Fiber-composite nonwoven fabric and method for manufacturing fiber-composite nonwoven fabric

Abstract

According to an embodiment of the present invention, provided is a fiber-composite nonwoven fabric comprising: a surface layer portion having a composition in which reinforcing fibers and thermoplastic resin fibers are mixed; and a deep layer portion, wherein the thermoplastic resin fibers included in the surface layer portion are provided in a molten state, a plurality of nodal points at which the molten thermoplastic resin fibers and the reinforcing fibers are fused are provided in the surface layer portion, and the thermoplastic resin fibers included in the deep layer portion are provided in an unmolten or partially molten state. According to the present invention, provided is a fiber-composite nonwoven fabric without a binder or with only a small amount of binder added thereto if necessary, and thus, there is no or little concern about high porosity and non-uniform pore formation in a composite material due to evaporation of a binder, in a high-temperature manufacturing process for composite materialization and productization using nonwoven fabric. Accordingly, the molded composite material can exhibit excellent mechanical properties of tensile strength and tensile rigidity, and excellent product quality.

Description

Fiber composite nonwoven fabric and method for manufacturing fiber composite nonwoven fabric

[0001] The present invention relates to a fiber composite nonwoven fabric in which reinforcing fibers and thermoplastic resin fibers are combined, and a method for manufacturing the same. The present invention is a technology for fixing a web within a nonwoven fabric by a bonding point formed by thermoplastic resin fibers and reinforcing fibers without a binder or needling process, thereby exhibiting excellent mechanical properties and quality.

[0002] According to ASTM (American Society for Testing and Materials), nonwoven fabrics are defined as “fiber aggregates that are bound together by chemical or mechanical action or by appropriate moisture and heat treatment without the process of spinning, weaving, or knitting, and have a fabric shape.”

[0003] Nonwoven fabrics have the advantages of unlimited raw material selection, high-speed and simplified processes, composites with heterogeneous fibers, and diversification of the final product's uses. Therefore, the nonwoven fabric material industry is a high value-added technology field with very high future growth potential, as it can replace existing textile products or create new uses across daily life and industry.

[0004] Nonwoven fabrics are classified by function and manufacturing method, and are manufactured using various raw materials such as natural materials, synthetic materials, metals, and glass, and are not limited to fibers such as short fibers or long fibers. Since the manufacturing process is relatively simple, it is easy to composite with heterogeneous fiber aggregates, and thus, due to its multifunctionality through composites with other materials, it is used in various industrial fields such as clothing, construction / civil engineering, hygiene / medical, and environment.

[0005] The manufacturing process of nonwoven fabrics can be broadly divided into three stages: web formation → web bonding → processing. In the web formation stage, it is further divided into two stages: dry and wet.

[0006] While the dry process forms fibers into a web in a standard atmosphere, the wet process obtains a web by dispersing fibers in water and floating them.

[0007] Dry-laid nonwovens are manufactured primarily by carding long fibers into a web, then bonding the resulting webs together through chemical, physical, and mechanical means. Wet-laid nonwovens are manufactured primarily by uniformly dispersing short fibers in water, floating them on a mesh, and bonding the resulting webs together through chemical and physical means to form sheets.

[0008] During this process, a binder is utilized to bond the fiber webs created during the manufacturing of wet and dry nonwovens. However, the large amount of binder added and sprayed can vaporize during the high-temperature molding process for composite material and product manufacturing, creating uneven pores within the composite. High porosity and uneven pores within the composite can lead to variations in mechanical properties and deterioration of properties, and can also be the cause of product quality problems.

[0009] The present invention aims to design a nonwoven structure and a manufacturing method so that a web can be fixed without using a binder in providing a nonwoven fabric in which reinforcing fibers and thermoplastic resin fibers are composited.

[0010] According to one embodiment of the present invention, a fiber composite nonwoven fabric is provided, which includes a surface portion and a deep portion of a composition in which reinforcing fibers and thermoplastic resin fibers are mixed, the thermoplastic resin fibers included in the surface portion are provided in a molten state, a plurality of nodal points are provided in the surface portion where the molten thermoplastic resin fibers and the reinforcing fibers are fused, and the thermoplastic resin fibers included in the deep portion are provided in a non-molten or partially molten state.

[0011] According to one embodiment of the present invention, the surface portion is provided with a fiber composite nonwoven fabric provided on each of the upper surface and the back surface of the deep portion.

[0012] According to one embodiment of the present invention, a fiber composite nonwoven fabric is provided, wherein the reinforcing fiber is at least one selected from the group consisting of carbon fiber, glass fiber, aramid fiber, Kevlar fiber, ceramic fiber, basalt fiber, boron fiber, and natural fiber.

[0013] According to one embodiment of the present invention, a method for manufacturing a fiber composite nonwoven fabric is provided, comprising: a first step of forming a nonwoven fabric by mixing reinforcing fibers and thermoplastic resin fibers; a second step of applying heat to the nonwoven fabric provided in the first step to melt thermoplastic resin fibers provided in a surface portion of the nonwoven fabric provided adjacent to a heat source, wherein a plurality of nodal points are provided in the surface portion where the molten thermoplastic resin fibers and the reinforcing fibers are fused, and the thermoplastic resin fibers included in a deep portion of the nonwoven fabric that is further from the heat source than the surface portion are provided in an unmelted or partially melted state.

[0014] According to one embodiment of the present invention, a method for manufacturing a fiber composite nonwoven fabric is provided, wherein the heat source for performing the second step is provided on the upper and lower surfaces of the nonwoven fabric.

[0015] According to one embodiment of the present invention, a method for manufacturing a fiber composite nonwoven fabric is provided, wherein in the first step, the nonwoven fabric is manufactured by supplying reinforcing fibers and thermoplastic resin fibers together with water on a wire belt to form a fiber web, and drying the nonwoven fabric through a dehydration process.

[0016] According to one embodiment of the present invention, a method for manufacturing a fiber composite nonwoven fabric is provided, in which the nonwoven fabric is manufactured by mixing reinforcing fibers and thermoplastic resin fibers in a first step, forming a sheet-like web through a carding process, and then overlapping the web in multiple layers using a cross-lay facility.

[0017] According to the present invention, the web within the nonwoven fabric can be fixed by the bonding points formed by the thermoplastic resin fibers and the reinforcing fibers even without a binder.

[0018] According to the present invention, a fiber composite nonwoven fabric is provided without a binder or with only a small amount of binder added as needed. Therefore, there is no or little concern about the occurrence of high porosity and uneven pores within the composite due to binder vaporization during the high-temperature manufacturing process for composite materials and products using the nonwoven fabric. Accordingly, the formed composite material can exhibit excellent mechanical properties such as tensile strength and tensile stiffness, as well as product quality.

[0019] FIG. 1 is a cross-sectional view of a fiber composite nonwoven fabric according to one embodiment of the present invention.

[0020] Figure 2 is an enlarged image of the nodal point formed between the reinforcing fiber and the thermoplastic resin fiber.

[0021] FIG. 3a and FIG. 3b illustrate a method for manufacturing a fiber composite nonwoven fabric according to one embodiment of the present invention. FIG. 3a is a cross-sectional view of a nonwoven fabric formed by mixing reinforcing fibers and thermoplastic resin fibers, and FIG. 3b is a cross-sectional view of a fiber composite nonwoven fabric formed by applying heat to the nonwoven fabric to melt thermoplastic resin fibers provided on the surface portion.

[0022] FIG. 4a and FIG. 4b illustrate a method for manufacturing a fiber composite nonwoven fabric including a binder according to one embodiment of the present invention. FIG. 4a is a cross-sectional view of a nonwoven fabric formed by mixing reinforcing fibers, thermoplastic resin fibers, and a binder, and FIG. 4b is a cross-sectional view of a fiber composite nonwoven fabric formed by applying heat to the nonwoven fabric to melt thermoplastic resin fibers provided on the surface portion.

[0023] Figure 5 shows the results of analyzing the properties and manufacturing method of a nonwoven fabric according to a conventional technology including a binder.

[0024] Figure 6 is a comparative analysis result of mechanical properties according to the reinforcing fiber content of a composite material using a nonwoven fabric manufactured according to the present invention.

[0025] Figure 7 shows the results of a comparative analysis of tensile strength and tensile stiffness of a composite material using a nonwoven fabric manufactured according to a conventional technology and the present invention.

[0026] Figure 8 shows the results of a cross-sectional analysis of a nonwoven fabric manufactured according to the prior art and the present invention.

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. In describing the present invention, detailed descriptions of related known functions or configurations will be omitted if it is determined that such detailed descriptions may unnecessarily obscure the gist of the present invention. In addition, the terms used in this specification are terms used to appropriately express preferred embodiments of the present invention, and may vary depending on the intention of the user or operator, or the customs of the field to which the present invention belongs. Therefore, the definitions of these terms should be determined based on the contents throughout this specification. The same reference numerals presented in each drawing represent the same elements.

[0028] Throughout the specification, when we say that an element is "on" another element, this includes not only cases where the element is in contact with the other element, but also cases where another element exists between the two elements.

[0029] Additionally, throughout the specification, when a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components.

[0030] FIG. 1 is a cross-sectional view of a fiber composite nonwoven fabric according to one embodiment of the present invention.

[0031] Referring to FIG. 1, the fiber composite nonwoven fabric according to the present invention includes a surface portion and a deep portion having a composition in which reinforcing fibers and thermoplastic resin fibers are mixed, the thermoplastic resin fibers included in the surface portion are provided in a molten state, a plurality of nodes are provided in the surface portion where the molten thermoplastic resin fibers and the reinforcing fibers are fused, and the thermoplastic resin fibers included in the deep portion are provided in a non-molten or partially molten state.

[0032] Fiber composite nonwoven fabrics are composed of a mixture of reinforcing fibers and thermoplastic resin fibers. Nonwoven fabrics can be defined as a fabric-like structure formed by bonding fiber aggregates together through chemical or mechanical action, or by appropriate moisture and heat treatment, without the use of spinning, weaving, or knitting processes.

[0033] The reinforcing fibers are included in the fiber composite nonwoven fabric and may be at least one selected from the group consisting of carbon fibers, glass fibers, aramid fibers, Kevlar fibers, ceramic fibers, basalt fibers, boron fibers, and natural fibers. Furthermore, the reinforcing fibers may be provided in the form of short fibers or long fibers, and may provide mechanical strength to the fiber composite nonwoven fabric. Here, short fibers may refer to fibers having a length of 50 mm or less, and long fibers may refer to fibers having a length of 50 mm or more.

[0034] According to the prior art, a wet nonwoven fabric manufacturing process was generally utilized to manufacture a nonwoven fabric containing reinforcing fibers in the form of short fibers. In the wet nonwoven fabric manufacturing process, a binder was added when reinforcing fibers in the form of short fibers were dispersed in a solvent such as water, or the binder was sprayed to fix the web containing the reinforcing fibers. In addition, according to the prior art, a dry nonwoven fabric manufacturing process was generally utilized to manufacture a nonwoven fabric containing reinforcing fibers in the form of long fibers. In the process of manufacturing a nonwoven fabric, the web containing reinforcing fibers was fixed and transported by needling the nonwoven fabric or spraying the binder during the process. In other words, according to the prior art, a binder had to be used to manufacture a nonwoven fabric whether the reinforcing fibers were long fibers or short fibers.

[0035] In contrast, according to the present invention, by mixing and using reinforcing fibers and thermoplastic resin fibers and configuring the thermoplastic resin fibers to form nodes with the reinforcing fibers within the surface layer, a fiber composite nonwoven fabric having excellent mechanical strength can be provided without using a binder or by adding a small amount of binder as needed.

[0036] Thermoplastic fibers are provided together with reinforcing fibers in fiber composite nonwoven fabrics. Thermoplastic fibers can refer to polymer compounds that melt and exhibit fluidity when heated above their glass transition temperature, and lose fluidity and return to a solid state when the temperature drops below their glass transition temperature. Materials that can be utilized as thermoplastic fibers include nylon, polyethylene, polypropylene, vinyl chloride resin, vinyl acetate resin, polystyrene, ABS resin, acrylic resin, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or copolymers or mixtures thereof.

[0037] Within the fiber composite nonwoven fabric, reinforcing fibers and thermoplastic resin fibers are provided in a mixed state. At this time, molten thermoplastic resin fibers are provided between the reinforcing fibers in the surface layer of the fiber composite nonwoven fabric and can form nodes together with the reinforcing fibers. The reinforcing fibers and thermoplastic resin fibers can be provided in a mixed weight ratio of about 10:90 to about 90:10.

[0038] Figure 2 is an enlarged image of the nodal point formed between the reinforcing fiber and the thermoplastic resin fiber.

[0039] Referring to Fig. 2, a node may refer to a point where reinforcing fibers and thermoplastic resin fibers are fused within a web constituting a nonwoven fabric. Since reinforcing fibers do not melt after heating, a node may be provided in the form of a molten thermoplastic resin weaving multiple reinforcing fibers at the node. At this time, each reinforcing fiber may be fixed by the multiple node points, and thus the web of the nonwoven fabric including the reinforcing fibers and thermoplastic resin fibers may be fixed as a single unit. Therefore, according to the present invention, reinforcing fibers and thermoplastic resin fibers may be fixed even without including a binder in the surface layer. According to the prior art, the binder that is added and sprayed vaporizes during a high-temperature process, thereby generating high porosity and uneven pores within the composite, and the pores within the composite cause deviations in mechanical properties and deterioration of properties.

[0040] Nodes within a fiber composite nonwoven fabric may be provided in the surface layer, and may not be provided in the deep layer located deeper than the surface layer. Here, the surface layer of the nonwoven fabric refers to the area from the surface of the nonwoven fabric to a certain thickness. For example, the surface layer may be the area from the surface of the nonwoven fabric to about 5% to 45% of the total thickness. However, the thickness of the surface layer may vary depending on the type and thickness of the nonwoven fabric, and the heat sources located on the upper and lower surfaces, and the criterion for dividing the surface layer and the deep layer may be the presence or absence of nodes.

[0041] As described above, the surface layer is the region where reinforcing fibers and thermoplastic resin fibers are bonded and fixed by knots. The surface layers may be provided on the upper and lower surfaces of the fiber composite nonwoven fabric. In this case, the fiber composite nonwoven fabric may have a depth layer provided between the two surface layers. The surface layers provided on the upper and lower surfaces can hold the depth layer provided internally. Accordingly, even if no knots are provided in the depth layer internally, the fiber composite nonwoven fabric can be fixed by the surface layer provided with knots. By providing knots only on the surface layer, it is not necessary to wait for all thermoplastic resin fibers contained in the entire nonwoven fabric to melt, so the heating process for melting the thermoplastic resin fibers by applying heat can be performed relatively quickly. This has the advantage of increasing the speed of the overall process and reducing the energy required for nonwoven fabric production. In addition, the reinforcing fibers and thermoplastic resin fibers provided internally have a certain level of fluidity, which can disperse stress applied to the nonwoven fabric.

[0042] The deep region is a region located inward in the thickness direction from the surface region within the nonwoven fabric, and as mentioned above, may be a region without knots. That is, the fiber composite nonwoven fabric according to the present invention may be composed of a surface region with knots and a deep region without knots. The deep region may be a region of about 5% to 45% of the total thickness of the nonwoven fabric.

[0043] According to the present invention, the web within the nonwoven fabric can be fixed by the bonding points formed by the thermoplastic resin fibers and reinforcing fibers, even without a binder or with the addition of a small amount of binder. For example, even when binder is added, the binder can be added in a small amount, at a ratio of 3 wt% or less relative to the total nonwoven fabric. Considering that prior art typically includes about 10 wt% of binder, the fiber composite nonwoven fabric of the present invention can use only a very small amount of binder, even if it includes it.

[0044] In the case of the present invention, since a large number of nodules formed by molten thermoplastic resin fibers and reinforcing fibers are provided in the surface layer to fix the surface layer, and the deep layer is covered and fixed by the surface layer provided with nodules, even if no binder or only a small amount of binder is provided, the mechanical stability is excellent. Furthermore, in the case of the present invention, since no binder or a small amount of less than 3 wt% is included, there is no or little concern that the vaporized binder will remain during the high-temperature molding process for composite materialization and productization, resulting in high porosity and uneven pores within the composite. In the case of the prior art, since the binder is included in a large amount of about 10 wt%, the vaporized binder remains during the high-temperature molding process in the composite, resulting in high porosity and uneven pores. Such high porosity and uneven pores have caused a deterioration in the overall mechanical properties of composites using nonwoven fabrics.

[0045] Whether or not a binder is provided in a fiber composite nonwoven fabric may vary depending on the method of manufacturing the nonwoven fabric. For example, if a nonwoven fabric is manufactured by mixing reinforcing fibers and thermoplastic resin fibers, forming a sheet-like web through a carding process, and then overlaying multiple layers using cross-lay equipment, a fiber composite nonwoven fabric can be manufactured without a binder. In contrast, if a nonwoven fabric is manufactured by forming a fiber web by supplying reinforcing fibers and thermoplastic resin fibers together with water on a wire belt, and then drying through a dehydration process, a small amount of binder, such as 1 to 3 wt%, may be used.

[0046] Referring to Fig. 1, the fiber composite nonwoven fabric may be composed of an upper surface layer accounting for approximately 34.5% of the total thickness, a lower surface layer accounting for approximately 29.5% of the total thickness, and a depth layer (approximately 36.0% of the total thickness) provided between the upper surface layer and the lower surface layer. As can be seen in the drawing, the thermoplastic resin fiber (nylon fiber) provided in the surface layer melts to form nodules, and accordingly, the color of the surface layer turns black. In contrast, the nylon fiber provided in the depth layer is not melted, and it can be seen that it is mixed with reinforcing fiber (carbon fiber) in a form without nodules.

[0047]

[0048] Next, a method for manufacturing a fiber composite nonwoven fabric according to one embodiment of the present invention will be examined.

[0049] FIG. 3a and FIG. 3b illustrate a method for manufacturing a fiber composite nonwoven fabric according to one embodiment of the present invention. FIG. 3a is a cross-sectional view of a nonwoven fabric formed by mixing reinforcing fibers and thermoplastic resin fibers, and FIG. 3b is a cross-sectional view of a fiber composite nonwoven fabric formed by applying heat to the nonwoven fabric to melt thermoplastic resin fibers provided on the surface portion.

[0050] FIG. 4a and FIG. 4b illustrate a method for manufacturing a fiber composite nonwoven fabric including a binder according to one embodiment of the present invention. FIG. 4a is a cross-sectional view of a nonwoven fabric formed by mixing reinforcing fibers, thermoplastic resin fibers, and a binder, and FIG. 4b is a cross-sectional view of a fiber composite nonwoven fabric formed by applying heat to the nonwoven fabric to melt thermoplastic resin fibers provided on the surface portion.

[0051] According to the method for manufacturing a fiber composite nonwoven fabric according to the present invention, there is provided a first step of forming a nonwoven fabric by mixing reinforcing fibers and thermoplastic resin fibers; a second step of applying heat to the nonwoven fabric provided in the first step to melt thermoplastic resin fibers provided in a surface portion of the nonwoven fabric provided adjacent to a heat source, wherein a plurality of nodal points are provided in the surface portion where the molten thermoplastic resin fibers and the reinforcing fibers are fused, and the thermoplastic resin fibers included in a deep portion of the nonwoven fabric that is further from the heat source than the surface portion are provided in a non-melted or partially melted state.

[0052] Looking at the step of forming a nonwoven fabric by mixing reinforcing fibers and thermoplastic resin fibers in the first step, the method of forming the nonwoven fabric can be performed by a dry or wet method.

[0053] When the first step is performed by a dry method, the nonwoven fabric can be manufactured by mixing reinforcing fibers and thermoplastic resin fibers, forming a sheet-like web through a carding process, and then overlapping multiple layers using a cross-lay facility. The carding process can refer to a process of forming a web by orienting fibers in a horizontal or vertical direction. Once a sheet-like web is formed through the carding process, the web can be overlaid into multiple layers using a cross-lay facility. According to the prior art, the multiple layers of web can be fixed by spraying a binder during the cross-lay process or the carding process, or by needling after the cross-lay process. Needling can be a process of repeatedly punching through multiple layers of web to intertwine the webs of each layer. However, according to the present invention, the web can be fixed by melting the thermoplastic resin fibers included in the surface portion in the second step described below without needling or binder injection and then allowing them to be fused with the reinforcing fibers (i.e., forming a node).

[0054] When the first step is performed using a wet method, the nonwoven fabric can be manufactured by supplying reinforcing fibers and thermoplastic resin fibers together with water on a wire belt to form a fiber web, and then drying them through a dehydration process. In this case, according to the prior art, a binder can be dispersed together when dispersing the reinforcing fibers and thermoplastic resin fibers together with water, or the binder can be sprayed onto the web before or after the dehydration process after forming the fiber web. However, according to the present invention, without mixing or spraying the binder, in the second step described below, a heat source is supplied to melt the thermoplastic resin fibers included in the surface portion during a series of drying processes, and then fuse them with the reinforcing fibers (i.e., form a knot), thereby fixing the web.

[0055] Depending on whether the first step is performed by a dry or wet method, the provision of a binder within the nonwoven fabric may vary. According to the present invention, a nonwoven fabric can be provided that contains only a small amount of binder or no binder. When the nonwoven fabric is produced by a dry method, the nonwoven fabric can be produced without a binder, as illustrated in FIG. 3a. On the other hand, when the nonwoven fabric is produced by a wet method, the nonwoven fabric can be produced without a binder, as illustrated in FIG. 3a, and the nonwoven fabric can be produced by mixing in about 1 wt% to about 3 wt% of a binder, as illustrated in FIG. 4a.

[0056] Referring to FIGS. 3a and 4a, the nonwoven fabric manufactured in the first step is in a state in which reinforcing fibers and thermoplastic resin fibers are uniformly dispersed and mixed, and the thermoplastic resin fibers may be mixed in the nonwoven fabric in the form of pellets, fibers, etc. while not yet melted.

[0057] Next, in the second step, the thermoplastic resin fibers provided on the surface layer of the nonwoven fabric, provided adjacent to the heat source, are melted. There are no restrictions on the heat source that can be used, and various types of heat sources, such as infrared heaters and hot plates, can be utilized.

[0058] Figures 3b and 4b show the results of manufacturing a fiber composite nonwoven fabric by performing the second step process on a nonwoven fabric without a binder and a nonwoven fabric containing a binder, respectively.

[0059] Since the heat source in the second stage is positioned adjacent to the surface of the nonwoven fabric, the thermoplastic resin fibers provided in the area close to the heat source are melted first. Therefore, as heat is transferred from the surface of the nonwoven fabric toward the inside, the thermoplastic resin fibers gradually begin to melt, and the melted thermoplastic resin fibers are fused to the reinforcing fibers dispersed together to form a node. In particular, when heat is applied in the second stage, the reinforcing fibers included in the nonwoven fabric function as thermal conductors, which can further promote heat diffusion within the nonwoven fabric. For example, carbon fibers, which can be utilized as reinforcing fibers, have excellent thermal conductivity and can function as a medium to transfer heat applied from the outside to the inside of the nonwoven fabric. Accordingly, the execution time of the second stage can be shortened, and energy consumption can also be reduced.

[0060] The heat source in the second stage can be positioned adjacent to each of the upper and lower surfaces of the nonwoven fabric, as needed. In this case, a surface layer can be formed on each of the upper and lower surfaces of the nonwoven fabric, as illustrated in FIGS. 3b and 4b.

[0061] At this time, as illustrated in Fig. 3b, if there is no binder in the nonwoven fabric manufactured in the first step, no binder remains naturally in either the surface or the deep region even after the second step is performed. In contrast, as illustrated in Fig. 4b, if there is binder in the nonwoven fabric manufactured in the second step, the binder remains in the deep region where sufficient heat to melt the thermoplastic resin fibers has not yet reached. In addition, some binder may remain in the surface region. However, since the amount of binder remaining in both the surface and the deep region is significantly less than that of the nonwoven fabric manufactured according to the prior art, the rate of pore generation can be reduced.

[0062] The execution time of the second step can be adjusted by considering factors such as the type of heat source, and the execution temperature can also vary depending on the composition of the nonwoven fabric, particularly the type and content of thermoplastic resin fibers. For example, the second step can be performed by applying a temperature of 200°C or higher to the nonwoven fabric.

[0063]

[0064] Above, we have examined a fiber composite nonwoven fabric and its manufacturing method according to one embodiment of the present invention. Below, we will examine the beneficial effects of the fiber composite nonwoven fabric according to the present invention through experimental examples.

[0065] Figure 5 shows the results of analyzing the properties of a composite using a prior art nonwoven fabric containing a binder. Referring to Figure 5, the nonwoven fabric was manufactured to contain a binder (VPB105) and a dispersant (CMC) and heated to 230-250°C. Referring to the cross-sectional analysis results on the right side of the figure, it can be confirmed that numerous irregular pores were formed as the binder vaporized. These uneven pores can deteriorate the mechanical properties of the composite or prevent it from exhibiting consistent properties.

[0066] Next, Fig. 6 shows the results of a comparative analysis of mechanical properties according to the reinforcing fiber content of a composite material using a nonwoven fabric manufactured according to the present invention.

[0067] Referring to Table 1 and Fig. 6 below, the tensile strength, tensile stiffness, and porosity according to the fiber content were evaluated for composites containing reinforcing fibers in fiber volume fractions of 20% (FVF20), 25% (FVF25), 30% (FVF30), and 35% (FVF35), respectively. Referring to the figure, the tensile strength according to the fiber content was found to be high when reinforcing fibers were contained in fiber volume fractions of 25% to 35%, and it can be confirmed that the tensile stiffness increased as the reinforcing fiber content increased. It was suggested that the porosity had a stable distribution within 1.0% regardless of the reinforcing fiber content.

[0068] Evaluation ItemsFVF20FVF25FVF30FVF35Fiber Volume Fraction [vol%]22.524.629.233.1Fiber Weight Fraction [wt%]31.634.239.644.5Tensile Strength [MPa]268334324353Tensile Stiffness [GPa]20.423.928.931.0Porosity [%]-0.20.0-0.61.0

[0069] Next, Fig. 7 shows the results of comparative analysis of tensile strength and tensile modulus of composites using nonwoven fabrics manufactured according to the prior art and the present invention. In addition, Fig. 8 shows the results of cross-sectional analysis of nonwoven fabrics manufactured according to the prior art and the present invention. Referring to Fig. 7 and Table 2, the results of comparative analysis of tensile strength and tensile modulus of nonwoven fabrics manufactured by mixing binder according to the prior art (B) and manufactured by forming a bonding point on the surface without a binder according to the present invention (A) can be confirmed for nonwoven fabrics in which reinforcing fibers are mixed at a fiber volume fraction of 30%.

[0070] Proposed Technology A Tensile strength [MPa] Tensile stiffness [GPa] FVF 30 Specimen 32428.9 Deviation [%] 181.4 Conventional Technology B Tensile strength [MPa] Tensile stiffness [GPa] FVF 30 Specimen 29728.8 Deviation [%] 732.0

[0071] It can be confirmed that the fiber composite nonwoven fabric manufactured according to the present invention has both higher tensile strength and tensile stiffness than the nonwoven fabric manufactured according to the prior art including a binder. In particular, it can be confirmed that the fiber composite nonwoven fabric manufactured according to the present invention has less variation in tensile strength and tensile stiffness depending on the location. This is because, as can be confirmed in Fig. 8, the fiber nonwoven fabric manufactured according to the present invention does not use a binder or contains only a small amount of binder as needed, and the binder vaporizes either absent or very little during the high-temperature molding process, resulting in low porosity within the composite. In contrast, the nonwoven fabric manufactured according to the prior art including a binder had lower tensile strength and tensile stiffness than the nonwoven fabric manufactured according to the present invention, and in particular, the variation in tensile strength and tensile stiffness depending on the location within the composite was large. This is understood to be due to the multiple pores (black portions of the cross-section) included in the cross-section, as can be confirmed in Fig. 8.

[0072] In this way, according to the present invention, a fiber composite nonwoven fabric structure composed of a surface layer including nodes and a deep layer without nodes can be provided without using a binder, thereby providing a nonwoven fabric having excellent tensile strength and tensile rigidity and small deviation in physical properties.

[0073] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that various modifications and changes to the present invention can be made without departing from the spirit and technical scope of the present invention as set forth in the claims to be described below.

[0074] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the patent claims.

Claims

1. Contains a surface layer and a deep layer of a composition mixed with reinforcing fibers and thermoplastic resin fibers, The thermoplastic resin fibers contained in the above surface layer are provided in a molten state, Within the above surface layer, a plurality of nodes are provided where the molten thermoplastic resin fibers and the reinforcing fibers are fused, A fiber composite nonwoven fabric, wherein the thermoplastic resin fibers contained in the above-mentioned deep layer are provided in a non-melted or partially melted state.

2. In paragraph 1, A fiber composite nonwoven fabric, wherein the surface layer is provided on each of the upper and lower surfaces of the deep layer.

3. In paragraph 1, A fiber composite nonwoven fabric, wherein the reinforcing fiber is at least one selected from the group consisting of carbon fiber, glass fiber, aramid fiber, Kevlar fiber, ceramic fiber, basalt fiber, boron fiber and natural fiber.

4. A first step of forming a non-woven fabric by mixing reinforcing fibers and thermoplastic resin fibers; A second step of applying heat to the nonwoven fabric provided in the first step and melting the thermoplastic resin fibers provided on the surface of the nonwoven fabric provided adjacent to the heat source, Within the above surface layer, a plurality of nodes are provided where the molten thermoplastic resin fibers and the reinforcing fibers are fused, A method for manufacturing a fiber composite nonwoven fabric, wherein the thermoplastic resin fibers contained in the deep portion of the nonwoven fabric, which is further from the heat source than the surface portion, are provided in an unmelted or partially melted state.

5. In paragraph 4, A method for manufacturing a fiber composite nonwoven fabric, wherein the heat source for performing the second step is provided on the upper and back surfaces of the nonwoven fabric.

6. In paragraph 4, A method for manufacturing a fiber composite nonwoven fabric, wherein in the first step, the nonwoven fabric is manufactured by supplying reinforcing fibers and thermoplastic resin fibers together with water onto a wire belt to form a fiber web, and drying the same through a dehydration process.

7. In paragraph 4, A method for manufacturing a fiber composite nonwoven fabric, wherein in the first step, the nonwoven fabric is manufactured by mixing reinforcing fibers and thermoplastic resin fibers, creating a sheet-like web through a carding process, and then superimposing the web in multiple layers using cross-lay equipment.

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