JP2023148924A - Method for manufacturing random sheet - Google Patents

Abstract

To provide a method for manufacturing a random sheet with better appearance.SOLUTION: A method for manufacturing a random sheet includes the steps of: laying flakes of fiber-reinforced resin consisting of a plurality of reinforcing fibers oriented and arranged in one direction and impregnated with a first polyolefin resin, in a planar shape; placing a film containing a second polyolefin resin, in contact with the laid flakes; and integrating the flakes with each other, by heating and pressurizing the flakes on which the film is placed.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a random sheet.

A thin film-like fiber-reinforced resin (hereinafter simply referred to as "Uni-Direction (UD)") containing a plurality of reinforcing fibers arranged in one direction and a resin composition (matrix resin) impregnated into the reinforcing fibers. (also called "sheet") are known. This UD sheet is cut into thin pieces, and the thin pieces are spread randomly in a two-dimensional shape, heated and pressurized, and molded into a sheet shape, so that blocks with reinforcing fibers oriented in one direction are randomly arranged. (for example, Patent Document 1). Random sheets have a unique marble-like appearance and are highly moldable (shapeable) by stamp molding, press molding, etc., so they are expected to be used in a variety of applications.

Patent Document 1 discloses that after the above-mentioned thin pieces containing carbon fibers as reinforcing fibers and polyamide resin etc. as matrix resin are spread in a flat shape, a transparent thermoplastic resin film made of polyamide resin etc. is rolled. A method for producing random sheets is described in which the sheets are temporarily bonded by molding, and then hot-pressed and cool-pressed. According to Patent Document 1, in the above method, when the transparent resin melted during heat pressing enters between the flakes, the carbon fibers are dragged and moved, so the shape of the flakes is distorted to create a random sheet with improved design. It is said that it is possible to obtain

International Publication No. 2020/009125

In Patent Document 1, a random sheet is produced using a thin piece containing a polyamide resin or the like as a matrix resin. However, polyamide resins have a high melting point and have a problem in that it takes time to produce random sheets. Therefore, the present inventors attempted to similarly produce a random sheet using a thin piece containing a polyolefin resin with a lower melting point. However, in the method described in Patent Document 1, when a thin piece containing a polyolefin resin is used, the appearance of the obtained random sheet is sometimes far from the appearance of flowing marble-like patterns.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a random sheet with better appearance.

A method for manufacturing a random sheet according to an embodiment of the present invention to solve the above problems is a thin piece of fiber reinforced resin obtained by impregnating a plurality of reinforcing fibers arranged in one direction with a first polyolefin resin. a step of placing a film containing a second polyolefin resin in contact with the spread thin pieces, and a step of heating and pressurizing the thin pieces on which the film is placed to integrate the thin pieces. and a step of converting the method into one.

According to the present invention, a method for manufacturing a random sheet with better appearance is provided.

FIG. 1 is a flowchart showing a method for manufacturing a random sheet according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration of a chopped sheet used for manufacturing a random sheet. FIG. 3 is a schematic diagram showing how chopped sheets are spread inside a mold in the first step of the random sheet manufacturing method according to an embodiment of the present invention. FIG. 4 is a schematic diagram showing how a second polyolefin resin film is placed in contact with chopped sheets spread inside a formwork in the second step of the random sheet manufacturing method according to an embodiment of the present invention. It is a diagram. FIG. 5 is a schematic diagram showing how a chopped sheet is heated and pressurized in the second step of the random sheet manufacturing method according to an embodiment of the present invention. FIG. 6 is a flowchart illustrating a flake integration sub-process in a random sheet manufacturing method according to an embodiment of the present invention. FIG. 7 is image data of the appearance of the chopped sheets scattered during the manufacture of the random sheet 1 in the example. FIG. 8 is image data of the appearance of the random sheet 1 obtained in the example. FIG. 9 is image data of the appearance of the random sheet 8 obtained in the example. FIG. 10 is image data obtained by imaging a marble.

Hereinafter, exemplary embodiments of the present invention will be described.

FIG. 1 is a flowchart showing a method for manufacturing a random sheet according to an embodiment of the present invention. As shown in FIG. 1, the manufacturing method according to the present embodiment includes a step of spreading thin pieces of fiber-reinforced resin (step S110), a step of placing a film in contact with the spread thin pieces (step S120), and heating and The method includes a step of integrating the thin pieces by pressure (step S130).

1. Spreading process (process S110)
In the first step, thin pieces of fiber-reinforced resin are spread in two dimensions.

1-1. Fiber-reinforced resin thin piece FIG. 2 is a schematic diagram showing an outline of the fiber-reinforced resin thin piece (hereinafter also simply referred to as "chopped sheet"). As shown in FIG. 2, the chopped sheet 100 is a thin piece of a UD sheet in which a matrix resin 120 is impregnated into a plurality of reinforcing fibers 110 oriented and arranged in one direction. The chopped sheet can be produced, for example, by cutting a UD sheet into a predetermined size.

The material of the reinforcing fibers 110 is not particularly limited. For example, carbon fibers, glass fibers, aramid fibers, alumina fibers, silicon carbide fibers, boron fibers, metal fibers, and the like can be used as the reinforcing fibers. Among these, carbon fibers and glass fibers are preferred, and carbon fibers are more preferred.

The average diameter of the reinforcing fibers 110 is preferably 1 μm or more and 20 μm or less, and more preferably 4 μm or more and 10 μm or less, from the viewpoint of sufficiently increasing the strength improvement effect of the reinforcing fibers.

Further, the reinforcing fibers 110 may be subjected to a sizing treatment using a sizing agent.

The sizing agent is not particularly limited, but is preferably a modified polyolefin, and more preferably a modified polyolefin containing a carboxylic acid metal salt. The above-mentioned modified polyolefin is produced by, for example, introducing a carboxylic acid group, a carboxylic acid anhydride group, or a carboxylic acid ester group into the polymer chain of an unmodified polyolefin, and forming a salt between the above-mentioned functional group and a metal cation. It is something that

The above-mentioned unmodified polyolefin is an ethylene polymer in which the content of structural units derived from ethylene is 50 mol% or more when the total amount of structural units derived from all monomers is 100 mol%, or an ethylene polymer derived from propylene. It is preferable that the propylene-based polymer has a content of 50 mol % or more of the structural unit. Examples of the ethylene polymers include ethylene homopolymers and copolymers of ethylene and α-olefins having 3 or more and 10 or less carbon atoms. Examples of the propylene-based polymer include propylene homopolymers and copolymers of propylene and ethylene or α-olefins having 4 or more and 10 or less carbon atoms. The unmodified polyolefin is preferably homopolypropylene, homopolyethylene, ethylene/propylene copolymer, propylene/1-butene copolymer, or ethylene/propylene/1-butene copolymer.

The content of reinforcing fibers 110 with respect to the total mass of the chopped sheet 100 is preferably 20% by mass or more and 80% by mass or less, more preferably 30% by mass or more and 75% by mass or less, and 35% by mass or more and 70% by mass or less. It is more preferable that it is less than % by mass.

The content of the reinforcing fibers 110 with respect to the total volume of the chopped sheet 100 is preferably 10 volume% or more and 70 volume% or less, more preferably 15 volume% or more and 60 volume% or less, and 20 volume% or more and 60 volume% or less. More preferably, it is less than or equal to % by volume.

The type of matrix resin 120 is not particularly limited as long as it is a polyolefin resin (first polyolefin resin).

The first polyolefin resin is a resin in which the content of structural units derived from α-olefin is 50 mol% or more when the total amount of structural units derived from all monomers is 100 mol%. Specifically, the first polyolefin resin can be a homopolymer or copolymer of α-olefin having 2 or more and 18 or less carbon atoms.

The α-olefin having 2 to 20 carbon atoms may be a linear α-olefin or a branched α-olefin.

Examples of the linear α-olefin having 2 to 20 carbon atoms include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1- Included are tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. The number of carbon atoms in the linear α-olefin is preferably 2 or more and 10 or less.

Examples of branched α-olefins having 3 to 20 carbon atoms include 2-methyl-1-butene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, and 3-methyl-1-butene. Pentene, 4-methyl-1-pentene, 3-ethyl-1-pentene, 4,4-dimethyl-1-pentene, trimethyl-1-butene, trimethyl-1-pentene, 4-methyl-1-hexene, 4, Included are 4-dimethyl-1-hexene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, methylethylpentene-1, diethylbutene-1, and propylpentene-1. The number of carbon atoms in the branched α-olefin is preferably 5 or more and 20 or less, more preferably 5 or more and 10 or less.

The olefin polymer may be a homopolymer of these α-olefins or a copolymer of two or more of these α-olefins.

The olefin polymer preferably has a structural unit derived from ethylene, propylene, butene, hexene, or octene as its main structural unit, and preferably has a structural unit derived from ethylene, propylene, or butene as its main structural unit. is more preferable, and it is even more preferable that the main structural unit is a structural unit derived from ethylene or propylene.

The olefin polymer may have structural units derived from the α-olefin in an amount of 51 mol% or more, but not less than 60 mol%, based on the number of moles of all structural units possessed by the olefin polymer. It is more preferable that the content is 70 mol% or more. Note that the upper limit of the amount of the structural unit derived from the α-olefin is not particularly defined and can be 100 mol%.

The olefin polymer may have a structural unit derived from other compounds of these α-olefins. Examples of the other compounds include α-olefins having 21 or more carbon atoms, aromatic vinyl compounds containing styrene, dienes, polyenes, and the like. The olefin polymer has structural units derived from the other compounds in an amount of 49 mol% or less based on the number of moles of all structural units possessed by the olefin polymer, but 1 mol% or more and 40 mol% or more. It is preferably less than mol%.

The above olefin polymer has a low melting point and can be molded in a short time, and from the viewpoint of lowering water absorption and further improving dimensional stability, the olefin polymer is a polymer whose main structural unit is a structural unit derived from propylene. Polypropylene (polypropylene) is preferred.

Examples of the above polypropylene include propylene/1-butene random copolymer, propylene/4-methyl-1-pentene random copolymer, propylene/ethylene random copolymer, propylene/ethylene/1-butene random copolymer. , propylene-octene random copolymers, and propylene homopolymers.

The polypropylene may have a content of structural units derived from propylene of 50 mol% or more when the total amount of structural units derived from all monomers is 100 mol%. The content of structural units derived from propylene is preferably 70 mol% or more and 100 mol% or less, more preferably 80 mol% or more and 100 mol% or less, and 100 mol% (i.e., homopolymer). It is even more preferable that there be. When it is a copolymer, the polypropylene may be a random copolymer or a block copolymer.

The above-mentioned polypropylene may have any stereoregularity of isotactic, syndiotactic, or atactic. Among these, isotactic and syndiotactic are preferred.

The polypropylene may be a modified polypropylene into which a carboxylic acid structure or a carboxylate structure has been introduced, or may be an unmodified polypropylene into which the above-mentioned structure has not been introduced, but preferably contains both of these. The mass ratio of unmodified polypropylene/modified polypropylene at this time is preferably 80/20 to 99/1, more preferably 89/11 to 99/1, and more preferably 89/11 to 93/7. More preferably, the ratio is from 90/10 to 95/5.

The weight average molecular weight (Mw) of the polypropylene is preferably 50,000 or more and 350,000 or less, more preferably 100,000 or more and 330,000 or less, and even more preferably 150,000 or more and 320,000 or less. Note that the weight average molecular weight (Mw) of polypropylene is the molecular weight measured by gel filtration chromatography (GPC) in terms of polystyrene.

The melt flow rate (MFR) of the above polypropylene measured at 230°C and a load of 2160 g in accordance with ASTM D-1238 is preferably 10.0 g/10 min or more, and preferably 50.0 g/10 min or more. is more preferable, and even more preferably 100.0 g/10 min or more. Although the upper limit of MFR of polypropylene is not particularly limited, it can be set to 400.0 g/10 min or less, and preferably 350.0 g/10 min or less.

The content of the structural units constituting the olefin polymer can be measured, for example, by ¹³ C-NMR method.

The matrix resin 120 may be a resin composition containing additives. Examples of the above additives include known fillers (inorganic fillers, organic fillers), pigments, dyes, weather-resistant stabilizers, heat-resistant stabilizers, antistatic agents, anti-slip agents, antioxidants, and anti-mold agents. , antibacterial agents, flame retardants, and softeners.

Further, the matrix resin 120 may contain other components such as a resin other than the first polyolefin resin and short fibers having a length shorter than the reinforcing fibers.

The content of matrix resin 120 with respect to the total mass of chopped sheet 100 is preferably 20% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 70% by mass or less, and 35% by mass or more and 70% by mass or less. It is more preferably at most 40% by mass and at most 65% by mass.

The chopped sheet 100 may be a single-layer thin piece, or may be a laminate of a plurality of aligned fiber layers in which reinforcing fibers 110 are oriented in different directions. When it is a laminate, the number of aligned fiber layers (number of laminated layers) included in one chopped sheet 100 is preferably 2 or more and 5 or less from the viewpoint of making it difficult to cause unevenness during molding of the random sheet. , more preferably two or more layers and three or less layers, and even more preferably two layers. In addition, when it is a laminate, the average value of the number of laminated layers of the entire chopped sheet spread is preferably 1.25 layers or more and 5.0 layers or less, and 1.5 layers or more and 4.0 layers or less. is more preferable, and even more preferably 1.75 layers or more and 2.5 layers or less. In addition, from the viewpoint of further increasing the randomness of the orientation direction of the reinforcing fibers in the random sheet, the plurality of arrayed fiber layers are arranged such that the orientation direction of the reinforcing fibers in the other arrayed fiber layers is different from the reinforcing fibers in one arrayed fiber layer. It is preferable that the angle formed is 180°/n (n is the number of aligned fiber layers) ±10°.

In the chopped sheet 100, the length (L) of the reinforcing fibers 110 in the orientation direction is preferably 1 mm or more and 80 mm or less, more preferably 3 mm or more and 60 mm or less, and more preferably 5 mm or more and 50 mm or less. preferable. By setting the length (L) of the chopped sheet 100 within the above range, the orientation direction of reinforcing fibers in the random sheet is made more random, the bending elastic modulus of the random sheet is further increased, and an appearance more similar to marble is produced. be able to. In addition, when the chopped sheet 100 is a laminate of a plurality of layers in which reinforcing fibers have different orientation directions, the orientation direction of the reinforcing fibers 110 measured for one layer determined so that the length (L) is the largest Let the length of the chopped sheet 100 be the length (L) of the chopped sheet 100. The length direction of the chopped sheet 100 means the direction in which the reinforcing fibers 110 are oriented, and the length of the chopped sheet 100 means the maximum distance between both ends in the length direction.

The width (W) of the chopped sheet 100 in the direction perpendicular to the length direction is preferably 1 mm or more and 50 mm or less, more preferably 3 mm or less and 30 mm or more, and further preferably 5 mm or more and 20 mm or less. preferable. Setting the width (W) of the chopped sheet 100 within the above range has the effect of further increasing the bending elastic modulus of the random sheet and producing an appearance more similar to marble.

Further, the chopped sheet 100 preferably has an aspect ratio (L/W), which is the ratio of the length (L) to the width (W), of 0.1 or more and 10.0 or less, and 0.3 or more and 8. It is more preferably 0 or less, and even more preferably 0.5 or more and 6.0 or less. By setting the aspect ratio (L/W) of the chopped sheet 100 within the above range, the bending elastic modulus of the random sheet can be further increased and an appearance more similar to marble can be produced.

The thickness of the chopped sheet 100 is preferably 0.1 mm or more and 1.0 mm or less, more preferably 0.2 mm or more and 0.5 mm or less. By setting the thickness to 0.1 mm or more, the productivity of the random sheet can be further improved. By setting the thickness to 1.0 mm or less, it is possible to prevent unevenness from occurring during molding of the random sheet.

The planar shape of the chopped sheet 100 is not particularly limited, and may include squares, rectangles, parallelograms, trapezoids and other quadrilateral shapes, equilateral triangles and other triangular shapes, other polygonal shapes, circles and ellipses, and other arbitrary shapes. It can be in the shape of

1-2. Spreading In this step, the chopped sheets 100 are spread in a flat shape. For example, the chopped sheet 100 may be spread without gaps inside a mold for press molding.

FIG. 3 is a schematic diagram showing how chopped sheets 100 are spread inside the formwork 212 in this step. As shown in FIG. 3, in this step, the chopped sheets 100 are randomly scattered inside the mold 212 without gaps. At this time, it is preferable to stack the chopped sheets 100 so as to form a plurality of layers so that no gaps are formed. Moreover, at this time, it is preferable to spread the chopped sheets 100 so that the directions of the reinforcing fibers included in the chopped sheets 100 are random so that the orientation directions of the reinforcing fibers included in each chopped sheet 100 are not aligned. . For example, the orientation of the chopped sheet 100 may be adjusted manually, or the chopped sheet 100 may be shaken in advance so as to have an uneven orientation and then scattered inside the formwork.

The planar shape and thickness of the spread chopped sheet 100 may be determined according to the shape of the random sheet to be molded.

2. Step of arranging the film (step S120)
Next, a sheet containing a polyolefin resin (second polyolefin resin) is placed in contact with the spread chopped sheets 100.

FIG. 4 is a schematic diagram showing how a film 410 containing the second polyolefin resin is applied in contact with the chopped sheet 100 spread inside the formwork 212 in this step. The method of arranging the film 410 is not particularly limited, and the film 410 may be arranged so as to cover the entire surface of the chopped sheet 100 spread out as shown in FIG. 4, or may be arranged so as to cover only a portion thereof.

The second polyolefin resin contained in the film 410 applied in this step melts and flows into the gaps in the chopped sheet 100 when the chopped sheet 100 is heated in the next step. Then, due to the above flow, the reinforcing fibers 110 are moved so as to be washed away from the matrix resin 120 of the chopped sheet 100, which is also melted. As a result, it is thought that a marble-like appearance with irregularly arranged streamlined patterns, which is different from the shape of the original chopped sheet 100, is produced. It is believed that the second polyolefin resin tends to produce an appearance that more closely resembles marble.

The type of the second polyolefin resin is not particularly limited as long as it is a polyolefin. The second polyolefin resin may be the same type of resin as the first polyolefin resin, or may be a different type of resin. Note that the same type of resin means resins in which the main structural units are the same, and more specifically, resins in which the types of monomers leading to the structural units having the highest molar ratio are the same.

Examples of the second polyolefin resin include various polyolefin resins similar to the first polyolefin resin described above.

Among these, from the viewpoint of improving fluidity during melting, the second thermoplastic resin is more preferably polypropylene.

From the viewpoint of more effectively causing movement of the reinforcing fibers 110 due to the flow of the second polyolefin resin, it is preferable that the second polyolefin resin has a larger melt flow rate (MFR). For example, when the second thermoplastic resin is polypropylene, the MFR of the polypropylene measured at 230°C and a load of 2160 g according to ASTM D-1238 is preferably 5.0 g/10 min or more, and 30.0 g /10min or more is more preferable, and even more preferably 100.0g/10min or more. Although the upper limit of MFR of polypropylene is not particularly limited, it can be 3000.0 g/10 min or less, and preferably 2000.0 g/10 min or less. For example, the MFR of polypropylene can be increased to the above range by heating polypropylene (or purchased commercially available polypropylene) with a low MFR once synthesized to cause appropriate thermal decomposition.

The amount of the film 410 applied is not particularly limited, but from the viewpoint of more effectively causing the change in appearance due to the flow, it is preferably 20.0 g/m ² or more, and 40.0 g/m ² or more. is more preferable, and even more preferably 100.0 g/m ² or more. Although the upper limit of the amount of the film 410 applied is not particularly limited, from the viewpoint of suppressing the occurrence of warping due to an excessive amount of resin, it can be set to 1000.0 g/m ² or less, and 500.0 g/m ² It is preferably at most 300.0 g/m ² , more preferably at most 300.0 g/m 2 .

3. Integrating process (process S130)
Next, the chopped sheets 100 on which the film 410 is placed are heated and pressurized to integrate the chopped sheets 100 together. As a result, a random sheet in which reinforcing fibers 110 are randomly oriented is obtained.

FIG. 5 is a schematic diagram showing how the chopped sheet 100 is heated and pressurized in this step. As shown in FIG. 5, the chopped sheet 100 is spread inside the formwork 212 by heating and pressurizing the lower mold 210 and the upper mold 220 of the press molding machine that hold the formwork 212. can be fused together and integrated.

FIG. 6 is a flowchart showing an exemplary flow of this process. As shown in FIG. 6, the integration of the thin pieces in this process includes a step of preheating the spread chopped sheet 100 and film 410 (step S610), a step of bumping the chopped sheet 100 (step S620), and a step of bumping the chopped sheet 100 (step S620). The process may include a step of heating and pressurizing the chopped sheet 100 (step S630), and a step of cooling the heated and pressurized chopped sheet 100 (step S640). Although FIG. 6 shows that bumping (step S620) is performed after preheating (step S610), the order is not limited, and bumping (step S620) may be performed before preheating (step S610). . Further, preheating (step S610) and bumping (step S620) may not be performed.

3-1. Preheating step (step S610)
In this step, the spread chopped sheets 100 and film 410 are preheated. Thereby, bumping and integration performed later can be performed more effectively in a shorter time.

Preheating conditions are not particularly limited. From the viewpoint of performing bumping and integration more effectively, the preheating temperature is preferably higher than the melting point of the first thermoplastic resin and the second thermoplastic resin, which have a higher melting point. On the other hand, the preheating temperature is preferably set to a temperature at which decomposition of the resin is unlikely to occur. For example, the preheating temperature is preferably 1°C or more and 80°C or less higher than the melting point of the above-mentioned high melting point, more preferably 3°C or more and 70°C or less, and 5°C or more and 60°C higher. It is more preferable to set the temperature to a higher temperature than below.

Similarly, the duration of preheating may be set to a condition that allows for more effective bumping and integration and less likely to cause decomposition of the resin. For example, the duration of preheating is preferably 2 minutes or more and 20 minutes or less, more preferably 4 minutes or more and 20 minutes or less, and even more preferably 6 minutes or more and 20 minutes or less.

Although the chopped sheet 100 and the film 410 may be pressurized during preheating, since it is not necessary to integrate the chopped sheet 100 in this step, pressurization is not necessarily necessary. For example, the pressure during preheating is preferably 0 MPa or more and 1 MPa or less, more preferably 0 MPa or more and 0.7 MPa or less, and even more preferably 0 MPa or more and 0.5 MPa or less.

3-2. Bumping step (step S620)
In this step, the spread chopped sheets 100 are repeatedly pressurized and depressurized in a short period of time. In this step, by removing the air between the chopped sheets 100, it is possible to suppress the generation of whitened areas due to the remaining air. The above-mentioned whitening site is more likely to occur due to the application of the film 410, and the more the weight of the film 410 is applied, the higher the frequency of occurrence tends to be. Therefore, from the viewpoint of suppressing the occurrence of whitening sites, it is preferable to include a bumping step.

Bumping conditions are not particularly limited. From the viewpoint of efficiently suppressing the occurrence of whitening sites, the pressure during pressurization is preferably 0.5 MPa or more and 20 MPa or less, more preferably 1 MPa or more and 20 MPa, and even more preferably 3 MPa or more and 20 MPa. preferable. The pressure at the time of depressurization can be atmospheric pressure, but may be 1/5 or less of the pressure at the time of pressurization.

The time required for one cycle of one pressurization and one depressurization may be determined depending on the air removal efficiency, but for example, it is preferably 0.1 seconds or more and 20 seconds or less, and 0.1 seconds or more and 10 seconds or less. The time is more preferably 0.1 seconds or more and 7 seconds or less. The number of cycles in this step may also be determined depending on the air removal efficiency, but for example, it is preferably 1 to 20 times, more preferably 3 to 20 times, and 5 to 20 times. More preferred.

3-3. Heating and pressurizing step (step S630)
In this step, the chopped sheets 100 spread inside the mold 212 are integrated with each other by heating and pressurizing the chopped sheets 100. In this step, when the chopped sheets 100 are integrated, the reinforcing fibers 110 are caused to move due to the flow of the second polyolefin resin described above, so that a molded product having a marble-like appearance can be obtained.

The heating temperature is a temperature higher than the melting point of the one having a higher melting point among the first thermoplastic resin and the second thermoplastic resin (a temperature higher than the melting point of the first thermoplastic resin and higher than the melting point of the second thermoplastic resin). temperature). On the other hand, the heating temperature is preferably a temperature at which decomposition of the resin is unlikely to occur. For example, the heating temperature is preferably 1°C or more and 80°C or less higher than the melting point of the above-mentioned high melting point, more preferably 3°C or more and 70°C or less, and 5°C or more and 60°C higher. It is more preferable to set the temperature to a higher temperature than below. The pressurizing pressure is preferably 0.5 MPa or more and 20 MPa, more preferably 1 MPa or more and 20 MPa, and even more preferably 3 MPa or more and 20 MPa.

The duration of heating and pressurization may be such that the chopped sheets 100 are sufficiently integrated, and for example, it is preferably 30 seconds or more and 20 minutes or less, and more preferably 50 seconds or more and 20 minutes or less. Preferably, it is more preferably 1 minute or more and 20 minutes or less.
Note that the method of heating and pressurizing is not limited to a press molding method using a press molding machine. Examples of other heating and pressurizing methods include a press molding method using a double belt press machine, an autoclave method using an autoclave device, and the like.

3-4. Cooling step (step S640)
In this step, the chopped sheet 100 integrated by the heating and pressurization described above is cooled. From the viewpoint of suppressing the occurrence of whitening sites due to thermal contraction of the first polyolefin and the second polyolefin, it is preferable to cool the chopped sheet 100 while pressurizing it in this step. The effect of suppressing the occurrence of whitened areas due to pressure tends to be more likely to occur as the amount of the second polyolefin applied is larger. The temperature during cooling is preferably 5°C or more and 90°C or less, more preferably 5°C or more and 70°C or less. The pressurizing pressure at this time is preferably 0.5 MPa or more and 20 MPa or less, more preferably 1 MPa or more and 20 MPa or less.

Thereafter, a random sheet can be obtained by sufficiently cooling and then taking it out. The obtained random sheet has an appearance closer to marble than a conventional random sheet in which the orientation direction of the reinforcing fibers 110 originating from each chopped sheet is changed randomly.

4. Other Embodiments It should be noted that the above-mentioned embodiments show an example of the present invention, and the present invention is not limited to the above-mentioned embodiments. It goes without saying that each embodiment is also possible.

For example, after arranging the film, chopped sheets may be spread over the film, and then the chopped sheets may be integrated by heating and pressurizing. Thereby, it is also possible to produce a random sheet with different degrees of marble-like appearance on the front and back sides.

Further, pigments such as pigments and dyes may be added to the matrix resin of the chopped sheet or the film to be placed. Thereby, it is also possible to produce random sheets having a wide variety of color tones.

5. Applications The applications of the random sheets manufactured by the above method are not limited, but are lightweight and relatively strong, such as electrical parts, PC cases, mobile covers, automobile parts, motorcycle parts, furniture, partitions, screen walls, doors, sliding doors, etc. It is very useful in the application of articles that require the following. Furthermore, it is also very useful in applications that require good design, such as building materials such as wallpaper, flooring, and decorative boards.

The present invention will be explained in detail based on Examples, but the present invention is not limited to these Examples.

1. Preparation of random sheet 1-1. Preparation of materials 1-1-1. Using a chopped sheet tape cutter (manufactured by Hashima Co., Ltd., H510), chop a UD sheet (Mitsui Chemicals Co., Ltd.) into a length of 13 mm in the direction of fiber orientation x 12.5 mm in width in the direction perpendicular to the length direction. A chopped sheet was obtained by cutting TAFNEX ("TAFNEX" is a registered trademark of the company) manufactured by the company. This UD sheet contained polypropylene and carbon fibers, had a fiber volume fraction (Vf) of 50% by volume, and a thickness of 160 μm.

1-1-2. film 1
0.1% by weight of peroxide (Perbutyl P-40, manufactured by NOF Corporation) was added to polypropylene (Prime Polypro J108M, manufactured by Prime Polymer Co., Ltd.) and thermally decomposed at 240°C to obtain a PP thermal decomposition product. . The melting point of this PP thermal decomposition product measured by the DSC method according to JIS K 7121 is 168°C, and the melt flow rate (MFR) measured at 230°C and a load of 2160 g according to ASTM D-1238 is 200. It was 0g/10min.

The above PP thermal decomposition product was heated and pressed for 10 minutes at 170° C. and 10 MPa using a press to obtain a polyolefin resin film 1 having a thickness of 55 μm.

1-1-3. film 2
A film 2 of polyolefin resin having a thickness of 100 μm was obtained in the same manner as in the production of film 1 except that the amount of the PP pyrolyzed product charged into the press was changed.

1-1-4. film 3
Polyamide 6 (manufactured by Toray Industries, Inc., Amilan CM1046, melting point announced by the manufacturer: 225°C) was heated and pressurized for 5 minutes at a temperature of 240°C and a pressure of 10 MPa using a press machine to form a thermoplastic resin film with a thickness of 100 μm. I got 1.

1-1-5. film 4
Terephthalic acid 2774g (16.7mol), isophthalic acid 1196g (7.2mol), 1,6-diaminohexane 2800g (24.1mol), benzoic acid 36.6g (0.3mol), hypophosphorous acid 5.7 g (5.4×10 ⁻² mol) of sodium monohydrate and 545 g of distilled water were placed in an autoclave having an internal capacity of 1 L, and the autoclave was purged with nitrogen. Stirring was started at 190°C, and the internal temperature of the autoclave was raised to 250°C over 3 hours. At this time, the internal pressure of the autoclave was increased to 3.03 MPa. After continuing the reaction for 1 hour, the low condensate was extracted by releasing it into the atmosphere from a spray nozzle installed at the bottom of the autoclave. The extracted low condensate was cooled to room temperature (23°C), then ground to a particle size of 1.5 mm or less using a grinder, and dried at 110°C for 24 hours. The water content of the obtained low condensate was 4100 ppm, and the intrinsic viscosity [η] was 0.15 dl/g. Next, this low condensate was placed in a plated solid phase polymerization apparatus, and after purging with nitrogen, the temperature was raised to 180° C. over about 1 hour and 30 minutes. Thereafter, the reaction was carried out for 1 hour and 30 minutes, and the temperature was lowered to room temperature (23°C). Thereafter, polyamide resin (PA6T6I) was obtained by melt polymerization using a twin-screw extruder with a screw diameter of 30 mm and L/D = 36 at a barrel setting temperature of 330°C, a screw rotation speed of 200 rpm, and a resin supply rate of 10 kg/h. Ta.

The resulting polyamide resin had an intrinsic viscosity [η] of 1.0 dl/g, a melting point Tm of 330°C, and a heat of fusion (ΔH) of 51 J/g.

In addition, the intrinsic viscosity [η] of the above polyamide resin is determined by dissolving 0.5 g of the polyamide resin in 50 ml of 96.5% sulfuric acid solution and flowing down the resulting solution in seconds at 25°C ± 0.05°C. The number was measured using an Ubbelohde viscometer and calculated based on the formula: [η]=ηSP/(C(1+0.205ηSP)).
[η]: Intrinsic viscosity (dl/g)
ηSP: Specific viscosity C: Sample concentration (g/dl)
t: Number of seconds for sample solution to flow down (seconds)
t0: Number of seconds for blank sulfuric acid flow (seconds)
ηSP=(t-t0)/t0

Further, the melting point Tm and heat of fusion (ΔH) of the polyamide resin were measured using a differential scanning calorimeter (Model DSC220C, manufactured by Seiko Instruments Inc.). Specifically, about 5 mg of polyamide resin was sealed in an aluminum pan for measurement, and the pan was set in a differential scanning calorimeter. Then, it was heated from room temperature to 350°C at a rate of 10°C/min. To completely melt the resin, it was held at 360°C for 3 minutes and then cooled to 30°C at 10°C/min. After leaving it at 30°C for 5 minutes, it was heated a second time to 360°C at 10°C/min. The temperature (°C) of the endothermic peak in this second heating was defined as the melting point (Tm) of the polyamide resin. The heat of fusion ΔH was determined from the area of the endothermic peak of crystallization during the first temperature raising process according to JIS K7122.

The polyamide resin was heated and pressurized for 5 minutes at 340° C. and 10 MPa using a press to obtain a thermoplastic resin film 3 having a thickness of 80 μm.

1-1-6. Thermoplastic resin pellets 1
The above PP thermal decomposition product was granulated and pelletized to obtain cylindrical thermoplastic resin pellets 1 having a length of 4000 μm, a diameter and width of 3000 μm.

1-2. Preparation of random sheet 1-2-1. Production of random sheet 1 (Example)
In a mold measuring 220 mm long x 220 mm wide, 65 g of the above chopped sheet was spread so that the orientation direction of the fibers was random. Thereafter, the film 1 cut to a length of 220 mm x width of 220 mm was placed on the spread chopped sheet.

The above mold was placed in a press machine (manufactured by Toyo Seiki Seisakusho Co., Ltd., mini test press machine), and press molding was performed under the following molding conditions to obtain a random sheet 1 with a length of 220 mm, a width of 220 mm, and a thickness of 1.1 mm. .
-Molding condition-
Preheating: Temperature 175°C, pressure 0.3MPa, 8 minutes Bumping: Temperature 175°C, pressure 10MPa, 5 times Pressure holding: Temperature 175°C, pressure 10MPa, 2 minutes Cooling: Temperature 15°C, pressure 10MPa, 3 minutes Note that preheating , bumping, pressure holding, and cooling were performed in this order.

1-2-2. Production of random sheet 2 (Example)
Random Sheet 2 was obtained in the same manner as in the production of Random Sheet 1 except that Film 1 was changed to Film 2. FIG. 7 shows image data obtained by imaging the appearance of the chopped sheets immediately after being spread. Further, image data obtained by capturing an image of the appearance of the random sheet 2 is shown in FIG.

1-2-3. Production of random sheet 3 (Example)
Random sheet 3 was obtained in the same manner as random sheet 1 except that bumping was not performed.

1-2-4. Production of random sheet 4 (comparative example)
Random Sheet 4 was obtained in the same manner as in the production of Random Sheet 1 except that Film 1 was not placed. FIG. 9 shows image data obtained by imaging the appearance of the random sheet 4.

1-2-5. Production of random sheet 5 (comparative example)
Random sheet 5 was obtained in the same manner as in the production of random sheet 1 except that the same amount of the above pellets was sprinkled instead of film 1.

1-2-6. Production of Random Sheet 6 to Random Sheet 7 (Example)
Random sheets 6 to 7 were obtained in the same manner as in the production of random sheet 1, except that film 1 was changed to films 2 to 4.

1-3. Evaluation 1-3-1. Appearance evaluation of degree of marble appearance The image data obtained by imaging marble (Figure 10) was set as the target appearance, and 5 trained scorers assigned 10 points to Figure 10 and 1 point to Figure 7 before pressing. The appearance of each random sheet was evaluated in units of one point. The average score of the evaluations by the five evaluators was taken as the appearance evaluation score of the random sheet.

1-3-2. Appearance evaluation of whitening site The surface of each random sheet was visually observed, and the whitening site on the surface of each sheet was evaluated according to the following evaluation criteria.
-Evaluation criteria-
◎: There are no visible whitening areas. ○: There are visible whitening areas, but all of them are less than 2.0 mm in size. △: There are 1 to 5 whitening areas with a size of 2.0 mm or more. Less than or equal to present ×: 5 or more whitening areas with a size of 2.0 mm or more are present

Table 1 shows the type of additive added to the chopped sheet, the resin type, MFR and amount of the additive added, the thickness of the film when it was placed, and the appearance evaluation score. Note that when polyamide resin is used as an additive, the MFR is not listed in the table because the standardized evaluation criteria for MFR are different from those for polypropylene, and comparison under the same conditions is not possible.

As is clear from Table 1, when chopped sheets containing polyolefin resin are laid down and then sheets containing polyolefin resin are arranged to produce a random sheet, the appearance becomes more marble-like. It is also seen that by performing bumping, it is possible to further suppress the occurrence of whitening sites.

The random sheets according to the invention have a better appearance than conventional random sheets. Therefore, the present invention is expected to expand the possibilities of using random sheets in applications that particularly require good design, and contribute to the development of various fields related to random sheets.

100 Chopped sheet 110 Reinforcing fiber 120 Matrix resin 210 Lower mold 212 Formwork 220 Upper mold 410 Film

Claims (5)

A step of laying thin pieces of fiber-reinforced resin in a flat shape, which are obtained by impregnating a plurality of reinforcing fibers arranged in one direction with a first polyolefin resin;
arranging a film containing a second polyolefin resin in contact with the spread thin pieces;
heating and pressurizing the thin pieces on which the film is placed to integrate the thin pieces;
Method of manufacturing random sheets. The method for producing a random sheet according to claim 1, wherein the amount of the film applied in the step of arranging the film is 20.0 g/m ² or more. The method for producing a random sheet according to claim 1 or 2, wherein the first polyolefin resin and the second polyolefin resin are both polypropylene. Any one of claims 1 to 3, wherein the second polyolefin resin is polypropylene having a melt flow rate (MFR) of 5.0 g/10 min or more as measured at 230° C. and a load of 2160 g in accordance with ASTM D-1238. The method for producing a random sheet according to item 1. The step of integrating the thin pieces includes a bumping step of removing air from gaps between the spread thin pieces;
heating and pressurizing the spread thin pieces and the film to a temperature higher than the melting point of the first polyolefin resin and higher than the melting point of the second polyolefin resin to integrate the thin pieces; including in order,
The method for producing a random sheet according to any one of claims 1 to 4.

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