| 摘要 |
Relates to resins produced by condensation of a hydrolyzed polyvinyl ester and a substance containing a reactive carbonyl group, e.g. an aldehyde or a cyclic ketone. Such resins are de-esterified to contain 3 per cent or less ester groups (calculated as polyvinyl ester), the content of hydroxyl groups calculated as polyvinyl alcohol being increased, preferably to about 10 to 20 per cent for higher (e.g. cyclohexanone or butyraldehyde) acetal groups, and to about 10 to 17 per cent for lower (e.g. acetaldehyde) acetal groups. Preferred de-esterification agents are alkalis, such as caustic alkali or alkali carbonate, or primary or secondary alcohols, such as lower fatty alcohols; and strong acid, e.g. sulphuric or hydrochloric, may be present with the latter; the process may be carried out at from room temperature to 70 DEG C. Suitable starting materials are polyvinyl acetal -acetate, -propionate, or -butyrate resins; polyvinyl formaldehyde-, acetaldehyde-, propionaldehyde-, butyraldehyde-, crotonaldehyde-, cyclohexanone-, acetal-ester resins; and polyvinyl acetaldehydebutyraldehyde-acetal ester resins. The products may be coated from solvents such as methyl alcohol alone or with acetone or methyl acetate to transparent, flexible, and moisture-resistant films; those from polyvinyl acetaldehydeacetal resins are particularly suitable for wrappings and for supports for photographic emulsions. The products are compatible with plasticizers, e.g. tricresyl phosphate; tri-(n- or iso-butyl or -amyl)phosphates; di-(n- or iso-butyl or amyl) phosphates; 2 : 4 : 6- or other tribromophenol; di- or triglyceryl esters such as acetins, propionins or butyrins; glycerol acetal esters such as the butyraldehyde acetal of mono-acetin, -butyrin, or -valerin; glycerol acetal ethers such as the acetaldehyde acetal of glycerol mono-ethyl or -dodecyl ether; a - or other monochlornaphthalene. The plasticized resins can be extruded to sheets or plates suitable for use in laminated safety glass, or otherwise moulded. In examples polyvinyl acetal-ester resins are de-esterified (a) by ethyl alcoholic caustic potash at 70 DEG C., (b) in pyridine solution by aqueous caustic soda at 40 DEG C., (c) by ethyl alcohol in the presence of sulphuric acid at 70 DEG C. Specification 351,082* is referred to. The Specification as open to inspection under Sect. 91 states that the de-esterification may be combined with the initial condensation, sulphuric acid being used as catalyst, and preferably a lower fatty alcohol as de-esterifying agent, at least 3 mols. per mol. of aldehyde being used. In an example, polyvinyl acetate, ethyl alcohol, and paraldehyde are reacted in the presence of sulphuric acid and water, the molar ratio of ethyl alcohol to paraldehyde being about 5 to 1, and the product contains 2,2 per cent polyvinyl acetate. This subject-matter does not appear in the Specification as accepted. |
