WO2025229656A1

WO2025229656A1 - A method of making scratch resistant tempered glass

Info

Publication number: WO2025229656A1
Application number: PCT/IN2025/050582
Authority: WO
Inventors: Srinivasprasad BS; Srivalli H; Jagadis S
Original assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Priority date: 2024-04-29
Filing date: 2025-04-11
Publication date: 2025-11-06
Anticipated expiration: 2026-10-29

Abstract

A method of making scratch resistant tempered glass is provided. e said method of making scratch resistant tempered glass comprising steps of i) coating of metal solution comprising water-soluble metal salt and water-soluble polymer binder on the said glass substrate, ii) drying the glass substrate, iii) heating the substrate above the pyrolysis temperature of polymer binder to diﬀuse metal ions into the substrate, followed by rapid quenching, thereby forming a transparent or coloured tempered glass substrate having an improved scratch resistance. e said method avoids multi-step deposition and immersion processes and improves the scratch resistance property of the tempered glass substrate in a shorter time. e present disclosure further relates to a scratch-resistant tempered glass substrate obtained by the said method.

Description

A METHOD OF MAKING SCRATCH RESISTANT TEMPERED GLASS

TECHNICAL FIELD

The present disclosure relates to a method of making scratch resistant tempered glass substrate and a scratch resistant tempered glass. More particularly, the present disclosure relates to method of making ion-exchangeable tempered glass substrates having an improved scratch resistant.

BACKGROUND

Silicate glasses primarily consist of a disordered network of silicon and oxygen atoms. Normally, monovalent and bivalent ions are embedded in the glass network, and this gives rise to some weaknesses. These monovalent ions are usually alkali ions and there exists a possibility of internal movement of these alkali ions within the glass matrix. This movement could be due to diffusion or due to application of an electric potential.

Ion exchange is caused in glasses when the mobile Na⁺ ions are replaced by other mobile ions and the activation energy for the reaction is overcome by thermal conditions. Sodium ions from the glass diffuse out of the sample and mobile ions at the source diffuse in and this diffusion is caused by a concentration gradient.

Ion diffusion is one of the easier options to alter glass surface composition. It is possible to modify many different properties of glass objects by ion exchange, e.g. mechanical, optical, electrical and chemical properties. By changing the mechanical properties, it is possible to alter properties related to hardness and strength. By changing optical properties, one can work on several properties such as luminescence, absorbance, reflectivity etc. Chemical properties directly impact surface energy, reactivity, and corrosion resistant. The most studied properties of these are probably chemical strengthening and colouration (glass staining).

Although ion exchange provides enhanced surface strength to the glass, the improvement in hardness is minimal, and the glass is still susceptible to scratches caused by exposure to materials that are harder than glass. For many applications, it is desirable to provide a substrate surface with improved scratch resistant. Soda lime glass does not inherently have a high scratch resistant, but the application of a suitable thin film can markedly improve the scratch resistant of the glass surface.

US9,670,088B2 describes a four-fold improvement of scratch resistant on glass using ion exchange method. It involves ion exchange of Corning Gorilla glass with molten bath of KN03 at a temperature of 390° C -480° C for 2-8 hours. Some of the glasses were also subject to acid treatment where the acid concentration used was 0.02 N H2SO4 or 1 molar (M) HN03 at 95° C and for a period of 24 hours. However, the exposure times are longer and involves a multi-step deposition/immersion process.

US10444408B2 describes a chemical tempering of glass by ion exchange of alkali metals present in the glass substrate through immersion in atleast one molten bath containing nitrates, sulphates or chlorides of a larger metal ion. Temperatures range from 380-450 deg C and the immersion time varies from 15 mins to 40 hours. The optical layers developed include a scratch resistant layer and optical interference layer. However, the exposure times are longer and involves a multi-step deposition/immersion process.

US3524737A describes a strengthening of glass by replacing the sodium ions in the glass surface with potassium ions. This is done by placing the glass at a temperature of about 35 deg C below the glass transformation range (between the strain point and annealing point of glass) for upto 24 hours. This is followed by immersion in a molten salt bath at 500 deg C and below the strain point of glass. Although thermochemical tempering is described, the process involves longer process time and does not discuss enhanced scratch resistant.

The prior arts discussed above describe the development of improved scratch resistant on glass, obtained due to chemical tempering. Although chemical tempering is established and widely used, the process involves multiple steps and takes hours (sometimes upto 24 hours) for completion. This can be addressed by the thermo-chemical tempering described in the present disclosure wherein the tempering process is complete in less than 7 minutes. This saves time and improves scratch resistant property significantly.

OBJECT OF INVENTION

The main object of the present invention is to provide a method of making scratch resistant tempered glass substrate, such that method to improves the scratch resistant property of the tempered glass substrate.

Another object of the present invention is to provide a method of making scratch resistant tempered glass substrate, such that method improves the scratch resistant property of the tempered glass substrate in a shorter time.

Yet another object of the present invention is to provide a method of making scratch resistant tempered glass substrate, such that method avoids a multi-step deposition.

Further, another object of the present invention is to provide a method of making scratch resistant tempered glass substrate, such that method avoids an immersion process.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a method of making scratch resistant tempered glass substrate is disclosed. Said method of making scratch resistant tempered glass involves coating material composition on the said glass substrate comprising water- soluble metal salt and water-soluble binder material, drying the glass substrate, and heating the substrate above the pyrolysis temperature to diffuse metal ions into the substrate and followed by rapid quenching to form a transparent or coloured tempered glass substrate having an improved scratch resistant in a shorter time. In another aspect of the present disclosure, the method of making scratch resistant tempered glass substrate comprising coating of metal salt solution on the said glass substrate having metal concentration of 0.1N and above.

In one another aspect of the present disclosure, the method of making scratch resistant tempered glass substrate imparting scratch resistant property of the tempered glass substrate in a shorter time.

In further aspect of the present disclosure, a scratch-resistant tempered glass substrate is disclosed. Said scratch-resistant tempered glass substrate obtained from said method having improved scratch resistant at upto ION measure according to ISO 4586-2.

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

DETAILED DESCRIPTION

The term ‘glass substrate’ or ‘transparent substrate’, as used herein, interchangeably, refers to a solid-like and transparent material that is used in numerous applications in our daily lives. As referred herein, the substrate is glass which is made from natural and abundant raw materials (sand, soda ash and limestone) that are melted at very high temperature to form a new material.

The present disclosure provides a method of making scratch resistant tempered glass substrate. Said method of making scratch resistant tempered glass involves coating of metal solution on the said glass substrate, drying the glass substrate, heating the substrate at a temperature above the pyrolysis temperature to diffuse metal ions into the substrate and followed by rapid quenching, thereby forming a transparent or coloured tempered glass substrate having an improved scratch resistance in a shorter time.

The said method of making scratch resistant tempered glass substrate avoids a multi- step deposition and immersion processes and improves the scratch resistant property of the tempered glass substrate in a shorter time. In every embodiment of the present disclosure, the metal solution comprising water- soluble metal salts and water-soluble polymer binder.

In every embodiment of the present disclosure, drying of said glass substrate happens at temperature from 50 to 70°C, preferably the curing temperature is 60°C.

In every embodiment of the present disclosure, curing time of said glass substrate is from 2 to 10 minutes, preferably 5 minutes.

In a preferred embodiment of the present disclosure, the water-soluble metal salt is selected from the group comprising silver nitrate or cupric chloride.

In a preferred embodiment of the present disclosure, the metal solution comprising water-soluble metal salt in an amount of 20 to 30 wt%.

In a preferred embodiment of the present disclosure, the concentration of the water- soluble metal salt in salt solution is 0. IN and above.

The first and foremost challenge in coating metal solution on glass is understanding challenges with regards to wetting on glass. Due to the contact angle differences and surface energies, the salt solutions are known to have poor wetting on glass making the coating non-homogenous and difficult to work with. It therefore became important to develop a binder system which would work with the salt solution that would provide enough wetting and make the coating uniform.

In a preferred embodiment of the present disclosure, the binder polymer material is water soluble polymers. Wherein the said water-soluble polymer is selected from group comprising polyvinyl alcohol (PVA), carboxy methyl cellulose or their combination thereof. In a preferred embodiment of the present disclosure, the metal solution comprising water-soluble polymer binder in an amount of 70 to 80 wt%.

In a preferred embodiment of the present disclosure, the metal solution comprising 25 wt% of silver nitrate and 75 wt% of polyvinyl alcohol (PVA).

In a preferred embodiment of the present disclosure, the coating of metal solution can be applied using spray coater or bar coater.

In every embodiment of the present disclosure, heating the glass substrate at temperature of from 680°C to 730°C which is above the pyrolysis temperature of the polymer for a period of from 2 to 5 minutes, preferably for a period of 180 seconds, followed by rapid quenching imparts a tempered glass substrate having an improved scratch resistance.

In a preferred embodiment of the present disclosure, the heating temperature of the glass substrate at top and bottom is between 705°C- 710°C.

In every embodiment of the present disclosure, heating the substrate at a temperature above the pyrolysis temperature of the polymer allows polymer to decompose and helps to diffuse metal ions into the substrate in order to form a glass substrate having an improved scratch resistance.

The present disclosure also provides a scratch -resistant tempered glass substrate obtained by the process comprising the steps of coating of a material composition on the said glass substrate comprising of metal salt solution and water-soluble binder material, curing the glass substrate, and heating the substrate at a temperature above the pyrolysis temperature of the polymer thus imparts the scratch-resistant tempered glass substrate.

In every embodiment of the present disclosure, the glass substrate having an improved scratch resistance of ION measured using a tungsten carbide tip. In one embodiment of the present disclosure, the scratch-resistant tempered glass substrate is colored glass substrate or transparent glass substrate.

Metal type and its concentration decides the colour of the glass. While silver led to an amber colour whose intensity varied with concentration of silver ions, time of tempering and temperature of the furnace, application of CuCh to glass led to an interesting ruby coloration of glass. Coloured glass produced from the said process also gives an aesthetic appearance to the scratch resistant tempered glass substrates of the present disclosure.

Preferably, the scratch-resistant tempered glass substrate according to the present disclosure, may be used exterior architectural applications like balustrades, railings, windows glass, door glass and facade as well as automotive applications such as windshield, sidelite windows, backlites, may be used in interior glasses such as shower glass, kitchen shutters, glass furniture and mirror, may also be used in value added glasses such as frosted (acid etched, sand blasted or grit blasted) glass and glass with ceramic frit coating.

EXAMPLES

Example 1

Experimental study of binder salt selectivity

The first and foremost challenge in coating salt solution on glass is understanding challenges with regards to wetting on glass. Due to the contact angle differences and surface energies, the salt solutions are known to have poor wetting on glass making the coating non-homogenous and difficult to work with. It therefore became important to develop a binder system which would work with the salt solution that would provide enough wetting and make the coating uniform. Four different binders were chosen for this study. PVA (Pyrolysis temperature of - 200 degC), a combination of setalux and DAA (Pyrolysis temperature of - 100 deg C) , a combination of setalux, tol onate and DAA (Pyrolysis temperature of - 100 deg C) and Carboxy methyl cellulose (CMC) (Pyrolysis temperature of - 200 degC). While PVA and CMC are aqueous systems, the other two binder systems chosen were non-aqueous in nature. The ratio of binder to salt system used the wet weight of the coating and drying conditions are provided in the table below. It can be understood from the table 1 that PVA worked best for silver nitrate solution and provided a uniform coating. It is also to be noted that the same binder systems were not effective in obtaining a uniform coating with copper salts, indicating a binder-salt selectivity existing in these systems.

Table 1. Experimental details of binder salt selectivity studies showing 4 different binder systems with salt: binder ratios

The coating was done using a bar applicator and dried at 60 deg C for 5 minutes in a drying oven. The weight of the coating deposited on the substrate is also captured. It is to be noted that aqueous systems formed a uniform coating due to solubility of silver nitrate solution in water compared to solvent based systems.

Example 2

Preparation of coating formulation

The formulation for coating on glass was prepared by mixing of silver nitrate solution in 3 different concentrations (0.01 N, 0. IN and IN) with a binder solution of 10% PVA (by weight). The ratio of Binder : salt was maintained at 75%: 25% by weight for all 3 concentrations mentioned above.

These 3 formulations were coated on glass using a bar applicator. The same can be applied on glass using spray coating method as well. Wet weight of coating was maintained the same for all 3 concentrations with +/-5% variation to ensure uniformity of coating across all the three samples. Coated glass substrates were dried at 60 deg C for 5 minutes in a drying oven and drying condition are listed in table 2. After drying, the coated glass substrates were tempered at temperature between 705°C- 710°C for about 3 minutes to obtain tempered glass substrate with improved scratch resistance.

Table 2: The list of experiments conducted along with drying conditions are listed

Scratch resistance test The coated and tempered samples are analysed for scratch resistance using a universal scratch tester and the testing procedure is carried out in accordance to ISO 4586-2. A 100 mm x 100mm glass of 4mm thickness is used for this purpose. The sample is placed at the centre of the horizontal table. A diamond tip is used for testing the scratch resistant of the glass. The height of the arm is adjusted so the arm of the equipment rests on the sample. Scratches are made starting from IN and repeated for 2N, 4N,6N and so on as per ISO 4586-2. The load at which continuous scratch mark appears on the surface is noted down. The test was repeated for annealed glass, tempered glass (without coating) and ion diffused glass of three different concentrations mentioned in Table 3.

It was found that scratch appeared on annealed glass at a load of 5N, whereas for the ion diffused glass starting from a concentration of 0.1 N silver nitrate, no scratch appeared even at 10N force that was applied. It is to be noted that 10N force is the maximum load for the instrument and additional force cannot be applied to check the yielding point at which scratch begins to appear on glass. The results were consistent for both copper and silver ions.

Table 3. Scratch test (UST) results showing how scratch improves between clear tempered glass and ion diffused glass from 0.1 N concentration to 1 N concentration

The improved scratch resistance of ion diffused glass post tempering can be attributed to conversion of silver ions to silver nano particles which in turn form nano particle clusters. The number of nanoparticles increase as the concentration of the silver nitrate solution increases. The threshold limit of 0.01 N silver nitrate solution does not provide enough silver particles to develop the scratch resistance required. This is an inter-ion diffusion process governed by time and temperature. The molten alkali metal ions diffuse out of the glass matrix while the silver ions replace the alkali ions and are reduced to silver metallic particles.

Claims

We Claim,

1. A method of making scratch-resistant tempered glass substrate, involves: a) coating of a metal solution on the said glass substrate comprising 20 to 30 wt% of water-soluble metal salt and 70 to 80 wt% of water-soluble polymer binder; b) drying the glass substrate; and c) heating the substrate at a temperature above the pyrolysis temperature of the polymer to form a tempered glass substrate having an improved scratch resistant.

2. The method of making scratch -resistant glass substrate as claimed in claim 1, wherein the water-soluble metal salt is selected from the group comprising silver nitrate or cupric chloride.

3. The method of making scratch-resistant glass substrate as claimed in claim 1 and 2, wherein the metal solution comprising silver nitrate solution in amount of 25 wt%.

4. The method of making scratch -resistant glass substrate as claimed in claim 1, wherein the glass substrate is dried at temperature from 50 to 70°C for 2 to 10 minutes.

5. The method of making scratch -resistant glass substrate as claimed in claim 1, wherein the glass substrate is heated at temperatures ranging from 680°C to 730°C period of 2 to 5 minutes to diffuse metal ions into the substrate, followed by rapid quenching for 2 to 5 minutes, thereby forming a transparent or coloured tempered glass substrate having an improved scratch resistant.

6. The method of making scratch-resistant tempered glass substrate as claimed in claim 1, wherein the concentration of the water-soluble metal salt is 0.1N and above.

7. The method of making scratch-resistant tempered glass substrate as claimed in claim 1, wherein the water-soluble polymer binder is selected from group comprising polyvinyl alcohol (PVA), Carboxy methyl cellulose or a combination thereof.

8. The method of making scratch-resistant glass substrate as claimed in claim 1 and 2, wherein the metal solution comprising polyvinyl alcohol (PVA) in amount of 75 wt%.

9. The method of making scratch-resistant tempered glass substrate as claimed in claim 1, wherein the coating of metal salt solution can be applied using spray coater or bar coater.

10. The method of making scratch-resistant tempered glass substrate as claimed in claim 1 and 4, wherein the heating temperature at top and bottom of the substrate is between 705°C and 710°C.

11. The method of making scratch-resistant tempered glass substrate as claimed in claim 1 and 4, wherein the heating time is 180 seconds.

12. A scratch -resistant tempered glass substrate obtained from a method as claimed in claim 1, characterized in that the glass substrate is free of scratches at upto ION measure according to ISO 4586-2.

13. The scratch-resistant tempered glass substrate as claimed in claim 12, wherein the glass substrate is colored or transparent.