JP2002126425A - Filter medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter medium for a filter by which foreign materials contained in a molten polymer and coarse particles and gelled materials contained in a filler or the like can be caught and removed at the same time. SOLUTION: This filter medium is obtained by dispersing a metallic fiber having 60-50,000 aspect ratio in a nonwoven fabric state and sintering it and has 2-70% change rate of air permeation resistance when pressurized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter medium used for filtering a high-viscosity liquid, and more particularly to a filter medium having an excellent ability to prevent gel-like substances and having a long filter life.

[0002]

2. Description of the Related Art When producing fibers or films from a solution having a high viscosity or a molten polymer, filtration is performed with a filter in order to remove coarse particles or gel-like substances contained in the polymer, foreign substances, fillers and the like. As a filter material for a filter, a material obtained by sintering metal particles (sintered metal particles) or a material obtained by sintering non-woven metal fibers (sintered metal fiber) is used.

[0003] Since sintered metal fibers generally have a higher porosity than sintered metal particles, they have low filtration resistance and are particularly suitable for microfiltration of polymers having high viscosity. However, when the thermoplastic polymer is melted and extruded, some of the polymer often becomes a gel and becomes a foreign matter defect of the extruded product. It is known that the capturing performance for removing the gel-like material differs depending on the filter medium for the filter, and the sintered metal particles are superior to the sintered metal fibers. Therefore, in order to carry out microfiltration of a high-viscosity polymer and to remove a gel-like substance, a method utilizing the respective advantages of the metal particle sintered body and the metal fiber sintered body (JP-A-9-11308, JP-A-9-11308) 9-39
No. 072) has been proposed.

That is, the filtration process is performed in two stages in series, and a metal fiber sintered filter is used for one of them and a metal particle sintered filter is used for the other. If a sintered filter is used, foreign matter in the molten polymer or coarse particles contained in fillers and the like can be captured by the filter, and a gel-like substance can be reliably captured by the sintered metal particle filter on the downstream side.

[0005] Another embodiment of the two-stage filtration is as follows.
There is also known a method in which the filter material of each filter element is formed of a laminate of a sintered metal fiber and a sintered metal particle, and the filtration is performed in substantially one step. When such a filter medium is a laminate of different kinds of sintered bodies, the volume of one filter is increased, so that the number of filters that can be incorporated in a filtration system having a fixed volume is reduced, and there is a disadvantage that the filtration area is substantially reduced.

As a method of reducing the reduction of the filtration area, there is also known a filter having a laminated structure in which small metal particles are sintered on a thin metal mesh to form a component of a filter material, and a metal particle layer of a different kind of sintered body is substituted. ing.

[0007] However, in the above-mentioned method in which the filtration step is divided into two stages and the filtration using a metal fiber sintered body and the filtration using a metal particle sintered body are individually performed, the capital investment is increased and the filtration step is not performed. Since the hysteresis time of the polymer at a high temperature is prolonged, a problem such as a new gelation occurring in a filtration step occurs in a polymer which easily forms a gel.

In the above-mentioned method, in which the filter medium of one filter is composed of a laminate of a sintered metal fiber and a sintered metal particle, the filtration area is substantially reduced, so that the amount of polymer per unit time is reduced. There is a problem that the amount of filtration is small, and in addition, there is a problem that it is difficult to regenerate and wash the filter.

In the above-described method in which the metal particle layer of the heterogeneous laminate is replaced with a filter medium formed by sintering small metal particles on a wire net, the gel-like substance trapping effect is improved as compared with a filter made of a single metal fiber sintered body. In some cases, the effect is not sufficient because the substitute layer is thin.

[0010]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and simultaneously captures and removes particulate matter such as foreign particles in a molten polymer and coarse particles contained in fillers and the like and a gel-like substance. It is an object to provide a filter material for a filter that can be used.

The present inventor has conducted various studies to solve the problems. As a result, when a metal fiber sintered body sintered so that the rate of change of the airflow resistance by the pressure treatment becomes a specific value is used as a filter medium, The inventors have found that the above problems can be solved at once, and arrived at the present invention.

[0012]

An object of the present invention is to provide a filter material obtained by dispersing and sintering a metal fiber having an aspect ratio of 60 to 50,000 into a nonwoven fabric, and to control the air flow resistance of the filter material by a pressure treatment. Is in the range of 2 to 70%.

Further, as a preferred embodiment of the present invention, a filter medium having a filtration accuracy of 1 to 50 μm can be mentioned.

As a further preferred embodiment of the present invention, a liquid substance having a viscosity of 5 to 5000 Pa · s is used for the object to be filtered, and as a particularly preferred embodiment, a molten polymer is used for the object to be filtered.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

(Filter Material) The filter material of the present invention is a filter material obtained by dispersing and sintering metal fibers having an aspect ratio of 60 to 50,000 into a non-woven fabric. It is in the range of 70%.

In the present invention, the metal fiber constituting the filter medium is a corrosion-resistant metal such as stainless steel or Hastelloy.
It is formed into a fibrous shape having a thickness of, for example, 1 to 50 μm. Further, the aspect ratio is a ratio of the length and thickness of the fiber, and the metal fiber in the present invention has an aspect ratio of 60 to
50,000. When the aspect ratio is less than 60, the mechanical strength of a filter medium obtained by arranging and sintering metal fibers in a nonwoven fabric shape becomes insufficient. On the other hand, if the aspect ratio exceeds 50,000, it becomes difficult to uniformly disperse the metal fibers into a nonwoven fabric. The lower limit of the aspect ratio of the metal fiber is preferably 100, more preferably 500, in order to further increase the mechanical strength of the filter medium. Further, the upper limit of the aspect ratio of the metal fiber is preferably 20,000, more preferably 10,000, in order to disperse the metal fiber more evenly when arranging the metal fiber in a nonwoven fabric shape.

The filter medium of the present invention is obtained by dispersing and sintering metal fibers having the above-mentioned aspect ratio into a non-woven fabric.
%. This ventilation resistance
One liter (liter) of air at 25 ° C. is applied to a unit area (1
cm ² ) is the pressure loss when passing through a filter medium.

The pressure treatment in the present invention means that a filter material cut out from a sheet-like filter material into a disk having a diameter of 50 mm is used as a sample, and a rubber hardness of 50 mm is cut out from both sides of the sample into a disk shape having a diameter of 50 mm. ~ 70 degree, thickness 5mm
The silicone rubber sheet or urethane rubber sheet is placed on top and placed on a mold of a pressing device such as a press with one rubber sheet facing down, and the other rubber sheet surface is placed on the surface of the filter medium sample per unit area. 14.7MPa (150K
gf / cm ² ) is applied and maintained for 10 minutes, and then the pressure load is released.

The filter medium sample subjected to the pressure treatment is subjected to measurement of air flow resistance after removing the rubber sheet. This pressure treatment and measurement of the ventilation resistance are repeated five times for the same sample, and ventilation is performed according to the following formula (1) from the maximum value (Rm) of the five measurement values of the ventilation resistance and the measurement value (Ri) of the ventilation resistance before the pressure treatment. The rate of change (X) in resistance is determined.

[0021]

X = 100 × (Rm−Ri) / (Ri) (1)

In the above formula (1), X is the rate of change (%) of the airflow resistance, Ri is the measured airflow resistance of the filter material sample before the pressure treatment, and Rm is the pressure treatment and the airflow resistance measurement. 5
This is the maximum value of the measured airflow resistance after the pressurization treatment when repeated.

The filter medium of the present invention has a rate of change in air flow resistance by a pressure treatment of 2 to 70%. This change rate is 2%
If less than, the elongation of the filter medium for tensile stress is small,
Problems such as cracks occurring on the surface of the filter medium when bending the filter medium occur. On the other hand, if the rate of change exceeds 70%, the effect of the present invention of simultaneously capturing and removing particulate matter such as coarse particles and gel-like substances contained in foreign substances and fillers does not appear.

The lower limit of the rate of change of the airflow resistance is preferably 3%, more preferably 4%. Also,
The upper limit of the rate of change in airflow resistance is preferably 50%, more preferably 40%, and particularly preferably 30%.

The filter medium of the present invention has a small rate of change due to pressure treatment, in other words, is excellent in compressive deformation, but such a filter medium can be obtained by, for example, changing the sintering temperature and time of the filter medium. And sintering while reducing the porosity of the filter medium.

The filter medium of the present invention preferably has a protective wire mesh sintered on at least one surface, and particularly preferably has a protective wire mesh sintered on both surfaces.

(Inhibiting performance of gel-like material) The filter medium of the present invention exhibits excellent performance in inhibiting gel-like material. The formation and filtration of a gel-like material will be described by taking, for example, polyester sheet molding as an example. The polyester polymer is melted by an extruder, and the molten polymer is transported by a piping system and guided to a filter housing, where it is extruded into a sheet form from a die through a filter such as a leaf disk filter, and cooled by a cooling drem. Formed into sheets.

It is believed that the gel is caused by thermal degradation of the polymer and occurs during the molten state from the extruder to the exit of the die. For example, a gel-like substance is generated at a location where the flow rate of the polymer is low, such as a wall surface of a pipe or a stagnant portion, by receiving a long-term heat history. For this reason, in general, means for avoiding generation of a gel-like substance after filtration as much as possible is provided by disposing the filter close to the die.

The gel-like substance flows more slowly in the stagnation section than the molten polymer, and the gel-like substance generated in the stagnation section separates from the stagnation section due to a slight change in the flow velocity of the piping system or separates from the pipe wall surface. Then, it flows together with the molten polymer and reaches the surface of the filter medium of the filter to be deposited. While the accumulation amount is small and the filtration differential pressure is small, the gel deposit does not move, but as time elapses and the filtration differential pressure increases, the pressing force acting on the deposit increases and the gel Objects may deform and pass through the filter media.

At this time, the filter medium of the present invention, in which the rate of change in airflow resistance due to the pressure treatment is small, has an effect of preventing the gel-like substance from being trapped and passing through even if the filtration differential pressure increases, or Has the effect of being cut into small pieces without causing actual harm and passing therethrough. On the other hand, in a filter medium in which the rate of change in airflow resistance due to the pressure treatment is larger than that of the filter medium of the present invention, when the differential pressure of filtration increases, the filter medium is deformed to such an extent that the deformed gel-like substance can penetrate, and a penetration path is formed. As a result, the gel-like material has poor blocking performance.

(Filtration performance after filter regeneration) When a sintered metal fiber filter is used for filtering a high-temperature and high-viscosity liquid such as a molten polymer, and then the filter is regenerated and washed and repeatedly used for filtering the molten polymer, the regeneration is performed. The filtration pressure of the subsequent filter is generally higher than the filtration pressure at the beginning of the polymer filtration. The reason for this is considered that when a high filtration pressure is applied to the filter medium sintered in the form of a nonwoven fabric, a compression deformation phenomenon occurs in the filter medium, and the thickness of the filter medium sheet becomes thinner and the porosity of the filter medium decreases. Can be

In particular, when a load of filtration pressure is applied to the filter medium in a high-temperature atmosphere, the compressive deformation phenomenon becomes more remarkable because the strength of the metal material is reduced. The squeezed and deformed filter medium sheet has a high pressure loss against the fluid, JISB8
The average pore diameter of the filter medium sheet measured by 356-1976 (ASTM-E-128-61) is reduced, and as a result, the filtration accuracy of the filter medium sheet changes in the direction of microfiltration (the filtration accuracy is improved). Are known.

However, the inventor of the present invention has found that a filter which has been repeatedly used and squeezed and deformed is more likely to pass through a gel than a new filter in which a sintered metal fiber filter is not squeezed and deformed. I found that.

The filtration accuracy of the filter, which captures solid foreign matter such as fine debris and metal fragments contained in the material to be filtered, has a high correlation with the average pore size of the filter medium sheet. In the filter material sheet which is no longer used, the filtration accuracy is improved. However, the trapping performance of the gel-like material has a low correlation with the average pore size of the filter medium sheet, and has a strong correlation with the compressive deformation of the filter medium sheet. Was found to be easy to pass through.

Although the mechanism of the phenomenon in which the gel-like material passes through a filter which is easily deformed by compression is not clear, the sintered fiber of metal fiber which is hardly deformed by compression can be subjected to a load by a pressure treatment. Seems to be in tension in the free space between its sintering points. However, it is considered that when a load is applied to a sintered body that is easily deformed by compression or has already been deformed by compression, the distance between the sintering points is shortened and the fibers are loosened. In addition, the sintering point of the metal fiber itself is not a fixed point in free space, but will be able to move freely under certain restrictions.

When the gel-like material passes through a sintered body that does not undergo squeezing deformation, the gel-like material may be caught by the tensioned fiber and stopped, or may be cut into small pieces and pass through. However, in a sintered body that is easily deformed by squeezing, the gel-like material deforms freely like an amoeba itself, making use of the looseness of the fibers and the ease of movement of the sintering point, while forming continuous air holes. It is thought that it can pass. Considering that the metal particle sintered body is a sintered body that does not undergo squeezing deformation, it is understood that the metal particle sintered body is excellent in the performance of capturing a gel-like material.

(Filtration Accuracy) The filter medium of the present invention has a filtration accuracy of 1
It is preferably from 50 μm to 50 μm. The filtration accuracy is as follows. A solution (suspension) in which a contaminant (ACFTD, UW White 90 (kaolin)) is suspended in water is guided to a filter medium, and subjected to suction filtration under a constant pressure (-4 kPa). The collection efficiency is calculated by measuring the number of particles of each particle size of the suspension, and the particle size corresponding to the collection efficiency of 95% is defined as the filtration accuracy.

If the filtration accuracy of the filter medium of the present invention is less than 1 μm, a high pressure is required for the filtration pressure, which is not practically preferable. If the filtration accuracy exceeds 50 μm, the constituent fibers of the sintered body become too coarse, and the effect of removing coarse particles and gel-like substances may be insufficient. The lower limit of filtration accuracy is 1.5μ
m, more preferably 2 μm. Further, the upper limit of the filtration accuracy is more preferably 40 μm, and particularly preferably 30 μm.

(Filtered Object) The filter medium of the present invention can be applied as a filtered object to a highly viscous fluid such as a molten polymer, a solution in which a solute is dissolved, a suspension in which a solid is suspended, and the like.

Among them, it is preferable to use a liquid substance having a viscosity of 5 to 5000 Pa · s as the object to be filtered, and it is particularly preferable to use a molten polymer as the object to be filtered.

When the material to be filtered is a molten polymer, for example, an aromatic polyester such as polyethylene terephthalate or polyethylene-2,6-naphthalate, a polyolefin such as polyethylene or polypropylene, a polyvinyl such as polystyrene, or a polyamide such as nylon; Preferable examples include a molten polymer of a thermoplastic polymer such as polycarbonate and polysulfone. Among them, a molten polymer of an aromatic polyester is particularly preferred.

Further, the filter medium of the present invention can be preferably applied to a material to be filtered having a viscosity in the range of 5 to 5000 Pa · s. When the viscosity of the object to be filtered is less than 5 Pa · s, it is not a target because the gel-like material can be relatively easily filtered without using the filter medium of the present invention. When the viscosity of the object to be filtered exceeds 5000 Pa · s, even when the filter medium of the present invention is used, the filter medium is squeezed and deformed due to a high filtration pressure, and the effect of the present invention is not exhibited. The lower limit of the viscosity of the object to be filtered is 8 Pa · s
Is more preferable, and 10 Pa · s is particularly preferable. Further, the upper limit of the viscosity of the object to be filtered is more preferably 2000 Pa · s, particularly preferably 1000 Pa · s.

Examples of the case where the object to be filtered is a solution include a methylene chloride solution in which polycarbonate is dissolved, a methylene chloride solution in which triacetyl cellulose is dissolved, and the like. These solutions often contain gels that are not completely dissolved, and these gels evaporate the solvent and become foreign matter defects in products such as formed films.

[0044]

EXAMPLES The present invention will be further described below with reference to examples. The physical property values in the present invention are measured and defined as follows. When a protective wire mesh is sintered on the filter material sheet, various characteristics of the filter material are measured with the protective wire mesh laminated.

1. Airflow resistance The airflow resistance of the filter medium is 1 liter (liter) of air at 25 ° C.
Pressure loss when passing through a filter medium of unit area (1 cm ² ) per minute. The airflow resistance is measured, for example, by mounting the airflow resistance measurement cell shown in the schematic diagram of FIG. 2 to the filter medium airflow resistance measurement device shown in the schematic diagram of FIG. The filter medium sample (11) shown in FIG.
m, and used as a sealing material (12:
(Upper seal material, 13: lower seal material, 14: side seal material) so that air can be prevented from flowing in from the side.
The diameter of the hole of the upper sealing material and the lower sealing material is 30 mm.
And the effective ventilation area of the filter medium in the cell is 7.1 cm ² .

The cell for measuring the airflow resistance was mounted on the airflow resistance measurement apparatus shown in FIG. 1, and the vacuum pump (6) was operated in an atmosphere controlled at 25 ° C., to thereby measure the amount of air to be passed through the filter medium ( The opening of the flow control valve (5) is adjusted so that the orifice flow meter (3) measures 1 L (liter) per minute per unit area (1 cm ² ). The air flows into the ventilation resistance measuring cell through the atmosphere opening pipe (7). The pressure loss at the time when the ventilation amount reaches a predetermined amount is measured by a ventilation resistance measuring manometer (2), and the value is defined as the ventilation resistance.

2. Pressure Treatment The pressure treatment of the filter medium is performed by using a filter medium cut out from a sheet-like filter medium into a disk having a diameter of 50 mm as a sample, and as shown in FIG. A urethane rubber sheet having a rubber hardness of 50 to 70 degrees and a thickness of 5 mm cut into pieces is superimposed, and one rubber sheet (23: lower cushion material) under an atmosphere controlled at 25 ° C.
Is placed on the mold (25: lower press mold) of a pressing device such as a press machine with the lower side facing down, and the other rubber sheet surface (2
2: Upper cushion material) and a press die (24: Upper press die) with a filter material sample of 14.7 per substantial unit area
A pressure of 150 kgf / cm ² (MPa) is applied and maintained for 10 minutes, and then the pressure load is released.

Example 1 A set of 30 leaf disk filters having a diameter of 177 mm and using a nonwoven fabric-like sintered body of metal fibers obtained by dispersing and sintering stainless fibers having an aspect ratio of 2000 into a nonwoven fabric as a filter material was set. Then, polyethylene-2,6-naphthalate was melt-extruded to form a polyester sheet having a thickness of 170 μm.

The filter medium used was composed of two fiber layers. The first layer from the upstream side had a fiber diameter of 12 μm and a basis weight of 500 g / m 2.
^2. The second layer has a fiber diameter of 6 μm and a basis weight of 1200 g /
m ² , the total porosity was 66%, and the rate of change in airflow resistance due to the pressure treatment was 15%. This filter 3
A set of 0 filters, polyethylene-2,
The initial pressure loss during 6-naphthalate melt extrusion is 1
It was 2.8 MPa, and no gel was found on the polyester sheet after continuous filtration for 5 days.

Comparative Example 1 The fiber structure of the filter medium was the same as that of Example 1, except that the filter medium used had a porosity of 76% and a rate of change in air flow resistance due to pressure treatment of 120%. A polyester sheet was formed in the same manner as in Example 1. The initial pressure loss of the filter was 11.2 MPa, and the operation 3
On the day, a gel-like substance was generated, and a defect caused by the gel-like substance was observed in the polyester sheet. Even if the filter material configuration is the same, a gel using a filter material having a high rate of change in airflow resistance can easily pass through a gel.

Example 2 The first layer from the upstream side has a fiber diameter of 8
400 g / m ² in basis weight and μm, fiber diameter 4 μm in the second layer
With a basis weight of 1000 g / m ² and a total porosity of 68%
A polyester sheet was formed in the same manner as in Example 1 except that a filter medium having a rate of change of 23% of the airflow resistance due to the pressure treatment was used for the leaf disk filter and polyethylene terephthalate was used as the polyester. As a result of performing continuous molding for 6 days, no gel-like substance was found on the polyester sheet.

[Comparative Example 2] The basis weight of the second layer of the filter medium was 1
Polyester in the same manner as in Example 2 except that a filter medium (filtration accuracy was almost equivalent to that in Example 2) was used, which had a porosity of 700 g / m ² , an overall porosity of 76%, and a change rate of air flow resistance by a pressure treatment of 140%. A sheet was formed. On the third day of operation, a gel-like substance was generated, and a defect due to the gel-like substance was observed in the polyester sheet. Even if the filtering media have the same filtration accuracy, a gel having a large rate of change in airflow resistance can easily pass through the gel.

[0053]

According to the filter using the filter medium of the present invention, a gel-like substance is simultaneously captured and removed for a long period of time in addition to particulate matter such as coarse particles contained in foreign matters and fillers in a molten polymer. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus for measuring a ventilation resistance of a filter medium.

FIG. 2 is a schematic view showing an enlarged cross section of a cell part for measuring a ventilation resistance.

FIG. 3 is a schematic view of an apparatus for performing a pressure treatment of a filter medium.

[Explanation of symbols]

 1: Cell for measuring air flow resistance 2: Manometer for measuring air flow resistance 3: Orifice flow meter 4: Vacuum container 5: Flow control valve 6: Vacuum pump 7, 15: Air release piping 11, 21: Filter material sample 12: Upper seal material 13: Lower seal material 14: Side seal material 16: Suction side piping 22: Upper cushion material 23: Lower cushion material 24: Upper press mold 25: Lower press mold

Claims (4)

[Claims] 1. A filter medium obtained by dispersing and sintering metal fibers having an aspect ratio of 60 to 50,000 into a nonwoven fabric, and having a rate of change of air flow resistance of 2 to 7 by pressurizing the filter medium.
A filter medium characterized by being in the range of 0%. 2. The filter according to claim 1, wherein the filtration accuracy is 1 to 50 μm.
3. The filter medium according to item 1. 3. The filter medium according to claim 1, wherein a liquid substance having a viscosity of 5 to 5000 Pa · s is used as the material to be filtered. 4. The filter medium according to claim 3, wherein the molten polymer is used as a member to be filtered.