JPH06218212A - Nonwoven fabric having gradient of pore size and its production - Google Patents

Abstract

PURPOSE:To obtain a nonwoven fabric useful as a cartridge filter low in production cost and superior in filter performance by winding the nonwoven fabric having the gradient of pore sizes in the longitudinal direction around a porous core. CONSTITUTION:The nonwoven fabric having the gradient of pore sizes in the longitudinal direction is produced by periodically changing discharge gas quantity in the production method of the nonwoven fabric by a melt-flow method. The nonwoven fabric is wound around the porous core to form the cartridge filter. Thus the useful nonwoven fabric whose production cost in low and filter performance is superior as the cartridge filter is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-woven fabric used in a cartridge filter for liquid filtration and a method for producing the same.

[0002]

2. Description of the Related Art A wind cartridge filter in which a spun yarn or a woolen yarn is wound around a porous core has a low manufacturing cost but a poor filtering performance. Further, the non-woven fabric laminated cartridge filter in which a plurality of non-woven fabrics having different average pore diameters are wound and laminated has good filtration life and filtration accuracy, but non-woven fabrics having different average pore diameters are manufactured separately and each is made to have a predetermined length. There is a problem that the manufacturing cost is high because a very complicated process of arranging and cutting and arranging in order from the one having the smallest average pore size after cutting is performed.

[0003]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a non-woven fabric which is useful as a cartridge filter having a low manufacturing cost and an excellent filtering performance, and a manufacturing method thereof.

[0004]

According to the invention of the present application, a nonwoven fabric having a pore diameter gradient in the longitudinal direction can be obtained by periodically changing the discharge air volume in the production of the nonwoven fabric by the melt blowing method. The non-woven fabric thus produced can be wound around a porous core to continuously produce a cartridge filter. With such a non-woven fabric, it is possible to manufacture a non-woven fabric having a pore diameter gradient in a wide range only by controlling the discharge air volume.

A conventional one is a cylindrical fibrous structure and a manufacturing method thereof (Japanese Patent Laid-Open No. 60-216818). However, there is no fiber adhesion and there is a change in physical properties due to a change due to pressure, resulting in a performance deterioration. It is difficult to obtain a uniform sheet because the fibers are scattered when the amount of discharged air is increased, and it is difficult to obtain a uniform sheet, and water must be sprayed when producing a fiber diameter of 2.5 μm or more. In that respect, there was a problem in the drying process and management. On the other hand, the nonwoven fabric having a pore diameter gradient and the method for producing the same of the present invention have excellent pressure resistance and dimensional stability because they have fiber adhesion, and post-processing such as heat compression can be easily performed, and It is now possible to combine it with other filter materials and reinforcing materials when manufacturing the cartridge. Also,
Up to now, non-woven fabrics having a pore diameter gradient in the longitudinal direction have not been implemented so far. In the production of a nonwoven fabric by the melt blow method, in addition to the method of periodically changing the discharge air volume, as a method of giving a pore diameter gradient in the longitudinal direction to the nonwoven fabric, for example, when using a thermoplastic fiber, the nonwoven fabric is a heat roll. There is a method in which the pore diameter is changed together with the thickness, the density, and the porosity by passing it while changing the heating and / or pressurizing conditions. Further, in the case of forming a web using a card machine, there is a method of changing the feed amount of the fiber to the card machine to change the hole diameter as well as the thickness, density and porosity.

The invention of this application will be specifically described below by taking as an example a method for producing a nonwoven fabric having a pore diameter gradient by the melt blow method. The melt-blowing method is a method in which a molten polymer extruded from an orifice is drawn and thinned by a heated air stream of air or another gas blown out from the vicinity of the orifice, and this is collected into a nonwoven fabric. In the invention of this application, the size of the holes formed in the nonwoven fabric is changed by periodically changing the discharge air volume of the heating airflow, and a pore diameter gradient is given in the production direction (longitudinal direction) of the nonwoven fabric. When the other spinning conditions are constant, the fibers become finer as the discharge air volume of the heated air stream increases, and the fibers become thin, and the size of the pores inside the nonwoven fabric surrounded by the fibers becomes small. On the contrary, when the discharged air volume decreases, the fibers become thicker and the holes become larger. Therefore, when the amount of discharged air is changed periodically, the hole diameter of the holes formed in the nonwoven fabric changes accordingly, and a hole diameter gradient occurs. In this case, since the discharge amount of the resin is constant, the basis weight of the obtained nonwoven fabric (weight per unit area)
Is almost constant, and the porosity is kept constant, though there is some variation.

The polymer used in the non-woven fabric may be any thermoplastic resin that can be melt-spun, and examples thereof include thermoplastic resins or thermoplastic elastomers such as polyolefins, polyamides, polyesters, and the like, or a mixture thereof. Those that are suitable are preferred. Further, the melt index (MI) of the polymer is not particularly limited, but is 20 to 1
It is preferably in the range of 000 g / 10 minutes. When the other spinning conditions are constant, the approximate fiber diameter at the maximum and minimum discharge air volume is determined by the type of polymer and MI, so the approximate range of fiber diameter when using that polymer Is determined. The discharge amount of polymer is 0.0
5 to 0.5 cc / min / orifice, and the spinning temperature is preferably set to a temperature higher than the melting point of the polymer by 20 ° C. or more. The discharge air volume of the heated air flow is controlled by an automatic valve or the like to be changed periodically. The discharged air volume may be changed continuously or in a stepwise manner, but continuous change is superior in filtration efficiency and filtration life when a cartridge filter is manufactured using the obtained nonwoven fabric. It will be a good thing. It should be noted that the discharge air volume is preferably automatically controlled by presetting the cycle of its change. 1 to 6 are graphs showing examples of periodic changes in the discharge air volume.

FIG. 1 shows that the amount of discharged air is increased from a set minimum amount to a set maximum amount and is continuously and proportionally decreased from the maximum amount state to the minimum amount state with the lapse of time. This is an example of cyclically changing after one cycle until it is stabilized with the minimum amount. In this way, the melt-blown nonwoven fabric obtained by changing the discharge air volume has a region in which the pore diameter changes continuously in the longitudinal direction from a small one to a large one, and a region where a constant large pore diameter is short appears alternately. A pore diameter gradient is formed in the longitudinal direction of the nonwoven fabric. In addition, as the pore diameter changes from a small one to a large one, the fiber diameter also changes from a thin one to a thick one. When a cartridge filter is manufactured using this melt-blown nonwoven fabric, the nonwoven fabric may be cut every cycle and wound on the porous core from the side having a smaller pore size.

FIG. 2 shows that when the discharge air volume is reduced from the set maximum volume state to the set minimum volume state,
In the example that is not continuous as shown in FIG. 1 but gradually decreased,
In the melt-blown nonwoven fabric obtained by changing the discharge air volume in this way, a pore diameter gradient that gradually changes from a small pore diameter to a large pore diameter is formed in the longitudinal direction.

FIG. 3 shows that the discharge air volume is proportionally and continuously increased with the passage of time from the state of the set minimum volume to the state of the set maximum volume, and then is stabilized at the maximum volume. Next, it is an example in which the cycle is periodically changed from one state of the maximum amount to a state of the minimum amount, which is proportionally and continuously decreased with the passage of time, and then set to be stabilized at the minimum amount as one cycle. The melt-blown non-woven fabric obtained by changing the discharge air volume in this way has a region where the pore size changes continuously in the longitudinal direction from one with a large pore size to a region where it changes continuously from one with a small pore size to a large one. By repeating the above, a pore diameter gradient is formed in the longitudinal direction of the nonwoven fabric. When a cartridge filter is manufactured using this melt-blown nonwoven fabric, the nonwoven fabric may be cut every ½ cycle and wound on the porous core from the side having a smaller pore diameter. In this case, since the loss of the nonwoven fabric for changing the discharge air amount from the minimum amount to the maximum amount does not occur at the minimum hole diameter, the nonwoven fabric can be used more efficiently.

4 to 6 show changes in the discharge air volume for one cycle. FIG. 4 shows a period in which the discharge air volume is constant during the continuous change of the discharge air volume, which is used particularly when it is desired to provide a nonwoven fabric with a large number of regions having a specific pore diameter. Further, FIG. 5 shows a change rate (gradient) changed midway when the discharge air volume is proportionally and continuously changed with the passage of time, and is produced long in a section with a gentle gradient. Therefore, for example, when the gradient is gentle in the section where the amount of discharged air is small as shown in FIG. 5, the resulting nonwoven fabric has more regions with large pore diameters. In addition, when continuously changing the discharge air volume, it is not always necessary to perform the discharge air quantity in proportion to the passage of time as shown in FIG. 1 or the like. For example, as shown in FIG. The change may be changed so as to be on a curve over time. Further, in the description of FIG. 1 and the like, an example in which the discharge air volume is continuously decreased with the passage of time has been shown, but conversely, the discharge air volume is continuously increased with the passage of time. May be manufactured as follows.

When used in a cartridge filter,
It is desirable that the melt-blown nonwoven fabric produced by periodically changing the discharge air volume as described above has an average pore diameter of 3 to 40 μm and an average fiber diameter of 0.5 to 5 μm.
It is preferably in the range of 0 μm. It should be noted that the porosity of the meltblown nonwoven fabric (substantially no change with changes in the amount of discharged air) is preferably in the range of 70 to 93%, and if the porosity is smaller than this, particles such as dust can be retained. Since the capacity inside the nonwoven fabric becomes small, the service life may be shortened. On the other hand, when the porosity is larger than this, the nonwoven fabric may be crushed or deformed by an external force. To manufacture a cartridge filter using the non-woven fabric of the invention of this application, the non-woven fabric of the invention of the present application is placed inside the porous core made of a perforated cylinder of metal, plastic, etc. Therefore, it is desirable to stack the layers so that the hole diameter becomes large.

For example, when a cartridge filter is manufactured using a melt-blown nonwoven fabric manufactured by periodically changing the discharge air volume as shown in FIG. 1, the nonwoven fabric is wound around a porous core at the end of the melt-blown nonwoven fabric manufacturing process. If the process is continued, the cartridge filter can be continuously manufactured. In this case, first, the portion of the meltblown non-woven fabric that has risen from the set minimum air volume to the maximum air volume is wound around the porous core, and then the maximum air volume to the minimum air volume is proportionally and continuously discharged over time. By winding the part (the pore size of the non-woven fabric changes from the minimum pore size to the maximum pore size), and then cutting the non-woven fabric in the middle of the part stabilized with the minimum air volume and thermally bonding the cut end. Manufacture cartridge filters. A cartridge filter can be continuously manufactured by exchanging the non-rolled porous core with the non-rolled porous core when the non-woven fabric is cut. It should be noted that when the rising portion comes to the innermost side, the cartridge filter does not have a structure in which the hole diameter increases from the inner side to the outer side completely, but since the rising portion has a large hole diameter, even if the rising portion is wound on the innermost side, the filtration accuracy is Has almost no effect.

When the strength of the non-woven fabric is weak,
It may be wound together with the reinforcing material because it may be damaged by tension applied to the step of winding the cartridge filter when manufacturing the cartridge filter. As the reinforcing material, a net having a coarser mesh than the average maximum pore diameter of the non-woven fabric,
A mesh, a woven fabric, a knitted fabric, a wire mesh, a non-woven fabric or the like can be used. In addition, another filter medium may be wound together with the non-woven fabric and used together. In particular, when more accurate filtration performance is required, it is preferable to use a melt-blown nonwoven fabric having a pore diameter gradient obtained by the above method, which is heat-compressed to have a smaller overall pore diameter.

[0015]

【Example】

Example 1 A polypropylene resin having MI (melt index) = 40 was melt-blown by using a melt-blowing device having a width of 750 mm in which an air slit width was adjusted to 0.3 mm, and a resin discharge rate of 0.15 cc / min / orifice and spinning were performed. At a temperature of 290 ° C, the air volume (discharge air volume) was 1.
The melt blown non-woven fabric having a pore diameter gradient in the longitudinal direction was manufactured by changing the pressure from ^{5 to} 5.5 Nm ³ / min and accumulating it on a conveyor having a distance (accumulation distance) from the nozzle of 20 cm. This was wound around a polypropylene-made porous core from the smaller average pore size to prepare a cartridge filter. (Cartridge: inner diameter 3.0 cm, outer diameter 6.4 c
m, length 25 cm) Table 1 shows the average pore diameter and fiber diameter of the filter medium for each air amount. The porosity is constant at about 90%.

[0016]

Table 1 Air amount [Nm ³ / min] Average pore diameter [μm] Average fiber diameter [μm] 1.5 24 13.6 1.9 23 9.7 2.7 22 8.8 3.5 21 6. 0 4.3 19 4.8 5.1 17 2.2 2.2 5.5 15 1.5 Maximum value of median average distribution Simple average (air amount is continuously changed, each value is within a predetermined width (80 cm ) The nonwoven fabric has a length of about 560 cm and is divided into 7 sections every 80 cm, and each value is measured.)

Comparative Example 1 Air amounts of 1.5, 1.9, 2.7, 3.5, 4.
Seven kinds of melt-blown nonwoven fabrics were manufactured under the same spinning conditions as in Example 1 while keeping the values constant at ^3, 5.1 and 5.5 [Nm ³ / min]. Cartridge filters were manufactured by cutting each of these seven types of melt-blown nonwoven fabrics into pieces each having a length of about 80 cm, and then winding and laminating the polypropylene porous cores in order from the one having the smallest average pore diameter and winding the joining portions. The porosity of the filter medium was about 90%.

Example 2 Using the same method as in Example 1, the amount of air is 1.5 to 5.
When changing to 5 Nm ³ / min, 5.5 Nm ³ / m
The average fiber diameter is 1.5μ by increasing the in time.
A melt-blown nonwoven fabric was produced in which m was 50% in area ratio and the remaining 50% was 2.2 to 13.6 μm. (The length of the non-woven fabric occupied by each average fiber diameter is
1.5 μm, 280 cm, 2.2, 4.8, 6.0,
8.8, 9.7 and 13.6 μm, respectively, about 46 cm. ) This was wound around the porous core from the smaller average pore size to prepare a cartridge filter.

Example 3 Using the same method as in Example 1, the amount of air is 1.5-3.
The fiber diameter is 6.0 to 1 by changing to 5 Nm ³ / min.
A melt blown non-woven fabric having a thickness of 3.6 μm was produced. (The length of the non-woven fabric occupied by the portion of each average fiber diameter is 6.0,
8.8, 9.7 and 13.6 μm, each 140 cm. ) This was wound around the porous core from the smaller average pore size to prepare a cartridge filter.

Example 4 The meltblown nonwoven fabric obtained in Example 1 was heated and compressed to obtain a filter medium having an average pore size of 7 to 15 μm. (The average pore size in each section (80 cm) is 14, 12, 10,
It was 9, 8, 7.5 and 7 μm. ) The porosity is about 7
It is constant at 0%. This was wound around a porous core from the smaller pore size to prepare a cartridge filter. The filtration accuracy and filtration life of the obtained cartridge filter were measured by the following methods and shown in the table. <Filtration accuracy> Concentration 10p with JIS 8 types of dust dispersed
While uniformly stirring the pm liquid, water was passed through the cartridge filter at a flow rate of 25 l / min, and a clean liquid was collected 1 minute after the start of liquid feeding, and the particle size was measured with a particle size distribution analyzer, and its maximum outflow Filtration accuracy was determined from particle size. <Filtration Lifetime> Concentration 100 with JIS 8 type dust dispersed
While the ppm solution is uniformly stirred, water is passed through the Cartridge filter at a flow rate of 25 l / min, the pressure loss is measured, and the treatment is performed until the pressure difference from the initial pressure loss becomes 2.0 kg / cm ^2. The total amount of water passed was measured and this was taken as the filtration life. The results of Examples and Comparative Examples are shown in Table 3.

[0021]

[Table 3] As is clear from the above Examples and Comparative Examples, the cartridge filter of this Example has a significantly longer filtration life when compared with those having the same filtration accuracy.

[0022]

The cartridge filter manufactured from the nonwoven fabric of the present invention has a low cost, and
It has excellent filtration life and filtration accuracy, and has an excellent effect that a cartridge can be produced in one step in manufacturing.

[Brief description of drawings]

FIG. 1 is a graph showing an example of periodic changes in discharge air volume.

FIG. 2 is a graph showing an example of a periodic change in discharge air volume.

FIG. 3 is a graph showing an example of a periodic change in discharge air volume.

FIG. 4 is a graph showing an example of a periodic change in discharge air volume.

FIG. 5 is a graph showing an example of a periodic change in discharge air volume.

FIG. 6 is a graph showing an example of a periodic change in discharge air volume.

Claims (3)

[Claims] 1. A non-woven fabric having a pore diameter gradient in the longitudinal direction. 2. A cartridge filter in which the nonwoven fabric according to claim 1 is wound around a porous core. 3. A method for manufacturing a non-woven fabric having a pore diameter gradient in the longitudinal direction, characterized in that the amount of discharged air is changed periodically in the method for manufacturing a non-woven fabric by the melt blow method.