Phosphorescent Marking Material

1. Field of Invention

The present invention relates to phosphorescent or photoluminescent materials and, more particularly, is directed to a non-toxic phosphorescent marking material and a method of marking same.

2. Description of the Prior Art

It has long been recognized that the appeal of certain toys can be enhanced by imparting phosphorescent properties to the various elements thereof. Crayons have become a standard teaching tool for children because they allow children to express themselves artistically. Crayons are clean, safe and easy to use. A need exists for a phosphorescent marker which is safe for children.

Heretofore it has been possible to impart phosphorescent properties to paint and chalk due to their thick viscosity. For example, phosphorescent pigments can be mixed in paint. U.S. Pat. No. 2,396,219 discloses a phosphorescent chalk writing material which is toxic and unsafe for use by children. In addition, chalk makes dust which is not optimal for a permanent clean marking material. The use of a phosphorescent material such as calcium sulphide phosphor in a crayon is not acceptable because calcium sulphide phosphor is toxic and it will settle out. The use of non-toxic phosphorescent pigments in a wax base marking material has been met with limited success because of the lack of a suitable suspension formula and an acceptable suspension process. Currently available phosphorescent pigment particles that are encapsulated in glass frit are heavy and cannot be effectively made into a phosphorescent crayon by conventional methods because the particles settle out of the formula and/or are not distributed throughout the crayon. Autoradiogram marking pens, such as the phosphorescent ink marking pen disclosed in U.S. Pat. No. 4,510,392, are sufficient for exposing film, but they have very low luminous properties for visual effects.

While non-toxic phosphorescent material is available, the pigment is generally unsuitable for use in wax base marking materials because of the problems and difficulties in suspending the phosphorescent material in the base mixture. U.S. Pat. No. 3,392,123 discloses an oxygen activated, wax based, chemiluscent marking material. The marking material is limited in use because it can be activated only once and the tetrakis (demethylamino) ethylene contained therein is corrosive. A need exists for a non-toxic wax base marking material containing suspended phosphorescent particles which can be molded or extruded.

It is an object of the present invention to provide a non-toxic phosphorescent marker which does not suffer from the disadvantages and limitations of existing phosphorescent markers.

Another object of the present invention is to provide an effective phosphorescent wax base marking material which can be utilized for a variety of applications including use as glow in the dark crayons for children.

A further object of the present invention is to provide a non-toxic phosphorescent pigment marker which is composed of a wax base and inert filler mixture, the filler being at least partially transparent to actinic radiation. Phosphorescent pigment particles are suspended in the wax base and filler mixture. The weight of phosphorescent particles is in the range of 10% to 50% of the total weight of the marking material. The composition of the marking material is such that a strip of the marking material is rubbed off or deposited on a surface when the marker is rubbed against the surface. The deposited material contains the suspended phosphorescent particles which luminesce when excited by light.

Yet another object of the present invention is to provide a method for making a non-toxic wax base phosphorescent marker. The process comprises the steps of mixing a plurality of phosphorescent particles with a wax base having an inert filler mixed therewith. The wax base and filler mixture are at least partially transparent to actinic radiation. The wax base and filler mixture is such that it is capable of keeping phosphorescent particles suspended therein, the particle sizes being in the range of 5 to 20 microns.

The invention accordingly comprises the method and apparatus, and together with their steps, parts, elements and interrelationships that are exemplified in the following disclosure, the scope of which will be indicated in the appended claims.

A fuller understanding of the nature and objects of the present invention will become apparent upon consideration of the following detailed description taken in connection with the accompanying drawing, wherein the drawing is a perspective view of a crayon embodying the invention.

Referring now to the drawing, there is shown a marking material 10 in the form of a crayon. Crayon 10 is composed of a carrier 12, which includes a base 14 and filler particles 16, and a plurality of phosphorescent pigment particles 18 are suspended in the carrier.

Base 14 is composed of a material which is suitable for molding or extrusion. In the preferred embodiment, base 14 is a wax base vehicle, for example micro-crystalline wax or bees wax, or a soap base or a blend thereof. In an alternative embodiment, base 14 is composed of a plastic that is compatible with the other components, for example, a plastic such as a low density plastic. Non-toxic petrolatum, such as petroleum jelly or mineral oil, is added to base 14 to form a base mixture that has a somewhat greasy configuration. Stearic acid or cetyl alcohol or stearyl alcohol or hydrogenated castor bean oil is added to the base mixture to impart a crumbly effect. A wax, for example, Fischer Traupe wax or paraflint or carnauba wax, is added to the base mixture for the purpose of imparting hardness to the base mixture. In an alternative embodiment, a low density plastic, for example a polyethylene such as that sold under the trade name AC6, is added to the base mixture to impart hardness and strength. Also, it has been found that a vinyl resin, such as that sold under the trade name ELVAX, imparts hardness and strength to the base mixture. The base wax mixture is then heated and melted to form a final base mixture or base 14, the mixture being heated to a temperature in the range of 160.degree. F. to 250.degree. F., preferably 175.degree. F. to 200.degree. F. It is preferred that the mixture is remained at a temperature in the range of 170.degree. F. to 200.degree. F. during processing.

Filler particles 16 are added to the melted base mixture 14. The filler particles 16 which are composed of an inert filler material such as magnesium silicate or powdered talc, having particle sizes in the range of 8-10 microns, are transparent or partially transparent to actinic radiation. In addition, filler particles 16 have a low density so that they remain suspended in the base mixture 14. The quantity of filler particles 16 by percent of total weight is in the range of 10% to 30% and preferably, 13% to 20%. The filler particles 16 are dispersed uniformly in the base material by mixing or milling or whipping. Preferably, the base/filler mixture is milled using, for example, a Tri-Homo colloid mill which is operating at 3700 rpm. The base/filler mixture exhibits anti-settling properties for the phosphorescent pigment particles 18 so that the phosphorescent particles remain suspended in the base/filler mixture and do not settle to the bottom of the base/filler mixture.

Next, phosphorescent pigment particles 18, for example, a non-toxic pigment having particle sizes in the range of 5-20 microns, are added and stirred or whipped into the base/filler mixture until the particles are evenly disbursed therein. In one embodiment, the base/filler/pigment particle mixture was whipped at approximately 1000 rpm for 2-3 minutes using a standard Lightning mixer that was equipped with a shear blade. The quantity of phosphorescent pigment particles by percent of total weight is in the range of 20% to 50% and, preferably, in the range of 25% to 35%. The resulting mixture is suited to be molded or extruded without settling over a temperature range of 170.degree. to 275.degree. F.

In a specific embodiment of the invention, approximately twelve phosphorescent crayons were made by first combining or mixing 20 grams of paraffin wax, 15 grams of Mobil 2305 micro wax, 7.5 grams of petroleum jelly, 5 grams of stearic acid and 2.5 grams of Fisher Traupe wax. Then, the mixture is heated to a temperature in the range of 195.degree. F. to 200.degree. F. to form a melted base mixture. Once heated, the mixture is maintained at a temperature in the approximate range of 170.degree. F. to 200.degree. F. until it is finally cooled. Next, 15 grams of No. 1250 micro talc is added to the base mixture and milled using a colloid mill to form a base/filler mixture. Next, 25 grams of phosphorous pigment, such as Hanovia Brand P1000, is added to the base/filler mixture and whipped at approximately 1000 rpm for 2-3 minutes to form a final marking mixture. The final marking mixture is poured into a mold and cooled. It is preferred that the poured mixture and/or mold is actively cooled. After cooling, the crayon is removed from the mold. The crayon marked well on a variety of surfaces. The phosphorescent pigment particles impart luminescent properties to the crayon and luminesce when excited by light. In one test, the marking material was rubbed onto a surface. The strip left on the surface luminesced brightly for four to ten seconds and continued to luminesce for approximately six hours. It is to be understood that, in another embodiment, the crayons are extruded rather than molded.

In another embodiment of the invention, a base mixture composed of a mixture of 20 grams of paraffin wax, 15 grams of Mobil 2305 micro wax, 9.5 grams of petroleum jelly, 5 grams of stearic acid and 2.5 grams of Fisher Traupe wax is heated to a temperature in the range of 195.degree. F. to 200.degree. F. until the mixture is melted. Once heated, the mixture is maintained at a temperature in the approximate range of 170.degree. F. to 200.degree. F. until final cooling. Next, 15 grms of No. 1250 micro talc is added to the melted mixture and milled using a colloid mill to form a base/filler mixture. Next, 35 grams of phosphorescent pigment particles (P1000) is added to the base/filler mixture and the resulting is whipped at at approximately 1000 rpm for 2-3 minutes to form a final marking mixture. Next, the final marking mixture is poured into a mold having a desired shape, for example the shape of a crayon. The poured mixture and/or mold is passively or actively cooled. Finally, after cooling, the finished crayon 10 is removed from the mold. Alternately, the resulting whipped mixture is fed to an extruder and extruded into a desired shape.

Since certain changes may be made in the foregoing disclosure without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description and depicted in the accompanying drawings be construed in an illustrative and not in a limiting sense.