Title of Invention

"A PROCESS FOR PREPARING A DESSICANT COATED SUBSTRATE"

Abstract A process for preparing a desiccant coated substrate comprising: - preparing a solution of desiccant and water in the proportion of 90- 110 % by weight depending upon the atmospheric conditions, emulsifying agent if defined of the kind as herein described in the proportion of 5-25 % of the dried desiccant weight for keeping the ingredients in suspension., - coating in any known manner the said desiccant solution onto the substrate of the kind as herein described using water based adhesive (solid contact) compound such as herein described , wherein the amount of adhesive added ranges between 10-25 % of weight of dry desiccant powder.
Full Text The present invention relates to a process for preparing a desiccant coated substrate for use in enthalpy wheels.
BACKGROUND
The invention relates to air-conditioning systems and more particularly to rotary air to air heat exchangers, also known as heat wheels. "Heat wheels" are well known in the air-conditioning art for their ability to transfer heat, water vapor or both between two counter flowing air streams. The ability to transfer water vapor (Latent Energy) is of particular interest since it dehumidifies the outdoor air during the cooling season and humidifies outdoor air during the heating season. This characteristic serves to reduce the energy demands required to condition outdoor air by as much as 95 %.
Known heat transfer devices have been described as falling into one of three types:
(1) those designed primarily for the removal of sensible heat
(2) those designed primarily for the removal of latent heat and
(3) those designed fro the removal of both sensible and latent heat also known as "enthalpy wheels".
Examples of sensible heat wheels are disclosed in US Patent Nos. (2,563,415 and 4,432,40. Examples of Latent heat wheels have been disclosed in US Patent Nos.{2,700,577 and 3,76,446. Enthalpy heat wheels are disclosed in US Patent Nos.'i3,307,617; 3,664,095,3,733,791; 4,172,164 and 4,255,171.



Enthalpy wheels rely on a coating of desiccant material on a substrate to transfer the latent energy. Examples of desiccants used for this application include silica gels, aluminium oxides and molecular sieves. Common substrates include aluminium foil, stainless steel strips,plastic films and organic and inorganic papers. Methods used to apply this desiccant coat include controlled corrosion of an aluminium substrate to produce aluminium oxide, 'in situ' formation of silica gels in ceramic paper and traditional coating methods, using solvent based binding agents. The coating method chosen must cause the desiccant to adhere tightly to the substrate while not effecting the breathibilty of the desiccant or its capacity to absorb more moisture. Also excessive coating during the process should be avoided so as

to prevent flaking problems. As the latent recovery performance is enhanced by a larger desiccant mass, having a relatively thick, well breathing desiccant coating is desirable. In many manufacturing processes for this product, the desiccant is coated onto the substrate before subsequent forming processes, such as corrugating and winding. Therefore, it is important that the coating layers are able to withstand these forming processes without damage.
The object of the present invention is to improve the breathibilty of the desiccant
Yet another object of the present invention is to allow the coated desiccant substrate to withstand the forming process without damage during the formation of the enthalpy wheels.
Summary of the invention
Accordingly the present invention provides a process for preparing a desiccant coated substrate comprising preparing a solution of desiccant and water in the proportion of 90 - 110% by weight depending upon the atmospheric conditions,if desired, adding emulsifying agent of the kind as herein described in the proportion of 5-25 % of the dried desiccant weight for keeping the ingredients in suspension., coating in any known manner the said desiccant mixture the substrate of the kind as herein described using water based adhesive compound such as herein described , wherein the amount of adhesive ( solid content) added ranges between. 10-25 % of weight of dry desiccant powder.
The water based adhesive is selected from styrene butadiene, copolymer latex's, polyvinyl acetate, vinyl chloride, vinylidene chloride, polyurethane's and polyacrylics.The said adhesive contains 4-12% of solid content, or 15-25% of liquid contents.
The emulsifying agent used in the process of the present invention is preferably is water soluble and the proportion of the said agent is preferably in the proportion of 5-15 % by weight of the dried desiccant.
The desiccant is selected from silica gel, aluminium oxide or molecular sieve.

The substrate is selected from aluminium foil plastic film, a metallic foil or paper, both organic or inorganic or a combination thereof

The thickness of the substrate ranges between 15µm to 150 µm.. The thickness of the coating ranges between 5 g/sq. m - 150g/sq.m.
The invention specifically relates to a method of coating the desiccant material onto substrate with water based binders, utilizing emulsion polymerization techniques
The water based adhesives include styrene butadiene, copolymer latex's, polyvinyl acetate, vinyl chloride, vinylidene chloride, polyurethane's and polyacrylics. These are either polymerized alone or in combination with other monomers, such as acrylonitrile.
Emulsion polymerization takes place within a mixture of water and monomer. In the process a surface active agent such as sodium dodecyl sulfate is dissolved in water to form colloidal agglomerates known as "micelles". The hydrocarbon portion of the micelle is capable of absorbing or solublizing organic monomers such as styrene, butadiene, vinyl chloride, vinyl acetate or acrylic which are normally not soluble in water. When free radicals are generated within the water phase polymerization of the monomer will be initiated within the micelle. As the polymer grows, it consumes monomer,and more monomer enters the micelle from the external phase to join the polymer.
To the prepared emulsion, the user adds any materials which incorporate the properties needed in the finished coating- in the preferred case water, desiccant powder, emulsifying agent,pH modifier and catalyzing agent to accelerate the curing of the coating. When the coating dries using heated air, the emulsified resin particles, which have been separated by water, move together and coalesce into a coating film.
In the known arts, solvent based binding agents were used for the purpose of coating a desiccant onto a substrate. U.S Patent No, 4,769,053 refers to the binder composition preferably including a "solvent such as toluene".

Use of water based emulsions in the manufacture of enthalpy wheels has the following advantages:
1. These binders generally perform well with most desiccants, allowing the adsorption characteristics of the desiccant to remain essentially unchanged after coating.
2. These binders have a very low levels of volatile organic compounds (V.O. C's) which makes the said process a negligible fire hazard and "environment friendly' and
3. Since no V.O.C are given off during the process, the need for expensive ventilation and fire safety equipment is reduced or eliminated as compared to conventional solvent based processes. . The only solvent used in the process is an emulsifying agent used to keep the desiccant /binder from separating. This solvent is water soluble, has a very high flash point and is classified as " non-flammable" by most agencies.
Latent capacity of the desiccant is regulatory preserved by virtue of the desiccant being prepared into a slurry with water prior to adding the binder and emulsion solvent to he mixture.This ensures that the all adsorption sites in the desiccant are filled with water molecules, which when the coating is dry. will provide maximum of adsorption sites in the coating that are not blocked with the binder and are able to hold water molecules.
With this process, very thick desiccant coatings are possible. Using 40jum thick aluminum foil as a substrate, coating thickness upto 120gsm on each side is possible. This might be desirable when it is necessary to absorb large amounts of water vapor, such as is the case of dehumidification. Under these conditions, the coating remains flexible enough to allow the corrugating and forming processes to occur without damaging the coating layers.



We claim:
A process for preparing a desiccant coated substrate comprising:
- preparing a solution of desiccant and water in the proportion of 90-
110 % by weight depending upon the atmospheric conditions,
emulsifying agent if defined of the kind as herein described in the proportion of 5-25 % of the dried desiccant weight for keeping the ingredients in suspension.,
- coating in any known manner the said desiccant solution onto the
substrate of the kind as herein described using water based adhesive (solid contact) compound such as herein described, wherein the amount of adhesive added ranges between 10-25 % of weight of dry desiccant powder.
2. A process as claimed in claim 1 wherein said water based adhesive is selected from styrene butadiene, copolymer latex's, polyvinyl acetate, vinyl chloride, vinylidene chloride, polyurethane's and polyacrylics.
3. A process as claimed in claim 1 wherein said emulsifying agent is water soluble .
4. A process as claimed in claim 1 wherein the emulsifying agent is in the proportion of 5-15 % of the dried desiccant.
5. A process as claimed in claim 2 wherein the said adhesive contains 4-12% of said content, or 15-25% of liquid contents.
6. A process as claimed in claim 1 wherein the desiccant is selected from silica gel, aluminium oxide or molecular sieve.
7. A process as claimed in claim 1 wherein the substrate is
an aluminium foil plastic film, a metallic foil or paper.


8. A process as claimed in claims 1 and 6 wherein said
substrate has a thickness ranging between 15 g/sq.m to 150 g/sq.m.
9. A process as claimed in claim 1 wherein the thickness of
the coating ranges between 5 g/sq. m - 150 g/sq.m.
10. A process for preparing a desiccant coated substrate substantially as
herein described.


Documents:

574-del-1996-abstract.pdf

574-del-1996-claims.pdf

574-del-1996-complete specification (granted).pdf

574-del-1996-correspondence-others.pdf

574-del-1996-correspondence-po.pdf

574-del-1996-description (complete).pdf

574-del-1996-description (provisional).pdf

574-del-1996-form-1.pdf

574-del-1996-form-2.pdf

574-del-1996-form-5.pdf

574-del-1996-form-6.pdf

574-del-1996-pa.pdf


Patent Number 197421
Indian Patent Application Number 574/DEL/1996
PG Journal Number 29/2008
Publication Date 26-Sep-2008
Grant Date 16-Mar-2007
Date of Filing 18-Mar-1996
Name of Patentee DEEPAK PAHWA
Applicant Address 20 RAJPUR ROAD, NEW DELHI-110054.
Inventors:
# Inventor's Name Inventor's Address
1 MR.MARK GOWAN CLARK 344 TENNESSEE NORTH EAST, ALBUQUERQUE, NEW MEXICO 87108, U.S.A.
2 MR. DEEPAK PAHWA 20 RAJPUR ROAD, NEW DELHI-110054, INDIA.
PCT International Classification Number C23C 16/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA