Filtering material and process for the production thereof,...

Details Filtering material and process for the production thereof,... Filtering material and process for the production thereof,...

1999-04-16

2001-05-08

Zirker, Daniel (Department: 1771)

Liquid purification or separation

Filter

Material

C210S506000, C210S502100, C442S150000, C428S143000, C428S402000, C055S521000, C055S524000

Reexamination Certificate

active

06227383

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to filter materials with adsorptive properties and to a method for their manufacture. Likewise, the present invention has as its subject matter adsorption filters which consist of at least two layers of these filter materials.
In the state of the art a variety of filter materials are known. For example, bulk filters are known, in which the filter material consists of a loose bulk of adsorption materials which necessarily must be held together by a housing or container. These classical bulk filters have a series of to some extent serious disadvantages. This is because there are limitations on the selection of the particle size in that if the adsorbent particles are of too small a diameter they offer too high a resistance to flow, and on the other hand too large a particle diameter results in poor adsorption kinetics. Since the adsorption material is present in the form of loose bulk material, breakthroughs regularly occur. Also, as a result of vibration or shaking in the use of such bulk filters, adsorption material can be lost through abrasion.
Attempts are made to get around these disadvantages of conventional bulk filters by making so-called sheet filters which consist of an air-permeable support material to which first a glue must be applied, discontinuously and generally in the form of dots or lines, onto which the adsorbent particles are then affixed. The air-permeable support material can be woven or knit goods, or also an open-pore, reticulated polyurethane foam. The disadvantage of these sheet filters lies in their generally expensive manufacture and in their not always sufficient stability of shape. Also, in their manufacture and in their subsequent use, a bad odor is produced time and again especially due to degradation products or solvent components of the glues used.
SUMMARY OF THE INVENTION
The problem to which the present invention is addressed is to offer an easily available filter material with adsorptive properties, which is especially stable in shape, but nevertheless easy to emboss and/or to fold, and avoids the disadvantages of the filter materials of the state of the art.
The subject of the present invention is likewise the offering of a method for the production of such filter material, one which especially succeeds without the use of conventional adhesives.
Another problem for the present invention is seen in the development of adsorption filters which contain at least two layers of these filter materials.
The purpose of the invention is achieved by a filter material with adsorptive properties, which comprises a support in sheet form, which is covered on one or both sides with a binder layer that becomes tacky when heated, and on which an adsorption material is affixed. In particular, the adsorption material is made to adhere thermally, i.e., with the heating of the binder layer.
The support material in sheet form can be a metal foil, especially an aluminum or copper foil, the thickness of the metal foil being able to vary according to its application. The thickness of the sheet should be, however, at least 5&mgr;m, and should amount preferably to at least 10&mgr;m, especially at least 40&mgr;m. A preferred support material is an aluminum foil coated with a polyolefin, such as is used, for example, in the packaging industry, although under certain circumstances a polyester film on its back and intended as reinforcement is not objectionable insofar as excessively high temperatures do not occur.
The support material in sheet form, however, can also be paper or cardboard. The paper or cardboard in this case has generally a thickness of 0.1 to 2 mm, preferably 0.2 to 1 mm. This corresponds to a surface weight of paper or cardboard of at least about 40 gm
2
. In particular, a stiff, embossable paper coated with plastic on one or both sides is used, the plastic becoming tacky upon heat treatment and serving as a binder composition for adhering the adsorptive material.
A certain minimum thickness of the support material is necessary in order to assure a certain minimum stability of the support material. On the other hand, a certain thickness should not be exceeded so that the material will be workable, and especially, embossable.
The binder layer that becomes tacky when heated is preferably a polyolefin coating, especially a polyethylene or polypropylene coating.
The binder layer that becomes tacky when heated generally has a layer thickness of at least 0.005 mm, preferably of at least 0.01 mm, and especially 0.02 mm.
A binder layer thickness of at least 0.005 mm is necessary in order to assure durable adhesion of the adsorption material even under stress, shaking or vibration. That is to say, the binder layer should not be thinner than 0.005 mm in order to achieve good adhesion, especially when using adsorbent granules with diameters of more than 0.2 mm.
The binder layer is applied to the support in the amount of at least 5 g/m
2
, preferably at least 10 g/mm
2
.
Adsorption materials suitable according to the invention are preferably selected from the group of active carbon, porous polymers, molecular sieves, ion exchangers and sustained release polymers (=polymers which are charged or filled with an active substance of a great variety of kinds and release it slowly).
For example, the adsorption material can consist of granular or pelleted adsorbent particles, which have preferably grain sizes of 0.1 to 2.0 mm, especially grain sizes of 0.2 to 1 mm, whereby the pressure loss can be controlled by the size and amount of the adsorbent grains and their quantity. The particles used in the invention generally have an internal surface area (BET) of at least 500 m
2
/g, preferably of at least 900 m
2
/g.
Adsorber particles suitable for use in the invention are particularly abrasion resistant.
The preferred adsorbent is active carbon. According to a special embodiment of the present invention, it can be spherical active carbon particles or granular carbon. In the selection of the active carbon, attrition-resistant types are recommendable, because otherwise dust would be formed when the excess adsorbent particles are vacuumed up and returned to the spreading apparatus, which would “dust,” so to speak, the hot and sticky adherent coating, which could lead to poorer adhesion of the active carbon.
Also, inorganic adsorbents, such as zeolites or special formulations, for example, can be used for the adsorption of H
2
S, NH
3
or carbon monoxide. Likewise, “porous polymers,”such as those offered under the name of “Sorbathene,” are suitable for the invention. In particular, the “porous polymers” may be spherical adsorbents.
Also polymer spheres carbonized at low temperature and activated, especially sulfonated, carbonized and activated polymer spheres, are suitable according to the invention as adsorbent particles.
Finally, ion exchangers, sustained-release polymers (i.e., polymers which are charged or filled with an active substance of a wide variety of kinds and release them slowly), but also silica gel beads, can be used, and a regenerative drying can be performed in connection with an electrically heated metal foil as support, for example.
If granular or spherical adsorbent particles are used as adsorption material, the filter materials according to the invention can be prepared by the following method:
a) First a support coated on one or both sides with a binder layer that becomes tacky when heated is passed through a bed of the hot adsorbents to be applied to the support, so that the adsorbents are brought in contact with the coating and are fixed thereon.
b) Optionally, the adsorbents are pressed on.
c) Then the excess adsorption particles are removed, for example by shaking or vibration or by aspiration.
d) Before or after the excess adsorbent particles are removed in step c), the material produced in this manner is allowed to cool.
If the adsorption material consists of granular or spherical adsorbent particles and is to be applied to only one side, the filter materials of the invention alternatively c

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