| 摘要 |
The process of the parent Specification is modified by carrying out the reaction for the preparation of polyvinyl benzals at a pH between 0.5 and 2.5 in the presence of a dispersing agent, and the polyvinyl alcohol may comprise up to 20 per cent by weight of the reaction mixture when a low viscosity polyvinyl alcohol is used. Aromatic aldehydes which may be used include benzaldehyde, halogeno-, nitro-, alkyl-, and alkoxy-benzaldehydes, corresponding naphthaldehydes, phenyl-acetaldehyde and cinnamic aldehyde. Non-aromatic aldehydes may also take part, paraldehyde, formaldehyde, n-butyraldehyde, n-heptaldehyde and stearaldehyde being specified. The polyvinyl alcohol may have up to 20 per cent of remaining acetyl groups. The desired acetal replacement varies from 20 to 75 per cent. The pH may be obtained by the use of acid catalysts such as hydrochloric, sulphuric, phosphoric, oxalic, tartaric, chloracetic, lactic, benzene sulphonic and naphthalene sulphonic acids. Specified dispersing agents are sodium lauryl and oleyl sulphates, sodium N-methyl tauride oleate and sodium dioctyl sulphosuccinate. The reaction mixtures are vigorously stirred and fine powders are obtained having a high affinity for dyes. |
