Method for producing a sheet

Abstract

The method for producing a electroconductive sheet having a substrate, in particular made of paper, and an electroconductive layer include the steps of: a/ preparing a multi-layer structure with an anti-adhesive coating inserted between a plastic film and a base layer, b/ cross-laminating the multi-layer structure and the substrate, and c/ removing the plastic film and the anti-adhesive coating from the base layer. The base layer is a layer of an electroconductive material or is covered with an electroconductive layer by an additional step consisting of: d1/ depositing an electroconductive film on the base layer; or d2/ printing the base layer with at least one ink having electrical properties, with the base layer being a printable layer with a binder base of which the rate is 15% greater in dry weight in relation to the total dry matter weight of this layer.

Claims

1. A method for producing a sheet comprising at least one electroconductive layer, said sheet comprising a substrate, wherein at least one side of the substrate is covered at least partially with a layer or several superimposed layers comprising the electroconductive layer, the method comprising the steps of: a/ preparing or providing a multi-layer structure comprising at least a plastic film, an anti-adhesive coating, and a base layer, with the anti-adhesive coating inserted between a side of the plastic film and the base layer; b/ applying an adhesive to at least one of (i) a side of the substrate and (ii) a side of the multi-layer structure located opposite to the plastic film, and applying said side of the substrate against said side of the multi-layer structure, so as to cross-laminate the multi-layer structure and the substrate; c/ removing the plastic film and the anti-adhesive coating from the base layer; and d/ covering the base layer with an electroconductive layer by printing the base layer with at least one ink having electrical properties, wherein the base layer is a printable layer having a binder base, wherein a ratio of the binder is greater than 15% in dry weight relative to the total dry matter weight of the base layer, then subjecting the printed sheet to an annealing heat treatment so as to form a layer of electroconductive ink, wherein step d/ is repeated at least once, and wherein each step d/ which follows another step d/ is separated from the other step d/ by an intermediary step of letting the sheet rest so as to substantially recover an initial humidity rate of the sheet.

2. The method according to claim 1, wherein the binder of the printable base layer comprises a main binder which is at least one of (i) a synthetic latex such as a styrene-butadiene copolymer (XSB) and (ii) a styrene-acrylate copolymer (SA).

3. The method according to claim 2, wherein the binder comprises a co-binder which is an adhesion promoter having an ethylene copolymeracrylic acid (EAA) base.

4. The method according to claim 1, wherein the printable base layer is printed by ink jet, rotogravure, flexography, screen printing or offset.

5. The method according to claim 1, wherein the electroconductive ink comprises at least one of (i) metal nanoparticles or microparticles, (ii) nanoparticles or microparticles of carbon, and (iii) at least one conductive polymer.

6. The method according to claim 1, wherein the printable base layer comprises pigments.

7. The method according to claim 1, wherein the printable base layer is formed from at least two underlayers.

8. The method according to claim 1, wherein the sheet comprises at least one of (i) a metal film and (ii) a barrier layer having a base of polyurethane (PU), polyvinyl alcohol (PVA), polyvinylidene chloride (PVDC), vinyl acetate ethylene copolymer (EVAC), cellulose nanofibres, or metal, wherein the barrier layer is located between the substrate and the base layer.

9. The method according to claim 1, wherein the substrate is a tracing paper, and wherein the printable base layer has a transparency and a binder rate greater than 30% in dry weight relative to the total dry matter weight of the base layer.

10. The method according to claim 1, comprising, before the step d/, a step of heat pre-treatment of the sheet in order to remove at least a portion of water contained in the sheet.

11. The method according to claim 1, wherein the annealing is carried out in an oven, on a hot plate, a photon oven or in an infrared dryer.

12. The method according to claim 1, wherein the step d/ is preceded by a step of subjecting the base layer to a plasma treatment.

13. The method according to claim 1, wherein the adhesive used in step b) is a single-component or two-component polyurethane adhesive.

14. The method according to claim 1, wherein the substrate comprises fillers that result in at least one of (i) increasing a thermal diffusivity of the sheet, (ii) increasing a wet strength of the sheet, and (iii) making the sheet fire-retardant.

15. The method according to claim 1, wherein at least one of: (i) in the multi-layer structure prepared in step a), the base layer extends over a surface area less than a surface area of the side of the plastic film; (ii) the multi-layer structure and the substrate are cross-laminated in step b) over a surface area less than a surface area of the side of the sheet; (iii) the plastic film removed in step c) has at least one dimension selected from a length and a width thereof which is less than a corresponding dimension or dimensions of the side of the sheet; and (iv) the sheet obtained in step c) is cut in pieces, then at least one of the pieces cut from the sheet is glued onto the substrate of another sheet, in such a way so that the sheet comprises at least one side having at least one zone of greater smoothness than the rest of the side, the zone comprising a smooth external layer which is formed by the base layer and which extends on the substrate of the sheet over a surface area less than a surface area of said side.

16. The method according to claim 15, comprising, between the steps a) and b), a step of cutting the multi-layer structure.

17. The method according to claim 16, wherein at least one cut piece of the multi-layer structure is cross-laminated to the substrate in step b), and the plastic film and the anti-adhesive coating are removed from the glued piece, in step c).

18. The method according to claim 15, wherein the application of the multi-layer structure onto the substrate is carried out in step b) using a stamp press which applies a pressure in the zone, or using a hot foil stamp press which softens the adhesive used in step b), wherein the adhesive used in step b) is a heat-sensitive adhesive.

19. The method according to claim 15, wherein the plastic film of the multi-layer structure prepared in step a) has at least one dimension selected from a length and a width thereof which is less than a corresponding dimension or dimensions of the side of the sheet.

20. The method according to claim 15, wherein the sheet is produced on line in a paper machine, or off line in a paper cutting or finishing machine.

21. The method according to claim 15, comprising, before the step c), a step of printing the side of the multi-layer structure located opposite the plastic film with electroconductive inks, or of depositing an electroconductive coating on said side.

22. The method according to claim 15, wherein, during the step a), the anti-adhesive coating deposited onto the plastic film is printed with electroconductive inks or is covered with an electroconductive coating.

23. The method according to claim 15, wherein (iv) the sheet obtained in step c) is cut in pieces, then at least one of the pieces cut from the sheet is glued onto the substrate of another sheet, and wherein the sheet to be cut or the cut piece is printed with electroconductive inks or is covered with an electroconductive coating, before the gluing onto the substrate of the other sheet.

24. The method for producing an electroconductive product comprising producing, using an electroconductive sheet obtained by the method according to claim 1, at least one component selected from a resistor, a capacitor, a transistor, an RFID chip, a logic circuit, a membrane switch (SWITCH), a photovoltaic cell, a battery, a means for collecting energy, a backlighting system, a means of solid-state lighting or display such as an organic or inorganic light-emitting diode (OLED), a membrane keyboard, a sensor, and combinations thereof.

Description

(1) The invention shall be better understood and other details, characteristics and advantages of this invention shall appear more clearly when reading the following description given by way of a non-restricted example and in reference to the annexed drawings wherein:

(2) FIG. 1 shows in a very diagrammatical manner steps of the method for producing a sheet according to the invention;

(3) FIG. 2 shows in a very diagrammatical manner an alternative embodiment of the method according to the invention;

(4) FIGS. 3 and 4 are images obtained by a scanning electron microscope (SEEM) of sheets, with FIG. 4 corresponding to a sheet obtained by the method according to the invention;

(5) FIGS. 5 and 6 show in a very diagrammatical manner steps of another alternative embodiment of the method according to the invention;

(6) FIGS. 7 to 11 show in a very diagrammatical manner several embodiments of the method according to the invention;

(7) FIG. 12 shows particular geometrical shapes for the plastic film, the multi-layer structure and/or the base layer during the implementation of the method according to the invention; and

(8) FIGS. 13 and 14 show in a very diagrammatical manner steps of an alternative embodiment of the method according to the invention;

(9) FIGS. 15 and 16 show in a very diagrammatical manner steps of another alternative embodiment of the method according to the invention;

(10) FIGS. 17 and 18 show sheets prepared by the method according to the invention, and

(11) FIG. 19 shows another sheet prepared by the method according to the invention.

(12) Reference is first made to FIG. 1 which shows in a very diagrammatical manner steps a/, b/ and c/ of the method for producing a sheet according to the invention.

(13) The step a/ of the method consists of preparing a multi-layer structure 12 comprising a lower plastic film 14, an anti-adhesive intermediary coating 16 and an upper base layer 18. The preparation of this structure 12 can be carried out in one step or several successive steps.

(14) The anti-adhesive coating 16 and the base layer 18 can be deposited simultaneously onto the plastic film 14, by a curtain coating technique for example.

(15) Alternatively, the anti-adhesive coating 16 is deposited onto the plastic film 14, then the base layer 18 is deposited on the anti-adhesive coating.

(16) The surface quality of the upper side 20 of the plastic film 14 is transmitted to the lower side 22 of the base layer 18 (by the intermediary of the anti-adhesive coating 16). The surface characteristics of the side 22 of the base layer are therefore defined by those of the side 20 of the plastic film 14.

(17) After drying and/or solidification of the base layer, the surface characteristics of the side 22 are frozen and are not intended to be modified during other steps of the method, and in particular the transfer of the base layer 18 onto a substrate 24, such as a paper, to be coated.

(18) The step b/ of the method consists of depositing a layer or a film of adhesive 26 onto the upper side 28 of the base layer 18 or onto the lower side 30 to be coated of the substrate 24, even on these two sides 28, 30, then in applying these sides 28, 30 against one another in order to laminate or cross-laminate the multi-layer structure 12 and the substrate 24, and as such form a laminated or cross-laminated product 32.

(19) The step c/ of the method consists of removing the plastic film 14 and the anti-adhesive coating 16 of the base layer 18, in such a way that only this layer 18 remains (with the adhesive 26) on the substrate 24.

(20) These steps b/ and c/ can be carried out simultaneously or one after the other. In this latter case, the adhesive 26 is advantageously in the dry state and/or solidified during the removal of the plastic film 14.

(21) At the end of the step c/, the side 22 of the base layer 18 is exposed, with this side being relatively smooth.

(22) FIG. 2 shows an alternative embodiment of the method according to the invention, and differs from the method described hereinabove in reference to FIG. 1, in particular in that the multi-layer structure 12 further comprises at least one additional layer 34 deposited onto the upper side 28 of the base layer 18.

(23) Several additional superimposed layers 34 can be deposited (simultaneously or successively) onto the side 28 of the base layer 18.

(24) During the step b/, the lower side 30 of the substrate 24 or the upper free side 36 of the additional layer 34 (the farthest away from the plastic film, in the case where the structure 12 comprises several additional layers) is covered with adhesive 26. Alternatively, these two sides 30, 36 are covered with adhesive 26.

(25) During the step c/, the multi-layer structure 12 and the substrate 24 are laminated or cross-laminated, in such a way as to form a laminated or cross-laminated product 32, then the plastic film 14 and the anti-adhesive coating are removed, in such a way as to expose the smooth or ultra-smooth side 22 of the base layer 18 of the sheet 10.

(26) The nature of the base layer 18 of the sheet can vary according to the embodiment of the method according to the invention.

(27) The base layer 18 can be carried out in an electroconductive material and for example metal. The base layer 18 is for example formed of a thin layer of gold which is deposited on the anti-adhesive coating 16 by vacuum depositing or by any other suitable technique.

(28) Alternatively, the base layer 18 can per se not be electroconductive and can then be coated with an electroconductive film (step d1/ of the method) or printed with an ink having electrical properties (step d2/).

(29) In the case where the base layer 18 is covered with a metal film, the latter can be formed in situ on the base layer or added and affixed, for example by gluing, onto the base layer. This film is for example a gold film.

(30) In the case where the base layer 18 is printable, it can be formed from a resin or from a printable varnish or from a paper coating comprising a binder and possibly pigments. The layer 18 is printable by any suitable technique, as the ink is intended to be deposited onto the smooth side 22 of the sheet 10.

(31) The ink can include metal particles, particles of carbon and/or conductive polymers, with the particles able to be micrometric or nanometric. The step d2/ can include a sub-step wherein the printed sheet is subjected to a step of annealing so that the layer of ink forms a continuous electroconductive layer. This is for example the case when the ink comprises metal particles which are intended to coalesce during the step of annealing.

(32) All of the embodiments make it possible to produce an electroconductive sheet, i.e. a sheet comprising at least one layer having good electrical conductivity, and in particular having a resistance per square less than 0.3 /sq, more preferably less than 0.15 /sq, and for example until a resistance of approximately 0.05 /sq.

(33) Measuring the resistance per square of a sheet according to the invention can be carried out by means of a 4-point device or apparatus. This method uses sporadic contacts arranged on the surface of the sheet. These contacts are carried out via metal tips. Two tips are used to supply a current and two other tips are used to measure a voltage. The four tips are arranged at the four corners of a virtual square at the surface of the sheet or are aligned one after the other on a virtual line at the surface of the paper. It is possible to use a Jandel 4-tip device (universal Probe) coupled to a Jandel RM3 current generator which provides a currant ranging from 10 nA to 99 Ma. The resistances measured are expressed in Ohms per square (ohm/ or /sq) and they are denoted as R. The device measures the V/I ratio that can be connected to the resistivity of the sheet. The case of a thin layer with thickness e and with resistivity is used. The thickness being negligible with regards to the other dimensions, a two-dimensional model for the conduction can be implemented and which gives: V/I=K.Math./e=K.R. K is a non-dimensional coefficient characteristic of the geometry 2D. The /e ratio characterises the layer, it is denoted as R(ohm/). The coefficient K can be calculated analytically in particular simple cases: K=log(2)/.

(34) Examples that illustrate this invention shall now be described in what follows.

EXAMPLE 1

Carrying Out Multi-Layer Structures and Sheets According to the Steps a/ to c/ of the Method According to the Invention

(35) Several multi-layer structures were carried out by reproducing the step a/ of the method according to the invention, using substrates made of paper (Bristol boards and Maine gloss from the Arjowiggins company).

(36) Tests were carried out in order to determine the most suitable adhesives for the carrying out of the step b/ of the method. The adhesive used must provide a fastening of the paper on the layer with regards to the multi-layer structure, that is sufficient in order to prevent it from become detached from this layer during the removal of the plastic film in step c/.

(37) We have tested three types of adhesive: a/ a two-component PU adhesive with solvent (reference AD 1048 from the Rexor company), b/ a single-component PU adhesive with solvent (reference NC 320 from the COIM company), and c/ a single-component PU adhesive without solvent (reference SF2930 from the COIM company).

(38) Tests were carried out using an adhesive tape in order to determine the level of adhesion of the papers on the multi-layer structures. The best results were obtained when the PU adhesive was applied onto the multi-layer structure rather than onto the paper, when the adhesive a/ was used to glue the Bristol board and when the adhesive b/ was used to glue the Maine gloss paper.

EXAMPLE 2

Preparation of a Sheet Comprising a Thin Film of Gold which is Formed In Situ on the Base Layer of the Sheet (Method with Step d1/)

(39) The depositing of a gold film onto the base layer of a sheet obtained by the method according to the invention, is carried out in a vacuum by means of a DEP280 machine. This machine makes it possible to vacuum deposit many metals such as titanium, copper or gold. In this case, a fine layer of gold is deposited on the base layer of the sheet. Beforehand, the sheet is placed in the oven in order to be degassed (100 C.). As such, the pressure decreases. The pressure in the enclosure stands at 9.5.Math.10.sup.7 mbar (for approximately 14 minutes) and at 8.10.sup.7 mbar (for approximately 25 minutes). A pre-spraying takes place first of all for 120 seconds. Spraying for 375 seconds then follows. The depositing of gold on the sheet in the end is 30 nm thick. It is possible to place up to three sheets to be treated simultaneously in the machine.

EXAMPLE 3

Carrying Out a Step of Photolithography Using a Sheet Coated with a Metal Layer, Such as that Obtained in Example 2

(40) A positive resin of 1.8 m of thickness (representing approximately 2 mL of resin) is deposited via spin-coating onto a sample (dimensions 11*11 cm) of a sheet coated with a metal layer, such as that obtained in example 2, by rotation at a speed of 3000 rpm. This operation lasts approximately 15 seconds. The difference between a positive resin and a negative resin is made during the development of zones subjected to the rays of photolithography (lighting). In the first case, it is the exposed zones which disappear during the development; in the second case, it is the unexposed zones.

(41) The sheet is placed in the oven for cross-linking of the resin. This is done at a temperature of 115 C. and for a duration of approximately 5 minutes. For the step of lighting, a quartz mask is arranged on the sheet, this mask comprising patterns, and the rays being intended to pass on zones where there is no pattern.

(42) The lighting is carried out at a power of 5 mW and lasts 10 seconds. This time depends on the thickness of the resin deposited and on the power of the rays. Once this step is complete, the mask is cleaned with acetone. The phase of development can then take place. A product called tetra-methylammonium hydroxide (MF-319) is used to develop after lighting. This step lasts one minute. This makes it possible to make the patterns that can be seen with the unaided eye appear on the sheet. As this here entails a positive resin, the developer removes the exposed resin. The sheet is then placed in an etching bath in order remove the exposed resin remaining on the metal layer. A mixture of potassium iodide/iodine (KI/I.sub.2) is used. This step lasts twenty seconds. After a rinsing with water, then only the metal layer and the unexposed resin remain. The sheet is annealed at 115 C. for a few minutes for the purposes of removing as much water as possible. The resin is then removed from the metal layer via stripping. For this, the sample is dipped into an acetone bath for fifteen minutes with ultrasound in order to remove the residual resin.

(43) The sheet has a very good thermal stability and is not altered by the successive heat treatments.

EXAMPLE 4

Carrying Out of a Step of Laser Ablation of a Metal Layer Deposited onto a Sheet, Such as that Obtained in Example 2

(44) The ablation laser can be carried out by means of a Tamarack Scientific machine. A laser ablates zones defined by an operator. The metal layer (such as gold) which undergoes the stress of the laser begins by absorbing the impact, then the heat of the latter propagates. A difference in dilatation is created due to this phenomenon, which results in the final ablation of the metal. This technique of ablation is subtractive and of the direct patterning type. This means that the pattern is carried out without adding any product. Here, it is the laser beam which passes through a mask and pulls off the matter from its support. The power of the beam is adjusted according to the material and the quantity of material to be sampled. The final results after laser ablation of the materials depend on the influence of the nature and of the thermal and mechanical properties of the materials.

(45) The tests showed good thermal and mechanical resistance of the sheet to laser ablation and a good definition of the patterns created via laser.

EXAMPLE 5

Example of Producing an Electronic Component Using Sheets Obtained in Examples 3 and 4

(46) The metal layers of the sheets obtained in examples 3 and 4 were coated with a layer of a dielectric material, then these dielectric layers were themselves coated with a thin layer of silver in order to carry out capacities.

(47) Other metal layers of the sheets obtained in examples 3 and 4 were printed with a carbon ink in order to carry out resistors.

EXAMPLE 6

Example of Producing Sheets Each Comprising a Printable Base Layer

(48) The method according to the invention is used to produce sheets each comprising a base layer which is printable, in particular with inks having electrical properties.

(49) Three different paper coatings were used, which are respectively identified by the letters A, B and C. These are layers with a finely ground calcium carbonate base (marketed under the brand Carbital 95) and binders. The other products of each layer are used to adjust the viscosity, to cross-link the binder or to favour the spreading of the layer.

(50) The difference between the layers A, B and C is primarily their binder rate, which is 16.2% for the layer A, 8.8% for the layer B, and 16.2% for the layer C (of which 8.1% binder and 8.1% co-binder or adhesion promoter), in dry weight in relation to the total dry weight (or total dry matter weight) of the layer.

(51) Details of the compositions of these layers are provided in the following table.

(52) TABLE-US-00001 Layer A Layer B Layer C Components Wet weight Dry weight Wet weight Dry weight Wet weight Dry weight Water 502.273 0.000 60.724 0.000 39.177 0.000 Alkali Ammonia 20% 2.623 0.000 0.317 0.000 0.205 0.000 Dispex N40 2.623 1.705 0.317 0.206 0.205 0.133 Dried purified fine salt 2.914 2.914 0.352 0.352 0.227 0.227 Calgon PTH 0.058 0.029 0.007 0.004 0.005 0.002 Empicol LZ 0.058 0.029 0.007 0.004 0.005 0.002 Defoamer 1512M 0.204 0.102 0.025 0.012 0.016 0.008 Agnique EHS 75E 2.331 1.247 0.282 0.151 0.182 0.097 Surfinol 420 0.729 0.342 0.088 0.041 0.057 0.027 Carbital 95 78% 474.565 727.366 57.374 87.937 37.016 56.734 Styronal D517 190.617 97.215 11.519 5.875 7.432 3.790 Acronal S305 94.066 48.444 5.683 2.927 3.666 1.888 AZC 29.141 19.816 3.523 2.396 2.273 1.546 Sterocoll FD 1.311 0.688 0.159 0.083 0.102 0.054 Defoamer 1512M 0.204 0.102 0.025 0.012 0.016 0.008 Diamond 0.000 0.000 0.000 0.000 28.392 5.678 Total dry weight (Kg) 900 100 70 Total wet weight (Kg) 1303 140 119 Binder rate 16.2% in dry weight 8.8% in dry weight 16.2% in dry weight (in relation to the total dry matter weight) Binder rate 20% in dry weight 10% in dry weight 20% in dry weight (in relation to the dry weight of pigments)

(53) Alkali Ammonia 20% is an aqueous solution. Dispex N40 is an anionic polyacrylate which is used as a dispersant and emulsifier in solution. Calgon PTH is a phosphate which is used as a dispersant in powder form. Empicol LZ is a wetting agent in the form of powder. Agnique EHS 75E is a liquid wetting agent. Surfinol 420 is used as an anti-foaming agent, dispersant and wetting agent. Carbital 95 78% represents pigments of calcium carbonates in a liquid medium. Styronal D517 and Acronal S305 are latexes that form binders. Styronal D517 is a styrene butadiene latex and Acronal S305 is a styrene/butyl acrylate (styrene-acrylic). AZC (ammonium-zirconium carbonate) is a liquid insolubilising agent. Sterocoll FD is an acrylic acid that is used as a rheology modifier. Defoamer 1512 M is a liquid anti-foaming agent and Diamond is a co-binder or adhesion promoter with an ethylene copolymeracrylic acid (EAA) base.

(54) Several papers marketed by the Arjowiggins company were used to produce sheets with the method according to the invention. Each sheet comprises a printable layer (A, B or C) or two superimposed printable layers (A+A, A+B or A+C). In the case of a sheet with two printable layers, a first layer A is deposited on the adhesive and is therefore located under the second layer or external layer (A, B or C) in the final product.

(55) Two plastic PET films, used as a donor in the method, were tested. The first is a standard PET film and the second is a smoother PET film (referenced as 42).

(56) The following table summarises the characteristics of the various sheets carried out by the method according to the invention.

(57) Printing tests via piezoelectric effect ink-jet by means of a Dimatix machine from Fujifilm and by screen printing were carried out. Two types of ink were used (Sunjet U5603 and SICPA 9SP7214), with a silver nanoparticle base.

(58) The base layer of a sheet can be printed by a layer of ink and then subjected to a step of annealing, before again being printed with another layer of ink and subjected to another step of annealing. In this case, after the first step of annealing, the sheet can be stored in a suitable location and/or subjected to a particular treatment, so that it recovers its initial humidity rate (before annealing), before being printed again.

(59) TABLE-US-00002 Thick- Num- ness ber Anneal- of the Paper Plastic Reference of Annealing ing Test paper weight Type of film Type of of the ink layers Annealing temperature time Raverage no. Paper (mm) (g/m.sup.2) layer Layer(s) (donor) printing used of ink method ( C.) (min) (/square) 1 Maine gloss 2858 117 135 porous B PET Ink jet Sunjet 2 IR dryer 150 to 200 3 0.588 offset hot standard U5603 chamber 2 Maine gloss 2933 111 135 porous A + B PET 42 Ink jet Sunjet 2 3.41 offset hot U5603 chamber 3 Maine 135 offset 102 191 porous without Ink jet Sunjet 2 0.287 base U5603 4 Maine 2934 111 135 closed A + C PET 42 Ink jet Sunjet 2 0.051 indigo without U5603 hot chamber 5 Bristol 2932 205 200 closed A + A PET 42 Ink jet Sunjet 1 0.3 electronic hot U5603 chamber 6 Maine gloss 2947 113 135 closed A + A PET 42 Ink jet Sunjet 1 2 0.3 electronic hot U5603 chamber 7 Maine gloss 2947 113 135 closed A + A PET 42 Ink jet Sunjet 2 3 0.07 electronic hot U5603 chamber 8 Bristol 2828 275 250 closed A PET Screen SICPA 1 No No 3 0.084 electronic 1 layer standard printing 9SP7214 annealing annealing 9 Bristol 2828 275 250 closed A PET Screen SICPA 1 Oven 165 3 0.078 electronic 1 layer standard printing 9SP7214 10 Bristol 2828 275 250 closed A + A PET Screen SICPA 2 No No 3 0.244 electronic 2 layers standard printing 9SP7214 annealing annealing 11 Bristol 2828 275 250 closed A + A PET Screen SICPA 2 Oven 165 3 0.078 electronic 2 layers standard printing 9SP7214 12 Maine 2828 64 80 closed A PET Screen SICPA 1 No No 3 0.126 electronic 1 layer standard printing 9SP7214 annealing annealing 13 Maine 2828 64 80 closed A PET Screen SICPA 1 Oven 165 3 0.074 electronic 1 layer standard printing 9SP7214 14 Maine 2828 64 80 closed A + A PET Screen SICPA 2 No No 3 0.322 electronic 2 layers standard printing 9SP7214 annealing annealing 15 Maine 2828 64 80 closed A + A PET Screen SICPA 2 Oven 165 3 0.144 electronic 2 layers standard printing 9SP7214 16 PEN Teonex 122 Ink jet Sunjet 2 IR dryer 150 to 200 2.5 0.141 Q65FA125 U5603

(60) The resistances of the layers of ink must be as low as possible. It is observed that the number of prints of a paper has an influence on its resistance. The more layers of ink the paper comprises, the lower its resistance is. When the tests 3, 4 and 7 concerning the papers coated with two layers of ink are compared, it is observed that the closed layers of tests 4 and 7 have a lower resistance than the porous layer of the test 3. The sheets comprising a closed external layer (A or C) have good results in terms of resistance. On the contrary, each sheet having a layer B, which is a porous or open layer, does not have good results in this regard (see the first two tests).

(61) This can be explained by the fact that the porous layers allow the ink to be absorbed in the sheet, with the layer of ink thus not being continuous on the surface.

(62) These differences in porosity between the sheets are clearly visible in FIGS. 3 and 4 which show SEM photographs of surfaces to be printed with Maine gloss 2858 (porous or open sheetfirst test) and Maine 2828 (closed or non porous sheettests 12 to 15) sheets, respectively.

(63) The porosity of a layer can be characterised by its binder rate and this can be measured by carrying out a test with pore size inks.

(64) The test with pore size inks makes it possible to measure the absorption capacity of a sheet and the ink speed penetration, by the depositing of a special ink (comprising a black colouring) on this sheet and by studying its behaviour over time. This test furthermore makes it possible to assess the change in the optical density of a sheet after printing.

(65) The ink used here is a pore size ink from the Lorilleux company, marketed under the reference 3809. This is a varnish wherein a low percentage of black colouring has been dissolved.

(66) The sheet is fixed onto a clean and smooth work surface using adhesive tape. A bronze metal stamp, with a diameter of 2.4 mm and a mass equal to 328 g, inked beforehand (thin film), deposits a button of ink on the surface to be tested. After a lapse of time of contact evaluated with the chronometer (t=0, 7, 15, 30, 60 and 120 s), the excess ink is completely wiped with a cloth (more preferably soft and lint-free). It is imperative that the operation be carried out in a single movement, in a single direction, with firmness in order to prevent leaving residue on the print. This movement as such generates, behind it, another clear print in the shape of a comet tail.

(67) The ink, by penetrating into the sheet, more or less tints its surface according to the quantity of ink absorbed. The optical density of the stains on the sheet is measured with a reflection densitometer. The change in the optical density can as such be assessed according to the penetration time of the ink and have a global indication on the speed and the capacity of absorption of the sheet.

(68) The following table shows the change in the optical density of the inks deposited onto the printable base layers of several sheets obtained par the method according to the invention, according to the time elapsed (in seconds) after the depositing of the ink onto these layers.

(69) TABLE-US-00003 Test t = t = t = t = t = t = no. Paper 0 s 7 s 15 s 30 s 60 s 120 s 12 to 15 Maine 2828 0.08 0.1 0.09 0.1 0.1 0.1 17 Opale 2858 0.15 0.17 0.23 0.27 0.32 0.4 8 to 11 Bristol 2828 0.08 0.09 0.09 0.1 0.09 0.11 1 Maine single 0.13 0.14 0.17 0.2 0.26 0.32 component 2858 18 Stoneywood 2935 0.08 0.09 0.11 0.1 0.1 0.1 19 Paper Chromolux 0.18 0.21 0.21 0.31 0.39 0.56 300 20 Paper Chromolux 0.13 0.16 0.17 0.26 0.32 0.44 180 21 Bristol 2930 0.18 0.19 0.21 0.27 0.32 0.33 hot chamber 22 Bristol 2931 0.14 0.14 0.18 0.16 0.2 0.19 hot chamber 5 Bristol 2932 0.05 0.06 0.06 0.08 0.08 0.09 hot chamber 2 Maine gloss 2933 0.21 0.22 0.27 0.28 0.32 0.37 hot chamber 4 Maine indigo 0.12 0.14 0.13 0.18 0.18 0.15 2934 hot chamber 6 Maine gloss 2947 0.09 0.09 0.09 0.09 0.11 0.12 hot chamber 3 Maine base 0.26 0.3 0.3 0.34 0.4 0.47

(70) A closed layer is characterised by a low density of ink at Os and no or little change in this density over time. On the contrary, a porous layer will have a higher density right from the start and especially an increase in the density over time.

(71) It is observed that the sheets with a porous base layer (tests 1 to 3 and 17 to 21) do not have good results (substantial variation in the optical density of the inks over time) contrary to sheets with a closed layer base (tests 4 to 15 and 22).

(72) It is therefore important to use sheets that each have a printable base layer. In the case of a printable base layer, this porosity is, as explained hereinabove, controlled by the binder rate of the base layer which must, according to the invention, be higher than 15% in dry weight in relation to the dry weight of the layer. No difference was observed for the type of film used for the donor.

EXAMPLE 7

Evaluation of the Surface Porosity of Sheets Obtained by the Method According to the Invention, by Measuring the Open Fraction of the Surfaces of these Sheets Determined Via Image Analysis

(73) SEM images such as those obtained in the example 6 and shown in FIGS. 3 and 4 were analysed in order to measure the surface fraction of the pores at the surface of the base layers of the sheets. It is observed that the surface fractions of porosity of the sheets are highly variable.

(74) TABLE-US-00004 Test Rate of binder(s) no. Paper in % (dry weight) Open fraction (%) 8 to 15 2828 16.2 0.08 1 2858 8.8 4.3 21 2930 8.8 5.27 22 2931 8.1 + 8.1 Diamond 1.55 2 2933 8.8 1.88 4 2934 16.2 0.81 6 to 7 2947 16.2 0.19

(75) We first observe that the open surfaces are all relatively low (<6%). There is a substantial influence of the binder rate on the open fraction of the sheets. Indeed, the sheets with a binder rate of 16.2% in dry weight or more have an open fraction less than or equal to 1.55% while papers with a binder rate of 8.8% in dry weight or less have an open fraction greater than or equal to 1.88%. In addition, if the sheet 2931 (test no. 22), which has 8.1% binder and 8.1% co-binder (Diamond) is excluded, the results are even more substantiating.

(76) The tableau hereinbelow summarises the influence of the binder rate on the properties of the sheets tested.

(77) TABLE-US-00005 Binder Density of the rates Open pore size inks Silver ink Test in % (dry fraction Delta resistance no. Paper weight) (%) 0 s 120 s 120-0 (/sq) 8-15 2828 16.2 0.08 0.08 0.1 0.02 1 2858 8.8 4.3 0.15 0.4 0.25 0.59 21 2930 8.8 5.27 0.18 0.33 0.15 22 2931 8.1 + 8.1 1.55 0.14 0.19 0.05 Diamond 2 2933 8.1 1.88 0.21 0.37 0.16 3.41 4 2934 16.2 0.81 0.12 0.15 0.03 0.051 6-7 2947 16.2 0.19 0.09 0.12 0.03 0.07

(78) The sheets that have layers with binder rates of 8.8% (in dry weight) have porous surfaces, since the open fraction of these surfaces is high (at least 1.88%), which causes a strong absorption of liquids such as pore size inks. As such, the difference in optical density of the inks between 120 s and 0 s is greater than 0.1 for these sheets with porous coatings, while for the sheets having layers with a binder rate of 16.2% (in dry weight), the open fraction is low and the difference in optical density between 120 s and Os for the test with pore size inks is low (less than 0.1).

(79) When these sheets are printed with inks comprising nanoparticles of silver, via a by ink jet, then when these sheets are subjected to a thermal annealing of about 150 C., we find that the resistance of the printed tracks is also linked to the binder rate of the sheets.

(80) The sheets with layers having a high binder rate, therefore with a closed layer, provide printed tracks which are not very resistive (respectively 0.13 /sq and 0.07 /sq for the papers 2934 and 2947tests 4 and 6-7). A value of 0.15 /sq or less is considered to be good for printed PEN plastic films.

(81) In the same conditions, the sheets with layer shaving a low binder rate, therefore with relatively open layers, provide printed tracks which are more resistant (respectively 0.59 /sq and 3.4 /sq). This can be explained by the fact that the conductive inks penetrate into the surface pores of the sheets and create defects in the tracks which make their resistivity increase.

(82) We can therefore conclude from this that the binder rate strongly influences the aptitude for printing of these papers by inks having electrical properties.

EXAMPLE 8

Carrying Out Sheets with Printable Base Layers, Using Various Pigments

(83) Additional tests were carried out in order to determine on the one hand the influence of the type of pigments and of the binder rate in the printable base layer, on the transfer carried out in the steps b/ and c/ of the method.

(84) Several multi-layer structures were prepared according to the step a/of the method, with each of these structures comprising a printable base layer.

(85) The tableau hereinbelow summarises the various pigments used in the base layers of the sheets as well as the binder rate of each of these couches. Thirteen different multi-layer structures were prepared (A to M).

(86) TABLE-US-00006 Binder Gloss at Test with pore size inks Test Fillers rate [%] 75 [%] 0 s 7 s 15 s 60 s 120 s A Kaolin 9.1% 8 1 1.2 1.3 1.4 1.4 B 16.7% 26 0.3 0.78 1.15 1.4 1.4 C 23.1% 44 0.25 0.45 0.8 1;1 1.1 D Calcium 9.1% 42 0.19 0.35 0.37 0.46 0.55 E carbonates 16.7% 87 0.06 0.07 0.07 0.11 0.14 F 23.1% 93 0.05 0.07 0.08 0.07 0.07 G Plastic 9.1% 17 H fillers 16.7% 36 0.46 0.53 0.65 0.3 0.3 I 23.1% 73 0.21 0.36 0.25 0.62 0.65 J Nano 9.1% 4 K TiO2 16.7% 85 L 23.1% 92 0.2 0.3 0.4 0.62 0.78 M Without 100% 103 0.07 0.07 0.07 0.07 0.07 filler

(87) The Kaolin is that marketed by the Golden Rock Kaolin company under the denomination Kaolin SC 90. The calcium carbonate is that marketed by the Imerys company under the name Carbital 95. The plastic fillers are marketed by the Rhom & Haas company under the name Ropaque Ultra E and the nanoparticles of titanium dioxide are marketed by the Kemira company under the reference US Titan L181.

(88) It was observed that each multi-layer structure comprising a base layer having a binder rate less than 15% was not correctly transferred onto the substrate paper during the steps b/ and c/ of the method. Moreover, better transfer results were obtained with base layers of which the pigments are mineral fillers rather than plastic fillers. The best results were obtained with base layers of which the pigments are calcium carbonates because these layers are very glossy (and therefore smooth) and are closed (values for optical density that are relatively low and constant over time). The base layer that does not comprise any filler further has the advantage of having a high gloss and also of defining a closed surface.

EXAMPLE 9

Carrying Out an Embossed Electroconductive Sheet, for Carrying Out a Transistor for Example

(89) FIG. 5 shows a multi-layer structure 40 carried out by the method according to the invention, with this multi-layer structure 40 comprising a plastic film 42 made of PET on a side whereon are superimposed the following layers: an anti-adhesive coating 44, an electroconductive layer 46 of ITO (indium tin oxide), a layer 48 of P-doped semiconductor material, a layer 50 of N-doped semiconductor material, and a layer of aluminium 52. This structure is obtained after the step a/ of the method.

(90) This multi-layer structure 40 is then glued on a substrate 54 made of paper (step b/), then the plastic film 42 is removed exposing the electroconductive layer 46 of ITO (step c/). An electroconductive sheet is thus obtained that can be used for the production of electronic components, such as a transistor.

(91) In an additional step of the method, the sheet is embossed by a suitable technique by exerting compression forces on the layer 46 of ITO (in a direction perpendicular to the plane of the sheet), in particular zones and by means of a suitable technique known to those skilled in the art. This creates recesses 56, as shown in FIG. 6, at the bottom of which are displaced portions of the layers 46 to 52, which remain superimposed on one another.

EXAMPLE 10

Carrying Out an Electroconductive Transparent Sheet

(92) The method according to the invention was used to produce an electroconductive transparent sheet, this sheet comprising a tracing paper of 65 g/m.sup.2 and having a transparency of 66%. A printable base layer with a calcium carbonate and comprising 50% in dry weight of binder in relation to the total dry matter weight of the base layer is transferred onto the tracing paper by the method. The tracing obtained has a transparency of 68.5% and a Bekk smoothness greater than 10,000 s. The transparent sheet was then printed with inks having electrical properties.

EXAMPLE 11

Measuring the Gloss and the Optical Density of Inks Printed on Sheets Prepared Using the Method According to the Invention

(93) Several sheets were prepared by the method according to the invention, these sheets are differentiated from one another by the binder rate of their printable base layers (with a calcium carbonate base), which varies between 9.1 and 23.1%.

(94) The table hereinbelow summarises the results of the gloss measurements and of the tests with pore size inks carried out on six sheets.

(95) TABLE-US-00007 Binder Test with pore size inks Tests rate Gloss 0 s 7 s 15 s 60 s 120 s D 9.1% 42 0.19 0.35 0.37 0.46 0.55 N 14% 70 0.09 0.15 0.17 0.2 0.23 O 15% 78 0.08 0.13 0.14 0.17 0.2 P 16% 84 0.06 0.09 0.1 0.12 0.15 E 16.7% 87 0.06 0.07 0.08 0.11 0.14 F 23.1% 93 0.05 0.07 0.08 0.07 0.07

(96) It is observed that, above 15% in dry weight of binder in the base layer, the sheet comprises a gloss higher than 80 and an optical density less than or equal to 0.15 to 120 s, which means that the layer is not very absorbent and this constitutes good results.

(97) Reference is now made to FIGS. 7 to 11 which show several embodiments of the method according to the invention for the production of a sheet of which at least one side comprises a zone of greater smoothness than the rest of this side, this zone extending on a surface less than that of the side.

(98) In the case of FIG. 7, a plastic film 100 having relatively substantial dimensions (width l and length L) is used, with these dimensions being for example similar to those of the sheet or of the paper 102 intended to receive the multi-layer structure. The plastic film is for example made of PET and has a width of 1.5 m, a length of several tens of meters and a thickness of 5 to 20 m approximately.

(99) The multi-layer structure is prepared (step a)) using this plastic film 100 of large dimensions, as indicated hereinabove. This multi-layer structure can include an anti-adhesive coating, an electroconductive base layer, a layer of adhesive and a barrier layer. The multi-layer structure is then cut into strips 104 of which the length is equal to the initial length of the plastic film 100 and of which the width is for example of a few millimeters or centimeters.

(100) One or several of these strips 104 are glued onto the paper 102 according to the step b). In the case of FIG. 7, the paper 102 receives three strips 104 which are substantially parallel and at a distance from one another. The portions of plastic film of these strips 104 can then be removed according to the step c) in such a way as to reveal independent base layers that define smooth zones and which each form an electroconductive layer or which are each intended to be covered with an electroconductive layer.

(101) The paper 102 prepared as such can have large dimensions and be intended to be cut in order to produce A4 format papers for example. In a particular case for carrying out the invention, the paper 102 is cut in such a way that the strips 104 extend along longitudinal edges of the cut papers.

(102) The embodiment shown in FIG. 7 is similar to the aforementioned case (iii) of the method according to the invention.

(103) In the case of FIG. 8, the plastic film 200 initially has an extended shape and therefore has the shape of a strip of which the length L can be similar to that of the paper 202 intended to receive the multi-layer structure, and of which the width is clearly less than that of this paper and is for example of a few millimeters or centimeters.

(104) The multi-layer structure is prepared (step a)) using this plastic film 200 and is then glued onto the paper 202 (step b)).

(105) In the first case of FIG. 8 (in the upper right corner), the paper 202 receives a strip which extends along one of its longitudinal edges. This particular case is similar to the aforementioned case (iii) of the method according to the invention.

(106) In the second case of FIG. 8 (in the lower right corner), the paper 202 receives a series of several portions of strip, which extends along one of the longitudinal edges of the paper. This paper 202 can be obtained in two ways. It can be obtained by arranging the adhesive on the multi-layer structure or the paper only in the zones where portions of strips must be glued (case (ii) and (iii) of the method according to the invention). As an alternative or additional characteristic, it would be possible to apply an adhesive pressure onto the strip only in the zones where corresponding portions of strips must be glued onto the paper. This can be carried out for example by means of an embossing press, a stamp press or a hot foil stamp press, which makes it possible to apply local pressures onto the paper when it is produced (in particular for a marking of the paper). In the second case of FIG. 8, the paper receives three separate portions of strips separated from one another, which each substantially have a square or rectangle shape.

(107) The plastic film or the portions of plastic film can then be removed according to the step c) in such a way as to reveal the independent base layers that define zones of greater smoothness.

(108) In the case of FIG. 9, the plastic film 300 has a square or rectangular shape of which the dimensions (width I and length L) are less than those of the paper 302 intended to receive the multi-layer structure.

(109) The multi-layer structure is prepared (step a)) using this plastic film 300 and is then glued onto the paper 302 (step b)), in its centre in the example of FIG. 9. The plastic film can then be removed in such a way as to reveal the base layer (step c)).

(110) The example embodiment shown in FIG. 9 is similar to the aforementioned cases (ii) and (iii) of the method according to the invention.

(111) In the case of FIG. 10, the plastic film 400 has the shape of a strip similar to that of FIG. 8. The multi-layer structure 406 is prepared (step a)) using this strip by superimposing an anti-adhesive coating and a base layer onto portions 408 of this strip only. The multi-layer structure 406 is then glued onto a paper 402 (step b)) and the plastic film 400 is removed in order to reveal separate base layers on the paper 402, such as is shown in FIG. 10.

(112) The example embodiment shown in FIG. 10 is similar to the aforementioned cases (i) and (iii) of the method according to the invention.

(113) In the case of FIG. 11, the plastic film 500 has a shape similar to that of FIG. 7. The multi-layer structure 506 is prepared (step a)) using this film by superimposing an anti-adhesive coating and a base layer onto a strip 408 only of this film. The multi-layer structure 506 is then glued onto a paper 502 (step b)) and the plastic film 500 is removed in order to reveal a base layer of elongated shape on the paper 502, as is the case in the first embodiment shown in the upper right corner of the FIG. 11. This example of an embodiment is similar to the aforementioned case (i) of the method according to the invention.

(114) In the alternative shown in the lower right corner of FIG. 11, the paper 502 receives a series of several portions of strips. This paper 502 can be obtained as explained hereinabove in relation with FIG. 8. The plastic film can then be removed according to the step c). This example of an embodiment can be similar to the aforementioned cases (i) and (ii) of the method according to the invention.

(115) As is diagrammatically shown in FIG. 12, the base layer and/or the electroconductive layer of the sheet prepared by the method according to the invention can have any shape such as a geometrical shape (circle, triangle, etc.) or the shape of a letter (F in the example shown). This shape can be imposed by the shape of the plastic film used (during the preparation of the multi-layer structure), of the multi-layer structure used (possibly after cutting), of the zone of the multi-layer structure or of the substrate whereon the adhesive is deposited, and/or of the support zones of the press used to cross-laminate the multi-layer structure and the substrate.

(116) FIGS. 13 and 14 show another alternative of the method according to the invention wherein the free side of the base layer 618 of the multi-layer structure 612 is printed with electroconductive inks 650 or is covered with an electroconductive coating. This printed or covered side is then glued and applied onto a side of a substrate of a sheet 610. The multi-layer structure 612 can be cut before the step of laminating.

(117) FIGS. 15 and 16 show another alternative of the method according to the invention wherein the anti-adhesive coating 616 deposited onto the plastic film 614 of the multi-layer structure is printed with electroconductive inks 650 or is covered with an electroconductive coating, before the base layer 618 is deposited. The base layer and this electroconductive layer (inks or coating) are then transferred onto the substrate of the sheet 610.

(118) FIG. 17 shows a sheet prepared by the method according to the invention in the aforementioned case (iv), i.e. in the case where the base layer is transferred onto the substrate of a first sheet, more preferably smooth, which is intended to be cut (into strips 700 in the example shown) and to be glued onto the substrate of another sheet 710.

(119) FIG. 18 shows another sheet prepared by the method according to the invention, in the form of a strip. The substrate of this sheet is formed by a paper covered with an anti-adhesive coating or by a plastic film. The plastic film or the anti-adhesive coating is here covered with four separate zones of a higher smoothness, i.e. with four zones comprising a smooth base layer which is electroconductive or which is associated or intended to be associated with an electroconductive layer. This sheet is particularly suitable for producing electronic labels.

(120) FIG. 19 shows another sheet prepared by the method according to the invention. This sheet 810 comprises a zone 812 of greater smoothness prepared in the manner described hereinabove. A portion of this zone 812 is covered by an electroconductive layer 814 whereon are deposited micro-diodes such as those described in document WO2012/031096, and other separate portions of the zone 812 are covered by coloured layers 816 of polymer (respectively yellow (Y), blue (B) and red (R)) each forming a wave guide in contact or connected to the layer 814 by at least one strip of the same polymer material as the layer under consideration. When the electroconductive layer 814 is powered by an electric current, the micro-diodes emit a light beam which is transmitted to the layers 816 of polymer that themselves diffuse coloured lights.

EXAMPLE 12

Evaluation of the Thermal Diffusivity of Sheets

(121) Sheets were tested in order to determine their thermal diffusivity on the surface (in XY) and in depth or in the mass (in Z).

(122) The first tests were carried out on the following sheets: 3382: Powercoat sheet (thickness 230 m) marketed by the Arjowiggins company and obtained by the steps of the method according to the invention (without electroconductive layer), 3384: Powercoat sheet with an aluminium film of 12 m inserted between the paper and the base layer (thickness 240 m) GD 28.09.12/1: Control sample with a Cnibra/pacifico mixture refined to 52 SR (thickness 193 m) GD 28.09.12/2: Sample with a Cnibra/pacifico mixture refined to 52SR and doped with 30% BN (thickness 193 m) GD 31.08.12/1: Control sample with a Cnibra/pacifico mixture refined to 40SR (thickness 229 m) GD 31.08.12/4: Sample with a Cnibra/pacifico mixture refined to 40SR doped with 20% Carbon fibres (thickness 355 m) GD 31.08.12/5: Sample with a Cnibra/pacifico mixture refined to 40SR doped with 60% carbon black (thickness 294 m)

(123) In the first test, a sufficient number of sheets are stacked in order to have a total thickness of about 1 mm. The sheets are then classed according to the diffusivity results.

(124) TABLE-US-00008 Number of Diffusivity Samples sheets Thickness [mm.sup.2/s] Classification GD310812-1 5 1.145 0.051 4 GD310812-4 3 1.065 0.082 1 GD310812-5 4 1.176 0.057 3 3382 5 1.150 0.040 7 3384 5 1.200 0.042 5 GD280912-1 7 1.001 0.042 5 GD280912-2 6 1.158 0.059 2

(125) In the second test, the stacks contain each time seven sheets (therefore the same number of air layers). The thicknesses of the packages of paper are therefore different.

(126) TABLE-US-00009 Number of Diffusivity Samples sheets Thickness [mm.sup.2/s] Classification GD310812-1 7 1.603 0.054 5 GD310812-4 7 2.485 0.116 1 GD310812-5 7 2.058 0.087 2 3382 7 1.610 0.046 6 3384 7 1.680 0.057 4 GD280912-1 7 1.001 0.042 7 GD280912-2 7 1.351 0.064 3

(127) In the third and last test, the stacks contain at each time seven sheets (therefore the same number of air layers), the thicknesses of the packages are therefore different. The packages of paper were compressed between the fingers before they were positioned in the device.

(128) TABLE-US-00010 Number of Diffusivity Samples sheets Thickness [mm.sup.2/s] Classification GD310812-1 7 1.603 0.057 4 GD310812-4 7 2.485 0.134 1 GD310812-5 7 2.058 0.085 2 3382 7 1.610 0.051 6 3384 7 1.680 0.056 5 GD280912-1 7 1.001 0.045 7 GD280912-2 7 1.351 0.085 2

(129) The sheets GD310812-4, GD310812-5 and GD280912-2 have the best results and the sheets 3382 and GD280912-1 do not have good results.

EXAMPLE 13

Characterisation of the Thermal Properties (Thermal Diffusivity) of Sheets of Paper by Infrared Thermography

(130) The purpose of the tests is to evaluate the differences in thermal properties of the sheets, and in particular their thermal diffusivity on the surface (in XY) and in depth or in the mass (in Z). Infrared thermography is the study of the thermal behaviour of a component by measuring surface the temperature and its temporal and spatial variations.

(131) The first tests (Test 1) consist in a temporal analysis. The samples are placed on a graphite plate and fixed using clamps. A camera is arranged 400 mm from the graphite plate. The lamps/graphite plate distance is 80 mm. Two IR 650 W lamps are spaced 45 mm. The whole is heated periodically (T=4 s, 6 s or 20 s) with an amplitude on the power of the lamps from 0 to 50% or 0 to 100%.

(132) The strategy adopted was to classify the various paper according to their performance (low response time=best performance). As the papers have different thicknesses, another classification was carried out by taking into consideration the thickness of the papers: the thickness at the square was divided by the response time, which provides information over a magnitude proportional to the thermal diffusivity (response time=characteristic length at the square/thermal diffusivity).

(133) The second tests (Test 2) consistent in an analysis in a stabilised regime. The conditions are the same as those during the temporal analysis. The setting on the graphite plate is set to 50 C.

(134) The last tests (Test 3) consist in an analysis in XY. A perforated insulating plate is placed (via a graphite rod) on an infrared lamp (650 W). The hole is located above one of the two filaments of the lamp. The sample paper with sufficient dimensions (75*75 mm) is placed on two graphite rods. The lamp is set to 10% of its maximum power. The treatment consists of extracting the longitudinal profiles when the temperature peak of 60 C. is reached. Each sample received the same treatment, as the profile is always in the same location.

(135) TABLE-US-00011 Test 1, dephasing Test 1, dephasing Thickness taken Test 2 Thickness not taken into account Stabilised into account Classification temperature Test 3 X Y Samples Classification index index Classification Classification 3382 3.75 4 6 6 3384 3 4 2 1 GD280912-1 5.5 6 3 7 GD280912-2 6.75 7 7 4 GD310812-1 3.25 4 4 5 GD310812-4 4 1.5 5 2 GD310812-5 1.75 1.5 1 3

(136) TABLE-US-00012 General Samples Classification GD310812-5 1.8 3384 2.5 GD310812-4 3.1 GD310812-1 4.1 3382 5 GD280912-1 5.4 GD280912-2 6.2

(137) The paper GD280912-1 seems to be one of the least best in the tests and the paper GD310812-4 seems to be one of the best in these tests (1st/2nd).

(138) A second series of sheets was prepared and compared to a tracing paper and to a plastic PET film (cfu=carbon fibres).

(139) TABLE-US-00013 Paper weight Thickness (g/m.sup.2) (m) Bulk VT_24.10.12.4 30% CaCO3 + 210 173 0.8 calendaring VT_24.10.12.6 30% CaCO3 + 220 203 0.92 PVA impregnation + calendaring VT_24.10.12.7 30% CaCO3 215 256 1.2 VT_24.10.12.8 20% cf 145 280 1.9 VT_24.10.12.9 20% cf + calendaring 142 180 1.27 VT_24.10.12.10 20% cf + calendaring 142 150 1.05 VT_24.10.12.11 20% cf + PVA 183 261 1.43 impregnation + calendaring VT_25.10.12.1 reference (fibres only) + 157 133 0.85 calendaring VT_25.10.12.2 reference (fibres only) 154 200 1.3 Tracing / 230 170 0.74 PT125 (PET) / 125

(140) The paper PT125 seems to be one of the least best in the tests and the paper VT_24.10.12.9 seems to be one of the best.

(141) The various tests have shown that the aluminium film made it possible to substantially improve the thermal diffusivity on the surface (x/y) of the sheet. With regards to the thermal diffusivity in depth (z), two parameters confirmed their very positive influence: the doping with carbon (fibres or fillers) and the calendaring of the papers in order to decrease the quantity of air.

(142) The best result is therefore to dope a paper (for example with a thickness of 200 m) with carbon, to calendar it then to insert an aluminium film (for example 12 m thick) between the base layer (for example 12 m thick) of the sheet and the paper.