Ink compositions and writing instruments including the compositions

A water-fast, shock resistant, shear-thinning ink composition having a shear-thinning index between about 0.01 to about 0.60, a viscosity of 50 cPs or greater at a shear rate of 30 sec.sup.-1 and a viscosity of 100 cPs or less at shear rates produced by writing and consisting essentially of:

• a. from about 50 to about 99 percent by weight of a polar solvent system including at least about 50 percent by weight water,
• b. an effective amount of a colorant material which is water insoluble when the composition is dry,
• c. from about 0.1 to about 5 percent by weight of a polymeric, shear-thinning material selected from the group consisting of xanthan gum, carageenan gum, locust bean gum, hydroxyethylcellulose, guar gum or mixtures of these, and
• d. from about 1 to about 20 percent by weight of a binder material which is water soluble when maintained at a given pH range and water insoluble when not maintained at that pH range and which is effective to improve the shock resistance of the composition, said composition providing a colored, water insoluble coalesced residue on drying.

A ball point pen comprising a reservoir including a water-fast, shock resistant, shear-thinning ink composition consisting essentially of:

• a. from about 50 to about 99 percent by weight of a polar solvent system including at least about 50 percent by weight water,
• b. an effective amount of colorant material which is water insoluble when the composition is dry,
• c. an amount of a water dispersible, polymeric shear-thinning material sufficient to provide an ink having a shear-thinning index between about 0.01 to about 0.6, a viscosity of 50 cPs or greater at a shear rate of 30 sec.sup.-1 and a viscosity of 100 cPs or less at shear rates produced by writing, and
• d. a water soluble polymeric binder material which is effective to improve the shock resistance of the composition and is water insoluble when the composition is dry in an amount ineffective to substantially affect the shear-thinning capability of the polymeric shear-thinning material, said composition providing a colored, water insoluble coalesced residue on drying.

A ball-point pen comprising a reservoir including a water-fast, shock resistant, shear-thinning ink composition having L a shear-thinning index between about 0.01 to about 0.60, a viscosity of 50 cPs or greater at a shear rate of 30 sec.sup.-1 and a viscosity of 100 cPs or less at shear rates produced by writing and consisting essentially of:

• a. from about 50 to about 99 percent by weight of a polar solvent system including at least about 50 percent by weight water,
• b. an effective amount of a colorant material which is water insoluble when the composition is dry,
• c. from about 0.1 to about 5 percent by weight of a polymeric, shear-thinning material selected from the group consisting of xanthan gum, carageenan gum, locust bean gum, hydroxyethylcellulose, guar gum or mixtures of these, and
• d. from about 1 to about 20 percent by weight of a binder material which is water soluble when maintained at a given pH range and water insoluble when not maintained at that pH range and which is effective to improve the shock resistance of the composition, said composition providing a colored, water insoluble coalesced residue on drying.