Field of technique

The invention relates to the production of the non-woven synthetic filter materials, specifically the invention relates to the method of production of filter material for filtration of high-dispersive substances, in particular of production of the fine fibrous and microfibrous non-woven filter materials used in individual protective means.

Background of the invention

It is a well known invention (CN102121137, Dalian University of Technology, published on 13.07.2011) which concerns the method of bipolar double spraying of electrospinning of production of nanofibrous material. In case of electrospinning from oppositely charged sprayers, the obtained nanofibres are interweaved over each other, receiving, due to the attraction, the charges of different polarities, and in this manner the two-fiber interweaved non-woven material is formed. The shortcoming of this solution is that if fibres are firmly attached to each other, the electric field formed by oppositely charged components of double fibre will have the form of a dipole electric field, leading to a standard electret charge of fibres using convential electrospinning.

It is known a triboelectric air filter (US20040177759, Tsai P.P. Chang Liang-Yu, published on 16.09.2004) which involves the mixing of fibres of polyolefin and melamine, where polyolefin preferably is made of a compound selected from a group that contains polyethylene, polypropylene, polybutylene and their mixtures. The obtained mixture of two obtained fibres is combed with a combing machine in order to generate a triboelectric charge. Polyolefin fibres acquire a negative charge which differs from the charge of polyamide fibres. The shortcoming of this solution is that the obtained fabric receives a triboelectric charge by friction, and fibres remain charged due to the subsequent mechanical influence applied to the fabric.

It is known the method of production of electrostatically charged filter material (US6811594, Hollingsworth & Vose Air Filter, published on 02.11.2004), comprising the mixing of polyester fibres at least with electrostatically charged fibres of another type, in order to produce filter material. The shortcoming of the solution is that the mixing of fibres and the forming of the material do not take place at the same time.

The method of making filter material (EP0829293B1 ,Esfil Limited, published on 18.03.1998.) is the closest solution by technical character to the present invention related to the method of making fine fibrous material with fibres having stable electret charge wherein fibres are formed in an electrostatic field from a solution having a solution dynamic viscosity of 0,1 to 3,5 Pa x s, a solution electrical conductivity of 10 ^"8 - 10 ^" "Ώ· ¹ x cm ¹ , a potential difference of 25 to 150 kV and a volume flow of solution of 10 ³ to 2 x 10 ² cm ³ x s ^"1 per fibre forming element and wherein additional processing of fibres takes place using saturated vapours of the solution in the fibre formation zone. The shortcoming of this solution is that the field of the electret charge forming on fibres is active at the smaller distances than the field charged with different polarity fibres when fibres are located at the distance of one another of 4-5 fibre diameters.

Summary of the invention

According to the invention the present method of production of filter material from fibres is represented where, in addition to a stable electret charge, fibres also additionally have a triboelectric charge. In order to carry out the present method fibres are formed in the electrostatic field from the such solution of two polymers, where the polymers during the contacting acquire the triboelectric charge. During the settling the fibres together on the collecting electrode and their mutual friction at the same time, these fibres acquire, in addition to the electret charge, the charge with the opposite signs, i.e. the triboelectric charge which corresponds to the sign of the charge obtained from mixing of two polymers located in different ends of the triboelectric series. The acquiring of the triboelectric charge increases the electric field inside the obtained material, respectively improving its filtering properties. In case of subsequent processing of the obtained material by using mechanical influence, for example, the obtained material is passed through the rolls of wrapping machine or the material is corrugated, etc, then the charge increases by mutual friction. If bipolar electrospinning is used thereat and the sign of charge given to fibre by high voltage device, corresponds to the sign of charge formed by the following mixing, then the charging process is more stable and the filtering properties are further improved. Also, in order to stabilize the spinning process, the zone of fibres formation is additionally treated with saturated vapours of the solvent.

Consequently, the shortcoming of the closest solution of EP 0829293 is eliminated where fibres obtained by the method of EP0829293 have only the electret charge, remaining generally electrically neutral while the charge has shorter range (as dipole charge) compared to the electrostatic (excess) charge. Since the remote influence increases the efficiency of the engaging of the aerosol particles by fibres also increases and the filtering properties of the material made of such fibres are improved.

The shortcomings of the method reported in the USA application US20040177759 and in the USA patent US6811594 are eliminated by present invention because the electrospinning process comprises both the mixing of fibres and the settling together of these fibres on the collecting electrode at the same time, i.e. the forming of filter material takes place by one operation.

Examples of realization of the invention

The present invention differs from the existing methods of production of the filters with the triboelectric charge by method of giving the triboelectric charge to fibre.

In case of the standard method two types of artificial fibres are produced separately and these artificial fibres differ by used polymers and in general the necessary operation is washing-off the oiler. The mixing process of these two types of fibres represents separate operation. The last operation is the forming of the filter material, for example, by the needle punching method. The triboelectric charge is given to fibres during these two operations.

In the present invention the operations of the production of fibres, i.e. the mixing of fibres and the forming of filter material are combined into one process, and in case of bipolar electrospinning the charging of fibres is improved.

In case of unipolar electrospinning the rotating cylinder passes through between two rows of the spinning elements. The personal polymer solution is fed to each row. The spinning elements are located along the conveyor on which the filter material is formed. One solution of polymer is fed to the even-numbered spinning elements, the another solution of polymer is fed to the odd-numbered spinning elements. In case of the mixing the fibres and the forming of the material take place contemporary with the forming of the triboelectric charge to fibres. In case of unipolar electrospinning the triboelectric charge should be increased by subsequent mechanical influence of the material, whether during the further processing of the material or during the rolling of the material between the rollers.

Example 1. In case of unipolar electrospinning the solutions of polystyrene and high chlorinated polyethylene are contained in the organic solution where tetramethylammonium iodide is added. The viscosity of both solutions is 6 ST, electrical conductivity is 7x 10 ^"5 Q ^"1 cnrr ¹ . The spinning is carried out on the rotating rollers, the voltage of both solution was -25 kV. The coefficient of the transmittance of oil aerosol of the obtained material at the rate of 6,8 cm/s without mechanical influence was 0,09%, in case of presence of mechanical influence, for example, after the passing of the obtained material through the rollers and/or after the corrugation of the obtained material, the coefficient of the transmittance of oil aerosol was 0,0025%. Consequently, the filtering properties of the obtained material are improved after using of subsequent mechanical influence more than 30 times.

In case of bipolar electrospinning the voltage was given with polarity corresponded to the location of the spun polymer in the triboelectric series and the mixing of fibres and the charging of fibres with differ polarity took place during electrospinning, i.e fibres are charged already during electrospinning and the charging process proceeds more stable and in addition to the filtering properties of the material are additionally improved, as seen from example 2.

Example 2. The solution of polystyrene is in the organic solution, which polarity is negative, and the solution of polymethyl metacrylate is in the organic solution which polarity is positive. The viscosity of the solutions is 6 ST, electrical conductivity is 7x 10 ^s Q ^"1 cm ^'1 . The obtained materials have the coefficient of the transmittance of the oil aerosol at the rate 3 cm/s: in case of unipolar electrospinning - 0,014%, in case of bipolar electrospinning - 0,00002%, i.e in case of bipolar electrospinning the filtering properties of the material are improved by 700 times. If mechanical influence of the obtained material will follow, for example, the material is passed through between the rollers or the material is corrugated, etc., then the coefficient of the transmittance of oil aerosol of the material is 0,00015% and the efficiency of the material increases 1 ,3 times by comparison in case of bipolar electrospinning without mechanical influence.