WO2009002024A2

WO2009002024A2 - Filtrate media for high- tension molding

Info

Publication number: WO2009002024A2
Application number: PCT/KR2008/003032
Authority: WO
Inventors: Dong-Gul Lee; Dong-Hyeop Lee
Original assignee: Dong-Gul Lee; Dong-Hyeop Lee
Priority date: 2007-06-25
Filing date: 2008-06-02
Publication date: 2008-12-31
Also published as: WO2009002024A3; KR100824214B1; JP2010531722A

Abstract

Disclosed is a filtration cloth for high-pressure molding. The filtration cloth comprises a mesh- type filter layer woven using one or more raw yarns selected from the group consisting of PET (polyethylene terephthalate) raw yarn, nylon-6 raw yarn and a mixed yarn thereof; a filtration layer needle-punched in one side of the filter layer and formed of fibers including one or more raw yarns selected from the group consisting of PET (polyethylene terephthalate) raw yarn, nylon raw yarn and a mixed yarn thereof; an absorption layer needle-punched on the other side of the filter layer and formed of fibers of PET raw yarns; and a coating layer formed in a high density, the coating layer being formed by melting the surface of the absorption layer.

Description

FILTRATE MEDIA FOR HIGH-TENSION MOLDING

Technical Field

[1] The present invention relates to a filtration cloth for high-pressure molding, more specifically to a filtration cloth for high-pressure molding, in which liquid is absorbed and discharged, and fine particles are filtered. Background Art

[2] An industrial filtration cloth is a filter member that passes liquidus particles such as water and oil and screens solidus particles through fine pores. This industrial filtration cloth is widely used in parts industries where water treatment / air-cleaning / press- forming are carried out through air, liquid or solid filtration.

[3] Among them, a filtration cloth is generally used in a set press-forming process, in which a mixture of slurry state is pressed to reduce moisture contents and then obtain a molded object.

[4] However, in case where the slurry is dehydrated by a mechanical pressure, the slurry particle moves along with liquid to block the filtration cloth. Thus, in order to avoid this, a considerable pressure must be exerted to damage the filtration cloth and also consume a great deal of energy.

[5] As one of conventional filtration cloth, Korean Patent Application Laid-open No.

1998-0029645 discloses a multi-layered non-woven fabric cloth, which is composed of a rear non- woven fabric layer, a synthetic fiber layer, a lsland-in-sea type composite fiber and the like. This filtration cloth can be applied to filtration of fine dust and liquid. However, repeated use easily causes damage on the filtration cloth.

[6] Further, Korean Utility Model Publication No. 20-0202148 discloses a high density filtration cloth using synthetic fibers, which is double-woven while regularly changing the latitude yarn in the surface layer and rear face layer to provide a high-density filtration cloth. This is developed in order to improve mainly filtration performance, and thus not suitable for repeated use in the high-pressure forming and embraces many problems. Disclosure of Invention

Technical Problem

[7] On the other hand, in a wet press-forming process, to which the present invention can be applied, a ferrite magnet is exemplified. The ferrite magnet is widely used in various areas such as automobiles, home appliances, industrial machinery and the like.

[8] In the manufacturing process of ferrite magnets, chlorine is separated from iron oxide, and mixed with water and boron acid is added in an appropriate amount to form a slurry. Moisture is dehydrated using a centrifugal separation. This mixture is supplied into a calcination rotary kiln and drying, dinger- forming and calcination reaction are carried out to form dingers, which are cooled and pulverized in a crasher to form ferrite powder. The ferrite powder is dispersed in a dispersing medium to prepare a slurry (for molding) having a certain concentration. The slurry is press-formed under magnetic field to form a molded object, which is then sintered.

[9] During the above course of actions, when moisture contained in the slurry is dehydrated, cracks occur in the molded ferrite, which lead to defective products, thereby significantly reducing production yield.

[10] Furthermore, in order to increase production yield and shorten the process time, various measures have been taken, for example, the injection rate of slurry into the die and the pressing speed is increased, or the moisture discharging passageway in the die is widened. However, in case where the injection rate of slurry or the pressing speed of the piston and the moisture discharging rate are higher than the moisture absorption rate, the pressure of slurry itself inside the die increases so that the raw materials flow backward the injection port. In addition, the slurry is not properly pressurized, etc., which lead to defective products due to low density of the molded objects

[11] In the above process, the filtration cloth, which is applied for wet anisotropic ferrite magnets, has the following functions. When the slurry is injected into a die and pressed, moisture contained in the slurry is absorbed and discharged to the outside through the filtration cloth, and solidus particles are screened by the filtration cloth to form a molded object according to the shape of the molding die.

[12] At this time, the die pressure is very high up to 300~350kg/cm2. Thus, where a conventional filtration cloth is used, it can be easily torn off and pores are widened to fail to perform the filtration functions, thereby discharging fine solid particles (for example, 1-2 microns) together with the moisture.

[13] Further, notwithstanding that the moisture discharging rate through the filtration cloth is directly related with the productivity of magnets, the die is slowly pressurized with a lower pressure in order to avoid tearing of the filtration cloth, thereby resulting in decrease in the productivity (for example, more than 70 seconds for one cycle time). Simultaneously, the slurry is not properly pressed, which leads to about 30% of defect rate for the total products due to low density in the texture after molding the magnets (for example, graded as being defective if the moisture residual is more than 15% after press-forming).

[14] In addition, when press-forming, the solid particles are pressed while making friction with the filtration cloth. Thus, the surface property of the filtration cloth affects directly the surface roughness of the molded object. That is, where the above conventional filtration clothes are used, their rough surface leads to roughness in the outer appearance of the molded object. Further, fine naps from the raw yarns are stuck to the molded object so that the filtration cloth is separated or peeled off when the die is open, thereby resulting in crashing of the molded object. Technical Solution

[15] Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the conventional art, and a primary object of the present invention is to provide a filtration cloth for high-pressure molding, which has high elasticity and mechanical strength and simultaneously rapidly discharges liquidus particles, thereby improving productivity in the wet press-forming process and providing a smooth appearance to the press-formed products.

[16] To accomplish the above object of the present invention, according to one aspect of the invention, there is provided a filtration cloth for high-pressure molding, the filtration cloth comprising: a mesh-type filter layer 10 woven using one or more raw yarns selected from the group consisting of PET (polyethylene terephthalate) raw yarn, nylon- 6 raw yarn and a mixed yarn thereof; a filtration layer 20 needle-punched in one side of the filter layer 10 and formed of fibers including one or more raw yarns selected from the group consisting of PET (polyethylene terephthalate) raw yarn, nylon raw yarn and a mixed yarn thereof; an absorption layer 30 needle-punched on the other side of the filter layer 10 and formed of fibers of PET raw yarns; and a coating layer 40 formed in a high density, the coating layer being formed by melting the surface of the absorption layer 30.

[17] In an embodiment, the filter layer 10 is woven using a longitude yarn formed in

400-440 denier and in a density of 13-15x2 per inch, and a latitude yarn formed either in 820-860 denier and in a density of 16-17 per inch or 420 denier x 2 and in a density of 15-16.

[18] In an embodiment, the filter layer 10 is woven in Reno texture.

[19] In an embodiment, the filter layer 10 has a shrinking rate of 15-17% when needle- punching the filtration layer 20 and the absorption layer 30.

[20] In an embodiment, the PET raw yarn and the nylon raw yarn in the filtration layer 20 is 3-6 denier raw yarn, and the mixed yarn thereof is mixed in a rate of 55-70% :30~45%.

[21] In an embodiment, the PET raw yarn in the absorption layer 30 is formed by optionally mixing two or more types of raw yarns selected within a range of 1-3 denier.

[22] In an embodiment, the coating layer is formed by heat-treating the surface of the absorption layer 30 with a heat source H of 280~330°C, and thereafter closely attaching a calendar roll R so as to reduce the fine protrusions, thereby having a high density.

Advantageous Effects

[23] As above, the fabric filter according to the invention has excellent absorption ability and elasticity, thereby sustaining continuous friction of a piston. The fabric filter rapidly absorbs and discharges moisture to avoid defective products which may be caused by low density. The fabric filter of the invention simplifies the production cycle of the press-forming process, thereby enabling mass- and low-cost production.

[24] These advantageous effects are further described as follows.

[25] First, a high strength yarn is used to significantly improve the elasticity and mechanical strength of the entire filtration cloth due to the filter layer woven in high- density reno texture. Thus, it can be flexibly shrunk and restored under high-pressure condition, in particular, under pressing condition under which a streamline object is molded, thereby supporting the filtration layer and absorption layer to be maintained in their initial states.

[26] Secondly, the filtration layer and absorption layer formed of dissimilar denier and materials are formed integrally at both sides of the filter layer. Thus, fine solidus particles are screened and liquidus particles such as moisture are rapidly absorbed and discharged, thereby significantly improving productivity of the wet press-forming process.

[27] Third, the absorption layer is formed of a low denier raw yarn so that the evenness thereof is improved and also the thermal forming can be easily performed to form a coating layer having a higher smoothness. Thus, the outer appearance of the molded object, which makes friction with the coating layer during the press-forming, remains in smooth state. In addition, crack is prevented from occurring in the surface of the molded object. Brief Description of the Drawings

[28] Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[29] FIGS. 1 to 3 are cross-sectional views illustrating the construction of a filtration cloth for high-pressure molding according to an embodiment of the invention;

[30] FIG. 4 is a cross-sectional view showing a process for forming a coating layer in a filtration cloth for high-pressure molding according to an embodiment of the invention;

[31] FIGS. 5 and 6 are cross-sectional views illustrating a process for press-forming a plate-shape or streamline object using a filtration cloth for high-pressure molding according to an embodiment of the invention; and

[32] FIGS. 7 to 10 are cross-sectional views illustrating a wet-process for manufacturing anisotropic ferrite magnets through press-forming using a filtration cloth for high- pressure molding according to an embodiment of the invention. Best Mode for Carrying Out the Invention

[33] Hereinafter, exemplary embodiments of the present invention will be described in detail, with reference to the accompanying drawings.

[34] FIGS. 1 to 3 are cross-sectional views illustrating the construction of a filtration cloth for high-pressure molding according to an embodiment of the invention. FIG. 4 is a cross-sectional view showing a process for forming a coating layer in a filtration cloth for high-pressure molding according to an embodiment of the invention. FIGS. 5 and 6 are cross-sectional views illustrating a process for press-forming a plate-shape or streamline object using a filtration cloth for high-pressure molding according to an embodiment of the invention. FIGS. 7 to 10 are cross-sectional views illustrating a wet-process for manufacturing anisotropic ferrite magnets through press-forming using a filtration cloth for high-pressure molding according to an embodiment of the invention.

[35] The present invention is directed to a filtration cloth for high-pressure molding

(hereinafter, referred to as a "high-pressure filtration cloth"). The high-pressure filtration cloth 100 is applied to high-pressure filtration in various industrial facilities such as wet-press forming machines, high-pressure dehydrators and the like. The high- pressure filtration cloth 100 includes a filter layer 10, a filtration layer 20, a suction layer 20 and a coating layer 40, so that solid particles are filtered and liquid (moisture) is rapidly absorbed and passes through under high-pressure.

[36] According to an embodiment of the invention, the filter layer 10 is formed by weaving at least one raw yarn selected from the group consisting of PET (polyethylene terephthalate) raw yarn, nylon-6 raw yarn and a mixed yarn thereof. The filter layer 10 is woven in a mesh-type. The weaving may be made using conventional methods such as twill- weaving, plain- weaving and the like. Preferably, a Reno- weaving may be used.

[37] The filter layer 10 acts as a reinforcement layer for supporting the high-pressure filtration cloth so that a good durability can be obtained. Preferably, the filter layer 10 employs a mixed yarn at a mixing ratio of 40-60% :40~60% so as to take advantages of both the good absorption property of PET raw yarns and the high-strength elasticity and flexibility of nylon-6 raw yarns.

[38] In addition, as illustrated in FIG. 3, the reno texture is characterized by a dense texture. In the reno texture, among plural slant yarns, one slant yarn is twisted to the right and left against the other slant yarn and a latitude yarn is disposed in-between.

[39] When the filter layer 10 is formed of a reno texture, inherently a good flexibility is obtained to improve the critical limit against elastic deformation. Therefore, during a high-pressure operation, the high-pressure filtration cloth is flexibly shrunk and recovered to thereby prevent the filtration cloth from tearing up. In addition, the reno texture is formed of a mesh-type structure. Thus, deformation of the texture due to repeated uses can be prevented to serving as a reinforcement member to maintain the initial state of the filtration cloth 100. According to an embodiment of the invention, the filter layer 10 may be formed through twill-weaving (weaving slant yarns in a protuberant form) or plain- weaving (weaving a latitude string and a longitude string in an off-set form), although the shrinkability is less than the reno texture.

[40] Here, the longitude yarn in the filter layer 10 is formed in 400-440 denier and in a density of 13-15x2 per inch, and the latitude yarn is formed in 820-860 denier and in a density of 16-17 per inch, or in 420 denier x2 and in a density of 15-16 per inch.

[41] Table 1 is an experimental result showing a moisture discharge rate (%) per hour with respect to weaving densities. As can be seen in Table 1 that as the weaving density of the latitude and longitude yarns are higher, the discharging rate of liquid becomes higher, and as the weaving density becomes lower, the discharging rate of liquid becomes relatively lower.

[42] Table 1: Experimental result showing a moisture discharge rate (%) per hour with respect to weaving densities

[43] Weaving density (12x2)xl3 (13x2)xl4 (14x2)xl5 (15x2)xl7

[44] Moisture discharging rate (%) 40 50 60 100

[45]

[46] Specifically, as the weaving density of the filter layer 10 becomes higher, the amount of moisture absorption increases due to swelling phenomena, so the moisture discharge can be rapidly performed. The swelling phenomenon is described by a phenomenon that when a fiber absorbs moisture, the lengthwise or diametric dimension increases due to an increase in the volume thereof.

[47] Therefore, considering the discharging rate of moisture according to the weaving density of the filter layer 10, preferably, the weaving is carried out in a density of 420 denier x 2 per inch for longitude yarns and in a density of (15x2)xl7 per inch for latitude yarns, thereby obtaining a maximum density of weaving.

[48] In addition, the filter layer 10 is formed in the filtration cloth 100 in 15-17% shrunk state when needle-punching a filtration layer 20 and an absorption layer 30 at both sides thereof. That is, if PET raw yarns and nylon raw yarns forming the filtration layer 20 and the absorption layer 30 is needle-punched on the filter layer 10, which is woven in a Reno texture, the PET raw yarns and nylon raw yarns are inserted between the longitude and latitude yarns in the filter layer 30 so that the filter layer 10 is shrunk. At this time, the needle-punching is performed so as to shrink the filter layer 10 by 15-17%, thereby improving elasticity for shrinking and restoring. Thus, the filtration cloth can be deformed with high flexibility, conforming to the mold shape, to thereby performing the filtration function, even under high pressure condition for press- forming an object, such as a plate-like object as illustrated in FIG. 5 and a streamline object as illustrated in FIG. 6.

[49] Here, if the shrinking rate of the filter layer 10 by the needle-punching is no more than 14%, it is likely to be torn off under pressing conditions due to a decrease in the range of shrinking and recovery. In addition, if the shrinking rate is no less than 18%, the density of the filter layer 10 becomes lower so not to properly perform the filtration function, along with an increase in the consumption of raw materials.

[50] Further, according to an embodiment of the invention, the filtration layer 20 is needle-punched in one side of the filter layer 10. The filtration layer 20 is formed of fibers constituting one or more raw materials selected from the group consisting of PET raw yarn, nylon raw yarn and a mixed yarn thereof. When it is used for wet- pressing an object, the filtration layer 20 is needle-punched so as to rapidly absorb and discharge moisture, which passes and is discharged through the filter layer 10 and the absorption layer 30. The absorption layer 30 will be further described hereinafter. Here, basically the needle-punching is performed in the surface or rear face of a laminated-fabric by moving various needles repeatedly up and down, such that the fabric is punched and tangled mechanically with each other to consequently form a fabric layer having a certain thickness and density.

[51] In addition, the PET raw yarns and nylon raw yarns forming the filtration layer 20 employ a 3-6 denier raw yarn, and the mixed yarn thereof is formed by mixing then at a mixing ratio of 55-70% :30~45%. The filtration layer 20 is formed, considering the respective physical properties of the PET raw yarns, the nylon raw yarns and the mixed yarns, such as their elasticity, and filtering and absorption properties. These properties can be obtained in combination by utilizing a mixed yarn of the PET raw yarns and the nylon raw yarns.

[52] Furthermore, the filtration layer 20 is formed of a relative high 3-6 denier so as to provide a good ventilation property and a good restoring force against a repeatedly exerted pressure. In case of the mixed yarns, preferably 60% of 6 denier raw yarns for the PET raw yarns are mixed to increase its absorption ability, and 40% of 3 denier raw yarns for the nylon raw yarns are mixed to improve filtration and elasticity thereof.

[53] In this way, the filtration layer 20 is formed of a mixed fiber of PET raw yarns and nylon raw yarns. Therefore, it cannot be easily deformed by a repeated high-pressure external force and restored to its original state, and thus rapidly absorb liquidus particles, i.e., moisture, which passes and is discharged through the filter layer 10.

[54] Further, according to an embodiment of the invention, the absorption layer 30 is needle-punched in the other side of the filter layer 10, and formed of fiber constituting PET raw yarns. When the filtration cloth 100 is used for wet-pressing an object, the absorption layer 30 makes friction with the object to be molded, having the coating layer in-between. The coating layer will be further explained hereinafter. The absorption layer 30 acts to filter primarily solidus particles and discharge moisture only.

[55] Here, the PET raw yarns in the absorption layer 30 is formed by selectively mixing two or more types of raw yarns having dissimilar deniers selected within a range of 1-3 denier. The absorption layer 30 is formed in a high density texture, using PET raw yarns of relatively low 1-3 denier having a good absorption property, thereby enabling to screen solidus particles up to 1 micron and simultaneously maintain the high ability of discharging moisture.

[56] Furthermore, if the absorption layer 30 is formed in a high density texture using a low denier of raw yarns considering the absorption ability only, the elasticity thereof may be lowered. Therefore, preferably, it is formed of a mixture of 1.5 denier PET ray yarns and 3 denier PET raw yarns at a mixing rate of 50:50%, to thereby obtain a self- elasticity while adversely affecting its absorption ability.

[57] Further, the PET raw yarns forming the absorption layer 30 is formed of a low denier of less than 3 deniers. Thus, it can be easily molded by heat during the melting treatment which will be further described hereinafter. Therefore, the surface of the coating layer 40 can have a good evenness uniformly throughout the entire surface thereof.

[58] Furthermore, according to an embodiment of the invention, the coating layer 40 is formed in high-density through a melting treatment of the surface of the absorption layer. When the filtration cloth 100 is used for wet-pressing an object, the coating layer 40 makes direct friction with the object to be molded. Thus, the coating layer 40 is formed in high density so as to provide a smooth appearance to the molded object after molding.

[59] As illustrated in FIG. 4, the coating layer 30 is formed by heating the surface of the absorption layer 30 in a temperature range of 280~330°C, preferably 31O⁰C, so as not to over-melt by the heat source or delay the melting process. Thereafter, a calendar roll T is closely contacted to reduce fine bumps and thus provide a high density. Thus, the surface of the absorption layer 30 is maintained in a high density of smooth surface, thereby enabling to obtain a good appearance of molded objects, while avoiding in advance defects such as peel-off s or fall-offs in the surface of molded objects, which may be caused by liens of the PET raw yarns.

[60] FIGS. 7 to 10 are cross-sectional views illustrating a wet-process for manufacturing anisotropic ferrite magnets through press-forming using a filtration cloth for high- pressure molding according to an embodiment of the invention. As illustrated in FIG. 7, a slurry raw material A is charged through a charging port 60. The slurry raw material A is composed of a mixture of ferrite powder and moisture. As shown in FIGS. 8 and 9, a piston 80 of a lower die 50 moves up to pressurize the slurry raw material A up to the filtration cloth 100 and an upper die 52. Then, the moisture C in the slurry raw material A is discharged through pores of the coating layer 40, the absorption layer 30, the filter layer 10 and the filtration layer 20. The solidus particles are screened and compressed in a cake form between the filtration cloth 100 and the piston 80, thereby forming a molded object having the form of ferrite magnets.

[61] At this time, the coating layer, which makes friction directly with the slurry raw material A, provides a smooth surface of molded objects due to its high roughness. Further, since the absorption layer 30 is formed of mixed fibers of PET raw yarns having different thicknesses, the moisture C is rapidly absorbed and discharged.

[62] In addition, the filter layer 10 is formed of a strong and easily extendable nylon-6 material to sustain the repeated compression and friction of the piston 80, thereby preventing deformation of the filtration cloth. Further, the filter layer 10 discharges moisture through pores, while screening solidus particles B. The discharged moisture C is absorbed into the filtration layer 20 and is discharged to the outside through the discharge hole 70 of the upper die 52.

[63] At this time, the filtration layer 20 has an elasticity sustaining friction, along with excellent absorption ability, thereby enabling to sustain frictional phenomenon by moisture absorption and pressurization of piston 80.

Industrial Applicability

[64] As described above, the filtration cloth 100 according to present invention is formed of a material having high elasticity and simultaneously excellent absorption ability. In the press-molding process for manufacturing wet anisotropic ferrite magnets, the moisture C within the slurry raw material A can be discharged with high efficiency. Thus, the press-forming process cycle can be sped up to improve production yield, while decreasing defects in the molded ferrite, which is caused by a low density of structure.

[65] While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.

Claims

[1] A filtration cloth for high-pressure molding, the filtration cloth comprising: a mesh-type filter layer 10 woven using one or more raw yarns selected from the group consisting of PET (polyethylene terephthalate) raw yarn, nylon-6 raw yarn and a mixed yarn thereof; a filtration layer 20 needle-punched in one side of the filter layer 10 and formed of fibers including one or more raw yarns selected from the group consisting of

PET (polyethylene terephthalate) raw yarn, nylon raw yarn and a mixed yarn thereof; an absorption layer 30 needle -punched on the other side of the filter layer 10 and formed of fibers of PET raw yarns; and a coating layer 40 formed in a high density, the coating layer being formed by melting the surface of the absorption layer 30. [2] The filtration cloth according to claim 1, wherein the filter layer 10 is woven using a longitude yarn formed in 400-440 denier and in a density of 13-15x2 per inch, and a latitude yarn formed either in 820-860 denier and in a density of

16-17 per inch or 420 denier x 2 and in a density of 15-16. [3] The filtration cloth according to claim 1, wherein the filter layer 10 is woven in

Reno texture. [4] The filtration cloth according to claim 1, 2 or 3, wherein the filter layer 10 has a shrinking rate of 15-17% when needle-punching the filtration layer 20 and the absorption layer 30. [5] The filtration cloth according to claim 1, wherein the PET raw yarn and the nylon raw yarn in the filtration layer 20 is 3-6 denier raw yarn, and the mixed yarn thereof is mixed in a rate of 55-70% :30~45%. [6] The filtration cloth according to claim 1, wherein the PET raw yarn in the absorption layer 30 is formed by optionally mixing two or more types of raw yarns selected within a range of 1-3 denier. [7] The filtration cloth according to claim 1 or 6, wherein the coating layer is formed by heat-treating the surface of the absorption layer 30 with a heat source H of

280~330°C, and thereafter closely attaching a calendar roll R so as to reduce the fine protrusions, thereby having a high density.