JPH05220313A - Filter - Google Patents

Abstract

PURPOSE:To prolong the filtration life and to improve the filtration accuracy and shape holding property by laminating extra fine composite fibers obtained by melt spinning in a density-gradient type, thermally bonding the nodes of fibers, roughing the filtration surface and further reinforcing the filter with a reinforcing material. CONSTITUTION:Two or more kinds of thermoplastic resins having >=20 deg.Cm.p. difference are melt-spun, this filter consists of the obtained extrafine composite fiber having <=10mum average fiber diameter, and the fibers are thermally bonded. At least one surface is roughed, and the density is graded in the thickness direction of the filter. The extra fine composite fibers are laminated while changing the density gradient in the thickness direction of the filter, when the filter is formed. A reinforcing material is provided on one or both surfaces of the filter or in the filter. Accordingly, microfiltration can be performed by this filter, the filtration life is prolonged, the strength is increased, and the shape is satisfactorily held.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter for microfiltration having a long filtering life, which is composed of ultrafine composite fibers obtained by a composite melt-blow spinning method and has a filtering surface formed in an uneven shape.

[0002]

2. Description of the Related Art A filter using ultrafine fibers obtained by a melt blow method has a high filtering accuracy, so that it can be used as a liquid prefilter used in the manufacture of pharmaceuticals and electronic devices, or as an air filter for clean rooms. -Adopted as such. Japanese Patent Laid-Open No. 58-89924 discloses a density gradient type in which a plurality of webs having different fiber diameters produced by a melt blow method are once made into a nonwoven fabric by a spunlace method or a thermal calendering method, and the nonwoven fabrics are laminated in the order of the fiber diameters. Is disclosed. Since this filter is of the density gradient type, it has the advantage of good filtration accuracy. On the other hand, when the non-woven fabric used as the filtering material is made by the spunlace method, the fibers are simply entangled with each other, so that the fibers may fall off during the filtration process, or the strength and shape retention may be insufficient. In addition, there is a problem that the thermal calendering method causes short film life due to film formation due to melting of fibers in the thermocompression bonding process, nonuniform pore size, etc., resulting in short filtration life and poor stability of filtration accuracy. ..

Japanese Patent Laid-Open No. 59-80313 discloses a density gradient type in which the mixing ratio of a mixed fiber composed of a fine-fineness fiber, a large-fineness fiber, and a heat-fusible fiber is sequentially changed, and the fibers are heated to each other. A filter bonded by fusing fibers is disclosed. However, the fine fiber used in this filter is a staple having a single yarn fineness of about 1 denier obtained by an ordinary spinning method, and the filtration accuracy is inferior at most about 20 μm. It cannot be used as a filter. Japanese Unexamined Patent Publication (Kokai) No. 53-114976 discloses a non-woven fabric composed of heat-fusible conjugate fibers obtained by a normal composite spinning method, and Japanese Unexamined Patent Publication (Kokai) 1-224021 discloses an ultrafine fiber obtained by an ordinary melt-blowing method. A filter is disclosed in which a nonwoven fabric made of fibers is formed into a wavy shape. Further, Japanese Patent Application Laid-Open No. 60-99057 discloses that
Disclosed is a mask formed of a non-woven composite fiber obtained by a composite melt-blow spinning method using two kinds of thermoplastic resins having different melting points, and a non-woven fabric in which the intersections of the fibers are heat-sealed is formed along the face. There is. However, the filters, masks, and the like disclosed in the above-mentioned publications, whether they use ordinary thick fineness staples or melt-blown ultrafine fibers, are not suitable for thermocompression bonding. There is a problem that the filtration life and the filtration accuracy are inferior due to the fact that there are drawbacks such as the formation of a film due to the melting of the fibers and the non-uniformity of the pore size, or that the fiber is not a density gradient type.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a microfiltration filter having a long filtration life, good filtration accuracy and good shape retention.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have used an ultrafine composite fiber web obtained by a composite melt-blow spinning method, and have a fiber in the thickness direction of a filter. It was found that the intended purpose can be achieved by providing a packing density gradient, increasing the surface area by molding the filtering surface in an uneven shape, and heat-sealing the intersections of the fibers, and completed the present invention. .. That is, (1) the first invention of the present application comprises ultrafine composite fibers obtained by spinning two or more kinds of thermoplastic resins having a melting point difference of 20 ° C. or more by a composite melt-blowing method, and heat fusion between fibers is performed. The present invention is a filter characterized in that at least one surface thereof is uneven and has a density gradient in the thickness direction of the filter. The filter according to (1) above, wherein the average fiber diameter of the fibers is 10 μm or less, and (3) the third invention of the present application has a density gradient in which the fiber diameter of the ultrafine composite fibers is changed in the thickness direction of the filter. While being laminated, the above (1)
Or the filter according to any one of (2), (4)
A fourth invention of the present application is the filter according to any one of the above (1) to (3), wherein the filter is reinforced with a reinforcing material.

The present invention will be described in detail below. The ultrafine composite fibers used in the filter of the present invention include polyolefin,
Among the thermoplastic resins capable of forming fibers, such as polyester and polyamide, two kinds of resins having different melting points of 20 ° C. or more are selected and composite melt-spun is used. Examples of such resin combinations include polyethylene / polypropylene, polypropylene / polyethylene terephthalate, polyamide / polyethylene terephthalate and the like. As a composite type, both resins are arranged in parallel, or a low melting point resin is placed on the sheath side, a high melting point resin is placed on the core side, or a sheath core type, or the low melting point resin is placed on the sea side and the high melting point resin is placed on the island side. An example is a sea-island type. When heat treating the web for the purpose of adhering the contact points between fibers with a resin with a low melting point, if the resin with a high melting point is softened or melted, the fibers tend to form a film, which leads to an uneven pore size of the filter and an increase in filtration resistance. Therefore, it is desirable that the difference between the melting points of the two resins is 20 ° C. or more in order to cause strong fusion by the low melting point component without melting or softening the high melting point component.
In addition, the composite ratio of the low melting point resin and the high melting point resin is 20/80 in terms of weight ratio in order to secure sufficient adhesion between the fibers.
To 80/20, preferably 30/70 to 70/30. As a method for spinning such fibers by a composite melt-blow spinning method, a plurality of thermoplastic resins are prepared by using a composite spinneret as disclosed in JP-A-60-99057 and JP-A-2-289107. Can be used from each extruder to the spinneret, and the molten resin extruded from the spinneret is blown off with high-speed hot air and deposited on the collecting conveyor as an ultrafine composite fiber web. In the composite melt-blowing method, the fiber diameter becomes thicker when the extrusion amount of resin is increased, and becomes thinner when the flow velocity of hot air is increased.
By changing either one or both of these conditions, a web having a changed fiber diameter can be obtained.
The fibers constituting the filter preferably have an average fiber diameter of 10 μm or less. If the average fiber diameter exceeds 10 μm, the filtration accuracy becomes worse than 10 μm, which is not preferable.

In the filter of the present invention, the filtering surface is formed in a concavo-convex shape, has a density gradient in the thickness direction, and the intersections between the fibers are heat-sealed. The unevenness referred to in the present invention means that the filtering surface of the filter is not smooth when viewed macroscopically, and the difference between the bottom point of the concave portion and the apex of the convex portion is about 1 m.
It means a state in which some unevenness of m or more is formed. Examples of the specific shape include linear or corrugated folds bent into an acute angle or a U shape, and shapes such as dotted or groove-like independent recesses scattered. By taking such a concavo-convex structure, the surface area of the filter medium is increased and the filtration life is lengthened. Filtration is performed with the uneven side as the introduction side of the fluid to be filtered. The density gradient type means a state in which the fiber packing density in the thickness direction of the filter changes stepwise or continuously. The fiber packing density is the following formula 1
The average value of 5 samples is shown. Fiber packing density (g / cm ³ ) = W / (V × ρ) Formula 1 W: Web / nonwoven fabric / filter weight (g / m ² ) V: Volume per 1 m ² (cm ³ / m ² ) ρ: Specific gravity of fiber (g / cm ³ ) The fiber packing density is about 0.01-0.35 for the entire filter.
In the range of 0.02 to 0.35 in the dense part and in the range of 0.01 to 0.25 in the rough part, it is preferable. If the fiber packing density in the dense portion is less than 0.01, microfiltration is impossible, and if it exceeds 0.35, the passage resistance of the fluid to be filtered becomes too large, which is not preferable.

The filter of the present invention can be manufactured by various methods. For example, two kinds of thermoplastic resins having a melting point difference of 20 ° C. or more are spun by a composite melt blow method to obtain an ultrafine fiber web having a constant average fiber diameter, and the web is heated at temperature, pressure, time and the like. There is a method in which after changing the conditions to make several types of heat-fusion type nonwoven fabrics with different fiber packing densities, this nonwoven fabric is laminated in order of density and the surface is made uneven by using a die or fold processing machine. .. Further, there is a method in which a plurality of ultrafine fiber webs having different average fiber diameters are obtained by sequentially changing spinning conditions such as an extrusion amount and a jet gas pressure at the time of spinning, and these are laminated in the order of average fiber diameter, and heated and molded. The ultrafine fiber web is directly sprayed and deposited on a porous and uneven molding material placed on the collection conveyor, and then heated by changing the temperature conditions on the front surface side and the back surface side to form a density gradient and heat molding. Method, or by utilizing the difference in suction force between the front side and the back side of the web, which is created when the gas blown to the collection conveyor is sucked and exhausted from the bottom of the collection conveyor-the back side is dense and the front side is rough. There is also a method of obtaining a fibrous web which is and heat-molding. Furthermore, ultrafine fiber webs with different average fiber diameters are spun on, and are deposited on a flat collecting material or on a porous and uneven molding base material in the order of the fiber diameters, and then heating conditions and molding conditions are applied. There is a method of changing and molding. Further, in the filter of the present invention, a reinforcing material may be provided on the surface of one side, both sides or inside of the filter for the purpose of further improving the strength and shape retention. Examples of such a reinforcing material include spunbonded non-woven fabric, heat-fusion type composite fiber non-woven fabric, heat-fusion type composite monofilament net, and wire netting. The reinforcing material may be one having a fiber diameter thicker than the ultrafine fibers and having air permeability. A product reinforced with the reinforcing material has even better shape retention after molding even with a low basis weight filter, and also has high strength.

The present invention will be described below with reference to examples. The methods for measuring filtration performance and the like used in each example are described below. Filtration accuracy: A circulation type filtration test device consisting of a water tank containing 30 liters of water, a pump, and a filter is used. 25 cm x 22 with honeycomb-shaped metal reinforcement on the filtrate discharge side
A sample filter is attached to the housing of a filter having a size of cm, and 5 g of a cake (Carborundum # 4000) is added to the water tank while circulating water at a flow rate of 10 liters per minute. 100 milliliters of filtered water collected 3 minutes after the addition of the cake is filtered with a membrane filter capable of collecting particles of 0.6 micron or more. The size of the particles collected on the membrane filter is measured by a particle size distribution analyzer, and the size of the largest particle (maximum outflow diameter, micron) is used as the filtration accuracy of the sample filter. Filtration life: A sample filter is attached to the filtration test device, and water is circulated at a flow rate of 30 liters per minute. Volcanic ash soil lower layer soil powder (average particle size 12.9 microns,
20 g of 99% by weight or more in a particle size range of 1.0 to 30 μm) is added and circulation filtration is continued, and when the water in the water tank becomes transparent, the differential pressure across the filter is measured. The operation of adding this powder and measuring the differential pressure is 3 kg
Repeat until / cm ² is reached. The time from the first powder addition until the differential pressure reaches 3 kg / cm ² was defined as the filtration life. Average fiber diameter: measured using a scanning electron microscope photograph of a sample piece cut from a web, a non-woven fabric, or a filter 1.
The average value of 00 fiber diameters.

(Example 1, Comparative Example 1) Melt flow rate 120 (g / 10 minutes: 230 ° C., 2160 g), melting point 1
63 ° C. polypropylene as the first component, melt floret 124 (g / 10 min: 190 ° C., 2160 g), melting point 122 ° C. linear low density polyethylene as the second component,
Using a parallel melt-blow spinneret with a hole diameter of 0.3 mm and a number of holes of 501, the composite ratio was 1/1 (weight ratio) and the spinning temperature was first.
Ingredient 260 ° C, 2nd ingredient 260 ° C, total discharge amount 120g /
1. The composite spinning was carried out under the condition of minutes, and the air at a temperature of 330 ° C. was pressured.
Introduced at 1 kg / cm ² and sprayed on the wire mesh conveyor,
A web having a basis weight of 130 g / m ² and an average fiber diameter of 1.8 μm was obtained. This web was heated at a temperature of 10 using a calendar roll.
Thermocompression bonded at 5 ° C, thickness 1.17 mm, fiber density 0.12
A non-woven fabric (non-woven fabric a) was obtained. Apart from this non-woven fabric, the web is flat stainless steel plate and the height of the mountain is 4 m.
m, mountain pitch 5 mm, sandwiched between corrugated corrugated stainless steel plates with an acute angle, and heat-treated at a temperature of 130 ° C. for 4 minutes,
A non-woven fabric (non-woven fabric b) having an uneven surface and a flat back surface was obtained. The non-woven fabric after molding had a peak height of 4 mm, a valley thickness of 1.2 mm, and a fiber density of 0.044. Nonwoven fabric a was laminated so as to be in contact with the flat surface of nonwoven fabric b, and heated for 1 minute at a temperature of 128 ° C. using a hot air heater to obtain a filter in which two layers were heat-sealed. The surface area on the irregular side of this filter was 1.89 m ² . When a filtration performance test was conducted using this uneven side as the liquid introduction side, the filtration accuracy was 1.0 μm and the filtration life was 14 minutes (Example 1). On the other hand, as a comparative example, when the filtration performance test was performed using only the nonwoven fabric a, the filtration accuracy was 1.1 μm, but the filtration life was 3 minutes, and the filtration life was short (Comparative Example 1). From the above results, it is understood that the filter of the present invention, which is a density gradient type and the filtering surface of which is formed in a concavo-convex shape, has better filtration accuracy and longer filtration life than the filter by the conventional melt blow method.

(Example 2, Comparative Example 2) Intrinsic viscosity 0.5
9. Polyethylene terephthalate with a melting point of 252 ° C
As an ingredient, melt florate 380 (g / 10 minutes: 23
0 ° C., 2160 g) and a melting point of 163 ° C. polypropylene was used as the second component, and the same spinning device as in Example 1 was used.
The compounding ratio is 1/1 (weight ratio) and the spinning temperature is the first component 320.
C., second component 240.degree. C., total discharge rate 120 g / min.
Introduced in kg / cm ² and sprayed on the wire mesh conveyor,
Web (A) having a basis weight of 90 g / m ² and a fiber diameter of 8.6 μm
Got Then, the air pressure was increased to 1.4 kg / cm ² , and a web (B) having a basis weight of 90 g / m ² and a fiber diameter of 4.1 μm was obtained. Further, the air pressure was raised to 1.9 kg / cm ² , and a web (C) having a basis weight of 190 g / m ² and a fiber diameter of 1.2 μm was obtained. The web (C) was heated to 155 using a calendar roll.
Thermocompression bonding was performed at 0 ° C. to obtain a nonwoven fabric having a thickness of 0.85 mm and a fiber density of 0.19 (nonwoven fabric C). Next, the web (B)
And the web (A) are laminated, and the laminated web is sandwiched between a flat stainless steel plate and a corrugated stainless corrugated plate having an acute angle with a mountain height of 4 mm and a mountain pitch of 5 mm, and heat-treated at a temperature of 165 ° C. for 5 minutes. , Surface (web (A) side)
A non-woven fabric (non-woven fabric D) having an uneven surface and a flat back surface (web (B) side) was obtained. Non-woven fabric after molding has a mountain height of 4 m
m, the valley thickness was 1.3 mm, and the fiber density was 0.047. The non-woven fabric C is laminated on the back side of the non-woven fabric D, and heated for 3 minutes at a temperature of 172 ° C. using a hot air heater to change the fiber diameter from the front side to the back side in three layers from thick to thin. A filter was also obtained in which the contact points of the fibers were heat-sealed. The surface area on the uneven side of this filter is 1.89 m ^2.
It was. When the filtration performance test was conducted using this uneven side as the liquid introduction side, the filtration accuracy was 0.9 μm and the filtration life was 11 minutes (Example 2). On the other hand, as a comparative example, when the filtration performance test was conducted using only the nonwoven fabric C, the filtration accuracy was 1.1 μm, but the filtration life was 2 minutes and the filtration life was short (Comparative Example 2).

(Example 3, Comparative Example 3) The polypropylene of the melt flow rate 380 used in Example 2 was used as the first component, and the linear low density polyethylene of the melt flow rate 124 used in Example 1 was used as the second component. Using the same spinning device as in Example 1, the composite ratio was 1/1 (weight ratio), the spinning temperature was 240 ° C. for the first component, 240 ° C. for the second component, and the total discharge amount was 120.
Spinning under the condition of g / min and air of temperature 330 ° C for 1.8k
It was introduced at a rate of g / cm ² and sprayed onto a molding substrate placed on a wire mesh conveyor to obtain a web having a basis weight of 420 g / m ² and an average fiber diameter of 2.4 μm. As a molding substrate,
A composite monofilament with a single yarn fineness of 800 d / f with polyethylene terephthalate as the core and high-density polyethylene as the sheath is plain woven with a warp and weft thread density of 12 threads / 25 mm, and this woven cloth has a mountain height. A crimped net was used in which the fibers were heat-molded into a waveform of 2.5 cm and the pitch between the mountains was 2.5 cm, and the fibers were heat-sealed. The air flow blown onto the molding substrate was removed by a suction device at the lower part of the conveyor by increasing the suction amount by 50% compared with the usual melt blow spinning. As the web deposits on the molded substrate. The lower part of the web has a high fiber density due to the suction action, and the upper part of the web has a weak suction action, so that the fiber density is low, and the web has a density gradient type as a whole. This web was heat-treated together with the molding substrate at a temperature of 130 ° C. for 5 minutes using a hot air heater to obtain a filter in which the intersections of the ultrafine fibers and the contact points between the ultrafine fibers and the molding substrate were sufficiently heat-sealed. .. This filter has an average thickness of 1.4 cm (excluding monofilament), a mountain pitch of 2.5 cm, an average fiber packing density of 0.014, a fiber density of 0.010 on the surface side of the mountain peak, and a back surface of the mountain peak. It was a density gradient type having a fiber density of 0.021. This filter had a surface area of 2.24 m ² on the uneven portion side. When a filtration performance test was conducted with the coarse density side of the filter as the liquid introduction side, the filtration accuracy was 4.0 μm and the filtration life was 19 minutes (Example 3). On the other hand, as a comparative example, the web was directly deposited on the wire mesh conveyor without using the molding substrate, and the blown airflow was removed by suction with a suction device below the conveyor with a weaker suction force than usual. The obtained web has a basis weight of 420 g / m ² and a fiber diameter of 2.4 μm.
It was. This web is heated to 130 ° C using a hot air dryer.
And heat-treated for 5 minutes to obtain a filter in which the intersections of the ultrafine fibers were sufficiently heat-sealed. This filter had an average fiber packing density and a fiber packing density on the front and back sides of 0.014, and had no density gradient. When the filtration performance test of this filter was conducted, the filtration accuracy was 7.9 μm,
The filtration life was 13 minutes, and the filtration life was short (Comparative Example 3).

[0013]

The filter of the present invention is a heat-fusion type ultrafine composite fiber obtained by the composite melt-blow spinning method, and is a density gradient type in which the fiber packing density changes in the thickness direction of the filter. Moreover, the fibers are firmly fused at their contact points. In addition, the filter has a filtering area increased by molding the introduction side of the fluid to be filtered into an uneven shape. Therefore, this filter is capable of microfiltration and has a long filtration life. Monofilament net, wire mesh,
A material reinforced with a reinforcing material such as a non-woven fabric composed of high-definition yarn has the effects described above, as well as high strength and good shape retention.

Claims (4)

[Claims] 1. A filter comprising ultrafine composite fibers obtained by spinning two or more kinds of thermoplastic resins having a melting point difference of 20 ° C. or more by a composite melt-blowing method, wherein the fibers are heat-sealed to each other. A filter characterized in that one surface thereof is uneven and has a density gradient in the thickness direction of the filter. 2. The filter according to claim 1, wherein the ultrafine composite fiber has an average fiber diameter of 10 μm or less. 3. The filter according to claim 1, wherein the density gradient is formed by laminating the ultrafine composite fibers while sequentially changing the fiber diameter in the thickness direction of the filter. 4. The filter according to claim 1, wherein the filter is reinforced with a reinforcing material.