CN114075045A

CN114075045A - Chemically strengthened glass with high safety stress and testing method

Info

Publication number: CN114075045A
Application number: CN202010833265.5A
Authority: CN
Inventors: 姜宏; 黄义宏; 覃文城; 王慧娟; 谈宝权; 李铭; 白一波; 胡伟
Original assignee: Huawei Technologies Co Ltd; Chongqing Aureavia Hi Tech Glass Co Ltd
Current assignee: Huawei Technologies Co Ltd; Chongqing Aureavia Hi Tech Glass Co Ltd
Priority date: 2020-08-18
Filing date: 2020-08-18
Publication date: 2022-02-22
Anticipated expiration: 2040-08-18
Also published as: CN114075045B; WO2022037335A1

Abstract

The invention discloses a chemically strengthened glass with high safety stress and a test method, wherein the chemically strengthened glass is obtained by ion exchange of precursor glass; when the following conditions are satisfied: putting precursor glass into a salt bath to perform chemical ion exchange for 1h at 440 ℃, wherein the mass ratio of sodium salt in the salt bath is the larger value of a numerical value and a numerical value b, a is 5 wt%, and b is K in the glass base material₂O/2(K₂O+Na₂O+Li₂O) molar ratio; the surface compressive stress of the obtained glass reaches more than 500MPa, and the depth DOL-0max of the compressive stress layer is more than 17% of the thickness of the glass. The invention not only strengthens the glass to a sufficient degree by accurately controlling the components of the precursor glass and the conditions of the sodium-containing salt bathThe obtained strengthened glass has the best compressive stress and tensile stress, and the strengthened glass has the maximum composite compressive stress in a tensile stress safety state. The chemically strengthened glass has high strength, hardness, scratch resistance and good drop resistance.

Description

Chemically strengthened glass with high safety stress and testing method

Technical Field

The invention belongs to the technical field of glass products, and particularly relates to chemically strengthened glass with high safety stress and a testing method.

Background

With the rapid development of the electronic information industry, electronic products such as mobile phones, bracelets, tablet computers and the like are increasingly necessary for daily life, and the electronic products all have display screens with glass cover plates. The consumer's accident of dropping the product by losing his hands while carrying or using it occurs due to the portability of the product. Since protective glass is often broken by surface tensile stress generated when it falls or collides with an object, or by damage due to collision of the surface with an acute angle object, etc., when consumers purchase products, products having good crashworthiness are more preferred under conditions satisfying basic functions, and thus the drop resistance of the products is an important characteristic of product quality and a competitive power of the products.

The chemically strengthened glass is characterized in that large alkali metal ions in high-temperature molten salt replace small alkali metal ions in the glass by utilizing a high-temperature ion exchange process so as to generate exchange plasma product difference, so that after the two alkali metal ions are subjected to ion exchange, the alkali metal ions with larger radius generate a 'squeezing plug' effect on the surface of the glass, and a compression stress layer with a certain depth is formed on the surface of the glass. The pressure stress layer can improve the surface hardness of the glass to a certain extent, offset external impact and prevent the expansion of microcracks, thereby improving the performances of scratch resistance, drop resistance and the like of the glass. However, chemically strengthened glass generates compressive stress on its surface and corresponding tensile stress in its interior. The tensile stress creates tension within the center of the glass and when the glass is impacted, it acts as a booster to the cracking of the glass, causing the glass to produce very fine fragments, even pelletized, of only 0.5 mm. The experience of the client is seriously influenced.

Tensile stress and compressive stress are the intergrowth relation, and chemically strengthened glass need have certain compressive stress just can keep high mechanical strength, so inside tensile stress is unavoidable, but when tensile stress was too big, stability was very poor, and the discreteness is big, and chemically strengthened glass takes place explosive fracture very easily under slight impact, can produce the spontaneous explosion phenomenon even, then can produce serious influence to the reliability and the personal safety nature of product, has greatly reduced chemically strengthened glass's factor of safety. In order to solve the above-mentioned contradiction, the compressive stress on the glass surface is mainly reduced by controlling the maximum value of the tensile stress inside the glass within a safe range, that is, reducing the tensile stress in the tensile stress concentration region to reduce the possibility of self-fracture collapse. The method is mainly characterized in that the internal tensile stress of a large tensile stress concentration area is not too large by reducing the surface compressive stress of the glass and sacrificing or reducing the strength of the whole glass, and the safety of a local area of the glass is guaranteed by sacrificing the strength of the whole glass. The problem with this is that the strength of the glass is sacrificed to ensure safety against "spontaneous explosion", and therefore the strength of the glass is not necessarily sufficient for design and use, or for maximum strength. However, if the strengthening degree of the glass is required to be increased on one side, the glass is likely to exceed the bearing range of the glass, and the glass is unsafe. And also may miss the optimum stress state to develop the glass properties. The strength of the glass may not be enhanced by the ultimate strengthening performance of the glass because the degree of strengthening is insufficient. The reason is that no proper method is available for judging the strengthening standard and safety method of the chemical strengthened glass at present, so that the optimal distribution of the compressive stress and the tensile stress safety of the current strengthened glass cannot be effectively balanced, and the strength and the drop resistance of the current chemical strengthened glass are considered, so that the practical application range of the current glass is limited. Moreover, there is no previous study on how to determine whether the chemically strengthened glass has high safety by the compressive stress and tensile stress of the chemically strengthened glass.

Therefore, how to achieve an effective balance between the optimal distribution of the compressive stress and the tensile stress safety of the chemically strengthened glass to obtain the maximum composite compressive stress in the tensile stress safety state has become a technical problem to be solved urgently by those skilled in the art.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to solve the problem of high safety and high pressure stress symbiosis contradiction and provides chemically strengthened glass with high safety stress, so that when the glass is impacted, the glass fragments are prevented from being finely crushed.

Furthermore, the invention also provides a test method for judging the high safety stress of the chemically strengthened glass, which is used for researching the safety balance point of the compressive stress and the tensile stress of the chemically strengthened glass and determining whether the high safety stress is met.

In order to solve the technical problems, the invention adopts the following technical scheme:

the present invention provides a chemically strengthened glass having a high safety stress, which is obtained by ion-exchanging a precursor glass, characterized in that when the following conditions are satisfied: putting precursor glass into a salt bath to perform chemical ion exchange for 1h at 440 ℃, wherein the mass ratio of sodium salt in the salt bath is the larger value of a numerical value and a numerical value b, a is 5 wt%, and b is K in the glass base material₂O/2(K₂O+Na₂O+Li₂O) molar ratio; the glass obtainedThe surface compressive stress of the glass reaches more than 500MPa, and the depth DOL-0max of the compressive stress layer is more than 17 percent of the thickness of the glass.

Further, the bifurcation threshold value of the chemically strengthened glass is more than 80% of the maximum tensile stress linear density value CT-LDmax.

The invention also provides a test method for judging the high safety stress of the chemically strengthened glass, the chemically strengthened glass is obtained by ion exchange of precursor glass, and the test method is characterized in that:

measuring the surface compressive stress, the depth DOL-0max of the compressive stress layer and the bifurcation threshold of the glass obtained under the following ion exchange conditions; wherein the ion exchange conditions are: putting precursor glass into a salt bath to perform chemical ion exchange for 1h at 440 ℃, wherein the mass ratio of sodium salt in the salt bath is the larger value of a numerical value and a numerical value b, a is 5 wt%, and b is K in the glass base material₂O/2(K₂O+Na₂O+Li₂O) molar ratio;

-the chemically strengthened glass has a high safety stress when the measured surface compressive stress reaches above 500MPa and the depth DOL-0max of the compressive stress layer is above 17% of the thickness of the glass. Furthermore, the bifurcation threshold value of the chemically strengthened glass is more than 80 percent of the maximum tensile stress linear density value CT-LDmax

Compared with the prior art, the invention has the following beneficial effects:

1. the invention relates to a method for increasing SiO of a glass substrate by researching the safety and the composition of a precursor glass₂With Al₂O₃The content improves the glass network framework strength, not only increases the quantity of glass bridge oxygen, but also is beneficial to reducing the stress relaxation effect of glass in ion exchange and slowing down the weakening effect of factors such as high temperature and long time in ion exchange on deep layer stress in composite compressive stress. Therefore, the chemically strengthened glass has the advantages that the components and the content thereof are controlled and adjusted to realize the synergistic interaction effect of the components, the precursor glass has high intrinsic strength, and the strengthened glass has the maximum composite compressive stress in a tensile stress safety state through the control of the components of a salt bath in the chemical strengthening treatment, and has excellent strength and drop resistanceAnd simultaneously has high safety.

2. By accurately controlling the components of the precursor glass and the sodium-containing salt bath, the invention not only strengthens the glass to achieve enough surface compressive stress, but also has high network structure strength, so that the compressive stress and the tensile stress of the obtained strengthened glass are in the best state, and the strengthened glass has the maximum composite compressive stress in the safe state of the tensile stress. The chemically strengthened glass has high strength, hardness, scratch resistance and good drop resistance. Moreover, the ion exchange process is easy to control, so that the production cost is low, the operability is high, the popularization and the application are easy, and the batch industrial production can be realized.

3. The tempered glass also has safety in the optimal stress state, can keep the stability and high strength of the glass in the using process, and is suitable for electronic display equipment, particularly the field of cover plate protection of the electronic display equipment.

4. The test method of the invention provides theoretical basis and new thought for the judgment of the strengthening standard and the safety method of the chemically strengthened glass, and has good application prospect. The method comprises the steps of determining the safety balance of the compressive stress and the tensile stress of the chemically strengthened glass and judging whether the chemically strengthened glass belongs to high-safety stress or not by researching the relationship between the bifurcation threshold value of the chemically strengthened glass obtained by ion exchange, the maximum tensile stress linear density value CT-LDmax, the depth DOL-0max of a compressive stress layer, the thickness of the glass and the surface compressive stress CS of the glass; and is consistent with the analysis result of the drop test.

Drawings

FIG. 1 is a schematic structural view of a chemically strengthened glass article according to the present invention.

Fig. 2 is a sectional view a-a of fig. 1.

Fig. 3 is a schematic front view of a consumer electronic device according to the present invention.

Fig. 4 is a schematic rear view of a consumer electronic device according to the present invention.

Detailed Description

The present invention will be described in further detail with reference to examples.

The following is an explanation of the related proper names and related measurement methods of the present invention:

the chemically strengthened glass is chemically strengthened glass treated by a high-temperature ion exchange process. The alkali metal ions with larger ionic radius in the molten salt replace the alkali metal ions with smaller ionic radius in the glass so as to generate exchange plasma product difference, and high-to-low pressure stress is generated in the surface layer of the precursor glass, so that the expansion of glass microcracks is hindered and delayed, and the purpose of improving the mechanical strength of the glass is achieved.

"depth of compressive stress layer DOL-0 max" is the distance from the surface of the strengthened glass to the position where the compressive stress is zero.

The depth of compressive stress layer DOL-0max can be determined by measuring the surface high and deep low compressive stress regions with FSM6000 and SLP1000 manufactured by Orihara, respectively, and fitting a stress curve with PMC software. Of course, other stress testers capable of measuring the surface high-pressure stress region and the deep-layer low-pressure stress region can be adopted.

The "bifurcation threshold" refers to the bifurcation of the glass by the self tensile stress when the glass is impacted by the tensile stress release test method, and the linear density value of the tensile stress at this time is the bifurcation threshold of the glass.

In the invention, the measurement of the bifurcation threshold of the chemically strengthened glass can adopt a Vickers diamond drill bit and a guide rail for fixing to ensure that the drill bit vertically impacts the surface of the glass, the impact adopts air pressure conduction, the air pressure is adjusted, the size of the impact force is controlled by combining a pressure sensor, and the height guide rail is adjusted according to the thickness of the glass so as to control the intrusion depth of the drill bit. When the glass is cracked, the crack is just split by the stress of the glass, and the linear density value of the tensile stress at the moment is the splitting threshold value of the glass.

"Tensile stress linear density (CT-LD)" means that the strengthened glass is a strengthened layer formed by ion exchange in salt bath, a stress layer is formed inside the glass during the ion exchange process, the tensile stress layer is provided with an upper boundary which is at a certain interval with the upper surface of the tempered glass and a lower boundary which is at a certain interval with the lower surface of the tempered glass, a curve which is drawn by taking the tensile stress at a certain point on a line segment which is perpendicular to the upper boundary and the lower boundary in the tensile stress layer and has upper and lower end points respectively falling on the upper boundary and the lower boundary as a Y axis and the distance between the corresponding point and the upper boundary as an X axis is taken as a tensile stress curve, and the ratio of the fixed integral of the tensile stress curve and the tempered thickness is taken as the tensile stress linear density, namely the ratio of the sum of the tensile stresses of the tempered glass measured by the SLP-1000 stress meter to the glass thickness.

The maximum tensile stress linear density value CT-LDmax refers to the strengthening of glass in a pure sodium nitrate salt bath at a fixed temperature (the temperature range can be 350-500 ℃), and has the rule that the CT-LD rapidly rises from 0 along with the increase of strengthening time and reaches a maximum value, the CT-LD slowly falls after strengthening, the CT-LDmax is in a parabola trend, and the maximum value is called as CT-Ldmax.

The "surface compressive stress CS" refers to the compressive stress generated on the surface of the glass due to the squeezing effect of the alkali metal ions with larger radius, which is generated by the alkali metal ions with smaller radius on the surface of the glass being replaced by the alkali metal ions with larger radius after the glass is chemically strengthened.

The surface compressive stress can be measured by FSM6000 and SLP1000 manufactured by Orihara corporation in the areas of high and low surface compressive stress, respectively, and the stress curves are fitted using PMC software. Of course, other stress testers capable of measuring the surface high-pressure stress region and the deep-layer low-pressure stress region can be adopted.

The 'complete machine drop test' refers to a method for testing the strength of the tempered glass, wherein a tempered glass sheet is attached to an electronic device sample such as a mobile phone and the like, falls down freely from a high position, the height of broken glass is recorded, the height value can reflect the strength of the glass, and the test method is called as the complete machine drop test.

Referring to fig. 1-2, the present invention provides a chemically strengthened glass 100 having a high safety stress, comprising a first major surface 1 and a second major surface 2; a compressive stress layer 3 and an intermediate tensile stress layer 4 are formed in the first main surface 1 and the second main surface 2 in the glass thickness inner direction, and the depth of the compressive stress layer 3 is 5. The distance between the first main surface and the second main surface is the thickness d of the glass.

The chemically strengthened glass is obtained by ion exchange of a precursor glass when the following conditions are satisfied: putting precursor glass into a salt bath to perform chemical ion exchange for 1h at 440 ℃, wherein the mass ratio of sodium salt in the salt bath is the larger value of a numerical value and a numerical value b, a is 5 wt%, and b is K in the glass base material₂O/2(K₂O+Na₂O+Li₂O) molar ratio; the surface compressive stress of the obtained glass reaches more than 500MPa, the depth DOL-0max of the compressive stress layer is more than 17% of the thickness of the glass, and the bifurcation threshold value is more than 80% of the maximum tensile stress linear density value CT-LDmax.

Under the conditions of 300g load and 10s pressure holding, the Vickers hardness value of the precursor glass of the invention is in all the following ranges and sub-ranges, 600kgf/mm²～630kgf/mm²And 600kgf/mm²～620kgf/mm²、610kgf/mm²～630kgf/mm²、620kgf/mm²～630kgf/mm²、600kgf/mm²、610kgf/mm²、620kgf/mm²Or 630kgf/mm²。

The precursor glass is formed by any one of a float method, an overflow method, a rolling method and a casting forming method; then ion exchange is carried out in salt bath to obtain:

IOX1：440℃*80wt％NaNO₃+20wt％KNO₃5h, placing the precursor glass in a glass containing 80 wt% NaNO₃And 20 wt% KNO₃In the mixed salt bath, strengthening is carried out for 5 hours at the temperature of 440 ℃;

IOX2：440℃*95wt％KNO₃+5wt％NaNO₃2h, placing the strengthened glass treated in the step 1) in a furnace containing 95 wt% of KNO₃And 5 wt% NaNO₃In the mixed salt bath, the strengthening is carried out for 2 hours at the temperature of 440 ℃.

In the IOX1 ion exchange process, when the surface pressure stress of the chemically strengthened glass is reduced to 5-20% of the first batch, lithium ion purified substances are added into the salt bath for purification; the adding amount of the lithium ion purified substance is 0.1-5 wt% or 0.2-2 wt% of the salt bath mass; for example, 0.1 wt%, 0.25 wt%, 0.5 wt%, 0.75 wt%, 1.5 wt%, 1.25 wt%, 2 wt%, etc. The purification temperature is 360-450 ℃, and the purification time is at least 4 h; for example, 360 ℃, 370 ℃, 380 ℃, 390 ℃, 400 ℃, 410 ℃, 420 ℃, 430 ℃, 440 ℃, or 450 ℃.

Wherein the precursor glass contains, in mole percent on an oxide basis: SiO2₂ 65mol％～75mol％、Al₂O₃8mol％～15mol％、Na₂O 1mol％～5mol％、Li₂O4 mol% to 13 mol% and K₂0.1 mol% -3 mol% of O; wherein, SiO₂/(SiO₂+Al₂O₃) At least 78 mol%, Na₂O+Li₂O is 7mol percent to 13mol percent.

The precursor glass also comprises a refining agent, wherein the content of the refining agent is not more than 1.5 wt% of the original components of the precursor glass, namely the addition amount of the refining agent is 1.5 wt% of the original components of the precursor glass; the clarifying agent is tin oxide and/or sodium chloride.

In the chemically strengthened glass of the present invention, SiO₂As the main glass forming oxide, is a glass network former capable of forming silicon-oxygen tetrahedra as the base network of the glass. The network structure strength of the glass can be improved, the high network structure strength is beneficial to reducing the stress relaxation effect of the glass in ion exchange, and the weakening effect of factors such as high temperature and long time in the ion exchange on the deep layer stress in the composite compressive stress is relieved. In some embodiments, the SiO in the glass composition₂The content of (b) is 65 mol% to 75 mol% and all ranges and subranges therebetween, for example 65 mol% to 70 mol%, 70 mol% to 75 mol%, 72 mol% to 75 mol%, 65 mol%, 66 mol%, 67 mol%, 68 mol%, 69 mol%, 70 mol% or 75 mol% and the like.

Al₂O₃Can also provide a stable network, is a glass network intermediate, and can form [ AlO ] in glass⁴⁺]Tetrahedrally linked [ SiO ]⁴⁺]Non-bridge oxygen of network architecture, tamping network architecture, further improving glass strengthDegree and stability, and [ AlO⁴⁺]The tetrahedron has larger volume, widens the gap of the network architecture and is beneficial to the subsequent chemical toughening process. Can improve the viscosity of the glass and inhibit crystallization. If the amount of alumina is too high and the alumina is more refractory than silica, the alumina cannot form a tetrahedral entry network, possibly to the extent that it cannot form a chain structure, without sufficient alkali to provide free oxygen, and the viscosity of the melt is generally increased. In some embodiments, Al is in the glass composition₂O₃The content of (b) is 8 mol% to 15 mol% and all ranges and subranges therebetween, for example, 8 mol% to 10 mol%, 8 mol% to 12 mol%, 8 mol% to 13 mol%, 9 mol% to 13 mol%, 10 mol% to 15 mol%, 8 mol%, 8.4 mol%, 9 mol%, 9.4 mol%, 9.6 mol%, 9.8 mol%, 10 mol%, 10.2 mol%, 10.4 mol%, 10.6 mol%, 10.8 mol%, 11 mol%, 11.2 mol%, 12 mol%, 13 mol%, 14 mol% or 15 mol%.

In another embodiment, ZrO may be included in the glass composition₂The amount of the surfactant is 0 to 1 mol% and all ranges and subranges therebetween, for example, 0 to 0.1 mol%, 0.1 mol% to 0.5 mol%, 0.5 mol% to 1 mol%, 0 mol%, 0.1 mol%, 0.5 mol% or 1 mol%.

In another embodiment, ZnO can be included in the glass composition in an amount of 0 to 2 mol% and all ranges and subranges therebetween, such as 0.1 mol% to 1 mol%, 0.1 mol% to 2 mol%, 1 mol% to 2 mol%, 0 mol%, 0.1 mol%, 0.5 mol%, 1 mol%, 1.5 mol%, or 2 mol%, and the like.

In another embodiment, the SiO in the glass composition₂/(SiO₂+Al₂O₃) At least 78%, preferably 80% or more and all ranges and subranges therebetween, e.g., 78% or more, 79% or more, 80% or more, 82% or more, 85% or more, 88% or more, 89% or more, up to 90.36%. This ratio ensures a more stable network structure than the aluminoxy tetrahedron, the higher the ratio, the greater the stability of the network structure of the glassThe better, the higher the bifurcation threshold, the more stress that can be safely contained, and the more the anti-falling performance of the glass can be exerted.

Na₂O is the primary component of the ion exchange and is the key exchange ion for creating high compressive stress on the surface, and in some embodiments, the glass composition may include Na₂O, in an amount of 1 to 5 mol% and all ranges and subranges therebetween, e.g., 1 to 3 mol%, 1.5 to 4 mol%, 2 to 5 mol%, 3 to 5 mol%, 4 to 5 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, or 5 mol%, etc.

Li₂O is the main component of ion exchange, is a key exchange ion for forming deep layer compressive stress, can obviously reduce the viscosity of the molten glass, and can cause low-temperature crystallization of the glass when too much O is introduced. Lithium oxide is generally used in the formation of glass ceramics, while other alkali metal oxides tend to reduce the formation of glass ceramics, forming aluminosilicate residual glass in the glass ceramic. In some embodiments, the glass composition can include Li₂O, in an amount of from 4 mol% to 13 mol% and all ranges and subranges therebetween. For example, 4 mol% to 5 mol%, 5 mol% to 8 mol%, 6 mol% to 10 mol%, 7 mol% to 11 mol%, 8 mol% to 12 mol%, 4 mol%, 5 mol%, 6 mol%, 8 mol%, 11 mol%, or 12 mol%.

By way of illustration, due to Na₂O、Li₂O is an alkali metal oxide, which is in a free state in the glass, and the excess oxygen ions can break bridge oxygen and break the network structure. Low content alkali metal component, high temperature single binary ion exchange to ensure the composite pressure stress with certain depth and high tensile stress linear density. In particular embodiments, the present invention employs low levels of alkali metal components. The glass composition may include Na₂O+Li₂O in an amount of 7 mol% to 13 mol% and all ranges and subranges therebetween, such as 7 mol%, 9 mol%, 10 mol%, 11 mol%, 12 mol%, or 13 mol%, and so forth.

K₂O is the main component of ion exchange. In some embodiments, the glass composition may include K₂O, content thereofFrom 0 to 3 mol% and all ranges and subranges therebetween. For example, 0 to 0.1 mol%, 0.2 mol% to 0.5 mol%, 0.3 mol% to 0.5 mol%, 0.5 mol% to 1 mol%, 1 mol% to 2 mol%, 2 mol% to 2.5 mol%, 2 mol% to 3 mol%, 0 mol%, 0.1 mol%, 0.8 mol%, 1.2 mol%, 2.6 mol% or 3 mol%.

B₂O₃Is a glass secondary network structure, the addition of which can promote the high-temperature melting of glass and reduce the melting difficulty, and B₂O₃The addition of (2) can increase the ion exchange rate of the glass, but the addition of boron leads to a weakening of the network structure. In some embodiments, the glass composition may include B₂O₃The amount is 0 to 3 mol% and all ranges and subranges therebetween, for example 0 to 1 mol%, 0 to 1.5 mol%, 0 to 2 mol%, 0 to 2.6 mol%, 1 mol% to 1.5 mol%, 1 mol% to 2.0 mol%, 1 mol% to 2.5 mol%, 0 mol%, 1.5 mol%, 1.8 mol%, 2 mol%, 2.5 mol% or 3 mol%.

MgO is used as a network intermediate, and has the effects of reducing the high-temperature viscosity of the glass and increasing the Young modulus of the glass. But alkaline earth metals and alkali metals are the main carriers of current in glass. In some embodiments, the glass composition can include MgO in an amount of 0 to 7.5 mol%, preferably 2 mol% to 7.5 mol% and all ranges and subranges therebetween, for example 0 to 1 mol%, 1 mol% to 2 mol%, 2 mol% to 3 mol%, 2 mol% to 5 mol%, 3 mol% to 7 mol%, 4 mol% to 6 mol%, 5 mol% to 7 mol%, 5 mol% to 7.5 mol%, 6 mol% to 7.5 mol%, 0 mol%, 1 mol%, 1.2 mol%, 2.0 mol%, 3 mol%, 4 mol%, 5 mol%, 7 mol%, or 7.5 mol%.

The precursor glass of the present invention may be a precursor glass sheet or a precursor glass block. The glass liquid can be made into a precursor glass plate by a rolling method, a floating method or an overflow method process in the processing process of the precursor glass, or can be made into a precursor glass brick by a casting method process. Specifically, the present invention mechanically cuts a precursor glass into a shaped precursor glass sheet, typically a rectangular glass sheet article. The raw materials are accurately weighed, and after the raw materials are sufficiently mixed, the raw materials are heated at a high temperature to be melted. Melting of glass is a very complex process that involves a series of physical, chemical, and physicochemical phenomena and reactions that result in the transformation of various raw materials from a mechanical mixture into a complex melt, i.e., molten glass. The melting of glass can be roughly divided into 5 stages of silicate formation, molten glass clarification, molten glass homogenization and molten glass cooling. The melting temperature of the glass frit is 1630-1700 ℃, for example 1630 ℃, 1650 ℃, 1660 ℃, 1680 ℃ or 1700 ℃.

The melting temperature is 1630-1700 ℃, so the clarifying agent is tin oxide or/and sodium chloride. In the present invention, the content of the refining agent is not more than 1.5 wt% of the raw components of the precursor glass. Preferably 0.5 wt%, 1 wt%, 1.2 wt% or 1.5 wt%.

Further, the chemically strengthened glass is formed by performing chemical ion exchange twice on the precursor glass in a salt bath. In this way, the compressive stress region generated at or near the first main surface and the second main surface of the chemically strengthened glass finally obtained is balanced with the tensile stress region at the central part of the glass, so that the chemically strengthened glass has the maximum composite compressive stress in a tensile stress safe state. Therefore, the chemically strengthened glass has high strength, hardness, scratch resistance and Young's modulus as well as drop resistance.

By way of illustration, the ion exchange process typically occurs at a temperature not exceeding the glass transition point. This process is carried out by: the glass is immersed in a molten bath containing an alkali metal salt (typically a nitrate) whose ions are larger than the bulk alkali metal ions in the glass. The bulk alkali metal ions are exchanged for larger alkali metal ions. For example, Na may be contained⁺Is dipped in potassium nitrate (KNO)₃) In a salt bath. Larger K in salt bath⁺Will replace the smaller Na in the glass⁺. Because of the presence of larger alkali metal ions at sites previously occupied by smaller alkali metal ions, a volume difference is formed on the surface of the strengthened glass article before and after ion exchange, and the volume difference is shaped on the surface of the chemically strengthened glass articleThe pressure stress layer with a certain depth can eliminate or inhibit the generation and the expansion of micro cracks on the surface of the chemically strengthened glass product, thereby achieving the purpose of improving the mechanical property of the chemically strengthened glass product.

By way of illustration, the strengthened glass can be chemically ion exchanged in at least one salt bath of potassium and sodium, and the depth of the compressive stress layer generated by potassium-sodium exchange determines the magnitude of the surface compressive stress of the strengthened glass. The higher the maximum value of the linear density of tensile stress (CT-LDmax) and the linear density of tensile stress (CT-LD) which can be obtained in the glass during the strengthening process, the higher the tensile stress, and the higher the compressive stress of the strengthened glass obtained because the compressive stress and the tensile stress are in a balanced equal relationship in the glass after the chemical strengthening. The strengthened glass has a bifurcation threshold of 80% of its maximum tensile stress linear density value.

In one or more embodiments, the salt bath that is ion exchanged may also include lithium ions in a molar ratio of less than 0.25%, e.g., 0.2% or less, 0.15% or less, 0.1% or less, 0.05% or less, 0.02% or less, 0.01% or less, to the total alkali metal ions in the salt bath. Because lithium ions in the salt bath are potassium-sodium and sodium-lithium exchange hindering ions, and the large amount of lithium ions can greatly reduce the ion exchange degree and weaken the strengthening state of the sample.

In some embodiments, the time and temperature of the ion exchange has an effect on the surface compressive stress of the chemically strengthened glass article. With the continuous increase of the ion exchange temperature (the same ion exchange time), the surface pressure stress shows the trend of increasing first and then decreasing; suitable ion exchange temperatures for the present invention are, for this reason, from 440 ℃ to 460 ℃, for example 440 ℃, 450 ℃ or 460 ℃. In addition, as the ion exchange time is prolonged (the ion exchange temperature is unchanged), the surface compressive stress tends to increase first and then decrease; based on this, suitable ion exchange times according to the invention are from 1h to 2h, for example 1h, 1.5h or 2 h.

In the glass strengthening process, the salt bath is recycled, i.e., multiple batches of precursor glass can be strengthened, but after the salt bath is used for a period of time, impurity metal ions (e.g., Li) are exchanged from the glass⁺) In salt bathThe more the number of the components is, the salt bath is deactivated, and the glass strengthening effect is weakened. Therefore, when the surface compressive stress of the chemically strengthened glass in the salt bath is reduced to 5-20% of that of the first batch of chemically strengthened glass in the multi-batch ion exchange process, a lithium ion purified product (see CN106000287A of the prior application) and other similar ion sieves are put into the salt bath for purification. For example, the lithium ion purification material can also be used, and comprises 215 to 55 percent of SiO, 5 to 50 percent of auxiliary material and 15 to 48 percent of at least one functional metal oxide based on the mol percent of the oxide, wherein the metal in the functional metal oxide is monovalent and/or divalent metal; for example, the monovalent metal is at least one of lithium, sodium, potassium and rubidium, and the divalent metal is at least one of magnesium, calcium, strontium and barium. The auxiliary material and SiO₂Forming polar covalent bond and ionic bond, and the adjuvant is at least one selected from phosphorus oxide, boron oxide, aluminum oxide, zirconium oxide, chromium oxide, iron oxide, zinc oxide, bismuth oxide, and cobalt oxide.

The lithium ion purified matter can extract or adsorb impurity ions Li in a deteriorated liquid salt bath mixture, can efficiently recover the activity of a molten salt compound, and does not introduce other impurity ions into the molten salt compound. Specifically, when the surface compressive stress of the chemically strengthened glass is reduced to 5% -20% of the chemically strengthened glass of the first batch and all ranges and subranges therebetween, such as 5% -10%, 5% -15%, 8% -18%, 10% -20%, 15% -20%, 5%, 10%, 15% or 20%, a lithium ion purified product is added into the salt bath for purification.

Preferably, the charged lithium ion purified product may be placed in the salt bath until the strengthening is completed, or the lithium ion purified product may be taken out when the concentration of the metal ions to be purified in the liquid salt compound to be melted is within a predetermined range.

In one or more embodiments, the lithium ion purification is added in an amount of 0.1 to 5 wt% of the salt bath and all ranges and subranges therebetween, such as 0.1 to 0.5wt, 0.5 to 1wt, 1 to 2wt, 1 to 4wt, 2 to 3wt, 3 to 4wt, 0.1wt, 0.5wt, 1wt, 2wt, 3wt, 4wt, or 5 wt.

In one or more embodiments, the lithium ion purification can combine with lithium ions at a temperature above the melting point of the molten salt compound to purify, enhance, or restore the activity of the salt bath. Preferably 360-450 ℃ and all ranges and subranges therebetween, such as 360-400 ℃, 400-450 ℃, 380-420 ℃, 410-450 ℃, 360 ℃, 370 ℃, 380 ℃, 390 ℃, 400 ℃, 410 ℃, 420 ℃, 430 ℃, 440 ℃ or 450 ℃. After a certain period of time, the lithium ion purification product adsorbs or extracts these impurity metal ions. In addition, the better the adsorption effect with longer purification times (temperature), the higher the activity of the salt bath recovery, on the basis of which suitable purification times according to the invention are at least 4h, further at least 5h, at least 6h, at least 7h or until the end of the strengthening reaction.

The invention also discloses a consumer electronics terminal comprising: a housing comprising a front surface, a rear surface, and side surfaces; and an electronic assembly partially located within the housing, the electronic assembly including a display located at or adjacent a front surface of the housing; the front surface or/and the back surface or/and the side surface comprise the chemically strengthened glass with high safe compressive stress.

The consumer electronic terminal comprises a mobile phone, a tablet computer or consumer electronic products thereof and the like. For example, consumer electronics, including mobile phones, tablets, computers, navigation systems, and the like, having a display; a construction article, a transportation article (e.g., an automobile, a train, an aircraft, an offshore vehicle, etc.), an appliance article, or any article that requires some transparency, scratch resistance, abrasion resistance, or a combination thereof. Exemplary articles comprising any of the glass articles disclosed herein are shown in fig. 3 and 4. In particular, FIG. 3 shows a front surface of a consumer electronic device, FIG. 4 shows a back surface of the consumer electronic device, which includes a housing comprising a front surface 6, a back surface 8, and side surfaces; and an electronic assembly partially or fully within the housing and including a display, and may also include a controller, memory, and other electronic components, wherein the display is located at or adjacent to the front surface of the housing. The front surface or/and the back surface or/and the side surface of the housing comprises tempered glass according to the invention. In some embodiments, a cover article 7 is also included, the cover article 7 overlying the front surface 6 of the housing or the cover article being positioned over the display, the cover article 7 and/or a portion of the housing including the strengthened glass of the present invention.

The chemically strengthened glass of the present invention can be applied to electronic devices, such as mobile phones (mobile phones), tablet computers (pads), computers, Virtual Reality (VR) terminal devices, Augmented Reality (AR) terminal devices, wearable devices, televisions, and the like. The electronic device includes a housing having a front surface, a rear surface, and side surfaces; an electronic component located within the housing; a display located at or adjacent to the front surface of the housing; and a cover substrate disposed on the display so as to isolate and protect the display panel from damage caused by external objects or forces. The cover substrate or housing comprises any of the strengthened glasses described above.

In some embodiments, further comprising a cover article 3, the cover article 3 covering the front surface 1 of the housing of the consumer electronic terminal or the cover article being positioned on a display, the cover article 3 and/or a portion of the housing comprising a strengthened glass according to the present invention. The cover article includes the chemically strengthened glass having a high safe compressive stress.

The invention also provides a test method for judging the high safety stress of the chemically strengthened glass, wherein the chemically strengthened glass is obtained by ion exchange of the precursor glass, and the test method comprises the following steps:

measuring the surface compressive stress, the depth DOL-0max of the compressive stress layer and the bifurcation threshold of the glass obtained under the following ion exchange conditions; wherein the ion exchange conditions are: putting precursor glass into a salt bath to perform chemical ion exchange for 1h at 440 ℃, wherein the mass ratio of sodium salt in the salt bath is the larger value of a numerical value and a numerical value b, and a is 5 wt%; b is K in the glass substrate₂O/2(K₂O+Na₂O+Li₂O) in a molar ratio. Wherein b of the examples 1, 2, 3, 4 and 5 is 7.7%, 5%, 6%, 0, respectively; therefore, the sodium salt mass ratios in the salt bath were 7.7%, 5%, 6%, 5%, and 5%, respectively.

-when the measured surface compressive stress reaches above 500MPa,

when the bifurcation threshold value of the chemically strengthened glass is more than 70 percent (such as 72 percent, 75 percent, 80 percent, 83 percent, 85 percent and the like) of the maximum tensile stress linear density value CT-LDmax, the depth DOL-0max of the compressive stress layer is more than 15 percent (such as 15.5 percent, 16 percent, 17 percent, 18 percent and 21 percent) of the thickness of the glass, and the surface compressive stress CS of the glass reaches more than 400MPa (such as 420, 440, 450, 500, 550, 600 and the like), the chemically strengthened glass is proved to have high safety stress.

Through the whole machine drop test of different heights, the height of the glass can reach 1.8m at most, the glass failure state is observed, only two cracks are extended instead of star burst, and the influence of external force on the failure state is avoided to the maximum extent, so that the glass is judged and determined to have better tensile stress safety, namely the glass meets the high safety stress standard.

The magnitude of the surface compressive stress formed by the strengthened glass disclosed herein depends on the thickness of the glass, and in some embodiments, the chemically strengthened glass has a thickness d of 0.2mm to 1.5mm, e.g., 0.5mm to 1.5mm, 0.5mm to 1mm, 1mm to 1.5mm, 0.4mm to 1mm, 1.2mm, 1mm, 0.8mm, 0.7mm, 0.6mm, 0.5mm, 0.4mm, 0.3mm, or 0.2mm, etc.; the tempered glass has a surface compressive stress of at least 500MPa, such as 550MPa, 600MPa, 660MPa, 700MPa, 750MPa, 780MPa, 900MPa, and up to 1200 MPa.

Example 1: a method for preparing chemically strengthened glass with high safe compressive stress comprises the following steps:

s1: firstly, accurately weighing the glass base materials according to the proportion (see table 1), then fully mixing the raw materials, and then preserving the heat for 4 hours at the high temperature of 1630 ℃ to melt the raw materials to obtain the glass melt.

S2: and casting the molten glass in a preheated stainless steel mold, putting the mold into an annealing furnace, and performing long-time gradient annealing around an annealing point to eliminate the internal stress of the glass. Cutting allowance on six surfaces of the annealed glass brick to obtain a glass brick with a proper size, and performing size fine cutting, flat grinding and edge sweeping by adopting a linear cutting machine, a CNC (computer numerical control) engraving machine and a flat grinding and polishing machine to obtain a precursor glass plate;

s3: preheating the precursor glass obtained in the step S2 at 300-400 ℃ for 10-30 min. Then it was subjected to a first step of ion exchange IOX1, 440 ℃ 80 wt% NaNO₃+20wt％KNO₃*5h；

S4: and (3) performing secondary ion exchange IOX2 on the glass obtained in the step S3, wherein the ion exchange IOX 2: 440 ℃ 95 wt% KNO3+5 wt% NaNO₃*2h。

Of course, the chemically strengthened glass of the present invention is not limited to the conditions (including composition, thickness, processing conditions, etc.) of the above examples 1 to 5, which are not listed herein. The chemically strengthened glass with high safe compressive stress can be obtained by adjusting the components, the processing conditions and the like according to the invention.

Examples 2 to 5

A precursor glass sheet was obtained in the same manner as in example 1, except that: (1) the glass substrate formulations were different (table 1); (2) the results of the tests were different (see Table 2)

TABLE 1

Note: "-" indicates that the precursor glass does not contain the component.

TABLE 2

TABLE 3

Note: "-" indicates that the glass article was not subjected to this step.

The results show that the overall falling height of the sand impact resistance of the embodiments 1 to 5 in the table 2 is 1.2 to 1.8m, and finally, the glass failure state is observed, only 2 to 3 cracks are extended without generating star burst, so that the influence of external force on the failure state is avoided to the maximum extent. The strengthened glass is fixed by a Vickers diamond drill and a guide rail to ensure that the drill vertically impacts the surface of the glass, the impact is conducted by air pressure, the air pressure is adjusted, and the impact force is controlled by combining a pressure sensor. The damage point only extends two cracks instead of star burst, the influence of external force on the damage state is avoided to the maximum extent, and finally, the tensile stress safety of the glass is judged by observing the damage state of the glass. And the single-rod static pressure strength can reach 410N.

While comparative example 1 is a conventional tempered glass (see table 1) on the market at present, and the process treatment method is adopted (see table 2), even if the thickness of the glass is 0.7mm, the surface CS is higher, but the CT-LD is reduced due to the surface CS; and the falling height of the sand surface impact resistance of the tempered glass is only 0.8 m. Indicating that the surface CS does not contribute much to its drop height, but is primarily CT-LD.

Comparative example 2, however, even with the same composition as in example 1, the strengthening process was carried out in a more conventional manner, such as strengthening IOX 1: 440 x 100 wt% NaNO₃*7h，IOX2：440*100wt％KNO₃2h, the CT-LD of the sample after fortification was 35000, because the IOX1 was over-fortified in the process, its CT-LD should have a downward trend, and the use of pure potassium salt would lead to a more impaired sodium-lithium exchange, resulting in a further decrease in CT-LD. The thickness of the glass is 0.7mm, the falling height of the sand-resistant surface impact strength of the strengthened glass is only 0.9m, tensile stress can generate tension in the center of the glass, and when the glass is impacted, the glass is taken as assistance of glass cracking, so that the glass is broken because the CT-LD is too high, and the bifurcation threshold is low. Will break into fragments.

The difference between the comparative example 3 and the comparative example 2 is that the thickness of the glass is 1.4mm, the falling height of the sand impact resistance of the strengthened glass is only 0.9m, tensile stress can generate tension in the center of the glass, and when the glass is impacted, the glass can generate fine fragments, even the glass can be granulated, the fragments are only 0.5mm, and the experience of customers can be seriously influenced.

Referring to table 3, the present invention also provides a test method for determining a chemically strengthened glass having a high safety stress, the chemically strengthened glass being obtained by ion-exchanging the above precursor glass, the test method comprising:

measuring the surface compressive stress, the depth DOL-0max of the compressive stress layer and the bifurcation threshold of the glass obtained under the following ion exchange conditions; wherein the ion exchange conditions are: putting precursor glass into a salt bath to perform chemical ion exchange for 1h at 440 ℃, wherein the mass ratio of sodium salt in the salt bath is the larger value of a numerical value and a numerical value b, a is 5 wt%, and b is K in the glass base material₂O/2(K₂O+Na₂O+Li₂O) in a molar ratio. Wherein b of the examples 1, 2, 3, 4 and 5 is 7.7%, 5%, 6%, 0, respectively; therefore, the sodium salt mass ratios in the salt bath were 7.7%, 5%, 6%, 5%, and 5%, respectively.

-the chemically strengthened glass has a high safety stress when the measured surface compressive stress reaches above 500MPa, the depth DOL-0max of the compressive stress layer is above 17% of the thickness of the glass, and the bifurcation threshold is above 80% of its maximum tensile stress line density value CT-LDmax.

The test results show that the chemically strengthened glass of each of examples 1 to 5 has a bifurcation threshold value which is more than 80% of the maximum tensile stress linear density value CT-LDmax, a compressive stress layer depth DOL-0max which is more than 17% of the thickness of the glass, and a surface compressive stress CS of the glass which is more than 500 MPa. The judgment and test method is consistent with the actual results in the table 2, namely the judgment and test method is the same as the observation and damage states of the actual sand surface impact strength test and the actual drop test, and the glass is proved to have better tensile stress safety, namely the glass meets the standard of detecting high safety stress.

The invention provides theoretical basis and new thought for the judgment of the strengthening standard and the safety method of the chemically strengthened glass, and has good application prospect. The safety balance of the compressive stress and the tensile stress of the chemically strengthened glass is determined by researching the relationship between the bifurcation threshold value of the chemically strengthened glass obtained by ion exchange under specific conditions and the maximum tensile stress linear density value CT-LDmax, the depth DOL-0max of a compressive stress layer, the thickness of the glass and the surface compressive stress CS of the glass, and whether the chemically strengthened glass belongs to the chemically strengthened glass with high safety stress is judged.

In conclusion, by adjusting the components and the content of the glass components and accurately controlling the conditions of the sodium-containing salt bath, the glass is strengthened to achieve sufficient surface compressive stress, and has high network structure strength, so that the compressive stress and the tensile stress of the obtained strengthened glass are in the optimal state, and the strengthened glass has the maximum composite compressive stress in the safe state of the tensile stress. The chemically strengthened glass has high strength, hardness, scratch resistance and good drop resistance; the glass has safety in the optimal stress state, can keep the stability and high strength of the glass in the using process, and is suitable for electronic display equipment, particularly the field of cover plate protection of the electronic display equipment.

The above description is only exemplary of the present invention and should not be taken as limiting, and any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A chemically strengthened glass having a high safety stress, which is obtained by ion-exchanging a precursor glass; characterized in that when the following conditions are satisfied: putting precursor glass into a salt bath to perform chemical ion exchange for 1h at 440 ℃, wherein the mass ratio of sodium salt in the salt bath is the larger value of a numerical value and a numerical value b, a is 5 wt%, and b is K in the glass base material₂O/2(K₂O+Na₂O+Li₂O) molar ratio; the surface compressive stress of the obtained glass reaches more than 500MPa, and the depth DOL-0max of the compressive stress layer is more than 17% of the thickness of the glass.

2. The chemically strengthened glass having high safety stress according to claim 1, wherein the chemically strengthened glass has a bifurcation threshold of 80% or more of its maximum tensile stress line density value CT-LDmax.

3. The chemically strengthened glass having high safety stress according to claim 1, wherein the precursor glass has a Vickers hardness of 600kgf/mm under a load of 300g and a dwell of 10s²～630kgf/mm²And all ranges and subranges therebetween.

4. Chemically strengthened glass with high safety stress according to claim 1, wherein the precursor glass contains, in mol% on oxide basis:

SiO₂ 65mol％～75mol％、Al₂O₃ 8mol％～15mol％、Na₂O 1mol％～5mol％、Li₂o4 mol% to 13 mol% and K₂0.1 mol% -3 mol% of O; wherein, SiO₂/(SiO₂+Al₂O₃) At least 78% of Na₂O+Li₂O is 7mol percent to 13mol percent.

5. The chemically strengthened glass with high safety stress as claimed in claim 4, wherein the precursor glass further comprises B₂O₃And MgO; wherein, B is₂O₃The molar percentage of the MgO is 0-3 mol%, and the molar percentage of the MgO is 0-7.5 mol%.

6. The chemically strengthened glass with high safety stress as claimed in claim 4 or 5, wherein the precursor glass further comprises a fining agent, wherein the fining agent is present in an amount of not more than 1.5 wt% of the original composition of the precursor glass.

7. Chemically strengthened glass with high safety stress according to claim 6, wherein the fining agent is tin oxide and/or sodium chloride.

8. The chemically strengthened glass having a high safety stress according to claim 6, wherein the precursor glass is formed by any one of a float method, an overflow method, a rolling method and a casting method; then ion exchange is carried out in salt bath to obtain:

IOX1：440℃*80wt％NaNO₃+20wt％KNO₃*5h；

IOX2：440℃*95wt％KNO₃+5wt％NaNO₃*2h。

9. the chemically strengthened glass having high safety stress according to claim 8, wherein the salt bath further comprises lithium ions, and the molar ratio of the lithium ions to the total alkali metal ions in the salt bath is less than 0.25%.

10. The chemically strengthened glass having a high safety stress according to claim 8, wherein a lithium ion purified product is charged into the salt bath for purification when the surface compressive stress of the chemically strengthened glass is reduced to 5 to 20% of the first batch in the IOX1 ion exchange process.

11. The chemically strengthened glass having high safety stress according to claim 8, wherein the precursor glass has a thickness of 0.4mm to 1.5 mm.

12. The chemically strengthened glass having high safety stress according to claim 10, wherein the lithium ion purified product is added in an amount of 0.1 to 5 wt% based on the mass of the salt bath.

13. The chemically strengthened glass having high safety stress according to claim 10, wherein the temperature of the refining is 360 ℃ to 450 ℃ and the time of the refining is at least 4 hours.

14. The chemically strengthened glass with high safety stress according to claim 11, wherein the chemically strengthened glass has a thickness of 0.7 mm.

15. The chemically strengthened glass having high safety stress according to claim 12, wherein the lithium ion purified product is added in an amount of 0.1 to 2 wt% based on the mass of the salt bath.

16. A consumer electronics terminal, comprising:

a housing comprising a front surface, a rear surface, and side surfaces;

and an electronic assembly partially located within the housing, the electronic assembly including a display located at or adjacent a front surface of the housing;

the front surface or/and the back surface or/and the side surface comprises the chemically strengthened glass with high safety stress as defined in any one of claims 1 to 15.

17. The consumer electronic terminal as recited in claim 16, further comprising a cover article covering a front surface of the housing or on the display, the cover article comprising the chemically strengthened glass with high safety stress as recited in any one of claims 1 to 15.

18. The consumer electronic terminal according to claim 16 or 17, wherein the consumer electronic terminal comprises a mobile phone, a tablet computer, or other electronic terminal.

19. A test method for judging high safety stress of chemically strengthened glass obtained by ion exchange of precursor glass,

when the measured surface compressive stress reaches more than 500MPa, the depth DOL-0max of the compressive stress layer is more than 17% of the thickness of the glass, and the chemically strengthened glass has high safety stress.

20. The test method according to claim 19, wherein the chemically strengthened glass has a bifurcation threshold of 80% or more of its maximum tensile stress linear density value CT-LDmax.

21. The test method according to claim 20, wherein the chemically strengthened glass has a high safety stress when the measured surface compressive stress reaches 550MPa or more, the depth DOL-0max of the compressive stress layer is 18% or more of the thickness of the glass, and the bifurcation threshold is 90% or more of its maximum tensile stress line density value CT-LDmax.

22. The test method according to claim 19, which is particularly suitable for chemically strengthened glass according to any one of claims 1 to 15.