WO2025116235A1 - Fiber-composite nonwoven fabric and method for manufacturing fiber-composite nonwoven fabric - Google Patents

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 producing fiber composite nonwoven fabric

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.

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."

Nonwoven fabrics have the advantages of unlimited raw material selection, high-speed and simplified processes, composites with different fiber assemblies, and diversification of the uses of the final product, so they can replace existing textile products or create new uses in everyday life and across industries. Therefore, the nonwoven fabric material industry is a high value-added technology field with very high future growth potential.

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 single fibers or long fibers. Since the manufacturing process is relatively simple, it is easy to composite with heterogeneous fiber aggregates, and is utilized in various industrial fields such as clothing, construction/civil engineering, hygiene/medical, and the environment due to its multifunctionality through composites with other materials.

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

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.

Dry nonwoven fabrics are mainly manufactured by forming long fibers into a web using carding methods and combining webs made by chemical, physical, and mechanical methods. Wet nonwoven fabrics are mainly manufactured by uniformly dispersing short fibers in water, floating them on a mesh, and combining webs made by chemical and physical methods to form sheets.

At this time, a binder is used to combine the fiber webs created during the manufacturing of wet nonwoven fabrics and dry nonwoven fabrics, but a large amount of added and sprayed binder may vaporize during the high-temperature molding process for composite material and product manufacturing, thereby generating non-uniform pores within the composite. High porosity and non-uniform pores within the composite cause deviations in mechanical properties and deterioration of properties, and may also be the cause of product quality deterioration.

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.

According to one embodiment of the present invention, a fiber composite nonwoven fabric is provided, which 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 at which 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.

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.

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.

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 nodes are provided in the surface portion at which 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.

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 back surfaces of the nonwoven fabric.

According to one embodiment of the present invention, a method for manufacturing a fiber composite nonwoven fabric is provided, wherein in a 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 nonwoven fabric through a dehydration process.

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 mixing reinforcing fibers and thermoplastic resin fibers, forming a sheet-like web through a carding process, and then superimposing the web in multiple layers using cross-lay equipment.

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.

According to the present invention, since a fiber composite nonwoven fabric is provided without a binder or with only a small amount of binder added as needed, there is no or little concern about high porosity and uneven pore generation in the composite due to binder vaporization during a high-temperature manufacturing process for composite materialization and productization using the nonwoven fabric. Accordingly, the molded composite material can exhibit excellent mechanical properties such as tensile strength and tensile stiffness, and product quality.

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

Figure 2 is an enlarged image of the nodules formed between the reinforcing fibers and the thermoplastic resin fibers.

FIGS. 3A and 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 layer.

FIGS. 4A and 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.

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

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.

Figure 7 shows the results of comparative analysis of tensile strength and tensile stiffness of composite materials using nonwoven fabrics manufactured according to conventional technology and the present invention.

Figure 8 shows the results of a cross-sectional analysis of a nonwoven fabric manufactured according to conventional technology and the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. In addition, the terms used in this specification are terms used to appropriately express the preferred embodiments of the present invention, and this 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 made based on the contents throughout this specification. The same reference numerals presented in each drawing represent the same members.

Throughout the specification, when it is said 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 there is another element between the two elements.

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.

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

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.

Fiber composite nonwoven fabrics have a composition of reinforcing fibers and thermoplastic resin fibers. Nonwoven fabrics can be defined as having a fabric shape in which fiber aggregates are bonded to each other by chemical or mechanical action or appropriate moisture and heat treatment without the process of spinning, weaving, or knitting.

The reinforcing fiber is included in the fiber composite nonwoven fabric, and may be 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. In addition, the reinforcing fiber may be provided in the form of short fiber or long fiber, and may provide mechanical strength to the fiber composite nonwoven fabric. Here, the short fiber may mean a fiber having a length of 50 mm or less, and the long fiber may mean a fiber having a length of 50 mm or more.

According to the prior art, a wet nonwoven fabric manufacturing process was generally utilized to manufacture a nonwoven fabric including 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 a web including the reinforcing fibers. In addition, according to the prior art, a dry nonwoven fabric manufacturing process was generally utilized to manufacture a nonwoven fabric including reinforcing fibers in the form of long fibers. In the process of manufacturing a nonwoven fabric, the nonwoven fabric was needled to fix and transport the web including the reinforcing fibers or the binder was sprayed during the process. That is, 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.

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.

Thermoplastic resin fibers are provided together with reinforcing fibers in fiber composite nonwoven fabrics. Thermoplastic resin fibers can refer to polymer compounds that melt and have fluidity when heated to a temperature higher than the glass transition temperature, and lose fluidity and return to a solid state when the temperature is lowered below the glass transition temperature. Materials that can be utilized as thermoplastic resin 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.

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

Figure 2 is an enlarged image of the nodules formed between the reinforcing fibers and the thermoplastic resin fibers.

Referring to FIG. 2, the node may refer to a point where reinforcing fibers and thermoplastic resin fibers are fused within a web constituting a nonwoven fabric. Since the reinforcing fibers do not melt after heating, the node may be provided in the form of a molten thermoplastic resin weaving a plurality of reinforcing fibers at the node. At this time, each reinforcing fiber may be fixed by the plurality of node points, and accordingly, the web of the nonwoven fabric including the reinforcing fibers and the thermoplastic resin fibers may be fixed integrally. Therefore, according to the present invention, the reinforcing fibers and the thermoplastic resin fibers may be fixed even without including a binder in the surface layer. According to the prior art, the added and sprayed binder 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.

The nodal point in the fiber composite nonwoven fabric may be provided in the surface portion, and may not be provided in the deep portion located inside the surface portion. Here, the surface portion of the nonwoven fabric means an area from the surface of the nonwoven fabric to a certain thickness. For example, the surface portion may be an area from the surface of the nonwoven fabric to about 5% to 45% of the total thickness. However, the thickness of the surface portion may vary depending on the type and thickness of the nonwoven fabric, and the heat source located on the upper and lower surfaces, and the criterion for dividing the surface portion and the deep portion may be the presence or absence of a nodal point.

The surface layer is a region where reinforcing fibers and thermoplastic resin fibers are bonded and fixed by the nodal points as described above. The surface layer may be provided on the upper and lower surfaces of the fiber composite nonwoven fabric, respectively. In this case, the fiber composite nonwoven fabric may be in a form where a deep layer is provided between the two surface layers. The surface layers provided on the upper and lower surfaces can hold the deep layer provided inside. Accordingly, even if nodal points are provided in the deep layer inside, the fiber composite nonwoven fabric can be fixed by the surface layer provided with nodal points. Since nodal points are provided only on the surface layer in this way, it is not necessary to wait for all thermoplastic resin fibers included in the entire nonwoven fabric to melt, and thus the heating process for melting the thermoplastic resin fibers by applying heat can be performed relatively short. Accordingly, the speed of the entire process increases, and there is an advantage in that the energy required for producing the nonwoven fabric can be reduced. In addition, the reinforcing fiber thermoplastic resin fibers provided inside have a certain level of fluidity, and thus can disperse stress applied to the nonwoven fabric.

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

According to the present invention, even without a binder or with a small amount of binder added, the web in the nonwoven fabric can be fixed by the bonding point formed by the thermoplastic resin fibers and the reinforcing fibers. For example, even when a binder is added, the binder can be added in a small amount at a ratio of 3 wt% or less with respect to the entire nonwoven fabric. Considering that the 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 when it includes it.

In the case of the present invention, since a large number of nodes formed by melted thermoplastic resin fibers and reinforcing fibers in the surface portion are provided to fix the surface portion, and the deep portion is covered and fixed by the surface portion provided with nodes, 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 3 wt% or less is included, there is no concern about or low concern about high porosity and uneven pores occurring in the composite due to the vaporized binder remaining during the high-temperature molding process for composite materialization and productization. In the case of the prior art, since a large amount of binder is included, about 10 wt% or so, the vaporized binder remains during the high-temperature molding process in the composite, which causes high porosity and uneven pores. Such high porosity and uneven pores caused the deterioration of the overall mechanical properties of the composite using the nonwoven fabric.

Whether or not a binder is provided to 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 overlapping multiple layers using cross-lay equipment, a fiber composite nonwoven fabric can be provided 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 of 1 wt% to 3 wt% may be used.

Referring to FIG. 1, the fiber composite nonwoven fabric may be composed of an upper surface layer occupying about 34.5% of the total thickness, a lower surface layer occupying about 29.5% of the total thickness, and a deep layer (about 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 fibers (nylon fibers) provided in the surface layer are melted to form nodes, and accordingly, the color of the surface layer turns black. In contrast, the nylon fibers provided in the deep layer are not melted, and are mixed with reinforcing fibers (carbon fibers) in a form without nodes.

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

FIGS. 3A and 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 layer.

FIGS. 4A and 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.

According to the method for manufacturing a fiber composite nonwoven fabric according to the present invention, the method comprises: 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 the thermoplastic resin fibers provided in a surface portion of the nonwoven fabric provided adjacent to a heat source, wherein a plurality of nodes are provided in the surface portion at which 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.

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

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-shaped web through a carding process, and superimposing multiple layers using a cross-lay facility. The carding process may refer to a process of forming a web by orienting fibers in a horizontal or vertical direction. Once a sheet-shaped web is formed through the carding process, the web can be superimposed into multiple layers using a cross-lay facility. According to the prior art, a binder can be sprayed during the cross-lay process or the carding process, or the multiple layers of web can be fixed through needling after the cross-lay process. Needling may be a process of punching multiple times through the multiple layers of web to interweave 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).

When the first step is performed by 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 drying them through a dehydration process. At this time, according to the prior art, when dispersing the reinforcing fibers and thermoplastic resin fibers together with water, a binder can be dispersed, or the binder can be sprayed on the web before or after the dehydration process is performed after forming the fiber web. However, according to the present invention, in the second step described below, without mixing or spraying the binder, the thermoplastic resin fibers included in the surface portion are melted by supplying a heat source during a series of drying processes, and then fused with the reinforcing fibers (i.e., forming a node), thereby fixing the web.

Depending on whether the first step is performed by a dry method or a wet method, whether a binder is provided in the nonwoven fabric may vary. According to the present invention, a nonwoven fabric can be provided that includes only a small amount of binder or without a binder. When a nonwoven fabric is produced by a dry method, a nonwoven fabric can be produced without a binder, as illustrated in FIG. 3a. On the other hand, when a nonwoven fabric is produced by a wet method, a nonwoven fabric can be produced without a binder, as illustrated in FIG. 3a, and a nonwoven fabric can be produced by mixing about 1 wt% to about 3 wt% of a binder, as illustrated in FIG. 4a.

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.

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 is no limitation on the heat source that can be used at this time, and various types of heat sources such as infrared heaters and hot plates can be utilized.

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.

Since the heat source of 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. Therefore, as heat is transferred from the surface of the nonwoven fabric to the inside, the thermoplastic resin fibers begin to melt gradually, 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, since the reinforcing fibers included in the nonwoven fabric function as a heat conductor, heat diffusion within the nonwoven fabric can be further promoted. For example, carbon fibers, which can be utilized as reinforcing fibers, have excellent thermal conductivity, and thus can function as a medium that transfers heat applied from the outside of the nonwoven fabric to the inside of the nonwoven fabric. Accordingly, the execution time of the second stage can be reduced, and the energy consumption can also be reduced.

The heat source of the second stage can be placed 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 shown in FIG. 3b and FIG. 4b.

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 portion 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 portion where sufficient heat to melt the thermoplastic resin fibers has not reached. In addition, some binder may remain in the surface portion. However, since the amount of binder remaining in both the surface and the deep portion is significantly less than that of the nonwoven fabric manufactured according to the prior art, the rate of pore generation can be reduced.

The execution time of the second step can be controlled by considering the type of heat source, etc., and the execution temperature can also be varied by considering the composition of the nonwoven fabric, especially the type and content of the thermoplastic resin fiber. According to one example, the second step can be performed by applying a temperature of 200° C. or higher to the nonwoven fabric.

In the above, a fiber composite nonwoven fabric and a manufacturing method thereof according to one embodiment of the present invention were examined. In the following, the advantageous effects of the fiber composite nonwoven fabric according to the present invention will be confirmed through experimental examples.

Fig. 5 is a result of analyzing the properties of a composite using a nonwoven fabric according to a prior art including a binder. Referring to Fig. 5, the nonwoven fabric was manufactured to include a binder (VPB105) and a dispersant (CMC), and was heated to 230 to 250°C. Referring to the cross-sectional analysis result on the right side of the drawing, it can be confirmed that a large number of irregular pores were generated as the binder was vaporized. Such uneven pores can deteriorate the mechanical properties of the composite, or prevent it from exhibiting consistent properties.

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.

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 20% (FVF20), 25% (FVF25), 30% (FVF30), and 35% (FVF35) of reinforcing fibers, respectively. Referring to the figure, the tensile strength according to the fiber content was found to be high when the reinforcing fibers were contained in an amount of 25 to 35% of the fiber volume fraction, and it could 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.

Evaluation items FVF20 FVF25 FVF30 FVF35 Fiber volume fraction [vol%] 22.5 24.6 29.2 33.1 Fiber weight fraction [wt%] 31.6 34.2 39.6 44.5 Tensile strength [MPa] 268 334 324 353 Tensile stiffness [GPa] 20.4 23.9 28.9 31.0 Porosity [%] -0.2 0.0 -0.6 1.0

Next, Fig. 7 shows the results of comparative analysis of tensile strength and tensile modulus of composites using nonwoven fabrics manufactured according to the conventional technology and the present invention. In addition, Fig. 8 shows the results of cross-sectional analysis of nonwoven fabrics manufactured according to the conventional technology 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 conventional technology (B) and manufactured according to the present invention so that a binding point is formed on the surface without a binder (A) can be confirmed.

Proposed Technology A Tensile strength [MPa] Tensile stiffness [GPa] FVF Psalm 30 324 28.9 Deviation [%] 18 1.4 Prior art B Tensile strength [MPa] Tensile stiffness [GPa] FVF Psalm 30 297 28.8 Deviation [%] 73 2.0

It can be confirmed that the fiber composite nonwoven fabric manufactured according to the present invention has higher tensile strength and tensile rigidity than the nonwoven fabric manufactured including a binder according to the prior art. 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 rigidity 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 necessary, and the binder does not vaporize or is very small during the high-temperature molding process, and thus the porosity within the composite is low. In contrast, the nonwoven fabric manufactured according to the prior art to include a binder had lower tensile strength and tensile rigidity than the nonwoven fabric manufactured according to the present invention, and in particular, the variation in tensile strength and tensile rigidity depending on the location within the composite was large. It is understood that this is due to the multiple pores (black portions of the cross-section) included in the cross-section, as can be confirmed in FIG. 8.

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 little deviation in physical properties.

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 may be made to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

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 scope of the patent claims.

Claims (7)

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