CN107903860B - Adhesive for solar cell backside protective film and application - Google Patents

Abstract

The invention belongs to the technical field of adhesives, and in particular relates to a water-resistant polyester resin adhesive used for the backside protective film of solar cells and its application. The adhesive for the back protective film of a solar cell comprises the following components by weight: 100 parts of polyester resin and 5-30 parts of melamine formaldehyde resin, and the gel fraction of the adhesive is more than 50%. The protective film for the backside of solar cells is formed by composite pressing of an electrical insulating layer, a moisture-proof layer, a weather-resistant layer and an adhesive layer, and the adhesive layer at least includes the above-mentioned adhesive for the backside protective film of solar cells. The technical scheme provided by the invention adds a specific melamine formaldehyde resin to form a chelating system, which greatly reduces the viscosity of the system by blocking polar groups such as carboxyl groups and hydroxyl groups on the branched chain, and has unexpected hydrolysis resistance. It has excellent processing and construction properties, and the interlayer peel strength is higher, and the service life is also greatly extended.

Description

Adhesive for solar cell backside protective film and application

technical field

The invention belongs to the technical field of adhesives, and in particular relates to a water-resistant polyester resin adhesive used for the backside protective film of solar cells and its application.

Background technique

Solar cells have attracted much attention as a renewable and clean energy source. One or several semiconductors that can directly convert the energy of sunlight into electrical energy can form a solar cell unit. Several or even dozens of the above-mentioned solar cell units are connected in series or parallel by wires and then sealed with resin, especially for protection. The solar cell unit that needs to work for a long time is packaged with various suitable materials to make a module, that is, a solar cell module. In general, the sun-irradiated surface is covered with a glass plate or a transparent plastic film, and thermoplastic resin is used as a filling material to embed the gap, while the back is protected by a plastic film (also known as a back film or a back plate protective film). Solar cell modules are outdoor-installed electrical equipment that can be used outdoors for decades. Therefore, during short-term processing and long-term mobile use, the protective film material constituting the module is required to have certain mechanical strength, electrical insulation, and weather resistance. , moisture resistance and heat resistance. However, it is difficult for a single plastic film to have these functions at the same time, so it is necessary to use adhesives to bond and laminate multiple materials that can share each function to form a composite protective film.

Chinese patent CN101805578A discloses a polyester resin adhesive, which is obtained by cross-linking reaction of 100 parts by weight of polyester resin and 3 parts of cross-linking agent polycarbodiimide resin V-05. The polyester resin is formed by polycondensation of polycarboxylic acid and polyol. In order to overcome the problem of poor hydrolysis resistance of the polyester resin itself, a cross-linking agent polycarbodiimide resin is introduced. There are branched chains containing many exposed carboxyl or hydroxyl groups, and the viscosity of the cross-linking system is high, up to 2000cps, which is difficult to process and use, and cannot be well applied to the protective film of solar cell modules. Therefore, there is an urgent need to develop a bonding material suitable for the protective film of solar cell modules, which can meet the requirements of current solar cell products and be easy to process.

SUMMARY OF THE INVENTION

The invention provides an adhesive for a solar cell backside protective film and its application, which are used to solve the problems of high viscosity of the current adhesive and difficult processing and construction.

In order to solve the above-mentioned technical problems, the technical scheme of the present invention is: the adhesive for the back protective film of solar cells includes the following components by weight: 100 parts of polyester resin and 5-30 parts of melamine formaldehyde resin, the The gel fraction of the binder is 50% or more.

Further, with 100 parts of polyester resin and 20 parts of melamine formaldehyde resin, the gel fraction of the binder is more than 60%.

Further, the preparation method of the melamine formaldehyde resin is as follows: add melamine to the formaldehyde solution with a pH value of 8-8.5, heat up to 70 ° C for insulation, continue to keep the reaction for half an hour after the system is clarified, and then cool down to 40 ° C, Methanol is added, then the pH value is adjusted to 5 to 6, the temperature is raised to 50° C. again to react for 1 hour, and the pH value is adjusted to 8 to 9 again to obtain the desired melamine formaldehyde resin.

Further, the molar ratio of the melamine to formaldehyde is 1:(3-6).

Further, the molar ratio of the melamine to methanol is 1:(15-20).

Further, the polyester resin is a copolymer of polycarboxylic acid and polyol, and the polycarboxylic acid is an aromatic dicarboxylic acid. The polycarboxylic acid contains at least 50 mol% to 90 mol% of aromatic It contains 25 mol % to 90 mol % of an alkylene glycol having 3 to 20 carbon atoms.

Further, the aromatic dicarboxylic acid is selected from one or more of phthalic acid, terephthalic acid, isophthalic acid and naphthalene dicarboxylic acid.

Further, the alkylene glycol having 3 to 20 carbon atoms is selected from 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol and 1,4-cyclohexane One or more of alkanedimethanol.

Further, the preparation method of the adhesive for the back protective film of the solar cell is as follows: at room temperature, the melamine formaldehyde resin is added dropwise to the polyester resin copolymer solution, the temperature is raised to 50° C., stirred for 0.5 to 1 hour, and cooled. The adhesive for the back surface protective film of the solar cell was obtained.

The invention also provides a solar cell backside protective film, which is formed by composite pressing of an electrical insulating layer, a moisture-proof layer, a weather resistance layer and an adhesive layer, and the electrical insulating layer is made of polyester film or polycarbonate film, so The weather-resistant layer is made of fluororesin and/or acrylic resin, the moisture-proof layer is made of metal aluminum or an inorganic oxide, and the adhesive layer at least includes the above-mentioned adhesive for a solar cell backside protective film.

The technical solution provided by the present invention adds a specific melamine formaldehyde resin to form a chelating system, which greatly reduces the viscosity of the system from about 2000cps to 150 cps by blocking polar groups such as carboxyl groups and hydroxyl groups on the branched chain. -200cps, and the hydrolysis resistance is unexpectedly greatly improved, so it has excellent processing and construction performance, and the interlayer peel strength is higher, and the service life is also greatly extended.

Detailed ways

For ease of understanding, the following describes the adhesive for solar cell backside protective film and its application with reference to the examples. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention.

The reagents used in the examples are all commercially available products unless otherwise specified.

The solar cell backside protective film provided by the present invention has a multi-layer structure, including an electrical insulating layer, a moisture-proof layer, a weather-resistant layer, and an adhesive layer formed between the electrical insulating layer, the moisture-proof layer, and the weather-resistant layer, which mainly plays an adhesive role. . in:

The electrical insulating layer is a polyester film or a polycarbonate film. The polyester can be made of one or more aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and aliphatic diols with 2 to 4 carbon atoms, such as ethylene glycol. Thermoplastic polyester resin obtained by esterification of alcohol, butanediol and/or aromatic diol. Representative polyesters are: polyethylene terephthalate, polybutylene terephthalate, polynaphthalene, terephthalic acid, copolyester of isophthalic acid and bisphenol A, polystyrene Copolyesters of oxyphthalates, aromatic diols, and aromatic dicarboxylic acids, etc. Among these polyesters, polyethylene terephthalate and polynaphthalene are the most desirable. These polyester resins can usually be formed into a polyester film by melt extrusion, and the mechanical properties of the polyester film can be further improved by stretching 2 to 4 times in the longitudinal and transverse directions and heat-setting at a higher temperature. Strength and thermal dimensional stability. In general, the thickness of the film can be 12 μm to 350 μm, preferably in the range of 50 μm to 250 μm. From the viewpoint of dielectric breakdown resistance and moisture resistance, a thickness of 100 μm to 250 μm is more desirable. In addition, polyester films with good hydrolysis resistance in which carboxyl groups are blocked, polyester films added with UV absorbers and pigments, and polyester films coated with coatings containing UV absorbers and pigments can also be used.

In terms of weight, polyester film occupies a particularly large proportion in the protective film. To achieve flame retardancy of the protective film, the polyester film must be flame retardant first. The flame retardant of polyester film can be achieved by copolymerizing flame retardant monomers or mixing flame retardants in polyester. When the solution of mixing flame retardants in polyester is chosen, the flame retardants can be inorganic compounds such as phosphides or aluminium hydroxide. Among them, mixing aluminum hydroxide is the common and most ideal method for preparing flame retardant films.

Polycarbonate resin is mainly composed of bisphenol and carbonic acid.

As the moisture-proof layer, metal oxides such as silicon and/or aluminum, metal thin films such as aluminum, and metal foils such as aluminum foil can be used. Among them, the most desirable is a coating of metal oxides such as silicon and/or aluminum, or an aluminum foil. The thickness of the coating is generally 10 nm to 300 nm, and the thickness of the metal foil is generally 5 μm to 25 μm. The adhesive layer in the present invention can be arranged between the metal oxide and metal vapor-deposited polyester resin film and the polycarbonate resin film, or can be vapor-deposited to form a moisture-proof layer with a thinner plastic film, and can pass through the present invention. The adhesive layer in the invention laminates this composite to the above-mentioned polyester resin film and polycarbonate resin film. It is also possible to use the adhesive layer in the present invention to directly laminate the metal foil to the above-mentioned polyester film in the same method, or to make a moisture-proof layer formed by composite lamination of the metal foil and a thinner plastic film in advance, This composite is then laminated to the above polyester resin film and polycarbonate resin film through the adhesive layer of the present invention.

The weather-resistant layer may be a film or coating film composed of fluororesin and/or acrylic resin. The fluororesin and the acrylic resin may be used alone, but the fluororesin and the acrylic resin may be copolymerized, blended, and grafted, or used by composite lamination. Among them, the fluororesin can be PTFE (polytetrafluoroethylene), ETFE (tetrafluoroethylene/ethylene copolymer), FEP (tetrafluoroethylene/hexafluoropropylene copolymer), PCTFE (polychlorotrifluoroethylene), PFA ( tetrafluoroethylene/perfluoroalkyl copolymer), PVF (polyvinyl fluoride), PVDF (polyvinylidene fluoride), etc.; propylene resin can be polymethyl methacrylate or methyl methacrylate and other propylene monomers of copolymer resin. Among them, films such as PVF, PVDF, ETFE, etc. are ideal, as well as coatings composed of the reactants of fluoropolymers containing hardening functional groups and hardeners such as functional isocyanates. The fluoropolymers containing hardening functional groups can be, for example, Copolymers of tetrafluoroethylene, isoethylene, vinyl ether and/or other monomers, copolymers of tetrafluoroethylene, polyvinylidene fluoride, vinyl ether and/or other monomers, chlorotrifluoroethylene, vinyl Copolymers of ethers, and/or other monomers, polyvinylidene fluoride, copolymers of vinyl ethers and/or other monomers, etc. Of course, various pigments, ultraviolet absorbers, and the like may be added to these fluororesin films or coating films.

The adhesive layer in the present invention will be described in detail below. The adhesive layer refers to functional layers that mainly share the electrical insulating layer, moisture-proof layer, weather-resistant layer, etc. constituting the protective film of the present invention, and a layer interposed between the functional layers and bonding all the functional layers together. The tie layer mainly includes an adhesive layer, and in some cases, also includes a surface pretreatment layer, a primer layer, an adhesion promoting layer, and the like. Among them, the electrical insulating layer is mainly made of polyester resin and polycarbonate resin film, the purpose is to make the electrical insulating layer have good electrical insulation and heat resistance; the weather-resistant layer is made of fluorine film; the moisture-proof layer is made of metal and metal oxides, and the above materials are all materials with good adhesion. At this time, it can be seen that the adhesive layer has all the above functions required in the solar cell module component, especially the heat and humidity resistance and heat resistance.

In the adhesive layer of the protective film of the present invention, organic or inorganic additives other than the above-mentioned components may be contained. For example: UV absorbers, UV protectors, adhesion promoters, cross-linking reaction catalysts, light reflectors, defoaming agents, pigments, moisture absorbers, etc.

Generally, the adhesive layer of the protective film for solar cells of this invention is produced by the following method. The prepared solar cell backside protective film is sprayed on the resin film or the metal film with an adhesive, and after drying, it is pressed with other films or metal films to form an adhesive layer through a heating roller. The above-mentioned series of steps can be implemented using existing equipment and methods.

The method for measuring the gel fraction (% by weight) of the binder is as follows: add 2.5 test samples and 50 ml of ethyl acetate into a 100 ml flask, and vacuum dry at 50° C. for 2 hours. Calculate the proportion of the weight of the insoluble part in the initial weight in the form of a percentage, which is the gel fraction.

The adhesive provided by the invention is specifically as the following examples:

Example 1

The adhesive for the back protective film of a solar cell comprises the following components by weight: 100 parts of polyester resin and 20 parts of melamine formaldehyde resin.

The preparation method of the melamine-formaldehyde resin is as follows: add melamine to an aqueous formaldehyde solution with a pH value of 8-8.5, heat up to 70 ° C for insulation, continue to keep the reaction for half an hour after the system is clarified, then cool down to 40 ° C, add methanol Then, the pH value is adjusted to 5-6, the temperature is again raised to 50° C. to react for 1 hour, and the pH value is adjusted to 8-9 again to obtain the desired melamine formaldehyde resin. The molar ratio of the melamine to formaldehyde is 1:3, and the molar ratio of the melamine to methanol is 1:15.

Wherein the polyester resin is a polycarboxylic acid and a polyol copolymer, the polycarboxylic acid contains 60 mol% of a mixture of phthalic acid, terephthalic acid and isophthalic acid, and the remainder is other types of polycarboxylic acids , such as: adipic acid, suberic acid, azelaic acid, sebacic acid, cyclohexanedicarboxylic acid, etc.; the polyol contains 30 mol% of 2-methyl-1,3-propanediol and 2,2-diol A mixture of methyl-1,3-propanediol, the rest are other types of polyols, such as: ethylene glycol, diethylene glycol, glycerol, polyethylene glycol, etc.

The specific preparation method of the adhesive for the back protective film of the solar cell is as follows: at normal temperature, drop the above-mentioned melamine formaldehyde resin into the polyester resin copolymer solution, raise the temperature to 50° C., stir for 0.5 to 1 hour, and cool to obtain the The adhesive for a solar cell backside protective film has a gel fraction of 60% or more.

By introducing the etherified melamine formaldehyde resin chelating system, a resin layer with a network structure with high humidity and heat resistance is formed, and this system effectively blocks the carboxyl groups and hydroxyl groups on the branched chains, which further improves the Hydrolysis resistance, and viscosity is also greatly reduced, improving processing and application properties.

Example 2

The adhesive for the back protective film of a solar cell comprises the following components by weight: 100 parts of polyester resin and 20 parts of melamine formaldehyde resin.

The preparation method of the melamine-formaldehyde resin is as follows: add melamine to an aqueous formaldehyde solution with a pH value of 8-8.5, heat up to 70 ° C for insulation, continue to keep the reaction for half an hour after the system is clarified, then cool down to 40 ° C, add methanol Then, the pH value is adjusted to 5-6, the temperature is again raised to 50° C. to react for 1 hour, and the pH value is adjusted to 8-9 again to obtain the desired melamine formaldehyde resin. The molar ratio of the melamine to formaldehyde is 1:6, and the molar ratio of the melamine to methanol is 1:20.

Wherein the polyester resin is a polycarboxylic acid and a polyol copolymer, the polycarboxylic acid contains 90 mol% of a mixture of phthalic acid, terephthalic acid and isophthalic acid, and the remainder is other types of polycarboxylic acids , such as: adipic acid, suberic acid, azelaic acid, sebacic acid, cyclohexanedicarboxylic acid, etc.; the polyol contains 80 mol% of 2-methyl-1,3-propanediol and 2,2-diol A mixture of methyl-1,3-propanediol, the rest are other types of polyols, such as: ethylene glycol, diethylene glycol, glycerol, polyethylene glycol, etc.

The specific preparation method of the adhesive for the back protective film of the solar cell is as follows: at normal temperature, drop the above-mentioned melamine formaldehyde resin into the polyester resin copolymer solution, raise the temperature to 50° C., stir for 0.5 to 1 hour, and cool to obtain the The adhesive for a solar cell backside protective film has a gel fraction of 70% or more.

Comparative Example 1

The difference from Example 1 is that methylol melamine replaces the melamine formaldehyde resin.

Comparative Example 2

The difference from Example 1 is that the melamine formaldehyde resin is replaced by polycarbodiimide resin V-05 (manufactured by Nissin Textile Co., Ltd.).

Comparative Example 3

The difference from Example 2 is that 80% of the polyol is a mixture of 1,3-propanediol and 1,4-butanediol.

Performance Testing:

1. Interlayer adhesion: AGS-J manufactured by Shimadzu, and measured according to ASTM D1876.

2. High temperature and high humidity experiment: 96 hours of treatment at 120° C., 2Kg atmospheric pressure, and 100% RH, using C340 produced by Weiss-Voetsh Environmental Testing Instruments, and according to IEC61215-10.13.

3. Liquid viscosity: use American BROOKFIELD DV-II+PRO digital viscometer to test according to ASTM D445-04 method.

The above experimental data are arranged in Table 1.

Table 1

It can be found that by adopting the technical solution of the present invention, the viscosity of the liquid is greatly reduced, and the interlayer adhesion is basically unchanged under the condition of high temperature and high humidity for a long time, and it has better hydrolysis resistance.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that the technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features thereof can be equivalently replaced, and These modifications or substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (7)

1. The adhesive for the solar cell back surface protective film is characterized by comprising the following components in parts by weight: 100 parts of polyester resin and 5-30 parts of melamine formaldehyde resin, wherein the gel fraction of the adhesive is more than 50%;

the polyester resin is a copolymer of polycarboxylic acid and polyhydric alcohol, wherein the polycarboxylic acid is aromatic dicarboxylic acid, the polycarboxylic acid at least comprises 50-90 mol% of aromatic dicarboxylic acid, and the polyhydric alcohol at least comprises 25-90 mol% of alkylene glycol with 3-20 carbon atoms;

the alkylene glycol with the carbon number of 3-20 is selected from one or more than two of 2-methyl-1, 3-propylene glycol, 2-dimethyl-1, 3-propylene glycol and 1, 4-cyclohexanedimethanol;

the preparation method of the melamine formaldehyde resin comprises the following steps: adding melamine into a formaldehyde aqueous solution with the pH value of 8-8.5, heating to 70 ℃, keeping the temperature, continuing to keep the temperature for reaction for half an hour after the system is clarified, then cooling to 40 ℃, adding methanol, adjusting the pH value to 5-6, heating to 50 ℃ again, reacting for 1 hour, and adjusting the pH value to 8-9 again to obtain the required melamine-formaldehyde resin.

2. The adhesive for a solar cell back surface protection film according to claim 1, wherein the adhesive has a gel fraction of 60% or more, and comprises 100 parts of a polyester resin and 20 parts of a melamine-formaldehyde resin.

3. The adhesive for a solar cell back surface protective film according to claim 1, wherein the molar ratio of melamine to formaldehyde is 1 (3 to 6).

4. The adhesive for a solar cell back surface protective film according to claim 1, wherein the molar ratio of melamine to methanol is 1 (15 to 20).

5. The adhesive for a solar cell back surface protective film according to claim 1, wherein the aromatic dicarboxylic acid is one or more selected from phthalic acid, terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid.

6. The adhesive for a solar cell back surface protection film according to claim 1, wherein the method for producing the adhesive for a solar cell back surface protection film is as follows: and at normal temperature, dropwise adding the melamine formaldehyde resin into a polyester resin copolymer solution, heating to 50 ℃, stirring for 0.5-1 hour, and cooling to obtain the adhesive for the solar cell back protective film.

7. A solar cell back surface protective film, which is formed by compounding and pressing an electric insulating layer, a moisture-proof layer, a weather-resistant layer and an adhesive layer, wherein the electric insulating layer is a polyester film or a polycarbonate film, the weather-resistant layer is made of fluororesin and/or acrylic resin, the moisture-proof layer is made of metal aluminum or inorganic oxide, and the adhesive layer at least comprises the adhesive for the solar cell back surface protective film according to any one of claims 1 to 6.