JP2001334549A - Method for manufacturing composite molded article, and composite molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of manufacturing a composite resin molded article reduced in weight, having a design surface excellent in optical and physical appearance, capable of being provided with arbitrary characteristics, arbitrary and wide in a selection range of two kinds of resins and excellent in strength and rigidity. SOLUTION: A primary molten resin is charged in the cavity of a mold to form a molded article having a design surface and, thereafter, the volume of the mold cavity is expanded and a secondary molten resin is injected in the mold cavity on the rear surface side of the design surface and gas is subsequently injected in the mold cavity to form a hollow part in the secondary molten resin at a desired place to manufacture the composite resin molded article.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a composite molded product and a composite molded product, and more particularly, to a composite molded product which is excellent in the appearance of a design surface by a two-stage injection molding and can be reduced in warp and reduced in weight. The present invention relates to a method for manufacturing a product and a composite molded product.

[0002]

2. Description of the Related Art Conventionally, thermoplastic resins and fiber-reinforced thermoplastic resins have been widely used in the fields of automobiles, home electric appliances, OA equipment, furniture, housing equipment, construction, and civil engineering. These molded products are mainly formed by injection molding in terms of productivity and the like. The feature of these molded products is that they are lighter in weight than other materials, but the industry demands further weight reduction from the viewpoint of resource saving and effective use of resin. This reduction in the weight of the resin molded product is a desirable use form from the viewpoint of high strength and rigidity per unit weight and effective utilization of resources.

[0003] In addition, to prevent the occurrence of sink marks, eliminate flow patterns, prevent uneven gloss, and improve mold transferability in molded products,
There is a need to eliminate appearance defects. Furthermore, from the viewpoint of utilizing the characteristics of the resin, the surface of the molded product is made of a resin material with excellent appearance and feel, and the core is made of a resin material with high strength and rigidity. The use of a multi-layer structure has been put to practical use.

[0004] In order to reduce the weight of an injection molded product, a foam injection molding method using a foaming agent, a molding method for forming a hollow portion by gas injection, and a method for reducing the thickness of the molded product are generally used. However, in the foam molding method, a gas flow is generated on the surface by the decomposition gas of the foaming agent, and it is very difficult to obtain a molded product having a satisfactory appearance, and the strength and rigidity are significantly reduced together with the expansion ratio. . In addition, the method for reducing the weight by gas injection has a problem that it is difficult to make the gas injection uniform and the appearance is not sufficient. further,
In the method of reducing the thickness of the molded article, it is difficult to secure the rigidity and strength of the molded article, and there is a problem of deformation such as warpage of the molded article.

[0005] Another problem with molded articles is that, in addition to improving the appearance of the design surface of the molded article, molded articles that satisfy properties such as physical properties such as hardness and chemical resistance, coloring, an antistatic effect, and a soft feeling. It has been demanded. That is, there is a particular need for a molded article that can simultaneously improve the appearance and physical properties of a design surface, as well as reduce weight, strength, and rigidity.

In order to achieve this object, gas injection is performed by setting a thermoplastic resin sheet having a decorative layer in an injection mold, and then sequentially injecting a molten thermoplastic resin and a high-pressure gas into the mold. Molding method for integrating a decorative sheet on the surface of a molded article (Japanese Patent Laid-Open No. 6-27019)
No. 5), after the surface material is set in the mold cavity, the molten resin is injected into the mold cavity, pressurized gas is injected into the molten resin, and the volume of the mold cavity is increased. Form a hollow part and discharge the pressurized gas in the hollow part,
Furthermore, there has been proposed a method of manufacturing a heat-insulating door in which a foamable resin is injected into a hollow portion to foam the resin (JP-A-6-198674).

Although this method is an excellent manufacturing method in that the surface material can be selected widely, it uses a preformed surface material and is generally limited to a sheet.
There are restrictions on the shape and design of the molded product. In addition, there is a problem that a step of setting a surface material in a molding die is required, and it is very difficult to reliably cover the entire design surface with the surface material in the outer peripheral portion of the molded product.

In the production of a hollow molded article, after the injection of the resin for forming the outer layer is started, the injection of the resin for forming the inner layer is started, and a predetermined amount is injected into the molding die cavity. Method for producing a hollow resin molded product in which a hollow portion is formed by blowing compressed gas (Japanese Patent Laid-Open No. 2-108511)
Japanese Patent Application Laid-Open No. Hei 3-284915) Injection molding method of a multilayered product in which two or more types of molding materials are sequentially injected into a mold and partially filled with a single or a plurality of molding materials. Thereafter, a cavity obtained by blowing a pressurized gas is filled with another type of molding material, and a pressurized gas is blown into the cavity to form a cavity and repeat the filling process.
308940).

In these molding methods, the strength and rigidity of the resin for the inner layer are changed by changing the types of the resin for the surface skin layer and the resin for the inner layer of the hollow molded article in the molded article having a hollow portion by gas injection. And the like, so as to obtain surface characteristics, for example, softness, as a skin layer resin.

However, in order to form a multilayer structure in a molten state while injecting the skin layer resin and the inner layer resin into a mold, the melt viscosity and melt fluidity of both resins, that is, the selection and combination of the resins are greatly restricted. There is a problem that it is difficult to make the thickness of the skin layer uniform on the surface of the molded product, and it is very difficult to uniformly cover the skin with the skin layer resin including the appearance. . Further, in some cases, the resin for the inner layer may break the skin layer and appear on the design surface. In addition, there is no change to the hollow molding method, and there is a difficulty in molding such as generation of ripples on the design surface of a molded product due to uneven cooling during cooling.

That is, in these hollow molding methods, a molded product having a design surface of an arbitrary shape, and a lightweight molded product excellent in the appearance of the design surface, has not yet been manufactured with high productivity. It is.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the weight of a resin molded product, to provide excellent optical and physical appearance of the design surface of the molded product, to provide arbitrary characteristics, and to provide two types of resin. It is an object of the present invention to provide a method for producing a composite molded product that can obtain a molded product excellent in strength and rigidity in which the selection range is arbitrary and wide.

[0013]

Means for Solving the Problems The present inventors have solved the above-mentioned problems by using a sheet for decorative skin, with respect to the formation of a surface layer having an excellent appearance of a design surface and the weight reduction by forming a hollow portion by gas injection. Intensive study was conducted including conventional manufacturing methods such as sandwich molding using various molding materials. as a result,
By forming the design surface and forming the hollow molded product in two steps using the same molding die, it is possible to secure an excellent appearance of the design surface and to make full use of the features of the hollow molded product. The inventors have found that a molded article can be manufactured with high efficiency and productivity, and have completed the present invention.

That is, the present invention provides: (1) After filling a cavity of a molding die with a primary molten resin to form a design surface of a molded product, the volume of the mold cavity is increased, and A method of manufacturing a composite molded article in which a hollow portion is formed at a desired position in the secondary molten resin by injecting a secondary molten resin and injecting a gas. (2) The method for producing a composite molded article according to (1), wherein the primary molten resin and the secondary molten resin are made of different materials. (3) The method for producing a composite molded article according to (1) or (2), wherein at least a part of the end face of the molded article is formed simultaneously with the design surface using the primary molten resin. (4) The method for producing a composite molded article according to any one of (1) to (3), wherein the secondary molten resin contains a filler and / or a fiber reinforced material. (5) A composite molded article obtained by the production method according to any one of (1) to (4). (6) The composite molded article according to claim 5, wherein the hollow portion is formed in at least 70% of the back surface area of the design surface of the molded article. (7) The composite molded article according to (5), wherein the hollow portion is formed in a rib-like portion on the back surface of the molded article.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The method for producing a composite molded article made of the thermoplastic resin of the present invention can be generally performed using an injection molding apparatus having gas injection equipment. As the injection mold used in the production method of the present invention, an injection mold capable of increasing and decreasing the cavity thickness in the opening and closing direction of the mold is used.

In the method of manufacturing a composite molded product according to the present invention, the mold is closed by injection molding as primary injection molding by providing a cavity clearance for forming a design surface (skin layer) of the molded product. Next, a primary molten resin composed of the first resin for the skin layer is injected into the mold cavity, and after a certain degree of cooling, the thickness of the final molded product is finally increased by expanding the mold cavity. And When the mold cavity is expanded, the design surface (skin layer) portion made of the first resin is already completely formed, and does not move due to the expansion of the cavity. After the start of expansion of the mold cavity, injection of a secondary molten resin made of the second resin and gas injection are performed on the back surface side of the design surface formed of the first resin. As a result, a composite molded article in which the skin layer and the hollow molded portion made of the second resin formed by gas injection are integrated is obtained.

In the present invention, when the skin layer is thin,
When it is difficult to fill the resin to the end of the mold cavity by injection, such as when the area is large, the primary molten resin is injected into the cavity thicker than the cavity thickness corresponding to the skin layer when the primary molten resin consisting of the first resin is injected. Injection compression means may be employed in which the movable mold is advanced to compress the incompletely filled molten resin from the start of the injection to the end of the injection after the injection is completed.

Further, the timing of expanding the volume of the molding die cavity, injecting the secondary molten resin, and injecting gas into the secondary molten resin in the mold cavity for forming the hollow portion by the secondary molten resin is as follows. The condition is not particularly limited as long as a hollow portion is formed at a desired portion of the next molten resin, and can be arbitrarily selected. For example, after the volume expansion of the mold cavity is completed, the injection of the secondary molten resin and the injection of the gas are performed.
After the start of volume expansion of the mold cavity, the injection of the secondary molten resin and the injection of gas are performed in parallel. After the secondary molten resin is completely filled in the middle of the expansion of the volume of the mold cavity, a method of expanding the cavity together with the injection of gas can be specifically mentioned.

Due to the injection of the secondary molten resin and the injection pressure of the gas, the molded article including the skin layer is cooled while being pressed against the molding die surface. For this reason, the shapeability of the outer surface of the molded article is improved, and sink and warpage do not occur on the surface.

Next, an injection molding method, which is one embodiment of the method for producing a composite molded article of the present invention, will be described with reference to the drawings. FIG. 1 is a sectional view in the mold opening and closing direction showing the concept of a molding die used in the method of manufacturing a composite molded article of the present invention, and shows a state after a design surface is formed. FIG. 2 shows a state after the composite in which a resin layer having a hollow portion is formed on the back side of the design surface. 1 and 2 also show two injection units for the sake of explanation.

In FIG. 1, 1 is a fixed mold, 2 is a movable mold, 3 is an intermediate mold, 4 is a molding mold cavity, 5 is a gas injection tube, 6 is a gas injection pin, and 7 is a first resin sprue. , 8
Is a second resin sprue, 9 is a first resin injection unit, 1
0 is an injection unit for the second resin, 11 is a design surface forming resin,
Reference numeral 12 denotes a hollow portion forming resin, and 13 denotes a hollow portion.

Hereinafter, a method of manufacturing a composite molded article using a polypropylene resin as the design surface forming resin and a talc-containing polypropylene resin pellet as the hollow portion forming resin will be described with reference to the drawings.

In FIG. 1, the mold movable in the mold opening and closing direction is the movable mold 2 on the left side of the drawing. However, if the thickness (volume) of the molding mold cavity can be increased or decreased. Where the movable mold is provided is optional. Also, in the case of FIG. 1, the movable mold 2 moves forward and backward as a whole. However, it is needless to say that the movable mold 2 may have a structure in which a movable core is provided inside the movable mold.

First, the movable mold 2 is advanced with respect to the fixed mold 1 on the molten resin injection side, the mold clamping is completed via the intermediate mold 3, and the molding mold cavity 4 is formed. Then
The primary molten resin (polypropylene resin) melt-kneaded in the first resin injection unit 9 is supplied to the primary molten resin sprue 7.
Is injected and filled into the molding die cavity 4. Thereafter, the molded product is cooled appropriately to obtain a molded product that forms the design surface of the molded product.

In the case of FIG. 1, the mold cavity 4
Shows an example in which the outer peripheral edge 11b of the final molded product can be formed simultaneously with the design surface 11a as the molded product design surface 11. By selecting such a molding die, the design property is further improved. FIG. 1 shows a state after the molded product design surface is formed.

Next, the movable die 2 is retracted, and the movable die 2 is retracted so as to be the molding die cavity 22 of the final molded product. An appropriate amount of the secondary molten resin (talc-containing polypropylene resin) melt-kneaded in the second resin injection unit 10 in consideration of the volume of the hollow portion in the final molded product after the start of the retreat of the movable mold 2 is subjected to secondary melting. It is injected into the mold cavity through the resin sprue 8.

After starting the injection of the secondary molten resin,
A gas is injected into the secondary molten resin from the gas injection pin 6 through the gas injection pipe 5, and the hollow portion 13 is formed by the hollow portion forming resin as the second resin. [Refer to FIG. 2] Although the enlarged mold cavity is formed by the retreat of the movable mold 2, the intermediate mold 3 is urged by an urging member (not shown) and pressed by the movable mold 2. In addition, the mold cavity is kept closed so that leakage of the molten resin does not occur. As a result, a composite molded product in which the design surface forming portion and the molded portion having the hollow portion are integrated is molded. After being appropriately cooled, the movable mold 2 is further retracted, and the composite molded product is taken out.

Since the formation of the hollow portion by the second resin is not a design surface as a molded product, appearance characteristics from the back side are not particularly required. Further, since the design surface is independently and reliably formed in advance by the former molding, it is possible to independently perform the forming having the hollow portion without considering the design surface. Therefore, it is possible to use a reinforced resin containing talc, glass fiber, or the like, which cannot be used for a design surface due to surface characteristics, and it is easy to improve the strength and rigidity as a whole.

When the hollow portion is formed, the adhesive force with the design surface forming resin is improved by the pressing force of the injection resin and / or the injection gas, and the molded product is pressed against the molding die surface. And the appearance and shapeability of the molded article are further improved.

In the above embodiment of the manufacturing method of the present invention, two completely independent injection units are used as the injection units as shown in FIG.
It may have two melt-kneading and metering sections, merge before the injection nozzle, and consist of one injection nozzle. In this case, it is generally preferable to inject a small amount of the primary molten resin following the end of the injection of the secondary molten resin. This is because at the start of forming the design surface in the next molding cycle, the generation of contamination by the secondary molten resin can be eliminated, and only the primary molten resin can be reliably injected.

In the method for producing a composite molded article of the present invention,
The position for injecting the gas is not particularly limited, and the shape of the molded product,
It is appropriately determined by the injection nozzle, the runner, the gate, the cavity wall near the gate, and the like as appropriate depending on the formation position, the length, and the like of the thick portion and the hollow portion. From the gas injection pin, a gas such as nitrogen is injected into the secondary molten resin in the cavity from an arbitrary position and, if necessary, from a plurality of gas injection pins. The timing of gas injection generally depends on the molding conditions such as the shape of the molded product, molding temperature, mold temperature, etc., but after the molten resin has been injected to some extent, the secondary melt measured in the mold cavity is measured. This is done to a certain extent after the resin has been injected. In particular, it is preferable to perform it several seconds after filling.

The shape of the hollow portion in the second resin can be appropriately determined in consideration of the use of the molded article, required characteristics, and the like. Specifically, for example, a thin and wide hollow portion can be formed in the entire molded product. In this case, in order to secure the strength and rigidity of the molded product, gas injection can be performed so as to form a rib-like material connecting between the hollow portions. In this case, the ribs can be formed by general gas injection molding or multi-layer gas injection molding, but the rib-equivalent portion becomes thick and cooling is delayed. For this reason, sink marks may occur on the design surface of the molded product, and it may be difficult to obtain a molded product having a high commercial value in which appearance is a problem.

Also, for example, a lattice-shaped core is used so that a thick portion for forming a rib is formed as a molding die cavity at the time of injection of the secondary molten resin, and a tip is formed at the time of injection of the primary molten resin. It is also possible to form a mold surface, retreat the core at the time of injection of the secondary molten resin, form a cavity having a groove shape, inject gas only into this thick portion of the groove shape, and form a hollow portion in the rib portion . Further, conversely, a portion other than the rib portion may be retracted to form a hollow portion by gas injection in the non-rib portion. The gas injection pressure is usually in the range of 5 to 30 MPa.

The thermoplastic resin used in the method for producing a composite molded article of the present invention is not particularly limited.
Polyolefin resins such as polypropylene, propylene-ethylene block copolymer, propylene-ethylene random copolymer, soft polypropylene resin, polyethylene, unsaturated carboxylic acid or its derivative-modified polyolefin resin, polystyrene homopolymer, rubber-modified polystyrene, Polystyrene resin such as polystyrene containing tactic structure, AS resin, ABS resin, polyvinyl chloride resin, polyamide resin, polyester resin, polyacetal resin, polycarbonate resin,
A polyaromatic ether or thioether resin, a polyaromatic ester resin, a polysulfone resin, an acrylate resin, or the like can be used. Here, the thermoplastic resin may be used alone, or two or more kinds may be used in combination.

If necessary, these thermoplastic resins include
Impact strength improving materials such as elastomers, reinforcing materials such as glass fiber, talc, calcium carbonate, fillers, antioxidants, ultraviolet absorbers, antistatic agents, weathering agents, light stabilizers, coloring agents, crystallization nucleating agents, etc. Can be added.

In the method for producing a composite molded article of the present invention, as described above, two kinds of resin materials are used as the design surface forming resin and the hollow portion forming resin, and the respective characteristics are used as the design surface and the hollow portion forming resin. It is preferable to obtain a combined effect according to the following. Therefore, a molding material containing a filler and / or a fiber reinforced material can be used as the secondary molten resin. However, the same resin can also be used when the molded article is mainly based on the appearance of the design surface. In this case, even if the resin is the same, the resin may be a resin having a different molecular weight or a different additive formulation or a recycled resin.

The composite molded article of the present invention is a composite molded article manufactured by the above-mentioned manufacturing method. Further, this composite molded product is a composite molded product in which the end surface of the molded product is formed at the same time as the design surface by the design surface resin. Further, the composite molded product in which the hollow portion of the composite molded product is formed in 70% or more, preferably 80 to 95% of the back surface area of the design surface of the molded product, or the rib-shaped portion on the anti-design surface side of the composite molded product Is provided.

The composite molded article of the present invention is lightweight and thin by gas injection, is excellent in the appearance of the design surface, and is free to select a resin for forming a hollow portion having excellent strength and rigidity independently of the appearance. What you can do becomes possible. Due to these features, the field of application is expanded as various molded articles in automobiles, home appliances, OA equipment, furniture, house equipment, miscellaneous goods, and the like.

[0039]

EXAMPLES Next, the present invention will be described based on examples, but the present invention is not limited to these examples. 1. Molding machine: Injection molding machine with 850 t movable mold advance / retreat function. 2. Resin used: Polypropylene resin [made by Idemitsu Petrochemical Co., Ltd., IDEMITSU P.P.
PJ-950HP, [melt flow rate: 32 g /
10 minutes (temperature: 230 ° C., load: 21.18 N)], and as the resin for forming the hollow portion, the J-950HP: 80
Inorganic filler-containing polypropylene resin consisting of 20% by mass and talc (average particle size: 5 μm) [melt flow rate: 30 g / 10 minutes: temperature: 230 ° C., load: 2]
1.18N)]. 3. Molding die: plate-shaped molded product (500 × 70) shown in FIG.
0 × height: 10 mm. In addition, the mold structure is capable of simultaneously forming an outer peripheral end portion having a thickness of 3 mm at the time of forming a design surface. 4. Molding Method (1) Primary Molding As shown in FIG. 1, the movable mold was advanced with respect to the fixed mold, and clamping was performed via an intermediate mold. At this time, the molding die clearance was 2 mm. The mold temperature was 40 ° C. The primary molten resin at 220 ° C., which was melt-kneaded and measured, was injected into the mold cavity.

(2) Secondary molding 15 seconds after the start of injection of the primary molten resin, the movable mold is
mm, and a secondary molten resin at 220 ° C., which was melt-kneaded and measured and corresponding to a clearance of 4 mm, was injected. At the same time as the completion of the injection of the secondary molten resin, the movable mold is further increased by 4 m.
m (the clearance between the dies is 10 mm in thickness of the final molded product)
Retreat) and start retreating and nitrogen gas at the same time
Injection was carried out at 3 MPa for 3 seconds, and cooling was performed while maintaining the gas pressure for 15 seconds. Next, after degassing, the movable mold was further retracted to take out the composite molded product. (3) Molding results: Under these molding conditions, a plate-shaped composite molded article having a hollow portion was obtained. The design surface of the composite molded article had an excellent appearance without sink marks, warpage, and flow pattern. When the molded product was cut, a hollow portion of about 50% was formed in the inorganic filler-containing resin layer on the non-design surface side over about 85% of the back surface area of the design surface.

[0041]

According to the present invention, after the molten resin for forming the design surface is injected and filled, the mold surface is surely transferred, and the design surface is securely formed. A hollow part-containing layer is formed by injection of a molten resin and gas injection, and a molded article in which the design surface and the hollow part-containing layer are integrally combined is obtained. The composite molded article of the present invention is lightweight by gas injection, is excellent in the appearance of the design surface, and can easily produce a composite molded article excellent in strength and rigidity.

[Brief description of the drawings]

FIG. 1 is a sectional view in the mold opening and closing direction showing the concept of a molding die used in a method of manufacturing a composite molded product according to the present invention, showing a state after a design surface is formed.

FIG. 2 shows a state after the composite in which a resin layer having a hollow portion is formed on the back surface side of the design surface.

[Explanation of symbols]

 1: Fixed mold 2: Movable mold 3: Intermediate mold 4: Mold cavity 5: Gas injection tube 6: Gas injection pin 7: First resin sprue 8: Second resin sprue 9: Injection for first resin Unit 10: Injection unit for second resin 11: Design surface forming resin 12: Hollow portion forming resin 13: Hollow portion

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29K 105: 16 B29K 105: 16 B29L 9:00 B29L 9:00 24:00 24:00 F term (reference) 4F202 AA11 AB11 AB25 AG03 AG06 AG28 AH17 AH33 AH47 AH51 AM34 AM35 CA11 CB01 CK19 4F206 AA11 AB11 AB25 AG03 AG06 AG28 AH17 AH33 AH47 AH51 AM34 AM35 JA05 JA07 JB28 JL02 JM04 JN12 JN27 JQ81

Claims (7)

[Claims] After a primary molten resin is filled in a cavity of a molding die to form a design surface of a molded product, the volume of the mold cavity is increased, and a secondary molten resin is injected to the back surface of the design surface and gas is injected. A composite molded article in which a hollow portion is formed at a desired position in the secondary molten resin by injecting the resin. 2. The method according to claim 1, wherein the primary molten resin and the secondary molten resin are made of different materials. 3. The molded product according to claim 1, wherein at least a part of the end surface of the molded article is formed simultaneously with the design surface using the primary molten resin.
A method for producing the composite molded article according to the above. 4. The method for producing a composite molded product according to claim 1, wherein the secondary molten resin contains a filler and / or a fiber reinforced material. 5. A composite molded article obtained by the production method according to claim 1. 6. The hollow part has a back surface area of 7% of the design surface of the molded product.
The composite molded article according to claim 5, wherein the composite molded article is formed at 0% or more. 7. The composite molded product according to claim 5, wherein the hollow portion is formed in a rib-like portion on the back surface of the molded product.