Patent Application
20110048513
The present invention relates to an adhesive composition and method for attaching a component to a substrate, and more particularly to a pressure sensitive adhesive compound for attaching a component to a substrate that cures in place under normal heat cycles.
The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Various components including, but not limited to, photovoltaic solar modules, solar preassemblies, roofing membranes, repair or seam patches, and mechanical equipment or other components are regularly attached directly to roofing and other substrates. One common method of securing these various components to a roofing substrate includes using mechanical fasteners such as screws or bolts. However, these mechanical fasteners can be expensive and penetrate the substrate, which can lead to, for example, water invasion of a roof. When the substrate is a solar preassembly, for example, water invasion can damage the photovoltaic cells. Another mechanical fastening method involves the use of ballast to hold down the components. Ballast, however, can greatly increase the load on a roofing substrate.
An alternate method of securing a component to a roofing substrate includes the use of chemicals or other agents. For example, a hot melt adhesive (e.g., asphalt) may be employed that is liquid or nearly liquid at high temperatures but that hardens upon cooling. However, hot melt adhesives require the use of specialized equipment that must be transported to each jobsite. The roofing materials or components must be brought together while the adhesive is still hot for the two pieces to permanently adhere. A two component liquid that is mixed at the jobsite may also be employed. Two component liquids require the use of specialized equipment and are very dependent on ambient conditions for the hardening to take place in the proper timeframe in order to achieve proper application. Extruded tapes or profiles may be employed and offer advantages over hot melt or two component liquid systems. Tapes do not require specialized equipment at the jobsite, require less training of application personnel, and offer instantaneous adhesive properties. However, non-hardening tapes either do not flow around irregularities or do not develop the ultimate properties needed for long term durability. For example, acrylic, butyl rubber, halobutyl rubber, ethylene propylene rubber, EPDM rubber, natural rubber, and other known non-hardening systems do not provide the necessary properties required in roofing environments. One solution to provide an adhesive that provides initially soft properties transitioning to hard properties includes using encapsulated curing agents. Encapsulated curing agents require physical rupturing of the encapsulants during application of the roofing materials. This rupturing requires that a minimum physical stress level be applied to the tape to break the encapsulated curing agent. However, uneven application of stress during application will result in inconsistent properties in the adhesive, resulting in possible sporadic failures. These curing agents may also require the use of toxic chemicals such as isocyanates or peroxides.
Accordingly, there is a need in the art for a pressure sensitive adhesive operable to secure a component to a substrate. The pressure sensitive adhesive should be initially soft or tacky to promote initial adhesion, and be able to cure in place without additional steps to a hard condition. Moreover, the adhesive composition should meet weatherability and strength criteria, such as resistance to ultra-violet radiation exposure, freeze and thaw cycles, rain, snow, sleet, and hail exposure, wind uplift forces, and extremes in temperature.
The present invention provides a pressure sensitive adhesive composition and a method for attaching a component to a substrate. The composition includes an uncured rubbery polymer blend, at least one of a tackifier or a curing agent blend, and a polybutene homopolymer. The tackifier includes a phenolic tackifier resin and the curing agent blend includes at least one of a cure accelerator, a sulfur activator, and a curing vulcanizing agent. The composition exhibits initial tackiness when uncured and high strength when cured. The composition is cured in situ on the substrate.
In one embodiment, the uncured rubbery polymer blend is present in an amount from about 10% to about 60% by weight, the at least one tackifier is present in an amount from about 5% to about 25% by weight, the curing agent blend is present in an amount from about 1% to about 6% by weight, and the polybutene homopolymer is present in an amount from about 20% to about 60% by weight.
In another embodiment, the uncured rubbery polymer blend is present in an amount from about 10% to about 60% by weight, the curing agent blend is present in an amount from about 1% to about 6% by weight, and the polybutene homopolymer is present in an amount from about 20% to about 60% by weight.
In yet another embodiment, the uncured rubbery polymer blend is present in an amount from about 10% to about 60% by weight, the at least one tackifier is present in an amount from about 5% to about 25% by weight, and the polybutene homopolymer is present in an amount from about 20% to about 60% by weight.
In yet another embodiment, the two separate molecular weight polyisobutylenes comprise a first polyisobutylene having an average viscosity molecular weight of greater than approximately 100,000 and a second polyisobutylene having an average viscosity molecular weight less than approximately 100,000.
In yet another embodiment, the cure accelerator comprises tetramethylthiuram disulfide and benzothiazyl disulfide, the sulfur activator comprises zinc oxide, and the curing vulcanizing agent comprises sulfur.
In yet another embodiment, the pressure sensitive adhesive composition includes a plasticizer.
In yet another embodiment, the plasticizer comprises paraffinic process oil.
In yet another embodiment, the pressure sensitive adhesive composition includes at least one filler and rheology modifier.
In yet another embodiment, the filler and rheology modifier is selected from the group consisting of one or more of calcium carbonate, talc, and fumed silica.
In yet another embodiment, the pressure sensitive adhesive composition includes a desiccant.
In yet another embodiment, the desiccant comprises calcium oxide.
In yet another embodiment, the pressure sensitive adhesive composition includes an antioxidant.
In yet another embodiment, the antioxidant comprises tetrakismethylene(3,5-di-t-butyl-4-hydroxyhydro-cinnamate) methane.
In yet another embodiment, the pressure sensitive adhesive composition includes an ultra-violet radiation absorber.
In yet another embodiment, the ultra-violet radiation absorber comprises carbon black.
In yet another embodiment, the pressure sensitive adhesive composition includes a stabilizer.
In yet another embodiment, the stabilizer comprises tetrachloro-p-benzoquinone.
A further embodiment of the pressure sensitive adhesive composition includes an uncured rubbery polymer blend present in an amount from about 10% to about 60% by weight, at least one of a tackifier present in an amount from about 5% to about 25% by weight or a curing agent blend present in an amount from about 1% to about 5% by weight, the tackifier comprising a phenolic tackifier resin, the curing agent blend comprising at least one of a cure accelerator, a sulfur activator, and a curing vulcanizing agent, and a polybutene homopolymer present in an amount from about 20% to about 60% by weight.
In one embodiment, the pressure sensitive adhesive composition includes a plasticizer present in an amount from about 1% to about 5% by weight.
In yet another embodiment, the pressure sensitive adhesive composition includes at least one filler and rheology modifier present in an amount from about 1% to about 5% by weight.
In yet another embodiment, the pressure sensitive adhesive composition includes a desiccant present in an amount from about 2% to about 8% by weight.
In yet another embodiment, the pressure sensitive adhesive composition includes an antioxidant present in an amount from about 0.1% to about 0.5% by weight.
In yet another embodiment, the pressure sensitive adhesive composition includes carbon black present in an amount from about 2% to about 5% by weight.
In yet another embodiment, the pressure sensitive adhesive composition includes a stabilizer present in an amount from about 0.1% to about 0.5% by weight.
In yet another embodiment, the uncured rubbery polymer blend is selected from the group consisting of ethylene propylene norbornadiene terpolymer, ethylene propylene dicyclopentadiene terpolymer, ethylene propylene hexadiene terpolymer, chlorobutyl rubber, polyisobutylene, halogenated butyl rubber, and a halogenated copolymer of p-methylstyrene and isobutylene.
In yet another embodiment, the uncured rubbery polymer blend comprises ethylene propylene norbornadiene terpolymers or ethylene propylene dicyclopentadiene terpolymer present in an amount from about 1% to about 5% by weight, ethylene propylene hexadiene terpolymer present in an amount from about 2% to about 10% by weight, chlorobutyl rubber present in an amount from about 5% to about 25% by weight, and a first polyisobutylene present in an amount from about 2% to about 10% by weight.
In yet another embodiment, the first polyisobutylene has an average viscosity molecular weight of greater than approximately 100,000.
In yet another embodiment, the pressure sensitive adhesive composition includes a second polyisobutylene having an average viscosity molecular weight less than approximately 100,000 and present in an amount from about 0.1% to about 3% by weight.
In yet another embodiment, the pressure sensitive adhesive composition has a tensile strength from about 5 pounds per square inch (psi) to about 40 psi when uncured and has a tensile strength from about 50 psi to about 100 psi when cured.
An assembly for adhering to a substrate is also provided. The assembly includes a component having a bottom surface, an adhesive layer disposed on at least a portion of the bottom surface of the component, the adhesive layer having an uncured rubbery polymer blend present in an amount from about 10% to about 60% by weight, at least one of a tackifier present in an amount from about 5% to about 25% by weight or a curing agent blend present in an amount from about 1% to about 5% by weight, the tackifier comprising a phenolic tackifier resin, the curing agent blend comprising at least one of a cure accelerator, a sulfur activator, and a curing vulcanizing agent, and a polybutene homopolymer present in an amount from about 20% to about 60% by weight. A release liner is disposed overtop the adhesive layer and the release liner is removable from the adhesive layer. The adhesive layer cures after the adhesive layer has been attached to the substrate. The adhesive layer has a peel strength from about 20 pounds per square inch to about 30 pounds per square inch after 24 hours of being applied to the substrate at room temperature.
The pressure sensitive adhesive composition is uncured prior to application on the substrate and has a tensile strength from about 5 pounds per square inch (psi) to about 40 psi. Once in place, the composition cures and hardens under the normal thermal environment or solar heating of the substrate to a tensile strength from about 50 psi to about 100 psi.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples and embodiments are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
With reference to
The component 14 may take various forms without departing from the scope of the present invention. For example, the component 14 may be a solar module that generally includes at least one photovoltaic cell (not shown) attached to a backing substrate (not shown). Exemplary photovoltaic cells for use with the present invention include, but are not limited to, thin film cells with a layer of cadmium telluride (Cd—Te), amorphous silicon, or copper-indium-diselenide (CuInSe2) or crystalline silicon wafers embedded in a laminating film or gallium arsenide deposited on germanium or another substrate. The photovoltaic cell is operable to generate an electrical current from sunlight striking the photovoltaic cell. The backing substrate may be comprised of any number of materials selected for their strength and weatherability. Other examples of components 14 include, but are not limited to, solar preassemblies, roofing membranes and other roofing materials, repair or seam patches, and mechanical equipment or other mechanical components or devices.
Turning to
With combined reference to
Once in place, the soft adhesive layer 10 is cured in place by heat from the normal environment of the substrate 12. More specifically, the composition polymers are vulcanized or crosslinked in order to harden the adhesive composition layer 10 in situ. As a cured, hardened composition, the adhesive layer 10 of the present invention exhibits greater shear properties and does not flow under the elevated temperatures that roofing materials experience. The hardened or cured adhesive layer 10 preferably has a tensile strength of about 50 psi to about 100 psi.
In an alternate embodiment, the adhesive layer 10 is fabricated in the form of an extruded tape wound in a roll on one or more of the release liners 18. The adhesive layer 10 is then applied to either the substrate 12 or the component 14. Then, the component 14 is pressed onto the substrate 12. The adhesive layer 10 then cures in place under the operating temperatures of the environment of the substrate 12, as described above.
As noted above, the adhesive layer 10 is soft and initially tacky, yet possesses high initial strength. Also, the composition of the adhesive layer 10 is able to adhere to the various kinds of substrates 12 and solar modules 14 described above while exhibiting necessary weatherability and strength criteria, such as resistance to ultra-violet radiation exposure, to freeze and thaw cycles, to rain, snow, sleet, and hail exposure, to wind uplift forces, and to extremes in temperature.
According to one aspect of the present invention, the adhesive layer 10 is comprised of a pressure sensitive adhesive composition that includes an uncured rubbery polymer blend and at least one of a tackifier and/or a curing agent blend. In one embodiment, the adhesive composition of the present invention includes an uncured rubbery polymer blend present in an amount from about 10% to about 60% by weight; at least one of a tackifier present in an amount from about 5% to about 25% by weight or a curing agent blend present in an amount from about 1% to about 5% by weight, and a polybutene homopolymer present in an amount from about 20% to about 60% by weight. The adhesive composition also preferably includes other components including plasticizers, water scavengers or desiccants, antioxidants, fillers and rheology modifiers, colorants and UV absorbers, and stabilizers.
The uncured rubbery polymer blend includes ethylene propylene norbornadiene or dicyclopentadiene terpolymer, ethylene propylene hexadiene terpolymer, chlorobutyl rubber, and two separate molecular weight polyisobutylenes. The polyisobutylenes preferably comprise a first polyisobutylene having an average viscosity molecular weight of greater than approximately 100,000 and a second polyisobutylene having an average viscosity molecular weight less than approximately 100,000. The uncured rubbery polymers impart strength and adhesion to the composition. Additionally, the chlorobutyl rubber acts as a crosslinking portion of the polymer blend during curing. Chemical derivatives and combinations of these uncured rubber polymers may also be used, for example, halogenated butyl rubber or a halogenated copolymer of p-methylstyrene and isobutylene.
The tackifiers preferably consist of polybutene homopolymer and phenolic tackifier resin. The polybutene homopolymer also acts as an adhesion promoter. Chemical derivatives and combinations of these tackifiers may also be employed in the composition without departing from the scope of the present invention.
The curing agent blend preferably consists of one or more of a cure accelerator, a sulfur activator, and a curing and vulcanizing agent. Exemplary cure accelerators include tetramethylthiuram disulfide and benzothiazyl disulfide. An exemplary sulfur activator includes zinc oxide. An exemplary curing and vulcanizing agent includes sulfur. Chemical derivatives and combinations of these cure accelerators, sulfur activators, and curing and vulcanizing agents may also be employed in the composition without departing from the scope of the present invention.
A suitable plasticizer for use in the present composition includes, but is not limited to, paraffinic process oil. Chemical derivatives and combinations of plasticizers may also be employed in the composition without departing from the scope of the present invention.
Suitable fillers and rheology modifiers for use in the present composition include, but are not limited to, one or more of calcium carbonate, talc, and fumed silica. Chemical derivatives and combinations of these fillers and rheology modifiers may also be employed in the composition without departing from the scope of the present invention.
A suitable water scavenger for use in the present composition includes, but is not limited to, calcium oxide. Chemical derivatives and combinations of calcium oxide may also be employed in the composition without departing from the scope of the present invention.
A suitable antioxidant for use in the present composition includes, but is not limited to, Tetrakismethylene(3,5-di-t-butyl-4-hydroxyhydro-cinnamate)methane. Chemical derivatives and combinations of compatible antioxidants may also be employed in the composition without departing from the scope of the present invention.
A suitable colorant and ultra-violet radiation absorber for use in the present composition includes, but is not limited to, carbon black. Chemical derivatives and combinations of compatible colorants and UV absorbers may also be employed in the composition without departing from the scope of the present invention.
A suitable stabilizer for use in the present composition includes, but is not limited to, Tetrachloro-p-benzoquinone. Chemical derivatives and combinations of compatible stabilizers may also be employed in the composition without departing from the scope of the present invention.
In order that the invention may be more readily understood, reference is made to the following example which is intended to illustrate the invention, but not limit the scope thereof:
The composition of the present invention was tested versus Sika 68. The results are summarized on the following chart:
The composition of the present invention exhibits a peel strength of at least 350 grams/cm at room temperature, at least 150 grams/cm at 70 degrees Celsius, and supports a static load of at least 23 grams/cm2 at 70 degrees Celsius, preferably for a minimum of 96 hours. As noted above, the composition is initially uncured having a tensile strength from about 5 psi to about 40 psi. Full curing of the composition occurs after placement on the substrate 12. Full curing is achieved when further exposure to elevated temperatures do not change the adhesivity, strength, or static load resistance of the composition. The fully cured composition has a tensile strength of about 40 psi to about 100 psi. The compositions described above are blends of polymers that contribute to the proper balance of properties through its cure potential. Polyisobutylene rubber has no cure potential and thus acts as a polymer diluent. Ethylene propylene terpolymers have unsaturation levels as high as 10%.
The present invention maintains properties after ageing as required by Underwriter's Laboratories and IEC regulations.
The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 61/041,760, filed on Apr. 2, 2008. The disclosure of the above application is incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US09/39312 | 4/2/2009 | WO | 00 | 11/10/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 61041760 | Apr 2008 | US |
