Physical recycling of silicified paper

Abstract

A method for physical reuse of silicified paper is described, the method comprising at least the following steps; a first step (a) of treating the at least one silicified paper by contacting the silicified paper with at least one alcohol and at least one alkali metal alkoxide under introduced heat without removing any appearing water from the reaction mixture, and then a second step (b) of removing the at least one desiliconized paper obtained from the first step (a) from the optionally pre-neutralized reaction mixture.

Description

Technical Field

[0001] The invention relates to the field of silicone and siliconized paper, and in particular to the physical recycling of siliconized paper. Background Art

[0002] In order to modify the surface of a sheet structure to produce a non-stick surface, for example, the silicone coating of certain sheet structures, more particularly paper and polymer sheet structures, is known practice. These are then referred to as siliconized sheet structures, i.e. a siliconized sheet structure is a sheet structure coated with silicone. Such silicone-coated papers or polymer films are available on the market and are used for a variety of end uses.

[0003] Silicone-coated papers, also referred to in the context of the present invention as siliconized papers, can be used, for example, as base papers for pressure-sensitive adhesive labels, self-adhesive films and tapes or as release papers for the production of PVC films. Such coated papers accumulate in large quantities at the manufacturers and users, and by far the largest proportion of such papers, after having completed their function, is sent to landfill or to thermal disposal, i.e. incineration. So far, only in exceptional cases has low-quality papers for packaging purposes been produced from these papers.

[0004] The importance of this topic for the goals of a circular economy is clear, for example from the work of M. The production data for 2008 and 2010 were obtained from PTS (Papiertechnische Stiftung) research report IGF_16407: "Development of a coating concept for producing silicone release papers using the multi-layer curtain coater technology" by H. Schmid at www.ptspaper.de. Page 6 of the report states that "In 2008, the global production of release paper was 33.7 billion square meters, which increased to 33.98 billion square meters in 2010. Of this, 52% in 2008 and 51.5% in 2010 were used for labels alone."

[0005] The prior art relates to various efforts to recycle silicone-coated paper. For example, the teaching of EP 0587000A1 claims a method for recovering silicone-coated paper by beating and reshaping the paper in a flotation deinking unit using a 10% strength sodium hydroxide solution, the method being characterized in that the beating is carried out in the presence of one or more salts of phosphoric acid esters of fluorinated alkanols. According to the teaching, the use of these external process aids is necessary to avoid typical problems in alkali recovery processes, such as poor pulp dissolution, incomplete resin dispersion, the formation of resin agglomerates and the associated risks of adhesion to drum surfaces and felts.

[0006] Another method for reusing silicone-coated, cellulose- and / or polymer-based carrier systems is claimed in EP 2542728 B1 by the company Reculiner (Belgium), but the method is only suitable for their use as material. Here, for example, silicone-coated release paper waste is used for cellulose fiber insulation (CFI), which is used in the construction sector for thermal and acoustic insulation. The release paper is treated, for example, with a flame retardant and then processed into lightweight sheets using specially developed equipment. The attached claims are cellulose fiber insulation materials obtained not from conventional waste paper (such as newspapers) but from such release paper, one of the most important advantages of which lies in the greater elasticity of the fibers it contains. This property is said to lead to better fixing, which means an increased resistance to possible sedimentation of the insulation material after it has been blown into the cavity wall. A further improvement on the part of the RecuLiner material is its increased fluidity, making it easier to apply, compared to conventional cellulose fiber insulation materials, which are preferably obtained from old newspapers.

[0007] WO2022 / 086456A1 teaches a method for deinking and desiliconizing paper products, comprising the steps of pulp screening and treating the paper with an aqueous solution comprising an alkylene glycol ether, sodium hydroxide, sodium silicate, hydrogen peroxide and a surfactant. According to the procedure of EP 0587000 A1, the silicone removal step is achieved using flotation so that silicone separated from the surface of the paper and printing ink are transported to the surface of an aqueous digestion solution by controlled introduction of air. The removed printing ink and removed silicone are then disposed of, for example, by incineration.

[0008] WO 2022 / 086456 A1 shows that the two-stage flotation process is only suitable for paper waste consisting mainly of used printing and writing paper, i.e. to an extent of 70% by weight or more, and silicone-coated paper to an extent of up to 30% by weight or preferably less, since otherwise there would be operationally disruptive mechanical blockages in the production line system of the paper processing plant. The multiphase aqueous digestion system here must be adjusted precisely with respect to the raw materials used and their effective concentrations in order to achieve good results in terms of printing ink removal and desiliconization. The residual silicone content of less than 100 ppm that can be achieved by the process under optimal conditions then allows the recycled paper to be used as printing paper.

[0009] EP 3885096 A1 describes a method for the physical recycling of siliconized sheetlike structures, in particular siliconized paper or siliconized polymer membranes, wherein the siliconized sheetlike structures are treated in a liquid digestion system comprising acetic anhydride and / or acetoxysiloxane and at least one Bronsted acid, optionally a solvent and preferably acetic acid. Desiliconization in this particular organic matrix is ​​carried out very efficiently, however, the use of Bronsted acids, in this case in particular sulfuric acid or an organic sulfonic acid, is always associated with the disadvantage of separating the desiliconized paper, namely that the desiliconized paper is more or less discolored after the liquid organic phase has been removed.

[0010] In view of the state of the art, there remains a fundamental need to provide an efficient desiliconization process which combines the advantages of efficient removal of silicone from paper coated solely with silicone, as disclosed in EP 3885096A1, for example, with the additional benefit of recovering a desiliconized paper carrier with as little discoloration as possible.

[0011] Likewise, it would be ideal if the desiliconization process could also offer the possibility of reusing the silicone components originating from the coating, with the result that the silicone-coated paper could be physically reused to a large extent.

[0012] In Zh.Obshch.Khim.1959,29,1528-1534 (Russian Journal of General Chemistry 1959,29,1528-1534), Vornokov and Shabarova describe the production of organoalkoxysilanes by cleavage of organosiloxanes with C4-C12 alcohols under alkaline conditions, using alkali metal hydroxides, alkali metal alkoxides or the alkali metal itself. The authors explain the reaction of organosiloxanes with alcohols as an equilibrium reaction, in which it is important to remove the water of reaction azeotropically from the reaction system or to use an inert water-insoluble solvent or preferably by adding a silicate (tetraalkoxysilane) as a dehydrating agent. If a dehydrating agent is not used, it is not possible to prepare alkoxysilanes derived from alcohols having a boiling point below 90° C. or to obtain high yields of alkoxysilanes. In contrast, this publication does not provide any solution for producing alkoxysiloxanes, since, as the skilled person will appreciate, in particular any remaining high-boiling tetraalkoxysilanes (e.g. tetraethoxysilane, bp 168° C.) and condensation products derived therefrom would require considerable separation and purification efforts.

[0013] The as yet unpublished European patent application with application reference number 22190105.1 describes a novel process for recycling waste silicones, for example old sprues and / or stamping scrap from silicone rubber production or discarded electronic scrap containing components / component groups of silicone seals, by chemical conversion thereof into alkoxysiloxanes, wherein the waste silicones are reacted thermally with alkali metal alkoxides and alcohols without removing any water present, and in a second step the reaction mixture resulting from this reaction is neutralized using a Brønsted acid, optionally with the addition of a solvent, and the solid components are then separated off, in particular by filtration and then the alkoxysiloxanes are separated off by thermal separation of the volatile compounds.

[0014] However, the recycling of siliconized sheet-like structures such as siliconized paper is not disclosed in said document.

[0015] Against this background, a particular object of the present invention is to provide a method for the physical recycling of siliconized paper, the purpose of which is to be able to recycle desiliconized paper with as little discoloration as possible. The particular object of the present invention is achieved by the subject matter of the present invention. Summary of the invention

[0016] The present invention provides a method for physical recycling of siliconized paper, comprising at least the following steps:

[0017] first step (a): treating at least one siliconized paper by contacting the siliconized paper with at least one alcohol and at least one alkali metal alkoxide under the introduction of heat, without removing any water present from the reaction mixture, preferably without using solvents which form azeotropes with water and / or without using other dehydrating agents,

[0018] And then,

[0019] Second step (b): removing the at least one desiliconized paper obtained from the first step (a) from the optionally pre-neutralized reaction mixture.

[0020] This therefore opens up a way to physically reuse the respective siliconized paper, which enables the desiliconized paper to be recovered with as little discoloration as possible.

[0021] The method according to the invention provides for the treatment of at least one siliconized paper. Siliconized papers that can be used in the method according to the invention also include, in particular, all siliconized papers known on the market. Paper and siliconized paper are both well known to the person skilled in the art. Paper is a sheet-like material known to the person skilled in the art, which can be produced in a manner known to the person skilled in the art, usually from a fiber material, such as, in particular, mechanical pulp, waste paper pulp and / or chemical pulp.

[0022] In the context of the present invention, siliconized papers are all papers with a silicone coating. These can be papers coated with silicone on one or both sides. Such siliconized papers are known to the person skilled in the art; they are commercially available and widely available on the market, for example as release papers or, for example, also as wrapping papers in food packaging.

[0023] The type of silicone coating is not critical and includes all silicone coatings known on the market and suitable for coating paper, in particular the established solvent-free or solvent-containing platinum-catalyzed systems, and UV-activated systems with free radical or cationic polymerization which are easy to process.

[0024] Preferably, the term "siliconized paper" in the context of the present invention refers to a paper which is silicone coated on one or both sides, wherein the silicone coating preferably fulfils the function of a release coating.

[0025] Therefore, preferred silicone coatings in the context of the present invention are release coatings made of silicone or silicone materials.

[0026] Anti-adhesive coatings made of silicone or silicone materials are known from the prior art and are described in the patent literature, for example in WO2020126655A1. They can be used, for example, in label laminates. They can preferably be used to protect adhesive surfaces from contamination or unwanted adhesion. For example, in particular in the case of paper, anti-adhesive coatings can be used to reduce the tendency of adhesive products to adhere to these papers.

[0027] Silicone coatings, preferably anti-adhesive coatings consisting of silicone or silicone materials, can be produced in a customary manner known from the prior art; they can preferably be prepared from one or more organosiloxanes by crosslinking.

[0028] The crosslinking can preferably be carried out via a hydrosilylation reaction between the compound having SiH groups and the ethylenically unsaturated compound, preferably in the presence of a catalyst, preferably thermally at relatively high temperatures, typically for example above 100°C.

[0029] For example, or preferably, the silicone coating can be prepared by crosslinking a silicone having ethylenically unsaturated free-radically polymerizable groups by means of high-energy radiation or thermal radiation in the presence of a suitable initiator or free-radical initiator.

[0030] The organosiloxanes that can be preferably used are, for example, silicones having ethylenically unsaturated free-radical polymerizable groups, such as (meth)acrylate-modified organosiloxanes. (Meth)acrylate-modified organosiloxanes are well known to those skilled in the art and are described in many patent specifications, such as US6211322 and US4978726.

[0031] Organosiloxanes, preferably (meth)acrylate-modified organosiloxanes, can be crosslinked three-dimensionally, preferably by free radicals, and can be cured thermally, for example, or under the influence of high-energy radiation, such as UV radiation or electron beams, preferably within a very short time, preferably with the addition of peroxides, preferably to give mechanically and chemically durable layers. In the case of using UV light as the radiation source, it is preferred that the crosslinking is preferably carried out in the presence of photoinitiators and / or photosensitizers, such as benzophenone, benzoin, α-hydroxyalkylphenone, acylphosphine oxide or derivatives thereof. Conventional photoinitiators are described, for example, in "A Compilation of Photoinitiators Commercially Available for UV Today" (K. Dietliker, SITA Technology Ltd, London 2002).

[0032] Neither the mere material utilization approach with cellulose- and / or polymeric siliconized carrier systems nor the above-described deinking approach with the use of external process auxiliaries (EP 0587000 A1) is used, thus for the first time the process of the present invention opens up new and previously unexplored possibilities for the physical recycling, preferably complete physical recycling, of siliconized papers, in particular cellulose-based siliconized release liner systems.

[0033] In the context of the present invention, a release liner is understood to mean a paper carrier which has the purpose of preventing premature adhesion of adhesive surfaces. These papers are coated on one or both sides with a silicone-based release agent. Release is understood to mean the separation of the coated paper carrier from adhesive materials, for example from self-adhesive labels.

[0034] In particular, the method according to the invention can be used to enable individualized recovery of valuable natural substances, preferably paper components, in particular cellulose, which have come into intimate contact with silicone materials.

[0035] Furthermore, the method according to the invention can also preferably additionally make it possible to reuse the coating silicone, in particular by chemically converting it into alkoxy-containing siloxanes and / or silanes. These compounds, optionally also in combination with other reactive silanes and / or silicones, can be further processed into a variety of valuable derivative silicone products. This is another very significant advantage of the present invention.

[0036] A major advantage of the present invention is that the silicone-coated paper emerges from the desiliconization step essentially white or without discoloration, so that nothing prevents its unlimited reuse in the papermaking field.

[0037] The method according to the invention and preferred embodiments of the method according to the invention will be described in more detail below.

[0038] The first step (a) of the process according to the invention provides for treating at least one siliconized paper by bringing it into contact with at least one alcohol and at least one alkali metal alkoxide under the introduction of heat.

[0039] This means that at least one alcohol together with at least one alkali metal alkoxide is allowed to act on the at least one siliconized paper to be treated under the introduction of heat, preferably under the introduction of mechanical energy. The at least one alcohol and the at least one alkali metal alkoxide are thus used together; in particular, the at least one siliconized paper is reacted by mixing together the at least one alcohol and the at least one alkali metal alkoxide under the introduction of heat.

[0040] Preferably, before the first step (a) is performed, the at least one siliconized paper may be optionally fragmented, for example, shredded with a cutting tool.

[0041] The first step (a) is for desiliconization of at least one siliconized paper, and thus at least one desiliconized paper is obtained from the first step (a). "Desiliconization" of siliconized paper means removing the silicone layer of the siliconized paper from the paper.

[0042] All of the at least one desiliconized paper obtained from the first step (a) is then removed from the optionally preneutralized reaction mixture in a second step (b).

[0043] That is, it is optionally possible, but not mandatory, to neutralize the reaction mixture before removing all of the desiliconized paper.

[0044] According to a very particularly preferred embodiment, the process according to the invention is carried out in step a) with addition of ethanol and potassium methoxide.

[0045] It is also applicable to the first step (a) to carry out the treatment without removing any water present from the reaction mixture.

[0046] Preferably, the first step (a) is carried out by introducing heat in a temperature range of 50° C. to 200° C., further preferably 80° C. to 180° C., in particular 80° C. to 120° C. This corresponds to a preferred embodiment of the present invention. The introduction of heat can be achieved by conventional methods known to those skilled in the art, in particular using a heating medium, for example via the reactor wall.

[0047] In the context of the present invention, alkali metal alkoxides are preferably understood to mean compounds of the following general formula:

[0048] [M + ][OR - ],

[0049] in

[0050] M is selected from Li, Na and K, preferably selected from Na and K

[0051] as well as

[0052] R is a straight-chain, branched or cyclic alkyl group, preferably having 1 to 10 carbon atoms, particularly preferably having 1 to 6 carbon atoms, very particularly preferably having 1 or 2 carbon atoms; according to a preferred embodiment of the invention, the at least one alkali metal alkoxide is therefore selected from the abovementioned compounds.

[0053] In the process according to the invention, at least one alkali metal alkoxide is used.

[0054] Particular preference is given to using potassium ethoxide, sodium ethoxide, potassium methoxide and / or sodium methoxide; potassium methoxide is particularly preferred.

[0055] Known methods for producing alkoxides include chlor-alkali electrolysis by the amalgam process, in which sodium amalgam is reacted with an alcohol [see, for example, Chemical and Engineering News 22, 1903-06 (1944)].

[0056] A further known method is the preparation of alkoxides, for example, from alkali metals and alcohols or from alkali metal hydroxides and alcohols. The production of alkoxides from alkali metals and tertiary alcohols is known, for example, from DE-23 33 634 (Dynamit Nobel) or from DE-26 12 642 (Degussa). The preparation of alkoxides from alkali metal hydroxides and tertiary alcohols is likewise known. The first variant of the method requires the use of expensive alkali metals, while the second variant from alkali metal hydroxides requires the removal of the water formed during the reaction by distillation, thus requiring a correspondingly high expenditure of heat.

[0057] Alkali metal alkoxides can also be prepared, for example, by electrolysis of salts, using electrolysis cells in which cation exchange membranes separate the electrode spaces, according to the teaching of DE-A-33 46 131. DE-42 33 191.9-43 describes a process by which alkali metal alkoxides can be produced from salts, for example, by electrodialysis.

[0058] Also described separately are processes for producing special alkoxides, for example alkoxides of higher and / or polyols.

[0059] It is known that alcohol salts of higher alcohols and / or polyols can be prepared in principle, for example, by transmutation, i.e. by replacing the alkoxy groups of lower alcohol salts ROM (wherein R and R' are alkyl groups of different carbon chain lengths and M represents a metal cation) by reaction with higher alcohols R'OH in a liquid reaction mixture under appropriate temperature and pressure conditions. In laboratory terminology, this reaction is also called "recooking".

[0060]

[0061] The position of the equilibrium depends on the acidity of the two alcohols, which decreases in the order methanol>primary alcohol>secondary alcohol>tertiary alcohol [RT McIver and JA Scott, J. American Chem. Soc., 96 (1973) 2706]. Therefore, it is said that the production of alcohol salts of secondary alcohols in this way is possible only in exceptional cases, while the production of alcohol salts of tertiary alcohols by alcohol exchange is completely unsuccessful ["Methoden der Organischen Chemie" (1963), volume 6 / 2, page 13]. However, DE-1 254 612 and DE-2726 491 (both Dynamit Nobel) also disclose the production of alcohol salts by reboiling higher alcohols. GB-1 143 897 (Metallgesellschaft) describes, for example, the reaction of monovalent alkali metal alcohol salts with C2-C18 alcohols or phenols containing up to 6 hydroxyl groups, wherein the solvent used is an excess of monohydric alcohols and / or hydrocarbons.

[0062] However, reboiling always leads to the formation of low-boiling alcohols ROH (for example methanol), which in some cases have to be removed from the reaction product mixture in order to isolate the desired alkoxide, optionally in addition to unconverted higher alcohols R′OH, thus with considerable thermal expenditure.

[0063] In addition to these thermal equilibrium shifts, EP 0 776 995 (B1) teaches, for example, a process for preparing alcohol salts under the action of an electric field, wherein an alcohol is converted into the desired alcohol salt by providing metal ions, which themselves originate from the electrochemical decomposition of another alcohol salt in an electric field; the formation and decomposition of the alcohol salt take place in chambers spatially separated by ion exchange membranes.

[0064] The at least one alkali metal alkoxide used in the first step (a) of the process according to the invention is preferably used in a total amount of 1-10% by mass, preferably 2-7% by mass, particularly preferably 3-6% by mass, based on the mass of all silicone used in the reaction, which corresponds to the mass of all silicone coating the at least one siliconized paper. This corresponds to a preferred embodiment of the present invention.

[0065] The process according to the invention is preferably carried out in the first step (a) at a temperature range of from 50° C. to 200° C., more preferably at a temperature range of from 80° C. to 180° C., further preferably at a temperature range of from 80° C. to 120° C., and over a period of preferably 1 to 12 hours, more preferably over a period of 2 to 8 hours, in each case preferably in the absence of a solvent. This corresponds to another particularly preferred embodiment of the present invention.

[0066] According to another preferred embodiment of the present invention, the at least one alcohol used in the first step (a) of the process according to the present invention is selected from linear, branched and cyclic C1-C10 alkanols, preferably methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, pentanol, hexanol, heptanol, octanol, nonanol and / or decanol, and / or their isomers, particularly preferably methanol and / or ethanol, in particular ethanol.

[0067] The at least one alcohol used in the first step (a) of the process according to the invention is preferably used in a total amount of 10-200% by mass, preferably 20-100% by mass, particularly preferably 30-80% by mass, based on the mass of all silicone used in the reaction, which corresponds to the mass of all silicones coated with the at least one siliconized paper. This corresponds to another particularly preferred embodiment of the present invention.

[0068] Ensuring good contact, in particular good mixing, of the at least one siliconized paper with the at least one alcohol and the at least one alkali metal alkoxide in the first step (a) of the process according to the invention is preferred and may have a preferably positive influence on the ease with which the dissolution process occurs.

[0069] Preferably, the reaction mixture obtained from the first step (a) and / or the at least one desiliconized paper removed in the second step (b) can be treated with at least one Bronsted acid. This corresponds to a further particularly preferred embodiment of the invention.

[0070] Preferably, the at least one desiliconized paper removed is treated with at least one Bronsted acid. This can be done in particular to neutralize the alkalinity on the surface of the paper, wherein the paper has been obtained from the reaction mixture of an alcoholic alkoxide solution.

[0071] For this optional treatment of the at least one desiliconized paper, preference is given to using at least one nonoxidizing Bronsted acid, particularly preferably at least one Bronsted acid diluted with water, the concentration of the diluted Bronsted acid in water preferably being 10 to 50% by weight, more preferably 15 to 40% by weight.

[0072] This can preferably be done in that at least one desiliconized paper, preferably one which has been shredded or which is present, for example, as a whole paper web, is brought into contact with the at least one Brønsted acid.

[0073] This optional treatment can be carried out, for example, in a conventional reactor, preferably in a reaction vessel with a stirrer, so that it results in contacting at least one desiliconized paper with at least one Bronsted acid. The liquid phase is then preferably separated from the desiliconized paper thus treated, and the paper is preferably subsequently washed with demineralized water, separated from the washing water phase and then preferably transferred to an industrial dryer, for example a drying oven, for dehumidification. Such an optional process corresponds to another particularly preferred embodiment of the present invention.

[0074] In the case of desiliconized paper present, for example, in the form of a paper web, in the context of a preferred embodiment of the present invention, the at least one desiliconized paper which is still alkaline on the surface can be subjected to an optional treatment, preferably in a roller mill, by first unrolling the desiliconized paper in question from a roll and drawing it through an impregnation bath of a Brønsted acid, preferably by subsequent washing with demineralized water, and then through a drying stage, preferably a drying oven, so that it is directed downstream of the impregnation bath in order to then be rolled up again on a roll. Such an optional process corresponds to a preferred embodiment of the present invention.

[0075] In the optional treatment with at least one Bronsted acid, the surface of the desiliconized paper wetted with the alcohol alkoxide solution undergoes neutralization, in particular to the extent that salt and alcohol are formed from the alkoxide and the acid.

[0076] In the optional treatment with at least one Bronsted acid, it is particularly preferred to use a Bronsted acid diluted with water, which is able to dissolve the resulting salt of the Bronsted acid and preferably ethanol or methanol of the alcohol type, which results from the preferably used potassium ethoxide, sodium ethoxide, potassium methoxide and / or sodium methoxide, in particular potassium methoxide. Particularly preferably used acids include diluted sulfuric acid (preferably 10-25% by weight in water), diluted perchloric acid (preferably 10-25% by weight in water), and / or diluted acetic acid (preferably 10-30% by weight in water).

[0077] As will be appreciated by those skilled in the art, oxidizing acids such as concentrated sulfuric acid, concentrated nitric acid, concentrated perchloric acid and concentrated sulfonic acid should be particularly avoided for direct treatment of desiliconized paper because these acids may result in at least color loss of dark pigmentations and even destruction of the paper due to oxidation of the cellulose in the paper.

[0078] Preferably, the reaction mixture separated from the at least one desiliconized paper is neutralized with at least one anhydrous Bronsted acid, which corresponds to another particularly preferred embodiment of the present invention. The at least one anhydrous Bronsted acid particularly suitable for the purpose is preferably selected from anhydrous inorganic acids and anhydrous organic acids, in particular from anhydrous sulfuric acid, anhydrous perchloric acid and anhydrous acetic acid. Such a procedure makes it possible to preferably obtain alkoxysiloxanes from the process according to the invention and corresponds to another particularly preferred embodiment of the present invention.

[0079] It also corresponds to a further particularly preferred embodiment of the present invention if, before removing the at least one desiliconized paper, the reaction mixture from the first step (a) is neutralized with at least one Bronsted acid, and this Bronsted acid is preferably selected from non-oxidizing Bronsted acids, particularly preferably Bronsted acids diluted with water, and in particular selected from dilute sulfuric acid, dilute perchloric acid and dilute acetic acid, and the concentration of the diluted Bronsted acid in water is preferably 10 to 50% by weight, more preferably 15 to 40% by weight.

[0080] Furthermore, it may be preferred to clean the at least one desiliconized paper obtained, for example to make it free of salts and acids. Thus, if the at least one desiliconized paper obtained is washed, preferably with demineralized water, preferably with demineralized water, this corresponds to a further particularly preferred embodiment of the present invention.

[0081] Furthermore, the desiliconized paper can preferably be dried. Thus, if at least one desiliconized paper, preferably a desiliconized paper treated with at least one Brønsted acid and particularly washed, is dried, preferably thermally and / or optionally dried by contacting it with at least one organic solvent, this corresponds to a further particularly preferred embodiment of the present invention.

[0082] The reaction in the first step (a) is carried out without removing any evolved water from the reaction mixture. No water is removed from the reaction mixture, preferably neither solvents which form an azeotrope with water nor other dehydrating agents are used.

[0083] If the treatment in the first step (a) of the process according to the invention is therefore carried out without the use of water-bound silicates, in particular without the use of tetraalkoxysilanes, this corresponds to a further particularly preferred embodiment of the invention.

[0084] According to another preferred embodiment of the present invention, the present invention can also be carried out using a rolling mill, if necessary, which preferably comprises unrolling the paper to be desiliconized from a roll so as to subject it to the first step (a) of the process according to the present invention, then removing it from the reaction mixture according to the second step (b) of the process according to the present invention, then preferably pulling it through a neutralization bath and a rinsing bath, and after passing through a drying zone on the other side of the rolling mill, preferably rolling up the desiliconized paper thus obtained again.

[0085] In the context of preferred embodiments, as described above, the present invention can provide for the optional use of at least one anhydrous inorganic acid. Where at least one anhydrous inorganic acid is actually used, its total addition amount is preferably calculated so as to achieve a stoichiometric equivalent based on the total alkoxide used.

[0086] In the context of a preferred embodiment, as described above, the present invention may provide for the optional use of at least one anhydrous organic acid. Where at least one anhydrous organic acid is actually used, it may be preferred to select a significant stoichiometric excess of the acid based on the total alkoxide used. This is preferably measured as a stoichiometric excess of at most 50%.

[0087] The amount of anhydrous organic acid used which may optionally be used in the context of the preferred embodiments should therefore preferably be chosen such that it is in the range from the stoichiometric equivalent to a 50% stoichiometric excess, based in each case on the total alkoxide used.

[0088] The amount of the Bronsted acid diluted with water which is optionally usable in the context of the preferred embodiment is preferably chosen so that it is in the range from the stoichiometric equivalent to a 50% stoichiometric excess, based in each case on the total alkoxide used.

[0089] For the possibility that the paper to be treated is a paper web, as is the case in the context of the preferred embodiment, the skilled person will appreciate that only a few exploratory preliminary tests are necessary in order to determine in a preferred manner the total amount of diluted Bronsted acid required to neutralize the paper web resulting from the second step (b) according to the invention. Since such paper webs removed from the reaction mixture in the context of this preferred embodiment are moistened only with an alcoholic alkoxide solution, the total amount of Bronsted acid diluted with water required for their alkoxide neutralization is naturally less than the total amount required to neutralize the alkoxide, which, according to another embodiment of the invention, is the amount required to neutralize the alkoxide in a mixture with desiliconized paper, preferably with shredded paper.

[0090] The use of at least one solvent should preferably be provided, in particular when the amount of salt expected from the optional neutralization step is present in an easily filterable form.

[0091] Suitable optional solvents which can be used in the optional neutralization step are preferably those which are chemically inert to the reaction system and promote the dilution or dispersion of the optional neutralization component. At least one optional solvent is preferably selected from alkanes, alkyl aromatic compounds and alcohols, particularly preferably from alkyl aromatic compounds, especially from toluene and xylene.

[0092] In the context of the present invention, in principle all silicones which are suitable for coating paper can be recycled.

[0093] According to a preferred embodiment of the invention, the method is performed by providing heat and / or preferably by introducing mechanical energy.

[0094] Preferably, in the context of the method according to the invention, the treatment of the siliconized paper is preferably carried out at between 50 and 200°C, more preferably between 80 and 180°C, in particular between 80 and 120°C.

[0095] According to another particularly preferred embodiment of the present invention, the first step (a) of the process according to the invention is carried out by introducing mechanical energy, which can be introduced in a conventional manner known to a person skilled in the art, preferably in the form of stirring energy or ultrasound.

[0096] On a production scale, it is preferred to use stirred reactors (stirred tanks) which are customary in chemical engineering.

[0097] Also suitable for introducing mechanical energy are preferably all devices which enable, for example, desiliconization of a paper web, in particular a paper web in the form of a roll, to be moved translationally through a mixture of at least one alcohol and at least one alkali metal alkoxide under introduction of heat, so that, for example, calenders can also be used successfully.

[0098] The process according to the invention can preferably be carried out at standard pressure (1013.25 hPa), at reduced pressure, or at elevated pressure, for example in order to achieve high heat treatment temperatures of up to 200° C. in a pressure-resistant apparatus.

[0099] The process according to the invention is preferably carried out at standard pressure, which corresponds to a particularly preferred embodiment of the invention.

[0100] According to another preferred embodiment of the present invention, the treatment of the at least one siliconized paper in the first step (a) may be carried out at a pressure greater than 1013.25 hPa.

[0101] If desired, the silanes and / or siloxanes which preferably have reactive alkoxy functions and are obtainable by the process according to the invention can be used again as adhesives and sealants, for example in the form of polymeric active substances, optionally also blended with other crosslinking silanes and / or siloxanes and unfilled and / or filled with fillers.

[0102] As is understood by the person skilled in the art, the respective type and chemical composition of the coating silicone used shapes the composition of alkoxy-containing siloxanes preferably obtained by the process according to the invention.

[0103] In the context of the present invention, the term "alkoxy-containing siloxanes" also relates in particular to substances which contain varying amounts of alkoxy-containing silanes or siloxanes, for example alkoxytrimethylsilane, dialkoxydimethylsilane, dialkoxytetramethyldisiloxane and the like.

[0104] Removing the desiliconized paper from the liquid phase can be done by conventional means, for example by filtration.

[0105] In the context of a preferred embodiment of the present invention, if, for example, the paper web to be desiliconized is treated by passing through a calender, in this case, the preferred separation of the liquid phase from the paper web in the sense of a pressing and squeezing operation can preferably already be achieved by setting a roll gap. It is preferably arranged directly downstream of the treatment bath to be passed, the treatment bath consisting of at least one alcohol and at least one alkali metal alkoxide. Such a process corresponds to a preferred embodiment of the present invention.

[0106] Further preferred embodiments of the method according to the invention are explained and / or illustrated in more detail below by means of examples.

[0107] In the context of a purely exemplary preferred embodiment of the method according to the invention, if, for example, 1.5 g of radiation-cured silicone / m 2 is applied on one side with stirring, 2Coating weight of paper support Siliconized yellowish blocky release paper is introduced into a matrix consisting, for example, of ethanol and potassium methoxide, heated, for example to gentle reflux for 4 hours and neutralized, for example with aqueous acetic acid, the solid components are separated by filtration, for example using a slot filter, washed with several portions of demineralized water until free of acid and salts and dried, for example by contact with ethanol, then a completely silicone-free white paper support can be obtained (see Example 1 of the invention), which has excellent water absorption and can be further processed to form all products obtained from cellulose recycling materials in the paper industry.

[0108] The desiliconization effect according to the invention, i.e. the detachment of the silicone layer from the paper carrier, can be demonstrated in the context of a further preferred embodiment of the invention preferably by infrared spectroscopy of the paper surface, since in the case of the paper desiliconized according to the invention the infrared spectroscopy at 1020 cm -1 and 1099cm -1 The positions of the bands characteristic of the presence of silicone are very significantly smaller than the corresponding bands of the siliconized paper at wave numbers between 3150 and 3750. Furthermore, the paper desiliconized according to the invention preferably exhibits the positions of the bands characteristic of water bound to the OH groups of cellulose at wave numbers between 3150 and 3750, whereas the siliconized paper has only relatively weak absorption at these positions.

[0109] In a further preferred embodiment of the invention, the digestion system consisting of at least one alcohol and at least one alkali metal alkoxide is contacted with the flake structure to be desiliconized not only once, but several times, in such a way that the concentration of alkoxy-containing siloxanes in the digestion system can be controlled. 29 Si NMR spectroscopy, for example also with the aid of viscosity measurements, can then characterize the alkoxy-containing siloxanes.

[0110] In the context of particularly preferred embodiments of the present invention, the chemical stripping of the silicone coating from the siliconized paper achievable according to the invention can preferably be even further promoted by preferably ensuring that the paper to be reused moves in a translational sense through a digestion system consisting of at least one alcohol and at least one alkali metal alkoxide during the thermal treatment.

[0111] According to this teaching, for example, in the context of another particularly preferred embodiment of the present invention, in the case of rolled paper, the invention can preferably also be implemented using a roll mill type arrangement, by, for example, stretching the paper to be desiliconized, which is wound into a roll, onto a roll mill, unrolling it, and pulling the unrolled paper through an immersion bath, which consists of at least one alcohol and at least one alkali metal alkoxide and has a controllable temperature. As is clear to the person skilled in the art, in such a preferred embodiment, the unwinding speed, the length of the immersion bath and the effective contact time of the carrier system obtained therefrom with the digestion system consisting of at least one alcohol and at least one alkali metal alkoxide, as well as the temperature and other parameters, will determine the efficacy of the desiliconization process in this case. If necessary, in such a preferred embodiment, for example, after passing through the digestion system, the paper can also preferably be pulled through a rinsing bath, and then optionally dried and rolled up again elsewhere on the roll mill.

[0112] As already mentioned further above, the process according to the invention preferably also enables the provision of alkoxysiloxanes. The alkoxysiloxanes obtainable according to the invention can preferably be used as starting material for polymerizing active substances and then preferably as sealants and / or adhesives with addition of suitable crosslinking catalysts, optionally also blended with further crosslinking silanes and / or siloxanes, optionally filled and / or unfilled with fillers and / or pigments.

[0113] The alkoxysiloxanes obtainable according to the invention are furthermore suitable, for example, as starting materials for producing SiOC-bonded polyethersiloxanes by transesterification with polyetherols in the presence of zinc acetylacetonate as catalyst, as disclosed in European Patent Application EP 3438158 (B1).

[0114] If, for example, a specific number-average siloxane chain length is desired prior to the optional further processing described herein, the alkoxysiloxanes obtainable according to the invention can preferably also be subjected to a downstream, preferably acid-catalyzed equilibration in order to establish the target chain length.

[0115] Likewise, as described in patent application EP 3663346 A1, it is preferably possible to convert the alkoxysiloxanes obtainable according to the invention into the corresponding siloxanes containing acetoxy groups, for example by reaction in a reaction medium comprising acetic anhydride, perfluoroalkanesulfonic acids (in particular trifluoromethanesulfonic acid) and preferably acetic acid, with continuous discharge of the corresponding acetates, and to use these likewise as reactive intermediates, for example for the production of SiOC-bonded polyether siloxanes or as starting materials for the polymerization of active substances.

[0116] The following embodiments are only used to further illustrate the present invention and do not constitute any limitation to the present invention. DETAILED DESCRIPTION

[0117] Example:

[0118] Infrared spectroscopy was used as a means to characterize the support surface. The measurements were performed on a Tensor27IR spectrometer from Bruker Optik GmbH equipped with a MIRacle from PIKE, a multi-crystal CRY ATR unit, and provided with an ATR crystal (Ge-Performance Crystal Plate), using OPUS 7.2 analysis software.

[0119] Embodiment 1 (present invention)

[0120] Desiliconization of Siliconized Release Paper

[0121] While stirring, first charge 100 g of ethanol and 5.0 g of potassium methoxide into a 500 ml four-necked round-bottom flask equipped with a precision glass paddle stirrer, an internal thermometer and an overhead reflux condenser. Then add 10.6 g of silicone release paper cut into pieces with a length of about 1 to 2 cm and a width of about 1 cm, and heat the mixture to reflux temperature (about 80° C.) for 4 hours.

[0122] The reaction mixture was cooled to 23° C., 100 ml of 25 wt % acetic acid were added with stirring and the mixture was allowed to stand for 30 minutes. The desiliconized paper was removed using a slot filter (MN 615) and rinsed with four 100 ml portions of demineralized water and finally with 50 ml of ethanol.

[0123] The white paper pieces thus separated were dried at 23°C overnight.

[0124] The surfaces of siliconized and desiliconized papers were characterized using infrared spectroscopy.

[0125] In the case of the paper desiliconized according to the invention, at 1020 cm -1 and 1099cm -1 At wave numbers between 3150 and 3750, the positions of the bands characteristic of the presence of silicone are very significantly smaller than the corresponding bands of the siliconized release paper. Furthermore, the release paper desiliconized according to the invention exhibits band positions between 3150 and about 3750 wave numbers, which are characteristic of water bound to the OH groups of cellulose, whereas the siliconized release paper has only relatively weak absorption at these positions.

[0126] The desiliconized paper absorbs water drops applied to its surface spontaneously and in a manner similar to absorbent paper, whereas the siliconized paper repels the water drops without any wetting at all.

Claims

1. A method for physical recycling of siliconized paper, comprising at least the following steps: first step (a): treating at least one siliconized paper by contacting the siliconized paper with at least one alcohol and at least one alkali metal alkoxide under the introduction of heat and without removing any water present from the reaction mixture, And then, Second step (b): removing said at least one desiliconized paper obtained from said first step (a) from the optionally previously neutralized reaction mixture.

2. The method according to claim 1, characterized in that The at least one desiliconized paper removed is treated with at least one Bronsted acid, preferably with at least one non-oxidizing Bronsted acid, particularly preferably with at least one Bronsted acid diluted with water, the concentration of the at least one Bronsted acid diluted with water preferably being 10 to 50% by weight, more preferably 15 to 40% by weight, very particularly preferably diluted sulfuric acid (preferably 10 to 25% by weight in water), diluted perchloric acid (preferably 10 to 25% by weight in water) and / or diluted acetic acid (preferably 10 to 30% by weight in water).

3. The method according to claim 1 or 2, characterized in that: The reaction mixture separated from the at least one desiliconized paper is neutralized using at least one anhydrous Bronsted acid, preferably selected from anhydrous mineral acids and anhydrous organic acids, in particular selected from anhydrous sulfuric acid, anhydrous perchloric acid and anhydrous acetic acid.

4. The method according to claim 1, characterized in that: Before removing the at least one desiliconized paper, the reaction mixture obtained from the first step (a) is neutralized using at least one Bronsted acid, preferably using at least one non-oxidizing Bronsted acid, particularly preferably using at least one Bronsted acid diluted with water, the concentration of the at least one Bronsted acid diluted with water preferably being 10 to 50% by weight, more preferably 15 to 40% by weight, very particularly preferably diluted sulfuric acid (preferably 10 to 25% by weight in water), diluted perchloric acid (preferably 10 to 25% by weight in water) and / or diluted acetic acid (preferably 10 to 30% by weight in water).

5. The method according to any one of claims 1 to 4, characterized in that Said at least one desiliconized paper obtained from said second step (b), preferably desiliconized paper treated with at least one Bronsted acid, is washed, preferably with demineralized water.

6. The method according to any one of claims 1 to 5, characterized in that The at least one desiliconized paper, preferably desiliconized paper treated with at least one Brønsted acid and in particular washed, is dried, preferably thermally and / or optionally dried by contacting it with at least one organic solvent.

7. The method according to any one of claims 1 to 6, characterized in that The first step (a) is performed by introducing mechanical energy, preferably in the form of stirring energy or ultrasound.

8. The method according to any one of claims 1 to 7, characterized in that The first step (a) is performed by introducing heat in a temperature range between 50°C and 200°C, preferably between 80°C and 180°C, in particular between 80°C and 120°C.

9. The method according to any one of claims 1 to 8, characterized in that The treatment in the first step (a) is carried out without the use of water-bound silicates, in particular without the use of tetraalkoxysilanes.

10. The method according to any one of claims 1 to 9, characterized in that The at least one alkali metal alkoxide used in the first step (a) conforms to the general formula [M + ][OR - ],in M is selected from Li, Na and K, preferably selected from Na and K, R is a linear, branched or cyclic alkyl group, preferably having 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, particularly preferably 1 or 2 carbon atoms, Preference is given to using potassium ethoxide, sodium ethoxide, potassium methoxide and / or sodium methoxide, in particular potassium methoxide.

11. The method according to any one of claims 1 to 10, characterized in that The at least one alcohol used in the first step (a) is selected from linear, branched and cyclic C1-C10 alkanols, preferably methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, pentanol, hexanol, heptanol, octanol, nonanol and / or decanol, and / or their isomers, particularly preferably methanol and / or ethanol, especially ethanol.

12. The method according to any one of claims 1 to 11, characterized in that The total amount of the at least one alcohol used in the first step (a) is 10-200% by mass, preferably 20-100% by mass, particularly preferably 30-80% by mass, based on the mass of all silicones used in the reaction, the mass of which corresponds to the mass of all silicones coated with the at least one siliconized paper.

13. The method according to any one of claims 1 to 12, characterized in that The total amount of the at least one alkali metal alkoxide used in the first step (a) is 1-10% by mass, preferably 2-7% by mass, particularly preferably 3-6% by mass, based on the mass of all silicones used in the reaction, the mass of which corresponds to the mass of all silicones coated with the at least one siliconized paper.

14. The method according to any one of claims 1 to 13, characterized in that The treatment in the first step (a) is performed for a period of 1-12 hours, preferably for a period of 2-8 hours.