IE20000079A1 - Process for preparing a glass master-batch - Google Patents

Abstract

A process for the preparation of a prilled or granulated component for the preparation of lead-containing glasses or alternative glasses having a density greater than 2.70g/cm3 and a refractive index of greater than 1.53 which process comprises:- i) mixing together the glass making components an amount of from 1.5 to 3% by weight of the glass making components of an aqueous solution of a binder which is selected from lithium silicate, sodium silicate, potassium silicate, or a mixture thereof which solution contains from 1.75 to 7 grams of Na20, K20, Li20 or a mixture thereof and 6 to 24 grams of Si02 per 100 grams of the aqueous solution; and ii) forming the mixture into into an agglomerated form in the absence of a heat treatment step.

Description

PROCESS FOR PREPARING A GLASS MASTER-BATCH The present invention relates to a process for preparing a glass master-batch and, in particular, to a process for preparing a glass master-batch for use in the production of lead containing glasses, such as, lead crystal glass or alternative glasses having a density greater than 2.70 g/cm3 and a refractive index greater than 1.53. These glasses may be colourless or coloured, as desired.

Lead crystal glass is traditionally prepared from four main components which are:(1) Silica sand which is a glass former and is the principal constituent of lead crystal glasses, comprising at least 50% by weight thereof; (2) Lead oxide which is incorporated to increase the density of the glass, to provide an increased refractive index which provides sparkle when the glass is cut and to facilitate cutting and polishing of the x glass. Lead oxide is generally incorporated in an amount of at least 24% by weight of the glass; (3) Alkali metal oxides, including potassium carbonate (potash) which are modifiers and are used to lower the melting temperature of the silica sand and reduce the melting point to a temperature of around 1400°C, and (4) Refining agents such as oxides of arsenic or antimony and alkali metal nitrates, or mixtures thereof, are used to remove gas bubbles from the melt.

The lead oxide and some of the refining agents :ated into the lead crystal glass are which are η ri (2 O f toxic and S Σ Their use, stcr bv ΙΕ η n ft 07 9 specific health, safety and environmental regulations.

The conventional process for the manufacture of lead crystal glass generally comprises weighing the individual chemicals in a batch plant and mixing the weighed chemicals to provide a batch of the mixed raw chemicals in powder form. As the chemicals are in a fine powdered form, any dust needs to be prevented from entering the atmosphere, or escaping from the plant. The collected dust must then be disposed of according to environmental regulations. The grain size of the individual chemicals used to form the batch is controlled so that the chemicals will blend with one another, in order to facilitate melting. Larger grains will generally melt more slowly than smaller grains, but if the grains are too small they can constitute a health hazard. However, because the batch consists of grains of individual chemicals, each with a different density and dimensions, it is possible for these chemicals to segregate due to agitation during transport and thereby to form layers which each have different chemical compositions. This can give rise to a different glass composition formed from each layer, resulting in non-uniform and unusable products .

Accordingly, in order to prepare satisfactory lead crystal glass from a batch of the raw chemicals, it is necessary to use the batch shortly after mixing in order that there is no time for the individual components of the batch to separate out. The batch is thus stored only for a short time before being transferred to the melting furnace where it is mixed with broken glass of the same formulation and melted for the required time period. At the end of the melting procedure the glass is in a molten state and ready to be blown or formed into glass products.

A further problem associated with forming lead crystal glass is not only that the batch materials may segregate after mixing, but that batch containing potassium carbonate in the form of potash is susceptible to absorbing moisture from the air since it is deliquescent. This makes the batch stick to the walls of any container or transportation chute and causes melting problems.

Accordingly, the problems associated with glass batches for the preparation of lead crystal glass are the handling, storage, transport and disposal of a number of individual toxic substances; the health and safety of the workers in the plants in which the chemicals are mixed and of the workers employed in loading the batch into the melting furnaces or pots, and other workers exposed to lead-containing dusts; the segregation of the mixed batch chemicals if not used immediately after mixing and the moisture absorption of the chemicals prior to and during processing.

GB-A-1430211 describes a process for preparing a granular glass-forming composition which comprises mixing lead suboxide and silica and/or a silicate in proportions such that the ratio of lead, expressed as PbO2, to silicon, expressed as SiO2, is from 93:7 to 30:70; moulding the mixture into granules and heat treating uhe granules in an oxygen-containing atmosphere. Various aqueous binders are suggested for use in preparing the granules. The granules which are produced according to this process comprise lead silicate which is produced during the heat treatment step by reaction of the components of the mixture.

DE-A-2604457 describes the preparation of dustless lead oxide granules for use in the glass industry by agglomerating lead oxide particles using a potassium silicate binder.

We have now developed a novel process for preparing granules for use in the preparation of leadcontainirg glasses, such as lead crystal glass, and 1E0 Ο03Ί 9 alternative glasses, which may be coloured or colourless, which overcomes the various problems discussed above and, in particular, enables the granules to be prepared at a site remote from the glass manufacturing facility and to be stored without separating into the individual glass making components .

Accordingly, the present invention provides a process for the preparation of a prilled or granulated component for the preparation of lead-containing glasses or alternative glasses having a density greater than 2.70 g/cm3 and a refractive index of greater than 1.53, which process comprises: i) mixing together the glass making components for the glass, other than silica sand, with an amount of from 1.5 to 3% by weight of the glass making components of an aqueous solution of a binder which is selected from lithium silicate, sodium silicate, potassium silicate, or a mixture thereof which solution contains from 1.75 to 7 grams of Na2O, K2O, Li2O or a mixture thereof and 6 to 24 grams of SiO2 per 100 grams of the aqueous solution; and ii) forming the mixture into an agglomerated form in the absence of a heat treatment step.

The agglomerates produced in accordance with the process may be in the form of prills, granules, tablets or briquettes.

In carrying out the process of the present invention for the manufacture of lead crystal glass, the lead crystal glass making components (other than silica sane) will generally comprise from 35 to 80% by weight leaf oxide (either present as PbO or Pb3O4), from 1 to 50% by weight of alkali metal compounds comprising oxides, carbonates o nitrates of lithium, IE Q 3 Q 3 ? 9 sodium or potassium, or mixtures thereof, from 0.1 to 5% by weight arsenic oxide, antimony trioxide, or a mixture thereof, optionally up to 5% by weight of one or more of boron, zinc, titanium, strontium, calcium or bismuth compounds and optionally up to 5% by weight of one or more colouring agents selected from gold, silver, manganese, nickel, cobalt, iron, cadmium, copper and uranium compounds.

The process of the present invention may also be used in the preparation of other lead-containing glasses including those used for the storage of nuclear waste which generally contain from 1% to 60% PbO.

The alternative glasses which have a density greater than 2.70 g/cm3 and a refractive index greater than 1.53 may be prepared from the following compositions : 50 to 68% by weight silica, to 24% by weight of one or more alkali metal compounds comprising oxides, carbonates or nitrates of lithium, sodium or potassium, or mixtures thereof, to 3% by weight boron compounds, to 2% by weight of arsenic oxide, antimony trioxide, or mixtures thereof, up to 30% by weight of one or more metal oxides selected from magnesium, calcium, strontium, barium, aluminium, germanium, tin, bismuth, titanium, zirconium, zinc and lanthanum, and optionally up to 5% by weight of one or more colouring agents selected from gold, silver, manganese, nickel, cobalt, iron, cadmium, copper and uranium compounds. with the percentages of the various components being chosen so as to provide a glass with the desired density and high refractive index.

IE 0 0 0 0 7 9 The process of the present invention preferably employs sodium silicate as the binder in an amount of about 2% by weight of the glass making components of an aqueous solution of sodium silicate. The sodium silicate solution preferably contains 3.5 grams of Na20 and 12 grams of SiO2 per 100 grams of solution.

In carrying out the process of the present invention the glass batch can be manufactured as any type of agglomerate, but preferably as prills or as granules.

In one embodiment of carrying out the process of the invention, the constituents are pre-weighed and transferred into a mixer, preferably a dispersive mixer. This mixer has two separate blending actions, low speed plough-shears which tumble blend the constituents, and high speed dispersers which break-up any agglomerates and also augment the blending process. The plough-shears and dispersers can operate simultaneously, or independently.

During the mixer loading cycle only the ploughshears may be used. Once all of the powder constituents have been added the dispersers are also operated to break up any agglomerates in the raw materials. At this point the liquid binder may then sprayed into the mixer, although other mixing techniques may be appropriate.

If the product is required as a granulate, the dispersers are stopped at this stage and the mixer discharged with only the plough-shears running. The mixed powder is then granulated by forcing the mix through a rotating profile-drilled ring die using a set of internal rollers rotating against the inside circumference of the die. The size of the granules is controlled by the size, feed rate, the dimensions of the die drillings, the speed of rotation of the die and rollers and the pressure exerted by the internal rollers, which is also a controlling factor in the tEomn hardness of the granules.

If the product is required in the form of prills then the mixing continues using both plough-shears and dispersers. By observing the power consumption of the plough-shears drive motor it is possible to achieve the desired prill size, the dispersers ensuring that oversize prills are avoided. The dispersers also increase the friction within the mixer, raising the temperature of the blend to around 35°C which assists in absorption of the binder into the powders.

If desired, the product may be produced in the form of tablets or briquettes by subjecting the prills or granules to an appropriate compression step. At the manufacturing facility the tablets or briquettes will then be crushed and comminuted, prior to use.

The agglomerates, e.g. prills or granules, produced according to the process of the present invention are suitable for use without requiring to be dried and, in particular, the agglomerates are not subjected to any heat treatment step. Accordingly, the chemical composition of the agglomerates is essentially the same as that of the starting composition as there is no chemical reaction of the components one with another. The glass making components are thus bound together, ready for use.

The agglomerates, e.g. prills or granules, may either be used directly in the production of glass or may be stored prior to use, for example the prills or granules may be filled into bags, bins, silos or tankers in order to enable transport to a different manufacturing site.

The product is essentially dust free for hygiene reasons and yet sufficiently free flowing to be suitable for pneumatic and mechanical handling systems. It must also be robust enough to prevent self-attrition during transport and handling etc.

In practice, for prills the product particle size |£0 0001 3 should be predominantly between 0.1 and 2.0mm diameter to satisfy the final mixing requirements.

For granules the product size will be around l-3mm diameter and 5-10mm length depending upon formulation, granulator dimensions and running conditions. Granule dimensions can be varied to accommodate specific bulk storage and handling installations, including automatic handling and transfer systems including bulk silos. At the glass manufacturing facility these granules are first reduced in size in an homogenising mixer to ensure particle size compatibility with the silica sand and then blended with the silica sand in the same mixer. This ensures that the total glass batch meets mixing, handling and melting criteria whilst reducing the risk of iron pick-up. The use of the masterbatch also increases the consistency of the mix as it reduces the need to weigh-out small amounts of minor components. Mixing times for the glassmaker are also reduced as the components have already been premixed to form the masterbatch, whilst at the same time increasing the flexibility of the glassmakers mixing plant (various masterbatches, various sand/masterbatch ratios) without complex weighing changes. Segregation of the prills or comminuted granules and sand must be avoided at all costs as this will lead to variations in glass workability and quality. The sand to masterbatch particle size is crucial to segregation avoidance and glass quality. Blending with sand should be carried out immediately before transfer to the furnace spreader or melting pot.

The agglomerates produced according to the process of the present invention overcome the problems encountered in handling the toxic components, including lead oxides, of the glass and facilitates the production of uniform, glass. Furthermore, the components used to form, the agglomerates do not ,£0 οοίπ · contain silica sand and thus problems of the pick-up of iron, chromium and other colouring metals from the processing equipment during the production of colourless glasses, and wear of the processing equipment because of the abrasive nature of silica sand, are avoided. Iron, chromium and nickel are colouring agents and thus must be avoided in the final glass mix during the production of colourless glasses. A further advantage of the agglomerates of the present invention is the overall absorption of moisture is restricted to their surfaces, thereby reducing total moisture pick-up. The agglomerates also allow for bulk storage and automated handling, which avoids health, safety and environmental problems, as well as improving the packaging of the product.

The present invention includes within its scope agglomerates of components for the preparation of lead crystal glass, which comprise the following components to 80% by weight lead oxide; to 50% by weight of alkali metal compounds comprising oxides, carbonates or nitrates of lithium, sodium or potassium, or mixtures thereof; up to 5% by weight of arsenic oxide, antimony trioxide, or a mixture thereof; optionally up to 5% by weight of one or more of boron, zinc, titanium, strontium, calcium or bismuth compounds, and optionally up to 5% by weight of one or more colouring agents selected from gold, silver, manganese, nickel, cobalt, iron, cadmium, copper and uranium compounds, bound together with from 1.5 to 3% by weight of the said components of lithium silicate, sodium silicate, potassium silicate, or a mixture thereof, which solution contains from 1.75 to 7 grams of Li,O, Na2O, K20 or a mixture thereof and 6 to 24 grams of SiO2 per 100 grams of the aqueous solution.

The present invention also includes within its scope agglomerates of the components for the preparation of a glass having a density greater than 2.70g/cm3 and a refractive index of greater than 1.53, which comprise the following components to 68% by weight silica, to 24% by weight of one or more alkali metal compounds comprising oxides, carbonates or nitrates of lithium, sodium or potassium, or mixtures thereof, to 3% by weight boron compounds, to 2% by weight of arsenic oxide, antimony trioxide, or mixtures thereof, up to 30% by weight of one or more metal oxides selected from magnesium, calcium, strontium, barium, aluminium, germanium, tin, bismuth, titanium, zirconium, zinc and lanthanum, and optionally up to 5% by weight of one or more colouring agents selected from gold, silver, manganese, nickel, cobalt, iron, cadmium, copper and uranium compounds, bound together with from 1.5 to 3% by weight of the said components of lithium silicate, sodium silicate, potassium silicate, or a mixture thereof, which solution contains from 1.75 to 7 grams of Li2O, Na20, K2O or a mixture thereof and 6 to 24 grams of SiO2 per 100 grams of the aqueous solution.

The present invention furthermore includes within its scope a process for the preparation of a leadcontaining glass or alternative glass having a density greater than 2.70 g/cm3 and a refractive index of greater than 1.53, which process comprises: a) optionally comminuting agglomerates prepared aotording to the process as defined above to form particles of from 0.1 to 2.0mm; b) mixing from 40 to 60% by weight of the particles from step (a) or the prills prepared according to the process as defined above with from 60 to 40% by weight of silica sand; c) feeding the mixture from step (b) to a glass melter and melting the mixture at a temperature in the range of 1300°C to 1600°C, preferably 1400°C to 1500°C, to form the glass.

When the glass produced by this process is a lead crystal glass it will preferably have a density of greater than 2.95g/cm3 and a refractive index of greater than 1.545.

The present invention, in summary, provides the following advantages: (i) reduction of health, safety and environmental risks; (ii) improvement of storage and handling, including bulk handling and storage, automatic and pneumatic handling and weighing; (iii) reduction of moisture pick up; (iv) reduciion of the risk of iron pick-up and other contaminants; (iv) maintenance of product in the as produced form during transport, storage and transfer to the blending facility.

The present invention will be further described with reference to the following Examples.

EXAMPLE 1 The following ingredients were dry mixed together: % by weight ) 63.5% 31% 2% 1% 1% 1.5% Lead oxide (litharge) Potassium carbonate Potassium nitrate Arsenic trioxide · Zinc oxide Borax 100 ;0 The mixed dry components were then mixed with 3% by weight, based on the weight of the mixture of a sodium silicate solution containing 3.5 grams Na2O and 12 grams SiO2 per 100 grams of the solution. After mixing, the blend was granulated using a rotating drilled-ring die using internal pressure rollers rotating against the inside circumference of the die. The resulting red like granules were sieved to remove both coarse and fine oowaers which were, reworked 4through the system. The granules had a length of from 5 to 15mm.

EXAMPLE 2 The following ingredients were dry mixed together: Lead oxide (litharge) Potassium carbonate Potassium nitrate Boric acid Arsenic trioxide % by weight . 5% 20% 0.3% 0.2% 1% \£0 0 OQ1 9 The mixed dry components were then treated as described in Example 1 to form granules.

EXAMPLE 3 The granules prepared according to Example 1 were weighed, the particle size of the granules was reduced to 95% by weight of less than 1.5mm and the particles were then mixed with silica sand in the weight ratio of 50:50.

The mixture was melted in a pot furnace for a period of 36 hours at a temperature of 1400°C and worked at 115O°C, resulting in a glass with the following characteristics.

Density Refractive Index

Claims (11)

CLAIMS :

1. A process for the preparation of a prilled or granulated component for the preparation of leadcontaining glasses or alternative glasses having a density greater than 2.70g/cm 2 3 and a refractive index of greater than 1.53 which process comprises i) mixing together the glass making components for the glass,, other than silica sand, with an amount of from 1.5 to 3% by weight of the glass making components of an aqueous solution of a binder which is selected from lithium silicate, sodium silicate, potassium silicate, or a mixture thereof which solution contains from 1.75 to 7 grams of Na 2 O, K 2 O, Li 2 O or a mixture thereof and 6 to 24 grams of SiO 2 per 100 grams of the aqueous solution; and ii) forming the mixture into an agglomerated form in the absence of a heat treatment step.

2. A process as claimed in claim 1 wherein the lead-containing glass is a Lead crystal glass and the lead crystal glass making components comprise from 35 to 80% by weight lead oxide, from 1 to 50% by weight of alkali metal compounds comprising oxides, carbonates or nitrates of lithium, sodium or potassium, or mixtures thereof, from 0.1 to 5% by weight of arsenic oxide, antimony trioxide, or a mixture thereof, optionally up to 5% by weight of one or more of boron, zinc, titanium, strontium, calcium or bismuth compounds, and optionally up to 5% by weight of cr.e or more colouring agents selected from gold, silver, manganese, nickel, cobalt, iron, cadmium, cccper and uranium compounds. IE::; 3 0 0 0379

3. A process as claimed in claim 1 wherein the glass is a glass having a density greater than 2.70g/cm 3 and a refractive index of greater than 1.53, and the glass making components comprise comprises 50 to 68% by weight silica, 12 to 24% by weight of one or more alkali metal compounds comprising oxides, carbonates or nitrates of lithium, sodium or potassium, or mixtures thereof, 0 to 3% by weight boron compounds, 0 to 2% by weight of arsenic oxide, antimony trioxide, or mixtures thereof, up to 30% by weight of one or more metal oxides selected from magnesium, calcium, strontium, barium, aluminium, germanium, tin, bismuth, titanium, zirconium, zinc and lanthanum, and optionally up to 5% by weight of one or more colouring agents selected from gold, silver, manganese, nickel, cobalt, iron, cadmium, copper and uranium compounds.

4. A process as claimed in any one of claims 1 to 3 wherein the binder comprises about 2% by weight of the glass making components of an aqueous solution of sodium silicate which contains 3.5 grams of Na 2 O and 12 grams of SiO 2 per 100 grams of solution.

5. A process as claimed in any one of the preceding claims wherein the agglomerated form comprises prills, granules, tablets or briquettes.

6. A process as claimed in claim 5 wherein the product is in the form of granules having a diameter of from 1 to 3mm and a length of from 5 to 10mm. A process as claimed in claim 5 wherein the tEO οοβι* product is in the form of prills having an average particle diameter of from 0.1 to 2.0mm.

7. 8. A process as claimed in any one of claims 5 to 7 wherein the prills or granules are ready for use without drying.

8. 9. Agglomerates of components for the preparation of lead crystal glass, which comprise the following components 35 to 80% by weight lead oxide; 1 to 50% by weight of alkali metal compounds comprising oxides, carbonates or nitrates of lithium, sodium or potassium, or mixtures thereof; up to 5% by weight of arsenic oxide, antimony trioxide, or a mixture thereof; optionally up to 5% by weight of one or more of boron, zinc, titanium, strontium, calcium or bismuth compounds, bound together with from 1.5 to 3% by weight of the said components of lithium silicate, sodium silicate, potassium silicate, or a mixture thereof, which solution contains from 1.75 to 7 grams of li 2 O, Na 2 O, K 2 O or a mixture thereof and 6 to 24 grams of SiO 2 per 100 grams of the aqueous solution.

9. 10. Agglomerates of the components for the preparation of a glass having a density greater than 2.70g/cm 3 and a refractive index of greater than 1.53, which comprise the following components 5C to 68% by weight silica, 12 to 24% by weight of one or more alkali metal compounds comprising oxides, carbonates or nitrates of lithium, sodium or potassium, or mixtures thereof, 0 to 3% by weight boron compounds, 0 to 2% by weight of arsenic oxide, antimony trioxide, or mixtures thereof, up to 30% by weight of one or more metal oxides selected from magnesium, calcium, strontium, barium, aluminium, germanium, tin, bismuth, titanium, zirconium, zinc and lanthanum,' and optionally up to 5% by weight of one or more colouring agents selected from gold, silver, manganese, nickel, cobalt, iron, cadmium, copper and uranium compounds, bound together with from 1.5 to 3% by weight of the said components of lithium silicate, sodium silicate, potassium silicate, or a mixture thereof, which solution contains from 1.75 to 7 grams of Li 2 O, Na 2 O, K 2 0 or a mixture thereof and 6 to 24 grams of SiO 2 per 100 grams of the aqueous solution.

10.

11. A process for the preparation of a leadcontaining glass or alternative glass having a density greater than 2.70 g/cm 3 and a refractive index of greater than 1.53, which process comprises: a) optionally comminuting agglomerates prepared according to the process of any one of claims 1 to 7 or as claimed in claim 9 or claim 10, to form particles having a particle size of from 0.1 to 2.0mm; b) mixing from 40 to 60% by weight of the parricles from step (a) or the prills prepared according to the process of any one of claims 1 to 7, or as claimed in claim 9 or claim 10 with from 60 to 40% by weight of silica sand; c) feeding the mixture from step (b) to a glass melter and melting the mixture at a temperature in the range of 1300°C to 1£OC : C, preferably 140Q-C to 1500°C, to form the glass.