Direct contact prints

There is also an increasing use of printing inks applied with or without a coating to the inner surfaces of packaging such that the ink touches the food directly. Some manufacturers do supply inks specially formulated for direct contact printing. However, given the technical requirements of printing inks it is difficult to see how all of the components used in an ink can be replaced with direct food additives. 

When there was no benzophenone in the packaging there was none detected in the food. However, there was not a clear numerical correlation between levels of benzophenone in cartonboard and food. Differences in the composition of the foods tested may have been important in this respect, along with other factors such as the storage time, the storage temperature, the extent of any direct contact made between the food and the package, and the presence or absence of any barrier material between the printed cartonboard and the food. 

Ink-jet printing is a noncontact method the sample solution is dispensed without direct contact between the print head and the substrate. In modern ink-jet technology, a... 

In direct thermal printing, a color former (colorless) and a developer (acidic) are brought into contact in the presence of heat, to... 

Films are either coextruded [12] or printed on the back of a very transparent material. The binder of these screen inks or gravure inks has to have a high melting point or crosslinking to form an elastic film to avoid being replaced by the hot injected polymer. It is also possible to coat the backside of the film with an adhesion promoter, which prevents direct contact between the printed area and the polymer. This coating can also improve the adhesion between the film and the injection-molded part [13]. 

The microarray manufacturing method that enables microarray printing without direct contact to the surface is termed non-contact printing. Piezoelectric, bubble-generated, and microsolenoid driven pipettes as shown in Fig. 3 work with the same physical principle as ink-jet printers and are capa-... 

Within the broad category of "printed electronics", there are various technologies for manufacturing conductive components, of which inkjet is one of them. These printing techniques are compared to each other in Table 3. Inkjet is the most commercially suitable of these methods for apphcations where rapid customization is required and where the substrate is dehcate or otherwise sensitive to direct contact. 

The resolution on packaging inks applies to layers of print situated at the non-food contact surface of any material intended for food contact. Inks in direct contact are excluded from the resolution. Neither does the resolution apply when there is evidence that a substrate stops the migration of any component, and set-off or transfer via the gas phase can be excluded. Consequently it does not apply to glass bottles, aluminium tins and corresponding materials. Its main objective is to regulate prints on fibrous or plastic materials. 

Johns et al have published a report on benzophenone in printed cardboard for food stored frozen. This substance was found at 0.4-3.0 mg/dm in four board samples out of seven. The authors suggest that UV-cured inks had been used with benzophenone as an initiator in the printing of these boards. Three of the corresponding foodstuffs contained benzophenone at a level of 0.6-2.9 mg/kg, though there was a polyethylene layer applied to the board. Model ink substances were added to the carton, which then was in direct contact with foodstuffs stored at -20 °C for a year. It was found that transfer of the volatile substances could be considerable even at low temperatures. 

Set-off can be avoided by the use of anti-set-off compoimds. These are spray powders that reduce the frictional contact between the sheets. Materials like silica and starch, which have a particle diameter slightly greater than the printed ink film thickness, can be used. Slow setting problems may be reduced by the use of less solvent or by a higher ratio of resin to oil. Varnishing with a formula that utilises polymerisation induced by radiation is another way to avoid set-off. The varnish covers the printed surface and direct contact between the layer of print and the iimer food contact surface of the substrate is avoided. 

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