WO2016071256A1

WO2016071256A1 - Plasma treatment of release layers

Info

Publication number: WO2016071256A1
Application number: PCT/EP2015/075400
Authority: WO
Inventors: Nikolay BELOV; Hermann Neuhaus-Steinmetz; Dennis Perlbach; Tobias Winkler
Original assignee: Tesa Se
Priority date: 2014-11-06
Filing date: 2015-11-02
Publication date: 2016-05-12
Also published as: DE102014222724A1; EP3215582A1

Abstract

The invention relates to a method for plasma treating a release layer, comprising the following steps: (i) introducing a plasma gas into a discharge chamber; (ii) exciting the plasma gas to a plasma state by discharge; and (iii) exposing the release layer to the plasma gas in a plasma state, said exciting of the plasma gas in a plasma state taking place by means of a electric high voltage having a frequency of between 2000 - 100.000 Hz and the high voltage being pulsed at a switching frequency of between 30 - 5000 Hz. The invention also relates to release layers which can be obtained according to said method, and to release liners comprising a support and the release layer. The invention also relates to adhesive strips comprising the thus described release liner and to an adhesive mass.

Description

Plasma Treatment of Release Layers Technical Field of the Invention

The present invention relates to a process for the plasma treatment of a release layer, comprising the steps of (i) introducing a plasma gas into a discharge space; (ii) exciting the plasma gas into a plasma state by discharge; and (iii) exposing the release layer to the plasma gas in a plasma state, wherein the plasma gas is excited into a plasma state via a high voltage electrical power having a frequency of 2000 to 100,000 Hz and the high voltage is pulsed at a switching frequency of 30 to 5000 Hz. The present invention further relates to release layers obtainable by the method described herein, as well as release liners comprising a support and the release layer. Also described are adhesive tapes comprising the release liner described herein and an adhesive.

General State of the Tech

Adhesive tapes are often wound into a roll in the form of an Archimedean spiral at the end of the manufacturing process. For this purpose, the adhesive is covered before winding the adhesive tape with a release liner (also referred to as release or covering). Release liners are also used for covering flat goods such as labels. In the case of double-sided adhesive tapes, release liners can be adjusted in such a way that one side of the adhesive tape is first exposed during the unwinding of the tape. This is possible if the release values between the respective release layer and the adhesive on the individual sides of the double-sided adhesive tape differ from one another.

As release liners, paper or film carriers are used, which are equipped with a release layer in order to reduce the adhesion tendency of adhering products to these surfaces (release-effective function). The release agents used are various substances such as silicones, fluorinated silicones, fluorinated alkanes and polyolefins, silicone copolymers, carbamates, waxes or mixtures thereof. Silicones have largely prevailed over the last few years due to their good processability and advantageous release properties. Due to the large number of different compositions, silicones can also be used to adjust the release values of release liners. The level of the respective peel force of a pressure-sensitive adhesive of a silicone-based release liner is usually adjusted by silicone resins and in particular by so-called MQ resins. D. Satas, Handbook of Pressure Sensitive Adhesive Technology, 3rd Edition, p. 664, provides a good overview of silicone resins and in particular MQ resins. The different release forces of the individual release layers compared to an adhesive are the result of different MQ resin contents in the respective release composition.

Although it is possible with the MQ resins to specifically adjust the release forces of a release liner and in particular the release forces of the release liner from the individual sides of a double-sided adhesive tape, a specific silicone composition must be selected for each desired release force coated on a carrier and cured. This makes it necessary to use and also stockpile multiple release liners with different MQ resin contents when there is a need for different release properties. Due to the large variety of different adhesive composition such storage is hardly feasible. Furthermore, the use of many different coating compositions can lead to increased waste material, since the individual coating compositions can not be permanently stored. Instead, the particular coating composition must be prepared just prior to application.

In addition, it is known that the use of MQ resins can change the release force profile of silicone-coated release liners. The separation force profile is the dependence of the release force on the withdrawal speed of the release liner from the adhesive. Typically, the force required to remove a release liner from an adhesive increases (or decreases) in the range of low take-off speeds (from 0 to, for example, 20 m / min) with increasing take-off speed before a release force sets in which is only slightly lower than the take-off force depends. Whether the release force increases in the range of low take-off speeds (rising profile) or decreases (sloping profile) depends on the content of MQ resin in the formulation. For high resin contents, sloping profiles are often observed and for low resin contents frequently rising profiles.

If the proportion of MQ resins in the silicone composition of the release coating is increased in order to increase the release forces of the release liner compared to a specific adhesive, the separating force profile may be reversed in the release force profile. Thus, the profile of the release force profile in silicone resin-containing formulations is difficult to predict, especially in the range of low take-off speeds. For example, it has been observed that in the low pull-off rate range of 0-20 m / min, the release values are high in the case of high MQ resin concentration and decrease with increasing drawdown speed, although the release values are low at low draw speeds for low MQ resin or resin free formulations and usually increase slightly with increasing take-off speed.

The use of MQ resins in silicone-based release coatings is therefore not always ideal for the specific adjustment of certain separation forces.

Also known from the prior art is the corona treatment of silicone-coated carrier materials. However, such known from the prior art materials are not release liners that could be used for strong pressure-sensitive acrylate adhesives with high bond strengths on steel. Because the effect achieved by the corona treatment leads to such a strong interaction between the above-mentioned strongly adhesive adhesives and the corona-treated surface that such a treated substrate is no longer suitable as a release material.

Object of the present invention The object of the present invention is therefore to address the disadvantages of the prior art and to provide an improved process with which the release values of release liners can be adjusted in a targeted manner, even for strongly tacky products, in a simple manner. without there being any significant change in the course of the release force profile compared to an untreated liner (reference liner) or excessive interaction between the corona-treated surface and the adhesive due to over-treatment.

Summary of the present invention

The present invention addresses this problem and the problems of the prior art by providing a process for the plasma treatment of a release layer, comprising the steps of: introducing a plasma gas into a discharge space;

- exciting the plasma gas into a plasma state by discharge; and

- exposing the release layer to the plasma gas in a plasma state; wherein the exciting of the plasma gas in a plasma state is pulsed with a switching frequency of 30 to 5000 Hz.

The present invention further relates to a release layer obtainable by the process according to the invention; Release liner, comprising a support and the release layer obtainable by the process according to the invention; and an adhesive tape comprising the release liner and an adhesive in contact with the release liner release layer.

In the method of plasma treatment of a release layer described herein, the release layer is exposed to a high voltage electrical discharge. For this purpose, an electrode or an electrode system by a high-frequency generator with an AC voltage of about 5-50 kV, and a frequency between 2 and 100 kHz, preferably supplied between 18-100 kHz.

The high-voltage discharge occurs between the lying at a high electrical potential electrode system and a counter electrode to ground potential. The counterelectrode at ground potential is preferably a roller having a metal body which is grounded. If the electrodes are not coated with a high voltage resistant insulator, the backing roll must be coated with a high voltage resistant layer, such as a layer of silicone rubber, ceramic or glass. Alternatively, bare metal rolls or rolls with conductive coatings may be used when the electrodes are coated with a high voltage resistant insulator. Furthermore, both the electrodes and the counter-roller can be coated with a high-voltage resistant insulator. The distance between the electrode system, which is preferably configured in the form of electrodes arranged parallel to the roller, and the track surface is typically between approximately 1 and 2 mm.

Can also be used so-called segment electrodes with fold-back individual segments, which typically have a width of 5 to 20 mm. Hereby, the treatment width can be adjusted by folding back the segments in the side areas as needed. Likewise, can be achieved by the targeted folding back of certain segments a strip-shaped treatment.

For the treatment, for example, the release layer applied to a support can be guided over a grounded treatment roller, so that the side of the release layer facing the electrode is treated.

Air between the treatment roller and the carrier may also cause a treatment effect on the back of the carrier. In order to suppress unwanted treatment of the back of the carrier, it is useful to avoid introduced by the web movement and roller rotation drag air between the material to be treated and the roller. For this purpose, the air before the treatment gap, i. before the gap between the electrodes and the release layer to be treated, by means of a pressure roller, an air nozzle, by electrostatic application, e.g. be extruded by means of a charging electrode R130 Fa. Eltex, or another measure. In a preferred embodiment of the invention, the carrier is thus guided over a treatment roller and pressed before the treatment gap on the treatment roller.

If necessary, ambient air can be passed through the electrode housing or even through the electrodes themselves during discharge in air for cooling and to remove the ozone created.

In the method according to the invention, the plasma treatment is preferably carried out at atmospheric pressure. By "atmospheric pressure", the present invention means a pressure of 0.5 to 2 times the ambient pressure, preferably 0.75 to 1 .5 times, more preferably from 0.9 to 1 .2 times the ambient pressure. In the case of a plasma treatment in which the individual steps of the method according to the invention are carried out at said pressures, the present invention also speaks of "atmospheric pressure plasma treatment", which is also referred to herein as "corona treatment".

In the case of such atmospheric pressure plasma treatment, the treatment effect is provided by the contact of arcs on the surface of the release layer. This discharge (also called "corona discharge") occurs as a characteristic glowing high-voltage discharge and it is believed that the electrons leaving the electrode experience high acceleration in the electric field In the case of air as a plasma gas, it is mainly emitted to oxygen and nitrogen molecules, in the case of air this leads to a dissociation or ionization of mainly oxygen and nitrogen molecules, since the energies of the electrons incident on the release layer Molecular cleavage may also be performed on the free energies of the corona discharge, but direct reactions between the components of the plasma gas and the non-activated surface may also take place.

When the plasma gas is excited into a plasma state by discharge (also referred to as "corona discharge" in the case of atmospheric pressure plasma treatment), a plurality of arcs are produced The corona discharge, which occurs when the plasma gas is excited into a plasma state by discharging, is therefore also referred to as a barrier discharge In principle, according to the invention uniform treatment effects are sought over the entire electrode width of the corona or plasma system . For a uniform discharge over the width of the electrodes is a relatively high minimum electrical power P _m in needed. This means that a certain minimum treatment effect at a certain speed under normal conditions not substeps n This minimum electrical power is typically one-fifth to one-tenth of the maximum useful generator power for a particular electrode design. On the one hand, this means that the possible power range of the generator can not be utilized due to the necessary minimum power for the electrodes. On the other hand, the treatment effect in the case of release layers is so pronounced that even with the smallest possible treatment strength separating forces against strongly pressure-sensitive adhesives, for example strong sticky acrylate adhesives are achieved, which no longer allow use of the treated surface as a release layer for such an adhesive. In other words, a conventional, ie unpulsed, plasma treatment is not suitable for producing release layers with low release values in a range from 2 to 100 cN / cm in contrast to strongly pressure-sensitive adhesives.

The invention is based on the finding that the limit for the minimum treatment effect can be broken by pulsing (rapid periodic switching on and off) of the high-frequency discharge, preferably by pulsing the corona discharge. During the switch-on time, an electrical power P is set equal to or above the minimum power of the plasma unit Pmin (see FIG. 1), so that a homogeneous discharge, preferably a homogeneous corona discharge, across the width of the electrodes is ensured during this time. Pulses can be used to reduce the minimum effective electrical power for uniform treatment across the web width to less than 1% of the minimum electrical power without pulses. A safe ignition over the entire web width occurs at each pulse, as long as the power during the on-time is at least as large as the minimum power Pmin for a uniform treatment across the web width.

The effective electrical power Petfektiv a pulsed discharge results from the ratio of the on time ti to repetition time T and from the power P during the on-time. For a set power of P = Pmin during the on-time an effective power of:

In a preferred embodiment of the invention, the repetition time T is varied at a fixed on-time ti for adjusting the effective power. Alternatively, the repetition time T can be varied at a fixed switch-on time ti. In another embodiment of the invention, both the on time and the reheat time are varied simultaneously.

In a particularly preferred embodiment of the invention, the discharge, i. the excitation of the plasma gas in a plasma state, pulse width modulated. In the case of pulse width modulation ("PWM"), the on-time t.sub.i is varied at a fixed recovery time T. The on-time t.sub.i is preferably 0.002 to 33 ms., By the pulse, ie the rapid periodically switching on and off of the discharge It is possible to choose the treatment dose, ie the energy incident on one square meter of treated surface, low and nevertheless to ensure a homogenous treatment over the entire width of the electrode.The calculation of the treatment dose is carried out according to the formula (1).

(1) j _ ^ effective

v * b

D: treatment dose in W ^* min / m ²

Peffekti _V : effective generator power in W

v: Machine speed in m / min, with which the surface to be treated is moved through the plasma atmosphere

b: electrode width in m By selectively adjusting the power, the dose can be regulated at a certain machine speed so that the resulting dose D corresponds to the target dose Dsoii.

¹ P soll = ¹ P effective = ^ D soll * v ^v * h ^υ

The pulsing of the high-frequency discharge is carried out according to the invention with a switching frequency of 30 to 5000 Hz. This ensures that the release layer can be exposed to a dose of 0.01 -6 W ^* min / m ² . In a preferred embodiment of the invention, the dose to which the release layer is exposed in the method according to the invention is 0.01 -6, preferably 0.01-3 W ^* min / m ² . By adjusting the treatment dose to the range mentioned, the separation behavior of the release layers described herein can be adjusted in a targeted manner, without reversing the course of the release force profile in the region of low take-off speeds. The release force of the treated release layer with respect to a particular adhesive surface increases with increasing treatment dose. Furthermore, the inventive method allows the treatment of release layers with a plasma discharge such that the treated release layers are also suitable as release materials against strongly adhesive surfaces such as acrylate-based PSAs. In particular, the method according to the invention allows the provision of release layers whose release forces are in the range from 2 to 100 cN / cm in relation to strongly adhesive adhesives.

By suitable switching frequencies and electrode designs with multiple electrode bars with suitable and possibly different distances further treatment interferences on the surface, due to the movement relative to the electrodes with pulsed power can be largely avoided. Likewise, electrodes which generate a broad, barely interrupted plasma zone in the web direction are advantageous for avoiding the treatment interferences.

Excitation of the plasma gas into a plasma state by discharge creates an atmosphere (also referred to herein generally as the "plasma atmosphere" and in the case of the corona). By the selective switching on and off of the high-frequency corona discharge, ie by the pulsed excitation of the plasma gas, the method according to the invention enables a gentle treatment of the release layer, which is suitable for the plasma treatment of the release layer. Such a gentle treatment with a comparatively low treatment effect would not be possible in the case of an unpulsed conventional plasma treatment and would not allow the provision of release layers with low release forces.

In a preferred embodiment of the invention, the plasma gas consists of nitrogen, carbon dioxide, argon, helium, air or a mixture of two or more of these gases. In a further embodiment of the invention, the plasma gas may further contain hydrogen.

In a likewise preferred embodiment of the invention, the release layer is applied to a carrier. Preferably, the support is over the entire area, i. Covering and not only selectively covered by the release layer, so that the thickness of the release layer is preferably in a range of 0.05 - 5 μηη.

In a further embodiment of the invention, the release layer contains at least one silicone, at least one fluorinated silicone, at least one fluorinated or partially fluorinated

Alkane or polyolefin, at least one silicone copolymer, at least one carbamate, at least one wax or mixtures of two or more of said substances.

The release layer is particularly preferably silicone-based. "Silicone-based" in the sense of the present invention means that the release layer contains at least one silicone-based polymer (hereinafter also "base polymer"). As base polymers are

Polysiloxanes, preferably functionalized and unfunctionalized polydimethylsiloxanes used.

Preferably, the composition underlying the release layer contains up to 80 parts by weight, more preferably up to 40 parts by weight of a silicone resin, based on 100 parts by weight of silicone resin and base polymer. Suitable silicone resins are known resins, preferably MQ resins. Suitable resins are described in D. Statas in: Handbook of Pressure Sensitive Adhesive Technology, 3rd Edition, page 664. Commercially available examples of particularly preferred resins are RCA 395 from Bluestar Silicones, Syl- ^Off® SL 40 from Dow Corning, and ^CRA® 17 from Wacker Silicones. In another Embodiment of the invention is the release layer underlying composition free of silicone resins.

The release layer to be treated by the method according to the invention can be based on solvent-containing and / or solvent-free systems. A "solvent-containing system" means that the system concerned is applied as an actual solvent-containing system, after which, however, only a maximum of traces of the solvent in the release layer are present after thermally initiated drying and crosslinking System "and thus indicates the special properties of such a solvent-based release layer.

The composition on which the release layer is based can be radiation-crosslinking (UV or electron beam), condensation-curing or addition-crosslinking. The composition which forms the release layer to be treated is preferably addition-curing.

The composition underlying the release layer is preferably a crosslinkable silicone system. These include mixtures of crosslinking catalysts, so-called thermally curable condensation or addition-crosslinking polysiloxanes and crosslinking component. For condensation-crosslinking silicone systems, tin compounds such as dibutyltin diacetate are frequently included in the composition as crosslinking catalysts. The composition underlying the release layer is particularly preferably an addition-crosslinking silicone system. Silicone-based release coatings on addition-curing basis can be cured by hydrosilylation. These release agents usually comprise the following components: · an alkenylated polydiorganosiloxane (especially linear and branched polymers having terminal and non-terminal alkenyl groups),

A polyorganohydrogensiloxane crosslinking agent as well

• a hydrosilylation catalyst. As catalysts for addition-crosslinking silicone systems (hydrosilylation catalysts), for example, platinum or platinum compounds, such as, for example, the Karstedt catalyst (a Pt (O) complex compound) have prevailed. Alternatively, rhodium compounds can be used.

Furthermore, it is also possible to use photoactive catalysts, so-called photoinitiators, in combination with UV-curable cationically crosslinking siloxanes based on epoxide and / or vinyl ethers or UV-curable free-radical crosslinking siloxanes, such as acrylate-modified siloxanes. Likewise, the use of electron beam curable silicones (e.g., silicone acrylates) is possible. Corresponding systems may also contain other additives, such as stabilizers or leveling agents, depending on the intended use.

Also useful are compositions in which the crosslinking reaction between organopolysiloxanes having hydrocarbyl substituted with mercapto groups bonded directly to the silicon atoms and organopolysiloxanes having vinyl groups bonded directly to the silicon atoms is in the presence of a photosensitizer. Such compositions are described for example in US 4,725,630 A1. When using the organopolysiloxane compositions described, for example, in DE 33 16 166 C1, which have epoxy groups substituted hydrocarbon radicals bonded directly to the silicon atoms, the crosslinking reaction is induced by release of a catalytic amount of acid which is obtained by photodecomposition of added onium salt catalysts. Other cationic-mechanism-curable organopolysiloxane compositions are materials having, for example, propenyloxysiloxane end groups.

In addition to the base polymer and a possible silicone resin, in the composition on which the release layer to be treated according to the invention is based, further constituents such as anchoring aids; organic and / or inorganic pigments; Fillers such as carbon black and organic and / or inorganic particles (eg polymethylmethacrylate (PMMA), barium sulphate or titanium oxide (ΤΊΟ2)); and organic and / or inorganic antistatics such as ionic polyelectrolytes, organic salts, ionic liquids, metal powders (eg silver powder), graphite and carbon nanotubes may be included. In a preferred embodiment of the invention, the composition on which the release layer to be treated according to the invention is based, in each case independently 0 to 5 parts by weight of one or more anchoring aids, one or more pigments, one or more fillers, and one or more antistatic agents, respectively based on 100 parts by weight of base polymer and silicone resin.

The inventive method is suitable for targeted adjustment of the release forces of release liners. The pulsed plasma treatment makes it possible to increase the separation forces without significantly changing the release force profile, ie the course of the release force as a function of the withdrawal speed, of the (untreated) release layer. In this respect, the method according to the invention allows the provision of release liners in which the absolute release force values can be set without significant change in the release force profile as a function of the dose. By the expression "setting the absolute release force values without substantially changing the release force profile", it is meant that the shape of the diagram does not change significantly when the release forces (Y-axis) are applied against the withdrawal speed (X-axis), but the profile merely shifts in its absolute values along the Y-axis as a function of the treatment dose, however, the shape of the separation force profile, ie the shape of the curve itself, remains substantially unchanged Starting from a surface to be treated, release layers with different degrees of separation behavior can be prepared in a simple manner with respect to one and the same adhesive mass, while retaining the release force profiles of the different release layers he release layers can thus be avoided both at low and at high take-off speeds. This has the advantage that, in the case of double-sided adhesive tapes, selective removal of exactly the side of the release liner with the lower release force from the adhesive is possible even with only a slight difference in the release values, without having to rely on different silicone compositions. Especially in the field of highly automated processes errors are thus avoided, since an identical or at least similar separation force profile ensures a safe and uniform difference in the separation forces between the two release layers and the adhesive over all take-off speeds. In addition, another advantage of the Maintaining known release force profiles in that adhesives can be transferred from a liner to a substrate, for example, without having to readjust process parameters such as pressure forces when changing the process speed.

Against this background, the present invention also relates to release layers, which are obtainable by the process according to the invention, and release liners, comprising a support and a release layer. In a preferred embodiment of the invention, this support is selected from the group consisting of polyethylene terephthalate (PET), polybutylene, polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC) and paper. Particularly preferred supports are glassine papers, clay-coated papers, Kraft papers, machine-grade papers and polyolefin-coated papers, and biaxially stretched PET, mono- and biaxially drawn PP, cast PP (extruded PP), HDPE and LDPE. Examples of suitable carriers which are provided with a release layer and are particularly suitable for treatment with the method according to the invention are siliconised glassine papers from Mondi (G-Liner), siliconized polyolefin-coated papers from Loparex (Polyslik ™), siliconized PET films from Siliconature (SILPHAN S), siliconized mono- and biaxially stretched PP films, as well as cast aluminum films from Siliconature (SILPROP S, SILPROP M, SILPROP K) and siliconized HDPE and LDPE films from the company Mondi.

In a further aspect, the present invention relates to adhesive tapes comprising a release liner whose release layer has been treated by the method described herein. In the case of these adhesive tapes, at least one side of the adhesive of the adhesive tape is in contact with the release layer obtainable by the process according to the invention. In a particularly preferred embodiment, the present invention relates to adhesive tapes in which the adhesive which is in contact with the release liner of the invention comprises an acrylate-based adhesive, preferably an acrylate-based adhesive having a bond strength to steel of 1 to 20, particularly preferably 5 Is -15 N / cm. In an exemplary embodiment of the invention, the coating weight of the adhesive is 50 g / m 2. The adhesive forces on steel mentioned herein are as follows determined: A 2 cm wide and 25 cm longer strip of adhesive tape is glued on the test plate by five times double rollover with the winding speed of 10 m / min using a 4 kg roll. The test plate is clamped in the lower clamping jaw of the tensile testing machine (BZ2.5 / TN1 S Zwick) and the adhesive tape is stretched over its free end by means of a tensile testing machine (BZ2.5 / TN1 S Zwick) at a peeling angle of 180 ° at a speed of 300 mm / min deducted. The necessary force is determined. The measurement results are averaged over three measurements and normalized to the width of the strip in N / cm.

The test plates are polished steel plates (material no. 1.4301, DIN EN 10088-2, surface 2R) with surface roughness Ra = 80-130 nm).

In a further, likewise preferred embodiment of the invention, the adhesive which is in contact with the release liner of the release liner of the adhesive tape described herein has a maximum proportion of acrylic acid and methacrylic acid (hereinafter also "(meth) acrylic acid content") 5, preferably 3, more preferably 1 percent by weight, based on the total composition of the adhesive, by which is meant that the proportion of acrylic acid and methacrylic acid units in the adhesive composition together does not exceed the stated values. Units "includes both copolymerized acrylic acid and methacrylic acid within possible (sticky) sticky polymers of the adhesive as well as a possible (residual) monomer content of acrylic acid and methacrylic acid in the composition. In other words, the proportion of polymerized acrylic acid and methacrylic acid units and possible residual monomers in its sum does not exceed the maximum proportions mentioned.

Experimental part

The following exemplary experiments are intended to illustrate the invention in more detail, without the invention being unnecessarily limited by the choice of the examples given.

Examples 1 -6

A double-sided siliconised glassine release paper G-Liner 1 12660 from Mondi Jülich GmbH with a width of 300 mm was used on a corona system with different thicknesses Web speeds of 10 m / min to 50 m / min treated. The very low required generator power of the corona system, type Corona Plus of the company Vetaphone was with the built-in pulse width modulation function to 10 watts and over the web speeds of 10-50 m / min to corresponding doses of 0.4-2 W min / m2 set. The gap between the electrodes and the release layer to be treated (treatment gap) was set to 2 mm. The electrode width was 500 mm. The treatment of the release paper has been carried out in a nitrogen atmosphere with a residual oxygen content of less than 50 ppm. As a comparative example, the same release paper was treated on the same equipment with the pulse width modulation function switched off at the manufacturer's determined and specified minimum corona power without pulses of 500 W for a homogeneous treatment effect across the web width without pulse width modulation. The calculation of the treatment dose is carried out according to the formula (1). (1) D = P / (v * b)

D: Corona dose in W min / m ²

P: generator power in W

v: machine speed in m / min

b: electrode width in m

The release force of the pretreated release papers is determined by bonding with three test strips each 20 mm wide. The test strips used are test tapes with the product numbers tesa 7475 and tesa 7476. Tesa 7475 is an adhesive tape with a PET film as a carrier, on which an acrylate compound is applied (adhesion to steel 12.5 N / cm). Tesa 7476 is an adhesive tape with a fabric tape as a support on which a natural rubber adhesive is applied (bond strength to steel 8 N / cm). The samples are stored for 24 hours at 70 ° C for tesa 7475 and at 40 ° C for tesa 7476 under a weight load of the bond of 2 N / cm 2 before the measurement. After storage, the test strips are cut to a length of 220 mm and stored for two hours under test conditions. For the measurement, the upper test strip of the bond is clamped in the upper jaw of a tensile testing machine, as used in AFERA 4001. The lower test strip is clamped in the lower jaw. The jaw distance is 50 mm. The measurement is made at a speed of 300 mm / min, with which the jaws are moved apart. The mean value determined over a distance of 100 mm three measurements of the force required for the separation of the bond corresponds to the separation force. The measurements are carried out at a test climate of 23 ± 1 ° C and 50 ± 5% rel. Humidity carried out. The measured release force of pulsed corona treated release paper is in Table 1. shown.

Table 1: Release force of untreated and treated Glassine release paper against acrylic adhesive tape tesa 7475 and natural rubber tape tesa 7476 with an electrode width of 500 mm.

For a grading of the release force of the release paper used, the minimum increase in release force with a classic corona treatment to 151 cN / cm against tesa 7475 is too strong even at web speeds of 50 m / min in corona treatment to be suitable for release application be. With the help of the pulse width modulation, the increase of the separation force can be adjusted from small increases. In the example, at a web speed of 50 m / min (0.4 W min / m ² at 10 W), an increase from 6 to 10 cN / cm was achieved against tesa 7475. With a possible reduction in power to about 1 W even smaller increases in the separation forces are possible. Examples 7-12

A double-sided siliconised PE-Coated release paper Poly Slik 603/80 gloss / gloss sf from Loparex BV with a width of 300 mm was treated on a corona machine with web speeds of 10 m / min to 50 m / min. The performance of the Corona system has been reduced to 10 watts and corresponding doses of 0.4-2 Wmin / m2 compared to classical corona treatment by a generator with built-in pulse width modulation function. The gap between the electrodes and the surface to be treated was set to 2 mm. The electrode width was 500 mm. The treatment of the release paper has been carried out in a nitrogen atmosphere, with a residual oxygen content of less than 50 ppm. As a comparative example, the same release paper was treated on the same equipment with pulse width modulation function switched off at the minimum corona power of 500 W for a homogeneous treatment effect across the web width without pulse width modulation. The calculation of the treatment dose is carried out according to the formula (1). The measurement of the separation forces was carried out as described for Examples 1-6. The measured separation forces are listed in Table 2.

Table 2: Release force of treated and untreated PE coated release paper against acrylic adhesive tape tesa 7475 and natural rubber adhesive tape tesa 7476

Example No. Type of V P release force release force

dose

Treatment tesa 7475 tesa 7476

[m / min] [W] [W

[cN / cm] [cN / cm] min / m ² ]

0

- 0 3 16

Reference.

(Classic 50 500

7 20 124 170

Corona)

(Classic 30 500

8 33 127 172

Corona)

(Classic 10 500

9,100,154,148

Corona)

10 (PWM Corona) 50 10 0.4 6 21

1 1 (PWM Corona) 30 10 0.7 8 25

12 (PWM Corona) 10 10 2 11 30

For a grading of the release force of the release paper used, the minimum increase in release force with a classic corona treatment to 124 cN / cm vs tesa 7475 is too strong even at web speeds of 50 m / min in the corona treatment to be suitable for release application. With the help of the pulse width modulation, the increase of the separation force can be adjusted from small increases. In the example, at a web speed of 50 m / min (0.4 W min / m ² at 10 W), an increase from 3 to 6 cN / cm was achieved with respect to tesa 7475. With a possible reduction in power to about 1 W even smaller increases in the separation forces can be achieved.

Claims

claims

1 . A process for the plasma treatment of a release layer, comprising the steps of: - introducing a plasma gas into a discharge space;

- exciting the plasma gas into a plasma state by discharge; and

- exposing the release layer to the plasma gas in a plasma state; wherein the exciting of the plasma gas into a plasma state via a high voltage electrical with a frequency of 2000 to 100,000 Hz and the

High voltage is switched on and off with a switching frequency of 30 to 5000 Hz.

2. The method of claim 1, wherein the plasma gas comprises nitrogen, carbon dioxide, argon, helium, air or mixtures thereof.

3. The method according to any one of claims 1 or 2, wherein the exciting of the plasma gas is pulse width modulated.

4. The method according to any one of claims 1 or 2, wherein the exciting of the plasma gas is pulsed at a variable repetition time and a fixed on-time or pulsed at variable repetition and variable on-time.

5. The method according to any one of claims 1 to 4, wherein the release layer is exposed to a dose of 0.01 to 6 W ^* min / m2.

6. The method according to any one of the preceding claims, wherein the release layer is applied to a support and covers the carrier over the entire surface.

7. The method of claim 6, wherein the carrier is passed over a treatment roller and is pressed before a treatment gap on the treatment roller.

8. The method according to any one of the preceding claims, wherein the release layer at least one silicone, at least one fluorinated silicone, at least one silicone copolymer, at least one carbamate, at least one fluorinated, partially fluorinated or unfluorinated alkane or polyolefin, at least one wax or mixtures of two or more of said substances.

9. The method according to any one of the preceding claims, wherein the release layer underlying composition contains at least one silicone-based polymer.

10. The method of claim 9, wherein the composition underlying the release layer contains up to 80 parts by weight of a silicone resin, based on 100 parts by weight of silicone resin and silicone-based polymer.

1 1. Release layer obtainable by the process according to any one of claims 1-10.

12. Release liner comprising a support and a release layer according to claim 11.

The release liner of claim 12, wherein the backing is selected from the group consisting of biaxially stretched polyethylene terephthalate, polybutylene, polypropylene, polyethylene, monoaxially stretched polypropylene, biaxially oriented polypropylene, PVC, cast PP, and paper.

14. An adhesive tape comprising a release liner according to any one of claims 12 and 13 and at least one adhesive.

15. Adhesive tape according to claim 14, wherein the at least one adhesive is in contact with the release layer of the release liner and / or with the release layer facing away from the release liner.

16. Adhesive tape according to claim 15, wherein the at least one adhesive is in contact with the release layer of the release liner and does not exceed a maximum (meth) acrylic acid content of 5, preferably 3, particularly preferably 1 weight percent, based on the total composition the at least one adhesive which is in contact with the release liner release layer.