WO2017041307A1

WO2017041307A1 - Method for producing a toughened glass article with a durable functional coating and a toughened glass article with a durable functional coating

Info

Publication number: WO2017041307A1
Application number: PCT/CN2015/089476
Authority: WO
Inventors: Yigang Li; Guangjun Zhang; Pengshu LIU; Hiroshi Kanda; Jochen Alkemper
Original assignee: Schott Glass Technologies (Suzhou) Co. Ltd.
Priority date: 2015-09-11
Filing date: 2015-09-11
Publication date: 2017-03-16
Also published as: CN108025962A; CN108025962B

Abstract

A method for producing a toughened glass article with a functional coating comprises providing a chemically toughened glass substrate with a first and a second face and a thickness (t) there between. The glass substrate has a surface layer with a compressive stress (CS) extending to a depth-of-layer (DoL) below the first and/or second face. The method further comprises applying a sol-gel coating to the first and/or the second face of said glass substrate and curing the sol-gel coating by heating it to curing temperatures above T _a-200 ^oC during a curing time t _c to produce the durable functional coating. The curing time t _c satisfies formula (I) wherein T _a is the temperature at the annealing point of the glass material of the glass substrate and T _c is the maximum curing temperature, where T _a and T _c are given in ^oC. Further provided is a toughened glass article with a durable functional coating, in particular produced by the method according to the invention.

Description

Method for producing a toughened glass article with a durable functional coating and a toughened glass article with a durable functional coating

Field of invention

The invention concerns toughened glass or glass ceramics articles with a durable functional coating and a method for production thereof， where the durable functional coating is a sol-gel coating.

Background of the invention

The market of consumer electronics， e.g. wearable devices as smart phones or tablets， requires glass articles with coated surfaces as e.g. cover glasses for touchscreens. Typical coatings are e.g. antireflection coatings (AR) ， anti-microbial coatings (AM) ， anti-glare coatings (AG) ， and anti-fingerprint coatings (AF) etc. The coatings need to have a high abrasive resistance in order to resist the mechanical strain occurring during daily use. The coated glass article should thereby be very thin in order to minimize volume and weight of the final product. Such coated glass articles should also exhibit very high durability during daily use and have the necessary strength and flexibility e.g. for sufficient protection of the underlying components. Common applications often also require only single-sided coatings， i.e. asymmetric coatings where only one of the surfaces of a glass sheet is coated， since the glass article needs to be directly bonded with a preferably uncoated surface to an underlying component as e.g. a display.

In order to improve the durability or strength of glasses， it is generally known to thermally or chemically pre-stress or toughen the glass. Thermal pre-stressing or toughening incorporates quickly quenching the glass from a heated state. During quenching， the surfaces of the glass cool quicker than the interior， resulting in solidification of the surface layers while the interior is still viscous. The temperature difference to the outer environment is thus larger in the interior than at the surfaces of the glass. The interior would therefore subsequently further contract which is prevented by the already solidified surface layers. As a result， a tensile stress builds up in the interior while a compressive stress forms in the surface layers. Chemical toughening or hardening， in contrast， is a result of exchanging smaller ions as e.g. lithium and/or sodium ions in a surface layer of the glass by larger ions as e.g. potassium， rubidium and/or cesium ions. Due to the larger volume required by the larger ions， a compressive stress is induced in the glass network in the ion-exchanged surface layers which is countered by a tensile stress in the interior of the glass where no ion-exchange occurred.

Thermal toughening is a rather low-cost method for achieving a higher durability or hardness of the glass but has some disadvantageous as compared to chemical toughening. In particular in the case of thin and very thin glass sheets it is not possible to establish a large enough temperature gradient in order to achieve the necessary tensile-compressive stress configuration. Furthermore， thermally toughened glasses cannot be cut after the toughening is completed.

A generally preferable and low-cost method for coating glasses or glass ceramics is coating by sol-gels. During sol-gel coating， a sol is applied to the surfaces of a glass substrate. An oxide layer is then produced from the sol or the sol-gel formed on the surface by densifying the sol or sol-gel via thermal curing where residual organics and other liquid components of the sol-gel are evaporated. The densifying typically requires annealing the wet sol-gel layer by heating the coated glass to temperatures up to 450℃for more than 1 hour. For example， SiO₂ layers can be produced by sols which comprise TEOS (Tetraethyl-orthosilicate， also known as Tetra-ethoxysilan) as a precursor. For high refractive layers， Titanium oxide layers can also be produced by sol-gel methods. A common precursor for such layers is TTIP (titanium-tetraisopropoxide) . Exemplary applications of sol-gel coatings comprise interference stacks of layers as e.g. anti-reflective coatings of glasses.

The necessary thermal curing for forming a durable sol-gel coating， however， is a particular problem for toughened glasses since the subsequent heating of thermally or chemically toughened glasses can lead to a relaxation of the stresses in the glass and thus can annihilate at least in part the stresses built-up during the toughening process.

In order to circumvent this problem， sol-gel coatings were proposed e.g. in DE 10 2007 009 786 A1 which allow ion-exchange after the sol-gel coating has been applied. The sol-gel coating is thereby at least partially permeable and allows the migration of larger ions as e.g. potassium ions to the surface of the glass substrate. However， such processes cannot be applied in the case of single-sided coatings where the coating is only applied to one of the surfaces of a glass sheet. The sol-gel coating， even though being permeable to the ion-exchange， inhibits the ion-exchange to a certain degree. As a result， asymmetric surface compressive stresses build up which， in particular in the case of thin or very thin glasses， result in uncontrollable warping of the glass sheet， ultimately rendering the coated glass unusable for many applications.

It is therefore an object of the present invention to overcome the disadvantages in the prior art. In particular， it is an object of the invention to provide a coated glass article and a method for producing such a coated glass article which has high durability and strength. It is a further object of the invention to provide a low-cost coated glass article and method for producing such a coated glass article which is easy and reliable to produce. Furthermore， it is an object of the invention to provide an asymmetrically coated glass article with sufficient durability or strength and negligible warp for the application in wearable or mobile consumer electronics and a method for producing such a glass article.

Description of the invention

The following terminologies and abbreviations are adopted herein：

- The term “glass article” is used in its broadest sense to include any object made of glass， ceramics and/or glass ceramics. As used herein， ″thin″ glass refers to thicknesses in the range of approx. 0.4 to 0.7 mm whereas “ultrathin glass” refers to glasses and glass sheets or articles with a thickness of equal or less than 0.4 mm， unless otherwise specified. Exemplary glass compositions optimized for thin and ultrathin forming and applications requiring ultrathin glasses are e.g. described in PCT/CN2013/072695 by

- Compressive stress (CS) ： A compressive stress that is chemically or thermally induced in a surface layer in the glass network by e.g. ion-exchange (chemical toughening) or thermal quenching (thermal toughening) which is sustained as additional stress in the glass network of the surface layer. CS can be measured by the commercially available stress measuring instrument FSM6000 based on an optical principle.

- Depth-of-layer (DoL) ： The thickness of the surface layer exhibiting the surface compressive stress CS. DoL can be measured by the commercially available stress measuring instrument FSM6000 based on an optical principle.

The objects of the invention are solved by a method for producing a toughened glass article with a durable functional coating and such a toughened glass article according to the independent claims. Further， the objects of the invention are solved by the use of such a toughened glass article according to a further independent claim.

The invention is based on the surprising insight that a sol-gel coating can be cured to the necessary density for relevant applications by rapidly heating the sol-gel coating to a comparatively high temperature， e.g. around or above the temperature T_a of the annealing point， for comparatively short times， e.g. tens of seconds or even seconds. The annealing point is hereby defined as the temperature T_a at which the viscosity of the glass material is η＝10¹³ dPas. Thereby， the sol-gel coating can be cured to the desired durability or hardness while the toughening parameters as surface compressive stress (CS) or depth-of-layer (DoL) can essentially be maintained with no significant deterioration of the toughness or hardness of the glass substrate.

The method for producing a toughened glass article with a functional coating according to the invention comprises：

- providing a， preferably chemically， toughened glass substrate with a first and a second face and a thickness there between，

- said glass substrate having a surface layer with a compressive stress (CS) extending to a depth-of-layer (DoL) below said first and/or second face，

- applying a sol-gel coating to the first and/or the second face of said glass substrate，

- curing the sol-gel coating by heating it to curing temperatures above T_a-200℃during a curing time t_c to produce said durable functional coating， where the curing time t_c satisfies

and T_a is the temperature at the annealing point of the glass material of the glass substrate and T_c is the maximum curing temperature， where T_a and T_c are given in ℃.

It has surprisingly been found that for such comparatively high curing temperatures with a maximum of T_c， curing times t_c satisfying the above mentioned condition are generally sufficient to cure the sol-gel coating to the desired density or hardness， in particular a pencil hardness≥7H， preferably≥9H. During such short times， it has also unexpectedly turned out that the toughening parameters in the toughened surface layer of the glass substrate can be maintained without significant deterioration， even at the comparatively high temperatures of T_c.

It has been found that， on the one hand， the higher T_c is chosen， the faster the toughening parameters deteriorate. On the other hand， higher T_c results in better coating durability. The same is true for longer t_c： longer curing allows for better densifying but also results in stronger deterioration of the toughening parameters. Based on this insight， numerous experiments were conducted in order to find the ideal conditions for the high-temperature curing of the sol-gel coating according to the invention. It has generally been found that higher curing temperatures T_c with the corresponding shorter curing times t_c are preferred than lower curing temperatures with longer curing times.

Whereas it is essentially possible that the curing only comprises heating and cooling to and from the maximum curing temperature T_c in the relevant temperature range， it has been found that the heating and cooling times are preferably chosen as short as possible while the maximum curing temperature T_c is maintained essentially constant for a peak time t_c′ . The peak time t_c′ preferably satisfies the condition

(T_c-T_a) +30 s. More preferably， the curing time t_c′ satisfies

s. Preferably， the heating from T_a-200℃ to T_c and the cooling from T_c to T_a-200℃occurs on negligible timescales and， in particular for industrial applications， is effected essentially instantaneously. In this case， the curing time t_c and the peak time t_c′ can essentially be identified.

It has surprisingly been found that the thus cured sol-gel coating can be sufficiently densified to excellent durability as can be shown in e.g. pencil hardness test and/or steel wool abrasion tests. It has been shown that the cured functional coating achieved by the method according to the invention can reach a pencil hardness≥7H and even≥9H. With an anti-fingerprint (AFP) coating on the top-most layer of the sol-gel coating， 10′000 abrasion cycles (1 kg weight on 2 cm x 2 cm area with 0000#steel wool) with critical water contact angle＞100° can be passed. It has also been found that the surface compressive stress (CS) of the toughened glass substrate as well as the depth-of-layer (DoL) can be maintained within a deviation of equal or less than 10％or even equal or less than 5 ％of the corresponding values prior to curing the sol-gel coating. As such， the method according to the invention offers a cost-effective method for applying a durable functional coating to a glass substrate.

It is to be understood that the method of the invention can generally also be applied in combination with other coating methods of the glass substrate which exemplarily comprise CVD or PVD coating methods or chemical or physical vapor deposition. It is also to be understood that the toughening of the glass substrate can either be thermal toughening or chemical toughening by ion-exchange. An advantage of chemically toughened glass substrates is that they can be further processed after the toughening， e.g. can be cut to the desired dimensions or shape. The coating of the glass substrate can in this case occur prior or after the cutting of the glass.

The presently preferred sol-gel process utilizes a reaction of metal-organic starting materials in the dissolved state to form the layers. As a result of controlled hydrolysis and condensation reaction of the metal-organic starting materials， a metal oxide network structure is built up， i.e. a structure in which the metal atoms are joined to one another by oxygen atoms， in tandem with the elimination of reaction products such as alcohol and water. The hydrolysis reaction here can be accelerated by addition of catalysts.

A common feature of all sol-gel reactions is that molecularly disperse precursors first undergo hydrolysis， condensation， and polymerization reactions to form particularly disperse or colloidal systems. Depending on the selected conditions， ″primary particles″ formed first of all may grow further， may undergo aggregation to form clusters， or may form more linear chains The resulting units cause microstructures which arise as a result of the removal of the solvent. In an ideal case， the material may be fully compacted thermally， but in reality there often remains a considerable degree of residual porosity.

The inorganic sol-gel material from which the sol-gel layers are produced is preferably a condensate， more particularly comprising one or more hydrolysable and condensable or condensed silanes and/or metal alkoxides， preferably of Si， Ti， Zr， Al， Nb， Hf and/or Ge， B， Sn， Zn. With preference， the groups cross-linked in the sol-gel process by way of inorganic hydrolysis and/or condensation may be， for example， the following functional groups： TiR₄， ZrR₄， SiR₄， AlR₃， TiR₃ (OR) ， TiR₂ (OR) ₂， ZrR₂ (OR) ₂， ZrR₃ (OR) ， SiR₃ (OR) ， SiR₂ (OR) ₂， TiR (OR) ₃， ZrR (OR) ₃， AlR₂ (OR) ， AlR (OR) ₂， Ti (OR) ₄， Zr (OR) ₄， Al (OR) ₃， Si (OR) ₄， SiR (OR) ₃ and/or Si₂ (OR) ₆， and/or one of the following substances or groups of substance with OR： alkoxy such as， preferably， methoxy， ethoxy， n-propoxy， isopropoxy， butoxy， isopropoxyethoxy， methoxypropoxy， phenoxy， acetoxy， propionyloxy， ethanolamine， diethanolamine， tiethanolamine， methacryloyloxypropyl， acrylate， methacrylate， acetylacetone， ethyl acetoacetate， ethoxyacetate， methoxyacetate， methoxyethoxyacetate and/or methoxyethoxyethoxyacetate， and/or one of the following substances or groups of substances with R： Cl， Br， F， methyl， ethyl， phenyl， n-propyl， butyl， allyl， vinyl， glycidylpropyl， methacryloyloxypropyl， aminopropyl and/or fluoroctyl.

A further improvement in the chemical stability and in the adhesion promoter layer function is achieved by treating the solution with small amounts of an admixture agent which is dispersed homogeneously in the solution and is also dispersed in the later layer， where it forms a mixed oxide. Suitable admixture agents are hydrolysable or dissociating inorganic salts， optionally with water of crystallization， of tin， aluminum， phosphorus， boron， cerium， zirconium， titanium， cesium， barium， strontium， niobium， or magnesium， e.g.， SnCl₄， SnCl₂， AlCl₃， Al (NO₃) ₃， Mg (NO₃) ₂， MgCl₂， MgSO₄， TiCl₄， ZrCl₄， CeCl₃， Ce (NO₃) ₃， and the like. These inorganic salts can be used both in hydrous form and with water of crystallization.

The admixture agent used may be one or more of the metal alkoxides of tin， aluminum， phosphorus， boron， cerium， zirconium， titanium， cesium， barium， strontium， niobium， or magnesium， preferably of titanium， zirconium， aluminum， or niobium. Also suitable are phosphoric esters， such as methyl phosphate or ethyl phosphate， phosphorus halides， such as chlorides and bromides， boric esters， such as ethyl， methyl， butyl， or propyl esters， boric anhydride， BBr₃， BCl₃， magnesium methoxide or ethoxide， and the like.

Complexing agents which can be used include， for example， ethyl acetoacetate， 2， 4-pentanedione (acetylacetone) ， 3， 5-heptanedione， 4， 6-nonanedione， or 3-methyl-2， 4-pentanedione， 2-methylacetylacetone， triethanolamine， diethanolamine， ethanolamine， 1， 3-propanediol， 1， 5-pentanediol， carboxylic acids such as acetic acid， propionic acid， ethoxy acetic acid， methoxy acetic acid， polyethercarboxylic acids (e.g.， ethoxyethoxy acetic acid) ， citric acid， lactic acid， methylacrylic acid， and acrylic acid.

The sol-gel composition for the coating can generally comprise hydrolysable compounds or salts of at least one of the elements of main-groups III to V of the periodic table， as e.g. Si or Al， and/or the transition element groups II to V of the periodic table， as e.g. Sn， Zn， Zr， Nb， Ta， V， and/or hydrolysable compounds of Lanthanides as e.g. Ce. Also， other hydrolysable compounds can be used as compounds of elements of e.g. main-groups I and II， as e.g. Li， Ca， Mg， and/or of the transition element groups VI to VIII， as e.g. Mn， Cr， Ni. The sol-gel coating after curing comprises the corresponding oxides of the above mentioned elements. Particular relevance for optical， in particular interference optical， coatings have oxides of the metals Ti， Si， Nb， Ta， Al， or Zr.

The sol-gel coating can further comprise a nanoparticle component which can improve the flexibility and tensile strength of the coating after curing. Layers with a nanoparticle component can be， dependent on the configuration of the nanoparticles， comparatively soft and porous. Preferably， the sol-gel condensate can be filled with the nanoparticle component and/or their thermal transformation or decay products. The nanoparticle can comprise nanowires and/or nanofibers and/or nano-chains and/or nano-tubes and/or nano-core-shell particles and/or hollow spheres. Further attributes of useful nanoparticles in this context can be found in the art.

The glass substrate preferably comprises an alkali containing glass composition. Preferred glasses are e.g. lithium aluminosilicate glasses， soda-lime glasses， borosilicate glasses， alkali metal aluminosilicate glasses， and aluminosilicate glass with low alkali content. Such glasses can be produced by e.g. drawing as e.g. down-draw processes， overflow-fusion or float processes. These glasses are particularly suitable for an ion-exchange treatment in order to provide the toughened glass substrate. In a preferred embodiment， the glass substrate comprises a lithium aluminosilicate glass with the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	55-69
Al₂O₃	18-25	SiO₂	55-69
Al₂O₃	18-25	Li₂O	3-5
Na₂O+K₂O	0-30	Li₂O	3-5
Na₂O+K₂O	0-30	MgO+CaO+SrO+BaO	0-5
ZnO	0-4	MgO+CaO+SrO+BaO	0-5
ZnO	0-4	TiO₂	0-5
ZrO₂	0-5	TiO₂	0-5
ZrO₂	0-5	TiO₂+ZrO₂+SnO₂	2-6
P₂O₅	0-8	TiO₂+ZrO₂+SnO₂	2-6
P₂O₅	0-8	F	0-1
B₂O₃	0-2	F	0-1

Preferably， the lithium aluminosilicate glass comprises the following glass composition in weight％：

Composition	weight-％
Composition	weight-％	SiO₂	57-66
Al₂O₃	18-23	SiO₂	57-66
Al₂O₃	18-23	Li₂O	3-5
Na₂O+K₂O	3-25	Li₂O	3-5
Na₂O+K₂O	3-25	MgO+CaO+SrO+BaO	1-4
ZnO	0-4	MgO+CaO+SrO+BaO	1-4
ZnO	0-4	TiO₂	0-4
ZrO₂	0-5	TiO₂	0-4
ZrO₂	0-5	TiO₂+ZrO₂+SnO₂	2-6
P₂O₅	0-7	TiO₂+ZrO₂+SnO₂	2-6
P₂O₅	0-7	F	0-1
B₂O₃	0-2	F	0-1

Further preferably， the lithium aluminosilicate glass comprises the following glass composition in weight％：

Composition	weight-％
Composition	weight-％	SiO₂	57-63
Al₂O₃	18-22	SiO₂	57-63
Al₂O₃	18-22	Li₂O	3.5-5
Na₂O+K₂O	5-20	Li₂O	3.5-5
Na₂O+K₂O	5-20	MgO+CaO+SrO+BaO	0-5
ZnO	0-3	MgO+CaO+SrO+BaO	0-5
ZnO	0-3	TiO₂	0-3
ZrO₂	0-5	TiO₂	0-3
ZrO₂	0-5	TiO₂+ZrO₂+SnO₂	2-5
P₂O₅	0-5	TiO₂+ZrO₂+SnO₂	2-5
P₂O₅	0-5	F	0-1
B₂O₃	0-2	F	0-1

In another preferred embodiment， the glass substrate comprises a soda-lime glass with the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	40-81
Al₂O₃	0-6	SiO₂	40-81
Al₂O₃	0-6	B₂O₃	0-5
Li₂O+Na₂O+K₂O	5-30	B₂O₃	0-5
Li₂O+Na₂O+K₂O	5-30	MgO+CaO+SrO+BaO+ZnO	5-30
TiO₂+ZrO₂	0-7	MgO+CaO+SrO+BaO+ZnO	5-30
TiO₂+ZrO₂	0-7	P₂O₅	0-2

Preferably， the soda-lime glass comprises the following glass composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	50-81
Al₂O₃	0-5	SiO₂	50-81
Al₂O₃	0-5	B₂O₃	0-5
Li₂O+Na₂O+K₂O	5-28	B₂O₃	0-5
Li₂O+Na₂O+K₂O	5-28	MgO+CaO+SrO+BaO+ZnO	5-25
TiO₂+ZrO₂	0-6	MgO+CaO+SrO+BaO+ZnO	5-25
TiO₂+ZrO₂	0-6	P₂O₅	0-2

Further preferably， the soda-lime glass comprises the following glass composition in weight％：

Composition	weight-％
Composition	weight-％	SiO₂	55-76
Al₂O₃	0-5	SiO₂	55-76
Al₂O₃	0-5	B₂O₃	0-5
Li₂O+Na₂O+K₂O	5-25	B₂O₃	0-5
Li₂O+Na₂O+K₂O	5-25	MgO+CaO+SrO+BaO+ZnO	5-20
TiO₂+ZrO₂	0-5	MgO+CaO+SrO+BaO+ZnO	5-20
TiO₂+ZrO₂	0-5	P₂O₅	0-2

In another preferred embodiment， the glass substrate comprises a borosilicate glass with the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	60-85
Al₂O₃	0-10	SiO₂	60-85
Al₂O₃	0-10	B₂O₃	5-20
Li₂O+Na₂O+K₂O	2-16	B₂O₃	5-20
Li₂O+Na₂O+K₂O	2-16	MgO+CaO+SrO+BaO+ZnO	0-15
TiO₂+ZrO₂	0-5	MgO+CaO+SrO+BaO+ZnO	0-15
TiO₂+ZrO₂	0-5	P₂O₅	0-2

Preferably， the borosilicate glass comprises the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	63-84
Al₂O₃	0-8	SiO₂	63-84
Al₂O₃	0-8	B₂O₃	5-18
Li₂O+Na₂O+K₂O	3-14	B₂O₃	5-18
Li₂O+Na₂O+K₂O	3-14	MgO+CaO+SrO+BaO+ZnO	0-12
TiO₂+ZrO₂	0-4	MgO+CaO+SrO+BaO+ZnO	0-12
TiO₂+ZrO₂	0-4	P₂O₅	0-2

Further preferably， the borosilicate glass comprises the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	63-83
Al₂O₃	0-7	SiO₂	63-83
Al₂O₃	0-7	B₂O₃	5-18
Li₂O+Na₂O+K₂O	4-14	B₂O₃	5-18
Li₂O+Na₂O+K₂O	4-14	MgO+CaO+SrO+BaO+ZnO	0-10
TiO₂+ZrO₂	0-3	MgO+CaO+SrO+BaO+ZnO	0-10
TiO₂+ZrO₂	0-3	P₂O₅	0-2

In another preferred embodiment， the glass substrate comprises an alkali metal aluminosilicate glass with the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	40-75
Al₂O₃	10-30	SiO₂	40-75
Al₂O₃	10-30	B₂O₃	0-20
Li₂O+Na₂O+K₂O	4-30	B₂O₃	0-20
Li₂O+Na₂O+K₂O	4-30	MgO+CaO+SrO+BaO+ZnO	0-15
TiO₂+ZrO₂	0-15	MgO+CaO+SrO+BaO+ZnO	0-15
TiO₂+ZrO₂	0-15	P₂O₅	0-10

Preferably， the alkali metal aluminosilicate glass comprises the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	50-70
Al₂O₃	10-27	SiO₂	50-70
Al₂O₃	10-27	B₂O₃	0-18
Li₂O+Na₂O+K₂O	5-28	B₂O₃	0-18
Li₂O+Na₂O+K₂O	5-28	MgO+CaO+SrO+BaO+ZnO	0-13
TiO₂+ZrO₂	0-13	MgO+CaO+SrO+BaO+ZnO	0-13
TiO₂+ZrO₂	0-13	P₂O₅	0-9

Further preferably， the alkali metal aluminosilicate glass comprises the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	55-68
Al₂O₃	10-27	SiO₂	55-68
Al₂O₃	10-27	B₂O₃	0-15
Li₂O+Na₂O+K₂O	4-27	B₂O₃	0-15
Li₂O+Na₂O+K₂O	4-27	MgO+CaO+SrO+BaO+ZnO	0-12
TiO₂+ZrO₂	0-10	MgO+CaO+SrO+BaO+ZnO	0-12
TiO₂+ZrO₂	0-10	P₂O₅	0-8

In another preferred embodiment， the glass substrate comprises an aluminosilicate glass with low alkali content with the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	50-75
Al₂O₃	7-25	SiO₂	50-75
Al₂O₃	7-25	B₂O₃	0-20
Li₂O+Na₂O+K₂O	0-4	B₂O₃	0-20
Li₂O+Na₂O+K₂O	0-4	MgO+CaO+SrO+BaO+ZnO	5-25
TiO₂+ZrO₂	0-10	MgO+CaO+SrO+BaO+ZnO	5-25
TiO₂+ZrO₂	0-10	P₂O₅	0-5

Preferably， the aluminosilicate glass with low alkali content comprises the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	52-73
Al₂O₃	7-23	SiO₂	52-73
Al₂O₃	7-23	B₂O₃	0-18
Li₂O+Na₂O+K₂O	0-4	B₂O₃	0-18
Li₂O+Na₂O+K₂O	0-4	MgO+CaO+SrO+BaO+ZnO	5-23
TiO₂+ZrO₂	0-10	MgO+CaO+SrO+BaO+ZnO	5-23
TiO₂+ZrO₂	0-10	P₂O₅	0-5

Further preferably， the aluminosilicate glass with low alkali content comprises the following composition in weight-％：

Composition	weight-％
Composition	weight-％	SiO₂	53-71
Al₂O₃	7-22	SiO₂	53-71
Al₂O₃	7-22	B₂O₃	0-18
Li₂O+Na₂O+K₂O	0-4	B₂O₃	0-18
Li₂O+Na₂O+K₂O	0-4	MgO+CaO+SrO+BaO+ZnO	5-22
TiO₂+ZrO₂	0-8	MgO+CaO+SrO+BaO+ZnO	5-22
TiO₂+ZrO₂	0-8	P₂O₅	0-5

The glasses used in the invention， in particular the above mentioned glasses， can also be modified. For example， the color can be modified by adding transition metal ions， rare earth ions as e.g. Nd₂O₃， Fe₂O₃， CoO， NiO， V₂O₅， MnO₂， TiO₂， CuO， CeO₂， Cr₂O₃. Inclusion of such modifying colorant can e.g. enrich the design of consumer electronics such as color requirements for back covers or can provide an additional function for the toughened glass article as e.g. as color filters. In addition， luminescence ions， such as transition metals and rare earth ions can be added in order to endow optical functions， such as optical amplifiers， LEDs， chip lasers etc. In particular， 0-5 weight-％of rare earth oxides can be added to introduce magnetic， photon or optical functions. Moreover， refining agents as e.g. As₂O₃， Sb₂O₃， SnO₂， SO₃， Cl， F， and/or CeO₂ can be added into the glass compositions in amounts of 0-2 weight-％.

The toughened glass article can also be provided with an anti-microbial function by applying an ion-exchange of the glass article in an Ag⁺-containing salt bath or a Cu²⁺-containing salt bath. After the ion-exchange the surface concentration of Ag⁺or Cu²⁺is higher than 10 μg/cm²， preferably higher than 50 μg/cm²， and more preferably higher than 100 μg/cm². The ultrathin glass with anti-microbial function could be applied for medical equipment such as computers or screens used in hospitals and consumer electronics.

It is to be understood that the sum of the components of the glass compositions amounts to 100 weight-％. Further preferred variations of such glasses can be found in e.g. PCT/CN2013/072695 and are hereby incorporated by reference.

The sol-gel coating can be cured by different heating means and the following exemplary setups can be envisaged as viable and， according to the requirements， preferred apparatus′ for implementing the method according to the invention.

Furnace： Since it takes some time for the heat to be transported from the face of the glass substrate to internal regions inside the glass substrate， the sol-gel coating can be heated while the glass substrate does not get significantly heated. In an industrial production setup， the sol-gel coated glass substrate can be quickly passed into a tunnel furnace (or similar) where a high temperature is maintained and the sol-gel coating immediately meets a very high temperature. Thereby， the heating time is negligibly short as compared to the time the sol-gel coating is cured at the curing temperature T_c. The coated glass-substrate is removed from the furnace before the toughened surface layer inside the glass can reach a temperature too high for maintaining the toughening parameters as e.g. CS and DoL of the stressed surface layer. Furnaces have the advantage of generally being cost-efficient and easy to setup and maintain.

UV irradiation： UV radiation is strongly absorbed at the faces of the glass substrate. UV irradiation can therefore be a very efficient way for curing the sol-gel coating. High power continues wave UV-lasers can be preferred. A certain amount of UV-energy is essentially only absorbed by the sol-gel coating which gets cured and densified whereas the glass substrate is negligibly heated. For example， TiO2 sol-gel coatings have proven to be a very good absorption material for UV-light.

CO₂-laser： CO₂-laser can be efficiently absorbed by glass material， so can essentially also be used for heating the glass surface. Due to the wavelengths of CO₂-lasers， a large amount of the irradiated energy is deposited by the glass substrate and not the sol-gel coating. However， an advantage of CO₂-laser can be that， as compared to furnaces， the irradiation time and doses to the glass faces can be precisely controlled. CO₂-laser can therefore be preferred but may require or elaborate fine tuning of the process parameters.

IR irradiation： IR irradiation suffers essentially of the same problem as mentioned above for CO₂-lasers. IR will rather heat the inside of the glass substrate and not only the coating. However， it has been found that IR-irradiation can be used indirectly， e.g. by way of a silicon wafer covering the coated glass substrate. The IR radiation heats the silicon wafer which in turn heats the coating. Direct IR irradiation yields a low efficiency.

Industrial microwave oven： Some glasses or glass-ceramics substrates do not absorb microwave radiation. For such glass substrates， heating by e.g. and industrial microwave oven can be a viable option. OH-groups in the sol-gel coating can efficiently absorb the microwaves thus improving the molecular dehydration process during sol-gel curing or densification.

Femtosecond laser： Femtosecond laser can also form a viable option due to the short pulsed extremely high energy release. The energy can thus be absorbed by sol-gel coating whereas the glass article is only marginally heated.

It has to be understood that the curing time and temperature in the case of locally applied heating， as it is e.g. case with lasers， correspond to the actual heating of the local area. Whereas the above examples from viable heating means for curing the sol-gel coating in a method according to the invention， it is to be understood that other heating means can also be applied and meet the requirements according to the invention.

As has already been stated in the above， it is generally advantageous if the heating time from T_a-200℃ to the maximum curing temperature T_c and/or the cooling time to cool the substrate from the curing temperature T_c to T_a-200℃ are as short as possible. The heating time from T_a-200℃ to the curing temperature T_c generally has to be less than the curing time t_c and is preferably equal or less than the peak time t_c′ . Preferably， the heating time is equal or less than 30 s， preferably equal or less than 20 s and further preferably equal or less than 10 s. The cooling time form T_c to T_a-200℃ generally has also to be less than the curing time t_c and is also preferably equal or less than the peak time t_c′ . Preferably， the cooling time is equal or less than 30 s， preferably equal or less than 20 s and further preferably equal or less than 10 s. More preferably， the heating and/or cooling time is of the order of seconds， in particular equal or less than 5 s. Subsequent to the cooling to T_a-200℃， the toughened glass article with the durable functional coating can be cooled to reom temperature at commonly applied cooling rates. In some setups， it might be preferable to pre-heat the sol-gel coating to a pre-heating temperature prior to the curing of the sol-gel. The pre-heating temperature should thereby be below T_a-200℃.

In a preferred embodiment of the method of the invention， the peak time t_c′ is equal or less than 40 s， preferably equal or less than 20 s， further preferably less than 10 s. In addition or alternatively， the curing temperature T_c is larger than 450℃， preferably equal or larger than 600℃， further preferably equal larger than 700℃. In further preferred embodiments， the maximum curing temperature T_c lies in the annealing range of the glass material and can preferably be equal or larger than T_a and/or T_g， where T_g is the glass transition temperature of the glass material. It is a surprising insight of the invention that the application of such high temperatures for the curing of a sol-gel coating on the face of an already toughened glass substrate essentially allows maintaining the toughening parameters as e.g. CS and DoL of the glass substrate whilst the sol-gel coating can be sufficiently densified to fulfill the requirements of the desired applications.

In a preferred embodiment of the method according to the invention， the glass substrate is provided with a thickness of the toughened glass substrate is equal or less than 1 mm， preferably equal or less than 0.7 mm， further preferably equal or less than 0.4 mm， further preferably equal or less than 0.2 mm， further preferably equal or less than 0.1 mm，further preferably equal or less than 0.05 mm， and further preferably equal or less than 0.01 mm. Selected preferred thicknesses for common applications are 5 μm， 10 μm， 15 μm， 25 μm， 30 μm， 35 μm， 55 μm， 70 μm， 80 μm， 130 μm， 145 μm， 160 μm， 190 μm， 210 μm， 250 μm， 280 μm， 500 μm， or 550 μm. It is to be understood， that the method according to the invention can also advantageously be applied to glasses with other thicknesses than the aforementioned.

In another embodiment of the method according to the invention， the functional coating comprises an anti-reflective and/or anti-glare and/or anti-microbial and/or a high-or semi-reflective coating.

Anti-reflective (AR) coating is a type of optical coating applied to the surface to reduce reflection and thereby improve the light transmission at a specific wavelength range. IR， visible or UV frequency are usual choices. The simplest interference AR coating consists of a single quarter-wave layer of transparent material whose refractive index is the square root of the substrate’s refractive index； this， theoretically， gives zero reflectance at the center wavelength and decrease reflectance for wavelengths in a broad band around the center. Multilayer AR coatings consist of transparent thin film structures with alternating layers of contrasting refractive index. Layers thicknesses are chosen to produce destructive interference in the beams reflected from the interfaces and constructive interference in the corresponding transmitted beams. Although being more complex and expensive， multilayer AR coatings can give special characteristics such as near-zero reflectance at multiple wavelengths or very low reflectivity over a broader band than single layer AR coating. AR coatings are used in a wide variety of applications where light passes through an optical surface and low loss or low reflection is desired.

According to the interference mechanism of AR coating， in principle， any known coatings may be used as an anti-reflection coating， only if their refractive index is appropriate. They may be applied by means of a liquid-phase coating， such as printing technology， spraying technology or sol-gel process. The anti-reflection coating may also be applied by means of a CVD coating， which may be， for example， a PECVD， PICVD， low-pressure CVD， or chemical gas-phase deposition at atmospheric pressure. The anti-reflection coating may also be applied by means of a PVD coating， which may be， for example， a sputtering， a thermal vaporization， or laser-beam， electron-beam， or light-arc vaporization.

According to the same interference mechanism of AR coating， high/semi reflective coatings can also be constructed by transparent thin film structures with alternating layers of contrasting refractive index. Layers thicknesses are chosen to produce constructive interference in the beams reflected from the interfaces and destructive interference in the corresponding transmitted beams. Such high/semi reflective coatings are used in a wide variety of applications where high/semi reflection is desired at some specific wavelength range， e.g. decorative colorful glass articles.

Anti-glare (AG) surface refers to a surface which can physically transform the light irradiating on it into a diffuse reflection rather than a specular reflection. AG surface is useful in situations where high transmission through a surface is not so important but low reflectivity is required. AG surfaces often work based on the scattering from their surface nanostructure. For instance， AG surface can be prepared by doping tiny particles into the coating layers or by making any texture or pattern on coating to increase the surface light diffusion.

Anti-microbial (AM) glass property usually is introduced to the glass surface by Ag-Na ion-exchange technology. Ag ions could diffuse into the glass surface under a depth around hundreds nanometers to tens micrometers by the ion-exchange mechanism between Ag ions and the alkali ions， usually Na ions， in the glass. Ag ions have a well-known cytotoxicity effect to microorganisms from inhibition of their growth to cell death. Antimicrobial glass surface may also be prepared by thermal tempering methods to diffuse heavy mental agents， e.g. Ag or Cu ions， into glass surface at high temperature.

Antimicrobial surface can also be prepared by coating technologies. In principle， all kinds of antimicrobial agents， from heavy metal materials like Ag or Cu mixtures or nanoparticles to complex organic drugs， could be deposited on glass surface as an antimicrobial coating.

In a further embodiment of the method according to the invention， the functional coating has a thickness of 50 nm to 1000 nm and/or comprises one or more， in particular four or six， layers. The layers can e.g. have an alternating sequence of high and low refractive indices as they are known in the art for functional coatings. It is to be understood that the one or more layer can also simultaneously fulfill several functions as e.g. interference layer and protective layer. The method according to the invention can also be applied for various functional coating configurations as they are known in the art and therefore not further described herein.

In an embodiment of the method according to the invention， the sol-gel coating is applied by a dip-coating process. Thereby， the glass substrate is submerged， i.e. dipped， into a sol-bath and then slowly removed from the sol-bath. The layer thickness can be chosen at very high precisions by adjusting the speed at which the glass substrate is removed from the sol-bath. However， other methods are also possible and can be preferred according to the requirements as e.g. spray coating which allows a comparatively quick application of the sol-gel coating. Other methods include e.g. spin-coating processes. In preferred embodiments， the sol-gel coating comprises several layers and during application， each layer is preferably applied with a pre-curing at about 200℃ for about 2 minutes prior to applying the subsequent layer in order to achieve sufficient stability and adhesion of the layers of the sol-gel coating.

In a further embodiment of the method according to the invention， the sol-gel coating is applied only to either the first or the second face of the glass substrate resulting in said glass article having the functional coating on only one of its faces. Such embodiments can only be achieved by the method according to the invention since the change in the toughening parameters as e.g. CS and/or DoL can be kept at a minimum during the sol-gel coating. In particular， it could be shown that the uncoated glass substrate and the coated glass substrate experience essentially the same change in toughening parameters during the curing process of the sol-gel coating according to the invention. This results in a minimized difference of the toughening parameters of the coated and uncoated faces of the glass article and， ultimately， resulting in a high precision one-sided coated glass article with minimal warp. Such high precisions cannot be achieved by conventional methods as e.g. chemically toughening the glass after a functional sol-gel coating has been applied and densified on onlyone face since even sol-gel coatings with very high permeability for the ion-exchange (after densifying) result in an unbalanced ion-exchange on the coated and uncoated face. As a result， the necessary precision of warp can generally not be achieved in this case.

In a further embodiment of the method according to the invention， the deviation of the compressive stress (CS) in the surface layer of the glass substrate after the curing of the sol-gel coating is at most 10％， preferably at most 5％of the corresponding value prior to the curing of the sol-gel coating. The deviation of the depth-of-layer (DoL) of the surface layer of the glass substrate after the curing of the sol-gel coating is at most 10％and preferably at most 5％of the corresponding value prior to the curing of the sol-gel coating. In particular in the case of one-sided coatings， the small deviations in the toughening parameters CS and DoL allow for a toughened glass article with a durable functional coating with deviations in warp that are smaller than could previously be achieved with glass articles having a sol-gel coating that were toughened after the coating.

In a further embodiment of the method according to the invention， the compressive stress (CS) in the surface layer of the toughened glass article after the curing of the functional coating is equal or larger than 250 MPa， preferably equal or larger than 400 MPa， further preferably equal or larger than 600 MPa， further preferably equal or larger than 800 MPa， further preferably equal or larger than 900 MPa， and/or the depth-of-layer (DoL) is equal or larger than 5 μm， preferably equal or larger than 10 μm， further preferably equal or larger than 20 μm， further preferably equal or larger than 30 μm， and further preferably equal or larger than 50 μm.

In a further embodiment of the method according to the invention the deviation in the warp of the toughened glass article after the curing of the sol-gel coating is at most 50％， preferably at most 30％， further preferably at most 10％of the corresponding value prior to the curing of the sol-gel coating.

For certain applications， for instance to introduce an AM property to the already coated surface， it may be advantageous to apply an ion-exchange procedure to the already toughened glass article with a functional coating. It is therefore well within the scope of the invention to apply an ion-exchange treatment to the toughened glass article after the curing of the sol-gel coating in a further embodiment of the method according to the invention.

The invention also concerns a toughened glass article with a durable functional coating， in particular a toughened glass article produced by a method according to the invention， comprising a， preferably chemically， toughened glass substrate with a first face and a second face and a thickness there between， where said glass substrate has a surface layer with a compressive stress (CS) extending to a depth-of-layer (DoL) below said first and/or second face， and where said glass substrate has a functional coating on at least one of the first or second face， wherein the durable functional coating is a result of a sol-gel coating process which is applied to the toughened glass substrate and has a pencil hardness≥7H， preferably≥9H.

In a preferred embodiment， the compressive stress (CS) in the surface layer of the toughened glass article is equal or larger than 250 MPa， preferably equal or larger than 400 MPa， further preferably equal or larger than 600 MPa， further preferably equal or larger than 800 MPa， further preferably equal or larger than 900 MPa， and/or the depth-of-layer (DoL) is equal or larger than 5 μm， preferably equal or larger than 10 μm， further preferably equal or larger than 20 μm， further preferably equal or larger than 30 μm， and further preferably equal or larger than 50 μm.

In a further preferred embodiment， the thickness of the glass substrate is equal or less than 1 mm， preferably equal or less than 0.7 mm， further preferably equal or less than 0.4 mm， further preferably equal or less than 0.2 mm， further preferably equal or less than 0.1 mm， further preferably equal or less than 0.05 mm， and further preferably equal or less than 0.01 mm.

In another preferred embodiment， the functional coating comprises an anti-reflective and/or anti-glare and/or anti-microbial and/or a high or semi-reflective coating.

In a further preferred embodiment， the toughened glass article has the functional coating only on either the first or the second face of the glass substrate.

In another preferred embodiment， the functional coating has a thickness of 50 nm to 1000 nm and comprises one or more， in particular four or six， layers.

Preferably， the functional coating is essentially free of Potassium and/or Rubidium and/or Cesium. Similar， the coating can also be essentially free of Lithium and/or Sodium. Since no further chemical toughening is necessary after the sol-gel coating has been cured， no ions from an ion-exchange accumulate in the functional coating. Thereby， it can be avoided that an enrichment of the corresponding ions in the functional coating alters the optical properties as e.g. refractive index or color of the layer (s) of the coating. Therefore， the otherwise necessary compensation-offset in the optical properties for anticipating the later deviations in the optical parameters caused by the ion enrichment is not necessary in the present invention. Hence， the invention allows for a greatly facilitated production of a coated glass article with excellent optical properties at ultimately less cost. However， it is within the scope of the present invention to provide a toughened glass article with a functional coating which has， after the curing of the sol-gel coating， experienced a further chemical toughening step if necessary. In this case， a certain enrichment of ions to be exchanged as e.g. Potassium， Rubidium and or Cesium may be found within the functional coating.

The invention further concerns the use of a toughened glass article with a functional coating according to the invention or a toughened glass article as produced by the method according to the invention， as display， display cover， in particular for cover lens of touch screens， preferably for LCD displays or OLED display， OLED lightning， sensors， in particular touch or fingerprint sensor， E-paper， optical devices， in particular optical lenses or optical filters， or MEMS/MOEMS， in particular optical switches or optical cross-connectors.

Brief description of the drawings

The exemplary figures used for illustration of the invention schematically show：

Fig. 1： a toughened glass substrate with a functional coating having three layers；

Fig. 2： the timeline for the curing process according to the method of the invention as applied in the sample preparation of the examples described herein；

Fig. 3： experimental data regarding the residual compressive stress CS_res obtained by varying curing parameters T_c and t_c；

Fig. 4a： a sample of a glass article with a durable functional coating according to the invention without protective anti-fingerprint top layer after a steel wool abrasion test；

Fig. 4b： magnification of the abraded area in Fig. 4a；

Fig. 5： spectral transmittance of a coated sample and an uncoated reference sample；

Fig. 6： water contact angle as a result of a steel wool abrasion test for several test samples with an additional anti-fingerprint coating on them.

The dimensions and aspect ratios in the figures are not to scale and have been oversized in part for better visualization. Corresponding elements in the figures are generally referred to by the same reference numerals.

Detailed description of figures and examples

Fig. 1 shows a chemically toughened glass substrate 1 with a functional coating 2 comprising three layers 2.1-2.3. The glass substrate 1 is a fiat glass pane or film having a thickness t. The layer 2.1 is directly adjacent to a first face 1.1 of the glass substrate 1. On top of layer 2.1 is the further layer 2.2 which is followed by the further and outermost layer 2.3. The layers 2.1 and 2.3 thereby form Iow-refractive index layers that were produced from an Aluminosilicate sol (see below) . The layer 2.2 is a high-refractive index layer produced from a Titania sol (see below) . The second face 1.2 of the glass substrate has no coating. The glass substrate 1 together with the coating 2 forms a toughened glass article 3 according to the invention. The setup of Fig. 1a is referred to as configuration A in the following. In a variation of the configuration A， the functional coating 2 is applied to both surfaces 1.1 and 1.2 (indicated by dashed lines) . Such a configuration is termed configuration AA in the following.

The glass substrate 1 of the glass article 3 is chemically toughened by ion-exchange prior to applying the coating 2. The chemical toughening is characterized by a surface compressive stress CS and a depth-of-layer DoL.

Glass composition

The glass composition used as glass substrates in the below described examples is as follows：

Composition	weight-％
Composition	weight-％	SiO₂	62
Al₂O₃	17	SiO₂	62
Al₂O₃	17	Na₂O	13
K₂O	3.5	Na₂O	13
K₂O	3.5	MgO	3.5
CaO	0.3	MgO	3.5
CaO	0.3	SnO₂	0.1
TiO₂	0.6	SnO₂	0.1

Table 1： Glass composition used in examples 1 to 11

The glass has a CTE _(20-300) of 8.3 x 10^-6/K and the glass annealing temperature is T_a＝635℃. The density of the glass is 2.4 g/cm³.

Sol preparation

Aluminosilicate sol： First， a mixture of 50 ml TEOS， 80 ml Ethanol and 10 ml 0.1N HCl was prepared and stirred for 3 hours (Component I) . Simultaneously， a mixture of 10 g Al(NO₃) ₃·9H₂O and 100ml Ethanol was prepared and stirred for 30 minutes (Component II) . Components I and II were mixed and stirred for further 30 minutes resulting in an Aluminosilicate sol. The Aluminosilicate sol was used for the low-refractive index layers 2.1 and 2.3 according Fig. 1.

Titania sol： A mixture of 15 ml Ti-isopropoxide and 10 ml acetic acid was prepared and stirred for 1 hour. After admixture of 200 ml Ethanol， the mixture was stirred for another hour， resulting in the Titania sol. The Titania sol is used for the high refractive index layer 2.2 according to Fig. 1.

Sample preparation

All samples were prepared with dimensions of 60 mm x 70 mm. Various samples were prepared according to configuration A (A) as described in the above. The corresponding sols were applied to the glass substrate 1 by a dip-coating process. Samples with AA configuration would be prepared be immersing only one single glass substrate into the sol-bath. Two A configuration samples were prepared by pasting a couple of glass substrates face to face and immersing them together in the sol-bath. The glass samples were then de-bonded when the three-layer dip-coating processes were completed. During application of layers 2.1-2.3， each layer was pre-cured at a temperature of 200℃ for 2 minutes before the subsequent layer was applied. After application of all layers according to configuration A (A) ， the coatings of all samples were cured according to the method of the invention in a RTP500 furnace using IR-irradiation heating a silicon wafer in contact with the coated glass substrate.

The timeline of the curing process is depicted in Fig. 2. In a first， pre-heating stage， the samples were pre-heated for about 90 seconds at 200℃ which is a necessary procedure for the particular type of experimental furnace that was used for sample preparation (from t₁ to t₂ in Fig. 2) . After the pre-heating stage， the temperature is rapidly increased to the maximum curing temperature T_c of 700℃. The heating time of about 10 s (from t₂ to t₃) is the fastest heating rate that can be achieved by the particular experimental furnace. In an industrial application， no preheating is necessary and the heating time can be much shorter and close to instantaneous heating. The maximum curing temperature T_c is maintained for a peak time t_c′ of 5 s (from t₃ to t₄) before the heat input is terminated and the samples cool naturally in the furnace chamber. At 300℃ (at t_s) ， the furnace chamber is opened and the samples are removed and naturally cool to room temperature. The total curing time t_c which corresponds to the time during which the coating is heated to above T_a-200℃ is also indicated in Fig. 2 and corresponds to approx. 22 s. In order to burn out all organic residuals in the sol-gel layers， an oxygen atmosphere is maintained in the furnace chamber during the curing process. For comparison， the temperature T_a-200℃ is indicated.

Figure 3 shows experimental data obtained by varying curing parameters T_c and t_c′ . All samples were prepared according to the curing timeline of Fig. 2， where T_c and t₄-t₃＝t_c′ have been varied.

Figure 3 shows the relative resulting residual surface compressive stress CS_res in the surface layers after the curing process. The relative residual CS_res value was calculated as follows： The CS_befcre of the chemically toughened glass substrate with a composition as described in the above was measured. Then the samples underwent a curing process as described in the above. During each curing process， T_c and t_c′ were varied， in other words， each curing process had a different maximum temperature T_c and peak time t_c′ . After the curing process， the CS_affer was measured and divided by the original CS_before in order to get the ratio CS_after/CS_before＝CS_res which is depicted in Fig. 3. ldeally， the residual CS_res is close to 100％which means that essentially no change in CS occurred during the curing process. In practice， however， it is expected that at least some minor change in CS occurs when heating to temperatures above T_a-200℃. A similar definition applies to DoL_before， DoL_after and DoL_res as used hereinafter.

Figure 3 shows that the higher the curing temperature T_c is chosen， the faster the CS decreases. In contrast， as has been shown with further experiments， higher T_c results in better coating durability. It is therefore desirable to determine the optimal compromise between high curing temperatures T_c and decrease in CS during the curing process. The specific choice of curing parameters T_c and t_c′ thereby can typically depend on e.g. the actual requirements of the coated glass substrate and/or the glass material. For the present glass samples， it has been determined that T_c＝700℃ at a peak time t_c′ of 5 s generally results in a residual CS_res of＞95％which is sufficient for most envisaged applications. A curing process at T_c＝800℃ for t_c′＝1 s may result in the same CS_res but， in practice， might be more difficult to be consistently repeated during industrial production. The specific choice of the process parameters depends on e.g. the possibilities of the production setup， the specific requirement for the desired glass article and the glass composition and can be adapted accordingly without major efforts.

Examples 1 to 2

Examples 1 to 2 were prepared to demonstrate the abrasion resistance and optical properties of a sol-gel coating applied by the method according to the invention. The samples of example 1 were provided with a double sided functional coating according to configuration AA. The samples of example 2 are the corresponding glass substrate with no functional coating and serve as reference samples for the optical transmittance.

Figure 4a shows a sample 4 of example 1 after 5000 cycles of steel wool abrasion test. The wool abrasion test was conducted with 1 kg weight on an area of 2 cm x 2 cm and 0000#steel wool. The samples of example 1 were not provided with a protective anti-fingerprint top layer. The abrasion direction 8 is indicated in Fig. 4a. The abraded area 6 is denoted by two black lines marked on the sample. All visible discolorations in Fig. 4a (streaks transverse to the abrasion direction 8) are a result from inhomogeneity of the coating. The inhomogeneity results partly from the difficulty to dip-coat a very small substrate and partly from the imperfect controlling of the coating environment during sample preparation.

Figure 4b shows a 40x magnified view of the worst affected area of the sample 4 after 5000 cycles. The samples of example 1 show almost no scratches at all besides some fine marks 10 with lengths of only tens to hundreds of μm. Such an excellent performance under 5000 steel wool abrasion cycles without any additional protective layer on top is better than common PVD deposited AR-coatings composed of SiO₂ and Nb₂O₅ as known in the art.

Figure 5 shows the optical properties of the coated samples according to examples 1 and 2. The structure of configuration AA of example 1 is designed to demonstrate an anti-reflective (AR) function at visible range as can be seen in the spectral transmittance in Fig. 5. The peak transmittance of example 1 is around 98.5％corresponding to only～1％reflection at each surface. Since example 1 is a three-layer coating， the AR band cannot be wide enough to cover the whole visible wavelength range. The AR property can easily be improved by adding more layers， typically four or six layers in total， and by optimizing the coating structure. As reference， the spectral transmittance of a corresponding uncoated glass substrate according to example 2 is also shown.

Examples 3 to 4

Examples 3 to 4 were prepared to demonstrate the abrasion resistance of a sol-gel coating applied by the method according to the invention and its compatibility with conventional anti-fingerprint coatings. The samples of example 3 were provided with a single sided functional coating according to configuration A where an AFP cover layer was applied by a conventional PVD deposition method. The samples of example 4 are the corresponding glass substrate with no functional coating but with the AFP coating and serve as reference samples.

The samples of examples 1 and 3 all passed the 9H pencil hardness test. The resulting water contact angles of a steel wool abrasion test are listed in the following table and are depicted in Fig. 6.

Abrasion cycles	Example 3 (degree)	Example 4 (degree)
Abrasion cycles	Example 3 (degree)	Example 4 (degree)	0	112.0	115.2
3000	112.4	109.2	0	112.0	115.2
3000	112.4	109.2	5000	108.3	109.3
8000	104.8	114.6	5000	108.3	109.3
8000	104.8	114.6	10000	103.7	108.9

Table 2： Steel wool abrasion test-critical water contact angle.

The data clearly shows that the samples of example 3 have a similar performance in steel wool abrasion test as the reference samples of example 4. All samples passed 10000 abrasion cycles.

Examples 5 to 6

Table 3： Selected parameters of examples 5 to 6

Examples 5 and 6 comprise samples with a single/double sided functional coating according to configuration A (A) where no additional layers were coated. Example 5 has a moderate DoL whereas example 6 has a deep DoL as can be gathered from table 3 above. The residual compressive stress CS_res of example 5 is 96％and the residual DoL_res is 104 ％whereas for example 6 CS_res is 100％and DoL_res is 96％.

Examples 7 to 8

Table 4： Selected parameters of examples 7 to 8

Examples 7 and 8 comprise samples that were prepared with a single-layer functional coating for comparison. The samples of example 7 were prepared having a single silicate layer functional coating whereas the samples of example 8 were prepared with a single Titania layer functional coating. As can be gathered from the table above， the residual CS_res and DoL_res are similar to the values as obtained with the multi-layer coatings according to configuration A (A) .

Example 9

Examples 9 comprises samples with a single sided functional coating according to configuration A where no additional layers were coated. Table 5 below shows comparative values for DoL and CS before and after the curing of the sol-gel coating on the coated and the uncoated sides.

Table 5： Single-side coated glass samples of example 9

The samples of example 9 clearly show that the change in the toughening parameters is essentially not influenced by the presence of the coating on one side.

Example 10

The samples of example 10 correspond to the samples of example 2 i.e. are only glass substrates without any coating. The samples of example 10 underwent the same curing procedure as was applied to the coated samples as described in the above.

Table 6： Uncoated reference glass samples

As can be gathered from the table 6 above， the uncoated samples of example 10 show comparable residual CS_res and DoL_res as the coated samples of examples 5-9.

Example 11

The samples of example 11 were prepared according to configuration A without additional cover layer. In order to demonstrate the permeability of the functional coating to a subsequent further ion-exchange process after the curing of the coating， the samples of example 11 were subjected to a further ion-exchange process after the functional coating was applied.

Table 7： Increase in CS and DoL after an ion-exchange treatment was applied after the functional coating

As can be gathered from table 7 above， the ion-exchange parameters of the uncoated as well as the coated surface were increased by the further ion-exchange treatment. The present example 11 shows that the coated glass article according to the invention can be further adjusted to the specific requirements after the functional coating has been applied. The coated glass article thus forms a versatile product that can be applied in various different applications and even allows for chemical toughening after the functional coating has been applied and cured. In particular， the ion-exchangeable property also allows for introducing an AM property at the coated surface.

Claims

A method for producing a toughened glass article with a functional coating， comprising：

- providing a， preferably chemically， toughened glass substrate with a first and a second face and a thickness (t) there between，

- said glass substrate having a surface layer with a compressive stress (CS) extending to a depth-of-layer (DoL) below said first and/or second face，

- applying a sol-gel coating to the first and/or the second face of said glass substrate，

- curing the sol-gel coating by heating it to curing temperatures above T_a -200℃ during a curing time t_c to produce said durable functional coating， where the curing time t_c satisfies

and T_a is the temperature at the annealing point of the glass material of the glass substrate and T_c is the maximum curing temperature， where T_a and T_c are given in ℃.
The method according to claim 1， wherein the maximum curing temperature T_c is maintained for a peak time t_c′ which satisfies
The method according to anyone of the preceding claims， wherein the durable functional coating is cured to a pencil hardness of ≥ 7H， preferably ≥ 9H.
The method according to anyone of the preceding claims， wherein the heating time from T_a -200℃ to the maximum curing temperature T_c is less than the curing time t_c， preferably less than the peak time t_c′， in particular equal or less than 30 s， preferably equal or less than 20 s， further preferably equal or less than 10 s， further preferably less than 5 s and/or the cooling time from the maximum curing temperature T_c to a temperature of T_a -200℃ is less than t_c， preferably equal or less than the peak time t_c′， in particular equal or less than 30 s， further preferably equal or less than 20 s， preferably equal or less than 10 s， further preferably equal or less than 5 s.
The method according to anyone of the preceding claims， wherein the peak time t_c′is equal or less than 40 s， preferably equal or less than 20 s， further preferably equal or less than 10 s， and/or the maximum curing temperature T_c is larger than 450℃， preferably equal or larger than 600℃， further preferably equal or larger than 700℃.
The method according to anyone of the preceding claims， wherein the maximum curing temperature T_c lies in the annealing range of the glass material and preferably is equal or larger than T_a.
The method according to anyone of the preceding claims， wherein the thickness of the toughened glass substrate is equal or less than 1 mm， preferably equal or less than 0.7 mm， further preferably equal or less than 0.4 mm， further preferably equal or less than 0.2 mm， further preferably equal or less than 0.1 mm， further preferably equal or less than 0.05 mm， and further preferably equal or less than 0.01 mm.
The method according to anyone of the preceding claims， wherein the functional coating comprises an anti-reflective and/or anti-glare and/or anti-microbial and/or a high-or semi-reflective coating.
The method according to anyone of the preceding claims， wherein the functional coating has a thickness of 50 nm to 1000 nm and/or comprises one or more， in particular four or six， layers.
The method according to anyone of the preceding claims， wherein the sol-gel coating is applied by a dip-coating， spray-coating or spin-coating process， where the sol-gel coating preferably comprises several layers and during applying the sol-gel coating， each layer is preferably applied with a pre-curing at about 200℃ for about 2 minutes prior to applying the subsequent layer.
The method according to anyone of the preceding claims， wherein the sol-gel coating is applied only to either the first or the second face of the glass substrate resulting in said glass article having the functional coating on only one of its faces.
The method according to anyone of the preceding claims， wherein the compressive stress (CS) in the surface layer of the toughened glass article after the curing of the functional coating is equal or larger than 250 MPa， preferably equal or larger than 400 MPa， further preferably equal or larger than 600 MPa， further preferably equal or larger than 800 MPa， further preferably equal or larger than 900 MPa， and/or the depth-of-layer (DoL) is equal or larger than 5 μm， preferably equal or larger than 10 μm，further preferably equal or larger than 20 μm， further preferably equal or larger than 30 μm， and further preferably equal or larger than 50 μm.
The method according to anyone of the preceding claims， wherein the deviation of the compressive stress (CS) in the surface layer of the glass substrate after the curing of the sol-gel coating is at most 10％， in particular at most 5％ of the corresponding value prior to the curing of the sol-gel coating.
The method according to anyone of the preceding claims， wherein the deviation in the depth-of-layer (DoL) of the surface layer of the glass substrate after the curing of the sol-gel coating is at most 10％， preferably at most 5％， of the corresponding value prior to the curing of the sol-gel coating.
The method according to anyone of the preceding claims， wherein the deviation in the warp of the coated toughened glass article after the curing of the sol-gel coating amounts to at most 50％， preferably at most 30％， further preferably at most 10％ of the corresponding value prior to the curing of the sol-gel coating.
The method according to anyone of the preceding claims， wherein an ion-exchange treatment is applied to the toughened glass article after the curing of the sol-gel coating.
A toughened glass article with a durable functional coating， in particular a toughened glass article produced by a method according to anyone of claims 1 to 16，comprising

- a， preferably chemically， toughened glass substrate with a first face and a second face and a thickness there between，

- said glass substrate having a surface layer with a compressive stress (CS) extending to a depth-of-layer (DoL) below said first and/or second face，

- where said glass substrate has a functional coating on at least one of the first or second face， wherein

- the durable functional coating is a result of a sol-gel coating process which is applied to the toughened glass substrate and has a pencil hardness ≥ 7H， preferably ≥ 9H.
The toughened glass article according to claim 17， wherein the compressive stress (CS) in the surface layer of the toughened glass article is equal or larger than 250 MPa， preferably equal or larger than 400 MPa， further preferably equal or larger than 600 MPa， further preferably equal or larger than 800 MPa， further preferably equal or larger than 900 MPa， and/or the depth-of-layer (DoL) is equal or larger than 5 μm， preferably equal or larger than 10 μm， further preferably equal or larger than 20 μm， further preferably equal or larger than 30 μm， and further preferably equal or larger than 50 μm.
The toughened glass article according to claim 17 or 18， wherein the thickness of the glass substrate is equal or less than 1 mm， preferably equal or less than 0.7 mm， further preferably equal or less than 0.4 mm， further preferably equal or less than 0.2 mm，further preferably equal or less than 0.1 mm， further preferably equal or less than 0.05 mm， and further preferably equal or less than 0.01 mm.
The toughened glass article according to anyone of claims 17 to 19， wherein the functional coating comprises an anti-reflective and/or anti-glare and/or anti-microbial and/or a high-or semi-reflective coating.
The toughened glass article according to anyone of claims 17 to 20， wherein the glass article has the functional coating only on either the first or the second face of the glass substrate.
The toughened glass article according to anyone of claims 17 to 21， wherein the functional coating has a thickness of 50 nm to 1000 nm and comprises one or more， in particular four or six， layers.
The toughened glass article according to anyone of claims 17 to 22， wherein the functional coating is essentially free of potassium and/or rubidium and/or cesium.
Use of a toughened glass article produced by a method according to anyone of claims 1 to 16 or a toughened glass article according to anyone of claims 17 to 23， as display， display cover， in particular for cover lens of touch screens， preferably for LCD displays or OLED displays， OLED lightning， sensors， in particular touch or fingerprint sensor， E-paper， optical devices， in particular optical lenses or optical filters， or MEMS/MOEMS， in particular optical switches or optical cross-connectors.