Non-aqueous ball point pen ink and ball point pen using the ink

Details Non-aqueous ball point pen ink and ball point pen using the ink Non-aqueous ball point pen ink and ball point pen using the ink

2000-11-09

2002-11-12

Jagannathan, Vasu (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S516000, C525S205000

Reexamination Certificate

active

06479568

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a non-aqueous ball point pen ink and a ball point pen using the ink. Specifically, the present invention relates to a non-aqueous ink provided with pseudoplasticity. The ink is provided by blending a non-Newtonian viscosity imparting and is provided with viscoelasticity by blending two types of polyvinyl pyrrolidone having different weight-average molecular weights to eliminate ink blobbing and scratching, and to a non-aqueous ball point pen using this ink.
BACKGROUND OF THE INVENTION
A conventional non-aqueous ball point pen has been designed by setting an ink viscosity in a range of 10,000 to 30,000 mPa·s (20° C.) to prevent leakage. However, when the viscosity during writing is high in this manner, the ball rotation resistance during writing automatically increases and writing smoothness was very low and fails to be satisfactory. Moreover, a high writing pressure was necessary during writing. In some cases, a load of 500 gf or more was applied to a pen point. The heavy load causes the pen point to be quickly damaged. Furthermore, ball breakage and writing defects frequently could occur as a consequence. On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 6-313143 (1994), 6-313144 (1994), 7-196972 (1995) or 9-48941 (1997), attempts were carried out to improve the above-described defects by creating inks having a pseudoplasticity viscosity property, where the ink viscosity is low when writing and where the ink viscosity is relatively high when writing is not performed. However, the attempts were not sufficient in enhancing the writing smoothness and completely preventing the leakage.
SUMMARY OF THE INVENTION
The present invention provides an ink which realizes a remarkably satisfactory writing smoothness, eliminates blobbing and feathering and which can completely prevent leakage, and further provides a non-aqueous ball point pen in which during ink transport by way of writing, no ink adheres to an ink reserving tube inner wall and an ink residual amount is clear. “Blobbing” is a phenomenon in which a surplus ink during writing is accumulated in a pen point. “Feathering” is blurring of the ink due to absorption by paper etc.
The present invention relates to a non-aqueous ball point pen ink which contains, as main components, a colorant, an organic solvent, a non-Newtonian viscosity imparting agent, and a total of 0.4 to 0.8 mass % of polyvinyl pyrrolidone, where 0.2 to 0.6 mass % of polyvinyl pyrrolidone has a weight-average molecular weight of about 1,000,000 to 1,500,000 and 0.1 to 0.4 mass % of polyvinyl pyrrolidone with a weight-average molecular weight of about 2,500,000 to 3,000,000. A non-Newtonian viscosity index of the ink may be in a range of 0.4 to 0.7, a viscosity in a shearing speed of 500 sec
−1
is in a range of 3,000 to 6,000 mPa·s (20° C.), and the viscosity in the shearing speed of 0.19 sec
−1
may be in a range of 20,000 to 60,000 mPa·s (20° C.). The non-Newtonian viscosity imparting agent may be a fatty acid amide wax with a melting temperature of 140° C. or more. The non-Newtonian viscosity imparting agent may be fatty acid amide wax. The blend amount of the fatty acid amide wax may be in a range of 1.0 to 2.0 mass %.
The non-aqueous ink above can be directly filled into an ink reserving tube of a ball point pen. The ink reserving tube can be a polypropylene tube. An inner wall of the ink reserving tube can be treated with silicone.
PREFERRED EMBODIMENT OF THE INVENTION
According to the present invention, there is provided an ink in which an ink viscosity in a shearing speed of 500 sec
−1
can preferably be in a range of 3,000 to 6,000 mPa·s. When the ink viscosity is less than 3,000 mPa·s, writing smoothness is satisfactory but drawn line blobbing can be remarkable, further feathering can be unsatisfactory, even though it is still acceptable. Moreover, when the viscosity exceeds 6,000 mPa·s, a low writing pressure and smooth stroke as the object of the present invention can be hardly embodied, even though it is still acceptable.
As a result of intensive studies on the writing stroke of a ball point pen, the present inventors found that the stroke largely depends on the ball rotation resistance during writing. As a result of experiments, when the ink viscosity in the shearing speed of 500 sec
−1
is less than 1,000 mPa·s, the ball rotation resistance is remarkably reduced, but a boundary lubrication area is constituted without forming an ink oil film between a ball and a ball seat and the intrinsic smoothness of the non-aqueous ball point pen is deteriorated. Moreover, when the viscosity exceeds 10,000 mPa·s, the ball rotation resistance tends to increase and the stroke obviously tends to become heavy. Specifically, when the ink viscosity is in a range of 1,000 to 10,000 mPa·s, the stroke becomes satisfactory. However, to prevent feathering and blobbing, and embody the intrinsic deep drawn line of the non-aqueous ball point pen, the ink viscosity should preferably be 3,000 mPa·s or more at minimum. Furthermore, not only to pursue touch smoothness, but also to enable a low pressure writing of about 100 gf like an aqueous ball point pen, the ink viscosity should preferably be 6,000 mPa·s or less. The ink viscosity described herein was measured in a measurement environment of 20° C. using a rheometer CSL manufactured by British Carrymay, Ltd.
Moreover, in the present invention, a non-Newtonian viscosity imparting agent is blended into an ink composition, and an ink non-Newtonian viscosity index is set to 0.4 to 0.7. As described above, to obtain the satisfactory stroke, the ink viscosity during writing, that is, during high shearing is set to be low. A likelihood of occurrence of leakage necessarily increases, and this cannot be prevented by a conventional ink design. To prevent this defect, pseudoplasticity is set as an ink viscosity property by containing the non-Newtonian viscosity imparting agent in the ink composition, and the ink viscosity when the ball point pen is not being used is set to be as high as possible. Moreover, adequate consideration was given also to the drawn line blobbing in the study of the ink viscosity, but it is also a fact that the drawn line blobbing is in an increase direction when the viscosity is set to be low. It is particularly mentioned that when the pseudoplasticity is set as the ink viscosity property, the cohesive force of the ink itself increases, the generation of a surplus ink in a pen point is reduced and an effect of eliminating the blobbing is brought about. When the non-Newtonian viscosity index is less than 0.4, the cohesive force of the ink itself excessively increases, an ink follow-up defect is caused, and a phenomenon of discontinuity, line cut and non-uniformity in line darkness (“scratching”). On the other hand, when the index exceeds 0.7, the cohesive force decreases and the effect of preventing the blobbing is weakened.
The non-Newtonian viscosity imparting agent for use in the non-aqueous ink includes a fatty acid amide wax and a derivative thereof, linear chain fatty acid ester polymer, polyethylene oxide, hardened castor oil, organic bentonite, silica, sulfate-based anion activator, and the like, but the fatty acid amide wax is preferable considering from stability. Further considering from the stability during the high-temperature preservation of the ball point pen, it is most preferable to select the fatty acid amide wax with a melting temperature of 140° C. or more as the non-Newtonian viscosity imparting agent. The amount of the fatty acid amide wax is in a range of 1.0 to 2.0 mass % in order to realize the non-Newtonian viscosity index of 0.4 to 0.7. The non-Newtonian viscosity index described herein was measured using the rheometer CSL manufactured by British Carrymay, Ltd. in a measurement environment of 20° C. with appropriate values of angle and diameter of a cone plate in a shearing speed range of 1 to 600 sec
−1
.
Furthermore, in the present invention, the viscosity in a shearing sp

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