JPH0240779B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a heat-resistant nonwoven fabric, and more specifically, the present invention relates to a heat-resistant nonwoven fabric that has an extremely low shrinkage rate at high temperatures, has excellent dimensional stability, and has excellent mechanical properties such as strength. Regarding nonwoven fabrics. [Prior Art] Conventionally, as for heat-resistant nonwoven fabrics, paper-like nonwoven fabrics made by a wet process, in which short aromatic polyamide fibers are mixed with pulp-like particles of the same composition, have been widely known. discloses a method for producing a heat-resistant nonwoven fabric using undrawn aromatic polyamide fibers as adhesive elements. In addition, regarding other heat-resistant nonwoven fabrics, needle punched felts made of novoloid fibers and aromatic polysulfide fibers, and JP-A-57-
Spunbond nonwoven fabrics using aromatic polysulfide such as No. 16954 are known. Furthermore, as the most similar to the present invention, there is known a nonwoven fabric in which fiber webs made of aromatic polyamide fibers are entangled by the action of water flow. [Problems to be Solved by the Invention] The paper-like nonwoven fabric produced by a wet process using the aromatic polyamide fibers described above is useful because it has excellent heat resistance, but it often wrinkles due to heat shrinkage in a high-temperature atmosphere. It has the disadvantage that it cannot hold its shape or has low tear strength because it uses short fibers with a fiber length of 10 mm or less, and it has poor impregnation properties with, for example, insulating varnish and unsaturated resin for FRP. . 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 layers to separate and bubbling occurs frequently, making it unsuitable for practical use. There was a drawback that there was no such thing. For heat-resistant nonwoven fabrics mainly composed of aromatic polyamide staple 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 above-mentioned wet method. For example, in a manufacturing method that utilizes the heat-adhesive properties 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. 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, a solvent exhaust or recovery device is required, which are both difficult to implement due to their poor versatility. The hydroentangled nonwoven fabric made of aromatic polyamide fibers has good heat resistance and excellent strength, but the fibers are mechanically entangled;
Because there is no bond between fibers, dimensional stability is poor, and
It has the disadvantage of causing frizz, and for this reason,
Attempts have been made to stabilize the dimensions by post-processing such as elongation, but these post-processing actually increase the heat shrinkage rate, which is not preferable. On the other hand, heat-resistant nonwoven fabrics made of other fibers are
Fiber felt made by the needle punch method and nonwoven fabric made by the spunbond method have been proposed, but both have poor shape retention and dimensional stability, and either have large heat shrinkage or wrinkles due to shrinkage. The disadvantage was that it caused Therefore, the present invention exhibits extremely little thermal shrinkage, no wrinkles or fuzzing, and excellent dimensional stability, strength, etc. under high-temperature atmospheres that were previously considered extremely difficult or impossible. The purpose of the present invention is to provide a heat-resistant nonwoven fabric that also has excellent mechanical properties. [Means for solving the problems] The present invention is characterized in that the fiber length is 80 to 20% by weight of heat-resistant fibers.
A nonwoven fabric in which a fiber web consisting of 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, the nonwoven fabric having a temperature of 200 to 375°C. The present invention relates to a heat-resistant nonwoven fabric having a dry heat shrinkage rate of 3% or less under certain conditions. [Function] As a result of intensive research aimed at obtaining a nonwoven fabric with an extremely low heat shrinkage rate and excellent heat resistance stability, the inventors of the present invention have found that by using heat resistant fibers, fiber entanglement due to the action of water flow can be achieved. By combining fiber-to-fiber bonding with non-stretched fibers, we have created a heat-resistant non-woven fabric that has extremely low shrinkage and no wrinkles when heated, and also has excellent mechanical properties such as strength. The present invention has been completed based on the discovery that the following 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 fibers, aromatic polyether fibers, and novoloid fibers, and fibers obtained by oxidizing synthetic fibers such as oxidized acrylic fibers. Any heat-resistant fiber that can be formed into a web, such as inorganic fibers such as glass fibers, asbestos fibers, carbon fibers, and metal fibers, can be used. Synthetic fibers, alone or in combination, facilitate web formation and allow these fibers to withstand temperatures up to 300°C.
It is suitable because it does not melt and forms a skeleton even at temperatures above, making it possible to obtain a variety of products, and in addition, product quality design and quality control can be carried out extremely easily and stably. 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 When used at high temperatures, or when the time required for heat resistance even at temperatures above the melting point is extremely short, it is possible to utilize these fibers by taking 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. Enhancement effect, effect of improving mechanical properties such as tensile strength,
Alternatively, it has the effect of preventing the nonwoven fabric from becoming fluffy and generating fiber dust, thereby improving the quality of the product. These undrawn fibers include undrawn polyester fibers, undrawn aromatic polysulfide fibers,
Undrawn aromatic polyester fibers, undrawn aromatic polyamide fibers, and the like are known, and can be appropriately selected and used depending on the required heat resistance conditions. In other words, for example, if long-term heat resistance is required,
It is preferable to use undrawn fibers that are inherently heat resistant, such as undrawn aromatic polysulfide fibers and undrawn aromatic polyester fibers, and even when heat resistance at high temperatures is required. When heat resistance for a short period of several minutes or hours is sufficient, 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-mentioned characteristics, but in the present invention, fibers with a length of 20 to 200 mm and a fineness of 0.5 to 10 are used.
It is preferable to use denier staple fibers because they have excellent uniformity in web formation and have good entanglement efficiency by water jetting.
A material with a diameter of 76 mm to 76 mm and a fineness of 1 to 6 denier is considered to be optimal because it provides the best web formation and entanglement efficiency. To briefly explain the reason why staple fibers are preferable in the present invention, they are made of, for example, non-woven fabrics produced by spunbond or melt-blown methods, or extremely long fibers with a fiber length exceeding 200 mm, such as those using long fiber tows. It is impossible or very difficult to use non-woven fabrics by mixing multiple raw materials and fibers with different properties such as fiber diameter and fiber length, so it is impossible to form a variety of non-woven fabrics, and The entanglement efficiency by water jetting is inferior, and on the other hand, short fibers used in the wet method, such as those with a fiber length of 20 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 staple fibers having the above-mentioned suitable fiber length and fineness ranges. Next, hydroentanglement, which is the most important aspect of the present invention, will be explained. Regarding hydroentanglement, it is sufficient to apply a known technique known, for example, in U.S. Pat. A water stream is sprayed onto the web mixed with drawn fibers through a large number of fine orifices, entangling each fiber. 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 possible reasons are as follows: First, each fiber that was arranged horizontally on the web is randomly arranged in three dimensions, including the vertical direction, by water jets. 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. As a result, the heat resistance stability of the undrawn fibers increases and the shrinkage rate decreases. Thirdly, the fibers in tension are locally stretched by the pressure of the water flow. The structural and molecular strain relaxation effect that results in a relaxation effect resulting in a decrease in heat shrinkage rate, and fourthly, the latent shrinkage of short fibers of heat-resistant fibers and undrawn fibers It is conceivable that the nonwoven fabric undergoes a treatment similar to wet heat heat setting during the drying process, resulting in a decrease in the thermal shrinkage rate of the nonwoven fabric. In any case, in the present invention, the hydroentanglement process is most important as a means for dramatically reducing the thermal shrinkage rate at temperatures of 200 to 375°C. The entangled nonwoven fabric is then thermo-compressed to fuse the fibers by the binding action of the undrawn fibers, resulting in excellent dimensional stability and mechanical properties such as strength that are significantly superior to conventional ones. This becomes the nonwoven fabric of the present invention. 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.
It also has the auxiliary effect of further reducing the dry heat shrinkage rate of the nonwoven fabric. 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
Suitable temperatures are 120 to 220°C, 140 to 240°C for undrawn polyphenylene sulfide fibers, or 250 to 350°C for undrawn aromatic polyamide fibers, and a linear pressure of 30 to 300 Kg/cm. it is conceivable that. In addition, any device can be used for these purposes, such as a flat plate heat press device, a rotating heat roll device, or an engraved heat roll device with an uneven surface, but using a rotating heat roll will improve continuous productivity and quality stability. It is advantageous because it is excellent in Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to these Examples. Example 1 Aromatic polyamide fiber (1.5 denier, 38 mm length)
50% by weight and 50% by weight of undrawn polyester fiber (5 denier, 44mm length) were uniformly blended, a web was formed by the carding method, and then the orifice diameter was
Using a 0.15 mm nozzle with 1000 orifices/m, a water stream was sprayed at a water pressure of 80 Kg/ ^cm2 and a water output rate of 120/min to entangle each fiber three-dimensionally, and then heated to a temperature of 100°C. A hydroentangled nonwoven fabric having a basis weight of 60 g/m ² and a thickness of 0.6 mm was obtained. Two sheets of this nonwoven fabric are layered and passed between rotating heat rolls with a smooth surface at a linear pressure of 70 kg/cm and at a temperature of
Passed twice under 200℃ condition, heat-compressed, and
A heat-resistant nonwoven fabric according to the present invention having a weight of 120 g/m ² and a thickness of 0.15 mm was obtained. In order to examine the heat resistance of the obtained nonwoven fabric, heat treatment was performed at a temperature of 200 to 375°C for 3 minutes using a hot air circulation furnace, 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 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 exhibited an extremely low shrinkage rate compared to other fabrics, and was of excellent quality with no occurrence of bubbling due to wrinkles or delamination. . In addition, the shrinkage rate and weight loss were measured by accurately marking 25 cm length at three points in the vertical and horizontal directions on a 30 x 30 cm test piece, and showing the weight loss after heat treatment and the average value of the shrinkage in the vertical and horizontal directions. The strength was measured by stretching a 5 cm wide test piece at a constant speed of 100 mm/min.

【table】

[Table] Example 2 Aromatic polyamide fiber (1.5 denier, 38 mm length)
40% by weight, polyphenylene sulfide fiber (3 denier, 51mm length), 40% by weight unstretched polyphenylene sulfide fiber (10 denier, 51mm length)
A hydroentangled nonwoven fabric having a basis weight of 80 g/m ² and a thickness of 0.5 mm was prepared by uniformly blending 20% by weight of the nonwoven fabric with the same method and conditions as in Example 1. Next, this nonwoven fabric was passed through the same rotating heat rolls as in Example 1 under the conditions of a linear pressure of 70 Kg/cm and a temperature of 220°C to be thermocompression bonded, thereby obtaining a heat-resistant nonwoven fabric of the present invention having a thickness of 0.13 mm. In order to examine the heat resistance of this nonwoven fabric,
As in Example 1, heat treatment was performed for 3 minutes at a temperature of 200 to 375° C. in a hot air circulation furnace, 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 thermocompressed by omitting only the hydroentangling process (Comparative Example 3) and an aromatic polyamide fiber.
The same test as in Example 2 was conducted on a nonwoven fabric (Comparative Example 4) in which a 100% web was hydroentangled 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 of the present invention exhibits an extremely low shrinkage rate compared to other fabrics, and has even better heat resistance. Since the rensulfide fiber has water resistance and chemical resistance, the wet heat shrinkage rate, which is a drawback of aromatic polyamide fibers, has been improved. The wet heat shrinkage rate was measured by accurately marking 25 cm long at three 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, it was heated at 170°C.
The shrinkage rate was measured after drying.

【table】

[Table] [Effects of the Invention] As mentioned above, the heat-resistant nonwoven fabric of the present invention has a shrinkage rate that is unprecedentedly low and completely prevents wrinkles due to shrinkage, which could not be avoided in the past. It is. 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. Effectively utilize undrawn polyester fibers that were previously unsuitable to dramatically improve workability, or utilize 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 has excellent productivity, workability, versatility, etc., and can provide products with stable quality and high safety, which is unprecedented and useful.

Claims (1)

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