Sandwiched glass article and method for sandwiching using thermoplastic polymer composition

Abstract

The present invention relates to a sandwiched article and a method for sandwiching glass substrates using a thermoplastic polymer composition. The sandwiched article comprises at least two glass substrates with at least one being non-transparent, and at least one surface coated with the thermoplastic polymer composition. The coated surfaces are adhered together to form a sandwiched glass product. The method involves applying the thermoplastic polymer composition to the glass substrates, drying the coated substrates, stacking them with the coated surfaces facing each other, optionally heating to form a bond, and then cooling to solidify the bond and complete the sandwiching process. The resulting sandwiched glass provides improved adhesion, durability, and strength, with potential applications in decorative glass and architectural glazing.

Description

[0001] SANDWICHED GLASS ARTICLE AND METHOD FOR SANDWICHING USING THERMOPLASTIC POLYMER COMPOSITION FIELD OF THE INVENTION

[0002] The present invention relates to the field of glass sandwiching, specifically to the sandwiching of glass substrates using a thermoplastic coating. More particularly, it relates to a sandwiched glass and a method for bonding glass substrates using a thermoplastic polymer composition.

[0003] BACKGROUND OF THE INVENTION

[0004] The concept of sandwiched glass involves the bonding of two or more layers of glass, typically with an interlayer material, to enhance the strength, safety, and aesthetic qualities of the final product. Sandwiched glass is commonly used in automotive windshields, architectural glazing, bulletproof glass, decorative glass, and solar panels. It is especially valued for its ability to hold together even when shattered, providing improved safety and security. The bonding between the glass layers is typically achieved by using interlayer materials that serve as adhesive layers, which are subjected to heat, pressure, or vacuum during the lamination process.

[0005] Polyvinyl butyral (PVB) is one of the most widely used materials for glass lamination due to its excellent impact resistance, optical clarity, and adhesion properties. It is particularly popular in automotive applications, where safety is a priority. The PVB interlayer also serves to reduce the transmission of sound and UV rays, making it ideal for many applications requiring both strength and safety. However, PVB lamination requires the use of an autoclave, a sealed pressure chamber that applies both heat and pressure to bond the glass layers. This autoclaving process is energy-intensive, involves expensive capital investment for autoclave equipment, and has long cycle times, making it less suitable for mass production. Additionally, PVB is incompatible with lacquered glass unless additional priming or preparation steps are taken, complicating the process and increasing manufacturing costs.

[0006] Ethylene-vinyl acetate (EVA) is another commonly used interlayer material, known for its flexibility, UV resistance, and durability. It is widely used in applications involving decorative glass, solar panels, and curved glass, where its ability to retain optical clarity and flexibility is highly valued. EVA laminates are typically processed in a vacuum sandwiching chamber, which requires precise control of temperature, pressure, and time. This vacuum process can becomplicated, requiring additional equipment and infrastructure. For lacquered glass, the use of EVA generally requires a vacuum lamination setup, which increases both energy consumption and manufacturing complexity. Despite its advantages, EVA lamination is still an expensive process when considering the associated equipment, energy costs, and the need for a vacuum chamber to achieve consistent bonding.

[0007] SGP (ethylene / methacrylic acid copolymers) is an advanced interlayer material used in high-performance applications that demand superior strength and impact resistance. SGP offers significantly higher tensile strength compared to PVB and EVA and is commonly used for structural applications such as large glass facades, skylights, and glass floors. However, the high performance of SGP comes at a significant cost, making it unsuitable for more costsensitive applications. In addition to the high material costs, SGP sandwiching also requires autoclaving or other specialized equipment, further increasing the overall cost of production. This makes it a premium solution that is typically reserved for specific, high-end applications.

[0008] Another method of bonding glass involves using an adhesive film placed between glass layers. This film can be either transparent or colored and is bonded under heat and pressure. While this method may seem cost-effective in certain cases, it has limitations in terms of performance and durability compared to PVB, EVA, or SGP interlayers. The adhesive film may not provide the same level of impact resistance, UV protection, or long-term durability as the aforementioned materials. Additionally, the adhesive film may not be suitable for high-stress applications where greater strength is required.

[0009] Lacquered glass, which is commonly used in decorative applications, presents unique challenges for lamination. The lacquer coating on the glass adds a layer of complexity to the bonding process, as many traditional interlayer materials (PVB, EVA, SGP) are incompatible with lacquered surfaces unless additional priming or treatment is applied. This requires manufacturers to implement additional steps, such as surface cleaning, priming, or adhesion promotion, which increases both the time and cost of production. In some cases, lacquered glass may require a specialized interlayer or film that can bond effectively with the lacquered surface, but this further complicates the lamination process.

[0010] Moreover, lacquered glass often needs to retain its aesthetic appeal while ensuring that the lamination process does not affect the color, transparency, or finish of the coating. This requirescareful selection of materials and processes to ensure that the final sandwiched glass product meets both the functional and aesthetic requirements of the end user.

[0011] US20150140301A1 discusses laminate structures with high adhesion between a polymer interlayer (such as PVB) and at least one glass sheet, which can be used in automotive glazing and other vehicle and architectural applications.

[0012] US10035331B2 discusses lightweight hybrid glass laminates using a polymer interlayer made of PVB.

[0013] In light of the above prior arts and the limitations of existing glass lamination techniques, there is a need for a new method that can efficiently sandwich glass with minimal energy consumption and without the need for complex or costly equipment. Furthermore, this method should maintain or improve the performance and durability of the sandwiched glass, while reducing costs associated with the manufacturing process and materials. The present invention addresses these challenges by introducing a novel approach that uses a thermoplastic polymer coating to bond glass substrates. This method eliminates the need for additional interlayers and offers a more cost-effective and efficient solution for sandwiching lacquered glass.

[0014] OBJECT OF THE INVENTION

[0015] The primary object of the present invention is to provide a sandwiched glass unit that does not require the direct use of a film interlayer for sandwiching.

[0016] Another object of the present invention is to provide an efficient method for sandwiching lacquered glass, eliminating the need for traditional interlayer materials such as PVB, EVA, or SGP, and avoiding complex processes like autoclaving or vacuum sandwiching.

[0017] Yet another object of the invention is to provide a simplified sandwiching process that directly bonds lacquered glass using a thermoplastic polymer coating, without the need for additional priming or specialized treatments, thereby reducing both time and complexity in the manufacturing process.

[0018] A further object of the present invention is to enable the efficient production of sandwichedlacquered glass at lower costs and with reduced energy consumption compared to traditional lamination techniques.

[0019] Another object of the present invention is to provide a sandwiching process for lacquered glass that overcomes the adhesion challenges typically encountered with traditional interlayer materials, offering a direct and effective bonding solution.

[0020] SUMMARY OF THE INVENTION

[0021] The primary aspect of the invention provides a sandwiched article comprising at least two glass substrates, with at least one being non-transparent, and at least one of the glass substrates coated with a thermoplastic polymer composition. The thermoplastic polymer coating adheres the glass layers together, and after optionally heating, forms a durable sandwiched glass product. The thickness of the thermoplastic polymer coating is in the range of 10 to 300 microns, which is specifically designed to ensure optimal adhesion and strength.

[0022] The thermoplastic polymer composition is a SEBS-based composition comprising 50 to 70 wt% o-Xylene, 10 to 30 wt% Styrene Ethylene Butylene Styrene (SEBS) and 10 to 30 wt% tackifier consisting of C5 and C9 hydrocarbon mixtures, which provides the necessary balance of tackiness, adhesion, and chemical resistance for effective lamination.

[0023] Another aspect of the invention provides a method for producing a sandwiched glass structure with enhanced durability and adhesion. The process begins by preparing a thermoplastic polymer composition. This composition is then applied to at least one surface of two glass substrates with at least one being non-transparent, to form a wet film. The coated glass substrates are subsequently dried at temperatures up to 250 °C to ensure proper adhesion. After drying, the glass substrates are stacked with their coated surfaces facing each other. The stacked glass is optionally heated to a temperature up to 250 °C to soften the thermoplastic coating, allowing the layers to bond together. Finally, the sandwiched glass structure is cooled to room temperature, solidifying the bond and resulting in a sandwiched glass unit with improved strength and durability. This method ensures superior adhesion between glass layers, offering a product that is resistant to mechanical stress and environmental factors.

[0024] The sandwiched article is specifically tailored to provide a sandwiched lacquered glass product, which is achieved by adhering the glass substrates and drying them at temperatures up to250°C. This method is highly versatile, offering a strong, durable bond without the need for additional interlayer materials such as PVB or EVA.

[0025] Overall, the invention offers a sandwiched glass product that is cost-effective, energy-efficient, and provides excellent adhesion, impact resistance, and durability, making it suitable for various applications in automotive, architectural, and decorative glass sectors.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Embodiments are illustrated by way of example and are not limited in the accompanying figures.

[0028] FIG. 1 illustrates a sandwiched article, in accordance with one aspect of the present invention disclosure.

[0029] FIG. 2 illustrates a flowchart representation of a method for sandwiching glass substrates, in accordance with one aspect of the present invention disclosure.

[0030] Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.

[0031] DETAILED DESCRIPTION OF THE INVENTION

[0032] As used herein, in every embodiment, the term 'non-transparent glass substrate' refers to a type of glass material that does not allow light to pass through it. Unlike transparent glass, which is clear and permits light to pass freely, non-transparent glass may appear opaque, frosted, or may have a coating or texture that blocks visibility or light transmission.

[0033] The term 'lacquered glass', as used herein, refers to glass that has been coated with a layer of colored or opaque lacquer (a type of protective or decorative coating). This coating is typically applied to the back side of the glass, making the front side smooth and clear, while the back side becomes colored or opaque.

[0034] The term ‘thermoplastic polymer’, as used herein, refers to a type of polymer material that becomes soft and moldable when heated and hardens when cooled. Unlike thermosetting polymers, which undergo a chemical change and cannot be remolded once set, thermoplastic polymers can be repeatedly heated and shaped without undergoing any permanent chemical alteration.The present invention provides a sandwiched article and a method for sandwiching nontransparent glass substrates using a thermoplastic polymer composition. The sandwiched glass product formed through this invention offers superior performance in terms of strength, durability, and adhesion, while also reducing the complexity and energy consumption typically associated with traditional lamination methods.

[0035] Referring to Fig.l the said sandwiched article(lOO) comprises at least two glass substrates with at least one of them non-transparent(l 10), where at least one surface of each substrate(120) is coated with thermoplastic polymer composition(130). The coated surfaces of the glass substrates are then adhered together and optionally heated, resulting in a sandwiched glass product. The thermoplastic polymer composition enhances the adhesive bond between the glass substrates and ensures the sandwiched article maintains high performance under various environmental conditions.

[0036] In one embodiment of the present disclosure, the coated thermoplastic polymer has a thickness ranging from 10 to 300 microns, ensuring the formation of a robust adhesive bond while maintaining the structural integrity of the sandwiched product. In a specific embodiment, the coated thermoplastic polymer has a thickness ranging from 25 to 150 microns.

[0037] In an embodiment of the present disclosure, the thermoplastic polymer is Styrene Ethylene Butylene Styrene (SEBS).

[0038] In an embodiment of the present disclosure, the thermoplastic polymer composition comprises o-Xylene, SEBS, and a tackifier. The precise proportions of these components ensure optimal adhesion, flexibility, and durability of the sandwiched glass.

[0039] In a specific embodiment of the disclosure, the thermoplastic polymer composition comprises o-Xylene in an amount ranging from 50 to 70% by weight.

[0040] In a specific embodiment, the thermoplastic polymer composition comprises SEBS in an amount ranging from 10 to 30% by weight.

[0041] In a specific embodiment, the thermoplastic polymer composition comprises a tackifier in an amount ranging from 10 to 30% by weight.In a specific embodiment, the tackifier comprises a mixture of C5 hydrocarbons selected from the group consisting of trans- 1,3 -pentadiene, cis-l,3-pentadiene, 2-methyl-2-butene, cyclopentadiene, cyclopentene, or a combination thereof, and C9 hydrocarbons selected from the group consisting of vinyl toluenes or their isomers, indene, methyl styrene, styrene, or a combination thereof. This hydrocarbon mixture contributes to the tackiness and adhesive properties of the composition and enhances the overall bonding strength and thermal stability of the sandwiched glass.

[0042] In an embodiment of the present disclosure, the coated surfaces are optionally heated at a temperature up to 250°C, ensuring that the adhesive properties of the thermoplastic polymer composition are fully activated and that the glass substrates are securely bonded together.

[0043] In a preferred embodiment of the present disclosure, the sandwiched article is a sandwiched lacquered glass, where the sandwiched glass has both decorative and functional coatings.

[0044] The present invention also provides a method for sandwiching lacquered glass using a thermoplastic polymer composition as the bonding layer. This innovative process provides a cost-effective and energy-efficient alternative to traditional glass lamination techniques, particularly for lacquered glass. The method eliminates the need for complex autoclaving or vacuum sandwiching processes, making it simpler and more economical, while still achieving high-performance sandwiched glass products.

[0045] Referring to Fig. 2, illustrates a flowchart representation of method for sandwiching glass substrates (200). At step 210 the method includes applying a thermoplastic polymer composition onto at least one surface of at least one non-transparent glass substrates to form a wet film. At step 220 the method includes drying the coated glass substrates at a temperature up to 250 °C. At step 230, the methods include placing the coated glass substrates together with the thermoplastic coating in between. At step 240 the method includes optionally heating the stacked glass substrates to form a substrates to form a bond between the glass substrates. At step 250 the method includes cooling the bonded glass substrates to solidify the bond and form a sandwiched glass

[0046] In an exemplary scenario, the method involves applying the thermoplastic polymer composition to at least one surface of at least two glass substrates with at least one of them non-transparent to form a wet film. The wet film is then dried at a temperature up to 250°C for10 to 20 minutes to activate the bonding properties of the composition and ensure its stability. The glass substrates are then stacked with the coated surfaces facing each other and optionally heated at a temperature up to 250°C. The heat causes the thermoplastic polymer composition to bond the glass substrates together, creating a strong and durable sandwiched product. Once the bond has formed, the stacked glass substrates are cooled to room temperature to solidify the adhesive bond and complete the sandwiching process. The cooling step ensures that the sandwiched glass retains its shape and the bond remains intact, resulting in a high-quality sandwiched glass product.

[0047] The thermoplastic polymer composition used in the method consists of three key components: o-Xylene, Styrene Ethylene Butylene Styrene (SEBS), and a tackifier mixture comprising C5 and C9 hydrocarbons. O-Xylene serves as a solvent, adjusting the viscosity of the composition for ease of application. SEBS, a thermoplastic elastomer, imparts flexibility, durability, and impact resistance to the sandwiched glass. The tackifier, which includes C5 and C9 hydrocarbons, controls the tackiness and adhesion of the coating, ensuring a strong bond between the glass layers.

[0048] For the sandwiching process, the coated glass substrates are stacked with their coated surfaces facing each other and clipped at the edges to maintain alignment. The stacked substrates are then optionally heated in an oven at temperatures up to 250°C, allowing the thermoplastic polymer coating to soften and form a bond between the glass layers. After heating, the bonded glass is allowed to cool to room temperature, where the thermoplastic polymer coating solidifies, securing the layers together to form a sandwiched glass.

[0049] In an embodiment of the present disclosure, the thermoplastic polymer composition is applied to at least one surface of at least two glass substrates with at least one being non-transparent, to form a wet film using a bar applicator, curtain coater, roller coater, spray coater and combinations thereof, ensuring an even and controlled coating thickness.

[0050] In a specific embodiment, the wet film has a thickness ranging from 10 to 300 microns.

[0051] In an embodiment of the present disclosure, the method optionally includes cleaning the glass substrates and priming with an amino silane primer to improve adhesion.In a specific embodiment, the tackifier comprising a mixture of C5 and C9 hydrocarbons is selected based on the requirements for optimal adhesion and performance.

[0052] The primary advantage of this method is its lower cost compared to traditional lamination techniques like EVA (Ethylene Vinyl Acetate) lamination, without compromising the durability or performance of the sandwiched glass. The process requires no additional vacuum or complex equipment, resulting in reduced energy consumption and capital expenditure (CAPEX) requirements. The adhesion strength of the sandwiched glass is comparable to EVA lamination, making it suitable for use in decorative glass, solar panels, and other applications.

[0053] The use of thermoplastic polymer composition not only improves the adhesion and durability of the sandwiched glass but also allows for enhanced aesthetic qualities, making the process suitable for various applications, including architectural glazing, automotive windshields, and decorative glass products.

[0054] In summary, the invention provides a cost-effective, efficient method for sandwiching nontransparent glass substrates, resulting in a sandwiched glass product with superior adhesion, strength, and durability. The ability to use a thermoplastic polymer in combination with carefully selected tackifiers and solvents ensures that the sandwiched glass meets the high-performance requirements of modem applications.

[0055] EXAMPLES

[0056] Example 1

[0057] Preparation of thermoplastic polymer composition

[0058] In the fumehood, a clean container or glassware was taken to prepare the thermoplastic polymer composition as detailed in Table 1. The weight of O-Xylene and tackifier was measured. Both were poured into the glass beaker and stirred gently until homogeneous. SEBS was gradually added to the solvent mixture while stirring. Stirring was continued until SEBS was completely dissolved, forming a clear or uniform solution. SEBS was compounded with other additives in precise proportions to achieve the desired properties. A balance of tackiness, adhesion, and chemical resistance was provided by the tackifier.

[0059] Table 1 : Thermoplastic polymer composition

[0060]

[0061] Coating Methodology:

[0062] To evaluate the effectiveness of the composition prepared and described above, a simple bar applicator was used to assess the coating quality and perform the tests. The painted side of the glass was washed in a glass washing machine (manual washing can also be performed). This was followed by a priming step, where amino silane was manually sprayed and allowed to cure for 2-3 minutes. After priming, the lacquered glass was ready to be coated.

[0063] The bar was set to a 250-micron wet film thickness and placed at the edge of the substrate. A small amount of the composition was poured in front of the bar. The bar was then drawn across the substrate at a consistent speed and pressure, ensuring that the coating thickness was uniform across the surface. The coated sample was then cured at 150°C for 15 minutes to ensure complete curing of the lacquered glasses.

[0064] Lacquered Glasses Sandwiching Methodology:

[0065] The lacquered glasses, coated as described above, were placed on top of each other and clipped at the sides to ensure proper adhesion between them. The glasses were then placed in an oven at 150°C for 15 minutes. The thermoplastic property of the material used in the formulation allowed it to soften or melt when heated and solidify when cooled, without undergoing any significant chemical changes. The technical benchmarking of the thermoplastic polymer composition is listed in Table 2.

[0066] Table 2: Technical benchmarking of the thermoplastic polymer composition

[0067]

[0068]

[0069] The table-2 compares the performance of three materials — Colored PVC-based adhesive films (Comparative Example- 1), Clear vinyl films (Comparative Example-2), and a thermoplastic polymer composition (Inventive Example- 1) — under various environmental and mechanical tests. In the High Humidity Test conducted over 56 days, the thermoplastic polymer coatings demonstrated the least degradation with a color difference (dE) of 0.32, significantly outperforming coloured PVC adhesive films (1.00) and Vinyl films (0.75). During the Bake Test at 100°C for 2 hours, the inventive composition exhibited superior thermal stability with no bubbles forming, unlike the multiple bubbles observed in both comparative examples, highlighting its resilience under elevated temperatures. The Adhesion Test revealed that the thermoplastic polymer coatings achieved the highest adhesion strength (2.7 MPa), surpassing PVC based adhesive films (2.3 MPa) and vinyl films (1.96 MPa), indicating enhanced bonding capability. The existing results suggest that the thermoplastic polymer composition offers superior durability, stability, and performance, making it an ideal candidate for applications requiring high reliability under challenging conditions.

[0070] It is clear from Table 2 that the thermoplastic polymer composition demonstrated better performance in terms of the high humidity test, bake test, and adhesion test compared to the colored PVC-based adhesive films and clear vinyl films. Therefore, the present invention not only provides an alternative to prefilms for sandwiching non-transparent glass but also exhibits superior performance.

[0071] The sandwiched glass of present invention has broad industrial applicability, particularly in sectors that utilize sandwiched glass to enhance strength, safety, and aesthetic qualities. The method for sandwiching lacquered glass with thermoplastic polymer composition offers significant advantages across various industries. In architectural glass, the process simplifies the production of decorative, high-strength sandwiched glass without the need for complex techniques such as autoclaving or vacuum lamination. This reduction in energy consumptionand simplification of the process makes it an attractive option for large-scale manufacturers of architectural glass.

[0072] The invention is also applicable to the production of sandwiched glass for solar panels, where durability, impact resistance, and UV resistance are critical. This method offers a cost-effective way to produce sandwiched glass for solar applications, helping to lower production costs and energy consumption for solar panel manufacturers. Furthermore, glass processors, such as fabricators and custom glass specialists, will find this method valuable, as it allows for the incorporation of sandwiched lacquered glass into their offerings without requiring significant capital investment.

[0073] Overall, this invention provides a simplified, cost-effective process for producing sandwiched lacquered glass, making it accessible to a wide range of industries. It reduces manufacturing costs, energy use, and capital expenditures while maintaining high performance in safety, durability, and aesthetic quality. The technology enhances production efficiency in sectors focused on energy conservation, safety, and decorative design, offering a versatile solution for various applications, including decorative glass, solar panels, and architectural glazing.

Claims

Claims:

1. A sandwiched article, comprising:at least two glass substrates, with at least one being non-transparent (110), and at least one of the glass substrates (120) coated with a thermoplastic polymer composition(130);wherein the coated glass substrates are adhered together to form a sandwiched glass product.

2. The sandwiched article as claimed in claim 1, wherein the thermoplastic polymer composition is Styrene Ethylene Butylene Styrene (SEBS) based composition.

3. The sandwiched article as claimed in claim 1 , wherein the coated thermoplastic polymer has a thickness of between 10 and 300 microns.

4. The sandwiched article as claimed in claim 2, wherein the SEBS-based composition comprises 50 to 70 wt% o-Xylene, 10 to 30 wt% Styrene Ethylene Butylene Styrene (SEBS), and 10 to 30 wt% tackifier comprising C5 and C9 hydrocarbon mixtures.

5. The sandwiched article as claimed in claim 4, wherein the C5 hydrocarbon is selected from the group consisting of trans- 1,3 -pentadiene, cis-l,3-pentadiene, 2-methyl-2- butene, cyclopentadiene, cyclopentene, or a combination thereof.

6. The sandwiched article as claimed in claim 4, wherein the C9 hydrocarbon is selected from the group consisting of vinyl toluenes or their isomers, indene, methyl styrene, styrene, or a combination thereof.

7. The sandwiched article as claimed in claim 1, wherein the coated glass substrates are brought in contact and adhered together and optionally heated to a temperature up to 250 °C.

8. The sandwiched article as claimed in claim 1, wherein the sandwiched glass product is a sandwiched lacquered glass.

9. A method for sandwiching glass substrates (200), comprising:(i) applying a thermoplastic polymer composition onto at least one surface of at least one non-transparent glass substrates to form a wet film (210);(ii) drying the coated glass substrates at a temperature up to 250 °C (220);(iii) placing the coated glass substrates together with the thermoplastic coating in between (230);(iv) optionally heating the stacked glass substrates to form a bond between the glass substrates (240);(v) cooling the bonded glass substrates to solidify the bond and form a sandwiched glass (250).

10. The method for sandwiching glass substrates as claimed in claim 9, wherein the thermoplastic polymer composition is SEBS-based composition comprising 50 to 70 wt% o-Xylene, 10 to 30 wt% Styrene Ethylene Butylene Styrene (SEBS), and 10 to 30 wt% tackifier.

11. The method for sandwiching glass substrates as claimed in claim 10, wherein the tackifier comprises a mixture of C5 hydrocarbons selected from the group consisting of trans-l,3-pentadiene, cis-l,3-pentadiene, 2-methyl-2-butene, cyclopentadiene, cyclopentene, or a combination thereof, and C9 hydrocarbons selected from the group consisting of vinyl toluenes or their isomers, indene, methyl styrene, styrene, or a combination thereof.

12. The method for sandwiching glass substrates as claimed in claim 9, wherein the thermoplastic polymer composition is coated using a bar applicator, curtain coater, roller coater, spray coater and combinations thereof.

13. The method for sandwiching glass substrates as claimed in claim 9, wherein the wet film has a thickness ranging from 10 to 300 microns.

14. The method for sandwiching glass substrates as claimed in claim 9, wherein the coated glass substrates are dried at 150 °C for 10 to 20 minutes.

15. The method for sandwiching glass substrates as claimed in claim 9, wherein the bonded glass substrates are optionally heated at a temperature up to 250 °C.

16. The method for sandwiching glass substrates as claimed in claim 9, wherein the bonded glass substrates are cooled to room temperature to form a sandwiched glass.

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