Patent Application
20120199200
This invention relates to an edge seal for solar modules, there being provided a sealant having carbon black for thermal and thermo-oxidative stability, while maintaining non-conductivity.
The construction of insulating glass units comprising two-pane or multi-pane glass is known. In addition to the glass panes, it is standard practice to use sealants and/or adhesives, spacers and desiccants or water scavengers for this purpose. Solar-module glazing (both photovoltaic solar modules and solar modules for heating water) is assembled in the same way, except that the two glass panes can be replaced partially or completely by sheet metal and/or plastic film.
The spacer consists primarily of metal (usually aluminum), is located in the edge area of the glass panes, and has the function of maintaining the two glass panes at the desired distance apart. A desiccant (e.g. a molecular sieve) is contained additionally within the hollow spacer in order to keep the air or gas trapped between the panes dry. To enable the desiccant to absorb moisture at all, the spacer is provided with small apertures (longitudinal perforation) on the side facing the interpane space. This arrangement prevents moisture from condensing on the inside of the glass panes at low ambient temperatures and impairing the transparency of the insulating glass unit.
Between the sides of the spacer that face the glass panes and the inner surfaces of the glass panes, a seal based on polyisobutylene and/or butyl rubber is provided. This seal is generally known as the primary seal. The function of the primary seal is during production of the insulating glass panes, to be a kind of “assembly aid” while the glass panes are being joined to the spacer, which has been pre-coated with primary sealant, in order to hold the assembly together during the next production stages, and later, during the service life of the insulating glass unit, to form a water-vapor barrier that prevents moisture from penetrating from the exterior inwards into the interpane space, and, if the insulating glass unit is filled with gas, to prevent loss of this gas outwards from the interpane space.
As the outward-facing edge of the spacer is a few millimeters inside of the outside edges of the glass panes, a “channel” is formed into which the secondary sealant, as it is generally known, is injected. The main purpose of the secondary seal is to elastically bond the edge of the insulating glass unit (glass panes and spacer) and also to form a seal—which is to some extent an additional seal—against water and water vapor from the outside and gas from the inside (interpane space). As a rule, the secondary seal consists of room-temperature-curing, two-part sealants and/or adhesives based on polysulfide, polyurethane or silicone. One-part systems, for example based on silicone, or a hot-melt butyl adhesive applied while hot, are also possible.
The systems described above, however, also have certain disadvantages. During production of the insulating glass units, a large number of materials have to be processed in a series of complicated and cost-intensive stages, some of which take place simultaneously.
As far as the thermal insulation properties of the edge seal are concerned, metal spacers used there have the disadvantage of being good heat conductors and thus having a negative influence on an insulating glass pane's desirable low K-value, which, in the case of double- or multi-pane insulating glass, has been improved substantially in recent years by filling the interpane space with inert gas and using glass panes coated with low-emission (low-E) layers.
Particularly as a consequence of the second disadvantage, increasing numbers of insulating glass systems have become available recently which, in place of aluminum as spacer, use: prefabricated stainless steel profiles (lower wall thickness possible and hence reduced heat flow); or prefabricated plastic profiles; or prefabricated thermoplastic profiles; or extrusion compound comprising thermoplastic materials extruded directly onto one of the glass panes. On account of the improved thermal insulation properties in the edge seal, these systems are also known as “warm-edge systems”. Examples of the above may be found in EP 517 067 A2, examples and application machinery for in EP 714 964 A1, EP 176 388 A1 and EP 823 531 A2.
The DE 196 24 236 A1 describes a hot-melt adhesive composition for insulating glass, containing a mixture of at least one reactive binder based on silane-functional polyisobutylene, hydrogenated polybutadiene and/or poly-α-olefins, and a non-reactive binder from the group comprising the butyl rubbers, poly-α-olefins, diene polymers, polybutene or styrene block copolymers, which composition may be used as 1- or 2-part adhesive/sealant in the production of insulating glasses. No separate spacers comprising metal or plastic profiles are needed here, and no additional, secondary sealants.
The DE 198 21 355 A1 describes a sealing compound for use in the production of multi-pane insulating glass; the compound contains silane-modified butyl rubber and serves as spacer between the individual panes of the multi-pane insulating glass. Here too, no secondary sealant is needed.
Particularly those spacers extruded directly onto one of the glass panes also overcome the problems relating to the manufacturing process. As a result, insulating glass panes can be made using an automated process which is much more flexible and more productive.
In the field of solar module manufacture, too, applying the spacer directly onto the module edges in this manner has proved to offer many advantages. Compared, for example, with the manual or semi-automatic fitting of pre-extruded butyl tapes, this solution brings not only optical advantages but also productivity advantages; in addition, it makes for a more reliable long-term barrier against water-vapor penetration and gas leakage. The EP 1 615 272 A1 (or DE 10 2004 032 604 A1) contains a description of an exemplary method and device for assembling solar modules.
The thermoplastic material used combines the function of the spacer with that of the primary seal, as it is called. It also contains the desiccant. The TPS system (TPS=thermoplastic spacer) is an example of such a system.
With these systems, too, the outward-facing edge of the spacer is a few millimeters inside of the outer edges of the glass panes, and the remaining space is filled by the secondary seal, as it is called, which bonds the units elastically.
Where silicone is used as the secondary sealant in combination with a thermoplastic spacer such as the TPS system, it has been found that insulating glass units, including those filled with inert gas, can be manufactured substantially more reliably and retain their gastightness in the edge seal even after a large number of weathering cycles (EP 916 801 A2). It is very difficult to obtain equally low gas-leakage rates when using metallic spacers combined with a standard primary seal and a silicone-based secondary seal.
Combined with polysulfide as secondary sealant, the TPS system has, over the past ten years, proved to be completely unproblematic in insulating-glass fenestration applications.
However, particularly in cases where silicone is used as a secondary sealant, there is a disadvantage that can, in certain cases, manifest itself as an optical defect within the insulating glass units. A combination of:
Proposals for creating a connection of such kind between the TPS and the silicone secondary seal as to achieve mechanical anchorage or a frictional connection by way of a specially shaped cross-section for the extruded TPS profile (DE 102 04 174 A1) unfortunately cannot be implemented due to the impossibility of obtaining a suitably shaped die for extruding such a profile cross-section. Another problem with this proposal that has not been solved is exactly how to join up the beginning and the end of the spacer profile extruded onto the glass pane. For a normal rectangular cross-section, this has been described and solved in the EP 823 531 A2. A further difficulty with this proposal is encountered while applying the secondary sealant and consists in how to completely fill the partially convex voids within the TPS strand without incorporating any air bubbles. All in all, therefore, this proposal is one that cannot be implemented as such in an everyday production process, and accordingly does not establish the desired objective.
Attempts to achieve chemical adhesion between the TPS sealant and the silicone sealant by selective addition of traditional, silane-based adhesion promoters to one and/or both sealants also fail. To this end, it is desirable to use grades and quantities which unfortunately have a negative influence on other desired properties, for example the working consistency of the TPS sealant, or which later on cause fogging in the insulating glass when the unit has been installed.
Superior edge seals strongly inhibit the movement of moisture from the atmosphere to the water-sensitive interior areas of the solar modules, even after experiencing severe weather exposures including high humidities, high temperatures, and temperature cycling. Accordingly, it is important to have edge sealants that exhibit good oxidative and heat stability as well as low conductivity.
The present invention provides an edge seal which is free of the disadvantages described and which, especially also under high stresses (external influences due to incompatible materials, extremely high temperatures and UV radiation), ensures permanent stability of the TPS edge seal and thereby reliably prevents any deformation of movement of the thermoplastic spacer profile into the interpane space. In addition, the edge seal includes carbon black for oxidative and heat stability and non-conductivity.
In one form, an edge seal for manufacturing two-pane or multi-pane insulating glass or solar modules includes a sealant and a bonding agent. The sealant contains a polymer modified with special reactive groups and has the following overall composition: olefinic polymers or combinations thereof included in an amount from about 10% to about 90% by weight of the total composition; at least one filler included in an amount from about 10% to about 65% by weight of the total composition; at least one inorganic filler that is a thermal and oxidative stabilizer in an amount from about 2% to about 30%; at least one of a desiccant or water scavenger included in an amount from about 2.5% to about 25% by weight of the total composition; and at least one aging resistor including an anti-oxidant or UV stabilizer included in an amount from about 0.1% to about 3% by weight of the total composition.
Further features, advantages, and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
In accordance with the principles of the invention, an edge seal includes a primary sealant that contains a polymer modified with special groups and has the following overall composition:
a) 30-60 wt. %, preferably 40 to 50 wt. %, olefinic polymers, number average molecular weight 400-1,000,000 D, preferably from 5,000 to 300,000 D
Thanks to the share of reactive groups bound to part of the primary sealant's polymer composition, the sealing compound according to the invention adheres markedly better to other materials, in particular glass, metals and plastic, than is the case with prior-art sealing compounds. In the invention, aside from the purely physical interactions which form the basis for glass adhesion in the prior art, chemical bonds are formed by hydrolysis-condensation reactions between the modified polymer constituents and the chemically active groups (—Z—OH) of the substrate surface. Where silicone is used as secondary sealant, the two sealants also bond additionally by way of cross-linking across the interface between the sealing compound and the silicone sealant during its curing. The TPS sealant and silicone secondary sealant thereby produce a seal which is substantially more stable toward external influences (e.g. plasticizer migration from incompatible materials), even at high temperatures and under exposure to alternating temperatures, so that any formation of “Girlande” is completely ruled out.
In some implementations, the olefinic polymers are selected from the group comprising polyisobutylene, polybutene, butyl rubber (polyisobutylene-isoprene), styrene block copolymers, especially SBS, SIS, SEBS, SEPS, SIBS, SBIBS, also in modified form, and amorphous copolymers and/or terpolymers of α-olefins (APAO).
The modified polymer can be selected from the group comprising polyisobutylene, polybutene, butyl rubber (polyisobutylene-isoprene), styrene block copolymers, especially SBS, SIS, SEBS, SEPS, SIBS, SBIBS, also in modified form, and amorphous copolymers and/or terpolymers of α-olefins (APAO), the polymer being modified with at least one group of formula (1) which is a terminal group or is distributed statistically within the chain
where -A- is
—(CH2)m— (2),
—S—(CH2)m— (3) or
and R1 and R2 are the same or different and are an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms or an aralkyl group having 7 to 20 carbon atoms,
The fillers can be selected from the group comprising ground and precipitated chalks, silicates, silicon oxides, lime, and carbon blacks or soots. In this connection, the invention also provides for the chalks to be surface-treated. However, it is also possible to use non-surface-treated chalks.
Further, in some forms, the composition includes a thermal and oxidative stabilizing inorganic filler, such as, for example, carbon black.
The silicates can be selected from the group comprising talc, kaolin, mica, silicon oxides, silicas and calcium or magnesium silicates. It is also with the scope of the invention for the water-binding substances to be selected from molecular sieves (zeolites) of types 3A to 10A. Of course, other substances that bond water chemically or physically may also be used. These include, but are not limited to, other desiccants such as silica gel, alumina, calcium sulfate, calcium chloride, magnesium sulfate, and potassium carbonate, and water scavengers such as calcium oxide.
It is possible to formulate the sealing compound either as a one-part sealing compound or as a two-part sealing compound. In the case of a one-part sealing compound, all the components are mixed together during the production process. In the case of a two-part sealing compound, the olefinic polymers (a) are mixed together with some of the fine-particle inert fillers (c) and the water-binding fillers (d) in one part, e.g. part A; a second part, part B, is manufactured from some of the fine-particle inert fillers together with some of the olefinic polymers (a) and/or the entire quantity of modified polymers (b) and the aging resistors (e). The two parts of the compound are then mixed together immediately prior to application.
The invention also provides for the aging resistors to be selected from the group comprising sterically hindered phenols, thioethers, mercapto compounds, phosphorus esters, benzotriazoles, benzophenones, HALS and antiozonants.
Last but not least, it is also within the scope of the invention to use the inventive sealing compound for fabricating insulating glass for windows, conservatories, structural and roof glazing, for glazing in land-bound vehicles, watercraft and aircraft, and for manufacturing solar modules, including thermoelectric solar modules.
Principles of the invention are further explained in detail below by reference to a comparative example and several examples in accordance with the invention.
The effect of the sealing compound of this invention compared to the prior art becomes evident from the following comparative test:
To one long edge in each case of test insulating-glass panes measuring 500×350 mm and constructed as 4 mm float glass/16 mm interpane space/4 mm float glass plus the edge seal consisting in the one instance of
After only about 4-5 weeks of the weathering-cycle test, test pane 1) showed deformation, i.e., movement, of the thermoplastic spacer profile into the interpane space. This was caused by the incompatibility reactions (plasticizer migration from the EPDM profile and the one-part silicone sealant).
Test pane 2), by contrast, showed no impairment of the edge seal whatsoever even after more than 50 weeks of the weathering-cycle test.
Similarly, the glass adhesion and the edge seal showed no recognizable impairment whatsoever after more than 4,000 hours of irradiation with UV lamps (Osram Ultravitalux) and temperatures at the pane surfaces of up to 110° C.
An edge seal that can withstand stresses of this kind is thus suitable not only for insulating-glass applications in particularly demanding situations, e.g. frameless glazing in facades or roofs (known as structural glazing), but also, for example, for the edge seal in solar modules.
In addition to the first application of a strand of reactive butyl compound, it is also possible to apply a second strand of butyl before the solar module is pressed. This is a particularly useful solution in cases where the electrical contacts of the photovoltaic cells contained in the module are made to pass through the edge seal to the outside. After the first strand has been applied, the contacts—usually in the form of thin tape‘are channeled to the exterior and the second butyl strand is then extruded directly on top of the first one. The contacts are thereby embedded in the butyl compound, thus ensuring that in the finished solar module, the contact leads across the edge seal to the outside are gastight and impermeable to water vapor. Since the contacts are usually in the form of non-insulated metal tapes, the edge seal must not show any electrical conductivity, as this can cause fault current or short circuits between the contacts. In the case of a silicone-based secondary seal, this is no problem, since silicones typically show very high volume resistivities, mostly >1014 Ohm·cm, and thus fall within the category of electrical insulators. However, butyl sealants with a high filler content of carbon black—as in the case of the reactive butyl compound described here—have volume resistivities of <106 Ohm·cm, meaning that the compound would be electrically conductive.
Reducing the carbon black content admittedly increases the volume resistivity, but also brings many disadvantages. Aside from mechanical reinforcement and viscosity regulation, the purpose of a high carbon black content in a butyl sealant is to make the mixture particularly stable toward high temperatures and UV irradiation. If the carbon black content were to be substantially reduced because of the volume resistivity, this would no longer be the case and the butyl sealing compound would no longer show the required long-term stability for applications in the field of solar modules, i.e. for applications involving high temperatures and solar radiation. By using a specialty carbon black in place of the carbon blacks generally used in butyl sealants, however, it is possible to obtain a reactive butyl compound that has all the required properties. It transpired that by selecting an oxidatively post-treated carbon black made by the furnace process and having a primary-particle size in the 50-60 nm range, a carbon black had been found which not only permitted filler contents of up to 20 wt. % for the reactive butyl compound, which are necessary for stabilization, mechanical reinforcement and viscosity regulation, but simultaneously result in a volume resistivity of >1010 Ohm·cm, which is fully adequate for the electrical insulating effect required of the reactive butyl sealing compound.
In addition, it has been found that the use of carbon black as an inorganic filler promotes thermal stability and oxidative stability within the edge sealant. By using Nurox Carbon Black, the carbon black content can be increased while maintaining low conductivity. More specifically, in polymer blends containing polybutene and polyisobutylene, carbon black acts as a thermal and oxidative stabilizer. These results were not expected, since the carbon black was put into the formulation to inhibit reactions due to absorption of UV and visible light.
Carbon black can affect the thermal decomposition of various polymers in an inert atmosphere by thermogravimetry/mass spectrometry (TGA-MS) and pyrolysis-gas chromatography/mass spectrometry (Pyrolosis-GC-MS). The nature of substituents on the hydrocarbon chain of the polymers affects the thermal behavior of the mixtures with carbon black. Carbon black exhibits no influence on the decomposition of poly(methyl methacrylate) (PMMA) which has quaternary carbon atoms in the polymer chain and decomposes by depolymerization. The decomposition of polypropylene (PP) is promoted, whereas, that of polyethylene (PE), polystyrene (PS) and polyacrylonitrile (PAN) is hindered in the presence of carbon black. The char yield of PAN is increased significantly, however, carbon black has no impact on the amount of residue of non-char-forming polymers. Analysis of the pyrolysis products indicate that carbon black has influence through the chain cleavage and H-transfer reactions. The promotion of the chain scission reactions in PP is indicated by the lower decomposition temperature and the increased formation of products originating from the primary macroradicals. It appears that carbon black participates in the termination of the chain reactions, too, thus, the yield of oligomers is significantly reduced from the vinyl polymers. The increased yield of hydrogenated products also confirms that carbon black participates in the H-transfer reactions.
It has been established that the effect of thermal stability depends on the volatile content of the carbon blacks. Carbon black of high volatile content is able to initiate the decomposition of PP and PIB, whereas carbon blacks of low volatile content increase the thermal stability of the polymers. Carbon blacks affect the product distribution of polymers, the magnitude of the changes increases with increasing volatile content of the carbon black. Lower amount of α,ω-alkadienes and more n-alkanes are released from PE/carbon black composite indicating the occurrence of a hydrogenation process.
In accordance with the principles of the invention, inclusion of carbon black as a oxidative and thermal stabilizer in a sealant or sealing compound provides a sealant or sealing compound with a relative thermal index (RTI) of at least about 105° C. when verified by Underwriters Laboratories Inc.® (UL).
The following examples include the use of carbon black for oxidative and thermal stability in accordance with the principles of the invention:
Where for each of the examples the components are selected from: Olefinic polymer: Polyethylene, polypropylene, polybutene, polyisobutene, butyl rubber (polyisobutene-isoprene) styrene block copolymers (in modified form as well): For all olefinic polymers Mol wt (Number average molecular weight 100-1,000, 000 Da, preferabaly 100-300,000 Da); Silanes: : DFDA-5451NT (silane grafted PE from Dow Chemical), DFDA-5481 NT (moisture curing catalyst from Dow Chemical), amorphous poly alpha olefins (such as and not restricted to Vestoplast 206, Vestoplast 2412), alkoxy silanes, amino silanes; Inert fillers: ground and precipitated chalks, silicates, lime, silicon oxides, and Carbon black, CaCO3, Ca(OH)2, titanium dioxide, silicates to be selected from the group comprising talc, kaolin, mica, silicon oxide, silicas, and calcium or magnesium silicates; Water Scavengers such as CaO or desiccants such as molecular sieves, silica gel, and calcium sulfate; Aging Resistors: Hindered phenols, hindered amines, thioethers, mercapto compounds, phosphorous esters, benzotriazoles, benzophenones, and antiozonants.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 045 104.2 | Sep 2007 | DE | national |
This patent application claims the benefit of U.S. Provisional Patent Application No. 61/251,551, filed on Oct. 14, 2009, and is a continuation-in-part of co-pending U.S. patent application Ser. No. 12/679,250, filed on Mar. 19, 2010, which claims the benefit of International Application No. PCT/DE/2008/001564, filed on Sep. 22, 2008, which claims the benefit of German priority document DE/10 2007 045 104.2, filed on Sep. 20, 2007. The contents of the above applications are incorporated herein by reference in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US10/52727 | 10/14/2010 | WO | 00 | 4/13/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61251551 | Oct 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12679250 | Oct 2010 | US |
| Child | 13501938 | US |
