RADIATION CURABLE SEALANT COMPOSITION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

60/850,598, filed on October 10, 2006. The disclosure of the above application is incorporated herein by reference.

FIELD

[0002] The present invention relates to a radiation curable sealant composition for use in sealing the edges of evaporative heat exchangers used in evaporative coolers, and more particularly, to a ultra-violet radiation curable sealant composition which can be applied and cured quickly to provide an effective seal against moisture and chemicals.

BACKGROUND OF THE INVENTION

[0003] Evaporative or swamp cooler systems are commonly used in warm climates having relatively low humidity to produce cool air for the purpose cooling the interior of houses and other structures at a relatively low cost. Such evaporative coolers typically comprise a housing including one or more layers of coated paper sheets that are adhered with an adhesive to form a heat and mass exchanger, herein referred to as an "exchanger." The exchanger is saturated with water and functions to cool warm air that flows through the cooling exchanger and into a cooling system. The edges of the laminated sheets are typically sealed to prevent the escape of water and to prevent the

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formation of mineral deposits which may form due to the use of water containing high mineral content. Current sealants used for this application include moisture curable MS Polymer® sealants and silicone sealants. However, the use of such sealants is costly and may require long cure times of up to 12 hours.

[0004] Accordingly, there is still a need in the art for a curable sealant composition which is capable of effectively sealing the edges of heat exchangers used in an evaporative cooler, which sealant may be quickly cured, which provides effective sealing, and which is cost effective to apply.

SUMMARY OF THE INVENTION

[0005] The present invention provides a sealant composition which may be applied to the edges of heat exchangers used in evaporative coolers. The sealant composition may be cured quickly by exposure to a radiation source. Once the composition is cured in place, the composition provides effective sealing against moisture and chemicals.

[0006] According to one aspect of the present invention, an ultra-violet (UV) curable liquid sealant composition is provided for use on the edges of a heat exchanger used in an evaporative cooler. The composition comprises UV curable oligomers and/or monomers and a thixotropic agent. Preferably, the composition comprises urethane acrylate oligomers and/or monomers. The thixotropic agent preferably comprises fumed silica. Preferably, the sealant further includes a wetting agent. The sealant preferably further includes a coloring agent to provide a visual indication that the heat

exchanger has been properly sealed. The sealant also preferably includes an odor masking agent to mask the odor of the composition.

[0007] The composition is preferably applied to the evaporative heat exchanger by either dipping the exchanger in a bath of the sealant composition or by rolling. The composition may then be cured within a few seconds by exposure to a suitable UV source such as a UV lamp. After curing, the composition effectively seals the edges of the cooling exchanger and prevents moisture and/or chemical infiltration. The sealant also exhibits sufficient flexibility to withstand normal vibrations and shock experienced during shipping and/or use of the evaporative cooler.

[0008] Accordingly, it is a feature of the present invention to provide a UV curable sealant composition for use in evaporative coolers which provides effective sealing properties. This, and other features and advantages of the present invention will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic cross-sectional view of an embodiment of a curable sealing composition applied as a sealant at an edge of an exemplary cooling exchanger in an evaporative cooler according to the principles of the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [00010] With reference to FIG. 1 , an article or heat exchanger is generally indicated by reference number 10. The heat exchanger 10 is preferably employed in an evaporative cooler to refrigerate air. The heat exchanger 10 includes a pair of stacked

sheets that include a first sheet 12A and a second sheet 12B. However, it should be appreciated that additional pairs of sheets 12 may be stacked without departing from the scope of the present invention. Each sheet 12A-B includes a cellulosic, porous, or paper substrate 14 coated with a protective or barrier layer of material such as a polyethylene layer 16 on one side thereof. A plurality of bonding members or adhesive beads 18 are adhered to the paper substrates 14 on a side of the paper substrates 14 opposite the polyethylene layers 16 to secure the first sheet 12A to the second sheet 12B. The adhesive beads 18 are preferably comprised of a hot melt ethylene vinyl acetate (EVA). Each adhesive bead 18 is spaced approximately one inch apart in the example provided, though various other amounts of spacing may be employed without departing from the scope of the present invention. The adhesive beads 18 and the paper substrates 14 of the first and second sheets 12A-B define a water chamber 13. Additional water chambers may be added by securing additional pairs of stacked sheets 12 to the first sheet 12A and/or the second sheet 12B. The additional pairs of sheets 12 are preferably secured using adhesive beads running perpendicular to the adhesive beads 18. The heat exchanger 10 further includes a radiation curable sealant composition 20 located on two opposite ends or edges of the stacked sheets 12A-B, only one side of which is illustrated in FIG. 1. The composition 20 is secured to a first substrate end portion 22 and a second substrate end portion 24 to seal the first sheet 12A to the second sheet 12B. Preferably, the composition 20 is at least partially wicked into the first and second substrate end portions 22, 24 of the paper substrates 14 on each sheet 12A-B and around one of the adhesive beads 18. The composition 20 seals

the edge of the cooling exchanger 10 such that water or debris is prevented from entering between the sheets 12A-B at the edges of the cooling exchanger 10. [00011] The composition 20 of the present invention comprises a radiation curable component, which preferably comprises a urethane acrylate oligomer or monomer. A preferred urethane acrylate oligomer/monomer is available from Shanghai Phichem Corp. under the designation KY 50-5B. However, it should be appreciated that other monomeric or oligomeric materials may be employed which provide the desired UV curable properties without departing from the scope of the present invention. [00012] The composition 20 also preferably includes a thixotrope, which functions to control the viscosity of the composition 20 when it is applied to the sheets 12A-B. The viscosity of the composition 20 in turn controls the amount of wicking of the composition 20 through the paper substrate 14, i.e., the depth to which the composition 20 saturates the paper substrate 14 when applied to the sheets 12A-B. It should be appreciated that the composition 20 should be sufficiently flowable when applied to the first and second substrate end portions 22, 24 to properly seal the edges of the sheets 12A-B. Preferably, the composition 20 has a viscosity of between about 2000 and 8000 centipoise (cps). A preferred thixotrope is fumed silica, available from Degussa under the designation Aerosil 200. Additionally, the composition 20 includes a wetting agent to aid in suspending the fumed silica. A preferred wetting agent is BYK 405 available from BYK Chemie.

[00013] The composition 20 preferably further includes a coloring agent to provide a visual indication that the heat exchanger 10 has been coated/sealed with the

composition 20. A preferred coloring agent is Blue Dye X17AB, available from Milliken

Chemical.

[00014] The composition 20 also preferably includes an odor masking agent which masks the odor of the composition 20 so that it does not emit an unpleasant odor when used in an evaporative cooling system or other systems which circulate air, such as heating, ventilating, and air conditioning systems. A preferred odor masking agent is

Odor Mask 96391 (vanilla scent) available from Stanley S. Schoenmann, Inc.

[00015] In an exemplary embodiment, the composition 20 comprises from about

80 to 99% by weight of the radiation curable urethane acrylate oligomer or monomer, from about 0.5 to 1.5% by weight of the thixotrope, from about 0.1 to 0.3% by weight of the coloring agent, from about 0.01 to 0.20% by weight of the wetting agent, and from about 0.01 to about 0.10% by weight of the odor masking agent.

[00016] A preferred formulation for use in the present invention comprises about

98.55% by weight of the urethane acrylate oligomers/monomers, about 1.0% by weight of the thixotrope, about 0.24% by weight of a coloring agent, about 0.16% by weight of a wetting agent, and about 0.05% by weight of an odor masking agent

[00017] The heat exchanger 10 is preferably constructed by first applying the adhesive beads 18 to the paper substrate 14 on the side opposite the polyethylene coating 16 of the first sheet 12A. The second sheet 12B is then stacked on top of the first sheet 12A such that the adhesive beads 18 adhere to both paper substrates 14 of each sheet 12A-B. The stacked sheets 12A-B are then heated in a press to activate the adhesive beads 18 thereby gluing the sheets 12A-B together to form the heat exchanger 10. Again, as noted above, further pairs of sheets 12 may be adhered by

applying another set of adhesive beads, this time on the protective layer 18, followed by another paper substrate with a protective layer, where the additional adhesive beads are heated to secure the protective layers together, preferably to form a dry chamber for air recirculation within the heat exchanger 10.

[00018] The composition 20 is preferably prepared by mixing all of the components using a high speed dispersion mixer. The composition 20 may be applied to the stacked pairs of sheets 12 by dipping the cooling exchanger 10 into a bath of the composition 20. Alternatively, the composition 20 may be applied or rolled directly onto the edges (i.e. the first and second substrate portions 22, 24 and around one of the adhesive beads 18) of the cooling exchanger 10. The composition 20 is wicked into the paper layer 20 of each pair of sheets 12A-B to a depth determined by the viscosity of the composition 20.

[00019] After application of the composition 20, a suitable radiation source is used to cure the composition 20. In a preferred embodiment, ultra-violet (UV) radiation or near-UV radiation may be used to cure the composition 20. Suitable UV sources include UV lights such as a UV lamp. Preferred wavelengths for the radiation source range from about 240 to about 400 nm. However, it should be appreciated that any other curing sources may be used to cure the composition 20 as long as the desired cure is achieved. Typically, the composition 20 is cured in a few seconds of exposure to the radiation source. Once cured, the composition 20 exhibits an effective seal against moisture and chemicals such as minerals used in the operation of evaporative coolers.

[00020] While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those persons skilled in the art that various changes in the methods and apparatus disclosed herein may be made witllOut departing from the scope of the invention.