Abstract: In an image-forming medium, a sheet of paper is coated with a layer of microcapsules which is composed of a binder material and a plurality of microcapsules filled with dye and uniformly distributed in the binder material. The binder material exhibits a predetermined thermal melting point, and the microcapsules exhibit a pressure-breaking characteristic so as to be squashed and broken under a predetermined pressure when said binder material is thermally softened or melted. When a leuco-pigment-based dye is used, a color developer is substituted for the binder material.

Abstract: An image-recording composition comprising: a microcapsule enclosing a leuco-dye; a phenol color-developing agent; and a reaction-accelerating agent catalyzing a color-developing reaction between the leuco-dye and the phenol color-developing agent, the reaction-accelerating agent being an organic compound having at least two carboxyl groups. An image-recording sheet comprising a substrate and a color-developing layer disposed by applying the image-recording composition to the substrate is also provided.

Abstract: A first heat-sensitive microcapsule of the present invention comprises a shell wall and a liquid coloring composition, and has such a temperature-breaking characteristic that the shell wall is broken by heating to a temperature equal to or higher than a boiling point of the liquid coloring composition. The first heat-sensitive microcapsule is stable to light and easy to handle. A second heat-sensitive microcapsule of the present invention comprises a shell wall, a coloring composition and a heat decomposition-type gas-developing agent, and has such a temperature-breaking characteristic that the shell wall is broken by heating to a temperature equal to or higher than a decomposition temperature of the gas-developing agent. The second heat-sensitive microcapsule can be sensitively broken even by heating in a short time.

Abstract: An image-recording composition comprising: a microcapsule enclosing a leuco-dye; a phenol color-developing agent; and a reaction-accelerating agent catalyzing a color-developing reaction between the leuco-dye and the phenol color-developing agent, the reaction-accelerating agent being an organic compound having at least two carboxyl groups. An image-recording sheet comprising a substrate and a color-developing layer disposed by applying the image-recording composition to the substrate is also provided.

Abstract: An ink composition includes an oil-based ink and a heat decomposition gas-developing agent that generates gas by a relatively small amount of heat. A thermal printer using the ink composition is not clogged with the composition even after a long-term storage, and provides a printed matter having excellent water resistance. Thus, the ink composition is remarkably useful for a thermal ink jet printer and a thermal ink permeation printer.

Abstract: A first heat-sensitive microcapsule of the present invention comprises a shell wall and a liquid coloring composition, and has such a temperature-breaking characteristic that the shell wall is broken by heating to a temperature equal to or higher than a boiling point of the liquid coloring composition. The first heat-sensitive microcapsule is stable to light and easy to handle. A second heat-sensitive microcapsule of the present invention comprises a shell wall, a coloring composition and a heat decomposition-type gas-developing agent, and has such a temperature-breaking characteristic that the shell wall is broken by heating to a temperature equal to or higher than a decomposition temperature of the gas-developing agent. The second heat-sensitive microcapsule can be sensitively broken even by heating in a short time.

Abstract: In a color image-forming medium, a substrate is coated with a color-developing layer which is composed of at least one kind of heat-sensitive color-developing component, and a plurality of pressure-sensitive microcapsules. Each of the pressure-sensitive microcapsules is filled with a dye exhibiting a first single-color, and features a pressure/temperature characteristic to be broken when being subjected to a predetermined pressure within a first temperature range. The heat-sensitive color-developing component features a thermal color-developing characteristic to develop a second single color within a second temperature range defined by a first critical temperature and a second temperature. The first critical temperature is in the first temperature range, and the second critical temperature exceeds an upper limit temperature of the first temperature range.

Abstract: An ink composition of the present invention comprises an oil-based ink and a heat decomposition-type gas-developing agent that generates gas by relatively small amount of heat. A thermal printer using the ink composition is not clogged with the composition even after a long-term storage, and provides a printed matter excellent in water resistance. Thus, the ink composition is remarkably useful for a thermal ink jet printer and a thermal ink permeation printer.

Abstract: In an image-forming medium, a sheet of paper is coated with a layer of microcapsules which is composed of a binder material and a plurality of microcapsules filled with dye and uniformly distributed in the binder material. The binder material exhibits a predetermined thermal melting point, and the microcapsules exhibit a pressure-breaking characteristic so as to be squashed and broken under a predetermined pressure when said binder material is thermally softened or melted. When a leuco-pigment-based dye is used, a color developer is substituted for the binder material.

Abstract: A charging method for transfer in an electrograph device having a phtosensitive drum uses a high voltage pulse train applied to a displaceable transferring sheet to effect transfer to the sheet of an image on the photosensitive drum. A detector for detecting the speed of feed of the sheet controls the frequency of the voltage pulse train so that the number of pulses per unit displacement of the sheet is independent of the speed at which the sheet moves.