Fiber-reinforced resin sheet, composite, and method for manufacturing a fiber-reinforced resin sheet

Abstract

The present invention provides a fiber-reinforced resin sheet that can reinforce an object by adhering to it appropriately, and that allows for easy removal of fibers from the object without leaving any residue when the object is recycled, as well as a method for manufacturing a fiber-reinforced resin sheet. [Solution] A fiber-reinforced resin sheet 1 that reinforces an object W by adhering to it, comprising: an adhesive layer 10 mainly containing a first polypropylene that adheres to the object W; a fiber layer 20 containing fibers that is laminated on the adhesive layer 10; and a protective layer 30 mainly containing a second polypropylene having a higher melting point than the first polypropylene, which is laminated on the fiber layer 20, wherein the adhesive layer 10 has a lower melting point than the protective layer 30.

Description

[Technical Field]

[0001] The present invention relates to a fiber-reinforced resin sheet, a composite, and a method for manufacturing a fiber-reinforced resin sheet, all suitable for applications such as reinforcing objects by adhering them to objects like automobile bumpers. [Background technology]

[0002] In recent years, resin bumpers have become popular for vehicles, primarily for weight reduction. In particular, automotive bumpers require heat resistance and impact resistance, so bumpers made from block polypropylene, which offers excellent heat and impact resistance, have become the mainstream. On the other hand, in order to comply with recent environmental regulations, automobile bumpers are required to use recycled materials. However, because recycled materials undergo thermal degradation of resin molecules due to heating during the recycling process, resulting in reduced mechanical properties, automobile bumpers made with recycled materials are weaker than those made with virgin materials, and there is a need to increase the strength of automobile bumpers. Furthermore, in recent years, numerous sensors have been installed on car bumpers to support the safety and comfort of drivers, pedestrians, and others. Therefore, it is especially necessary to support the weight of these sensors against gravity. Therefore, there is a need for reinforcing materials that can be bonded to automobile bumpers to increase their strength, particularly their strength against gravity.

[0003] For example, Patent Document 1 discloses a fiber-reinforced resin sheet, which is a composite of continuous fibers and a matrix resin, as a reinforcing material against uniaxial forces. Specifically, it discloses that the strength of a substrate can be increased by bonding a fiber-reinforced resin sheet, which includes an open fiber sheet aligned in one direction and a thermoplastic matrix resin, to a substrate. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-62758 [Overview of the project] [Problems that the invention aims to solve]

[0005] As mentioned above, environmental regulations have become stricter in recent years, and there is a demand for the recycling of automobile bumpers. However, as shown in Patent Document 1, when a fiber-reinforced resin sheet is used, if the reinforcing fibers contained in the fiber-reinforced resin sheet remain attached to the automobile bumper, it hinders the recycling of the resin automobile bumper. Therefore, in the recycling process of automobile bumpers reinforced with fiber-reinforced resin sheets, the fiber-reinforced resin sheet is peeled off and removed from the automobile bumper. However, there is a problem that the reinforcing fibers remain on the automobile bumper during the peeling process, making it impossible to recycle the automobile bumper.

[0006] The present invention aims to provide a fiber-reinforced resin sheet that can reinforce an object by adhering to it appropriately, and that can be easily removed from the object when recycling the object without leaving any fibers such as glass fibers attached to it, and a method for manufacturing a fiber-reinforced resin sheet. [Means for solving the problem]

[0007] The present invention is essentially based on the following (1) to (7) fiber-reinforced resin sheets. (1) A fiber-reinforced resin sheet that reinforces an object by adhering to it, comprising: an adhesive layer mainly containing a first polypropylene that adheres to the object; a fiber layer containing fibers that is laminated on the adhesive layer; and a protective layer mainly containing a second polypropylene having a higher melting point than the first polypropylene, which is laminated on the reinforcing layer, wherein the adhesive layer has a lower melting point than the protective layer. (2) The fiber-reinforced resin sheet according to (1) above, characterized in that the first polypropylene is random polypropylene and the second polypropylene is homopolypropylene or block polypropylene. (3) The fiber-reinforced resin sheet according to (1) above, wherein the object is made of resin, and the adhesive layer has a lower melting point than the object. (4) The fiber-reinforced resin sheet according to (1) above, characterized in that the adhesive layer or the protective layer contains a modified polyolefin as an additive. (5) The fiber-reinforced resin sheet according to (1) above, characterized in that the fiber layer contains glass fibers aligned in one direction as the fibers. (6) The fiber-reinforced resin sheet according to (1) above, characterized in that the difference in melting points between the first polypropylene and the second polypropylene is 20 degrees or more. Furthermore, the present invention is essentially based on the composite described in (7) below. (7) A composite characterized in that the adhesive layer of the fiber-reinforced resin sheet described in any of (1) to (6) above is welded to the object, and the fiber-reinforced resin sheet and the object are integrated. Furthermore, the present invention is essentially a method for producing a fiber-reinforced resin sheet as described in (8) below. (8) A method for manufacturing a fiber-reinforced resin sheet that reinforces an object by adhering to it, comprising the steps of: forming a laminate in which a protective layer mainly containing a second polypropylene and a fiber layer containing fibers are laminated; and forming an adhesive layer mainly containing a first polypropylene having a lower melting point than the second polypropylene on the fiber layer of the laminate. [Effects of the Invention]

[0008] According to the present invention, since the adhesive layer in contact with the object has a lower melting point than the protective layer, the protective layer does not soften or melt. By bonding the fiber-reinforced resin sheet to the object at a temperature at which the adhesive layer softens or melts, the fiber-reinforced resin sheet adheres well to the object without deformation due to heat, thereby increasing the strength of the object. Furthermore, when recycling the object, by heating it to a temperature at which the adhesive layer softens or melts but the protective layer does not soften or melt, the fiber-reinforced resin sheet can be peeled off the object while the fibers remain fixed to the protective layer. As a result, the fiber-reinforced resin sheet can be easily removed from the object without any fibers remaining on it. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view showing a fiber-reinforced resin sheet according to this embodiment. [Figure 2] This flowchart shows an example of the manufacturing of a fiber-reinforced resin sheet according to this embodiment. [Modes for carrying out the invention]

[0010] The following describes embodiments of the fiber-reinforced resin sheet according to the present invention. In this embodiment, a fiber-reinforced resin sheet 1 for reinforcing an automobile bumper is described as an example, but the fiber-reinforced resin sheet according to the present invention is not limited to the use of reinforcing automobile bumpers, but can also be used as a reinforcing member in other fields where mechanical properties and impact resistance are required, such as in the construction field, aerospace field, sports applications, automobile components other than automobile bumpers, and wind turbine blades. Furthermore, in the present invention, "mainly contains" means that it is contained in a proportion of 50% by weight or more of the components constituting each part, or that it is contained in the largest proportion, preferably 60% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight.

[0011] Figure 1 is a schematic cross-sectional view showing the fiber-reinforced resin sheet 1 according to this embodiment. As shown in Figure 1, the fiber-reinforced resin sheet 1 according to this embodiment has an adhesive layer 10, a fiber layer 20, and a protective layer 30. Figure 1 also shows the state in which the fiber-reinforced resin sheet 1 according to this embodiment is adhered to and reinforced on an automobile bumper W, which is the object to be reinforced.

[0012] In this embodiment, the automobile bumper W will be described as having a composition mainly containing block polypropylene (hereinafter also referred to as b-PP). Block polypropylene is a propylene polymer copolymerized with α-olefins other than propylene, and has polymer blocks made of propylene and polymer blocks made of α-olefins other than propylene. Examples of α-olefins other than propylene include ethylene and α-olefins having 4 to 20 carbon atoms. Furthermore, impact copolymer, which is a mixed component of propylene homopolymer and EPR (ethylene propylene rubber), can be used as block polypropylene.

[0013] (adhesive layer 10) The adhesive layer 10 is a layer that contacts the object and can be melted by heating to fuse the fiber reinforced resin sheet 1 to the object. The adhesive layer 10 mainly contains (contains as a base resin) the first polypropylene with a low melting point and is configured to have a lower melting point than the protective layer 30. In the present embodiment, random polypropylene (hereinafter also referred to as r-PP) can be used as the first polypropylene. Random polypropylene is a propylene polymer copolymerized with other α-olefins other than propylene, and other α-olefins other than propylene are randomly incorporated into the propylene chain. Examples of other α-olefins other than propylene include ethylene and α-olefins having 4 to 20 carbon atoms. The melting point of random polypropylene varies depending on the composition, but is mostly 125°C to 150°C. Also, the thickness of the adhesive layer 10 is not particularly limited, but can be 500 μm or less, can be 200 μm or less, and can also be 100 μm or less. Note that a recycled raw material of a propylene-based resin may be used for the adhesive layer 10. When using a recycled raw material, the recycled raw material and virgin random polypropylene can be blended to adjust the melting point of the adhesive layer 10. The melting point can be measured in accordance with JIS K-7121.

[0014] The content of ethylene monomer or α-olefin monomer in random polypropylene is not particularly limited, but is preferably 2% by weight or more and 40% by weight or less, more preferably 2% by weight or more and 30% by weight or less, still more preferably 2.5% by weight or more and 25% by weight or less, and even more preferably 3% by weight or more and 20% by weight or less. Also, the content of propylene monomer in random polypropylene is preferably more than 60% by weight and less than 98% by weight, more preferably 70% by weight or more and less than 98% by weight, still more preferably 75% by weight or more and 97.5% by weight or less, and even more preferably 80% by weight or more and 97% by weight or less.

[0015] In addition, the α-olefins having 4 to 20 carbon atoms are not particularly limited. For example, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene and the like can be mentioned. As the α-olefin, an α-olefin having 4 to 12 carbon atoms is preferable, and 1-butene, 3-methyl-1-butene, 1-hexene and 4-methyl-1-pentene are more preferable. The α-olefin may be used alone or in combination of two or more. Further, ethylene and an α-olefin having 4 to 20 carbon atoms may be used in combination.

[0016] The MFR (230 ° C, 2.16 kg) of the random polypropylene which is the base resin of the adhesive layer 10 is not particularly limited, but is preferably 0.5 to 50 g / 10 min, more preferably 1 to 30 g / 10 min, and particularly preferably 6 to 25 g / 10 min. By setting the MFR of the random polypropylene within the range of 0.5 to 50 g / 10 min, the adhesive layer 10 can be appropriately impregnated into the fiber layer 20 and the weldability to the object can be enhanced. The MFR can be measured in accordance with JIS K 6921-2.

[0017] Furthermore, in the adhesive layer 10, the content of the random polypropylene which is the base resin is not particularly limited, but is preferably 80% by weight or more of the entire adhesive layer 10, more preferably 90% or more, and preferably 95% by weight or more. Also, in the adhesive layer 10, the content of the random polypropylene which is the base resin can be made substantially 100% by weight.

[0018] Furthermore, in this embodiment, the adhesive layer 10 can be configured to contain one or more additives such as acid-modified polyolefin, silane-modified polyolefin, modified polyolefin, and chlorinated polyolefin. In this embodiment, the amount of additives is preferably 20% by weight or less of the total adhesive layer 10, more preferably 10% by weight or less, and even more preferably 5% by weight or less. By adding these additives to the adhesive layer 10, the strength of the fiber-reinforced resin sheet 1 can be increased, and the strength of the composite formed by laminating the fiber-reinforced resin sheet 1 to the automobile bumper W can be increased. In addition, by adding these additives to the adhesive layer 10, the adhesion between the automobile bumper W to be reinforced and the fiber layer 20 can be increased. Furthermore, by adjusting the type and amount of additives (thermoplastic resin) added to the adhesive layer 10, it is possible to adjust the temperature when removing the fiber-reinforced resin sheet 1 from the automobile bumper W and adjust the peel strength, thereby improving recyclability.

[0019] The acid-modified polyolefin is not particularly limited, and examples include acid-modified polyolefins modified with unsaturated carboxylic acids or their anhydrides, such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid, and acid-modified polyolefins composed of monomers such as polyethylene, polypropylene, and polybutene. Examples of silane-modified polyolefins include resins obtained by graft polymerization of silane compounds onto polyolefins such as polyethylene and polypropylene. Examples of modified polyolefins include modified polyolefins obtained by reaction with alkylphenol resins. Furthermore, examples of chlorinated polyolefins include chlorinated polypropylene, acid-modified chlorinated polypropylene, acrylic-modified chlorinated polypropylene, chlorinated polyethylene, and chlorinated ethylene vinyl acetate copolymer. However, the additives are not limited to those described above, and known additives that can be used to improve adhesion to the fiber layer 20 can be used.

[0020] (Fiber layer 20) The fiber layer 20 is an interposed layer between the adhesive layer 10 and the protective layer 30, and contains fibers as a reinforcing material. The fibers are not particularly limited, but examples include fiber sheets composed of fibers such as glass fibers, carbon fibers, aramid fibers, boron fibers, basalt fibers, metal fibers, and cellulose nanofibers. Fiber sheets made of highly elastic fibers such as polyarylate fibers, heterocyclic polymer fibers, high molecular weight polyethylene fibers, and polyvinyl alcohol fibers can also be used. Among these, glass fibers are preferred, and examples of glass fiber materials include E glass (glass with alkali content of 2.0% or less), AR glass (alkali-resistant glass), C glass (acid-resistant alkali-lime-containing glass), D glass (low dielectric constant glass), S glass (high-strength, high-modulus glass), T glass (high-strength, high-modulus glass), NE glass (low dielectric constant, low dielectric loss tangent glass), and H glass (high dielectric constant glass). These fiber sheets come in various types depending on the weaving method, including unidirectional cloth (where fibers are aligned in one direction), plain weave cloth (where fibers are plain woven), and nonwoven fabrics. However, it is preferable to use unidirectional cloth. By using unidirectional cloth, the strength in one direction, such as the direction of load (the direction of fiber orientation), can be increased.

[0021] The fiber sheet used in the fiber layer 20 may contain auxiliary fibers in addition to the main fibers. As auxiliary fibers, the fibers exemplified above, such as carbon fibers, glass fibers, and aramid fibers, can be used. Furthermore, the auxiliary fibers can be arranged at an angle different from the longitudinal direction (fiber orientation direction or MD direction) of the main fibers. In addition, the fiber sheet used in the fiber layer 20 may be an open fiber sheet, and the fiber sheet may further contain bridge fibers oriented in a direction transverse to the main fibers. Furthermore, the fibers of the fiber sheet are preferably long fibers, and may be twisted, but are preferably untwisted roving yarns. In addition, the fiber sheet may or may not be surface treated with a silicone-based surface treatment agent.

[0022] The thickness of the fiber sheet in the fiber layer 20 is not particularly limited, but from the viewpoint of handling properties and maintaining the strength of the fiber sheet itself, it is preferably 0.01 mm or more, more preferably 0.2 mm or more, and even more preferably 0.3 mm or more, and from the viewpoint of the drape properties of the fiber sheet, it is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less.

[0023] Furthermore, the basis weight of the fiber sheet used in the fiber layer 20 is not particularly limited, but is generally 50 to 500 g / m². 2 It is preferable to use 100-500 g / m². 2 It is more preferable to do so, at 150-450 g / m². 2 It is even more preferable to do so, at 200-400 g / m². 2 It is particularly preferable to do so. Furthermore, in the fiber sheet used for the fiber layer 20, the thickness of the fibers (single fiber diameter) is not particularly limited, but can be, for example, 5 to 50 μm or 7 to 30 μm.

[0024] (Protective layer 30) The protective layer 30 is a layer laminated on the side of the fiber layer 20 opposite to the adhesive layer 10, and has the function of protecting the fiber layer 20. In this embodiment, the protective layer 30 has a higher melting point than the adhesive layer 10, and even when the fiber-reinforced resin sheet 1 is heated to the temperature at which the adhesive layer 10 softens or melts, the protective layer 30 does not soften or weld, and the fibers of the fiber layer 20 remain fixed to the protective layer 30, making it possible to grasp the protective layer 30 and peel the fiber-reinforced resin sheet 1 together with the fiber layer 20 from the automobile bumper W. Preferably, the protective layer 30 has a melting point 10°C or higher than the adhesive layer 10, more preferably 15°C or higher, even more preferably 20°C or higher, and particularly preferably 25°C or higher.

[0025] In this embodiment, the protective layer 30 mainly contains a second polypropylene (used as the base resin) which has a higher melting point than the first polypropylene forming the protective layer 30, in order to have a higher melting point than the adhesive layer 10. Specifically, as the second polypropylene, homopolypropylene (hereinafter also referred to as h-PP) or block polypropylene, which have a higher melting point than random polypropylene, can be used as the base resin. Homopolypropylene is a polymer consisting only of polypropylene. Furthermore, the block polypropylene used in the fiber-reinforced resin sheet 1 is a propylene polymer copolymerized with other α-olefins other than propylene, similar to the block polypropylene that constitutes the automobile bumper W. It is a block polymer having polymer blocks made of propylene and polymer blocks made of other α-olefins other than propylene, and examples include block copolymers of propylene and ethylene, and block copolymers of propylene and α-olefins having 4 to 20 carbon atoms. In addition, impact copolymer, which is a mixed component of propylene homopolymer and EPR (ethylene propylene rubber), can also be used as the block polypropylene used in the fiber-reinforced resin sheet 1. The melting points of homopolypropylene and block polypropylene vary depending on their composition, but are often around 150-170°C, and tend to be higher than those of random polypropylene. Recycled polypropylene resin can also be used for the protective layer 30. When using recycled materials, the melting point of the protective layer 30 can be adjusted by blending recycled materials with virgin homopolypropylene or block polypropylene.

[0026] The content of ethylene monomer or α-olefin monomer in block polypropylene is not particularly limited, but is preferably 2% to 40% by weight, more preferably 2% to 30% by weight, even more preferably 2.5% to 25% by weight, and even more preferably 3% to 20% by weight. The content of propylene monomer in block polypropylene is preferably more than 60% to less than 98% by weight, more preferably 70% to less than 98% by weight, even more preferably 75% to 97.5% by weight, and even more preferably 80.5% to 97% by weight. In block polypropylene, the above-mentioned α-olefins with 4 to 20 carbon atoms can also be used as α-olefins.

[0027] The MFR (230°C, 2.16 kg) of homopolypropylene or block polypropylene, which is the base resin of the protective layer 30, is not particularly limited, but is preferably 0.5 to 50 g / 10 min, more preferably 2 to 45 g / 10 min, and can also be 20 to 45 g / 10 min. By setting the MFR of homopolypropylene or block polypropylene within the range of 0.5 to 50 g / 10 min, the protective layer 30 can be appropriately impregnated into the fiber layer 20, thereby improving the adhesion between the protective layer 30 and the fibers. Furthermore, by setting the MFR to 50 g / 10 min or less, the protective layer 30 becomes less susceptible to deformation by heat, so when the fiber-reinforced resin sheet 1 is heated and bonded to the automobile bumper W, the protective layer 30 may deform due to heat, disrupting the orientation of the fibers in the fiber layer 20 that adheres to the protective layer 30, and thus preventing a decrease in the strength of the fiber-reinforced resin sheet 1.

[0028] Furthermore, in the protective layer 30, the content of homopolypropylene or block polypropylene, which is the base resin, is not particularly limited, but similar to the adhesive layer 10, it is preferably 80% by weight or more of the total protective layer 30, more preferably 90% or more, and preferably 95% by weight or more. In addition, in the protective layer 30, the content of homopolypropylene and block polypropylene, which are the base resins, can be approximately 100% by weight. Furthermore, in the protective layer 30, a resin mixed with homopolypropylene and block polypropylene can also be used as the base resin.

[0029] The protective layer 30, like the adhesive layer 10, can contain one or more additives such as acid-modified polyolefin, silane-modified polyolefin, modified polyolefin, and chlorinated polyolefin. Furthermore, like the adhesive layer 10, the additives in the protective layer 30 are not limited to those described above, and any known additives that can be used to improve adhesion with the fiber layer 20 can be used. Moreover, like the adhesive layer 10, the additive content of the protective layer 30 is preferably 10% by weight or less of the total protective layer 30, more preferably 8% by weight or less, and even more preferably 5% by weight or less. However, when additives are added to the protective layer 30, compared to when no additives are added, the fibers of the fiber layer 20 tend to adhere more easily to the automobile bumper W during recycling (leading to a decrease in recyclability). Therefore, if recyclability is a priority, it is preferable to use a configuration without additives.

[0030] (Method for manufacturing the fiber-reinforced resin sheet 1 according to this embodiment) Next, a method for manufacturing the fiber-reinforced resin sheet 1 according to this embodiment will be described. The method for manufacturing the fiber-reinforced resin sheet 1 is not particularly limited, but an adhesive layer 10 and / or protective layer 30 can be formed by impregnating a fiber-containing fiber layer 20 with softened or molten polypropylene using methods such as extrusion lamination or hot press molding. Specifically, in the case of the extrusion lamination method, a molten polypropylene resin that will form the adhesive layer 10 and / or protective layer 30 is extruded onto the fiber-containing fiber layer 20, the molten resin is impregnated into the fiber layer 20, and then cooled and solidified to extrude-laminate the adhesive layer 10 and / or protective layer 30 onto the fiber layer, thereby manufacturing the fiber-reinforced resin sheet 1.

[0031] Furthermore, in this embodiment, as shown in Figure 2, it is preferable to form a fiber-reinforced resin sheet 1 by impregnating a fiber sheet with a matrix resin mainly containing molten second polypropylene to form a laminate in which a protective layer 30 mainly containing second polypropylene and a fiber layer 20 are laminated (step S101), cooling and solidifying (step S102), and then impregnating a surface of the laminate different from the surface on which the protective layer 30 is formed with a matrix resin mainly containing first polypropylene to form an adhesive layer 10 mainly containing first polypropylene (step S103), thereby forming a fiber-reinforced resin sheet 1 in which the protective layer 30, fiber layer 20 and adhesive layer 10 are laminated. By laminating in this order, the fiber layer 20 is impregnated with the protective layer 30, so when recycling the object, the fiber-reinforced resin sheet 1 can be peeled off the object while the fibers remain firmly fixed by the protective layer 30, and the fiber-reinforced resin sheet 1 can be easily removed from the object without any fibers remaining on the object.

[0032] Furthermore, when manufacturing the fiber-reinforced resin sheet 1, it is preferable to have a configuration in which a roll-to-roll process is used to continuously manufacture the fiber-reinforced resin sheet 1 in a single line by drawing a long roll of fiber sheet from the roll, extruding and coating a matrix resin mainly containing molten second polypropylene onto the fiber sheet to form a protective layer 30 on the fiber layer 20, and then extruding and coating an adhesive layer 10 onto the side of the fiber sheet opposite to the protective layer 30.

[0033] (Method of using the fiber-reinforced resin sheet 1 according to this embodiment) The method of using the fiber-reinforced resin sheet 1 according to this embodiment will now be described. The method of use is not particularly limited, but for example, one method is to heat the adhesive layer 10 of the fiber-reinforced resin sheet 1 until it softens or melts, and then press the molten adhesive layer 10 against the surface of an object such as an automobile bumper W to weld the fiber-reinforced resin sheet 1 to the automobile bumper W, or to heat the fiber-reinforced resin sheet 1 while the adhesive layer 10 of the fiber-reinforced resin sheet 1 is in contact with the surface of the automobile bumper W to weld the fiber-reinforced resin sheet 1 to the automobile bumper W. The temperature at which the fiber-reinforced resin sheet 1 is bonded to the automobile bumper W is not particularly limited as long as it is the temperature at which the adhesive layer 10 softens or melts (for example, a temperature higher than the melting point of random polypropylene), but it is preferable to set the temperature close to the melting point of the protective layer 30, which mainly contains homopolypropylene or block polypropylene, and the automobile bumper W, which mainly contains block polypropylene (for example, a temperature range of 5 to 10°C above or below the melting point of homopolypropylene or block polypropylene). For example, if the melting point of the adhesive layer 10 is 130°C and the melting points of the protective layer 30 and the automobile bumper W are 160°C, it is preferable to set the temperature at which the fiber-reinforced resin sheet 1 is bonded to the automobile bumper W to 150°C to 170°C.

[0034] (Recycling of automotive bumpers) If the automobile bumper W is made of block polypropylene, and fibers such as glass fibers are attached to the automobile bumper W, it becomes difficult to recycle the automobile bumper W. Therefore, when recycling the automobile bumper W, the fiber-reinforced resin sheet 1 is peeled off from the automobile bumper W. Specifically, in this embodiment, the fiber-reinforced resin sheet 1 is heated at a temperature lower than the temperature at which it was bonded (a temperature at which the protective layer 30 does not melt, for example, 120 to 140°C), and the fiber-reinforced resin sheet 1 is peeled off from the automobile bumper W while the adhesive layer 10 is softened or melted. In the fiber-reinforced resin sheet 1 according to this embodiment, even if the adhesive layer 10 softens or melts, the protective layer 30 does not soften or melt. Therefore, even if a part of the adhesive layer 10 melts and remains attached to the automobile bumper W, the protective layer 30 remains fixed to the fibers of the fiber layer 20, and the fibers can be peeled off together with the protective layer 30. Thus, with the fiber-reinforced resin sheet 1 according to this embodiment, the fiber-reinforced resin sheet 1 can be peeled off the automobile bumper W without any fibers adhering to or remaining on the automobile bumper W, thus enabling the automobile bumper W to be recycled. [Examples]

[0035] Next, we will describe some test examples of the present invention. In these test examples, fiber-reinforced resin sheets according to Examples 1-6 and Comparative Examples 1-7 were prepared, and in addition to the strength of the prepared fiber-reinforced resin sheets (tensile load at 0.5% elongation, tensile modulus), the heat resistance, adhesiveness, and recyclability of the fiber-reinforced resin sheets were measured.

[0036] Table 1 below shows the composition of the fiber-reinforced resin sheets for Examples 1-6 and Comparative Examples 1-7, and the measurement results for the tensile load at 0.5% elongation, tensile modulus, heat resistance, adhesion, and recyclability of these fiber-reinforced resin sheets. In Table 1, items for Comparative Example 1-7, where the desired properties were not obtained, are shown in gray. In this test example, the fiber-reinforced resin sheets for Examples 1-6 and Comparative Examples 1-7 were manufactured using a hot press machine (AWFA-50, manufactured by Shinto Metal Industries Co., Ltd.). The hot press machine has a heating plate on the upper side and a rubber plate on the lower side, and the heating plate can be lowered to heat-press and bond objects placed on the rubber plate. The composition and measurement results of the fiber-reinforced resin sheets for Examples 1-6 and Comparative Examples 1-7 are described in detail below.

[0037] [Table 1]

[0038] In this test example, the fiber-reinforced resin sheets for Examples 1-6 and Comparative Examples 1-7 were prepared as follows: A PET film (product name: A4100, manufactured by Toyobo) was treated to create a release sheet. A fiber sheet measuring 200 mm in length and 80 mm in width was placed on top of the fiber sheet, and a resin film measuring 200 mm in length, 80 mm in width, and 60 μm in thickness was placed on top of the fiber sheet to form a protective layer. After placing the same release sheet on top, the sheets were pressed using a hot press at a temperature of 200°C and a pressure volume of 1.2 (displayed as 20 kg / cm² on the hot press). 2 The laminate, consisting of a fiber layer and a protective layer, was then formed by hot pressing for 10 seconds. Next, the formed laminate was inverted, the release sheet in contact with the fiber layer was removed, and a resin film measuring 200 mm in length, 80 mm in width, and 60 μm in thickness was placed on top of the fiber layer to form an adhesive layer. A release sheet was then placed on top of that, and the laminate was hot-pressed using a hot press machine under the same conditions as above. This produced a fiber-reinforced resin sheet in which the adhesive layer, fiber layer, and protective layer were laminated in that order.

[0039] As described above, in these test examples, the fiber-reinforced resin sheets of Example 1-6 and Comparative Example 1-7 have a three-layer structure consisting of an adhesive layer, a fiber layer, and a protective layer, but the combinations of the adhesive layer, fiber layer, and protective layer differ in each case. The specific configurations of the fiber-reinforced resin sheets of Example 1-6 and Comparative Example 1-7 are described below.

[0040] In this test example, fiber-reinforced resin sheets according to Examples 1-6 and Comparative Examples 1-7 were prepared using the following polypropylene resins for the adhesive layer and protective layer. Homopolypropylene: h-PP1 (MFR: 42g / 10min, Melting point: 163℃) Block polypropylene: b-PP1 (MFR: 2g / 10min, Melting point: 166℃) Random polypropylene: r-PP1 (MFR: 7.5g / 10min, melting point 138℃) r-PP2 (MFR: 22g / 10min, Melting point: 134℃) Furthermore, in this test example, acid-modified polypropylene (melting point: 142°C, acid value 26 mg KOH / g) or silane-crosslinkable polypropylene (MFR: 9 g / 10 min, melting point: 77°C) modified with carboxylic anhydride was used for some of the protective or adhesive layers. In the following, the above acid-modified polypropylene will be referred to as acid-modified PP, and the above silane-crosslinkable polypropylene will be referred to as silane-crosslinkable PP.

[0041] Specifically, the fiber-reinforced resin sheets according to Examples 1-6 were constructed as follows. In the fiber-reinforced resin sheet according to Example 1, the protective layer was composed solely of h-PP1, and the adhesive layer was composed solely of r-PP1. In the fiber-reinforced resin sheet according to Example 2, the protective layer was composed solely of h-PP1, and the adhesive layer was composed of r-PP1 with 5% by weight of acid-modified PP added to the total adhesive layer. In the fiber-reinforced resin sheet according to Example 3, the protective layer was composed solely of h-PP1, and the adhesive layer was composed of r-PP2 with 5% by weight of acid-modified PP added to the total adhesive layer. In the fiber-reinforced resin sheet according to Example 4, the protective layer was composed solely of h-PP1, and the adhesive layer was constructed by adding silane-crosslinkable PP to r-PP2 at a concentration of 10% by weight of the total adhesive layer. In the fiber-reinforced resin sheet according to Example 5, the protective layer was constructed by adding 5% by weight of acid-modified PP to h-PP1, and the adhesive layer was constructed by adding 5% by weight of acid-modified PP to r-PP2. In the fiber-reinforced resin sheet according to Example 6, the protective layer was composed solely of b-PP1, and the adhesive layer was composed of r-PP2 with 5% by weight of acid-modified PP added to the total adhesive layer. Furthermore, in Examples 1-6, the fibers of the fiber layer were unidirectional cross glass fiber sheets (basis weight: 385g / m²). 2 ) was used.

[0042] As described above, in the fiber-reinforced resin sheets according to Examples 1-6, a protective layer was formed using homopolypropylene or block polypropylene, which has a high melting point, as the base resin, and an adhesive layer was formed using random polypropylene, which has a low melting point, as the base resin. As a result, in the fiber-reinforced resin sheet 1 according to Examples 1-6, as shown in Table 1 above, the difference between the melting point of the base resin of the protective layer and the base resin of the adhesive layer (melting point of the base resin of the protective layer - melting point of the base resin of the adhesive layer) was 25-32°C.

[0043] Next, the structure of the fiber-reinforced resin sheet relating to Comparative Examples 1-7 will be described. In the fiber-reinforced resin sheet of Comparative Example 1, both the protective layer and the adhesive layer were composed solely of h-PP1. In the fiber-reinforced resin sheet of Comparative Example 2, the protective layer was composed solely of r-PP2, and the adhesive layer was constructed by adding 5% by weight of acid-modified PP to r-PP2. In the fiber-reinforced resin sheet of Comparative Example 3, both the protective layer and the adhesive layer were constructed by adding 5% by weight of acid-modified PP to r-PP2 in each layer. In the fiber-reinforced resin sheet of Comparative Example 4, both the protective layer and the adhesive layer were composed solely of r-PP2. In the fiber-reinforced resin sheet of Comparative Example 5, both the protective layer and the adhesive layer were composed solely of r-PP1. In Comparative Examples 1-5, a unidirectional cross-patterned glass fiber sheet was used as the fiber constituting the fiber layer 20.

[0044] Furthermore, in the fiber-reinforced resin sheets of Comparative Examples 6 and 7, both the protective layer and the adhesive layer were composed solely of r-PP1. In addition, in the fiber-reinforced resin sheet of Comparative Example 6, the fibers constituting the fiber layer were plain weave cloth glass fiber sheets (basis weight: 220 g / m²). 2 In the fiber-reinforced resin sheet of Comparative Example 7, the fibers constituting the fiber layer are made of a nonwoven fabric (basis weight: 70g / m²) using yarn with a polyester (PET) core and a polyethylene (PE) sheath. 2 ) was used.

[0045] Thus, in the fiber-reinforced resin sheets of Comparative Examples 1-7, both the protective layer and the adhesive layer are constructed using the same base resin. Therefore, in the fiber-reinforced resin sheet of Comparative Example 1-5, the difference between the melting point of the base resin of the protective layer and the melting point of the base resin of the adhesive layer (melting point of the base resin of the protective layer - melting point of the base resin of the adhesive layer) is 0°C. Furthermore, while the fiber-reinforced resin sheet of Comparative Example 1-5 used a unidirectional cross glass fiber sheet as the fibers constituting the fiber layer 20, the fiber-reinforced resin sheets of Comparative Examples 6 and 7 used a plain weave cross glass fiber sheet or a nonwoven fabric fiber sheet made of polyester and polyethylene.

[0046] In this test example, a resin molded product using block polypropylene (hereinafter referred to as b-PP molded product) was produced. Specifically, a dumbbell-shaped b-PP molded product was produced by injection molding block polypropylene (b-PP1) using a hand truder (M-1, manufactured by Toyo Seiki Seisakusho). The b-PP molded product was shaped like a dumbbell, corresponding to the small test piece in Annex A of JIS K 7161-2, with a length of 80 mm, a width of 10 mm, and a thickness of 4 mm. The tensile modulus of the produced b-PP molded product alone was measured to be 1.8 GPa.

[0047] Using the fiber-reinforced resin sheets prepared in Examples 1-6 and Comparative Examples 1-7, the tensile load at 0.5% elongation of the fiber-reinforced resin sheet alone, and the tensile modulus of the laminate formed by laminating the fiber-reinforced resin sheet to a b-PP molded product were measured. In addition, the heat resistance, adhesiveness, and recyclability of the fiber-reinforced resin sheet were evaluated. Details are described below.

[0048] (Tensile load at 0.5% elongation) In this test, the tensile load required to elongate the fiber-reinforced resin sheets of Examples 1-6 and Comparative Examples 1-7 by 0.5% was measured as the tensile load at 0.5% elongation. Specifically, the fiber-reinforced resin sheets of Examples 1-6 and Comparative Examples 1-7 were molded into strips measuring 170 mm in length and 10 mm in width. The molded fiber-reinforced resin sheets were mounted on an Autograph (AGX-50kNV, Shimadzu Corporation) and stretched in the width direction at a speed of 50 mm / min under conditions of 23°C. The tensile load at which the fiber-reinforced resin sheet elongated by 0.5% was measured for 5 samples (n=5), and the average value was determined as the tensile load at 0.5% elongation. For the fiber-reinforced resin sheets of Examples 1-6 and Comparative Examples 1-5, which used unidirectional cross-grain glass fiber sheets, the length direction of the fiber-reinforced resin sheet was defined as the orientation direction of the glass fibers, and the tensile load at 0.5% elongation was measured when the sheet was stretched in the orientation direction of the glass fibers.

[0049] As a result of the measurement, in the fiber reinforced resin sheets according to Comparative Examples 6-7, the tensile load at 0.5% elongation was 30 N / 10 mm or less. In contrast, in the fiber reinforced resin sheets according to Examples 1-6 and Comparative Examples 1-5, the tensile load at 0.5% elongation was as high as 306 N / 10 mm or more. From this, it was found that in the fiber reinforced resin sheets according to Examples 1-6 and Comparative Examples 1-5, by using unidirectional cross glass fibers, high strength can be obtained in the fiber orientation direction. Also, compared with the fiber reinforced resin sheets according to Example 1 and Comparative Examples 1, 4-5 in which no additive was added to the protective layer and the adhesive layer, in the fiber reinforced resin sheets according to Examples 2-6 and Comparative Examples 2-3 in which an additive was added to the protective layer or the adhesive layer, the tensile load at 0.5% elongation tends to be high. In particular, it was found that in the fiber reinforced resin sheets according to Example 5 and Comparative Example 3 in which an additive was added to both the protective layer and the adhesive layer, the tensile load at 0.5% elongation tends to be even higher.

[0050] (Tensile modulus of elasticity) Also, in this test example, the tensile modulus of elasticity of the laminate obtained by laminating the fiber reinforced resin sheets according to Examples 1-6 and Comparative Examples 1-5, 7 on the b-PP molded product was measured. Specifically, the b-PP molded product was placed on a release sheet, and the fiber reinforced resin sheets according to Examples 1-6 and Comparative Examples 1-5, 7 with a length of 170 mm and a width of 10 mm were respectively stacked on the b-PP molded product, and then a release sheet was placed on top of them and bonded together with a hot press machine. The hot press was performed with the upper hot plate at 170°C, the pressure volume at 1.00 (indicated as 15 kg / cm 2 ) and the press time at 10 seconds. Then, the laminate of the bonded fiber reinforced resin sheet and the b-PP molded product was attached to an autograph (AGX-50kNV, manufactured by Shimadzu Corporation), and pulled at a speed of 1 mm / min in an environment of 23°C, and the tensile modulus of elasticity was measured for 2 samples (n = 2) each, and the average value was determined as the tensile modulus of elasticity. The cross-sectional area used when obtaining the tensile modulus of elasticity was 10 mm × 4 mm, which is the value of the b-PP molded product. Also, for the fiber reinforced resin sheets according to Examples 1-6 and Comparative Examples 1-5 using unidirectional cross glass fiber sheets, they were pulled in the fiber orientation direction of the glass fibers, and the tensile modulus of elasticity was measured.

[0051] The measurement results showed that the tensile modulus of the composite when the fiber-reinforced resin sheets of Examples 1-6 and Comparative Examples 1-5 were laminated with the b-PP molded product was 3.2 GPa or higher, while the tensile modulus of the laminate when the fiber-reinforced resin sheet of Comparative Example 7 was laminated with the b-PP molded product was 1.6 GPa. Since the b-PP molded product produced in this test example has a tensile modulus of 1.8 GPa on its own, it was found that by laminating the fiber-reinforced resin sheets of Examples 1-6 and Comparative Examples 1-5 to the b-PP molded product, the tensile modulus of the laminated product increased by 1.4 GPa or more (approximately 1.78 times or more), which is sufficient to reinforce the automobile bumper W. On the other hand, in the case of the fiber-reinforced resin sheet of Comparative Example 7, the tensile modulus of the laminate when it was laminated with the b-PP molded product was lower than the tensile modulus of the b-PP molded product alone, indicating that a unidirectional cross fiber sheet is preferable as the fiber constituting the fiber layer 20.

[0052] (Heat resistance of fiber-reinforced resin sheets) Furthermore, in this test example, after laminating the fiber-reinforced resin sheets according to Examples 1-6 and Comparative Examples 1-5 onto b-PP molded products, we evaluated whether the laminated fiber-reinforced resin sheets were deformed by heat and whether the fiber-reinforced resin sheets were welded to the release sheet. Specifically, a strip-shaped b-PP molded product was placed on the release sheet, and the fiber-reinforced resin sheets according to Examples 1-6 and Comparative Examples 1-5, each measuring 170 mm in length and 10 mm in width, were placed on top of the b-PP molded product, and then the release sheet was placed on top of that, and the products were laminated using a hot press machine. The hot press was performed with the upper heating plate set to 150°C to 170°C and the pressure volume set to 1.00 (indicated as 15 kg / cm²). 2The process was carried out with a pressing time of 10 seconds. The fiber-reinforced resin sheets were then visually inspected and evaluated to see if they had deformed due to the pressure and heat of the heat press (e.g., whether the orientation of the glass fibers was disrupted), or if the fiber-reinforced resin sheet (protective layer) had fused to the release sheet. In Table 1 above, deformation of the fiber-reinforced resin sheet after bonding is indicated as "deformed," if the fiber-reinforced resin sheet (protective layer) had fused to the release sheet after bonding is indicated as "fused," and if neither deformation nor fusion was observed it is indicated as "shape maintained." If deformation occurs, the orientation of the fibers in the fiber layer may be disrupted, potentially reducing strength, and if fusion occurs, it may hinder continuous production.

[0053] The evaluation results showed that the fiber-reinforced resin sheets of Examples 1-6 and Comparative Example 1 were evaluated as having "shape retention," and even when bonded by hot pressing, no deformation of the fiber-reinforced resin sheet or welding to the release sheet was observed, indicating excellent heat resistance. On the other hand, in the fiber-reinforced resin sheet of Comparative Example 2-5, deformation of the fiber-reinforced resin sheet and welding of the fiber-reinforced resin sheet to the release sheet were observed when the hot pressing temperature was 160°C or higher. Furthermore, in the fiber-reinforced resin sheet of Comparative Example 3-4, deformation of the fiber-reinforced resin sheet and welding of the fiber-reinforced resin sheet to the release sheet were observed even when the hot pressing temperature was 150°C. This is because, in the fiber-reinforced resin sheet of Comparative Example 2-5, random polypropylene with a low melting point was used as the base resin in both the adhesive layer and the protective layer, and when heated to 150°C or higher (or 160°C or higher), the protective layer, which also uses the same random polypropylene as the base resin, melted. On the other hand, in the fiber-reinforced resin sheets according to Examples 1-6, by using random polypropylene as the base resin for the adhesive layer and homopolypropylene or block polypropylene, which has a higher melting point than random polypropylene, for the base resin of the protective layer, it was possible to effectively prevent deformation of the fiber-reinforced resin sheet or welding of the fiber-reinforced resin sheet (protective layer) to the release sheet, even at temperatures at which the adhesive layer melts.

[0054] Thus, it was found that by using polypropylene with a lower melting point than the protective layer in the adhesive layer, a fiber-reinforced resin sheet with good heat resistance can be formed. From another perspective, in order to form a fiber-reinforced resin sheet with good heat resistance, it is preferable to use homopolypropylene or block polypropylene as the base resin for the protective layer and random polypropylene as the base resin for the adhesive layer. Furthermore, in this embodiment, the difference between the melting point of the polypropylene used as the base resin for the protective layer and the polypropylene used as the base resin for the adhesive layer was 25 to 32°C, and from this, it is considered preferable that the difference between the melting points of the protective layer and the adhesive layer be 20°C or more.

[0055] (Adhesion of fiber-reinforced resin sheets) In addition, in this test example, after laminating the fiber-reinforced resin sheets according to Example 1-6 and Comparative Example 1-5 onto a b-PP molded product, the laminated fiber-reinforced resin sheet and the b-PP molded product were pulled in opposite directions at room temperature, and the peel load at which the fiber-reinforced resin sheet peeled off from the b-PP molded product was measured. The state in which the composite consisting of the fiber-reinforced resin sheet and the b-PP molded product broke was also observed and evaluated as the adhesiveness of the fiber-reinforced resin sheet. For the evaluation of the adhesiveness of the fiber-reinforced resin sheet, the fiber-reinforced resin sheets according to Example 1-6 and Comparative Example 1-5 were laminated onto the b-PP molded product under the same conditions as for the heat resistance of the fiber-reinforced resin sheet. Then, the b-PP molded product and the fiber-reinforced resin sheet were each gripped using the gripping device of the Autograph (AGS-500NX, manufactured by Shimadzu Corporation). The fiber-reinforced resin sheet and the b-PP molded product were then pulled in opposite directions at a speed of 300 mm / min in an environment with a temperature of 23°C and a relative humidity of 50% (180° peeling was performed). The maximum load at which the fiber-reinforced resin sheet peeled from the b-PP molded product was measured as the peeling load, and the fracture state was visually observed. When bonding the fiber-reinforced resin sheet and the b-PP molded product, a release sheet was placed between the fiber-reinforced resin sheet and the b-PP molded product up to a position of 30 mm from the edge, and then heat-pressed to form the unbonded portion of the fiber-reinforced resin sheet and b-PP molded product as the gripping area of ​​the Autograph.

[0056] Furthermore, the fracture state of the composite consisting of the b-PP molded product and the fiber-reinforced resin sheet was evaluated as follows. Specifically, when the fiber-reinforced resin sheet was peeled from the b-PP molded product, if the peeling occurred at the interface between the b-PP molded product and the fiber-reinforced resin sheet, it was evaluated as "interfacial peeling." If the adhesive layer 10 of the fiber-reinforced resin sheet was destroyed and the sheet peeled off, it was evaluated as "cohesive failure." If the fiber layer of the fiber-reinforced resin sheet was destroyed and the sheet peeled off, it was evaluated as "material failure." Note that if the fracture shape is "material failure," it can be evaluated that the adhesive layer 10 is more firmly adhered to the b-PP molded product and the fiber layer compared to "interfacial failure" and "cohesive failure."

[0057] As shown in Table 1 above, in the fiber-reinforced resin sheet of Comparative Example 1, when bonded at 150°C, the peel load at room temperature between the fiber-reinforced resin sheet and the b-PP moldable material was 1.3 N / 10 mm, and the fracture shape was "interfacial peeling". When bonded at 160°C or higher, the peel load at room temperature between the fiber-reinforced resin sheet and the b-PP moldable material was 3.0 to 4.3 N / 10 mm, and the fracture shape was "cohesive fracture". In contrast, in the fiber-reinforced resin sheets of Examples 1-4, 6 and Comparative Examples 2, 5, when bonded at 150°C, the peel load at room temperature between the fiber-reinforced resin sheet and the b-PP moldable material was 5.2 to 12.6 N / 10 mm, and the fracture shape was "interfacial peeling". When bonded at 160°C or higher, the peel strength at room temperature between the fiber-reinforced resin sheet and the b-PP moldable material was 10.7 to 22.2 N / 10 mm, and the fracture shape was "material fracture". Thus, the fiber-reinforced resin sheets of Examples 1-4, 6 and Comparative Examples 2, 5 showed higher peel loads at room temperature between the fiber-reinforced resin sheet and the b-PP moldable material than the fiber-reinforced resin sheet of Comparative Example 1, and the fracture shape was "material fracture" at 160°C or higher, indicating high adhesion to b-PP molded products. Furthermore, in the fiber-reinforced resin sheets of Example 5 and Comparative Examples 3, 4, when bonded at 150°C or higher, the peel load at room temperature between the fiber-reinforced resin sheet and the b-PP moldable material was 15.0-23.4 N / 10mm, and the fracture shape was "material fracture," indicating that higher adhesion to b-PP molded products was obtained compared to the fiber-reinforced resin sheets of Examples 1-4, 6 and Comparative Examples 2, 5.

[0058] From these findings, it was found that when homopolypropylene, which has a high melting point, is used as the base resin in the adhesive layer, as in the fiber-reinforced resin sheet of Comparative Example 1, the adhesive layer does not melt sufficiently at a hot pressing temperature of 150°C, resulting in decreased adhesion of the fiber-reinforced resin sheet to the b-PP molded product. On the other hand, when random polypropylene, which has a low melting point, is used as the base resin in the adhesive layer, as in the fiber-reinforced resin sheets of Examples 1-6 and Comparative Example 2-5, the adhesive layer melts sufficiently even at a hot pressing temperature of 150°C, resulting in high adhesion of the fiber-reinforced resin sheet to the b-PP molded product. Furthermore, comparing the adhesion of the fiber-reinforced resin sheets of Examples 1-6 and Comparative Example 2-5, it was found that the peel load tended to be higher when bonded at 170°C in Examples 2-6 and Comparative Example 2-3, which contain acid-modified polypropylene or silane-crosslinkable polypropylene as additives in the adhesive layer, compared with Examples 1 and Comparative Example 4, which do not contain additives in the adhesive layer.

[0059] (Recyclability) Furthermore, in this test example, after laminating the fiber-reinforced resin sheets of Examples 1-6 and Comparative Examples 1-5 onto b-PP molded products, the laminated fiber-reinforced resin sheets and b-PP molded products were pulled in opposite directions at a high temperature (120-140°C) (180° peeling was performed). The tensile load at which the fiber-reinforced resin sheets peeled from the b-PP molded products was measured, and the state of the fracture of the laminate consisting of the fiber-reinforced resin sheets and b-PP molded products was observed to evaluate the recyclability of the fiber-reinforced resin sheets. In the evaluation of recyclability, the fiber-reinforced resin sheets and b-PP molded products were laminated under the same conditions as the evaluation of adhesion, except that the lamination was performed at 170°C. Furthermore, when evaluating recyclability, the grips of the Autograph (AGS-500NX, manufactured by Shimadzu Corporation) were preheated in a constant temperature bath. Then, the bonded laminated b-PP molded product and the fiber-reinforced resin sheet were each gripped with the Autograph's grips, and in that state, heated in the constant temperature bath for 3 minutes to 120-140°C. After that, the fiber-reinforced resin sheet and the b-PP molded product were pulled in opposite directions at a speed of 300 mm / min (performing a 180° delamination), and the maximum load at which the fiber-reinforced resin sheet peeled off from the b-PP molded product was measured as the delamination load, and the fracture state was observed visually. The evaluation of the fracture state was performed in the same manner as when evaluating adhesion.

[0060] As shown in Table 1 above, in the case of the fiber-reinforced resin sheets of Comparative Examples 2-3, it was found that when the fiber-reinforced resin sheet was peeled off from the b-PP molded product at a temperature of 130°C or lower for recycling, the fracture shape was "material fracture". This means that during recycling, some of the fibers remained attached to the b-PP molded product, suggesting that the fiber-reinforced resin sheet of Comparative Examples 2-3 cannot solve the problem of removing the fiber-reinforced resin sheet from the bumper without any fibers remaining attached to the bumper. In contrast, in the case of the fiber-reinforced resin sheets of Examples 1-4, 6 and Comparative Examples 1, 4-5, even at temperatures of 130°C or lower, the fracture shape was not "material fracture", and the fiber-reinforced resin sheet could be removed from the b-PP molded product during recycling without any of the fibers remaining attached to the b-PP molded product. In the case of the fiber-reinforced resin sheet according to Example 5, at temperatures of 130°C or higher, the fracture shape was not "material fracture," and the fiber-reinforced resin sheet could be removed from the b-PP molded product without any fibers remaining attached to the b-PP molded product. However, at a temperature of 120°C, the fracture shape was "material fracture," and some fibers remained attached to the b-PP molded product.

[0061] From this, it was found that when a configuration using random polypropylene with a relatively low melting point is used as the base resin of the protective layer, as in the fiber-reinforced resin sheet of Comparative Example 2-3, the protective layer tends to soften during recycling, and the fibers tend to remain on the b-PP molded product side together with the adhesive layer. In particular, it was found that when the adhesive layer contains acid-modified polypropylene or the like as an additive, the adhesion between the adhesive layer and the fibers increases, making it more likely for the fibers to remain on the b-PP molded product. Furthermore, it was found that when an additive such as acid-modified polypropylene is added to the protective layer, as in the fiber-reinforced resin sheet of Example 5, the fibers tend to remain adhered to the b-PP molded product compared to when no additive is added to the protective layer, as in the fiber-reinforced resin sheets of Examples 1-4 and 6.

[0062] From the results of this test example, as shown above, by making the adhesive layer 10 have a lower melting point than the protective layer 30, or by using a resin with a lower melting point than the base resin of the protective layer 30 as the base resin of the adhesive layer 10, it is possible to provide a fiber-reinforced resin sheet with excellent heat resistance, excellent adhesion, and excellent recyclability, as shown in the fiber-reinforced resin sheet 1 of Example 1-6. Furthermore, by adding additives such as acid-modified polypropylene or silane-crosslinkable polypropylene to the adhesive layer 10, as shown in the fiber-reinforced resin sheet 1 of Example 2-6, the strength of the fiber-reinforced resin sheet 1 and the degree to which the fiber-reinforced resin sheet 1 reinforces the automobile bumper W can be increased, and the adhesion of the fiber-reinforced resin sheet 1 to the automobile bumper W can be further improved. Moreover, when additives are added to the protective layer 30, as shown in the fiber-reinforced resin sheet 1 of Example 5, the strength of the fiber-reinforced resin sheet 1 and the strength of the composite formed by laminating the fiber-reinforced resin sheet 1 to the bumper are increased, but the recyclability tends to decrease.

[0063] Furthermore, as shown in Examples 1-6, the heat resistance, adhesiveness, and recyclability of the fiber-reinforced resin sheet 1 change depending on the composition of each layer of the fiber-reinforced resin sheet 1. The adhesiveness and recyclability of the fiber-reinforced resin sheet 1 also change depending on the temperature at which the fiber-reinforced resin sheet 1 is bonded to the automobile bumper W (bonding temperature) and the temperature at which the fiber-reinforced resin sheet 1 is peeled off the automobile bumper W (peeling temperature). For this reason, it is preferable to adjust the composition of each layer constituting the fiber-reinforced resin sheet 1 according to the temperature at which the fiber-reinforced resin sheet 1 is bonded to the bumper and the temperature at which the fiber-reinforced resin sheet 1 is peeled off the bumper during recycling. It is also preferable to adjust the temperature at which the fiber-reinforced resin sheet 1 is bonded to the automobile bumper W and the temperature at which the fiber-reinforced resin sheet 1 is peeled off the automobile bumper W during recycling according to the composition of each layer constituting the fiber-reinforced resin sheet 1.

[0064] Thus, a fiber-reinforced resin sheet 1 that can reinforce an automobile bumper W and improve the recyclability of the automobile bumper W is preferably one that has a high peel strength at room temperature, as evaluated for adhesiveness, and a low peel strength when heated, as evaluated for recyclability. In this regard, for example, the fiber-reinforced resin sheet 1 according to Example 3 has high adhesiveness with a peel strength of 20.1 N / 10 mm at room temperature when bonded to a bumper at 170°C, and is easy to peel off with a peel strength of 1.1 N / 10 mm when heated at 140°C for recycling, thus solving the problem of the present invention.

[0065] As described above, in this embodiment, a fiber-reinforced resin sheet 1 that reinforces an object by adhering to it comprises an adhesive layer 10 for adhering to the object, a fiber layer 20 containing fibers which is laminated on the adhesive layer 10, and a protective layer 30 which is laminated on the fiber layer 20, wherein the adhesive layer 10 has a lower melting point than the protective layer 30, or the adhesive layer 10 mainly contains a first polypropylene such as random polypropylene, and the protective layer 30 mainly contains a second polypropylene such as homopolypropylene or block polypropylene which has a higher melting point than the first polypropylene. As a result, by bonding the fiber-reinforced resin sheet 1 to the object at a temperature where the protective layer 30 does not soften or melt, and the adhesive layer 10 softens or melts, the fiber-reinforced resin sheet 1 adheres to the object without deformation, thereby increasing the strength of the object. Furthermore, when recycling the object, by heating it to a temperature where the protective layer 30 does not soften or melt, and the adhesive layer 10 softens or melts, the fiber-reinforced resin sheet 1 can be peeled off the object while the fibers remain fixed to the protective layer 30. In particular, in the fiber-reinforced resin sheet 1 according to this embodiment, by setting the difference in melting points between the first polypropylene and the second polypropylene, or the difference in melting points between the adhesive layer 10 and the protective layer 30 to 20°C or more, 25°C or more, or 30°C or more, a wide range of temperatures can be used when bonding the fiber-reinforced resin sheet 1 to the automobile bumper W and when peeling the fiber-reinforced resin sheet 1 off the automobile bumper W, thereby facilitating workability.

[0066] Furthermore, when the automobile bumper W, which is the object to be reinforced, is mainly composed of block polypropylene, in the fiber-reinforced resin sheet 1 according to this embodiment, the adhesive layer 10 is composed of random polypropylene, which has a lower melting point than the block polypropylene that is the base resin of the automobile bumper W. Therefore, the fiber-reinforced resin sheet 1 can be peeled off from the automobile bumper W more efficiently by peeling it off at a temperature at which the automobile bumper W does not soften or melt, but the adhesive layer 10 softens or melts.

[0067] Furthermore, in the fiber-reinforced resin sheet 1 according to this embodiment, the adhesive layer 10 can be configured to contain additives such as acid-modified polyolefin or silane-crosslinkable polyolefin, thereby increasing the strength of the fiber-reinforced resin sheet 1 and the degree to which the fiber-reinforced resin sheet 1 reinforces the automobile bumper W, as well as further improving the adhesion of the fiber-reinforced resin sheet 1 to the automobile bumper W. In addition, in the fiber-reinforced resin sheet 1 according to this embodiment, the protective layer 30 can be configured to contain additives such as acid-modified polyolefin, which tends to increase the strength of the fiber-reinforced resin sheet 1 and the degree to which the fiber-reinforced resin sheet 1 reinforces the automobile bumper.

[0068] In addition, in the fiber-reinforced resin sheet 1 according to this embodiment, the fiber layer 20 is configured to contain glass fibers aligned in one direction, thereby increasing the strength in one direction (the orientation direction of the fibers). Furthermore, in the fiber-reinforced resin sheet 1 according to this embodiment, by using the same polypropylene resin as the automobile bumper W for the adhesive layer 10, even if a portion of the adhesive layer 10 remains attached to the automobile bumper W, it does not hinder the recyclability of the automobile bumper W. Moreover, in the fiber-reinforced resin sheet 1 according to this embodiment, by using the same polypropylene resin for both the adhesive layer 10 and the protective layer 30, handling during the manufacturing process can be improved.

[0069] Although preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the embodiments described above. Various modifications and improvements can be made to the above embodiments, and such modified or improved forms are also included in the technical scope of the present invention.

[0070] For example, in the embodiment described above, the fiber-reinforced resin sheet 1 was exemplified as a three-layer film consisting of an adhesive layer 10, a fiber layer 20, and a protective layer 30. However, the configuration is not limited to this, and for example, in order to further increase the strength of the fiber-reinforced resin sheet 1, the adhesive layer 10, fiber layer 20, protective layer 30, etc., can be further laminated on top of the protective layer 30 to create a layer structure of four or more layers.

[0071] Furthermore, in the embodiments described above, a fiber-reinforced resin sheet 1 was illustrated in which an adhesive layer 10, a fiber layer 20, and a protective layer 30 were laminated in that order. However, as long as the fiber layer 20 is laminated on top of the adhesive layer 10 and the protective layer 30 is laminated on top of the fiber layer 20, another layer may be provided between the adhesive layer 10 and the fiber layer 20, and similarly, another layer may be provided between the fiber layer 20 and the protective layer 30.

[0072] Furthermore, in the embodiments described above, a configuration using a fiber sheet was illustrated when forming the fiber layer 20. However, for example, the fiber layer 20 can also be formed by scattering fibers on a resin film for forming the adhesive layer 10 or protective layer 30.

[0073] In addition, while the example shown in Figure 1 above illustrates the state in which the adhesive layer 10, fiber layer 20, and protective layer 30 are laminated, the fiber-reinforced resin sheet according to the present invention can be configured such that a portion of the protective layer 30 penetrates between the fibers of the fiber layer 20, forming an integral layer with the fiber layer 20. In particular, in the present invention, by forming the protective layer 30 on the fiber layer 20 before the adhesive layer 10, a portion of the protective layer 30 can penetrate more easily between the fibers of the fiber layer 20, further improving the adhesion between the protective layer 30 and the fibers of the fiber layer 20, and making it easier to remove the fibers together with the protective layer 30, thereby further improving the recyclability of the automobile bumper W. [Explanation of symbols]

[0074] 1…Fiber-reinforced resin sheet 10...adhesive layer 20…Fiber layer 30…Protective layer

Claims

1. A fiber-reinforced resin sheet that reinforces an object by adhering to it, A first adhesive layer mainly containing polypropylene, which adheres to the aforementioned object, A fiber layer containing fibers is laminated on the adhesive layer, The fiber layer comprises a protective layer mainly containing a second polypropylene having a higher melting point than the first polypropylene, which is laminated on top of the fiber layer. The adhesive layer is characterized by having a lower melting point than the protective layer, and is a fiber-reinforced resin sheet.

2. The first polypropylene is random polypropylene, The fiber-reinforced resin sheet according to claim 1, characterized in that the second polypropylene is homopolypropylene or block polypropylene.

3. The aforementioned object is made of resin, The fiber-reinforced resin sheet according to claim 1, characterized in that the adhesive layer has a lower melting point than the object.

4. The fiber-reinforced resin sheet according to claim 1, characterized in that the adhesive layer or the protective layer contains a modified polyolefin as an additive.

5. The fiber-reinforced resin sheet according to claim 1, characterized in that the fiber layer contains glass fibers aligned in one direction as the fibers.

6. The fiber-reinforced resin sheet according to claim 1, characterized in that the difference in melting points between the first polypropylene and the second polypropylene is 20 degrees or more.

7. A composite characterized in that the adhesive layer of the fiber-reinforced resin sheet according to any one of claims 1 to 6 is welded to the object, and the fiber-reinforced resin sheet and the object are integrated.

8. A method for manufacturing a fiber-reinforced resin sheet that reinforces an object by adhering it to the object, A step of forming a laminate in which a protective layer mainly containing a second polypropylene and a fiber layer containing fibers are laminated together, A method for producing a fiber-reinforced resin sheet, comprising the step of forming an adhesive layer on the fiber layer of the laminate, the adhesive layer mainly containing a first polypropylene having a lower melting point than the second polypropylene.

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