SURFACE TREATMENT OF GLASS AND SIMILAR MATERIALS

The present invention relates to a method of treating a glass body, vitrocristalline material, ceramic or rock, 03 ℮ % ^ which has been chemically tempered, so that the material located within an outer portion of the body is in a compressive stress, and an apparatus for carrying out the method.

It is known that the tensile strength of an article made of glass, vitrocristalline material, ceramic or rock is less than that theoretically that the item should have, with regard to the dimensions of its cross-section.

For example, the effective resistance-pull glass article made from a composition ordinary, such as sodium silicate and calcium, is about 6 kg/mm2.

The resistance that that item should have by virtue of the theoretical calculations is higher by several hundreds times to the actual value.

It is known that the glass can be strengthened or hardened by bringing a substance into the glass from a contact agent and by appropriately setting the temperature during and after said penetration, so that the outer layers of the glass are brought in a state of tension or compression in a state of tension increased compression. Such a method, for establishing or increasing surface compressive stresses is known as chemical tempering method.

Typically, the chemical tempering involves replacement of ions from the glass by ions from the contact agent treatment. It is possible, for example, establish compressive stresses in substituent at ions in the outer layers of the glass, ions that provide, to these outer layers, a smaller coefficient of thermal expansion; the substitution is made at a temperature that is high enough and which is maintained for a period of time sufficient to produce a trigger voltage; is then enables the glass to cool. An alternative, surface compressive stresses may be established by substituting ions in the outer layers of the glass, larger ions, while the surface layers of the glass are at an elevated temperature, which, however, is too low to enable release substantial or, at least, a full release voltages, for the time during which this temperature the bare eet hand, the glass is cooled to the normal temperature, so that the set voltage are "frozen". Furthermore, it is possible to insert the surface compressive stresses by bringing ions into the glass through one of its surfaces, from a contact agent, under the influence of an electric field, without concomitant equal movement of ions from the glass to the contact agent at travere the same surface.

A method of chemical tempering can be applied not only to a glass body, but also to a material body vitrocristalline. In its application to such a body, the quenching treatment provides the best results when the phase of the material vitrocristalline, which is capable of scattering more or most of the medium from the contact agent, is well dispersed on the entire surface of the body. A method of chemical tempering may also be applied to a ceramic body or rock, provided that there is a sufficiently uniform distribution of a phase or of glass phases in the surface of the material, to permit the establishment of or increase the surface compressive stresses by introducing or exchange of substances, as said above.

The invention provides a simple method, by which a property (or properties) of a glass body, vitrocristalline material, ceramic or rock, which has been chemically toughened, can be changed.

According to the present invention " this change is obtained by subjecting the body chemically toughened to a post-treatment or post-treatment removing a surface layer of the material which is under compressive stress.

Since the vehicle, obtained by the chemical tempering, is due to the fact that the outer layers of the body are in a state of compressive stress, is can be expected that the partial removal of such layers is beneficial; on the contrary, would be expected to a seriously weaken such removal the body.

In fact, after removing surface, the body, for example, a glass sheet, is more resistant. In general, the same body has superior resistance to breakage. The removing surface is surprising.

does pent body treated according to the invention form an article of manufacture. An alternative, the body may be

"" ' Level i ** * _AOE280A2AO> _AOE280A2AO>

a portion of an article, for example, the body can form a coating carried by a substrate. In the latter case, the compressive stresses, due to the chemical tempering., may be confined to the outer layers of the exposed surface of the body.

The invention is intended more particularly, but not exclusively, to be applied to the processing of the glass sheet. The invention can be applied to a sheet which has been chemically tempered over its entire surface or a sheet having a certain portion or portions have been chemically hardened, such as edges or edge portions of the sheet, wherein the frequently break may begin. Even if the set of the sheet has been chemically toughened, the methods of the invention, in which a surface layer is otêe of the material under compressive stress, can be confined to a portion or portions of the sheet, for example, to its edges or its edge portions.

It has been found that it is advantageous, for the final mechanical resistance of the body, of removing a surface layer, the thickness of which is between 0.1 and 20 microns of the outer layer or outer layers are under compressive stress. Below this interval, the effectiveness of the treatment is not so marked and, above this interval, the increase in mechanical hardness gradually decreases, as the thickness increases removed.

The removal of the surface layer is performed, preferably by dissolving the layer using a fluorine containing agent. The agents containing fluorine are recommended in that they enable processing very quickly.

In particular, by treating the glass, preferably use of an acidic agent, fluorine-containing. If the agent used has sufficient acidity, the optical properties of the surface are not détérioriées. Preferably, the agent has a pH of less than 4. Tests have shown that the transparent glass can be treated by such agent without sacrificing transparency, while, using less acidic agents, the surface of the glass is likely to change to a where it diffuses light.

A jydes treating agents that are very advantageously, an aqueous solution of hydrofluoric acid " Another suitable agent is ammonium bifluoride. As another example, include the use of an agent that comprises a fluorine compound, for example sodium fluoride (NaF) with sulfuric aeide. A particularly efficacious agent is that which includes both hydrofluoric acid and sulfuric acid. For example, a satisfactory result has been obtained within a treatment period of a few minutes only by using an aqueous solution containing 6% by volume of each thereof.

While the preferred are agents containing fluorine, the removal of the surface layer can be obtained by other etchants. Therefore, for example, a surface layer of the outer layers can be removed, being in tension compression, of a body of chemically toughened glass, using an agent containing QH ions, for example a sodium hydroxide solution. When using a basic agent, it is preferable that the agent, in contact with the body, is continuously renewed, to prevent degradation of optical properties of the surface.

Preferably, the temperature of the treatment agent is between 0 °C and 80 °C. The rate of removal of the material of the surface of the body may be accurately controlled by corresponding choice of the temperature within this gap.

The treatment may be advantageously applied constantly by discharging the treatment agent that is brought into contact with the surface of the body, by spraying or by providing otherwise, continuously, to the latter the treatment agent and allowing the agent flows along the surface to be treated.

This provides the advantage of rapidly renew the agent polluted by the reaction with the surface of the body. The same processing can also be applied by means of a fluorine-containing compound having the form of a gas or vapour.

An alternative embodiment of the process includes immersing the body chemically dipped in a bath of treating agent. The reaction products are effectively transported away from the surface when being treatment is performed in this manner.

Advantageously, is given to the treatment agent to the body and the oscillating motion of a frequency sound or ultrasound. It has been found that this movement accelerates the action _AOE296A0AO> benefit of the treatment agent; which provides a -5 tended " pixels given the mechanical strength in a shorter time.

It is advantageous monitoring the treatment of driven, which removes a surface layer, by treatment with water or with a basic agent. The advantage of this is that, by this post-processing, the mechanical strength of the body may be increased by 10-core more. The post-processing can be performed by exposing the body to a humid atmosphere, by exemplê an environment which is saturated or close to saturation, or by immersing " the body in water or in an aqueous solution of a base, by 'example sodium hydroxide, post-processed is' 15' continued for a time sufficient for the reinforcing effect has 1ieu. If a base is used, the reaction products ^ so & tf ', "' preferably, continuously discharged in cases where the

- - " tVà' nspVf in is to be preserved. The period the _AOE296A0AO> ^ pôs' t-treating can easily be determined by tests and

Depends on-£ 0' recess, in any given case, the composition of

' the^{T treatment agent} and its temperature. When processing a regular glass sodium and calcium to, good results have been ' obtained by immersion in a bath consisting of an "^" w aqueous solution at 20 % sodium hydroxide 30 °C.

25 _AOE280A2AO> "" Treatment with which a surface layer is ètéê"of" external showers have compressive stresses, preferably takes place shortly after the chemical tempering

- * _AOE280A2AO> '~ £tt'^{, , '} to' e-^{s '} pi^{, refers}, the process is executed in

_AOE280A2AO>^v- ' forStfe -^ d * a portion of a continuous process in which

_AOE280A2AO> '-_AOE296A0AO>' 3o^{i-i-: è_AOUNI167AO}> iifps. ~ s6ùt successively chemically hardened (preferably by '_AOE280A2AO> uii 4' method that involves exchange of alkali metal ions or,

^ ·^{1! '} * _AOE296A0AO>' mfeÜX' éncore, by a process which involves substitution with alkali metal ions of the body, of alkali metal ions larger' _AOE280A2AO> _AOE280A2AO> èf' iont subjected to the treatment for removing surface.

-Si *^< '£ e *' pôet -treatment with water or with a base is executed, this treatment may be also carried out immediately following the

* - _AOE296A0AO> " 'previous'. In treatment of glass, preference is given

to^{: of} th 'to continuous processes in which performs processing^D3--' Îréttpê chemical, involving the exchange of metal ions alca' % (ÿ^{K % ïNrre end} the glass and a contact agent, and wherein a surface layer of the outer layers is Ôtée, seats compressive stresses, in a few minutes from the end of the chemical tempering. In avoiding or reducing handling the body between the quenching and the following processing, the risk of damage to the surface of the body is also; includes discarded or reduced.

After which a surface layer is Ôtée to following the chemical tempering, and after the subsequent treatment with water or with a base (if the use is made of such treatment), at least a portion of the treated surface of the body may be coated with one or more layers that alter a surface property of the body, and, for example, its surface hardness. The improvement in tensile strength is greatly increased by treatments of the quenching and removing surface, but the other properties and, for example, the surface hardness of the body, are not necessarily improved by these treatments. Therefore, it is very advantageous body to have some protection by applying urn or more layers that provide the properties and improved méeaniques body, for example, a hard layer or a layer with viscoelastic properties adapted to give the surface of the resilience in a localized pressure. The improvement obtained by applying the layer or protective layers is greater than the improvement which would be obtained by applying the same or of the same layers without quenching had treatments and removing previous surface*

One or more protective layers may be deposited by various methods and, for example, by evaporation under vacuum, by the sputtering or by the application of the coating material in liquid form, for example by dipping the body in a solution containing a substance and, then, subjecting the deposited film and to a heat treatment. It is advantageous to apply one or more coating layers comprising at least one or more of the following substances: ^ TiO, SiO ^, 2 A1 ° 3 '^{Cr 2} ° 3'^{Fe 2} ° 3 '^{Zr0 2}'^{Ta 0,V 2} ° 5 '^{Th0 2}'^{Y ° 3*2} * 2^*Ce0Zl10 SiC, TiN, TaC, ZrC, BgC, TiC, A^B, B^C, zircon, beryl, topaz, ^ ZnCrO, ZrBg. The layers formed by these compounds have a significant hardness. It is advantageous to perform the tempering traii. coatings, surface removal of the coating and, successively-, in a continuous process wherein the contact (if any) between the cbrps and other bodies, after removing surface and before the coating treatment, is minimized.

5 Preferably, the processes are carried out in an apparatus comprising means for spraying the etchant, a reservoir, for collecting the etchant after that it will have firefighting along the body, and means for supporting the body to be processed in the area of action of the sprinkling means.

10 Such apparatus continuously renews the etching liquid in contact with the surface of the body and may also capture the firefighting solution after that it will have on the body.

Advantageously, the apparatus also comprises means for to be sprayed by the treatment agent ion exchange the body

15 subjected to the treatment, and a reservoir for collecting the firefighting agent after it will have on the body. Such apparatus allows the treatment of attack and ion exchange v a continuous process.

Advantageously, the reservoir for collecting

20 the or each of the tanks is connected to a recycling circuit which recirculates the liquid by sprinkler devices' or sparged, for re-use. The apparatus may include a '' ' means " for filtering and/or regenerate the agent during its' recycling.

25 "" " The carrying out a method according to the invention by 1 'use of a fluorine-containing etchant, and its' result' , can also be determined by examining the body itself. If ion exchange has occurred, which involves replacement of ions contained by the body for other ions, these other ions '3Ô will have a higher level in an outer layer' of the body and, in a surface depth of such a "" outer layer, the body will contain fluorine ions. ~ In the case of a " body which a. been chemically toughened by ion exchange between

'the "sodium ion glass and potassium ions of a con -3 $2" "tact ^ the body is characterized, after the etch,^r" v^{: të} that it contains sodium ions and, in an outer layer^{5 "} due" cores ","* potassium ions in a concentration greater than^{u *i "}' "^{: in} " ïnè' pàrtie internal body (wherein the ion concentration of

z-£ "^ L-j pQ- fcâfssfêtre zero), and in that there are fluorine ions^{; in}" a ~ thickness surface of the outer layer. The surface of such body is hydrophobic. L^{3 in.ren.tion} includes a body having these characteristics.

The invention will now be illustrated by a number of examples, that is, in no way limiting. In all these examples, the thickness of the surface layer removed was determined by measuring the weight loss of the material as a result of the removal process.

Example I

Vitrocristalline A sheet of material, produced from the following composition by weight:

potassium. The breakdown voltage obtained A 8θ kg/ram ' near four times higher than before the quenching treatment.

A sheet having the same composition was subjected to similar processing to 20 °C and was then immersed in a bath having the following composition:

8,8 liters of water

0,6 HgSO litre of^

0,6 litre HF (to 70 $).

Treatment dura 3 minutes. MOR

p

of the sheet, determined by bending, was 110 kg/mm.

A layer of 2 microns thickness been removed by treating the surface of the sheet, on each of its faces. By continuing the acid treatment to 20 minutes, surface layers of 14 microns thick were removed and modulus of rupture obtained was only 94 kg/mm^2.

During a comparative test, a modulus of rupture comparable to that held the treated sheet by the acid for 3 minutes, as described above, obtained by treating ftt like sheet by the acid for one minute to 20 °C, in accompanying the processing of vibration

mechanical a frequency of 45 cycles per second and a

2

vatts power/cm 2. However, in this case, the thickness removed from the surface was that of 0.9 microns.

A sheet of soda-lime glass, formed from the following major components:

SiOg: 71 %

A1 " 0:2,3 2 %

Ha_{2 0}: 13 %

CaO: 12 %

was subjected to an ion exchange process. Ions Li^{+ of} a bath containing 2 % ofLiïïQ and 98 of NaNO % ^ ^ j were substituted 10 in Na^{+ glass}, at a temperature of 580 °C. Treatment dura 20 minutes. The glass was removed from the bath, cooled and dried. The glass was then placed in an aqueous solution containing 10 % by volume of hydrofluoric acid, maintained at 50 °C.

After a treatment that dura 30 seconds, the glass was removed from the

15 acid bath, washed with distilled water and dried at alcohol vapor

isopropyl. A thickness of 3 microns was removed from

ïî ; each surface by the acid treatment. MOR eta. it of 4' 5 kg/mm^2. Before processing in the acid bath, the module-. was that of 15 kg/mm. The treated sheet officc disseminated 20.quelque reduced light.

rv L-:-^{1 '} _AOE280A2AO> Example III'

Sodocalique A sheet of glass was subjected to an ion exchange process in a bath of ^ ·ΚΝ0 As a result of the quenching; the surface layers of glass-* 25,25 of a thickness of microns, were in a state of compression and the re-

s is. strength pulling the glass was 100 kg/mm. The glass was subjected to a treatment in an acid bath identical to that

example in the I; the treatment was stopped after 2 mi. QiteSjiJlpe surface layer of a thickness of 2 microns

30. was removed from each side of the sheet by the treatment. The glass obtained had a tensile strength of 130 kg/mm2.

A ZrOg layer was then deposited on a sample of treated glass by immersing the sample in an alcoholic solution of the corresponding acetate and then subjecting

35 the coating film, thus formed, to a heat treatment, to 3P0°C. The tensile strength had slightly exporters-

_AOE280A2AO> ued, -but the surface hardness was higher than àvant 1' operation of the coating.

'-j ;; s-s' L-Example IV

The fig. 1 shows schematically an apparatus for carrying out the ion exchange treatments and acid in a continuous process.

A sheet of glass 17 was deposited vertically on a support 18 which was advanced by a mechanism (not shown), for example by a chain or by a carriage. In a first compartment 19, the glass sheet was heated to the temperature of the ion exchange treatment, i.e. 450 °C, by heating elements by radiation (not shown).

In the same compartment 19, spray pipes 20,21, differently oriented and having holes 6, 7, 8 are connected to a line for supplying molten potassium nitrate.

The glass 17 thus was sprayed on all its surfaces by jets 9 of the salt exchange. 2k The treatment was continued for hours. The salt used was collected at the base of the compartment 19 by a gutter 10 that carries the salt to a regenerator and a return device (not shown). After this treatment, the glass was kept in an adjacent compartment 11 for one hour at a temperature of 450 °C to allow the salt to drop completely. The glass was then cooled in such compartment by cooling devices 12.

When the glass reached a temperature of 50 °C, the partition 13 was raised and the glass 17 was inserted in a compartment l4, constructed similarly to the compartment 19 * The compartment l4, the treatment is orchestrated to the agent acid using spray tubes or sparged 15,16. The acid mixture, consisting of hydrofluoric acid and sulfuric acid, was sprayed onto the surfaces of the glass for one minute. The glass was then cooled and was then ready to be coated with a protective layer, . if necessary. The acid treatment removed a layer of 2.5 microns thick of each face of the glass sheet. The acid treatment increased the resistance of the glass tensile 90 to 120 kg/mm ^. Dana a comparative test, wherein a like sheet was subjected to a treatment like, but discontinuously, the surface of the sheet being handled ' after quenching chemi-

and that before the acid treatment, the tensile strength was o

only increased to 105 kg/mm.

Example V

A ceramic, formed from! compoaition of the following:

-.

sio 2_: 55 %

Ka_{2 0}: 0.5

CaO, MgO; Fe_{2 3 0,} TiO

4" 5 %

was immersed in a train of KNO ^ to 450 °C during 48 hours.

After the chemical tempering, the workpiece was treated with an aqueous solution of sulfuric acid and hydrofluoric acid, as a result of which a surface layer of 12 microns thick was removed from the outer layer in a state of compressive stress. The part clearance and a tensile strength twice that it had before the acid treatment.

Example VI

A sheet of soda-lime glass was treated for hours in a bath of 4θ KNO ^, containing 0.2 % ofKgCO ^. The bath was kept at 450^{o C}. The tensile strength of the sheet after the treatment was 90 kg/mm. The potassium ions penetrated up to 30 microns in the sheet. In a comparative test, a sheet of the mime glass was subjected to the same chemical strengthening treatment and was then immersed for one hour in an aqueous solution at 20 % ofHaOH to 30 °C. The tensile strength of the glass after the treatment was 110 kg/mm.

A surface layer with a thickness of 1.5 micron was Ôtée by co-treatment of the surface of the glass sheet, on each of its faces.

_AOE280A2AO> Example VII

_AOE296A0AO> * A rock nepheline (Ua ^ KAl If O ^ ^ ^), was üùUmïise to an ion exchange process in a bath of ^ ΚΝ0 to 500 °C. After 30 hours, the sample was removed from the bath, cooled di and then immersed for three minutes in an acidic agent containing 6 % by volume HF. The acid treatment removed a surface layer, having compressive stresses, rock, * and the rock strength was significantly increased by the treatment.

Example VIII

^ ~ _AOE280A2AO> sheets were hardened soda-lime glass

-immersion for twenty hours in a bath of ^ ΚΚ0 to 470 °C, treatment which was followed by cooling of the sheets. The tensile strength of the hardened sheets was 90 kg/mm2 Al ef > ixi chemically hardened The sheets were sprayed for 2 minutes with an aqueous solution containing 6 % and 6 % of EF of H SOjj, the temperature of the solution being 20 °C. The treatment removed of each face of each sheet a surface layer of 1.5 micron thick. Following the heat treatment, the sheets had a tensile strength of

5. 115 kg/mm^2.

The sheets were then immersed for 5 minutes in water touillante. The final treatment increased re-

2

such to the sheet to 135 kg/mm.

It is obvious that the invention is not limited to

-10 embodiments which have been described and illustrated example, and modifications can be made without departing from the invention.