urethane acrylates (MW =3000 g/mol) with soft polyol segment ... Screen difunctional urethane acrylate oligomers with trifunctional urethane acrylate.
How does it feel ?
MOST RECENT DEVELOPMENTS IN UV CURABLE SOFT TOUCH COATINGS Xavier Drujon, Radtech Europe Conference, October 13-15 2015, Prague, Czech Republic Authors: Xavier Drujon, Lisa Spagnola, Gunter Moeller
Applications for Soft Touch Coatings Soft-touch coatings are unique finishes that deliver the feel and appearance of a velvet or flocked fabric substrate
Packaging
Consumer Electronics
Automotive
Small Appliance
Aerospace
Soft Touch Coatings Value Analysis
Packaging
Definitions
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FMOT: First Moment Of Truth
•
SMOT: Second Moment Of Truth
Colleen Twomey, Cal. Poly. Univ., Radtech USA 2015 « … there is evidence that integration of soft touch coatings increases « FMOT » and « SMOT », particularly in beauty and cosmetics. » « Customers are willing to pay 5% price increase for packaging with soft touch tactile coatings over packaging with no tactile coatings »
3
Conventional Soft Touch Coatings Conventional soft touch coatings are two part isocyanate based chemistries in either solvent or water. ● A large portion is 2K solvent borne which uses a difunctional polyol with a trifunctional hardener (isocyanate)
Strengths: ● Excellent tactile/haptic properties
Weaknesses: ● Limited pot life ● Extended bake / cure ● Limited coating properties
Voice of Customer: ● Interest in a UV-curable system that can replace current 2K soft touch coating technology ● Need for increase mar, abrasion, stain, and chemical resistance
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Technical Challenges (1) But what is soft ? ● Quantitative assessment of soft touch performance of a coating remains elusive… Effect of age1 and sex2 on tactile perception Effect of visual appearance on tactile perception3 Effect of body sites, velocities and force of application2 ● We confirm that perception of feel varies from person to person Experimental Soft Touch panel samples were evaluated by a panel of people selected among our R&D and headquarters staff. They were selected to create a range of background, age and gender. Example: Results for eleven people evaluating “sample 19” ( 1= hard and 5 =soft) Rating
1
2
3
4
5
Number of responses
2
4
1
1
3
What feels rubbery to on person might feel silky to another
•
Conclusions: Need a way to quantify the “Soft Touch Experience”
1. « The effect of age on neural processing of pleasant soft touch stimuli » A. May et al., Frontiers in Behavioral Neuroscience (2014) 2. « Effect of visual expectation on perceived tactile perception » H. Yanagisawa et al. International Journal of Design Vol. 9, No 1 (2015) 3. « Quantitative assessment of pleasant touch », G. Essick et al., Neurosciences and Biobehavioral Reviews 34 (2010) 192-203
Surface mechanical properties measurements of coatings surface by AFM Oscillatory loading nanoindentation technique
indenter P
measures mechanical properties at the surface
z uz sample
a
r
The techniques can be combined with surface imaging
2πµ P= χ (u ) du ∫ 1−υ 0 a
µ = Shear modulus
S.Cohen and Estelle Kalfon-Cohen, Dynamic nanoindentation by instrumented nanoindentation and force microscopy: a comparative review, Beilstein J Nanotechnol. 2013; 4: 815–833
“Soft-touch” feel and adhesion via AFM
Preliminary results suggest good correlation between “touch feel” and adhesion forces Adhesion forces are estimated from nano indentation data
P adhesion
1 = Rubbery feel 2 = Velvety feel 3 = Silky feel
“Soft-touch” feel and adhesion via AFM: Some method limitations and alternatives Surface roughness, phase separation - Causes large standard deviations and may invalidate results Treatment of Adhesion - Ad hoc assumptions are made to account for how adhesion forces alter G’ and G’’. Is the size of the probe / indenter (nano) relevant to the soft feel « experience » (micro/macro) ?
Quantification of the “soft touch experience”: Preliminary conclusions AFM nano-indendation method(s) are valuable to study and understand “soft touch” coatings, but should be used with great care due to their “nano” character and many built in assumptions
Probe diameter 25 mm Surface contact r = 1-5 mm Microscope CDD for in situ observation of indenter/sample contact
“The friction induced in (soft touch) contact ….. a complex combination of phenomena: adhesion, elastic ratio of bodies in contact, viscous flow, plasticity occurrence, and topography occurrence” 1 Alternative (?) method to study friction induced in contact with rough soft matter has been recently described by Le Houérou et al. 1
1. V.Le Houérou et al., Proceedings of the ASME 2014 12th Biennial Conference on Engineering Systems Design and Analysis, June 25-27 2014, Copenhagen
Technical Challenges (2) Increasing crosslinking density to improve mar, abrasion, stain, and chemical resistance results in loss of soft touch properties ● Evaluation of the haptic properties of a homogeneous series of aliphatic urethane acrylates (MW =3000 g/mol) with soft polyol segment
The Chemistry Design Of Experiments (DOE): ● Screen difunctional urethane acrylate oligomers with trifunctional urethane acrylate crosslinkers – Difunctional urethane acrylates: UA1, UA2, UA3, UA4, UA5 – Trifunctional crosslinkers: M1, M2, M3, M4, M5
● Ratio of difunctional to trifunctional material screened at 90:10 and 60:40 ● All formulations contained: – Silica: matting agent and surface modifier – Photoinitiator – Solvent: viscosity reduction Mass (g)
Percent
Percent based on:
Difunctional Urethane Oligomer
24 or 36
60 or 90
of total resin
Trifunctional Crosslinker
16 or 4
40 or 10
of total resin
59.7
125
on solids
Disperbyk 2008
0.35
10
on silica
Acematt 3300
3.4
8.5
on resin
PL-HMPP
2
5
on resin
Solvent 50:50 MEK: BuAcetate
Measurements
Feel
Stain Resistance
● Rubbery, Velvety, Silky ● Soft (5) to Hard (1)
● Delta E ● Coffee, red wine, and ketchup (19-20hr) ● Mustard (1hr)
Hardness ● Persoz pendulum hardness ● Pencil hardness Gloss ● 60 degree Adhesion ● Cross hatch – Tape (%) – Finger rub (pass/fail)
Material Resistance ● MEK double rubs ● 50:50 IPA:Water double rub ● Sunscreen and bug spray (1hr at 80°C) – 1=no change, 2=slight change, 3= significant change – Test adhesion with wooden scraper – pass/fail Abrasion Resistance ● RCA abrader – Wear through on glass – Stop at 300 cycles
Using DOE Extremes to Understanding Feel
DOE 4
DOE 18
Properties
+
Selected six sample from DOE for further analysis DOE 9
-
DOE 38
DOE 26
DOE 3
-
+
Feel
abrasion
5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
solvent resistance
Feel
pencil hardness
2K 4 9 18
stain resistance
adhesion
abrasion
Feel 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
solvent resistance
pencil hardness
2K 3 26 38
stain resistance
adhesion
Using DOE Extremes to Understanding Feel Selected six sample from DOE for further analysis
DOE 4
-
Properties
+
● DMA- Tg and modulus ● AFM- surface roughness and modulus
DOE 18
DOE 38 DOE 26
DOE 3
-
+ FEEL
Oligomer Backbone
Oligomer Loading
Monomer Structure
3
UA3
0.9
M1
4
UA1
0.6
M1
9
UA4
0.6
M4
18
UA2
0.6
M1
26
UA3
0.6
M5
38
UA5
0.9
M2
Experiment #
DOE 9
DMA Analysis of Selected Samples Storage Modulus at 25°C (MPa)
Loss Modulus at 25°C (MPa)
2K
16
3
Tg storage modulus 1
2
4
-30
NA
3
0.3
-43
NA
4
731
57
-11
78
9
335
31
-21
82
18
701
77
18
69
26
3
0.1
-49
NA
38
4
0.5
-24
NA
Experiment #
Comparison of DMA for Rubbery vs Silky Sample
Expanding the DOE Promising products from DOE : ● Oligomers: UA4 and UA5 ● Crosslinkers: M1 and M4 Expanded DOE to screen combinations with M1:
Oligomer Loading
Crosslinker
Feel (rubbery, velvety, silky)
UA5
0.9
M1
2
4.5
B
26
47
UA5
0.6
M1
3
4
H
200+
42
UA4
0.9
M1
3
3
B
17
58
UA4
0.6
M1
3
4
F
190
39
Oligomer
Feel rating
Pencil Hardness
MEK double rubs
Sum Stain (∆E)
Soft Touch UV Curable Coatings Demonstrate Soft Touch and Feel with
M1/UA5
M1/UA5 Aromatic Urethane Acrylate Designed for Soft Touch Coatings ● Typical liquid properties: – Contains 25% butyl acetate as solvant – Viscosity at 25°C: 1660 mPa.s – Color: 67 APHA – Haze: 14% ● Typical solid properties: – Pencil Hardness H – Solvent resistance MEK rub 200+ – Stain resistance
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Formulation Recommendation
Formulation (%wt) Oligomer Acrylate Oligomer Acrylate
Products M1/UA5
"Silky“ Feel 62,00
Main features "Velvety“ Feel 38,50 17,50
UA2
Acematt 3300 Disperbyk Silica dispersant 2008
4,00
4,00
0,40
0,40
Solvent
MEK
31,00
37,00
Speedcure 84
2,60
2,60
Matting Silica
Photoinitiator
● Spray application ● Can be formulated “as is” without additional resin to yield a solvent resistant, “silky” coating. ● Can be formulated with other resins UA2 to yield “velvety” coatings with another level of touch sensation
The two formulations applied on ABS panels with a target thickness of 36µm. The solvent was flash off at 60°C / 5 minutes. The coatings were cured 3 x 10 m/min using a Mercury vapor 120W lamp. The panels exhibited a soft feel, characterized as “silky” and “velvety”, good adhesion on ABS (6x6 crosshatch) and good resistance to solvent. 19
Outlooks Multigenerational approach ● solvent based ● 100% UV curable under development ● Waterborne UV-PUD under investigation
Obtaining tactile effects through 3D ● In mold coating/skinning decorative processes are used to produce soft feel plastic parts, with a good replication of mold surface structure ● UV screen printing and inkjet printing are decoration process that enable the creation of 3D tactile finishes (Braille effect)
Switch cover prototype, illustrating in mold skinning, 2K PUR system (Bayer/Polytec/Krauss Mafei/Mankiewicz)
Outlook: Bio-Inspired Soft Touch Coatings - Duvet and Tactile effects
Observation
Understanding
Inspiration
SEM view of ptterned polyimide foils obtained by dry etching in polymer plasma M.Moreno-Couranjou et al., Plasma Process.Polym. 2014, 11, 647-654
Acknowledgements
Lisa Spagnola, Jeff Klang, - Sartomer North Ameria Gunter Moeller, Manjuli Gupta, Sriraj Srinivasanr – Arkema North America Armelle Dehureaux – Sartomer Europe Ming Fan – Sartomer Asia
