JPS6328860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to lead glass compositions suitable for mechanical forming. For example, lead crystal glass used in high-grade glass tableware is required to contain 24% by weight or more of PbO, for example, according to British standards.
Traditional lead crystal glass has a gentle temperature-viscosity curve due to its high lead content, and is commonly known as long glass. It was also convenient depending on the work. However, in recent years, with advances in mechanical molding technology, it has become possible to final mold the blow-molded parison by mechanical blowing in a mold. When the product is a container such as a tumbler, final molding by blowing eliminates the roughening of the glass surface caused by the molding and the leaving of mold seam marks that are seen in conventional press-molded products, making it comparable in quality to hand-blown products. It is possible to efficiently manufacture products with no difference in quality. However, mechanical blow molding requires less time for molding, so
Because the temperature drop of the glass base during molding is small and deformation occurs after molding, it is necessary to use a so-called short glass with a steep temperature-viscosity curve. Mechanical blow molding is only performed on glass, potash crystal glass, or semi-crystal glass containing less than 20% PbO.
Although mechanical blow molding is desired for lead glass containing 20% or more of lead glass, mechanical blow molding has not been used because the glass has a gentle temperature-viscosity curve. The present invention is based on the above-mentioned reasons and provides a lead glass composition containing 20% by weight or more of PbO, which has a relatively steep temperature-viscosity curve suitable for mechanical blow molding. %in
_SiO2 50-60%, _{Al2O3 0-3} %, _{B2O3 1-8} %,
ZrO ₂ 0-3%, CaO 0-8%, Li ₂ O 0-3%,
_Na2O0 ~15%, _K2O0 ~15%, PbO20~30%,
SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ + ZrO ₂ 55-65%, B ₂ O ₃ +
This is a lead glass composition characterized by having a composition of 5 to 10% CaO and 9 to 16% _Li2O + _Na2O + _K2O . The characteristic of the lead glass composition of the present invention is that the PbO content is 20 to 30%.
Despite containing a large amount (by weight%), the temperature-viscosity curve is relatively steep, and the difference (Tw - Ts) between the glass temperature Tw when the viscosity is 10 ⁴ poise and the glass temperature Ts when the viscosity is 10 ^7.6 poise is 270°C. It lies in the following. That is, the viscosity range of glass suitable for glass molding, whether by hand blow molding or mechanical blow molding, is approximately constant and is within the range of 10 ⁴ to 10 ^7.6 poise. In the case of hand-blowing, since the forming process is slow, Tw−Ts is required to prevent the glass from solidifying during forming.
While it is said that a temperature of about 300°C is preferable, in the case of mechanical blow molding, it is necessary to solidify immediately after the molding is completed, and the temperature for Tw-Ts is preferably 270°C or less. Further, the molten glass is maintained at a temperature near the working temperature (Tw) in the working tank and is sent to the gob feeder. Normally, while the molding machine is operating, the molten glass flows sequentially, so no devitrification is generated, but especially in the case of mechanical molding, for example, when replacing the mold, the flow stops and the molten glass flows. Due to stagnation, devitrification is likely to occur. Once devitrification occurs, even if the molding machine is restarted, the devitrification does not disappear immediately, but gradually melts and flows into the product as semi-molten foreign matter, significantly reducing the yield of the product. become. In addition, the temperature of the molten glass in the work tank is not necessarily constant at Tw, so it may be set a little higher than Tw in anticipation of the temperature drop while being sent to the gob feeder, or conversely, when molding a product that requires an extremely short molding time, Tw Or make it a little lower. Further, it is sufficient to consider that the stagnation time of the molten glass due to mold replacement etc. is usually 3 hours or less. Therefore, (Tw−100)℃~(Tw+100)
It is desirable that no devitrification is generated even if the glass is kept in the temperature range of .degree. C. for 3 hours, and the glass having the composition of the present invention satisfies this requirement. Next, we will discuss the reason for limiting each component of the lead glass composition of the present invention. SiO ₂ becomes a network former together with Al ₂ O ₃ , B ₂ O ₃ , and ZrO ₂ , and if it is less than 50%, the chemical durability of the glass will deteriorate. If it goes down and exceeds 60%, the glass tends to devitrify. Al ₂ O ₃ and ZrO ₂ improve the devitrification resistance and chemical durability of the glass, but if both exceed 3%, they increase the viscosity of the molten glass, which is undesirable. B ₂ O ₃ lowers the high-temperature viscosity of the glass, increases the low-temperature viscosity, and shortens the glass, so it is effective to add 1% or more, but if it exceeds 8%, the volatilization of B ₂ O ₃ will cause the formation of veins in the glass. 1 to 8 because it makes it easier to understand
%. If the total of the above SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ and ZrO ₂ is less than 55%, the chemical durability of the glass decreases, and if it exceeds 65%, it is difficult to melt. CaO increases chemical durability and shortens the glass, so B ₂ O ₃
Similarly, it is a preferable component for the present invention, but if it exceeds 8%, the glass tends to devitrify. Also B ₂ O ₃ ,
When the total amount of CaO is less than 5%, the effect of shortening the glass is small, and when it exceeds 10%, the glass tends to devitrify. Li ₂ O, Na ₂ O, and K ₂ O are effective as fluxes when melting glass, and Li ₂ O shortens the glass, so it is a preferred component for the present invention, but it is effective even in small amounts, and it is not expensive. Therefore, it is limited to 0 to 3%. When each of Na ₂ O and K ₂ O exceeds 15%, it reduces the chemical durability of the glass. Also,
If Li ₂ O + Na ₂ O + K ₂ O is less than 9%, it will have little effect as a flux, and if it exceeds 16%, chemical durability will decrease. If PbO is less than 20%, the refractive index of the glass will not be very high and the shine as crystal glass will be insufficient, and if it exceeds 30%, the glass will easily devitrify. In addition to the above limited ingredients, SO ₃ as a clarifying agent,
As ₂ O ₃ , Sb ₂ O ₃ , Cl, and F are each 1% or less, MgO, ZnO, and SnO ₂ are each 3% or less to increase chemical durability, and BaO and SrO are used as fluxes during glass melting. 3% or less, and Fe ₂ O ₃ and TiO ₂ are each 0.05% as impurities from raw materials.
You can enter the following. In addition, _NiO , _CoO , and
Se may be included. Next, regarding the examples of the present invention, Table 1 shows the glass composition and measurement results of Tw and Ts for the examples of the present invention and comparative examples, and the results of measurements from Tw-100°C to Tw.
The results of a devitrification test after being held at +100°C for 3 hours are shown. Silica sand, aluminum hydroxide, borax, zircon powder, calcium carbonate,
Basic magnesium carbonate, barium carbonate, lead oxide, soda carbonate, potassium carbonate, lithium carbonate,
Antimony oxide was prepared and mixed according to the target composition of each example and comparative example, and heated at 1350℃6 in a crucible.
After being heated and melted for a period of time, it was cast into a mold and slowly cooled, which was then used as a sample for viscosity measurement and devitrification measurement. The viscosity was measured by the ball pull-up viscosity measurement method for Tw, and the penetrating viscosity measurement method for Ts, to determine the temperature at each viscosity. To measure devitrification, the sample was crushed and classified, and glass grains with a particle size of 10 to 14 mesh were arranged on a platinum foil and heated in an electric furnace with an internal temperature gradient of (Tw-100) to (Tw+100)°C. After maintaining the temperature in the temperature range for 3 hours, the presence or absence of devitrification was examined by microscopic observation using transmitted light at a magnification of 40 times. Comparing Examples and Comparative Examples, all of Examples 1 to 8 had Tw-Ts≦270°C, whereas the glass of Comparative Example had Tw-Ts=300°C. This is because B ₂ O ₃ +CaO in the composition exceeds 5% by weight in the examples, whereas it is only 2.6% by weight in the comparative examples. Regarding devitrification properties, no devitrification was observed in any of Examples 1 to 7 and Comparative Examples. 【table】

Claims (1)

[Claims] 1% by weight: SiO ₂ 50-60%, Al ₂ O ₃ 0-3%,
_B2O3 1-8%, _ZrO2 0-3%, _CaO0-8 %,
_Li2O0 ~3%, _Na2O0 ~15%, _K2O0 ~15%,
SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ + ZrO ₂ 55 ~ with PbO20~30%
65%, _B2O3 +CaO5~10%, _Li2O + _{Na2O + K2O9}
A lead glass composition characterized in that it has a composition of ~16%. 2. The glass composition according to claim 1, wherein the temperature difference (Tw - Ts) between the temperature (Tw) at which the viscosity of the glass composition is 10 ⁴ poise and the temperature (Ts) at which the viscosity is 10 ^7.6 is 270°C or less Lead glass composition.