A writing instrument configured to apply a writing material or liquid to a surface, comprising a socket, and a ball arranged in the socket, characterized by at least one first component which is arranged to come into contact with the ball, wherein the at least one first component comprises a first material having surface properties such that the friction coefficient between the ball and the at least one first component decreases when the force acting from the ball on the at least one first component increases at least within a certain range of forces.

A writing tip assembly for dispensing a free-flowing low-viscosity ink from a writing instrument may include a micro-spring, a writing ball configured to transfer ink to a substrate, and a second ball between the writing ball and the micro-spring. The second ball is configured to transfer ink to the writing ball. A writing instrument for dispensing a free-flowing low-viscosity ink includes an ink reservoir, the writing tip assembly, and a feeder fluidically coupling the ink reservoir to the writing tip assembly.

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 reservoir unit for a writing instruments using an ink reservoir tube with which low contamination can be achieved considering environmental problems; and a writing instruments using the same. The ink reservoir tube is composed of a composite material in which a raw material is layered on a paper substrate having paper as a substrate. One end section of the ink reservoir tube is coupled to a connection part formed on a writing member or a relay member that holds the writing member to constitute the ink reservoir unit for a writing instrument. In one preferred aspect, a locking device using a male thread formed on an outer peripheral surface is provided to the connection part to be connected to the ink reservoir tube, and the ink reservoir tube is coupled to the relay member that holds the writing member by the locking device.

A ball point tip comprising a ball holder having an ink conduit and a ball house, a ball accommodated into the ball house and a leaf spring axially disposed between the ball and an axial end of the ink conduit, the leaf spring having a main body and a plurality of tongues extending radially from the main body, ink passages being formed between the tongues in order to fluidly connect the ink conduit and the ball house, wherein the ball holder and the leaf spring are made of plastic and unitary formed.

A water-based ballpoint pen contains an aqueous ink composition in which resin particles having an average particle diameter of at least 0.3 μm are blended. The water-based ballpoint pen is provided with a ballpoint pen tip including a writing ball. The writing ball is formed from a mixture that includes a hard phase component comprising tungsten carbide, a binder phase component comprising cobalt and nickel, and chromium.

An ink reservoir unit for a writing instruments using an ink reservoir tube with which low contamination can be achieved considering environmental problems; and a writing instruments using the same. The ink reservoir tube is composed of a composite material in which a raw material is layered on a paper substrate having paper as a substrate. One end section of the ink reservoir tube is coupled to a connection part formed on a writing member or a relay member that holds the writing member to constitute the ink reservoir unit for a writing instrument. In one preferred aspect, a locking means using a male thread formed on an outer peripheral surface is provided to the connection part to be connected to the ink reservoir tube, and the ink reservoir tube is coupled to the relay member that holds the writing member by the locking means.

A writing tool includes a refill having an ink reservoir tube formed to be a straight cylinder whose wall thickness is less than 0.56 mm; and a writing tip or a relay member holding the writing tip attached to a first end of the ink reservoir tube, wherein the refill is detachably attached to a barrel, wherein in the refill, amounting strength between the writing tip or the relay member holding the writing tip and the ink reservoir tube is set higher than a mounting strength between the barrel and a connecting portion of the ink reservoir tube. There is provided a writing tool that can prevent the occurrence of a problem such as leakage of ink at a time of replacement of refills and perform replacement of refills smoothly.

Provided are a reversibly thermochromic aqueous ink composition having excellent writability and few problems such as aggregation of a colorant, an increase in viscosity of the composition, or a decrease in handwriting density, and a refill or an aqueous ballpoint pen using the reversibly thermochromic aqueous ink composition.

A reversibly thermochromic composition is a reversibly thermochromic aqueous ink composition containing a reversibly thermochromic microcapsule pigment encapsulated in a microcapsule formed from an organic resin, an N-vinyl-2-pyrrolidone polymer, glycerin, and water, in which when contents (% by mass) of the reversibly thermochromic microcapsule pigment, the N-vinyl-2-pyrrolidone polymer, and the glycerin with respect to a total mass of the ink composition are P.sub.MC, P.sub.PVP, and P.sub.G, respectively, 0.3≤P.sub.MC/(P.sub.PVP+P.sub.G)≤4, and 0.2≤P.sub.PVP/P.sub.G≤5, and a refill or an aqueous ballpoint pen incorporating the reversibly thermochromic aqueous ink composition.

A writing tool includes a refill having an ink reservoir tube formed to be a straight cylinder whose wall thickness is less than 0.56 mm; and a writing tip or a relay member holding the writing tip attached to a first end of the ink reservoir tube, wherein the refill is detachably attached to a barrel, wherein in the refill, amounting strength between the writing tip or the relay member holding the writing tip and the ink reservoir tube is set higher than a mounting strength between the barrel and a connecting portion of the ink reservoir tube. There is provided a writing tool that can prevent the occurrence of a problem such as leakage of ink at a time of replacement of refills and perform replacement of refills smoothly.