Description

The present invention relates to a brown-red glass for containers of wine, beer and similar alcoholic drinks. Just since the early century, a similar glass was ma¬ nufactured by using dyeing compounds in an oxidative environment. Said process is no more practised for economical as well as environmental reasons and for grounds connected to the production technology. But the main reason is depending on the fact that a similar glass could not at present satisfy the market requirements, especially in the field of the spectro- photo etric properties of said glass.

Particularly the brown-red glass, which was manufactured in this early century, could not satisfied what the market is to-day requiring in terms of filtering power (i.e. protection against the consequences of the photo-chemical energy on the food contained inside such a glass). Indeed, the only care of the manufacturers in this early century was to prod- duce a glass container as such. The production was ranging from green, half-white, white glass containers for wine, alcoholic (or not) beverages, to amber glass containers for beer. The brown-red glass, which was ma¬ nufactured in this early century represented the typi¬ cal attempt to diversify the glass colour. Nowadays the experts pay their attention to a glass, which is adapted to protect the contents (also taking into account the value of some beverages), in addition to that it should have a colour, which could be welcomed by the sight.

A recently granted European patent No.O 249 651 to AVIR FINANZIARIA S.p.A. - Asti ITALY, claims a green glass, which has filtering power higher than 95% for samples of 5 mm. thickness, whereas another European patent No. _O 347 945 to NORDVETRI S.p.A. - Pergine Valsugana (TN) ITALY, claims an amber-green glass, which has a filtering power higher than 99,5% for samples of 3 or

5 mm. thickness. It is well known that the brown-amber glass, which is usually used for beer containers, pre¬ sents the highest protection against the action of the U.V. rays, but it does not represent the best solution for containers of a vintage wine, of a champagne, of a barolo wine, of a cognac, etc.

Therefore, the most recently searches of the glass ma¬ nufacturers were developed towards two aims: the first one to improve the glass filtering power and the second one to satisfy also the sight requirements of the market.

The problem, which the glass according to the invention intends to solve, is to offer to the market, besides the recently offered choices, a further opportunity of choice by means of a glass, which:

- could be manufactured with raw materials and dyeing compound, which are easily found in the market and which don't compromise the production process;

- offers a substantial protection against the action of the U.V. radiation the beverages inside a contai¬ ner, which is made of said glass and

- substantially satisfies the sight requirements of the market.

_S aid problem is solved by the glass according to the invention, which is characterized in that it presents a

dominant wave length, which is substantially equal to at least 950 rim. for 3 mm. thickness samples and therefore it is amber-red coloured, a filtering power of said glass being substantially provided higher than

99,5% for 3 mm. thickness samples.

Said and further characteristics will be apparent according to the following description and to the alleged drawings, where:

Fig.l represents a transmission curve of the glass according to the invention, which is compared with the transmission curves of a light-amber glass and of a brown-amber glass, for 3 mm. thickness samples;

Fig.2 represents the transmission curve of a brown-red glass, which was manufactured in the early century.

A' brown-red glass, which is amber-red coloured, is a glass, which has a dominant wave length (i.e. the property, which defines the glass colour tonality) substantially higher than 590 nm. for 3 mm. thickness samples, with respect to 580-583 nm. of an amber glass and to 573 nm. of an amber-green glass. In addition, the filtering power of such a glass (i.e. the glass protective capacity against the action of the U.V. radiations, which are the most dangerous, because they are provided with the highest energy) is adapted to

reach a value, which is at least equal to 99,5% for 3 mm. thickness samples.

It is well known that the definition of the total parameters of a glass and of its behaviour are depending on its following parameters:

- dominant wave length, which defines its colour tona¬ lity;

- purity, which defines its colour intensity;

- brilliance, which defines the light, which is trans¬ mitted with respect to the air;

- filtering power, which defines the protective capa¬ city of the glass under examination, i.e. the capa¬ city to absorb the radiation, which is in particu¬ lar comprised within the so-called "actinic area", i.e. in the area, which is comprised within the range of 350-450 nm.

Therefore, the first three parameters give the colorimetric properties of the glass, which can be ap¬ preciated by the eye and which don't provide any idea about the protective action of the glass under examination, whereas the index of such a protection is given by the fourth parameter. All of glasses, compri¬ sed the white one, are able to absorb the radiation be¬ low 300-350 n ., but not all of them are able to protect from the radiations, which are dangerous for

the content, i.e. the radiations, which have a higher energetic content and which are comprised within the so-called "actinic area". The glasses, which present a high filtering power, are claimed in many patents. If the transmission curve 1 of Fig.l is examined, i. e. the curve regarding the glass according to the invention, it could be seen that the ordinate is substantially null, independently of the incident light intensity, up to a value of wave length substantially equal to 450-470 nm. The consequence is that the filtering power of the glass according to the invention is comparable with the light-amber glass filtering power (represented by transmission curve 2) and with the brown-amber filtering power (represented by the transmission curve 3).

If the transmission curves 1, 2, 3 Fig.l are examined, it could interest to see the value of their transmission in correspondence of the wave length equal to 550 n ., this value being depending on the sulphide content, which is present in the glass bath. In addition, the amber-red glass is keeping a good trans¬ parency, allowing in such a way not only to ascertain the presence of a liquid inside the container, but also to establish its more or less brown colour.

The glass according to the invention allows to obtain in lack of chromium oxide the development of brown- amber chromophores (which the value of the filtering power with regard to the U.V. radiations is depending on) and of red chromophores, which allow to obtain a dominant length value substantially equal to 590 nm. for 3 mm. thickness samples, with respect to about 580 nm. of the amber glass. In order to obtain in the melting tank the formation of the a.m. chamophores, the vitrifiable mixture should present an oxido-reductive state with a Redox number (according to Simpson) substantially lower than -20 up to -25. In such a way the iron polysulphide chromophore is obtained even in presence of iron-oxide percentages substantially comprised in the range of 0,10-0,25% in a substantially reductive ambient.

It is just the oxido-reductive glass state, which allows the second chromophore formation, just the red one. Selenium, in the state of metallic selenium, or a selenium compound, zinc selenite, is reduced to Se—, by reacting with the bivalent iron, from which the ferrous selenide is obtained, which is (according to Volf) responsible of the red chromophore. Therefore this reason is why the reducing power of the vitrifiable mixture, which is expressed in Redox

unities, should be comprised inside the range of -20 and -25.

A good control of the furnace and of the vitrifiable mixture allows to keep substantially uniform the colour of the finished product.

The oxido-reductive, substantially lightly reducing state of the vitrifiable mixture in a melting tank, in order to ensure no variation of the ferrous-ferric balance, can be obtained with the traditional raw materials: blast furnace slag, coal, pyrite, etc. The transmission curve 1 Fig.l, relating to the glass according to the invention, is showing how the trans- mittance increases towards the infra-red wave lengths. This fact is depending on the total iron content (par¬ ticularly on bivalent iron content) , which is substan¬ tially lower than the amber glass iron content. Therefore the amber-red glass allows a higher heat con¬ duction and consequently it requires a lower energy consumption, due to the melting of the vitrifiable mixture. The temperature of the tank bottom could be comprised within a range of 1200 and 1220 ^* C. T _h e _b asic compounds of the vitrifiable mixture are adapted to comprise: siliceous sand, calcium carbonate, dolomite, or just one of the following compounds: sodium carbonate or furnace slag.

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PCT/EP95/00080

The refining and dyeing compounds are: coal, pyrite, selenium (or its compounds) or a mixture of said com¬ pounds with presence of sulphate, in order to assure the pre-arranged Redox number.

The amount of the above mentioned raw materials are such to obtain a glass, which has the following percen¬ tage composition:

Si02 = (70-72)% Fe203 = (0,10-0,25)%

A1203 = (1-2,5) FeO = (80-90)%

Na20 = (13,5-14,5)% S03 = ( 0,04-0,07)%

K20 = (0,5-1)% S— - 80-90% of S tot

CaO = (7-9)% Selenium 50-70 ppm

MgO = (3-4)%

In addition, the dyeing substances assure a filtering power, which is substantially equal to or even higher than 99,5% for 3 mm. thickness samples. Fig.2 shows the transmission curve of a brown-red glass, which is obtained with a dyeing mixture of man¬ ganese-iron. The filtering power of the glass with mangenese could be lower than the filtering power of the glass 1 Fig.l, as it presents a lower absorption within the range U.V.-first visible and it could be less protective with regard to photo-bioligic action of the above mentioned "actinic area".

In addition it is apparent from the curve 1 Fig.l that the transmittance value in the field of infra-red radiation having a wave length of 1000 nm. (always with regard to the glass according to the invention) is substantially higher than 30% for 3 mm. thickness samples.