Treatment of metal surfaces

摘要

A coating or cleaning and polishing composition for application to a substrate of a metal lying below and including magnesium in the electromotive series or alloys thereof comprises a mercapto organo silicon compound which is (A) a mercapto organo silane having the general formula wherein R is a divalent hydrocarbon radical free of aliphatic unsaturation, a is 1 or 2, R1 is a monovalent hydrocarbon radical free of aliphatic unsaturation, b is 0, 1, or 2, (a + b) has a value not greater than 3, and X is a halogen atom or an acetoxy, acryloxy, or hydrocarbyloxy radical (e.g. OR1); (B) a siloxane homopolymer of units having the general formula wherein R, R1, a, b and (a + b) are as above; or (C) a siloxane copolymer containing from 0.1 to 99.9 mole per cent of units of Formula II and from 99.9 to 0.1 mole per cent of at least one other siloxane unit which unit can be a different species of Formula II or a unit having the general formula wherein R111 is a hydrogen atom or an alkyl, aryl, monovalent olefinically unsaturated hydrocarbon, epoxyalkyl, acryloxyalkyl or methacryloxyalkyl radical and e is 0, 1 or 2. The copolymer may contain at least 25 mole per cent of the units of Formula (II). In a modification, the mercapto organo silicon compound may be a mercapto hydro carbyl polysiloxane containing the unit where R is as above, Z is a hydroxy or alkoxy radical and c has an average value of from 0 to 2. Examples of mercapto organo silicon compounds are given. The compound may be cured on the substrate to form an adherent coating thereon. An intimate blend of a curable polysulphide polymer and the mercapto organo silicon compound may be formed, the blend applied to the substrate and thereafter the polysulphide cured. A composition comprising the mercapto organo silicon compound and an abrasive (Example 10) may be used to clean and provide a protective coating for the substrate, the abrasive component being thereafter removed from the coating. The mercaptoorganosilanes of Formula I, except those in which the HS-group is attached to silicon through the beta carbon atom of the divalent hydrocarbon moiety (R) can be formed by the reaction of NaSH with a chlorinated precursor of formula in an inert dry solvent medium e.g. methanol, under ambient room temperature conditions (Examples 1 to 4). Other Formula I mercapto organo silanes may be prepared by the reaction of H2S with a silane of formula wherein R11 is hydrogen or an R1 group, advantageously at elevated pressures in an inert organic medium in the presence of a free radical generating catalyst. The polysiloxanes of Formula II and (III) may be prepared (Examples 5 to 7) by the hydrolysis and condensation of the mercapto organosilanes of Formula I, or the cohydrolysis and cocondensation thereof with di, tri or mono-mercaptoorgano silanes, examples of which are given.ALSO:A cleaning composition for metal surfaces comprises an abrasive e.g. precipitated chalk and a mercapto organo silicon compound which is (A) a mercapto organo silane having the general formula wherein R is a divalent hydrocarbon radical free of aliphatic unsaturation, a is 1 or 2, R1 is a monovalent hydrocarbon radical free of aliphatic unsaturation, b is 0, 1, or 2, (a+b) has a value not greater than 3, and X is a halogen atom or an acetoxy, acryloxy, or hydrocarbyloxy radical; (B) a siloxane homopolymer of units having the general formula wherein R, R1, a, b and (a + b) are as above: or (C) a siloxane copolymer containing from 0.1 to 99.9 mole per cent of units of formula II and from 99.9 to 0.1 mole per cent of at least one other siloxane unit which unit can be a different species of formula II or a unit having the general formula wherein R111 is a hydrogen atom or an alkyl, aryl, monovalent olefinically unsaturated hydro-carbon epoxyalkyl, acryloxyalkyl or meth-acryloxyalkyl radical and e is 0, 1 or 2. The mercapto organo silane may have the general formula The copolymer may contain at least 25 mole per cent of the units of formula (II). In a modification, the mercapto organo silicon compound may be a mercapto hydro carbyl polysiloxane containing the unit where R is as above, Z is a hydroxy or alkoxy radical and c has an average value of from 0 to 2. The metal surface may be of aluminium, brass, bronze, copper, chromium, iron, magnesium, nickel, lead, silver, silverplate, sterling silver, tinplate, tin, bronze, beryllium, and zinc. Examples of mercapto organo silicon compounds are given. (Example 10 relates). The composition comprising the mercapto organo silicon compound and abrasive is used to clean and provide a protective coating for the metal surface, the abrasive component being thereafter removed from the coating.ALSO:A coated substrate comprises a substrate of a metal lying below and including magnesium in the electromotive series or alloys thereof and a cured coating adhered thereto of a mercapto organo silicon compound which is (A) a mercapto organo silane having the general formula: I wherein R is a divalent hydrocarbon radical free of aliphatic unsaturation, a is 1 or 2, R1 is a monovalent hydrocarbon radical free of aliphatic unsaturation, b is 0, 1, or 2, (a + b) has a value not greater than 3, and X is a halogen atom or an acetoxy, acryloxy, or hydrocarbyloxy radical; (B) a siloxane homopolymer of units having the general formula II wherein R, R1, a, b and (a + b) are as above; or (C) a siloxane copolymer containing from 0.1 to 99.9 mole per cent of units of formula II and from 99.9 to 0.1 mole per cent of at least one other siloxane unit which unit can be a different species of formula II or a unit having the general formula III wherein R111 is a hydrogen atom or an alkyl, aryl, monovalent olefinically unsaturated hydrocarbon, epoxyalkyl, acryloxyalkyl or methacryloxyalkyl radical and e is 0, 1 or 2. The mercapto organo silane may have the general formula: IV The copolymer may contain at least 25 mole per cent of the units of formula (II). In a modification, the mercapto organo silicon compound may be a mercapto hydro carbyl polysiloxane containing the unit V where R is as above, Z is a hydroxy or alkoxy radical and c has an average value of from 0 to 2. The substrates may be of aluminium, brass, bronze, copper, chromium, iron, magnesium, nickel, lead, silver, silverplate, sterling silver, tinplate, tin, bronze, beryllium, and zinc. Examples of mercapto organo silicon compounds are given. The compound may be cured on the substrate to form an adherent coating thereon. The mercapto hydro carbyl silicon compound may be applied in a solvent solution, dispersion in liquid systems, or by using undiluted compounds, by, for example, spray application as from aerosol bombs, dipping or brushings. The coated substrate may be further coated with a cured polysulphide polymer. The polysulphide may be applied as a curable coating which is subsequently cured. Alternatively, an intimate blend of a curable polysulphide polymer and the mercapto organo silicon compound may be formed, the blend applied to the substrate and thereafter the polysulphide cured. A composition comprising the mercapto organo silicon compound and an abrasive may be used to clean and provide a protective coating for the substrate, the abrasive component being thereafter removed from the coating.