KR100513667B1 - Galss composition, chemically tempered glass substrate and methoos for producing and using said glass substrate - Google Patents

Abstract

An object of the present invention is a glass composition intended to be chemically transformed into a glass ribbon, comprising the following components.

SiO ₂ 55-71 wt%

Al ₂ O ₃ > 2% by weight

MgO 4-11 weight percent and Al ₂ O ₃ <5 weight percent,> 8 weight percent

Na ₂ O 9-16.5% by weight

K ₂ O 4-10 wt%

Description

Glass compositions, substrates made of chemically toughened glass, and methods of producing and using the glass substrates {GALSS COMPOSITION, CHEMICALLY TEMPERED GLASS SUBSTRATE AND METHOOS FOR PRODUCING AND USING SAID GLASS SUBSTRATE}

The present invention relates to compositions that can be converted into glass ribbons. The glass composition according to the present invention is more specifically intended for the application of the aviation windowpane type, but is not correspondingly limited to this application.

With respect to the application of the aviation type, the present invention is more particularly intended for window panes which can exhibit high compressive stress over a significant depth after chemical toughness treatment.

For these applications, in particular for aircraft or helicopter windowpanes, the requirements for mechanical strength are so great that strength strengthening operations are generally carried out by chemical means, rather than simply thermal means, for example for automotive windshields. Chemical toughness treatment may also be used in other applications that require significant chemical toughness treatment, such as, for example, glass armored railroad or windshields for marine vehicles or otherwise automotive windshields.

As in the case of the thermal toughness treatment, the chemical toughness treatment puts the glass surface in a compressed state, where the bursting strength of the glass is increased by an amount approximately equal to the magnitude of the compressive surface stress produced by the treatment, in which case And by replacing some of the alkali metal ions in the glass surface layer with other less bulky ions that are inserted into the glassy network.

In the case of forces exerted throughout the pane, for example by pressure into the air of a pressurized cockpit, also more dynamic forces such as bird strikes, ie, glass, can cause surface defects. In the case of an impact which generates a very high force that causes breakage in terms of the range indicated, the properties of the mechanical strength are, on the one hand, defined by the value of the compressive surface stress, and on the other hand by the treated depth. do. Ideally, the purpose of the chemical toughening operation is thus to place the surface layer of the glass article which is processed under very high compressive stress over a very significant depth, ie over the depth of the largest bond.

For a given glass composition, the depth exchanged depends on the duration of the ion exchange treatment and the temperature performed. However, as the temperature rises, the stress relaxation rate increases and as a result, the break stress is lowered. Likewise, prolonging the treatment for too long results in an unsatisfactory degree of toughness, requiring stress relaxation time.

These considerations have led to the development of new glass compositions that are more advantageous for ion exchange than conventional windowpane compositions, especially new glass compositions that allow greater exchange depths with treatment times of less than several hours. Thus, French Patent Application No. FR-A-2,128,031 provides silica-soda glasses which satisfy the following composition using oxides commonly encountered in conventional industrial glass.

SiO ₂ 65.0-76.0 wt%

Al ₂ O ₃ 1.5-5.0 wt%

MgO 4.0-8.0 wt%

CaO 0.0-4.5 wt%

Na ₂ O 10.0-12.0 wt%

K ₂ O 1.0-4.0 wt%

B ₂ O ₃ 0.0-4.0 wt%

These components represent 96% by weight or more of glass and moreover satisfy 0 or 0.45 (% by weight) of CaO / [CaO + MgO] and 0.05 or 0.35% by weight of K ₂ O / [Na ₂ O + K ₂ O]. These limits are included.

The composition defined above gives a strengthening depth after 24 hours of 1.8 or 3.3 times greater than the depth obtained with normal glazing.

However, in French patent application FR-A-2,128,031, the ion exchange process is relatively short, which is systematically limited at most 24 hours, which attains approximately 100 microns at most (for 400 ° C. treatment temperature) the thickness of the reinforced layer Do it. However, especially for the aviation sector, the thickness must be much larger, for example approximately 300 microns, which returns to the aforementioned problem with conventional glass compositions.

In European Patent EP-0,665,822, the glass compositions are also suitable for long-term treatment, which in some cases may be at least about 20 days, typically at least 72 hours, in particular at least 10 days or even at least 15 days, and consequently a considerable depth, It can also be used to obtain strength-enhanced glass articles by ion exchange, for example to a depth of 200 microns or more, while maintaining a very satisfactory strength level, for example, a compressive surface stress of 400 MPa or more. It has already been proven. Thus, glass products having a composition satisfying the chemical formula known from French patent FR-A-2,128,031 are subjected to strength strengthening by ion exchange at the same temperature, resulting in a compressive surface stress of at least 400 MPa for a treated depth of at least 200 microns. An article is described which preferably has a compressive surface stress of at least 500 MPa and, alternatively, at least 650 MPa for a treated depth of at least 75 microns.

By the way pointed out, the treatment carried out can be, for example, for 18 days at a temperature of 415 ° C., resulting in a compressive surface stress of approximately 500 MPa and an exchanged depth of approximately 265 microns. If an application that allows for a thinner treatment depth is possible, substantially using a lower treatment temperature (eg 350 ° C.) for a time somewhat consistent with the previous case, i.e. with a treatment depth of approximately 80 microns, It is also possible to obtain higher strength levels, for example approximately 700 MPa or higher levels of compressive surface stress.

Although the mechanical properties obtained are satisfactory, it is nevertheless the same that these properties require a relatively long toughness treatment time.

Moreover, apart from the requirements for mechanical properties, it is more particularly necessary to obtain good chemical resistance, in particular good hydrolytic resistance. This is because the consumption of glass used in this type of product is relatively low compared to the production capacity of the furnace in the glass industry, so it is not necessary to keep the glass and maintain the properties of the glass for a period of up to several years. desirable.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows four curves which show a burst coefficient (unit: MPa) vertically and indentation load (unit; N) horizontally.

It is therefore an object of the present invention to provide glass compositions having good hydrolysis resistance with the ability to undergo chemical toughness treatments that produce stresses such as those required for the application of aviation glazing types, which are necessary to obtain these stresses. The treatment time is shorter than the treatment time for known compositions.

The above object is achieved according to the invention by a glass composition which is intended to be converted into a glass ribbon and comprises the following components.

SiO ₂ 55-71 wt%

Al ₂ O ₃ > 2% by weight

MgO 4-11 weight percent and Al ₂ O ₃ <5 weight percent,> 8 weight percent

Na ₂ O 9-16.5% by weight

K ₂ O 4-10 wt%

Preferably, the composition according to the invention satisfies Na ₂ O / K ₂ O <1.8% by weight, preferably <1.4% by weight. These preferred compositions allow much shorter processing times while generating satisfactory stress equivalent to those of the prior art. This is because these compositions show a better diffusion of tolerance during the toughening operation without greater stress relaxation.

The composition defined above has the advantage that in particular, for the purposes of the aviation arts, a good hydrolysis resistance can be achieved with the chemically strengthened properties.

According to a preferred embodiment of the present invention, the sum of the weight ratios of the alkali metal oxides is less than 23% by weight, preferably less than 21% by weight. If the content of alkali metal oxide is too high, the hydrolysis resistance decreases.

The Na ₂ O content is advantageously less than 14%, and the K ₂ O content is preferably 7% or more. The oxides Na ₂ O and K ₂ O make it possible to maintain the melting point and high temperature viscosity of the glass according to the invention within acceptable limits. The presence of these two oxides simultaneously in a limited ratio causes the glass's chemical resistance, more specifically the resistivity as well as the hydrolysis resistance to be significantly increased.

The inventor further defines the composition as having an alkalinity of less than 15, preferably less than 10.

In the context of the present invention, the SiO ₂ content should not exceed approximately 71%, and above that carrying out the dissolution of the batch and the smelting of the glass requires high temperatures to accelerate the wear of the furnace refractory bricks. Below 55%, the glasses according to the invention do not have sufficient stability. The glass according to the invention having the most suitable viscosity for glass that can be suspended in a bath of molten metal, exhibiting good hydrolysis resistance and excellent properties for strengthening chemical strength, the most easily soluble glass according to the invention being 60 or 65% SiO. ₂ is included.

The MgO content is preferably at least 7%. The element leads to dissolution of these glass compositions, thereby improving hot viscosity and also increasing the hydrolysis resistance of the glass. Although other alkaline earth metal elements are present in the composition, it is preferred that CaO, a compound that is detrimental to chemical toughness, is present only in the form of impurities having a content of less than 0.5% by weight.

Alumina acts as a stabilizer. The oxide increases to some extent the chemical resistance of the glass. The Al ₂ O ₃ content should not exceed 18% so as not to make the glass too difficult to melt and to increase the high temperature viscosity of the glass to unacceptably high levels. Al ₂ O ₃ content is advantageously less than 14%.

The glass composition according to the invention may further comprise an oxide B ₂ O ₃ . Subsequently, the B ₂ O ₃ content does not exceed 4%, because above this value, the volatilization of boron in the presence of alkali metal oxides occurs significantly during glass production, causing corrosion of the refractory brick. Moreover, higher B ₂ O ₃ content impairs the quality of the glass. If B ₂ O ₃ is present in the glass composition in an amount of at least 2%, Al ₂ O ₃ is advantageously at least 10%.

According to a preferred embodiment of the invention, the B ₂ O ₃ content is less than 2% and in this case the Al ₂ O ₃ content is less than 10%.

Moreover, the glass compositions may contain colorants, in particular for automotive windshield type applications, which may be, for example, iron oxide, chromium oxide, cobalt oxide, nickel oxide, selenium oxides and the like. The present invention also provides a glass composition having a light transmittance and an energy transfer rate that can be adopted according to principles known to those skilled in the art, depending on the intended application. The light transmittance is advantageous at least 71%.

Among the compositions according to the present invention, the selected composition will be a composition having a formation range of about 1050 or 1150 ° C., and in the float process the formation range is 1585 (log η = glass viscosity, expressed in poise). 3.2) or 5000 (log η = 3.7).

More preferably, the composition used has a temperature corresponding to a greater viscosity (log η = 3.5) than the liquidus temperature (T _liq ), wherein these two preferred temperature differences are at least 10 ° C., more preferably 20 It is more than ℃. In this way, the glass can be obtained using the float method without the risk of becoming opaque.

Another property of the composition according to the invention is that the coefficient of expansion of the composition is at least 90 * 10 ⁻⁷ ° C. ⁻¹ . These properties show that these compositions are suitable for thermal toughness.

More particularly, for aviation type applications, the glazing is coated with a layer deposited for example by pyrolysis. The present invention advantageously provides a composition that allows the coating to be deposited without relieving stress unacceptably. The composition according to the invention advantageously has an upper unwinding temperature (T _S ) of at least 500 ° C., preferably at least 540 ° C. (the very point on the expansion curve defined in the book “Glass” by Horst Scholze).

The subject of the invention is also a glass substrate in which the matrix satisfies one of the above compositions and which has been strengthened by ion exchange for the purpose of aviation type application. For the person skilled in the art, the compositions according to the invention have a significant compressive surface stress level for shorter toughness treatment times than the most recent prior art mentioned, but the relaxation of the compressive stress is as much as the skilled person considered the treatment time. It's not big. After chemical toughening, it is in fact possible to obtain a glass substrate having a compressive stress level of at least 400 MPa, which is suitable for the intended application.

According to the first embodiment of the present invention, the glass substrate is strengthened by surface ion exchange at a surface exchange depth of 200 microns or more, and has a compressive surface stress of 400 MPa or more.

According to another embodiment, the glass substrate is strengthened by surface ion exchange to a surface exchange depth of at least 50 microns and has a compressive surface stress of at least 700 MPa.

The invention furthermore provides a process for obtaining a glass substrate, which forms a glass in a float-type plant and then treats the substrate by potassium ion exchange for at least 24 hours at a temperature of 350 or 500 ° C. to provide.

Further details and advantageous features of the invention will emerge from the following examples presented according to the invention.

Tests were performed on various glass matrices that satisfied the following formula (units by weight).

Example 1 illustrates a composition according to the prior art and meets the criteria required for aviation applications. The composition according to example 1 is an example illustrated in European patent EP-0,665,822.

The last three columns of the table are, in the first case, the temperature corresponding to the viscosity (log η = 2), which is the temperature in the melt bath, and in the second case, the bath of the metal in which the glass is dissolved. Is the temperature corresponding to the viscosity (log η = 3.5), which is the selected temperature entering the column, and finally, in the third case, the temperature T _liq corresponding to the liquid phase.

The first information already indicates that these glass compositions according to the invention can constitute glass substrates obtained using float techniques.

The following table shows various types of toughness treatments in potassium nitrate baths, with different temperatures and durations of treatment. These various treatments were carried out on the compositions according to the invention, defined by Example 2.

The second table shows the treatments for examples of the compositions 3, 4, 5 and 6.

The table shows that the compositions according to the invention are particularly advantageous for ion exchange in potassium nitrate baths. It is clearly evident that the glass of the present invention enables very high compressive stress levels to be obtained at exchanged depths satisfactory for aeronautical applications. While the expected decrease in the value of the burst strength is indeed confirmed as the treatment time increases, the decrease due to the first occurrence of stress relaxation is not so much, resulting in low levels.

In the following table, the chemical toughness treatments performed with the composition according to Example 1 are compared with the various treatments performed with the composition according to Example 2.

In view of the table, it is clear that the composition according to the invention produces at least as satisfactory results as the results obtained using the composition according to example 1, or even better results.

It is also clear that treatment at a temperature of 425 ° C. for a time of 6 days produces better results than that obtained by treatment at a temperature of 425 ° C. for a time of 12 days using a composition such as that of Example 1. . The latter result is considered satisfactory for the application of the aviation type. Therefore, it is clearly evident that the composition according to the invention enables the result to be obtained on par with that of Example 1 using a shorter treatment time, and therefore at a lower cost.

The following table shows the hydrolysis resistance properties of the glass according to the invention. The table gives the residual amounts and alkalinities of the compositions according to the invention, these values being obtained by water-digestion of the glass in a granular form.

The soaking or "DGG" of glass in granular form consists of dipping 10 grams of ground glass in 100 milliliters (ml) of heated water to break for 5 hours. Between 360 and 400 microns. After rapid cooling, the solution is filtered and a limited amount of filtrate is evaporated to dryness. The weight of the dry matter obtained allows the amount of glass dissolved in water, i.e. the residual amount, to be calculated, the amount being in milligrams (mg) for the initial glass mass equivalent to four times the relative density (ie 10 g for 2.5 relative density). It is expressed as

Regarding alkalinity, this is the average mass (in mg) of the alkaline substance dissolved relative to the initial glass mass equivalent to four times the relative density.

It is also clear that the pane according to the invention exhibits very high resistance to local damage, for example resistance to impact by small hard particles.

The curves in the figures appended here illustrate these properties. These curves were obtained from tests conducted with 70 × 70 mm test pieces. The test involves using a three-point bending test, ie, applying a load to a ring of 10 mm diameter and 1 mm rim on a support consisting of three equally spaced balls placed on a 20 mm radius circle to measure the rupture coefficient. For each type of test piece, these bursting coefficients are also measured after forming the defect. To do this, Vickers indentation is made with a given load (3 or 100 N) at the center of the specimen, and the face of the specimen is widened during the test. The result is shown in the figure with four curves which show a rupture coefficient (unit: Mpa) lengthwise and an indentation load (unit; N) transversely.

Curve 1 shows the test results for test pieces made of soda-lime glass that is not strengthened.

Curve 2 shows the test results for a test piece made of glass according to Example 1, reinforced to 425 ° C. for 12 days.

Curve 3 shows the test results for a test piece made of glass according to Example 4 reinforced to 406 ° C. for 10 days.

Curve 4 shows the test results for a test piece made of glass according to Example 5, reinforced to 406 ° C. for 15 days.

These curves demonstrate the superior performance of chemically strengthened glass compared to ordinary soda-lime glass. The curve also shows a nearly equivalent or even better performance in the case of high indentation loads, especially in Examples 4 and 5, compared to Example 1.

The pane according to the invention is most often applied to composite panes, such as aircraft windshields, and more generally to any general purpose of any aerospace or toughening glass, in particular automotive panes, glass reinforced panes or railway panes.

Claims (18)

A glass composition intended to be converted to a glass ribbon, the glass composition comprising the following components. SiO ₂ 55-71 wt% Al ₂ O ₃ > 2% by weight MgO 4-11 weight percent and Al ₂ O ₃ <5 weight percent,> 8 weight percent Na ₂ O 9-16.5% by weight K ₂ O 4-10 wt% The glass composition according to claim 1, wherein Na ₂ O / K ₂ O <1.8% by weight is satisfied. The glass composition according to claim 1 or 2, wherein the sum of the weight ratios of alkali metal oxides is less than 23% by weight. 3. The glass composition according to claim 1, wherein the alkalinity is less than 15. 4. The method of claim 1 or 2, characterized in that it contains boron oxide (B ₂ O ₃ ) having a content of 2 to 4% by weight, the alumina (Al ₂ O ₃ ) content is greater than 10% by weight , Glass composition. The glass composition according to claim 1 or 2, wherein the Al ₂ O ₃ content is less than 10% by weight and the B ₂ O ₃ content is less than 2% by weight. The glass composition of claim 1, wherein calcium oxide (CaO) is present only in the form of impurities. The glass composition of claim 1, wherein the glass can be chemically transformed into a glass ribbon using a float process that is passed over a tin melting bath. The glass composition of claim 1, wherein the coefficient of expansion of the glass composition is greater than 90 * 10 ⁻⁷ ° C ⁻¹ . 4. 3. The glass composition of claim 1, wherein the annealing temperature T _s of the glass composition is greater than 500 ° C. 4. As a glass substrate, The matrix of glass substrates satisfies one of the compositions according to claim 1, Wherein the glass is formed in a float-type plant and is treated by potassium ion exchange for at least 24 hours at a temperature of 350 to 500 ° C. As a glass substrate, The matrix of glass substrates satisfies one of the compositions according to claim 1, A glass substrate, characterized by being strengthened by surface ion exchange to a surface exchange depth of greater than 200 microns and having a compressive surface stress of greater than 400 MPa. As a glass substrate, The matrix of glass substrates satisfies one of the compositions according to claim 1, A glass substrate, characterized by being strengthened by surface ion exchange to a surface exchange depth of greater than 50 microns and having a compressive surface stress of greater than 700 MPa. In the method for producing a glass substrate according to claim 11, Wherein the glass is formed in a float-type plant and treated by potassium ion exchange for at least 24 hours at a temperature of 350 to 500 ° C. In the method using the glass substrate according to claim 11, A method for using a glass substrate, characterized in that for producing laminated composite windows such as aviation windows. The glass composition according to claim 1, wherein Ma ₂ O / K ₂ O <1.4 wt% is satisfied. The glass composition of claim 1, wherein the alkalinity is less than 10. 3. The glass composition of claim 1, wherein the annealing temperature T _s of the glass composition is greater than 540 ° C. 4.