Strong UV absorber glass

Recently, a great deal of attention has been directed to the harmful effects of ultraviolet (UV) radiation on humans. Much of the attention has concerned the effect of such radiation on the eye. Accordingly, the value of strong UV absorption by eye glasses has been recognized.

It is well known that UV radiation can also cause degradation and discoloration in such items as paints, fabrics and plastics. Therefore, strong UV absorption by architectural glazing materials is beneficial. The sun is not the only light source that emits UV. Various types of artificial lighting, such as halogen lamps, may also emit UV radiation. Accordingly, there is an interest in minimizing UV radiation emitted by artificial sources as well. This may be achieved by utilizing UV absorbing glass in the fabrication of lamp envelopes, reflectors and lenses.

It is common knowledge that photochromic glasses are activated by absorption of UV radiation. The most evident utility of such glasses has been in control of visible light transmission. Inherently, however, they also strongly influence the intensity of UV transmission. This behavior is readily understood in terms of the Grotthus-Draper Law which states that: Only light that is absorbed can produce chemical change.

Photochromic glasses containing silver halide crystals absorb strongly at wavelengths shorter than 320 nm, but only absorb weakly in the interval between 320 and 400 nm. Even though radiation in the wavelength range of 320-400 nm is much less harmful than that in the shorter wavelength region, for some applications it is desirable to eliminate transmission of this radiation as well. Therefore, several suggestions have been advanced for accomplishing this. For example, it has been proposed to dope the above glasses with ions which provide additional absorption of UV radiation.

Photochromic glasses containing halides of copper and/or cadmium are also known, but not commercially available. Such glasses were originally disclosed in U.S. Pat. No. 3,325,299 (Araujo I). The transmission cutoff in these glasses occurs at approximately 400 nm, and is much sharper than that in silver halide glasses. Consequently, protection against UV radiation is complete in these glasses without additional doping. The precipitation of the copper halide phase in these glasses is like that of the silver halide phase in the silver halide photochromic glasses. It may require heating of a glass containing in solution the copper and halogen ions of interest. As taught in the patent, the glass is maintained for a short time at a temperature somewhat above the annealing point.

U.S. Pat. No. 4,166,745 (Araujo II) discloses copper-cadmium photochromic glasses that have a refractive index of 1.52-1.54, and that may be strengthened by an exchange of sodium ions for lithium ions.

U.S. Pat. No. 4,222,781 (Morse et al.) discloses photochromic glasses based on copper halide wherein good optical clarity and photochromic properties are provided by controlling the alkali metal oxide, the Al2 O3 and the B2 O3 concentrations in the base glass, and/or by adding MoO3 or WO3 to the composition.

European Publication Number 0 456 351 A2 [U.S. Pat. No. 5,145,805] (Tarumi et al) discloses two glass families containing up to 15% copper halide. The non-phosphate family comprises, in percent by weight, 20-85% SiO2, 2-75% B2 O3, up to 15% Al2 O3, up to 30% alkali metal oxides, up to 10% divalent metal oxides and up to 10% of at least one of ZrO2, La2 O3, Y2 O3, Ta2 O3 and Gd2 O3. The broad ranges of this disclosure fail to disclose critical features of the present invention.

There are numerous applications for glasses having the sharp UV cutoff inherent in the copper or copper-cadmium halide glasses. Frequently, however, such applications require avoiding any change in visible absorption such as occurs in photochromic glasses exposed to UV radiation, e.g., sunlight. Many UV materials exhibit yellow color which is unacceptable for certain applications. U.S. Pat. No. 5,322,819 (Araujo III) disclosed a non-photochromic, copper halide containing UV Absorber glass which exhibits a sharp cutoff in transmission in the wavelength interval between visible and UV radiation. Specifically, the Araujo III reference ('819) disclosed a non-photochromic R2 O--B2 O3 --SiO2 glass which contains a precipitated cuprous or cuprous-cadmium halide crystal phase and has a sharp spectral cutoff at about 400 nm, the glass composition consisting essentially of, in cation percent, 35-73% SiO2, 15-45% B2 O3, 0-12% Al2 O3, the Al2 O3 being less than 10% when the SiO2 is over 55%, 0-12% Li2 O, 0-20% Na2 O, 0-12% K2 O, the Li2 O+Na2 O+K2 O being 4.75-20%, 0-5% CaO+BaO+SrO, 0.125-1.0% Cu2 O, 0-1% CdO, 0-5% ZrO2, 0-0.75% SnO2, 0-1% As2 O3, and/or Sb2 O3, the glass containing 0-1.25% Cl, 0-1.0% Br, 0.25-2.0% Cl+Br and 0-2% F by weight.

For certain applications such as for protecting the human skin and articles having complex shapes and sizes, currently available UV absorber glass may not be practical for providing the needed protection. Thus, while the glasses disclosed in the '819 patent have been shown to be very effective in absorber UV radiation, such glasses are generally available in bulk form, making then impractical for certain applications such as UV absorber paints and varnishes as well as UV absorbing skin creams for example. Accordingly, it is a principal object of the present invention to provide UV absorbing glass in a form which can be readily utilized in such applications.

SUMMARY OF THE INVENTION

The object of the present invention is achieved by providing UV absorbing glass in a form suitable for protecting from UV radiation, articles having complicated shapes. Examples suitable forms of the inventive UV absorbing glass material include, (1) a liquid such as a lotion or cream for protecting the skin, (2) paints and varnishes for applying over articles having complicated shapes and sizes, and (3) a solution with which clothing can be impregnated to form UV absorbing clothing.

Briefly, the invention relates to a strong UV absorbing glass consisting essentially of, in cation percent, 15-30% SiO2, 50-60% B2 O3, 2-5% Al2 O3, 0-6% Li2 O, 0-3.0% Na2 O, 14-20% K2 O, 0.5-1.0% CuO, 0.4-0.7% SnO2, 0.5-1.5% Cl, and 0.7-1.5% Br.

In another aspect, the invention relates to a method of making UV absorbing liquid or gel by:

a) providing a UV absorbing glass;

b) grinding the glass into fine powder having average particle size in the range of 1-5 microns; and

c) suspending the fine powder in a matrix to form a liquid.

In still another aspect, the invention relates to a method of producing essentially haze-free (i.e., transparent), strong UV absorbing glass by:

a) providing a strong UV absorbing glass having a known refractive index, and containing copper and halides;

b) melting the glass;

c) quenching the glass by rolling said glass into a thin roll or ribbon; and

d) heat treating said ribbon to form an essentially haze-free, UV absorbing glass.

The heating process leads to the growth of copper halide crystals in the glass.

Optionally, for applications where it is not practical to apply the roll or ribbon of glass over the article, the UV absorbing glass ribbon can be ground into a fine powder which can subsequently be suspended in a matrix to form a UV absorbing liquid which can then be applied to the surface of the article to be protected. For applications requiring transparency, the refractive index of the matrix is preferably the same or substantially the same as that of the UV absorbing glass. A particularly useful matrix for such applications is index matching oil. Examples of applications where use of the liquid form may be useful include, UV absorbing paints and varnishes, UV absorbing body lotions or creams, as a spray for such objects as automobiles and boats, and other similar applications. In a further aspect, the invention relates to a method of making a transparent UV absorbing liquid by:

a) providing a strong UV absorbing glass composition consisting essentially of, in cation percent, 15-30% SiO2, 50-60% B2 O3, 2-5% Al2 O3, 0-6% Li2 O, 0-0.7% Na2 O, 14-20% K2 O, 0.5-1.0% CuO, 0.4-0.7% SnO2, 0.5-1.5% Cl, and 0.7-1.5% Br;

b) melting the glass;

c) forming the melt into a thin sheet of glass to quench the glass;

d) heat treating the glass to grow tiny crystals of CuCl in the glass;

e) grinding the heat-treated sheet of glass into fine powder having average particle size in the range of 1-5 microns;

f) suspending the fine powder in a transparent liquid to form a transparent UV absorbing liquid.

In still a further aspect, the invention relates to a method of protecting an article from UV radiation by applying a coating of the inventive UV absorbing liquid on the surface of the article to be protected.