IN PLASTIC MATERIALS, PAPER AND ALUMINIUM
FLAME TREATMENT VS CORONA TREATMENT
EsseCI flame treaters borns during period ’60 to ’70.
Several quality inconveniences on “CORONA” treatment,
was rised up, by generating problems, as poor adhesion on :
lacquering, inking, coating, metallizing, gluing,
so, by rising doubts, on the reliability about “CORONA” technology,
used on industrial process of POYPROPYLENE web production.
In that time, PP web was designated to :
Film for electronic components (capacitors etc.)
Plastic films have low surface tensions, so they have non-receptive anchor substrate such as printing inks, adhesives and coatings.
Polyethylene and polypropylene have lowest surface energy. They are subjected to SURFACE TREATMENTS to improve their adhesion characteristics.
Surface treatment can also be used to improve adhesion capacity of all plastic materials as well as of some non-plastic materials: aluminum and paper or metallized .
It increases surface tension to prepare them for subsequent processing printing, laminating, coating adhesive, etc.
Surface treatment principal processes are:
Atmospheric plasma treatment
Vacuum Plasma treatment
Cleaning with acid
CORONA TREATMENT AND FLAME TREATMENT COMPARISON
A corona treatment station consists of a high-frequency generator, a step-up transformer connected to a fixed electrode rectilinear and electrically grounded by a roller, coated by an insulating material. In the air gap between the film and the electrode that is established that regime of discharges effluvium called “crown effect” that leads to activation of the film. The treatment is normally carried out on the lines of extrusion of the film, but its effectiveness tends to decrease over time; therefore, we find the corona treatment also at the entrance of the rotary printing and coating lines and laminating, to freshen the material.
A flame treatment station is designed individually on specific needs, built and installed at the headquarters of the client.
To observe the different components of a treatment station click: flame treatment station
DEPTH OXIDATION IN TREATED POLYPROPYLENE
flame treatment: 5 e 10 nanometers
corona treatment: 50 nanometers
Measuring by ESCA technique (XPS – X-ray photoelectron spectroscopy) the surface of a flame treated film, it is possible to read an O / C ratio higher than when using the corona treatment.
So with flame there is a more extensive oxidation concentrated in a shallower surface reginon, that results in an higher wettability.
Delamination is a weakening phenomena of oxidized layer that only with corona treatment happens.
OXYGEN RADICALS ON OXIDIZED SURFACE
Corona treated polypropylene and in general all polymers PET, PE, and others are characterized by the presence, on their surface, of LMWOM (acronym of oxidized materials of low molecular weight). These oxidized materials are produced by the rupture of CC bonds (in literature is known as β–cleavage). The LMWOM are soluble with water or acetone or methanol because weakly bound to the surface PP.
In a flame treated surface of POLYPROPYLENE instead, there are radicals IMWOM (oxidized material of good molecular weight), which are larger than the LMWOM. The IMWOM have greater weight, are not soluble in water and in other polar solvents because they are strongly bound to the surface PP.
Film wettability is measured through the specific ASTM D2578. This test is very simple and very quick to perform but incomplete. Two films that have the same level dyne ASTM D2578 can have a big difference in terms of surface energy.
In terms of workability after the treatment, the surface energy is more important than the wettability.
A corona treated films show a good wettability, thanks to the presence of oxidized material on its surface (LMWOM). The main weakness of the corona treated film is the DELAMINATION : decay treatment (aging phenomenon) in a few weeks.
The energy surface of a film flame treated is greater than a film corona treated.
PRINTING APPLICATION: THE COLORING
The “coloring“ is a fault which consists in the presence of ink in NO PRINTED areas . The coloration appears on the cylinder, after several minutes of printing. The coloration is a phenomenon produced by delamination LMWOM film surface corona treated. The coloring wasn’t observed on the film flame treated.
We analyzed two samples of the same film:
corona treated film
flame treated film
According to specification ASTM D2578 they had the same level of treatment: 40 dynes / cm
Sun Chemical inks (Demachem, Blades), nitrocellulose, modified USED ando resins of polyurethanes
metering rod (wire size 06), according to the specification TAPPI: T552pm- 92
In our tests we did not use any adhesion promoter, to highlight the real differences of treatment in terms of energy and surface resistance.
The samples were then dried in an oven equipped with a system of forced air circulation, at 70 ° C for 10 seconds, according to the recommendations of manufacturers of inks. After preparation of the samples, these have been used two types of tests:
1) manual peeling test
according to the specifications of the producers inks, the test was performed using a tape ASTM, 45 ° inclined with respect to the sample surface.
2) automatic peeling test
to measure the adhesion strength of the samples we used a dynamometer – type Zwick Roell – ASTM tape was attached to a terminal of the dynamometer and the sample on the other terminal.
Behavior difference between surface flame treated and corona treated is absolutely macroscopic both in manual peeling test and in automatic one.
Only flame treatment technology
can ensure ink coating on film surface
without using any adhesion promoter
METALLIZATION and BARRIER EFFECT
FILM BOPP COEX for applications metallization is a typical application of a flame treatment.
the market leader BOPP,
produce BOPP coex for metallization,
using only flame treatment for surface activation of the film.
ExxonMobil prefers the flame treatment because
it guarantees the barrier effect.
Using flame treatment you can get a higher bond strength lamination and better adhesion of metal. The flame treated surface has higher energy content, compared to the corona treated.
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FLAME TREATMENT vs CORONA TREATMENT ultima modifica: 2014-03-19T11:00:51+00:00 da