Coating processes – Medical or dental purpose product; parts; subcombinations;... – Flexible web – sheet – film – or filament base
Reexamination Certificate
2000-11-16
2002-08-27
Beck, Shrive P. (Department: 1762)
Coating processes
Medical or dental purpose product; parts; subcombinations;...
Flexible web, sheet, film, or filament base
C427S245000, C427S246000, C427S439000, C427S374100, C427S398100
Reexamination Certificate
active
06440489
ABSTRACT:
The present invention relates to the dehumidification of air with the aid of a moisture exchanging element, such as a heat exchanging element and dehumidifying element. An inventive moisture exchanging element is comprised of a fibre matrix that has been impregnated with waterglass. More specifically, the invention relates to a dehumidifying element that has bacteriostatic properties, and to a method of its manufacture.
BACKGROUND OF THE INVENTION
It is necessary to control the humidity of the air in conjunction with certain manufacturing processes and in the storage of moisture-sensitive products. A control of this nature is also often applied in order to avoid corrosion of expensive equipment. It is normally necessary to dehumidify the air, which can be achieved with the aid of different types of air dehumidifiers. The so-called rotary sorption dehumidifier is an example of a typical air dehumidifier. Such dehumidifiers are described in SE-B-462 671, SE-B-501 507 and WO 93/08910, among other documents.
FIG. 5
outlines a rotary sorption dehumidifier of this kind.
Swedish Patent Application 9804152-8, which was published after the filing date of the present application, describes an advantageous process for the manufacture of dehumidifying elements, in which paper is impregnated with a highly concentrated waterglass solution. The advantage with this process is that no energy consuming drying stage is required.
The rotor is a cylinder that has a matrix which is comprised of alternate thin pleated and planar walls that contain an hygroscopic substance, such as silica gel. The walls form in the direction of airflow narrow channels through which the air flows. Heated air that releases moisture that has fastened to the walls is conducted through a smaller sector, This air flow is then passed outside the space that shall be kept dry, via a channel system. Dry air is obtained continuously as the rotor rotates between the two air flows.
The hygiene requirements are very high in certain applications, for instance in the manufacture of pharmaceutical products and the production of foodstuffs. This will not normally constitute a problem, as it is difficult for bacteria to grow in the rotor. Most rotors have an inorganic composition and thus contain no bacteria nutrients. Furthermore, the rotor is heated at regular intervals during operation between temperatures of 100 and 140° C., and is very dry during the whole of the cycle. Consequently, the environment is sufficiently hostile to microorganisms to satisfy hygiene requirements in operation.
However, it is difficult with conventional techniques to guarantee low bacterial growth in dehumidifying elements over long periods of inactivity. Organic material, for instance in the form of dust particles, may have fastened in the rotor and favourable conditions for microorganisms can occur locally because no heating or drying of the element takes place.
Problems can also occur when exchanging heat from air to air, including bad odours and spreading of bacteria among other things, since the moisture content of the air shall also be transferred in rotary heat exchangers (enthalpy exchange). Some of these problems may have connection with bacterial growth in the heat exchange element, which is very similar to that described above.
There is thus a need for a moisture exchange element that includes one or more components which actively counteract the growth of microorganisms.
SUMMARY OF THE INVENTION
It has now been found that a bacteriostatic moisture exchange element that solves the aforesaid problems of malodours and the growth of microorganisms can be produced by a method comprising the steps of:
a) providing paper, such as facing paper and/or fluted paper,
b) immersing the paper in a highly concentrated waterglass solution at a temperature in
the range of 45-95° C., where said highly concentrated waterglass solution has a viscosity of at least 350 mPa·s at a temperature of 45° C.
c) cooling the immersed paper with air at a temperature of 35° C. at the highest, and preferably at 25° C. at the highest;
d) producing a waterglass impregnated fibre matrix with a starting point from the paper in step c), followed by chemical conversion of the waterglass on said paper with the aid of known processes for the manufacture of a moisture exchange element; and
e) impregnating the moisture exchange element in step d) with one or more aqueous solutions of an hygroscopic salt and a water soluble substance that inhibits the growth of microorganisms.
Definitions
The term “moisture exchange element” as used in this document refers to elements that are able to reduce the moisture content of air. Examples of moisture exchange elements are heat exchange elements in rotary heat exchangers for air-to-air heat exchange, and air dehumidifying elements. An inventive moisture exchange element is comprised of a fibre matrix that has been impregnated with waterglass.
The term “waterglass”, as used in this document, relates to aqueous solutions of sodium silicate (“soda waterglass”) or potassium silicate (“potash waterglass”). Soda waterglass and potash waterglass are often designated as (Na
2
O)
m
(SiO
2
)
n
and (K
2
O)
m
SiO
2
)
n
respectively, and the mole ratio between the two oxides (n/m) can vary, as will be apparent. In the case of the present invention, soda waterglass with n/m in the range of 3.2-3.5 is preferred, and waterglass with n/m from 3.3 to 3.4 is particularly preferred.
The term “highly concentrated waterglass” as used in this document refers to waterglass that has a viscosity of at least 350 mPa·s at 45° C. The upper viscosity limit is 800 mPa·s at 95° C. The viscosity of highly concentrated waterglass at room temperature is so high as to make it extremely difficult to immerse paper in the waterglass at this temperature in practice and therewith cause the waterglass to wet the paper. Typically concentrated waterglass according to known technology has a viscosity of up to 200 mPa·s at 20° C. Highly concentrated waterglass, on the other hand, has a much higher viscosity at 20° C. and in its lowest concentrated form can be likened to cold syrup.
The term “paper” as used in this document relates to sheets produced from organic fibres, such as cellulose, or from inorganic fibres, such as ceramic fibres, glass fibres, slag fibres, carbon fibres, mineral fibres and mixtures thereof. Inorganic fibres are preferred. It is also preferred to use glass fibres and/or mineral fibres with an admixture of up to 20% cellulose fibres or synthetic fibres. The paper will have a typical thickness of 0.1-0.3 mm. The flute height of the fluted or corrugated paper is typically 1-5 mm and its flute length is typically 1.5-7 mm. The weight of the paper is typically 20-50 g/m
2
.
The term “hygroscopic salt” as used in this document refers to salts that are able to absorb air-carried water. According to the invention, the absorption capacity of hygroscopic salts shall be such that the salts will be in a dissolved state at the relative humidities in which bacteria thrive. Examples of such salts are chlorides, bromides and iodides of lithium, sodium, potassium, magnesium and calcium. Lithium chloride, calcium chloride and sodium chloride are particularly preferred.
The expression “water soluble substances capable of inhibiting the growth of microorganisms” as used in this document refers to water soluble substances that have a growth inhibiting ability. Examples of such substances are azides, such as sodium azide, and water soluble silver and copper salts, such as silver nitrate, copper nitrate and copper sulphate. In principle, the invention can be practised with any water soluble substance whatsoever, provided that said substance will inhibit the growth of microorganisms.
With regard to the selection of hygroscopic salts and water soluble substances that are capable of inhibiting the growth of microorganisms, it is necessary that their use in conjunction with moisture exchanging elements will not endanger human beings and the environment. Neither should they have a negative effe
Beck Shrive P.
Kolb Michener Jennifer
Proflute AB
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