FR2984770A1 - METHOD AND DEVICE FOR CHROMATOGENIC GRAFT PROCESSING OF A HYDROXYL SUBSTRATE - Google Patents

Abstract

The invention relates to a process for the chromogenic grafting treatment of a substrate (1) having a hydroxylated surface (Sh), characterized in that it comprises the following successive stages: - continuous deposition of a grafting reagent on a support (2), said transmitting support, running, said support (2) being distinct from the substrate (1) to be treated, - juxtaposition of said emitter carrier (2) to at least a part of the hydroxylated surface (Sh) of the substrate ( 1), at a temperature adapted to cause the transfer of the reagent from the emitter carrier to the substrate and the grafting reaction of the reagent on the hydroxyl groups of the surface (Sh) of the substrate (1), for a period of time suitable for the development of the grafting reaction and in ventilation conditions adapted to the evacuation of the products of the grafting reaction, - separation of the emitter carrier (2) and the substrate (1).

Description

The present invention relates to a method and a device for treating a hydroxylated substrate by chromogenic grafting. BACKGROUND OF THE INVENTION It is of interest for many applications to modify the surface properties of a material, in particular to render it hydrophobic and to give it barrier properties. Such properties are particularly sought in the field of packaging, and more particularly for food packaging. Molecular grafting, which involves reactogenic functions present on the surface of the material and a reagent capable of reacting with the latter to form a covalent bond, is a particularly suitable means. Various embodiments of such a molecular grafting have been reported, either under standard conditions of chemistry in solution, or in solid-gas conditions with the chromatogenic technique. In particular, the document WO 99/08784 proposes to graft hydrophobic groups onto a support having hydrophilic functions. The document WO 2009/083525 more specifically proposes to graft a fatty acid onto a film of polyvinyl alcohol (PVA), thus rendering it hydrophobic. Said PVA film can be attached to a substrate that is to be sealed. These two documents propose to implement a grafting by chromatogenic chemistry. Unlike the so-called "classical" chemistry, where the reaction must be carried out in a solvent capable of contacting the surface of the substrate and the reagent and trapping released hydrochloric acid, the chromatogenic chemistry uses the vapor pressure of the reagents and a gas flow to diffuse the reagent inside the substrate, which eliminates solvents. A particularly advantageous grafting chromatogenic reaction typically consists in reacting a hydroxylated S substrate with a long chain fatty acid chloride and can be written according to the formula: K 1 S -OH + RCO Cl S -O-CO-R + HC1 K2 where K1 and K2 are respectively the constants of association and dissociation velocity. However, the industrial implementation of the chromatogeny faces several difficulties.

On the one hand, the substrate to be treated is not necessarily in the form of a sheet or a strip, that is to say a flat substrate of regular thickness. In some particularly interesting applications of chromatogeny, the substrate may have a complex shape, such as a tray, a cup, etc. or structured, such as corrugated cardboard or honeycomb containing interleaf sheets. It is then difficult - if not impossible - to apply the reagent homogeneously, for example with printing or nebulization methods. In addition, the substrate may have glued or printed elements. In this case, performing the chromatogenic treatment prior to assembly or printing of the substrate could affect the surface condition of the substrate and affect the quality of subsequent bonding and / or printing operations. On the other hand, the reagent may have impurities that may cause problems from the point of view of the food or the coloration of the substrate. To avoid such drawbacks, it would be possible to use a distilled reagent, but this would generate significant additional costs because of the very high boiling points of the reagents considered and their corrosive nature. An object of the invention is therefore to design a method and a device for overcoming the aforementioned problems. In particular, an object of the invention is to make it possible to modify the surface properties of a material irrespective of the shape and / or the structure of the substrate. BRIEF DESCRIPTION OF THE INVENTION According to the invention, there is provided a process for the chromatogenic grafting treatment of a substrate having a hydroxylated surface, characterized in that it comprises the following successive stages: - continuous deposition of a a grafting reagent on a support, said transmitting support, running, said support being distinct from the substrate to be treated, juxtaposing said emitter carrier with at least a portion of the hydroxylated surface of the substrate, at a temperature suitable for causing the transfer of the reagent from the emitter carrier to the substrate and the reagent grafting reaction on the hydroxyl groups of the surface of the substrate, for a period of time suitable for the development of the grafting reaction and in ventilation conditions adapted to the evacuation of the reaction products grafting, - separation of the emitter carrier and the substrate.

Preferably, said emitter support is absorbent, porous or fibrous, so as to absorb the deposited reagent. In some embodiments of the invention, said emitter carrier has a grammage adapted to conform to the shape of the hydroxylated surface of the substrate. The transmitter support can advantageously be fiberglass and can be reused. Thus, the transmitting medium can form a continuous band. According to another embodiment, the emitter carrier is made of cellulose. The deposition of the reagent can be carried out by heliography or flexography. Preferably, the reagent comprises a fatty acid chloride.

Moreover, the reagent may advantageously comprise a mixture of at least two fatty acid chlorides having distinct boiling points. According to preferred embodiments, the substrate has a concave and / or convex shape and / or a three-dimensional structure. In particular, the substrate may have a stackable form and the emitter carrier is, in this case, the bottom of another substrate that is nested in the substrate to be treated to transfer the deposited reagent and develop the grafting reaction. According to one embodiment, the step of juxtaposing the transmitter support and the substrate is implemented in a ventilated oven. In another embodiment where the substrate is plane, during the juxtaposition, said substrate is on a heating roller. In one embodiment where the substrate has a three-dimensional structure, the emitter carrier is a face of another substrate that is juxtaposed to one side of the substrate to be treated to transfer the deposited reagent and develop the grafting reaction. Another object of the invention relates to a hydrophobic substrate having a concave and / or convex shape and / or a three-dimensional structure, obtainable by the method described above. By three-dimensional structure is meant that the substrate is not homogeneous, which is for example the case of a honeycomb or corrugated cardboard. According to particularly preferred applications, said hydrophobic substrate consists of a molded cellulose vase, a food-grade container whose inner surface intended to be in contact with food is covered with a layer of PVA, made of corrugated cardboard, or a honeycomb carton. Another subject of the invention relates to a device for the chromatographic grafting treatment of a substrate having a hydroxylated surface, characterized in that it comprises: a device for scrolling a support, said transmitting support, a device for continuous deposition of a reagent on the emitter carrier; a device for juxtaposing the emitter carrier to at least a portion of the hydroxylated surface of the substrate, said device comprising a heating element and generating a ventilation adapted for the evacuation of the products of the chromogenic grafting reaction. According to one embodiment, said juxtaposition device comprises a ventilated oven. According to another embodiment, said juxtaposition device comprises a heating roller.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which: FIG. 1 is a schematic view of a treatment device according to a first embodiment of FIG. embodiment of the invention, - Figure 2 is a schematic view of a processing device according to a second embodiment of the invention, - Figure 3 is a schematic view of a treatment device according to a third embodiment of the invention. Embodiment of the invention FIG. 4 is a schematic view of a processing device according to a fourth embodiment of the invention DETAILED DESCRIPTION OF THE INVENTION FIGS. 1 to 4 illustrate various embodiments of the method according to FIG. invention which will be described in detail hereinafter. However, these embodiments are not limiting and it is possible in particular, particularly as a function of the shape and / or the structure of the substrate to be treated, to combine elements of an embodiment with elements of a another embodiment.

In general, instead of directly applying the reagent to a hydroxylated surface of the substrate to be treated, the reagent is first deposited continuously on a so-called "transmitting carrier" in scrolling. Next, the emitter carrier is juxtaposed to at least a portion of the hydroxylated surface to be treated, called the "receiving surface" of the substrate. By "juxtaposition" is meant in the present text that ensures between the transmitter support and at least a portion of the substrate surface the closest spatial proximity possible without there being physical continuity between the surfaces. By way of illustration, said juxtaposition corresponds to the placement of two sheets of paper on one another without the application of a force other than gravity, these two sheets not then being in intimate contact with each other. one with the other. The juxtaposition thus formed is then placed under chromatogenic development conditions (ie high temperature and gas flow) so as to ensure the diffusion of the reagent of the emitter support towards the receiving surface and the development of the grafting reaction. of the reagent on the hydroxylated terminations of the substrate. Alternatively, it is also possible to use two emitter carriers which are then placed on either side of the substrate to be treated. As will be seen below, it is not necessary, for the grafting takes place, to juxtapose the emitter carrier to the entire hydroxylated surface to be treated.

Indeed, because of the phenomenon of diffusion of the reagent on the hydroxylated surface, it may be sufficient to juxtapose the emitter carrier to only a portion of the hydroxylated surface of the substrate, the appropriate temperature and ventilation conditions can be provided by an oven ventilated by a heating roller associated with a ventilation nozzle, by infrared heating associated with a scroll of the substrate to be treated and the transmitter support, etc. When the reaction has finished developing, the transmitting support and the receiving surface of the substrate are separated and, after returning to ambient temperature, the treated substrate can be conditioned for transport and subsequent use. Figure 1 schematically illustrates the implementation of a first embodiment. In this, the transmitter support 2 scrolls in the direction of the arrow. According to an embodiment where the support 2 is not intended to be reused, said support is supplied in the form of a reel and unwound by a suitable reel (not shown) before being presented to the deposition device 10. reagent.

The device 10 shown schematically herein is a flexographic or heliographic device, comprising a reagent application roller 10b and a counteracting roller 10a, for applying the carrier 2 against the roller 10b. The surface of the emitter-coated emitter support 2 is designated by the mark Sr.

If the substrate 1 to be treated is in the form of a plane substrate, which is the case in FIG. 1, said substrate may be supplied in the form of a coil and unwound by a suitable reel (not shown here). and driven in scrolling by a heating roller 20. The hydroxylated surface is designated by the reference Fh and is opposite to the surface in contact with the heating roller 20.

Advantageously, the substrate 1 is preheated to a temperature close to the grafting temperature. For this purpose, a heating roller, an infra-red radiator or any other suitable heating device (not shown here) may be used upstream of the heating roller 20. The surface Sr of the emitter support 2 and the surface Fh of the substrate 1 are juxtaposed at the level of the heating roller 20. A loading system is provided to ensure sufficient tension of the support 2 and the substrate 1. The temperature of the heating roller 20 is chosen at least equal to the development temperature of the chromatogenic reaction.

The speed of travel of the emitter carrier 2 and rotation of the heating roller 20 are chosen so that the chromatogenic reaction can develop completely during the contact time between the emitter carrier 2 and the substrate 1. Due to the dynamic nature of this method, the products of the grafting reaction (in particular hydrochloric acid) can be evacuated.

Optionally, it is possible to implement an additional heating of the substrate 1 and the support 2, for example by means of one or more infra-red radiants 21 placed above the heating roller 20. After its separation from the substrate 1, the transmitter support 2 can be reused continuously, as shown schematically by the dotted line, possibly being cleaned by a thermal device 30. Alternatively (not shown), the transmitter support 2 can be wound in the form of a coil so as to be sent to a processing center, for example for recycling. Figure 2 schematically illustrates another embodiment of the invention.

Unlike the previous embodiment, the substrate 1 is in the form of a relief piece, schematized here by a cylinder of circular section. Due to its elongated hollow shape, it would be difficult to homogeneously apply reagent over the entire surface of the substrate.

This difficulty is overcome by the use of two transmitting media 2, 2 'scrolling. On each of the emitter carriers 2, 2 'is deposited by a deposition device 10, 10' of the reagent on a surface Sr, Sr '. The deposition devices 10, 10 'are similar to that described with reference to FIG. 1 and will therefore not be further described. Furthermore, upstream of the deposition of the reagent, the transmitting supports can be unwound from a coil or scroll continuously (as shown schematically by the dotted lines), subject to periodic cleaning if necessary. The Sr and Sr 'surfaces of the transmitting supports are fed on either side of a plurality of substrates 1 arranged side by side, so as to be juxtaposed tangentially to the cylindrical wall of said substrates. The juxtaposition thus formed runs in a ventilated furnace 22. The duration of presence in the furnace of the substrates 1 juxtaposed to the Sr, Sr 'surfaces of the emitter supports 2, 2' is determined so that the chromogenic grafting reaction can proceed completely. At the outlet of the oven, the substrates 1 are separated from the emitter supports 2, 2 'and cooled for packaging. Figure 3 schematically illustrates a third embodiment of the invention.

In this case, the substrate 1 has a three-dimensional structure, that is to say in which the surface to be treated is not directly accessible. This is particularly the case of corrugated cardboard, for which it is desirable to treat not only the outer sheets but also the sheets constituting the inner structure of the cardboard.

In this embodiment, the cartons 1 are put in place in a charger 11, from which a handling device takes them to present them to a device for depositing the reagent 10. The depositing device 10 is similar to that already described. with reference to Figures 1 and 2 and will therefore not be described further.

The device 10 deposits reagent on the Sr surface of each carton.

Then, a handling device successively takes each carton to place it against another carton, the reagent-coated surface of a carton being against the uncoated surface of the adjacent carton. This stack of cartons 1 is placed in a ventilated oven 22 scrolling.

The duration of presence of the cartons in the oven 22 is adapted so that the chromatogenic grafting reaction can proceed completely. Particularly advantageously, the cartons are placed in the oven in a vertical position. Thus, the flow of ventilation can circulate inside the corrugations of the cardboard and makes it possible to promote the diffusion of the reagent from the outer sheet on which the reagent has been transferred to the internal sheets constituting the structure of the cardboard. At the outlet of the oven 22, the cartons may be placed on a conveyor on which they cool before being packaged. Figure 4 schematically illustrates a fourth embodiment of the invention. In this, the substrate 1 to be treated is a non-plan stackable object, such as a tray. In the case where said tray is for food use, the inner surface Fh is preferably covered with a layer of PVA.

In a particularly advantageous manner, the stackable nature of the trays is used to overcome a specific transmitter support. For this purpose, the reagent is deposited on the bottom Sr of each tray. For example, a deposition device of the heliography or flexography type may be used, comprising a roll 10b for applying the reagent and a roll 10a having bosses 101a intended to each support a tray 1 during the application of the reagent. Then, a handling device grasps each tray and stacks it on another tray, the bottom Sr on which the reagent was deposited being juxtaposed to the inner surface Sh to treat the underlying tray.

The stack thus formed is placed in a ventilated oven 22. The duration of presence in the oven is determined so that the chromatogenic grafting reaction can take place entirely. Then the trays are extracted from the oven and cooled separately, before packaging and / or use.

Alternatively (not shown), the reagent could be deposited on a specific emitter carrier, for example in the form of a strip, depositing said strip in individual sheets of dimensions greater than the developed surface of the substrates 1, and perform a successive stack of a tray and an emitting sheet.

Due to the low basis weight of the emitting sheets, these can conform, with some wrinkles, to the shape of the substrate. Substrate to be treated The substrate to be treated is typically a porous substrate of variable form whose surface has hydrophilic functions (as described in WO 99/08784), which are either carried by the substrate itself or by a coating of a layer having hydrophilic functions. The hydroxylated surface Sh may be flat or not; it can also have a three-dimensional structure (in the case of corrugated cardboard or honeycomb, for example). On the other hand, the hydroxylated surface may represent some or all of the surface of the substrate. According to a particular embodiment of the invention, the substrate has a surface coated with a polyvinyl alcohol (PVA) film, as described in WO 2009/083525. Reference is therefore particularly made to these documents for more details concerning the preparation of the hydroxyl substrate, which is not the subject of the present invention. According to a preferred application of the invention, the substrate is a cellulosic material, such as paper or cardboard. According to another preferred application of the invention, the substrate is made of molded cellulose. Transmitter Support The emitter carrier is preferably non-reactogenic with respect to reagents such as acid chlorides, so that the grafting reaction does not take place on the transmitting support but on the receiving substrate. Furthermore, the emitter carrier is absorbent, so as to absorb the amount of reagent necessary for complete grafting.

For this purpose, a porous or fibrous emitter carrier is chosen. In addition, the emitter carrier has a sufficiently low basis weight to conform to the receiving substrate which may have a concave or convex complex shape.

Depending on the applications, it may indeed be desirable for the emitter carrier to conform as much as possible to the shape of the receiving surface of the substrate, so as to promote homogeneous transfer of the reagent. The porosity, the thickness and the weight of the emitter support are chosen in particular according to the amount of reagent to be deposited on the substrate and the shape of said substrate. The grammages are usually between 10 and 100 g / m2. According to a preferred application of the invention, the emitter support is fiberglass and can be reused several times for subsequent grafting, with periodic cleaning if necessary.

Indeed, from a temperature of the order of 450 ° C, all the organic compounds are destroyed. Therefore, to clean the fiberglass support, it is sufficient to expose it periodically to a heat source at a temperature above 450 ° C, such as a heat gun, a burner, a pyrolysis device, etc.

Such a device is designated by the reference numeral 30 in FIG. 1. Moreover, although the cellulose is reactogenic with respect to the fatty acid chlorides, the emitter carrier can also be made of cellulose. Indeed, the amounts of reagent consumed in the case of a low basis weight cellulose sheet (i.e. <15 g / m 2) are very small (i.e. <0.15 g / m 2) and can therefore be practically neglected. In addition, cellulose sheets of this type are, because of their low basis weight, very flexible and are therefore capable, if necessary by being creased locally, to deform to conform to a concave or convex complex surface of the substrate. The emitting cellulose carriers generally can not be reused for subsequent grafting but can be used for other applications, such as agricultural mulching, or recycled. According to a particular embodiment, the emitter carrier may be a surface of a substrate to be treated, the reagent deposited on said surface being transferred to the hydroxylated surface of another substrate to be treated during the juxtaposition of these two substrates.

Thus, even if the emitter function is filled by a substrate, the grafting is still obtained after transfer of the reagent onto a substrate separate from the emitter substrate. Examples of this embodiment are illustrated in FIGS. 3 and 4. Deposition of the Reagent on the Transmitter Support As will be seen below, the deposited reagent may be composed of a single compound, in particular a fatty acid chloride, such as described in WO 99/08784 cited above, or a mixture of at least two compounds, including two fatty acid chlorides. In the appropriate case, said compounds advantageously have different boiling points.

In particular, the reagent may comprise stearic acid chloride and / or palmitic acid chloride. The deposition of reagent on the emitter carrier is carried out in a controlled manner using known printing techniques by heliography or flexography. The grafting reagent is thus deposited in the liquid state on the emitter support, in the manner of an ink. For this purpose, it is therefore carried in the deposition device at a temperature greater than its melting temperature in order to have a viscosity compatible with the deposition system (a temperature that is 20 to 30 ° C. higher than the temperature reagent melting is considered appropriate).

It is possible to precisely control the density and amount of the deposited grafting reagent by means of a particular etching of the anilox roll which is used to apply the reagent. In practice, the amount of reagent required for the grafting of the destination substrate is increased on the transmitting support, increased if necessary by the consumption of reagent due to the emitter carrier. Optionally, it proceeds, prior to the deposition of the reagent, a heating of the emitter carrier. Such heating may for example be carried out by infrared or by a heating roller.

It may be useful for drying the support before the reaction, and / or for raising the temperature of the support to a temperature similar to that of the grafting reagent. Transfer of the reagent Said emitter carrier, loaded with excess reagent, is then juxtaposed to at least a portion of the receiving surface of the substrate to be treated.

It is not necessary to ensure an intimate physical contact between the emitter carrier and the substrate; indeed, as will be described below, the transfer of reagent occurs as soon as the emitting and receiving surfaces are juxtaposed, that is to say as close as possible to one another, and that the thermal conditions are met.

Moreover, as indicated above, it is not necessary to juxtapose the emitter carrier with all of the hydroxylated surface on which it is desired to perform the grafting. Indeed, thanks to the large diffusion of the reagent on the hydroxylated surface, it may be sufficient to juxtapose only a portion of the surface of the substrate to be treated to the emitter carrier. This property is used in the embodiment illustrated in FIG. 2, in which the two emitter supports 2, 2 'are only juxtaposed tangentially with the substrates 1 of cylindrical shape.

It has been experimentally verified that grafting occurs on the entire outer surface of said cylindrical substrates. In some cases, a plurality of substrates are stacked one on top of the other, optionally by interposing a specific emitter carrier between two substrates. According to a preferred embodiment, illustrated in Figures 2 to 4, the juxtaposition thus formed is placed in a ventilated oven, maintained at the temperature necessary for the development of the reaction. According to another embodiment, illustrated in FIG. 1, the stack of the substrate to be treated and the emitter carrier, both of which are planar, are brought into contact with a heating roller maintained at the temperature necessary for the development of the reaction. .

In this case, thanks to the dynamic nature of this step, sufficient ventilation occurs to allow the evacuation of the products of the reaction. In accordance with the principle of chromatogeny, there is then a so-called transfer mechanism where the reagent migrates through gaseous exchange of the emitter carrier to the receiving surface of the substrate and reacts with the reactogenic sites of said surface.

This transfer mechanism is to some extent related to the mechanism of molecular distillation. In the case of molecular distillation, the product to be distilled is placed in an emitter compartment which is heated to a high temperature but below its boiling point at the pressure under consideration.

There is thus above the surface of the liquid present in the emitter compartment a gas phase containing a certain partial pressure of the product to be distilled, called "vapor pressure". The higher the temperature, the higher the vapor pressure. Next to the transmitter compartment is a receiver compartment which is placed at a lower temperature than the transmitter compartment.

At this receiving compartment, the vapor pressure is lower and the product to be distilled condenses. Molecular distillation is a powerful technique because it allows to distil products with very high boiling points but it is a slow phenomenon because the low value of the vapor pressure significantly limits the material transfer speed. In the case of the chromatogenic transfer carried out in the process described here, the transfer mechanism is analogous in that a gaseous phase characterized by a certain concentration of reagent molecules is present; however, the condensation is obtained in this case not by a thermal effect and a lowering of the vapor pressure but by a chemical mechanism of consumption of the reagent. The observation of diffusion rings in the DSMT test (which is described in the article by S. Berlioz et al., SFGP 2007 - Investigation of a Novel Principle of Chemical Grafting for Cellulose Fibers Modification, International Journal of Chemical Reactor Engineering 6 (2008)) of fatty acid chlorides and the demonstration of a very frank hydrophobicity edge indeed indicates that the reaction rate is very fast with respect to the diffusion phenomena. It can thus be considered that the concentration of residual reagent on the receiving surface of the substrate is practically zero. The system therefore functions as a highly efficient chemical pump as long as reactogenic sites remain on the receiving surface of the substrate. When the substrate is chemically saturated and there are no more reactogenic sites available, this pumping mechanism ceases completely. Once the substrate is saturated, additional (excess) reagent transfer can occur only if there is a positive temperature difference between the emitter carrier and the substrate. However, the emitter carrier and the substrate being at the same temperature, the transfer becomes virtually zero once the substrate is saturated, which avoids applying an excess of reagent on the substrate. If it were necessary to further reduce this reagent transfer phenomenon, it would be possible to subject the receiving substrate to a temperature higher than that of the emitter carrier. For this purpose, it could for example be applied, by the surface of the substrate opposite to the receiving surface, infrared heating at a temperature higher than that of the ventilated oven or that of the heating roller in the case illustrated in Figure 1.

The transfer of reagent from the emitter carrier to the substrate is thus automatically controlled. In addition, any excess reagent is removed by the gas flow of the ventilated oven. This method also ensures a high homogeneity of grafting on the entire receiving surface. It could be feared that the treatment speed is slowed down prohibitively but it has been found that, although the grafting reaction is slowed down compared to a direct deposit of the reagent on the substrate to be grafted, this slowdown remains moderate with times. treatment that can go down to a few seconds.

Indeed, the large dispersion of the reagent on the surface of the emitter carrier ensures a high rate of vaporization of the latter. Moreover, the almost instantaneous reactivity of the reagent on the receptor substrate generates a high concentration gradient of the reagent in the gas phase. In addition, this slowdown can be compensated, where possible, by stacking the substrates to be grafted between which emitter carriers are interposed. In this respect, it is advantageous to have a continuous furnace system ensuring a constant residence time. Finally, the transfer rate can be increased by using relatively low boiling point reagents, such as palmitic acid chloride.

Particularly advantageously, if the deposited reagent comprises in mixture several reagents of different boiling points, these reagents will diffuse proportionally to their vapor pressure. Thus, longer-chain and higher-boiling reagents, which diffuse less, will preferentially be grafted on the emitter carrier, while short-chain and low-boiling reagents, which diffuse more, will be grafted preferentially on the receiving substrate. This property can be used in some applications described below. Moreover, the slowing down of the duration of the reaction is related to the average distance separating the transmitting and receiving parts.

Indeed, as already mentioned above, an intimate contact between the transmitting carrier and the receiving substrate is not sought and in practice, there may be greater or smaller distances between them. However, it is advantageous to reduce as far as possible the distance between the transmitting carrier and the receiving substrate.

According to one embodiment of the invention, flat substrates can be processed by the transfer method which has just been described. In this case, an advantage of this process is in particular to avoid the coloration of the substrate and / or the deposit thereon of non-volatile impurities that would be present in the reagent. In this context, the reagent is continuously deposited on the emitter carrier in scrolling, and then said support is placed on the substrate to be treated, itself positioned on a heating roller, which provides the temperature necessary for the grafting reaction. The running speed of the juxtaposed transmitting and receiving substrate and the circumference of the roll are calculated so that the transfer has time to take place between the transmitting medium and the receiving substrate. The time required for the transfer is shorter as the receiving substrate is already at a temperature close to the reaction development temperature. It may therefore be advantageous to heat the substrate before juxtaposing it with the emitter support. Such heating may be carried out by passing the substrate over a heating roller, and / or by applying infrared heating thereto. Combined or alternatively, infrared heating of the transmitter support also makes it possible to increase the transfer speed by increasing the temperature rise rate of said support. In practice, it is thus possible to perform the grafting with speeds close to those that can be obtained by depositing the reagent directly on the surface to be treated. Determining the Time Required for Transfer To determine the time required for transfer for a given substrate and reagent, the following procedure can be implemented. A given quantity of reagent is deposited on the emitter support and put in contact with the receiving surface of the substrate, and then the stack thus formed is placed under the conditions chosen to carry out the transfer (for example, a ventilated oven at 150 ° C). The experiment is repeated by varying the exposure time in the oven. Just after the end of the exposure, for each experiment, the emitter carrier is separated from the substrate and a new stack is formed with the emitter carrier already used and a blank control receiver sheet. For this purpose, a virgin sheet which is very hydrophilic and very reactive with respect to the chromatogenic reaction, such as Wattman paper, is preferably chosen.

The new stack is then placed in the ventilated oven for a period of about 10 minutes. The stack is then taken out of the oven, the emitter support is separated from the control receiving sheet and the control receiving sheet is tested by wetting it with water to find traces of hydrophobicity. If traces of hydrophobicity are observed, this means that the transfer reaction was not complete. If on the contrary, no trace of hydrophobicity is observed, it means that the reaction was well completed and that there was more reagent on the emitter carrier.

From these results, the minimum duration of exposure is determined to obtain the complete disappearance of the hydrophobicity on the control receiver sheet. This minimum duration corresponds to the time necessary for the transfer of the reagent. Care must be taken, however, that a very high transfer rate may result in a lowering of the grafting rate, since a large quantity of reagent may then be lost through evaporation. Application to the treatment of structured materials According to a particular embodiment of the invention, the method makes it possible to treat the internal parts of structured materials such as corrugated board. In this case, the emitter carrier consists of the outer sheet of the corrugated board and the receiving substrate of the insert sheet. The reagent is deposited on the outer surface of the carton and the plates are then placed vertically against each other in an oven. Preferably, the cartons are placed so that the flutes are vertical to allow better ventilation. Particularly advantageously, the grafting can be further improved by using mixed reagents having different boiling points. The high-boiling reagent, which diffuses less, is then preferentially grafted onto the emitting outer surface which needs to be the most protected in terms of hydrophobicity while the reagent of lower boiling point, which diffuses better, graft preferentially on the spacer sheet which needs less protection. Application to the treatment of stackable containers Another particular embodiment of the invention relates to any containers whose shape allows stacking, for example trays for food use.

One can naturally interpose a transmitting sheet between each tray but if the edges of the tray are low enough, it is also possible to simply deposit the reagent on the rear part of the tray which then acts as the transmitter. The reagent will diffuse on the inner bottom of the tray and will also diffuse on the edges. Here again, the appropriate use of a mixture of high and low boiling point reagents makes it possible to optimize the grafting with a preferential grafting of the high boiling point reagent at the bottom of the tray and a preferential grafting of the reagent of low boiling point on the edges.

Examples of conditions of implementation Example n ° 1 The table below shows the variation of the transfer time (in seconds) according to the nature of the reagent (palmitic acid chloride (C16Cl) and stearic acid chloride ( C18CI)) and temperature between 120 and 180 ° C: Temperature 120 ° C 140 ° C 160 ° C 180 ° C C16CI 180 120 60 30 C18CI> 600 600 300 150 Example No. 2 A dosage of the percentages of reagents grafted onto the transmitter support and the receiver substrate has been realized. The initial ratio of the mixture deposited between the palmitic acid chloride and the stearic acid chloride is 1/1.

After transfer and grafting, the grafted reagents are assayed by saponification of the fatty acids and analyzed by HPLC. It is measured that the ratio between stearic acid and palmitic grafted on the emitter carrier is of the order of 60/40 while it is 40/60 on the receiving substrate. It is observed that the emitter carrier has been enriched in stearic acid, which is the least volatile reagent, and that the receptor substrate has been enriched in palmitic acid, which is the most volatile reagent. Examples of Treated Substrates A particularly interesting first example is that of a molded cellulose vessel.

Despite the elongated hollow shape of such an object, it suffices to apply the reagent to two parallel emitting supports and to juxtapose them tangentially to the external wall of the vessel, as illustrated in FIG.

Thanks to the diffusion of the reagent, the entire external surface of the vase is grafted. The vase thus obtained has the advantage of being watertight while remaining permeable to air (and therefore to oxygen), which makes it possible to avoid the development of populations of anaerobic bacteria in the water of the water. vase.

A second particularly advantageous example is that of a tray for food use, made of molded cellulose and thus the inner surface intended to be in contact with food is covered with a layer of PVA. For such a tray, it is particularly advantageous to take advantage of the stackable nature of the trays, to apply the reagent on the bottom of each tray and stack a series of trays in a ventilated oven, as shown in Figure 4. Thus, it s' clears a specific issuer support. Furthermore, this process allows, in the case where the reagent contains impurities, not to transfer these impurities on the inner surface of the tray, the reagent remaining on the bottom of the tray on which the reagent was deposited and n ' therefore not affecting the properties of the inner surface of the tray. A third example is that of corrugated cardboard or honeycomb. Due to the diffusion of the reagent, the treated board has hydrophobic properties not only at the outer sheets but also at the level of the sheets forming the inner structure.

The resulting board is therefore more resistant to moisture. Furthermore, the treatment being implemented after the manufacture and possibly the printing of the cardboard, it is freed from the constraints related to the strength of the bonding and the quality of the printing. Naturally, the examples given above are only for information only and the person skilled in the art can define applications to other substrates and adapt accordingly the operating conditions of the transfer of the reagent and the development of the reaction of chromatogenic grafting without departing from the scope of the present invention.

REFERENCES WO 99/08784 S. Berlioz et al., SFGP 2007 - Investigation of a Novel Principle of Chemical Grafting for Cellulose Fibers Modification, International Journal of Chemical Reactor Engineering, Vol. 6 (2008) 35

Claims (19)

REVENDICATIONS1. Process for the chromogenic grafting treatment of a substrate (1) having a hydroxylated surface (Sh), characterized in that it comprises the following successive stages: - continuous deposition of a grafting reagent on a support (2), said carrier, in scrolling, said carrier (2) being distinct from the substrate (1) to be treated, - juxtaposition of said emitter carrier (2) to at least a part of the hydroxylated surface (Sh) of the substrate (1), at a temperature adapted to cause the transfer of the reagent from the emitter carrier to the substrate and the grafting reaction of the reagent to the hydroxyl groups of the surface (Sh) of the substrate (1) for a period of time suitable for the development of the grafting reaction and in ventilation conditions adapted to the evacuation of the products of the grafting reaction, - separation of the emitter carrier (2) and the substrate (1). 2. Method according to claim 1, characterized in that said transmitting support (2) is absorbent, porous or fibrous. 3. Method according to one of claims 1 or 2, characterized in that said transmitting support (2) has a basis weight adapted to match the shape of the hydroxylated surface of the substrate (1). 4. Method according to one of claims 1 to 3, characterized in that the transmitter support (2) is fiberglass. 5. Method according to claim 4, characterized in that the transmitter support (2) forms a continuous band. 6. Method according to one of claims 1 to 3, characterized in that the transmitter support (2) is cellulose. 7. Method according to one of claims 1 to 6, characterized in that the deposition of the reagent is carried out by heliography or flexography. 8. Method according to one of claims 1 to 7, characterized in that the reagent comprises a fatty acid chloride. 9. Method according to one of claims 1 to 8, characterized in that the reagent comprises a mixture of at least two fatty acid chlorides having distinct boiling points. 10. Method according to one of claims 1 to 9, characterized in that the substrate (1) has a concave and / or convex shape and / or a three-dimensional structure. 11. Method according to one of claims 1 to 10, characterized in that the substrate (1) has a stackable shape and in that the emitter carrier is the bottom of another substrate that is nested in the substrate ( 1) to be treated to transfer the deposited reagent and develop the grafting reaction. 12. Method according to one of claims 1 to 11, characterized in that the step of juxtaposing the transmitter support (2) and the substrate (1) is implemented in a ventilated oven. 20 13. Method according to one of claims 1 to 10, characterized in that the substrate (1) is flat and in that during juxtaposition, said substrate (1) is on a heating roller (20). 14. Method according to one of claims 1 to 10, characterized in that the substrate 25 (1) has a three-dimensional structure and in that the emitter support is a face of another substrate that is juxtaposed to one side substrate (1) to be treated to transfer the deposited reagent and develop the grafting reaction. 15. Hydrophobic substrate having a concave and / or convex shape and / or a three-dimensional structure, obtainable by the method according to one of claims 1 to 14. Substrate according to claim 15, consisting of a molded cellulose vase, a food-grade container whose inner surface for contact with food is coated with a PVA layer, a corrugated cardboard, or a cardboard honeycomb. 17. Apparatus for the treatment by chromatographic grafting of a substrate (1) having a hydroxylated surface (Sh), characterized in that it comprises: a device for scrolling a support (2), said transmitting support; device (10, 10 ') for continuously depositing a reagent on the emitter carrier (2), - a device for juxtaposing the emitter carrier with at least a part of the hydroxylated surface (Sh) of the substrate (1), said device comprising a heating element and generating ventilation adapted for evacuation of the products of the chromogenic grafting reaction. 18. Device according to claim 17, characterized in that said juxtaposition device comprises a ventilated oven (22). 19. Device according to claim 17, characterized in that said juxtaposition device comprises a heating roller (20).