Abstract A method of increasing the dimensional stability of cellulosic material by impregnating the cellulose with a composition including a cellulose swelling agent and a compound capable of crosslinking with the cellulose molecules. The swelling agent is capable of swelling the cellulose beyond its full water swollen condition and the crosslinking compound crosslinks with the cellulose molecules to thereby reduce the number of potential water absorbing sites and render the cellulose more dimensionally stable. The cross-linking takes place at elevated temperatures in the absence of an acidic catalyst and the cross-linked cellulosic materials are useful as insulators in electrical apparatus. Aminoplasts may be used as cross-linkers and, among others, nitrogen containing compounds such as dimethyl formamide and various amines may be used as swelling agents.
The transformer of claim 1, wherein the swelling agent is employed in the weight ratio of 33:1 to 1:10 with respect to the aminoplast resin, based on 100 percent concentration.
Claim 2
Dependent Claim
33 words
The transformer of claims 1, wherein the combined weight of the swelling agent and aminoplast resin, based on 100 percent concentrations, comprises at least 3.7 percent by weight of the dry cellulose pressboard.
Claim 3
Dependent Claim
27 words
The transformer of claim 1, wherein the aminoplast resin is selected from the group consisting of dimethylolethylene urea, dihydroxyethylene urea; dimethylolpropylene urea; melamine-formaldehyde; urea-formaldehyde; and mixtures thereof.