JP3449430B2 - Fine particle filter media - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter material for removing fine particles of micron or submicron order contained in a gas or liquid, and a filter cartridge using the filter material. The present invention relates to a filter material capable of filtering particles having an average particle diameter of 0.5 to 5.0 μm with a long life.

[0002]

2. Description of the Related Art Conventionally, in the development of a filter medium, if the filter medium is set so that the filter precision is increased, the filter life is shortened, and conversely, if the filter life is lengthened, the filter precision is decreased, and an effort is made to solve the problem. It has been.

As a device for solving such a problem and increasing the filtration accuracy of the filter and prolonging the filtration life, as described in JP-A-60-216818, the fiber diameter of the filter medium is set in the depth direction of the filter medium. Change, again
No. 8009, the packing density of the fibers is made to have a gradient in the depth direction, and further, as described in JP-A-1-297113, the fiber diameter and the average pore diameter are simultaneously changed in the depth direction. Has been.

However, changing the fiber diameter requires holding many kinds of non-woven fabrics made under different spinning conditions, and there is a problem that a large loss occurs when changing the setting of the manufacturing conditions of the filter medium. It was In addition, JP-A-60-21
The method of winding the filter medium around the filter core (tubular core member) while changing the production conditions as shown in 6818 can solve such a problem, but the spinning conditions are not stable, so that the polymer flows into the polymer pipe. Fluctuations and non-uniformity, resulting in uneven polymer retention time, resulting in uneven polymer viscosity, clogging of orifices, unstable spinning, and fluctuations in fiber diameter and yarn breakage. there were. In addition, there is a problem in that a new process is required to adjust the filling rate, which increases the cost. Furthermore, the effect of these measures was not sufficient.

In spite of such efforts, a method for efficiently filtering particles having a diameter smaller than the fiber diameter with a good balance between filtration accuracy and life is not well known. A method of increasing the filling rate to about 0.4 to 0.85 in order to improve the filtration accuracy is also known, but it is not preferable from the viewpoint of prolonging the life, and even if such a filter medium is laminated, its lamination It is known to be less effective.

[0006] In particular, even in the filtration of particles having an average particle diameter of 0.5 to 5 µm used as a prefilter for a microfiltration membrane, there has been a great demand for improvement in life. In addition, when these filter materials whose packing ratio is not so large are stored in a roll, the packing ratio of the filter material changes between the surface layer and the filter core side, which causes a problem that the filtering performance varies when the cartridge is made. There was also.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the drawbacks of the conventional filter media, to provide a filter media and a filter cartridge which have high filtration accuracy for fine particles and enable filtration with a long filtration life.

[0008]

The present invention adopts the following means in order to solve the above problems. That is, according to the present invention, 10-40 superfine fibers having an average fiber diameter of 1.5 μm or more and 5 μm or less are stacked in the thickness direction, and the basis weight is 5 g / m ² or more
A fiber aggregate in the range of less than 40 g / m ² ,
In the fiber assembly, the bonding points between the fibers are partially present in the thickness direction.
There is no difference between the surface layer and the inner layer, the maximum pore size of the fiber assembly is in the range of 28 μm to 40 μm, and the ratio of the maximum pore size to the average flow pore size is in the range of 1.5 to 2.5. And a packing ratio of fibers in the range of 0.05 to 0.35, which is a filtering material for fine particles (claim 1), and a tubular core member having a liquid passage hole, and its surroundings. A filter cartridge having a filter material layer disposed on the end of the filter cartridge,
This filter material layer is a filter cartridge (claim 2) in which at least three layers of the filter material according to claim 1 are wound.

The present invention will be described in detail below. In order to highly accurately filter and collect particles smaller than the average diameter of the ultrafine fibers forming the filter medium in the filter medium used in the present invention,
It is necessary to use a filter medium composed of ultrafine fibers having a fiber diameter of between 1.5 μm and 5 μm. Generally, the finer the fiber used for depth filtration, the more preferable it is, and the average value is 5 μm.
Hereafter, it is more preferably 3 μm or less. If the average fiber diameter is 5 μm or more, it is difficult to increase the filtration efficiency. It is preferable to reduce the fiber diameter, but the fiber diameter is 1.5
If it is less than μm, the filter material is deformed by the force of being pressed against the core member and the filter material is liable to be clogged, resulting in a shorter life. In addition, the manufacturing cost of the filter medium is high.

When a thermoplastic polymer is used as a material for producing the ultrafine fibers constituting these filter materials, for example, a composite spinning method, a spunbond method, a melt blow method,
Electrostatic spinning method and the like can be mentioned. Among these methods, the spunbond method and the melt blow method are considered to be advantageous in terms of cost because the filter medium can be directly formed without a post-processing step. The form of the fiber aggregate may be a woven fabric or a non-woven fabric, but the non-woven fabric is more effective in improving filtration accuracy because the fibers are randomly dispersed. The cross-sectional shape of the fiber may be circular or any other shape, and in some cases, a modified cross-section is more preferable.

The basis weight of the fiber assembly is preferably in the range of 5 to 40 g / m ² , and more preferably 25 to 35 g.
/ M ² is preferable. When the basis weight is less than 5 g / m ² , problems such as an increase in the cost of winding the fiber assembly around the tubular core material and an increase in the risk of the filter material being cut for some reason during the processing step are likely to occur. On the other hand, if the fabric weight is more than 40 g / m ² , there are many problems in operability, such as wrinkles when wound around the filter medium.

In the present invention, it is important that 10 to 40 ultrafine fibers are stacked in the depth direction. The number of fibers in the depth direction is given by the following formula in which the basis weight is divided by the product of the specific gravity of the fiber constituent substance and the fiber diameter. Depth direction number of fibers = filtration weight (g / m ² ) / [fiber density (g / cm ³ ) × fiber diameter (μm)]

Conventionally, as disclosed in Japanese Patent Laid-Open No. 58-186412, it was considered that the number of fibers in the depth direction should be large, but the present inventors have found that the number of fibers in the depth direction is 40. It has been clarified that it becomes difficult to uniformly disperse the fibers in the filter medium as the size becomes larger. Especially in the non-woven fabric composed of ultrafine fibers produced by the melt-blowing method, suction is made to work from the lower surface of the collector so that the fibers collected in the collector are not blown off by the traction air jet flow, but the fiber layer depth is deep. Then, when the fiber is pulled due to the pressure loss of the fiber layer, the suction force acting to prevent the fiber from being blown off is weakened, and unevenness such as ropes is generated near the top of the sheet, so it is not possible to improve filtration accuracy by experiments. confirmed. Further, if the fiber layer is too deep, there is a problem that it becomes difficult to uniformly wind the fiber layer around the filter core. On the other hand, if the number of fibers in the depth direction is too small, it means that the basis weight is reduced, and problems such as strength tend to occur.

The filling factor of the fiber is 0.05 or more and 0.
It may be 35 or less. If the filling rate is less than 0.05, it becomes difficult to perform highly efficient filtration of particles smaller than the average fiber diameter, which is the object of the present invention. On the other hand, when the filling rate is higher than 0.35, the filtration accuracy is slightly improved, but even if the filter media are laminated, the life is hardly changed and it is difficult to achieve a long filtration life. When the particle size is larger than the fiber gap (pore size) of the filter medium, when the fibers are uniformly dispersed in the filter medium,
Since there is no difference in structure between the surface layer and the inside of the filter medium (cross-sectional direction), large particles are filtered only on the surface of the filter medium by the sieving effect, so the cake layer is formed on the surface layer of the filter medium on the most upstream side. To significantly increase the filtration resistance,
The problem was that the filtration life was shortened.

Further, since most of the particles to be filtered of the filter material used in industry are polydisperse and the particle size distribution is large, these problems become remarkable, which makes the design of the filter material difficult. In addition, the fact that the operating conditions for filtration are significantly different depending on the purpose also changes the mechanism for collecting the particles to be filtered, further complicating the problem. That is, the submicron particles contained in polydisperse particles have a large collection rate by Brownian diffusion, while the micron size has a large contribution due to direct interruption or inertia. However, there was a problem in that the unique design of the multi-filter material could not be changed.

In the present invention, by grasping the characteristics of the particles to be filtered and the filtration operation conditions, and by realizing the fiber diameter, filling rate, and fiber dispersion state corresponding to them, a more effective long life,
High accuracy can be achieved.

When the particles to be filtered include a large number of particles larger than the fiber diameter and are a polydisperse system having a wide distribution of particle diameters, several kinds of the filtering materials of the present invention are used in combination to collect each filtering material. A more effective filtration can be realized by previously determining the collection target particle diameter and then stacking a filter material having a corresponding fiber diameter, filling rate, and maximum pore diameter on the upstream side of the filter material having a larger target particle diameter.

In the present invention, it is important to control the dispersed state of the fibers. As one of the methods for controlling the dispersed state, for example, in the melt blow method, a die for discharging a polymer and a collector of a nonwoven fabric are used. This can be easily achieved by changing the distance between them. The appropriate distance between the die and the collector varies depending on the spinning conditions and the size of particles to be filtered, but is generally preferably 3 to 60 cm, and more preferably 10 to 30 cm.

The dispersibility of the fiber is evaluated by preventing the filter material from being deformed and cutting the cross section (for example, by cutting in liquid nitrogen), and observing the cross section with a scanning electron micrograph to melt the fiber. The number of places where multiple fibers are entangled in a rope shape and the number of fused fibers is counted, or the size of the pores formed by the fibers with a porometer is uniform, but for example, the maximum pore diameter (maximum pore size) It can be easily confirmed by measuring and comparing the ratio of the mean flow pore size with the mean flow pore size. When the fiber assembly is a non-woven fabric, since the morphology of the fibers is not so uniform, it is necessary to increase the number of measurement points and perform the measurement, and to evaluate with an average value of at least 3 points.

The value of the ratio between the maximum pore diameter and the average flow rate diameter is influenced not only by the dispersed state of the fibers but also by the average fiber diameter and the fiber diameter dispersion. The smaller the average fiber diameter and the smaller the fiber diameter standard deviation, the more preferable. In particular, the average fiber diameter is 4 μm or less and the fiber diameter standard deviation is 50% or less of the average fiber diameter, and more preferably,
It is preferably 35%.

In order to carry out filtration treatment of particles of 0.5 to 5 μm with a long life, in order to widen the distribution of pore diameters, the ratio of the maximum pore diameter to the average pore diameter is between 1.5 and 2.5. It is important to be. Therefore, for example, in the meltblown nonwoven fabric, it is necessary to appropriately control the fiber dispersion by means such as intentionally introducing a rope-like material in which fibers are gathered in a bundle, which is usually a problem. If the maximum pore size at this time is too small, the pores will be blocked more quickly by the trapped particles, and therefore it is necessary that the pore size is larger than 28 μm, and more preferably larger than 30 μm. On the other hand, if the maximum pore size is larger than 40 μm, the filtration accuracy will be significantly reduced.

In the present invention, it is preferable that the fiber diameter distribution is narrow, but in the melt blow method, as a method for reducing the fiber distribution, the discharge amount per single hole is set to 0.01 or more and 0.75 g / min or less, and the traction is performed. It was found that this can be achieved by making the distribution of the air flow, which is a fluid, in the nozzle width direction as small as possible.

The filter material used in the present invention has a fiber diameter changed in the depth direction, as has been used conventionally.
It is also possible to construct the filter cartridge by a method such as changing the filling rate in the depth direction.

As a proper condition for the filtration operation carried out in the present invention, it is preferable to perform the filtration at a linear velocity of 0.5 to 20 cm / min. When the filtration rate is less than 0.5 cm / min, the effect of the present invention is not sufficiently shown in improving the life, probably because the collecting mechanism changes. In addition, a low filtration rate means a reduction in the amount of filtration treatment, which is not industrially preferable. On the other hand, when it is higher than 20 cm / min, the filtering accuracy of the filter material of the present invention cannot be sufficiently increased.

As the particles to which the filter material of the present invention is most effectively used, not only particles having a nearly spherical shape such as polystyrene latex but also non-spherical particles are useful. A large effect was also observed on irregular particles such as blood cells and bacteria (particles that are deformed by external stimuli). If anything, polydisperse particles having a larger particle size distribution are considered to be more effective.

Next, in order to eliminate the difference between the inside and the outside of the performance of the filter medium wound and stored in a roll, the filter medium is linearly pressured by a calender roller or the like at 5 to 100 kgf / c.
It is preferable to press at a temperature of ½ or less of the melting point of the nonwoven fabric constituent material under a pressure of m ² . The calendering process slightly increased the accuracy and tended to shorten the life, but there was no difference in the characteristics between the inside and outside of the roll, and therefore no difference was found in the filtration characteristics. If the linear pressure when using a calender is less than 5 kgf / cm ² , its effect is small and it is difficult to control, while 100 kgf / cm ²
When it was larger than cm ^2, it became clear that the filter medium was crushed too much, the life was too short, and the lamination effect was small. If the temperature at the time of calendering is too close to the melting point, the surface of the sheet will be melted and the surface of the filter material will be clogged with trapped particles to shorten the filtration life, which is not preferable. According to the experience of the inventors, it is preferable to carry out the treatment at a temperature between half the melting point and room temperature. In the present invention,
It is preferable to evenly disperse the weakly adhered portions on the filter medium due to the partial pressure deformation. At this time, JP-A-3-6
It is necessary that the bonding points are not dispersed only on the surface of the sheet as in 9654, but are weakly bonded in the entire depth direction of the filter medium. This is extremely difficult to achieve at the high calendering temperature conditions described in that patent.

Although the ventilation resistance is slightly increased by calendering and the life is also slightly decreased as a result, when the cartridge is made, the filter medium is deformed by the winding tension and the ventilation resistance is increased. This problem is not so important. There is no problem in processing by laminating two or more filter media in order to improve the processing efficiency. The number of bonding points may be adjusted by a hydroentangling method or heat treatment. Such a filter medium calendered at a relatively low temperature may be wall-folded (pleated) to be used by laminating 2 to 10 layers. Even if the filter material of the present invention is laminated with another material such as a porous film or a membrane, or subjected to post-processing such as hydroentangling treatment or electret processing, the effect is the same. Further, it is also one of the preferable modes to perform adsorption treatment at the same time by providing a layer made of granular or fibrous activated carbon or other porous material in the middle or before and after. The filter material of the present invention is also useful as a heat retaining material or a bacterial barrier material because of its ultrafine fiber characteristics and appropriate fluid permeability.

[0028]

【Example】

Examples 1 to 3 and Comparative Examples 1 to 3 The present invention will be specifically described with reference to Examples. The characteristic values described in the examples were determined by the following measuring methods. Fiber diameter Scanning electron micrograph of fiber with magnification of 1000 to 5000
The width of the side surface of 200 fibers arbitrarily taken from the photograph was measured and determined by arithmetic mean. Fiber filling rate A 20 cm square sample is weighed and the fiber areal weight is converted into a basis weight per 1 m ² . Further, the thickness of 5 arbitrary points of the sample was measured according to JIS L1096 under a load of 7 g / cm ² . The value obtained by dividing the basis weight by the specific gravity of the polymer was further divided by the thickness to obtain a dimensionless volume filling rate. Fiber Dispersion State Using Coulter Porometer II, ASTMF3
Measurement was carried out according to 16-86, and the ratio of the maximum pore diameter to the average flow pore diameter was obtained. Particle filtration accuracy and filtration life An aqueous solution in which 0.025 g / 1 of particles obtained by mixing JIS11 seed particles and JIS8 seed particles in a mass ratio of 8: 2 is supplied at a linear velocity of 5 cm / min, and after 3 minutes have elapsed The turbidity of the liquid before and after the filter material was measured, and the collection efficiency was calculated by the following formula. Collection efficiency (%) = (1-outlet concentration / inlet concentration) × 100 Further, as for the filtration life, the differential pressure before and after the filter medium is measured with a digital manometer, and the time until the filtration pressure becomes 5 kgf / cm ² is measured. I asked.

A polypropylene resin having a melt flow rate of 300 to 1000 is used, and a basis weight of ultrafine fibers having a fiber diameter of 0.8 to 6.0 μm is 30 by a melt blow method.
A nonwoven fabric of g / m ² was prepared and a filtration test was performed. The results are shown in Table 1.

[0030]

[Table 1]

In Table 1, the pore size ratio is shown by the formula: pore size ratio = maximum pore size / average pore size.
The proportion of the mixture of IS8 seed particles and JIS11 seed particles is shown in%.

Example 4 The non-woven fabric used in Example 2 was prepared in a roll of 1000 m and left for 3 months, then the surface layer and core of the roll were sampled and the linear pressure was 20 kgf by a calender roller.
/ Cm at 20 ° C. room temperature. When the filtration test was carried out 5 times for each of them, the collection efficiency was 95% and the life was 32 minutes for both, and no significant difference was observed between the two results. Comparative Example 4 The nonwoven fabric used in Example 2 was prepared with a roll of 1000 m and left for 3 months, then the roll was rewound and the surface layer portion and the core portion were sampled 10 m each and a filtration test was performed 5 times for each. As a result, the surface layer part had no difference in performance from Example 1, but the sample on the core side had a significant difference with a collection efficiency of 89% and a life of 33 minutes, showing a significant difference in filtration performance. It became an administrative problem.

[0033]

EFFECTS OF THE INVENTION A filter medium satisfying the requirements of the present invention, when used as a filter because of its controlled dispersibility of fibers, has high filtration accuracy of desired fine particles and enables filtration with a long filtration life. The cost is significantly improved, and the effect is extremely large.

Claims (2)

(57) [Claims] 1. A basis weight , in which 10 to 40 ultrafine fibers having an average fiber diameter of 1.5 μm or more and 5 μm or less are stacked in the thickness direction.
Of fibers having a weight ratio of 5 g / m ² or more and less than 40 g / m ²
The fiber assembly is composed of fibers
Mutual adhesion points exist so that there is no difference between the surface layer and the inner layer
And a maximum pore size of the fiber aggregate is in the range of 28μm~40μm and that the ratio of the mean flow pore size and said maximum pore diameter 1.5
.About.2.5, and the filling factor of the fibers is 0.05 to 0.
A filter material for fine particles, which is in the range of 35. 2. A tubular core member having a liquid passage hole,
A filter cartridge in which a filter material layer disposed around the filter material is fixed at an end thereof, and the filter material layer is formed by winding at least three layers of the filter material according to claim 1. A filter cartridge characterized by being present.