Process for preparing polyamide based, titanium dioxide pigmented pulverulent coating compositions having at least ten aliphatically bound carbon atoms per carbonamide group

Claim 2

In a method for preparing a pulverulent coating composition pigmented with titanium dioxide and based on polyamide having at least ten aliphatically bound carbon atoms per carbonamide group or copolyamide or a mixture of homopolyamide and copolyamide containing at least 70% by weight of said polyamide by precipitation of said polyamide from solution, the improvement comprising adding titanium dioxide pigment having a nucleating effect less than or equal to 3° C. where said nucleating effect is determined by the formula ΔT=(T.sub.max p)-(T.sub.o) wherein ΔT is the nucleating effect; (T max p) is the maximum precipitation temperature of a solution of polyamide and pigment; and (T o ) is the maximum precipitation temperature of a solution of said polyamide free of said pigment.

Claim 3

In the method of producing polyamide powder from polyamide having a relative viscosity of 1.4 to 1.8 as measured in 0.5% metacresol solution at 25° C. and at least 70% of said polyamide consisting of polyamide with at least ten aliphatically bound carbon atoms per carbonamide group, comprising: (a) dissolving said polyamide in at least twice the amount by weight of ethanol in a closed vessel at a temperature between about 130° to 150° C. to form a solution of said polyamide (b) cooling said solution to a precipitation temperature between about 100° and 125° C.; (c) precipitating said polyamide powder from said cooled solution of (b) with agitation and under an inert atmosphere; and (d) separating said precipitated polyamide powders of (c) from said ethanol; the improvement comprising: (e) rapidly cooling said solution of about 130° to 150° C. to a saturation limit of about 125° C. inside temperature with stirring and distillation of said ethanol under its own pressure; (f) further cooling said solution below said saturation limit with distillation of said ethanol and cooling with a jacket wherein the jacket temperature is at most 3° C. below said inside temperature up until a precipitation temperature within the range of 90° to 113° C. is reached; and (g) maintaining said solution in the isothermal state during the ensuing precipitation stage by further distillation of ethanol, the further improvement comprising: (h) adding titanium dioxide pigment after step (a) having a nucleating effect less than or equal to 3° C. where said nucleating effect is determined by the formula ΔT=(T.sub.max p)-(T.sub.o) wherein ΔT is the nucleating effect; (T max p) is the maximum precipitation temperature of a solution of polyamide and pigment; and (T o ) is the maximum precipitation temperature of a solution of said polyamide free of said pigment.

Claim 4

In the method of producing polyamide powder from polyamide having a relative viscosity of 1.4 to 1.8 as measured in 0.5% metacresol solution at 25° C. and at least 70% of said polyamide consisting of polyamide with at least ten aliphatically bound carbon atoms per carbonamide group, comprising: (a) dissolving said polyamide in at least twice the amount by weight of ethanol in a closed vessel at a temperature between about 130° to 150° C. to form a solution of said polyamide (b) cooling said solution to a precipitation temperature between about 100° and 125° C.; (c) precipitating said polyamide powder from said cooled solution of (b) with agitation and under an inert atmosphere; and (d) separating said precipitated polyamide powders of (c) from said ethanol; the improvement comprising: (e) rapidly cooling said solution of about 130° to 150° C. to a saturation limit of about 125° C. inside temperature with stirring and distillation of said ethanol under its own pressure; (f) further cooling said solution below said saturation limit with distillation of said ethanol and cooling with a jacket wherein the jacket temperature is at most 3° C. below said inside temperature up until a precipitation temperature within the range of 90° to 113° C. is reached; and (g) maintaining said solution in the isothermal state during the ensuing precipitation stage by further distillation of ethanol, the further improvement comprising: (h) adding titanium dioxide pigment after step (a) having a nucleating effect less than or equal to 3° C. where said nucleating effect is determined by the formula ΔT=(T.sub.max p)-(T.sub.o) wherein ΔT is the nucleating effect; (T max p) is the maximum precipitation temperature of a solution of polyamide and pigment; and (T o ) is the maximum precipitation temperature of a solution of said polyamide free of said pigment.

Claim 5

The method of claim 2, wherein said pigment is added before step (c).

Claim 6

The method of claim 2, wherein said pigment is added after step (c).

Claim 7

The method of claim 2, wherein said pigment has a particle size less than 10 microns.

Claim 8

The method of claim 5, wherein said pigment has a particle size less than 2 microns.

Claim 9

In a method for preparing a pulverulent coating composition pigmented with titanium dioxide and base on polyamide having at least ten aliphatically bound carbon atoms per carbonamide group or copolyamide or a mixture of homopolyamide and copolyamide containing at least 70% by weight of said polyamide by precipitation of said polyamide from solution, the improvement comprising adding titanium dioxide pigment having a nucleating effect less than or equal to 3° C. where said nucleating effect is determined by the formula ΔT=(T.sub.max p)-(T.sub.o) wherein ΔT is the nucleating effect; (T max p) is the maximum precipitation temperature of polyamide and pigment; and (T o ) is the maximum precipitation temperature of a solution of said polyamide free of said pigment, wherein a mixture of 400 grams of said polyamide in granular form and 32 grams of said titanium dioxide are added to 2,400 grams of ethanol and heated to 1450° C. to dissolve said polyamide and form a solution and said soulution is cooled to 110° C. by distillation of said ethanol at a rate of 60° C. per hour.

Claim 10

In a method for preparing a pulverulent coating composition pigmented with titanium dioxide and base on polyamide having at least ten aliphatically bound carbon atoms per carbonamide group or copolyamide or a mixture of homopolyamide and copolyamide containing at least 70% by weight of said polyamide by precipitation of said polyamide from solution, the improvement comprising adding titanium dioxide pigment having a nucleating effect less than or equal to 3° C. where said nucleating effect is determined by the formula ΔT=(T.sub.max p)-(T.sub.o) wherein ΔT is the nucleating effect; (T max p) is the maximum precipitation temperature of polyamide and pigment; and (T o ) is the maximum precipitation temperature of a solution of said polyamide free of said pigment, wherein a mixture of 400 grams of said polyamide in granular form and 32 grams of said titanium dioxide are added to 2,400 grams of ethanol and heated to 1450° C. to dissolve said polyamide and form a solution and said soulution is cooled to 110° C. by distillation of said ethanol at a rate of 60° C. per hour.

Claim 11

A pigmented pulverulent composition obtained by the process of claim 2 having a grain size between 40 to 250 microns, a bulk density greater than 400 grams/liter and an impact dent test value in excess of 1800 mm/7.6 kg.

Claim 12

The pigmented pulverulent composition of claim 7 having a bulk density within the range 500 to 700 grams per liter.