JPH0415003B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to the improvement of a filter cloth used in a wet molding device that filters and compresses slurry-formed magnetic material powder such as hard ferrite magnet material or soft ferrite magnet material and molds it into a desired shape. The present invention relates to a filter cloth for wet molding which has excellent releasability from a molded body after molding, uniformizes the density of the molded body, and has the effect of improving productivity such as reducing cracking, without using in combination with a filter cloth. BACKGROUND ART Generally, when manufacturing ferrite magnets by a wet molding method, a molding apparatus as shown in FIG. 4 is used, and magnetic material powder is slurried in a molding space formed by a die 1 and a lower punch 2. That is, a slurry-like raw material 3 is filled, a filter paper 5 and a filter cloth 6 are arranged between the slurry-like raw material 3 and the upper punch 4, and then compressed with a required pressure and water is filtered and discharged. Obtain a molded body of the desired shape. In the production of anisotropic ferrite magnets, a magnetic field in a desired direction is formed at least within the molding space during compression. Moisture in the compression process of this slurry raw material 3 passes through the filter paper 5 and the filter cloth 6, and the upper punch 4
Water is drained to the outside through a drain hole 7 provided in the drain hole 7 . Therefore, it is essential for the filter paper 5 and the filter cloth 6 to be able to remove water uniformly and sufficiently during the water removal process, and to prevent the raw material powder from flowing out. In order to prevent this, various studies have been made on the structure of the filter paper 5 and the filter cloth 6, etc. As conventional filter cloths, woven fabrics made of natural or synthetic fibers, or so-called woven fabrics made of short synthetic fibers, etc. have been used. In addition, for the purpose of improving the mechanical strength of the nonwoven fabric, short synthetic fibers are bonded and integrated by needling on both sides of the base fabric 11 woven from synthetic multifilament yarns, as shown in FIG. A filter cloth 10 having a configuration in which nonwoven fabric layers 12 and 13 are provided has been proposed. Problems to be Solved by the Invention When any of the above-mentioned filter cloths is brought into direct contact with the slurry raw material in a molding device and filtered and compressed,
The raw material powder tends to flow out along with the moisture in the raw material, leading to early clogging, so it is necessary to replace it after using it for several compression processes, considering the water removal effect and uniform density of the resulting compact. In addition, there was a problem of poor detachability from the molded body. For this reason, in order to extend the life of the filter cloth and improve the ease with which it can be separated from the molded body, a filter paper has been interposed. However, filter paper has low mechanical strength and is easily damaged, so it is replaced after each compression process.In industrial production, the increased replacement work reduces productivity and a large amount of filter paper is used and discarded. There is an economical problem with this, and it is also a factor in reducing the yield due to biting into the molded body. In addition, in order to improve the strength of the filter paper itself so that it can withstand multiple uses, for example, by mixing chemical fibers or creating a multi-layer structure made of different materials, the structure becomes similar to that of filter cloth, which reduces the cost and the molded product. This caused difficulty in separating from the system. On the other hand, as a filter cloth that does not use filter paper at all,
A structure in which the surface of the filter cloth that comes into contact with the slurry raw material is subjected to a frizz treatment or a calender treatment has also been proposed, but compared to the case of a filter cloth that also uses filter paper, it is still less likely to clog. Considering the water removal effect and uniform density of the resulting molded product, there was a limit to the number of times it could be used. As mentioned above, the water removal rate and its uniformity of the molded body in the wet molding method have a large effect on the density of the molded body, and non-uniformity of the density of the molded body makes the magnetic properties of the obtained ferrite magnet unstable. In addition, since this can cause cracks in molded bodies and sintered bodies, there is a strong need for a filter cloth whose initial performance can be maintained even after many compression steps in consideration of the economic efficiency of mass production. In view of the current situation, this invention is capable of maintaining a uniform density of a molded body with excellent detachability from a molded body and excellent water drainage without using a filter paper in a wet molding method, and a molded body and a sintered body. The aim is to create a filter cloth that has the effect of preventing body cracks, and also maintains this initial performance, withstands the same number of uses as before, and improves industrial productivity by eliminating the need to replace filter paper. purpose. Means for Solving the Problems The present invention aims to provide a filter cloth that has excellent detachability from a molded article, excellent water drainage ability, and can maintain a uniform density of a molded article in a wet molding method without using a filter paper in combination. As a result of various studies, we have developed a hygroscopic woven fabric in which hygroscopic fiber yarns made of multifilament are used as the warp and/or weft on the side of the filter cloth made of nonwoven fabric that comes into contact with the slurry raw material powder (the side of the molded object). It was discovered that by providing filter cloth, it is possible to obtain a filter cloth that has a lifespan equal to or longer than conventional filter cloth that uses filter paper, has the required performance as a filter cloth, and is highly economical in mass production. . That is, the present invention provides at least one hygroscopic fiber yarn in which at least one of the light warp and weft yarns is a multifilament yarn.
This filter cloth for wet molding is characterized in that a sheet of hygroscopic woven cloth is placed on the side of the object to be molded and is entangled and integrated with short chemical fibers by needling. Function In this invention, a hygroscopic woven fabric refers to hygroscopic fiber yarns made of multifilaments as warp and/or
Or, it refers to a woven fabric that is made hygroscopic by using the weft. As the hygroscopic fiber yarn, synthetic fibers such as polyamide, hygroscopic chemical fibers such as regenerated fibers such as human silk, hygroscopic natural fibers such as cotton, and other known hygroscopic fiber yarns can be used. Further, according to the inventor's experiments, hygroscopic fiber yarns having an official moisture content of 8.0% to 12.0% exhibited preferable characteristics. In addition, the structure of the woven fabric should be selected from plain weave, twill weave, and satin weave, depending on which type of hygroscopic fiber yarn is used in the weave, the yarn type, the properties of the slurry-like raw material powder, the filtration and compression conditions, etc. Weaving can also be applied, and various innovations can be added to the weaving method, such as changing the thread count and denier. As short chemical fibers to be entangled and integrated into the above-mentioned hygroscopic woven fabric by needling, known fibers such as synthetic fibers such as polyester and polypropylene, recycled fibers, and semi-synthetic fibers can be used. It is desirable that the length etc. be appropriately selected depending on the filtration molding conditions, and it is not always necessary to use only the same type of fibers or the same length fibers. As short chemical fibers, known fibers having a fiber thickness of 0.5 to 3 deniers and a fiber length of 50 to 80 mm can be used. The needling conditions are not particularly limited, but as will be described later, when integrating by bonding, the needling conditions may be short or short depending on the cross-sectional configuration of the filter cloth, that is, the number and position of hygroscopic woven fabrics, or the juxtaposition of non-hygroscopic woven fabrics. The amount of chemical fibers in the fibers, the amount of needling, and the order thereof may be appropriately selected. A plurality of hygroscopic woven fabrics may be used as long as at least one woven fabric is disposed near the surface of the filter cloth that comes into contact with the slurry-like raw material, and the stacking position in the filter cloth can also be arbitrarily selected. Furthermore, it is also possible to arrange a hygroscopic woven fabric in the center of the thickness of the filter cloth, and in this case as well, there is no need to use a filter paper in combination. The filter cloth according to the present invention is composed of at least one hygroscopic woven fabric and a nonwoven fabric layer intertwined with this by needling, and the hygroscopic woven fabric serves as a base fabric and has the necessary mechanical strength. Additionally, other non-hygroscopic fabrics can be provided to improve mechanical strength. As non-hygroscopic woven fabrics, woven fabrics made of monofilament yarns, multifilament yarns, spun yarns, etc. of known fibers such as polyethylene and polyester can be used, depending on the properties of the slurry raw material powder, filtration and compression conditions, etc. The material may be selected as appropriate, but in consideration of mechanical strength and economic efficiency, a woven fabric using polyethylene monofilament yarn is preferable. In this invention, when a non-hygroscopic woven fabric is arranged, the hygroscopic woven fabric is arranged near the slurry raw material contact surface, and the non-hygroscopic woven fabric is arranged at the center or on the upper punch side. However, if the texture of the non-hygroscopic fabric is coarser than that of the hygroscopic fabric, its properties as a filter fabric will improve. Further, it is desirable to subject each surface of the filter cloth to a surface treatment such as a fuzzy treatment or a calender treatment depending on the properties of the slurry-like raw material powder, filtration compression conditions, etc. Further, the thickness of the filter cloth according to the present invention is preferably about 1 mm to 2 mm, considering the official moisture content, mechanical strength, and sealing performance of the molding space, and the air permeability is
Approximately 3 to 6 c.c./cm ² /sec is desirable. Disclosure of the Invention Based on Drawings FIGS. 1 to 3 are cross-sectional explanatory views of a filter cloth according to the present invention. The filter cloth 20 shown in FIG. 1 is made by placing a required amount of polyester short fibers 22 on a hygroscopic woven fabric 21 using hygroscopic fiber yarns made of polyamide multifilament yarns, and entangling them by required needling. It is integrated into one filter cloth 20, and the surface 23 on the side of the hygroscopic woven cloth 21 becomes the contact surface with the slurry raw material, and the surface is calendered. The filter cloth 30 shown in FIG. 2 is produced by placing a required amount of polyester short fibers 32 on a hygroscopic woven fabric 31 using hygroscopic fiber yarn made of polyamide multifilament yarn, and subjecting it to required needling. Furthermore, a similar hygroscopic woven fabric 33 and a small amount of short polyester fibers 32 are placed and needled to form a single filter cloth 30, and the surface 34 on the outermost hygroscopic woven fabric 31 side becomes slurry. This is the surface that comes into contact with the shaped raw material, and the surface is calendered. The filter cloth 40 shown in FIG. 3 is produced by placing a required amount of polyester short fibers 42 on a hygroscopic woven fabric 41 using hygroscopic fiber yarn made of polyamide multifilament yarn, and subjecting it to the required needling. Furthermore, a non-hygroscopic woven fabric 43 using a non-hygroscopic fiber yarn made of polyethylene monofilament yarn and a required amount of polyester short fibers 42 are placed and needled to form one filter cloth 40. , non-hygroscopic woven fabric 4 arranged to improve mechanical strength
3 is located approximately at the center of the cross section, and the surface 44 on the outermost hygroscopic fabric 41 side is the contact surface with the slurry raw material, and this surface is calendered. Note that the layered structure of the filter cloth and the entangling method are not limited to the above-mentioned methods, and any known method can be selected as appropriate. Example A conventional filter cloth (corresponding to Fig. 5, filter cloth No. 1) in which short fibers were needled on both sides of a non-hygroscopic base cloth,
A filter cloth according to the present invention in which a hygroscopic woven fabric is arranged on the surface that comes into contact with the slurry-like raw material powder (corresponding to Fig. 1, filter cloth
No. 2) and 3 of the filter cloth according to the present invention (corresponding to Fig. 3, filter cloth No. 3) in which a hygroscopic woven fabric is arranged on the surface in contact with the slurry-like raw material powder and a non-hygroscopic base fabric is arranged in the center.
A seed filter cloth was manufactured using a woven cloth having the properties shown in Table 1 and short polyester fibers (fiber thickness: 1.5 denier, fiber length: 76 mm). The surface of each filter cloth that comes into contact with the slurry raw material is calendered. Table 1 shows the properties of each filter cloth. Using these three types of filter cloth, the average particle size was 0.7 μm.
A slurry-like raw material powder of ~0.8 μm was molded in a magnetic field to obtain a large number of bow-shaped molded bodies in multiple lots. During compression molding, each filter cloth was used until the variation in density of the compact began to exceed 5.0% of the unit weight of the compact, and the number of times it was used (number of moldings) up to that point, as well as the crack occurrence rate of the obtained compact measure,
The results are shown in Table 2 along with the observed detachability from the molded body. As is clear from Table 2, the filter cloth according to the present invention has a stable density of the molded product even after being used for the same number of times as compared to the conventional filter cloth that uses filter paper in combination, and is free from defects such as cracks. It can be seen that this has been significantly reduced.

【table】

[Table] Effects of the Invention The filter cloth according to the present invention uses hygroscopic fiber yarns made of multifilament as the warp and/or weft on the contact surface on the slurry raw material side (to-be-molded object side) of the filter cloth made of nonwoven fabric. Due to the structure in which the hygroscopic woven fabric is arranged, it is possible to maintain a uniform density of the molded product with excellent detachability from the molded product and excellent water removal property without using filter paper in the wet molding method. , it has the effect of preventing cracks in the sintered body, maintains the initial performance, can withstand the same number of uses as before, and has the advantage of being able to improve industrial productivity by eliminating the need to replace filter paper. have By not using filter paper, it is economical and has the advantage of improving productivity by eliminating the need to replace it, as well as providing more stable air permeability compared to filter paper, which reduces the variation in air permeability between moldings. It can be made small, which is advantageous in stabilizing the compact density uniformly, and the effect of preventing cracks in the compact and sintered compact can be obtained. In addition, compared to filter paper, the sealing performance under high compression is improved, the protrusion of slurry-like raw material powder is prevented, and the occurrence of burrs in the compact state is reduced, which improves the processing yield of sintered compacts. is obtained. In addition, it has excellent releasability from the molded body, eliminates the filter paper getting caught in the filter paper as in the conventional case, and has the effect of improving the yield in combination with the above-mentioned crack prevention effect. Furthermore, in configurations using multiple hygroscopic woven fabrics or in combination with non-hygroscopic woven fabrics, the mechanical strength of the filter cloth can be greatly improved, making it possible to obtain extremely economical filtration cloths. I can do it.

[Brief explanation of drawings]

1 to 3 are cross-sectional explanatory views of the filter cloth according to the present invention. FIG. 4 is an explanatory diagram of the main parts of the wet molding apparatus. FIG. 5 is an explanatory cross-sectional view of a conventional filter cloth. 20,30,40...filter cloth, 21,31,3
3, 41... Hygroscopic woven fabric, 22, 32, 42...
Short fiber, 43...Non-hygroscopic base fabric, 23, 34, 4
4...Surface.

Claims (1)

[Claims] 1. At least one hygroscopic woven fabric, in which at least one of the light warp and weft yarns is a hygroscopic fiber yarn made of multifilament yarn, is placed on the side of the molded object and entangled and integrated with short chemical fibers by needling. A filter cloth for wet molding characterized by comprising: