Thermally sensitive recording medium

Details Thermally sensitive recording medium Thermally sensitive recording medium

1999-06-16

2001-07-10

Hess, Bruce H. (Department: 1774)

Record receiver having plural interactive leaves or a colorless

Having a colorless color-former, developer therefor, or...

Identified organic electron acceptor other than phenolic resin

C106S031190, C106S031210, C503S220000

Reexamination Certificate

active

06258747

ABSTRACT:

BACK GROUND OF THE INVENTION
The present invention relates to a thermally sensitive recording medium which develops russet or wine red color.
DESCRIPTION OF THE PRIOR ART
Generally, the thermally sensitive recording medium possessing a thermally sensitive recording layer mainly comprising a colorless or a pale colored electron donating dye precursor (hereinafter shortened to dye precursor) and a color developer which develops color when heated together with said dye precursor was disclosed in Japanese Patent publication 45-14035 and had been widely utilized practically. As a recording apparatus for this thermal sensitive recording medium, a thermally printer to which a thermal head is installed can be used. The recording method mentioned above has strong points in comparison with other conventional recording methods, namely, noiseless during recording, a developing and a printing procedure are not needed, maintenance free, apparatus is relatively low price and compact and a recorded pattern is very vivid. Therefore, along with the growth of information industry, the application of this method is widely expanded, for instance, applications for a facsimile or a computer, for many kinds of measuring equipment and for a label. The developed color image of these thermally sensitive recording medium is mainly black color, however, a red color developing type, a blue color developing type, a green color developing type, a full color developing type and a dual color developing type are also well known.
The developed color of thermally sensitive recording medium is comparatively sharp and close to a photograph, and recently has been used as an output means of image which is taken by a camera attached to a game machine. Accompanied with the extension of uses, a thermally sensitive recording medium which develops neutral color such as russet color or wine red color is becoming to be desired. However, in the conventional field of thermally sensitive recording medium, there is still a need for a thermally sensitive recording medium which develops these neutral color.
The object of this invention is to provide a thermally sensitive recording medium which has a sufficient color density and develops russet or wine red color.
To accomplish the above mentioned object, the present invention provides a thermally sensitive recording medium having a thermally sensitive color developing layer containing a colorless or a pale colored dye precursor and a color developer as a main component on a substrate, wherein the color difference a* value regulated by JIS-Z-8729 of developed image of said thermally sensitive recording medium is 0~50, and the color difference b* value regulated by JTS-Z-829 of developed image of said thermally sensitive recording medium is −15~10.
The color difference a* value is a parameter which indicates green color, and when the minus value of a* is big, the greenish tone is strong. And when the value approaches to 0, the greenish tone becomes weak. Further, plus a* value indicates the reddish tone. Meanwhile, the color difference b* value is a parameter which indicates blue tone and when the minus value of b* is big, the bluish tone is strong. When the value approaches to 0, the bluish tone becomes weak, and plus b* value indicates yellowish tone. In the thermally sensitive recording medium of this invention, the color difference a* value of developed image is 0~50 and b* value is −15~0, and the required russet or wine red color tone can be obtained. Further, more vivid tone can be obtained when color difference a* value is 10~50 and b* value is −15~0, more desirably a* value is 15~45 and b* value is −10~0. When these color difference values are out of the region regulated in this invention, the color of developed image becomes red or black and the object color tone can not be obtained.
In addition to a* and b* value regulating in this invention, the color tone can be also indicated by L* value which displays brightness. L* value is not limited in this invention, however, when L* value is too low, color tone becomes dark. Therefore, desirably the practical L* value is to be 20~60, and more desirably to be 20~50.
In a preferred embodiment, the present invention provides the thermally sensitive recording medium as described above, wherein dye precursor is comprises at least one kind of an orange color developing leuco dye whose maximum absorption wave length is 480~570 nm and at least one kind of a black color developing leuco dye whose maximum absorption wave length is 420~480 nm and 550~640 nm. The maximum absorption wave length of this invention is measured in 99% acetic acid solution. Thus, by the combination use of leuco dyes whose maximum absorption wave lengths are different, the thermally sensitive recording medium which develops neutral color such as russet color or wine red color can be easily obtained.
In another embodiment, the invention provides the thermally sensitive recording medium containing 0.05~1 parts of black color developing leuco dye whose maximum absorption wave length is 420~480 nm and 550~640 nm to 1 part of red color developing leuco dye whose maximum absorption wave length is 480~570 nm. When the content of black color developing leuco dye is smaller than 0.05 parts to 1 part of red color developing leuco dye, the aimed color tone can be obtained, however, the color density becomes slightly low. This is not a problem in a practical use, but the contrast of developed image is slightly bad. Conversely, when the content is bigger than 1 part, the contrast of developed image is good, but the black color tone becomes slightly strong. Therefore, it is desirable that the black color developing leuco dye is contained in the above mentioned ratio to the red color developing leuco dye to obtain the thermally sensitive recording medium whose developed image is vivid russet or wine red color and the contrast of image is good.
Preferebly, the thermally sensitive recording medium contains at least one kind of chemical compound indicated by general formula (1) as red color developing leuco dye whose maximum absorption wave length is 480~570 nm.
The use of these leuco dyes is effective to obtain the russet or wine red color which is the object of this invention. Further, the preserving ability of the developed image is improved, and especially the resistance to the plasticizer is remarkably improved. The reason for above mentioned improvement can not be clearly explained, however, in this invention, it is assumable that the polarity of the compound represented by general formula (1) is high, and the solubility of developed image formed by the reaction with a color developer to the plasticizer becomes low.
It is also preferred that the thermally sensitive recording medium which displays the developed color image of russet or wine red color. In this invention, the term “russet ” or “wine red ” color means dim and dark neutral tone developing of red, which is disclosed e.g. from page 32 to 33, in item “8 Dull & Dark red” of “Color one point 10, color naming and it's episode” (Japan Standard Society, issued on Nov. 19, 1993). These colors are expressed as dim red or dark red by JIS common name, or are expressed as russet, reddish brown or garnet color by idiomatic color naming. Further, the expression of color becomes different by a subjectivity of inspector or by an illumination, and in this invention, the expression of russet color or wine red color are typically used containing commonly expressed wine red color, rose color or reddish purple color, however, not limited to them.
As a leuco dye which develops red color used in this invention, the leuco dye whose maximum absorption wave length in 99% acetic acid solution is from
480~570 nm can be used. As the concrete examples,
3-diethylamino-6-methyl-7-chlorofluoran,
3-diethylamino-benzo[a]fluoran,
3-diethylamino-7-chlorofluoran,
3-diethylamino-7-methylfluoran,
3-N-ethyl-N-isoamylamino-benzo[a]fluoran,
3-N-ethyl-N-p-methylphenylamino-7-methylfluoran,
3-dibutylamino-6-me

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