RECYCLABLE MOISTUREPROOF PAPER HAVING LIGHT-SHIELDING PROPERTY

摘要

PROBLEM TO BE SOLVED: To obtain a light-shielding moistureproof paper suitable as a packaging paper for photosensitive materials, etc., by forming a defiberable and heat- sealable moistureproof layer on a surface of a paper substrate having a light- shielding layer composed mainly of a pigment and free from aluminum foil or aluminized film. SOLUTION: A light-shielding layer having a brightness index of 25-70 and a light transmittance of <=0.5% over the whole wavelength range of 200-800nm is produced by coating a kraft paper with a liquid mixture obtained by compounding 5-300 pts.wt. (in terms of solid) of an aqueous binder such as polyvinyl alcohol to 100 pts.wt. of a light-shielding agent composed mainly of a pigment consisting of 2-50wt.% of graphite, 10-70wt.% of a color pigment such as red iron oxide and 10-70wt.% of a white pigment such as titanium oxide at a coating weight of 3-25g/m<2> . A moistureproof layer having defiberability and heat-sealability is formed by coating the light-shielding layer with 3-25g/m<2> of a mixed liquid produced by mixing 100 pts.wt. of an acrylic emulsion having a gel fraction of 90-100% with 1-5 pts.wt. of a wax emulsion to obtain the objective light-shielding moistureproof paper.