Patent GB-823003-A (GB)
Title: Magnesium-zinc paint pigments
IPC: C09C1/62
Filed: 1957-10-25
Abstract: A pigment for pigmenting coating compositions consists of (a) between 80% and 20% by volume of a particulate binary alloy consisting of magnesium in an amount between 30% and 15% by weight and zinc in an amount between 70% and 85% by weight; and (b) between 20% and 80% by volume of a zinc chromate or a chromate of an alkaline earth metal. The alloy may be formed by melting magnesium in the presence of a flux consisting of the chlorides of potassium, magnesium, barium and sodium, and calcium fluoride and adding thereto sufficient pre-heated zinc to form either of the intermetallic compounds MgZn or MgZn2, holding the temperature at 1400 DEG  F. for 30 minutes, then pouring into moulds, cooling, breaking up and pulverizing.  The powdered alloy may be mixed with the powdered chromate in a suitable vehicle, e.g. a drying oil such as linseed oil, or a linseed oil-modified alkyd resin or a mixture thereof with a phenol-formaldehyde resin, containing thinners such as mineral spirit and xylene and if desired an anti-skinning agent, e.g. dipentene; a gelling agent, e.g. 1% to 10% aluminium stearate gel in xylene; an extender, e.g. asbestine; and a drier such as manganese, lead or cobalt naphthenate or oleate. Examples are given of coating mild steel, an aluminium-base alloy, and a magnesium-base alloy with paints in which 25%, 50% and 75% of the pigment was alloy, the remainder being zinc chromate, and the results compared with coatings formed from paints containing the alloy only, and containing zinc chromate only.  The chromates of barium, strontium and calcium may replace zinc chromate.ALSO:A pigment for pigmenting coating compositions consists of (a) between 80 and 20% by volume of a particulate binary alloy consisting of magnesium in an amount between 30 and 15% by weight and zinc in an amount between 70 and 80% by weight; and (b) between 20 and 80% by volume of a zinc chromate or a chromate of an alkaline earth metal. The alloy may be formed by melting p  magnesium in the presence of a flux consisting of the chlorides of potassium, magnesium, barium and sodium, and calcium fluoride and adding thereto sufficient pre-heated zinc to form either of the intermetallic compounds MgZn or MgZn2, holding the temperature at 1400 DEG  F. for 30 minutes, then pouring into moulds, cooling, breaking up and pulverizing.  The powdered alloy may be mixed with the powdered chromate in a suitable vehicle, e.g. a drying oil such as linseed oil, or a linseed oil-modified alkyd resin or a mixture thereof with a phenol-formaldehyde resin dissolved in aliphatic hydrocarbons (primarily heptane) containing thinners such as mineral spirit and xylene and if desired an anti-skinning agent, e.g. dipentene; a gelling agent, e.g. 1 to 10% aluminium stearate gel in xylene; an extender, e.g. asbestine; a drier such as manganese, lead or cobalt naphthenate or oleate; pigments such as iron oxides or organic dyes; and malic acid.  The chromates of barium, strontium and calcium may replace zinc chromate. Uses.-Coating metals, e.g. Fe, Al, Mg and their alloys.ALSO:A pigment for pigmenting coating compositions consists of (a) between 80 and 20% by volume of a particulate binary alloy consisting of magnesium in an amount between 30 and 15% by weight and zinc in an amount between 70 and 85% by weight and (b) between 20 and 80% by volume of a zinc chromate or a chromate of an alkaline earth metal.  The alloy may be formed by melting magnesium in the presence of a flux consisting of the chlorides of potassium, magnesium, barium and sodium, and calcium fluoride and adding thereto sufficient pre-heated zinc to form either of the intermetalic compounds MgZn or MgZn2, holding the temperature at 1400 DEG F. for 30 minutes, then pouring into moulds, cooling, breaking up and pulverizing.