BOPP2015 presentation comments

Stefano Mancinelli -‐ esseCI srl Sales & Process Manager 1

1. FLAME CHEMISTRY AND OXIDATION MECHANISM

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.

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.



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) °⎯⎯→⎯ R M k1 ; chain initiation step (2) 'k2 R MMR +⎯→⎯+ °°° α ; chain branching step (3) R° +M k3! →! R° +P ; propagating step forming product (4) PMR k4⎯→⎯+° ; propagating step forming product (5) "P R →° ; 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.


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.

When 2

54CRIT k

kk1αα

++=> , the explosion condition is reached by the

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) °° +→+° OHOOH 2 (7) °°°° +→+ OHHHO 2 (8) °° +→+ HOHOHH 2

2 (9) °°°° +→+ OHOHOHO 2 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).


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.

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



2. FLAME vs. CORONA OXIDATION MECHANISMS

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:

q 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

CH3 CH3 PP SURFACE CH2-CH-CH2-CH-CH2

CH3 CH3

CH2-C-CH2-CH-CH2

CH2-C-CH2-C-CH2

CH3 CH3

OOH

OXYGEN

CORONA TREATMENT

CHEMICAL COMPOSITION OF A CORONA TREATED SURFACE

CHEMICAL COMPOSITION OF CORONA TREATED SURFACES

CH2-C-CH2-C-CH2

CH3 CH3

OOH

β-scission reaction

CH2-C

OOH

CH3

O ⇒ alkoxy radicals RO° ⇒ LMWOM

Low molecular weight

C-OH

C=O

C=O O


oxidation depth, when using corona, causes also delamination phenomenon (weakening of oxidized layer), not observed when treating PP by flame.

q 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


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.

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,

What is staining ? oxygen level vs Power

0

2

4

6

8

10

12

14

0 5 10 15 20 25 30 35 40

Power density (Wmin/m²)

Oxyg

en le

vel %

Threshold for formation of LMWOM in litterature = 8,3 Wmin/m²

Anchored oxygen level = 4,8%

Threshold for formation of LMWOM= 9,8 Wmin/m²

CORONA TREATMENT SURFACE OXIDATION


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.

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.

PP SURFACE FLAME OXIDATION MECHANISM

! O/C RATIO !  IMWOM vs. LMWOM

INCREASED SURFACE ENERGY

!  Chain Scission behaviour

!  �Aging��behaviour

!  Metallizing barrier effect & Metal Bond Strength



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



CORONA 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.



FLAME TREATED


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).

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.



CORONA TREATED

FLAME TREATED


3. FLAME TREATER COMPONENTS AND LAST DEVELOPMENTS

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.




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



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.



s.r.l.Societa' Costruzioni IndustrialiesseCI

The information shown on this drawing is confidential and must not be copied reproduced or comunicatedto a third party wholly or in part without Our written consent

MaterialeMaterial

Customer/JobCliente/Comm.

Rugosità Gen.Roughness

FormFormato File

NameScalaScale Sheet

Foglio diof

DenominationDenominazione

ProgettoProject

Rev.DisegnatoreDrwg.

CheckContr.

DataDate

Toll.Gen

De Divitiis M.

Gioia A.A1

1:20

IT93.2

1 1

Drwg. No.Disegno Num.

FLAME TREATER LAYOUTFLAME TREATER PLANT

5553.LO.1.003.09.2013

BRUECKNER GSU / 5553

5553.lo.1.0.dft

A

Detail A1:10

B

Detail B1:10

180

170

100 ±0.2

39 +0.10

102±0.2

14

30.5±0.1

40

1.5

29 +0.2+0.1

97.9±0.12+0.2

+0.1

4.6

+0.2

+0.1

20 ±0.1

15.5

Burner 406 Type

FILM FLOW

8800BURNER FACE LENGTH = (+2x50mm SIDE PLATE)

9200ROLL FACE LENGTH =

2391

870.5±1

185

425

O600

O475

826 920

9690 ±2

9290

870.5

185

2036

650

660

100

9301184

650

1300

15

240 120

280

18

225

450 ±0.5

180

30

120

240

520

Num. 2+2 M20x40

Num. 2 Ø6H12

185±0.5

35

32.5

230

750

290

280

280

230

4785

4845

4785

4845

C.L.

280

370

290

280

1744

C

Detail C1:10

310141287

230

280

775

230

12°

OPERATOR SIDEDRIVE SIDE

(*) Mixture InletFlange UNI DN 125

(*) Water OutletFlange UNI DN 50

(*) Water InletFlange UNI DN 50

By esse C.I. s.r.l.

By Customer

SUPPLY EXTENSION

(*) = COUNTER FLANGES INCLUDEDIN SELLERS SUPPLY

Exhaust Duct660x650x9000

824 920 200


The above three slides represent top burner system, including the exhaust system for the top installation.




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


s.r.l.Societa' Costruzioni IndustrialiesseCI

The information shown on this drawing is confidential and must not be copied reproduced or comunicatedto a third party wholly or in part without Our written consent

MaterialeMaterial

Customer/JobCliente/Comm.

Rugosità Gen.Roughness

FormFormato File

NameScalaScale Sheet

Foglio diof

DenominationDenominazione

ProgettoProject

Rev.DisegnatoreDrwg.

CheckContr.

DataDate

Toll.Gen

De Divitiis M.

Gioia A.A3

1:20

IT93.2

1 1

Drwg. No.Disegno Num.

TYPICAL FOR INSTALLATIONMIXTURE GENERATOR TYPE 036.900/1200

036.900/120008/04/2013

esse C.I. s.r.l.

036.900/1200.dft

100

2100

1000400 1000 600

2000

892 225

892 413

154586 464

Num. 2 FlangesUNI DN40Cooling WaterInlet / Outlet

FlangeUNI DN125Mixture Outlet Flange

UNI DN50Gas Inlet

CableInlet

CableInlet

Mixture OutletOptional



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.


φ = EQUIVALENCE

RATIO

MIXTURE COMPOSITION

λ = LAMBDA =

= 1 / φ



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).


λ = LAMBDA

(A/G)USED/(A/G)STOICHIOMETRIC

λ >1 mixture lean; λ < 1 mixture rich;

λ = 1 mixture stoich.

JCS 122 Oxygen analyzer


4. FLAME PROCESS LAST DEVELOPMENTS

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

DDBS DIFFERENTIATED DOUBLE BURNER SYSTEM



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 (450- 470m/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 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

WET & DRY PROCESS

BOPP FILM 2015 - Berlin – June 24th., 2015


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.

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.

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.



5. SUMMARIZING…

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.

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).



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

Documents

BOPP2015 presentation comments