Transparent glass manufacturing and thermoforming

Abstract

The present invention relates to a method for producing a transparent glass article, the method comprising the following steps (a) to (f): step (a) preparing a nanocomposite; step (b) applying an external stimulus to the nanocomposite to make it reshapeable; step (c) reforming the nanocomposite into a predetermined shape to obtain a primary structure; step (d) degreasing the primary structure to obtain a secondary structure having voids formed therein; optional step (e) filling the voids in the secondary structure with at least one additive; and step (f) sintering the secondary structure to obtain a transparent glass article. The glass particles include spherical glass particles having a diameter in the range of 5 nm to 400 nm.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a transparent glass article and to a transparent glass article obtainable by said method. [Background technology]

[0002] Transparent glass is an important material because it combines high thermal, chemical, and mechanical stability with optical transparency. However, forming transparent glass into glass articles is complicated because transparent glass has a high melting point, especially when the transparent glass is formed from fused silica. Currently, transparent glass is mostly formed into glass articles using melt processing, grinding, or etching, but none of these processes allows for high-throughput replication of transparent glass articles.

[0003] Recently, a concept has been proposed that allows the molding of transparent glass using additive manufacturing, i.e., 3D printing and similar techniques, by selectively applying heat or radiation, based on nanocomposites containing a binder matrix and glass particles dispersed therein. However, the above-mentioned processes are only suitable for rapid prototyping and are limited to very small series in the production of glass articles. In other words, such processes do not scale well industrially.

[0004] In this regard, U.S. Patent No. 5,999,623 describes a method for producing glass or glass-ceramic articles by powder injection molding of glass powder. Specifically, the method includes mixing an organic binder, glass powder, and wax together in a continuous mixing process to obtain a mixture, forming the mixture into a first formed structure, and debinding and sintering the first formed structure. However, based on the size and relatively low density of the glass powder used, one must conclude that the glass or glass-ceramic articles obtained in U.S. Patent No. 5,999,623 are not transparent.

[0005] US Patent No. 5,999,623 describes silicate glass honeycomb articles containing up to about 9% titanium dioxide, which are produced by an extrusion process utilizing high-purity fused silica soot particles dispersed in a rubbery paste formulation containing Elvanol™ or Methocel™, i.e., the silica soot particles are dispersed in an aqueous suspension containing a thickener, requiring extensive drying after extrusion of the article.

[0006] Patent Document 3 discloses a method for producing an ultra-thin glass sheet, which comprises extruding a polymer / glass compound containing 30% to 80% by volume of an inorganic component consisting of glass particles and optionally ceramic particles, and 20% to 70% by volume of an organic component consisting of one or more thermoplastic polymers and one or more processing aids selected from the group consisting of surfactants, waxes, and plasticizers, into a composite polymer / glass sheet, followed by gradually heating to a temperature of 500°C to 1600°C so that the organic component first burns out and then the glass particles of the inorganic component sinter together, thereby obtaining a glass sheet. However, as demonstrated by the examples in Patent Document 3, this method is limited to producing an ultra-thin glass sheet having a thickness of approximately 200 μm.

[0007] Patent Document 4 discloses a method for producing a quartz glass molded article, in which silica having a specific particle size is blended with a binder composition containing a thermoplastic material, such as EVA copolymer (poly(ethylene-vinyl acetate)) or polypropylene, an acrylic resin, a plasticizer, and a lubricant. This blended mixture is injection-molded, degreased, and then sintered at a temperature of 1000°C to 1800°C. However, the resulting glass molded article is not transparent, but is considered to be translucent or opaque.

[0008] Furthermore, Patent Document 5 describes a composition and method for producing compacts from high-purity transparent quartz glass by additive manufacturing. Specifically, the composition includes an organic binder that exists in liquid form at room temperature and is polymerizable / crosslinkable upon exposure to heat or radiation; a polymerization initiator / crosslinker that initiates polymerization / crosslinking of the organic binder upon application of heat or radiation; and at least one type of spherical quartz glass particles dispersed in the organic binder. However, Patent Document 5 requires the organic binder to be liquid at room temperature so that the composition can be processed with high spatial resolution by selectively applying heat or radiation. This makes the organic binder unsuitable for replication processes such as injection molding. Furthermore, the organic binder must be polymerizable / crosslinkable to achieve sufficient mechanical stability during the formation of the powder compact. Otherwise, the powder compact will be too soft and unable to withstand the load during processing. Again, this makes the organic binder disclosed in Patent Document 5, which requires a liquid state at room temperature, unsuitable for replication processes. A similar process is described in Non-Patent Document 1. In Non-Patent Document 1, amorphous silica nanopowder with a diameter of 100 nm was dispersed in a monomer mixture containing hydroxyethyl methacrylate (HEMA) and phenoxyethanol (POE). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent Application Publication No. 2007 / 0154666 [Patent Document 2] International Publication No. 00 / 48775 [Patent Document 3] European Patent Application Publication No. 3081541 [Patent Document 4] Japanese Patent Application Publication No. 04-349130 [Patent Document 5] International Publication No. 2018 / 065093 [Non-patent literature]

[0010] [Non-Patent Document 1] F. Kotz et al., Adv. Mater. 2018, 30, 1707100 Summary of the Invention [Problem to be solved by the invention]

[0011] In view of the above, the present invention aims to overcome the above-mentioned drawbacks associated with forming transparent glass known in the art. In particular, the present invention has as its basic technical problem the provision of a method for manufacturing transparent glass articles that allows transparent glass to be easily formed into glass articles in a replication process that is industrially scalable. [Means for solving the problem]

[0012] The basic technical problem of the present invention as stated above has been solved by providing the embodiments characterized in the claims.

[0013] In particular, in one aspect, the present invention provides a method for producing a medicament comprising: The following steps (a) to (f): (a) providing a nanocomposite comprising an organic thermoplastic binder matrix that is solid at room temperature and glass particles dispersed therein; (b) applying an external stimulus to the nanocomposite to render the nanocomposite reshapeable; (c) Reshaping the nanocomposite into a predetermined shape to obtain a primary structure; (d) degreasing the primary structure by removing the organic thermoplastic binder matrix to obtain a secondary structure having voids formed therein; (e) optionally filling the voids of the secondary structure with at least one additive; (f) obtaining a transparent glass article by sintering the secondary structure; A method for producing a transparent glass article, preferably consisting of these steps, comprising: The method of manufacture is provided, wherein the glass particles comprise spherical glass particles having a diameter in the range of 5 nm to 400 nm.

[0014] Advantageously, the manufacturing method according to the present invention, characterized by the process steps defined above, allows transparent glass to be easily formed into glass articles using an industrially scalable replication process, such as injection molding. Consequently, the manufacturing method according to the present invention allows for high-throughput replication of transparent glass articles, which is not possible using the above-described processes established in the art. Advantageously, as will be explained in more detail below, the predetermined geometric shape is not further limited, since the moldable nanocomposite can be formed into the predetermined geometric shape by any suitable means known in the art. Accordingly, the geometric shape of the transparent article finally obtained after debinding and sintering is also not further limited. According to the present invention, the transparent glass article produced is understood to be an article having any shape. Its thickness is preferably 0.5 mm (500 μm) or more, more preferably 0.6 mm (600 μm) or more, even more preferably 0.8 mm (800 μm) or more, and most preferably 1.0 mm (1000 μm) or more.

[0015] Steps (a) to (f) of the production method according to the present invention will be described in detail below with reference to FIG. 1, which schematically shows steps (a) to (f).

[0016] In step (a) of the method for producing a transparent glass article as defined above, a nanocomposite is provided. The nanocomposite provided in step (a) comprises an organic thermoplastic binder matrix and glass particles dispersed therein (the latter indicated by open circles in Figures 1(a) to 1(e)). The organic thermoplastic binder matrix is ​​solid at room temperature. In this specification, room temperature is understood to be a temperature of 25°C.

[0017] According to the present invention, the organic thermoplastic binder matrix is ​​solid at room temperature. At elevated temperatures, when exposed to an external stimulus, such as heat or radiation, preferably heat, the organic thermoplastic binder matrix can soften, e.g., partially or completely melt. When the external stimulus is removed, the organic thermoplastic binder matrix becomes solid again. Because the organic thermoplastic binder matrix used in the present invention is organic, it is derived from monomers with a hydrocarbon backbone. These monomers react with each other to form, for example, polyolefins by polymerization, polyesters or polyamides by polycondensation, or polyurethanes by polyaddition. Because the organic thermoplastic binder matrix used in the present invention is thermoplastic, it is neither polymerizable nor crosslinkable. That is, when exposed to an external stimulus, the organic thermoplastic binder matrix simply softens and does not undergo any chemical reaction. With the organic thermoplastic binder matrix in its softened state, the nanocomposite can be remolded into a desired shape. This remoldability is unique to nanocomposites containing the organic thermoplastic binder matrix prepared in step (a). As used herein, the nanocomposite may be prepared in any suitable form, including, but not limited to, in the form of granules, also referred to as granules.

[0018] According to the present invention, the composition of the organic thermoplastic binder matrix is ​​not limited. For example, the organic thermoplastic binder matrix may be composed of, but is not limited to, polyesters based on aromatic or aliphatic dicarboxylic acids and diols and / or hydroxycarboxylic acids, polycarbonates based on aliphatic or aromatic diols, polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, and polyisobutene, ethylene propylene rubber (EPR) and poly(vinyl butyral), cycloolefin polymers, and polyamides, polyethers or polyurethanes including aromatic polyethers based on bisphenols, or combinations thereof. Specifically, the organic thermoplastic binder matrix may be composed of poly(vinyl butyral).

[0019] As explained further below, the average molecular weight of the polymer constituting the organic thermoplastic binder matrix must be sufficiently high, i.e., at least several hundred grams per mole, to impart sufficient mechanical stability to the primary structure obtained in step (c). At a minimum, the polymer constituting the organic thermoplastic binder matrix has an average molecular weight such that the organic thermoplastic binder matrix is ​​solid at room temperature but softens at elevated temperatures when subjected to an external stimulus. However, if the average molecular weight of the polymer constituting the organic thermoplastic binder matrix is ​​too high, the organic thermoplastic binder matrix may not soften at elevated temperatures, e.g., may decompose without partially or completely melting. The organic thermoplastic binder matrix typically has a melting temperature in the range of 50°C to 200°C, preferably in the range of 100°C to 150°C. Herein, the melting temperature of the organic thermoplastic binder matrix is ​​determined according to DIN 51006 or DIN 51007, depending on the crystallinity of the polymer constituting the organic thermoplastic binder matrix.

[0020] The nanocomposite prepared in step (a) contains glass particles as an essential component in addition to an organic thermoplastic binder matrix. The glass particles are dispersed in the organic thermoplastic binder matrix. Dispersion of the glass particles can be achieved by any means known in the art. For example, to disperse the glass particles, the organic thermoplastic binder matrix can be softened before adding the glass particles, or the polymer that constitutes the organic thermoplastic binder matrix can be dissolved in a suitable organic solvent.

[0021] In a preferred embodiment of the present invention, the glass particles are fused silica glass particles. Fused silica glass is characterized by being composed of high-purity amorphous silicon dioxide. That is, fused silica glass is substantially free of any components that are typically added to other types of glass to lower their melting points. As a result, fused silica glass exhibits high thermal stability, which in turn makes it difficult to process using conventional processes such as melt processing. This drawback is overcome by the manufacturing method of the present invention, which does not require any melt processing. Fused silica glass exhibits high light transmittance in the wavelength range of 340 nm to 400 nm and is therefore widely used in the optical field, for example, as a lens substrate. In this specification, fused silica glass is understood to mean glass having a mass fraction of silicon dioxide of at least 99% relative to the total mass of the glass, and containing less than 15 ppm of typical impurities, such as Al, Ca, Cu, Fe, Na, K, Li, and Mg.

[0022] As an alternative to or in addition to fused silica glass particles, any other type of glass particles can be used in the present invention without limitation.

[0023] In the present invention, the glass particles include spherical glass particles having diameters in the range of 5 nm to 400 nm, preferably 7 nm to 400 nm, more preferably 10 nm to 200 nm, and even more preferably 50 nm to 100 nm. These glass particles are also referred to as "first type glass particles" in this specification. The first type glass particles having diameters in the nanometer range make a composite comprising an organic thermoplastic binder matrix and glass particles dispersed therein into a nanocomposite.

[0024] In the present invention, the glass particles can further include spherical glass particles having a diameter in the range of 2 μm to 50 μm, preferably in the range of 2 μm to 40 μm. These glass particles are also referred to herein as "second-type glass particles." When the glass particles include a first-type glass particle and a second-type glass particle, i.e., a bimodal mixture of glass particles, the smaller-sized glass particles can fill the gaps between the larger-sized glass particles. This achieves a denser packing of the glass particles. This, in turn, results in less shrinkage during sintering in step (f), as further explained below. In principle, the glass particles can further include any other type of glass particle having a diameter different from the diameters of the first-type glass particle and the second-type glass particle. Such multimodal mixtures of glass particles are also within the scope of the present invention.

[0025] In this specification, the diameter of the first, second, and any other type of glass particles is understood to be the average diameter measured in accordance with ISO 9276-2. The term "spherical" is also understood to encompass spheroidal glass particles, i.e., glass particles having a sphere-like geometric shape. For example, for the first type of glass particles having a diameter in the range of 5 nm to 400 nm, this means that these glass particles may not substantially have dimensions less than 5 nm in diameter and may not substantially have dimensions greater than 400 nm in diameter.

[0026] Although not limited thereto, the content of glass particles in the nanocomposite is at least 5 parts by volume, preferably at least 30 parts by volume, and more preferably at least 50 parts by volume, per 100 parts by volume of organic thermoplastic binder matrix. The higher the content of glass particles in the nanocomposite, the more densely packed the glass particles will be in the resulting transparent glass article. The inventors have surprisingly discovered that even if the content of glass particles in the nanocomposite relative to the organic thermoplastic binder matrix is ​​significantly higher, for example, 55 parts by volume or more per 100 parts by volume of organic thermoplastic binder matrix, it is still possible to reshape the nanocomposite in step (b), as further described below. The upper limit of the content of glass particles in the nanocomposite is not particularly limited, and is preferably 75 parts by volume or less, more preferably 70 parts by volume or less, and most preferably 60 parts by volume or less, per 100 parts by volume of organic thermoplastic binder matrix. Therefore, the content of glass particles in the nanocomposite is preferably 30 to 75 parts by volume, more preferably 50 to 70 parts by volume, and most preferably 55 to 60 parts by volume, per 100 parts by volume of the organic thermoplastic binder matrix.

[0027] In addition to the organic thermoplastic binder matrix and glass particles dispersed therein, the nanocomposite may optionally include one or more additional agents that facilitate the manufacture of the resulting transparent glass article.

[0028] For example, a dispersing agent can be added to facilitate dispersion of the glass particles in the organic thermoplastic binder matrix. Examples of dispersing agents include, but are not limited to, nonionic surfactants, such as polyoxyethylene alkyl ethers or polyoxymethylenes, and anionic surfactants, such as fatty acids and their salts or aliphatic carboxylic acids and their salts, such as stearic acid and its salts or oleic acid and its salts. However, the nanocomposite preferably does not contain any such dispersing agents or any solvents.

[0029] To facilitate debinding of the primary structure in step (d), according to a preferred embodiment of the present invention, the nanocomposite further comprises a phase former dispersed in the organic thermoplastic binder matrix. The phase former, which is solid or viscous at room temperature, forms an internal phase in the organic thermoplastic binder matrix. Examples of phase formers include alcohols, ethers, and silicone oils, as well as combinations thereof. These substances have a sufficiently high molecular weight and / or appropriate functional groups so as to be solid or viscous at room temperature. As used herein, the term "viscous" is understood to mean a viscosity at room temperature of at least 5 mPa·s, as measured according to DIN 53019. The phase former can be removed from the organic thermoplastic binder matrix before or during debinding of the primary structure in step (d), for example, by a heat treatment that results in evaporation or sublimation of the phase former or decomposition of the phase former, as described further below. Furthermore, the phase former can also be removed by solvent extraction.

[0030] A specific example of a phase former is phenoxyethanol. Phenoxyethanol has a viscosity of approximately 30 mPa·s at room temperature, making it a viscous substance. Phenoxyethanol can evaporate at atmospheric pressure at a temperature of 242°C. However, due to its high vapor pressure, a significant amount is already removed at lower temperatures. A preferred example of a phase former is polyethylene glycol (PEG). Thus, in a preferred embodiment of the present invention, the nanocomposite comprises an organic thermoplastic binder matrix, such as poly(vinyl butyral), glass particles, and a phase former, such as poly(ethylene glycol), the latter two components dispersed in the organic thermoplastic binder matrix, where at least one phase former is solid or viscous at room temperature.

[0031] The molecular weight (polymer chain length) of polyethylene glycol (PEG) used as a phase former is not particularly limited as long as the phase former is solid or viscous at room temperature. Preferred examples of PEG include low-molecular-weight PEGs, such as commercially available products PEG300 to PEG20000, preferably PEG400 to PEG10000.

[0032] In step (b) of the method for producing the above-defined transparent glass article, an external stimulus (indicated by an arrow in FIG. 1(b)) is applied to the nanocomposite, which allows the nanocomposite to be reshaped. Since the nanocomposite prepared in step (a) of the method for producing the above-defined transparent glass article does not contain any solvents, etc., but only contains a solid organic thermoplastic binder matrix together with glass particles and any phase former, according to the present invention, there is no need to perform any drying process to remove any solvents, such as water.

[0033] According to the present invention, the external stimulus may be any stimulus capable of reshaping the nanocomposite, but is not limited thereto. To achieve this, the external stimulus must soften, e.g., partially or completely melt, the organic thermoplastic binder matrix, thereby enabling the nanocomposite, including the organic thermoplastic binder matrix and the glass particles dispersed therein, to be shaped in a desired manner. Typically, the external stimulus is heat or radiation, preferably heat. Suitable means for applying the external stimulus to the nanocomposite are known to those skilled in the art and are applied conventionally depending on the organic thermoplastic binder matrix. Once the nanocomposite is reshapeable, the external stimulus may be further applied to the extent that the organic thermoplastic binder matrix remains softened and does not immediately resolidify. As will be further described below, when a mold-based replication process is used in step (c), the external stimulus may be applied to the nanocomposite via the mold. That is, the mold transfers the energy provided by the external stimulus to the organic thermoplastic binder matrix in the nanocomposite.

[0034] As mentioned above, the external stimulus may be any stimulus that can render the nanocomposite remoldable, but is not limited thereto. To achieve this, the external stimulus must be capable of softening the organic thermoplastic binder matrix. For example, if the external stimulus is heat, a heat source having an appropriate temperature and sufficient energy density to soften the organic thermoplastic binder matrix can be used. Furthermore, if the external stimulus is radiation, a radiation source having an appropriate wavelength and sufficient energy density to soften the organic thermoplastic binder matrix can be used. Naturally, the conditions applied to render the nanocomposite remoldable depend on the organic thermoplastic binder matrix used. The temperature required to render the nanocomposite remoldable is typically less than 400°C, preferably less than 200°C, and particularly preferably less than 150°C. Because the organic thermoplastic binder matrix must be solid at room temperature, the temperature required to render the nanocomposite remoldable is greater than 25°C, typically greater than 40°C.

[0035] In step (c) of the method for producing a transparent glass article as defined above, the nanocomposite is reshaped into a predetermined shape, thereby obtaining a primary structure, also called a green compact. The predetermined shape into which the nanocomposite is reshaped in step (c) already reflects the shape of the resulting transparent glass article.

[0036] According to the present invention, the reshaping of the nanocomposite in step (c) is not limited to any specific method, as long as the nanocomposite can obtain a predetermined shape. In step (c), the nanocomposite is preferably reshaped into a predetermined shape by injection molding, extrusion molding, or blow molding, each of which can be considered a replication process. Other exemplary replication processes for reshaping the nanocomposite in step (c) include hot embossing, thermoforming, calendaring, hot and cold pressing, or injection compression molding. These replication processes can be performed at relatively low temperatures because they only require softening of the organic thermoplastic binder matrix, not the glass particles. Therefore, the present invention allows high-throughput replication of transparent glass articles, which facilitates industrial scale-up of the production of transparent glass articles. According to the present invention, the term "reshaping" does not imply the presence of a mold in step (c) to obtain a primary structure having a predetermined shape. It is also contemplated herein that the nanocomposite can be reshaped into a predetermined shape in step (c) by, but not limited to, extrusion-based additive manufacturing, for example, fused deposition modeling.

[0037] If necessary, the primary structure obtained in step (c) may be subjected to post-processing. For example, if the primary structure has visible artifacts resulting from the replication process and the mold used therein, such post-processing may be readily applied. Suitable means for post-processing are known to those skilled in the art and include, but are not limited to, drilling, sawing, milling, turning, grinding and polishing. In principle, any type of additive or subtractive post-processing may be applied.

[0038] In step (d) of the method for producing a transparent glass article as defined above, the primary structure is degreased by removing the organic thermoplastic binder matrix, resulting in a secondary structure, also referred to as a degreased body. As a result of the degreasing, i.e., removal of the organic thermoplastic binder matrix, the secondary structure has voids formed therein.

[0039] Depending on the organic thermoplastic binder matrix, the primary structure can be degreased in step (d) by heat treatment, chemical reaction, reduced pressure, solvent extraction, or a combination thereof. For example, before heat treatment, the primary structure can be first immersed in a solvent to perform solvent extraction. In principle, any means can be applied that can remove the organic thermoplastic binder matrix without adversely affecting the glass particles that make up the secondary structure. In this context, those skilled in the art will routinely select appropriate conditions to apply to remove the organic thermoplastic binder matrix in step (d).

[0040] For example, when debinding is performed by heat treatment, the applied temperature is typically in the range of 150°C to 600°C. The heating rate is typically in the range of 0.1°C / min to 2°C / min, e.g., 0.5°C / min to 1°C / min. The holding time depends on the size of the resulting transparent glass article, but typically ranges from 2 minutes to 10 hours. If the size is quite small, even a few seconds may be sufficient to debinding the primary structure in step (d). The heat treatment can also be carried out in stages. In accordance with the above considerations, debinding by heat treatment can be further facilitated by reduced pressure, i.e., a pressure lower than atmospheric pressure, which makes the organic thermoplastic binder matrix more volatile.

[0041] After removal of the organic thermoplastic binder matrix, the glass particles are bonded together by hydrogen bonds, which provide mechanical stability to the secondary structure. Considering the size of the glass particles, which have diameters in the nanometer range, the glass particles have a large specific surface area, which allows sufficient interactions to keep the secondary structure mechanically stable.

[0042] Before or during removal of the organic thermoplastic binder matrix in step (d), the phase former, if present, is removed from the primary structure, for example by evaporation or sublimation, or by decomposition. Removal of the phase former, if present, can also be achieved by solvent extraction. In principle, the same measures as those described above in connection with the removal of the organic thermoplastic binder matrix can be applied.

[0043] When a phase former is present, removal of the phase former facilitates debinding of the primary structure in step (d). This is because removal of the internal phase in the organic thermoplastic binder matrix formed by the phase former creates pores in the primary structure. The remaining organic thermoplastic binder matrix can then be removed in a more controlled manner through these pores. This makes the secondary structure less susceptible to damage, especially when thick structures, such as 1.0 mm or thicker, are employed.

[0044] In step (e) of the method for producing the transparent glass article defined above, the voids of the secondary structure can be filled with at least one additive. According to the present invention, step (e) is optional. The at least one additive, also called a filler, must have an appropriate particle size so that it can be introduced into the voids formed in the secondary structure. In this specification, the at least one additive is not further limited and can be selected appropriately.

[0045] For example, at least one additive can be selected from pigments, such as gold(III) chloride (AuCl) or chromium(III) nitrate (Cr(NO)), to impart a particular color to the resulting transparent glass article. As explained further below, the secondary structures are exposed to fairly high temperatures during sintering in step (f), and the pigments must be able to withstand these temperatures. Therefore, inorganic pigments such as those described above are preferred over organic pigments, which tend to decompose when heated to the fairly high temperatures applied during sintering.

[0046] Typically, to impart particular optical properties to the resulting transparent glass article, the at least one additive can be selected from doping agents that decompose upon sintering in step (f) to yield dopants such as Ti, F, Na, K, Ca, Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Pm, Sm, Sc, Tb, Tm, Yb, Y, Ge, Pb, Ba, Zr, Zn, Al, and Mg, as further described below. Suitable doping agents are known to those skilled in the art.

[0047] To increase the density of the resulting transparent glass article, at least one additive can be selected from glass precursors, such as silicon-based precursors, such as tetraethyl orthosilicate (Si(OC2H5)4), also known as TEOS. In particular, glass precursors that form glasses indistinguishable from those of the glass particles in the nanocomposite can be used herein, but glass precursors that form glasses different from those of the glass particles in the nanocomposite can also be used herein. For example, when the nanocomposite contains fused silica glass particles as the glass particles, titanium-based precursors, such as tetraethyl orthotitanate (Ti(OC2H5)4), can also be used. Other metal alkoxides that can be used herein include titanium isopropoxide, titanium ethoxide, zirconium ethoxide, aluminum isopropoxide, vanadyl isopropoxide, niobium ethoxide, tantalum ethoxide, and potassium tert-butoxide. Further suitable glass precursors are known to those skilled in the art and can be used herein as well.

[0048] As further described below, in step (f), the glass particles and optional additives are converted into a dense glass during sintering of the secondary structure to form a transparent glass article. Filling the secondary structure with a glass precursor can reduce shrinkage of the secondary structure during sintering.

[0049] When the glass particles in the nanocomposite are fused silica glass particles and the voids in the secondary structure are filled with a silicon-based precursor such as TEOS, a transparent glass article formed from high-purity fused silica glass having a density equivalent to that of fused silica glass processed by conventional methods can be obtained.Even if the secondary structure is not filled with a glass precursor in step (e), the transparent glass article obtained after sintering has an optical transmittance in the wavelength range of 200 nm to 1000 nm and a Vickers hardness equivalent to that of fused silica glass processed by conventional methods.

[0050] In step (e), the voids of the secondary structure can be filled with at least one additive by immersing the secondary structure in a solution containing at least one additive, by exposing the secondary structure to physical vapor deposition or chemical vapor deposition in an atmosphere containing or generating at least one additive, or by a combination thereof. However, in principle, any other filling process can be applied in this regard as well. For example, a sol-gel process can also be applied.

[0051] Optionally, the voids of the secondary structure can be filled with at least one additive even before the debinding of the primary structure is complete, in which case the at least one additive is filled into the partially debound primary structure.

[0052] Depending on the at least one additive to be filled into the voids of the secondary structure in step (e), the secondary structure may first be immersed in a solution containing the at least one additive, e.g., a pigment, and then exposed to physical vapor deposition or chemical vapor deposition containing or producing the at least one additive, e.g., a glass precursor.

[0053] In step (f) of the method for producing a transparent glass article as defined above, the secondary structure is sintered, thereby obtaining a transparent glass article.

[0054] Appropriate sintering conditions are known to those skilled in the art and are selected routinely as appropriate. For example, the temperature applied is typically in the range of 700°C to 1500°C. The heating rate is typically in the range of 1°C / min to 10°C / min, for example, 5°C / min. The holding time depends on the size of the resulting transparent glass article, but is typically in the range of 0.5 hours to 4 hours. When the doping reagent and / or glass precursor is filled into the voids of the secondary structure in step (e), the secondary structure can be pre-sintered at an intermediate temperature to decompose it or convert it into glass. For example, pre-sintering can be performed at a temperature in the range of 400°C to 700°C.

[0055] In this specification, sintering does not require the application of pressure. On the contrary, the sintering in step (f) can be suitably carried out at a pressure lower than atmospheric pressure, for example, at a pressure of at most 0.1 mbar, preferably at a pressure of at most 0.01 mbar, particularly preferably at a pressure of at most 0.001 mbar. Since sintering can be carried out at atmospheric pressure or even lower pressure, there are no specific requirements to be met in the present invention regarding the sintering furnace.

[0056] After sintering, the resulting transparent glass article can be cooled to room temperature. When the glass particles in the nanocomposite are fused silica glass particles, both a relatively high heating rate and a relatively high cooling rate can be selected, taking into account the low thermal expansion coefficient and high thermal shock resistance of fused silica glass.

[0057] The transparent glass article obtainable by the manufacturing method of the present invention is characterized by a light transmittance of more than 70%, preferably more than 85%, and particularly preferably more than 90% in the wavelength range of 200 nm to 1000 nm for a layer thickness of 1.0 mm. It should be noted that the transparent glass article obtainable by the manufacturing method of the present invention is not limited to ultrathin glass sheets. In a preferred embodiment, the transparent glass article has a thickness of at least 0.5 mm, preferably at least 0.6 mm, more preferably at least 0.8 mm, and most preferably at least 1.0 mm. The transparent glass article can also have a thickness of up to 500 mm, preferably up to 100 mm. Furthermore, the transparent glass article obtainable by the manufacturing method of the present invention is characterized by a Vickers hardness of more than 700 HV, measured according to DIN EN ISO 6507. Therefore, the material properties of the transparent glass article obtainable by the manufacturing method of the present invention meet the standards that fused silica glass must meet for many applications.

[0058] The transparent glass article obtainable by the method for manufacturing a transparent glass article according to the present invention can be used for various applications. For example, the transparent glass article can be applied in the optical field, for example, as a substrate for a lens. Due to the specific process steps of the manufacturing method according to the present invention, the transparent glass article according to the present invention can be easily manufactured by a replication process that can be expanded to an industrial scale.

[0059] Advantageously, based on the organic thermoplastic binder matrix used in the present invention, which is solid at room temperature and capable of dispersing large amounts of glass particles, the present invention enables for the first time the formation of transparent glass into glass articles by low-temperature replication processes such as injection molding, thereby achieving high-throughput replication of the resulting transparent glass articles, which is not possible with processes established in the art. [Brief explanation of the drawings]

[0060] [Figure 1]1 is a diagram illustrating steps (a) to (f) of a method for producing a transparent glass article according to the present invention. In step (a), a nanocomposite is prepared. In step (b), an external stimulus is applied to the nanocomposite to make it reshapeable. In step (c), the nanocomposite is reshaped into a predetermined shape to obtain a primary structure. In step (d), the primary structure is degreased to obtain a secondary structure having voids formed therein. In optional step (e), the voids in the secondary structure are filled with at least one additive. Then, in step (f), the secondary structure is sintered to obtain a transparent glass article. [Figure 2] 1A and 1B are photographs of (a) a nanocomposite, (b) a green compact, and (c) a transparent glass article obtained in Example 1 described below. [Figure 3] 1 is a graph showing the light transmittance spectrum of the transparent glass article obtained in Example 1 described below, together with the light transmittance spectrum of a commercially available transparent glass article for comparison. [Figure 4] 1 is a photograph of the glass article obtained in Example 4 described below. [Figure 5] 1 is a photograph of a glass article obtained in Comparative Example 1 described below. [Figure 6] 1A is a photograph of a glass article obtained in Comparative Example 2, which will be described below, and FIG. 1B is a graph showing a light transmittance spectrum thereof. [Figure 7] 1A is a photograph of a glass article obtained in Comparative Example 3, which will be described below, and FIG. 1B is a graph showing a light transmittance spectrum thereof. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0061] The present invention is further illustrated by the following examples, but is not limited thereto.

[0062] Example 1 Injection molding of nanocomposites containing fused silica glass particles Variation 1 (premixing of fused silica glass particles with an organic thermoplastic binder): 25 g of fused silica glass particles with an average diameter of 50 nm to 100 nm were dispersed in a solution of 6 g of poly(vinyl butyral) and 6 g of poly(ethylene glycol) (PEG 1500) in 60 mL of tetrahydrofuran using a laboratory dissolver. The mixture was then dried in an oven at 70 °C to yield a nanocomposite comprising an organic thermoplastic binder matrix and silica glass particles dispersed therein.

[0063] Variation 2 (premixing of fused silica glass particles with an organic thermoplastic binder): 25 g of fused silica glass particles with an average diameter of 50 nm to 100 nm were dispersed in a solution of 6 g of poly(ethylene glycol) (PEG 1500) in 60 mL of water using a laboratory dissolver. This mixture was then dried in an oven at 70 °C. After grinding, the dried mixture was mixed with 6 g of poly(vinyl butyral) using a twin-screw mini-kneader to obtain a nanocomposite containing an organic thermoplastic binder matrix and silica glass particles dispersed therein.

[0064] The nanocomposite obtained in Variation 2 shown in Figure 2(a) was injection molded using a small injection molding machine (DSM's X-Plore) at a temperature of 130°C and a pressure of 8 bar for 4 seconds. The holding pressure was 8 bar. The mold of the small injection molding machine was set to a temperature of 55°C to maintain the nanocomposite in a remoldable state. By injection molding the nanocomposite, a green compact having the desired shape was obtained.

[0065] The resulting green compact shown in FIG. 2(b) was then immersed in water at 40° C. for 4 hours to remove the poly(ethylene glycol) used as the phase former by solvent extraction.

[0066] The organic thermoplastic binder matrix of the immersed powder compact was then removed by thermal debinding using the following protocol to obtain a debound body. Heating rate: 0.5℃ / min: 25℃→150℃ Holding time: 4 hours Heating rate: 0.5℃ / min: 150℃→280℃ Holding time: 4 hours Heating rate: 1℃ / min: 280℃→600℃ Holding time: 2 hours Cooling rate: 5℃ / min: 600℃ → 25℃ End

[0067] The resulting degreased body was then sintered to full density under vacuum at a residual pressure of 0.001 mbar, to obtain a transparent glass article, applying the following protocol. Heating rate: 5℃ / min: 25℃→1300℃ Holding time: 2 hours Cooling rate: 5℃ / min: 1300℃ → 25℃ End

[0068] The resulting transparent glass article, shown in Figure 2(c), was formed from fully dense fused silica glass. Specifically, the light transmittance of the transparent glass article at a layer thickness of 1.0 mm in the wavelength range of 300 nm to 400 nm was greater than 85%. As can be seen from the light transmittance spectrum shown in Figure 3, the light transmittance of the transparent glass article obtained by injection molding in Example 1 ("injection-molded glass") was comparable to that of a commercially available transparent glass article formed from fused silica ("fused silica glass").

[0069] Example 2 Continuous extrusion of nanocomposites containing fused silica glass particles 25 g of fused silica glass particles with an average diameter of 50 nm to 100 nm were dispersed in a mixture of 6 g of poly(vinyl butyral) and 6 g of poly(ethylene glycol) (PEG4000) using a twin-screw mini-kneader to obtain a nanocomposite containing an organic thermoplastic binder matrix and silica glass particles dispersed therein.

[0070] The resulting nanocomposite was extruded using a capillary rheometer equipped with an annular gap nozzle with an outer diameter of 16 mm and an inner diameter of 15 mm. The temperature was set at 130 °C, and the nanocomposite, which contained a molten organic thermoplastic binder matrix and glass particles dispersed therein, was continuously extruded at a piston speed of 1 mm / s. A continuous tubular compact was obtained by extrusion through the annular gap nozzle.

[0071] The resulting tubular green compact was then immersed in water at 40° C. for 4 hours to remove the poly(ethylene glycol) used as the phase former by solvent extraction.

[0072] The organic thermoplastic binder matrix of the immersed tubular compact was then removed by thermal debinding using the following protocol to obtain a continuous tubular debound body. Heating rate: 0.5℃ / min: 25℃→150℃ Holding time: 4 hours Heating rate: 0.5℃ / min: 150℃→280℃ Holding time: 4 hours Heating rate: 1℃ / min: 280℃→600℃ Holding time: 2 hours Cooling rate: 5℃ / min: 600℃ → 25℃ End

[0073] The resulting tubular debound bodies were then sintered to full density under vacuum at a residual pressure of 0.001 mbar applying the following protocol. Heating rate: 5℃ / min: 25℃→1300℃ Holding time: 2 hours Cooling rate: 5℃ / min: 1300℃ → 25℃ End

[0074] In this way, a transparent fused silica glass tube was obtained.

[0075] Example 3 Fabrication of injection-molded binary-doped fused silica glass. The green compact obtained by injection molding in Example 1 was partially degreased by immersion in water at 40°C for 4 hours. The partially degreased green compact was then immersed in a 25 mM Eu(NO3)3 aqueous solution and a 10 mM Ce(NO3)3 aqueous solution for 24 hours, respectively. The partially degreased and immersed green compact was then dried at 70°C.

[0076] The organic thermoplastic binder matrix of the immersed powder compact was then removed by thermal debinding using the following protocol to obtain a debound body. Heating rate: 0.5℃ / min: 25℃→150℃ Holding time: 4 hours Heating rate: 0.5℃ / min: 150℃→280℃ Holding time: 4 hours Heating rate: 1℃ / min: 280℃→600℃ Holding time: 2 hours Cooling rate: 5℃ / min: 600℃ → 25℃ End

[0077] The resulting debound bodies were then sintered to full density under vacuum at a residual pressure of 0.001 mbar applying the following protocol. Heating rate: 5℃ / min: 25℃→1300℃ Holding time: 2 hours Cooling rate: 5℃ / min: 1300℃ → 25℃ End

[0078] As a result, a transparent and colorless fused silica glass article was obtained. This fused silica glass article emitted fluorescence when irradiated with ultraviolet light of 254 nm (Eu 3+ produces red fluorescence, and Ce 3+ produces blue fluorescence).

[0079] Example 4 Effect of phase formers on the production of injection-molded fused silica glass. Twenty-one grams of fused silica glass particles with an average diameter of 90 nm were dispersed in a solution of 2.06 g of poly(ethylene glycol) (PEG1500) and 8.01 g of poly(vinyl butyral) in 72 g of acetone using a laboratory dissolver. The mixture was then dried in an oven at 70°C to yield a nanocomposite with a low content of phase former (9 wt% of the total raw materials).

[0080] Twenty-one grams of fused silica glass particles with an average diameter of 90 nm were dispersed in a solution of 5.15 g of poly(ethylene glycol) (PEG1500) and 5.02 g of poly(vinyl butyral) in 45 g of acetone using a laboratory dissolver. The mixture was then dried in an oven at 70°C to obtain a nanocomposite with a sufficiently high content of phase former (17 wt% of the total raw materials).

[0081] The resulting nanocomposites containing high and low amounts of phase former were injection molded using a small injection molding machine (DSM X-Plore) at a temperature of 130°C and a pressure of 8 bar for 4 seconds. The holding pressure was 8 bar. The mold of the small injection molding machine was set at a temperature of 55°C to keep the nanocomposite remoldable. By injection molding the nanocomposite, a green compact with the desired shape was obtained.

[0082] The resulting green compact was then immersed in water at 40° C. for 4 hours to remove the poly(ethylene glycol) used as the phase former by solvent extraction.

[0083] The organic thermoplastic binder matrix of the immersed powder compact was then removed by thermal debinding using the following protocol to obtain a debound body. Heating rate: 0.5℃ / min: 25℃→150℃ Holding time: 4 hours Heating rate: 0.5℃ / min: 150℃→280℃ Holding time: 4 hours Heating rate: 1℃ / min: 280℃→600℃ Holding time: 2 hours Cooling rate: 5℃ / min: 600℃ → 25℃ End

[0084] The resulting degreased body was then sintered under vacuum at a residual pressure of 0.001 mbar, to obtain a transparent glass article, applying the following protocol: Heating rate: 5℃ / min: 25℃→1300℃ Holding time: 2 hours Cooling rate: 5℃ / min: 1300℃ → 25℃ End

[0085] The resulting glass articles, both of which had a thickness of 2.0 mm, are shown in Figure 4. As can be seen from Figure 4, the glass article obtained using a small amount of phase former cracked during degreasing, while the glass article obtained using a larger amount of phase former showed no cracks.

[0086] Comparative Examples 1 to 3 Variation in glass particle size In Comparative Examples 1 to 3, the following glass types were used to produce nanocomposites. Glass type 1 G018-354 (Schott) SiO2 (10% to 50% by weight), Al2O3 (1% to 10% by weight), Y2O3 (1% to 10% by weight), B2O3 (1% to 10% by weight), MgO (1% to 10% by weight), BaO (over 50% by weight) Average diameter d 50 = 3 μm Glass type 2 GM31107 (Schott) SiO2 (1% to 10% by weight), Al2O3 (10.50% by weight), CaO (1% to 10% by weight), B2O3 (10% to 50% by weight), BaO (over 50% by weight) Average diameter d 50 = 3 μm Glass type 3 Duran 8330 (Schott) SiO2 (over 50 wt%), Al2O3 (1 wt% to 10 wt%), K2O (0.1 wt% to 1 wt%), B2O3 (10 wt% to 50 wt%), Na2O (1 wt% to 10 wt%), NaCl (1 wt% to 10 wt%) Average diameter d 50 =700nm

[0087] Using a laboratory dissolver, the given amounts of each glass type listed in the table below were dispersed in a thermoplastic binder consisting of poly(hydroxyethyl methacrylate) (obtained by photo-induced radical polymerization of 15 ml of hydroxyethyl methyl acrylate using 2,2-dimethoxy-2-phenylacetophenone as the initiator) and phenoxyethanol (5 ml). Green sheets with thicknesses ranging from 400 μm to 1000 μm were obtained from this thermoplastic nanocomposite.

[0088] [Table 1]

[0089] The organic thermoplastic binder matrix of the compact was then removed by thermal debinding using the following protocol to obtain a debound body (glass type 3) or dense sintered glass parts (glass types 1 and 2). Heating rate: 0.5℃ / min: 25℃→150℃ Holding time: 4 hours Heating rate: 0.5℃ / min: 150℃→280℃ Holding time: 4 hours Heating rate: 1℃ / min: 280℃→600℃ Holding time: 2 hours Cooling rate: 5℃ / min: 600℃ → 25℃ End

[0090] The resulting degreased body of glass type 3 was then sintered under atmospheric pressure using the following protocol to obtain a dense glass article. Glass Type 3: Heating rate: 5℃ / min: 25℃→800℃ Holding time: 1 hour Cooling rate: 5℃ / min: 800℃ → 25℃ End

[0091] The resulting glass article of Comparative Example 1, using glass type 1 and having a thickness of 400 μm, is shown in Figure 5. As can be seen from Figure 5, the glass article of Comparative Example 1 is not transparent.

[0092] The resulting glass articles of Comparative Example 2, using Glass Type 2 and having a thickness of 340 μm, are shown in Figure 6a. As can be seen from Figure 6a, none of the resulting glass articles of Comparative Example 2 are transparent. Specifically, as can be seen from the light transmittance spectrum shown in Figure 6b, the light transmittance of the glass articles in the wavelength range of 200 nm to 1000 nm is less than 15%.

[0093] By using glass type 3 with an average diameter of 700 nm in Comparative Example 3, it is clear that glass particles with this diameter also do not produce a transparent glass article, even though the glass sheet has a thickness of 175 μm, as shown on the left side of Figure 7a. Specifically, as can be seen from the light transmittance spectrum shown in Figure 7b, the light transmittance of the glass article with a thickness of 175 μm is less than 30% in the wavelength range of 200 nm to 1000 nm. The light transmittance of the glass article with a thickness of 480 μm is a maximum of about 10% in the wavelength range of 200 nm to 1000 nm, while the glass article with a thickness of 1.0 mm shows essentially no transmission.

Claims

1. The following steps (a) to (d) and step (f): (a) providing a nanocomposite comprising an organic thermoplastic binder matrix that is solid at room temperature and glass particles dispersed therein; (b) applying an external stimulus to the nanocomposite to render the nanocomposite reshapeable; (c) reforming the nanocomposite into a predetermined shape to obtain a primary structure; (d) degreasing the primary structure by removing the organic thermoplastic binder matrix to obtain a secondary structure having voids formed therein; (f) obtaining a transparent glass article by sintering the secondary structure; 1. A method for producing a transparent glass article, comprising: The glass particles include spherical glass particles having an average diameter measured in accordance with ISO 9276-2 in the range of 5 nm to less than 100 nm, the nanocomposite further comprises at least one phase former dispersed in the organic thermoplastic binder matrix and does not comprise water as a solvent; the phase former is solid or viscous at room temperature and forms an internal phase in the organic thermoplastic binder matrix; and The thickness of the transparent glass article is 1.0 mm or more. Manufacturing method.

2. The method of claim 1 , wherein the nanocomposite provided in step (a) is in granular form.

3. 3. The process of claim 1 or 2, wherein the organic thermoplastic binder matrix is ​​composed of polyesters based on aromatic or aliphatic dicarboxylic acids and diols and / or hydroxycarboxylic acids, polycarbonates based on aliphatic or aromatic diols, polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, polyisobutene, ethylene propylene rubber (EPR) and poly(vinyl butyral), cycloolefin polymers and polyamides, polyethers or polyurethanes including aromatic polyethers based on bisphenols, or combinations thereof.

4. The method according to any one of claims 1 to 3, wherein the glass particles are fused silica glass particles.

5. The method according to any one of claims 1 to 4, wherein the spherical glass particles have an average diameter measured in accordance with ISO 9276-2 in the range of 50 nm or more and less than 100 nm.

6. The method according to any one of claims 1 to 5, wherein the glass particles further comprise spherical glass particles having an average diameter measured in accordance with ISO 9276-2 in the range of 2 µm to 40 µm.

7. The method according to any one of claims 1 to 6, wherein the content of the glass particles in the nanocomposite is at least 30 parts by volume per 100 parts by volume of the organic thermoplastic binder matrix.

8. The process according to any one of claims 1 to 7, wherein the at least one phase former is selected from the group consisting of polyethylene glycol (PEG).

9. The method according to any one of claims 1 to 8, wherein in step (c), the nanocomposite is reshaped into a predetermined shape by injection molding, extrusion molding or blow molding.

10. The method according to any one of claims 1 to 9, wherein the primary structure obtained in step (c) is subjected to one of drilling, sawing, milling, turning, grinding and polishing as post-processing.

11. The method according to any one of claims 1 to 10, wherein in step (d), the primary structure is degreased by heat treatment, chemical reaction, reduced pressure, solvent extraction, or a combination thereof.

12. The method according to any one of claims 1 to 11, comprising, between step (d) and step (f), step (e) of filling the voids of the secondary structure obtained in step (d) with at least one additive.

13. The method of claim 12 , wherein the at least one additive is selected from pigments, doping agents, and glass precursors.

14. 14. The manufacturing method according to claim 12 or 13, wherein in step (e), the voids of the secondary structure are filled with the at least one additive by immersing the secondary structure in a solution containing the at least one additive, exposing the secondary structure to physical vapor deposition or chemical vapor deposition in an atmosphere containing or producing the at least one additive, or a combination thereof.

15. 15. The method according to any one of claims 1 to 14, wherein the transparent glass article has a light transmittance of more than 70% in the wavelength range of 200 nm to 1000 nm for a layer thickness of 1.0 mm, and a Vickers hardness of more than 700 HV measured in accordance with DIN EN ISO 6507.

Images