Photocurable adhesive liquid and photovoltaic module

Abstract

The present application aims at the problems of poor processing performance, large energy consumption and low efficiency of PVB solid adhesive film, and provides a photocuring PVB adhesive solution, which adopts a special diluent with good solubility for PVB, and the diluent can be quickly cured by LED light, greatly shortening the module packaging cycle. The photocuring adhesive film formed by the photocuring adhesive solution of the present application does not need high-temperature heating in the packaging process, significantly reducing the energy consumption and photovoltaic power generation cost, so that it can greatly play its excellent properties such as adhesion, strong water permeability resistance, high light transmittance, high weather resistance, impact resistance, corrosion resistance and the like in the photovoltaic field.

Description

Technical Field

[0001] This invention relates to encapsulating films for photovoltaic modules, specifically to a photocurable liquid PVB encapsulating film for photovoltaic modules and a photovoltaic module. Background Technology

[0002] Solid encapsulants used for encapsulating photovoltaic modules typically include EVA, POE, EPE, and PVB, with thicknesses ranging from 0.35 to 1.52 millimeters. The long-term reliability of photovoltaic modules is significantly affected by the encapsulant. The key performance characteristic of ideal encapsulation materials is their adhesion to the glass module, followed by strong water resistance, good weather resistance, long service life, and high transparency.

[0003] EVA film is the most widely used due to its advantages such as high transparency, low melting point, easy processing, and low price. However, it has poor water resistance, poor weather resistance, and short service life. In recent years, it has been gradually replaced by products with better performance, such as POE film (including co-extruded type).

[0004] PVB exhibits excellent adhesion to glass, metals, and ceramics, and has been a superior bonding material in the fields of architectural and automotive safety glass since its introduction in the 1930s, withstanding the test of time for over 70 years. As an encapsulation material, PVB's advantages, including high adhesion, high transparency, high water permeability resistance, high weather resistance, impact resistance, non-toxicity, and non-corrosiveness, are leading to its increasing penetration in the photovoltaic film field. Its application in BIPV (Building Integrated Photovoltaics) is expected to see breakthroughs first, potentially becoming the primary encapsulation material for future building-integrated photovoltaics. According to national standards, photovoltaic modules for building curtain walls must be encapsulated with PVB film to ensure product safety and durability.

[0005] Under the same testing conditions, PVB film modules exhibit significantly better water permeability resistance than POE and EVA, and also show significantly better performance in acid, alkali, and salt spray resistance, high temperature resistance, and impact resistance. Furthermore, the excellent weather resistance and resistance to extreme environments result in a significantly longer service life for PVB films compared to EVA and POE (referencing traditional architectural-grade PVB films, which can last for 50 years or more).

[0006] The reason why PVB films exhibit extremely strong water resistance and adhesion is that during the bonding process between PVB and glass, the hydroxyl groups in the film can form strong hydrogen bonds with the oxygen atoms in the glass, causing the hydrophilic groups on the interface to disappear, making it difficult for water vapor to penetrate and resulting in excellent adhesion. EVA or POE are low-polarity materials, requiring the use of coupling agents in the formulation to achieve the connection between the film and the glass. However, the relatively loose connection of the coupling agent results in lower interfacial bond energy, making water vapor penetration easier and the adhesion strength significantly weaker than that of PVB films.

[0007] While solid PVB film boasts excellent performance, its processing properties are poor. Traditional lamination processes struggle to achieve effective adhesion between PVB and glass, requiring a lamination temperature of 170℃ and necessitating the use of an autoclave or a combination of roll pressing and high-pressure encapsulation. Domestically, there has been no significant breakthrough in processing equipment and encapsulation processes. The complexity of the processing technology and the lack of equipment are key factors restricting the application of PVB film in photovoltaic module encapsulation. Furthermore, the module lamination cycle is primarily determined by the characteristics of the solid film; the hot lamination process takes 25-35 minutes, consuming almost half of the photovoltaic module production time, severely limiting module production efficiency.

[0008] Liquid PVB films offer unique advantages in terms of energy consumption and processing time. However, the inherent material properties of PVB itself provide little incentive for those skilled in the art to conduct research on PVB liquid films. For example, PVB is a white powder with a glass transition temperature (Tg) of 65-117℃. Its molecular structure contains a large number of polar hydroxyl, acetyl, and acetal groups. The more hydroxyl groups, the stronger the bond to glass, but the more hygroscopic and less water-resistant it is. More acetyl groups reduce solution viscosity and Tg. A larger molecular weight reduces solubility and significantly increases solution viscosity. In existing technologies, PVB resin is typically dissolved in highly polar alcohols or alcohol ethers to form a liquid, such as methanol, ethanol, butanol, 1,2-propanediol-1-monomethyl ether, and propylene glycol methyl ether. The resulting coatings contain a large amount of volatile organic solvents, are easily flammable, and emit significant amounts of VOCs during the drying process.

[0009] Photoactive diluents are usually low molecular weight acrylic monomers with relatively low polarity and poor compatibility with PVB. In particular, low polar UV monomers are completely insoluble. Therefore, to make solid PVB resin into a photosensitive liquid adhesive, it is necessary to select a matching type of photoactive diluent and construction process, which must take into account compatibility, low viscosity, as well as the photocuring performance, weather resistance and flexibility of the adhesive film. Summary of the Invention

[0010] The purpose of this invention is to address the problems of poor processing performance, high energy consumption, and low efficiency of PVB solid films by providing a photocurable PVB adhesive. This adhesive uses a special diluent with excellent solubility for PVB, and this diluent can be rapidly cured under LED light, significantly shortening the module encapsulation cycle. Therefore, in this invention, it is referred to as a photoactive diluent. The photocurable film formed by the photocurable adhesive of this invention eliminates the need for high-temperature heating during the encapsulation process, significantly reducing energy consumption and photovoltaic power generation costs. This allows PVB to fully utilize its inherent excellent properties in the photovoltaic field, such as strong adhesion, strong water penetration resistance, high light transmittance, high weather resistance, impact resistance, and non-corrosiveness.

[0011] The aforementioned special diluent is a (meth)acrylic acid hydroxy ester compound with the structural formula: R1-CH=CHCOOR2-OH, where R1 is H or CH3; R2 is a compound group with 2 to 9 carbon atoms. The mass percentage of hydroxyl groups is 7.94-14.64%. This diluent has low viscosity, contains hydroxyl and (meth)acryloyloxy photosensitive groups, exhibits good solubility for PVB, does not contain volatile organic solvents, and can rapidly cure into a film under ultraviolet light. The cured film has excellent adhesion to glass and maintains the original excellent weather resistance of PVB.

[0012] Furthermore, the different chain lengths of ester hydroxyl groups, i.e., the different numbers of carbon atoms they contain, result in significantly different photocuring speeds and noticeable differences in their solubility in PVB. If the alkyl chain is too long and the hydroxyl content in the molecule is too low, the compatibility with PVB resin deteriorates, even to the point of immiscibility, leading to a very slow photocuring speed. Conversely, if the molecular chain is too short and the hydroxyl content is too high, the photocuring speed is fast. For example, hydroxy methacrylates have inferior dilution effects, photocuring speed, and yellowing resistance compared to hydroxy acrylates.

[0013] The hydroxyl groups described above can exist in the form of primary or secondary hydroxyl groups. In some preferred embodiments of the present invention, the (meth)acrylate hydroxyl ester compounds contain at least primary hydroxyl groups, including but not limited to: hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), 4-hydroxybutyl acrylate (4-HBA), 6-hydroxyhexyl acrylate (4-HHA), 9-hydroxynonyl acrylate (9-HNA), hydroxyethyl caprolactone acrylate (HECLA), hydroxyethyl dicaprolactone acrylate (HEDCLA), 1-hydroxymethyl-2-nonylphenoxyethyl acrylate; hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), hydroxybutyl methacrylate (4-HBMA), 6-hydroxyhexyl methacrylate (4-HHMA), 9-hydroxynonyl methacrylate, 1-hydroxymethyl-2-nonylphenoxyethyl methacrylate, hydroxyethyl caprolactone methacrylate (HECLMA), and hydroxyethyl dicaprolactone methacrylate (HEDCLMA). The photocuring speed of primary hydroxyl monomers is greater than that of secondary hydroxyl monomers.

[0014] In the photocurable adhesive of this invention, the mass ratio of polyvinyl butyral resin to photoactive diluent is 20-70:30-80. If the PVB resin content is too high, the performance of the cured film will be closer to that of PVB, and the viscosity of the adhesive will be too high, making it difficult to coat. If the photoactive diluent content is too high, the viscosity of the adhesive will be lower, the photocuring speed will be faster, the leveling speed during the coating process will be faster, and bubbles will be easier to eliminate, but the performance of the cured adhesive film will deteriorate, the elongation at break will decrease, and the bonding strength to glass will be worse.

[0015] In some embodiments of the present invention, the polyvinyl butyral resin has a molecular weight of 5,000-150,000, a hydroxyl value of 15-35 wt%, and an acetal content of 65-85%.

[0016] In some embodiments of the present invention, 0 to 5 parts by weight of photosensitizers are also included, including but not limited to 1173, 184, TPO, 819, and TPO-L.

[0017] In the system of this invention, the adhesive is sealed inside the photovoltaic module and is isolated from the air during photocuring. The oxygen inhibition effect is very small. After the photosensitizer absorbs the ultraviolet light of the LED, it can quickly trigger the photopolymerization reaction of the reactive diluent, and the PVB adhesive is cured instantly. The thickness of the cured film can reach several millimeters.

[0018] Ultra-clear glass yellows under short-wavelength (below 360nm) ultraviolet light, affecting its light transmittance and reducing photoelectric conversion efficiency. Therefore, selecting photosensitizers that absorb long wavelengths is essential to ensure rapid drying of the liquid film without causing yellowing. LED photosensitizers capable of absorbing long-wavelength ultraviolet light include TPO, 819, and TPO-L.

[0019] The photocuring refers to drying the liquid adhesive film by irradiating it with ultraviolet light with a wavelength of 350-500 nm, and the irradiation energy is 25-3000 mJ / cm. 2 Preferably, single-wavelength LED light curing is used, such as 365nm, 385nm, 395nm, 405nm, or a combination of two or more wavelengths, to rapidly cure the adhesive film, with an irradiation energy of 100-1500 mJ / cm². 2 .

[0020] The preparation method of the photocurable PVB adhesive of the present invention includes: weighing polyvinyl butyral (PVB) resin and photoactive diluent in proportion, stirring evenly, heating to dissolve into a transparent liquid, adding appropriate amounts of photosensitizer and additives as needed, including but not limited to defoamers, leveling agents, ultraviolet light absorbers, antioxidants, multifunctional crosslinking agents, coupling agents, etc., and finally degassing under vacuum to obtain LED photocurable liquid adhesive for later use.

[0021] This invention also relates to a photovoltaic module that uses the aforementioned adhesive for bonding, including but not limited to bonding between the power generation layer and the glass panel, and bonding between the power generation layer and the photovoltaic backsheet. The adhesive undergoes a rapid photocuring reaction under LED ultraviolet light irradiation, instantly transforming into a flexible, transparent solid film, thereby bonding and encapsulating the transparent cover plate, power generation glass or solar cells, and transparent backsheet into a single unit.

[0022] Furthermore, the adhesive is uniformly applied to the surface of the photovoltaic glass panel or backsheet using one of the following methods: spray coating, roller coating, screen printing, slot coating, dispensing coating, scraping coating, injection coating, or bar coating.

[0023] Heating the adhesive can reduce the viscosity of the product, quickly eliminate air bubbles in the coating, facilitate leveling, and improve the overall performance of the UV-curable film. The coating temperature can be controlled within the range of 30-110 degrees Celsius. For example, before coating an LED UV-curable liquid adhesive film, preheating can be performed, with the temperature controlled within the range of 35-90 degrees Celsius.

[0024] The photocurable PVB adhesive of the present invention can be colorless and transparent, or it can be colored by adding pigments, preferably pearlescent pigments.

[0025] Preferably, the thickness of the adhesive layer based on the present invention can be 0.1-2.0 mm; more preferably, it is 0.3-1.55 mm.

[0026] The power generation layer can be photovoltaic glass (thin-film battery), perovskite battery layer, or crystalline silicon battery string (crystalline silicon battery). The panel and backsheet can be photovoltaic glass or transparent plastic.

[0027] Compared with existing technologies, the advantages of this invention are as follows: The special photoactive diluent of this invention has excellent solubility for PVB and can be rapidly cured by LED light, greatly shortening the component encapsulation cycle. The encapsulation process does not require high-temperature heating, significantly reducing energy consumption and photovoltaic power generation costs. Detailed Implementation

[0028] Example 1

[0029] The formulation for LED light-curing liquid adhesive film is as follows:

[0030] PVB resin (hydroxyl content wt 29%, molecular weight 5000) 54g;

[0031] HEA (hydroxyl mass percentage 14.64%) 45g;

[0032] TPO 1g;

[0033] The structural formula of HEA is:

[0034] The components in the above formula are stirred evenly and heated to 80-100℃ until completely dissolved. After vacuum degassing, an LED light-curing liquid adhesive film is obtained for later use. Before coating, the adhesive is preheated to 90℃. First, the liquid adhesive film adhesive layer B is applied to the surface of the glass backplate with a coating thickness of 0.38 mm. Then, the cadmium telluride power generation glass layer is laid. Next, the liquid adhesive film adhesive layer A is applied to the surface of the battery layer with a thickness of 0.38 mm. The transparent glass panel is then covered. After vacuum degassing, the adhesive is irradiated simultaneously from both sides with 405nm LED light at an irradiation energy of 630mJ / cm². 2 After obtaining the bonded double-glass module, the photovoltaic module is obtained by installing the leads and frame.

[0035] Example 2-1

[0036] The formulation for LED light-curing liquid adhesive film is as follows:

[0037] PVB resin (hydroxyl content wt 19%, molecular weight 5500) 52g;

[0038] 3-HPA (OH content 13.06%) 47.5g;

[0039] 819 0.5g;

[0040] The structural formula of the 3-HPA used is:

[0041] The components in the above formula are stirred evenly and heated to 50-80℃ until completely dissolved. After vacuum degassing, an LED light-curing liquid adhesive film is obtained for later use. Before coating, the adhesive is preheated to 50℃. First, liquid adhesive film adhesive layer B is applied to the surface of the glass backplate with a coating thickness of 0.38 mm. Then, a cadmium telluride power generation glass layer is laid. Next, liquid adhesive film adhesive layer A is applied to the surface of the battery layer with a thickness of 0.38 mm. A transparent glass panel is then covered. After vacuum degassing, the adhesive is cured simultaneously on both sides using 395nm LED light with an irradiation energy of 650mJ / cm². 2 After obtaining the bonded double-glass module, the photovoltaic module is obtained by installing the leads and frame.

[0042] Example 2-2

[0043] The formulation for LED light-curing liquid adhesive film is as follows:

[0044] PVB resin (hydroxyl content wt 19%, molecular weight 5500) 52g;

[0045] 2-HPA (OH content 13.06%) 47.5g;

[0046] 819 0.5g;

[0047] The structural formula of the 2-HPA used is:

[0048] The components in the above formula are stirred evenly and heated to 50-80℃ until completely dissolved. After vacuum degassing, an LED light-curing liquid adhesive film is obtained for later use. Before coating, the adhesive is preheated to 50℃. First, liquid adhesive film adhesive layer B is applied to the surface of the glass backplate with a coating thickness of 0.38 mm. Then, a cadmium telluride power generation glass layer is laid. Next, liquid adhesive film adhesive layer A is applied to the surface of the battery layer with a thickness of 0.38 mm. A transparent glass panel is then covered. After vacuum degassing, the adhesive is cured simultaneously on both sides using 395nm LED light with an irradiation energy of 710 mJ / cm². 2 After obtaining the bonded double-glass module, the photovoltaic module is obtained by installing the leads and frame.

[0049] Example 3

[0050] The formulation for LED light-curing liquid adhesive film is as follows:

[0051]

[0052] The structural formula of 4-HBA is:

[0053] The components in the above formula are stirred evenly and heated to 50-80℃ until completely dissolved. After vacuum degassing, an LED light-curing liquid adhesive film is obtained for later use. Before coating, the adhesive is preheated to 50℃. First, the liquid adhesive film adhesive layer B is applied to the surface of the glass backplate with a coating thickness of 0.38 mm. Then, the cadmium telluride power generation glass layer is laid. Next, the liquid adhesive film adhesive layer A is applied to the surface of the battery layer with a thickness of 0.38 mm. The transparent glass panel is then covered. After vacuum degassing, the adhesive is cured simultaneously on both sides using 385nm LED light with an irradiation energy of 280mJ / cm². 2 After obtaining the bonded double-glass module, the photovoltaic module is obtained by installing the leads and frame.

[0054] Example 4

[0055] The formulation for LED light-curing liquid adhesive film is as follows:

[0056] PVB resin (hydroxyl content wt 29%, molecular weight 5000) 30g;

[0057] 6-Hydroxyhexyl acrylate (4-HHA) 70g;

[0058] TPO 0.5g;

[0059] The structural formula of 6-hydroxyhexyl acrylate (4-HHA) is: The hydroxyl content is 9.87% by mass;

[0060] The components in the above formula are stirred evenly and heated to 80-100℃ until completely dissolved. After vacuum degassing, an LED light-curing liquid adhesive film is obtained for later use. Before coating, the adhesive is preheated to 90℃. First, the liquid adhesive film adhesive layer B is applied to the surface of the glass backplate with a coating thickness of 0.38 mm. Then, the cadmium telluride power generation glass layer is laid. Next, the liquid adhesive film adhesive layer A is applied to the surface of the battery layer with a thickness of 0.38 mm. The transparent glass panel is then covered. After vacuum degassing, the adhesive is irradiated simultaneously from both sides with 405nm LED light at an irradiation energy of 500mJ / cm². 2 After obtaining the bonded double-glass module, the photovoltaic module is obtained by installing the leads and frame.

[0061] Example 5

[0062] The formulation for LED light-curing liquid adhesive film is as follows:

[0063] PVB resin (hydroxyl content wt 29%, molecular weight 5000) 20g;

[0064] 9-Hydroxynonyl acrylate (9-HNA, hydroxyl content 7.94%) 80g;

[0065] TPO 0.5g;

[0066] The structural formula of 9-hydroxynonyl acrylate is:

[0067] The components in the above formula are stirred evenly and heated to 80-100℃ until completely dissolved. After vacuum degassing, an LED light-curing liquid adhesive film is obtained for later use. Before coating, the adhesive is preheated to 90℃. First, liquid adhesive film adhesive layer B is applied to the surface of the glass backplate with a coating thickness of 0.38 mm. Then, a cadmium telluride power generation glass layer is laid. Next, liquid adhesive film adhesive layer A is applied to the surface of the battery layer with a thickness of 0.38 mm. A transparent glass panel is then covered. After vacuum degassing, the adhesive is irradiated simultaneously from both sides with 405nm LED light at an irradiation energy of 910 mJ / cm². 2 After obtaining the bonded double-glass module, the photovoltaic module is obtained by installing the leads and frame.

[0068] Comparative Example 1

[0069] The same photovoltaic modules were produced by replacing the photocurable liquid film in the example with a PVB film of the same thickness and using conventional autoclave heat lamination (170°C / 30 minutes).

[0070] Comparative Example 2

[0071] The photoactive diluent in Example 5 was replaced with 1-hydroxymethyl-2-nonylphenoxyethyl methacrylate, the structural formula of which is:

[0072] The hydroxyl content is 5.12% by mass;

[0073] The test results showed that 80g of 1-hydroxymethyl-2-nonylphenoxyethyl-methacrylate could not completely dissolve 20g of PVB resin, and after stirring for 30 minutes, a large amount of visible precipitate remained.

[0074] The performance test results of Examples 1-5 and Comparative Example 1 are shown in Table 1.

[0075] Table 1 Performance test results of LED light-curing liquid encapsulating film

[0076]

[0077] As shown in Table 1, Examples 1-5 obtained the same PVB film as Comparative Example 1 using PVB adhesive in a short time with low energy consumption. Tests showed that Examples 1-5 retained the advantages of the PVB solid film in terms of glass adhesion, light transmittance, and water resistance. Furthermore, compared to Comparative Example 1, the encapsulation of components using the photocurable liquid film of this invention has advantages of high efficiency and low carbon footprint. The process is simple, requires no high-pressure equipment, and the overall cost is significantly better than that of the PVB solid film. In particular, Example 3 showed good solubility of 4-HBA with PVB, the fastest photocuring speed, and the lowest energy consumption.

[0078] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A light-curing adhesive, characterized in that, The product comprises: 20-70 parts by weight of polyvinyl butyral resin, and 30-80 parts by weight of a photoactive diluent, wherein the photoactive diluent dissolves the polyvinyl butyral resin and enables rapid photocuring; the photoactive diluent is a (meth)acrylate hydroxyl ester compound with the structural formula: R1-CH=CHCOOR2-OH, wherein R1 is H or CH3; R2 is a compound group with 2-9 carbon atoms; and the hydroxyl group has a mass percentage of 7.94-14.64%. The (meth)acrylate hydroxy ester compounds are hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), 4-hydroxybutyl acrylate (4-HBA), 6-hydroxyhexyl acrylate (4-HHA), and 9-hydroxynonyl acrylate (9-HNA).

2. The photocurable adhesive according to claim 1, characterized in that, The (meth)acrylate hydroxyl ester compound contains a primary hydroxyl group.

3. The photocurable adhesive according to claim 1, characterized in that, The polyvinyl butyral resin has a molecular weight of 5,000-150,000, a hydroxyl value of 15-35 wt%, and an acetal content of 65-85%.

4. The photocurable adhesive according to claim 1, characterized in that, It also includes 0 to 5 parts by weight of a photosensitizer, wherein the photosensitizer is at least one of 1173, 184, TPO, 819, TPO-L or a mixture of both.

5. The photocurable adhesive according to claim 1, characterized in that, The aforementioned photocuring refers to irradiating a liquid adhesive with ultraviolet light of wavelength 350-420 nanometers to cure it, with an irradiation energy of 25-2500 mj / cm².

6. A photovoltaic module, characterized in that, Bonding is achieved using the adhesive as described in any one of claims 1-4.

7. The photovoltaic module according to claim 6, characterized in that, The adhesive is applied by one of the following methods: spray coating, roller coating, screen printing, slot coating, dispensing coating, scraping coating, injection coating, or bar coating.

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