CN104276756A - Alkali-free glass - Google Patents

Abstract

The invention discloses an alkali-free glass. The mole percentage of each chemical component in the glass is: SiO ₂ 68.5-72%, Al ₂ O ₃ 12.6-15%, B ₂ O ₃ 1-3.7%, MgO0.1-5.5%, CaO4-7%, ZnO0.05-4%, SrO1-3.5%, SnO0.05-0.1%. It has the advantages of high chemical stability, high strain point, high Young's modulus, low expansion coefficient, low melting temperature, and low liquidus temperature. melting temperature. This material can be widely used in the production of glass substrates for flat-panel displays, photovoltaic devices or other optoelectronic devices, especially for TFT-LCD and OEL glass substrates using low-temperature polysilicon LTPS technology.

Description

a non-alkali glass

technical field

The invention belongs to the technical field of glass production, and relates to a formula widely applicable to the production of glass substrates for plane displays, lighting, photovoltaic devices or other optoelectronic devices, in particular to an alkali metal-free alkaline earth aluminosilicate glass .

Background technique

With the rapid development of the optoelectronic industry, the demand for various display devices is increasing, such as active matrix liquid crystal display AMLCD, organic light-emitting diode OLED and active matrix liquid crystal display LTPS TFT-LCD devices using low-temperature polysilicon technology. The devices are based on TFT technology using thin-film semiconductor materials to produce thin-film transistors. The mainstream silicon-based TFT can be divided into amorphous silicon (a-Si) TFT, polycrystalline silicon (p-Si) TFT and single crystal silicon (SCS) TFT, among which amorphous silicon (a-Si) TFT is the current mainstream TFT-LCD The applied technology, amorphous silicon (a-Si) TFT technology, can be processed at a temperature of 300-450°C during the production process. LTPS polysilicon (p-Si) TFT needs to be processed multiple times at higher temperatures during the manufacturing process, and the substrate must not be deformed during multiple high-temperature treatments, which puts forward higher requirements on the performance of the substrate glass. The preferred strain The point is higher than 650°C, more preferably higher than 670°C, 700°C. At the same time, the expansion coefficient of the glass substrate needs to be similar to that of silicon to minimize stress and damage. Therefore, the preferred linear thermal expansion coefficient of the substrate glass is between 28-39×10-7/°C. In order to facilitate production and reduce production costs, the glass used as a display substrate should have a lower melting temperature and liquidus temperature.

Glass substrates for flat display need to form transparent conductive films, insulating films, semiconductor (polysilicon, amorphous silicon, etc.) Photo-etching technology forms various circuits and graphics. If the glass contains alkali metal oxides (Na ₂ O, K ₂ O, Li ₂ O), alkali metal ions diffuse into the deposited semiconductor material during heat treatment and damage The characteristics of the semiconductor film, therefore, the glass should not contain alkali metal oxides, the first choice is to use SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , alkaline earth metal oxide RO (RO=Mg, Ca, Sr) and other main components alkaline earth aluminosilicate glass.

The strain point of most silicate glasses increases with increasing glass former content and decreasing modifier content. But at the same time, it will cause high-temperature melting and clarification difficulties, resulting in intensified erosion of refractory materials, increasing energy consumption and production costs. Therefore, improving the low-temperature viscosity while ensuring that the high-temperature viscosity does not increase significantly through component improvement, or even lower is the best breakthrough to increase the strain point.

In the process of glass substrate processing, the substrate glass is placed horizontally, and the glass sags to a certain extent under its own weight. The degree of sagging is proportional to the density of the glass and inversely proportional to the elastic modulus of the glass. With the development of substrate manufacturing towards large size and thinning, attention must be paid to the sagging of glass plates during manufacturing. The composition should therefore be designed so that the substrate glass has as low a density as possible and as high a modulus of elasticity as possible.

With the popularity of smart phones and tablet computers, the era of smart mobility has opened. In the past, mobile phones were limited to communication functions, but now the performance of smart devices including smartphones and tablet computers is close to that of notebooks, allowing people to perform and enjoy high-level business and entertainment activities all the time with the convenience of wireless communication. Under such a trend, the requirements for display performance are also continuously increasing, especially for the picture quality of mobile smart devices and the requirements for outdoor visual performance. Thinning has become an inevitable trend. Under the guidance of this development trend, the display panel is developing in the direction of thinner and ultra-high-definition display, and the panel manufacturing process is developing at a higher processing temperature; at the same time, the monolithic glass has been processed to a thickness of 0.25mm, 0.2mm, and 0.1mm. even thinner. The way to make glass thinner is mainly chemical thinning. Specifically, the glass substrate is corroded with hydrofluoric acid or hydrofluoric acid buffer solution. The thinning principle is as follows:

Main chemical reaction: 4HF+SiO ₂ =SiF ₄ +2H ₂ O

Secondary chemical reaction: RO+2H ⁺ =R ²⁺ +H ₂ O (R stands for alkaline earth metal, etc.)

The chemical thinning process and the surface quality of the thinned glass substrate have a certain relationship with the composition of the basic glass. The existing TFT-LCD substrate glass frequently appears in the process of chemical thinning. production cost. Glass with high chemical stability has better surface quality after thinning. Therefore, the development of TFT-LCD substrate glass with high chemical stability can reduce production costs such as secondary polishing and improve product quality and yield. For large Industrialized production has great benefits.

With the development of the trend of thinning and thinning, in the production of higher-generation glass substrates such as G5, G6, G7, and G8, the sagging and warping of horizontally placed glass substrates due to their own weight has become an important research topic. For glass substrate producers, after the glass plate is formed, it has to go through various steps such as annealing, cutting, processing, inspection, cleaning, etc. The drooping of large-sized glass substrates will affect the loading, Ability to take out and divide. For panel manufacturers, similar problems also exist. Larger sag or warpage will lead to increased fragmentation rate and CF process alarm, seriously affecting product yield. If both sides of the substrate are supported at both ends, the maximum sag (S) of the glass substrate can be expressed as follows:

        

k is a constant, ρ is the density, E is the modulus of elasticity, l is the support interval, and t is the thickness of the glass substrate. Among them, (ρ/E) is the reciprocal of the specific modulus. Specific modulus refers to the ratio of material elastic modulus to density, also known as "specific elastic modulus" or "specific stiffness", which is one of the important requirements of structural design for materials. A higher specific modulus means that the material is lighter for the same stiffness, or more rigid for the same mass. It can be seen from the above formula that when l and t are constant, the sag can be reduced when ρ becomes smaller and E is increased. Therefore, the substrate glass should have as low a density as possible and as high a modulus of elasticity as possible, that is, it should have a specific modulus as large as possible . Due to the sharp reduction in thickness, the thinned glass has a reduced mechanical strength and is more easily deformed. Reducing density, increasing specific modulus and strength, and reducing glass brittleness have become factors that glass producers need to consider.

In order to obtain non-foaming alkali-free glass, the gas produced during the glass reaction is expelled from the molten glass by using the clarifying gas. In addition, during homogenization and melting, the clear gas generated needs to be reused to increase the diameter of the bubble layer so that it By floating up, the participating microbubbles are taken out.

However, molten glass used as a glass substrate for flat panel displays has a high viscosity and needs to be melted at a relatively high temperature. In such a glass substrate, vitrification reaction usually occurs at 1300-1500°C, and defoaming and homogenization are performed at a high temperature of 1500°C or higher. Therefore, among fining agents, As ₂ O ₃ capable of generating fining gas in a wide temperature range (range of 1300-1700 degrees) is widely used.

However, As ₂ O ₃ is very toxic, and may pollute the environment and cause health problems in the glass manufacturing process or waste glass disposal, and its use is being restricted.

Attempts have been made to use antimony fining instead of arsenic fining. However, antimony itself poses environmental and health concerns. Although the toxicity of Sb ₂ O ₃ is not as high as that of As ₂ O ₃ , Sb ₂ O ₃ is still toxic. Also, compared with arsenic, antimony produces clearing gas at a lower temperature and is less effective in removing such glass bubbles.

Contents of the invention

The purpose of the present invention is to provide an environment-friendly, more perfect component design of flat-panel display glass substrates, and to provide a clarifying agent that does not exist as a surface clarifier even if As ₂ O ₃ and/or Sb ₂ O ₃ are not used. The formula of the defective glass substrate, designed an alkali-free glass, the glass substrate prepared by using this formula meets the requirements of environmental protection, does not contain As ₂ O ₃ , Sb ₂ O ₃ and their compounds, and the glass does not contain heavy metal barium and their compounds , has higher chemical stability, has higher strain point, has higher Young's modulus, has higher transmittance, has lower melting temperature, has lower liquidus temperature, has The lower density is in line with the development trend of the flat panel display industry. It is suitable for the production and manufacture of various forming methods such as the down-draw method and the float method.

The technical solution adopted in the present invention is: a kind of alkali-free glass, the molar percentage of each chemical composition in the glass is:

SiO ₂ 68.5-72%,

Al ₂ O ₃ 12.6-15%,

B ₂ O ₃ 1-3.7%,

MgO 0.1-5.5%,

CaO 4-7%,

ZnO 0.05-4%,

SrO 1-3.5%,

SnO 0.05-0.1%.

The beneficial effects of the present invention are: 1), the present invention is environmentally friendly and does not contain any toxic and harmful substances. The clarifier uses stannous oxide SnO. SnO is an easy-to-obtain substance and is known to have no harmful properties. It is used alone as a When used as a glass clarifying agent, it has a relatively high temperature range for producing clear gas, which is suitable for the elimination of glass bubbles; 2), by controlling SiO ₂ +Al ₂ O ₃ >83%, SrO/R'O<0.25, (MgO +ZnO)/R'O>0.35, 0.8<R'O/Al ₂ O ₃ <1.2, which can make the glass have higher chemical stability, strain point, Young's modulus and lower melting temperature, liquid 3) The glass substrate produced with the help of the glass component formula provided by the present invention can reach the following technical indicators after testing: 10% HF acid solution (22°C/20min) erosion amount <4.8mg/ cm2; the coefficient of thermal expansion at 50-350 degrees is 28-34×10 ^-7 /°C; the strain point is above 700°C; the density is less than 2.5g/cm ³ , and the liquidus temperature is lower than 1150°C. The number of bubbles with a diameter greater than 0.1 mm is invisible; 4) Due to the relatively high amount of SiO ₂ and Al ₂ O ₃ contained in the composition of the present invention, it ensures excellent chemical corrosion resistance, and at the same time, it is matched with a certain proportion of SiO 2 and Al 2 O 3 MgO+ZnO can effectively reduce the melting temperature, bring more space for the improvement of production line yield, and reduce the production costs of fuel and electricity at the same time.

Detailed ways

A kind of alkali-free glass, the molar percentage of each chemical composition in the described glass is:

SiO ₂ 68.5-72%,

Al ₂ O ₃ 12.6-15%,

B ₂ O ₃ 1-3.7%,

MgO 0.1-5.5%,

CaO 4-7%,

ZnO 0.05-4%,

SrO 1-3.5%,

SnO 0.05-0.1%.

Preferably, the sum of the molar percentages of SiO ₂ and Al ₂ O ₃ is greater than 83%.

Preferably, SrO/(MgO+CaO+ZnO+SrO)<0.25.

Preferably, (MgO+ZnO)/(MgO+CaO+ZnO+SrO)>0.35.

Preferably, 0.8<(MgO+CaO+ZnO+SrO)/Al ₂ O ₃ <1.2.

Preferably, the mole percentage of Al ₂ O ₃ is 13-14.5%.

Preferably, the molar percentage of ZnO is 0.5-3%.

Preferably, the molar percentage of B ₂ O ₃ is 1.5-3.5%.

Preferably, the molar percentage of _SiO2 is 69-71%.

Preferably, the molar percentage of SrO is 1.5-3.0%.

During implementation, the raw materials including the corresponding oxide mole percentage components of the above-mentioned glass substrates are uniformly stirred and mixed, and then the mixed raw materials are melted and processed, and the bubbles are discharged and the glass liquid is homogenized by stirring with a platinum rod, and then its temperature Reduce the forming temperature range of the glass substrate required for forming. Through the annealing principle, the thickness of the glass substrate required by the flat-panel display is produced, and then the formed glass substrate is subjected to simple cold processing, and finally the basic physical properties of the glass substrate are tested. Qualified product.

In the present invention, the molar content of _SiO2 is 68.5-72%. SiO ₂ is a glass former. If the content is too low, it is not conducive to the enhancement of chemical and corrosion resistance, and the expansion coefficient will be too high, and the glass will be easily devitrified; increasing the SiO ₂ content will help reduce the weight of the glass and reduce the thermal expansion coefficient. The strain point increases, the chemical resistance increases, but the high temperature viscosity increases, which is not conducive to melting, and the general kiln is difficult to meet, so the content of SiO ₂ is 68.5-72%, and the preferred mole percentage of SiO ₂ is 69-71 %.

The molar content of Al ₂ O ₃ is 12.6-15%, which is used to improve the strength of the glass structure. If the content is lower than 12.6%, the glass is prone to devitrification and is also easily corroded by external moisture and chemical reagents. A high content of A1 ₂ O ₃ helps to increase the strain point and bending strength of the glass, but the glass is prone to crystallization if it is too high, and it will make the glass difficult to melt, so the content of A1 ₂ O ₃ is 12.6-15%. The preferred molar percentage of Al ₂ O ₃ is 13-14.5%.

The content of B ₂ O ₃ is 1~3.7mol%. The function of B ₂ O ₃ is quite special. It can form glass alone, and it is also a good flux. It is difficult for B ₂ O ₃ to form [BO ₄ ], can reduce high-temperature viscosity, B has the tendency to capture free oxygen to form [BO ₄ ] at low temperature, make the structure more compact, increase the low-temperature viscosity of the glass, and prevent crystallization from occurring. But too much B ₂ O ₃ will greatly reduce the glass strain point, so the content of B ₂ O ₃ is 1-3.7%, and the preferred mole percentage of B ₂ O ₃ is 1.5-3.5%.

MgO has the characteristics of greatly increasing the Young's modulus and specific modulus of the glass, reducing the viscosity at high temperature, and making the glass easy to melt. When the amount of alkaline earth metals in the alkali-free silicate glass is small, the introduction of Mg ²⁺ ions outside the network with high electric field strength is easy to produce local accumulation in the structure and increase the range of short-range order. In this case, more oxides such as Al ₂ O ₃ and B ₂ O ₃ are introduced, and when they exist in the state of [AlO ₄ ] and [BO ₄ ], since these polyhedrons are negatively charged, they attract some cations outside the network, The accumulation degree and crystallization ability of the glass are reduced; when the amount of alkaline earth metal is high and the network fracture is serious, the introduction of MgO can reconnect the broken silicon-oxygen tetrahedron and reduce the crystallization ability of the glass. Therefore, when adding MgO, pay attention to the proportion with Al ₂ O ₃ and B ₂ O ₃ . The presence of MgO leads to lower expansion coefficient and density, higher chemical resistance, strain point and modulus of elasticity relative to other alkaline earth metal oxides. If MgO is greater than 5.5 mol%, the chemical resistance of the glass will be deteriorated, and the glass will be easily devitrified. A too low MgO content is disadvantageous for an increase in the modulus. Therefore its content is 0.1-5.5 mol%.

The molar content of CaO is 4-7%. Calcium oxide is used to promote the melting of glass and adjust the formability of glass. If the calcium oxide content is less than 4%, the viscosity of the glass will not be reduced. If the calcium oxide content is too high, the glass will be prone to crystallization, and the thermal expansion coefficient will also increase significantly, which is not conducive to the subsequent process. Therefore, the content of CaO is 4-7%.

The molar content of SrO is 1-3.5%. Strontium oxide is used as a flux and prevents crystallization of the glass. If the content is too much, the glass density will be too high, resulting in excessive molar weight of the product. Therefore, the content of SrO is determined to be 1 to 3.5%.

The molar content of ZnO is 0.05-4%. Divalent metal oxides can be divided into two categories according to their status in the periodic table and their influence on properties: one is alkaline earth metal oxides in the main group, and its ion R ²⁺ has 8 outer electron structures; the second type is located in the subgroup of the periodic table (such as ZnO, CdO, etc.), and its ion R ²⁺ has 18 outer electron structures. The impact is different. ZnO can reduce the high-temperature viscosity of glass (such as 1500 degrees), which is beneficial to eliminate bubbles; at the same time, it can improve the strength and hardness below the softening point, increase the chemical resistance of the glass, and reduce the thermal expansion coefficient of the glass. In the alkali-free glass system, adding an appropriate amount of ZnO helps to inhibit crystallization and lower the crystallization temperature. In theory, after ZnO is introduced into the glass as an exosome in the alkali-free glass, it generally exists in the form of [ZnO ₄ ] at high temperature, which is looser than [ZnO ₆ ] glass, and is in the same position as the glass without ZnO. Compared with the high temperature state, the glass containing ZnO has lower viscosity and higher atomic motion speed, and cannot form crystal nuclei. It is necessary to further reduce the temperature to facilitate the formation of crystal nuclei. Therefore, the upper limit temperature of crystallization of the glass is lowered. Too much ZnO content will greatly reduce the strain point of the glass. Therefore, the content of ZnO is determined to be 0.05-4 mol%, more preferably, the content of ZnO is 0.5-3%.

In the present invention, 0.05-0.1% stannous oxide SnO can also be added to the glass composition as a clarifying agent or defoaming agent when the glass is melted, so as to increase the melting mole of the glass. If the content is too much, the glass substrate will be devitrified, so the added amount should not exceed 0.1mol%.

The concrete embodiment that each component in the formula is measured by mole percentage is given below, referring to Table 1, 2:

Table 1

Table 2

It can be seen from Table 1 and Table 2 that the alkali-free glass prepared by the formula of the present invention meets the requirements of environmental protection, and has high chemical stability, high strain point, high Young's modulus, low expansion coefficient, low melting temperature, and low liquid phase line temperature etc.

Claims (10)

1. an alkali-free glass, characterized in that: the molar percentage of each chemical composition in the glass is: SiO ₂ 68.5-72%, Al ₂ O ₃ 12.6-15%, B ₂ O ₃ 1-3.7%, MgO 0.1-5.5%, CaO 4-7%, ZnO 0.05-4%, SrO 1-3.5%, SnO 0.05-0.1%. 2. An alkali-free glass according to claim 1, characterized in that the sum of the molar percentages of SiO ₂ and Al ₂ O ₃ is greater than 83%. 3. An alkali-free glass according to claim 1, characterized in that: SrO /(MgO+CaO+ZnO+SrO)<0.25. 4. An alkali-free glass according to claim 1, characterized in that: (MgO+ZnO)/(MgO+CaO+ZnO+SrO)>0.35. 5. The alkali-free glass according to claim 1, characterized in that: 0.8<(MgO+CaO+ZnO+SrO)/Al ₂ O ₃ <1.2. 6. The alkali-free glass according to claim 1, characterized in that: the mole percentage of Al ₂ O ₃ is 13-14.5%. 7. The alkali-free glass according to claim 1, characterized in that the molar percentage of ZnO is 0.5-3%. 8 . The alkali-free glass according to claim 1 , wherein the molar percentage of B ₂ O ₃ is 1.5-3.5%. 9. A kind of alkali-free glass according to claim 1, characterized in that: the molar percentage of _SiO2 is 69-71%. 10. The alkali-free glass according to claim 1, characterized in that: the molar percentage of SrO is 1.5-3.0%.