JP2003159507A - Filter medium for air filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter medium for an air filter with high stiffness and high strength against delamination, low increase of pressure loss and excellent in pleating processability. <P>SOLUTION: In a filter medium for an air filter consisting of a nonwoven fabric of a basis weight 25-150 g/m<SP>2</SP>, the filter medium for an air filter wherein a polyvinyl alcohol fiber-like binder adhering component fibers is not completely dissolved and swells while holding a fiber form and uniformly exists in the thickness direction of the filter medium. <P>COPYRIGHT: (C)2003,JPO

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 an air filter, which is mainly made of glass fiber and is used in various clean rooms such as semiconductor manufacturing, air conditioning for buildings, and air cleaning applications.

[0002]

2. Description of the Related Art Conventionally, a filter material for an air filter, which is mainly composed of ultrafine glass fiber or chopped glass fiber, has no adhesive strength to the glass fiber itself and does not exhibit the strength of the filter material. A fibrous binder or the like is used alone or in combination to impart strength. Among them, the polyvinyl alcohol fibrous binder is used in the “internal addition method” in which it is mixed with the raw glass fibers and dispersed in water at the time of manufacturing the filter medium, and is made into a sheet by wet papermaking. The sheet has a good yield and does not require a post-process for impregnating the binder like a synthetic resin binder. However, in the polyvinyl alcohol fibrous binder, since it once dissolves in the hot water in the sheet in the drying step during manufacturing, the binder gradually moves in the outward direction of the sheet thickness in the same step, so-called "migration". Easy to cause.

As a result, a resin puddle is formed on the surface of the sheet, which blocks the eyes of the filter medium to increase the pressure loss and the rigidity of the sheet is lowered due to the lack of binder in the sheet. It is also known that when this is subjected to pleat folding pleating and the filter medium is assembled as a unit, troubles such as cracking, layer peeling, and defective folded mountain shape are caused.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and problems, to obtain a filter material for an air filter which has a high Gurley rigidity, a low pressure loss, and good pleat folding pleating properties, particularly peel strength. Is to provide.

[0005]

SUMMARY OF THE INVENTION The inventor of the present invention maintains the semi-molten state, that is, the morphology of the fiber, although the problem occurs as described above when the fibrous binder is completely melted as in the conventional case. It was found that these problems can be solved by controlling the state and using it as a binder.

That is, the present invention has a basis weight of 25 to 150 g / m.
^{In the} filter material for an air filter composed of the non-woven fabric of ^2, the polyvinyl alcohol fibrous binder for adhering the constituent fibers swells while maintaining the fiber morphology without being completely dissolved, and is present evenly in the thickness direction of the filter material. The present invention relates to a filter material for an air filter, which is characterized.

In a preferred embodiment of the present invention, the fiber diameter of the polyvinyl alcohol fibrous binder after swelling is 7.5 to 110 μm. In another preferred embodiment of the present invention, the fiber diameter of the polyvinyl alcohol fibrous binder is 1.1 to 7.0 times the fiber diameter before swelling. Advantageously, the polyvinyl alcohol fibrous binder in the filter medium is from 0.1 to 10% by weight, based on the weight of the filter medium.

The air filter material of the present invention is advantageously a non-woven fabric composed mainly of glass fibers. The filter material for an air filter is mainly composed of ultrafine glass fibers or chopped glass fibers having an average fiber diameter of 6 μm or less, but if necessary, organic fibers such as polyethylene, polypropylene, polyester, polyaramid, acrylic, vinylon and rayon are blended. May be.

The method of applying the binder in the process of manufacturing the filter material for the air filter includes an external addition method which is applied after forming the fiber sheet and an internal addition method which is added in the step of dispersing the raw material fibers. In the present invention, polyvinyl is used. In order to uniformly disperse the alcohol fibrous binder, it is necessary to carry out the internal addition method. Further, when the filter medium of the present invention is manufactured, the moisture content of the wet paper containing the polyvinyl alcohol fibrous binder before drying needs to be 50 to 80% by weight for the reason described below.

That is, in the filter medium for an air filter of the present invention, raw material fibers are slurried in water, a polyvinyl alcohol fibrous binder is added during this slurrying step, and the resulting slurry is paper-made by a paper machine. Produced by a process characterized in that a wet paper web with a water content of 80% by weight is formed and dried. This method is also the subject of the present invention.

The present invention will be described in more detail below. When the polyvinyl alcohol fibrous binder is used in the internal addition method, when the sheet enters the drying step and the temperature of the water held by the sheet reaches the melting temperature, the fibrous binder is melted from its surface and mixed with other materials. It adheres to the intersections with the fibers and solidifies as the water content of the sheet evaporates, providing strength. At that time, the diameter of the fibrous binder was thickened before and after melting, that is, "swelling" was observed, and the present inventors found that there is a high correlation between this phenomenon and the effect of the present invention.

That is, the diameter of the polyvinyl alcohol fibrous binder in a semi-molten state is 1.1 to 7 times as large as that before the melting, and if the swelling state can be controlled, the fibrous binder migrates in the drying step. I found that it does not cause. When the fibrous binder swells more than 7 times, it completely dissolves and causes migration, and when the degree of swelling is less than 1.1 times, there is almost no dissolved portion,
The binder effect is not exhibited. This swelling state can be observed under an electron microscope, or as described later, by coloring the fibrous binder and observing under a real microscope, and the degree of swelling can be calculated from the relationship with the fiber diameter before swelling. Further, the fibrous binder having a swelling degree of 1.1 times or less does not show fusion at the intersection of the fibrous binder and the glass fiber, or the fibrous binders, when observed with an electron microscope or an actual microscope.

The polyvinyl alcohol fibrous binder used in the present invention usually has a diameter of 7 μm to 15 μm. These are common fibrous binders. By the way, since the number of particles of 15 μm or more is small per unit weight, the number of adhesive intersections is small and the binder effect is low, while those of 7 μm or less are
The production cost of the polyvinyl alcohol fibrous binder increases. These have swelling degrees of 1.1 to 7.
By controlling to 0 times, the effect of the present invention can be exhibited. The swelled diameter of the polyvinyl alcohol fibrous binder can be in the range of 7.5 to 110 μm.

There are various types of polyvinyl alcohol fibrous binders used in the present invention having different structural formulas and melting temperatures, and it is necessary to pay attention to their selection in order to exert the effects of the present invention. Polyvinyl alcohol fibrous binders with various melting temperatures are known, but if the melting temperature of itself is too low, it will completely dissolve in the drying process due to the wet heat effect, causing migration, lowering the rigidity and pressure loss. Will increase. On the other hand, if the melting temperature is too high, the adhesive force between the fibers becomes low and the strength of the filter medium becomes low.

The method for maintaining the shape of the fiber is not particularly limited to one, but for example, it is necessary to pay sufficient attention to the water content of the wet paper. The preferred melting temperature is
The temperature is usually 50 ° C to 80 ° C, although it is selected depending on the drying ability of the paper machine, the conditions, and the like. If the water content is too low, it will not dissolve and the adhesive force between the fibers will decrease, resulting in a low strength of the filter medium. Further, if the water content is too high, it will be completely dissolved, causing migration, lowering the rigidity and increasing the pressure loss. In the present invention, it is desirable that the moisture content of the wet paper sheet immediately before entering the drying step be 50% to 80%, preferably 55% to 70%.

Further, one method is to select a polyvinyl alcohol fibrous binder having a high hot water dissolution temperature. In addition, the polyvinyl alcohol fibrous binder takes a certain amount of time to dissolve in hot water, so that the wet paper web is rapidly heated at a high temperature to quickly remove the moisture, or the drying process is started as described above. Before doing so, sufficiently reduce the water content of the wet paper by press dehydration or vacuum suction,
Examples include a method of drying. However, in any of the methods, if the conditions are too strict, the fibers will not dissolve or expand at all, and the binder effect will not be exhibited.

The content of the polyvinyl alcohol fibrous binder is preferably 0.1% by weight to 10% by weight, more preferably 0.5% by weight to 7% by weight. If the content of the polyvinyl alcohol fibrous binder is less than 0.1% by weight based on the weight of the filter medium, the effect is small, and if it exceeds 10% by weight, the pressure loss of the filter medium for an air filter is significantly increased.

The polyvinyl alcohol fibrous binder can be used alone by the internal addition method to achieve the object of the present invention, but when it is desired to impart water resistance, water repellency and chemical resistance which are usually required for a filter medium. It is desirable to use a synthetic resin binder latex or a water repellent together. The total content of the polyvinyl alcohol fibrous binder in these filter media is 10% by weight or less, preferably 7% by weight or less. Since many synthetic resin binder latexes form a film-like substance between fibers and easily cause an increase in pressure loss, the smaller the amount, the better.

The synthetic resin binder latex is not particularly limited, but examples thereof include acrylic latex, vinyl acetate latex, urethane latex, epoxy latex, SBR latex and NB.
R-based latex, olefin-based latex and the like can be used alone or in combination of two or more kinds, but one having good adhesiveness to the substrate and difficult to form a film-like substance should be selected.

The filter medium of the present invention can be produced by a paper machine for producing general paper or wet non-woven fabric, for example, a wet paper machine such as a Fourdrinier paper machine, a cylinder paper machine or a tilted wire paper machine. A dryer such as a cylinder dryer, a Yankee dryer, a through dryer or an infrared dryer can be used for drying. Further, there is no problem in drying the filter medium of the present invention by using two or more kinds of dryers.

[0021]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The basis weight, sheet thickness, Gurley rigidity, peel strength and pressure loss in the examples and comparative examples were measured by the following methods.

The basis weight and sheet thickness measured in the present invention were measured in accordance with JIS L-1096. For Gurley stiffness, TAPPI STANDARD T5
The measurement was carried out in accordance with 43 pm-84, but the length of the sample was 2.5 inches and the width was 1 inch. The peel strength was measured according to TAPPI UM569.
The pressure loss (Pa) was measured according to JIS B9908, and the ventilation resistance when air was passed through the filter medium at a wind speed of 5.3 cm / sec was measured. The diameter of the polyvinyl alcohol fibrous binder before and after the sheet is dried is determined by the type of paper pulp and its test method (edited by the Japan Paper Pulp Technology Association, “Type of Paper Pulp and Its Test Method”, PVA iodine boric acid test, 1966,
Coloring was performed using p301), and the diameters of the colored fibers were arbitrarily measured with a stereomicroscope, and the average value of the fiber diameters was calculated. Regarding the suitability for pleating, the state of cracking, peeling, and folding when passing through a processing machine was visually determined.

Example 1 90% by weight of ultrafine glass fibers having an average fiber diameter of 6 μm or less and 10% by weight of chopped glass fibers
And polyvinyl alcohol fibrous binder (SPG 056, manufactured by Kuraray Co., Ltd.
(7.3 μm × 3 mm) was disaggregated with a pulper using acidic water having a pH of 3.5 to prepare an aqueous slurry, and a sheet was formed from these slurries using a standard square handmade paper machine. . Acrylic latex (SFA-3
3. Dainippon Ink and Co., Ltd. was applied to the wet paper to make the wet paper have a water content of 55%, and then dried at once with a rotary dryer at 130 ° C., a basis weight of 70 g / m ² , a binder resin content of 6. A sheet having a fiber diameter of the swollen polyvinyl alcohol fibrous binder after sheet drying of 8.1 mm was obtained at 2% by weight.

Example 2: Except that the wet paper has a water content of 70%
Example 1 was repeated. Polyvinyl acetate after sheet drying
The fiber diameter of the lucol fibrous binder is 40 μm,
Basis weight 70g / m ², Binder resin content of 5.8% by weight
I got a card.

Example 3: Polyvinyl alcohol fibrous binder (VPB101 manufactured by Kuraray Co., Ltd .: 12.9 μm)
m x 3 mm) is 6.0% by weight, and the moisture content of the wet paper is 55%
Example 1 was repeated except that Basis weight 70g / m
² , the binder resin content is 6.5% by weight, and the fiber diameter of the polyvinyl alcohol fibrous binder after sheet drying is 1
A 4.2 μm sheet was obtained.

Example 4: Polyvinyl alcohol fibrous binder (VPB101, manufactured by Kuraray Co., Ltd., 12.9 μm)
m × 3 mm) is 6.0% by weight, and the moisture content of the wet paper is 70%
Example 2 was repeated except that Basis weight 70g /
A sheet having m ² and a binder resin content of 6.8% by weight was obtained.
A sheet having a fiber diameter of the polyvinyl alcohol fibrous binder after drying the sheet was 88.7 μm was obtained.

Comparative Example 1: 90% by weight of ultrafine glass fibers having an average fiber diameter of 6 μm or less and 10% by weight of chopped glass fibers
And polyvinyl alcohol fibrous binder (SPG 056, manufactured by Kuraray Co., Ltd.
(7.3 μm × 3 mm) was disaggregated with a pulper using acidic water having a pH of 3.5 to prepare an aqueous slurry, and a sheet was formed from these slurries using a standard square handmade paper machine. . Acrylic latex (SFA-3
3, Dainippon Ink and Co., Ltd.) was applied to the wet paper, the moisture content of the wet paper was set to 35%, and then it was dried at once with a rotary dryer at 130 ° C., the basis weight was 70 g / m ² , and the binder resin content was 6.1. By weight%, a sheet having a fiber diameter of the polyvinyl alcohol fibrous binder after sheet drying of 7.3 μm was obtained.

Comparative Example 2: 90% by weight of ultrafine glass fibers having an average fiber diameter of 6 μm or less and 10% by weight of chopped glass fibers
And a polyvinyl alcohol fibrous binder (SPG 056 manufactured by Kuraray Co., Ltd.
(7.3 μm × 3 mm) was disaggregated with a pulper using acidic water having a pH of 3.5 to prepare an aqueous slurry, and a sheet was formed from these slurries using a standard square handmade paper machine. . Acrylic latex (SFA-3
3, Dainippon Ink and Chemicals, Inc.) was applied to the wet paper, the wet paper had a water content of 95%, and then dried at once with a rotary dryer at 130 ° C., the basis weight was 70 g / m ² , and the binder resin content was 6.8. By weight%, a sheet was obtained in which the polyvinyl alcohol fibrous binder after sheet drying was not in fibrous form.

Comparative Example 3: Example 3 was repeated except that the moisture content of the wet paper was 35%. The fiber diameter of the polyvinyl alcohol fibrous binder after sheet drying is 13 μm,
The resulting sheet had a basis weight of 70 g / m ² and a binder resin content of 6.7% by weight.

Comparative Example 4: Example 3 was repeated except that the wet paper had a water content of 90%. The polyvinyl alcohol fibrous binder after sheet drying is not in fiber form.
The obtained sheet had a basis weight of 70 g / m ² and a binder resin content of 6.9% by weight.

Comparative Example 5: 90% by weight of ultrafine glass fibers having an average fiber diameter of 6 μm or less and 10% by weight of chopped glass fibers
And a polyvinyl alcohol fibrous binder (SPG 056 manufactured by Kuraray Co., Ltd.
(7.3 μm × 3 mm) was disaggregated with a pulper using acidic water having a pH of 3.5 to prepare an aqueous slurry, and a sheet was formed from these slurries using a standard square handmade paper machine. . Acrylic latex (SFA-3
3, Dainippon Ink and Co., Ltd.) was applied to the wet paper to make the wet paper have a water content of 55%, and then dried at once with a rotary dryer at 130 ° C., a basis weight of 70 g / m ² , and a binder resin content of 13.0. By weight%, a sheet having a fiber diameter of the polyvinyl alcohol fibrous binder after drying the sheet of 8.1 μm was obtained.

The physical properties of the sheet are summarized in Table 1.

[0033]

[Table 1]

The filter media shown in Examples 1 to 4 were air filter media having high Gurley rigidity and peel strength, little increase in pressure loss, and good pleating characteristics.

In Comparative Example 1, the pressure loss did not increase, but the Gurley rigidity and peel strength were low, and the pleat pleating processability was poor.

In Comparative Example 2, the pressure loss increased remarkably,
Gurley stiffness and peel strength are low. Also, the pleat processing suitability for pleat folding is poor.

In Comparative Example 3, the pressure loss did not increase, but the Gurley rigidity and peel strength were low. Also, the pleat processing suitability for pleat folding is poor.

In Comparative Example 4, the pressure loss increased remarkably,
Gurley stiffness and peel strength are low. Also, the pleat processing suitability for pleat folding is poor.

In Comparative Example 5, the pressure loss increased sharply,
Gurley rigidity and peel strength are high. Also, the pleat processing suitability for pleat folding is poor.

[0040]

INDUSTRIAL APPLICABILITY The present invention relates to a filter medium for air filters, which is a novel filter medium which does not impair its suitability as a filter medium for air filters by controlling the degree of melting of the polyvinyl alcohol fibrous binder in the internal addition method. Is provided.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomohiko Soyama             3-5-1, Nishi-Zao, Nagaoka-shi, Niigata Hokuetsu             Research Institute of Paper Manufacturing Co., Ltd. F-term (reference) 4D019 AA01 BA04 BB03 CB06 DA10                 4L047 AA05 BA09 BA21 BB03

Claims (6)

[Claims] 1. A filter medium for an air filter comprising a nonwoven fabric having a basis weight of 25 to 150 g / m ² , wherein the polyvinyl alcohol fibrous binder for adhering the constituent fibers swells while maintaining the fiber morphology without being completely dissolved. A filter medium for an air filter, characterized by being uniformly present in the thickness direction. 2. The filter medium for an air filter according to claim 1, wherein the swollen polyvinyl alcohol fibrous binder according to claim 1 has a fiber diameter of 7.5 to 110 μm. 3. The fiber diameter of the polyvinyl alcohol fibrous binder after swelling according to claim 1 is 1.
The filter material for an air filter according to claim 1, which is 1 to 7 times. 4. The polyvinyl alcohol fibrous binder in the filter medium is 0.1 to 10% by weight based on the weight of the filter medium.
The filter material for an air filter according to any one of claims 1 to 3, which is 5. The filter medium for an air filter according to claim 1, wherein the filter medium for an air filter is a non-woven fabric mainly composed of glass fibers. 6. The method for producing a filter medium for an air filter according to claim 1, wherein raw material fibers are slurried in water, and a polyvinyl alcohol fibrous binder is added during the slurrying step. Then, the resulting slurry is subjected to papermaking with a paper machine to form a wet paper having a water content of 50 to 80% by weight and drying.