Resin and Colorant - A Flexiproof Role
By Tom Kerchiss, RK Print Coat Instruments
A resin, sometimes synthetic, sometimes of an organic origin is a non-coloured vehicle used to carry the various elements associated with a flexographic ink direct to the anilox roller and ultimately on to the substrate. Resins can provide the ink with a matte finish or with a required level of gloss. Resins also help to anchor an ink or coating to the substrate, or not, as the case may be. Why would you not want an ink or coating to adhere permanently to the surface of a substrate? For some applications the sole purpose of the item is to reveal what is hidden. An example, one that most of us would be familiar with would be scratch card lottery tickets. The coating on the surface of the scratch card is formulated so that with a certain degree of pressure and typically using a coin the surface can be rubbed off the reveal win or lose.
Resins are versatile. If a resin is mixed with a suitable amine: the latter a clear liquid that helps a resin to stay in a wet state, but flashes off when subjected to hot air, the result is a varnish. Resin quietly goes about its business its not a media headline grabber but resin rules. Well almost. Colorant, usually a pigment but sometimes a dye provides the colour that the printer will match. A perfect looking colour, one that meets expectations is only part of the story. No one wants an ink that when laid down beads up on the surface. No one wants ink that comes off when the customer handles a printed product. To prevent this and to ensure ink and coating goes smoothly much care and attention goes into providing the correct vehicle or resin and varnish combination.
Oil based resin such as soybean and petroleum hydrocarbons may be used in litho inks, whereas polyamides and polyurethanes might be used in solvent based flexo or gravure applications. Styrene acrylic emulsion polymers may be selected and used for aqueous ink applications, but modified resins and other options are up for consideration and for use when applications are demanding.
As with other vehicle ingredients the chemical functionality of the resin is carefully matched to the print process and the intended application. To take an example: cheese slices are to be packed in a laminated flexible structure with peel back capability. This laminate is comprised of laminate layers that protect product contents with a printed layer that promotes the product and the brand.
The laminates in this instance provide protection against environmental spoilage, there is however, a reverse flexo printed outer layer. A polyurethane resin based systems is selected, which provides the high bond strength necessary to avoid delamination. A drawback is that the dispersion properties of the pigment are not so effective. To overcome this the formulator or resin producer has factored for this by employing complimentary co-resins in the mix that improve the dispersion properties of the pigment but without compromising other ink components or additives.
In flexo film printing, inks containing nitro cellulose still have a role to play. In this instance the formulator uses a mixture of nitro cellulose with a modifying resin such as a polyamide, polyvinyl butyral or a urethane, whichever is appropriate to ensure balanced performance properties. Nitro cellulose has good heat resistance and, for instance: a polyamide or one of the other mentioned resin provides good adhesion of the ink on many plastic films.
Irrespective of the ink type the need for consistency is important, another requirement is the increasing need, where possible to meet environmental dictates, and with that comes the need to reduce or exclude solvents or seek alternatives. As a result and over time ink chemists and ink additive, resin and other providers have abandoned many time tested recipes, in some instances replacing organic solvents with water, which in turn has led to the introduction of new surfactants, polymers and other materials and the adaptation or reformulation of existing materials.
When a resin or surfactant or another element such as pigments are modified or new additives or resin and vehicles are introduced formulations change, process variables occur and trialling, product monitoring is necessary. If one element changes through addition or subtraction, if the percentage of a resin in the vehicle is lowered or raised ink adhesion or print appearance may be affected. Much depends upon the type of ink and application but many tests are undertaken using various techniques and systems to prevent, resolve or monitor quality and performance over time are associated with print quality, block resistance, light fastness, bleeding, foam ability shear stability, gloss, water resistance, tape adhesion testing and drying in air. Also of importance is printability, colour appearance, and the look of a colour or colours on a substrate, taking into account polar and non polar surfaces, surface receptive treatment processes, and of course the conditions under which a colour is viewed.
Colour communication, proofing or as they are sometimes referred too as sample preparation systems are used throughout the supply chain to ensure consistency of results, resolve ink related issues and to speed new products to market. Devices such as the FlexiProof can be utilised by everyone involved in the production and use of flexo inks, including resin manufactures.
Resin manufacturers in the United States, in Italy and in Belgium have purchased RK Print Coat Instruments FlexiProof colour communication devices for quality control and product development purposes.
The FlexiProof 100 and variants FlexiProof UV and FlexiProof LED UV are multi-tasking devices providing real world test, monitoring and product development capability for those involved directly or indirectly with the flexographic process including the inks, materials and components. The FlexiProof is also in operation in a number of Universities and in some educational establishments engaged in research and in the advancement of the flexo process.
A scaled down but component critically exact version of a production flexo press the FlexiProof can be used to determine printability, i.e., gloss, durability, flexibility, chemical resistance, rub resistance, etc. It can be used for batch processing trialling unfamiliar materials, formulations, etc., and for colour matching, computer colour matching, data sampling and to evaluate how various elements interact and perform over time. Assessing the viability of product, processes and materials and formulations off press saves on press downtime, minimises waste, speeds product development and makes for a more efficient use of resources. The FlexiProof UV and LED UV incorporate an integral miniaturised UV system so that printing and curing can be undertaken seamlessly and without impacting on other workflow practices.
To a large degree there is an overlap with ink manufacturers test evaluations and with on the job print assessment and testing in that tight quality control must run right through the process of manufacture and the use of the ink itself on press. Variability is inherent in any process including one as complex as producing an ink. The issue is one of controlling that variability and the FlexiProof is a useful tool in that regard.
RK Print Coat Instruments Ltd
Litlington, Royston, Hertfordshire SG8 0QZ
www.rkprint.com sales@rkprint.com
Source: RK Print Coat Instruments Ltd
