Technical Bulletin Surface Treatment - ENCRES DUBUIT

June 2014
Light Fastness
TECHNICAL BULLETIN
Headquarter, Mitry Mory, FRANCE
Tel : 01 64 67 41 60
Fax : 01 64 67 41 89
email : [email protected]
web : www.edubuit.fr
Dubuit Paint, BRASIL
Tel : +55 12 36 44 15 50
Fax : +55 12 36 44 15 50
email : [email protected]
web : www.dubuit.com.br
Encres Dubuit Shanghai, CHINA
Tel : +86 21 6722 3661
Fax : +86 21 6722 3668
email : [email protected]
web : encresdubuit.com.cn
Dubuit Of America, USA
Tel : +1 630 894 95 00
Fax : +1 630 894 96 00
email : [email protected]
Tintas Dubuit, SPAIN
Tel : +34 934 770 990
Fax : +34 934 771 398
email : [email protected]
Surface Treatment
The Encres Dubuit company, ink manufacturer, is worldwide renowned for the quality,
the reliability and the relevance of its products.
We meet our clients’ needs in 4 areas:
• Industry
• New technologies
• Graphic
• Label
using 3 printing processes:
• Screen printing
• Ink jet
• Pad printing
And manufacturing on 3 continents (factories in France, Spain, China and Brazil).
Encres Dubuit is especially well positioned on the UV ink market, whether it’s for
screen or digital printing.
Encres Dubuit has been complying with ISO 9001 Standards since 1994.
Encres Dubuit Pune, INDIA
Publivenor, BELGIUM
Tel : +91 98 23 71 09 00
email : [email protected]
web : www.edubuit.fr
Tel : +32 2 363 09 20
Fax : +32 2 361 89 59
email : [email protected]
web : www.publivenor.be
Introduction
Contents :
Introduction
1
Surface Tension /
Energy
1
Plastics
Intro
2
Plastics
Flame
2
Plastics
Corona and plasma
2
Glass&metals
Intro
3
Glass&metals
Hardener
3
Glass
Primer
3
Glass
Flame&silane
3
Fig 2. Encres Dubuit sells
Dyne Pens,
the easiest way to control
your substrate!
In the ink industry, the major
technical demand, whatever the
industry, is to have a good adhesion of the ink on the substrate.
For every application, in every
country, the prints are tape tested
24h hours after the printing process.
Good adhesion is dependent on
many parameters:
- the ink must be suitable for the
application
- traces of pollution like oily
products, dust or condensation
should be avoided
- the ink must be well dried
(please refer to our Technical
Data Sheets for more details).
- the nature of the substrate and
its quality
- the surface treatment
Through this Technical Bulletin,
Encres Dubuit wish to help you
to understand the necessity of
surface treatment for some kind
of substrates: polyolefins plastics,
glass and metals, and also give
you some tips to be able to control and improve the quality of
your surface treatment.
One of the first technical concept
to understand is the surface tension and surface energy.
The surface energy of a substrate,
measured by dyne/cm shows the
wettability of a substrate to be
printed. (fig 1)
Surface Tension / Energy
The surface energy of a substrate
is defined as the sum of all the
intermolecular forces that are on
the surface of a substrate.
High energy results in attraction
forces to another material, low
energy results in the repulsion of
another material.
The surface tension of a liquid
(the ink) can be defined as the
resistance of the liquid to deform
or break.
When a substrate has a high surface energy, (ie it tends to attract), and an ink has a low surface tension, (ie has little resistance to deformation), a good
wetting of the ink on the substrate
is produced, as well as a good
adhesion.
As a general rule, we found that a
good wetting of an ink is possible
if the Surface Energy is higher
than 40 dynes per cm.
The most accurate way to control
the surface energy is to use tools
like Dyne Pens (fig 2 and 3)
If you don’t have any, you can
immerse the treated object into
water, then take it out and observe if the water comes to drops
or remain as a uniform layer of
water.
untreated
Fig.1. example of bad wettability
Surface treatment aims
to have good ink
ADHESION on specific
substrates
treated
Fig.3. dyne pen on untreated and treated subs-
Surface Treatment
Plastics and surface treatment
Material
Name
Surface
energy
mN/m
Polytetrafluorethylene
PTFE
18
Polypropylene
Polyethylene
29
31
PP
PE
Polymethylmethacrylate
PMMA
Polystyrene
PS
33...44
33...35
Polycarbonate
40...46
PC
Polyvinylchloride PVC
38...41
Polyethylene terephtalate
PETP
41 ...45
Polyamide 11
PA
43
Fig. 4. surface energy of various plastics
Fig 7. flame machine for cylindrical objects manufactured by Machine Dubuit.
Main plastics have chemically
inert and nonporous surfaces
with low surface tensions. This
makes them non receptive to
bonding with inks, adhesives
and coatings.
Polyethylene and polypropylene for example have very low
surface energy (fig 4).
Pretreatment is essential.
Depending on the plastic shape,
and the final application, there are
4 different standard ways for
treating them:
- Flame: perfect for 3D objects
with curved and uneven surfaces.
Glass, metals and surface treatment
- Corona or plasma: perfect for
flat objects and thin sheets with
low temperature resistance.
- Primers wiped with a soft
cloth for low cost solution.
Flame treatment
Flame treatment uses a mixture
of air and gas such as butane,
propane or methane.
The flame has 2 actions:
1. Burning contaminents such
as oil, grease and mold release
agents.
2. Oxidizing the surface to increase the surface energy and
wettability.
The result is a clean substrate
with chemical functionalities as
hydroxyl on its surface.
Tips for improving flame
treatment:
1.Check the distance to the
flame. The object must be in
the « Luminous zone », the
hottest flame region. (fig.5)
2. Control the mixture ratio
gas / air which depends on the
gas you use. (fig.6)
3. Manage the dwell time: the
slower the better, but avoid to
damage the substrate.
4. Adjust the air flow so the
flame’s shape is straight.
5. Check if there is any pollution into the capillary tubes by
placing a white paper in front of
the air/gas mixture without
starting the fire.
Then check the treatment with
Dyne pen!
Fig 5.. object’s best distance to the flame
Mixing rao air/gas
Air
Gas
Methane
10
1
Propane
25
1
Butane
32
1
Fig.6. mixture ratio air/gas
well as for large and flat substrates like plastic sheets. The
main difference between Corona and plasma is that plasma
treats only 1 face, while corona
must treat 2 faces , which
means that you must place elec-
trodes on both sides of the surface. This is easy for plastic
sheets, but much more difficult
when it comes to containers.
1. clean the substrate of all
contamination with alcohol and
dry thoroughly
nutes, depending on the nature
of the adhesion promoter.
Primers
Fig 8. plasma electrode
Page 2
Adhesion promoters or primers
are solvent based, UV or waterborne liquids, that can provide
good adhesion and superior
resistance properties to difficult
substrates, such as PP, PE and
TPO. The most widely used
primers are Chlorinated Polyolofins (CPO) based on an
aromatic
solvent.
The
procedure for applying primers
are:
2. apply 2.5 to 5 µm of primer
by spraying or wiping with soft
cloth
3.ink can be printed immediately after the primer coating has dried, that is to say
within few seconds to few mi-
ink molecules, which is not the
case, as inks are organic molecules. This is why in order to
adhere on inorganic substrates
(glass, metals) with the organic
ink, we must add adhesion promoters or coupling agents between inorganic materials (glass,
minerals, and metals) and organic polymers of the ink.
(thermosets,
thermoplastics,
and elastomers) such as organofunctional silanes (fig.9).
of AM9192 into solvent based
inks and 4% in UV inks. Please
note that after adding hardener,
the pot life is reduced as the ink
viscosity in increasing over
time. (please refer to our Technical Data Sheets for more
details). The use of hardener is
the most widely used way of
improving adhesion as well as
chemical and mechanical resistance.
silane chemistry. The procedure
for applying primers are:
3.ink can be printed immediatly
after the primer coating has
dried that is to say within few
seconds to few minutes, depending on the nature of the adhesion promoter.
There are 3 ways of introducing
these adhesion promoters:
1. add organofunctional silanes
hardener into the ink
2. wiped a silane-based primer
on the surface
3. use flame + silicate treatment
Solutions 1 and 2 can be mixed.
Fig 9. organofunctional silane
Hardeners
Corona and plasma
Corona and plasma treatment
use a high voltage discharge to
change the surface energy of
the substrate. We prefer these
high-voltage treatment to the
flame when the substrate cannot
resist to high temperature, as
Glass and metals are inorganic
materials. It means they are not
carbon based as organic materials, like plastics for example.
Surface energy is usually high
enough to allow the ink to have
good wettability (290 dynes/cm
for glass, around 500 dynes/cm
for aluminum), but tto have a
good ink adhesion, a support
must have intermolecular and
chemical interactions with the
Be aware that this kind of products are usually considered as
harmful and need specific handling and storage.
The easiest way to add silane
based compounds is to add
hardener directly into the ink.
Those hardener are available
for both solvent and UV based
inks, but the % to add to the ink
is different. For Dubuit inks, we
recommend the addition of 10%
AM9192
Fig 10. Encres Dubuit supplies hardeners and primers
Primers
When the process does not
allow to add any hardener in the
ink that will increase the ink
viscosity, the best solution is to
add an adhesion promoter or
primer. This is the case for
digital inks, it is impossible to
add any hardener into the ink
cartridges. Those adhesion
promoters are also based on the
1. clean the substrate of all
contamination with alcohol and
dry thoroughly
2. apply 2.5 to 5 µm of primer
by spraying or wiping with soft
cloth
Inorganic substrates as
glass and metals need
adhesion promoters based on silicon chemistry
to bond to organic coatings, such as inks.
Flame (Pyrosil®) treatment
Many glass containers are cold
end coated (CEC) in order to
improve the scratch resistance
and obtain a transport protection. This means that they have a
wax, usually Polyethylene, coated on the surface.
Therefore, to achieve good ink
adhesion onto glass, flaming the
glass surface is necessary in
order to destroy the wax.
In addition, a gas mixture of
silicon-compounds is added in
order to obtain silicon dioxides
agglutinate who form a thin
layer (20 - 40 nm) that bounds
the ink. (fig.11)
How to identify silicon particles?
A flame containing a silicon
compound can be identified by
its reddish colour.
The layer of silicon dioxide
deposited is absolutely transparent but you can identify its rough
touch feeling.
The main suppliers of these gas
mixtures is Pyrosil®.
This treatment is traditionally
widely used for glass containers
but can also be used for metallic
containers (fig.12)
Fig 12. adhesion improvement on metal
while using Pyrosil flame treatment
Fig 11. flame with particles of silicate
Page 3