Low trauma grafted psa silicone compositions with high adhesion

Abstract

Silicone adhesives useful in medical applications combine the properties of soft silicone adhesive and pressure sensitive adhesives, and are soft gels formed by hydrosilative addition of a linear or lightly branched SiH-functional silicone on to a resin hybrid containing ethylene unsaturation, which has been produced by condensing a silicone resin with a silanol-functional organopolysiloxane. The adhesives can simultaneously exhibit high adhesion to the skin and low trauma upon removal.

Description

LOW TRAUMA GRAFTED PSA SILICONE COMPOSITIONS WITH HIGH ADHESIONBACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention is directed to silicone compositions which are curable to form pressure sensitive adhesives, and the pressure sensitive adhesives prepared therefrom. The silicone compositions exhibit high levels of adhesion, good cohesion and shear, and also exhibit low trauma when utilized as medical dressings or coverings, or for adhering wearable medical devices (“wearables”). The peel strength of the adhesives is tunable over a wide range as a result of combining the cure chemistries of condensation curing and hydrosilylative addition curing.

[0003] 2. Description of the Related Art

[0004] Medical dressings, which may also be called bandages, wound covers, inter alia, desirably require properties which are often conflicting. For example, a bandage which is to be applied to cover a wound or following surgery is generally desired to adhere strongly to the skin adjacent to the damaged area, often for long periods of time. At the same time, it is highly desirable that such bandages are capable of being removed without trauma to the patient, in other words as painlessly as possible and without causing damage to the skin or to the damaged area. Finally, it is important that the adhesive, generally a pressure sensitive adhesive or “PSA,” be relatively inert. Medical wearables such as oximeters and glucose monitors not only must adhere to the skin, but unlike wound dressings, medical pads, and the like, also present significant shear forces due to the weight of the devices, even though small, and also peel forces due to accidental contact of the device with clothing, furniture, walls, and the like.

[0005] There are many pressure sensitive adhesives commercially available. Many of these are based on vinyl addition polymers such as polyvinyl acetate, polyvinyl butyrate, styrene acrylates, styrene / butadiene copolymers and the like. Many of such copolymers also contain copolymerized ethylene and / or vinyl chloride. By suitable selection of these monomers, tackyadhesives which generally have a low glass transition temperature are easily and economically manufactured. However, it has been found that some of these pressure sensitive adhesives cause allergic reactions or skin irritation. Moreover, many of such adhesives have a relatively low permeability for oxygen and water vapor. It is difficult to formulate a pressure sensitive adhesive which can maintain its adhesion to the skin for long periods of time, especially in the presence of water, soaps, and the like. Many of these PSAs have such strong adhesion to the skin that the user experiences considerable pain and discomfort when the dressings are removed (high “trauma”). In addition, there is the danger that if the non-adhesive portion of the dressing, which is often a thin, non-tacky polymer film or gauze, does not completely cover the damaged area, the adhesive- coated portion of the dressing may adversely affect the wound when the dressing is removed.

[0006] Silicones have been used for some years as adhesive coatings for medical dressings. Silicones have several advantages over other types of adhesives, in that they are highly biocompatible and also exhibit high permeability for oxygen and water vapor. Thus, the skin is much less likely to suffer damage when a dressing is to be applied for a long period of time when silicone PSAs are used. Due to the biocompatibility of silicones, the skin is also much less likely to suffer from irritation or allergic reactions. Such silicone adhesives have been supplied as soft silicone adhesives (“SSA”) and pressure sensitive adhesives (“PSA”). These two classes of adhesives are fundamentally different. SSAs are generally solvent free, two component systems, whereas PSAs are one component systems often including considerable organic solvent. SSAs are applied to substrates in greater thicknesses than PSAs, have only low to moderate peel strength, are low trauma adhesives, and can be repositioned after initial application and removal. PSAs, on the other hand, have high peel strength, are not repositionable, and are painful to remove from the skin (high trauma).

[0007] It would be desirable to provide silicone adhesives which have the desirable characteristics of both SSAs and PSAs: high peel strength, low coating thickness, low trauma, and repositionability. Such silicone adhesives, when used on medical dressings, should preferably provide dressings and bandages which exhibit little or no edge peel for as much as 5 days or longer. It would be further desirable if the adhesiveness and softness could be adjusted over a wide range.

[0008] U.S. Patent 11,396,616 B2 discloses silicone adhesives principally for use in assembling electronic components. The patent describes prior attempts to employ hydrosilylative crosslinking for silicone adhesives as being deficient, and proposes a two curing step adhesive where a liquid organopolysiloxane mixture containing both silanol and alkenyl functionality, a condensation catalyst, adhesion promoter, crosslinkable silane, and organic peroxide is first condensed at low temperature to form a liquid of low viscosity and no tack, and then cured at a high temperature which activates the organic peroxide to form a very adhesive, hard product. The use of organic peroxides and their decomposition products is not desired in medical products which will contact the skin, especially for long periods of time, and the high hardness and adhesiveness are incompatible with the desired characteristics of low trauma silicone adhesives. The silicone adhesive for electronic components is thus of no relevance to medical adhesives.

[0009] U.S. Published Application 2015 / 0376482 Al discloses silicone hot melt adhesives which contain as a first ingredient an alkoxy functional silicone resin hybrid prepared by hydrosilylative addition of an alkoxysilyl-functional organopolysiloxane onto an alkenyl- functional silicone resin, and an alkoxy-functional silicone prepared by hydrosilylative addition of an alkoxy-functional polysiloxane also bearing at least one SiH group onto a linear organopolysiloxane terminated at both ends with alkenyl groups. The composition further requires a condensation catalyst and crosslinker. The viscosity is too high, being a hot melt adhesive, for general use as a medical adhesive, and the preparation process, involving two separate hydrosilylations, is not economical.

[0010] U.S. Patent 5,696,209 discloses dual cure, solvent-free, liquid silicone adhesives containing an alkenyl-functional silicone resin, an SiH functional organopolysiloxane having at least 1.7 SiH groups per molecule, an alkoxysilane, a hydrosilylation catalyst and a condensation catalyst. The composition first cures by hydrosilylation to produce a viscous, tacky pressure sensitive adhesive with high green strength, followed by condensation curing over a considerable period of time to provide an immovable bond. Such compositions are clearly unsuitable for use as medical adhesives. The lengthy moisture-induced second curing stage is a distinct disadvantage.

[0011] U.S. Patent 6,201,055 Bl discloses a highly silica- filled addition-curable silicone pressure sensitive adhesive stated to be useful for bonding electronic components, but also useful for pressure sensitive tapes, bandages and labels. The composition is based on an alkenyl- functional linear organopolysiloxane, a silicone resin containing up to 2 mol percent alkenyl groups, and organopolysiloxane bearing SiH groups, a hydrosilylation catalyst, and coarse silica filler in an amount of 25-200 parts per 100 parts of curable ingredients. The compositions are of high viscosity.

[0012] U.S. Published Application 2022 / 0177756 Al states that hydrosilylation-curable silicone adhesives lose their adhesiveness under hot humid conditions, and proposes to solve this problem by incorporating special adhesion promoters which are linear or cyclic organopolysiloxanes bearing an epoxy group which is an alicyclic vicinal cyclohexane epoxy (cyclohexene oxide) radical. The base components are typical addition-curable, linear vinylfunctional organopolysiloxanes and SiH functional organopolysiloxanes, employed at an SiH / alkenyl ratio of from 0.8 to 1.5. The incorporation of the special epoxy-group containing alicyclic species increases the cost of the composition. Peel strength is not specified, but adhesives employing epoxy groups as adhesion enhancers typically exhibit very high adhesion.

[0013] U.S. Published Application 2022 / 0002601 Al discloses silicone pressure-sensitive adhesives containing a reaction product of a silanol end group-containing linear organopolysiloxane, in excess of 25 parts by weight of a non-functional linear organopolysiloxane, and greater than 30 weight percent of a silicone resin. Minimization of trauma is stated to be achieved through the use of non-functional linear organopolysiloxanes having a viscosity of 100,000 mPas or higher, which renders the adhesives softer. The adhesives are preferably crosslinked using electron beam radiation, as used in all of the examples, but may also be cross-linked employing an organic peroxide free radical initiator or hydrosilylation with an SiH functional linear organopolysiloxane or silicone resin having 3 or more SiH groups per molecule. The inclusion of a non-functional linear organopolysiloxane is disadvantageous, as these can bleed out of the adhesive over time, especially when used in such large amounts.

[0014] U.S. Patent 10,662,330 B2 discloses silicone adhesives with increased adhesiveness, useful in medical applications. The adhesive compositions cure by hydrosilylation and include an alkenyl-functional component which includes an organopolysiloxane having minimally two alkenyl groups per molecule and a viscosity of 200-500,000 mPa-s, and optionally about 20 wt. % or less of a silicone resin having at least 0.01 wt. % alkenyl groups and not more than 1 wt. % hydroxy groups; an SiH-functional organosilicon crosslinker component having on average from 2.5 to 3.5 SiH groups per molecule, and a high molecular weight such that the weight percent of silicon-bonded hydrogen is not more than 0.025 wt. %, and a hydrosilylation catalyst. The comparative examples show that use of a,co-SiH-terminated organopolysiloxanes of higher silicon-bonded hydrogen content fails to provide adequate adhesion.SUMMARY OF THE INVENTION

[0015] It has now been surprisingly and unexpectedly discovered that silicone pressure sensitive adhesives can be formulated with a wide range of adhesive strengths while being able to maintain low trauma when utilized in medical dressings and for the securing of medical devices and like uses, thus providing the benefits of both SSAs and PSAs simultaneously. The silicone pressure sensitive adhesives employ a “hybrid” condensation product of a linear or lightly branched organopolysiloxane bearing terminal silanol groups and / or a substantially linear or lightly branched organopolysiloxane bearing terminal silanol groups and also optionally bearing ethylenically unsaturated groups, with at least one organopolysiloxane resin to provide a tacky condensed product bearing ethylenically unsaturated groups, and as a gel-former, an SiH functional linear or lightly branched organopolysiloxane. The adhesive is prepared in a two-step reaction, where the substantially linear organopolysiloxane bearing silanol and optional ethylenically unsaturated groups is condensed with a silicone resin employing a condensation catalyst, and from 5 weight percent to 95 weight percent of this condensed product is admixed with the SiH functional organopolysiloxane, optionally with further alkenyl-functional organopolysiloxanes, and crosslinked using a hydrosilylation catalyst. The adhesives can also be used in non-medical applications.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. In the claims, a component preceded by the grammatical article “a” means that one of such a component or a plurality of such a component may be used. The terms “organopolysiloxane” and “polyorganosiloxane” are to be interpreted as synonyms.

[0017] The pressure sensitive adhesives of the present invention are prepared by a two- step process, wherein first, a silanol end-stopped organopolysiloxane and / or a silicone fluid bearing both terminal silanol groups and also alkenyl groups, and a silicone resin bearing condensable groups and optionally also bearing alkenyl groups, are condensed in the presence of a condensation catalyst to prepare a partial vinyl-functional “hybrid” prepolymer. At least one of the condensable ingredients must contain ethylenically unsaturated groups. In addition to these necessary components, the prepolymer may also have been prepared employing additional optional components, in particular a nonreactive or reactive solvent, an alkoxysilane chain extender and / or cross-linker, and other components which do not detract from the nature of the prepolymer, which when cured, is a tacky substance bearing ethylenically unsaturated groups. In a second step, an SiH-functional organopolysiloxane is added. The resulting curable composition is curable by hydrosilylation to form a pressure sensitive adhesive. The adhesive may be formulated to include medical ingredients such as antibiotics, vitamins, and the like, or may be free of such ingredients.

[0018] Organopolysiloxanes (“silicones”), whether linear, lightly branched, cyclic, resinous, or combinations of these, contain siloxy units known in the art as M, D, T, and Q siloxy units. M groups have the general formula XsSiOi 2 where X can be a nonfunctional or functional substituent bonded to silicon. M units are terminal units. When all the X substituents are nonfunctional hydrocarbon groups R such as alkyl groups, cycloalkyl groups, aryl groups, or thelike, then the M unit as a whole is nonfunctional. To provide functional M groups, at least one X must contain a reactive functional group or must be a reactive functional group. These functional groups may vary widely depending upon the use of the particular silicone. If the functional group is a hydroxyl group bended to silicon, then the M group is termed a silanol group. In general, silanol groups are monofunctional, in other words have one hydroxyl group and two nonfunctional groups such as methyl groups. If the functional group is an alkoxy group such as a methoxy or ethoxy group, then the M end group is an alkoxysilyl group. Alkoxysilyl -functional M groups may contain from 1 to 3 alkoxy groups. The functional group may also be an unsaturated group such as a vinyl, allyl, propenyl, or other unsaturated group. The functional group may also be silicon-bonded hydrogen. In this case, the M group may contain a single silicon-bonded hydrogen or up to 3 silicon-bonded hydrogen atoms, any remaining X substituents generally being nonfunctional hydrocarbon groups. Other types of functional groups are well known to those skilled in the art, and include, by way of example but not by limitation, halogens, epoxyalkyl, ester, hydroxyalkyl, amino alkyl, and the like. The X substituents are preferably non-functional hydrocarbon, alkoxy, or silicon-bonded hydrogen. The M groups are preferably free of each of the further functional groups not mentioned. Silicon-bonded hydroxy groups and alkoxy groups are considered “condensable” groups.

[0019] Similarly with respect to the M groups described above, D groups have the general formula X2SiC>22 where X is described as above. T groups have the general formula XSiCh / 2, while Q units have the formula SiC>42 Thus, M units are monovalent chain terminators, D units are divalent chain extending units, T units are trivalent branching units, and Q units are tetravalent branching units. The types and amounts of these siloxy units which are present in any given silicone will determine the nature of the silicone. For example, linear organopoly siloxanes have the broad formula MDnM where n is an integer from 0 to very high values. When n = 0, the resulting disiloxane M-M is the shortest of the linear siloxanes. Simple cyclic siloxanes have the formula Dn, and lightly branched organopoly siloxanes contain a large majority of D units, M terminal units, and a very small amount, less than 10 mol percent, of T and / or Q branching units. A very special category of organopolysiloxanes are the silicone resins. As is well known to those skilled in the art, the term “silicone resin” or the term “resinous” when describing a silicone, is different from the use of this term in other polymer arts. Silicone resins are highly cross-linked,network-like organopolysiloxanes made up substantially of T and Q units, with M units serving as terminating units, and with only a minor amount, if any, of D units. Because of their highly crosslinked, network-like nature, silicone resins have physical and chemical characteristics which are considerably different from conventional linear and cyclic organopolysiloxanes. Common silicone resins include T resins, MT resins, MQ resins, DT resins, and MDQ resins. Silicone resins may be liquid, but are commonly solids soluble in organic solvents such as toluene.

[0020] In the organopolysiloxanes of the present invention, nonfunctional X groups are preferably substituted or unsubstituted, saturated or aromatically unsaturated hydrocarbon groups, for example, alkyl groups, cycloalkyl groups, aryl groups, arylalkyl groups, and combinations of these. Examples of unsubstituted radicals X are “R” groups, for example alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, and tert-pentyl radicals, hexyl radicals such as the n-hexyl radical, heptyl radicals such as the n-heptyl radical, octyl radicals such as the n-octyl radical and isooctyl radicals such as the 2,2,4- trimethylpentyl radical, nonyl radicals such as the n-nonyl radical, decyl radicals such as the n- decyl radical; cycloalkyl radicals such as cyclopentyl, cyclohexyl, 4-ethylcyclohexyl, cycloheptyl radicals, norbornyl radicals and methylcyclohexyl radicals; aryl radicals such as the phenyl, biphenylyl, and naphthyl radicals; alkaryl radicals such as o-, m-, p-tolyl radicals and ethylphenyl radicals; and aralkyl radicals, such as the benzyl radical and the a- and the B-phenylethyl radicals. Preferred aryl groups are the phenyl group and the naphthenyl group, the phenyl group being much preferred. The preferred arylalkyl group is the ethylphenyl group. Examples of substituted hydrocarbons as radicals R are halogenated hydrocarbons such as the chloromethyl, 3- chloropropyl, 3 -bromopropyl, 3,3,3 -trifluoropropyl and 5,5,5,4,4,3,3-heptafluoropentyl radicals and the chlorophenyl-, dichlorophenyl- and trifluorotolyl radicals. The alkyl groups are preferably alkyl groups having 1-20 carbon atoms, more preferably 1-4 carbon atoms, and most preferably methyl, ethyl, or propyl groups. Methyl groups are much preferred. The alkenyl groups are preferably alkenyl groups containing from 2 to 18 carbon atoms, and may contain only one or more than one ethylenically unsaturated group. The ethylenically unsaturated groups which may be present as functional X groups may also be alkynyl groups although this is not preferred. Most preferably, the alkenyl groups are vinyl groups, allyl groups, methallyl groups, 5-hexenyl,butadienyl, cyclopentenyl, cyclohexenyl, cyclopentadienyl and the like, preferably vinyl or allyl groups and / or propenyl groups, most preferably vinyl groups.

[0021] The silanol-stopped organopolysiloxanes are linear organopolysiloxanes or very lightly branched organopolysiloxanes having no more than 1-3 mole percent of branching siloxane units relative to the total amount of D units, preferably substantially linear organopolysiloxanes which contain only inadvertent amounts of branching units due to their method of preparation. These organopolysiloxanes bear silanol groups at each linear chain terminus, thus containing almost exclusively two silanol groups per molecule, although the use of linear or lightly branched polyorganosiloxanes with both terminal and pendent, or with only pendent hydroxy groups is also possible. The silanol groups are preferably dimethylsilanol groups for ease of preparation. The silanol stopped organopolysiloxanes may have weight average molecular weights ranging from about 500 g / mol to about 500,000 g / mol, more preferably from about 1000 g / mol to about 250,000 g / mol, yet more preferably about 10,000 g / mol to about 200,000 g / mol, and most preferably about 50,000 g / mol to about 150,000 g / mol. These silanol-stopped organopolysiloxanes are commercially available or can be prepared by methods common in organosilicon chemistry.

[0022] In addition to or in lieu of silanol (silicon-bonded hydroxyl) groups, these condensable linear or lightly branched polyorganosiloxanes may also contain other condensable groups such as Ci-6 alkoxy groups, preferably methoxy, ethoxy, or butoxy groups, most preferably methoxy and / or ethoxy groups.

[0023] The organopolysiloxanes bearing both silanol groups and ethylenically unsaturated groups and / or other condensable groups can be prepared by equilibration of a silanol-stopped organopolysiloxane with a vinyl-functional siloxane such as divinyltetramethyldisiloxane in the presence of an equilibration catalyst such as PNCh. Equilibration is stopped prior to elimination of all silanol groups. A preferred weight average molecular weight of these “vinyl / silanol” organopolysiloxanes is from 8000 g / mol to 150,000 g / mol, more preferably 12,000 g / mol to 85,000 g / mol, and most preferably 15,000 g / mol to 80,000 g / mol. The ratio of vinyl groups to silanol groups and / or other condensable groups may be as much as 5000:1, preferably 2500: 1 to 10: 1, and most preferably 1000: 1 to 10:1. A vinyl-terminated fluid with a molecular weight ofabout 16,000 and containing 0.0025 mol percent of residual terminal silanol groups has been found to be satisfactory.

[0024] Silicone resins are generally prepared by condensation / hydrolysis of mixtures of appropriate chlorosilanes and / or alkoxysilanes. By choosing hydrolysable and condensable silanes also bearing a desired functional group, appropriate functionalized silicone resins can be obtained. Alternatively, a silicone resin bearing a reactive functionality may be prepared and then the functionality may be changed by reacting the functional groups present with a compound containing another functional group. Due to their method of preparation, silicone resins generally contain residual silanol and / or silicon-bonded alkoxy groups. The silicone resins useful in the partial vinyl-functional prepolymer, or “hybrid,” are silicone resins which do contain residual condensable groups, preferably silicone resins which bear condensable groups as well as ethylenically unsaturated groups, preferably vinyl groups. The hydrocarbon groups which are present in the silicone resins may be any of the hydrocarbon groups previously discussed, but are preferably alkyl or aryl groups, most preferably methyl groups. A preferred MQ resin is MQ resin 804, a methyl silicone resin available from Wacker Chemical Corporation, Adrian, Mich., which also contains approximately 1.8 weight percent vinyl functionality. A preferred silicone resin containing no ethylenic unsaturation is MQ resin 803, also available from Wacker Chemical Corporation, containing trimethylsilyl terminal groups, containing residual ethoxy and silanol groups, and an M / Q ratio of about 0.67. MQ resins having unsaturation other than vinyl, including vinyloxy, allyl, allyloxy, propenyl, etc., are less commonly available, but may be used also. The various resins may be used alone or in admixture with other saturated or unsaturated resins.

[0025] The condensation of the silanol-stopped fluid, the optional organopolysiloxanes bearing both silanol groups and ethylenically unsaturated groups, and the silicone resin(s) takes place in the presence of a condensation catalyst. Condensation catalysts are well known to those skilled in the art of organosilicon chemistry, and may be selected from a variety of acids and bases, including sodium and potassium hydroxide, alkali metal alkoxides, guanidines, organic amines, and ammonia, from a variety of metal catalysts including specifically tin catalysts such as dibutyl tin dilaurate, dibutyl tin diacetate, tin octoate, and the like, and mixed catalysts such as mixtures of neodecanoic acid and tetramethylguanidine. Bismuth catalysts are also useful. Condensationcatalysts are available commercially or can be prepared by methods common in organic chemistry. The amount of condensation catalyst depends on the type of catalyst employed, but is generally less than one weight percent, more preferably less than 0.5 weight percent, based on the total weight of the mixture being condensed.

[0026] The condensation reaction may take place neat, or in the presence of a solvent. Suitable organic solvents are any solvents in which reaction ingredients are soluble, preferably solvents such as aromatic solvents, for example toluene, mixed aromatic solvents, aliphatic solvents, mixed aliphatic solvents such as ISOPARE available from Exxon, ester solvents such as ethyl acetate, glycol ethers, and other solvents well known to the skilled chemist. Whether a solvent is needed or not is largely dependent upon the viscosity of the system both prior to and following condensation. A viscosity which is high enough to render subsequent steps difficult can be lowered through the use of a suitable organic solvent. When organic solvents are employed, they are generally employed in amounts of less than 80 weight percent based on the total condensable mixture, more preferably less than 60 weight percent, still more preferably less than 50 weight percent, yet more preferably less than 30 weight percent, and most preferably in the range of 1 -20 weight percent. Solvents may also be totally absent. The duration of the reaction is dependent upon numerous factors which are well known and easily managed by those skilled in the art of organosilicon condensation reactions, in particular the nature and amount of catalyst. The reaction may take place at room temperature (e.g., 25° C) or below, but preferably takes place at elevated temperatures such as 40° C to 180° C, more preferably 60° C to 150° C, and most preferably 85° C to 130° C. A condensation time of approximately 180 minutes at 130° C has proven to be quite acceptable. The condensation is preferably conducted in an inert atmosphere, for example an atmosphere of nitrogen. To facilitate the condensation, water may optionally be added.

[0027] The resulting condensation product is a partially vinyl-functional prepolymer which can be cured at elevated temperature, for example in the form of an approximately 100 pm thick film, for 15 minutes at 120° C to form a very tacky film.

[0028] In a second step, the tacky vinyl-functional prepolymer prepared as described above is admixed with an SiH organopolysiloxane. The functionality of the SiH-functional organopolysiloxane depends at least to some extent on the amount of the tacky prepolymer containing both silanol and ethylenically unsaturated functionality. When the tacky prepolymer is present in amounts greater than 50 weight percent of the formulation, preferably, greater than 60% by weight, more preferably greater than 70% by weight, and most preferably greater than 80% by weight, then the SiH functional organopolysiloxanes may contain on average less than 2.5 SiH groups per molecule, preferably 2.4 SiH or less per molecule, more preferably less than 2.2 SiH groups per molecule, yet more preferably 2 SiH groups per molecule, and optionally from 1.5-2, 1.6-1.9, or 1.7-1.9 SiH groups, on average. Most preferably, the SiH-functional gel former contains two SiH groups per molecule, more preferably in terminal positions, and is thus free of chainpendent SiH groups. If the tacky prepolymer is present in amounts of 50 weight percent or less, then SiH functional organopolysiloxanes with a higher number of SiH groups per molecule, for example 2.5 or more, preferably 2.5 to 5, and most preferably 2.5 to 4 SiH groups may be present per molecule. A subsequent hydrosilylation reaction between the alkenyl-functional prepolymer and the SiH-functional organopolysiloxane causes a soft gel product to be formed. The silicon- bonded hydrogen content of the SiH-functional gel former can vary over a wide range, so long as a soft gel is obtained. The active hydrogen content may be, for example, from 0.005 weight percent to 0.5 weight percent, more preferably 0.005 weight percent to 0.1 weight percent. In the case of organopolysiloxanes containing only two SiH groups, the weight percent of active hydrogen is inversely proportional to the molecular weight of the organopolysiloxanes. As one skilled in the art readily recognizes in view of the disclosure herein, the use of SiH-functional organopolysiloxanes having very short chain lengths, or too high a weight percentage of silicon- bonded hydrogen, for example 1 to 1.7 weight percent, will tend to form polymers which may be too hard for use in the present invention. The proper chain length and silicon-bonded hydrogen content is easily determined by simple experiments easily performed by one skilled in the art. The amount of SiH-functional organopolysiloxane in the curable compositions of the invention, with exclusion of any solvent present, in other words, based on the sum of the alkenyl-functional prepolymer, any other alkenyl-functional ingredients, and SiH-functional organopolysiloxanes, is preferably from 5 weight percent to 95 weight percent, more preferably from 90 weight percent to10 weight percent, yet more preferably from 80 weight percent to 20 weight percent, and most preferably from 60 weight percent to 40 weight percent.

[0029] The curable composition may also contain further ethylenically unsaturated substances to aid in the development of the soft gel portion of the final product. For example, alkenyl-functional organopolysiloxanes may be added. These alkenyl-functional organopolysiloxanes may bear vinyl or other ethylenically unsaturated groups at the chain termini of the organopolysiloxanes or may contain pendent ethylenically unsaturated groups, and may also be cyclic, although the latter are not preferred. The molecular weight of these vinyl-functional organopolysiloxanes may vary over a wide range, for example, from about 5000g / mol to higher values of about 150,000 g / mol, more preferably from about 8000 g / mol to about 85,000g / mol, and yet more preferably from about 15,000 g / mol to about 80,000 g / mol. An example of such an ethylenically unsaturated substance is a linear a, co-divinyl polydimethylsiloxane. The amount of these substances can also vary over a wide range, for example from none to from 0.01-80 weight percent, more preferably from 1-70 weight percent, and most preferably from 30-70 weight percent, based on the total weight of curable components. By the term “curable components” is meant the ethylenically unsaturated prepolymer, SiH-functional organopolysiloxane, and any other components which react in a hydrosilylation reaction. The SiH / alkenyl ratio of the present curable adhesive composition is preferably 0.3:1 to 4:1, more preferably 0.5: 1 to 2: 1 and most preferably 0.5:1 to 1: 1. If this ratio is too low, cohesive strength may suffer, whereas if too high, tack may suffer.

[0030] The curable compositions must contain a hydrosilylation catalyst. Most hydrosilylation catalysts are based on noble metals, their compounds, and complexes, and are well known to those skilled in the art. Suitable hydrosilylation catalysts are well-known, and widely available from numerous sources. Preferred hydrosilylation catalysts are platinum compounds such as those disclosed in U.S. Pat. Nos. 3,159,601; 3,159,662; 3,220,972; 3,715,334; 3,775,452; and 3,814,730, and German published application DE 195 36176 Al, generally supplied in a solvent suitable for use in the adhesive formulation. Karstedt’s catalyst is preferred. The amount of catalyst can be readily determined by one of ordinary skill in the art. Conventional amounts of catalyst range from 1 ppm to 1000 ppm, more preferably 5 ppm to 150 ppm, yet more preferably10 ppm to 100 ppm, and most preferably 15 ppm to 50 ppm, based on the total weight of the hydrosilatable mixture and calculated as elemental metal.

[0031] The curable composition may contain a hydrosilylation reaction inhibitor. Such inhibitors are generally employed when the mixture, which is curable by hydrosilylation and which contains a hydrosilylation catalyst, is not to be used immediately. Addition curing silicon compositions have a limited pot life which is also temperature dependent. If the curable composition is prepared just prior to the coating operation, then in general, no hydrosilylation inhibitor will be necessary, and this is preferred. However, if the curable composition is to be prepared and then stored or shipped prior to use, then conventional hydrosilylation inhibitors which are well known to those skilled in the art can be employed. Examples of these are the acetylenic alcohols such as that known as dehydrolinalol, available from BASF S.E. Divinyltetramethyldisiloxane may also be useful for this purpose.

[0032] The curable mixture described above can be coated onto any desired substrate by coating operations well known to those skilled in the art, for example by casting, neat or from solvent, spraying, knife blade coating, gravure printing, jet printing, and the like. The thickness of the coating, following removal of any solvent present, can vary according to the particular application. The thickness of the coating can also vary to accommodate differences in pressure sensitivity, with thicker coatings being generally more adhesive. Coating thicknesses can preferably range from 10 pm to 1 mm, more preferably 20 pm to 500 pm, yet more preferably 20 pm to 200 pm, and most preferably 40 pm to 150 pm. Preferable substrates include woven and nonwoven fabrics, plastic films such as Mylar films, plastics, metals, and the like. Typical substrates as are commonly used for medical bandages are eminently suitable, for example. For medical devices which are intended to be wearable, the substrate may be a plastic or may be made of metal. These examples of potential substrates are illustrative, and not limiting.

[0033] The curable compositions are preferably free of nonfunctional organopolysiloxanes, especially when used in large concentrations. Such nonfunctional organopolysiloxanes, not being covalently bonded to the polymer network, may exude over time. The result may be substantially unpredictable change in adhesive and trauma performance, whichis undesirable. When nonfunctional organopolysiloxanes are present, these are preferably trimethylsilyl-terminated poly dimethylsiloxanes having molecular weights below 100,000 g / mol, more preferably below 80,000 g / mol, and most preferably below 50,000 g / mol. The amounts of such organopolysiloxanes should be low such that they remain well below the solubility limit so as to limit exudation. Thus, the amounts are preferably below 15 weight percent based on the total weight of the adhesive, more preferably below 10 weight percent, and yet more preferably less than five weight percent. Preferably, such nonfunctional organopolysiloxanes are present only in amounts which are unavoidable or are not present whatsoever. Silicone resins, however, even when essentially or wholly non-functional, may be present, and may be used, for example, to adjust properties of the cured composition, e.g. modulus, tack, etc. For example such silicone resins may be present in amounts of from less than 1% by weight to 65% by weight based on the total weight of the curable composition, more preferably from 1% to 60% by weight, and most preferably from 1% to 30% by weight. Such silicone resins may also be totally absent.

[0034] The curable compositions may contain, or may be free of, additional substances such as tack improvers, tack modifiers other than silicone resins, emollients, active medical ingredients such as vitamins, antibiotics, biocides, and antifungals, and also dyes, pigments, fragrances, and the like. Such ingredients are preferably absent.

[0035] Following application to a substrate, it is necessary to cure the composition. Due to the nature of the components, it is believed that a composition having both the properties of an SSA and also the properties of a PSA is obtained, one portion of this network being composed substantially of the condensation cured “hybrid” components which are responsible in large degree for the tack of the composition, and a second portion created as a gel in the hydrosilylation reaction. Due to the fact that the condensation-derived prepolymer still contains ethylenic unsaturation, it is bonded to the gel portion of the composition by covalent bonding. As a result, adhesives with high cohesive strength, high but tunable adhesion, and low trauma are all able to be obtained, in particular, simultaneously. Cure is generally obtained by heating the compositions to an elevated temperature, for example from 40°C to 170°C, more preferably from 70°C to 150°C, and most preferably from about 70°C to about 130°C. The cure time is dependent, as is well known to those skilled in the art, upon the amount of catalyst, the presence or absence of inhibitors, and thereactivity of the ingredients both in terms of the nature of the unsaturated group still present, and also the concentration of these groups. Cure times of from one minute to about 30 minutes are generally suitable, more preferably from two minutes to 20 minutes. A cure time of about 15 minutes at 120°C has been found to be highly suitable. The cure temperature may be selected so as to volatilize any solvent present. In some cases, for example when low viscosity organopolysiloxanes are present, these may serve as a solvent and may remain in the composition provided their concentration is low enough to avoid exudation over time.

[0036] Thus, in one aspect, the invention pertains to a curable silicone composition which is curable to a pressure sensitive adhesive composition, the curable composition containing hydrosilylation-curable components which include 5 to 95 wt. %, of a condensation product of a silicone resin bearing condensable group(s) and a linear or lightly branched polyorganosiloxane also bearing condensable group(s), at least one of these further bearing at least one alkenyl group; and from 95 to 5 wt. %, of at least one SiH-functional linear or lightly branched polyorganosiloxane preferably containing on average less than 3.5 SiH groups per molecule, more preferably less than 2.5 SiH groups per molecule, and having a wt. % of silicon-bonded hydrogen in the range of 0.005 wt. % to 0.5 wt. %, a hydrosilylation catalyst, optionally, a hydrosilylation inhibitor, and optionally, a solvent, wherein the amounts of the respective hydrosilylation-curable components are selected so as to provide an SiH / alkenyl ratio in the range of 0.3: 1 to 4: 1, and wherein following curing to a pressure sensitive adhesive and application to skin, the pressure sensitive adhesive exhibits a Wong-Baker face analysis pain level of less than 3 upon removal after 24 hours. The pressure sensitive adhesive is preferably in the form of a gel, and preferably has a peel strength from a steel substrate of greater than 2 N / 2.54 cm as measured according to ASTM D903, 180 degree Peel Strip Strength of Adhesive Bonds

[0037] The invention further pertains in particular, to a silicone pressure sensitive adhesive, comprising the cured product of the curable silicone composition. The silicone pressure sensitive adhesive is preferably an adhesive for a medical dressing or medical wearable. By “medical wearable” is meant any medical or other device which monitors any physiological characteristic, such as but not limited to glucose level, oxygen level, pulse rate, blood pressure, heart rhythm, temperature, and the like. The invention also pertains to a process for themanufacture of the silicone composition curable to a pressure sensitive adhesive as described above, by condensing a silicone resin bearing condensable group(s) with a linear or lightly branched polyorganosiloxane bearing condensable group(s) in the presence of a condensation catalyst, at least one of the silicone resin and linear or lightly branched polyorganosiloxane also bearing at least one alkenyl group, to form a resin hybrid composition, and adding to the resin hybrid composition to provide a pressure sensitive sufficient SiH functional linear or lightly branched polyorganosiloxane bearing on average less adhesive gel following curing - adding a hydrosilylation catalyst; and optionally adding a hydrosilylation inhibitor, wherein the process optionally takes place in the presence of a solvent, and the amount of the SiH-functional linear or lightly branched polyorganosiloxane constitutes from 5 to 95 weight percent of the total of resin hybrid composition and linear or lightly branched SiH-bearing polyorganosiloxanes, thereby forming a curable silicone composition curable to a pressure sensitive adhesive. Pressure sensitive adhesive articles, can be prepared by applying the curable silicone composition to a substrate and curing.

[0038] The invention will no be further described through the use of several examples, which should not be construed as limiting the invention in any way.

[0039] For adhesion testing the samples are coated on polyester substrates such as MYLAR™, in a thickness typically ranging from 1 to 10 mils (25.4 pm to 254 pm) thick and cured. Then they are applied to a stainless steel substrate for 30 min dwell time to measure the peel force between the adhesive layer and the stainless steel panel. The samples are peeled at a speed of 30.5 cm / minute in a tensile testing instrument at a 180 degree angle under ordinary temperature and humidity. The trauma on skin resulting from the removal of many conventional wound dressing tapes varies with the length of time the tape is worn and can be related to the peel test described above. This is not true for the pressure sensitive adhesives of the present invention, however. Trauma to the skin can be lessened by the wound dressing tape chemistry and design. By "low trauma" it is meant that the adhesive compositions have a peel strength of less than or equal to 3 N / cm on skin and a pain rating of less than 3 on the Wong -Baker pain scale, a facial observation pain assessment scale recognized and widely used in the medical field to quantify pain intensity measurement. See, e.g. E. Akgun et al., “Measurement of the pain levels of patients withextremity traumas and assessment of the attitudes of emergency physicians to pain management,” ANNALS OF MEDICAL RESEARCH 2018:25(4) 553.8.

[0040] Comparative Example 1

[0041] An organopolysiloxane mixture containing silicon-bonded alkenyl groups is prepared from 95.6 parts of a vinyl-terminated poly dimethylsiloxane also having 0.0025 mol percent terminal hydroxyl groups and a weight average molecular weight of approximately 16,000 g / mol, 4.0 parts of an approximately 2:3 weight ratio mixture of silicone resin MQ804 available from Wacker Chemicals, Adrian, Michigan; and a vinyl terminated organopolysiloxane having a viscosity of 20,000 mPa-s, a hydrosilylation inhibitor, and a hydrosilylation catalyst. The mixture is stirred with a Speedmixer™ at 2550 rpm for 5 minutes. To 10 parts of the mixture just described is added 5 parts of silicone resin MQ 803 TF, a methyl MQ silicone resin containing some residual silicon-bonded ethoxy and hydroxy groups, available from Wacker Chemicals, Adrian, MI. To this mixture is added 10 parts of an SiH containing mixture prepared by mixing 29.1 parts of a 16,000 g / mol organopolysiloxane terminated by vinyl groups and also containing 0.0025 mol % residual terminal hydroxy groups, 69.7 parts of an SiH functional organopolysiloxane having a viscosity of 1000 mPa-s, 1.2 parts of an SiH functional crosslinker having a viscosity of 180 mPa-s and 0.17 wt. % of silicon-bonded hydrogen. The curable mixture is rendered homogenous using a Speedmixer™ mixer at 2350 rpm for 30 seconds.

[0042] The curable mixture described above is coated onto a Mylar film at a thickness of 15 mils (50.1 pm) and cured at 120°C for 15 minutes. When the cured adhesive film is contacted with a finger or with a steel probe, a large amount of residue transfers to the probe.

[0043] Comparative Example 2

[0044] To 3 parts of the organopolysiloxane mixture containing alkenyl groups described in Comparative Example 1 is added 6 parts of a condensation product of 106 parts of MQ resin 803 available from Wacker Chemicals, Adrian, Michigan, and 100 parts of dimethylsilanol- terminated poly dimethylsiloxane dissolved in ISOPAR™ E solvent, and mixed for 5 minutes at 2350 rpm on a Speedmixer™ mixer. To this homogenous mixture is added 3 parts of the SiH-containing mixture described above, stirring with a Speedmixer™ mixer at 2350 rpm for 30 seconds. A 15 mil (50.1 pm) film is cast onto a Mylar substrate and cured at 120°C for 15 minutes. When contacted with a finger or with a steel probe, a large amount of adhesive remained adhered to the probe.

[0045] Inventive Examples

[0046] Example 1

[0047] A partially vinyl-functionalized organopolysiloxane fluid is prepared by equilibrating a silanol-terminated polydimethylsiloxane with 1,3-divinyltetramethyldisiloxane in the presence of PNCh as an equilibration catalyst. The equilibration is terminated prior to conversion of all terminal silanol groups to vinyl groups, leaving a portion of the polymer chains being terminated by vinyl groups at one terminus and silanol groups at the other terminus. The concentration of silanol groups is found to be 0.0025 mol percent calculated as OH, and the molecular weight is about 16,000 g / mol.

[0048] A vinyl-functional prepolymer is prepared by condensing 28.5 g of MQ resin 804 with 29.7 g of a silanol-terminated polydimethylsiloxane having a molecular weight of about 120,000 g / mol and 55.4 of the partially vinyl-functionalized organopolysiloxane fluid described above, dissolved in 30 g of ISOPARE solvent, employing 0.1 mL of a 63.1 weight percent solution of a 1:1 mixture of neodecanoic acid and tetramethylguanidine dissolved in ISOPAR E as the condensation catalyst. The condensation proceeds for approximately 3 hours at a temperature of about 150°C. The vinyl-functional prepolymer is used as synthesized, without removing the solvent.

[0049] To 16 g of the vinyl -functional prepolymer described above is added 20.2 g of a linear SiH-terminated organopolysiloxane having an active hydrogen content of 0.012 weight percent, 4.2 g of a linear vinyl-terminated organopolysiloxane having an iodine number of 3, 0.02 g of 1,3-divinyltetramethyldisiloxane, and these ingredients are mixed intensively at 2350 rpm to provide a homogeneous, clear, colorless liquid. To this liquid is added an amount of a solution of Karstedt’s catalyst to provide a platinum concentration of 15 ppm based on the weight of the totalmixture, and this admixture is mixed at 2350 rpm for 30 seconds to provide a curable adhesive composition.

[0050] The curable adhesive composition is coated onto a mylar substrate film at a thickness of approximately 100 pm (4 mils) and cured at 120°C for 15 minutes. The adhesive side of the cured film is applied to a stainless steel substrate and the peel strength is measured after 30 minutes and is approximately 1.1 N / 2.54cm. in a separate test, the adhesive is pressed onto the skin of a human subject and worn for 24 hours prior to removal. No pain is observed upon removal according to the Wong-Baker test [must be described above],

[0051] Example 2

[0052] A vinyl-functional prepolymer is prepared by condensing 7 g of MQ resin 804 with 53.9 g of MQ resin 803 and 80.5 g of a silanol-terminated poly dimethylsiloxane having a molecular weight of approximately 120,000 g / mol, dissolved in 80 g of ISOPARE solvent. Unlike the prepolymer of Example 1, which contained both aliphatic and resinous vinyl functionality, in this example, all of the vinyl functionality is derived from MQ resin 804, thus being exclusively resinous vinyl functionality. The condensation is conducted as in Example 1. When this prepolymer is cast onto a Mylar film at a thickness of approximately 75 pm (3 mils) and heated for 15 minutes at 120°, the peel strength from a stainless steel substrate is very high at 11.5 N / 2.54 cm.

[0053] The vinyl-functional prepolymer described above, 4.4 g, is mixed with 0.53 g of a linear SiH-terminated organopolysiloxane having an active hydrogen content of 0.012 weight percent, and 0.02 g of 1,3-divinyltetramethyldisiloxane and is intensively mixed at 2350 rpm to provide a homogeneous, clear, colorless liquid. To this liquid is then added sufficient Karstedt catalyst to provide 15 ppm of platinum based on the total weight of the mixture, and the catalystcontaining mixture is stirred at 2350 rpm for 30 seconds. The curable mixture is then cast onto a Mylar film at a thickness of approximately 100 pm (4 mils) and cured at 120°C for three minutes, forming a solid, tacky film. The peel strength from a stainless steel substrate is approximately 6.4 N / 2.54 cm. After applying the substrate to the skin of a subject and wearing for 24 hours, no pain is observed upon removal according to the Wong-Baker test described above.

[0054] Example 3

[0055] An “A” component is prepared by mixing 1.3 g of the vinyl -prepolymer described in Example 2 with 20.1 g of the partially vinyl-functionalized organopolysiloxane fluid described in Example 1, 0.3 g of a higher molecular weight version of the partially vinyl-functionalized polymer with a molecular weight of 46,000 g / mol, 0.05 g of 1,3 divinyltetramethyldisiloxane and sufficient Karstedt catalyst to provide 15 ppm of platinum calculated as the metal and based on the total weight of the mixture. The mixture is stirred intensively at 2350 rpm to provide a homogenous, clear and colorless liquid. A “B” component is prepared by mixing 11.62 g of an a,co-SiH terminated poly dimethylsiloxane having a viscosity of 1000 mPa-s and 0.2 g of a polydimethylsiloxane containing in-chain hydrogen methylsiloxy units, with a molecular weight of about 7000 g / mol and 0.18 weight percent of silicon-bonded hydrogen and intensively mixed at 2350 rpm until homogenous. Parts A and B are combined in a 1: 1 weight ratio, mixed at 2350 rpm for 30 seconds and coated onto a Mylar® polyester film at a thickness of about lOOum (4 mils). The coating cures to a solid, tacky film.

[0056] Examples 1 and 2 show that a wide range of adhesive peel strengths can be obtained without significantly increasing trauma. In prior art adhesives which are commercially available, an increase in adhesive peel strength is generally associated with a considerable increase in pain upon removal.

[0057] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.

Claims

WHAT IS CLAIMED IS:

1. A curable silicone composition which cures to a pressure sensitive adhesive, comprising: hydrosilylation-curable components a) 5 to 95 wt. %, based on the weight of a) and b) of a condensation product of a)i) a silicone resin bearing condensable group(s) and a)ii) a linear or lightly branched polyorganosiloxane also bearing condensable group(s), at least one of a)i) and a)ii) further bearing at least one alkenyl group; and b) from 95 to 5 wt. %, based on the weight of a) and b) of at least one SiH- functional linear or lightly branched polyorganosiloxane having a wt. % of silicon bonded hydrogen in the range of 0.005 wt. % to 0.5 wt. %, c) a hydrosilylation catalyst, d) optionally, a hydrosilylation inhibitor, and e) optionally, a solvent, wherein SiH groups and alkenyl groups are present in an SiH / alkenyl ratio in the range of 0.3:1 to 4: 1, and wherein following curing to a pressure sensitive adhesive and application to skin, the pressure sensitive adhesive exhibits a Wong-Baker face analysis pain level of less than 3 upon removal after 24 hours.

2. The curable silicone composition of claim 1, wherein the pressure sensitive adhesive is in the form of a gel following curing.

3. The silicone composition of claim 1, wherein the peel strength of the pressure sensitive adhesive from a steel substrate is greater than 2 N / 2.54 cm as measured according to ASTM D903.

4. The curable silicone composition of claim 1 , wherein the SiH functional linear or lightly branched polyorganosiloxane component has on average less than 3.5 SiH groups per molecule.

5. The curable silicone composition of claim 1, wherein the SiH-functional linear or lightly branched polyorganosiloxane component has on average less than 2.5 SiH groups per molecule.

6. The curable silicone composition of claim 1, wherein component a) is present in an amount of greater than 50 weight percent and component b) has, on average, less than 2.5 SiH groups per molecule.

7. The curable silicone composition of claim 1, wherein component a) is present in an amount of 5 to 50 weight percent and component b) has, on average, 2.5-5 SiH groups per molecule.

8. A silicone pressure sensitive adhesive, comprising the cured product of the silicone composition of claim 1.

9. The silicone pressure sensitive adhesive of claim 7, which is an adhesive for a medical dressing or medical wearable.

10. A process for the manufacture of the silicone composition which cures to a pressure sensitive adhesive of claim 1, comprising: a) condensing a silicone resin bearing condensable group(s) with a linear or lightly branched polyorganosiloxane bearing condensable group(s) in the presence of a condensation catalyst, at least one of the silicone resin or linear or lightly branched polyorganosiloxane also bearing at least one alkenyl group, to form a resin hybrid composition, and b) adding to the resin hybrid composition a), sufficient SiH functional linear or lightly branched polyorganosiloxane having a silicon-bondedhydrogen content of from 0.005 to 0.5 wt. % to provide an SiH / alkenyl group ratio of from 0.3: 1 to 4:l; c) adding a hydrosilylation catalyst; and d) optionally adding a hydrosilylation inhibitor, wherein the process optionally takes place in the presence of a solvent, and the amount of the SiH- functional linear or lightly branched polyorganosiloxane added in step b) constitutes from 5 to 95 weight percent of the total of resin hybrid composition and linear or lightly branched SiH-bearing polyorganosiloxanes added in step b), thereby forming a curable silicone composition curable to a pressure sensitive adhesive.

11. The silicone composition of claim 10, wherein the peel strength of the pressure sensitive adhesive from a steel substrate is greater than 2 N / 2.54 cm as measured according to ASTM D903.

12. The curable silicone composition of claim 10, wherein component a) is present in an amount of greater than 50 weight percent and component b) has, on average, less than 2.5 SiH groups per molecule.

13. The curable silicone composition of claim 10, wherein component a) is present in an amount of 5 to 50 weight percent and component b) has, on average, 2.5-5 SiH groups per molecule.

14. A process for the manufacture of a pressure sensitive adhesive article, comprising applying the curable silicone composition of claim 1 or the curable silicone composition prepared by the process of claim 10 to a substrate and curing the curable silicone composition.

15. The process of claim 14, wherein following curing, the composition has a peel strength greater than 2 N / 2.54 cm.