JPH0732851B2 - Glass fiber filter paper for high performance air filter - Google Patents

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 a high-performance air filter for air cleaning used in a clean room of a semiconductor manufacturing factory.

[0002]

2. Description of the Related Art Conventionally, high-performance air is used in fields such as clean rooms, clean benches, aseptic chambers that require a highly clean environment, or in fields where it is necessary to remove radioactive ultrafine dust emitted from nuclear reactors. Glass filter paper for filters is used. For high-performance air filter glass filter paper, HEPA (high-performance air filter) filter paper that collects 99.97% or more of DOP (dioctyl phthalate) particles with a particle size of 0.3 μm and DOP particles with a particle size of 0.1 μm are targeted. There is a filter paper for ULPA (Ultra High Performance Air Filter) which has a collection efficiency higher than HEPA. Filter media with various collection efficiencies are prepared by filter media manufacturers according to the cleanliness requirements of these filter papers such as in a clean room.
In order to improve the collection efficiency, it is possible to deal with it by increasing the compounding ratio of the ultrafine glass fiber having a smaller fiber diameter, but the pressure loss also increases accordingly, and ULPA and U
In the current situation, the pressure loss also rises as the collection efficiency of LPA becomes higher. By the way, the pressure loss of the glass fiber for high-performance air filters currently in practical use is 24 to 63 m under the condition that the surface wind velocity is 5.33 cm / sec.
It is in the range of mH ₂ O. It is said that the ULPA filter paper with a pressure loss of 60 mmH ₂ O or more can sufficiently support the air cleanliness of the clean room required when manufacturing a 16-megabit LSI, but the operating load due to the high pressure loss is large. Reduction of pressure loss is desired for the purpose of energy saving. Further, as the HEPA filter paper, one having a trapping efficiency of 99.97% specified by the MIL standard and a pressure loss of 24 mmH ₂ O or less has not yet been put into practical use.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is to maintain the collection efficiency of conventional glass fiber filter papers for HEPA and ULPA while maintaining a pressure loss of 4 to 8 mmH ₂ O as compared with conventional products.
It is to provide a low-performance filter paper for an air filter.

[0004]

Means for Solving the Problems The inventors of the present invention have made diligent studies on the relationship between filter characteristics such as pressure loss and collection efficiency and physical properties of filter paper. The present invention has been made paying attention to the fact that the characteristics are greatly affected.

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

The glass fiber filter paper for high performance air filters referred to in the present invention is a glass fiber having a collection efficiency of 0.3 μm DOP particles of 99.97% or more under the condition that the surface wind velocity is 5.33 cm / sec. Means filter paper, usually HEPA and UL
It means a glass fiber filter paper for air filters called PA.

The maximum pore size of the glass fiber filter paper is determined by using a pore size / size distribution measuring device which is mainly used for measuring the maximum pore size related to a liquid filter and a battery separator, and is used as a solvent for porphyll (trade name; Coulter Electro
nics).

[0008] maximum pore size P _m measured by the above method in the present invention, with respect to the maximum pore size is calculated by _{P c = -0.135 × ΔP + 15} , must be a P _m ≦ P _c,
The lower P _m is compared with P _c , the better the performance.

The above expression P _c = -0.135 × ΔP + 15 is an expression found as a result of analysis of a commercially available glass fiber filter paper for high performance air filters and filter papers prepared by changing pressure loss with an extra fine glass fiber content. Is. That is, the pressure loss and the maximum pore diameter of the glass fiber filter paper are inversely proportional to each other.The higher the pressure loss, the smaller the maximum pore diameter, and the same pressure loss, the smaller the maximum pore diameter, the higher the collection efficiency. I found it. As shown in FIG. 1, the analysis results of the conventional product, the maximum pore size P _m to be measured whereas P _c calculated from pressure loss was in relation P _m> P _c.

FIG. 2 shows an actual paper machine with different papermaking conditions.
Maximum pore size and pressure loss of manufactured filter paper for air filter.
This is the relationship between loss and collection efficiency. Maximum hole of the present invention
Diameter P _m<P_cThe difference is great in the glass fiber filter paper
It was found that the collection efficiency increases with increasing pressure loss.
It was. Also, P_m<P_cThe glass fiber filter paper is
Lost 26 mmH₂Collection of 0.3 μm DOP particles in O
Efficiency meets 99.97% or more required for HEPA class
In contrast, P_m> P_cThe filter paper of 99.97% or more
It is below. UL with 0.1 μm DOP particles
The same thing can be observed even if it carries out with PA filter paper.

Various methods are conceivable for making the maximum pore diameter P _m of the glass fiber filter paper smaller than P _c , and particularly 1
Although not limited to one method, in order to reach the maximum pore size level specified in the glass fiber filter paper of the present invention, it is extremely necessary to keep the raw material blending, especially the blending ratio of the ultrafine glass fiber and the chopped strand fiber within a certain range. The present inventor has found that it is effective. That is, a filter paper for a high-performance air filter in which the content of chopped strand fibers having a fiber diameter of 10 μm or less and the content of ultrafine glass fibers in the composition of glass fiber is 90 to 50% by weight is advantageous in the present invention. It is an embodiment. In general, it is possible to reduce the maximum pore diameter P _m by increasing the fiber diameter of the ultrafine glass fibers constituting the filter paper, and thereby to improve the collection efficiency. However, simply reducing the fiber diameter causes an increase in pressure loss of the filter paper, and is not suitable as a method for obtaining the filter paper satisfying P _m ≤P _c of the present invention. In the present invention, the proportion of chopped glass fibers, which is usually blended by several percent for the purpose of maintaining strength, is increased to a specified value or more, whereby pressure loss can be prevented from increasing and the maximum pore diameter can be reduced to P _m ≤P The filter paper of _c can be obtained. As the proportion of chopped glass fibers becomes higher, the finer glass fibers having a smaller fiber diameter can be blended, so that the maximum pore diameter becomes smaller and the filter performance improves. In order to satisfy P _m ≤P _c , it is necessary that the compounding ratio of chopped strand glass fibers is 10% or more. More preferably, it is 15% or more.

The glass fiber filter paper for a high performance air filter of the present invention contains a binder in addition to the ultrafine glass fiber and the chopped glass fiber. This binder is an organic binder, and the amount thereof is 10% or less, preferably 7% or less, and it is preferable that the amount is as small as possible within the range in which the required strength is maintained. As the amount of binder increases, the pressure loss increases, reducing the collection efficiency.

[0013]

The mechanism of action of increasing the collection efficiency by reducing the maximum pore size of the air filter has not been theorized so far, but it is estimated as follows.

It is said that the mechanism of collecting glass fiber filter paper for high performance air filters using ultrafine glass fiber is related to the variation in the filling of the glass fiber constituting the filter paper. Therefore, if the variation of the filling is large, the variation of the pores formed in the filter paper is increased accordingly, the maximum pore diameter is increased, and the collection efficiency is lowered. It is considered that if the variation in pores is controlled so as to reduce the maximum pore diameter, the filling of the fibers becomes uniform and the filter performance is improved. It is considered that the increase in the mixing ratio of the chopped strands has an effect on the filling uniformity as well as the decrease in the size of the entire pores due to the increase in the usage ratio of the ultrafine glass fibers having a smaller fiber diameter. Conventionally, no attention was paid to the maximum pore size of an air filter, but by controlling this, the trapping effect is effectively exhibited, and as a result, the filter performance is improved.

[0015]

Example 1 90% by weight of ultrafine glass fibers having an average fiber diameter of 1 μm or less and 10% by weight of chopped glass fibers having an average fiber diameter of 6 μm were acidified with a pulper at pH 3.5 to 1% at a concentration of 0.5%.
Disaggregated for 0 minutes. Next, the inlet concentration is 0.05% by weight
Paper was made using a paper machine. Acrylic latex (HA-
16, manufacturer: Japan Acrylic) is applied to a wet paper, then dried with a drier, and P _m <P _{c as shown in} Table 1 below.
A glass fiber filter paper for HEPA having a basis weight of 69 g / m ² was obtained.

Example 2 In Example 1, the chopped glass fiber content was 30%.
%, And the same as in Example 1 except that the glass fiber component having an average fiber diameter of 0.65 μm in 70% by weight of the ultrafine glass fibers having an average fiber diameter of 1 μm or less was increased to adjust the pressure loss to the same level. Then, as shown in Table 1 below, P _m
A glass fiber filter paper for HEPA having a basis weight of 71 g / m ² of <P _c was obtained.

Example 3 In Example 1, the chopped glass fiber content was 45%.
%, And the same as Example 1 except that the glass fiber component having an average fiber diameter of 0.65 μm in 55% by weight of the ultrafine glass fibers having an average fiber diameter of 1 μm or less was increased to adjust the pressure loss to the same level. Then, as shown in Table 1 below, P _m
A glass fiber filter paper for HEPA having a basis weight of 70 g / m ² of <P _c was obtained.

Example 4 The same as Example 1 except that 5% by weight of ultrafine glass fibers having an average fiber diameter of 0.32 μm in 90% by weight of the ultrafine glass fibers having an average fiber diameter of 1 μm or less was added. As shown in Table 1, 73 g / m ^{2 of} basis weight with P _m <P _c
To obtain a glass fiber filter paper for ULPA.

[0019]Example 5 In Example 1, the chopped glass fiber content was 30.
Ultrafine glass fiber 7 with an average fiber diameter of 1 μm or less in weight%
Glass fiber component with an average fiber diameter of 0.32 μm in 0% by weight
Is increased so that the pressure loss becomes the same level as in Example 4.
Described in Table 1 below in the same manner as in Example 1 except that
Street P_m<P_cThe unit weight is 74g / m ²For ULPA
A glass fiber filter paper 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, 10 μm or less of ultrafine glass fiber was used.
And 0 wt%, as described in the following Table 1, except that the pressure loss is adjusted to reduce the glass fiber component of the average fiber diameter 0.65μm to the same level in the same manner as in Example 1 P _m
A glass fiber filter paper for HEPA having a basis weight of 68 g / m ² of> P _c was obtained.

Comparative Example 2 Extra fine glass fiber 97 having an average fiber diameter of 1 μm or less with the chopped glass fiber content of 3% by weight in Example 1.
P _m > as described in Table 1 below in the same manner as in Example 1 except that the pressure loss was adjusted to the same level.
A glass fiber filter paper for HEPA having a basis weight of 70 g / m ² of P _c was obtained.

Comparative Example 3 In Example 1, the compounding ratio was 6 for chopped glass fiber.
And 0 wt%, ultrafine glass fibers and 40 wt%, except that the pressure loss is adjusted to the same level are as P _m> P _c according to the following Table 1 in the same manner as in Example 1 having a basis weight 6
8 g / m ² of glass fiber filter paper for HEPA was obtained.

Comparative Example 4 The same procedure as in Example 4 was repeated except that chopped glass fiber was 3% by weight, ultrafine glass fiber was 97% by weight, and pressure loss was adjusted to the same level. 72 g / m ² with a basis weight of P _m > P _c as described in 1.
To obtain a glass fiber filter paper for ULPA.

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 size P _max Coulter Electronics Coulter Porometer was used to measure 3 points at different locations, and the average of these was used as the maximum pore size.

(2) Pressure loss Using a self-made device, air was passed through a filter paper having an effective area of 100 cm ^{2 at} a surface wind velocity of 5.33 cm / sec (= S), and the pressure loss at that time was measured by a fine differential pressure gauge.

(3) DOP collection efficiency Air containing polydisperse DOP particles generated by a Ruskin nozzle was filtered through a filter paper having an effective area of 100 cm ^{2 at} a surface wind velocity of 5.33.
The DOP collection efficiency when ventilated at cm / sec was measured using a laser particle counter manufactured by Rion. still,
0.3μm for glass fiber filter paper for HEPA, UL
The glass fiber filter paper for PA was measured for 0.1 μm DOP particles.

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

(5) Tensile strength A test piece having a width of 25 mm sampled from the longitudinal and lateral directions of the filter paper had a span length of 100 mm and a pulling speed of 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 the filter paper, was calculated from the following equation based on the measured values of (2) and (3). (The higher the α value, the higher the collection efficiency with the same pressure loss.)

[0031]

[Table 1]

[0032]

[Effect] The present invention is a novel glass fiber filter for HEPA and ULPA which has been conventionally used for clean rooms. It has a new low pressure loss and a high collection efficiency by controlling the maximum pore size to a specified value or less in relation to the pressure loss. The following effects can be expected. (1) When the collection efficiency is the same level as the conventional product, pressure loss can be reduced, and when used in a clean room,
It contributes to energy saving and fan noise reduction without lowering the air cleanliness of the clean room. (2) If the pressure loss is at the same level, the collection efficiency will increase and the air cleanliness of the clean room can be increased with the same energy consumption. (3) Compared with conventional products, it can be manufactured at almost the same cost. (4) Since the strength is improved, the weight per unit area of the filter paper can be reduced, and the amount of the filter paper used in the processed filter product can be reduced.

As described above, the practical value of the present invention is extremely high, and contributes not only to the semiconductor industry but also to other industries such as the food industry using a clean room and the medical industry.

[Brief description of drawings]

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

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

Claims (2)

[Claims] 1. The maximum pore size P of the filter paper._mIs calculated by the following formula (a)
Maximum pore size calculated P _cOn the other hand, P_m≤P_cHave a relationship
Glass fiber filter for high performance air filters characterized by
paper. P_c= −0.135 × ΔP + 15 (a) P_c: Maximum pore diameter (unit: μm) ΔP: Pressure loss at surface wind velocity 5.33 cm / S (mm
H₂O) 2. The glass fiber composition has a fiber diameter of 10
The chopped strand glass fiber content of μm or less is 1
0-50% by weight, ultrafine glass fiber content 90-50
The glass fiber filter paper for a high performance air filter according to claim 1, wherein the glass fiber filter paper is characterized by being in a weight percentage.