Record receiver having plural interactive leaves or a colorless – Having a colorless color-former – developer therefor – or... – Method of use – kit – or combined with marking instrument or...
Reexamination Certificate
2001-10-10
2003-06-17
Hess, B. Hamilton (Department: 1774)
Record receiver having plural interactive leaves or a colorless
Having a colorless color-former, developer therefor, or...
Method of use, kit, or combined with marking instrument or...
C503S209000
Reexamination Certificate
active
06579826
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reversible thermosensitive recording medium, and more particularly to a reversible thermosensitive recording medium utilizing a coloring reaction of an electron donating coloring compound with an electron accepting compound. In addition, the present invention relates to an image forming and erasing method using the reversible thermosensitive recording medium.
2. Discussion of the Background
In view of environmental problems such as increase of dust and destruction of forests, considerable attention is currently placed on reversible thermosensitive recording media which can reversibly record and erase an image many times. Therefore various reversible thermosensitive recording media have been proposed, and some of the recording media are marketed now.
For example, Japanese Laid-Open Patent Publications Nos. (hereinafter referred to as JOP) 63-107584 and 4-78573 have disclosed polymer-type reversible thermosensitive recording media utilizing a physical change, in which a transparent state and an opaque state are reversibly achieved upon application of heat thereto.
In addition, JOPs 60-193691 and 2-188293 have disclosed dye-type reversible thermosensitive recording media utilizing a chemical change, in which a combination of gallic acid with phloroglucinol is used, or a salt of a higher aliphatic amine and bis(hydroxyphenyl)acetic acid or gallic acid is used as a color developer.
Some of the present inventors and other inventors propose a reversible thermosensitive recording medium using a coloring agent and a color developer in JOP 5-124360, etc. Namely, by using a combination of a specific color developer (i.e., an electron accepting compound) with a specific coloring agent (i.e., a leuco dye, or an electron donating coloring compound), a color image can be easily formed and erased reversibly when properly controlling heating and cooling conditions. The reversible thermosensitive recording medium can reversibly achieve a colored state and a non-colored state many times, and the colored state and non-colored state can be stably maintained at room temperature.
Such a reversible thermosensitive recording medium has been improved as disclosed in JOP 6-210954, and is now used for, for example, point cards in which information of the amounts of points given to a user proportionally to the total purchase amounts in a shop is displayed.
Reversible thermosensitive recording media including a combination of a color developer and a leuco dye have a drawback in that when the recording media are exposed to light for a long period of time, the media tend to color blown and the color cannot be erased. The reason is considered to be that the molecular structure of the leuco dye changes due to irradiation of light, resulting in formation of irreversible colored materials.
Conventional irreversible thermosensitive recording media including a combination of a leuco dye and a color developer also have such a coloring problem. In attempting to solve the problem, an ultraviolet absorbent is typically included in the irreversible thermosensitive recording media to prevent the leuco dye being exposed to ultraviolet light.
For example, JOP 62-48585 discloses an irreversible thermosensitive recording medium in which an intermediate layer including a low molecular weight ultraviolet absorbent is formed between a recording layer and a protective layer.
The present inventors find that when this technique is applied to a reversible thermosensitive recording medium, a problem which occurs is that the coloring/erasing properties of the recording medium are changed because the main component of the ultraviolet absorbent migrates to the recording layer. In addition, it is also found that big problems tend to occur such that the ultraviolet absorbent migrates to the surface of the protective layer, resulting in deterioration of ultraviolet light absorbability of the recording medium, and image qualities deteriorate because the migrated ultraviolet absorbent adheres to a thermal printhead serving as an image writing device.
JOP 7-68937 discloses a reversible thermosensitive recording medium including a protective layer which includes a microencapsulated ultraviolet absorbent which is liquid at room temperature. This microencapsulated ultraviolet absorbent is used to prevent the ultraviolet absorbent from bleeding out. However, the protective layer has a drawback of having poor film strength because of including a liquid phase, and thereby the protective layer deforms after long repeated use. In addition, if the microcapsule is damaged, various problems occur such that the coloring/erasing properties deteriorate; a thermal printhead is contaminated, resulting in deterioration of image qualities; and users are contaminated. Therefore, this method can fully solve the coloring problem.
JOP 10-100541 discloses a reversible thermosensitive recording medium in which a particulate inorganic pigment having ultraviolet-ray masking ability is included in an intermediate layer or a protective layer. Since the particulate inorganic pigment has a controlled particle size, the resultant layer has ultraviolet scattering ability. Therefore the layer has a combination of ultraviolet absorbing ability and ultraviolet scattering ability, and thereby the recording layer is prevented from being exposed to ultraviolet rays.
However, in this method a large amount of a very fine inorganic pigment has to be included in the intermediate or protective layer. Therefore, the layer is brittle. When a reversible thermosensitive recording medium including such a brittle layer is processed so as to be a sheet or a card, a problem such that the edges of the sheet or card have burrs. In addition, such reversible thermosensitive recording medium has high manufacturing costs because the fine inorganic pigment is very expensive. Further, the properties of such a recording medium largely change depending on the dispersion of the very fine inorganic pigment, and therefore problems with image qualities often occur.
In addition, JOPs 8-224960 and 9-207437 have disclosed reversible thermosensitive recording media which include a protective layer including a polymer having ultraviolet absorbability.
In general, the protective layer of a reversible thermosensitive recording medium has to have high heat resistance and durability, and therefore a resin layer crosslinked upon application of heat or ultraviolet rays is typically used as the protective layer. When a polymer which has ultraviolet absorbability and which is not crosslinked is used for the protective layer, the resultant recording medium has poor heat resistance and durability.
Even when a combination of a polymer having ultraviolet absorbability with a crosslinkable resin is used to form a protective layer in which the polymer is fixed by the crosslinked resin, the film strength of the protective layer deteriorates similarly to the protective layer including a microcapsule mentioned above, and thereby the non-crosslinked polymer having ultraviolet absorbability is firstly damaged and then the surface of the recording medium deforms after long repeated use. Therefore, bad image formation/erasure problems occur, resulting in shortage of the life of the recording medium.
As can be understood from the above-description, a reversible thermosensitive recording medium having a good combination of light resistance and durability has not yet been developed.
In JOPs 13-180188 and 13-180116, the present inventors have proposed a reversible thermosensitive recording medium which includes a combination of an electron donating coloring compound and an electron accepting compound and which is used for forming a temporary document such as documents for a meeting.
Such a document-use reversible thermosensitive recording medium has a function in which plural images stored in a computer as digital information are illustrated in plural sheets of the recording medium, which a user can see while comparing the plural images. Therefo
Arai Satoshi
Furuya Hiromi
Shibuya Takeshi
Tatewaki Tadafumi
Tsutsui Kyoji
Hess B. Hamilton
Ricoh Company Limited
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