FR2950352A1 - MIXER-MASTER COMPOSITION USEFUL IN PHOTOVOLTAIC MODULES - Google Patents

Abstract

The present invention relates to a composition useful as a masterbatch, comprising: a copolymer (a) of ethylene and an ethylenic monomer carrying a polar function; ▪ and at least one solution (b) of organic peroxide selected from tert-butyl 2-ethylperhexanoate, tert-amyl 2-ethylperhexanoate and dilauroyl peroxide; the mass quantity of peroxide solution (b) being in the range of 5 to 30% relative to the total weight of the composition (I). The invention also relates to the use of this masterbatch for the crosslinking of a photovoltaic cell encapsulant.

Description

Field of the invention

The invention relates to a thermoplastic composition comprising an organic peroxide, its method of manufacture and the use of this composition for crosslinking polymers. In particular, the subject of the invention is the use of this composition for the crosslinking of film encapsulating photovoltaic cells.

STATE OF THE ART Organic peroxides are commonly used for the crosslinking of thermoplastic resins or elastomers, these resins and elastomers being grouped together in the present description under the term "polymers". To crosslink a polymer, a peroxide is generally mixed with the polymer to be crosslinked in a first step, then a second polymer forming step is carried out and a third crosslinking step, for example by a heat treatment. At room temperature, the peroxides can be in liquid or solid form. When the peroxides are mixed with these polymers, they are mixed at high temperature, that is to say a temperature above the softening point of the polymer, for example by extrusion or kneading; the peroxides are then usually in a liquid form. A first problem is that the peroxides in this liquid form are difficult to mix with the polymer and a peroxide demixing phenomenon can be observed. In addition, a long mixing time at high temperature is necessary to allow the mixing of the peroxide in the polymer. We can then observe a crosslinking phenomenon at this stage, that is to say a premature crosslinking of the polymer before shaping. This phenomenon decreases the transparency of the crosslinked polymer. To mitigate these problems, peroxide in liquid form can be incorporated at room temperature beforehand into porous fillers such as silica or talc. However, when these porous peroxide-bearing fillers are mixed with the polymer, they are difficult to distribute uniformly and rapidly in the polymer; the use of these porous fillers can also reduce certain properties of the polymer, such as its transparency. In order to facilitate the mixing of the peroxides with the polymer to be crosslinked, it is also possible to use compositions comprising an additional polymer and peroxides in high concentration, which are well known to those skilled in the art under the name "masterbatch". "Master batch").

In addition, the photovoltaic modules comprise light-sensitive cells, called "photovoltaic cells", which are capable of converting light into current. These cells are protected from their environment (moisture, oxygen, etc.) by protective layers which are usually made of glass or polymer. One or more layers of encapsulant allow to adhere the cells to the protective layers. The encapsulant must perfectly match the shape of the space existing between the cells and the other layers of protection of the module and this in order to avoid the presence of air which limits the efficiency of the photovoltaic module.

This encapsulant is generally a composition comprising an encapsulating polymer, generally a copolymer of ethylene and vinyl acetate, which is crosslinked with an organic peroxide. The various constituent layers of the panel are assembled (cells, encapsulant layer (s) comprising peroxide, protective layers) and the panel thus assembled undergoes a firing step allowing the crosslinking of the encapsulant layer. One can refer for example to the Handbook of Photovoltaic Science and Engineering, Wiley, 2003 which describes the operation and constitution of photovoltaic modules. In addition, one of the problems encountered by the photovoltaic module manufacturing industry is that this baking step decreases the efficiency of the module manufacturing process.

It is therefore necessary to find new compositions making it possible to improve the yields of the photovoltaic module manufacturing processes.

There is also a need to find a new composition to limit the phenomenon of premature crosslinking in order to improve the efficiency of the photovoltaic cells.

SUMMARY OF THE INVENTION The invention is directed to a novel composition useful as a masterbatch which solves at least one of the above disadvantages. This composition (I) comprises: a copolymer (a) of ethylene and an ethylenic monomer carrying a polar function; and at least one solution (b) of organic peroxide selected from tert-butyl 2-ethylperhexanoate, tert-amyl 2-ethylperhexanoate and dilauroyl peroxide; the mass quantity of peroxide solution (b) being in the range of 5 to 30% relative to the total weight of the composition (I).

This new composition can be advantageously used as a masterbatch for the crosslinking of polymer encapsulating in photovoltaic panels. Indeed, the crosslinking is fast and the introduction of the peroxide in the form of masterbatch makes it possible to improve the transparency of the encapsulating polymer. In addition, the introduction of organic peroxide by a masterbatch is easier than the direct introduction of liquid or solid peroxide into the encapsulating polymer.

Preferably, the polar-functional ethylenic monomer comprises from 3 to 20 carbon atoms, preferably from 4 to 8 atoms.

Advantageously, the polar-bearing ethylenic monomer is chosen from vinyl esters of saturated carboxylic acid, unsaturated carboxylic acids of carbon or (meth) acrylic acid esters of unsaturated carboxylic acid.

Preferably, the ethylenic monomer may be chosen from vinyl acetate and methyl, ethyl or butyl (meth) acrylates. Most preferably, it is vinyl acetate.

Advantageously, the copolymer (a) comprises from 10 to 60% by weight of ethylenic monomer carrying a polar function relative to the total weight of the copolymer, preferably from 25 to 45% by weight. The dispersion of the peroxide is improved when the copolymer comprises this range of ethylenic monomer.

In one embodiment, the mass amount of peroxide included in the composition (I) is in the range of 7 to 16%.

Preferably, the peroxide (b) is tert-butyl 2-ethylperhexanoate.

The invention also relates to a process for producing a composition (I) according to the invention comprising: a first step of contacting the peroxide solution (b) chosen from tert-butyl 2-ethylperhexanoate; tert-amyl 2-ethylhexanoate and dilauroyl peroxide with copolymer (a); a second step of total absorption of the peroxide solution (b) by the copolymer (a) with stirring; a third step of recovering the composition (I). An advantage of this method is that the phenomenon of premature crosslinking of the composition is even more limited and that the manufacturing process is simple.

According to an advantageous embodiment, the temperature of the second process step is lower than the softening temperature of the copolymer, which is measured in the present application by the method is described in ASTM E 28-99 (2004), better known under the name "Ring and Bali".

According to a first advantageous embodiment, the copolymer is in the form of particles having an average volume of 1 to 1000 mm 3, preferably 3 to 120 mm 3. In this case, the composition (I) is obtained directly in the form of particles without the need to reform particles. It can then easily be used as a masterbatch. By using particles having this particular volume, the uptake of the peroxide by the copolymer is excellent and there is little agglomeration between the particles.

According to one version of the process for producing the composition of the invention, there are several contacts or a continuous contact of the peroxide solution (b) with the copolymer (a), that is to say that There are several injections or continuous injection of the peroxide solution (b) during the process.

Another subject of the invention is a composition obtained by the process according to the invention.

Another subject of the invention is a film comprising a mixture of the thermoplastic composition (I) and a second polymer chosen from polyolefins. This film can be advantageously used as a film encapsulating photovoltaic cells.

Advantageously, the mass quantity of composition (I) relative to the total mass of the film is 3 to 30%, preferably 8 to 25%. The invention also relates to a method of manufacturing a photovoltaic module comprising the steps of assembling the photovoltaic cell layers, encapsulating films and protective layers, at least one of the encapsulating films being a film according to the invention. invention; cooking of the module, preferably at a temperature greater than or equal to the degradation temperature of the peroxide (b).

By using the composition according to the invention to form the encapsulant film of the invention, the efficiency of the photovoltaic panel manufacturing processes is rapid and the encapsulant layer retains a high transparency, which makes it possible to obtain a photovoltaic panel exhibiting a very good return.

Detailed Description of the Invention The composition (I) produced by the process according to the invention comprises a copolymer (a) and an organic peroxide solution (b).

The copolymer (a) is a copolymer of ethylene and an ethylenic monomer carrying a polar function. The term "ethylenic monomer" is understood to mean a monomer comprising an unsaturation capable of reacting with ethylene in a radical process. By polar function is meant a function having a dipole moment, such as amine, alcohol, urethane, acid or ester functions. Preferentially, the polar function is an acid function or an ester function.

The polar-functional ethylenic monomer preferably comprises from 3 to 20 carbon atoms, preferentially from 4 to 8 carbon atoms. By way of example of copolymer (a), mention may be made of copolymers of ethylene and of a vinyl ester of carboxylic acid, copolymers of ethylene with an unsaturated carboxylic acid or copolymers of ethylene and of an alkyl acrylate and or methacrylates, grouped together in the present application under the term (meth) acrylate. Advantageously, the ethylenic monomer may be chosen from vinyl acetate and methyl, ethyl or butyl (meth) acrylates. The quantity by mass of ethylenic monomer relative to the total weight of the copolymer (a) can be in the range of from 1 to 70%, advantageously from 10 to 60% and preferably from 20 to 45%. According to the invention, the amounts of the various monomers present in the copolymer (a) can be measured by infrared spectroscopy using the ISO8985 (1998) standard. The softening temperature of the copolymer can be measured by ASTM Standard E 28-99 (2004).

The so-called radical polymerization processes, usually operating at pressures between 200 and 2500 bar, may be used. These processes are carried out industrially using two main types of reactors: an autoclave type reactor or a tubular type reactor. These polymerization processes known to those skilled in the art and can be used for example the methods described in documents FR2498609, FR2569411 and FR2569412. Those skilled in the art know in what proportions to use each of the monomers to obtain the copolymer (a) used in the invention. These copolymers are marketed by the applicant under the trade name EVATANE® and LOTRYL®.

The copolymer may also include additives or inorganic fillers. By way of example of an additive, mention may be made of plasticizers, antioxidants or anti-ozone agents, antistatic agents, coloring materials, pigments, optical brighteners, thermal stabilizers, light stabilizers, retarders of flame. Coupling agents may be advantageously added in order to improve the adhesion power on another support of the composition (I) or the polymer to be crosslinked. It can be organic, mineral and more preferably semi-inorganic semi-organic. Among these, mention may be made of titanates or organic silanes, for example monoalkyl titanates, trichlorosilanes and trialkoxysilanes.

As fillers, there may be mentioned clay, silica, talc, carbonates such as calcium carbonate, silicates such as sodium silicate.

The copolymer (a) is in the form of "particles", that is to say that pieces of polymer can have any type of geometry, for example, spherical, spheroidal or cylindrical. The volume of a particle is advantageously in the range from 1 to 1000 mm 3, preferably from 3 to 120 mm 3. In these preferred volume ranges, excellent peroxide uptake is obtained while having little agglomeration of the particles. Preferably, at least 90% by weight of these particles have a volume included in these preferred ranges of volume.

The organic peroxide solution (b) comprises at least one organic peroxide optionally with an organic solvent thereof.

Any type of solvent miscible with peroxide can be used. For example, solvents of the alkane, aromatic, alkene, halogenated or alcohol type are used. Preferably, the solvent molecules comprise from 1 to 12 carbon atoms. As an example of a solvent, mention may be made of decane, dodecane, 2,4,4-trimethylpentene, α-methylstyrene, trichlorethylene, toluene, benzene, ethylbenzene or (1-methylethenyl) benzene, 2-ethylhexanol, isopropanol, t-butyl alcohol or acetone. It is also possible to use a mixture of solvents, for example a mixture of the solvents listed above. Preferably, the amount of solvent is less than or equal to 25% of the total mass of the organic peroxide solution (b), or even less than or equal to 10%. The solvent used is preferably not a solvent of the copolymer, especially when the amount of solvent in the peroxide solution is greater than 20% by weight. By solvent of the copolymer is meant a polymer concentration greater than or equal to 0.05 g per ml of solvent when 1 g of copolymer per ml of solvent is brought into contact for one hour at 23 ° C.

The composition (I) produced by the process according to the invention comprises a mass quantity of peroxide in the range from 5 to 30%, for example from 7 to 16%.

The manufacturing method according to the invention comprises the following steps: a first step of contacting the peroxide solution (b) with the copolymer (a); a second step of total absorption of the peroxide solution (b) by the copolymer (a); a third step of recovering the thermoplastic composition (I).

The first contacting step can be carried out in any type of container. The container may be left open or closed after contacting. The container can be closed tightly or not. Preferably, the container is sealed and is equipped with a valve. The solution (b) of peroxide is contacted with the copolymer (a) by pouring directly onto the particles or by a drip system or by a spraying system such as a spray.

The second step is a stirring absorption step of the peroxide solution (b) with the copolymer (a). This is a total absorption. By "total absorption" is meant that the remaining volume (b) unabsorbed solution in the container after the absorption step is less than 5%, preferably less than 2%, most preferably less than 1%. The absorption step is carried out at a temperature at which the solution (b) remains liquid, i.e. at a temperature greater than or equal to the melting temperature of the peroxide when it is used without solvent .

However, it is advantageous for the absorption temperature to be lower than the softening temperature of the copolymer (a) measured according to the ASTM E 28-99 (2004) standard. The duration of the absorption is at least until the complete absorption of the peroxide. The absorption time is generally in the range of 10 to 600 minutes, preferably 20 to 240 minutes. The absorption step is carried out with stirring. This stirring can be carried out by any stirring system, such as for example a system with pale, helical, screw or ultrasonic or in a rotary type device or drum, such as a dryer. Several peroxide solution (b) can be contacted with the copolymer (a), i.e., the process can comprise at least 2 peroxide injections. The first and second steps of the process according to the invention can also be carried out simultaneously by putting the solution of peroxide (b) in continuous contact with the copolymer (a), for example by means of a drip system or again by a spraying system such as a spray.

In the third step of the process, the thermoplastic composition (I) is recovered in the form of copolymer particles comprising peroxide. Optionally, it is possible to carry out a step of drying the particles recovered during the third step, for example in an oven or any other type of dryer. This is carried out at a temperature below the decomposition temperature of the peroxide of the composition (I).

The thermoplastic composition (I) can be used to crosslink a useful polymer as encapsulant in the photovoltaic modules. As an example of encapsulating polymers, there may be mentioned polyolefins such as copolymers (a) of ethylene and a polar functional ethylenic monomer described above.

According to one embodiment, the copolymer (a) is a copolymer of ethylene and vinyl acetate and the polymer to be crosslinked is a copolymer of ethylene and vinyl acetate. In order to crosslink the encapsulating polymer, it is generally mixed in a first step with the composition (I) of the invention, and then, in a second shaping step, the encapsulating film which is cross-linked in a third stage is shaped. . In the first step, conventional mixing techniques are used, in particular in tools for using thermoplastics, such as extruders or mixers. It can be mixed at a temperature below the degradation temperature of the peroxide (b). The second forming step is carried out at a temperature below the degradation temperature of the peroxide (b). Any type of apparatus for shaping such as presses, injectors or calenders can be used. It is also possible to perform the shaping simultaneously with the first step, for example by extrusion of film by placing a flat die at the end of the extruder. The third step is generally carried out at a temperature above the degradation temperature of the peroxide.

In the particular case of a photovoltaic panel, a first layer of lower encapsulant, photovoltaic sensors, a second upper encapsulant layer and then an upper protective layer are successively placed on a rear protection layer. These different layers are assembled to form the module and then performs the third crosslinking step. It is specified that the compositions can be used to crosslink the encapsulants of all types of photovoltaic modules and are obviously not limited to those presented in this description.

The thermoplastic composition (I) is advantageously used to crosslink polymers for the manufacture of transparent encapsulants.

According to the invention, a part or a film is transparent when it has a level of disorder (in English "Haze") less than or equal to 20%, for example less than or equal to 10%. The haze level of the film is evaluated according to the ASTM D1003 standard, on a film of 500 μm thickness of the composition which constitutes the part or the film, and for at least one wavelength of the visible range (from 380 to 780 nm), for example 500 nm.

Claims (10)

REVENDICATIONS1. Composition (I) comprising: a copolymer (a) of ethylene and an ethylenic monomer carrying a polar function; and at least one solution (b) of organic peroxide selected from Tert-butyl 2-ethylhexanoate, tertamyl 2-ethylperhexanoate and dilauroyl peroxide; the mass quantity of peroxide solution (b) being in the range of 5 to 30% relative to the total weight of the composition (I). 2. Composition according to claim 1 wherein the polar-functional ethylenic monomer comprises from 3 to 20 carbon atoms, preferably from 4 to 8 atoms. 3. Composition according to one of the preceding claims wherein the ethylenic monomer may be selected from vinyl acetate and methyl (meth) acrylates, ethyl or butyl. 4. Composition according to one of the preceding claims wherein the copolymer (a) comprises from 10 to 60% by weight of ethylenic monomer carrying a polar function relative to the total weight of the copolymer, preferably from 25 to 45% by weight. 5. Composition according to one of the preceding claims wherein the mass amount of peroxide included in the composition (I) is in the range of 7 to 16%. 6. Composition according to one of the preceding claims wherein the peroxide (b) is tert-butyl 2-ethylperhexanoate. 7. A method of manufacturing a composition (I) according to one of the preceding claims comprising: a. a first step of contacting the peroxide solution (b) selected from tert-butyl 2-ethylperhexanoate, tert-amyl 2-ethylperhexanoate and dilauroyl peroxide with the copolymer (a); b. a second step of total absorption of the peroxide solution (b) by the copolymer (a) with stirring; vs. a third step of recovering the composition (I). 8. Film comprising a composition according to one of claims 1 to 6 or obtained according to the process according to claim 7 and an encapsulant polymer chosen from polyolefins. 9. Use of the film according to the preceding claim as a film encapsulating photovoltaic cells. 10. A method of manufacturing a photovoltaic module comprising the steps of: assembling the photovoltaic cell layers, encapsulating films and protective layers, at least one of the encapsulating films being a film according to claim 9; for cooking the module, preferably at a temperature greater than or equal to the degradation temperature of the peroxide (b).