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...
Reexamination Certificate
2000-05-18
2003-04-01
Jagannathan, Vasu (Department: 1714)
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...
C523S160000, C522S155000, C522S909000, C427S493000, C427S143000, C430S308000, C525S309000
Reexamination Certificate
active
06541561
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to cross-linkable printing inks and coatings which have particular usefulness in the manufacture of transfers, plastic films and stencils.
In recent years, the use of monomers and oligimers, both separately and as admixtures, curable by ultra violet light or by electron beam radiation has given rise to a new range of materials which are mainly used in the surface coatings industry.
The great advantage of these materials is that by blending low viscosity monomers or oligimers with high viscosity oligimers, or by suitably compounding the oligimers, it has been possible to formulate a large range of compositions which are at the correct viscosity for processing by the normal processes of coating or printing without requiring solvents.
The ability to provide surface coating compositions which are 100% non-volatile has been of great importance for a number of reasons:
First, the absence of volatile solvents ensures an environmentally friendly product.
Secondly, the use of solvents represents an additional cost since they are totally lost having once performed their purpose of reducing viscosity.
Thirdly the loss of solvents in conventional compositions such as, for example printing inks, causes variability during processing which demands greater processing control and these 100% non-volatile liquid compounds remain perfectly stable during the coating or printing processes. After the coating or printing processes have been performed, these compositions can be rapidly or instantly converted by crosslinking using ultra violet light or electron beams.
It is symptomatic of these compositions that the low viscosity monomers or oligimers which are used to adjust viscosity are not removed and are therefore finally part and parcel of the final coating or ink and affect the physical characteristics of the composition.
The formulation of inks and coatings has therefore to take into account the physical properties of the compounds both as processible liquids and finally as crosslinked coatings or inks.
In general, the availability of a range of monomers having various functionalities enables the viscosity to be adjusted whilst also controlling the softness or hardness and the flexibility or strength of the final crosslinked product. In general, monofunctional monomers do not have the high density of crosslinking as multifunctional monomers and are as a consequence more soft and flexible. Similarly the oligimers which have higher molecular weight components also vary in functionality with similar consequences.
Crosslinking of the compounds occurs either by incorporating various well known photo sensitisers which respond to particular wavelengths of light when ultra violet light is used or require no catalyst when the energy for crosslinking is derived from electron beams.
Whilst it is possible to achieve very hard, tough cross-linked films from the use of these compositions, it has, in practice, been impossible to provide tough, hard films which are also free from cracking on flexing. The resulting films do not have the resilience which can be obtained by extruded plastics in which the toughness and flexibility is provided by not only the type of polymer used but by the orientation achieved by extrusion in the molten state.
It is believed that the reason for this ultimate lack of flexibility lies in the fact that the crosslinked molecules are not orientated and are of relatively low molecular weight and are, therefore, in the form of clusters rather than extended linear molecules.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that the disadvantage of the lack of flexibility in otherwise strong and tough UV or electron beam cured films can be overcome by incorporating into the liquid compositions polymeric materials in the form of powders.
According to one aspect of the present invention there is provided a cross-linkable printing ink which comprises a dispersion of a powdered polymer or resin in a liquid composition comprising at least one polymerisable monomer or oligimer.
The invention also includes a method of making a plastics film or transfer which comprises mixing a powdered polymer into a curable liquid composition comprising at least one oligimer or monomer to form an ink, printing said ink on a substrate, heating the printed ink to cause the powdered polymer to dissolve in said composition and then causing said oligimer or monomer to polymerise to form a solid, flexible, cured ink film.
DETAILED DESCRIPTION OF THE INVENTION
In its simplest form the inks of the invention may consist of one or more powdered polymers dispersed in a single liquid polymerisable monomer. The monomer will be polymerisable to form a cured ink film or coating and the toughness and flexibility of the resulting film will depend on a number of factors, including the functionality of the monomer and its interaction with other components of the ink composition. Monofunctional monomers give very soft and sometimes tacky adhesive type cured coatings in compositions with the powdered polymer. Where the functionality is more than one a cross-linked, cured structure is normally obtained. By varying the functionality, it is possible to vary the properties of the film or coating from soft, tacky films to tough, flexible films. It is convenient to prepare a blend of liquid monomers and/or oligimers and to select components which in admixture with the powdered polymer give an ink composition of the desired viscosity and yield a final, cured ink film having the desired physical properties. For example, a monomer of low functionality will tend to introduce softness and flexibility into the cured film, while a multifunctional monomer or oligimer will cause the cured film to exhibit toughness and high strength.
The selection of the monomers and oligimers follows the above stated rules but the addition of polymeric materials in powder form requires further consideration which influence both the viscosity of the liquid form and the final crosslinked coating or ink.
If, for example, the powdered polymer is soluble in the monomer or oligimer, then the viscosity will be affected with the degree of dissolution of the powder. In practice, it is found that certain powdered polymers can be incorporated and remain in a discrete form without noticeable effect on the viscosity, provided the compositions are kept at a relatively low temperature. It is most convenient to use combinations in which the viscosity can be maintained without change for some period of time at room temperature and the powdered polymer is very soluble in the monomers or oligimers at higher temperatures.
It has been found that by selecting the monomers and oligimers or mixtures thereof and equally selecting types of powdered polymers it is possible to enhance the properties of the crosslinked coatings of inks to achieve levels of toughness combined with flexibility hitherto not possible by conventional methods.
Basically, this achievement is thought to be due to the molecular structure which can be introduced by the performed powdered polymer which is not possible when monomers or oligimers crosslink conventionally as clusters, non-linearly.
It is an object of this invention to change the normal consequences of formulation of ultra violet or electron beam curing compositions by the inclusion of powdered polymers or resins such that:
1) the compositions can be converted by coating, printing, or extruding whilst maintaining their viscosity within tolerable processing limits;
2) the powdered polymers or resins can be allowed to modify the final result by being partially or completely dissolved in the monomers or oligimers by the application of heat or other non crosslinking form of energy;
3) the solubilised polymer is permanently incorporated in the crosslinked monomer, oligimer or mixtures thereof.
Whereas it is usually preferable that the compositions covered by this invention contain no solvent whatsoever and are, indeed, 100% non-volatile and are thus extremely friendly to the environment,
Burns Doane Swecker & Mathis L.L.P.
Jagannathan Vasu
Shosho Callie E
Trip Industries Holding B.V.
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