the role of surface modification in digital printing on polymer-coated packaging boards.

Brief introduction due to the variable amount of information involved, packaging is an ideal application for digital printing.
Traditionally, packaging materials are printed with offset, recessed or Flexo (1)
But in this study, printing is done with digital printing technology. e. , dry-
Carbon powder for electronic photography
In digital printing, information can be changed flexibly or updated easily.
Digital printing allows customization and customization for selected target groups.
Compared with the traditional printing technology, its volume is very small;
Digital printing is mainly suitable for short packaging in highly personalized packaging.
The obvious benefit of digital printing is the low amount of waste, printingon-demand.
The position of digital printing in the packaging industry is still quite mild, but the future looks bright and it is estimated that the use of this method will increase more than traditional printing technology (2).
The quality of digital printing will also be close to traditional technology.
Extrusion coatings used in packaging applications include polyolene (
Polyethylene, PE;
Polypropylene (PP), copolymers (e. g.
(E/MA), adhesives (e. g.
(Acid)
Barrier polymer (e. g. , PA)
And other polymers (e. g.
PET, PET)(3).
According to a pilot test of polymers containing each of these groups, three polymers were selected for more detailed examination: Low-
Density Polyethylene (PE-LD)
Ethylene, methyl propylene ester (E/MA)
, And pet (PET). PE-
LD is the highest
Extrusion of bulk polymers used in the paint industry.
It is easy to process, provides sufficient moisture resistance and has excellent chemical resistance and heat resistance
Sealing performance.
In addition to these advantages, low cost (3, 4).
Only problem with PE
The LD observed during the trial is low digital print quality.
E/MA is a polymer of ethylene and methyl propylene, and usually contains 5%-
20% methyl acetate.
E/MA can adhere well to various substrates, and its heat
Better sealing performance than PE-LD (3).
E/MA is the best print quality among all polymers used in pilot trials.
As an excellent pet movie
Packaging materials have excellent chemical resistance and stability in a wide range of temperature (-60[degrees]C to220[degrees]C)(3, 4).
PET also has good printing performance.
For extrusion coatings, a common problem is the lack of adhesion between the polymer coating and the printing ink.
The most common way to improve the adhesion properties of polymer coatings is different surface treatments.
Including flame, Corona and ozone treatment (3). The corona-
Discharge treatment is widely used to improve the wetting and adhesion properties of extrusion coating plates (5,6).
The surface energy of the printed material is treated by the Corona-
Voltage charge.
Previously randomly arranged surface molecules are brought into a common pattern by this charge.
In the process of Corona treatment, the following three phenomena will occur :(a)
Chemical effects ,(b)
Physical effects (micropitting), and (c)
Electrostatic effect (Resident effect)(7-10).
Chemical effects include surface oxidation and flow formation. molecular-
Compound of weight. The corona-
The treatment effect is based on bombarding the polymer surface with electrons.
When they are in contact with the surface of the polymer, they have so much energy that they destroy the carbon-
Hydrogen or carbon
Carbon, therefore, forms a very lively free radical on the surface.
At the same time, ozone and oxygen radicals react with free radicals on the surface.
Therefore, chemical functional groups are formed on the underlying surface.
The polar functional bases that can form and enhance bonding include carbonyl (C=O), carboxyl (COOH)Hydrogen peroxide (-OOH), hydroxyl (-OH), and amide (-CONH[. sub. 2])groups.
Even if a small number of these active functional groups are added to the polymerization scan, it is very beneficial to improve the surface properties and humidity (3, 7, 9, 11-15).
Some polymers already contain these active bases in their basic structures, such as the acrylic base of E/MA is highly polar (see Fig. 1)(3).
In contrast, like PE-
LD, it is necessary for the Corona treatment to form these regiments into their structures.
With olefin, the treatment is polarized for a long time-
Chain polymer molecules into shorter-
The ends of these smaller parts are fragmented and oxidized by chains, mainly resulting in ether and Tuan (16).
The surface energy depends largely on the molecules on the surface of the polymer coating.
In general, the more polarity the sublayer contains, the easier it gets wet (8).
According to Stenlund (17)
These functional bases are mainly formed in the amorphous part of the polymer, where oxygen can spread.
Therefore, the effect of Guannan treatment on the polymer coating depends, among other things, on the degree of crystal of the polymer (18).
Some micropits may also occur during the corona treatment: surface topography may change and some contaminants may be removed from the surface (3, 7).
Corona treatment can also cause permanent charges on good insulators such as polymer coatings (3).
When a dielectric material, such as a polymer coating, is subjected to a strong DC electric field, long
Induction of charged charges in the medium.
This is the so-called resident effect.
In the DC field, the induced polarization of the medium generates an abnormal charge (
Surface charges relative to adjacent electrodes)
, Will decay when removed on the spot.
However when electrode/dielectric gap happened discharge when ahomocharge (
Similar to the surface charge of adjacent electrodes)
I also produce.
Homosexuality is relatively permanent and sometimes
Living at room temperature for many years.
The solar corona can be detected by dust removal-
Treat the surface with very fine polar powder.
This reveals a discrete mode of charge.
Such patterns are called \"Lichtenberg characters\" after their discoverers \"(9, 19). [
Figure 1 slightly]
In this study, the surface chemistry of the polymer coating was modified with Corona treatment.
The effects of the Corona were evaluated by contact angle measurement and polar powder.
In addition, the microscopic method is used when analyzing the polymer surface.
Electrostatic force microscope (EFM)
Surface Charges and atomic force microscopy that have been used to study polymer surfaces (AFM)
Define surface roughness.
The effect of surface chemical composition on the adhesion of carbon powder was determined by tapepeeland rub-
Turn off the measurement.
The printing quality is analyzed from both visual and digital aspects.
The experimental polymer film is suitable for Cupforma classics (grammage 170g/[m. sup. 2])
The polymer extrusion-coated guide inboretro Oyj Oy of the stoura ENSO.
Bleached SBS (
Solid bleaching sulfuric acid)
Cup board for food-
Packaging applications. Corona post-
For surface modification. Corona post-
Treatment refers to the discharge treatment performed outdoors under atmospheric pressure on the pilot line.
The principle of Corona treatment is that the moving Net passes through the air gap between the electrode and the ground backing roller.
The potential difference between the electrode and the support roller causes the air to ionize in the air gap.
The main effects of the corona are discussed above.
Generator (Vetaphone)output was 4. 5 kW. The corona-
According to the equation, the processing efficiency depends on the width of the electrode and the wire speed.
1: efficiency of Corona treatment (W min/[m. sup. 2])= [
Generator power (W)]/[
Electrode width (m)X Line speed (m/min)](1)
Three commercial polymers were used in this study: Low-
Density Polyethylene (PE-LD)
Ethylene, methyl propylene ester (E/MA)
Poly Vinyl ester (PET).
Figure 1 shows the molecular structure of the polymer.
Coat weight target 20g /[m. sup. 2].
Figure 2 is cross
Cross section image of extrusionCoating Cup.
The sample was confirmed as PE-
LD, E/MA and PET (without corona)andPE-L[D. sub. cor], E/M[A. sub. cor]and PE[T. sub. cor](corona-treated). [
Figure 2:The polymer-
Print the coating layer grade with XeikonDCP/50
SP digital printing machine.
The printing method in xeiikon is based on dryingtoner web-
Federal Reserve electronic photography.
During electrophotography, the powder Toner is transferred to the printed substrate through an electric field, after which the toner particles are melted to the substrate at heat and/or pressure.
Printing on one side, four process colors--
Yellow, cyan, magenta and black--are used.
Figure 3 shows the mechanical configuration (20).
There are some modifications to the printer compared to basicXeikon/50
SP machine configuration.
In order to achieve a more direct paper path, the pretreatment unit was modified and the fuser unit was modified.
The Fuser unit is a non-contact fuser based on IR-radiation;
It is 1000 adjustable by six-
W ceramic module (In 2 × 3 matrix).
The distance between the module and the printed substrate is adjustable (
Of these trials, about 70mm
The maximum surface heat of the substrate obtained is 130 [degrees]C-140[degrees]C.
This unit is necessary when printing on polymer
Coating substrate because in nip-
The polymer will stick to the user drum.
The adhesion of carbon powder is determined by adhesive tape-
How to peel and rub-offmeasurement.
In the tape test, the tape was pressed on the print surface for 5 minutes, after which the tape was opened at a1 80 [degrees]angle.
The standard for measuring the adhesion of toner is the percentage (%)
This is equal to the density ratio of the printing area before and after the test. Rub-
Off indicates the wear and durability of dry print images.
It is determined by rubbing the image against an unprinted surface.
The amount of toner that has been transferred is measured by a change in brightness (%).
Printing quality, mainly prints, is visually analyzed (ranking list)
And numbers (mottle value).
Visual assessments were conducted for six different people trained for this type of assessment.
Numerical evaluation using Umax PowerLook II scanner and analysis using shuttle viewersoftware.
According to experience, the most critical evaluation is visual impression. [
Figure 3 slightly]
Surface properties include smoothness (PPS)
And surface energy.
Contact angle measurements made with Panasonic AG-define the surface energy of the polymer coating
Use 2-7355 devicesliquids method.
Surface energy ([gamma])
As shown in equation 2, consists of dispersion and polar components.
D refers to the polar components of dispersion and P-to-surface energy (5). [gamma]= [[gamma]. sup. D]+ [[gamma]. sup. P](2)
Determination of field performance by polar powder (Porapak[R]Type Q).
This powder is made of balls.
Shaped Poly particles with particle size of 80-100 mesh (ca. 150-180[micro]m).
Electrical properties including surface and volume resistivity, charge half are determined
Time and maximum surface voltage.
Electrostatic force microscope (EFM)
Can be used for non-contact imaging of conductive and insulating materials (21);
For the study of semiconductor and piezoelectric materials (22-25)
Iron and electricity material (26, 27), and light-
Launch assembly (LEDs and lasers)(28-31). Also, real-
Time evolution of charge trappedSi [O. sub. 2]
With EFM (32, 33)
And Scanning capacitance microscope (34).
The EFM measurement was performed with a thermal microscope automatic probe cp stm/AFM/EFM research system.
Use the non-contact silicon cantilever scraping tip coated with Pt to collect AFM and efmimage, respectively.
The back of the cantilever reflection beam is coated with Cr-Au layer.
The principle of the EFM is to detect changes in electrical properties on the surface of the sample.
For efm measurement, voltage [V. sub. dc]
Applied to tips. Byvarying [V. sub. dc]
Depending on the change in signal strength, changes caused by static power between the sample and the tip can be observed, which means changes in the observed mean height values of the EFM signal (Fig. 4).
The greater the signal strength, the greater the surface charge.
The symbols and absolute values of these symbols are difficult to determine accurately, but the comparison between these symbols is possible. [
Figure 4 slightly]
The observation signal is the first harmonic EFM signal ([F. sub. [omega]1])
, Proportional to the surface potential ,[V. sub. s]
Therefore, for the surface charge (24).
The area of measurement is chosen after the polar powder measurement, and in the polar powder measurement, the electrical attraction does combine the powder. Also, the non-
The charging area was measured but the proper signal was not obtained.
Three images were taken at each tip bias value and the average signal strength was calculated from these images.
The first harmonic signal is defined (24)[F. sub. [omega]1]= [[
Partial derivativeC/[
Partial derivative]z]([V. sub. dc]-[V. sub. s])[V. sub. ac]sin([omega]t)(3)
Where C is the capacitor, z is the distance between the tip and the sample ,[V. sub. ac]
Is the AC voltage applied to the tip, herechosen, making the amplitude 1. 0 V, [omega]= 2[pi]
F, where f is the iscanantiover resonance frequency and t is the time.
EFM signals can be implemented using Eq 3, which is a function of applying tip bias [V. sub. dc](Fig. 4)
And determine the slope k. [
Figure 5 Slightly]k = [[[
Partial derivativeEF[M. sub. signal]]/[[
Partial derivative][V. sub. dc]]]= [a/x](4)
Where a corresponds to the height of the charge condensation from the signal, x corresponds to the charge of the force level caused by the [change]V. sub. dc].
In fact, these values are measured from efm images taken with different [V. sub. dc]
Then compare with the change of the EFM signal.
Finally, it is possible to convert the efm profile [V. sub. s]-profile.
Results and discussion of the effects of surface properties and electrical properties on TonerAdhesion and the visual quality surface and electrical properties in the process of digital printing affect the operational and printing suitability of the printed substrate.
Surface properties include surface energy and smoothness.
The contact angle measurement shows that the surface energy of the polymer coating is significantly increased by the corona treatment (Fig. 5). With PE-
An increase of about 13 mN/m, an increase of about 6 mN/m for E/MA and PET.
Corona treatment introduces a polar mass on the polymer surface, increasing the polarity of the surface.
Therefore, due to the increase in the value of the polar component, the surface energy increases.
However, the corona-
Therapeutic effects, especially surface energy, are habitually reduced over time.
Some researchers have studied this phenomenon. 5, 35)
Sameresult was also observed in this study (Fig. 5).
After treatment, the reduction of surface energy is mostrapid, after which surface energy settles more or less to a certain level.
Temperature, humidity, pressure, transfer and oxygen can cause the disposal to rot.
Despite the reduction, the surface
Energy levels of the Corona-
The processed sample is more stable than the unprocessed sample.
Polymer not treated and treated
The coating plate is digitally printed, and after melting, the adhesive tape for toner adhesion is definedpeel method.
The test shows that when the surface area of the polymer coating is higher than the surface area of the carbon powder (e. g.
Magentatoner 38 mN/m of Sai Kang)
The adhesion of toner is close to 100% (Fig. 6a).
According to the measurement of contact angle.
E/MA and PET have reached the required level without corona treatment.
Surface required-
The energy level refers to the surface energy required for sufficient toner adhesion. WhenPE-
The LD with poor adhesion is corona-
After the pilot treatment of the extrusion coating, the adhesion was significantly improved.
With all of them-
The surface energy of the treated sample is above 38 mN/m.
What\'s not important is toner.
According to the tape test, the adhesive value of these methods is 100% (Fig. 6b).
Wear durability is a measure of the adhesion of toner.
Determination of wear durability of printed samples by frictionTurn off the measurement.
These measurements show that wear durability increases when the sample is the coronatreated (Fig. 7).
PET has good wear durability even if there is no Corona because of the surface height-energy level (see Fig. 6). [
Figure 6 slightly]
Electrical properties of printed substrates, I. e.
Surface and volume resistivity, charge half
Time and maximum surface voltage play an important role in electro-photographic printing, at least in coated paper/uncoated paper.
This is because of the electrical properties involved in Toner
Transfer process.
In order to avoid electrical accumulation in the substrate, the conductivity must be sufficient.
Static and operational problems can lead to the accumulation of charges.
Observations made with paper grades show that the conductivity on the top and back of the board should be as low as possible, and the conductivity of the board layer should be as high as possible.
In addition, the conductivity value should be as uniform as possible throughout the printing surface.
On the other hand, a certain resistivity is required from the substrate to maintain the charge in the carbon powdertransfer stage.
Fluctuations in electrical properties may leadg. , mottling (20, 37).
In general, polymers have low conductivity and they can be classified as dual-electrical materials (36).
Table 1 lists the surface and electrical properties of the polymer and the print quality valuescoated samples.
As reported in Table 1, there is not much difference in electrical properties between different polymer coatings, and corona treatment does not appear to have a significant impact on these properties.
There was also no significant change in the smoothing value, and no obvious correlation between smoothing, electrical properties and spots was observed.
Visual assessment is considered to be more important than a shuttle scan measurement.
When assessing this impression, the best coating that has not been treated with the Corona is proved to be E/MA.
Pet after coronatreatment, E/Marle second with sample.
Pets are considered to be the best impression.
However, the results of PET are still average if there is no Corona treatment.
Because the effect of Corona in Corona will not last, but will disappear over time, PET will lose E/MA in practical application, if Corona treatment is not carried out,
Heating in packaging applications
Sealing performance is also an important factor, and E/MA has better sealing performance than PET.
The interpretation of the difference in printing quality is based on the resident effect and surface-
Charge uniformity on the surface of the polymer. [
Figure 7 Slightly]
As shown in the figure, the effect of the resident effect on the surface of the polymer
6 it is stated that although the surface of E/MA is low, it has good ink adhesionenergy values (
And the lower polar component)than PET.
This shows that in addition to surface oxidation to enhance the adhesion of carbon powder, there must be other phenomena
Resident formation.
As mentioned above, the corona treatment can generate permanent charges on the surface of the polymer.
This electrical effect can be studied with polar powder.
Powder is poured onto a sample of the extruded coated board.
The sample swings back and forth carefully and excesspowder is poured out of the surface.
The charge caused by discharge treatment results in uneven distribution of the powder on the surface.
The powder forms a graphic on the surface of the polymer.
When studying samples that were not Corona treated, it was found that the powder was not attached to these surfaces at all except E/MA.
When poured into a sample with a Corona
After treatment, the powder is more or less connected to each sample.
Figure 8 the Corona-treated PE-
Coating Plates for LD, PET and E/MA.
Significant differences in powder diffusion can be observed between polymers.
It is found that the most uniform and close adhesion of the powder can be achieved with E/MA. With PE-
The adhesion of LD and PET powder is quite uneven.
Tonerparticipants observed the same pattern.
The study of the powder shows that the corona treatment has different effects on different polymer coatings, and the uniformity of the coating varies depending on the polymer type.
The surface analysis of polymer was carried out by microscope, and the surface morphology of polymer coating was studied.
Rms roughness of the sample (
Standard deviation from optimal deviation
Fitting plane of data)
The mean values of the five image regions that were measured as randomly selected, as shown in Table 2.
Scan the area of 30X30 [micro][m. sup. 2]
Show only the Corona-
The surface treated E/MAhas is clearly the largest feature.
The analysis conducted with EFM showed that trap charges on the polymer surface vary depending on the type and distribution of the polymer, and are associated with observations made with polar powders. The tip bias[V. sub. dc]
From-1. 5 V to +1. 5 V in 0. 5-V steps, and[V. sub. s]
Calculated as a function on [V. sub. dc].
Figure 9 shows the value [V. sub. s]
In different coatings when [V. sub. dc]= 1. 5 V.
There is no Corona treatment, only E/MA coating [V. sub. s]signal.
This means the charge level of PE-
LD and PET substrates are not important.
After the corona treatment, the value [V. sub. s]for PE-
LDand PET is 3 to 4 times higher than the value of pure E/MA, but thecorona treatment of E/MA is almost 80 times higher than the average charge level before treatment.
According to print quality analysis, surface-
The charge level and uniformity appear to be very clearly related to print spots and visual quality, in which case the results of the efm measurements are good proof that the E/MA coating is suitable for digital printing.
When the surface charge is high and the surface charge distribution is uniform, the ink powder has good adhesion and uniform printing quality. [
Figure 8:
Conclusion The conversion process of the packaging board put forward high requirements for polymer surface and printed image.
When it comes to extrusion coating packaging applications, sufficient toner adhesion and wear durability are essential.
The quality of visual printing is also an important factor in packaging applications.
This study shows that sufficient high-energy surfaces and surfaces-
For uniform print quality and adhesion of toner, charging uniformity is necessary.
E/MA and PET have the necessary surface
There is no Corona treatment, but PE-
In order to succeed in the digital printing process, LD requires surface modification.
Printing suitability of PE
LD can be significantly improved by Corona treatment.
If it is not processed, the adhesion value of carbon powder will be very poor.
PET, especially E/MA, due to its high enough surface-energy level.
Observations of polar powders and EFM measurements show that the charge on the surface of theE/MA is very uniform during the corona treatment.
Due to the uniform distribution of charge, the toner is attached to the surface very evenly and the printing quality is high. [
Figure 9 omitted
Received confirmation funding from Dr. International. D.
Science and technology projects (PaPSaT)
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Johanna lahti * and antti savolainen paper Institute, Tampere University of TechnologyO. Box 541, FIN-
33101 Tampere, Finland
Oyj RASANEN, consumer Bords tail
55800 Physical Laboratory of imtra, Tandja suminning, Finland and Hanu hudingning weihuli
20014, Turku, Finland *, who should communicate.