PPC - PVDF
There are two principal technologies that are the backbone of the coatings industry:
Liquid coating technology (wet)
Powder coating technology (dry)
PPC - Polyester Powder Coating
Powder coating is the technique of applying dry paint to a part in the form of a fine powder which is electrically charged. The part is electrically ‘earthed’ so the powder is attracted to the part and stays in place through static electricity. The part is then placed in an oven and is subject to temperature which melts the polyester and allows the finish to flow and cure before the part is cooled and ready to use.
Powder coating differs from ‘wet paints’ which typically use a solvent where the solids are in suspension in a liquid carrier which must fully evaporate before the finish is ready to use.
Polyester powder coating is available in a wide range of finishes from solid colours in various gloss levels, through to textured or
metallic effects.
Aluminium supplied direct from the extrusion process is often contaminated with oil and other residues which will effect the
longevity of the final coating. Unfinished aluminium supplied from stock will have traces of natural oxidisation on the surface. It is vital therefore that the pretreatment is correctly carried out to a very high standard.
The vast majority of powder coat failures can be put down to poor or inconsistent pre-treatment methods. The Pre-treatment offers two main benefits:
• Offers an air and watertight ‘seal’ to the aluminium
• Offers a good ‘key’ surface to the powder to adhere to
The basic procedure carried out in either immersion baths or vertical spray method is:
1. Clean
2. Rinse
3. Etch
4. Rinse
5. Desmut (only when using an alkaline etch)
6. Rinse
7. Chromate or Chrome Free Conversion
8. Rinse
9. Demin Rinse
10. Dry
Once dry the pretreated aluminium is placed on a moving overhead gantry which transfers the aluminium to a spray booth. Powder
coating guns coat the aluminium extrusions, cast aluminium or sheet with a fine but controlled surface thickness of powder. Any over-sprayed powder can be collected and re-used giving a coating efficiency that can be in excess of 95%.
Without being handled the aluminium is transferred by the gantry into a continuous oven at between 160 to 210C. In the oven the temperature heats the aluminium and the powder undertakes four basic stages to full cure, Melt, Flow, Gel and Cure. Once cooled the finished aluminium can be used immediately.
The current British Standard and European Standard for powder coating is covered in:
BS EN 12206-1:2004‘Paints and varnishes - Coating of aluminium and aluminium alloys for architectural purposes’
This replaces the earlier British Standard BS 6496:1984.
The 2004 BS EN standard covers primarily the pre-treatment process and the testing of suitable test samples which accompany the material throughout the process.
All powder coatings, however, will age over time and using higher durability powders will ensure that the surface finish looks better for longer. Higher durability powders can be used on high rise applications, or other places where access could be difficult or where there is a particularly harsh environment.
Powders for architectural coatings fall into three basic classes:
Class 1
- 1 year ‘Florida’ - weather exposure - standard
Class 2
- 3 year ‘Florida’ - weather exposure
Class 3
- 10 year ‘Florida’ - weather exposure
In class 1 the sample must retain at least 50% of its original gloss level at the end of the test, whereas for class 2 powders they must retain at least 75% and class 3 powders at least 90% over the same period of exposure. Colour variation over time is similarly more stringent on classes 2 and 3.
PVDF - Polyvinylidene Flouride
Fluoropolymers have been used in a multitude of high performance coating applications for over thirty five years
1. Poly(vinylidene fluoride) (PVDF) has been used especially in architectural applications, where both excellent appearance and substrate protection must be maintained over a very long period of time
2. PVDF is preferred among the fluoropolymers for these applications, because it has enough solvency in ester and ketone solvents to
be able to be formulated into solvent dispersion coatings. These coatings can be applied by conventional coil or spray coating
techniques, and baked at temperatures of 230-250 ºC.
The microscopic phase structure that is formed in PVDF coatings is very complicated
3. PVDF is a semi-crystalline polymer. Pure PVDF homopolymer has a crystalline phase with a typical melting point in the 160-170 ºC range, and an amorphous phase with a glass transition temperature of approximately –40 ºC. In a PVDF dispersion coating, during baking the PVDF crystallites melt, and a high temperature miscible alloy of the PVDF resin and acrylic is formed. Upon cooling, some of the PVDF reforms into crystallites, and the remaining PVDF plus the acrylic form a second amorphous, miscible alloy phase. This
combination of crystalline and amorphous phases gives PVDF coatings many of their superior properties, such as flexibility
combined with solvent resistance.
Quality and testing standards
CHALK RESISTANCE
No chalking greater than #8 rating per ASTM D 4214, Method ASTM D 659 test procedure after a 2000 hour weatherometer test.
COLOR CHANGE
Finish color coat change not to exceed 5 Hunter units per ASTM D 2244 test procedure, after 2000 hour weatherometer test.
ABRASION RESISTANCE
Per ASTM D 968, Method A, PVDF will pass 65±5 liters/mil, minimum of falling sand.
SPECULAR GLOSS
Specular gloss is to be determined per ASTM D 523 at a glossmeter angle of 60°. PVDF has a standard gloss range of approximately 20–35°.
HARDNESS TEST
Minimum pencil hardness is HB to 2H, using Eagle Turquoise pencils per ASTM D 3363.
CURE TEST
PVDF will withstand 100 double rubs of an MEK soaked cloth before exposing primer coat per ASTM D 5402.
CROSS-HATCH ADHESION TEST
No paint removal with cellophane tape after cross-scoring with eleven horizontal and eleven vertical lines 1/8" apart per ASTM D 3359.
DIRECT AND REVERSE TEST
No visible paint removal with cellophane tape after direct and reverse impact of 80-inch pounds, using 5/8" steel ball on a Gardner Impact Tester (Not to include Zinc coating failures), per ASTM D 2794.
BEND ADHESION TEST
Per ASTM D 4145, no loss of adhesion when taped with cellophane tape when subjected to a 0T-2T diameter 180° bend test on 0.017" G-90 (grade D) galvanized steel or fabricator’s roll forming operation. (Not to include Zinc failures).
HUMIDITY RESISTANCE TEST
No blistering, cracking, peeling, loss of gloss of softening of the finish after 2000 hours of exposure to 100% humidity at 100°F ±5°F, per Federal Test Method Standard 141, Method 6201 or ASTM D 2247.
SALT SPRAY RESISTANCE TEST
Samples diagonally scored and subjected to 5% neutral salt spray per ASTM B 117, then taped with cellophane tape: 1000 hours-no blistering, and no loss of adhesion greater than 1/8" from score line. Samples taped 1 hour after removal from test cabinet.
WEATHEROMETER TEST
No checking, blistering or adhesion loss of coating system after 2000 hours of accelerated weathering, per ASTM 822/G23.
FLAME SPREAD RATE
PVDF displays a flame spread classification of A (Class 1), when tested in accordance with ASTM E84.
CHEMICAL RESISTANCE TEST
No significant color change after 24 hours exposure to 10% solutions of hydrochloric and sulfuric acids, per ASTM D 1308.
Liquid coating technology (wet)
Powder coating technology (dry)
PPC - Polyester Powder Coating
Powder coating is the technique of applying dry paint to a part in the form of a fine powder which is electrically charged. The part is electrically ‘earthed’ so the powder is attracted to the part and stays in place through static electricity. The part is then placed in an oven and is subject to temperature which melts the polyester and allows the finish to flow and cure before the part is cooled and ready to use.
Powder coating differs from ‘wet paints’ which typically use a solvent where the solids are in suspension in a liquid carrier which must fully evaporate before the finish is ready to use.
Polyester powder coating is available in a wide range of finishes from solid colours in various gloss levels, through to textured or
metallic effects.
Aluminium supplied direct from the extrusion process is often contaminated with oil and other residues which will effect the
longevity of the final coating. Unfinished aluminium supplied from stock will have traces of natural oxidisation on the surface. It is vital therefore that the pretreatment is correctly carried out to a very high standard.
The vast majority of powder coat failures can be put down to poor or inconsistent pre-treatment methods. The Pre-treatment offers two main benefits:
• Offers an air and watertight ‘seal’ to the aluminium
• Offers a good ‘key’ surface to the powder to adhere to
The basic procedure carried out in either immersion baths or vertical spray method is:
1. Clean
2. Rinse
3. Etch
4. Rinse
5. Desmut (only when using an alkaline etch)
6. Rinse
7. Chromate or Chrome Free Conversion
8. Rinse
9. Demin Rinse
10. Dry
Once dry the pretreated aluminium is placed on a moving overhead gantry which transfers the aluminium to a spray booth. Powder
coating guns coat the aluminium extrusions, cast aluminium or sheet with a fine but controlled surface thickness of powder. Any over-sprayed powder can be collected and re-used giving a coating efficiency that can be in excess of 95%.
Without being handled the aluminium is transferred by the gantry into a continuous oven at between 160 to 210C. In the oven the temperature heats the aluminium and the powder undertakes four basic stages to full cure, Melt, Flow, Gel and Cure. Once cooled the finished aluminium can be used immediately.
The current British Standard and European Standard for powder coating is covered in:
BS EN 12206-1:2004‘Paints and varnishes - Coating of aluminium and aluminium alloys for architectural purposes’
This replaces the earlier British Standard BS 6496:1984.
The 2004 BS EN standard covers primarily the pre-treatment process and the testing of suitable test samples which accompany the material throughout the process.
All powder coatings, however, will age over time and using higher durability powders will ensure that the surface finish looks better for longer. Higher durability powders can be used on high rise applications, or other places where access could be difficult or where there is a particularly harsh environment.
Powders for architectural coatings fall into three basic classes:
Class 1
- 1 year ‘Florida’ - weather exposure - standard
Class 2
- 3 year ‘Florida’ - weather exposure
Class 3
- 10 year ‘Florida’ - weather exposure
In class 1 the sample must retain at least 50% of its original gloss level at the end of the test, whereas for class 2 powders they must retain at least 75% and class 3 powders at least 90% over the same period of exposure. Colour variation over time is similarly more stringent on classes 2 and 3.
PVDF - Polyvinylidene Flouride
Fluoropolymers have been used in a multitude of high performance coating applications for over thirty five years
1. Poly(vinylidene fluoride) (PVDF) has been used especially in architectural applications, where both excellent appearance and substrate protection must be maintained over a very long period of time
2. PVDF is preferred among the fluoropolymers for these applications, because it has enough solvency in ester and ketone solvents to
be able to be formulated into solvent dispersion coatings. These coatings can be applied by conventional coil or spray coating
techniques, and baked at temperatures of 230-250 ºC.
The microscopic phase structure that is formed in PVDF coatings is very complicated
3. PVDF is a semi-crystalline polymer. Pure PVDF homopolymer has a crystalline phase with a typical melting point in the 160-170 ºC range, and an amorphous phase with a glass transition temperature of approximately –40 ºC. In a PVDF dispersion coating, during baking the PVDF crystallites melt, and a high temperature miscible alloy of the PVDF resin and acrylic is formed. Upon cooling, some of the PVDF reforms into crystallites, and the remaining PVDF plus the acrylic form a second amorphous, miscible alloy phase. This
combination of crystalline and amorphous phases gives PVDF coatings many of their superior properties, such as flexibility
combined with solvent resistance.
Quality and testing standards
CHALK RESISTANCE
No chalking greater than #8 rating per ASTM D 4214, Method ASTM D 659 test procedure after a 2000 hour weatherometer test.
COLOR CHANGE
Finish color coat change not to exceed 5 Hunter units per ASTM D 2244 test procedure, after 2000 hour weatherometer test.
ABRASION RESISTANCE
Per ASTM D 968, Method A, PVDF will pass 65±5 liters/mil, minimum of falling sand.
SPECULAR GLOSS
Specular gloss is to be determined per ASTM D 523 at a glossmeter angle of 60°. PVDF has a standard gloss range of approximately 20–35°.
HARDNESS TEST
Minimum pencil hardness is HB to 2H, using Eagle Turquoise pencils per ASTM D 3363.
CURE TEST
PVDF will withstand 100 double rubs of an MEK soaked cloth before exposing primer coat per ASTM D 5402.
CROSS-HATCH ADHESION TEST
No paint removal with cellophane tape after cross-scoring with eleven horizontal and eleven vertical lines 1/8" apart per ASTM D 3359.
DIRECT AND REVERSE TEST
No visible paint removal with cellophane tape after direct and reverse impact of 80-inch pounds, using 5/8" steel ball on a Gardner Impact Tester (Not to include Zinc coating failures), per ASTM D 2794.
BEND ADHESION TEST
Per ASTM D 4145, no loss of adhesion when taped with cellophane tape when subjected to a 0T-2T diameter 180° bend test on 0.017" G-90 (grade D) galvanized steel or fabricator’s roll forming operation. (Not to include Zinc failures).
HUMIDITY RESISTANCE TEST
No blistering, cracking, peeling, loss of gloss of softening of the finish after 2000 hours of exposure to 100% humidity at 100°F ±5°F, per Federal Test Method Standard 141, Method 6201 or ASTM D 2247.
SALT SPRAY RESISTANCE TEST
Samples diagonally scored and subjected to 5% neutral salt spray per ASTM B 117, then taped with cellophane tape: 1000 hours-no blistering, and no loss of adhesion greater than 1/8" from score line. Samples taped 1 hour after removal from test cabinet.
WEATHEROMETER TEST
No checking, blistering or adhesion loss of coating system after 2000 hours of accelerated weathering, per ASTM 822/G23.
FLAME SPREAD RATE
PVDF displays a flame spread classification of A (Class 1), when tested in accordance with ASTM E84.
CHEMICAL RESISTANCE TEST
No significant color change after 24 hours exposure to 10% solutions of hydrochloric and sulfuric acids, per ASTM D 1308.
Other useful information
PVF contains only one fluorine atom. Because its fusion and decomposition temperatures are so close, PVF can decompose during the baking process when used as a coating. Consequently, the baking cycle operating range is very small and requires close control.
PTFE with four fluorine atoms has no specific crystalline melting point, and has a high sintering point; consequently, it forms a relatively porous surface. The sintering point is well above the temperature that typical coating substrates can withstand before losing their mechanical properties. In addition, PTFE has no known commonly used solvents that could be used to prepare a practical formulation.
PVDF contains alternating carbon/fluorine and carbon/hydrogen bonds, which provide a polarity that enables the formulation of a practical coating that resists environmental degradation and dirt retention. This structure enables PVDF to resist oxidation, photochemical deterioration, fading, chalking, cracking and airborne pollutants. Thus, PVDF has a balance of properties
that makes it particularly suitable for use in coatings, especially for architectural uses.
PVDF 2 is a 2-coat system which includes pretreatment+primer+top coat, it is suitable for normal environmental conditions
PVDF 3 is a 3-coat system which includes pretreatment+primer+colour coat+clear top coat, it is suitable for normal and agressive environmental conditions
Fluorinated Ethylene Vinyl Ether
A relatively new coating for architectural use is based on a copolymer of fluoroethylene alkyl vinyl ether (FEVE). Fluoroethylene reportedly confers weathering resistance and durability to the polymer. Alkyl vinyl ether units provide solubility in various organic solvents, as well as transparency, gloss, hardness and flexibility. Coatings based on FEVE are generally two-component, thermosetting systems, which require a high degree of crosslinking to achieve final coating properties.
FEVE-based coatings are being evaluated on outdoor exposure in Florida. Results show that FEVE-based coatings have excellent gloss retention for about five years, but then the gloss decreases precipitously. The rapid decrease in weathering after five years is most likely due to degradation of the alkyl vinyl ether groups.
PVDF-2 Coat Finish
Duranar
Ideal for architectural applications
Suited for normal environments
Contains %70 Kynar 500 or Hylar 5000
Meets or exceeds the performance requirements of AAMA 2605
PVDF-3 Coat Finish
Duranar XLE
Ideal for architectural applications
Suited for normal and aggressive environments
Offers exotic colors as well as bright metallics using aluminum flakes
Protective clear coat offers increased graffiti resistance
Provides increased abrasion resistance
Contains 70% Kynar 500 or Hylar 5000 resins
Meets or exceeds the performance requirements of AAMA 2605
FEVE/FLUOROPOLYMER-2 or 3 Coat Finish
Megaflon
Ideal for corporate identity applications and image programs
Provides bright, vivid colors
Attains higher gloss levels
Meets or exceeds the performance requirements of AAMA 2605
PTFE with four fluorine atoms has no specific crystalline melting point, and has a high sintering point; consequently, it forms a relatively porous surface. The sintering point is well above the temperature that typical coating substrates can withstand before losing their mechanical properties. In addition, PTFE has no known commonly used solvents that could be used to prepare a practical formulation.
PVDF contains alternating carbon/fluorine and carbon/hydrogen bonds, which provide a polarity that enables the formulation of a practical coating that resists environmental degradation and dirt retention. This structure enables PVDF to resist oxidation, photochemical deterioration, fading, chalking, cracking and airborne pollutants. Thus, PVDF has a balance of properties
that makes it particularly suitable for use in coatings, especially for architectural uses.
PVDF 2 is a 2-coat system which includes pretreatment+primer+top coat, it is suitable for normal environmental conditions
PVDF 3 is a 3-coat system which includes pretreatment+primer+colour coat+clear top coat, it is suitable for normal and agressive environmental conditions
Fluorinated Ethylene Vinyl Ether
A relatively new coating for architectural use is based on a copolymer of fluoroethylene alkyl vinyl ether (FEVE). Fluoroethylene reportedly confers weathering resistance and durability to the polymer. Alkyl vinyl ether units provide solubility in various organic solvents, as well as transparency, gloss, hardness and flexibility. Coatings based on FEVE are generally two-component, thermosetting systems, which require a high degree of crosslinking to achieve final coating properties.
FEVE-based coatings are being evaluated on outdoor exposure in Florida. Results show that FEVE-based coatings have excellent gloss retention for about five years, but then the gloss decreases precipitously. The rapid decrease in weathering after five years is most likely due to degradation of the alkyl vinyl ether groups.
PVDF-2 Coat Finish
Duranar
Ideal for architectural applications
Suited for normal environments
Contains %70 Kynar 500 or Hylar 5000
Meets or exceeds the performance requirements of AAMA 2605
PVDF-3 Coat Finish
Duranar XLE
Ideal for architectural applications
Suited for normal and aggressive environments
Offers exotic colors as well as bright metallics using aluminum flakes
Protective clear coat offers increased graffiti resistance
Provides increased abrasion resistance
Contains 70% Kynar 500 or Hylar 5000 resins
Meets or exceeds the performance requirements of AAMA 2605
FEVE/FLUOROPOLYMER-2 or 3 Coat Finish
Megaflon
Ideal for corporate identity applications and image programs
Provides bright, vivid colors
Attains higher gloss levels
Meets or exceeds the performance requirements of AAMA 2605