WO2023073729A1

WO2023073729A1 - A sealant composition for substrates

Info

Publication number: WO2023073729A1
Application number: PCT/IN2022/050934
Authority: WO
Inventors: Indraneel ZOPE; Nirmalya MOITRA
Original assignee: Saint-Gobain Glass France
Priority date: 2021-10-29
Filing date: 2022-10-20
Publication date: 2023-05-04
Also published as: CO2024006601A2; MX2024005115A; EP4423206A1

Abstract

The present application provides a sealant composition for substrates. Said sealant composition comprises 60 to 80 wt % of silanol hydroxysilane; 5 to 25 wt% of an oil; 2 to 10 wt% of fumed silica; and 5 to 7 wt% of crosslinking agent. Said sealant composition is mixed with 0.05 to 5 wt% of UV responsive additive such that the sealant composition exhibits fluorescence when exposed to ultraviolet light and improved mechanical shear strength in the range of 526 to 867 kPa.

Description

A SEALANT COMPOSITION FOR SUBSTRATES

TECHNICAL FIELD

The present disclosure relates in general to a sealant composition for substrates, and more particularly to a sealant composition for glass substrates, such that the sealant exhibits excellent mechanical shear strength and displays fluorescence when exposed to ultraviolet light.

BACKGROUND

Sealants are generally used at a juncture of at least two substrates or at least one substrate and a surface, which further adhere to each other by preventing the passage of moisture, fluids, dust etc., therein. For example, sealants are widely used in construction of buildings to seal joints, ceiling joints, floors, roofs, cladding, in sealing materials such as glass, wood, aluminum, bridges, roads, canal linings etc. Generally, sealants when applied to a substrate undergo a curing process, where the applied sealant hardens and sets in a way that it adheres at least two substrates together or at least one substrate and a surface to each other.

Specifically, silicone based sealants, in view of its unique properties, make it resistant to heat, moisture, and weathering, hence suitable for applications in sealing windows to frames, automobiles, appliances, sealing cables and sensors in electronic devices and the like. The sealant on curing, becomes impermeable to all materials, thereby sealing at least two substrates or at least one substrate and a surface together. Generally, silicone based sealants are cured when exposed to atmospheric moisture at a temperature between 40°F and 120°F, and a humidity between 5% and 95%. Silicon based sealants of the type neutral cured (alkoxy or oxime) and acetic cured are well known in the art. Irrespective of their curing mechanism i.e. alkoxy or oxime or acetic, the cured silicone sealant is, essentially, a cross-linked network of siloxane, becomes completely indistinguishable upon curing, i.e., the end user will not be able to identify the type of cured silicone which has been used for a particular application. Silicone sealants involving different types of curing mechanisms have different applications, owing to their differential mechanical properties and chemical properties. For example, neutral cured silicone sealants find its application in load bearing applications, specifically in mirror/glass mounting, gap filling applications where sealant is exposed to external weather, window and door glazing and sealing, decoration filling and sealing, frame and floor filling, construction substrates, such as glass, anodized aluminum, GMS steel, ceramic, and some surface treated materials. Whereas, acetic cured silicone sealants find its application in non-load bearing applications such as, general sealing application, general glazing applications, signage and display boards, internal fixtures/fittings, doors frame sealing, etc. Therefore, using inappropriate silicone sealant based on its curing mechanism, usually leads to defects and failure in end application. For example, use of acetic cure silicone sealant for high load bearing applications such as glass mounting or mirrors or lacquered glass / mirrors, etc., will corrode mirrors and damage lacquered paint layer in lacquered glass.

Specifically, using such inappropriate silicone sealant on lacquered glasses, leads to mirror corrosion and visual defects, thereby negatively impacting the aesthetics of the environment at large. Also, it becomes tough or substantially next to impossible to identify the type of sealant that was used in a particular end application, due to absence of any existing methods or means to differentiate the sealant once the sealant is completely cured. Henceforth, increasing the chemical analysis to be performed in order to understand the type of silicone sealant and therefrom the root cause of the failure that led to such a damage. Although there are numerous brands of silicone sealants available in market, currently it is impossible to differentiate such sealants from each other sealants, especially in cases where there arises a customer complaint. Specifically, there arises a need for sealant compositions which can not only be distinguished between neutral cure and acetic cure, post curing, but also ensure that such composition displays or exhibits excellent mechanical properties.

Existing prior art teaches the addition of a variety of silicone compositions with fluorescence additive and photo initiators to sealants as such, however, such inclusion is either for the purpose of curing of silicones or cure through volume or decorative purpose.

Referring to a Chinese patent application CN110229647A, teaches a kind of glass decoration fluorescence silicone sealant, and a preparation method thereof. Specifically, the sealant disclosed in this application focuses on the use of acetic cure silicone and a fluorescence additive. Here, the fluorescence additive is inorganic in nature and does not require ultraviolet light to fluorescence.

European patent application EP1833884A4 discloses curable silicone compositions having an improved depth of cure and which also incorporates a fluorescent agent for detection. The major objective here to include appropriate fluorescent additive, which does not interfere the photo-curing effectiveness. Accordingly, the fluorescent additive described, does not absorb the ultraviolet light in same wavelength range as that of a photo-initiator.

US patent publication US2015/0376481 Al discloses stable thermal radical curable silicone adhesive composition comprising a clustered functional polyorganosiloxane, a reactive resin and polymer, a radical initiator, a moisture cure initiator; and a cross linker.

The above references prior art compositions address a very specific requirement of the improved depth of cure or a sealant composition inclusive of a fluorescence only for decoration purpose or obtaining thermally stable curable adhesive compositions. The above disclosed prior art do not address the surprising mechanical shear strength that is achieved because of using a specific UV responsive additive. None of the existing state of art, differentiates the neutral cure silicone sealant from an acetic cure silicone sealant, once it is completely cured. The above sealants are targeted for electronics applications, specifically for thermal interface material applications, macro-electronics applications, opto-electronics applications and thermally conductive electronics applications.

There is definitely a need to address the above discussed limitations and enable the end user to identify the neutral silicone sealant used, in order to find out the root cause of the failure, and reduce the time for root-cause analysis for any defects arising due to the usage of inappropriate acetic cure silicone sealant for glass, mirror or lacquered glass applications. And so, it is desirable to develop a sealant composition, specifically for substrates, with a visual indicator or some kind of responsiveness to ultraviolet light, post curing of the silicone sealant, at the same time ensuring that improved mechanical shear strength. With the proposed invention, specifically the problem and disadvantages outlined above, are circumvented with the use of a sealant composition.

OBJECT OF INVENTION

The main object of the present invention is to provide a sealant composition for a substrate, said sealant composition upon curing when exposed to ultraviolet light exhibits fluorescence, thereby making it a visual indicator which helps in identifying a neutral cure sealant from an acetic cure sealant, used for adhering a substrate on a surface.

Another object of the present invention is to provide a sealant composition for glass substrates, ensuring that the sealant upon curing, displays an improved mechanical shear strength to hold the substrates against each other or a substrate onto a surface.

Yet another object of the present invention is to provide a sealant composition, which upon fluorescence, displays improved visual detection, and enables the end user to identify the root cause involved in the failure due to use of an acetic cure silicone sealant, thereby reducing the time involved in performing any chemical analysis.

The present disclosure was developed by outlining the above objectives.

SUMMARY OF THE DISCLOSURE

In an aspect of the present disclosure, a sealant composition for glass substrates is disclosed. Said sealant composition comprising 60 to 80 wt % of silanol hydroxysilane; 5 to 25 wt% of an oil; 2 to 10 wt% of fumed silica; and 5 to 7 wt% of crosslinking agent. The sealant composition is mixed with 0.05 to 5 wt% of UV responsive additive such that the sealant composition exhibits fluorescence when exposed to ultraviolet light and improved mechanical shear strength in the range of 526 to 867 kPa.

Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and are not limited in the accompanying figures. FIG. 1(a) and (b) illustrates images, of a plywood substrate with and without UV responsive molecules exposed to UV, in accordance with one embodiment of the present disclosure.

FIG. 2(a) and (b) illustrates images, of a glass substrate with and without UV responsive molecules exposed to UV, in accordance with one embodiment of the present disclosure.

FIG. 3 represents the effect of loading level of UV responsive molecule on shear strength, using an alkoxy cure silicon sealant as per inventive example 1 , in accordance with one embodiment of the present disclosure.

FIG. 4 represents the effect of loading level of UV responsive molecule on shear strength, using an oxime cure silicon sealant as per inventive example 2, in accordance with one embodiment of the present disclosure.

FIG. 5 represents the sample dimensions of plywood and glass, for evaluating the mechanical shear strength, in accordance with one embodiment of the present disclosure.

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

DETAILED DESCRIPTION

As used herein, in every embodiment, it must be understood that the term ‘cured’ or ‘curing’, refers to a process where the sealant is allowed to toughen or settle down effectively over a period of time, when applied on a substrate. The term ‘neutral cure silicone’, as used herein, refers to a sealant which releases alcohol or other non-acidic substance whilst curing. The ‘neutral cure silicone’ include the oxime and alkoxy silicones, where methyl ethyl ketoxime is released with the oxime curing systems, and an alcohol is released with the alkoxy curing systems. Whereas the term ‘acetic cure silicone’ refers to a sealant which releases acetic acid whilst curing.

The term ‘UV responsive molecules’ or ‘fluorescence additive’ or ‘UV responsive additive’ which are used interchangeably herein, refer to compounds that absorb light in the ultraviolet and violet region and re-emit light in blue region, when exposed to light.

As used herein, and unless defined otherwise, the phrase ‘% by weight’ or ‘wt%’ is meant to denote % by weight of the total sealant composition. The present application provides a sealant composition for a substrate. Said sealant composition comprises by weight: 60 to 80 wt % of silanol hydroxysilane; 5 to 25 wt% of an oil; 2 to 10 wt% of fumed silica; and 5 to 7 wt% of crosslinking agent. The sealant composition, in accordance with the present disclosure is mixed with 0.05 to 5 wt% of fluorescence additive or UV responsive additive, which post curing of the sealant exhibits fluorescence. Beneficially, the sealant composition in accordance with the present disclosure, enables an end user to identify the neutral cure silicone sealant from an acetic cure silicone sealant, in a particular application, due to the displayed fluorescence. Further, beneficially, the disclosed sealant composition displays an improved or in fact surprisingly enhanced mechanical shear strength, by adhering at least two substrates together or at least one substrate onto a surface, such as wall, wood, laminate, etc. The silanol hydroxysilane polymer forms the base ingredient of the disclosed sealant composition. As used herein the term ‘silanol hydroxysilane’ is meant to include any of a variety of silanol polymers including hydroxyl terminated polydimethylsiloxane. The base silanol hydroxysilane is generally present in an amount ranging from 60 to 80 wt% of the total composition. In some embodiments, the silanol hydroxysilane may be present in the sealant composition in an amount of 65 to 75% by weight of the composition. In a specific embodiment, the silanol hydroxysilane is present in the amount of 70 wt% of the total composition. The hydroxyl terminated polydimethylsiloxane undergoes condensation reaction in the presence of the crosslinking agent and catalyst to form a three dimensional network with alcohol based by-products.

The disclosed sealant composition comprises an oil which functions as a plasticizer. Plasticizers in the form of oil are incorporated in the disclosed composition to adjust flexibility and elasticity of the silicone sealant. It also aids in mixing by adjusting the rheological properties on silicone mix, specifically, viscosity of the mix during manufacturing. It also influences the cost owing to its lower price. The plasticizer in accordance with the present disclosure imparts better extrudability of silicone during end application.

In accordance with the present disclosure the oil can either be a mineral oil or a silicone oil. The oil is generally present in an amount ranging from 5 to 25 wt% of the total composition, when the sealant composition is a neutral cured system. In a specific embodiment, when the sealant composition in an alkoxy cured system, the oil is a silicone oil, which is present in an amount of 15 to 25% by weight of the composition. In a preferred embodiment, the silicone oil is present in the range of 18 wt% of the composition. The silicone oil in accordance with the present disclosure can be selected from the group comprising trimethyl terminated polydimethylsiloxane, polymethyloctadecylsiloxane, dimethyl-methyloctadecyl siloxane copolymer, polymethyltetradecyl siloxane or dimethyldodecyltetrasiloxane terpolymer.

In another specific embodiment, in accordance with the present disclosure when the sealant composition is an oxime cured system, the oil is a mineral oil, which is present in an amount of 5 to 20% by weight of the composition. In a preferred embodiment, the mineral oil is present in the range of 12 wt% of the composition. The mineral oil in accordance with the present disclosure can be selected from the group comprising paraffinum liquidum, petrolatum, paraffin, or a combination thereof. In an alternate embodiment, the oil can be selected from petroleum-based oils, naphthenic oils, paraffinic oils and combinations thereof.

Specifically, using silicone oil and mineral oil as plasticizers in neutral cured systems, depends on factors like, long term yellowing resistance, thermal stability of silicone, mold and fungal resistance, color stability, volatility and lastly shrinkage of cured silicone. Alkoxy cured silicones are used in more critical applications like load-bearing application wherein use of silicone oil is required. Accordingly, based on the end application either silicone oil or mineral oil is chosen as a suitable plasticizer to be incorporated in the disclosed neutral cure sealant composition.

Fumed silica is present in the disclosed sealant composition, in an amount ranging from 2 to 10 wt% of the composition. The fumed silica in a preferred embodiment is present in an amount of 8 wt%, which promotes the thickening of the sealant once applied onto a substrate and also reinforces the sealant composition. It provides thixotropic reinforcements providing non-slump properties, and also held in adjusting mechanical properties including cohesion of cured silicone and toughness. The disclosed sealant composition, comprises a crosslinking agent in an amount ranging from 5 to 7 wt% of the total composition. The crosslinking agent of the sealant composition, is a silane based crosslinker which is selected from the group consisting methyltrimethoxysilane, trialkoxysilanes and ketoximosilanes. Specifically, the trialkoxysilanes are exemplified by propyltrimethoxysilane, phenyltrimethoxysilane, glycidoxypropyltrimethoxysilane, ethyltrimethoxysilane, aminopropyltrimethoxysilane, aminoethylaminopropyltrimethoxysilane, phenyl trimethoxysilane, and methyltrimethoxysilane.

Further, ketoximosilanes include methyltri (methylethylketoximo)silane, tetra(methylethylketoximo)silane, methyltris(methylethylketoximo)silane, and vinyltris(methylethylketoximo) silane. In a preferred embodiment the crosslinking agent is methyltrimethoxysilane for alkoxy-cured silicone and methyltris(methylethylketoxime)silane for oxime-cured silicones.

In every embodiment of the present disclosure, the crosslinking agent is responsible for the neutral cure silicone, i.e., alkoxy cure or oxime cure. When the crosslinking agent is selected from methyltrimethoxysilane, the silanol group from polydimethylsiloxane reacts with methoxy group from crosslinker leading to liberation of methanol and Si-O-Si linkage. Similarly, using methyltris(methylethylketoxime)silane as the crosslinking agent in the sealant composition according to the present disclosure, the silanol group from polydimethylsiloxane reacts with methylehtylketoxime group from crosslinker leading to liberation of methylethylketoxime and Si-O-Si linkage.

In accordance with the present disclosure, the sealant composition further comprises an adhesion promoter in the range of 0 to 2% by weight of the total composition. In a preferred embodiment the adhesion promoter is present in an amount of 1%. In an embodiment the adhesion promoter is selected from the group consisting of aminopropyltrimethoxy silane, aminopropyltri ethoxy silane, 3- gly ci doxypropyltrimethoxy silane, 3-glycidoxypropyltriethoxysilane. In a preferred embodiment the adhesion promoter is aminopropyltriethoxysilane. The adhesion promoter as per the present disclosure enhances the adhesion of the sealant over the substrate and simultaneously improves the adhesion between the components of the sealant. Specifically, the adhesion promoter aminopropyltriethoxysilane reacts chemically and forms a chemical bridge between the sealant and the substrate, thereby improving the adhesion of the sealant over the substrate.

In a further embodiment, in accordance with the present disclosure the sealant composition also comprises a catalyst in the range of 0.05 to 0.1% by weight of the total composition. In a preferred embodiment the catalyst is present in an amount of 0.05%. In an embodiment the catalyst is selected from the group consisting of dibutyl tin dilaurate, dibutyl tin diacetate or dibutyl tin oxide. The base silanol hydroxysilane polymer structure is dependent on the catalyst that is used. The catalyst may indirectly affect the curing kinetics and mechanical strength of the sealant, due to changes in polymer properties. It can influence the skin formation time, complete curing time and depth of cure. Hence in a preferred embodiment the catalyst is dibutyl tin dilaurate, which enhances the complete curing of the silicone sealant.

The sealant composition in accordance to an inventive aspect of the present disclosure, is further mixed with an UV responsive additive or a fluorescence additive in an amount ranging from 0.05 to 5 wt% of the total composition. In an embodiment the UV responsive additive is selected form the group comprising benzenesulfonic acid, disodium, 5 - [ [4- [bis(2-hydroxy ethyl)amino] -6-(3 -sulfonatoanilino)- 1,3,5 -triazin-2- yl]amino] -2- [(E)-2- [4- [ [4- [bis(2-hy droxy ethyl)amino] -6-(3 -sulfonatoanilino)- 1,3,5- triazin-2-yl]amino]-2-sulfonatophenyl]ethenyl]benzenesulfonate; 4,4'-Bis[(4-anilino- 6-morpholino-s-triazin-2-yl)amino]-2,2'-stilbenedisulfonic acid disodium salt; 2-(4- Styryl-3-sulfophenyl)-2H-naphtho[l,2-d]triazole sodium Salt; 2,2'-(l,2- Ethenediy l)b is [5 - [ [4-(diethy lamino)-6- [(2, 5-disulfophenyl)amino] -1,3,5 -triazin-2- yl]amino]benzenesulfonic acid] hexasodium salt; dipotassium;disodium;5-[[4-[bis(2- hydroxy ethyl)amino] -6-(4-sulfonatoanilino)- 1,3,5 -triazin-2-y 1] amino] -2- [(E)-2- [4- [ [4- [bis(2-hy droxyethy l)amino] -6-(4-sulfonatoanilino)- 1 , 3 , 5-triazin-2-yl]amino] -2- sulfonatophenyl]ethenyl]benzenesulfonate; 2,2 ’-Stilbenedisulfonic acid, 4,4'-bis[[4- [bis(2-hydroxyethyl)amino]-6-(p-sulfoanilino)-s-triazin-2-yl]amino]-, tetrasodium salt; 2,2'-(l,2-Ethenediyl)bis[5-[[4-(4-morpholinyl)-6-[(4-sulfophenyl)amino]-l,3,5- triazin-2-yl] amino] -benzenesulfonic Acid Sodium Salt; 4,4'-Bis[4-[bis(2- hydroxyethyl)amino]-6-anilino-l,3,5-triazin-2-yl]amino]stilbene2,2'-disulphonic acid; 2,2’-Stilbenedisulfonic acid, 4,4'-bis[(4-anilino-6-methoxy-s-triazin-2- yl)amino]-, disodium salt; 4,4'-Bis(2-sulfostyryl) biphenyl disodium salt; 2, 2' -(1,2- Ethenediy l)b is [5 - [ [4-(diethy lamino)-6- [(2, 5-disulfophenyl)amino] -1,3,5 -triazin-2- yl]amino]benzenesulfonic acid] hexasodium salt. In a specific embodiment the UV responsive additive is disodium,5-[[4-[bis(2-hydroxyethyl)amino]-6-(3- sulfonatoanilino)-l,3,5-triazin-2-yl]amino]-2-[(E)-2-[4-[[4-[bis(2- hydroxy ethyl)amino] -6-(3 -sulfonatoanilino)- 1,3,5 -triazin-2-y 1] amino] -2- sulfonatophenyl]ethenyl]benzenesulfonate, i.e., Tinopal 2B, which is preferred in the amount ranging from 0.05 to 0.375 wt%. The sealant composition, being a neutral cure silicone system, is mixed with Tinopal 2B using common mixing means such as speed mixer at 2000 rpm for 1 min.

In a specific embodiment, the UV responsive additive, Tinopal 2B, reacts with the alkoxy crosslinker. It was surprisingly found by the inventors of the present invention that the crosslinker simultaneously reacted with OH-polymer increasing the cross-link density. This reaction of Tinopal 2B extra with silicone was reasoned to enhance the mechanical properties of cured silicone. The presence of UV responsive additive in the sealant composition affects the chemical and mechanical properties such as shear strength. The UV responsive additive when added in a preferred amount of 0.05 to 0.25 wt%, provides improved optical clarity to the sealant. In a most preferred embodiment, the UV responsive additive or the fluorescence additive is added in an amount of 0.15 wt% of the total composition.

The sealant composition comprising the UV responsive additive when exposed to the ultraviolet light at a wavelength of 365nm, triggers ultraviolet fluorescence. This visual indication helps the end user in identifying the neutral silicone sealant used for a particular application. In cases where an inappropriate sealant has been used for glass mounting, or mirror or lacquered glass adhesion onto another substrate or wall; for ex., if an acetic cure silicone sealant is used for such adhesion, this will lead to damages such as corrosion, forming streaks etc. Whilst using the silicone sealant in accordance with the present disclosure, which is a neutral cure silicone sealant inclusive of the UV responsive additive when exposed to ultra violet light will fluorescence, thereby enabling the end user to seamlessly identify the sealant that has been used for adhesion of the glass onto wall or glass onto wood, etc.

Also in case of any failures due to inappropriate use of silicone sealant, i.e., using a silicone sealant which is not appropriate for a certain load bearing application, the visual indicator in terms of fluorescence will help in easy identification of the neutral sealant used, which will help the end user to immediately resolve the issue by not performing a deep chemical analysis to figure out the root cause involved in such failures.

In alternative embodiment other UV responsive additives can be added which can emit the light in different wavelengths for e.g. red, orange where in improvement in mechanical properties may or may not be intended, but enables in fluorescence of the sealant post curing, which again ensures that the end user identifies the neutral silicone sealant used for a particular application.

The sealant composition may, for example, be in the form of paste. The sealant composition in the form of a paste, has a viscosity in the range of 10000 to 100000 cSt. In certain embodiments, the sealant composition paste may have a viscosity of less than about 50000 cSt, for example, in the range of from 35000 to 45000 cSt. In further preferred embodiments, the sealant composition paste may have a viscosity of less than about 42000 cSt, for example in the range of from 38000 cSt to 40000 cSt.

The sealant composition usually in the form of a paste is applied on to a substrate manually, using a sealant applicator, known to an ordinary person in the art. The sealant in accordance with the present disclosure, once applied, cures to form a hardened material and settles down, such that it adheres or holds at least two substrates together, or at least one substrate onto another surface. In an embodiment the sealant, hardens and settles down on to the substrate at a temperature of less than 120 °F. The sealant takes at least 24 hours to complete the curing process. The time required to reach the improved mechanical shear strength in accordance with the present disclosure is usually not more than 24 hours.

The sealant on curing post application, becomes impermeable to any constituents, thereby sealing at least two substrates together. The substrate in an embodiment, for example, may be but not limiting to, a wood, glass, metal, ceramic, plywood, laminates, mirror, lacquered glass, colored glass, tinted glass, patterned glass or a tempered glass.

In accordance with the present disclosure, the sealant thus formed has a mechanical shear strength in the range of 526 to 867 kPa. In specific embodiment, the UV responsive additive, for example, Tinopal 2B containing four ethyl alcohol moieties reacts with the alkoxy crosslinker. It was surprisingly found by the inventors that this crosslinker would also simultaneously react with OH-polymer increasing the crosslinking density. This reaction of Tinopal 2B with silicone was reasoned to enhance the mechanical properties of cured silicone. In another specific embodiment, the UV responsive molecule, for example, Tinopal 2B containing four ethyl alcohol moieties reacts with the oxime crosslinker. This crosslinker would also simultaneously react with OH-polymer increasing the cross-linking density. This reaction of Tinopal 2B with silicone enhances the mechanical properties of the neutral cured silicone systems.

In accordance with an inventive aspect of the present disclosure, it was quite surprisingly found by the inventors that the mechanical shear strength of the sealant, increases with increase in the loading level of the UV responsive additive. In some embodiments, the shear strength was found increased up to 732kPa (39%) with loading level of 0.15 w% of UV responsive additive. With a further increase in the loading level of the UV responsive additive, the mechanical shear strength was found to reduce to 639 kPa (21%). Although after a certain level of increase in the loading of the UV responsive the mechanical shear strength has dropped down, but still it is pertinent to note that the achieved mechanical shear strength is higher than the value achieved for a conventional sealant alone, without UV responsive additive.

Thus, the sealant formed as per the disclosed composition, is beneficial in ways, that it helps the end user to identify the sealant used and simultaneously provides better optical clarity and improved mechanical shear strength.

EXAMPLES

Inventive Example 1 Preparation of Sealant Composition:

Table 1 discloses a sealant composition according to an inventive Example 1, which was prepared following the steps produced below:

Commercially available alkoxy-cure silicone sealant containing silanol hydroxysilane polymer was used as a base, to which the components including oil, fumed silica, methylmethoxysilane, aminopropyltriethoxysilane, dibutyl tin dilaurate and Tinopal 2B were thoroughly mixed together using a speed mixer. Mixing was carried out using SpeedMixer by Hauschild Engineering (Model DAC 150.1 FVZ-K). 100g material was mixed, which was subsequently used for shear test sample preparation and to cast thin strips for visual observation.

Table 1

The above disclosed, Inventive sealant composition was then tested for the following properties:

Optical Clarity: The glass strips were coated with the silicone sealant as disclosed in Table 1, and were adhered on to the surface of a wood. The entire surface of one side of the glass strip is provided with the silicone sealant. UV fluorescence additive when added in loading levels i.e. 0.05 to 0.25 w% provided excellent visual clarity. The enhancement of optical clarity achieved can be seen from Table 2.

Table 2

UV Fluorescence:

Casted strips when exposed to UV lamp (365 nm, 4 Watt) displayed fluorescence as seen from Table 3. Intensity of fluorescence was found to increase with increasing loading levels of Tinopal 2B. It is therefore inferred that Tinopal 2B when added in low loading levels i.e. 0.05 to 0.25 wt% not only displayed observable fluorescence but also retained good visual clarity.

Table 3

Silicone sealant with 0.25wt% Tinopal 2B when applied to different substrates i.e. plywood and lacquered glass did not deteriorate the displayed fluorescence in any manner (Figures 1(b) and 2(b) with UV responsive additive). This confirms that UV fluorescence is not affected by nature of substrate and can indeed be a quick visual tool to identify the sealant. It is also observed from these Figures 1(a) and 2(b) that the sealants without UV responsive additive does not fluorescence when exposed to ultra violet light.

Mechanical shear strength:

The mechanical shear strength was evaluated using the standard method ASTM C961- 15.

1) The plastic head from the cartridge was cut and screwed in a plastic nozzle over the sealant tube in order to control the flow of the sealant.

2) A single overlap joint samples were prepared using plywood and glass. Sample dimensions are shown in Figure 5.

3) 0.5-0.6 g of sealant was used and spread across 50 x 25 mm area for making single lap joint. Here the press time was maintained for about 5 seconds.

4) The sample under constant load of 150-160 g was stored (typically, clear glass of size 100 x 100 x 6 mm can be used as load)

5) The mechanical shear strength was determined using UTM. After the determination of the mechanical shear strength it was interestingly found that the mechanical shear strength of the sealant which is incorporated with the UV responsive additive was excellent. Specifically, the shear strength obtained was even more than that of the conventional sealant without UV responsive additive.

From Figure 3, it is evident that the mechanical shear strength increased with increase in loading level of Tinopal 2B. It has surprisingly increased to 39% for formulation with loading level of 0.15 w% later reduced the magnitude of increase to 21%. This suggested the existence of a maxima at 0.15w% that optimally affect the cross-linking density.

Table 4

Inventive Example 2

Preparation of Sealant Composition:

Similar to inventive example 1, commercially available oxime-cure silicone sealant containing silanol hydroxysilane polymer was used as a base, to which the components including oil, fumed silica, methyltris(methylethylketoxime)silane, aminopropyltriethoxy silane, dibutyl dilaurate and Tinopal 2B were mixed using a speed mixer. Mixing was carried out using SpeedMixer by Hauschild Engineering (Model DAC 150.1 FVZ-K). 100g material was mixed which was subsequently used for shear test sample preparation and to cast thin strips for visual observation.

Table 5

Optical Clarity:

The glass strips were coated with the silicone sealant as disclosed in Table 5, and were adhered on to the surface of a wood. The entire surface of one side of the glass strip is provided with the silicone sealant. UV fluorescence additive when added in loading levels i.e. 0.05 to 0.25 w% provided excellent visual clarity.

UV Fluorescence:

Casted strips when exposed to UV lamp (365 nm, 4 Watt) displayed fluorescence as seen from Figure 4. Intensity of fluorescence was found to increase with increasing loading levels of Tinopal 2B. It is therefore inferred that Tinopal 2B when added in low loading levels i.e. 0.05 to 0.25 wt% not only displayed observable fluorescence but also retained good visual clarity.

Mechanical shear strength:

5) The mechanical shear strength was determined using UTM.

After the determination of the mechanical shear strength it was interestingly or quite surprisingly found that the mechanical shear strength of the sealant which is incorporated with the UV responsive additive was excellent. Specifically, the shear strength obtained was even more than that of the conventional sealant without the UV responsive additive, thereby proving enhanced inventive aspect, as per the present disclosure.

From Figure 4, it is evident that the mechanical shear strength increased by 9%, 15%, 12% and 14% for 0.05w%, 0.15w%, 0.25w% and 0.375w% loading levels of Tinopal 2B.

Factor of Safety Factor of safety is calculated based on the shear strength. A minimum shear strength required is evaluated by assuming 5 % area coverage of the silicone on the glass/mirror panel. Based on the gravitational force on the glass panel, the minimum shear bond strength required for the silicone was found to be 3kPa. Further, a force equivalent to a person pulling on the glass panel was added. The pulling force was assumed to be 1000N, in an example. In such a case, the required bond strength was found to be equal to 23 kPa. Based on end application requirements, minimum factor of safety is defined to be 10. Hence, silicone sealant should have minimum shear bond strength of >230 kPa. Addition of UV additive increases the shear bond strength i.e. for same quantity of silicone used for mounting glass panel, the factor of safety is enhanced.

Following table summarizes the effect of UV additive on factor of safety for 0.15% loading of UV additive (as it gives best performance in both cure systems).

Table 6

It is evident that by addition of UV additive in both, alkoxy-cured silicone and oxime- cured silicone, the shear bond strength increased i.e. for same quantity of silicone used for mounting glass panel, the factor of safety is enhanced.

INFERENCE

It is thus evident from the above examples that addition of UV additive i.e. Tinopal 2B, to neutral cure silicone sealants can not only fluoresce and thereby being a visual indicator, but also display additional technical advantage of excellent increase in mechanical shear strength. Specifically, the enhancement in mechanical shear strength, in fact, has shown improvement over a conventional sealant without UV responsive additive. In order to differentiate the cured sealant between a neutral cure sealant and acetic cure sealant, loading level of Tinopal 2B can either be varied from 0 to 0.375 w%. Alternatively, UV responsive additives such as Tinopal AMS, Tinopal RBS 200, Tinopal SCP, Tinopal ABP, Tinopal ABP-X, Tinopal UNPA-GX, Tinopal MSP, Tinopal AS, Tinopal UP, Tinopal ABP-X, Tinopal WHN, Tinopal MST, Tinopal BHT, Tinopal CBS-X, Tinopal DMS, Tinopal OB, Tinopal 2BT also work in the same manner, and the scope is not limited only to the disclosed UV responsive additives.

INDUSTRIAL APPLICABILITY

Thus from the above inventive and comparative examples, the sealant composition of the present disclosure is very unique with significantly improved visual clarity, mechanical shear strength and acts as a visual indicator to identify the type of sealant, thereby making it economically viable for end users and suitable for various load bearing applications. Specifically, the disclosed sealant is preferred for mirror mounting, lacquered glass mounting, sky-light gap filling, weather sealant, gap filling silicone sealant and the like. Note that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described. Still further, the order in which activities are listed is not necessarily the order in which they are performed.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims.

The specification and illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The specification and illustrations are not intended to serve as an exhaustive and comprehensive description of all of the elements and features of apparatus and systems that use the structures or methods described herein. Certain features, that are for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in a sub combination. Further, reference to values stated in ranges includes each and every value within that range. Many other embodiments may be apparent to skilled artisans only after reading this specification. Other embodiments may be used and derived from the disclosure, such that a structural substitution, logical substitution, or another change may be made without departing from the scope of the disclosure. Accordingly, the disclosure is to be regarded as illustrative rather than restrictive. The description in combination with the figures is provided to assist in understanding the teachings disclosed herein, is provided to assist in describing the teachings, and should not be interpreted as a limitation on the scope or applicability of the teachings. However, other teachings can certainly be used in this application.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive-or and not to an exclusive-or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

Also, the use of "a" or "an" is employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural, or vice versa, unless it is clear that it is meant otherwise. For example, when a single item is described herein, more than one item may be used in place of a single item. Similarly, where more than one item is described herein, a single item may be substituted for that more than one item.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent that certain details regarding specific materials and processing acts are not described, such details may include conventional approaches, which may be found in reference books and other sources within the manufacturing arts.

While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.

Claims

Claims:

1. A sealant composition for a substrate, comprising:

60 to 80 wt % of silanol hydroxysilane;

5 to 25 wt% of an oil;

2 to 10 wt% of fumed silica; and

5 to 7 wt% of crosslinking agent; characterized in that the sealant composition is mixed with 0.05 to 5 wt% of UV responsive additive such that the sealant composition exhibits fluorescence when exposed to ultraviolet light and improved mechanical shear strength in the range of 526 to 867 kPa. The sealant composition as claimed in claim 1, further comprises 0 to 2 wt% of an adhesion promoter selected from the group consisting of aminopropyltrimethoxysilane, aminopropyltriethoxysilane, 3- glycidoxypropyltrimethoxysilane or 3 -gly ci doxypropyltri ethoxy silane. The sealant composition as claimed in claim 1, wherein the oil is selected from mineral oil or silicone oil. The sealant composition as claimed in claim 1, further comprises 0.05 to 0.1 wt% of a catalyst selected from the group consisting dibutyl tin dilaurate, dibutyl tin diacetate or dibutyl tin oxide. The sealant composition as claimed in claim 1, wherein the crosslinking agent is a silane based crosslinker selected from the group consisting of methyltrimethoxysilane, trialkoxysilanes, or ketoximosilanes.

27 The sealant composition as claimed in claim 5, wherein the trialkoxysilane comprises the compounds selected from propyltrimethoxysilane, phenyltrimethoxysilane, glycidoxypropyltrimethoxysilane, ethyltrimethoxysilane, aminopropyltrimethoxysilane, aminoethylaminopropyltrimethoxysilane, phenyl trimethoxysilane or methyltrimethoxysilane. The sealant composition as claimed in claim 5, wherein the ketoximosilanes comprises the compounds selected from methyltri (methylethylketoximo)silane, tetra(methylethylketoximo)silane, methyltris(methylethylketoximo)silane, or vinyltris(methylethylketoximo) silane. The sealant composition as claimed in claim 1, wherein the UV responsive additive is selected from the group consisting of benzenesulfonic acid; disodium, 5-[[4- [bis(2-hydroxyethyl)amino]-6-(3-sulfonatoanilino)-l,3,5-triazin-2-yl]amino]-2- [(E)-2- [4- [ [4- [bis(2-hy droxyethyl)amino] -6-(3 -sulfonatoanilino)- 1,3,5 -triazin-2- yl]amino]-2-sulfonatophenyl]ethenyl]benzenesulfonate; 4,4'-Bis[(4-anilino-6- morpholino-s-triazin-2-yl)amino]-2,2'-stilbenedisulfonic Acid Disodium Salt; 2-(4- Styryl-3-sulfophenyl)-2H-naphtho[l,2-d]triazole Sodium Salt; 2,2'-(l,2- Ethenediyl)bis[5-[[4-(diethylamino)-6-[(2,5-disulfophenyl)amino]-l,3,5-triazin-2- yl]amino]benzenesulfonic acid] hexasodium salt; dipotassium;disodium;5-[[4- [bis(2-hydroxyethyl)amino]-6-(4-sulfonatoanilino)-l,3,5-triazin-2-yl]amino]-2- [(E)-2- [4- [ [4- [bis(2-hy droxyethyl)amino] -6-(4-sulfonatoanilino)- 1,3,5 -triazin-2- yl]amino]-2-sulfonatophenyl]ethenyl]benzenesulfonate; 2,2’-Stilbenedisulfonic acid, 4,4'-bis [ [4- [bis(2-hydroxy ethyl)amino] -6-(p-sulfoanilino)-s-triazin-2- yl]amino]-, tetrasodium salt; 2,2'-(l,2-Ethenediyl)bis[5-[[4-(4-morpholinyl)-6-[(4- sulfophenyl)amino]-l,3,5-triazin-2-yl]amino]-benzenesulfonic Acid Sodium Salt; 4,4'-Bis[4-[bis(2-hydroxyethyl)amino]-6-anilino-l,3,5-triazin-2- yl]amino]stilbene2,2'-disulphonic acid; 2,2’-Stilbenedisulfonic acid, 4,4'-bis[(4- anilino-6-methoxy-s-triazin-2-yl)amino]-, disodium salt; 4,4'-Bis(2-sulfostyryl) biphenyl Disodium Salt; 2,2'-(l,2-Ethenediyl)bis[5-[[4-(diethylamino)-6-[(2,5- disulfophenyl)amino]-l ,3,5-triazin-2-yl]amino]benzenesulfonic acid] hexasodium salt. The sealant composition as claimed in claim 1 hardens and settles onto the substrate at a temperature in the range of 40°F to 120°F. The sealant composition as claimed in claim 1, is a neutral cured silicone. The sealant composition as claimed in claim 10, wherein the neutral cured silicone is either an alkoxy cure or oxime cure silicone. The sealant composition as claimed in claim 1 , wherein the substrate is glass, wood, metal, ceramic, plywood or laminate. The sealant composition as claimed in claim 12, wherein the glass substrate is one of a mirror, a lacquered glass, a colored glass, a tinted glass, a patterned glass or a tempered glass. The sealant composition as claimed in claim 1 has a viscosity in the range of 10000 cSt to 100000 cSt. The sealant composition as claimed in claim 1, exhibits a load bearing capacity at 867 kPa. The sealant composition as claimed in claim 1, wherein the mechanical shear strength increases up to 867kPa for a maximum load bearing capacity of 1162 N.