Adhesives

Details Adhesives Adhesives

1998-03-26

2001-02-06

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

C522S006000, C522S120000, C522S121000, C522S904000, C522S905000, C427S516000, C427S208400, C428S041700, C428S041800, C428S042300, C428S3550RA, C156S272200, C156S273300, C156S275500, C156S275700

Reexamination Certificate

active

06184264

ABSTRACT:

The present invention relates to adhesives, to methods for producing adhesives and to articles comprising adhesives. In particular this invention relates to ‘switchable’ adhesives, that is, adhesives which may be influenced to change from a tacky to a non-tacky state thereby reducing the peel strength of the adhesive.
Adhesive products such as adhesive surgical or medical dressings and bandages normally comprise a layer of a pressure sensitive adhesive. However, when conventional adhesive dressings and/or bandages are removed they often cause localised trauma to the patient.
There has therefore long been a desire to provide, for example, adhesive dressings which can exhibit a reduction in peel strength of the adhesive, and therefore cause less localised trauma, than conventional adhesives when the dressing is removed. Hereinafter, adhesives which can be changed from a tacky to a non-tacky state will be referred to as 'switchable adhesives'.
Switchable adhesives are known. For example, U.S. Pat. Nos. 5,032,637, 5,352,516, 4,331,576 and 5,182,323 describe adhesives which become less tacky, ie. are switchable, in contact with water. However, such adhesives are unsuitable, for example, if used on a wound dressing and the patients wound needs to be kept dry. UV switchable adhesives are described in U.S. Pat. Nos. 4,286,047, 4,968,559 and 5,118,567 and Japanese Patent No.3043988. Such adhesives suffer from the disadvantage that they may require high doses of UV radiation or may need to be used in conjunction with photoinitiators which result in undesirable bi-products. Since it remains undesirable to expose patients to too much ultra violet radiation, there remains a need for a switchable adhesive which can undergo a reduction in peel strength at low dosages of UV radiation or more preferably by exposure to visible light irradiation and/or which removes or mitigates the need for the use of photoinitiators.
We have now surprisingly found an adhesive which is switchable when exposed to, inter alia, visible light, ie. is visible light switchable, or low dosages of UV light. Such visible light switchable or low dosage UV light switchable adhesives generally comprise an adhesive polymeric group with bound-in polymerisable or curable group.
Thus according to the invention we provide a switchable adhesive composition comprising an adhesive polymeric moiety and a plurality of bound-in curable moieties.
The bound-in curable moieties are preferably photocurable moieties. By the term curable moieties we mean moieties which are capable of undergoing a reaction, eg. photo curing to produce a polymer comprising the adhesive polymeric group, which polymer has greatly increased molecular weight. The preferred curable moieties are those which produce a polymer of increased molecular weight by way of cross-linking the adhesive polymeric moiety.
The bound-in curable moiety may be introduced into the adhesive polymeric moiety by forming a polymer comprising the adhesive polymeric moiety and the bound-in curable moiety, eg. the curable moiety is chemically bound to the adhesive polymeric moiety.
The adhesive polymeric moiety will generally comprise a polymeric ‘backbone’. Any conventionally known adhesive polymers may be used provided that such polymers are, where desirable, reactable to produce adducts with curable moieties such that the curable moieties are bound-in.
Preferred adhesive polymeric moieties include polyurethanes, polyacrylates and free radical polymerisable vinyl moieties. Polyacrylates are especially preferred.
When the adhesive polymeric moiety comprises a polyurethane adhesive it may be a lightly cross-linked or linear polyurethane adhesive. When the adhesive polymeric moiety is a polyurethane the bound-in curable groups may form end groups on the polyurethane backbone, may be incorporated into the polymer backbone or may be pendant groups, eg. along the backbone.
Desirably the bound-in curable groups in the polyurethane adhesives are located at or close to free ends of the backbone and curing causes these ends to become linked together.
Particularly preferred adhesives are acrylates. By the term acrylate adhesives we include acrylates, methacrylates and acrylate copolymer adhesives. Indeed acrylate copolymer adhesives are especially preferred, eg. alkyl acrylate copolymers. The ‘backbone’ polymer may be a copolymer with one or more acrylates. Alternatively the ‘backbone’ polymer may be a copolymer with one or more acrylates and a free radical polymerisable vinyl moiety. Such vinyl moieties include compounds such as itaconic anhydride, maleic anhydride or vinyl azlactone or glycidyl methacrylate. Especially preferred acrylate adhesives are those wherein the polymeric ‘backbone’ includes a proportion of unreacted carboxylic acid residues, eg. acrylic acid residues. Unreacted acid residues are particularly advantageous since they may be derivatised, eg. esterifled, with curable groups. Thus especially preferred acrylate copolymers are acrylate tricopolymers. A particularly preferred adhesive moiety is an alkyl acrylate/alkyl acrylate/acrylic acid tri-copolymer. An especially preferred adhesive moiety is an n-butyl acrylate/2-ethylhexyl acrylate/acrylic acid tri-copolymer. The most preferred tri-copolymer is n-butyl acrylate/2-ethylhexyl acrylatelacrylic acid in the ratios 47147/6. Such an adhesive composition is hereinafter referred to as A8 adhesive.
Any conventionally known unsaturated compounds, eg. olefinic or aromatic compounds, may be used as the bound-in curable moiety provided that they are able to react with the polymeric ‘backbone’. Free radical curable moieties are preferred, such groups include acrylates and methacrylates which may form, for example, esters or amides with any unreacted acid groups in the polymeric ‘backbone’. Curable groups which are photodimerisable may also be used and include groups such as anthracenes, cinnamates, maleimides and coumarin groups. Mixtures of all of the aforesaid may also be used. Preferred bound-in curable groups are selected from acrylates, methacrylates and anthracenes. Especially preferred bound-in curable groups are free radical curable groups such as acrylates and/or methacrylates. Most preferred are methacrylates such as hydroxyalkyl methacrylates wherein the hydroxyalkyl group possesses from 1 to 6 carbon atoms, eg. 1 to 4 carbon atoms and especially 1 or 2 carbon atoms. Especially preferred is hydroxyethylmethacrylate.
Altematively, when the polymeric ‘backbone’ comprises an acrylate moiety then the bound-in curable moiety may be a free radical polymerisable vinyl moiety as hereinbefore described.
The amount of the bound-in curable moiety present in the switchable adhesive composition may vary, depending, inter alia, upon the amount of tackiness desired in the switchable adhesive when it is switched from it's tacky to it's non-tacky state. Thus, the amount of the bound-in curable moiety, eg. hydroxyethyl methacrylate, present in the switchable adhesive composition may be from 0.4 to 50% by weight of polymer backbone preferably from 0.4 to 40% by weight and more preferably from 0.4 to 20% by weight. The free radical curable moieties are preferably present as from 0.4 to 5% by weight. The photodimerisable moieties are preferably present as from 10 to 15% by weight, eg. 13% by weight.
The switchable adhesive compositions of the invention may also include a free radical initiator. Any conventionally known free radical initiators may be used. Particularly preferred are those initiators which react to visible light radiation, although initiators which react under longer or shorter wavelength light may be used in compositions of the invention. Thus, free radical initiators which may be mentioned include titanocene photoinitiators; dye/co-initiator systems, eg. thionine/triethanolamine; dye/borate salt systems; dye/peroxide systems and 1,2-diketonelco-initiator systems, eg. camphorquinone/tertiary amine. Preferred free radical initiators are the titanocene initiators such as bis(y
5
-cyclopentadienyl) bis [2,6-di

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