Polyamide powder and method for coating an object by melting said powder

Abstract

The present invention relates to a coating composition in the form of a loose powder including the following by weight: 50% to 99.99% of polyamide powder, and 0.01% to 0.5% of polypropylene glycol, out of the total weight of the composition. The present invention relates in particular to a coating composition in the form of a powder including the following by weight: 50% to 99.9% of polyamide powder, 0.01% to 10% of at least one pigment and 0.01% to 0.5% of polypropylene glycol, out of the total weight of the composition. The present invention relates in particular to the use of said composition in methods for coating objects, in particular metal, by means of stuccoing.

Claims

1. A coating composition in free powder form comprising, by weight: from 50% to 99.99% of polyamide powder, from 0.01% to 0.5% of polypropylene glycol, relative to the total weight of the composition, wherein the composition is obtained by dry mixing of the polyamide powder and the polypropylene glycol.

2. The coating composition according to claim 1, in powder form comprising, by weight: from 50% to 99.9% of polyamide powder, from 0.1% to 10% of at least one pigment, from 0.01% to 0.5% of polypropylene glycol, relative to the total weight of the composition.

3. The coating composition according to claim 1, in powder form comprising, by weight: from 50% to 99.9% of polyamide powder, from 0.1% to 5% of at least one optical-effect pigment, from 0.01% to 0.5% of polypropylene glycol, relative to the total weight of the composition.

4. The composition as claimed in claim 3, in which said at least one optical-effect pigment is a diffractive pigment, an interference pigment, a reflective pigment, or a mixture thereof.

5. The composition as claimed in claim 1, in which the polyamide is PA 11, PA 12, PA 6.10, PA 6.12, PA 6.14, PA 6.18, PA 10.10, PA 10.12, a copolyamide thereof, or mixtures thereof.

6. The composition as claimed in claim 1, in which the molar mass of the polypropylene glycol is within the range of from 1000 to 3000 g/mol.

7. The composition as claimed in claim 1, also comprising from 0.1% to 0.3% by weight of at least one metallic pigment.

8. A process for manufacturing a powder composition in accordance with claim 1, comprising the dry blending of polyamide, polypropylene glycol and an optional pigment.

9. The process as claimed in claim 8, in which the polyamide, the polypropylene glycol and the optional pigment are added in this order during the dry blending.

Description

EXAMPLES

(1) The examples below illustrate the present invention without limiting its scope. In the examples, unless otherwise indicated, all the percentages and parts are expressed on a weight basis.

(2) Although the tests refer to a composition based on polyamide 11, it is clearly understood that the compositions according to the present invention are not limited to this embodiment, but may comprise any type of polyamide, alone or as a mixture.

(3) Manufacture of the Compositions of Tests 1 to 17.

(4) A polyamide 11 powder Rilsan (PA 11) with an inherent viscosity in the range from 1.05 to 1.15 (measured at 0.5% by weight in meta-cresol, at 20 C.) is used. The polyamide powder has a D50 substantially equal to 100 m.

(5) The following pigments are used: Black, yellow and red pigments (iron oxide) of brand Bayferrox and of respective particle size: 0.6 m, 0.2-0.8 m and 0.17 m. Interference pigments, of brand Iriodin from Merck: for tests 1 to 14: mica/TiO.sub.2/SnO.sub.2 pigment of particle size ranging from 1 to 15 m, for tests 15 and 16: mica/TiO.sub.2/SnO.sub.2 of particle size ranging from 20 to 100 m. Aluminum pigment: 15 m of brand Standart PCS 1500 from Eckart.

(6) Various types and contents of polyether (PEG, PPG, PTMG or PEG-PPG copolymer) are tested in the reference composition (Table 1, Ref column): in the comparative tests 1 to 6: polyethylene glycol (PEG) of respective molar masses (in g/mol) 600 (contents of 0.05% and 0.1%), 1500 (0.05% and 0.1%) and 8000 (0.05% and 0.1%); in tests 7 to 12: polypropylene glycol (PPG) of respective molar masses (in g/mol): 450 and 2000 (0.05%; 0.1% and 0.2%); in comparative test 13: polytetramethylene glycol (PTMG) of molar mass (in g/mol) 2000 (content of 0.2%); in comparative test 14: PEG/PPG copolymer (80/20 ratio) of molar mass 8000 (content 0.1%).

(7) The polyether is added to the polyamide powder by dry blending. The pigments are then added by dry blending to the mix thus obtained. A 10 L Henschel mixer is used. The PA powder is introduced into the mixer and stirring is started. The polyether is added and the mixture is blended (60 seconds at 900 rpm). All the pigments are then added and the mixture is again blended (100 seconds at 900 rpm).

(8) Each composition is used in a coating process according to the invention, by dipping in a fluidized bed.

(9) Needless to say, the device for dipping in a fluidized bed is given merely as an example, and any other device for coating an object with a film, such as spraying or electrostatic powdering, may also be employed in the process of the invention.

(10) Each coating powder composition is applied by powdering onto 5 steel plates 100503 mm in size. The application conditions comprise: heating of the plates for 10 minutes at 330 C., followed by dipping them for 4 seconds in the fluidized bed, and then cooling them in air.

(11) The compositions with a high content of pigments generally form a cloud of pigment(s) above the fluidized bed and leave a deposit on the edge of the tank after only a few seconds of fluidization, this deposit consisting essentially of pigments.

(12) It is noted that the formula containing PPG does not form a cloud of pigments above the fluidized bed and gives only the deposit of polyamide powder usually found during the fluidization of a pigment-free polyamide powder.

(13) Microscopy images did not demonstrate any bonding or impregnation of the pigments onto the grains of powder in the compositions of the invention.

(14) Evaluation of the fisheyes on the coatings obtained: Table 1 notes the presence (yes or no) of fisheyes on the coating obtained on each plate.

(15) Among the products tested, only: PPG 2000 when it is used at contents of 0.05%, 0.1% or 0.2% in the composition (Examples 10 to 12), and PPG 450 used at 0.2% (Example 9) make it possible to totally eliminate fisheyes.

(16) No improvement of this defect that remains present on the coatings obtained by powdering with compositions comprising PEG, PTMG or PEG/PPG copolymer is observed (comparative tests 1 to 6 and 13 to 14). On the contrary, even additional defects (craters) are observed with polyethers of molar mass 8000 g/mol (PEG and PEG/PPG copolymer) and with PTMG. A phase separation between the polyamide and PEG is also noted on the films obtained in comparative tests 5 and 6.

(17) TABLE-US-00001 TABLE 1 Tests 1 to 14 Test Test Test Test Test Test Test Test Test Test Test Test Test Test 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Ref Comp Comp Comp Comp Comp Comp Ex Ex Ex Ex Ex Ex Comp Comp 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Polyamide 11 98.76 98.71 98.66 98.71 98.66 98.71 98.66 98.71 98.66 98.56 98.71 98.66 98.56 98.56 98.66 Rilsan Interference 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 pigment Yellow 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 pigment Black 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 pigment Red pigment 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 PEG 600 0.05 0.1 PEG 1500 0.05 0.1 PEG 8000 0.05 0.1 PPG 450 0.05 0.1 0.2 PPG 2000 0.05 0.1 0.2 PTMG 2000 0.2 PEG/PPG 0.1 copolymer (80/20) 8000 Presence of yes yes yes yes yes yes + yes + rare rare no no no no yes + yes + fisheyes PA/PEG PA/PEG other other phase phase coating coating separa- separa- defects defects tion tion

(18) Tests on other formulations detailed in Table 2 below show that PPG contents of 0.05% or 0.075% may suffice to eliminate fisheyes.

(19) TABLE-US-00002 TABLE 2 Examples 15 to 17 Ex 15 Ex 16 Ex 17 PA 11 powder 98.85 98.025 Blue colored PA 11 99.4 powder PPG 2000 0.05 0.075 0.1 Interference 1 1.6 pigments Iron oxide black 0.1 0.2 pigment Iron oxide red 0.5 pigment Aluminum pigment 0.1 Flyaway/depositions no no no of pigments Presence of no no no fisheyes

(20) The presence of PPG in the polyamide powder composition according to the invention does not alter the other performance qualities of the polyamide coatings (abrasion resistance, corrosion resistance, etc.). In addition, crossed contamination tests showed that traces of grades of PPG-supplemented PA powder (compositions according to the invention) did not contaminate the grades of PA powders that do not comprise any anti-crater agent.

(21) The use of a powder composition according to the invention (Examples 9 to 12 and 15 to 17) in a powder coating process makes it possible to obtain components coated with a homogeneous film free of defects and of fisheyes.