Physical recycling of siliconized sheets

Abstract

The invention relates to the physical recycling of siliconized sheets. The method for the physical recycling of siliconized sheets comprises treating the siliconized sheets in a liquid digestion system comprising acetic anhydride and / or acetoxysiloxane and at least one Bronsted acid, optionally with a solvent, preferably with the addition of acetic acid, and removing the desiliconized sheets from the liquid phase.

Description

Technical Field

[0001] The present invention relates to the field of silicones and sheet-like, silicone-coated structures and more particularly to the physical recycling of such structures. Background Art

[0002] Silicone coating of certain sheet-like structures, more particularly both paper and polymer structures, is a known practice in order to modify the surface of the structure in order to produce, for example, a non-stick surface. Such silicone-coated paper or polymer films are commercially available for various end uses.

[0003] Papers coated with silicones are used, for example, as base papers for pressure-sensitive adhesive labels, self-adhesive films and self-adhesive tapes or as release papers for the production of PVC films. Such coated papers accumulate in large quantities both at the sites of manufacturers and users and, to date, after having fulfilled their function as base papers or release papers, the largest proportion of such papers has been sent to landfills or thermally disposed of (i.e. incinerated). To date, low-quality papers for packaging purposes have been produced from these papers only in exceptional cases.

[0004] The importance of this topic for the goals of the circular economy is shown, for example, in PTS (Papiertechnische Stiftung) Research Report IGF-16407, Development of a Coating Concept for Producing Silicone Release Papers Using the Multi-layer Curtain Coater Technology, M. and H. Schmid, www.ptspaper.de, production data for 2008 and 2010 are evident. Page 6 of the report states: "In 2008, global production of release paper was 33.7 billion square meters, which only 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] In addition to paper-based systems, polymer films, such as polyolefins and here more particularly monoaxially oriented polypropylene films (MOPP), biaxially oriented polypropylene films (BOPP) and polyester release films (PETP), are increasingly provided with silicone coatings.

[0006] MOPP systems are often used to protect adhesive surfaces, for example, in the linings of self-adhesive closures, but also in envelopes, pouches and cartons, as well as in the linings of self-adhesive cable ducts or in components assembled by automotive and smartphone manufacturers.

[0007] Polyester release films (PETP) equipped with silicone release systems are increasingly used in the electrical industry as release films for the pressing and molding of pre-impregnated insulated conductors, in the plastics industry as release films in the production of sheets from cast compounds, in the chemical industry as release films, which are siliconized on both sides, for packaging such as waxes and resins that exhibit adhesion and adhesive effects, and also as release films in the production of adhesive tapes, as well as in the rubber industry (as protection against adhesion in rubber manufacturing operations) and in the electronics industry as release films during the production of multilayer PCBs.

[0008] The prior art mentions various efforts to recycle silicone-coated paper. For example, the teaching of EP0587000 A1 claims a method for recycling silicone-coated paper in a flotation deinking plant, using a sodium hydroxide solution with a concentration of 10%, by beating and forming new paper, the method being characterized in that beating takes place in the presence of one or more salts of phosphoric acid esters of fluorinated alkanols. According to this teaching, it is necessary to use these special process aids in order to avoid the typical problems of alkali recycling operations, such as poor pulp dissolution, incomplete resin dispersion and the formation of resin agglomerates and the associated risk of sticking to the cylinder surface and felt.

[0009] Reculiner (Belgium) claims in EP 2542728 B1 another operation for recycling cellulose-based and / or polymer-based carrier systems coated with silicone, but this operation only adapts to their application as materials. Here, for example, waste release paper coated with silicone is used for cellulose fiber insulation, for thermal insulation and sound insulation in the construction industry. The release paper is treated with a flame retardant, for example, and then processed into lightweight sheets using a specially developed device. The accompanying claim is that one of the most important advantages of cellulose fiber insulation materials obtained not from conventional waste paper (e.g., newspapers) but from this type of release paper is that the fibers it contains have greater elasticity. This property is said to lead to better fixing, meaning that there is an improved tolerance to possible sinking of the insulation material after it is blown into the cavity wall. Compared with traditional cellulose fiber insulation materials, which are preferably obtained from old newspapers, a further improvement of the material of RecuLiner is said to be its increased flowability, which makes it easy to apply.

[0010] In the as yet unpublished European patent application with application number 19176869.6, a new process is described for recycling silicones, more particularly silicone rubbers and / or silicone oils, by chemically converting them into acetoxy-containing silanes and / or siloxanes, wherein the silicone to be recycled is thermally treated in a digestion system comprising acetic anhydride and / or acetoxysiloxanes and at least one Brønsted acid, preferably with the addition of acetic acid.

[0011] However, there is no disclosure of recycling of sheet-like siliconized structures, such as siliconized release papers and siliconized polymer films, respectively. Summary of the invention

[0012] Against this background, it is an object of the present invention to provide a method for the physical recycling of sheet-like siliconized structures, more particularly siliconized paper or siliconized polymer films.

[0013] The inventors have surprisingly found that the process described in the as yet unpublished European patent application with the application number 19176869.6 also allows the recycling of silicones applied as release coatings to sheet-like structures such as cellulose-based supports (paper, etc.) and polymer films, such as polyolefins, and more particularly among them uniaxially oriented polypropylene films (MOPP) and biaxially oriented polypropylene films (BOPP) and polyester release films (PETP). Thus, in this way the path to the physical reuse of various sheet-like siliconized structures is opened up.

[0014] A subject of the present invention is therefore a method for the physical recycling of sheet-like siliconized structures, more particularly siliconized paper or siliconized polymer films, comprising at least the following steps:

[0015] a) treating the flaky siliconized structure in a liquid digestion system comprising acetic anhydride and / or acetoxysiloxane and at least one Bronsted acid, optionally with a solvent, preferably with the addition of acetic acid,

[0016] b) Removal of the desiliconized platelets from the liquid phase.

[0017] The silicone coatings to be collected by the method according to the invention include not only all silicone coatings known on the market, in particular the established solvent-free or solvent-containing platinum-catalyzed systems, but also the easily processable UV-activated systems using free radical or cationic polymerization. For the purposes of the present invention, the flaky siliconized structures are in particular silicone-coated papers or polymer films.

[0018] By avoiding the approach of mere material application and deinking using special process aids (EP 0587000 A1) and operating on cellulose-containing and / or polymeric siliconized carrier systems, the method according to the invention offers for the first time new, previously unexplored opportunities for the complete physical recycling of sheet-like siliconized structures, such as in particular siliconized release liner systems.

[0019] More particularly, the process of the invention allows the separate recovery of valuable natural substances (such as cellulose) and synthetic polymers (such as polypropylene) that have come into intimate contact with the organosilicon material.

[0020] It also allows the recycling of the coated silicone by chemically converting them into acetoxy-containing silanes and / or siloxanes. 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 a very important advantage of the present invention.

[0021] For example, European patent applications EP3611214A1, EP3611216A1, EP3611217A1, EP3611215A1 and the as yet unpublished European patent application with application number 18210035.4 show the production and processing of siloxanes carrying acetoxy groups to give polyether siloxanes based on SiOC, and similarly, the processing thereof to give siloxanes carrying (meth)acrylic groups, for example for release applications, is also shown in European patent application 19200055.2, also as yet unpublished.

[0022] The method of the present invention is described in more detail below.

[0023] Step a) employs a liquid digestion system comprising acetic anhydride and / or acetoxysiloxane and at least one Bronsted acid and optionally a solvent. According to a particularly preferred embodiment, the process of the invention is carried out in step a) with addition of acetic acid.

[0024] In a preferred embodiment of the present invention, the digestive system used comprises

[0025] i) acetic anhydride and Bronsted acids, ii) acetic anhydride, siloxane rings and / or hydroxy-functional siloxanes and Bronsted acids, iii) acetoxysiloxanes and Bronsted acids, or iv) acetoxysiloxanes, siloxane rings and / or hydroxy-functional siloxanes, acetic anhydride and Bronsted acids, preferably in each case with added acetic acid.

[0026] Preferably, according to the invention, the Bronsted acids used are protic acids with a pKa of less than -1.30, such as preferably nitric acid, methanesulfonic acid and p-toluenesulfonic acid, preferably protic acids with a pKa of less than -2.90, such as preferably concentrated sulfuric acid, more preferably protic acids with a pKa of less than -4.90, such as preferably perfluoroalkanesulfonic acids such as heptafluoropropanesulfonic acid, pentafluoroethanesulfonic acid, trifluoromethanesulfonic acid and also perchloric acid and chlorosulfonic acid, of which perfluoroalkanesulfonic acids are particularly preferred, trifluoromethanesulfonic acid being very particularly preferred here, and furthermore sulfonic acid or perfluoroalkylsulfonic acid ion exchange resins are also preferred, for example commercially available and products, but also in the form of perfluoroalkyl sulfonic acid resins such as (e.g., NR50 type).

[0027] Particularly preferred Bronsted acids for use according to the invention are perfluoroalkanesulfonic acids, and most preferably trifluoromethanesulfonic acid.

[0028] Within the scope of the present invention, it is in principle possible to recycle all siloxanes which come into consideration for the coating of sheet-like paper or polymer structures.

[0029] According to a preferred embodiment of the invention, the method is carried out with supply of heat and / or preferably with introduction of mechanical energy.

[0030] It is preferred according to the invention that the flaky siliconized structure is subjected to a heat treatment in a digestion system, preferably between 50°C and 200°C, more preferably between 80°C and 160°C, more particularly between 120°C and 150°C.

[0031] Mechanical energy can be introduced into the digestion system in particular in the form of stirring energy or ultrasound. On a production scale, use can be made in particular of stirred reactors (stirred tanks) customary in chemical engineering.

[0032] The process of the invention can advantageously be carried out at standard pressure (1013 hPa), at reduced pressure or, to achieve high heat treatment temperatures of up to 200° C., at elevated pressure in a rated pressure apparatus. The process of the invention is preferably carried out at standard pressure.

[0033] Preferably, according to the invention, the Bronsted acid used in the digestive system is advantageously used in an amount of 0.1-1.5 mass %, preferably in an amount of 0.15-1.0 mass %, more preferably in an amount of 0.2-0.8 mass %, based on the total mass of the respective digestive system.

[0034] If desired, the silanes and / or siloxanes with reactive acetoxy functions obtained 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 blended with other crosslinking silanes and / or siloxanes and unfilled and / or filled with fillers.

[0035] It is obvious to the person skilled in the art that the respective nature and chemical composition of the silicone used and intended for recycling determines the composition of the acetoxy-containing siloxanes obtained by the process according to the invention.

[0036] In a preferred embodiment of the invention, the digestion system contains acetic anhydride. The amount of acetic anhydride used here is advantageously guided by the amount of organosilicon used for recycling and the desired target structure of the silanes / siloxanes carrying acetoxy groups (definition of the average chain length desired in each case based on the amount of organosilicon substrate to be recycled by the amount of acetic anhydride used).

[0037] In the context of the present invention, the term "siloxanes comprising acetoxy groups" especially also relates to substances which comprise varying amounts of silanes having acetoxy groups, such as trimethylsilyl acetate, diacetoxydimethylsilane and the like.

[0038] The polymerization behavior of the silanes and / or siloxanes provided with reactive acetoxy groups which have been obtained according to the invention can be demonstrated in a simple manual experiment simply by applying a small volume of about 0.5-2 ml to a black Bakelite cover. In particular, the still Brönsted-acidic acetoxysilanes / siloxanes polymerize very rapidly under the influence of air moisture and leave an opaque white silicone film.

[0039] Alternatively, the high reactivity of the acetoxysilanes and / or siloxanes obtained by the process according to the invention also allows, for example, their conversion into the corresponding alkoxysilanes / -siloxanes.

[0040] Removal of the desiliconized platelets from the liquid phase may be accomplished by conventional techniques, such as by filtration.

[0041] The possibilities of the method according to the invention are further explained and illustrated below.

[0042] For example, if according to the present invention, a base weight of 135 g / m 2 A white, one-sided siliconized release paper (from Neptun Technologies GmbH) was introduced into an acetoxysiloxane and the silicone coating was peeled off from the paper support within an exposure time of only 3 hours at a reaction temperature of 130° C. (inventive example 1). What remained was a slightly brownish discolored desiliconized paper which, even in this form and / or after optional bleaching, can be further processed into any product obtained from cellulose recycled material in the paper industry.

[0043] The desiliconization effect of the invention, meaning the detachment of the silicone layer from the paper carrier, can be impressively demonstrated by infrared spectroscopy of the paper surface.

[0044] The desiliconized paper according to the invention has a 1020 cm -1 and 1099cm -1 The band positions at the wavenumbers between 3150 and 3750 are much smaller than the corresponding bands of the siliconized release paper. In addition, the release paper desiliconized according to the present invention shows the band positions at the wavenumbers between 3150 and 3750 as the characteristic of water bound to the OH groups of cellulose, while the siliconized release paper has no signal positions at those points.

[0045] The effect of the desiliconization which has surprisingly been found according to the invention could likewise be convincingly demonstrated using siliconized biaxially oriented polypropylene films (BOPP films) (inventive example 2).

[0046] It was completely unexpected and unforeseeable to the person skilled in the art that the method claimed according to the invention is also suitable for the effective reuse of siliconized PETP (polyethylene terephthalate) films. Although concentrated sulfuric acid is used in the digestion system according to the invention, the desiliconization in this case is not accompanied by ester cleavage disintegration of the polyethylene terephthalate film (Example 3 of the invention).

[0047] In a preferred embodiment, the digestion system claimed according to the invention is contacted with the sheet-like structure to be desiliconized several times instead of once, and in this way the concentration of acetoxy-containing siloxanes in the digestion system can be controlled. By using analytical techniques such as 29 Si-NMR spectroscopy and, for example, viscosity measurements can subsequently characterize the acetoxy-containing siloxanes to the extent that they have been processed, in the sense of European patent applications EP 3611214 A1, EP 3611216 A1, EP 3611217 A1, EP 3611215 A1 and the likewise unpublished European patent application with application number 18210035.4, into valuable derivative products such as SiOC-linked polyether siloxanes or in the sense of the unpublished European patent application with application number 19200055.2 into SiOC-linked siloxane (meth)acrylates.

[0048] According to the invention, chemical release of the silicone layer from the siliconized release paper or from the siliconized polymer film can be facilitated by ensuring that the carrier system to be reused is mobilized in the sense of being transformed in the digestive system during the thermal treatment.

[0049] According to this teaching, in the case of a rolled carrier system, the invention can also be implemented according to the invention using an arrangement like a roller mill, by winding the release paper or polymer film to be desiliconized into a roll, stretching it on a roller mill, after which the roll is unwound and the unwound carrier is pulled through an immersion bath which consists of the digestion system according to the invention and has a controllable temperature.

[0050] It will be clear to the person skilled in the art that in this case the unwinding speed, the length of the immersion bath and the resulting effective contact time of the carrier system with the digestion system as well as the temperature and other parameters are co-determinants of the efficiency of the desiliconization procedure. If desired, after passing through the digestion system, the paper and / or film can additionally be pulled through a rinsing bath, thereafter optionally dried and wound up again elsewhere on the rolling mill.

[0051] In another preferred embodiment of the present invention, the siliconized release paper or siliconized polymer film is heat-treated in the digestive system with the introduction of mechanical energy, when the siliconized release paper or siliconized polymer film is in sheet form.

[0052] Another subject of the present invention is the use of a liquid digestion system comprising acetic anhydride and / or acetoxysiloxane and at least one Bronsted acid, optionally a solvent, preferably with the addition of acetic acid, for desiliconizing sheet-like siliconized structures, in particular siliconized paper or siliconized polymer films. With regard to preferred embodiments of this subject matter, reference is made to the preceding description in its entirety. DETAILED DESCRIPTION

[0053] Example

[0054] Infrared spectroscopy was used as a means to characterize the support surface.The measurements were performed on a Tensor 27 infrared spectrometer from Bruker Optik GmbH equipped with a MIRacle, Multiple Crystals CRY ATR unit from PIKE and fitted with a $106D0000 diamond ATR crystal using OPUS 7.2 analysis software.

[0055] Embodiment 1 of the present invention

[0056] Desiliconization of cellulose-based siliconized release papers

[0057] In a 500 ml four-necked round-bottom flask with an internal thermometer, a KPG stirrer and a top-mounted reflux condenser, 100 g of decamethylcyclopentasiloxane were heated with 12.5 g of acetic anhydride and 3.7 g of acetic acid and also 0.23 g of trifluoromethanesulfonic acid (0.2% by mass, based on the reaction mixture) at 150° C. for 6 hours with continuous stirring. The mixture was allowed to cool to 130° C. and 15.4 g of a 135 g / m slurry having a basis weight of 150 g / m slurry were introduced in the form of short strips with continuous stirring. 2 The mixture was placed under stirring at 130° C. for 3 hours, after which it was cooled to 25° C., at which point the desiliconized paper strips with a slightly brownish discoloration were removed from the acetoxysiloxane by means of a fluted filter, while the acetoxysiloxane passed through the fluted filter as a clear filtrate.

[0058] After rinsing the paper strips with a small amount of acetone, the dried paper surface was analyzed by vibrational spectroscopy (IR analysis).

[0059] It can be seen here that in the case of the desiliconized paper according to the invention, the presence of silicones at 1020 cm -1 and 1099cm -1The band positions at the wavenumbers between 3150 and 3750 are much smaller than the corresponding bands of the siliconized release paper. In addition, the desiliconized release paper of the present invention shows the band positions at the wavenumbers between 3150 and about 3750 as the characteristic of water bound to the OH groups of cellulose, while the siliconized release paper has no signal positions at those points.

[0060] Embodiment 2 of the present invention

[0061] Desiliconization of silicone-coated BOPP films

[0062] a) Production of BOPP film coated with silicone on one side (not in the present invention)

[0063] A BOPP film ( CR, a corona-treated transparent biaxially oriented polypropylene film for release film application) was corona pretreated and then coated on one side with a commercial radiation-curable silicone acrylate by: RC 711 and 68g A mixture of RC 902 and 2g of photoinitiator A18 combination, and use from The five-roll coating unit of Coating Machinery GmbH, Dormagen (Germany) has a coating capacity of about 1 g / m 2 The combined mixture was applied at a coating weight of 1000 g and exposed to a stream of 100 m / min of water at 60 W / cm in a nitrogen atmosphere having a residual oxygen content of less than 50 ppm. The coating was cured using UV light from medium-pressure mercury vapor lamps from Metz GmbH, Nürtingen (Germany).

[0064] b) Desiliconization of BOPP film coated with silicone on one side (the present invention)

[0065] In a 500 ml four-necked round-bottom flask with an internal thermometer, a KPG stirrer and a top-mounted reflux condenser, 70 g of decamethylcyclopentasiloxane and 12.5 g of acetic anhydride and 3.7 g of acetic acid and 0.60 g of sulfuric acid (0.6% by mass, based on the reaction mixture) were introduced under stirring, and then a total of 10.0 g of the biaxially oriented polypropylene (BOPP) film coated with silicone on one side from a) was cut into a nearly rectangular piece of about 10 mm x 20 mm in size and heated at 120° C. for 4 hours. The mixture was allowed to cool to 25° C., at which time the desiliconized polypropylene strips were removed from the acetoxysiloxane using a groove filter, and the acetoxysiloxane passed through the groove filter as a clear filtrate.

[0066] After rinsing the polypropylene strips with a small amount of ethanol, the dried polypropylene surface was analyzed by vibrational spectroscopy (IR analysis).

[0067] In addition, the infrared spectrum of an untreated (= not treated according to the invention) BOPP film was recorded as a reference. -1 and 1088.0cm -1 At , the position of the band of the untreated release liner film that is characteristic of the silicone coating is seen.

[0068] In contrast, in the case of the desiliconized film of the present invention, these characteristic band positions completely disappeared.

[0069] Embodiment 3 of the present invention

[0070] Desiliconization of silicone-coated PETP films

[0071] a) Production of PETP film coated with silicone on one side (not in the present invention)

[0072] 50μm chemically pre-treated on one side to improve adhesion of solvent-based coatings and printing inks The pretreated side of a polyethylene terephthalate film of WDW / WDW CSRE 36-65 (white, biaxially oriented film) was coated with a commercial radiation-curable silicone acrylate by mixing 30 g of RC 711 and 68g A mixture of RC 902 and 2g of photoinitiator A18 combination, and use from The five-roll coating unit of Coating Machinery GmbH, Dormagen (Germany) has a coating capacity of about 1 g / m 2 The combined mixture was applied at a coating weight of 1000 g and exposed to a stream of 100 W / cm2 of water at a web speed of 100 m / min and 60 W / cm2 in a nitrogen atmosphere having a residual oxygen content of less than 50 ppm. The coating was cured using UV light from medium-pressure mercury vapor lamps from Metz GmbH, Nürtingen (Germany).

[0073] b) Desiliconization of a PETP film coated with silicone on one side (the present invention)

[0074] In a 500 ml four-necked round-bottom flask with an internal thermometer, a KPG stirrer and a top-mounted reflux condenser, 70 g of decamethylcyclopentasiloxane were introduced with stirring together with 12.5 g of acetic anhydride and 3.7 g of acetic acid and 0.60 g of sulfuric acid (0.6% by mass, based on the reaction mixture), and then a total of 10.0 g of biaxially oriented polyethylene terephthalate (PETP) coated on one side with silicone from a) was cut into almost rectangular pieces of about 10 mm x 20 mm in size and heated at 120° C. for 4 hours. The mixture was allowed to cool to 25° C., at which point the desiliconized polyester strips were separated from the acetoxysilane using a fluted filter, which passed through the fluted filter as a clear filtrate.

[0075] After rinsing the polyester strips with a small amount of ethanol, the dried polyester surface was analyzed by vibrational spectroscopy (IR analysis).

[0076] In addition, the infrared spectrum of an untreated (= not treated according to the invention) PETP film was recorded as a reference. -1 and 1087.4cm -1 At , the position of the band of the untreated release liner film that is characteristic of the silicone coating is seen.

[0077] In contrast, in the case of the desiliconized film of the present invention, these characteristic band positions completely disappeared.

Claims

1. A method for physical reuse of a flaky siliconized structure, comprising the following steps: a) treating the platelet-shaped siliconized structure in a liquid digestion system comprising acetic anhydride and / or acetoxysiloxane and at least one Bronsted acid and optionally a solvent, b) Removal of the desiliconized platelets from the liquid phase. 2 . The method according to claim 1 , wherein the sheet-like siliconized structure is a siliconized paper or a siliconized polymer film.

3. The method of claim 1, wherein the liquid digestion system is supplemented with acetic acid.

4. The method according to claim 1, wherein step a) takes place with supply of heat and / or with introduction of mechanical energy.

5. The method according to claim 4, wherein the mechanical energy is introduced into the digestive system in the form of stirring energy or ultrasound.

6. The method according to one of claims 1 to 5, wherein the heat treatment in step a) is carried out in a temperature range between 50°C and 200°C.

7. The method according to claim 6, wherein the heat treatment in step a) is carried out at a temperature ranging between 80°C and 160°C.

8. The method according to claim 6, wherein the heat treatment in step a) is performed at a temperature ranging from 120°C to 150°C.

9. The method according to claim 1, characterized in that The digestive system used includes a) acetic anhydride and Bronsted acid, b) acetic anhydride, siloxane rings and / or hydroxy-functional siloxanes and Bronsted acids, c) acetoxysiloxane and Bronsted acid, or d) Acetoxysiloxanes, siloxane rings and / or hydroxy-functional siloxanes, acetic anhydride and Bronsted acids.

10. The process according to claim 9, wherein a digestion system is used to which acetic acid is in each case added.

11. The method according to claim 1, characterized in that The Bronsted acid used was a protic acid with a pKa of less than -1.

30.

12. The method according to claim 11, characterized in that The Bronsted acid used was a protic acid with a pKa of less than -2.

90.

13. The method according to claim 11, characterized in that The Bronsted acid used was a protic acid with a pKa of less than -4.

90.

14. The method according to claim 11, characterized in that The Bronsted acids used are nitric acid, methanesulfonic acid, p-toluenesulfonic acid, concentrated sulfuric acid, perfluoroalkanesulfonic acid, perchloric acid, chlorosulfonic acid, sulfonic acid or perfluoroalkanesulfonic acid ion exchange resins.

15. The method according to claim 14, characterized in that The perfluoroalkanesulfonic acid is heptafluoropropanesulfonic acid, pentafluoroethanesulfonic acid, or trifluoromethanesulfonic acid.

16. The method according to claim 1, characterized in that The Bronsted acid used in the digestive system is used in an amount of 0.1 to 1.5% by mass, based on the total mass of the respective digestive system.

17. The method according to claim 16, characterized in that The Bronsted acid used in the digestive system is used in an amount of 0.15-1.0 mass %.

18. The method according to claim 16, characterized in that The Bronsted acid used in the digestive system is used in an amount of 0.2-0.8 mass %.

19. The method according to claim 16, characterized in that The corresponding digestion system includes added acetic acid.

20. The method according to claim 1, characterized in that The lamellar siliconized structure includes a polymer film.

21. The method according to claim 20, characterized in that The polymer film is formed of polyethylene PE, polyethylene terephthalate PET or polypropylene PP.

22. The method according to claim 20, characterized in that The polymer film is uniaxially or biaxially oriented polypropylene MOPP / BOPP.

23. Use of a liquid digestion system comprising acetic anhydride and / or acetoxysiloxane and at least one Bronsted acid, optionally with a solvent, for desiliconizing lamellar siliconized structures.

24. The use according to claim 23, wherein the liquid digestion system is supplemented with acetic acid.

25. The use according to claim 23, wherein the sheet-like siliconized structure is a siliconized paper or a siliconized polymer film.