EP0339487B1 - Active carbon filter layer for gas masks and gas mask containing said active carbon filter layer - Google Patents

Abstract

The active carbon filter layer for gas masks is essentially composed of highly air-permeable sheet-like structures placed one on top of the other and having a layer fixed thereon and consisting of particulate or spherical active carbon particles having a diameter of 0.1 to 1 mm, and its pressure loss is less than 10 mm (water column) for a thickness of 4 cm and with a circular cross-section of 100 cm<2> when 1 l/sec of air flows through.

Description

The present invention relates to an activated carbon filter layer for gas masks, a hood mask and their use.

All common mask filters consist of a replaceable filter cartridge that contains at least one activated carbon filter layer. Activated carbon for mask filters usually has a specific or "inner" surface determined by the BET method from 500 to over 2000 m² / g. It is a special property of activated carbon that it can permanently adsorb a large number of substances in its micropores, which can make up up to 50% of the total volume, very unspecifically. Toxic gases such as HCN, which are only weakly bound by normal physical adsorption, can be bound with the aid of applied metal compounds, for example silver, copper or chromium, by means of a superimposed chemisorption. The activated carbon filter layer of mask filters is usually designed as a bulk filter, in which the medium to be cleaned flows through a fixed bed of the activated carbon particles. In order to ensure a sufficient period of operation of the filter, a sufficient amount or mass of the adsorber material must be available. At the same time, however, the adsorption kinetics are proportional to the "outer" surface of the particles, so that small particles are cheaper in this respect. In addition, larger activated carbon particles are often only fully used in the outer areas. These are usually already saturated - which requires an interruption and replacement of the filter cartridge - if the coal inside is only weakly loaded. However, the use of the smallest possible particles in a bulk filter necessarily leads to a high pressure loss. In practice, the particle size is limited downwards by the associated pressure loss. Another disadvantage of bulk filters is that the activated carbon particles rub against each other, and the pulverulent coal further increases the resistance to flow.

It is generally believed that good filter performance necessarily requires a high volume resistance, because only then would there be good contact between the gas to be cleaned and the adsorber grains, in order to also rule out breakthroughs through cavities caused by settling particles, the packing must be firm be compressed. This means that a high flow resistance of the activated carbon filter for gas masks is pre-programmed. However, it not only means an effective physiological load on the gas mask wearer, but also increases the feeling of tightness.

It is therefore an object of the present invention to provide an activated carbon filter layer for gas masks, i.e. to provide a mask filter with low flow resistance and high adsorption capacity.

This object is achieved by a special arrangement of the support structures and a special choice of the support structure and the activated carbon particles contained therein.

The invention thus relates to an activated carbon filter layer for gas masks, which is essentially composed of superimposed, highly air-permeable support structures with an attached layer of granular or spherical activated carbon particles with a diameter of 0.1 to 1 mm, and that their pressure loss at a thickness of 4 cm is circular Cross-section of 100 cm² when flowing with an air flow of one liter per second is less than 10 mm, preferably less than 5, in particular less than 2 mm water column.

Another object of the present invention is to provide a hood mask which contains such an activated carbon filter layer or the support structure made of fibrous material or rubber hair exists or is a textile fabric, such as preferably fleece, fabric or plush.
It is also an object of the present invention to provide a gas mask with the above features, in which the filter layer is plate-shaped in order to be worn on the chest or on the back and which is connected to the mask body by a flexible tube. Alternatively, this filter layer with a diameter of a few centimeters can be arranged in a flexible hose.
Finally, it is an object of the present invention to use the carrier structures defined above in gas masks.

Support structures with attached granular or spherical activated carbon particles are known as so-called area filters. According to the teaching of the present invention, they can be modified by the person skilled in the art in such a way that they are highly permeable to air and covered with the required amount of granular or spherical activated carbon particles of the desired size, in the required number, when superimposed, give an activated carbon filter of the thickness of a few centimeters customary for gas masks.

With finely divided substances with specific protective or adsorption properties, e.g. Surface filters loaded with activated carbon, in particular textile surface filters, are also known. However, they have not been used for mask filters because, for the reasons explained at the outset, only activated carbon filter was considered suitable.

DE-B-28 04 154 describes a filter material made of an open-pore, flexible foam carrier and adsorber particles carried by its pore walls. The adsorber grains can also be spherical and consist of activated carbon. However, their size is considerably smaller than is required for a surface filter from which a mask filter according to the invention could be produced.

DE-C-28 29 599 describes a multi-layer composite material for protective clothing with a non-flammable textile fabric as the outer layer, a mineral fiber layer and an inner layer made of air-permeable, heat-insulating polyurethane foam with a thickness of 2 mm, the pores of which are occupied by activated carbon particles, which are at least partially spherical porous activated carbon bodies exist. In order for such a layer of polyurethane foam to be useful for the purposes of the invention, the foam would have to have a very open-pore structure and these pores should not be occupied by the activated carbon particles. Rather, these would have to be fixed in the correct size on the walls of the foam in order to ensure the high air permeability that surface filters require, so that when placed on top of one another, they result in a mask filter with the required low pressure loss.

DE-C-29 51 827 describes, inter alia, a protective material against chemical pollutants and short-term exposure to heat from an air-permeable flexible carrier layer, for example a woven fabric, scrim, knitted fabric or non-woven fabric, on which spherical adsorber grains of one diameter are made from a solidified adhesive mass on at least one side on supporting columns are fixed from about 0.1 to 0.7. Such a surface filter can be useful for the purposes of the invention if granular or spherical activated carbon is selected as the adsorption grains and the support layer, for example as a mesh, is designed to be very loose and the activated carbon beads are attached in the manner described on both sides of the air-permeable support layer, which is used for the purposes the invention can be made of glass fibers or metallic fibers. In order to be usable as an activated carbon filter layer for gas masks, such a surface filter must also be highly permeable to air and provided with the required amount of activated carbon so that the required number of packages placed on top of one another results in a mask filter with low flow resistance and high adsorption capacity.

The use of a flexible surface filter of DE-C-29 51 827 but with a carrier layer made of foam or rubber hair in an air cleaning device for removing odors and pollutants in vehicle cabins is the subject of EP-B-100 907.

What was said above for the material of DE-C-29 51 827 in order to make it useful for the purposes of the invention also applies to the material of EP-B-118 618, in which a surface filter made of an air-permeable textile carrier material and thereupon with an adhesive in an even distribution fixed activated carbon particles with a diameter of 0.1 to 1 mm, that a hot melt adhesive, a solvent-free polyurethane or a self-crosslinking acrylate by means of a template as a point or line pattern with a height of 0.05 to 0, 5 mm and a diameter or a width of 0.2 to 1 mm is printed on an air-permeable textile carrier material that only covers 30 to 70% of the surface of the carrier material, spherical activated carbon is then fixed in this printed adhesive.

DE-A-32 00 959 discloses a textile surface filter made of a textile fabric, for example a fleece, a woven fabric or a plush, which contains fibers which become temporarily sticky at elevated temperature without melting. These can be heterofil fibers made of two coaxially arranged components, the outer one of which has a lower melting point than the inner one, fibers or undrawn amorphous polyester fibers that become soft and sticky up to about 85 ° C without crystallizing at higher temperatures and finally crystallize assume the thermal stability of a normal polyester fiber. While the fibers mentioned are temporarily sticky, granular activated carbon with a size of 0.1 to 0.5 mm can also be attached to them. In this way, in contrast to a fixation of the activated carbon on the top and bottom of the textile fabrics, the exposed fibers can be covered completely and accordingly achieve high adsorption performance with low flow resistance.

Finally, DE-A-12 79 917 describes an extractor device with an adsorption filter made of a fibrous material, on the fibers of which are coated with highly viscous glue, activated carbon grains of 0.5 to 1 mm in diameter are glued. The fibers prepared in this way are contained in the known extractor device between air-permeable fabrics to form fiber mats. Such a material could also be designed according to the teaching of the invention so that it can be used to produce a mask filter with the required low pressure drop and high adsorption capacity.

In the known textile support structures or those designed according to the invention, the distance of the threads, fibers, monofilaments or wires from one another should be at least twice as large as the diameter of the activated carbon particles used in each case. It is preferably about three to ten times. If the carrier structure consists of a highly air-permeable open-pore foam layer, its pores should have a diameter of 1 to 5 mm, preferably 1.5 to 2.5 mm.

The known or suitable for the purposes of the invention support structures usually have a thickness of a few millimeters, for example 1 to 5 mm. If they are made up of monofilaments, wires or threads, their diameter is preferably 0.1 to 0.8 mm.

The highly air-permeable support structures can be flexible, but also rigid. If the granular, in particular spherical, activated carbon particles are fixed thereon and they are preferably completely covered with the activated carbon particles, the rigidity increases and the highly air-permeable support structures are even more so than that activated carbon filter layer for gas masks made of relatively rigid, pressure-resistant structures.

Instead of building up the mask filter from the superimposed surface filters, for which a few or many layers are required depending on their thickness and the thickness of the activated carbon filter layer of the gas mask, it is also possible to retrofit the surface filters loaded with activated carbon balls or granules into elementary filters in the form of strips or chips about the size of a few square centimeters. This means that you are completely independent of the shape of the objects to be filled and the elementary filters can be introduced into the cavities to be filled together with heterofil fibers or threads made of hot-melt adhesive. The whole can be solidified after filling, so that no settling or abrasion as with bulk filters is to be feared even with high mechanical stress.

Depending on the material from which the support structure is built, the activated carbon particles can be fixed directly to it or an adhesive is required. Plastic materials, in particular fiber materials, are commercially available which have the property of initially becoming superficially sticky at an elevated temperature in a certain temperature interval without melting. This property, which could be called a built-in hot melt adhesive, can be used to fix the activated carbon particles to it, as described in detail in DE-A-32 00 959.

Another possibility preferred for the purposes of the invention is that the activated carbon particles are fixed to the carrier structure with an adhesive. This gives the person skilled in the art more choice with regard to the material from which the carrier structure is constructed and the adhesive.

In the two possibilities, the diameter of the wires, monofilaments or threads of the surface structure, alone or with the adhesive, is dimensioned such that a complete covering with the activated carbon particles is possible in order to produce a filter element completely covered with the activated carbon particles in a preferred embodiment of the invention.

In order to fix the activated carbon particles to the carrier, both inorganic and organic adhesive systems can be used. The latter include polymers, in particular acrylic acid derivatives, polyurethanes, polystyrenes, polyvinyl acetates and hot melt adhesives. Preference is given to adhesive compositions which consist of crosslinkable polymers which pass through a minimum viscosity before their crosslinking. Such adhesive systems, e.g. The IMPRANIL® high solid PUR reactive products from BAYER® are initially highly viscous, i.e. they offer good initial adhesion if the carrier skeleton is sprinkled with the activated carbon particles. With the increase in temperature, they show a sharp drop in viscosity, which results in better wetting of the activated carbon particles and thus, after curing through crosslinking, particularly good adhesion. As the viscosity minimum is passed through, small constrictions form at the contact points between the support structure and activated carbon particles due to the capillary forces. Because of the practically punctiform fixation of the activated carbon beads, almost their entire surface is accessible to the gas to be cleaned after curing. If the highly air-permeable support structure consists of glass, metal or carbon fibers, adhesive materials made from enamel or glazes can be used, and because of the high temperatures required to melt these coatings, an inert atmosphere has to be used so that the activated carbon particles are not adversely affected by oxidation or even be destroyed.

The activated carbon particles must be free-flowing and wear-resistant. Their diameter is suitably three to five times smaller than that Diameter of the pores or openings of the highly air-permeable support structure. Commercial activated carbon beads with a diameter of 0.1 to 1 mm are not only the most free-flowing shape, but also withstand the highest loads due to their symmetry. Granular activated carbon particles are also suitable, provided they are not too angular or irregular in shape because it is important that the activated carbon particles can penetrate structures of several centimeters in thickness when they are fixed to the support structure.

Activated carbon particles suitable for mask filters should have an inner surface area of 600 to 2000 m 2 / g, preferably 1000 to 1600 m 2 / g, determined by the BET method. The activated carbon particles should be very pressure-resistant and are preferably highly insensitive to moisture. A very abrasion-resistant spherical activated carbon can be produced, for example, from coal tar pitch or petroleum distillation residues. Additional hardening of the surface and remarkable insensitivity to moisture can be achieved through a special post-treatment. The production of suitable activated carbon spheres is described for example in EP-B-118 618, DE-B-29 32 571 and DE-A-30 41 115.

In order to increase the abrasion resistance, the surface of the activated carbon can also be impregnated in a plastic dispersion or a coal tar pitch solution or bitumen solution and subjected to a slight post-activation. The sensitivity to water vapor can be significantly reduced by adding ammonia gas during the after-activation and cooling to 100 ° C in the absence of air.

The activated carbon particles can be impregnated with metal compounds, in particular the metals silver, copper and chromium. Next to it encapsulated enzymes which break down toxins are also present, as described in EP-B-118 618.

With the filters described, excellent separation effects of pollutants and gases were achieved with extremely low pressure drops. Surprisingly, it has been shown that the activated carbon grains do not have to be flowed through for high effectiveness with little pressure loss, but only need to be flowed through. The Brownian motion of the gas molecules is sufficient to achieve a high adsorption rate. A loosened activated carbon filter layer according to the invention has a larger volume than a bulk filter with the same performance but a considerably lower flow resistance. The amount of 100 g of activated carbon which is customary today for an activated carbon filter layer of a gas mask can be accommodated in a volume of about 350 ml in the support structures according to the invention. The carrier layer preferably contains 50 to 300 g of activated carbon per liter.

Because of the diverse possibilities of shaping the filter layer according to the invention, the shape of the mask filter can also be adapted to a wide variety of needs. The filter can be placed in a hood mask, for example around the head or neck, and then serves as an additional head or neck protection against impacts. The filtered air should flow past the eyes to prevent the clear windows from fogging up. A plate-shaped filter can be worn on the chest or back and connected to the mask body by a flexible tube. Cylindrical filter elements with a diameter of a few centimeters can preferably also be accommodated directly in a flexible hose or can be coupled together to form a tubular structure using suitable means. Such interchangeable filter elements can also have different functions. The inlet opening of the filter elements Containing or composed of hoses is conveniently located on the inside of a protective suit.

Claims (23)

1. An activated charcoal filter layer for gas masks, characterized in that it is essentially formed of superimposed, highly air-permeable support structures with a layer of granular or spherical activated charcoal particles with a diameter of 0.1 to 1 mm affixed to such structures, the filter layer having a pressure drop of less than 10 mm water column at a thickness of 4 cm with a circular cross-section of 100 cm² at an air flow of 1 l/sec.
2. An activated charcoal filter layer according to claim 1, characterized in that the support structure is a highly air-permeable foam layer.
3. An activated charcoal filter layer according to claim 2, characterized in that the openings or pores of the foam have a diameter of 1 to 5 mm, preferably from 1.5 to 2.5 mm.
4. An activated charcoal filter layer according to claim 1, characterized in that the support structure consists of a fiber-like material or rubber hair, or is a textile surface structure or a nonwoven, woven or plush textile.
5. An activated charcoal filter layer according to claim 1, characterized in that the support structure contains textile fibers which temporarily become sticky at elevated temperatures, without melting.
6. An activated charcoal filter layer according to claim 5, characterized in that the fibers are heterophilic fibers of two coaxially arranged components, the outer one of which has a lower melting point as the inner fiber.
7. An activated charcoal filter layer according to claim 6, characterized in that the fibers are unstretched amorphous polyester fibers which become soft and sticky up to about 85 °C.
8. An activated charcoal filter layer according to one of claims 1 to 7, characterized in that the support structure is completely covered with the activated charcoal particles.
9. An activated charcoal filter layer according to one of claims 1 to 8, characterized in that the activated charcoal particles are affixed on the support structure with an adhesive mass.
10. An activated charcoal filter layer according to one of claims 1 to 9, characterized in that the adhesive mass comprises polymers, in particular acrylic acid derivatives, polyurethanes, polystyrenes, polyvinyl acetates or hot-melt glues.
11. An activated charcoal filter layer according to one of claims 1 to 10, characterized in that the adhesive mass consists of cross-linked polymers which pass through a viscosity minimum before being cross-linked.
12. An activated charcoal filter layer according to one of claims 1 to 11, characterized in that the support layer comprises 50 to 300 g activated charcoal per liter.
13. An activated charcoal filter layer according to one of claims 1 to 12, characterized in that the activated charcoal particles are very pressure-resistant.
14. An activated charcoal filter layer according to one of claims 1 to 13, characterized in that the activated charcoal particles are extremely moisture-resistant.
15. An activated charcoal filter layer according to one of claims 1 to 14, characterized in that the activated charcoal particles are impregnated with metal compounds, in particular with metals like silver, copper and chromium.
16. An activated charcoal filter layer according to one of claims 1 to 15, characterized in that it carries encapsulated enzymes in addition to the activated charcoal particles.
17. An activated charcoal filter layer according to one of claims 1 to 16, characterized in that the activated charcoal filter layer has a pressure drop of less than 5 mm, preferably less than 2 mm water column at a thickness of 4 cm with a circular cross-section of 100 cm² at an air flow of 1 l/sec.
18. A hood gas mask characterized in that it comprises an activated charcoal filter layer according to one or more of claims 1 to 17.
19. A hood gas mask according to claim 18, characterized in that the activated charcoal filter layer is formed as a head or neck protection.
20. A gas mask characterized in that the activated charcoal filter layer according to one or more of claims 1 to 17 is formed in the shape of a plate, so that it can be worn on the chest or back, the filter layer being connected with the mask element by way of a flexible hose.
21. A gas mask characterized in that the activated charcoal filter layer according to one or more of claims 1 to 17 forms cylindrical filter elements with a diameter of several centimeters and arranged in a flexible hose.
22. A gas mask according to one of claims 18 to 21, characterized in that replaceable, preferably cylindrical filter elements, which may have different functions, are joined to a hose.
23. Use of an activated charcoal filter layer according to one or more of claims 1 to 17 for gas masks.