Patent GB-1365230-A (GB)
Title: Soft absorbent fibrous sheet material and a method for making same
IPC: B31F1/12
Filed: 1972-06-06
Abstract: 1365230 Paper SCOTT PAPER CO 6 June 1972 [24 June 1971] 26347/72 Headings D2A and D2B [Also in Division F4] A soft, absorbent, creped fibrous sheet is made by forming a web from stock of lignocellulosic fibres, an elastomeric bonding material and water, removing water from the web without mechanical compression until the web is at least 80% dry, adhering the web to a creping surface and removing it from the surface by a creping blade. The stock is supplied through a tapered manifold 11 and tubes 12 to a chamber 13 feeding a Fourdrinier wire 16 which extends over table rolls 18 and may be associated with vacuum boxes and hydrofoils. The formed web is transferred to a foraminous drying fabric 24 by means of a steam or air jet 26 and a suction roll 25 and-is carried by the fabric 24 through a dryer 27 which may be preceded by vacuum boxes. The dryer preferably comprises a hood 34 from which air which may be heated is passed through the web and the fabric and into and through a drum 35 for removal by a second hood 36, but it may alternatively comprise radiant heat lamps or tunnel dryers. Since the web leaving the dryer is at least 80% dry a creping adhesive such as starch may be applied to the surface of the web or the surface of the creping drum 32 by a sprayer 37. The creping drum may be a yankee dryer and the web is creped from the drum by the creping blade 38. In alternative constructions the adhesive is applied by a roll dipping into a reservoir, Figs. 2 and 3 (not shown), and the adhesive may be or may contain an elastomeric bonding material and may be printed onto the web or the drum surface in the form of specified patterns. The drum 32 may be heated for drying or curing the bonding material. The elastomeric bonding material in the stock may be of the butadiene acrylonitrile type or may be buta diene-styrene, neoprene, acrylic copolymers, polyvinyl chloride, vinyl copolymers, or nylon, or plasticizers added to polymers such as polyvinyl alcohol or carboxy-methyl-cellulose. Debonding agents which may be added to the stock to reduce the number of interfibre hydrogen bonds are in the class of long chain cationic surfactants, preferably with at least twelve carbon atoms in at least one alkyl chain, such as fatty dialkyl quaternary amine salts, mono fatty alkyl tertiary amine salts, primary amine salts, and unsaturated fatty alkyl amine salts, or are in specified classes of cation-active tertiary amine oxides or cationactive amino compounds. The bonding material applied to the surface of the web or the surface of the drum 32 and which can be dried or cured to set it may be acrylate latex rubber emulsion, emulsions of resins such as acrylates, vinyl acetates, vinyl chlorides and meth-acrylates, or water soluble resins such as carboxy methyl cellulose, polyvinylalcohol, and polyacrylamide, or any of these materials mixed with a low molecular weight starch, e.g. dextrine, or a low molecular weight polymer, e.g. carboxymethyl-cellulose or polyvinylalcohol. Wet strength additives may be used with these materials. In an example the stock included Softwood Bleached Kraft and Hardwood Bleached Kraft, are specified debonding agent, a specified cationic polyelectrolyte used for beater deposition of anionic materials, and a specified anionic acrylic latex as an elastomeric bonding agent. The web was dried to more than 90% dry and transferred to a heated creping drum by means of a press nip formed between the drum and an elastomeric roll having a neoprene cover of a stated thickness and hardness, a specified adhesive being sprayed into the nip. The formed web has a basis weight of from 10 to 30 lbs per 2,880 square ft., a T.E.A. (tensile energy absorbtion)- to-stiffness ratio greater than 1.5 x 10<SP>-4</SP>, and an average calculated density throughout its thickness under no load of less than 0.3 gms per cubic cm.