Daylight/nightglow colored phosphorescent plastic...

Details Daylight/nightglow colored phosphorescent plastic... Daylight/nightglow colored phosphorescent plastic...

1998-11-10

2002-04-23

Baxter, Janet (Department: 1752)

Compositions

Organic luminescent material containing compositions

With inorganic luminescent material

C524S408000, C524S433000, C524S437000, C524S439000, C252S301350

Reexamination Certificate

active

06375864

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to phosphorescent plastic compositions and articles that have an attractive bright fluorescent daylight color and a strong glow-in-the-dark phosphorescence of a color similar to that of the daylight color. In particular, the invention relates to the direct use of polymer-soluble fluorescent dyes, in combination with phosphorescent pigments, to provide an expanded and customizable palette of daylight and glow-in-the-dark colors.
The use of phosphorescent materials in the production of luminescent materials is very well known, having been used for such diverse “glow-in-the-dark” items as golf balls, rubber shoe soles, many varieties of toys, safety helmets, safety tape for bicycle visibility, directional indicators and signs, backlight for liquid crystal clocks, and the like. Phosphorescent materials have been reported for use as nighttime illumination for vehicle parts, such as wheel valve stem caps, gear shift knobs, or for phosphorescent tabs for illuminating keyholes. They have also been used for night-time illumination of plastic electronic key pads that contain informational indicia.
Phosphorescent phosphors are substances that emit light after having absorbed visible or ultraviolet radiation or the like, and the afterglow of the light that can be visually observed continues for a considerable time, ranging from several minutes to several hours after the source of the stimulus is cut off. Until recently, the most commonly known non-radioactive phosphorescent phosphor pigments were sulfides of zinc, calcium, strontium and cadmium, such as CaS:Bi (which emits violet blue light), CaSrS:Bi (which emits blue light), ZnCdS:Cu (which emits yellow or orange light) and ZnS:Cu (which emits green light). The color palette of the phosphorescent afterglow, however, has been limited to these colors.
The daylight appearance of plastic articles containing sulfide-based phosphorescent phosphor pigments is an aesthetically unappealing pale greenish or grayish white. Therefore, daylight color pigments are often added to plastic compounds containing these phosphorescent phosphor pigments. However, the added color pigments, by virtue of their particle size (e.g., about one to six microns), interfere with both the absorption of light and the emission of light by the phosphorescent phosphors, resulting in a diminished luminescence and shortening of the afterglow duration.
To attempt to overcome the interfering effects of the color pigments, it is necessary to employ large quantities of the relatively expensive phosphorescent pigments (e.g., 20% to 30% by weight) in plastic compositions containing daylight color pigments. Therefore, it has not heretofore been economical for suppliers of color concentrates to prepare plastic phosphorescent/daylight color concentrate compositions for use by end users in the manufacture of plastic articles. Another disadvantage of the sulfide-based phosphorescent phosphors is that they are sensitive to ultraviolet light, such as that of sunlight or moonlight, and thus are not weatherable. Therefore their use has, for the most part, been restricted to indoor applications.
Recently, a new group of phosphorescent phosphors that both absorb and emit light in the visible spectrum has become available. (See, for example, U.S. Pat. Nos. 5,424,006 and 5,686,022). These phosphors have a crystalline structure and are highly chemically stable metal oxide aluminates, containing one or more of strontium, calcium, magnesium, and barium, activated by europium and at least one co-activator, such as ytterbium, dysprosium, neodymium, samarium, thorium, thulium, erbium, and the like, to form a phosphorescent phosphor, such as SrAl
2
O
4
; Eu, Dy, which emits green light (about 520 nm), CaAl
2
O
4
:Eu, Nd or Sm, which emits blue light (about 442 nm), SrO.5CaO.5Al
2
O
4
:Eu, Dy, which emits blue-green light (about 490 nm), and BaAl
2
O
4
:Eu, Nd, which emits green light (about 500 nm). These new phosphors are weatherable, ie. they do not readily decompose upon exposure to ultraviolet light, such as sunlight or moonlight, and they can be used outdoors as well as indoors. The new phosphors have an afterglow that is about three to more than twelve times brighter than that of the comparable sulfide phosphorescent phosphors at 10 minutes after stimulation, and about 17 to more than 37 times brighter at 100 minutes after stimulation; moreover, the afterglow of these phosphors is still visible 15 to 24 hours or more after a single stimulation. Depending on the chemical nature of the phosphor selected, however, the color of the afterglow is limited to green, blue-green, or violet, and the daytime appearance of plastics containing these phosphors is also an aesthetically unappealing pale greenish white or grayish white.
In view of the foregoing advantages of the metal oxide aluminate, europium-activated phosphorescent phosphors, it would be desirable to provide an aesthetically pleasing daylight color to plastic articles containing these phosphorescent pigments without diminishing either the brightness or the duration of the afterglow. The following description sets forth unexpected results obtained when daylight fluorescent color dyes, rather than daylight color pigments, were added to resin compositions containing the metal oxide aluminate-based phosphorescent phosphors.
SUMMARY OF THE INVENTION
The invention provides compositions, and molded, extruded or formed phosphorescent plastic articles produced therefrom, that contain non-radioactive, non-sulfide phosphorescent phosphor pigments that emit light in the visible spectrum, preferably metal oxide aluminate:europium-activated phosphorescent phosphor pigments, in combination with polymer-soluble daylight color dyes, preferably daylight fluorescent dyes, in transparent or translucent resins.
The plastic articles produced from the compositions of the invention exhibit a remarkably rich, attractive, clear (preferably almost transparent), brilliant daylight appearance, especially a brilliant fluorescent daylight appearance, in addition to a strong, brightly colored, long-lasting luminescent afterglow in the dark. It has been discovered herein that by using dyes, especially fluorescent dyes, rather than color (or fluorescent) pigments, to provide daytime color to the plastic articles, the brightness and duration of the afterglow of the phosphorescent phosphor pigments is not diminished. Moreover, it has been discovered herein that by employing fluorescent dyes rather than fluorescent pigments, and by employing transparent or translucent resins, the phosphorescent glow of the preferred metal oxide aluminate:europium-activated pigments in transparent or translucent plastics is so strong that it illuminates the plastic article such that the color of the glow-in-the-dark luminescence appears to take on a color that is very similar to that of the daylight fluorescent dye. The “acquired” glow-in-the-dark color may be entirely different than the color of the natural luminescence of the phosphorescent phosphor. For example, an article having a clear fluorescent pinkish red daylight color has a clear bright pink glow-in-the-dark luminescence, even when the natural luminescence of the phosphorescent phosphor is bright green. Similarly, an article having a clear fluorescent orange daylight color has a clear bright orange glow-in-the-dark luminescence, when the natural luminescence of the phosphor is bright green.
Further, by varying the concentration of the daylight fluorescent dyes, and/or by mixing together two or more daylight fluorescent dyes, and/or by mixing daylight fluorescent dye(s) with conventional dye(s), the invention provides bright and strong, new and unique glow-in-the-dark hues in a palette of colors and shades that were not previously available (e.g., red, pink, orange, yellow, white, reddish violet, yellow-green, and the like). Thus, the invention compositions may be customized to create a variety of daylight, preferably fluorescent, and glow-in-the-dark colors, including pastels.
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