Methods of preparing polyurethane adhesives, adhesives...

Details Methods of preparing polyurethane adhesives, adhesives... Methods of preparing polyurethane adhesives, adhesives...

1999-01-25

2002-03-19

Gorr, Rachel (Department: 1711)

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

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C528S905000

Reexamination Certificate

active

06359100

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to a process for producing polyurethane adhesives, especially pressure sensitive adhesives utilizing a hydroxy-terminated urethane extended polyether (ester) polyol and a moderate range molecular weight diisocyanate. The resulting adhesives provide excellent adhesive and wear characteristics and are essentially non-cytotoxic making them particularly useful for medical applications such as in ostomy and wound care.
BACKGROUND OF THE INVENTION
The present invention is generally directed to the field of synthetic polymeric adhesive compositions, especially polyurethane adhesive compositions, particularly adapted for medical devices such as in the areas of ostomy, wound care and the like.
Adhesives have been used to affix ostomy appliances and wound dressings to the human body. Such appliances require a skin-contacting layer having an adhesive thereon which must be compatible with the skin. The cytotoxicity of the adhesive, measured by methods described in U.S. Pharmacopeia XXII, pp. 1495-1496, (1990) and supplement 9, pp. 3575-3576 (Sep. 15, 1993) incorporated herein by reference, cannot exceed a rating of 2 for use in such medical devices. In addition, many wound care applications use pressure-sensitive adhesives for adhesion of wound dressings to the patient's skin. Medical applications of this type require that the adhesive exhibit low cytotoxicity (i.e. grade levels of 2 or less, preferably zero).
Pressure-sensitive adhesives made with polyurethane polymers based on aliphatic, cycloaliphatic and araliphatic polyisocyanates, or prepolymers thereof, are especially attractive for use in medical devices. Such adhesives are transparent, non-discoloring, have a high degree of skin-tack and exhibit excellent adhesive and cohesive strength even after repeated removal and repositioning on the skin.
However, the polymerization of such polyisocyanates or prepolymers thereof, with hydroxyl-terminated polyols to form pressure-sensitive polyurethane adhesives must be performed in the presence of a catalyst. A variety of urethane-forming catalysts are disadvantageous because they are typically cytotoxic, not sufficiently active, catalyze undesirable oxidative degradation reactions and/or generate undesirable isocyanate trimers.
For example, most tertiary amines are not active enough for the polymerization of pressure-sensitive polyurethane adhesives from polyisocyanates or prepolymers thereof. Tertiary amines which are sufficiently active generally cause severe skin irritation and therefore cannot be used in medical applications. In addition, most tertiary amines have unacceptable grade levels of cytotoxicity.
Transition metal catalysts are also well known for use in the production of polyurethane adhesives. These catalysts are very potent but exhibit unacceptable cytotoxicity levels and often catalyze undesirable side reactions such as isocyanate trimerization. These undesirable side reactions tend to increase crosslink density and decrease desirable adhesive properties such as elongation, tear resistance and cohesive strength.
It is known in the art that transition metal catalysts formed from organic tin (II) salts and organotin (IV) compounds are highly efficient catalysts for the formation of polyurethane adhesives. They are advantageous because they do not catalyze the formation of isocyanate trimers.
Efforts have been made to employ acceptable catalysts for the formation of polyurethane adhesives. Much attention has been focused on the organic tin (II) salts and organotin (IV) compounds in the search for low cytotoxicity level catalysts for the formation of polyurethane adhesives.
For example, Melvin H. Gitlitz et al. “Kirk Othmer Encyclopedia of Chemical Technology”, 3
rd
Edition (1979) volume 23, pages 69-77 disclose that the toxicity of organic tin compounds is a reflection of their biological activity. The most toxic compounds are lower trialkyl organotin compounds such as trimethyl and triethyl tin derivatives. Di-organotin compounds as a class are substantially less toxic than the analogous tri-organotin compounds. It is stated that dialkyl tin chlorides and oxides generally show decreasing oral toxicity with increasing length of the alkyl chain. Mono-organotin compounds (e.g., monobutyltin sulfide) show decreasing toxicity with increasing alkyl chain length but have a lower order of toxicity than di-organotin compounds. Mono-alkyltin derivatives, however, do not exhibit as high a catalytic activity as dialkyl tin derivatives.
Further efforts have been made to identify transition metal catalysts which can polymerize polyisocyanates and polyols to form acceptable, non-toxic polyurethane adhesives. For example, U.S. Pat. No. 3,930,102 discloses a method of preparing pressure-sensitive polyurethane adhesives using tin (II)-ethyl hexoate, ferric acetyl acetonate, tin (II) naphthenate, or dibutyltin (IV) dilaurate. While the adhesives are stated to be optionally clear and color-stable, these catalysts exhibit unacceptable cytotoxicity even at moderate catalyst concentrations. They are therefore unacceptable for use in the production of polyurethane adhesives, especially for medical applications.
U.S. Pat. No. 4,661,099 discloses a method of producing polyurethane adhesives in the presence of catalysts which accelerate polyurethane formation. Dibutyltin dilaurate is used in high concentrations to catalyze the reaction. There is no mention of cytotoxicity testing of the pressure sensitive adhesive.
U.S. Pat. No. 4,332,927 discloses non-pressure sensitive polyurethane compositions for use in the manufacture of blood filters. The catalysts employed to form the adhesive include dialkyltin dicarboxylated compounds comprising linear or branched alkyl groups having less than 18 carbon atoms per molecule and carboxylate groups derived from monocarboxylic acids having from 2 to 18 carbon atoms per molecule, aliphatic carboxylic acids having from about 14 to about 20 carbon atoms per molecule and mixtures of the above. A major proportion of the carboxylate moiety comprises carboxylic acid derivatives. The hydroxy-function catalysts disclosed in the '927 Patent become part of the urethane matrix and may therefore require high cure temperatures on the order of 150 to 160° C. At such high temperatures, oxidative degradation of the polyether polymer chains likely occurs.
It would therefore be a significant advance in the art of the formation of polyurethane adhesives if a method could be employed to obtain polyurethane adhesives having exceptional properties including non-cytotoxicity.
It would be a further advance in the art to provide polyurethane adhesives, especially pressure adhesives which are non-cytotoxic and have excellent wear and strength properties.
SUMMARY OF THE INVENTION
The present invention is generally directed to polyurethane compositions, especially pressure-sensitive polyurethane compositions and to processes of making the same employing hydroxy-terminated urethane-extended prepolymers in which the formation of the prepolymer and of the polyurethane adhesive composition is performed in the presence of non-cytotoxic catalysts.
In particular, the present invention is, in part, directed to a method of preparing a polyurethane adhesive composition comprising:
a) reacting a polyol component selected from the group consisting of polyether polyols, polyester polyols and combinations thereof having at least 1.75 hydroxy groups per molecule with a diisocyanate compound selected from the group consisting of aliphatic, cycloaliphatic, and araliphatic diisocyanate compounds and combinations thereof in the presence of a non-cytotoxic catalyst to form an intermediate product having a viscosity of at least 5,000 cps when measured at a temperature of from about 25 to 35° C.; and
b) reacting greater than a stochiometric amount of the intermediate product with an isocyanate compound having a functionality of at least 2.0 in the presence of a non-cytotoxic catalyst.
Polyurethane compositions prepared by the method are also encom

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