CZ142492A3 - Batch for lead-free crystal glass - Google Patents

Abstract

Leadless crystal glass with refraction index equal or higher as 1,52, determined mainly for manufacturing of glass jewelry semiproducts, chandelier appendages, pressed glass for household and glass bars and beads with possibility to use it for bevel and ball cut of glass, which contains 64 to 73 per cent weight of silicon dioxide (SiO/sub_2/), 6 to 12 per cent weight of sodium oxide (Na/sub_ 2/O), 4 to 10 per cent weight of potassium oxide (K/sub_2/O), 4,5 to 9,5 per cent weight of magnesium oxide (MgO) and/or calcium oxide (CaO), 2 to 6 per cent weight of barium oxide (BaO), 1 to 3 per cent weight of zinc oxide (ZnO), 0,2 to 1,5 per cent weight of boron oxide (B/sub_2/O/sub_3), 0,2 to 15 per cent weight of lithium oxide (Li/sub_2/O) and/or fluorides (F/exp_1-/), 0,2 to 0,8 per cent weight of antimonius oxide (Sb/sub_ 2/O/sub_3/) and/or arsenous oxide (As/sub_ 2/O/sub_3/), at which the total amount of zinic oxide (ZnO), potassium oxide (K/sub_2/O) and barium oxide (BaO) is more then 10 per cent weight. Glass with advantage contains 0,5 to 2 per cent weight of aluminum oxide (Al/sub_2/O/sub_3/), respectively traces of sulfates ((SO/sub_4/)/exp. 2-/) to 0,4 per cent weight.

Description

The invention relates to a charge for lead-free crystal glass which comprises silica SiO 2 from sodium Na ₂ O, potassium K 2 O, calcium CaO and / or magnesium MgO, barium Bao, zinc ZnO, boron ^Β 2θ3 'lithium Li ₂ 0, antimony As ₂ O ₂ and / or arsenic As ₂ O ₂ .

BACKGROUND OF THE INVENTION

Japanese Patent No. 3,074,936 discloses a composition of crystal glass comprising by weight of a glass composition. % SiO ₂ 65 to 75, MgO 1 to 7, CaO 5 to 15, Na ₂ O and potassium K ₂ O 10 to 20, more than 90 wt. is the sum of SiO ₂ , Al ₂ O ₂ , magnesium MgO, sodium Na ₂ O and potassium K ₂ O.

This type of crystal glass is particularly suitable for glass pressing.

Polish Patent No. 76 646 discloses a colorless glass composition having the following composition in% by weight: silica SiO ₂ 65 to 75, alumina Al ₂ O ₂ 0 to 3.0, calcium oxide CaO 0.1 to 12, oxide of magnesium MgO 1 to 6, boron oxide ^B 20 0,1 0.1 to 2.5. sodium oxide Na-O 42 to 17, potassium oxide KO 0 to 5 and to 0.5

1fluoride F. The glass has a coefficient of linear thermal expansion

84,72.10? mm. ° C in a temperature range of 25 to 90 ° C, a Littleton softening point of 727 θθ and a working temperature of 1235 ° C.

Glass as well as unleaded glass is suitable especially for automatic production of household glass, glasses, cups etc.

Lead-free crystal glasses include the so-called " Bohemian crystal, which is a silica-sodium-potassium glass, where the sum of potassium K ₂ O and sodium Na ₂ 0 is equal to or greater than 10% by weight.

This type is particularly accentuated by its low price and is used for cheap crystal glass products. The refractive index is around 1.51.

in w Τ '

Crystal glasses conforming to EEC Directiveswith glass containing PbO in varying amounts.

Special crystal glass with a refractive index of 1.51 to 1.52 intended for the noble products has a sum of potassium oxide K ₂ O, zinc ZnO, barium BaO and lead PbO equal to or higher than% by weight.

For luxury products refined by grinding, lead crystal is used, where the content of lead oxide PbO is about 24% by weight. or higher, and further a highly lead crystal, wherein the lead oxide content of PbO is about 30% by weight. and more. Both types of glass usually have a refractive index higher than 1.545. This increased refractive index is achieved mainly by an increased content of lead oxide PbO or barium BaO.

For the manufacture of costume jewelery blanks, utility glass especially for edge cut and pressing of household glass as well as illuminating glass especially chandelier trimmings, two types of low-lead glasses with lead oxide content PbO lower than 10% by weight are presently preferred. They contain about 70% by weight of SiO2, alkali metal and alkaline earth metal oxides, usually έ of arsenite oxide As ^ O ^ and fluorides F. This basic type of glass is intended for manual processing of glass. Alumina and boron oxide additions of up to about 2% by weight are suitable for machining.

The refractive index of these glasses is less than 1.52, so it lies below the limit of special crystal glasses according to the applicable EEC standards. The low content of lead oxide PbO does not significantly improve their characteristics and extends the length of the glass, which results in a decrease in the performance of the forming machines and in the mechanical production of products of more demanding shapes. Lead oxides cause complications in the electric melting of the glass, increase the susceptibility of glass to scab, and cause environmental problems.

SUMMARY OF THE INVENTION

These disadvantages are eliminated or substantially reduced in the case of the lead-free crystal glass of the batch according to the invention, which is characterized in that the batch contains in wt. silica SiOg 64 to 73, sodium Na 2 O 6 to 12, potassium I 4 O 4 to 10, calcium Cao and / or magnesium MgO 4.5 to 9.5, barium BaO 2 to 6, zinc ZnO 1 to 3, boron B ~ 0.2 to 0.2

1.5, lithium LigO and / or fluoride F. 0.2 to 1.6 and the antimony $ ^ 2 ^ 3 ^and / bo ^no arsenic AS2O3 0.2 to 0.3. The sum of zinc oxide ZnO, potassium K ₂ O and barium BaO is greater than 10% by weight.

Preferably, the feed further comprises Al2O2 in an amount of 0.5 to 2% by weight.

It is further preferred that the feed contains traces of up to 0.4 wt.

2Sulfur SC> ₄

Compared to low-lead glasses, the unleaded crystal obtained from this batch exhibits better optical properties, with a refractive index equal to or greater than 1.52. The optimum charge composition ensures the acquisition of special crystal glass according to the relevant EEC standards. The glass from this charge can be melted on the glass electric melting units, thereby eliminating the emission of lead oxides to the atmosphere and improving the hygienic conditions in the working environment of the glassworks.

The combination of lithium oxide 10 with fluoride F 4 reduces the surface tension of the glass, facilitates fining and is suitable for electrical melting of the glass. Increasing the proportion of lithium oxide L ^ O at the expense of fluoride F ^ ”reduces the corrosion of the refractory refractory material.

The addition of alumina reduces the risk of devitrification of the glass and has a beneficial effect on shaping.

The addition of SO4 sulphates in combination with arsenic trioxide ASgO4 or antimony trioxide SbgO4 represents a suitable clarifying combination.

DETAILED DESCRIPTION OF THE INVENTION

The invention is illustrated by the following examples.

Example 1 2 3 Charge components % wt. % wt. % wt. SiO2 70.55 68.5 70.3 sodium oxide NagO 9.8 10.0 10.1 potassium oxide 5.5 5.5 5.5 calcium oxide CaO 6.5 5.8 6.0 barium oxide BaO 3.2 3.8 3.4 Zinc oxide ZnO 1.6 1.6 1.6 magnesium oxide MgO 0.8 1,8 1.0 boron oxide Β ₂ Ο ^ 0.8 0.8 0.8 lithium oxide Li ₂ O 0.2 0.3 0.3

fluorides 0.55 0.45 0.3 antimony trioxide Sb ₂ O ^ - 0.1 - arsenic trioxide As ₂ O ₂ 0.5 0.35 0.4 alumina al ₉ 0. - 1.0 - 2- ^ZJ siranv SO. - - 0.2

100.0 100.0 100.0

All glasses melted from exemplary batches have a refractive index greater than 1.52.

The glass melted from the charge pc according to example 1 is suitable for the production of glass tubes or tubes for grinding glass beads with a quality hole.

Example 2 shows a charge from which the melted glass is intended especially for manual processing in the production of utility and lighting glass.

From the batch in Example 3, a glass of viscosities of relatively short viscosity, suitable for machine processing, is obtained, allowing the performance of the forming machines to be increased. This glass is also suitable for processing touches and chandelier bowls.

Overall, compared to low-lead glass types, the luminosity and maximum melting temperatures are reduced. Products can be machine-polished and polished. Hydrolithic resistance of glass determined according to ČSN No. 700531 corresponds to the third class of resistance.

Industrial applicability

The solution of the charge composition for unleaded crystal enables melting of glass on all types of glass melting units, gas and electric and processing of glass and machine and hand glass, especially in the production of jewelery semi-products, lighting, utility or technical glass. The glass can be further refined by grinding and polishing.

In the case of illuminated glass, the solution is suitable for the production of shades and chandelier trimmings intended especially for grinding.

In the case of utility glass, the solution is intended mainly for ball and edge grinding and for mechanical processing of pressed household glass.

In technical glass, the charge can be applied to glass tubes and beads.

Claims (3)

PATENT CLAIMS Charge for lead-free crystal glass, consisting of SiO ₂ , sodium Na ₂ O, potassium K ₂ O, calcium CaO and / or magnesium MgO, barium BaO, zinc ZnO, boron B 2 O 4, lithium Li ₂ O % of antioxidant Sb ₂ O ₃ and / or arsenite As ₂ O ₂ and fluorides F 1, characterized in that it contains in wt. SiO ₂ 64 to 73, Na ₂ O 6 to 12, K ₂ O 4 to 10, CaO ·> and / or magnesium MgO 4.5 to 9.5, barium Bao 2 to 6, zinc ZnO 1 to 3, boron B-0 _q 0.2 to 1.5, lithium LiO 2 'and / or fluorides F 0.2 to 1,5, antimony Sb ₂ O ₃ and / or arsenic As ₂ O ₃ 0.2 to 0.8, the sum of zinc oxide ZnO, potassium K ₂ O, and barium BaO are greater than 10 wt. 2. The charge of claim 1, further comprising 0.5 to 2 wt. aluminum oxide Al ₂ O ₃ · Third batch according to claim 1 or 2, wherein _M O - further contains from traces up to 0.4% by weight. sulphate SO4.