Fiber Marker Including an Erasable Ink

The invention relates to aqueous-based erasable inks.

Aqueous-based erasable inks typically include a film-forming elastomeric polymer and colorant dispersed in water. When the inks are applied to paper, the water evaporates and the polymer provides a coalesced residue on the surface of the paper. The inks are erasable in that the residue can be removed from the paper surface for some period of time after formation without leaving a visible residue or damaging the paper.

In one aspect, the invention features a pen including a body, a writing tip at one end of the body, a reservoir included within the body, and an aqueous-based, erasable marking composition having a viscosity of between 10cps and 30cps (preferably between 10 cps and 20cps) within the reservoir. The marking composition includes a latex emulsion (a rubber dispersed in water) and a water insoluble colorant, preferably a fluorescent pigment like those commonly used in highlighters. In a preferred embodiment, the pen is a marker, having a porous tip, and the marking composition is delivered to the tip by capillary action.

Preferred compositions for use in the marker include a release agent (preferably a silicone), an anti-oxidant (preferably a cresol), and a latex with a rubber solids content of between 20% and 40% and a viscosity of less than 50cps (more preferably less than 40cps). The composition preferably includes between about 60% and 90% (most preferably 70% and 80%) of the latex by weight. The preferred latexes include a polystyrene-butadiene copolymer having a Mooney value of at least 90.

In another aspect, the invention features an aqueous-based, erasable marking composition that includes a a styrene-butadiene copolymer having a Mooney value of greater than 100.

In another aspect, the invention features an aqueous-based, erasable marking composition that includes a styrene-butadiene copolymer, a water insoluble colorant, and a release agent.

In another aspect, the invention features an aqueous-based, erasable marking composition that includes a styrene/butadiene copolymer, a water-insoluble colorant, and an anti-oxidant.

In another aspect, the invention features an aqueous-based, erasable marking composition that includes a styrene/butadiene copolymer, a water-insoluble colorant, and sufficient water that the viscosity of the composition (at room temperature) is between about 10cps and 30cps, preferably between about 10cps and 20cps.

The erasable inks of the invention provide markings that can be readily removed from paper for a lengthy period of time (more than a year) after the ink is applied, without damaging the paper or leaving a visible residue. The inks are storage-stable, easy to manufacture, and easy to apply. The inks preferably have a low viscosity and as a result are particularly suitable for use with standard felt-tip markers that rely on a capillary feed system to draw ink from a reservoir. Thus, the inks are suitable for use in markers, which typically use fluorescent-colored pigments. One significant advantage to using the inks in markers is that when textbook pages are highlighted by a student, the highlighted portions can be erased a year later when the book is given or sold to a different student.

Other features and advantages of the invention will be apparent from the description of the preferred embodiments thereof, and from the claims.

The preferred compositions include a styrene/butadiene copolymer, a water-insoluble colorant, a release agent, an anti-oxidant, and water.

The styrene/butadiene copolymer is the film-forming material in the composition. The preferred copolymers are unsubstituted, i.e., they lack chemical groups such as carboxyl, sulfonyl, or amino groups, and have a high modulus of elasticity. The preferred copolymers have a Mooney viscosity of greater than 90, preferably greater than 100. Copolymers with a high Mooney value are preferred because generally they tend to be less crumbly on the paper once the water evaporates, and have a greater rub resistance.

The preferred copolymers have a styrene:butadiene ratio of between 10:90 and 35:6.5, more preferably between 20:80 and 30:70. In general, the higher the styrene content, the more erasable the ink. If the styrene content is lower than 10%, the erasability of the ink tends to deteriorate. If the styrene content is greater than 35%, the inks may have an undesirably high viscosity.

The preferred copolymers are available as latex emulsions from Goodyear Chemicals of Akron, Ohio under the tradename PLIOLITE. The emulsion has a solids content of 30-50% and a Brookfield viscosity (25.degree. C.) of less than about 50cps, more preferably about 30cps or less. The viscosity of the latex preferably is less than 50cps, more preferably less than 40cps. Normally, the ink compositions will include between 60% and 90%, more preferably between about 70% and 80%, of the emulsion by weight. Typically, the composition should include between about 20% and 40% of solid rubber by weight. The most preferred latex emulsion is PLIOLITE LPF-2108.

The preferred colorants are fine grain sized, organic or inorganic pigments or dyes that are insoluble in water. Examples of suitable pigments include carbon blacks and prussian blues; suitable dyes include those that are nitro- or anthroquinone-based. The amount of colorant can vary but usually will not exceed about 5% of the composition by weight. The preferred colorants have a particle size of less than 3 .mu.m.

The more preferred colorants are fluorescent pigments that provide a vibrant, read-through, erasable tracing and which can be photocopied without observing the highlighted material. The especially preferred read-through tracings are provided by including from about 3% to 5% by weight of the fluorescent pigment. Examples of suitable fluorescent pigments include the Day-Glo pigments available from the Day-Glo Color Corp. of Cleveland, Ohio and "Lumikol", from Nippon Keiko Kagaku LTD.

The release agents used in the composition provide a film between the paper surface and the marking, which may be liquid, semi-solid or solid. This film aids in lifting the marking from the surface by a rubbing action with an elastomeric eraser, providing substantially complete removal of the marking from the surface without significant detectable damage to the surface. Preferred release agents include water dispersible silicone oils or silicone surfactants. Especially preferred release agents include combinations of silicone oils and silicone surfactants and particularly combinations of glycol polysiloxanes and silicone glycol copolymers. Normally, amounts of release agents between about 1 to about 10 percent by weight are suitable; for the more preferred release agents amounts between about 4 to about 8 percent by weight are suitable.

The anti-oxidant inhibits the oxidation, and resultant cross-linking, of the styrene/butadiene copolymer. Cross-linking is undesirable because it adversely effects the erasability performance characteristics of the ink, particularly after the inks have been exposed to direct sunlight for a significant period of time. Especially preferred are rubber antioxidants, in particular 4,4'-thiobis (6-tert-butyl-m-cresol) and 4,4'-butylidenebis (6-tert-butyl-m-cresol). Amounts of rubber antioxidant between about 1 to about 2 percent by weight of the rubber solids are normally suitable.

The compositions can include other conventional ingredients. For example, emulsifying agents such as fatty acids (preferably fatty acid diethanolamides) are normally included in the ink in amounts between about 0.3 to about 1 percent by weight to thoroughly disperse the colorant and release agent in the aqueous phase. Dispersing agents also may be included particularly to help disperse the antioxidant.

Sufficient water should be included in the composition so that its Brookfield viscosity (25.degree. C.) is less than about 30cps, more preferably between about 10cps and 20cps. If the viscosity is too low, the ink will tend to absorb into the paper, making erasability difficult. If the viscosity is too high, the compositions may be too thick for practical use, particularly in capillary feed systems.

The compositions generally can be prepared by blending the ingredients under conditions of high shear. The following examples illustrate the invention. Of these examples, the most preferred compositions are those described in Examples 8, 10, 15 and 17.

The preferred inks can be used in conventional capillary feed markers that preferably include a polyester fiber tip (or nib) connected to an ink reservoir, preferably also made of polyester fiber. Other types of nibs (e.g., acrylonitrile fibers) and reservoirs (e.g., polyethylene fibers and cellulose acetate fibers) can be used. The reservoir is surrounded by, e.g., a polypropylene barrel, and is capped at the end opposite the nib with, e.g., a polypropylene plug; the marker also includes a polypropylene cap for covering the nib. The reservoirs are available from, e.g., American Filtrona Co. of Richmond, Va., or Baumgartner. The nibs are available from e.g., Aubex Co. of Tokyo, Japan, Teibow or Porex. During use, because the ink has a relatively low viscosity, the ink is drawn from the reservoir by the tip by capillary action. Passages from, for example, a textbook can be highlighted with the inks, which provide a uniform, transparent covering over the passage. The inks are erasable when applied.

The most preferred composition exhibit erasability characteristics that do not appreciably deteriorate for lengthy periods of time (at least a year). Compositions can be tested for such properties by making a mark on standard 60 lb. offset printing paper and exposing the mark to six hours of sunlight for six consecutive days. The most preferred compositions exhibit approximately the same ease of erasability of the mark using a standard Pink Pearl eraser, (available from Eberhard Faber) after seven days as two hours after application.

Other embodiments are within the claims. For example, the marking composition of the invention may be used in other types of writing instruments, e.g. ball-point pens, and in other suitable applications, e.g. bottle and brush ink dispensers.