UV-curable powder coatings containing interpenetrating polymer networks (IPNs)

Saeid Bastani , Siamak MoradianProgress in Organic Coatings, 56, (2006), 248–251

Presented By- Nikita Mhadeshwar

Advantages of UV-curable powdercoatings

Essentially no emission of VOCFast curing speed Minimal health riskIndependency of the flow system from the cure

system

Interpenetrating Polymer Networks

A polymer comprising two or more networks which are at least partially interlaced on a molecular scalebut not covalently bonded to each other and cannot be separated unless chemical bonds are broken

It can be made by two techniques 1. Sequential IPN 2. Simultaneous IPN

Simultaneous Interpenetrating Network (SIN)

One of the methods of synthesizing IPNMonomers, oligomers, crosslinkers and initiators are mixed

together and the polymerization and crosslinking is forced to occur simultaneously

EXPERIMENTAL

Curing Systems of UV-curable powder coatings

Radical cure systems

Eg. unsaturated polyester,

polyurethane acrylate and

maleate vinylether

Cationically cured systems

Eg. epoxy type resins including,

bisphenols, novalac modified

bisphenols, cycloaliphatic

epoxides, glycidylmethacryla

tes and glycidyl acrylics

Raw Materials

COMPONENT COMPOSITION SUPPLIERS

Uracross P3125 DSM

Uracross P3307 DSMCyracure UVI 6974 (onium salt photoinitiator) Union Carbide

BYK 361 BYK ChemieVEctomer (aromatic urethane divinyl ether) Allied Signal Co.GT 6259 (bisphenol A/epoxy cresol novalac) Ciba-GeigyPhotosensitizer (cumene hydroperoxied) -Plastisizer (epoxidized soya oil) -Araldite GT 7004 (epoxy resin) Ciba-GeigyUralac 5125 (polyester) Ciba-GeigyBYK 365 BYK Chemie

Irgacure 184 Ciba-Geigy

Preparation of free radical UV-curable powder coatings (FRUVPC)

COMPONENTS Wt%

Uracross P3125 81.6

Uracross P3307 16.7

Iragacure 184 1

BYK 361 0.66

Preparation of cationic UV-curable powder coatings (CUVPC)

Equal parts of “VEctomer” and “GT6259” were mixed together and then 3 wt% of UVI 6974, together with the photosensitizer and the palsticizer were added.

Finally these composites were mixed by melt extrusion

Preparation of IPN UV-curable powder coatings

SAMPLE NO.

Free radical UV-curable

powder coatings (parts

by weight)

Cationic UV-curablepowder coatings(parts by weight)

FRUVPC 100 0

IPN-1 90 10

IPN-2 80 20

IPN-3 70 30

IPN-4 60 40

IPN-5 50 50

IPN-6 40 60

IPN-7 30 70

IPN-8 20 80

IPN-9 10 90

CUVPC 0 100

Extrusion of the premix took place at 80 ⁰C, 200 rpm in a twin-screw extruder.

The powder coatings were sprayed electrostatically with a corona gun on to the substrate.

The flowing and curing conditions were as follows:Flow: IR-radiations (32 kw/m2) (100 sec).Cure: UV exposure (7 m/min at 2×80 w/cm medium pressure

Hg lamp). The coatings were then postcured in a 100 ⁰C oven for 5 h.

Hybrid PE-Epoxy

The formulation contains 50:50 Uralac 5125 and epoxy resin (Araldite GT 7004), flow additive BYK 365 and benzoin. Cured 12 min at 180 ⁰C.

Testing of IPN powder coatingsGardner impact resistance (ASTM D 2794-69)pendulum hardnessCross hatch adhesion MEK resistance Salt spray resistance (ASTM B117)Tg

Samples Direct impact (in. lbs)

Konig hardness

(sec)

Cross hatch

adhesionFlow (⁰C) MEK

resistance

Salt spray (mm)

(240 h)FRUVPC 5 210 1B 110 100 2

IPN-1 20 210 2B 110 100 2

IPN-2 35 203 3B 110 100 2

IPN-3 78 201 4B 110 100 2

IPN-4 112 194 5B 110 100 2

IPN-5 140 183 5B 110 100 2

IPN-6 150 177 5B 110 87 2

IPN-7 160 169 5B 110 74 4

IPN-8 160 133 5B 110 40 5

IPN-9 160 104 5B 110 32 10

CUVPC 160 99 5B 110 20 15

Hybrid PE-Epoxy 60 210 5B 180

Surface slightly

damaged12

Samples Tg Ѳ

FRUVPC 320 -

IPN-1 318 0.009

IPN-2 319 0.008

IPN-3 321 0.004

IPN-4 324 −0.002

IPN-5 331 −0.021

IPN-6 336 −0.033

IPN-7 332 −0.020

IPN-8 326 0.001

IPN-9 327 0.0006

CUVPC 328 -

CONCLUSIONThe properties of IPN UV-curable powder coatings such as

adhesion, hardness, impact strength, solvent (MEK) resistance and the resistance to salt spray were better than the separate individual UV-curable powder coating compositions.

It seems that through careful selection of the type and the amount of free radical and cationic components to form IPN UV curable powder coatings it is possible to engineer the required properties.