JPH04284803A - Glass fiber filter sheet for use in air filter of high performance - Google Patents

Abstract

PURPOSE:To provide a glass fiber filter sheet for use in an air filter of high performance. CONSTITUTION:A maximum bore diameter Pm of a glass fiber sheet is required to satisfy the relationship Pm<=Pc, wherein Pc is calculated by an equation Pc=-0.135XDELTAP+15. Smaller the Pm is in comparison with the Pc, higher the performance of a filter can be attained, wherein the Pc is a maximum bore diameter (mum) and the DELTAP is pressure loss (mmH2O) at a surface air velocity 5.33cm/S. A filter sheet for air filter of high performance having pressure loss of 4-8mmH2O lower than that of conventional ones can be obtained, which is very useful from the viewpoint of energy saving.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass fiber filter paper for use in high-performance air filters for air purification used in clean rooms of semiconductor manufacturing plants and the like.

0002

[Prior Art] High performance air has been used in fields that require a highly clean environment such as clean rooms, clean benches, and sterile rooms, or in fields where it is necessary to remove radioactive ultrafine dust emitted from nuclear reactors, etc. Glass filter paper for filters is used. Glass filter papers for high-performance air filters include HEPA (high-performance air filter) filter paper that captures 99.97% or more of DOP (dioctyl phthalate) particles with a particle size of 0.3 μm, and DOP with a particle size of 0.1 μm.
ULPA targets particles and has higher collection efficiency than HEPA.
There is filter paper for (ultra high performance air filter). Depending on the cleanliness of the clean room etc. required for these filter papers,
Filter papers with various collection efficiencies are prepared by filter media manufacturers. In order to increase the collection efficiency, it is possible to increase the blending ratio of ultrafine glass fibers with smaller fiber diameters, but this also increases the pressure loss, making it more difficult to use ULPA than HEPA, or U
The current situation is that the higher the demand for collection efficiency among LPAs, the higher the pressure loss. By the way, the pressure loss of glass fiber for high-performance air filters currently in practical use is 24 to 63 m at a surface wind speed of 5.33 cm/sec.
mH2O range. It is said that ULPA filter paper with a pressure loss of 60 mm H2 O or more can adequately meet the air cleanliness required in clean rooms when manufacturing 16 megabit LSIs, but the high pressure loss results in a large operating load, making it difficult to save energy. For this purpose, it is desired to reduce pressure loss. Regarding HEPA filter paper, one that satisfies the collection efficiency of 99.97% specified by the MIL standard and has a pressure loss of 24 mmH2O or less has not yet been put into practical use.

0003

[Problems to be Solved by the Invention] An object of the present invention is to maintain the collection efficiency of conventional glass fiber filter paper for HEPA and ULPA while reducing pressure loss by 4 to 8 mmH2 compared to conventional products.
An object of the present invention is to provide a filter paper for a high-performance air filter with low O.

0004

[Means for Solving the Problems] As a result of intensive study on the relationship between the filter characteristics of pressure loss and collection efficiency and the physical properties of filter paper, the present inventors have found that the above-mentioned filter The present invention was developed based on the fact that the characteristics are greatly affected.

The filter paper of the present invention will be explained in more detail.

[0006] The glass fiber filter paper for a high-performance air filter as used in the present invention is a glass fiber that exhibits a collection efficiency of 0.3 μm DOP particles of 99.97% or more under the condition of a surface wind speed of 5.33 cm/sec. means filter paper, usually HEPA and U
This refers to glass fiber filter paper for air filters called LPA.

[0007] The maximum pore diameter of glass fiber filter paper was determined using a pore size/size distribution measuring device, which is mainly used for measuring the maximum pore diameter of liquid filters and battery separators.
Electronics).

In the present invention, it is necessary that the maximum pore diameter Pm measured by the above method satisfies Pm ≦Pc with respect to the maximum pore diameter calculated by Pc = -0.135×ΔP+15, and Pm is compared with Pc. The lower the value, the better the performance.

The formula Pc = -0.135 x ΔP + 15 was found as a result of analyzing commercially available glass fiber filter papers for high-performance air filters and filter papers made by changing the amount of ultrafine glass fibers for pressure loss. be. In other words, the pressure drop and maximum pore diameter of glass fiber filter paper are inversely proportional; the higher the pressure drop, the smaller the maximum pore diameter, and at the same pressure drop, the smaller the maximum pore diameter, the better the collection efficiency. I found it. As shown in FIG. 1, in the analysis results of the conventional product, the actually measured maximum pore diameter Pm had a relationship of Pm > Pc with respect to Pc calculated from the pressure loss.

FIG. 2 shows the relationship between maximum pore diameter, pressure loss, and collection efficiency for air filter paper produced using an actual paper machine under different papermaking conditions. It has been found that in the glass fiber filter paper of the present invention having a maximum pore diameter Pm <Pc, the larger the difference, the higher the collection efficiency at the same pressure loss. In addition, glass fiber filter paper with Pm < Pc has a DOP of 0.3 μm at a pressure loss of 26 mmH2O.
Particle collection efficiency is 99.97%, which is required for HEPA class.
On the other hand, the filter paper with Pm>Pc is 99.97% or less. D of 0.1μm
The same thing can be observed when using OP particles and using ULPA filter paper.

The maximum pore diameter Pm of the glass fiber filter paper is Pc
Various methods can be considered to make the pores smaller, and it is not limited to one method in particular, but in order to reach the maximum pore size level specified in the glass fiber filter paper of the present invention, the raw material composition, especially the ultrafine glass fibers and The present inventor has found that it is extremely effective to keep the blending ratio of chopped strand fibers within a certain range. That is, a filter paper for a high performance air filter in which the content of chopped strand fibers with a fiber diameter of 10 μm or less in the glass fiber composition is 10 to 50% by weight and the content of ultrafine glass fibers is 90 to 50% by weight is advantageous in the present invention. This is an embodiment. Normally, by reducing the fiber diameter of the ultrafine glass fibers constituting the filter paper, it is possible to lower the maximum pore diameter Pm and thereby increase the collection efficiency. However, simply reducing the fiber diameter increases the pressure loss of the filter paper, which is inappropriate as a method for obtaining a filter paper that satisfies Pm≦Pc according to the present invention. In the present invention, the ratio of chopped glass fiber, which is usually mixed in at a few percent for the purpose of maintaining strength, is increased to a specified value or more, thereby preventing an increase in pressure loss and reducing the maximum pore diameter.
A filter paper with ≦Pc can be obtained. As the proportion of chopped glass fibers increases, ultrafine glass fibers with a smaller fiber diameter can be blended, so the maximum pore diameter becomes smaller and the filter performance improves. In order to make Pm > Pc, the blending ratio of chopped strand glass fiber is 10
% or more. More preferably 1
5% or more.

The glass fiber filter paper for high performance air filters of the present invention contains a binder in addition to ultrafine glass fibers and chopped glass fibers. This binder is an organic binder, and its amount is 10% or less, preferably 7% or less, and as long as the required strength is maintained, it is preferably as small as possible. As the amount of binder increases,
Pressure drop increases and reduces collection efficiency.

[0013]

[Operation] The mechanism of increase in collection efficiency by reducing the maximum pore diameter of the air filter has not been theorized so far, but it is estimated as follows.

It is said that the collection mechanism of glass fiber filter paper for high-performance air filters using ultrafine glass fibers is related to variations in the filling of glass fibers constituting the filter paper. Therefore, if the filling variations are large, the pores formed within the filter paper will vary widely, the maximum pore diameter will increase, and the collection efficiency will decrease. It is thought that if the pore size is controlled to reduce the variation in pores so that the maximum pore diameter becomes smaller, the fiber filling becomes uniform and the filter performance improves. It is thought that the increase in the blending ratio of chopped strands affects the uniformity of filling as well as the decrease in the overall pore size due to the increase in the usage ratio of ultrafine glass fibers with a smaller fiber diameter. Conventionally, the maximum pore diameter of air filters has not received much attention, but we believe that by controlling this, the collection effect can be effectively exerted, which will lead to improved filter performance.

[0015]

[Examples] Example 1 90% by weight of ultrafine glass fibers with an average fiber diameter of 1 μm or less,
10% by weight of chopped glass fiber with an average fiber diameter of 6 μm
Using acidic water with pH 3.5 in a pulper, the concentration is 0.5%.
The mixture was disintegrated for 10 minutes. Then, paper was made using a paper machine with an inlet concentration of 0.05% by weight. Acrylic latex (
HA-16 (manufacturer: Nippon Acrylic) was applied to the wet paper,
After that, dry it with a dryer, and as shown in Table 1 below, Pm
A glass fiber filter paper for HEPA with a basis weight of 69 g/m2 and <Pc was obtained.

Example 2 In Example 1, the blending ratio of chopped glass fiber was changed to 30
% by weight, and the same as Example 1 except that the glass fiber component with an average fiber diameter of 0.65 μm in 70% by weight of ultrafine glass fibers with an average fiber diameter of 1 μm or less was adjusted so that the pressure loss was at the same level. As shown in Table 1 below, HE with a basis weight of 71 g/m2 where Pm < Pc
A glass fiber filter paper for PA was obtained.

Example 3 In Example 1, the blending ratio of chopped glass fiber was changed to 45%.
% by weight, and the same as in Example 1 except that the glass fiber component with an average fiber diameter of 0.65 μm in 55% by weight of ultrafine glass fibers with an average fiber diameter of 1 μm or less was adjusted so that the pressure loss was at the same level. As shown in Table 1 below, HE with a basis weight of 70 g/m2 where Pm < Pc
A glass fiber filter paper for PA was obtained.

Example 4 The same procedure as in Example 1 was repeated except that 5% by weight of ultrafine glass fibers with an average fiber diameter of 0.32 μm were blended in 90% by weight of ultrafine glass fibers with an average fiber diameter of 1 μm or less. As shown in Table 1, the basis weight is 7 where Pm < Pc
A glass fiber filter paper for ULPA of 3 g/m2 was obtained.

Example 5 In Example 1, the blending ratio of chopped glass fiber was changed to 30
% by weight, except that the glass fiber component with an average fiber diameter of 0.32 μm in the ultrafine glass fibers with an average fiber diameter of 1 μm or less was increased and adjusted to the same level as in Example 4. In the same manner as Example 1, the fabric weight is 74 g/m2 where Pm<Pc as described in Table 1 below.
A glass fiber filter paper for ULPA was obtained.

Comparative Examples Comparative Examples 1, 2 and 3 correspond to Examples 1 to 3, and Comparative Example 4 corresponds to Examples 4 and 5.

Comparative Example 1 In Example 1, ultrafine glass fibers of 1 μm or less were
Pm > Pc as shown in Table 1 below in the same manner as in Example 1 except that the glass fiber component with an average fiber diameter of 0.65 μm was adjusted so that the pressure loss was at the same level. HEP with a basis weight of 68g/m2
A glass fiber filter paper for A was obtained.

Comparative Example 2 Same as Example 1 except that the blending ratio of chopped glass fiber was 3% by weight, and 97% by weight of ultrafine glass fiber with an average fiber diameter of 1 μm or less, and the pressure loss was adjusted to the same level. HEPA with a basis weight of 70 g/m2 where Pm > Pc as described in Table 1 below.
A glass fiber filter paper was obtained.

Comparative Example 3 In Example 1, the blending ratio of chopped glass fiber was changed to 6
0% by weight, and 40% by weight of ultrafine glass fiber.
Example 1 except that the pressure loss was adjusted to the same level.
In the same manner as described in Table 1 below, a glass fiber filter paper for HEPA with a basis weight of 68 g/m2 where Pm > Pc was obtained.

Comparative Example 4 In Example 4, chopped glass fiber was added in an amount of 3% by weight.
The fabrication weight was 72 as described in Table 1 below, except that the ultrafine glass fiber was 97% by weight and the pressure loss was adjusted to the same level.
A glass fiber filter paper for ULPA of g/m2 was obtained.

The filter papers of Examples 1 to 5 and Comparative Examples 1 to 4 were analyzed by the following method, and the results are shown in Table 1. (1) Maximum pore diameter Pmax Using a Coulter porometer manufactured by Coulter Electronics, measurements were taken at three different locations, and the average was taken as the maximum pore diameter.

(2) Pressure loss Using a self-made device, air was blown through a filter paper with an effective area of 100 cm 2 at a surface velocity of 5.33 cm/sec (=S), and the pressure loss at that time was measured using a differential pressure gauge.

(3) DOP collection efficiency DOP collection efficiency when air containing polydisperse DOP particles generated by a Raskin nozzle is passed through a filter paper with an effective area of 100 cm2 at a surface wind speed of 5.33 cm/sec. The measurement was carried out using a laser particle counter manufactured by Kawasaki. The measurement was performed on DOP particles of 0.3 μm for the glass fiber filter paper for HEPA and 0.1 μm for the glass fiber filter paper for ULPA.

(4) Combustible material was heated in an electric furnace at 925±25° C. for 10 minutes, and the difference in weight before and after heating was divided by the weight before heating to obtain a percentage.

(5) Tensile Strength For 25 mm wide test pieces taken from the longitudinal and transverse directions of the filter paper, the span length was 100 mm and the tensile speed was 12.5.
It was measured using a constant speed tensile tester at mm/min.

(6) α value The α value, which is an index of the filter performance of filter paper, is expressed by (2) and (
3) Based on the measured value, it was calculated from the following formula. (The higher the α value, the higher the collection efficiency at the same pressure loss.)

0
031]

[Table 1]

[0032]

[Effects] The present invention provides a new method for glass fiber filter paper for HEPA and ULPA, which has been conventionally used for clean rooms, by controlling the maximum pore diameter to below a specified value in relation to pressure loss. The following effects can be expected. (1) When the collection efficiency is made to the same level as conventional products, it is possible to reduce pressure loss, and when used in a clean room, it contributes to energy savings and fan noise reduction without reducing the air cleanliness of the clean room. . (2) When the pressure loss is kept at the same level, the collection efficiency increases, and the air cleanliness of the clean room can be improved with the same amount of energy consumption. (3) Compared to conventional products, it can be manufactured at almost the same cost. (4) Since the strength is improved, the basis weight of the filter paper can be lowered, and the amount of filter paper used in processed filter products can be reduced.

As described above, the practical value of the present invention is extremely high, and it will fully contribute not only to the semiconductor industry but also to other industries that use clean rooms, such as the food industry and the medical industry.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between pressure loss and maximum pore diameter for glass fiber filter papers with different pressure losses.

FIG. 2 is a graph showing the relationship between pressure loss and collection efficiency for glass fiber filter papers with different maximum pore diameter conditions.

Claims (2)

[Claims] [Claim 1] The maximum pore diameter Pm of the filter paper is expressed by the following formula (a):
A glass fiber filter paper for a high-performance air filter, characterized in that, with respect to the maximum pore diameter Pc calculated as follows, Pm≦Pc. Pc = −0.135×ΔP+15
(a) Pc: Maximum pore diameter (unit: μm) ΔP: Pressure loss at surface wind speed 5.33 cm/S (mm
H2O) Claim 2: In the glass fiber composition, the fiber diameter is 1
The content of chopped strand glass fibers of 0 μm or less is 10 to 50% by weight, and the content of ultrafine glass fibers is 90% by weight.
The glass fiber filter paper for high performance air filters according to claim 1, characterized in that the content is 50% by weight.