Patent GB-616171-A (GB)
Title: Improvements in or relating to fixing the form of cellulosic fibrous materials
IPC: D06Q1/08
Filed: 1946-04-08
Abstract: Cellulose fibrous materials are impregnated with a water-soluble or water-dispersible polyvinyl alcohol, an aqueous solution of an aldehyde and preferably a catalyst, dried to dampness, a mechanical finish imparted thereto and the resin cured in situ.  The curing takes place as or after the mechanical finish is applied.  The drying is carried out until there is about 10 per cent moisture in the cloth.  The polyvinyl alcohol may be obtained by acid or alkaline hydrolysis of a polyvinyl ester, particularly the acetate, and the hydrolysis may be partial or complete.  Other suitable methods of preparation such as the reduction of polymerized methyl vinyl ketone may also be employed.  The molecular weight of the polymer may be as high as 14,500, but only those polymerized alcohols soluble or readily dispersible in water should be used.  The water solutions may if desired be treated with sodium perborate to increase the degree of polymerization. Suitable aldehydes are formaldehyde, acetaldehyde (including metaldehyde) glyoxal, and acrolein, but it is preferred to use formaldehyde or those compounds which readily produce formaldehyde such as paraformaldehyde, hexamethylene tetramine.  The catalyst may be ammonium thiocyanate (preferred) zinc chloride, ammonium dihydrogen phosphate or ammonium nitrate.  The pH of the solution should be adjusted by the addition of a volatile base (ammonia, isopropylamine) so that the cured fabric has a pH of 3-6. The solution may be prepared by any method, and softening, stiffening or wetting agents may be added as well as other compounds which may form a permanent part of the finished product such as glue, casein, albumen, urea, melamine, phenol and acetone.  In practice the proportion of aldehyde should be more than that required to react with the polyvinyl alcohol.  In glazing and calendering fabrics two or three passages of the material through the machine at about 350 DEG  F. will ordinarily be sufficient to cure the resin. In other cases, an oven cure at 300 DEG -400 DEG  F. for 4 minutes is desirable.  In a typical example polyvinyl alcohol of medium polymerization and containing no acid radicles is added to 400 parts cold water and heated till completely dissolved and after cooling 15.9 parts Carbowax 4000, 30 parts 37 per cent formaldehyde and 6 parts ammonium thiocyanate added.  The cloth is impregnated, squeezed, dried to a moist feel and glazed by three runs through a glazer at 350 DEG  F., followed by curing at 300 DEG  F. for 4 minutes, soaping, washing and drying.  Specification 503,414 is referred to.ALSO:Cellulose fibrous materials are impregnated with a water-soluble or water-dispersible polyvinyl alcohol, an aqueous solution of an aldehyde and preferably a catalyst, dried to dampness, a mechanical finish imparted thereto and the resin cured in situ. The curing takes place as or after the mechanical finish is applied. The drying is carried out until there is about 10 per cent moisture in the cloth.  The polyvinyl alcohol may be obtained by acid or alkaline hydrolysis of a polyvinyl ester, particularly the acetate, and the hydrolysis may be partial or complete.  Other organic and inorganic polyvinyl esters may be hydrolysed; if the hydrolysis is incomplete, the organic acid radicle has a marked influence on the hardness of the resin obtained, in that the longer the carbon chain in the radicle, the softer is the resin obtained.  Other suitable methods of preparation such as the reduction of polymerized methyl vinyl ketone may also be employed.  The molecular weight of the polymer may be as high as 14,500, but only those polymerized alcohols soluble or readily dispersible in water should be used.  The partially hydrolysed esters are less soluble than those completely hydrolysed.  The more highly polymerized alcohols give stiffer fabrics than those of lower degree of polymerization.  The water solutions may, if desired, be treated with sodium perborate to increase the degree of polymerization.  Suitable aldehydes are formaldehyde, acetaldehyde (including metaldehyde), glyoxal, and acrolein, but it is preferred to use formaldehyde or those compounds which readily produce formaldehyde such as paraformaldehyde, hexamethylene tetramine.  The catalyst may be ammonium thiocyanate (preferred), zinc chloride, ammonium dihydrogen phosphate or ammonium nitrate.  The pH of the solution p  should be adjusted by the addition of a volatile base (ammonia, isopropylamine) so that the cured fabric has a pH of 3-6.  The solution may be prepared by any method, and softening, stiffening or wetting agents may be added as well as other compounds which may form a permanent part of the finished product such as glue, casein, albumen, urea, melamine, phenol and acetone.  In practice, the proportion of aldehyde should be more than that required to react with the polyvinyl alcohol.  In glazing and calendering fabrics two or three passages of the material through the machine at about 350 DEG  F. will ordinarily be sufficient to cure the resin. In other cases, an oven cure at 300-400 DEG  F. for 4 mins. is desirable.  In Schreinering, the oven cure may be at 280-350 DEG  F. for 10-3 minutes.  In beetling and embossing the entire curing is carried out in the oven at 280-350 DEG  F. for 10-3 minutes.  The procedure may be varied by first embossing and then impregnating, drying, embossing again and then curing, this giving very durable results and being very satisfactory for bookcloth.  In a typical example, polyvinyl alcohol of medium polymerization and containing no acid radicles is added to 400 parts cold water and heated till completely dissolved, and after cooling 15.9 parts Carbowax 4000, 30 parts 37 per cent formaldehyde and 6 parts ammonium thiocyanate added.  The cloth is impregnated, squeezed, dried to a moist feel and glazed by three runs through a glazer at 350 DEG  F. followed by curing at 300 DEG  F. for 4 minutes, soaping, washing and drying.  Specification 503,414 is referred to.