurethane material to form a shell-shaped surface portion.   2. The RIM polyurethane molding method according to claim 1, further comprising a step of injecting an internal material into the cavity after forming the surface portion and forming the inside inside the surface portion. 3. Depressurizing the mold cavity;
Injecting polyurethane material into the cavity under reduced pressure, foaming the polyurethane material and flowing into the cavity;
During the curing from the start to the completion of the curing of the polyurethane material, the decompression of the cavity is released or relaxed, the polyurethane material is defoamed by the shrinkage of the foam, and a part of the polyurethane material is adhered to the cavity surface. And the step of making the remainder of the polyurethane material continuous in a thread or band form with respect to the part;
Forming a shell-shaped surface portion by completing the partial curing, and forming a bridge portion inside the surface portion by completing the curing of the remaining portion.   A polyurethane material is formed by once foaming under reduced pressure and then defoamed by releasing or relaxing the reduced pressure, and has a shell-like surface portion and a bridge portion connected in a string or band form inside the surface portion. Polyurethane molded product.

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