Patent GB-1315192-A (GB)
Title: Coated paper and method of making same
IPC: D21H17/00
Filed: 1970-06-22
Abstract: 1315192 Coated paper SCOTT PAPER CO 22 June 1970 [25 June 1969 22 May 1970] 30265/70 Heading B2E A coated paper having high bulk and a glass value of at least 50 is produced by (1) applying to the surface of at least one side of a sized paper web an aqueous top coating composition having a total solids content of 60-70% by weight, the solids comprising a paper-coating grade pigment, a thermoplastic binder present in an amount equivalent to 10-20% on a dry weight basis, and an antisticking agent, (2) conveying the coated web to a gloss calendar nip while causing only minimal evaporation of water from the coated surface whereby the coating retains enough moisture so that in the absence of the antisticking agent the coating would stick to the heated surface of the calender drum, and (3) calendering the coated paper web between a gloss calender drum having a smooth finishing surface heated to 82-150‹C and a resilient backing roll the pressure in the nip being 400-800 pounds per linear inch, and removing the paper web from contact with the drum as it emerges from the nip. Preferably the temperature of the coated surface prior to calendering does not exceed 70-‹C and the time interval between the application of the top coating composition and calendering does not exceed 5 seconds. The top coating may comprise a mixture of glossing and non-glossing paper-coating grade pigments. The glossing pigment can be a mixture of coating clay and aluminium hydrate, precipitated calcium carbonate and titanium dioxide and preferably comprises 80-90% by weight of the total pigment. Suitable non-glossing pigments are ground natural barytes, waterground calcium carbonate. Preferred thermoplastics binders are styrene-butadiene and styrene-isoprene rubbers optionally carboxylated by incorporation of acrylic acid. A minor proportion of a non-thermoplastic adhesive may be incorporated, e.g. casein, soy protein and starch. Suitable anti-sticking agents are sulphonated castor oil and potassium oleate, preferably a mixture of predispersed calcium stearate and emulsified oleic acid. Additives such as de-foaming agents, dyes, optical brighteners and insolubilizers, e.g. melamine-formaldehyde resin may be present in the composition. A preferred top coating composition comprises a pigment mixture comprising 80-90% by weight glossing pigment with the remainder of the pigment being ground calcium carbonate, anti-sticking agent comprised of dispersed calcium stearate in an amount equivalent to 0.75-2.0% by weight of the total pigment and emulsified oleic acid in amount equivalent to 0.2-0.7% by weight of the total pigment, and a thermoplastic binder comprising styrene-butadiene, styrene-isoprene or styrenebutadiene-acrylic acid copolymer. Preferably sizing is accomplished by applying an intermediate coating comprising a paper-coating grade pigment, the particle size of which is less than 5 microns and a non-thermoplastic binder, e.g. casein, gelatin and soy protein, starch and vegetable gums, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose and styrene-maleic anhydride copolymer.