ERHO, Tomi (P.O. Box 1000, VTT, FI-02044, FI)
1. Printing ink comprising thermoplastic carbohydrate polymer as pigment.
2. Printing ink according to claim 1, wherein the carbohydrate polymer has a glass transition point less than 210 0C, in particular less than 170 0C.
3. Printing ink according to claim 1 or 2, wherein the carbohydrate polymer is starch or starch derivative, in particular a hydrophobic starch ester having a degree of substitution of at least 1.7, in particular at least 2.0.
4. Printing ink according to any of the preceding claims, wherein the polymer is biodegradable.
5. Printing ink according to any of the preceding claims, wherein the thermoplastic carbohydrate polymer forms 10 - 100 wt-%, typically 50 - 100 wt-%, in particular essentially 100 wt-% of the pigments of the ink.
6. Printing ink according to any of the preceding claims, further comprising coloured pigment, in particular white, black, red, green, blue, cyan, magenta or yellow pigment, typically forming 10 - 90 wt-%, in particular 50 - 90 wt-% of the pigments of the ink.
7. Printing ink according to any of the preceding claims, comprising
- 40 - 80 parts by weight water and/or water-based resin primer, - 20 - 60 parts by weight said thermoplastic carbohydrate polymer, and
- optionally, 1 - 20 parts by weight other additive(s), such as viscosity control agent(s) and/or stability control agent(s).
8. Printing ink according to any of the preceding claims, wherein the thermoplastic carbohydrate pigment particles have size of 100 nm - 10 μm, in particular 200 - 500 nm in average.
9. Printing ink according to any of the preceding claims, wherein the thermoplastic carbohydrate pigment particles are spherical.
10. A printed product comprising
- a substrate, and
- a printing on the substrate, wherein the printing is at least partly formed of printing ink according to any of the preceding claims.
11. A printed product according to claim 10, wherein the substrate is fiber-based, such as a paper or board.
12. A printed product according to claim 10 or 11, wherein the thermoplastic carbohydrate polymer forms on the substrate a layer having a thickness of 0.1 - 50 μm.
13. A printed product according to any of claims 10 - 12, comprising a visually identifiable marking, in particular a microstructured marking, such as a diffractive marking, embossed on the printing.
14. A printed product according to any of claims 10 -13, wherein the printing covers only a fraction of the surface area of the substrate.
15. A printed product according to any of claims 10 - 14, which is a packaging blank or a package.
16. A printed product according to any of claims 10 - 15, comprising optically detectable microstructures embossed in the printing layer.
17. A printed product according to claim 16, wherein the optically detectable microstructures form a visually identifiable diffractive marking.
18. A method for marking products, comprising
- providing a printable substrate,
- printing onto the substrate printing ink according to any of claims 1 - 9 for forming a marking layer comprising thermoplastic carbohydrate polymer on the substrate,
- embossing a marking comprising microstructures on the marking layer.
19. A method according to claim 18, wherein the printing ink is printed using offset, gravure, flexo, serigraphic, or ink-jet printing.
20. A method according to claim 18 or 19, wherein the marking is visually identifiable diffractive marking.
21. A method according to any of claims 18 - 20, comprising providing a fibrous substrate, in particular a coated paper or cardboard, - printing the printing ink on at least a portion of the surface of the substrate,
- letting the printing ink dry for forming said marking layer,
- embossing, using a microfabricated embossing member, a visually identifiable microstructure on the marking layer at an elevated temperature.
The invention relates to thermoplastic polymer films, which can be applied on fibrous products, such as papers or cardboards, for example. In particular, the invention concerns optically identifiable microstructures produced in such films. The invention also concerns methods of the producing polymer films of the present kind and manufacturing the optically identifiable microstructures on the film.
There is a growing interest in providing means for identification of fibrous materials and for verifying the origin thereof. An object is to prevent or at least making more difficult the production and distribution of counterfeit goods packed in such materials. A further object is to increase the attractiveness of goods by manufacturing unique visually identifiable patterns thereon. As specific examples of important goods can be mentioned, medicines and tobacco products packed in cardboard packages.
Examples of safety features (in the following also "safety markings") incorporated into fibrous materials include various tags and labels allowing for optical or electrical identification of the materials. In particular, there are a number of RFID and barcode tag solutions known in the art. One problem related to present day tags and labels is that they have to be attached to the surface of, e.g., the cardboard, in a separate process step. Depending on how they are fixed to the cardboard surface, for example by use of adhesives, there is always a risk that they might fall off during handling or conversion. There is also a considerable risk that separate safety markings are copied and used for counterfeiting of the product.
In contrast to separate labels, safety markings and decorative markings can be applied directly on the product, provided that the product as such comprises a layer capable of receiving and maintaining the marking. Most of these techniques are based on coating of paper or board using a specialized coating composition during the manufacturing stage of the paper or board and embossing the marking in the coating layer. Some techniques are also known, in which a marking is produced on a varnish layer applied on a printed product.
It is an aim of the present invention to eliminate at least a part of the problems related to the known art and to provide a novel material which is suitable as a base for diffractive safety markings and decorative markings and the like. It is also an aim of the invention to provide a novel packaging product comprising and marking layer formed of the abovementioned material.
It is a further aim of the invention to provide a novel method for producing markings on substrates.
The invention is based on the idea of including thermoplastic carbohydrate polymer or a derivative thereof as pigment in printing ink. Such printing ink is capable of forming on a printable substrate a marking layer capable of receiving various types of optically identifiable microstructures, including diffractive marking patterns. The layer formed is thermoplastic and thus embossable using hot-pressing.
In particular, the pigment is a thermoplastic carbohydrate polymer having a glass transition point of less than 210 0 C. Most advantageously, the pigment is starch or starch derivative.
The marking layer according to the invention is produced using printing ink of the above kind on a substrate. The marking layer may comprise microstructures, that is, micro-protrusions or microgrooves or a combination thereof so as to form a marking. The marking is visually identifiable provided that the density of microstuctures is high enough, such as in a diffractive marking. However, also plain (untreated) marking layers are within the scope of the invention as they in every case have a unique composition and appearance due to the polymeric pigment and are capable of receiving a marking by embossing.
The method according to the invention comprises providing a printable substrate, - printing onto the substrate printing ink comprising thermoplastic carbohydrate polymer pigment for forming a thermoplastic carbohydrate polymer film on the substrate, - embossing a marking comprising microstructures on the thermoplastic carbohydrate polymer film.
More specifically, the invention is characterized by what is stated in the independent claims. Considerable advantages are obtained by means of the invention. In contrast to prior technologies requiring a substrate coated with a special coating during the manufacturing stage of the product, the present film can be applied to practically any printable substrate using conventional and common printing techniques. Moreover, local application of the marking layer is possible, providing versatility and considerable savings as well as a possibility to form various shapes of the marking layer, such as text or graphics including e.g. a company logo. The marking layer can be applied in the printing stage of the product or in a separate stage.
Thus, the invention provides an inexpensive and reliable way of incorporating into various products decorative markings and safety markings, which allow for visual inspection or detection e.g. based on polychromatic light or based on the use of laser beams and other monochromatic light. Microstructures capable of diffracting light in the visual range, in the ultraviolet range, in the infrared range or in a broad wavelength range comprising visual, ultraviolet and/or infrared light can be manufactured to the present marking layer.
The invention also provides novel possibilities for decorating products. As the marking layer can easily be applied on parts of the substrate only, a single embossing member can be used to produce diverse-shaped identifiable patterns on the products (no patterns are reproduced on areas not containing the present polymer pigment). For example, a single embossing plate or roll comprising a specific identifiable micropattern (e.g. a pattern unique to a particular brand) can be used to mark several products of the same product family (e.g. packages of different size or packages of a chocolate bar and an ice-cream stick, for example, by the same manufacturer and/or sold under the same trademark). Printing allows for the production of marking layers of practically any shape on packaging blanks, for example.
The polymers used in the invention are biocompatible and, in some cases, even biodegradable materials. The bio compatibility allows for the use of the polymer layers in foodstuff packagings and wrappings of other products which must meet stringent requirements, e.g. as cigarette papers. The cost for the application of the marking is small compared to the cost of the product and its package. Further, no additional processing of the embossed surfaces is required for achieving visually complete and mechanically durable decorations. However, additional treatment of the surface, for example by varnishing, is not excluded. Thermoplastic polymers based on starch are of particular interest as they generally are intermixable with common ink solvents, are printable, and form an embossable surface structure on various substrates, including paper and board. In addition, starch is easily available and inexpensive and various techniques for the production of thermoplastic starch and derivatives suitable for printable ink mixtures are known in the art (see below).
Further features and advantages of the invention will become apparent from the following detailed description of particularly preferred embodiments.
By "printing ink" we mean material comprising at least one solvent and one pigment blended with the solvent and capable of being applied on a printable substrate by some printing technique, such as offset, gravure, flexo, serigraphic, or ink-jet printing. In addition to the abovementioned components, the printing ink may comprise one or more additional solvents or pigments, along with other components, such as dyes, resins or other binders, lubricants, solubilizers, surfactants, particulate matter, fluorescers, stabilizers, or the like additives.
By "pigments" we mean particle-form substances capable of being blended with a solvent so as to form printable ink. Generally, pigments are used for affecting the spectral appearance of ink. The thermoplastic carbohydrate polymers used in the present invention are typically bleak or very light-coloured, that is, they are unsaturated in colour. They can be used as secondary (< 50 wt% of all pigments) the primary (> 50 wt-% of all pigments) or even as the only pigment of the ink. Conventional coloured pigments (toners) can be included in the composition for giving the ink a specific colour.
By a "printable substrate" we mean any substrate capable of receiving and maintaining a printing from printing ink thereon. The substrate may, for example, be capable of absorbing solvent of printing ink and binding pigments of the printing ink onto its surface layer, the solvent of the ink can be evaporated from the surface of the substrate by warming, or the binder system may be polymerized using UV-light onto the surface of the substrate, to mention some examples. In particular, the printing substrate may be a fiber-based web or sheet, such as a coated or uncoated paper or board, or a polymer film.
As was discussed above, the present invention provides a novel printing ink and novel marking layers comprising thermoplastic carbohydrate polymers and polymers derived from such materials and applicable by printing. The marking layers can be used as microstructured safety markings, identification markings or for decorative purposes (e.g. for producing "rainbow colours" on a substrate). They are useful also for brand promotion. The ink can also be used as a printing ink as such without micropatterning the layer formed.
The marking layer is generally formed by applying and drying the present ink composition on a porous substrate. In the drying process, a first portion of the ink volatilizes and a second portion of the ink adheres to the substrate. The polymer pigment adheres to the surface of the substrate, forming the embossable marking layer. The ink typically contains also other components, such as binders, which may absorb and adhere to deeper portions of the substrate too. Consequently, the present printed product can be distinguished from other products by analyzing the surface layer and/or the ink residues.
The marking layer typically has a thickness of about 0.1 to 50 micrometres.
The polymer pigment typically has a moderately high to high glass transition point, e.g. up to about 210 0 C, in particular 200 0 C or less, preferably from about at least 30 or 60 up to 170 0 C.
For the purpose of the invention, the thermoplastic polymer is in particular selected from thermoplastic, biocompatible or biodegradable polymers derived from carbohydrate materials. This group of carbohydrate materials comprises native starch, dextrin, native hemicellulose, native cellulose as well as derivatives thereof, viz. starch derivatives, dextrin derivatives, hemicellulose derivatives, cellulose derivatives, and mixtures thereof.
In order to convert the carbohydrate polymer into a thermoplastic polymer, the polymer material is plasticized. The plasticization can be effected by incorporating suitable substituents (internal plasticization) or by blending or melt-blending the native polymer with conventional ("external") plasticizers, typically monomeric plasticizers. It is also possible to combine these two approaches.
As a specific example of the latter alternative, the working embodiment can be mentioned wherein the carbohydrate polymer is plasticized with a hydroxyl compound selected from the group of C 2 to C 4 alcohols having 1 - 5 hydroxyl groups, in particular glycerol or sorbitol or mixtures thereof. Other plasticizers are water, acetic glycerol esters, propylene glycol, dipropylene glycol, citric acid alkyl esters and mixtures thereof.
Internally plasticized polymers, e.g. starch or cellulose derivatives, are generated from starch or cellulose by a chemical reaction, and at least part of the anhydroglucose units of the molecule comprises groups that modify the hydroxyl functions of said units.
It should be noted that for some applications it is particularly preferred to use chemical derivatives of biopolymers. Thus, e.g. esterifϊcation (for instance acetylation) improves the thermal stability of the product, when compared with native starches. This is advantageous especially when the product is used as a pigment at an elevated temperature.
The esters or ethers or mixed ester/ethers of starch are typically prepared from native starch, hydrolyzed starch, oxidized starch, cross-linked starch or gelatinized starch. The starch, in turn, can be based on any natural starch, the amylose content of which is 0-100 % and the amylopectin content 100-0 %. Accordingly, the starch can be sourced from barley, potato, wheat, oats, pea, corn, tapioca, sago, and rice, or similar tuber vegetables and cereal crops.
According to a preferred embodiment, the starch-based component is an ester formed of starch and one or several aliphatic C2-24 carboxylic acids. The carboxylic acid residue of the ester can be derived from a lower alkane acid, such as acetic acid, propionic acid or butyric acid, or a mixture of them. According to a preferred embodiment, the starch component is an esterifϊed starch, most suitably a starch acetate, the degree of substitution of which is 0.5-3, preferably 1.5-3 and most suitably 2-3. Suitable starch acetates are disclosed in, e.g. FI 113875, FI 107386 and WO 05/037864.
The starch ester can also be derived from natural saturated or unsaturated fatty acids. Examples of these are palmitinic acid, stearic acid, oleic acid, lino lie acid, and mixtures of them. The ester may also comprise both long (C16-24) and short chain (C 2 _ 14 ) carboxylic acid components. An example of these is a mixed ester of acetate and stearate. Besides acids, corresponding acid anhydrides, and acid chlorides and other corresponding reactive acid derivatives, too, can be used to form esters in a way which is known per se. The production of fatty acid esters of starch can be carried out as described for instance in the following documents: Wolff, LA. , Olds, D.W. and Hubert, G.E., The acylation of Corn Starch, Amylose and Amylopectin, J. Amer. Chem. Soc. 73 (1952) 346-349 or Gros, A.T. and Feuge, R.O., Properties of Fatty Acid Esters of Amylose, J. Amer. Oil Chemists' Soc 39 (1962) 19 - 24.
Lower ester derivatives, such as starch acetate, can be prepared by bringing the starch to react with an acid anhydride which corresponds to the ester group, for instance acetic anhydride, in the presence of a catalyst. Starch acetate can be produced for instance with the methods according to FI Patent No. 107386 or US Patent No. 5667803, or with other methods which are commonly used in acetylation of starch.
Another important starch component of the invention is represented by an ether formed by starch and a hydroxy alkyl group, the hydroxy alkyl component of which is preferably derived from ethylene oxide or propylene oxide. The molecular substitution of such an etherized starch is ca 0.05 - 6, preferably 0.1 - 3, in particular 0.3 - 2.
Other suitable polymers include cellulose derivatives and hemicellulose derivatives, such as cellulose esters and xylan esters.
According to a preferred embodiment, the thermoplastic carbohydrate polymer is a hydrophobic starch ester having a degree of substitution of at least 1.7, in particular at least 2.0. According to another preferred embodiment, the thermoplastic starch polymers are native starch, hydrolyzed starch and ether derivatives thereof or esters having a low DS of less than 0.5.
A method for producing porous particles from starch-based raw-materials (for example starch esters or starch ethers) is described in our previous patents and patent applications (FI 20035172, FI 20035173, FI 20050833 and FI 20040741 (FI 118179)). In that method, the particles are prepared using a two-stage method in which the starch-based material is first dissolved in an organic solvent or a mixture of an organic solvent and a non-solvent, for instance water, from which mixture the starch component is subsequently precipitated by diluting the solution with a non-solvent. Said method generates essentially round, porous particles. The derivatives are thermoplastic; Tg is typically approximately 150-160 0 C. According to one embodiment of the invention, the thermoplastic polymer pigment is in the form of particles of the above-indicated kind. The particle size typically lies within the range of 100 nm - 10 μm, in particular 200 - 500 nm in average. The particle form is preferably spherical.
According to a preferred embodiment, the thermoplastic carbohydrate polymer forms 10 - 100 wt-%, typically 50 - 100 wt-%, in particular essentially 100 wt-% of the pigments of the ink. That is, coloured pigments can be replaced with the present pigment or the ink may comprise both types of pigments. Depending on the shade of the carbohydrate pigment and on the amount and shade of other (optional) pigments, the ink can produce a non-transparent white or whitish or even coloured marking layer. At the same time, the marking layer is microfabricable, which allows the production of diffractive patterns.
According to one embodiment, the ink comprises, in addition to the thermoplastic carbohydrate polymer a coloured pigment, in particular white, black, red, green, blue, cyan, magenta or yellow pigment either in normal or pearlescence form, typically forming 10 - 90 %, in particular 50 - 90 % of the pigments of the ink. Such pigments are known in the art. Provided that the amount of coloured pigment is sufficient, it is thus possible to replace conventional non-embossable inks in ordinary one-, two-, three- or four-colour printing and to achieve an embossable coloured printing pattern without any additional processing steps.
Printing of the present printing ink is basically similar to printing of conventional printing inks. The viscosity of the ink depends on the printing method used but is typically in the range of 1 - 200 cp (centipoise), in particular 1 - 100 cp. For gravure printing, the preferred viscosity is 15 - 60 seconds (Shell Cup Viscometer, #3 Cup), 15 - 60 seconds (Shell Cup Viscometer, #2 Cup) and less than 30 seconds (Shell Cup Viscometer, #1 Cup) for ink-jet printing. It is to be noted that in particular for other printing methods the viscosity can be more or less than what is indicated above.
In addition to pigment, the ink comprises liquid carrier (vehicle), which can be water, oil, or another solvent. Typically, the total amount of pigments in the printing ink is 5 - 50 wt-%, depending on the intended printing method. The ink may also contain binder resins which help to adhere the pigment to the surface being printed, viscosity control agents, such as CMC, stabilizing agents, or other additives.
According to one embodiment, the printing ink comprises - 40 - 80 parts by weight water and/or water-based resin primer,
- 20 - 60 parts by weight said thermoplastic carbohydrate polymer pigment, such as starch pigment, and
- optionally, 1 - 20 parts by weight other additive(s), such as viscosity control agent(s) and/or stability control agent(s).
Detailed examples of printing compositions falling within this general formula are given below. According to a further embodiment, the ink comprises 20 - 60 parts by weight of second pigment. Water-based inks of the above kind are inexpensive and easy to manufacture. They are also sufficiently stable at embossable pigment amounts. They have also been found to be printable, provided that the viscosity of the ink is suitable for the printing method used.
It should be pointed out that it is not necessary to provide the substrate with an integral marking layer which covers the whole substrate. For the purpose of the invention it is sufficient that the layer is present at the point where the embossing is carried out. Thus the thermoplastic carbohydrate polymer need only cover the part of the substrate where the marking pattern is applied.
The substrate fibrous material is selected from cellulosic, lignocellulosic and thermoplastic fibres and mixtures thereof. Typically, the substrate comprises a web or sheet of paper or cardboard or a layer formed by natural fibres, such as cotton. It may comprise a base paper or cardboard, which optionally contains fϊller(s). The grammage can vary freely but is usually in the range of about 30 to 750 g/m 2 , for example about 40 to 500 g/m 2 , and the thickness is about 1 to 100 micrometres.
The printing is allowed to dry before embossing so that a stable marking layer is formed on the substrate. The marking layer is preferably embossed at a temperature of at least 100 0 C, in particular at least 150 0 C, and a pressure of 1.5 bar (abs.) or more. Generally speaking, the marking typically comprises a plurality of mechanical deformations, which upon reflection of incident waves of light, in particular light having a wave length within the range of visible light, will produce a diffractive pattern. The pattern can produce varying visual effects depending on the observation angle relative to the light sources present.
A suitable pattern can be formed of engravings, i.e., pits or microgrooves, which extend from the surface of the marking layer to the marking layer. It can also be formed by rises, i.e., micro-protrusions which project away from the surface of the marking layer.
The grooves or protrusions can also be of variable depth, breadth and height, respectively. Typically they have a smallest dimension in the range of light, i.e. visible only or the range from UV to visible or visible to IR or in the broad range from UV to IR. Dimensions outside the indicated ranges are also possible. Thus, generally, the smallest dimension of the grooves and ridges of the microstructures are in the range of about 10 nm to 1500 nm, in particular about 50 nm to 1000 nm, and preferably about 75 to 800 nm.
Based on the foregoing, the present diffractive microstructures can comprise cinegrams, exelgrams or holograms and other structures (barcodes), which are detectable by visual inspection. In one preferred embodiment, the diffractive pattern comprises a holographically imaged pattern (a hologram), which gives a three dimensional impression to the viewer.
In practice, embossing can be carried out as known in the art. Thus, the layer can be embossed using an embossing device comprising an embossing device and a backing member and further comprising means for adjusting the temperature of the embossing device.
The embossing device can be static or dynamic, as will be discussed below in connection with the examples. In case of dynamic embossing, the embossing member is placed on a roll. Typical, roll-on-roll embossing requires that there is an embossing device comprising in combination an embossing roll and a backing roll for exerting embossing pressure on the surface layer of a substrate which is pressed between the rolls.
Flat-bed embossing is done using embossing means, which comprise at least one embossing plate. The working surface of the plate can be, for example, of metal having a microfabricated negative of the desired embossing. Generally, in both static and dynamic embossing, the embossing member used for achieving the desired pattern has a structure corresponding to the diffractive microstructure which is to be produced. It can be made on a thin metal sheet, in particular a thin nickel sheet, by, for instance, optical exposure combined with electrochemical deposition or by electron lithography. An embossing member also known as a shim is thus obtained and by using this shim, the desired diffractive microstructures is produced by pressing the shim onto the surface of the thermoplastic layer.
To achieve the shaping action, the surface needs to be soft, which can be obtained by increasing the temperature of the layer to about or above the glass transition point of the polymer.
The embossed products, sheets and webs, produced according to the present invention can be employed, for example, in the packaging industry to give the product a safety-marking for warranting the authenticity of the product or for graphically enriching the exterior decorative image of the packages. Examples of typically applications are daily consumer goods, cigarettes, digital media, pharmaceuticals, cosmetics, and consumer electronics, including fast moving consumer goods (FMCG) and food products. Visual markings can be replaced or complemented with codes which are invisible to the naked eye but which can be read with a separate optical reader.
It is highly advantageous for the package converter, product packager or brand owner that the microstructure can be applied to the surface during the processing, e.g. during last or penultimate step of the converting process, before or even during cutting, since this will do away with the need for further separate marking steps.
In the Examples, acetate starch pigment AP2 manufactured according to a process described FI 118179 is used.
Printing Ink Example A 40,0 parts Starch pigment AP2
50,0 parts Joncryl 1602 (water-based Styrene / acrylic emulsion)
2,0 parts Joncryl wax9 (PE-wax, white)
8,0 parts tap water 100,0 parts total
Thus, the compositon of the ink resembles a typical flexographic ink, with the exception that a coloured pigment is replaced with the starch pigment. Joncryl is a trademerk of BASF.
The measured viscosity (Brookfϊeld, spindle RV5, T=21 0 C) was 1008 mPas at 25 rpm and 944 mPas at 50 rpm.
Printing Ink Example B
33,3 parts Starch pigment AP2
66,6 parts tap water
100,0 parts total
The ink consists essentially of starch pigment mixed in water. The measured viscosity (Brookfϊeld, spindle RV3, T=21 0 C) was 12 mPas at 25 rpm and 16 mPas at 50 rpm.
Printable ink compositions were also achieved using different mixing ratio. However, for achieving good embossability the amount of pigment is preferably more than 10 parts and for keeping the ink stabile, the amount of starch should not exceed about 35 parts (without stabilizers or other additives).
Printing Ink Example C
29,5 parts starch pigment AP2 4,5 parts CMC
66,0 parts tap water
100,0 parts total This composition comprises carboxymethyl cellulose mainly for increasing the viscosity of the ink. This is beneficial in particular for gravure and flexographic printing.
The measured viscosity (Brookfϊeld, spindle RV5, T=21 0 C) was 176 mPas at 25 rpm and 136 mPas at 50 rpm.
All the ink compositions given above were manufactured by mixing their components in a magnetic mixer from 2 to 24 hours at 50 0 C. A test printing was carried out using an IGT Fl - laboratory scale printing machine using anilox-rolls having ink for 6.5 ... 20 ml/m 2 in cups thereof for ink transfer. All ink compositions A, B and C showed good printability at these conditions. A mineral-coated board was used as the printing substrate. All printed samples were succesfully embossed using static embossing at 6 bar pressure and 150 ... 170 0 C temperature for 25 seconds.
The advantageous embodiments and examples given above are not intended to limit the scope of the invention, which should be interpreted according to the appended claims taking equivalents into account.