Colloid systems and wetting agents; subcombinations thereof; pro – Continuous or semicontinuous solid phase – The solid phase contains organic material
Reexamination Certificate
2000-04-07
2002-05-21
Lovering, Richard D. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous or semicontinuous solid phase
The solid phase contains organic material
C137S205000, C401S217000, C422S043000, C516S099000, C516S101000, C516S924000, C516S928000
Reexamination Certificate
active
06391927
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for manufacturing ink follower, which follows water-base ink filled in an ink reservoir of a ballpoint pen.
BACKGROUND ART
The ink for a water-base ballpoint pen has a viscosity of as low as 50 mPa sec to 3 Pa sec, while the ink for an oil-base ballpoint pen, though it has a similar structure to a water-base one, has a viscosity of 3 to 20 Pa sec. Consequently, the ink filled in a water-base ballpoint pen may leak out when the pen is left upward or sideways. Moreover, even a small impact made on the pen may cause its ink to scatter and to stain the hand or the clothes.
There have been conventional arts for a water-base ballpoint pen with its ink in its ink reservoir that it is equipped with an ink follower composed of a gelled material, or a mixture of the gelled material and solid material.
The aims of the arts are to make the ink follower follow the ink smoothly, to make the pen endure the impact when dropped, to prevent the ink from back flow, to give the pen a good appearance, and so on.
A common feature of such arts is that the ink follower, which has pseudo-plasticity, is made from hardly-volatile or non-volatile solvent which is supplemented with some kind of thickener in order that the ink follower may not flow backward when the pen is left sideways or upward.
Moreover, conventional ink follower for water-base ballpoint pens often has very low viscosity and tenacity, as compared with that for conventional oil-base ballpoint pens, which often has equal viscosity to common grease used for lubricant. That is because of making the following property to the ink better.
Amount of the ink of a ballpoint pen necessary for writing varies depending upon the diameter of the ball. In an oil-base ballpoint pen for fine (0.5 mm) to bold (1.0 mm) letters, the amount is 10-30 mg per 100 m. On the other hand, in a water-base ballpoint pen for fine (0.3 mm) to bold (0.7 mm) letters, the amount is 50-300 mg per 100 m. Since the amount of the ink consumed for a water-base ballpoint pen is more than five- to ten-fold of that for an oil-base ballpoint pen, severe ink-following properties are requested for the ink follower for a water-base ballpoint pen. Thus the follower having low viscosity and tenacity has been used as compared with that for an oil-base ballpoint pen.
Lubricant grease with low viscosity and consistency generally has such low stability that oily matter likely separates when left to stand. In addition, if the thickener component in the lubricant grease is likely to move, it causes the grease to lose homogeneity easily by forming a mixture of coarse and dense portions. The lower the viscosity of the thickener of the grease, the less effectively the thickener is dispersed by a disperser such as a double-roll mill, a triple-roll mill, a kneader or a planetary mixer, any one of which is suitable for substances with high viscosity. The thickener is, however, not so low in viscosity as to be capable of being mixed effectively by a disperser such as a bead mill, a sand mill or a homogenizer, any one of which is suitable for substances with low viscosity. Inefficient dispersion causes not only time-dependent instability but also lot-to-lot instability in viscosity and uniformity.
The ink follower for the water-base ballpoint pens consists of materials similar to the lubricant grease, and exhibits time-dependent behaviors based on similar physical laws.
Once the oil is separated due to a time-dependent change, it affects the surfactant in the ink. It weakens the effect of the ink in the surfactant and blocks the ink passage as oil droplets resulting in a bad influence on writing.
Moreover, if the thickener component in the ink follower lacks homogeneity, the ink follower is separated into a portion following the ink and portions adhering to the inner wall of the ink reservoir. The adhering portions not only give the pen an unpleasant appearance, but also mean a corresponding loss of the ink follower, resulting eventually in its failure to perform its function of, for example, preventing the ink from volatilizing or from leaking.
The objects of this invention are to dissolve the defect that conventional ink follower for a water-base ballpoint pen has lot-to-lot and time-dependent instability of quality, and to provide a method for manufacturing the ink follower which has a better following property than the conventional ink follower for water-base ballpoint pens.
DISCLOSURE OF THE INVENTION
As a result of our diligent study of above problems, we have found that, reduced viscosity and surface tension of the base oil under elevated temperature make it easy for particulate thickener such as silica, alumina and titanium oxide and clay thickener to disperse. We have also found that thickener, when homogenized very highly microscopically, always shows its best performance and that it produces increased time-dependent stability and reduced lot-to-lot difference. Thus we have completed our present invention.
Lubricant grease and ink follower for a water-base ballpoint pen are prepared from similar materials by similar processes, but are clearly different from each other from a technical standpoint.
The lubricant grease is usually used only for lubricating, and is, therefore, made to have high structural viscosity and yield value lest the oily constituent of the grease drip from a point where the grease is applied. On the other hand, the ink follower for a water-base ballpoint pen is held in a reservoir with no opening except its rear end, and is used in an environment in which there is no sliding matter except itself. Therefore, the structural viscosity and yield value of the ink follower may be low. It would rather be correct to say that it is necessary for the ink follower to be low in structural viscosity and yield value in order to follow the ink smoothly.
Fine particulate powder such as inorganic thickener (particulate silica, alumina or titanium dioxide), inorganic or organic pigment and fine resin particulate, which gains structural viscosity in liquid, generally shows a lower thickening effect and a lower yield value when it is well-dispersed.
The solvent used for the base oil for the ink follower is selected from polybutenes, liquid paraffin, highly purified mineral oil such as spindle oil, silicone oil such as dimethyl polysiloxane and methyl phenyl polysiloxane and so on. They do not dissolve in a water-base ink, and has only a small volatile loss. They generally have a better wetting property with resins such as polypropylene, polyethylene and so on, used for an ink reservoir than that of water-base ink. Thus the consumption of the ink is easy to recognize.
Polybutenes and silicone oils, though some kinds of them are highly volatile, can withstand for two years or more at room temperature if their volatile loss is not more than about 0.2% by weight under a JIS C-2320 method at 98° C. for five hours.
The volatility of polybutenes largely depends upon their molecular weight. Polybutenes with average molecular weight more than about 500 may satisfy the above volatile loss.
Since the volatile loss of silicone oils also depends upon their molecular structure, it cannot be determined only by their molecular weight. Therefore, the volatile loss of silicone oils is recommended to be measured practically by the method as described above.
Aerozyl R-972, R-974D, R-976D and RY-200 (trade names, Nippon Aerozyl) are preferable material for the thickener for the present invention. They may be used either solely or jointly and the total additional amount to the total amount of the ink follower is 1-10% by weight.
Although pseudo-plasticity can be given even when the amount is less than 1%, quantitative lack of the thickener is evident and separation of oil cannot be prevented. In addition, even if viscosity is increased using particulate silica, titanium oxide or aluminum as well as other powder such as inorganic and organic pigment whose BET specific surface area is around 50 m
2
/cm, to which pseudo-plasticity is most unlikely given, t
Iwamoto Kiyoshi
Kamagata Tadashi
Ogura Norio
Shiraishi Katsuhiko
Takeuchi Youji
Kubovcik & Kubovcik
Lovering Richard D.
Mitsubishi Pencil Kabushikikaisha
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