To compare dot gain of various hardcopies, we have proposed a new dot gain definition as “Dot area expansion caused by dot thickness reduction compared with the one at the solid area”. According to this definition, the amount of dot gain can be estimated both from cross sectional dot structures and by colorimetric measurement. The latter is preferred as for evaluation efficiency. The present report describes in detail the principle of colorimetric dot gain analysis based on the new definition and further proposes practically effective procedures. The amount of dot gain is evaluated by the degree of deviation from the straight line representing the Murray-Davies relationship on a color coordinate plane. Such a deviation takes place with the change of the ratio of main absorption to sub-absorption of the colorant caused by the dot thickness reduction. Accordingly, in the case of a step wedge comprising a typical magenta pigment which has the main absorption at the y region accompanied with a relatively large sub-absorption at the z region, a colorimetric analysis on the y-z plane is most desirable. Slight differences in dot gain depending on screen structure have become detectable due to the appropriate selection of plane.

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In laser thermal transfer printing using dye sublimation type medium, a high definition and continuous tone image can be obtained easily because a laser light is focused to small spot and heat energy can be controlled by the pulse width modulation of laser light. In this report, we focus on the laser light absorbing layer of double layered dye donor sheet. Carbon black, metal-phthalocyanine pigment and dye, metal complex organic compound, and cyanine dye are used as light-heat conversion materials. As experimental results of dye transfer from dye donor layer to receiving sheet by laser heating, each sample exhibits different dye transfer characteristics according to kind of light-heat conversion materials. By the measurement of absorption spectra of laser light absorbing layers after laser heating, it becomes clear that the phenomena such as the decomposition reaction and the crystal phase transformation of light-heat conversion materials are caused by laser heating. We have concluded that it is necessary for a high heat generation efficiency to have no change of IR light absorption by laser heating.

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A novel electronic reflective display by an electrical movement of conductive toner has been investigated. The sandwich type display cell consists of two ITO (Indium Tin Oxide) plates coated with charge transport layer (CTL) and a spacer. There are conductive toners and dielectric white particles in this display cell. In this display, toner movement is controlled by the change of an external electric field applied between two ITO electrodes. The conductive toners in contact with the CTL on the anode are charged positively by the hole injection from the CTL, and then move to the cathode by a coulomb attraction. In addition, the toners can move to the counter electrode by an applying a reverse electric field and the cell displays the white by the light scattering of white particles. The cell displays the black and white pixel by switching of electrical polarity. The reflection density in the image area to display black was 0.9, and it was 0.6 in the non-image area to display white. The maximum contrast was obtained when mixing weight ratio of the conductive toner to the white particle is 1:1.

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A video printer using thermal dye transfer method makes high quality images with its half tone control system. Recently a few kinds of printed images with a little bit of density difference in gray balance, such as graphic images or overlaid images are reported. In case of printing many identical images continuously, there are some differences in image quality, especially in gray balance, between the first print and the last one. So we have checked the reason and investigated the method for improving the quality of gray balance.
Before trying to examine the half tone control system, we have studied the relationship between the printed image and the detected temperature of the thermal head. We have made investigation into compensating the optical density with switching the data banks for gamut according to the head temperature. To realize this new method to compensate the optical density, it was important to clarify the limit of the density step caused by data switching. It is very effective for density compensation to increase the number of data banks and the key data for the compression of gamut data in half tone control. After all these investigations, we have reduced the density error by half.

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4, 4', 7, 7'-tetrachlorothioindigo (TCTI) and 4, 4', 5, 5', 7, 7'-hexachlorothioindigo (HCTI) are thionated derivatives of indigo that are known as reddish purple pigments as well as photoconductors. Although these molecules are quite similar in structure, TCTI is less soluble in organic solvents and more photoconductive than HCTI by about one order of magnitude. Intermolecular interactions are obviously responsible for these differences in physical properties. As a tool for evaluating intermolecular interactions, we have focused on the two-center energy which is involved in MO calculations and which relates to the bond energy within a molecule. We believed the two-center energy to be a powerful measure of intermolecular interactions when applied to non-bonded atom-pairs between two molecules. On the basis of this idea, we have extracted typical molecule pairs from the crystal lattice and evaluated their two-center energies. As a result, we found a two-dimensional CH…O hydrogen bond network both in TCTI and HCTI as well as other intermolecular forces. These results suggest that the intermolecular interactions are appreciably stronger in TCTI than in HCTI, indicating the insolubility of TCTI for organic solvents.

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