Abstract: A thermal transfer sheet having a back coating layer excellent in heat-resistance is provided by using a styrene-acrylonitrile copolymer as a resin constituting the back coating layer. A thermal transfer material having an excellent heat-resistance and having a back coating layer having considerable strength is provided by incorporating at least two species of heat-resistant particles having different particle sizes in the back coating layer, since the larger species of particle imparts excellent heat-resistance to the back coating layer, the smaller species of particle enhances the total amount of the fillers, and the larger and smaller species of particles function so as to provide a synergistic effect.

Abstract: A thermal transfer sheet has a substrate film, a heat-fusible ink layer formed on one surface side of the substrate film, and an antisticking layer formed on the other surface side of the substrate film. The heat-fusible ink layer comprises a carbon black having toluene-coloring transmittance of 60% or more, and, therefore, there is provided a thermal transfer sheet containing a heat-fusible ink layer having an uniform thickness and being capable of providing printed letters improved in blackness and durability such as solvent resistance.

Abstract: A copolymer of formaldehyde with a cyclic formal is continuously prepared by feeding formaldehyde, the cyclic formal and 0.1-20 weight parts, per 100 weight parts of formaldehyde, of an inert organic solvent to a biaxial mixer where the formaldehyde is copolymerized with the cyclic formal in the presence of boron trifluoride or an ether complex thereof.

Abstract: A method of stabilizing oxymethylene copolymers which comprises heating an oxymethylene copolymer in a hydrocarbonaceous mixed medium consisting of about 50 - 92% by weight of a hydrocarbon having 5 - 7 carbon atoms, about 6 - 48% by weight of an alcohol and about 2 - 20% by weight of water based on the total amount of the medium, at a temperature of from about 100.degree. to about 170.degree. C. in the presence of a salt selected from the group consisting of the sodium and potassium salts of ethylenediaminetetraacetic acid under the conditions of a pH value of from about 4 to about 7.