be preferably used include rosin alkylketene dimers higher fatty acid salts paraffin wax and alkenylsuccinic acid the weight ratio of the softening agent to the sizing agent is preferably from 1 100 to 10 1 more preferably 1 20 to 5 1 from the viewpoint of a balance between the desired effect and a reduction in the strength of the paper the base paper that is used in the present invention is produced mainly from wood pulp such as nbkp lbkp nbsp and lbsp in addition it can be produced from mixtures of wood pulp and synthetic fibers such as vinylon or synthetic pulp such as polyethylene from the viewpoint of flexibility it is preferred that the freeness of the pulp be such that it is not almost beaten however taking into consideration the formation and paper production suitability the canadian standard freeness of the pulp is preferably from 200 to 500 cc c s f fillers such as clay talc calcium carbonate and urea resin fine particles sizing agents such as rosin alkylketene dimers higher fatty acid salts paraffin wax and alkenylsuccinic acid and fixing agents such as aluminum sulfate and cationic polymers may be added if desired in addition surface sizing using pigments such as calcium carbonate and kaolin starch polyvinyl alcohol and sbr latexes may be applied furthermore the back of the base paper may be coated with a coating solution such as a film forming polymer for the purpose of preventing curling the heat sensitive coating solution as used herein will hereinafter be explained a color former and a color developer are dispersed independently in the respective water soluble polymer solutions for example by means of a ball mill.