JPH11309739A - Method for molding lightweight resin molded product and lightweight resin molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate defective appearance and the nonuniformity of molding density when a molten resin is injected into a mold cavity, and the cavity is expanded to mold a lightweight resin molded product. SOLUTION: A molten resin is injected/packed into a mold cavity which is formed by a mold in which the volume the cavity can be expanded in the mold opening/closing direction and in the direction crossing the mold opening/ closing direction. Next, the cavity is expanded dimensionally to the volume of a final molded product, the molten resin is expanded, and the lightweight resin molded product is molded. To expand the molten resin, a molten resin in which fibers are entangled and which exhibits expandability, a molten resin containing a foaming agent, a molten resin into which gas is injected, and others can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a lightweight resin molded article and a lightweight resin molded article, and more particularly, to an injection molding method, which has sufficient mold transferability, a dense surface and a good appearance. TECHNICAL FIELD The present invention relates to a method for molding a lightweight resin molded article capable of making the density, strength and strength uniform and a lightweight resin molded article.

[0002]

2. Description of the Related Art Conventionally, thermoplastic resins and fiber-reinforced thermoplastic resins have been widely used as automobile parts, home appliances, OA fields, members for construction and civil engineering, and the like. 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. On the other hand, on the other hand, prevention of sink marks in molded products,
There is a need for eliminating appearance defects such as improved mold transferability.

[0003] In injection molding (including injection compression molding; the same applies hereinafter), methods for reducing the weight of a resin molded product include a method using a resin containing a foaming agent, a method of injecting a gas, and a method of using a fiber in a resin containing a fiber. There is known a method that utilizes the expandability, which is a restoring force of entanglement. Among them, the usual injection molding using a foaming agent-containing resin, that is, a method of injecting a resin in an amount smaller than the volume of the cavity to foam the resin cannot be uniformly molded to the end portion of the molded product, or There is a problem that a molded article having an excellent appearance cannot be obtained, for example, silver is generated on a product surface by a foaming agent. As a method for solving this problem, a counter pressure method for suppressing foaming at the time of injection has been proposed, but there is a problem in economy, and a problem in which molding of a thin end portion is difficult is not solved.

On the other hand, in a gas injection (including gasification by liquid injection) molding method, similarly, after injecting a smaller amount of molten resin than the volume of a mold cavity, a gas is injected to form a hollow in a molded article. There is a molding method for forming a part. However, in this method, since the flow of the resin on the surface of the mold is intermittent, there is a problem of poor appearance such as generation of a flow mark on the surface of the molded product. In addition, even in the molding method utilizing the expandability of a fiber-containing resin such as glass fiber, as in a normal molding method, molding in a fixed mold cavity tends to cause poor appearance of a molded product, Also, the mold transferability at the end of the molded product may not be sufficient depending on the degree of weight reduction.

In the above-mentioned molding method for the purpose of reducing the weight of a resin molded product in injection molding, improvements have been made to solve the respective problems. For example, the molten foamable plastic composition is injected into a cavity having a volume of 10 to 95% of the volume of the intended molded article,
After forming a solidified layer in contact with the mold surface, expand the foam to the volume of the desired molded article and foam it (Japanese Unexamined Patent Publication No. Hei 8-3).
00391) has been proposed. Also, in the gas injection molding method, it is known that the cavity is expanded at the time of gas injection in order to form a large hollow portion. Further, the present applicant has proposed a method of expanding a cavity in a light-weight molding method utilizing expansion property due to entanglement of fibers by a specific fiber-containing resin (International Publication W
P97 / 29896).

That is, in these improved molding methods, a resin is injected and filled into a mold cavity smaller than the volume of the final molded product, the surface is cooled and hardened to a certain extent, and the surface transfer of the mold is completed. The purpose of the present invention is to improve the appearance of a molded product by expanding the volume of the final molded product to a lighter weight.

[0007]

However, in these improved methods, the expansion of the volume of the final molded product after injection filling of the resin into the mold cavity is generally carried out in the mold opening / closing method. Only has been done. In this case, there is little problem particularly when the degree of weight reduction is low or when a simple molded product such as a plate-shaped molded product is used. However, as a shape of a lightweight resin molded product, a box-shaped molded product having a rising portion on an outer peripheral portion,
In the case of a container-shaped molded product, etc., it is easy to reduce the weight of the bottom portion, but it is substantially impossible to reduce the weight of the rising portion.
Therefore, in such a molded product, since there is naturally a limit in reducing the weight, the molded product can be uniformly reduced in weight as a whole, that is, the density can be made uniform and the physical properties can be made uniform. A molding method is desired.

According to the present invention, after injecting and filling a molten resin,
An object of the present invention is to provide a molding method and a lightweight resin molded product capable of obtaining a lightweight resin molded product having excellent uniformity in density and physical properties when molding a lightweight resin molded product by enlarging a mold cavity. .

[0009]

Means for Solving the Problems The inventors of the present invention have made intensive studies on the above-mentioned problems, and as a result, a mold for forming a mold cavity has a three-dimensionally reducing and enlarging mold cavity volume. By using a mold, transferability, appearance,
It has been found that a lightweight resin molded product excellent in uniformity such as density and strength can be obtained. That is, by providing a sliding mold for reducing and enlarging the mold cavity volume so as to slide in the mold opening / closing direction and in a direction intersecting the mold opening / closing direction, a box-shaped molded product is provided. However, it has been found that a lightweight resin molded article having excellent uniformity in appearance, density, strength, and the like can be obtained, and the present invention has been completed.

That is, the present invention provides the following: (1) A molten resin is injected and filled into a mold cavity, and a part of the mold is moved in a mold opening / closing direction and a direction intersecting with the mold opening / closing direction. A method for molding a lightweight resin molded product, comprising expanding the mold cavity volume to the volume of the molded product, expanding the molten resin, and removing the molded product after cooling. (2) The method for molding a lightweight resin molded article according to the above (1), wherein the molten resin contains entangled fibers. (3) The above (1), wherein the molten resin is obtained by melting a raw material containing at least a part of a resin pellet containing fibers having a length of 2 to 100 mm, and has a fiber content of 5 to 80% by weight. (2) The molding method of the lightweight resin molded article according to (2). (4) The above (2) or (3), wherein the fibers are glass fibers.
The molding method of the lightweight resin molded article according to the above. (5) The method for molding a lightweight resin molded article according to the above (1), wherein the molten resin contains a foaming agent. (6) The method for molding a lightweight resin molded product according to the above (1), wherein a gas is injected into the molten resin in the mold cavity. (7) The method for molding a lightweight resin molded product according to any one of the above (1) to (6), wherein the lightweight molded product has a rising portion on an outer peripheral portion; Fiber length is 2
An object of the present invention is to provide a lightweight resin molded product containing 5 to 60% by weight of 20 mm glass fiber and having a porosity in a rising portion of 20% or more.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. As a molding method of the lightweight resin molded article of the present invention, any of an injection molding method and an injection compression molding method can be adopted. The molding die used in the molding method of the present invention has a structure capable of three-dimensionally reducing and enlarging the mold cavity by sliding the volume of the mold cavity in the mold opening / closing direction and the direction intersecting the mold opening / closing direction. belongs to. In addition, many mold cavities have a complicated mold structure than the functions and applications required for various molded products. In this case, the sliding mold is not necessarily used for injection and filling of molten resin. It is not necessary that the shape of the mold cavity be similar to the shape of the mold cavity, and it is sufficient that the mold cavity can be reduced or enlarged as a whole.

First, the mold has a part which can slide in the mold opening / closing direction and a direction intersecting the mold opening / closing direction, and can reduce and enlarge the clearance of the mold cavity. That is, it is a molding die having a sliding die that moves forward and backward to make the cavity volume variable. The basic structure of the mold includes a sliding mold and other molds that combine to form a cavity. As a specific example, first, the sliding mold movable in the mold opening / closing direction includes (1) a fixed mold and a movable mold, and the cavity volume is made variable by sliding movement of the movable mold. There is a mold of the structure to do. In this case, the movable mold corresponds to a sliding mold. That is, the sliding die is moved forward or backward using a die clamping mechanism such as a toggle mechanism or a die moving device provided between the movable die plate and the movable die. Further, (2) the whole mold may be constituted by a fixed mold, a movable mold and a sliding mold provided in the movable mold. In this case, a cavity is formed by members of a fixed mold, a movable mold, and a sliding mold. Generally, the movable mold and the fixed mold are clamped by a mold clamping mechanism. The sliding die is moved forward and backward by a sliding die moving device provided between the movable dies. That is, the cavity is formed by the sliding die and the fixed die, or the sliding die, the fixed die and the movable die. In this case,
There may be two or more sliding dies depending on the structure of the lightweight resin molded product.

Next, a mold that slides in a direction intersecting with the mold opening and closing direction generally slides in a direction orthogonal to the mold opening and closing direction. In addition, in this case, it is generally incorporated into the side of the movable mold cavity, and the number thereof is plural. In order to form the entire outer periphery of the molded product, the sliding mold preferably has a shape close to a quadrangle, and depending on the shape of the molded product, employs a combination with a non-sliding portion. You can also.

In the sliding mold used in the present invention, a mold having a heat insulating structure on a cavity forming surface adjacent to another mold may be used. Here, the portion adjacent to the other mold is the same as the other mold fixed when the sliding mold retreats from the position of the sliding mold filled with resin. It means the boundary part, and is the part that is most strongly affected by the cooling of the fixed mold. Specifically, it is a peripheral portion corresponding to a peripheral portion of a sliding die or a cylindrical portion for forming a hole or the like in a molded product. Therefore, the term “adjacent” refers to not only the case where the ends of the sliding molds are in direct contact with each other, but also the case where they are adjacent to each other with a gap. The formation range of the heat insulating structure is usually in the range of 3 to 20 mm from the sliding end of the sliding die, and an optimal range is appropriately selected depending on the size of the molded product, the molding material resin, the type of the molding method, and the like. Here, if the width of the heat insulating structure is widened, it becomes difficult to cool the molded product. Therefore, optimal conditions are selected in consideration of the molding cycle.

Next, the heat insulation structure is not limited to a structure having a heat insulation layer on the surface of a mold, but a metal layer,
Alternatively, a multi-layer structure such as a thin heat-resistant resin layer having a small heat insulating effect can be exemplified. Here, the reason why the metal layer is provided on the heat insulating layer is to make the surface of the mold as uniform as the metal layer when the molten resin is injected, thereby minimizing the influence on the flow of the resin, This is because it is preferable that the heat insulating effect appears after the start of cooling after filling. That is, the purpose of forming the heat insulating structure at a specific position is to make the cooling speed of the molten resin in the specific portion slower than that of other general portions.

The molding die is generally made of a metal material such as general steel, nickel, aluminum, copper, zinc or an alloy thereof. General metallic materials have high thermal conductivity and good thermal conductivity, and the injected molten resin is rapidly cooled, and the surface of the molded product is solidified. Examples of the material for forming the heat insulating structure (layer) include heat-resistant resins such as polyimide, polysulfone, polyethersulfone, polyarylate, polyallylsulfone, polyphenylene ether, and epoxy resins. Among these resins, the glass transition temperature is 1
A resin or a thermosetting resin having a heat resistance of 40 ° C. or higher, preferably 170 ° C. or higher, or a melting point of 220 ° C. or higher, preferably 240 ° C. or higher can be used.

Other heat-insulating structure (layer) forming materials include metal compounds such as glass, alumina, zirconia, silica, magnesium oxide and titanium nitride, and heat-resistant materials such as ceramics. The materials used to form these heat-insulating structures (layers) include melt spray coating, solution or paste coating, curing or sintering, chemical vapor deposition, physical vapor deposition, and film-like simple substance. Can be formed in advance and bonded, and a plurality of these can be combined to form a heat insulating structure including formation of a metal layer.

The thickness of the heat insulating layer in the heat insulating structure is as follows:
There is no particular limitation, and it can be appropriately set in consideration of the type of the resin to be molded, the shape of the molded product, the molding method, molding conditions, and the like. For example, the heat insulation layer portion is 0.1 to 5 mm,
The case where the surface metal layer is 0.01 to 0.5 mm can be exemplified. Here, if the thickness of the surface metal layer is 0.01 mm or less, the strength of the metal layer may be insufficient, and the protection effect of the heat insulating layer may be inferior. If it is 0.5 mm or more, the heat insulating effect may be reduced. Note that a surface layer can be further formed on the surface metal layer. The effect of the surface layer in this case is to improve the releasability, and examples thereof include fluororesin, silicone resin, and fluororesin-dispersed metal plating. With this layer, even if the cooling is delayed more than other general parts, the molding cycle is shortened and the molded product is released from the mold without hindering the overall cooling after the cooling.

Next, an example of the injection molding method for a lightweight resin molded product 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 mold which is a main part of the present invention in the injection molding method. The mold is mounted between a fixed die plate and a movable die plate of an injection molding machine (not shown). FIG. 2 is a cross-sectional view taken along the line XX in FIG. 1, and is a cross-sectional view in a direction intersecting the mold opening and closing direction of the cavity portion. In the figure, 1 is a fixed mold, 2 is a movable mold, 3 is a sliding mold that moves in the mold opening and closing direction, 4 is a sliding mold that moves in a direction intersecting the mold opening and closing direction, and 5 is a resin. Flow path, 6 is the initial mold cavity, 6
6 is a mold cavity to be a molded product, 7 is a gas injection path, 8
Denotes a gas discharge path, and 9 denotes a heat insulating portion on the surface of the mold. As for the sliding molds 3 and 4, the position when forming the mold cavity volume at the time of injection of the molten resin is indicated by a solid line to form the cavity of the final molded product. The position is indicated by a two-dot chain line.

In the drawing, a sliding die 3 is mounted between a movable die plate (not shown) and a movable die.
Can be moved forward and backward with respect to the cavity 6 by a mold moving device (not shown). First,
By operating a mold opening / closing mechanism such as a toggle mechanism (not shown), the movable mold 2 is clamped with respect to the fixed mold 1 and the sliding molds 3 and 4 are moved forward before or after clamping. Thus, the initial mold cavity 6 at the time of injection of the molten resin.
Determine the volume of. 1 and 2 show a mold for molding a box-shaped lightweight resin molded product. The mold cavity 6 at the time of injecting the molten resin has a clearance in the mold opening and closing direction, that is, a cavity clearance at a lower portion of the box-shaped molded product is D1, and a clearance in a direction intersecting the mold opening and closing direction, that is, the box-shaped molded product. R on the side clearance
1, the sliding mold 3 and the sliding mold 4 (4
1.42.43.44).

Next, the molten resin is injected into the mold cavity 6 through the resin flow path 5 and fills the cavity 6. As a result, details of the mold surface, such as ribs and surface textures, are reliably transferred by the injection resin pressure. At the time of injection, the molten resin has expandability due to entanglement of fibers and expandability due to the inclusion of a foaming agent. Also,
Inflatability can also be imparted by injecting a gas after injection filling.

After the injection filling of the molten resin is completed, after a suitable time, when the filled resin still has fluidity, the sliding dies 41 and 42 are retracted (H) to the position of the clearance R2 (H). Let it. After retreating the sliding dies 41, 42, the sliding dies 43, 44 are similarly retracted (H) to the position of the clearance T2. Thereafter, the sliding die 3 is retracted (H) to the position of the clearance D2. Due to the retreat of the respective sliding dies, the molten resin expands to have a cavity volume 66 in the shape of the final molded product. After the cooling process, the mold is opened by the operation of a mold opening mechanism such as a toggle mechanism. Is opened, and the lightweight resin molded product is taken out.

In this case, when the expandability due to the entanglement of the fiber contained such as glass fiber as the molten resin is exhibited, and when the degree of expansion is more than a certain degree (1.5 times or more), the expansion after expansion is caused by the expansion. Continuous voids are generated inside the molten resin. In this case, a relatively low pressure (3 MPa) is utilized inside the expanded molten resin by utilizing the continuous voids.
The following gas can be injected from the gas injection path 7. Due to the gas pressure of this gas injection, the molded product is pressed against the mold surface even after expansion, and the mold surface is reliably transferred even during the cooling process, and it is possible to obtain a molded product with excellent appearance. Become. The gas injected here can be discharged from the gas discharge path 8 while maintaining a pressure at which the molded product can be pressed against the surface of the mold, so that cooling can be accelerated. By doing so, the weight is reduced due to expansion and voids are generated, so that it becomes a heat insulator, cooling only from the mold surface makes it difficult to cool, the molding cycle becomes longer, and it is possible to improve the disadvantage that productivity is reduced. It becomes possible.

In the molding method of the lightweight resin molded product, as an example, the sliding die 3 and the sliding die 4 (41.
42.43.44), the case where each operation is performed stepwise has been described. However, the operation order and the timing of performing the operation stepwise (including the case where the respective operations are overlapped) are described in the following. Optimal conditions can be selected by changing conditions such as the shape, thickness, and expansion ratio. In addition, in the case of FIG. 1, the enlargement is performed by one sliding die, and in the case of FIG. 2, the entire outer peripheral portion of the molded product is enlarged. The above may be sufficient, or the outer peripheral part may be partially enlarged.

Although the injection molding method has been specifically described above, it is desired to prevent the flow orientation of the molten resin when the cavity thickness at the time of injection of the molten resin is small, or when the flowability of the molten resin is low. In some cases, injection compression molding can be employed. That is, after the injection of the molten resin into the mold cavity larger than the injection volume of the molten resin in advance, the sliding mold is advanced, preferably before the injection is completed, to compress the molten resin, and this compression The mold resin is completely filled with the molten resin. Hereinafter, a lightweight resin molded product is molded by enlarging the cavity according to the injection molding method.

The thermoplastic resin used in the method for molding a lightweight resin molded article of the present invention is not particularly limited. Examples thereof include polypropylene, propylene-ethylene block copolymer, propylene-ethylene random copolymer, and polyethylene. Such as polyolefin resin, polystyrene resin, ABS resin, polyvinyl chloride resin, polyamide resin, polyester resin, polyacetal resin,
Polycarbonate resins, polyaromatic ether or thioether resins, polyaromatic ester resins, polysulfone resins, acrylate resins, and the like can be used. Here, the thermoplastic resin may be used alone, or two or more kinds may be used in combination.
Among such thermoplastic resins, polypropylene, block copolymers of propylene and other olefins, random copolymers, or polypropylene-based resins such as mixtures thereof, high-density polyethylene, polyamide-based resins, polycarbonate-based resins It is particularly preferable to use a thermoplastic resin containing an acid-modified polyolefin resin modified with an unsaturated carboxylic acid or a derivative thereof, a polyolefin resin, and particularly a polypropylene resin.

The acid-modified polyolefin resin modified with an unsaturated carboxylic acid or a derivative thereof improves the interfacial adhesive strength between a filler such as glass fiber and the resin, and as a result, the physical properties and long-term stability of the molded product are improved. It is preferable because it contributes to improvement and promotes resin impregnation into the fiber bundle. Further, as the unsaturated carboxylic acid used for the modification,
For example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, citraconic acid, sorbic acid, mesaconic acid, angelic acid and the like, and as derivatives thereof, acid anhydrides, esters, amides, imides And metal salts, such as maleic anhydride, itaconic anhydride, citraconic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, monoethyl maleate, acrylamide,
Maleic acid monoamide, maleimide, N-butylmaleimide, sodium acrylate, sodium methacrylate and the like can be mentioned. Among these, unsaturated dicarboxylic acids and derivatives thereof are preferred, and maleic anhydride is particularly preferred. As the acid-modified polyolefin-based resin, the amount of the unsaturated carboxylic acid or derivative thereof added is 0.0.
The content is preferably in the range of 1 to 20% by weight, preferably 0.02 to 10% by weight, and particularly preferably a maleic anhydride-modified polypropylene resin.

In the method for molding a lightweight resin molded article of the present invention, in the case of a molding method utilizing expansion due to entanglement of fibers, the inclusion of fibers is essential. As a fiber,
Ceramic fiber: boron fiber, silicon carbide fiber, alumina fiber, silicon nitride fiber, zirconia fiber, inorganic fiber: glass fiber, carbon fiber, metal fiber: copper fiber, brass fiber, steel fiber, stainless steel fiber, aluminum fiber, aluminum alloy Fiber, organic fiber: polyester fiber, polyamide fiber, aramid fiber, polyarylate fiber and the like can be exemplified. Among these, glass fibers are preferably used.

Here, as the glass fibers, glass fibers such as E-glass and S-glass having an average fiber diameter of 25 μm or less, particularly in the range of 3 to 20 μm can be preferably employed. When the diameter of the glass fiber is less than 3 μm, the glass fiber does not adapt to the resin at the time of pellet production, and it becomes difficult to impregnate the resin. On the other hand, when the diameter exceeds 20 μm, the glass fiber is liable to be cut or chipped during melt kneading.

For the method of molding a lightweight resin molded article containing fibers in the present invention, for example, a pellet-like raw material reinforced by a pultrusion method using a thermoplastic resin and continuous fibers can be used. As a preferred example of this raw material pellet, the total length is 2 to 100 mm,
Fibers having a length equal to the total length are arranged in parallel with each other, and the pellets contain 20 to 80% by weight or a mixture of the pellets and other resin pellets, and the fibers have a total weight of 5 to 80% by weight. %, Preferably 10 to 75% by weight. The use of pellets in which the fibers are arranged in parallel to each other and contained 20 to 80% by weight of the total makes it difficult for the fibers to break even when plasticizing and kneading with the screw of the injection device, and to disperse the fibers. The property is also good. Thereby, the length of the fiber present in the injection molten resin can be kept relatively long, and the expansion property of the molten resin can be easily improved. In addition, the physical properties and surface appearance of the molded product are improved.

In the case where the fibers are glass fibers, when producing pellets by a pultrusion molding method or the like, the glass fibers are surface-treated with a coupling agent and then treated with a sizing agent.
100 to 10000, preferably 150 to 5000
It is desirable to bundle them in the range of the book. The coupling agent can be appropriately selected from so-called silane coupling agents and titanium coupling agents that have been conventionally used. For example, γ-aminopropyltriethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxy Amino silane such as silane or epoxy silane can be employed. In particular, it is preferable to employ the amino silane compound.

By adhering and impregnating the thermoplastic resin to the glass fibers converged by the above-mentioned converging agent, resin pellets containing glass fibers are produced. As a method of attaching and impregnating a thermoplastic resin to glass fibers, for example, a method of passing a fiber bundle through a molten resin and impregnating the resin with the fiber, a method of impregnating the fiber bundle through a coating die, or a method using a die A method in which the molten resin adhering around the fibers is spread and impregnated into the fiber bundle can be adopted.

Here, in order to make the fiber bundle and the resin well blended, that is, to improve the wettability, the fiber bundle is passed through a die having an uneven portion on the inner periphery and a plurality of rods alternately up and down. By pulling out through the tensioned fiber bundle, the fiber bundle is opened, the molten resin is impregnated into the fiber bundle, and further, the fiber bundle is pressed with a pressure roller. A molding method can also be adopted. If the glass fiber and the molten resin are compatible with each other and have good wettability, the molten resin can be easily impregnated into the glass fiber and the pellets can be easily manufactured. May be omitted.
Here, as a method of making the resins compatible with each other, a method of imparting polarity to the resin or grafting a functional group that reacts with the coupling agent on the surface of the glass fiber is effective. Furthermore, after treating the glass fiber bundle with a liquid material such as liquid paraffin having a boiling point equal to or higher than the melting temperature of the molten resin at the time of impregnation, a plurality of fiber bundles are introduced in a separated state into the resin impregnation section, and the A method of integrating the bundle is also preferable. According to this method, the impregnation property of the resin can be improved and high-speed pultruding can be performed.

By cutting a resin-impregnated strand or the like along the longitudinal direction of the fiber by the above-described method, a resin pellet containing a long fiber having the same length as the entire length of the pellet can be obtained. . At this time, as resin pellets,
The fiber bundle is made into a strand, and the cross-sectional shape is not limited to a cut resin-containing long fiber bundle whose shape is substantially circular.By arranging the fibers flat, a resin in a sheet shape, tape shape or band shape The long fiber bundle may be cut into a predetermined length.

In the method for molding a lightweight resin molded product of the present invention, when foaming is used, a molding material containing, for example, about 0.1 to 5% by weight of a foaming agent is used. Here, the type of the foaming agent is not limited as long as it decomposes by heat to generate gas. For example, oxalic acid derivatives, azo compounds, hydrazine derivatives, semicarbazide, azide compounds, nitroso compounds, triazoles,
Urea and its related compounds, nitrite, hydride, carbonate, bicarbonate and the like can be employed. More specifically, azodicarbonamide (ADCA), benzenesulfohydrazide, N, N-dinitropentamethylenetetramine, terephthalazide and the like can be used.

Next, when a gas injection molding method is employed as a method for molding the lightweight resin molded article of the present invention, a gas such as nitrogen is injected from an injection nozzle, a runner, or a gas injection nozzle provided on the cavity wall. Inject into the molten resin in the cavity. Injection of gas is generally performed after the retreat of the sliding mold starts. In the present invention, the gas injection is performed while retracting the sliding mold, unlike a general gas injection molding method. Therefore, the pressure in the cavity is relatively low, and the pressure of the injected gas is usually 20 MPa. Hereinafter, in particular, a low gas pressure of 3 Mpa or less is sufficient.

In order to mold the lightweight resin molded article of the present invention, an antioxidant, an ultraviolet absorber, an antistatic agent, a weathering agent, a light stabilizer, a colorant,
Additives such as nucleating agents and fillers such as short glass fibers and talc can also be added. In the method for molding a lightweight resin molded product of the present invention, a molten resin is injected into a narrowed mold cavity in advance, or is injected and compressed to fill the mold cavity with the molten resin. Then, the sliding mold 3 moving in the mold opening / closing direction and the sliding mold 4 moving in the direction intersecting, usually perpendicular to, the mold opening / closing direction are moved in the expanding direction so that the cavity has the volume and shape of the final molded product. Move to and hold. After the lightweight resin molded product is cooled, the mold is opened by operating the mold opening / closing mechanism to take out the lightweight resin molded product. Here, the operation of the sliding mold 3 and the sliding mold 4 can be arbitrarily set depending on the shape of the lightweight resin molded product. That is, when both the sliding dies 3 and 4 are operated at the same time, the operation of the sliding dies 4 may be prioritized over the sliding dies 3 in some cases. For example, when the lightweight resin molded article has a rising portion on the outer peripheral portion, the sliding mold 3 is started after the movement and enlargement of the sliding mold 4 is started or after the movement and enlargement is completed.
May be preferred. This is because, when the sliding die 3 moves, a new interface between the mold surface and the resin does not occur due to the movement. However, when the sliding die 4 is moved or enlarged in a direction intersecting with the die opening / closing direction, a new interface between the die and the molten resin is generated in the outer peripheral direction. Therefore, when the sliding mold 4 moves, the molten resin needs to have fluidity on the surface of the mold.

After the injection of the molten resin, the timing at which the movement of the sliding mold is started depends on the shape, thickness, size,
It is appropriately determined according to the temperature of the mold and the like. The first object of the method for molding a lightweight resin molded article of the present invention is to make the mold cavity smaller than the shape and volume of the final molded article, and inject and fill the molten resin to the end and details of the mold cavity. To spread the word. In this way, it is possible to ensure the transfer of fine ribs and grain on the surface of the mold and to obtain a molded product having excellent appearance. Further, by this, the molded product surface forms a dense structure while the final molded product is lightweight, and from this point, the molded product is excellent in appearance and strength. However, in the molding method of the present invention, depending on the relationship between the shape of the molded article and the shape of the sliding mold, the surface formed surface of the molded article may be expanded by moving and enlarging the sliding mold. In this case, it is preferable to move the sliding mold at a time when the cooling of the molten resin in the corresponding portion does not proceed.
Further, in this case, as described above, a heat insulating structure is provided in the sliding mold portion where the fixed mold and the sliding mold are in contact with each other, so that cooling of the resin in this portion is suppressed. You can also. Furthermore, the movement of the sliding mold is substantially uniform throughout the molded product, a solid molded product having different surface and center densities, and one or more relatively There is a molded product having a large hollow portion.

As described above, in the molding method of the present invention, the use of fiber-containing raw material resin, the use of a foaming agent-containing resin, the use of a normal resin other than these, and the use of gas injection are used independently. In addition to the case, the case where two or more kinds are combined and molded is naturally included. In addition, when injecting a gas, the injected gas is maintained at a certain pressure (ensure shapeability) during the cooling process of the molded product.
It is preferable to circulate the gas while exhausting the gas to the outside. As a result, while being a lightweight resin molded product, the inside of the molded product is uniformly cooled by the flowing gas, and the cooling efficiency,
The molding cycle can be improved.

As the lightweight resin molded article molded by the method of molding a lightweight resin molded article of the present invention, there is a box-shaped lightweight resin molded article having a rising portion on the outer periphery. It can be more suitably molded. Among them, the outer periphery has a rising portion, the average fiber length contains 2 to 20 mm glass fiber 5 to 60 wt%,
The average porosity of the rising portion is 20% or more, preferably 3%.
There is a lightweight resin molded product that is 0% or more. In this case, the general portion other than the rising portion has the same or higher porosity. In the molding method of the lightweight resin molded article and the lightweight resin molded article of the present invention, if necessary, a skin material such as a resin sheet, an eratosummer sheet, a foam sheet, a woven fabric, or a nonwoven fabric is previously placed in the mold cavity. By setting it on the surface, a skin-integrated lightweight resin molded product can be obtained.

As described above in detail, the method for molding a lightweight resin molded article of the present invention has high uniformity in density as a whole including the peripheral portion of the molded article, and as a result, has a good balance of strength, It has excellent mold transferability. In particular, even in the case of a molded product having a rising portion on the outer peripheral portion of the molded product, for example, a box-shaped molded product, the densities of the side wall portion and the lower body portion can be substantially equal or arbitrarily adjusted, and the weight can be reduced Is achieved. Therefore, it can be applied to various molded products that emphasize appearance, and the application field is expected to be expanded. Due to these features, the application fields thereof are expanded as various molded articles such as the automobile parts, home appliances, OA equipment fields, furniture, architecture, and civil engineering fields described above. In particular, application to molded articles having a high degree of weight reduction, which has been difficult in the past, is expected.

[0042]

Next, the effects of the present invention will be described based on specific examples, but the present invention is not limited to these examples. Example 1 Glass fibers are arranged in parallel, the content is 60% by weight,
A glass fiber reinforced polypropylene pellet having a length of 12 mm (glass fiber length = 12 mm, containing 3% by weight of maleic anhydride-modified polypropylene) and a melt index (MI: 230 ° C., 2.16 kg load) of 3
A raw material for molding was obtained by dry blending 40% by weight of 0 g / 10 min polypropylene pellets. The injection molding machine is provided with a screw having a mold clamping force of 850 t and a compression ratio of 1.9,
A compression unit (for moving the sliding mold 3 forward and backward) that allows the sliding mold 3 that slides in the movable mold to move forward and backward, and four sliding molds 4 provided in the movable mold (41. 42.43.44)
Was used. Fig. 1
This is to produce a box-shaped molded article as shown in FIG. Initial cavity 6 at the start of injection is 300 × 300 × 30
mm (height) and clearance (D1, R1, T
In 1), both the lower part and the side part were 3 mm. In addition, on the cavity surface adjacent to the movable mold and the fixed mold of the sliding mold 4,
One having a width (5 mm) and a heat insulating structure was used. The heat insulation structure includes a 1.0 mm thick epoxy resin layer and a 0.2 mm thick nickel layer thereon.

First, a resin corresponding to the initial mold cavity volume 6 was melt-plasticized and injection-filled. Two seconds after the completion of filling, two of the sliding molds 41.42 and then the remaining 43.42.
44 were retracted and enlarged until the side wall thickness (R2, T2) became 9 mm, and then the sliding mold 3 was similarly retracted and enlarged to a position where the lower wall thickness (D2) became 9 mm. Gas pin (gas injection path 7) 2 seconds after the start of retreat of sliding mold 3
Then, a nitrogen gas of 1 MPa was injected. After cooling, the mold was opened and the lightweight resin molded product was taken out. The obtained lightweight resin molded product expanded three-fold, and the porosity at the rising portion was about 65%, indicating almost the same expansion in any part of the box-shaped molded product. In addition, the entire outer surface of the molded product was well transferred, including the corners. The surface of the molded product also had uniform smoothness. The glass fiber length was examined with a microscope after incineration of the molded product. The average fiber length was 4.9 mm, and the glass fiber content was 36% by weight.

[0044]

According to the present invention, there is provided a molding method for injecting and filling a molten resin, reliably transferring a mold surface, and then retreating a sliding mold to increase the cavity volume and reduce the weight. The sliding mold is operated three-dimensionally to expand the shape and volume of the final molded product. Therefore, the density is expanded not only in the thickness direction of the molded product but also in the lateral direction, so that the density of the entire molded product can be made uniform, and the object of weight reduction can be further achieved. In particular, the expansion of the rising portion of a molded product having a rising portion on the outer peripheral portion of the molded product, such as a box-shaped molded product, is reliably achieved, and the uniformity and transferability of the lightweight resin molded product are secured. You. Therefore, it is possible to easily mold a molded article with a particularly high weight reduction, the degree of freedom of design is widened, and the application field is expected to be greatly expanded.

[Brief description of the drawings]

FIG. 1 is a conceptual sectional view showing one embodiment of the operation of a mold used in a molding method of the present invention.

FIG. 2 is a sectional view taken along line XX of FIG.

[Explanation of symbols]

 1: Fixed mold 2: Movable mold 3: Sliding mold 4: Sliding mold 5: Resin channel 6: Initial mold cavity 66: Mold cavity 7: Gas injection path 8: Gas discharge path 9: Heat insulation structure

Claims (8)

[Claims] A mold is injected and filled into a mold cavity, and a part of the mold is moved in a mold opening / closing direction and a direction intersecting with the mold opening / closing direction, so that the mold reaches the volume of the final molded product. A method for molding a lightweight resin molded article, comprising expanding a molten resin by expanding a cavity volume, and removing the molded article after cooling. 2. The method according to claim 1, wherein the molten resin contains entangled fibers. 3. A molten resin obtained by melting a raw material containing at least a part of resin pellets containing fibers having a length of 2 to 100 mm, and having a fiber content of 5 to 80% by weight.
3. The method for molding a lightweight resin molded product according to claim 1 or 2. 4. The fiber according to claim 2, wherein the fiber is glass fiber.
The molding method of the lightweight resin molded article according to the above. 5. The method according to claim 1, wherein the molten resin contains a foaming agent. 6. The method for molding a lightweight resin molded product according to claim 1, wherein a gas is injected into the molten resin in the mold cavity. 7. The method for molding a lightweight resin molded product according to claim 1, wherein the lightweight resin molded product has a rising portion on an outer peripheral portion. 8. A glass fiber having a rising portion on an outer peripheral portion and having an average fiber length of 2 to 20 mm in an amount of 5 to 60% by weight,
A lightweight resin molded product having a porosity of 20% or more at the rising portion.