MXPA98009564A - Multiple layer sheet indicating indeb handling - Google Patents

Abstract

The present invention relates to a multi-layer sheet (1) comprising a flexible support (2) and a layer of pressure-sensitive adhesive (3) for joining the multi-layer sheet to a smooth and rigid surface (5) , wherein the pressure sensitive adhesive is completely removed from the surface (5) and selected so as to exhibit an adhesive layer with a thickness of 300 mm at an adhesion of 90 ° of between 20 and 85 N / inch of glass after a drying time of 3 days at a temperature of 70 ° C. The flexible support (2) preferably comprises at least one damaged layer (4) and shows intralayer faults when the multilayer sheet (1) is detached from the surface (5). The present invention further relates to a pressure sensitive adhesive which can be obtained by polymerizing a precursor comprising a) a monomeric component which contains one or more alkyl acrylates, the alkyl groups of which have an average of 4-14 atoms of C, and 2-8 percent of at least one copolymerizable monomer having a polar group, b) 5-15 percent of hydrophobic silica, c) one or more polymerization initiators, and d) one or more crosslinking compounds in a concentration which results in a crosslinking density obtainable by the use of hexandiol diacrylate as a reference crosslinking compound in a concentration of between 0.06 and 0.14 percent. The present invention further relates to a pressure sensitive adhesive which can be obtained by polymerizing a precursor comprising a) a monomeric component which contains one or more alkyl acrylates, the alkyl groups of which have an average of 4-14 atoms of C, and 8-20 percent of at least one copolymerizable monomer having a polar group, b) 5-15 percent of hydrophobic silica, c) one or more polymerization initiators, and d) one or more crosslinking compounds in a concentration that results in a crosslinking density obtainable by the use of hexandiol diacrylate as a reference crosslinking compound in a concentration of between 0.06 and 0.11 percent

Description

MULTIPLE LAYER SHEET THAT INDICATES UNFAIR HANDLING Field of the Invention The invention relates to a multi-layered sheet coated with pressure-sensitive adhesive useful as removable labels for application to smooth and rigid surfaces such as glass or painted metal surfaces, whereby the labels preferably exhibit characteristics a tamper proof. The invention is further related to pressure sensitive adhesive materials, which are useful in those multi-layer sheets.

BACKGROUND OF THE INVENTION Multilayer sheets for tamper-resistant labels and labels are known. WO 95/29474 describes, for example, a label that can be attached to the inner side of a vehicle window. DE 44 C5 945 also discloses a tamper-evident label to be applied to a transparent surface such as a windshield. DE 43 14 579 describes a tamper-proof windshield label containing a hologram. The tamper-evident labels known in the art are designed to have a very strong adhesion to smooth surfaces such as REF. 28788 glass and to give a permanent bond, and can be removed only with the aid of solvents and / or mechanical release. In some cases, transparent polymeric sheets or sheets such as, for example, thin sheets of polyurethane are laminated on the inner surface of the windscreens. Making use of solvents and / or mechanical tools for temporary labels is inconvenient, and the sheets or polymer sheets can be easily damaged by solvents and detachment. Thus there is a need to provide a multi-layer sheet useful, for example, as a label, which is easily removable from the rigid flat surface and preferably also exhibits tamper-proof features. Multilayer sheets that are useful for the preparation of a label having sufficiently high adhesion to tamper-proof, and at the same time removable without the aid of solvents or mechanical release, are not available in the prior art.

Brief description of the invention. The present invention relates to a multi-layer sheet (1) comprising a flexible support (2) and a layer of pressure-sensitive adhesive (3) for joining the multi-layer sheet to a smooth and rigid surface (5) , wherein the pressure sensitive adhesive can be easily removed from the surface (5) and selected to exhibit an adhesive layer with a thickness of 300 μm at a 90 ° adhesion of between 7.9 and 33.5 N / centimeter (20 and 85 N / inch) of the glass after a drying time of 3 days at a temperature of 70 ° C. In a preferred embodiment, the flexible support (2) comprises at least one damaging layer (4) and shows intralayer failure when the sheets of multiple layers (1) are detached from the surface (5). The present invention further relates to a pressure sensitive adhesive which can be obtained by polymerizing a precursor comprising a) a monomeric component which contains one or more alkyl acrylates, the alkyl groups of which have an average of 4-14. C atoms, and 2-8 percent of at least one copolymerizable monomer having a polar group, b) 5-15 percent hydrophobic silica, c) one or more polymerization initiators, and d) one or more crosslinking compounds in a concentration which results in a crosslinking density obtainable by the use of hexandiol diacrylate as a reference crosslinking compound in a concentration of between 0.06 and 0.14 percent.

The present invention further relates to a pressure sensitive adhesive which can be obtained by the polymerization of a precursor comprising a) a monomer component which contains one or more alkyl acrylates, the alkyl groups of which have an average of 4-14 carbon atoms, and more than 8-20 percent of at least one copolymerizable monomer having a polar group, b) 5-15 percent hydrophobic silica, ) one or more polymerization initiators, and d) one or more crosslinking compounds in a concentration which results in a crosslinking density obtainable by the use of hexanediol diacrylate as a reference crosslinking compound in a concentration of between 0.06 and 0.10 per hundred.

Detailed Description of the Invention The multi-layer sheet (1) of the present invention comprises a substrate (3) and a layer of pressure-sensitive adhesive (3)] to bond the film to a smooth and rigid surface (5) such as as, for example, surfaces of glass, metal or painted metal. When it comes to removing the multilayer sheet (1) from the surface, the flexible substrate (2) preferably shows intralayer failure, thereby imparting tamper-proof characteristics to the multilayer sheet (1). The flexible substrate (2) may comprise one or more layers and preferably at least two layers. The flexible substrate (2) preferably comprises at least one damaging layer (4) which is designed to be the weakest point of the multi-layer sheet (1) of the present invention and consequently the predetermined failure point when peeling off the multi-layer sheet (1) of the surface (5). The damaging layer (4) is preferably an inner, unexposed layer of the multi-layer sheet (1) and has two adjacent layers of multi-layer sheets. The flexible substrate may further comprise layers such as, for example, a pigment layer (6) (not shown) or a retroreflective layer (7). The multilayer sheet (1) of the present invention can be easily removed from the substrate (5) without any residue. The term "easily removable" means that the pressure sensitive adhesive can be removed from the surface (5) after a period of use without using chemical agents such as organic solvents or mechanical tools such as knives or scrapers. Due to the chemical formulation of tamper-evident characteristics and ease of removal of surfaces such as glass or painted metal, the multi-layer films of the present invention comprising a damaging layer (4) are especially suitable for preparation of temporary labels such as vehicle toll booths or anti-counterfeit product labels. The pressure-sensitive adhesive useful for the multilayer sheet (1) of the present invention is selected to exhibit high adhesion to the flexible substrate (2), that is, to the layer of the flexible substrate (2) that is adjacent to it. to the layer of pressure-sensitive adhesive (3). The multi-layer sheets according to the present invention comprising a damaging layer (4), this adhesion must be greater than the internal or cohesive strength of the damaged layer (4) to prevent the flexible substrate from being easily removed from the adhesive layer without destroying the flexible substrate (2). The adhesion of the pressure sensitive adhesive to the smooth and rigid surface (5) must also be greater than the internal strength of the damaged layer (4) to prevent the multi-layer sheet (1) from detaching from the surface without destroying it. . The adhesive should not only be resistant to easy peeling at room temperature, but should also adhere well and resist the point of removing the multilayer sheet (1) intact at elevated temperature. On the other hand, the adhesion between the pressure-sensitive adhesive layer and the smooth and rigid surface should not be too great to result in permanent bonding of the pressure-sensitive adhesive layer to the surface (5). It was found that the pressure-sensitive adhesives that are useful in the multi-layer sheets (1) of the present invention exhibit, for a layer of a pressure-sensitive adhesive of a thickness of 300 microns, a 90 ° adhesion at glass after a drying time of 3 days at 70 ° C measured by the test method specified below, between 7.9 and 33.5 N / centimeter (20 and 85 N / inch), and, especially, between 11.8 and 29.5 N / centimeter (30 and 75 N / inch), and more particularly between 11.8 and 27.6 N / centimeter (30 and 70 N / inch). The pressure-sensitive adhesive materials identified by this test method are useful for glass surfaces and other smooth and rigid surfaces, such as metal or painted metal surfaces. The pressure-sensitive adhesive materials are especially useful for glass surfaces. The pressure-sensitive adhesives according to the present invention preferably exhibit a high optical transmission so that the indentations (4d) such as the printed patterns that are part of the flexible substrate (2), can be seen through the layer adhesive (3). Pressure sensitive adhesives that exhibit a visible light transmission of at least 80% and preferably at least 90% are preferred. The pressure sensitive adhesives to be used in the multilayer films of the present invention are more preferably optically transparent, ie, uncolored. It was found that a specific class of pressure sensitive adhesives satisfying the above requirements can be obtained by polymerizing a precursor comprising a) a monomer component which comprises one or more alkyl acrylates, the alkyl groups of which has an average of 4 -14 C atoms, and 2-8 percent of at least one copolymerizable monomer having a polar group, b) 5-15 percent hydrophobic silica, c) one or more polymerization initiators, d) one or more crosslinking compounds in a concentration which results in a crosslinking density obtainable by the use of hexandiol diacrylate as a reference crosslinking compound in a concentration of between 0.06 and 0.14 percent. The pressure sensitive adhesives are novel and are the subject matter of the present invention. Pressure-sensitive adhesive tapes containing hydrophobic silica are generally described in US 4,749,590. The tapes are said to be initially repositionable, "but within a few days they usually can not be removed" (US 4,749,590, column 4, lines 49-50). US 4,895,745 discloses dark pressure-sensitive acrylic adhesives comprising hydrophobic silica and pigments such as, for example, carbon black pigments which can not be used, for example, for the front face type labels described below, which require highly transmissive pressure-sensitive adhesives. The average term of 4-14 C atoms means that the average number of C atoms of the alkyl acrylate compounds, weighted by their respective percentage by weight with respect to the mass of the alkyl acrylate component, is between 4-14 and, in particular, between 4-12 carbon atoms. Useful alkyl acrylates (ie, acrylic ester monomers of alkyl acid) include linear or branched monofunctional unsaturated acrylates or methacrylates of non-tertiary alkyl alcohols, the groups alkyl of which are from 4 to 14, and in particular, from 4 to 1 carbon atoms. Examples of those lower alkyl acrylates used in the invention include but are limited to n-butyl acrylate, isobutyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, n-octyl acrylate. , n-octyl methacrylate, 2-methylbutyl acrylate, isononyl acrylate, n-nonyl acrylate, isoamyl acrylate, n-decyl acrylate, isodecyl acrylate, isodecyl methacrylate, isobornyl acrylate, 4-acrylate, methyl-2-pentyl, and dodecyl acrylate. Preferred lower acrylate and methacrylate esters include isooctyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate and dodecyl acrylate. The precursor preferably contains up to 5, and in particular, 1-4 alkyl acrylates. The average number of carbon atoms in the alkyl groups of the alkyl acrylates as defined above is preferably 4-14, especially between 4-12 and very particularly between 5-10. The concentration of the alkyl acrylate component with respect to the mass of the precursor of the pressure sensitive adhesive is at least preferably 75% by weight, and, in particular, of at least 85% by weight. The PSA precursor can not contain alkyl esters of unsaturated aliphatic carboxylic acids other than acrylic acid such as, for example, alkyl maleate and alkyl fumarate (based, respectively, on maleic and fumaric acid). In this regard, dibutyl maleate, dioctyl maleate, dibutyl fumarate and dioctyl fumarate are preferred. The amount of ester compounds of unsaturated aliphatic carboxylic acids other than acrylic acid is preferably not too high and, in particular, does not exceed 25% by weight with respect to the mass of the alkyl acrylate component. The term polar monomers includes both moderately polar and strongly polar monomers. Polarity (that is, the ability to bind hydrogen) is often described by the use of terms such as "strongly", "moderately" and "poorly". References describing these and other terms of solubility include "Solvents", Paint Testing Manual, 3rd ed., GG Seward, Ed., American Society for Testing and Materials, Philadelphia, Pennsylvania, and "A Three-Dimensional Approach to Solubility" , Journal of Paint Technology, Vol. 38, No. 496, pp. 269-280. Examples of highly polar copolymerizable monomers are acrylic acid, methacrylic acid and acrylamides while N-vinyl lactams such as, for example, N-vinyl pyrrolidone, N-vinyl caprolactam, acrylonitrile and dimethyl aminopropyl methacrylate are typical examples of moderately polar monomers. The precursors contain between 2 and 8 percent of one or more copolymerizable polar monomers. If the amount of the copolymerizable polar monomers exceeds 8 percent, the 90 ° adhesion of the glass pressure sensitive adhesive is too high and the pressure sensitive adhesive is permanently bonded. If the amount of copolymerizable polar monomers is less than 2 percent, the adhesion at 90 ° in glass is too low to ensure that the multilayer sheet (1) is not removed intact from a glass surface when applied for example, high temperatures . The amount of copolymerizable polar monomer is preferably 2-7 percent and especially preferably 3-6 percent. The pressure sensitive adhesive to be used in the multilayer films of the present invention therefore comprises 5-15 percent hydrophobic silica. In an especially preferred embodiment, the amount of hydrophobic silica is between 7.5 and 15 percent and especially between 10 and 15 percent. Hydrophobic silica is commercially available, for example, from Degussa, as "Aerosil" R972, R974 or R9976. According to the Degussa bulletin entitled "Product Information" of June 4, 1984, the hydrophobic silicas "Aerosil" R972, R974 and R976 are prepared from the hydrophobic silicas denoted as "Aerosil" 130, 200 and 300, respectively, which exhibits a surface area of 130, 200 and 300 m2 / g, respectively. Hydrophobic silica is also commercially available, for example, as TS-720 from Cabot Cab-O-Sil Division, Tuscola, Illinois, USA. In US 2,859,198 (Sears et al.), It is proposed that the surface of finely divided inorganic solid silicon-containing materials, such as silica, can be made hydrophobic by treating the material with an organosiloxane material. According to US 4,136,081 (Schultz) the silica "can be treated with organosilicon materials such as chlorosilanes, silazanes, alcosisilanes and cyclic siloxanes to produce hydrophobic surfaces" (column 6, lines 47-52). The enumeration of the hydrophobic silica materials given above, and the description of some of the methods selected for preparing hydrophobic silica materials, should be understood as illustrative and not as a limitation. The hydrophobic silica used to prepare the PSA materials according to the present invention, preferably it exhibits a surface area of at least 10 m2 / g and especially of at least 50 m2 / g. The surface area of the hydrophobic silica is preferably especially between 50 to 400 m2 / g (surface area of B.E.T.). The addition of the hydrophobic silica to the precursor of the pressure sensitive adhesive in the specified amount imparts sufficient cohesive or internal strength to the pressure sensitive adhesive, so that the adhesive is thought to have a character similar to rubber. This allows the adhesive residues to be removed, for example, from glass surfaces, by holding the edge of the adhesive residue and pulling to effect complete removal of the glass substrate. All sections of adhesive residue or label residue coated with adhesive can then be removed manually. If the concentration of the hydrophobic silica is chosen to be less than 5 percent, it was found that the pressure sensitive adhesive breaks after attempts to remove large sections of the adhesive mass, thus necessitating the use of tools mechanical and / or chemical agents such as organic solvents. The increase in the concentration of the hydrophobic silica above 15 percent adversely affects the properties of adhesion against detachment at 90 ° in glass The addition of hydrophobic silica in an appropriately selected amount to the precursor of the pressure sensitive adhesive is therefore essential to establish the desired removal capacity of pressure sensitive adhesive (3) from the surface (5). It was found that other fillers such as, for example, hydrophilic silica or polysaccharide fillers adversely affect optical properties such as clarity and / or mechanical properties such as the mechanical strength of the pressure sensitive adhesive. The precursor of the pressure sensitive adhesive useful in the multilayer films of the present invention further contain one or more crosslinking compounds to increase the cohesive strength and tensile strength of the resulting PSA material. Useful crosslinkers include benzaldehyde, acetaldehyde, anthraquinone, various compounds of the benzophenone and vinyl-halomethyl-s-triazine type such as, for example, 2,4-bis (trichloromethyl) -6-p-methoxystiryl-s- triazine. Preferred are polyacrylic functional monomers such as, for example, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, 1,2-ethylene glycol diacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate or 1,2-diacrylate. dodecandiol. The compounds listed above, which may be substituted or unsubstituted, are intended to be illustrative and not limiting. The crosslinking component to be used in the present invention preferably contains 1-5, especially between 1-3 and very particularly 1-2 crosslinking compounds. Particularly preferred crosslinking compounds are 1,6-hexanediol diacrylate and tripropylene glycol diacrylate.

The degree of crosslinking (crosslinking density) that can be expressed as the number of crosslinks per gram or per unit volume of the polymer can be theoretically estimated and experimentally determined, for example, by volume increase measurements or via stress curves. of traction (see Encyclopedia of Polymer Science and Engineering, 2nd ed., New York 1988, vol.4, p.355-357). A detailed description of the volume increase measurements that are preferred is given in P.J. Flory, Principles of Polymer Chemistry, Cornell University Press, Ithaca and London, 1953, pg. 579. When two different precursors are reacted which differ with respect to the crosslinking component but are in other identical circumstances, under identical external reaction conditions (polymerization method such as block polymerization, solution, emulsion or suspension, temperature, pressure , radiation in the case of UV polymerization, etc.), the density of the crosslinking obtained depends on the chemical nature of the crosslinking agent used, its functionality and its respective concentrations. In the present application, the crosslink density was reported with respect to the crosslink density that can be obtained using varying amounts of hexanediol diacrylate (HDDA) as a reference crosslinking component under standardized reaction conditions (block light-cured, photoinitiator: Irgacure 651 , distributed by Ciba Geigy, in a concentration of 0.24 percent, UV radiation with an exposure of 900-1500 mJ / cm2 of a UV lamp, 90% of the emissions of which are between 300 and 400 nm, with a maximum at 351 nm, ambient temperature, normal pressure, oxygen exclusion). The precursor to be used in the multilayer sheets according to the present invention preferably contains one or more crosslinking compounds in a concentration to give a crosslink density obtained by the use of HDDA at a concentration of between 0.06 and 0.14 percent. The concentration of HDDA is preferably between 0.08 and 0.14 percent, and especially preferably between 0.09 and 0.13 percent. If the crosslinking compounds are used in a concentration to give a crosslink density obtained by the use of HDDA at a concentration of less than 0.06 percent, the resistance to cohesion and the tensile strength of the resulting pressure sensitive adhesive is too low. In this case, it was found that the adhesive layer can be cut, for example, with a scraper blade, which allows the intact removal of the multilayer film from the surface, without destruction, and allows the re-adhesion of the layer sheet multiple to other surface. If the crosslinking compounds are used in a concentration to give a crosslinking density obtainable by the use of HDDA at a concentration of more than 0.14 percent, the 90 ° adhesion of the surface (5) was too low to ensure the destruction of the surface. flexible support (2) comprising a damaging layer (4) when detached from the multilayer film of the substrate. The pressure sensitive adhesive materials to be used in the multi-layer sheets of the present invention can be obtained by applying generally known polymerization methods such as block polymerization, solution, emulsion or suspension. Due to environmental reasons, block polymerization is often preferred to avoid the use of organic solvents. The polymerization reaction preferably starts by means of a polymerization initiator and preferably proceeds via a radical polymerization mechanism. Useful examples of polymerization initiators include photoactivatable initiators such as, for example, benzoin ethers (eg, benzoin, ether, benzoin isopropyl ether, substituted benzoin ethers such as anisoin methyl ether), acetophenones (e.g., 2,2-diethoxyacetophenone) or alpha-ketoles (e.g., 2-methyl-2-hydroxy-propiophenone), and / or thermally activatable initiators such as, for example, organic peroxides (e.g., benzoyl peroxide) and lauryl peroxide) and 2, 2 > -azobis (isobutyronitrile). The photopolymerization and the addition of photoactivatable initiators are preferred. The initiator component preferably comprises between 1-3 and, in particular, between 1-2 initiator compounds; especially preferred are initiator components that contain only a photoinitiator. The initiator component is preferably present in an amount of 0.01-2.00 percent, in particular, between 0.05-1.00 percent and very specifically between 0.1-0.5 percent. In a preferred method of preparation, a portion of the initiator component is added to the alkyl acrylate component which is partially polymerized to a degree of typically 2-30% to form a syrup of a coatable viscosity of, for example, 300-20,000. cps (Brookfield) at ordinary room temperatures. The viscosity of the syrup is preferably adjusted to the amount of hydrophobic silica to be added. For high loads with hydrophobic silica of, for example, 12-15 percent, the viscosity of the syrup is preferably not higher than 1,000 cps, and in particular, between 250 and 1.00 cps. For lower charges with hydrophobic silica, the viscosity is preferably not less than 1,500 cps and, in particular, 1750 cps or more. The viscosity of the precursor can also be adjusted by adding a small amount typically less than 5 percent of a polymeric additive, which is preferably a photopolymerizable polyacrylate as described, for example, in WO 94/00, 052. The polymerization preferably proceeds as a photopolymerization which is described, for example, in US 4,182,752. In a preferred embodiment, the polymerization is carried out with black UV lights having more than 60 percent, and more preferably more than 75 percent of its emission spectrum of between 280 and 400 nm, with an intensity of between about 0.1 to about 25 mW / cm2. The exposure is typically between 900-1,500 mJ / cm2. The polymerization can be stopped either by removal of the heat source radiation and / or introduction of, for example, oxygen radical scavenger. The filler components, which essentially comprise hydrophobic silica, are subsequently added to the prepolymerized syrup. When the amount of hydrophobic silica exceeds about 8 percent, it has been found necessary to employ a high-cut mixer such as a paint mill to obtain uniform dispersions. By doing this and appropriately adjusting the viscosity of the prepolymerized syrup, essentially uniform dispersions can be obtained for loads as high as 25 percent. The pressure sensitive adhesive used in the multiple layer sheets of the present invention comprises up to 15 percent hydrophobic silica. The dispersion obtained is mixed with the remaining part of the initiator component and, optionally, with other adjuvants such as, for example, chain transfer agents, polymeric additives such as, for example, those described in EP 0,349,216 or EP 0,352,901, solvents, flame retardants, odor masking agents and / or other adjuvants known in the tape art. The addition of pigments and dyes is not preferred because the pressure sensitive adhesives useful for the multilayer sheets of the present invention preferably exhibit high optical transmission and clarity. If pigments / dyes and / or paints are added, those are preferably selected so as to impart color to the resulting PSA materials without adversely affecting their transfer and clarity. An example of a suitable paint is Permalink Yellow CTL-Druckfarbe (primer) which can be obtained from SICPA Druckfarben, Backnang. In order to produce the PSA films useful in the multilayer sheets of the present invention, the dispersion or mixture obtained is coated on a support, a carrier fabric or a release liner and polymerized in an inert, ie, oxygen-free atmosphere. , for example a nitrogen atmosphere. Previously and subsequently, the term film is used to describe a structure whose thickness is substantially less than any of its length or width and which has two opposite, essentially parallel surfaces. As used herein, the term films includes, for example, sheets, slats, tapes and discs. Damaging layers (4) for tamper-proof multiple layer sheets (1) that are irreversibly destroyed or deformed when detached from the multilayer sheet (1), have been described in the literature. The incorporation of a damaging layer or damaging layers (4) in the multi-layer sheets (1) of the present invention is optional but preferred. The present invention also comprises multi-layered sheets comprising a flexible backing (2) and a layer of pressure-sensitive adhesive (3) for joining the multi-layered sheet to a smooth and rigid surface (5) that does not comprise a damaged layer (4) . The damaging layer (4) may comprise, for example, a pattern of adhesion regulating material (4a), which may be applied to the inner surface of the layer of pressure sensitive adhesive and / or of the other layers of adhesive. the multi-layer sheet (1) in a non-continuous form. The adhesion regulating material covers only a part of the internal surface of one or more of these layers, thereby creating surface areas with different adhesion properties. The adhesion regulating material can be any of a substance that reduces adhesion such as a release agent or, alternatively, an adhesion promoting substance such as a primer. The pattern that reduces the adhesion (4a) can be applied, for example, on the inner surface of the layer of pressure-sensitive adhesive (3). While the adhesion of the layer of pressure-sensitive adhesive (3) to the adjacent layer of the flexible substrate is high in areas where the material that reduces adhesion is absent, the adhesion between the pressure-sensitive adhesive (3) and the material that reduces adhesion is very low in areas where the material that reduces adhesion is present. In areas where the material that reduces adhesion is present, there is often virtually no adhesion between the pressure sensitive adhesive layer (3) and the adjacent layer of the flexible substrate. Various materials can be used as substances that reduce adhesion and repel the adhesive to create a pattern (4a). Examples of those materials include carbamates such as polyvinyl carbamate octadesyl, available under the name "Kalle removable coating K" from Hoechst AG, Germany, or "Escoat 20" from Aderson Development Company, USA. Additional suitable materials include silicone systems such as UV curable free radical silicone acrylate release coatings, silicone adhesion systems, silicone condensation systems and silicone systems that cure cationically. A more complete description of both materials that reduce silicone-based and silicone-free adhesion and their use to create patterns can be found, for example, in US 5,061,535. The adhesion regulating material used in the multilayer sheets (1) of the present invention can also be a substance that promotes adhesion. Layers on either side of the pattern of a substance that promotes adhesion exhibit greater adhesion in areas where the adhesion-promoting substance is present. In areas where the adhesion promoting substance is absent, there is limited adhesion or occasionally there is no adhesion between the adjacent layers. Various types of materials are used as adhesion promoters. Those must be designed specifically for the two adjacent layers, since the adhesion promoting substance must have good adhesion to both adjacent layers, which may be very different in their chemical nature. It has been found that polyurethane-based primers and ethylene-acrylic acid-based primers are suitable for use in the present invention. The type of pattern used for the application of the adhesion revealing substance of the present invention is not critical. The pattern that regulates the adhesion (4a) is preferably that substance which promotes adhesion and is preferably applied using a method of printing by engraving. The pattern that regulates the adhesion (4a) provides areas with different adhesion properties for the adjacent layers of the flexible support (2) resulting in a deformation and / or destruction of the adjacent layer or layers. In this sense, the pattern that regulates adhesion (4a) is known as a damaging layer in the multi-layered sheets of the present invention. The damaging layer (4) may also comprise certain fragile optical elements or layers such as a cinegram (4b) or a hologram (4b) as described, for example, in EP 0,253,089; EP 0,401,466 and US 5,066,041. During an attempted tampering, the hologram could be destroyed. The cinegrams, which are commercially available from Landis & Gyr, Zug, Switzerland, and others, and holograms are attractive from an aesthetic point of view and can be used to incorporate specific graphics or information for the user in the movies. The cinegramas or holograms can be used in restricted areas of the film of multiple layers only, but it is also possible to use extended holographic layers that comprise a structured layer? an optional reflective layer. The structured layer can be formed by several methods that are well known in the art, described in US 4,856,857. This can be made from materials such as polymethyl methacrylate, nitrocellulose, and polystyrene. The structured layer includes an embossed, microstructured pattern of holographic or diffraction images in the form of logos or patterns that reflect light. In one embodiment, a patterned microstructured layer can be formed by contacting the material of which the structured layer will be made as a non-deformable embossing plate having a pattern and a microstructured relief, and applied heat and pressure. Alternatively, the structured layer can be made by any other suitable processes, such as radiation curing and can be made of materials such as urethane, epoxy, polyester, and acrylate monomers and oligomers, which are formulated with photoinitiators, They mold with a non-deformable tool that has a pattern in microstructured relief, and are cured by radiation. The optional reflective layer is coated on the structured layer of the holographic layer (4b) either before or after stamping. The reflective layer preferably has a refractive index greater than that of the structured layer. In a preferred embodiment, the reflective layer is substantially transparent and colorless. Illustrative examples of suitable reflector layer materials include but are not limited to bismuth trioxide, zinc sulfide, titanium dioxide, and zirconium oxide, which are described in US 4,856,857. Transparent materials such as tin, aluminum or silver, or structured reflectors can also be used. The reflective layer omits the reflection of light through the structured layer due to the difference in the refractive index between the structured and reflective layers. In this way, the structured holographic pattern is more easily visible to the unmeasured eye once the reflective layer is coated on the structured layer, and the pressure sensitive adhesive can be applied directly to the structured layer without diminishing the visibility of the pattern structured.

The transparent multilayer film described in DE 44 24 148.8 comprises an irreversibly destructible or deformable layer (4c) comprising, for example, a hot-melt adhesive or a pressure-sensitive adhesive, which can also be used in the multilayer sheets (1) of the present invention. The irreversibly destructible or damageable layer (4c) can also comprise, for example, a paper layer, whereby the internal strength and the thickness of the paper layer is selected such that the paper layer is at a certain point. of predetermined breaking of the multi-layer sheet (1). The damaging layer may also comprise indications (4d) which may be applied by any number of processes, including transfer processes or direct printing processes. The indications are preferably applied by standard printing processes, such as screen printing. Serigraphy printing inks commonly used for this purpose include 3M screen printing inks (800 series, 900 series), dried in a forced air oven at 45 ° C for 30 minutes (800 series) or for 45 seconds at 65 ° C (900 series). Inks can preferably be selected which can be dried or cured at relatively low temperatures for short periods of time, to facilitate rapid manufacture and prevent damage to the thermally sensitive layers that may be present. Printed patterns and other indications may operate as damaging layers only when they are used as an inner layer having two adjacent layers of the multilayer sheet. Overlapping impressions, for example, usually do not operate as damaging layers. The use of printed patterns as a damaging layer is described, for example, in US 4,184,701. The specific embodiments of the damaging layer described above are intended to be illustrative and not limiting. The term "damaging layer" is used in the present invention to characterize easily damaged, i.e. destructible and / or inelastic deformable layers which may be continuous or discontinuous. The damaging layer exhibits internal or cohesion resistance and low is at the predetermined breaking point of the multilayer sheet after removing or tampering unduly. It should be noted, however, that multiple fault patterns are observed for the multi-layered sheet of the present invention in practice. This failure process is relatively complex and is influenced by various parameters such as the elasticity or brittleness, respectively of the different layers, the tensile strength of the materials used and the adhesion between the adjacent layers, the thickness of the different layers, the respective pattern of the discontinuous layers if present, the direction of the coating and the peel angle, the peel strength and release rate and the temperature peel. The fault pattern can change when one or more of the parameters vary. With tampering, the internal resistance of damaging layers of type (4c), for example, may increase in some cases is the result of stretching and simultaneous orientation of the macromolecules in the damaging layer, so that one or more of other areas of the multi-layer sheet have internal strength and / or adhesion similar or even less with respect to the adjacent layer or layers than the damaging layer. This means in practice that a layer or layers of the multi-layered sheet other than the damaged layer can be deformed and / or irreversibly destroyed before the damaged layer and / or in addition and / or instead of the damaged layer, the sheets of multiple layers (1) with one or more of the damaged layers (4) are the subject matter of the present invention, regardless of the actual failure mode, ie regardless of whether the failure paper depends on the damage in the layer or damaging layers and / or other layers.

The multi-layer sheet (1) may further comprise a cover layer (6) (not shown), which forms the exposed layer opposite the adhesive layer. The cover layer (6) (not shown) of the multilayer sheet according to the invention is typically a polymeric film in which it is preferably dimensionally stable, wear resistant, tear resistant, abrasion resistant and / or resistant to solvents. The cover layer can be treated by corona, flame treated, treated with plasma or treated with a chemical primer. Methods of surface treatment are described, for example, in G. Habenicht et al., Adhesion, 1992 (5), pp. 21-36 and in K. W. Gestenberg, Coating, 1990, pp. 260-263. A material which is preferred for this purpose is, for example, a polyethylene terephthalate (PET) polymer film. The dimensionally stable, wear-resistant, tear-resistant, abrasion-resistant and / or solvent-resistant cover layer protects the underlying layers of the multilayer sheet (1) from wear, dust, moisture and other undesirable influences during its lifetime. The cover layer preferably has a thickness of 10 to 200 microns and more preferably 10 to 150 microns. Especially preferred is a thickness of about 10 to about 75 microns. To improve the adhesion of the underlying layer, the film is preferably treated with a corona discharge or with a chemical primer. The primer can be applied in the customary manner, for example with a coating rod, to a useful thickness of up to about 1 micron. The multi-layer sheet (1) according to the invention can further comprise a reflective layer (7) which improves its visibility. The incorporation of a reflective layer (7) is optional but preferred. The reflective layer can be a metal layer such as a thin sheet of metal, for example, or it can comprise one or more types of retroreflective materials, including retroreflective materials of the microsphere type and retroreflective materials of the cube corner type. The retroreflective layer described in US 2,407,680 may comprise a monolayer encased in glass microspheres which are coated in the spacer resin comprising, for example, polyvinyl butyral or polyester. The spacer resin conforms to the microspheres. A reflective layer which is below the spacer resin may comprise opaque materials such as silver, aluminum, chromium, nickel or magnesium, or transparent materials with a high refractive index such as those described above for use on the holographic structured layer. , such as zinc sulfide or multi-layer reflectors as described in US 3,700,305. In this way, the light entering the reflecting layer is focused by the glass microspheres through the spacer resin and is reflected by the glass reflecting layer through the spacer resin and the glass microspheres to an observer. Other retroreflective materials using glass microspheres are described in US 3,801,183. Microsphere-type retroreflective materials are commercially available, for example, from 3M, St. Paul, USA, as 3M® High-Intensity Masking Coating SCOTCHLITE® Series No. 790; 3M® SCOTCHLITE® Validation Safety Coating Series Nos. 5300, 5350, 5390, 4250, and 4290; 3M® SCOTCHLITE® Label Coating Serial No. 5330; and 3M® SCOTCHLITE® Front Adhesive Verification Coating No. 2500. The retroreflective layer (7) may also include a multiplicity of cubic corner retroreflective elements, instead of glass and resin microspheres, which may be made from materials such as such as vinyl, polycarbonate or acrylic polymers for retroreflective elements of cubic corners stamped, and urethane, epoxy, polyester and oligomers of retroreflective elements of cubic corners cured by radiation. The cube corner elements typically have three mutually perpendicular faces with surface areas of between about 1.9 x 10-3 mm2 to 0.1 mm2. The cubic corner retroreflective elements can be stamped by a master mold in a coating material under suitable temperature and pressure. The element can also be treated by coating a radiation curable resin in a master mold, laminating the coating film under sufficient pressure, gelling the resin by curing it with radiation. The thicknesses of each of the different layers forming the flexible substrate (2) is preferably selected so that they are within the range of 10 to 1000 microns, preferably 15-500 microns, and more preferably 20-200 microns . The materials forming the layers of the multilayer sheet (1) of the invention can be put together and bonded together using a variety of known coating and lamination processes. Typically, the layer of pressure sensitive adhesive (3) is laminated to a flexible substrate (2) by means of a transfer process using only pressure. The layers of the flexible substrate (2) are commonly combined using lamination equipment at ambient or elevated temperatures. In cases of non-continuous layers, such as patterns that form indications or patterns that form layers of substances that regulate adhesion, those patterns can be applied by standard printing techniques such as printing by engraving or screen printing. The non-continuous layers may also be formed separately on a temporary substrate, such as a release liner for example, and transferred to other component layers of the multilayer film by lamination as well. Figure 1 shows a multi-layer sheet (1) according to the present invention, comprising a layer of pressure-sensitive adhesive (3), which adheres to a destructible or irreversibly deformable layer (4c), which It has a layer of indications (4d) on its inner surface. The destructible or irreversibly deformable layer (4c) can be, for example, a paper layer. After attempts to remove the multilayer film from the substrate, the indication layer (4d) is broken, followed or accompanied by an irreversible deformation and / or destruction of the layer (4c) and / or the adhesive layer (3) .

When a paper layer is used as the destructible or irreversibly deformable layer (4c), the paper type and thickness of the paper should be selected so that the paper layer is broken and irreversibly damaged after being tampered with improperly. If the destructible or irreversibly deformable layer (4c) is an opaque layer similar to, for example, a paper layer, the multi-layer sheet of the Figure can be applied, for example, to a glass surface or to the surface of another transparent, smooth and rigid material, such as, for example, a polymethacrylate coating and viewed from the opposite side of the transparent material through the transparent adhesive. This construction, which were called and will later be called construction of the front face type, can be used, for example, for a windshield label which is applied to the windshield from the inside of the vehicle and viewed from the outside. Figure lb shows a multilayer film similar to that of Figure la, whereby the sequence of the layer (4c) and the indication layer (4d) have been inverted. This construction, which was previously called and will subsequently be called a back face type construction, can be used, for example, as a tamper-proof tag or label, which is adhered via a layer of pressure-sensitive adhesive (3). ) to a non-transparent surface such as a painted metal surface. In this case, the observer sees the printed pattern or the indication layer (4d). In this construction, the printed pattern or indication layer (4d) does not form a predetermined breaking point, because this layer is applied on top of the layer (4c) and does not form an internal layer as in the case of Figure la. In another modality, which is derived from the modalities shown in Figure la and lb but not shown, the destructible or irreversibly deformable layer (4c) is replaced by a retroreflective layer, and the tamper-proof properties are mainly based on the indication layer (4d). Figure 2a shows a multi-layered sheet (1) according to the present invention comprising a layer of pressure sensitive adhesive (3) containing an indication layer (4d). The adhesive layer is attached to a transparent or semitransparent holographic layer (4b), such as a microstructured holographic layer. The transparent holographic layer is attached to the surface of a retroreflective layer (7) into which the light enters using a pattern coating of an adhesion promoting substrate (4a) such as a primer. The coating of the primer pattern promotes the adhesion of the fragile, thin holographic layer in areas where it is present, thus giving the irreversible destruction of the holographic layer (4d) and any indications (4d) it may contain, after the attempts of undue manipulation. The embodiment of Figure 2a is a construction of the front face type, which is seen through the layer of pressure sensitive adhesive and the transparent material to which it is adhered. Figure 2b is a construction of the back face type, which corresponds to the construction of the Figure 2a. In this construction the printed pattern or indications (4d) or forms a predetermined breaking point because this layer is applied on top of the layer (4b) and does not form an internal layer as in the case of Figure 2a. The failure modes described for the embodiment of Figures 1 and 2 are illustrative and not limiting, and in practice additional failure patterns are observed which are, for example, intermediate between the failure modes described. It was further found by the present inventors that the pressure sensitive adhesive obtainable by the polymerization of a precursor comprising: a) a monomeric component which contains one or more alkyl acrylates, the alkyl groups of which have an average of 4-14 carbon atoms, and more than 8-20 percent of at least one copolymerizable monomer having a polar group, b) 5-15 percent hydrophobic silica, ) one or more polymerization initiators, and d) one or more crosslinking compounds in a concentration which results in a crosslinking density obtainable by the use of hexanediol diacrylate (HDDA) as a reference crosslinking compound in a concentration of between 0.06 and 0.11 percent, exhibit advantageous 90 ° release values on smooth and rigid surfaces, such as glass or painted metal surfaces, and those pressure sensitive adhesive materials are the subject matter of the present invention. The concentration of the reference crosslinker HDDA is preferably 0.06-0.10 and especially preferably 0.06-0.09. Although the pressure sensitive adhesive material described above, which is useful for the preparation of the pressure-sensitive adhesive layer (3) of the multilayer sheet (1), comprises an amount of copolymerizable monomer or monomers from 2-8 percent, it was found that useful pressure-sensitive adhesive materials with high adhesion values at 90 ° in glass were obtained when the amount of copolymerizable monomers having a polar group of more than 8-20 was varied percent, preferably more than 8-15 percent, and especially preferably more than 8-10 percent. The pressure sensitive adhesives are novel and are the subject matter of the present invention. In those pressure-sensitive adhesive materials, the alkyl acrylates, the copolymerizable monomers having a polar group, the polymerization initiators and the crosslinking compounds can be selected as described above for the pressure sensitive adhesive useful for the polymer layer. pressure sensitive adhesive (3) and those materials can be prepared as indicated above. The multi-layer sheets (1) of the present invention are easily removable from rigid surfaces, such as glass or painted metal and are especially useful for the preparation of temporary labels and tags, such as right vignettes, which can be removed afterwards. of a specific period of use. In a preferred embodiment, the multi-layer sheets (1) comprise one or more damage layers (4) and exhibit a unique combination of tamper-proof features, and complete and easy removability. The present invention is better explained by the following examples, which are illustrative, but not limiting. The following test methods were used to characterize the materials used in the examples.

Test Methods 90 ° Adhesion of Glass The 90 ° adhesion test is a modified version of the PSTC-3, which is available from the Council of Pressure Sensitive Tapes in Glenview, Illinois, USA.

A flexible retroreflective coating (3M® Scotchlite® 4780A without EEA top film, available from 3M, St, Paul, USA) replaced by the polymer film normally used as support in this test. The adhesive layer to be tested was produced by photopolymerizing the prepolymerized precursor between two layers of siliconeized biaxially oriented polyethylene terephthalate (PET) film having a thickness of 50 microns. Strips of the adhesive material were cut between the two sheets of polyester at widths of 2.54 cm and lengths of 11 cm for use in this test.

One of the polyester sheets was removed and the exposed adhesive face laminated to the retroreflective side of a commercially available retroreflective coating (see above) with a rubber coated roll. The roller was passed over the sample 5 times with a pressure that can be exerted by the hand. The adhesive / reflector coating sheet thus prepared was then stored at 23 ° C for 24 hours. The second polyester sheet was then removed and the exposed adhesive side applied to a glass plate (the side not exposed to the metal bath during production), which had been cleaned with isopropyl alcohol. The adhesive / retroreflective coating sheet was pressed onto the glass surface using a conventional mechanical laminate. The lamination was carried out with a roller coated with rubber with a weight of 6.8 kg., Which was passed over the sample 4 times at a speed of 300 m / min. The samples were then stored under various conditions before the adhesion measurements were made. The adhesion with a 90 ° release angle was then determined at 23 ° C, with a release rate of 300 mm / min, using a tensile tester.

Three measurements were made for each sample. The values were then averaged and recorded in N / in IN / 2.54 cm).

Removal Capping Test The pressure sensitive adhesive compositions were light-cured between two transparent, siliconized polyester sheets. Once the polyester film was removed from the adhesive layer thus formed and the exposed adhesive surface applied to a multilayer support (2). All the materials were laminated together using a roller coated with rubber. The roller was passed over the sample 5 times with a pressure that can be exerted by the hand. The adhesive / reflector coating sheet thus prepared was then stored at 23 ° C for 24 hours. The remaining polyester sheet protecting the pressure sensitive adhesive layer was then removed. The final multilayer sheet (1) was then adhered to a glass substrate using a conventional mechanical laminator. The lamination was carried out with a roller coated with rubber weighing 6.8 kg., Which was passed over the sample 4 times at a rate of 300 rpm.

The behavior of the multilayer sheet (1) was evaluated qualitatively during attempts to detach the multi-layered sheet from the glass by hand.

Examples 1-5 and Comparative Examples 1-5 A mixture of 0.04 percent Irgacure 651 (commercially available from Ciba-Geigy) and 100 parts by weight of isooctyl acrylate (IOA) was partially polymerized by UV light to form a syrup with a coatable viscosity of approximately 2,000 mPas. Next, as indicated in Table 1, various amounts of hydrophobic silica, hexanediol diacrylate (HDDA) and, in each case, 0.2 percent Irgacure 651 (commercially available from Ciba-Geigy) were added to the syrup, followed by mixing with a laboratory shaker for 90 minutes. The coating and curing of the syrup were carried out between two transparent siliconized polyester films. The level of the radiation dose was approximately 1,300 mJ / cm2. The radiation was supplied from lamps that had approximately 90% emissions between 300 and 400 nm, and an emission peak at 351 nm. The thickness of the adhesive samples was chosen to be 300 or 800 μm.

Table 1. Adhesive compositions used in the examples (1) Fumid hydrophobic silica, available as R-972 from Degussa. (2) HDDA = hexanediol diacrylate Examples 1-5 The 90 ° adhesion was measured for the adhesives of Examples 1-5 and Comparative Examples 1-5 as described above. It is evident that high adhesion values were initially present for the adhesives of Examples 1-5 and were maintained after aging and the adhesive bonded under various conditions. The bonded adhesive could still be broken if enough strength was applied and the adhesive could be completely removed. Contrary to this, the pressure sensitive adhesive compositions of Comparative Examples 1-5 exhibit adhesion to glass which is very high (C2-C5) or very low (Cl) to be useful for the particular application contemplated.

Table 2. Results of adhesion tests Table 2. Results of adhesion tests (continued) * breakage of the construction, the adhesion was too high to be measured, the adhesive could not be removed completely without solvents and / or mechanical tools.

Examples 6-8 and Comparative Example 6 The pressure sensitive adhesive materials shown in Table 3 were obtained using the method of Examples 1-5.

Table 3 The adhesion was measured at 90 ° for the adhesives of Examples 6-8 and Comparative Example 6 using the test method specified above. The results are summarized in Table 4.

Table 4 Example 9 The multilayer support (2) was prepared by the following procedure: 1. A polyester film (= backing) was hot rolled on the aluminum side of a retroreflective coating based on microspheres. Coree sheet / retroreflective coating is available from 3M, St. Paul, USA as 2005E 3M® Scotchlite® FAVS coating. 2. An ethylene-acrylic acid pattern based on the adhesion-promoting primer was then applied, which is a 70: 30% by weight mixture of Neocryl A45 (commercially available from Zenica, The Netherlands) and Adcoate 50 T 4990 (commercially available) from Morton, USA) to the front or side of the face of the retroreflective coating previously used by a simplified manual printing process to generate a regular arrangement of spots or spots approximately 3 cm in diameter. A sheet of material prepared in this way was cut into a sample of approximately 6 cm by 4 cm. 3. A thin transparent film containing a hem was then laminated, aggravating the front surface of the reflective coating having a stamped adhesion promoting substance. The holographic film which is commercially available from Crown Roll, Leaf, Inc. of Peterson, New Jersey, was a thin, transparent hologram transfer film, which consisted of a polyester coating, a structured layer of methacrylate based of polymethyl, a high-index zinc sulfide reflector, and a thin adhesive. The lamination was carried out at approximately 130 ° C, with a pressure of 2 bar and a speed of 5 cm per minute using a commercially available thermal laminator (Sallmetal, Raalte, Holland). 4. An image on the top of the transparent holographic layer was printed by screen printing using a commercially available silkscreen printing ink (screen printing ink 3M 882 (red)). The ink was dried 30 minutes at 45 ° C. A thick layer of 300 microns of pressure sensitive adhesive was applied from Example 2 by first removing one of the protective coatings and then laminating the PSA to the printed surface by screen printing using a rubber coated roll that was passed over the sample 5 times using the pressure that could be exerted by the hand, thus preparing the multi-layered sheet of the front face type (1) of the invention. The effectiveness of the construction of the multilayer sheet coated with full adhesive was evaluated first by removing the second protective coating, adhering the multi-layer sheet to a glass test surface and qualitatively evaluating the removal behavior as described under the "Removal Capability Test" method above. After the removal of the multi-layer sheet, several areas were examined for the presence of residues: 1) the glass substrate; 2) areas of the retroreflective layer where the adhesion promoting substance had been applied; and 3) areas of the retroreflective layer where no adhesion promoter was applied. The results of the removal capacity test are given in Tables 6 and 7.

Example 10 Example 10 was prepared in an identical manner to that of Example 9, except that the pressure sensitive layer of the Example 3 was applied to the face of the multilayer sheet at a thickness of 300 microns. The results of the removal capacity test are given in Tables 6 and 7.

Example 11 Example 11 was prepared in a form identical to that of Example 9, with the exception that a 300 micron layer of the PSA of Example 4 was applied to the multilayer sheet. The results of the removal capacity test are given in Tables 6 and 7.

Example 12 Example 12 was prepared in an identical form to that of Example 9, with the exception that a different screen printing ink was used. The screen printing ink applied to the coating of the primer pattern on the retroreflective layer was 3M 910 screen ink (blue), dried 45 seconds at 65 ° C. The results of the removal capacity test are given in Tables 6 and Example 13 Example 13 employed a multilayer sheet as described in Example 12, with the exception that the polyester film present on the aluminum coated side of the retroreflective sheeting was omitted. As in Example 12, a 300 micron layer of the pressure sensitive adhesive denoted by B was present. The adhesive layer was laminated to the aluminum coated side or the back side of the retroreflective coating, however, instead of the front face , thereby creating a multi-layered sheet of the back face type suitable for being applied to a painted metal surface such as the body of a motorcycle.

Examples 14-15 Examples 14 and 15 were prepared in the same manner as in Example 13, with the exception that pressure sensitive adhesives denoted as C and D, respectively, were employed at a thickness of 300 microns.

Table 5. Construction of Examples 9-15 (The order in the Table reflects the construction of the multilayer sheet) Ink 1. 3M 882 screen printing ink (red), dried 30 minutes at 45 ° C Ink 2. Serial printing ink 3M 910 (blue), dried 45 seconds at 65 ° C *) 2005E 3M® Scotchlite® coating FAVS without polyester support Table 6. Results of the proofing capacity tests (1 hour at 23 ° C) Table 6. Results of the removal capacity tests (1 hour at 23 ° C) (sontinuasión) TABLE 7 The bonded multilayer sheets of Examples 9-15 were stored for a variety of conditions as indicated in the Table and then removed from the glass. All failures indicated that tamper-proof features of multiple layer sheets such as separation were operational. The adhesive residues and / or support residues on the glass substrate were completely removable manually.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, property is claimed as contained in the following:

Claims (9)

1. A multi-layered sheet, characterized in that it comprises a flexible backing and a layer of pressure-sensitive adhesive for joining the multi-layered sheet to a smooth and rigid surface, wherein the pressure-sensitive adhesive is easily removable from the surface, and is selected so that an adhesive layer with a thickness of 300 μ exhibits a 90 ° adhesion of between 20 and 85 N / 2.54 cm of the glass after a drying time of 3 days at a temperature of 70 ° C.

2. The multi-layered sheet according to claim 1, characterized in that the support comprises at least one damageable layer and exhibits a layered failure when shedding from the multi-layered surface. The multi-layer sheet according to any of claims 1 6 2, characterized in that the layer of pressure sensitive adhesive comprises a pressure sensitive adhesive, which can be obtained by the polymerization of a precursor comprising a) a monomeric component which contains one or more alkyl acrylates, the alkyl groups of which have an average of 4-14 carbon atoms, and more than 2-8 percent of at least one copolymerizable monomer having a polar group, b) 5-15 percent hydrophobic silica, c) one or more polymerization initiators, and d) one or more crosslinking compounds in a concentration that results in a crosslinking density obtainable by the use of hexanediol diacrylate as a compound reference crosslinker at a concentration between 0.06 and 0.14 percent. 4. The multi-layer sheet according to claims 2-3, characterized in that the damaging layer comprises a pattern of material that regulates the adhesion, cinegrams and / or holograms, a destructible or reversibly deformable layer and / or patterns and / or printed indications. 5. The multi-layer sheet according to any of claims 2-4, characterized in that it additionally comprises a reflective layer and / or a cover layer. 6. The multi-layer sheet according to any of claims 2-5, with a sequence of layers (3) / (4d) / (4a) / (7) f (3) / (7) / (4a) / (4cD, (3) / (4d) / (4a) / (7) or (6) / (4d) / 0 *) / (4a) / (7) / (3). 7. The use of a multi-layer sheet in accordance with any of claims 1-6 to prepare labels or temporary labels such component vignettes of rights. 8. A pressure sensitive adhesive, characterized in that it can be obtained by the polymerization of a precursor comprising a) a monomeric component which contains one or more alkyl acrylates, the alkyl groups of which have an average of 4-14 atoms of C, and more than 2-8 percent of at least one copolymerizable monomer having a polar group, b) 5-15 percent of hydrophobic silica, c) one or more polymerization initiators, and d) one or more compounds crosslinking agents in a concentration that results in a crosslinking density obtainable by the use of hexandiol diacrylate as a reference crosslinking compound at a concentration of between 0.06 and 0.14 percent. 9. A pressure sensitive adhesive, characterized in that it can be obtained by the polymerization of a precursor comprising a) a monomeric component which contains one or more alkyl acrylates, the alkyl groups of which have an average of 4-14 atoms of C, and more than 8-20 percent of at least one copolymerizable monomer having a polar branch, b) 5-15 percent of hydrophobic silica, c) one or more polymerization initiators, and d) one or more crosslinking compounds in a concentration that results in a crosslinking density obtainable by the use of hexandiol diacrylate as a reference crosslinking compound at a concentration of between 0.06 and 0.11 percent. SUMMARY OF THE INVENTION The present invention relates to a multi-layer sheet (1) comprising a flexible support (2) and a layer of pressure-sensitive adhesive (3) for joining the multi-layer sheet to a smooth and rigid surface (5), wherein the pressure-sensitive adhesive is completely removed from the surface (5) and selected so as to exhibit an adhesive layer with a thickness of 300 μm at a 90 ° adhesion of between 20 and 85 N / inch of glass after a drying time of 3 days at a temperature of 70 ° C. The flexible support (2) preferably comprises at least one damaged layer (4) and shows intralayer faults when the multilayer sheet (1) is detached from the surface (5). The present invention further relates to a pressure sensitive adhesive which can be obtained by polymerizing a precursor comprising a) a monomeric component which contains one or more alkyl acrylates, the alkyl groups of which have an average of 4-14. C atoms, and 2-8 percent of at least one copolymerizable monomer having a polar group, b) 5-15 percent hydrophobic silica, c) one or more polymerization initiators, and d) one or more crosslinking compounds in a concentration which results in a crosslinking density obtainable by the use of hexandiol diacrylate as the reference crosslinking compound in a concentration of between 0.06 and 0.14 percent. The present invention further relates to a pressure sensitive adhesive which can be obtained by polymerizing a precursor comprising a) a monomeric component which contains one or more alkyl acrylates, the alkyl groups of which have an average of 4-14. C atoms, and 8-20 percent of at least one copolymerizable monomer having a polar group, b) 5-15 percent of hydrophobic silica, c) one or more polymerization initiators, and d) one or more crosslinking compounds in a concentration which results in a crosslinking density obtainable by the use of hexandiol diacrylate as the reference crosslinking compound in a concentration of between 0.06 and 0.11 percent.