1. Field of the Invention
The present invention relates to an ink follower composition which is used at the rear end of ink in oil-based ballpoint pens which house the ink in an ink reservoir tube.
2. Description of Related Art
As for a gel-like ink follower, followers for use in aqueous ballpoint pens of a type where ink is directly housed in an ink reservoir tube have been heretofore disclosed in Japanese Unexamined Patent Publication (Kokai) Nos. 57-153070, 57-200472, 61-57673, 61-145269, 61-151289, 61-200187, 61-268786, 62-50379, 62-148581, 5-270192 and 5-270193. In the case of a ballpoint pen using an aqueous ink having low viscosity, these ink followers prevent the ink from leaking out when the pen tip is allowed to stand in the vertically upward or horizontal direction, and prevent the ink from splashing upon receipt of a light impact. Also, in the case of using an aqueous ink having high viscosity, when a mechanical impact is imposed or writing is performed while the pen tip is higher than the opposite end, the ink follower prevents the ink from entraining air and flowing out from the end of the ink reservoir tube (this is usually called xe2x80x9creverse flowxe2x80x9d) to soil human bodies, clothes and the like. In order to prevent this reverse flow, various ink reverse-flow inhibitors have been heretofore proposed.
On the other hand, the reverse-flow inhibitors for oil-based ballpoint pens include those where a plug for preventing the leakage of ink, using a sponge or plaster, is provided at the end of the ink reservoir tube of a ballpoint pen, and those where an ink follower capable of moving with the ink, along with the consumption of ink in the ink reservoir tube, is used at the ink end. The former case has a problem in that if the ink once contacts with the leakage-preventing plug, a vent hole provided in the plug is clogged and therefore, unless the plug is removed, the ballpoint pen cannot revert to its reusable state whatever method may be used. Even if the plug is removed to retrieve the reusable state, there arises a problem that when a reverse flow occurs, the ink leaks out from the back end.
In the latter case, some ink followers for oil-based ballpoint pens use a gelled grease, however, these are disadvantageous in that during storage at a high temperature or for a long period of time, the grease not only separates or becomes compatible with ink to cause deterioration in the quality, but it also becomes opaque and hardly distinguishable from ink to indicate to the user, when writing cannot be performed any more, that some ink remains. Moreover, when these ink followers are used as they are for oil-based ballpoint pens, the gelling agent transfers to the ink to cause oil separation and this gives rise to a failure in maintaining the effect as a reverse-flow inhibitor or, in many cases, to deterioration in the effect of the pen itself.
Oil-based ballpoint pens usually use a solvent having low vapor pressure and therefore, it is not necessary, in most cases, to provide an ink follower at the back end and thereby prevent the ink solvent from evaporating. However, in the case of an oil-based ballpoint pen using an ink containing a solvent having high vapor pressure, some countermeasure against the volatilization of the solvent is required. The simplest method for preventing the volatilization of solvent from the rear part of a refill or the like is to seal the rear part using a fixing member, however, this renders the pressure inside the refill or the like negative during writing and, as a result, writing cannot be performed.
As described above, the development of ink followers for oil-based ballpoint pens is accompanied by peculiar problems different from those in the case of an aqueous ballpoint pen. Accordingly, the ink follower for oil-based ballpoint pens must have all of the following qualities:
(1) to be stable without separating or becoming compatible with ink even after storage at a high temperature or for a long period of time;
(2) to have an improved resistance against a strong impact;
(3) to have appropriate follow-up performance to the ink;
(4) to be capable of shutting out the outside air from the ink and thereby preventing the volatilization of ink (this quality is important particularly in the case of an oil-based ballpoint pen using a quick drying ink obtained by incorporating a solvent having high vapor pressure into an ink);
(5) to have a capability of preventing leakage of ink from the back end of the ink reservoir tube after tip up writing; and
(6) to not move to the distal end of the tip due to position to thereby cause reversal between the ink and the ink follower (occurrence of reversal phenomenon), even if there is a difference in the specific gravities.
The object of the present invention is to provide an ink follower composition which is an ink follower for oil-based ballpoint pens and has high suitability for inks enhanced in quick drying properties.
As a result of extensive investigations, the present inventors have found that the above-described problems can be overcome by an ink follower composition for oil-based ballpoint pens which is characterized by the following points. The present invention has been accomplished based on this finding.
More specifically, the present invention resides in the following matters (1) to (7).
(1) An ink follower composition for oil-based ballpoint pens, comprising at least one organic solvent selected from the group consisting of a sparingly volatile organic solvent and a non-volatile organic solvent, said solvent having an evaporation loss of 0.4% by weight or less under the conditions of 98xc2x0 C. and 5 hours, a gelling agent comprising inorganic fine particles, and from 10 to 60% by weight of a resin soluble in the organic solvent used.
(2) The ink follower composition for oil-based ballpoint pens as described in (1) above, which is used for an oil-based ballpoint pen having housed therein an ink using an ink solvent containing from 10 to 100% by weight of a solvent selected from the group consisting of alcohols, glycols and glycol monoethers each having a vapor pressure of 0.01 to 50 mmHg at 25xc2x0 C.
(3) The ink follower composition for oil-based ballpoint pens as described in (1) or (2) above, wherein the organic solvent is a liquid paraffin.
(4) The ink follower composition for oil-based ballpoint pens as described in any one of (1) to (3) above, wherein the resin is a resin insoluble in or forming a two phase region with a solvent having one or more hydroxyl groups within the molecular structure.
(5) The ink follower composition for oil-based ballpoint pens as described in any one of (1) to (3) above, wherein the resin contains at least one resin selected from the group consisting of terpene-base resins and phenol-base resins.
(6) The ink follower composition for oil-based ballpoint pens as described in any one of (1) to (5) above, wherein the inorganic fine particle is fine particulate silica.
(7) An oil-based ballpoint pen comprising an ink reservoir tube having housed therein:
(a) an ink containing at least a coloring material, a resin and a solvent, said solvent containing from 10 to 100% by weight of a solvent selected from the group consisting of alcohols, glycols and glycol monoethers each having a vapor pressure of 0.01 to 50 mmHg at 25xc2x0 C., and
(b) an ink follower composition containing at least one or more organic solvent selected from the group consisting of a sparingly volatile organic solvent and a non-volatile organic solvent, said solvent having an evaporation loss of 0.4% by weight or less under the conditions of 98xc2x0 C. and 5 hours, a gelling agent comprising inorganic fine particles, and from 10 to 60% by weight of a resin which is soluble in the organic solvent used and is in a solid state at 25xc2x0 C.