Pressure roll, and molding apparatus using the pressure roll

A molding apparatus for molding a plastic sheet, said molding apparatus comprising:

• a main cooling roll;
• a pressure roll comprising a cylindrical core member having a center shaft;
• an intermediate layer of a flexible material formed on a peripheral surface of said cylindrical core member, said intermediate layer having a thickness of 5-25 mm, and at least one internal cavity for receiving a pressure transmission medium to modify the pressure applied to the plastic sheet by said pressure roll, wherein said internal cavity extends over almost the whole length of said intermediate layer in an axial direction;
• and
• an outermost layer formed on a peripheral surface of said intermediate layer, said outermost layer having a thickness of not less than 0.6 mm and being made of a metal;
• and
• a cooling means for cooling a surface of said pressure roll with a liquid or gaseous medium,
• wherein aid pressure roll has an outer diameter of 250 to 700 mm and a ratio of a mean thickness of said outermost layer to said outer diameter of said pressure roll is 0.1 to 1.5%, and
• wherein the thicknesses of said outermost layer and said intermediate layer are selected from the above ranges so that they can deform when said pressure roll is pressed against said cooling roll so as to increase a contacting area of said outermost layer with plastic material, thereby obtaining a thin plastic sheet.

A pressure roll for coacting with a cooling roll to press a molten or softened plastic material introduced therebetween to form a plastic sheet saving a reduced uniform thickness, said pressure roll comprising:

• a cylindrical core member having a center shaft;
• an intermediate layer of a flexible material formed on a peripheral surface of said cylindrical core member, said intermediate layer having a thickness of 5-25 mm, and at least two internal cavities for receiving a pressure transmission medium to modify the pressure applied to the plastic sheet by said pressure roll, wherein each of sail at least two internal cavities extends over almost the whole length of said intermediate layer in an axial direction;
• and
• an outermost layer formed on a peripheral surface of said intermediate layer, skid outermost layer having a thickness of not less than 0.6 mm and bring made of a metal,
• wherein said pressure roll has an outer diameter of 250 to 700 mm and a ratio of a mean thickness of said outermost layer to said outer diameter of said pressure roll is 0.1 to 1.5%, and
• wherein the thicknesses of said outermost layer and said intermediate layer are selected from the above ranges so that they can deform when said pressure roll is pressed against the cooling roll so as to increase a contacting area of said outermost layer with the plastic material, thereby obtaining a thin plastic sheet.

A molding apparatus for molding a plastic sheet, said molding apparatus comprising:

• a main cooling roll;
• a pressure roll comprising a cylindrical core member having a center shaft;
• an intermediate layer of a flexible material formed on a peripheral surface of said cylindrical core member, said intermediate layer having a thickness of 5-25 mm, and at least two internal cavities for receiving a pressure transmission medium to modify the pressure applied to the plastic sheet by said pressure roll, wherein each of said internal cavities extends over almost the whole length of said intermediate layer in an axial direction;
• and
• an outermost layer formed on a peripheral surface of said intermediate layer, said outermost layer having a thickness of not less than 0.6 mm and being made of a metal;
• and
• a cooling means for cooling a surface of said pressure roll with a liquid or gaseous medium,
• wherein said pressure roll has an outer diameter of 250 to 700 mm and a ratio of a mean thickness of said outermost layer to said outer diameter of said pressure roll is 0.1 to 1.5%, and
• wherein the thicknesses of said outermost layer and said intermediate layer are selected from the above ranges so that they can deform when said pressure roll is pressed against said cooling roll so as to increase a contacting area of said outermost layer with plastic material, thereby obtaining a thin plastic sheet.