William Schaeffer & Sarah Cotts UV/EB West

February 26 & 27, 2013

“Radiation Curable Components and Their Use

in Corrosion Resistant Applications"

Outline of Discussion Topics  Economic Impact of Corrosion   Types of Chemistry Commonly Used   Industry Trend  Corrosion Resistance Test Methods  Oligomer Performance as it Relates to Backbone

Structure  Monomer Performance as it Relates to Functionality  Effect of Film Thickness on Corrosion Protection   The Importance of Corrosion Inhibiting Pigments (CIP)  Weather Resistance Test Results  Conclusions & Observations Made Based on this Study

Economic Impact of Metallic Corrosion Across U.S. Sectors, Cost of Damage, $276 Billion (Federal Highway Administration Survey, 2000)  

Typical Chemistries Currently Used

  These range from alkyd and epoxy ester coatings that are baked or air dried to promote crosslinking.

 Solvent-borne two-part coatings employing polyurethanes or latexes based on vinyl, acrylic or styrene combinations.

 Water based compositions, including aqueous alkyds, epoxy esters, polyesters, and polyurethanes.

 High solids or powder coatings based on vinyl, polyester, or epoxy ester compositions are also favorable alternatives.

Industrial Market Technology Distribution, 2004, 58 MM Gallons

Market Distribution of Technologies for Direct to Metal Applications

Typical Metal Applications Now Using Radiation Cured Coatings to Provide Corrosion or Processing Protection

Examples of Poor Corrosion Resistance

  The most widely used corrosion control technique.   Means for separating the surfaces that are susceptible

to corrosion from the factors in the environment which cause corrosion to occur.

  Can be used in combination with other methods of corrosion protection   Cathodic Protection   Corrosion Inhibitors

  Can be used as a primer, secondary, topcoat, or combination

Protective Coatings

How Do Coatings Protect Metal?   3 Basic Mechanisms

  More than one of these mechanisms may be used by a coating   Barrier Protection

  Organic coatings act as a barrier to a corrosive solution or electrolyte   Forming a barrier relatively impermeable to moisture   The barrier should be as impermeable, thick, and continuous as practical.

  Cathodic Protection   High loading of fine zinc particles, so the particles in the cured film are in

electrical contact with each other and with the underlying steel. This permits a type of cathodic protection.

  Organic and inorganic products are used for zinc-rich coatings on steel   Inhibitive Pigments

  Added to primers to inhibit corrosion at the coating/metal interface.

Corrosion Resistant Testing  Ongoing project to understand

(meth)acrylate monomer and oligomer performance in ASTM B117 Salt/Fog Testing  Ability to withstand corrosive environment  Protect metal surface from corrosion

 Testing focused on cold rolled steel (CRS)  Common construction and durable good

component  Substrate very susceptible to corrosion

Salt/Fog Testing ASTM B117   Test protocol

 5% NaCl solution  pH of 6.5 to 7.2  Temperature set to

35 °C  Fog rate of 1.0 to

2.0 mL per hour per 80 cm2

 Q-Lab 4x8” CRS

Test Panel Preparation   Each monomer tested contained 5.0 %

photoinitiator (Daracure 1173).  Substrate: Cold Rolled Steel (CRS)  Film Thickness: 1.0 mil unless otherwise

stated.  1600 mJ/cm2 of total UV energy with two

Hg arc lamps (400 w/in.) as measured using the UV Power Puck radiometer.

Corrosion Protection Using Radiation Curable Acrylates

Data & Results

Oligomer Backbone Comparison Ranking: 5 is best

Oligomer Designation

Description B117 Rank

O1 AR Epoxy Acrylate 2 O2 AL Epoxy acrylate 0 O3 Linseed epoxy acrylate 0 O4 Polybutadiene acrylate 1 O5 Amine acrylate 0 O6 Acrylic oligomer 3 O7 Acrylic oligomer 1 O8 Polyester acrylate 0 O9 Polyester acrylate 0

O10 Zn oligomer 0 O11 Brominated epoxy acrylate 2 O12 Novolac epoxy acrylate 1

O1

O6 O7

O9 O8

Oligomer Backbone Comparison Ranking: 5 is best  

  Test series comprised varied backbone structures.  Epoxy acrylates, polyester acrylates, and specialty

acrylics in acrylate monomers.   A Bis phenol A aromatic (AR) epoxy acrylate was used

as the control in this round of testing and received a rating of 2.

 Despite its hydrophobic nature, the polybutadiene acrylate performed very poorly (1 rating).

  The polyester oligomers performed likewise due poor adhesion caused by high functionality.

  The best performer was an acrylic oligomer (3 rating).

Urethane Acrylate Comparison

Sample Designation

Oligomer Description B117 Rank

UA1 Lower MW polyester ALUA 1

UA2 Higher MW polyester ALUA 0

UA3 Low viscosity polyester ALUA 1

UA4 Polyester ARUA 0

UA5 Polyether ALUA 3

UA6 Low MW ARUA 3

UA7 Polyester ALUA 4

UA8 Polycarbonate ALUA 4

UA9 Polyester ARUA 4

Ranking: 5 is best

UA9

UA8 UA4

UA7

Urethane Acrylate Comparison  

 Based  on  this  tes,ng  generally,  aroma,c  urethanes  offer  an  advantage  over  alipha,c  urethanes.    

 The  study  also  demonstrated  that  alipha,c  urethanes  based  on  polyester  or  polycarbonate  polyols  offer  significantly  improved  corrosion  resistance.    

Relative Corrosion Protection Based on Oligomer Type  

Comparison of Commonly used Monomers

Sample Designation

Description B117 Rank

M1 IBOA 0

M2 HDDA 1

M3 Tricyclodecane Dimethanol Diarcylate (TCMDA)

2

M4 TMPTA

0

M5 PETA

0

M6 Cyclic Trimethylolpropane Formal Acrylate (CTFA)

0

Ranking: 5 is best

Testing of Commonly Used Monomers  Monomers impart less corrosion protection compared to

oligomers – possibly due to significantly lower molecular weight.

 Performance differences may also be linked to functionality.

 Mono functional monomers are low in cross link density making them subject to moisture attack.

 Higher functionality makes the film too brittle when cured resulting in poor adhesion and surface cracking.

 Difunctional monomers seem to offer more protection owing to a balance of cured film properties.

Corrosion Resistant Pigment Testing Inhibitor Weight % B117 Rank

Pigment 1 5% 4

Pigment 2 5% 5

Pigment 3 3% 4

Pigment 4 3% 3

Ranking: 5 is best

TCDMDA P1 P3 P2 P4

Corrosion Resistance of a Difunctional Monomer (TCDMDA)   as it Relates to Film Thickness  

0.5 mil

3.0 mil

Corrosion Resistance of a Difunctional Monomer as it Relates to Film Thickness  

 Corrosion resistance improves with coating film thickness.

 No added benefit from 2-4 mil.

 Application of two thin coating layers is more effective than one thick coating layer.

 Second layer fills any voids or defects in the first, providing a higher quality coating.

Accelerated Weathering Testing of Corrosion Resistant Formulations

QUV Equipment & Conditions   8 hours of UV radiation @

60 C.   Followed by 4 hours dark

condensation @ 40 C.   The lamps were replaced

every 400 hours to ensure constant UV intensity.

  The bulb used was a UVA 340 from Q-Panel. The output is from 300 - 400 nanometers centered at 340 nm.

Cure & Application Conditions

Gloss Retention &Yellowing Resistance

Gloss : ASTM D523-89

@ 60 °

Yellowness Index: ASTM E 313-98 geometry: 45/0

illuminant/observer: D65/10°

Effects of Corrosion Inhibiting Pigments on Weathering Resistance (Yellowness Index as it Relates to Hours of QUV Exposure)

Weathering Resistance of Corrosion Protective Urethanes (YI as it relates to QUV exp.)

Weathering Resistance of Corrosion Protective Urethanes (gloss retention @ 60 degrees as it relates to QUV exp.)

Conclusions & Observations Coating Market Trends(2000 – 2004)  Chemistries vary widely, including polyurethanes,

acrylics, and alkyds. Epoxy-based coatings are common.   The industry is trending toward “green” coating

technologies.  Solvent-borne direct-to-metal coatings decreased from

84% to 61%.  Over this period the use of waterborne coatings

increased from 13% to 35%.  UV/EB curable 100% solids coatings represent a small

but growing portion of the market for direct-to-metal coatings.

Conclusions & Observations Corrosion Protection from Acrylate Chemistries

  UV/EB curable coatings based on aromatic backbone structure resist corrosion better than their aliphatic analogs.

  Polyester acrylates should not be used to formulate corrosion protective coatings.

  Aromatic epoxy acrylates contribute mid-range performance to corrosion protective coatings.

  Urethane acrylate oligomers provide the best corrosion protection.   Aromatic urethanes are generally superior to aliphatic, there are exceptions

based on backbone structure.   Proper selection and use of corrosion inhibiting pigments can greatly

enhance performance of acrylate-based protective coatings.   Coating application technique has an impact on the performance of

corrosion protective coatings, e.g., two thin layers are more effective than an equivalent single layer.

Conclusions & Observations, Effect of Weathering on Acrylate-Based Corrosion Protective Coatings   ARUA’s offer better corrosion protection than ALUA’s.   ARUAs do not resist yellowing as well as ALUAs.   Addition of a HALS to coatings based on ARUAs can dramatically

improve weathering resistance.   Corrosion inhibiting pigments did not appear to affect weathering

resistance.   Over coating an ARUA-based coating with one based on an ALUA may

produce a weathering advantage compared to the use of the ARUA-based coating alone.

  Offers concurrent benefit to weathering resistance and corrosion resistance.

Future Work Plans

Expand Coatings Durability Knowledge Base

Prohesion Testing (ASTM D 5894)  Combined testing

using :  Cyclic salt spray

(ASTM G85).  QUV accelerated

weathering testing (ASTM D4587).

Questions Please!