DE102008042882A1 - Photovoltaic modules containing plasticized interlayer films of high polyvinyl acetate polyvinyl acetals - Google Patents

Abstract

The invention relates to the use of plasticized polyvinyl acetal based films comprising polyvinyl acetal having a polyvinyl acetate content greater than 3% by weight for the manufacture of photovoltaic modules.

Description

Technical area

The The invention relates to the production of photovoltaic modules under Use of plasticized films based on polyvinyl acetal with high polyvinyl acetate content.

State of the art

photovoltaic modules consist of a photosensitive semiconductor layer, for protection against external influences with a transparent Cover is provided. As a photosensitive semiconductor layer monocrystalline Solar cells or polycrystalline, thin semiconductor layers be used on a support. Thin film solar modules consist of a photosensitive semiconductor layer on top of a Substrate such. As a transparent plate or a flexible carrier film z. B. by vapor deposition, vapor deposition, sputtering or wet separation is applied.

Both Systems are often placed between a glass pane and a glass pane rigid, rear cover plate z. B. made of glass or plastics Help of a transparent adhesive laminated.

Of the transparent adhesive must be the photosensitive semiconductor layer and completely enclose their electrical connection lines, UV-stable and insensitive to moisture and after the lamination process completely free of bubbles.

As transparent adhesives, curing resins or crosslinkable ethylene vinyl acetate (EVA) based systems are often used, such as in DE 41 22 721 C1 or DE 41 28 766 A1 disclosed.

A Alternative to curing adhesive systems is the use of plasticized films based on polyvinyl acetals such as the polyvinyl butyral (PVB) known from laminated glass production. The solar cell units are made with one or more PVB films covered and these under increased pressure and elevated Temperature with the desired cover materials to a Laminate connected.

Process for the production of solar modules by means of PVB films are z. B. by DE 40 26 165 C2 . DE 42 278 60 A1 . DE 29 237 70 C2 . DE 35 38 986 C2 or US 4,321,418 known. The use of PVB films in solar modules as laminated safety glazings is z. In DE 20 302 045 U1 . EP 1617487 A1 , and DE 35 389 86 C2 disclosed. However, these documents contain no information about the mechanical, chemical and electrical properties of the PVB films used.

The Preparation of the interlayer films usually used polyvinyl butyrals takes place on an industrial scale by saponification of polyvinyl acetate to polyvinyl alcohol with a desired residual acetate content and its subsequent implementation with an aldehyde to the corresponding polyvinyl acetal with the desired Acetalization.

Polyvinyl alcohol is made from polyvinyl acetate by direct hydrolysis or by alcoholysis. The reaction can be catalyzed by strong acids or bases (cf. Encyclopedia of Polymer Science and Engineering, Wiley, New York 1989, Vol ). On an industrial scale, the alcoholysis of polyvinyl acetate with methanol under alkaline catalysis to form methyl acetate and polyvinyl alcohol is preferred. Excess solvent and methyl acetate are distilled off after reaching the desired degree of hydrolysis. The degree of hydrolysis of the polyvinyl alcohol can be adjusted via residence time, catalyst concentration and temperature. The production costs of polyvinyl alcohol generally increase with increasing degree of hydrolysis, since on the one hand the yield of polyvinyl alcohol based on polyvinyl acetate decreases and, on the other hand, the amount of catalyst, residence time and the amount of solvent to be distilled increases.

ever higher the degree of hydrolysis of the polyvinyl alcohol, the higher are also the process costs of producing a polyvinyl acetal. This is partly due to the increasing costs with the degree of hydrolysis the polyvinyl alcohol itself. On the other hand, the required Amount of aldehyde to achieve a given content of OH groups (expressed as polyvinyl alcohol content of the polyvinyl acetal in weight percent) with the degree of hydrolysis.

The systems described in the prior art contain low-residue polyvinyl acetals Actual content, ie the polyvinyl acetals are made from highly saponified polyvinyl alcohols. This is unfavorable for the above energetic and economic reasons.

It is also known that the volume resistivity of PVB films fall steeply with increasing moisture content, what the occurrence of leakage currents in photovoltaic modules strongly favored. In the edge area of the photovoltaic module the foils are open as encapsulating material to the environment and the environmental conditions such. B. exposed to high ambient humidity. As a result, the water content of the films in the edge region strong increase and assume values up to the equilibrium moisture content (about 3% by weight). Of the increased water content in the edge region of the film reduced their electrical resistance in this area strong. The water content Although it decreases to the middle of the film, but to avoid leakage can the photosensitive semiconductor layers therefore not to the edge region the film or the module are laid. This reduces the area occupation and thus the current efficiency of the module.

Adhesive films for photovoltaic modules must therefore have the highest possible volume resistivity. Describes this DE 102007000816.5 Adhesive films of polyvinyl acetals with increased volume resistivity and reduced plasticizer content, the glass transition temperatures Tg of more than 20 ° C.

adversely in such systems, the increased product cost, since the plasticizer is usually cheaper than the polyvinyl acetal is. Furthermore, it deteriorates due to the reduction of the plasticizer content the flowability of the film, causing problems can result in the lamination of the photovoltaic modules.

Farther decreases with increasing glass transition temperature of the adhesive films also the tendency to embrittlement at low ambient temperatures to. This results in low outdoor temperatures and simultaneous mechanical loading of photovoltaic modules to an increased risk of breakage of the modules.

task

task Therefore, it was the object of the present invention to produce at low cost plasticized films based on polyvinyl acetal with high specific volume resistance for the production of photovoltaic modules to provide.

It was found to be polyvinyl acetals having a high polyvinyl acetate content meet these requirements.

Presentation of the invention

• a) einer transparenten Frontabdeckung
• b) einer oder mehreren photosensitiven Halbleiterschichten
• c) mindestens eine weichmacherhaltige, auf Polyvinylacetal basierenden Folie und
• d) einer rückwärtigen Abdeckung

wobei das Polyvinylacetal einen Polyvinylacetatgehalt von mehr als 3 Gew.% aufweist.The present invention therefore relates to photovoltaic modules comprising a laminate

• a) a transparent front cover
• b) one or more photosensitive semiconductor layers
• c) at least one plasticized, based on polyvinyl acetal film and
• d) a rear cover

wherein the polyvinyl acetal has a polyvinyl acetate content of more than 3% by weight.

Prefers have the films used in the invention at an ambient humidity of 85% rh at 23 ° C a specific Resistance of at least 5E + 11 ohm.cm, preferably at least 1E + 12 ohm.cm, preferably at least 5E + 12 on. These Values should be achieved at each point of the film, in particular in the edge area of the module.

The Glass transition temperature Tg of the invention used Films is less than 20 ° C, in particular preferably not more than 19.5 ° C, more preferably not more than 18 ° C, in particular maximum 16 ° C or maximum 14 ° C. When Lower limit for the glass transition temperature Tg can be specified 0 ° C.

to Preparation of polyvinyl acetal is polyvinyl alcohol with a for the polyvinyl acetal corresponding polyvinyl acetate content dissolved in water and with an aldehyde such as butyraldehyde acetalated with the addition of an acid catalyst. The precipitated polyvinyl acetal is separated off, washed neutral, if necessary in an alkaline aqueous medium suspended, then washed neutral again and dried.

The acid used for the acetalization must be neutralized again after the reaction. If an excess of base (for example NaOH, KOH or Mg (OH) ₂ ) is used here, the alkalititer increases and, as described below, the addition of a basic substance can be completely or partially omitted.

Of the Polyvinyl alcohol content of the polyvinyl acetal may be reduced by the amount of the aldehyde used in the acetalization can be adjusted.

It It is also possible to acetalize with others or more Aldehydes with 2-10 carbon atoms (eg valeraldehyde) perform.

The contained on plasticized polyvinyl acetal based films preferably uncrosslinked polyvinyl butyral (PVB) obtained by acetalization is obtained from polyvinyl alcohol with butyraldehyde.

The use of crosslinked polyvinyl acetals, especially crosslinked polyvinyl butyral (PVB) is also possible. Suitable crosslinked polyvinyl acetals are, for. In EP 1527107 B1 and WO 2004/063231 A1 (thermal self-crosslinking of carboxyl-containing polyvinyl acetals), EP 1606325 A1 (crosslinked with polyaldehydes polyvinyl acetals) and WO 03/020776 A1 (Crosslinked with glyoxylic polyvinyl acetals) described. The disclosure of these patent applications is fully incorporated by reference.

When Polyvinyl alcohol can be used in the context of the present invention also terpolymers of hydrolyzed vinyl acetate / ethylene copolymers be used. These compounds are usually more than 93 mol% hydrolyzes and contains 1 to 10 wt. Based on ethylene Units (eg type "Exceval" of Kuraray Europe GmbH).

When Polyvinyl alcohol can be used in the context of the present invention furthermore hydrolyzed copolymers of vinyl acetate and at least used another ethylenically unsaturated monomer become.

The Polyvinyl alcohols can be used in the context of the present invention pure or as a mixture of polyvinyl alcohols with different Degree of polymerization or degree of hydrolysis are used.

polyvinyl contain in addition to the acetal units still from vinyl acetate and vinyl alcohol resulting units. The inventively used Polyvinyl acetals preferably have a polyvinyl alcohol content of less than 18% by weight, less than 17% by weight, less than 16% by weight or 15% by weight and in particular less than 14% by weight. A polyvinyl alcohol content of 10% by weight should not be undercut.

Of the Polyvinyl acetate content of the invention used Polyvinyl acetal is preferably above 5% by weight, especially preferably above 7% by weight, and especially above 8% by weight. The upper limit can be 15% by weight in each case. A preferred range is between 8 and 14 weight percent polyvinyl acetate content.

Out the polyvinyl alcohol content and the residual acetate content, the degree of acetalization be determined by calculation.

Prefers the films have a plasticizer content of at most 40% by weight, 35 wt.%, 32 wt.%, 30 wt.%, 28 wt.%, 26 wt.%, 24 wt.% Or 22% by weight, with a plasticizer content of 15% by weight for reasons the processability of the film should not be fallen below (in each case based on the entire film formulation). invention Slides or photovoltaic modules can one or more Contain softener.

• – Ester von mehrwertigen aliphatischen oder aromatischen Säuren, z. B. Dialkyladipate wie Dihexyladipat, Dioctyladipat, Hexylcyclohexyladipat, Mischungen aus Heptyl- und Nonyladipaten, Diisononyladipat, Heptylnonyladipat sowie Ester der Adipinsäure mit cycloaliphatischen oder Etherbindungen enthaltenden Esteralkoholen, Dialkylsebazate wie Dibutylsebazat sowie Ester der Sebazinsäure mit cycloaliphatischen oder Etherbindungen enthaltenden Esteralkoholen, Estern der Phthalsäure wie Butylbenzylphthalat oder Bis-2-butoxyethylphthalat
• – Ester oder Etter von mehrwertigen aliphatischen oder aromatischen Alkoholen oder Oligoetherglykolen mit einem oder mehreren unverzweigen oder verzweigten aliphatischen oder aromatischen Substituenten, wie z. B. Estern von Di-, Tri- oder Tetraglykolen mit linearen oder verzweigten aliphatischen oder cycloaliphatischen Carbonsäuren; Als Beispiele für letztere Gruppe können dienen Diethylenglykol-bis-(2-ethylhexanoat), Triethylenglykol-bis-(2-ethylhexanoat), Triethylenglykol-bis-(2-ethylbutanoat), Tetraethylenglykol-bis-n-heptanoat, Triethylenglykol-bis-n-heptanoat, Triethylenglykol-bis-n-hexanoat, Tetraethylenglykoldimethylether und/oder Dipropylenglykolbenzoat
• – Phosphate mit aliphatischen oder aromatischen Esteralkoholen wie z. B. Tris(2-ethylhexyl)phosphat (TOF), Triethylphosphat, Diphenyl-2-ethylhexylphosphat, und/oder Trikresylphosphat
• – Ester der Zitronensäure, Bernsteinsäure und/oder Fumarsäure

Suitable plasticizers for the films used according to the invention are one or more compounds selected from the following groups:

• Esters of polyhydric aliphatic or aromatic acids, e.g. As Dialkyladipate as Dihexyladipat, Dioctyladipat, Hexylcyclohexyladipat, mixtures of heptyl and nonyl adipates, Diisononyladipat, Heptylnonyladipat and esters of adipic acid with cycloaliphatic or ether-containing ester alcohols, dialkyl sebacates such as dibutyl sebacate and esters of sebacic acid with cycloaliphatic or ether bonds containing ester alcohols, esters of phthalic acid such as butyl benzyl phthalate or bis-2-butoxyethyl phthalate
• Esters or ethers of polyhydric aliphatic or aromatic alcohols or oligoether glycols having one or more straight-chain or branched aliphatic or aromatic substituents, such as B. esters of di-, tri- or tetraglycols with linear or branched aliphatic or cycloaliphatic carboxylic acids; As examples of the latter group may be used diethylene glycol bis (2-ethylhexanoate), triethylene glycol bis (2-ethylhexanoate), triethylene glycol bis (2-ethylbutanoate), tetraethylene glycol bis-n-heptanoate, triethylene glycol bis-n heptanoate, triethylene glycol bis-n-hexanoate, tetraethylene glycol dimethyl ether and / or dipropylene glycol zoate
• - Phosphates with aliphatic or aromatic ester alcohols such. Tris (2-ethylhexyl) phosphate (TOF), triethyl phosphate, diphenyl 2-ethylhexyl phosphate, and / or tricresyl phosphate
• - esters of citric acid, succinic acid and / or fumaric acid

Especially suitable as a plasticizer for the invention used Slides are one or more compounds selected from the following group di-2-ethylhexyl sebacate (DOS), di-2-ethylhexyl adipate (DOA), dihexyl adipate (DHA), dibutyl sebacate (DBS), triethylene glycol bis-n-heptanoate (3G7), tetraethylene glycol bis-n-heptanoate (4G7), triethylene glycol bis-2-ethylhexanoate (3GO or 3G8) tetraethylene glycol bis-n-2-ethylhexanoate (4GO or 4G8) di-2-butoxyethyl adipate (DBEA), di-2-butoxyethoxyethyl adipate (DBEEA) Di-2-butoxyethyl sebacate (DBES), di-2-ethylhexyl phthalate (DOP), di-isononyl phthalate (DINP) triethylene glycol bis-isononanoate, triethylene glycol bis-2-propylhexanoate, Tris (2-ethylhexyl) phosphate (TOF) 1,2-diisononyl cyclohexanedicarboxylate (DINCH) and dipropylene glycol zoate.

All particularly suitable as a plasticizer for the invention used Films are plasticizers whose polarity is expressed by the formula 100 × O / (C + H) is less than or equal to 9.4, where O, C and H are the number of oxygen, carbon and and hydrogen atoms in the respective molecule.

The following table shows plasticizers which can be used according to the invention and their polarity values according to the formula 100 × O / (C + H). Surname 100 × O / (C + H) Di-2-ethylhexyl sebacate (DOS) 5.3 Di-2-ethylhexyl adipate (DOA) 6.3 Di-2-ethylhexyl phthalate (DOP) 6.5 Triethylene glycol-bis-2-propylhexanoat 8.6 Triethylene glycol-bis-i-nonanoate 8.6 Di-2-butoxyethyl sebacate (DBES) 9.4 Triethylene glycol bis-2-ethylhexanoate (3G8) 9.4 1,2-Diisononyl cyclohexanedicarboxylate (DINCH) 5.4

Furthermore, the ion mobility which may be dependent on the water content of the film and thus the specific resistance can be influenced by the addition of SiO ₂ , in particular fumed silica. The plasticizer-containing films based on polyvinyl acetal preferably contain 0.001 to 15% by weight, preferably 2 to 5% by weight, of SiO ₂ .

The Avoidance of traces of acid in the production of the film material is a possibility of corrosion tendency of the invention used Reduce foils compared to photosensitive semiconductor layers. Slides of this type are usually elevated by extrusion under Temperatures produced, causing a thermal decomposition of polymeric material or the plasticizer may occur. Furthermore, can by diffused water cleavage of the residual acetate groups of the polyvinyl alcohol, thereby liberating acetic acid becomes. In both cases acid traces, which can attack the photosensitive semiconductor layers.

Prefers have the films used in the invention therefore a certain basicity, expressed as Alkali titers of about 5 or 10, preferably about 15 and especially over 20, 30 or 40 should be. A maximum alkali titre of 100 should not be exceeded become.

Of the Alkaline titer is, as described below, by back titration determined by the film and can by addition of basic substances, such as As metal salts of organic carboxylic acids with 1 to 15 carbon atoms, especially alkali or alkaline earth salts as magnesium or potassium acetate are adjusted. The basic Compound is usually in a concentration of 0.005 to 2 wt.% In particular 0.05 to 1 wt.%, Based on the entire mixture used.

Farther the films of the invention may additionally also conventional additives, such as oxidation stabilizers, UV stabilizers, dyes, pigments and anti-adhesive included.

The basic preparation and composition of films based on polyvinyl acetals is z. In EP 185 863 B1 . EP 1 118 258 B1 WO 02/102591 A1 . EP 1 118 258 B1 or EP 387 148 B1 described.

The Lamination of the photovoltaic modules takes place under fusion of Foils, allowing a bubble- and streak-free inclusion of the photosensitive Semiconductor layer is obtained with the films.

In a variant of the photovoltaic modules according to the invention become the photosensitive semiconductor layers on the cover d) applied (eg by vapor deposition, vapor deposition, sputtering or wet separation) and through a film c) with the transparent Front cover a) glued.

In In another variant, the photosensitive semiconductor layers on the transparent front cover a) applied and through the Foil c) glued to the rear cover d).

alternative For example, the photosensitive semiconductor layers may be sandwiched between two foils c) embedded and so with the covers a) and d) be glued.

The Thickness of plasticized polyvinyl acetal based films is usually 0.38, 0.51, 0.76, 1.14, 1.52 or 2.28 mm.

Used according to the invention Films fill during the lamination process on the photosensitive semiconductor layers or their electrical Compounds existing cavities.

The transparent front cover a) is usually made of glass or PMMA. The back cover d) (so-called backsheet) of the photovoltaic module according to the invention can made of glass, plastic or metal or their composites, wherein one of the carriers can be transparent. It is too possible, one or both covers as composite glazing (ie as a laminate of at least two glass panes and at least a PVB film) or as insulating glazing with a gas gap perform. Of course, the combination is also these measures possible.

The used in the modules, photosensitive semiconductor layers do not need to have any special properties. It can mono-, polycrystalline or amorphous systems are used.

at Thin-film solar modules is the photosensitive semiconductor layer applied directly to a support. An encapsulation is not possible here. Therefore, the composite becomes from a carrier (eg the rear one Cover) with the photosensitive semiconductor layer and the transparent Front cover by at least one intermediate, on plasticized Polyvinyl acetal based film of the invention collapsed and through this at elevated temperature bonded. Alternatively, the photosensitive semiconductor layer may be on the transparent front cover applied as a carrier and with the rear cover by at least an intermediate, based on plasticized polyvinyl acetal Bonded inventive film.

to Lamination of the laminate thus obtained can the methods familiar to the person skilled in the art, with and without preceding ones Production of a pre-bond can be used.

So-called autoclave processes are carried out at an elevated pressure of about 10 to 15 bar and temperatures of 130 to 145 ° C for about 2 hours. Vacuum bag or vacuum ring method z. B. according to EP 1 235 683 B1 work at about 200 mbar and 130 to 145 ° C

Preferably are used to produce the photovoltaic modules according to the invention Vacuum laminators used. These consist of a heatable and evacuable chamber in which bonded glazing inside of 30-60 minutes can be laminated. decreased Pressures of 0.01 to 300 mbar and temperatures of 100 to 200 ° C, in particular 130-160 ° C have proven in practice.

alternative may be a laminated body thus described above between at least one roller pair at a temperature of 60 to 150 ° C to an inventive Module be pressed. Plants of this type are for the production known from laminated glazing and usually have at least a heating tunnel before or after the first press shop in plants with two pressing plants.

Furthermore, the invention relates to the use of plasticized polyvinyl acetal-based films, which in an ambient climate of 85% r. F./23°C a specific electrical Volume resistivity of more than 1E12 ohm · cm and a glass transition temperature Tg of less than 20 ° C, or with the said preferred embodiments for the production of photovoltaic modules.

invention Photovoltaic modules can be used as façade components, roof surfaces, Winter garden cover, sound insulation wall, balcony or parapet element or used as part of window surfaces.

Measurement Methods:

The determination of the glass transition temperature of the film is carried out by means of differential scanning calorimetry (DSC) according to DIN 53765 using a heating rate of 10 K / min in the temperature range -50 ° C-150 ° C. A first heating ramp is followed, followed by a cooling ramp followed by a second heating ramp. The position of the glass transition temperature is reflected by the second heating ramp associated measurement curve DIN 51007 determined. The DIN midpoint (Tg DIN) is defined as the intersection of a horizontal halfway up the grade with the trace. The step height is defined by the vertical distance of the two points of intersection of the central tangent with the baseline of the trace before and after glass transition.

The determination of the flow behavior of the film takes place as a melt index (mass flow: MFR) ISO 1133 on a corresponding device, eg. B. the company Göttfert, model MI2. The MFR value is given at 100 ° C with the 2 mm nozzle at a weight load of 21.6 kg in grams per 10 minutes (g / 10 min).

Alkaline titer

3 to 4 gr. Of the plasticized polyvinyl acetal film is dissolved in 100 ml of a mixture of ethanol / THF (80:20) in a magnetic stirrer overnight. To this is added 10 ml of dilute hydrochloric acid (c = 0.01 mol / liter) and then potentiometrically potentiometric with a solution of tetrabutylammonium hydroxide (TBAH) in 2-propanol (c = 0.01 mol / liter) with a Titroprocessor against a blank titrated. The alkali titre is calculated as follows: Alkali titre = ml HCl per 100 gr of a sample = (Consumption TBAH blank - TBAH sample × 100 by weight of sample in gr.)

The measurement of the volume resistivity of the film is carried out according to DIN IEC 60093 at a defined temperature and ambient humidity (23 ° C and 85% RH) after the film has been conditioned for at least 24 hours under these conditions. To carry out the measurement, a plate electrode type 302 132 from Fetronic GmbH and an ohmmeter ISO-Digi 5 kV from Amprobe were used. The test voltage was 2.5 kV, the waiting time after application of the test voltage up to the data acquisition 60 sec. In order to ensure sufficient contact between the flat plates of the measuring electrode and the foil, its surface roughness R _z should be measured after measurement DIN EN ISO 4287 not greater than 10 microns, ie, if necessary, the original surface of the PVB film must be smoothed by thermal transfer before the resistance measurement.

The polyvinyl alcohol and polyvinyl alcohol acetate content of the polyvinyl acetals was determined according to ASTM D 1396-92 certainly. The analysis of the metal ion content was carried out by atomic absorption spectroscopy (AAS).

Of the Water or moisture content of the films is determined by the Karl Fischer method certainly. To simulate the wetting behavior under humid Conditions, the film is previously 24 h at 23 ° C and 85% rf stored. The method can be applied both to the unlaminated film as well as on a laminated photovoltaic module in dependence from the distance to the edge of the film.

Examples:

Production of polyvinyl acetals with different residual acetate content

pVB1:

100 parts by weight of the polyvinyl alcohol Mowiol 28-99 (commercial product of Kuraray Europe GmbH) were dissolved in 1075 parts by weight of water with heating to 90 ° C. There were at a temperature of 40 ° C 56.8 parts by weight of n-butyraldehyde and at a temperature of 12 ° C with stirring 75 parts by weight 20% hydrochloric acid added. The mixture was heated to 69 ° C after precipitation of the polyvinyl butyral (PVB) and stirred at this temperature for 2 hours. The PVB was separated after cooling to room temperature, washed neutral with water and dried. A PVB having a polyvinyl alcohol content of 20.2% by weight and a polyvinyl acetate content of 1.3% by weight was obtained.

PVB 2:

The PVB production was carried out according to PVB 1, with 59.8 Parts by weight of n-butyraldehyde were used. It became a PVB with a Polyvinylakoholgehalt of 18.2 wt.% And a polyvinyl acetate content of 1.7% by weight.

PVB 3:

The PVB production was carried out according to PVB 1, with 63.2 Parts by weight of n-butyraldehyde were used. It became a PVB with a Polyvinylakoholgehalt of 16 wt.% And a polyvinyl acetate content of 1.7% by weight.

PVB 4:

The PVB production was carried out according to PVB 1, with 100 Parts by weight of the polyvinyl alcohol Mowiol 30-92 (commercial product by Kuraray Europe GmbH) and 52.3 parts by weight of n-butyraldehyde used were. It became a PVB with a Polyvinylakoholgehalt of 16.7 % By weight and a polyvinyl acetate content of 9.2% by weight.

PVB 5:

The PVB production was carried out according to PVB 4, with 56 Parts by weight of n-butyraldehyde were used. It became a PVB with a Polyvinylakoholgehalt of 14.8 wt.% And a polyvinyl acetate content of 9% by weight.

PVB 6:

The PVB production was carried out according to PVB 4, with 60.3 Parts by weight of n-butyraldehyde were used. It became a PVB with a Polyvinylakoholgehalt of 13.1 wt.% And a polyvinyl acetate content of 9.2% by weight.

PVB 7:

The PVB production was carried out according to PVB 4, with 66 Parts by weight of n-butyraldehyde were used. It became a PVB with a Polyvinylakoholgehalt of 12 wt.% And a polyvinyl acetate content of 9.1% by weight.

PVB 8:

The PVB production was carried out according to PVB 1, with 100 Parts by weight of the polyvinyl alcohol Mowiol 26-88 (commercial product by Kuraray Europe GmbH) and 60 parts by weight of n-butyraldehyde used were. It became a PVB with a Polyvinylakoholgehalt of 11.9 % By weight and a polyvinyl acetate content of 12.7% by weight.

PVB 9:

The PVB production was carried out according to PVB 8, with 66 Parts by weight of n-butyraldehyde were used. It became a PVB with a Polyvinylakoholgehalt of 10.7 wt.% And a polyvinyl acetate content of 13.2% by weight.

Table 1 lists the chemical compositions of the abovementioned polyvinyl butyrals and of the polyvinyl alcohols used. Table 1 PVB Polyvinyl alcohol content PVB [wt.%] Polyvinyl acetate content PVB [wt.%] Degree of acetalization (= butyral content) [% by weight] Polyvinyl alcohol content PVB [mol%] Polyvinyl acetate content PVB [mol%] Degree of acetalization (= butyral content) [mol%] 1 20.2 1.3 78.5 29.1 1 70 2 18.2 1.7 80.1 26.5 1.3 72.2 3 16 1.7 82.3 23.6 1.3 85.1 4 16.7 9.2 84.1 24.8 7 68.2 5 14.8 9 76.2 22.2 6.9 70.9 6 13.1 9.2 77.7 19.9 7.1 73 7 12 9.1 78.9 18.3 7.1 74.6 8th 11.9 12.7 75.4 18.3 10 71.7 9 10.7 13.2 76.1 16.6 10.5 73

Table 2 shows the economic advantages that result from the use of a polyvinyl alcohol with a reduced degree of hydrolysis (higher yield based on polyvinyl acetate, reduced amount of aldehyde to achieve a comparable OH group content of the polyvinyl acetal). Table 2 PVB Used polyvinyl alcohol (PVA) Hydrolysis degree PVA [mol%] Yield of PVA based on 100 parts of polyvinyl acetate [%] Butyraldehyde [parts by weight per 100 pb PVA] Polyvinyl alcohol content PVB [w%] 1 Mowiol 28-99 99.2 51.5 56.8 20.2 2 Mowiol 28-99 99.2 51.5 59.8 18.2 3 Mowiol 28-99 99.2 51.5 63.2 16 4 Mowiol 30-92 93.1 54.5 52.3 16.7 5 Mowiol 30-92 93.1 54.5 56 14.8 6 Mowiol 30-92 93.1 54.5 60.3 13.1 7 Mowiol 30-92 93.1 54.5 66 12 8th Mowiol 26-88 87.8 57.1 60 11.9 9 Mowiol 26-88 87.8 57.1 66 10.7

Production of plasticizer-containing Films based on polyvinyl acetal

Comparative Example 1

290 g PVB 1, 100g plasticizer 3G8 and 10g softener DBEA in a laboratory mixer (manufacturer: Brabender, Model 826801) mixed. The resulting mixture became a flat film having a thickness of 0.8 mm extruded. The extrusion took place on a twin-screw extruder with counter-rotating screws (manufacturer: Haake, System Rhecord 90), equipped with melt pump and slot die. The cylinder temperature of the extruder was 220 ° C, the Nozzle temperature was 150 ° C.

Comparative Examples 2-4

at 304 g of PVB 1 or 2 and 3 and 96 g of plasticizer were used for the extrusion DOA used. The other procedure was carried out according to the comparative example 1.

Examples 1-6

at 304 g of PVB 4 or 5, 6, 7, 8 and 9 and 96 g of plasticizer DOA used. The other procedure took place according to Comparative Example 1.

It were films of the composition listed in Table 3 prepared and their glass transition temperature Tg, the Water content and the volume resistivity studied.

DBEEA:

Di-2-butoxyethoxyethyladipat

3G8:

Triethylenglykol-bis-2-ethylhexanoat

DOA:

Di-2-ethylhexyladipat

It means

DBEEA:

Di-2-butoxyethoxyethyladipat

3G8:

Triethylene glycol-bis-2-ethylhexanoate

DOA:

Di-2-ethylhexyl

It shows that films from the standard PVB 1 with medium plasticizer content (VB1) one for photovoltaic applications too low volume resistance exhibit. PVB films of fully hydrolyzed PVOH with reduced Plasticizer content up to a PVOH content of at least 16 wt.% Although a high volume resistance but also a high Glass transition temperature Tg of over 20 ° C on (VB2-4).

The Reduction of the PVOH content causes partially hydrolyzed PVB Polyvinyl alcohols a significant reduction in the glass transition temperature below 20 ° C with sufficiently high volume resistivity (Examples 1 and following).

Ex. 1 and following show that by the inventively used Films using inexpensively manufacturable PVB a combination of high specific resistance and low glass transition temperature can be achieved. Films of this type are particularly suitable for photovoltaic applications suitable.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

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• - EP 1118258 B1 [0043, 0043]
• WO 02/102591 A1 [0043]
• - EP 387148 B1 [0043]
• - EP 1235683 B1 [0054]

Cited non-patent literature

• Encyclopedia of Polymer Science and Engineering, Wiley, New York 1989, Vol. 17 [0009]
• - DIN 53765 [0059]
• - DIN 51007 [0059]
• - ISO 1133 [0060]
• - DIN IEC 60093 [0062]
• - DIN EN ISO 4287 [0062]
• ASTM D 1396-92 [0063]

Claims (10)

Photovoltaic module, comprising a laminate of a) a transparent front cover b) one or more photosensitive semiconductor layers c) at least one plasticizer-containing polyvinyl acetal-based film and d) a rear cover characterized in that the polyvinyl acetal has a polyvinyl acetate content of more than 3 wt.% , Photovoltaic module according to claim 1, characterized that the plasticizer-containing, based on polyvinyl acetal films c) have a plasticizer content of not more than 40% by weight. Photovoltaic module according to one of the claims 1 to 2, characterized in that the film c) has a glass transition temperature Tg of less than 20 ° C has. Photovoltaic module according to one of the claims 1 to 3, characterized in that the polyvinyl acetal a Polyvinylalkoholanteil of less than 18% by weight. Photovoltaic module according to one of the claims 1 to 4, characterized in that as plasticizer one or more Connections are used whose polarity, expressed by the formula 100 × O / (C + H) is less than or equal to 9.4, where O, C and H are the number of oxygen, carbon and and hydrogen atoms in the respective molecule. Photovoltaic module according to one of the claims 1 to 5, characterized in that the plasticizer-containing on Polyvinyl acetal-based films c) a metal salt of a carboxylic acid containing 1 to 15 carbon atoms as the basic compound. Photovoltaic module according to one of claims 1 to 6, characterized in that the plasticizer-containing polyvinyl acetal-based film contains 0.001 to 5 wt.% SiO ₂ . Photovoltaic module according to one of the claims 1 to 7, characterized in that one or more photosensitive Semiconductor layers b) on a transparent front cover a) or a rear cover d) are applied and by at least one plasticizer-containing, on polyvinyl acetal based film c) are glued together. Use of plasticizer-containing, on polyvinyl acetal based films containing the polyvinyl acetal a polyvinyl acetate content of more than 3% by weight for the production of photovoltaic modules. Use of photovoltaic modules according to a of claims 1 to 8 as a facade component, roof surfaces, Winter garden cover, sound insulation wall, balcony or parapet element or as part of window surfaces.