JP2005144405A - Filter cloth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter cloth excellent in filtration efficiency, alkaliproof, etc. in filtering sludge generated from construction and civil engineering sites. <P>SOLUTION: The filter cloth in which polyester multifilament where the relative viscosity is not less than 1.50, the amount of carboxylic terminal group is 15 eq/Ton or less, the strength is 3.0 cN/dtex or more, and the cutting extensibility is 30% or less is used at least partly is provided. Since in the filter cloth, the relative viscosity of the polyester is 1.50 or more and the strength of the multifilament is 3.0 cN/dtex or more, the mechanical property is excellent, and since the carboxylic terminal group amount of the polyester is 15 eq/Ton or less, the alkaliproof is good. Accompanied with the dissolution of polyester component, fine particles are also flowed simultaneously, by which clogging is less liable to occur, the cake detachability is good also, and a long-term use is possible. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a filter cloth that has durability even under alkaline conditions and is excellent in sludge filtration efficiency.

  Sludge (sludge) generated from construction and civil engineering sites is subjected to pressure dehydration using a special filter press and disposed of and reused as cake. In order to make it easy to peel the cake after dehydration from the filter cloth, slaked lime is added to the sludge to make the cake easier to harden.

  The filter cloth used in this filter press is required to have strength and rigidity and good dimensional stability because the mechanical action during pressure dehydration is severe, and with the addition of the slaked lime to the sludge Excellent alkali resistance is also required.

  From such a background, many filter cloths for filter presses are composed of fibers excellent in alkali resistance, such as polyamide fibers and polyolefin fibers. However, both are excellent in alkali resistance, but the filter cloth using polyamide fiber has poor dimensional stability due to dry and wet, and the filter cloth is wrinkled by repeating the process of the filter, resulting in problems such as tearing. Often occurs.

  In the case of a filter cloth using polyolefin fibers, fine particles of sludge tend to remain in the filter cloth in the dehydration step, and clogging occurs during long-term use, resulting in a decrease in filtration efficiency.

  In addition, filter cloth composed of polyester fiber is also used, but originally the polyester component has low durability against alkali, and gradually undergoes hydrolysis and dissolves by contact with alkali for a long time, It is said that it is not suitable for long-term use. However, the inventors have confirmed that the fine particles are also caused to flow simultaneously with the dissolution of the polyester component, so that clogging is difficult and the cake peelability is good.

Aramid fibers (for example, see Patent Document 1) and polyphenylene sulfite fibers (for example, see Patent Document 2) do not have such a problem, but are expensive because they are expensive.
Japanese Unexamined Patent Publication No. 09-052007 Japanese Patent Laid-Open No. 08-192018

  The present invention has been made in view of such a current situation, and an object thereof is to provide a filter cloth which is excellent in mechanical properties and dimensional stability, hardly clogged, and excellent in alkali resistance. It is.

  The present invention solves the above-mentioned problems, with a relative viscosity of 1.50 or more, a carboxyl end group amount of 15 eq / Ton or less, a strength of 3.0 cN / dtex or more, and a breaking elongation of 30% or less. The gist of the present invention is a filter cloth comprising at least a part of a certain polyester multifilament.

  Since the filter cloth of the present invention is composed of multifilaments made of polyester, it has excellent dimensional stability, the relative viscosity of the polyester is 1.50 or more, and the strength of the multifilament is 3.0 cN / dtex or more. Therefore, it is excellent in mechanical properties, and the carboxyl end group amount of the polyester is 15 eq / Ton or less, so the alkali resistance is good, and the fine particles are also caused to flow at the same time as the polyester component is dissolved, so that clogging is difficult. Cake peelability is also good, and long-term use is possible.

  Hereinafter, the present invention will be described in detail. The polyester multifilament used in the present invention is made of a polyester mainly composed of polyethylene terephthalate having a relative viscosity of 1.50 or more and a carboxyl end group amount of 15 eq / Ton or less. When the relative viscosity is 1.50 or more, preferably 1.55 or more, strength as a filter cloth and durability under severe conditions are improved. However, if the relative viscosity is too high, spinning becomes difficult, so the relative viscosity preferably does not exceed 2.0.

  Further, when the amount of carboxyl end groups is 15 eq / Ton or less, preferably 13 eq / Ton or less, excellent physical properties can be maintained even when a filter cloth is used under conditions where temperature and humidity change drastically. A multifilament made of polyester having a terminal group amount exceeding 15 eq / Ton has poor alkali resistance and is not practical in terms of strength. The carboxyl end group amount is better as it is closer to 0 from the viewpoint of the performance of the filter cloth, but is preferably 10 eq / Ton or more in consideration of productivity. Therefore, 10-15 eq / Ton is preferable and 10-13 eq / Ton is more preferable.

  As a method for obtaining a polyester multifilament having a relative viscosity of 1.50 or more and a carboxyl end group amount of 15 eq / Ton or less, a prepolymer having a relative viscosity of 1.25 to 1.45 is produced, and then solid-phase polymerization is performed. For example, a melt spinning method, a carbodiimide compound or a copolymer of ethylene and glycyl methacrylate as a carboxyl end group blocking agent after solid-phase polymerization, and a melt spinning method may be used.

  The single yarn fineness of the polyester multifilament used in the present invention is preferably 0.5 to 50 dtex. If the single yarn fineness is less than 0.5 dtex, it becomes possible to filter out finer sludge. On the other hand, if it exceeds 50 dtex, clogging is less likely to occur, but sludge filtration efficiency deteriorates and is not suitable. Preferably it is 1-30 dtex.

  The total fineness is preferably 30 to 2000 dtex. If the total fineness is less than 30 dtex, the strength of the filter cloth will be low. On the other hand, if it exceeds 2000 dtex, the thickness of the filter cloth will be too large, and the filtration efficiency will be unfavorable.

  The strength of the polyester multiphyllant used in the present invention needs to be 5.0 cN / dtex or more, and preferably 8.0 cN / dtex or more. If the strength is less than 5.0 cN / dtex, mechanical properties such as tensile strength and tear strength required for a filter cloth cannot be sufficiently satisfied. The upper limit of the strength is preferably about 10 cN / dtex.

  Further, the cut elongation of the polyester multifillant used in the present invention needs to be 30% or less, and preferably 25% or less. When the filament has a cut elongation exceeding 30%, sufficient dimensional stability cannot be obtained, and the filter cloth is likely to wrinkle during use, leading to liquid leakage and tearing of the filter cloth. The lower limit of the cutting elongation is preferably about 5%.

  The properties of the multifilament may be flat yarn, twisted yarn, false twisted yarn, or air processed yarn. The cross-sectional form of the filament may be any, and is not particularly limited, such as a round shape, a triangular shape, an L shape, a T shape, a Y shape, a W shape, and a flat shape. In consideration of the strong surface, it is preferable to use flat yarn or twisted yarn having a round cross section.

  The filter cloth of the present invention is configured using at least a part of the polyester multifilament. Other fibers can be used depending on the expected filtration level such as alkali resistance and filtration efficiency. Further, the mixing ratio is not particularly limited. The ratio may be taken into account depending on the level expected. This ratio can be adjusted by performing twisting, union knitting, etc. during the manufacture of the filter cloth.

  The method for making the filter cloth of the present invention into a cloth is not particularly limited. Ordinary weaving and weaving techniques can be used to weave and weave so that the fabric is suitable for the expected filtration level. However, considering the filtration process, if priority is given to misalignment, dimensional stability, filtration efficiency, etc., it is preferable to use plain weave, twill weave, satin weave, or a woven fabric having a structure such as a deformed structure or a multiple structure.

EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to these. The polyester multifilament yarn in the examples was evaluated by the following method.
(1) Relative viscosity (ηrel)
The polyester multifilament was dissolved in a solution of phenol / tetrachloroethane (mass ratio = 1/1) to a concentration of 0.05 g / l, and the relative viscosity was measured at 20 ° C.
(2) Amount of carboxyl terminal group A sample of 150 mg was dissolved in 10 ml of benzyl alcohol and 10 ml of chloroform, and titrated with an aqueous potassium hydroxide solution for measurement.
(3) Strength and Cutting Elongation Measured according to JIS L 1013 7-5.
(4) Dry heat shrinkage rate Measured according to JIS L 1013 7-15 (2) B method (filament shrinkage rate).

The filter cloth was evaluated by the following method.
(5) Tensile strength and cut elongation Measured according to JIS L1096 6-12 A method (strip method).
(6) Air permeability Measured according to JIS L1096 6-27 A method (Fragile method).
(7) Clogging According to the appearance of the filter cloth after use, the evaluation was made in three stages: ○: almost no clogging was observed, Δ: clogging was slightly observed, and x: clogging was remarkable.

(Example 1)
Relative viscosity 1 obtained by melt spinning and stretching using a tip with a relative viscosity of 1.64 and a carboxyl end group amount of 10 eq / Ton, solid phase polymerization of polyethylene terephthalate having a relative viscosity of 1.44 and a carboxyl end group amount of 35 eq / Ton. .64, carboxyl end group content 12 eq / Ton, strength 8.0 cN / dtex, elongation at break 25%, dry heat shrinkage 4.0%, single yarn denier 8.6 dtex, total fineness 1100 dtex, number of filaments 128 polyester Multifilament yarn is twisted with S twist of 150 T / M, and this twisted yarn is used as warp and weft, and weaved with a warp density of 60 / 2.54 cm, a weft density of 60 / 2.54 cm, and a 2/2 twill structure. The filter cloth of Example 1 of the present invention was obtained by heat setting at 180 ° C. for 1 minute.

(Example 2)
The warp yarn is a polyester multifilament yarn S twist 150 T / M twist yarn having a total fineness of 1100 dtex used in Example 1, and a weft yarn having a relative viscosity of 1.44 and a carboxyl end group weight of 35 eq / Ton. Relative viscosity 1.64 obtained by melt spinning and drawing using a tip having a relative viscosity of 1.57 obtained by solid-phase polymerization of terephthalate and a carboxyl end group amount of 18 eq / Ton, a carboxyl end group amount of 20 eq / Ton, and a strength of 8.0 cN / Dtex, cutting elongation 25%, dry heat shrinkage 4.2%, single yarn denier 8.6 dtex, total fineness 1100 dtex, 128 filaments polyester multifilament yarn S twist 150T / M twisted yarn Weaving in the same manner as in Example 1 and performing heat setting to It was obtained over cloth.

(Comparative Example 1)
Weaving was performed in the same manner as in Example 1 using the twisted polyester multifilament yarn used as the weft in Example 2 as the warp and weft, and heat setting was performed to obtain the filter cloth of Comparative Example 1.

(Comparative Example 2)
Using a polypropylene multifilament yarn S twist 150 T / M twist yarn of total fineness 1100 dtex, number of filaments 120, strength 7.2 cN / dtex, cut elongation 30%, dry heat shrinkage 6.5% as warp and weft, Weaving was performed in the same manner as in Example 1, and heat setting was performed to obtain a filter cloth of Comparative Example 2.

(Comparative Example 3)
A nylon 6 multifilament yarn S twist 150T / M twist yarn with a total fineness of 1100dtex, 128 filaments, strength of 7.6cN / dtex, cutting elongation of 30%, dry heat shrinkage of 6.2% was used as warp and weft. Weaving was performed in the same manner as in Example 1, and heat setting was performed to obtain a filter cloth of Comparative Example 2.

(Filtration test)
The filter cloths of the above examples and comparative examples are cut, and the upper and lower end parts are folded and sewn, so that a cylindrical part for passing a rod is provided as a 1200 mm wide x 2000 mm filter cloth on the top and bottom. It was installed between filter plates for pressing and used for sludge filtration. A sludge having a pH of about 11 mixed with a cement component was injected into a filter press using a pump, and after reaching a specified injection amount (390 m ³ ), dehydration was performed with compressed air (about 4 MPa) to prepare a cake. Next, the pressure was released, the filter plate was opened, the cake was dropped by its own weight, the filter cloth was washed with water by automatic spraying, and then the sludge was injected again. Thus, the filtration process of 1000 cycles in total was repeated for about 3 months.

  About the filter cloth of obtained Example 1- Example 2 and Comparative Example 1- Comparative Example 3, it shows in Table 1 together with the performance before and behind use for a filtration test.

As is clear from Table 1, the filter cloths of Example 1 and Example 2 have a stable performance with little change in strength and air permeability before and after filtration, and with a small degree of clogging after filtration. Met. On the other hand, Comparative Example 1 using a polyester multifilament yarn having a large amount of carboxyl end groups for both the warp and weft yarns had a large decrease in strength but a large decrease in air permeability, which was a concern for long-term use. Comparative Example 2 using polypropylene multifilament yarn for both warp and weft has large clogging, and Comparative Example 3 using nylon multifilament yarn for both warp and weft has large cut elongation, lacks dimensional stability, and clogging also occurs. It was a little big.

Claims (1)

A polyester multifilament having a relative viscosity of 1.50 or more, a carboxyl end group amount of 15 eq / Ton or less, a strength of 5.0 cN / dtex or more, and a cut elongation of 30% or less is used at least in part. A filter cloth characterized by