The Effects of Flame Treatment on Clay Coated Paperboard in Extrusion Coating Mikko Tuominen, M.Sc. (Eng) and Jurkka Kuusipalo, Professor Tampere University of Technology Roland Bothor, Ph.D. SIG Combibloc Systems GmbH and Timo Lankinen, M.Sc. (Eng) Stora Enso Packaging Boards ABSTRACT The target was to study the adhesion between extrusion coated PE-LD and clay coated paperboard, where flame and corona were used as pretreatments. The focus was to find out the influence of following flame treatment parameters: gas rate, air-gas ratio, burner vs. substrate distance. Test trials were carried out in extrusion coating pilot lines at TUT (Tampere University of Technology), Finland and BP Köln GmbH in Dormagen, Germany. The results showed how strongly the flame treatment parameters are affecting adhesion and what are the optimum value ranges and combination of parameters. The effect of flame and corona treatments on adhesion was established to be equal, whereas the mechanisms seem to be partly different. Based on the whole series of trials, a model to predict adhesion was created, and it will be tested at production lines in the near future. INTRODUCTION The key factor in the lamination of paperboard with polyethylene is efficiency. In a modern production line the efficiency is obtained mainly by increasing the line speed. However, the quality of product must be maintained. This trend sets high demands especially for adhesion. The flame treatment parameters must be optimized in order to achieve the best possible pretreatment result. The optimum value ranges and combination of gas rate, air-gas ratio, burner vs. substrate distance and line speed can be discovered by trials. Sufficient adhesion between different surfaces is often difficult to achieve, because of low surface energy, incompatibility, chemical inertness, or the presence of contaminants and weak boundary layers. Surface treatments are used to change the chemical composition, increase the surface energy, modify the crystalline morphology and surface topography, or remove the contaminants and weak boundary layers. Many processes have been developed to modify substrate surfaces, including chemical solvents, corona treatments, plasma treatments, heat and flame treatments. These processes generally cause physical or chemical changes in a thin surface layer without affecting the bulk properties. On the other hand surface treatment of substrate does not ensure automatically acceptable adhesion, e.g. polyolefins require also adequate oxidation during extrusion coating. The topography of substrate surface has also an effect on the wetting and adhesion properties. Rougher surface provides more area for wetting and mechanical interlocking, which leads to better adhesion. In smoother surface e.g. pigment coated paper or paperboard acceptable adhesion is more difficult to achieve [1–5]. Flame treatment is basically a simple method to improve adhesion between substrate and polymer in extrusion coating. Substrate is exposed to direct flame which modifies the surface of substrate. In the combustion reaction different thermally activated atoms and molecules, e.g. oxygen ions and atoms, as well as free electrons are formed. These react with the surface of substrate composing carbonyl, carboxyl and hydroxyl groups among others. Consequently polarity and oxidation of the surface increases and leads into improved wetting and adhesion. The flame treatment clearly improves adhesion on surfaces of paperboard or polymer. However, the mechanism behind this adhesion improvement is not necessarily the same. In the surface of polymer occurs crosslinking, breaking of the long-chain molecules and some micro roughening. In the surface of paperboard micro roughening as well as surface activation takes place. Additionally, the flame treatment removes possible contaminants or sticking fibers from the surface of substrate [1–7]. For obtaining the best possible flame treatment results burner design and flame treatment parameters must be controlled and optimized. The geometry of flame is mainly controlled by ribbon or drilled ports of burner nozzle. Consistent and uniform flame treatment must be ensured for long periods of time. This is mostly done by using flame analyzer or in-line mass flow measurement, depending on the manufacturer of equipment [8–10]. The most important flame treatment parameters are:

• The gas rate (output/volume) • The air-gas ratio • The burner vs. substrate distance • The line speed (exposure time)

The gas rate is simply the flow rate of air-gas mixture fed to the burner. It defines the physical expansion and thermal capacity of flame but is not affecting to the flame composition or temperature. Lifting of gas rate eventually destroys or over-oxidizes the surface depending on substrate. Over-oxidation can generate weak boundary layer which leads to adhesion failure [3–4, 9] The air-gas ratio: The combustion reaction of flame treatment is a rapid exothermic reaction between fuel gas and oxygen of air. The most used gases in flame treatment are natural gas/methane (CH4) and propane (C4H10). For a stoichiometric combustion the air-gas ratio for natural gas is approximately 10:1 and for propane 24:1. Common practice is that at least stoichiometric ratio or even excess oxygen is used in combustion reaction for obtaining more “oxidizing” flame treatment [1–4, 6–10]. The burner vs. substrate distance: The structure of a single flame can be divided into three conical shaped zones. In the heating zone (1st) the mixture of air and gas is heated into its ignition temperature. In the primary combustion zone (2nd) actual combustion begins and is seen as a deep blue, shining cone (Figure 1). Just above the primary combustion zone flame has its highest temperature, in which ion activity and concentration are in maximum levels. This “active” area is used for the surface treatment. In the secondary combustion zone (3rd) temperature decreases as well as treatment efficiency [8–9].

Figure 1. Paperboard is flame treated. The primary combustion zone is seen as a deep blue, shining cone. The line speed mainly determines the exposure time in which substrate is under the influence of flame treatment. Sufficient contact time between flame and substrate is required in order to achieve adequate treatment level. For accomplishing this in high line speed multiple burner heads can be used. The best possible pretreatment result is obtained when the value ranges and optimum combination of flame treatment parameters are established. These optimum parameter settings are influenced also by the substrate. EXPERIMENTAL Considerable amount of information was obtained in the research work. In this paper the main points of research work are presented, along with some of the most interesting results. To begin with, the results demonstrated how strongly the flame treatment parameters are affecting adhesion and what are the optimum value ranges and combinations of parameters. Experimental designing (DoE) was used as a help in the planning of trials and in the evaluating and presenting results. Therefore, it was possible to reduce the total number of test points in each test trial, without losing the information. A model for adhesion was also created. The model should not be complicated, basically the parameter settings are entered into the model and an adhesion value is obtained. In addition, the effects of flame and corona treatments were compared. Test trials were carried out at TUT [11] and BP, Dormagen. In the trials at TUT single and double clay coated paperboard was extrusion coated with 15 g/m² of PE-LD at extruder temperature of 300°C. In addition, the effects of flame and corona treatments were compared. The idea was that, the effects of parameters are examined in the trials at TUT, and subsequently the obtained results are confirmed in the trial at BP. This way the effects of larger pilot line and higher line speeds could be seen. The line speeds were up to 500 m/min in the

trial at BP, which equals roughly with production line speeds. Flame treatment equipment of Hill GmbH was used in all the trials and propane as treatment gas.

Figure 2. The extrusion coating pilot line in TUT [11]. Adhesion was the main interest in the research work. Adhesion was measured using 90°-peel test. As a part of the research work many other measurements were also made e.g. X-ray Photoelectron Spectroscopy (XPS), surface energy (contact angle), roughness of surface, Scanning Electron Microscopy (SEM) and Atomic Force Microscope (AFM). Some of the results are presented in this paper. RESULTS AND DISCUSSION

Scaled and centered coefficients for adhesion

0

1

2

3

Gas Rate Ratio Distance Line Speed Board Grade

Figure 3. The effects of flame treatment parameters on adhesion. Gas rate, air-gas ratio (Ratio), burner vs. substrate distance (Distance), line speed and board grade (single vs. double coated). Figure 3 shows how strongly different flame treatment parameters are affecting adhesion. The coefficients are scaled and centered so they do not have any adhesion unit. However, the degree of effect of gas rate, air-gas ratio, burner vs. substrate distance, line speed and board grade on adhesion can definitely be seen. The research work also showed existence of interactions between the parameters e.g. in higher line speeds the effects of parameters on adhesion are stronger than in lower line speeds. The interactions are not included in Figure 3. The

gas rate has minor effect on adhesion compared to other parameters. The air-gas ratio and burner vs. substrate distance has moderate effect on adhesion. The line speed has the strongest effect on adhesion. The board grade has a clear effect on adhesion, so a smooth double clay coated paperboard has negative influence on adhesion compared to rougher single clay coated. The surface of single coated paperboard provides larger area for wetting and adhesion forming.

0,5

1

1,5

Adhesion (N/15m

m)

Air-Gas Ratio Distance Gas Rate Line Speed

Relative ranges of flame treatment parameters

Figure 4. The adhesion as a function of value ranges of air-gas ratio, burner vs. substrate distance (Distance), gas rate and line speed. In Figure 4 the adhesion is presented as a function of value ranges of flame treatment parameters. The increase of gas rate improves adhesion, whereas the increase of line speed impairs adhesion. There are significant optimum value ranges of the air-gas ratio and burner vs. substrate distance.

The Optimum Combination of Burnervs. Substrate Distance and Air-Gas Ratio

Adhesion

Distance Air-Gas RatioOptimum observed

TheoreticalOptimum

Figure 5. The combination of burner vs. substrate distance (distance) and air-gas ratio for an optimised adhesion. The optimum combination of air-gas ratio and burner vs. substrate distance is presented as a calculated model of adhesion in Figure 5. On the left axis is the burner vs. substrate distance and on the right the air-gas ratio. The best adhesion area is illustrated as red colour in Figure 5.

1,5

2

Adhesion (N/15m

m)

Distance Air-Gas Ratio Line Speed

Relative Ranges of Flame Parameters (Trials at BP Line)

Figure 6. The adhesion as a function of value ranges of burner vs. substrate distance (Distance), air-gas ratio and line speed. The optimum values showed in the Figure 4 and 5 are dependent on the line speed so they were tested also at higher line speeds, up to 500 m/min at BP. The results showed quite similar effects and optimum ranges as the previous trials at TUT. Due to mechanical reasons a small burner vs. substrate distance like at the TUT trials could not be adjusted at the BP line. So the optimum value already appeared at the minimum distance as shown in Figure 6. The optimum combination of parameters is also influenced by the materials used and the equipment, so for each material or machine the optimum combination has to be established individually. The gas rate, has only a minor effect compared to the other parameters. Increasing the gas rate does not improve adhesion essentially but it does define the consumption of gas, which is targeted to be at its minimum in production lines. This makes the role of other flame treatment parameters even more important. The air-gas ratio has a major effect on adhesion. In the previous studies [1–4, 6–10] an oxidizing flame has been preferred, on the contrary in this work the optimum value range was founded to be below the stoichiometric ratio, in the gas rich area. This results most likely from the excess air from surroundings or from the air moving with substrate. Therefore even if the settings of flame are not oxidizing the treatment might be. In a way, air-gas ratio is the most important flame treatment parameter. The burner vs. substrate distance affects strongly adhesion and oxidation of paperboard. The optimum distance between the burner and substrate is in the “active” zone (Figure 1), where temperature and ion activity is the highest. The optimum value range is affected strongly by the treatment level and so by the gas rate and line speed. The line speed has the strongest influence on adhesion. On the other hand, the influence on oxidation and surface energy of the paperboard is just moderate. The line speed has interactions with the other parameters i.e. the effects of other parameters depend on the line speed. The trials at BP with high line speeds up to 500 m/min showed that the obtained results from the trials at TUT are comparable regarding the main effects and optimum of parameters. The board grade, the considerable difference between single and double clay coated paperboard proves the importance of substrate, from adhesion point of view at least. The rougher surface of single clay coated paperboard leads to better adhesion, by providing more area for wetting and adhesion bonding between the polymer and paperboard. Figures 7 and 8 show the effects of flame and corona treatment on adhesion. Figure 9 shows surface energy and oxidation (XPS) measurements of paperboard. The flame and corona treatment coefficients are based on a long test trial series, whereas the XPS and surface energy measurement are made from the selected representative test points.

Scaled and centered coefficient for adhesion

0

5

0

5

0

5

Flame Corona Flame+Corona Figure 7. The effects of flame and corona treatment on adhesion.

0,5

1

1,5Adhesion (N/15m

m)

Air Rate of Flame Corona Power

Relative Ranges of Flame and Corona Treatment

Figure 8. The adhesion as a function of flame and corona treatment.

Oxidation (XPS) and surface energy measurements of paperboard

+15,0 +11,3

+7,2+14,4

+23,0

+11,8

+66,8

+38,5

15

25

35

45

55

65

75

No treatment Flame Corona Flame+Corona

C oxidised(%)

Surfaceenergy (%)

Polarcomponent(%)

+6,6

Figure 9. The effects of flame and corona treatment on oxidation and surface energy of paperboard. The gas rate of flame 21,7 l/min and the power of corona 2,6 kW. Predictably, flame and corona treatments increase adhesion, oxidation and surface energy (polarity). Flame and corona treatments have equal effects on adhesion, whereas the corona treatment increases surface energy and oxidation more than the flame treatment. In contrast to flame treatment the corona treatment with high power leads to decreasing adhesion after reaching an optimum, as seen in Figure 8. The co-effect of flame and corona

treatments has minor positive influence on adhesion but clear positive influence on surface energy and oxidation of paperboard. However, flame and corona treatments combined do not oxidize the surface as much as the corona treatment by itself. , Scanning Electron Microscopy (SEM), Atomic Force Microscope (AFM) and roughness measurements from the surface of paperboard indicate that the pretreatment causes physical and topographical changes on the surface. The roughness of clay coated surface decreases due to the pretreatment. In previous studies [3–5], where the effects of pretreatment on paper or paperboard have been investigated, quite similar results have been obtained. In the previous studies done at TUT [3, 4], it has also been detected that the corona treatment increases the polarity and oxidation of surface more than the flame treatment. In some studies [3] the corona treatment improves adhesion more than the flame treatment, while in other investigations [4, 5] the effects are quite equal. It is also perceived that the co-effect of flame and corona treatments gives additional benefit for adhesion [4]. The decrease of adhesion in high power levels has also been observed previously [4]. Even if the effects of flame and corona treatment on adhesion were equal, the surface measurements proved that the mechanism behind it is not exactly the same theoretically, although some correlation was detected between adhesion, oxidation and surface energy. Therefore, it is case-specific which of the pretreatment provides a better result. CONCLUSIONS The best possible flame treatment result is obtained by using parameters as showed qualitatively in this paper. Naturally, the settings are only valid in this case but it is possible to establish the optimum settings for each case, all is needed are know-how, test trials and time. The optimum of adhesion is also depending on many different details in a production line e.g. melt temperatures, chill roll settings, line pressures, equipment or burner type. But these results presented show that it is worth to check the optimum for each coating line, if it is not done so far. ACKNOWLEDGMENTS This work has been a part of research and development project between Paper Converting Institute at Tampere University of Technology, SIG Combibloc Systems GmbH and Stora Enso Packaging Boards. Thank you to Mr. Manfred Hill, Hill GmbH, Germany for the supply of flame treatment equipment & know-how, BP Köln GmbH, Germany for the support and availability of the pilot coating line, the lab staff of TUT, Stora Enso and SIG Combibloc for all the measurements and the trial support. References 1. Wu, S., Polymer interface and adhesion, Marcel Dekker, Inc., New York, 1982, 630 p. 2. Lindland, T., Peach, A., “Substrate preparation trough direct flame”, proceedings from the 1985 Tappi Polymers, Laminations and Coatings Conference, Chicago. 3. Junnila, J., Savolainen, A., Forsberg, D., “Adhesion improvements between paper and polyethylene by pretreatment of substrate”, proceedings from the 1989 Tappi Polymers, Laminations and Coatings Conference, Orlando. 4. Savolainen, A., Kuusipalo, J., “The optimization of corona and flame pretreatment in multilayer coating”, proceedings from the 1991 Tappi Extrusion Coating Short Course, Dusseldorf. 5. Laiho, E., Ylänen, T., “Flame, corona, ozone –do we need all pretreatments in extrusion coating?”, proceedings from the 1997 Tappi Polymers, Laminations and Coatings Conference, Toronto, Ontario, Canada. 6. Brewis, D.M., Surface analysis and pretreatment of plastics and metals, Appl. Sci. Publishers Ltd., Essex, 1982, 268 p. 7. Chan, C-M., Polymer surface modification and characterization, Hanser Publishers, 1994, 285 p.

8. Eckert, W., “Improvement of adhesion on polymer film, foil, and paperboard by flame treatment”, proceedings from the 2003 European Tappi Polymers, Laminations and Coatings Conference, Roma. 9. Hill, M., “Flame treatment meets quality management”, proceedings from the 2002 Tappi Place Conference, Boston. 10. DiGiacomo, J., “Fundamentals of flame plasma surface treating”, proceedings from the 2001 Tappi Polymers, Laminations and Coatings Conference, Barcelona. 11. http://www.tut.fi/units/ymp/pap/

1

The Effects of Flame Treatment on Clay The Effects of Flame Treatment on Clay Coated Paperboard in Extrusion CoatingCoated Paperboard in Extrusion Coating

Mikko TuominenMikko TuominenTampere University of Technology (TUT), Finland Tampere University of Technology (TUT), Finland

Institute of Paper ConvertingInstitute of Paper Converting

Prof. Jurkka Kuusipalo, TUT, Finland Prof. Jurkka Kuusipalo, TUT, Finland Roland Bothor, SIG Combibloc Systems GmbH, GermanyRoland Bothor, SIG Combibloc Systems GmbH, Germany

Timo Lankinen, Stora Enso Packaging Boards, FinlandTimo Lankinen, Stora Enso Packaging Boards, Finland

2005 TAPPI European PLACE Conference2005 TAPPI European PLACE ConferenceMay 25, 2005, Vienna, AustriaMay 25, 2005, Vienna, Austria

Why carry out these investigations?Why carry out these investigations?

Line speed is increasing in production lines Line speed is increasing in production lines This sets high demands especially for adhesionThis sets high demands especially for adhesionBest possible flame treatment is requiredBest possible flame treatment is requiredThe effects of flame treatment parameters must be The effects of flame treatment parameters must be establishedestablished

Not much published informationNot much published informationNot on clay coated paperboardNot on clay coated paperboardNot in high line speeds, up to 500 m/minNot in high line speeds, up to 500 m/min

Questions and TargetsQuestions and Targets

How How stronglystrongly is adhesion affected by flame is adhesion affected by flame treatment parameters?treatment parameters?What is the What is the optimum value rangeoptimum value range and and combinationcombination of flame treatment parameters?of flame treatment parameters?What are the What are the differencesdifferences between flame and between flame and corona treatment?corona treatment?

2

Why is the paperboard flame treated?Why is the paperboard flame treated?

Sufficient adhesion to polymer is often difficult to Sufficient adhesion to polymer is often difficult to achieve because of achieve because of ……

Low surface energyLow surface energyIncompatibilityIncompatibilityChemical inertnessChemical inertnessPresence of contaminants or weak boundary layersPresence of contaminants or weak boundary layers

The flame treatment The flame treatment ……Changes the chemical compositionChanges the chemical compositionIncreases the surface energyIncreases the surface energyModifies the surface topographyModifies the surface topographyRemoves the contaminants, weak boundary layers and Removes the contaminants, weak boundary layers and sticking fiberssticking fibers

How flame treatment improves adhesion?How flame treatment improves adhesion?

The paperboard is exposed to direct flameThe paperboard is exposed to direct flameThermally activated atoms and molecules are Thermally activated atoms and molecules are formed e.g. oxygen ions and atoms and free formed e.g. oxygen ions and atoms and free electronselectronsThese react with the surface composing carbonyl, These react with the surface composing carbonyl, carboxyl and hydroxyl groupscarboxyl and hydroxyl groupsThe surface activation, polarity and oxidation The surface activation, polarity and oxidation increases and leads into improved wetting and increases and leads into improved wetting and adhesionadhesion

The important flame treatment parameters?The important flame treatment parameters?

For obtaining the best possible flame treatment For obtaining the best possible flame treatment result the parameters must be optimizedresult the parameters must be optimized

The most important parameters are:The most important parameters are:The gas rate (output/volume)The gas rate (output/volume)The airThe air--gas ratiogas ratioThe burner vs. substrate distanceThe burner vs. substrate distanceThe line speed (exposure time)The line speed (exposure time)

3

How is it done?How is it done?

Test trials at TUT and BP pilot linesTest trials at TUT and BP pilot linesThe effects of parameters are The effects of parameters are examinedexamined in TUTin TUTThe obtained results are The obtained results are confirmedconfirmed in BPin BP

Grammage of PEGrammage of PE--LD 15g/mLD 15g/m²²Extruder temp. 300Extruder temp. 300°°C at TUT, 320C at TUT, 320°°C at BPC at BPThe flame treatment equipment supplied by Hill GmbH The flame treatment equipment supplied by Hill GmbH Propane as burner gasPropane as burner gasMeasurements: Measurements:

Adhesion (90Adhesion (90°°--peel test) peel test) Others: XOthers: X--ray Photoelectron Spectroscopy (XPS), surface energy, ray Photoelectron Spectroscopy (XPS), surface energy, roughness of surface, Scanning Electron Microscopy (SEM) and roughness of surface, Scanning Electron Microscopy (SEM) and Atomic Force Microscope (AFM) Atomic Force Microscope (AFM)

How How stronglystrongly flame treatment parameters flame treatment parameters are affecting adhesion?are affecting adhesion?

What are the most important parameters? What are the most important parameters? The existence of interactionsThe existence of interactionsBenefits of experimental design (DoE)Benefits of experimental design (DoE)A model for adhesion?A model for adhesion?

Scaled and centered coefficients for adhesion

0

1

2

3

Gas Rate Ratio Distance Line Speed Board Grade

What is the What is the optimum value rangeoptimum value range of flame of flame treatment parameters?treatment parameters?

How each parameters is improving adhesion?How each parameters is improving adhesion?Clear optimum value ranges in airClear optimum value ranges in air--gas ratio and gas ratio and burner vs. board distance burner vs. board distance

0,5

1

1,5

Adhesion (N/15m

m)

Air-Gas Ratio Distance Gas Rate Line Speed

Relative ranges of flame treatment parameters

4

What is the What is the optimum combinationoptimum combination of flame of flame treatment parameters?treatment parameters?

Maximum line speed Maximum line speed and minimum gas and minimum gas consumptionconsumptionOptimum combination Optimum combination of airof air--gas ratio and gas ratio and burner vs. substrate burner vs. substrate distancedistanceThe optimum must be The optimum must be tested in higher line tested in higher line speed, up to 500 m/minspeed, up to 500 m/min

The Optimum Combination of Burnervs. Substrate Distance and Air-Gas Ratio

Adhesion

Distance Air-Gas RatioOptimum observed

TheoreticalOptimum

What is the What is the optimum combinationoptimum combination at higher at higher line speeds?line speeds?

1,5

2

Adhesion (N/15m

m)

Distance Air-Gas Ratio Line Speed

Relative Ranges of Flame Parameters (Trials at BP Line)

The main effects and optimum ranges are quite similar to the The main effects and optimum ranges are quite similar to the results of TUTresults of TUTThe optimums are influenced by differences in equipment and The optimums are influenced by differences in equipment and materialsmaterials

The gas rateThe gas rate

Flame treatment improves adhesion, oxidation Flame treatment improves adhesion, oxidation and surface energyand surface energyGas rateGas rate has has minorminor effect on adhesion effect on adhesion compared to other parameterscompared to other parameters

But it defines the consumption of gas (propane)But it defines the consumption of gas (propane)

The role of other parameters becomes more The role of other parameters becomes more importantimportant

5

The airThe air--gas ratiogas ratio

MajorMajor influence on adhesioninfluence on adhesionThe stoichiometric airThe stoichiometric air--gas ratio for propane is gas ratio for propane is 24:1 and for methane 10:124:1 and for methane 10:1The optimum The optimum belowbelow the stoichiometric ratiothe stoichiometric ratio

Excess air from surroundings or with substrateExcess air from surroundings or with substrateIn previous studies In previous studies ““oxidizingoxidizing”” flame has been flame has been preferredpreferred

Definitely important to be Definitely important to be optimizedoptimized

The burner vs. substrate distanceThe burner vs. substrate distance

Affects Affects greatlygreatly adhesion, oxidation and surface energyadhesion, oxidation and surface energyThe The optimumoptimum in the in the ““activeactive”” zone , shining coneszone , shining cones

Flame temperature and ion activity the highestFlame temperature and ion activity the highest

The optimum is influenced by treatment level (gas rate The optimum is influenced by treatment level (gas rate & line speed) and gas quality or type& line speed) and gas quality or type

The line speedThe line speed and and board gradeboard grade

The line speedThe line speedaffects affects greatlygreatly on adhesion but not so strongly on on adhesion but not so strongly on oxidation and surface energyoxidation and surface energyInteractions with other parametersInteractions with other parameters

The board gradeThe board gradeSingleSingle clay coated paperboard has clearly a clay coated paperboard has clearly a betterbetteradhesion than adhesion than doubledouble clay coatedclay coated

•• Rougher surfaceRougher surface•• More area for wetting and adhesion formingMore area for wetting and adhesion forming

No mechanical adhesion with clay coated No mechanical adhesion with clay coated paperboardpaperboard

6

What are the What are the differencesdifferences between flame between flame and corona treatment?and corona treatment?

Both treatments improve adhesion quite equallyBoth treatments improve adhesion quite equallyThe flame The flame improvesimproves adhesion in higher treatment levelsadhesion in higher treatment levelsThe corona leads to a The corona leads to a decreasedecrease of adhesion at too high treatment of adhesion at too high treatment levelslevelsThe coThe co--effect gives an additional but minor adhesion improvementeffect gives an additional but minor adhesion improvement

Scaled and centered coefficient for adhesion

0

5

0

5

0

5

Flame Corona Flame+Corona

0,5

1

1,5Adhesion (N/15m

m)

Air Rate of Flame Corona Power

Relative Ranges of Flame and Corona Treatment

What are the What are the differencesdifferences between flame between flame and corona treatment?and corona treatment?

CoronaCorona treatment increases treatment increases oxidation oxidation moremore than than flameflametreatmenttreatmentCoronaCorona treatment increases treatment increases surface energy surface energy moremore than than flameflame treatmenttreatment

Especially the polar Especially the polar componentcomponent

The coThe co--effect increases effect increases oxidation more than flame oxidation more than flame but less than coronabut less than coronaThe coThe co--effect increases the effect increases the surface energy the mostsurface energy the most

Oxidation (XPS) and surface energy measurements of paperboard

+15,0 +11,3

+7,2+14,4

+23,0

+11,8

+66,8

+38,5

15

25

35

45

55

65

75

No treatment Flame Corona Flame+Corona

C oxidised(%)

Surfaceenergy (%)

Polarcomponent(%)

+6,6

What are the What are the differencesdifferences between flame between flame and corona treatment?and corona treatment?

Flame and corona treatments cause physical and Flame and corona treatments cause physical and topographical changes in the surfacetopographical changes in the surface

Roughness of surfaceRoughness of surfaceScanning Electron Microscopy (SEM)Scanning Electron Microscopy (SEM)Atomic Force Microscope (AFM)Atomic Force Microscope (AFM)

Previous studies show similar resultsPrevious studies show similar resultsSome correlationSome correlation between adhesion, surface energy between adhesion, surface energy and oxidation was detectedand oxidation was detectedEven if the treatments improve adhesion quite equally Even if the treatments improve adhesion quite equally the mechanismthe mechanism is is notnot exactly exactly the samethe same

7

The The bestbest possible flame treatment resultpossible flame treatment result

Is obtained by using parameters as showed Is obtained by using parameters as showed qualitativelyqualitatively in this presentationin this presentationThe optimum of adhesion is also depending on other The optimum of adhesion is also depending on other parameters in production line e.g.parameters in production line e.g.

Material usedMaterial usedMelt temperaturesMelt temperaturesChill roll settingsChill roll settingsLine pressuresLine pressures

It is worth to It is worth to check the optimumcheck the optimum for for your system if it is not done so far !!!your system if it is not done so far !!!

AcknowledgmentsAcknowledgments

Thank you to Thank you to ……

Mr. Manfred Hill, Hill GmbH, GermanyMr. Manfred Hill, Hill GmbH, Germanyfor the supply of flame treatment equipment & knowfor the supply of flame treatment equipment & know--howhow

BP KBP Kööln GmbH, Germanyln GmbH, Germanyfor the support and availability of the pilot coating linefor the support and availability of the pilot coating line

The lab staff of TUT, Stora Enso and SIG CombiblocThe lab staff of TUT, Stora Enso and SIG Combiblocfor all the measurements and trial supportfor all the measurements and trial support

Questions?Questions?

Thank you for your attention!Thank you for your attention!