Method for manufacturing a fiber-reinforced thermoplastic resin sheet

Abstract

To provide a production method of a fiber-reinforced thermoplastic resin sheet from preformed bodies already impregnated with a thermoplastic resin between fibers by using a double belt press apparatus, wherein the fiber-reinforced thermoplastic resin sheet has very few internal voids because the fully laminated preformed bodies closely contact with the inside of the sheet while avoiding damage on a surface of the sheet.SOLUTION: A production method of a fiber-reinforced thermoplastic resin sheet containing reinforcing fibers and a thermoplastic resin, has various processes. In particular, the method is performed continuously by using a double belt press apparatus. The double belt press apparatus has, in an area to be pressed by an upper belt and a lower belt, in this order: a preheat section for preheating preformed bodies laminated from an inlet side of the apparatus; a heating section for simultaneously heating and pressurizing the laminated preformed bodies to remelt them; and a cooling section for simultaneously cooling and pressurizing the remelted preformed bodies to solidify them closely. Each section meets specific conditions.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a fiber-reinforced thermoplastic resin sheet using a double-belt press device. More specifically, after opening continuous reinforcing fibers and continuously impregnating them with a thermoplastic resin through a thermoplastic resin bath, cutting is performed, and using a preform, in a double-belt press device, the cut preforms are laminated and deposited, the thermoplastic resin in the preform is remelted while heating and pressurizing, and the preforms are adhered to each other, cooled and solidified to form a continuous sheet. The present invention relates to a method for manufacturing a fiber-reinforced thermoplastic resin molded body characterized by this.

Background Art

[0002] In recent years, fiber-reinforced thermoplastic resin sheets have been widely used as molding intermediates or molded products. In particular, the molding intermediate is called a stampable sheet. For example, it is cut into a predetermined shape, heated to near the softening point or melting point of the thermoplastic resin, or to a temperature higher than that, by far-infrared heating or the like, placed in a mold at a predetermined temperature, and then pressurized and cooled and solidified to form a final molded product.

[0003] Such a fiber-reinforced thermoplastic resin sheet molding intermediate has conventionally been produced by melt-impregnating a mat-like material (e.g., chopped strand mat) or an aligned product of reinforcing fibers (e.g., glass fiber, carbon fiber) with a powder, film, or sheet of a thermoplastic resin at a temperature at least higher than the softening point or melting point of the thermoplastic resin.

[0004] As an intermediate for forming a fiber-reinforced thermoplastic resin sheet, from the viewpoints of energy and environmental issues, fiber-reinforced resins with high rigidity, high strength, and a high weight-reducing effect have attracted attention. In particular, fiber-reinforced thermoplastic resins using a thermoplastic resin as a matrix resin are excellent in processability and impact resistance, and their application to vehicle fields such as automobiles and the construction field is being studied. At that time, due to the characteristics of the shape of the final product, there is a strong demand for a large size in the intermediate for forming. In this regard, although the TD direction of the machine base of the double-belt press device is restricted by the belt width of the machine base, the MD direction is not restricted by length, so it is suitable for manufacturing the intermediate for forming.

[0005] As a method for manufacturing an intermediate for forming a fiber resin-reinforced thermoplastic resin sheet, examples of the manufacturing method using a double-belt press device are as follows.

[0006] For example, in Patent Document 1, a method of forming a fiber-reinforced thermoplastic resin papermaking web into a sheet by a double-belt press method aims to continuously produce a high-strength sheet-shaped molded product with a uniform thickness and excellent surface shape. However, in the double-belt press device, the heating region is only at one top roll, and the subsequent four rolls are all cooling regions. Therefore, a preheating device is required in front of the device, and it is difficult to form a fiber-reinforced resin thermoplastic resin sheet only with the double-belt press device.

[0007] Patent Document 2 is an invention characterized in that, in a double-belt press device, when manufacturing various press-molded products with different pressing forms during the diversification of press-molded products, the pressing unit in each zone of the machine base is selected for each press-molded product to be manufactured. However, there is no specific disclosure regarding the selection of each zone when laminating and depositing a preform in which a thermoplastic resin has been impregnated between the cut reinforcing fibers, remelting the thermoplastic resin in the preform while heating and pressurizing, and closely adhering, cooling, and solidifying the preform to form a sheet.

[0008] Patent Document 3 is an invention related to the production of fiber-reinforced plastics with high strength and little variation in producing a fiber-reinforced thermoplastic resin sheet. It is a method of laminating a unidirectional prepreg containing reinforcing fibers and a thermoplastic resin so that the fibers become random. Similar to Patent Document 2, there is no description of a method of forming a sheet using a double-belt press device by laminating and depositing a preform in which the thermoplastic resin is already impregnated between the cut reinforcing fibers.

[0009] Patent Document 4 is a method for producing a fiber-reinforced thermoplastic resin sheet using a double-belt press device assuming a nonwoven fabric as the reinforcing fiber and a polyimide as the matrix resin, and is a patent that defines the distance between the lower belt and the upper belt in the heating zone and the cooling zone. Specifically, in the heating zone, the distance between the upper and lower belts gradually decreases from the machine inlet side to the outlet side, and in the cooling zone, it is parallel without an inclination between the upper and lower belts. It is not a machine condition setting assuming that a discontinuous preform in which the thermoplastic resin is impregnated between the fibers in advance is laminated on the belt and good products are produced using a double-belt press device.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0011] In the above method, particularly the method of Patent Document 4, in the production of a fiber-reinforced thermoplastic sheet using a double-belt press machine, it is divided into two zones, a heating zone and a cooling zone, and the distance between the upper and lower belts is defined in each zone. First, regarding the heating zone, the distance between the upper and lower belts is narrowed toward the outlet side. However, when using a different material from that of Patent Document 4, specifically, when laminating and integrating preforms in which impregnation of a thermoplastic resin between reinforcing fibers is completed to form a fiber-reinforced thermoplastic resin sheet, if the distance between the upper and lower belts is unreasonably narrowed at a stage where sufficient heat has not been applied to the preform, the surface of the fiber-reinforced thermoplastic resin sheet will be disturbed and damaged by the belts. A fiber-reinforced thermoplastic resin sheet with a damaged surface may also cause a problem called springback, in which the reinforcing fibers pop out in the out-of-plane direction during heating when performing forming processing in a subsequent process. Also, if the distance between the upper and lower belts is set to be equal in the cooling zone, sufficient pressure cannot be applied during the process of shrinkage after forming of the fiber-reinforced thermoplastic resin sheet during the cooling process, which may cause defects such as the remaining of fine voids in the fiber-reinforced thermoplastic resin sheet and sink marks on the surface of the fiber-reinforced thermoplastic resin sheet.

[0012] The present invention has been made to solve the above conventional problems. The object is to produce good-quality fiber-reinforced thermoplastic resin sheets using a double-belt press device and using preforms in which thermoplastic resin has been impregnated between fibers. It is to provide a method for manufacturing a good-quality sheet with extremely few internal voids by avoiding damage to the sheet surface and ensuring close adhesion of the preforms sufficiently laminated to the inside of the sheet.

Means for Solving the Problems

[0013] As a result of intensive studies, the present inventor has improved the method for producing a good-quality fiber-reinforced thermoplastic sheet by using a double-belt press device, particularly by optimizing the conditions of each part in the double-belt press device.

[0014] The present invention is as follows. [1] A method for manufacturing a fiber-reinforced thermoplastic resin sheet containing reinforcing fibers and a thermoplastic resin, a fiber opening step of opening a fiber bundle of continuous reinforcing fibers, an impregnation step of passing the opened fiber bundle of continuous reinforcing fibers through a tank containing a molten thermoplastic resin to impregnate the thermoplastic resin, a cooling and solidifying step of crushing the fiber bundle of continuous reinforcing fibers impregnated with the thermoplastic resin with a shaping roller and cooling and solidifying it into a tape-shaped prepreg, a cutting step of cutting the tape-shaped prepreg into a preform, a laminating step of laminating the preforms so that the direction of the reinforcing fibers is random in the plane, and an integrating step of integrating the laminated preforms into a fiber-reinforced thermoplastic resin sheet characterized by comprising: the integrating step is continuously performed using a double-belt press device, and the double-belt press device has, in the region pressed by the upper belt and the lower belt, from the device inlet side, a preheating section for preheating the laminated preforms, a heating section for simultaneously heating and pressing the laminated preforms to remelt them, and a cooling section for simultaneously cooling and pressing the remelted preforms to closely adhere and solidify them in this order, and the following conditions are satisfied in each section. A method for manufacturing a fiber-reinforced thermoplastic resin sheet. Preheating section: The clearance between the upper belt and the lower belt varies following the variation in the thickness of the laminated preforms. Heating section: The clearance between the upper belt and the lower belt is 0.5 mm to 10 mm smaller on the device outlet side than on the device inlet side. Cooling section: The clearance between the upper belt and the lower belt is 0.2 mm to 5 mm smaller on the device outlet side than on the device inlet side. [2] The method for manufacturing a fiber-reinforced thermoplastic resin sheet according to [1], characterized in that the preform is in the shape of a strip having a length of 5 mm to 100 mm, a width of 4 mm to 60 mm, and a thickness of 0.05 mm to 0.4 mm. [3] The method for manufacturing a fiber-reinforced thermoplastic resin sheet according to [1] or [2], wherein the mass ratio of the reinforcing fibers to the thermoplastic resin contained in the fiber-reinforced thermoplastic resin sheet is in the range of 85 / 15 to 30 / 70. [4] The reinforcing fiber contained in the fiber-reinforced thermoplastic resin sheet is glass fiber and / or carbon fiber, and the method for producing a fiber-reinforced thermoplastic resin sheet according to any one of [1] to [3]. [5] The fiber-reinforced thermoplastic resin sheet has a thickness in the range of 1 to 10 mm, and the method for producing a fiber-reinforced thermoplastic resin sheet according to any one of [1] to [4]. [Advantages of the Invention]

[0015] According to the present invention, a fiber-reinforced thermoplastic resin sheet having a good appearance and extremely few internal voids can be obtained. By avoiding excessive pressure in a state where the preform is not sufficiently heated, damage to the sheet surface is avoided, and by effectively discharging the voids in the sheet to the outside, there are also effects such as high process stability and a reduction in the amount of preform to be discarded. [Embodiments for Carrying Out the Invention]

[0016] In this specification, the "preform" contains continuous reinforcing fibers and a thermoplastic resin, and is cut into strip shapes. Therefore, after laminating the preforms in a double-belt press device, which is a subsequent process, and forming them into a fiber-reinforced thermoplastic resin sheet, it is possible to re-form them into a desired final molded article.

[0017] [Reinforcing Fiber] The reinforcing fiber is not particularly limited, but representative examples include inorganic fibers such as carbon fiber, silicon carbide fiber, and glass fiber, metal fibers such as boron fiber, and organic fibers such as aramid fiber. From the viewpoints of cost and the elastic modulus and mechanical strength of the obtained molded article, inorganic fibers such as glass fiber and carbon fiber are preferred.

[0018] [Thermoplastic Resin] The thermoplastic resin is not particularly limited. Representative examples include polyamide resins such as polyamide 6, polyamide 12, polyamide 66, and polyamide 46; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polyolefin resins such as polyethylene and polypropylene; polyether ketone resin, polyphenylene sulfide resin, polyetherimide resin, polycarbonate resin, etc. These thermoplastic resins may be modified ones.

[0019] Representative examples of particularly preferred thermoplastic resins are as follows. These can be appropriately used according to the application (or desired properties) of the molded article. (1) When low cost, fluidity during molding, water resistance, hot water resistance, or chemical resistance is required, polyolefin resins are preferred. Due to easy availability, polypropylene is particularly preferred, and in the present invention, it is preferable to use acid-modified polypropylene. This is because the adhesion to the aforementioned reinforcing fibers is particularly excellent. (2) When abrasion resistance, oil resistance, or long-term heat resistance characteristics are required, polyamide resins are preferred, and polyamide 6, polyamide 66, and polyamide MXD6 resins are particularly preferred. (3) When heat resistance, mechanical strength, creep characteristics, chemical resistance, or oil resistance is required, polyester resins are preferred, and polyethylene terephthalate is particularly preferred.

[0020] [Fibrillation process] The present invention has a fibrillation process for fibrillating a fiber bundle of continuous reinforcing fibers. The fibrillation process is preferably carried out in a state where there is almost no twist. Usually, a roller and an air fibrillation process are used, but it is not limited thereto.

[0021] [Impregnation process] The present invention has an impregnation step of impregnating a thermoplastic resin by passing a fiber bundle of opened continuous reinforcing fibers through a tank containing the molten thermoplastic resin. The impregnation apparatus used in the present invention impregnates continuous reinforcing fibers in a high-pressure tank (hereinafter, may also be referred to as a resin tank) filled with molten thermoplastic resin at a temperature equal to or higher than the melting point of the thermoplastic resin.

[0022] In order to continuously and efficiently impregnate the thermoplastic resin, it is preferable to pass through a resin tank having a pressure of 0.1 MPa or more. When it is less than 0.1 MPa, it becomes difficult to sufficiently obtain impregnability. The higher the pressure in the resin tank, the more preferable it is for improving impregnability, more preferably 0.3 MPa or more, and still more preferably 0.5 MPa or more. Although the higher the pressure in the resin tank, the more preferable it is for improving impregnability, the equipment cost also increases, so it is preferably 2 MPa or less. Further, before the continuous reinforcing fibers enter the resin tank, it is preferable to bring them into contact with a curved die having a resin discharge slit. By discharging the molten thermoplastic resin from the resin discharge slit and impregnating a part of the thermoplastic resin from the side where the fiber bundle of the continuous reinforcing fibers is in contact with the curved die, pre-impregnation can be favorably performed while maintaining the state where the continuous reinforcing fibers are opened.

[0023] [Cooling and solidifying step] The present invention has a cooling and solidifying step of crushing a fiber bundle of continuous reinforcing fibers impregnated with a thermoplastic resin with a shaping roller and cooling and solidifying it into a tape-shaped prepreg. The continuous reinforcing fibers that have passed through the resin tank are likely to be gathered by the drawing tension, and in this state, the thermoplastic resin has not completely impregnated the details of the continuous reinforcing fibers. By crushing, cooling, and solidifying with a shaping roller, the resin impregnability and handleability can be improved.

[0024] [Tape-shaped prepreg] The mass ratio of the reinforcing fiber to the thermoplastic resin contained in the tape-shaped prepreg (reinforcing fiber / thermoplastic resin) is preferably 85 / 15 to 30 / 70, more preferably 85 / 15 to 50 / 50, and even more preferably 85 / 15 to 60 / 40. This mass ratio is the same for the preform and the fiber-reinforced thermoplastic resin sheet. The size of the tape-shaped prepreg is not particularly limited in length, and preferably has a width of 4 mm to 60 mm and a thickness of 0.05 mm to 0.4 mm. The width is more preferably 10 mm to 50 mm. The thickness is more preferably 0.07 mm to 0.2 mm.

[0025] [Cutting Process] The present invention has a cutting process of cutting a tape-shaped prepreg into a preform. Cutting is usually performed with a fan cutter, but is not particularly limited.

[0026] [Preform] The produced tape-shaped prepreg is cut into a preform for easy use. The size of the preform is preferably 5 mm to 100 mm in length, 4 mm to 60 mm in width, and 0.05 mm to 0.4 mm in thickness.

[0027] When the thickness is less than 0.05 mm, the production efficiency is poor, and when it exceeds 0.4 mm, the impregnation property tends to be insufficient. The thickness is more preferably in the range of 0.07 mm to 0.2 mm. Also, when the width is less than 4 mm or exceeds 60 mm, the production efficiency tends to be poor when producing the fiber-reinforced thermoplastic resin sheet in the subsequent process. The width is more preferably in the range of 10 mm to 50 mm. Regarding the length, when it is less than 5 mm or exceeds 100 mm, the productivity tends to be poor when producing the fiber-reinforced thermoplastic resin sheet in the subsequent process. The length is more preferably in the range of 10 mm to 50 mm. When the mass ratio of the contained reinforcing fiber exceeds 85%, the resin impregnation property becomes insufficient and it tends to be a starting point for fracture. When it is less than 30%, it becomes difficult to obtain the reinforcing effect of the reinforcing fiber.

[0028] In addition, the tape-shaped prepreg and the preform may contain additives such as a thermal degradation inhibitor, an oxidation degradation inhibitor, and an ultraviolet absorber, as necessary. The content of these additives can vary depending on the purpose, but usually, it is preferably 0.5% by mass or less, more preferably added in the range of 0.2 to 0.5% by mass, respectively, based on the mass of the tape-shaped prepreg or the preform. The same applies to the fiber-reinforced thermoplastic resin sheet with respect to the additives.

[0029] [Laminating Process] The present invention has a laminating process of laminating the preform so that the direction of the reinforcing fibers is random in the plane. The spraying unit provided with a spraying port for spraying and laminating the preform is not particularly limited in its configuration as long as it can spray a predetermined amount of the preform from the spraying port onto the surface to be sprayed. For example, the spraying port for spraying the preform may be provided with a weighing unit for adjusting the weight of the preform to be dropped, a storage tank for storing the preform, a transport unit for transporting the preform from the storage tank to the weighing unit, and the like. In this apparatus, the preform stored in the storage tank is supplied to the weighing unit via the transport unit, the weight is adjusted at the weighing unit, and the preform freely falls from the spraying port onto the surface to be sprayed. At this time, the environment from the spraying port to the surface to be sprayed is preferably an environment where no external force other than gravity is applied. When adjusting the weight of the preform at the weighing unit of the apparatus, it may also be adjusted by a method based on the rotation speed of the gears of the weighing unit. The laminating unit for laminating the preform is not particularly limited in its configuration as long as it is an apparatus in which the preform sprayed from the spraying port is laminated on the surface to be laminated. The surface to be laminated is usually located below the spraying port and is set so that the preform dropped by gravity from the spraying port is laminated on the surface to be laminated. In the present invention, this laminating process is preferably performed on the lower belt on the inlet side of the double-belt press apparatus. Therefore, as the structure of the double-belt press apparatus to be used, it is more preferable to adopt an apparatus in which the lower belt side is longer in the inlet side direction compared to the upper belt side (lower belt length > upper belt length), so that the preform can be directly sprayed on the extended lower belt on the apparatus inlet side, which is preferable from the viewpoint of the design of the manufacturing process.

[0030] [Integrated Process] The present invention has an integrated process of integrating a laminated preform into a fiber-reinforced thermoplastic resin sheet. The integrated process is continuously performed using a double-belt press device. The double-belt press device has, in the region pressed by the upper belt and the lower belt, from the device inlet side, a preheating section for preheating the laminated preform, a heating section for simultaneously heating and pressurizing the laminated preform to remelt it, and a cooling section for simultaneously cooling and pressurizing the remelted preform to closely solidify it, in this order. It is important to satisfy the following conditions in each of the above sections. Preheating section: The clearance between the upper belt and the lower belt varies following the thickness variation of the laminated preform. Heating section: The clearance between the upper belt and the lower belt is 0.5 mm to 10 mm smaller on the device outlet side than on the device inlet side. Cooling section: The clearance between the upper belt and the lower belt is 0.2 mm to 5 mm smaller on the device outlet side than on the device inlet side.

[0031] [Double-Belt Press Device] The double-belt press device used in the present invention is a device equipped with two belts, an upper and a lower one. The lower belt is mounted on an inlet-side drum and an outlet-side drum each pivotally supported by a rotating shaft at the device inlet side and the outlet side, respectively. Similarly, the upper belt is also mounted on an inlet-side drum and an outlet-side drum each pivotally supported by a rotating shaft at the device inlet side and the outlet side, respectively. The belts mounted are steel endless belts that circulate endlessly in synchronization with the rotation of the drums. Between the lower belt inlet-side drum and the lower belt outlet-side drum, and between the upper belt inlet-side drum and the upper belt outlet drum, a preheating section, a heating section, and a cooling section are provided.

[0032] In the present invention, by supplying the sprayed preform into the belt around which the lower belt and the upper belt circulate, the thermoplastic resin in the preform melts due to the heat and pressure applied from the double belt press device, and the layers of the preform are adhered to each other. Then, while maintaining that state, it is cooled and pressure is applied to obtain a laminated fiber-reinforced thermoplastic resin sheet without gaps.

[0033] As the pressurizing mechanism of the double belt press device used in the present invention, generally used press rolls, hydraulic pressure, presses using vibration pressurizing plates, etc. are used. In the process of obtaining a laminated fiber-reinforced thermoplastic resin sheet from the sprayed preform, since it is necessary to apply pressure while rapidly reducing the thickness to about one-tenth, a press roll method with good followability to large thickness changes is preferable. Further, as the heating means, there is no particular limitation, and it is possible to use an IR heater, a hot air heater, or a heat medium heater using oil.

[0034] In the present invention, by heating and pressurizing, the sprayed preform is cooled and pressurized while being sandwiched between steel belts to obtain a fiber-reinforced thermoplastic resin sheet. As the cooling means, there is no particular limitation, and there are cold air, a cooling water circulation method, a refrigerant circulation method, etc.

[0035] In the present invention, after the fiber-reinforced thermoplastic resin sheet is peeled from the steel belt, it is cut in a direction perpendicular to the device. The length in the longitudinal direction of the device can be arbitrarily set, and there is no particular limitation on the cutting method, and there are a slitting blade, a coping saw blade, etc.

[0036] The double-belt press device used in the present invention having the above-described features stacks preforms on the lower belt on the device inlet side. The stacking amount is controlled by the weight corresponding to the target thickness of the formed body. Thereafter, the preforms stacked on the lower belt are conveyed into the double-belt press device by the conveyance of the belt. The inside of the device is set by dividing it into three forming regions (preheating section, heating section, cooling section) as described above. Each region is, from the device inlet side, a preheating section for preheating the stacked preforms, a heating section for simultaneously heating and pressing the stacked preforms to remelt them, and a cooling section for simultaneously cooling and pressing the remelted preforms to closely solidify them. Such a region setting and the condition setting of the device are also features of the specific improvement points this time.

[0037] In the preheating section of the device that preheats the stacked preforms close to the inlet side, heat is applied to the preforms introduced from the device inlet side, and the thermoplastic resin contained in the preforms is melted by heat to adhere the stacked preforms to each other. At this time, in the process of the preforms adhering to each other, the thickness of the stacked preforms gradually decreases from the device inlet side toward the outlet side. As a setting on the device side, in the region for preheating the stacked preforms, the clearance of the device (the distance between the upper and lower belts) is not particularly set, and it is characterized by not actively pressing the sheet with a hydraulic jack or the like. As the stacked preforms proceed through the preheating process, the thickness decreases, and the position of the upper belt follows in a form that relies on the self-weight of the upper belt.

[0038] For example, if the clearance is narrowed more than the thickness of the preform stacked from the device inlet side to the outlet side decreases as the preheating process progresses, and pressure is set with a hydraulic jack or the like, or if the clearance is uniformly adjusted to a thickness corresponding to the target thickness and pressure is applied with a hydraulic jack or the like to preheat the stacked preform, the preform stacked in the device will become clogged, leading to a problem that causes the device to stop. Even if the device does not stop, when performing forming processing in a subsequent process, damage to the surface of the obtained fiber-reinforced thermoplastic resin sheet by the belt and fuzzing will also lead to a problem called springback, in which the reinforcing fibers pop out in the out-of-plane direction during heating. As the preform stacked passes through the preheating section, the thickness decreases, and by setting the clearance between the upper and lower belts to naturally decrease, the stacked preform can pass through the preheating section without difficulty, and damage to the surface of the obtained fiber-reinforced thermoplastic resin sheet can be minimized.

[0039] As described above, no particular setting of the clearance is required in the preheating process. As the stacked preform progresses through the preheating process, the thickness decreases, and the position of the upper belt follows by relying on the self-weight of the upper belt. Therefore, no particular pressure setting is required either.

[0040] The set temperature in the preheating section is set such that the center temperature of the stacked preform becomes the melting point (Tm) of the thermoplastic resin contained in the preform to Tm + 100 °C while passing through the preheating section. Due to the characteristics of the apparatus, the belt cooled at the apparatus outlet is reheated on the apparatus inlet side and heat is applied from the belt to the stacked preform. Therefore, when the belt surface temperature is low, heat is not sufficiently applied to the center of the preform sufficiently stacked in the preheating process, and the adhesion between the preforms stacked due to insufficient heating becomes incomplete, resulting in defects such as a large number of fine voids in the fiber-reinforced thermoplastic resin sheet after molding. Conversely, when the belt surface temperature is too high, the preform is overheated centering on the contact portion with the belt, resulting in defects such as burning of the thermoplastic resin contained and sticking to the belt. In addition, the adjustment of the belt surface temperature includes not only the adjustment of the set temperature of the direct heating apparatus and the adjustment of the air volume, etc., but also the adjustment of the conveying speed, etc.

[0041] In the heating section of the apparatus that simultaneously heats and presses the preform stacked in the apparatus, it is characterized by a setting in which the clearance between the upper and lower belts decreases from the apparatus inlet side to the outlet side, and pressurization by a hydraulic jack or the like. This apparatus setting is for heating the preform heated from the inlet side to a temperature of the melting point (Tm) of the thermoplastic resin + 50 °C or higher and actively discharging the voids contained in the preform to the apparatus inlet side. The upper limit of the temperature in the heating section is preferably the melting point (Tm) of the thermoplastic resin + 100 °C or lower. It is important that the inclination of the clearance between the upper and lower belts is 0.5 mm to 10 mm smaller on the apparatus outlet side than on the apparatus inlet side. Although it depends on the target thickness of the obtained fiber-reinforced thermoplastic resin sheet, when it is less than 0.5 mm, it is not possible to effectively discharge the voids in the stacked preform. When it is more than 10 mm, there is a possibility that a gap may occur between the preform stacked on the inlet side and the belt, which is not preferable. The inclination of the clearance between the upper and lower belts (the difference between the apparatus inlet side and the apparatus outlet side) is preferably 0.5 mm to 5 mm, more preferably 1 mm to 3 mm, and even more preferably 1 mm to 2 mm.

[0042] The clearance adjustment in the heating section is characterized in that the clearance between the upper and lower belts decreases from the inlet side to the outlet side of the apparatus as described above. Specifically, it is preferably from the thickness equivalent of the fiber-reinforced thermoplastic resin sheet obtained on the outlet side of the apparatus to the thickness equivalent + 1.0 mm, and from the clearance on the outlet side of the apparatus + 0.5 mm to 10 mm on the inlet side of the apparatus. Even with appropriate pressure and temperature conditions, if the clearance is set in a direction narrower than the appropriate setting, the preform laminated in the heating section will be clogged, causing problems such as equipment stoppage. Conversely, if the clearance is set in a direction wider than the appropriate setting, voids in the laminated preform cannot be effectively removed to the inlet side of the apparatus, resulting in defects such as a large number of fine voids in the fiber-reinforced thermoplastic resin sheet after molding.

[0043] The pressure in the heating section is for actively removing the voids contained in the laminated preform to the inlet side of the apparatus as described above. As the clearance between the belts decreases from the inlet side to the outlet side, it is sufficient if the pressure is equal to or greater than the pressure that would cause the preform to expand more than the set clearance in the thickness direction. That is, it is sufficient if the pressure is greater than the pressure due to the self-weight of the upper belt. When the pressure is low, the voids contained in the preform cannot be effectively removed to the inlet side of the apparatus, resulting in defects such as a large number of fine voids in the fiber-reinforced thermoplastic resin sheet after molding. When the pressure is high, there are no particular problems if the clearance setting is appropriate. However, if the clearance setting is inappropriate, the preform laminated in the apparatus in the heating section will be clogged, leading to problems such as equipment stoppage. Specifically, it is a clearance setting below the target thickness of the sheet. Even if it does not lead to equipment stoppage, the surface of the obtained fiber-reinforced thermoplastic resin sheet will be damaged by the belt and fuzzed, which also causes a problem called springback where the reinforcing fibers pop out in the out-of-plane direction during heating when performing molding processing in the subsequent process. From the above, the pressure applied in the heating section is empirically 0.1 kg / cm 2 or more, and more preferably 1 kg / cm 2 or more.

[0044] The temperature setting in the heating section is such that the belt surface temperature is set so that the central temperature of the laminated preform maintains a temperature range of Tm + 50°C to Tm + 100°C of the thermoplastic resin also contained in the preform while passing through the heating section. When the belt surface temperature is low, heat is not sufficiently applied to the center of the preform that has been sufficiently laminated in the heating process, resulting in incomplete adhesion between the laminated preforms due to insufficient heating, and defects such as a large number of fine voids in the fiber-reinforced thermoplastic resin sheet after molding. Conversely, when the belt surface temperature is too high, the preform is overheated around the contact part with the belt, causing defects such as charring from the contained thermoplastic resin and sticking to the belt. Note that the heating methods for the preheating section and the heating section are not particularly limited, but for example, an IR heater, a hot air heater, or a heat medium heater using oil can be used. Specifically, when using a hot air heater, in addition to directly adjusting the set temperature of the heating device and the air volume, there is also adjustment of the conveying speed, etc. for adjusting the belt surface temperature.

[0045] In the cooling section where the cooling and pressurization of the preform laminated in the apparatus are carried out simultaneously, the clearance between the upper and lower belts is smaller on the apparatus outlet side than on the apparatus inlet side, and it is characterized by active pressurization using a hydraulic jack or the like. This apparatus setting is for actively removing the fine voids in the obtained fiber-reinforced thermoplastic resin sheet due to the post-molding shrinkage during cooling and solidification by pressurizing while cooling the preform remelted after heating and pressurization from the inlet side. It is important that the inclination of the clearance between the upper and lower belts is 0.2 mm to 5 mm smaller on the apparatus outlet side than on the apparatus inlet side. Although it depends on the target thickness of the obtained fiber-reinforced thermoplastic resin sheet, when it is smaller than 0.2 mm, it is not possible to effectively remove the voids in the remelted preform. When it is larger than 5 mm, there is a possibility of a gap occurring between the preform remelted at the inlet side and the belt, which is not preferable. The inclination of the clearance between the upper and lower belts (the difference between the apparatus inlet side and the apparatus outlet side) is preferably 0.2 mm to 3 mm, more preferably 0.3 mm to 2 mm, and even more preferably 0.4 mm to 1 mm.

[0046] The clearance adjustment in the cooling section is characterized in that the clearance between the upper and lower belts decreases from the inlet side to the outlet side of the apparatus as described above. Specifically, it is preferably from the thickness equivalent of the fiber-reinforced thermoplastic resin sheet obtained on the outlet side of the apparatus to the thickness equivalent + 0.5 mm, and from the clearance on the outlet side of the apparatus + 0.2 mm to 5 mm on the inlet side of the apparatus. Even if the appropriate pressure and temperature conditions are provided, if the clearance is set narrower than the appropriate setting, the preform laminated in the cooling section will become clogged, resulting in problems such as equipment stoppage. Conversely, if the clearance is set wider than the appropriate setting, voids associated with volume shrinkage during cooling and solidification in the laminated preform cannot be effectively removed to the inlet side of the apparatus, resulting in defects such as a large number of fine voids in the fiber-reinforced thermoplastic resin sheet after molding.

[0047] The pressure in the cooling section is for the purpose of actively removing voids associated with volume shrinkage during cooling and solidification in the laminated preform to the inlet side of the apparatus as described above. As the clearance between the belts decreases from the inlet side to the outlet side, it is sufficient if the pressure is greater than the pressure at which the preform to be laminated tends to expand more than the set clearance in the thickness direction. That is, it is sufficient if the pressure is greater than the pressure due to the self-weight of the upper belt. When the pressure is low, voids contained in the preform cannot be effectively removed to the inlet side of the apparatus, resulting in defects such as a large number of fine voids in the fiber-reinforced thermoplastic resin sheet after molding. Conversely, when the pressure is high, no particular problem occurs if the clearance setting is appropriate. However, if the clearance setting is set narrower than the appropriate setting, for example, the preform laminated in the apparatus in the cooling section cannot pass through, leading to problems resulting in equipment stoppage. Alternatively, although it does not lead to equipment stoppage, it also causes a problem called springback in which the reinforcing fibers protrude in the out-of-plane direction during sheet heating when performing molding processing in the subsequent process due to damage to the surface of the obtained fiber-reinforced thermoplastic resin sheet by the belt and fuzzing. The pressure during heating is equivalent to the surface pressure applied to the preform to be laminated and is empirically 0.5 kg / cm 2 or more, and more preferably 2 kg / cm 2 or more is sufficient.

[0048] The temperature in the cooling section is set such that the central temperature in the laminated preform reaches the melting point (Tm) - 20°C to the melting point (Tm) - 120°C (for amorphous resins, the glass transition temperature (Tg) - 20°C to the glass transition temperature (Tg) - 120°C) of the thermoplastic resin also contained in the preform as it passes through the cooling section. When the belt surface temperature is higher than the appropriate set temperature, problems such as difficulty in peeling the fiber-reinforced thermoplastic sheet after molding from the apparatus belt due to insufficient cooling and warping of the sheet occur at the apparatus outlet. Conversely, when the belt surface temperature is lower than the appropriate set temperature, no particular problems occur with the apparatus and the fiber-reinforced thermoplastic resin sheet after molding, but productivity is sacrificed. A set temperature in the cooling section of Tm - 30°C to Tm - 100°C (for amorphous resins, Tg - 30°C to Tg - 100°C) of the thermoplastic resin contained in the laminated preform as the central temperature in the preform passes through the cooling section is more preferable. The cooling mechanism of the cooling section is not particularly limited, and for example, an air-cooling method using a blower, a water-cooling method using a chill roll, etc. can be used. The adjustment of the belt surface temperature includes direct adjustment of the set temperature of the cooling device, adjustment of the air volume, adjustment of the water volume, etc., as well as adjustment of the conveying speed, etc.

[0049] The speed setting of the device depends on the target thickness of the resulting fiber-reinforced thermoplastic resin sheet. Generally, in the case of a sheet with a thin target thickness, since the distance from the device belt to the center in the preform laminated from the device belt is short, the heat transmitted from the device belt is likely to be transmitted, and it tends to warm up and cool down easily. Therefore, if the device speed is set slow, the time taken to pass through each of the preheating section, heating section, and cooling section becomes long. As a result, especially in the preheating section and heating section, the preform laminated is prone to overheating, leading to problems such as charring on the surface of the resulting fiber-reinforced thermoplastic resin sheet. Also, when forming a sheet with a thick target thickness, since the distance from the device belt to the center of the preform laminated from the device belt is long, the heat transmitted from the device belt is difficult to be transmitted, and it tends to be difficult to warm up and cool down. Therefore, if the device speed is set fast, the time taken to pass through each of the preheating section, heating section, and cooling section becomes short. As a result, in the preheating section and heating section, the preform laminated is prone to insufficient heating, and in the cooling section, the preform laminated is prone to insufficient cooling. Insufficient heating leads to problems such as insufficient adhesion between preforms in the fiber-reinforced thermoplastic resin sheet, defects such as interlayer void content, and insufficient cooling leads to difficulties in releasing the fiber-reinforced thermoplastic resin sheet from the device belt, warping, and other problems. Therefore, for the speed setting in this device, it is advisable to set it fast when the thickness of the resulting fiber-reinforced thermoplastic resin sheet is thin and slow when it is thick. As a specific method for adjusting the device speed, it depends on the performance of the device, especially the heating method (heating capacity of the fiber-reinforced thermoplastic resin sheet) of the preheating section and heating section, and the cooling method (cooling capacity of the fiber-reinforced thermoplastic resin sheet) of the cooling section. However, after optimizing the temperature setting of each section, it is preferable to optimize the device speed. At that time, in order to grasp the center temperature of the preform laminated passing through each section of the device, it is advisable to measure the temperature with a device capable of directly measuring the temperature such as a thermocouple. In the said examination device, when forming a fiber-reinforced thermoplastic resin sheet with a thin thickness (thickness 1.0 to 3.0 mmt), the set speed of the device is preferably 1.0 to 2.0 m / min, and when forming a fiber-reinforced thermoplastic resin sheet with a thick thickness (thickness 3.0 to 10.0 mmt), the set speed of the device is preferably 0.2 to 1.0 m / min.

[0050] By optimizing the setting conditions of each part as described above, it becomes possible to stably produce good products by the method for manufacturing a fiber-reinforced thermoplastic resin sheet using a double-belt press device.

[0051] [Fiber-reinforced thermoplastic resin sheet] The thickness of the fiber-reinforced thermoplastic resin sheet is preferably in the range of 1 to 10 mm. When the sheet thickness after molding is less than 1 mm, holes in the sheet due to uneven spraying of the laminated preform are likely to occur. Also, when the sheet thickness after molding is greater than 10 mm, the distance from the device belt to the center of the laminated preform becomes long, and heat from the belt is less likely to be transmitted in the preheating section and the heating section, resulting in defects due to insufficient heating, or in the cooling section, heat is less likely to be transmitted to the belt, and defects due to insufficient cooling are likely to occur. The width of the fiber-reinforced thermoplastic resin sheet depends on the belt width of the device used. Although it is also related to the thickness of the preform laminated on the belt, generally, the width of the fiber-reinforced thermoplastic resin sheet is about the used belt width - 50 mm. Since the shape of the original laminated preform remains at the sheet ends in the width direction, it is advisable to appropriately trim and shape them after molding from the device. The fiber-reinforced thermoplastic resin sheet is discharged in a continuous sheet shape after being peeled off from the steel belt at the device outlet for laminating the preform at the device inlet. Therefore, as it is, its handling property is poor, so it is advisable to cut the fiber-reinforced thermoplastic resin sheet in a direction perpendicular to the device after peeling it off from the steel belt. Therefore, the length of the fiber-reinforced thermoplastic resin sheet can be set arbitrarily, and there is no particular limitation on the cutting method, and there are a slitting blade, a coping saw blade, etc. The molded fiber-reinforced thermoplastic resin sheet is, as described above, a sheet-like material obtained by using a preform in which reinforcing fibers are impregnated with resin in advance, laminating it with the said device, and making the layers between the preforms adhere. Therefore, in a customer corresponding to the post-process, the fiber-reinforced thermoplastic resin sheet is cut out according to the size of the molded product, reheated to Tm~Tm + 100°C of the contained thermoplastic resin, and put into a molding die and pressurized to be molded into an arbitrary shape. As a molding method, there are a stamping molding method in which the cut fiber-reinforced thermoplastic resin sheet is heated using an external heat source such as an IR heater and put into a die adjusted in advance near the crystallization temperature for pressure molding, or a heat & cool molding method in which the fiber-reinforced thermoplastic resin sheet cut out in the same die is continuously heated, cooled, and pressurized.

Example

[0052] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

[0053] (Example 1) As the reinforcing fiber, a fiber bundle of continuous glass fiber (manufactured by Nippon Electric Glass Co., Ltd., ER2310-431N, 2310 Tex, 4000 f) was passed through a roller with a diameter of 2 cm, opened, and then passed through a resin tank at 240 °C made of an acid-modified polypropylene resin (manufactured by Prime Polymer Co., Ltd., J139, and a blend of MMP006 (blend mass ratio J139:MMP006 = 3:1, MI after blending = 40 g / 10 min), melting point 160 °C) having a pressure of 0.6 MPa to continuously impregnate the resin. Thereafter, after being crushed, cooled, and solidified by a shaping roller, it was cut to produce a strip-shaped preform having a width of 15 mm, a length of 35 mm, and a thickness of 0.1 mm, in which 25 parts by mass of polypropylene resin was impregnated with 75 parts by mass of glass fiber. This preform was formed into a fiber-reinforced thermoplastic resin sheet using a double-belt press device (manufactured by SANDVIK). The device outline and manufacturing conditions of each part of the double-belt press device are described below. Total device length: 7500 mm Press length of the lower belt: 5220 mm (between the inlet-side drum and the outlet-side drum) Press length of the upper belt: 4000 mm (between the inlet-side drum and the outlet-side drum) Device belt width: 500 mm Effective spreading width: 450 mm (width capable of spreading the laminated preform) Pressing method: Roll type Total length of the preheating section: 1500 mm Total length of the heating section: 750 mm Total length of the cooling section: 750 mm Pressing method: Press the four corners of each part (preheating section, heating section, cooling section) with a hydraulic jack and transmit pressure to the four rolls stored inside Conveying speed: 0.20 m / min Preheating section clearance: Not specifically set (temporarily set to 8.0 mm, which is significantly wider than the target forming thickness of 6 mm. The thickness at the time of substrate input is approximately 60 mm) Heating section clearance: 8.0 mm on the inlet side, 6.5 mm on the outlet side (-1.5 mm towards the outlet side) Cooling section clearance: 6.5 mm on the inlet side, 6.0 mm on the outlet side (-0.5 mm towards the outlet side) Preheating section pressure: No pressure (only the self-weight of the upper belt) Heating section pressure: 15 MPa (gauge pressure of the hydraulic jack cylinder section) Cooling section pressure: 15 MPa (gauge pressure of the hydraulic jack cylinder section) Preheating section set temperature: 260 °C (belt surface temperature, measured) Heating section set temperature: 260 °C (belt surface temperature, measured) Cooling section set temperature: 40 °C (belt surface temperature, measured) The target clearance was adjusted at the device outlet (cooling section outlet) to correspond to the target sheet thickness. On the inlet side belt of the double belt press device with the above settings, a preform equivalent to a target sheet thickness of 6 mm was laminated and scattered. As a result, the pre-laminated body did not clog in the device, and a fiber-reinforced thermoplastic resin sheet with good appearance was obtained. Also, for inspection, the inside of the sheet was observed, and there were no obvious voids and it was a good product.

[0054] (Comparative Example 1) In Example 1, the clearance conditions of the double belt press device were changed to the same clearance corresponding to the target sheet thickness from the inlet side to the outlet side. Also, the pressure condition was such that 15 MPa pressure was applied equally in all parts from the preheating section to the cooling section. Below, the clearance and pressure conditions of the double belt press device of Comparative Example 1 are described. The set temperature and conveyance speed of each part are the same as those in Example 1. Preheating section clearance: 6.0 mm on the inlet side, 6.0 mm on the outlet side (no inclination towards the outlet side. The thickness at the time of substrate input is approximately 60 mm) Heating section clearance: 6.0 mm on the inlet side, 6.0 mm on the outlet side (no inclination towards the outlet side) Cooling section clearance: 6.0 mm on the inlet side, 6.0 mm on the outlet side (no inclination towards the outlet side) Preheating section pressure: 15 MPa (gauge pressure of the hydraulic jack cylinder) Heating section pressure: 15 MPa (hydraulic jack cylinder gauge pressure) Cooling section pressure: 15 MPa (hydraulic jack cylinder gauge pressure) To the double belt press apparatus with the above settings, a preform was laminated and sprayed in the same manner as in Example 1 to produce a fiber reinforced thermoplastic resin sheet equivalent to a target thickness of 6 mm. As a result, sheet clogging occurred in the preheating section and the apparatus was stopped. The sheet surface was severely damaged and had fluff.

[0055] (Comparative Example 2) In Comparative Example 1, the clearance conditions of the double belt press apparatus were the same, but the pressure conditions were changed to a condition where no pressure was applied in the preheating section for production. The preform used was the same as in Example 1. Hereinafter, the clearance and pressure conditions of the double belt press apparatus of Comparative Example 2 will be described. The set temperature and conveyance speed of each section are the same as in Example 1. Preheating section clearance: 6.0 mm on the inlet side, 6.0 mm on the outlet side (no inclination towards the outlet side. The thickness at the time of substrate input is approximately 60 mm) Heating section clearance: 6.0 mm on the inlet side, 6.0 mm on the outlet side (no inclination towards the outlet side) Cooling section clearance: 6.0 mm on the inlet side, 6.0 mm on the outlet side (no inclination towards the outlet side) Preheating section pressure: No pressure applied (only the self - weight of the upper belt) Heating section pressure: 15 MPa (hydraulic jack cylinder gauge pressure) Cooling section pressure: 15 MPa (hydraulic jack cylinder gauge pressure) To the double belt press apparatus with the above settings, a preform was laminated and sprayed in the same manner as in Example 1 to produce a fiber reinforced thermoplastic resin sheet equivalent to a target thickness of 6 mm. As a result, the preform passed through the preheating section, but then sheet clogging occurred in the subsequent heating section and the apparatus was stopped. The sheet surface was significantly damaged and had fuzz.

[0056] (Comparative Example 3) In Example 1, the clearance conditions of the double-belt press device were the same, but the pressure condition was set such that no pressure was applied in the cooling section. The preform used was the same as that in Example 1. The clearance and pressure conditions of the double-belt press device of Comparative Example 3 are described below. The set temperature and conveying speed of each section are the same as those in Example 1. Preheating section clearance: Not specifically set (temporarily set to 8.0 mm, which is significantly wider than the target forming thickness of 6 mm. The thickness at the time of substrate input is approximately 60 mm) Heating section clearance: 8.0 mm on the inlet side, 6.5 mm on the outlet side (-1.5 mm toward the outlet side) Cooling section clearance: 6.5 mm on the inlet side, 6.0 mm on the outlet side (-0.5 mm toward the outlet side) Preheating section pressure: No pressure applied (only the self-weight of the upper belt) Heating section pressure: 15 MPa (hydraulic jack cylinder gauge pressure) Cooling section pressure: No pressure applied (only the self-weight of the upper belt) Under the condition that there is no pressurized area in the cooling section, the preform was laminated and sprayed in the same manner as in Example 1 to produce a fiber-reinforced thermoplastic resin sheet equivalent to a target thickness of 6 mm. As a result, the sheet substrate did not clog in the apparatus, but a large number of irregularities due to insufficient pressure were generated on the sheet surface. Further, when the produced sheet was cut and internally observed, it was found that it contained a large number of fine voids.

Industrial Applicability

[0057] According to the present invention, when a fiber-reinforced thermoplastic resin sheet using a preform in which a thermoplastic resin is impregnated between fibers is produced by a double-belt press device, it is possible to stably produce good products that avoid damage to the sheet surface and have extremely few voids inside the sheet. As a result, it is possible to provide a method for manufacturing a fiber-reinforced thermoplastic resin sheet having high impregnability and little variation in physical properties.

Claims

1. A method for manufacturing a fiber-reinforced thermoplastic resin sheet containing reinforcing fibers and a thermoplastic resin, comprising: a fiber-opening step of opening a fiber bundle of continuous reinforcing fibers; an impregnation step of passing the opened fiber bundle of continuous reinforcing fibers through a tank containing a molten thermoplastic resin to impregnate the thermoplastic resin; a cooling and solidifying step of crushing the fiber bundle of continuous reinforcing fibers impregnated with the thermoplastic resin with a shaping roller, cooling and solidifying it to form a tape-shaped prepreg; a cutting step of cutting the tape-shaped prepreg into a preform; a laminating step of laminating the preforms so that the direction of the reinforcing fibers is random in the plane; and an integrating step of integrating the laminated preforms into a fiber-reinforced thermoplastic resin sheet ; wherein the integrating step is continuously performed using a double-belt press device, and the double-belt press device has, in the region pressed by the upper belt and the lower belt, from the device inlet side, a preheating section for preheating the laminated preforms, a heating section for simultaneously heating and pressing the laminated preforms to remelt them, and a cooling section for simultaneously cooling and pressing the remelted preforms to closely solidify them, in this order, and each section satisfies the following conditions. A method for manufacturing a fiber-reinforced thermoplastic resin sheet is characterized in that. Preheating section: The clearance between the upper belt and the lower belt varies following the variation in the thickness of the laminated preforms. Heating section: The clearance between the upper belt and the lower belt is 0.5 mm to 10 mm smaller on the device outlet side than on the device inlet side. Cooling section: The clearance between the upper belt and the lower belt is 0.2 mm to 5 mm smaller on the device outlet side than on the device inlet side.

2. The method for manufacturing a fiber-reinforced thermoplastic resin sheet according to claim 1, wherein the preform is in the shape of a strip having a length of 5 mm to 100 mm, a width of 4 mm to 60 mm, and a thickness of 0.05 mm to 0.4 mm.

3. The method for manufacturing a fiber-reinforced thermoplastic resin sheet according to claim 1 or 2, wherein the mass ratio of the reinforcing fibers to the thermoplastic resin contained in the fiber-reinforced thermoplastic resin sheet is in the range of 85 / 15 to 30 / 70.

4. The method for manufacturing a fiber-reinforced thermoplastic resin sheet according to any one of claims 1 to 3, wherein the reinforcing fibers contained in the fiber-reinforced thermoplastic resin sheet are glass fibers and / or carbon fibers.

5. The method for manufacturing a fiber-reinforced thermoplastic resin sheet according to any one of claims 1 to 4, wherein the fiber-reinforced thermoplastic resin sheet has a thickness in the range of 1 to 10 mm.