JPS6340124B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-performance filter that has high collection efficiency and less clogging, and therefore has a large dust holding capacity and a long life. Conventionally, filters with high collection efficiency and low clogging have been manufactured using nonwoven fabrics with different fiber materials, fiber fineness, fiber density, thickness, etc., depending on the dust to be removed. There are laminated filters that have a suitable combination of fiber densities. This laminated filter can be manufactured by laminating various types of non-woven fabrics, or by polymerizing multiple webs and processing them with resin, so it is possible to manufacture filters with desired performance. It is used in air filters, liquid filters, such as fuel filters and oil filters for automobiles and aircraft. These laminated filters are less likely to clog and retain a large amount of dust compared to single-layer nonwoven filters, but when looking at the amount of dust retained from the space volume of the filter, there is still a considerable amount of unused space left. Clogging occurs, ventilation resistance increases rapidly, and the service life tends to be shortened, so that space utilization efficiency is not always satisfactory. The reason for this is that a cake layer of dust is likely to form on the inflow side of the laminated surface of the laminated filter, and this is caused by the fact that the laminated filter is manufactured by polymerizing various single layers of nonwoven fabric with uniform fiber density. It was an unavoidable problem. In view of this point, the inventors of the present invention have conducted intensive studies on filters with high collection efficiency and less clogging, and as a result, have discovered the present invention. Fibers are thermally bonded together using a binder,
The fiber density on the mixed dust air inflow side is 0.01 to 0.1, the fiber density on the outflow side is 0.05 to 0.4, and the change in fiber density from the inflow side to the outflow side has an exponentially continuous density gradient. Moreover, the filter is characterized in that the fiber forming material is distributed homogeneously in the thickness direction. The filter of the present invention has a step-like fiber density in which conventional laminated filters are made by laminating a large number of nonwoven fabrics with uniform fiber density, but the filter of the present invention has a continuously changing density gradient and the forming material is uniformly distributed. It is characterized by being a single layer filter. Homogeneously distributing the material forming the fibers constituting the filter means, for example, that the fiber distribution is uniform throughout the thickness. In the case of a filter made of two types of fibers, 1 denier fibers and 3 denier fibers, these fibers are uniformly mixed at any point in the thickness direction of the filter. This point will be explained with reference to FIG. FIG. 1A shows the fiber density distribution in the thickness direction of a conventional laminated filter, for example, a three-layer laminated filter, and FIG. 1B shows the fiber density distribution in the thickness direction of the filter according to the present invention. The fiber density of the filter in the present invention is 0.01 to 0.1 on the inflow side and 0.05 to 0.4 on the outflow side, and the distribution preferably has a density gradient with a gentle slope on the inflow side 1 and a steep slope on the outflow side 2. The fiber density of the filter in the present invention can be controlled by the type of dust and particle size distribution, but the shape of the density gradient is generally a curve connecting the inflow side and the outflow side.
It is preferable to show an exponential function change, and to give a specific example, a curve with a density gradient expressed by the following equation is preferable. Here, α: Thickness of the filter, fiber density at l αi: Fiber density at the inlet side of the filter a: Constant 0.35 to 0.64 lo: Thickness of the filter l: Distance in the thickness direction from the inlet side of the filter This is because if the fiber density gradient on the inflow side is large, the amount of dust retained will be reduced, while if the density gradient on the outflow side is small, the collection efficiency will be reduced. The fiber density in the present invention is
It is expressed as the ratio of the volume occupied by the fibers to the spatial volume occupied by the filter, and its unit is cm ³ /cm ³ . The fibers constituting the filter in the present invention are:
Examples include regular threads with round cross-sections and special threads with irregular cross-sections other than round cross-sections, such as Y-section, Inorganic fibers such as rocks are used. Further, the fineness of the fibers used is not particularly limited. The aggregate of fibers constituting the filter in the present invention includes short fiber webs and long fiber webs. The fibers constituting the filter in the present invention are not limited to only one type of fiber, but may be a mixture of at least two types of fibers, and the mixed state is preferably uniform. That is, it is essential that the forming material of the filter in the present invention is uniformly distributed in any part thereof. The filter in the present invention itself is a single-layer filter with high collection efficiency and less clogging. By polymerizing nonwoven fabrics, it is possible to obtain filters that exhibit more accurate collection performance. The filter of the present invention is novel in that it is a single-layer filter in which the fiber density, which is a fiber aggregate characteristic, is controlled by a continuous density gradient from the inflow side to the outflow side by utilizing the thermal adhesion between the fibers by a powder binder. In addition, the fiber fineness of the fibers themselves constituting the fiber aggregate and the fiber characteristics such as the fiber cross-sectional shape coefficient give the filter of the present invention a high collection efficiency, less clogging, and therefore a lower amount of dust retained. This is significant in order to more effectively enhance performance over a long life and to maintain a continuous density gradient of fiber density in the present invention. FIG. 2 shows a dust removal filter and a conventional laminated filter as one example of the filter of the present invention.
For example, it is a filter cross-sectional schematic diagram showing a dust collection state in a three-layer laminated filter. Dust is collected in conventional laminated filters, and ventilation resistance begins to increase rapidly. In other words, the schematic cross-sectional view of the filter in the dust-collecting state just before the end of the filter's life is shown in FIG. The figure is Figure 2B
It is. In the dust removal filter of the present invention, the dust particles 1 are captured in a well-dispersed state in the thickness direction, whereas in the conventional laminated filter, dust-containing air flows into each polymerized single layer. Dust particles are trapped on the side 2, and this uneven distribution of dust develops in the cake layer 3, resulting in a significant increase in the ventilation resistance of the filter. The reason why such a cake layer is not generated in the dust removal filter of the present invention is that the fiber density has a continuous density gradient, and the filter collection performance changes from low collection performance to high collection performance from the dust-containing air inflow side to the outflow side. This is because performance changes continuously. The present invention will be specifically explained below using Examples. Example 1 Fabric weight made of 3 denier polyester fiber
400g/ ^m2 of air containing a low melting point polyester powder binder perpendicular to the surface of the carded web at a linear velocity
Spray powder at 0.5m/pass through this web,
When a low melting point polyester powder binder is captured by the polyester fibers constituting the web, this powder binder adheres to the surface layer of the web,
The adhesion concentration tended to decrease toward the front and back sides of the web. After that, this web was heat pressed for 10 minutes at 130°C, the temperature at which the powder binder can be fused, to a gauge thickness of 4 mm, and then the heat press was released to recover the compressive elasticity of the web, resulting in a single layer with a thickness of 5 mm. A filter was obtained. The average fiber density of this filter is 0.07, the fiber density on the dust-containing air inflow side is 0.03, and the fiber density on the outflow side is
It was 0.11. Also, the changes in fiber density at 1 mm intervals from the inflow side to the outflow side are 0.03, 0.04, 0.06,
0.08 and 0.11, and the constant a was 0.4. This filter was attached to a dust tester with a filtration area of ^79cm2 , and JIS class 8 test dust was supplied to the filtration surface at a wind speed of dust-containing air of 30cm/sec.
The average collection efficiency and dust retention amount in mm water column were measured. The measurement results are shown in Table 1.

[Table] For comparison, the above powder binder was dispersed so as to adhere uniformly in the thickness direction to a card web made of 3 denier polyester fibers with a basis weight of 400 g/m ² and the above and the above were prepared at a gauge thickness of 2.5 mm. A single-layer filter molded under the same heat press conditions, a 2 mm thick nonwoven fabric (fabric weight 110 g/m 2 ) made of 6 denier polyester fibers, and a 1 mm thick nonwoven fabric (basis weight 120 g/m ² ) made of 3 denier polyester fibers.
^m2 ) and thickness made of 1.5 denier rayon fiber
The dust collection performance of a multilayer filter consisting of three layers of 0.5 mm nonwoven fabric (fabric weight 150 g/m ² ) was measured under the same conditions as above, and the results are shown in Table 2.

[Table] It is clear from these results that although the filter of this example has the same collection efficiency as the laminated filter of Comparative Example 2, the amount of dust retained is approximately twice as high as that of the laminated filter of Comparative Example 2. demonstrated. The single-layer filter with uniform fiber density of Comparative Example 1 was also inferior to the present example in terms of dust retention and collection efficiency. Furthermore, the powder binder was dispersed in a carded web with a basis weight of 400 g/m ² made of 3 denier polyester fibers so as to be linearly adhered in the thickness direction, and the powder binder was applied to a card web made of 3 denier polyester fibers with a basis weight of 400 g/m 2 to form a linear adhesion in the thickness direction. A molded single-layer filter was produced. The fiber density of the filter is 0.05 on the inflow side and 0.11 on the outflow side.
It was hot. When the dust collection performance was measured, it was as shown in Table 3 and was not satisfactory (Comparative Example 3).

[Table] Example 2 On the surface of a carded web with a fabric weight of 140 g/m ² and a uniform denier distribution in the thickness direction, it was made of 60% by weight of 1-denier polyester fibers and 40% by weight of 3-denier polyester triangular cross-section fibers. The air containing the same powder binder as in Example 1 was passed vertically at a linear velocity.
Spray at 0.3m/sec and pass through this web.
When the powder binder was captured by the polyester fibers constituting the web, the powder binder adhered in large amounts to the surface layer of the web, and the adhesion concentration tended to decrease toward the back layer of the web. After that, this web was heat pressed for 2 minutes at 140°C, the temperature at which the powder binder can be fused, to a gauge thickness of 1 mm, and then the hot press was released to recover the compressive elasticity of the web, resulting in a single layer filter with a thickness of 1.2 mm. was gotten. This filter has a fiber density on the dust-containing air inlet side.
It had a continuous density gradient of 0.02 and fiber density on the outflow side of 0.09. Table 4 shows the results of measuring the collection efficiency and dust retention amount of the obtained filter. For comparison, the surface layer side of the web consists of 100% by weight of 1 denier polyester fibers, the proportion of 3 denier polyester triangular cross section fibers increases linearly towards the surface layer side, and the proportion of 3 denier polyester triangular cross section fibers on the back layer side increases linearly. Using a web with a non-uniform distribution of fibers in the thickness direction (fabric weight of 140 g/m ² ), the fabrication of a filter was attempted in the same manner as above (Comparative Example 4).
The performance of this filter is also listed in Table 4.

[Table] In conventional filters, if the initial collection efficiency is increased, the amount of dust retained cannot be avoided, but in Example 2, the amount of dust retained per 1 mm of filter thickness is 408 g. /m ² , and compared with 584 g/m ² in Example 1, a high initial collection efficiency was obtained without causing a significant decrease in the amount of dust retained per 1 mm of filter thickness. In addition, the amount of dust retained per 1 mm thickness of the filter of Comparative Example 3
Compared to 402 g/m ² , the superior performance of Example 2 was obvious. Comparative Examples 5 to 8 Using the carded web of Example 2, adopting the same filter manufacturing method as in Example 2, and changing the heat press temperature and gauge thickness conditions, the inflow of dust-containing air into the filter as shown in Table 5 was achieved. Four types of continuous gradient type filters with different fiber densities on the side and outflow side were obtained. The results of performance evaluation of these four types of filters are also listed in Table 5.

[Table] From these comparative examples, it can be seen that if the collection efficiency as in Example 2 is attempted to be ensured, the amount of dust retained will be extremely reduced.

[Brief explanation of drawings]

FIG. 1A shows the fiber density distribution in the thickness direction of a conventional laminated filter, for example, a three-layer laminated filter, and FIG. 1B shows the fiber density distribution in the thickness direction of the dust removal filter of the present invention. There is. 1...Dust-containing air inflow side, 2...Outflow side. FIG. 2A is a schematic cross-sectional view of a conventional laminated filter, for example, a three-layer laminated filter, in a dust-collecting state, and FIG. 2B is a cross-sectional schematic diagram of the filter in a dust-collecting state in the present invention. 1...Dust particles, 2...Dust-containing air inflow side of each single layer, 3...Cake layer.

Claims (1)

[Claims] 1. Fibers are thermally bonded together using a binder, and the fiber density on the dust-containing air inflow side is 0.01 to 0.1, the fiber density on the outflow side is 0.05 to 0.4, and from the inflow side to the outflow side. A filter characterized in that the change in fiber density has an exponentially continuous density gradient, and the material forming the fibers is uniformly distributed in the thickness direction. 2. Claim 1 in which the fibers constituting the filter are a mixed fiber of at least two types of fibers.
Filter as described in section. 3. The filter according to claim 1 or 2, wherein at least two layers of filters are stacked. 4 Claim 1 in which nonwoven fabrics are layered
3. The filter according to item 2, item 2, or item 3. 5. The filter according to claim 1, 2, 3, or 4, which is made of fibers having an irregular cross-sectional shape.