Thin film electric heater, and method and apparatus for injection molding of plastics using the same

A thin film electric heater comprising:

• a thin film electric resistor to be formed directly on a surface of an object to be heated;
• said thin film electric resistor having terminal portions to supply thereto electric power to thereby heat the surface of the object;
• said thin film electric resistor having a surface resistivity r of a value defined by:
• ##EQU2## wherein L is a length between said terminal portions as measured along said thin film electric resistor, D is length of said thin film electric resistor in a direction perpendicular to the direction between said terminal portions, V.sub.a is a maximum value of allowable voltage applied between said terminal portions, I.sub.a is a maximum value of allowable current flowing between said terminal portions, and W.sub.r is an input power per unit area of said thin film electric resistor determined to obtain a desired rate of increase of temperature of the surface of the object.