JP4245421B2 - Powder slush molding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a powder slush molding method.
[0002]
[Prior art]
In the powder slush molding method, a plastic powder is attached to the mold surface of a heated mold to form a molten plastic film, and then cooled to harden the molten plastic film to form a plastic film having a mold surface shape. The coating is peeled off from the mold surface, and is widely used as a molding method for various plastic coatings such as an automobile instrument panel skin (see Patent Document 1).
[0003]
In addition, for the skin of the airbag door integrated instrument panel in which the airbag door portion is integrally formed, as a tearing portion when the airbag is inflated, a back surface of the skin is provided with a strength reduction portion made of a groove or a cut, A so-called invisible type has been proposed in which the cleavage portion is not visible from the skin surface side in normal times (see Patent Document 2).
[0004]
[Patent Document 1]
JP 2000-102938 [Patent Document 2]
JP-A-2002-347557
[Problems to be solved by the invention]
However, in the conventional powder slush molding method, air is blown between the molten plastic film 50 and the mold surface 41 at the pin corner portion (the portion where the radius of the curved surface is small) 43 in the mold surface recess 42 as shown in FIG. Air trapping is likely to be confined, and as a result, pinholes that deteriorate the appearance and performance tend to occur on the surface of the plastic coating. In particular, when the plastic powder has a high melt viscosity, the air accumulation tends to occur, and the generation of pinholes tends to increase.
[0006]
As a method of making the air accumulation difficult to occur, the melt viscosity is reduced using a plastic powder added with a plasticizer. However, depending on the type of the plastic powder, there are some cases where good physical properties and quality cannot be obtained when a plasticizer is added. In a powder slush molding method using such a plastic powder, the pinhole should be prevented. It was difficult. For example, a non-crosslinked type TPU (thermoplastic polyurethane) mentioned as a preferred material for the invisible type airbag panel integrated instrument panel skin is easily damaged when a plasticizer is added, so a plasticizer is added. It was not possible to reduce the melt viscosity.
[0007]
It is also conceivable to increase the temperature of the mold surface 41 to lower the melt viscosity of the plastic powder. In this case, however, the time for heating and cooling the mold surface 41 increases, and the molding cycle of the plastic film is increased. It becomes longer and productivity decreases. Therefore, in particular, when a plastic film is formed by a powder slush molding method using non-crosslinking type TPU powder, it is difficult to prevent the occurrence of pinholes at the pin corners while suppressing an increase in molding time.
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the above points, and provides a powder slush molding method in which pinholes are unlikely to occur at the corners of the pins, and a reduction in productivity can be suppressed.
[0009]
[Means for Solving the Problems]
According to the present invention, a plastic powder is adhered to a mold surface of a heated mold to form a molten plastic film, and then cooled to harden the molten plastic film to form a plastic film, and the plastic film is removed from the mold surface. In the powder slush molding method to be peeled off, the plastic powder attached to the pin corner portion of the concave portion of the mold surface is made to have a lower melt viscosity than the plastic powder attached to the other portion of the mold surface.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing from plastic powder adhesion to a molten plastic film forming step in a powder slush molding method according to one embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a peeling step in the same embodiment.
[0011]
In the powder slush molding method in this invention, at least two types of plastic powders having different melt viscosities are used. As said plastic powder, the well-known thermoplastic powder conventionally used for the powder slush molding method can be used. In particular, in the case of molding an invisible airbag door integrated instrument panel skin, a non-crosslinking type TPU as described above is preferable.
[0012]
As the mold used in the powder slush molding method of the present invention, a known mold used in the powder slush molding method can be used, and at least a recess is formed on the mold surface for forming the plastic film in the mold. In addition, a pin corner portion having a small radius (R) or chamfer width is formed in the concave portion. A mold 10 shown in FIG. 1 (A) is used for powder slush molding of an invisible type airbag panel integrated instrument panel skin as a plastic film, and is formed on a mold surface 11 for forming a plastic film. A small pin corner portion 13 is formed in the recessed portion 12 formed. The radius (R) of the pin corner portion 13 is set to an appropriate value according to the shape of the instrument panel skin. In the present invention, the pin corner portion 13 is particularly 1.5 mm or less. The effect of preventing the occurrence of pinholes is remarkable.
[0013]
The mold 10 is provided with known heating means for heating the mold surface 11. In the illustrated example, a pipe 15 for circulating a heating medium such as oil is disposed on the outer surface of the mold 10 and connected to a heating medium supply device (not shown).
[0014]
In the powder slush molding method of the present invention, as shown in FIGS. 1A and 1B, first, the first plastic powder is applied to the pin corner portion 13 of the recess 12 in the mold surface 11 of the mold 10. P1 is attached.
[0015]
The first plastic powder P1 attached to the pin corner 13 has a lower melt viscosity than the second plastic powder P2 attached to the other part (general part) 14 of the mold surface 11 later. Specifically, 250 to 400 Pa · S (190 ° C.) is preferable. When the temperature is less than 250 Pa · S (190 ° C.), the difference in physical properties is increased near the boundary with the second plastic powder P2, and the plastic film is likely to be warped. On the other hand, 400 Pa · S (190 ° C.) is increased. When exceeding, the air confined between the pin corner portion 13 of the mold surface 11 and the layer of the first plastic powder P1 adhering to the pin corner portion 13 becomes the subsequent second plastic powder P2. This makes it difficult to escape to the outside when forming the molten coating, and pinholes are likely to occur on the surface of the plastic coating formed by the pin corners 13.
[0016]
The first plastic powder P1 adheres to the pin corner 13 by placing the first plastic powder P1 on the pin corner 13 manually or automatically using powder coating, a handle, a cylinder, or the like. This is performed by softening or melting the first plastic powder P1 by the heat of the mold surface 11. The adhesion amount of the first plastic powder P1 varies depending on the amount of the second plastic powder P2 to be subsequently adhered to the other portion 14 of the mold surface 11, but at least the pin corner portion 13 is the first portion. The amount is covered with the plastic powder P1. The temperature of the mold surface 11 is preferably such that the first plastic powder P1 is softened and adhered, and differs depending on the melt viscosity of the first plastic powder P1, but the first plastic powder P1. As an example of the case where is made of non-crosslinked TPU, about 160 to 260 ° C. is shown.
[0017]
Since the first plastic powder P1 is attached to the pin corner portion 13 prior to the second plastic powder P2 attached to the other portion 14 of the mold surface 11, the first plastic powder is used. P1 can be reliably adhered to the pin corner 13 without being obstructed by the second plastic powder P2.
[0018]
Next, the second plastic powder P2 is attached to the other portion 14 as shown in FIGS. The second plastic powder P2 has a higher melt viscosity than the first plastic powder P2, specifically 350 to 900 Pa · S (190 ° C.) and the first plastic powder P1 It is preferable from the viewpoint that the difference in physical properties can be reduced.
[0019]
The second plastic powder P2 adheres to the other portion 14 of the mold surface 11 by replacing the mold 10 having the first plastic powder P1 attached to the pin corner portion 13 with the second plastic powder P2. The mold 10 and the bucket 20 are rotated so as to be alternately inverted by a rotating device (not shown), and the bucket 20 is inverted above the mold surface 11 during the rotation. Thus, the second plastic powder P2 is dropped and deposited on the mold surface 11, and the deposited second plastic powder P2 is softened or melted by the heat of the mold surface 11. At this time, the second plastic powder P2 is deposited on the first plastic powder P1 because the first plastic powder P1 is already attached at the pin corner 13 of the mold surface 11, The other portion 14 of the mold surface 11 is directly deposited on the mold surface without being disturbed by the first plastic powder P1. Therefore, the second plastic powder P2 adheres to the required thickness due to the heat of the mold surface in the other portion 14 that is in direct contact with the mold surface 11, but the mold surface is present due to the presence of the first plastic powder 11a. The pin corner portion 13 that cannot directly contact 11 is thinly attached to the first plastic 11a or hardly attached. Accordingly, the mold surface 11 constitutes an adhesion layer in which the first plastic powder P1 adhered to the pin corner portion 13 and the second plastic powder P2 adhered to the other portion 14 are continuous.
[0020]
The mold surface temperature during rotation of the mold 10 and the bucket 20 is set to a temperature at which the first plastic powder P1 and the second plastic powder P2 are melted, and the first plastic powder P1 and the second plastic powder. Although it differs depending on the type of the powder P2, etc., 190-260 ° C. is given as an example when the first plastic powder P1 and the second plastic powder P2 are made of non-crosslinked type TPU.
[0021]
The mold 10 and the bucket 20 are rotated a required number of times while being heated to form a molten plastic film P3 having a required thickness on the mold surface 11 of the mold 10, and then the rotation of the mold 10 is stopped, The second plastic powder P <b> 2 that has become surplus in the mold 10 is collected in the bucket 20. Further, the mold surface 11 of the mold 10 is cooled by lowering the temperature of the heat medium of the pipe 15 or the like, and the molten plastic film P3 is cured to form a plastic film. After that, as shown in FIG. 2, the plastic slush molding is finished by peeling the plastic coating 30 from the mold surface 11. The plastic coating 30 thus obtained has a good appearance with no or few pin holes in the pin corner portions 31 formed by the pin corner portions 13 of the mold surface 11.
[0022]
【Example】
Specific examples will be described below. General-purpose TPU resin (trade name: E785QSDH, manufactured by Nihon Milactolan Co., Ltd.) 100 parts by weight, ultraviolet absorber (trade name: Tinuvin 120, manufactured by Nagase Sangyo Co., Ltd.), 0.3 part by weight, light stabilizer (trade name: Tinuvin 622, Nagase Sangyo Co., Ltd.) 0.5 parts by weight, antioxidant (Irganox 1010, Ciba Specialty Chemicals Co., Ltd.) 0.3 parts by weight of mixture, non-crosslinked type normal melt viscosity TPU pellets by extrusion molding machine Formed. Non-crosslinked type low melt viscosity TPU pellets were formed on the normal melt viscosity TPU pellets thus obtained by repeating the melt-to-pellet process twice with the extruder. The two types of TPU pellets were frozen and pulverized to form a second plastic powder P2 from the normal melt viscosity TPU pellets, and a first plastic powder P1 was obtained from the low melt viscosity TPU pellets. When the melt viscosity at 190 ° C. was measured for each of the first plastic powder P1 and the second plastic powder P2 by a Koka type flow tester, the first plastic powder P1 was 300 Pa · S (190 On the other hand, the second plastic powder P2 was 600 Pa · S (190 ° C.).
[0023]
Thereafter, the mold 10 for molding the invisible airbag door-integrated instrument panel skin is heated to 220 ° C., and the pin corner 13 (radius R is 1.0 mm) of the mold surface 11 The plastic powder P1 was placed with a thickness so that the pin corner portion 13 was covered with a handle.
[0024]
Next, the bucket 20 containing the second plastic powder P2 and the mold 10 having the first plastic powder P1 attached to the pin corner 13 are combined and combined to form the mold surface 11 of the mold 10. The mold 10 and the bucket 20 are rotated twice in one direction and the opposite direction so that the mold 10 and the bucket 20 are alternately inverted, and the mold surface 11 is melted with plastic. After forming the film, the heating was stopped and cooled, the coalescence was released, and the plastic film was peeled from the mold surface 11 to obtain an example product.
[0025]
On the other hand, the step of attaching the first plastic powder to the pin corner portion 13 is omitted, and the bucket 20 in which the second plastic powder is accommodated and the mold 10 are combined and combined, The temperature of the mold surface 11 of the mold 10 is heated to 220 ° C., and the mold 10 and the bucket 20 are rotated twice each in one direction and in the opposite direction so that the mold 10 and the bucket 20 are alternately inverted. After forming the molten plastic film on the mold surface 11, the heating was stopped and cooled, the coalescence was released, and the plastic film was peeled off from the mold surface 11 to obtain a comparative product.
[0026]
As a result of observing the appearance of the example product and the comparative example product thus obtained, the example product had a good appearance with no pinholes including the portion formed by the pin corners. On the other hand, the comparative product had a pinhole in the portion formed at the pin corner, and the appearance was inferior.
[0027]
【The invention's effect】
As illustrated and described above, according to the powder slush molding method of the present invention, it is possible to obtain a plastic film having a good appearance without a pinhole in a portion formed by pin corners of a mold surface. In addition, since it is not necessary to lower the melt viscosity of the plastic powder by setting the temperature of the mold surface to be higher than usual, the heating and cooling time of the mold surface is not prolonged, and the decrease in productivity can be suppressed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing steps up to formation of a melt film in an embodiment of a powder slush molding method of the present invention.
FIG. 2 is a cross-sectional view showing a plastic film peeling step in the same embodiment.
FIG. 3 is a cross-sectional view showing a pin corner portion in a concave portion of a mold surface where pinholes are likely to occur.
[Explanation of symbols]
10 Mold 11 Mold surface 12 Recess 13 Pin corner 14 Other portion 20 of mold surface Bucket P1 First plastic powder P2 Second plastic powder P3 Molten plastic coating 30 Plastic coating

Claims (5)

Powder slush molding in which plastic powder is attached to the mold surface of a heated mold to form a molten plastic film, then cooled to harden the molten plastic film to form a plastic film, and the plastic film is peeled off from the mold surface In the method
A powder slush molding method characterized in that the plastic powder adhered to the pin corners of the recesses formed on the mold surface has a lower melt viscosity than the plastic powder adhered to the other part of the mold surface. 2. The powder slush molding method according to claim 1, wherein the plastic powder is attached to the pin corner portion of the mold surface before the other portion of the mold surface. The melt viscosity of the plastic powder attached to the pin corner of the mold surface is 250 to 400 Pa · S (190 ° C.), and the melt viscosity of the plastic powder attached to the other portion of the mold surface is 350 to 900 Pa · S (190 ° C.). The powder slush molding method according to claim 1 or 2, wherein The powder slush molding method according to any one of claims 1 to 3, wherein a radius of the pin corner is 1.5 mm or less. The powder slush molding method according to any one of claims 1 to 4, wherein the plastic powder is non-crosslinked TPU.

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