Production of multilayered thin plasters comprising a...

Details Production of multilayered thin plasters comprising a... Production of multilayered thin plasters comprising a...

2001-09-20

2003-09-09

Crispino, Richard (Department: 1734)

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

C156S310000, C156S323000, C156S324000, C264S175000, C427S002310

Reexamination Certificate

active

06616793

ABSTRACT:

This invention relates to a process for producing multilayered thin plasters comprising a carrier material based on polyurethane.
BACKGROUND OF THE INVENTION
Multilayered thin plasters comprising a carrier material based on polyurethane are customarily produced by the polyurethane composition being spread coated on a carrier material and being laminated together with an adhesive composition, preferably likewise a polyurethane, using a doctor blade before it has cured. It has hitherto not been possible to produce very thin carrier layers of polyurethane. This is because when the doctor blade gap is set to a very low height, although it produces a thin polyurethane layer, the high viscosity of the polyurethane causes a buildup of material upstream of the doctor blade. This buildup of reactive polyurethane becomes blocked in time, rendering continuous operation impossible.
Foam wound contact materials as obtainable for example from Beiersdorf under the name of Cutinova® thin and Cutinova® hydro will be used by way of example to explain the production process in more detail. They are described inter alia in DE 42 33 289 A1, in DE 196 18 825 A1 and WO 97/43328.
According to these references, the polyurethane gel foam consists of a polyaddition product of a polyetherpolyol (Levagel® from Bayer AG) with an aromatic or aliphatic diisocyanate (Desmodur® Bayer AG), into which a polyacrylate superabsorbent powder (Favor®, Stockhausen) has been incorporated. The polyurethane gel can be made weakly or strongly self-adherent to skin depending on the ratio of OH equivalents of the polyol to reactive isocyanate groups.
The sheetlike polyurethane gel foam from 1 to 6 mm in thickness is covered by a polyurethane film on one side upstream of a doctor blade. Plasters of appropriate size are punched out of the bale material.
The punched-out large-area wound contact materials are very useful for managing chronic or slow-healing wounds of patients who have to be treated in hospital.
It is an object of the present invention to provide a process capable of producing very thin, single- or multilayered plasters comprising a polyurethane carrier in a continuous operation.
SUMMARY OF THE INVENTION
The invention accordingly provides a process for producing multilayered thin plasters comprising a carrier material based on polyurethane, which comprises
a) applying at least one layer of a polyurethane to a transfer,
b) applying an adhesive composition to a release layer,
c) laminating the uncured polyurethane on the transfer and the adhesive composition on the release layer together using a doctor blade in particular,
d) passing the laminate downstream of the doctor blade into a roll nip in which the polyurethane and the adhesive composition are rolled out to the ultimate thickness.
DETAILED DESCRIPTION
In a first advantageous embodiment of the process, the roll nip is formed by two smooth rolls.
In a further preferred embodiment, the roll nip is formed by a top embossing roll and a smooth bottom roll.
The embossing makes it possible, first, to adjust the polyurethane layer on the moving carrier web to the desired thickness and, secondly, to create specific accumulations of material in the coherent polyurethane layer in order that plasters of any shape may be punched out as a result.
The embossing roll may comprise various embossments to provide a change in the polyurethane layer. These embossments may have the shape of a semiconcave lens for example, This leads to raised centers in the polyurethane layer, which are beveled off toward the edge. Other possibilities include ellipsoids, cuboids, cubes or other geometric shapes in order that specific shapes may be created in the PU layer.
For example, in the case of the lens, the result is a polyurethane layer which, after punching, is beveled off from a point in the center toward the edge.
This point is situated In the area's middle in particular in order that a symmetrical appearance may be obtained for the beveled layer. But the beveling may also be irregular, depending on the requirements and application scenario of the plaster.
The height of the edge zone is not more than 50% of the overall height of the product, preference being given to edge zone heights of less than 0.2 mm. The contouring profile from the center to the edge is defined by the mold chosen, i.e, the casting mold determines the design of the contour.
To provide the desired thickness reduction, the roll nip preferably generates a pressure of at least 4 bar, especially 5 bar.
The polyurethane layer, furthermore, preferably has a post roll nip thickness of 10 to 100 &mgr;m, especially 40 to 60 &mgr;m.
The adhesive, furthermore, preferably has a post roll nip thickness of 20 to 100 &mgr;m, especially 40 to 60 &mgr;m.
The carrier film preferably comprises a transparent multilayered moisture vapor pervious polyurethane, polyethylene, polypropylene, polyamide or polyester film. But this enumeration is not to be understood as conclusive in that, it will be appreciated, one skilled in the art is able to come up with other suitable films without inventive step. In an advantageous embodiment, these films have a thickness of 10 to 100 &mgr;m, especially 40 to 60 &mgr;m.
The advantageous thickness results from the need for a flexurally stiff material which resists curling when subjected to mechanical loading.
In a further advantageous embodiment, it comprises a skin friendly pressure sensitive adhesive composition comprising polyacrylate into which a tackifier (a hydrocarbon resin for example) is incorporated to enhance the adhesion to skin.
The release layer is preferably a release paper which has been siliconized on one side.
The polyurethane layer is in particular transparent, highly moisture vapor pervious and adhesive. To store fluid, it is preferable to incorporate a superabsorbent polymer as a powder.
The polyurethane layer serves as good cushioning and as a storage medium for exudate from the wound.
Useful polyurethanes form part of the subject matter of DE 196 18 825, which discloses hydrophilic, self-adhesive polyurethane gels consisting of
a) polyetherpolyols with 2 to 6 hydroxyl groups and having OH values of 20 to 112 and an ethylene oxide (EO) content of ≧10 weight %,
b) antioxidants,
c) bismuth(III) carboxylates soluble in the polyols a) and based on carboxylic acids having 2 to 18 carbon atoms as catalysts and also
d) 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 weight %, relative to the polyol a), the quantity of antioxidants b) is in the range from 0.1 to 1.0 weight %, based on polyol a), and the ratio of free NCO groups of component d) to the free OH groups of component a) (isocyanate index) is selected within the range from 0.30 to 0.70.
Preference is given to using polyetherpolyols having 3 to 4, most preferably 4, hydroxyl groups and an OH number in the range from 20 to 112, preferably 30 to 56. The ethylene oxide content in the polyetherpolyols used according to the invention is preferably ≧20% by weight.
Polyetherpolyols are known per se and are prepared for example by polymerization of epoxides, such as ethylene oxide, propylene oxide, butylene oxide or tetrahydrofuran, with themselves or by addition of these epoxides, preferably of ethylene oxide and propylene oxide—optionally mixed with each other or separately in succession—to 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 useful high molecular weight polyhydroxy compounds mentioned are recited for example in High Polymers, Vol. XVI, “Polyurethanes, Chemistry and Technology” (Saunders-Frisch, Interscience Publishers, New York, volume 1, 1962, pages 32-42).
The isocyanate component used is monomeric or trimerized hexamethylene diisocyanate or hexamethylene diisocyanate modified by

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