JP7567289B2 - Nonwoven fabric structure and method of manufacture thereof - Google Patents

Description

The present invention relates to a nonwoven fabric structure and a method for manufacturing the same.

Nonwoven fabrics with excellent moldability and mechanical strength properties are suitable for use in industrial materials, building materials, automobiles, and other applications. In particular, when used as molded nonwoven fabrics that are lightweight and have excellent rigidity after molding, such as automobile undercovers and dash silencers, they are lightweight and easily conform to the shape of the molding die, such as sound absorption and cushioning properties and uneven protrusions, making it possible to significantly improve energy conservation and workability by reducing the weight of automobiles. In addition, nonwoven fabrics that are a mixture of inorganic fibers and thermoplastic resin fibers are expected to have particularly high bending rigidity, making it possible to replace part of metal materials.

Conventionally known high basis weight moldable nonwoven fabrics are mainly made from short fibers and require the use of a large amount of thermally adhesive fibers, which poses problems in terms of heat resistance and cost. In addition, nonwoven fabrics with high mechanical strength such as tensile strength and tear strength have poor moldability (elongation when heated) due to excessive fiber entanglement, while nonwoven fabrics with high moldability generally have poor rigidity.

Patent Document 1 discloses a nonwoven fabric made of sheath-core composite long fibers that has excellent stretchability and moldability despite its low basis weight and thin thickness. Patent Document 2 proposes a method for producing a dense semi-finished product for automotive trim materials in which a web of sheath-core composite long fibers is needle-punched to three-dimensionally entangle it, and discloses that the heating temperature range is wide when heating and compression molding. Patent Document 3 discloses a prepreg sheet containing carbon fibers and thermoformable resin fibers.

Japanese Patent Application Publication No. 3-241054 JP 2018-9256 A JP 2017-95662 A

However, with the technology of Patent Document 1, it is difficult to obtain a nonwoven fabric with high rigidity, and long preheating is required to prevent delamination. Furthermore, Patent Document 2 does not specify the specific rigidity, and it is cost-effective because it requires special components, and it is not easy to bond to polypropylene, which is used as a general-purpose product in automobiles. In Patent Document 3, it is difficult to manufacture a single-layer sheet with a high basis weight, and it is necessary to stack nonwoven fabrics with low basis weight, and nonwoven fabrics containing highly rigid carbon fibers have problems with fiber dropout and fiber breakage during handling, making it difficult to work with. As can be seen from this, no high-density nonwoven fabric structure that combines light weight, excellent rigidity, and high moldability has been proposed so far.

In view of the above problems, the present invention aims to provide a nonwoven fabric structure having high moldability and excellent mechanical strength properties, and a method for producing the same.

Means for Solving the Problems The present inventors have conducted extensive research to solve the above problems and have completed the present invention having the following configuration.
1. A nonwoven fabric structure formed by thermally fusing a long-fiber nonwoven fabric and a short-fiber nonwoven fabric containing a mixture of inorganic fibers and thermoplastic resin fibers, the nonwoven fabric structure having a basis weight of 100 to 4000 g/ ^m2 and an apparent density of 0.4 to 1.3 g/ ^cm3 .
2. The nonwoven fabric structure according to 1, wherein the long fibers constituting the long-fiber nonwoven fabric are core-sheath type fibers, the core component being made of polyester, and the sheath component being made of the thermoplastic resin.
3. The nonwoven fabric structure according to 1 or 2, wherein the inorganic fibers are carbon fibers.
4. The nonwoven fabric structure according to any one of 1 to 3, wherein the weight ratio of the long fiber nonwoven fabric to the entire nonwoven fabric structure is 30% to 85%.
5. A method for producing a nonwoven fabric structure, comprising the steps of: entangling a long-fiber nonwoven fabric by a needle punching method; laminating a short-fiber nonwoven fabric containing a mixture of inorganic fibers and thermoplastic resin fibers on the entangled long-fiber nonwoven fabric; and heat-treating the laminate at 140 to 255°C and a pressure of 0.1 to 5 MPa.

The nonwoven fabric structure of the present invention has high moldability and excellent mechanical strength properties due to the above-mentioned configuration.

1 is a photograph of a three-point bending test measuring device.

The present invention will be described in detail below.
The nonwoven fabric structure of the present invention is a nonwoven fabric structure in which a long-fiber nonwoven fabric and a short-fiber nonwoven fabric in which inorganic fibers and thermoplastic resin fibers are mixed are thermally fused together, and has a basis weight of 100 to 4000 g/ ^m2 and an apparent density of 0.4 to 1.3 g/ ^cm3 .

The total basis weight of the nonwoven fabric structure of the present invention can be appropriately set in consideration of the mechanical strength properties required for the final product, but must be 100 to 4000 g/ ^m2 . If the basis weight is too low, the fabric will be lighter, but it will be difficult to expect high rigidity. The greater the basis weight, the higher the rigidity will be, but the larger the required installation space will be, so it must be set appropriately.

The weight fraction of the long fiber nonwoven fabric relative to the entire nonwoven fabric structure is 30% or more, preferably 50% or more, and more preferably 70% or more. The weight fraction is preferably 85% or less. If it exceeds 85%, the effect of improving the rigidity, which is the objective of the present invention, may be reduced. The long fiber nonwoven fabric may be made of long fibers with good thermal formability, and it is preferable that at least a part of the constituent fibers of the long fiber nonwoven fabric is a core-sheath type fiber. Furthermore, crimp-free long fibers are often arranged in the nonwoven fabric without slack or bending with few bending points, and as a result, the strength of each fiber directly contributes to the strength of the nonwoven fabric, so high rigidity can be expected. It is believed that the fibers of the long fiber nonwoven fabric are mainly arranged in the two-dimensional in-plane direction rather than the thickness direction, which makes it easier to increase the bending rigidity and initial modulus.

Next, the long fiber nonwoven fabric may be used in a single layer, or two or more layers of nonwoven fabric may be laminated. When using a single layer of long fiber nonwoven fabric, it is necessary to have many fibers aligned in the thickness direction to prevent delamination within the layer. Also, care must be taken when using a single layer, as the number of fiber constraint points increases and moldability may decrease. The nonwoven fabric laminated to the long fiber nonwoven fabric may be a long fiber nonwoven fabric or a short fiber nonwoven fabric.

When stacking nonwoven fabrics, single-component nonwoven fabrics may be stacked, but as an example, two or more layers of single-component nonwoven fabric and core-sheath type fibrous nonwoven fabric may be stacked. Three layers, in which a core-sheath type fibrous nonwoven fabric is sandwiched between single-component nonwoven fabrics, are also preferred. The stacked nonwoven fabrics are preferably entangled by penetrating a water flow or needle from the core-sheath type fibrous nonwoven fabric using a water punching method or a needle punching method. Since the degree of freedom of the fibers in the long fiber nonwoven fabric is small, problems such as peeling may occur even after needle punching. The needle density (penetration number) and needle depth must be appropriately set depending on the type of needle used, the desired mechanical strength characteristics, and the basis weight of each layer, and are not limited. If a core-sheath type fibrous nonwoven fabric is used on at least one side and a single-component nonwoven fabric is present in the middle layer, a composite structure with a high rigidity surface layer and a flexible fiber structure in the inner layer can be formed in one thermoforming, and the inner layer can reduce tapping sounds while the surface layer can suppress wear and other abrasion. It is also expected to have excellent sound absorbing properties. A preferred lamination method is to first loosely entangle the fibers of multiple layers using a needle punching method or the like, and then finish the laminate into a single layer using a needle punching method. This makes it easy to obtain high moldability while providing appropriate fiber restraint and preventing delamination. The smaller the basis weight per layer, the more the fibers are aligned in the in-plane direction, making it possible to increase bending rigidity.

Resins used for the long fibers constituting the long fiber nonwoven fabric are preferably polyester, polyolefin, or polyamide, and are particularly preferably inexpensive general-purpose thermoplastic resins such as polyester and polyolefin. Examples of polyester include homopolyesters such as polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polybutylene naphthalate (PBN), polyethylene naphthalate (PEN), polycyclohexane dimethyl terephthalate (PCHT), and polytrimethylene terephthalate (PTT), as well as their copolymer polyesters. Examples of polyolefins include polyethylene (PB), polypropylene (PP), and polyethylene (PE). Polyamide fibers such as nylon 6 (NY6) and nylon 66 can also be used. In addition, it may contain commonly used additives such as paints, pigments, matting agents, antistatic agents, flame retardants, and reinforcing particles. It is also possible to mix small amounts of other polymers, such as nylon and olefin, within a range that does not impair the purpose of the present invention. It is also preferable to use core-sheath or side-by-side composite fibers. In particular, combinations of PP/PET, copolymerized PET/PET, PBT/PET, and PE/PP are preferred. For automotive applications, the use of composite fibers such as PP/PET, NY6/PET, and copolymerized PET/PET is particularly suitable.

The fineness of the long fibers that make up the long fiber nonwoven fabric is not particularly limited, but it is preferably 1 dtex to 10 dtex, and more preferably 2.5 dtex to 7 dtex, because this makes it easier to obtain productivity and mechanical strength properties.

Next, the short fiber nonwoven fabric in the nonwoven fabric structure of the present invention will be described. Short fiber nonwoven fabric is made of a mixed fiber of inorganic fibers and thermoplastic resin fibers. Carbon fibers, glass fibers, basalt fibers, etc. can be used as inorganic fibers, and fibers with a length of 2 to 10 cm are preferably used. Inorganic fibers are mainly used to improve rigidity, and the longer the fiber, the higher the rigidity can be expected, but if the fiber length exceeds 10 cm, the improvement effect is small and it becomes more difficult to manufacture short fiber nonwoven fabric. Furthermore, even if long fibers are used, they often break during the manufacturing process of short fiber nonwoven fabric (especially the fiber blending process).

As the thermoplastic resin fiber, polypropylene, polyester, polyamide, polyphenylene sulfide, PTFE, etc. can be used. The fiber length of the thermoplastic resin fiber is, for example, 2 to 10 cm, but is not limited to this. In order to increase the composite strength of the short fiber nonwoven fabric and the long fiber nonwoven fabric, it is particularly preferable from the viewpoint of preventing delamination (interlayer peeling) that the thermoplastic resin fiber is the same or similar to the material component of the long fiber that constitutes the long fiber nonwoven fabric. "The same or similar" is understood as common knowledge that it can be discussed in the same chemical classification, such as polyester, and that there are few molecular functional groups that repel each other. This makes it possible to thermally bond the long fiber nonwoven fabric and the short fiber nonwoven fabric without using a special adhesive, solving the problem of peeling at the interface.

In the nonwoven fabric structure of the present invention, by using composite fibers in which inorganic fibers and thermoplastic resin fibers are mixed with a short fiber nonwoven fabric, it is possible to prevent problems such as wear and cracks caused by pebbles kicked up by tires, etc., when the nonwoven fabric structure is used for, for example, an automobile fender cover or undercover. In addition, the nonwoven fabric structure can be used as a structure to replace metals, engineering plastics, etc.

Next, a method for producing the nonwoven fabric structure of the present invention will be described. Long fiber nonwoven fabrics can be produced by conventional methods, but the spunbond method is preferably used because the fibers are arranged in the in-plane direction (two-dimensional surface direction), making it easy to increase the bending rigidity and to obtain mechanical strength properties. Short fiber nonwoven fabrics can be produced by mixing fibers using a carding method, an air-laid method, or the like. If necessary, integration processing may be performed using a needle punch method, a water flow entanglement method, or the like. The short fiber nonwoven fabric can be used as a reinforcing layer, and recycled carbon fibers, for example, may be used as the inorganic fibers. In this case, when using the carding method in the production of short fiber nonwoven fabrics, care must be taken to set the processing speed low so that the carbon fibers do not break.

Next, a method for thermally bonding a long-fiber nonwoven fabric and a short-fiber nonwoven fabric will be described. Any of the usual heated press processes can be used for bonding. For example, it may be a press process of a veneer sheet, or it may be processed by passing it through heated metal press rolls capable of producing long pieces (such as Yuri Roll Co., Ltd.'s calendar processing equipment), or it may be processed using a high-temperature metal belt press machine. The conditions are set according to the thermoplastic resin contained in the short-fiber nonwoven fabric, but the apparent density of the nonwoven fabric structure can be controlled by pressing it under conditions of 140 to 330°C and a pressure of 0.1 to 5 MPa. It is also preferable to first create a nonwoven fabric structure in a flat plate shape, and then to again three-dimensionally mold it using a press machine to create a three-dimensional structure.

The following are examples of the present invention. The present invention is not limited to these examples. First, we will explain how to measure the physical properties of the samples prepared in the following examples and comparative examples.

<Metaku>
The sample was cut into a 20 cm square, the weight was measured, and the weight was converted into mass per m ² to give the basis weight (g/m ² ).

<Apparent density>
The thickness of the sample was measured under a load of 20 g/cm ² in accordance with JIS L1913 (2010). The apparent density (g/cm ³ ) was calculated by dividing the basis weight measured above by the thickness measured above.

<Peeling>
A sample was cut into a size of 5 cm wide x 30 cm long, and the sample was folded by hand in the longitudinal direction to about 90 degrees 20 times, and visually evaluated for the occurrence of peeling.

<Bending rigidity>
A three-point bending test was carried out in accordance with JIS K7017 (see Figure 1).
The sample was measured with a support width of 32 mm, an indenter radius of 5 mm, and a speed of 1 mm/min. When the short fiber nonwoven fabric was laminated on only one side, the short fiber nonwoven fabric was placed on the bottom and the measurement was performed.

Example 1
Four layers of long-fiber nonwoven fabric (Volance (registered trademark) manufactured by Toyobo Co., Ltd.) made of polyethylene terephthalate long fibers having a fineness of 5.0 dtex and a basis weight of 250 g/ ^m2 were laminated and needle-punched twice with an Organ FPD220 (40SM) at a penetration number of 32 and a needle depth of 11 mm to obtain a long-fiber web. The converted apparent density of the obtained long-fiber web was about 0.09 g/ ^cm3 .
Next, carbon fibers (average fiber length 5 cm, average diameter approximately 5 μm), copolymer polyester short fibers (fineness 3.3 dTex), and polyethylene terephthalate short fibers (fineness 4.4 dTex) were mixed in weight ratios of 50%, 25%, and 25% by carding to produce two short fiber nonwoven fabrics with a basis weight of 250 g/ ^m2 .
Thereafter, short fiber nonwoven fabrics were laminated on both sides of the long fiber web, and pressed at 220° C. and a pressure of 0.1 MPa using a metal belt press (manufactured by KBK Steel Products Co., Ltd.) to obtain a nonwoven fabric structure. The physical properties of the obtained nonwoven fabric structure are shown in Table 1. Then, a moldability test was conducted.

Example 2
A long-fiber nonwoven fabric (Volance (registered trademark) manufactured by Toyobo Co., Ltd.) made of polyethylene terephthalate long fibers having a fineness of 5.0 dtex and a basis weight of 180 g/ ^m2 was needle-punched with an Organ FPD220 (40SM) at a penetration number of 50 and a needle depth of 11 mm to obtain a long-fiber web. The converted apparent density of the obtained long-fiber web was 0.91 g/ ^cm3 .
Next, carbon fibers (average fiber length 5 cm, average diameter approximately 5 μm), copolymer polyester short fibers (fineness 3.3 dTex), and polyethylene terephthalate short fibers (fineness 4.4 dTex) were mixed in weight ratios of 50%, 25%, and 25% by carding to produce two short fiber nonwoven fabrics with a basis weight of 180 g/ ^m2 .
Thereafter, short fiber nonwoven fabrics were laminated on both sides of the long fiber web, and pressed at 220° C. and a pressure of 0.1 MPa using a metal belt press (manufactured by KBK Steel Products Co., Ltd.) to obtain a nonwoven fabric structure. The physical properties of the obtained nonwoven fabric structure are shown in Table 1. Then, a moldability test was conducted.

Example 3
Six sheets of long-fiber nonwoven fabric (Volance (registered trademark) manufactured by Toyobo Co., Ltd.) made of polyethylene terephthalate long fibers with a fineness of 5.0 dtex and a basis weight of 250 g/ ^m2 were laminated and needle-punched twice using an Organ FPD220 (40SM) with a penetration number of 70 and a needle depth of 11 mm to obtain a long-fiber web. The converted apparent density of the obtained long-fiber web was about 0.10 g/ ^cm3 .
Next, carbon fibers (average fiber length 5 cm, average diameter approximately 5 μm), copolymer polyester short fibers (fineness 3.3 dTex), and polyethylene terephthalate short fibers (fineness 4.4 dTex) were mixed in weight ratios of 50%, 25%, and 25% by carding to produce two short fiber nonwoven fabrics with a basis weight of 250 g/ ^m2 .
Thereafter, short fiber nonwoven fabrics were laminated on both sides of the long fiber web, and pressed at 220° C. and a pressure of 0.1 MPa using a metal belt press (manufactured by KBK Steel Products Co., Ltd.) to obtain a nonwoven fabric structure. The physical properties of the obtained nonwoven fabric structure are shown in Table 1. Then, a moldability test was conducted.

Example 4
Five sheets of long fiber nonwoven fabric (manufactured by Toyobo Co., Ltd.) with a basis weight of 250 g/ ^m2 and consisting of long fibers with a fineness of 5.5 dtex, the core of which is polyethylene terephthalate and the sheath of which is polypropylene (weight ratio in the long fibers: 50/50), were laminated and needle punched twice using an Organ FPD220 (40SM) with a penetration number of 32 and a needle depth of 11 mm to obtain a long fiber web. The converted apparent density of the obtained long fiber web was 0.09 g/ ^cm3 .
Next, carbon fibers (average fiber length 5 cm, average diameter approximately 5 μm) and polypropylene short fibers (average diameter 20 μm) were mixed in a weight ratio of 50%:50% by carding to prepare a single short fiber nonwoven fabric having a basis weight of 250 g/ ^m2 .
Thereafter, a short fiber nonwoven fabric was laminated on the long fiber web, and pressed at 190°C and a pressure of 0.1 MPa using a metal belt press (manufactured by KBK Steel Products Co., Ltd.) to obtain a nonwoven fabric structure. The physical properties of the obtained nonwoven fabric structure are shown in Table 1. Thereafter, a moldability test was conducted. In Example 4, the IR heat treatment in the moldability test was conducted at 200°C for 90 seconds.

(Comparative Example 1)
Six sheets of long-fiber nonwoven fabric (Volance (registered trademark) manufactured by Toyobo Co., Ltd.) made of polyethylene terephthalate long fibers having a fineness of 5.0 dtex and a basis weight of 250 g/ ^m2 were laminated, and needle punched twice using an Organ FPD220 (40SM) with a penetration number of 38 and a needle depth of 12 mm to obtain a long-fiber web. The converted apparent density of the obtained long-fiber web was 0.09 g/ ^cm3 .
The long fiber web was then pressed at 190°C and a pressure of 0.1 MPa using a metal belt press (manufactured by KBK Steel Products Co., Ltd.) to obtain a nonwoven fabric structure. The physical properties of the obtained nonwoven fabric structure are shown in Table 1. Then, a moldability test was conducted. In Comparative Example 1, the IR heat treatment in the moldability test was conducted at 250°C for 45 seconds.

(Comparative Example 2)
A long-fiber nonwoven fabric (Volance, manufactured by Toyobo Co., Ltd.) made of polyethylene terephthalate long fibers having a fineness of 5.0 dtex and a basis weight of 80 g/ ^m2 was needle-punched with an Organ FPD220 (40SM) at a penetration number of 38 and a needle depth of 11 mm to obtain a long-fiber web. The converted apparent density of the obtained long-fiber web was 0.10 g/ ^cm3 .
The long fiber web was then pressed at 190°C and a pressure of 0.1 MPa using a metal belt press (manufactured by KBK Steel Products Co., Ltd.) to obtain a nonwoven fabric structure. The physical properties of the obtained nonwoven fabric structure are shown in Table 1. Then, a moldability test was conducted. In Comparative Example 2, the IR heat treatment in the molding test was conducted at 250°C for 45 seconds.

(Comparative Example 3)
A long-fiber nonwoven fabric (Volance (registered trademark) manufactured by Toyobo Co., Ltd.) made of polyethylene terephthalate long fibers with a fineness of 5.0 dtex and a basis weight of 250 g/ ^m2 was needle-punched once using an Organ FPD220 (40SM) with a penetration number of 38 and a needle depth of 11 mm, and eight sheets of this needle-punched long-fiber nonwoven fabric were stacked and needle-punched a second time under the same conditions as the first time to obtain a long-fiber web. The converted apparent density of the obtained long-fiber web was 0.10 g/ ^cm3 .
Next, carbon fibers (average fiber length 5 cm, diameter approximately 5 μm) and polypropylene short fibers (diameter approximately 20 μm) were mixed in a weight ratio of 50% and 50% by carding to produce a single short fiber nonwoven fabric having a basis weight of 250 g/ ^m2 .
Thereafter, a short fiber nonwoven fabric was laminated on the long fiber web, and pressed at 190°C and a pressure of 0.1 MPa using a metal belt press (manufactured by KBK Steel Products Co., Ltd.) to obtain a nonwoven fabric structure. The physical properties of the obtained nonwoven fabric structure are shown in Table 1. Thereafter, a moldability test was conducted. In Comparative Example 3, the IR heat treatment in the moldability test was conducted at 250°C for 45 seconds.

From the above, it can be seen that the examples have higher bending rigidity and better moldability than the comparative examples.

The nonwoven fabric structure obtained by the present invention is lightweight and highly rigid, and can be effectively used as building materials, industrial materials, automobile parts such as automobile undercovers, fender liners, hood silencers, and tonneau covers, as well as sound absorbing and sound insulating materials. In addition, when the inorganic fibers are carbon fibers or glass fibers with high tensile rigidity, they can be used in structural members that require strength. Furthermore, the present invention can effectively utilize recycled carbon fibers extracted from CFRP using thermosetting resins. From the above, it is believed that the present invention will make a significant contribution to industry.

Claims (5)

A long fiber nonwoven fabric made of polyester and/or olefin resin ;
A nonwoven fabric structure in which a short fiber nonwoven fabric containing a mixture of inorganic fibers and thermoplastic resin fibers is thermally fused to the nonwoven fabric,
A nonwoven fabric structure having a basis weight of 100 to 4000 g/m2 and an apparent density of 0.4 to 1.3 g/cm3. 2. The nonwoven fabric structure according to claim 1, wherein the long fibers constituting the long-fiber nonwoven fabric are core-sheath fibers and have one of the following characteristics (1) or (2) .
(1) The resin of the thermoplastic resin fiber is polyester, and the sheath component of the long fiber is polyester, or
(2) The resin of the thermoplastic resin fiber is polyolefin, and the sheath component of the long fiber is polyolefin. The nonwoven fabric structure according to claim 1 or 2, characterized in that the inorganic fibers are carbon fibers. The nonwoven fabric structure according to any one of claims 1 to 3, characterized in that the weight ratio of the long fiber nonwoven fabric to the entire nonwoven fabric structure is 30% to 85%. A step of entangling the long fiber nonwoven fabric by a needle punch method;
a step of laminating a short-fiber nonwoven fabric containing a mixture of inorganic fibers and thermoplastic resin fibers on the entangled long-fiber nonwoven fabric, and heat-treating the laminate at 140 to 255° C. and a pressure of 0.1 to 5 MPa.