Expert Voices
Testing and measuring
Learing from mistakes
Experience and specifications play an important role for a perfect coatings
Detecting failures and interpreting them correctly, is the first step to avoid them in the future and to guarantee
a good application. Different parameters as well as experience are necessary for this. As a consequence the
failure ranges from low interest to hughe dramatic impact. Derrick Twene from DSM and Steven Houghton, GKN
Aerospace, think both that the right mixing provides failures from the upscale to production and that the different technologies drives the performance of a coating as well.
Derrick Twene
Global Industry Manager
Flooring and Construction
DSM Coating Resins
Waalwijk, The Netherlands
Derrick.Twene@dsm.com
1
Which measurements do you use to detect failures in coating/raw material production?
When we produce a resin/polymer we as standard measure and monitor the viscosity, pH, particle size, solid content
and general appearance in the wet and dry state applied
on glass. Additional measurements of quality such as, acid
value free monomer content to name a few are in place
and depend heavily on the type of resin/polymer produced.
In all cases, we as standard take and store a representative
sample for future reference. With respect to our raw materials used as the building blocks, quality safe guards such
as molecular weight, reactivity, colour and appearance to
name few are in place in close cooperation with the supplier, QC and our analytical department. A final check for us
would be to produce a lacquer or paint and look and measure the chemical and mechanical properties of the coating.
In most cases a significant amount of defects such as poor
wetting, haze in the film, low gloss, and particles can be
visually picked up and acted on. The extent and type of
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European Coatings Journal
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10 l 2012
“In most cases a significant amount of
defects can be visually picked up”
the testing depends greatly on the end application of the
coating.
2product
Please share your experiences: after the first
test you recognise that the product doesn’t
show its performance. What kind of failures could
have occurred and how can they be solved?
The development of a new product would involve customer
or customers to validate the concept. Meaning, if problems
or failures occur in the first production it is possible to work
together quickly to find the route cause which can often
be a simple case of additive package used in formulating.
However, it is safe to say that the scale up from a lab to a
plant setup does involve a number steps which depending
on the technology and how specialised the polymer architecture can be very challenging. For instance, differences
in the size relation of the reactor compared to the mixer,
results in different shear forces the volume and the heat
distribution can be different, as can the speed of dosing.
This requires a specialised team of process engineers working closely with the research department to ensure accurate
translation irrespective of scale or equipment used. In a lot
of instances the failure mechanism itself usually indicates
the origin of the problem.
Our first approach would logically be to determine the differences between the lab setup (where the correct properties were obtained) with the pilot plant and the production plant setup. Checks such as batches of raw materials
used and quality of these would be cross referenced often
leading to a reproduction on lab and production scale with
subsequent internal and customer testing for validation
of the desired performances. If needed, the new product
would be altered to boost performance. In some instances the coating formulation must be altered to maximize
performance. Because of this feedback during product
development and our customer intimacy we are usually
very confident that, when commercialized, the new product will perform to customer expectations.
í
European Coatings J OURNAL10 l 2012 www.european-coatings.com
Expert Voices
Testing and measuring
“The mixing process is quite complicated and specifications
are produced which define parameters”
1
Which measurements do you use to detect failures in coating/raw material production?
As we supply bespoke products, they require bespoke
coatings to meet stringent customer requirements, and
so we find ourselves formulating our own coatings to
this end.
To meet such requirements, our coatings typically contain
a multitude of resins and additives, some of which would
usually be seen as mutually incompatible, and so more
often than not, the mixing process is quite complicated
and specifications are produced for our operators which
define parameters such as: checking of base materials as
supplied; environment of mixing room; mixing equipment
to use; material addition sequence; mixing speeds; mixing times; standing times; filtration equipment and process; and other offline processes sometimes also including
synthesis. Many of the coated products we supply to our
customers are optical products, requiring a high degree
of transparency and minimum optical distortion. Failures
at the mixing stage can be defined as falling under three
main causal areas although in reality, these areas subdivide into many more. These are: quality of materials as
supplied, eg. viscosity, solubility and reactivity aspects;
inadequately defined specification (early stages in new
product launch where operator does not fully understand
certain requirements from the draft specification and clarification is required); and specification not followed correctly (not only human error, but other elements such as
wrong environmental conditions).
Steven Houghton
Chief Chemist
GKN Aerospace
Luton, UK
dr_steven_houghton@yahoo.co.uk
ness in coating due to inadequate mixing (sometimes
seen in mix as well as on product); surface defects – either from inadequately mixed additive or wrong viscosity due to under/over mixing; or air bubbles due to overmixing or too-short stand time, as seen in mix as well
as on product. In extreme cases, adhesion issues may
also occur, but this is usually solved at the development
stage, where the mixing process is gradually defined.
Failures observed by the customer and as we formulate
our own coatings to coat our own products, I would define operations here as the customer, would typically be
those described above, and additionally the presence
and effect of foreign particulates (as the product is coated in a clean room) and any errors in processing of the
coating. The problem solving approach begins with assessment of the defect visual and sometimes by microscopy or spectrophotometer, and of the extensive documentation which travels with the product which records
all elements of the process), to determine key areas in
the process where an error may have occurred. If it is
determined that all elements of the process have been
correctly followed, and the defect can be reproduced offline, the tolerance of the parameter which can reproduce the defect when manipulated will be tightened.
í
2product
Please share your experiences: after the first
test you recognise that the product doesn’t
show its performance. What kind of failures could
have occurred and how can they be solved?
An inadequately processed coating mix generally manifests itself in three ways for our optical products: hazi-
“Accelerated Testing”
Ulrich Schulz
www.european-coatings.com/books
www.european-coatings.com
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l 2012 European Coatings Journal
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European Coatings Journal
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