EP1856197A1

EP1856197A1 - Method for modifying the bulk properties of materials by dielectric barrier discharges, materials and two-dimensional and three-dimensional articles obtainable by the method, and apparatus for implementing the method

Info

Publication number: EP1856197A1
Application number: EP06706662A
Authority: EP
Inventors: Marion Sterner; Leonardo Andreotti; Illya Kulyk; Giorgio Trani
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-02-07
Filing date: 2006-02-06
Publication date: 2007-11-21
Also published as: ITVE20050007A1; WO2006082090A1

Abstract

A method for modifying the bulk properties of materials by dielectric barrier discharges (DBDs), characterised by: preparing within the material, cayities filled with a mixture of gases and/or vapours in which a dielectric barrier discharge can take place, subjecting said material to plastic and/or viscoplastic deformation during a step which, depending on the material, can precede, follow or be simultaneous with that of forming said cavities, and subjecting said material to dielectric barrier discharge treatment during a step following the commencement of said plastic and/or viscoplastic deformation, such that said discharge takes place within said filled cavities.

Description

METHOD FOR MODIFYING THE BULK PROPERTIES OF MATERIALS BY DIELECTRIC BARRIER DISCHARGES, MATERIALS AND TWO- DIMENSIONAL AND THREE-DIMENSIONAL ARTICLES OBTAINABLE BY THE METHOD, AND APPARATUS FOR IMPLEMENTING THE METHOD The present invention relates to a method for modifying the bulk properties of materials by dielectric barrier discharges, materials and two- dimensional and three-dimensional articles obtainable by the method, and an apparatus for implementing the method.

In industry there is often the need to modify characteristics of materials to render them suitable for particular applications and uses which would otherwise not be possible.

One of the known methods for modifying certain material characteristics is based on the use of dielectric barrier discharges or DBDs.

These are obtained between two electrodes, at least one of which presents that surface facing the other electrode coated with a thin layer of dielectric material (generally glass or alumina). A microdischarge takes place between the two electrodes, to generate a cold plasma. The potential which has to be applied to obtain the discharge increases with the distance between the electrodes. For example at a distance apart of a few mm, and applying an AC voltage of some kVolt at a frequency of 0.1-10 MHz, the discharge generated is characterised by a low power consumption (from 0.1 to 10

W/cm², depending on the specific modalities of the treatment).

From the physical viewpoint the plasma generated by the DBD in gas at atmospheric pressure is pf non-thermal, non-stationary type and consists of a series of discharges during each cycle of the feed voltage.

The most important property of the DBD from the applicational viewpoint is that in particular it generates radical species from the molecules present in the plasma, because of which the interaction mechanisms between the DBD plasma and the substrates relate more to radical chemistry than to ion chemistry.

An important characteristic of the DBD is that it does not heat the substrate (in effect the temperature increase of a material subjected to DBD does not exceed 10-20°C). Because of this "cold" treatment, the DBD at atmospheric pressure converts the electrical energy into radical chemical reactions with greater efficiency, hence enabling energy consumption to be contained. The effect of treatment by plasma in general and by DBD plasma in particular, in air, in oxygen or in inert gases, consists of increasing the surface energy of the substrate, this phenomenon being widely utilized in industry.

Moreover if suitable chemical precursors are present, even nanometric layers can be deposited on the most varied substrates by virtue of the plasma. For example, nanolayers of silicon oxides, diamond-like carbon (DLC) or polymer claddings can be deposited with DBD plasma.

Again from the industrial viewpoint, a DBD generated at atmospheric pressure is much more easily obtainable than conventional plasma treatments, which require low pressures, and achieves significant advantages, namely:

- the DBD can take place within interspaces or in internal cavities of minimal dimensions (a few microns);

- for equal treatment and/or deposition rates, compared with low pressure plasmas a DBD does not require vacuum chambers; the discharge region need merely be isolated from the environment; - as the distance between the electrodes is only a few millimetres, the volume of the treatment apparatus is much smaller than the vacuum chambers traditionally used for plasma treatments;

- an atmospheric pressure DBD virtually does not heat the treated material; - the DBD power supply units for alternating current, low frequency and low power are more economical than radiofrequency feeders conventionally used for low pressure treatments (PECVD);

- given its relatively simple structure, the plant for generating the DBD can be easily dimensioned on the basis of the dimensions of the material to be treated;

- in the case of solid materials the DBD treatment can be implemented simultaneously on several superposed layers, to afso modify those surfaces not directly exposed to the electrodes.

Plasma-based techniques are mostly used to modify the surface characteristics of materials.

In order to modify the characteristics of a solid material throughout its entire thickness, it has already been proposed to apply the DBD technique to porous materials, which can be modified throughout their mass by virtue of the fact that the dielectric barrier discharges are developed within their internal cavities, to modify their surfaces.

However the DBD technique is difficult to apply on materials intended to undergo plastic and/or viscoplastic deformations during their productive process, as these could alter the characteristics conferred by the DBD treatment. An object of the invention is to bulk-modify by the DBD technique materials containing internal cavities or cavitable materials processed - A -

industrially by means of plastic and/or viscoplastic deformations, without the modifications induced by the dielectric barrier discharges being altered by said deformations and consequently without preventing the use of said materials modified in accordance with the typical requirements of industrial transformation processes.

To attain this object the invention confronts the problem of modifying by dielectric barrier discharges the chemical-physical characteristics throughout the mass of a plastic and/or viscoplastic material containing cavities or cavitable, which is to be subjected to plastic and/or viscoplastic deformations, such that: a) the deformed material modified by dielectric barrier discharges presents at least one characteristic improved compared with the deformed but non- modified material, and b) the deformed material modified by dielectric barrier discharges presents characteristics at least equal to those of the modified but non-deformed material.

These and other objects which will be apparent from the ensuing description are attained, according to the invention, by a method for modifying the bulk properties of materials by dielectric barrier discharges (DBDs) as claimed in claim 1.

The present invention is further clarified hereinafter in general terms and in terms of some non-limiting embodiments with reference to the accompanying drawings, in which:

Figure 1 is a block diagram essentially illustrating the method of the invention, Figures 2a, 2b and 2c are schematic illustrations showing three different steps in the application of the method of the invention to a porous material with open cells,

Figures 3a and 3b are schematic illustrations showing the application of the method of the invention to the formation of pleated paper holders,

Figure 4 is a schematic illustration showing the application of the method of the invention to the formation of a closed cell expanded polyethylene film,

Figures 5a and 5b are schematic illustrations showing in general and detailed view the application of the method of the invention to the formation of an open cell expanded polyethylene film, and Figure 6 is a schematic illustration showing the application of the method of the invention to the formation of a flexible laminate. As stated, the method of the invention consists essentially of subjecting the material to be treated, which can be solid, molten or liquid, to three treatments, of which the first treatment 2 can be defined as preparation of cavities filled with a mixture of gases and/or vapours sensitive to DBD treatment, the second treatment 4 as plastic and/or viscoplastic deformation, and the third treatment 6 as dielectric barrier discharge (DBD) The first step 2 differs depending on whether the material to be treated already presents microcavities or cells, i.e. is either a porous or non-porous material and, in the first case, whether the cells are open or closed.

If the material to be treated is of open cell type (fabric, non-woven fabric of natural or artificial fibres, paper, open cell polymer foam), cell filling is achieved by: - subjecting the material to a flow of treatment gases or a mixture of gases and/or vapours, possibly able to act as chemical precursors;

- impregnating the material with a liquid consisting at least partly of a precursor, then eliminating those liquid components other than the precursor and then, at the appropriate moment, evaporating the precursors, which permeate the material cavity. Said solution can carry in suspension particles, even of nanometric dimensions, which are deposited on the surface of the cavities.

If instead the material to be treated is of closed cell type, the gas or gas mixture must already be contained in the material cavity. This can be obtained by using as the expanding agent in the expanded material production process the same mixture which is then subjected to DBD treatment, or by making this mixture permeate into the previously formed cavities, evidently in this case with a much slower process. In the case of materials which are liquid, semisolid or under solidification (e.g. polyurethane foams), the gas mixture chosen for the discharge can be insufflated by known methods.-

Microcapsules containing the gas or gas mixture concerned can also be used, mixing them with liquid or molten materials such that they are able to act as internal cavities; the dielectric barrier discharge then takes place within the microcapsules.

The second step of the method of the invention is the plastic and/or viscoplastic deformation step, being the variation on a macroscopic scale of the geometric shape and/or morphology and/or physical state of the material. This is due to the application of an external force to the material and, as stated, can take place before, during or after the formation of said cavities in the material or, if these cavities are already present, after their filling.

The plastic deformation step can be effected either to obtain the material to be subjected to DBD treatment in a state different from that of the starting material, or to obtain three-dimensional articles.

The plastic deformation step can consist for example of a forming or extrusion or spreading treatment.

The forming process (or thermoforming if accompanied by material heating) is generally used to obtain three-dimensional articles (trays, blister strips, etc.) used in different packaging methods, starting from two- dimensional sheets or plates. The materials usable for thermoforming according to the present invention are porous (expanded materials, cavited materials, fabrics, non-woven fabrics), including laminated with other materials. The porous material can contain particles of various types (for example CaCC>₃, TiO₂ and silicates are often used in paper production) including of nanometric dimensions, or containing in their cavities molecules which are non-volatile but are potentially able to react with or be modified by a dielectric barrier discharge (for example residual lignin or that reintroduced into the paper). Three-dimensional articles usable as food packaging can also be obtained by folding processes. These processes are automated and of various types; examples include drawing (folding a poorly extendable material such as aluminium or paper in a male-female mould to obtain a three- dimensional container), crease-lining (creation of a recess in a flat material to render it foldable and, in the paper article manufacturing industry, form price tags for boxes) and flow packs (continuous forming of three-dimensional packs by folding a flexible film about a forming tube, then closing by welding).

An extrusion process is used to transform thermoplastic granulates into threads, fibres, films or panels. If extruding an expanded polymer, an expanding agent is added to the molten polymer material, the cavities then forming within the molten polymer material itself at the extruder exit, at a determined moment of the process, as a result of the sudden pressure change. In particular, solid particles of various types (CaCθ₃, silicates, etc.) including of nanometric dimensions can be mixed in, which in addition to conferring specific properties on the final material can act as bubble nucleation points and influence the morphology of the expanded product.

A polymer containing a mixture of expanding gases can also be formed in a two-dimensional panel or in a three-dimensional article by methods known in the art (e.g. injection moulding). Several layers with different polymer formulations can also be coextruded.

In order for the bubbles to contain the desired gas for the dielectric barrier discharge, this must form part of or constitute the expanding agent fed into the molten polymer material prior to the extruder exit. A non-volatile chemical precursor can also be fed into the molten polymer material, to then react with the gas on the inner surface of the cavities during dielectric barrier discharge.

The DBD treatment is hence applicable when the bubbles form but before the gas prepared for the discharge escapes from the cavited polymer by permeation or before other gases, originating from the outside, penetrate into the cavities to alter the composition of their contents. Spreading treatment consists of spreading a coat of liquid formulation

(adhesive, ink, varnish) onto a fiat, solid, rigid or flexible support (paper, plastic film). This spreading can be done by various methods, generally using rollers which collect the formulation from a tank and deposit in onto the moving substrate, or can be done by a dispenser.

The formulations can also be applied to a defined extent.

Liquid formulations can also be spread by spray processes, which can also simultaneously effect the process of insufflating into the liquid formulation the gases (or gas mixtures) chosen for the dielectric barrier discharge. The third step of the method of the invention consists of the DBD treatment for modifying certain bulk characteristics of the material, in which the cavities filled with gases or gas mixtures sensitive to DBD treatment have previously been prepared, and which has been subjected to the deformation process. The DBD treatment is effected in such a manner as not to lose effectiveness because of the deformations undergone by the material during the usual production processes, these being at precise moments of the production process. These moments are chosen such as to maximize the synergic effect between deformation and DBD treatment. In the case of deformation by forming, the DBD treatment is applied after the material has been permeated by the gas concerned and deformed by the mould; the electrodes used are the half-moulds themselves. In this manner a three-dimensional article is directly obtained on which the dielectric barrier discharge has acted with maximum efficiency. A similar procedure can be used in the case of folding by drawing or crease-lining; in the case of a flow pack, the forming tube or a segment thereof can constitute one of the two electrodes.

In the case of deformation by extrusion, if the extruded product comprises bubbles generated by an expanding agent introduced into the molten polymer material, it is subjected to DBD treatment at the extruder exit, this modifying the bulk properties of the material.

The point at which the DBD treatment is applied (and the polymer temperature) can be chosen on the basis of the treatment itself and the characteristics to be imparted to the material. The electrodes can be integrated into the extrusion mouth if the expanded polymer is treated when still semisolid or, for treating an already cooled expanded material, they can take the form of rollers at a certain distance from the extrusion mouth.

In the case of injection moulding, the material can be subjected to dielectric barrier discharge while still in the mould, provided that: - the article walls comprise at least one porous or cavited layer,

- the mould walls can act as DBD electrodes, i.e. that they are electrically conducting material and at least one of the two is covered by a dielectric,

- a suitable. power supply is connected to the mould walls.

In this manner three-dimensional articles can be treated rapidly without difficulty for the productive process.

In the case of material deformation by spreading, the dielectric barrier discharge treatment can be effected using as electrodes the actual rollers used for depositing the formulation or, if laminating the substrate spread with a second film, the coupling rollers. In the case of deformation by spraying, the liquid material containing the gas bubbles can be passed through two preferably vertical electrodes, or can be sprayed on a web which passes between two horizontal electrodes.

Depending on the starting material and the gas or mixture of gases used, the method of the invention enables various modifications to be obtained concerning the mass of the material, the DBD treatment being applied at a moment subsequent to the commencement of the deformation step to which the material is subjected, so that its effectiveness is not decreased by the deformation process. In greater detail, the advantages obtainable by the method of the invention can be listed as follows:

- the treatments and depositions can concern the entire mass of the material and not only its surface layers directly exposed to the electrodes,

- the method is applicable to a wide variety of materials containing cavities, and possibly with the addition of particles of various kinds (calcium carbonate, silicates, etc.) including of nanometric dimensions, in particular: a) open cell materials: fibrous materials in general (paper, yarns, fabrics, non-woven fabrics), natural, artificial or synthetic materials in thread, strip, sheet, slab or film form, sintered materials; b) expanded solid materials with closed cells, possibly containing mixtures of gas and/or precursors; c) materials in the liquid, molten, semisolid state or undergoing thickening/solidification, foamed or expanded by gas or mixtures of gas and precursors; d) viscous liquid materials, with microspheres dispersed throughout their bulk and filled with suitable gas and/or precursors; - the discharge and hence the treatments or depositions occur not only on the outer surfaces of the material, but also within its internal porosity (for example within the spaces between the threads or fibres, within the inner cavities of an expanded or sintered material, or within the gaseous inclusions of a liquid substance), and can interact with substances or particles present at the interface which bounds the cavity;

- the treatment is applicable directly to two-dimensional or three-dimensional solid articles obtained by deformation processes (forming, extrusion, spreading, etc.), and enables them to be provided with characteristics which would normally be deteriorated by or not be obtainable in traditional productive processes;

- special substances can be synthesized which could not be produced in another manner within the material;

- materials can be obtained which are modified in their interior, i.e. in parts most protected from wear and from mechanical or chemical attack, with properties which are more stable with time;

- minimum quantities of gaseous precursors are required to be fed to the treatment gas;

- the use of solvents can be avoided, hence making the treatment more ecological;

- the method is very simple and economical;

- the inner surfaces of the material (the microcavities) can be activated in the presence of suitable gases;

- nanolayers of particular substances can be obtained, deposited not only on the outer surfaces but also in the microcavities of the materials. This nanolayer deposit can itself induce an improvement in properties such as solvent or flame resistance, or reaction to mechanical stresses in the material, such as increased rigidity or increased ultimate tensile stress in solids and improved rheologicai behaviour in liquids or molten substances; or a variation in optical properties of the material, such as transparency, opacity, reflection, colour, refraction index, etc., including for anti- counterfeiting purposes;

- modifications can be made to a defined extent, as the DBD treatment can be carried out using suitable masks to define the regions of interest, again for anti-counterfeiting purposes; - radical processes can be activated to obtain effects such as molecular scavenging (oxygen scavenging), accelerated material degradation, controlled release of substances from microcapsules contained in the materia);

- the discharge can vary the quantity of gaseous molecules in a cavity, to increase pressure and expand the material without varying the temperature;

- light emission from the cavities can be triggered in the presence of suitable gases (again as an anti-counterfeiting method);

- grafting/copolymerisation reactions can be activated on the inner surface of the cavities; - an increase in potential energy and hence wettability of the material in its microcavities can be obtained, to hence accelerate material impregnation with various chemical substances (in the case of open cell material). In particular, if the material is biodegradable, biodegradation can be accelerated; - a sterilization effect can be obtained even within the depth of the material mass, in particular of fabrics to be used in the pharmaceutical field; - preservation effects can be obtained on paper against mildew attack;

- water and oil repellence can be obtained throughout the entire bulk of the material.

The following examples will further clarify the invention. Example 1: Forming and DBD treatment on open cell porous material

(fibrous material).

The starting open cell porous material is yieldable paper, for example of the type described in EP-0824619-B1.

The method combines forming and DBD treatment. The forming mould, shown in Figures 2a-2c, is composed of two parts, a lower 8 and an upper 10, movable in the sense of approaching the lower part. To effect dielectric barrier discharge, both parts are clad with a conductor layer, for example of metal, and at least one of these parts with a layer of dielectric material (glass, quartz, ceramic, etc.). The material to be treated 12 is introduced between the two parts 8 and 10 of the mould. The gas mixture 14 is introduced into the mould on only one side of the material 12 (Figure 2a).

To prepare the internal cavities of the material 12 (first step in the process of the invention) the upper part 10 is made to approach the lower part 8, so that this compresses the mixture 14 and causes it to pass through the material 12, so replacing the air within the pores thereof (see Figure 2b).

The second step (material deformation) commences when the upper part 10 begins to press on the material 12 and terminates at the moment the two parts have approached each other to their maximum extent, to leave a minimum space between them (see Figure 2c). When the mould has been closed the power supply unit 16 is activated to effect DBD treatment on the three-dimensional article already formed within the mould.

The specific property modifications to the material, created by the dielectric barrier discharge, are conferred by this process to the final three- dimensional article, which does not have to be further deformed.

According to the invention, this process is effected simultaneously with the forming (in its final stage) within the mould, and hence does not require substantial modifications to a traditional forming line, but only modification to the mould in that part necessary for gas feed/discharge (this part can already be provided in plants which combine deformation by male/female half-moulds with air deformation) and for effecting the DBD treatment.

The described treatment according to the invention is applicable to a whole series of materials in three-dimensional forms such as film, strips, plates etc., during or after the productive forming process. The porous starting materials can be monomaterials or multi-layer materials obtained by coextrusion or rolling.

Example 2: Preparation of pleated paper holders for oven and/or confectionery use.

The starting material (see Figure 3a) consists of paper discs 18 of dimensions suitable for the confectionery products to be contained.

Each disc is interposed between the male part 20 and female part 22 of a mould able to cold-deform it by pressing and to transform it into a pleated holder 24. During this stage the male half-mould 20 presses the paper disc into the cavity in the female half-mould 22 to form the holder 24 thereby. The deformation by pressing takes place before filling the microcavities of the paper disc with the gas concerned. For pore filling, a stack of already formed holders 24 is inserted into a mould of shape corresponding to the stack and provided, on its female half- mould 26, with a seal gasket 28 (see Figure 3b).

The two halves of this mould form a pair of DBD electrodes. The male half-mould 30 is provided with a conduit 32 for gas entry and is initially spaded from the female part 26, in which the stack of holders 24 is inserted.

The gas outlets 34 are positioned in the female part 26 below the edge of the stack of holders 24.

The mixture for the DBD treatment consists of inert gas and a fluorinated monomer (chemical precursor).

The male half-mould 30 is lowered onto the female half-mould 26 and presses the edges of the stacked holders 24 against the gasket 28 of the female half-mould 26. The gas mixture is then fed into the mould and, to escape from the cell, has to pass through the various paper layers of the stacked holders 24, saturating their pores, before leaving through the conduits 34.

On termination of this stage the DBD treatment is effected, this enabling holders to be obtained which comprise on the surface of the fibres a nanometric layer of water and oil repellent polymer, giving the article moisture resistance and water and oil repellent properties.

Example 3: Preparation of modified film of open cell expanded polyethylene.

Powdered, granular or molten polyethylene is used and is extruded in the presence of an expanding agent (see Figure 4). Pressurized gas is fed through a conduit 38 into the mass of the molten polymer contained in an extruder 36, the gas containing as chemical precursor a monomer able to deposit on a surface, as a result of DBD treatment, a nanometric layer of polymer with a light refractive index different from that of polyethylene.

At the exit of the extruder 36 the sudden pressure change causes the gas to evolve and form bubbles within the mass of the material, these being hence already filled with the gas mixture concerned.

After the film 38 has emerged from the extruder mouth 40 (see Figure 4), at a distance from this latter sufficient to ensure film expansion and stabilization of the expanded film, the film is passed between a pair of roller- electrodes 42, between which the dielectric barrier discharge occurs.

In this manner the chemical precursor contained in the pressurized gas within the forming cavities gives rise to modification of the polymer material, which on termination of the process becomes stabilized at ambient temperature and consists of an expanded plastic film which, by virtue of the fact that on the inner surface of the cavities a nanometric polymer layer has been formed having a light refractive index different from that f polyethylene, displays optical iridescence properties.

Example 4: Preparation of modified film of closed or open cell polyethylene. Again in this example, as in the preceding example, the starting material is powdered, granular or molten polyethylene, which is extruded in the presence of an expanding agent to obtain an expanded material.

For this purpose, CO₂ or a mixture of CO₂ and other gases such as helium, argon, etc. is fed into the molten polymer contained in an extruder 36 (see Figures 5a and 5b) through a conduit 38. At the exit of the extrusion mouth 40 the sudden pressure decrease causes the gas to expand, giving rise to the formation of bubbles within the material mass. in proximity to the extrusion mouth 40 two electrodes 44 are positioned with an interspace sufficiently wide to allow polymer expansion, the dielectric barrier discharge being produced between these. The discharge causes functional groups, preferably of carboxyl nature, to form on the inner surface of the cavities. As functionalization takes place only on polymer molecules having exposed segments at the surface, it is important to treat the expanded polymer while still at a sufficiently high temperature to possess an intense molecular mobility. In this manner the functionalized molecular segments can more rapidly change place with those not yet functionalized, so enabling more homogeneous functionalization to be obtained.

If an ionomer is specifically to be obtained, the average percentage of functionalized structural units per polymer molecule must be less than 15%.

In a preferred embodiment of the extrusion line of the present example, the two electrodes 44 for DBD treatment are directly integrated into the extrusion mouth 40 and extend in the extrusion direction to form between them an interspace of a certain width, suitable to allow expansion of the molten polymer 46. These are isolated from the rest of the plant and are maintained at optimum temperature for effecting the DBD treatment. Example 5: Preparation of a flexible laminate.

A UV-crosslinkable liquid adhesive containing a photoinitiator is brought to a foamed state by injecting into its mass a gas (for example xenon) able to generate light (e.g. UV) when subjected to dielectric barrier discharge. Alternatively the gas can be contained in microcapsules dispersed within the adhesive.

The adhesive 48 containing internal cavities prepared in this manner is then applied by spreading or spraying onto a support 50, consisting for example of a plastic film.

This support is then subjected to DBD treatment by passage between two electrodes which, if the adhesive is applied in a lamination process, can also consist of the coupling rollers 52, which cause a second film 54 to adhere to the adhesive. Depending on the situation, a small interspace, less than the adhesive thickness, can be maintained between the rollers 52, in order not to cause the cavities to collapse.

Following the DBD treatment the gas contained in the cavities generates UV-vis radiations, which cause crosslinking of the adhesive and entrapment of the gas filled cavities.

In an alternative embodiment of the method, not shown in the drawings, the layer of cavited and crosslinked adhesive can be coupled to films having a layer of dielectric material in contact with the adhesive and a layer of transparent conductive material on the opposite side; at least one of the two films must be transparent. In this manner, if the two conductive layers are connected to a generator, the gas within the cavities of the crosslinked adhesive can be subjected to subsequent DVD treatment, to obtain a flexible laminate able to emit UV light and usable for example to sterilize the contents of a package formed with the film. The film can further be printed on the transparent side with fluorescent inks, transforming the laminate into a flexible light source, with wide application (furnishing, publicity, etc.).

When the laminate with the emitting layer has been formed, it can be spread with further UV-crosslinkable formulations. By using spreading rollers able to act as electrodes, this formulation can be immediately crosslinked, it also being possible to immediately fix a surface micromarking impressed by the spreading roller.

If the laminate is used in an external environment, it can be printed with a UV-crosslinkable hydrophobic coating, the print roller, which also acts as the electrode, conferring lotus leaf morphology. Light emission by the bubbles fixes the lotus leaf morphology, giving the surface self-cleaning properties.

Claims

C L A I M S

1. A method for modifying the bulk properties of materials by dielectric barrier discharges (DBDs), characterised by:

- preparing within the material, cavities filled with a mixture of gases and/or vapours in which a dielectric barrier discharge can take place,

- subjecting said material to plastic and/or viscoplastic deformation during a step which, depending on the material, can precede, follow or be simultaneous with that of forming said cavities, and

- subjecting said material to dielectric barrier discharge treatment during a step following the commencement of said plastic and/or viscoplastic deformation, such that said discharge takes place within said filled cavities.

2. A method as claimed in claim 1 , characterised by subjecting the material, already subjected to DBD treatment, to degassing.

3. A method as claimed in claim 1 , characterised by repeating at least one of the steps of the process.

4. A method as claimed in claim 1, characterised by using an open cell, porous material and subjecting it to a gaseous flow containing chemical precursors and able to fill said cells.

5. A method as claimed in claim 1 , characterised by using an open cell porous material, impregnating it with a liquid consisting at least partly of at least one precursor, then evaporating said precursor.

6. A method as claimed in claim 5, characterised by evaporating those components of the liquid other than the precursor before evaporating the precursor itself.

7. A method as claimed in claim 6, characterised by using a solution having solid particles in suspension.

8. A method as claimed in claim 7, characterised by using a solution having solid particles of nanometric dimensions in suspension.

9. A method as claimed in claim 1 , characterised by using a closed cell porous material and permeating said mixture of gases and/or vapours into the interior of its already formed cells.

10. A method as claimed in claim 1 , characterised by filling the closed cells with said mixture of gases and/or vapours during cell formation.

11. A method as claimed in claim 10, characterised by subjecting to DBD treatment a closed cell porous material obtained from a molten material, into which said mixture of gases and/or vapours has been introduced as expanding agent.

12. A method as claimed in claim 1 , characterised by using a closed cell porous material consisting of microcapsules containing said mixture of gases and/or vapours.

13. A method as claimed in claim 12, characterised by using a closed cell porous material obtained by mixing the microcapsules with a liquid material, from which the material to be subjected to DBD treatment is obtained.

14. A method as claimed in claim 1 , characterised by subjecting the material with its cavities filled with said mixture of gases and/or vapours to plastic and/or viscoplastic deformation, prior to the formation of said filled cavities.

15. A method as claimed in claim 1 , characterised by subjecting the material with its cavities filled with said mixture of gases and/or vapours to plastic and/or viscoplastic deformation, during the formation of said filled cavities.

16. A method as claimed in claim 1 , characterised by subjecting the material with its cavities filled with said mixture of gases and/or vapours to plastic and/or viscoplastic deformation, after the formation of said filled cavities.

17. A method as claimed in claim 1 , characterised by effecting said plastic and/or viscoplastic deformation by forming.

18. A method as claimed in claim 1 , characterised by effecting said plastic and/or viscoplastic deformation by thermoforming.

19. A method as claimed in claim 1 , characterised by effecting said plastic and/or viscoplastic deformation by extrusion.

20. A method as claimed in claim 1 , characterised by effecting said plastic and/or viscoplastic deformation by coextrusion of different molten polymers.

21. A method as claimed in claim 1, characterised by effecting said plastic and/or viscoplastic deformation by spreading a coat of a cavited liquid formulation onto a substrate.

22. A method as claimed in claim 1 , characterised by effecting said plastic and/or viscoplastic deformation by spraying a cavited liquid formulation onto a substrate.

23. A method as claimed in claim 22, characterised by simultaneously spraying the liquid formulation and insufflating the mixture of gases and/or vapours.

24. A method as claimed in claims 21 to 23, characterised by applying said liquid formulation to the substrate to a defined extent.

25. A method as claimed in claim 1, characterised by effecting said plastic and/or viscoplastic deformation by folding.

26. A method as claimed in claim 22, characterised by effecting said plastic and/or viscoplastic deformation by folding a flexible film and closing the flexible film obtained thereby by welding.

27. A method as claimed in claim 1 , characterised by effecting said plastic and/or viscoplastic deformation by drawing.

28. A method as claimed in claim 1 , characterised by effecting said plastic and/or viscoplastic deformation by crease-lining.

29. A method as claimed in claim 17, characterised by effecting the dielectric barrier discharge between two electrodes formed by the halves of the mould in which the plastic and/or viscoplastic deformation of the material by forming takes place.

30. A method as claimed in claim 19, characterised by subjecting the material leaving the extruder to dielectric barrier discharge.

31. A method as claimed in claim 29, characterised by effecting the DBD treatment with electrodes integrated into the polymer extrusion mouth.

32. A method as claimed in claim 29, characterised by effecting the DBD treatment with electrodes in the form of rollers applied at a predefined distance from the extrusion mouth.

33. A method as claimed in claim 18, characterised by effecting the DBD treatment with electrodes consisting of the walls of an injection mould in which the plastic and/or viscoplastic deformation of the material to be treated takes place.

34. A method as claimed in claim 21 , characterised by effecting the DBD treatment using as electrodes the same rollers used to deposit the formulation.

35. A method as claimed in claim 21 or 22 in which deposition of the liquid formulation is followed by lamination with a second film on the substrate on which deposition has taken place, characterised by effecting DBD treatment using as electrodes the actual coupling rollers.

36. A method as claimed in claim 21 , characterised by effecting the DBD treatment using two electrodes, between which the liquid material containing gas bubbles is made to pass.

37. A method as claimed in claim 36, characterised in that the electrodes, between which the liquid material flows, are integrated into the liquid dispenser.

38. A method as claimed in claim 21 , characterised by effecting the DBD treatment using two horizontal electrodes, between which a strip is made to pass on which the liquid material containing air bubbles has been spread.

39. A method as claimed in claim 1 characterised by effecting said plastic and/or viscoplastic deformation by dispensing a coat of a liquid formulation.

40. Material obtainable by the method claimed in one or more of claims 1 to 39, characterised by consisting of a film.

41. Material obtainable by the method claimed in claim 40, characterised by consisting of a thread.

42. Material obtainable by the method claimed in claim 40, characterised by consisting of a fibre.

43. Material obtainable by the method claimed in claim 40, characterised by consisting of a sheet.

44. Material obtainable by the method claimed in claim 40, characterised by consisting of a panel.

45. Material obtainable by the method claimed in claim 40, characterised by consisting of an extruded mass in general.

46. An article obtainable by the method claimed in one or more of claims 1 to 39, characterised by consisting of a tray.

47. An apparatus for implementing the method claimed in claims 1 to 39, characterised by comprising:

- a material preparation station for obtaining cavities filled with a mixture of gases and/or vapours sensitive to DBD treatment,

- a forming mould, - a power supply unit for DBD.

48. An apparatus as claimed in claim 47, characterised by comprising a degassing station.

49. An apparatus as claimed in claim 47, characterised in that the forming mould is composed of two parts, namely a lower (8) and an upper (10), this latter being movable in the sense of approaching the lower part.

50. An apparatus as claimed in claim 49, characterised in that the two parts are clad with a conductive layer.

51. An apparatus as claimed in claim 47, characterised in that the forming mould consists of an extruder, at the exit mouth of which there is provided a pair of rollers (42) between which the dielectric barrier discharge takes place.

52. An apparatus as claimed in claim 51 , characterised in that the two electrodes are integrated directly into the extrusion mouth and extend in the extrusion direction to form between them an interspace suitable for allowing the molten polymer material to expand.