Photocurable acrylic glass sealant

Abstract

The invention provides a photocurable acrylic glass sealant that can be cured completely in depth within 1 hour The glass sealant has a composition comprising (a) an acrylate- terminated photocurable prepolymer with at least one branching point having four or more acryl or methacryl functional groups at the ends of the prepolymer backbone, and preferably having a molecular weight in the range of 5000 to 120,000 Da, (b) a photoinitiator, (c) optionally a filler, (d) optionally a plasticizer, (e) optionally an adhesion promoter, (f) optionally a UV stabilizer, (g) optionally additional components.

Description

[0001] Title: Photocurable acrylic glass sealant

[0002] Technical Field

[0003] The present invention relates to a photocurable acrylic glass sealant that can be cured completely in depth (at least 10 mm) within 1 hour, preferably within 10 minutes. This glass sealant may be used as an insulating glass sealant. For instance, it may be used as edge seal for manufacturing two-pane or multi-pane insulating glass or solar modules. For example, it may be used as secondary glass sealant, when producing two-pane or multi-pane insulating glass units or solar modules.

[0004] Background Art

[0005] Glass sealants are compositions applied on glass that should be able to seal. Adhesion and barrier properties are therefore important. However, in many applications it is desirable that the barrier properties survive aging and that the sealant does not become tacky. This is particularly important in insulating glass units and solar modules where the glass sealant is exposed to light and where it may have to withstand very harsh outside conditions. Moreover, the glass sealant, when used in insulating glass units and similar applications, should provide elasticity, adhesion and cohesive strength and cannot be brittle. Preferably, it meets the requirements of standard EN 1279-4:2018.

[0006] Insulating glass units (IG units) typically consist of two or more glass panes separated from each other by a spacer (spacer bar or spacer frame), wherein the arrangement may be sealed by a glass sealant, typically with a combination of two different glass sealants (a so-called primary sealing material and a so-called secondary sealing material). The IG units are preferably filled with various gases (e.g. noble gases such as argon, krypton or xenon, or heavy gases such as sulphur hexafluoride) to improve the heat and sound insulation. The primary sealing material serves to seal the unit against penetrating atmospheric humidity and against emergent filling gases and is usually based on isobutylene polymers which have only low cohesive strength. The primary sealing material is arranged between the spacer and the glass. If a separate, secondary sealing material is used, then it ensures elasticity, adhesion, and cohesive strength, filling the joint formed between the glass panes and the spacer and providing mechanical stability to the unit. The secondary sealing material is typically in the form of glass sealants based on polyurethane, polysulphide or silicone. These glass sealants can be used as single-component glass sealant which cure by means of atmospheric humidity or atmospheric oxygen. More commonly, two-component glass sealants that cure at room temperature are used in which one part contains the polymer component and the other part contains a crosslinker or hardener component. The secondary sealing material can additionally contain silanes for improved glass adhesion. The combination of spacer, and sealing material, e.g., primary sealing material, and secondary sealing material, is usually referred to as a so-called edge seal.

[0007] Background information may be found in an article by S. Van den Bergh et al., “Window Spacers and Edge Seals in Insulating Glass Units: A State-of-the-Art Review and Future Perspectives”, published in Energy and Buildings 58 (2013) 263-280, http: / / dx.doi.Org / 10.1016 / i.enbuild.2012.10.006, which is included herein by reference.

[0008] For instance, US2022195263 relates to a system for producing a glass sealant composite made of a primary sealing material and a curable secondary sealing material, the use of the system for producing insulating glass or solar modules, an edge seal for producing doublepane or multi-pane insulating glass or solar modules comprising the glass sealant composite, and an insulating glass unit comprising at least two glass panes and the edge seal. In this system, the secondary sealing material is based on polyurethane or polysulphide.

[0009] GB2454584 provides a two-part glass sealant, comprising a first part and a second part, wherein the first part comprises a polymer selected from silane-terminated polyurethane or silane-terminated polyether. In use, the first and second parts are mixed to achieve a cured substance having a 48 hour Shore A hardness in the range of 25-70. Also disclosed is use of the glass sealant in insulating glass units. EP3606996 provides insulating glass sealants based on polyurethanes and organically-modified nanoclays. W02009036752 relates to a composite edge for producing double or multiple pane insulating glass or solar modules, wherein a special primary glass sealant and a silicone-based composition as secondary glass sealant are provided. EP0916801 describes and claims an insulating glass unit and a process for making such. The unit comprises two glass panes spaced apart by a spacer of thermoplastic material adherent to the panes, an inert or heavy gas trapped within the unit and a layer of silicone elastomer located at the periphery of the unit between the edge portions of the glass panes and in contact with the external surfaces of the spacer. The thermoplastic material has a water vapor permeability of not more than about 0.2 l / m2 / day (measured at 20 degrees Centigrade for 4 mm thickness) and a shear strength of more than 0.2 MPa as determined at a glass sealant thickness of 0.5 mm at 23 degrees Centigrade and a shear speed of 100 mm / min. The process described for making these units comprises providing between two glass panes an endless strip of the thermoplastic material in a plastic state applied as a hot melt containing a dehydrating material, urging the two glass panes towards each other against the thermoplastic material to form a spacer comprising the thermoplastic material adherent to the panes, introducing to the cavity defined by the two panes and the spacer an inert or heavy gas and applying a layer of silicone elastomer located at the periphery of the unit in contact with external surfaces of the spacer.

[0010] In addition, WO2015086457 discloses an insulating glazing for a building, comprising at least two panes, a circumferential polymer or metal spacer, appropriate glass sealants between the panes and the spacers, and appropriate glass sealants in the external intermediate space between the panes and an intermediate space filled with air or gas. The connection between two spacers on the corners of the insulating glazing unit is implemented by a corner connector, especially a plastic molded part, in which two miter-cut spacers are adjoined to each other. The inner chamber between the panes is filled with an inert gas before the assembly is pressed together.

[0011] From US2020408032, insulating glass units (1) are known, wherein the insulating glass unit includes at least one first and one second glass pane, at least one spacer consisting of glass, which is connected to each glass pane by at least one glass sealant, at least one other spacer which is gas-tight or comprises a gas-tight layer and is connected to each glass pane by at least one second glass sealant, and at least one joining region for a glass spacer and another spacer. The at least one glass spacer, the at least one other spacer and the glass panes form a closed inner chamber that does not affect the visual appearance. To this end, the at least one joining region is closed by a third glass sealant in a gas-tight manner, with the glass sealant containing polyisobutylene and being guided over the joining region. According to an advantageous embodiment of this insulating glass unit, the first glass sealant, by means of which the glass spacer is connected to the glass panes, or the second glass sealant, by means of which the additional spacer is connected to the glass panes, or both of the glass sealants mentioned consist(s) of a primary glass sealant, which is disposed on the side facing the inner chamber, and a secondary glass sealant which is disposed on the side facing the external region. At least one of the primary and secondary glass sealants mentioned is transparent. In addition, one of the primary glass sealants or both primary glass sealants may contain acrylic. According to an advantageous embodiment, one of the primary glass sealants or both primary glass sealants takes / take the form of a double-sided adhesive tape. One of the secondary glass sealants or both secondary glass sealants preferably contains / contain polyisobutylene.

[0012] A moisture-curable sealant containing also a radiation-curable meth(acrylic) functionality has been described in US2004181007A1. The prepolymer used therein is made from a linear polyol with a functionality of 2 and a molecular weight of 2000. This is reacted with a mixture composed of 98% 4,4’-diphenylmethane diisocyanate and 2 percent 2,4’-diphenylmethane diisocyanate, having a functionality of 2, and subsequently with 2-hydroxylethylacrylate. Moreover, some of the diisocyanate groups will react with aminosilane. This prepolymer will therefore have a functionality (number of acrylate groups) of less than two and a molecular weight of around 2730. There are no branching points. Such prepolymers are well-known, but found less suitable for photocurable acrylic glass sealants that can be cured completely in depth (at least 10 mm) within 1 hour. This is shown in the comparative experiments 14-16 included herein.

[0013] Moreover, the dual-cure glass sealant of US2004181007A1 requires two curing steps - a fast initial treatment with radiant energy providing the initial minimum mechanical performance (green strength) and slow moisture-curing phase resulting in the final strength. Such moisture-curing phase can take many days under poorly controlled conditions and thus the final product performance can be poorly reproducible. Furthermore, as may be known to those practicing the art of moisture-curable sealants, the presence of excessive moisture in contact with moisture-curable sealants can lead to uneven curing and bubble formation inside the sealant, which is unacceptable for the gas and moisture barrier function.

[0014] Production of laminated glass articles including photovoltaic modules and laminated glazing having a radiant- or heat cured acrylic edge seal has been revealed by WO2010 / 146389. In that embodiment, the thickness of the film is proportional to the amount of applied material and thicker films may be produced by repeated application, with typical thickness claimed to be less than 2 mm. This is not satisfactory for the production of insulating glass units according to EN1297 standard, where sealant thickness in the range of 5-10 mm is typically used, and the preferred sealant curing depth limit is at least 10 mm.

[0015] US5945462 concerns temporary protective coatings for precision surfaces. The reference is not concerned with glass sealant compositions, but rather with an aqueous-based composition which cures to form a reaction product which is suitable for use as a strippable protective coating for protection of surfaces, e.g., precision optical surfaces. In this reference use is made of a (meth)acrylate-capped organic prepolymer resin having at least one pendent hydrophilic group. A clear selection for using an acrylate-terminated photocurable prepolymer with at least one branching point, four or more acryl or methacryl functional groups at the ends of the prepolymer backbone, and preferably having a molecular weight in the range of 5000 to 120,000 Da is missing. Rather, from the description and the desirable resin shown in column 8 of this reference it is clear that the prepolymer is a bifunctional linear prepolymer without branching points. Apparently, this linear resin is the component present in Neorad™ NR-3709 used in the examples of US5945462.

[0016] US2022119586 provides a UV-curable resin for forming a chemical-mechanical polishing pad comprising: (a) one or more acrylate blocked isocyanates; (b) one or more acrylate monomers; and (c) a photoinitiator. The invention also provides a method of forming a chemical-mechanical polishing pad using the UV-curable resin. It does not concern glass sealant compositions. This reference describes in detail the acrylate blocking agent that may be used. There is no teaching to use and / or prepare a prepolymer having at least one branching point, four or more acryl or methacryl functional groups at the ends of the prepolymer backbone, and preferably having a molecular weight in the range of 5000 to 120,000 Da. In the examples PET95A is used, which is a prepolymer of polyether TDI type with an NCO content of 5.4. There is no suggestion to create a branching point.

[0017] In WO9408788 a method is disclosed for manufacturing ophthalmic, telescopic, microscopic, etc. lenses. Also disclosed is the use of a radiation (e.g., UV or visible light) curable adhesive (2) formulation containing a predominant amount of an acrylic capped organic prepolymer; a lesser amount of an ethylenically unsaturated diluent monomer; a minor amount of a non-reactive releasing agent and a suitable photoinitiator for blocking (bonding) and deblocking (debonding) a lens blank (3) to a support member (1). The prepolymer is a polyester urethane that is acrylate terminated. There is no indication or teaching that this is a prepolymer with at least one branching point, four or more acryl or methacryl functional groups at the ends of the prepolymer backbone, and preferably having a molecular weight in the range of 5000 to 120,000 Da.

[0018] The demand for insulating glazing or insulating glass units is increasing with the need to preserve energy. A large body of art exists on the preparation of such units. Nonetheless, a need remains for alternative systems that can be used as sealing material. Such systems should be easy to apply, provide the required elastic adhesion, ability to fill the joint formed between the glass panes and the spacer and provide mechanical stability to the unit. A suitable glass sealant should be curable, without loss of solvents creating fogging inside the unit, and without interacting adversely with the isobutylene polymers or similar if used as primary glass sealant, and with long-lasting chemical stability. Moreover, the currently used secondary glass sealants for insulating glass units take several hours to cure chemically (typical glass sealant types are polyurethanes, polysulphides, and silicones). During this time, glass units must be supported and not moved because structural integrity takes time to build. During this time, argon gas can leak out from the insulating glass units and product may be lost if deformation of seal occurs. It costs space, time, and labour productivity to wait for product curing. Also, there is interest in a one-component product that simplifies application on the insulating glass units compared to the currently used two-component polyurethanes, polysulphides, and silicones that require two-component mixing at a precise ratio, which may fail and produce defective product. Handling of two-component products requires more space, logistics, and labour. In a co-pending patent application therefore an edge seal and a photocurable acrylic glass sealant are proposed that overcome most of the problems described above.

[0019] What remains is the need for a glass sealant that has excellent barrier properties and adhesion properties, that is not brittle even at temperatures of -30 °C, and that moreover is not tacky after curing or upon age. Summary of the Invention

[0020] Accordingly, there is now provided a glass sealant with a composition that overcomes the problems described above. The glass sealant is defined in claim 1. Also claimed is the edge seal, the method of preparing the edge seal and two-pane or multi-pane insulating glass or solar modules provided with the edge seal according to the present invention. The glass sealant may be a single component system (“1 K”), a 2 component system (“2K”) or a multiple component system. Finally, some of the polyacrylates used in the glass sealant are believed to be novel. Accordingly, the present invention also relates to such new polyacrylates.

[0021] Detailed description of the Figures.

[0022] Figure 1 provides a schematic representation of the acrylate-terminated photocurable prepolymer used in the new glass sealant.

[0023] Figure 2 provides a schematic representation of the acrylate-terminated photocurable prepolymer when cured.

[0024] Figure 3 provides a schematic representation of a two-pane sealed insulating glass, wherein a spacer (5) containing a desiccant (4) is adhered to the glass panes (1) with an inner or primary sealant (3) and which is provided with an outer or secondary sealant (6). The secondary sealant (6) is applied to a height (u) on the back of the spacer and to a height (s) on the inner surface of the glass panes (1).

[0025] Figure 4 provides a schematic representation of a potentially suitable route to prepare acrylate-terminated photocurable prepolymer.

[0026] Detailed description of the Invention

[0027] The glass sealant according to the present invention is particularly suitable for IG units. Indeed, the glass sealant is particularly suitable for use as a secondary glass sealant, as discussed below. However, it should be noted that the glass sealant may also be used as a primary sealant in IG units or even in entirely other applications. The below description of its use in IG units is therefore not intended as limitation.

[0028] As indicated in the review paper by Van Den Bergh et al. mentioned above, IG units may be prepared with separate primary and secondary glass sealants or with a single (secondary) sealant. Edge seals consist of a number of components, typically including a spacer, a desiccant, and the glass sealant.

[0029] In the edge seal according to the present invention, a spacer, a desiccant, and / or a primary glass sealant may be used. The current patent application focusses on secondary glass sealants which are applied around the perimeter of the glass. The secondary glass sealant functions as the adhesive that unites the glass panes and spacer and prevents excessive movement under different environmental stresses. Polyurethane (Pll), silicone (Si), and polysulphide (PS) are widely used as secondary glass sealants, but hot-melt butyl- or epoxybased glass sealants may also be used. The present invention provides a further alternative. Although the photocurable acrylic glass sealant proposed in this application is referred to as secondary glass sealant, it is to be understood that it can also be used as single glass sealant, e.g., without a conventional primary glass sealant. The technology for applying glass sealants onto glass panes is well known, as are the thickness and width of the glass sealant to provide a suitable seal.

[0030] Throughout this application, the expression “spacer” is used to define spacer bars and frames, which may be pre-formed, but also spacers made of thermoplastic materials.

[0031] Photocurable acrylic compositions are well-known in applications as paints, varnishes, glues, and electronics potting. However, such photocurable compositions have not yet found large-scale use in the production of insulating glass units due to the limits of curing depth, adhesion, moisture and gas barrier performance, and the hazards of short-wave UV radiation to workers and equipment. The photocurable acrylic glass sealants comprise one or more photocurable compounds carrying one or more acryl or methacryl functional groups per molecule (component a) and a photoinitiator (component b). As used herein, the expression acryl functional group also encompasses methacryl functional group.

[0032] It is also important to notice that the photocurable composition used in the present invention does not rely on moisture cure. The photocurable compounds are cured, and moreover cured almost instantly to full depth, with the use of radiant energy that through the photoinitiator interacts with the acryl functional groups. In an embodiment, the photocurable composition used in the present invention is isocyanate free.

[0033] The photocurable compound is an acrylate-terminated photocurable prepolymer with at least one branching point as discussed hereafter. Moreover, having four or more acryl or methacryl functional groups at the ends of the prepolymer backbone, preferably six or more acryl or methacryl functional groups, more preferably nine or more acryl or methacryl functional groups at the ends of the prepolymer backbone. Preferably, the photocurable compound has a molecular weight in the range of 5000 to 120,000 Da.

[0034] Acrylate-terminated photocurable prepolymers with the appropriate number of functional endgroups and appropriate molecular weight may be commercially available. Moreover, prepolymers having one or more, preferably two or more branching points are believed to be novel. It has been found of particular interest to produce the more suitable acrylate-terminated photocurable prepolymers by the method described hereafter.

[0035] For instance, starting from a linear or branched, endgroup functionalized reagent forming the core of the prepolymer and reacting this with a polyfunctional reagent with more than two functionalities, a branching point is created preferably at each endgroup and accordingly a form of branching can be created. The product of this reaction can then be used as intermediate with the appropriate chemistry to attach arms and form acrylate- terminated photocurable prepolymers with four or more acryl or methacryl functional endgroups and the appropriate molecular weight. Prior to this, the process of branching may be repeated, creating a hyperbranched acrylate-terminated photocurable prepolymer, i.e. , an acrylate-terminated dendrimeric photocurable prepolymer.

[0036] The acrylate-terminated photocurable prepolymer may be represented by the general formula A-(B)n

[0037] wherein the multifunctional core A corresponds to the backbone of the prepolymer and each B represents a (meth)acrylate-terminated arm connected via a branching point to the backbone. The core may be linear (n=2), triangular (n=3), cross-shaped (n=4) or star-shaped (n=5 and larger). The acrylate-terminated photocurable prepolymer will preferably have a branching point at each endpoint of the core, and in that case has at least two branching points.

[0038] Preferably the core has a molecular weight in the range of 4000 to 90,000 Da, more preferably in the range of 8000 to 15,000 Da. Preferably the core is linear or triangular.

[0039] Preferably, the core is generated by a sequential addition of commercially available reagents to a liquid telechelic polymer, building up the desired molecular weight in several reaction cycles or generations.

[0040] The core of the prepolymer may be hydrophilic or hydrophobic.

[0041] Examples of hydrophilic core include e.g. the reaction products of polyester, polyether or polycarbonate polyols with electrophilic reagents, branched via subsequent Michael addition steps, including thiol-acrylate or amino-acrylate reactions.

[0042] Examples of hydrophobic core include e.g. similar reaction products derived from telechelic polydienes or hydrogenated polydienes, styrene-containing block copolymers, polyfarnesenes, dimeric fatty acid polyesters or triglycerides. These prepolymer cores have functional groups which may be used to attach the (meth)acrylate-terminated multi-armed dendrimer blocs, for example, via Michael addition reactions.

[0043] As mentioned above, each B individually represents a (meth)acrylate- terminated arm that is connected via a branching point to the backbone A. Each branching point may connect 2 or more arms, preferably 2 to 4 arms to the backbone A. Moreover, the arms may be branched themselves, having an arm, a branched arm or a hyperbranched arm branching therefrom. If the arm is in the form of a dendron, then the prepolymer so defined is a dendrimer. Whereas dendrimers generally are highly structured symmetric molecules, within the scope of the present invention also imperfect molecules with “trailing generations” (shorter arms) may be used.

[0044] Figure 1 is a schematic representation of an acrylate-terminated photocurable prepolymer that may be used as component (a) of the glass sealant. What is characteristic of component (a) is that the acrylate-terminated photocurable prepolymer has at least one, preferably at least two branching points.

[0045] The preparation of dendrimers is well-known. A photocurable compound as shown in Figure 1 may therefore be made by any suitable route. Suitably, the photocurable compound is made by way of a diverging method, starting with a compound having at least 2 end-terminated functional groups, preferably hydroxyl or other nucleophilic groups.

[0046] A potentially suitable route is schematically depicted in Figure 4. The acrylate-terminated photocurable prepolymer prepared according to Fig. 4 is believed to be novel. Accordingly, this product is claimed as well.

[0047] The acrylate-terminated photocurable prepolymer may be the only component (a) in the composition of the glass sealant. Figure 2 is a schematic representation of the cured glass sealant. As is shown in Figure 2, a product is formed with the arms (B) in a matrix formed by the backbone (A).

[0048] However, also a mix of photocurable compounds may be used, wherein the acrylate-terminated photocurable prepolymer having at least one, preferably at least two branching points, having four or more acryl or methacryl functional groups at the ends of the prepolymer backbone, and having a molecular weight in the range of 5000 to 120,000 Da comprises at least 50 % by weight of the component (a) mixture. For instance, Component (a) may be a mixture further comprising an alkyl ester of acrylic or methacrylic acid, aliphatic urethane acrylate, polyether polyacrylate, epoxidized fatty acid triglyceride polyacrylate, and acryl or methacryl-functionalized non-hydrogenated polydiene, or similar, each carrying one or more acryl or methacryl functional groups, or a mixture of such components.

[0049] Suitable alkyl ester of acrylic or methacrylic acid may be a C1-12 alkyl ester, preferably a C4-12 alkyl, more preferably selected from 2-ethylhexyl methacrylate, 2-ethylhexyl acrylate, lauryl acrylate, and 4-(t-butyl)cyclohexyl acrylate, commercially available as Laromer™ UA 9072 from BASF.

[0050] Suitable aliphatic urethane derivatives carrying one or more acryl or methacryl functional groups have a molecular weight greater than 1000 Da. For instance, the following aliphatic urethane acrylates may be used: Sartomer™ CN966H90, Sartomer CN965, Sartomer CN9002 from Arkema or Laromer™ PR9000 from BASF. A very suitable photocurable polyether polyacrylate is propoxylated neopentyl glycol diacrylate, commercially available as Sartomer SR9003.

[0051] Suitable fatty acid triglycerides carrying one or more acryl or methacryl functional groups have a molecular weight greater than 1000. A very suitable photocurable fatty acid triglyceride is acrylated epoxidized soybean oil.

[0052] Suitable non-hydrogenated polydienes carrying one or more acryl or methacryl functional groups have a molecular weight greater than 1000. For instance, a very suitable non-hydrogenated polydiene carrying methacryl functional groups is Polyvest™ EP MAT from Evonik.

[0053] In addition to the one or more photocurable compounds carrying one or more acryl or methacryl functional groups per molecule (component a), also minor amounts, e.g., up to 5, suitably up to 2 mass % copolymerizable monomers, e.g., as reactive diluent, may be included. For example, up to 5% methacryl-functional silane (MEMO), or vinyl trimethoxysilane (VTMO) may be used.

[0054] By using a mixture of photocurable components, it may be possible to change the viscosity of the photocurable composition and the hardness of the cured sealant.

[0055] In addition to the photocurable component (a), a photoinitiator (component b) is applied. The component (b) is selected from one or more photoinitiators that are suitable for inducing the polymerization of acrylates and / or methacrylates upon irradiation with visible or nearultraviolet light, where near-ultraviolet light is selected from wavelengths that do not create workplace hazard to exposed personnel. For instance, this photoinitiator may operate at 300-480 nm wavelength, suitably 300-450 nm wavelength. Preferably, this is a photoinitiator that operates at 380-470 nm wavelength, suitably 380-410 nm wavelength. This may be a Norrish type I photoinitiator or a Norrish type II photoinitiator in combination with an appropriate amine synergist. Preferably, a photoinitiator is selected that readily dissolves in the photocurable compound or in the other components included in the photocurable composition. Examples of suitable photoinitiators available from the Arkema company include Speedcure™ TPO-L, Speedcure TPO, Speedcure BPO, Speedcure DETX in combination with ethyl 4-(dimethylamino)benzoate. A very suitable photoinitioator is ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, commercially available as Speedcure TPO-L. An alternative is diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide, available as Speedcure TPO. Suitable photoinitiators from Ciba include for instance Irgacure™ 819, Irgacure 651, and Irgacure 184, which may be used even below 380 nm. Also combinations may be used.

[0056] The amount of photoinitiator depends on the particular photocurable compound. For instance, for a component (a) with a molecular weight below 200 a sufficient amount is in the range of 1-5% from the mass of component (a). For a component (a) with a higher molecular weight, a sufficient amount is in the range of 0.1-1%. Preferably, the amount of photoinitiator is in the range of 0.4-4.6% from the mass of component (a).

[0057] The curing may be completed with the use of additional radical initiators and / or with additional energy sources. In addition to the photoinitiators mentioned above, chain transfer agents and cross-linking agents may be used.

[0058] In addition, the photocurable composition may comprise one or more plasticizers as component (c). The plasticizer provides flexibility and lowers glass transition temperature that improves cold weather performance of edge seal. Preferably, the plasticizer has low volatility to avoid fogging inside insulating glass unit. Suitable plasticizers for photocurable acrylic glass sealants include phthalates, terephthalates, benzoates, dibenzoates, and benzyl phthalates. A particularly suitable class of plasticizers are esters selected from one or more alkyl, aralkyl or mixed phthalate, alkyl or aralkyl terephthalate, alkyl or aralkyl benzoate or dibenzoate. Preferably a dialkyl phthalate is used, still more preferably dialkyl phthalate where the alkyl substituents each contain at least 9 carbon atoms, still more preferably diisononyl phthalate.

[0059] The amount of plasticizer, if any, may be up to an amount less than 50% by mass on the photocurable composition. For instance, it may be used in an amount in the range of 1-10% by mass.

[0060] To reduce the cost, it is preferable to add a translucent filler as component (d). This may be an organic filler or an inorganic filler. Note in this regard that a filler such as calcium carbonate as used in US2004181007A1 will not work. Component (d) may be selected from one or more translucent fillers with an optical refractive index l(fiiiei) that is equal to the optical refractive index of the composition of the product, I (product), plus or minus 0.05, still more preferably selected from powdered polyacrylates, polymethacrylates, polyolefins, cellulose-based materials, silica or their mixtures. Moreover, the organic filler preferably has particle size distribution with D90 less than 100 pm so as to prevent settling or precipitation from the mixture. Preferred classes of fillers include polymethylmethacrylate (PMMA) and polypropylene (PP).

[0061] The amount of filler, if any, may be up to an amount of less than 80% by mass on the photocurable composition. For instance, it may be used in an amount in the range of 10-30% by mass.

[0062] In addition, the photocurable composition may comprise one or more adhesion promoters as component (e). The adhesion promoter ensures adhesion to the glass panes and to the spacer, if any. Whether an adhesion promoter is needed depends on the adhesive bond formed by the photocured composition. Preferably, the photocurable composition has adhesion strength of at least 0.3 MPa. Metal based adhesion promotors e.g., Chartsil™ or Chartwell™ range from Synthron, or Titanates and Zirconates may be used. Suitable adhesion promoters for photocurable acrylic glass sealants may also be selected from, for instance, tackifying resins and / or silanes and silane-terminated polymers. A particularly suitable class of adhesion promoters includes vinylsilanes. Silane based adhesion promotors like an epoxy-silane (Silquest™ A-187, Momentive), an amino-silane (Dynasylan™ 1189, Evonik) or a methacrylate based silane (silane A-174, Momentive) may be used. For instance, this may be selected from di- or trialkoxyvinylsilanes, trialkoxymethacryloylalkylsilanes, and di- or trialkoxysilyl-terminated polymers. Some vinyl silane based adhesion promoters may co-react with component (a), and are therefore preferred. Preferably, vinyltrimethoxysilane (VTMO) can be used. A further alternative includes commercially available silane-terminated pre-polymers, e.g., from Wacker, Evonik, Kaneka, and Momentive. For instance, the silyl-terminated polymer marketed as Silyl™ SAX 400 from the Kaneka company may be used. In addition, MA-series (e.g. MA 490) or MAX-series (e.g. MAX 602) from Kaneka may be used.

[0063] The amount of adhesion promoter, if any, may be up to an amount of less than 10% by mass. For instance, it may be used in an amount in the range of 1-5% by mass.

[0064] Moreover, the acrylate-terminated photocurable prepolymer having one or more, preferably two or more branching points with four or more acryl or methacryl functional groups at the ends of the prepolymer backbone, and having a molecular weight in the range of 5000 to 120,000 Da may have been silylated in whole or in part. For instance, the addition of secondary aminosilanes such as Dynasylan™ 1189 from Evonik results in a facile Michael addition to acrylate groups and produces partially or fully silylated prepolymers.

[0065] Moreover, to achieve sufficient UV stability, the photocurable composition may and preferably does comprise one or more UV stabilizers as component (f). It has been found that not all typical UV stabilizers perform adequately. In particular for compositions that are cured by UV radiation, the nature and amount of UV stabilizer must be optimised to avoid interference with the photoinitiator. Suitable examples of UV stabilizers are selected from one or more UV stabilizers that do not inhibit the curing process by absorption of the effective curing light wavelength or quenching of acrylate polymerization, still more preferably selected from nonphenol type UV stabilizers, still more preferably / V-(2-ethoxyphenyl)- / V’-(2-ethylphenyl)oxamide (Tinuvin™ 312 available from BASF) and similar oxalanilide-based UV-stabilizers. The UV stability of photocurable acrylic sealant may be also enhanced by the addition of hindered amine light stabilizer (HALS), for example, Tinuvin™ 765 from BASF. The amount of these additive(s), may be up to an amount less than 3% by mass. For instance, a UV stabilizer or combination thereof may be used in an amount in the range of 0.3-1% by mass.

[0066] Furthermore, the photocurable composition may comprise one or more rheological additives as component (g). Suitable examples include organic thixotropes that allow for the light transmission during photocuring to the depth of up to 5 mm. Of these, the commercially available Thixatrol™ PM 8056 from Elementis is preferred.

[0067] The amount of rheological additives, if any, may be up to an amount of less than 5% by mass. For instance, it may be used in an amount in the range of 0.5-2% by mass.

[0068] As indicated, the photocurable composition may be a single component system (1 K), a 2 component system (2K) with e.g. the photoinitiator separated from the photocurable component, or even a multicomponent system. If a dual or multiple component system is used, then the components should be mixed prior to its use.

[0069] Typically, the edge seal prepared by curing the glass sealant is in the form of a layer having a thickness in the range of 1 to 5 mm. The layer thickness preferably is 3±1 mm. Upon curing it preferably has a Shore A hardness that is in the range of 25 to 70, more preferably 45 to 70, measured according to EN 1279-6:2016. Moreover, preferably the acrylic glass sealant, upon curing, has water vapour transmission rate for a 2 mm film no greater than 2.7 g / (m224h), measured according to EN 1279-4:2018 (Annex D.1). In addition, the acrylic glass sealant, upon curing, has argon gas permeation rate for 2 mm film no greater than 0.64 g / (m224h), as measured according to EN 1279-4:2018 (Annex D.2).

[0070] The glass sealant according to the present invention can be applied directly onto a glass pane and / or onto a spacer. Curing of the glass sealant is effected by irradiation, more preferably at the visible or near-ultraviolet wavelength range, still more preferably between 380 and 410 nm. Curing may, for instance, be effected at 385-400 nm wavelength using an Onforu™ 50W LED floodlight or another appropriate light source at, for instance, 10 cm distance. Irradiation time depends on the nature and amount of the photoinitiator and intensity of the light source. Initiation may already start after a few milliseconds. For instance, the irradiation time may be in the range of 1 to 60 seconds, for instance, 5 to 25 s, preferably about 15 s at each 10 cm segment of edge seal. However, irradiation may also be performed simultaneously, for instance in a UV cabinet, in a tunnel or similar station.

[0071] The method for preparing the edge seal according to the present invention therefore comprises the following steps:

[0072] (i) attaching a spacer on appropriately sized glass pane;

[0073] (ii) attaching another glass pane to the spacer, forming a cavity that may be filled with inert gas or a gas that is denser than air, and forming an outer edge gap, optionally repeating these steps for obtaining multi-pane insulating glass units;

[0074] (iii) filling the outer edge gap between spacer(-s) and glass panes with uncured acrylic glass sealant as defined herein above, and

[0075] (iv) curing the acrylic glass sealant, preferably by irradiation, more preferably at the visible or near-ultraviolet wavelength range, e.g., between 380 and 410 nm.

[0076] The glass sealant may also be used for the preparation of solar modules. This can be achieved, for instance, according to the following steps:

[0077] (i) spreading a layer of photocurable acrylic glass sealant on glass;

[0078] (ii) positioning of solar cells on the glass sealant layer with sunward face down;

[0079] (iii) electrically connecting the cells into circuit;

[0080] (iv) spreading a layer of glass sealant on the back side of cells and circuits;

[0081] (v) placing a second transparent sheet, such as glass, on the back side of the panel; (vi) curing of the acrylic glass sealant by irradiation through glass with visible or nearultraviolet light, e.g., between 380 and 410 nm. The current invention is illustrated by the following examples. A Hauschild Speedmixer™ DAC 150.3 FVZ has been used.

[0082] Example 1

[0083] Synthesis of photocurable acrylate dendrimer

[0084] Krasol™ F3000 (Cray Valley) polyol (22.17 g) was mixed on a Speedmixer at 20°C with Ongronat™ 1080 (Borsodchem) polyisocyanate (2.83 g) and Tib™ Kat 318 (TIB Chemicals) catalyst (0.025 g). The mixture was maintained at the same temperature for 12 h and pentaerythritol triacrylate (Allnex™) hydroxyacrylate (5.29 g) was added, followed by mixing on the same equipment. After 2 h, ethylene glycol dimercaptoacetate (TCI Chemicals) polythiol (22.35 g) and Lupragen™ N600 catalyst (0.52 g) were added and mixed in, followed after 15 min by pentaerythritol triacrylate (Allnex) used as polyacrylate (59.46 g).

[0085] Example 2

[0086] Synthesis of photocurable acrylate dendrimer

[0087] Krasol F3000 (Cray Valley) polyol (21.64 g) was mixed on a Speedmixer at 20°C with Desmodur™ I (Covestro) polyisocyanate (3.36 g) and Tib Kat 318 catalyst (0.025 g). The mixture was maintained at the same temperature for 12 h and pentaerythritol triacrylate (Allnex) hydroxyacrylate (4.73 g) was added, followed by mixing on the same equipment. After 2 h, pentaerythritol tetrakis(3-mercaptopropionate) (Bruno Bock) polythiol (40.63 g) and Lupragen N600 catalyst (0.71 g) were added and mixed in, followed after 1 min by Sartomer™ SR9003 (Arkema) polyacrylate (116.79 g).

[0088] Example 3

[0089] Synthesis of photocurable acrylate dendrimer

[0090] POLIOS 55 / 20N (Purinova) polyol (21.40 g) was mixed on a Speedmixer at 20°C with Desmodur I (Covestro) polyisocyanate (4.99 g) and Tib Kat 318 catalyst (0.025 g). The mixture was maintained at the same temperature for 12 h and pentaerythritol triacrylate (Allnex) hydroxyacrylate (7.02 g) was added, followed by mixing on the same equipment. After 2 h, pentaerythritol tetrakis(3-mercaptopropionate) polythiol (56.52 g) and Lupragen N600 catalyst (0.91 g) were added and mixed in, followed after another 1 h by pentaerythritol triacrylate (Allnex) used as polyacrylate (145.98 g).

[0091] Example 4

[0092] Synthesis of photocurable acrylate dendrimer

[0093] Priplast 3186 (Cargill) polyol (20.00 g) was mixed on a Speedmixer at 20°C with Ongronat 1080 polyisocyanate (5.00 g) and Tib Kat 318 catalyst (0.025 g). The mixture was maintained at the same temperature for 12 h and pentaerythritol triacrylate (Allnex) hydroxyacrylate (9.33 g) was added, followed by mixing on the same equipment. After 2 h, ethylene glycol dimercaptoacetate (TCI Chemicals) polythiol (39.44 g) and Lupragen N600 catalyst (0.73 g) were added and mixed in, followed after another 1 h by pentaerythritol triacrylate used as polyacrylate (111.93 g).

[0094] Example 5

[0095] Synthesis of photocurable acrylate dendrimer

[0096] Castor oil (Polynatura™) polyol (16.16 g) was mixed on a Speedmixer at 20°C with Ongronat 1080 polyisocyanate (8.84 g) and Tib Kat 318 catalyst (0.025 g). The mixture was maintained at the same temperature for 12 h and 2-hydroxyethyl acrylate (SigmaAldrich) hydroxyacrylate (6.43 g) was added, followed by mixing on the same equipment. After 2 h, pentaerythritol tetrakis(3-mercaptopropionate) polythiol (37.93 g) and Lupragen N600 catalyst (0.69 g) were added and mixed in, followed after another 10 min by Sartomer SR9003 polyacrylate (95.41 g).

[0097] Examples 6-10

[0098] Preparation of photocurable acrylic sealant

[0099] Acrylate dendrimer (10 g) from any of the Examples 1-5 according to the Table below (10 g) was mixed on a Speedmixer with Laromer LIA9072 from BASF (2.0 g), Laromer PR9000 from BASF (2.0 g), DINP (0.2 g), Dynasylan™ MEMO (0.6 g), Dynasylan VTMO (0.4 g), Silyl SAX 520 from Kaneka (1.0 g), Cab-O-Sil TS 610 from Cabot (3.4 g), Thixatrol™ PM8056 (0.1 g), Tinuvin™ 312 (0.06 g), Sabostab™ LIV65 (0.14 g), and TPO-L (0.10 g). The obtained mixture was cured in an H-block form by irradiation at 395 nm wavelength (exposure about 1 J / cm2), producing a white, rubber-like sealant, having an adhesion of approximately 0.3 MPa or larger and in some cases with very strong adhesion to glass.

[0100] Photocurable Acrylate Shore A Adhesion to Appearance acrylic sealant dendrimer used hardness after glass /

[0101] curing elongation

[0102] Example 6 Example 1 95 1.40 MPa White, not / 18.73% tacky, not oily Example 7 Example 2 82 0.64 MPa / White, not 24.25% tacky, not oily Example 8 Example 3 85 0.60 MPa White, not / 19.77% tacky, not oily

[0103]

[0104] Example 9 Example 4 92 0.39 MPa / White, not 12.12% tacky, not oily Example 10 Example 5 90 0.27 MPa / White, not 18.19% tacky, not oily

[0105]

[0106] Comparative Examples 11- 13

[0107] A photocurable acrylic glass sealant formulation according to Example 1 was prepared, but now applying the UV stabilizer and filler employed in US2004181007A1. The glass sealant were applied on a glass pane, similar to Example 6. The results are in Table 2. What is immediately apparent, is that the compositions do not provide sufficient depth of cure for the application as secondary sealant, as illustrated by Example 6.

[0108] Table 2

[0109] Component Comparative Comparative Comparative example 11 example 12 example 13

[0110] Propoxylated neopentyl (a) 900 g 900 g 900 g

[0111] glycol diacrylate

[0112] (Sartomer™ SR9003)

[0113] Acrylated epoxidized (a) 400 g 400 g 400 g

[0114] soybean oil

[0115] Diphenyl (2,4,6- (b) 60 g 60 g 60 g trimethylbenzoyl)phosphine

[0116] oxide (Speedcure™ TPO)

[0117] Diisononyl phthalate (c) 100 g 100 g 100 g

[0118] Calcium Carbonate (d) - 400 g 400 g (Omyacarb™ 1T)

[0119] Vinyltrimethoxysilane (e) 80 g 80 g 80 g

[0120] Tinuvin™ 400 (f) - - 20 g

[0121] Thixatrol™ PM 8056 (g) 40 g 40 g 40 g

[0122] Curing depth after 5.5 mm 2.0 mm 0.4 mm

[0123] irradiation according to

[0124] Example 6

[0125]

[0126] The production time when applying the compositions according to the present invention therefore compares favourably to that of a conventional edge seal using commercially available two-component polyurethane or polysulphide glass sealants where for a similar IG unit typically at least 3 hours are required to reach Shore A hardness of at least 45. Since the 3 hour curing time with Pll and PS glass sealants is comparable to the time required for all other basic operations at IGU factory (glass cutting, washing, drying, spacer bending, desiccant filling, butylation, assembly of IGU, gas filling and secondary glass sealant application), about one half of IGU factory floor is typically reserved for stands containing IGUs during the curing process. By elimination of the slow curing chemistry, it is possible to free up to one half of the factory floor, reduce facility size or double the productivity at existing facilities. The use of a one-component glass sealant described in this invention eliminates possibilities for mechanical failure or damage of IGUs during curing, prevents loss of product due to incorrect mixing ratio of two-component glass sealants, prevents stoppage of production line due to chemical curing of two-component glass sealants inside the glass sealant application machinery, and avoids the contact toxicity of isocyanates typically used in polyurethane glass sealants. Immediate curing of photocurable acrylics enables immediate quality control and shipment of the finished IGUs, providing an opportunity for superior implementation of just-in-time inventory strategy at IGU factories.

[0127] Comparative Example 14

[0128] A prepolymer as disclosed in US2004181007A1 was made with a few minor deviations replacing reactants no longer available with the closest alternative. The dimer acid-based polyester diol Priplast™ 3187 was replaced with the currently available Priplast 3199 of the same hydroxyl number. The plasticizer Jayflex™ DTDP (ExxonMobil), was replaced with Jayflex DINP. Silquest™ A-Link™ 15 was replaced by the equivalent Dynasylan™ 1189 .The organotin catalyst Tib™ Kat 318 was used, to speed up the reaction. None of these changes will affect the degree of branching when preparing a prepolymer. Moreover, the procedure was attempted in a 1L round-bottom glass flask under vacuum, as described in US2004181007A1 , but the resulting material was too viscous to discharge from the flask and solidified upon standing. For this reason, the procedure was scaled down using 100 mL polypropylene Speedmixer™ vessels.

[0129] Thus, Priplast 3199 (50.26 g, 0.02513 mol) was mixed with DINP (7.42 g) on Speedmixer, then Irganox™ 1010 (0.07 g) and Isonat 125M (9.31 g, 0.0372 mol) were added. The mixture was mixed on Speedmixer, then Tib Kat 318 (60 mg) was added and mixed again. The mixture was maintained in water bath at 55°C for 45 minutes, then 2-hydroxyethyl acrylate (2.59 g, 0.02231 mol) was added and mixed. The mixture was maintained at 55°C for 45 minutes. Dynasylan 1189 (0.42 g, 0.00177 mol) was added, the mixture was mixed on Speedmixer and submitted for NMR analysis after 2 h. NMR analysis indicated the presence on average of 0.99 acrylate groups per Priplast 3199 molecule. Theoretically expected 0.02231 mol acrylate / 0.02513 mol Priplast = 0.89 acrylate groups per Priplast 3199 molecule. The NMR data are in reasonable agreement with the prepolymer PP1 of Table 1 of US2004181007A1.

[0130] Comparative Examples 15 and 16,

[0131] A photocurable acrylic glass sealant formulation was prepared, but now applying the prepolymer employed in US2004181007A1, as made in Comparative Example 14. Example 15 was made with fumed silica (Cab-O-Sil™ TS 610), and Example 16 was made without fumed silica.

[0132] The prepolymer of Example 14 (10 g) was mixed on a Speedmixer with Laromer™ LIA9072 from BASF (2.0 g), Laromer PR9000 from BASF (2.0 g), DINP (0.2 g), Dynasylan MEMO (0.6 g), Dynasylan VTMO (0.4 g), Silyl™ SAX 520 from Kaneka (1.0 g), Cab-O-Sil TS 610 from Cabot (3.4 g, optional - two variants, with and without), Thixatrol™ PM8056 (0.1 g), Tinuvin™ 312 (0.06 g), Sabostab LIV65 (0.14 g), and TPO-L (0.10 g). The obtained mixture was cured in an H-block form by irradiation at 395 nm wavelength (exposure about 1 J / cm2), producing a white, rubber-like sealant with oily surface (oil remains on a cotton swab when wiping off the surface), and insufficient adhesion to glass. The mechanical properties of the tested materials were as follows:

[0133] 1) Variant with CabOSil TS 610, tested 10 min after curing (Comparative Example 15):

[0134] Shore A hardness 54, adhesion 0.09 MPa, elongation 18%, oily surface.

[0135] 2) Variant without CabOSil TS 610, tested 10 min after curing (Comparative Example 16 minus fumed silica): Shore A hardness 43, adhesion 0.1 MPa, elongation 25%, oily surface.

[0136] The new acrylate-terminated photocurable prepolymer with at least one branching point, four or more acryl or methacryl functional groups at the ends of the prepolymer backbone, and preferably having a molecular weight in the range of 5000 to 120,000 Da therefore clearly outperforms commercial prepolymers having insufficient acrylate groups per prepolymer and a lacking branching point.

Claims

CLAIMS1. A photocurable acrylic glass sealant having a composition comprising:(a) an acrylate-terminated photocurable prepolymer with at least one branching point having four or more acryl or methacryl functional groups at the ends of the prepolymer backbone, and preferably having a molecular weight in the range of 5000 to 120,000 Da, (b) a photoinitiator,(c) optionally a filler,(d) optionally a plasticizer,(e) optionally an adhesion promoter,(f) optionally a UV stabilizer,(g) optionally additional components.

2. The glass sealant of claim 1 , wherein the acrylate-terminated photocurable prepolymer has six or more acryl or methacryl functional groups, more preferably nine or more acryl or methacryl functional groups at the ends of the prepolymer backbone.

3. The glass sealant of claim 1 or 2, wherein the acrylate-terminated photocurable prepolymer has a molecular weight in the range of 10,000 to 50,000 Da.

4. The glass sealant of any one of claims 1-3, wherein the acrylate-terminated photocurable prepolymer is the product of the reaction of a linear or branched, endgroup functionalized reagent forming the core of the prepolymer with a polyfunctional reagent with more than two functionalities forming the at least one branching point, preferably forming two or more branching points, which product is transformed into the acrylate-terminated photocurable prepolymer with four or more acryl or methacryl functional endgroups.

5. The glass sealant of any one of claims 1-4, wherein the acrylate-terminated photocurable prepolymer is represented by the general formulaA-(B)nwherein the multifunctional core A corresponds to the backbone of the prepolymer and each B represents a (meth)acrylate-terminated arm connected via a branching point to the backbone, and wherein the core may be linear (n=2), triangular (n=3), cross-shaped (n=4) or star-shaped (n=5 and larger), wherein the core preferably has a molecular weight in the range of 4000 to 90,000 Da, more preferably in the range of 8000 to 15,000 Da, and / or wherein the core is hydrophilic or hydrophobic.

6. The glass sealant of claim 9, wherein each branching point connects 2 or more arms, preferably 2 to 4 arms to the backbone A, and / or wherein one or more of the arms are branched themselves, having an arm, a branched arm or a hyperbranched arm branching therefrom.

7. The glass sealant of any one of claims 1-6, which is isocyanate free and is curable by photocuring, preferably at 380-470 nm wavelength.

8. The glass sealant of any one of the preceding claims, having the following overall composition:a) 20%-99%, preferably 40-70%, most preferably 50-65% by mass, of one or more photocurable compounds;b) less than 5%, preferably 0.4-4.6% by mass of one or more photoinitiators;c) optionally one or more fillers, which must be translucent if present;d) optionally one or more plasticizers ;e) optionally one or more adhesion promoters;f) less than 3% by mass of one or more UV stabilizers; andg) optionally one or more rheological additives,adding up to 100% by mass,wherein at least 50% by mass of component (a) comprises the acrylate-terminated photocurable prepolymer of any one of claims 1-11.

9. The glass sealant of any one of the preceding claims, wherein component (b) is selected from one or more photoinitiators that are suitable for inducing the polymerization of acrylates upon irradiation with visible or near-ultraviolet light, preferably at a wavelength range between 300 and 450 nm, more preferably between 380 and 410 nm, more preferably ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate.

10. The glass sealant of any one of the preceding claims, wherein component (d) is present in an amount less than 50%, preferably 1-10% by mass, and preferably selected from one or more of alkyl, aralkyl or mixed phthalate, alkyl or aralkyl terephthalate, alkyl or aralkyl benzoate or dibenzoate, still more preferably dialkyl phthalate wherein the alkyl substituents each contain at least 9 carbon atoms.

11. The glass sealant of any one of the preceding claims, wherein component (c) is present in an amount of less than 80%, preferably 10-30% by mass, more preferably selected from one or more translucent fillers with an optical refractive index I (finer) that is equal to theoptical refractive index of the composition of the product, l(prOduct), plus or minus 0.05, still more preferably selected from powdered polyacrylates, polymethacrylates, polyolefins, cellulose-based materials, silica or their mixtures.

12. The glass sealant of any one of the preceding claims, wherein component (e) is present in an amount less than 10%, preferably 1-5% by mass, more preferably selected from one or more adhesion promoters effective for creating chemical bonding between polyacrylates and glass or metal surfaces, still more preferably selected from di- or trialkoxyvinylsilanes, trialkoxymethacryloylalkylsilanes, and di- or trialkoxysilyl-terminated polymers.

13. The glass sealant of any one of the preceding claims, wherein component (f) is present in an amount of 0.3-1% by mass, more preferably selected from one or more UV stabilizers that do not inhibit the curing process by absorption of the effective curing light wavelength or quenching acrylate polymerization, more preferably selected from non-phenol type UV stabilizers, more preferably comprising an oxalanilide-based UV absorbent, still more preferably / V-(2-ethoxyphenyl)- / V’-(2-ethylphenyl)oxamide.

14. The glass sealant of any one of the preceding claims, wherein component (g) is present in an amount of less than 5%, preferably 0.5-2%, more preferably selected from organic thixotropes.

15. An edge seal prepared upon curing the glass sealant of any one of claims 1-14, having has a Shore A hardness that is in the range of 45 to 70, measured according to EN 1279-6:2016, and / orhaving a water vapour transmission rate for a 2 mm film that is no greater than 2.7 g / (m2'24h), measured according to EN 1279-4:2018 (Annex D.1), and / orhaving an argon gas permeation rate for 2 mm film that is no greater than 0.64 g / (m224h), as measured according to EN 1279-4:2018 (Annex D.2).

16. The edge seal of claim 15, further comprising a spacer and / or a primary glass sealant.

17. The edge seal of claims 15 or 16, in the form of a layer having a thickness in the range of 1 to 10, preferably 1 to 5 mm.

18. The edge seal of any one of claims 15-17, comprising at least one photocured acrylic glass sealant as secondary sealant.

19. Use of the edge seal according to claims 15-18, for manufacturing insulating glass for windows, conservatories, structural glazing and roof glazing; for glazing in landbound vehicles, watercraft and aircraft, or for fabricating solar modules.

20. Method for preparing the edge seal according to any one of claims 15-19, comprising the following steps:(i) attaching a spacer and / or a primary glass sealant on appropriately sized glass pane; (ii) attaching another glass pane to the spacer, forming a cavity that may be filled with inert gas or a gas that is denser than air, and forming an outer edge gap, optionally repeating these steps for obtaining multi-pane glass units;(iii) filling the outer edge gap between spacer(-s) and glass panes with uncured acrylic glass sealant with a composition according to any one of claims 1-19, and(iv) curing the acrylic glass sealant, preferably by irradiation, more preferably at the visible or near-ultraviolet wavelength range between 300 and 450 nm, preferably between 380 and 410 nm.

21. Two-pane or multi-pane insulating glass or solar modules provided with an edge seal as claimed in any one of claims 15-18.

22. An acrylate-terminated photocurable prepolymer with at least one branching point and four or more acryl or methacryl functional endgroups, and having a molecular weight in the range of 5000 to 120,000 Da as defined in any one of claims 1-11.

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