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...
Reexamination Certificate
2002-02-01
2003-11-04
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...
C528S065000, C528S076000, C525S403000, C525S440030, C106S031130, C156S277000, C428S423100
Reexamination Certificate
active
06642343
ABSTRACT:
The present invention relates to a polyurethane resin, to a coating composition comprising said polyurethane resin, to the use of said polyurethane resin for printing plastic substrates, to a method of producing a polyurethane resin and to a method of producing a laminate carrying a printed image, according to the preamble of the independent claims.
Polyurethane resins are the binders of choice in solvent borne coating compositions for plastic films and in the production of image carrying laminates. Laminates are multilayered shaped articles in which—according to the needs of the final article—each of the layers consist either of the same or of different materials. The preferred materials are paper, wood, textiles, metal and plastic films. In the field of food packaging, the laminates are mostly made from plastic or metal films, in particular metallized films, or a combination of both. Film materials are chosen such that the laminates can be subjected to sterilization processes without deterioration of the film and/or the laminate. As a further advantage laminates impart to prints or generally images a satisfying appearance with respect to gloss and color fastness. Generally laminates are produced by either joining two or more layers by means of adhesives or by adhesive-free extrusion coating. Irrespective of the production process a print or generally any kind of image which does not necessarily have to be printed can be applied to one or both of the layers prior to applying the next layer (Römpp Lexikon, Lacke und Druckfarben, ed. U. Zorll, Georg Thieme Verlag, Stuttgart, New York 1998, p.214 and 318).
Coating compositions for laminates, which are mainly in the form of printing inks, have to satisfy high standards. The resin as the film forming part of the composition must provide the dried layer with the required adhesive strength both to the underlying substrate and to the adhesive or to the extruded layer. As a further requirement the resin must impart to the dried layer stability during and after sterilization processes and/or treatment in boiling water even over a prolonged period of time (e.g. during food preparation). Further the dried layer must show blocking resistance and stability during sealing of the laminate (e.g. in the production of bags). The composition—as a printing ink—must be printable in flexo and gravure printing processes which are the techniques commonly used for printing plastic films. Thus, the resin must allow the printing ink to be thinly liquid, rapidly drying and to be soluble in esters and in alcohols, in particular in ethanol.
EP-604 890 teaches a printing ink (for printing laminates) based on a polyurethane resin. The polyurethane resin is the reaction product of a high molecular weight polyol compound of a molecular weight in the range of between 3000 to 10000, a low molecular weight polyol compound of a molecular weight of less than 200, an organic diisocyanate compound, a chain extender and optionally a reaction terminating agent. The polyol compounds are chosen such that the whole of the high molecular weight polyol compound and the low molecular weight polyol compound has an average molecular weight in the range of between 1500 and 2700, the isocyanate index of the diisocyanate being more than 2.0 and the nitrogen content of the polyurethane resin derived from the isocyanate groups of the diisocyanate being from 1.3 to 1.95% by weight.
Whereas printed and dried layers produced with the ink of EP-604 890 show in most of the cases the required bond strength, the initial adhesiveness of the layers to the underlying substrate, i.e. the adhesiveness within the first 30 seconds after drying, is poor. A lack of initial adhesiveness results in at least partial transfer of the printed layers to the back side of the substrate/film to which the layer has been applied during storage on rollers or stacks. A further drawback of the prints/layers produced with the ink of EP 604 890 is their lack in heat resistance in particular on coextruded polypropylene and polyester. The latter results in damages on edges of the layers during heat treatment of the laminate. In addition the printing ink shows poor compatibility with alcohols as the solvent of choice in flexographic applications. All these drawbacks are mainly due to lack of performance of the polyurethane resin.
The object of the present invention is to overcome the drawbacks of the prior art.
In particular it is an object to provide polyurethane resins applicable as film forming binders in coating compositions. The coating compositions must be suitable for producing—in the broadest sense—any kind of dried layers on plastic films and/or laminates. The polyurethane resin must provide the dried layer with an excellent initial adhesiveness in particular such that the layer is not damaged during storing and further processing of the substrate/film and during finishing of the laminate. Further, the resin has to reduce the risk of delamination during sealing of the plastic film or laminate, has to be heat resistant and soluble in alcohols and ester.
A further object is to provide a method for producing said polyurethane resin.
It is still another object of the present invention to provide a printing ink for plastic substrates and laminates wherein the printed and dry layers adhere initially well to the substrate and wherein the ink is printable by flexographic and/or gravure printing processes.
These objects are solved by the features of the independent claims.
In particular, they are solved by a polyurethane resin being the reaction product of at least one diisocyanate and components having isocyanate reactive functional groups, said components comprising a first group of at least one polyol, a second group of at least one polyol and a third group of at least one polyol and optionally at least one amine and a reaction terminating agent wherein all polyols of said first group are of an average molecular weight in the range of between 1000 to 10000 g/mol, wherein all polyols of said second group are of an average molecular weight in excess of 10000 up to 20000 g/mol, wherein all polyols of said third group are of an average molecular weight of equal or less than 800 g/mol and wherein the ratio of the equivalent weights of the diisocyanate to the components having isocyanate reactive functional groups is selected such that essentially all of the isocyanate groups of the diisocyanate are present as the reaction product with one of the isocyanate reactive functional groups. This means that there are essentially no free unreacted isocyanate groups left.
The polyurethane resin is obtained by first reacting a mixture comprising a first group of at least one polyol and a second group of at least one polyol with at least one diisocyanate to a first isocyanate terminated prepolymer, wherein all polyols of said first group are of an average molecular weight in the range of between 1000 to 10000 g/mol, wherein all polyols of said second group are of an average molecular weight in excess of 10000 up to 20000 g/mol and wherein the ratio of the equivalent weights of the diisocyanate to the entirety of the polyols of the first and of the second group is in the range of between 3.6:1 to 2.3:1, in a second step reacting said first isocyanate terminated prepolymer with a third group of at least one polyol, all polyols of said third group are of an average molecular weight of equal or less than 800 g/mol to a saturated polyurethane resin.
In a preferred embodiment the first isocyanate terminated prepolymer is reacted with the said third group of polyols to a second isocyanate terminated prepolymer and in a third step said second prepolymer is reacted with at least one diamine and optionally with a terminating agent to a saturated polyurethane resin. Saturated in this context means that the polyurethane resin has essentially no free unreacted isocyanates left.
In a preferred embodiment of the present invention the average molecular weight of the polyols of said second group are in the range of between 10500 to 18000 g/mol an
Denis Eugène
Gilles Catherin
Gilles Eiselé
Gorr Rachel
Shoemaker and Mattare
Sicpa Holding S.A.
LandOfFree
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