EP1132492A2 - Web-shaped plasma-processed materials - Google Patents

Abstract

Production of a strip-like metallic or polymeric material comprises subjecting the surface of the material to an atmospheric plasma produced by an indirect plasmatron optionally with the introduction of a gas or aerosol. Preferred Features: The atmospheric plasma is produced by an indirect plasmatron having a neutrode with a permanent magnet pair to influence the shape and position of the plasma arc.

Description

The present invention relates to sheet-like materials, in particular polymers or metallic foils using an atmospheric plasma are treated.

Many finishing steps, such as printing, coating, painting, Gluing, etc., is only possible with plastic and metal foils if one sufficient wettability with solvent or water-based printing inks, Lacquers, primers, adhesives, etc. is given. In general, therefore, in or Corona treatment performed offline with the film processing.

Such as B. in the publications DE-A 4212549, DE-A 3631584, DE-A 4438533, EP-A 497996 and DE-A 3219538 describe the web-shaped Materials exposed to an evenly distributed electrical discharge. Prerequisite are two working electrodes, one with a dielectric Material (silicone, ceramic) is encased. One is between the two electrodes high AC voltage with a frequency typically between 10 and 100 kHz placed so watery a uniform spark discharge takes place. That too treating material is carried out between the electrodes and the discharge exposed. This results in "bombardment" of the polymer surface Electrons, whose energy is sufficient to create bonds between carbon-hydrogen and break up carbon-carbon. The radicals formed react with the corona gas and thereby form new functional groups. Furthermore, the polymer or metal surface is cleaned because Foil additives and rolling oils are oxidized and distilled off.

Despite the wide range of applications and constant further development the corona treatment has significant disadvantages. So it happens especially at higher ones Orbital velocities to a parasitic backside corona discharge if the sheet-like materials do not rest on the roller-shaped electrode. Furthermore, the corona treatment leads to a clear one electrostatic charge of the sheet-like materials that are winding the Materials difficult, the subsequent processing steps, such as painting, Printing or gluing hindered and especially in the manufacture of Packaging film is responsible for powdery materials such as Stick coffee or spices to the film and, in the worst case, leak Seal seams contribute. After all, corona treatment is always one Filament discharge that does not produce a homogeneously closed surface effect. It is also found over time that there is a loss of surface properties occurs due to the migration of film additives and aqueous a molecular Rearrangement based on minimizing surface energy takes place.

The corona treatment is limited to thin substrates such as Plastic films and papers. For thicker materials, the total resistance is too large between the electrodes to ignite the discharge. But then it can individual punctures also occur. Corona discharge should not be used for electrically conductive plastics. They also show dielectric Electrodes in metallic or metal-containing webs are often limited Effect. The dielectrics can easily due to the permanent stress run away. This is particularly the case with silicone-coated electrodes. Ceramic electrodes are very resistant to mechanical stress sensitive.

In addition to the corona discharge, surface treatments can also be caused by flames or light can be performed. The flame treatment is usually at Temperatures around 1700 ° C and intervals between 5 and 150 mm. There the foils heat up briefly to high temperatures of around 140 ° C, effective cooling must be carried out. To further improve the anyway the treatment results are good compared to the chill roll be brought to an electrical potential that the ions of the flame towards treating web accelerates (polarized flame). As a disadvantage for the Surface treatment of foils are particularly those that must be strictly observed View process parameters. A treatment intensity that is too low leads to minor, insufficient, effects. Too strong intensities lead to one Melting of the surfaces, the functional groups submerge inwards and are therefore inaccessible. The high temperatures are also disadvantageous and evaluate the necessary safety precautions. The applicable ones Safety regulations, for example, do not allow pulsed operation of a Flame pretreatment plant too. It is known that the selection of the burner gas allows only certain reactive species (ions and radicals) and that the cost of Flame treatment are significantly higher than with corona treatment.

The main disadvantage of the corona treatment, the localized micro-discharges (Filaments) can be avoided by using a low pressure plasma become. These mostly "cold" plasmas are by means of equal, alternating or High frequency current or generated by microwaves. With only low thermal Loading of the - usually sensitive - material to be treated energetic and chemically active particles provided. These cause one targeted chemical reaction with the material surface, since the processes are in the gas phase at low pressure in a particularly effective manner and the Represents discharge as a homogeneous space discharge cloud. With microwave excitations whole reactor vessels can be used in the Giga-Hz range Fill in the plasma discharge. Compared to wet chemical processes are extreme small amounts of process agents are necessary.

In addition to the targeted activation (modification) of surfaces, in Such processes also polymerizations (coating) and grafts become. As a result of exposure to plasma, classic polymerization monomers, such as ethylene, acetylene, styrenes, acrylates or vinyl compounds as well as such starting materials for crosslinking and thus for Polymer or layer formation are stimulated, which in classic chemical Cannot polymerize reactions. For example, these are saturated Hydrocarbons such as methane, silicon compounds such as tetramethylsilane or Amines. This creates excited molecules, radicals and molecular fragments, which polymerize from the gas phase onto the materials to be coated. The The reaction normally takes place in an inert carrier gas such as argon. Reactive gases, such as hydrogen, can advantageously be used for various purposes. Nitrogen, oxygen, etc. can be added.

Established physical and chemical plasma coating processes such as cathode sputtering or plasma-activated chemical deposition from the gas phase ( PACVD ) usually take place in a vacuum at pressures between 1 and 10 ^-5 mbar. The coating processes are therefore associated with high investment costs for the required vacuum chamber and the associated pump system. In addition, due to the geometric limitations of the vacuum chamber and the necessary, sometimes very long pumping times, the processes are usually carried out as batch processes, resulting in long, watery process times and the associated high unit costs.

Coating processes using corona discharge advantageously require no vacuum at all, they expire at atmospheric pressure. Such a thing Process (ALDYNE ™) is described in DE 694 07 335 T 2. The difference to the conventional corona, which works with the ambient air as a process gas with the corona coating, a defined process gas atmosphere in the discharge area in front. Layered systems of the following structure can be selected by selected precursors be obtained: e.g. SiOx-based layers made of organosilicon Compounds such as tetramethylsilane (TMS), tetarethoxysilane (TEOS) or hexamethyldisiloxane (HMDSO), polymer-like hydrocarbon layers Hydrocarbons such as methane, acetylene or propargyl alcohol as well as fluorinated Carbon layers from fluorinated hydrocarbons such as Tetrafluoroethene.

However, this is not a serious disadvantage of the existing processes closed surface deposition, caused by the filament-shaped discharge characteristic the corona. Accordingly, the process for Application of barrier coatings unsuitable. For surface polarization by introducing functional groups compared to simple ones Corona discharge is too expensive.

For punctiform, partial surface coatings, such as those used for corona coating, Avoiding can also occur due to atmospheric plasmas Arc discharges are generated in a plasma torch. With conventional Torch types are based on the electrode geometry with a pin-shaped cathode and Concentric hollow anode only almost circular attachment surfaces of the emerging Plasma jets can be reached on the surface to be processed. With large-scale For applications, the process requires an enormous amount of time and delivers because of the relatively small starting point very inhomogeneous surface structures.

DE 19532412 C2 describes a device for pretreating surfaces Described with the help of a plasma jet. Through a special design of the A highly reactive plasma jet is obtained which approximately has the shape and has the dimensions of a candle flame and thus also the treatment of Profile parts with a relatively deep relief permitted. Because of the high Reactivity of the plasma jet is sufficient for a very short pretreatment, so that the workpiece at a correspondingly high speed on the plasma jet can be passed. For a treatment of larger surfaces is in the mentioned publication a battery of several staggered Plasma nozzles have been proposed. In this case, however, is a very high one apparatus expenditure required. Since the nozzles partially overlap, it also becomes strip-like in the treatment of sheet-like materials Treatment patterns are coming.

DE 29805999 U1 describes a device for the plasma treatment of surfaces described, which is characterized by a rotary head, the at least one Eccentrically arranged plasma nozzle for generating a parallel to the axis of rotation directed plasma beam. If the workpiece is relatively high Speed rotating rotating head is moved, the plasma jet sweeps a strip-like surface zone of the workpiece, the width of which corresponds to the diameter corresponds to the circle described by the plasma nozzle during rotation. In this way it is possible with a comparatively small apparatus A relatively large surface can be rationally pretreated. Yet the surface dimensions do not correspond to those, as usually with the Processing of film materials on an industrial scale.

In DE-A 19546930 and DE-A 4325939 there are so-called corona nozzles for the indirect treatment of workpiece surfaces is described. In such Corona nozzles oscillate or rotate between the electrodes guided air flow, so that you get a flat discharge zone in which the Surface of the workpiece to be treated with the corona discharge tufts can be painted over. The disadvantage of this process was that aqueous mechanical to equalize the electrical discharge Moving component must be provided, which has a high constructive Effort required. The cited documents also do not describe in what maximum widths such corona nozzles are manufactured and used can be.

For the present invention, the object was plastic and metal foils To be made available, which are processed or modified homogeneously, so that subsequent finishing steps, such as printing, coating, Painting, gluing, etc. without wetting problems and with good ones Have adhesive properties carried out.

The aim was to use a method that the through Low-pressure plasmas (batch operation, costs), corona (filament-shaped discharge, Backside treatment, electrostatic charging, etc.) and plasma nozzles (strip-like surface treatment) given disadvantages.

According to the invention, this is achieved by treating the entire or part of the surface homogeneously sheet-like metallic materials with a thickness of less than 100 µm or sheet-like polymeric materials which are obtained by passing through an indirect plasmatron generates atmospheric plasma on the surface of the Material can act.

An indirect plasmation suitable for the method according to the invention is e.g. described in EP-A-851 720 (incorporated by reference).

The burner is characterized by two coaxially spaced apart Electrodes. A direct current arc burns between these, through an cascaded arrangement of freely adjustable length is wall stabilized. Through a Blowing transversely to the arc axis can be a band-shaped, laterally flowing Exit the plasma jet. This burner, also called plasma broad-beam burner, is also characterized in that a magnetic field exerts a force on the arc that is exerted by the flow of the plasma gas on the arc Counteracts force. The burner can also be of various types Plasma gases are supplied.

These materials can be obtained in particular by the fact that an atmospheric Plasma from an indirect plasmatron with an elongated plasma chamber, which in cascaded structure a plurality of electrically isolated from each other Neutrodes includes, which are required to generate the plasma light gas Electrodes are arranged coaxially to the longitudinal axis of the plasma chamber and the Plasma jet outlet opening runs parallel to the longitudinal axis of the plasma chamber, is used.

In particular, at least one neutrode with a permanent magnet pair to influence the shape and position of the plasma arc. Due to the number, placement and field strength of the magnets used, you can Operating parameters such as gas volume and gas speed be taken. Furthermore, at least individual neutrodes with one Possibility of supplying a gas to the plasma chamber, e.g. a channel be provided. This allows this plasma gas to target the arc in a particularly targeted manner and fed homogeneously. By blowing transversely to the arc axis a band-shaped plasma free jet flowing out to the side can emerge. Through the Applying a magnetic field becomes a deflection and the resulting one Preventing the arc from breaking.

The sheet-like materials described according to the invention can be used both in Connection to a film production as well as before further processing, i.e. before the Treat printing, laminating, coating, etc. of foils. The thickness of the polymeric film materials is essentially irrelevant and moves in the thickness range of 0.5 µm and 2 cm, preferably in the range between 10 and 200 µm.

The materials described according to the invention can be polymeric materials, but also metallic substrates, in particular also plastic and metal foils. In particular, the materials according to the invention also include polymeric sheet materials, which are optionally vapor-coated with metal, metal oxides or SiO _x .

In the context of the present invention, plastic films are understood in particular to be those which consist of a thermoplastic material, in particular of polyolefins such as polyethylene (PE) or polypropylene (PP), of polyester such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) or liquid-crystalline polyesters (LCP) , made of polyamides such as nylon 6,6; 4.6; 6; 6.10; 11; 12; Made of polyvinyl chloride (PVC), made of polyvinyl dichloride (PVDC), made of polycarbonate (PC), made of polyvinyl alcohol (PVOH), made of polyvinyl vinyl alcohol (EVOH), made of polyacrylonitrile (PAN), made of polyacrylic butadiene styrene (ABS), made of polystyrene-acrylonitrile (SAN), made of polyacrylic ester-styrene-acrylonitrile (ASA), made of polystyrene (PS), made of polyacrylates, such as polymethyl methacrylate (PMMA), made of cellophane, or made of high-performance thermoplastics, such as fluoropolymers, such as polytetrafluoroethylene (PTFE) and polyvinyl difluoride (PVDF) Polysulfones (PSU), polyether sulfones (PES), polyphenyl sulfides (PPS), polyimides (PAI, PEI), polyaryl ether ketones (PAE),
in particular, however, also those which are made from mixtures or from copolymers or terpolymers and those which are produced by coextruding homopolymers, copolymers or terpolymers.

Plastic films are also understood to mean those which consist of a thermoplastic material and with a metal of the 3rd main group or the 1st or 2nd subgroup or with SiO _x or a metal oxide of the 2nd or 3rd main group or the 1st or 2nd subgroup are steamed.

Metal foils are understood to be foils made of aluminum, copper, gold, Silver, iron (steel) or alloys of the metals mentioned.

In particular, sheet-like materials according to the invention include such understood, which are so surface-treated by an atmospheric plasma, that by interacting with the plasma gas, an increase in surface tension the polymer surface takes place. Furthermore, by certain types of plasma gas and / or aerosol a plasma graft or a Plasma coating (plasma polymerization) on or on the surface be performed. The extremely reactive species of plasma gas can do this have a cleaning and even disinfectant effect on the surface.

Web-like materials according to the invention, which are polarized, thus receive an increase in surface tension. This will ensure complete wetting with polar liquids such as alcohols or water. The Polarization occurs when atoms or molecular fragments - excited by the Plasma - react with surface molecules and consequently into the surface to be built in. Since these are mostly fragments containing oxygen or nitrogen, also speaks of surface oxidation.

Sheet-like materials according to the invention are provided with a surface graft provided if a targeted incorporation of molecules, preferably by a reaction on the polymer surface. For example, carbon dioxide reacts with hydrocarbon compounds to form carboxyl groups.

Web-like materials according to the invention with a plasma coating are characterized in that a reactive plasma gas by a kind of polymerization is deposited more or less closed on the surface. That’s it among other things possible release, barrier, antifog or in general To create protective layers on the plastic and metal foils.

Web-like materials according to the invention, for surface cleaning are characterized by being on the surface deposited impurities, additives or low molecular weight components are oxidized and be vaporized. Disinfection occurs when the number of germs in the Kind is reduced, watery it lies below the critical germ concentration.

The plasma gas for the treatment of the web-shaped according to the invention Materials is used, is characterized in that it is made of Mixtures of reactive and inert gases and / or aerosols. Through the high energy in the arc leads to excitation, ionization, fragmentation or radical formation of the reactive gas and / or aerosols. Due to the Flow direction of the plasma gas are the active species from the Burner chamber carried out and can be used to interact with the Surface of plastic and metal foils are brought.

The oxidizing process gas and / or aerosol can be used in concentrations of 0 to 100%, preferably between 5 and 95%.

Oxygen-containing gases and / or aerosols such as oxygen (O ₂ ), carbon dioxide (CO ₂ ), carbon monoxide (CO), ozone (O ₃ ), hydrogen peroxide gas (H ₂ O ₂ ), water vapor are preferably used as oxidizing plasma gases and / or aerosols (H ₂ O), evaporated methanol (CH ₃ OH), nitrogen-containing gases and / or aerosols such as nitrous gases (NO _x ), nitrous oxide (N ₂ O), nitrogen (N ₂ ), ammonia (NH ₃ ), hydrazine (H ₂ N ₄ ), sulfur-containing gases and / or aerosols such as sulfur dioxide (SO ₂ ), sulfur trioxide (SO ₃ ), fluorine-containing gases and / or aerosols such as terafluorocarbon (CF ₄ ), sulfur hexafluoride (SF ₆ ), xenon difluoride (XEF ₂ ), nitrogen trifluoride (NF ₃ ), boron trifluoride (BF ₃ ), silicon tetrafluoride (SiF ₄ ), hydrogen (H ₂ ) or mixtures of these gases and / or aerosols. Inert gases are preferably noble gases, and argon (Ar) is particularly preferred.

Crosslinkable plasma gases and / or aerosols are preferably unsaturated hydrocarbons such as ethylene, propylene, butene, acetylene; saturated hydrocarbons with the general composition C _n H _{2n + 2} , such as methane, ethane, propane, butane, pentane, iso-propane, iso-butane; Vinyl compounds such as vinyl acetate, methyl vinyl ether; Acrylates such as acrylic acid, methacrylic acid, methyl methacrylate; Silanes with the general composition Si _n H _{2n + 2} , halogenated silicon hydrides such as SiCl ₄ , SiCl ₃ H, SiCl ₂ H ₂ , SiClH ₃ , alkoxysilanes such as teraethoxysilane; Hexamethyldisilazane; Hexamethyldisiloxane used.

Maleic anhydride, acrylic acid compounds, vinyl compounds, carbon dioxide (CO ₂ ) are preferably used as graftable process gases and / or aerosols.

The active and the inert gas and / or aerosol is preferably used in a preliminary stage mixed and then introduced into the zone of the arc discharge. Out For safety reasons, certain gas and / or aerosol mixtures such as, for example Oxygen and silanes immediately before introduction into the zone of the Arc discharge mixed.

Such used for the treatment of the sheet-like materials according to the invention Plasmas are characterized in that their temperatures are in the range of Arc at several 10,000 Kelvin. Because the escaping plasma gas is still Having temperatures in the range of 1000 to 2000 Kelvin is sufficient Cooling of the temperature-sensitive polymeric materials necessary. This can generally done by an effectively working chill roll.

The contact time of plasma gas and foil material is very important. This should preferably be reduced to a minimum so that a thermal No damage to the materials. A minimal contact time is always through reached an increased web speed. The web speeds of the foils is usually higher than 1 m per minute, it is preferably between 20 and 600 m per minute.

Because the lifetime of the active species (radicals and ions) under atmospheric pressure is limited, it is advantageous the plastic and metal foils in very little Pass the distance past the burner opening (nozzle). This is preferably done at a distance of 0 to 40 mm, particularly preferably at a distance of 1 to 15 mm.

The following examples are intended to illustrate the invention: Examples

Plastic and metal foils according to the invention succeeded in the atmospheric Plasma by using the described plasma broad-beam burner to produce treated surfaces. This was achieved with a - compared to other processes - only a small outlay on equipment, and at the same time low Litigation costs. Since in the example each neutrode of the plasma torch has an outlet opening for the plasma gas, this can target the arc and be fed homogeneously. The laterally flowing, band-shaped plasma free jet therefore leads to a particularly homogeneous processing of the surface.

Surprisingly, by means of the burner described above Atmospheric pressure on various substrates reached surface tensions that are otherwise only possible in low-pressure plasma.

Surprisingly, it was also found that despite the use of one by one Arc discharge generated "hot" plasma with sufficient cooling and reasonable contact time no thermal damage to the processed plastic and metal foils appeared.

For this purpose, the relevant properties of the following film samples were as follows measured. The thermal damage to the film sections was visual or by Microscopic examinations assessed. The determination of the surface tension was carried out with commercially available test inks from Arcotec Oberflächentechnik GmbH according to DIN 53364 or ASTM D 2587. The specification of the surface tension was done in mN / m. The measurements were carried out immediately after treatment. The measurement errors are ± 2 mN / m. The The element distribution on the film surface was determined by means of ESCA measurements (Photoelectron spectroscopy). The specification of the element distribution was done in percent.

The following film materials were used in different examples Application of the method described and treated on their surface properties examined:

example 1

PE 1 :

Single-layer, 50 µ thick, one-sided corona-pretreated, transparent blown film made of an ethylene-butene copolymer (LLDPE, <10% butene) with a density of 0.935 g / cm ³ and a melt flow index (MFI) of 0, 5 g / 10 min (DIN ISO 1133 Condition D).

Example 2

PE 2 :

Single-layer, 50 µ thick, one-sided corona-pretreated, transparent blown film made of an ethylene-vinyl acetate copolymer (3.5% vinyl acetate) with approx. 600 ppm lubricant (erucic acid amide (ESA)) and approx. 1000 ppm antiblocking agent (SiO ₂ ), with a density of 0.93 g / cm ³ and a melt flow index (MFI) of 2 g / 10 min (DIN ISO 1133 Condition D).

Example 3

BOPP 1:

Single-layer, 20 µ thick, one-sided corona-pretreated, transparent, biaxially oriented film made of polypropylene with approx. 80 ppm antiblocking agent (SiO ₂ ), with a density of 0.91 g / cm ³ and a melt flow index (MFI) of 3 g / 10 min at 230 ° C.

Example 4

BOPP 2:

Co-extruded, three-layer, 20 µ thick, one-sided corona-pretreated, transparent, biaxially oriented film made of polypropylene with approx. 2500 ppm antiblocking agent (SiO ₂ ) in the outer layers), with a density of 0.91 g / cm ³ and a melt Flow index (MFI) of 3 g / 10 min at 230 ° C.

Example 5

PET:

Commercial, single-layer, 12 µ thick, corona-pretreated on one side, biaxially oriented film made of polyethylene terephthalate.

Example 6

PA :

Commercially available, single-layer, 15 µ thick, corona-pretreated on one side, biaxially oriented film made of nylon 6.

Only the untreated film sides were subjected to the plasma treatment. To the The plasma gases oxygen, nitrogen and carbon dioxide were used, each in Connection with argon as an inert carrier gas. Within the test series the gas concentration and the distance to the plasma torch vary. The slides were visually examined for their thermal damage. The surface tensions were determined using test inks, the element distribution on the Surface was determined using an ESCA measurement. A summary overview Table 1 gives the results.

Using the example of PE 1 (No. 4 to 7, Table 1) it could be shown that up to a distance (film - burner opening) of 10 mm comparable pretreatment effects be achieved. This only falls above a distance of 15 mm Pretreatment level significantly.

The materials listed in Table 1 were also pretreated by means of corona discharge and tested for their surface tension with test inks immediately after the treatment. Energy cans in the range from 0.1 to 10 J / m ² - as are common in industrial corona systems - were used.

The results of the corona discharge and the plasma treatment are in Table 2 juxtaposed.

Polypropylene in particular produced a significantly higher surface tension when using atmospheric plasma. However, higher values were also determined for PE compared to corona pretreatment.

Claims (7)

Web-like treated homogeneously with an atmospheric plasma metallic material with a thickness of less than 100 µm or web-shaped polymeric material, obtainable by using an indirect Plasmatrons generated atmospheric plasma if necessary under Delivery of a gas or aerosol to the surface of the material can act. Material according to claim 1, obtainable in that the material atmospheric plasma acting through a plasmatron, which with an elongated plasma chamber, which is cascaded in structure of neutrodes electrically isolated from one another, the for Generation of the plasma light gas required electrodes coaxial to the longitudinal axis the plasma chamber are arranged and the plasma jet outlet opening runs parallel to the longitudinal axis of the plasma chamber. Material according to one of the preceding claims, obtainable in that the atmospheric plasma acting on the material is determined by an indirect one Plasmatron, in which at least one neutrode with a permanent magnet pair to influence the shape and position of the plasma arc is provided. Material according to one of the preceding claims, obtainable in that the atmospheric plasma acting on the material is determined by an indirect one Plamatron, in which at least individual neutrodes with a Possibility of supplying a gas to the plasma chamber, generated. Material according to one of the preceding claims, obtainable in that the atmospheric plasma with the addition of a mixture of one Inert gas and an oxidizing gas and / or aerosol, a crosslinkable Gas and / or aerosol or a graftable gas and / or Aerosol. Material according to one of the preceding claims, obtainable in that the atmospheric plasma at a distance of 1 to 40 mm on the Lets material act. Material according to one of the preceding claims, characterized in that the polymeric materials are optionally plastic films vapor-coated with metal, metal oxide or SiO _X.