A thermochromic writing instrument including a writing body, storing a thermochromic ink therein, stored in a barrel; an operation body provided in the barrel to be operated to longitudinally move the writing body; a nib of the writing body configured to be capable of appearing from a front end of the writing instrument, wherein the writing instrument 1 further includes a friction unit, for rubbing handwriting in the thermochromic ink and capable of thermally changing the color of the handwriting by frictional heat generated at that time, and at least one clip body as the operation body, the friction unit 10 is provided at a rear end of the barrel, and the clip body is provided in an area other than the rear end of the barrel.

A thermochromic writing instrument including a writing body, storing a thermochromic ink therein, stored in a barrel; an operation body provided in the barrel to be operated to longitudinally move the writing body; a nib of the writing body configured to be capable of appearing from a front end of the writing instrument, wherein the writing instrument 1 further includes a friction unit, for rubbing handwriting in the thermochromic ink and capable of thermally changing the color of the handwriting by frictional heat generated at that time, and at least one clip body as the operation body, the friction unit 10 is provided at a rear end of the barrel, and the clip body is provided in an area other than the rear end of the barrel.

A refill for writing implements has an ink reservoir tube (1) made of resin material and formed to be a straight cylinder and a writing tip (2) attached to one end of the ink reservoir tube (1), and a value of an expression of D.sup.4−(D−2t).sup.4 is selected to be 45 or greater, where D denotes an outer diameter of the ink reservoir tube (1) and t denotes a thickness of the ink reservoir tube (1). It is possible to secure the necessary storage amount of ink in the ink reservoir tube (1) without increasing the outer diameter thereof, and is also possible to provide a refill for a writing implement and a writing implement which allow one to keep writing comfortably without feeling of discomfort in writing.

A refill for writing implements has an ink reservoir tube (1) made of resin material and formed to be a straight cylinder and a writing tip (2) attached to one end of the ink reservoir tube (1), and a value of an expression of D.sup.4−(D−2t).sup.4 is selected to be 45 or greater, where D denotes an outer diameter of the ink reservoir tube (1) and t denotes a thickness of the ink reservoir tube (1). It is possible to secure the necessary storage amount of ink in the ink reservoir tube (1) without increasing the outer diameter thereof, and is also possible to provide a refill for a writing implement and a writing implement which allow one to keep writing comfortably without feeling of discomfort in writing.

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.

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.

A compensation membrane and a pen or the equivalent including a compensation membrane. The compensation membrane being configured for compensating a pressure difference between the outside and the inside of a free ink reservoir of a pen or the equivalent. The membrane including a first portion having a first rigidity and a second portion having a second rigidity, the first rigidity being less than the second rigidity.

A compensation membrane and a pen or the equivalent including a compensation membrane. The compensation membrane being configured for compensating a pressure difference between the outside and the inside of a free ink reservoir of a pen or the equivalent. The membrane including a first portion having a first rigidity and a second portion having a second rigidity, the first rigidity being less than the second rigidity.

A liquid ink instrument, including: a pen body, a writing element mounted on the head of the pen body, an ink absorber mounted at the rear end of the writing element; a fiber ink feeder mounted in the body penetrates the ink absorbing body, the front end in contact with the writing element, the rear end communicated with the ink cartridge; at least one air-liquid balancer in the axial direction, the air-liquid balancer installed between the recited fiber ink feeder and the body; having one or more air-liquid exchange grooves penetrating through the outer circumferential surface; having an overflow groove on a radial surface of the air-liquid balancer, one end contacted to fiber ink feeder, and the other end communicating with air-liquid exchange groove; a gas-free fit or an interference fit adopted between the outer circumferential surface of the fiber ink feeder and the inner wall of the air-liquid balancer.

A liquid ink instrument, including: a pen body, a writing element mounted on the head of the pen body, an ink absorber mounted at the rear end of the writing element; a fiber ink feeder mounted in the body penetrates the ink absorbing body, the front end in contact with the writing element, the rear end communicated with the ink cartridge; at least one air-liquid balancer in the axial direction, the air-liquid balancer installed between the recited fiber ink feeder and the body; having one or more air-liquid exchange grooves penetrating through the outer circumferential surface; having an overflow groove on a radial surface of the air-liquid balancer, one end contacted to fiber ink feeder, and the other end communicating with air-liquid exchange groove; a gas-free fit or an interference fit adopted between the outer circumferential surface of the fiber ink feeder and the inner wall of the air-liquid balancer.