Description

FIELD OF INVENTION

The present invention relates to a method for the manufacture of a flat filter material, flat filter material from polymer blends, in particular a flat filter material obtained as in described process and a filter comprising a flat filter material.

BACKGROUND OF INVENTION

Flat non-woven filter fabrics are a basic material for the production of various types of air filters. Such fabrics are formed from the natural fibers and present primarily from various types of plastics. The choice of material for the construction of the filter beside the price of crucial importance are other properties, such as filtration efficiency, pressure drop, temperature range of application etc.

For the production of flat filter materials are used different plastic materials, typically polypropylene is used because it can readily form fibers. Such uniform nonwoven filter does not have a specific internal electrical charge. The idea of using electrostatic phenomena to improve the effectiveness of the filter flat materials was known. Some postulated the preparation of such nonwoven materials from electrets i.e. materials endowed by stable net charge forming the constant electric field in the interfiber space. However, the production of electrets and forming from them the nonwoven fabrics have proven to be difficult.

From the PL277835 semi-mask is known, which comprises a fine filter which is a mixture of uniformly distributed in the space of the fibers of at least two materials with different dielectric constants and the structure limit of the filter porosity is less than 30%.

US2012097035 discloses a filter material comprising a blend of polypropylene and acrylic fibers in the shape of a rounded, flat, a dog bone, oval or bean-like size from 0.08 to 3.3 dtex. A preferred blend comprises about 50 weight percent polypropylene fibers and about 50 percent by weight of acrylic fibers. The fibers may be mixed in the range of from 90:10 to 10:90 for acrylic polypropylene. The shape contains 25 percent by weight of a rounded shape, a flat, dog bone, oval or bean-like. The mixture of fibers comprises about 25 weight percent of at least one size of between 0.08 and 3.3 dtex.

The electret fibers added to these mixtures comprise from 0.02 to 33 percent by weight of the charge control agent. These fibers may be used in the manufacture of the electret material with corona methods, or triboelectric methods for entering the charge.

US2002121194 describes a process for the preparation of triboelectrically charged nonwoven material, wherein the blend of fibers made from fibers having a coefficient of poliacrylnitrile <= 1.7 dtex and polyolefin fibers having a coefficient of <= 1.7 dtex is free of antistatic agents and lubricants in result of rinsing. The mixture is dried to a moisture content <1% by weight.

US2004177758 presents triboelectric air filter medium formed as a mixture of polyolefin fibers and polyamide fibers. A blend of polyolefin fibers and polyamide fibers is carded to charge the polyamide and polyolefin fibers with the electrical charges. The ratio by weight of polyamide fibers to polyolefin fibers is in the range from 10:90 to 90:10.

US5368734 discloses an electrically charged air filter which comprises a blend of clean expanded fibers of elongated porous polytetrafluoroethylene and polyamide fibers.

The document GB2329598 shows a composite comprising a first electrostatic filter with a filter layer , layer 2 comprising a second mechanical filter, and a third layer 3 having different electrostatic filter. Electrostatic layers preferably comprises a blend of polypropylene and modacrylic fibers, with the ratio of their masses being preferably of 2: 1 , and may include a thin woven fabric made of polypropylene, which is intended to strengthen and protect these layers. The second layer may for example be obtained by means of polypropylene meltblown layer of lower weight than electricity.

US4965034 discloses an extrusion linear ethylene polymers such as low density polyethylene (LLDPE) with minor amounts (less than 5 weight percent), thermoplastic polyurethane. These polymers are used to extrude film having improved surface structure.

DE 10022889 describe a method wherein a stream of molten polyester, which is divided into second and third stream of polyester. To the second stream is introduced additional polyester polymer melt to obtain a polymer blend of a second polymer containing from 3 to 50% by weight. The first polymer mixture is fed to the third stream of the polyester, wherein the first and third stream of the polyester blend into a second polymer blend. This blend is formed into fibers, which can create non-woven fabrics.

US4518744 concerns a process for melt spinning fiber-forming thermoplastic polymer, more particularly polyethylene terephthalate, adipic acid, hexamethylene or polypropylene. In this method, the fiber-forming polymer is added in the range of from 0.1 % to 10% by weight of another polymer which is immiscible in a melt of the fiber- forming polymer. This other polymer has a particle size of 0.5 to 3 microns in the melt with the fiber-forming polymer immediately prior to spinning. Also described are new the melt spun fibers produced in the process, in which another polymer is in the form of microfibrils.

US4945125 describes a method for preparing partially interpenetrating polymer network of polytetrafluoroethylene and silicone elastomers. The articles produced by this method have improved physical properties as compared to extruded fibers as polytetrafluoroethylene only dispersing resin.

The prior art also considered providing additives to the nonwoven fabrics such as resin particles or the formation of nonwovens composed of two types of polymers to triboelectric phenomenon generated by the electric charges in the nonwoven fabric. However, it turn out to be difficult to provide effect mixing together of the fibers of these materials. The first attempts to produce non-woven filter of a mixture of two different polymers fed into an extruder did not give the expected results.

From the viewpoint of air pollution is the most important filtration efficiency of the filter material. To improve the filtration efficiency, electrostatic effects, as many aerosol particles have a resultant electric charges can be used. Electrically charged aerosol particle moving with the air flow in proximity to the filter fibers also experience the impact of charged electrostatic forces, which greatly enhance the effects of particle deposition on the fibers. So are produced masks and filters for personal protection. The production of filter fabric from a mixture of two different polymers fed to the extruder failed. The blends, such as nonhomogenous fibril blendsconsisting of irregularly spaced layers of these two types of polymers could not be received. Blends were tested for different combinations and proportions of the various polymers used. The resulting blends were then tested for filtration efficiency and pressure drop. By appropriate selection of the starting polymer system the method for obtaining a flat filter material that is characterized by high efficiency filtration through continuous triboelectric charging of fibril at the point of their contact was obtained. This material has highly improved filtration efficiency in comparison with the conventional planar non-woven polypropylene fibers. Interestingly triboelectric effect persisted for a long time and provide long-term effect to improve filtration efficiency, especially in the critical research aimed at the acquisition of new knowledge and skills for developing new products, in this case, an innovative method for obtaining a flat filter material with polymer blend was provided.

SUMMARY OF THE INVENTION

The present invention relates to a method for the manufacture of a flat filter material, characterized in forming the fibers from a mixture of granulates from at least two polymers wherein one polymer is selected from the group consisting of polymers having negative tribolectric charge and another polymer selected from the group consisting of polymers having a positive tribolectric charge, melting and mixing a mixture of granulates in an extruder, then hot forming polymer fibers, which are fed to the receiver system to form thereon a layer fleece. Preferably, the temperature of the molten polymer blend in the range of 220 to 255°C. Preferably, the temperature of the air in the head for forming fiber is in the range: 350-420/°C, preferably at temp: 380°C. In a preferred embodiment, the ratio of used air streams directed to the polymer fibers in the forming head zakresie2,0 to 3.0 kg/kg of polymer.

In the method according to the invention, the first polymer is selected from the group consisting of: polyacrylonitrile, polyethylene, polypropylene, polyvinyl chloride and another polymer selected from the group consisting of: polyformaldehyde, polyester, polyamides, poly(methyl methacryiate) and polystyrene, poly (methyl methacrylate). Preferred is a mixture of polypropylene and polyester or polypropylene, and Nylon 66, Preferred is a mixture of two polymers used in a ratio of 80:20 to 20:80.

In another embodiment, a mixture of polypropylene having a high melt index, nylon 66, polystyrene and methyl methacrylate, or a mixture of polypropylene having a high melt index, nylon 66, polystyrene and methyl methacrylate, preferably polymethyl methacrylate content in blends is less than 30%.*-

The present invention also relates to a flat filter material obtained by the method according to the invention. A flat filter material consists of fibers comprising a mixture of at least two polymers, one polymer selected from the group consisting of polymers having negative tribolectric charge and another polymer selected from the group consisting of polymers having a positive tribolectric charge.

Preferably, the first polymer is selected from the group consisting of: polyacrylonitrile, polyethylene, polypropylene, polyvinyl chloride and the other polymer is selected from the group consisting of: poliformaldehyde, polyester, polyamides, poly (methyl methacrylate). More preferably flat filter material consists of a mixture of polypropylene and polyester or polypropylene and Nylon 66, wherein the mixture of two polymers is used in a ratio of 80:20 to 20:80.

In a preferred embodiment, the flat filter material comprises a mixture of

polypropylene having a high melt index, nylon 66, polystyrene and methyl

methacrylate. In another preferred embodiment, the flat filter material comprises a mixture of polypropylene having a high melt index, nylon 66, polystyrene and methyl methacrylate. Preferably the content of polymethyl methacrylate in blende is less than 30%.

The present invention also provides a filter comprising a flat filter material according to the invention.

The solution according to the invention is shown in the figures as follows:

Fig. 1 shows schematically the connection of the polymer fibers (polymer blends) of the prior art

Fig. 2 shows schematically a possible connection of polymers (polymer blends) of the invention.

Fig. 3 shows a comparison of filtration efficiency for materials produced according to the Examples. The graph clearly shows that the polymer blends of the invention permit the production of filter material of substantially higher filtration efficiency. The invention was illustrated in the examples which are intended to merely a detailed explanation of certain preferred embodiments of the invention.

EXAMPLES

Example 1 (no blend no tribolectric phenomena)

To the extruder feeder homogeneous granulate of polypropylene having a high melt index was introduced. The heating portion of the extruder at a temperature of 210°C was applied for melting and mixing the polymer. The melted polymer was further heated to a temperature of 252°C forced through into the spray head where the melt blown hot-molded polymer fibers form. The air used to blow the polymer melt temperature was 345°C.

Formed, hot fibers were directed to the receiver system, formed in the layer of fleece and cooled down from sticking together in mutual contact of a fiber. In result a stable and uniform nonwoven fabric was obtained. The thickness of the nonwoven fabric was controlled by the rate of receiving a pile forming at the outlet of the spray nozzle. Control of the size of the fibers was achieved by appropriately selecting the temperature of the molten polymer blend, the temperature of the air stream used in forming the head and the ratio of fibers and air streams directed to the head of the polymer forming the fibers. The temperature to which the molten polymer was heated is 252°C. The air stream used to blow in the head of molten fiber forming polymer and had a temperature of 345°C. The air used to form the polymeric fibers of the spray head was administered in an amount of 2.6 kg/kg of polymer. The resulting nonwoven fabric was subjected to filtration tests using a test aerosol. The test results are shown in Table 1. The tests were subjected obtained nonwovens flat sample area of 50.2 cm2 at air flow of 30 l/min.

Table 1. Results of quality nonwovens filtration technique obtained from melt-blown polypropylene

Example 2 (Use of pure polyamide)

- Melting of polyamide 66: temperature: 216°C

- Final heating of polyamide 66: temperature: 245°C

- Spray air temperature: temperature: 360°C

- Volume of air: 2.85 kg/kg of polyamide 66

To the feeder of the extruder, the granulate of fresh Nylon 66 was introduced. In the heating portion of the extruder the polymer was melted and mixed. The melted polymer was further pushed to the spray head where the hot polymer fibers were formed with the melt blown process. These fibers were placed on the receiver system, formed in the layer of fleece and while cooling down, stuck together in result of the contact of the fibers. In result a stable and compact cylindrical nonwoven fabric composed of fibers was obtained. The thickness of the nonwoven fabric was controlled by the rate of receiving a pile formed at the outlet of the spray nozzle. Control of the size of the fibers was achieved by appropriately selecting the temperature of the molten polymer blend, the temperature of the air stream used in forming the head and the ratio of fibers and air streams directed to the head of the polymer forming the fibers. The resulting nonwoven fabric was subjected to filtration tests using a test aerosol. The test results are shown in Table 2. The tests were conducted with the obtained nonwovens flat sample area of 50.2 cm ² at air flow of 30 l/min.

Table 2. Test results of qualitative filter nonwoven material obtained with melt-blown technique from Nylon-66.

Example 3 (PP and PET)

- Melting of polymers: temperature: 255°C

- Final heating of polyamide 66: temperature: 276°C

- Spray air temperature: temperature: 380°C

- Volume of air: 2.35 kg/kg of polymer mixture 66

To the feeder of the extruder, the granulates of a mixture of polypropylene and polyester (PET) in a suitable weight ratio were introduced. In the heating portion of the extruder the two polymers were melted and mixed. No studies were done whether the system was a homogeneous or heterogeneous mixture. The molten, liquid mixture was further pumped to the spray head where the melt blown formed into a hot polymer fibers. These fibers were placed on the receiver system, formed into a fleece layer and while cooling down the fibrils were sticking together. The result is a stable non-woven polymer.

The thickness of the nonwoven fabric was controlled by the rate of receiving a pile forming at the outlet of the spray nozzle. Control of the size of the fibers was achieved by appropriately selecting the temperature of the molten polymer blend, the temperature of the air stream used in forming the fiber head and the proportion of air flow directed to the polymer fibers forming head. The resulting nonwoven fabric was subjected to filtration tests using a test aerosol. The test results averaged from the measurements of five samples are shown in Table 3. The tests were subjected obtained nonwovens flat sample area of 50.2 cm ² at air flow of 30 l/min.

Table 3. Results of the qualitative research of filtrated nonwoven fabrics derived

Example 4 (PP, Nylon)

- Melting of polymers: temperature: 255°C

- Final heating of the polyamide 66: temperature: 275°C - Spray air temperature: temperature 380°C

- Volume of air: 2.7 kg/kg of polymers

To the feeder of the extruder, the granulates of a mixture ofnbpolypropylene and Nylon 66 in a suitable weight ratio were introduced. In the heating portion of the extruder the two polymers were melted and mixed. No studies were done whether the system was a homogeneous or heterogeneous mixture. The molten, liquid mixture was further pumped to the spray head where the melt blown formed into a hot polymer fibers. These fibers were placed on the receiver system, formed into a fleece layer and while cooling down the fibrils were sticking together. The result is a stable non-woven polymer.

The thickness of the nonwoven fabric was controlled by the rate of receiving a pile forming at the outlet of the spray nozzle. Control of the size of the fibers was achieved by appropriately selecting the temperature of the molten polymer blend, the temperature of the air stream used in forming the fiber head and the proportion of air flow directed to the polymer fibers forming head. The resulting nonwoven fabric was subjected to filtration tests using a test aerosol. The test results averaged from the measurements of five samples are shown in Table 4. The tests were subjected obtained nonwovens flat sample area of 50.2 cm ² at air flow of 30 l/min.

Table 4. Results of the quality non-woven filter technique from blend of

Example 5 (PP + PS + Nylon 66 + methyl methacrylate)

- Melting of polymers: temperature: 235°C

- Final heating of the polyamide 66: temperature: 265°C

- Spray air temperature: temperature: 380°C

- Volume of air: 2.7 kg/kg of polymer

In the feeder of the extruder granules was introduced a mixture of four polymers: polypropylenes, high melt index nylon 66, polystyrene and methyl methacrylate in various proportions by weight. The heating portion of the extruder was melting and mixing these polymers. Not determined whether the resulting system is a mixture of homogeneous or heterogeneous. The molten, liquid mixture was further pumped to the spray head where the melt blown formed into a hot polymer fibers. These fibers were placed on the receiver system, formed on the layer of fleece and cooling down from sticking together in mutual contact of a fiber. The result is a durable and relatively flexible non-woven polymer. The thickness of the nonwoven fabric was controlled by the rate of receiving a pile forming at the outlet of the spray nozzle. Control of the size of the fibers was achieved by appropriately selecting the temperature of the molten polymer blend, the temperature of the air stream used in forming the fiber head and the proportion of air flow directed to the polymer fibers forming head. The resulting nonwoven fabric was subjected to filtration tests using a test aerosol. The test results averaged from the measurements of five samples are shown in Table 5.

Table 5. The results of the qualitative nonwovens filtration technique obtained from melt-blown polypropylene blend, nylon 66, polystyrene and methyl methacrylate.

11 40:10:20:30 248 196 90.0 94.3

12 40:10: 10: 40

13 30:50:10:10 262 96 93.6 96.3

14 30:10:50:10 259 185 94.0 96.7

15 30: 10:10:50 _

In cases where the content of polymethyl methacrylate in blend was greater than 30% it was not possible to obtain nonwoven fabric. The fibers were not formed in spray head.