Process for producing a multilayer molded article

1

PROCESS FOR PRODUCING A MULTILAYER
MOLDED ARTICLE

FIELD OF THE INVENTION 5

The present invention relates to a process for producing a multilayer molded article comprising a thermoplastic resin and a skin material. More particularly, it relates to a process for producing a multilayer molded article comprising a thermoplastic resin and a skin mate- 10 rial which covers a desired part of the article

DESCRIPTION OF THE RELATED ART

The above described multilayer molded article comprising the thermoplastic resin and the skin material 15 which covers only a desired part of the article is used as a door trim or a rear trim of an automobile and the like. As a process for producing such multilayer molded article comprising the thermoplastic resin and the skin material which covers only the desired part of the arti- 2° cle (hereinafter referred to as "skin material partially laminated article"), practically used are a process which comprises molding the thermoplastic resin by, for example, injection molding and laminating the skin material having a desired shape on the molded article with an 25 adhesive and the like, and a process which comprises making a part by laminating the skin material on a hard board and attaching said part to the molded article with small screws and the like. These processes require postprocessing of the article, which is troublesome and 30 increases the production cost of the article.

As processes for integrally molding the skin material partially laminated article, Japanese Patent Publication No. 28704/1981 and Japanese Patent Kokai Publication No. 177332/1983 disclose processes for integrally pr.o- 35 ducing a skin material partially laminated article by injection molding which comprise fixing the skin material at a desired position on an inner wall of a mold with a fastener or a magic band, closing the mold and then injecting the thermoplastic resin. These processes re- 40 quire special means for fixing the skin material to the mold. Further, since the resin melt is supplied after closing the mold, it flows at a very high flow rate in a very narrow clearance which corresponds to a difference between a thickness of the article and the thickness 45 of the skin material, a rear face of the skin material receives a large shear rate so that the skin material tends to be easily displaced even though the fastener or the magic band is used. In addition, the skin material is largely influenced by heat, and after the supply of the 50 resin melt, a large pressure is applied to the skin material in a dwell time so that grain pattern, texture, hand and feeling (hereinafter referred to as "feeling") of the skin material tend to be impaired.

DESCRIPTION OF THE INVENTION 55

As a result of the extensive study on a process for producing a skin material partially laminated article having good feeling without displacement of the skin material, it has been found that conditions for supplying 60 the resin melt are important and the present invention has been completed.

Accordingly, the present invention provides a process for producing a multilayer molded article which comprises supplying at least one piece of a skin material 65 having a desired shape and a resin melt between upper and lower molds and closing the molds to form a multilayer molded article, wherein the resin melt is supplied

at or near a center area of a rear face of the skin material, or wherein after the skin material is lifted to a position at which the skin material contacts a cavity surface of the upper mold by a vertically movable rod or bar which is positioned at a part of the lower mold on which the skin material is placed, the resin melt is supplied between the upper and lower molds and the rod or bar is returned to a determined position at least before the molding is completed.

That is, the present invention provides a method for economically producing the skin material partially laminated article wherein the skin material is not moved and the article has good feeling by supplying the resin melt at or near the center area of rear face of the skin material through a passage for the resin melt provided in the upper or lower mold, or by lifting the skin material to the position at which the skin material contacts the cavity surface of the upper mold by the vertically movable rod or bar which is positioned at a part of the lower mold, supplying the resin melt between the upper and lower molds and then returning the rod or bar to the determined position at least before the completion of molding.

The process of the present invention will be illustrated by making reference to the accompanying drawings.

FIG. 1 shows a perspective view of a molded article produced by the process of the present invention, and FIG. 2 shows a cross sectional view of the article of FIG. 1 along the line A—A'. In the figures, numeral 1 stands for a multilayer molded article, 2 stands for a thermoplastic resin and 3 stands for a skin material.

FIGS. 3 to 14 show vertical cross sectional views of apparatuses for explaining the process of the present invention. In these figures, 6 and 8 stand for upper and lower platens of a mold closing machine, respectively, and 7 and 9 stand for upper and lower molds, respectively.

On a cavity surface of the lower mold 9, a shallow depression 10'is provided for determining a position on which the skin material 3 is placed.

By using such apparatus, the process of the present invention is carried out according to the following four steps:

1. The skin material 3 which has been cut to a desired size is placed with the surface down in the depression 10 of the lower mold 9.

2. A lifting mechanism (not shown) of the mold closing machine is actuated to lift the lower mold 9, and then the lower mold 9 is temporarily stopped at a position where the clearance between the cavity surfaces of the upper and lower molds 7 and 9 is larger than the thickness of the article to be molded. At said position, the resin melt 4 is supplied at or near the center area of the rear face of the skin material 3 through a resin passage (not shown) provided in the upper mold 7 by means of a conventional resin melt supplier (not shown) such as an extruder (FIG. 3).

3. Thereafter, the lifting mechanism is reactuated to further lift the lower mold 9 so as to press the skin material 3 against the lower mold 9 and spread the resin melt 4 in the mold cavity, whereby the skin material 3 and the thermoplastic resin 2 are integrated and the molding is completed (FIG. 4).

4. After cooling the mold, the lower mold 9 is lowered to open the upper and lower molds, and then the molded article 1 is removed from the mold.

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In the process of the present invention, the timing for supplying the resin melt 4 is not limited to the above described timing, and the resin melt can be supplied at any time after the skin material 3 is placed on the lower mold 9 and before the upper and lower molds are closed 5 to the final position. Namely, besides the timing at which the mold is stopped at the intermediate position, the resin melt can be supplied before the mold closing is started, or during a continuous closing of the mold without stopping, if desired, while decreasing the mold 10 closing rate.

Preferably, the resin melt 4 is supplied when the mold closing action is temporarily stopped after the start of the mold closing or the mold closing rate is decreased to 30 mm/sec. or less, and the cavity clearance between 15 the upper and lower molds 7 and 9 is not larger than (C+ 100) mm and not smaller than (C + 5) mm wherein "C" represents the cavity clearance when the molding is completed. Thereby, the feeling of the skin material is maintained. 20

When the resin melt 4 is supplied through two or more passages, it is necessary to prevent confluence of the resin melt 4 from the passages on the skin material by adjusting an amount of the resin melt supplied from 25 each passage based on the size and other properties of the skin material 3 so as to prevent penetration of the resin melt between the skin material 3 and the lower mold 9.

According to the process of the present invention, ^ since the resin melt 4 is supplied at or near the center area of the rear face of the skin material when the clearance between the upper and lower molds is still large, the resin melt 4 flows over the skin material 3 at a small shear rate (stress) and spreads from the center area 35 towards a periphery of the skin material. Therefore, the skin material 3 is hardly moved out of position.

During the supply of the resin melt 4, a larger clearance between the upper and lower molds is preferred to decrease the shear rate when the resin melt 4 flows over ^ the skin material 3. However, if the clearance is too large, a shape of the supplied resin melt is deformed and therefore the resin melt 4 is non-uniformly spread, which may cause movement of the skin material. Further, it takes longer from the supply of the resin melt till 45 the closing of the mold, so that the center area of the skin material 3 is heated for a longer period of time than other part and the feeling of the skin material 3 tends to be deteriorated. In addition, a surface condition of a part of the article where no skin material is laminated 50 tends to be deteriorated. Thus, the clearance of the mold is adjusted to a suitable value based on the kinds of the materials, a shape of the molded article, etc.

The present invention further provides a process which comprises placing the skin material 3 with the 55 surface up on the cavity surface of the lower mold 9, and supplying the resin melt 4 at or near the rear face of the skin material 3 through a passage (not shown) which is provided in the lower mold 9.

The skin material.3 is lifted by the resin melt 4 apart 60 from the lower mold 9 and pressed to a predetermined part of the upper mold 8. In such a case, if supply balance of the resin melt is not adequate, the skin material tends to be displaced. Therefore, the clearance between the upper and lower molds during the supply of the 65 resin melt is set narrower than the former process in which the ■ ^ a melt is supplied from the passage provided in the upper mold 7.

Instead of supplying the resin melt 4 from the passage provided in the mold, the resin melt may be supplied from a resin passage which can inserted in and removed from the clearance between the upper and lower molds. However, this method is used only in a very limited case since it is very difficult to adjust the clearance of the mold during the resin supply as described above.

Since the skin material is hardly displaced as explained above, means for preventing displacement of the skin material is not necessarily used. However, it is still preferred to co-use means for preventing displacement of the skin material in order to more precisely position the skin material. As such the displacement preventing means, various means such as shown in FIG. 5 can be used. For example, as shown in FIG. 5A, the depth of the depression 10 is made substantially the same as the thickness of the skin material, as shown in FIG. 5B, a low wall 11 surrounding the skin material 3 is provided, as shown in FIG. 5C, a part of the mold on which the skin material is positioned is modified to form a telescopic element 13, which is pressed against the resin supply side by means of an expansion element 14 such as a spring, a hydraulic cylinder, a pneumatic cylinder and the like during the supply of the resin melt and being returned to the original position as the supply of the resin melt 4 proceeds, or in case where the skin material 3 is a fabric type one such as a fabric or a nonwoven fabric, the part of the mold on which the skin material is placed is provided with minute unevenness 12 as shown in FIG. 5D. In the case of FIG. 5D, not only the displacement of the skin material is prevented, but also the feeling of the skin material is maintained effectively.

To supply the resin melt 4 at or near the center area of the skin material 3, the resin melt may be supplied from at least two inlets for the resin melt and integrated with each other to reach the center area of the skin material, in addition to the above described method in which the resin melt is supplied from one point near the center area. •

When the position at which the skin material 3 is placed on the article is deviated from the center of the article, in addition to the inlet provided near the center area of the rear face of the skin material, another inlet for supplying the resin melt 4 is provided at a position for balancing the flows of resin melt. In this case, it is important that the flows of the resin melts 4,5 do not meet each other on the skin material 3.

According to the present invention, the laminated molded article can be produced by lifting the skin material 3 by a vertically movable rod 16 or bar 17 which is provided in the lower mold 9 up to a position at which at least a part of the skin material 3 contacts with the cavity surface of the upper mold, thereafter supplying the resin melt 4 between the skin material 3 and the lower mold 9 and returning the rod 16 or the bar 17 to the original position at least before the molding is completed. By this method, since the skin material 3 is held by the rod 16 or the bar 17, it is hardly displaced and therefore, the resin melt 4 is not necessarily supplied at the center area of the rear face of the skin material.

The timing at which the rod 16 or the bar 17 is returned to the original position is any time after the start of resin melt supply and before the completion of molding. When plural number of the rods 16 and the bars 17 are used, it is not necessary to return all of them to their original positions at the same time.