JP2016141074A - Method for producing molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molded product excellent in bending characteristics.SOLUTION: A method for producing a molded product includes: a step of extrusion molding a composition containing a discontinuous carbon fiber and a thermoplastic resin to produce a prepreg; and a step of hot press molding the prepreg to produce a molded product. The discontinuous carbon fiber has a number average fiber diameter of 5 μm or more and 15 μm or less, the composition has a content of the discontinuous carbon fiber of 1 vol.% or more and 50 vol.% or less, and the prepreg has a ratio, in which an angle to the extrusion direction of the discontinuous carbon fiber is oriented in a range of 0° or more and 20°or less, of 70% or more.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a molded body, a molded body, and an article having the molded body.

  A prepreg containing discontinuous carbon fibers and a thermoplastic resin is more flexible than a prepreg containing continuous carbon fibers and a thermoplastic resin. It is possible to easily produce a molded body having the same.

  However, if the discontinuous carbon fibers are not sufficiently oriented, there is a problem that the mechanical properties become insufficient.

  Patent Document 1 discloses a method for producing a carbon fiber reinforced plastic in which discontinuous carbon fibers having an average fiber length of 10 mm or more are formed on a sheet-like substrate, and then the sheet-like substrate is impregnated with a matrix resin. At this time, the sheet-like base material is formed by carding so that the average value of the degree of orientation of the carbon fibers contained in the base material is in the range of 2 to 10.

WO2012 / 165076

  However, there is a problem that bending characteristics are insufficient.

  An object of one embodiment of the present invention is to provide a molded body having excellent bending characteristics in view of the problems of the above-described conventional technology.

  One embodiment of the present invention is a method for producing a molded body, in which a step of producing a prepreg by extruding a composition containing discontinuous carbon fibers and a thermoplastic resin, and hot press molding the prepreg to produce a molded body The discontinuous carbon fiber has a number average fiber diameter of 5 μm or more and 15 μm or less, and the composition has a content of the discontinuous carbon fiber of 1 vol% or more and 50 vol% or less, The prepreg has a ratio of 70% or more in which the angle with respect to the extrusion direction of the discontinuous carbon fibers is in the range of 0 ° to 20 °.

  According to one embodiment of the present invention, a molded article having excellent bending characteristics can be provided.

  Next, the form for implementing this invention is demonstrated.

  The method for producing a molded body includes a step of producing a prepreg by extruding a composition containing discontinuous carbon fibers and a thermoplastic resin, and a step of producing a molded body by subjecting the prepreg to hot press molding.

  The discontinuous carbon fiber can be produced by cutting the continuous carbon fiber using a guillotine cutter or the like.

  The carbon fiber may be a virgin fiber or a reuse / recycle fiber, or both may be used in combination.

  The carbon fiber may be any of fibers whose surface is coated with a sizing agent and whose surface is not coated with a sizing agent, or both may be used in combination.

  The sizing agent is not particularly limited as long as it can improve the adhesion between the thermoplastic resin and the carbon fiber.

  The number average fiber diameter of the discontinuous carbon fibers is 5 to 15 μm, and preferably 5 to 10 μm. When the number average fiber diameter of the discontinuous carbon fibers is less than 5 μm, the discontinuous carbon fibers are easily broken. On the other hand, when the number average fiber diameter of the discontinuous carbon fibers exceeds 10 μm, the flexibility of the discontinuous carbon fibers is lowered and the moldability of the composition and the prepreg is lowered.

  Content of the discontinuous carbon fiber in a composition is 1-50 volume%, and it is preferable that it is 16-40 volume%. When the content of the discontinuous carbon fibers in the composition is 1% by volume or less, the bending characteristics of the molded body are deteriorated. On the other hand, when the content of the discontinuous carbon fibers in the composition exceeds 50% by volume, the moldability of the composition and the prepreg deteriorates.

  The proportion of the discontinuous carbon fibers included in the prepreg that are oriented in the range of 0 to 20 ° with respect to the extrusion direction is 70% or more, and preferably 80% or more. If the proportion of the discontinuous carbon fibers contained in the prepreg is less than 70% of the angle with respect to the extrusion direction of the discontinuous carbon fibers is less than 70%, the bending properties of the molded article are deteriorated.

  The thermoplastic resin is not particularly limited, but polyamide, polypropylene, polyethylene, polystyrene, acrylic resin, polyethylene terephthalate, polyacetal, polyester, polycarbonate, polyolefin, polyphenylene sulfide, polybutylene terephthalate, polyphenylene ether, polyether ether ketone, polyamideimide , Polysulfone, ABS resin, fluororesin, and the like, and two or more of them may be used in combination.

  The composition may be produced by melt-kneading a composition containing carbon fibers and a thermoplastic resin.

  The carbon fiber used when producing the composition may be either a discontinuous carbon fiber or a continuous carbon fiber.

  Although it does not specifically limit as an extruder used when extruding a composition, A pressure extruder provided with the heating mechanism for softening a thermoplastic resin, a kneader, etc. are mentioned.

  The method for hot press molding the prepreg is not particularly limited, and examples thereof include a method in which the prepreg is laminated on a mold in a predetermined direction and then molded using a hot press machine.

  When the prepreg is laminated on the mold, it may be manual or a machine may be used.

  Note that the prepreg may be stretched before being laminated on the mold. Thereby, the residual amount of the space | gap in a molded object can be reduced.

  Next, a method for laminating the prepreg in a predetermined direction will be described.

  For example, if the prepregs are stacked so that the extrusion direction of the (n + 1) th layer prepreg is parallel to the extrusion direction of the nth layer prepreg, the bending characteristics against the force perpendicular to the extrusion direction of the prepreg can be obtained. Can be improved.

  Further, when the prepregs are laminated so that the angle between the extrusion direction of the (n + 1) -th layer prepreg and the extrusion direction of the n-th layer prepreg is 45 °, it is perpendicular to the extrusion direction of the n-th layer prepreg. The bending characteristic with respect to a special force can be improved.

  Further, when the prepregs are stacked so that the extrusion direction of the (n + 1) th layer prepreg is perpendicular to the extrusion direction of the nth prepreg, a force perpendicular to the extrusion direction of the nth prepreg is obtained. The bending characteristic with respect to can be improved.

  The angle between the number of prepregs stacked and the extrusion direction of the (n + 1) th prepreg and the extrusion direction of the nth prepreg are not particularly limited.

  The temperature at which the prepreg is subjected to hot press molding is usually 180 to 350 ° C.

  The pressure for hot press molding the prepreg is usually 0.5 to 4 MPa.

  The number average fiber length of the discontinuous carbon fibers contained in the molded body is 0.1 to 5 mm, and preferably 0.1 to 4 mm. When the number average fiber length of the discontinuous carbon fibers contained in the molded body is less than 0.1 mm, the degree of freedom of the discontinuous carbon fibers contained in the prepreg is increased, and the discontinuous carbon is formed when the prepreg is subjected to hot press molding. The fiber orientation is disturbed, and the bending properties of the molded body are deteriorated. On the other hand, when the number average fiber length of the discontinuous carbon fibers contained in the molded body exceeds 5 mm, the discontinuous carbon fibers are easily entangled and the moldability of the composition is lowered.

  The bending elastic modulus of the molded body is usually 15 to 30 GPa, preferably 18 to 30 GPa.

  The bending strength of the molded body is usually 250 to 340 MPa, preferably 280 to 340 MPa.

  The specific rigidity of the molded body is usually 1.0 to 2.3 Mm, and preferably 1.2 to 2.3 Mm.

  The ratio in which the angle of the discontinuous carbon fibers contained in the molded body with respect to the extrusion direction of the prepreg is oriented in the range of 0 to 20 ° is usually 70% or more, and preferably 80% or more. When the proportion of the discontinuous carbon fibers contained in the molded body is 70% or more of the ratio of the angle with respect to the extrusion direction of the prepreg in the range of 0 to 20 °, the bending characteristics of the molded body can be further improved. .

  The thickness of the molded body is usually 1 to 10 mm.

  The shape of the molded body may be a flat surface or a curved surface.

  Moreover, you may repeat high-order shaping | molding with respect to a molded object.

  Furthermore, you may heat-press-mold a prepreg with a reinforcing material.

  The molded body can be applied to transportation devices such as automobiles, electronic mobile devices, medical devices, assistance products, and the like.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples.

Example 1
Using a biaxial kneader, a composition comprising 20% by volume of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.) and 80% by volume of CM1017 (manufactured by Toray Industries, Inc.) as polyamide 6 is melt-kneaded to obtain a kneaded product. Obtained. At this time, the kneading temperature was 240 ° C., and the screw rotation speed was 15 rpm.

  Using a pressure extruder, the kneaded product was heated to 250 to 280 ° C., and the extrusion ratio was 28, and extrusion molding was performed to obtain a prepreg. In the prepreg, the degree of orientation of discontinuous carbon fibers was 94%.

  Two layers of prepreg are laminated on a 70 mm long and 90 mm wide mold so that the extrusion direction of the prepreg is in the horizontal direction of the mold, and then molded at 0.6 MPa and 235 ° C. for 20 minutes using a hot press machine. Thus, a molded body having a thickness of 4 mm was obtained. The molded body had an orientation degree of discontinuous carbon fibers of 87%, a flexural modulus of 21 GPa, a flexural strength of 286 MPa, and a specific rigidity of 1.5 Mm.

(Comparative Example 1)
Using a biaxial kneader, a composition comprising 20% by volume of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.) and 80% by volume of CM1017 (manufactured by Toray Industries, Inc.) as polyamide 6 is melt-kneaded to obtain a kneaded product. Obtained. At this time, the kneading temperature was 240 ° C., and the screw rotation speed was 15 rpm.

  After the kneaded material was filled in a metal mold having a length of 70 mm and a width of 90 mm, it was molded at 0.6 MPa and 235 ° C. for 20 minutes using a hot press machine to obtain a molded body having a thickness of 3 mm. The number average fiber length of the discontinuous carbon fibers was 0.8 mm, the degree of orientation of the discontinuous carbon fibers was 38%, the flexural modulus was 11 GPa, the flexural strength was 154 MPa, and the specific rigidity was 0.9 Mm.

(Comparative Example 2)
Using a uniaxial kneader, CM1017 (manufactured by Toray Industries, Inc.) as polyamide 6 was melt-kneaded twice to obtain a kneaded product. At this time, the kneading temperature was 240 ° C., and the screw rotation speed was 25 rpm.

  After the kneaded material was filled in a 70 mm long and 90 mm wide mold, it was molded at 1.2 MPa and 235 ° C. for 20 minutes using a hot press machine to obtain a molded body. The molded body had a flexural modulus of 4 GPa, a flexural strength of 123 MPa, and a specific rigidity of 0.3 Mm.

(Example 2)
Instead of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.), chopped carbon fiber T008-003 (manufactured by Toray Industries, Inc.) having a surface with a number average fiber length of 3 mm and a number average fiber diameter of 7 μm coated with a sizing agent is used. A molded body having a thickness of 4 mm was obtained in the same manner as in Example 1 except that it was used. In the prepreg, the degree of orientation of discontinuous carbon fibers was 85%. The molded body had an orientation degree of discontinuous carbon fibers of 80%, a flexural modulus of 18 GPa, a flexural strength of 291 MPa, and a specific rigidity of 1.4 Mm.

(Comparative Example 3)
Instead of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.), chopped carbon fiber T008-003 (manufactured by Toray Industries, Inc.) having a surface with a number average fiber length of 3 mm and a number average fiber diameter of 7 μm coated with a sizing agent is used. A molded body having a thickness of 3 mm was obtained in the same manner as in Comparative Example 1 except that it was used. The number average fiber length of the discontinuous carbon fiber was 1.1 mm, the degree of orientation of the discontinuous carbon fiber was 33%, the flexural modulus was 11 GPa, the bending strength was 113 MPa, and the specific rigidity was 0.9 Mm.

(Example 3)
Example 1 except that chopped carbon fiber T010-006 (manufactured by Toray Industries, Inc.) having a number average fiber length of 6 mm and a number average fiber diameter of 7 μm was used instead of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.) Similarly, a molded body having a thickness of 4 mm was obtained. In the prepreg, the degree of orientation of the discontinuous carbon fibers was 91%. The number average fiber length of the discontinuous carbon fibers was 1.9 mm, the degree of orientation of the discontinuous carbon fibers was 86%, the flexural modulus was 23 GPa, the flexural strength was 351 MPa, and the specific rigidity was 1.8 Mm.

(Comparative Example 4)
Comparative Example 1 except that chopped carbon fiber T010-006 (manufactured by Toray Industries, Inc.) having a number average fiber length of 6 mm and a number average fiber diameter of 7 μm was used instead of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.) Similarly, a molded body having a thickness of 3 mm was obtained. The number average fiber length of the discontinuous carbon fibers was 2.1 mm, the degree of orientation of the discontinuous carbon fibers was 35%, the bending elastic modulus was 12 GPa, the bending strength was 120 MPa, and the specific rigidity was 0.8 Mm.

Example 4
Instead of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.), chopped carbon fiber T008-006 (manufactured by Toray Industries, Inc.) having a surface with a number average fiber length of 6 mm and a number average fiber diameter of 7 μm coated with a sizing agent is used. A molded body having a thickness of 4 mm was obtained in the same manner as in Example 1 except that it was used. In the prepreg, the degree of orientation of the discontinuous carbon fibers was 91%. The molded body had an orientation degree of discontinuous carbon fibers of 83%, a flexural modulus of 26 GPa, a flexural strength of 336 MPa, and a specific rigidity of 2.0 Mm.

(Comparative Example 5)
Instead of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.), chopped carbon fiber T008-006 (manufactured by Toray Industries, Inc.) having a surface with a number average fiber length of 6 mm and a number average fiber diameter of 7 μm coated with a sizing agent is used. A molded body having a thickness of 3 mm was obtained in the same manner as in Comparative Example 1 except that it was used. The number average fiber length of the discontinuous carbon fiber was 2.3 mm, the degree of orientation of the discontinuous carbon fiber was 27%, the flexural modulus was 10 GPa, the flexural strength was 112 MPa, and the specific rigidity was 0.9 Mm.

(Example 5)
Example 1 except that chopped carbon fiber T010-012 (manufactured by Toray Industries, Inc.) having a number average fiber length of 12 mm and a number average fiber diameter of 7 μm was used instead of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.) Similarly, a molded body having a thickness of 4 mm was obtained. In the prepreg, the degree of orientation of discontinuous carbon fibers was 93%. The molded body had a discontinuous carbon fiber number average fiber length of 3.4 mm, discontinuous carbon fiber orientation of 89%, flexural modulus of 23 GPa, flexural strength of 314 MPa, and specific rigidity of 1.8 Mm.

(Comparative Example 6)
Comparative Example 1 except that chopped carbon fiber T010-012 (manufactured by Toray Industries, Inc.) having a number average fiber length of 12 mm and a number average fiber diameter of 7 μm was used instead of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.) Similarly, a molded body having a thickness of 4 mm was obtained. The number average fiber length of the discontinuous carbon fibers was 5.5 mm, the degree of orientation of the discontinuous carbon fibers was 49%, the flexural modulus was 10 GPa, the flexural strength was 101 MPa, and the specific rigidity was 0.8 Mm.

(Example 6)
Instead of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.), chopped carbon fiber CS-2516 (manufactured by Formosa Plastic) having a number average fiber length of 48 mm and a number average fiber diameter of 9 μm coated with a sizing agent A molded body having a thickness of 2 mm was obtained in the same manner as in Example 1 except that was used. In the prepreg, the degree of orientation of the discontinuous carbon fibers was 91%. The number average fiber length of the discontinuous carbon fibers was 1.2 mm, the degree of orientation of the discontinuous carbon fibers was 80%, the flexural modulus was 24 GPa, the flexural strength was 297 MPa, and the specific rigidity was 1.8 Mm.

(Comparative Example 7)
Instead of chopped carbon fiber T010-003 (manufactured by Toray Industries, Inc.), chopped carbon fiber CS-2516 (manufactured by Formosa Plastic) having a number average fiber length of 48 mm and a number average fiber diameter of 9 μm coated with a sizing agent A molded body having a thickness of 3 mm was obtained in the same manner as in Comparative Example 1 except that was used. The number average fiber length of the discontinuous carbon fiber was 1.9 mm, the degree of orientation of the discontinuous carbon fiber was 31%, the flexural modulus was 13 GPa, the flexural strength was 156 MPa, and the specific rigidity was 1.0 Mm.

  Table 1 shows the manufacturing conditions of the molded body.

  Next, the number average fiber length and orientation degree of the discontinuous carbon fibers in the molded body, and the bending characteristics of the molded body were evaluated.

<Number average fiber length of chopped carbon fiber>
Chopped carbon fiber was placed on a glass slide. Next, after the chopped carbon fiber was unwound with tweezers, the chopped carbon fiber was photographed with a scale, the length of the chopped carbon fiber was manually measured, and the number average fiber length was obtained.

<Number average fiber diameter of chopped carbon fiber>
The cross section of the chopped carbon fiber was photographed using a scanning electron microscope, the fiber diameter was manually measured, and the number average fiber diameter was obtained.

<Number average fiber length of discontinuous carbon fibers contained in the molded body>
The molded body was immersed in formic acid to dissolve polyamide 6, and the remaining polyamide 6 was washed away with formic acid while filtering. Next, discontinuous carbon fibers were extracted by washing out formic acid with distilled water. The number average fiber length of the discontinuous carbon fibers was determined in the same manner as the chopped carbon fibers except that the extracted discontinuous carbon fibers were placed on a slide glass.

<Orientation degree of discontinuous carbon fiber in prepreg>
Using an optical microscope, the surface of the prepreg was two-dimensionally photographed at a magnification of 15 times, and then the direction of 250 discontinuous carbon fibers was measured at an angle of −90 ° to + 90 ° with an extrusion direction of 0 °. did. Next, after convolving the angle of −90 ° to 0 ° to 0 ° to 90 ° and creating a histogram in the range of 0 to 90 ° with an interval of 10 °, the orientation that is oriented in the range of 0 to 20 ° is obtained. The ratio of continuous carbon fibers was calculated and used as the degree of orientation of discontinuous carbon fibers.

<Orientation degree of discontinuous carbon fiber in molded body>
Using an optical microscope, the magnification was set to 15 times, and the surface of the molded body was photographed two-dimensionally. Then, the direction of 125 discontinuous carbon fibers per side, a total of 250 discontinuous carbon fibers, the prepreg extrusion direction as 0 °, − Measurements were made at an angle of 90 ° to + 90 °. Next, the angle of −90 ° to 0 ° is convolved with 0 ° to 90 °, a histogram in the range of 0 ° to 90 ° with 10 ° intervals is created, and then the orientation that is oriented in the range of 0 to 20 ° is obtained. The ratio of continuous carbon fibers was calculated and used as the degree of orientation of discontinuous carbon fibers.

<Bending characteristics of molded body>
In accordance with JIS K 7171, after placing the molded body so that the extrusion direction of the molded body is perpendicular to the indenter, a three-point bending test is performed to measure the flexural modulus, bending strength and specific rigidity. did.

  Table 2 shows the evaluation results of the number average fiber length and orientation degree of the discontinuous carbon fibers in the molded body and the bending characteristics of the molded body.

  From Table 2, it turns out that the molded object of Examples 1-6 is excellent in a bending characteristic.

  On the other hand, since the molded objects of Comparative Examples 1 and 3 to 7 produced kneaded materials instead of producing prepregs, the degree of orientation of the discontinuous carbon fibers was lowered, and the bending characteristics were lowered.

Since the molded body of Comparative Example 2 does not include discontinuous carbon fibers, the bending characteristics are deteriorated.

Claims (5)

A step of extruding a composition containing discontinuous carbon fibers and a thermoplastic resin to produce a prepreg;
Having a step of heat-pressing the prepreg to produce a molded body,
The discontinuous carbon fiber has a number average fiber diameter of 5 μm or more and 15 μm or less,
In the composition, the content of the discontinuous carbon fibers is 1% by volume or more and 50% by volume or less,
The prepreg has a ratio in which the angle with respect to the extrusion direction of the discontinuous carbon fibers is in the range of 0 ° to 20 ° is 70% or more. A molded body manufactured by the method for manufacturing a molded body according to claim 1,
The discontinuous carbon fiber contained in the molded body has a number average fiber length of 0.1 mm to 5 mm. The flexural modulus is 15 GPa or more and 30 GPa or less,
The bending strength is 250 MPa or more and 340 MPa or less,
The molded product according to claim 2, wherein the specific rigidity is 1.0 Mm or more and 2.3 Mm or less.   The discontinuous carbon fiber contained in the molded body has a ratio of 70% or more in which the angle with respect to the extrusion direction is oriented in a range of 0 ° or more and 20 ° or less. The molded body described. An article comprising the molded body according to any one of claims 2 to 4.