Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Patent
1998-12-03
2000-09-05
Seidleck, James J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
522182, 522 75, 522909, 522 39, 522 28, 522 59, 427514, 427517, 106 3127, 106 3128, 106 316, C08F 248, C08F 250, C08J 718, C09D 1100
Patent
active
061144061
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a radiation-curable ink jet composition.
Ink jet printing is well suited to applications such as short-run label printing. The inks used for this process are of generally low viscosity and are based on organic or aqueous solvent systems. In either case, the solvent content is relatively high.
When high levels of organic solvents are employed, evaporation of such solvents in the drying process potentially presents both environmental and health and safety hazards.
On the other hand, aqueous-based systems also present problems. It is relatively difficult to drive-off the water in the drying process. Such aqueous systems also tend to have a poor affinity for non-absorbent surfaces.
One potential solution to these problems, particularly in relation to the solvent base, is to use hot melt inks. However, the durability of the resultant coatings is inadequate for various applications.
The applicants have conjectured that a better solution to the foregoing problems would be to utilise an ink jet process using an ink which is UV-curable.
In another context, it is relevant to note that it is common to print direct onto polyethylene or PET bottles by means of silk-screen printing as a less expensive alternative to labelling. However, this technique results in a lower print quality than can be achieved with conventional printing on a paper label. Thus, there is a need for a high quality printing process capable of printing direct onto curved polymer substrates, with a fast drying time.
One process which potentially also lends itself to solving this objective is ink-jet printing using an ink which is radiation-curable, for example UV-curable.
It is usual to formulate UV-curable inks using a monomeric or oligomeric base vehicle. However, such polymer materials do not give the low viscosity required for a UV-curable ink-jet ink suitable for the aforementioned application, without the use of organic solvents. Although polymerisable monomers are in principle better-suited to achieving low viscosity, it is a problem to find a suitable monomer which would have sufficiently low toxicity and high thermal stability yet which gives a sufficiently flexible and durable film upon curing.
This problem has now been solved in accordance with the present invention by formulating a UV ink which contains an alkoxylated or polyalkoxylated acrylate monomer, a photoinitiator and a colourant.
A UV-curable ink-jet ink which contains a polar conductive component and a polymerisable monomer is disclosed in EP-A-0 465 039. However, this does not meet the aforementioned requirements. This ink contains the polar conductive component because it relies on so-called continuous heads which direct the ink by means of an electrostatic process. Moreover, many of the particular monomers and oligomers said to be usable in this process have serious health and safety implications. Thus, avoidance of the polar conductive material and accompanying viscosity modifiers used in the inks disclosed in EP-A-0 465 039 would be highly desirable on environmental and toxicity grounds.
Analogous non-conductive inks are disclosed in EP-A-0 540 203 which cross-references EP-A-0 465 309. Both of the latter documents envisage use of monofunctional and polyfunctional acrylate monomers. Ethoxylated monofunctional and trifunctional (but not difunctional) materials are recited. These documents also teach that the inks may optionally contain up to 70% by weight of difunctional material and optionally up to 10% by weight of trifunctional material.
Another monomer-based composition is described in U.S. Pat. No. 4,303,924 but this is said to require application in an inert atmosphere.
UV-curable photoresists for printed circuit board applications and which contain low levels of ethoxylated acrylate monomers are disclosed in U.S. Pat. No. 5,270,368.
Thus, there remains a need for a low viscsity radiation-curable ink jet composition with low toxicity and/or irritancy and which produces high quality print.
A new form of ink has now been devised which ove
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Caiger Nigel Antony
Selman Hartley David
Coates Brothers PLC
McClendon Sanza L.
Seidleck James J.
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