WO2017187200A1

WO2017187200A1 - Process for producing frits

Info

Publication number: WO2017187200A1
Application number: PCT/GB2017/051215
Authority: WO
Inventors: Simon BRIGHAM
Original assignee: Glassflake Ltd
Priority date: 2016-04-29
Filing date: 2017-04-28
Publication date: 2017-11-02
Also published as: GB201607544D0; GB2596023A8; GB201819465D0; GB2589270B8; GB2589270A8; GB2596023B; GB202113897D0; GB2596023A; GB2596023B8; GB202101798D0; GB2565705A; GB2589270A; GB2565705B; GB2589270B

Abstract

The present invention relates to a method of producing a frit; the method comprising: milling a plurality of glass flakes to provide a frit, use of glassflake in the production of frit and frit obtained by the methods of the invention.

Description

Process for producing frits

[0001] This invention relates to a process for the production of frits. The process uses as a starting material glass flakes and takes less time, uses fewer resources and costs less than traditional methods.

BACKGROUND

[0002] Glass frits are homogeneous mixtures of inorganic materials which have been fused, quenched to form a gas and granulated. Frits are widely used in the production of glazes and enamels, they can be used as colourants (known as stains) to add to glass formulations and they can also be used to produce glasses and ceramics directly for use in the electronics industry.

[0003] Frits are often used to render soluble and hazardous compounds inert, by combining them with silica and/or other oxides. Thus, the use of frits allows the introduction of certain desired materials to change the appearance (e.g. colour or finish) of a glass based component or coating or to add functionality. Forming the desired material into a frit before glass formation can reduce the solubility of the material, allowing pre- reaction of materials that otherwise would not have time to react and be incorporated under the glass formation conditions. The use of frits also allows for even dispersion of the materials and can minimise the processing problems associated with the toxicity of certain materials, and importantly add colour and functionality. Frits allow for the formation of a homogenous glass that will exhibit the intended properties.

[0004] A frit is generally prepared by fusing a variety of minerals and metal oxides in a furnace and then rapidly quenching the molten material.

[0005] The desired raw materials are weighed out according to a specific theoretical composition. The composition is formulated in batches prior to the smelting process. Typically the batch consists of raw materials such as silica, fluorspar, soda ash, borax, feldspar, zircon, aluminium oxide, lithium carbonate, magnesium carbonate, and titanium oxide. Other oxides, metal oxides and inorganic materials may be introduced to give the desired properties for specific applications.

[0006] Typically the raw materials are blended to form a batch mix, the mixed charge or batch is fed directly into the melter; melters can be continuous or batch and are typically of the Rotary Kiln type, although chambers, tanks and tunnel kilns can and have been used. Melters, kilns or furnaces used for melting such materials typically operate at temperatures around 1050°C to 1450 °C, but the time and temperature varies significantly depending on the frit or glass composition. When smelting is complete, the molten material is cooled to a solid. Typically it is poured into a trough with a water stream where it solidifies and breaks up into chunks of between 3 and 15mm. Alternatively it is passed between water-cooled metal rollers that limit the thickness of the material to around 3mm and then quenched with a water spray that shatters the material into smaller glass particles referred to as unground frit. Alternatively the molten glass is dropped directly into a cooling bath to quench the molten glass and results in large chunks of material requiring significant further processing. All of these water quenching methods result in effluent which needs recycling or disposing of in a safe manner.

[0007] The frit can be supplied in the thus formed unground form however the large size and inconsistent morphology renders it useless for most applications. It is therefore highly desirable to further reduce the particle size of the frit. The particle size required depends upon the end use of the frit but is usually less than 30 microns and generally in the range of 2 to 12 microns. Ideally, for example, inorganic pigments for ceramics should not have particles less than 2 microns. In addition to this the particles need to have a narrow size distribution in order to have good diffused reflection; dependent on the colour and chemical stability. Therefore the process of particle reduction must be able to readily produce a defined particle size with a consistent narrow distribution. On the other hand, for functional materials, it may be desirable to have a particle of around 500 nanometres and the amount of grinding time required to achieve this can be very lengthy.

[0008] The current technology used to produce frits or coloured stains involves an intensive process to reduce the quenched glass from sizes ranging from tens of millimetres to a few microns or less. The technology used to reduce the particle size to a usable form from the precursor frit has not undergone major efficacy improvements for a significant time. To reduce the unground frit particle size to a more appropriate size for application, the fritted particles typically go through a multi-step process that can take more than 7 days to achieve a final product. In addition to size reduction, energy is required to dry frits at multi points during the process to make it ready for use in the next step.

[0009] A typical process involves the following procedure: after quenching, the frit is dried using heating and/or forced air. Typically rotary dryers are most commonly used for drying frit but drying beds and conveyors using radiant heat may also be used. Drying tables and stationary dryers are also employed for small batch materials.

[0010] After drying, the frit is typically passed through a crusher to bring the size to below 2mm and magnetic separation may be used to remove iron-bearing material that has been introduced as a contaminant via the reduction process. Typically the material is then transferred to a ball mill to reduce the particle size further, commonly to 1.0 mm. A further ball mill is then used typically to reduce the material to 0.2 mm milled by either wet or dry grinding processes or combination of both.

[0011] Typically the next stage is to further mill using a variety on milling operations such as ball mills, jet mills etc., to achieve a D90 of circa 8 microns.

[0012] The present methods of frit production are environmentally unsound for other reasons in addition to the high energy usage.

[0013] The processes involve the formation of particulate pollution, arising during the melting and during the multi-step milling process due to the impact milling and the transfer of product between steps. These emissions of particulate matter (PM) can include particulate matter of less than 10 micrometers (PM-10). The emission can also contain condensed metallic oxide fumes that have volatilized from the molten charge, mineral dust and sometimes hydrogen fluoride.

[0014] A further environmental hazard is produced in traditional frit production in the form of water used in the quenching and milling processes are produced albeit often in closed systems. Usually however, these systems require purging to prevent build-up of salts or other contaminants resulting in an aqueous effluent requiring disposal. Also suspended particles and heavy metals dependent on the composition are contained within these waters and these need to be removed by solids separation techniques. This results in a solid effluent requiring disposal.

BRIEF SUMMARY OF THE DISCLOSURE

[0015] In a first aspect of the present invention there is provided a method of producing a frit; the method comprising:

milling a plurality of glass flakes to provide a frit.

[0016] A glass flake is a glass particle that has a largest transverse length that is larger than its thickness, e.g. a largest transverse length that is more than two times or more than three times, preferably more than five times as large as its thickness.

[0017] By using glass flakes produced using known methods, the process of becoming a frit becomes quicker and more energy efficient. A glass flake with a mean particle diameter between 5-500 microns and a mean thickness of 1-10 microns is already within the range of desired particle size for frits in many applications but it is in sheet form rather than in granular form. Such flakes typically require simply breaking up rather than extensive resizing. This can be achieved by conventional milling processes. The process also allows the production of uniformly and significant smaller size particles than that of conventionally made frit. [0018] Examples of milling methods useful in the methods of the invention include: a mortar and pestle, ball milling, planar milling, pressurised fluid milling, air jet milling, roll milling, spin milling, high speed revolution milling (e.g. using collision between particles and vessel pins or forcing the particles to pass through small holes at high energy), and bead milling. Dry milling processes are preferred. In most cases the required particle size can be obtained by a single step dry milling process optionally followed by sieving through an appropriate size sieve.

[0019] The method may comprise the step of passing the frit produced from the milling process (which may also comprise particles that are larger than desired) through a sieve to remove any particles that are larger than desired to provide a sieved frit. The size of the mesh of the sieve will be chosen as appropriate for the desired particle size of the frit. This will depend on the precise application to which the frit is to be put.

[0020] The preferred method is rotary ball milling, as other types of milling generally require particle to particle impact for size reduction. With particles that are already very small the kinetic energy imparted in the milling process can be insufficient to cause sufficient breakdown, particularly with flake/ granules that are produced having at least one dimension below 2 microns. The density of such small flakes is such that it is difficult to ensure that particle to particle impact is sufficient to reduce the dimension as desired in an efficient way. Ball mills which work on the principle of continuous direct impact on the flakes is more effective in reducing the flakes to granules and in reducing the granule size further. The preferred process is ball mill using a ceramic ball media.

[0021] Due to the substantially reduced precursor thickness, the milling processes required to produce a particle of a useable size are significantly reduced along with the number of steps and transfer operations required. The reduction in the number of transfer processes can lead to a reduction in the particulate matter released as emissions from the process plant. The surprisingly small amount of generated particulate matter may also arise from a change in fracture mechanics relative to the milling of larger non-flake like particles

[0022] The length of time of the milling process will depend on the size of the particles desired in the frit. The glass flakes may be milled for up to 48 hours in total. The glass flakes may be milled for up to 36 hours in total. The glass flakes may be milled for up to 24 hours in total. The glass flakes may be milled for up to 18 hours in total. The glass flakes may be milled for longer than 30 minutes in total. The glass flakes may be milled for longer than 1 hour in total. The glass flakes may be milled for longer than 2 hours in total. In this context, the term 'in total' is intended to mean that the mentioned length of time is the total length of time the glass flakes are milled, with said total being the sum of the lengths of time of all of the individual milling steps to which said flakes are subjected between formation of the flakes and arrival and the desired frit.

[0023] It may be that the glass flakes used in the methods of the invention are formed of the material that it is desired the frit be formed of. It may be that the glass flakes are coated with one or more components of the desired frit with the remaining components being comprised in the glass flakes. It may be that the glass flakes are milled along with one or more components of the desired frit with the remaining components being comprised in the glass flakes, although this is less preferred.

[0024] The process typically also comprises the step of forming the glass flakes.

[0025] Illustrative methods of forming glass flakes are described in WO88/08412 and WO2009/040520 (herein incorporated by reference in their entirety). For very thin flakes (i.e. those below 500 nm), the methods of WO2009/040520 are preferred.

[0026] The method of forming the glass flakes may comprise feeding a stream of molten glass into a spinning cup; and allowing the molten glass to emanate radially over the rim of said cup. The molten glass may pass over the rim in such a manner as to be forced into the gap between a pair of plates surrounding the cup, such movement of the molten glass being in a radial direction and effected by a flow of air passing between the plates so as to pull the stream of material in said radial direction in such manner as to keep it flat and also to pull it so that, as solidification of the molten glass occurs, the material is broken into flakes. Said cup may include an insulating means and/or it may include a means for heating the cup while it is rotating. The equipment may include a vessel for holding molten glass, said vessel being provided with a nozzle for controlling flow therefrom, wherein the distance between the control nozzle and the entry to the spinning cup. The equipment may be provided with plates forming an annular venturi and for receiving the film of molten glass. The equipment may include a means for applying an air pressure of from 180 to 580 mm water gauge. The equipment may include a means for providing a mass flow of the glass from a source thereof to the cup of between 0.4 and 4.5 kilograms of glass per minute, the glass temperature at the exit from said source being from 600 to 1800 °C and the glass temperature at the spinning cup being from 580 to 1580 °C dependent on the viscosity profile and melt characteristics of the frit composition. It may be that the following parameters are used: the mass flow of the glass from the vessel is between 0.5 and 4.5 kilograms of glass per minute, the glass temperature at the control nozzle is from 1200 to 1400°C and the glass temperature at the spinning cup is from 1080 to 1380°C.

[0027] Such methods not only accurately control the flake thickness, but also enables the flake cross-sectional dimensions to be controlled, from 10's of microns across to many 100's of microns across, with narrow size distributions. Such narrow size distributions of the starting flakes mean that the granule size of the resultant frit is likewise controlled, with the resultant granules having a likewise narrow size distribution.

[0028] The spinning cup methods of forming glass flakes and the milling of the resultant glass flakes do not involve any water quenching and therefore these combined processes involve neither energy consuming drying processes nor the generation of contaminated water.

[0029] An alternative method of forming the glass flakes is to pass molten glass through a bushing or nozzle to form a molten tube of glass, and passing air through the tube to expand the tube until it has the desired wall thickness. It may be that the distal end of the tube is allowed to close, in this case when the air is blown into the tube, bubbles of glass are formed. The bubbles are air cooled, solidified and carried away by a vacuum collector. A variant of this is where a tube is formed and drawn down towards a collection vessel or between two intermeshing rotating drums. The advantage of these glass bubble or tube methods is that they have lower production costs than the spinning cup method. The thickness of the flakes formed is more variable than the spinning cup method and the thicknesses of the flakes that can be obtained are limited to between about 2 μηι and about 15 μηι.

[0030] The composition of the glass flakes may be the same as the composition of the desired frit. Likewise, the composition of the molten glass may be the same as the composition of the desired frit. The frit, the glass flakes and/or the molten glass will typically comprise at least one of silica, fluorspar, soda ash, borax, feldspar, zircon, aluminium oxide, lithium carbonate, magnesium carbonate, and titanium oxide.

[0031] The molten glass may be selected from an aluminaborate glass; an aluminasilicate glass; a borate glass, a borosilicate glass, a fluoroborate; a fluorogermanate glass, a phosphate glass, and a silicate glass.

[0032] The flakes may be treated by coating with an additive. In the spinning cup method, the flakes may be treated by coating with an additive either as the material leaves the spinning cup or as it leaves the gap between the two plates. In the glass bubble method, the tube can be coated once it has expanded and/or the flakes can be coated before or after they are collected. The additive will typically be a desired component of the resultant frit.

[0033] The additives may be, for example, colourants such as metal oxides and complex inorganic pigments directly to the flakes during the forming process. As these are bonded to the precursor flakes they are retained in the frit that results from the milling process. This reduces the number of steps required in the manufacturing process and can overcome problems of transport vibration separation often observed with such materials manufactured by conventional processes.

[0034] Exemplary metal oxide colourants which can be used as additives to provide a coloured frit (a stain) include:

Fe2C>3 Yellow - Pink (Coordination VI)

Red - Brown (Coordination IV)

Cr₂C>3 Green

CuO Blue (Coordination VI)

Green (Coordination VI)

C03O4 - Blue (Coordination IV)

^Co° At about 900C Co₃0₄ decomposes to CoO and 0₂

MnC>2 - Brown

Mn₂0₃

NiO - Yellow - Purplish

Ni₂0₃

[0035] Where one or more component of the desired frit is added as an additive coating to the flakes or where one or more component of the desired frit is mixed with the glass flakes at the milling stage, the molten glass will typically comprise all the remaining components of the desired frit but not the one or more components of the frit that are subsequently added.

[0036] The process may comprise the step of forming the molten glass from the component materials.

[0037] The process may comprise the step of forming the molten glass from the component materials.lt may be that the molten glass is prepared from a blend of the component materials using direct electrical melting (in which the glass is melted over a very short residence time by radiant heat between two electrodes; see EP0289240), gas fired top heat or a combination thereof. In certain embodiments, the molten glass is prepared from a blend of the component materials using direct electrical melting. This gives further efficiency savings over the rotary kiln processes typically used in frit manufacture. The process may comprise the step of blending the component materials prior to melting. [0038] The size of the particles of the frit will depend on the desired use of the frit and the size of the glass flakes will likewise depend on the desired particle size of the frit..

[0039] It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a diameter (i.e. a largest transverse distance) of from 5 to 500 μηι. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a diameter from 10 to 200 μηι. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a diameter from 15 to 100 μηι. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a diameter from 20 to 30 μηι.

[0040] It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a thickness from 10 nm to 10 μηι. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a thickness from 50 nm to 50 μηι. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a thickness from 200 nm to 20 μηι. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a thickness from 1 μηι to 10 μηι. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a thickness from 100 nm to 1 μηι.

[0041] It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have an aspect ratio (i.e. the ratio of the largest transverse distance to thickness) of from 2: 1 to 100000: 1 ; preferably 5: to 100000: 1. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have an aspect ratio of from 10: 1 to 25000: 1. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have an aspect ratio of from 50: 1 to 1500: 1.

[0042] It is preferred that glass flakes of the present invention are of a substantially uniform thickness. Thus, it may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a thickness within 50% of the nominal mean thickness. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a thickness within 20% of the nominal mean thickness. It may be that greater than 50% by weight (e.g. greater than 75% by weight, greater than 90% or greater than 98%) of the glass flakes have a thickness within 10% of the nominal mean thickness.

[0043] Glass frits and stains may be used in many areas including but not limited to Appliance glass, Automotive, Architectural glass, cosmetic glassware, container glass, tableware , ceramic glazes and enamels

[0044] Frits made according to the methods of the invention may be used for decorating enamels or glass packaging, sanitaryware, refractories, speciality coatings and traditional pottery glazes.

[0045] The frit may be added to an organic vehicle and mixed (e.g. using a 3-roll mill) to form an coating formulation.

[0046] The frit may be applied to an object. The frits substrate may be coated over at least a portion of its surface with the frit. The frit may be applied manually or automatically, either as the dry powder or more preferably as a coating formulation in an organic vehicle. Suitable techniques include screen printing, spraying, rolling or pre-printed decals.

[0047] Frits for electronics are typically printed onto a substrate either as the dry powder or more preferably as a coating formulation in an organic vehicle. Suitable techniques include screen printing or inkjet printing by forming a paste or a ceramic ink. The chemistry of glass for such applications may be modified to yield different properties such as thermal expansion coefficient, the glass transition point (Tg), the softening point, the glass may also be vitreous or devitrifying with varying chemical functionality such as nonstick properties. Particle diameter of such frits for electronics application range from D50 0.5 - 50microns, in frit or powder form. Such frits are used in electronic assemblies, communication equipment, automotive and automotive glass such as the obscuration band, power generation and storage as well display equipment.

[0048] Once the frit has been applied to an object (either as a coating or by printing), the frit may be fired to form a glass.

[0049] The frit may be used as an additive in the production of a glass or plastic. This is particularly the case where the frit comprises a colourant.

[0050] In a second aspect of the invention is provided a frit obtainable by or obtained by a method of the first aspect.

[0051] In a third aspect of the invention is provided a use of glass flakes in the production of a frit.

[0052] In a fourth aspect of the invention is provided glass flakes suitable for the production of a frit. [0053] The invention may provide a plurality of glass flakes comprising three or more of the following components: S1O2; B2O3; AI2O3; Na20; and MgO and optionally a colourant. The glass flakes may comprise four or more of the listed components. The glass flakes may comprise all of the listed components.

[0054] It may be that the S1O2 is present in an amount from 30 to 60 wt% (e.g. from 40 to 50 wt%). It may be that the B2O3 is present in an amount from 10 to 40 wt% (e.g. from 20 to 30 wt%). It may be that the AI2O3 is present in an amount from 2 to 8 wt% (e.g. from 3 to 6 wt%). It may be that the Na20 is present in an amount from 10 to 40 wt% (e.g. in an amount from 20 to 30 wt%). It may be that the MgO is present in an amount from 0.1 to 3 wt% (e.g. from 0.5 to 1.5 wt%).

[0055] The invention may provide a plurality of glass flakes comprising three or more of the following components: Colemanite; Pb Oxide; CaCOs; ZnOx; Dolomite; Silica; feldspar; Alumina; and K2CO3 and optionally a colourant. The glass flakes may comprise four or more of the components listed in the first sentence of this paragraph. The glass flakes may comprise six or more of the components listed in the first sentence of this paragraph. The glass flakes may comprise all of the components listed in the first sentence of this paragraph.

[0056] It may be that the colemanite is present in an amount from 0.1 to 5 wt% (e.g. from 1 to 3 wt%). It may be that the Pb Oxide is present in an amount from 0.1 to 4 wt% (e.g. from 1 to 2 wt%). It may be that the CaC03 is present in an amount from 5 to 30 wt% (e.g. from 12 to 24 wt%). It may be that the ZnOx is present in an amount from 4 to 10 wt% (e.g. from 6 to 8 wt%). It may be that the Dolomite is present in an amount from 1 to 7 wt% (e.g. from 3 to 5 wt%). It may be that the silica is present in an amount from 40 to 80 wt% (e.g. from 50 to 60 wt%). It may be that the feldspar is alkaline. It may be that the feldspar is present in an amount from 2 to 8 wt% (e.g. from 4 to 6 wt%). It may be that the alumina is present in an amount from 0.1 to 10 wt% (e.g. from 1 to 5 wt%). It may be that the K2CO3 is present in an amount from 1 to 10 wt% (e.g. from 2 to 6 wt%).

[0057] The invention may provide a plurality of glass flakes comprising three or more of the following components: Colemanite; CaCOs; Dolomite; feldspar ; ZnOx; Silica; Alumina and optionally a colourant. The glass flakes may comprise four or more of the components listed in the first sentence of this paragraph. The glass flakes may comprise six or more of the components listed in the first sentence of this paragraph. The glass flakes may comprise all of the components listed in the first sentence of this paragraph.

[0058] It may be that the Colemanite is present in an amount from 1 to 8 wt% (e.g. from 2 to 6 wt%). It may be that the CaC03 is present in an amount from 5 to 20 wt% (e.g. from 7 to 10 wt%). It may be that the Dolomite is present in an amount from 10 to 50 wt% (e.g. from 20 to 40 wt%). It may be that the feldspar is alkaline. It may be that the feldspar is present in an amount from 2 to 10 wt% (e.g. from 5 to 8 wt%). It may be that the ZnOx is present in an amount from 0.1 to 3 wt% (e.g. from 0.5 to 1.5 wt%). It may be that the silica is present in an amount from 20 to 50 wt% (e.g. from 30 to 40 wt%). It may be that the alumina is present in an amount from 5 to 25 wt% (e.g. from 10 to 20 wt%).

[0059] The invention may provide a plurality of glass flakes comprising two or more of the following components Si0₂ ZnO; CaO; ZnO B₂0₃ Si02; BaO BaOs ZnO BiaOs; ZnO B₂0₃ and optionally a colourant. The glass flakes may comprise three or more of the components listed in the first sentence of this paragraph. The glass flakes may comprise all of the components listed in the first sentence of this paragraph.

[0060] If present, a colourant may be present in an amount from 0.1 to 20 wt%. A colourant may be present in an amount from 0.5 to 10 wt%. A colourant may be present in an amount from 1 to 5 wt%.

[0061] The embodiments described above in relation to the first aspect of the invention apply equally to the second, third and fourth aspects of the invention as appropriate.

[0062] The glass flakes used in the methods of the first aspect of the invention may be the glass flakes of the fourth aspect of the invention. Likewise, the glass flakes used in the second aspect of the invention may be the glass flakes of the fourth aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a process diagram illustrating a typical prior art method of making a frit.

Figure 2 is a process diagram illustrating a typical method of the invention.

DETAILED DESCRIPTION

[0064] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0065] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0066] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

EXAMPLES

Example 1

[0067] Based on a flake precursor with a mean thickness of 5 microns and an average planar measurement of 120 microns, each flake was formed of an ECR based (borosilicate) composition that was pre-doped during production with a colorant metal oxide to produce a frit with a D90 of 12 microns.

Iron oxide doped frit Time in ball mill 4.0hrs

Manganese doped frit Time in ball mill

Magnesium Oxide doped frit d90: 11.256. Time in ball mill 5.5 hrs.

Copper oxide doped frit d90: 11.427 Time in ball mill 8.5 hrs

[0068] These times are several days shorter than known production method times for a similar materials.

[0069] The following frits have been made according to the methods of the invention:

1) Base (glossy) frit:

Si0₂ (45%); B₂0₃ (26%); AI2O3 (4%); Na₂0 (24%); and MgO (1 %)

2) Crystalline (glossy) frit

Colemanite (2.0%); Pb Oxide (1.4%); CaCOs (18.0%); ZnOx (6.7%); Dolomite (3.8%); Silica Sand (56.%; Si0₂ 95-96% - AI2O3 2.5%); alkaline feldspar (4.8%); alumina (anhydrous; low calcined grade; 3.3%); and K2CO3 (4.0%) 3) Frit used for opaque glazes

Colemanite (3.8%); CaCOs (8.8%); Dolomite (29.7%); alkaline feldspar (6.4%); ZnOx (0.7%); Silica flour (35.65; S1O2 99%); and alumina (anhydrous; low calcined grade; 15.0%).

Claims

1. A method of producing a frit; the method comprising:

milling a plurality of glass flakes to provide a frit.

2. A method of claim 1 , wherein the glass flakes are milled by rotary ball milling.

3. A method of claim 1 or claim 2, wherein the glass flakes are milled for up to 48 hours in total.

4. A method of any one of claims 1 to 3, wherein the method comprises passing the frit produced from the milling process through a sieve to remove any particles that are larger than desired and to provide a sieved frit.

5. A method of any one of claims 1 to 4, wherein the method also comprises the step of forming the glass flakes by feeding a stream of molten glass into a spinning cup; and allowing the molten glass to emanate radially over the rim of said cup.

6. A method of claim 5, wherein the flakes are coated with an additive, the additive being one of the components of the product frit, as the material leaves the spinning cup.

7. A method of claim 6, wherein the additive is a colourant.

8. A method of any one of claims 1 to 4, wherein the method also comprises the step of forming the glass flakes by passing molten glass through a bushing or nozzle to form a molten tube of glass, and passing air through the tube to expand the tube until it has the desired wall thickness.

9. The method of any one of claims 5 to 8, wherein the molten glass is prepared from the component materials using direct electrical melting

10. A method of claim 5 or claim 8 or a method of claim 9, when dependent on claims 5 or 8, wherein the molten glass contains all of the components of the product frit.

1 1. A method of any one of claims 1 to 10, wherein greater than 75% by weight of the glass flakes have an aspect ratio of from 2: 1 to 100000: 1.

12. A use of glass flakes in the production of a frit.

13. A use of claim 12, wherein greater than 75% by weight of the glass flakes have an aspect ratio of from 2: 1 to 100000: 1.

14. A plurality of glass flakes comprising three or more of the following components: S1O2, B2O3; AI2O3; Na20; and MgO and optionally a colourant.

15. A plurality of glass flakes comprising three or more of the following components: Colemanite; Pb Oxide; CaCC ; ZnOx; Dolomite; Silica; feldspar; Aluminaand K2CO3 and optionally a colourant.

16. A plurality of glass flakes comprising three or more of the following components: Colemanite; CaCC ; Dolomite; feldspar; ZnOx; Silica; Alumina and optionally a colourant.

17. A plurality of glass flakes comprising two or more of the following components SiC>2- ZnO; CaO; ZnO-B₂0₃-Si0₂; BaO BaOs ZnO BiaOs; ZnO B₂0₃ and optionally a colourant.

18. Glass flakes of any one of claims 14 to 17, wherein greater than 75% by weight of the glass flakes have an aspect ratio of from 2: 1 to 100000: 1.

19. A method of any one of claims 1 to 1 1 , wherein the glass flakes are glass flakes of any one of claims 14 to 17.

20. A frit obtainable by or obtained by a method of any one of claims 1 to 11 and 19.

21. A use of claim 12 or claim 13, wherein the glass flakes are glass flakes of any one of claims 14 to 17.