WO2014179153A1 - Surface treatments for low electrostatic discharge fusion drawn glass - Google Patents

Surface treatments for low electrostatic discharge fusion drawn glass Download PDF

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Publication number
WO2014179153A1
WO2014179153A1 PCT/US2014/035383 US2014035383W WO2014179153A1 WO 2014179153 A1 WO2014179153 A1 WO 2014179153A1 US 2014035383 W US2014035383 W US 2014035383W WO 2014179153 A1 WO2014179153 A1 WO 2014179153A1
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WO
WIPO (PCT)
Prior art keywords
glass sheet
treatment
glass
surface roughness
average surface
Prior art date
Application number
PCT/US2014/035383
Other languages
French (fr)
Inventor
Yunfeng Gu
Kai Ming Kiang
Jonathan Michael Mis
Nicholas James Smith
Louis Joseph STEMPIN, Jr.
Wanda Janina Walczak
Original Assignee
Corning Incorporated
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Corning Incorporated filed Critical Corning Incorporated
Priority to KR1020157032444A priority Critical patent/KR20160004302A/en
Priority to JP2016511770A priority patent/JP2016522144A/en
Priority to CN201480024285.0A priority patent/CN105164079A/en
Publication of WO2014179153A1 publication Critical patent/WO2014179153A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C15/00—Surface treatment of glass, not in the form of fibres or filaments, by etching

Definitions

  • the present specification generally relates to surface treatments for glass surfaces and, more specifically, to methods of strategically texturing the b-side of glass sheets without compromising the performance attributes of the a-side of the glass sheet.
  • Flat panel display (FPD) glass which may be used for thin film transistor (TFT) - liquid crystal display (LCD) substrates, may consist of two sides.
  • the first side may be a functional side upon which TFTs are built (a-side), and the second side may be a nonfunctional backside (b-side).
  • a-side functional side upon which TFTs are built
  • b-side nonfunctional backside
  • the b-side of the FPD glass may contact a variety of materials, such as, for example, plastics, rubbers, or ceramics and, as such, the surface quality and uniformity of the b-side surface need not be as high as the a-side surface.
  • a method for improving the electrostatic discharge properties of a glass sheet including treating at least one side of the glass sheet with a treatment solution that increases an average surface roughness, and removing the treatment solution.
  • An average surface roughness of the at least one treated side of the glass sheet may be from about 0.3 nm to about 100 nm.
  • a percent reduction in voltage between the glass sheet before the treatment and the glass sheet after the treatment may be from about 1.5% to about 40%.
  • a glass sheet having a first side with an average surface roughness of from about 0.3 nm to about 100 nm, and a second side with an average surface roughness of from about 0.1 nm to about 100 nm is provided.
  • the glass sheet may have a length of at least about 100 mm, and a thickness of less than about 1.0 mm.
  • a glass sheet may include a side having a surface roughness of about 0.2 nm, or even about 0.15 nm for a 2 x 2 ⁇ atomic- force microscope (AFM) scan, and another side having a surface roughness of from about 0.3 nm to about 1.3 nm.
  • 0.2 nm may be defined as Ra or Rq as determined by AFM measurement.
  • Ra and Rq may be represented by equations (1) and (2):
  • n is number of points at which measurement occurs
  • z is height at each point
  • zbar is average of height collected at each point in the line scan.
  • Ra is often designated as "average” surface roughness
  • Rq is often called the “root-mean-square” (RMS) surface roughness.
  • the a length of the glass sheet may be greater than about 100 mm, and a thickness of the glass sheet may be less than about 1 mm
  • FIG. 1 is a schematic showing an embodiment of a fusion draw method
  • FIG. 2 is a graph of voltages measured after contact separation plotted against glass type and treatment process for a glass sheet having dimensions of 180 mm x 230 mm x 0.5 mm, according to embodiments;
  • FIG. 3 is a graph showing percent reduction in voltage for the data shown in FIG. 2;
  • FIG. 4 is a graph of voltages measured after contact separation plotted against glass type and treatment process for a glass sheet having dimensions of 127 mm x 127 mm x 0.5 mm, according to embodiments;
  • FIG. 5 is a graph showing percent reduction in voltage for the data shown in FIG. 4;
  • FIG. 6 is a graph average surface roughness according to embodiments plotted against glass type and treatment process
  • FIG. 7 is a graph of voltages measured after contact separation plotted against average surface roughness for a glass sheet having dimensions of 180 mm x 230 mm x 0.5 mm, according to embodiments;
  • FIG. 8 is a graph of voltages measured after contact separation plotted against average surface roughness for a glass sheet having dimensions of 127 mm x 127 mm x 0.5 mm, according to embodiments;
  • FIG. 9 is a graph of voltages measured after contact separation plotted against glass type and treatment process for a glass sheet having dimensions of 730 mm x 920 mm x 0.5 mm, according to embodiments;
  • FIG. 10 is a graph showing percent reduction in voltage for the data shown in FIG. 9;
  • FIG. 11 is a graph of voltages measured after contact separation plotted against glass type and treatment process for a glass sheet having dimensions of 730 mm x 920 mm x 0.5 mm, according to embodiments.
  • FIG. 12 is a graph showing percent reduction in voltage for the data shown in FIG. 11.
  • Glass sheets treated in accordance with the methods disclosed herein may be formed by any suitable method.
  • the glass sheets may be formed by a fusion draw process.
  • the fusion draw process is a down draw process, also referred to as the overflow process.
  • a glass-forming melt flows into a refractory trough and then overflows in a controlled manner from either side of the trough.
  • An advantage of this process is that the surface of the sheet glass formed therefrom does not come in contact with any refractory material or other forming equipment.
  • the fusion draw process yields a very flat and uniformly thick sheet of glass. As a result, no secondary processing is needed to obtain a smooth, flat, and uniform sheet of glass for display applications.
  • the fusion draw process requires that glasses used in the process have a relatively high viscosity at the liquidus temperature.
  • the fusion draw process is further described below with reference to FIG. 1. Similar fusion draw processes are described in U.S. Pat. Nos. 3,338,696 and 3,682,609, which are incorporated herein by reference in their entirety.
  • an exemplary glass manufacturing apparatus 100 for forming glass sheet material from molten glass is schematically depicted in which a fusion draw machine is used to form the molten glass into glass sheets.
  • the glass manufacturing apparatus 100 includes a melting vessel 101, a fining vessel 103, a mixing vessel 104, a delivery vessel 108, and a fusion draw machine (FDM) 120.
  • Glass batch materials are introduced into the melting vessel 101 as indicated by arrow 102.
  • the batch materials are melted to form molten glass 106.
  • the fining vessel 103 has a high temperature processing area that receives the molten glass 106 from the melting vessel 101 and in which bubbles are removed from the molten glass 106.
  • the fining vessel 103 is fluidly coupled to the mixing vessel 104 by a connecting tube 105. That is, molten glass flowing from the fining vessel 103 to the mixing vessel 104 flows through the connecting tube 105.
  • the mixing vessel 104 is, in turn, fluidly coupled to the delivery vessel 108 by a connecting tube 107 such that molten glass flowing from the mixing vessel 104 to the delivery vessel 108 flows through the connecting tube 107.
  • the delivery vessel 108 supplies the molten glass 106 through a downcomer 109 into the FDM 120.
  • the FDM 120 comprises an enclosure 122 in which an inlet 110, a forming vessel 111 and at least one draw assembly 150 are positioned. As shown in FIG. 1, the molten glass 106 from the downcomer 109 flows into an inlet 110 which leads to the fonning vessel 111.
  • the forming vessel 1 11 includes an opening 112 that receives the molten glass 106 which flows into a trough 113 and then overflows and runs down two converging sides 114a and 114b before fusing together at a root, where the two sides join, before being contacted and drawn in a downstream direction 151 by the draw assembly 150 to form a continuous glass sheet 148. Thereafter, the continuous glass sheet 148 may be segmented into discrete glass sheets.
  • the surface treatment methods have been described herein as being used in conjunction with glass sheets formed by the fusion draw process, it should be understood that the surface treatment methods may be used on glass sheets formed from other processes in which glass batch materials are melted to form molten glass and the molten glass is then formed into a glass sheet.
  • the pulling rolls described herein may also be utilized in conjunction with up-draw processes, slot-draw processes, and other, similar processes.
  • the dimensions of the glass sheets made by the fusion draw process are not particularly limited, and the treatment methods described herein may be applied to glass sheets having any dimensions.
  • the length of the glass sheet to be treated may be greater than about 100 mm, or even greater than about 200 mm. In some embodiments, the length of the glass to be treated may be greater than about 300 mm, or even greater than about 400 mm. In other embodiments, the length of the glass sheet may be greater than 500 mm or even greater than 600 mm. In further embodiments, the length of the glass sheet may be greater than 700 mm, or even greater than 800 mm. In still further embodiments, the length of the glass sheet may be greater than about 900 mm, or even about 1000 mm.
  • the width of the glass sheet to be treated may be greater than about 100 mm, or even greater than about 200 mm. In some embodiments, the width of the glass to be treated may be greater than about 250 mm, or even greater than about 300 mm.
  • the thickness of the glass sheet to be treated is not particularly limited, and the method of treating a glass sheet disclosed herein may be used on thin glass sheets. In embodiments, the thickness of the glass sheet to be treated may be about 1.0 mm or less, or even about 0.7 mm or less. In some embodiments, the thickness of the glass sheet to be treated may be about 0.5 mm or less, or even about 0.4 mm or less. In other embodiments, the thickness of the glass sheet to be treated may be about 0.3 mm or less, or even 0.1 mm or less.
  • the composition of the glass sheet to be treated is not particularly limited, and the treatments disclosed herein may be applied to any glass composition.
  • the glass to be treated may be an alkali aluminosilicate glass, an alkali boroaluminosilicate glass, an alkaline-earth aluminosilicate glass, or an alkaline-earth boroaluminosilicate glass.
  • alkali refers to alkali metals (e.g., Li, Na, K, Rb and Cs)
  • alkaline- earth refers to alkaline-earth metals (e.g., Be, Mg, Ca, Sr and Ba), unless the context clearly indicates otherwise.
  • the a-side of the glass sheet may generally have an average surface roughness of from about 0.1 nm to about 100 nm.
  • the a-side surface may have an average surface roughness of from about 0.1 nm to about 100 nm, from about 0.16 nm to about 0.27 nm, from about 0.20 nm to about 0.27 nm, or even from about 0.22 nm to about 0.25 nm.
  • the average surface roughness of the a-side of the glass sheet may be such that it does not affect the visual properties of the glass sheet that are perceivable by the human eye.
  • the glass sheet to be treated in accordance with this disclosure may comprise an a-side and a b-side. Because the b-side surface of the glass sheet may be subject to mechanical contact during manufacture and subsequent handling, the b-side surface quality requirements may not be as stringent as the a-side surface quality requirements, which allows for more flexibility in converting b-side texturing concepts into practice.
  • the main concern with modifications to the b-side of a glass sheet is defects discernable with the human eye. For example, defects on the b-side that are greater than about 100 ⁇ may not be acceptable. In embodiments, defects on the b-side of the glass sheet that are greater than about 150 ⁇ may not be acceptable.
  • the glass sheets used in the methods described herein are initially obtained using forming processes as described herein above.
  • the glass sheets may not have the thickness dimension required for the specified application.
  • Panel thinning techniques may be used to achieve a desired thickness and/or thickness uniformity of the glass sheet.
  • Panel thinning techniques may include chemical or mechanical methods for reducing the thickness of the glass substrate from the b-side without diminishing the quality of the a-side surface. Mechanical thinning may mitigate a wide range of b-side surface features, defects, and contaminants because of the process of planarization. Chemical thinning may open up features such as dents and dimples.
  • the glass chemistry on the b-side surface does not particularly limit the use of thinning processes. Accordingly, thicknesses as discussed above may be achieved through the use of thinning processes, if necessary.
  • At least one side of the glass sheet may be texturized using a treatment solution comprising an acid, a base, a neutral solution, or mixtures thereof.
  • a treatment solution comprising an acid, a base, a neutral solution, or mixtures thereof.
  • Texturizing the glass sheet with the solutions disclosed in embodiments improve the electrostatic discharge (ESD) performance of the glass sheet.
  • Exposure to the treatment solution may also alter the glass surface chemistry and modify the surface of the glass sheet within acceptable b-side tolerance limits.
  • the glass sheet may be washed with any suitable cleaner to remove particulate matter and other surface contaminants before or after the treatment with the treatment solution.
  • the cleaners may be SemiClean KG (manufactured by Yokohama- Yushi-Kogyo), or other, similar cleaners.
  • the cleaners may include other detergents, acids, bases, peroxides, or mixtures thereof.
  • Detergents may combine surfactants, acid, bases, chelators and the like.
  • cleaning agents may be much simpler in nature, such as, for example, single bases, or bases with peroxides, single acids, or single acids with peroxides.
  • the duration and method of cleaning the glass sheet is not particularly limited and may be any suitable method, such as spraying, dipping, or a washing process used in the manufacture of glass sheets.
  • the glass sheet may be treated with a treatment solution to modify the ESD performance of the glass sheet.
  • the treatment solution may be hydrochloric acid (HC1).
  • the molarity of the HC1 may be from about 0.15 M to about 0.35 M, or even from about 0.2 M to about 0.3 M. In other embodiments, the molarity of the HC1 may be about 0.25 M.
  • the treatment solution may be a mixture of sulfuric acid (H 2 SO 4 ) and water.
  • the sulfuric acid:water mixture may be a 1 :4 mixture, or even a 1 :3 mixture.
  • the mixture of sulfuric acid and water may be a 1 :2 mixture.
  • the treatment solution may be a dilute mixture of sodium fluoride (NaF) and phosphoric acid (H 3 PO 4 ).
  • An exemplary mixture of NaF and H 3 PO 4 may be a mixture of 0.2 M NaF and 1M H 3 PO 4 , which may be diluted in water in a 4:5 mixture.
  • the treatment solution may be a mixture of HC1 and hydrofluoric acid (HF).
  • the molarity of the HC1 may be from about 0.15 M to about 0.35 M, or even from about 0.2 M to about 0.3 M.
  • Other suitable acids include HN0 3 , ammonium bifluoride, ammonium fluoride, HF:NH 4 F, HF:NH 4 HF mixtures, or others. It should be understood that other formulations of the treatment solution may be possible.
  • the glass sheet may be exposed to the treatment solution by any known method, such as, for example, dip coating, roller coating, or spray coating.
  • a mask may be placed over the a-side of the glass sheet to prevent texturization of the a-side of the glass sheet.
  • the mask material is not particularly limited, and may include any material that is capable of adhering to the glass sheet and protecting the glass sheet from the effects of the treatment solution.
  • the mask material should also be easily removed from the glass sheet after the treatment process is complete.
  • Exemplary masks include protective films (Visqueen or Kapton), which if they leave residue behind may be washed off in a subsequent cleaning process.
  • the duration of the treatment is not particularly limited, and the treatment should be conducted for the amount of time necessary to achieve the desired texturization.
  • the duration of the treatment may be from about 0.5 min to about 90 min, or even from about 1 min to about 60 min, or from about 5 min to about 30 min.
  • the duration of the treatment may be from about 10 min to about 20 min.
  • treatment times may be be less than 0.5 min, or even less than 0.25 min.
  • the treatment time may be less than 0.1 min.
  • the temperature at which the treatment is conducted may vary depending on the composition of the glass sheet and the composition of the treatment solution. In some embodiments, the temperature at which the treatment is conducted may be from about 20°C to about 100°C, or even from about 40°C to about 90°C. In other embodiments, the temperature at which the treatment is conducted may be from about 40°C to about 80°C, or even from about 50°C to about 70°C.
  • the treatment solution may be removed from the glass sheet by any suitable method.
  • the treatment solution may be removed by washing the treated glass sheet, as discussed above.
  • the treatment solution may be removed by heating, evaporation, or any other suitable means.
  • the treatment solution may be physically removed by, for example, forced air, a roller, a blade, or the like. It should be appreciated that the treatment solution may be removed by any method or apparatus without deviating from the scope of this disclosure.
  • the average surface roughness of the glass sheet may be measured before and after the treatment process.
  • the average surface roughness may be measured using an atomic force microscope (AFM).
  • Roughness is measured using standard values of Ra or Rq as defined above.
  • the average surface roughness of the glass sheet before the treatment process is from about 0.1 nm to about 100 nm, from about 0.1 nm to about 0.3 nm, or even from about 0.15 nm to about 0.25 nm.
  • the average surface roughness before the treatment process is from about 0.2 nm to about 0.23 nm.
  • the average surface roughness may be increased by the treatment process.
  • the average surface roughness may be measured after the treatment process to determine the increase in the average surface roughness as a result of the treatment process.
  • the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.3 nm to about 100 nm, or even from about 0.3 to about 75 nm
  • the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.3 nm to about 50 nm, or even from about 0.3 nm to about 25 nm.
  • the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.3 nm to about 15 nm, or even from about 0.4 nm to about 10 nm.
  • the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.4 nm to about 5 nm, or even from about 0.5 nm to about 1.3 nm. In still other embodiments, the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.5 nm to about 1.15 nm In other embodiments, the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.5 nm to about 1.0 nm, or even from about 0.7 nm to about 0.9 nm.
  • the increase in the average surface roughness caused by the treatment process may be affected by any number of conditions including, but not limited to, the composition of the glass sheet, the composition of the treatment solution, the duration of the treatment process, and/or the temperature of the treatment process. It should be understood that each of the above parameters may be modified in the treatment process to obtain a desired increase in the average surface roughness after the treatment process.
  • a correlation may be drawn between the average surface roughness of the glass sheet and electrostatic discharge (ESD) properties.
  • ESD electrostatic discharge
  • the ESD properties of the glass sheet may be determined by measuring the voltage on a treated side of the glass sheet. As discussed above, one side surface of the glass sheet may accumulate charge which negatively impacts the ESD properties of the glass sheet. The voltage across the sheet is a measure of the accumulated charge. Thus, as the voltage on a treated side the glass sheet approaches zero, the ESD properties of the glass sheet generally improve.
  • the measured voltage of a glass sheet after contact separation may vary depending, for example, on the composition of the glass sheet, the size of the glass sheet, the composition of the treatment solution, and combinations thereof.
  • a reduction in voltage is realized as surface roughness of one side of the glass sheet is increased.
  • This reduction in voltage may be calculated as a percentage by measuring the voltage after contact separation before treatment and measuring the voltage after contact separation after treatment.
  • the percentage of reduction of voltage may be from about 1.5% to about 40%), or even from about 2.0% to about 35%.
  • the percentage of reduction of voltage after contact separation may be from about 3.0% to about 30%, or even from about 4.0%> to about 25%).
  • the percentage of reduction of voltage after contact separation may be from about 5.0%) to about 20%, or even from about 7.0%) to about 15%).
  • the percentage of reduction of voltage after contact separation may be about 12%, or even about 10%.
  • the increases in both a treated side roughness and glass sheet voltage may vary depending on the composition of the glass, the size of the glass, the composition of the treatment solution, the duration of the treatment process, and the temperature at which the treatment process is operated, increases in the average surface roughness may be achieved for each glass composition using each treatment solution discussed herein. Thereby, the ESD properties of the glass sheet may be improved.
  • Glass Type I an alumino silicate glass manufactured by Corning Incorporated, was stripped of its protective Visqueen film and washed with 4% SemiClean KG (manufactured by Yokohama- Yushi-Kogyo) wash using a standard washing process. The glass was then dipped in various acids at various lengths of time and temperature as listed in Table 1 below, where each glass sheet had a thickness of 0.5 mm.
  • FIGS. 2-6 four glass types were treated using a treatment process as described herein.
  • Four differing glass compositions were tested; Glass Type I, as mentioned above, Glass Type II, Glass Type III, and Glass Type IV.
  • the four glass types have similar compositions and, generally, fall within the category of aluminosilicate glasses.
  • Various treatment solutions were used, and the treated glass sheets were prepared as shown in Table 1, but using the four different glass compositions, as mentioned above. After the treatment process was completed, the glass sheets were tested for average surface roughness and voltage after contact separation as follows.
  • the chuck and pins that were used were HEPA vacuumed and wiped down with DI cleanroom wipe 1 hour before testing.
  • One sample of Glass Type II was used to contact clean chuck and pins at the start of testing, side b then side a, using 6 reps per side.
  • FIGS. 2-6 The results of the tests are shown in FIGS. 2-6.
  • ten different results are shown: 2-1 shows Glass Type IV before treatment; 2-2 shows Glass Type I before treatment;
  • 2- 3 shows Glass Type I after treatment with a diluted mixture of NaF and H 3 PO 4 ; 2-4 shows Glass Type I after treatment with H 2 SO 4 ; 2-5 shows Glass Type I after treatment with HCl; 2- 6 shows Glass Type I after treatment with HCl and HF; 2-7 shows Glass Type II before treatment; 2-8 shows Glass Type II after treatment with a mixture of NaF and H 3 PO 4 ; 2-9 shows Glass Type III before treatment; and 2-10 shows Glass Type III after treatment with a mixture of NaF and H 3 P0 4 .
  • the graph in FIG. 2 plots glass type versus voltage measured after contact separation for 180 mm x 230 mm x 0.5 mm glass sheets, and shows that for each type of glass, the voltage approaches 0 with any type of treatment.
  • FIG. 3 shows voltage data from FIG. 2 as a percent reduction in voltage.
  • the percent reduction in voltage is calculated by the following equation:
  • V 0 is the average voltage measured after contact separation of the glass sheet before treatment and V is the average voltage measured after contact separation of the glass sheet after treatment.
  • FIG. 3 ten different results are shown: 3-1 shows Glass Type IV before treatment; 3-2 shows Glass Type I before treatment; 3-3 shows Glass Type I after treatment with a diluted mixture of NaF and H 3 PO 4 ; 3-4 shows Glass Type I after treatment with H 2 SO 4 ;
  • 3- 5 shows Glass Type I after treatment with HCl; 3-6 shows Glass Type I after treatment with HCl and HF; 3-7 shows Glass Type II before treatment; 3-8 shows Glass Type II after treatment with a mixture of NaF and H3PO4; 3-9 shows Glass Type III before treatment; and
  • 3- 10 shows Glass Type III after treatment with a mixture of NaF and H 3 PO 4 .
  • the graph in FIG. 3 shows that there is a reduction in voltage measured for each glass type after each treatment is conducted.
  • 4-1 shows Glass Type IV before treatment
  • 4- 2 shows Glass Type I before treatment
  • 4-3 shows Glass Type I after treatment with a diluted mixture of NaF and H 3 PO 4
  • 4-4 shows Glass Type I after treatment with H 2 SO 4
  • 4-5 shows Glass Type I after treatment with HCl
  • 4-6 shows Glass Type I after treatment with HCl and HF
  • 4-7 shows Glass Type II before treatment
  • 4-8 shows Glass Type II after treatment with a mixture of NaF and H 3 P0 4
  • 4-9 shows Glass Type III before treatment
  • FIG. 3 plots glass type versus voltage measured after contact separation for 127 mm x 127 mm x 0.5 mm glass sheets, and shows that for each type of glass, the voltage approached zero with any type of treatment.
  • FIG. 5 shows voltage data from FIG. 4 as a percent reduction in voltage. The percent reduction in voltage is calculated using equation (3).
  • 5-1 shows Glass Type IV before treatment
  • 5-2 shows Glass Type I before treatment
  • 5- 3 shows Glass Type I after treatment with a diluted mixture of NaF and H 3 P0 4 ;
  • 5-4 shows Glass Type I after treatment with H 2 SO 4 ;
  • 5-5 shows Glass Type I after treatment with HCl;
  • 5- 6 shows Glass Type I after treatment with HCl and HF; 5-7 shows Glass Type II before treatment; 5-8 shows Glass Type II after treatment with a mixture of NaF and H 3 P0 4 ; 5-9 shows Glass Type III before treatment; and 5-10 shows Glass Type III after treatment with a mixture of NaF and H 3 PO 4 .
  • the graph in FIG. 5 shows that there is a reduction in voltage measured for each glass type after each treatment is conducted.
  • 6-1 shows Glass Type IV before treatment
  • 6- 2 shows Glass Type I before treatment
  • 6-3 shows Glass Type I after treatment with a diluted mixture of NaF and H 3 P0 4
  • 6-4 shows Glass Type I after treatment with H 2 S0 4
  • 6-5 shows Glass Type I after treatment with HCl
  • 6-6 shows Glass Type I after treatment with HCl and HF
  • 6-7 shows Glass Type II before treatment
  • 6-8 shows Glass Type II after treatment with a mixture of NaF and H 3 P0
  • 6-9 shows Glass Type III before treatment
  • 6-10 shows Glass Type III after treatment with a mixture of NaF and H 3 P0 4 .
  • the graph in FIG. 6 plots glass type versus average surface roughness, and shows that, for each type of glass, the treatment process produced an increase in the average surface roughness.
  • FIGS. 2-6 show that each type of treatment conducted in this example provides increases in average surface roughness and causes the voltage to approach zero. However, FIGS. 2-6 also show that various treatments work particularly well with various types of glass.
  • FIG. 7 shows a graph of the average surface roughness versus voltage measured after contact separation for 180 mm x 230 mm x 0.5 mm glass sheets.
  • the circle in FIG. 7 indicates Glass Type I before treatment
  • the square in FIG. 7 shows Glass Type I after treatment with a diluted a mixture of NaF and H 3 P0 4
  • the diamond in FIG. 7 shows Glass Type I after treatment with H 2 S04
  • the triangle in FIG. 7 indicates Glass Type I after treatment with HCl
  • the arrow in FIG. 7 indicates Glass Type I after treatment with HCL and HF.
  • FIG. 8 shows a graph of the average surface roughness versus voltage after contact separation for 127 mm x 127 mm x 0.5 mm glass sheets.
  • the circle in FIG. 8 indicates Glass Type I before treatment
  • the square in FIG. 8 shows Glass Type I after treatment with a diluted a mixture of NaF and H 3 PO 4
  • the diamond in FIG. 8 shows Glass Type I after treatment with H 2 S04
  • the triangle in FIG. 8 indicates Glass Type I after treatment with HCl
  • the arrow in FIG. 8 indicates Glass Type I after treatment with HCl and HF.
  • the line in FIG. 8 shows a linear regression analysis for the plot.
  • Example 3 tests were conducted on Glass Type II and Glass Type III using the methods discussed in the examples above.
  • a commercially available lift tester having a modified chuck to support the size of the glass sheet was used on 730 mm x 920 mm x 0.5 mm glass sheets using a grounded 304 SS chuck.
  • a -39 kPa vacuum was created and insulative Vespel pins (5 mm R) were used.
  • the lift pin speed was 10 mm/sec and the apparatus had 20 vacuum ports.
  • Three samples per glass type were sampled and run in random order. Six lift cycles per sample were conducted with ionization used between lift cycles. Values were reported at 80 mm pin height Probe tracks with glass during lift pin movement.
  • the Samples were cleaned using a standard wash process with 4% SemiClean KG, and conditioned in cleanroom for 1 hour prior to test execution at a relative humidity of about 12%.
  • the chuck and pins were HEPA vacuumed and wiped down with DI cleanroom wipe 1 hour before testing.
  • One Glass Type II sample was used to contact clean chuck and pins at start of testing, side b then side a; 6 reps per side.
  • FIG. 9 shows the results of the tests.
  • 9-1 indicates Glass Type II before treatment
  • 9-2 indicates Glass Type II after treatment with a mixture of NaF and H 3 PO 4
  • 9-3 indicates Glass Type III before treatment
  • 9-4 indicates Glass Type III after treatment with a mixture of NaF and H 3 PO 4
  • FIG. 9 shows voltage measured after contact separation versus glass type and indicates that that the voltage increased (i.e., approaches 0) with treatment.
  • FIG. 10 shows voltage data from FIG. 9 as a percent reduction in voltage.
  • the percent reduction in voltage is calculated using equation (3).
  • 10-1 indicates Glass Type II before treatment
  • 10-2 indicates Glass Type II after treatment with a mixture of NaF and H 3 PO 4
  • 10-3 indicates Glass Type III before treatment
  • 10-4 indicates Glass Type III after treatment with a mixture of NaF and H 3 PO 4 .
  • the graph in FIG. 10 shows that there is a reduction in voltage measured for each glass type after each treatment is conducted.
  • Example 4 tests were conducted on Glass Type IV, Glass Type II, and Glass Type V, using methods discussed in the examples above.
  • a commercially available lift tester having a modified chuck to support the size of the glass sheet was used on 730 mm x 920 mm x 0.5 mm glass sheets.
  • the chuck was grounded 304 SS.
  • a vacuum of -39 kPa vacuum was created, and insulative Vespel pins (5 mm R) were used.
  • the lift pin speed was 10 mm/sec, and the apparatus had 20 vacuum ports.
  • Three samples per glass type were tested and run in random order. Three lift cycles per sample were conducted with ionization used between lift cycles. Values were reported at 80 mm pin height.
  • FIG. 11-1 indicates Glass Type IV before treatment
  • 11-2 indicates Glass Type II before treatment
  • 11-3 indicates Glass Type II after treatment with a mixture of NaF and H 3 PO 4
  • 11-4 indicates Glass
  • FIG. 11 shows voltage measured after contact separation versus glass type and indicates that that the voltage increased (i.e., approaches 0) with treatment.
  • FIG. 12 shows voltage data from FIG. 11 as a percent reduction in voltage.
  • the percent reduction in voltage is calculated using equation (3).
  • 12-1 indicates Glass Type II before treatment
  • 12-2 indicates Glass Type II after treatment with a mixture of NaF and H 3 PO 4
  • 12-3 indicates Glass Type III before treatment
  • 12-4 indicates Glass Type III after treatment with a mixture of NaF and H 3 PO 4 .
  • the graph in FIG. 12 shows that there is a reduction in voltage measured for each glass type after each treatment is conducted.

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Abstract

A method for improving the electrostatic discharge properties of a glass sheet including treating at least one side of the glass sheet with a treatment solution that increases an average surface roughness, and removing the treatment solution. An average surface roughness of the at least one treated side of the glass sheet may be from about 0.3 nm to about 100 nm. A percent reduction in voltage between the glass sheet before the treatment and the glass sheet after the treatment may be from about 1.5% to about 40%. A glass sheet having a first side with an average surface roughness of from about 0.3 nm to about 100 nm, and a second side with an average surface roughness of from about 0.1 nm to about 100 nm. The glass sheet may have a length of at least about 100 mm, and a thickness of less than about 1.0 mm.

Description

SURFACE TREATMENTS FOR LOW ELECTROSTATIC DISCHARGE
FUSION DRAWN GLASS
PRIORITY
[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S.
Provisional Application Serial No. 61/817518 filed on 4/30/2013, the content of which is relied upon and incorporated herein by reference in its entirety.
BACKGROUND FIELD
[0001] The present specification generally relates to surface treatments for glass surfaces and, more specifically, to methods of strategically texturing the b-side of glass sheets without compromising the performance attributes of the a-side of the glass sheet.
Technical Background
[0002] Flat panel display (FPD) glass, which may be used for thin film transistor (TFT) - liquid crystal display (LCD) substrates, may consist of two sides. The first side may be a functional side upon which TFTs are built (a-side), and the second side may be a nonfunctional backside (b-side). Previously, focus has been on the a-side of the FPD glass because formation of TFT structures may be sensitive to surface inconsistencies when deposited over large areas. The b-side of the FPD glass may contact a variety of materials, such as, for example, plastics, rubbers, or ceramics and, as such, the surface quality and uniformity of the b-side surface need not be as high as the a-side surface. However, during processing, contact between the FPD glass and these various other materials may cause triboelectrification. For example, two dissimilar materials are charged from contact separation due to their differences in intrinsic work function values or the ability to transfer charge based on their Fermi energy levels. The more charge that is accumulated at a surface, the higher the surface voltage. Moreover, when two charged surfaces separate, the capacitance decreases as the separation distance increases, which may result in even higher surface voltages. Glass contact separation is unavoidable in TFT-LCD manufacturing. These high voltages may damage the TFT structures deposited on the a-side surface of the FPD glass.
[0003] Accordingly, a need exists for lowering the total charge accumulation at the glass surface. SUMMARY
[0004] According to one embodiment, a method is disclosed for improving the electrostatic discharge properties of a glass sheet including treating at least one side of the glass sheet with a treatment solution that increases an average surface roughness, and removing the treatment solution. An average surface roughness of the at least one treated side of the glass sheet may be from about 0.3 nm to about 100 nm. A percent reduction in voltage between the glass sheet before the treatment and the glass sheet after the treatment may be from about 1.5% to about 40%.
[0005] In other embodiments, a glass sheet having a first side with an average surface roughness of from about 0.3 nm to about 100 nm, and a second side with an average surface roughness of from about 0.1 nm to about 100 nm is provided. The glass sheet may have a length of at least about 100 mm, and a thickness of less than about 1.0 mm.
[0006] In other embodiments, a glass sheet may include a side having a surface roughness of about 0.2 nm, or even about 0.15 nm for a 2 x 2 μιη atomic- force microscope (AFM) scan, and another side having a surface roughness of from about 0.3 nm to about 1.3 nm. According to embodiments, 0.2 nm may be defined as Ra or Rq as determined by AFM measurement. Ra and Rq may be represented by equations (1) and (2):
Figure imgf000004_0001
where n is number of points at which measurement occurs, z is height at each point and zbar is average of height collected at each point in the line scan. Ra is often designated as "average" surface roughness, while Rq is often called the "root-mean-square" (RMS) surface roughness. The a length of the glass sheet may be greater than about 100 mm, and a thickness of the glass sheet may be less than about 1 mm
[0007] Additional features and advantages of the disclosure will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.
[0008] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic showing an embodiment of a fusion draw method;
[0010] FIG. 2 is a graph of voltages measured after contact separation plotted against glass type and treatment process for a glass sheet having dimensions of 180 mm x 230 mm x 0.5 mm, according to embodiments;
[0011] FIG. 3 is a graph showing percent reduction in voltage for the data shown in FIG. 2;
[0012] FIG. 4 is a graph of voltages measured after contact separation plotted against glass type and treatment process for a glass sheet having dimensions of 127 mm x 127 mm x 0.5 mm, according to embodiments;
[0013] FIG. 5 is a graph showing percent reduction in voltage for the data shown in FIG. 4;
[0014] FIG. 6 is a graph average surface roughness according to embodiments plotted against glass type and treatment process;
[0015] FIG. 7 is a graph of voltages measured after contact separation plotted against average surface roughness for a glass sheet having dimensions of 180 mm x 230 mm x 0.5 mm, according to embodiments;
[0016] FIG. 8 is a graph of voltages measured after contact separation plotted against average surface roughness for a glass sheet having dimensions of 127 mm x 127 mm x 0.5 mm, according to embodiments; [0017] FIG. 9 is a graph of voltages measured after contact separation plotted against glass type and treatment process for a glass sheet having dimensions of 730 mm x 920 mm x 0.5 mm, according to embodiments;
[0018] FIG. 10 is a graph showing percent reduction in voltage for the data shown in FIG. 9;
[0019] FIG. 11 is a graph of voltages measured after contact separation plotted against glass type and treatment process for a glass sheet having dimensions of 730 mm x 920 mm x 0.5 mm, according to embodiments; and
[0020] FIG. 12 is a graph showing percent reduction in voltage for the data shown in FIG. 11.
DETAILED DESCRIPTION
[0021] Glass sheets treated in accordance with the methods disclosed herein may be formed by any suitable method. In embodiments, the glass sheets may be formed by a fusion draw process. The fusion draw process is a down draw process, also referred to as the overflow process. In the fusion draw process, a glass-forming melt flows into a refractory trough and then overflows in a controlled manner from either side of the trough. An advantage of this process is that the surface of the sheet glass formed therefrom does not come in contact with any refractory material or other forming equipment. In addition, the fusion draw process yields a very flat and uniformly thick sheet of glass. As a result, no secondary processing is needed to obtain a smooth, flat, and uniform sheet of glass for display applications. The fusion draw process requires that glasses used in the process have a relatively high viscosity at the liquidus temperature. The fusion draw process is further described below with reference to FIG. 1. Similar fusion draw processes are described in U.S. Pat. Nos. 3,338,696 and 3,682,609, which are incorporated herein by reference in their entirety.
[0022] Referring to FIG. 1 by way of example, an exemplary glass manufacturing apparatus 100 for forming glass sheet material from molten glass is schematically depicted in which a fusion draw machine is used to form the molten glass into glass sheets. The glass manufacturing apparatus 100 includes a melting vessel 101, a fining vessel 103, a mixing vessel 104, a delivery vessel 108, and a fusion draw machine (FDM) 120. Glass batch materials are introduced into the melting vessel 101 as indicated by arrow 102. The batch materials are melted to form molten glass 106. The fining vessel 103 has a high temperature processing area that receives the molten glass 106 from the melting vessel 101 and in which bubbles are removed from the molten glass 106. The fining vessel 103 is fluidly coupled to the mixing vessel 104 by a connecting tube 105. That is, molten glass flowing from the fining vessel 103 to the mixing vessel 104 flows through the connecting tube 105. The mixing vessel 104 is, in turn, fluidly coupled to the delivery vessel 108 by a connecting tube 107 such that molten glass flowing from the mixing vessel 104 to the delivery vessel 108 flows through the connecting tube 107.
[0023] The delivery vessel 108 supplies the molten glass 106 through a downcomer 109 into the FDM 120. The FDM 120 comprises an enclosure 122 in which an inlet 110, a forming vessel 111 and at least one draw assembly 150 are positioned. As shown in FIG. 1, the molten glass 106 from the downcomer 109 flows into an inlet 110 which leads to the fonning vessel 111. The forming vessel 1 11 includes an opening 112 that receives the molten glass 106 which flows into a trough 113 and then overflows and runs down two converging sides 114a and 114b before fusing together at a root, where the two sides join, before being contacted and drawn in a downstream direction 151 by the draw assembly 150 to form a continuous glass sheet 148. Thereafter, the continuous glass sheet 148 may be segmented into discrete glass sheets.
[0024] While the surface treatment methods have been described herein as being used in conjunction with glass sheets formed by the fusion draw process, it should be understood that the surface treatment methods may be used on glass sheets formed from other processes in which glass batch materials are melted to form molten glass and the molten glass is then formed into a glass sheet. By way of example and not limitation, the pulling rolls described herein may also be utilized in conjunction with up-draw processes, slot-draw processes, and other, similar processes.
[0025] The dimensions of the glass sheets made by the fusion draw process are not particularly limited, and the treatment methods described herein may be applied to glass sheets having any dimensions. However, in some embodiments, the length of the glass sheet to be treated may be greater than about 100 mm, or even greater than about 200 mm. In some embodiments, the length of the glass to be treated may be greater than about 300 mm, or even greater than about 400 mm. In other embodiments, the length of the glass sheet may be greater than 500 mm or even greater than 600 mm. In further embodiments, the length of the glass sheet may be greater than 700 mm, or even greater than 800 mm. In still further embodiments, the length of the glass sheet may be greater than about 900 mm, or even about 1000 mm. Likewise, the width of the glass sheet to be treated may be greater than about 100 mm, or even greater than about 200 mm. In some embodiments, the width of the glass to be treated may be greater than about 250 mm, or even greater than about 300 mm. The thickness of the glass sheet to be treated is not particularly limited, and the method of treating a glass sheet disclosed herein may be used on thin glass sheets. In embodiments, the thickness of the glass sheet to be treated may be about 1.0 mm or less, or even about 0.7 mm or less. In some embodiments, the thickness of the glass sheet to be treated may be about 0.5 mm or less, or even about 0.4 mm or less. In other embodiments, the thickness of the glass sheet to be treated may be about 0.3 mm or less, or even 0.1 mm or less.
[0026] The composition of the glass sheet to be treated is not particularly limited, and the treatments disclosed herein may be applied to any glass composition. In some embodiments, the glass to be treated may be an alkali aluminosilicate glass, an alkali boroaluminosilicate glass, an alkaline-earth aluminosilicate glass, or an alkaline-earth boroaluminosilicate glass. As used herein, the term "alkali" refers to alkali metals (e.g., Li, Na, K, Rb and Cs) and "alkaline- earth" refers to alkaline-earth metals (e.g., Be, Mg, Ca, Sr and Ba), unless the context clearly indicates otherwise.
[0027] In some embodiments, the a-side of the glass sheet may generally have an average surface roughness of from about 0.1 nm to about 100 nm. For example, in some embodiments, the a-side surface may have an average surface roughness of from about 0.1 nm to about 100 nm, from about 0.16 nm to about 0.27 nm, from about 0.20 nm to about 0.27 nm, or even from about 0.22 nm to about 0.25 nm. In some embodiments, the average surface roughness of the a-side of the glass sheet may be such that it does not affect the visual properties of the glass sheet that are perceivable by the human eye.
[0028] As discussed briefly above, the glass sheet to be treated in accordance with this disclosure may comprise an a-side and a b-side. Because the b-side surface of the glass sheet may be subject to mechanical contact during manufacture and subsequent handling, the b-side surface quality requirements may not be as stringent as the a-side surface quality requirements, which allows for more flexibility in converting b-side texturing concepts into practice. The main concern with modifications to the b-side of a glass sheet is defects discernable with the human eye. For example, defects on the b-side that are greater than about 100 μιη may not be acceptable. In embodiments, defects on the b-side of the glass sheet that are greater than about 150 μιη may not be acceptable.
[0029] The glass sheets used in the methods described herein are initially obtained using forming processes as described herein above. When in as formed conditions (i.e., without any additional surface treatments or the like), the glass sheets may not have the thickness dimension required for the specified application. Panel thinning techniques may be used to achieve a desired thickness and/or thickness uniformity of the glass sheet. Panel thinning techniques may include chemical or mechanical methods for reducing the thickness of the glass substrate from the b-side without diminishing the quality of the a-side surface. Mechanical thinning may mitigate a wide range of b-side surface features, defects, and contaminants because of the process of planarization. Chemical thinning may open up features such as dents and dimples. The glass chemistry on the b-side surface does not particularly limit the use of thinning processes. Accordingly, thicknesses as discussed above may be achieved through the use of thinning processes, if necessary.
[0030] In accordance with some embodiments, after a glass sheet having suitable dimensions and composition for its intended use has been obtained, at least one side of the glass sheet may be texturized using a treatment solution comprising an acid, a base, a neutral solution, or mixtures thereof. Texturizing the glass sheet with the solutions disclosed in embodiments improve the electrostatic discharge (ESD) performance of the glass sheet. Exposure to the treatment solution may also alter the glass surface chemistry and modify the surface of the glass sheet within acceptable b-side tolerance limits.
[0031] According to some embodiments, the glass sheet may be washed with any suitable cleaner to remove particulate matter and other surface contaminants before or after the treatment with the treatment solution. In some embodiments, the cleaners may be SemiClean KG (manufactured by Yokohama- Yushi-Kogyo), or other, similar cleaners. In other embodiments, the cleaners may include other detergents, acids, bases, peroxides, or mixtures thereof. Detergents may combine surfactants, acid, bases, chelators and the like. In some other embodiments, cleaning agents may be much simpler in nature, such as, for example, single bases, or bases with peroxides, single acids, or single acids with peroxides. The duration and method of cleaning the glass sheet is not particularly limited and may be any suitable method, such as spraying, dipping, or a washing process used in the manufacture of glass sheets.
[0032] The glass sheet may be treated with a treatment solution to modify the ESD performance of the glass sheet. In some embodiments, the treatment solution may be hydrochloric acid (HC1). The molarity of the HC1 may be from about 0.15 M to about 0.35 M, or even from about 0.2 M to about 0.3 M. In other embodiments, the molarity of the HC1 may be about 0.25 M. In some embodiments, the treatment solution may be a mixture of sulfuric acid (H2SO4) and water. In some embodiments, the sulfuric acid:water mixture may be a 1 :4 mixture, or even a 1 :3 mixture. In other embodiments, the mixture of sulfuric acid and water may be a 1 :2 mixture. In some embodiments, the treatment solution may be a dilute mixture of sodium fluoride (NaF) and phosphoric acid (H3PO4). An exemplary mixture of NaF and H3PO4 may be a mixture of 0.2 M NaF and 1M H3PO4, which may be diluted in water in a 4:5 mixture. In yet other embodiments, the treatment solution may be a mixture of HC1 and hydrofluoric acid (HF). In these embodiments, the molarity of the HC1 may be from about 0.15 M to about 0.35 M, or even from about 0.2 M to about 0.3 M. HF may be added to the HC1 in concentrations from about 1 x 10 3 M (M= moles/liter) to about 1M, or even from about 2 x 10~3 M to about 1 x 10"4 M. In some embodiments 2.5 x 10"3 M of HF may be added to HC1. Other suitable acids include HN03, ammonium bifluoride, ammonium fluoride, HF:NH4F, HF:NH4HF mixtures, or others. It should be understood that other formulations of the treatment solution may be possible.
[0033] The glass sheet may be exposed to the treatment solution by any known method, such as, for example, dip coating, roller coating, or spray coating. In embodiments where the glass sheet is dip coated in the treatment solution, a mask may be placed over the a-side of the glass sheet to prevent texturization of the a-side of the glass sheet. The mask material is not particularly limited, and may include any material that is capable of adhering to the glass sheet and protecting the glass sheet from the effects of the treatment solution. The mask material should also be easily removed from the glass sheet after the treatment process is complete. Exemplary masks include protective films (Visqueen or Kapton), which if they leave residue behind may be washed off in a subsequent cleaning process. Other suitable mask materials include photoresist, waxes, or other removable coatings. [0034] The duration of the treatment is not particularly limited, and the treatment should be conducted for the amount of time necessary to achieve the desired texturization. In some embodiments, the duration of the treatment may be from about 0.5 min to about 90 min, or even from about 1 min to about 60 min, or from about 5 min to about 30 min. In some embodiments, the duration of the treatment may be from about 10 min to about 20 min. In other embodiments, treatment times may be be less than 0.5 min, or even less than 0.25 min. In yet other embodiments, the treatment time may be less than 0.1 min.
[0035] The temperature at which the treatment is conducted may vary depending on the composition of the glass sheet and the composition of the treatment solution. In some embodiments, the temperature at which the treatment is conducted may be from about 20°C to about 100°C, or even from about 40°C to about 90°C. In other embodiments, the temperature at which the treatment is conducted may be from about 40°C to about 80°C, or even from about 50°C to about 70°C.
[0036] In some embodiments, after the treatment has concluded, the treatment solution may be removed from the glass sheet by any suitable method. For example, in some embodiments, the treatment solution may be removed by washing the treated glass sheet, as discussed above. In other embodiments, the treatment solution may be removed by heating, evaporation, or any other suitable means. In yet other embodiments, the treatment solution may be physically removed by, for example, forced air, a roller, a blade, or the like. It should be appreciated that the treatment solution may be removed by any method or apparatus without deviating from the scope of this disclosure.
[0037] The average surface roughness of the glass sheet may be measured before and after the treatment process. The average surface roughness may be measured using an atomic force microscope (AFM). Roughness is measured using standard values of Ra or Rq as defined above. In some embodiments, the average surface roughness of the glass sheet before the treatment process is from about 0.1 nm to about 100 nm, from about 0.1 nm to about 0.3 nm, or even from about 0.15 nm to about 0.25 nm. In some embodiments, the average surface roughness before the treatment process is from about 0.2 nm to about 0.23 nm. In some embodiments, the average surface roughness may be increased by the treatment process. Accordingly the average surface roughness may be measured after the treatment process to determine the increase in the average surface roughness as a result of the treatment process. In some embodiments, the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.3 nm to about 100 nm, or even from about 0.3 to about 75 nm In other embodiments, the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.3 nm to about 50 nm, or even from about 0.3 nm to about 25 nm. In yet other embodiments, the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.3 nm to about 15 nm, or even from about 0.4 nm to about 10 nm. In still other embodiments, the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.4 nm to about 5 nm, or even from about 0.5 nm to about 1.3 nm. In still other embodiments, the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.5 nm to about 1.15 nm In other embodiments, the average surface roughness of the glass sheet after being exposed to the treatment process may be from about 0.5 nm to about 1.0 nm, or even from about 0.7 nm to about 0.9 nm. The increase in the average surface roughness caused by the treatment process may be affected by any number of conditions including, but not limited to, the composition of the glass sheet, the composition of the treatment solution, the duration of the treatment process, and/or the temperature of the treatment process. It should be understood that each of the above parameters may be modified in the treatment process to obtain a desired increase in the average surface roughness after the treatment process.
[0038] In accordance with some embodiments, a correlation may be drawn between the average surface roughness of the glass sheet and electrostatic discharge (ESD) properties. Particularly, as the average surface roughness of the glass sheet increases, the ESD properties of the device may improve. The ESD properties of the glass sheet may be determined by measuring the voltage on a treated side of the glass sheet. As discussed above, one side surface of the glass sheet may accumulate charge which negatively impacts the ESD properties of the glass sheet. The voltage across the sheet is a measure of the accumulated charge. Thus, as the voltage on a treated side the glass sheet approaches zero, the ESD properties of the glass sheet generally improve. Without being bound by any particular theory, it is generally thought that by increasing the average surface roughness of a treated side of the glass sheet, there will be less contact between a treated side of the glass sheet and the components made of different materials. Thus, triboelectrification may be reduced or minimized by increasing the roughness of a treated side of the glass sheet. The final composition of the glass surface imparted by the treatment of embodiments described herein may also play a role in the tribo electrification mechanism.
[0039] According to some embodiments, and as shown in the examples below, the measured voltage of a glass sheet after contact separation may vary depending, for example, on the composition of the glass sheet, the size of the glass sheet, the composition of the treatment solution, and combinations thereof. However, according to embodiments, a reduction in voltage is realized as surface roughness of one side of the glass sheet is increased. This reduction in voltage may be calculated as a percentage by measuring the voltage after contact separation before treatment and measuring the voltage after contact separation after treatment. In some embodiments, the percentage of reduction of voltage may be from about 1.5% to about 40%), or even from about 2.0% to about 35%. In other embodiments, the percentage of reduction of voltage after contact separation may be from about 3.0% to about 30%, or even from about 4.0%> to about 25%). In yet other embodiments, the percentage of reduction of voltage after contact separation may be from about 5.0%) to about 20%, or even from about 7.0%) to about 15%). In some other embodiments, the percentage of reduction of voltage after contact separation may be about 12%, or even about 10%.
[0040] Although, in embodiments, the increases in both a treated side roughness and glass sheet voltage may vary depending on the composition of the glass, the size of the glass, the composition of the treatment solution, the duration of the treatment process, and the temperature at which the treatment process is operated, increases in the average surface roughness may be achieved for each glass composition using each treatment solution discussed herein. Thereby, the ESD properties of the glass sheet may be improved.
Examples
[0041] The disclosure will be further clarified by the following examples.
EXAMPLE 1
[0042] Glass Type I, an alumino silicate glass manufactured by Corning Incorporated, was stripped of its protective Visqueen film and washed with 4% SemiClean KG (manufactured by Yokohama- Yushi-Kogyo) wash using a standard washing process. The glass was then dipped in various acids at various lengths of time and temperature as listed in Table 1 below, where each glass sheet had a thickness of 0.5 mm.
[0043] Table 1
Figure imgf000014_0001
[0044] The 127 mm x 127 mm x 0.5 mm glass sheets were tested on a commercially available lift tester manufactured by the Harada Corporation, and the 180 mm x 230 mm x 0.5 mm glass sheets were tested on a similar lift tester that was modified to support glass sheets of this size. After exposure to the acid identified in Table 1, the surfaces were again washed with 4% SemiClean KG using a washing process. The voltage after contact separation was measured at 12% relative humidity in a class 100 clean room. The results are obtained by conducting 3 lifts per sample, 3 samples per glass type. The same trend was measure irrespective of the test apparatus used. Surface composition (XPS) and average surface roughness were determined on the tested glass sheets. It was determined that a linear function existed between measured voltage after contact separation and average surface roughness. On average, the measured voltage after contact separation differed between glass types. The difference between voltages measured after contact separation was larger when the size of the glass sheet was larger. This is believed to result from multiple vacuum port use on the larger glass sheets. Initial contact at a vacuum port causes tribo electrification for both 180 mm x 230 mm x 0.5 mm and 730 mm x 920 mm x 0.5 mm glass sheets. 730 mm x 920 mm x 0.5 mm sheets were also tugged back and forth in the horizontal direction between vacuum ports causing further triboelectrification and magnification of the voltage signal resulting in larger differences between glass types.
EXAMPLE 2
[0045] Referring now to FIGS. 2-6, four glass types were treated using a treatment process as described herein. Four differing glass compositions were tested; Glass Type I, as mentioned above, Glass Type II, Glass Type III, and Glass Type IV. The four glass types have similar compositions and, generally, fall within the category of aluminosilicate glasses. Various treatment solutions were used, and the treated glass sheets were prepared as shown in Table 1, but using the four different glass compositions, as mentioned above. After the treatment process was completed, the glass sheets were tested for average surface roughness and voltage after contact separation as follows.
[0046] 180 mm x 230 mm x 0.5 mm glass sheets were tested by a lift tester with a grounded 304 SS chuck. A vacuum of -39 kPa was created and insulative Vespel pins (5 mm R) were used. The testing also used 10 mm/sec lift pin speed and a single vacuum port. Three samples were conducted per glass type and run in random order. Three lift cycles were conducted per sample. Ionization was used between lift cycles, and values were reported at 80 mm pin height. Probe tracks were used with the glass during lift pin movement.
[0047] 127 mm x 127 mm x 0.5 mm glass sheets were tested by a lift tester commercially available from Harada Corporation and using an insulative black anodized Al chuck. A vacuum of -90 kPa vacuum was created, and insulative POM pins (2.5 mm R) were used. The testing also used 27 mm/sec lift pin speed and double channel vacuum port feed by single supply. Three samples per glass type were tested and run in a random order. Three lift cycles were conducted per sample with ionization used between lift cycles. Values were reported at 29 mm pin height. The probe did not track with glass during lift pin movement.
[0048] Samples were cleaned in a washing process with 4% SemiClean KG and were conditioned in a cleanroom for 1 hour prior to test execution at a relative humidity of about
12%. The chuck and pins that were used were HEPA vacuumed and wiped down with DI cleanroom wipe 1 hour before testing. One sample of Glass Type II was used to contact clean chuck and pins at the start of testing, side b then side a, using 6 reps per side.
[0049] The results of the tests are shown in FIGS. 2-6. In FIG. 2, ten different results are shown: 2-1 shows Glass Type IV before treatment; 2-2 shows Glass Type I before treatment;
2- 3 shows Glass Type I after treatment with a diluted mixture of NaF and H3PO4; 2-4 shows Glass Type I after treatment with H2SO4; 2-5 shows Glass Type I after treatment with HCl; 2- 6 shows Glass Type I after treatment with HCl and HF; 2-7 shows Glass Type II before treatment; 2-8 shows Glass Type II after treatment with a mixture of NaF and H3PO4; 2-9 shows Glass Type III before treatment; and 2-10 shows Glass Type III after treatment with a mixture of NaF and H3P04. The graph in FIG. 2 plots glass type versus voltage measured after contact separation for 180 mm x 230 mm x 0.5 mm glass sheets, and shows that for each type of glass, the voltage approaches 0 with any type of treatment.
[0050] FIG. 3 shows voltage data from FIG. 2 as a percent reduction in voltage. The percent reduction in voltage is calculated by the following equation:
[(Vo - V)/Vo] x l 00 (3)
Where V0 is the average voltage measured after contact separation of the glass sheet before treatment and V is the average voltage measured after contact separation of the glass sheet after treatment. In FIG. 3, ten different results are shown: 3-1 shows Glass Type IV before treatment; 3-2 shows Glass Type I before treatment; 3-3 shows Glass Type I after treatment with a diluted mixture of NaF and H3PO4; 3-4 shows Glass Type I after treatment with H2SO4;
3- 5 shows Glass Type I after treatment with HCl; 3-6 shows Glass Type I after treatment with HCl and HF; 3-7 shows Glass Type II before treatment; 3-8 shows Glass Type II after treatment with a mixture of NaF and H3PO4; 3-9 shows Glass Type III before treatment; and
3- 10 shows Glass Type III after treatment with a mixture of NaF and H3PO4. The graph in FIG. 3 shows that there is a reduction in voltage measured for each glass type after each treatment is conducted.
[0051] In FIG. 4, ten different results are shown: 4-1 shows Glass Type IV before treatment;
4- 2 shows Glass Type I before treatment; 4-3 shows Glass Type I after treatment with a diluted mixture of NaF and H3PO4; 4-4 shows Glass Type I after treatment with H2SO4; 4-5 shows Glass Type I after treatment with HCl; 4-6 shows Glass Type I after treatment with HCl and HF; 4-7 shows Glass Type II before treatment; 4-8 shows Glass Type II after treatment with a mixture of NaF and H3P04; 4-9 shows Glass Type III before treatment; and
4- 10 shows Glass Type III after treatment with a mixture of NaF and H3PO4. The graph in FIG. 3 plots glass type versus voltage measured after contact separation for 127 mm x 127 mm x 0.5 mm glass sheets, and shows that for each type of glass, the voltage approached zero with any type of treatment.
[0052] FIG. 5 shows voltage data from FIG. 4 as a percent reduction in voltage. The percent reduction in voltage is calculated using equation (3). In FIG. 5, ten different results are shown: 5-1 shows Glass Type IV before treatment; 5-2 shows Glass Type I before treatment;
5- 3 shows Glass Type I after treatment with a diluted mixture of NaF and H3P04; 5-4 shows Glass Type I after treatment with H2SO4; 5-5 shows Glass Type I after treatment with HCl;
5- 6 shows Glass Type I after treatment with HCl and HF; 5-7 shows Glass Type II before treatment; 5-8 shows Glass Type II after treatment with a mixture of NaF and H3P04; 5-9 shows Glass Type III before treatment; and 5-10 shows Glass Type III after treatment with a mixture of NaF and H3PO4. The graph in FIG. 5 shows that there is a reduction in voltage measured for each glass type after each treatment is conducted.
[0053] In FIG. 6, ten different results are shown: 6-1 shows Glass Type IV before treatment;
6- 2 shows Glass Type I before treatment; 6-3 shows Glass Type I after treatment with a diluted mixture of NaF and H3P04; 6-4 shows Glass Type I after treatment with H2S04; 6-5 shows Glass Type I after treatment with HCl; 6-6 shows Glass Type I after treatment with HCl and HF; 6-7 shows Glass Type II before treatment; 6-8 shows Glass Type II after treatment with a mixture of NaF and H3P0 ; 6-9 shows Glass Type III before treatment; and 6-10 shows Glass Type III after treatment with a mixture of NaF and H3P04. The graph in FIG. 6 plots glass type versus average surface roughness, and shows that, for each type of glass, the treatment process produced an increase in the average surface roughness.
[0054] FIGS. 2-6 show that each type of treatment conducted in this example provides increases in average surface roughness and causes the voltage to approach zero. However, FIGS. 2-6 also show that various treatments work particularly well with various types of glass.
[0055] Referring now to FIG. 7, this graph provides a comparison of the average surface roughnesses and voltages measured after contact separation for Glass Type I as shown in FIGS. 2 and 6. Specifically, FIG. 7 shows a graph of the average surface roughness versus voltage measured after contact separation for 180 mm x 230 mm x 0.5 mm glass sheets. The circle in FIG. 7 indicates Glass Type I before treatment, the square in FIG. 7 shows Glass Type I after treatment with a diluted a mixture of NaF and H3P04, the diamond in FIG. 7 shows Glass Type I after treatment with H2S04, the triangle in FIG. 7 indicates Glass Type I after treatment with HCl, and the arrow in FIG. 7 indicates Glass Type I after treatment with HCL and HF. As can be seen from FIG. 7, as the average surface roughness increases, voltage measured after contact separation increases (i.e., approaches 0), thereby verifying a correlation between the average surface roughness and voltage. The line in FIG. 7 shows a linear regression analysis for the plot.
[0056] Referring now to FIG. 8, this graph provides a comparison of the average surface roughness and voltage measured after contact separation for Glass Type I shown in FIGS. 4 and 6. FIG. 8 shows a graph of the average surface roughness versus voltage after contact separation for 127 mm x 127 mm x 0.5 mm glass sheets. The circle in FIG. 8 indicates Glass Type I before treatment, the square in FIG. 8 shows Glass Type I after treatment with a diluted a mixture of NaF and H3PO4, the diamond in FIG. 8 shows Glass Type I after treatment with H2S04, the triangle in FIG. 8 indicates Glass Type I after treatment with HCl, and the arrow in FIG. 8 indicates Glass Type I after treatment with HCl and HF. As can be seen from FIG. 8, as the average surface roughness increases, voltage measured after contact separation increases (i.e., approaches 0), thereby verifying a correlation between the average surface roughness and voltage. The line in FIG. 8 shows a linear regression analysis for the plot.
EXAMPLE 3
[0057] In Example 3 tests were conducted on Glass Type II and Glass Type III using the methods discussed in the examples above. A commercially available lift tester having a modified chuck to support the size of the glass sheet was used on 730 mm x 920 mm x 0.5 mm glass sheets using a grounded 304 SS chuck. A -39 kPa vacuum was created and insulative Vespel pins (5 mm R) were used. The lift pin speed was 10 mm/sec and the apparatus had 20 vacuum ports. Three samples per glass type were sampled and run in random order. Six lift cycles per sample were conducted with ionization used between lift cycles. Values were reported at 80 mm pin height Probe tracks with glass during lift pin movement. The Samples were cleaned using a standard wash process with 4% SemiClean KG, and conditioned in cleanroom for 1 hour prior to test execution at a relative humidity of about 12%. The chuck and pins were HEPA vacuumed and wiped down with DI cleanroom wipe 1 hour before testing. One Glass Type II sample was used to contact clean chuck and pins at start of testing, side b then side a; 6 reps per side.
[0058] Referring now to FIG. 9, this figure shows the results of the tests. In FIG. 9, 9-1 indicates Glass Type II before treatment, 9-2 indicates Glass Type II after treatment with a mixture of NaF and H3PO4, 9-3 indicates Glass Type III before treatment, and 9-4 indicates Glass Type III after treatment with a mixture of NaF and H3PO4. FIG. 9 shows voltage measured after contact separation versus glass type and indicates that that the voltage increased (i.e., approaches 0) with treatment.
[0059] FIG. 10 shows voltage data from FIG. 9 as a percent reduction in voltage. The percent reduction in voltage is calculated using equation (3). In FIG. 10, 10-1 indicates Glass Type II before treatment, 10-2 indicates Glass Type II after treatment with a mixture of NaF and H3PO4, 10-3 indicates Glass Type III before treatment, and 10-4 indicates Glass Type III after treatment with a mixture of NaF and H3PO4. The graph in FIG. 10 shows that there is a reduction in voltage measured for each glass type after each treatment is conducted.
EXAMPLE 4
[0060] In Example 4 tests were conducted on Glass Type IV, Glass Type II, and Glass Type V, using methods discussed in the examples above. A commercially available lift tester having a modified chuck to support the size of the glass sheet was used on 730 mm x 920 mm x 0.5 mm glass sheets. The chuck was grounded 304 SS. A vacuum of -39 kPa vacuum was created, and insulative Vespel pins (5 mm R) were used. The lift pin speed was 10 mm/sec, and the apparatus had 20 vacuum ports. Three samples per glass type were tested and run in random order. Three lift cycles per sample were conducted with ionization used between lift cycles. Values were reported at 80 mm pin height.
[0061] Referring now to FIG. 11, this figure shows the results of the test. In FIG. 11, 11-1 indicates Glass Type IV before treatment, 11-2 indicates Glass Type II before treatment, 11-3 indicates Glass Type II after treatment with a mixture of NaF and H3PO4, 11-4 indicates Glass
Type V before treatment, and 11-5 indicates Glass Type V after treatment with a mixture of NaF and H3P04. FIG. 11 shows voltage measured after contact separation versus glass type and indicates that that the voltage increased (i.e., approaches 0) with treatment.
[0062] FIG. 12 shows voltage data from FIG. 11 as a percent reduction in voltage. The percent reduction in voltage is calculated using equation (3). In FIG. 12, 12-1 indicates Glass Type II before treatment, 12-2 indicates Glass Type II after treatment with a mixture of NaF and H3PO4, 12-3 indicates Glass Type III before treatment, and 12-4 indicates Glass Type III after treatment with a mixture of NaF and H3PO4. The graph in FIG. 12 shows that there is a reduction in voltage measured for each glass type after each treatment is conducted.
[0063] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:
1. A method for improving the electrostatic discharge properties of a glass sheet comprising: treating at least one side of the glass sheet with a treatment solution that increases an average surface roughness of the at least one side of the glass sheet; and
removing the treatment solution, wherein
an average surface roughness of the at least one treated side of the glass sheet is from about 0.3 nm to about 100 nm after the treatment, and
a percent reduction in voltage between the glass sheet before the treatment and the glass sheet after the treatment, measured after contact separation, is from about 1.5% to about 40%.
2. The method of claim 1, wherein the glass sheet comprises alkali alumino silicate, alkali boroaluminosilicate, alkaline-earth alumino silicate, alkaline-earth boroaluminosilicate, or combinations thereof.
3. The method of claim 1, wherein a length of the glass sheet is greater than about 100 mm
4. The method of claim 1, wherein a thickness of the glass sheet is less than about 1.0 mm.
5. The method of claim 1, wherein the average surface roughness of the at least one treated side of the glass sheet is from about 0.4 nm to about 10 nm
6. The method of claim 1, wherein the average surface roughness of the at least one treated side of the glass sheet is from about 0.5 nm to about 1.3 nm.
7. The method of claim 1, wherein the percent reduction in voltage between the glass sheet before the treatment and the glass sheet after the treatment, measured after contact separation, is from about 2.0 % to about 35%>.
8. The method of claim 1, wherein the percent reduction in voltage between the glass sheet before the treatment and the glass sheet after the treatment, measured after contact separation, is from about 3.0% to about 30%.
9. The method of claim 1, wherein a duration of the treating step is from about 0.5 min to about 90 min.
10. The method of claim 1 , wherein a temperature during the treating step is from about 20°C to about 100°C.
11. The method of claim 1, wherein the treatment solution comprises at least one selected from the group consisting of HC1, H2S04, a mixture of HC1 and HF, ammonium bifluoride, ammonium fluoride, and a mixture of NaF and H3P04.
12. The method of claim 11, wherein the treatment solution comprises HC1 in a molar concentration from 0.15 moles/liter to 0.35 moles/liter.
13. The method of claim 12, wherein the treatment solution comprises HF in a molar concentration from 1 x 10"3 moles/liter to about 1 mole/liter.
14. The method of claim 11, wherein the treatment solution comprises sulfuric acid (H2S04) and water in a 1 :4 mixture of H2S04 to water.
15. The method of claim 11, wherein the treatment solution comprises sulfuric acid (H2S0 ) and water in a 1 :3 mixture of H2S0 to water.
16. The method of claim 11, wherein the treatment solution comprises sulfuric acid (H2S0 ) and water in a 1 :2 mixture of H2S0 to water.
17. The method of claim 11, wherein the treatment solution comprises 0.2 moles/liter NaF sodium fluoride (NaF) and 1 mole/liter H3P04.
18. The method of claim 1, wherein an average surface roughness of the glass sheet before the treating step is from about 0.1 nm to about 0.3 nm.
19. The method of claim 1, further comprising thinning the glass sheet prior to treating the glass sheet.
20. The method of claim 1, wherein a first side of the glass sheet is treated with the treatment solution and has an average surface roughness of from about 0.3 nm to about 100 nm after treatment, and
a second side of the glass sheet is not treated with the treatment solution and has an average surface roughness of from about 0.1 nm to about 0.3 nm.
21. A glass sheet comprising:
a first side having an average surface roughness of from about 0.3 nm to about 100 nm; and
a second side having an average surface roughness of from about 0.1 nm to about 100 nm, wherein
a length of the glass sheet is at least about 100 mm, and
a thickness of the glass sheet is less than about 1.0 mm.
22. The glass sheet of claim 21, wherein the glass sheet comprises alkali alumino silicate, alkali boroaluminosilicate, alkaline-earth aluminosilicate, alkaline-earth boroalumino silicate, or combinations thereof.
23. The glass sheet of claim 21, wherein the length of the glass sheet is greater than about 200 mm
24. The glass sheet of claim 21, wherein the thickness of the glass sheet is less than about 0.5 mm.
25. The glass sheet of claim 21, wherein the first side of the glass sheet has an average surface roughness of about 0.4 nm to about 10 nm, and the second side of the glass sheet has an average surface roughness of about 0.1 nm to about 0.3 nm.
26. The glass sheet of claim 25, wherein the first side has an average surface roughness of about 0.5 nm to about 1.3 nm.
PCT/US2014/035383 2013-04-30 2014-04-25 Surface treatments for low electrostatic discharge fusion drawn glass WO2014179153A1 (en)

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TW201446668A (en) 2014-12-16

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