JP2014105245A - Method for producing thermoplastic molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a thermoplastic molding, in which a minute void derived from a prepreg can be prevented from being generated when the prepreg containing a thermoplastic resin is molded.SOLUTION: The method for producing the thermoplastic molding comprises: a step of aligning a plurality of carbon fibers in a sheet-like state; a step of impregnating the aligned carbon fibers with the thermoplastic resin so that an impregnation rate becomes 50-90% and a thermoplastic prepreg is obtained; a preheating step (1) of heating the thermoplastic prepreg to the temperature higher than the melting point of the thermoplastic prepreg by 5-30°C; a heating/pressurizing step (2) of heating the heated thermoplastic prepreg to the temperature higher than the melting point of the thermoplastic prepreg by 30-80°C while exerting the pressure of 0.4-10.0 MPa on the thermoplastic prepreg; and a cooling/pressurizing step (3) of exerting the pressure of 0.4-10.0 MPa on the thermoplastic prepreg while setting the temperature within 30-80°C.

Description

  The present invention relates to a method for producing a thermoplastic molded article using a thermoplastic prepreg.

  In recent years, carbon fibers, which are reinforcing fiber materials, have been compounded with various matrix resins, and the resulting fiber-reinforced plastics have been widely used in various fields and applications. And in the aerospace field and general industrial fields where high mechanical properties and heat resistance are required, conventionally, thermosetting resins such as unsaturated polyester resin, epoxy resin, and polyimide resin have been used as matrix resins. It has been. However, especially in the aerospace field, these matrix resins have the drawbacks of being brittle and inferior in impact resistance, and therefore, improvement has been demanded. In the case of a thermosetting resin, when this is used as a prepreg, there is a problem in storage management due to the short lifetime of the resin, poor followability to the product shape, long molding time and productivity There were also problems such as low. On the other hand, in the case of a thermoplastic resin prepreg, the impact resistance when made into a composite material is excellent, the storage management of the prepreg is easy, the molding time is short, and the molding cost may be reduced.

The thermoplastic prepreg using a thermoplastic resin as a matrix and the thermoplastic molded article obtained by molding them include the following in terms of the form of carbon fibers in the thermoplastic prepreg and the orientation thereof. (1) A thermoplastic prepreg in which continuous carbon fibers are used, unidirectionally aligned fiber sheets are prepared, and these are heated and impregnated with a thermoplastic resin. The thermoplastic molded body using such a thermoplastic prepreg is excellent in mechanical strength and in-plane by laminating the thermoplastic prepreg so that the thickness direction fiber axis direction does not overlap because the thermoplastic physical property is isotropic. It is characterized by having isotropic properties. (2) As a non-continuous carbon fiber, a small piece obtained by cutting a thermoplastic prepreg obtained by heat impregnating a unidirectionally arranged strand or a unidirectionally arranged fiber sheet with a thermoplastic resin into a fiber length of, for example, about 25 mm to 50 mm There is a thermoplastic prepreg. As an example of a molded body using such a thermoplastic prepreg, there is a thermoplastic molded body obtained by laminating and molding small pieces of a thermoplastic prepreg on a mold by free-falling, and such a molded body is a small piece of a thermoplastic prepreg. Since the layers are randomly laminated, the mechanical properties are in-plane isotropic and the moldability is excellent.
Such thermoplastic prepreg is often molded by a conventionally known method, and in particular, it is actually molded under the same molding conditions as the glass fiber material.

  For example, Patent Document 1 proposes a fiber-reinforced thermoplastic resin sheet made of a thermoplastic resin and reinforcing fibers. However, although patent document 1 has description of the manufacturing conditions of the shaping | molding board which consists of a prepreg using glass fiber as a reinforced fiber, there is no description of the manufacturing conditions of the shaping | molding board which consists of prepregs using carbon fiber. Glass fibers tend to have a larger fiber diameter than carbon fibers, and therefore tend to be less dependent on the mechanical properties of the molded product obtained by molding a prepreg and the manufacturing conditions during molding. The manufacturing conditions of the thermoplastic molded plate obtained by molding a thermoplastic prepreg using the above are not optimal and need to be improved. In addition, molded articles made of general prepregs including thermoplastic prepregs always have the problem of voids that occur during production, and there is a method of producing them without generating voids and eliminating the generated voids. It is anxious.

  For example, in Patent Document 2, a thermoplastic fiber nonwoven fabric in which a thermoplastic resin fiber is a nonwoven fabric in a non-woven state is superposed on a reinforcing fiber sheet in which a plurality of reinforcing fiber bundles are aligned in one direction, and pressure is applied while heating. Thus, a technique for obtaining a fiber-reinforced thermoplastic resin sheet with few voids has been proposed. However, this method is an example of trying to reduce voids by reducing the amount of resin to be supplied, and is not a fundamental void elimination measure. That is, there is no description about the countermeasure when a void remains, and when a micro void remains at the time of manufacture of a prepreg, the micro void derived from a prepreg remains also in a thermoplastic molded board obtained from such a prepreg. there is a possibility.

Japanese Patent No. 2885038 Japanese Patent Laid-Open No. 2003-165851

  An object of the present invention is to prevent prepreg-derived microvoids that are generated when thermoplastic prepreg is formed.

The gist of the present invention is that a thermoplastic prepreg in which a plurality of carbon fibers are arranged in a sheet shape and impregnated with a thermoplastic resin so as to have an impregnation rate of 50% to 90% is obtained by the following (1) to ( A method for producing a thermoplastic molded article obtained by the step 3) as a thermoplastic molded article.
(1) Preheating step: a step of heating the thermoplastic prepreg at a temperature 5 to 30 ° C. higher than the melting point of the thermoplastic resin,
(2) heating the thermoplastic prepreg while applying a pressure of 0.4 MPa or more and 10.0 MPa or less to a temperature 30 to 80 ° C. higher than the melting point of the thermoplastic resin;
(3) Cooling and pressurization step: Step of adding a pressure of 0.4 MPa or more and 10.0 MPa or less to the thermoplastic prepreg with a temperature setting of 30 to 80 ° C. Here, the impregnation ratio is determined by using a thermoplastic resin prepreg with a polyester resin (Kurzer) Manufactured, product name: Technobit 4000), and the cross-sections were polished with water-resistant paper counts # 200, 400, 600, 800, 1000 in order of each count for 5 minutes, and then a digital microscope (manufactured by Keyence Corporation, product) Name: VHX-100) is used to photograph the cross section at 150 times, measure the area ratio of the normal part and void of the photographed cross section, and subtract the void ratio from 100%.

  According to the method for producing a thermoplastic molded body of the present invention, a fine void that has been easily retained by molding a thermoplastic prepreg impregnated so as to have an impregnation rate of 50% to 90% under specific molding conditions. In addition, a thermoplastic molded plate having excellent mechanical strength can be provided.

  The thermoplastic prepreg that can be used in the method for producing a thermoplastic molded body of the present invention refers to a prepreg in which a plurality of carbon fibers are arranged in a sheet shape and impregnated with a thermoplastic resin. The thermoplastic prepreg refers to a molded plate obtained through a molding process comprising (1) a preheating process, (2) a heating and pressing process, and (3) a cooling and pressing process.

(Thermoplastic resin)
The thermoplastic resin that can be used in the method for producing the thermoplastic molded article of the present invention includes polypropylene and polypropylene acid-modified products, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, aromatic or aliphatic polyamide, aromatic Resin selected from the group consisting of aromatic polyester, aromatic polycarbonate, polyetherimide, polyarylene oxide, thermoplastic polyimide, polyamideimide, polybutylene terephthalate, polyethylene terephthalate, polyethylene, acrylonitrile butadiene styrene, and used alone. It is also possible to use a mixture of two or more. Depending on the application, it can be used by mixing with a thermosetting resin. Particularly preferred are polyamides, polypropylenes and polypropylene acid modified products, polycarbonates and acrylonitrile butadiene styrene (ABS) resins, which are excellent in heat resistance, elastic modulus and chemical resistance.

  These thermoplastic resins include commonly used flame retardants, weather resistance improvers, other antioxidants, heat stabilizers, UV absorbers, plasticizers, lubricants, colorants, compatibilizers, fillers, and conductive fillers. Carbon black or the like may be added as appropriate.

  The carbon fibers that can be used in the method for producing the thermoplastic molded article of the present invention are preferably opened as much as possible when they are aligned, regardless of whether or not they are twisted.

  The method for producing a thermoplastic prepreg that can be used in the method for producing a thermoplastic molded article of the present invention is not particularly limited, and a conventionally known method can be used. For example, a directly melted thermoplastic resin is made from a plurality of carbon fibers. A method of impregnating a sheet-like material, a film-like thermoplastic resin is laminated on one or both sides of a plurality of carbon fibers arranged in a sheet shape, and the film-like thermoplastic resin is melted and impregnated. There are methods, such as a method of melting and impregnating a powdered thermoplastic resin, but from the viewpoint of impregnation and degree of freedom of opening, and from the viewpoint of the appearance quality of the resulting prepreg, a plurality of carbon fibers are formed into a sheet. A method of laminating a film-like thermoplastic resin on one side or both sides of those arranged in order to melt and impregnate the film-like thermoplastic resin is preferable. In particular, from the viewpoint of preventing warping of the resulting thermoplastic prepreg, a film-like thermoplastic resin is laminated from both sides of the carbon fiber strand, and melt impregnation under conditions of a roll temperature of 150 to 400 ° C. and a roll pressure of 10 to 1000 MPa. Particularly preferred is a method of making them.

  The impregnation rate of the thermoplastic prepreg that can be used in the method for producing a thermoplastic molded body of the present invention needs to be 50% or more and 90% or less. By keeping the impregnation rate within the above range, it becomes possible to intentionally provide an air pass line, and when a subsequent pressurizing step is performed, it is possible to prevent the presence of minute voids, and such heat A thermoplastic molded plate obtained from a plastic prepreg has a feature that it has no voids and has excellent mechanical properties. Furthermore, the fiber volume content (Vf) is preferably 10% or more and 60% or less. If the fiber volume content (Vf) exceeds 60%, the carbon fiber tends to inhibit the pass line through the remaining microvoids, and the mechanical properties of the thermoplastic molded plate obtained from such a thermoplastic prepreg. Tend to decrease. Furthermore, since carbon fiber is expensive compared with other conventionally known reinforcing fibers, it is not preferable from the viewpoint of cost. On the other hand, when the fiber volume content (Vf) is less than 10%, the number of cases where voids are hindered from being reduced and the carbon fiber cost can be reduced, but the thermoplastic molded plate obtained from such a prepreg Mechanical properties tend to be insufficient.

  The thickness of the thermoplastic prepreg that can be used in the method for producing a thermoplastic molded article of the present invention needs to be 0.03 mm or more and 0.50 mm or less. When the thickness of the thermoplastic prepreg exceeds 0.50 mm, the dispersion of the carbon fiber strands in the prepreg tends to be incomplete, and when a thermoplastic molded plate is prepared using such a thermoplastic prepreg, There is a tendency for mechanical properties to decrease and variations in physical properties to increase. The upper limit of the thickness is more preferably 0.40 mm or less, and still more preferably 0.35 mm or less. On the other hand, when the thickness of the prepreg is less than 0.03 mm, the rigidity of the prepreg tends to decrease significantly, and it is difficult to form a sheet of carbon fiber strand or to apply a thermoplastic resin for producing such a prepreg. Therefore, it tends to be difficult to obtain a high-quality prepreg. The lower limit of the more preferable thickness is 0.04 mm or more, and more preferably 0.05 or more.

One or more thermoplastic prepregs that can be used in the method for producing a thermoplastic molded body of the present invention are laminated, and then processed through the following steps (1) to (3) to become a thermoplastic molded plate.
(1) Preheating step, (2) Heating and pressing step, (3) Cooling and pressing step

  When the production method of the thermoplastic molded body is a batch process, various temperatures are different depending on the thermoplastic resin to be used. For example, the temperature of the heating part of the molding machine is higher by 5 to 30 ° C. than the melting point of the thermoplastic resin. A laminated body in which one or more thermoplastic prepregs are laminated is introduced into a molding machine heating section, and the temperature of the laminated body is within a range of 30 to 80 ° C. higher than the melting point of the thermoplastic resin, for example. Preheat to the extent that Thereafter, as the heating and pressing step, the thermoplastic prepreg is pressurized for 1 to 10 minutes while maintaining the temperature of the heating unit of the molding machine, and then the thermoplastic prepreg is transferred to the cooling unit of the molding machine and added as a cooling and pressing step. There is a method of obtaining a thermoplastic molded plate by applying pressure.

  On the other hand, in the case of a continuous process, a laminate obtained by laminating one or more thermoplastic prepregs is placed on a steel belt, and the temperature varies depending on the thermoplastic resin to be used, but is 5 to 30 ° C higher than the melting point of the thermoplastic resin. After preheating up to, it is heated and pressurized by passing between hot rolls that have been heated to 30 to 80 ° C. higher than the melting point of the thermoplastic resin in advance, and then cooled and pressurized to make thermoplasticity There is a method for obtaining a molded plate. In addition, for example, the process can be appropriately selected depending on the material, for example, heating / pressurization / cooling / pressurization is performed by a belt press, or preheating is performed by a far infrared heater method, an electromagnetic induction method, or a Joule heating method.

The pressure setting range in the heating and pressing step of the method for producing a thermoplastic molded body of the present invention requires that the pressure around the heating surface of the obtained thermoplastic molded body be 0.4 MPa or more and 10.0 MPa. If it is less than 0.4 MPa, it becomes difficult to completely expel the air of the unimpregnated portion in the thermoplastic prepreg out of the system, so that the mechanical properties of the thermoplastic molded plate obtained under such molding conditions deteriorate. Therefore, it is not preferable. A more preferable lower limit of the pressure is 0.6 MPa or more. On the other hand, if it exceeds 10.0 MPa, the flow of the thermoplastic resin generated during the heating and pressurizing step increases, and the fiber volume content of the thermoplastic molded plate obtained with respect to the charging is not preferable. A more preferable upper limit of the pressure is 8.0 MPa.
Similarly, the temperature in the heating and pressing step needs to be heated at a temperature 30 to 80 ° C. higher than the melting point of the thermoplastic resin. When the temperature is lower than 30 ° C, the resin is not in a molten state sufficient for molding, and it is difficult to completely expel the air in the unimpregnated portion in the thermoplastic prepreg out of the system. It is not preferable because the mechanical properties of the thermoplastic molded plate obtained under the conditions are lowered. On the other hand, when molding is performed in a temperature range exceeding 80 ° C., when a general-purpose thermoplastic resin such as modified polypropylene is used, the decomposition temperature may be reached. Also, if heating at such a temperature, the viscosity of the resin becomes unnecessarily low, and burrs are generated, or the fiber volume content of the thermoplastic molded plate obtained for the preparation is shifted due to the generated burrs. This is not preferable.

  The pressurization time in the heating and pressurizing step varies depending on the material and size of the mold used, but is preferably 1 minute or more and 10 minutes or less, for example. The pressurization time is less than 1 minute, and the difference between the temperature of the heating part of the molding machine after the heating and pressurizing step and the temperature of the laminated body of the thermoplastic prepreg is remarkable, and the heating tends to be insufficient. On the other hand, if the pressurization time exceeds 10 minutes, there will be no difference between the temperature of the heating section of the molding machine after the heating and pressurizing step and the temperature of the laminate of the thermoplastic prepreg, but the heating will be sufficient, but the total molding time will be longer. Therefore, the productivity tends to deteriorate.

The pressurizing pressure in the cooling and pressurizing step of the method for producing a thermoplastic molded body of the present invention requires that the pressure around the heating surface of the obtained thermoplastic molded body be 0.4 MPa or more and 10.0 MPa. If the pressure is less than 0.4 MPa, the thermal shrinkage of the thermoplastic resin that occurs during cooling cannot be followed, and microvoids tend to be newly generated in the system, and the heat obtained under such molding conditions. The plastic molded plate tends to have lower mechanical properties. On the other hand, if the pressure exceeds 10.0 MPa, the amount of burrs generated during the heating and pressing step increases, and the fiber volume content of the thermoplastic molded plate obtained as a result tends to shift.
The cooling temperature in the cooling and pressurizing step varies depending on the material and size of the mold used, the type of thermoplastic resin used, and the difference in heat capacity between the mold used and the molding machine cooling section, but is 30 ° C. or higher and 80 ° C. or lower. Need to be. When the temperature is less than 30 ° C., the temperature difference between the outer surface and the inside of the molded body becomes noticeable due to rapid cooling, which may cause generation of microvoids due to a difference in thermal expansion or warpage of the molded body. Absent. Further, when a crystalline resin is used, there is a tendency that crystallization is hindered by rapid cooling, and therefore there is a possibility that the mechanical properties of the thermoplastic molded plate obtained under such production conditions may be lowered. On the other hand, when the temperature exceeds 80 ° C., the cooling rate is slow, and particularly the cooling rate inside the material is dramatically slowed. Therefore, internal stress relaxation tends to occur more easily than crystallization promotion, and local carbon fibers and resins Due to the degree of freedom, microvoids tend to occur during stress relaxation, and peeling at the resin fiber interface tends to occur. In addition, it is not preferable from the viewpoint of safety because it takes time to manufacture and handles a high-temperature object when the molded body is taken out.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by these Examples.
In the following examples and comparative examples, the following were used as raw materials.
(Carbon fiber)
Carbon fiber (Mitsubishi Rayon Co., Ltd., product name: TR50S15L, 12,000, density 1.82 g / cm ² )
(Thermoplastic resin film)
Using modified polypropylene (Mitsubishi Chemical Corporation, product name: Modic <registered trademark> P958), it was prepared by the following method.
The modified polypropylene which had been sufficiently dried was sandwiched by a heating plate heated to 220 ° C. using a heating and cooling two-stage press (F-37, manufactured by Shinfuji Metal Industry Co., Ltd.), pressed and thinned. Then, the thermoplastic resin film was obtained by cooling with a cooling board.
The basis weight of the obtained thermoplastic resin film was 28.0 g / m ² .

[Production Example 1]
A resin film was laminated on both surfaces of a carbon fiber sheet-like material (basis weight 98.0 g / m ² ) in which carbon fibers were oriented in one direction to obtain a laminate. This laminate was heated to 200 to 250 ° C., and a thermoplastic resin film was melt-impregnated into a carbon fiber sheet to obtain a thermoplastic prepreg. The obtained thermoplastic prepreg had a thickness of 115 μm, a basis weight of 153.0 g / m ² , a fiber deposition content of 47.0%, and an impregnation rate of 75%.

[Example 1]
Eighteen thermoplastic prepregs obtained in Production Example 1 were laminated so that the fiber axis directions coincided, and the laminate was placed in a mold. Furthermore, it was put into a heating / cooling two-stage press machine (product name: F-37, manufactured by Shindo Metal Industry Co., Ltd.) with a heating plate set at 220 ° C. in advance, and preheating was performed until the internal temperature of the mold reached 180 ° C. Subsequently, after heating and pressing with a pressure plate of 0.6 MPa for 7 minutes using a heating plate at 220 ° C., a cooling press was performed with a cooling plate at 30 ° C. at a pressure of 0.6 MPa to obtain a molded plate 1. The cooling disk was heated to 50 ° C. at the end of molding due to heat transfer from the mold. The fiber volume content Vf, thickness, mechanical properties, and void ratio of the obtained molded plate 1 are shown in Table 1.

[Examples 2-3]
Molded plates 2-3 were obtained by the same method as described in Example 1 except that the pressure of the heating / cooling press and the cooling press was changed to 1.0 MPa in Example 2 and 2.0 MPa in Example 3. . Table 1 shows the fiber volume content Vf, thickness, mechanical properties, and void ratio of the obtained molded plates 2 to 3.

[Comparative Example 1]
A molded plate 4 was obtained by the same method as described in Example 1 except that the pressure of the heating / cooling press and the cooling press was changed to 0.3 MPa. The fiber volume content Vf, thickness, mechanical properties, and void ratio of the obtained molded plate 4 are shown in Table 1.

(Evaluation method)
(Measurement of fiber volume content)
The density of the test piece for the bending test was measured by a method according to JIS K7112. Thereafter, the fiber deposition content was calculated from the density of the carbon fiber and the resin film.

(0 ° bending test)
The obtained molded plate was cut into a size of 100.0 mm (0 ° direction) × 12.7 mm width (90 ° direction) with a wet diamond cutter to prepare a test piece. The obtained test piece was compliant with ASTM D790 (indenter R = 5.0, L / D = 40) using a universal testing machine (manufactured by Instron, product name: Instron 5565) and analysis software (product name: Bluehill). A three-point bending test was performed to obtain strength and elastic modulus.

(90 ° bending test)
The obtained molded plate was cut into a size of 60.0 mm (0 ° direction) × 12.7 mm width (90 ° direction) with a wet diamond cutter to prepare a test piece. The obtained test piece was compliant with ASTM D790 (indenter R = 5.0, L / D = 16) using a universal testing machine (manufactured by Instron, product name: Instron 5565) and analysis software (product name: Bluehill). A three-point bending test was performed to obtain strength and elastic modulus.

(Impregnation rate)
The prepreg is embedded in a polyester resin (product name: Technobit 4000, manufactured by Kultzer), and the cross section is polished for 5 minutes with each count in the order of water-resistant paper counts # 200, 400, 600, 800, 1000, then digital micro Using a scope (manufactured by Keyence Corporation, product name: VHX-100), a cross section was photographed at 150 times. It is obtained by measuring the area ratio of the normal part and void of the photographed cross section and subtracting the void ratio from 100%.

(Void occurrence rate)
The resulting molded plate was embedded in a polyester resin (product name: Technobit 4000, manufactured by Kultzer), and the sections were polished for 5 minutes with each count in the order of counts of water-resistant paper # 200, 400, 600, 800, 1000 Thereafter, a cross section was photographed at a magnification of 150 using a digital microscope (manufactured by Keyence Corporation, product name: VHX-100). The area ratio of the normal part and void of the photographed cross section was measured, and the void generation rate was calculated. The evaluation index is ◯ when the void generation rate is less than 1%, ◯ when it is 1% or more and 4% or less, Δ when it is more than 4% and 7% or less, and × when it is more than 7%.

(Measurement of melting point)
The melting point of the thermoplastic resin was measured and analyzed using DSC (TA Instruments, product name: Q1000) and analysis software (TA Universal Analysis) to obtain a melting point. The operating conditions of the DSC were 5 mg of a thermoplastic resin, heated at 5 ° C./min, and measured from room temperature to 300 ° C.

Claims (1)

A thermoplastic prepreg in which a plurality of carbon fibers are arranged in a sheet form and impregnated with a thermoplastic resin so as to have an impregnation rate of 50% to 90% is formed into a thermoplastic article by the following steps (1) to (3). A method for producing a thermoplastic molded body.
(1) Preheating step: a step of heating the thermoplastic prepreg to a temperature 5-30 ° C. higher than the melting point of the thermoplastic resin,
(2) Heating and pressing step: a step of heating the thermoplastic prepreg while applying a pressure of 0.4 MPa or more and 10.0 MPa or less to a temperature 30 to 80 ° C. higher than the melting point of the thermoplastic resin,
(3) Cooling and pressurizing step: a step of setting the temperature to 30 to 80 ° C. and applying a pressure of 0.4 MPa or more and 10.0 MPa or less to the thermoplastic prepreg

Here, the impregnation rate is obtained by embedding the thermoplastic prepreg in a polyester resin (product name: Technobit 4000, manufactured by Kultzer Co.), and the cross-sections in the order of water resistant paper counts # 200, 400, 600, 800, 1000, respectively. After polishing for 5 minutes with a count, a cross section was photographed at a magnification of 150 times using a digital microscope (manufactured by Keyence Corporation, product name: VHX-100), and the area ratio of normal portions and voids of the photographed cross section was measured. It is obtained by subtracting the void ratio from%.