WO1997039190A1 - Procedure and equipment for processing paper documents using supercritical pressure fluid - Google Patents

Abstract

This invention concerns a procedure for processing paper documents, including books. The procedure's characterizing feature is that it comprises an initial stage in which the documents to be processed are exposed to the effects of a supercritical pressure fluid formed from a mixture of a gas with 1 % to 20 % mass of an alcohol. The invention also concerns a solvent and equipment for applying the procedure.

Description

 METHOD AND INSTALLATION FOR PROCESSING PAPER DOCUMENTS WITH SUPERCRITICAL PRESSURE FLUID

The present invention relates to a process for treating paper, books and documents which it is desired to improve the condition and to promote preservation, as well as an installation and a solvent making it possible to implement this process.

We know that very many books and paper documents, such as newspapers and posters, and especially those printed on paper manufactured since the mid-19th century, are rapidly degrading and that treatment is necessary on millions of works if we want to avoid their destruction. Several treatments are currently implemented, with the main aim of deacidifying the paper and of stopping the irreversible degradation of the cellulose fibers which ensure its texture. Some of these processes require the use of a chlorofluorocarbon (CFC) type fluid as a vector of a treatment agent, which it is imperative to replace in view of the cessation of the manufacture of these products following international conventions banning the use of the molecules they use and which are suspected of destroying stratospheric ozone.

It has also been proposed to use carbon dioxide at supercritical pressure as a carrier fluid for treatment agents, with the advantages linked to its abundance, its harmlessness and its chemical inertness. We will first recall what are a supercritical fluid and a subcritical liquid. It is known in fact that bodies are generally known under three states, namely solid, liquid and gaseous, and that one passes from one to the other of these states by varying the temperature and the pressure. However, there is a point beyond which one can pass from the liquid state to the gaseous state, in a continuous way, without passing by a boiling (or conversely one can pass from the gaseous state to the state liquid without going through condensation). This point is called a critical point.

In the case of a pure body, a fluid in the supercritical state is in a state characterized by a? pressure and a temperature respectively higher than the critical pressure and the critical temperature. In the case of a mixture, a fluid in the supercritical state is in a state characterized, on a pressure / temperature diagram, by a point located beyond

K) the envelope of critical points. Similarly, in the case of a pure body, a liquid said in a subcritical state is characterized by a pressure higher than the critical pressure and by a temperature below the critical temperature. In the case of a mixture, a

15 said liquid in a subcritical state is characterized by a pressure above the critical pressures and by a temperature below the critical temperatures of the components of the mixture. It will be considered, in the remainder of this text, that a fluid at supercritical pressure is 0 either a fluid in the supercritical state or a so-called subcritical liquid as defined above.

French patent FR-A-2,674,872 describes a deacidification / reinforcement process for paper products based on the use of carbon dioxide at supercritical pressure without, however, the proposed procedure being optimized, effectively leading to to a very high consumption of treatment agents. One of the main advantages of this process lies in the ease of carrying out the separation between the solvent, 0 constituted by the fluid at supercritical pressure, with the extracts and solutes.

In addition, in such a process, this separation can be carried out so as to impregnate a porous matrix which will have been previously contacted with a solution of the product to be impregnated in a fluid at supercritical pressure, as has been described in many previous documents. Besides the fact that the supercritical fluid leaves no residue in the matrix thus impregnated, the homogeneous impregnation of said matrix is facilitated by the very high value of the diffusivity of these fluids, generally ten to one hundred times higher than those of liquids, and by the very low viscosity of these fluids, close to those of gas and therefore about a hundred times weaker than that of liquids. This method does not, however, offer any solution to the problem of reinforcement required for documents which are already seriously damaged. The object of the present invention is to improve the efficiency of the processes for processing paper documents using fluids at supercritical pressure, such as in particular carbon dioxide.

The subject of the present invention is thus a method for processing paper documents, and in particular books, comprising at least one step consisting in subjecting the documents to be treated to the action of a fluid at supercritical pressure, this fluid possibly being the vehicle of at least one treatment agent, characterized in that the fluid at supercritical pressure consists of the mixture of a gas with 1% to 20% by mass of an alcohol.

In one embodiment of the invention, the gas consists of carbon dioxide, and the alcohol consists of ethanol.

The Applicant has in fact found that the fact of producing a fluid at supercritical pressure from a mixture formed of carbon dioxide and an alcohol made it possible to obtain results which could not be achieved by the process according to the state. Prior art in which the supercritical pressure fluid consisted only of carbon dioxide.

In particular, it has been found that a mixture at supercritical pressure consisting of carbon dioxide and alcohol proves to be much more effective as regards the elimination of microorganisms. The present invention thus makes it possible to eliminate the document sterilization operation which is currently practiced on a large scale and which uses agents, such as in particular ethylene oxide, the implementation of which is potentially dangerous.

It has also been found that adding alcohol to the gas brought to supercritical pressure makes it possible to significantly increase the pH of the treated paper from 0.5 to 1.5 units. If such an increase in pH is of course insufficient to achieve the objectives set by the librarians, it nevertheless constitutes an interesting step in the invention.

It has also been found that degraded papers, which usually have a yellowed appearance, tend, after having been treated according to the process of the invention, to regain a lighter appearance. It has also been found that treatment according to said method made it possible to eliminate the odor of "old books" from the treated papers.

It has also been found that in certain cases the mechanical strength of the treated papers is improved by this step.

The present invention is also particularly advantageous in that it achieves a modification of the internal porosity of the paper which facilitates better diffusion of the treatment agents inside the latter, and in particular deacidification and reinforcing agents which are eventually used later.

The present invention makes it possible to complete the deacidification of paper documents started during the extraction step with a specific deacidification step.

It is known, from French patent FR-A-2,674,872, cited above, that it is possible to use, as deacidifying agents, organometallic compounds, such as magnesium alkylcarbonates which will lead to the precipitation of magnesium oxide, hydroxide and carbonate, capable of neutralizing the acidity present and constituting a alkaline reserve. These magnesium alkylcarbonates are known to have a very low solubility in pure carbon dioxide, even when the latter is at supercritical pressure, so that the impregnation operation of the paper cannot be carried out under economically conditions acceptable. By using a solvent consisting of a fluid at supercritical pressure obtained from a mixture of carbon dioxide and alcohol, it has been found that the solubility of the deacidifying agents mentioned above is much higher than that it was according to the aforementioned technique, which makes it possible to carry out a more effective impregnation consequently of the treated paper. The present invention also makes it possible to use certain active agents which have not previously been usable because of their low solubility in pure carbon dioxide at supercritical pressure.

In a variant implementation of the invention, the efficiency of this deacidification operation is improved by making the phase during which the fluid at supercritical pressure is brought into contact with the documents to be treated at a given pressure, a decompression phase which causes the precipitation of the deacidification agent in the porous material constituted by the paper documents, and a rapid recompression phase. These phases can be repeated several times to carry out several identical cycles. The following phases will therefore preferably be carried out: - Contacting the deacidification agent solution in the fluid at supercritical pressure with the documents to be treated, either in static mode, or more favorably by continuous percolation of this solution, - Decompression resulting the precipitation of the deacidification agent in the documents,

- Rapid recompression by adding fluid without deacidification agent, to restore solution of the fraction precipitated outside the document,

- New phase of bringing the deacidification agent solution into contact with the high pressure fluid, favorably by continuous percolation of this solution.

As can be seen in the examples which will be described later, it is thus possible to bring the pH of the paper documents to a value greater than 7, and thus to constitute an alkaline reserve forming a buffer which will preserve the documents against future re-acidification.

Furthermore, it has been found by analyzes carried out with a scanning microscope that by using a fluid at supercritical pressure according to the invention, the homogenization of the impregnation of the documents is improved, in particular in the thickness direction.

The present invention also makes it possible to reinforce the documents processed. One of the difficulties of this operation resides in the fact that it calls for the introduction into the cellulose fibers of the documents treated with a reinforcing agent which does not however have to stick together the various sheets of the documents. We have proposed, in patents GB-A-2,156,830 and

US-A-4,724,158, to impregnate the documents with an acrylic monomer which is then polymerized in situ by irradiation by means of γ rays. Such a method is however complex and costly to implement. According to the present invention, a fluid at supercritical pressure is used as the carrier fluid for transporting within the paper a reinforcing agent. The fluid at supercritical pressure can be formed from a gas alone or, preferably, from the mixture of a gas and an alcohol and in particular ethanol.

The reinforcing agent can belong to several families of polymers which are soluble in dioxide. carbon at supercritical pressure. We note in particular:

- Polyethylene glycols whose molar mass is between 0.2 kg and 0.6 kg, - Silicones whose molar mass is between 0.5 kg and 50 kg and in particular polydimethylsiloxane and polymethylphenylsiloxane,

- Functionalized silicones of the same nature and of the same molar masses as the previous ones, but the chain ends of which are functionalized to facilitate their chemical attachment to the cellulose fibers, for example by functions which will react easily with the hydroxyl functions of the cellulose, such as, for example, 3-isocyanatopropyltriethoxysilane, - Cellulose derivatives, from which one will favorably choose those which may have substantial solubility in a fluid at supercritical pressure obtained from a mixture of carbon dioxide added from 5% to 15 % by mass of an alcohol such as ethanol. In particular, ethyl cellulose, hydroxypropylmethylcellulose, methylcellulose and hydroxypropylcellulose will be used.

The implementation of the strengthening step is comparable to that of deacidification. It will also be possible, in certain cases, to carry out these two operations concomitantly by dissolving in the fluid at supercritical pressure the two deacidification and reinforcement agents respectively, then by impregnating the documents in the manner described above. However, it is sometimes preferable to carry out these two stages successively, in order to optimize their implementation separately, in particular the pressure for dissolving and impregnating the documents with the solution at supercritical pressure, and the drop in pressure causing precipitation of the reinforcement or deacidification agent in the heart of the paper constituting the documents. In addition, certain treatment agents have both deacidification and reinforcement functions. This is thus the case with modified silicones such as polydimethylsiloxanes or polymethylphenylsiloxanes, the hydroxyl ends of which are substituted by an alkali or alkaline earth metal, favorably by magnesium, calcium or barium, the chain of said silicone polymer having a mass average molar of between 0.5 kg and 5 kg, these compounds having both a deacidification power by release of a strong base during the hydrolysis occurring after impregnation of the paper and a reinforcing power in the same way as the previous silicones. According to the invention, the efficiency of the process can be improved, both with regard to the deacidification step and the strengthening step, by carrying out several successive impregnations. To do this, a counter-current can be produced between several batches of documents and the impregnation solution constituted by the mixture of the fluid at supercritical pressure and one or more active agents.

The present invention makes it possible to carry out at the end of the treatment process a step of "stripping" of the treated documents in order to eliminate from them the deacidification and reinforcing agents which have precipitated outside the pore volume of the treated document. It is understood that such an operation must be carried out under conditions making it possible, on the one hand, to dissolve in the fluid at supercritical pressure the treatment agents which are outside the pore volume without, however, extracting from that the treatment agents who precipitated it. To do this, a fluid at supercritical pressure consisting of a mixture of carbon dioxide and alcohol in proportion of 1% to 15% by mass at a pressure between 8 MPa and 50 MPa and at a temperature between 20 ° C and 80 ° C. In order to avoid re-extracting agents from deacidification and reinforcement which permeate the treated document, the quantity of fluid at supercritical pressure used may be reduced if necessary to bring it to a value lower than that used at the start of treatment, and in particular around 10 kg to 40 kg of fluid per kilogram of documents processed.

It is also possible, according to the invention, to complete the treatment with a second "stripping" phase in which carbon dioxide, without the addition of alcohol, is used as the fluid at supercritical pressure, at a pressure and at a temperature. identical to the previous ones. This operation eliminates the traces of alcohol present in the documents processed. For this last treatment step, a low level of solvent, between 2 kg to 20 kg of fluid per kilogram of documents, is sufficient.

The present invention also relates to a solvent intended for the treatment of paper documents characterized in that it consists of a fluid at supercritical pressure obtained from a mixture of a gas with 1% to 20% by mass of an alcohol.

Advantageously, the gas consists of carbon dioxide, and the alcohol consists of ethanol.

The present invention also aims to propose an installation allowing the implementation of the treatment method described above. An original feature of the installation according to the invention is that the documents remain, during the various processing steps, inside the same processing enclosure. Interestingly, the documents are arranged on supports made, for example, of metal cloths, so as to promote the circulation of the treatment fluid and the penetration of the latter inside these documents. Preferably, the enclosures are cylindrical in shape and the fluid is distributed at several levels thereof and preferably along the axis of the cylinder of the enclosure, either by using a fluid supply pipe pierced with holes or is made of a sintered material allowing the fluid to pass along the axis, or of distribution rings which are distributed on several levels in the enclosure or finally of any device avoiding making "short -circuits "from the fluid to the outlets which are preferably located at the periphery of the enclosure.

The present invention also relates to an installation for processing paper documents using a solvent consisting of a fluid at supercritical pressure obtained from the mixture of a gas with 1% to 20% by mass of an alcohol. , this fluid possibly being the vector of at least one treatment agent, characterized in that it comprises at least one treatment enclosure provided with means for receiving the documents to be treated, with means for supplying at least solvent, switching means capable of controlling the admission and expulsion of said solvent into the enclosure according to a desired processing mode, so that the documents can undergo the entire processing in the same enclosure.

The present installation can comprise several treatment enclosures containing documents to be treated which are arranged in cascade and which are successively traversed at least by said fluid at supercritical pressure, so as to constitute a treatment against the current.

An embodiment of the present invention will be described below, by way of non-limiting example, with reference to the appended drawing in which:

The single figure is a schematic view of a treatment installation according to the invention.

The processing method according to the invention was applied to a series of paper documents which were placed in an autoclave so as to be subjected to a first stage, or extraction stage, during which they underwent the action of a fluid at supercritical pressure obtained from a mixture consisting of 90% by weight of carbon dioxide and 10% by weight of ethanol, this mixture being brought to a pressure of 10 MPa and to a temperature of 45 ° C.

The documents used for this extraction step are designated from I to VII in Table I below, on which the characteristics of these documents have also been recorded,

TABLE I

It is noted that after percolation of 34 kg of fluid at supercritical pressure per kilogram of documents, the mass loss of the documents is between 2% and 4.6%. Additional measurements have shown that the extraction product is composed of organic products (0.3% to 2.3% of the mass of documents) and water, 15% to 40% of the water present in the documents thus being extracted. Surprisingly, it will be noted that this extraction is accompanied by a significant increase in the pH values of the various documents and, what is even more surprising, improvements, admittedly variable depending on the paper, in their mechanical properties, as specified below.

The pH measurements were carried out hot according to French standard NF Q03-005, the maximum tensile strength measurements before rupture are obtained on five to ten samples of 15 mm in width and 50 mm in length at a speed of 5 mm / min extension. Double-ply measurements are performed on a Lorentzen & Wettre device on a minimum of ten samples per test.

The results of the tests carried out on the paper documents mentioned above have been grouped in Table II below.

TABLE II

La résistance maximale à la traction avant rupture, qui renseigne sur la solidité des feuilles à l'arrachement, est améliorée pour la plupart des types de papiers. Le nombre de double-plis, qui est caractéristique de la souplesse de la feuille, est également augmenté considérablement dans la majorité des cas .

The maximum tensile strength before rupture, which provides information on the strength of the sheets when torn off, is improved for most types of paper. The number of double folds, which is characteristic of the flexibility of the sheet, is also increased considerably in the majority of cases.

Regarding the reduction of acidity, the average increase in pH is 0.4 units. It was noted that the extracts collected during this stage have pH values between 4 and 5. One can reasonably assume that this is the extraction of organic acids initially present in the paper or resulting from its degradation over time. We also note that the seven works thus treated no longer give off the characteristic smell of "old books" and that the improvement in the appearance of the leaves is obvious, especially on the edges of the pages where the usual yellow / brown color has partially disappeared.

Furthermore, it has been demonstrated that such a treatment has an antifungal effect. To highlight this, we seeded, with cellulolytic fungi of the genera Trichoderma and Chaetomium, (standard NF T 72-101) a sample of 10 g of paper which was then subjected to the following treatment:

Extraction with 1 kg of fluid at supercritical pressure according to the invention at a pressure of 30 MPa, - Rapid decompression up to 10 MPa, - Decompression to atmospheric pressure.

Samples taken from the treated sample were cultured according to standard NF T 72-101 and observations made 3, 6 and 10 days after seeding showed a non-development of the fungal strains.

The first extraction step is optionally followed by a second step, or deacidification step.

An example of such a deacidification step will be described below, in which an active deacidification agent of magnesium ethylmethyl carbonate (designated by EMC in the text below) is used. dissolved in absolute ethanol and which is injected into a stream of a fluid at supercritical pressure consisting of a mixture of carbon dioxide and ethanol which is brought to a pressure of 30 MPa and to a temperature of 45 ° C and of which the composition is identical to that of the fluid used in the extraction step.

In the present example of implementation of the invention, the impregnation necessary for the deacidification stage is carried out by a kind of "niche modulation", that is to say a treatment carried out in three phases, namely a first phase during which the enclosure containing the paper documents to be treated by the EMC agent is filled at high pressure, of the order of 30 MPa, a second phase during which the enclosure is isolated and decompresses around 20 MPa, and a third phase during which the pressure inside it is increased to a value close to the initial pressure, namely of the order of 30 MPa. The cycle of these three phases is resumed several times during the treatment, eight times in this case. In this mode of implementation, an amount of 90 kg of EMC agent was used per tonne of documents to be treated, and an amount of 80 kg of carbon dioxide-ethanol mixture per kilogram of documents to be treated.

The results obtained are recorded in Table III below:

TABLE III

It can be seen that an increase in the pH of the documents treated is thus obtained, beyond the neutrality value for six documents out of the seven treated. It is also noted that this mode of implementation makes it possible to constitute an alkaline reserve intended to play a role of buffer, making it possible to limit any increase future acidity of documents. The pH measurements were carried out hot according to standard NF Q03-005, and the alkaline reserve is expressed as a percentage by mass of calcium carbonate equivalent evaluated according to standard ISO / TC 6N822.

It is noted that the impregnation protocol by "modulation in slots" of the pressure, as described previously, allows an average increase in pH of 2.85 units as well as a satisfactory incorporation of the active deacidification agent until heart of the cellulosic matrix of paper documents. It has in fact been observed, by observation by scanning electron microscopy of the documents treated, that the treatment method according to the invention makes it possible to obtain a constant content of alkaline agent from one side to the other of the sheet of documents. , and this without decrease in the center of it.

Furthermore, in Table IV shown below, the treatments carried out respectively by the methods according to the prior art using a fluid at supercritical pressure and by the method according to the present invention using a mixture of gas and alcohol at supercritical pressure. It should be noted that, in this table, the alkaline reserve is expressed as a percentage by mass of calcium carbonate equivalent according to ISO / TC6N822 standard.

It can be seen from this table that the total quantities of carbon dioxide used for a complete processing of paper documents according to the two methods are substantially identical. It is also noted that the quantity of active agents, namely the EMC agent, necessary for the complete deacidification of paper documents, is notably reduced in the process according to the invention, which represents a saving of 30% compared to the amount used in the prior art. So the following process the invention not only is more effective in terms of treatment but on the other hand makes it possible to achieve a very substantial saving in the cost of treatment, when it is known that the active agent EMC alone represents, on the one hand significant cost of overall document processing.

TABLE IV

It is also noted that the method according to the invention makes it possible to produce a much greater alkaline reserve than the method according to the prior art.

The treatment method according to the invention can also include a strengthening step during which a product intended to improve their mechanical resistance is introduced into the cellulose fibers to be treated.

As mentioned previously, it is known that such a reinforcement step is particularly difficult to implement since it is necessary to impregnate the paper with a treatment agent making it possible to re-agglomerate the cellulose fibers without as much paste between them the sheets of the document. It is possible, according to the invention, to use a polymer which, after having been dissolved in a "vector" fluid, will be deposited by impregnation in the paper documents. According to the invention, the carrier fluid consists of a fluid at supercritical pressure obtained from a mixture of carbon dioxide and alcohol.

In the example used by the applicant, four reinforcing agents were used, namely: - PEG agent consisting of polyethylene glycol with an average molar mass of 0.2 kg,

- MePhSi agent consisting of methylphenylsilicone consisting of 50% methyl radicals and 50% phenyl radicals with an average molar mass of 4 kg, - HPC agent E consisting of hydroxypropylcellulose type E with an average molar mass of 80 kg,

- Agent HPC L consisting of hydroxypropylcellulose type L with an average molar mass of 95 kg.

Each of these four reinforcing agents was made to act on documents II and VII of table I.

The reinforcing agent in solution in ethanol was injected into a supercritical fluid of composition identical to that of the fluid used during the extraction step. 1 g of each reinforcing agent was used per kilogram of documents to be processed.

The variations in the essential mechanical characteristics of the paper documents are shown in Table V below, namely the number of double plies and the maximum tensile force before rupture. These variations are respectively denoted Δ double-ply and Δ traction.

TABLE V

Ces mesures ont été effectuées sur des documents II et VII qui ont subi, préalablement à l'étape de renforcement, un traitement d'extraction réalisé dans des conditions identiques à celles décrites précédemment. La mesure du nombre de double-plis a été réalisée sur un appareil Lorentzen & Wettre sur un minimum de 10 échantillons par test, et la mesure de la résistance maximale à la traction avant rupture a été effectuée sur 5 à 10 échantillons de papier de 15 mm de largeur et 50 mm de longueur à une vitesse d'allongement de 5 mm/min. Avec les agents de traitement cités on obtient des améliorations similaires sur tous les autres types de papiers traités.

These measurements were carried out on documents II and VII which underwent, prior to the strengthening step, an extraction treatment carried out under conditions identical to those described above. The measurement of the number of double-plies was carried out on a Lorentzen & Wettre device on a minimum of 10 samples per test, and the measurement of the maximum tensile strength before rupture was carried out on 5 to 10 paper samples of 15 mm wide and 50 mm long at an extension speed of 5 mm / min. With the processing agents mentioned, similar improvements are obtained on all the other types of paper treated.

According to the invention, it is also possible to use several reinforcing agents simultaneously. Such an embodiment will be described below, in which the reinforcing agents PEG and MePhSi have been made to act, after they have been dissolved in a fluid at supercritical pressure identical to that used in the previous example, on the documents I, II, III, IV, and VII of Table I. The two reinforcing agents were mixed in an ethanolic solution, at a rate of 5% of polyethylene glycol for 1% of methylphenylsilicone. The measurement methods used were the same as in the previous example and the results were reported in Table VI below.

TABLE VI

On a également réalisé un traitement de renforcement avec un autre couple d'agents de renforcement, à savoir l'agent PEG et un autre agent le MeCel, qui est constitué de méthylcellulose. On a ainsi utilisé une solution éthanolique à 5% de PEG et 1% de MeCel, suivant un protocole identique à celui mis en oeuvre dans l'exemple précédent. Les résultats obtenus sont consignés dans le tableau VII ci-après.

A reinforcing treatment was also carried out with another pair of reinforcing agents, namely the agent PEG and another agent MeCel, which consists of methylcellulose. So we have used an ethanolic solution containing 5% PEG and 1% MeCel, according to a protocol identical to that used in the previous example. The results obtained are reported in Table VII below.

TABLE VII

The treatment process may include a final step in which a “stripping” of the documents having undergone deacidification and reinforcement treatment is carried out, and which has the aim of eliminating the deacidification and reinforcement agents which have precipitated outside the pore volume of the processed document. It will be understood that such an operation must be carried out under conditions which allow on the one hand to dissolve the external treatment agents in the fluid at supercritical pressure and on the other hand not to extract the treatment agents which have precipitated within paper. The "stripping" operation is usually carried out in two phases. A first phase consists of processing paper documents using a fluid at supercritical pressure made from a mixture of carbon dioxide and alcohol, at a pressure of the order of 8 MPa to 50 MPa and more favorably between 10 Mpa and 30 MPa, at a temperature between 20 ° C and 80 ° C. The alcohol used to constitute the fluid at supercritical pressure is preferably ethanol, but it can also be constituted by methanol, propanol or isopropanol. The proportion of this alcohol in the fluid at supercritical pressure is of the order of 1% to 15% by mass. In order to avoid extracting the deacidifying and reinforcing agents which impregnate it from paper, the quantity of fluid at supercritical pressure will be limited to a value of approximately 5 kg to 50 kg of fluid per kilogram of documents processed.

The second phase of the "stripping" operation consists in treating the paper documents with a fluid at supercritical pressure consisting of pure carbon dioxide. The main purpose of this phase is to remove traces of alcohol from the documents processed. To do this, it is preferable to use a quantity of fluid at a lower supercritical pressure than previously and comprised between approximately .2 kg and 20 kg of fluid per kilogram of documents to be processed.

Finally, by way of example, a complete treatment was carried out comprising each of the different treatment stages described above, on samples of documents II, III, IV and VIII, the characteristics of which are defined in Table I.

This treatment thus includes:

- An extraction step at a pressure of 10 MPa, with a solvent consisting of a fluid at supercritical pressure consisting of a mixture of carbon dioxide with 10% by mass of ethanol. The rate of solvent that has been used is 30 kg per kilogram of paper,

- A simultaneous deacidification and reinforcement step with the deacidification agent EMC in solution in ethanol and the mixture of reinforcing agents PEG (lg per kilogram of paper) and MePhSi (lg per kilogram of paper) also in solution in ethanol, - A final stripping step in two phases, namely a first phase in which a fluid at supercritical pressure is made to act on the paper documents, made from a mixture of carbon dioxide with 10% mass of ethanol, under a pressure of 30 MPa, with a solvent content of 10 kg of fluid per kilogram of documents and a second phase in which a supercritical pressure fluid made up of dioxide is acted on the documents pure carbon, at a pressure of 30 MPa with a solvent content of 15 kg of carbon dioxide per kilogram of documents. The measurements were carried out under conditions identical to those carried out previously. The results of this treatment are recorded in Table VIII below.

TABLE VIII

On constate que les améliorations obtenues par un tel traitement, à savoir augmentation du pH, création d'une réserve alcaline, assouplissement et consolidation des feuilles traitées sont particulièrement sensibles comme en attestent les valeurs consignées dans ce tableau.

It is noted that the improvements obtained by such a treatment, namely increase in pH, creation of an alkaline reserve, softening and consolidation of the treated leaves are particularly sensitive as evidenced by the values recorded in this table.

The implementation of the various steps for processing the paper documents described above can advantageously be carried out in an installation as described below. This installation consists of a series of cylindrical autoclaves with vertical axis, five in the embodiment shown in the figure, which are referenced from A1 to A5. The autoclave A1 has a pipe 1 for admitting a fluid at supercritical pressure and an outlet pipe 3, which is joined to the inlet 4 of the autoclave A2. In this pipe 3 open two pipes, namely a pipe 5 for admitting a deacidification agent and a pipe 7 for admitting a reinforcing agent. The output 9 of the autoclave A2 is joined by a pipe 11 to the inlet 13 of the autoclave A3 and the outlet 15 thereof is joined, by a pipe 17, to the inlet 19 of the autoclave A4. The outlet 21 thereof is provided with a pipe 23 which connects it to separators.

The documents to be processed are loaded into the autoclaves and the processing phases are carried out successively in them. The originality of the installation resides in the fact that the documents do not undergo any displacement from one autoclave to another during the various stages of treatment. This preserves the documents which are most often of the greatest fragility.

Favorably, said documents are installed inside the autoclaves on supports, made of metal fabrics promoting the circulation of the fluid in order to facilitate the penetration of the fluid between the pages, said documents are favorably arranged vertically and not stacked one on the other. the others horizontally. The fluid is preferably distributed on several levels of the autoclave, and very favorably along the axis of the cylinder of one autoclave.

The present form of implementation makes it possible to produce a sort of counter current between the fluid and the documents, not by moving the documents from one autoclave to the other, but by simulating this movement by the judicious operation of valves, as is commonly used in so-called simulated moving bed chromatographic processes or in extraction processes treating solid charges.

The implementation of a treatment process comprising all of the steps described above will be described below, the deacidification and reinforcement steps being carried out concomitantly, and the stripping step being carried out in two phases.

The figure schematically represents the state of the five autoclaves at a given time in a step of treatment. As will be explained below, the autoclave connections will be different in the next step. In the configuration shown in the figure, the fluid at high supercritical pressure according to the invention (carbon dioxide + alcohol) is introduced into the autoclave Al containing documents having already undergone the stages of extraction, deacidification and reinforcement, thus carrying out the first phase of the final stripping step. The fluid leaving the autoclave A1 is supplemented with at least one deacidification agent through line 5 and at least one reinforcing agent through line 7. Also introduced into autoclace A2, through line 1 *, a supplement of fluid at high supercritical pressure, of the order of 30 MPa, then the assembly is sent, via line 3, to the autoclave A2 which contains documents having already undergone an extraction step and a first phase of deacidification and reinforcement. In the autoclave A2, the second phase of the deacidification-reinforcement stage is carried out. The fluid from this autoclave is then sent to the autoclave A3, via line 11, under the same pressure and temperature conditions, this autoclave containing documents having already undergone the extraction step. In this autoclave A3, the first phase of the deacidification / reinforcement step is carried out. The fluid from the autoclave A3 is sent to the autoclave A4 via the line 13. This fluid is at the pressure where the deacidification and reinforcing agents are precipitated in the fibers of the documents. This fluid is used to carry out in the A4 autoclave the extraction step on the documents contained therein and which have not yet undergone treatment.

It will be noted that, for the optimal implementation of the deacidification / reinforcement steps, as has been described above, the injection of fluid at supercritical pressure containing no agents of deacidification and strengthening is necessary at certain times in the treatment cycle.

When the quantities of fluid and treatment agents necessary for the optimal realization of the four stages have been used, the configuration of the installation is changed. To do this, the autoclave A1 is isolated, then decompressed to atmospheric pressure, so that the documents processed can be recovered and replaced by a new batch of documents to be processed.

The autoclave A2 then undergoes the stripping operation and is therefore connected, as was the autoclave Al during the previous cycle. The autoclave A3 undergoes the second phase of deacidification and reinforcement and is therefore connected, as was the autoclave A2 during the previous cycle. The A4 autoclave underwent the first deacidification and reinforcement phase and is therefore connected as was the A3 autoclave during the previous cycle. The autoclave A5, loaded with documents which have not yet undergone any treatment, is subjected to the extraction operation and is therefore connected as was the autoclave A4 during the previous cycle.

One proceeds thus on. In the third cycle, the autoclave A2 is emptied and reloaded, the autoclave A3 is subjected to the stripping step, the autoclave A4 to the second phase of the deacidification and strengthening step, the autoclave A5 to the first phase of this step and the autoclave A1, with its loading of documents not yet processed, in the extraction step. Under these conditions we see that everything happens as if the fluid and the documents were flowing against the current.

This implementation is very favorable economically by reducing handling, and therefore labor, as well as the necessary flow rates of fluid at supercritical pressure, the processing times and the consumption of deacidification agents and enhancement. Such an implementation is also very favorable in terms of the quality of the treatment by reducing the always problematic handling of documents, the periods of exposure to the fluid under supercritical pressure, and therefore the possible damage caused to covers and certain inks, and limiting the deposition of agents reinforcement and deacidification on the pages or covers of documents.

Claims

1.- Process for processing paper documents, and in particular books, characterized in that it comprises a first step consisting in subjecting the documents to be treated to the action of a fluid at supercritical pressure, formed from the mixture of a gas with 1% to 20% by mass of an alcohol. 2.- Method according to claim 1, characterized in that the gas is carbon dioxide. 3.- Method according to one of claims 1 or 2, characterized in that the alcohol is ethanol. 4.- Method according to any one of the preceding claims, characterized in that it comprises a treatment step during which at least one deacidification and / or reinforcement agent is dissolved in the fluid at supercritical pressure and on puts this solution in contact with the documents to be processed, so that said solution permeates them. 5.- Method according to claim 4 characterized in that said step comprises an additional phase during which the pressure is rapidly reduced and then it is restored to the value of the initial pressure. 6.- Method according to claim 5 characterized in that the above-mentioned treatment step is repeated several times. 7.- Method according to any one of claims 4 to 6 characterized in that the deacidifying agent consists of an organometallic compound and in particular of magnesium alkylcarbonate. 8.- Method according to claim 7 characterized in that the deacidifying agent consists of ethylmethyl-magnesium carbonate. 9.- Method according to any one of claims 4 to 6 characterized in that the reinforcing agent is a polyethylene glycol. 10.- Method according to any one of claims 4 to 6 characterized in that the reinforcing agent is a silicone and in particular a polydimethylsiloxane or a polymethylphenylsiloxane. 11.- Method according to claim 10 characterized in that the reinforcing agent is a modified silicone such as polydimethylsiloxanes or polymethylphenylsiloxaneε whose hydroxyl endings are substituted by an alkali or alkaline-earth metal, favorably with magnesium, calcium or barium. 12.- Method according to one of claims 4 to 6 characterized in that the reinforcing agent is a functionalized silicone and in particular 3-isocyanatopropyltriethoxysilane. 13.- Method according to one of claims 4 to 6 characterized in that the reinforcing agent is a derivative of cellulose and in particular ethyl cellulose, 1 hydroxypropylmethylcellulose, methylcellulose or 1 hydroxypropylcellulose. 14.- Method according to any one of the preceding claims, characterized in that the treatment process ends with a "stripping" step comprising at least one phase in which the documents having previously undergone deacidification treatment and / or reinforcement by a fluid consisting of a mixture of gas and alcohol at supercritical pressure. 15.- Method according to claim 14 characterized in that the "stripping" step comprises a second phase in which said documents are treated with a fluid at supercritical pressure free of alcohol. 16. Solvent intended for the treatment of paper documents, characterized in that it consists of a fluid at supercritical pressure obtained from a mixture of a gas with 1% to 20% by mass of an alcohol. 17. Solvent according to claim 16 characterized in that the gas is carbon dioxide. 18. Solvent according to one of claims 16 or 17 characterized in that the alcohol is ethanol. 19.- Installation for processing paper documents using a solvent consisting of a fluid at supercritical pressure obtained from the mixture of a gas with 1% to 20% by mass of an alcohol, this fluid possibly being the vector of at least one processing agent, characterized in that it comprises at least one processing enclosure (A1, A2, A3, A4, A5) provided with means for receiving the documents to be processed, with supply means , at least in solvent (1,1 ′, 5,7), of switching means able to control the admission and the expulsion of said solvent into the enclosure (A1, A2, A3, A4, A5) according to a mode processing, so that the documents can undergo the entire processing in the same enclosure. 20.- Installation according to claim 19 characterized in that it comprises several treatment chambers (Al, A2, A3, A4, A5) containing documents to be treated which are arranged in cascade and which are successively traversed at least by said fluid at supercritical pressure, so as to constitute a counter-current treatment.