1. flame chemistry and oxidation mechanism

Transcription

1. FLAME CHEMISTRY AND OXIDATION MECHANISM FLAME CHEMISTRY
Chain/Radical reactions:
!  M ⇒ R
; Initiating step – k1
!  R+M ⇒ αR+M ; Chain Branching – k2
!  R+M ⇒ R+P ;
Propagating step – k3
!  R+M ⇒ P
;Terminating/Production – k4
!  R ⇒ P
;
Wall destruction – k5
M = reactants; P,P',P= reaction products
Multiplication factor αcrit = 1 + [(k4 + k5) / k2]
Brueckner meeting - Siegsdorf - Oct 9th., 2013
H2 – O2 COMBUSTION SYSTEM
Chain Branching ⇒ RADICAL POOL
H+O2 ⇒ OH+O;
OH+H2 ⇒ H+H2O;
O+H2 ⇒ OH+H;
O+H2O ⇒ 2OH.
Flame treatment is an industrial process used to improve wetting and adhesion
properties of polyolefin films (BOPP Bioriented Polypropylene; OPP – Oriented
Polypropylene; PE, PET, PS, etc.) and 3D components, such as automobile body
parts(bumpers, dashboards, headlights, etc.) and blow-molded bottles.
Polyolefin materials, and in particular PP (polypropylene) have many good
properties as: low cost; can be worked and shaped quite easily; can get good
mechanical properties, if properly worked; are very good electric insulators.
Anyway they are apolar on their surfaces, which are characterized by very poor
energies. This is the reason why they need to be treated, in order to make
possible their coating with inks, paints, adhesives, metal, and other materials
typically coupled with polyolefins, in industrial applications as flexible packaging
or automotive production.
Activation of polyolefin surfaces by flame is realized by means of two actions:
breaking of Carbon – Hydrogen links along the polymer surface, thanks to
flame high temperature, developed by the combustion process.
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 1 -
Theorical temperatures, reached using C1–C3 hydrocarbon combustibles,
are between 1700 °C and 1900 °C. As first step in the surface oxidation
process, hydrogen abstraction is far the more likely one, in comparison
with breaking of a C – C link along the macromolecular backbone.
Links C–C type are infact shielded, from radicals external attacks, by
means of hydrogen and metyl groups surrounding the molecule backbone
(cage effect). In addition, the mobility of radicals –C° type, coming from
an eventual scission of C–C links, is really reduced (because of radicals –C°
dimensions), so high is the probability of a recombination, after the
scission, between radicals –C° and °C-.
Insertion of oxygen based groups – contained inside the flame area - in
correspondence of broken links points, along the macromolecular chains.
The oxygen so transferred to the polymer surface acts as a bridge
between the polymer itself and the second material to be coupled with it.
In order for flames to propagate, their reaction kinetics must be fast; i.e. the
mixture must be explosive.
Premixed laminar flame - in which the fuel and the oxidizer are thoroughly
mixed prior to combustion - is produced by radical/chain reactions occurring in
a combustion system, formed by an oxidizer (generally air) and a combustible (in
a solid, liquid or gaseous state). Here will be considered just the last case, being
only gaseous combustibles
typically hydrocarbons (natural gas, methane,
propane, LPG, etc.) – used for polyolefins surface flame treatment .
Main steps of combustion radical reactions are the following:
(1)
(2)
(3)
(4)
k1
M → R ° ; chain initiation step
k2
αR °° + M ' ; chain branching step
R° + M →
R° + M !k3!
→ R° + P ; propagating step forming product
k4
R° + M →
P ; propagating step forming product
(5)
R ° → P " ; termination step forming product
Where:
M, M’ = reactant molecules
R° = different radicals species = OH, O2, O, HO2, H (RADICAL
POOL)
P, P’, P” = reaction products
α = MULTIPLICATION FACTOR
k1, k2, k3, k4, k5 = reaction rates
The chain initiation step (1) is endothermic and quite slow, it is not important in
determining the explosive condition, nor is it important in determining the
products formed.
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 2 Its duty is to provide the radical that develops the radical pool of reaction (2).
Radicals are chemicals species characterized by high reactivity and mobility.
The combustion system undergoes, then, to exothermic reactions and, if
sufficient heat is not removed from the system itself, it becomes self –
heating. Since the rate of reaction, and thus rate of heat release, will both
increase exponentially with temperature (Arrhenius mode), the reactions rapidly
runs away; that is, the system explodes – step (3) of the reaction: the
propagating step.
k + k5
When α > α CRIT = 1 + 4
, the explosion condition is reached by the
k2
combustion system and , if the mixture is inside its flammability limits (i.e. it
has a right composition) and within its explosive conditions (i.e. within right
pressure-temperature boundaries for a certain composition) the flame is
generated and can propagate. At this point flame is a subsonic combustion wave
(running at a speed around 40/45 cm/s in case of systems air/hydrocarbons).
According to the formula representing αCRIT, the higher is the rate of chain
branching step (k2) and the lower the rates of termination steps (k4, k5), the
more likely will be the explosion of the combustion system. Termination steps
are determined by radicals recombination (4) or their contact with cold
surfaces of reaction vessel (wall destruction) (5).
α has a value between 1 and 2, since during these steps, from one radical,
depending on the chain branching reaction (see below), one or two radicals can
be formed. Chain branching step produces a radical pool, according to the
following oxyhydrogenation reactions:
(6)
H° + O 2 → O ° + OH°
(7)
O°° + H2 → H° + OH°
(8)
H2 + OH° → H2 O + H°
(9)
O°° + H2 O → OH° + OH°
The sequence [Eqs. (6) – (9)] is of great importance in the oxidation reaction
mechanics of any hydrocarbon, in that it provides the essential chain branching
and propagating steps as well as the radical pool for fast reaction to occur.
It is this radical pool that develops the oxygen based groups inside the flame,
used to activate the polyolefin surface (2nd factor of action of the flame).
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 3 PP SURFACE FLAME OXIDATION MECHANISM
!  C-H link breaking vs. C-C link breaking;
!  OH > O > H >> HO2
RH+OH ⇒ R°+H2O;
Initiating step
RH+H ⇒ R°+H2
R°+OH ⇒ ROH;
R°+HO2 ⇒ ROOH;
Propagating step
R°+O2 ⇒ ROO;
R°+H2O2 ⇒ ROO+OH
R°+O ⇒ RO
R°+H ⇒ RH;
Terminating step
BOPP surface oxidation by flame is in Literature defined as a Free
Radical Degradation, beginning with radicals attack on tertiary carbon of
the macromolecular backbone.
The initial step in the oxidation of polymers by a flame is so passing
through polymer-radical formation by hydrogen abstraction. H
abstraction along macromolecular chain is far more likely to occur respect
to carbon-carbon link breaking, because of cage effect exerted by
methyl and hydrogen group towards C-C link and because of lack of
mobility of the C atoms, after the link breaking, so they form again the
link. Polymer-radical formation occurs primarily by reaction with the O
atoms, H atoms and OH radicals found in the flame. Thermal energy from
the flame could also generate polymer radicals (alkyl radicals R). Hydroxyl
OH radicals are considered from literature the ones playing most
important role in the film surface oxidation, since are the ones
characterized by highest concentration and highest reactivity (reaction
rate constant for OH radical is at least two order of magnitude higher
than the ones of the other radicals present in the flame, as molecular and
atomic oxygen radical or peroxyl radical).
H radicals will tend to compete with the OH and O species terminating
the oxidation step, so, basically H tends to compete to generate less
wettable PP surfaces.
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 4 2. FLAME vs. CORONA OXIDATION MECHANISMS CHEMICAL COMPOSITION OF A CORONA TREATED SURFACE
CH3
CH3
CH2-CH-CH2-CH-CH2
PP SURFACE
CORONA TREATMENT
CH3
CH3
CH2-C-CH2-CH-CH2
OXYGEN
CH3
CH3
CH2-C-CH2-C-CH2
OOH
CHEMICAL COMPOSITION OF CORONA TREATED SURFACES
CH3
CH3
CH2-C-CH2-C-CH2
OOH
β-scission reaction
C=O
O
CH3
CH2-C
OOH
C-OH
Low molecular
weight
C=O
O ⇒ alkoxy radicals RO° ⇒ LMWOM
When comparing flame treatment to corona treatment (that are the two
most commonly used pretreatment methods for improving polymers
surface adhesion), even if both based on oxidation of polymer surface,
following differences can be underlined:
When using flame, the depth of Oxygen incorporation in the
treated PP is between 5 and 10 nanometers versus a depth of about
50 nanometers in case of corona treatment. So with flame there is
a more extensive oxidation concentrated in a shallower surface
region, that results in an higher wettability. Moreover, the higher
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 5 

oxidation depth, when using corona, causes also delamination
phenomenon (weakening of oxidized layer), not observed when
treating PP by flame.
Most important, using flame treatment is not possible only to get
an higher and more concentrated oxygen quantity, but also a better
oxidation quality. Corona treated PP (and in general polymers as
PET, PE, and others) are characterized by the presence, on their
surface, of LMWOM. This presence is much higher when increasing
corona watt density applied to the material (literature refers this
as overtreatment). LMWOM stands for Low Molecular Weight
Oxidized Materials. These oxidized materials are produced on
corona treated PP surface because of C-C links breaking (this
reaction is known in literature as β-scission reaction) and
consequent weight lowering of this oxidized materials. LMWOM are
water soluble or other solvent (as acetone or methanol) soluble and
generally more weakly anchored to the PP surface. Atomic oxygen
radical is the precursor of LMWOM formation, passing through
alcoxy radicals (RO) formation. Literature states that when an hot
flame impinges the cold (at about 400 K) PP surface, many radicals
present in the flame (that is produced by a radical reaction) are
destroyed. This destruction doesn’t affect OH radicals
concentration – since they are far the more present radicals in the
flame, but there is a big impact on atomic oxygen radicals, that
strongly diminish their concentration. The following formation of
alcoxy radicals – from which LMWOM develop – is so negligible in
case of flame; with flame LMWOM could eventually form (as an
alternative way respect to the one represented by RO radicals)
starting from carboxilate/peroxy groups (COO), but these groups
scission to form alkoxy groups is too slow to account for a
significant formation amount of LMWOM. Moreover formation of
COO groups can be kept under control with flame, working with an
air/gas ratio not too gas lean (so not too oxygen rich). The same
phenomenon doesn’t occur with corona treatment, where alcoxy
radicals, that are present in a large extent, are involved up to 50%
in the β-scission reaction types, so forming LMWOM. In a PP flame
treated surface, instead IMWOM (Intermediate Molecular Weight
Oxidized Material) are present, that are bigger than LMWOM,
with higher weight, not soluble to water and other polar solvents
and so more strongly anchored to the PP surface. This fundamental
difference between corona and flame treatments, along with the
fact that corona produces a deeper treatment than on a web treated
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 6 by flame, is the cause for an higher surface energy of a flame treated
film than a corona treated one. Among web producers there is the
folk to measure the wettability after treatment on the web,
through the specification ASTM D2578. This test is very simple to
perform, very fast also and can give to the operator immediately
the idea if his machine is correctly working. By the way ASTM D
2578 doesn’t tell everything about the web surface after
treatment. Two films having same ASTM D2578 dyne level can
have a huge difference in terms of surface energy. And what really
cares in terms of processability of the web after the treatment is
the surface energy it has, not the wettability. A corona treated
web can show a good wettability, thanks to the presence of
oxidized material on its surface (LMWOM), but these materials are
weakly tied to the film surface, so they are easily taken away from
the surface itself, according to typical delamination phenomenon.
This means that using corona you get a good fresh (on line)
treatment, but then you get a poor treatment for applications as
printing, laminating and metallising and you get a strong decay of
treatment (aging phenomenon) few weeks after the treatment.
CORONA
SURFACE
What
is TREATMENT
staining
? OXIDATION
oxygen level vs Power
14
Threshold for formation of LMWOM in litterature = 8,3 Wmin/m²
12
Oxygen level %
10
8
Anchored oxygen level = 4,8%
6
4
Threshold for formation of LMWOM= 9,8 Wmin/m²
2
0
0
5
10
15
20
25
30
35
40
Power density (Wmin/m²)
Flame treatment is characterized by an higher anchored oxidation type
of the polymer surface, than the one possible treating the web by corona,
as measured by ESCA (XPS–X ray photoelectron spectroscopy) technique.
Using corona treatment is possible to get, as shown on the above slide an
oxygen level % measured by ESCA in the order of 14 and higher,
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 7 increasing the treater watt density; but just a minor amount - about 5%
is the anchored one; the rest is given by LMWOM.
In the case of flame treatment all the oxidized material is well anchored
on the film surface.
This corona issue is underlined by a simple test: water washing of corona
and flame treated samples. Surface chemistry of corona treated film is
strongly affected by water washing, with a significant loss of surface
oxidation and a noticeable increase in the advancing contact angle of
water. Corona treated surfaces have an O/C ratio, at ESCA , up to 0,23,
becoming, after water washing, 0,08. In the case of flame O/C ratio is
0,18 before washing and still 0,18 after washing. This is a clear evidence
of the presence of water soluble LMWOM on the corona treated PP, while
flame treated PP has no detectable LMWOM, since the O/C ratio does
not vary with the water washing.
PP SURFACE FLAME OXIDATION MECHANISM
!  O/C RATIO
!  IMWOM vs. LMWOM
INCREASED SURFACE ENERGY
!  Chain Scission behaviour
!  Agingbehaviour
!  Metallizing barrier effect & Metal Bond Strength
Basing on this basic difference in surface chemistry, and, at the end of
the day, in surface energy after flame treatment and after corona
treatment, much different is also the film behaviour in its performances,
Presence of LMWOM first of all can explain high treatment decay
observed in corona treated surfaces respect to flame treated ones.
Treatment decay or aging depends much also on film composition and
additives presence inside it, but, considering same type of film, corona
treated will always decay faster than flame treated, because of the
presence of the above reported LMWOM.
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 8 Metallised film after corona will present poor performances both in
terms of barrier to water vapour and to oxygen if compared to the ones
of flame treatment.
Also metal adhesion after flame will be at least 30% higher after flame
than after corona and also much more lasting with the time. This last
difference is well underlined by REXAM tests, from which it is possible
to see that starting metal adhesion to substrate is much lower and also
much faster dropping when film is corona treated than one it is flame
treated. This is confirmed by the fact that if flame treated film is then
corona treated (for example for refreshing treatment, as in use in many
converters facilities) REXAM test will give poor adhesion of the metal if
compared to the adhesion coming from just flame treated film. This
because corona is introducing LMWOM materials on the flame treated
surface, modifying its chemistry.
FLAME vs. CORONA SURFACE ADHESION
CORONA TREATED – SLOW PEELING
FLAME TREATED – SLOW PEELING
CORONA TREATED – FAST PEELING
FLAME TREATED – FAST PEELING
FLAME vs. CORONA SURFACE ADHESION
CORONA TREATED
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 9 FLAME vs. CORONA SURFACE ADHESION
FLAME TREATED
For printing applications particularly significant to explain the difference
in surface adhesion between corona and flame treatments is the results
of an experimentation run in esseCI lab. Different samples of the same
film, both corona and flame treated were analysed. The corona and flame
treated samples presented same treatment level, according to ASTM
D2578 specification.
On the two samples series (flame and corona treated) were then spread
different types of SUN CHEMICAL inks (Demachem, Multilam),
nitrocellulose based inks, modified using polyurethanes resins, by means
of a metering rod (wire size 06), according to TAPPI T552pm-92
specification. The samples were then dried, cured in an oven equipped
with a forced air circulating system, at 70°C for 10 seconds, as per the
ink producer recommendations. After the samples preparation, these
were used in two kinds of tests:
1) manual peeling test: according to the inks producer specifications
was performed both slow and fast peeling, using an ASTM tape,
45° inclined respect to the sample surface;
2) automatic peeling test: using a tensile strength testing machine
(dynamometer) – Zwick Roell type – in order to measure the
adhesion strength of the samples. The ASTM tape has been fixed
at one clamp of the dynamometer, and the sample on the other
clamp.
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 10 The inks used in the tests are generally used with a diluent (ethil acetate)
and an adhesion promoter. In the case of the test here reported no
adhesion promoter has been used, to underline the film treated surface
strength and energy, coming just from the surface treatment (corona or
flame), so to check just the treatment contribute to adhesion.
Absolutely macroscopic is the difference in behaviour between corona
treated and flame treated surfaces, both in the manual and in the
automatic peeling test, in terms of ink surface removed by the tape, and
in terms of bond strength (in case of flame treated ink/film bond
strength keeps around 400g; with corona treated samples well lower than
200g). FLAME vs. CORONA SURFACE ADHESION
CORONA TREATED
FLAME TREATED
In the above slide the samples (film + tape) on the top were coming after
corona treatment, while the samples on the bottom after flame
treatment.
The figure evidences how in the corona treated film, ink has moved from
the film to the tape, while in flame treated film it has been the tape glue
to move from the tape to the ink, thanks to film high adhesion values.
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 11 3. FLAME TREATER COMPONENTS AND LAST DEVELOPMENTS Brueckner meeting - Siegsdorf - Oct 9th., 2013
The 2 above slides represent a bottom flame treater system.
Flame treatment station is actually fully integrated, both from a
mechanical, electrical and electronical point of view in Brueckner PRS,
after a continuous info exchange between BMS and esseCI technical
offices. In the flame treaters, top or bottom, operator side and drive
side are actually irrelevant. Next step could be to have also top or bottom
position irrelevant in terms of flame treater design.
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 12 Burner positioning resolution is today equal to 0.15mm, so half of the
minimum variation in gap relevant in terms of treatment level.
Also from a point of view of electrical/electronical interface the flame
treatment station is actually completely integrated in the BMS line,
thanks to last version signal exchange protocol. Flame treatment unit can
be completely controlled not only locally, but also from the remote (from
the remote it can be also switched on and switched off).
Bottom flame treater configuration is the one to be used when
metallisable film has to be treated. If metallisable film is treated on the
top side, so the side in touch with the chill roll, surface defects as halos,
spots appear on the web after metallisation. This has nothing to do with
the barrier properties (water vapour and oxygen).
On the water bath side web is rougher than on the chill roll side.
Roughness, does play an important role, during the metallization phase,
since the lower it is (web surface in contact with the chill roll) and the
better the Aluminum copies, transfers the surface itself, amplifying more
all surface defects, working as an upsetting of the surface.
This is the reason why it is suggested to treat by bottom treater
metallisable film.
The above slide shows new standard exhaust system for bottom flame
treaters. Exhaust system plays a fundamental role in flame treatment,
for two main reasons: first of all it removes the produced heat (about
50% of the whole combustion energy is going to the exhausts), so avoiding
to stress film surface and components in the treatment area; secondly,
exhaust system removes used air coming from combustion allowing air
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 13 renewal in the flame treatment area. These are the reasons why last
standard in exhaust system is based on the concept to have the lateral
hoods very close to the film treated surface, so to the treater roll.
Hoods are overturnable for maintenance needs, manually, as standard and,
when requested, also pneumatically, through suitable cylinders.
9690 ±2
824
660
9290
920
200
100
2036
185
185
2391
650
Exhaust Duct
660x650x9000
870.5
930
425
870.5 ±1
1184
B
O
O
47
5
60
0
12°
BURNER FACE LENGTH = 8800 (+2x50mm SIDE PLATE)
920
650
ROLL FACE LENGTH = 9200
(*) Water Outlet
Flange UNI DN 50
1300
(*) Water Inlet
Flange UNI DN 50
FILM FLOW
(*) Mixture Inlet
Flange UNI DN 125
230
230
370
290
750
290
280
DRIVE SIDE
280
OPERATOR SIDE
1744
826
230
775
280
120
240
280
A
15
Num. 2+2 M20x40
C
4785
4785
4845
4845
Detail A
1:10
C.L.
20 ±0.1
520
240
120
Burner 406 Type
30
225
450 ±0.5
180
280
+0.2
+0.1
180
+0.2
+0.1
4.6
2
29 +0.1
+0.1
39 0
100 ±0.2
170
141
(*) = COUNTER FLANGES INCLUDED
IN SELLERS SUPPLY
310
15.5
1.5
287
+0.2
Detail B
1:10
97.9 ±0.1
30.5 ±0.1
40
102 ±0.2
230
14
32.5
280
185 ±0.5
18
35
Num. 2 Ø6H12
Denominazione
Denomination
Progetto
Project
Detail C
1:10
Cliente/Comm.
FLAME TREATER LAYOUT
FLAME TREATER PLANT
Materiale
Material
Disegnatore
Drwg.
SUPPLY EXTENSION
By Customer
By esse C.I. s.r.l.
esseCI
s.r.l.
Societa' Costruzioni Industriali
BRUECKNER GSU / 5553
Customer/Job
The information shown on this drawing is confidential and must not be copied reproduced or comunicated
to a third party wholly or in part without Our written consent
Rev.
Gioia A.
De Divitiis M.
Data
Date
Rugosità Gen.
Roughness
Formato
Form
Scala
Scale
Contr.
Check
03.09.2013
3.2
Toll.Gen
IT9
A1 File
Name
Foglio
1:20 Sheet
5553.lo.1.0.dft
1
di
of
1
Disegno Num.
Drwg. No.
5553.LO.1.0
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 14 Brueckner meeting - Siegsdorf - Oct 9th., 2013
The above three slides represent top burner system, including the
exhaust system for the top installation.
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 15 100
2000
2100
Flange
UNI DN125
Mixture Outlet
Cable
Inlet
400
1000
Mixture Outlet
Optional
Cable
Inlet
1000
464
225
154
586
892
600
Flange
UNI DN50
Gas Inlet
Num. 2 Flanges
UNI DN40
Cooling Water
Inlet / Outlet
Denominazione
Denomination
Progetto
Project
Cliente/Comm.
TYPICAL FOR INSTALLATION
MIXTURE GENERATOR TYPE 036.900/1200
Disegnatore
Drwg.
892
413
esseCI
s.r.l.
Societa' Costruzioni Industriali
Materiale
Material
Rev.
Gioia A.
De Divitiis M.
Data
Date
Rugosità Gen.
Roughness
Formato
08/04/2013
3.2
Toll.Gen
A3 File
Name
Form
Scala
Foglio
1:20 Sheet
Scale
Contr.
Check
esse C.I. s.r.l.
Customer/Job
The information shown on this drawing is confidential and must not be copied reproduced or comunicated
to a third party wholly or in part without Our written consent
IT9
036.900/1200.dft
1
di
of
1
Disegno Num.
Drwg. No.
036.900/1200
In the above three slides is reported new mixture generator design.
New mixture generator design has been already implemented starting
from 2 years ago; it allows complete maintenance access from the front
and behind and not from the sides, so that it can be placed aside the
auxiliary board in the PRS area. The generator is equipped with its own
operator panel, for collecting info on working variables and on system
alarms. One very important improvement respect to the past is the
introduction af an air dehumidifier system. It is given by a chilled
water/combustion air heat exchanger that works using about 5m3/h of
chilled water to remove about 30g of water per each kg of the
combustion air flow. The results, as represented in the above
psychrometric chart are the following: without the dehumidifier two
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 16 possible working point for the combustion air are A1 and A2 points;
considering 90% as bypass factor (so 90% of the combustion air passing
through the heat exchanger and the 10% not passing through), if C is the
point representing water condition, points A1 and A2 will move
respectively to points B1 and B2, new air combustion working points. So
looking to the diagram it is evident how the effect of the dehumidifier is
to dampen combustion air conditions dispersion and so to get higher
constancy in flame treatment working conditions.
MIXTURE COMPOSITION
φ = EQUIVALENCE
RATIO
λ = LAMBDA =
=1/φ
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 17 JCS 122 Oxygen
analyzer
λ = LAMBDA
(A/G)USED/(A/G)STOICHIOMETRIC
λ >1 mixture lean;
λ < 1 mixture rich;
λ = 1 mixture stoich.
Mixture composition, that is air to gas ratio is most important parameter
in flame treatment technology; it represents quality of the energy given
to the film by flame. Flame has to be a stocihiometric or close to
stoichiometric one, in order to achieve best yield from treatment.
In esseCI flame treaters traditionally mixture composition is controlled
through a calorimetric system, the Jonoflame. Recently esseCI, in order
to improve the control on this parameter has also introduced oxygen
analysis, that monitors air to gas ratio parameter as controlled by
Jonoflame. In this way it is possible to get a tight check on the
parameter as well as to get an absolute reference for the air to gas ratio
parameter (the lambda value).
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 18 4. FLAME PROCESS LAST DEVELOPMENTS DDBS
DIFFERENTIATED DOUBLE BURNER SYSTEM
The Energy Saving project, firstly implemented on January 2011 on
ExxonMobil Chemical Europe Sud facility (Line # 603) confirmed the
target to save gas, so energy, on the actually installed L#603 flame
treater, using a different flame treater configuration. In the pre-project
condition (Standard Double Burner Configuration - SDBS), at a max speed
value of 470 m/min, a total mixture flow of 1350/1400m3 per working
hour was used. An energy saving higher than 40% of this energy has been
obtained from the start-up of the new flame treater configuration, i.e.
Differentiated Double Burner System (DDBS). This means a money
saving, per year and at italian natural gas costs, higher than € 120000,00.
Moreover, thanks to new design for the exhaust hoods and for the
insulating properties of new exhaust main duct, it is possible to recover a
good percentage of the combustion energy contained in the exhausts
(that represents roughly 50% of the total combustion energy), that, in
SDBS is instead wasted in the room.
In the pre-project situation the PRS was equipped with a Standard
Double Burner System (SDBS), bottom position mounted. So the system
was equipped with two burners, 206 type, mounting grids no.7, 22 mm
wide. The flame treater was completed by exhaust system, composed by
3 exhaust hoods, one in central position and the other two at the edges
of the two burners. With this configuration, the two burners work
simultaneously, so at the same time.
After the modification the PRS is now equipped with a Differentiated
Double Burner System (DDBS), bottom position mounted. In the DDBS
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 19 the two burners never work at the same time, they are excluding each
other; if I work with burner no.1, I will not use burner no.2 and vice versa.
DDBS burner no.2, so the downstream one, is equipped with a ribbon, no.7
but 34mm wide, in order to cope with higher production speeds (450470m/min). Burner no.1 is instead equipped with a narrower grid, that can
be used when running at lower speeds (300m/min), for thicker products.
DDBS exhaust system is conceived in order to suck just hot air, so,
through motorized exhaust valves system, the exhaust side
corresponding to the burner not used is excluded, in order to have
available, at the exhaust fan outlet, in form of exhausts, energy at higher
quality level, that can be reused for warming up refreshing air used for
TDO or for the WIP area.
WET & DRY PROCESS
BOPP FILM 2015 - Berlin – June 24th., 2015
Wet&Dry process has been recently developed by esseCI to get a better
exchange of heat when treating CPP film.
What can happen infact when treating CPP by flame is formation of
wrinkles when the materiali s passing under the flame. Infact thermal
deformation of the film produced by the heat make the film overlapping,
since it cannot slide over the roll surface. Using suitable nozzles it is
possible to apply and to keep present over treater roll surface, in form of
atomized water a thin layer of water, that works as a cushion, allowing
the film to slide over roll surface, so avoiding its overlapping and the
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 20 following wrinkle formation. Also heat exchange between roll surface and
film is significantly increased.
Film surfaces are then clearly dried up through suitable air knifes to have
a film completely dry rewinded in the mother roll, so the name WET &
DRY used for this process.
Thanks to this new process development it is possible to apply flame
benefits on CPP, for example on the one for metallisation (widely used in
the chinese market) without producing thermal deformations over it.
esseCI enriched flame Process
!  Enriched flame;
!  Film surface modified in line, through a low cost
process at industrial speeds, to deliver high barrier
metallized film;
!  large food company based in Dallas very interested
in this technology esseCI is developing.
We have a tradition in enriching flame by third components, recently we
have focused over an third added element that allows to modify, in line,
film surface, through a low cost process applied at industrial speeds
(higher than 500mpm), to deliver high barrier metallised film.
The whole effect is as applying a primer on the BOPP surface while flame
treating it.
A large food company is cooperating with esseCI in developing this
technology.
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 21 5. SUMMARIZING… Summarizing…
!  Flame treatment technology can warrant higher quality on
film treated surfaces (higher surface energy and higher
adhesion);
!  Flame particularly useful in treating films for tape and for
metallization. Also used with good results on sealable and
cavitated webs (but with necessary higher attention on
process conditions);
!  Flame process is a mature one but still with very high
improvement potential;
!  Flame treatment system actually improved in its typical point
of weakness and fully electronically and mechanically
integrated in BMS lines;
!  Best 5 layers extrusion line, the one where you can
produce and treat with best results all film types, should
be equipped both with corona and flame treater (flame
in bottom position).
Actually flame treatment technology is a mature one, but still
characterized by high improvements margin, as last process developments
are demonstrating. Moreover esseCI has recently focused on what have
been traditionally considered weak points as influence of room conditions
on flame and as mixture composition control/monitoring system.
Flame treater system is actually fully integrated in a Brueckner line, both
from a mechanical and electrical/electronical point of view, thanks to a
continuous information exchange between Brueckner and esseCI technical
offices.
There is no machine able to do everything.
Starting from this consideration it is anyway out of any question that
flame treatment can warrant higher quality on film treated surfaces,
respect to corona, thanks to its higher surface adhesion and surface
energy. This is particularly true in applications as:
•
•
•
metallisation: where flame treated surfaces, compared to corona,
allow significantly increased barriers to water vapour (WVTR) and
to oxygen (OTR), as well as improved and longer lasting adhesion of
metal to the film, as widely demonstrated by REXAM tests;
printing: where flame treated surfaces allow, compared to corona,
to get better printing quality, improved toner adhesion and
improved visual quality, as well as improved rub-off and abrasion
resistance in flexo, rotogravure and digital printing applications;
tapes films.
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 22 When treating heat sealable film flame treater presents a narrower
working range and, depending on process conditions and film type
sealability on treated/treated sides (TR/TR or external/external) can be
not as good as when corona is used.
Concerning this point it is important anyway to underline the following:
in the flexible packaging industry treated/treated or EXT/EXT
sealability is requested only in uncommon applications (as overwrapping
just for certain kind of biscuits and tobacco films) or to form bellows. In
these cases it is not requested an high sealing strength, since the
resistance of the package is given by the paper pack, wrapped by the
sealing. So in these cases flame can warrant requested sealing strength
also on TR/TR sides.
On all the other flexible packaging applications FIN SEAL (sealing is on
untreated/untreated, that is internal/internal side) , is always used when
Horizontal Form Fill Seal (HFFS) machines are run (for example with
biscuits or long pasta as spaghetti).
In the case of snacks or short pasta used is LAP SEAL with Vertical Form
Fill Seal (VFFS) machines, where the seal is on treated/untreated sides,
so external/internal. In FIN SEAL and LAP SEAL cases, that are the
far majority in flexible packaging applications, as it is possible to see
visiting a supermarket, flame can warrant better results than corona,
since it doesn’t affect, despite corona, the untreated side of the
film. In the case of chips are used VFFS machines, but with laminates
structures, where printed/treated sides are placed internally, so they do
not interfere with sealability.
In not so common application also a lacquer layer is used on the sides to
be sealed, in this case, again, no issues on sealability coming from flame
treatment.
So, flame treatment issues with sealable films is a false problem, in
the name of which makes no sense to renounce to the higher
performances of flame treament over corona treatment as above
described.
This is the reason why on an high performances 5 layer BOPP extrusion
line flame treatment has to be present, in bottom position (corona on the
top), for getting best results on all produced type films.
Stefano Mancinelli
Stefano Mancinelli ‐ esseCI srl Sales & Process Manager 23

1. flame chemistry and oxidation mechanism

Transcription

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