Latex containing papers

Claim 1

A method for the continuous manufacture of fibrous paper sheet material from an aqueous fibrous pulp containing at least 7% latex solids comprising the following steps: (1) providing water which contains no more than abut 22 mg/l of chlorine, no more than about 46 mg/l of sulfate, no more than about 0.2 mg/l of sulfamate and no more than about 0.2 mg/l of aluminum, (2) suspending fibrous material having an anionic charge in said water, (3) measuring the pH and the Zeta potential of said fibrous suspension, (4) adding to said fibrous suspension a compound which will alter the pH of said fibrous suspension, to adjust the pH of said fibrous suspension to the pH value of the aqueous suspension of latex particles to be added later, the nature and amount of said compound which will alter the pH being such that the suspension will continue to contain no more than about 22 mg/l of chlorine, no more than about 46 mg/l of sulfate, no more than about 0.2 mg/l of sulfamate and no more than about 0.2 mg/l of aluminum, (5) providing an aqueous solution comprising as bridging agent a condensate of diamide and formaldehyde having the formula: ##STR3## the ratio x/y being between 0.1 and 3, the molecular weight being between 400 and 1500, and adjusting the Zeta potential of said agueous solution to an absolute value between 60-120% of that of the fibrous suspension and the latex suspension, said adjusting of the Zeta potential being effected by controlling the quantity of said condensate in said aqueous solution, (6) adjusting the pH of said bridging agent solution to that of the aqueous suspension of latex and the fibrous suspension, (7) adding the latex suspension to the fibrous suspension in an amount to provide, in the final paper product, at least 7% latex solids, (8) adding the bridging agent solution to the obtained mixture of latex and fibrous suspension in a quantity such that the obtained mixture has a Zeta potential substantially equal to that of the aqueous starting fibrous suspension and the latex particles remain generally unflocculated, and (9) forming a paper sheet from the resultant mixture.

Claim 2

A method for the continuous manufacture of fibrous paper sheet material from an aqueous fibrous pulp containing at least 7% latex solids comprising the following steps: (1) providing water which contains no more than abut 22 mg/l of chlorine, no more than about 46 mg/l of sulfate, no more than about 0.2 mg/l of sulfamate and no more than about 0.2 mg/l of aluminum, (2) suspending fibrous material having an anionic charge in said water, (3) measuring the pH and the Zeta potential of said fibrous suspension, (4) adding to said fibrous suspension a compound which will alter the pH of said fibrous suspension, to adjust the pH of said fibrous suspension to the pH value of the aqueous suspension of latex particles to be added later, the nature and amount of said compound which will alter the pH being such that the suspension will continue to contain no more than about 22 mg/l of chlorine, no more than about 46 mg/l of sulfate, no more than about 0.2 mg/l of sulfamate and no more than about 0.2 mg/l of aluminum, (5) providing an aqueous solution comprising as bridging agent a condensate of diamide and formaldehyde having the formula: ##STR3## the ratio x/y being between 0.1 and 3, the molecular weight being between 400 and 1500, and adjusting the Zeta potential of said agueous solution to an absolute value between 60-120% of that of the fibrous suspension and the latex suspension, said adjusting of the Zeta potential being effected by controlling the quantity of said condensate in said aqueous solution, (6) adjusting the pH of said bridging agent solution to that of the aqueous suspension of latex and the fibrous suspension, (7) adding the latex suspension to the fibrous suspension in an amount to provide, in the final paper product, at least 7% latex solids, (8) adding the bridging agent solution to the obtained mixture of latex and fibrous suspension in a quantity such that the obtained mixture has a Zeta potential substantially equal to that of the aqueous starting fibrous suspension and the latex particles remain generally unflocculated, and (9) forming a paper sheet from the resultant mixture.