EP4359463A1

EP4359463A1 - Biodegradable pressure-sensitive adhesive

Info

Publication number: EP4359463A1
Application number: EP22735868.6A
Authority: EP
Inventors: Philipp WEGENER; Ernesto Rafael OSORIO BLANCO; Sara Schröder
Original assignee: Beiersdorf AG; Tesa SE
Current assignee: Beiersdorf AG; Tesa SE
Priority date: 2021-06-21
Filing date: 2022-06-21
Publication date: 2024-05-01
Also published as: WO2022268837A1; AU2022299275A1; TW202311483A

Abstract

The invention aims to provide a pressure-sensitive adhesive which has good adhesive performance parameters and is biodegradable as defined by current standards. This is achieved with a pressure-sensitive adhesive which comprises at least one polyhydroxyalkanoate and which is characterized in that the polyhydroxyalkanoate - comprises 20% to 70% by weight structural units derivable from 3-hydroxybutyric acid (3-HB); and - comprises at least one further structural unit derivable from a hydroxyalkanoic acid selected from the group consisting of 4-hydroxybutyric acid (4-HB), 3-hydroxyvaleric acid (3-HV), 4-hydroxyvaleric acid (4-HV), 3-hydroxyhexanoic acid (3-HX) and/or 4-hydroxyhexanoic acid (4-HX). The invention further provides - a multilayer composite system comprising at least one carrier material and a pressure-sensitive adhesive according to the invention; - a skin-wearable medical device (wearable device) that comprises a pressure-sensitive adhesive according to the invention and a medical system; and - the use of a pressure-sensitive adhesive according to the invention as an adhesive for producing adhesive bonds on the skin.

Description

BIODEGRADABLE ADHESIVE

The invention relates to the technical field of pressure-sensitive adhesives, such as are used in many areas of technology for the temporary or permanent bonding of a wide variety of substrates and also in medicine for providing dressings for bonding to the skin. More specifically, the invention proposes a pressure-sensitive adhesive based on a polyhydroxyalkanoate, which has significantly improved biodegradability compared to conventional pressure-sensitive adhesives.

In almost all areas of life, increasing efforts to achieve more sustainability have been evident for several years. In this context, awareness of the ecological problems associated with the entry of persistent plastic particles into the environment has also grown. There is therefore increasing demand for products that can be quickly and easily transformed into harmless decomposition products after disposal. So-called biodegradable plastics or materials based on biodegradable polymers receive the greatest attention.

"Biodegradable polymers" is a term for natural, bioidentical and synthetic polymers which, in contrast to conventional plastics, are broken down by a large number of microorganisms in a biologically active environment (compost, sludge, soil, waste water); this does not necessarily happen under normal household conditions (composting in the garden). A definition of biodegradability can be found in the European standard DIN EN 13432 (biological degradation of packaging) and the international standard ISO 14855-1 (aerobic biodegradability of plastics).

The expert distinguishes between disintegration (decomposition) and biodegradability. Disintegration (decomposition) refers to the physical decomposition into very small fragments.

The determination of the ability to disintegrate or the degree of decomposition of polymers is described in DIN EN ISO 20200, among others. Here, the sample to be examined is stored in a defined artificial solid waste at 58 ± 2 °C for at least 45 and at most 90 days. Subsequently, the entire sample through l sieved through a 2 mm sieve and the degree of decomposition D determined according to equation (1) below:

Where m 1 : the initial dry mass of the sample material and m _r : the dry mass of the remaining sample material obtained by sieving.

Biodegradability is generally understood to mean the ability of microorganisms to decompose a chemical compound or an organic material in the presence of oxygen into carbon dioxide, water and salts of other elements present (mineralization) with the formation of new biomass or in the absence of oxygen into carbon dioxide, methane, mineral salts and new biomass. Biological degradation takes place extra- and/or intracellularly by bacteria, fungi and microorganisms and their enzymes. The biodegradability of plastic materials is described, among other things, in ISO 14855-1:2012 "Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions" or in the related DIN EN 13432 "Requirements for the recycling of packaging through composting and biological degradation ) normatively regulated. The material to be tested is subjected to an aerobic degradation test, and a degree of degradation of at least 90% compared to a suitable reference substance must be achieved within a maximum of six months. The degree of degradation is determined by the measured development of carbon dioxide. The comminuted sample is stored with vermiculite or well-performing aerated compost as inoculum in an air-fed vessel at 58 ± 2°C and CO ₂ evolution continuously recorded. Due to the complexity of the equipment, there are a number of testing institutes that have specialized in testing and then issue a corresponding certificate. At the end of the test, the degradation rate D is found according to equation (2) below as:

(CC^jj -(C02)g 4nn

Dt = - - ^ x 100

* ThC0 _{2 2} )

there is

(C0 ₂ )T: the cumulative amount of carbon dioxide evolved in each composting vessel containing the test substance, in grams per vessel;

(C0 ₂ )B: the average cumulative amount of carbon dioxide formed in the blank vessels, in grams per vessel;

ThC0 ₂ : the theoretical amount of carbon dioxide that can be formed by the test substance, in grams per vessel.

In addition to biodegradability, DIN EN 13432 also includes a test to determine the quality of the compost resulting from degradation. This must not have any negative effects on plant growth. As a rule, biodegradable components also have a high rate of disintegration, whereas the disintegration of a material does not necessarily indicate biodegradability.

Other relevant standards for determining and evaluating the biodegradability of plastics include ISO 17088 "Plastics - Organic recycling - Specifications for compostable plastics" and ASTM D6400 "Standard Specification for Labeling of Plastics Designed to be Aerobically Composted in Municipal or Industrial Facilities". .

In the context described above, biodegradability is also becoming increasingly important for pressure-sensitive adhesive tapes and medical products, with the possibilities for producing suitable pressure-sensitive adhesives being very limited in this regard. Pressure-sensitive adhesives are amorphous materials with a low glass transition point. The classic framework polymers such as natural rubber, styrene block copolymers or polyacrylates are not biodegradable according to the underlying European standards such as DIN EN 13432. The same applies to the usual tackifier resins such as rosin derivatives, hydrocarbon resins or terpene-phenolic resins. Silicone pressure-sensitive adhesives are completely out of the question due to their excellent aging stability. Pressure-sensitive adhesives find a wide range of uses in the manufacture of products for wound care and for other medical applications. A prerequisite for this is that such adhesives are skin-friendly. For example, they may only contain very small amounts of residual monomers and should not have any irritating or allergenic potential.

The main task of the adhesives used is secure adhesion of the article intended to be placed on the skin to the skin, and at the end of the application time easy and painless detachment and removal from the skin. The first property is often regarded as the most important property of a plaster or similar article, but it is not always achievable, since perspiration, secretion of sebum, skin fat or sweat lead to undesired premature detachment from the skin. How quickly the bond detaches itself is generally dependent on the liquid absorption capacity of the wound dressing and/or the adhesive and on the water vapor permeability of the article as a whole. An objective criterion for differentiating the breathability of plaster adhesives is the determination of the water vapor permeability (MVTR), whereby a certain amount of water, e.g. in a period of 24 hours and at a temperature of 35°C, evaporates through an area covered with the plaster and is quantified by differential weighing. (The MVTR is measured according to various standards, including the DIN EN 13726-2 standard, the measured values of which are not comparable with each other.

In addition to the requirements described above, which plasters must meet in use, there are other properties and regulations that must be taken into account. These are defined in the current guidelines of UNEP and ECHA.

The problem of disposal is becoming increasingly important, especially in the case of medical products that are generally available and are to be regarded as consumer goods. This has a very strong impact on the manufacture and marketing of such products. Sustainable approaches and, in this context, the biodegradability of products are becoming increasingly important for consumers and are therefore increasingly becoming the focus of manufacturers.

The presence of heteroatoms in the main carbon chain is generally regarded as a structural condition for biodegradability. This is due to the higher polarity of the bond and the existing lone pairs of electrons

Heteroatoms have higher reactivity than CC bonds, often in better Accessibility to microbial degradation results, for example through hydrolysis. Advantageous polymers as a basis for biodegradable adhesives are therefore those that have functional groups such as ester, amide, imine or enamine groups, which can then act as points of attack for biological degradation.

In this context, CN 102867459 A describes a biodegradable sticker label which comprises a surface material layer, an adhesive layer and a backing paper, with the adhesive layer forming the middle layer.

The backing paper consists of silicone oil-coated glassine paper; the surface material layer includes the following composition:

- 30 to 70 parts by weight of polyhydroxyalkanoate up to 150 parts by weight of polylactic acid

- up to 50 parts by weight starch

1 to 15 parts by weight plasticizer

0.3 to 1 part by weight of nucleating agent and

1 to 10 parts by weight of lubricant; and the adhesive layer comprises the following composition:

- 20 to 60 parts by weight starch

- 90 to 110 parts by weight of water

- 5 to 50 parts by weight of polyhydroxyalkanoate

- 0.5 to 20 parts by weight of alkaline matter

- 0.5 to 10 parts by weight of impregnating agent, 0.1 to 5 parts by weight of crosslinking agent and

0.1 to 5 parts by weight antibacterial material.

Complete biodegradation should be achieved without compost treatment.

In a broader context, EP 2305324 A1 relates to a biocompatible medical implant for soft tissue applications comprising a poly(4-hydroxybutyrate-co-hydroxyalkanoate) copolymer composition, the copolymer having a weight average molecular weight of 10,000 to 10,000,000 daltons. Overall, it can be stated that there is a continuing need for high-performance PSAs that can be used widely and take sustainability aspects into account.

It was an object of the invention to provide a pressure-sensitive adhesive which has good technical adhesive parameters and is biodegradable within the meaning of the applicable standards. It was a supplementary object of the invention to provide such a pressure-sensitive adhesive which can be produced at least in part and ideally entirely from bio-based raw materials.

A first and general subject of the invention, with which the object is achieved, is a pressure-sensitive adhesive which comprises at least one polyhydroxyalkanoate and which is characterized in that the polyhydroxyalkanoate

- comprises from 20 to 75% by weight of structural units deriving from 3-hydroxybutyric acid (3-HB); and at least one further structural unit which is based on a hydroxyalkanoic acid selected from the group consisting of 4-hydroxybutyric acid (4-HB), 3-hydroxyvaleric acid (3-HV), 4-hydroxyvaleric acid (4-HV), 3-hydroxyhexanoic acid (3- HX) and/or 4-hydroxyhexanoic acid (4-HX).

PSAs of this type have proven to be high-performing and reliably biodegradable.

In accordance with the general understanding, a “pressure-sensitive adhesive” is understood to mean a material which has the property of forming a permanent connection to an adhesion substrate even under relatively weak pressure. Pressure-sensitive adhesives are generally permanently inherently tacky at room temperature, i.e. they have a certain viscosity and tack. This is attributed in particular to the fact that they wet the surface of a substrate even with little pressure.

Without wishing to be bound by this theory, it is often assumed that a pressure-sensitive adhesive can be regarded as an extremely highly viscous liquid with an elastic portion, which consequently has characteristic viscoelastic properties that lead to the permanent inherent tack and pressure-sensitive adhesiveness described above. It is assumed that, in the case of pressure-sensitive adhesives, mechanical deformation leads both to viscous flow processes and to the build-up of elastic restoring forces. Of the The proportionate viscous flow serves to achieve adhesion, while the proportionate elastic restoring forces are necessary in particular to achieve cohesion. The relationships between rheology and pressure-sensitive tack are known in the prior art and are described, for example, in "Satas, Handbook of Pressure Sensitive Adhesives Technology", Third Edition, (1999), pages 153 to 203.

The storage modulus (G') and the loss modulus (G") are usually used to characterize the degree of elastic and viscous content, which can be determined by means of dynamic mechanical analysis (DMA), for example using a rheometer, as is described, for example, in WO 2015/189323 A1 is disclosed.

In the context of the present invention, an adhesive is preferably understood as pressure-sensitive adhesive and thus as pressure-sensitive adhesive if at a temperature of 23 ° C in the deformation frequency range of 10 ° to 10 ¹ rad / sec G 'and G "are each at least partially in the range of 10 ³ to 10 ⁷ Pa.

Polyhydroxyalkanoates, also known as PHAs for short, are polyesters that can formally be traced back to a monomer base of one or more hydroxyalkanoic acids. They accordingly have a structure of the formula H-[-0-RC(0)-] _n -0H, where R is a branched or unbranched and functionalized or unfunctionalized alkylene radical. Technically, however, PHAs are generally not synthesized by way of a polymerization of hydroxyalkanoic acids, but biologically produced by bacterial cultures. The composition of the PHAs is controlled by the biological material made available to the bacteria and in particular by the selection of the bacteria.

The hydroxyalkanoic acids on which the polyhydroxyalkanoate of the PSA of the invention is formally based are preferably hydroxylated in the 3- or 4-position. The polyhydroxyalkanoate thus has a side functionalization of alkyl groups on its main chain in part. According to the invention, the polyhydroxyalkanoate comprises 20 to 75% by weight of structural units which can be traced back to 3-hydroxybutyric acid. The PHA thus has methyl groups protruding from the main chain on these structural units.

The polyhydroxyalkanoate of the pressure-sensitive adhesive of the invention also has structural units based on 4-hydroxybutyric acid (4-HB), 3-hydroxyvaleric acid (3-HV), 4-hydroxyvaleric acid (4-HV), 3-hydroxyhexanoic acid (3-HX) and/or 4- Hydroxyhexanoic acid (4-HX) can be attributed, so that structural units without side functionalization and other methyl or propyl side chains protruding from the main chain are also possible.

The polyhydroxyalkanoate preferably comprises structural units (3-HB) at 30 to 65% by weight, particularly preferably at 35 to 60% by weight. In this way, a substantial part of the pendant functionalization consists of short alkyl residues. This is advantageous because such a side functionalization expresses an amorphous character of the polymer.

In one embodiment, the polyhydroxyalkanoate also comprises structural units attributable to (4-HB), and the weight ratio (3-HB):(4-HB) is from 5.5:4.5 to 2:3, preferably from 1.05: 0.95 to 0.95 : 1.05. As has been shown, polymers with a particularly amorphous character and a comparatively low glass transition temperature are obtained in this way, which, with their rheological profile, are therefore very suitable for use in pressure-sensitive adhesives.

Overall, in the sense of the best possible PSA properties, it is preferred if the at least one polyhydroxyalkanoate of the PSA of the invention has only very low crystallinity. In this sense, the at least one polyhydroxyalkanoate of the PSA of the invention preferably has an enthalpy of fusion of <15 J/g, particularly preferably <10 J/g. The at least one PHA of the pressure-sensitive adhesive of the invention very particularly preferably has no crystallinity.

The polyhydroxyalkanoate of the pressure-sensitive adhesive of the invention also preferably has a glass transition temperature of less than 0.degree. This property has an advantageous effect on what is known as the flowability of the pressure-sensitive adhesive and ultimately also on its adhesive strength.

The polyhydroxyalkanoate of the pressure-sensitive adhesive of the invention can, in principle, comprise further structural units which are attributable to hydroxyalkanoic acids in addition to those previously mentioned. However, these structural units are preferably present in minor proportions. Examples of such further structural units are 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxyundecanoic acid, 3-hydroxydodecanoic acid, 4-hydroxyhexanoic acid, 4-hydroxyheptanoic acid, 4-hydroxyoctanoic acid, 4-hydroxynonanoic acid, 4-hydroxydecanoic acid, 4-hydroxyundecanoic acid and 4-hydroxydodecanoic acid. Preferably, however, the PHA comprises excluding structural units based on 3-hydroxybutyric acid (3-HB), 4-hydroxybutyric acid (4-HB), 3-hydroxyvaleric acid (3-HV), 4-hydroxyvaleric acid (4-HV), 3-

Hydroxyhexanoic acid (3-HX) and/or 4-hydroxyhexanoic acid (4-HX).

The polyhydroxyalkanoate of the PSA of the invention is preferably crosslinked. This means that the originally individual macromolecules of the PHA are at least partially connected to one another by chemical bonds in such a way that they are present as a more or less continuous, three-dimensional network.

In a preferred embodiment, the crosslinking is initiated by free radicals. Accordingly, the polyhydroxyalkanoate of the PSA of the invention is preferably free-radically crosslinked,

In this case, the composition to be crosslinked for producing the pressure-sensitive adhesive of the invention preferably comprises one or more initiators which can initiate a crosslinking reaction proceeding via free radical formation. Suitable initiators are known in principle to those skilled in the art. Examples of suitable radical sources or initiators are peroxides, hydroperoxides, azo compounds and compounds with benzophenone substructures. Crosslinking is preferably initiated by at least one compound selected from the group consisting of peroxides and compounds with benzophenone substructures. In this sense, the PSA of the invention preferably comprises at least one compound selected from the group consisting of peroxides and compounds with benzophenone substructures. It is clear to the person skilled in the art that this formulation, in the strict sense, rather addresses the composition to be crosslinked for the production of the pressure-sensitive adhesive of the invention, while the decomposition products of the initiator would actually be expected in the pressure-sensitive adhesive itself.

Crosslinking is particularly preferably initiated by a compound selected from the group consisting of dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, dicumyl peroxide (DCP) and 4-benzoylphenyl acrylate. In the sense mentioned above, the pressure-sensitive adhesive of the invention therefore particularly preferably contains at least one compound selected from the group consisting of dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, dicumyl peroxide (DCP) and 4-benzoylphenyl acrylate.

The pressure-sensitive adhesive or the composition to be crosslinked to produce the pressure-sensitive adhesive preferably contains one or more free-radical initiators in a total amount of from 0.1 to 10% by weight, more preferably from 0.5 to 7% by weight, in particular from 1 to 5% % by weight, based in each case on the total weight of PSA or of the composition.

The activation of the initiators and thus of the free-radical crosslinking is preferably carried out by means of UV radiation or heat. It can be advantageous to use, in addition to the initiators, one or more auxiliaries to avoid or at least to reduce chain degradation processes caused by free radicals. These auxiliaries or stabilizers improve the efficiency of the initiators by suppressing undesirable chain degradation reactions. Suitable stabilizers are multifunctional organic compounds with high reactivity towards free radicals. Preferred stabilizers are triallyl isocyanurate (TAIC) and tetraethylthiuram disulfide (TEDS).

In another embodiment, the polyhydroxyalkanoate is chemically crosslinked. This means that the crosslinking is effected by means of a chemical crosslinker. This is a linear or branched compound with at least two reactive centers, ie at least two functionalities in the molecule, which can react with suitable functional groups of the polyhydroxyalkanoate to form chemical bonds. Preferred crosslinkers are compounds containing one or more epoxide groups, isocyanate groups, carbodiimide groups, C-C double bonds, aldehyde groups, OH groups, carboxylic acid groups and/or amino groups.

In the simplest case, such crosslinkers are mixed into the composition containing the polyhydroxyalkanoate to be crosslinked; then the crosslinking reaction is initiated. The initiation usually takes place through temperature input, but can also start at room temperature. In order to accelerate or generally enable the crosslinking reaction, it may be necessary to use a crosslinking catalyst or a substance with an accelerating effect.

In the simplest case, the chemical crosslinking takes place via the terminal functional groups of the polymer chains of the PHA, ie usually via terminal COOH and/or OH groups. In addition, it is possible for the polyhydroxyalkanoate to have functional groups suitable for a crosslinking reaction. The PHA can be used in the non-networked io 0.1 to 25% by weight, more preferably 2 to 15% by weight, in particular 5 to 12% by weight, of structural units containing functional groups suitable for crosslinking.

The functional groups suitable for a crosslinking reaction can also be contained in the side functionalizations of the structural units. The functional groups of the structural units of the PHA are preferably selected from the group consisting of C-C double bonds, hydroxy groups, carboxy groups and amino groups; most preferably they are terminal hydroxy and/or carboxy groups of the PHA polymer chains.

Some possible chemical crosslinking processes are described in more detail below by way of example.

For polyhydroxyalkanoates that are functionalized with C-C double bonds, 1 to 2 g of radical initiator, e.g. 2,2'-azobis(2 -methylbutyronitrile) are given. Crosslinking can be carried out directly with this composition, but it is also possible to add 5 to 10% by weight, based on the PHA to be crosslinked, of monoethylenically unsaturated compounds as reactive diluents or co-substrates, for example (meth)acrylic esters , cyclic ketene acetals or itaconates. The crosslinking reaction is carried out under a nitrogen atmosphere and is started either by UV radiation or by heating the reaction mixture to 80.degree. The mixture is stirred for 5 hours and the crosslinked composition formed is purified by precipitation or dialysis or used without further purification.

PHAs that are functionalized with carboxyl and/or hydroxyl groups and have a weight-average molecular weight M _w of <50,000 g/mol, preferably from 10,000 to 30,000 g/mol, can be crosslinked with a diisocyanate (NCO), for example with hexamethylene diisocyanate , isophorone diisocyanate and/or methylene diphenyl isocyanate. The amount of diisocyanate to be used depends on the amount of carboxyl and hydroxyl groups in the PHA (OH number). An NCO:OH ratio of approx. 1 is aimed for. In a final crosslinking step, the network obtained can be converted to the desired final crosslinking by adding typical COOH crosslinking agents, for example difunctional or multifunctional epoxy crosslinking agents such as tetraglycidyl-m-xylenediamine degree of networking are brought. The degree of crosslinking is preferably 0.5 to 1% and is based on the carboxy groups.

For correspondingly functionalized PHAs with a weight-average molecular weight M _w of >50,000 g/mol, crosslinking preferably takes place with a polyisocyanate, for example with trimerized hexamethylene diisocyanate. In this case, an NCO:OH ratio of 0.6 to 1 is aimed for.

The final crosslinking described can also take place via polycarbodiimides; this is also possible, in particular, for PHAs containing amino groups. Typically, from 0.1 to 2% by weight of polycarbodiimide, based on the total weight of the PHA to be crosslinked, is used.

In addition to the crosslinking already described, the polyhydroxyalkanoate of the pressure-sensitive adhesive of the invention can also be crosslinked by physical methods, for example by forming blend systems with one or more substances selected from the group consisting of polylactic acid, cellulose, starch, sorbitol, mannose and polyglycerol.

The pressure-sensitive adhesive of the invention can in principle comprise one or more polyhydroxyalkanoates as described above. All of the above statements relating to “the polyhydroxyalkanoate” obviously apply if the PSA comprises a plurality of polyhydroxyalkanoates as described above, equally for all conceivable subsets and for all of these polyhydroxyalkanoates.

In addition to the constituents mentioned up to this point, the pressure-sensitive adhesive of the invention can have further components which are preferably likewise biodegradable. The PSA of the invention preferably comprises one or more components selected from the group consisting of UV stabilizers, antioxidants, hydrophilizing agents, tackifiers, fillers, pigments, dyes, flame retardants, foaming agents, antistatic agents, plasticizers, surfactants, breathability improvers and sugar esters. In particular, the PSA of the invention comprises one or more tackifiers and/or plasticizers. In one embodiment, the PSA of the invention comprises antibacterial (antiseptic) and/or skin care substances.

The term “tackifier” or also “adhesive resin” or “tackifier” is understood by the person skilled in the art to mean a resin-based substance that increases the stickiness of the pressure-sensitive adhesive. Examples of tackifiers are hydrocarbon resins (for example polymers based on unsaturated C5 or C9 monomers), terpene-phenolic resins, polyterpene resins based on α- and/or β-pinene and/or d-limonene, aromatic resins such as coumarone-indene resins or resins based on styrene or o-methylstyrene and rosin and its derivatives, for example disproportionated, dimerized or esterified resins, for example reaction products with glycol, glycerol or pentaerythritol. Natural resins such as colophony resins and derivatives thereof are preferably used.

The addition of tackifiers in small amounts of up to 1% by weight is possible without the biodegradability of the PSA of the invention being lost. With larger amounts that are added to the PSA, however, it is possible that its biodegradability is no longer given. Tackifiers are therefore preferably avoided.

Examples of suitable miscible plasticizers are aliphatic and aromatic mineral oils, polyethylene and polypropylene glycol, di- or polyesters of phthalic acid, citric acid, trimellitic acid or adipic acid, liquid rubbers (e.g. low molecular weight nitrile or polyisoprene rubbers), liquid polymers of butene and/or isobutene , acrylic acid esters, polyvinyl ether, liquid and soft resins based on the raw materials of adhesive resins, wool wax and other waxes or liquid silicones. Plasticizers from renewable raw materials are particularly preferably used, such as bio-based polyoxytrimethylene glycol, vegetable oils, preferably refined vegetable oils such as rapeseed oil and soybean oil, fatty acids or fatty acid esters, or epoxidized vegetable oils, for example epoxidized soybean oil. In particular, biodegradable plasticizers are used, preferably di- or poly-esters of citric acid or adipic acid. The plasticizer, in particular the biodegradable one, is more preferably used in amounts of up to 10% by weight (based on the total weight of the PSA), particularly preferably in amounts of up to 5% by weight (based on the total weight of the PSA) , very particularly preferably in amounts of up to 2.5 wt .-% (based on the total weight of the pressure-sensitive adhesive). As with the tackifiers, the addition of any plasticizers is in minor amounts up to 1% by weight is possible without the biodegradability of the pressure-sensitive adhesive of the invention being lost. Here, too, it is possible that when larger amounts are added to the pressure-sensitive adhesive, it is no longer biodegradable. Plasticizers are therefore preferably dispensed with, or biodegradable plasticizers are used.

A “breathability improver” is understood as meaning an additive that increases the water vapor permeability of the adhesive compared to an otherwise identically composed adhesive. Preferred breathability enhancers are sorbitan esters.

What has already been said about the tackifiers and plasticizers applies to the other additives already mentioned above: in small amounts of up to 1% by weight, it is also possible to add non-biodegradable additives without the biodegradability of the pressure-sensitive adhesive being significantly impaired. With larger amounts that are added to the pressure-sensitive adhesive of the invention, it is possible that the pressure-sensitive adhesive is no longer sufficiently biodegradable. Additives, in particular non-biodegradable additives, are therefore preferably dispensed with. On the other hand, biodegradable additives, for example biodegradable fillers, can also be used in larger amounts.

The pressure-sensitive adhesive of the invention can comprise at least one further polymer (B) which is different from the polyhydroxyalkanoate(s) and is likewise a polyester. The polyester (B) can be another polyhydroxyalkanoate, but also a polyester other than a polyhydroxyalkanoate.

In principle, the pressure-sensitive adhesive of the invention can be prepared in any manner conceivable for the person skilled in the art.

For example, to make the pressure-sensitive adhesive, the components can simply be dispersed and mixed in a solvent, which is then removed.

However, as has been shown, the PSA of the invention can also be obtained from the melt. The components are melted and mixed in the melt or partly incorporated into the melt of the copolymer. Another In this respect, the invention relates to a process for producing a pressure-sensitive adhesive according to the invention, which comprises the melting of at least one polyhydroxyalkanoate which comprises o to 20 to 70% by weight of structural units which can be traced back to 3-hydroxybutyric acid (3-HB); and o comprises at least one further structural unit which reacts to an acid selected from the group consisting of 4-hydroxybutyric acid (4-HB), 3-

Hydroxyvaleric Acid (3-HV), 4-Hydroxyvaleric Acid (4-HV), 3-

hydroxyhexanoic acid (3-HX) and/or 4-hydroxyhexanoic acid (4-HX); initiating crosslinking of the polyhydroxyalkanoate; and forming the composition so obtained into a web. The process is carried out in particular at low temperatures, preferably at less than 60°C, in particular at less than 50°C and very particularly preferably at less than 40°C. In particular, this also enables the incorporation of temperature-sensitive substances, e.g. proteins. The other potential components of the PSA of the invention described herein can also be incorporated, in particular homogeneously, into the melt.

A further subject matter of the invention is a multilayer composite system which comprises at least one backing material and a PSA of the invention. The multilayer composite system according to the invention is preferably an overlay for adhesion to the skin or an adhesive tape.

In one embodiment, the multilayer composite system is an overlay for bonding to the skin (hereinafter also “skin overlay” or “overlay”), preferably human skin. Pads according to the invention thus offer access to biodegradable skin pads that meet all adhesive and medical requirements.

In principle, all rigid, flexible and elastic fabrics made of synthetic and natural raw materials are suitable as carrier material for the pad to be bonded to the skin. The carrier material preferably consists of an air and water vapor permeable but water-impermeable polymer layer with a thickness of about 10 to 200 p.m. Preference is given to backing materials which, after application of the adhesive, can be used in such a way that they meet the requirements for a functional skin contact. Textiles such as wovens, knits, scrims or fleeces, further nets, foils, foams and laminates made from the above materials and papers may be mentioned by way of example. The carrier material is preferably a film, a woven fabric or a fleece, particularly preferably with a thickness of 20 to 200 μm, in particular with a weight per unit area of 20 to 200 g/m ² .

Furthermore, these materials can be pre-treated or post-treated. Common pre-treatments are plasma or corona treatment and hydrophobing; Common post-treatments are calendering, tempering, laminating, punching, covering and sterilizing.

In principle, both natural and synthetic carrier materials can be considered. The carrier material is preferably selected from the group consisting of cotton; Viscose; polypropylene; Polyesters, in particular selected from polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyisosorbate terephthalate (PIT) and copolymers of these; polyamides; PVC; polyethylene; polyurethanes; silicones and polylactic acid. The carrier material is preferably selected from the group consisting of cotton, viscose, polyesters, polyethylene and polyurethanes.

The carrier material is particularly preferably a polyurethane film, a polyethylene film, a polyester fleece, a woven fabric made from viscose, polyester or cotton or a woven fabric made from any mixtures of viscose, polyester and/or cotton.

The pressure-sensitive adhesive of the invention can be applied to the backing material by conventional methods. It is usually covered on one side with the carrier material, and the structure created in this way is applied as a composite. Depending on the substrate used, the moisture vapor transmission rate, strength of a wound dressing, cushioning against pressure, and other physical properties of the dressing can be controlled.

In order to ensure easy handling, the skin patch is preferably covered with a protective layer, for example siliconized paper or a siliconized film (release liner).

The skin dressing may also include a substrate for absorbing wound exudate. The pad can basically be used as a full-surface self-adhesive or partial self-adhesive skin pad (dressing), in particular as a wound pad, plaster, hygiene item, cosmetic and/or dermatological pad, patch, tape, bandage, colostomy bag, fixation bandage, kinesio tape, cataplasma, bandage, Surgical cover or mask be designed. The overlay is preferably a patch. In addition, it can also be in the form of a less adhesive patch or pad, for example, with the adhesive strength being able to be set specifically according to the particular application.

The pressure-sensitive adhesive of the invention is preferably present in the overlay as a layer with a layer thickness of up to 120 gm, particularly preferably up to 100 gm, in particular up to 80 gm.

In a further embodiment, the multilayer composite system according to the invention is an adhesive tape.

For the purposes of this invention, the general expression “adhesive tape” includes all flat structures such as tapes or tape sections extended in two dimensions, tapes with extended length and limited width, diecuts, labels and the like. The adhesive tape can be made available in fixed lengths such as by the meter or as endless goods on rolls (Archimedean spiral) or as cross-wound spools. A layer or optionally several layers of adhesive can be applied to one or both sides of the carrier material.

The backing materials used for the adhesive tape are the usual backing materials familiar to the person skilled in the art, such as paper, fabric, fleece or foils, the latter made, for example, from polyesters such as polyethylene terephthalate (PET), polyethylene, polypropylene, stretched polypropylene or polyvinyl chloride. The carrier material is particularly preferably based on renewable raw materials such as paper, fabrics made from, for example, cotton, hemp, yurt, nettle fibers or bio-based and/or biodegradable polymers, for example polylactic acid.

The backing material can be provided with a pressure-sensitive adhesive on one or both sides. In the case of two-sided finishing with pressure-sensitive adhesive, both pressure-sensitive adhesives are preferably pressure-sensitive adhesives of the invention. The adhesive tape is preferably formed by applying the pressure-sensitive adhesive to some or all of the surface of the backing. The coating can also take place in the form of one or more strips in the longitudinal direction (machine direction), optionally in the transverse direction, but in particular it is all-over. Furthermore, the PSA can be applied in grid dot form by screen printing, in which case the adhesive dots can also be of different sizes and/or distributed differently, by gravure printing in longitudinally and transversely connected webs, by grid printing or by flexographic printing. The pressure-sensitive adhesive can be in the form of a dome (produced by screen printing) or else in another pattern, such as a grid, stripes, or zigzag lines. Furthermore, it can also be sprayed on, for example, which results in an irregular application pattern.

The coating thickness of the PSA is preferably between 10 and 200 g/m ² , more preferably between 15 and 75 g/m ² and particularly preferably between 20 and 50 g/m ² .

It is advantageous to use an adhesion promoter, a so-called primer layer, between the backing material and the pressure-sensitive adhesive, or to physically pretreat the backing surface to improve the adhesion of the adhesive to the backing material. The above-described application of the pressure-sensitive adhesive to the backing also encompasses application to a backing provided with a primer layer. The known dispersion and solvent systems can be used as primers, for example those based on isoprene- or butadiene-containing rubber, acrylate rubber, polyvinyl, polyvinylidene and/or cyclo rubber. Isocyanates or epoxy resins as additives improve adhesion and in some cases also advantageously increase the shear strength of the adhesive tape. The adhesion promoter can also be applied to the carrier film by means of a coextrusion layer.

Flame treatment, corona or plasma treatment, for example, are suitable as physical surface treatments.

Furthermore, the carrier material can be subjected to an anti-adhesive physical treatment or coating on the rear or top side, ie opposite the adhesive side, in particular equipped with a release agent or release system (if appropriate mixed with other polymers). Examples of separating or - synonymous referred to - release layers are those made of stearyl compounds, for example polyvinylstearyl carbamate, stearyl compounds of transition metals such as Cr or Zr, ureas of polyethyleneimine and stearyl isocyanate; or from polysiloxanes. The term "stearyl" is a synonym for all straight or branched alkyl or alkenyl radicals with a carbon number of at least 10, such as an octadecyl radical. Suitable release agents also include surface-active release systems based on long-chain alkyl groups such as stearyl sulfosuccinates or stearyl sulfosuccinamates, but also polymers selected from the group consisting of polyvinyl stearyl carbamates, polyethyleneimine stearyl carbamates, chromium complexes of C14 to C28 fatty acids and stearyl copolymers. Release agents based on acrylic polymers with perfluorinated alkyl groups, silicones, for example based on polydimethylsiloxanes, and fluorosilicone compounds are also suitable.

The carrier material can also be pre-treated or post-treated in some other way. Other common pre-treatments are hydrophobing, common post-treatments are calendering, tempering, laminating, punching and covering.

The adhesive tape can be laminated with a commercially available release film or release paper, which is usually composed of a base material made of polyethylene, polypropylene, polyester or paper, which is coated on one or both sides with polysiloxane. Such a structure is usually also referred to as a release liner.

A further subject matter of the invention is a medical device that can be worn on the skin, in particular on human skin, and which comprises a pressure-sensitive adhesive of the invention and a medical system. A "medical system" is understood to mean a sequence of elements that, in their entirety and in their interaction, fulfill a medical function, which can consist, for example, of releasing an active substance, stimulating certain areas of the body or recording medically relevant data . In this respect, the medical device that can be worn on the skin is preferably a device for releasing an active substance, for stimulating areas of the body or for acquiring medical data. The release of an active ingredient can be provided in particular transdermally; for example, patients with type 2 diabetes can be injected with insulin via a microneedle, eg in a three-day rhythm.

The stimulation is particularly preferably an electronic stimulation, e.g. an electronic muscle stimulation (electronic muscle stimulation (EMS)).

Medical data can be, in particular, body temperature, heart rhythm, blood pressure, number of steps or respiratory rate as well as chemical concentrations such as pH, lactate, glucose or chloride values. The medical system can preferably derive and output specific information such as sleep status, stress level or training status from this data.

The structure of the medical system can in particular include a protective layer, one or more adhesive intermediate layers, one or more stamped parts, one or more insulating layers, in particular against electromagnetic radiation or interference (EMI shielding), and one or more sensors.

A further subject of the invention is the use of a pressure-sensitive adhesive of the invention as an adhesive for producing bonds on the skin, in particular on human skin. The adhesive of the invention can be used in particular in an overlay for bonding to the skin or in a medical device that can be worn on the skin, in each case as set out above.

In addition, the pressure-sensitive adhesive of the invention can also be used as an adhesive in the production of labels for medical products or for the production of bonds in medical devices.

examples

Measurement and test methods Method 1 - Determination of Molecular Weight

The details of the number-average molar mass M _n and the weight-average molar mass M _w in this document relate to the determination by gel permeation chromatography (GPC), which is known per se. The determination is carried out on a 100 ml sample that has been filtered clear (sample concentration 4 g/l). Tetrahydrofuran with 0.1% by volume of trifluoroacetic acid is used as the eluent. The measurement takes place at 25 °C.

A column type PSS-SDV, 5 pm, 10 ³ Å, 8.0 mm ^* 50 mm is used as a pre-column (details here and below in the order: type, particle size, porosity, inner diameter ^* length; 1 Å = 10 ¹ ° m) used. A combination of columns of the type PSS-SDV, 5 μm, 10 ³ Å and 10 ⁵ Å and 10 ⁶ Å, each with 8.0 mm ^* 300 mm, is used for the separation (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer ). The flow rate is 1.0 ml per minute. The calibration is carried out using the commercially available ReadyCal kit poly(styrene) high from PSS Polymer Standard Service GmbH, Mainz. The values are universally converted to polymethyl methacrylate (PMMA) using the Mark-Houwink parameters K and alpha, so that the data are given in PMMA mass equivalents.

Method 2 - Adhesion steel

The adhesive strength was determined in a test atmosphere of 23 °C +/- 1 °C temperature and 50% +/- 5% rel. humidity. The samples were cut to 20mm width and glued to a steel plate (ASTM). The steel plate was cleaned and conditioned before the measurement. For this purpose, the plate was first wiped with solvent and then left in the air for 5 minutes so that the solvent could evaporate. The side of the adhesive tape facing away from the test substrate was then covered with 25 μm thick, etched PET film, which prevented the sample from stretching during the measurement. The test sample was then rolled onto the substrate. For this purpose, the tape was rolled back and forth five times with a 4 kg roller at a winding speed of 10 m/min. 1 min after rolling, the plate was pushed into a special holder. The bond strength was measured using a Zwick tensile testing machine; the samples were peeled off at an angle of 180° at a speed of 300 mm/min. The measurement results are given in N/cm and are averaged from five individual measurements. Method 3 - Determination of Shear Life

The shear strength was determined in a test climate of 23 +/- 1 °C temperature and 50% +/- 5% rel. humidity.

The test samples were cut to a width of 13 ± 0.2 mm and stored in a climatic environment for at least 16 hours. For the test, 50 x 25 mm ASTM steel plates with a thickness of 2 mm and a 20 mm marking line were used, which were intensively cleaned several times with acetone before bonding and then left to dry for 10 minutes. The bond area was 13 x 20 ± 0.2 mm. The test strip was applied to the middle of the substrate by rubbing it with a wiper in the longitudinal direction, avoiding air pockets, so that the upper edge of the test sample lay exactly on the 20 mm marking line.

The back of the test sample was masked with aluminum foil. The free protruding end was taped off with paper. The adhesive strip was then rolled back and forth twice with a 2 kg roller. After rolling, a strap loop (weight 5-7 g) was attached to the protruding end of the adhesive tape.

An adapter plate was then attached to the front of the shear test panel with a screw and nut. To ensure that the adapter plate was firmly seated on the plate, the screw was tightened firmly by hand.

The plate prepared in this way was attached to a counter clock via the adapter plate by means of a hook; A 1 kg weight was then hung smoothly into the belt loop.

The pull-up time between rolling and loading was 12 minutes. The time in minutes before the bond failed was measured; the measurement results are the average of three measurements. A shearing life of at least 5,000 minutes is considered a good result.

Table 1: Chemicals used Production of the PSAs

The constituents for producing the PSAs were initially taken in the amounts stated in Table 2 in ethyl acetate (solids content 15%) and stirred at 45° C. for 3 hours. The resulting solution was then homogenized overnight using a roller bench. The dispersions obtained were applied to backings (etched PET film, 23 gm thick), the solvent was removed and the sheet-like PSAs obtained in this way (layer thickness 25 gm) were left to stand for one day in a test atmosphere. Then the tests were carried out.

Table 2: Composition of the PSAs (data in g) and test results

The PSAs of Examples 1-3 were all biodegradable according to DIN EN 13432.

Claims

patent claims

1 . Pressure-sensitive adhesive comprising at least one polyhydroxyalkanoate, characterized in that the polyhydroxyalkanoate comprises o to 20 to 75% by weight of structural units which can be traced back to 3-hydroxybutyric acid (3-HB); and o comprises at least one further structural unit which is based on a hydroxyalkanoic acid selected from the group consisting of 4-hydroxybutyric acid (4-HB), 3-hydroxyvaleric acid (3-HV), 4-

Hydroxyvaleric acid (4-HV), 3-hydroxyhexanoic acid (3-HX) and/or 4-hydroxyhexanoic acid (4-HX).

2. PSA according to claim 1, characterized in that the polyhydroxyalkanoate comprises structural units attributable to (4-HB) and the weight ratio (3-HB):(4-HB) is from 5.5:4.5 to 2:3.

3. Pressure-sensitive adhesive as claimed in either of claims 1 and 2, characterized in that the polyhydroxyalkanoate comprises from 35 to 60% by weight of structural units (3-HB).

4. Pressure-sensitive adhesive according to any one of the preceding claims, characterized in that the polyhydroxyalkanoate is crosslinked.

5. PSA according to claim 4, characterized in that the polyhydroxyalkanoate is free-radically crosslinked.

6. Multilayer composite system, comprising at least one backing material and a pressure-sensitive adhesive as claimed in any of claims 1 to 5.

7. Multi-layer composite system according to claim 6, characterized in that the multi-layer composite system is an overlay for adhesion to the skin.

8. Multi-layer composite system according to claim 6, characterized in that the multi-layer composite system is an adhesive tape.

9. A medical device that can be worn on the skin (wearable device), comprising a pressure-sensitive adhesive according to any one of claims 1 to 5 and a medical system.

10. The use of a pressure-sensitive adhesive as claimed in any of claims 1 to 5 as an adhesive for producing bonds on the skin.