Hydrophilic, self-adhesive polyurethane gel substances

Details Hydrophilic, self-adhesive polyurethane gel substances Hydrophilic, self-adhesive polyurethane gel substances

1998-11-03

2001-02-20

Cooney, Jr., John M. (Department: 1711)

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

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C523S111000, C524S839000, C524S871000, C524S873000, C524S875000

Reexamination Certificate

active

06191216

ABSTRACT:

The present invention relates to improved hydrophilic, self-adhesive polyurethane gel compositions and foams prepared therefrom, to the use of the polyurethane gel compositions for pressure-distributing, in particular self-adhesive, polyurethane (foam) gels prepared therefrom and to the use of the polyurethane gel compositions for self-adhesive and pressure-distributing materials and adhesive layers.
Polyurethane gels and foams produced therefrom are known, for example, from EP 0 057 839, EP 0 147 588 or U.S. Pat. No. 4,661,099 and from applications DE 43 08 445 or DE 43 08 347. Some of the polyurethane gels described therein and the foams produced therefrom are self-adhesive systems which are capable of absorbing aqueous fluids in a range from a few percent of the weight thereof to more than 100 times the weight thereof, if fillers such as for example fluid-absorbing polymers are optionally incorporated therein.
The structural components in the gels and foam gels described in the stated documents, apart from polyhydroxy compounds, are aromatic or aliphatic polyisocyanates (but in fact in practice only aromatic polyisocyanates are used). However, if the gels are intended for use as adhesive layers for skin contact, then gels produced with aliphatic isocyanates are preferable to aromatically based gels. However, if an attempt is made to produce hydrophilic gels on the basis of aliphatic isocyanates using the formulations described in the above documents, due to the low reactivity of aliphatic NCO groups, only very slowly reacting mixtures are obtained if, in order to avoid skin incompatibility problems, it is possible to use only low concentrations of the amines or metal salts cited therein as catalysts. Another disadvantage of the aliphatic gels produced according to the above patent publications is that they are extremely sensitive to oxidative degradation, which very rapidly results in complete destruction of the gel (liquefaction) and renders these gels unusable for commercial applications.
In specific applications, for example in the medical sector, there is also a requirement for material sterility.
There are various ways in which sterile material may be obtained, such as for example radiation sterilisation, gas sterilisation with ethylene oxide or steam sterilisation.
The stated sterilisation processes are all used in the production of medical products or consumables, but they all have specific advantages and disadvantages.
One important method is &ggr; radiation sterilisation. This method has the advantage that the material to be sterilised may already be in a tightly sealed package and no residues from the sterilisation process remain in the material to be sterilised. The disadvantage is that in many materials, such as for example materials of organic origin or synthetic polymers, free radicals are formed which subsequently result in degradation of the material. This thus results in immediate decomposition or a distinct reduction in the storage life of the material after sterilisation.
In polyurethane gels or polyurethane foam gels, this is manifested by a loss of cohesion of the gel material. In extreme cases, &ggr; sterilisation transforms the gel or foam gel back into a highly viscous liquid.
An object of the invention was accordingly to provide aging-resistant polyurethane gels on the basis of aliphatic isocyanates while avoiding amine catalysts, which gels, despite the low reactivity of the aliphatic NCO groups, react as least as fast as conventional products produced with aromatic isocyanates and furthermore to provide polyurethane foam gels and &ggr;-sterilisable polyurethane gels and polyurethane foam gels.
The present invention accordingly provides hydrophilic, self-adhesive polyurethane gels consisting of
a) polyether polyols with 2 to 6 hydroxyl groups and having OH values of 20 to 112 and an ethylene oxide (EO) content of ≧10 wt. %,
b) anti-oxidants,
c) bismuth(III) carboxylates soluble in the polyols a) and based on carboxylic acids having 2 to 18 C atoms as catalysts together with
d) hexamethylene diisocyanate or a modified hexamethylene diisocyanate,
wherein the product of the functionalities of the polyurethane-forming components a) and d) is at least 5.2, the quantity of catalyst c) amounts to 0.005 to 0.25 wt. %, relative to the polyols a), the quantity of anti-oxidants b) is in the range of ≧0.1 wt. %, relative to the polyols a) and a ratio of free NCO groups in component d) to the free OH groups in component a) (isocyanate index) in the range from 0.30 to 0.70 is selected.
According to the invention, preferred polyether polyols are those with 3 to 4, particularly preferably 4, hydroxyl groups and having an OH value in the range from 20 to 112, preferably from 30 to 56. The ethylene oxide content in the polyether polyols used according to the invention is preferably ≧20 wt. %.
The polyether polyols according to the invention are known per se and are produced, for example, by polymerising epoxides, such as ethylene oxide, propylene oxide, butylene oxide or tetrahydrofuran with themselves or by addition of these epoxides, preferably ethylene oxide and propylene oxide (optionally mixed together or separately in succession), onto starter components having at least two reactive hydrogen atoms, such as water, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, glycerol, trimethylolpropane, pentaerythritol, sorbitol or sucrose. Representatives of the stated relatively high molecular weight polyhydroxyl compounds to be used according to the invention are listed, for example, in High
Polymers, volume XVI, Polyurethanes, Chemistry and Technology, (Saunders-Frisch, Interscience Publishers, New York, volume 1, 1962, pp. 32-42).
The isocyanate component used according to the invention is monomeric or trimerised hexamethylene diisocyanate or also hexamethylene diisocyanate modified by biuret, uretidione, allophanate groups or by prepolymerisation with polyether polyols or mixtures of polyether polyols based on known starter components having 2 or >2 reactive H atoms and epoxides, such as ethylene oxide or propylene oxide, and of an OH value of ≦850, preferably of 100 to 600. It is preferred to use modified hexamethylene diisocyanate, in particular hexamethylene diisocyanate modified by prepolymerisation with polyether diols of an OH value of 200 to 600. Very particularly preferred modification products of hexamethylene diisocyanate are those with polyether diols of an OH value of 200-600 and having a residual content of monomeric hexamethylene diisocyanate of below 0.5 wt. %.
Catalysts which may be considered for the polyurethane gels according to the invention are bismuth(III) carboxylates soluble in the anhydrous polyether polyols a) and based on linear, branched, saturated or unsaturated carboxylic acids having 2 to 18, preferably 6 to 18 C atoms. Bismuth(III) salts of branched saturated carboxylic acids having tertiary carboxyl groups are preferred, such as those of 2,2-dimethyloctanoic acid (for example versatic acids, Shell). Preparations of these Bi(III) salts in excess quantities of these carboxylic acids are very suitable. A solution of 1 mole of the Bi(III) salt of versatic 10 acid (2,2-dimethyloctanoic acid) in an excess of 3 moles of this acid and having a Bi content of 17% has proved outstandingly suitable.
According to the invention, the catalysts are preferably used in quantities of 0.01 to 0.3, in particular of 0.03 to 0.15 wt. %, relative to the polyol a).
Anti-oxidants (stabilisers) which may be considered for the polyurethane gels and polyurethane foam gels according to the invention are in particular sterically hindered phenolic stabilisers, such as BHT (2,6-di-tert.-butyl-4-methylphenol), Vulkanox BKF (2,2′-methylene-bis-(6-tert.-butyl-4-methylphenol)) (Bayer AG), Irganox 1010 (pentaerythrityltetrakis[3-(3,5-di-tert.-butyl-4-hydroxyphenyl) propionate]), Irganox 1076 (octadecyl-3-(3,5-di-tert.-butyl-4-hydroxyphenyl) propionate), Irganox 1330 (1,3,5-trimethyl-2,4,6-tris(3′,5′-di-t

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