JPS6328962A - Heat resistant nonwoven fabric - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a heat-resistant nonwoven fabric, and more specifically, it has an extremely low shrinkage rate at high temperatures, excellent dimensional stability, and mechanical properties such as mechanical strength. The present invention relates to a heat-resistant nonwoven fabric with excellent physical properties.

[Prior Art] Conventionally, with regard to heat-resistant nonwoven fabrics, paper-like nonwoven fabrics produced by a wet process, in which short aromatic polyamide fibers are mixed with bulb-shaped particles having the same composition, have been widely known.
No. 18 and the like disclose a method for producing a heat-resistant nonwoven fabric using undrawn aromatic polyamide fibers as adhesive elements.

As for other heat-resistant nonwoven fabrics, needle bunch felts made of novoloid m fibers and aromatic polysulfide fibers, and spunbond nonwoven fabrics using aromatic polysulfide as disclosed in JP-A-57-16954 are known. .

Furthermore, as the most similar to the present invention, a nonwoven fabric is known in which a fiber web made of aromatic polyamide fibers is entangled by the action of water flow.

[Problems to be solved by the invention] The paper-like nonwoven fabric produced by the wet process using aromatic polyamide fibers described above is useful because it has excellent heat resistance, but wrinkles frequently occur due to heat shrinkage in high-temperature atmospheres. It has the disadvantage that it cannot hold its shape, or that it uses short fibers with a fiber length of 10 mm or less, so its tear strength is low, and its impregnability with, for example, insulating varnish and unsaturated resin for FRP is poor. . Furthermore, with this wet method, it is difficult to produce thick nonwoven fabrics, and thick ones are made by laminating multiple thin sheets, so heating causes the spaces between the eyebrows to peel off and bubbling occurs, making it impractical for practical use. There was a drawback that it was not.

For heat-resistant nonwoven fabrics mainly composed of aromatic polyamide stable fibers, a manufacturing method that does not reduce heat resistance and is suitable for mass production has not yet been developed, except for paper-like fabrics produced by the wet method described above. For example, in a manufacturing method that utilizes the heat-sealability of undrawn aromatic polyamide fibers, thermocompression bonding at a high temperature of 300°C or higher is required in order to obtain sufficient strength of the nonwoven fabric, so it is not possible to apply a normal calender or the like. difficult,
In addition, the use of plasticizing solvents such as 2-dimethylpyrrolidone and methylformamide is being considered to lower the thermocompression bonding temperature, but this also requires processing at higher temperatures than the range applicable to ordinary calenders. Otherwise, solvent exhaust and recovery equipment will be required.1. All of these methods lacked versatility and were difficult to implement.

The hydroentangled nonwoven fabric made of aromatic polyamide fibers has good heat resistance and excellent strength, but although the fibers are mechanically entangled, there is no bond between the fibers. It has the disadvantage of poor dimensional stability and the formation of fluff. Therefore, attempts have been made to stabilize the dimensions through post-processing such as stretching, but these post-processing have the effect of increasing the heat shrinkage rate. This was not a desirable increase.

On the other hand, as for heat-resistant nonwoven fabrics made of other fibers, fiber felt made by needle bunching method and nonwoven fabric made by spunbond method have been proposed, but both of them are inferior in shape retention and dimensional stability. Further, there is a drawback that the thermal shrinkage is large or wrinkles are generated due to the shrinkage.

Therefore, the present invention has extremely little thermal shrinkage and no wrinkles or fuzzing under high-temperature atmospheres, which was considered extremely difficult or impossible in the past, and
The purpose is to provide a heat-resistant nonwoven fabric that also has excellent mechanical properties such as dimensional stability and strength.

c) Means for Solving Problems] The present invention involves entangling a fiber web having a fiber length of 80 to 20% by weight of heat-resistant fibers and 20 to 80% by weight of unstretched edges by the action of a water stream, and then The present invention relates to a heat-resistant nonwoven fabric whose fibers are fused together by compression bonding, and which has a dry heat shrinkage rate of 3% or less under a temperature condition of 200 to 375°C.

[Function] As a result of intensive research aimed at obtaining a nonwoven fabric with extremely low heat shrinkage and excellent heat resistance stability, the present inventors found that
Utilizing heat-resistant m-fibers, the structure combines inter-fiber entanglement due to the action of water flow and inter-fiber bonding due to unstretched fibers, resulting in extremely low shrinkage and no wrinkles when heated. Furthermore, the present invention was completed based on the discovery that a heat-resistant nonwoven fabric with excellent mechanical properties such as strength can be obtained.

The present invention will be explained in detail below. First, the heat-resistant fibers used in the present invention form the skeleton of the heat-resistant nonwoven fabric, and are entangled with other fibers by the action of water to form the nonwoven fabric. It imparts mechanical properties such as tensile or tear strength, and has inherent heat resistance.

These fibers include synthetic fibers such as aromatic polyamide fibers, aromatic polysulfide fibers, aromatic polyester m fibers, aromatic polyether fibers, novoloid fibers,
Synthetic fibers such as oxidized acrylic fibers, glass fibers, and asbestos l! Heat resistance '1a that allows formation of webs such as inorganic fibers such as male, carbon fibers, metal fibers, etc.
IIi1: Any material can be used, but if synthetic fibers selected from aromatic polyamide fibers, novoloid fibers, and oxidized acrylic fibers are used alone or in combination, web formation is easy; It does not melt and forms a skeleton even at temperatures above ℃, making it possible to obtain a wide variety of products. Moreover, product quality design and quality control are extremely easy and stable.

It can be said that it is suitable for the purpose of In particular, aromatic polyamide fibers are optimal because they provide the best products in terms of heat resistance and productivity.

In addition, in the case of thermoplastic heat-resistant fibers such as aromatic polysulfide fibers and aromatic polyester fibers, nonwoven fabrics with various properties can be formed by mixing them with the above-mentioned non-melting fibers, or nonwoven fabrics with a temperature below the melting point of these Falti fibers can be formed. When used at high temperatures, or when the time required for heat resistance even at temperatures above the melting point is extremely short, these fibers can be used to take advantage of their characteristics, so they can be said to have high utility value.

Next, to explain the undrawn fibers, the undrawn fibers are plasticized or melted by heat and pressure to bond the heat-resistant fibers that are the skeleton and the undrawn fibers, thereby improving the dimensional stability of the heat-resistant nonwoven fabric. It has the effect of increasing the mechanical properties such as tensile strength, and the effect of preventing the generation of fluff and fiber dust in the nonwoven fabric, thereby improving the quality of the product.

Known examples of these undrawn fibers include undrawn polyester fibers, undrawn aromatic polysulfide fibers, undrawn aromatic polyester fibers, and undrawn aromatic polyamide fibers, which are appropriately selected and used depending on the required heat resistance conditions. be able to. In other words, for example, if long-term RP7 heat resistance is required, use undrawn aromatic polysulfide fiber or undrawn aromatic polyester! a! It is preferable to use undrawn fibers that are inherently heat resistant, such as fibers, and even if high temperature heat resistance is required, it is suitable for short-term heat resistance of several minutes or hours. If this is acceptable, it is advantageous to use undrawn polyester fibers that can be easily formed into a web or fused and bonded by pressure and heating.

In addition, although this undrawn polyester fiber has excellent workability and productivity, it has the disadvantage of poor heat resistance. Because entanglement is also performed by water flow rather than using polyester as a binding element, even if undrawn polyester fibers deteriorate or decompose due to heating, they will still maintain a certain degree of strength and shape retention due to entanglement. Therefore, it is fully applicable to heat-resistant applications such as honeycomb cores, electrical insulating materials, etc., which are impregnated with thermosetting resin or varnish.

These heat-resistant and undrawn fibers may be of any type as long as they have the above characteristics, but in the present invention, they are stable fibers with a fiber length of 20 to 200 mnt and a fineness of 0.5 to 20 denier. However, it is preferable because it has excellent web formation properties and good entanglement efficiency by water jetting. In particular, fiber length of 38 to 76III11 and fineness of 1 to 6 denier produces the best web. It can be said to be the optimal one because it provides formation and entanglement efficiency.

To briefly explain the reason why stable wfItI is preferable in the present invention, for example, nonwoven fabrics produced by spunbond method or melt blow method, or extremely long fibers with a fiber length exceeding 200+ nm, such as those using long fiber tow, can be used. Because it is impossible or extremely difficult to mix multiple raw materials, fibers with different properties such as IaI fiber diameter, fiber length, etc., it is not possible to form a variety of nonwoven fabrics. In addition, the entanglement efficiency by water jetting is inferior, and on the contrary, when the fiber length is 2, as used in the wet method,
Short fibers with a diameter of 0 mm or less are not effective because even if they are entangled, only a product with low strength can be obtained. Therefore, when using these long fibers or short fibers, it is necessary to mix them with stable fibers having the above-mentioned suitable fiber length and fineness ranges.

Next, hydroentanglement, which is the most important gist of the present invention, will be explained. Regarding hydroentanglement, for example, US Pat.
, 088, 859, etc., in which a water stream is injected through a large number of fine orifices to the web in which the heat-resistant fibers and undrawn fibers are mixed, and the water flow is applied between each fiber. Intertwine. The heat shrinkage rate of the nonwoven fabric is greatly improved by the entanglement treatment using these water jets.

The reason for this is not yet clear, but the following are possible reasons: First, each fiber that was arranged horizontally on the web is randomly arranged in three dimensions, including the vertical direction, by the water jet. The second reason is that undrawn fibers generally have very high shrinkage, but these undrawn fibers partially shrink due to the action of water flow. Molecular action that causes unstretched fibers to be stretched and molecularly oriented, resulting in increased heat resistance stability of unstretched fibers and reduced shrinkage rate
Thirdly, the fibers under tension undergo a local relaxation effect due to the pressure of the water flow, and as a result, the heat shrinkage rate decreases. It is conceivable that the latent shrinkage of the short fibers of the undrawn fibers undergoes a treatment similar to moist heat heat setting during the drying process after hydroentanglement, resulting in a decrease in the thermal shrinkage rate of the nonwoven fabric.

In any case, in the present invention, the step of hydroentanglement is
It is most important as a means to dramatically reduce the thermal shrinkage rate at temperatures of 0 to 375@C.

Intertwined infidels! The fabric is then thermocompressed to fuse the fibers by the bonding action of the undrawn fibers, resulting in the nonwoven fabric of the present invention having excellent dimensional stability and mechanical properties such as strength that are significantly superior to conventional fabrics. Become. In addition, this thermocompression bonding is thought to have not only a bonding effect but also a heat setting effect on heat-resistant fibers and undrawn fibers, and thermocompression bonding also has an auxiliary effect of further reducing the dry heat shrinkage rate of the nonwoven fabric. have

The temperature and pressure in this thermocompression bonding are appropriately selected so that the undrawn fibers can be plasticized or melted under pressure to bond each fiber.For example, if the undrawn polyester fiber is a 〜220″'C1
140 for unstretched polyphenylene sulfide fiber
240″C1 or unstretched aromatic polyamide 1
For m-fibers, a temperature of 250 to 350"C and a linear pressure of 30 to 300 cm are considered appropriate. In addition, devices used for these include a flat plate hot press device, a rotating heat roll device, Alternatively, any device such as an engraved heat roll device with an uneven surface may be used, but it is advantageous to use a rotating heat roll because it has excellent continuous productivity and quality stability.

Hereinafter, the present invention will be explained in more detail based on Examples.
The present invention is not limited to these examples.

[Example 1] Aromatic polyamide fiber mU, s denier, 38n+m length)
50% by weight and 1tt unstretched polyester (5 denier).

44 mm length) and 50% by weight were uniformly mixed together to form a web using a carding method, and then a web with an orifice diameter of 0.15 m was formed.
m, using a nozzle with 1000 orifices/m, water pressure 80kg/cn+2 water discharge fil120ffi/
After spraying a water stream under the conditions of
A hydroentangled nonwoven fabric having a thickness of 0.6 mm and a thickness of 0.6 mm was obtained.

Two sheets of this non-woven fabric are layered and passed between rotating heat rolls with a smooth surface at a linear pressure cuff of 0 kg/cm and a temperature of 200°C.
Passed twice under the following conditions and bonded under heat to obtain a fabric weight of 120 g/m.
2. A heat-resistant nonwoven fabric according to the present invention having a thickness of 0-15 mm was obtained.

In order to examine the heat resistance of the obtained nonwoven fabric, heat treatment was performed for 3 minutes at a temperature of 200 to 375°C using a hot air circulation furnace.
The yield wI rate and tensile strength after heat treatment were measured.

The results are shown in Table 1.

In addition, for comparison, a web with the same composition as in Example 1 was thermocompressed by omitting only the hydroentangling process (Comparative Example 1) and a commercially available aromatic polyamide wet-laid nonwoven fabric (Comparative Example 2). The same test as in Example 1 was conducted. The results are also shown in Table 1.

As is clear from Table 1, the heat-resistant nonwoven fabric according to the present invention exhibits an extremely low shrinkage rate compared to other fabrics, and is of excellent quality with no occurrence of bubbling due to wrinkles or delamination. Ta.

In addition, the shrinkage rate and weight loss were measured by accurately marking 25 cm long at 3 points each length and width on a 30 x 30 cm test piece, and showing the weight loss after heat treatment and the average value of the shrinkage length and width.
In addition, the tensile strength is measured using a 5cm wide test piece at 100mm/m.
The measurement was performed by stretching at a constant speed.

[Margins below] Table 1 [Example 2] Aromatic jlx e') 7 40% by weight of MiF fiber & TI (1.5 denier, 38 mm length) and 40 layers of polyphenylene sulfide fiber (3 denier, 51 mm length) were placed on fire. and,
Unstretched polyphenylene sulfide fiber (10 denier, 51 mm length) was uniformly blended with 2 Offi amount % and processed in the same manner and under the same conditions as Example 1 to obtain a fabric weight of 80 g/II+2.
A hydroentangled nonwoven fabric having a thickness of o and smm was prepared.

Next, this nonwoven fabric was passed through the same rotating heat rolls as in Example 1 under the conditions of a linear pressure cuff of 0 kg/am and a temperature of 220°C and thermocompression bonded to obtain a heat-resistant nonwoven fabric according to the present invention having a thickness of 0 to 13 nv. Ta.

In order to examine the heat resistance of this nonwoven fabric, Example 1
Similarly, heat treatment was performed for 3 minutes at a temperature of 200 to 375''C in a hot air circulating oven, and the shrinkage rate and tensile strength after the heat treatment were measured.

The results are shown in Table 1.

In addition, for comparison, a web with the same composition as in Example 2 was bonded under heat by omitting only the hydroentanglement process (Comparative Example 3), and a web made of 100% aromatic polyamide fiber was bonded by hydroentanglement. The same test as in Example 2 was conducted on the nonwoven fabric (Comparative Example 4) that was laminated and consolidated with a rotating heat roll. The results are also shown in Table 2.

As is clear from Table 2, the heat-resistant nonwoven fabric according to the present invention exhibits an extremely low shrinkage rate compared to other fabrics, and has even better heat resistance. Since the fibers have water resistance and chemical resistance, the thermal shrinkage rate, which is a drawback of aromatic polyamide fibers, has been improved.

In addition, the wet heat shrinkage rate was measured by accurately marking 25 cm long at 3 points in the vertical and horizontal directions on a 30 x 30 cm test piece, and after applying 200% water by weight to the nonwoven fabric, the test piece was heated at 170°C.
The sample was placed in a hot air circulation dryer, and the yield rate after drying was measured.

[Table 2] Effects of the Invention As mentioned above, the heat-resistant nonwoven fabric according to the present invention has a shrinkage rate that is unprecedentedly low, and completely eliminates wrinkles due to shrinkage that could not be avoided in the past. This was to prevent this.

For this reason, in all industries where heat-resistant nonwoven fabrics have traditionally been used, such as heat-resistant electrical insulation, fiber-reinforced plastics, building structures, and the aerospace industry, it is important not only to improve workability but also to improve quality and safety. It is very useful for improving sexual performance.

Moreover, since it employs two bonding methods, hydroentanglement and thermal fusion, it is possible to select a wider range of heat-resistant fibers and undrawn fibers than ever before, so for example, for heat-resistant applications. Effective use of undrawn polyester fibers, which were previously unsuitable, to significantly improve workability, or aromatic polysulfide fibers with excellent water and chemical resistance for use in high-temperature liquid filters, etc. It is also an advantageous feature of the nonwoven fabric of the present invention that has not been found in the past.

Therefore, the heat-resistant nonwoven fabric of the present invention is excellent in productivity, workability, versatility, etc., and can provide products with stable quality and high safety, which is unprecedented and useful.

Claims (5)

[Claims] (1) A fiber web consisting of 80 to 20% by weight of heat-resistant fibers with a fiber length of 20 to 200 mm and 20 to 80% by weight of undrawn fibers is entangled by the action of water flow, and then the fibers are fused by thermocompression bonding. A heat-resistant nonwoven fabric having a dry heat shrinkage rate of 3% or less under a temperature condition of 200 to 375°C. (2) The heat-resistant nonwoven fabric according to claim 1, wherein the heat-resistant nonwoven fabric contains at least 40% by weight of aromatic polyamide fibers. (3) The heat-resistant nonwoven fabric contains 20 to 60 weight of one or more undrawn fibers selected from undrawn polyester fibers, undrawn aromatic sulfide fibers, undrawn aromatic polyester fibers, and undrawn aromatic polyamide fibers. % of the heat-resistant nonwoven fabric according to claim 1. (4) The heat-resistant nonwoven fabric according to claim 1, wherein the heat-resistant fibers and the undrawn fibers are staple fibers having a fiber length of 20 to 200 mm and a fineness of 0.5 to 10 deniers. (5) Claim 1, wherein the heat-resistant nonwoven fabric has a dry heat shrinkage rate of 1.5% or less under a temperature condition of 325°C or less.
Heat-resistant nonwoven fabric as described in Section 1.