WO2009138990A1

WO2009138990A1 - Encapsulation material

Info

Publication number: WO2009138990A1
Application number: PCT/IL2009/000493
Authority: WO
Inventors: Izhar Halahmi; Itay Baruchi
Original assignee: Pythagoras Solar Inc.
Priority date: 2008-05-15
Filing date: 2009-05-17
Publication date: 2009-11-19

Abstract

An encapsulant for functional elements is provided to reduce humidity and heat-associated damage.

Description

ENCAPSULATION MATERIAL

FIELD OF THE INVENTION

This invention relates to an encapsulation material for use, e.g., in protection of functional elements and in construction of non-hermetic enclosures, e.g., photovoltaic modules and cells.

BACKGROUND OF THE INVENTION

It is well known that solar radiation may be utilized to produce useable energy. One approach involves the use of a photovoltaic cell, which is adapted to convert solar radiation to electricity. The cost per unit power for producing electricity through the use of photovoltaic cells may be decreased by concentrating the sunlight. In this way, the same amount of sunlight can impinge a smaller, and thus cheaper, photovoltaic cell, from which a similar or equal amount of electricity may be extracted.

Low concentration solar panels which incorporate photovoltaic cells are designed and manufactured to operate for at least 20 years. This requirement compels the design to deal with both thermal and encapsulation issues so as to prevent system degradation.

In low concentration photovoltaic systems, the irradiation density on the cell may reach a level up to 10 times higher than that observed in regular panels. This typically results in an increase in the cell temperature, if excess heat is not dissipated properly, to levels that both harms the cell itself and the optical materials to which it is attached. Moreover, the high cell temperature reduces its efficiency in converting solar energy into electricity, thus leading to a lower level of electrical power generated by the solar panel. The silicon PV cells incorporated in such systems are also highly susceptible to humidity and oxygen that cause corrosion (manly on the conductor ribbons).

It has thus been the understanding that the combination of high temperatures and humidity negatively influence the long term functionality and performance of not only silicon cells and interconnections thereof but also of a great variety of other electronic, electric or otherwise heat-generating devices which are exposed during their operation or idle state to environmental conditions, thus requiring a protective coating which, on one hand, provide suitable protection and, on the other hand, would not disturb their normal operation routine.

SUMMARY OF THE INVENTION

It has thus been the inventor's intent to provide a low cost packaging for a non- hermetic enclosure and/or functional components disposed therein which permits heat dissipation from within the enclosure, which limits to a minimum or prevents humidity build-up therein and optionally also minimizes stress build-up in the enclosure. As is further disclosed hereinbelow, such an exemplary functional element or device is or contains a photovoltaic cell.

The enclosure of a functional element is typically in the form of a barrier coating protective layer, namely a layer that operates to protect one or multiple layers or parts of the enclosure from the exposure to air and continuous interaction with oxygen and e.g., moisture, contaminants, and heat. The invention is thus concerned with a most generic encapsulating material permitting the dissipation of heat and preventing humidity buildup (e.g., by way of humidity trapping) in non-hermetic enclosures, e.g., photovoltaic modules and cells, PV, and different electronic and electric devices, during operation or otherwise rest periods.

The encapsulation material of the invention, herein referred to as an "encapsulant" is, in most general terms, suitable for protection of such functional elements or enclosures in which such elements are disposed. As will be further demonstrated, the encapsulant of the invention is additionally useful for prevention of corrosion in elements of such non-hermetic enclosures.

Thus, in one aspect of the present invention there is provided an encapsulant material, e.g., for encapsulating at least one functional element in, e.g., a non-hermetic enclosure, said encapsulant comprising at least one heat conductive material, at least one desiccant and at least one thermoplastic and/or thermosetting polymer.

The encapsulant of the invention is suitable for encapsulating at least one functional element of an enclosure, typically a non-hermetic enclosure, the element being typically susceptible to any type of structural or operational damage upon continuous or short term contact with one or more of humidity, particulate or gaseous materials and heat. The "functional element" in most general terms, is any such element which function is crucial for the well-functioning of the device in which it is disposed or with which it is associated. In other words, malfunction of the functional element, e.g., due to such damage, would bring about the permanent or short-term malfunctioning of the device as a unit. Non-limiting examples of such functional elements are those disposed in or associated with military and non-military devices; any element of a stationary or non-stationary device; image sensors such as a micro-relay, a micro- switch, a pressure sensor, an acceleration sensor, a high-frequency filter, a micro-mirror and the like; an audio sensor; an electronic circuit; an optoelectronic element; a power supply unit; a generator; a sensor device; an audio device; a camera; and any other element or device which are under continuous exposure (short term or long term) or intermittent exposure to humidity, sun-light and/or generated heat. In some embodiments, the functional element is a photovoltaic cell or a device containing thereof.

The "non-hermetic enclosure" is any enclosure which houses at least one such functional element and which, due to, e.g., structural or other considerations is non- hermetic to the permeation of one or more of gases, humidity, particulate material, light, heat and other opportunistic contaminants. The non-hermetic enclosure may be completely exposed to such conditions, may only partially be exposed to such or may under certain extreme temperature, pressure, etc be exposed to such permeation.

The enclosure may house one or more elements, some of which may be functional and others may be non-functional. Where the enclosure is a device having housing and a plurality of elements, the encapsulant of the invention may be selected to best encapsulate one or more of the elements and/or the device as a whole. In other words, different encapsulant materials may be utilized in a single device (enclosure) to protect different elements thereof. It may also be required to encapsulate only one of many such elements. Factors determining the composition of the encapsulant of choice and the elements to be encapsulated may vary and may depend on such factors as: the element itself, its size, its position in the device, its three-dimensional structure, its connectivity to other elements of the device, any parameter associated with its operation (such as light transmittance, sensitivity to light or heat, etc), cost associated with encapsulation, shelf-life, expected service lifetime, expected position of the device in the ambient and expected exposure to damaging conditions and other factors as known to a person skilled in the art. As stated above, the encapsulant of the invention comprises at least of the following: at least one heat conductive material, at least one desiccant and at least one thermoplastic and/or thermosetting polymer. The encapsulant may also comprise additional components as further detailed below.

The at least one heat conductive material is selected to enable dissipation of heat generated on the PV during operation. In some embodiments, the heat conductive material is selected to have a bulk heat conductivity of quartz or higher. In further embodiments, the heat conductive material is in the form of a particulate material, i.e., particles, referred to herein as heat conductive particles, HCP. Typically, the HCP are electrically insulative. In other embodiments, the HCP is conductive, and may thus be selected amongst suitable metal powders such as cupper, nickel, aluminum, silver and other conductive metals, salts, oxides or mixtures thereof (either homogenous or heterogeneous mixtures).

In some embodiments, the HCP is selected to also trap humidity collected in the functional element or prevent humidity from collecting therein (or on its surface). The at least one heat conductive material is at least one inorganic material. In other embodiments, the at least one heat conductive is a particulate inorganic material, which may be selected, in a non-limiting fashion, from molecular sieves, silica gel, calcium sulfate, calcium chloride, silicates, alumosilicates, clay and magnesium sulfate.

The at least one heat conductive material may act as a filler that is incorporated to a liquid polymeric mixture, so as to obtain a paste or putty. The filler may thus be further selected from any desirable form, such as spherical or irregular, in the form of flakes, fibers, or whiskers, and may have an averaged particle size of between 0.01 to 100 microns. In such embodiments, the material, i.e., filler, may be selected from molecular sieves, silica gel, calcium sulfate, calcium chloride, metal or non-metal silicates, clay, magnesium sulfate, boron nitride, silicone nitride, metal oxide, such as aluminum oxide and alumina; an alumosilicate; a metal carbonate; a metal phosphate; a metal sulfate; a metal borate; or any mixture thereof. In some additional embodiments, the material is in the form of metal particles coated by a hard coating such as a ceramic coating.

In further embodiments, the material is characterized by a high absorbance capacity, e.g., of water, and the lack of release of corrosive ions. Non-limiting examples of such materials are silica gel, zeolites, molecular sieves, clay, carbon black and calcium aluminum silicates. In some embodiments, the filler is or composes molecular sieves, being optionally made or composed of sodium potassium or calcium aluminum silicate.

Typically, the encapsulant is composed of between 5 and 95% filler (by weight).

As stated above, the encapsulant of the present invention comprises at least one desiccant, i.e., a humidity trapping material, usually in form of fine powder, dispersed in polymer or oligomer. In some embodiments, the HCP and the desiccant are the same, namely the HCP or the desiccant is capable of heat dissipation and humidity trapping, under such embodiments, the encapsulant of the invention may or may not comprise one or more other desiccant. In other embodiments, independently of the nature of the HCP, the encapsulant of the invention comprises at least one desiccant.

The desiccant employed may be in the form of particulate material, referred herein as humidity trapping particles, HTP. The HTP may be selected amongst such materials which are physical desiccants, such as molecular sieves, which absorb water (humidity) without undergoing any chemical reaction (oxidation, hydroxylation, etc) and without release of any soluble compounds or amongst reactive desiccants, chemisorbents such as CaO, Portland cement and Gypsum, which chemically interact with the humidity and thereby reducing (or diminishing) its concentration.

As a person skilled in the art would appreciate, the humidity trapping material is selected so as to continuously interact (by physical or chemical interaction over a short or long period of time) with humidity that diffuses into the enclosure during its service lifetime. The humidity, however, may also be associated with that which is initially present during enclosure assembly. In fact, in some embodiments, in order to minimize exposure to long-term permeating humidity, the humidity trapping material is provided as paste or putty that remains greasy or cross-linked to a soft mass, designed to encapsulate the humidity sensitive functional elements, e.g., the PV cell.

The ability of the encapsulant material of the invention to also avoid or minimize heat build-up in a functional element, e.g., the PV, may be imparted also by the inclusion of at least one phase change material, PCM. The encapsulant comprising said PCM may thus be characterized by a high heat capacity (namely increased ability to store high levels of thermal energy with a relatively small temperature increase) being in the range of at least 20 kJ/kg. In some embodiments, the heat capacity of the encapsulant of the invention is between 20 and 100 kJ/kg. In some other embodiments, the heat capacity is between 20 and 200 kJ/kg.

The at least one PCM is selected to have a melting point in the range of the service temperature of the application (i.e., at the temperature that is generated in the PV module during exposure to sunlight). In other words, the PCM is selected to have a melting temperature, during which phase change (i.e., melting), thermal energy is consumed without an increase in the temperature of the PV, hence providing protection to the device from overheating. In some embodiments, the melting point is at least 10°C. The PCM may also be selected to have a melting point of at most 70°C, or between 10 and 70°C. The at least one PCM is further selected to be non-corrosive, of low volatility, hydrophobic and have a relatively low modulus of elasticity (so as to avoid stress on the PV and wires during phase change cycles).

In some embodiments, the at least one PCM is selected to have a melting point greater than 20°C, and a heat capacity greater than 30 kJ/Kg.

The PCM materials may be blended with the remaining components of the encapsulant or be applied as a separate layer or layers. Notwithstanding, the at least one PCM is selected amongst materials which are either solids or liquids at room temperature. Non-limiting examples of PCM include paraffin, O-mannitol, methyl palmitate, stearic acid, pentaerythritol and mixtures thereof with paraffin and/or a polyamine; an olefin oligomer such as an alkane, an alkene and an alkyn having from 4 to 100 carbon atoms per molecule; an alcohol including mono-, di-, tri- and poly- alcohols; an esters; an amides; an aldehyde; a ketone; a sugar; a glycol; a poly hydroxyl; and a fatty acid including an ether, an ester, an amide, and a carbamate thereof.

As further disclosed, the encapsulant of the invention also comprises at least one thermoplastic and/or thermosetting polymer for dispersing therein the other components of the encapsulant, i.e., HTP, HCP and optionally PCM. In other words, the polymer employed acts as a continuous phase of the encapsulant and is therefore selected to endow the encapsulant with the desired elasticity, adhesion, with the ability to minimize bleeding and for ease of application as a paste or putty form. The polymers may be present in the encapsulant in their pure (or neat) forms or as formulations comprising them.

The polymer or oligomer may be by itself reactive to water (in the form of water vapor of any degree of humidity). In such embodiments, the polymer and/or oligomer is selected to comprise such reactive groups as isocyanate and/or alkoxy silane groups. Non-limiting examples for such polymers and oligomers are polyisocyanate such as Desmodur™ manufactured by Bayer, and siloxane terminated polymer, known as MS- polymer manufactured by Kaneka.

In some further embodiments, the thermoplastic polymer is selected from ethylene copolymers and terpolymers, ethylene-vinyl acetate (EVA), ethylene acrylate and methacrylate such as Lotryl and Lotader manufactured by Arkema, ethylene-alpha olefin, styrene ethylene butadiene block copolymer (SEBS), styrene butadiene block copolymer (SBS)₅ styrene isobutylene block copolymer (SIBS), ethylene-propylene, polyester, polyamide, polyurethane, epoxy, vinyl polymer, styrenic polymer, polycarbonate, silicone polymer, silane grafted polyolefin, silane terminated polymer (known as MS polymer) and polyvinyl butyral, natural rubber, butyl rubber, nitrile rubber, acrylic rubber, polysulfide rubber, chloroprene and neoprene.

The thermosetting polymer may be selected from polyester, polyamide, polyurethane, epoxy, amino resin, alkyd, silicone, siloxane modified polymer (MS polymer), unsaturated polyester, phenolic resins and vinyl ester.

The polymer component typically is between 5% and 90% (weight percent) of the total weight of the encapsulant material. In some embodiments, the polymer is a thermoplastic polymer.

The encapsulant of the invention may optionally further comprise at least one monomer and/or oligomer to endow the encapsulant with a desired adhesion, lowered viscosity, wetting of the HTP, HCP and PCM particles and with increased thermal resistance, creep resistance and mechanical strength. The at least one monomer and/or oligomer is thus selected from acrylic and methacrylic acid and esters thereof, styrene, isocyanates, diols, polyols, silanes, siloxanes, glycidyl containing compounds and glycidyl ethers and esters, phenolic resins and amino resins.

The encapsulant of the invention may optionally further comprise at least one additive to enable softening of the encapsulant so as to lower stress on the enclosure or functional element to be encapsulated, e.g., the PV cell, and on electrical conductors, as well as to improve adhesion. The additive may be one or more selected from a plasticizer such as a phthalic acid ester (including ortho, meta and para isomers) and amide, and an ester and amide of a aliphatic mono and polyacid; at least one tackifier; a silicone oil; a mineral oil; a vegetable oil; and a polyhydric alcohol and any ester thereof. Typically, the encapsulant of the invention is composed of between 0 and 50% (by weight) of said at least one additive, being in some embodiments at least one plasticizer.

The present invention further provides an encapsulant material comprising at least one heat conductive material, at least one desiccant, at least one thermoplastic and/or thermosetting polymer and optionally at least one of (a) at least one phase change material, (b) at least one monomer and/or oligomer, (c) at least one additive and (d) at least one additional filler.

In some embodiments, the encapsulant of the invention comprises between 5% to 95% by weight of at least one thermoplastic or thermosetting polymer, 0% to 80% by weight PCM and 5% to 95% filler, wherein said filler is molecular sieves acting both as HCP and HTP.

The encapsulant of the invention has been shown to exhibit adhesion to a surface such as glass, metal and silicon. According to one example, the encapsulant has peel strength to degreased aluminum of at least 1 pound per linear inch (PLI), in accordance with ASTM D903, D395, D1876, and D3167.

The encapsulant of the invention may be prepared by admixing the components of the encapsulant in the required ratios. In some embodiments, the filler is incorporated into the encapsulant last by employing any one method of mixing; employing for example a mechanical mixer, e.g., high speed mixer, sigma mixer, planetary mixer, extruder, co-kneader, two and three roll mill or media mill.

In some embodiments, the encapsulant is prepared by kneading the ingredients in a mixer, blender, or co-kneader, or by using an extruder. In some further embodiments, where the polymer is thermoplastic, the kneading is performed in a co- kneader, twin screw extruder — especially co-rotating twin screw extruder, at a temperature between 50°C and 250°C.

When the at least one filler is mixed into the encapsulant, heat conductivity is increased and opportunistic humidity which was absorbed by the encapsulant is trapped by the filler and thus deactivated. This process of deactivation is very crucial where electric, electronic, optic, photoelectric or photovoltaic modules or devices are concerned, particularly when exposed to harsh environments in a non-hermetic enclosure or package. Under such conditions, the encapsulant may be applied onto the PV module or between the module and its back enclosure to reduce exposure to humidity and increase protection from corrosion.

For PV related applications, and as may be suitable also to others, the encapsulant of the invention may be applied as a bead, putty or sheet (layer) of a thickness ranging from 10 microns to 5 millimeters, between the PV module and the back plate or foil or in any void or cavity in the PV module that is not requiring light transmission. The layer of encapsulant applied is flexible with a low modulus of elasticity. It may be cross-linked (elastic) or plastic and even greasy. In some embodiments, the layer of the encapsulant has a secant modulus of elasticity, measured at ambient conditions, in accordance with ISO 527-2, of between 0.05 and 0.25% strain of less than about 250 MPa. In other embodiments, the secant modulus of elasticity is less than about 100 MPa, or less than about 75 MPa.

In another aspect of the present invention, there is provided the use of an encapsulant of the invention in the construction of a device selected from electric, electronic, optic, photoelectric and photovoltaic module or device which may be disposed in any enclosure for any application. The encapsulant is typically employed for preventing or minimizing heat buildup, e.g., due to the high heat capacity of the encapsulant, in a PV module. There is also provided the use of the encapsulant in preventing or minimizing collection of humidity in a PV module.

Generally, the at least one functional element, e.g., PV, may be encapsulated wholly or only in one or more of its faces. The encapsulation may be together with a substrate or onto a substrate, such as a metal film with the bonding to the substrate being achieved at a temperature suitable to suppress occurrence of thermal expansion of the substrate (one or more) and/or the functional element (one or more). This improves air-tightness reliability of the sealing space. Further, the bonding at such selected temperature also prevents the functional element from being damaged by heat.

According to another aspect of the invention, characteristic change of the functional element by external stress or heat stress can be kept to the minimum. That is, even if the functional element, e.g., an electronic component, is exposed to an environment having a temperature change, the encapsulant characteristics are able to prevent deformation and thereby the characteristic change of the functional element caused by external stress or heat stress can be suppressed. The invention additionally discloses a method for fabricating a photovoltaic cell module comprising bringing into contact at least one encapsulant of the present invention with a photovoltaic cell or an array of photovoltaic cells and/or at least one substrate, e.g., under conditions permitting the encapsulant, to adhere to said photovoltaic cell(s) and/or to said substrate to form a photovoltaic cell module.

As used herein, the expression "...under conditions permitting the encapsulant to adhere..." reflects on the conditions necessary to provide tight seal around the cell. Such conditions are flow of the encapsulant, wetting of substrate, low (minimal or complete lack of) voids and bubbles, curing or drying at conditions that are not harmful to PV cell and conductors and low stress applied to substrates after completion of curing or drying

In some embodiments, the PV is a silicon module. In other embodiments, the substrate is a metallic surface acting as a heat sink or of a material selected from metallized polymeric film, polymeric film and a polymer composite. In further embodiments, the silicon module is adhered to said metallic substrate.

The invention further provides a photovoltaic cell module comprising a photovoltaic cell or an array of photovoltaic cells encapsulated in an encapsulant material according to the present invention, said encapsulant being optionally adhered to a supporting substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic representation of a PV module utilizing an encapsulant of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Solar or photovoltaic cell modules comprise a single photovoltaic cell or a planar array of electrically interconnected photovoltaic cells on a superstrate and/or substrate. The cells are generally adhered to the superstrate and/or substrate using an encapsulant which acts to generally protect the cells from the environment (e.g. wind, rain, snow, dust and the like and in accordance with general current practice is used to both encapsulate the cells and laminate them to the substrate and/or superstate to form an integral photovoltaic cell module.

Typically a series of photovoltaic cell modules may be interconnected to form a solar array which functions as a single electricity producing unit. Usually wafer based photovoltaic cell modules are designed using a superstate in combination with a substrate and having one or more layers of encapsulant as a cell adhesive for adhering the cells to the superstate and when present to the substrate. Hence, light passes through the transparent superstate and encapsulant/adhesive before reaching the semiconducting wafer.

The prerequisites from an encapsulant material used to adhere the transparent (front) superstate to the cells are quite different from those associated with the adherence of the photovoltaic cells to the back substrate. Each of the substrate and superstate may be rigid and may be selected from the same or a similar material, e.g. a glass plate, or a flexible material e.g. a metallic films and/or sheets or suitable plastic materials such as polyimides, although the choice of an encapsulant for intimately bonding the superstate or the substrate to the photovoltaic cells is restricted by the need to be transparent to sunlight if used to bond the superstate. The encapsulant used in the back of the photovoltaic cells may not be transparent but must be protective from the environment, particularly where a substrate may not be present.

As Fig. 1 generally demonstrates, a PV module is presented having three optical units (10, 11, 12) in the front end of the module, a series of PV cells (20, 21, 22) associated with each optical unit and a substrate (30) at the back side of the module. Encapsulating the PV cells from the back and acting as a protective layer between the cells and the substrate is a layer (40) of an encapsulant material of the invention. As a person skilled in the art would appreciate, the module of Fig. 1 is merely a representation of an exemplary use of the encapsulant of the invention, which alternatively may be used in different compositions in other devices and enclosures and in a multitude of other (symmetric or asymmetric) three-dimensional forms. Other numbers of PV cells may also be used.

The encapsulant of the invention, as disclosed herein, has demonstrated a combination of (a) consistency of liquid or paste or putty in its un-cured or un-dried state (b) wetting of substrate (c) curing at conditions that are not harmful to PV cell and conductors (d) heat conductivity to enable dissipation of heat from PV cell to external surface of module (e) adsorption of humidity so humidity becomes inactive at service conditions and unavailable for corrosion and (f) low stress applied to substrates after completion of curing or drying. Exemplary encapsulants of the invention exhibiting such characteristics are listed in Table 1.

The following encapsulants have also been prepared. The following provides non-limiting examples for the encapsulants, their preparation and use.

EXAPMLE 1: Addition cured silicone-based encapsulant

To 1,000 grams of Dow Corning PV6010 (mixed A and B components), 1,500 grams of molecular sieves 4A powder were introduced and the mixture was mixed in planetary mixer under dry nitrogen atmosphere. The molecular sieves 4A powder used are of an averaged particle size of 3 micrometers manufactured by Huiying Chemistry Industry (Xiamen) Co. Ltd under the trade name ANTEN™.

The resulting thixotrophic paste, referred to as TCHA-I, was applied between an aluminum plate (simulating the back sheet of a solar PV) and PV cell. The thickness of paste was 100-200 microns and the curing was for 60 minutes at 85⁰C.

The Aluminum-cured paste-PV cell laminate was exposed to sun (summer time, Tel-Aviv, Israel, noon) and temperature on cell front side was measured to 44°C.

A control comprising only Dow Corning PV6010 between the aluminum and the PV cell provided cell front side temperature of 72°C, under same conditions.

In order to measure the humidity capturing capabilities of the TCHA-I, a cured sheet, 1 mm thick of TCHA-I , was exposed to 100% relative humidity at 45°C for 2 weeks and found to adsorb humidity from atmosphere, by about 12% of its weight at saturation; the humidity adsorption only negligibly impacting on adhesion and elasticity.

EXAPMLE 2: Silicone grease-based encapsulant

To 1,000 grams of Dow Corning 44 grease, 2,000 grams of molecular sieves 4A powder were introduced and the mixture was mixed in a planetary mixer under dry nitrogen atmosphere. The molecular sieves 4A powder used are of an averaged particle size of 3 micrometers, manufactured by Huiying Chemistry Industry (Xiamen) Co. Ltd, under the trade-name ANTEN™.

The resulting thixotrophic paste, referred to as TCHA-2, was applied between an aluminum plate (simulating the back sheet of a solar PV) and PV cell. The thickness of paste was 100-200 microns. The Aluminum-greasy paste-PV cell laminate was exposed to sun (summer time in Tel-Aviv Israel, noon) and temperature on cell front side was measured to 40°C.

A control comprising only silicone grease between the aluminum and the PV cell, provided cell front side temperature of 68°C, under same conditions.

In order to measure the humidity capturing capabilities of the TCHA-2, a cured sheet, 1 mm thick of TCHA-2 was exposed to 100% relative humidity at 45⁰C for 2 weeks and was found to adsorb humidity from atmosphere, by about 15% of its weight at saturation.

EXAPMLE 3; Thermoplastic tacky encapsulant

500 grams Eastman APP M-5K amorphous polypropylene, 200 grams Eastotac

H-100 hydrocarbon resin tackifier 200 grams Polystix 85 rosin tackifier (Hercules) 100 grams Epolene N- 14 Polyethylene wax and 2 grams hindered phenol antioxidant (IrganoxlOlO) were melt kneaded together with 2,000 grams of molecular sieves 4A at 220 Celsius in co-rotating twin screw extruder havin vacuum vent at 30RPM. The molecular sieves 4A powder used are of an averaged particle size of 3 micrometers, manufactured by Huiying Chemistry Industry (Xiamen) Co. Ltd, under the trade-name ANTEN™.

The resulting soft pellets, referred to as TCHA-S, were applied between an aluminum plate (simulating the back sheet of a solar PV) and PV cell as a melt at 180 Celsius. The Aluminum- thermoplastic compound-PV cell laminate was exposed to sun (summer time in Tel-Aviv Israel, noon) and temperature on cell front side was measured to 50⁰C.

In order to measure the humidity capturing capabilities of the TCHA-S, a solid sheet, 1 mm thick of TCHA-S was exposed to 100% relative humidity at 45°C for 2 weeks and was found to adsorb humidity from atmosphere, by about 12% of its weight at saturation.

Table 1

Claims

CLAIMS:

1. An encapsulant for encapsulating a functional component in a non-hermetic enclosure, said encapsulant comprising at least one heat conductive material, at least one desiccant and at least one thermoplastic and/or thermosetting polymer.

2. The encapsulant according to claim 1, wherein said at least one heat conductive material is selected to enable dissipation of heat generated on said functional component.

3. The encapsulant according to claim 2, wherein said heat conductive material is selected to have a bulk heat conductivity of quartz or higher.

4. The encapsulant according to claim 1, wherein said heat conductive material is in the form of heat conductive particles, HCP.

5. The encapsulant according to claim 4, wherein said HCP are electrically insulative or electrically conductive.

6. The encapsulant according to claim 4, wherein said HCP is selected to also trap humidity collected within the enclosure or to prevent humidity from collecting therein.

7. The encapsulant according to claim 1, wherein said at least one heat conductive material is at least one inorganic material.

8. The encapsulant according to claim 6, wherein said at least one heat conductive material is inorganic HCP, being selected from molecular sieves, silica gel, calcium sulfate, calcium chloride, silicates, alumosilicates, clay and magnesium sulfate.

9. The encapsulant according to claim 1, wherein said at least one heat conductive material is a filler having an averaged particle size of between 0.01 to 100 microns.

10. The encapsulant according to claim 9, wherein said heat conductive material is selected from molecular sieves, silica gel, calcium sulfate, calcium chloride, metal or non-metal silicates, clay, magnesium sulfate, boron nitride, silicone nitride; metal oxide; an alumosilicate; a metal carbonate; a metal phosphate; a metal sulfate; a metal borate; a zeolite; carbon black and calcium aluminum silicates.

11. The encapsulant according to claim 10, wherein said heat conductive material is silica gel, a zeolite, molecular sieves, clay, carbon and calcium aluminum silicates.

12. The encapsulant according to claim 11, wherein said heat conductive material is or composes molecular sieves, being optionally made or composed of sodium potassium or calcium alumosilicate.

13. The encapsulant according to claim 1, wherein said encapsulant being composed of between 5 and 95% heat conductive material (by weight).

14. The encapsulant according to claim 1, wherein said at least one heat conductive material and said at least one desiccant are the same.

15. The encapsulant according to claim 1, wherein said at least one heat conductive material and said at least one desiccant are the different.

16. The encapsulant according to claim 1, wherein said desiccant is in the form of humidity trapping particles, HTP.

17. The encapsulant according to claim 16, wherein said HTP is selected amongst physical desiccants and chemisorbents.

18. The encapsulant according to claim 1, further comprising at least one phase change material, PCM.

19. The encapsulant according to claim 18, wherein said PCM is selected to avoid or minimize heat build-up in said enclosure.

20. The encapsulant according to claim 18, wherein said PCM having a high heat capacity in the range of at least 20 kJ/kg.

21. The encapsulant according to claim 20, wherein said heat capacity is between 20 and 100 kJ/kg.

22. The encapsulant according to claim 21 , wherein said heat capacity is between 20 and 200 kJ/kg.

23. The encapsulant according to claim 18, wherein said at least one PCM is selected to have a melting point in the range of the service temperature of the application.

24. The encapsulant according to claim 23, wherein the melting point is at least 1O⁰C.

25. The encapsulant according to claim 24, wherein the melting point is of at most 7O⁰C, or between 10 and 70°C.

26. The encapsulant according to claim 18, wherein said at least one PCM is further selected to be non-corrosive, of low volatility, hydrophobic and have a relatively low modulus of elasticity.

27. The encapsulant according to claim 18, wherein said at least one PCM is selected to have a melting point greater than 20°C, and a heat capacity greater than 30 kJ/Kg.

28. The encapsulant according to claim 18, wherein said at least one PCM is selected from paraffin, 0-mannitol, methyl palmitate, stearic acid, pentaerythritol and mixtures thereof with paraffin and/or a polyamine; an olefin oligomer; an alcohol; an ester; an amide; an aldehyde; a ketone; a sugar; a glycol; a poly hydroxyl; and a fatty acid.

29. The encapsulant according to claim 1, wherein said at least one thermoplastic and/or thermosetting polymer is selected to allow dispersion therein of said HTP, HCP and optionally PCM.

30. The encapsulant according to claim 29, wherein said polymer is in the form of a continuous phase.

31. The encapsulant according to claim 1, wherein said thermoplastic polymer is selected from ethylene copolymers and terpolymers, ethylene-vinyl acetate (EVA), ethylene acrylate and methacrylate, ethylene-alpha olefin, styrene ethylene butadiene block copolymer (SEBS), styrene butadiene block copolymer (SBS), styrene isobutylene block copolymer (SIBS), ethylene-propylene, polyester, polyamide, polyurethane, epoxy, vinyl polymer, styrenic polymer, polycarbonate, silicone polymer, silane grafted polyolefin, silane terminated polymer (MS polymer) and polyvinyl butyral, natural rubber, butyl rubber, nitrile rubber, acrylic rubber, polysulfide rubber, chloroprene and neoprene.

32. The encapsulant according to claim 1, wherein said thermosetting polymer is selected from polyester, polyamide, polyurethane, epoxy, amino resin, alkyd, silicone, siloxane modified polymer (MS polymer), unsaturated polyester, phenolic resins and vinyl ester.

33. The encapsulant according to claim 1, comprising between 5% and 90% (weight percent) of at least one polymer.

34. The encapsulant according to claim 33, wherein said polymer is a thermoplastic polymer.

35. The encapsulant according to claim 1, further comprising at least one monomer and/or oligomer.

36. The encapsulant according to claim 35, wherein said at least one monomer and/or oligomer is selected from acrylic and methacrylic acid and esters thereof, styrene, isocyanates, diols, polyols, silanes, siloxanes, glycidyl containing compounds and glycidyl ethers and esters, phenolic resins and amino resins.

37. The encapsulate according to claim 1, further comprising at least one additive.

38. The encapsulant according to claim 37, wherein said additive is selected to enable softening of the encapsulant so as to lower stress on the enclosure to be encapsulated and on electrical conductors, and to improved adhesion.

39. The encapsulant according to claim 37, wherein said additive being selected from a plasticizer; a tackifier; a silicone oil; a mineral oil; a vegetable oil; and a polyhydric alcohol and any ester thereof.

40. The encapsulant according to claim 1, comprising at least one conductive material, at least one desiccant, at least one thermoplastic and/or thermosetting polymer and optionally at least one of (a) at least one phase change material, (b) at least one monomer and/or oligomer, (c) at least one additive and (d) at least one additional filler.

41. The encapsulant according to claim 40, comprising between 5% to 95% by weight of at least one thermoplastic or thermosetting polymer, 0% to 80% by weight PCM and 5% to 95% filler, wherein said filler is molecular sieves acting both as HCP and HTP.

42. The encapsulant according to any of the preceding claims having an adhesion to a surface such as glass, metal and silicon.

43. The encapsulant according to any of the preceding claims having peel strength to degreased aluminum of at least 1 pound per linear inch (PLI)₅ in accordance with ASTM D903, D395, D1876, and D3167.

44. The encapsulant according to any one of the preceding claims, being in a form selected from a bead, putty, a sheet, a paste and a bulk concentrate.

45. The encapsulant according to any one of the preceding claims for use in the construction of sealed enclosures.

46. The encapsulant according to claim 45, wherein said enclosure is selected from an electric, electronic, optic, photoelectric or photovoltaic modules or devices.

47. The encapsulant according to claim 46, wherein said enclosure is a PV module.

48. The encapsulant according to claim 47, for application onto the PV module or between the module and its back enclosure.

49. The encapsulant according to claim 48, being applied as a sheet having a thickness of between 10 microns to 5 millimeters.

50. The encapsulant according to claim 49, wherein said sheet being flexible with a low secant modulus of elasticity.

51. The encapsulant according to claim 50, wherein said modulus of elasticity, measured at ambient conditions, in accordance with ISO 527-2, is of between 0.05 and 0.25% strain of less than about 250 MPa.

52. The encapsulant according to claim 51, wherein the secant modulus of elasticity is less than about 100 MPa, or less than about 75 MPa.

53. Use of an encapsulant according to any one of claims 1 to 52 for the construction of a device selected from electric, electronic, optic, photoelectric and photovoltaic module or device.

54. The use according to claim 53, wherein said encapsulant is for preventing or minimizing heat buildup, and/or for preventing or minimizing collection of humidity in said device.

55. A process for fabricating a photovoltaic cell module, said process comprising bringing into contact at least one encapsulant according to any one of claims 1 to 52 with a photovoltaic cell or an array of photovoltaic cells and/or at least one substrate under conditions permitting the encapsulant to adhere to said photovoltaic cell(s) and/or to said substrate to form a photovoltaic cell module.

56. The process according to claim 55, wherein said PV is a silicon module.

57. The process according to claim 55, wherein the substrate is a metallic surface or of a material selected from metallized polymeric film, polymeric film and a polymer composite.

58. A photovoltaic cell module comprising a photovoltaic cell or an array of photovoltaic cells encapsulated in an encapsulant according to any one of claims 1 to 52, said encapsulant being optionally adhered to a supporting substrate.

59. A process for protecting a functional element from exposure to at least one condition selected from humidity, heat, thermal expansion, heat related damage, and humidity related damage, said process comprising encapsulating said functional element, partially or wholly with an encapsulant according to any one of claims 1 to 52.

60. A process for reducing the exposure of a functional element to at least one condition selected from humidity, heat, thermal expansion, heat related damage, and humidity related damage, said process comprising encapsulating said functional element, partially or wholly with an encapsulant according to any one of claims 1 to 52.

61. A process for decreasing permeating of humidity into a non-hermetic enclosure, said process comprising encapsulating said enclosure, partially or wholly with an encapsulant according to any one of claims 1 to 52.

62. A process for decreasing damage to a functional element associated with exposure of said element to one or more of humidity and heat, said process comprising encapsulating said element, partially or wholly with an encapsulant according to any one of claims 1 to 52.