Thermally sensitive recording medium

Details Thermally sensitive recording medium Thermally sensitive recording medium

1999-05-19

2001-09-04

Hess, Bruce H. (Department: 1774)

Record receiver having plural interactive leaves or a colorless

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

Identified color-former

C503S204000, C503S216000, C503S217000, C503S218000, C503S220000, C503S221000

Reexamination Certificate

active

06284706

ABSTRACT:

BACK GROUND OF THE INVENTION
The present invention relates to a thermally sensitive recording medium which develops sepia or light brown 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 thermal 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 kind of measuring equipment and for a label. The developed color image of these thermally sensitive recording media 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 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 sepia color or light brown color is coming to be desired. In the conventional field of thermally sensitive recording medium, it is commonly observed that the developed color changes to sepia or light brown color by the effect of environment such as sun light and temperature, or by the effect of chemicals, however, this color change is a phenomenon which is recognized as a problem caused by poor color preserving. And the thermally sensitive recording medium whose original developed color is sepia or light brown is not developed yet.
The object of this invention is to provide a thermally sensitive recording medium which has a sufficient color density and develops sepia or light brown color.
To accomplish the above mentioned object, a thermally sensitive recording medium is provided 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 measured by JIS-Z-8729 of developed image of said thermally sensitive recording medium is 0 to 40, and the color difference b* value measured by JIS-Z-8729 of developed image of said thermally sensitive recording medium is 0 to 55.
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 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 is close 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 to 40 and b* value is 0 to 55, and the required sepia or light brown color tone can be obtained. Further, more vivid tone can be obtained when color difference a* value is 0 to 40 and b* value is 3 to 55, more desirably, a* value is 0 to 30 and b* value is 10 to 40. When these color difference values are out of the region regulated in this invention, the color of developed image becomes orange or black and the aimed color tone cannot be obtained.
In addition to a* and b* values in this invention, the color tone can be also obtained 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 30 to 60, and more desirably is 30 to 50.
In a preferred embodiment, the thermally sensitive recording medium comprises a dye precursor composed by at least one kind of an orange color developing leuco dye whose maximum absorption wave length is 460 to 560 nm and at least one kind of a black color developing leuco dye whose maximum absorption wave lengths are 420 to 480 nm and 550 to 640 run. The maximum absorption wave length of this invention is measured in 99% acetic acid solution. Thus, by the combined use of leuco dyes whose maximum absorption wave lengths are different, the thermally sensitive recording medium which develops sepia color or light brown color can be easily obtained.
In another embodiment, the thermally sensitive recording medium contains 0.05 to 1 parts of black color developing leuco dye whose maximum absorption wave lengths are 420 to 480 nm and 550 to 640 nm to 1 part of orange color developing leuco dye whose maximum absorption wave length is 460 to 560 nm. When the content of black color developing leuco dye is smaller than 0.05 parts to 1 part of orange color developing leuco dye, the color of developed image becomes reddish brown which is the aimed color tone, however, the color density becomes slightly low. This is not a problem in a practical use, however, the contrast of developed image is slightly bad. In the meanwhile, when the content is bigger than 1 part, the contrast of developed image is good, but the color tone becomes slightly dark and looks like dark brown. Therefore, it is desirable to contain the black color developing leuco dye in the above mentioned ratio to the orange color developing leuco dye to obtain the thermally sensitive recording medium whose developed image is vivid sepia or light brown color and the contrast of image is good.
Further, in still another embodiment, the thermally sensitive recording medium contains at least one leuco dye selected from the group composed by 3-cyclohexylamino-6-chlorofluoran and 3-diethylamino-6,8-dimethylfluoran as an orange color developing leuco dye whose maximum absorption wave length is 460 to 550 nm. The use of these leuco dyes is effective to obtain the sepia or light brown color which is the object of this invention.
In another aspect of this invention a thermally sensitive recording medium is provided which displays the developed color image of sepia or light brown color. In this invention, the term of sepia or light brown color means dim and dark neutral tone developing of yellowish red or light brown, which is disclosed, e.g., from page 42 to 51 of “Color one point 10, color naming and it's episode”) (Japan Standard Society, issued on Nov. 19, 1993) in items of “13 DULL ORANGE”, “14 REDDISH BROWN”, “15 BROWN”, “16 YELLOWISH BROWN” or “17 GRAYISH BROWN”. These colors are expressed as dim yellowish red, dim red, dark red, dark yellowish red and dark gray by JIS common name, or are expressed as cinnamon color, wheat color, fox color, brick color, reddish brown, light brown, nut-brown color, dark-brown color, yellowish brown and earth-brown 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 sepia color or light brown color are typically used to mean commonly expressed sepia or light brown color, however, the invention is not limited to them.
As a leuco dye which develops orange color used in this invention, the leuco dye whose maximum absorption wave length in 99% acetic acid solution is from 460 to 550 nm can be used. As the concrete examples, 3-cyclohexylamino-6-chlorofluoran and 3-diethylamino-6,8-dimethylfluoran

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