1. Field of the Invention
The present invention relates to an image-forming medium used in image-forming apparatuses such as printers, etc.
2. Description of the Related Art
An image-forming apparatus with the following type of structure is used for practical purposes.
In this image-forming apparatus, first, an image-forming medium in a sheet form that has been coated with microcapsules in which a dye precursor and a photocuring composition have been encapsulated is exposed to light according to image data by using an exposure means and the photocuring composition inside the microcapsules is cured according to the image data.
Then, ordinary paper, etc., that has been coated with a developer that will change colors when it reacts with the dye precursor encapsulated in the microcapsules, etc., and a photosensitive sheet that has been exposed are made to come in contact therewith and are pressed to perform a development, the microcapsules that have not been cured are broken with a crushing roller, and an image is formed when the dye precursor that flows out of the microcapsules reacts with the developer.
This image-forming apparatus uses an image-forming medium in which 3 types of microcapsules, which are shown below, are supported on a film, and once the medium has been exposed to light in accordance with image data, the medium is overlapped with an image-receiving sheet that has been coated with a developer and pressed and developed in this state.
The microcapsules in the uncured part are broken when they are pressed. The colorless dye flows out therefrom and reacts with the developer and coloration takes place to form an image. The exposure means is an analog exposure system, in which a pattern sheet transmits or reflects light and exposure is performed all at once with image data light of a wavelength of from blue to red (approximately 400 to 700 nm)
(1) Microcapsules encapsulating a photocuring composition sensitive to light of the blue wavelength region and a colorless dye that turns yellow when it reacts with developer.
(2) Microcapsules encapsulating a photocuring composition sensitive to light of the green wavelength region and a colorless dye that turns magenta when it reacts with developer.
(3) Microcapsules encapsulating a photocuring composition sensitive to light of the red wavelength region and a colorless dye that turns cyan when it reacts with developer.
Nevertheless, the image-forming medium used in conventional image-forming apparatuses poses a problem in that, when the medium is exposed in succession by using image data light of the blue (approximately 400 to 500 nm), green (approximately 500 to 600 nm), and red (approximately 600 to 700 n) wavelength regions, there is a reduction in the density of the 3 primary colors of yellow, magenta and cyan.
This problem is caused by so-called crosstalk at the photosensitive wavelength region of the microcapsules,
That is, the photosensitivity of each microcapsule used in the conventional image-forming medium is as shown in FIG. 26. For instance, microcapsules for magenta coloration are desired to be photosensitive to only light of the green wavelength region (approximately 500 to 600 nm).
However, as shown in FIG. 26, since microcapsules for magenta coloration are sensitive to light of from approximately 430 nm to approximately 640 nm, they are also photosensitive to light of the blue wavelength region (approximately 400 to 500 nm), etc.
Therefore, it appears that when light that has been resolved to the 3 colors of blue, green, and red is used for exposure, a curing reaction proceeds with exposure to light other than green light, to which the microcapsules should not be originally sensitive, and this leads to a reduction in the density of the 3 primary colors.
This type of overlapping of wavelength regions where there is photosensitivity is called crosstalk.
In order to solve this problem with crosstalk, the digital image-forming apparatus of Japanese Patent Application Laid-open No. 2-82234 has a means for irradiating light that does not reach the crosstalk wavelength region of microcapsule sensitivity, as the digital image data light, onto an image-forming medium coated with 3 types of microcapsules having a sensitivity peak in the respective wavelength regions of blue, green, and red.
A combination of a halogen tungsten lamp and color filter is used, or a metal halide lamp with an emission spectrum at a specific wavelength is used, in the above-mentioned publications in order to prevent crosstalk.
Nevertheless, there are many cases when the crosstalk wavelength region of actual microcapsules is broad as shown in FIG. 1, and if light that does not reach crosstalk is to be used with microcapsules for magenta coloration that are photosensitive to green, in particular, this light will be very limited at 540 to 580 nm, and it will be difficult to actually make this type of light using a color filter.
Moreover, although it is possible to emit light of a certain single wavelength using a metal halide lamp, realistically, it is difficult to use metal halide lamps in printers, etc., because they are expensive and they require large amounts of energy.
The present invention has solved the above-mentioned problems, its object is to provide an image-forming medium with no reduction in image density, even though exposure is performed using light that has been resolved by a simple, inexpensive device such an a filter, etc.
In order to accomplish this object, the present invention provides an image-forming medium comprising a substrate and several types of photo-curing compositions with sensitivity peaks in different wavelength regions supported thereon. Each of the several types of photocuring compositions contains a spectral sensitizer that is designed so that there is apparently no crosstalk in an image which is formed using the image-forming medium.
The xe2x80x9capparentlyxe2x80x9d used here means that crosstalk is controlled to such an extent that there is no reduction in image density, even when exposure is performed with light that has been resolved to 3 colors.
Using the best sensitivity as the criterion, crosstalk is actually present when sensitivity in 1/1,000 or 1/10.000 the best sensitivity.
However, crosstalk at a sensitivity that differs by even 3 to 4 digits essentially has no effect an the image. It, therefore, is quite possible to apparently eliminate crosstalk to such an extent that there will be no problems with the image, although it is difficult to completely eliminate crosstalk of a photocuring composition.
In the image-forming medium of the present invention, each of the above-mentioned several types of photocuring compositions contains a spectral sensitizer, which is designed so that there will be apparently no crosstalk in the image that has been formed using the image-forming medium. Therefore, even if exposure in performed using light that has been resolved by a simple, inexpensive device such as a filter, etc., a reduction in image optical density (hereinafter merely referred to as xe2x80x9cimage densityxe2x80x9d) can realistically be prevented.
In the image-forming medium of the present invention, it is preferable that the half-width of the wavelength absorption peak of each spectral sensitizer of the image-forming medium is 50 nm or less, so that crosstalk is hardly present and a reduction in image density can realistically be prevented.
Moreover, in the image-forming medium of the present invention, it is preferable that 3 types of photocuring compositions are supported on a substrate in the image-forming medium, and that spectral sensitizer with a maximum absorption wavelength in the blue, green, or red wavelength regions is contained in the respective photocuring composition, so that full-color printing is possible and a reduction in density of the 3 primary colors can be prevented.
In addition, in the image-forming medium of the present invention, it is preferable that the spectral sensitizers contained in the image-forming medium have a maximum absorption wavelength of 400 to 470 nm, 530 to 570 nm, or 630 to 700 nm, respectively, so that a reduction in density of the 3 primary colors can be reliably prevented.
Moreover, in the image-forming medium of the present invention, it is preferable that the photocuring compositions are supported on a substrate in a microcapsule-encapsulated state, so that it is possible to provide an inexpensive image-forming medium with which full-color printing is possible and a reduction in density of the 3 primary colors, etc., can be prevented using microcapsules that can be easily produced by conventional methods.
This and other objects, features and advantages of the present invention are described in or will become apparent from the following detailed description of the invention.