JP2000317972A - Injection molding simultaneous decorating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a decorative sheet from releasing from a molded product by the decorative sheet step by step in the preliminary molding. SOLUTION: A decorative sheet S inserted between a female and a male mold is held by clamping by a receiving chuck 23, and the whole peripheral edge of a cavity face is press fixed on a parting face of a male mold 20 mounted on a movable platen 22 by sheet clamps 50, and a sealed spacer V is formed by the cavity face of the female mold and the sheet S. The sheet S is heat softened by a hot platen 60, and the sheet is sucked while reducing the pressure in multi-stages by vacuum pump 70 through a vacuum suction hole 21 of the male mold 20, and the sheet S is made to suction-adhere on the cavity face of the female mold. After the preliminary molding of the sheet S, the upper end side of the sheet S is cut in the width direction by a sheet cutter 81, and the sheet S is cooled and the hot platen 60 is retracted, and a molded product forming resin is injected from a male mold gate 32 into a cavity formed by the female and male molds 20 and 30 and bonded with the sheet S and laminated thereon. Thus the decorative sheet S of superior heat resistance not to be released from the molded product is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of an injection molding simultaneous decorating method in which a decorative sheet is bonded and laminated on the surface of a resin molded product to provide a picture.

[0002]

2. Description of the Related Art Conventionally, as a method of providing a pattern on the surface of a resin molded product, a decorative sheet is inserted between male and female molds of injection molding, and the molds are engaged and clamped. In general, a method of injection-filling a resin sheet and bonding a decorative sheet to the surface of a resin molded product is generally performed. In particular,
The female mold cavity surface is provided with an intake hole, and the decorative sheet is fixed to the peripheral parting surface of the female mold cavity surface with a decorative sheet clamp to form a closed space between the decorative sheet and the female mold cavity surface, After evacuating from the suction hole connected to the vacuum pump and reducing the pressure, the decorative sheet is brought into close contact with the surface shape of the female mold cavity surface, preformed and then closed. A resin in a flowing state is injected and filled into the cavity space to be formed, and the resin is solidified, and at the same time, a decorative sheet is adhesively laminated on the surface of the molded product (Japanese Patent Publication No. 50-1913).
No. 2, JP-A-6-315950 and the like).

[0003]

In the above-mentioned conventional simultaneous injection-molding and decorating method, since the stress at the time of preliminary molding of the decorative sheet remains in the decorative sheet, when the sheet is heated again, the sheet tends to shrink due to release of the residual stress. In some cases, the decorative sheet was peeled off from the molded product by the force.

Recently, polypropylene (hereinafter referred to as PP) has been used as a resin for injection molding from the viewpoint of so-called environmental problems.
Although the heat-sensitive adhesive for PP typified by chlorinated polyolefin retains necessary and sufficient adhesive strength as an industrial product at room temperature,
Adhesive strength at high temperatures is inferior to BS resin, PC (polycarbonate) resin, etc., and in decorative molded products using decorative sheets based on acrylic resin, etc., the decorative sheets shrink at high temperatures depending on the product shape. Shearing stress is generated at the interface between the decorative sheet and the molded product due to the force to be applied, and the decorative sheet may be peeled off from the molded product, so that it cannot be said that the heat resistance is sufficient.

[0005]

As a result of various studies to solve the above problems, the following has been found. That is, when the decorative sheet is stretched by heating, a force to return is generated, and when the temperature of the decorative sheet is reduced at a stretch in that state, the stress remains in the decorative sheet. When heated again, the decorative sheet tends to contract due to the residual stress. It has been found that this residual stress is the cause of peeling of the decorative sheet at high temperatures.

The inventor of the present invention has noticed that the force for shrinkage caused by the stretching of the decorative sheet decreases with time under a sufficiently high temperature. Therefore, in the present invention, the decompression at the time of preliminary forming of the decorative sheet is performed stepwise, and the decorative sheet is formed while relaxing the residual stress caused by the initial stretching of the decorative sheet. This makes it possible to produce a product having excellent heat resistance as compared with a conventional decorative molded product.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a decorative sheet is inserted between a pair of open male and female molds in order to bond and laminate a decorative sheet on the surface of a molded article simultaneously with injection molding. By fixing the female mold cavity surface and the decorative sheet in a sealed manner with a clamp or the like on the parting surface of the peripheral edge of the surface, the decorative sheet is heated and softened, and the sealed space is depressurized. After the decorative sheet is brought into close contact with the surface shape of the female mold cavity surface and preformed, the molds are closed, and then the resin in the fluid state is injected and filled into the cavity space formed between the male and female molds. In addition, in the simultaneous injection molding and decorating method in which the resin is solidified and the decorative sheet is adhered and laminated on the surface of the molded article, the pressure reduction is performed stepwise.

FIG. 1 shows an example of an injection molding machine used in the present invention. In this injection molding machine 10, the female mold 20
Has a structure in which a vacuum suction hole 21 or a vacuum suction groove is provided so as to be applicable to vacuum suction molding. One of the shapes of a molded product formed by injection molding by being combined with the male mold 30 is provided. The portion is shaped as a female cavity surface 24. The male mold 30 is fixed to a fixed platen 31 and also to a tie bar 40 (a total of four). on the other hand,
The female die 20 is fixed to a movable platen 22, and the movable platen 22 is slidably penetrated by a tie bar 40.

First, at the time of preforming, the decorative sheet S inserted between the male and female dies is sandwiched and held by the receiving chuck 23, and the decorative sheet S is attached to the sheet clamp 50 on the parting surface of the female die 20 mounted on the movable platen 22. Then, the entire periphery of the cavity surface is pressed and fixed, and a sealed space V (see FIG. 3) is formed between the female mold cavity surface and the decorative sheet S. Next, after the decorative sheet S is heated and softened by the hot platen 60, the decorative sheet S is sucked by the vacuum pump 70 through the vacuum suction holes 21 of the female mold 20 to make the decorative sheet S adhere to the female mold cavity by suction (this state is shown in FIG. 1). ). At this time, the pressure in the sealed space is not reduced monotonically from the atmospheric pressure to a vacuum state at once, but is reduced in multiple steps (at least two steps) as shown in FIG. That is, for example, at time t = t ₁ , the valve 71 interposed between the vacuum pump 70 and the suction hole 21 is opened only for the time Δt, and the pressure is changed from P = P ₀ (= atmospheric pressure) to P = P ₁ (<
P ₀ ) and left to stand until t = t ₂ , during which time the residual stress is released. Next, at time t = t _2, the valve is opened again for a time Δt, the pressure is reduced to P = P ₂ (<P ₁ ), and the pressure is left as it is until t = t ₃ , and the residual stress is further released. Thereafter, at time t = t ₃ , the valve is fully opened, and the air pressure is reduced to a vacuum or a state close thereto. Then, at the stage of t> t ₃ , the decorative sheet S completely adheres to the female mold cavity surface, and the preforming is completed.
FIG. 3 shows the progress of the preliminary forming of the decorative sheet S with the passage of time t. Here, t ₁ , t ₂ , t ₃ , Δt,
The specific values of P ₁ and P ₂ may be determined by experiments, and the optimum values may vary depending on the material of the decorative sheet, the shape and size of the mold, and the like. , T ₁ = 5 to 20 seconds, t ₂ = t ₁ + (2 to 5 seconds), t
₃ = t ₂ + (2 to 5 seconds), Δt = 0.5 to 1 second, P ₁ =
400~600mmHg, P ₂ = 200~400mmH
g.

FIG. 4 is a graph showing a change in the strength of a force (or stress) for the decorative sheet to contract when the sealed space V between the female cavity surface and the decorative sheet is depressurized. Since this intensity is actually difficult to measure, FIG. 4 is only a conceptual illustration. The time-intensity curves obtained when the pressure in the sealed space V is reduced at once and when the pressure is reduced in multiple stages as shown in FIG. As indicated by the mark, the decorative sheet is in close contact with the female mold cavity surface, and the strength at which the decorative sheet tends to shrink becomes residual stress.

After the preliminary forming of the decorative sheet S is completed, the decorative sheet S is nipped by the sheet chuck 80 for conveyance, and the decorative sheet S is cut in the width direction by the sheet cutter 81. As the sheet cutter 81, cutting tools,
A heating wire or the like is used. In the example of FIG. 1, the sheet cutter 81 is installed on the hot platen 60, and cuts the decorative sheet S in conjunction with bringing the hot platen 60 close to the decorative sheet S. It is also possible to cut the decorative sheet by installing it on the clamp 50 and interlocking with the pressing and fixing of the sheet. Thereafter, the decorative sheet S is cooled. (Alternatively, resin injection, which will be described later, may be performed without waiting for the cooling of the decorative sheet S.) As the hot platen 60 for heating and softening the decorative sheet S, the hot plate 60 comes into close contact with the decorative sheet S and contacts with the decorative sheet S to conduct heat conduction Contact heating type, or non-contact type (heating plate 60 shown in FIG. 1 is this type) in which heating is performed by radiant heat from a position distant from decorative sheet S or by dielectric heating.

After completion of the preforming of the decorative sheet S as shown in FIG. 1, the hot platen 60 is retracted to an external standby position (not shown) between the male and female molds as shown in FIG. By operating the piston 91, the female die 20 with the decorative sheet S in close contact therewith is combined with the male die 30 while sliding on the tie bar 40, and the die is clamped. Injection molding is performed by filling the cavity C with the molded product forming resin P in a flowing state through the male gate 32. And the injected resin P
Is solidified, and the decorative sheet S and the resin molded product P 'are bonded and laminated, and then, as shown in FIG.
Is opened, and the resin molded product P ′ whose surface is decorated by the decorative sheet S is taken out of the mold. The female mold 20 and the male mold 30
Is formed of metal such as iron or ceramics.

As the decorative sheet, a sheet which has a base sheet as a minimum element and which has been subjected to a decorative treatment by kneading a colorant, printing a pattern, forming a metal thin film or the like as necessary is used. The base sheet is made of polyolefin resin such as polyethylene, polypropylene, olefin-based thermoplastic elastomer, polymethyl (meth) acrylate, methyl (meth)
Acrylic resin such as acrylate-butyl (meth) acrylate, polyethylene terephthalate, polyester resin such as polybutylene terephthalate, vinyl chloride resin,
It consists of a sheet of thermoplastic resin such as polycarbonate resin, polystyrene, ABS resin, etc., and the thickness is usually 20-30.
It is about 0 μm.

[0014] When sufficient adhesion with the injection molded article cannot be obtained on the base sheet or the decoration treatment itself, an adhesive layer is formed on the molded article side. The adhesive is selected according to the combination of the decorative sheet and the material of the molded article. For example, in the case of a combination of a base sheet of a polyolefin resin and a molded product of a polyolefin resin, a chlorinated polyolefin resin (such as chlorinated polypropylene) is used. A two-component curable urethane resin layer is formed on a material sheet, and a chlorinated polyolefin resin layer is formed thereon in this order.

The resin in the flow state injected from the male gate is a resin for injection molding, and is actually selected in accordance with required physical properties of the product, cost, and the like. Specifically, polyethylene, polypropylene, polybutene, polyolefin resins such as olefin-based thermoplastic elastomers, acrylonitrile-butadiene-styrene copolymer (ABS), polystyrene resin, acrylonitrile-styrene copolymer, polyvinyl chloride resin, polycarbonate, A resin such as an acrylic resin, which is heated and melted and injected, and cooled to be solidified; a polyurethane resin comprising a polyol and an isocyanate crosslinking agent; an epoxy resin having an amine as a curing agent; an isocyanate; In some cases, an uncured liquid component of a two-component reaction-curable resin such as an unsaturated polyester using a sulfonate, benzoyl peroxide or the like as a curing agent is injected and solidified by a chemical reaction. However,
In the method of the present invention, among these resins, various decorative sheets and a high temperature immediately after being removed from the mold (normally 40 to
This is effective in the case of a polyolefin resin in which it is difficult to obtain an adhesive having a strong adhesive force at about 60 ° C.).

[0016]

EXAMPLES (Example) A two-part curing type obtained by adding 10 parts by weight of 1,6-hexamethylene diisocyanate to 100 parts by weight of acrylic polyol on one side of an acrylic resin (polymethyl methacrylate) sheet having a thickness of 125 μm. A urethane resin primer was coated at 1 μm, and an adhesive made of chlorinated polypropylene was further coated at 4 μm on the primer to prepare a decorative sheet.

Using the decorative sheet prepared as described above, simultaneous decoration was performed by an injection molding machine shown in FIG. First, the decorative sheet S was pressed and fixed on the female parting surface by the sheet clamp 50 to form a sealed space V surrounded by the decorative sheet S and the female mold cavity surface. Then
The heating was started by bringing the hot plate 60 of infrared radiation type having a surface temperature of 350 ° C. inserted from outside of both molds close to the decorative sheet S at a distance of 40 mm. This heating start time is set to t = 0 seconds. Then, when t = 10 seconds and the sheet temperature reached 140 ° C., suction by the vacuum pump 70 was started. This suction was performed while controlling the valve 71 connected to the vacuum pump 70 by an electric signal sent via a control signal line 72 from a control panel (not shown) in which opening and closing times were programmed in advance. Specifically, the pressure in the sealed space is increased to 760 m
mHg to 570 mmHg, and left in this state for 2.5 seconds to release the residual stress of the decorative sheet S,
Next, at time t = 13 seconds, the valve 71 was opened again and closed after 0.5 seconds to reduce the pressure in the sealed space to 390 m.
mHg and left for 2.5 seconds in this state to further release the residual stress of the decorative sheet S, and then t = 1
At the time of 6 seconds, the valve 71 is fully opened and suction is performed for 1 second, the pressure in the sealed space is reduced to 10 mmHg or less, and the decorative sheet S
Was completely brought into close contact with the cavity surface of the female mold to complete the preforming.

Next, the hot platen 60 is retracted to a standby position (not shown) outside the male and female molds.
After closing the mold 1, the male and female molds are closed and the molds are closed as shown in FIG. 5, and 10 parts by weight of ethylene propylene rubber is added to 100 parts by weight of 220 ° C. polypropylene melted from the male gate 32 in the cavity space between the two molds. The mixed resin was injection-filled and solidified by cooling. The temperature of both molds at this time was 60 ° C. Subsequently, as shown in FIG. 6, both molds were opened, and a molded product having a decorative sheet laminated and integrated on the surface was taken out.

(Comparative Example) A decorative molded article was manufactured in the same manner as in Example except that the pressure reduction during the preliminary molding of the decorative sheet was performed at once. Specifically, the heating start time of the decorative sheet S by the hot platen 60 is set to t = 0 seconds, and when t = 10 seconds and the sheet temperature reaches 140 ° C., the suction by the vacuum pump 70 is started, and is performed for 7 seconds. Then, the pressure in the sealed space was reduced from 760 mmHg at atmospheric pressure to 10 mmHg or less at once, and the decorative sheet S was completely adhered to the female mold cavity surface. After completion of the preliminary molding, injection molding was performed.

Each of the decorative molded products obtained in Examples and Comparative Examples was left in an atmosphere of 110 ° C. for 10 minutes,
When the decorative sheet was cooled to ℃ and the presence or absence of peeling of the decorative sheet from the molded article was visually checked, peeling of the decorative sheet was observed in the molded article of the comparative example, but peeling of the decorative sheet was not observed in the molded article of the example. I couldn't.

[0021]

As described above, according to the present invention,
When performing injection molding simultaneous decoration, by performing the pressure reduction during the preliminary molding of the decorative sheet in a stepwise manner, since the molding is performed in a state where the residual stress caused by the initial stretching of the decorative sheet is relaxed, Even in a temperature environment in which a decorative molded product manufactured by a conventional method is likely to cause peeling, a decorative article having excellent heat resistance without peeling can be produced.

[Brief description of the drawings]

FIG. 1 is a partially cutaway view showing an example of an injection molding machine used in the present invention.

FIG. 2 is a graph showing a change in air pressure in a closed space between a female cavity surface and a decorative sheet during sheet molding.

FIG. 3 is an explanatory diagram showing the progress of preliminary forming of a decorative sheet over time.

FIG. 4 is a graph showing a change in the strength of a force that causes the decorative sheet to contract when the sealed space between the female mold cavity surface and the decorative sheet is depressurized.

FIG. 5 is a partially cutaway view of an injection molding machine showing a state in which a molding resin is injected after preliminary molding of a decorative sheet is completed.

FIG. 6 is a partially cutaway view of an injection molding machine showing a state in which both male and female molds are opened and a resin molded product is taken out after injection molding.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Injection molding machine 20 Female mold 21 Suction hole 22 Movable board 23 Reception chuck 30 Male mold 31 Fixed board 32 Gate 40 Tie bar 50 Sheet clamp 60 Hot plate 70 Vacuum pump 71 Valve 80 Sheet chuck 81 Sheet cutter 90 Fluid pressure cylinder 91 Piston S Decorative sheet C Cavity P Molded resin P 'Resin molded

Claims (1)

[Claims] 1. A decorative sheet is inserted between a pair of opened male and female molds, and the decorative sheet is clamped between the female mold cavity surface and the decorative sheet on a parting surface of a peripheral edge of the female mold cavity surface. After being preliminarily molded, the decorative sheet is heated and softened, and the decorative sheet is brought into close contact with the surface shape of the female cavity surface by depressurizing the sealed space so that the decorative sheet is sealed and fixed. After the molds are closed, the resin in the fluid state is injected and filled into the cavity space formed between the male and female molds, and the resin is solidified, and at the same time, the decorative sheet is bonded and laminated on the surface of the molded article by injection molding. In the decorating method, the injection molding simultaneous decorating method is characterized in that the decompression is performed stepwise.