METHOD FOR ALTERING ADHESION PROPERTIES OF A SURFACE BY PLASMA COATING

Abstract

A method for altering adhesion properties of a surface of a substrate by a coating, comprising the steps of: a) ionizing a plasma gas at low temperature and at atmospheric pressure, thereby creating a plasma with a plasma temperature of at most 50° C.; b) introducing a precursor into a plasma gas afterglow of the plasma; c) subjecting the surface of the substrate to the plasma including the precursor, thereby forming a coating onto the surface. The plasma gas is essentially completely comprised of inert gas. The coating alters the adhesion properties of the surface.

Claims

1.-15. (canceled)

16. A method for altering adhesion properties of a surface of a substrate with respect to a second surface by a coating, comprising the steps of: a) ionizing a plasma gas at low temperature and at atmospheric pressure, thereby creating a plasma with a plasma temperature of at most 50° C.; b) introducing a precursor into a plasma gas afterglow of said plasma; c) subjecting the surface of the substrate to said plasma comprising said precursor, thereby forming a coating onto said surface, wherein said plasma gas is essentially completely comprised of inert gas, and wherein said coating alters the adhesion properties of the surface, wherein the substrate is not in a plasma zone and/or does not pass through a plasma zone, said plasma zone being a zone where plasma is induced.

17. The method according to claim 16, wherein the precursor is selected to increase the adhesion of the surface by the coating.

18. The method according to claim 16, wherein the precursor is introduced as an aerosol or as a gas.

19. The method according to claim 16, wherein said plasma gas comprises inert gas for at least 99% by volume.

20. The method according to claim 16, wherein said plasma gas comprises 02 for at most 1% by volume.

21. The method according to claim 16, wherein said inert gas is a noble gas.

22. The method according to claim 16, wherein said inert gas is a non-noble gas.

23. The method according to claim 16, wherein the plasma temperature is at most 50° C.

24. The method according to claim 16, wherein said plasma gas is ionized by means of electrodes.

25. The method according to claim 16, wherein the substrate moves during step c.

26. The method according to claim 16, wherein the substrate is static during step c.

27. The method according to claim 16, wherein said substrate undergoes a plasma pre-treatment step prior to being subjected to the plasma comprising the precursor.

28. The method according to claim 16, wherein the precursors comprises any or any combination of the following groups: hydroxyl-functional groups, amines, primary amines, isocyanates and/or epoxy-functional groups.

Description

BRIEF DISCUSSION OF THE FIGURES

[0031] FIG. 1: at t=t0 the plasma is on. A precursor R—X is added to the plasma gas and the plasma is contacted with the substrate. Hereby the precursor R—X is radicalized, and the substrate is activated.

[0032] FIG. 2: at t=t1 the plasma is on. Radical recombination reactions are taking place on the surface, resulting in a covalent bond between substrate and precursor.

[0033] FIG. 3: at t=t2, the plasma is on. Film growth and thickness depend on treatment time. Also cross-linking is taking place.

[0034] FIG. 4: at t=t3 the plasma is off. After the plasma treatment, a functional plasma deposited film remains which is grafted onto the substrate.

DETAILED DISCUSSION OF THE INVENTION AND ITS EMBODIMENTS

[0035] The present invention concerns a method for altering adhesion properties of a surface of a substrate by a coating, comprising the steps of: [0036] a) ionizing a plasma gas at low temperature and at atmospheric pressure, thereby creating a plasma; [0037] b) introducing a precursor into said plasma; [0038] c) subjecting the surface of the substrate to said plasma comprising said precursor, thereby forming a coating onto said surface,
whereby said plasma gas is essentially completely comprised of inert gas, and whereby said coating alters the adhesion properties of the surface.

[0039] In an embodiment, the adhesion is increased. In another embodiment, the adhesion is decreased. In yet another embodiment, the adhesion properties are altered according to a predetermined surface modification profile. Hereby, the adhesion properties may for instance be increased on a first portion of the surface and may be decreased on a second portion of the surface. Preferably the precursor is selected to increase the adhesion of the surface by the coating or the precursor is selected to de crease the adhesion of the surface by the coating. The present method allows to deposit a coating on a large number of substrates and using a large number of precursors, in particular due to the low temperature of the plasma, preferably of at most 50° C., and due to the preferable introduction of the precursor in the plasma afterglow. Hence, this allows a skilled person to easily test which precursors lead to a coating which increases adhesion of the surface and which precursors lead to a coating which decreases adhesion of the surface. This can be easily tested by applying the coated surface to a second surface and compare the adhesion strength between the coated surface to the second surface with the adhesion strength between the uncoated surface to the second surface. It should be clear that such procedure would not constitute an undue burden.

[0040] In a preferred embodiment, the precursor is introduced as an aerosol or as a gas.

[0041] In a preferred embodiment, the plasma gas comprises inert gas for at least 99 vol. %.

[0042] In a preferred embodiment, the plasma gas comprises O2 for at most 1% by volume.

[0043] In embodiments, the said inert gas is a noble gas, preferably Ar or He. In other embodiments, the inert gas is a non-noble gas, preferably N2. In yet other embodiments the inert gas is a gas mixture of inert gasses, such as noble gasses and/or inert non-noble gasses, e.g. a gas mixture of He, Ar and/or N2.

[0044] In a preferred embodiment, the plasma gas is ionized by means of electrodes, more preferably the plasma gas is ionized by said electrodes with a power of at most 10 Watt per cm.sup.2 of the electrode surface, most preferably at most 7.5 W/cm.sup.2.

[0045] The plasma deposition process of the present invention is based on the simultaneous generation of surface radicals (i.e. activation of the difficult-to-treat substrate) and radicalized species in the plasma gas phase, leading to radical recombination reactions of the species to the substrate (i.e. grafting based on covalent bonding). The chemical nature of the precursor can range from classic monomers to saturated molecules, from organic to inorganic molecules, from low molecular weight (e.g. monomers, oligomers) to high molecular weight (e.g. polymers being dissolved or emulsified).

[0046] The scheme outlined in FIGS. 1 to 4 indicate the different phases during the atmospheric plasma deposition process:

[0047] FIG. 1: at t=t0 the plasma is on. A precursor R—X is added to the plasma gas and the plasma is contacted with the substrate. Hereby the precursor R—X is radicalized, and the substrate is activated.

[0048] FIG. 2: at t=t1 the plasma is on. Radical recombination reactions are taking place on the surface, resulting in a covalent bond between substrate and precursor.

[0049] FIG. 3: at t=t2, the plasma is on. Film growth and thickness depend on treatment time. Also cross-linking is taking place.

[0050] FIG. 4: at t=t3 the plasma is off. After the plasma treatment, a functional plasma deposited film remains which is grafted onto the substrate.

[0051] In Step 1, the plasma is generated (can be based on direct or indirect plasma configurations, using an inert plasma gas such as N2, Argon, Helium, or any mixtures thereof), instantaneously generating radicalized species in the plasma gas phase. These species can be added to the plasma as a gas (or gas mixture), or a liquid (e.g. an aerosol, a spray, a liquid mixture, an emulsion, a dispersion, or polymer solution), preferably as a gas or as an aerosol. In the scheme outlined in FIGS. 1-4, we used the connotation “R—X” to denote the initial precursor, and “R—X.” the radicalized form of the precursor. “R” being the targeted functionality, and “X” being a part of the molecule being able to be radicalized. For example, “X” can be reactive (such as C═C double bonds, C═O, epoxy, isocyanate, . . . ), but can also be unreactive (i.e. saturated), in this specific case, the radical will be formed based on hydrogen abstraction.

[0052] In addition to the radicalized species in the gas phase, also surface radicals are formed on the substrate which is also in contact with the plasma. The generation of these surface radicals can be mainly based on hydrogen abstraction or breaking of covalent bonds located at the surface of the substrate.

[0053] In Step 2, radical recombination reactions are taking place between the radicalized species and surface radicals. This radical recombination reaction results in a permanent grafting of the precursor to the surface by the formation of a covalent bond. It must be remarked that presence of reactive gasses such as 02, needs to be avoided during this phase.

[0054] In Step 3, film growth is taking place by the continuous incorporation of species by radical recombination. It must be remarked that the plasma process is ‘non-specific’, meaning that a specific precursor can be built in on the surface on any location, leading to a heterogeneous conformation of the plasma deposited film on a molecular level. Furthermore, the film growth can take place in a ‘continuous’ plasma or in a ‘pulsed’ plasma process. This pulsed plasma has a specific plasma off time, where recombination reactions are favoured, similar to propagation in conventional polymer synthesis.

[0055] In the final phase of the plasma deposition process (Step 4), the plasma is switched off, or similarly the substrate has left the plasma afterglow zone, leading to a fully functional coating layer which is covalently linked to the substrate.

[0056] The resulting plasma deposited film has the following unique features:

[0057] Covalently bonded to the surface of the substrate;

[0058] Functional with respect to adhesion properties. For instance: [0059] (i) This functionality can be a reactive functional group that can participate in a curing reaction with a curable ‘reactive’ adhesive or topcoat. For example, primary amines or epoxies in the case of an epoxy-amine glue or topcoat, or hydroxyls or isocyanates in the case of a PU resin as glue or topcoat. In such an application, the applied coating increases adhesion of the surface to a glue or topcoat, which can further be used to attach the substrate to another component. [0060] (ii) This functionality can also be ‘unreactive’, simulating a similar chemistry as an ‘unreactive’ topcoat (e.g. a pressure sensitive adhesive or overmoulded thermoplastic). The target of the plasma deposited layer is to guarantee compatibility between the difficult-to-bond substrate and the unreactive topcoat, and facilitate chain entanglement between the plasma deposited film and the topcoat to increase the adhesion to the maximum.

[0061] Heterogeneous:

[0062] Compared to polymeric analogues having a distinct repeat unit, the plasma deposited film is heterogeneous in nature. This means that besides a main carbon chain in the polymeric backbone, also other elements can be incorporated (originating from the introduced precursor).

[0063] Cross-Linked:

[0064] During the film growth phase of the plasma deposited film, also radical sites are generated on the surface of the growing film itself. These radical sites are created randomly, leading to the creation of cross-links.

[0065] High Molecular Weight:

[0066] The molecular weight of the fully functional plasma deposited film is high (comparable to conventional thermosets), due to the cross-linked nature of the film. It must be remarked that the presence of O.sub.2 needs to be avoided in the treatment area of the plasma process. When there is a significant amount of O.sub.2 present (>100 ppm), radical recombination reactions will be quenched, leading to low molecular weight fragments residing in the plasma deposited film, having a plasticizing effect. Hence, in most preferred embodiments, the plasma gas comprises at most 0.01 vol % O.sub.2.

[0067] Durable:

[0068] Due to the cross-linked nature and high molecular weight of the plasma deposited film, the durability of the film is greatly enhanced compared to conventional primers. Overall, it was tested that the time between the plasma deposition process and the application of an adhesive or topcoat can be extended to a period of minimum 6 months.

[0069] Dry:

[0070] After the plasma deposition process, the resulting film does not require any subsequent drying step. A subsequent curing step may also not be necessary, but may lead to improvement of the molecular weight of the film.

[0071] In a preferred embodiment, the plasma temperature is at most 50° C., more preferably at most 40° C., still more preferably at most 30° C. and most preferably around room temperature.

[0072] In a preferred embodiment, the plasma temperature is controlled, more preferably by cooling electrodes used for ionizing the plasma gas. This can be e.g. water-cooled or air-cooled electrodes. Preferably the temperature of the electrodes is measured and/or the temperature of the substrate is measured in order to allow better control the temperature of the plasma gas. Typically this can be achieved by using a temperature control system, e.g. a PID controlling system, which allows to steer the cooling of the plasma, e.g. by cooling the electrodes, by checking how a predetermined desired plasma temperature relates to the measured temperature. Preferably the temperature of the electrodes and of the substrate is measured and the temperature control system ensures that the desired plasma temperature lies between the electrode temperature and the substrate temperature.

[0073] The substrates which can be treated with the present invention may have any type of shape and size, and may be substrates which are difficult to bond, due to their inert nature or their extreme fragility (such as natural materials, or biodegradable/water soluble materials), for example:

[0074] Polymers: [0075] Commodities (e.g. PE, PP, PVC, PS, EPDM, polyolefins . . . ) [0076] Engineering thermoplastics (e.g. PET, PBT, PMMA, PC, PES, polyamides, aramides, Acrylonitrile styrene acrylate (ASA), acrylonitrile butadiene styrene (ABS), . . . ) [0077] Fluorinated polymers (e.g. PTFE, PVDF, Fluorinated ethylene propylene (FEP), . . . ) [0078] Biodegradable polymers (e.g. PLA, PCL, . . . ) [0079] Cross-linked polymers (e.g. epoxy-amines, polyurethanes, silicones, . . . ) [0080] Carbon fibres [0081] Water soluble polymers (PEG, polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyacrylamides, divinyl ether-maleic anhydride (DIVEMA), polyoxazoline, polyphosphates, polyphosphazenes, . . . ) [0082] Natural materials: rayon or viscose, polysaccharides, chitosan, collagen, proteins, xanthan gum, pectins, dextran, carrageenan, guar gum, hyaluronic acid (HA), leather . . . [0083] Metals: Gold, silver, iron, brass, lead, iron, copper, tin, stainless steel, aluminium, zinc, . . . (including all possible alloys) [0084] Ceramics: Glass, silicon wafers, metal oxides (e.g. Al2O3, ZnO, . . . ), carbides (e.g. SiC, titanium carbide, . . . ), nitrides (e.g. Si3N4, . . . )

[0085] In preferred embodiments, the substrates comprise any or any combination of the following: [0086] polymer materials such as polymers, co-polymers, co-extruded polymers, e.g. polyamide (PA) fiber, PA staple fiber, PA yarn, PA fabric, PA6 fiber, PA6 staple fiber, PA6 yarn, PA6 fabric, PA66 fiber, PA66 staple fiber, PA66 yarn, PA66 fabric, polybutadiene terephthalate (PBT), Polyethylene terephthalate (PET) foil, PET fabric, PET fiber, aramid fabric, aramid textile, aramid fiber, polycarbonate, Poly(methyl methacrylate) (PMMA), rayon fiber, silicone, Teflon, Teflon foil, carbon fiber, unsized carbon fiber, Ethylene Fluorinated Ethylene Propylene (EFEP), EFEP films, para-aramid fabric, acrylonitrile styrene acrylate (ASA), acrylonitrile butadiene styrene (ABS), polyvinylchloride (PVC), ethylene-tetrafluorethylene copolymer (ETFE), ETFE film, polypropylene (PP), [0087] and combinations thereof, such as co-extruded PA6 and PBT, co-extruded PBT and PC, co-extruded ASA and PC, co-extruded PC and ABS [0088] ceramic materials such as glass and/or enamel, glass fiber, unsized glass fiber [0089] metallic materials such as alloys, more preferably steel, low-tinned steel (LTS)

[0090] The precursor used in the present invention preferably is an organic precursor. If an increased adhesion is desired, the precursor preferable comprises any or any combination of the following groups: hydroxyl-functional groups, amines, primary amines, isocyanates and/or epoxy-functional groups. In a preferred embodiment, the precursor comprises any of the following substances as arranged in the table below:

TABLE-US-00001 Name CAS nr Chemical composition Hydroxyl-based Acrylic acid 79-10-7 [00001] 2-Hydroxyethyl methacrylate (HEMA) 868-77-9 [00002] Poly(ethylene glycol) methacrylate (PEGMA) 25736-86-1 [00003] N-Hydroxyethyl acrylamide (HEAA) 7646-67-5 [00004] cis-2-Butene-1,4-diol (BUDIOL) 6117-80-2 [00005] Pentaerythritol triacrylate (PETA) 3524-68-3 [00006] Polyvinylalcohol (PVA) 9002-89-5 [00007] Poly(vinyl alcohol-co- ethylene) (EVOH) 25067-34-9 [00008] Amine-based (3-Aminopropyl) triethoxysilane 919-30-2 [00009] N-[3-(Trimethoxysilyl) propyl]ethylenediamine 1760-24-3 [00010] N-(3-Trimethoxysilylpropyl) diethylenetriamine 35141-30-1 [00011] Isocyanate-based 2,6-dimethylphenyl isocyanate 28556-81-2 [00012] Toluene 2,4- diisocyanate 584-84-9 [00013] 4,4′-Methylenebis (phenylisocyanate) 101-68-8 [00014] (Trimethylsilyl)isocyanate (TMOS-ISO) 1118-02-1 [00015] 3-(Triethoxysilyl)propyl isocyanate (TEOS-ISO) 24801-88-5 [00016] Epoxy-based Glycidyl methacrylate 106-91-2 [00017] (3-Glycidyloxypropyl) trimethoxysilane 2530-83-8 [00018]

[0091] Also the following substances can be used as precursor: methacrylic acid, allylamine, allylmethacrylate, hydroxyethylacrylate, 2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (CAS 2554-06-5), 3-Mercaptopropyl trimethoxysilane (CAS 4420-74-0), Vinyltriethoxysilane (CAS 78-08-0), Maleic anhydride (CAS 108-31-6).

[0092] The precursors mentioned here above are particularly suitable for increasing the adhesion properties of a multitude of substrates, in particular of glass and/or ceramics. Substrates treated with the method according to the present invention using any of said precursors show particularly strong adhesion to a polyurethane (PU) layer, a 1-component PU layer and/or a 2-component PU layers. Such PU layers may typically be adhesive layers, such as gluing layers, which can be used to glue different components together. In cases where the PU glue does not stick very well to one of the components, this component can be treated with the method according to the present invention such that the adhesion to the PU glue improves.

Example 1: Plasma Treated Textile Reinforcement Material and Method of Producing Such Reinforcement Material

[0093] The invention can be applied for manufacturing a reinforcement material, in particular a tire cord or tire cord fabric, whereas a textile cord is being provided, the textile cord is being treated by atmospheric plasma in combination with an organic precursor, preferably comprising a poly-isocyanate in accordance with the invention, to be grafted on the plasma treated and therefore modified surface of the cord, resulting in an increased adhesive capability to a latex/rubber comprising matrix, and the cord being treated in such a way is then contacted with the latex/rubber matrix.

[0094] Textile cords have been widely used as reinforcement materials in radial tires, conveyor belts, hoses or driving belts. The reinforcing character of the material is mainly effected by the structure of the cord consisting of several filaments being twisted together. Besides such more or less linear cord structures (so called “single end cords”), cords can also be used in the form of laminar structures, e.g. as woven structures (so called “fabric”).

[0095] The filaments can be made of different types of synthetic high-tenacity polymeric fibers like e.g. polyesters such as polyethylene terephthalate (PET) or polyethylene naphthalene (PEN), aromatic or aliphatic polyamides like Aramid or Nylon, respectively, but also of regenerated cellulose fibers. Non-textile materials like steel fibers, carbon fibers or glass fibers can also be taken into consideration as reinforcing material. Fiber blends e.g. commingled yarns or hybrid constructions of different fiber types can also be used as well as monofilament constructs of one fiber type wrapped with filaments of another fiber type. Due to the different chemical structure of the polymer fibers, those reinforcement materials show different adhesive properties with respect to the tire rubber to which they are bonded in the vulcanization step.

[0096] It is of course the intention to have a strong bonding between the textile cord and the rubber in order to guarantee structural integrity of the tire in use and to avoid separation of the cord from the rubber.

[0097] In order to improve the adhesion between the textile cord and the tire rubber during the vulcanization process, currently the cord is dipped with a mixture, mostly comprising Resorcinol, Formaldehyde and Latex (RFL-dip), before vulcanization. In many cases—depending on the nature of the fibers used—the additional application of a pre-dip coating consisting of in particular a mixture of blocked isocyanates and low molecular epoxides to the fiber, followed by the said RFL-dip is necessary to increase the reactivity of the reinforcement material which then guarantees an adequate adhesion between the tire cord and the rubber. This is the case for aramid and polyester cords, and their combinations (e.g. hybrids, commingled materials).

[0098] However, the additional pre-dipping step leads to the unwanted effect of an increased weight of the dipped cord, besides higher process complexity and higher costs compared to single-bath dipping with an RFL dip only. Regarding the RFL dip, resorcinol as well as formaldehyde are said to negatively affect human health due to potential detrimental i.a. carcinogenic effects. Therefore, it has been the goal to develop alternatives to improve adhesion without the need of hazardous substances like resorcinol and/or formaldehyde and without the need of a multi-stage dipping process.

[0099] Wet chemistry methods using highly concentrated acid or alkali, as well as plasma treatment methods using different kinds of plasma have been applied for surface activation or modification of textile fibers in order to improve their hydrophilicity and therefore adhesion of the cord to the RFL dip and rubber, respectively. Both treatment methods may have an etching effect on the fiber, morphological and topological changes are not limited to the fiber surface but can also occur inside of the fiber which then results in a weakening of physical fiber properties e.g. breaking force and tenacity.

[0100] However, the use of atmospheric plasma has the advantage that due to the low energy input needed, it does not negatively affect the dynamometric properties and the structure of the fibers. Besides the further advantage that no high pressure or—on the other hand—no vacuum and therefore no specific installation regarding pressure or vacuum generation is needed, this method allows plasma generation at low temperature, from room temperature to 250° C., but preferably limited to at most 50° C. One way to use such plasma is the plasma-assisted polymerization and deposition of organic precursor substances onto the fiber surface.

[0101] It has now surprisingly been found that by using polyisocanates, preferably diisocyanates as precursor substance in a plasma-assisted polymerization and deposition step, in combination with a subsequent latex dipping step, the use of hazardous substances like resorcinol and formaldehyde in a subsequent dip solution as well as the need for an additional pre-dip can be completely avoided.

[0102] The present invention provides a method for treating textile reinforcement materials, in particular tire cords in such a way that the fibers of the reinforcement material can be modified and/or coated with an organic precursor material to be polymerized on the surface of the fibers during plasma treatment to improve their adhesion to the rubber matrix in one single dipping step, without the use of resorcinol/formaldehyde.

[0103] One way to generate atmospheric plasma is via dielectric barrier discharges (DBD) whereby—either in a cylindrical or in a rectangular arrangement—at least two concentric or parallel electrodes are separated by a gap of some millimeters and a dielectric barrier is disposed between the electrodes. A power source is providing alternating current (ac) voltage to the electrodes with the effect that a dielectric barrier discharge takes place between the dielectric barrier and the inner electrode. The electrical power applied is in the range of between 20 and 500 W, preferably between 50 and 450 W. The generation of the atmospheric plasma typically occurs in the presence of an oxidizing or non-oxidising gas (“plasma gas”), like N.sub.2, Ar, He, Ne, O.sub.2, CO.sub.2, O.sub.2, N.sub.2O, CF.sub.4, SF.sub.6, or mixtures thereof. Preferably, the gas is non-oxidizing and/or free of oxygen, e.g. N2, Ar, He or Ne in order to better control the adhesion properties and/or to avoid incorporation of plasma gas molcules or plasma gas atoms int the coating. The plasma gas is fed to the plasma reactor and is being excited by the electric discharge which results in a conversion to the plasma state. The plasma propagates through the elongated space through which the plasma gas is fed, towards the lower open end of the plasma reactor where it can be ejected through a nozzle to treat the tire cord. An example of a device used for this invention is disclosed in WO2006081637A1.

[0104] The flow rate of the plasma gas is between 1 and 100 slpm, preferably between 40 and 90 slpm, most preferably between 50 and 80 slpm.

[0105] In a preferred embodiment, the plasma generated via DBD has a temperature <100° C. (“cold plasma”) and even more preferred <50° C. In a most preferred embodiment, plasma generation is performed at room temperature.

[0106] Regarding the use of polyisocyanates as organic precursor compounds, they preferably comprise “unblocked” or “blocked” isocyanates. “Blocked” isocyanates are reaction products of isocyanates with, for example, phenols, oximes, caprolactam or β-dicarbonyl compounds, which thermally dissociate at higher temperature to set free the original isocyanate group. Furthermore the blocked isocyanates are stable when in contact with water e.g. in dip solutions. Since during the atmospheric plasma treatment no water is present, unblocked polyisocyanates can be used as well.

[0107] Preferably, the polyisocyanates are diisocyanates. More preferably, the polyisocyanates are from the group of diphenyl diisocyanates, most preferably from the group of methylene diphenyl diisocyanates (MDI).

[0108] As latex, there is used at least one compound selected from the group of vinyl-pyridine (VP) latex, styrene-butadiene (SBR) latex, carboxylated styrene-butadiene (XSBR) latex, natural rubber (NR) latex or combinations thereof, e.g. a styrene butadiene vinylpyridine latex. The total solid content inside the latex compound is between 10 to 40 wt %, preferably between 10 and 20 wt %. The latex dip is prepared by diluting the concentrated latex emulsion with soft water to a total solid content of 20 wt %.

[0109] Experimental Design:

[0110] The following commercially available cord materials were treated according to this invention: Polyester (3340×2 dtex), Aramid (1670×2 dtex).

[0111] 50 cm of each cord sample were irradiated by plasma generated in a PlasmaSpot® device from Molecular Plasma Group, Luxembourg, using a custom-made fiber nozzle at a treatment line speed of 4 m/min. The cord samples were passed between 1 and 10 times through the plasma. The Power applied was varied between 60 Watt and 250 Watt.

[0112] As a precursor, Yokohama Hamatite GPI-1650-B primer comprising methylene diphenyl diisocyanate was used. It was fed into the plasma device at a rate of 1 to 10 g per hour per cord in liquid state in the form of an aerosol. The treated cords were then dipped in a dipping bath containing a styrene butadiene vinylpyridine latex (Omnova Pliocord VP106S) with a total solid content of 20% on a standard tire cord dipping line and dried in three subsequent ovens at 150° C., 230° C. and 230° C. respectively with a residence time of 50 seconds in each oven.

[0113] Yokohama Hamatite GPI-1650-B primer is a mixture comprising 25-50% ethyl acetate and 10-25% 4,4′-methylene diphenyl diisocyanate.

[0114] The effect of the plasma-assisted polymerization of the polyisocyanates in combination with the latex-dip on the adhesion of the tire cord was measured by cord-to-rubber adhesion (CRA). CRA was tested by preparing a test sample where five cords were embedded within a surface layer of a rubber sheet and vulcanized for 30 minutes at a temperature of 150° C. while applying pressure to the rubber. Subsequently, a load was applied to the cords until they were peeled from the rubber sheet. The value of this load therefore corresponds to the cord-to-rubber adhesion.

[0115] For comparison, adhesion values of plasma treated cords without subsequent dipping in a latex comprising solution were measured. Such direct bonding showed remarkably lower and therefore unsatisfactory adhesion values. The subsequent application of a dip containing latex to the plasma treated cords is hence essential in the context of this example.

[0116] Further reference samples were prepared and tested without the step of plasma-polymerization/deposition, but with the subsequent latex dipping step.

[0117] Experimental results:

[0118] PET 3340x2 dtex

TABLE-US-00002 Concentration of precursor Plasma (% of original Power Plasma gas flow Number Yokohama Latex CRA value (W) Gas (slm) of passes primer solution) dip (N/cord) Sample 1 250 N.sub.2 80 10 100% yes  8,7 Sample 2 60 Ar 60 10  25% yes 10,0 Sample 3 60 Ar 60 1  25% yes  5,2 Comparative 250 N.sub.2 80 10 100% no  1,8 sample 1 Comparative 60 Ar 60 10  25% no  1,6 sample 2 Comparative 60 Ar 60 1  25% no  1,5 sample 3 Comparative No plasma   yes  3,3 sample 4

[0119] Aramid 1670x2 dtex

TABLE-US-00003 Plasma Concentration of precursor Power Plasma gas flow Number (% of original Latex CRA value (W) Gas (slm) of passes Yokohama primer solution) dip (N/cord) Sample 1 60 Ar 60 1 100% yes 4,7 Sample 2 60 Ar 60 3 100% yes 5,2 Sample 3 60 Ar 60 6 100% yes 5,0 Sample 4 250 N.sub.2 80 1 100% yes 5,2 Sample 5 250 N.sub.2 80 3 100% yes 11,7  Sample 6 250 N.sub.2 80 6 100% yes 8,9 Sample 7 250 N.sub.2 80 1  25% yes 9,2 Sample 8 250 N.sub.2 80 3  25% yes 11,7  Sample 9 250 N.sub.2 80 6  25% yes 8,0

[0120] All comparative aramid samples (direct bonding without latex dip) showed adhesion values between 0.6 and 1.6 N/cord. The reference sample without plasma treatment but with latex dip resulted in an adhesion value of only 2.8 N/cord.

[0121] For both cord materials an increased adhesion could be observed by the combined effect of plasma assisted polymerization/deposition using polyisocyanates as precursor and a latex dip. Regarding PET, low power value for plasma generation (60 W) and a relatively low precursor amount (25% of the original concentration) were sufficient to reach adhesion values more than five times higher than the comparative sample with no latex dip.

[0122] Regarding the aramid cord, best adhesion results could be reached by using a power value of 250 W and a relatively low number of passes through the plasma. Also in this case, a relatively low precursor concentration (25% of the original concentration) seems to be sufficient to reach the same adhesion values as with the original concentration.

Example 2: Further Examples

[0123] Adhesion between a PA6 substrate and a 1-component (1K) PU glue was seen to improve by treating the substrate with the method according to the present invention using (3-Aminopropyl) triethoxysilane (CAS 919-30-2) and/or 4,4′-Methylenebis(phenyl isocyanate) (CAS 101-68-8) as precursor. Stress tests showed that the failure was a cohesive failure, i.e. a failure within the different components, and was not due to the adhesion between substrate and glue.

[0124] Adhesion between a PBT substrate and a 1-component (1K) PU glue was seen to improve by treating the substrate with the method according to the present invention using 4,4′-Methylenebis(phenyl isocyanate) (CAS 101-68-8) as precursor. Stress tests showed that the failure was a cohesive failure, i.e. a failure within the different components, and was not due to the adhesion between substrate and glue.

[0125] Adhesion between a glass substrate and a 1-component (1K) PU glue was seen to improve by treating the substrate with the method according to the present invention using (3-Aminopropyl) triethoxysilane (CAS 919-30-2) and/or 1-(3-Trimethoxysilylpropyl)diethylenetriamine (CAS 35141-30-1) as precursor. Stress tests showed that the failure was a cohesive failure, i.e. a failure within the different components, and was not due to the adhesion between substrate and glue.

[0126] Adhesion between an enamel substrate and a 1-component (1K) PU glue was seen to improve by treating the substrate with the method according to the present invention using (3-Aminopropyl) triethoxysilane (CAS 919-30-2) and/or 1-(3-Trimethoxysilylpropyl)diethylenetriamine (CAS 35141-30-1) as precursor. Stress tests showed that the failure was a cohesive failure, i.e. a failure within the different components, and was not due to the adhesion between substrate and glue.

[0127] Adhesion between a glass substrate and a 2-component (2K) PU glue was seen to improve by treating the substrate with the method according to the present invention using 1-(3-Trimethoxysilylpropyl)diethylenetriamine as precursor. Stress tests showed that the failure was a cohesive failure, i.e. a failure within the different components, and was not due to the adhesion between substrate and glue.

[0128] Adhesion between an enamel substrate and a 2K PU glue was seen to improve by treating the substrate with the method according to the present invention using (3-Aminopropyl) triethoxysilane (CAS 919-30-2) and/or 1-(3-Trimethoxysilylpropyl)diethylenetriamine (CAS 35141-30-1) as precursor. Stress tests showed that the failure was a cohesive failure, i.e. a failure within the different components, and was not due to the adhesion between substrate and glue.

[0129] Adhesion between a PC substrate and a 2K PU glue was seen to improve by treating the substrate with the method according to the present invention using (3-Aminopropyl) triethoxysilane (CAS 919-30-2) and/or 1-(3-Trimethoxysilylpropyl)diethylenetriamine (CAS 35141-30-1) as precursor. Stress tests showed that the failure was a cohesive failure, i.e. a failure within the different components, and was not due to the adhesion between substrate and glue.

[0130] Adhesion between a PMMA substrate and a 2K PU glue was seen to improve by treating the substrate with the method according to the present invention using 2-Hydroxyethyl methacrylate (CAS 868-77-9) and/or 1-(3-Trimethoxysilylpropyl)diethylenetriamine (CAS 35141-30-1) as precursor. Stress tests showed that the failure was a cohesive failure, i.e. a failure within the different components, and was not due to the adhesion between substrate and glue.

[0131] Adhesion between a PET fabric and Nitrilbutadiene elastomer (NBR) was seen to improve by treating the substrate with the method according to the present invention using 1-(3-Trimethoxysilylpropyl)diethylenetriamine as precursor. Stress tests showed slight improvement.

[0132] Adhesion between a Aramid fabric and ethylene propylene diene monomer rubber (EPDM) was seen to improve by treating the substrate with the method according to the present invention using 2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (CAS 2554-06-5) and/or 3-Mercaptopropyl trimethoxysilane (CAS 4420-74-0) as precursor. Stress tests showed significant improvement.

[0133] Adhesion between a Aramid fabric and fluorinated silicone was seen to improve by treating the substrate with the method according to the present invention using Vinyltriethoxysilane (CAS 78-08-0) as precursor. Stress tests showed significant improvement.

[0134] Adhesion between rayon and natural rubber was seen to improve by treating the substrate with the method according to the present invention using 4,4′-Methylenebis(phenyl isocyanate) (CAS 101-68-8) and/or 3-Mercaptopropyl trimethoxysilane (CAS 4420-74-0) as precursor. Stress tests showed significant improvement.

[0135] Adhesion between aramid and natural rubber was seen to improve by treating the substrate with the method according to the present invention using 4,4′-Methylenebis(phenyl isocyanate) (CAS 101-68-8) as precursor. Stress tests showed significant improvement.

[0136] Adhesion between PET and natural rubber was seen to improve by treating the substrate with the method according to the present invention using 4,4′-Methylenebis(phenyl isocyanate) (CAS 101-68-8) and/or 3-Mercaptopropyl trimethoxysilane (CAS 4420-74-0) as precursor. Stress tests showed significant improvement.

[0137] Adhesion between an EFEP substrate and a Nitrilbutadiene elastomer (NBR) was seen to improve by treating the substrate with the method according to the present invention using 2-Hydroxyethyl methacrylate (CAS 868-77-9) as precursor. Stress tests showed drastic improvement.

[0138] Adhesion between a PET substrate and overmoulded PP was seen to improve by treating the substrate with the method according to the present invention using Maleic anhydride (CAS 108-31-6) as precursor. Stress tests showed clear improvement.

[0139] Adhesion between a substrate of co-extruded PBT and PC material and 1K and 2K PU glue was seen to improve by treating the substrate with the method according to the present invention using 2-Hydroxyethyl methacrylate (CAS 868-77-9) and/or 4,4′-Methylenebis(phenylisocyanate) (CAS 101-68-8) as precursor. Stress tests showed clear improvement.

[0140] Adhesion between a substrate of co-extruded PC and ABS material and 1K and 2K PU glue was seen to improve by treating the substrate with the method according to the present invention using 2-Hydroxyethyl methacrylate (CAS 868-77-9) and/or 4,4′-Methylenebis(phenylisocyanate) (CAS 101-68-8) as precursor. Stress tests showed clear improvement.

[0141] Adhesion between a substrate of co-extruded ASA and PC material and 1K and 2K PU glue was seen to improve by treating the substrate with the method according to the present invention using 2-Hydroxyethyl methacrylate (CAS 868-77-9) and/or 4,4′-Methylenebis(phenylisocyanate) (CAS 101-68-8) as precursor. Stress tests showed clear improvement.