Prepreg for de-autoclaving applicable to large structures and its manufacturing method

Abstract

The present invention relates to a prepreg for autoclave-free applications applicable to large structures and a method for manufacturing the same. More specifically, it relates to a semi-impregnated prepreg for autoclave-free processes and a method for manufacturing the same, which enables the production of large composite materials for high-altitude work at a relatively low cost by improving shape stability and molding impregnation properties through different control of the viscosity and flowability of the impregnation resin applied to both sides of the fiber.

Description

Technology Field

[0001] The present invention relates to a prepreg for autoclave-free applications applicable to large structures and a method for manufacturing the same. More specifically, it relates to a semi-impregnated prepreg for autoclave-free processes and a method for manufacturing the same, which enables the production of large composite materials for high-altitude work at a relatively low cost by improving shape stability and molding impregnation properties through different control of the viscosity and flowability of the impregnation resin applied to both sides of the fiber. Background Technology

[0002] Generally, prepreg is an abbreviation for Pre-impregnated material, meaning a raw material that has been impregnated in advance. It is an intermediate material for molding composite materials in the form of a sheet in which a matrix resin for impregnation is impregnated into reinforcing fibers at a certain ratio. It is a material that has the advantage of being able to mold composite materials capable of precise control of the fiber-resin ratio, excellent fiber orientation, and the application of various resin properties.

[0003] Fiber reinforced composites, which have a high strength-to-weight ratio, are widely applied to small structures for sports and leisure, such as fishing rods and golf clubs, as well as large structures ranging from wind turbine blades and utility poles to aircraft fuselages. Molding methods for these fiber reinforced composites include Sheet Molding Compound (SMC), Resin Transfer Molding (RTM), Filament Winding, Pultrusion, Hot Press, and Autoclave. Among these, for molded products requiring excellent physical properties, such as aircraft, large blades for wind turbines, utility poles for high-voltage transmission towers, and electrical / electronic mechanical parts, products are mostly formed using prepreg produced through the autoclave process.

[0004] Among these, the autoclave method is a vacuum, pressurized, and heated furnace capable of simultaneously applying heat, pressure, and vacuum. Since vacuum and pressurization are applied simultaneously, it enables the effective removal of pores and volatile components from within the molded product during the molding of composites using prepreg. Furthermore, as a facility capable of producing molded products with the densest structure through the application of high pressure, it is the most commonly applied method for molding composites requiring excellent quality, such as those for aircraft and electronic components.

[0005] However, despite the advantages of the autoclave process, it is often not applied to composite products requiring mass production due to the disadvantages of high equipment and operating costs. In the autoclave process, pressurization conditions are typically set to 1 to 7 atmospheres; while this poses no significant problem for autoclaves molding small products, as the molded product grows larger, the thickness of the metal outer wall of the autoclave increases exponentially to maintain internal pressure, leading to a very high cost for the autoclave equipment. Additionally, there is a disadvantage in that the manufacturing cost of the product increases due to the use of a considerable amount of auxiliary materials and a long molding cycle time.

[0006] For this reason, research on out-of-autoclave processes is actively underway to reduce the high equipment and manufacturing costs, which are cited as drawbacks, while maintaining the advantages of the autoclave method.

[0007] Typically, the autoclave-free process follows a prepreg stacking sequence similar to that of an autoclave, but instead of a high-pressure autoclave chamber, it utilizes an ambient pressure oven, hot air blower, or surface heating element to raise the prepreg temperature during molding.

[0008] However, since the autoclave-free process applies pressure to the prepreg solely through vacuum without a pressurization process, it becomes very difficult to effectively remove pores and volatile components from the prepreg. Active attempts are being made to overcome the disadvantages of this process through material improvements, resulting in the development of semi-impregnated prepregs.

[0009] FIG. 1 is a conceptual diagram of a conventional prepreg and a semi-impregnated prepreg. FIG. 1(a) is a prepreg in which the matrix resin (2) for impregnation is completely impregnated into the reinforcing fiber (1), and FIG. 1(b) is a semi-impregnated prepreg in which the reinforcing fiber (1') that is not impregnated into the matrix resin (2) remains in a partially impregnated form.

[0010] Therefore, if the impregnation rate of a general prepreg is 97% or higher, the impregnation rate of a semi-impregnated prepreg is approximately 20-70% because there are unimpregnated void areas (3) remaining. Through this intentional non-impregnation, it is possible to secure a flow channel for the resin through the unimpregnated portion during vacuum / heating in the autoclave-free process, and through this, stable discharge from the internal pores of the prepreg to the outside enables the molding of a dense molded product with few pores.

[0011] As such, while the autoclave-free method is harmoniously applied to a material called semi-impregnated prepreg, conventional semi-impregnated prepreg not only suffers from reduced shape stability due to reinforcing fibers in the unimpregnated portion, but also experiences further degradation of shape stability because the resin strength decreases at room temperature due to the use of low-viscosity, high-flowability resins to improve impregnation.

[0012] For this reason, if the impregnation matrix is ​​changed to a high-viscosity resin to improve the shape stability of the semi-impregnated prepreg, the flowability decreases, resulting in reduced molding impregnation during autoclave-free molding, making it difficult to completely remove pores. Consequently, there is a problem in that a dense molded product cannot be obtained. The problem to be solved

[0013] The present invention was devised to resolve the aforementioned problems and aims to provide a semi-impregnated prepreg for an autoclave-free process and a method for manufacturing the same, which can improve shape stability at room temperature and molding impregnation properties during autoclave-free molding. means of solving the problem

[0014] The present invention provides a prepreg applicable to large structures for non-autoclave use, comprising, as a means to achieve the above objective: a sheet-shaped fiber; a first thermosetting resin having high viscosity and low flowability coated on a release liner to be pressed onto one side of the fiber to maintain the shape stability of the prepreg at room temperature; and a second thermosetting resin having lower viscosity and high flowability than the first thermosetting resin, coated on a release liner to be pressed onto the other side of the fiber to be impregnated into the fiber during molding to improve molding impregnation properties, wherein the second thermosetting resin is formed thicker than the first thermosetting resin.

[0015] delete

[0016] delete

[0017] The present invention relates to a method for manufacturing a prepreg for autoclave-free applications applicable to large structures, comprising a fiber supply step, a prepreg-formed fiber formation step, and a semi-impregnated prepreg manufacturing step.

[0018] The fiber supply step above is,

[0019] The process comprises a step of continuously supplying or feeding sheet-shaped fibers between pressure rollers using a spinning device or the like to open the fibers.

[0020] The prepreg fiber formation step is,

[0021] The method comprises the step of simultaneously and continuously supplying a first thermosetting resin of high viscosity and low flowability coated on a release liner to stabilize the shape of the fiber on one side of the fiber, and a second thermosetting resin of low viscosity and high flowability coated on a release liner on the other side, and compressing both sides of the fiber by a first compression roller, and then passing through a heater to be heated and pressed with an appropriate pressure by another second compression roller above, thereby integrally bonding the first thermosetting resin of high viscosity and the second thermosetting resin of low viscosity to both sides of the fiber to form a prepreg fiber.

[0022] The manufacturing step of semi-impregnated prepreg is,

[0023] The present invention provides a method for manufacturing a prepreg for autoclave-free applications applicable to large structures, characterized by comprising the step of obtaining a semi-impregnated prepreg by passing a prepreg-formed fiber, formed by heat-pressing a first thermosetting resin of high viscosity on one side of the fiber and heat-pressing a second thermosetting resin of low viscosity on the other side, through release paper peeling rolls to peel off the release paper laminated to the first thermosetting resin of high viscosity, and winding the fiber onto a winding roll. Additionally, the thickness ratio of the first thermosetting resin and the second thermosetting resin is characterized as being 1:2 to 4.

[0024] delete

[0025] delete

[0026] delete Effects of the invention

[0027] According to the present invention, a high-viscosity / low-flow resin is applied to one side of the fiber for shape stability, so that excellent shape stability is maintained during operations at room temperature such as tailoring, lay-up, and rolling of the semi-impregnated prepreg, making the operation easy. Additionally, the possibility of shape defects occurring, such as the fiber orientation being disrupted or unidirectional fibers splitting, is reduced, thereby enabling the production of a molded product with higher physical properties. Furthermore, a low-viscosity / high-flow resin with high molding impregnation is applied to the other side, so that when manufacturing a molded product using an autoclave-free process, the flowability of the resin and the wetting of the fiber are increased, resulting in a lower porosity and enabling the production of a molded product with excellent physical properties. Brief explanation of the drawing

[0028] FIG. 1 is a conceptual diagram of a conventional prepreg and a semi-impregnated prepreg. FIG. 2 is a manufacturing process diagram for manufacturing a semi-impregnated prepreg according to a preferred embodiment of the present invention. FIG. 3 is a block diagram of the manufacturing process of the present invention. FIG. 4 is a conceptual diagram of a semi-impregnated prepreg according to a preferred embodiment of the present invention. Fig. 5 is a conceptual cross-sectional view of an autoclave-free molded material according to the resin applied to a semi-impregnated prepreg. Specific details for implementing the invention

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings, focusing on the parts necessary to understand the operation and function according to the present invention.

[0030] The embodiments described in this specification and the configurations illustrated in the drawings are merely one preferred embodiment of the present invention and do not represent all of the technical concepts of the present invention; therefore, it should be understood that various modifications capable of replacing them may exist at the time of filing this application.

[0031] In describing embodiments of the present invention, unnecessary technical details that are well known in the technical field to which the present invention belongs and are not directly related to the present invention are omitted to ensure clearer communication without obscuring the essence of the invention. The present invention will be described in detail below with reference to the attached drawings illustrating specific embodiments.

[0032] A semi-impregnated prepreg for an autoclave-free process according to a preferred embodiment of the present invention comprises a sheet-shaped fiber (100), a first thermosetting resin (110) of high viscosity and low flowability coated on a release paper (111) that is pressed against one side of the fiber (100) to stabilize its shape, and a second thermosetting resin (120) of low viscosity and high flowability coated on a release paper (111) that has a viscosity relatively lower than that of the first thermosetting resin (110) and penetrates into the fiber (100) to improve molding impregnation.

[0033] Hereinafter, the manufacturing process of a preferred embodiment of the present invention will be described in detail with reference to the attached FIG. 2 and FIG. 3.

[0034] The method for manufacturing a semi-impregnated prepreg for an autoclave-free process according to the present invention is divided into a fiber supply step (S100), a prepreg-formed fiber formation step (S200), and a semi-impregnated prepreg manufacturing step (S300), as illustrated.

[0035] First, the fiber supply step (S100) is,

[0036] A step of continuously supplying or feeding a sheet-shaped fiber (100) through a compression roller using a spinning device or the like to open the fiber (100), wherein the fiber (100) may be selected from the group consisting of carbon fiber, glass fiber, aramid fiber, basalt fiber, boron fiber, and mixtures thereof. Additionally, the fiber (100) may be applied in the form of a unidirectional semi-impregnated prepreg (UD) where the fiber (100) is aligned in one direction, or in the form of a fabric-type semi-impregnated prepreg where the fiber (100) is formed in a fabric shape.

[0037] Next, the prepregned fiber forming step (S200) is,

[0038] A first thermosetting resin (110) having high viscosity and low flowability to stabilize the shape of the fiber (100) is coated on a release liner (111) and pressed onto one side of the fiber (100), and a second thermosetting resin (120) having low viscosity and high flowability, having a relatively lower viscosity than the first thermosetting resin (110) to penetrate the fiber (100) and improve molding impregnation, is coated on the release liner (111) and pressed onto the other side of the fiber (100) to form a prepreg fiber.

[0039] More specifically, a high-viscosity first thermosetting resin (110) coated on a release liner (111) is supplied to one side of the fiber (100), and a low-viscosity second thermosetting resin (120) coated on a release liner (111) is supplied to the other side, and is compressed on both sides of the fiber (100) by a first compression roller (130). As it passes through a heater (140) and is heated, it is pressed with an appropriate pressure by another second compression roller (131) above, so that the high-viscosity first thermosetting resin (110) and the low-viscosity second thermosetting resin (120) are integrally bonded to both sides of the fiber (100).

[0040] At this time, when a large amount of pressure is applied by the first and second compression rollers (130) (131), it becomes a shape similar to a completely impregnated prepreg, so it is desirable to maintain the impregnation rate of the fiber (100) at a level of 20 to 70% by adjusting the spacing of each of the first and second compression rollers (130) (131).

[0041] Next, the semi-impregnated prepreg manufacturing step (S300) is,

[0042] The step of manufacturing a semi-impregnated prepreg (300) by peeling off the release paper (111) on one side of the prepreg-treated fiber (100) in the above step.

[0043] In the previous step, a prepreg fiber formed by heat-pressing a high-viscosity first thermosetting resin (110) on one side of the fiber (100) and heat-pressing a low-viscosity second thermosetting resin (120) on the other side is passed through release paper peeling rolls (150) to peel off the release paper (111) laminated to the high-viscosity first thermosetting resin (110) and wound onto a winding roll (160) to obtain a semi-impregnated prepreg (300).

[0044] Next, the first thermosetting resin (110) and the second thermosetting resin (120), which are features of the present invention, will be described in more detail.

[0045] The first thermosetting resin (110) and the second thermosetting resin (120) of the present invention must be of the same type and may be selected from the group consisting of epoxy resin, phenolic resin, unsaturated polyester resin, cyanate ester resin, melamine resin, bismaleimide resin and mixtures thereof.

[0046] First, the first thermosetting resin (110), which has a viscosity of 90,000 to 110,000 cps at 75 to 85°C and a melt flow index of 75 to 85 g / min, is a high viscosity / low flow resin that is characterized by having almost no stickiness at room temperature and high viscosity at a curing temperature of 80 to 150°C, so that there is not much flow of resin.

[0047] Second, the second thermosetting resin (120), which has a viscosity of 4,000 to 6,000 cps and a melt flow index of 450 to 800 g / min at 75 to 85°C, is characterized by being a low-viscosity / high-flow resin that is sticky and weak at room temperature, but has a very low viscosity within the curing temperature, making it easy to penetrate into each individual fiber of the fiber in a semi-impregnated state, and thus has very high impregnation in the process.

[0048] For example, the first thermosetting resin (110) may be a resin having a viscosity of 100,000 cps at 80°C and a melt flow index of 80, and the second thermosetting resin (120) may be a resin having a viscosity of 5,000 cps at 80°C and a melt flow index of 500 or higher.

[0049] However, the melt flow index of the resin is a numerical value representing the number of grams of resin that pass through a hole with a constant cross-sectional area for 10 minutes at a specific temperature and pressure. A higher melt flow index indicates that the fluidity of the resin is higher, but the viscosity is lower, so the resin lacks strength and becomes sticky at room temperature, resulting in poor shape stability and handling.

[0050] FIG. 4 is a conceptual diagram of a semi-impregnated prepreg according to a preferred embodiment of the present invention.

[0051] Referring to FIG. 4, a cross-sectional view of a semi-impregnated prepreg for an autoclave-free manufacturing process of the present invention is shown, in which a first thermosetting resin (110) having high viscosity / low flowability is bonded to one side of a fiber (100), and a second thermosetting resin (120) having low viscosity / high flowability is bonded to the other side of the fiber (100).

[0052] Here, the ratio of the void (101) is preferably about 10 to 70% due to the characteristics of the present invention. If the void ratio is less than 10%, the first thermosetting resin (110) and the second thermosetting resin (120) on the upper and lower sides are connected to each other during autoclave molding, and the flow path of the resin becomes blocked, thereby increasing the likelihood of voids occurring in the molded product. If it exceeds 70%, the reaction rate between the fiber (100) and the resin decreases, and the shape stability of the semi-impregnated prepreg (300) is likely to be significantly worse.

[0053] Accordingly, in the semi-impregnated prepreg (300), the first thermosetting resin (110), which is high viscosity / low flowability, is mainly responsible for shape stability, and the second thermosetting resin (120), which is low viscosity / high flowability, is responsible for penetrating and impregnating the unimpregnated fibers of the semi-impregnated prepreg (300). It is preferable that the amount of the second thermosetting resin (120), which is low viscosity / high flowability, be greater than the amount of the first thermosetting resin (110), which is high viscosity / low flowability. That is, the thickness of the second thermosetting resin (120), which is low viscosity / high flowability, is formed to be thicker than the thickness of the first thermosetting resin (110), which is high viscosity / low flowability.

[0054] Figure 5 is a conceptual cross-sectional view of an autoclave-free molded material according to the resin applied to a semi-impregnated prepreg.

[0055] Referring to FIG. 5, this figure is illustrated to explain the superiority of the semi-impregnated prepreg molding for the autoclave-free process of the present invention compared to conventional products.

[0056] FIG. 5(a) is a conceptual diagram of an example in which only a low-viscosity / high-flow thermosetting resin (120) with high flowability is applied to manufacture a semi-impregnated prepreg for a conventional autoclave-free process. In this case, shape stability is significantly reduced, so there are many cases where inconvenience must be endured during operation. In addition, if the flowability of the resin becomes excessively high, resin (102) may escape due to excessive resin flow during molding, so the volume ratio of fibers to resin originally planned changes, and a disadvantage may occur where the molded thickness is thinner than the expected thickness.

[0057] FIG. 5(b) is a conceptual diagram of an example in which only a high-viscosity / low-flow thermosetting resin (110) is applied to increase shape stability. In this case, there is a problem in that the flowability is significantly reduced during autoclave-free molding, so the entire area of ​​the fiber is not impregnated even after molding, and the probability of unimpregnated pores being formed increases, which may lead to a decrease in the physical properties of the molded product.

[0058] FIG. 5(c) illustrates that when manufacturing a semi-impregnated prepreg for an autoclave-free process, a high-viscosity / low-flow thermosetting resin (110) that maintains the shape stability characteristic of the present invention and a low-viscosity / high-flow thermosetting resin (120) that can improve molding impregnation are mixed, and that by applying the same resin, not only is the shape stability before molding excellent and workability good, but when molding using an autoclave-free process, the low-viscosity / high-flow thermosetting resin (120) easily penetrates the fibers, resulting in excellent impregnation. Therefore, a composite molded product (400) with few pores and well-controlled thickness can be obtained, and the thickness ratio of the high-viscosity / low-flow first thermosetting resin (110) and the low-viscosity / high-flow second thermosetting resin (120) is preferably about 1:2 to 4.

[0059] As described above, the most significant feature of the method for manufacturing a semi-impregnated prepreg for an autoclave-free process according to the present invention is that resins with different viscosity and flow properties are applied to both sides of a fiber (100), wherein a high-viscosity / low-flow resin that is easy to maintain shape stability at room temperature is applied to one side, and a low-viscosity / high-flow resin that has excellent molding impregnation properties during molding is applied to the other side.

[0060] Therefore, when using the semi-impregnated prepreg (300) which is the product of the present invention, excellent shape stability and workability at room temperature and excellent molding impregnation during molding, which are required characteristics of a semi-impregnated prepreg for an autoclave-free process, can be simultaneously secured, and it is expected that it can be widely utilized in the manufacture of various autoclave-free molded products.

[0061] In particular, since there is no need to use an expensive autoclave, not only can production time and costs be reduced, but in addition, while conventional prepregs require pressure to eliminate pores within the laminate, the present invention creates a passage for air to pass through the prepreg, thereby producing the same effect as applying pressure without actually applying pressure, thus enabling the production of prepreg of the same quality as that produced by molding in an autoclave.

[0062] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. The scope of protection of the present invention shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention. Explanation of the symbols

[0063] 100 : Fiber 101 : Pore 102 : Resin 111 : Release paper 110 : 1st class thermosetting resin (high viscosity / low flow thermosetting resin) 120 : Secondary thermosetting resin (low viscosity / high flow thermosetting resin) S100: Fiber supply stage S200: Prepregized fiber formation step S300: Semi-impregnated prepreg manufacturing stage 130: 1st compression roller 131: 2nd compression roller 140: Heater 150: Peel-off roll 160 : Rolling Roll 300 : Semi-impregnated Prepreg 400 : Composite molded product

Claims

Claim 1 A prepreg for autoclave-free application applicable to large structures, comprising: a sheet-shaped fiber; a first thermosetting resin having high viscosity and low flowability coated on a release liner to be pressed onto one side of the fiber to maintain the shape stability of the prepreg at room temperature; and a second thermosetting resin having lower viscosity and high flowability than the first thermosetting resin, coated on a release liner to be pressed onto the other side of the fiber to be impregnated into the fiber during molding to improve molding impregnation properties; wherein the second thermosetting resin is formed thicker than the first thermosetting resin. Claim 2 A method for manufacturing prepreg for autoclave-free applications applicable to large structures, comprising a fiber supply step, a prepreg fiber formation step, and a semi-impregnated prepreg manufacturing step, wherein the fiber supply step comprises a step of continuously supplying or feeding sheet-shaped fibers between compression rollers using a spinning device, etc., for opening the fibers, and the prepreg fiber formation step comprises a step in which a first thermosetting resin of high viscosity and low flowability coated on a release liner to stabilize the shape of the fiber is simultaneously and continuously supplied to one side of the fiber, and a second thermosetting resin of low viscosity and high flowability coated on a release liner is supplied to the other side, and the fibers are compressed on both sides by a first compression roller, and while being heated by passing through a heater, are pressed with an appropriate pressure by another second compression roller above, so that the high-viscosity first thermosetting resin and the low-viscosity second thermosetting resin are integrally bonded to both sides of the fibers to form prepreg fibers, and semi-impregnated prepreg A method for manufacturing a prepreg for autoclave-free application applicable to large structures, characterized in that the manufacturing step comprises a step of obtaining a semi-impregnated prepreg by passing a prepreg-formed fiber, formed by heat-pressing a high-viscosity first thermosetting resin on one side of the fiber and heat-pressing a low-viscosity second thermosetting resin on the other side, through release paper peeling rolls to peel off the release paper laminated with the high-viscosity first thermosetting resin, and winding the fiber onto a winding roll. Claim 3 A prepreg for autoclave-free application applicable to large structures, characterized in that, in claim 1, the thickness ratio of the first thermosetting resin and the second thermosetting resin is 1:2 to 4. Claim 4 delete

Images