JPH10337744A - Manufacture of fiber reinforced thermoplastic resin molded product, and molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing advantageously from the economical point of view a fiber reinforced thermoplastic resin molded product having a hollow section and provided with the good outer appearance even at the time of not being coated, by utilizing the gas assist injection molding method. SOLUTION: When a molded product is manufactured by using a fiber reinforced thermoplastic resin composition in the gas assist injection method, the injection of molten resin is started while reducing the pressure to 1/2 atmospheric pressure or under in the state of closing a mold cavity, and in the middle of injection or after the completion of injection, a pressurized fluid is injected from a pressurized fluid injection device 11 into molten resin injected into a mold cavity to form a hollow section.

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-reinforced thermoplastic resin molded product and a molded product. More specifically, the present invention relates to a method for producing a fiber-reinforced resin molded article having a good appearance by a gas assist molding method, and a fiber-reinforced thermoplastic resin molded article produced by this method.

[0002]

2. Description of the Related Art Conventionally, when a molded article having a good appearance, for example, a molded article such as a home appliance, a furniture article, an office, an OA apparatus, and an automobile part, is manufactured from a thermoplastic resin as a raw material, the conventional injection molding is used. to produce a good molded article appearance by law, varies depending on the kind of structure and the thermoplastic resin in the mold cavity, it should be about 1000 kgf / cm ² before and after the injection pressure, is a directly a hollow molded article I couldn't get it.

As another method for producing a hollow molded article having a good appearance, a core molding method is known. In this core molding method, a core made of a low-melting-point metal or resin is placed in advance in a mold cavity where the appearance of a molded product is desired to be beautiful, and a sufficiently high injection pressure and By maintaining a high holding pressure, it is possible to obtain a molded article having the same good appearance as a normal injection molded article. However, it is unavoidable that a special core needs to be created and the cost increases, which is disadvantageous.

Techniques for improving the appearance of products by injection molding (preventing warpage and sink marks) include those described in "Molding", Vol. 8, No. 4, 213-219 (1996). A gas assist injection molding method has been proposed and put into practical use. The gas assist molding method is classified into a full shot method and a short shot method according to the amount of molten resin to be injected into a mold cavity in advance.

[0005] The full shot method is a method of filling a mold cavity for injection molding with a resin and then injecting a pressurized fluid into the molten resin while the resin is in a molten state. In this method, an insufficient amount of resin is filled to fill the mold cavity, and a pressurized fluid is injected into the molten resin while the resin is in a molten state.

Even if the mold cavity for injection molding is full-shot and filled with molten resin, when the molded product cools, the resin undergoes volume shrinkage, causing warpage of the molded product and sinking of the surface of the molded product. The full-shot method in the above-described gas assist molding method has a meaning of compensating for the volume contraction by injecting a pressurized fluid. When using the short shot method, a sufficient amount of pressurized fluid was injected into the molten resin to fill the mold cavity, the molten resin was pressed and held on the surface of the mold cavity, cooled, and removed from the mold. When the resin contains almost no reinforcing fibers, it is possible to obtain a light-weight molded product having a hollow portion inside and having the same appearance as a normal injection-molded product.

When a product is produced by an injection molding method, a thermoplastic resin as a raw material often contains reinforcing fibers such as glass fibers. Among the thermoplastic resins, polyamide MXD6 is said to be easy to obtain a molded article having a good glossy appearance while being fiber-reinforced. However, even in such a fiber-reinforced thermoplastic resin composition in which a molded article having a good appearance is easily obtained in such general injection molding, finally, the pressure applied to the cavity surface is controlled to be low as in the gas assist molding method. In this case, the surface of the molded article has a rough surface and is rough, and it is difficult to obtain a molded article having a gloss and a good appearance similar to a product by a normal injection molding method.

[0008] A molded product produced from a fiber-reinforced thermoplastic resin composition by the short shot method has a noticeable roughness on the surface of the molded product. There is. If this is to be used in places where it can be seen, it is necessary to apply a paint after performing pretreatment such as sanding on the surface of the molded article, which has the drawback of causing high cost.

As another method for improving the appearance when a molded article is produced by a short shot method using a fiber reinforced thermoplastic resin composition as a molding raw material, it is effective to increase the pressure of an injection fluid. In the case of a large molded product, the size of the pressurized fluid injection device increases, the amount of pressurized fluid used increases, and the like, which is not preferable because the cost increases.

[0010]

SUMMARY OF THE INVENTION In view of such circumstances, the present inventors have made intensive studies and as a result, produced a fiber-reinforced molded article by a gas-assisted injection molding method using a thermoplastic resin composition containing reinforcing fibers as a raw material. In this case, it has been found that the cause of the poor appearance of the surface of the molded article is the residual air in the cavity, and the present invention has been completed based on this finding.

When the mold cavity is filled with the molten resin, the flow end (melt front) of the molten resin is said to advance while the resin is ejected from the center and adheres to the side surface. In the case of fiber reinforced thermoplastic resin, when the resin squirted from this center spreads on the wall,
Irregularities occur in the flowing molten resin due to the fibers, and air is taken into the irregularities. When the molten resin is pressed against the mold cavity surface by a pressurized fluid having a low pressure compared to the injection pressure, in the case of normal injection molding, at a pressure of about 400 to 1500 kgf / cm ² of the injection pressure and the holding pressure, The volume of air remaining in the gap between the wall surfaces is reduced to 1/400 to 1/1500, and the surface is solidified as it is.

However, in the case of the gas-assisted injection molding method, the trapped air is reduced to 1/10 to 1/100 by the residual pressure of about 10 to 100 kgf / cm ² when the mold cavity is completely filled with the molten resin. Is reduced to When the maximum and minimum volume ratios are calculated, it can be seen that there is a volume difference of 4 to 150 times. The trapped air is so small that it cannot be removed only from the parting line of the mold and is trapped. It has been found that the cause of the poor appearance of the molded article of the fiber-reinforced thermoplastic resin is the trapped residual air.

The objects of the present invention are as follows. 1. Provided is a method for producing a molded article made of a fiber-reinforced thermoplastic resin composition having a good appearance and having a hollow portion by a gas-assisted injection molding method. 2. Provided is a method for producing a molded article made of a fiber-reinforced thermoplastic resin composition having a hollow portion, which has a good appearance even without painting and has a low painting cost even when painting is required, by a gas-assisted injection molding method.

[0014]

Means for Solving the Problems In order to solve the above problems, the present invention provides a method for producing a fiber-reinforced thermoplastic resin molded article by injection molding using a thermoplastic resin composition containing reinforcing fibers as a raw material. The molten resin is melted while melting the fiber-reinforced thermoplastic resin composition containing the reinforcing fiber and reducing the pressure in the mold cavity to 1/2 atmosphere or less in a state where the mold cavity for injection molding is closed. Injection is started, and during or after the injection is completed, a pressurized fluid is injected into the molten resin injected into the mold cavity to form a hollow portion in the molded product. Provided is a method for producing a fiber-reinforced thermoplastic resin molded product.

In addition, in a fiber-reinforced thermoplastic resin molded article produced by injection molding from a thermoplastic resin composition containing reinforcing fibers, a reinforcing fiber having a blending amount of 7% by volume or more with the thermoplastic resin. Is melted, and in a state where the mold cavity for injection molding is closed, while reducing the pressure in the mold cavity to 1/2 atmosphere or less, start injection of the molten resin, A fiber having a good appearance, characterized in that a hollow part is formed in a molded product by injecting a pressurized fluid into a molten resin injected into a mold cavity during or after injection. Provide a reinforced thermoplastic resin molded product.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The thermoplastic resin in the present invention, polyethylene, olefinic resin such as polypropylene, polystyrene, rubber-reinforced polystyrene, acrylonitrile-styrene copolymer, styrene-based resin such as ABS resin, polycarbonate, polyacetal, polyamides, polyethylene terephthalate, Examples include polyesters such as polybutylene terephthalate, modified polyphenylene oxide, polyphenylene sulfide, and polymethyl methacrylate. These may be a mixture of two or more. The thermoplastic resin is not limited to those exemplified above.

Examples of polyamides include nylon 6, nylon 66, nylon 69, nylon 610, and nylon 6.
12, a polyamide resin obtained from nylon 12, a mixed diamine compound with meta-xylylenediamine alone or 40% by weight or less of para-xylylenediamine, and α, ω-linear aliphatic dibasic acid or aromatic dibasic acid, Examples thereof include polyamide resins obtained from a linear aliphatic diamine such as tetramethylene diamine and hexamethylene diamine octamethylene diamine and an aromatic dibasic acid, and a mixture thereof. Polyamides are not limited to those exemplified.

The polyamide obtained from meta-xylylenediamine and adipic acid is called polyamide MXD6. Linear diamine alone or branched diamine
0% by weight or less of mixed diamine compound and α, ω-linear aliphatic dibasic acid alone or aromatic dibasic acid at 40% by weight
A molded article having a relatively good appearance can be obtained even with a polyamide resin obtained from a mixed dicarboxylic acid comprising: Still more preferred polyamides are polyamide MXD6,
Nylon 6, Nylon 66, or a mixture or copolymer thereof.

In the present invention, the reinforcing fiber means glass fiber, carbon fiber or a mixture thereof. The average diameter of the reinforcing fibers is in the range of 3 to 23 μm, more preferably 6 to 13 μm for glass fibers, and 5 to 13 μm for carbon fibers. Fiber length is 1mm-10
Any of chopped strands having a length of about mm and having been subjected to a convergence treatment with a surface treatment agent such as a long fiber, a roving, and a sizing agent may be used. The average diameter of the fibers can be measured by observing with a microscope.

When the amount of the reinforcing fibers to be compounded in the thermoplastic resin composition is small, the appearance of the obtained molded article does not deteriorate so much. Therefore, it is not necessary to apply the production method according to the present invention. When the compounding amount of the reinforcing fiber is 7% by volume or more (about 13% by weight for glass fiber and about 10% by weight for carbon fiber), the appearance of the obtained molded product is deteriorated. By applying the manufacturing method, not only can the appearance of the molded article be significantly improved,
At the same time, strength and elastic modulus are improved, which is preferable. If the upper limit of the reinforcing fiber exceeds 35% by volume, the moldability is extremely lowered, which is not preferable.

In the thermoplastic resin composition, fine fibers or fine plate-like or powder-like fillers can be blended in addition to the reinforcing fibers as long as the effects of the present invention are not impaired. Specifically, glass wool, milled glass fiber, milled carbon fiber, talc, fine mica, fine glass flake, wollastonite, potassium titanate, magnesium sulfate, sepiolite, zonolite, aluminum borate, glass beads, glass beads , Calcium carbonate, silica, kaolin, clay, titanium oxide, barium sulfate, zinc oxide, magnesium hydroxide, and the like, but are not limited thereto.

To the extent that the effects of the present invention are not impaired, the thermoplastic resin composition may further contain, in addition to the above-mentioned filler, various resin additives which are generally used, for example, a lubricant, a flame retardant, a heat stabilizer, Pigments, dyes, release agents, nucleating agents, light stabilizers, ultraviolet absorbers and the like can be added. The above fillers and resin additives may be used alone or as a mixture of two or more.

To form a thermoplastic resin composition in which reinforcing fibers, and if necessary, fillers and resin additives are blended with the thermoplastic resin, a conventionally known kneading method can be used. For example, a resin, reinforcing fibers, and, if necessary, a filler, various resin additives, and the like are each weighed and mixed in a predetermined amount to form a mixture, and the mixture is kneaded with a normal vent-type extruder, or Pellets can be formed by a method in which a reinforcing fiber and a filler are kneaded while melting a resin component using a kneading apparatus similar to that described above. The long fiber reinforced type pellets can be produced by a known pellet production method, for example, a pultrusion method. A method of blending a pellet containing reinforcing fibers and a pellet not containing reinforcing fibers can also be used.

When a molded article is manufactured by the method of the present invention, while the mold cavity for injection molding is closed, the pressure in the mold cavity is reduced to 1/2 atmosphere or less while the molten resin Injection is started, and during or after completion of injection, it is essential that a pressurized fluid is injected into the molten resin injected into the mold cavity to form a hollow portion in the resin.

Conventionally, a technique for reducing the pressure and vacuum in the mold cavity is based on a technique for improving the transferability of transferring a concavo-convex pattern engraved in the mold cavity by blow molding to the surface of a molded article, and an injection molding method. It has been known as a technique for improving transferability of signal bits when manufacturing a compact disc. However, for the purpose of improving the appearance of a fiber-reinforced resin molded product, it has not been known to apply the invention to a gas assisted injection molding method, particularly to combine it with a short shot method.

According to the present invention, as a result of various experiments, the pressure in the mold cavity is preferably higher as the degree of pressure reduction (the lower the pressure), but in molding by the short shot method, the pressure in the mold cavity is reduced by 1 /. It was found that a molded article having a good appearance can be obtained by injecting and molding the molten resin in a state where the pressure is reduced to 2 atm or less. As a result of further experiments, it is more preferable that the pressure be 1/4 atm or less in consideration of many factors that weaken the effect of decompression such as air flowing into the gap between the molds and gas generated from the resin, a molding cycle, and feasibility. I understood that.

In order to maintain a reduced pressure of less than 1/2 atmosphere in the mold cavity, it is necessary to prevent air from flowing around the mold cavity and from the nozzle side. In order to prevent air inflow from around the mold cavity, it is effective to provide an air inflow prevention means such as packing around the mold cavity. For example, resilient packing is placed on the entire outer periphery of the mold cavity, the packing is completely sealed with the mold opened about 1 mm, and the hole of the decompression line and the cavity Reduce the pressure through the gap between the ring surfaces. Immediately before molding, the mold is completely tightened, and the gap between the cavity parting surface and the hole leading to the pressure reducing section is closed by completely closing the mold, and the operation of reducing the pressure is also completed.

The method of reducing the pressure in the mold cavity is as follows.
Any method such as (a) a method using an oil vacuum pump, (b) a method using a water-sealed vacuum pump, and (c) a method using a piston may be used. For the purpose of preventing molten resin from reaching the pump, (1) provide a decompression opening / closing unit in the mold cavity that opens in the mold cavity, (2) use a decompression port in the mold cavity without providing an opening / closing unit. (3) Insert a pressure-resistant empty container (vacuum chamber) between the vacuum pump and the decompression line of the mold cavity. (4) Combine these (1) to (3) appropriately. , Etc.

In order to prevent air from flowing into the mold cavity from the nozzle side of the molding machine, it is desirable that the molding machine is equipped with a shut-off nozzle by bringing the nozzle of the molding machine into contact with the mold gate. A method of reducing the pressure by delaying the time until the molten resin is injected into the mold cavity after the nozzle touch may be used. It is possible to reduce the pressure inside the mold cavity by increasing the time until injection after the nozzle touch, but during this time some molten resin flows into the mold cavity, so a cold slug well that prevents this inflow It is effective to attach such equipment to the spool or runner.

When the opening / closing section (1) is provided in a mold, the air passage for decompression is ideally preferably closed immediately before the molten resin reaches the opening / closing section entrance. If measures are taken to prevent the air passage from being blocked by the molten resin, the air passage may be blocked by the molten resin, or may be closed after the molten resin reaches the air passage. It is safe and preferable to close the opening / closing section before injecting the molten resin into the mold cavity. When a porous metal material is used for the pressure reducing port in the above (2), the air passage may or may not be opened or closed.

In the method of the present invention, the pressurized fluid is injected into the molten resin injected into the mold cavity because the molten resin is pressed against the surface of the mold cavity, and the surface of the molded product has an uneven pattern on the surface of the cavity. The purpose of this is to accurately transfer the film and form a hollow portion inside the molded article.

In the method of the present invention, there are no particular restrictions on the injection position, the number of injection ports, and the like when the pressurized fluid is injected into the molten resin. The size of the molded product, the structure of the molded product, and the formation of the hollow portion It can be appropriately selected according to the position to be formed, the size of the hollow portion, and the like. The injection position of the pressurized fluid is (1) located inside the molten resin injection section (injection nozzle), (2) located near the molten resin injection section, (3) located at a position away from the molten resin injection section Or (4) a plurality of the above (1) to (3) are combined and arranged.

When a plurality of pressurized fluid injection sections (nozzles) are arranged, the pressurized fluid injected from the injection section presses the molten resin while forming a hollow portion, and presses from the adjacent injection sections. It is possible to form resin partition walls (ribs or pillars connecting opposing surfaces such as upper and lower, left and right of the molded product) at a portion where the formed resin meets, and it is possible to reinforce an injection molded product having a hollow portion. It is suitable.

When the injection part (gas nozzle) for pressurized fluid is attached to the mold, either the movable mold or the fixed mold may be used, or both may be attached. It is preferable to make the gap between the mold and the gas nozzle as small as possible, or to completely eliminate the gap when the nozzle is not movable. Also, when pressurized fluid is injected only from the injection nozzle of the molding machine,
The attachment of the pressurized fluid injection nozzle to the mold need not be considered.

The timing of injection of the pressurized fluid in the production of a molded article by the method of the present invention may be during injection of the molten resin into the mold cavity or immediately after injection is completed (including simultaneously with injection completion). I do. When the mold for manufacturing a molded product is composed of a fixed mold portion and a movable mold portion, the mold cavity is formed between the start of the injection of the molten resin and the completion of the injection of the pressurized fluid into the molten resin. The fixed mold part and the movable mold part may be kept in a tightened state so that the volume does not change.

When a molded article is manufactured by the method of the present invention, the molten resin is injected into the mold cavity in order to change the size and thickness of the hollow portion formed inside the molded article.
Alternatively, immediately after the injection is completed, the movable mold portion can be retracted to increase the volume of the mold cavity. Also in this case, the injection of the pressurized fluid is started during or immediately after the injection of the molten resin into the mold cavity. When the volume of the mold cavity is increased, the injection of the pressurized fluid may be started before, during, or after the expansion of the volume.

The molded article obtained by the method of the present invention has a hollow portion in a thick portion. The hollow portion may extend over the entire main portion of the molded product or may be a part of the main portion. You may. As a molded article in which a hollow portion is a main portion, a tubular structure (for example, a pipe) can be given. In this case,
The hollow portion constitutes, for example, a fluid flow path. In addition, as a molded product in which the hollow portion is a part, an injection molded product in which the surface of the hollow portion constitutes a sliding surface, for example, the hollow portion constitutes a hole through which an electric wire or a drive wire passes, and the electric wire or the drive wire is used. An injection-molded product that slides in contact with the inner surface of the hole can be given.

As the pressurized fluid that can be used when producing a molded article by the method of the present invention, an inert fluid that is gaseous or liquid at ordinary temperature and ordinary pressure and does not react with or mix with the molten resin during molding is desirable. Specifically, nitrogen gas, air, carbon dioxide gas, helium, water and the like can be mentioned, and among them, nitrogen gas is preferable.

The product (PV) of the volume (V) of the molten resin injected into the mold cavity and the pressure (P) may be an amount capable of molding a desired injection molded product. Depends on. In general, the higher the pressure of the pressurized fluid remaining after the injection of the pressurized fluid into the molten resin and the formation of the hollow portion in the molten resin, the better the mold transferability and the appearance. Therefore, it is preferable that the pressure of the pressurized fluid is high.

The molded articles according to the present invention are used, for example, in automobile exterior parts such as roof rails, door handles, bumpers, etc., and in the OA field, shafts requiring dimensional accuracy of copiers and printer parts require surface smoothness. Can be used. In addition, warpage and burrs do not occur in the molded product, and the imprint transferability is improved even for a molded product with a grain. In particular, in the case of automotive roof rails,
Since strength and elastic modulus are required, it is necessary to mix a considerably large amount of reinforcing fibers, and it is difficult to obtain a molded article having a good appearance by the conventional gas assist injection molding method. Although multi-layer coating or sanding is required, the method of the present invention does not require surface coating, or can reduce cost even when coating.

FIG. 3 is a longitudinal sectional view of one example of a roof rail for an automobile, which is one of molded articles suitable for production by the method of the present invention, and FIG. 4 is a bottom view thereof. FIG. 5 is a longitudinal sectional view taken along the line VV in FIG. In the roof rail 30 for a vehicle, a hollow portion 35 is formed in the inside 32 of the rail main body 31 and the leg portions 33 and 34 along the length direction. 36 is a mark of the resin injection gate, and 37 is a mark of the injection port of the pressurized fluid. When the rail main body 31 having the same size as that shown in FIG. 3 is manufactured from aluminum, the weight is about twice as large as that manufactured from the fiber-reinforced thermoplastic resin composition.

[0042]

EXAMPLES Hereinafter, the content of the present invention will be specifically described with reference to examples, but the present invention is not limited to the following description examples unless the gist is exceeded.

The injection mold used in the following Examples and Comparative Examples has a diameter of 25 mm as shown in FIG.
A molded product having a handle shape having a length of 350 mm and a total length of 350 mm was used. For the evaluation of the appearance, the mold cavity surface was polished for # 1500. Due to the small size of the mold, no packing was used to prevent air leakage, but it was possible to reduce the inside of the mold cavity to about 50 mmHg by connecting to a vacuum pump. FIG.
FIG. 1 shows a schematic diagram of a vacuum pump line and a pressurized fluid injection line of the injection mold shown in FIG.

1 and 2, 1 is a handle-shaped mold cavity, 2 is a resin injection gate, 3 is an inlet for pressurized fluid, 4 is a surface roughness measuring position, 5 is an injection mold, 6 Is a sprue runner, 7 is a vacuum pump, 8 is a vacuum chamber, 9 is a pipeline, 10 is a valve, 11 is a pressurized fluid injection device, and 12 is a pipeline.

The surface appearance of the obtained molded article was evaluated by the following method. (1) Appearance: The surface appearance is visually observed. "Good" means no surface roughness is observed, "Almost good" means slight surface roughness is observed, and considerable surface roughness is observed. The thing was judged as "with roughness". (2) Surface roughness: "Surfacecom 554"
A ”and Ra (μm) according to JISB0601.
m) and Rx (μm) were measured at the measurement positions shown in FIG. (3) Flexural modulus: Measured according to JIS K7171.

Example 1 As a fiber-reinforced thermoplastic resin composition pellet, Lenny 1022F (manufactured by Mitsubishi Engineering-Plastics Co., Ltd., 50% by weight of glass fiber (3
(Trade name) of polyamide MXD6 blended (3% by volume). After bringing the nozzle of the injection molding machine into contact with the gate of the injection molding mold in the mold clamped state, open the valve of the vacuum pump leading to the mold cavity, and check that the pressure gauge in the mold cavity has dropped to about 50 mmHg. After confirmation, the passage to the vacuum pump was closed, and at the same time, injection of the molten resin into the mold cavity was started. The molding conditions are as follows: molding machine temperature setting =
280 ° C, injection pressure = 1200 kgf / cm ² , injection rate = about 7
0 cc / sec, residual pressure after gas injection = 23 kgf / cm ² , mold temperature = 135 ° C.

The injection of the molten resin was terminated 1.4 seconds after the start of the injection of the molten resin into the mold cavity. Immediately thereafter, the injection of nitrogen gas into the molten resin was started. Formed. The pressure of the nitrogen gas was maintained for 60 seconds, during which time the molded article was cooled, the residual nitrogen gas was released to the atmosphere, the mold was opened, and the molded article was taken out. The weight of the molded article is 126 grams, and after the molded article is released from the mold and left to cool to room temperature, the appearance of the molded article is visually observed, and the surface roughness is measured by a shape measuring instrument, and Table 1 shows the flexural modulus and the like.

Example 2 In the example described in Example 1, except that the pressure gauge of the vacuum pump was changed so that the pressure gauge in the mold cavity was 250 mmHg, which was about ３ of 760 mmHg in the room. A molded article was manufactured in the same manner as described in Example 1, and the results of visual observation of the appearance, the results of surface roughness measurement by a shape measuring instrument, and the flexural modulus were shown in the same manner as in Example 1. 1 is shown.

Example 3 In the example described in Example 1, Novapet 63 was used as a fiber-reinforced thermoplastic resin composition.
08G30 (manufactured by Mitsubishi Engineering-Plastics Co., Ltd.) A molded article is manufactured in the same manner as described in the above example, except that the trade name is polyethylene terephthalate containing 30% by weight (18% by volume) of glass fiber. Table 1 shows the results of visual observation of the appearance, the results of surface roughness measurement using a shape measuring instrument, the flexural modulus, and the like, as in the same example.

[Comparative Example 1] In the same manner as in Example 1, except that the passage of the vacuum pump was closed and no vacuum was applied in the mold cavity. A molded product was manufactured, and the visual observation result of the appearance, the measurement result of the surface roughness by a shape measuring instrument, the bending elastic modulus, and the like of the molded product are shown in Table 1, as in the same example.

[Comparative Example 2] In the same manner as in Example 3, except that the passage of the vacuum pump was closed and no vacuum was applied in the mold cavity. A molded product was manufactured, and the visual observation result of the appearance, the measurement result of the surface roughness by a shape measuring instrument, the bending elastic modulus, and the like of the molded product are shown in Table 1, as in the same example.

REFERENCE EXAMPLE 1 The injection amount of the molten resin into the mold cavity was the same as that described in Example 1, except that the passage of the vacuum pump was closed and no vacuum was applied to the mold cavity. Example 1 except that the pressure was increased (full shot), the pressurized fluid was not injected, and the holding pressure was 700 kgf / cm ^2.
A molded article was manufactured in the same manner as described in Table 1, and the visual observation results of the appearance, the measurement results of the surface roughness using a shape measuring instrument, and the flexural modulus of the molded article were measured in the same manner as in Example 1. It was shown to.

REFERENCE EXAMPLE 2 Novamid 1012, a reinforced fiber (non-reinforced) nylon, which is said to provide a molded article having good gloss and excellent appearance even under normal injection molding conditions.
A molded article was produced in the same manner as described in Comparative Example 1 using C2 (trade name of nylon 6, manufactured by Mitsubishi Engineering-Plastics Corporation), and the appearance of the molded article was visually observed in the same manner as in the same example. Table 1 shows the results of the observation, the measurement of the surface roughness using a measuring instrument, and the flexural modulus.

[0054]

[Table 1]

From Table 1, the following becomes clear. (1) The molded article obtained by the method according to the present invention is a non-reinforced polyamide MXD which is said to obtain a molded article having an excellent appearance despite being blended with a large amount of glass fiber,
The appearance is excellent similarly to the molded product of nylon 6 (see Reference Example 1 and Reference Example 2). In addition, when the pressure inside the mold cavity is reduced, the appearance of the molded product becomes more excellent as the pressure is increased (Examples 1 and 2). (2) A glass fiber molded product molded without depressurizing the inside of the mold cavity has a noticeable appearance of roughness and sink marks (see Comparative Examples 1 and 2). (3) The molded article of Reference Example 1 was formed by a normal injection molding method without injecting a pressurized fluid, and was heavy because there was no hollow portion. Example 1
However, the flexural modulus was inferior, and sink marks were observed on the surface of the molded product. (4) The molded article obtained by the method according to the present invention is high in flexural modulus and excellent in strength despite being lightweight (Examples 1, 2 and Reference Example 1).

[0056]

As described above, the present invention has the following particularly advantageous effects, and its industrial utility value is extremely large. 1. According to the method of the present invention, a fiber-reinforced thermoplastic resin composition is used as a raw material, and a gas-assisted injection molding method is used. Can be manufactured. 2. According to the method of the present invention, since the molten resin is injected under reduced pressure in the mold cavity, residual air trapped on the mold cavity surface can be reduced, and a molded article having a good appearance and having a hollow portion can be obtained. Can be manufactured. 3. The molded article according to the method of the present invention is not only excellent in appearance without sink marks and roughness but also excellent in strength despite having a hollow portion and being lightweight.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a mold used in Examples and Comparative Examples.

FIG. 2 shows the vacuum pump line of the mold shown in FIG.
Figure 3 shows a schematic diagram of a pressurized fluid injection line.

FIG. 3 is a longitudinal sectional view of an example of a roof rail for a vehicle along a length direction.

FIG. 4 is a bottom view of the automobile roof rail shown in FIG. 3;

FIG. 5 is a longitudinal sectional view taken along a line VV in FIG. 3;

[Explanation of symbols]

 1: Mold cavity 2: Resin injection gate 3: Pressurized fluid injection port 4: Surface roughness measurement position 5: Injection molding die 6: Sprue runner 7: Vacuum pump 8: Vacuum chamber 9, 12: Pipeline 10 : Valve 11: Pressurized fluid injection device 30: Roof rail for automobile 31: Rail body 32: Inside 33, 34: Leg 35: Hollow 36: Resin injection gate 37: Pressurized fluid injection port

Claims (7)

[Claims] When producing a fiber-reinforced thermoplastic resin molded article by injection molding using a thermoplastic resin composition containing reinforcing fibers as a raw material, a fiber-reinforced thermoplastic resin composition containing reinforcing fibers is melted, In a state in which the mold cavity for injection molding is closed, the injection of the molten resin is started while the pressure inside the cavity is reduced to 気 圧 atm or less, and the resin is injected into the cavity during or after the injection is completed. A method for producing a fiber-reinforced thermoplastic resin molded article having a good appearance, wherein a pressurized fluid is injected into a molten resin to form a hollow portion in the molded article. 2. The method for producing a fiber-reinforced thermoplastic resin molded article according to claim 1, wherein the injection amount of the fiber-reinforced resin composition into the mold cavity is smaller than the volume of the mold cavity. 3. The fiber-reinforced thermoplastic resin molding according to claim 1, wherein the reinforcing fiber is glass fiber or carbon fiber, and the compounding amount in the thermoplastic resin is 7% by volume or more. Product manufacturing method. 4. The thermoplastic resin according to claim 1, wherein the thermoplastic resin has a polyamide as a main component.
The method for producing a fiber-reinforced thermoplastic resin molded product according to the above item. 5. The method for producing a fiber-reinforced thermoplastic resin molded article according to claim 4, wherein the polyamide is polyamide MXD6. 6. A fiber-reinforced thermoplastic resin molded article produced by injection molding using a thermoplastic resin composition containing reinforcing fibers as a raw material, wherein the compounding amount of the thermoplastic resin is 7%.
When the mold cavity for injection molding is closed, the pressure inside the mold cavity is reduced to さ せ in a state where the fiber-reinforced thermoplastic resin composition containing the reinforcing fiber of not less than% by volume is melted.
While the pressure is reduced to the atmospheric pressure or less, the injection of the molten resin is started, and during or after the injection, a pressurized fluid is injected into the molten resin injected into the mold cavity to form a hollow portion in the molded product. A fiber-reinforced thermoplastic resin molded article having a good appearance, characterized in that the molded article has a good appearance. 7. The molded article is an automobile roof rail.
The fiber-reinforced thermoplastic resin molded product according to claim 6.