HK1173478B - Ultra smooth and recyclable printing sheet and its manufacturing process - Google Patents

Description

The present invention relates to a smooth or ultra-smooth recyclable printed sheet and its manufacturing process, which can be used in such distinct fields as packaging, electronics, optics, or graphic arts, for example as a printing medium, particularly photographic image.

In the known technique, an ultra-smooth sheet can be made by rolling a plastic film onto one side of a paper, this plastic film defining an ultra-smooth face on the paper. The base paper is made of a fibrous material whose faces have a relatively high roughness, of the order of about 20μm, i.e. each of its faces is formed of bumps and hollows whose height separating them is of the order of 20μm. Rolling a plastic film on one side of such paper allows to give this face a very low roughness, of the order of 1μm in the case of a PET (polyethylene terephthalate) film.

Paper is a relatively expensive and widely produced material, so it is important that it is recyclable. However, a paper-based sheet, ultra-smooth because it has a plastic film, is not recyclable or is difficult to recycle, which is not environmentally friendly or economical. When paper-based sheets are recycled, these sheets are ground and mixed with water in a pulper to form a paste. If these sheets include plastic films, these films are shredded in the pulper and their plastic material pollutes the paste.

It is therefore not possible, with current technology, to produce an ultra-smooth sheet that is recyclable, preferably completely recyclable.

In addition, such ultra-smooth sheet is not printable and a printable resin must be deposited on the plastic film of the sheet to make it printable. e technique is used in particular to manufacture resin-coated photographic papers, which contain a PE film and have a smooth Bekk of 6000s.

A smooth sheet can also be made by laying a coating composition on one side of a paper, this composition defining after drying a smooth face on the paper. This technique allows to make a smooth sheet without plastic film. The composition is laid on the paper by a curtain coating technique, by dragging or scraping blade, by air blade, by heliogravure or by rolls (size, film press, etc.) The face of the base paper, on which the coating composition is laid, has an alternation of holes and bumps, the holes being filled by the coating composition and the bumps being flattened during the coating, which reduces the roughness of the paper. However, this technique does not allow to obtain a coating, for example, if the sheet is also covered with a film, due to the coating of the plastic sheet.

The current method used to produce a smooth, shiny sheet consists of depositing a coating composition on a base paper by means of a mechanical roller with a very smooth cylindrical surface and a layer of chromium.

It is also difficult to obtain a smooth sheet by laying a composition on relatively rough paper, because when the above-mentioned holes on the paper face are too large or too numerous, the coating composition does not fully fill these holes or too large a quantity of this composition is required to do so.

For example, a paper with a relatively large hand, for example over 1.10 cm3/g, which has relatively rough faces and low printability, is not able to produce a smooth sheet even if it is applied in large quantities, and also reduces the hand considerably.

It is therefore also not possible, with the known technique, to produce under satisfactory conditions a smooth sheet from rough paper and/or with a relatively large hand.

The purpose of the invention is in particular to provide a simple, efficient and economical solution to the problems of earlier techniques.

It concerns a process for the manufacture of a smooth sheet, also called ultra-smooth within the meaning of the invention, the smoothness of which is independent of the roughness of the paper or more generally of the base material used, and the sheet contains no plastic film and is therefore at least partly recyclable or even biodegradable.

It proposes a process for the manufacture of a printed sheet having at least one smooth and preferably ultra-smooth face, the sheet containing a substrate, in particular paper, at least one side of which is at least partly covered by one or more layers, the process consisting of the following steps: al prepare or provide a multilayer structure comprising at least, or consisting of, a smooth plastic film, an anti-adhesive layer and a printable layer by printing Offset, inkjet, laser, helium, flexo, dry toner, liquid toner, electrophotography and/or lithography, the anti-adhesive layer being interspersed between the plastic film and the printable layer,b/ glue a side of the substrate and/or the face of the multilayer structure, located on the side opposite the plastic film, and apply the above-mentioned side of the substrate against the above-mentioned side of the multilayer structure, thus smoothing the multilayer structure and the substrate, etc. / remove the plastic film from the layer, thus defining the ultra-printable side of the plastic or printed sheet.

In a particular embodiment of the invention, the multilayer structure is prepared prior to the implementation of the printed sheet manufacturing process, in which case the multilayer structure is provided for the implementation of the printed sheet manufacturing process.

The smoothness of the sheet is induced by the smoothness of the plastic film in the multilayer structure, and is therefore not dependent on the substrate used. The invention therefore allows the surface state of a plastic film to be transferred onto a plastic substrate. Otherwise, the invention allows the manufacture of an ultra-smooth or smooth sheet from a substrate, such as paper or plastic, without a significant advantage in the inclusion of any paper or film, such as a roughness of the paper or plastic, equal to or greater than 1.10/cm3.

The paper prepared by the process of the invention is therefore both printable and recyclable.

For the purposes of this application, 'printable sheet' and 'substrate for the preparation of the printable sheet' means a thin (not more than 500 μm thick) element, preferably flexible and/or flexible.

A printable sheet or layer is a sheet or layer that can be printed by any printing technique, and in particular by offset printing, inkjet, laser, helium, flexo, dry toner, liquid toner, electrophotography, lithography, etc. A printable layer typically comprises a mixture of pigments and at least one binder, or is made of a printable varnish made of polymer (s) such as acrylic, vinyl, polyethylene, styrene, amide, polyvinyl alcohol, ethylene, or a mixture of these polymers. The ink is intended to be applied to the smooth or smooth free surface of the sheet or layer.

According to a feature of the invention, printing the printable layer does not lead to any structural change of the layer, and in particular no change of state or phase of the layer (such as a change from a solid to a liquid state and then back to the solid state).

A multilayer structure of the invention prepared or made by the process of the invention includes, or consists of, a plastic bottom film, an anti-adhesive intermediate layer and a printable top layer.

The plastic film is used as a fabrication medium for the printed layer. This film does not remain in the final product, namely the sheet, which is therefore recyclable. The top face of the film (located on the side of the printed layer) is advantageously as smooth as possible, because the surface quality of the smooth face of the sheet, defined by the printed layer, is a function of the surface quality of this top face of the plastic film.

The plastic film is chosen from a film of polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polymer based on polylactic acid (PLA), any polymer based on cellulose, etc. The film has for example a thickness of about 12μm.

The advantage is that the plastic film is free of and/or not coated with PVDF (polyvinylidene fluoride), PP (polypropylene), Teflon, silica, boron nitride, chromium stereochlorides or any other product with anti-stick/anti-adhesive properties.

The film face on the side of the printable layer is preferably smooth and may have a smoothness of Bekk greater than 10 000s Bekk.

The thickness, hardness and glass transition temperature of the plastic film have little or no influence on the characteristics of the printed layer. Only the smoothness, or a contrario, the roughness of the plastic film has an influence on the smoothness or roughness of the printed layer. The smoother the plastic film, the smoother the printed layer. However, the professional is able to determine which characteristics of the plastic film are likely to influence the surface condition of the printed layer, and to optimize these characteristics according to the final smoothness desired to obtain this printed layer.

The anti-adhesive layer of the multilayer structure is applied to the plastic film by some technique, for example by heligraphy. The purpose of this anti-adhesive layer is to limit the adhesion of the printable layer to the plastic film and to facilitate the separation and removal of the plastic film from the printable layer at step c/ of the above-defined process. The anti-adhesive layer does not alter the smoothness and surface quality of the plastic film surface on which this layer is applied.

The non-adhesive layer may adhere more to the plastic film than to the printable layer, so that most or all of the non-adhesive layer remains on the plastic film when it is removed from the printable layer.

Alternatively, the non-adhesive layer can adhere more to the printable layer than to the plastic film, and is then intended to remain at least partially on the printable layer when the plastic film is removed.

In yet another variant, the non-adhesive layer is intended to be significantly split into two parts when the plastic film is removed, with one part remaining on the plastic film and the other part remaining on the printable layer.

The multilayer structure may comprise two anti-adhesive layers superimposed between the plastic film and the printable layer, these two layers being intended to separate from each other when the plastic film is removed (one of the anti-adhesive layers remaining on the plastic film and the other anti-adhesive layer remaining on the printable layer).

Leaving part or all of an anti-adhesive layer on the printable layer is particularly advantageous when the sheet is intended to be used as a support in a casting application. The casting application involves extruding and casting at least one polymer (such as polyurethane (PU), polyvinyl chloride (PVC), etc.) onto a support coated with an anti-adhesive layer. This polymer may have a textured surface to give the sheet a particular appearance (e.g. leather-like). Leaving an anti-adhesive layer on the sheet according to the invention avoids having to re-deposit such a layer on that sheet for a casting application, and is therefore particularly advantageous in terms of preparation time and cost for the application of the casting support.

The non-adhesive layer has a thickness of 5μm or less and preferably 1μm. The non-adhesive layer may be composed of silicone (s), siloxane (s), polysiloxane (s) or its Werner complex derivatives, such as chromium chloride stearates, or waxes of polyethylene, propylene, polyurethane, polyamide, polytetrafluoroethylene, etc.

The advantage is that the non-adhesive layer does not contain PVDF.

The printed layer of the multilayer structure can be chosen from printed varnish, paper coating, etc.

For the purposes of this application, a printed varnish is a substance made from polymer acrylic, polyurethane, polymethyl methacrylate, styrene butadiene, vinyl acetate, polyamide, nitrocellulose or any other cellulose, polyvinyl alcohol, starch, etc. This substance is generally deposited in liquid form and solidified by drying/heating or UV or electronic irradiation.

Paper coating or coating composition is a composition that includes a binder and pigments. The binder may be acrylic, polyurethane, polymethyl methacrylate, styrene butadiene, vinyl acetate, polyamide, nitrocellulose or any other cellulose, polyvinyl alcohol, starch, or a mixture thereof. The pigments may be chosen from calcium carbonates, kaolins, titanium dioxide, silicon talc, papaya, mica, nacre particles, plastic pigments (polystyrene (PS), polyurethane (PU), etc.) to create their mixture. The ratio of binding pigments to coatings is generally between 5% and 8%, as opposed to pigments, which are used in a majority of the coatings, in order to create a porous porous layer, as opposed to pigments, which are used in a porous layer, as they are used in a porous layer, but are not used in a porous layer.

The plastic material used in the printable layer (as binder and/or pigment) is easily fragmentable and does not pollute the pulp when recycled. On the contrary, the plastic films retain cohesion and clog filters when the pulp is resuspended. Water-soluble binders (such as starch, polyvinyl alcohol (PVA), etc.) are particularly advantageous in this regard as they disperse into water during recycling.

The paper coating may also include a dispersant and/or rheological modifier and/or a dye and/or surface or spreading agent and/or a conductive additive, which may be used to reduce the surface resistivity of the sheet.

Preferably, the printable coating is free of anti-adhesive agent and/or product that may reduce the surface energy of the coating, such as silicone or similar material, PVDF, PP, Teflon, silica, boron nitride, etc. This type of agent or product may be required for thermal transfer printing of a coating, in particular to prevent the paper from adhering to the printer tape.

The printable layer may consist of several layers superimposed on each other, each layer being printable and selected from the above types (printable varnish, paper coating, etc.).

The printed layer may have a thickness of less than or equal to 30μm, preferably less than or equal to 15μm, and more preferably less than or equal to 10μm. Its weight is advantageously less than or equal to 30g/m2, preferably less than or equal to 15g/m2, and more preferably less than or equal to 10g/m2.

The printable layer can be deposited on the non-adhesive layer by any technique, for example by heligraphy.

The printable layer can be deposited on the non-stick layer in a liquid or semi-liquid state and then solidified by drying, heating, or UV or electronic radiation. After solidification and/or drying, the printable layer, which is in contact with the smooth surface of the plastic film via the non-stick layer, has a smooth surface, located on the side of the plastic film.

The printable layer is therefore dried and/or solidified before transfer to the substrate, in particular to avoid altering the surface state of this layer conferred by the plastic film. In other words, the multilayer structure is prepared prior to the transfer of the printable layer to the substrate, and the printable layer is in solid and/or dry state during its transfer to the substrate, i.e. at steps b/ and c/ of the process according to the invention. The surface state of the printable layer is therefore created during the preparation of the multilayer structure.

In the process according to the invention, the manufacture of the printable layer is therefore carried out independently of that of the base substrate. This makes it possible, in particular, to implement the process with standard industrial tools, which allows for optimal production speeds. According to another feature, the process includes, before step a, a preliminary step consisting of making, for example by engraving, hollow and/or embossed patterns on the surface of the plastic film intended to receive the non-adhesive layer and the printable layer, the printable layer being intended to use the shape of these patterns in such a way as to understand an impression of the aforementioned surface of the plastic film.

The multilayer structure may comprise at least one additional layer deposited on the printable layer on the side opposite the plastic film, the free side of this additional layer or the furthest additional layer from the plastic film being intended, in step b/, to be glued and applied to the above-mentioned side of the substrate.

The additional layer (s) may be functional or non-functional, for example insulating (dielectric) or barrier (to gases, e.g. oxygen, liquids, e.g. water, fats, etc.).

In the case of a multilayer structure with only one additional layer, this layer is deposited on the top surface of the printable layer, i.e. on the surface of the printable layer, which is on the opposite side of the plastic film of the multilayer structure. This additional layer may be of any nature, and is therefore not necessarily printable. In the case of a multilayer structure with two or more additional layers, these additional layers are superimposed on each other and deposited on the aforementioned top surface of the printable layer. The technique or techniques used to deposit the additional layer (s) on the layer may be of the above types or any other type.

The multilayer structure may therefore include in addition to the three elements above (a plastic film, an anti-adhesive layer, and a printable layer), one or more additional layers, which are printable or non-printable, on the printable layer (on the side opposite the plastic film).

Step b/ of the invention process consists in gluing the surface of the substrate to receive the printable layer, or the surface of the multilayer structure, on the side opposite the plastic film and applying these surfaces to each other in order to fix them.

The substrate can be chosen from paper, sheet paper, cardboard, and coated or pre-coated paper. The paper can have a relatively large hand size of 1.10 cm3/g or more, preferably 1.2 cm3/g or more, more preferably 1.3 cm3/g or more, more particularly 1.4 cm3/g or more, and even more particularly 1.5 cm3/g or more.

The process of the invention allows for the production of a sheet with both a large hand and a smooth surface, which was not possible with the earlier technique. It was not possible in the earlier technique to produce a sheet with a large hand and a high surface quality. A substrate with a large hand can be formed from an inexpensive material. In the case of paper, the pulp used may include cellulose fibers, a binder, and a low proportion of fillers and/or adjuvants, such as starch.

In one particular example of the invention, the process according to the invention results in a small reduction of the paper substrate hand by about 2 to 5%.

A sheet of paper, which is smooth or ultra-smooth and has a large handle, made with the invention process, has good printability and low weight, which makes it possible to make lightweight packaging with a relatively high stiffness.

In step b/ of the process, the surface to be coated with the substrate or the free surface of the printable layer or an additional layer of the multilayer structure is glued with an appropriate glue.

Alternatively, the two above-mentioned sides of the substrate and the multilayer structure are glued together simultaneously or one after the other.

Glue is applied to the surface of the adhesive by any technique, such as heliogravure. The glue can be of thermal, non-thermal, UV-glue or chemical reaction. The glue can be applied to the surface of the adhesive in liquid or non-liquid form (in the case of a thermo-adhesive film). The glue is chosen from the following polymers: acrylic, polyurethane, polymethyl methacrylate, styrene butadiene, vinyl acetate, polyamide, nitrocellulose or other cellulose, polyvinyl alcohol or starch. Each layer of the glue can be 10 μm or less thick and any other cellulose, vinyl alcohol or starch.

In a particular case of the invention, the glue is deposited on the above-mentioned face of the multilayer structure during the preparation of this structure, and this glue becomes an integral part of the multilayer structure. The glue can be formed by a thermoactive adhesive layer, which is activated by heating when the multilayer structure is applied to the substrate (receiver).

The nature of the glue and the bonding process (on film and/or on paper) can have a significant influence on the final surface condition of the paper.

In terms of the uniformity of the glue deposition, the glue deposition is preferably homogeneous to avoid excess and/or lack of glue per place, which would result in a final sheet with surface roughness.

The method of adhesive coating may also be important. Induction methods that generate the least possible heterogeneity of deposition, such as reverse roll or kiss coating, are preferred. The coating is preferred to fill as much as possible the pores or surface irregularities of the paper. For example, when a paper has an average surface roughness (e.g. Sa) of about 20μm, a glue coating at least 10μm thick is preferred to fill the pores.

The adhesive layer deposited on the paper and/or the printable layer is preferably at least half the average surface roughness (e.g. Ra or Sa) of the paper. In one embodiment of the invention, the adhesive is deposited on at least one side of the substrate at step b/, and the thickness of the layer of adhesive deposited is at least half the average surface roughness of the substrate, and is preferably equal to this average roughness.

The glue may be aqueous, solvent, non-solvent, bi- or mono-component.

The glue allows the printable layer (or an additional layer) to be fixed to the substrate and, if necessary, to compensate for surface irregularities of the substrate.

The printed layer is then sandwiched between the substrate and the glue (and, if necessary, one or more additional layers) on the one hand and the plastic film and the non-adhesive layer on the other.

In the case where the glue used to bond the substrate to the multilayer structure is thermo-adhesive, the application of the substrate to the multilayer structure is carried out hot, at a given temperature, which is for example between 50 and 200 °C approx. Alternatively, the application and bonding of the substrate to the multilayer structure can be carried out at room temperature.

A slight pressure may be required to ensure proper adhesion of the printable layer to the substrate via the glue.

However, the temperature and/or pressure used during application and bonding must not alter the characteristics of the printable layer, and in particular the surface condition of its face on the plastic film side. e.g. the printable layer must not be softened by applying a high temperature, as this could lead to a change and/or a decrease in the surface quality of its face on the plastic film side.

The next step in the process is to remove the plastic film from the printable layer and substrate so that the printable layer (and where appropriate the additional layer (s) of the multilayer structure mentioned above) remains on the substrate.

As explained above, at least part and preferably the majority or even the whole of the non-adhesive layer can remain on the plastic film and is then removed from the printable layer when the plastic film is removed.

The transfer of the printable layer of the multilayer structure onto the substrate at step (b) and step (c) of the process can be carried out as follows, when the substrate and the multilayer structure are in continuous bands.

The lamination or back-gluing of the multilayer structure and substrate can be achieved by passing these two elements between two parallel and adjacent mechanical rollers, rotating in opposite directions. The thickness of the resulting product is in particular a function of the distance between the rollers.

Alternatively, either the multilayer structure or the substrate can be glued, the glue allowed to dry, and then the two elements can be brought into contact with each other by applying a specified temperature and pressure.

The process may also consist of pre-coating the above-mentioned surface of the substrate with at least one smoothing layer containing one or more thermoplastic polymers (such as at least one polystyrene, polyurethane, acrylic, etc.) or a mixture of pigments (such as kaolins, calcium carbonates, talc, titanium dioxide, etc., and mixtures thereof) and at least one binder (such as acrylic, polyurethane, polymethyl methacrylate, styrene butadiene, vinyl acetate, polyamide, nitrocellulose or any other cellulose, amide or PVA).

This pre-coated side of the substrate can also be calendered before step b/ to increase its smoothness.

The process of the invention may include an additional step of printing the sheet with an ink having electrical and/or optical properties.

The present invention also relates to a process for preparing a multilayer structure comprising at least, or consisting of, a plastic film, an anti-adhesive layer, and a printable layer, the anti-adhesive layer being interspersed between the plastic film and the printable layer.

The present invention also relates to a process for printing sheet prepared by the process described above, which involves a step of printing sheet without changing the state of its printable layer, i.e. without softening or melting of this layer during printing.

The present invention also relates to a process for the manufacture of a sheet for casting applications having at least one smooth face, the sheet containing a substrate, in particular paper, at least one side of which is at least partly covered by one or more layers of overlapping, the process consisting of the steps: a) prepare or provide a multilayer structure comprising at least, or consisting of, a plastic film, an anti-adhesive layer and a layer for casting application, the anti-adhesive layer being interspersed between the plastic film and the layer for casting application,b) glue a side of the substrate and/or the face of the multilayer structure on the side opposite the plastic film and apply the above-mentioned side of the substrate to the above-mentioned side of the multilayer structure, so as to back up the multilayer structure and the substrate, etc.

The coating for application casting is for example a PVA coating.

The present invention also relates to a printed sheet having at least one smooth and preferably ultra-smooth face, such sheet comprising a substrate, in particular paper, at least one side of which is at least partially covered by one or more layers, including a layer of printing by offset, inkjet, laser, helium, flexo, dry toner, liquid toner, electrophotography and/or lithography and defining the said smooth or ultra-smooth face, characterized by the smooth or ultra-smooth face having a Bekk smoothness greater than 2000s, and preferably greater than 5000s.

The smooth or ultra-smooth side of the sheet may have a gloss of more than 70% and preferably more than 80%, for example measured at 75° using the TAPPI T480 om-92 method.

The printed sheet layer may have a thickness of 30μm or less, preferably 15μm or less, and preferably 10μm or less. The printed sheet layer may have a weight of 30g/m2, preferably 15g/m2, and preferably 10g/m2 The printed sheet may, for example, have a thickness and weight that are less than or equal to the following combined values: 10μm and 10g/m2, 3μm and 10g/m2, 2μm and 10g/m2, 5μm and 5g/m2, 3μm and 3g/m2, 2μm and 5μm2, 2μm and 5μm2, 2μm2 and 2μm2, 2μm2 and 2μm2, 2μm2 and 2μm2, 2μm2 and 2μm2, 2μm2 and 2μm2, 2μm2 and 2μm2 and 2μm2.

The present invention also relates to the use of a printable sheet as described above for the manufacture of an electronic and/or optical component, this sheet being printed by means of an ink having electrical and/or optical properties.

The sheet according to the invention may be compatible with electronic organic inks for electronic applications, such as the manufacture of RFID (Radio Frequency Identification) chips, display or detection systems, etc., directly on the sheet.

In the earlier technique, an RFID chip could be made on a sheet of plastic film made of polyethylene terephthalate (PET). However, this plastic film has relatively low mechanical and temperature strength, which limits the possible applications of the chip and prevents the film from being printed with inks at relatively high temperatures.

A sheet printed with an ink with electrical properties, which has the advantage of a flexible substrate and a printable layer with little or no electrical conductivity, can be used to make thin-film organic transistors using conductive or semiconducting organic inks.

The sheet according to the invention can also be used to make optical components, such as waveguides, holographic patterns, etc.

For example, the process defined above may include, before step a/, a preliminary step consisting of making, for example by engraving, hollow and/or relief patterns on the plastic film surface for the non-adhesive layer and the printable layer, the printable layer being intended to match the shape of these patterns so as to comprise an impression of the aforementioned plastic film surface.

In this case, the transfer of the surface state from the film to the printable layer includes both a transfer of the smooth and patterns of the plastic film. The patterns transferred to the printable layer themselves have smooth-looking surfaces and/or walls and are defined precisely.

Finally, the present invention relates to the use of a printable sheet as described above for the printing of a photographic image, for the manufacture of a packaging, and/or for a casting application.

The invention will be better understood and further details, features and advantages of the present invention will be more clearly seen by reading the following description made as a non-limiting example and by reference to the attached drawings in which: Figure 1 shows very schematically the steps of the process according to the invention of manufacturing a smooth or ultra-smooth printed sheet; Figure 2 shows very schematically a variant of the process according to the invention; Figures 3 and 4 show very schematically the means of carrying out the transfer step of the process according to the invention; and Figures 5 and 6 are images obtained by a scanning electron microscope (SEM) of one side of a base paper and one side of a smooth or ultra-smooth sheet obtained by the invention.

First, reference is made to Figure 1 which shows in a very schematic way the steps a, b and c of the process according to the invention for the manufacture of a smooth or ultra-smooth 10 and fully recyclable printed sheet.

Step a/ of the process consists of preparing a multilayer structure 12 with a plastic film bottom 14, an anti-adhesive intermediate layer 16 and a printable top layer 18.

The non-adhesive layer 16 and the printable layer 18 can be applied simultaneously to the plastic film 14, for example by curtain coating.

Alternatively, non-adhesive layer 16 is applied to plastic film 14 and then printable layer 18 is applied to the non-adhesive layer.

The surface quality of the upper face 20 of plastic film 14 is transmitted to the lower face 22 of the printable layer 18 (via the non-adhesive layer 16). The surface characteristics of the face 22 of the printable layer are therefore defined by those of the face 20 of the plastic film 14.

The first film tested has a roughness (e.g. Sa) of 1μm. This film was used to transfer a printable layer onto Bristol® paper from Arjowiggins. The measured roughness of this printable layer is 1.1μm. The second film has a roughness of 0.5μm. This film was used to transfer a printable layer onto another Bristol® paper. The measured roughness of this printable layer was 0.7μm. The roughness (or film solidity) was therefore transferred to 24 layers of the paper. After being transferred to the surface of a particular layer of paper, the film and 22 other characteristics are not changed.

The printed layer 18 may consist of a resin or a printed varnish or paper coating containing a binder and pigments. Alternatively, the printed layer may comprise two or more sub-layers which are chosen from a printed varnish and a paper coating. In the case where the printed layer has two sub-layers: a printed varnish and a paper coating, the printed varnish is located above or below the paper coating, so that the lower face 22 is pre-mentioned of the printed layer defined by the printed varnish or paper coating.

Step b/ of the process consists of laying a layer or film of glue 26 on the upper face 28 of the printable layer 18 or on the lower face 30 to be coated with substrate 24 or on both of these faces 28, 30 and then applying these faces 28, 30 against each other to laminate or back-glues the multilayer structure 12 and substrate 24 to form a laminated or back-glued product 32.

Step c/ of the process is to remove plastic film 14 and non-adhesive layer 16 from printable layer 18 so that only layer 18 remains (with glue 26) on substrate 24.

In the latter case, the adhesive 26 is preferably dry and/or solidified when the plastic film 14 is removed.

At the end of step c/, the face 22 of printable layer 18 is stripped bare, this face being smooth or ultra-smooth.

However, part of the non-adhesive layer 16 may remain on the face 22 of the printable layer 18 after removal of the plastic film.

Layer 18 is printable by any appropriate technique, the ink being intended to be applied to the smooth or ultra-smooth face 22 of sheet 10.

Alternatively, substrate 24 may be coated or pre-coated paper, i.e. paper on which a layer or pre-layer 33 is laid on one side, which contains one or more thermoplastic polymers or a mixture of pigments and binder. This layer or pre-layer 33 is intended to be laid on the above-mentioned side 30 of the substrate and is advantageously smoothed by calendering. It is then intended to be glued on side 28 of the printable layer 18.

Figure 2 is a variant of the process of the invention and differs from the process described above in reference to Figure 1 in that the 12' multilayer structure also includes at least one additional layer 34 deposited on the top 28 of the printable layer 18.

Several additional layers 34 overlapping may be deposited (simultaneously or successively) on the face 28 of the printable layer 18.

In step b/, the lower side 30 of substrate 24 or the free upper side 36 of additional layer 34 (the furthest from the plastic film, where the structure 12' contains several additional layers) is covered with glue 26.

In step c/, the multilayer structure 12' and substrate 24 are glued or laminated to form a 32' laminated or laminated product, then the plastic film 14 and the non-adhesive layer are removed to expose the smooth or ultra-smooth face 22 of the printable layer 18 of the 10' sheet.

As in Figure 1, the sheet in Figure 2 may contain a substrate 24 pre-coated on its side 30 to increase its smoothness.

Figures 3 and 4 show schematically the means of implementing the process step c/ transfer according to the invention.

A first roll 40 is intended to drive a continuous strip of the multilayer structure 12 (composed of plastic film 14, non-adhesive layer 16 and printable layer 18 - and possibly additional layers) 34).

The rolls 40, 42 rotate in opposite directions and are close apart, the multilayer structure 12 and the substrate 24 being forced to pass between these rolls and being applied to each other at a given pressure to ensure their rolling or backing.

Glue 26 may be applied to the multilayer structure 12 and/or substrate 24 as shown above, prior to or during this back-glue step, in which case glue 26 may be injected between the structure 12 and the substrate prior to their passage between the rollers, as schematically shown by the double arrow in Figure 3.

A third roll 44 draws sheet 10 formed by substrate 24 and printable layer 18 in one direction, while plastic film 14 and non-adhesive layer 16 are drawn in another direction to separate them from sheet 10.

Figures 5 and 6 are images obtained by scanning electron microscope (SEM) of one face of a base paper or substrate 24 and one smooth or ultra-smooth face of a sheet 10, produced by the process of the invention, respectively.

The base paper (Figure 5) is here made up of cellulosic fibres interwoven with each other and defining a rough face.

The sheet according to the invention (Figure 6) has a smooth or ultra-smooth face defined by its printable layer which has a roughness Sz of the order of 1.01μm, this being comparable to that of a paper coated with a plastic film, according to the previous technique, which has a roughness Sz of the order of 1.5μm.

This value of roughness of the sheet of 1,01 μm according to the invention is given for guidance purposes and is a particular example of the implementation of the invention.

Further examples illustrating the present invention will now be described in the following

Example 1: Preparation of a smooth or ultra-smooth sheet of paper for offset printing

A smooth or ultra-smooth sheet according to the invention has been prepared for offset printing from a printable A-layer having the following composition: - What?

Composition de la couche A
Pigments	Carbonate de calcium	1248g
	Liant	Dispersion aqueuse de copolymère n-butyl acrylate-acrylonitrile-styrène	300g
Dispersant		Acide sulfoccinique - isooctylester, sel de sodium	3g
	Modificateur rhéologique	Dispersion aqueuse de copolymère acrylique	0,6g
Agent d'étalement		Tensio-actif non-ionique	0,2g

The final concentration by weight of printable layer A is 50% and the viscosity is 100 cps, measured by a Brookfield® viscosimeter.

The A-layer is applied to a PET plastic film, which is coated with an anti-adhesive layer of chromium chloride stereo. The deposition of the A-layer on the film is about 10 g/m2. The A-layer is then dried in a 70°C oven. A multilayer structure is then obtained consisting of the PET plastic film, an anti-adhesive layer of chromium chloride stereo and the printable A-layer.

The free side of layer A, i.e. the side opposite the plastic film, is glued with Super-Lok® 364 glue from National Starch. The glue is deposited at 3 g/m2 on layer A. The glued side of layer A is applied to a substrate formed by Bristol® 335 g/m2 paper manufactured by Arjowiggins and then the whole is dried in an oven at 70 °C. Step b/ of the process is then completed.

The plastic film and the non-adhesive layer are then removed (in step c/) leaving only the printable layer A and the glue on the paper substrate.

The prepared sheet is offset printable. It is not offset printable. This was confirmed by a sheet printing test obtained in example 1 with a Canon Selphy CP800 heat transfer printer. The transfers of yellow, cyan and magenta were poor, and the black did not transfer at all. The final image was not acceptable. Example 2 : Preparation of a smooth or ultra-smooth sheet offset printable, from a puffy or relatively large hand paper

The printable layer A in example 2 is prepared and applied in the same manner and under the same conditions as discussed in example 1 on Elementa bulk foam paper from Arjowiggins.

Example 3: Preparation of a smooth or ultra-smooth sheet of offset printing paper from pre-coated paper

The printable layer A in Example 3 is prepared and applied in the same manner and under the same conditions as discussed in Example 1 on Maine Gloss® pre-coated paper from Arjowiggins.

Example 4: Preparation of smooth or ultra-smooth coloured sheet for offset printing

A smooth or ultra-smooth coloured sheet according to the invention was prepared for offset printing from a printable B-layer having the following composition: - What?

Composition de la couche imprimable B
Pigments	Carbonate de calcium	1248g
	Liant	Dispersion aqueuse de copolymère n-butyl acrylate-acrylonitrile-styrène	300g
Dispersant		Acide sulfoccinique - isooctylester, sel de sodium	3g
	Modificateur rhéologique	Dispersion aqueuse de copolymère acrylique	0,6g
Agent d'étalement		Tensio-actif non-ionique	0,2g
	Colorant	0,1g

The final concentration by weight of printable layer B is 50% and the viscosity is 100 cps, measured by a Brookfield® viscosimeter.

The B layer is applied to a PET plastic film face which is previously coated with an anti-adhesive layer of chromium chloride stereo The deposition of the B layer on the film is about 10 g/m2 The B layer is then dried in a kiln at 70°C. A multilayer structure is then obtained consisting of the PET plastic film, an anti-adhesive layer of chromium chloride stereo and the printable B layer.

The free side of the B-layer, the side opposite the plastic film, is glued with Super-Lok® 364 glue from National Starch. The glue is deposited at a rate of 3 g/m2 on the B-layer. The glued side of the B-layer is applied to a substrate made of Bristol® 335 g/m2 paper manufactured by Arjowiggins and then the whole is dried in an oven at 70°C.

The plastic film and the non-adhesive layer are then removed to leave only the printable layer B and the glue on the paper substrate.

The resulting paper has a very homogeneous colour.

Example 5: Preparation of a smooth or ultra-smooth sheet of low surface resistivity and offset printable

A smooth or ultra-smooth sheet according to the invention with low surface resistivity and for Offset printing was prepared from a C printable layer having the following composition: - What?

Composition de la couche imprimable C
Pigments	Carbonate de calcium	1248g
	Liant	Dispersion aqueuse de copolymère n-butyl acrylate-acrylonitrile-styrène	300g
Dispersant		Acide sulfoccinique - isooctylester, sel de sodium	3g
	Additif conducteur	Dispersion aqueuse d'un polymère conducteur	3g
Modificateur rhéologique		Dispersion aqueuse de copolymère acrylique	0,6g
	Agent d'étalement	Tensio-actif non-ionique	0,2g

The final concentration by weight of the C-printable layer is 50% and the viscosity is 100 cps, measured by a Brookfield® viscosimeter.

The C-layer is applied to a PET plastic film face which is previously coated with an anti-adhesive layer of chromium chloride stereo The deposition of the C-layer on the film is about 10 g/m2 The C-layer is then dried in a kiln at 70°C. A multilayer structure is then obtained consisting of the PET plastic film, an anti-adhesive layer of chromium chloride stereo and the printable C-layer.

The free side of layer C, the side opposite the plastic film, is glued with Super-Lok® 364 glue from National Starch, which is applied at a rate of 3 g/m2 to layer C. The glued side of layer C is applied to a substrate made of Bristol® 335 g/m2 paper from Arjowiggins and then dried in an oven at 70°C.

The plastic film and the non-adhesive layer are then removed to leave only the printable C-layer and the glue on the paper substrate.

The resistivity of the paper thus obtained is relatively low, and is of the order of 3.107, which is lower than that of the paper in example A, which is of the order of about 1.1010.

Example 6 - Preparation of a smooth or ultra-smooth sheet that can be printed by inkjet

A smooth or ultra-smooth sheet according to the invention has been prepared for inkjet printing from a printable D-layer having the following composition:

Composés
Pigments	Alumine	1000g
	Liant	Polyvinyl Alcool	100g
Agent d'étalement		Tensio-actif non-ionique	1g

The final concentration by weight of printable layer D is 14% and the viscosity is 50 cps, measured by a Brookfield® viscosimeter.

The D-layer is applied to a PET plastic film face which is previously coated with an anti-adhesive layer of chromium chloride stereo. The deposition of D-layer on the film is about 15 g/m2. The D-layer is then dried in a 70°C furnace.

The free side of layer D, i.e. the side opposite the plastic film, is glued with Super-Lok® 364 glue from National Starch. The glue is deposited at a rate of 3 g/m2 on layer D. The glued side of layer D is applied to a substrate made of Bristol paper 335 g/m2 manufactured by Arjowiggins and then the whole is dried in an oven at 70 °C.

The plastic film and the non-adhesive layer are then removed to leave only the printable D-layer and the glue on the paper substrate.

Results: The different sheets prepared for examples 1 to 6 were analysed and the following parameters of the sheet were measured: weight, thickness, hand, smoothness, shine, resistivity and printability.

The measures were implemented as follows: the weight was measured in accordance with ISO 536 (1976) by means of a Sartorius® scale with a range of 2200 g and with an accuracy of 0,1 g; the thickness was measured in accordance with ISO 534 (1988) by means of a MTS MI20 micrometer; the hand (or mass volume) was measured in accordance with NFQ 03-017; the Bekk smoothness was measured in accordance with ISO 5627 (1984) by means of a Büchel® 131 ED apparatus; the brightness was measured at 75° by the TAPPI® T480 om-92 method; the surface resistivity was measured in accordance with the Bykner® Gardner® micro-gloss 75° 4553 model; the surface meshes were measured in accordance with ASTM D257-83 method;Err1:Expecting ',' delimiter: line 1 column 221 (char 220)

The table below summarises all measurements and analyses carried out on sheets of examples 1 to 6.

Support		Papier Bristol@	Papier Elementa® bulk	Papier Maine Gloss®	Exemples
					Exemple 1 : Couche A sur Bristol@	Exemple 2 : Couche A Elementa® bulk	Exemple 3 : Couche A Maine Gloss®	Exemple 4 : Couche B sur Bristol®	Exemple 5 : Couche C sur Bristol@	Exemple 6 : Couche D sur Bristol@
		270	100	250	304	130	290	396	311	294
Epaisseur (µm)		250	140	220	273	173	240	310	314	334
		0,92593	1,4	0,88	0,9	1,33	0,83	0,78	1,01	1,14
Lissé Bekk (s : secondes)		60	20	400	7705	5035	9436	9532	6036	996
Brillance (à 75°, en %)		x	x	x	85,1	86,3	87	85,9	86,6	85,4
Résistivité surfacique		x	x	x		x	x			x
Test des encres porométriques (densité optique en fonction du temps de contact)	15 secondes	x	x	x	V 0,36	V 0,33	V 0,34	C 0,95	V 0,37	x
	30 secondes	x	x	x	V 0,37	V 0,30	V 0,33	C 1,22	V 0,41	x
	60 secondes	x	x	x	V 0,37	V 0,31	V 0,34	C 1,06	V 0,40	x
	120 secondes	x	x	x	V 0,38	V 0,32	V 0,35	C 1,04	V 0,46	x

(x : paramètres non mesurés)

The increase in weight is in the order of 30 to 40 g/m2 in the case of layer A, 126 g/m2 in the case of layer B, 41 g/m2 in the case of layer C, and 24 g/m2 in the case of layer D. The increase in thickness is in the order of 20 to 33 μm in the case of layer A, 60 μm in the case of layer B, 64 μm in the case of layer C, and 84 μm in the case of layer D. The increase in weight and thickness is mainly due to the addition of the glue layer to the media and the transfer of the printing medium.

A paper has a relatively large hand when it has a value of 1.10cm3/g or more. In the examples above, only Elementa® bulk paper has a large hand (1.4cm3/g).

Deposition of the printable layer A on a support causes a decrease in its hand. When the support initially has a large hand, as in the case of Elementa® bulk in example 2, the transfer of the layer A on this support causes a slight decrease in its hand (of the order of 5%).

Depositing the printable layer B on a support causes a decrease in his hand, whereas depositing the printable layer C on a support has little influence on his hand. Depositing the printable layer D on a support causes an increase in his hand because the printable layer here is an inkjet layer which is very porous and therefore has a low density.

Bristol® and Elementa® bulk papers have a relatively low initial smoothness of less than 100s. Maine Gloss® pre-coated paper has a relatively high initial smoothness of 400s, due to its calcium carbonate pre-coating and butadiene styrene latex.

The transfer of a printable layer onto a support by the process of the invention gives the support a smooth or ultra-smooth surface, as explained above.

The transfer of the printable layer A onto a paper support makes it possible to increase its smoothness considerably. It is noted that the printable layer A makes it possible to give a paper with a strong hand a very large smoothness (5035s in example 2).

It is also noted that the greater the initial smoothness of the support, the greater the smoothness of the support on which layer A is transferred.

The transfer of layer D onto a Bristol® support increases its smoothness to about 1000s.

The sheets prepared in examples 1 to 6 all have a high gloss of over 80%, so the process makes it possible to produce sheets with both a high smoothness and a high gloss.

The presence of a conductive additive in layer C makes it possible to significantly reduce the surface resistivity of the sheet. The sheet in example 5 has a surface resistivity about a factor of 1000 lower than that of the sheets in examples 1 and 4.

As regards the offset printability of the sheets prepared in examples 1 to 5, the porometric ink test shows that the papers have relatively correct optical density values after inking, even if these do not increase over time, thus showing limited absorption.

As regards the inkjet paper prepared in example 6, tests on Epson and Canon inkjet printers show correct results despite low deposition.

Example 7 : Preparation of a smooth or ultra-smooth printable sheet containing a printing varnish or resin

A smooth or ultra-smooth sheet according to the invention has been prepared from a printable layer formed by a lacquer or an acrylic printable resin E having the following composition. - What?

Composition du vernis imprimable E
Liant	Dispersion aqueuse de copolymère n-butyl acrylate-acrylonitrile-styrène	300g
	Dispersant	Acide sulfoccinique - isooctylester, sel de sodium	3g
Modificateur rhéologique		Dispersion aqueuse de copolymère acrylique	0,6g
	Agent d'étalement	Tensio-actif non-ionique	0,2g

Printable varnish E has a final concentration by weight of 50% and a viscosity of 50 cps, measured with a Brookfield® viscosimeter.

The varnish is applied to a PET plastic film, which is coated with an anti-adhesive layer of chromium chloride stereo. The deposition of the varnish on the film is about 5 g/m2. The varnish is then dried in an oven at 70 °C. A multilayer structure is then obtained consisting of the PET plastic film, an anti-adhesive layer of chromium chloride stereo and acrylic varnish.

The free side of the varnish is glued with Super-Lok® 364 glue from National Starch. The glue is applied at a rate of 3 g/m2 to the varnish. The glued side of the varnish is applied to a substrate formed by Bristol® 335 g/m2 paper made by Arjowiggins, and then the whole is dried in an oven at 70 °C. The plastic film and non-adhesive layer are then removed (in step c/) to leave only the printable varnish and the glue on the paper substrate.

The table below summarises the measurements and analyses carried out on the sheets prepared by this example 7. - What?

Support	Exemple 7 : Vernis imprimable E sur Bristol@
	280
Epaisseur (µm)	260
	0,93
Lissé Bekk (s : secondes)	> 10 000
Brillance (à 75°, en %)	99

The transfer of the printable varnish E to the support does not change the weight, thickness and hand of the support, which makes it possible to produce a sheet with a very high smoothness (> 10 000s) and gloss (99%), but the printability of this sheet is lower than those prepared in examples 1 to 6 because of the absence of pigments in the printable layer.

Example 8 : Preparation of smooth or ultra-smooth printing sheets by offset, indigo or electrically conductive inks

Each sheet prepared here comprises two printable layers AA, AB or AC, a first layer (A, B or C) deposited (by kiss coating) on the non-adhesive layer of the multilayer structure and a second layer (A) deposited (by kiss coating) on the first layer. The first layer, i.e. the layer closest to the plastic film in the multilayer structure, is the layer intended to receive the inks directly during printing. It is it that defines the printability of the printing process.

The plastic film used is a 12μm thick PET film. The printable layers for preparing a sheet of paper by Offset are a first layer B, and a second layer A. The printable layers for preparing a sheet of paper by HP Indigo are a first layer C, and a second layer A. The printable layers for preparing a sheet of paper by electrically conductive inks (Electronic Printing) are a first layer A, and a second layer A. The prepared multilayer structures are PET/anti-adhesive layer/A&A or C&A or B&A layers. The A, B and C layers are deposited at a ratio of 6 g/m2.

The composition of these layers is detailed in the following tables. - What?

Composition de la couche imprimable A
Pigments	Carbonate de calcium	475ml
	Liant 1	Dispersion aqueuse de copolymère styrène-Butadiène	190ml
Styronal® D517 (BASF)
Liant 2	Dispersion aqueuse de copolymère n-butyl acrylate-acrylonitrile-styrène	94ml
	Dispersant	Acide sulfoccinique - isooctylester, sel de sodium	3g
Modificateur rhéologique		Dispersion aqueuse de copolymère acrylique	0,6g
	Agent d'étalement	Tensio-actif non-ionique	0,2g

Composition de la couche imprimable B
Pigments	Carbonate de calcium	475ml
	Liant 1	Dispersion aqueuse de copolymère styrène-Butadiène	95ml
Styronal® D517 (BASF)
Liant 2	Dispersion aqueuse de copolymère n-butyl acrylate-acrylonitrile-styrène	47ml
	Dispersant	Acide sulfoccinique - isooctylester, sel de sodium	3g
Modificateur rhéologique		Dispersion aqueuse de copolymère acrylique	0,6g
	Agent d'étalement	Tensio-actif non-ionique	0,2g

Composition de la couche imprimable C
Pigments	Carbonate de calcium	475ml
	Liant 1	Dispersion aqueuse de copolymère styrène-Butadiène	95ml
Styronal® D517 (BASF)
Liant 2	Dispersion aqueuse de copolymère n-butyl acrylate-acrylonitrile-styrène	47ml
	Promoteur d'adhérence	Dispersion aqueuse d'acide Acrylique -	280 ml
Ethylène Diamond® 63001 (NALCO)
Dispersant	Acide sulfoccinique - isooctylester, sel de sodium	3g
	Modificateur rhéologique	Dispersion aqueuse de copolymère acrylique	0,6g
Agent d'étalement		Tensio-actif non-ionique	0,2g

Each of the three multi-layer structures and an Arjowiggins 200 g/m2 Opal® paper were back-glued with a two-component polyurethane glue, applied at a rate of 10 g/m2.

The resulting sheets are printable for their applications, i.e. offset, digital HP Indigo and conductive inks (electronic printing).

Claims (15)

1. A method of fabricating a printable sheet (10) presenting at least one smooth face (22), the sheet comprising a substrate (24), in particular made of paper, having at least one face covered at least in part in a layer or a plurality of superposed layers, the method comprising the steps consisting in:

   a) preparing or providing a multilayer structure (12) comprising at least, or constituted by, a plastics film (14), an anti-adhesive layer (16), and a smooth layer (18) printable by offset printing, ink jet printing, laser printing, heliogravure, flexography, dry toner printing, liquid toner printing, electrophotography, lithography, the anti-adhesive layer being interposed between the plastics film and the printable layer;

   b) pasting adhesive on a face (30) of the substrate and/or the face (28) of the multilayer structure situated opposite from the plastics film, and applying said face of the substrate against said face of the multilayer structure so as to laminate the multilayer structure and the substrate; and

   c) withdrawing the plastics film from the printable layer, the printable layer (18) defining said smooth face (22) of the sheet.
2. A method according to claim 1, characterized in that the printable layer (18) is in the solid state and/or dry in step b) and/or step c).
3. A method according to claim 1 or 2, characterized in that, prior to step b), the said face of the substrate is precoated with at least one smoothing layer including one or more thermoplastic polymers or a mixture of pigments and at least one binder, the precoated layer of the substrate being optionally calendered in order to increase its smoothness.
4. A method according to any preceding claim, characterized in that the anti-adhesive layer (16) is withdrawn at least in part from the printable layer (18) while withdrawing the plastics film (14) in step c).
5. A method according to one of claims 1 to 3, characterized in that the anti-adhesive layer (16) remains on the printable layer (18) when the plastics film (14) is withdrawn in step c).
6. A method according to any preceding claim, characterized in the that the printable layer (18) comprises a mixture of pigments and at least one printable varnish or binder, e.g. based on acrylic polymer, polyurethane, polymethyl methacrylate, styrene butadiene, vinyl acetate, polyamide, nitrocellulose or any other cellulose, polyvinyl alcohol, starch, or a mixture thereof.
7. A method according to any preceding claim, characterized in that the multilayer structure (12') comprises at least one additional layer (34) deposited on the printable layer (18) on its side opposite from the plastics film (14), the free face of said additional layer or of the additional layer farthest from the plastics film being for pasting and applying against said face of the substrate during step b).
8. A method according to any preceding claim, characterized in that it comprises an additional step consisting in printing the sheet (10) with an ink having electrical and/or optical properties.
9. A method according to any preceding claim, characterized in that it comprises, before step a), a preliminary step consisting in making indented and/or projecting patterns on the face of the plastics film that is to receive the anti-adhesive layer and the printable layer, e.g. by etching, the printable layer being for fitting closely to the shape of these patterns so as to include an imprint of the said face of the plastics film.
10. A method according to any preceding claim, characterized in that the printable layer (18) has a thickness less than or equal to 30 µm, preferably less than or equal to 15 µm, and more preferably less than or equal to 10 µm, and/or grammage less than or equal to 30 g/m², preferably less than or equal to 15 g/m², and more preferably less than or equal to 10 g/m².
11. A method according to any preceding claim, characterized in that the adhesive is deposited at least on one face of the substrate in step b), and in that the thickness of the deposited layer of adhesive is not less than half the mean roughness of the face of the substrate, and is preferably equal to said mean roughness.
12. A printable sheet (10) or printed sheet, in particular with an electrically conductive ink, having at least one smooth face (22), the sheet comprising a substrate (24), in particular a paper substrate, having at least one face covered at least in part in a layer or a plurality of superposed layer, including a printable layer (18) or printed by offset printing, ink jet printing, laser printing, heliogravure, flexography, dry toner printing, liquid toner printing, electrophotography, lithography and defining said smooth face, the sheet being characterized in that said smooth face has Bekk smoothness greater than 2000 s, and more preferably greater than 5000 s, and/or a gloss greater than 70%, and preferably greater than 80%.
13. A printable sheet according to claim 12, characterized in that the printable layer (18) has thickness less than or equal to 30 µm, preferably less than or equal to 15 µm, and more preferably less than or equal to 10 µm, and/or grammage less than or equal to 30 g/m², preferably less than or equal to 15 g/m², and more preferably less than or equal to 10 g/m².
14. The use of a printable sheet according to claim 12 or 13, for making an electronic and/or optical component, the sheet being printed by means of an ink having electrical and/or optical properties.
15. Electronic and/or optical component comprising a sheet according to claim 12 or 13, where the smooth face is printed with an ink having electrical or optical properties.