DE2034381A1 - Method for strengthening a glass article - Google Patents

Description

Patent attorney Dipl.-Phys. Gerhard Liedl 8 Munich 22 Steinsdorfstr. 21-22 Tel. 298462

B 4742

ASAHI GLASS CO., LTD., No. 1-2, Marunouchi 2-chome, Chiyoda-ku, TOKYO / Japan

Method for strengthening a glass article

The invention relates to a method for solidifying a glass article, at the alkali metal ions present in the surface layer of the glass article by larger alkali metal ions at a temperature be replaced, which is increased, but still below the relaxation temperature of the glass article lies.

C / W

ÖÖ908S / 1S78

It is ζ. B ₀ from an article by Kistler "Stress in Glass Produced by the Non-Uniform Exchange of Monovalent Ions" published in the Journal of the American Ceramic Society Vo. 45, No ₀₂ , February 1962, pages 59-67, a process for solidifying a glass article by ion exchange is known, in which the glass article containing alkali metal ions, such as lithium ions, is brought into contact with a molten salt which contains other alkali metal ions, namely such ,, having a larger lonendurchmesser than the first mentioned, so that the first-mentioned ions can be replaced by the latter. As a result, a compressive stress surface layer develops on the glass article. This very pronounced surface stress resistance increases the mechanical strength of the glass article. However, if the process is applied to conventional sheet glass, ie to normal soda-lime glass, for example window glass, drawn glass, floating glass, rolled glass or plate glass, the rate of ion exchange is extremely slow. In order to produce an ion exchange layer with a thickness of 30 to 40 microns, treatment times are required which are extremely long, for example 15 to 20 hours. It is now possible to increase the thickness of the ion exchange layer by either lengthening the treatment time or by dl ® treatment temperature increases "Jeel © these two options, however, is unsatisfactory essentially, w as the strength of the glass article dsm uiteder reduced * rd IIRU ζ was due to the pressure Naehlassene voltage or negative voltage.

According to the invention, a method for solidifying ®ineo glass articles of the type in Hede is now to be proposed, white & i w

4742 Q0988S / 1578

BAD ORIOSNAL

on various processes for the continuous production of flat glass, e.g. can be applied to Froucault, Pennvernon, Pittsburgh or Colburn processes. The ion exchange treatment time should be relatively short, nevertheless the glass article should be sufficient Maintain strength.

The criteria for using the method according to the present Invention to be produced glass articles correspond to the usual the shaping of a conventional flat glass, i.e. the viscosity reference point and the liquidus temperature of the glass according to the present invention Invention is intended to fall into the following areas:

Relaxation temperature 450 - 55O ⁰ C

. Processing point 980-115O ⁰ C

Liquidus temperature below HOO ⁰ C

The relaxation temperature should be understood as the temperature

14 5

the one at which the viscosity of the glass is 10 'poise. The processing point is the temperature at which the viscosity of the glass

4th
10 poise.

It has now been found, surprisingly, that glass articles accordingly the components and weight proportions given below can be prepared which meet these conditions and which by a short-term ion exchange treatment can be sufficiently solidified.

The object on which the invention is based is accordingly achieved

009885/1578

solved that a glass article is used, which consists essentially of 55-70% SiO ₂ , 10-20% Al ₂ O ₃ ; 0-3% TiO _£ ; 0 - 3% ZrO _3, wherein the total amount of SiO ,,, _o Al 0 ", TiO and ZrO _{0 0} 75-85 wt -.%

Cl Ci O & L

the glass composition; from 3-4% by weight of Li ₀ O;

Ct

7-15% by weight Na ₀ O; 1-8 wt -.% RO, wherein RO at least one divalent oxide from the group 0-7 wt -.% MgO, 0-7 wt -.% ZnO, 0-5 wt -.% CaO and 0-2 wt. -% means PbO, BaO, SrO or a mixture thereof, and consists of 0-4% by weight B ₀ O ₉ , the total amount of SiO ₃ , Al ₃ O ₃ , TiO ₃ , ZrO ₃ , Li ₃ O, Na ₃ O, RO and B ₃ O ₃ makes up at least 98% of the glass composition.

Of the desired shape having and in accordance with the above information composite glass article is subjected to ion exchange treatment, in which are published in the Glasartikel'enthaltenen lithium ions by sodium ions from a molten salt is', which is brought into contact with the glass article. In this way the glass article is solidified.

The accompanying drawings and the following description are used the further explanation of the subject matter of the invention,

On the drawings show:

1 shows a viscosity curve corresponding to the low temperature range for a glass to be treated according to the method of the invention and the curve of a Schv & nxijgases ,, The vertical axis shows the logarithmic values of the viscosity in. Poise for both curves, while the horizontal axis the reciprocal of the absolute temperature ( ⁰ IC) indicates;

⁴⁷⁴² '009885/1 ^ 78. . .

203A381

2 shows a viscosity curve which shows the high temperature range for the two types of glass. The vertical axis shows the logarithmic values of the viscosity in poise for both curves. The horizontal axis shows the temperature in ⁰ C.

The following reasons are decisive for the selected composition range of the glass to be treated according to the present invention.

salary

The SiOn content should be selected as large as possible in order to ensure a satisfactory ion exchange rate. However, if the SiO "content is too high, the viscosity of the glass becomes too high. The glass becomes hard with the result that its melting and deformation properties are deteriorated. On the other hand, if the SiO ₀ content is too small, then the glass devitrifies too easily. From this consideration, after lengthy tests, the preferred range for the SiO ₂ content between 55 and% by weight resulted.

Al ₀ O ,, salary

The proportion of Al O, must be higher than 10 wt -.% Be, o- to the ion-2 ■■

to increase exchange speed. However, if the proportion is over. 20% by weight, the glass tends to devitrify easily. The viscosity of the glass also increases.

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20.3 A 381

TiO ₀ content

TiO ₀ makes the glass soft. However, if the TKX content exceeds 3% by weight, the glass appears somewhat colored.

ZrO ₂ content

A small amount of ZrO ₀ acts to prevent devitrification of the glass. However, if the ZrO ₀ content is too high, it will crystallize and the crystals will precipitate in the glass. Accordingly, the ZrO ₁₅ content should not exceed 3% by weight.

The total amount of SiO _2, Al ₂ O _3, TiO ₂ raid ZrO ₂ be in the range of 75 to 85 wt -.% Are, with regard to the best combination of devitrification tendency with respect to the Viskositätscharäkteristiken, the melting and forming properties as well as to achieve the lonenaustauschverfestigungseffektes.

Li _rt 0 salary

Li ₀ O is the lithium source required for the ion exchange reaction. However, if the Li ₀ O content exceeds 4% by weight, the. The viscosity of the glass is reduced. The glass tends to devitrify. For this reason, shaping the glass also becomes difficult. The purging temperature. is lower and, accordingly, the negative voltage in the surface of the glass article, which is achieved by the ion exchange, also decreases. If the LiJO content is below 3% by weight

009885/1578

is, the ion exchange ratio becomes too low. The viscosity of the glass rises. This means that the melting and molding properties of the glass are deteriorated.

Na ₂ O content

Na ₂ O acts to increase the ion exchange rate. However, if the Na "0 content exceeds 15% by weight, the relaxation temperature of the glass becomes lower. On the other hand, when the Na "0 content is below 7% by weight, the viscosity of the glass becomes higher. The glass article tends to devitrify.

Bivalent metal oxide content

AIsRO, i.e. divalent metal oxides, are MgO, ZnO, CaO, PbO or SrO is used. In any case, the corresponding metal oxide should be used in an amount of more than 1% by weight. Through this the melting properties of the glass are improved. Furthermore, the viscosity curve thereof is properly adjusted so that it is suitable for glass working. However, if any of these metal oxides is used in an amount greater than 8% by weight, then increases the liquidus temperature of the glass. The viscosity curve runs then almost parallel to the vertical axis. This means that a Deforming the glass is extremely difficult. The ion exchange rate becomes slower. Of all RO's, MgO and ZnO are den superior to others in increasing the rate of ion exchange. Accordingly, MgO and / or ZnO should be preferred can be used in the glass. MgO or ZnO can contain up to a

4742.

009885/1578

% of the glass used - ge of 7 wt.. At about 7 wt -.%, The glass tends to easily Entglasungi The CaO content is used to adjust the viscosity curve that the glass can be deformed in a suitable manner, without the liquidus temperature of the glass is extremely increased. If the cap content exceeds 5% by weight, the ion exchange rate becomes slower. Accordingly, CaO can be up to 5 weight - be contained in the glass.%. In other's RO, PbO, BaO and SrO ie - the ion exchange rate decreases - be used% - if the same in an amount of about 2 wt..

B ₀ O ₀ salary

The viscosity curve of the glass can be correspondingly determined by B _{0 On}

ouch

set without causing an extreme increase in the liquidus temperature of the glass results. However, if the B "0" content exceeds 4% by weight, the glass article becomes slightly uneven. Furthermore, the ent voltage temperature. of the same humiliated with the result that the Effect of ion exchange strengthening may be reduced again.

The listed ingredients should in its entirety at least 98 wt -.% Make the glass mixture.

There are always sub-components in the raw materials of the glass " Contamination, cleaning agents or coloring agents present, If the proportion of subcomponents is too high, the properties will of the glass modified to a large extent. Accordingly, the possibility of such modification should be largely avoided

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to prevent the sub-component content being kept as low as possible. Thus, for example, should the proportion of kgO, F, As and Sb ₃ O _{3 0} O, preferably not depending 1 wt -.% Exceed. The total amount of sub-components should be at most 2 wt -% amount..

In practicing the method according to the invention So a glass with the above composition is produced, i.e. that a batch consisting of a mixture of the raw materials is prepared in the desired proportion according to a conventional method. The batch is melted, the melted glass is cleaned and homogenized. The molten glass is then brought into the desired shape. If desired, the ion exchange treatment can also can only be carried out after the glass article has been quenched. Since the glass to be treated according to the present invention the temperature-viscosity characteristics and liquidus temperature given above has, .can be continuous in flat glass or sheet glass are processed. The glass sheet is then subjected to a suitable ion exchange treatment, if necessary after it was bent accordingly. Bending becomes necessary when the glass panel is to be used as safety glass for front or rear windows of automobiles.

To carry out the ion exchange treatment, the glass article, e.g. a sheet of glass immersed in a molten salt bath containing sodium and / or potassium ions and which are higher Temperature is maintained, which, however, must not exceed the relaxation temperature of the glass. Such baths preferably exist

009886/1578

from sodium nitrate and also from potassium nitrate, a mixture of Potassium nitrate and sodium nitrate, from sodium sulfate, potassium sulfate or a mixture of the latter. Satisfying results are also achieved when a paste consisting of a mixture of an inert solid material, e.g. clay, and a salt is applied to the surface of the glass article with subsequent heating.

The treatment temperature depends on the composition of the glass article, in particular on the relaxation temperature, ie the temperature should be in the range between about 850 ° C. and the relaxation temperature of the glass article. Preferably remains to 5O ⁰ C below the strain point of the glass.

The thickness of the ion exchange layer increases roughly in proportion to Square root of the treatment time. It should be mentioned, however, that the compressive stress occurring on the surface of the glass article is restored subsides if the treatment time is too long. Accordingly prolonged treatment is generally not favorable. The preferred time for treatment is between about 5 to 60 minutes. In this case, the thickness of the ion exchange layer is about

35 to 130 microns. The compressive stress is between 30 and 45 kg / mm

In the ion exchange treatment, the lithium ions or sodium ions present in the surface layer of the glass article become replaced by other sodium ions or potassium omea, which ' have a larger ion diameter than the züerat mentioned.

009885/1578

- i-

When the other ions are sodium ions, the lithium ions are replaced with sodium ions. If the other ions are potassium ions the lithium ions are replaced by the potassium ions and the sodium ions by the potassium ions. Because of their ion mobility the ion exchange reaction between the sodium ions and potassium ions proceeds later than the other ion exchange reaction, so that accordingly, this ion exchange reaction hardly contributes to the strengthening of the glass. If both sodium ions and also potassium ions in contact with the surface of the glass article come, the lithium ions present on the surface of the glass article are essentially replaced by the sodium ions.

The higher the compressive stress on the glass article, and the greater the thickness of the compressive stress layer, the stronger the strengthening effect brought about by the ion exchange reaction.

According to the method according to the present invention it is possible a compressive stress surface layer with a thickness of

■ 2

over 30 microns and with a compressive stress over 30 kg / mm, although the ion exchange treatment is only a short one Time, namely less than 30 minutes must be made.

The glass to be treated according to the present invention becomes continuous in a flat glass ribbon or in a board by means of a conventional Formed sheet glass molding process. A solidified by an ion exchange treatment according to the present invention

⁴⁷⁴² 009885/1578

Individual pane of glass can also be used in a suitable manner as a security window glass, e.g. for transport purposes, such as automobiles, airplanes, or Ge used in buildings. However, it can also be such a single one Glass sheet with an unsolidified sheet of glass or with one that has been strengthened by physical annealing or by ion exchange Glass pane can be combined to make a laminated safety glass for to achieve the same purpose.

The application of the present invention is not to tabular or plate-shaped glass articles. You can also with same effectiveness for treating other shaped glass articles, e.g. Common glass was used.

The following examples provide details on how to do it of the method according to the invention.

example 1

As can be seen from Table 1 below, 11 glass samples, each of which had a different composition, were produced. In the first process step, the raw materials, namely silica sand, magnesium carbonate, borax, lithium carbonate, feldspar, aluminum oxyhydrate, boric acid, petalite and the like were mixed in the necessary proportions in order to achieve the desired glass composition. The mixture was then melted, ie a batch of the same was placed in a 500 ecm platinum melting pot. This was heated ^{to 1500 °} C. in an electric furnace for about 10 hours. The melt was then poured in the form of a sheet

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presses. The Qassdbdbe thus produced was in test pieces with the dimensions 1Φ χ 10 χ 0.2 cm cut to then ion exchange to be treated.

List of 1

Glass sample glass composition wt -.%

No. SiO ₂ Al ₂ O ₃ ZrO ₂ TiO ₂ Li ₃ O Na ₃ O MgO ZnO CaO B ₃ O ₃

1 70 12th 2 55.5 17th 3 65 .10 4th 62, 6 20th 5 .69 16 6th 68.2 17th 7th 65.5 13th 8th 64.5 15th 9 64, 5 17th

3 11 4th 4th 3.5 15th 6th 1 3 15th 7th 7th 3.4 12th 2. 2 4th 7th 3.8 10 3.5 11 3.5 9 2 3.5 10 2

10 64.1 17 0.5 3.4 10 2.5 2.5

11 67.1 15 3.4 10 4

For each of the samples 1 to 11, the upper relaxation temperature, the processing point and also the liquidus temperature measured. The results are compiled in Table 2 below.

The liquidus temperature was measured using a glass rod for 15 hours.

⁴⁷⁴² 009885/1578

was maintained in the furnace einexnelektrischen was in a temperature gradient from 800 ⁰ C to HOO ⁰ C adjustable. The maximum temperature at which devitrification occurs was read.

List of 2 1120 s »liquidus tempera» Glass sample Viscosity reference point 1020 - 1000 No. upper relaxation processing
temperature C point C 980 ' 1070 1 480 1120 - 900 2 480 . 1150 1050 3 450 1150 1070 4th 510 1010 960 5 510 1090 1040 6th 480 1100 970 7th 480 1100 970 8th 470 1060 970 9 470 950 10 490 11 476

To carry out the ion exchange treatment, each glass sample was immersed in a bath of molten sodium nitrate (NaNO ₉ ), which on

on

380 ° C to 430 ° C, immersed for 15 to 60 minutes. Afterward the sample was taken out of the bath and washed with water. Table 3 below shows the ion exchange treatment time, the temperature that is on the surface

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the solidified glass sheet occurring compressive stress and also the thickness of the compressive stress layer.

List 3 400 15th 'Compressive stress
value (kg / mm) Strength of
Pressure-
tense
schichf in
micron Glass sample
No. Treatment conditions
Salt bath temperature time
° C (min.) 430 15th 30th 50 1 NaNO ₃ 380 30th 35 50 2 H 430 15th 30th 40 3 H 400 15th 40 80 4th Il 400 15th 35 60 5 ti 400 15th .35 70 6th It 400 30th 35 50 .. 7th Il 430 15th 40 50 8 _t It 380 15th 35 80 9 It 430 15th 45 50 10 It 460 60 40 60 11 ti 40 135 11 dd

Regarding the viscosity curve of glass No. 11 in table 1 reference is made to Figs.

For comparison purposes, the viscosity curve is in this figure compared with that of a flat glass or a sdivhi ^ gjaaes, like it is commercially available in accordance with the swimming pool procedure

009885/1578

The composition of the swimming glass was as follows:

Weight %

SiO ₂ 72.2

Al ₂ O ₃ 1.8

CaO 7.3

MgO 3.8

Na ₂ O 13.7

K ₂ O 0.7

SO ₃ 0.3

Fe ₂ O ₃ 0.1

TiO ₂ 0.1

The liquidus temperature of this glass was 97O ⁰ C.

From Figs. 1 and 2 it can be seen that according to the present Invention treated glass for a temperature-viscosity characteristic which is similar to that of a conventional sheet glass or flat glass.

Example 2

A glass that has the composition No. 10 according to the list was gradually melted in a small glass tank furnace. It was made from the melted by the Fourcault method Glass mass produced a glass sheet. The examination showed that the glass panel had no defects such as e.g. B. devitrification, Glass streaks or pebbles, as they sometimes appear on a plate glass occur according to the usual glass drawing process. The plate glass

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furthermore showed an excellent surface quality. The one made in this way Sheet glass was consolidated by means of an ion exchange treatment as described in Example 1.

Example 3

From a glass which has the composition according to the example No. 9 in Setup 1, a glass panel measuring 30 30 χ 0.2 cm was formed. In the meantime, according to a glass plate with the dimensions 30 30 χ 0.3 cm is made using a conventional flow process. Subsequently were The two sheets of glass are bent so that they are a laminated composite glass form. The explained in position 1 No. 9 curved glass panel was subsequently diarch ion exchange in the same manner as in Example 1 solidified. Then she was with the river glass plaque laminated. Between the two glass plates was used to bind them a polyvinyl butyral film with a thickness of 0.7 mm inserted.

The mechanical strength of the laminated glass thus produced was tested and measured in the following ways:

On a steel plate, which has a hole with a diameter of 200 mm, with the interposition of a rubber ring with a thickness of 2 mm, the laminated glass panel to be tested was placed in such a way that that the solidified sheet of glass was at the bottom. A steel bolt, which one 50 mm in diameter and one at the distal end half spar is before mold was down on the center of the laminated glass pushed until the laminated glass was under the concentrated

⁴⁷⁴² 009885/1578

Load was destroyed. Then the compressive stress of the glass plate measured at the time of their destruction by a compressive tension meter.

Between the compressive stress ε, the Young's modulus E and the Poisson's ratio γ, the compressive stress δ is as follows Relationship:

E.
δ =

T -

When the breaking stress of the laminated glass sheet is in the above The way it is measured, it reaches up to 60 kg / mm. In comparison in addition, the breaking stress of a laminated glass panel, which consists of two non-solidified glass panels with a thickness of 2 mm and 3 mm exists, only 10 kg / mm.

A 'swimming glass' - as in the previous description is mentioned - is produced by applying a glass melt to a liquid metal melt, which has a higher specific Has weight than glass. ·

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Claims (5)

• 2Q34381 claims 1. A method for strengthening a glass article in which the alkali metal ions present in the surface layer of the glass article are replaced by larger alkali metal ions at a temperature which is elevated but below the upper relaxation temperature of the glass article, so that a compressive stress layer is formed on the surface of the glass article is, characterized in that a glass article is used which consists essentially of 55 to 70 wt.% SiQ ₂ J 10 to 20 wt.% Al ₃ O ₃ ; 0 to 3% by weight of TiO ₂ ; . 0 to 3 wt .-% ZrO, wherein the total amount of SiO _3, Al ₃ O _3, TiO ₃ and ZrO ₃ 75 to 85 wt -% of the glass composition; 3 to 4% Li ₃ O; 7 to. 15% Na ₃ O; 1 to 8% RO, where RO is at least one divalent oxide from the group 0 to 7% MgO, 0 to 7% ZnO, 0 to 5% CaO and 0 to 2% PbO, BaO, SrO or a mixture thereof and of O up to 4% B _o 0 ", the total amount of SiO ₀ , ti ι- · ύ α Al ₃ O ₃ , TiO ₂ , ZrO ₂ , Li ₃ O, Na ₃ O, RO and B ₃ O _{3 make up} at least 98% of the glass composition. 2. The method according to claim 1, characterized in that the in the surface layer of the glass article to be replaced ions lithium ions and that the larger alkali metal ions are sodium ions. 3. The method according to claim 1, characterized in that the glass article is brought into contact with a molten salt which contains the larger alkali metal ions and which is kept at a temperature which is 30 to 50 ⁰ C lower than the upper relaxation temperature of the Glass article. 009885/1578 4. Glass article which contains lithium ions and sodium ions and the surface of which has a compressive stress layer and in which the concentration of sodium ions in the surface layer of the solidified glass article is also greater than in the interior of the glass article, characterized in that the interior of the glass article consists essentially of 55 to 70% SiO ₃ ; 10 to 20% Al ₃ O ₃ ; 0 to 3% TiO ₃ ; 0 to 3% ZrO ₀ , the total amount of SiO ₀ , Al ₀ Q ₉ , TiO ₀ and a Ci Ci ό ti ZrO _{0 make up} at least 75 to 85 percent by weight of the glass composition; 3 to 4% Li ₀ O, 7 to 15% NaO; 1 to 8% RO, whereby RO is less Ci at least one divalent oxide from the group of O to 7% MgO, O to 7% ZnO, O to 5% CaO and O to 2% PbQ, BaO, SrO or a mixture thereof and from O to 4% B _O O " consists, wherein the total amount of SiO ₃ , Al ₃ O ₃ , TiO ₃ , ZrO ₃ , Li ₃ O, Na ₃ O, RO and B ₀ O _{3 make up} at least 98% of the glass composition. 5. Glass article according to claim 4, characterized in that the thickness of the compressive stress surface layer is at least about 30 microns and that the compressive stress value is at least about 30 kg / mm. 009885/1578