JPS62225218A - Production of filter medium - Google Patents

Abstract

PURPOSE:To control an increase in the initial pressure drop of the titled medium and to obtain a medium-performance filter medium for an air filter provided with a high a layer-to-layer adhesive property by overlapping a staple web cong. hot-melt fibers on an electret raising nonwoven fabric, and hot-pressing both materials. CONSTITUTION:A staple web contg. at least 30% hot-melt fiber and having <=0.05% fiber packing rate is overlapped on an electret raising nonwoven fabric composed of whiskery fibrous fluff having at least 3mm length from the surface of the nonwoven fabric and raised over the whole surface of the nonwoven fabric. When both materials are overlapped with the raising surface of the nonwoven fabric as the adhesion surface, the raising fluff eats into the staple web, the respective fibers are tangled with each other, and a layer-to-layer adhesive property stronger than the surface adhesion by the mere melting due to hot pressing can be obtained. Hot press is carried out at <=1kg/cm<2> pressure and at a temp. lower than the m.p. of the electret raising nonwoven fabric and higher than the m.p. of the hot-melt fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a filter medium, and more specifically, to a method for manufacturing a filter medium, and more specifically to a method for producing a multilayer P material with improved interlayer adhesion of a medium-performance air filter medium used for various types of air purification. It is related to the manufacturing method.

[Prior art]

In recent years, there have been attempts to apply electret nonwoven fabrics as filter media for medium-performance air filters.

Electret nonwoven fabric attempts to attract and collect dust using permanently charged electrostatic force, and even if low basis weight and low fiber filling rate are used to achieve low pressure loss, it still exhibits high collection efficiency. However, on the other hand, there was a problem that the rigidity as a filter medium was insufficient. In order to improve this lack of rigidity, it is possible to polymerize a highly rigid nonwoven fabric with a high fiber filling rate to a low basis weight electret nonwoven fabric and bond it with liquid adhesive, powdered adhesive, heat-sealable fiber, etc. Methods such as bonding by welding using sound waves or high frequencies were used. However, when the interlayer adhesion is increased using the above adhesive method,
This was not an excellent bonding method because it required a large amount of adhesive and increased the welding area, resulting in increased pressure loss.

[Problem that the invention seeks to solve]

Currently, filter media manufactured using such bonding methods tend to emphasize low pressure loss, so the interlayer adhesion of the P material is sacrificed to some extent, and delamination may occur during the bending process of the P material. There is a problem that arises.

The present invention was made as a result of intensive studies in order to solve such problems, and provides a method for manufacturing a medium-performance p-material for air filters that suppresses the increase in initial pressure loss of the filter medium and provides high interlayer adhesion. This is what we intend to provide.

[Means to solve the problem]

The present invention relates to a method for producing a filter medium, which comprises polymerizing a short fiber web containing heat-fusible fibers and an electret raised nonwoven fabric, and then thermocompression bonding.

In the present invention, the raised electret nonwoven fabric is not a loop-shaped continuous fiber, but is a whisker-like fiber fluff having a length of at least 311 m or more from the surface of the nonwoven fabric, and is raised over the entire surface of the nonwoven fabric. It is something that exists.

In the present invention, the electret nonwoven fabric is raised by a raising machine such as a wire raising machine, an emery raising machine, or a brushing machine (brush roll).

In the present invention, a short fiber web containing heat-fusible fibers is a short-fiber web having a heat-fusible fiber content of at least 30% and a fiber filling rate of 0.05% or less. The content of heat-fusible fibers is more preferably 50% or more, and may be 100% in some cases.

When such an electret raised nonwoven fabric is polymerized with a short fiber web containing heat-fusible fibers using the raised surface as an adhesive surface, the raised fluff bites into the short fiber web containing heat-fusible fibers, causing the fibers to become entangled with each other. Therefore, in addition to surface adhesion between fibers due to mere melting, stronger interlayer adhesion can be obtained due to the physical anchoring effect.

In the present invention, thermocompression bonding refers to forming the F material at a pressure of IKp/cd or less at a temperature below the melting point of the fibers of the electret raised nonwoven fabric and above the melting point of the heat-sealable fibers. Examples of this method include conventionally used hot plate pressing and a method in which the P material is sandwiched between porous materials and hot air is passed through.

Furthermore, the material of the nonwoven fabric to be processed into electret may be of a known type, and includes fibers obtained from insulating polymers, such as polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, and polyester fibers, but is preferred. is polypropylene fiber.

In the present invention, the fibers used in the short fiber web to be superposed on the electret raised nonwoven fabric include natural fibers and synthetic fibers in the form of short fibers such as polyester staple, cotton, polynosic, and polyacrylonitrile. Examples of heat-fusible fibers include fibers made of composites of different types of synthetic polymers with different melting points, such as fibers made of polypropylene/polyethylene, polyester/modified polyester, etc. in a sheath core type or bimetal type composite.

In the present invention, the raised nonwoven fabric may be processed to become an electret before or after heat fusion bonding, or may be processed to become an electret before or after thermocompression bonding.

(Example〕 Next, the present invention will be explained in detail with reference to Examples.

Example 1 A 3-denier polypropylene spunbond nonwoven fabric (fabric weight ff 140P/rrt) was brushed using a synthetic fiber brushing machine to create fluff with an average fiber length of 15 mm.

3 denier core/sheath (sheath core) on the raised surface of this nonwoven fabric
Webs of 6-denier polyester short fibers (805F-/I) having a structural heat-fusible fiber content of 80% were overlapped and thermocompression bonded at a hot plate temperature of 145°C. Then,
The spunbond nonwoven fabric was subjected to charging treatment by corona discharge for 20 seconds with an applied DC voltage of -20 KV and a distance of 10 m between the electrodes to form an electret, thereby creating a p material (Example 1) according to the present invention. The p material of Example 1 was
The interlayer peel strength was measured in accordance with 116. The results are shown in Table 1.

For comparison, Table 1 shows that the spunbond nonwoven fabric used in Example 1 was not brushed and the content of heat-sealable fibers with a core-sheath structure of 3 denier was 80% as in Example 1. A certain 6 denier polyester short fiber web (80P/ld
), thermocompression bonded at a hot plate temperature of 145°C, and then subjected to electret treatment to create Comparative Example 1.

The peel strength of the member of Comparative Example 1 was measured in the same manner as in Example 1, and the results are shown in Table 1.

Table 1 The P material of Comparative Example 1 has a width of 130++g+ and easily peels between layers when folded by hand, whereas the filter material of Example 1 could be folded without any problems.

Example 2 A 0.07 denier polypropylene ultrafine fiber nonwoven fabric (fabric weight 1i155'/rrt) produced by melt blow spinning was brushed by rubbing with a synthetic fiber brush roll to create fluff with an average fiber length of 8 m.

This non-woven fabric is coated with a short fiber web (100%
F/yf) was polymerized and thermocompression bonded at a hot plate temperature of 140°C to create the filter medium of Example 2.

For comparison, a filter medium of Comparative Example 2 was created with the same configuration as Example 2 without raising the ultrafine fiber nonwoven fabric used in Example 2.

Next, in the same manner as in Example 1, the interlayer peel strength of Example 2 and Comparative Example 2 was measured.

The results are shown in Table 2.

Table 2 In the P material of Example 2, material breakage occurred in the ultrafine fiber nonwoven fabric in the 180° peel test. Since the tensile strength at break of this microfiber nonwoven fabric was 800P/25m width, it is thought that the peel strength was higher than this value.

Example 3 8 denier polypropylene spunbond nonwoven fabric (basis weight fi 30P/i) was made with an emery raising machine to create an average fiber length of 5 m.
It has a brushed finish. This non-woven fabric is a short fiber web of 100% heat-sealable fibers with a core-sheath structure of 6 denier <80P/d)
was polymerized and thermocompression bonded at a hot plate temperature of 150°C. For comparison, Comparative Example 3 was prepared using the same configuration and manufacturing method as Example 3 without raising the nap.Next, the peel strength of Example 3 and Comparative Example 3 was measured in the same manner as Example 1. The results are shown in Table 3.

Table 3 When the filter medium of Example 3 was folded to a width of 308 mm using an accordion pleat machine, no peeling between the layers of the filter medium was observed. On the other hand, in material F of Comparative Example 3, delamination occurred between the spunbond nonwoven fabric and the thermocompression bonding layer of heat-sealable fibers during the folding process, and continuous folding process was not possible.

Claims (1)

[Claims] 1. A method for producing a filter medium, which comprises polymerizing an electret raised nonwoven fabric and a short fiber web containing heat-fused fibers and bonding them under heat.