Patent Description:
The present specification generally relates to strengthened glass articles, in particular strengthened glass articles having high mechanical strength and low internal tension, and methods of strengthening the glass articles.

Historically, glass has been used to produce a variety of articles. For example, because of its hermeticity, optical clarity, and excellent chemical durability relative to other materials, glass has been a preferred material for pharmaceutical applications, including, without limitation, vials, syringes, ampoules, cartridges, and other glass articles. The glass used in pharmaceutical packaging must have adequate mechanical and chemical durability so as to not affect the stability of the pharmaceutical formulations contained therein. Glasses having suitable chemical durability include those glass compositions within the ASTM standard 'Type IA' and 'Type IB' glass compositions which have a proven history of chemical durability.

A concern for food and drug manufacturers is providing glass containers having sufficient strength to minimize damage and breakage caused by external sources of damage, such as handling and/or transport of the glass containers. While glass containers are superior to many alternative materials, they are not unbreakable and occasionally experience damage from handling and/or transport. Cracks are severe damage flaws that extend through the wall thickness, compromising content sterility but not leading to catastrophic failure of the package.

The documents <CIT>, <CIT> and <CIT> describe chemically strengthened glass articles.

The present disclosure provides a strengthened glass article, such as a package, container, or vessel comprising a glass and adapted to contain pharmaceutical products or vaccines, and foodstuff containers (e.g., bottles, baby food jars, etc.) in a hermetic and/or sterile state. The strengthened glass articles are strengthened by a method of strengthening that produces compression stress in a surface region of the glass and tensile stress in a central region of the glass. The strengthening process is designed such that the compressive stress at the surface and the depth of layer are sufficient to provide mechanical strength and resistance to external sources of damage. However, the method strengthening the glass is also designed to maintain the central tension less than a threshold central tension below which flaw damage extending into a central region of the glass (i.e., the central region is the region of the glass under a central tension) does not propagate through the thickness of the wall or laterally across the surfaces of the glass. Thus, the method of strengthening glass may produce a glass article having mechanical strength to resist flaw damage from external sources of damage, but also exhibits minimal delayed breakage risk.

The present invention is directed to a glass article as defined in independent claim <NUM>. Preferred embodiments are defined in dependent claims <NUM>-<NUM>.

These and other aspects, advantages, and salient features will become apparent from the following detailed description, the accompanying drawings, and the appended claims.

Reference will now be made in detail to embodiments of methods of strengthening glass articles and the strengthened glass articles, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. The present disclosure is directed to a method of strengthening glass articles and the strengthened glass articles made therefrom. Referring to <FIG>, a glass article <NUM> strengthened by the method disclosed herein is schematically depicted. The glass article <NUM> includes a glass <NUM> having a first surface <NUM>, a second surface <NUM>, and a thickness t measured between the first surface <NUM> and the second surface <NUM>. The glass <NUM> includes one or more compression regions <NUM> that extend from the first surface <NUM>, the second surface <NUM>, or both to a depth of compression (DOC) and is under a compressive stress, and a central region <NUM> that extends inward from the DOC and is under a central tension. Each of the compression regions <NUM> includes a surface region <NUM> proximate the first surface <NUM> and/or the second surface <NUM> and an interior compression region <NUM> extending from the surface region <NUM> to the DOC. The method of strengthening is a three-stage strengthening process that includes introducing potassium ions into the surface region <NUM> of the glass <NUM>, thermally treating the glass <NUM> at a temperature and for a time sufficient to diffuse at least a portion of the potassium ions into the glass <NUM> to a depth within the glass sufficient to produce the DOC, and then introducing a compressive stress that may be greater than or equal to <NUM> megapascals (MPa) to the surface regions <NUM> of the glass <NUM>. The method of strengthening the glass article <NUM> may produce a glass article <NUM> having a compressive stress and DOC sufficient to provide mechanical strength to resist damage from external sources while also having a central tension that is low enough that flaws extending into the central region <NUM> of the glass <NUM> do not self-propagate through the glass <NUM>, which may result in destruction of the article.

In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that, unless otherwise specified, terms such as "top," "bottom," "outward," "inward," and the like are words of convenience and are not to be construed as limiting terms. In addition, whenever a group is described as comprising at least one of a group of elements and combinations thereof, it is understood that the group may comprise, consist essentially of, or consist of any number of those elements recited, either individually or in combination with each other. Similarly, whenever a group is described as consisting of at least one of a group of elements or combinations thereof, it is understood that the group may consist of any number of those elements recited, either individually or in combination with each other. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range as well as any ranges therebetween. As used herein, the indefinite articles "a," "an," and the corresponding definite article "the" mean "at least one" or "one or more," unless otherwise specified.

As used herein, "glass article" may refer to an article comprising a glass, such as a glass container for example.

As used herein, "depth of compression" (abbreviated DOC) may refer to a depth within the glass at which the stress in the glass transitions from compressive stress in the compression layer to tensile stress in the central region. The DOC is related to the depth in the glass to which the potassium or other ions diffuse during the strengthening process.

As used herein, "depth of layer" (abbreviated DOL) may refer to a depth within the glass at which the concentration of potassium ions is reduced to the bulk concentration of potassium ions in the glass. The DOC is proportional to the DOL and may be slightly less in magnitude than the DOL.

As used herein, "threshold central tension" may refer to a value of the central tension in the central region of the glass above which central tension flaws that extend into the central region exhibit self-propagation through the thickness of the glass from the first surface to the second surface and laterally across the glass.

As used herein, the terms "borosilicate glass" and "borosilicate glass composition," may refer to glass compositions which comprise boron at concentrations in excess of <NUM> wt. % of the glass composition.

Referring to the drawings in general and to <FIG> in particular, it will be understood that the illustrations are for the purpose of describing particular embodiments and are not intended to limit the disclosure or appended claims thereto. The drawings are not necessarily to scale, and certain features and certain views of the drawings may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.

Glass is a preferred material for pharmaceutical packaging for several reasons, including optical clarity, hermeticity, and chemical inertness. However, it is possible for a glass package to exhibit a through-thickness crack which can compromise the contents' hermeticity or sterility and yet still effectively contain the contents. To prevent through-thickness cracks, glass may be strengthened to improve the mechanical strength of the glass and the ability to resist flaws caused by external sources of damage. The glass may be strengthened by the introduction of a compressive stress. The compressive stresses produced in the glass must be overcome to produce flaws that extend into the central region of the glass or all the way through the thickness of the glass. Such compressive stress may be introduced, for example, by thermal tempering, chemical tempering by ion exchange, lamination of glasses or glasses and plastics (e.g., glass/glass or glass/plastic/glass lamination) having different moduli and/or coefficients of thermal expansion (CTE), and/or coatings of materials having moduli and/or CTE that differ from those of the glass.

Referring to <FIG>, a conventional process <NUM> for strengthening glass includes a single-step ion-exchange process. The conventional process <NUM> includes converting the glass into a glass article <NUM>, subjecting the glass to the single-step ion-exchange process <NUM>, rinsing the ion-exchange reagents from the glass <NUM>, and washing the glass <NUM>. The single-step ion-exchange process <NUM> may include submerging the glass in an ion-exchange bath comprising an alkali metal salt, such as potassium nitrate (KNO<NUM>) or sodium nitrate (NaNO<NUM>) for example. The ion-exchange bath may be maintained at a temperature of at least <NUM>. The larger alkali metal ions, such as potassium ions, from the ion-exchange bath diffuse into the glass, replacing smaller ions, such as lithium and/or sodium. Replacement of the smaller ions in the glass with the larger alkali metal ions creates a compressive stress in the glass. The glass may be maintained in contact with the ion-exchange bath for a period of time sufficient to diffuse the larger alkali metal ions (e.g., potassium) into the glass to a depth in the glass sufficient to produce a given DOC.

One consequence of the introduction of compressive stress is the complementary buildup of tensile stress in opposing regions of the glass article, such as a container. For physical force balance to be maintained, the amount of stored elastic energy (SEE) in the compression regions <NUM> (compression) and in the central region <NUM> (tension) must be equal. In most cases, the glass surface experiences a large compressive stress, and the interior experiences a smaller magnitude tensile stress. Accordingly, the large compressive stresses at the surfaces of the glass are focused over a shallow depth, while the smaller tensile stress is distributed over the majority of the thickness of the glass.

The compressive stress in the compression regions <NUM> (e.g., first compression layer and second compression layer) is balanced by tensile stress, also referred to herein as "central tension" or "CT," in a central region of the glass, which extends inward from the DOC. For glass strengthened using a single-step ion-exchange process, the total compressive stress (e.g., the sum of the compressive stresses in the first compression region and the second compression region) is equal to the total central tension. The following Equation <NUM> (EQU. <NUM>) provides an expression for the relationship between the compressive stress (CS) and central tension (CT) in a glass strengthened by conventional ion-exchange. <MAT> In EQU. <NUM>, L is the thickness of the glass, DOC is the depth of compression from a first surface of the glass, and (L-DOC) is the depth of compression from the second surface of the glass. CS(x) is the compressive stress as a function of depth x, and CT(x) is the tensile stress as a function of depth x.

For a conventional single step ion-exchange process, the compressive stress may follow the error function profile CS(x) = CS * ERFC(x). Additionally, the central tension distribution CT(x) could be considered constant as a close approximation of the actual central tension distribution within the central tension region. Thus, the relationship between CS and CT for a single-step ion-exchange process can be modeled by the following Equation <NUM> (EQU. <NUM>): <MAT>.

In one integration of EQU. <NUM>, the following relationship between CS and central tension CT in Equation <NUM> (EQU. <NUM>) is obtained: <MAT> In EQU. <NUM>, DOCFSM is the depth of compression in millimeters measured according to the FSM method described below, t is the thickness of the glass, and a is a constant equal to <NUM>. Unless otherwise specified, central tension CTerfc and compressive stress CS are expressed herein in megaPascals (MPa), whereas thickness t and depth of layer DOCFSM are expressed in millimeters. As shown above in EQU. <NUM> and EQU. <NUM>, the CT is determined from the CS and the DOC. For a single-step ion-exchange process, the CT, CS, and DOC are all interdependent. For example, for a glass having a thickness of <NUM>, a CS of <NUM> MPa and a DOC of <NUM> micrometers (µm), the CT calculated from EQU. <NUM> would be about <NUM> MPa. Thus, for a single-step ion-exchange, a change in either the CS or the DOC results in a change in the CT.

Commercially-available borosilicate glass compositions have been used in conventional pharmaceutical packaging applications. However, ion-exchange of commercially-available borosilicate glass compositions is difficult and requires greater temperatures and longer ion-exchange times to produce a compressive stress sufficient to improve the mechanical strength of the glass compared to other types of glass. For example, ion-exchange of a commercially-available borosilicate glass in an ion-exchange bath comprising KNO<NUM> may require an ion exchange temperature of at least <NUM> and an ion exchange time of at least <NUM> hours to produce a compression of at least <NUM> MPa and a DOC of <NUM>.

Aluminosilicate glass compositions may be ion-exchanged to increase the compressive stress and depth of compression to a much greater extent compared to borosilicate glass compositions. For example, single-step ion-exchange of aluminosilicate glass in a bath of KNO<NUM> at a temperature of <NUM> and for a time of less than <NUM> hours (e.g., from <NUM> hours to <NUM> hours) may produce a compressive stress of greater than <NUM> MPa, or even greater than <NUM> MPa, at the surface of the glass and a DOC of greater than <NUM>. As previously discussed, in a single-step ion-exchange process, the CS, DOC, and CT are interrelated so that increasing the CS, the DOC, or both results in a corresponding increase in the central tension (CT). Thus, increasing the CS and DOC of a <NUM> thick aluminosilicate glass to <NUM> MPa and <NUM>, respectively, may increase the CT of the glass to <NUM> MPa.

It has been found that central tensions in excess of about <NUM> MPa are sufficient to cause flaws that penetrate into the central region of the glass to self-propagate through the thickness of the glass and laterally across the glass. Self-propagation of flaws in glass having central tensions of greater than <NUM> MPa is discussed in co-pending <CIT>. At central tensions greater than about <NUM> MPa, self-propagation of flaws through the thickness of the glass from the first surface to the second surface and laterally across the glass may proceed spontaneously and may render the glass article, such as a pharmaceutical container (e.g., vial, ampoule, cartridge, syringe, jar, etc), unusable for its intended purpose. In other words, self-propagation of flaws through the glass may cause the glass article to completely fail. When the CT is greater than <NUM> MPa, self-propagation of flaws may result in complete destruction/breakage of the glass article immediately or in a short amount of time, such as less than <NUM> hours, less than <NUM> hours, or even less than <NUM> hour. In some applications, complete failure of the glass article resulting from self-propagation of flaws may provide an indication of a defective glass article, such as identification of a defective pharmaceutical container in which a through crack has compromised the sterility of the container and exposed the contents to the atmosphere. In these applications, the damage to the glass article is easily apparent to the human eye such defective or damaged articles can be removed from inventory before the contents are administered to a patient. In some cases, complete destruction of the glass article (e.g., container) may result in complete loss of the contents.

However, in some applications, self-propagation of flaws rendering the glass article completely unusable for its intended purpose is not desired. For example, in the field of emergency medical response, complete failure of a glass pharmaceutical container in response to flaw damage may result in completely loss of the contents, which may render a critical pharmaceutical composition unavailable in an emergency situation, such as a situation of life or death. Under these circumstances, the availability of the contents of the glass container may outweigh the contamination of the contents resulting from loss of hermeticity or sterility. Thus, in certain circumstances, a glass article having a high compressive stress and DOC with a central tension less than the threshold central tension may be more suitable by providing high mechanical strength to resist flaw damage caused by external sources of damage and improved sharp damage response (i.e., reduced self-propagation of flaws resulting in reduced delayed breakage risk). Thus, the glass articles, such as glass pharmaceutical containers, having high CS and DOC and low CT may be resistant to flaw damage and may maintain the ability to contain the contents even in the event of a through crack developing in the glass.

Single-step ion-exchange processes for strengthening glass articles may be limited in their ability to produce glass articles having high CS and DOC with low CT below the threshold central tension, due to the interdependence of the CS, DOC, and CT. As previously discussed, for single-step ion-exchange processes, the CS, DOC, and CT are interdependent such that changing the CS and/or DOC changes the CT. Therefore, when a glass is ion-exchanged using a single-step ion-exchange process to increase the CS and DOC to improve the mechanical strength of the glass, the central tension also increases. Increasing the CS and DOC to a degree sufficient to improve the mechanical strength of the glass may increase the central tension above the threshold central tension, which results in self-propagation of flaws and increased risk of delayed breakage. There is, therefore, an ongoing need for methods of strengthening glass articles to produce glass articles having high CS, high DOC and reduced CT to minimize self-propagation of flaws and reduce the breakage rate of the glass articles.

Two-step ion-exchange processes have been proposed for engineering the stress profile to reduce the CT in the central region of the glass. In these two-step ion-exchange processes, the first step includes submersing the glass in a poisoned ion-exchange bath to produce a stress profile with a low CS extending to the DOC. As used herein, the term "poisoned ion-exchange bath" may refer to an ion-exchange bath having a substantial concentration of ions other than the alkali metal ions of the ion exchange bath, the other ions reducing the effectiveness of the ion-exchange bath for ion-exchanging the glass. For example, a typical poisoned ion-exchange bath may include concentrations of the smaller sodium or lithium ions replaced by the larger potassium ions or may include other ions, such as calcium ions for example, that reduce the effectiveness of the ion-exchange bath. A poisoned ion-exchange bath may have a poisoning level of greater than <NUM>% of the ions in the ion-exchange bath. In the second step, the glass is submersed in a fresh ion-exchange bath to spike the surface of the glass with potassium ions to increase the CS at the surface. In order to get the desired DOC and CT level, the salt poisoning level must be controlled, such as by adding by adding foreign salts (i.e., salts that do not include the ion intended to be exchanged into the glass) to the ion-exchange bath to increase the poisoning level to the desired level. Thus, the two-step ion-exchange process requires two separate ion-exchange baths.

The methods for strengthening a glass article of the present disclosure are designed to eliminate the interdependence of CS, DOC, and CT so that strengthened glass articles having a high CS, high DOC, and a CT less than the threshold CT can be produced. Referring to <FIG>, a flowchart illustrating the method <NUM> for strengthening glass articles of the present disclosure is depicted. The method <NUM> for strengthening glass articles is a three-step process that may include step <NUM> of providing a glass article comprising a glass having the first surface, the second surface, and thickness t measured from the first surface to the second surface. The method <NUM> includes step <NUM> of introducing potassium ions into the surface region of the glass, step <NUM> of thermally treating the glass at a temperature and for a time sufficient to diffuse at least a portion of the potassium ions into the glass to a depth of layer, and then step <NUM> of introducing a compressive stress that may be greater than or equal to <NUM> megapascals (MPa) to the surface region <NUM> of the glass <NUM>. The DOL of the potassium ions after introducing the compressive stress to the surface region may be sufficient to produce a DOC of at least <NUM>. In some embodiments, the method <NUM> may optionally include step <NUM> of rinsing the glass article after step <NUM> and before step <NUM>. Additionally, in some embodiments, the method <NUM> may optionally include the step <NUM> of rinsing the glass after introducing the compressive stress of <NUM> MPa to the surface region and/or step <NUM> of washing the glass article.

As previously discussed, eliminating the interdependence of the CS, DOC, and CT may enable any one of the CS, DOC, and CT to be independently controlled. For example, the methods of strengthening the glass article of the present disclosure enable strengthening of the glass to achieve compressive stress at the first surface and/or the second surface of greater than <NUM> MPa and a DOC of greater than or equal to <NUM>, while maintaining the CT less than the threshold central tension of <NUM> MPa, above which flaws exhibit self-propagation. Thus, the CT can be controlled independent of the DOC and CS. The methods for strengthening glass articles of the present disclosure may produce strengthened glass articles exhibiting mechanical strength sufficient to resist damage from external sources as well as improved sharp damage response (i.e., reduced risk of delayed breakage caused by self-propagation of flaws). For example, the higher CS at the surface of the glass may increase the insult force necessary to create flaws in the first surface <NUM> and/or second surface <NUM> of the glass <NUM> and may reduce and/or prevent flaws that do develop in the compression regions <NUM> from propagating further into the glass <NUM>. The greater DOC may increase the depth to which a flaw must penetrate into the glass <NUM> to reach the central region <NUM> under tension. Thus, the higher CS and greater DOC make it more difficult for a flaw to propagate through the DOC to the central region <NUM>. However, if a flaw does propagate into the central region, the decreased CT may preserve the ability of the strengthened glass article to contain liquids and solids by reducing propagation of the flaw so that the glass article is not completely destroyed. Additionally, the method of strengthening disclosed herein can be accomplished with a single ion-exchange bath and does not require control of a poisoning level in a separate poisoned ion-exchange bath. Each step of the method of strengthening glass articles will now be described in further detail.

The method of making the glass article described hereinabove may include providing a glass having a first surface and a second surface separated by a thickness. The glass may comprise those compositions previously described herein, and be formed by those methods known in the art such as, but not limited to, down-drawing, including slot and/or fusion drawing, float methods, casting methods, molding processes such as, but not limited to, Vello, Danner, and blow-molding processes, or the like. The method of strengthening glass articles is performed on glass articles that have already been converted into the final shape of the article. The step <NUM> of providing the glass articles may include processing a piece of glass, such as a length of glass tubing, sheet of glass, or other glass, into the glass article. The glass may be processed through one or more thermal conversion steps in which the glass is heated and then mechanically deformed to shape the glass into the desired glass article, such as a container, for example. In some embodiments, the glass article may be a glass container (i.e., container comprising a glass), such as a vial, cartridge, ampoule, syringe, jar, or other container. Although described in the context of pharmaceutical containers, the methods of strengthening glass articles may be applied to other strengthen glass articles, such as bottles or other containers for foodstuffs, cover glass for portable electronics or glass for automotive or aerospace applications, for example.

Introducing the potassium ions to the glass article in step <NUM> of the method <NUM> in <FIG> may include subjecting the glass article to an initial ion-exchange process. During the initial ion-exchange process, the glass may be submersed in an initial ion-exchange bath that may include an alkali metal salt, such as alkali metal nitrates, alkali metal sulfates, or other alkali metal salts. During the initial ion-exchange, the larger alkali metal ions from the initial ion-exchange bath may diffuse into the surface regions of the glass to replace smaller metal ions, such as smaller alkali metal ions like lithium or sodium ions. The initial ion-exchange process introduces the amount of potassium ions into the surface regions of the glass, such as the surface region proximate the first surface of the glass and the surface region proximate the second surface of the glass.

In some embodiments, the alkali metal salt of the initial ion-exchange bath may be potassium nitrate. In some embodiments, the initial ion-exchange bath may be a fresh ion-exchange bath or a poisoned ion-exchange bath. Alkali metal ions, such as potassium ions, diffuse faster into the glass when a fresh ion-exchange bath is used for the ion-exchange, resulting in a reduced ion exchange time compared to submersion in a poisoned ion-exchange bath. The initial ion-exchange may be conducted using a poisoned ion-exchange bath, but the time required for the initial ion-exchange may be greater compared to a fresh ion-exchange bath. Additionally, submersing the glass in a fresh ion-exchange bath during the initial ion-exchange may enable the use of the same bath for the initial ion-exchange process and the final ion-exchange process, as well as for other single-step ion-exchange processes.

The initial ion-exchange bath may be maintained at an initial ion-exchange temperature of greater than or equal to <NUM>, greater than or equal to <NUM>, greater than or equal to <NUM>, or even greater than or equal to <NUM>. The initial ion-exchange temperature of the initial ion-exchange bath may be less than or equal to <NUM>, less than or equal to <NUM>, or even less than or equal to <NUM>. In some embodiments, the initial ion-exchange bath may be maintained at the initial ion-exchange temperature of from <NUM> to <NUM>, or from <NUM> to <NUM>, from <NUM> to <NUM>, or even from <NUM> to <NUM>. In some embodiments, the initial ion-exchange bath may be maintained at the initial ion-exchange temperature of from <NUM> to <NUM>. At temperatures greater than about <NUM>, thermal relaxation in the glass may be more significant, which may reduce the compressive stress in the surface region resulting from introduction of the potassium ions to the surface region. The upper temperature range of the initial ion-exchange process may be further limited by the chemistry of the initial ion-exchange bath and side reactions with the components. For example, potassium nitrate may thermally decompose or react with other constituents of the initial ion-exchange bath at temperatures greater than about <NUM>.

The glass of the glass article may be submersed in the initial ion-exchange bath for an initial ion-exchange time sufficient to introduce the amount of potassium ions into the surface regions of the glass at the initial ion-exchange temperature. In some embodiments, the initial ion-exchange time may be greater than or equal to <NUM> hour (hr), greater than or equal to <NUM> hr, or even greater than or equal to <NUM> hr. In some embodiments, the initial ion-exchange time may be less than or equal to <NUM> hr, such as less than or equal to <NUM> hr, or even less than or equal to <NUM> hr. For example, in some embodiments, the initial ion-exchange time may be from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, or even from <NUM> hr to <NUM> hr. At initial ion-exchange times greater than about <NUM> hour, thermal relaxation of the glass caused by exposure of the glass to the initial ion-exchange temperature for the extended period of time may reduce the compressive stress in the surface regions created by introduction of the larger alkali metal ions. Maintaining the initial ion-exchange time at less than or equal to <NUM> hour may minimize thermal relaxation in the glass, thereby preserving the compressive stress resulting from introduction of the potassium ions. The initial ion-exchange time at high temperature may also be limited by the chemistry of the initial ion-exchange bath and side reactions with components of the initial ion-exchange bath.

In some embodiments, introducing potassium ions into the surface regions of the glass may include subjecting the glass to the initial ion-exchange at the initial ion-exchange temperature of greater than or equal to <NUM> and for an initial ion-exchange time long enough to introduce the amount of potassium ions to the surface regions of the glass sufficient to attain the DOC of greater than <NUM> and the central tension of less than <NUM> MPa following thermal treatment and the final ion-exchange process. In some embodiments, the initial ion-exchange of the glass may be conducted at an initial ion-exchange temperature of from <NUM> to <NUM> and for an initial ion-exchange time of from <NUM> hours to <NUM> hours.

The amount of potassium ions introduced to the surface regions of the glass by the initial ion-exchange process may be determined based on the target values of the DOC and the CT. The amount of potassium ions may be sufficient to enable the potassium ions to diffuse into the glass to a depth in the glass sufficient to produce the target DOC during the thermal treatment step while maintaining compressive stress in the compression regions of the glass. In other words, enough potassium may be deposited in the surface regions during the initial ion-exchange to prevent the compressive stress from dropping below required level during the thermal treatment step conducted to diffuse the potassium ions further into the glass.

The amount of potassium ions to introduce to the surface regions of the glass during the first ion-exchange to produce the target values of DOC and CT in the glass may be estimated by modeling the initial ion exchange process as a single step ion exchange process using EQU. <NUM> and/or EQU. <NUM> previously discussed. The amount of potassium ions introduced to the surface regions may be further fine-tuned by adjusting the initial ion-exchange temperature, the initial ion-exchange time, or both. In some embodiments, the method of strengthening the glass article may include subjecting the glass article to the initial ion-exchange process, determining the amount of the potassium ions to introduce to the surface region of the glass, and adjusting the initial ion-exchange temperature, the initial ion-exchange time, or both of the initial ion-exchange process to introduce the determined amount of potassium ions into each of the surface regions of the glass.

At the conclusion of the initial ion-exchange time, the glass article comprising the glass may be removed from the initial ion-exchange bath. In some embodiments, the glass of the glass article may be rinsed to remove the reagents from the initial ion-exchange bath from the surfaces of the glass (e.g., the first surface and the second surface).

Referring again to <FIG>, the method of strengthening the glass article includes thermally treating the glass article (step <NUM>) after introducing the potassium ions to the surface regions of the glass, such as after subjecting the glass article to the initial ion-exchange process. Thermally treating the glass article after introducing the potassium ions to the surface regions may cause the potassium ions in the surface regions of the glass to diffuse further into the glass to a DOL (i.e., towards the center of the glass). The DOL to which the potassium ions are diffused during the thermal treatment may be sufficient to produce the target DOC in the glass. Diffusion of the potassium ions further into the glass may produce compressive stress in interior compression regions of the glass, each of which extends from one of the surface regions to the DOC. Diffusion of the potassium ions further into the glass to the DOL may increase the DOC, which may improve the deep flaw region load bearing performance of the glass. In other words, increasing the DOC may increase the depth to which flaws must penetrate into the glass to reach the central region of the glass, which is under tensile stress. The load bearing performance of the glass relates to the mechanical strength of the glass and refers to the amount of force exerted on the glass required to cause breakage or catastrophic failure of the glass. Load bearing performance of the glass will be discussed in further detail in relation to the Examples presented herein.

Thermally treating the glass of the glass article may include subjecting the glass to a thermal treatment temperature for a thermal treatment time sufficient to diffuse at least a portion of the potassium ions from the surface regions to a DOL sufficient to produce the DOC greater than or equal to <NUM>. Heat may be removed from the glass article at the conclusion of the thermal treatment time. In some embodiments, the glass of the glass article may be thermally treated by placing the glass articles in an oven or other heating apparatus maintained at the thermal treatment temperature and removing the glass articles from the oven at the conclusion of the thermal treatment time. The thermal treatment temperature may be greater than or equal to <NUM>, greater than or equal to <NUM>, or even greater than or equal to <NUM>. In some embodiments, the thermal treatment temperature may be less than or equal to <NUM>, less than or equal to <NUM>, or even less than or equal to <NUM>. In some embodiments, the thermal treatment temperature may be from <NUM> to <NUM>, such as from <NUM> to <NUM>, from <NUM> to <NUM>, or even from <NUM> to <NUM>. The process window for the thermal treatment temperature may be greater than the process window for the first ion-exchange temperature of the first ion-exchange process due to removal of the salt bath chemistry limitation from the thermal treatment. Not intending to be bound by any specific theory, it is believed that during thermal treatment, the glass is not subjected to high surface stress such as the high surface stress experienced in an ion-bath. Since thermal relaxation in the glass is driven by temperature, time, and stress, a reduction in the surface stress experienced in the glass may enable the glass to withstand greater thermal treatment temperatures and thermal treatment times without experiencing substantial thermal relaxation compared to the ranges of temperature and time appropriate for the initial ion-exchange.

The thermal treatment time may be sufficient to diffuse at least a portion of the potassium ions in the surface regions of the glass to the DOL and may be short enough to minimize thermal relaxation of the glass to maintain the compressive stress in the compression region caused by introducing the potassium ions and diffusing the potassium ions to the DOL. For example, in some embodiments, the thermal treatment time may be sufficient at the thermal treatment temperature to diffuse potassium ions from the surface regions into the glass to a DOL that is sufficient to produce a DOC of at least <NUM> in the glass. In some embodiments, the thermal treatment time may be greater than or equal to <NUM> hr, greater than or equal to <NUM> hrs, or even greater than or equal to <NUM> hrs. In some embodiments, the thermal treatment time may be less than or equal to <NUM> hrs, less than or equal to <NUM> hrs, less than or equal to <NUM> hrs, or even less than or equal to <NUM> hrs. In some embodiments, the thermal treatment time may be from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, or from <NUM> hr to <NUM> hr.

The thermal treatment time to achieve a specific DOC may depend on the thermal treatment temperature. For example, as the thermal treatment temperature increases, the thermal treatment time for achieving the specific DOC decreases. Likewise, as the thermal treatment temperature decreases, the thermal treatment time for attaining the specific DOC increases. Increasing the thermal treatment temperature may, therefore, reduce the thermal treatment time to achieve the specific DOC, which may reduce the cycle time and increase the production rate of the glass articles. However, increasing the thermal treatment temperature may result in increased thermal relaxation within the glass, which can reduce the compressive stress produced by the potassium ions introduced to the glass and diffused to the DOL. The reduction in compressive stress in the compression region caused by thermal relaxation may reduce the mechanical strength of the glass and degrade the load bearing performance and damage resistance of the glass. Therefore, the thermal treatment temperature and thermal treatment time may be modified to balance production rate with thermal relaxation.

Thermally treating the glass may include varying the thermal treatment temperature during the thermal treatment. In some embodiments, thermally treating the glass may include continuously increasing or decreasing the thermal treatment temperature throughout the thermal treatment time. In other embodiments, thermally treating the glass may include subjecting the glass to a plurality of thermal treatment temperatures during the thermal treatment time. For example, in some embodiments, the glass may be subjected to first thermal treatment at a first thermal treatment temperature for a first thermal treatment time and a second thermal treatment at a second thermal treatment temperature for a second thermal treatment time. The glass may be subjected to <NUM>, <NUM>, <NUM>, <NUM>, or more than <NUM> different thermal treatment temperatures during the thermal treatment.

In some embodiments, the glass may be rinsed to remove the ion-exchange materials from the surfaces (e.g., first surface and second surface) of the glass after the initial ion-exchange process and before thermally treating the glass (<FIG>, step <NUM>). However, failure to rinse or wash the glass surfaces before the thermal treatment has been found to have very little influence on the final stress profile and load bearing performance of the glass. Rinsing the glass article (step <NUM>) may include dip rinsing (i.e., submersing the glass of the glass article in a solvent such as water or other organic solvent to rinse off the ion-exchange reagents).

As shown in <FIG>, following thermal treatment of the glass (step <NUM>), the method may include introducing a compressive stress of greater than or equal to <NUM> MPa to the surface regions of the glass, such as the surface region proximate the first surface and the surface region proximate the second surface. In some embodiments, introducing the compressive stress into the surface regions of the glass may include subjecting the glass to a final ion-exchange process to produce the compressive stress of greater than or equal to <NUM> MPa, as determined at the first surface and/or the second surface of the glass. In other words, the final ion-exchange process may be used to "spike" the surface regions of the glass with a high concentration of larger alkali metal ions, such as potassium ions, to increase the compressive stress in the surface regions of the glass.

The final ion-exchange process may include submersing the glass of the glass article into a final ion-exchange bath maintained at a final ion-exchange temperature. The final ion-exchange bath may include an alkali metal salt, such as alkali metal nitrates, alkali metal sulfates, or other alkali metal salts. The alkali metal of the alkali metal salt may be larger in size than other metal ions of the glass composition (e.g., other smaller alkali metal ions, such as sodium and lithium ions). During the final ion-exchange, the larger alkali metal ions from the final ion-exchange bath may diffuse into the surface regions of the glass to replace smaller metal ions, such as smaller alkali metal ions like lithium or sodium ions. The final ion-exchange process introduces an additional amount of potassium ions or other larger alkali metal ions into the surface regions of the glass. In some embodiments, the final ion-exchange bath may include potassium nitrate. In some embodiments, the final ion-exchange bath may be a fresh ion-exchange bath or a slightly poisoned ion-exchange bath. As used herein, a "slightly poisoned ion-exchange bath" refers to an ion-exchange bath has a low poisoning level of less than about <NUM>% by weight compared to a "poisoned ion-exchange bath" having a poisoning level greater than <NUM>% by weight. The slight poisoning of the bath may result from continued use of the bath, which may accumulate small concentrations of smaller alkali metal ions from the glass that are replaced during the ion-exchange.

The final ion-exchange bath may be maintained at a final ion-exchange temperature of less than or equal to <NUM>, such as less than or equal to <NUM>, less than or equal to <NUM>, or even less than or equal to <NUM>. Maintaining the final ion-exchange bath at a final ion-exchange temperature less or equal to <NUM> may minimize the degree of thermal relaxation that occurs in the compression regions during the final ion-exchange. In some embodiments, reducing the thermal relaxation in the glass during the final ion-exchange may reduce or prevent decreases in the compressive stress in the interior compression regions between the surface regions and the DOCs. In some embodiments, the final ion-exchange temperature may be greater than or equal to <NUM>, greater than or equal to <NUM>, or even greater than or equal to <NUM>. In some embodiments, the final ion-exchange bath may be maintained at the final ion-exchange temperature of from <NUM> to <NUM>, or from <NUM> to <NUM>, from <NUM> to <NUM>, or even from <NUM> to <NUM>.

The glass of the glass article may be submersed in the final ion-exchange bath for a final ion-exchange time sufficient to produce a compressive stress at the first surface, second surface, or both of at least <NUM> MPa. In some embodiments, the final ion-exchange time may be greater than or equal to <NUM> hr, greater than or equal to <NUM> hr, or even greater than or equal to <NUM> hr. In some embodiments, the final ion-exchange time may be less than or equal to <NUM> hr, such as less than or equal to <NUM> hr, or even less than or equal to <NUM> hr. For example, in some embodiments, the final ion-exchange time may be from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, from <NUM> hr to <NUM> hr, or even from <NUM> hr to <NUM> hr. At final ion-exchange times greater than about <NUM> hour, thermal relaxation of the glass caused by exposure of the glass to the final ion-exchange temperature for an extended period of time may reduce the compressive stress in the compression regions, in particular the interior compression regions between the surface region and the DOC, thereby reducing the deep flaw region load bearing performance of the glass article. Maintaining the final ion-exchange time at less than or equal to <NUM> hour may minimize thermal relaxation in the glass, thereby preserving the compressive stress in the interior compression regions. The glass of the glass article may be removed from the final ion-exchange bath at the conclusion of the final ion-exchange time.

In some embodiments, the method may include subjecting the glass article to a final rinse (step <NUM>) and/or final wash following the final ion-exchange process to remove excess alkali metal salts and other reagents from the surfaces of the glass. The final rinse may include dip rinsing the glass article.

Referring again to <FIG>, the method of strengthening may produce a glass article <NUM> having improved mechanical strength to resist damage from external sources and having a reduced central tension to reduce delayed breakage caused by self-propagation of flaws extending into the central region <NUM> of the glass <NUM>. The glass article <NUM> comprises the glass <NUM> having the first surface <NUM>, the second surface <NUM>, and the thickness t measured as the distance between the first surface <NUM> and the second surface <NUM>. The glass <NUM> has compression regions <NUM> extending from the first surface <NUM>, the second surface <NUM>, or both to the DOC. The compression regions <NUM> are under a compressive stress. The glass may have a first compression layer extending from the first surface <NUM> to a first DOC and a second compression layer extending from the second surface <NUM> to a second DOC. It is intended for the compression regions <NUM> to represent either or both of the first compression layer proximate the first surface <NUM> and the second compression layer proximate the second surface <NUM>. The glass <NUM> further includes the central region <NUM> under a central tension (CT) and extending inward from the DOC and disposed between the compression regions <NUM> (i.e., between the first compression layer and the second compression layer).

The thickness t of the glass <NUM> may be sufficient to form a container, such as a glass container. In some embodiments, the thickness of the glass <NUM> may be greater than or equal to <NUM>, such as greater than or equal to <NUM>, greater than or equal to <NUM>, or even greater than or equal to <NUM>. In some embodiments, the thickness t of the glass <NUM> may be sufficient to conform to the standards for pharmaceutical containers. The thickness t of the glass <NUM> may be less than or equal to <NUM>, such as less than or equal to <NUM>, less than or equal to <NUM>, less than or equal to <NUM>, less than or equal to <NUM>, less than or equal to <NUM>, or even less than or equal to <NUM>. In some embodiments, the thickness t of the glass may be from <NUM> to <NUM>, such as from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>. It is understood that complex packaging geometries such as vials, cartridges, and bottles may have a variety of wall thicknesses throughout the container.

The DOC (e.g., first DOC and/or second DOC) may be sufficient to increase the depth to which flaws must extend into the glass to reach the central region <NUM>, which is under a tensile stress. Flaws extending into the compression regions <NUM> can be arrested by the compressive stress in the compression regions <NUM>. As the DOC of the compression regions <NUM> increases, the depth to which a flaw must extend to penetrate through the compression regions <NUM> to reach the central region <NUM> increases. Thus, increasing the DOC of the compression regions <NUM> may increase the damage resistance of the glass by reducing the probability of a flaw extending through the compression regions <NUM> and into the central region <NUM>. In some embodiments, the DOC (e.g., the first DOC and/or the second DOC) of the glass <NUM> may be greater than or equal to <NUM>, such as greater than or equal to <NUM>, or even greater than <NUM>. In some embodiments, the DOC (e.g., the first DOC and/or the second DOC) of the glass <NUM> may be from <NUM> to <NUM>, such as from <NUM> to <NUM>, from <NUM> to <NUM>, or even from <NUM> to <NUM>. In some embodiments, each DOC may be from <NUM>% to <NUM>% of the thickness t of the glass <NUM>.

The compression regions <NUM> may have a compressive stress sufficient to provide the mechanical strength to the glass to resist damage from external sources of damage, such as handling, filing, transporting. Increasing the compressive stress in the compression regions <NUM> increases the insult forces necessary to create flaws in the first surface <NUM> and/or second surface <NUM> of the glass <NUM>. Increasing the compressive stress in the compression regions <NUM> may also reduce and/or prevent flaws in the compression regions <NUM> from propagating further into the glass <NUM>, such as into the central region <NUM> of the glass <NUM>. The first, the second or both of the compression regions <NUM> of the glass <NUM> has or have a compressive stress of greater than or equal to <NUM> MPa, greater than or equal to <NUM> MPa, or even greater than or equal to <NUM> MPa as determined at the first surface <NUM> and/or the second surface <NUM>. In some embodiments, the compression regions <NUM> may have a compressive stress less than or equal to <NUM> MPa, less than or equal to <NUM> MPa, less than or equal to <NUM> MPa, or even less than or equal to <NUM> MPa as determined at the first surface <NUM> and/or the second surface <NUM>. In some embodiments, the compression regions <NUM> of the glass <NUM> may have a compressive stress of from <NUM> MPa to <NUM> MPa, such as from <NUM> MPa to <NUM> MPa, as determined at the first surface <NUM> and/or the second surface <NUM> of the glass <NUM>.

Referring still to <FIG>, each compression region <NUM> may include the surface region <NUM> and the interior compression region <NUM>. The surface region <NUM> may be proximate the surface, such as the first surface <NUM> and/or the second surface <NUM>, and may extend from the surface of the glass <NUM> inward toward the center of the glass <NUM> (i.e., in the + or -Z direction of the coordinate axis in <FIG>). The surface region <NUM> may be defined by the distance into the glass <NUM> to which the potassium ions from the final ion-exchange process penetrate into the glass. The surface region <NUM> may have a surface region thickness that is less than the DOC. Each interior compression region <NUM> may extend from the corresponding surface region <NUM> to the corresponding DOC. Each interior compression region <NUM> may comprise the potassium ions introduced during the initial ion-exchange process and diffused into the glass <NUM> during the thermal treatment. At least a portion of the potassium ions in the surface region <NUM> resulting from the initial ion-exchange process may further diffuse into the interior compression region <NUM> during the final ion-exchange process. The surface region <NUM> may have a greater concentration of potassium ions and greater compressive stress compared to the potassium ion concentrations and compressive stress in the interior compression region <NUM>.

Additionally, the magnitude of the slope of the potassium ion concentration as a function of depth in the glass in the surface region <NUM> may be greater than the magnitude of the slope of the potassium ion concentration as a function of depth in the interior compression region <NUM>. Referring to <FIG>, the potassium ion concentration as a function of depth in the glass is graphically depicted for an aluminosilicate glass subjected to a single stage ion-exchange (<NUM>), and borosilicate glass subjected to a single stage ion-exchange process (<NUM>), and an aluminosilicate glass subjected to the three stage method of strengthening glass disclosed herein (<NUM>). For the aluminosilicate glass subjected to the single stage ion-exchange (<NUM>), the potassium ion concentration decreases steadily with increasing depth. Likewise, for the borosilicate glass subjected to the single stage ion exchange (<NUM>), the potassium ion concentration also decreases steadily with increasing depth. For the aluminosilicate glass subjected to the three-stage strengthening process disclosed herein (<NUM>), the potassium ion concentration decreases rapidly in the surface region as indicated by the greater average slope in the surface region (represented by the first region <NUM> of curve <NUM>) from the surface (depth = <NUM>) to a depth of the surface region (i.e., the depth at which the slope of potassium concentration as a function of depth changes). In <FIG>, the depth of the surface region (<NUM>) is about <NUM>, though this depth may vary depending on the conditions selected for the first ion-exchange process, thermal treatment, and/or the final ion-exchange process. In the interior compression regions of the glass, indicted by the second region <NUM> of curve <NUM>, the potassium ion concentration decreases with increasing depth at a lesser rate compared to the surface region, first region <NUM> of curve <NUM>. Thus, <FIG> shows that the three-stage strengthening process disclosed herein produces an aluminosilicate glass having two distinct regions within the compression regions of the glass.

Referring still to <FIG>, the potassium ion concentration at the surface for the aluminosilicate glass subjected to the three-stage strengthening process of the present disclosure may be less than the potassium ion concentration at the surface of the aluminosilicate glass subjected to the single-stage ion exchange. However, the aluminosilicate glass produced using the three-stage strengthening process may exhibit a greater compressive stress at the surface compared to the glass made with the single-stage ion exchange due to less thermal relaxation during the final ion exchange. During the longer ion-exchange time of the single stage ion exchange, exposure to the ion exchange bath at temperatures in excess of <NUM> may result in thermal relaxation, which decreases the compressive stress at the surface of the glass strengthened by the single stage ion exchange. <FIG> also shows that the aluminosilicate glass produced by the three-stage strengthening process disclosed herein may exhibit a greater DOC and a greater compressive stress at the surface (as demonstrated by the greater potassium ion concentration at the surface) compared to borosilicate glass strengthened by a single stage ion exchange.

Referring again to <FIG>, the central region <NUM> of the glass may have a CT below a threshold CT, above which flaws penetrating into the central region <NUM> exhibit self-propagation through the thickness of the glass (i.e., in the +/-Z direction of the coordinate axis in <FIG>). Above the threshold central tension, flaws penetrating into the central region <NUM> may exhibit self-propagation of the flaw laterally through the glass (i.e., in the +/-X and/or +/-Y directions of the coordinate axis of <FIG>). Self-propagation of flaws penetrating into the central region <NUM> of the glass <NUM> may cause complete destruction of the glass <NUM> immediately, or within a time period after introduction of the flaw. The influence of central tension on the self-propagation behavior of flaws extending into the central region <NUM> of the glass <NUM> is described further in <CIT>, and co-pending <CIT>. The breakage caused by self-propagation of the flaws in the central region <NUM> may render the glass article, such as a glass container, useless for its intended purpose.

As previously discussed herein, in some applications, self-propagation of flaws resulting in complete destruction of the glass article is not desired. For example, in some applications, glass articles, such as glass containers, that can sustain a through crack without complete breakage/destruction of the glass article may be more desirable. The glass articles <NUM> produced from the method of strengthening glass disclosed herein has a central tension in the central region <NUM> less than the threshold CT below which flaws extending into the central region <NUM> do not experience self-propagation of the flaw through the thickness of the glass <NUM> and laterally through the glass <NUM>. Thus, the glass articles <NUM> subjected to the method of strengthening glass disclosed herein sustain flaw damage extending into the central region <NUM> of the glass <NUM> without self-propagation of the flaws that result in complete destruction the glass article <NUM>, such as a The central tension in the central region <NUM> of the glass <NUM> is less than <NUM> MPa, such as less than or equal to <NUM> MPa, or even less than or equal to <NUM> MPa. In some embodiments, the glass <NUM> may have a central tension in the central region <NUM> of from <NUM> MPa to <NUM> MPa.

As previously discussed, the three-stage strengthening process disclosed herein may eliminate the dependence of CT on the CS and DOC and enable independent control of the CT, CS, and DOC. For example, the DOC may be increased or decreased by increasing or decreasing the thermal treatment temperature and/or the thermal treatment time of the thermal treatment step. The CT may be increased or decreased by increasing or decreasing the initial ion exchange time of the initial ion exchange. To modify the CT independent of the DOC, the increase or decrease in the ion exchange time may be accompanied by a corresponding change in the thermal treatment temperature and/or thermal treatment time. For example, to increase the CT, the initial ion exchange time may be increased to increase the amount of potassium ions introduced to the surface region <NUM> in the initial ion exchange. To compensate for the greater penetration of potassium ions into the glass resulting from the increased initial ion-exchange time, the thermal treatment temperature and/or the thermal treatment time of the thermal treatment may be reduced to achieve the same target DOC with increased CT. The CS can be increased or decreased by increasing or decreasing the final ion-exchange time and/or final ion-exchange temperature. Increasing or decreasing the CS may also be accompanied by modifications to the thermal treatment to maintain the same DOC and CT. Thus, each of the CT, DOC, and CS can be independently controlled.

This independent control of the CT relative to the DOC and CS enable the glass to be strengthened to provide increased mechanical strength to resist damage without increasing the CT above the threshold at which flaws penetrating into the central region <NUM> exhibit self-propagation of flaws through the thickness and laterally across the glass.

The article comprises a glass. The glass includes first surface and the second surface. The glass includes a compression region extending from the first surface, the second surface, or both to the DOC, wherein the compression region is under a compressive stress, and a central region under a central tension, wherein the central region extends inward from the DOC. The compressive stress measured at the first surface, the second surface, or both is greater than or equal to <NUM> megapascals (MPa), the DOC may be at least <NUM> micrometers (<NUM>), and the central tension is less than a threshold central tension above which a stored elastic energy in the central region is sufficient to cause flaws extending into the central region to self-propagate through a thickness of the glass from the first surface to the second surface and laterally through the glass The central tension is less than <NUM> MPa. In some embodiments, the glass may include the first compression region proximate the first surface and the second compression region proximate the second surface.

Commercially available Borosilicate glasses (ASTM E438-<NUM> (Standard Specification for Glasses in Laboratory Apparatus) Type <NUM>, class A glasses - <NUM> ppm/K, Type <NUM>, class B glasses -<NUM> ppm/K) that are typically used as containers for pharmaceuticals, serum, vaccines, and the like, may only be strengthened to achieve a compressive stress in a range of from <NUM> MPa to <NUM> MPa when ion exchanged for periods that are typically used. To obtain a compressive stress of <NUM> MPa or greater, such borosilicate glasses must be ion exchanged for at least <NUM> hours at temperatures of greater than <NUM>, which greatly increases the processing time for making the strengthened borosilicate glasses. Thus, these commercially-available borosilicate glasses may not be easily ion-exchanged to achieve high compressive stress. Such glasses are thus less resistant to damage from external sources of damage compared to strengthened glass having a compressive stress greater than <NUM> MPa. Consequently, the failure rate of borosilicate glass containers due to damage caused by handling, transportation and other sources of external damage may be greater. In contrast, the glasses strengthened by the three-stage strengthening method disclosed herein may achieve a compressive stress of greater than <NUM> MPa or even greater than <NUM> MPa in a practical amount of time while maintaining the CT less than the threshold CT, above which self-propagation of flaws extending into the central region <NUM> causes breakage of the glass.

In some embodiments, the glass article, such as a container comprising a glass, may include at least one aluminosilicate glass. In some embodiments, the aluminosilicate glass may include at least one alkali metal oxide. In some embodiments, the glass article, such as a container, may include a glass composition that is within the ASTM standard type 1b glass compositions.

In some embodiments, the glass article, such as a container, may comprise a chemically durable glass such as that described in <CIT> et al. , entitled "Alkaline Earth Alumino-Silicate Glass Compositions with Improved Chemical and Mechanical Durability," which claims priority from <CIT>, and having the same title. This exemplary glass composition generally includes SiO<NUM>, Al<NUM>O<NUM>, at least one alkaline earth oxide, and alkali oxides including at least Na<NUM>O and K<NUM>O. In some embodiments, the glass compositions may also be free from boron and compounds containing boron. The combination of these components enables a glass composition which is resistant to chemical degradation and is also suitable for chemical strengthening by ion exchange. In some embodiments, the glass compositions may further comprise minor amounts of one or more additional oxides such as, for example, SnO<NUM>, ZrO<NUM>, ZnO, or the like, which may be added as fining agents and/or to further enhance the chemical durability of the glass composition. In some embodiments, the glasses described therein include from about <NUM> mol% to about <NUM> mol% SiO<NUM>; from about <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% alkali oxide; and from about <NUM> mol% to about <NUM> mol% of alkaline earth oxide. The alkali oxide comprises at least NazO and K<NUM>O. In other embodiments, the glasses described therein comprise from about <NUM> mol% to about <NUM> mol% SiOz; from about <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% alkali oxide; and from about <NUM> mol% to about <NUM> mol% of alkaline earth oxide. The alkaline earth oxide comprises at least one of SrO and BaO.

In some embodiments, the glass article, such as a container, may comprise a chemically durable glass such as that described in described in <CIT>et al. , entitled "Glass Compositions with Improved Chemical and Mechanical Durability," which claims priority from <CIT>, and having the same title. The alkali aluminosilicate glass generally includes SiOz, Al<NUM>O<NUM>, at least one alkaline earth oxide, and one or more alkali oxides, such as NazO and/or K<NUM>O, and is free from boron and compounds containing boron. The alkali aluminosilicate glass composition may also be free from phosphorous and compounds containing phosphorous. The combination of these components enables a glass composition which is resistant to chemical degradation and is also suitable for chemical strengthening by ion exchange. In some embodiments, the glass compositions may further include minor amounts of one or more additional oxides such as, for example, SnO<NUM>, ZrO<NUM>, ZnO, TiOz, As<NUM>O<NUM> or the like, which may be added as fining agents and/or to further enhance the chemical durability of the glass composition. In some embodiments, such glasses may include from about <NUM> mol% to about <NUM> mol% SiO<NUM>; from about <NUM> mol% to about <NUM> mol% alkaline earth oxide; X mol% Al<NUM>O<NUM>; and Y mol% alkali oxide. The alkali oxide may include Na<NUM>O in an amount greater than <NUM> mol% and a ratio of Y:X which is greater than <NUM>. In other embodiments, such glasses may include from about <NUM> mol% to about <NUM> mol% SiO<NUM>; from about <NUM> mol% to about <NUM> mol% alkaline earth oxide, wherein the alkaline earth oxide may include CaO in an amount greater than or equal to <NUM> mol% and less than or equal to <NUM> mol%; X mol% Al<NUM>O<NUM>, wherein X is greater than or equal to <NUM> mol% and less than or equal to about <NUM> mol%; Y mol% alkali oxide, wherein a ratio of Y:X is greater than <NUM>. The glass compositions described in <CIT> and <CIT> are free from boron and compounds of boron and are ion exchangeable, thereby facilitating chemically strengthening of the glass to improve mechanical durability.

In other embodiments, the alkali aluminosilicate glass may include: from about <NUM> mol% to about <NUM> mol% SiO<NUM>; from about <NUM> mol% to about <NUM> mol% Na<NUM>O; from about <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from <NUM> mol% to about <NUM> mol% B<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% K<NUM>O: from about <NUM> mol% to about <NUM> mol% MgO; and from <NUM> mol% to about <NUM> mol% CaO; wherein: <NUM> mol% ≤ SiO<NUM> + B<NUM>O<NUM> + CaO ≤ <NUM> mol%; Na<NUM>O + K<NUM>O + B<NUM>O<NUM> + MgO + CaO + SrO > <NUM> mol%; <NUM> mol% ≤ MgO + CaO + SrO ≤ <NUM> mol%; (Na<NUM>O + B<NUM>O<NUM>)-Al<NUM>O<NUM> ≥ <NUM> mol%; <NUM> mol% ≤ Na<NUM>O - Al<NUM>O<NUM> ≤ <NUM> mol%; and <NUM> mol% ≤ (NazO + K<NUM>O) - Al<NUM>O<NUM> ≤ <NUM> mol%. The glass is described in <CIT>, and claiming priority to <CIT>.

In other embodiments, the alkali aluminosilicate glass may include: at least one of alumina, and at least one of an alkali metal oxide and an alkali earth metal oxide, wherein-<NUM> mol% ≤ (R<NUM>O + R'O - Al<NUM>O<NUM> - ZrO<NUM>) - B<NUM>O<NUM> ≤ <NUM> mol%, where R is one of Li, Na, K, Rb, and Cs, and R' is one of Mg, Ca, Sr, and Ba. In some embodiments, the alkali aluminosilicate glass may include: from about <NUM> mol% to about <NUM> mol. % SiO<NUM>; from <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from <NUM> mol% to about <NUM> mol% B<NUM>O<NUM>; from <NUM> mol% to about <NUM> mol% LizO; from <NUM> mol% to about <NUM> mol% Na<NUM>O; from <NUM> mol% to about <NUM> mol% K<NUM>O; from <NUM> mol% to about17 mol% MgO; from <NUM> mol% to about <NUM> mol% CaO; and from <NUM> mol% to about5 mol% ZrOz. The glass is described in <CIT>, and claiming priority to <CIT>.

In other embodiments, the alkali aluminosilicate glass may include: from about <NUM> mol% to about <NUM> mol% SiO<NUM>; from about <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from <NUM> mol% to about <NUM> mol% B<NUM>O<NUM>; from <NUM> mol% to about <NUM> mol% Li<NUM>O; from <NUM> mol% to about <NUM> mol% Na<NUM>O; from <NUM> mol% to about <NUM> mol% K<NUM>O; from <NUM> mol% to about <NUM> mol% MgO; from <NUM> mol% to about <NUM> mol% CaO; from <NUM> mol% to about <NUM> mol% ZrO<NUM>; from <NUM> mol% to about <NUM> mol% SnO<NUM>; from <NUM> mol% to about <NUM> mol% CeO<NUM>; less than about <NUM> ppm As<NUM>O<NUM>; and less than about <NUM> ppm Sb<NUM>O<NUM>; wherein <NUM> mol% ≤ Li<NUM>O + Na<NUM>O + K<NUM>O ≤ <NUM> mol% and <NUM> mol% ≤ MgO + CaO ≤ <NUM> mol%. The glass is described in <CIT>, and claiming priority to <CIT>.

In other embodiments, the alkali aluminosilicate glass may include SiO<NUM> and NazO, wherein the glass has a temperature T35kp at which the glass has a viscosity of <NUM> kilo poise (kpoise), wherein the temperature Tbreakdown at which zircon breaks down to form ZrOz and SiOz is greater than T35kp. In some embodiments, the alkali aluminosilicate glass may include: from about <NUM> mol % to about <NUM> mol% SiO<NUM>; from about <NUM> mol % to about <NUM> mol% Al<NUM>O<NUM>; from <NUM> mol% to about <NUM> mol% B<NUM>O<NUM>; from about <NUM> mol % to about <NUM> mol% NazO; from <NUM> mol % to about <NUM> mol% KzO; from <NUM> mol% to about <NUM> mol% MgO; and <NUM> mol% to about <NUM> mol% CaO. The glass is described in <CIT>, and claiming priority to <CIT>.

In other embodiments, the alkali aluminosilicate glass may include at least <NUM> mol% SiOz and at least one modifier selected from the group consisting of alkali metal oxides and alkaline earth metal oxides, wherein [(Al<NUM>O<NUM> (mol%) + B<NUM>O<NUM>(mol%))/(Σalkali metal modifiers(mol%))] > <NUM>. In some embodiments, the alkali aluminosilicate glass may include: from <NUM> mol% to about <NUM> mol% SiOz; from about <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% B<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% NazO; and from <NUM> mol% to about <NUM> mol% KzO. The glass is described in <CIT>, and claiming priority to <CIT>.

In other embodiments, the alkali aluminosilicate glass may include SiO<NUM>, Al<NUM>O<NUM>, P<NUM>O<NUM>, and at least one alkali metal oxide (RzO), wherein <NUM> ≤ [(P<NUM>O<NUM>(mol%) + R<NUM>(mol%))/M<NUM>O<NUM>(mol%)] < <NUM>, where M<NUM>O<NUM> = Al<NUM>O<NUM> + B<NUM>O<NUM>. In some embodiments, the alkali aluminosilicate glass may include: from about <NUM> mol% to about <NUM> mol% SiO<NUM>; from <NUM> mol% to about <NUM> mol% B<NUM>O<NUM>; from <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% P<NUM>O<NUM>; and from about <NUM> mol% to about <NUM> mol% R<NUM>O; and, in certain embodiments, from about <NUM> to about <NUM> mol% SiO<NUM>; from <NUM> mol% to about <NUM> mol% B<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from about <NUM> mol% to about <NUM>% P<NUM>O<NUM>; and from about <NUM> mol% to about <NUM> mol% R<NUM>O. The glass is described in <CIT>, and claiming priority to <CIT>.

In still other embodiments, the alkali aluminosilicate glass may include at least about <NUM> mol% P<NUM>O<NUM>, wherein (M<NUM>O<NUM>(mol%)/RxO(mol%)) < <NUM>, wherein M<NUM>O<NUM> = Al<NUM>O<NUM> + B<NUM>O<NUM>, and wherein RxO is the sum of monovalent and divalent cation oxides present in the alkali aluminosilicate glass. In some embodiments, the monovalent and divalent cation oxides are selected from the group consisting of Li<NUM>O, Na<NUM>O, KzO, Rb<NUM>O, CszO, MgO, CaO, SrO, BaO, and ZnO. In some embodiments, the glass may include <NUM> mol% B<NUM>O<NUM>. The glass is described in <CIT>, entitled "Ion Exchangeable Glass with High Crack Initiation Threshold," and claiming priority to <CIT>.

In still other embodiments, the alkali aluminosilicate glass may include at least about <NUM> mol% SiO<NUM> and at least about <NUM> mol% Na<NUM>O. In some embodiments, the glass further comprises Al<NUM>O<NUM> and at least one of B<NUM>O<NUM>, KzO, MgO and ZnO, wherein -<NUM> + <NUM>·Al<NUM>O<NUM> - <NUM>·B<NUM>O<NUM> + <NUM>·Na<NUM>O - <NUM>·K<NUM>O + <NUM> (MgO + ZnO) ≥ <NUM> mol%. In particular embodiments, the glass may include: from about <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from <NUM> mol% to about <NUM> mol% B<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% NazO: from <NUM> mol% to about <NUM> mol% K<NUM>O; from <NUM> mol% to about <NUM> mol% MgO; and from <NUM> mol% to about <NUM> mol% CaO. The glass is described in <CIT>, and claiming priority from <CIT>.

In other embodiments, the alkali aluminosilicate glasses described hereinabove are ion exchangeable and may include at least about <NUM> mol% SiOz; at least about <NUM> mol% R<NUM>O, wherein R<NUM>O comprises Na<NUM>O; Al<NUM>O<NUM>, wherein Al<NUM>O<NUM>(mol%) < RzO(mol%); and B<NUM>O<NUM>, and wherein B<NUM>O<NUM>(mol%) - (RzO(mol%) - Al<NUM>O<NUM>(mol%)) ≥ <NUM> mol%. In some embodiments, the glass comprises: at least about <NUM> mol% SiOz, from about <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% B<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% Na<NUM>O; from <NUM> mol% to about <NUM> mol% KzO; at least about <NUM> mol% MgO, ZnO, or combinations thereof, wherein <NUM> ≤ MgO ≤ <NUM> and <NUM> ≤ ZnO ≤ <NUM> mol%; and, optionally, at least one of CaO, BaO, and SrO, wherein <NUM> mol% ≤ CaO + SrO + BaO ≤ <NUM> mol%. These glasses are described in <CIT>, and entitled "Zircon Compatible, Ion Exchangeable Glass with High Damage Resistance".

In other embodiments, the alkali aluminosilicate glasses described hereinabove are ion exchangeable and may include: at least about <NUM> mol% SiOz; at least about <NUM> mol% RO, wherein RzO comprises Na<NUM>O; Al<NUM>O<NUM>, wherein -<NUM> mol% ≤ Al<NUM>O<NUM>(mol%) - R<NUM>O(mol%) ≤ <NUM> mol%; and B<NUM>O<NUM>, wherein B<NUM>O<NUM>(mol%) - (R<NUM>O(mol%) - Al<NUM>O<NUM>(mol%)) ≥ <NUM> mol%. In some embodiments, the glasses comprise: at least about <NUM> mol% SiO<NUM>, from about <NUM> mol% to about <NUM> mol% Al<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% B<NUM>O<NUM>; from about <NUM> mol% to about <NUM> mol% NazO; from <NUM> mol% to about <NUM> mol% K<NUM>O; at least about <NUM> mol% MgO, ZnO, or combinations thereof, wherein <NUM> mol% ≤ MgO <NUM><NUM> and <NUM> ≤ ZnO < <NUM> mol%; and, optionally, at least one of CaO, BaO, and SrO, wherein <NUM> mol% ≤ CaO + SrO + BaO ≤ <NUM> mol%. These glasses are described in <CIT>, and entitled "Ion Exchangeable Glass with High Damage Resistance".

In some embodiments, the alkali aluminosilicate glasses described hereinabove may be substantially free of (i.e., contain <NUM> mol% of) of at least one of lithium, boron, barium, strontium, bismuth, antimony, and arsenic.

In some embodiments, the three-stage method disclosed herein for strengthening glass may be conducted on ion-exchangeable borosilicate glass having a composition that may be more easily ion-exchanged compared to existing, commercially-available borosilicate glasses, which are not easily strengthened through ion-exchange. In some embodiments, the three-stage method for strengthening glass may be applied to an ion-exchangeable borosilicate glass. In some embodiments, the ion-exchangeable borosilicate glass may include greater than or equal to <NUM> mol. % and less than or equal to <NUM> mol. % SiO<NUM>; greater than or equal to <NUM> mol. % and less than or equal to <NUM> mol. % Al<NUM>O<NUM>; greater than or equal to <NUM> mol. % and less than or equal to <NUM> mol. % B<NUM>O<NUM>; greater than or equal to <NUM> mol. % and less than or equal to <NUM> mol. % Na<NUM>O; greater than or equal to <NUM> mol. % and less than or equal to <NUM> mol. % K<NUM>O; greater than or equal to <NUM> mol. % and less than or equal to <NUM> mol. % MgO; and greater than or equal to <NUM> mol. % and less than or equal to <NUM> mol. The ion-exchangeable borosilicate glass may be capable of being strengthened by ion-exchange and may have a thickness t. The concentration(s) of the constituent components of the ion-exchangeable borosilicate glass may be such that: <NUM> ≤ <NUM> * (<NUM> + ((<NUM>*Al2O3)+(-<NUM>*B2O3) + (<NUM>*Na2O) + (-<NUM>*K2O)) + ((Na2O-<NUM>)<NUM>*(-<NUM>) + (Al2O3-<NUM>)*(K2O-<NUM>)*(<NUM>) + (B2O3-<NUM>)*(K2O-<NUM>)*(-<NUM>)))/t. These glasses are described in <CIT>, and entitled "Ion Exchangeable Borosilicate Glass Compositions and Glass Articles Formed from the same".

In some embodiments, the alkali aluminosilicate glasses described hereinabove may be down-drawable by processes known in the art, such as slot-drawing, fusion drawing, re-drawing, and the like, and may have a liquidus viscosity of at least <NUM> kilopoise. In some embodiments, the alkali aluminosilicate glasses described hereinabove may be suitable for tube drawing and re-forming from tubes and the like and may have a liquidus viscosity of at least <NUM> kilopoise and, in some embodiments, at least about <NUM> kilopoise.

The glass articles strengthened by the method disclosed herein may be used for glass containers, such as pharmaceutical containers, having the mechanical strength to resist external damage but do not experience destruction of the glass article in response to flaws penetrating into the central region or all the way through the thickness of the glass. Although a through crack may expose the composition, such as a pharmaceutical composition, to the atmosphere, which may violate the integrity of the composition, the container may remain intact and capable of containing the composition. Thus, the contents may be retained in the glass container, despite the through crack, to enable the contents to be available when needed. As used herein, terms such as "container" and "vessel" refer to any article that is adapted to hold a solid or fluid for storage. The container may, in some embodiments, be sealable. The glass articles may be used for containers or vessels, such as vials for holding sterile substances such as a vaccine, biologic, pharmaceutical, foodstuff, solution, or the like. Nonlimiting examples of such containers include glass vials, bottles, food jars, cartridges, syringes, ampules, or the like. The glass articles strengthened by the methods disclosed herein may also be used for other articles, such as cover glass for personal electronics or strengthened glass for aerospace or automotive applications, for example.

Compressive stress and DOC may be measured using those means known in the art. Such means include, but are not limited to, measurement of surface stress (FSM) using commercially available instruments such as the FSM-<NUM>, manufactured by Luceo Co. (Tokyo, Japan), or the like, and methods of measuring compressive stress and depth of compression are described in ASTM 1422C-<NUM>, entitled "Standard Specification for Chemically Strengthened Flat Glass," and ASTM <NUM> "Standard Test Method for Non-Destructive Photoelastic Measurement of Edge and Surface Stresses in Annealed, Heat-Strengthened, and Fully-Tempered Flat Glass". Surface stress measurements rely upon the accurate measurement of the stress optical coefficient (SOC), which is related to the birefringence of the glass. SOC in turn is measured by those methods that are known in the art, such as fiber and four point bend methods, both of which are described in ASTM standard C770-<NUM> (<NUM>), entitled "Standard Test Method for Measurement of Glass Stress-Optical Coefficient," and a bulk cylinder method.

The composition of the glass, in particular the concentration profile of potassium ions in the glass as a function of depth within the glass, can be determined using electron probe micro-analysis (EPMA) using an electron probe microanalyzer.

The chemical durability of the glass can be determined by conducting surface hydrolytic resistance (SHR) testing according to the hydrolytic testing methods known in the art and described in United States Pharmacopeial Convention (USP) <NUM>. The results of the surface hydrolytic resistance testing under USP <NUM> are reported as the amount of hydrochloric acid (HCl) consumption needed to titrate the volume of water in the container and is given in units of milliliters (mL) of <NUM> Molar (M) HCl per <NUM> milliliters (mL) of water.

The mechanical strength of the glass articles, such as cartridges for pharmaceutical compositions, may be evaluated by conducting a cone crush test. Referring to <FIG>, the cone crush test for evaluating the mechanical strength of a glass cartridge <NUM> is depicted. The glass cartridge <NUM> includes a sidewall <NUM>, a neck <NUM>, a flange <NUM>, and an open end <NUM> opposite the neck <NUM> and flange <NUM>. The cone crush test includes placing a conical or frustoconical stopper <NUM> into the open end <NUM> of the cartridge <NUM> and applying a force F to the end <NUM> of the stopper <NUM> protruding from the cartridge <NUM> in a direction parallel to the center axis A of the cartridge (i.e., in the -Z direction of the coordinate axis in <FIG>). The force F is increased until the cartridge <NUM> fails at the open end <NUM>, and the force F required to produce failure is recorded. Standard equipment may be utilized to apply and measure the force F. The cone crush test may be performed on any container or article that includes an open end, such as a cartridge, syringe, or other open ended article.

The mechanical strength of the glass articles, such as cartridges for pharmaceutical compositions, may also be evaluated by conducting a horizontal compression test. Referring to <FIG>, the horizontal compression test may include positioning the cartridge <NUM> between a first plate <NUM> and a second plate <NUM> and applying opposing forces F to the first plate <NUM> and second plate <NUM> at a point midway between the flange <NUM> and the open end <NUM> of the cartridge <NUM>. The forces F are applied in a direction normal to the sidewall <NUM> (i.e., in the +/-X or +/-Y direction of the coordinate axis of <FIG> and perpendicular to the center axis A). The force F is increased until the cartridge <NUM> fails, and the force F required to produce failure is recorded. Standard equipment may be utilized to apply and measure the force F. The horizontal compression test may be performed on cartridges, vials, syringes, ampouls, jars, containers, or other articles.

The mechanical strength of the glass articles, such as cartridge <NUM>, may also be evaluated by conducting a cartridge cantilever test. Referring to <FIG>, the cartridge cantilever test may include securing the cartridge <NUM> in a fixed position between the first plate <NUM> and the second plate <NUM> in contact with the sidewalls <NUM> of the cartridge <NUM>. A third plate <NUM> is placed against the flange <NUM>, and a force F is applied to the third plate <NUM> in a direction normal to the outer surface of the flange <NUM> (i.e., in the +/-X or +/-Y direction of the coordinate axis of <FIG> and perpendicular to the center axis A). The force F is increased until the cartridge <NUM> fails at the neck <NUM>, and the force F required to produce the failure is recorded. Standard equipment may be utilized to apply and measure the force F. The horizontal compression test may be performed on cartridges, as well as vials and other articles having a neck and flange structure at one end.

The mechanical strength of the glass articles, such as cartridge <NUM> or other container, may also be evaluated by conducting a barrel crush test. Referring to <FIG>, the barrel crush test test may include supporting the cartridge <NUM> or other container by a first support plate <NUM> proximate the neck <NUM> and flange <NUM> and a second support plate <NUM> positioned proximate the open end <NUM> of the cartridge <NUM> and on the same side of the cartridge <NUM> as the first support plate <NUM>. A third plate <NUM> is placed against the sidewall <NUM> proximate the open end <NUM> of the cartridge <NUM> and opposite the second support plate <NUM>. Force F is then applied to the third plate <NUM> in a direction normal to the outer surface of the sidewall <NUM> and perpendicular to the surface of the second support plate <NUM> (i.e., in the +/-X direction of the coordinate axis of <FIG> and perpendicular to the center axis A). The force F is increased until the barrel of the cartridge <NUM> proximate the open end <NUM> failed, and the force F required to produce the failure is recorded. Standard equipment may be utilized to apply and measure the force F. The horizontal compression test may be performed on cartridges, as well as vials and other articles having a neck and flange structure at one end.

The following examples illustrate the features and advantages of the glasses described herein and are in no way intended to limit the disclosure or appended claims thereto.

In Example <NUM>, alkali aluminosilicate glass articles were strengthened by the three-stage strengthening method of the present disclosure. The alkali aluminosilicate glass articles were <NUM> cartridges having a sidewall glass thickness of <NUM>. The glass cartridges were submersed in an initial ion-exchange bath that included potassium nitrate (KNO<NUM>) maintained at the initial ion-exchange temperature of <NUM> for an initial ion-exchange time of <NUM> hr. The glass cartridges were removed from the initial ion-exchange bath, dip rinsed, and placed in an oven, in which the glass cartridges were subjected to a thermal treatment temperature of <NUM> for a thermal treatment time of <NUM> hrs. The glass cartridges were removed from the oven and submersed in a final ion exchange bath comprising KNO<NUM> maintained at a final ion-exchange temperature of <NUM> for a final ion-exchange time of <NUM> hrs. Following removal from the final ion-exchange process, the alkali aluminosilicate glass cartridges of Example <NUM> were dip rinsed and washed to remove residual ion-exchange reagents from the surfaces of the cartridges.

In Comparative Example <NUM>, commercially-available borosilicate glass cartridges were obtained for comparison to the strengthened cartridges of Example <NUM>. The borosilicate glass cartridges of Comparative Example <NUM> were <NUM> cartridges having a glass thickness at the sidewall of <NUM>. The commercially-available borosilicate glass cartridges of Comparative Example <NUM> were strengthened by a single ion-exchange process introducing potassium ions into the borosilicate glass to the depth of layer.

In Comparative Example <NUM>, alkali aluminosilicate glass cartridges were strengthened by a conventional single-stage ion-exchange process. The alkali aluminosilicate glass cartridges of Comparative Example <NUM> were <NUM> cartridges having a glass thickness at the sidewall of <NUM>. The alkali aluminosilicate glass cartridges of Comparative Example <NUM> were strengthened by submersing the glass cartridges in a single ion-exchange bath comprising KNO<NUM> maintained at an ion-exchange temperature of <NUM> and for a time of <NUM> hours. The alkali aluminosilicate glass cartridges were removed from the single ion-exchange bath and then dip rinsed and washed to remove the ion-exchange reagents from the surfaces of the cartridges.

The potassium ion concentration profiles for the alkali aluminosilicate glass cartridges of Example <NUM>, the borosilicate glass cartridges of Comparative Example <NUM>, and the alkali aluminosilicate glass cartridges of Comparative Example <NUM> were determined by EPMA. Referring to <FIG>, the potassium ion concentration as a function of depth in the glass (depth equals <NUM> at the surface) is depicted for the alkali aluminosilicate glass cartridges of Example <NUM> (<NUM>), the borosilicate glass cartridges of Comparative Example <NUM> (<NUM>), and the alkali aluminosilicate glass cartridges of Comparative Example <NUM> (<NUM>). As shown in <FIG>, for the borosilicate cartridges of Comparative Example <NUM> (<NUM>) and alkali aluminosilicate glass cartridges of Comparative Example <NUM> (<NUM>), the concentration of potassium ions in the glass decreases with increasing depth at a consistent rate. In contrast, the potassium ion concentration profile for the aluminosilicate glass cartridges of Example <NUM> exhibits two distinct regions within the compression layer. First region <NUM> corresponds to the surface region of the glass and is characterized by a greater magnitude of the average slope of potassium ions as a function of depth. The second region <NUM> corresponds to the interior compression region between the surface region and the DOL (i.e., the depth to which the potassium concentration decreases to the bulk concentration of potassium ions in the glass). In the second region <NUM>, the magnitude of the average slope of potassium ion concentration as a function of depth in the glass is less than the magnitude of the average slope in the first region <NUM>.

<FIG> also shows that the concentration of potassium ions at the surface of the alkali aluminosilicate cartridges of Example <NUM> is less than the concentration of potassium ions at the surface of the alkali aluminosilicate cartridges of Comparative Example <NUM>. Due to the relationship between compressive stress and concentration of potassium ions, it would be expected for the alkali aluminosilicate cartridges of Comparative Example <NUM> to have a greater compressive stress at the surface compared to the alkali aluminosilicate cartridges of Example <NUM> because of the greater potassium ion concentration. However, the CS determined at the surface of the alkali aluminosilicate cartridges of Example <NUM> was found to be greater than the CS determined at the surface of the alkali aluminosilicate cartridges of Comparative Example <NUM>. Not intending to be bound by any particular theory, it is believed that the greater CS of the alkali aluminosilicate cartridges of Example <NUM> may be the result of reduced thermal relaxation in the glass. The final ion-exchange process for the alkali aluminosilicate cartridges of Example <NUM> was conducted at a temperature of <NUM> which resulted in less thermal relaxation compared to the alkali aluminosilicate cartridges of Comparative Example <NUM>, which was ion-exchanged at a much greater temperature for a longer period of time. The greater thermal relaxation in the alkali aluminosilicate cartridges of Comparative Example <NUM> may have caused a reduction in the CS at the surface of the glass. This demonstrates that the three-stage strengthening process disclosed herein in which the final ion-exchange process is conducted at temperatures less than <NUM> may result in less thermal relaxation and greater CS compared to glass articles strengthened with a convention single-stage ion-exchange.

The CS and potassium ion concentration at the surface of the alkali aluminosilicate cartridges of Example <NUM> were both substantially greater than the CS and potassium ion concentration at the surface of the borosilicate glass cartridges of Comparative Example <NUM>. The CS, DOL, and CT determined for the aluminosilicate cartridges fo Example <NUM> and the borosilicate cartridges of Comparative Example <NUM> are provided in the following Table <NUM>.

The DOL for the alkali aluminosilicate cartridges of Example <NUM> (<NUM> in <FIG>) was less than the DOL for the alkali aluminosilicate cartridges of Comparative Example <NUM> (<NUM> in <FIG>). However, the DOL for the alkali aluminosilicate cartridges of Comparative Example <NUM> was greater than <NUM> and sufficient to produce a DOC of at least <NUM>. The DOL (and, thus, the DOC) for the alkali aluminosilicate cartridges of Example <NUM> were also greater than the DOL for the borosilicate glass cartridges of Comparative Example <NUM> (ref. <NUM> in <FIG>). Thus, compared to commercially available borosilicate glass cartridges, such as those in Comparative Example <NUM>, the alkali aluminosilicate glass cartridges of Example <NUM> strengthened by the three-stage strengthening process disclosed herein exhibit greater CS and greater DOC. The DOC for borosilicate glass articles can be increased by increasing the ion-exchange time, but the CS of borosilicate glass cannot be increased without making substantial changes to the glass composition.

The mechanical strengths of the alkali aluminosilicate cartridges of Example <NUM>, the borosilicate glass cartridges of Comparative Example <NUM>, and the alkali aluminosilicate cartridges of Comparative Example <NUM> were evaluated by subjecting the cartridges to a cone crush test, horizontal compression test, cantilever cartridge test, and barrel crush test, as described herein. The results of these mechanical strength tests are presented in <FIG>, which are Weibull distribution plots of the failure load in kilograms of force (kg-f). The borosilicate cartridges of Comparative Example <NUM> are represented by data series <NUM> in <FIG>, data series <NUM> in <FIG>, data series <NUM> in <FIG>, and data series <NUM> in <FIG>. The alkali aluminosilicate cartridges of Comparative Example <NUM> are represented by data series <NUM> in <FIG>, data series <NUM> in <FIG>, data series <NUM> in <FIG>, and data series <NUM> in <FIG>. The alkali aluminosilicate cartridges of Example <NUM> are represented by data series <NUM> in <FIG>, data series <NUM> in <FIG>, data series <NUM> in <FIG>, and data series <NUM> in <FIG>.

As shown in <FIG>, the alkali aluminosilicate cartridge of Example <NUM> strengthened by the three-stage method disclosed herein exhibited substantially greater mechanical strength compared to the commercially-available borosilicate cartridges of Comparative Example <NUM> in each of the cone crush, horizontal compression, cantilever cartridge, and barrel crush tests. Also, the alkali aluminosilicate cartridge of Example <NUM> exhibited mechanical strength comparable to and even slightly superior to the alkali aluminosilicate cartridges of Comparative Example <NUM>, which were strengthened by a single-stage ion-exchange process. Thus, <FIG> demonstrate that the three-stage strengthening process comprising a first ion-exchange, a thermal treatment, and a final ion-exchange can produce glass articles having equivalent or even superior mechanical strength compared to alkali aluminosilicate glass articles strengthened by a single ion-exchange process and substantially superior to the mechanical strength of commercially available borosilicate glass articles.

In Example <NUM>, the influence on the thermal treatment conditions on the potassium ion concentration profile in the glass and on the mechanical performance of glass cartridges were investigated. For Example <NUM>, <NUM> alkali aluminosilicate glass cartridges having a glass thickness at the sidewall of <NUM> were subjected to the three-stage strengthening process of the present disclosure. The first ion-exchange process and the final ion-exchange process were maintained constant and the thermal treatment time and the thermal treatment temperature were varied. The thermal treatment time and thermal treatment temperature for Examples 4A, 4B, 4C, and 4D are provided below in Table <NUM>.

For each of Examples 4A, 4B, 4C, and 4D, the potassium ion concentration profile was determined using EPMA, and the results are presented in <FIG>. As shown in <FIG>, the potassium ion concentration profile for Examples 4A, 4B, 4C, and 4D are all similar, with similar depths of layer at around <NUM> to <NUM>. <FIG> demonstrates the relationship between the thermal treatment temperature and thermal treatment time and shows that the same potassium ion concentration profile with the same depth of layer can be obtained at different thermal treatment temperatures by changing the thermal treatment time accordingly. Thus, the thermal treatment temperature and the thermal treatment time can be modified to balance reduced thermal relaxation with the processing time.

The cartridges of Examples 4A, 4B, 4C, and 4D were also subjected to the cone crush test to evaluate the effects of thermal treatment conditions on the mechanical strength of the glass cartridges. The cone crush test results are shown in <FIG>, which is a Weibull plot of the failure load in kilograms of force for each of Examples 4A, 4B, 4C, and 4D. As shown in <FIG>, the cartridges for each of Examples 4A, 4B, 4C, and 4D exhibited similar mechanical strength performance as evaluated by the cone crush test, which indicates that the thermal treatment conditions by themselves may not have a great effect on the mechanical strength of the glass articles strengthened by the three-stage strengthening process of the present disclosure. Thus, the mechanical strength of the glass articles produced by the disclosed method may not be highly sensitive to changes in the thermal treatment conditions.

For Comparative Example <NUM>, commercially available unstrengthened borosilicate glass cartridges were obtained. The unstrengthened borosilicate glass cartridges of Comparative Example <NUM> were <NUM> borosilicate cartridges. The unstrengthened borosilicate glass cartridges of Comparative Example <NUM> were not subjected to a strengthening process.

In Comparative Example <NUM>, a subset of the commercially available unstrengthened borosilicate glass cartridges of Comparative Example <NUM> were subjected to a single-stage ion-exchange strengthening process to produce strengthened borosilicate glass cartridges. In particular, the subset of borosilicate glass cartridges of Comparative Example <NUM> were immersed in an ion-exchange bath comprising KNO<NUM> maintained at a temperature of <NUM>. The borosilicate glass cartridges were immersed in the ion-exchange bath for an ion-exchange time of <NUM> hours. After <NUM> hours, the strengthened borosilicate glass cartridges of Comparative Example <NUM> were removed and rinsed to remove the excess ion-exchange reagents.

In Example <NUM>, the effects of the ion-exchange conditions in the initial ion-exchange and the final ion-exchange processes on the mechanical strength of alkali aluminosilicate glass cartridges subjected to the three-stage method of strengthening disclosed herein were evaluated. In Example <NUM>, <NUM> alkali aluminosilicate glass cartridges having a glass thickness of <NUM> were subjected to the three-stage method of strengthening glass articles disclosed herein. The thermal treatment time and thermal treatment temperature during the thermal treatment step were maintained constant throughout each of Examples 7A, 7B, 7C, 7D, 7E, 7F, and <NUM>.

For Examples 7A, 7B, 7C, and 7D, the final ion-exchange temperature was constant at <NUM>, and the final ion-exchange time was maintained constant at <NUM> hours (<NUM> minutes). The initial ion-exchange temperatures and initial ion-exchange times of the initial ion-exchange process for Examples 7A, 7B, 7C, and 7D are provided below in Table <NUM>. For Examples 7E, 7F, and <NUM>, the initial ion-exchange temperature and initial ion-exchange time were maintained at <NUM> and <NUM> hour (<NUM>), respectively. The final ion-exchange temperatures and final ion-exchange times of the final ion-exchange process for Examples 7E, 7F, and <NUM> are provided below in Table <NUM>.

The cartridges of Examples 7A through <NUM>, Comparative Example <NUM>, and Comparative Example <NUM> were subjected to horizontal compression test and cone crush testing to evaluate the effects of the ion-exchange conditions in the initial ion-exchange process and final ion-exchange process on the mechanical strength of the glass cartridges. The results of the horizontal compression tests are provided in <FIG>, which is a Weibull plot of the failure load in kilograms of force for each of Examples 7A through <NUM>, Comparative Example <NUM>, and Comparative Example <NUM>. The results of the cone crush test are shown in <FIG>, which is a Weibull plot of the failure load in kilograms of force for each of Examples 7A through <NUM>, Comparative Example <NUM>, and Comparative Example <NUM>.

As shown in <FIG> and <FIG>, the alkali aluminosilicate glass cartridges of Examples 7A through <NUM>, which were strengthened by the disclosed three-stage strengthening method, exhibited superior mechanical strength compared to the unstrengthened borosilicate glass cartridges of Comparative Example <NUM> and the strengthened glass cartridges of Comparative Example <NUM>.

<FIG> and <FIG> also indicate that variability in the mechanical strength of the alkali aluminosilicate glass cartridges strengthened by the disclosed method increases with decreasing initial ion-exchange time. The degree of variability in the mechanical strength of the alkali aluminosilicate glass cartridges strengthened by the disclosed method in response to changes in final ion-exchange time are less than the variability resulting from changes in initial ion-exchange time.

In Example <NUM>, strengthened alkali aluminosilicate glass cartridges were prepared for hydrolytic testing. For Samples 8A, 8B, 8C, 8D, and 8E (8A-8E), <NUM> cartridges were strengthened by subjecting the cartridges to the three-stage method of strengthening. For Samples 8F, <NUM>, <NUM>, 8I, and 8J (8F-8J), <NUM> cartridges were strengthened according to the three-stage method of strengthening. The thermal treatment was maintained constant for each of Samples 8A-8J. The initial ion-exchange temperature, initial ion-exchange time, final ion-exchange temperature, and final ion-exchange time for each of Samples 8A-8J are provided below in Table <NUM>.

In Comparative Example <NUM>, alkali aluminosilicate glass cartridges were prepared for hydrolytic testing by strengthening the cartridges by a single-step ion-exchange process. For Samples CE9A, CE9B, and CE9C, <NUM> cartridges were strengthened, and for Samples CE9D, CE9E, and CE9F, <NUM> cartridges were strengthened. The ion-exchange temperature of the single ion-exchange process was <NUM> and the ion-exchange time was <NUM> hour for Samples CE9A and CE9D, <NUM> hours for Samples CE9B and CE9E, and <NUM> hours for Samples CE9C and CE9F.

In Example <NUM>, the alkali aluminosilicate glass cartridges of Example <NUM> (Samples 8A-8J) and Comparative Example <NUM> (Samples CE9A-CE9F) were subjected to hydrolytic testing to demonstrate that the three-stage method of strengthening glass articles produces glass articles that comply with the chemical sensitivity standards for Class 1B glass. The surface hydrolytic resistance testing was conducted according to the methods described in USP <<NUM>> and referenced herein. Referring to <FIG>, the alkali aluminosilicate glass cartridges of Example <NUM> strengthened by the three-stage strengthening method disclosed herein exhibited SHR values well below the limit for Type <NUM> glass for pharmaceutical containers (line <NUM> in <FIG>) and comparable to the SHR exhibited by the alkali aluminosilicate glass cartridges of Comparative Example <NUM> strengthened by a single ion exchange step. Thus, the disclosed method of strengthening glass articles disclosed herein does not degrade the chemical durability of the glass composition and is capable of strengthening glass articles while maintaining compliance with the SHR standards for Type <NUM> glass for pharmaceutical containers.

Claim 1:
An article comprising a glass, the glass comprising:
a first surface and a second surface;
a compression region extending from the first surface, the second surface, or both to a depth of compression (DOC), wherein the compression region is under a compressive stress and includes a surface compression region and an internal compression region between the surface compression region and the DOC and having a compressive stress profile different than the surface compression region; and
a central region under a central tension, wherein the central region extends inward from the DOC, wherein:
the compressive stress measured at the first surface, the second surface, or both is greater than or equal to <NUM> megapascals (MPa);
the DOC is at least <NUM> micrometers (<NUM>);
the central tension is less than a threshold central tension above which a stored elastic energy in the central region is sufficient to cause flaws extending into the central region to self-propagate through a thickness of the glass from the first surface to the second surface and laterally through the glass, the threshold central tension being <NUM> MPa; and
wherein the glass article is a container adapted to hold a pharmaceutical product, a vaccine, a biologic, a foodstuff, or a solution.