Title of Invention	BOROSILICATE GLASS OF HIGH HYDROLYTIC STABILITY
Abstract	The invention relates to borosilicate glasses having a composition (in % by weight, based on oxide) of Sio2 70.5 - < 73. B2o3 8 -10, al2o3 4-5. 6, Li2o 0-<0.5, Na2O 7-9. k2O 1.2 - 2.5, Mgo 0 - 1, CaO 0 -2, with MgO +Cao 0 -2, BaO 0.5 -4, ZrO2 0 -2, CeO2 0 -1, F 0 - 0.6. On account of their high hydrolytic stability, the glasses are particularly suitable for pharmaceutical purposes.

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FORM 2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE SPECIFICATION (See Section 10; rule 13) TITLE "BOROSILICATE GLASS OF HIGH HYDROLYTIC STABILITY" APPLICANT SCHOTT AG Hattenbergstrasse 10 55122 Mainz Germany Nationality : Germany The following specification particularly describes the nature of this invention and the manner in which it is to be performed The invention relates to a borosilicate glass of high hydrolytic stability. The invention also relates to uses of the glass. For use as primary pharmaceutical packaging materials, such as ampoules or vials, there is a need for glasses which in particular have a very high hydrolytic stability. An important parameter for characterization of the workability of a glass is the working point VA at which the viscosity of the glass is 10' dPas. This working point should be low, since even slight reductions in V^ lead to a significant drop in production costs, since the melting points can be lowered. This working point should also be low for glasses to be used as primary pharmaceutical packaging materials to ensure that any evaporation of alkali metal borate which may occur during the deformation of the alkali-containing borosilicate glasses is as low as possible. This is because these vaporized products form deposits in glass containers made from tube and have an adverse effect on the hydrolytic stability of the containers. The patent literature has already described glasses which have high chemical resistances but which also have disadvantageously high working points. DE 42 30 607 CI proposes chemically highly resistant borosilicate glasses which have low alkali metal and AI2O3 contents and which can be fused to tungsten. They have expansion coefficients a(2G°C;300°C) of at most 4.5 X 10"^/K and according to the examples have working points of > 1210°C. The borosilicate glasses described in laid-open specification DE 37 22 130 Al also have low expansions and high working points. They are relatively susceptible to crystallization on account of the absence of K2O. The Li20-containing glasses with a high SiOe content described in 1482/MAS/96 CI are also highly chemically stable but likewise have disadvantageously high working points and low thermal expansions. The glasses described in DE 44 30 710 CI have a high Si02 content, namely > 75% by weight and > 83% by weight of Si02 + B2O3 in combination with an 8102/6203 weight ratio of > 8, which does make them highly chemically resistant but also leads to disadvantageously high working points. Therefore, it is an object of the invention to find a glass which fulfils the abovementioned high demands on the hydrolytic resistance combined, at the same time, with a low working point VR. This object is achieved by the Borosilicate glass of high hydrolytic stability, having a composition (in % by weight, based on oxide) of: Si02 70.5 - B2O3 8-10 AI2O3 4-5.6 Li20 0 - Na20 7-9 K2O 1.2-2,5 0-1 0-2 0-2 0.5 - 4 MgO CaO with MgO + CaO BaO Zr02 0-2 Ce02 0-1 F" 0-0.6 and if appropriate conventional refining agents in standard quantities. For a chemically highly resistant glass, the glass according to the invention has a relatively low Si02 content of 70.5 to The glass contains 8 to 10% by weight, preferably 8.5 to 9.5% by weight, of B2O3 in order to reduce the thermal expansion, the working point and the melting point while at the same time improving the chemical resistance, in particular the hydrolytic stability. The boric acid binds the alkali metal ions which are present in the glass more strongly into the glass structure, leading to a reduced release of alkali metal ions in contact with solutions, for example when determining the hydrolytic stability. Whereas lower contents would significantly reduce the hydrolytic stability and would not sufficiently lower the melting point, higher contents would have an adverse effect on the acid resistance. The glass according to the invention contains at least 4% by weight and at most 5.6% by weight, preferably at most > 4 - 5.5% by weight, of AI2O3. This makes the glass very resistant to crystallization, i.e. during cooling during the shaping process, for example during 4 the tube drawing, no devitrification crystals which would remain at the glass surface and would adversely affect the shaping of the glass are formed. Also, AI2O3, like boric acid, bonds the alkali metal oxides, in particular Na20, more strongly into the glass. At higher contents, the melting point and the working point would rise without the improved resistance to crystallization which is thereby achieved being of any further benefit. For the glass according to the invention, it is important for the levels of the individual alkali metal oxides to be kept within very tight limits, allowing a balanced ratio between them to be achieved. Consequently, the glass contains 7 - 9% by weight of Na20, preferably at least 7.5% by weight of Na20, 1.2 -2.5% by weight of K2O, preferably 1.5 - 2.3% by weight of K2O, and 0 - The alkali metal oxides, in particular Na20 and Li20, reduce the working point of the glass, and in addition K2O improves the devitrification stability. The release of alkali metal ions increases disproportionately above the corresponding upper limit of the alkali metal oxide. Therefore, these specific contents ensure a minimum release of alkali metal ions, which leads to the different excellent chemical resistances. The glass contains 0.5 - 4% by weight of BaO, preferably at least 2.5% by weight of BaO, particularly preferably at least 3% by weight of BaO, and as further components may contain MgO in an amount of 0 - 1% by weight and CaO in an amount of 0 - 2% by weight. These components vary the "length of the glass", i.e. the temperature range within which the glass can be worked. On account of the different network-modifying actions of these components, it is possible to match the viscosity characteristics to the requirements of the particular production and working process by exchanging these oxides for one another. Moreover, CaO improves the acid resistance. CaO and MgO reduce the working point and are strongly bonded into the glass structure. The sum of CaO and MgO should be between 0 and 2% by weight, since the thermal expansion increases at higher levels. The presence of BaO reduces the working point without the hydrolytic stability being adversely affected. Crucial factors in the differing levels of release of alkali metal ions are firstly the different ionic radii of the alkali metals. Secondly, the contents of the different alkaline-earth elements are also responsible for the release of alkali metal ions. The ionic radii of sodium and calcium are lower than those of potassium and barium. This firstly means that more sodium is released than potassium. However, by using suitable amounts of AI2O3, which compresses the glass structure, the release of the small Na ion is also prevented or at least made more difficult. To ensure that AI2O3 has a sufficient action with respect to NaaO, there should not be too much CaO, since this component occupies the same sites in the glass as NaaO. For example, it is preferable for the ratio of the Al203/(Na20 + CaO) contents by weight to be > 0.55. The glass may contain 0 - 2% by weight of Zr02. It is particularly preferable for it to contain at least 0.5% by weight of Zr02. Zr02 improves the hydrolytic stability and in particular the alkali resistance of the glass. Higher contents would increase the working point excessively, whereas the chemical resistances would no longer be significantly improved. The glass may contain up to 1% by weight of Ce02. In low concentrations, Ce02 acts as a refining agent, while in higher concentrations it prevents the discoloration of the glass by radioactive radiation. Therefore, primary packaging materials which have been produced using a Ce02-containing glass of this type and filled can still be visually checked for the presence of any particles even after radioactive loading. Still higher Ce02 concentrations make the glass more expensive and lead to an undesirable yellow-brownish intrinsic colour. For uses in which the ability to avoid discoloration caused by radioactive radiation is not crucial, a Ce02 content of between 0 and 0.3% by weight is preferred. Furthermore, the glass may contain up to 0.6% by weight of F~. This reduces the viscosity of the melt, thereby accelerating the melting of the batch and the refining of the melt. Moreover, increasing the F content of the glass enables the pH of an aqueous solution which is in contact with the glass to be buffered, i.e. the increase in the pH of the contents caused by the release of alkali metal ions from the inner surface of the glass after injectable liquids have been introduced into glass containers is partially neutralized by F ions. In addition to the abovementioned Ce02 and fluorides, for example CaF2, the glass can be refined using standard refining agents, such as chlorides, for example NaCl, and/or sulphates, for example Na2S04 or BaSO^, which are present in standard quantities, i.e. depending on the quantity and type of refining agent used, in quantities of from 0.0003 to 1% by weight, in the finished glass. If AS2O3 and Sb203 are not used, the glasses, apart from inevitable impurities, contain no AS2O3 and Sb203, which is particularly advantageous for their use as primary pharmaceutical packaging materials. Examples Two examples of glasses according to the invention (A) and three comparative examples (V) were melted from standard raw materials. Table 1 gives the corresponding composition {in % by weight, based on oxide), the coefficient of thermal expansion a(20°C;300°C) [10"VK], the transformation temperature Tg [°C], the working point V^ [°C] and the hydrolytic stability, the acid resistance and the alkali resistance of the glasses. The chemical resistances were determined in the following way: • the hydrolytic stability H in accordance with DIN ISO 719. The table in each case indicates the base equivalent of the acid consumption as (xg NaaO / g of glass grit. The maximum value for a chemically highly resistant glass belonging to Hydrolytic Class 1 is 31 ^g Na20/g. • The acid resistance S in accordance with DIN 12116. The table in each case indicates the weight loss in mg/dm^. The maximum loss for a glass belonging to Acid Class 2 is 1.5 mg/dm^. • The alkali resistance L in accordance with DIN ISO 695. The table in each case indicates the weight loss in mg/dm^. The maximum loss for a glass belonging to Alkali Class 2 is 175 mg/dm^. The particular requirements for at least Class 2 are satisfied by the glasses according to the invention. In particular with regard to the hydrolytic stability, which is especially important for pharmaceutical purposes, the glasses give excellent results, with base equivalents of Therefore, the glasses according to the invention are eminently suitable for all applications in which chemically resistant glasses are required, e.g. for laboratory applications, for chemical installations, for example as tubes, and in particular also for containers for medical purposes, for primary pharmaceutical packaging materials, such as ampoules or vials. The very low working points V^ of at most 1130 °C characterize their good working properties. The melting points of the glasses are very low, at between 1450°C and 1520°C. The favourable melting and working range which results reduces the energy consumption in the production process. In a preferred embodiment, the glasses contain no AS2O3 and Sb203, which is particularly advantageous for use as primary pharmaceutical packaging materials. The glasses have a coefficient of thermal expansion a(20°C;300°C) of between 5.8 and 7.0 x 10"VK. Therefore, their linear expansion is well matched to the thermal expansion characteristics of sapphire, of which a(20°C;300°C) is approx. 6.7 x lO'^^K. Therefore, they are likewise eminently suitable for use as sealing glass for sapphire. The glasses have a crystallization resistance which is even suitable for tube drawing. Table 1: Compositions (in % by weight, based on oxide) of exemplary embodiments (A) and comparative examples (V) and their main properties: Al A2 VI V2 V3 SiOz 72.0 71.8 72.7 73.5 69.6 B2O3 8.9 8.8 10.0 5.2 8.5 AI2O3 5.0 5.0 6.1 4.7 4.3 LizO - 0.3 - - - Na20 8.0 7.6 7.2 8.8 9.9 K2O 1.8 2.2 1.3 2.1 3.1 MgO 0.2 - - - 0.1 CaO 0.5 0.3 1.1 3.4 2.3 BaO 3.4 2.5 1.6 2.3 2.2 Zr02 - 1.5 - - - Ce02 0.2 - - - - a(20°C;300'C) 6.27 6.33 5.53 5.41 7.02 [10'VK] Tg['C] 545 556 566 553 552 VAE'C] 1084 1105 1145 1169 1014 HE^g Na20/g] 11 11 13 22 29 S [mg/dm^] 0.7 0.7 0.7 0.8 0.9 L[nig/dm^] 121 85 126 132 142 The exemplary embodiments make it clear that the glasses according to the invention combine a very low working point and optimum hydrolytic stability, two properties which are contradictory requirements in known glasses. For example, although comparative example VI has a similarly good hydrolytic stability, its working point is too high, whereas V3 has a low working point but a poor hydrolytic stability. V2 demonstrates a high working point and a relatively poor hydrolytic stability. WE CLAIM : Borosilicate glass of high hydrolytic stability, having a composition (in % by weight, based on oxide) of: Si02 70.5 - B2O3 8-10 AI2O3 4-5.6 LiaO 0 - NazO 7-9 K2O 1.2-2.5 MgO 0-1 CaO 0-2 with MgO + CaO 0-2 BaO 0.5-4 Zr02 0-2 Ce02 0-1 F' 0-0.6 and if appropriate conventional refining agents in standard quantities. The borosilicate glass according to Claim 1, characterized by a composition (in % by weight, based on oxide) of: Si02 71 - 72.5 B2O3 8.5 - 9.5 AI2O3 > 4 - 5.5 LiaO 0-0.3 Na20 7.5-9 K2O 1.5-2.3 MgO 0-1 CaO 0-2 with MgO ( CaO 0-2 BaO 2.5 - 4 Zr02 0-2 CeOz 0-0.3 F' 0-0.6 and if appropriate conventional refining agents in standard quantities. The borosilicate glass according to Claim 1 or 2, characterized in that the ratio of the Al2O3/(Na20 + CaO) contents by weight is > 0.55. The borosilicate glass according to at least one of Claims 1 to 3, characterized in that apart from inevitable impurities it contains no AS2O3 and SbzOs. The borosilicate glass according to at least one of Claims 1 to 4, having a coefficient of thermal expansion a{20°C;300°C) of between 5.8 and 7.0 x lO'^/K and a working point V^ of at most 1130"C.

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