SWITCHABLE ADHESIVE COMPOSITIONS

Abstract

This invention relates to polyurethane-based pressure sensitive adhesive compositions that comprise curable moieties. The adhesive compositions are “switchable” from a tacky state to a non-tacky state by initiating curing of the curable moieties. The adhesive compositions comprise the reaction product of: (A) a polymer component containing at least 2 nucleophilic functional groups containing an active hydrogen atom; and (B) a crosslinking component that is obtainable by reacting a polyisocyanate component and a ompound comprising a functional group that is curable by free-radical polymerisation and further comprising a nucleophilic functional group containing an active hydrogen atom.

Claims

1. An adhesive polyurethane composition comprising the reaction product of: (A) a polymer component having a weight average molecular weight in the range of 500 to 100,000 Dalton, and containing an average per molecule of X nucleophilic functional groups containing an active hydrogen atom, wherein X represents a number having a value of at least 2; and (B) a cross-linking component obtained by reacting: (i) a polyisocyanate component having an average of at least Y isocyanate functions per molecule, wherein Y represents a number in the range from 1.8 to 6; (ii) at least one compound comprising a functional group that is curable by free-radical polymerisation and further comprising a nucleophilic functional group containing an active hydrogen atom; and (iii) optionally at least one compound comprising a nucleophilic functional group containing an active hydrogen atom and which does not include a functional group that is curable by free-radical polymerisation; wherein the total degree of substitution of the polyisocyanate component (i) by the compounds (ii) and (iii) is at least 0.2 and no more than the lesser of 0.3Y and 0.8.

2. An adhesive polyurethane composition according to claim 1, wherein the total degree of substitution of the polyisocyanate component (i) by the compounds (ii) and (iii) is no more than the lesser of 0.28Y and 0.8.

3. An adhesive polyurethane composition according to claim 1, wherein the total degree of substitution of the polyisocyanate component (i) by the compounds (ii) and (iii) is at least 0.3.

4. An adhesive polyurethane composition according to claim 1, wherein the cross-linking component (B) is obtained by reacting the polyisocyanate component (i) with both the compound (ii) and the compound (iii).

5. (canceled)

6. (canceled)

7. An adhesive polyurethane composition according to claim 1, wherein Y represents a number in the range from 2 to 4.

8. An adhesive polyurethane composition according to claim 1, wherein the polyisocyanate component (i) comprises one or more polyisocyanate compounds selected from the group of polyisocyanates containing from 2 to 10 isocyanate functions per molecule.

9. (canceled)

10. An adhesive polyurethane composition according to claim 8, wherein the polyisocyanate component (i) comprises a trimerized diisocyanate of the formula D(R-NCO).sub.3, wherein D represents a ring structure selected from isocyanurate and iminooxadiazindione and mixtures thereof, and each R independently represents a straight chain, branched or cyclic alkylene group having from 2 to 15 carbon atoms or an aryl group having from 6 to 20 carbon atoms.

11. An adhesive polyurethane composition according to claim 1, wherein the at least one compound (ii) comprises an olefin moiety as the functional group that is curable by free-radical polymerization and/or is selected from hydroxy-substituted acrylate esters, hydroxy-substituted methacrylate esters, and mixtures thereof.

12. (canceled)

13. An adhesive polyurethane composition according to claim 1, wherein the at least one compound (iii) comprises or consists of one or more C.sub.1-C.sub.30 aliphatic alcohols; linear, branched or cyclic C.sub.1-C.sub.18 aliphatic alcohols; linear, branched or cyclic C.sub.1-C.sub.12 aliphatic alcohols; branched C.sub.3-C.sub.12 aliphatic alcohols; or branched C.sub.6-C.sub.18 aliphatic alcohols; and/or comprises or consists of one or more hydroxyl-substituted photoinitiators.

14. (canceled)

15. An adhesive polyurethane composition according to claim 1, wherein X represents a number of at least 2.2.

16. An adhesive polyurethane composition according to claim 1, wherein the polymer component (A) is selected from hydroxy-terminated polyethers, hydroxy-terminated polyesters, amine-terminated polyethers, and amine-terminated polyesters.

17-19. (canceled)

20. An adhesive polyurethane composition according to claim 1, wherein the polymer component has a weight average molecular weight in the range of 1,000 to 50,000 Dalton.

21. An adhesive polyurethane composition according to claim 1, wherein the polymer component has an equivalent weight per nucleophilic functional group of from 200 to 5,000 and/or has a mono-ol content of no more than 2 mol %.

22. (canceled)

23. An adhesive polyurethane composition according to claim 1, wherein the sum of X and Y is at least 4.5.

24. An adhesive polyurethane composition according to claim 1, wherein the molar ratio of unsubstituted isocyanate functions in the cross-linking component (B) to nucleophilic groups in the polymer component (A) is from 0.3 to 0.8.

25. An adhesive polyurethane composition according to claim 1, wherein the ratio of unsubstituted isocyanate functions in the cross-linking component (B) to nucleophilic groups in the polymer component (A) is at least 0.8n and no more than the lesser of 1.2n and 0.8, where n represents the total degree of substitution of the polyisocyanate component (i).

26. An adhesive polyurethane composition according to claim 1, comprising from 0.05 to 1 meq/g of the functional group that is curable by free-radical polymerisation.

27. An adhesive polyurethane composition according to claim 1, further comprising a photoinitiator that is reactive to UV light, wherein the photoinitiator is selected from the group consisting of benzoin and derivatives; benzophenone and derivatives; acetophenone; 4-phenoxyacetophenone; 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone; 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one; 2-ethyl anthraquinone; benzil dimethyl ketal; 2-hydroxy-2-methyl propiophenone; and ethyl-4-(dimethylamino) benzoate.

28. (canceled)

29. (canceled)

30. An adhesive polyurethane composition according to claim 1, further comprising a solvent and/or a stabilizer.

31. (canceled)

32. An adhesive polyurethane composition according to claim 1, wherein the reduction in peel force of the adhesive after switching is from 30 to 99%.

33. A method of preparing an adhesive polyurethane composition comprising: (a) a first step of reacting: (i) a polyisocyanate component having an average of at least Y isocyanate functions per molecule, wherein Y represents a number in the range from 1.8 to 6; with (ii) at least one compound comprising a functional group that is curable by free-radical polymerisation and further comprising a nucleophilic functional group containing an active hydrogen atom; and optionally with (iii) at least one compound comprising a nucleophilic functional group containing an active hydrogen atom and which does not include a functional group that is curable by free-radical polymerisation; wherein the total degree of substitution of the polyisocyanate by the compounds (ii) and (iii) is at least 0.2 and no more than the lesser of 0.3Y and 0.8, to form a cross-linking component (B); (b) a second step of combining the product of step (i) with a polymer component (A) having a weight average molecular weight in the range of 500 to 100,000 Dalton, and containing an average per molecule of X nucleophilic functional groups containing an active hydrogen atom, wherein X represents a number greater than 2.

34. A method according to claim 33, wherein step (a) and/or step (b) is carried out in the presence of a catalyst and/or a solvent.

35. (canceled)

36. (canceled)

37. An adhesive medical product comprising a switchable adhesive polyurethane composition as defined in claim 1 disposed between a first carrier film and a release liner, wherein the first carrier film is UV translucent, optionally wherein a removable UV occlusive layer is laminated to the first carrier film on the surface opposite the adhesive composition.

38. (canceled)

39. A method of treating a wound using an adhesive dressing as defined in claim 37, the method comprising removing the release liner and applying the adhesive dressing to the wound site.

Description

[0269] The invention will be further described by way of example only and without limitation by reference to the drawings in which:

[0270] FIG. 1 is a cross-sectional view through an adhesive dressing in accordance with a first embodiment of the invention;

[0271] FIG. 2 is a perspective view showing the attempted removal from a patient's forearm of an adhesive dressing in accordance with the first embodiment of the invention and includes an enlargement bubble showing in partial cross- section how removal of the adhesive dressing causes the adhesive composition to extrude;

[0272] FIG. 3 is a perspective view showing the adhesive dressing in accordance with the first embodiment of the invention undergoing irradiation to effect switching of the adhesive;

[0273] FIG. 4 is a perspective view showing how the adhesive dressing in accordance with the first embodiment of the invention may be easily removed after switching of the adhesive;

[0274] FIG. 5 is a graph showing the peel force measurements for examples 7 to 11.

DETAILED DESCRIPTION OF THE DRAWINGS

[0275] An adhesive medical product using the switchable adhesive composition of the present invention will now be described with reference to FIGS. 1 to 4. The adhesive medical product in this example is an adhesive medical dressing.

[0276] FIG. 1 is a cross-sectional view through an adhesive medical dressing 100 attached to a patient's skin 20. The adhesive medical dressing 100 is a multi-layer product having the following structure. The dressing 100 comprises a wound facing absorbent layer 130 disposed beneath a protective backing layer 140. At opposed edges 150, the backing layer 140 is provided with a switchable adhesive composition 170 which includes curable molecules that can be cross-linked under the influence of UV and/or visible light.

[0277] The backing layer 140 is optionally provided with a light occlusive cover layer 180 which is releasably secured to the backing layer 140 by a weak adhesive 190. For ease of removal, the light occlusive cover layer 180 overlaps the backing layer 140 at its edges 110. In the case that the switchable adhesive composition 170 contains a photoinitiator that is actuated by UV radiation, the light occlusive cover layer 180 may be omitted.

[0278] FIG. 2 is a perspective view showing the attempted removal of an adhesive dressing 100 from the forearm 14 of a patient, prior to switching of the switchable adhesive composition. Before switching, the adhesive composition 171 is very tacky and sticks the adhesive dressing 100 to the patient's skin 20 quite firmly. Hence, when the patient attempts to peel the dressing 100 from the forearm 14, the the dressing 100 remains attached to the skin 20 unless the dressing is peeled with some force.

[0279] FIG. 3 is a perspective view showing the adhesive dressing undergoing irradiation, in this example from a lamp 60, to effect cure of the curable molecules in the adhesive composition 170. The light from the lamp 60 (UV light or visible light, preferably long wavelength UV) causes the photoinitiator in the adhesive composition 170 to generate free radicals that initiate curing of the curable molecules in the adhesive composition. Curing transforms (switches) the adhesive composition 170 from its tacky state to a non-tacky or low-tack state.

[0280] FIG. 4 is a perspective view showing how, after switching of the adhesive composition, the patient is easily able to remove adhesive dressing 100 from the forearm 14 without the need for excessive force.

EXAMPLES

Examples 1-5—Compositions Comprising Cross-linking Component (B)

[0281] The reaction was carried out at room temperature under stirring. The components shown below in Table 1 except for the catalyst were added into a reagent bottle and mixed into a homogeneous solution, after which the catalyst was added. The mixture was left overnight for the reaction to be completed. After confirming by GPC measurements that no unreacted hydroxypropyl methacrylate or 2-ethyl-1-hexanol remained, the isocyanate functional acrylate oligomer was ready to be used.

[0282] GPC was carried out by diluting samples with tetrahydrofuran in a ratio of 1:100 and injected in an amount of 20 μl into the injection valve of a Waters HPLC 1515 pump using a flow rate of 1 ml/min of tetrahydrofuran. The instrument was equipped with a Styragel HR1 column connected to a Waters 2414 refractive index detector.

[0283] The components shown in Table 1 are as follows:

[0284] A Polyisocyanate component (i)

[0285] B Solvent.

[0286] C Catalyst

[0287] D Stabiliser

[0288] E Compound (ii)

[0289] F Compound (iii)

TABLE-US-00001 TABLE 1 Reagent Ex. 1 Ex 2 Ex. 3 Ex. 4 Ex. 5 A Baymedix AP536 115.8 g 109.2 g 54.7 g 54.7 g 54.8 g (i) (Y = 3.2) B Ethyl acetate 24.43 g   32 g 16.0 g 16.0 g 16.0 g C Zirconium (IV)  0.01 g  0.01 g 0.01 g 0.01 g 0.01 g pentanedionate D Irganox 1010  0.7 g  0.50 g 0.25 g 0.25 g 0.25 g E Hydroxypropyl  59.1 g  16.2 g 4.00 g 3.02 g 2.03 g methacrylate (ii) F 2-Ethyl-1-hexanol    0 g  36.2 g 21.8 g 22.8 g 23.6 g (iii) Degree of subst. of 0.650 0.189 0.093 0.07 0.047 polyisocyanate (i) by compound (ii) Total degree of subst. 0.650 0.655 0.654 0.657 0.653 of polyisocyanate component (i) by (ii) and (iii)

Example 6—Compositions Comprising Polymer Component (A)

[0290] Under protection from ultraviolet sources all components in Table 2 except for Baymedix AR602 were loaded into a sealable glass jar and mixed until all solid materials had been dissolved using a magnetic stirrer. Baymedix AR602 was then added and the mixture was stirred until it become homogenous.

[0291] The components shown in Table 2 are as follows:

TABLE-US-00002 H Polyol I Photoinitiator B Solvent C Catalyst D Stabilizer for preventing premature switch during storage J Surfactant

TABLE-US-00003 TABLE 2 Reagent Example 6 H Baymedix AR602 (X = 4) 1797 g I Irgacure 369 12 g B Ethyl acetate 190 g C Borchi Kat 22 2.5 g D Irganox 1010 2 g J BYK377 2.45

Examples 7 to 11—Switchable Adhesive Compositions

[0292] Examples 7 to 11 are examples of switchable adhesive compositions in accordance with the present invention formulated to include the compositions comprising cross-linking component (B) from Examples 1 to 5 and the composition comprising polymer component (A) from Example 6 in the amounts shown in Table 3.

[0293] In Examples 7 to 11, both compositions were loaded into a sealable glass jar and mixed to a homogenous solution using a magnetic stirrer over a period of approximately 10 minutes under protection from ultraviolet sources. The resulting adhesive solution was then spread onto a flexible medical polyurethane film having a removable carrier film (medical film 48938) using a spreader having a gauge of 150 μm. The adhesive coating was then cured in a ventilated fan assisted oven at 130° C. for 10 minutes. After this step, the thickness of the adhesive coating was about 60-80 μm.

TABLE-US-00004 TABLE 3 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Cross-linking Ex. 1 Ex. 2 Ex. 3 Ex. 4 .sup. Ex. 5 component (B) 9.81 g 11.6 g 13.3 g 12.4 g 12.5 g Polymer Ex. 6 Ex. 6 Ex. 6 Ex. 6 .sup. Ex. 6 component (A) 28.9 g 33.1 g 33.1 g 33.2 g 33.2 g NCO/OH* 0.643 0.635 0.742 0.680 0.696 *NCO/OH represents the molar ratio of unsubstituted isocyanate functions in the cross-linking component (B) to nucleophilic hydroxyl groups in the polymer component (A)

[0294] Peel Force Measurements

[0295] Peel force before and after switching was determined for each of the adhesives of Examples 7 to 11. In preparation for peel force measurements, a very easy release liner was transferred to the exposed side of the adhesive. The removable carrier film was then removed from the medical film and replaced by a high adhesion PET tape. The PET film is fixed to the medical film in order to cancel out the elasticity effect of the medical film on the measured peel force.

[0296] Peel strengths were determined after a dwell time of 20 minutes using an Instron 5943 testing rig, equipped with a 100 N load cell, according to FINAT test method FTM1, with the exception that high density polyethylene (HDPE) panels were used as the substrate surface and that a peeling rate of 100 mm/min, crosshead speed 200 mm/s, was used in order to collect all of the necessary data within the time frame of one peel force measurement.

[0297] Adhesive switching was achieved by exposing the adhesive (adhered to the HDPE plate) to light through the PET tape and medical film backing with a light intensity of approximately 5 mW/cm2 from a XeLED-Ni3UV-R4-365-E27-SS lamp having a narrow spectrum around 365 nm. Switching times for the different coatings were measured as the time between the starting time of irradiation and the time when the substantially instantaneous loss of tack occurred, during a continuous peel strength test of about 1.5 minutes (i.e., the adhesive was peeled for a period of time whilst being irradiated). The peel force measurement was continued under irradiation until the peel force reached a plateau value, which typically occurred 5-10 seconds after the switch time. Peel strengths and switch times were measured in quadruple and the average values of switch time and peel strength (before and after switch) are reported in Table 4.

[0298] Results of the peel force measurements are shown in Table 4 alongside the meq curable groups (i.e. the olefin moiety of the methacrylate esters). The meq of curable groups is easily calculated from the mmol of hydroxypropyl methacrylate added to the adhesive and the total dry weight of the adhesive (i.e. excluding the solvent).

TABLE-US-00005 TABLE 4 Methacrylate Peel force Peel force meq/g before switch after switch Switch (mmol HPMA/g Example (N/25 mm) (N/25 mm) time (s) dry adhesive) 7 1.56 0.025 1.8 0.578 8 1.61 0.020 1.8 0.167 9 1.12 0.045 2.2 0.093 10 2.64 0.203 2 0.067 11 1.86 0.297 2.1 0.045

[0299] From Table 4, it can be seen that a reduction in peel force of over 80% is obtained in all cases. As expected, the peel force after switching is highest for the adhesive of Example 11, which has the lowest content of the curable methacrylate moieties. However, the reduction in peel force is nonetheless significant even when the content of curable groups is relatively low. Once the methacrylate content of the adhesive exceeds ca. 0.05 meq/g the reduction in peel force easily exceeds 90%. A comparison of Examples 7 and 8 shows that the switched peel force is essentially once the content of curable groups is above ca. 0.1 meq/g. This demonstrates that excessive amounts of curable groups are not essential to good switching performance. This provides the possibility of replacing some of the curable groups with non-curable groups from the compound (iii), without impairing (or even improving) the performance of the adhesive. In examples 7 and 8 the reduction in peel force is close to 99%, demonstrating that the switched adhesive may be removed from a substrate with essentially no damage to the substrate (and no pain in the case of removal of the switched adhesive from the skin). The results of the peel force measurements are shown graphically in FIG. 5.

Examples 12 to 17—Cross-linking Components Having Different Degrees of Substitution of the Isocyanate

[0300] Compositions comprising cross-linking components (B) having different degrees of substitution of the polyisocyanate component (i) were prepared according to the procedure set out in example 1, using the amounts of the different components set out in Table 5. Optional component (iii) is not used in examples 12 to 17.

TABLE-US-00006 TABLE 5 Reagent Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 A Baymedix 71.0 g 51.4 g 40.0 g 51.2 g 40.0 g 71.0 g AP536 (i) (Y = 3.2) B Ethyl acetate 12.4 g 10.7 g  9.0 g 11.5 g  9.0 g 17.0 g C Dibutylin 0.01 g 0.01 0.01 g 0.01 g 0.01 g 0.01 g dilaurate D Irganox 1010 0.33 g 0.33 g 0.25 g 0.36 g 0.24 g 0.45 g E Hydroxypropyl 14.0 g 20.1 g 19.0 g 26.3 g 22.0 g 42.0 g methacrylate (ii) Degree of subst. of 0.251 0.498 0.605 0.654 0.700 0.753 polyisocyanate (i) by compound (ii)

Examples 18 to 31—Switchable Adhesive Compositions

[0301] Examples 18 to 31 are examples of switchable adhesive compositions in accordance with the present invention formulated to include the compositions comprising cross-linking components (B) from Examples 12 to 17 and the composition comprising polymer component (A) from Example 6 in the amounts shown in Table 6. The adhesives were formulated according to the method of Example 7, except that the adhesives were spread onto film using a gauge of 200 μm, resulting in adhesive coatings with a coat weight of 90-100 g/m.sup.2. Peel force was measured as described above in quadruple samples per adhesive and is reported in Table 6. The measured values represent adhesive failure. No cohesive failure was observed in these tests. In other words, the maximum measured peel force represents the force necessary to separate the adhesive from the substrate and not internal breakdown of the adhesive structure (which would leave a residue on the surface).

[0302] It will be appreciated that as the degree of substitution of the polyisocyanate component increases, it is necessary to increase the relative amount of the cross-linking component (B) to ensure sufficient unreacted isocyanate groups are available for reaction with the polymer component (A).

TABLE-US-00007 TABLE 6 Peel force (B) Degree of Amount Amount before switch Ex. from substitution (A)/g (B)/g Ratio* (N/25 mm) 18 Ex. 12 25% 33.00 2.19 0.31 0.89 19 Ex. 13 50% 29.02 4.40 0.44 1.03 20 Ex. 13 50% 29.02 4.21 0.42 1.21 21 Ex. 14 60% 33.04 8.15 0.53 2.74 22 Ex. 14 60% 33.03 8.41 0.55 2.04 23 Ex. 14 60% 33.05 8.71 0.57 1.71 24 Ex. 15 65% 29.00 9.00 0.57 4.27 25 Ex. 15 65% 28.99 9.57 0.61 2.25 26 Ex. 15 65% 29.00 9.41 0.60 3.18 27 Ex. 16 70% 29.02 13.00 0.71 4.55 28 Ex. 16 70% 29.02 13.54 0.74 3.47 29 Ex. 16 70% 29.04 14.03 0.77 2.57 30 Ex. 17 75% 25.01 18.99 0.94 6.88 31 Ex. 17 75% 25.00 19.21 0.95 7.07 *Ratio of unsubstituted isocyanate functions in the cross-linking component (B) to nucleophilic groups in the polymer component (A)

[0303] As shown in Table 6, the degree to which the isocyanate functions of the cross-linking component (B) are substituted with either curable groups (such as acrylate/methacrylate) or non-curable groups affects the adhesive properties of the adhesive composition. While it might be expected that the cross-linking component (B) could be made simply with a sufficient amounts of unsaturated moieties and excluding the non-curable moieties (from compound (iii)), it is found that the adhesiveness of the formed composition is lower when the cross-linking component (B) has only a low degree of substitution. The distribution and density of cross links in the formed polymer matrix, and thus the properties of the adhesive, can be tuned for a polyol-isocyanate oligomer pair, or mix thereof, by substituting part of the isocyanate component (i) with a non-curable compound (iii). Accordingly, the minimum degree of substitution of the polyisocyanate component (i) is at least 0.2, and preferably at least 0.3, more preferably at least 0.4, and most preferably at least 0.45 or at least 0.5.

[0304] On the other hand, while a strong adhesive may be formed using cross-linking components (B) with very high levels of isocyanate substitution, the amount of cross-linking component (B) required to form sufficient cross-links with the polymer component (A) is very high, which is not cost-effective. For example, the maximum degree of substitution of the polyisocyanate component (i) is no more than the lesser of 0.3Y and 0.8, for example no more than the lesser of 0.28Y and 0.75.

Example 32—Pumping of Composition Comprising Cross-linking Component (B)

[0305] The ratio between the polymer component (A) and cross-linking component (B) will determine the tackiness of the adhesive, and at the same time a small variation of the ratio may have a large impact on the adhesion performance. Therefore, one of the best ways to sustain a stable ratio during coating of the adhesive is to use a cogwheel pump (gear metering pump). In the examples below a 2K GMM e2 mixer from Scanrex Industriservice AB equipped with a GM301D-30R-110Z 3.0 cc and a GM601D-30R-110Z 6.0cc pumps from Oerlikon Barmag for the cross-linking and polymer component, respectively.

[0306] In a production trial, 20 kg of the composition comprising the cross-linking component (B) from Example 1 (ca. 65% substitution of isocyanate by curable groups) and 40 kg of the composition comprising polymer component (A) from Example 6 were prepared and charged into their respective vessels. The mixer was set at a total flow rates displayed below in Table 7. The mixing process was then started and proceeded under intermittent conditions until the cross-linking component (B) 3.0 cc pump stopped due to too high torque. When dissembling the cross-linking component pump head, a white rubber-like material was noticed on the cogwheel as well as on the pump house surrounding it. Since it is well known that high shear forces can initiate polymerization it is believed that this was the reason to the clogging of the pump.

[0307] In a second trial, 5 kg of the composition comprising the cross-linking component (B) made according to Example 2 (ca. 19% substitution of isocyanate by curable groups) was charged into its corresponding vessel where after arranging a recirculation setup the cross-linking component pump (with the polymer component pump disconnected) was started at a flow rate of 2.5 ml/s. After pumping 970 litres around in the system without any pump failure, no visible matters could be detected in the pump head after dissembling it which clearly demonstrates that polymerization can be avoided in the pump head by keeping the amounts of curable moieties below a certain concentration, while maintaining the total degree of substitution of the polyisocyanate component (i) by way of the compound (iii).

TABLE-US-00008 TABLE 7 Pump head Cross-linking Flow Pumped Running condition component (B) rate ml/s volume L condition after stop Example 1 2.4 5 Intermittent Clogged Example 1 1.3 9 Intermittent Clogged Example 1 1.3 13 Intermittent Clogged Example 2 2.5 970 Continuous Ok

Example 33—Adhesives Including A Photoinitiator As Compound (iii)

[0308] A composition comprising a cross-linking component (B) in which a photoinitiator is used as compound (iii) was prepared by the method of example 1 using the components set out in Table 8.

TABLE-US-00009 TABLE 8 Reagent Amount (g) A Baymedix AP536 (i) (Y = 3.2) 103.11 B Ethyl acetate 29.3 C Zirconium (IV) pentanedionate 0.04 D Irganox 1010 0.39 E Hydroxypropyl methacrylate (ii) 15.01 F 2-Ethyl hexanol (iii) 20.89 I Irgacure 127* 20.00 Degree of subst. of polyisocyanate (i) 0.185 by compound (ii) Total degree of subst. of polyisocyanate 0.679 component (i) by (ii) and (iii) *hydroxyl-substituted photoinitiator

[0309] A composition comprising polymer component (A) was prepared by the method of example 6 using the components set out in Table 9.

TABLE-US-00010 TABLE 9 Reagent Amount (g) H Baymedix AR602 (X = 4) 719.1 B Ethyl acetate 76.01 C Borchi Kat 22 1.04 D Irganox 1010 1.15 J BYK 377 1.04

[0310] An adhesive composition was prepared by combining 33.9 g of the polymer component (A) and 9.94 g of the cross-linking component (B) according to the method of Example 7. The NCO/OH ratio of this adhesive was 0.465. The adhesive gave an initial peel force of 1.45 N/25 mm, a peel force after switch of 0.10 N/25 mm and a switch time of 9.6 son HDPE. A particular advantage of the adhesive of example 33 is that the potentially hazardous photoinitiator becomes chemically bonded to the adhesive polymer matrix such that it is unable to be absorbed by the skin.

Example 34—Adhesives Including A Photoinitiator As Compound (iii)

[0311] A composition comprising a cross-linking component (B) in which a photoinitiator is used as compound (iii) was prepared by the method of example 1 using the components set out in Table 10.

TABLE-US-00011 TABLE 10 Reagent Amount (g) A Baymedix AP536 (i) (Y = 3.2) 46.6 B Ethyl acetate 13.3 C Zirconium (IV) pentanedionate 0.01 D Irganox 1010 0.19 E Hydroxypropyl methacrylate (ii) 8 F 2-Ethyl hexanol (iii) 5.6 I Omnirad 2959* 10.6 Degree of subst. of polyisocyanate (i) 0.219 by compound (ii) Total degree of subst. of polyisocyanate 0.574 component (i) by (ii) and (iii) *hydroxyl-substituted photoinitiator

[0312] A composition comprising polymer component (A) was prepared by the method of example 6 using the components set out in Table 11.

TABLE-US-00012 TABLE 11 Reagent Amount (g) H Baymedix AR602 (X = 4) 900.8 B Ethyl acetate 66.7 C Borchi Kat 22 1.1

[0313] An adhesive composition was prepared by combining 20.05 g of the composition comprising polymer component (A) and 7.82 g of the composition comprising cross-linking component (B) according to the method of Example 7. The NCO/OH ratio of this adhesive was 0.841. The adhesive gave an initial peel force of 2.9 N/25 mm, a peel force after switch of 0.08 N/25 mm and a switch time of 5.5 s on HDPE. A particular advantage of the adhesive of example 34 is again that the potentially hazardous photoinitiator becomes chemically bonded to the adhesive polymer matrix such that it is unable to be absorbed by the skin.

Examples 35 to 38—Cytotoxicity of the Adhesive

[0314] A composition comprising cross-linking component (B) was prepared by the method of Example 1 using the components set out in Table 12. Optional component (iii) was not used.

TABLE-US-00013 TABLE 12 (Example 35) Reagent Amount (g) A Baymedix AP536 (i) (Y = 3.2) 51.3 B Ethyl acetate 10.8 C Zirconium (IV) pentanedionate 0.002 D Irganox 1010 0.3 E Hydroxypropyl methacrylate (ii) 26.2 F 2-Ethyl-1-hexanol (iii) 0 Degree of subst. of polyisocyanate (i) 0.650 by compound (ii)

[0315] A composition comprising polymer component (A) was prepared by the method of Example 6 using the components set out in Table 13.

TABLE-US-00014 TABLE 13 (Example 36) Reagent Amount (g) H Baymedix AR602 (X = 4) 88.0 I Irgacure 369 0 B Ethyl acetate 9.0 C Borchi Kat 22 0.06 D Irganox 1010 0 J BYK 377 0.13

[0316] Adhesives were formulated according to the method of Example 7 using the compositions comprising polymer components (A) and cross-linking components (B) in the proportions set out in Table 14.

TABLE-US-00015 TABLE 14 Example 37 Example 38 Cross-linking Ex. 35 Ex. 2 component (B) 11.85 g 12.15 g Polymer component (A) Ex. 36 Ex. 6 28.9 g 33.0 g NCO/OH 0.777 0.669

[0317] The cytotoxicity of the Examples 37 and 38 (measured according to cytotoxicity tests complying with the methods described in the guidelines of ISO 10993-5, Biological Evaluation of Medical Devices) is set out in Table 15. To determine whether less concentrated examples would show more favourable cytotoxicity, the adhesive composition extracts were diluted. In Table 15, dilution ratio indicates to what extent the extract was diluted before performing the cytotoxicity test. The ratio extract:culture media is tabulated. It should be noted that it is only if the undiluted, 1:0, sample shows a viability above 70% that decides if the sample has passed the test or not.

TABLE-US-00016 TABLE 15 Dilution ratio Example Undiluted 1:2 1:4 1:8 38 75 81 90 94 37 39 73 83 88

[0318] As can be seen in Table 15, the sample from example 38 passed the cytotoxicity test whilst the sample from example 37 failed, despite its lack of photoinitiator and approximate halved catalyst concentration, both of which were expected to exert a certain toxicity to living cells. This demonstrates that a reduction in the concentration of curable moieties in the adhesive has a beneficial effect on the cytotoxicity of the adhesive, without impairing the switching properties of the adhesive.

[0319] In circumstances in which the medical skin covering will be in contact with a patient's skin for a prolonged period, or in which the medical skin covering will be replaced with a new medical skin covering several times over a prolonged period, it is particularly important for the switchable adhesive compositions that are used in the medical skin coverings to be of low cytotoxicity.

Example 39

[0320] A composition comprising cross-linking component (B) was prepared by the method of Example 1 using the components set out in Table 16. Optional component (iii) was not used.

TABLE-US-00017 TABLE 16 Reagent Amount (g) A Baymedix AP501 (i) (Y = 2) 63.29 B Ethyl acetate 10.00 C Zirconium (IV) pentanedionate 0.02 D Irganox 1010 0.1 E Hydroxypropyl methacrylate (ii) 7.07 Degree of subst. of polyisocyanate (i) 0.252 by compound (ii)

Example 40

[0321] An adhesive was formulated according to the method of Example 7 using the composition comprising polymer component (A) of Example 6 and the composition comprising cross-linking component (B) of Example 39 in the proportions set out in Table 17.

TABLE-US-00018 TABLE 17 Cross-linking component (B) Example 39 6.38 g Polymer component (A) Example 6 33.17 g NCO/OH 0.592

[0322] The adhesive gave an initial peel force of 3.38 N/25 mm, a peel force after switch of 0.03 N/25mm and a switch time of 1.8 s on HDPE. An advantage of adhesives produced in combination with cross-linking components (B) similar to those in example 39 is that considerably less amount of the isocyanate component is required. This is more cost effective as the isocyanate component is expensive in relation to the polymer component (A).

[0323] Materials

[0324] The following materials were used in the examples described above.

TABLE-US-00019 Material [function] Description Supplier Baymedix AR602 Tetra-functional hydroxy-terminated Covestro AG [Polymer component A] polyether polyol; equivalent weight per hydroxyl group of ca. 1600 Da. X = 4 Baymedix AP501 Aliphatic NCO terminated Covestro AG [Polyisocyanate prepolymer based on component (i)] hexamethylene diisocyanate NCO content 12.8 w/w % Y = 2 Baymedix AP536 Trimerized hexamethylene Covestro AG [Polyisocyanate diisocyanate NCO content 23 w/w % component (i)] Y = 3.2 Borchi Kat 22 Polyurethane catalyst Borchers BYK 377 Surfactant BYK-Chemie GMBH Songnox1010 Pentaerythritol Tetrakis(3-(3,5-di- IGM Resins tert-butyl-4-hydroxyphenyl) propionate (antioxidant) Omnirad 127 2-hydroxy-1-{4-[4-(2-hydroxy-2- IGM Resins methyl-propionyl)-benzyl]-phenyl}- 2-methylpropan-1-one (photoinitiator) Omnirad 2959 1-[4-(2-Hydroxyethoxyl)-phenyl]-2- IGM Resins hydroxy-2-methylpropanone (photoinitiator) Omnirad 369 2-Benzyl-2-(dimethylamino)-4′- BASF AG morpholinobutyrophenone (photoinitiator) Code 48938 Medical film Shanghai ISO Medical Products Co. Ltd. HDPE panels Panels for peel test measurements ChemInstrument Inc. Release liner Transparent PET Release film, 50 Huhtamaki Oyj μm, silicone 1720, quality 1876