Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2000-01-03
2002-10-01
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031580, C106S031640, C106S031860
Reexamination Certificate
active
06458192
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel erasable ink composition.
BACKGROUND OF THE INVENTION
Erasable ink is characterized in that when letters, drawings or the like are written or made on paper, the lines drawn with the ink can be erased with a rubber eraser. The ink is used in felt-tip pens or the like.
Known as such an erasable ink is an ink composition for paper, the composition being prepared by uniformly dispersing a pigment such as carbon black in a solution of a high molecular weight polyethylene oxide in an aqueous medium, in the presence or absence of a surfactant. This ink composition comprises 1-20% by weight of a pigment and 0.01 to 5% by weight of a high molecular weight polyethylene oxide, so that letters and drawings formed with the ink composition on paper can be erased with a rubber eraser (Japanese Examined Patent Publication No. 39470/1989).
However, since the above ink composition has an extremely high adhesion to the paper surface, it is not always easily erasable with a rubber eraser. The problem of erasability becomes more serious when the ink is used in ballpoint pens with which great writing pressure tends to be applied. On the other hand, if the adhesion of the ink composition is reduced to increase erasability, fixability will inevitably decline. When the ink composition has lower fixability, mere rubbing with a finger may easily erase the drawn lines. Until now, no technology has been established that provides good erasability and high fixability.
The conventional erasable ink compositions have another problem that erasability declines with the lapse of time due to the deterioration of the inks. The lines are relatively easy to erase immediately after drawing but will become difficult to erase with the lapse of time.
A main object of the present invention is to provide an ink composition particularly excellent in erasability and fixability. Another object of the present invention is to provide an ink composition which can draw lines whose erasability does not decline with the lapse of time.
SUMMARY OF THE INVENTION
The present inventors carried out extensive research to solve the prior art problems and found that the above objects can be accomplished with a specific ink composition. The present invention has been accomplished based on this finding.
The present invention provides an erasable ink composition that comprises a colorant, a film-forming resin and a release agent.
DETAILED DESCRIPTION OF THE INVENTION
Any colorant may be used as long as the effects of the present invention are not sacrificed. Colorants used in known aqueous ink compositions or the like can be used. Useful colorants include, for example, inorganic pigments such as titanium oxide, carbon black, ultramarine blue, cobalt blue, chromium oxide, iron oxide red and graphite, and organic pigments such as C.I. pigment black 1, C.I. pigment green 7, C.I. pigment blue 15, C.I. pigment red 112 and C.I. pigment violet 19. In addition, fluorescent pigments, luminescent pigments and the like can be used. Furthermore, the so-called colored resin beads can be used as a colorant in the practice of the present invention. Examples of colored resin beads are resin beads (e.g., of an acrylic resin or a styrenic resin) containing a dye or pigment, resin beads colored with a dye, etc. Further, in the practice of the present invention, toners for copying may also be used. These colorants may be used either singly or in combination of two or more. Among them, the use of colored resin beads is preferred.
There is no specific limitation on the particle size of the colorant in the practice of the present invention. The colorant usually has an average particle size of about 0.3 to 20 &mgr;m, preferably 0.5 to 10 &mgr;m. In other words, according to the present invention, a fine colorant having an average particle size of less than 1 &mgr;m can also be used as an erasable ink. The particle size distribution can be controlled by a known classification technique such as spontaneous sedimentation, centrifugation or filter filtration.
The term “average particle size” used herein means weight average particle diameter, which was determined as follows. The weight cumulative distribution was determined by the liquid phase centrifugal sedimentation method in the light transmission mode (measuring apparatus “CAPA-700”, manufactured by Horiba Seisakusho K.K.). The average particle size was expressed by the particle size corresponding to 50% by weight in cumulative distribution. The specific gravity of the colorant particles was calculated using the true specific gravity.
The shape of the colorant is not critical but may be spherical, polyhedral, flaky or fibrous, for instance. In the practice of the present invention, however, a basically spherical form is preferred and, in particular, it is preferred that the shape be as close as possible to the true sphere.
The content of the colorant may be judiciously selected in consideration of the other components used. It is usually about 1 to 40% by weight, preferably 3 to 20% by weight. When the content is more than 40% by weight, the viscosity will be excessively high, so that the ink will flow out with difficulty. When it is less than 1% by weight, sufficient coloration may not be attained in some instances.
Any resin that has film formability may be used as a film-forming resin. Resins known or commercially available can be used. Examples are polyethylene oxide, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, sodium polyalginate, sodium polyacrylate, dextrin, gum arabic and the like. These resins may be used either singly or in combination of two or more. Among them, polyethylene oxide or like resins having film formability, stringiness and cohesion are preferred. The molecular weight of the film-forming resin is not limited specifically and may be adequately selected according to the resin used. For example, polyethylene oxide for use as a film-forming resin usually has a molecular weight of about 150,000 to 4,800,000 (preferably 500,000 to 4,000,000).
The content of the film-forming resin may be judiciously selected in consideration of the film-forming resin and release agent used. It is usually about 0.1 to 5% by weight, preferably 0.5 to 2% by weight. When the content is too low, the desired film formability may not be provided. When it is too high, the adhesion of the ink composition will be excessively high and poor erasability may result.
Any release agent may be used as long as it is soluble in water and is solid or semi-solid (more specifically, in a hard to soft wax state) at normal temperatures. Release agents known or commercially available can be used. Examples are polyethylene glycol, soap (fatty acid salt), polyoxyethylene fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkylarylether, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, sucrose fatty acid ester, water-soluble lanolin, water-soluble wax and the like. These release agents may be used either singly or in combination of two or more. The most preferable among them is polyethylene glycol (particularly the one having a molecular weight of 500 or more, preferably 700 to 2,800, more preferably 950 to 2,100). The release agents having such a molecular weight provide particularly excellent erasability. The molecular weight used herein means a weight average molecular weight, which was determined by gel penetration chromatography (GPC).
The content of the release agent may be judiciously selected in consideration of the film-forming resin and release agent used. It is usually about 3 to 30% by weight, preferably 7 to 20% by weight. When the content is too low, sufficient erasability may not be attained. When it is too high, poor fixability may result. The ratio of the film-forming resin to the release agent may be judiciously selected in consideration of their molecular weights and the other components used. The film-forming resin:release agent ra
Faison Veronica F.
Klemanski Helene
Rader & Fishman & Grauer, PLLC
Sakura Color Products Corporation
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