JPH03224720A - Vacuum molding method - Google Patents

Abstract

PURPOSE:To form a shape skin of uniform wall thickness and without defects on the surface by varying the retaining position correspondingly to the mold dividing surface shape of projected mold in the state of retaining the skin, bringing the skin into contact with the projected mold, releasing all retentions after mold clamping and vacuum molding. CONSTITUTION:A skin 1 consisting of a vinyl chloride resin skin layer and a backing layer composed of flexible PP foamed bodies laminated on the rear surface side of the skin layer is heated, and when the same is in the state of being able to deform, a bottom force 3 which is a projected mold is lifted up. When clamps C and B on the side of a high dividing surface 30 are lifted up from a position where the skin 1 is pushed up by 100mm following the rising of the bottom force 3, said clamps are on the positions higher than those of clamps D and A. When the bottom force 3 and a top force 4 are brought into contact with each other and mold clamped, clamps A-D are opened and the skin 1 comes into a clamping section by means of the pressing force from the bottom force 3. Then, the inside of the cavity is vacuumized by a vacuum pump 5 through an air exaust path 40 provided on the top force 4, and the skin 1 is vacuum molded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for vacuum forming thermoplastic resin.

The vacuum forming method of the present invention is useful when vacuum forming a large, complex-shaped molded article such as an automobile instrument panel.

[Prior Art] Automobile instrument panels and the like are constructed of a hard base, a backing layer made of foam, and a skin made of a resilient skin material made of vinyl chloride resin or the like. Then, the skin is formed into a predetermined shape by vacuum forming, and is integrally covered with a base formed by injection molding or the like.

When shaping the skin into a predetermined shape, the peripheral edge of the sheet-like skin is held with a plurality of clamps and heated to a softening temperature. Then, it is shaped into a predetermined shape by being held between a mold consisting of a convex mold and a concave mold having a predetermined shape.

By the way, internal stress may remain when forming the skin into a sheet shape, and this stress may act during vacuum forming, causing the skin after molding to shrink significantly in the roll direction. Therefore, conventionally, after vacuum forming, the skin is held with clamps until it is cooled and solidified. However, when shaping the skin into the shape of an instrument panel with large irregularities, the thickness of the skin material becomes thinner because the convex parts are extremely stretched, and in extreme cases, it may even tear. . Furthermore, since the thickness of the backing layer of the epidermis also differs locally, there has been a problem in that the tactile sensation differs locally. In addition,
By increasing the size of the sheet-shaped skin and keeping it in a relaxed state, it is possible to prevent the sheet from becoming thicker and tearing. However, it is still strongly stretched locally, and it is inevitable that differences in wall thickness will occur. In addition, there is a lot of material loss and the yield is poor.

Therefore, Japanese Unexamined Patent Publication No. 59-120456 discloses a vacuum forming method in which a plurality of clamps are opened in stages depending on the degree of pressing against the convex skin. That is, by opening the clamp near the convex portion before the other clamps, the skin in that area is not stretched, thereby preventing the skin from becoming thinner.

[Problems to be Solved by the Invention] In the vacuum forming method, as shown in FIG. 5, the white portion 102 of the convex mold 101 first comes into contact with the heated skin 100. Here, it is assumed that the distance from the white portion 102 to one end 103 of the convex mold 101 is longer than the distance from the white portion 102 to the other end 104. If the convex mold 101 is further raised in this state, the length of the skin 100 from the white part 102 to one end 103 will be a little short, and the length of the skin 100 from the white part 102 to the other end 104 will be a little too long. .

Therefore, when the clamp 105 on the other end 104 side is opened according to the method disclosed in the above publication, the skin 100 is shifted toward the one end 103 side (in the direction of the arrow shown in the figure) as shown in FIG. 6, and the lengths on both sides of the white portion 102 are balanced. Therefore, the thickness of the skin 100 becomes uniform.

However, in FIG. 5, the epidermis 100 has a white part 1
02 contacts first, the contacting portion of the skin 100 cools down and becomes difficult to deform locally.

As shown in FIG. 6, the portion that is difficult to deform is shifted toward the end 103, resulting in a problem that local swelling remains on the surface of the shaped skin 100.

The present invention was made in view of these circumstances, and
The purpose is to mold a shaped skin that has a uniform thickness and no surface defects.

[Means and effects for solving the problems] The vacuum forming method of the present invention that solves the above problems includes a step of holding and heating a plurality of peripheral parts of a sheet-like skin with a plurality of holding members, and a step of heating In a vacuum forming method that consists of a forming process in which a softened skin is placed between a convex mold and a concave mold, the convex mold and the concave mold are clamped, and vacuum forming is performed, the molding process involves placing a softened skin between a convex mold and a concave mold, and vacuum forming the convex mold while holding the skin in a holding member. The holding position of at least one holding member is changed in the mold clamping direction according to the shape of the mold splitting surface of the mold to bring the skin into contact with the convex mold, and after the mold is clamped, the skin is released from being held by all the holding members to perform vacuum forming. It is characterized by

As the skin, a thermoplastic resin material such as polyvinyl chloride or polyolefin, or a cloth material lined with a sheet made of these resin materials is used. It is also possible to use one having a backing layer made of a soft foam such as foamed urethane, foamed PP, or foamed PVC on the back side.

The outer skin is heated to about its softening temperature while its peripheral edge is held by a plurality of holding members. This softens the epidermis and allows it to be plastically deformed.

Note that a surface heater or the like is used to heat the epidermis, and the plurality of holding members are located on the same plane, so that the epidermis is generally held in a horizontal state.

Subsequently, the convex white portion comes into contact with the softened skin and presses the skin. At this time, in the vacuum forming method of the present invention, at least one holding member is held according to the shape of the convex mold parting surface. Change the position in the mold clamping direction. In other words, if the skin is held in the horizontal direction and the mold is clamped in the vertical direction, and the lower mold is convex, the height of at least one holding member is changed according to the height of the cutting surface of the lower mold. let The height, the number of holding members to be changed, and their positions are generally determined by trial and error, but usually the holding members are changed so that the holding members corresponding to the mold parting surfaces at higher positions are at higher positions.

This prevents a large pressing force from acting locally on the epidermis from the lower mold.

The height of the holding member may be changed as the lower die approaches the outer skin, or may be changed in advance before the lower die comes into contact with the outer skin. Note that although a part of the holding member can be opened before mold clamping, the skin is held as a whole by the holding member.

Then, the convex and concave molds are clamped together, all the holding members are opened, and the skin is the convex and concave mold clamping parts (PL part).
Get into it. At this time, a tensile force that is approximately uniform over the entire circumference of the skin is applied to the skin, so that the skin enters the mold clamping portion almost uniformly over the entire circumference.

The skin is then vacuum-formed by being attracted to the mold surface under negative pressure. Therefore, the thickness of the epidermis becomes uniform, and local variations in thickness are prevented. Further, the part of the skin that is in contact with the image part of the convex surface is vacuum-formed while maintaining its position. This prevents bulges from occurring on the surface of the skin after molding and impairing the appearance quality.

[Effects of the Invention] Therefore, according to the vacuum forming method of the present invention, a skin having a uniform wall thickness and excellent appearance quality can be easily produced with stable quality. In addition, since the area of the sheet-like skin required for molding is the minimum necessary amount, the yield is improved. Furthermore, the degree of stretching of the backing layer is uniform and the soft feel is increased, so even if the thickness of the backing layer is made thinner than in the past, it is possible to maintain the same tactile feel as in the past, thereby reducing costs.

[Example] Hereinafter, this will be explained in detail using examples.

First, a skin 1 consisting of a skin layer made of vinyl chloride resin and a backing layer made of a soft PP foam laminated on the back side of the skin layer is prepared, and as shown in Figure 2, the skin 1 is held horizontally and heated. Heat from both sides in step 2. Here, the skin 1 has a sheet shape as shown in FIG. 4, and is held by six clamps A to F at each of the four corners and both peripheral edges in the longitudinal direction.

At this time, the clamps A to F are located in the same plane, and the skin 1 is held horizontally. In addition, Figures 1 to 3
The figure shows the state seen from the direction of the arrow in FIG.

When the skin 1 is heated to a softening temperature (160'C) and becomes plastically deformable, the heater 2 is removed and the convex lower mold 3 is raised toward the skin 1. In this lower mold 3, the mold parting surface 30 on the side of clamp C and clamp B is higher by 180 mm than the parting surface 31 on the side of clamp D and clamp A. Then, the image part 32 of the lower mold 3 covers the epidermis 1 by 100 mm.
When it is pushed up to a certain extent, clamp E and clamp F are released.

From a position where the skin 1 is pushed up about 100 mm, as shown in FIG. 1, as the lower die 3 rises, the clamps C and B on the side of the higher die parting surface 30 are raised. As a result, clamp C and clamp B become clamp D and clamp A.
It will be in a higher position.

The lifting of the lamp C and the clamp B is performed by an air cylinder device, and the lifting speed is 100 to 1 of the lifting speed of the lower die 3.
It has been adjusted to be 20%.

That is, the condition is such that the peripheral edge of the skin 1 held by the clamps C and B reaches the position of the upper mold 4 first and waits for the lower mold 3 to rise.

As shown in FIG. 3, when the lower mold 3 and the upper mold 4 are brought into contact and clamped, the clamps A to D are respectively located at the mold cutting surface of the lower mold 3. In this state, clamps A to D are opened. Then, the skin 1, on which the tensile force is acting due to the pressure from the lower mold 3, enters the mold clamping portion as shown by the arrow in FIG. At this time, the entire circumference of the skin 1 is located at the cutting surface of the lower die 3, so the skin 1 enters the cavity almost uniformly, and no strong force is applied locally, resulting in uniform meat. It becomes thick.

Then, the skin 1 is vacuum-formed by reducing the pressure in the cavity with the vacuum pump 5 via the exhaust passage 40 provided in the upper mold 4.

The thickness of the skin 1 formed into a predetermined shape is 25 ± 0° 2 mm.
It was within the range of This is 2.5 to 1.5 times smaller than the conventional method in which the skin is molded while keeping it in the same plane.
mm~2.5+0.2 mm, the variation width was much smaller in the direction of thinning, and a uniform tactile sensation was obtained. And because the backing layer had a sufficient thickness, it had an excellent soft feel. In addition, the required area of the sheet-like skin to be used is reduced by 20 to 30% compared to the conventional method, and the yield is improved. In addition, there was no swelling of the surface of the skin, which occurs when molding is performed by gradually opening a plurality of clamps as shown in FIG. 6, and the appearance quality was excellent.

[Brief explanation of drawings]

Figures 1 to 4 relate to a vacuum forming method according to an embodiment of the present invention, with Figure 1 being an explanatory diagram showing the relationship between the lower mold and the clamped state of the skin before mold clamping, and Figure 2 heating the skin. FIG. 3 is an explanatory diagram showing the mold clamping state, and FIG. 4 is a plan view showing the sheet-like skin used together with the clamp. FIGS. 5 and 6 are explanatory diagrams each illustrating the relationship between the lower die and the skin in the conventional vacuum forming method. 1...Skin 2...Heater 3...Lower mold (convex) 4...Upper mold (concave) A, B, C, D, E
, F... Clamp (holding member) 30° 31... Mold splitting surface

Claims (1)

[Claims] (1) A step of holding and heating a plurality of peripheral parts of a sheet-like skin with a plurality of holding members, and placing the skin softened by heating between a convex mold and a concave mold, In a vacuum forming method comprising a molding step of clamping and vacuum forming, in the molding step, at least one of the retainers is held in the holding member according to the shape of the convex mold parting surface while the skin is held in the holding member. A vacuum forming method characterized by changing the holding position of the member in the mold clamping direction to bring the skin into contact with the convex mold, and after the mold is clamped, releasing the retention of the skin by all the holding members and performing vacuum forming. .