JP2013053245A - Thin-wall molding having uniform thickness, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-wall molding having a uniform thickness, which is constituted of a fiber-reinforced composite material containing a reinforcing fiber and a thermoplastic resin, and has a smooth surface; and to provide a method for manufacturing the same.SOLUTION: The thin-wall molding is constituted of a fiber-reinforced composite material containing a reinforcing fiber of ≥5 mm and ≤100 mm in average fiber length, and a thermoplastic resin, wherein the reinforcing fiber volume content (Vf=100×reinforcing fiber volume/(reinforcing fiber volume+thermoplastic resin volume)) is 5 to 80%; the thickness is uniformly 1.5 mm; and the proportion of a reinforcing fiber bundle (A) constituted of a critical single yarn number or more defined by the expression (1): critical single yarn number=600/D (wherein, D is an average fiber diameter (μm) of the reinforcing fiber) is ≥20 vol% and ≤99 vol% with respect to the total amount of the reinforcing fiber.

Description

  The present invention relates to a thin molded article having a uniform thickness, which is made of a fiber-reinforced composite material containing reinforcing fibers and a thermoplastic resin, and a method for producing the same.

  In recent years, there has been an increasing demand for weight reduction in various fields such as electrical and electronic equipment, automobiles, medical equipment, aircraft, building materials, and general industrial parts. It has come to be required. As such a thin-walled and highly rigid housing or member, a molded body obtained by press-working a rolled plate of an aluminum alloy or a magnesium alloy, or a molded body formed by die-cast molding has been used, and glass fiber or carbon is used. A molded body in which a fiber-reinforced composite material filled with fibers is injection-molded or a molded body in which a thermoplastic resin is integrated with a fiber-reinforced composite material plate by injection molding has been used.

  Aluminum alloys and magnesium alloys are excellent in strength and rigidity, but have limited formability, and it is difficult to form a complex shape by itself. In addition, metal members (especially magnesium alloys) have a problem that the corrosion resistance is inferior, and the surface is corroded by moisture or salt contained in the moisture in the atmosphere or the user's sweat, resulting in a problem of poor appearance.

  Therefore, Patent Document 1 proposes a method of manufacturing a housing having a covering step of covering the entire member made of a magnesium alloy with a resin layer and a forming step of integrally forming the member and a resin component. This makes it possible to form a complicated shape and impart corrosion resistance, but the process is complicated and the specific strength of aluminum alloy, magnesium alloy, and resin is high for iron, but will be described later. Since it is lower than the fiber reinforced composite material, there is a limit to the weight reduction that can be achieved.

  The fiber reinforced composite material is excellent in specific strength, specific rigidity, and excellent in corrosion resistance. Therefore, the fiber reinforced composite material is widely used in the above-mentioned applications. In particular, molded products made by injection molding of fiber reinforced composite materials filled with glass fiber or carbon fiber are widely used due to their high degree of freedom in shape and high productivity, but the fiber length remaining in the molded product is shortened. Therefore, problems remain in applications that require high strength and rigidity.

  On the other hand, fiber reinforced composite materials reinforced with continuous fibers are particularly excellent in specific strength and specific rigidity, and thus have been used mainly for applications that require high strength and rigidity. However, the degree of freedom in shape is low as compared with resin and fiber-reinforced composite materials by injection molding, and it has been difficult to form a complex shape alone. In addition, since it is manufactured by laminating a plurality of reinforcing fibers in a woven form, there is a problem that productivity is low. Patent Document 2 proposes a composite molded product in which a resin member is bonded to the outer edge of a plate-like member made of a sheet containing reinforcing fibers, particularly continuous fibers. As a result, it is possible to realize a molded product having a complicated shape, but it is difficult to say that productivity is high because it is manufactured through a plurality of processes. In addition, a fiber-reinforced composite material using continuous fibers is usually obtained by heating and pressurizing a material called a prepreg in which a reinforcing fiber base is impregnated with a thermosetting resin for 2 hours or more using an autoclave. .

  In recent years, an RTM molding method in which a thermosetting resin is poured after a reinforcing fiber base not impregnated with resin is set in a mold has been proposed, and the molding time has been greatly reduced. However, even when the RTM molding method is used, it takes 10 minutes or more to mold one part, and productivity is not improved.

Therefore, a fiber reinforced composite material using a thermoplastic resin as a matrix in place of a conventional thermosetting resin has attracted attention (for example, Patent Document 3). However, research and development of fiber reinforced composite materials using thermoplastic resin as a matrix is still in the process of development, and this is molded to provide good surface smoothness and uniform thickness of the molded body. A technique for obtaining a molded article having a quality that can withstand practical use has not been sufficiently established.

The fiber-reinforced thermoplastic resin with a fiber length of 1 mm or less is a field where injection molding is still in progress, but it is a thin panel of ² mm or less and a large-area panel body exceeding 1 m ² or a shape close to a panel body As for the thin-walled molded article, the technology is not well established even by injection molding.

JP 2010-147376 A JP 2010-14180 A International Publication No. 2007/097436 Pamphlet

  An object of the present invention is to provide a thin-walled molded article having a uniform thickness, which is made of a fiber-reinforced composite material containing reinforcing fibers and a thermoplastic resin, and a method for producing the same.

  As a result of intensive studies on the above problems, the inventors of the present invention consisted of a fiber-reinforced composite material composed of a random reinforcing fiber containing a fiber bundle that satisfies a specific opening condition and a thermoplastic resin, and this fiber-reinforced composite material. It was found that the thin-walled molded body molded while flowing the powder had a uniform thickness and excellent strength.

That is, the present invention
A thin-walled molded article composed of a fiber-reinforced composite material comprising a reinforcing fiber having an average fiber length of 5 mm or more and 100 mm or less and a thermoplastic resin,
Reinforcing fiber volume content (Vf = 100 × volume of reinforcing fiber / (volume of reinforcing fiber + volume of thermoplastic resin)) is 5 to 80%,
Having a uniform thickness of 1.5 mm or less,
Following formula (1)
Critical number of single yarns = 600 / D (1)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)
The reinforcing fiber bundle (A) constituted by the number of critical single yarns or more defined in (1) relates to a thin-walled molded product characterized in that the ratio to the total amount of reinforcing fibers is 20 Vol% or more and 99 Vol% or less.

The present invention also provides:
A random mat composed of a reinforcing fiber having an average fiber length of 5 mm or more and 100 mm or less and a thermoplastic resin, wherein the reinforcing fiber has a basis weight of 25 to 3000 g / m ² , and the following formula (1)
Critical number of single yarns = 600 / D (1)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)
With respect to the reinforcing fiber bundle (A) composed of the number of critical single yarns or more defined in (1), the ratio of the reinforcing fiber to the total amount of reinforcing fibers in the random mat is 20 Vol% or more and 99 Vol% or less, and the following step A-1) To A-3)
A-1) A random mat is heated and pressurized between the melting point and the decomposition temperature when the thermoplastic resin is crystalline, or the glass transition temperature to the decomposition temperature when amorphous, and the thermoplastic resin is put into the reinforcing fiber bundle. Step of impregnating to obtain a prepreg A-2) The prepreg obtained in the above A-1) is gold whose temperature is adjusted to below the melting point when the thermoplastic resin is crystalline, and below the glass transition temperature when the thermoplastic resin is amorphous. The following formula (3)
Charge rate (%) = 100 × base material area (mm ² ) / mold cavity projection area (mm ² ) (3)
(Here, the substrate area is the projected area in the extraction direction of all the arranged random mats or prepregs, and the mold cavity projected area is the projected area in the extraction direction.)
A-3) Step of placing the prepreg placed in the mold in the above A-2) and performing impregnation to molding in the step of molding, or the following Steps B-1) to B-4)
B-1) A random mat is represented by the following formula (3)
Charge rate (%) = 100 × base material area (mm ² ) / mold cavity projection area (mm ² ) (3)
(Here, the substrate area is the projected area in the extraction direction of all the arranged random mats or prepregs, and the mold cavity projected area is the projected area in the extraction direction.)
Step B-2) When the thermoplastic resin is crystalline, the melting point to the thermal decomposition temperature of the thermoplastic resin, the amorphous In this case, the temperature is raised from the glass transition temperature to the thermal decomposition temperature of the thermoplastic resin, and the pressure is impregnated (first pressing step).
B-3) A step of pressurizing so that the pressure in the final step is 1.2 to 100 times the pressure in the first press step (second press step).
B-4) Impregnation to molding by the step of molding by adjusting the mold temperature below the melting point when the thermoplastic resin is crystalline, and below the glass transition temperature when amorphous, the thin resin is characterized in that The present invention relates to a method for producing a molded body.

  The thin molded article comprising a fiber reinforced composite material including a reinforcing fiber and a thermoplastic resin according to the present invention and having a uniform thickness of 1.5 mm or less, an electric / electronic device, an automobile, a medical device, an aircraft, a building material, It can meet demands for weight reduction of materials in various fields such as industrial parts.

  Hereinafter, although embodiment of this invention is described sequentially, this invention is not restrict | limited to these.

<Thin wall molding>
The present invention is a molded body composed of a fiber-reinforced composite material comprising a reinforcing fiber having an average fiber length of 5 mm or more and 100 mm or less and a thermoplastic resin,
Reinforcing fiber volume content (Vf = 100 × volume of reinforcing fiber / (volume of reinforcing fiber + volume of thermoplastic resin)) is 5 to 80%,
Having a uniform thickness of 1.5 mm or less,
Following formula (1)
Critical number of single yarns = 600 / D (1)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)
About the reinforcing fiber bundle (A) constituted by the number of critical single yarns or more defined in (1), the ratio is 20 Vol% or more and 99 Vol% or less of the total amount of reinforcing fibers.

  The thin molded article of the present invention is a thin molded article having a thickness of 1.5 mm or less, more precisely, a thickness exceeding 0 mm to 1.5 mm or less. The thickness of the thin molded article of the present invention is more preferably 0.2 to 1.5 mm.

  The reinforcing fibers constituting the thin molded article of the present invention are discontinuous having an average fiber length of 5 mm or more and 100 mm or less. As a result, a thin molded article that exhibits high physical properties not only against static strength and rigidity but also against shock loads and long-term fatigue loads. When the average fiber length is less than 5 mm, there is a problem that the physical properties of the molded product are lowered. When the average fiber length is longer than 100 mm, there is a problem that the handleability of the reinforcing fiber is deteriorated. The average fiber length of the reinforcing fibers is preferably 10 mm or more, more preferably 15 mm or more, and further preferably 20 mm or more. Further, the fiber length of the reinforcing fiber is preferably 80 mm or less, and more preferably 60 mm or less. A particularly preferable average fiber length is 5 mm to 80 mm.

  The reinforcing fiber contained in the fiber reinforced composite material constituting the molded body of the present invention is not particularly limited, and is an inorganic fiber such as carbon fiber, glass fiber, stainless steel fiber, alumina fiber, mineral fiber, polyether ether ketone fiber, polyphenylene. Examples thereof include at least one selected from the group consisting of organic fibers such as sulfide fibers, polyethersulfone fibers, aramid fibers, polybenzoxazole fibers, polyarylate fibers, polyketone fibers, polyester fibers, polyamide fibers, and polyvinyl alcohol fibers. Among these, in applications where the molded body is required to have strength and rigidity, it is preferably at least one selected from the group consisting of carbon fibers, aramid fibers, and glass fibers. For applications that require electrical conductivity, carbon fibers are preferred, and carbon fibers coated with a metal such as nickel are more preferred. In applications that require electromagnetic wave transparency, glass fibers and organic fibers are preferred, and aramid fibers and glass fibers are more preferred from the balance of electromagnetic wave permeability and strength. In applications where impact resistance is required, organic fibers are preferable, and polyamide fibers and polyester fibers are more preferable in consideration of cost. Among these, carbon fibers are preferable in that they can provide a fiber-reinforced composite material that is lightweight and excellent in strength.

  The average fiber diameter of the reinforcing fibers contained in the fiber reinforced composite material constituting the thin molded article of the present invention is not particularly limited. For example, in the case of carbon fibers, the preferable average fiber diameter is 3 to 12 μm, more preferably. Is 5 to 7 μm. In the case of polyester fibers, the preferred average fiber diameter is 10 to 50 μm, more preferably 15 to 35 μm. These can be used in combination, and it is also possible to use different types of reinforcing fibers depending on the part of the thin-walled molded body, and the thin-walled molded body in a state where fiber reinforced composite materials using different reinforcing fibers are laminated in whole or in part It is also possible to produce.

  Examples of the thermoplastic resin contained in the fiber reinforced composite material constituting the thin molded article of the present invention include vinyl chloride resin, vinylidene chloride resin, vinyl acetate resin, polyvinyl alcohol resin, polystyrene resin, acrylonitrile-styrene resin (AS resin). ), Acrylonitrile-butadiene-styrene resin (ABS resin), acrylic resin, methacrylic resin, polyethylene resin, polypropylene resin, polyamide 6 resin, polyamide 11 resin, polyamide 12 resin, polyamide 46 resin, polyamide 66 resin, polyamide 610 resin, polyacetal Resin, polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, boribylene terephthalate resin, polyarylate resin, polyphenylene ether resin, polypheny Nsurufido resins, polysulfone resins, polyethersulfone resins, polyether ether ketone resin, and at least one member selected from the group consisting of such as polylactic acid resins as preferred. Especially, it is more preferable in it being at least 1 sort (s) chosen from the group which consists of polyolefin, polyamide, a polycarbonate, and polyester from the improvement effect of a physical property, and ease of use. The polyamide referred to here is preferably at least one selected from the group consisting of polyamide 6 resin, polyamide 11 resin, polyamide 12 resin, polyamide 46 resin, polyamide 66 resin, and polyamide 610 resin. The polyester referred to here is preferably at least one selected from the group consisting of polyethylene terephthalate resin, polyethylene naphthalate resin, and boribylene terephthalate resin.

It is important that the thin-walled molded product of the present invention has a reinforcing fiber volume content (Vf) defined by the following formula (4) of 5 to 80% with respect to the fiber-reinforced composite material to be formed.
Reinforcing fiber volume content (Vf) = 100 × reinforcing fiber volume / (reinforcing fiber volume + thermoplastic resin volume) (4)

  The reinforcing fiber volume content (Vf) indicates the composition of the reinforcing fiber and the thermoplastic resin contained in the fiber reinforced composite material, that is, the molded body constituted thereby. If the reinforcing fiber volume content is lower than 5%, the reinforcing effect may not be sufficiently exhibited. On the other hand, if it exceeds 80%, voids are likely to be generated in the fiber-reinforced composite material, and the physical properties of the thin molded article may be lowered. The reinforcing fiber volume content is more preferably 20 to 60%.

  As a specific method for calculating the above-mentioned reinforcing fiber volume content (Vf), the thermoplastic resin is removed from the sample of the thin molded article, and the masses of the reinforcing fiber and the thermoplastic resin are obtained. Can be obtained by converting the volume into the volume using the density of each component and applying these volume values to the above formula.

  As a method for removing the thermoplastic resin from the thin-walled molded product sample, when the reinforcing fiber is an inorganic fiber such as carbon fiber or glass fiber, a method using combustion (pyrolysis) removal can be used as a simple and preferable method. . In this case, the weight of the well-dried thin-walled molded body sample is weighed and then treated at 500 to 700 ° C. for 5 to 60 minutes using an electric furnace or the like to burn the thermoplastic resin component. The mass of each component can be calculated by weighing the reinforcing fibers remaining after the combustion in a dry atmosphere and then weighing them.

As a method for removing the thermoplastic resin from the thin molded body sample, a method in which the thermoplastic resin is decomposed or dissolved using a chemical substance that is easily decomposed or dissolved is also preferable. More specifically, the mass of a thin-walled molded product sample having an area of 1 cm ² to 10 cm ² may be weighed, and a dissolved component may be extracted using a chemical substance that dissolves or decomposes a thermoplastic resin. Thereafter, the residue can be weighed after washing and drying, and the mass of each component can be determined. For example, when the thermoplastic resin is polypropylene, the polypropylene can be dissolved by using heated toluene or xylene. When the thermoplastic resin is polyamide, the polyamide can be decomposed by heated formic acid. When the thermoplastic resin is polycarbonate, the polycarbonate can be dissolved by using heated chlorinated hydrocarbon.

  When the abundance of the reinforcing fiber and the thermoplastic resin contained in the fiber reinforced composite material constituting the thin molded article of the present invention is shown on a mass basis, it is preferably 50 to 1000 parts by mass, more preferably 100 parts by mass with respect to the reinforcing fiber. Is 50 to 500 parts by mass, and more preferably 60 to 300 parts by mass of the thermoplastic resin with respect to 100 parts by mass of the reinforcing fiber. If the ratio of the thermoplastic resin to 100 parts by mass of the reinforcing fibers is less than 50 parts by mass, voids are likely to be generated in the fiber-reinforced composite material, and the strength and rigidity may be lowered. On the contrary, if the ratio of the thermoplastic resin is more than 1000 parts by mass, the reinforcing effect of the reinforcing fiber may not be easily exhibited.

  The thin molded article of the present invention preferably has a smooth surface. The term “smooth surface” as used herein means that when the surface of the thin molded article is visually observed, a rough shape, wrinkles, irregularities, etc. are not confirmed, and the surface is flat and smooth.

Furthermore, the thin molded article of the present invention has a uniform thickness of 1.5 mm or less.
The thickness of the thin molded article of the present invention is preferably 0.1 mm or more and 1.5 mm or less, more preferably 0.3 mm or more and 1.5 mm or less, and further more preferably 0.4 mm or more and 1.2 mm or less. preferable.

As an example of the uniform thickness referred to here, the thickness of the thin molded article is measured at multiple points, and the arithmetic average value (hereinafter, unless otherwise noted, simply means “average value” means the arithmetic average value). When calculated, the thickness variation is within ± 10% from the average value, that is, the thickness variation (%) of each measurement point represented by the following formula (5) is minus 10 or more plus 10 or less, More preferably, it is from minus 5 to plus 5.
Variation in thickness (%) = 100 × (measured thickness−average thickness) / average thickness (5)

  Further, when another expression is given for the uniform thickness of the thin molded article of the present invention, the standard deviation calculated from the thickness of each part of the thin molded article measured as described above and the average value thereof is 0. Is preferably 0.1, more preferably 0 to 0.08, still more preferably 0 to 0.07, and most preferably 0 to 0.01. When the value of this standard deviation is 0, it is particularly preferable that the thickness is completely uniform in each part of the molded body.

The number of measurement points for the thickness of the thin molded product when confirming whether the molded product has a uniform thickness is naturally better, but in consideration of accuracy and measurement effort, the number of points is 5 or more and 100 or less. It is preferable to measure the thickness of the film, and it is more preferable to measure the thickness of 10 to 50 points.
As a matter of course, it is preferable to uniformly measure each part of the thin molded body for the part where the thickness of the molded body is measured.

The thin molded article of the present invention has the following formula (1)
Critical number of single yarns = 600 / D (1)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)
The reinforcing fiber bundle (A) composed of the number of critical single yarns or more defined in the above is characterized in that the ratio to the total amount of reinforcing fibers is 20 Vol% or more and 99 Vol% or less.
When the ratio of the reinforcing fiber bundle (A) to the total amount of the reinforcing fibers is less than 20 Vol%, there is an advantage that a thin molded article having excellent surface quality can be obtained, but it is difficult to obtain a thin molded article having excellent mechanical properties. When the ratio of the reinforcing fiber bundle (A) exceeds 99 Vol%, the entangled portion of the fibers becomes locally thick and it is difficult to obtain a thin-walled one. The proportion of the reinforcing fiber bundle (A) is preferably 30 Vol% or more and less than 90 Vol%, more preferably 30 Vol% or more and less than 80 Vol%.

  In addition, if another expression is made for the above-mentioned reinforcing fiber bundle (A), the thin-walled molded product of the present invention is 20% by volume or more and 99% by volume or less of the reinforcing fiber in the fiber-reinforced composite material constituting the above-mentioned formula. The reinforcing fiber bundle (A) composed of the number of critical single yarns or more defined in (1), and the remaining reinforcing fibers of 1 vol% or more and 80 vol% or less are composed of a single yarn state or less than the above critical single yarn number. The fiber bundles are dispersed in the thermoplastic resin.

Moreover, in the fiber reinforced composite material which comprises the thin molded object of this invention, the average fiber number (N) in the reinforced fiber bundle (A) comprised by more than a critical single yarn shall satisfy | fill following formula (2). Particularly, the surface is smooth and has a uniform thickness, which is preferable.
0.7 × 10 ⁴ / D ² <N <1 × 10 ⁵ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)

  Specifically, when the reinforcing fiber is a carbon fiber and the average fiber diameter of the carbon fiber is 5 to 7 μm, the critical single yarn number is 86 to 120, and when the average fiber diameter of the carbon fiber is 5 μm, the fiber The average number of fibers in the bundle is in the range of more than 280 and less than 4000, among which 600 to 2500 is preferable, and 600 to 1600 is more preferable. When the average fiber diameter of the carbon fibers is 7 μm, the average number of fibers in the fiber bundle is in the range of more than 142 and less than 2040, and in particular, it is preferably 300 to 1600. More preferably, the number is 300 to 800.

When the average number of fibers (N) in the reinforcing fiber bundle (A) is less than 0.7 × 10 ⁴ / D ² , it may be difficult to obtain a high fiber volume content (Vf). Further, when the average number of fibers (N) in the reinforcing fiber bundle (A) is 1 × 10 ⁵ / D ² or more, a locally thick portion is generated, which may cause a void. As average fiber number (N) in said reinforced fiber bundle (A), it is more preferable in following Formula (2 ') to satisfy | fill.
0.7 × 10 ⁴ / D ² <N <6 × 10 ⁴ / D ² ( ^{2 ′} )
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)

  In the thin molded article of the present invention, the larger value of the tensile elastic modulus in an arbitrary direction and a direction orthogonal thereto (hereinafter sometimes referred to as a 0 degree direction and a 90 degree direction, respectively) The ratio divided by the value (hereinafter sometimes abbreviated as Eδ) is preferably 1.0 to 1.3. Eδ is an index of isotropic property of the material. When Eδ is less than 2, it is considered isotropic, and when it is 1.3 or less, isotropic property is particularly excellent.

  By imparting such characteristics to the reinforcing fibers, the fluidity of the fiber-reinforced composite material in the softened and melted state is increased, the moldability is improved, and a thin molded article having excellent surface quality can be obtained. The shape of the thin molded body can be a wide range of shapes from a large-area panel body to a complex shape. Conventionally, it has been difficult to obtain a thin molded article made of a fiber reinforced thermoplastic resin having a long reinforcing fiber length and high physical properties. However, in the present invention, such a thin molded article can be easily obtained.

  As long as the object of the present invention is not impaired, the fiber reinforced composite material constituting the thin molded article of the present invention contains functional fillers and additives in addition to the reinforcing fibers and the thermoplastic resin. Also good. Examples of such fillers and additives include, but are not limited to, organic / inorganic fillers, flame retardants, UV-resistant agents, pigments, mold release agents, softeners, plasticizers, and surfactants. . Particularly in electronic / electric equipment applications and automotive applications, high flame retardancy may be required, so it is preferable to include a flame retardant in the thermoplastic resin. As an example of a flame retardant, a well-known thing can be used, and if it can give a flame retardance to the thermoplastic composition of this invention, it will not specifically limit. Specific examples include phosphorus flame retardants, nitrogen flame retardants, silicone compounds, organic alkali metal salts, organic alkaline earth metal salts, bromine flame retardants, etc. These flame retardants can be used alone. Alternatively, a plurality of them may be used in combination. The content of the flame retardant is preferably 1 to 40 parts by mass and more preferably 1 to 20 parts by mass with respect to 100 parts by mass of the thermoplastic resin from the balance of physical properties, moldability, and flame retardancy.

<Method for producing thin molded article>
The present invention is a random mat composed of a reinforcing fiber having an average fiber length of 5 mm or more and 100 mm or less and a thermoplastic resin, wherein the reinforcing fiber has a basis weight of 25 to 3000 g / m ² , and the following formula (1)
Critical number of single yarns = 600 / D (1)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)
With respect to the reinforcing fiber bundle (A) composed of the number of critical single yarns or more defined in (1), the ratio of the reinforcing fiber to the total amount of reinforcing fibers in the random mat is 20 Vol% or more and 99 Vol% or less, and the following step A-1) To A-3)
A-1) A random mat is heated and pressurized between the melting point and the decomposition temperature when the thermoplastic resin is crystalline, or the glass transition temperature to the decomposition temperature when amorphous, and the thermoplastic resin is put into the reinforcing fiber bundle. Step of impregnating to obtain a prepreg A-2) The prepreg obtained in the above A-1) is gold whose temperature is adjusted to below the melting point when the thermoplastic resin is crystalline, and below the glass transition temperature when the thermoplastic resin is amorphous. The following formula (3)
Charge rate (%) = 100 × base material area (mm ² ) / mold cavity projection area (mm ² ) (3)
(Here, the substrate area is the projected area in the extraction direction of all the arranged random mats or prepregs, and the mold cavity projected area is the projected area in the extraction direction.)
A-3) Step of placing the prepreg placed in the mold in the above A-2) and performing impregnation to molding in the step of molding, or the following Steps B-1) to B-4)
B-1) A random mat is represented by the following formula (3)
Charge rate (%) = 100 × base material area (mm ² ) / mold cavity projection area (mm ² ) (3)
(Here, the substrate area is the projected area in the extraction direction of all the arranged random mats or prepregs, and the mold cavity projected area is the projected area in the extraction direction.)
Step B-2) When the thermoplastic resin is crystalline, the melting point to the thermal decomposition temperature of the thermoplastic resin, the amorphous In this case, the temperature is raised from the glass transition temperature to the thermal decomposition temperature of the thermoplastic resin, and the pressure is impregnated (first pressing step).
B-3) A step of pressurizing so that the pressure in the final step is 1.2 to 100 times the pressure in the first press step (second press step).
B-4) When the thermoplastic resin is crystalline, it is impregnated to molded by a step of molding by adjusting the mold temperature below the melting point, and when amorphous, below the glass transition temperature. It is also related to the manufacturing method of the thin molded article.

The method of impregnation to molding including the above steps A-1) to A-3) is a so-called cold press method. The method of impregnating to forming including the above steps B-1) to B-4) is a so-called hot press method. Although both press moldings can be applied to the thin molded article of the present invention, the cold press method is more preferably used from the viewpoint of further shortening the molding time.
The above process can be performed continuously following the manufacturing process of the random mat, or may be performed individually after obtaining the random mat.

  Moreover, in this invention, it arrange | positions with a low charge with respect to a metal mold | die shape, A base material (random mat or prepreg) is made to flow by pressurizing. By setting the reinforcing fiber to the above-described opening degree, the fluidity of the fiber-reinforced composite material in the softened and melted state is increased and the moldability is improved. This effectively works not only on the molding size and shape but also on the appearance and thickness, has excellent surface quality, and can obtain a thin molded body having a complex shape from a thin and large panel shape. Conventionally, it has been difficult to obtain a thin molded article having a long reinforcing fiber length and made of a fiber reinforced thermoplastic resin having high physical properties. However, in the present invention, such a thin molded article can be obtained.

  Also, normally, when a fiber reinforced composite material is flowed, the reinforcing fibers tend to be oriented in the flow direction, and anisotropy may occur in the physical properties, but in the present invention, by using the random mat described above, In addition, a complicated shape can be obtained while maintaining the isotropy of the reinforcing fiber. The charge rate of the base material is preferably 5 to 100%, more preferably 20 to 95% in the formula (3). A more preferable base material charge rate is 50 to 90%.

  If the charge rate of the base material is lower than 5%, the base material is cooled in the process of flowing during molding, and a thin molded article having a desired thickness may not be obtained. On the contrary, when the charge rate of the base material exceeds 100%, the feature of the present invention that the material is made to flow to some extent is not realized. Further, if the charge rate of the base material exceeds 100%, not only the loss of the base material is increased, but also post-processing such as trimming is required, which is disadvantageous in terms of productivity and cost.

  In addition, there is almost no problem when forming a thin molded product with a panel shape or a relatively simple shape close to this, but a thin molded product with a complicated shape having branches, deep drawing, deep standing surfaces, rising parts, etc. In this case, wrinkles are generated around the branch intersection point and the angle of the surface, so that it becomes easy to form a thick and thin portion. Therefore, when placing a prepreg or a random mat as a base material in the mold cavity, more precisely, in the mold cavity in the steps A-2) and B-1), avoid the portion where the thickness tends to change as described above. When the base material is disposed, a thin molded body with a remarkably uniform thickness can be obtained, which is more preferable.

<< Random mat >>
The random mat used in the production method of the present invention is composed of a reinforcing fiber having an average fiber length of 5 mm or more and 100 mm or less and a thermoplastic resin, and the reinforcing fiber has a basis weight of 25 to 3000 g / m ^2. About the reinforcing fiber bundle (A) composed of the number of critical single yarns or more defined in 1), the ratio of the random mat to the total amount of fibers is 20 Vol% or more and 99 Vol% or less, and the average fiber in the reinforcing fiber bundle (A) The number (N) satisfies the formula (2). The details of the reinforcing fiber, the thermoplastic resin, and the reinforcing fiber bundle (A) in the random mat are as described above for the fiber-reinforced composite material constituting the thin-walled molded article, and are supplemented as follows.
In the plane of the random mat, the reinforcing fibers are not oriented in a specific direction and are dispersed in a random direction.

  The random mat used in the production method of the present invention is preferably an isotropic material. When a thin molded article is obtained from the random mat, the isotropy of the reinforcing fibers in the random mat is maintained even in the thin molded article. By obtaining a thin molded body from the random mat and obtaining the ratio (Eδ) of the larger value of the tensile modulus of elasticity in two directions perpendicular to each other to the smaller value (Eδ) of the thin molded body. It is possible to quantitatively evaluate the isotropic property of the thin molded article. Thin-walled molded products having an Eδ of less than 2 are considered isotropic, and thin-walled molded products having an Eδ of 1.3 or less are considered to be particularly excellent in isotropic properties.

  In the random mat used in the production method of the present invention, when the proportion of the reinforcing fiber bundle (A) with respect to the total amount of fibers of the random mat is less than 20 Vol%, there is an advantage that a thin molded article having excellent surface quality can be obtained. It becomes difficult to obtain a molded article having excellent mechanical properties. When the proportion of the reinforcing fiber bundle (A) exceeds 99 Vol%, the entangled portion of the fibers becomes locally thick, and it becomes difficult to obtain a thin molded body. The ratio of the reinforcing fiber bundle (A) in the random mat is preferably 30 Vol% or more and less than 90 Vol%, more preferably 30 Vol% or more and less than 80 Vol%.

As described for the reinforcing fiber composite material constituting the thin molded article of the present invention, the average number of fibers (N) in the reinforcing fiber bundle (A) also satisfies the formula (2) for the random mat. preferable. When a random mat having an average number of fibers (N) of less than 0.7 × 10 ⁴ / D ² is used, it is difficult to obtain a thin molded body having a high reinforcing fiber volume content (Vf). In addition, when a random mat having an average number of fibers (N) of 1 × 10 ⁵ / D ² or more is used, a locally thick portion is generated, which tends to cause voids. As average fiber number (N) in said reinforced fiber bundle (A), it is more preferable in following Formula (2 ') to satisfy | fill.
0.7 × 10 ⁴ / D ² <N <6 × 10 ⁴ / D ² ( ^{2 ′} )
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)

  Further, when impregnation to molding is performed using a random mat used in the production method of the present invention to obtain a thin molded body of 1.5 mm or less, preferably 1 mm or less, a fiber that is simply separated is used. If used, the density is large and good physical properties cannot be obtained. Further, when all the fibers are opened, it becomes easy to obtain a thinner one, but the fiber entanglement increases, and a fiber having a high fiber volume content cannot be obtained. The reinforcing fiber bundle (A) having a critical single yarn or more defined by the above formula (1) and the reinforcing fiber (B) having a single yarn state or less than the number of critical single yarns are simultaneously present in the molded body, thereby reducing the thickness. In addition, it is possible to realize a thin molded body having a high physical property expression rate. The production method of the present invention can provide molded articles having various thicknesses, but can obtain a thin molded article having a thickness of 1.5 mm or less, which is difficult to obtain by conventional molding methods. It is particularly suitable for obtaining a thin molded body having a thickness of about 1 mm.

  There is no restriction | limiting in particular in the thickness of the random mat used with the manufacturing method of this invention, The thing of 1-150 mm thickness can be obtained. In view of the effect of the present invention that a thin molded body can be obtained from the random mat of the present invention, the thickness is preferably 2 to 100 mm. In addition, the random mat may be used in the next step after the volume is reduced to an easy-to-use thickness using an appropriate pressurization or decompression device.

  The ratio of the reinforcing fibers and thermoplastic resin in the random mat can be determined from the ratio of the amount of each component charged at the time of manufacturing the random mat, but as described above for the thin molded article, the thermoplastic resin in the sample is burned and decomposed. It can also be measured by removing it by decomposition or dissolution with chemical substances. The procedure for obtaining the volume of each component by using the density of each component from the mass of each component and calculating the reinforcing fiber volume content (Vf) is also as described above for the thin molded article.

The random mat used in the production method of the present invention preferably has a reinforcing fiber volume content (Vf) defined by the following formula (4) of 5 to 80% with respect to the reinforcing fiber and thermoplastic resin contained therein.
Reinforcing fiber volume content (Vf) = 100 × reinforcing fiber volume / (reinforcing fiber volume + thermoplastic resin volume) (4)

  This reinforcing fiber volume content (Vf) indicates the composition of the reinforcing fibers and the thermoplastic resin contained in the random mat, as described above for the thin molded article. If the reinforcing fiber volume content is lower than 5%, the reinforcing effect may not be sufficiently exhibited. On the other hand, if it exceeds 80%, voids are likely to occur in the resulting molded article, and the physical properties of the thin molded article may be reduced. The reinforcing fiber volume content is more preferably 20 to 60%.

  When the abundance of the reinforcing fiber and the thermoplastic resin contained in the random mat used in the production method of the present invention is shown on a mass basis, it is preferably 50 to 1000 parts by mass, more preferably 50 to 100 parts by mass with respect to 100 parts by mass of the reinforcing fiber. It is 500 mass parts, More preferably, it is 60-300 mass parts of thermoplastic resins with respect to 100 mass parts of reinforced fiber. When the ratio of the thermoplastic resin to 100 parts by mass of the reinforcing fibers is less than 50 parts by mass, voids are likely to be generated in the obtained fiber-reinforced composite material, and the strength and rigidity may be lowered. On the contrary, if the ratio of the thermoplastic resin is more than 1000 parts by mass, the reinforcing effect of the reinforcing fiber may not be easily exhibited.

  The random mat used in the production method of the present invention contains a solid thermoplastic resin and serves as a preform for obtaining a thin molded article. In the random mat, the thermoplastic resin is preferably present in the form of fibers and / or particles. Since the reinforcing fiber and the fibrous and / or particulate thermoplastic resin are mixed and close to each other, it is not necessary to flow the fiber and the resin greatly in the mold of the impregnation step, and the thermoplastic resin can be easily impregnated. . Two or more types of thermoplastic resins can be used as long as they are compatible with each other, and fibrous and particulate materials may be used in combination.

  The fibrous thermoplastic resin preferably has a fineness of 100 to 5000 dtex, more preferably 1000 to 2000 dtex, an average fiber length of 0.5 to 50 mm, and an average fiber length of 1 to 10 mm. Is more preferable.

  The particulate thermoplastic resin is preferably spherical, strip-shaped, or cylindrical, such as pellets, and is preferably a strip-shaped product obtained by cutting the film into thin strips. Preferred examples of the spherical thermoplastic resin include a perfect circle or ellipse, or an egg shape. The preferable average particle diameter of the spherical thermoplastic resin is 0.01 to 1000 μm, the more preferable average particle diameter is 0.1 to 900 μm, and the more preferable average particle diameter is 1 to 800 μm. The particle size distribution is not particularly limited, but a sharp particle size distribution is more preferable for the purpose of obtaining a thinner thin molded article, and it is used as a particulate thermoplastic resin having a desired particle size distribution by an operation such as classification. I can do it.

  As the flaky thermoplastic resin, a cylindrical shape such as a pellet, a prismatic shape, and a flake shape are preferable. In this case, it may have a certain aspect ratio, but the preferred length is about the same as that of the above fibrous form.

About the method for manufacturing the above-mentioned random mat used in the present invention, in particular, an isotropic random mat, a manufacturing method including the following series of steps is exemplified as a preferable one.
Cut process: A process of cutting reinforcing fibers.
-Opening process: A process of opening a fiber bundle by introducing cut reinforcing fibers into a pipe and blowing air onto the fibers.
・ Sprinkling process: A spraying process in which the reinforced fibers that have been opened are sprayed together with a fibrous or powdery thermoplastic resin.
Each process will be described in more detail below.

-Cutting process The cutting method of the reinforcing fiber in said cutting process is a process of specifically cutting a reinforcing fiber using a knife. As the knife, a rotary cutter or the like is preferable.
In order to obtain a fiber bundle of a desired size, it is also preferable to use a fiber having a narrow strand width as a reinforcing fiber to be cut, or to cut the strand width in the longitudinal direction. In that case, it is also preferable to use a cutter having a blade parallel to the fiber direction to cut the fiber bundle in the longitudinal direction simultaneously with cutting to a specific fiber length.
As the rotary cutter, it is preferable to use a spiral knife or a splitting knife with a specified angle. In order to obtain a random mat for reinforcing a thermoplastic resin having excellent surface quality, the density of fibers is greatly affected. In the conventional rotary cutter, the fiber cut is discontinuous, and when it is introduced into the spraying process as it is, spots on the fiber basis weight are formed. For this reason, it is possible to apply with small density spots by continuously cutting the fibers using a knife with a specified angle without interrupting the fibers. The knife angle for continuously cutting the reinforcing fiber is geometrically calculated from the width of the reinforcing fiber to be used and the fiber length after cutting, and the relationship between them is the following formula (6) Is preferred.
Fiber length of reinforcing fiber (pitch of blade) = Reinforcing fiber strand width × tan (90−θ) (6)
(Here, θ is an angle formed by the circumferential direction and the arrangement direction of the knife.)

-Opening process The above-mentioned opening process is a process of opening a fiber bundle by introducing cut reinforcing fibers into a pipe and blowing air onto the fibers. The degree of opening can be appropriately controlled by air pressure or the like. The reinforcing fiber opening method in the production of the random mat of the present invention is characterized by blowing air onto the reinforcing fibers. In the opening step, the reinforcing fibers can be opened more completely by blowing air directly onto the fiber bundle at a wind speed of 5 to 500 m / sec, preferably from the compressed air blowing hole. Specifically, several holes with a diameter of about 1 mm are drilled in the tube through which the reinforcing fibers pass, pressure of about 0.2 to 0.8 MPa is applied from the outside, and compressed air is blown directly onto the fiber bundle to facilitate the fiber bundle. Can be opened.

-Application | coating process The said application | coating process is a process of spraying the opened reinforcing fiber with a fibrous or particulate thermoplastic resin. In the spreading step, an isotropic random mat can be obtained by spreading the opened reinforcing fibers and the fibrous or particulate thermoplastic resin on a flat surface such as a table or a sheet.
In the spraying step, the thermoplastic resin is preferably supplied in an amount of 50 to 1000 parts by weight with respect to 100 parts by weight of the reinforcing fiber. More preferably, it is 55 to 500 parts by weight of the thermoplastic resin with respect to 100 parts by weight of the reinforcing fiber, and more preferably 60 to 300 parts by weight of the thermoplastic resin with respect to 100 parts by weight of the reinforcing fiber.

In applying the reinforcing fiber, it is preferable to use a tapered pipe having a conical shape or the like. In a tube such as a cone, air diffuses and the flow velocity in the tube is reduced. At this time, a rotational force is applied to the reinforcing fibers. The reinforcing fibers opened using this venturi effect can be preferably diffused and dispersed.
According to the above preferred method for producing a random mat, there are few fibers whose major axes are oriented in the three-dimensional direction, and a random mat having a two-dimensional orientation can be obtained.

<< prepreg >>
In the present invention, when impregnation to molding is performed including the steps A-1) to A-3), the random mat is amorphous up to a temperature not lower than the melting point and lower than the thermal decomposition temperature when the thermoplastic resin is crystalline. In this case, by heating to a temperature not lower than the glass transition temperature and lower than the thermal decomposition temperature, a thermoplastic resin is impregnated to obtain a prepreg and used for molding. The form of the reinforcing fiber in the prepreg is kept in the random mat. That is, the reinforcing fibers in the prepreg maintain the fiber length, isotropy, and degree of opening in the random mat, and are the same as those described in the random mat.

In the prepreg, the step A-2) may be performed as it is without cooling, or the step of A-2) may be performed after the step of once impregnating and solidifying the thermoplastic resin. In the prepreg, the thermoplastic resin is infiltrated into the reinforcing fiber bundle and between the reinforcing fiber single yarns. As described above, the random mat is characterized in that the reinforcing fiber and the fibrous or particulate thermoplastic resin are mixed and exist in close proximity so that the thermoplastic resin can be easily impregnated. The prepreg is 1 to 10 times, preferably 1 to 5 times the thickness of the thin molded article to be obtained. The thickness is not limited, but preferably 0.1 mm
It is above, and an upper limit should just be arrange | positioned and shape | molded in a metal mold | die, and is substantially about 30 mm.

The prepreg used in the production method of the present invention preferably has a void ratio of 0 to 30%, more preferably 0 to 10%. The void ratio is more preferably 0 to 5%, and the most preferable void ratio is 0 to 3%. The void ratio of the prepreg is calculated by observing the cross section of the prepreg with an optical microscope and dividing the existing area of the void by the cross sectional area of the observation substrate. In the observation, n = 5 per prepreg, and the average value is defined as the void ratio.
The value obtained by subtracting the above void ratio from 100 is the degree of resin impregnation (%), which is a measure that the thermoplastic resin is impregnated between the reinforcing fiber bundles in the prepreg.

<< Production Method by Cold Press Method in Steps A-1) to A-3) >>
Hereinafter, the cold press method in which impregnation to molding is performed in steps A-1) to A-3) will be specifically described.
As described above, in the step A-1), the random mat is heated to a melting point or higher and lower than the decomposition temperature when the thermoplastic resin is crystalline, or to a glass transition temperature or higher and lower than the decomposition temperature when the thermoplastic resin is amorphous. The prepreg is obtained by applying pressure to impregnate the thermoplastic resin in the reinforcing fiber bundle and between the reinforcing fiber single yarns. The obtained prepreg is used for the next step A-2) while being kept at the temperature at the time of impregnation or after being allowed to cool and then reheated. The temperature of the prepreg can be measured by, for example, a measuring instrument in which a K-type thermocouple is attached to the prepreg surface and installed outside the heating furnace.

  In the next step A-2), the temperature of the prepreg obtained in A-1) is adjusted to below the melting point when the thermoplastic resin contained therein is crystalline, and below the glass transition temperature when amorphous. In the mold (more precisely, in the mold cavity), the charge rate represented by the above formula (3) is arranged to be 5% or more. In this case, one or 2 to 100 superimposed prepregs can be placed in the mold. When superposing, a part or the whole is superposed and used depending on the thin molded body to be obtained. Here, it is desirable that a part or all of the surface of the end portion of the prepreg is not in contact with the mold cavity edge portion. Moreover, when superimposing, all the prepregs do not need to be the same shape, What is necessary is just to superimpose one part or all part, respectively.

The charge rate when placing the prepreg in the mold is preferably 5 to 100%, more preferably 20 to 95% in the formula (3). A more preferable prepreg charge rate is 50 to 90%.
When placing the prepreg in the mold, if the charge rate is less than 5%, when the prepreg pressurized during molding flows in the mold, the mold tends to lose heat and before forming the desired shape There is a risk of solidifying.

  When placing the prepreg in the mold, if the charge rate exceeds 100%, a thin molded body filled with fibers up to the end of the mold can be obtained, but when molding a product with a complicated shape, the material There are cases in which it is difficult to obtain a thin molded body having a uniform thickness because the wall thickness changes with respect to the product design thickness due to the drawing or tensioning, and it is difficult to control. In addition, an unnecessary part remains at the end of the thin molded body, and trimming by machining or the like in post-processing is necessary, which not only complicates the process but also causes material loss. .

  As described above, in the step A-2), when the prepreg is arranged in the mold, the charge rate is set to 5% or more and 100% or less to secure a layer in which the reinforcing fibers are substantially in-plane two-dimensionally oriented. Thus, it is possible to manufacture a light-weight thin molded body with high productivity without generating material loss and labor of trimming.

  In this step A-2), the location of the prepreg is a mold, more precisely, a mold cavity, or a horizontal part (0 degree) or an inclined part whose angle to the horizontal part is 70 degrees or less. preferable. If the prepreg is placed on an inclined part with an angle of more than 70 degrees with the horizontal part of the mold, the standing surface of the mold contacts the prepreg when the mold is clamped during molding, and the position is shifted. There is a possibility that the prepreg may be drawn into the portion and normal molding cannot be performed.

  Further, in this step A-2), when the prepreg is arranged as a base material in the mold, more precisely in the mold cavity, the prepreg gathers at the time of molding and becomes thick or wrinkles occur. If the base material is disposed so as to avoid the branching portion of the thin molded body to be obtained and the surroundings where the surface angle changes, it is possible to obtain a thin molded body with a significantly uniform thickness, which is more preferable. .

  The thickness of the prepreg in the mold can be appropriately selected according to the thickness of the shape to be obtained. However, when the charging rate of the base material to the mold is 5% or more and 80% or less, the total thickness of the prepreg or the laminated thickness of the prepreg may be 1.0 mm or more in order to appropriately flow. preferable.

Note that the temperature of the above mold is from melting point −200 ° C. or higher and melting point −10 ° C. or lower when the thermoplastic resin is crystalline, and when amorphous, it is glass transition temperature −200 ° C. or higher and glass transition temperature −10 ° C. or lower. It is preferable that By doing so, the thin molded body obtained from the prepreg in step A-3) can be cooled to a temperature at which the shape is stabilized and taken out from the mold. Next, in step A-3), the above A-2 ) Pressurize and mold the prepreg placed in the mold. The pressure at this time is preferably 0.1 MPa to 100 MPa, more preferably 0.2 MPa to 40 MPa, and still more preferably 0.5 to 20 MPa. The time required to reach the target pressure is preferably 0.01 to 10 seconds.

  After reaching the target pressure, the prepreg is pressed for 5 to 200 seconds to be molded as described above. A more preferable pressurization time is 10 to 60 seconds. In the meantime, the prepreg is flowed to perform molding, and at the same time, it is cooled to a temperature at which the shape is stabilized by heat exchange with the mold. Thereafter, the mold is opened to obtain a thin molded body.

<< Production Method by Hot Press Method in Steps B-1) to B-4) >>
Hereinafter, the hot press method in which impregnation to molding is performed in steps B-1) to B-4) will be specifically described.
In step B-1), the random mat is placed in the mold so that the charge rate represented by the formula (3) is 5% or more. One or 2 to 100 stacked random mats can be placed in the mold. At this time, the random mat may be used after being heated and / or pressurized in advance to reduce the volume. When superposing, a part or the whole is superposed and used depending on the thin molded body to be obtained. Here, it is desirable that a part or all of the surface of the random mat end does not contact the mold cavity edge. In the case of overlapping, the random mats need not all have the same shape, and may be partially or entirely overlapped. The significance of the charge rate range and the problem when it is outside the range are the same as those described for the prepreg in step A-2) of the cold press method, and the charge when placing the random mat in the mold The rate is preferably 5 to 100%, more preferably 20 to 95% in the formula (3). A more preferable charge rate of the random mat is 50 to 90%.

  In this step B-1), the arrangement place of the random mat is a mold, more precisely, a horizontal part (0 degree) or an inclined part with an angle of 70 degrees or less with the horizontal part of the mold cavity. And preferred. The problem when the random mat is arranged in the inclined part where the angle formed by the horizontal part of the mold exceeds 70 degrees is as described for the prepreg in the step A-2) of the cold press method.

  In this step B-1), as described above with respect to the arrangement of the prepreg in the step A-2) of the cold press method, as shown in the patchwork arrangement of FIG. When a random mat is placed in the mold cavity as a base material, the random mat gathers during molding and becomes thick or wrinkles easily. It is very preferable to arrange the base material so as to avoid locations such as surroundings where the angle changes, because a thin molded body with a remarkably uniform thickness can be obtained.

In the next step B-2), when the thermoplastic resin contained in the random mat is crystalline, the glass transition of the thermoplastic resin from the melting point to the thermal decomposition temperature of the thermoplastic resin, and if amorphous, the glass transition of the thermoplastic resin This is a step (first pressing step) in which the temperature is raised from the temperature to the thermal decomposition temperature, and the pressure is impregnated.
The next step B-3) is a step (second press step) in which pressurization is performed so that the pressure in the final step is 1.2 to 100 times the pressure in the first press step.

  In the first pressing step, the random mat is pressurized to a predetermined target pressure, and is preferably held for 0.5 to 20 minutes. If the thermoplastic resin contained in the random mat is crystalline, the melting point of the thermoplastic resin or higher is used. Heat up to a temperature below the thermal decomposition temperature, or if it is amorphous, to a temperature above the glass transition temperature of the thermoplastic resin and below the thermal decomposition temperature, and put the thermoplastic resin in the reinforcing fiber bundle and between the reinforcing fiber single yarns Impregnate. Next, the time during which the process proceeds to the second pressing step can be appropriately selected depending on the performance of the molding machine, but is preferably 0.01 to 200 seconds in order to shorten the molding time.

The second pressing step is a step of performing single-stage or multi-stage pressurization, but it is preferably one stage for the purpose of simplifying the molding. The mold temperature in the second pressing step may be the same as the mold temperature in the first pressing step or may be raised to 1 ° C. or higher and lower than the thermal decomposition temperature. When the second pressing step is multistage, the temperature may be raised or cooled as the latter stage, and the temperature raising and cooling may be performed alternately.
The total pressing time in the second pressing step is not particularly limited, but is preferably 0.5 to 10 minutes from the viewpoint of shortening the molding time.

  Moreover, the target pressure of a 1st press process is 0.1MPa-10MPa, Preferably it is 0.2MPa-8MPa. The final target pressure in the second pressing step can be appropriately selected depending on the performance of the molding machine, but is preferably 0.2 to 100 MPa, more preferably 0.3 to 50 MPa, and more preferably 0.5 to 20 MPa. The final target pressure in the second pressing step is 1.2 to 100 times that in the first pressing step. That is, it is preferable that the molding pressure in B-2 to B-3 is 0.1 MPa to 100 MPa.

  In step B-4), the thermoplastic resin contained in the random mat is molded by adjusting the mold temperature below the melting point when the thermoplastic resin is crystalline, and below the glass transition temperature when amorphous. When the thermoplastic resin is crystalline, the temperature of the mold after the adjustment is melting point −200 ° C. or higher and melting point −10 ° C. or lower, and when amorphous, the glass transition temperature −200 ° C. or higher, glass transition temperature −10 ° C. The following is preferable. The time required for this step can be appropriately controlled depending on cooling conditions and the like, but is preferably 0.5 minutes to 20 minutes from the viewpoint of shortening the molding time. The method for adjusting the temperature of the mold is not particularly limited, and it may be appropriately cooled by a method of flowing a cooling medium through the temperature control circuit in the mold.

EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not limited to these.
Polyamide 66 (hereinafter, abbreviated as PA66, crystalline resin) used in the following reference examples has a melting point of 265 ° C. and a decomposition temperature (in the air) of 300 ° C., and polypropylene (hereinafter abbreviated as PP, crystalline resin). ) Has a melting point of 170 ° C., a decomposition temperature (in air) of 300 ° C., a polycarbonate (hereinafter abbreviated as PC, amorphous resin) has a glass transition point of 150 ° C., and a decomposition temperature (in air) of 420 ° C. . The above decomposition temperature is a measurement result by thermogravimetric analysis.
The thin molded bodies of the present example and comparative example are flat plates of 350 mm × 350 mm in length and width, and the design thickness is 0.4 mm in Example 1, 0.8 mm in Example 2 and Comparative Example 2, and Example 3 and Comparative Example 1 were 1.2 mm.

0) Analysis of volume content of reinforcing fiber and resin in random mat Mass ratio of reinforcing fiber and resin in random mat is the ratio of reinforcing fiber and resin supplied (mass basis) at the time of making random mat. The volume content of the reinforcing fiber and the resin was calculated using the density of each component based on the mass ratio. The reinforcing fiber volume content in the random mat is represented by Vf.

1) Analysis of reinforcing fiber bundle in random mat Cut out the random mat to about 100 mm x 100 mm.
From the cut-out mat, all the fiber bundles are taken out with tweezers, and the number (I) of bundles of reinforcing fiber bundles (A) and the length (Li) and mass (Wi) of reinforcing fiber bundles are measured and recorded. When the fiber bundle is so small that it cannot be taken out with tweezers, the mass is finally measured (Wk). For measuring the mass, a balance capable of measuring up to 1/100 mg (0.01 mg) is used.
The number of critical single yarns is calculated from the fiber diameter (D) of the reinforcing fibers used in the random mat, and is divided into a reinforcing fiber bundle (A) having a number of critical single yarns or more and the other. In addition, when two or more types of reinforcing fibers are used, it is divided for each type of fiber, and measurement and evaluation are performed for each.
The method for obtaining the average number of fibers (N) of the reinforcing fiber bundle (A) is as follows.
The number of fibers (Ni) in each reinforcing fiber bundle is obtained by the following equation from the fineness (F) of the reinforcing fibers used.
Ni = Wi / (Li × F)
The average number of fibers (N) in the reinforcing fiber bundle (A) is obtained from the number of bundles (I) of the reinforcing fiber bundle (A) by the following formula.
N = ΣNi / I
The ratio (VR) of the reinforcing fiber bundle (A) to the total amount of fibers of the mat can be obtained by the following equation using the density (ρ) of the reinforcing fibers.
VR = Σ (Wi / ρ) × 100 / ((Wk + ΣWi) / ρ)

2) Analysis of reinforcing fiber bundle in thin-walled molded body For reinforcing fiber bundle contained in thin-walled molded body, the resin was burned and removed in a furnace at 500 ° C. for 1 hour, and then measured in the same manner as in the above random mat method. did.

3) Analysis of average fiber length of reinforcing fibers contained in thin molded article The average fiber length of reinforcing fibers contained in the obtained thin molded article is about 500 ° C x 1 hour after removing the resin in the furnace. The length of 100 randomly extracted reinforcing fibers was measured and recorded with a caliper and loupe to the 1 mm unit, and from the lengths of all the reinforcing fibers measured (Li, where i = 1 to an integer of 1 to 100), The average fiber length (La) was determined by the following formula.
La = ΣLi / 100
In addition, it can measure by the method similar to the above also about the average fiber length of the reinforced fiber in a random mat.

4) Analysis of fiber and resin volume content in thin-walled molded body The thin-walled molded body was burned and removed from the resin in a furnace at 500 ° C. for 1 hour, and the weight of the sample before and after treatment was weighed. The mass of the resin component was calculated. Next, the volume content of the reinforcing fiber and the resin was calculated using the specific gravity of each component. Also regarding a thin molded object, the reinforcing fiber volume content to contain is represented by Vf.

5) Tensile test A test piece was cut out from the horizontal portion of the thin molded article using a water jet, and the tensile strength and tensile modulus were measured using a Tensilon universal testing machine manufactured by A & D with reference to JIS K 7164. The shape of the test piece was an A-type test piece. The distance between chucks was 115 mm, and the test speed was 2 mm / min. In addition, about the test piece, it cut out about the arbitrary direction (0 degree direction) of the horizontal part of a thin molded object, and the direction (90 degree direction) orthogonal to this, respectively, and measured the tensile strength and tensile elasticity modulus of both directions. . Further, for the tensile modulus, a ratio (Eδ) obtained by dividing the larger value by the smaller value was calculated.

6) Evaluation of surface smoothness For the purpose of evaluating the smoothness of the surface of the thin molded article, the surface of the thin molded article was evaluated by touching it with the naked eye, an optical microscope, and a hand. Good (symbol ○) when the resin is not sufficiently impregnated with resin (dry) and wrinkles in the reinforcing fiber, and the surface is smooth (symbol ○). Slightly dry parts and wrinkles are visible or rough. A case where the case was defective (symbol Δ), a lot of dry parts and wrinkles were observed, or the surface of the thin molded body was uneven was defined as a serious failure (×).

7) Evaluation of formability For the purpose of evaluating formability, shape observation was performed. Filled with fiber-reinforced composite material up to the end of the thin-walled molded product, good when no defect is seen (symbol ○), poor when part is missing or defective (symbol Δ), many missing or defective The case was regarded as a serious defect (×).

8) Evaluation of variation in thickness of thin molded body The thickness of the obtained thin molded body was measured at 10 locations from the whole thin molded body using a micrometer, and (arithmetic) average value and standard deviation were obtained.
Furthermore, among the measured values of the thickness at 10 locations of the thin molded body, the minimum value and the maximum value, and the average value of the above thickness, respectively, are defined by the following formulas (7) and (8), respectively. Value variation ”and“ maximum thickness variation ”were calculated, and it was confirmed whether the thickness variation of the thin molded body satisfied within ± 10% of the average value.
Variation in minimum thickness value (%) = 100 × (minimum value of thickness of horizontal part and standing surface−average value of thickness) / average value of thickness (7)
Variation in maximum thickness value (%) = 100 × (maximum value of horizontal part and standing surface thickness−average value of thickness) / average value of thickness (8)

9) Degree of resin impregnation in prepreg and molded body The degree of resin impregnation in prepreg and molded body was evaluated by measuring the void ratio in these and then subtracting this void ratio from 100 as the degree of resin impregnation (%). The void ratio of the prepreg and the molded body was calculated by observing the cross section of these test pieces with an optical microscope and dividing the existing area of the void by the cross sectional area of the test piece used for observation. In the observation, n = 5 per one sample, and the average value was taken as the void ratio of the sample.

[Reference Example 1]
Carbon fiber as a reinforcing fiber (manufactured by Toho Tenax Co., Ltd .: Tenax STS40-24KS (fiber diameter 7 μm, fiber width 10 mm)) is expanded to a width of 20 mm, cut to a fiber length of 10 mm, and the carbon fiber supply rate is 250 g / min. It introduced into the taper pipe | tube, and sprayed on the table installed in the lower part of the taper pipe | tube exit, spraying air on carbon fiber in a taper pipe | tube, and opening a fiber bundle partially.
In addition, as a matrix resin, PA66 fiber (Asahi Kasei Polyamide 66 fiber: T5 nylon, fineness 1400 dtex) dry-cut to 2 mm is supplied into the taper tube at 357 g / min and dispersed simultaneously with the carbon fiber to obtain an average fiber length. A random mat in which 10 mm carbon fiber and PA66 were mixed was obtained. This random mat had a reinforcing fiber (carbon fiber) volume content (Vf) of 30%, and the basis weight of the reinforcing fiber was 263 g / m ² .
When the average fiber length (La) and the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) of the obtained random mat were examined, the average fiber length (La) was defined as 10 mm and the formula (3). The number of critical single yarns was 86, and with respect to the reinforcing fiber bundle (A), the ratio of the mat to the total amount of fibers was 35%, and the average number of fibers (N) in the reinforcing fiber bundle (A) was 240. When the form of the reinforcing fiber in the random mat was observed, the fiber axis of the reinforcing fiber was almost parallel to the surface and was randomly distributed in the surface.

[Reference Example 2]
Carbon fiber (manufactured by Toho Tenax Co., Ltd .: Tenax IMS 60-12K (average fiber diameter 5 μm, fiber width 6 mm)) as a reinforcing fiber was cut into a length of 20 mm, and the carbon fiber supply rate was introduced into the tapered tube at 195 g / min. Then, air was blown onto the carbon fiber in the taper tube, and the fiber bundle was partially opened, and was then sprayed on a table installed at the lower part of the taper tube outlet.
Also, PP resin (polypropylene polymer polypropylene: Prime Polypro J108M) frozen and ground to an average particle diameter of about 1 mm is supplied as a matrix resin into the tapered tube at 404 g / min, and sprayed simultaneously with the carbon fiber to obtain an average fiber. A random mat in which 20 mm long carbon fiber and PP were mixed was obtained. This random mat had a reinforcing fiber (carbon fiber) volume content (Vf) of 20% and a basis weight of the reinforcing fiber of 169 g / m ² .
When the average fiber length (La) and the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) of the obtained random mat were examined, the average fiber length was 20 mm and the critical unit defined by the formula (3) was used. The number of yarns was 120. Regarding the reinforcing fiber bundle (A), the ratio of the mat to the total amount of fibers was 86%, and the average number of fibers (N) in the reinforcing fiber bundle (A) was 900. When the form of the reinforcing fiber in the random mat was observed, the fiber axis of the reinforcing fiber was almost parallel to the surface and was randomly distributed in the surface.

[Reference Example 3]
Glass fiber as a reinforcing fiber (Nippon Electric Glass Co., Ltd .: EX-2500 (average fiber diameter 15 μm, fiber width 9 mm) is cut into a length of 50 mm, and the supply amount of glass fiber is introduced into the tapered tube at 342 g / min. The air was blown onto the glass fiber in the taper tube, and the fiber bundle was partially opened while being spread on a table installed at the lower part of the taper tube outlet.
In addition, as a matrix resin, a PC resin (polycarbonate manufactured by Teijin Chemicals: Panlite L-1225L) frozen and pulverized to an average particle size of about 710 μm is supplied into the tapered tube at 656 g / min, and sprayed simultaneously with the glass fiber. A random mat in which glass fibers having an average fiber length of 50 mm and PC were mixed was obtained. This random mat had a reinforcing fiber (glass fiber) volume content (Vf) of 20% and a basis weight of the reinforcing fiber of 249 g / m ² .
When the average fiber length (La) and the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) of the obtained random mat were examined, the average fiber length (La) was defined by the formula (3) as 50 mm. The number of critical single yarns was 40, and with respect to the reinforcing fiber bundle (A), the ratio of the mat to the total amount of fibers was 68%, and the average number of fibers (N) in the reinforcing fiber bundle (A) was 60. When the form of the reinforcing fiber in the random mat was observed, the fiber axis of the reinforcing fiber was almost parallel to the surface and was randomly distributed in the surface.

[Reference Example 4]
Carbon fiber as a reinforcing fiber (manufactured by Toho Tenax Co., Ltd .: Tenax STS40-24KS (fiber diameter 7 μm, fiber width 10 mm)) is expanded to a width of 20 mm, cut to a fiber length of 10 mm, and the carbon fiber supply rate is 250 g / min. It introduced into the taper pipe | tube, and it sprayed on the table installed in the lower part of the taper pipe | tube exit, without blowing air on carbon fiber in a taper pipe | tube.
In addition, as a matrix resin, PA66 fiber (Asahi Kasei Fibers polyamide 66 fiber: T5 nylon, fineness 1400 dtex) dry-cut to 2 mm is fed into the tapered tube at 357 g / min, and dispersed simultaneously with carbon fiber, resulting in an average fiber length of 10 mm. A random mat in which the carbon fiber and PA66 were mixed was obtained. This random mat had a reinforcing fiber (carbon fiber) volume content (Vf) of 30%, and the basis weight of the reinforcing fiber was 263 g / m ² .
When the average fiber length (La) and the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) of the obtained random mat were examined, the average fiber length (La) was defined as 10 mm and the formula (3). The number of critical single yarns was 86, and with respect to the reinforcing fiber bundle (A), the ratio of the mat to the total amount of fibers was 100%, and the average number of fibers (N) in the reinforcing fiber bundle (A) was 24000.
As shown in Examples 1 to 3 and Comparative Examples 1 and 2 below, the random mats produced in Reference Examples 1 to 4 were impregnated and molded using a 500-ton hydraulic press machine manufactured by Kawasaki Oil Works.

[Example 1]
The random mat produced in Reference Example 1 was hot-pressed at 300 ° C. and 4 MPa for 5 minutes using a press machine made by Kawasaki Yoko Co., Ltd. in which a flat plate mold for impregnation was set, then cooled to 50 ° C., and impregnated with resin A prepreg having a degree of 99%, a thickness of 0.5 mm, a reinforcing fiber (carbon fiber) volume content of 30%, and a basis weight of the reinforcing fiber of 263 g / m ² was obtained.
Next, one obtained prepreg was heated to 300 ° C. using an IR oven made by NGK Kiln Tech, and the mold temperature was set to 120 ° C. 350 × 350 mm size flat plate mold, charge rate 60% Then, cold pressing was performed at a pressure of 10 MPa for 60 seconds to obtain a thin molded body having a length and width of 350 × 350 mm and a design thickness of 0.4 mm.
The resulting thin molded body was well filled with fiber reinforced composite material up to the end, and the moldability was good (◯). When the thickness of the thin molded article was measured at 10 points and the average thickness was calculated, the thickness variation was within ± 5% of the average thickness, indicating that the thin molded article had a very uniform thickness. It could be confirmed. Further, no wrinkles or the like were observed on the surface of the thin molded article, and the surface smoothness was good (◯). The reinforcing fiber (carbon fiber) volume content (Vf) of the thin molded article was 30%. As a result of examining the average fiber length (La) and the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) of the reinforcing fibers (carbon fibers) in the thin molded article, the average fiber length (La) was 10 mm, critical. The number of single yarns was 86, the proportion of the reinforcing fiber bundle (A) was 35%, and the average number of fibers (N) of the reinforcing fiber bundle (A) was 240. Table 1 shows the evaluation results of the thin molded article.

[Example 2]
The random mat produced in Reference Example 2 was hot-pressed at 220 ° C. and 3 MPa for 5 minutes using a Kawasaki Yoko press equipped with a flat plate mold for impregnation, cooled to 50 ° C., and impregnated with resin. A prepreg having a degree of 99%, a thickness of 0.5 mm, a reinforcing fiber (carbon fiber) volume content of 20%, and a basis weight of the reinforcing fiber of 169 g / m ² was obtained.
Next, the obtained two prepregs were heated to 220 ° C. using an IR oven made by NGK Kiln Tech, and then stacked, and a 350 × 350 mm molding flat plate mold having a mold temperature set to 120 ° C. Then, it was placed at a charge rate of 80% and cold pressed at a pressure of 10 MPa for 60 seconds to obtain a thin molded body having a length and width of 350 × 350 mm and a design thickness of 0.8 mm.
The resulting thin molded body was well filled with fiber reinforced composite material up to the end, and the moldability was good (◯). When the thickness of the thin molded article was measured at 10 points and the average thickness was calculated, the thickness variation was within ± 5% of the average thickness, indicating that the thin molded article had a very uniform thickness. It could be confirmed. Further, no wrinkles or the like were observed on the surface of the thin molded article, and the surface smoothness was good (◯). The reinforcing fiber (carbon fiber) volume content (Vf) of the thin-walled molded product was 20%. As a result of examining the average fiber length (La) and the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) of the reinforcing fibers (carbon fibers) in the thin molded article, the average fiber length (La) is 20 mm, critical. The number of single yarns was 120, the proportion of the reinforcing fiber bundle (A) was 86%, and the average number of fibers (N) of the reinforcing fiber bundle (A) was 900. Table 1 shows the evaluation results of the thin molded article.

[Example 3]
Three random mats produced in Reference Example 3 were stacked, set to a flat plate mold for molding of 350 × 350 mm size at a charge rate of 90%, and at 300 ° C. and 5 MPa using a Kawasaki Oil Works press. After pressurizing for 7 minutes (first pressing step), the pressure was gradually increased over 2 minutes, and pressing was performed at 10 MPa for 1 minute (second pressing step). Cooled to 50 ° C, resin impregnation degree 99%, reinforcing fiber (glass fiber) volume content 20%, reinforcing fiber basis weight 747g / m ² , thin and thick molded body 350x350mm length and design thickness 1.2mm Got.
The resulting thin molded body was well filled with fiber reinforced composite material up to the end, and the moldability was good (◯). When the thickness of the thin molded article was measured at 10 points and the average thickness was calculated, the thickness variation was within ± 5% of the average thickness, indicating that the thin molded article had a very uniform thickness. It could be confirmed. Further, no wrinkles or the like were observed on the surface of the thin molded article, and the surface smoothness was good (◯). The volume content (Vf) of reinforcing fibers (glass fibers) of the thin molded article was 20%. As a result of examining the average fiber length (La) and the ratio of the reinforcing fiber bundle (A) of the reinforcing fibers (glass fibers) in the thin molded article and the average number of fibers (N), the average fiber length (La) is 50 mm, The number of critical single yarns was 40, the proportion of reinforcing fiber bundles (A) was 68%, and the average number of fibers (N) of reinforcing fiber bundles (A) was 60.

[Comparative Example 1]
The random mat produced in Reference Example 4 was hot-pressed at 300 ° C. and 4 MPa for 5 minutes using a Kawasaki Yoko press machine in which a flat plate mold for impregnation was set in the same manner as in Example 1, and then 50 ° C. The prepreg having a resin impregnation degree of 99%, a thickness of 0.5 mm, a reinforcing fiber (carbon fiber) volume content of 30%, and a basis weight of the reinforcing fiber of 263 g / m ² was obtained.
Next, three prepregs obtained by heating to 300 ° C. using an IR oven made by NGK Kilntec were stacked in the same manner as in Example 1, and the mold temperature was set to 120 ° C. It was arranged in a flat plate mold for molding so as to have a charge rate of 80% and cold pressed at a pressure of 10 MPa for 60 seconds to obtain a thin molded body having a length and width of 350 × 350 mm and a design thickness of 1.2 mm.
The obtained thin molded article was not filled with the fiber reinforced composite material in a part of the end portion, and the moldability was poor (Δ). When the thickness of the thin molded body was measured at 10 points and the average value of the thickness was calculated, the thickness variation was barely within ± 10% of the average thickness value. Further, the surface of the thin molded article had a slight roughness and the surface smoothness was poor (Δ). The reinforcing fiber (carbon fiber) volume content (Vf) of the thin molded article was 30%. As a result of examining the average fiber length (La) and the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) of the reinforcing fibers (carbon fibers) in the thin molded article, the average fiber length (La) was 10 mm, critical. The number of single yarns was 86, the proportion of the reinforcing fiber bundle (A) was 100%, and the average number of fibers (N) of the reinforcing fiber bundle (A) was 24,000.

[Comparative Example 2]
Impregnation and molding were carried out in the same manner as in Comparative Example 1, except that the number of prepregs used in the cold pressing was changed from 3 to 2 and the design thickness of the thin molded body was changed to 0.8 mm.
The obtained thin molded article was not filled with a fiber reinforced composite material at the end, and the moldability was extremely poor (×). In addition, when the thickness of the thin molded article was measured at 10 points and the average value of the thickness was calculated, the thickness variation exceeded ± 10% of the average thickness, and in the thin molded article having a uniform thickness, There wasn't. Further, the surface of the molded product was rough, and the smoothness of the surface was seriously poor (×). The reinforcing fiber (carbon fiber) volume content (Vf) of the thin molded article was 30%. As a result of examining the average fiber length (La) and the ratio of the reinforcing fiber bundle (A) and the average number of fibers (N) of the reinforcing fibers (carbon fibers) in the thin molded article, the average fiber length (La) was 10 mm, critical. The number of single yarns was 86, the proportion of the reinforcing fiber bundle (A) was 100%, and the average number of fibers (N) of the reinforcing fiber bundle (A) was 24,000.
The thin molded bodies of Examples 1 to 3 had good moldability because the fiber-reinforced composite material flowed well at the time of molding, the surface smoothness was also good, and the thickness was uniform with a thin thickness of 1.5 mm or less. .

  The thin molded article of the present invention can be suitably used in various fields such as electrical / electronic equipment, automobiles, medical equipment, aircraft, building materials, and general industrial parts.

Claims (14)

A thin-walled molded article composed of a fiber-reinforced composite material comprising a reinforcing fiber having an average fiber length of 5 mm or more and 100 mm or less and a thermoplastic resin,
Reinforcing fiber volume content (Vf = 100 × volume of reinforcing fiber / (volume of reinforcing fiber + volume of thermoplastic resin)) is 5 to 80%,
Having a uniform thickness of 1.5 mm or less,
Following formula (1)
Critical number of single yarns = 600 / D (1)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)
A thin-walled molded product characterized in that the ratio of the reinforcing fiber bundle (A) constituted by the number of critical single yarns or more defined in (2) to the total amount of reinforcing fibers is 20 Vol% or more and 99 Vol% or less. The thin molded article according to claim 1, wherein the average number of fibers (N) in the reinforcing fiber bundle (A) satisfies the following formula (2).
0.7 × 10 ⁴ / D ² <N <1 × 10 ⁵ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)   The ratio (Eδ) obtained by dividing the larger value by the smaller value of the tensile elastic modulus in an arbitrary direction and a direction perpendicular thereto is 1.0 to 1.3. The thin-walled molded product according to crab.   The thin molded article according to any one of claims 1 to 3, wherein the thickness is 0.3 to 1.5 mm.   The thin molded article according to any one of claims 1 to 4, wherein the thickness variation is within ± 10% of the average value.   The thin-walled molded product according to any one of claims 1 to 5, wherein the reinforcing fiber is at least one selected from the group consisting of carbon fiber, glass fiber, and aramid fiber.   The thin molded article according to any one of claims 1 to 6, wherein the thermoplastic resin is at least one selected from the group consisting of polyolefin, polyamide, polycarbonate, and polyester. A random mat composed of a reinforcing fiber having an average fiber length of 5 mm or more and 100 mm or less and a thermoplastic resin, wherein the reinforcing fiber has a basis weight of 25 to 3000 g / m ² , and the following formula (1)
Critical number of single yarns = 600 / D (1)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)
With respect to the reinforcing fiber bundle (A) composed of the number of critical single yarns or more defined in (1), the ratio of the reinforcing fiber to the total amount of reinforcing fibers in the random mat is 20 Vol% or more and 99 Vol% or less, and the following step A-1) To A-3)
A-1) A random mat is heated and pressurized between the melting point and the decomposition temperature when the thermoplastic resin is crystalline, or the glass transition temperature to the decomposition temperature when amorphous, and the thermoplastic resin is put into the reinforcing fiber bundle. Step of impregnating to obtain a prepreg A-2) The prepreg obtained in the above A-1) is gold whose temperature is adjusted to below the melting point when the thermoplastic resin is crystalline, and below the glass transition temperature when the thermoplastic resin is amorphous. The following formula (3)
Charge rate (%) = 100 × base material area (mm ² ) / mold cavity projection area (mm ² ) (3)
(Here, the substrate area is the projected area in the extraction direction of all the arranged random mats or prepregs, and the mold cavity projected area is the projected area in the extraction direction.)
A-3) Step of placing the prepreg placed in the mold in the above A-2) and performing impregnation to molding in the step of molding, or the following Steps B-1) to B-4)
B-1) A random mat is represented by the following formula (3)
Charge rate (%) = 100 × base material area (mm ² ) / mold cavity projection area (mm ² ) (3)
(Here, the substrate area is the projected area in the extraction direction of all the arranged random mats or prepregs, and the mold cavity projected area is the projected area in the extraction direction.)
Step B-2) When the thermoplastic resin is crystalline, the melting point to the thermal decomposition temperature of the thermoplastic resin, the amorphous In this case, the temperature is raised from the glass transition temperature to the thermal decomposition temperature of the thermoplastic resin, and the pressure is impregnated (first pressing step).
B-3) A step of pressurizing so that the pressure in the final step is 1.2 to 100 times the pressure in the first press step (second press step).
B-4) When the thermoplastic resin is crystalline, it is impregnated to molded by a step of molding by adjusting the mold temperature below the melting point, and when amorphous, below the glass transition temperature. The manufacturing method of the thin molded object in any one of 1-7. The method for producing a thin molded article according to claim 8, wherein the average number of fibers (N) in the reinforcing fiber bundle (A) satisfies the following formula (2).
0.7 × 10 ⁴ / D ² <N <1 × 10 ⁵ / D ² (2)
(Here, D is the average fiber diameter (μm) of the reinforcing fibers)   The prepreg in A-2) or the random mat arrangement in B-1) is a horizontal part (0 degree) of the mold or an inclined part having an angle of 70 degrees or less with the horizontal part. 9. A method for producing a thin molded article according to 9.   The method for producing a thin molded article according to any one of claims 8 to 10, wherein a charge rate represented by the formula (3) is 5% to 100%.   The method for producing a thin molded article according to any one of claims 8 to 10, wherein a charge rate represented by the formula (3) is 50% to 90%.   The random mat having a reinforcing fiber volume content (Vf = 100 × volume of reinforcing fiber / (volume of reinforcing fiber + volume of thermoplastic resin)) of 5 to 80% is used according to any one of claims 8 to 12. A method for producing a thin molded article.   The manufacturing method of the thin molded object in any one of Claims 8-13 whose abundance of the thermoplastic resin in a random mat is 50-1000 weight part with respect to 100 weight part of reinforcement fibers.