Thermoclad Duravin ES Vinyl

New powders for electrostatic applications

Electrostatic coating systems use a process by which electrically charged powder particles are sprayed on to a grounded part. Due to the electrostatic attraction, the powder adheres to the part and with application of heat fuses or cures and flows out to a smooth coat. There are many types of electrostatic powder applications which require different coating properties. In choosing powder materials, the inherent spray characteristics, performance specifications, and ultimate end use properties should match the demands of the application as well as the coater's budget. Thermoclad is pleased to introduce DURAVIN ES as a practical and economical thermoplastic alternative for electrostatic applications.

Customer demand initiated research and product development efforts at Thermoclad to conceive this unique vinyl powder for introduction to the thermoset dominated electrostatic market. In many applications DURAVIN ES is not considered a direct competitor to the thin film thermosets ( epoxies, polyesters, and hybrids) as their properties differ significantly, on the other hand, vinyl offers many unique characteristics and advantages associated with thermoplastics.

Duravin and Duravin ES

The predominate method of applying vinyl powder has been and continues to be by the fluidized bed process. Preheated parts are dipped into the fluid bed, then fused smooth in a post heat oven. Popular applications by this method include dishwasher racks, fencing, conduit, closet shelving, and other fabricated wire products. DURAVIN's strength lies primarily in its thick protective coating which displays excellent weather and corrosion resistance.

DURAVIN ES compounds have for the most part the same properties as their fluidized bed counterparts. Unlike fluidized bed however, this electrostatic vinyl can be applied as thin as 5 to 6 mils while thicknesses over 20 mils may be achieved if necessary. When applied with a preheat, coatings of higher thicknesses may be obtained. DURAVIN ES formulations are also available in varying degrees of hardness and flexibility as required by specific end use applications.

Presently, this electrostatic vinyl is applied to welded wire fencing, fencing components, expanded metal panels, castings, and stampings. Suitability for different applications can be determined by comparing DURAVIN ES properties with those of other electrostatic powders as shown below.

Thermoclad has developed a series of no-primer self adhering or alloyed products to eliminate the use of vinyl primers for those customers who have difficulty using them.  Although they are higher priced, it sometimes can eliminate the primer application step.

New Product - DURALLOY-EV Technical Data Sheet

Application procedures

DURAVIN ES compounds can be sprayed using both corona and tribo charged systems. Wire goods spray well with the corona system and the highly polar vinyl particle charges equally in both positive and negative modes. The frictionally charged tribo system performs excellently with DURAVIN ES on complicated substrates because of the larger particle size which aids particle projection. Faraday cage effect is evident in both thermoset and vinyl spray, but the effect may be easier to overcome with the free flowing vinyl. Due to polarity and particle size, DURAVIN ES requires somewhat stricter controls than most thermosets in order to maintain consistently smooth and easy application. The basic guidelines for electrostatically coating with DURAVIN ES are as follows.

Corona Charging

Charging:
DURAVIN ES requires a lower charge (40-70 Kv) than most thermosets for the best performance. At higher charges (typical for thermosets) the highly polar and large vinyl particles have a tendency to adhere to one another, not just to the substrate. This creates a mottling effect or technically, back ionization. Cross contamination with other powders such as thermosets should be avoided by thorough cleaning between any powder changes.
 
Atomization:
For smoothest finishes and proper powder/air mixtures, DURAVIN ES sprays best at low atomization, 25-40 PSIG. Higher pressures can result in a dusting of powder which will deliver light and spotty coatings. Pressure settings may vary and are unique to each manufacturer's equipment.
 
Ejection:
Also due to its relatively large particle size DURAVIN ES may impinge itself at high ejection rates. The optimal range is 50-70 PSIG, although higher pressures may aid in reaching deep recessed areas and corners.
 
Hopper:
The rule of thumb for fluidized bed coatings also applies to bed pressures for the hopper. A gentle rolling boil is best. It may be necessary to screen the compound to insure an unrestricted flow and clear powder lines.

Tribo Charging

Powder Flow:
DURAVIN ES requires a powder flow of 15 to 30 PSIG for optimal results. Cross contamination with other powders such as thermosets should be avoided by thorough cleaning between any powder changes. Pressure settings may vary and are unique to each manufacturer's equipment.
 
Air Flow:
For the smoothest finishes DURAVIN ES sprays best in the range of 20-40 PSIG. Higher pressures can aid in reaching recessed areas and corners, but due to the powder's large particle size, impingement may occur, resulting in an uneven and pock-marked surface.
 
Hopper:
The rule of thumb for fluidized bed coating also applies to bed pressures for the tribo hopper. A gentle rolling boil is best. It may be necessary to re-screen the compound to insure an unrestricted flow and clear powder lines.

Cleaning and Oven Parameters

Cleaning:
Standard electrostatic coating substrate preparation practices should be followed.
 
Priming:
Thermoclad presently produces both solvent and volatile free water based primers to insure proper coating adhesion. Primers can be dipped, sprayed, or flow coat applied. The entire part must be wetted by the primer and pre-heated to insure crosslinking and a chemical bond to the vinyl coating.
 
Preheat:
The main function of the preheat is to crosslink the vinyl primer. A minimum substrate temperature of 350º F (176º C) is required. Warmer substrates will improve the conductivity and help apply thicker coatings, but heating is not necessary and the powder will spray satisfactorily on cool substrates as well.
 
Postheat:
Vinyl begins to melt at 390º F to 400º F (200º C to 205º C), but higher oven temperatures must be used to attain a practical production cycle. Finer and less massive substrates are most efficiently processed at higher temperatures, 430º F to 450º F (221º C to 232º C) and relatively short cycles, 2-5 minutes, whereas more massive substrates such as a 1/8" steel panel will require a much lower temperature/fusion cycle to prevent the coating's degradation and sag, 410-420º F (210º C to 215º C) for 10-15 minutes. Complex substrates of different gauge materials should use the lower temperature cycles. Vinyl, being a thermoplastic, does not require a cure. When the material is fused and appears smooth, it is finished.
 
Cooling:
After the fusion process is complete, the part may be air cooled or water quenched by immersion or spray.

The above suggestions offer a brief application guide. Since every piece of equipment is slightly different, it is best to evaluate various equipment settings and conditions to establish the operating latitude and the optimal coating results. Thermoclad's technical staff will be pleased to review any idiosyncrasies of your coating line. If necessary, compounds can be modified to suit particular requirements.

In conclusion...

Electrostatic powder coating is currently one of the most widely used coating process and it continues to grow at a steady rate. Along with this expansion, the types of different electrostatic powders have also grown. Over the last quarter of a century, Thermoclad has maintained its reputation as the technological innovator in the field of fluidized bed vinyl. Using this experience, DURAVIN ES has been created as a cost efficient alternative in the thermoset dominated electrostatic coating market. DURAVIN ES is the protective and decorative coating for applications which require vinyl's distinct properties and advantages in an electrostatic powder.