JP4990203B2 - Air filter medium for hot emboss molding and air filter using the same - Google Patents

Description

The present invention relates to a filter medium for air filters, particularly semiconductor, liquid crystal, bio-food industry related clean rooms, clean benches, etc., air filters for building air conditioning, and air emboss moldable air filter filter media. And an air filter using the filter medium.

  Conventionally, in order to efficiently collect submicron or micron particles in the air, an air filter collecting technique is used. Air filters are broadly classified into coarse dust filters, medium performance filters, HEPA filters, ULPA filters, etc., depending on the target particle size and dust removal efficiency. Many of these air filters use non-woven fabric, woven fabric, mat-like fiber layer air filter media, especially non-woven glass fiber air filter media for medium performance filters, HEPA filters, and ULPA filters. Is often used. This originates in the characteristic of the pressure loss and the collection efficiency which are the basic performance of an air filter in addition to the nonflammability which glass fiber has.

  Usually, in order to increase the filtration area, a filter medium for an air filter is used as an air filter by placing a pack pleated in a zigzag shape with a valley in an aluminum frame, a wooden frame, or the like. Here, if the pleated filter media come into contact with each other, structural resistance will occur during ventilation, so insert a separator made of aluminum plate, paper, etc., or attach a hot melt ribbon, thread, etc. By holding the filter medium, the filter media are prevented from contacting each other directly.

  A method different from this is proposed in which a heat embossing process is performed on the air filter medium to form a shallow recess in the filter medium, and this is used as a spacer (Patent Document 1, Patent Document 2, and Patent Document 3). .

  When this method is used, the air filter can have a large filtration area, and at the same time, the structural resistance due to the separator and the spacer can be reduced, so that the air filter can be reduced in pressure loss.

  However, since the air filter medium is directly molded to give a dent, there are problems that the depth of the embossment is not sufficient and the filter medium is cracked or cracked depending on the heat processing method and conditions of the heat processing machine. It was. This effect is small when organic fibers, especially thermoplastic synthetic fibers, are used as the fibers that make up the air filter medium, but this problem is not the case when the filter medium is composed of glass fibers that are rigid and brittle. Is serious. A hot embossing method for solving this problem has been proposed (Patent Documents 4 and 5).

  However, on the other hand, improvement in workability such as emboss depth is also demanded for air filter media. However, as a result of investigations by the present inventors, the sheet of the filter material for air filter is preheated at a predetermined temperature, and if it is embossed immediately after processing, a "return phenomenon" of the embossed portion occurs during the subsequent cooling. It turned out that the depth of an embossing part will become shallow. This is presumably because a force to restore the filter material sheet to its original state by the strain energy of the embossed part worked until the filter medium sheet was allowed to cool and the surface temperature cooled to room temperature. Since the emboss depth is shallow, the number of pleats in the completed air filter becomes too large, and the filter does not become as designed. For this reason, measures such as increasing the preheating temperature and increasing the height of the embossing roll protrusions were taken, but there were problems such as increased running costs and excessively high protrusions that could break the embossed part. It was.

  In addition, the air filter may be used in a high-temperature atmosphere, and even at this time, the embossed part depth “return phenomenon” occurs, and the pressure loss of the air filter increases over time, making it unusable. There was a problem.

Therefore, there is a need for improvements on these issues.
JP-A-3-101804 Japanese Patent Laid-Open No. 3-196805 (Japanese Patent No. 2935432) Japanese Patent Laid-Open No. 3-196807 (Japanese Patent No. 2935433) JP 09-212269 (Patent No. 2865606) Japanese Patent Laid-Open No. 09-212270 (Patent No. 2865607)

  An object of the present invention is to provide a filter medium for an air filter that can be embossed at low cost, and even if the protrusion is high, the embossed part is not torn and the embossing processability is better than before. To provide a filter medium for an air filter that suppresses an increase in pressure loss over time when an air filter using the present filter medium that does not cause a phenomenon is used in a high-temperature atmosphere of 70 ° C., and an air filter using the filter medium. It is.

This invention is a filter medium for an air filter whose main fiber is glass fiber, whose composition is 97 to 90% by mass of fiber mainly composed of glass fiber and 3 to 10% by mass of thermoplastic binder having a glass transition temperature of 80 ° C. or more . And the decreasing rate of the storage elastic modulus in 80 degreeC with respect to the storage elastic modulus in 40 degreeC of the said filter medium shall be 5% or less. Further, the thermoplastic binder is a thermoplastic resin having a glass transition temperature of 80 ° C. or higher. Further, the filter medium for air filter was hot embossed and pleated to prepare a filter cartridge, and then a 70 ° C. hot air was applied at a surface wind speed of 2.5 m / sec. Even if it ventilates on the conditions of this, it is set as the structure where an embossing molding part does not return.

  By using the filter medium for an air filter of the present invention, the embossing processability is better than the conventional one because the embossed part is not torn even at a low cost even if the protruding part is high. Since there is no need to use separators, spacers, etc., and this “return phenomenon” does not occur, the pressure over time when an air filter using this filter medium is used in a high-temperature atmosphere of 70 ° C. Loss increase can be suppressed.

The filter medium for an air filter of the present invention is a filter medium for an air filter mainly composed of glass fibers, and the structure is composed of 97 to 90% by mass of glass fibers and 3 to 10% by mass of a thermoplastic binder having a glass transition temperature of 80 ° C. or higher. Is done. Since the filter medium for air filters using glass fiber as the main fiber has a very low strength even if it is made of glass fiber alone, it usually has a predetermined strength by adding an organic binder. In addition to the above-described strength properties, the air filter medium for embossing processing needs to have a thermoforming function in this binder. With glass fiber alone, the sheet cannot be embossed even if hot embossing is performed, or it can be broken by processed protrusions / edge portions. Only when a binder having a thermoforming function is added to glass fiber, the thermal fluidity of the sheet is manifested. Therefore, a binder that is thermoplastic is used. In order to perform thermoforming without any problem, it is necessary to blend 3% by mass or more of a binder, and the higher the binder content, the better the heat flow characteristics. However, increasing the binder adversely deteriorates the incombustibility and flame retardancy of the filter medium, so a blending ratio of 10% by mass or less is desirable. More preferably, it is 4-7 mass%.

  Here, as a result of intensive studies by the present inventors, the "return phenomenon" of the filter medium at the time of embossing molding and when the air filter is used in a high-temperature atmosphere is the result of measuring the filter medium with a dynamic viscoelastic device It was found that there is a relationship with the storage elastic modulus of the formula (1) obtained by

Storage elastic modulus E '= | σ / ε | cosδ (1)
In the formula, σ means stress, ε means strain, and δ means phase difference.

  In general, when a sinusoidal stress is applied to a polymer material, the strain has the same frequency and the phase has a sine waveform delayed by δ. Storage modulus is a measure of the energy stored and fully recovered per cycle and can be considered as an elastic element of matter. That is, the larger the storage elastic modulus, the stronger the force that pushes back when a force is applied.

When the temperature of the filter medium is increased by heating, the thermoplastic binder softens and the storage elastic modulus decreases. At the time of hot embossing, after preheating so that the surface temperature of the filter medium is usually 100 to 200 ° C., embossing is performed using an embossing roll or the like. Since a certain amount of time is required for the cooling time until the surface temperature of the filter medium after processing returns to room temperature, the aforementioned “return phenomenon” occurs before the filter medium hardens from the softened state. The inventors have newly found that the “return phenomenon” can be suppressed when the difference in storage modulus between 40 ° C. and 80 ° C. is small. Specifically, the rate of decrease in storage elastic modulus at 80 ° C. relative to the storage elastic modulus at 40 ° C. of the filter medium for air filter (hereinafter abbreviated as “the rate of decrease in storage elastic modulus”) is preferably 5% or less. . When the rate of decrease in the storage elastic modulus is 5% or more, the “return phenomenon” clearly starts to occur, and thus the emboss depth becomes shallow. More preferably, it is 3% or less. Further, the absolute value of the storage elastic modulus is not particularly limited in the present invention, but if the storage elastic modulus at 40 ° C. is too low, the softening state until the filter medium surface temperature after processing returns to room temperature continues for a long time. ”Is likely to occur, and is preferably at least 1.0 × 10 ⁸ Pa or more. More preferably, it is 5.0 × 10 ⁸ Pa or more.

    In the air filter medium, the method of reducing the storage elastic modulus reduction rate to 5% or less is not limited to one, but it is particularly effective to set the composition of the thermoplastic binder of the air filter medium to a glass transition temperature of 80 ° C. or higher. Is the method. By increasing the glass transition temperature to 80 ° C or higher, the glass-like state of the filter medium is maintained at a relatively high temperature, so that the so-called thermal responsiveness that solidifies immediately before the "return phenomenon" during cooling is good. The depth of the embossed part is maintained as set. The index of the glass transition temperature of 80 ° C. is an empirical value obtained as a result of the study by the present inventors.

  The above-mentioned thermoplastic binder having a glass transition temperature of 80 ° C. or higher is styrene-acrylate resin, acrylate resin, vinyl acetate resin, ethylene vinyl acetate resin, polyester resin, polyvinyl chloride resin, polyvinylidene chloride resin, urethane resin. Etc. Of these, styrene-acrylic ester resins are particularly preferred. Styrene-acrylic acid ester resins have particularly good thermal fluidity and thermal responsiveness among the above resins, and it is considered that the “return phenomenon” hardly occurs.

  Styrene-acrylic acid ester resin is a resin composed of a combination of styrene monomer and ethyl acrylate monomer, a combination of styrene monomer and butyl acrylate, a combination of styrene monomer and 2-ethylhexyl acrylate, etc. Can be mentioned. The glass transition temperature varies slightly depending on the molecular weight of the resin, the degree of crosslinking, the degree of crystallinity, etc., but it varies most depending on the copolymer composition, and the glass transition temperature of the homopolymer constituting the basic skeleton and the monomer Theoretically calculated from the weight fraction using the Fox equation. From this, the composition ratio (weight fraction) of the styrene monomer at a glass transition temperature of 80 ° C. or higher is 83.7% or higher, 87.0% or higher, or 88.2% or higher in the above order as a theoretical calculation value. It becomes. Further, if the effect of the present invention is not changed, each monomer component such as methyl methacrylate, acrylonitrile, ethyl methacrylate, vinyl acetate, butyl methacrylate, -COOH group, and other functional groups are added to these basic skeletons. You may use together suitably for the purpose of changing.

  The glass fiber used as the main fiber in the present invention can be freely selected from ultrafine glass fibers and chopped glass fibers having various fiber diameters and fiber lengths according to required filtration performance and other physical properties. In particular, the ultrafine glass fiber is a woolen glass fiber manufactured by a flame stretching method or a rotary method, and is an essential component for maintaining the pressure loss of the filter medium at a predetermined value and achieving an appropriate collection efficiency. As the fiber diameter becomes smaller, the collection efficiency becomes higher. Therefore, in order to obtain a high-performance filter medium, it is necessary to blend ultrafine glass fibers having a fine average fiber diameter. However, since the pressure loss may increase excessively when the fiber diameter is reduced, an appropriate fiber diameter should be selected within this range. In addition, you may blend and mix the thing of several types of fiber diameters. Moreover, low boron glass fiber and silica glass fiber can also be used for the purpose of preventing boron contamination of silicon wafers in semiconductor process applications. Further, natural fibers, organic synthetic fibers, and the like may be blended in the glass fiber as a secondary material within a range that does not affect the embossing processability. The blending ratio is desirably 20% by mass or less in the main fiber, and more desirably 10% by mass or less.

  The filter medium for an air filter of the present invention can be obtained using the following production method or the like. That is, the glass fibers constituting the filter medium are dispersed in water using a dispersing machine such as a pulper, and the slurry is subjected to wet paper making with a paper machine to obtain a wet paper. Next, there is a method in which the binder of the present invention is adhered to the aforementioned wet paper and then dried. Moreover, even if these treatment liquids are applied to dry paper once dried with wet paper, the effect does not change.

  In the raw fiber dispersion step, in order to improve the dispersibility, a method of adjusting to pH 2 to 4 with sulfuric acid acid is preferable, but a surfactant such as a dispersant having a neutral pH may be used. Further, in order to impart water repellency and / or flame retardancy, it is possible to add a water repellant and / or a flame retardant to the binder liquid within the scope of the object of the present invention.

  The method for applying the binder liquid is not particularly limited, but is a method in which wet paper or dry paper is immersed in the binder liquid, a method in which the binder liquid is sprayed on the wet paper or dry paper, and the binder liquid is adhered to the roll. Examples thereof include a method of transferring to wet paper or dry paper.

As a drying method, a hot air dryer, a roll dryer or the like is used, and a drying temperature of 120 ° C. or higher, preferably 140 ° C. or higher is desirable.
[Example]

Next, although an Example and a comparative example demonstrate this invention more concretely, this invention is not limited at all by this.
As an example of the heat embossing method of the air filter medium of the present invention, as shown in FIG. 1, the air filter medium is heated at a heating station and passes through an embossing marking roll. This continuously forms embossing and marking (= folding lines). It has been found that the air filter medium of the present invention has a surface temperature of 150 to 175 ° C. before passing through the embossing marking roll, and cracks and cracks are generated in the embossed molded part at temperatures lower than 150 ° C.
In addition, as a method of heating the air filter medium, a roll heated by electric heat, steam, or a press die may be passed.

65% by mass of ultrafine glass fiber with an average fiber diameter of 0.65 μm, 30% by mass of ultrafine glass fiber with an average fiber diameter of 2.70 μm, 5% by mass of chopped glass fiber with an average fiber diameter of 6 μm, concentration of 0.5% by mass, sulfuric acid acidity Disaggregation using a mixer at pH 3.5. Subsequently, paper was made using a hand-drawing apparatus to obtain wet paper. Next, a commercial product A of an emulsion product having a composition of polystyrene-ethyl acrylate resin at a glass transition temperature of 85 ° C. is diluted to an aqueous solution having a solid concentration of 2.0% by mass, and this is applied to the wet paper as a binder liquid. Then, it was dried with a hot air dryer at 120 ° C. to obtain a filter medium for an air filter having a basis weight of 70 g / m ² and a binder adhesion amount of 6.0% by mass.

In Example 1, instead of the commercial product A of the emulsion product, the commercial product B of the emulsion product composed of polystyrene-ethyl acrylate resin at a glass transition temperature of 86 ° C. was diluted to an aqueous solution with a solid content concentration of 2.0% by mass. A filter medium for an air filter having a basis weight of 70 g / m ² and a binder adhesion amount of 6.0% by mass was obtained in the same manner as in Example 1 except that this was used as a binder liquid.

In Example 1, instead of the commercial product A of the emulsion product, the commercial product C of the emulsion product composed of polystyrene-ethyl acrylate resin at a glass transition temperature of 92 ° C. was diluted to an aqueous solution with a solid content of 2.0% by mass. A filter medium for an air filter having a basis weight of 70 g / m ² and a binder adhesion amount of 5.9% by mass was obtained in the same manner as in Example 1 except that this was used as a binder liquid.
[Comparative Example 1]

In Example 1, instead of the commercial product A of the emulsion product, the commercial product D of the emulsion product having a composition of polystyrene-ethyl acrylate resin at a glass transition temperature of 75 ° C. was diluted to an aqueous solution with a solid content of 2.0% by mass. A filter medium for an air filter having a basis weight of 70 g / m ² and a binder adhesion amount of 5.9% by mass was obtained in the same manner as in Example 1 except that this was used as a binder liquid.
[Comparative Example 2]

In Example 1, instead of the commercial product A of the emulsion product, the commercial product E of the emulsion product having a composition of polystyrene-ethyl acrylate resin at a glass transition temperature of 60 ° C. was diluted to an aqueous solution with a solid content of 2.0% by mass. A filter medium for an air filter having a basis weight of 70 g / m ² and a binder adhesion amount of 6.1% by mass was obtained in the same manner as in Example 1 except that this was used as a binder liquid.
[Comparative Example 3]

In Example 1, instead of the commercial product A of the emulsion product, the commercial product F of the emulsion product composed of polystyrene-ethyl acrylate resin at a glass transition temperature of 35 ° C. was diluted to an aqueous solution with a solid content concentration of 2.0% by mass. A filter medium for an air filter having a basis weight of 70 g / m ² and a binder adhesion amount of 5.9% by mass was obtained in the same manner as in Example 1 except that this was used as a binder liquid.

In Example 1, the blended raw material of Example 1 was disaggregated using 10 m ³ pulper disperser in sulfuric acid acidic pH 3.5 water. Next, paper is continuously produced by a paper machine, and a binder liquid obtained by diluting the commercial product A of the emulsion product of Example 1 to an aqueous solution having a solid content of 2.0% by mass is applied to the wet paper obtained by paper making. Was dried with a roll dryer at 120 ° C. to prepare a wound product of a continuous sheet of filter media for an air filter having a basis weight of 80 g / m ² , a binder adhesion amount of 6.0% by mass and a width of 610 mm and a length of 300 m. Next, a filter cartridge was prepared by the hot embossing method shown in FIG. 1, and this filter cartridge was fitted into an aluminum support frame to produce an air filter of the present invention having outer dimensions of 610 mm, a width of 610 mm, and a depth of 292 mm.
[Comparative Example 4]

In Example 4, instead of the commercial product A of the emulsion product, the commercial product E of the emulsion product having a composition of polystyrene-ethyl acrylate resin at a glass transition temperature of 60 ° C. was diluted to an aqueous solution with a solid content of 2.0% by mass. In the same manner as in Example 4 except that this was used as a binder liquid, a wound product of a continuous filter medium for air filter having a basis weight of 70 g / m ² and a binder adhesion amount of 6.1% by mass was obtained. Next, a filter cartridge was prepared by the same hot embossing method as in Example 4, this filter cartridge was fitted into the same aluminum support frame as in Example 4, and processed by a filter medium molding device for air filter. An air filter having a length of 610 mm, a width of 610 mm, and a depth of 292 mm was prepared.

  In addition, the glass transition temperature in these Examples and Comparative Examples is a manufacturer's nominal value.

  The physical properties of Examples and Comparative Examples were evaluated by the following methods.

(1) Filter media pressure loss About the filter media of Examples 1 to 3 and Comparative Examples 1 to 3, the pressure loss when passing through a filter paper with an effective area of 100 cm ^{2 at} a surface wind speed of 5.3 cm / sec. Measured with a differential pressure gauge.

(2) 0.3 μm filter medium DOP permeability For the filter mediums of Examples 1 to 3 and Comparative Examples 1 to 3, air containing polydisperse DOP particles generated by a Ruskin nozzle was applied to filter paper having an effective area of 100 cm ² with a surface wind speed of 5 The transmittance of DOP was measured by using a laser particle counter manufactured by Rion Co., Ltd. from the number ratio of upstream and downstream when ventilated at 3 cm / sec. The target particle size was 0.3 μm, and the transmittance was determined from the geometric mean of the particle size classification 0.2-0.3 μm transmittance and 0.3-0.4 μm transmittance.

(3) Storage elastic modulus and decrease rate of storage elastic modulus About the filter media of Examples 1 to 3 and Comparative Examples 1 to 3, an 8 × 40 mm test piece was cut out from a sample, and a viscoelasticity measuring device (DMS210 manufactured by Seiko Instruments Inc.) was used. The temperature was raised from the initial 28 ° C., and the storage elastic modulus at 40 ° C. and 80 ° C. was measured.
Further, from these measured values, the rate of decrease in storage elastic modulus was also obtained by calculation.

(4) Embossing evaluation In order to evaluate the return of the embossed part at the time of processing a filter medium, two types of concave and convex molds having a width of 10 mm, a length of 70 mm, a depth of 2 mm, a width of 10 mm, a length of 70 mm, and a depth of 3 mm are used. The filter media of Examples 1 to 3 and Comparative Examples 1 to 3 were prepared and sandwiched between concavo-convex molds heated to 150 ° C., and pressurized at a predetermined pressure for 5 seconds. The embossing at this time was evaluated by visual evaluation with ○ (withstanding practical use), Δ (not withstanding practical use), and × (not withstanding practical use).

(5) Evaluation of air filter embossing For the air filters of Example 4 and Comparative Example 4, hot air at 70 ° C. was applied with a surface wind speed of 2.5 m / sec. Measure the depth of the embossed part before and after 48 hours of ventilation under the above conditions, and evaluated that the emboss depth did not change as ○ (withstands practical use), and the shallower as x (not into practical use). .

実施例１、２、３と比較例１、２、３との比較によれば、ガラス転移温度８０℃未満では、貯蔵弾性率の低下率が５％以上と大きく、ガラス転移温度７５℃である比較例１のエンボス評価では、エンボス深さ２ｍｍでやや不良程度であったが、更に厳しい深さ３ｍｍでエンボスの戻り現象が顕著であった。また、更にガラス転移温度の低い比較例２，３では、エンボス深さ２ｍｍと３ｍｍでともにエンボスの戻り現象が顕著であった。一方、本発明のガラス転移温度８０℃以上である実施例１、２及び３では、貯蔵弾性率の低下率が５％以下であり、エンボスの戻り現象が見られず、本発明の効果のあることが分かる。

According to the comparison between Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3, when the glass transition temperature is less than 80 ° C., the decrease rate of the storage elastic modulus is as large as 5% or more, and the glass transition temperature is 75 ° C. In the embossing evaluation of Comparative Example 1, although the embossing depth was 2 mm, it was slightly poor, but the embossing return phenomenon was remarkable at a more severe depth of 3 mm. Further, in Comparative Examples 2 and 3 having a lower glass transition temperature, the embossing return phenomenon was remarkable at both emboss depths of 2 mm and 3 mm. On the other hand, in Examples 1, 2 and 3 having a glass transition temperature of 80 ° C. or higher according to the present invention, the reduction rate of the storage elastic modulus is 5% or less, the embossing return phenomenon is not observed, and the present invention is effective. I understand that.

  According to a comparison between Example 4 and Comparative Example 4, the air filter of Example 4 using a filter medium having a storage elastic modulus reduction rate of 5% or less to which a binder having a glass transition temperature of 80 ° C. or higher was applied was 70 ℃ hot air was applied to the surface wind speed 2.5m / sec. It can be seen that the embossing return phenomenon does not occur after ventilating under the above conditions. On the other hand, in the air filter of Comparative Example 4, the emboss depth is shallow, and it can be seen that the emboss return phenomenon is remarkable.

These are the perspective views of the filter medium cartridge manufacturing apparatus for air filters in embodiment of this invention. These are the perspective views of the embossing marking roll part in the filter medium cartridge manufacturing apparatus for air filters in embodiment of this invention. These are the graphs of the storage elastic modulus measurement data of the filter medium in Example 1. These are the graphs of the storage elastic modulus measurement data of the filter medium in Comparative Example 2.

Explanation of symbols

A: Filter media supply station
B ... Heating station
C ... Embossing marking station
D ... Cooling station
E ・ ・ ・ Adhesive application station
F ... Filter media width cutting station
G ・ ・ ・ Pleating station
I ... Curing station
J: Constant length cutting station

Claims (3)

The filter medium for an air filter using glass fiber as a main fiber, the constitution of which is 97 to 90% by mass of fiber mainly composed of glass fiber and 3 to 10% by mass of a thermoplastic binder, and the storage elasticity of the filter medium at 40 ° C. For an air filter for hot embossing processing , characterized in that the rate of decrease in storage modulus at 80 ° C. relative to the modulus is 5% or less, and the thermoplastic binder is a thermoplastic resin having a glass transition temperature of 80 ° C. or higher Filter media. 2. The air filter medium for hot emboss molding according to claim 1, wherein the thermoplastic resin is a styrene-acrylate resin. After the claim 1 or 2 medium for an air filter according to create a filter cartridge with hot embossing molding, a hot air of 70 ° C. face velocity 2.5 m / sec. The air filter is characterized in that the embossed part does not return even when ventilated under the conditions described above.

Images