JP3573019B2 - Manufacturing method of urethane molded product - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a urethane molded product in which a coating material is applied in advance to a cavity in a mold in order to simultaneously perform molding and coating, and then a urethane material is injected and foamed.
[0002]
[Prior art]
As this type of molded product, for example, there is a steering wheel for a vehicle. The steering wheel is subjected to foam molding by setting a core metal in a mold cavity (a cavity for forming a molded product) and then injecting a urethane material into the mold cavity. In the case of a steering wheel made of a urethane material, it is necessary to form a skin layer on the surface of the steering wheel in order to improve the appearance, feel, abrasion resistance, and the like. A method of injecting a urethane material into the material has been put to practical use by the present applicant (Japanese Patent No. 2518481).
[0003]
Specifically, when a urethane material is injected into a mold cavity under reduced pressure, the gas contained in the urethane material is bumped under reduced pressure to form gas bubbles. It is filled while flowing. A urethane reaction starts in parallel with the foaming of the urethane material, and reaction hardening proceeds. At this time, since the reaction heat escapes to the mold in the portion close to the cavity surface, the urethane reaction is delayed, and the increase in the viscosity of the urethane material is suppressed. Therefore, the gas bubbles on the surface are degassed under reduced pressure to form a low foaming skin layer. On the other hand, in the interior away from the cavity surface, the thickening due to the urethane reaction progresses, the gas bubbles are held as they are, and a highly foamed core portion is formed. In this case, a low-foaming skin layer is formed on the surface of the high-foaming core portion, and the appearance, tactile sensation, wear resistance, and the like of the steering wheel surface are improved.
[0004]
However, since the urethane resin molded by the foam molding as described above has a defect of being inferior in light resistance and yellowing, it is necessary to form a coating film having light resistance on the surface of the urethane resin portion.
[0005]
As a method of forming the coating film, a method of applying a coating material in advance to a cavity in a mold and then molding a product is applied. Specifically, the mold is opened, and a coating solution is applied to the cavity by a spray gun (mold coating). Thereafter, the mold is closed, and a urethane material is mixed and injected into the cavity to be cured by reaction. Thereby, a coating film is formed on the surface of the molded article. The coating solution used here is composed of, for example, methyl ethyl ketone (MEK) and isopropyl alcohol (IPA) as solvents, and a urethane resin having excellent light resistance.
[0006]
[Problems to be solved by the invention]
By the way, in the above-mentioned urethane resin foam molding, the urethane material injected first into the cavity becomes a low-foaming skin layer, and the urethane material injected later becomes the highly foamed core portion. Therefore, a molding method for reducing the pigment by injecting a urethane material containing a pigment to form a low-foaming skin layer and injecting a urethane material containing no pigment to form a highly foamed core portion. It has been proposed by the present applicant (Japanese Patent Application Laid-Open No. 9-183138). Further, in this molding method, as a measure to prevent the uncolored core portion from being exposed on the surface by cutting off the gate remaining portion, a urethane material containing a pigment is injected in the final step of foam molding. ing.
[0007]
However, when the coating solution is applied (mold coated) by the spray gun as described above, the coating cannot be applied to the cavity accurately. Therefore, the paint applied to portions other than the cavities causes burrs in the foam molding. Since the burrs have a cross-sectional structure in which a core portion containing no pigment penetrates between skin layers containing pigments, when the burrs are removed by a burr treatment process, an uncolored core portion is exposed on the surface to deteriorate the appearance. I will.
[0008]
The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing a urethane molded article capable of reducing the amount of pigment contained in a urethane material without deteriorating the appearance. .
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is a method for producing a urethane molded product in which a urethane material is injected and foamed, wherein a solvent and a solvent are mixed in a mold cavity in a state where a mold is closed. A coating in which a coating solution containing a urethane resin is boiled, and the coating is applied to the surface of the mold cavity by increasing the volume at the time of boiling and breaking bubbles, and the vaporized solvent is exhausted to form a coating layer on the surface of the mold cavity. A first injecting step of injecting a first urethane material containing a pigment into the mold cavity, and a second injecting step of injecting a second urethane material containing more pigment than the first urethane material The gist is that it consists of:
[0010]
According to a second aspect of the present invention, in the first aspect of the invention, the gist is that the coating step is performed under reduced pressure.
According to a third aspect of the present invention, in the first aspect, the first injection step is performed under reduced pressure.
[0011]
In the invention according to claim 4, in the invention according to claim 1, between the first injection step and the second injection step, the pigment is further reduced from the first urethane material, or the pigment is contained. The gist of the present invention is to include a third injection step of injecting a third urethane material.
[0012]
(Action)
According to the first aspect of the present invention, a paint solution containing a solvent and a urethane resin is boiled in a mold cavity in a state where the mold is closed. The solvent applied to the surface of the cavity and the vaporized solvent are exhausted to form a coating layer on the mold cavity. Then, the first urethane material having a reduced pigment concentration is injected into the mold cavity in a reduced pressure state, and foam molding of the urethane material is performed. Thereafter, a second urethane material containing more pigment than the first urethane material is injected, and the vicinity of the gate is foamed. As described above, when the coating layer is formed in the mold cavity with the mold closed, the generation of burrs during foam molding is suppressed, so that the amount of pigment contained in the urethane material can be reduced.
[0013]
According to the second aspect of the present invention, the coating solution is boiled in the mold cavity by setting the mold cavity in a reduced pressure state, and the coating layer is formed in the mold cavity due to an increase in volume at the time of boiling and breakage of bubbles. It is formed with a substantially uniform thickness. In this case, a coating layer having a desired thickness is formed almost uniformly on the surface of the urethane material to be foam-molded by controlling the injection amount of the coating solution. Therefore, the pigment contained in the first urethane material can be reduced.
[0014]
According to the third aspect of the present invention, when the first urethane material is injected into the mold cavity under reduced pressure, a low-foaming skin layer is formed by the first injected urethane material, and then the injection is performed. The highly foamed core portion is formed by the urethane material to be used. When molded in this manner, the pigment concentration of the skin layer is lower than that of the urethane resin in the vicinity of the gate, but since there are almost no bubbles, the degree of coloring is substantially equal to that of the vicinity of the gate. Further, unlike the prior art, the coating material is not applied to a portion other than the cavity, and burrs generated by foam molding are reduced. Therefore, the exposure of the core portion due to the removal of burrs is prevented, and the amount of pigment contained in the first urethane material can be reduced. .
[0015]
According to the invention as set forth in claim 4, a low-foaming skin layer is formed on the surface of the molded article by the first urethane material, and the pigment is further reduced or contains the pigment than the first urethane material. The inner core of the skin layer is formed by the third urethane material.
[0016]
In the first urethane material for the surface, it is preferable to lower the pigment concentration to 40% to 80% of the reference concentration. In the internal third urethane material, it is preferable to lower the pigment concentration to 30% to 70% of the reference concentration.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 3 are partial cross-sectional views of an injection molding machine according to the present embodiment, and FIG. 4 is a perspective view of a vehicle steering wheel 1 molded by the injection molding machine.
[0018]
As shown in FIG. 4, the steering wheel 1 has a ring portion 2, spoke portions 3, 4, 5, and a boss portion 6, and a die 7 (a lower die 8, 8) of an injection molding machine shown in FIGS. The upper mold 9) is for covering the core metal 10 of the ring portion 2 and the spoke portions 3, 4, and 5 with urethane resin. In this embodiment, the urethane resin is foamed in a state where the steering wheel 1 shown in FIG. 4 is turned upside down.
[0019]
As shown in FIGS. 1 to 3, the mold 7 is disposed in a box 13 including a frame 11 and a lid 12. Specifically, the lower die 8 of the die 7 is fixed to the frame 11, and the upper die 9 of the die 7 is fixed to the lid 12. In addition, a seal member 14 is provided at a joint of the lid 12 and the frame 11. Then, the frame 11 and the lower mold 8 are moved upward from the state where the mold 7 is opened as shown in FIG. 1, and the mold 7 is moved in a state where the core metal 10 is set as shown in FIG. Closed and clamped. At this time, a box 13 is formed by the frame 11 and the lid 12, and the inside of the box 13 is sealed by the sealing member 14. The core 10 of the present embodiment is manufactured by die-casting of aluminum die-cast, magnesium die-cast, or an alloy thereof, and the cross-sectional shape of the ring portion 10a of the core 10 is U-shaped as shown in FIG. It has become.
[0020]
Recesses 15 and 16 are formed in the lower die 8 and the upper die 9, and the depressions 15 and 16 serve as cavities 17 for forming a molded product. In order to fix the metal core 10 of the steering wheel 1 at the time of molding, a fixing member 18 is protruded from the center of the lower die 8 and a fixing member 19 is protruded from the center of the upper die 9. . Further, a discharge hole 20 (for example, a cross-sectional area = 4 mm ² ) is formed in the concave portion 16 of the upper die 9, and the cavity 17 communicates with the hollow portion 21 in the box 13 through the discharge hole 20.
[0021]
A discharge pipe 31 is provided on one side wall (left side wall in the drawing) of the frame body 11, and the discharge pipe 31 is connected to a vacuum pump 34 via a pipe 32 and a valve 33. When the vacuum pump 34 is driven, the air in the box 13 is discharged from the discharge pipe 31, and the pressure in the box 13 is reduced.
[0022]
An injection nozzle 41 of the urethane injection device 40 is provided on the other side wall (the right side wall in the drawing) of the frame body 11, and the urethane material mixed by the urethane injection device 40 is discharged from the injection nozzle 41. It is injected into the cavity 17 through the gate 23. The urethane material is liquid and includes a polyol component, an isocyanate component, and a coloring component, and is configured such that the three components are mixed in the urethane injection device 40.
[0023]
Here, a schematic configuration of the urethane injection device 40 will be described with reference to FIG.
As shown in FIG. 5, the urethane injection device 40 includes a cylinder 42 and a body 43 disposed at the tip of the cylinder 42. The injection nozzle 41 is provided on the tip side of the body 43, and the injection nozzle 41 is disposed on the side wall of the frame 11.
[0024]
A through hole 44 is formed in the center of the body 43, and a spool 46 attached to a piston (not shown) reciprocating in the cylinder 42 is slidably inserted into the through hole 44. A pair of long grooves 47a and 47b extending in the longitudinal direction are formed on the outer periphery of the spool 46. Then, the spool 46 slides between the forward position shown by the two-dot chain line and the retreat position shown by the solid line in FIG. 5 due to the reciprocating motion of the piston, and the leading end face of the spool 46 and the through hole 44 at the retreat position. A mixing chamber 48 is formed by the wall surfaces of the mixing chamber 48.
[0025]
A cylindrical nozzle body 49 and a nozzle body 50 are disposed inside the body 43 at positions facing each other, so that the polyol component is discharged from the nozzle body 49 and the isocyanate component is discharged from the nozzle body 50. ing. Each nozzle body 49, 50 has an orifice 51 that opens into the mixing chamber 48 or the long groove 47a, 47b. A holder (not shown) holding the nozzle bodies 49 and 50 is mounted on the outer surface of the body 43, and the tip of the needle 52 inserted through the holder adjusts the opening of the orifice 51. A reflux hole 53 for the polyol component and a reflux hole 54 for the isocyanate component are formed adjacent to the nozzle bodies 49 and 50 of the body 43, and both the reflux holes 53 and 54 are open to the long grooves 47a and 47b. .
[0026]
A tank 57 for the polyol component and a pump 58 are connected to the nozzle body 49 and the reflux hole 53 by a hose 56, and the polyol component is supplied in the order of the tank 57 → the pump 58 → the nozzle body 49 → the long groove 47a → the reflux hole 53 → the tank 57. It is circulating. A tank 60 for an isocyanate component and a pump 62 are connected to the nozzle body 50 and the circulation hole 54 by a hose 60, and the tank 61 → the pump 62 → the nozzle body 50 → the long groove 47b → the circulation hole 54 → the tank 61 in this order. The components circulate.
[0027]
A discharge hole 64 for discharging a coloring component is formed at the center of the spool 46. More specifically, the distal end of the discharge hole 64 opens to the distal end surface of the spool 46, and the rear end opens to the outer peripheral surface of the spool 46. An introduction hole 65 is formed in the rear portion of the body 43 and communicates with the opening at the rear end of the discharge hole 64 only when the spool 46 is retracted. A tank 69 for a coloring component is connected to the introduction hole 65 via a flow control device 67 and a valve 68 by a hose 66, and the inside of the tank 69 is constantly pressurized by an air pressurizing device 70. The opening and closing timing of the valve 68 is controlled by a timer or the like, and the opening and closing timing of the valve 68 and the flow rate adjusting device 67 adjust the discharge amount from the discharge hole 64. In the present embodiment, a coloring material in which a pigment as a coloring component is dispersed in a polyol component is stored in a tank 69, and the coloring material is discharged from a discharge hole 64 via a valve 68, a flow control device 67, and the like. You.
[0028]
As described above, the coloring material discharged from the discharge holes 64, the polyol component discharged from the nozzle body 49, and the isocyanate component discharged from the nozzle body 50 are collision-mixed in the mixing chamber 48, and the spool 46 is moved forward. By sliding to the position, the urethane material is injected into the cavity 17 from the injection nozzle 41.
[0029]
Next, a method of molding the urethane resin of the steering wheel 1 in the present embodiment will be described with reference to FIGS.
First, as shown in FIG. 1, the mold 7 is opened, and a mold release agent is applied to the wall surfaces of the cavity 17 (the concave portion 15 of the lower die 8 and the concave portion 16 of the upper die 9). The release agent is made of wax, silicone oil, or the like, and is applied for the purpose of preventing the molded product from sticking to the mold 7 and facilitating removal of the molded product.
[0030]
Next, the liquid paint M (in this embodiment, 170 g) is poured into the concave portion 15 of the lower die 8 while keeping the die 7 horizontal. The solution of the coating material M in the present embodiment contains methyl ethyl ketone (MEK) and isopropyl alcohol (IPA) as solvents, and a urethane resin as a solid content. In addition, when the ratio of each component in the coating material M is represented by% by weight, MEK = about 85%, IPA = about 10%, and urethane resin = 2.5%. The urethane resin contained in the paint M is colored in the same color as the urethane resin to be foam-molded.
[0031]
Then, as shown in FIG. 2, the core metal 10 is set in the mold 7, and the mold 7 is closed and the mold is clamped. At this time, the frame 11 and the lid 12 are joined via the seal member 14, and the inside of the box 13 is closed. In the present embodiment, a coating process on the cavity surface is performed with the mold 7 closed.
[0032]
Specifically, the inside of the box 13 is depressurized by driving the vacuum pump 34 to discharge the air in the box 13 from the discharge pipe 31. At this time, the air in the cavity 17 is sucked into the hollow portion 21 in the box 13 through the discharge hole 20 and the pressure in the cavity 17 is also reduced. When the pressure in the cavity 17 is reduced, the boiling point of the solvent (MEK, IPA) of the coating material M decreases. As a result, the paint M boils and breaks bubbles with an increase in volume. Specifically, the temperature of the mold 7 is maintained at 55 ° C., and when the pressure in the cavity 17 is reduced to 300 torr or less, the solvent boils. The paint M is applied to the wall surface of the cavity 17 due to the increase in volume and the breakage of bubbles at the time of boiling.
[0033]
Then, the solvent of the paint M is vaporized, and the urethane resin of the paint M is applied to the wall surface of the cavity 17. That is, a coating layer is formed on the wall surface of the cavity 17. At this time, the surface of the core 10 in the cavity 17 is washed with the solvent of the coating M, and the coating M serving as an adhesive is applied to the surface of the core 10. In the present embodiment, the pressure in the cavity 17 is reduced to 50 torr, and the solvent is vaporized in about 60 seconds. Then, the vaporized solvent is exhausted from the vacuum pump 34 from the discharge hole 20 through the hollow portion 21 in the box 13 and the discharge pipe 31.
[0034]
Then, while maintaining the reduced pressure, the urethane material mixed by the urethane injection device 40 is injected into the cavity 17 from the injection nozzle 41 through the gate 23, and the material is injected into the cavity 17 as shown in FIGS. The reaction hardens. Thus, a low-foaming skin layer U2 and a high-foaming core U3 are formed inside the urethane resin U1 of the paint M. FIG. 6 is an enlarged sectional view of the ring portion 2 of the steering wheel 1.
[0035]
Specifically, the spool 46 is retracted to discharge the polyol component from the nozzle body 49 and the isocyanate component from the nozzle body 50 to the mixing chamber 48, respectively. At the same time, the valve 68 is opened to discharge the coloring material from the discharge holes 64 into the mixing chamber 48, and these are collided and mixed. At this time, the pigment concentration in the urethane material is adjusted, for example, to be 40% of the reference concentration. When the spool 46 is advanced, the mixed urethane material is injected from the injection nozzle 41 into the cavity 17. That is, the first urethane material whose pigment concentration is reduced to 40% of the reference concentration is injected into the cavity 17 (first injection step).
[0036]
Then, the gas contained in the urethane material is suddenly boiled under reduced pressure and becomes a myriad of gas bubbles, so that the urethane material foams in a short time and fills the cavity 17 while flowing into the cavity 17. In parallel with the foaming of the urethane material, a reaction between the polyol component and the isocyanate component in the urethane material (urethane reaction) starts. Along with this, heat is generated and reaction hardening proceeds. At this time, since the heat of reaction escapes to the mold 7 in the portion close to the wall surface of the cavity 17, the urethane reaction is delayed as compared with the inside, and the thickening of the urethane material is suppressed. For this reason, the gas bubbles on the surface are easily broken and degassed under reduced pressure, resulting in a very low foaming dense skin layer U2 in which no minute gas bubbles remain. On the other hand, in the interior away from the wall surface of the cavity 17, the thickening due to the urethane reaction proceeds rapidly, and the gas bubbles are held as they are to form the highly foamed core portion U3. As described above, by forming the skin layer U2 on the surface of the highly foamed core portion U3, the steering wheel 1 is given not only a soft feeling but also a firm touch.
[0037]
Thereafter, a urethane material whose pigment concentration is adjusted to the reference concentration (100%) by increasing the amount of the coloring component discharged from the discharge hole 64 into the mixing chamber 48 is injected into the cavity 17 from the injection nozzle 41. That is, a second urethane material containing more pigment than the first urethane material is injected (second injection step). Thereby, the urethane resin U4 near the gate is formed as shown in FIG. Therefore, even if the urethane resin U5 as the gate remaining portion is cut off, the urethane resin U4 containing the pigment of the reference concentration is exposed, so that the appearance is prevented from being deteriorated.
[0038]
FIG. 7 is a timing chart of a change in pigment concentration in the molding. That is, as shown in FIG. 7, in the first injection step in the period from t1 to t2, the pigment concentration is 40% with respect to the reference concentration, and the skin layer U2 and the core portion U3 are formed. In the second injection step during the period from t2 to t3, the urethane resin U4 near the gate is formed with the pigment concentration as the reference concentration (100%).
[0039]
When molded in this manner, the pigment concentration of the skin layer U2 provided below the coating layer is 40%, which is lower than the reference concentration, and the core portion U3 is foamed, so that the pigment concentration is lower than that of the skin layer U2. The pigment concentration is low and the color is light. Therefore, since the color of the coating layer, the color of the skin layer U2, and the color of the core portion U3 are visually recognized as the added density, the coloring looks almost the same as the pigment reference density of the urethane resin U4 exposed on the surface.
[0040]
The dashed line shown in FIG. 7 is a comparative example in which the coating material M was applied by a spray gun and then the urethane material was subjected to foam molding. In this case, burrs are generated on the parting line, and the highly foamed core is exposed as the burrs are removed. Therefore, in the period from t1 to t2 when the skin layer and the core portion are formed, it is necessary to increase the pigment concentration (for example, 65%) to such an extent that the appearance is not deteriorated. However, according to the present embodiment, the coating material M is prevented from being applied to portions other than the cavity 17, and the occurrence of burrs on the parting line is suppressed, so that the pigment concentration can be reduced.
[0041]
In this manner, the molding and coating of the urethane resin of the ring portion 2 and the spoke portions 3, 4, and 5 of the steering wheel 1 are performed simultaneously. That is, a low-foaming skin layer U2 made of urethane resin and a high-foaming core portion U3 are formed, and the surface of the low-foaming skin layer U2 is coated with a light-resistant urethane resin U1 having a substantially uniform thickness (for example, , 10 μm).
[0042]
Then, the mold 7 is opened, and as shown in FIG. 4, the steering wheel 1 in which the ring portion 2 and the spoke portions 3, 4, and 5 are covered with the urethane resin is taken out, and the molding process is completed.
[0043]
As described above, in the foam molding using the liquid urethane material, the resin molding is performed under the condition of low temperature and low pressure in the cavity 17 as compared with the injection molding of a general thermoplastic resin. Therefore, it is possible to prevent the coating layer formed on the wall surface of the cavity 17 from being broken by the pressure and temperature during molding. Further, since the urethane material is injected into the cavity 17 in the reduced pressure state, the wraparound failure of the material is reduced.
[0044]
As described above, the present embodiment has the following advantages.
(1) The pigment concentration of the skin layer U2 is lower than that of the urethane resin U4 in the vicinity of the gate. However, since there are almost no bubbles, the degree of coloring is almost equal to that of the urethane resin U4. Further, the coating material M is not applied to a portion other than the cavity 17, and burrs generated by foam molding can be reduced. Therefore, exposure of the core portion U3 due to the removal of burrs can be prevented. Further, when applied with a spray gun (mold coating), the coating material M cannot be applied uniformly to the cavity 17, and in particular, the application to the parting line portion becomes insufficient, and the coating film at that portion becomes insufficient. It will be thin. However, in the present embodiment, a coating film of a desired thickness can be formed substantially uniformly on the surface of the foamed skin layer U2 by controlling the injection amount of the coating solution. Therefore, since the urethane resin can be hidden by this coating film, the concentration of the pigment contained in the skin layer U2 and the core portion U3 to be foam-molded can be reduced. Further, even if the urethane resin U5 as a gate remaining portion is cut off, the urethane resin U4 having the pigment concentration as a reference concentration is exposed, so that the appearance can be prevented from being deteriorated.
[0045]
As described above, the pigment contained in the urethane material can be reduced without deteriorating the appearance, and the material cost can be reduced. In addition, the pigment particles wear the passing portion in the urethane injection device 40. However, since the pigment can be reduced as described above, the wear can be reduced. Therefore, the maintenance cost of the urethane injection device 40 can be reduced.
[0046]
(2) Since the low-foaming skin layer U2 is formed outside the high-foaming core portion U3 by foam molding using a urethane material, wear resistance, tactile sensation, and the like can be improved. Further, a coating film of the urethane resin U1 having excellent light resistance can be formed on the surface of the resin portion of the steering wheel 1 with a substantially uniform thickness. As a result, light resistance can be uniformly obtained at any place, and discoloration of the urethane resin skin layer U2 can be prevented. In addition, there is no unevenness in color on the product surface, so that poor appearance can be prevented. Therefore, the steering wheel 1 has excellent product performance such as wear resistance, tactile sensation, and light resistance. Further, even if the coating film is worn by using the steering wheel 1 for a long time, the skin layer U2 is formed inside, so that the performance such as the appearance and the touch can be maintained.
[0047]
(3) In the closed mold 7, the coating material M is applied almost uniformly without uneven application on the wall surface of the cavity 17 due to the boiling of the solvent and the increase in volume and foam breakage. In this case, the coating efficiency can be increased and the material cost of the coating material M can be reduced as compared with the case where the coating material M is applied (mold coated) by a spray gun. Further, the paint M is prevented from scattering to the outside, the workplace can be kept clean, and the deterioration of the surrounding environment can be prevented.
[0048]
(4) In foam molding using a urethane material, resin molding is performed under low-temperature and low-pressure conditions in the cavity 17 as compared with injection molding of a thermoplastic resin. The layer can be prevented from breaking. Further, if the inside of the cavity 17 is brought to a normal pressure state after forming the coating layer by reducing the pressure inside the cavity 17, there is a possibility that the coating layer may be broken depending on the pressure change at that time, but as in the present embodiment, By injecting the urethane material while maintaining the reduced pressure, the coating layer can be prevented from being broken. Further, since the urethane material is foamed under a reduced pressure, it is possible to reduce wraparound defects of the material. Therefore, the product yield can be improved.
[0049]
(5) The surface of the core 10 is washed with a solvent of the coating M, and the surface of the core 10 is coated with a urethane resin-based coating M having excellent adhesiveness, so that the core 10 and the urethane resin are strongly bonded. Can be fixed.
[0050]
The above embodiment may be implemented in the following modes.
In the above embodiment, in the first injection step (t1 to t2 in FIG. 7), the first urethane material having a pigment concentration of 40% is injected to form the skin layer U2 and the core portion U3. In the second injection step (t2 to t3 in FIG. 7), the second urethane material having the pigment concentration as the reference concentration (100%) is injected to form the urethane resin U4 as a portion near the gate. It is not limited to. For example, depending on the shape, color, etc. of the molded product, the skin layer U2 and the coating film (urethane resin U1) can reliably cover the inner core portion U3. May be performed.
[0051]
Specifically, a skin layer U2 is formed by injecting a first urethane material having a pigment concentration of 40% in a period from t1 to t10 shown in FIG. % And a pigment-free urethane material is injected to form an inner core portion U3. Further, during a period from t2 to t3, a second urethane material having a pigment concentration as a reference concentration (100%) is injected to form a urethane resin U4 as a portion near the gate. Of course, in the period from t10 to t2, it is not necessary to inject a urethane material having a pigment concentration of 0%, and at least the urethane material in which the pigment is reduced compared to the first urethane material injected in the period from t1 to t10 (the second urethane material). 3 urethane material). In the molding method shown in FIG. 8, the injection step in the period from t1 to t10 corresponds to the first injection step, and the injection step in the period from t2 to t3 corresponds to the second injection step. Further, an implantation step between the first implantation step and the second implantation step, that is, an implantation step in a period from t10 to t2 corresponds to a third implantation step.
[0052]
Further, the pigment concentration of the skin layer U2 and the core portion U3 can be appropriately changed according to the shape, color, and the like of the molded product. Specifically, for example, during the period from t1 to t2 when the skin layer U2 and the core portion U3 are formed, the foaming may be performed by gradually lowering the pigment concentration.
[0053]
However, when the steering hole is formed as in the above embodiment, it is preferable to reduce the pigment concentration of the urethane material for the surface to 40% to 80% of the reference concentration. In the urethane material for the inside, it is preferable to lower the pigment concentration to 30% to 70% of the reference concentration.
[0054]
In the above embodiment, the paint solution is injected with the mold 7 opened. However, a paint injecting device is separately provided, and the paint is injected from the paint injecting device into the cavity 17 with the mold 7 clamped. M may be configured to be injected. By doing so, the coating solution can be injected while the cavity 17 is being depressurized, and the resin molding can be performed in a short time. Further, since the coating solution is injected into the closed cavity 17, the solvent of the coating material M can be prevented from leaking outside the injection molding machine.
[0055]
The molded product is not limited to the steering wheel 1, but may be applied to other parts such as an instrument panel, a console box, a glow box, a headrest, an armrest, a door cover, an air spoiler, and a bumper. Of course, the present invention may be applied to molded articles such as home electric appliances in addition to automobile parts.
[0056]
-The components of the coating material M may be changed as appropriate. Specifically, another thermosetting resin may be used instead of the urethane resin. Further, as the solvent of the coating material M, a solvent other than methyl ethyl ketone (MEK) and isopropyl alcohol (IPA), for example, water may be used. Alternatively, toluene or the like may be added to the MEK or IPA solvent. Practically, any solvent using a solvent having a boiling point of about 160 ° C. or less may be used.
[0057]
In the above embodiment, the inside of the cavity 17 is depressurized to 50 torr by driving the vacuum pump 34, but the invention is not limited to this. The pressure reduction state in the cavity 17 may be appropriately changed according to conditions such as the drying time of the coating solution, the application state, and the thickness of the skin layer U2.
[0058]
Further, technical ideas other than the claims grasped by the above embodiment will be described below together with their effects.
(A) In the method for producing a urethane molded article according to claim 1, the foam molding includes a step of injecting a urethane material having a predetermined concentration lower than a reference concentration to form a low-foaming skin layer. Forming a highly foamed core portion by injecting a urethane material having a predetermined concentration lower than the reference concentration to form a highly foamed core portion, and forming the vicinity of the gate by injecting a urethane material having the pigment concentration as the reference concentration And a process for producing a urethane molded article. When the urethane material is injected into the cavity in the reduced pressure state and foam molding is performed, a low foam skin layer is formed outside the high foam core. Even if the pigment concentration of the skin layer is reduced, the color is almost the same as that of the vicinity of the gate having the reference concentration because there are almost no bubbles. Further, a coating film having a substantially uniform thickness is formed on the outer side of the skin layer, and the core portion can be hidden by the coating film and the skin layer. Therefore, the pigment concentration in the step of forming the skin layer and the step of forming the core can be reduced.
[0059]
(B) The method for producing a urethane molded product according to the technical concept (a), wherein the pigment concentration in the step of forming the core portion is lower than that in the step of forming the skin layer. Manufacturing method. That is, when the inner core portion is hidden by the coating film and the skin layer, the pigment concentration in the step of forming the core portion can be further reduced.
[0060]
【The invention's effect】
As described in detail above, according to the present invention, the pigment contained in the urethane material can be reduced without deteriorating the appearance.
[Brief description of the drawings]
FIG. 1 is a view for explaining a method of forming a steering wheel according to an embodiment.
FIG. 2 is a diagram for explaining a steering wheel forming method according to the embodiment.
FIG. 3 is a view for explaining a method of forming the steering wheel according to the embodiment.
FIG. 4 is a perspective view of the steering wheel of the embodiment.
FIG. 5 is a schematic configuration diagram of a urethane injection device of the embodiment.
FIG. 6 is an enlarged sectional view of a ring portion of the steering wheel according to the embodiment.
FIG. 7 is a timing chart showing a change in pigment concentration in foam molding according to the embodiment.
FIG. 8 is a timing chart showing a pigment concentration change in another foam molding.
[Explanation of symbols]
1 ... Steering wheel as urethane molded product, 7 ... Mold, 17 ... Cavity, M ... Paint, U4 ... Urethane resin as gate vicinity.

Claims (4)

In a method for producing a urethane molded product in which a urethane material is injected and subjected to foam molding,
In a mold cavity with the mold closed, a paint solution containing a solvent and a urethane resin is boiled. A coating process of evacuating and forming a coating layer on the surface of the mold cavity,
A first injection step of injecting a first urethane material containing a pigment into the mold cavity;
A second injection step of injecting a second urethane material containing more pigment than the first urethane material. The method for producing a urethane molded product according to claim 1,
The method for producing a urethane molded product, wherein the coating step is performed under reduced pressure. The method for producing a urethane molded product according to claim 1,
The method for producing a urethane molded product, wherein the first injection step is performed under reduced pressure. The method for producing a urethane molded product according to claim 1,
A third injection step of injecting a third urethane material containing less or no pigment than the first urethane material is included between the first injection step and the second injection step. A method for producing a urethane molded product.

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