jpcl webinar - uv stabilization final v1

UV Stabilization of Organic Coatings

Mervin G. Wood, Ph.D.

Technical Expert

JPCL Webinar

November 11, 2015

Outline

Ultraviolet Component of Light Sources

Degradation and UV Light

Ultraviolet Absorbers (UVA)

Hindered Amine Light Stabilizers (HALS)

Weathering Test Methods

Conclusions

2


UV-C Region (up to 280 nm)

Found only in outer space

Filtered out by Earth’s atmosphere

UV-B Region (280 to 315 nm)

Responsible for polymer damage

Absorbed by window glass to 290 nm

UV-A Region (315 to 400 nm)

Also responsible for polymer damage

Dose is proportionally higher than C or B

3


‒ Natural Sunlight*

4

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

250 270 290 310 330 350 370 390 410 430 450

Irrad

ianc

e (W

atts

/sq.

met

er)

Wavelength (nm)

Miami, Florida (June 17, 1983)

UVC UVB UVA

Visible

Increasing Energy per photon

Energy = h=hc/

Shorter = Higher Energy per photon, lower intensity (fewer photons in solar radiation)

Longer = Lower Energy per photon, higher intensity, higher total energy in sunlight

*UV-B will increase with altitude

5



Light Energy

Energy can be...

absorbed

reflected

scattered

transmitted

Absorbed energy can...

cause photolysis of polymers, impurities

be transferred from one molecule to another

be emitted as heat or light6

7

/ nm Bonding Type Bond Energy

UV

-B

230 -C-C- Aromatic 520 kJ/mol

286 R-O-H Alcohol 420 kJ/mol

290 R-CR2-H prim. / sec. / tert. H 410 / 395 / 385 kJ/mol

310 C-O-H Alcohol 385 kJ/mol

320 -C-O- Ether 365 - 390 kJ/mol

UV

-A

340 R-CH2-CH3 Aliphatic 335 - 370 kJ/mol

350 -CR2-Cl aliphatic Chloride 330 - 350 kJ/mol

360 -CH2-NR2 Amine 330 kJ/mol

400 -O-O- Peroxide 270 kJ/mol

References: Morrison Boyd, Lehrbuch d. Org. Chemie, 3rd Ed., VCH, 1985

Absorbed UV light can break bonds


8

Absorbed UV light can break bonds


9

• Initiation Polymer-P free radicals (P•, PO•, HO•, HOO•,...)

• Propagation / P• + O2 POO•

Branched chains POO• + PH POOH + P•

PO• + PH POH + P•

HO• + PH H2O + P•

• Auto catalytic POOH PO• + •OH

Chain reaction 2 POOH PO• + POO• + H2O

• Termination / P• + P• P-P

Recombination P• + POO• POOP (Peroxide bridge)

PO• + PO• POOP (Peroxide bridge)

P• + PO• POP (Ether bridge)

fast

slow

DT, h

DT, h

DT, h

Mechanism of photo-oxidation


10

Ultraviolet Absorbers (UVAs)

UV Absorbers

UVAs – How they work

Prevent polymer degradation by absorbing light and converting to heat

Tautomeric mechanism allows long-term activity

Subject to Beer-Lambert Law – thickness dependent

Not very efficient in highly pigmented systems

11

12

O2h

PH

h or D

UV Absorbers work here

R R* R. ROO.

ROO. ROOH + P.

RO. + .OH

UVAs ‒ Degradation and UV Light

HALS work here

UV Absorbers

13

hR1

R2

R1

R2

+-

Energy dissipation

Conversion of the absorbed UV light

takes place in the excited singlet state

“Enol form” (S0) “Keto form” (S1)

D

Benzotriazole UVA ‒ Mode of Action

UV Absorbers

Beer-Lambert Law

A = ebc

where A = absorbance

e = molar extinction coefficient

b = path length

c = concentration of UV absorber

Absorption (A) = -log T

T = Transmission

Competitive absorption of harmful UV light14

UV Absorbers

Governed by Beer-Lambert Law

Extinction Coefficient

UVA Concentration

Film Thickness

Range of Absorption

290 nm ‒ 400 nm

Properties

Compatibility

Regeneration

Photopermanence15

16

UV Absorbers – Various Commercial Classes

Oxanilide

Benzophenone

Benzotriazole

Triazine

Cyanoacrylate

17

UV Absorbers ‒ UV absorbance spectra

of UVA types

0.00

0.50

1.00

1.50

290 310 330 350 370 390 410 430

Wavelength / nm

Ab

so

rban

ce

Cyanacrylate

Oxalanilide

Benzophenone

Benzotriazole

Triazine

c = 20 mg/liter in Toluene(Xylene), path = 1cm

UV-A VISUV-B

Cyanoacrylates, Oxalanilides absorbs efficiently only in UV-B

Benzotriazoles show best spectrum coverage

18

UV Absorbers ‒ Photopermanence

Photopermanence = f(UVA type, Mw)

50

60

70

80

90

100

110

0 500 1000 1500 2000 2500

Xe-WOM CAM 180 exposure / hrs

UV

-A r

eta

ine

d / %

0.8% Triazine C

1.5% Triazine B

1.5% Triazine A

1.5% Benzotriazole B

1.5% Benzotriazole A

30mm Clear Coat with UVA + 1% N-Alkyl HALS on fused quartz plates

(% UV-A determined at 345nm)

98.2%

94.2%

89.6%

83.9%

76.2%Decreasing Photopermanence

UVAs – Synergy with HALS

19

0

10

20

30

40

50

60

70

80

90

100

0 500 1000 1500 2000 2500 3000 3500 4000

20

De

g G

loss

Hours

Polyester Urethane Clearcoat/Bronze Metallic Basecoat, XeWOM = J2527

Unstabilized

2% UVA

1% N-Alkyl HALS

2% UVA/1.5% N-Alkyl HALS

UV Absorbers ‒ Proper UV Absorber

Choice

Substrate Sensitivity

UV wavelength sensitivity of resin binder or underlying resin

UV wavelength sensitivity of pigment

Sensitivity of color change (yellowing or pigment fading) for resulting article

Environmental Factors

Environmental conditions

Interior versus exterior

Duration of service (warranty)

Formulation Details

Solventborne, waterborne, 100% solids or UV cured

Basecoat/clearcoat, monocoat, etc.

20

21

Hindered Amine Light Stabilizers (HALS)

Hindered Amine Light Stabilizers

Photostabilization with HALS

Regenerative

Effective in maintaining physical properties

Effective in pigmented as well as low Pigment to Binder (P/B) ratio

formulations

Not thickness dependent

22


23

How much effect can HALS have?

Scanning electron micrographs

of a white polyester

polyurethane after 1300 hours

QUVB (313 nm)

Unstabilized Unstabilized

X 1,000 X 10,000

X 10,000 X 10,000

1% HALS 2% HALS

HALS Function in Coatings

Gloss retention

Reduce cracking

Reduce chalking

24

O2h

PH

h or D

HALS work here

R R* R. ROO.

ROO. ROOH + P.

RO. + .OH

HALS ‒ Degradation and UV Light

UV Absorbers work here


25

OC N

R

H

R

O NN R

N+

O O

O C R

RHC

R

O

RC

R

O

OCR

O

H

OR

H

O OC

O

R

O OR

R

Oxidation

'

-'+

'or

'

'

or

Mechanism of Action – Modified Denisov Cycle


26

HALS Basicity

P i p er i d i n e

A l k y l P iper id in e

A l k y l P i p er i d i n e / AO hyb r i d

A l kox y P i p er i d i n e

p K b

5 . 0

5. 1

5 . 5

9. 6

R1 = “Head Group”

Activity

Basicity

Compatibility

R2 = “Backbone”

Solubility/Compatibility

Equivalent Weight

Basicity

HALS – Weathering Performance of HALS Type

27

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

20

De

g G

loss

Months

HSTSA Clearcoat/Silver Metallic Basecoat, Weathering = South FL

Unstabilized

2% UVA/1% N-Acyl HALS

2% UVA/1% N-Alkyl HALS

2% UVA/1% N-OR HALS

HSTSA = High Solids

Thermoset Acrylic

Weathering Test Methods

28

Natural Weathering

Florida

Arizona

Australia

Other

Accelerated Weathering

QUV-B (for high altitude simulation)

Xenon with various light filters

QUV-A (for terrestrial simulation)

Many others

Substrate Weathering Considerations

Environmental Factors

Interior versus exterior

Environmental conditions & pollutants

Duration of service (warranty)

Conclusions

UV Absorbers ...

Competitively absorb UV light to hinder radical initiation

Regenerate

Retard color change in low P/B formulations

Shield polymer from UV light and degradation

Exhibit synergism with HALS

29

Conclusions Continued

Hindered Amine Light Stabilizers ...

Terminate free radicals to prevent further chain reactions

Are effective in high pigmented as well as low P/B formulations

Regenerate

Are not thickness dependent

Reduce cracking and loss of tensile properties

Exhibit synergism with UVAs

30

Acknowledgements

Many thanks to Lori Boggs and Diane Langer for their contribution and

support

31

32

While the descriptions, designs, data and information contained herein are presented in good faith and

believed to be accurate, they are provided for guidance only. Because many factors may affect processing

or application/use, BASF recommends that the reader make tests to determine the suitability of a product for

a particular purpose prior to use. NO WARRANTIES OF ANY KIND, EITHER EXPRESSED OR IMPLIED,

INCLUDING, BUT NOT LIMITED TO, WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A

PARTICULAR PURPOSE, ARE MADE REGARDING PRODUCTS DESCRIBED OR DESIGNS, DATA OR

INFORMATION SET FORTH, OR THAT THE PRODUCTS, DESCRIPTIONS, DESIGNS, DATA OR

INFORMATION MAY BE USED WITHOUT INFRINGING THE INTELLECTUAL PROPERTY RIGHTS OF

OTHERS. In no case shall the descriptions, information, data or designs provided be considered a part of

BASF's terms and conditions of sale. Further, the descriptions, designs, data, and information furnished by

BASF hereunder are given gratis and BASF assumes no obligation or liability for the descriptions, designs,

data or information given or results obtained all such being given and accepted at the reader's risk.

© BASF Corporation, 2015

jpcl webinar - uv stabilization final v1

Documents