WO2019023444A1

WO2019023444A1 - Frit paste and method for sealing a glass assembly therewith

Info

Publication number: WO2019023444A1
Application number: PCT/US2018/043883
Authority: WO
Inventors: Diane Kimberlie Guilfoyle; Hyung Soo Moon; Pei-Lien TSENG; Lu Zhang
Original assignee: Corning Incorporated
Priority date: 2017-07-28
Filing date: 2018-07-26
Publication date: 2019-01-31
Also published as: TW201910286A

Abstract

A glass-based frit paste is disclosed, wherein a ratio of the total weight percent of high boiling point organic material to the total weight percent of low boiling point organic materials is in a range from about 3.0 to about 5.0, and a maximum weight % of low boiling point organic materials is equal to or less than 10%. A method of forming a glass article is also disclosed. Specific sintering schedules to minimize and/or eliminate dark spots formed by incomplete burn-off of volatile paste constituents are also disclosed.

Description

FRIT PASTE AND METHOD FOR SEALING A GLASS ASSEMBLY

THEREWITH

Cross-Reference to Related Applications

[0001] This application claims the benefit of priority of U.S. Provisional Application Serial No. 62/538,017 filed on July 28, 2017 the contents of which are relied upon and incorporated herein by reference in their entirety as if fully set forth below.

BACKGROUND

Field

[0002] The present disclosure is directed to a glass-based frit paste suitable for sealing a glass assembly.

Technical Background

[0003] The sealing of glass components with glass-based frits is well known. However, the physical characteristics of the components being sealed, and the application to which the sealed components are applied, can dictate very different frit compositions to ensure acceptable sealing methods, and satisfactory performance of the sealed components.

[0004] Organic light emitting diode (OLED) displays, for example, utilize a sealed glass package to protect the sensitive organic material enclosed therein. For example, the temperature sensitivity of the organic electroluminescent component of the OLED display panel limits processing temperatures to less than about 125°C, and more conservatively to temperatures not exceeding 100°C. Accordingly, the frit employed for sealing an OLED display panel is typically sealed with a laser that irradiates the frit positioned between the glass substrates without heating the organic electroluminescent material to a degradation temperature. Thus, work on frits for OLED devices has focused on developing low temperature frits (low T_g) to ensure temperature rise within the package from the localized laser energy used for sealing is minimal. In addition to providing less likelihood for damage to the organic components of the OLED device, for example an OLED display panel, low temperature (low T_g) frits may require a lower pre-sintering temperature (thus assuring less opportunity for devitrification and for oxidation of chemical elements such as vanadium), a shorter process cycle for pre-sintering, and less likelihood for damage to leads and electrodes during laser-sealing. As used herein, pre-sintering refers to initial heating of a frit deposited on a glass substrate to sinter and adhere the frit to the substrate, for example prior to placing an opposing glass substrate in position on the frit wall formed in the pre-sintering step and is to be distinguished from sintering that might occur during a subsequent heating step, e.g., a sealing step. Because pre-sintering can be performed prior to the inclusion of organic material in a glass package, pre-sintering can be performed in an oven.

[0005] However, whether a frit can be used to successfully seal a glass package, for example a display panel, depends not only on the properties of the glass powder itself, but also on the behavior of the frit paste formulation, both during and after the dispensing operation. For example, OLED frit seal geometries can involve a relatively thin frit seal between two sheets of glass, and that thin frit seal must be formed with minimal anomalies, such as voids, that might allow atmospheric gases to penetrate through the seal. The frit paste used in forming the frit seal may be pen-dispensed on one or both of two glass plates, but is typically screen- printed, and must therefore perform satisfactorily under the respective process constraints. For example, a suitable frit paste in a screen printing operation should easily infiltrate the printing screen and form a consistent, preferably void-free, pattern on the glass substrate. Moreover, a suitable frit paste should provide a reasonable working time so that the frit paste does not quickly dry on the printing screen and cause clogging of the screen, and yet should also be capable of complete, or nearly complete, burn-out of organic components of the frit paste to prevent eruptions of such organic component vapors during the sintering processes.

SUMMARY

[0006] In one embodiment, a glass frit paste is disclosed comprising a glass frit (particulate), at least one low boiling point organic material, at least one high boiling point organic material and

wherein a ratio of a total weight percent of high boiling point materials to a total weight percent of low boiling point materials is in a range from about 3.0 to about 5.0.

[0007] The glass frit paste may comprise a total weight percent of low boiling point materials less than about 10 wt. %.

[0008] In various embodiments, glass frit paste may include an inorganic filler. For example, the inorganic filler may be a coefficient of thermal expansion (CTE) lowering filler, such as an inorganic filler comprising zirconium. For example, the inorganic filler can be zirconium phosphate or zirconia.

[0009] In some embodiments the total weight percent of solid material in the glass frit paste is equal to or greater than about 75 weight percent. For example, the total weight percent of solid material in the glass frit paste may be in a range from about 75 weight percent to about 77.5 weight percent.

[0010] The glass frit may comprise, on an oxide basis in mole percent,

ZnO 0 - 10,

Ti02 0 - 10,

[0011] In various embodiments the sum P2O5 + Te0₂ of the glass frit can be in a range from about 20 mole % to about 40 mole %.

[0012] A particle size distribution of the glass frit may include a D50 in a range from about 1 micrometer (μηι) to about 3 μηι, for example in a range from about 1 μιη to about 1.5 μηι. A maximum particle size of the glass frit can be equal to or less than about 5 μηι.

[0013] A T_g of the glass frit can be in a range from about 295°C to about 310°C.

[0014] In another embodiment, a method of forming a glass article is disclosed, comprising a) dispensing a frit paste onto a first glass substrate, a ratio of high boiling point materials to low boiling point materials in the frit paste in a range from about 3.0 to about 5.0; b) heating the glass substrate from step a) at a first ramp rate to a first hold temperature, the first hold temperature in a range from about 335°C to about 345°C and for a first hold time of 60 ± 5 minutes; c) heating the glass substrate after step b) at a second ramp rate to a second hold temperature, the second hold temperature in a range from about 375°C to about 385°C and for a second hold time of 30 ± 5 minutes; d) heating the glass substrate after step c) at a third ramp rate to a third hold temperature, the third hold temperature in a range from about 395°C to about 405°C and for a third hold time of 30 ± 5 minutes; and e) cooling the glass substrate after step d) at a fourth ramp rate.

[0015] In some embodiments, the heating in step b) is performed in air.

[0016] In some embodiments, the heating in step c) is performed in nitrogen.

[0017] In some embodiments, the heating in step d) is performed in nitrogen.

[0018] In some embodiments, the second ramp rate is equal to the first ramp rate.

[0019] In some embodiments, the third ramp rate is equal to the second ramp rate. [0020] In some embodiments, the first, second and third ramp rates are equal.

[0021] In some embodiments, a T_g of a glass powder comprising the frit paste is equal to or greater than 310°C, for example equal to or greater than about 320°C, such as equal to or greater than about 330°C.

[0022] In still another embodiment, a method of forming a glass article is described, comprising a) dispensing a frit paste onto a first glass substrate, a ratio of high boiling point materials to low boiling point materials in the frit paste in a range from about 3.0 to about 5.0; b) heating the glass substrate from step a) at a first ramp rate to a first hold temperature, the first hold temperature in a range from about 320°C to about 330°C and for a first hold time of 30 ± 5 minutes; c) heating the glass substrate after step b) at a second ramp rate to a second hold temperature, the second hold temperature in a range from about 335°C to about 345°C and for a second hold time of 30 ± 5 minutes; d) heating the glass substrate after step c) at a third ramp rate to a third hold temperature, the third hold temperature in a range from about 375°C to about 385°C and for a third hold time of 30 ± 5 minutes; and e) cooling the glass substrate after step d) at a fourth ramp rate.

[0023] In some embodiments, the heating in step b) can be performed in air.

[0024] In some embodiments, the heating in step c) can be performed in air.

[0025] In some embodiments, the heating in step d) is performed in nitrogen.

[0026] In some embodiments, the second ramp rate is equal to the first ramp rate.

[0027] In some embodiments, the third ramp rate is equal to the second ramp rate.

[0028] In some embodiments, the first, second and third ramp rates are equal.

[0029] In some embodiments, the frit paste comprises a glass powder with a T_g equal to or greater than about 310°C, for example equal to or greater than about 320°C, such as equal to or greater than about 330°C.

[0030] It is to be understood that both the foregoing general description and the following detailed description present embodiments of the present disclosure, and are intended to provide an overview or framework for understanding the nature and character of the embodiments as they are claimed. The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the present disclosure, and together with the description serve to explain the principles and operations of the

embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is a cross sectional view of an exemplary OLED assembly according to embodiments described herein;

[0032] FIG. 2 are photographs (a) - (d) of frit paste deposited by screen printing on a glass substrate over the course of 30 minutes, illustrating the effects of screen clogging due to evaporation of low boiling point constituents of the frit paste;

[0033] FIG. 3 are photographs (a) - (e) of frit paste deposited by screen printing on a glass substrate over the course of 30 minutes, illustrating the effects of an addition of high boiling point constituents to a frit paste;

[0034] FIG. 4 are a series scanning electron microscopy images (a) and (b) showing the results of sintering an example frit paste at different sintering temperatures;

[0035] FIG. 5 is an exemplary sintering schedule for processing frit pastes according to embodiments of the present disclosure;

[0036] FIG. 6 is a plot graphically showing the weight change in percent of the frit paste of FIG.5 as a function of temperature, illustrating the organic materials were completely eliminated by a temperature of 380°C;

[0037] FIGS. 7A and 7B show profile plots illustrating the cross sectional shape profile of the sintered frit paste according to an embodiment of the present disclosure;

[0038] FIG 8 is a plot graphically illustrating height after sintering for a frit paste according the an embodiment of the present disclosure at different printing speeds and down stop positions;

[0039] FIG 9 is a plot graphically illustrating the height after sintering for a frit paste according the an embodiment of the present disclosure at different solids loading (percent weight) and three sintering temperatures;

[0040] FIG. 10 is a plot graphically illustrating the change in print height of a deposited frit paste line, after sintering, at different solids loading (percent weight) and three sintering temperatures;

[0041] FIG. 11 is an optical microscopy photograph of a sintered frit line in accordance with an embodiment of the present disclosure;

[0042] FIG. 12A is an optical microscopy image of a "black spot" within a sintered line of frit;

[0043] FIG. 12B is an SEM image of a black spot within a sintered line of frit; [0044] FIG. 12C is another optical microscopy image of a "black spot" within a sintered line of frit;

[0045] FIG. 13 is another exemplary sintering schedule for processing frit pastes according to embodiments of the present disclosure; and

[0046] FIG. 14 is still another exemplary sintering schedule for processing frit pastes according to embodiments of the present disclosure;

[0047] FIG. 15 shows optical microscopy and scanning electron microscopy images of sintered frit lines according to the indicated two stage sintering schedules;

[0048] FIG. 16 shows optical microscopy and scanning electron microscopy images of sintered frit lines according to the indicated two stage sintering schedules;

[0049] FIG. 17 shows optical microscopy and scanning electron microscopy images of sintered frit lines according to the indicated two stage sintering schedules;

[0050] FIG. 18 shows optical microscopy and scanning electron microscopy images of sintered frit lines according to the indicated three stage sintering schedule;

[0051] FIG. 19 is a TGA plot showing percent weight of oleic acid as a function of temperature; and

[0052] FIG. 20 is a TGA plot showing percent weight of Oxsoft® as a function of

temperature.

DETAILED DESCRIPTION

[0053] Apparatus and methods will now be described more fully hereinafter with reference to the accompanying drawings in which example embodiments of the disclosure are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, this disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0054] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment.

[0055] Directional terms as may be used herein - for example up, down, right, left, front, back, top, bottom - are made only with reference to the figures as drawn and are not intended to imply absolute orientation. [0056] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; the number or type of embodiments described in the specification.

[0057] As used herein, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a "component" includes aspects having two or more such components, unless the context clearly indicates otherwise.

[0058] As used herein, and to avoid confusion, glasses disclosed herein may be referred to in a substantially solid (bulk form), or in a particulate form that can be produced, for example, by grinding and/or milling the bulk glass. The glass in a particulate form will be referred to as glass frit.

[0059] As used herein, a frit paste is to be construed to mean a material made using a glass powder (glass frit) and having a paste-like constituency. For example, typical frit pastes, without limitation, can comprise a solvent material (e.g., an organic solvent) and a binder material (e.g., an organic binder material). Typical frit pastes may include other materials as well, such as filler materials (e.g., used to vary a CTE of the sintered frit) and dispersants.

[0060] As used herein, a frit seal shall be interpreted to mean a glass-containing seal formed with a frit (e.g., frit paste) on at least one glass article, for example a glass plate, by the consolidation (sintering) of the frit. For a frit paste, such sintering processes are used to burn off the organic materials and consolidate the glass particles. To produce a frit seal including a desired CTE different than a CTE of the base glass frit, the frit paste before sintering may include one or more materials selected to vary the CTE of the base glass frit, for example a CTE lowering filler material.

[0061] As used herein, the term "frit" used in isolation shall refer generically to a glass frit or a frit paste made with the glass frit.

[0062] FIG. 1 illustrates an exemplary OLED device 10 comprising a first glass substrate 12 and a second glass substrate 14 sealed to the first glass substrate by a frit seal 16. The OLED device further includes an electroluminescent material and associated electronic components 18 disposed between the first and second glass substrates and sealed therein with the frit seal. For example, the electroluminescent material and associated electronic components (e.g., thin film transistors) may be formed on first glass substrate 12, while the second glass substrate 14 is an encapsulating substrate, which, when sealed with first glass substrate 12, forms an hermetically sealed volume therebetween. To wit, a glass package. The first glass substrate may be referred to as the backplane substrate, or simply backplane. The frit seal is typically formed by depositing a frit paste, for example via pen dispensing or screen printing, around an edge portion of one or both first and second glass substrates. For example, the frit paste may be deposited on the second glass substrate and pre-sintered to the second glass substrate in a furnace or oven. The first and second glass substrates may then be positioned in opposing relationship with the pre-sintered frit positioned therebetween. A laser may then be used to heat the pre-sintered frit, softening the frit and forming a frit seal that adheres together the first and second substrates.

[0063] Disclosed herein are glass-based frit pastes suitable for use in different applications, with different sealing methods. The glass-based frit pastes of the present disclosure may include, for example, vanadium-phosphate glasses, and may be selected as appropriate from the family of vanadium-phosphate glasses to meet the needs of the specific application. For example, a glass may be selected from the compositional ranges (described in mole % on an oxide basis) shown in Table 1 below.

Table 1

[0064] Referring to Table 1, while in some embodiments the sum of P2O5 and TeCh can be in a range from about 20 mole % to about 40 mole %, in other embodiments the sum of P2O5 and TeCh can be in a range from about 20 mole % to about 35 mole %, for example in a range from about 20 mole % to about 30 mole %. In some embodiments, the sum of Fe2Cb and B12O3 can be in a range from about 20 mole % to about 30 mole %.

[0065] The major components in the family of low glass transition temperature (T_g) glasses perform very specific roles and determine major properties of the frit. As is the case with any multi-component glass composition, the components in the frits suitable for use in the sealing of glass packages for OLED devices provide both positive and negative contributions to frit performance. For example, V2O5 both lowers T_g and increases near-infrared absorbance, but on the other hand degrades aqueous durability. P2O5 improves glass stability (decreases devitrification tendency), but at the same time raises T_g. Fe2Cb stabilizes the vanadium oxidation state, minimizes aqueous attack on vanadium and lowers CTE, but like P2O5, raises Tg.

[0066] Although P2O5 and Fe2Cb perform important roles in determining frit performance, the key component for OLED sealing is V2O5, since this species provides for both low T_g and laser-absorbance necessary during laser sealing processes. Because traditional routes for achieving lower T_g, such as alkali and/or halide addition, are typically not permitted in OLED frit compositions, since these components could result in poisoning of the TFT (thin film transistor) layer of the active OLED device, one strategy is to incorporate other low T_g glass formers into the frit composition. A list of inorganic oxides that will form glasses by themselves, or with small amounts of a second component include S1O2, B2O3, P2O5, Ge02, B12O3, V2O5, Sb₂03, AS2O3 and Te0₂.

[0067] Of the preceding list, S1O2 and Ge02 may be excluded because of very high T_g, while Sb203, and AS2O3 may be undesirable because of environmental concerns. V2O5 and P2O5 are already components in the OLED frit, while past work with B2O3 has shown that additions of this component in amounts greater than about 5 mole % can result in decreased aqueous durability. Thus, B12O3 and Te02, both of which are low T_g glass formers, are favored additions. B12O3, in particular, has the attractive feature that the Bi cation is sesquivalent, and may well play a role in the frit similar to other sesquivalent cations (Sb⁺³ in Sb203, and Fe⁺³ in Fe203) in which V2O5 is stabilized by an oxide capable of oxygen loss or reduction.

[0068] Several criteria can be used to evaluate glasses and frits as potential OLED-suitable sealing materials. These are: • T_g: T_g, as measured by differential scanning calorimetry (DSC) in accordance with ASTM El 356, can, in some embodiments, be no greater than about 310°C for OLED sealing, for example, no greater than about 305°C, for example in a range from about 290°C to about 310°C, for example in a range from about 295°C to about 300°C. However, as described herein, T_g can, in other embodiments, be greater than 310°C, even for OLED applications.

• Glass stability:

(a) as-poured (cullet) - the poured patty should be free of any devitrification, oxidation or other defects indicative of poor glass stability.

(b) after heat-treatment (cullet) - a piece of cullet heated to 375°C should appear vitreous, without surface devitrification, and should also exhibit evidence of viscous flow, such as rounding of edges.

(c) after air jet-milling to a Dso particle size in a range from about 1 micrometer (μπι) to about 3 μπι (with no added filler material), a flow button sintered at 380°C should exhibit substantial flow and rounding of edges and remain glossy, without devitrification or oxidation, both by visual inspection and by x-ray diffraction (XRD).

(d.) after air jet-milling to a Dso particle size in a range from about 1 μπι to about 3 μπι (and optionally as a blend, with filler material in a range from about 10 wt. % to about 30 wt. %, for example a CTE-modifying filler, such as a CTE lowering filler), a flow button sintered at 380°C should exhibit flow and rounding of edges and remain glossy, without evidence of devitrification or oxidation, both by visual inspection and by XRD.

• Aqueous durability (beaker test): The standard beaker test consists of immersing a test sample of the glass in 40 milliliters of deionized water at 90°C for 48 hours, and then visually evaluating the appearance of the supernatant and the condition of the sample after the test.

(a) as poured (cullet) - a piece of cullet should yield a supernatant that is clear to only slightly tinted, and the sample should also be intact, without residue from partial disintegration.

(b) after air jet-milling to a Dso particle size in a range from about 1 μπι to about 3 μπι (with no added filler material), a flow button sintered at 380°C should yield a supernatant that is clear to only slightly tinted, and the sample should be intact, without evidence of residue from partial disintegration. (c) after air jet-milling to a D50 particle size in a range from about 1 μιη to about 3 μπι (as a blend comprising a filler in a range from about 10 weight % to about 30 weight %), a flow button sintered at 380°C should yield a supernatant that is clear to only slightly tinted, and the sample should be intact, without evidence of residue from partial disintegration.

[0069] A parameter termed the "durability index" has been found to be a useful predictor of aqueous durability in a 48 hr 90°C beaker test and emerged as a key composition design tool, where:

[0070] Durability index = (∑(components which are susceptible to aqueous attack)/(∑( components which protect against aqueous attack).

[0071] Durability index = (∑ (V2O5 + P2O5 + B₂0₃))/(∑ (Fe₂0₃ + Bi₂0₃))

[0072] For durable, low T_g frit compositions in the V₂05-P205-Fe20₃-Te02-Bi₂0₃ pentenary, for example, the durability index should be as low as possible (consistent with low T_g and other properties such as flow, and resistance to devitrification), such as in a range from about 2.0 to about 3.5. Glasses in this range were rated acceptable (clear or light tint) in beaker durability testing. Aqueous durability appreciably degraded for glasses with durability indices higher than this range, with beaker test results deteriorating to medium tint (3.9), and dark, disintegrated (> 4.0).

[0073] Typically, cullet from glass melts is first evaluated for both as-poured glass stability and stability following heat-treatment at 375°C. If acceptable glass stability is demonstrated (e.g., lack of devitrification), T_g of the cullet can then be measured by DSC. If the cullet T_g is equal to or less than about 310°C, for example equal to or less than about 300°C, then pieces of the bulk glass may be evaluated for aqueous durability. Assuming successful performance in this test, the cullet can then be air jet-milled to a D50 particle size in a range from about 1 μπι to about 3 μπι, and evaluated in remaining stability and aqueous durability tests.

Accordingly, in certain instances data may not be collected if tests early in the testing sequence suggest undesirable OLED sealing performance. As used herein, D50 is the median value of the particle size distribution, i.e., it is the value of the particle diameter at 50% in the cumulative distribution. For example, if Dso=2 μπι, then 50% of the particles in the sample are larger than 2 μπι, and 50% are smaller than 2 μπι.

[0074] Modification of the basic V₂05-P205-Fe₂0₃ composition with low T_g glass formers TeC , and ΒΪ2θ₃ resulted in identifying two broad compositional groupings that meet the foregoing performance characteristics: 1) glasses with partial replacement of TeCh by P2O5, with only minimal partial replacement of Fe₂Cb by Bi₂Cb, and; 2) glasses with partial replacement of P₂Os by Te0₂, and greater replacement of Fe₂Cb by Bi₂Cb.

[0075] For glasses comprising partial replacement of Te0₂ by P₂0s,Te0₂ was found to play the same role in maintaining glass stability as does P₂Os, but with the advantage of lower T_g. Fe₂Cb was held at relatively high levels to maintain aqueous durability.

[0076] The broad compositional ranges (in mole %) described in Table 1 represent glasses in this series with T_g equal to or less than about 310°C , for example equal to or less than about 305°C, for example in a range from about 290°C to about 300°C, although in further embodiments, T_g may be greater than 310°C. Example compositions (expressed in mole %) are shown in Tables 2 and 3. Compositions were obtained that possessed T_g values in a range from about 295°C to about 300°C, and that also exhibited excellent aqueous durability as both cullet and as a fired flow button. These compositions also exhibited good fired flow as a fine powder.

Table 2

Table 3

[0077] Tables 2 and 3 describe compositions with partial replacement (up to 15 mole %) of Te02-for-P20₅, with only minimal (< 5%) partial replacement of Fe2Cb by B12O3. Table 2, in particular, illustrates that for some compositional groupings, e.g., Group II, TeC should be greater than about 10 mole % for low T_g, exemplified by sample B5 containing TeC at 5 mole % and exhibiting a T_g of 328°C; but less than 20 mole % for glass stability, as shown by sample B7 having TeC at 20 mole % and exhibiting poor flow and significant

devitrification. For Group III, T_g was sacrificed at V2O5 levels equal to or less than about 45 mole %, as evidenced by the relatively high T_g of sample B8 (318°C). While the Group II and Group III glasses may be appropriate frit glasses in some circumstances, the Group I glasses represent more attractive compositions for most OLED sealing applications.

Accordingly, in some embodiments, glass compositions as described herein may comprise V2O5 in a range from about 45 mole % to about 50 mole % including all ranges and subranges therebetween; P2O5 in a range from about 5 mole % to about 15 mole % including all ranges and sub-ranges therebetween, for example in a range from about 10 mole % to about 15 mole %, for example in a range from about 12.5 mole % to about 15 mole %; Fe2Cb in a range from about 12.5 mole % to about 17.5 mole %; B2O3 in a range from about 0 mole % to 5 mole % including all ranges and sub-ranges therebetween; ZnO in a range from about 0 mole % to 7.5 mole % including all ranges and sub-ranges therebetween; T1O2 in a range from about 0 mole % to about 5 mole % including all ranges and sub-ranges therebetween; TeC in a range from about 5 to about 20 mole % including all ranges and sub-ranges therebetween, for example in a range from about 10 mole % to about 20 mole %, for example in a range from about 15 mole % to 20 mole %, and; B12O3 in a range from about 0 mole % to about 5 mole % including all ranges and sub-ranges therebetween. Glasses in Table 2 can exhibit a ratio of TeCh/I^Os in a range from about 0.3 to about 4.0 including all ranges and sub-ranges therebetween, for example in a range from about 0.3 to about 1.2, for example from about 0.6 to about 1.2, for example from about 1.0 to about 1.2. Glasses in Table 2 can also exhibit a ratio of Bi₂03/Fe₂03 in a range from about 0 to about 0.4 including all ranges and sub-ranges therebetween, for example in a range from about 0 to about 0.35.

[0078] Turning to Table 3, for the Group IV glasses B12O3 should be maintained equal to or less than 5 mole % to achieve lower T_g. As shown, samples B9, B 10, B13, B14, B 15, B16 and B17 exhibited dark supernatant after the 48 hour cullet beaker test, but low T_g. Thus, these compositions may be useful as sealing frits for applications that do not require prolonged aqueous durability. Also, as indicated by the Group V glasses, suitable examples with V2O5 levels greater than 50% are possible, but only if Fe₂03 is increased to at least 17.5 mole % to maintain aqueous durability. However, at these higher Fe₂03 levels, Te0₂ should be maintained equal to or less than about 15 mole % to achieve the low T_g desired for OLED sealing. Examples Bl 1 and B 12, with higher T_g, are less desirable for OLED sealing applications, but may, for example, be applicable to the sealing of vacuum insulated glazing (VIG) panels. Accordingly, in some embodiments, glass compositions as described herein may comprise V2O5 in a range from about 50 mole % to about 52.5 mole % including all ranges and sub-ranges therebetween; P2O5 in a range from about 12.5 mole % to about 17.5 mole % including all ranges and sub-ranges therebetween, for example in a range from about 15 mole % to about 17.5 mole; Fe₂03 in a range from about 10 mole % to about 17.5 mole % including all ranges and sub-ranges therebetween; B2O3 in a range from about 0 mole % to about 5 mole % including all ranges and sub-ranges therebetween; ZnO in a range from about 0 mole % to about 2.5 mole % including all ranges and sub-ranges therebetween; T1O2 in a range from about 0 mole % to about 5 mole % including all ranges and sub-ranges therebetween; Te0₂ in a range from about 10 mole % to about 15 mole % including all ranges and sub-ranges therebetween, for example in a range from about 12.5 mole % to about 15 mole %, and; B12O3 in a range from about 0 mole % to about 7.5 mole % including all ranges and sub-ranges therebetween, for example in a range from about 0 mole % to about 2.5 mole %, for example in a range from about 0 mole % to 5 mole %, for example in a range from about 2.5 mole % to about 5 mole %, for example in a range from about 2.5 mole % to about 7.5 mole %, for example in a range from about 5 mole % to about 7.5 mole %. Glasses in Table 3 can exhibit a ratio of Te0₂/P₂05 in a range from about 0.5 to about 1.2 including all ranges and sub-ranges therebetween, for example in a range from about 0.65 to about 1.2, for example in a range from about 0.8 to about 1.2. Glasses in Table 3 can also exhibit a ratio of Bi₂03/Fe₂03 in a range from about 0 to about 1.5 including all ranges and sub-ranges therebetween, for example in a range from about 0.2 to about 0.5, for example in a range from about 0.3 to about 0.5, for example in a range from about 0.4 to about 0.5.

[0079] Note in particular that, for example, while holding Fe₂03 at 15 mole % to maintain durability, B12O3 can only be tolerated at equal to or less than about 5 mole % from a T_g standpoint, since 7.5 mole % B12O3 was found to raise T_g to greater than 310°C. However, higher levels of B12O3 can be tolerated from a low T_g standpoint in the family of glasses where simultaneous Bi₂03-for-Fe₂03 and Te0₂-for-P₂05 substitutions are made. This distinguishes both families of glasses as distinct composition groups.

[0080] For glasses with partial replacement of P2O5 by Te0₂, and of Fe₂03 by B12O3, B12O3 was found to have a similar role as Fe₂03 in stabilizing V2O5 and in maintaining aqueous durability, and also had the advantage of producing a lower T_g. The combination of a partial replacement of P2O5 by Te0₂, and of Fe₂03 by B12O3 was used in tandem to obtain lower T_g and durable compositions. Example glasses within this category are shown in Tables 4, 5, and 6.

[0081] Compositions (expressed in mole % on an oxide basis) were obtained that possessed T_g values in a range from about 295°C to about 300°C, and excellent aqueous durability as both cullet and as a fired flow button, as exemplified by C3. These compositions also possessed good fired flow as a fine powder.

[0082] The composition ranges shown in Table 4 (given in mole %) exhibit low T_g (defined in the context of OLED sealing as having a T_g equal to or less than about 310°C), excellent aqueous durability (measured by the 48 hour beaker test) as both cullet and as a fired flow button, and good fired flow as a fine powder at temperatures equal to or less than about 400°C.

Table 4

[0083] Table 5 describes compositions, in mole % on an oxide basis, with partial replacement of Te0₂-for-P₂05 and Bi₂03-for-Fe₂03. The Group VI glasses represent good sealing characteristics for OLED sealing, while for the Group VII glasses B1O2 should be less than about 20 mole % for good glass stability. Accordingly, in some embodiments, glass compositions as described herein may comprise V2O5 in a range from about 47.5 mole % to about 52.5 mole % including all ranges and sub-ranges therebetween, for example in a range from about 50 mole % to about 52.5 mole %; P2O5 in a range from about 10 mole % to about 17.5 mole % including all ranges and sub-ranges therebetween, for example in a range from about 10 mole % to about 12.5 mole%, for example in a range from about 10 mole % to about 15 mole %, for example in a range from about 12.5 mole % to about 15 mole %, for example in a range from about 12.5 mole % to about 17 mole %, for example in a range from about 15 mole % to about 17.5 mole %; Fe₂03 in a range from about 5 mole % to about 10 mole % including all ranges and sub-ranges therebetween; B2O3 in a range from about 0 mole % to about 5 mole % including all ranges and sub-ranges therebetween; ZnO in a range from 0 mole % to about 7.5 mole % including all ranges and sub-ranges therebetween; T1O2 in a range from about 0 mole % to about 5 mole % including all ranges and sub-ranges therebetween; Te0₂ in a range from about 5 mole % to about 20 mole % including all ranges and sub-ranges therebetween, for example in a range from about 5 mole % to about 15 mole %, for example in a range from about 15 mole % to about 20 mole %, and; B12O3 in a range from about 10 mole % to about 20 mole % including all ranges and sub-ranges therebetween. The durability index may range, for example, between about 2.8 to about 3.25. Glasses in Table 5 can exhibit a ratio of TeCh/I^Os in a range from about 0.2 to about 2.0 including all ranges and sub-ranges therebetween, for example in a range from about 0.5 to about 2.0, for example in a range from about 1.0 to about 1.6, for example in a range from about 1.0 to about 1.4, for example in a range from about 1.0 to about 1.2. Glasses in Table 14 can also exhibit a ratio of BiiCb/FeiCb in a range from 1.0 to about 4.0 including all ranges and subranges therebetween, for example in a range from about 1.0 to about 3.0, in a range from about 1.0 to about 2.0, for example in a range from about 1.0 to about 1.2.

Table 5

[0084] Table 6 describes compositions, in mole % on an oxide basis, with partial replacement of Te0₂-for-P₂05 and BiiCb-for-FeiCb. For the Group VIII glasses TeCte should be maintained equal to or less than about 27.5 mole % to obtain good aqueous stability, while for the Group IX glasses the durability index should be less than about 3.4. Accordingly, in some embodiments, glass compositions as described herein may comprise V2O5 in a range from about 45 mole % to about 55 mole % including all ranges and sub-ranges therebetween, for example from about 45 mole % to about 52.5 mole %; P2O5 in a range from 0 mole % to about 15 mole % including all ranges and sub-ranges therebetween, for example in a range from about 0 mole % to about 5 mole %, for example in a range from about 5 mole % to about 15 mole %, for example in a range from about 10 mole % to about 15 mole %; Fe2Cb in a range from about 5 mole % to about 15 mole % including all ranges and sub-ranges therebetween, for example in a range from about 10 mole % to about 15 mole %, for example in a range from about 12.5 mole % to about 15 mole %; B2O3 in a range from about 0 mole % to about 5 mole % including all ranges and sub-ranges therebetween; ZnO in a range from about 0 mole % to about 2.5 mole % including all ranges and sub-ranges therebetween; T1O2 in a range from about 0 mole % to about 5 mole % including all ranges and sub-ranges therebetween; TeCh in a range from about 10 mole % to about 27.5 mole % including all ranges and sub-ranges therebetween, for example in a range from about 15 mole % to about 25 mole %, for example in a range from about 15 mole % to about 22.5 mole %, and; B12O3 in a range from about 5 mole % to about 10 mole % including all ranges and sub-ranges therebetween, for example in a range from about 7.5 mole % to about 10 mole %. Glasses in Table 6 can exhibit a ratio of Te02/P20s in a range from about 0.5 to about 10.0 including all ranges and sub-ranges therebetween, for example in a range from about 0.5 to about 5.0, for example in a range from about 0.5 to about 2.5, for example in a range from about 0.5 to about 1.5. Glasses in Table 6 can also exhibit a ratio of Bi203/Fe203 in a range from 0.4 to about 2.0 including all ranges and sub-ranges therebetween, for example in a range from about 0.5 to about 1.2, for example in a range from about 0.7 to about 1.2

Table 6

[0085] Table 7 describes compositions, in mole % on an oxide basis, with partial replacement of Te02-for-P20₅ and Bi203-for-Fe203. For the Group X glasses V2O5 should be maintained greater than about 40 mole % to obtain low T_g and equal to or less than about 55 mole % for aqueous stability. Accordingly, in some embodiments, glass compositions as described herein may comprise V2O5 in a range from about 40 mole % to about 55 mole % including all ranges and sub-ranges therebetween; P2O5 in a range from about 5 mole % to about 15 mole % including all ranges and sub-ranges therebetween, for example in a range from about 12.5 mole % to about 15 mole %; Fe2Cb in a range from about 10 mole % to about 12.5 mole % including all ranges and sub-ranges therebetween; B2O3 in a range from about 0 mole % to 5 mole % including all ranges and sub-ranges therebetween; T1O2 in a range from about 0 mole % to about 5 mole %; ZnO in a range from about 0 mole % to about 5 mole %; TeC in a range from about 5 mole % to about 15 mole % including all ranges and sub-ranges therebetween, for example in a range from about 10 mole % to about 15 mole %, and; B12O3 in a range from about 10 mole % to about 15 mole % including all ranges and sub-ranges therebetween. Glasses in Table 7 can exhibit a ratio of Te02/P20s in a range from about 0.4 to about 3.0 including all ranges and sub-ranges therebetween, for example in a range from about 0.4 to about 2.0, for example in a range from about 0.4 to about 2.0, for example in a range from about 0.4 to about 1.2. Glasses in Table 7 can also exhibit a ratio of Bi203/Fe203 in a range from 1.0 to about 1.2 including all ranges and sub-ranges therebetween.

Table 7

[0086] The frit glasses described herein above may be combined with one or more solvents and/or one or more binder materials to produce a frit paste with desired dispensing and sealing properties. It should be noted that in the context of paste performance, e.g., the rheology of the frit paste, the chemical composition of the glass powder provides little influence. Accordingly, the foregoing glass compositions are presented and described as suitable glass compositions for the manufacture of frit pastes for the sealing of OLED devices. However, the disclosure is not limited to these few glass compositions. Nor is the sealing of OLED devices limited thereto. Additionally, frit pastes disclosed herein may further contain one or more filler materials selected to modify a CTE of the frit seal upon sintering. Filler materials may include, for example, one or more of beta quartz (β quartz), zirconium phosphate, zirconium tungsten-phosphate and zirconia, to name a few, typically in a range from about 0 weight % to about 20% weight percent, for example in a range from about 0 weight % to about 10 weight %. In still further embodiments, the frit paste may include one or more other additives, including dispersants and/or plasticizers, selected to obtain appropriate properties for the paste. Various dispersants can include BYK® Anti- Terra 202®, BYK® 354, Solsperse® 9000 and Dextrol® OC-60, or combinations thererof. The frit paste may include one or more binders, for example Aqualon® ethylcellulose ether (T-100) or Ethocel Standard 200 Industrial Ethylcellulose (Dow 200) from Dow Chemical, or combinations thereof. Frit pastes described herein can exhibit improved viscosity and stability, where stability in the present context is intended to mean the ability of the frit paste to resist evaporation of volatile components of the frit paste, such as the solvent in which the particulate materials such as glass powder and filler materials are suspended. Loss of solvent can cause the frit paste to become less workable for the purposes of dispensing the frit paste onto the one or more glass substrates. Stability, then, is closely related to workability.

[0087] During screen printing processes in particular, it may be necessary for the frit paste to remain on the screen for an extended period of time. For example, a given amount of frit paste may be added to the printing screen and thereafter a plurality of glass substrates may be screen printed before additional frit paste is added to the screen. Additionally, screen printing processes are typically performed in open air, for example a clean room, and often with considerably air flow to help ensure a clean environment. Thus, volatile components of the paste, such as low boiling point organic materials, can evaporate from the paste during the printing process, thereby reducing the workability of the paste. This may lead to clogging of the screen and an inability to suitably dispense the frit paste. For example, the frit paste can be formed on the substrate with height discrepancies, voids and other discontinuities that would render a seal formed therefrom unsuitable to hermetically seal sensitive components, such as OLED components, between glass substrates.

[0088] Accordingly, frit pastes disclosed herein have additional, high boiling point organic materials (e.g., oils) added to the paste composition. The addition of high boiling point organic materials has been found to increase the period of time during which the frit paste can be worked in a screen printing process. As used herein, the term "high boiling point" (HBP) refers to a boiling point equal to or greater than about 255°C, and "low boiling point" (LBP) refers to a boiling point less than 255°C. Typically, the low boiling point components are liquid solvents, for example butyl carbitol™ acetate (BCA) or an ester alcohol such as Texanol™, or combinations thereof. High boiling point materials can include plasticizers, such as oleic acid, triacetin (1,2,3-triacetoxypropane), dibutyl sebacate and Oxsoft® (a phathalate-free plasticizer from OXEA GmbH), or combinations thereof. High boiling point materials can also include a poiyoS such as Poly G® 20-56. To avoid clogging, the frit pastes disclosed herein should have no more than about 10% by weight (wt. %) of low boiling point organic materials, for example, equal to or less than about 5 wt. %. Suitable frit pastes may include a ratio of high boiling point organic materials to low boiling point organic materials (HBP/LBP) in a range from about 3.0 to about 5.0. It should be understood that the addition of high boiling point organic materials may improve workability in other frit dispensing operations, such as pen dispensing. The frit pastes disclosed herein are capable of providing good cross sectional profiles (e.g., consistent height and side wall formation) and long working times.

[0089] Tables 8 and 9 list several frit pastes that were evaluated for workability and sealing performance. Example 1 represents a conventional frit paste formed with a low boiling point solvent, Texanol (boiling point 254°C), a binder T-100, and dispersant additives, and was made with glass frit CI . Example 2 similarly employed Texanol solvent and T-100 binder, but further included dispersant additives and a POLY G 20-56 high boiling point oil (boiling point 290°C). The frit paste in Example 2 was also made with glass frit C 1. The frit paste of Example 3 used a Texanol solvent and a Dow 200 binder, an additive (e.g., dispersant), an oleic acid plasticizer high boiling point material (boiling point 286°C) and a triacetin

(glycerin triacetate, boiling point 259°C) plasticizer. Example 4 utilized Texanol solvent, Dow 200 binder, dispersant additives and an oleic acid plasticizer high boiling point material (boiling point 286°C) and a triacetin (glycerin triacetate, boiling point 259°C) plasticizer. Example 3 through Example 8 frit pastes were made using glass frit B 18. The ratio HBP/LBP is calculated based on the high boiling point plasticizers and HBP additives (e.g., Poly G 20-56) and the low boiling point solvents. All values for Tables 8 and 9 are given in weight percent.

Table 8

Table 9

Dibutyl Sebacate 13.15

Acetyl Tributyl

Citrate 12.05

Oxysoft 12.3

Dispersants 0.68 1.17 0.45 0.42

HBP/LBP 3.16 1.58 1.17 1.06

[0090] Table 10 includes further data related to Example 1 through Example 4.

Table 10

[0091] A paste clogging test was applied to evaluate workability of the samples from Table 8. A line of frit was first deposited on an exposed surface of a glass substrate. To simulate the air flow in an industrial production clean room environment, air flow from a fan was directed at the substrate surface on which the frit paste had been printed. After a first printing, the air flow was continued for 10 minutes, after which a second glass substrate was printed. The same process was repeated 3 additional times, resulting in a total of 5 printed substrates. As shown in FIG. 2, when the frit paste contains a large amount of low boiling solvent, the solvent evaporated rapidly during the process. The solvent evaporation leads to more viscous paste. When the viscosity is too high, the paste does not flow easily, workability is reduced and clogging of the screen pores can result. For example, Examples 6 - 8 show an increased amount of solvent that was added to decrease viscosity and flow. As indicated, the ratio of high boiling point materials to low boiling point materials was thereby decreased, and Examples 6 - 8 exhibited a reduced workability time.

[0092] FIG. 2 is an optical photograph (reflected light) of an unsintered printed frit paste line made with frit paste Example lfrom Table 8. The figure illustrates a progression of frit lines ((a) through (d)) printed through a 400 mesh printing screen during intervals of 10 minutes under the blowing air conditions described above. Frit paste on the screen was not renewed during the test. As shown in FIG. 2, image (a), the initial frit line appears to be well applied, with a width of about 681 micrometers (μιη). FIG. 2, image (b) similarly shows a frit paste line printed 10 minutes after the initial frit paste line shown in image (a). The frit paste line of image (b) shows more inconsistency in the edge of the frit paste line (more ragged), and a more dimpled surface, suggesting less frit paste was passing through the screen. In addition, the width of the frit paste line is decreased relative to the initial frit paste line of image (a). At image (c), showing a third frit paste line printed 20 minutes after the initial frit paste line of image (a) was printed, a breaking up of the printed line due to on-screen drying of the frit paste is clearly illustrated. The screen pore pattern is clearly observed as discrete "dots" of frit paste, depicting poor coverage of the substrate. Finally, a frit line printed 30 minutes after the initial frit past line was printed is shown at image (d). Image (d) shows significant breaking up of the frit paste line. Frit paste deposition has been severely compromised, with little if any frit paste infiltrating the screen to be deposited on the glass substrate.

[0093] In contrast to the results illustrate in FIG. 2, FIG. 3 illustrates a plurality of transmitted light optical images ((a) through (e)) of printed frit paste lines employing frit paste Example 4 of Table 8. Unlike the frit paste of Example 1, the frit paste of Example 4 contained a high boiling point material (e.g., oleic acid) and, in comparison to Example 1, significantly less low boiling point materials (e.g., Texanol and dispersants). Similarly to the foregoing test conducted on the Example 1 sample, an initial frit paste line from Example 4 was printed on a glass substrate (image (a)). A width of the frit paste line was about 657 μιη. Ten minutes later, a second frit paste line of the Example 4 frit paste was printed, as shown in image (b), and so forth for images (c), (d) and (e), each frit paste line printed after a ten minute interval from the preceding frit paste line. Widths of each frit paste line ((a) - (e)) are remarkably consistent, with a difference between a maximum width and a minimum width of only 11 μπι, suggesting an even, consistent pattern deposited over a period of forty minutes, again without renewal of the frit paste on the printing screen.

[0094] The scanning electron microscopy images of FIG. 4 show cross sections of sintered frit (Example 4) disposed on a glass substrate. Each line of sintered frit was printed to the same uniform thickness. Image (a) is a cross sectional view of the frit paste Example 4 after sintering to a glass substrate at a sintering temperature of 380°C. The sintered frit is densified, with no evidence of crystallization. A thickness of the sintered frit was 9.35 μιη. The sintering schedule is shown in FIG. 5. For comparison, a second cross sectional image (image (b)) of the same frit paste (Example 4) after sintering to a glass substrate at a sintering temperature of 400°C is also shown in FIG. 4. The frit was fully densified, with no evidence of crystallization. A thickness of the sintered frit was 6.5 μπι. The images of FIG. 4 illustrate that frit pastes of the present disclosure can be successfully sintered at sintering temperatures as low as at least 380°C, and while the sintering schedule of FIG. 5 shows at least partial sintering in nitrogen (N₂), testing has shown frit pastes disclosed herein can be fully sintered in an air atmosphere, significantly easing the requirements for sintering. The images further show that although a sintering temperature of 400°C produced optimal densification, as evidenced by the reduced thickness after sintering, sintering results at 380°C were found to still be acceptable.

[0095] FIG. 6 is a graph depicting thermal gravimetric analysis (TGA) results on the frit paste of Example 4, showing that the organic materials of the frit paste were burned off at a sintering temperature of about 380°C and illustrating that a sintering temperature of equal to or greater than 380°C is capable of burning off the organic materials, and, together with the results shown in FIG. 5, produces a densified and amorphous sintered material.

[0096] FIGS. 7A and 7B show cross sectional profiles of a frit paste according to Example 4 that was screen printed as a line of frit paste on glass substrates. The plots show good height consistency and a flat top profile across the entire width of each sintered frit line. As shown, the average frit height above the glass substrate varied between about 6.5 μπι for the sintered frit line shown in image (a), about 5.1 μιη shown for the sintered frit line in image (b) and about 4.7 μπι for the frit line shown in image (c). The flat top profile can provide advantages for laser sealing and adhesion due to its high contact area with the encapsulation substrate. The height of the profile can be tuned by changing the solids loading (amount of solid materials) in the frit paste. As used herein, solid materials are materials that exhibit structural rigidity and resistance to changes in shape or volume at standard temperature and pressure. Solids may be crystalline, or amorphous. In the context of the present disclosure and unless otherwise indicated, solids, e.g., solids loading, typically refers to glass particles (e.g., amorphous solids) or filler particles (e.g., crystalline solids), and amounts thereof. When the solids loading changes from 76% to 71% for example, the average height of the frit line changes from 6.5 micrometers to 4.7 micrometers. Alternatively, or in addition, the printing conditions e.g., printing speed and pressure can be varied - typically by changing printing speed and/or pressure (downstop), as shown in FIG. 8. When the printing speed changes from 100 millimeters/second to 200 millimeters/second, the printing height increases from 12.7 micrometers to 13.8 micrometers with 0 micrometer downstop. At the same speed of 200 millimeters/second, the frit height changes from 13.8 micrometers to 12.4 micrometers when the downstop increases from 0 micrometers to 400 micrometers.

[0097] As shown in FIG. 9, which is a plot of print height (height of frit line from the surface of the substrate) after pre-sintering (prior to sealing) for three pre-sintering temperatures 360°C, 380°C and 400°C and for different solids loading of the Example frit paste 4, in general, the greater the solids loading in wt. %, the greater the after-sintering print height. The solids loading used, in percent by weight, are provided in Table 11. This can be further seen with the aid of FIG. 10 showing a plot of the change in print height for before pre- sintering and after pre-sintering as a function of the change in solids loading for three pre- sintering temperatures 360°C, 380°C and 400°C, again in weight percent. Print heights were measured using a Keyance measurement instrument.

Table 11

[0098] FIG. 11 is an optical photograph of a sintered frit line using a frit paste of Example 4. The frit paste was presintered to a first glass substrate in a plurality of closed loop cells at a presintering temperature of 380°C, then the glass substrate was sealed to a second glass substrate positioned on the presintered frit by exposing the presintered frit to a laser beam operating at a central wavelength of 810 nanometers at a sealing speed (traverse speed along the frit) of about 20 mm/second at a power of 11.5 watts to sinter the frit and attached the two glass substrates. The beam size at the surface of the frit was about 1.1 mm. The sealed glass substrate was then tested for hermeticity in an environment of 85°C and 85% relative humidity. As shown in Table 12, after 90 hours at 85°C and 85% humidity, the percentage of good cells (cells not having lost hermeticity) was about 86%, and was still about 83% after 330 hours. It was determined the failures were due to extrinsic sources (e.g. contamination during sealing preparation, for example particulate contamination), indicating that the percentage of good cells may have been higher without the extrinsic contamination.

Table 12

[0099] During testing of the frit compositions, a sintering issue that was encountered was the appearance of "dark spots" within the sintered frit after completion of sintering. An exemplary dark spot is shown in FIGS. 12A (optical microscopy) and 12B (scanning electron microscopy, SEM). The SEM image of FIG. 12B depicts an empty void structure, with additional protruding structures arranged around the void. FIG. 12C is another image of a dark spot by optical microscopy, showing the spot relative to at least a portion of a sintered frit line. It is believed the protruding structures of a dark spot may potentially contact metal film on an OLED panel and lead to damage of the panel during laser sealing. Black spots are believed to be the result of incomplete burn-off of organic materials during the burn-off phase of a sintering heat treatment cycle. Thus, organic materials are trapped within the frit melt and then erupt when pressure within pores containing the organic material builds during the higher temperature sintering phase.

[00100] Increasing the burn-off time from about 20 minutes to about 60 minutes at 325°C may not be sufficient to reduce the occurrence of black spots, particularly for low T_g glasses. It has also been found that high boiling point organic species have a tendency to leave a residue at such low burn-off temperatures. Moreover, the extended burn-off time, even at such a low temperature, can be sufficient to produce melting of the glass and subsequent trapping of the organic materials the burn-off is intended to eliminate. The trapped organic material can then outgas during a subsequent sintering step, leading to increased volume of the seal material due to an increase in pore size, and even explosive rupturing of pores containing the organic material that produces black spots. Conversely, raising the burn-off temperature from about 325°C to about 340°C can produce a significant reduction in black spots by increasing volatilization of the organic material. However, a higher burn-off temperature can result in a frit that is not as densely packed when compared with a 325°C burn-off The occurs because, for reasons similar to the lower burn-off temperature, burn-off may not yet be complete, and some organic materials can still become trapped and create pores that impede consolidation. Still further, raising the peak sintering temperature to 400°C without addressing the burn-off phase may aid sintering, but may also increase the occurrence of black spots, since, without assuring complete burn-off of the organic paste materials, explosive outgassing can still occur. Accordingly, additional sintering cycles are disclosed that have been shown to produce good sintering results and to reduce the occurrence of black spots.

[00101] In a first alternative sintering schedule, temperature hold times are 340°C for 60 minutes in air, 380°C for 30 minutes in N2 and 400°C for 30 minutes in N2. As shown in FIG. 13, temperature ramp times to the hold temperatures are conducted at 5°C/minute, the first ramp to 340°C in air, with the second and third ramp times to 380°C and 400°C, respectively, in N2. Temperature ramp down is conducted at 10°C/minute, in N2, to below 300°C, and can be performed at furnace rate thereafter. Indeed, during testing, a 340°C burn- off temperature exhibited the lowest number of dark spots and good sintering. Hold temperatures can vary by ± 5°C. In a second alternative sintering schedule, temperature hold temperatures and times are 325°C for 30 minutes in air, 340°C for 30 minutes in air and 380°C for 60 minutes in N2. Again, hold temperatures can vary by ±5°C. As shown in FIG. 14, temperature ramp times to the hold temperatures are conducted at 5°C/minute, the first ramp to 325°C in air and the second ramp time to 380°C also in air. The third ramp time, to 380°C, is performed in N2. Temperature ramp down is conducted at 10°C/minute, in N2, to below 300°C, and can be performed at an uncontrolled furnace rate thereafter. Temperature ramp times to the hold temperatures are 5°C. Temperature ramp down is conducted at 10°C/minute to below 300°C, and can be performed at furnace rate thereafter. It should be noted that ramp up and ramp down times can vary at least within ± 5 minutes without necessarily affecting frit performance. For example, ramp up rates can vary from about 3°C/minute to about 7°C/minute. Ramp down rates may vary in a range from about

5°C/minute and 15°C/minute. In some embodiments, the sintering furnace may simply be turned off at the conclusion of the peak temperature cycle (conclusion of sintering), and allowed to cool at an uncontrolled furnace rate.

[00102] Another method to reduce dark spots is to use a high T_g glass powder, for example with a T_g equal to or greater than 330°C. A high T_g frit glass softens and sinters at higher temperatures compared to low T_g glass, thus enabling a higher burn-off temperature or longer time before glass sintering phase. Such higher burn-off temperature or longer time before sintering using a high T_g glass can allow more complete burn-off of organic materials from the frit paste without significant entrapment of organic material and subsequent outgassing issues. In addition, a higher T_g also allows a higher sintering temperature, which can help frit densification. However, the use of a high T_g glass frit powder must be weighed against the increased sealing time and temperature, and potential damage to any organic material, e.g., OLED material, being intentionally sealed within the package.

[00103] Referring now to FIGS. 15, 16, and 17, various images of frit lines sintered under the indicated conditions are shown. In particular, FIGS. 15 - 17 depict optical microscopy (OM) images and scanning electron microscopy (SEM) images for different two stage sintering schedules and the number of dark (black) spots observed after sintering.

[00104] In contrast to FIGS. 15 - 17, FIG. 18 illustrates OM and SEM images of frit lines sintered using a three stage sintering cycle. As is evident from the data, overall the three stage sintering cycles provide significantly reduced occurrences for dark spots.

[00105] It should be apparent in view of the present disclosure that reducing the burn out temperature of organic materials can be effective in minimizing or preventing excessive outgassing during sintering. While oleic acid was used in a majority of experiments, substitution of Oxsoft®, a phthalate-free plasticizer manufactured by OXEA showed improved results. Why this is so can be seen by comparing the TGA plots shown in FIGS. 19 and 20, where FIG. 19 is a plot showing the TGA results for oleic acid as residual weight percent plotted as a function of temperature, and FIG. 20 is a plot of the TGA results for Oxsoft. The data show that while oleic acid exhibits a tail that extends well past 300°C, Oxsoft shows complete burn off by 300°C. Accordingly, the use of a plasticizer that exhibits complete burn off, as demonstrated by TGA, for example equal to or less than about 300°C, may be favored over plasticizers exhibiting complete burn off only at higher temperatures. Another suitable plasticizer includes dibutyl sebacate.

[00106] It will be apparent to those skilled in the art that various modifications and variations can be made to embodiments of the present disclosure without departing from the spirit and scope of the invention. Thus, it is intended that the present disclosure cover the modifications and variations of such embodiments provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A glass frit paste comprising:

a glass frit;

at least one low boiling point organic material;

at least one high boiling point organic material; and

2. The glass frit paste according to claim 1, wherein the total weight percent of low boiling point materials is less than 10 wt. %.

3. The glass frit paste according to claim 1 or claim 2, wherein the glass frit paste comprises an inorganic filler.

4. The glass frit paste according to claim 3, wherein the inorganic filler comprises zirconium.

5. The glass frit paste according to claim 4, wherein the inorganic filler is zirconium phosphate or zirconia.

6. The glass frit paste according to any one of claims 1 to 5, wherein the total weight percent of solid material in the glass frit paste is equal to or greater than about 75 weight percent.

7. The glass frit paste according to claim 6, wherein the total weight percent of solid material in the glass frit paste is in a range from about 75 weight percent to about 77.5 weight percent.

8. The glass frit paste according to any one of claims 1 to 7, wherein the glass frit comprises on an oxide basis in mole percent:

ZnO 0 - 10, Ti02 0 - 10,

9. The glass frit paste according to claim 8, wherein P2O5 + TeC is in a range from about 20 mole % to about 40 mole %.

10. The glass frit paste according to any one of claims 1 to 9, wherein the glass frit comprises a particle size distribution with a D50 in a range from about 1 μιη to about 3 μιη.

11. The glass frit paste according to any one of claims 1 to 9, wherein the glass frit comprises a particle size distribution with a D50 in a range from about 1 μιη to about 1.5 μιη

12. The glass frit paste according to any one of claims 1 to 11, wherein a maximum particle size of the glass frit is equal to or less than about 5 μιη.

13. The glass frit paste according to any one of claims 1 to 12, wherein a T_g of the glass frit is in a range from about 295°C to about 310°C.

14. A glass assembly comprising a first glass substrate, a second glass substrate, the first glass substrate and the second glass substrate sealed by a glass seal formed by the glass frit paste of any one of claims 1 to 13.

15. A method of forming a glass article, comprising:

a) dispensing a frit paste onto a first glass substrate, a ratio of high boiling point materials to low boiling point materials in the frit paste in a range from about 3.0 to about 5.0;

b) heating the glass substrate from step a) at a first ramp rate to a first hold temperature, the first hold temperature in a range from about 335°C to about 345°C and for a first hold time of 60 ± 5 minutes;

c) heating the glass substrate after step b) at a second ramp rate to a second hold temperature, the second hold temperature in a range from about 375°C to about 385°C and for a second hold time of 30 ± 5 minutes; d) heating the glass substrate after step c) at a third ramp rate to a third hold temperature, the third hold temperature in a range from about 395°C to about 405°C and for a third hold time of 30 ± 5 minutes; and

e) cooling the glass substrate after step d) at a fourth ramp rate.

16. The method according to claim 15, wherein the heating in step b) is performed in air.

17. The method according to claim 16, wherein the heating in step c) is performed in nitrogen.

18. The method according to claim 17, wherein the heating in step d) is performed in nitrogen.

19. The method according to any one of claims 15 to 18, wherein a T_g of a glass powder comprising the frit paste is equal to or greater than 330°C.

20. A method of forming a glass article, comprising:

b) heating the glass substrate from step a) at a first ramp rate to a first hold temperature, the first hold temperature in a range from about 320°C to about 330°C and for a first hold time of 30 ± 5 minutes;

c) heating the glass substrate after step b) at a second ramp rate to a second hold temperature, the second hold temperature in a range from about 335°C to about 345°C and for a second hold time of 30 ± 5 minutes;

d) heating the glass substrate after step c) at a third ramp rate to a third hold temperature, the third hold temperature in a range from about 375°C to about 385°C and for a third hold time of 30 ± 5 minutes; and

e) cooling the glass substrate after step d) at a fourth ramp rate.

21. The method according to claim 20, wherein the heating in step b) is performed in air.

22. The method according to claim 21, wherein the heating in step c) is performed in air.

23. The method according to claim 22, wherein the heating in step d) is performed in nitrogen.

24. The method according to claim 23, wherein the second ramp rate is equal to the first ramp rate.

25. The method according to any one of claims 20 to 24, wherein the frit paste comprises a glass powder with a T_g equal to or greater than about 330°C.