New Coatings

Author:European Union Publications Office, 2006

1. New Coatings Studied at Voestalpine. 1.1. Materials. 1.2. Scratch testing. 1.3. Evaluation of physical properties related to scratch resistance. 1.4. Comparative evaluation of scratch tests. 1.5. Comparative evaluation of coating systems. 2. New Coatings Studied at Arcelor. 2.1. Materials. 2.2. Characterizations. 2.3. Conclusions. 3. New Coatings Studied at Doc. 3.1. Choice of coatings.


1. New Coatings Studied at Voestalpine

1.1. Materials

Clearcoats for the application on organic coated steel which are based on an acrylat backbone with isocyanate crosslinking agents have been supplied by BASF. A standard version of this clearcoat has been modified by varying types and ratio of the crosslinking agents and - in one case - nano particles have been added in a small portion to increase scratch resistance (table 5-1). These coatings have been applied on a black basecoat according to the layer sequence as shown in figure 1-2.

Table 5-1: Experimental high-gloss clearcoats from BASF

To work out the effect of the nano particles more in detail, the BASF Standard-Clearcoat V1 has been supplied with increasing contents of nanoparticles (SiO2-based) and samples as described in table 5-2 have been prepared by bar coating and thermal curing. Subsequent T-bend-testing revealed that the addition of nanoparticles in the given concentration range has no influence on the adhesion and flexibility of the top clearcoat.

Table 5-2: Characterization of BASF - Clearcoats with nanoparticles

Layer-Sequence T-bend Test [ T ]
Sample Basecoat Clear-coat 1 Clearcoat 2 Adhesion Fissure
BC+1+1 black Standard 0.0% Nanoparticles 1 2
BC+1+2 black Standard 0.8% Nanoparticles 1 1,5
BC+1+3 black Standard 1.6% Nanoparticles 1 1,5
BC+1+4 black Standard 2.4% Nanoparticles 1 1,5

Particle-distribution within the "Nano-Coatings" was investigated by FE-SEM and EDAX-Analysis. As it can bee seen in the figures 5-1 and 5-2, there is a homogenious distribution of the SiO2-particles within the top clearcoat. The semiquantitative EDAX-results of the Si-content in the dry film (table 5-3) are in reasonable agreement with the specifications given from BASF for the varnish (table 5-2).


Table 5-3: EDAX-Analysis (dry film) of BASF-top-clearcoats with nanoparticles

Sample Elemental Content (EDAX) [Wt %]
C O Si
BC+1+1 87,9 12,0 0,1
BC+1+2 86,6 13,0 0,4
BC+1+3 88,4 10,3 1,3
BC+1+4 89,5 8,4 2,1

1.2. Scratch testing


Clear Coats for Coated Carbon Steel V1 - V5

Gloss mesurement of the tested samples (figures 5-3 and 5-4) result in the following ranking of mar- resistance:

V1 = V5 (identical top-clearcoat)

All samples exhibit a moderate increase in gloss due to a thermal treatment ("reflow"). All of the formulation tested here exceed the performance of spray coated serial automotive clearcoats [5], only one experimental coating shows a similar mar resistance like these coil coating systems.

The addition of nano-particles in a concentration range between 0 - 2,4% revealed no significant improvement of mar resistance as shown in figure 5-5. A significant ageing effect that has been observed with hardness measurements does not affect the mar resistance (table 5-3).



Table 5-4: Nano particle coatings - Influence of ageing on AMTEC test-results

Series 1: Amtec-testing several weeks after the coating process

  20°-Gloss Gloss after Amtec-Test Gloss after Reflow (2h/80°C) nplast Amtec Residual Gloss [%] Residual Gloss [%] after Reflow
BC+1+1 87,2 76,8 -- 63,2 88,1 --
BC+1+2 87,0 77,8 -- 62,7 89,4 --
BC+1+3 86,9 77,4 -- 61,4 89,1 --
BC+1+4 86,1 78,0 -- 62,1 90,7 --

Series 2: Amtec-testing approx. 12 hours after the coating process

  20°-Gloss Gloss after Amtec-Test Gloss after Reflow (2h/80°C) nplast Amtec Residual Gloss [%] Residual Gloss [%] after Reflow
BC+1+1 88,1 80,3 79,9 76,5 91,1 90,7
BC+1+2 87,9 79,0 78,8 71,4 89,9 89,6
BC+1+3 86,1 75,5 77,1 64,3 87,7 89,6
BC+1+4 85,8 75,0 75,4 67,3 87,4 87,8

Clear Coats on Stainless Steel

All protection layers applied to the stainless steel samples (Senocoil-Coating on TKS, PET-Film on USINOR, thermal curing Clearcoat form BASF [CQ3-2814] and UV-curing clearcoat from BASF [CQ3-2652]) show a lower residual gloss at 20° after the Amtec-Test than the clearcoats for coated carbon steel (figure 5-3). The reflow treatment results in a strong recovery of Senocoil and the thermal BASF system (CQ32-814) while the PET-foil and the UV-curing (CQ32-652) system exhibit no significant reflow effect.

A comparison between black carbon steel samples and bright stainless steel samples has to be made with care since the reflectivity of the two substrate is completely different (see absolute gloss values in figure 5-4) and for a more detailed evaluation all clearcoats for stainless steel should be applied on a substrate with a black basecoat, additionally an evaluation at a gloss angle of 85° turned out to give the best results on stainless steel.

Amtec-Testing of the optimised coating-systems for stainless steel revealed the following details (figure 5-6):

- the protective system favoured by DOC has the best resistance against marring,

- the sample "CSM-F/04/04" has a lower marring resistance but is still on an acceptable absolute level

- with the system of Arcelor (which shows a typical mat and microstructured surface) a polishing effect is found on both substrates (stainless steel "AFP" and coated carbon steel "Arcelor auf BC") which results in an enhanced residual gloss.


Erichsen single scratch test

In the initial phase of the project a lot of studies have been made on the geometry and crack-pattern obtained with this special stylus test. Various information can be deduced from evaluations like figure 5-7. The "hard" clearcoat (V2) shows pronounced brittle behaviour which is reflected in the lowest critical load of all coatings tested as well as a strong increase in permanent scratch width with increasing load: Deformation energy is transformed to a great extent into irreversible brittle failure while other coatings show significant contributions of elastic (i.e. reversible) deformation leading to lower scratch width.


Throughout the work it turned out that great care has to be taken about the tip geometry. A crack in the diamond cone which can only be observed under a microscope leads to significant reductions in the critical load. The final results as presented in figure 5-8 have been obtained with a carefully inspected test stylus:

The Critical load of the standard clear coat V1 and the modifications V4 + V5 are all in a similar region and even the addition of various concentrations of nanoparticles do not result in a significant change of the cracking behaviour of the coatings. An obvious explanation for this results is the fact that binding and crosslinking agent are the same for all of these coatings. On the other hand changes in the crosslinking agent lead to strong reduction of the critical load in the case of the hard (V2) as well as the soft (i.e. undercured - V3) modification of the coating.


Optimised clear coats on stainless steel form all partners have been investigated in a round robin scratch test in the last semester of the project. On the basis of the data given in the table 5-5 it can be said that:

* Critical loads of the coatings on stainless steel are generally on a low level (> 100g) compared to coated carbon steel (typically - 150 g).

* The system favoured by DOC is (independent of the coating thickness) on a slightly lower level compared to CSM an Arcelor.

* Applying the same protective coating from Arcelor on stainless steel and on coated carbon steel results in significant enhanced critical loads in the latter substrate (figure 5-9). This effect is mainly dominated by the better adhesion on coated carbon steel (see pictures in figure 5-9).

Table 5-5: Erichsen Single Scratch Test - summary of critical load results

  sample identification critical load [g]
CSM CSM - F/04/04 70
DOC DOC - 4016M_15,5µ 45,6
DOC - 4016M_3µ 43,8
DOC - 4016B_15,5µ 45,6
DOC - 4301M_15,5µ 59,7
Acelor Acelor auf BC > 350
B&K B&K Ref auf BC 240


Falling sand test

Clear Coats for Coated Carbon Steel V1 - V5

A volume of 20 liter of sand is necessary to erode approximately 50% of the top clearcoat layer. At this point the susceptibility for abrasive wear of clearcoats on coated carbon steel can be determined in figure 5-10 as follows:

V3 (Soft) > V1 (Standard) - V4 (Nano Particles) - V5 (Different Sub-layer) > V2 (Hard).

Detailed explanation of this behaviour is given before, generally speaking we find an increasing abrasion behaviour with increasing brittleness of the coating.

The testing series of coating V1 with increasing concentrations of nano particles (table 5-6) shows no abrasion at all, only a surface roughening is observed. This roughening decreases with increasing particle content. From the pronounced ageing behaviour of this series we conclude that curing was incomplete in this case which makes a direct comparison with the results from figure 5-10 impossible. However the ranking within the results of table 5-6 implies that the addition of nano particles in the given concentration range has no significant influence on the abrasion behaviour of the coating. This conclusion is also in accordance with the ranking found above {V1 (Standard) - V4 (Nano Particles)}.

On stainless steel substrates evaluation of the erosion-depth with lasertopography was impossible due to the highly reflective substrate.



Table 5-6: Falling Sand Test - Surface profile after 20 l of falling sand

Sample Basecoat Clearcoat 1 Clearcoat 2 Ra [µm] (arithmetic average of deviation of roughness-profile)
BC+1+1 black Standard 0.0% Nanoparticles 1,81
BC+1+2 black Standard 0.8% Nanoparticles 1,09
BC+1+3 black Standard 1.6% Nanoparticles 0,92
BC+1+4 black Standard 2.4% Nanoparticles 0,91

1.3. Evaluation of physical properties related to scratch resistance

Universal Hardness (micro-scale instrumented indentation)

Testing the experimental clearcoats from BASF (V1 - V5) with a Fischerscope H100, similar correlations as reported in [1] have been found between abrasion behaviour in the falling sand test and various parameters of the universal hardness measurements (figure 5-12).


In contrast to the results given above no clear correlation has been found between the wet marring test (Amtec-Test) and the same parameters of the universal hardness measurements (figure 5-13).

We attribute this behaviour to a different evaluation mode in both tests.

The measure of the falling sand test is the abrasion depth after the application of a certain volume of abrasive (usually 20 litre of silica sand) i.e. a direct measure for the abrasion of the coating. The correlation in figure 5-12 is quite good because the mechanism of coating degradation is obviously similar in both cases: the universal hardness and the abrasion depth are measures against penetration of the coating network structure.

On the other hand the term "marring" refers primarily to the optical degradation of a surface and consequently the loss of gloss is used as a measure with the Amtec marring test. From literature we know [12] that it's not only the depth of a scratch but also the cracking mode of the coating (plastic deformation or brittle fracture) that contributes to the degradation of the reflective properties. This additional information (type of fracture) is obviously not covered by the universal hardness measurement and therefore we find no clear correlation in the case of figure 5-13.

Universal hardness measurements on the "Nano-Coatings" revealed the following ageing behaviour of all samples: storage in a room climate leads to a pronounced increase in hardness (figure 5-14) and to a reduction in elasticity. Ageing phenomenons like this are known with coil coatings but the unusual high increase in hardness with time is a strong indication for incomplete curing.


Dynamic viscoelasticity measurements

The average values (from three measurements) of the Storage Modulus G' and of the Loss Tangent tan S (= G''/ G') for the Clearcoats V1 - V3 are given in figure 5-15 and table 5-7.

These results allow a differentiation between the clearcoats using the Storage Modulus G' in the low frequency regime or the maximum of the Loss Tangent tan S.S-S-

The latter is the ratio between the Loss Modulus G'' and Storage Modulus G' and can also be referred as the "relative plastic network fraction".


Table 5-7: Average values of the Loss Tangent tan for the BASF-Clearcoats V1-V3 at 40°C

  Single-Scratch 2g-Critical Load Falling Sand Amtec Max. tan delta
Clearcoat [g] [µm] after 20 l of Sand Residual 20°-Gloss  
V1 (Standard)
V2 (Hard)
V3 (Soft)

A comparison of these mechanical parameters of the coatings with the results of previous scratching tests (table 5-7) imply the following relationship:

A low maximum in tan S which can also be referred as a low plastic network fraction (i.e. a brittle coating) corresponds to more severe scratching than higher tanS (figure 5-16). This trend seems to be true for all types of scratch tests.


1.4. Comparative evaluation of scratch tests

To check the transferability of scratch test results, a round robin tests with samples from all partners has been performed in the 6th semester. Good agreement has been observed between the DOC scratch test and the AMTEC-test at Voestalpine provided that evaluation is done in both cases in the same manner (measurement of the 85°-residual gloss after scratch testing) - figure 5-17.

Looking at the results in detail it is evident that:

* scratch resistance of the favoured coating systems from CSM and DOC is at the same level for this type of degradation and

* the matt protective coating from Arcelor shows a polishing-effect after wet abrasive treatment.


1.5. Comparative evaluation of coating systems

Clearcoats for coated carbon steel

As anticipated previously the initial experimental clear coat formulation V1 supplied by BASF can be regarded already as an optimised protective coating for coated carbon steel. Variations in the coating formulation as described in table 5-1 resulted in an overall reduction of scratch resistance. A different approach - the enhancement of scratch resistance via addition of hard SiO2 nano particles - did not lead to an improved performance either: Due to the homogeneous distribution of particles both - formability and scratch resistance - where not affected at all. Looking at the results given in [5] the potential for a further improvement of scratch resistance coatings exists but in the case of coil coatings sufficient flexibility for post forming operations has to be considered which might be a limiting requirement in respect of scratch resistance.

2. New Coatings Studied at Arcelor

Apart from reference materials, other coatings have been studied: some have been found on the market, other have been developed by suppliers for contract partners. Arcelor has studied X different products found on the market or given by partners and it has studied also the effects of coating parameters on the coating properties by using a roll coating pilot.

Here are presented the products that had been studied and all the characterizations that had been made on them.

2.1. Materials

Other materials on the market

Arcelor has characterized 9 samples. 3 of them are co-laminated with a film and thermo-cured or UV- cured varnishes coat the others. The suppliers are: Plalam, Zanussi, Avesta, KTN, Liber paint and Von Roll-Isola. In the following table are presented details of these samples.

Table 5-8: Materials on the market

Supplier Substrate Coating
Grade Finish Coating Nature
Plalam 1,4016 Brushed Film Polyphtalate
Zanussi 1,4301   Varnish Epoxy
Avesta 1 1,4016 Brushed 2 layers film Polymetacrylate/PET
Avesta 2 1,4016 Brushed 2 layers film Polymetacrylate/PET
KTN 1,4301 Brushed Varnish Polyphtalate
Liber Paint 1 1,4301 Annealed and pickled PL4 (varnish) Acrilic/polyurethane
Liber Paint 2 1,4016 Bright PL1 (varnish) Acrilic/polyurethane
Von Roll-Isola 1 1,4301 Brushed GV412 (UV varnish ?
Von Roll-Isola 2 1,4301 Brushed GV415 (UV varnish ?

Other material supplied by partners

Arcelor, CSM and DOC/TKS have sent us several samples. Samples coming from DOC/TKS have been developed with collaboration of BASF and Henkel. All the products are UV-cured coatings. In the following table are summarized the samples characteristics:

Table 5-9: Materials supplied by partners

Supplier Substrate Coating
Grade Finish Coating Nature
BASF 1,4301 Brushed 2694 D Polyester
BASF 1,4016 Bright 2652 D Polyester
BASF 1,4301 Bright 2652 D Polyester
BASF 1,4301 Brushed 2814 D Polyester
BASF 1,4301 Brushed 2652 D Polyester
Henkel 1,4016 Brushed 4016M ?
Henkel 1,4016 Bright 4016B3 ?
Henkel 1,4301 Brushed 4301M ?
Henkel 1,4301 Bright 4301B3 ?
CSM 1,4301 Brushed   ?

Contribution of Arcelor - use of roll-coating pilot

Other samples have been supplied via Arcelor. First 2 samples comes from BASF : they are UV-cured coatings. And two other samples comes from Valspar: they are thermo-cured varnishes. In the following table are represented the samples information.

Table 5-10: Materials supplied by Arcelor

Supplier Substrate Coating
Grade Finish Coating Nature
BASF C-steel   3219 D Polyester
BASF C-steel   2652 D + Ximer Polyester
Valspar 1,4016 Brushed VE 822 S Epoxy
Valspar 1,4016 Brushed KCA 24 010 35 Polyester

With the last varnish (Valspar KCA 24 010 35), trials have been made on the Arcelor roll-coating pilot (see in Annex 2 the pilot construction). We studied the effect of coating parameters on coating properties. The studied parameters are: the coating speed, the distance between applicator and carrying rolls and the way of quenching.

2.2. Characterizations

All the samples collected for this study underwent several tests. Following are presented all the results and conclusions of these tests. A summary table is given in the table 5-17.

Surface analysis

IR analysis

8 coatings have been analysed by IR spectroscopy and by GDOES : BASF 2652 D, BASF 2694 D, BASF 2814 D, Plalam, Zanussi, Avesta 1, Avesta 2, KTN. Spectra are given in annex 3.

Table 5-11: FTIR analysis of several coatings

Coating Comments Main absorption Frequencies
BASF 2694 D Polyester Standard UV Curing Aromatics : 1631cm-1, 1511cm-1, 831cm-1
CH3-CH2 : 2955cm-1, 1464cm-1, 1391cm-1
Ester : 1735cm-1, 1249cm-1, 1050cm-1
BASF 2652 D Polyester UV Curing developed  for stainless steel Aromatics : 1608cm-1, 1511cm-1, 831cm-1
CH3-CH2 : 2933cm-1, 1464cm-1, 1388cm-1
Ester : 1735cm-1, 1249cm-1, 1048cm-1
BASF 2814 D Polyester Thermoset coating Aromatics : 1608cm-1, 1507cm-1, 727cm-1
CH3-CH2 : 2967cm-1, 1375cm-1
Ester : 1760cm-1, 1267cm-1, 1043cm-1
Plalam Polyphtalate film  (2 layers) Aromatics : 3055cm-1, 1615cm-1, 725cm-1
CH3-CH2 : 2964cm-1, 1456cm-1, 1372cm-1
Ester/Ether : 1716cm-1, 1239cm-1, 1093cm-1
Zanussi Epoxy varnish Aromatics : 3060cm-1, 1608cm-1, 1509cm-1
-OH : 3406cm-1
Epoxide : 3060cm-1, 938cm-1
Amide/Imide  :  1650cm-1,  1244cm-1,  1183cm-1,
Ether : 1041cm-1, 1244cm-1, 1183cm-1, 1085cm-1
Avesta 1 Polymethacrylate film  + PET (2 layers) Aromatics : 3055cm-1, 725cm-1
CH3-CH2 : 2967cm-1, 1456cm-1, 1374cm-1
Ester/Ether : 1718cm-1, 1242cm-1, 1094cm-1
Avesta 2 Polymethacrylate  film  + PET (2 layers Aromatics: 1616cm-1, 725cm-1
CH3-CH2 : 2962cm-1, 1455cm-1, 1371cm-1
Ester/Ether : 1733cm-1, 1245cm-1, 1100cm-1
KTN Polyphtalate varnish Aromatics : 3075cm-1, 1609cm-1, 728cm-1
CH3-CH2 : 2965cm-1, 1376cm-1
Ester/Ether : 1723cm-1, 1243cm-1, 1098cm-1

Some problems have been encountered for Plalam and Avesta samples because of their 2 layers composition. Except for Zanussi spectrum, all the other spectra are similar. It seems that all the coatings have the same base (polyester).

GDOES analysis

5 coatings have been analysed by IR spectroscopy and by GDOES : Plalam, Zanussi, Avesta 1, Avesta 2, KTN Spectra are given in ANNEX 4. The GDOES analysis gives indications on the composition and the thickness of the coatings.

The coatings are composed of carbon, oxygen and hydrogen in majority. But we can observe that some samples present a Siliceous or Nitrogen or Phosphor peak at the interface. It is probably due to a surface treatment before the coating.

A correlation between erosion time and thickness can tell us what is the coating thickness. They are summarized in the following table:

Table 5-12: Coating thickness evaluated by GDOES

Sample Plalam Zanussi Avesta 1 Avesta 2 KTN
Thickness 20 µm 3 µm 20 µm 20 µm 5 µm

Scratch resistance

The scratch resistance of an uncoated surface is 50g (load above which the scratch becomes visible).


Several coatings do not improve the scratch resistance of the surface. Film coatings and BASF 2652 D coating with Excimer treatment present the best scratch resistance. They reach the value of 400g. We must note that on a brush surface, we can observe a difference in scratch resistance in function of the scratch direction (in the brush direction or crossing the brush direction). With some coatings, we can also observe that the scratch is more visible on the bright substrate than on the brushed substrate.

Fingerprint perception

Fingerprint results are presented in the following figure:


Quite all the samples present an improvement of the fingerprint resistance. The perception of the fingerprint depends on the surface finish (a dull surface allow to improve the anti- fingerprint properties), the light incidence (results can be different with the observation angle). A lot of samples have a good behaviour with a quotation of 1. It concerns as well film coating and varnish coating (UV or thermo-cured varnishes). Best results are obtained by BASF 2652 D with Excimer treatment. Unfortunately, it cannot be compared to the other because of its really dull surface.

Vapour resistance

Only few samples present a good vapour resistance. The other samples present white stains more or less visible and/or non-adherence areas of the coating.


Anti soiling properties

Films and some varnishes (Valspar, KTN) present good anti-soiling properties. Regarding to BASF samples, we can note the importance of the substrate nature (grade and finish). The same varnish does not have the same behaviour with two different grades or two different finish. The surface under the coating has a real importance.


Draw forming tests

Draw forming tests have been realized on several samples:

- samples from roll coating pilot

- samples from BASF

- samples from Henkel

- samples from CSM Before being formed, a cross scratch has been drawn on some samples to study the effect of a damage on the ability to be formed.


* Arcelor samples: Tests have been made on quite all the samples prepared on the pilot. Samples of the speed study present a good behaviour during forming. Samples of he roll spacing study present non adhering areas and whitening of the coating.

* BASF samples:

The three samples present a very bad aspect with a whitening of the coating and non-adherence areas except sample 3219 D, which present only a dull aspect on the side.

* CSM sample:

As 3219 D, this sample is one the best. A dullish aspect appears on the side but there is no whitening and no non-adherence area.

* Henkel samples: Samples 4016M is the better one with only a dull aspect and some little white areas. The other samples present large non-adherence areas.

Effect of thickness on properties

Thickness has been measured for all the substrate than are magnetic. In the following table are summarized the results.


Thickness are very different: the range goes from 3 to 200um. The thicker coatings are the film ones. We can notice that below 15um, the samples keep the "metallic aspect". All the film coatings present a plastic aspect.

Thanks to the samples realized on the roll-coating pilot, we have studied the effect of thickness on fingerprint and scratch resistance. All the conditions are the same : same substrate, same varnish, same coating parameters, except the speed coating in the first case and except the rolls spacing in the second case.

In the table 5-16 are summarized the fingerprint perception and the scratch resistance in function of the coating thickness. These results show that the thickness has no effect on the fingerprint perception whereas it has an effect on the scratch resistance: the thinner the coating, the better the scratch resistance. It seems that until 6um the scratch resistance is relatively good and when the thickness is higher, the scratch resistance decrease rapidly.

Table 5-16: Effect of the coating thickness on the anti-fingerprint and anti-scratch properties

Speed coating (m/min) Thickness (µm) Fingerprint perception Scratch resistance:  load (g)
30 4,5 2 300
40 5,5 2 200
50 7 2 300
60 11 2 100


Way of quenching

4 ways of quenching have been studied: - by immersion in industrial water

- by immersion in deionised water

- by spraying on the coated surface with industrial water - by spraying on the uncoated surface with industrial water.

We saw that using industrial water directly on the coating can cause stains on the surface whether it is made by immersion or by spraying. Using deionised water by immersion can be a solution to avoid stains. Another way to avoid them is to spray water on the uncoated surface. The strip could be cooled without contact between water and coating.


2.3. Conclusions

Main conclusions are the following:

The analysis signal is mainly composed of C, O, and H. The coatings are organic products and FTIR confirms that they are polymers like PET, epoxy or polyester. We can see also picks of Si, N or P, which indicate a surface treatment before coating. The scratch resistance of an uncoated surface is 50g (by Clemen test, load above which the scratch is visible). The scratch resistance of the studied coating is really variable. Some coatings do not improve at all the scratch resistance whereas others hide or resist to scratch. We can note a correlation between scratch resistance and thickness: the thinner the coating, the better the scratch resistance. It seems that below 6um the scratch resistance is relatively good, upper the scratch resistance becomes rapidly as bad as the uncoated surface. Moreover, the surface finish is really important : a brushed surface allow to hide the scratches if they are made in the same direction than the brushing direction. All the coatings present a fingerprint resistance improvement. The perception of the fingerprint depends on the surface finish (a dull surface allow to improve the fingerprint resistance), the light incidence and the nature of the coating. The thickness does not seem to have an effect on fingerprint resistance. Only few samples present a good vapour resistance. Often samples present white stains more or less visible and/or non-adherence areas. Films and some tested varnishes have good anti-soiling properties. As for scratch resistance we can note an effect of the grade and the finish of the substrate. Draw forming tests have been realized on several samples. Most of them present whitening or non- adherence areas.

Quenching means have also been studied by the way of the roll coating pilot. Using an appropriate quenching allow to have a surface without stains. The better way of quenching is to cool without contact with the coated surface.

It is really difficult to choose only one product because each coating has its own qualities. As an example: there is no coating which has good anti-soiling properties and in the same time a good vapour resistance.

Films (Plalam or Avesta) seem to have good global properties but a drawback is the plastic aspect of this type of coating.

Another point has to be discussed: the fingerprint resistance. In this report we only consider the fingerprint perception. But the cleaning ability of the coating may also been considered. A coating can have a bad fingerprint perception but a good cleaning ability. This could also been an interesting property.

3. New Coatings Studied at Doc

3.1. Choice of coatings

In order to develop scratch and fingerprint resistant coatings, in a first screening phase the applicability of different coating systems was evaluated. This screening was done by BASF as a subcontractor of DOC.

The following lacquer types were considered: - thermal curing clear coat based on acrylates - thermal curing clear coat based on standard polyesters - thermal curing clear coat based on high molecular polyesters - UV curing clear coat based on acrylates

According to BASF, in all systems a good adjustment of hardness is combined with a reasonable flexibility. The thermal curing acrylates deliver the highest gloss range, followed by polyester systems. The UV curing system exhibit a medium gloss range. Whereas all lacquers showed good adhesion on organically precoated substrates, the thermal curing acrylate system and the standard polyester system adhered insufficiently on stainless steel. Thus, for further examinations on clear coats for stainless steels two systems were chosen: a thermal curing clear coat based on high molecular polyesters (identifier: CQ3-2814D) and a UV curing coat based on acrylates (identifier: CQ3-2652D). The two lacquers were applied on different stainless steel surfaces.

In the second phase of the project, many different coating companies were addressed for supplying clear coats which could be suitable as scratch resistant antifingerprint coatings for stainless steel surfaces.

The following different coating systems were regarded: - thermal curing organic coatings

- UV curing organic coatings

- inorganic sol-gel coatings

The tests on the different coating systems have been performed in several steps: firstly, different clear coats were tested and compared, and secondly, from the most promising systems optimised versions have been regarded in several optimisation cycles. The results presented in this report correspond to the best versions tested from each company. A list of the coatings to be discussed in this section is given in table 5-18. Due to the fact that in some cases the amount of sample material was not sufficient, not all tests could be performed with all variants.

Samples coated with "Novacoat 1000 UV" by Henkel were sent to the project partners for the round robin test. A list of these specimens is given in table 5-19. On the other hand, specimens from the project partners were tested in the round robin test (table 5-20).

The thickness of the coatings applied on stainless steels ranged from approximately 0.6 um to 15.5 um. Generally, the thicker the coating, the higher was its visibility. However, one demand of stainless steel industry is not to derogate the impression of the stainless steel surface. Regarding this point, the best optical appearance was reached by the coatings from Henkel (thickness: 3 um) and Nano-X.

Table 5-18: Coatings analysed at DOC

supplier sample code substrate coating
    grade finish code thickness type production
TKN Senocoil 1.4301 brushed Senocoil 2.5 µm thermal curing technical line
ANNP ANNP 1 1.4301 bright NMC 20 B 3.75 µm thermal curing laboratory
ANNP ANNP 2 1.4301 brushed NMC 20 B 0.88 µm thermal curing laboratory
ANNP ANNP 3 1.4301 brushed PVDF-A 4.35 µm thermal curing laboratory
ANNP ANNP 4 1.4301 brushed PVDF-A 5.13 µm thermal curing laboratory

Table 5-19: List of the specimens sent to the project partners for the round robin test

partner identifier
VASL 4016M_15.5
Arcelor 4016M_3
CSM 4016M_3