Random sheet manufacturing method

Abstract

The present invention provides a method for manufacturing a random sheet having a better external appearance. This random sheet manufacturing method comprises: a step for spreading, in a planar manner, thin pieces of a fiber-reinforced resin obtained by impregnating a plurality of reinforcing fibers arranged oriented in one direction with a first thermoplastic resin; a step for adding a powder of a second thermoplastic resin to the thin pieces which have been spread; and a step for heating and pressurizing the thin pieces to which the powder has been added and unifying the thin pieces with each other.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a random sheet. [Background technology]

[0002] A thin-film fiber-reinforced resin (hereinafter simply referred to as a "Uni-Direction (UD) sheet") is known, which contains a plurality of reinforcing fibers oriented in one direction and a resin composition (matrix resin) impregnated into the reinforcing fibers. This UD sheet is cut into thin pieces, which are then randomly arranged in a two-dimensional pattern and heated and pressurized to form a sheet. This produces a random sheet, in which blocks of reinforcing fibers oriented in one direction are randomly arranged (see, for example, Patent Document 1). Random sheets have a unique marble-like appearance and are highly moldable (shapeable) by stamp molding, press molding, and other processes, and are therefore expected to be used in a variety of applications.

[0003] Patent Document 1 describes a method for producing a random sheet, in which the above-mentioned flakes using carbon fiber as the reinforcing fiber are laid out in a plane, a thermoplastic resin film of a transparent resin is temporarily attached by roll molding, and then hot pressing and cold pressing are performed. According to Patent Document 1, in the above method, when the molten transparent resin enters between the flakes during hot pressing, the carbon fibers are pulled and moved, so that the shape of the flakes can be distorted to obtain a random sheet with improved design. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 009125 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 describes that a highly decorative random sheet can be obtained by temporarily adhering a transparent thermoplastic resin film by roll molding and then performing hot press molding. However, according to the inventors' investigations, even with the method described in Patent Document 1, the appearance of the obtained random sheet was sometimes far from the appearance of a flowing marble-like pattern.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for producing a random sheet with a better appearance. [Means for solving the problem]

[0007] One embodiment of the present invention for solving the above problems relates to the following methods for producing a random sheet [1] to [6]. [1] A step of laying out thin pieces of fiber-reinforced resin in a plane, the thin pieces being formed by impregnating a plurality of reinforcing fibers oriented in one direction with a first thermoplastic resin; applying powder of a second thermoplastic resin to the spread flakes; A method for producing a random sheet, comprising a step of heating and pressurizing the flakes to which the powder has been applied to integrate the flakes together. [2] In the step of applying the powder, the amount of the powder applied is 20.0 g / m 2 The method for producing a random sheet according to [1] is as described above. [3] The method for producing a random sheet according to [1] or [2], wherein the first thermoplastic resin and the second thermoplastic resin are both polyolefin resins. [4] The method for producing a random sheet according to any one of [1] to [3], wherein the first thermoplastic resin and the second thermoplastic resin are both polypropylene. [5] The method for producing a random sheet according to any one of [1] to [4], wherein the second thermoplastic resin is polypropylene having a melt flow rate (MFR) of 5.0 g / 10 min or more measured at 230°C under a load of 2160 g in accordance with ASTM D-1238. [6] The step of integrating the flakes together includes a bumping step of removing air from gaps between the spread flakes and the powder; and a step of heating and pressurizing the spread flakes and the powder to a temperature equal to or higher than the melting point of the first thermoplastic resin and equal to or higher than the melting point of the second thermoplastic resin to integrate the flakes together, in this order. A method for producing a random sheet according to any one of [1] to [5]. [Effects of the Invention]

[0008] The present invention provides a method for producing random sheets with better appearance. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a flowchart showing a method for manufacturing a random sheet according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the structure of a chopped sheet used in the production of a random sheet. [Figure 3] FIG. 3 is a schematic diagram showing how chopped sheets are laid out inside a mold in the first step of the random sheet manufacturing method according to one embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing how thermoplastic resin powder is applied to chopped sheets spread inside a mold in the second step of the random sheet manufacturing method according to one embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram showing how the chopped sheet is heated and pressed in the second step of the random sheet manufacturing method according to one embodiment of the present invention. [Figure 6] FIG. 6 is a flowchart showing the flake integration sub-process in the random sheet manufacturing method according to one embodiment of the present invention. [Figure 7] FIG. 7 shows image data of the appearance of the chopped sheets scattered during the production of the random sheet 1 in the example. [Figure 8] FIG. 8 shows image data of the appearance of the random sheet 1 obtained in the example. [Figure 9] FIG. 9 shows image data of the appearance of the random sheet 9w obtained in the example. [Figure 10] FIG. 10 shows image data obtained by capturing an image of a marble. DETAILED DESCRIPTION OF THE INVENTION

[0010] Exemplary embodiments of the present invention will now be described.

[0011] Fig. 1 is a flowchart showing a method for manufacturing a random sheet according to one embodiment of the present invention. As shown in Fig. 1, the manufacturing method according to this embodiment includes a step of laying out thin flakes of fiber-reinforced resin (step S110), a step of applying powder to the laid out thin flakes (step S120), and a step of integrating the thin flakes by applying heat and pressure (step S130).

[0012] 1. Spreading process (process S110) In the first step, thin pieces of fiber-reinforced resin are laid out in two dimensions.

[0013] 1-1. Fiber-reinforced resin thin pieces Fig. 2 is a schematic diagram showing an outline of the above-mentioned thin piece of fiber-reinforced resin (hereinafter simply referred to as "chopped sheet"). As shown in Fig. 2, chopped sheet 100 is a thin piece of UD sheet in which a plurality of reinforcing fibers 110 aligned in one direction are impregnated with matrix resin 120. Chopped sheets can be produced, for example, by cutting a UD sheet to a predetermined size.

[0014] The material of the reinforcing fibers 110 is not particularly limited. For example, carbon fiber, glass fiber, aramid fiber, alumina fiber, silicon carbide fiber, boron fiber, metal fiber, etc. can be used as the reinforcing fibers. Of these, carbon fiber and glass fiber are preferred, and carbon fiber is more preferred.

[0015] From the viewpoint of sufficiently enhancing the effect of improving strength by the reinforcing fibers, the reinforcing fibers 110 preferably have an average diameter of 1 μm or more and 20 μm or less, and more preferably 4 μm or more and 10 μm or less.

[0016] The reinforcing fibers 110 may also be subjected to a sizing treatment using a sizing agent.

[0017] The sizing agent is not particularly limited, but a modified polyolefin is preferred, and a modified polyolefin containing a metal carboxylate is more preferred. The modified polyolefin is, for example, an unmodified polyolefin in which a carboxylic acid group, a carboxylic anhydride group, or a carboxylic ester group is grafted onto the polymer chain of the unmodified polyolefin, and a salt is formed between the functional group and a metal cation. The α-olefin constituting the modified polyolefin may be derived from a fossil fuel, a biomass material, or a mixture thereof.

[0018] The unmodified polyolefin is preferably an ethylene polymer containing 50 mol% or more of structural units derived from ethylene, or a propylene polymer containing 50 mol% or more of structural units derived from propylene. Examples of the ethylene polymer include ethylene homopolymers and copolymers of ethylene with an α-olefin having from 3 to 10 carbon atoms. Examples of the propylene polymer include propylene homopolymers and copolymers of propylene with ethylene or an α-olefin having from 4 to 10 carbon atoms. The unmodified polyolefin is preferably homopolypropylene, homopolyethylene, ethylene-propylene copolymer, propylene-1-butene copolymer, or ethylene-propylene-1-butene copolymer. The α-olefins constituting these modified polyolefins may be derived from fossil fuels, biomass materials, or mixtures thereof.

[0019] The content of the reinforcing fibers 110 relative 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 even more preferably 35% by mass or more and 70% by mass or less.

[0020] The content of reinforcing fibers 110 relative to the total volume of chopped sheet 100 is preferably 10% by volume or more and 70% by volume or less, more preferably 15% by volume or more and 60% by volume or less, and even more preferably 20% by volume or more and 60% by volume or less.

[0021] The type of matrix resin 120 is not particularly limited as long as it is a thermoplastic resin (first thermoplastic resin). The first thermoplastic resin may be a crystalline resin or an amorphous resin. These thermoplastic resins may be derived from fossil fuels, biomass materials, or a mixture thereof.

[0022] Examples of the first thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, polybutene, and poly4-methyl-1-pentene, polyamide resins, polyester resins, polystyrene resins, thermoplastic polyimide resins, polyamideimide resins, polycarbonate resins, polyphenylene ether resins, polyphenylene sulfide resins, polyacetal resins, acrylic resins, polyetherimide resins, polysulfone resins, polyether ketone resins, polyether ether ketone resins, polyarylate resins, polyether nitrile resins, vinyl chloride resins, ABS resins, and fluororesins.

[0023] Of these, polyamide resins and polyolefin resins are preferred, and polyolefin resins are more preferred from the viewpoint of enabling molding at lower temperatures and further increasing production efficiency, and polypropylene is even more preferred from the viewpoint of being lightweight, having high rigidity, low water absorption, and further having improved chemical resistance and chemical stability.

[0024] The matrix resin 120 may be a resin composition containing additives, such as known fillers (inorganic fillers and organic fillers), pigments, dyes, weather-resistant stabilizers, heat-resistant stabilizers, antistatic agents, antislip agents, antioxidants, antifungal agents, antibacterial agents, flame retardants, and softeners.

[0025] Furthermore, the matrix resin 120 may contain other components such as resins other than those mentioned above, or short fibers having a length shorter than the reinforcing fibers mentioned above.

[0026] The content of matrix resin 120 relative 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, even more preferably 35% by mass or more and 70% by mass or less, and particularly preferably 40% by mass or more and 65% by mass or less.

[0027] The chopped sheet 100 may be a single-layered thin piece, or may be a laminate of multiple aligned fiber layers with different orientation directions of the reinforcing fibers 110. When the chopped sheet 100 is a laminate, the number of aligned fiber layers (number of layers) included in one chopped sheet 100 is preferably 2 to 5, more preferably 2 to 3, and even more preferably 2, from the viewpoint of preventing unevenness during molding of the random sheet. Furthermore, when the chopped sheet 100 is a laminate, the average number of layers of the entire stack of chopped sheets is preferably 1.25 to 5.0, more preferably 1.5 to 4.0, and even more preferably 1.75 to 2.5. Furthermore, from the viewpoint of further increasing the randomness of the orientation direction of the reinforcing fibers in the random sheet, the angle between the orientation direction of the reinforcing fibers of one aligned fiber layer and the orientation direction of the reinforcing fibers of another aligned fiber layer is preferably 180° / n (n is the number of aligned fiber layers) ±10°.

[0028] The length (L) of the chopped sheet 100 in the orientation direction of the reinforcing fibers 110 is preferably 1 mm to 80 mm, more preferably 3 mm to 60 mm, and even more preferably 5 mm to 50 mm. By setting the length (L) of the chopped sheet 100 within the above range, the bending modulus of the random sheet can be increased and an appearance closer to that of marble can be achieved. Note that when the chopped sheet 100 is a laminate of multiple layers with different orientation directions of the reinforcing fibers, the length (L) of the chopped sheet 100 is defined as the length in the orientation direction of the reinforcing fibers 110 measured for one layer determined to have the longest length (L). The length direction of the chopped sheet 100 refers to the direction in which the reinforcing fibers 110 are oriented, and the length of the chopped sheet 100 refers to the maximum distance between both ends in the length direction.

[0029] The width (W) of the chopped sheet 100 in the direction perpendicular to the longitudinal direction is preferably 1 mm to 50 mm, more preferably 3 mm to 30 mm, and even more preferably 5 mm to 20 mm. By setting the width (W) of the chopped sheet 100 within the above range, the bending modulus of the random sheet can be increased and an appearance closer to that of marble can be produced.

[0030] Furthermore, the aspect ratio (L / W) of chopped sheet 100, which is the ratio of length (L) to width (W), is preferably 0.1 or more and 10.0 or less, more preferably 0.3 or more and 8.0 or less, and even more preferably 0.5 or more and 6.0 or less. By setting the aspect ratio (L / W) of chopped sheet 100 within the above range, the bending modulus of elasticity of the random sheet can be further increased, and an appearance closer to that of marble can be produced.

[0031] The thickness of the chopped sheet 100 is preferably 0.1 mm or more and 1.0 mm or less, and more preferably 0.2 mm or more and 0.5 mm or less. By making the thickness 0.1 mm or more, the productivity of the random sheet can be further improved. By making the thickness 1.0 mm or less, it is possible to make it difficult for unevenness to occur during the molding of the random sheet.

[0032] The planar shape of the chopped sheet 100 is not particularly limited, and can be a square, a rectangle, a parallelogram, a trapezoid and other quadrilateral shapes, an equilateral triangle and other triangular shapes, other polygonal shapes, a circle, an oval, and any other shape.

[0033] 1-2.Paving In this step, the chopped sheet 100 is spread out flatly. For example, the chopped sheet 100 may be spread out tightly inside a press molding frame or the like.

[0034] FIG. 3 is a schematic diagram showing how chopped sheets 100 are laid inside a formwork 212 in this step. As shown in FIG. 3, in this step, chopped sheets 100 are scattered randomly inside the formwork 212 without any gaps. At this time, it is preferable to lay chopped sheets 100 so that they are stacked in multiple layers to prevent gaps from forming. Furthermore, it is preferable to lay chopped sheets 100 so that the orientation of the reinforcing fibers in each chopped sheet 100 is random (the orientation of the reinforcing fibers contained in the chopped sheets 100). For example, the orientation of chopped sheets 100 may be adjusted manually, or chopped sheets 100 that have been shaken in advance to have uneven orientations may be scattered inside the formwork.

[0035] The planar shape and thickness of the chopped sheets 100 laid out may be determined in accordance with the shape of the random sheet to be formed.

[0036] 2. Powder application step (step S120) Next, a powder of thermoplastic resin is applied to the chopped sheets 100 that have been spread out.

[0037] 4 is a schematic diagram showing how thermoplastic resin powder 410 is applied to chopped sheet 100 spread inside mold 212 in this process. The method of applying powder 410 is not particularly limited, and powder 410 may be applied from a spreader 420 as shown in FIG. 4, or may be applied manually.

[0038] The powder 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. This flow then causes the reinforcing fibers 110 to flow and move from the matrix resin 120 of the chopped sheet 100, which is also melting. This is thought to result in a marble-like appearance with irregularly arranged streamlined patterns that deviate from the original shape of the chopped sheet 100. The powder 410 is more likely to penetrate into the gaps in the chopped sheet 100 than a resin film. Therefore, the molten powder 410 is more likely to penetrate into the gaps in the chopped sheet 100 before the matrix resin 120 melts and flows, which is thought to more effectively move the reinforcing fibers 110 and create an appearance closer to marble.

[0039] The type of thermoplastic resin (second thermoplastic resin) constituting the powder is not particularly limited. The second thermoplastic resin may be a crystalline resin or a non-crystalline resin.

[0040] Examples of the second thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, polybutene, and poly4-methyl-1-pentene, polyamide resins, polyester resins, polystyrene resins, thermoplastic polyimide resins, polyamideimide resins, polycarbonate resins, polyphenylene ether resins, polyphenylene sulfide resins, polyacetal resins, acrylic resins, polyetherimide resins, polysulfone resins, polyether ketone resins, polyether ether ketone resins, polyarylate resins, polyether nitrile resins, vinyl chloride resins, ABS resins, and fluororesins.

[0041] Among these, from the viewpoint of improving fluidity during melting, the second thermoplastic resin is preferably a polyolefin resin, more preferably polypropylene. In this specification, polyolefin resin means a resin in which the proportion 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%, and polypropylene means a resin in which the proportion of structural units derived from propylene is 50 mol% or more when the total amount of structural units derived from all monomers is 100 mol%. The same applies to other resins.

[0042] Furthermore, from the viewpoint of making the appearance of the random sheet more similar to marble, the second thermoplastic resin preferably has a melting point in the range of 0° C. to 30° C. inclusive, more preferably in the range of 0° C. to 15° C. inclusive, and even more preferably in the range of 0° C. to 10° C. inclusive. Furthermore, from the viewpoint of making the appearance of the random sheet more similar to marble, the melting point of the second thermoplastic resin is preferably such that the absolute value of the difference in melting points is within a predetermined range and is equal to or lower than the melting point of the first thermoplastic resin.

[0043] If the melting points of the first thermoplastic resin and the second thermoplastic resin are not too far apart, the melting of the matrix resin 120 of the chopped sheet 100 and the melting and flow of the powder 410 can occur almost simultaneously when the chopped sheet 100 is heated and pressurized in the next step. This makes it possible to more effectively change the appearance due to the flow of the powder 410. Furthermore, if the melting points are not too far apart, the thermal decomposition of one resin can be suppressed when the heating temperature is increased to melt the other resin with a higher melting point.

[0044] In addition, the second thermoplastic resin is preferably compatible with the first thermoplastic resin from the viewpoint of suppressing the occurrence of whitened areas due to insufficient mixing of the resins. In this specification, "compatible" means that a single phase is formed when the two resins are heated and mixed above their melting points and cooled to 25°C. Furthermore, it is more preferable that the two resins are identical. In this specification, "same" means that the monomer composition, weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the two resins are identical within the measurement error range.

[0045] For example, it is preferable that the first thermoplastic resin and the second thermoplastic resin are both polyolefin resins, and it is more preferable that they are both polypropylene, from the viewpoint of improving the visibility of the marble-like appearance formed by the multiple fibers and of reducing water absorbency and further improving dimensional stability.

[0046] From the viewpoint of more effectively causing the movement of the reinforcing fibers 110 due to the flow of the powder 410, it is preferable that the second thermoplastic resin have a higher melt flow rate (MFR). For example, when the second thermoplastic resin is polypropylene, the MFR of the polypropylene measured in accordance with ASTM D-1238 at 230°C under a load of 2160 g is preferably 5.0 g / 10 min or more, more preferably 30.0 g / 10 min or more, and even more preferably 100.0 g / 10 min or more. Although there are no particular limitations on the upper limit of the MFR of polypropylene, it can be set to 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 a synthesized polypropylene with a low MFR (or a commercially available polypropylene) to cause moderate thermal decomposition.

[0047] The smaller the powder 410, the easier it is for it to penetrate into the gaps in the chopped sheet 100 during heating, and the easier it is for the reinforcing fibers 110 to move due to flow. Furthermore, the smaller the powder, the easier it is to distribute uniformly over the chopped sheet 100. From the above viewpoint, the powder 410 preferably has a median diameter (D50) of 700 μm or less, more preferably 600 μm or less, and even more preferably 500 μm or less, at which the cumulative amount of particles based on mass in the particle size distribution is 50%. From the same viewpoint, the powder 410 preferably has a particle diameter (D90) of 1400 μm or less, more preferably 1500 μm or less, and even more preferably 1000 μm or less, at which the cumulative amount of particles based on mass is 90%.

[0048] On the other hand, larger powder 410 makes it easier to move reinforcing fibers 110 during flow, and can more effectively change the appearance. Also, larger powder 410 is less likely to scatter on the scattering surface and is easier to scatter uniformly. From the above viewpoint, the median diameter (D50) of powder 410, at which the cumulative amount of particles based on mass in the particle size distribution is 50%, is preferably 50 μm or more, more preferably 80 μm or more, and even more preferably 100 μm or more. From the same viewpoint, the particle diameter (D10) of powder 410, at which the cumulative amount of particles based on mass is 10%, is preferably 40 μm or more, and even more preferably 50 μm or more.

[0049] The amount of powder 410 applied is not particularly limited, but from the viewpoint of more effectively causing the change in appearance due to the flow, it is set to 20.0 g / m 2 It is preferable that the content is 40.0 g / m or more. 2 More preferably, it is 100.0 g / m or more. 2 Although the upper limit of the amount of powder 410 to be applied is not particularly limited, from the viewpoint of suppressing the occurrence of warping due to an excessive amount of resin, it is preferable that the upper limit be 1000.0 g / m 2 and 500.0 g / m 2 It is preferable that the density is 300.0 g / m or less. 2 It is more preferable to set the following:

[0050] 3. Integration step (step S130) Next, the chopped sheets 100 that have been spread out and to which the powder 410 has been added are heated and pressurized to integrate the chopped sheets 100. This results in a random sheet in which the reinforcing fibers 110 are randomly oriented.

[0051] Fig. 5 is a schematic diagram showing the state in which chopped sheet 100 is heated and pressurized in this process. As shown in Fig. 5, by heating and pressing lower mold 210 and upper mold 220 of the press molding machine, which hold mold frame 212, together, chopped sheet 100 spread inside mold frame 212 can be fused together and integrated.

[0052] 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 may include a step of preheating the laid chopped sheet 100 and powder 410 (step S610), a step of bumping the chopped sheet 100 (step S620), 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). Note that FIG. 6 shows that bumping (step S620) is performed after preheating (step S610), but the order of these steps is not limited, and bumping (step S620) may be performed before preheating (step S610). Also, preheating (step S610) and bumping (step S620) may not be performed.

[0053] 3-1. Preheating step (step S610) In this step, the chopped sheet 100 and the powder 410 that have been laid out are preheated, which allows the subsequent bumping and integration to be carried out more efficiently and in a shorter time.

[0054] The preheating conditions are not particularly limited. From the viewpoint of more effective bumping and integration, the preheating temperature is preferably higher than the melting point of either the first thermoplastic resin or the second thermoplastic resin, whichever has the higher melting point. On the other hand, the preheating temperature is preferably set to a temperature at which decomposition of the resins is unlikely to occur. For example, the preheating temperature is preferably 1°C to 80°C higher than the melting point of the resin with the higher melting point, more preferably 3°C to 70°C higher, and even more preferably 5°C to 60°C higher.

[0055] Similarly, the duration of preheating should be set so that bumping and integration are performed effectively and decomposition of the resin is unlikely to occur. 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.

[0056] During preheating, chopped sheet 100 and powder 410 may be pressed, but pressurization is not necessarily required because there is no need to integrate chopped sheet 100 in this step. 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.

[0057] 3-2. Bumping step (step S620) In this process, the chopped sheets 100 are repeatedly pressurized and depressurized in a short period of time. In this process, air is removed from between the chopped sheets 100, thereby preventing the occurrence of whitened areas due to remaining air. The application of powder 410 makes the above-mentioned whitened areas more likely to occur, and the more powder 410 is applied, the more frequently they occur. Therefore, from the perspective of preventing the occurrence of whitened areas, it is preferable to include a bumping process.

[0058] The bumping conditions are not particularly limited. From the viewpoint of efficiently suppressing the occurrence of whitened portions, 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 or less, and even more preferably 3 MPa or more and 20 MPa or less. The pressure during depressurization can be atmospheric pressure, but may also be 1 / 5 or less of the pressure during pressurization.

[0059] The time required for one cycle of one pressurization and one depressurization may be determined depending on the efficiency of air removal, but is, for example, preferably from 0.1 to 20 seconds, more preferably from 0.1 to 10 seconds, and even more preferably from 0.1 to 7 seconds. The number of cycles in this step may also be determined depending on the efficiency of air removal, but is, for example, preferably from 1 to 20 times, more preferably from 3 to 20 times, and even more preferably from 5 to 20 times.

[0060] 3-3. Heating and pressurizing step (step S630) In this step, the chopped sheets 100 and the powder 410 are heated and pressurized to integrate the chopped sheets 100 laid inside the mold 212. In this step, when the chopped sheets 100 are integrated, the reinforcing fibers 110 are moved by the flow of the powder 410 described above, and a molded body having a marble-like appearance can be obtained.

[0061] The heating temperature is set to a temperature equal to or higher than the melting point of the first thermoplastic resin or the second thermoplastic resin that has the higher melting point (a temperature equal to or higher than the melting point of the first thermoplastic resin and a temperature equal to or higher than the melting point of the second thermoplastic resin). On the other hand, the heating temperature is preferably set to a temperature at which decomposition of the resins is unlikely to occur. For example, the heating temperature is preferably set to a temperature 0°C to 80°C higher than the melting point of the resin with the higher melting point, more preferably a temperature 3°C to 70°C higher, and even more preferably a temperature 5°C to 60°C higher. The pressure applied is preferably 0.5 MPa to 20 MPa, more preferably 1 MPa to 20 MPa, and even more preferably 3 MPa to 20 MPa.

[0062] The duration of heating and pressurization should be sufficient to ensure that the chopped sheet 100 is sufficiently integrated, and is preferably, for example, between 30 seconds and 20 minutes, more preferably between 50 seconds and 20 minutes, and even more preferably between 1 minute and 20 minutes. The method of heating and pressurizing is not limited to the press molding method using a press molding machine. Examples of other methods of heating and pressurizing include a press molding method using a double belt press machine and an autoclave method using an autoclave device.

[0063] 3-4. Cooling step (step S640) In this step, the chopped sheet 100 integrated by the above heating and pressurization is cooled. From the viewpoint of suppressing the occurrence of whitened areas due to thermal shrinkage of the first thermoplastic resin and the second thermoplastic resin, it is preferable to cool the chopped sheet 100 while applying pressure in this step. The effect of suppressing the occurrence of whitened areas due to the above pressure tends to be more easily achieved as the amount of the second thermoplastic resin applied increases. The temperature during cooling is preferably 5°C or higher and 90°C or lower, more preferably 5°C or higher and 70°C or lower. The pressure applied at this time is preferably 0.5 MPa or higher and 20 MPa or lower, more preferably 1 MPa or higher and 20 MPa or lower, and even more preferably 3 MPa or higher and 20 MPa.

[0064] The random sheet is then removed after being sufficiently cooled to obtain a random sheet. The random sheet obtained has an appearance closer to marble than conventional random sheets, in that the orientation directions of the reinforcing fibers 110 derived from each chopped sheet are randomly varied.

[0065] 4. Other embodiments It should be noted that the above-described embodiment is merely an example of the present invention, and the present invention is not limited to the above-described embodiment. It goes without saying that various other embodiments are possible within the scope of the concept of the present invention.

[0066] For example, powder can be applied to a limited area, then a chopped sheet can be laid on top of it, and the chopped sheet can be integrated by heating and pressing. This can also produce random sheets with different degrees of marble texture. In this case, powder can be first laid inside a frame, then a chopped sheet can be laid on top, and powder can be sprinkled on top again. Sheets with different degrees of marble texture can be produced by changing the amount of powder sprinkled on the front and back.

[0067] Furthermore, pigments and dyes may be added to the matrix resin of the chopped sheet or to the powder to be applied, which allows random sheets with a wide variety of colors to be produced.

[0068] 5.Applications The random sheet produced by the above method is not limited to specific applications, but is extremely useful for applications requiring light weight and relatively high strength, such as electrical components, PC housings, mobile phone covers, automobile parts, motorcycle parts, furniture, partitions, screen walls, doors, sliding doors, etc. It is also extremely useful for applications requiring design, such as building materials, wallpaper, flooring materials, and decorative boards. [Example]

[0069] The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

[0070] 1. Creating a random sheet 1-1.Preparing ingredients 1-1-1. Chopped Sheet 1 Using a tape cutter (Hashima Corporation, H510), a UD sheet (Mitsui Chemicals, Inc., TAFNEX ("TAFNEX" is a registered trademark of the company)) was cut into a size of 13 mm in the fiber orientation direction and 12.5 mm in width in the direction perpendicular to the length direction, to obtain chopped sheet 1. This UD sheet contained polypropylene and carbon fiber, had a fiber volume fraction (Vf) of 50% by volume, and was 160 μm thick.

[0071] 1-1-2. Chopped Sheet 2 Using a tape cutter (Hashima Corporation, H510), a UD sheet (Maruhachi Corporation, MCP1223) was cut into a size of 13 mm in the fiber orientation direction and 12.5 mm in width in the direction perpendicular to the length direction to obtain chopped sheet 2. This UD sheet contained polyamide 6 and carbon fiber, and had a fiber volume fraction (Vf) of 52% by volume and a thickness of 170 μm.

[0072] 1-1-3. Thermoplastic resin powder 1 Polypropylene (Prime Polypro J108M, manufactured by Prime Polymer Co., Ltd.) was pyrolyzed at 240°C with the addition of 0.1% by weight of peroxide (Perbutyl P-40, manufactured by NOF Corporation) to obtain a PP pyrolyzate. The melting point of this PP pyrolyzate, as measured by DSC in accordance with JIS K 7121, was 168°C, and the melt flow rate (MFR), as measured in accordance with ASTM D-1238 at 230°C under a load of 2160 g, was 200.0 g / 10 min.

[0073] This PP pyrolyzate was frozen to -90°C with liquid nitrogen and then pulverized using a 6875D freezer mill (manufactured by Spex). The pulverized product was then passed through a sieve with 1400 μm openings to remove unpulverized material, yielding Powder 1. The particle size of Powder 1 was measured using a dry sieving device, Air Jet Sieve e200LS (manufactured by Hosokawa Micron Corporation). The particle size of Powder 1 was found to have a mass-based D50 of 190 μm, a mass-based D90 of 458 μm, and a mass-based D10 of 68 μm.

[0074] 1-1-4. Thermoplastic resin powder 2 Polypropylene (Prime Polypro J106G, manufactured by Prime Polymer Co., Ltd.) was powdered in the same manner as for Powder 1 to obtain Thermoplastic Resin Powder 2. The melting point, melt flow rate (MFR), and mass-based particle size were measured in the same manner as for Powder 1. The melting point of this polypropylene was 168°C, and the melt flow rate (MFR) was 15 g / 10 min. The particle sizes of Powder 2 were D50 by mass of 245 μm, D90 by mass of 475 μm, and D10 by mass of 87 μm.

[0075] 1-1-5. Thermoplastic resin powder 3 Polyamide 6 (Amilan CM1046, manufactured by Toray Industries, Inc., melting point: 225°C) was frozen to -90°C with liquid nitrogen and then pulverized using a pulverizer (6875D freezer mill, manufactured by Spex). The pulverized material was then passed through a 1400 μm mesh sieve to remove any unpulverized material, yielding powder 3. The particle size of powder 3 was measured using a dry sieving device (Air Jet Sieve e200LS, manufactured by Hosokawa Micron Corporation). The mass-based D50 was 270 μm, the mass-based D90 was 491 μm, and the mass-based D10 was 71 μm.

[0076] 1-1-6. Thermoplastic resin film 1 The PP thermal decomposition product was heated and pressed for 10 minutes at 170° C. and a pressure of 10 MPa in a press to obtain a thermoplastic resin film 1 having a thickness of 55 μm.

[0077] 1-1-7. Thermoplastic resin film 2 Polyamide 6 (Amilan CM1046, manufactured by Toray Industries, Inc., melting point published by the manufacturer: 225°C) was heated and pressed in a press at a temperature of 240°C and a pressure of 10 MPa for 5 minutes to obtain a thermoplastic resin film 1 having a thickness of 100 μm.

[0078] 1-1-8. Thermoplastic resin film 3 Terephthalic acid 2774 g (16.7 mol), isophthalic acid 1196 g (7.2 mol), 1,6-diaminohexane 2800 g (24.1 mol), benzoic acid 36.6 g (0.3 mol), sodium hypophosphite monohydrate 5.7 g (5.4 × 10 -2 545 g of ethanol (mol) and distilled water were placed in a 1-L autoclave and purged with nitrogen. Stirring was initiated 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 raised to 3.03 MPa. The reaction was continued for 1 hour, and then the low condensation polymer was discharged into the atmosphere through a spray nozzle installed at the bottom of the autoclave and extracted. The extracted low condensation polymer was cooled to room temperature (23°C), crushed to a particle size of 1.5 mm or less in a crusher, and dried at 110°C for 24 hours. The obtained low condensation polymer had a water content of 4100 ppm and an intrinsic viscosity [η] of 0.15 dL / g. Next, this low condensation polymer was placed in a tray-type solid-state polymerization reactor, purged with nitrogen, and then heated to 180°C over approximately 1 hour and 30 minutes. The reaction was then continued for 1 hour and 30 minutes, and the temperature was then lowered to room temperature (23°C). Thereafter, melt polymerization was carried out in a twin-screw extruder with a screw diameter of 30 mm and L / D=36 at a barrel temperature of 330°C, a screw rotation speed of 200 rpm, and a resin feed rate of 10 kg / h to obtain a polyamide resin (PA6T6I).

[0079] The polyamide resin obtained 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.

[0080] The intrinsic viscosity [η] of the polyamide resin was calculated by dissolving 0.5 g of the polyamide resin in 50 ml of a 96.5% sulfuric acid solution, measuring the flow time of the resulting solution at 25°C ± 0.05°C using an Ubbelohde viscometer, and then calculating the intrinsic viscosity [η] 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 to flow (seconds) ηSP=(t-t0) / t0

[0081] The melting point (Tm) and heat of fusion (ΔH) of the polyamide resin were measured using a differential scanning calorimeter (DSC220C, manufactured by Seiko Instruments Inc.). Specifically, approximately 5 mg of polyamide resin was sealed in a measurement aluminum pan and placed in the differential scanning calorimeter. The polyamide resin was then heated from room temperature to 350°C at 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 the resin 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 during this second heating was taken as the melting point (Tm) of the polyamide resin. The heat of fusion (ΔH) was calculated from the area of ​​the endothermic peak of crystallization during the first heating process in accordance with JIS K7122.

[0082] The polyamide resin was heated and pressed for 5 minutes at 340° C. and a pressure of 10 MPa using a press to obtain a thermoplastic resin film 3 having a thickness of 80 μm.

[0083] 1-1-9. Thermoplastic resin pellets The PP thermal decomposition product was granulated and pelletized to obtain cylindrical thermoplastic resin pellets having a length of 4000 μm and a diameter of 3000 μm.

[0084] 1-2. Making a random sheet 1-2-1. Preparation of Random Sheet 1 (Example) 65 g of the above chopped sheet 1 was spread in a mold measuring 220 mm long x 220 mm wide so that the fiber orientation direction was random. Then, 8.8 g of powder 1 was evenly sprinkled on the spread chopped sheet. Image data obtained by photographing the appearance of the sprinkled chopped sheet are shown in Figure 7.

[0085] The above mold was placed in a press (a mini test press manufactured by Toyo Seiki Seisakusho Co., Ltd.) and press-molded under the following molding conditions to obtain a random sheet 1 measuring 220 mm in length, 220 mm in width, and 1.1 mm in thickness. Image data obtained by photographing the appearance of the random sheet 1 is shown in Figure 8. - Molding conditions - Preheating: 175°C, 0.3 MPa, 8 minutes Bumping: After five bumpings at a temperature of 175°C and a pressure of 10 MPa, Pressure retention: Temperature 175°C, pressure 10MPa, 2 minutes Cooling: 15°C, 10 MPa, 3 minutes The steps were carried out in the following order: preheating, bumping, pressure holding, and cooling.

[0086] 1-2-2. Preparation of Random Sheets 2 to 5 (Examples) Random Sheets 2 to 5 were obtained in the same manner as in the production of Random Sheet 1, except that the amount of Powder 1 to be sprinkled was changed.

[0087] 1-2-3. Preparation of Random Sheets 6 to 7 (Examples) Random Sheets 6 to 7 were obtained in the same manner as in the production of Random Sheet 1, except that Powder 1 was changed to Powder 2 and the amount of powder applied was changed.

[0088] 1-2-4. Preparation of random sheet 8 (Example) Random sheet 8 was obtained in the same manner as random sheet 1, except that bumping was not performed.

[0089] 1-2-5. Preparation of random sheet 9 (Example) In a mold measuring 220 mm long x 220 mm wide, 71 g of chopped sheet 2 was spread so that the fiber orientation direction was random. Then, 4.0 g of powder 3 was evenly spread on the spread chopped sheet.

[0090] The mold was placed in a press (a mini test press manufactured by Toyo Seiki Seisakusho Co., Ltd.) and press-molded under the following molding conditions to obtain a random sheet 9 measuring 220 mm in length, 220 mm in width and 1.1 mm in thickness. - Molding conditions - Preheating: 240°C, 0.3 MPa, 8 minutes Bumping: After five bumpings at a temperature of 240°C and a pressure of 10 MPa, Pressure retention: Temperature 240°C, pressure 10MPa, 2 minutes Cooling: 15°C, 10 MPa, 4 minutes The steps were carried out in the following order: preheating, bumping, pressure holding, and cooling.

[0091] 1-2-6. Preparation of random sheet 10 (comparative example) Random sheet 9 was obtained in the same manner as random sheet 1, except that powder 1 was not sprinkled. Image data obtained by photographing the appearance of random sheet 10 is shown in FIG.

[0092] 1-2-7. Preparation of random sheet 11 (comparative example) Random sheet 11 was obtained in the same manner as random sheet 1, except that powder 1 was not sprinkled, and instead film 1 (weighing 2.4 g) measuring 220 mm in length and 220 mm in width was placed on the chopped sheet.

[0093] 1-2-8. Preparation of random sheet 12 (comparative example) Random sheet 12 was obtained in the same manner as random sheet 1, except that the same amount of the above pellets was scattered instead of powder 1.

[0094] 1-2-9. Preparation of random sheet 13 (comparative example) Random sheet 13 was obtained in the same manner as random sheet 1, except that powder 1 was not sprinkled, and instead a film 2 (weighing 5.1 g) measuring 220 mm in length and 220 mm in width was placed on the chopped sheet.

[0095] 1-2-10. Preparation of random sheet 14 (comparative example) Random sheet 14 was obtained in the same manner as random sheet 1, except that powder 1 was not sprinkled, and instead a film 3 (weighing 5.1 g) measuring 220 mm in length and 220 mm in width was placed on the chopped sheet.

[0096] 1-2-11. Preparation of random sheet 15 (comparative example) Random sheet 15 was obtained in the same manner as random sheet 9, except that powder 3 was not sprinkled, and instead a film 2 (weighing 5.1 g) measuring 220 mm in length and 220 mm in width was placed on the chopped sheet.

[0097] 1-3.Evaluation 1-3-1. Marble appearance evaluation The image data (Fig. 10) obtained by photographing the marble was used as the target appearance, and five trained graders evaluated the appearance of each random sheet in increments of 1 point, with Fig. 10 being given a score of 10 and Fig. 7 before pressing being given a score of 1. The average score of the five graders was used as the appearance evaluation score for that random sheet.

[0098] 1-3-2.Evaluation of the appearance of the whitened area The surface of each random sheet was visually observed, and the whitened areas on the surface of each sheet were evaluated according to the following evaluation criteria. -Evaluation criteria- ◎: No visible whitening areas ○: Visible white areas are present, but all are less than 2.0 mm in size △: There are 1 to 5 white spots of 2.0 mm or more in size ×: There are five or more whitened areas of 2.0 mm or larger.

[0099] Tables 1 and 2 show the type of additive added to the chopped sheet, the type of resin of the additive, MFR and amount added, the thickness of the film if one was placed, and the appearance evaluation points. Note that when polyamide resin is used as the additive, the evaluation criteria for the standardized MFR differ from that of polypropylene, making it impossible to compare under the same conditions, so the MFR is not listed in the tables.

[0100] [Table 1]

[0101] [Table 2]

[0102] As is clear from Table 1, when a random sheet is made by adding thermoplastic resin powder to a chopped sheet, the appearance becomes more marble-like. Also, it can be seen that bumping can further reduce the occurrence of whitened areas.

[0103] This application claims priority from Japanese Patent Application No. 2022-057209, filed March 30, 2022. The entire disclosures of the specification, claims, and drawings of that application as originally filed are incorporated herein by reference. [Industrial Applicability]

[0104] The random sheet of the present invention has a better appearance than conventional random sheets. Therefore, the present invention is expected to broaden the possibilities for using random sheets, particularly in applications where design is required, and to contribute to the development of various fields related to random sheets. [Explanation of symbols]

[0105] 100 chopped sheets 110 Reinforced Fiber 120 Matrix Resin 210 Lower mold 212 Formwork 220 Upper mold 410 powder 420 Spreader

Claims

1. A step of laying thin pieces of fiber-reinforced resin in a plane, the thin pieces being formed by impregnating a plurality of reinforcing fibers oriented in one direction with a first thermoplastic resin; applying a powder of a second thermoplastic resin to the spread flakes; and applying heat and pressure to the powder-applied flakes to integrate the flakes together. The powder has a median diameter (D50) of 700 μm or less, at which the cumulative amount of particles based on mass in the particle size distribution becomes 50%. Manufacturing method of random sheet.

2. In the step of applying the powder, the amount of the powder applied was 20.0 g / m ２ The method for producing a random sheet according to claim 1, wherein the method is as described above.

3. The method for producing a random sheet according to claim 1 , wherein the first thermoplastic resin and the second thermoplastic resin are both polyolefin resins.

4. The method for producing a random sheet according to claim 1 , wherein the first thermoplastic resin and the second thermoplastic resin are both polypropylene.

5. The second thermoplastic resin is polypropylene having a melt flow rate (MFR) of 5.0 g / 10 min or more 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 claim 1.

6. The step of integrating the flakes together includes a bumping step of removing air from gaps between the spread flakes and the powder. and a step of heating and pressurizing the spread flakes and the powder to a temperature equal to or higher than the melting point of the first thermoplastic resin and equal to or higher than the melting point of the second thermoplastic resin to integrate the flakes together, in this order. The method for producing the random sheet according to any one of claims 1 to 5.

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