Patent GB-431956-A (GB)
Title: Improved manufacture of fibrous sheet material having a basis of partially hydrolysed cellulose
IPC: D21J1/08
Filed: 1934-05-14
Abstract: 431,956. Compound paper. SOC. OF CHEMICAL INDUSTRY IN BASLE, Basle, Switzerland. May 14, 1934, Nos. 14561 and 14562. Convention dates, May 12, 1933 and Oct. 30, 1933. [Class 96] In the manufacture of fibrous sheet material of the kind consisting of a number of superimposed sheets having a basis of partially hydrolyzed cellulose, there is added to the cellulosic material before, during or after its partial hydrolysis a primary aromatic amineformaldehyde resin. The product has a high resistance to water. Suitable cellulosic material is unsized paper from sulphite, sulphate or soda cellulose or cotton rag stock. Suitable hydrolizing agents are zinc chloride, aluminium chloride, sulphuric acid, phosphoric, a mixture of sulphuric and phosphoric acids, or a mixture of sulphuric, phosphoric and acetic acids. Preferably the resin is formed by condensing the amine with the formaldehyde or substance yielding formaldehyde in the presence of an acid. The term primary aromatic amine includes not only aniline and its homologues but substances such as anhydroformaldehydeaniline, formyl aniline or their homologues which react like aniline. After condensation in an acid medium, the resin is precipitated by addition of a base or by dilution. The nature of the resin depends on the ratio of the amine to the aldehyde. Preferably the resin used in the invention is infusible, but sufficiently fluid at the temperature used for pressing the film, and generally the ratio of formaldehyde to aniline should not exceed 1À4-1À5 mols. to 1 mol. For a fusible resin the ratio should be 0À8-1 mol. to 1 mol. The fibrous material may be impregnated with the fusible resin, and then treated with an aldehydic compound before drying and pressing. The resin may be used as a solution or suspension, suitable solvents for the infusible resins being ethylenechlorhydrin, or glycerinedichlorhydrin. When employing a solution, the solvent may be removed after impregnation by evaporation. In an example wherein the resin is added to the material after the partial hydrolysis, 652 litres of aniline hydrochloride solution containing 28À56 per cent of aniline is made up to 1000 litres and 202 litres of 38À6 per cent formaldehyde solution are added. The washed and piled sheets of hydrolized cellulose (32 mm. thick) are immersed in 3 per cent caustic soda solution for 72-96 hours, and the material is washed free from electrolytes and dried for 24 hours at 50-60‹ C. The dried sheets are pressed for about 2 minutes at 170‹ C. and a pressure of 7 kilos/sq. cm. The sheets are then cooled and calendered and treated to cause the resin to become thermoplastic, e.g. for 10 minutes at 160-170‹ C. and 7 kilos/sq. cm. Tubes formed of layers of fibrous material may be similarly treated. In an example according to a second method the sheets are immersed in a hydrolyzing solution which contains the resin in solution. The sheets are then superimposed, and the mass washed, dried and subjected to the heat treatment as described above. In a third method the resin may be associated with the fibrous material before hydrolysis, the resin being added either to the pulp or to the sheets. When added to the pulp the resin may be precipitated in the beater from an acid solution or added as an aqueous suspension, and when added to the sheets it may be precipitated from an acid solution or applied as a solution in a solvent of chlorhydric type. The content of resin may be 5 to 40 per cent, but generally 5-15 per cent is sufficient. After incorporation of the resin the sheet material is hydrolyzed and superimposed to form flat sheets or tubes which are washed and dried and then subjected to heat treatment. In all the above methods the sheets are superimposed while wet. They may, however, after hydrolysis and incorporation of the resin be dried and then superimposed by heat and pressure. This method is particularly suitable where high resin contents are being employed since by this method the resin is active in uniting the several layers. It also facilitates washing which is performed on the single sheets. The union of the sheets is done at 140-160‹ C. under a pressure of 70-200 kilos /sq. cm. or more. This form of the process is also suitable for producing a resinous parchment of desired thickness by employing 60-70 per cent sulphuric acid as the hydrolyzing agent for a paper containing resin. The products obtained according to the invention have a particularly low capacity for absorbing moisture and are useful for electrical insulation purposes. U.S.A. Specification 1,894,907 is referred to.