JPH11333878A - Production of fiber-containing lightweight resin molding, and molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfy strength, rigidity, and appearance in a lightweight resin molding having voids and to provide a production method for reducing the weight of the plate-shaped molding and the molding. SOLUTION: A molten resin comprising 20-70 wt.% of fibers 2-100 mm in average length and 80-30 wt.% of a thermoplastic resin with ultrahigh flowability is injected into a mold cavity, compressed, and packed, and a movable mold is retracted in a direction in order to expand the cavity. By molding the mixture of polypropylene pellets containing 30-80 wt.% of glass fibers of equal length to that of the pellets and polypropylene pellets at least 100 g/10 min in melt index as a molding material, a lightweight molding 1.2-20 mm in thickness and 0.4 cm<2> or below in surface weight can be produced.

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 fiber-containing lightweight resin molded product and a molded product.
The present invention relates to an efficient method for producing a fiber-containing lightweight resin molded article free from appearance defects such as deformation, low gloss and uneven gloss, and to a molded article.

[0002]

2. Description of the Related Art Fiber-reinforced resin molded articles reinforced by incorporating fibers such as glass fibers have been known. This fiber reinforced resin molded product has tensile strength, bending strength,
Because of its excellent mechanical properties such as flexural modulus and heat resistance, automotive parts such as instrument panel cores, bumper beams, door steps, roof racks, rear quarter panels and air cleaner cases, and exterior wall panels,
Widely used as architectural and civil engineering members such as partition wall panels and cables and troughs. In producing such a fiber-reinforced resin molded product, an injection molding method of injecting a molten resin containing fibers into a mold can be used. According to this injection molding method, it is possible to mold even a complicated shape, and since a predetermined molding cycle can be repeated continuously, there is an advantage that the same shape can be mass-produced.

[0003] In a fiber-reinforced resin molded product formed by injection molding, if the amount of fiber such as glass fiber is increased in order to improve strength and rigidity, the weight of the molded product increases,
Warpage tends to increase. For this reason, in order to reduce the weight, a foam injection molding method has been proposed in which a foaming agent is mixed into a raw material and molding is performed while foaming a resin as a molded product (JP-A-7-247679). In this foam injection molding method, it is not easy to obtain a sufficient expansion ratio even if a considerable amount of a foaming agent is used to achieve weight reduction. Moreover, even if the expansion ratio is sufficiently obtained, the appearance is impaired such as generation of silver in the molded product, and the uniformity is poor, and the performance may not be sufficiently secured.

[0004] In order to solve these problems, in order to reduce the weight while maintaining mechanical properties such as strength, rigidity and impact resistance and appearance quality, (1) a fiber having a relatively long length is used. (2) The above-mentioned (1), wherein a fiber-reinforced resin pellet containing the resin is used, a springback phenomenon is caused by the contained fiber, and the resin being molded is expanded by the springback phenomenon to obtain a lightweight molded product. An expansion molding method has been proposed in which a foaming agent is mixed into the fiber-reinforced pellets described in the above, and the expansion of the resin is supplemented by the foaming agent, and the weight of the molded article is further reduced (International Publication WO97 / 2).
No. 9896). According to these methods, the molded product can be sufficiently reduced in weight without impairing the mechanical properties.
It can be said that this is effective in reducing the weight of the fiber-reinforced resin molded product.

[0005]

However, in the molding methods shown in the above (1) and (2), it is sometimes difficult to obtain a good lightweight resin molded product depending on the shape of the molded product. That is, in the case of a molded article having a relatively large area as a lightweight molded article, the cavity thickness is set to 2 mm or less, particularly 1 mm, when the filling of the molten resin into the mold cavity is completed in order to reduce the weight of the molded article. There is a need to: However, it is difficult to completely fill such a thin mold cavity with a resin not only in normal injection molding but also in injection compression molding.

For example, in the case of using polypropylene as a raw material for general injection molding in consideration of the strength of a molded product, it depends on the flow length of the molten resin (the size of the molded product). 1 mm or less was impossible.
This was especially true for fiber-containing resins containing fibers such as glass fibers. That is, even if the shape of the molded article, for example, the area is large, a thin mold cavity can be sufficiently filled with the molten resin, and then a method for producing a molded article having a high porosity and a high degree of weight reduction by expanding is desired. ing. An object of the present invention is to provide a fiber-containing lightweight material having excellent strength, rigidity, heat resistance, etc., and improved appearance defects such as sink marks, warpage, deformation, low gloss, and uneven gloss even when the area of the molded product is large. It is an object of the present invention to provide a method for manufacturing a resin molded product and a molded product.

[0007]

Under these circumstances, the present inventors have developed a method for producing a fiber-containing lightweight resin molded article, which includes molding conditions, molding raw materials and moldability, molded article physical properties,
We conducted intensive research on the relationship between appearances. As a result, in relation to the melt fluidity and expandability of the thermoplastic resin as a molding raw material, the strength of the molded product, the moldability is improved by adopting a thermoplastic resin that is not usually used for injection molding or injection compression molding. It has been found that a fiber-containing lightweight resin molded product can be obtained well. In addition, they found that such a raw material having excellent moldability was excellent not only in injection and compression filling properties but also in expandability in a subsequent expansion step, and was able to achieve strength, rigidity and good appearance. The invention has been completed.

That is, the present invention provides: (1) a molten resin comprising 20 to 70% by weight of a fiber having an average fiber length of 2 to 100 mm and 80 to 30% by weight of an ultra-high-flowability thermoplastic resin in a mold cavity; A method for producing a fiber-containing lightweight resin molded product, which comprises injecting, compressing and filling, and then retracting a movable mold in a direction in which the mold cavity volume increases. (2) The method for producing a fiber-containing lightweight resin molded product according to the above (1), wherein the cavity thickness at the time of compression filling is 2 mm or less. (3) The ultra-high-flowability thermoplastic resin containing fibers is injected into a cavity having a thickness of 2 mm or less and a flow area per nozzle of 500 cm ² or more, and fills the cavity when compressed. The method for producing a fiber-containing lightweight resin molded article according to the above (1) or (2), which has sufficient fluidity. (4) The method for producing a fiber-containing lightweight resin molded article according to any one of the above (1) to (3), wherein the thermoplastic resin is a polypropylene resin and the melt index is 100 g / 10 minutes or more. (5) The fiber-containing lightweight resin molding according to any one of the above (1) to (4), wherein after the movable mold starts retreating in the direction in which the mold cavity volume increases, gas is injected into the resin in the cavity. Product manufacturing method. (6) The fiber-containing heat in which the molten resin has a total length in the range of 2 to 100 mm and fibers of the same length as this total length are arranged in parallel with each other and contained 30 to 80% by weight of the whole. The method for producing a fiber-containing lightweight resin molded article according to any one of the above (1) to (5), using a raw resin composed of a plastic resin pellet (A) and an ultra-high fluidity thermoplastic resin pellet (B). (7) The above (1) wherein an expansion aid is mixed with the molten resin.
The method for producing a fiber-containing lightweight resin molded product according to any one of (1) to (6). (8) A fiber containing 20 to 70% by weight of a fiber having an average fiber length of 1 to 10 mm, 80 to 30% by weight of a polypropylene resin having a melt index of 100 g / 10 minutes or more, and having a porosity of 5 to 90%. A lightweight resin molded product; and (9) having a plate-like portion, wherein the thickness of the plate-like portion is 1.2 to 20 m.
It is an object of the present invention to provide a fiber-containing lightweight resin molded product according to the above (8), wherein the surface weight of the main part is 0.4 g / cm ² or less.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, as a method for producing a fiber-containing lightweight resin molded product, a molding die capable of reducing and expanding the volume (thickness) of a mold cavity is used, and a fiber-containing molten thermoplastic resin is injected, compressed, and filled into the mold cavity. . That is, a specific fiber-containing molten thermoplastic resin is first filled into an initial mold cavity by injection compression molding. Next, the movable mold is retracted to increase the thickness so that the mold cavity volume becomes the volume of the final molded product. Then, the molten thermoplastic resin expands to an enlarged volume due to a springback phenomenon caused by entanglement of the contained fibers, and a lightweight resin molded article containing fibers is obtained. In the present invention, at this time, as the specific fiber-containing raw material resin, 20 to 70% by weight of the fiber having an average fiber length of 2 to 100 mm and an ultrahigh fluidity thermoplastic resin 80 to 3
A molten resin consisting of 0% by weight is used.

[0010] The production method of the present invention is particularly aimed at producing a molded article having a plate-like portion, having a relatively large area, and a low surface weight of the main portion of the plate-like portion. The fiber-containing lightweight resin molded product can be manufactured by expanding the molten resin by injecting and compressing the molten resin containing the fiber, filling the mold cavity, and then expanding the cavity. However, the weight per unit area (surface weight) is irrelevant to the weight reduction due to expansion, and is fixed by the weight per area of the molten resin before expansion. Therefore, it is necessary to reduce the thickness of the molten resin before expansion in order to truly reduce the weight.

[0011] For this purpose, the production method of the present invention is applied to the case where the initial thickness is usually 2 mm or less, preferably 1.5 mm or less, particularly preferably 1.0 mm or less when the cavity is completely filled with the molten resin. It is applied to. However, even if an attempt was made to mold using a conventional molding resin material for ordinary injection molding, it was not possible to fill the molten resin up to the end of a thin cavity of 1 mm or less. Therefore, no matter how much the thickness exceeds 2 mm, there is a limit to the weight reduction as a molded product.
The true goal of weight reduction has not been achieved.

In the method for producing a molded article of the present invention, the thickness of the molten resin under the respective blending conditions and molding conditions for molding the molded article in a state in which the ultra-high-flowability thermoplastic resin contains fibers is described. It is preferable that the material be injected into a mold cavity having a flow area per nozzle of ² cm or less and having a flow area of 500 cm ² or more, and have sufficient fluidity to fill the cavity when compressed.

More specifically, the thermoplastic resin has a melt index (MI) of 1.3 times or more of a high fluidity injection molding for each thermoplastic resin. , Low molecular weight with low strength and no use
It is a resin that has ultra-high fluidity. Since the MI has different measurement conditions depending on the thermoplastic resin, the specific MI differs depending on the type of the thermoplastic resin and is determined individually for each.

In the polypropylene resin to which the present invention can be preferably applied, MI is specifically 100 g / 1.
0 minutes or more, preferably 150 to 2000 g / 10 minutes,
More preferably, it is 200 to 1000 g / 10 minutes. Note that the upper limit of MI includes a range from the measurement method to a range where high MI cannot be substantially measured.
0 g / 10 minutes. In addition, M of the polypropylene resin
I was measured according to JIS K 7210 (230 ° C., 2.16
It is a value measured according to the kg load (hereinafter the same).

Here, the ultra-high-flowability polypropylene resin used in the present invention is based on the type of fiber contained therein,
The MI can be appropriately selected according to the length, content, cavity thickness during injection compression, cavity shape, flow length (area) from the nozzle (gate), molding conditions, and the like. In this case, resins having different MI can be mixed and used, and a part of MI of the mixed polypropylene is 100 g.
Even if the time is less than / 10 minutes, the total MI is 100 g / 1
What is necessary is just to make it 0 minutes or more. However, it is not necessary to use an extremely large MI as long as the formability is satisfied.

In the present invention, even if the above-mentioned thermoplastic resin alone does not form a molded product in terms of strength, it can be reduced in weight by applying to the production method of the present invention. This also makes the molded product sufficiently practical for practical use. It is considered that the reason for this is that fibers having a specific length are contained in order to impart expandability. Further, the fiber-containing lightweight resin molded article of the present invention is a polypropylene resin 8 having an average fiber length of 1 to 10 mm, 20 to 70% by weight, and a melt index of 100 g / 10 min or more.
A fiber-containing lightweight resin molded product comprising 0 to 30% by weight and having a porosity of 5 to 90%, particularly having a plate-like portion, wherein the plate-like portion has a thickness of 1.3 to 20 mm and a plate-like portion. Is a fiber-containing lightweight resin molded article having a surface weight of the main part of 0.4 g / cm ² or less. That is, a fiber-containing lightweight resin molded article having a weight per area of 0.4 g / cm ² or less regardless of the degree of weight reduction due to expansion.

The fiber-containing lightweight resin molded product of the present invention has a plate-like thin thickness, and the thickness of the plate-like portion is in the range of 1.3 to 20 m.
Generally, it is in the range of 1.5 to 10 mm. The fiber-containing lightweight resin molded product is composed of a skin layer / expansion layer / skin layer in the thickness direction, and the expansion layer is strictly composed of an intermediate layer having a high degree of expansion and outer layers having a relatively low degree of expansion. ing. In this layered structure, when the area of the molded product is large, rigidity is insufficient, and local stress or torsion may be insufficient. In this case, in order to solve this problem, the skin layers on both surfaces can be partially connected with a non-expanded or low-expansion resin, that is, ribs can be provided.

Further, after the movable mold starts retreating in the direction in which the mold cavity volume increases, that is, a gas such as nitrogen can be injected into the resin in the cavity after the start or end or after the end. . This assists the expansion of the fiber-containing resin, and also presses the molten thermoplastic resin toward the molding surface of the mold. Does not occur. In addition, if this gas is circulated, the cooling of the molded article is promoted, and the molding cycle is shortened. At this time, if a liquid such as volatile water is accompanied, the cooling effect can be further improved.

Further, as a preferred production method of the present invention,
Fiber-containing thermoplastic resin pellets in which the molten resin has a total length in the range of 2 to 100 mm and fibers having a length equal to the total length are arranged in parallel with each other and contained 30 to 80% by weight of the whole. It can be manufactured using a raw material resin composed of (A) and an ultrahigh-flowability thermoplastic resin pellet (B). Here, the method of producing the fiber-containing thermoplastic resin pellet (A) will be described later, but the MI in the case of a polypropylene resin is usually 50 g / 1.
It is preferable to use a resin having good flowability for 0 minutes or more.

The mixing ratio between the fiber-containing thermoplastic resin pellet (A) and the ultra-high-flowability thermoplastic resin pellet (B) is 95/5 to 30/70 (weight ratio), preferably 90/10 70/30. This can be appropriately determined in consideration of the fiber content in the pellet (A), the physical properties of the molded article, and the moldability. This selection of the raw material is preferable because it excels in the springback phenomenon, that is, keeps the fiber length of the glass fiber and the like in the plasticized molten thermoplastic resin at the time of injection molding long and improves the dispersibility. If necessary, a small amount (5% by weight or less) of an expansion aid (foaming agent) can be added to this raw material resin to supplement expansion.

The weight reduction of the fiber-containing lightweight resin molded article of the present invention varies depending on the type and content of the contained fiber and the required characteristics of the target molded article.
It is selected in the range of 5-90%, preferably 20-80%. If the porosity is less than 5%, the effect of weight reduction is small, and 90%
%, The smoothness of the surface is reduced, the dense skin layer on the surface is thinned, and the strength is weak. The average fiber length in the molded article is in the range of 1 to 10 mm, preferably 2 to 8 mm. Here, if it is less than 1 mm, the entanglement of the fibers becomes insufficient, the expandability becomes insufficient, and the strength, rigidity and impact resistance are not preferred. Also, 10
If it exceeds mm, the dispersibility will be insufficient and the fluidity at the time of melting will be insufficient, making it difficult for the resin to flow to the thin part and the terminal part of the molded product, which may cause molding failure. Further, the fiber content is usually in the range of 10 to 70% by weight, preferably 15 to 60% by weight. If it is less than 10% by weight, the expandability, strength, rigidity and heat resistance are not sufficient, and if it exceeds 70% by weight, the fluidity at the time of melting is reduced, and the expandability and moldability may be reduced. Glass fibers are most preferred as the fibers. In the above, the porosity is
[(Volume of molded article−volume without voids) / volume of molded article] × 100.

The thermoplastic resin used in the present invention is not particularly limited. For example, polypropylene, propylene-ethylene block copolymer, propylene-ethylene random copolymer, polyolefin resin such as polyethylene, polystyrene , Rubber-modified impact-resistant polystyrene, polystyrene resin such as polystyrene containing syndiotactic structure, ABS resin, polyvinyl chloride resin, polyamide resin, polyester resin, polyacetal resin, polycarbonate resin, polyaromatic ether Alternatively, a 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.

Among such thermoplastic resins, polypropylene resins such as polypropylene, block copolymers of propylene and other olefins, random copolymers, and mixtures thereof are preferred. The polypropylene resin is preferably a polypropylene resin containing an acid-modified polyolefin resin modified with an unsaturated carboxylic acid such as maleic anhydride or fumaric acid, or a derivative thereof. In addition, high-density polyethylene, low-density polyethylene, ethylene-α
-Olefin copolymer resin, other thermoplastic resin such as polyamide resin, elastomer for improving impact strength such as ethylene-α-olefin copolymer elastomer, phenolic type, phosphorus type, antioxidant such as sulfur type, Light stabilizers, ultraviolet absorbers, weathering agents, crosslinking agents, nucleating agents, coloring agents, fillers such as short fibers, talc, calcium carbonate and the like can also be added.

Next, as the fibers, ceramic fibers:
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, polyarylate fiber and the like can be exemplified. Of these, glass fibers are most preferably used, and other organic fibers and inorganic fibers can be used in combination with the glass fibers.

Further, as described above, the raw material of the fiber-containing thermoplastic resin has a total length in the range of 2 to 100 mm and fibers having a length equal to this total length are arranged in parallel with each other. 30-80% by weight of the whole
In the fiber-containing thermoplastic resin pellets (A) or a mixture with other pellets, the fibers are 10 to 10
It is preferably 70% by weight, and preferably exhibits ultra-high fluidity. The use of pellets in which the fibers are arranged in parallel to each other and contained 30 to 80% by weight of the whole 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. The use of the pellet (A) improves the springback phenomenon of the molten resin in the cavity, increases the fiber length remaining in the final molded product, improves the physical properties, and improves the surface appearance. In addition, as a plasticizing screw of an injection molding machine, the use of a relatively low compression type having a compression ratio of 2.5 or less, particularly 2 or less is preferable in terms of suppressing fiber breakage.

Here, as the glass fiber, E-glass or S-glass glass fiber having an average fiber diameter of 25 μm or less, preferably in the range of 3 to 20 μm can be preferably employed. Glass fiber diameter is 3μ
If it is less than m, the glass fiber does not adapt to the resin during pellet production, and it becomes difficult to impregnate the resin. If it exceeds 20 μm, cutting and chipping are liable to occur during melt-kneading.
Using these thermoplastic resins and glass fibers, in producing pellets by a pultrusion method or the like, glass fibers are surface-treated with a coupling agent, and then by 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 which have been conventionally used. For example, γ-aminopropyltriethoxysilane, N-β-
(Aminoethyl) -γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane,
Aminosilane and epoxysilane such as β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane can be employed. In particular, it is preferable to employ the amino silane compound.

As the sizing agent, for example, urethane type, olefin type, acrylic type, butadiene type, epoxy type and the like can be used, and among these, urethane type and olefin type can be used. Among these, urethane-based sizing agents are usually polyisocyanate 50 obtained by polyaddition reaction of a diisocyanate compound and a polyhydric alcohol.
If it is contained in a proportion of at least% by weight, an oil-modified type,
One component type such as moisture curing type and block type, and
Either a two-pack type such as a catalyst-curable type and a polyol-curable type can be employed. On the other hand, a modified polyolefin resin modified with an unsaturated carboxylic acid or a derivative thereof can be used as the olefin sizing agent.

By adhering and impregnating a 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-fitted, that is, in order to improve the wettability, the molten resin is pulled out through the tensioned fiber bundle into the inside of the die provided with the uneven portion on the inner periphery. After impregnating the fiber bundle,
A pultrusion method incorporating a step of pressing the fiber bundle with a pressure roller can also be employed. In addition, if the glass fiber and the molten resin are compatible with each other, and have good wettability,
Since the glass fiber is easily impregnated with the molten resin and the production of pellets is facilitated, the step of converging the fiber with the above-mentioned sizing agent may be omitted in some cases. Here, as a method of well-matching each other, a method of imparting polarity to the resin, grafting a functional group that reacts with the coupling agent on the surface of the glass fiber, or heating the fiber bundle to the melting temperature of a molten resin such as liquid paraffin or more A method of pre-treating with a liquid having a boiling point is effective.

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

In addition, a foaming agent as an expansion aid of 5 parts by weight or less can be added to the raw material. If the foaming agent is included, even if the restoring force (expansion) of the fiber due to the springback phenomenon is insufficient, the foaming force of the foaming agent complements the restoring force of the fiber. As a result, the fiber-containing thermoplastic molten resin expands to a volume corresponding to the molded product. If the content of the foaming agent is more than 5 parts by weight, a silver mark may be formed, which may cause a defect in appearance quality, and a large hollow portion may be formed inside the molded product, resulting in strength and rigidity. May be significantly reduced. For these reasons, the content of the foaming agent is intended to complement the springback phenomenon, so that its content is preferably kept to the minimum necessary.

Specifically, it is preferable to contain 0.01 to 2, preferably 0.02 to 0.5, more preferably 0.05 to 0.3 parts by weight of a foaming agent. 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, semicarbazides, azide compounds, nitroso compounds, triazoles, ureas and related compounds, nitrites, hydrides, carbonates, bicarbonates and the like can be employed. More specifically, azodicarbonamide (ADCA), benzenesulfohydrazide, N, N-dinitropentamethylenetetramine, terephthalazide and the like can be used. As the foaming agent, not only these chemically decomposed foaming agents, but also water, alcohol, propane, as long as they generate gas when the resin is melted and heated.
Physical foaming agents such as butane, fluorine compounds and organic solvents can also be used. These physical foaming agents are added to the resin raw material in a state of being impregnated in a thermoplastic resin, an inorganic powder or the like.

Next, the gas to be injected into the fiber-containing molten thermoplastic resin in the cavity is nitrogen, air or the like. When cooling is desired, the temperature is 15 ° C. or lower, preferably 0 ° C. or lower. It is preferable to use a cooling gas. The gas to be injected is preferably an inert gas such as nitrogen gas. Further, the gas is a gas injection nozzle provided inside a nozzle of an injection device for plasticizing and injecting the fiber-containing molten thermoplastic resin, or a sprue, a runner and a cavity provided inside the mold. The gas can be injected into the interior of the molten resin from a gas injection pin that is opened on either side. Among these, it is preferable to inject from a gas injection pin provided in the mold, particularly from a gas injection pin opened in the cavity.

The pressure of the gas is 0.01
It is preferably set in the range of 20 MPa, particularly in the range of 0.1０．１3 MPa. That is, the pressure value of the gas to be injected depends on the size, shape and expansion ratio of the molded product,
And, the fluidity of the molten resin, the viscosity and the content of fiber
Furthermore, it is set according to the shape of the mold and the like.
In general, when the gas pressure is reduced, the possibility of forming a large hollow portion inside the molten resin is reduced, the strength is more reliably secured, and the surface of the molten resin and the molding surface of the mold are reduced. Gas is less likely to leak into the gap between them, and the possibility of occurrence of defects such as silver marks is reduced.

The reason why the gas can be injected at a relatively low pressure is that a large number of mutually continuous voids are secured inside the molded product by utilizing the springback phenomenon of the fiber. On the other hand, in the conventional lightweighting of the short fiber with a foaming agent, only closed cells can be formed. Therefore, in order to inject a predetermined amount of gas, it is necessary to expand the closed cells. A part is formed. That is, the form of weight reduction is completely different depending on the large hollow portion or continuous uniform dispersion. When the gas pressure is 2
If it exceeds 0 MPa, gas often leaks between the surface of the molten resin and the mold molding surface, or a large hollow portion often occurs, and appearance defects such as silver marks,
Although there is a high possibility that a functional defect such as a decrease in strength due to a large hollow portion will occur, gas injection in the present invention is complementary to expansion and does not require such high pressure. Also,
In the cooling step of the molded article, it is preferable to cool the molten resin in a short time by flowing and discharging the gas.

Further, a skin material for covering and integrating the surface of the molded article can be attached to the mold before molding. As described above, by using a mold in which a skin material is mounted before molding, a fiber-reinforced lightweight resin laminated molded product whose surface is covered with the skin material can be obtained. Here, examples of the skin material include cloths such as woven fabrics and nonwoven fabrics, thermoplastic resin sheets, films, foamed sheets of thermoplastic resin, and single-layer materials such as films on which patterns are printed, and thermoplastic elastomers. A multilayer material in which a backing material formed of a thermoplastic resin or a foamed sheet of a thermoplastic resin or the like is used as a skin material such as vinyl chloride resin or the like can be used. The skin material can be entirely coated on the molded product or can be partially coated.

One embodiment of the method for producing a fiber-containing lightweight resin molded product of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a sectional view of a mold conceptually showing an embodiment of a method for producing a fiber-reinforced lightweight resin molded product of the present invention, and shows a state where a cavity of the molding die is enlarged and reduced. In FIG. 1, 1 is a fixed mold, 2 is a movable mold, 3 is a mold cavity, 4 is a sprue, 5 is a molten resin when molten resin is injected, 6 is a gas inlet, and 7 is a gas outlet. The thickness of the mold cavity is indicated by a two-dot chain line at the start of molten resin injection, by a three-dot chain line at compression and filling completion, and by a solid line at the time of expansion and expansion to the volume of the molded product.

In the production of the fiber-containing lightweight resin molded article of the present invention, a molding die and a molding apparatus having a special function are used. That is, as shown in FIG. 1, the movable mold 2 can be moved forward and backward with respect to the fixed mold 1 to make the thickness (volume) of the mold cavity variable. FIG. 1 shows a movable type that compresses and expands the entire surface of the cab. However, depending on the shape of the molded product, only the main part may be advanced and retracted. Moving the movable mold
A direct pressure type mold opening and closing mechanism, and a mold moving device that allows the sliding mold provided between the movable platen and the movable mold or inside the movable mold independently of the injection molding machine to move back and forth. This can be implemented.

Next, the manufacturing method will be described based on the movement of the mold. First, the fixed mold 1 and the movable mold 2 are clamped and positioned so that the compression allowance C is left so that the mold cavity thickness becomes D1, and the cavity volume at the time of injection of the molten resin is determined. The fiber-containing molten thermoplastic resin is injected into the mold cavity in the initial state from a nozzle of a plasticizing device (not shown) via a sprue 4 to become a molten resin 5. Then, the injected molten resin is
Normally, before the injection is completed, the movable mold 2 is advanced so that the cavity thickness is at the position of D2, and the molten resin is compressed to fill and fill the mold cavity. For this purpose, a plasticized melted and weighed molten resin having a cavity thickness corresponding to D2 is injected. The advance of the movable mold in this case may be performed by position control or may be controlled by pressure. When controlling the pressure, it is preferable to leave a clearance H when the movable mold advances and the resin is completely compressed. As a result, even when the volume of the injection resin is delicately changed and becomes insufficient, the compressive force of the movable mold acts and the entire cavity can be reliably filled.

An apparatus (not shown) for controlling the mold temperature on the mold surface of the mold cavity is incorporated in the molding mold.
In the method for producing a fiber-containing lightweight resin molded product of the present invention, the mold temperature is preferably set relatively high because the thickness of the mold cavity is small. The mold temperature is 60 to 120 ° C. when a polypropylene resin is used,
Preferably it is 80-110 degreeC. If the mold temperature is lower than 60 ° C., the cooling of the molten resin proceeds too much during the molding, and the moldable conditions may be narrowed.

The molten resin filled and filled in the mold cavity reliably transfers the shape of the mold and fine irregularities such as grain on the surface of the mold by compression by the movable mold. Next, before the molten resin starts to cool from the contact portion with the mold and completely cools and hardens, the movable mold reaches a position where the thickness of the final molded product whose mold cavity thickness is D3 is indicated by a solid line in FIG. The mold 2 is retracted. Due to the retreat of the movable mold 2, the fiber-containing thermoplastic resin in a molten state expands due to the springback phenomenon due to the entanglement of the contained fibers and becomes a final molded product, and is pressed against the mold wall surface by the expansion force. Shaped. Here, the retreat of the movable mold
Although it differs depending on the molding conditions, molding raw materials, and the shape of the mold, it is preferable that the compression, filling, and filling steps of the molten resin be completed and the step be performed immediately after the formation of the surface layer. That is, when the cooling proceeds and the viscosity of the molten resin increases, the expansion of the molten resin becomes difficult to follow the retraction of the movable mold, and there is a possibility that the volume of the final molded product cannot be reliably formed.

In the present invention, depending on the degree of weight reduction of the molded product, it is necessary to inject the highly expansive molten resin into the cavity. It is desirable that the fibers, for example, glass fibers, have a long average fiber length. Also, in order to obtain a molded product having a high porosity, a small amount of a foaming agent is added to complement the expansion force and to prevent sink marks due to pressing and shaping of the resin against the mold surface. Can also. Further, after the retreat of the movable mold is started, the gas injection port 7 is closed with the gas exhaust port 8 closed.
And a relatively low-pressure gas of 1 Mpa or less can be injected. Further, by discharging and flowing the gas while maintaining the pressure of the gas discharge port at a certain pressure, the cooling of the molded article is promoted, and the occurrence of sink marks on the surface can be prevented. The fiber-containing lightweight resin molded article of the present invention is different from closed cells in the case of weight reduction using a general foaming agent, and the molten resin has continuous voids based on the fibers due to the recovery of entanglement of the contained fibers. There is a great feature that the gas can be injected while uniformizing the inflated portion of the formed product, and a feature is that the molding cycle can be greatly shortened because the gas can be cooled from the inside by flowing the gas.

[0043]

EXAMPLES 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 fiber reinforced polypropylene pellets in which glass fibers (13 μm; the same applies hereinafter) are arranged in parallel and having a content of 75% by weight and a length of 15 mm [polypropylene containing 3% by weight of maleic anhydride-modified polypropylene (MI = 6
0 g / 10 min as raw material] 50 wt% and polypropylene pellets (MI = 500 g / 10 min) 50 wt%
Is dry-blended into raw materials for molding (total MI =
300 g / 10 min). The polypropylene melt index (MI) is JIS K7210.
(230 ° C., 2.16 kg load). same as below.

The injection molding machine used a screw having a mold clamping force of 850 t and a compression ratio of 1.9 in order to reduce breakage of glass fibers. In the apparatus, a movable mold can be moved back and forth with respect to a mold cavity by a mold moving device (see FIG. 1). The molding die was a flat plate having a size of 600 × 300 × (variable in product thickness) mm and a center direct gate was used. The mold temperature was set at 90 ° C.

The mold was clamped so that the mold cavity gap was 3 mm, leaving a compression allowance, and the cavity gap was 0.9 mm.
The molten resin (resin temperature: 250 ° C.) of the raw material, which was plasticized and weighed to a value of mm, was injected. The injection time was 1.9 seconds. 1.5 seconds after the start of the injection, the movable mold was advanced, and the molten resin was filled (2 seconds). Immediately after the completion of the compression, the movable mold was retracted until the cavity gap became 2.0 mm in the thickness of the final molded product, and then cooled, the mold was opened, and the fiber-containing lightweight resin molded product was taken out. Table 1 shows the evaluation results of the obtained molded articles. In addition, the average glass fiber length in a molded article was calculated | required from the enlarged photograph by the microscope after incineration.

Example 2 In Example 1, the thickness of the final molded product was 3.0 mm.
One second after the start of the retreat of the movable mold, a fiber-containing lightweight resin molded product was obtained in the same manner as in Example 1 except that 2 MPa of nitrogen gas was injected into the molten resin from a gas injection pin. Table 1 shows the evaluation results of the obtained molded articles.

Comparative Example 1 In Example 1, the cavity gap was fixed at 0.9 mm, the molten resin was injected, the mold was opened after cooling, and the molded product was taken out. That is, this is a case where a normal injection molding method is adopted. The mold temperature was 30 ° C. Table 1 shows the evaluation results of the obtained molded articles.

Comparative Example 2 In Example 1, the melt index (MI) was 50
MI instead of 0 g / 10 min polypropylene is 60
Example 1 except that g / 10 minutes of polypropylene was used.
A fiber-containing lightweight resin molded product was obtained in accordance with Table 1 shows the evaluation results of the obtained molded articles.

Reference Example 1 A molded product was obtained in the same manner as in Example 1 except that the time for moving the movable mold forward and compressing the resin was changed from 2 seconds to 10 seconds. Table 1 shows the evaluation results of the obtained molded articles. When the molded article and molding conditions of Example 1 are employed, the compression time of the resin, that is, the time until the movable mold retreats, that is, the cooling time of the molten resin greatly affects the expansion of the molten resin. I understand.

Example 3 Glass fibers are arranged in parallel and the content is 70% by weight.
Glass fiber reinforced polypropylene pellets having a length of 12 mm [3% by weight of maleic anhydride-modified polypropylene
Containing polypropylene (produced using MI = 60 g / 10 min as raw material) and 60% by weight of polypropylene pellets (MI = 60 g / 10 min).
A foaming agent (Eiwa Chemical Co., Ltd., as an expansion initiator) was used as an expansion initiator for 100 parts by weight of a dry blend of 40% by weight (300 g / 10 minutes) and 40% by weight (total MI = 200 g / 10 minutes).
Polystyrene EE115 (foaming agent content: 10% by weight) to which 2 parts by weight was added was used as a raw material for molding.

The injection molding machine used a screw having a mold clamping force of 850 t and a compression ratio of 1.9 to reduce breakage of glass fibers. In the apparatus, a movable mold can be moved in and out of a mold cavity by a mold moving device. As a molding die, a door panel type having an approximate size of 720 × 500 × (variable product thickness) mm was used, and a center direct gate was used. The door panel has the shape and dimensions shown in FIG. 2 [W1 = 720 mm, W2 = 40 mm, H1 = 5.
00 mm, H2 = 280 mm]. The mold temperature was set at 100 ° C.

The mold is clamped so that the mold cavity gap is 3 mm, leaving a compression allowance, and the cavity gap is 0.8 mm.
The molten plastic (resin temperature: 260 ° C.) of the raw material, which was plasticized and weighed, was injected. The injection time was 2.3 seconds. 2.0 seconds after the start of the injection, the movable mold was advanced to fill (1 second) the molten resin. Immediately after the completion of the compression, the movable mold was retracted until the cavity gap became 2.0 mm in thickness of the final molded product. One second after the movable mold starts to retract, 3
A nitrogen gas of MPa was injected into the resin in the mold cavity from a gas injection pin. Thereafter, the mold was opened, the mold was opened, and the molded product (door panel) was taken out. Table 2 shows the evaluation results of the obtained molded articles.

Reference Example 2 Using polypropylene having an MI of 60 g / 10 min, using the mold of Example 3, the mold temperature was fixed at 40 ° C., and the cavity thickness was fixed at 2.5 mm. The resin was plasticized, weighed, injection-molded and filled to form a polypropylene door panel having a good appearance. This door panel is common at the moment. Table 2 shows the evaluation results.

Comparative Example 3 A door panel was obtained in the same manner as in Example 3 except that polypropylene having an MI of 80 g / 10 min was used instead of 300 g / 10 min of MI. Table 2 shows the evaluation results. Comparative Example 4 Polypropylene having an MI of 300 g / 10 min and chopped strands of 3 mm glass fiber were melt-kneaded by an extruder to obtain pellets having a glass fiber content of 42% by weight and an average fiber length of 0.46. A door panel was manufactured in the same manner as in Example 3, except that the short fiber-reinforced polypropylene pellets were used instead of the forming raw material of Example 3. Table 2 shows the evaluation results. Comparative Example 5 A door panel was manufactured in the same manner as in Example 3, except that instead of the glass fiber-reinforced polypropylene pellets, only polypropylene having an MI of 300 g / 10 minutes was used. Table 2 shows the evaluation results.

Example 4 Glass fibers are arranged in parallel and the content is 70% by weight.
Glass fiber reinforced polypropylene pellets having a length of 12 mm [3% by weight of maleic anhydride-modified polypropylene
Containing polypropylene (produced using MI = 60 g / 10 min as raw material) and 60% by weight of polypropylene pellets (MI = 60 g / 10 min).
As a swelling initiator, 4 parts by weight of a water-absorbent resin pellet having absorbed 5% by weight of water was used as a swelling initiator, based on 100 parts by weight of a dry blend of 40% by weight (150 g / 10 minutes) of 40% by weight (total MI = 120 g / 10 minutes). The added material was used as a raw material for molding.

The same injection compression molding machine and mold were used as in Example 3, and the mold temperature was set at 100.degree. The mold was clamped so that the mold cavity gap was 3 mm, leaving a compression allowance, and a plasticized and weighed molten resin (resin temperature: 260 ° C.) having a cavity gap of 1.3 mm was injected. The injection time was 2.6 seconds. 2.4 seconds after the start of injection, the movable mold was advanced, and the molten resin was filled (3 seconds). Immediately after the completion of the compression, the movable mold was retracted until the cavity gap became 3.0 mm in the thickness of the final molded product. Two seconds after the start of the retreat of the movable mold, a nitrogen gas of 1 MPa was injected into the resin in the cavity from a gas injection pin. Thereafter, the mold was opened, the mold was opened, and the molded product (door panel) was taken out. Table 2 shows the evaluation results of the obtained molded articles.

[0057]

According to the present invention, it is possible to satisfactorily mold a light-weight molded product having a relatively large main portion in a plate shape. A molded product excellent in strength, rigidity and appearance can be obtained while having good moldability and light weight. In particular, due to excellent moldability, the gap between the mold cavities during injection and compression is 2 mm or less, and even 1.5 m.
m, which is expanded, so that the thickness increases, but there is no change in weight, and the surface weight of the plate-shaped molded product can be reduced. The molded article of the present invention satisfies the strength, rigidity, and appearance, and achieves sufficient weight reduction, so that it is used for automobile parts and the like and contributes to resource saving.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mold conceptually showing an embodiment of a method for producing a fiber-reinforced lightweight resin molded product of the present invention, showing a state where a cavity of the molding die is enlarged and reduced.

FIG. 2 shows an automobile door panel formed in Examples and Comparative Examples.

[Explanation of symbols]

 1: fixed mold 2: movable mold 3: cavity 4: sprue 5: molten resin 6: gas inlet 7: gas outlet

Claims (9)

[Claims] A fiber having an average fiber length of 2 to 100 mm.
A molten resin consisting of 70% by weight and an ultra-high-flowability thermoplastic resin of 80 to 30% by weight is injected into a mold cavity, compressed and filled, and then the movable mold is retracted in a direction to increase the mold cavity volume. A method for producing a fiber-containing lightweight resin molded product. 2. The thickness of a cavity when compressed and filled is 2
The method for producing a fiber-containing lightweight resin molded product according to claim 1, which is not more than mm. 3. An ultra-high-flowability thermoplastic resin containing fibers is injected into a cavity having a thickness of 2 mm or less and a flow area per nozzle of 500 cm ² or more. The method for producing a fiber-containing lightweight resin molded product according to claim 1 or 2, which has sufficient fluidity to fill. 4. The method for producing a fiber-containing lightweight resin molded article according to claim 1, wherein the thermoplastic resin is a polypropylene resin and has a melt index of 100 g / 10 minutes or more. 5. The fiber-containing lightweight resin molded product according to claim 1, wherein the movable mold starts retreating in the direction in which the mold cavity volume increases, and then gas is injected into the resin in the cavity. Manufacturing method. 6. A fiber in which the molten resin has a total length in the range of 2 to 100 mm and fibers having a length equal to the total length are arranged in parallel with each other and contained 30 to 80% by weight of the whole. The method for producing a fiber-containing lightweight resin molded product according to any one of claims 1 to 5, wherein a raw material resin comprising a thermoplastic resin pellet (A) and an ultra-high fluidity thermoplastic resin pellet (B) is used. 7. The method for producing a fiber-containing lightweight resin molded product according to claim 1, wherein an expansion aid is mixed with the molten resin. 8. Fibers 20 to 7 having an average fiber length of 1 to 10 mm.
0% by weight and a melt index of 80 to 30% by weight of a polypropylene resin having a melt index of 100 g / 10 minutes or more,
A fiber-containing lightweight resin molded product having a porosity of 5 to 90%. 9. A plate-like part having a thickness of 1.2 to 2
9. The fiber-containing lightweight resin molded article according to claim 8, wherein the surface weight of the main part is 0 g / cm ² or less.