Pens comprise a non-aqueous writing ink comprising a solvent, a coloring agent, a resin, a gelling agent, and a homo or copolymer of vinylpyrrolidone and/or a polyvinyl alcohol which is acetalized with an aldehyde comprising between 1 and about 6 carbon atoms, wherein the gelling agent is a mixture of silica particles and of a fatty acid amide wax, wherein the homo or copolymer of vinylpyrrolidone, if present, is present in amounts of between about 0.05 and about 0.6 wt.-%, relative to the total weight of the ink and wherein the polyvinyl alcohol which is acetalized with an aldehyde comprising between 1 and about 6 carbon atoms, if present, is present in amounts of between about 0.05 and about 1.0 wt.-%, relative to the total weight of the ink.

Pens comprise a non-aqueous writing ink comprising a solvent, a coloring agent, a resin, a gelling agent, and a homo or copolymer of vinylpyrrolidone and/or a polyvinyl alcohol which is acetalized with an aldehyde comprising between 1 and about 6 carbon atoms, wherein the gelling agent is a mixture of silica particles and of a fatty acid amide wax, wherein the homo or copolymer of vinylpyrrolidone, if present, is present in amounts of between about 0.05 and about 0.6 wt.-%, relative to the total weight of the ink and wherein the polyvinyl alcohol which is acetalized with an aldehyde comprising between 1 and about 6 carbon atoms, if present, is present in amounts of between about 0.05 and about 1.0 wt.-%, relative to the total weight of the ink.

A thermochromic pigment composition including: (A) at least one electron-donor organic dye compound, (B) at least one electron-acceptor compound, and (C) at least one compound corresponding to the following formula (I): in which: X is 0 or a single bond, Z is COO or OCO, R.sub.1 is O-alkyl or (CH.sub.2).sub.mCH.sub.3—R.sub.2 is OCO(CH.sub.2).sub.nCH.sub.3 or H, —y=0-3, —m=12-18; —p=8-18, and on the condition that, when X is 0, y is other than 0. The thermochromic pigment composition are also useable in thermochromic pigment microcapsules ink compositions including the thermochromic pigment microcapsules, and writing instruments including the ink compositions.

A thermochromic pigment composition including: (A) at least one electron-donor organic dye compound, (B) at least one electron-acceptor compound, and (C) at least one compound corresponding to the following formula (I): in which: X is 0 or a single bond, Z is COO or OCO, R.sub.1 is O-alkyl or (CH.sub.2).sub.mCH.sub.3—R.sub.2 is OCO(CH.sub.2).sub.nCH.sub.3 or H, —y=0-3, —m=12-18; —p=8-18, and on the condition that, when X is 0, y is other than 0. The thermochromic pigment composition are also useable in thermochromic pigment microcapsules ink compositions including the thermochromic pigment microcapsules, and writing instruments including the ink compositions.

An ink composition for a water-based ballpoint pen and a water- based ballpoint pen, which have stable ink flowability even in a so-called fine ballpoint pen, have excellent luster of drawn lines, and do not cause a ball to fall off. The ink composition for a water-based ballpoint pen according to the present invention contains at least an aluminum pigment and 8 to 25 mass% of solid urethane particles with an average particle size of 0.3 to 10 μm. In addition, a water-based ballpoint pen according to the present invention is provided with the ink composition for a water-based ballpoint pen that has the above composition.

An ink composition for a water-based ballpoint pen and a water- based ballpoint pen, which have stable ink flowability even in a so-called fine ballpoint pen, have excellent luster of drawn lines, and do not cause a ball to fall off. The ink composition for a water-based ballpoint pen according to the present invention contains at least an aluminum pigment and 8 to 25 mass% of solid urethane particles with an average particle size of 0.3 to 10 μm. In addition, a water-based ballpoint pen according to the present invention is provided with the ink composition for a water-based ballpoint pen that has the above composition.

Provided is a thermochromic writing instrument, including thermochromic ink; and a friction unit configured to cause handwriting in the thermochromic ink to undergo a thermochromic change by frictional heat. The thermochromic ink includes a metallic luster pigment added thereto. The thermochromic writing instrument is provided with an attachment hole to attach the friction unit. The friction unit includes an attachment portion to be inserted into the attachment hole and a friction portion in a convex curved surface shape projecting from the attachment hole. The friction portion has a volume Ve and the metallic luster pigment has a volume Vp, the volume Ve and the volume Vp satisfying 5 □ Ve/Vp □ 35, the friction portion 32 has a maximum outer diameter D and a projection length L, the diameter D and the length L satisfying 0.1 □ L/D □ 1.5, and a material for the friction unit 3 has a value of Shore A hardness in accordance with JIS K 7215 of Japan Industrial Standard measured immediately after starting contact with an indenter in a range of 60 or more and 85 or less and has a value (ΔHS) of the Shore A hardness defined by a following equation of 0 or more and less than 5, ΔHS=(Shore A Hardness Value immediately after Starting Contact with Indenter)−(Shore A Hardness Value 15 seconds after Starting Contact with Indenter).

Provided is an oil-based ink composition for writing instruments which has good properties for writing on writing surfaces of various materials and which has improved friction resistance against friction from retracing of letters that have already been written and against stronger friction forces.

An ink composition for a water-based ballpoint pen including at least a black pigment and borneol, the black pigment satisfying requirements X to Z below: X: 50% particle size (D50) in a cumulative particle size distribution in terms of volume being 0.2 to 1.0 μm, Y: 10% particle size (D10) in a cumulative particle size distribution in terms of volume being 0.1 to 0.3 μm, and Z: 90% particle size (D90) in a cumulative particle size distribution in terms of volume being 1.0 to 5.0 μm.

An ink composition for a water-based ballpoint pen including at least a black pigment and borneol, the black pigment satisfying requirements X to Z below: X: 50% particle size (D50) in a cumulative particle size distribution in terms of volume being 0.2 to 1.0 μm, Y: 10% particle size (D10) in a cumulative particle size distribution in terms of volume being 0.1 to 0.3 μm, and Z: 90% particle size (D90) in a cumulative particle size distribution in terms of volume being 1.0 to 5.0 μm.