JP7658196B2 - Fiber-reinforced thermoplastic resin laminate and method for producing same - Google Patents

Description

The present invention relates to a fiber-reinforced thermoplastic resin laminate and its manufacturing method.

Molded articles made of fiber-reinforced thermoplastic resin, which is a composite of thermoplastic resin and reinforcing fibers such as carbon fiber, are lightweight and have high mechanical properties, and are used in a variety of fields, including automobiles and building materials. Molded articles made of such fiber-reinforced thermoplastic resin are often manufactured by injection molding, since fiber-reinforced thermoplastic resin has excellent moldability.

For example, JP 2013-133378 A (Patent Document 1) describes a molded article containing carbon fibers with a mass average fiber length of 0.4 to 10 mm, which is obtained by injection molding a carbon fiber reinforced thermoplastic resin containing 10 to 70 mass% of carbon fibers with a mass average fiber length of 1 to 10 mm, in which the carbon fibers are two-dimensionally randomly oriented in the thermoplastic resin and have a length of 3 mm to 30 mm, a width of 1 mm to 10 mm, and a thickness of 0.5 mm to 10 mm. However, because the carbon fibers in this molded article are randomly dispersed, the mechanical properties (especially bending properties) are not necessarily sufficient in applications where a large impact is applied.

On the other hand, JP 2016-98271 A (Patent Document 2) describes a prepreg in which the discontinuous fibers are sufficiently oriented in the thermoplastic resin, the prepreg being obtained by extrusion molding a composition containing discontinuous fibers having a number average fiber length of 1 μm to 5 mm and a number average fiber diameter of 5 nm to 30 μm and a thermoplastic resin under conditions in which the pressure gradient with respect to the stroke is 0 Pa/mm to 1.0 Pa/mm in the plastic region. However, in this prepreg, the discontinuous fibers are oriented in one direction near the surface, but are randomly dispersed in the center, so that the mechanical properties (particularly the bending properties) are not necessarily sufficient in applications where a large impact is applied.

In addition, Japanese Patent Application Laid-Open No. 2000-108236 (Patent Document 3) describes a fiber-reinforced thermoplastic resin laminate in which reinforcing fibers are oriented, which is obtained by alternately laminating fiber-reinforced thermoplastic resin layers and thermoplastic resin layers reinforced with reinforcing fibers and press-molding them under pressure. Furthermore, Japanese Patent Application Laid-Open No. 2016-180037 (Patent Document 4) describes a molded body obtained by thermoforming a carbon fiber-reinforced thermoplastic resin composite material having a layer containing carbon fibers and thermoplastic resin with an average fiber length of 5 to 50 mm oriented in one direction and a layer containing continuous carbon fibers and thermoplastic resin oriented in one direction. However, in these laminates and molded bodies, since a large number of extremely thin layers are laminated and thermoformed, even if heat and pressure are applied uniformly over the entire surface, deflection and height differences occur in each layer, which tends to cause variations in the fiber orientation, and in particular, the degree of fiber orientation in the center of the laminates and molded bodies was not sufficiently high. For this reason, in applications where a large impact is applied, the mechanical properties (especially bending properties) were not necessarily sufficient. Furthermore, compared to laminates manufactured by injection molding, these laminates and molded bodies were inferior in terms of cost, formability, reworkability, mass production (short molding cycle), adaptability to complex shapes, etc. Furthermore, to manufacture laminates and molded bodies with a thickness of more than 2 mm, it is necessary to stack and thermoform an extremely large number of layers, which not only complicates the manufacturing process but also tends to make it more difficult to uniformly orient the fibers, even when uniform press molding is performed.

JP 2013-133378 A JP 2016-98271 A JP 2000-108236 A JP 2016-180037 A

The present invention was made in consideration of the problems with the above-mentioned conventional technology, and aims to provide a molded body made of a fiber-reinforced thermoplastic resin that has excellent mechanical properties (particularly, flexural modulus and flexural strength) and a method for manufacturing the same.

As a result of intensive research conducted by the inventors to achieve the above object, they discovered that when a fiber-reinforced thermoplastic resin, which is a composite of a thermoplastic resin and reinforcing fibers, is injection molded, an injection molded body having a thickness of 2 mm or less has high mechanical properties (particularly, flexural modulus and flexural strength), whereas a single-layer injection molded body having a thickness of more than 2 mm has reduced mechanical properties (particularly, flexural modulus and flexural strength). Furthermore, the inventors discovered that even if injection molded bodies having a thickness of 2 mm or less are stacked or bonded with an adhesive, the mechanical properties (particularly, flexural modulus and flexural strength) of the resulting laminated molded body are not improved.

As a result of further intensive research, the inventors discovered that a laminated molded product with excellent mechanical properties (particularly flexural modulus and flexural strength) can be obtained by injection molding a fiber-reinforced thermoplastic resin on top of an injection molded product with a thickness of 2 mm or less, which is made of a fiber-reinforced thermoplastic resin that is a composite of a thermoplastic resin and reinforcing fibers, and laminating the injection molded product with a thickness of 2 mm or less, thereby completing the present invention.

That is, the fiber-reinforced thermoplastic resin laminated molded body of the present invention contains polyamide and fibers having a number average fiber length of 0.05 to 20 mm, and the fiber content is 1 to 70 mass%. It is a laminated molded body in which two or more layers consisting of injection molded bodies having a thickness of 0.5 to 2 mm are laminated, and the laminated molded body is formed by injection molding or injection press molding of the upper injection molded body on the surface of the lower injection molded body, and the orientation degree of the fibers in the direction parallel to the surface direction of the laminated molded body is 0.75 or more for the entire laminated molded body, and at least a part of the surface of each layer is directly fused to each other.

In the fiber-reinforced thermoplastic resin laminate of the present invention, it is preferable that the thickness of the entire laminate is 2.0 mm or more. It is also preferable that the ratio of the surface of each layer that is directly fused to the adjacent layer is 10% or more. Furthermore, it is preferable that the fibers are carbon fibers.

The method for producing a fiber-reinforced thermoplastic resin laminated molded body of the present invention is characterized in that a lower layer molded body containing a thermoplastic resin and fibers with a number average fiber length of 0.05 to 20 mm, the fiber content being 1 to 70 mass%, and the thickness being 0.5 to 2 mm is injection molded or injection press molded, and then an upper layer molded body containing the thermoplastic resin and the fibers, the fiber content being 1 to 70 mass%, and the thickness being 0.5 to 2 mm is injection molded or injection press molded on the surface of the lower layer molded body, thereby obtaining a laminated molded body in which the layers made of the molded bodies are directly fused to each other at least in part of the layer surface.

In the manufacturing method of the fiber-reinforced thermoplastic resin laminate of the present invention, it is preferable to heat the lower layer molded body so that the surface temperature is 30 to 280°C while injection molding or injection press molding the upper layer molded body, and it is more preferable to preheat the lower layer molded body so that the surface temperature is 5 to 100°C higher than the glass transition temperature (Tg) of the thermoplastic resin (Tg + 5°C to Tg + 100°C), and then injection molding or injection press molding the upper layer molded body.

Although the reason why the present invention provides a fiber-reinforced thermoplastic resin laminate having excellent mechanical properties (particularly, flexural modulus and flexural strength) is not entirely clear, the present inventors speculate as follows. That is, the fiber-reinforced thermoplastic resin laminate of the present invention is obtained by injection molding a fiber-reinforced thermoplastic resin on an injection molded body having a thickness of 2 mm or less made of a fiber-reinforced thermoplastic resin, and laminating the injection molded body having a thickness of 2 mm or less. When the fiber-reinforced thermoplastic resin is injection molded to a thickness of 2 mm or less, the flow path of the fiber-reinforced thermoplastic resin is narrow, so that the fibers tend to be aligned in a certain direction. In the obtained injection molded body, as shown in FIG. 1, the fibers 2 in the thermoplastic resin 1 are highly oriented in a direction parallel to the surface direction of the molded body throughout the entire body from the surface to the center, and it is speculated that high mechanical properties (particularly, flexural modulus and flexural strength) are obtained. In the fiber-reinforced thermoplastic resin laminate of the present invention, such injection molded bodies are laminated by injection molding, and each layer made of the injection molded body is directly fused to at least a portion of its surface. It is therefore presumed that the laminated body as a whole has high mechanical properties (especially flexural modulus and flexural strength).

On the other hand, in a single-layer molded body having a thickness of more than 2 mm produced by injection molding a fiber-reinforced thermoplastic resin, the flow path of the fiber-reinforced thermoplastic resin is wide, so that the orientation of the fibers varies. As shown in Figure 2, in the thermoplastic resin 1, the fibers 2 are oriented in a direction parallel to the surface direction of the molded body near the surface of the molded body, but are randomly oriented in the center, which is presumably responsible for the deterioration of the mechanical properties (especially the flexural modulus and flexural strength).

In addition, when injection molded bodies made of fiber-reinforced thermoplastic resin and having a thickness of 2 mm or less are stacked on top of each other, the layers of the injection molded bodies are not directly fused together, so it is believed that each layer behaves as if it were an independent molded body, and the mechanical properties (especially the flexural modulus and flexural strength) do not improve.

Furthermore, when an injection molded body made of fiber-reinforced thermoplastic resin and having a thickness of 2 mm or less is bonded using an adhesive, an interface is generated between the layer made of the injection molded body and the adhesive layer, and it is presumed that the mechanical properties (particularly the flexural modulus and flexural strength) do not improve.

The present invention makes it possible to obtain molded articles made of fiber-reinforced thermoplastic resins that have excellent mechanical properties (particularly flexural modulus and flexural strength).

FIG. 2 is a schematic diagram showing the internal structure of the fiber-reinforced thermoplastic resin laminate of the present invention. FIG. 1 is a schematic diagram showing the internal structure of a conventional single-layer molded body made of fiber-reinforced thermoplastic resin. FIG. 2 is a schematic diagram showing a manufacturing process of a fiber-reinforced thermoplastic resin laminate produced in an example.

The present invention will be described in detail below with reference to preferred embodiments.

[Fiber-reinforced thermoplastic resin laminate]
First, the fiber-reinforced thermoplastic resin laminated molded body of the present invention will be described. The fiber-reinforced thermoplastic resin laminated molded body of the present invention (hereinafter also simply referred to as "laminated molded body") contains a thermoplastic resin and fibers having an average fiber length of 0.05 to 20 mm, and the fiber content is 1 to 70 mass%. It is a laminated molded body in which two or more layers made of injection molded bodies having a thickness of 0.5 to 2 mm are laminated, and the orientation degree of the fibers in the direction parallel to the surface direction of the laminated molded body is 0.75 or more for the entire laminated molded body, and at least a part of the surface of each layer is directly fused to each other.

The thermoplastic resin used in the present invention is not particularly limited, and examples thereof include polyamide, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polystyrene, styrene-butadiene resin, acrylonitrile-styrene resin, acrylonitrile-butadiene-styrene resin, acrylic resin, methacrylic resin, polyolefin such as polyethylene and polypropylene, polyester such as polyacetal, polycarbonate, polyethylene terephthalate and polybutylene terephthalate, polyarylate, polyphenylene ether, polyphenylene sulfide, polysulfone, polyether sulfone, polyether ether ketone, polylactic acid, etc. These thermoplastic resins may be used alone or in combination of two or more. Among these thermoplastic resins, polyamide and polypropylene are preferable.

The fibers used in the present invention are not particularly limited as long as they are reinforcing fibers used in fiber-reinforced thermoplastic resins, and examples thereof include inorganic fibers such as carbon fiber, glass fiber, alumina fiber, silicon carbide fiber, boron nitride fiber, and metal fiber; natural fibers such as pulp, lignin, hemicellulose, cellulose, and cellulose nanofiber; and organic fibers such as aramid fiber and vinylon fiber. These fibers may be used alone or in combination of two or more types. Recycled fibers and reused fibers may also be used. Among these fibers, carbon fiber, glass fiber, pulp, and cellulose nanofiber are preferred.

The number average fiber length of the fibers used in the present invention must be 0.05 to 20 mm, preferably 0.10 to 20 mm, more preferably 0.15 to 15 mm, even more preferably 0.20 to 10 mm, particularly preferably 0.25 to 5 mm, and most preferably 0.3 to 4 mm. If the number average fiber length of the fibers is less than the lower limit, the aspect ratio decreases and the fibers are randomly oriented, and the mechanical properties (particularly the flexural modulus and flexural strength) of the resulting laminated molded product tend not to be sufficiently improved. On the other hand, if the number average fiber length exceeds the upper limit, the variation in mechanical properties due to fiber aggregation and curved orientation increases, and the reliability of the mechanical properties of the resulting laminated molded product tends to decrease.

The injection molded body constituting each layer of the laminate molded body of the present invention contains such a thermoplastic resin and fiber. In such an injection molded body, the fiber content must be 1 to 70 mass%, preferably 2 to 65 mass%, more preferably 3 to 60 mass%, and even more preferably 5 to 50 mass%. If the fiber content is below the lower limit, the mechanical properties (particularly the flexural modulus and flexural strength) of the obtained laminate molded body tend not to be sufficiently improved. On the other hand, an injection molded body with a fiber content exceeding the upper limit may have a decreased flowability of the fiber-reinforced thermoplastic resin due to an increase in viscosity, which may decrease the injection moldability.

The thickness of the injection molded body must be 0.5 to 2 mm, preferably 0.6 to 1.9 mm, more preferably 0.7 to 1.8 mm, and even more preferably 0.8 to 1.7 mm. Injection molded bodies with a thickness less than the lower limit may experience a decrease in the fluidity of the fiber-reinforced thermoplastic resin upon cooling and solidification, resulting in a decrease in injection moldability. On the other hand, if the thickness of the injection molded body exceeds the upper limit, the degree of fiber orientation in the resulting laminated molded body decreases, and the mechanical properties (particularly the flexural modulus and flexural strength) tend not to be sufficiently improved.

In the laminated molded product of the present invention, the number of layers made of the injection molded product is not particularly limited as long as it is two or more layers, and may be three or more layers, but from the viewpoint of productivity (shortening the total molding time), it is preferable that it is two layers.

The total thickness of the laminated molded product of the present invention is not particularly limited, but is preferably 1.1 mm or more, more preferably 1.2 mm or more, even more preferably 1.5 mm or more, even more preferably 2.0 mm or more, particularly preferably 2.5 mm or more, and most preferably 3.0 mm or more. In particular, if the total thickness of the molded product exceeds 2.0 mm, it is difficult to obtain a single-layer injection molded product with excellent mechanical properties (particularly flexural modulus and flexural strength), and it is necessary to laminate the injection molded products by injection molding.

In the laminated molded product of the present invention, the degree of fiber orientation in the direction parallel to the surface direction of the laminated molded product must be 0.75 or more for the entire laminated molded product, preferably 0.76 or more, more preferably 0.77 or more, and even more preferably 0.78 or more. If the degree of fiber orientation is below the lower limit, the mechanical properties (particularly the flexural modulus and flexural strength) of the resulting laminated molded product tend not to be sufficiently improved.

The degree of fiber orientation can be determined by the following method. In other words, five measurement areas (2 mm long x 2 mm wide) are randomly extracted and cut out from the laminated molded body, and these are used as test pieces. A three-dimensional image of each test piece is obtained using a three-dimensional measurement X-ray CT device. The obtained three-dimensional images are subjected to fiber orientation analysis using CT data analysis software, and the fiber orientation tensor and its maximum eigenvalue in each test piece are calculated. Here, the maximum eigenvalue of the fiber orientation tensor can be used as a measure of the strength of fiber orientation. Therefore, in the present invention, this is taken as the degree of fiber orientation, and the degree of fiber orientation in the direction parallel to the surface direction is determined in each of the five measurement areas (test pieces), and the average value is taken as the degree of fiber orientation in the direction parallel to the surface direction in the laminated molded body. The upper limit of the degree of fiber orientation is 1.0, which means that all fibers are oriented in a direction parallel to the surface direction of the laminated molded body.

In addition, in the laminated molded product of the present invention, it is necessary that each layer made of the injection molded product is directly fused to each other at least in a portion of its surface, and in each layer, the proportion of the layer surface that is directly fused to the adjacent layer is preferably 10% or more, more preferably 30% or more, even more preferably 50% or more, particularly preferably 90% or more, and most preferably 95% or more. If the proportion of the layer surface that is directly fused to the adjacent layer is less than the lower limit, the mechanical properties (particularly the flexural modulus and flexural strength) of the laminated molded product as a whole tend not to be sufficiently improved.

[Method for producing fiber-reinforced thermoplastic resin laminate]
Next, the manufacturing method of the fiber-reinforced thermoplastic resin laminated molded body of the present invention will be described. The manufacturing method of the fiber-reinforced thermoplastic resin laminated molded body of the present invention contains a thermoplastic resin and fibers having a number average fiber length of 0.05 to 20 mm, the fiber content is 1 to 70 mass%, and the thickness is 0.5 to 2 mm. After injection molding or injection press molding of a lower layer molded body having a thermoplastic resin and fibers having a number average fiber length of 0.05 to 20 mm, the fiber content is 1 to 70 mass%, and the thickness is 0.5 to 2 mm, the upper layer molded body is injection molded or injection press molded on the surface of the lower layer molded body, and the layers made of the molded body are directly fused to each other at least in a part of the layer surface. In addition, in the manufacturing method of the fiber-reinforced thermoplastic resin laminated molded body of the present invention, it is also possible to manufacture a laminated molded body in which three or more layers made of the molded body are laminated by repeating such injection molding or injection press molding.

In the manufacturing method of the fiber-reinforced thermoplastic resin laminate of the present invention, first, a lower layer molded body containing the thermoplastic resin and the fibers, having a fiber content of 1 to 70% by mass, and having a thickness of 0.5 to 2 mm is produced by injection molding or injection press molding (preferably injection molding). Specifically, the fiber-reinforced thermoplastic resin containing the thermoplastic resin and the fibers and having a fiber content of 1 to 70% by mass is injection molded or injection press molded (preferably injection molding) so that the thickness of the resulting lower layer molded body is 0.5 to 2 mm, thereby producing the lower layer molded body.

There are no particular limitations on the fiber-reinforced thermoplastic resin, so long as it contains the thermoplastic resin and the fibers in a specified ratio. It may be a commercially available fiber-reinforced thermoplastic resin, or it may be prepared by mixing the thermoplastic resin and the fibers in a specified ratio immediately before molding.

There are no particular limitations on the mold used during molding, but a mold having multiple molds for molded bodies that can perform injection molding and preheating as necessary is preferred. By using such a mold, it is possible to simultaneously perform injection molding of multiple molded bodies and preheating as necessary in one molding cycle. In addition, by using a mold that allows the thickness of the molded bodies to be changed, such as a mold that employs a core-back system, it is possible to create an upper layer molded body without removing the lower layer molded body from the mold by changing the set thickness of the mold after creating the lower layer molded body.

The melting temperature of the resin during molding can be set appropriately depending on the resin used, but is preferably 150 to 450°C. The mold temperature can also be set appropriately depending on the resin used, but is preferably 30 to 280°C, more preferably 40 to 200°C, and even more preferably 50 to 150°C.

Next, an upper layer molded body containing the thermoplastic resin and the fibers, having a fiber content of 1 to 70% by mass, and having a thickness of 0.5 to 2 mm is produced on the surface of the lower layer molded body produced in this manner by injection molding or injection press molding (preferably injection molding). Specifically, the fiber-reinforced thermoplastic resin containing the thermoplastic resin and the fibers and having a fiber content of 1 to 70% by mass is injection molded or injection press molded (preferably injection molding) on the surface of the lower layer molded body so that the thickness of the upper layer molded body obtained is 0.5 to 2 mm, thereby producing the upper layer molded body. In this way, by producing an upper layer molded body on the surface of the lower layer molded body by injection molding or injection press molding, the layers made of molded bodies can be directly fused to each other at least in part of the layer surfaces, and a laminated molded body with excellent mechanical properties (particularly, bending modulus and bending strength) can be obtained.

The melting temperature of the resin during molding can be set appropriately depending on the resin used, but is preferably 150 to 450°C. The mold temperature can also be set appropriately depending on the resin used, but is preferably 30 to 280°C, more preferably 40 to 200°C, and even more preferably 50 to 150°C.

The surface temperature of the lower layer molded body when preparing the upper layer molded body is not particularly limited, but is preferably 30 to 280°C, more preferably 40 to 200°C, and even more preferably 50 to 150°C. If the surface temperature of the lower layer molded body is below the lower limit, the layers of the molded body will not be sufficiently fused together, and the mechanical properties (particularly the flexural modulus and flexural strength) of the laminated molded body as a whole will tend not to be sufficiently improved. On the other hand, if the surface temperature exceeds the upper limit, the lower layer molded body will be thermally deformed and the fiber orientation will be disturbed, so that the mechanical properties (particularly the flexural modulus and flexural strength) of the resulting laminated molded body will tend not to be sufficiently improved.

In addition, in the manufacturing method of the fiber-reinforced thermoplastic resin laminate of the present invention, it is preferable to preheat the lower layer molded body at a temperature below the melting point or softening point of the thermoplastic resin, and then injection mold or injection press mold the upper layer molded body. This allows the layers of molded bodies to be directly fused to each other at least in part of their layer surfaces, and a laminated molded body with excellent mechanical properties (particularly flexural modulus and flexural strength) can be obtained.

Specifically, the preheating temperature is preferably a temperature at which the surface temperature of the lower laminate is 5 to 100°C higher than the glass transition temperature (Tg) of the thermoplastic resin (Tg + 5°C to Tg + 100°C), more preferably a temperature at which the surface temperature is 10 to 60°C higher than the Tg (Tg + 10°C to Tg + 60°C), even more preferably a temperature at which the surface temperature is 15 to 50°C higher than the Tg (Tg + 15°C to Tg + 50°C), and particularly preferably a temperature at which the surface temperature is 20 to 45°C higher than the Tg (Tg + 20°C to Tg + 45°C). If the preheating temperature is below the lower limit, the layers of the molded body will not be sufficiently fused together, and the mechanical properties (particularly the flexural modulus and flexural strength) of the laminated molded body as a whole will tend not to be sufficiently improved. On the other hand, if the preheating temperature exceeds the upper limit, the lower molded body will be thermally deformed and the fiber orientation will be disturbed, so the mechanical properties (particularly the flexural modulus and flexural strength) of the resulting laminated molded body will tend not to be sufficiently improved.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
First, a carbon fiber reinforced polyamide 6 having a carbon fiber (CF) content of 30 mass% ("long fiber CF reinforced 6 nylon Torayca TLP1060" manufactured by Toray Industries, Inc.) was mixed with polyamide 6 ("Amilan CM1001" manufactured by Toray Industries, Inc.) to prepare a carbon fiber reinforced polyamide 6 having a CF content of 10 mass%.

Next, using this carbon fiber reinforced polyamide 6, injection molding was performed under conditions of a melting temperature of 280°C and a mold temperature of 80°C, and a lower layer molded body 3 with a multipurpose test piece shape and a thickness of 2 mm was produced as shown in Figure 3 (A). The obtained lower layer molded body 3 was inserted into a mold, and while heating the surface temperature of this lower layer molded body 3 to 50°C, as shown in Figure (B), the carbon fiber reinforced polyamide 6 (CF content: 10 mass%) was injection molded on the surface of the lower layer molded body 3 under conditions of a melting temperature of 280°C, and an upper layer molded body 4 with a thickness of 2 mm was laminated, and as shown in Figure (C), a laminated molded body (total length: 170 mm, length of parallel part: 80 mm, width of end: 20 mm, width of central parallel part: 10 mm, thickness: 4 mm) with a multipurpose test piece shape in which the lower layer molded body 3 and the upper layer molded body 4 are directly fused was produced.

Example 2
Carbon fiber reinforced polyamide 6 with a CF content of 20 mass% was prepared by mixing polyamide 6 with a CF content of 30 mass% (long fiber CF reinforced 6 nylon Torayca TLP1060 manufactured by Toray Industries, Inc.) and polyamide 6 with a CF content of 20 mass% (Amilan CM1001 manufactured by Toray Industries, Inc.).

A laminated molded body (thickness: 4 mm) in the shape of a multipurpose test piece was produced in the same manner as in Example 1, except that this carbon fiber reinforced polyamide 6 (CF content: 20% by mass) was used instead of the carbon fiber reinforced polyamide 6 with a CF content of 10% by mass, in which the lower layer molded body 3 (thickness: 2 mm) and the upper layer molded body 4 (thickness: 2 mm) were directly fused together. A laminated molded body was produced.

Example 3
A multipurpose test piece-shaped laminated molded body (thickness: 4 mm) in which the lower layer molded body 3 (thickness: 2 mm) and the upper layer molded body 4 (thickness: 2 mm) were directly fused to each other was produced in the same manner as in Example 1, except that a carbon fiber reinforced polyamide 6 having a CF content of 30 mass% ("long fiber CF reinforced 6 nylon Torayca TLP1060" manufactured by Toray Industries, Inc.) was used as is without mixing it with polyamide 6 instead of the carbon fiber reinforced polyamide 6 having a CF content of 10 mass%.

Example 4
A multipurpose test piece-shaped laminated molded body (thickness: 4 mm) in which the lower layer molded body 3 (thickness: 2 mm) and the upper layer molded body 4 (thickness: 2 mm) were directly fused to each other was produced in the same manner as in Example 3, except that the lower layer molded body was inserted into a mold and preheated so that the surface temperature of the lower layer molded body was 80°C. The carbon fiber reinforced polyamide 6 (CF content: 30% by mass) was then injection molded onto the surface of the lower layer molded body at a melting temperature of 280°C.

(Comparative Example 1)
Carbon fiber reinforced polyamide 6 (CF content: 10% by mass) prepared in the same manner as in Example 1 was injection molded under conditions of a melt temperature of 280°C and a mold temperature of 80°C to produce a single-layer molded body in the shape of a multipurpose test specimen (total length: 170 mm, parallel portion length: 80 mm, end width: 20 mm, central parallel portion width: 10 mm, thickness: 4 mm).

(Comparative Example 2)
Carbon fiber reinforced polyamide 6 (CF content: 20% by mass) prepared in the same manner as in Example 2 was injection molded under conditions of a melt temperature of 280°C and a mold temperature of 80°C to produce a single-layer molded body in the shape of a multipurpose test specimen (total length: 170 mm, parallel portion length: 80 mm, end width: 20 mm, central parallel portion width: 10 mm, thickness: 4 mm).

(Comparative Example 3)
Carbon fiber reinforced polyamide 6 with a CF content of 30 mass% ("long fiber CF reinforced 6 nylon Torayca TLP1060" manufactured by Toray Industries, Inc.) was injection molded at a melt temperature of 280°C and a mold temperature of 80°C to produce a single-layer molded body in the shape of a multipurpose test specimen (total length: 170 mm, length of parallel portion: 80 mm, width of end portion: 20 mm, width of central parallel portion: 10 mm, thickness: 4 mm).

(Comparative Example 4)
Using carbon fiber reinforced polyamide 6 with a CF content of 30% by mass ("long fiber CF reinforced 6 nylon Torayca TLP1060" manufactured by Toray Industries, Inc.), injection molding was performed under conditions of a melt temperature of 280° C. and a mold temperature of 80° C. to produce two molded bodies in the shape of a multipurpose test piece with a thickness of 2 mm. These two molded bodies were stacked together to produce a laminated molded body in the shape of a multipurpose test piece (total length: 170 mm, length of parallel part: 80 mm, width of end part: 20 mm, width of central parallel part: 10 mm, thickness: 4 mm).

(Comparative Example 5)
Two molded bodies having a multipurpose test piece shape and a thickness of 2 mm were prepared in the same manner as in Comparative Example 4. The two molded bodies were bonded together using an adhesive ("SuperX" manufactured by Cemedine Co., Ltd.) to prepare a laminated molded body having a multipurpose test piece shape (total length: 170 mm, length of parallel portion: 80 mm, width of end portion: 20 mm, width of central parallel portion: 10 mm, thickness: 4 mm).

<Number average fiber length of fibers>
A test piece (10 mm long x 10 mm wide x 4 mm thick) was cut out from the parallel part of the multipurpose test piece-shaped laminate and heated at 500°C under air flow to remove the resin part by incineration. The remaining fibers were photographed and the fiber lengths of 6,000 randomly selected fibers were measured using image analysis software to determine the number average value, which was used as the number average fiber length of the fibers. The results are shown in Table 1.

<Degree of fiber orientation in laminated molded body>
From the obtained laminated molded body, five randomly extracted measurement areas (2 mm long x 2 mm wide) were cut out, and these were used as test pieces (2 mm long x 2 mm wide x 4 mm thick). A three-dimensional measurement X-ray CT device (Yamato Scientific Co., Ltd. "TDM1000H-II") was used to obtain three-dimensional images of each test piece. For the obtained three-dimensional images, fiber orientation analysis was performed using CT data analysis software (Volume Graphics Co., Ltd. "VGSTUDIO MAX") to calculate the fiber orientation tensor and its maximum eigenvalue in each test piece. The maximum eigenvalue of the fiber orientation tensor can be used as a measure of the strength of fiber orientation, and in the present invention, this was taken as the degree of fiber orientation. The degree of fiber orientation in the direction parallel to the surface direction was determined in each of the five measurement areas (test pieces), and the average value was taken as the degree of fiber orientation in the direction parallel to the surface direction in the laminated molded body. The results are shown in Table 1.

<Proportion of fused area>
The layers of the obtained laminated molded body were peeled away from each other, and the peeled surface was observed using a digital microscope ("VHX-7000" manufactured by Keyence Corporation). The fused regions were identified based on the difference in brightness of the peeled surface, and the proportion of the fused regions in the entire peeled surface was calculated. The results are shown in Table 1.

<Flexural modulus and flexural strength>
The obtained laminate was subjected to a three-point bending test at a test speed of 2 mm/min, a support distance of 64 mm, and a temperature of 23° C. to measure the flexural modulus and flexural strength. The results are shown in Table 1.

As shown in Table 1, it was found that by injection molding a lower layer molded body of a specific thickness containing thermoplastic resin and carbon fiber, and then injection molding an upper layer molded body of a specific thickness containing thermoplastic resin and carbon fiber on top of this lower layer molded body, it is possible to obtain a laminated molded body with a high degree of carbon fiber orientation in the planar direction and excellent mechanical properties (especially bending properties) (Examples 1 to 4).

In addition, it was found that when the lower layer molded body was preheated to a specified temperature and then the upper layer molded body was injection molded (Example 4), the mechanical properties (especially the bending properties) were improved compared to when the lower layer molded body was not preheated to the specified temperature (Example 3).

On the other hand, it was found that the single-layer injection molded products containing thermoplastic resin and carbon fiber (Comparative Examples 1 to 3) had a lower degree of carbon fiber orientation in the planar direction and were inferior in mechanical properties (especially bending properties) compared to the laminated molded products obtained in Examples 1 to 3.

In addition, when injection molded bodies of a specific thickness containing thermoplastic resin and carbon fiber were stacked (Comparative Example 4) or bonded with an adhesive (Comparative Example 5), a laminated molded body with a high degree of orientation of the carbon fibers in the planar direction was obtained, but it was found that this laminated molded body had inferior mechanical properties (particularly bending properties) compared to the laminated molded bodies obtained in Examples 1 to 3.

As described above, according to the present invention, it is possible to obtain a molded product made of fiber-reinforced thermoplastic resin with excellent mechanical properties (particularly flexural modulus and flexural strength). Therefore, the fiber-reinforced thermoplastic resin laminate molded product of the present invention is particularly useful as a component that is subjected to a large impact, such as an automobile component, a train component, an aerospace component, an industrial machinery component, a construction component, a material for home appliances, a material for sports and leisure, a pressure vessel, a material for protective equipment, etc.

1: Thermoplastic resin, 2: Fiber, 3: Lower layer molded body, 4: Upper layer molded body

Claims (7)

a laminated molded article including two or more layers of injection molded articles each containing polyamide and fibers having a number average fiber length of 0.05 to 20 mm, the fiber content being 1 to 70 mass %, and the thickness being 0.5 to 2 mm;
the laminated molded body is formed by forming an upper layer injection molded body on a surface of a lower layer injection molded body by injection molding or injection press molding,
With respect to the entire laminated molded body, the orientation degree of the fibers in a direction parallel to the surface direction of the laminated molded body is 0.75 or more,
A fiber-reinforced thermoplastic resin laminate, characterized in that at least a portion of the surface of each layer is directly fused to the other layer. The fiber-reinforced thermoplastic resin laminate according to claim 1, characterized in that the overall thickness of the laminate is 2.0 mm or more. The fiber-reinforced thermoplastic resin laminate according to claim 1 or 2, characterized in that in each layer, the proportion of the layer surface that is directly fused to the adjacent layer is 10% or more. The fiber-reinforced thermoplastic resin laminate according to any one of claims 1 to 3, characterized in that the fibers are carbon fibers. A method for producing a fiber-reinforced thermoplastic resin laminated molded body, comprising: injection molding or injection press molding a lower layer molded body containing a thermoplastic resin and fibers with a number average fiber length of 0.05 to 20 mm, the fiber content being 1 to 70% by mass, and a thickness of 0.5 to 2 mm; and then injection molding or injection press molding an upper layer molded body containing the thermoplastic resin and the fibers, the fiber content being 1 to 70% by mass, and a thickness of 0.5 to 2 mm, on the surface of the lower layer molded body, thereby obtaining a laminated molded body in which layers made of the molded bodies are directly fused to each other at least in part of the layer surface. The method for manufacturing a fiber-reinforced thermoplastic resin laminated molded body according to claim 5, characterized in that the upper layer molded body is injection molded or injection press molded while the lower layer molded body is heated so that the surface temperature is 30 to 280°C. The method for manufacturing a fiber-reinforced thermoplastic resin laminate according to claim 5 or 6, characterized in that the lower layer molded body is preheated so that the surface temperature is 5 to 100°C higher than the glass transition temperature (Tg) of the thermoplastic resin (Tg + 5°C to Tg + 100°C), and then the upper layer molded body is injection molded or injection press molded.