Curable polyorganosiloxane composition for use as an encapsulant for a solar cell module

Abstract

The invention relates to curable polyorganosiloxane compositions for the use as an encapsulant for a solar cell module, in particular, for the encapsulation of photovoltaic modules, cured polyorganosiloxane composition made therefrom and photovoltaic modules comprising the same as encapsulant.

Claims

1. A curable polyorganosiloxane composition for the use as an encapsulant, said composition consisting of: (A) at least one polyorganosiloxane having at least two unsaturated hydrocarbyl residues, (B) at least one polyorganohydrogensiloxane having at least seven Si atoms, wherein the molar ratio of SiH-groups to all Si-atoms in the polyorganohydrogensiloxane is 0.7, (C) at least one hydrosilylation catalyst, adhesion promoter (D1), wherein (D1) is a compound of formula (3c): ##STR00010## and ring position isomers thereof, and and adhesion promoter (D2), wherein (D2) is at least one organosilane, comprising at least one alkoxy silyl group, selected from compounds of the formula (4):
X(CR.sup.6.sub.2).sub.eY(CH.sub.2).sub.eSiR.sub.d(OR.sup.3).sub.3d(4) wherein X is selected from the group consisting of halogen, unsaturated aliphatic group with up to 14 carbon atoms, epoxy-group-containing aliphatic group with up to 14 carbon atoms, cyanurate-containing group, and an isocyanurate-containing group, Y is selected from the group consisting of a single bond, a heteroatomic group selected from COO, O, S, CONH, HNCONH, e is 0, 1, 2, 3, 4, 5, 6, 7, or 8, and may be identical or different, R may be the same or different, and is selected from optionally substituted alkyl with up to 30 carbon atoms, optionally substituted aryl with up to 30 carbon atoms, poly(C.sub.2-C.sub.4)-alkylene ether with up to 1000 alkylene oxy units, the groups R being free of aliphatic unsaturation, R.sup.3 is selected from H (hydrogen) and alkyl radicals having 1 to 6 carbon atoms, and may be identical or different, R.sup.6 is selected from hydrogen and R, d is 0, 1, or 2, (E) at least one reinforcing filler, and optionally auxiliary or conventional additives selected from the group consisting of stabilizers against hot air, oils, solvents, process aids, mold release agents, wetting agents, pigments, functional fillers for increased heat or electrical conductivity, low surface or inert fillers, extenders for extended volume, natural or synthetic fibers, blowing agents, anti-microbial agents, fungicides, additives for increasing mildew resistance, opaque non-transparent fillers, plasticizers, release oils, hydrophobicizing oils, and inhibitors for controlling the crosslinking reaction, wherein the molar ratio of the total of SiH groups in component (B) to the total of the unsaturated hydrocarbyl residues in component (A) in the formulation is between 0.7 and 4.

2. The curable polyorganosiloxane composition according to claim 1, wherein the encapsulant is for a photovoltaic module.

3. The curable polyorganosiloxane composition according to claim 1, wherein component (A) is a compound of formula (1):
R.sup.1.sub.aR.sub.3aSiO[R.sub.2SiO].sub.m[R.sup.1RSiO].sub.nSiR.sup.1.sub.aR.sub.3a(1) wherein R is selected from optionally substituted alkyl with up to 30 carbon atoms, optionally substituted aryl with up to 30 carbon atoms, or poly(C.sub.2-C.sub.4)-alkylene ether with up to 1000 alkylene oxy units, the groups R being free of aliphatic unsaturation, wherein R.sup.1 is selected from aliphatic or aromatic groups with up to 30 carbon atoms, comprising CC-group-containing groups (alkenyl groups) or CC-group-containing groups (alkinyl groups), optionally comprising one or more O- or F-atoms, a=0-3 m=0-2000 n=0-500.

4. The curable polyorganosiloxane composition according to claim 1, wherein component (B) is a compound of formula (2a):
H.sub.a1(R).sub.3a1Si[RHSiO].sub.x[R.sub.2SiO].sub.y[RR.sup.1SiO].sub.zSi(R).sub.3a1H.sub.a1(2a) wherein R is selected from optionally substituted alkyl with up to 30 carbon atoms, optionally substituted aryl with up to 30 carbon atoms, or poly(C.sub.2-C.sub.4)-alkylene ether with up to 1000 alkylene oxy units, the groups R being free of aliphatic unsaturation, wherein R.sup.1 is selected from aliphatic or aromatic groups with up to 30 carbon atoms, comprising CC-group-containing groups (alkenyl groups) or CC-group-containing groups (alkinyl groups), optionally comprising one or more O- or F-atoms, a1 is 0-1, and 7x+y+z<1000.

5. Curable polyorganosiloxane composition according to claim 4, wherein R comprises at least one phenyl group.

6. Curable polyorganosiloxane composition according to claim 1, wherein component (C) is at least one transition metal compound, wherein the transition metal is selected from group consisting of nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum.

7. Curable polyorganosiloxane composition according to claim 1, wherein component (E) is selected from silica having a BET-surface of at least 150 m.sup.2/g.

8. Curable polyorganosiloxane composition according to claim 1, said composition comprising: 100 parts by weight of component (A), 0.1 to 200 parts per weight of component (B), 0.5 to 1000 ppm of component (C), wherein component (C) is at least one transition metal compound, based on the amount of the transition metal in the component (C) and based on the total of components (A) and (B), 0.01 to 5 parts by weight of component (D), up to 50 parts by weight of component (E).

9. A photovoltaic module comprising the cured polyorganosiloxane composition according to claim 1.

10. A photovoltaic module comprising the cured polyorganosiloxane composition according to claim 2.

11. A photovoltaic module comprising the cured polyorganosiloxane composition according to claim 3.

12. A photovoltaic module comprising the cured polyorganosiloxane composition according to claim 4.

13. A photovoltaic module comprising the cured polyorganosiloxane composition according to claim 5.

14. A photovoltaic module comprising the cured polyorganosiloxane composition according to claim 6.

15. A photovoltaic module comprising the cured polyorganosiloxane composition according to claim 7.

16. A photovoltaic module comprising the cured polyorganosiloxane composition according to claim 8.

Description

EXAMPLES

Test Procedures

(1) Test Procedure for Adhesion on Glass

(2) The test method follows essentially ASTM C 794-06. Standard float glass plates 50 mm150 mm with 2 mm thickness were used for the adhesion tests if not indicated otherwise. The glass plates were cleaned with 2-propanol and air-dried. A micromesh steel wire grid (Rocholl GmbH; 25 mm wide and 300 mm long; wire thickness: 0.5 mm; mesh width 1 mm1 mm) was used for the preparation of the specimens.

(3) Procedure: The glass plate is coated 4 mm thick with the silicone encapsulant. The grid is pressed into the coating and a second layer of the silicone encapsulant is applied on top. The grid overlaps on one side. Silicone encapsulant outside the grid is wiped off. The specimens are placed in an oven for 10 minutes, which has been pre-heated to 90 C. The specimens are stored under ambient conditions for at least 12 hours before they are tested. For adhesion testing the silicone is cut away from the glass by means of a scalpel 2 to 3 mm deep at the side of the specimen where the grid overlaps. The specimens are vertically clamped into a tensile testing machine. The free end of the grid is clamped into a suitable clamp of the load cells. The grid is pulled with 50 mm/minute forming an angle of 180 with the glass plate.

(4) In the case of pure cohesive failure within the silicone adhesion was rated positive. In the case of initial adhesion the specimen was subjected to accelerated ageing and retested after different time spans. For accelerated ageing under heat and moisture the specimens were placed in a climate chamber at 85 C. and 85% relative humidity. The above adhesion test was repeated after 1000 hours. Three samples were tested for each material if not mentioned otherwise.

(5) Test Procedure for Adhesion on Plastic

(6) Tedlar foil was used as a representative example for a plastic backskin of a solar module. The test specimens were prepared and tested similarly as described above for glass. The metal grid was replaced by foil. The glass plate is coated 4 mm thick with the silicone encapsulant then the foil is well pressed onto the coating. Silicone paste outside the foil is wiped off. For the accelerated ageing tests the specimens were subjected to 85 C. and 85% relative humidity for 1000 hours.

(7) Preparation of the Encapsulants

(8) The encapsulants were prepared in plastic beakers with a kitchen mixer. The filler batch was carefully diluted with the polyorganosiloxane having at least two alkenyl groups and then the other ingredients were added. The mixtures were de-aerated under vacuum before use.

(9) Preparation of Filler Batch (F 1)

(10) A filler batch (F 1) was produced as follows: 22.5 kg of a vinyl terminated linear polydimethylsiloxane with a viscosity of 10 Pa.Math.s at 25 C. was placed in a planetary mixer and mixed with 2.8 kg of hexamethyldisilazane and 0.9 kg of water. 12.0 kg of fumed silica with a BET surface of 300 m.sup.2/g were gradually added and mixed in until a stiff mixture was obtained. This mixture was stirred and heated to reflux for 30 minutes. The volatiles were distilled off and subsequently vacuum was pulled for 30 minutes. The mixture was diluted with 7.8 kg of the above polydimethylsiloxane. When the resulting filler batch was used for the preparation of the following encapsulants it was calculated as having 28.3% of silica and 71.7% of vinyl terminated polymer with a viscosity of 10 Pa.Math.s.

EXAMPLE 1

Encapsulants with Different Crosslinkers

(11) 52 g of filler batch (F 1) were mixed with the amount of the different crosslinker components (B) in g as listed in the tables 1 in %, 0.12 g of a platinum solution of the Karstedt type with 1% of platinum, 10.5 l of inhibitor ethinylcyclohexanol-(1) (ECH) and then the mixture was completed up to 100 g with ca. 46.5-47.5 g of a vinyl terminated linear polydimethylsiloxane having a viscosity of 10 Pa.Math.s.

(12) All examples 1.1-1.4 contained ca. 14.7 wt. % of filler, 12 ppm of platinum and 100 ppm of inhibitor ECH. The materials had a liquid to pasty, slightly sagging consistency.

(13) TABLE-US-00001 TABLE 1 Initial Type of mol. ratio Crosslinker SiH/ adhesion Adhesion after crosslinker SiH/all Si [%] SiVi on glass 1000 h 85/85 1.1 M.sub.2D.sup.H.sub.52 0.96 0.38 1.38 Yes Yes 1.2 M.sub.2D.sup.H.sub.26D.sup.Ph.sub.5.5D.sub.2 0.73 0.75 1.38 Yes Yes 1.3* M.sub.2D.sup.H.sub.12D.sub.28 0.29 1.39 1.38 No No 1.4* M.sub.2D.sup.H.sub.25D.sub.25 0.48 0.83 1.38 No No *comparative examples

(14) The comparative examples 1.3 and 1.4 demonstrate that the linear crosslinkers outside the inventive range of the SiH ratio do not adhere to glass not even under the test conditions of the initial phase, whereas the examples 1.1 and 1.2 adhere well in the fresh state and even after the accelerated ageing for 1000 hours at 85 C. and 85% relative humidity. The encapsulants 1.1 and 1.2 were also tested on Tedlar foil (PVF) and failed adhesively after 1000 hours at 85 C. and 85% relative humidity. This observation indicates that composition without further adhesion promoters cannot completely deliver adhesion both to glass and to plastics such as PVF of the backskin as required.

EXAMPLE 2

Encapsulants with Different Crosslinkers and the Adhesion Promoter (D1)

(15) The composition in this example uses an additional siloxane adhesion promoter (D1), which in this example is an addition product of methacryloxypropyltrimethoxysilane and D.sup.H.sub.3D in a 1:1 molar ratio according to formula (3c).

(16) 52 g of filler batch (F 1) were mixed with the amount of the different crosslinker components (B) in g as listed in the tables 2 in %, 0.12 g of a platinum solution of the Karstedt type with 1% of platinum, 10.5 l of inhibitor ethinylcyclohexanol-(1) (ECH), 0.7 g of adhesion promoter (D1) and then the mixture was completed up to 100 g with ca. 44.7-46.8 g of a vinyl terminated linear polydimethylsiloxane having a viscosity of 10 Pa.Math.s.

(17) All examples 2.1 to 2.10 contained ca. 14.7 wt. % of filler, 12 ppm of platinum and 100 ppm of inhibitor ECH and 0.7 g of adhesion promoter (D1). The materials had a liquid to pasty, slightly sagging consistency.

(18) TABLE-US-00002 TABLE 2 Type of mol. ratio Crosslinker SiH/ Initial Adhesion after crosslinker SiH/all Si [%] SiVi adhesion 1000 h 85/85 2.1 M.sub.2D.sup.H.sub.33 0.94 0.38 2.0 Yes Yes 2.2 M.sub.2D.sup.H.sub.32D.sub.5 0.82 0.50 2.0 Yes Yes 2.3 M.sub.2D.sup.H.sub.27D.sub.7 0.75 0.52 2.0 Yes Yes 2.4 M.sub.2D.sup.H.sub.26D.sub.9 0.70 0.56 2.0 Yes Yes 2.5 M.sub.2D.sup.H.sub.26D.sup.Ph.sub.5.5D.sub.2 0.73 0.74 2.0 Yes Yes 2.6 M.sub.2D.sup.H.sub.33D.sup.Ph.sub.2.9D.sub.5.3 0.76 0.56 2.0 Yes Yes 2.7* M.sub.2D.sup.H.sub.7D.sub.4 0.54 0.72 2.0 Yes No 2.8* M.sub.2D.sup.H.sub.25D.sub.25 0.48 0.82 2.0 Yes No 2.9* M.sub.2D.sup.H.sub.12D.sub.28 0.29 1.38 2.0 Yes No 2.10* M.sub.2D.sup.H.sub.20D.sub.105 0.16 2.55 2.0 Yes No *Comparative examples

(19) The comparative examples 2.7 to 2.10 wherein the crosslinker structure is outside of the inventive range but with the adhesion promoting siloxane (D1) adhered well to glass in the initial state. However, all samples failed after 1000 hours at 85 C. and 85% humidity, although the samples of example 2.7-2.10 survived 250 hours at 85 C. and 85% relative humidity.

(20) The samples of example 2.1 to 2.6 comprising a component (B) according to the definition of the inventive passed the test of 1000 hours at 85 C. and 85% relative humidity without adhesive failure in this peel adhesion test.

(21) In addition the adhesion to a Tedlar foil (PVF) was tested with the example 2.6. The encapsulant adhered in the initial test and survived 1000 hours at 85 C. and 85% relative humidity without any loss of adhesion to the foil.

EXAMPLE 3

Encapsulants with Different Crosslinkers and Adhesion Promoters

(22) In the examples 3 the adhesion promoter component (D2) the siloxane of examples 2 and silanes as component (D2) are combined: Memo=Methacryloxypropyltrimethoxysilane, CH.sub.2C(CH.sub.3)COO(CH.sub.2).sub.3Si(OCH.sub.3).sub.3 Glymo=Glycidoxypropyltrimethoxysilane, (C.sub.2H.sub.3O)CH.sub.2O(CH.sub.2).sub.3Si(OCH.sub.3).sub.3

(23) Encapsulants were prepared as described in the examples 1 and 2 having incurporated ca. 14.7% of filler, the vinyl terminated polysiloxane with a viscosity of 10 Pa.Math.s, 12 ppm of platinum, 100 ppm of ECH and the amounts of crosslinkers and adhesion promoters as listed in table 3.

(24) TABLE-US-00003 TABLE 3 Adhesion after Crosslinker Adhesion 1000 hours mol. ratio promoter SiH/ 85 C. 85% rel. SiH/all Si [%] [%] SiVi humidity 3.1 M.sub.2D.sup.H.sub.33 0.94 0.64 (B) 1.0 1.9 Yes Glymo 0.9 Memo 0.75 3.2 M.sub.2D.sup.H.sub.27D.sub.7 0.75 0.87 (B) 1.0 1.9 Yes Glymo 0.9 Memo 0.75 3.3 M.sub.2D.sup.H.sub.26D.sub.9 0.70 0.93 (B) 1.0 1.9 Yes Glymo 0.9 Memo 0.75 3.4 M.sub.2D.sup.H.sub.33D.sup.Ph.sub.2.9D.sub.5.3 0.76 0.93 (B) 1.0 1.9 Yes Glymo 0.9 Memo 0.75 3.5* M.sub.2D.sup.M.sub.25D.sub.25 0.48 1.37 (B) 1.0 1.9 No Glymo 0.9 Memo 0.75 3.5 M.sub.2D.sup.H.sub.33 0.94 0.55 Glymo 0.7 2.0 Yes 3.7* M.sub.2D.sup.H.sub.12D.sub.28 0.29 2 Glymo 0.7 2.0 No 3.8 M.sub.2D.sup.H.sub.33 0.94 0.53 Memo 0.3 1.5 Yes 3.9 M.sub.2D.sup.H.sub.33D.sup.Ph.sub.2.9D.sub.5.3 0.76 1.07 Memo 0.35 2.0 Yes *Comparative examples

(25) The examples 3.1 to 3.4 show sufficient adhesion under the 1000 h test conditions if 2 or 1, i.e. if at least the adhesion promotors of (D2) are present, whereas e.g. example 3.5 having a component (B) with a molar ratio of SiH of less than 0.5 shows insufficient adhesion over 1000 h at 85 C. and 85% humidity.

(26) Example 3.4 e.g. shows in addition also good adhesion to Tedlar foil i.e. Polyvinylfluorid (PVF DuPont) over 1000 h. The encapsulant adhered in the initial test and passed the 1000 hours at 85 C. and 85% relative humidity without any loss of adhesion to the PVF-foil.

EXAMPLE 4

Encapsulants with a Light Activatable Metal Catalyst

(27) 52 g vinyl-terminated polydimethylsiloxane polymer having a viscosity of 10 Pa.Math.s at 25 C. as component (A) was admixed with 29 g of hexamethyldisilazane treated Aerosil 300 obtained according to the process of preparation of filler batch (F 1). Then to the resulting mixture further 16.7 g of the vinyl-terminated polydimethylsiloxane having a viscosity of 10 Pa.Math.s was added. Then 0.9 g Dynasilan GLYMO (Glycidoxypropyltrimethoxysilane), 0.25 g Dynasilan MEMO (Methacryloxypropyltrimethoxysilane) as components (D2), 1 g of an adhesion promoter (D1) according to formula 3c, 0.9 g of a trimethylsilyl-terminated poly(co-diphenyl-methylhydrogendimethylsiloxane) M.sub.2D.sup.Ph.sub.2D.sup.H.sub.25D.sub.4 as component (B) were added. In a sealed darkened glove box under red or yellow light of a bulb lamp (excluding at least blue and UV-light) the light activatable metal catalyst which was trimethyl(methylcyclopentadienyl)-platium(IV) dissolved in a vinylterminated polydimethylsiloxane of 1 Pa.Math.s at 25 C. was admixed using 10 g of this component as to establish a platinum concentration of 24 ppm Pt in the total composition of this example. The ratio of the D.sup.H units to all Si units in component (B) was 0.76, the SiH:Si-vinyl ratio in this example was 1.9.

(28) The composition was irradiated for 10 sec at 120 mW/cm.sup.2 (=1200 mJ/cm.sup.2) at a distance of 5 cm with a UV lamp Panacol UV-H255 type LH365E 250 W 320-405 nm as light source.

(29) The cured composition adheres with a peel force of 10-12 N/mm and cohesive failure upon sheets of PVC (polyvinylchloride), PA 6.6 (polyamide), PBT (polybutylenterephtalat) after a storage of 7d at 25 C.

(30) The cured composition adheres with a peel force of 8 N/mm after a storage of 90 min at 25 C. upon glass.

(31) Peel forces were measured by the test method mentioned above (ASTM C 794-06).

(32) Example 4 demonstrates that also light-activatable compositions using the adhesion promotors (D1) adhere to various substrates.