Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-02-28
2003-10-07
Barr, Michael (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S398100, C427S430100, C427S439000, C427S443200, C427S337000
Reexamination Certificate
active
06630206
ABSTRACT:
The present invention relates to the dehumidification of air with the aid of a dehumidifying element that comprises a fibre matrix which has been impregnated with waterglass and which also includes a molecular sieve. More specifically, the invention relates to a method of manufacturing a dehumidifying element.
TECHNICAL BACKGROUND
Air dehumidification is conventionally achieved with a type of dehumidifying element that can be produced by joining together flat and corrugated or fluted fibre material having moisture absorbent properties, to form a laminate that is rolled-up into a rotor-form or stacked in the form of a block. Such laminates are shown in FIG.
3
. The dehumidifying element can be likened to corrugated board that has been rolled-up to provide a rotor, or corrugated board that has been cut into lengths and stacked in block form. This element includes a structure that has many parallel channels. The corrugations or flutes are normally from 1.5 to 3 mm high and the channels have a length of from 50 to 400 mm.
FIG. 4
shows a part-sector of one such rotor.
A rotor is cut from the roll or block of rolled material and ground, and is often provided with a hub, spokes and/or a skirt. The rotor constitutes “the heart” of an air dehumidifier, wherewith the air is driven through the multiple of channels in the rotor by means of a blower. Because the channel walls contain a moisture absorbing substance, the air will be dry after having passed through the rotor. A small heated air flow passes through a smaller sector of the rotor and expels the air present in this sector. Dry air can be produced continually, by continuously rotating the rotor between the sectors with air to be dehumidified and heated air. The expelled moisture is carried away with the heated air flow in a separate channel system. This principle is also shown in FIG.
5
.
SE B 460 705 describes a method of producing a dehumidifying element in which paper that contains ceramic fibres is impregnated with a waterglass solution prior to or subsequent to lamination, wherein the paper is heated and dried subsequent to impregnation, to form hydrated waterglass having a water content of 3-20%. The matrix thus formed is then immersed in acid so as to form a silica-hydrogel.
SE B 460 021 also relates to a dehumidifying element that is comprised of a laminate of sheet of ceramic fibres that is fluted on one side and that has a paper thickness of 0.18-0.25 mm, a flute length of 2.5-4.2 mm and a flute height of 1.5-2.3 mm. This laminate is impregnated with an active silicon dioxide-aluminium oxide-aerogel consisting of 97-85% silicon dioxide and 3-15% aluminium oxide. The element is produced by immersing ceramic paper in an aqueous solution of waterglass and then drying the paper. The paper is then immersed in an aqueous solution of aluminium sulphate and then dried again.
SE B 462 671 also describes a method of producing a dehumidifying element in which a laminate comprising a corrugated or fluted sheet and a facing sheet is impregnated with an aqueous solution of waterglass, followed by drying and heating the laminate to a water content of 5-45% and thereafter immersing the laminate in an aqueous metal salt solution, and finally further drying and heating the laminate.
SE B 469 976 teaches a method of producing dehumidifying elements in which paper webs that contain a mouldable material, such as fibre glass or cellulose, are saturated with concentrated waterglass solution and dried to a dry solids content of 45-65% with respect to waterglass, and then corrugated, whereafter the resultant laminate is dried to a dry solids content of about 60-95%.
EP B 0 642 384 relates to a method of treating dehumidifying elements with the aim of influencing the pore size of the silica gel. This is achieved by treating the elements with an acid, base and a stabilising solution that contains salts of zinc, aluminium and phosphate. Waterglass is applied to the paper and the waterglass then dried, also in this case.
All of the above applications disclose an impregnation step followed by a drying step in conjunction with manufacture of dehumidifying elements that consist of a silica gel matrix. Drying stages are energy demanding and thereby lead to high costs. Moreover, it is difficult to apply sufficient quantities of waterglass when the solution has the low concentration required by known techniques, meaning that the dehumidifying elements produced will have a limited silica gel content and therewith a less than optimal capacity. There is thus a need for improved methods that will lower production costs and increase performance and the quality of the end product.
In certain applications of dehumidifying elements, it is necessary for the dehumidified air to be very dry. For example, a dew point of beneath −40° C. is required when drying plastic granules for the manufacture of PET-products, while still lower moisture contents are sometimes required in respect of dehumidifying air in chambers where moisture sensitive products are tested.
A rotor that contains silica gel as a hydroscopic substance can not reach these states without unreasonably high energy consumption by the regeneration process. Thus, there is also a need for novel dehumidifying elements that are able to generate still drier air than that which can be achieved with a dehumidifying element based on silica gel.
SUMMARY OF THE INVENTION
It has now been found possible to completely eliminate the drying stage after immersion of paper in the waterglass solution while, at the same time, increasing the amount of silica gel matrix applied and to produce finally a dehumidifying element that is able to dry air to a dew point beneath −40° C., by means of a method comprising the steps of
a) providing a piece of paper, such as facing paper and/or fluted paper;
b) immersing said paper in a highly concentrated waterglass solution in which a molecular sieve has been suspended, at a temperature within the range of 45-95° C., wherein said suspension of highly concentrated waterglass/molecular sieve has a viscosity of at least 350 mPa.s at a temperature of 45° C.; and
c) cooling the immersed paper with air having a temperature of at most 45° C. and preferably at most 25° C.
DETAILED DESCRIPTION OF THE INVENTION
A moisture adsorbent that enables air to be dried to very low moisture contents is a molecular sieve. The adsorbent is also called molecular screen, mole screen or zeolite. According to the present invention, a molecular sieve is a highly porous crystalline aluminium silicate which contains in its crystalline structure a large number of very small pores of equal pore opening diameters. Moisture is attracted to the surface and the attraction force is high, particularly on the inside of the pores. In order for molecules to fasten within the pores, it must be possible for the molecules to enter through the pore openings, which have a diameter of between 3 and 10 Å in respect of different molecular sieves. The water molecule is small and is able to enter the pores, whereas larger molecules are unable to enter and instead pass by the sieve.
Molecular sieves based on aluminium silicate attract polar substances, such as water, with greater or lesser power. A molecular sieve of this nature is thus hydrophilic. The attractive force of the sieve diminishes when the aluminium content decreases. The silicate crystal becomes hydrophobic when containing only a small amount of aluminium or no aluminium at all, and can be used for the adsorption of hydrophobic substances, such as organic solvents for instance. Thus, it is necessary in conjunction with the present invention to utilise hydrophilic molecular sieves, for instance sieves that have a high aluminium silicate content.
The vapour pressure across a hydrophilic molecular sieve that has a given moisture content is much lower than, for instance, the vapour pressure across silica gel that has the same moisture content in a range where said moisture content is relatively low. Expressed in another way, a molecular sieve is able to tak
Barr Michael
Proflute AB
Young & Thompson
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