MXPA00005329A - Low light-transmitting neutral grey glass composition - Google Patents

Abstract

The invention relates to a glass comprised of silicon, sodium and calcium of neutral grey colour with low light transmission (less than 20%). The glass reduces the solar energy transmission such as for example the transmission of near infrared radiation (less than 14%) and to a large extent the transmission of ultraviolet radiation transmission (less than 12%). This glass comprises the following components expressed in percentages by weight:Fe2O3 between 1.20 and 2.0%;FeO between 18 and 28%(reduction percentage);Co3O4 between 0.020 and 0.030%;selenium between 0.0025 and 0.010%;CuO between 0.0050 and 0.050%. The glass of the invention avoids using colorant compounds such as nickel, chromium and manganese.

Description

COMPOSITION OF NEUTRAL GRAY GLASS OF LOW TRANSMISSION OF LIGHT. BACKGROUND OF THE INVENTION. A. FIELD OF THE INVENTION. The present invention relates to a composition and a method for the commercial production of a privacy glass, of neutral gray color, which has a low light transmission (less than 20%), and low solar energy transmission, which shows a low transmission of infrared radiation (less than 14%), and especially a low ultraviolet transmission (less than 12%), for use in the construction industry and mainly in the automotive industry. B. DESCRIPTION OF THE RELATED ART. Several patents have been developed for obtaining gray glass, for purposes of "ppvacity", which have low light transmission and low transmission of infrared and ultraviolet radiation. The glasses described in virtually all patents that refer to a neutral gray type of glass for privacy purposes, are based on three basic components: iron oxide, cobalt oxide and selenium, using different proportions and, in conjunction with the formulation typical of a silica-sodium-calcium glass, they constitute the basic composition of glass. Such is the case of the glasses of the North American patents Nos. 4,873,206 of James Jones, issued on October 10, 1989, the patent No. 5,393,593 of Gulotta et al., Issued on February 28, 1995, and the patent No. 5,278,108 of Cheng et al., issued on January 11, 1994, in which these components are used without any other additional component.

Some other panes of other patents, such as those mentioned below, use, in addition to the three mentioned components, different metallic elements that give the final product the characteristics that allow it to be classified as privacy glasses to be used in the industries of construction and automotive. U.S. Patent No. 5,308,805 to Baker et al., Issued May 4, 1994, discloses a low-transmission neutral gray glass, in which one of the claimed components is nickel oxide in proportions of 100 to 500 ppm. In the past, gray heat-absorbing glass containing nickel in its structure often had nickel inclusions in the form of sulfur that, during the melting of the glass, formed until they appeared as small invisible particles that could not be distinguished by the naked eye in a glass already formed. The problem with such inclusions of nickel sulphide, is due to its high coefficient of thermal expansion that can cause sufficient thermal stress to fracture a glass plate. This is a singular problem in glass pieces where it is subjected to a thermal treatment such as tempering, in which the presence of nickel sulphide causes an excessive percentage of part breakage during or consequently to the tempering process. An additional disadvantage of the glasses containing nickel is the color change suffered by these after the thermal process, such as after tempering.

U.S. Patent No. 5,023,210 to Krumwide et al., Issued June 11, 1991, discloses a composition of neutral low-transmission gray glass, which does not use nickel. In order to achieve the characteristics similar to those of a neutral gray glass, it uses chromium oxide in quantities of 220 to 500 ppm of Cr2O3, of its composition, which in these proportions produces a gray tone and adjusts the levels of selenium and cobalt to make it neutral tone. However, in prior references a preference for not using these compounds is mentioned due to the problems presented by the difficulty of melting the chromium compounds (U.S. Patent No. 4,837,206), and additionally because they have difficulties in discarding the solid materials containing said compounds. Also, in the North American Patent No. 5No. 308,805 the drawback of chromium oxide used as a coloring agent is mentioned, since it requires the use of operations and apparatus additional to the conventional ones inside the foundry furnaces, in order to reach the necessary conditions to produce the desired glasses. U.S. Patent No. 5,346,867 to Jones et al., Issued September 13, 1994, discloses a neutral gray heat-absorbing glass composition utilizing manganese and titanium oxide to increase selenium retention (which is a high cost component), during the production process. Although from previous references (U.S. Patent No. 4,873,206), it is known that the use of manganese has a tendency to form yellowish brown coloration when exposed to ultraviolet radiation, for example, that received by solar radiation, making it difficult to maintain uniformity of the product, and the use of titanium causes a yellowing when the glass comes into contact with the liquid tin of the float process. This is what makes these two aspects undesirable during glass production because it makes color control critical to obtain the desired shade during manufacturing. Jones and others mention in their '867 patent that the process of solarization is a phenomenon associated with the change from Fe3 + to Fe2 + which causes an undesirable change in color, mentioning that they found that this does not happen in the glass described and Additionally, the use of titanium oxide is incorporated into the glass to obtain the desired range of dominant wavelength, as well as to reduce the transmission of ultraviolet radiation. On the other hand, it is well known to those skilled in the art, that the addition or substitution of one or more dyes by another or others, or by the change of the relative proportional amount in the composition of the glass, affects not only the color of the product, such as for example the dominant wavelength of the color or the purity of excitation, but also the light transmission, the absorption of heat and additional properties such as the transmission of ultraviolet and infrared radiation. Since ancient times copper has played an important aspect in the production of glass, ceramics and colored pigments. It has been recognized, for example, the coloring of Persian ceramics by its tonality conferred by Copper. Of special interest to the artists of ceramics, are turquoise blue and especially the dark blue Egyptian and Persian (Waldemar A.Weil; Colored Glasses, Society of Glass Technology, Great Bretain, P.154-167, 1976). Copper has been used within glass compositions, not only in those of the silica-sodium-calcium type, but in some others such as those containing, for example, borosilicate. Thus, the color developed depends on the base of the glass, its concentration and its state of oxidation. For the case of the glass mentioned as a base, the copper in the form of oxide imparts a blue coloration of a greenish tone, specifically turquoise, however, inside the glass, the copper may be in its monovalent state, which does not give color. Thus, the blue-green coloration depends not only on the amount of copper present, but on the ionic balance between the cuprous and cupric states. The maximum absorption of copper oxide is in a band centered at 780 [mu] m and a secondary weak peak is present at 450 [mu] m, which disappears at high soda contents (around 40% weight) (CR Bamford Color Generation and Control in Glass, Glass Science and Technlogy, Elsevier Scientific Publishing Company, P.48-50, Amsterdam, 1977). In the production of ruby red glass, a mixture containing copper oxide together with some reducing agent (SnO is commonly used), is melted under reducing conditions. The initial mix shows the characteristic blue color of copper II, but as soon as the melting begins, the color changes to a pale straw yellow, which is produced during this stage. Due to a thermal treatment at a temperature between the annealing point and the softening point, the ruby red color develops. Yes, during the merger, the reduction state is carried beyond a critical stage, the color changes to coffee and appears opaque or "off". On the other hand, if the copper is insufficiently reduced, some blue traces remain and the ruby red color does not develop (Amal Paul, Chemistry of Glasses, Chapman and Hall, P.264-270, London, 1982). US Patent No. 2,922,720 to Parks et al., Issued June 20, 1957, mentions the use of copper in glass as: "... Copper has been used as a coloring agent for glass by developing a ruby red coloration. , but to be able to obtain the color in an open melting furnace, it has been necessary to use cyanogens as a reducing agent ... ", he also mentions the effect of copper on the coloration of the glass, as due to the colloidal suspension of particles of metallic copper in the glass, and by analogy it is believed that a particle size produces ruby red colors, depending on the intensity of the color, of the copper concentration. For smaller particle sizes, the color effect is zero. The glass of the present invention, avoids the use of some metals that the patents mentioned above describe as very important, such is the case of nickel, chromium and manganese. In the glass of the present invention, copper oxide (CuO) is used in addition to the use of iron oxide, cobalt oxide and selenium, as an alternative to obtain a slightly greenish gray hue within the neutral color region frequently used in the automotive and construction industry. Additionally providing a reduction in the transmission of ultraviolet radiation and a reduction in the near infrared region by absorption bands around 800 nanometers that helps reduce infrared solar transmission. Therefore, in the present invention, obtaining a neutral gray glass with a light transmission less than 20% and preferably between 15 and 18% for a glass thickness between 3.9 and 4.1 mm, and a transmission reduction is achieved of solar energy that manifests as a transmission of infrared radiation less than 14%, and a transmission of ultraviolet radiation less than 12%. SUMMARY OF THE INVENTION It is therefore a principal objective of the present invention to provide a composition of a neutral gray glass, by using copper in the form of oxide as an alternative for obtaining the typical greenish-gray color in the privacy glasses used in the construction industry and, preferably, in the automotive industry. It is also a principal object of the present invention to provide a composition of a neutral gray glass, based on a typical composition of a silica-sodium-calcium glass, including the compounds of cobalt oxide, iron oxide and selenium, as well as oxide copper, by which the use of the following components is avoided: nickel, chromium and manganese. It is still a principal object of the present invention to provide a composition of a neutral gray glass, of the aforementioned nature, by using copper in the form of an oxide, which has an absorption in the near infrared regions, but mainly in the ultraviolet region, due to its combination with iron oxide, cobalt oxide and selenium, to be able to replace nickel, chromium and manganese within the existing formulations, since these chemical elements present 5 characteristics of the undesirable product or process under certain circumstances. It is a further main objective of the present invention to provide a neutral gray glass with a luminous transmission of less than 20% and preferably between 15 and 18% for a glass thickness between 3.9 and 4.1 mm, and a reduction in the transmission of solar energy that manifests with a transmission of infrared radiation less than 14%, and a transmission of ultraviolet radiation less than 12%. It is further a main objective of the present invention to provide a neutral gray glass having a dominant wavelength of 15 480 to 575 μm, preferably 500 to 570 μm, and a color excitation purity of less than 10% , preferably less than 8% These and other objects and advantages of the neutral gray privacy glass of the present invention will be disclosed to those skilled in the art from the following detailed description thereof DETAILED DESCRIPTION OF THE INVENTION Typical composition of a silica-sodium-calcium glass used in the construction industry and automotive, and formed by the well-known process of glass float, is characterized by the following formulation based on percentage by weight with respect to the total weight of the glass. glass Components% weight S¡O2 68 to 75 AI2O3 0 to 5 CaO 5 to 15 MgO 0 to 10 Na2O 10 to 18 K2O 0 to 5 The neutral gray glass composition of the present invention is based on the position described above to which the following coloring compounds have been added: Components% weight Fe2O3 1,200 to 2,000 CuO 0.005 to 0.050 Se 0.0025 to 0.010% reduction 18.0 to 28.0 It is common in the glass industry to refer the total iron content in the composition of glass or of the mixture to melt glass, as the total iron expressed as Fe2O3. When a batch of glass is melted, part of that total iron quantity is reduced to FeO, while the rest is kept as Fe2O3. The balance between the ferric and ferrous oxidation states in the molten mixture is the result of a final oxide-reduction equilibrium that is a mixture between the use of oxidizing or reducing agents in the feed mixture and the combustion characteristics, example the air-gas ratio used inside the furnace to melt said mixture. The reduction of Fe2O3 produces not only FeO, but also oxygen, reducing the combined weight of the two iron compounds in the resulting glass. Consequently, the weight combination of FeO and Fe2O3 contained in a resulting glass composition will be less than that fed during mixing, or of the total of the initial iron used expressed as Fe2O3. For this reason, it is understood that the total iron is the iron expressed in the form of Fe2O3, as used in the description of this patent application, meaning the amount of iron fed into the mixture before its reduction. And it should be understood that the reduction value of the ferrous state is defined as the weight of the ferrous oxide (FeO) expressed as Fe2O3 in the glass product, divided by the weight percentage of total iron expressed as Fe2O3. This amount in the glass industry is commonly expressed as a percentage of reduction. The physical properties such as the transmission of light correspond to variables calculated based on internationally accepted standards. So that the transmission of light is evaluated using the illuminant "A" and standard observer of 2o known also as of 1931 [Publication C.I.E. 15.2, ASTM E-308 (1990)]. The range of wavelength used for these purposes is 380 to 780? M, integrating values in numerical form with intervals of 10? M. The transmission of solar energy represents the heat that the glass gains directly, evaluating from 300 to 2150? M with intervals of 50? M, the numerical form of calculation uses as recognized standard values those reported by Parry Moon in "Proposed Standard Solar Radiation Curves for Engineer Use "', Franklin Institute, Vol. 230, p. 604, table II, 1940. The calculation of the transmission of ultraviolet (UV) radiation, involves only the participation of solar UV radiation, so it is evaluated in the range of 300 to 400 μm wavelength using intervals of 10? M. For the transmission of infrared (IR) radiation, only the range in which the solar spectrum has influence is contemplated, as is UV radiation, which is why the range of the near infrared region is used from 800 to 2150? M , with intervals of 50? m. Both calculations employ the Parry Moon solar radiation values mentioned above. The amount of solar heat that is transmitted through the glass can also be calculated by the contribution of thermal energy with which each of the regions where the solar spectrum has influence, which is from the ultraviolet region (280? M), participates. ), up to the region of the near infrared (2150? m), which is 3% for UV, 44% for the visible and in the order of 53% for IR, however, the values of transmission of direct solar energy, in the present invention, are calculated based on a numerical integration taking into account the entire range of the solar spectrum from 300 to 2150 μm, with intervals of 50 μm and using the solar radiation values reported by P. Moon. The specifications for the determination of color such as the dominant wavelength and the excitation purity, have been derived from the Tristimulus values (X, Y, Z) that have been adopted by the International Commission of Illumination (CIE), as a direct result of experiments involving many observers. These specifications can be determined by calculating the trichromatic coefficients x, y, z of the Tristimulus values that correspond to the colors red, green and blue respectively. The trichromatic values are plotted in the chromaticity diagram and compared with the coordinates of the illuminant "C" considered as the lighting standard. The comparison provides the information to determine the color excitation purity and its dominant wavelength. The dominant wavelength defines the wavelength of the color and its value is in the visible range, from 380 to 780? M, while for the purity of excitation, the lower its value, the closer it tends to be a neutral color. A deeper understanding of these issues can be obtained in the "Handbook of Colorimetry" published by the "Massachusetts Institute of Technology" by Arthur C. Hardy, issued in 1936.

Claims (1)

1. CLAIMS. 1. A neutral gray silica-sodium-calcium glass that includes as unique coloring components, in weight percentage: Fe203 from 1.20 to 2.0%; FeO from 18 to 28%, as a percentage of reduction; Selenium from 0.0025 to 0.010%; and CuO from 0.0050 to 0.050% the glass has a light transmission less than 20%, a transmission of near infrared radiation less than 14%, a transmission of ultraviolet radiation less than 12%, a dominant wavelength of 480 to 575? m and an excitation of color purity of less than 10%.