Patent GB-896610-A (GB)
Title: Improvements in or relating to the production of photoconductive layers for electrophotographic processes
IPC: C08G18/42
Filed: 1958-06-06
Abstract: Products are made by reacting isocyanates with resins containing hydroxyl groups so that some or all of the latter are reacted.  When using mono-isocyanates 10-100% of the hydroxyl groups may react, while di-isocyanates are used in sufficient proportion to combine with up to 20% of the hydroxyl groups. Mixtures of the two can be employed.  The reaction takes 0,1 to 4 hours at 80 DEG -200 DEG C., preferably in a hydrocarbon, ester or ketone as solvent.  In the examples the following are reacted:- (1) cyclohexyl isocyanate and the polyester from phthalic anhydride, trimethylolpropane and penta-erythritol; (2) as in (1) where the polyester contains some C9-C10 fatty acid; (3) cyclohexyl isocyanate and the polyester from phthalic anhydride, adipic acid and trimethylol-propane; (4) as in (2) using benzyl isocyanate instead of cyclohexyl isocyanate; (5) cyclohexyl isocyanate and the benzoic acid esterification product of an epoxide resin prepared from 4:41-dihydroxydiphenylpropane and epichlorhydrin; (6) hexamethylene diisocyanate and the polyester from phthalic anhydride, trimethylol-propane, pentaerythritol and castor oil; and (7) cyclohexyl isocyanate with m-xylylene di-isocyanate and p  the polyether from 4:41-dichloromethyl-diphenylether and trimethylol-propane (prepared in presence of ethylene oxide).  For use as electrophotographic layers (see Group XXXVI), the products are converted into organic solutions or aqueous dispersions and mixed with an aqueous dispersion of the photoconductive material containing a protective colloid such as gum arabic, gelatine or polyvinylalcohol.  Suitable organic solvents are alcohol, acetone and methoxyethyl acetate.  Aqueous dispersions are made by dissolving the product in a solvent such as toluene or trichlorethylene, adding it to a molten emulsifier (e.g. abietic acid ethylene oxide reaction product) and then adding water. Specified photoconductive materials are the oxides, sulphides, selenides, tellurides and iodides of Cd, Hg, Sb, Bi, Tl, Mo, AP Pb and Zn (especially ZnO), arsenic trisulphide, cadmium arsenide, lead chromate, selenium, anthracene, acenaphthene, chrysene, terphenyl, benzanthrone, 1:4- or 1:5-dicyanonaphthalene, aminophthalonitrile and nitrophthalonitrile. In general the hydroxylated resins that can be reacted with isocyanates are (A) polyesters from di- and poly-carboxylic acids and di- or poly-hydric alcohols, with or without minor proportions of mono-carboxylic acids or monohydric alcohols; (B) epoxide resins which contain hydroxyl groups present from their production or obtained by subsequent reaction of the epoxide group with acids, alkalis, carboxylic acids, phenols or amines; (C) the polyethers of Specification 877,913 obtained by reaction of polyalcohols with compounds having two or more aromatically bound -CH2-O-R- groupings; (D) products obtained by condensing aldehydes with di- and poly-hydric alcohols that do not form cyclic acetals, e.g. paraformaldehyde, butane-1:4-diol and 2:21-bis-(4:41-di-hydroxyethoxyphenyl)-propane.  Many components are specified as suitable for forming resins of these types. Specifications 518,057, 579,698, 675,169, 675,171, 730,670, 798,184, 798,209, 818,068 and 828,820 also are referred to.