FLAME TREATMENT vs CORONA TREATMENT

SURFACE FLAME TREATMENT

TO IMPROVE

COATING ADHESION 

IN PLASTIC MATERIALS, PAPER AND ALUMINIUM

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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 :

  • Food packaging

  • Film for electronic components  (capacitors etc.)

  • Tapes production

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.

SOME APPLICATIONS OF FLAME TREATMENT

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:

  • Flame treatment

  • Atmospheric plasma treatment

  • Vacuum Plasma treatment 

  • Corona treatment

  • Cleaning with acid

  • Priming

 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

 

 

trattamento cornoa vs trattamento a fiamm

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 βcleavage). 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.

WETTABILITY 

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). T
he main weakness of the corona treated film is the DELAMINATION : decay treatment (aging phenomenon) in a few weeks.

 

ENERGY SURFACE

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.


 

PEELING TEST

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

We used:

  • 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.

ExxonMobil,

the market leader BOPP

produce BOPP coex for metallization,

using only flame treatment for surface activation of the film.
Why?

ExxonMobil prefers the flame treatment because

it guarantees the barrier effect.

effetto barriera del film metallizzato coex

ADHESION SURFACE

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.

 

energia superficiale film : trattamento corona vs trattamento a fiamma

 

technical articles :

Flame vs Corona treatment

The fundamentals of flame treatment process and its main parameters

 

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FLAME TREATMENT vs CORONA TREATMENT ultima modifica: 2014-03-19T11:00:51+00:00 da Ufficio Stampa