Technical Information 50.G.003 Radiation-curing Systems General Information, Services

Transcription

1 Technical Information 50.G.003 Radiation-curing Systems General Information, Services NewV UV curing inks and varnishes for flexo printing Direction for use NewV flex_direction for use 06/2017 en

2 TABLE OF CONTENT Composition of UV-curing inks and varnishes... 3 Curing... 3 Hindrance of reaction... 4 Technical requirements... 4 Printing plates for flexo printing... 4 Mounting tape... 4 Anilox rollers... 4 Blade... 4 Washup solution... 4 UV lamps... 5 Cooling... 5 Extraction... 5 Shutter... 5 Using UV-curing inks... 5 Handling UV-curing inks, varnishes and wash-up solutions... 5 Disposing of inks and varnishes... 6 Recycling of UV prints... 6 Recommended application parameters... 6 Substrates... 6 Adhesion on films, foils, metals and cast-coated substrates... 6 Using UV-curing inks and varnishes on thermal papers... 6 Printing on solvent based ink surface... 7 UV varnishing of UV ink surface... 7 Cracking of cured UV ink and varnish films... 7 Set-off in the reel... 7 Suitability for gluing... 7 Heat-seal resistance... 7 Hot-foil stamping... 7 Greying of the cardboard surface... 8 Water and weather resistance of UV-curing inks and varnishes... 8 Thermal transfer, laser printing on UV-cured ink and varnish films... 8 Shrink foil applications... 8 Fittings and bearings for varnish and ink pumps... 8 Auxiliaries... 9 Food and confectionery packaging... 9 Classification... 9 Shelf life... 9 NewV flex_direction for use 06/2017 Page 2/9

3 Composition of UV-curing inks and varnishes The special drying method of these products requires special formulation. The UV inks and varnishes are made from pigments, vehicles, additives and photoinitiators. Pigments (in inks) Vehicles (acrylates) Pre-polymers high viscosity Vehicles (acrylates) Monomers low viscosity Photoinitiators Additives Stabilizer Lubricant Extender With a few exceptions, the applied pigments are the same types which are used in conventional flexographic inks. The pigment uptake of UV vehicles is limited and this has a negative effect on the consistency and intensity of the inks. By this reason the UV flexo inks are short, compact and have different flow characteristics. The vehicles are manufactured from purely synthetic basis. These are acrylates with different chemical structures and varying viscosity. Together with the photoinitiators, they are highly reactive. These photoinitiators are responsible for triggering and finishing the crosslinking reaction. The used additives can be stabilisers, extenders and lubricants. UV inks are not miscible either with solvent or water based flexographic inks or with auxiliaries for these ink systems, only with products that are recommended for UV ink systems. In addition to process and standard spot colours, chromatic colours, opaque white, metal-pigmented UV-curing inks and fluorescent versions are also available. Curing Curing is a photochemical reaction, a polymerization of the ink/varnish, the transformation from liquid to solid. There are two types of reactions: cationic and radical. The hubergroup NewV inks and varnishes are radical curing products. Cationic reaction: Acid is formed and reacts slowly with the binders. The reaction is completed after hours. Radical reaction: Formed right after UV irradiation, free radicals react with unsaturated groups of acrylates % of the crosslinking is done within a fraction of a second. UV rays Liquid vehicle with initiator Initiator forms radicals Effect of radicals on vehicle Polymerisation Hard, tack-free ink film The energy potential of electromagnetic rays is inversely proportional to their wavelength. The shorter the wavelength, the higher is the energy potential of the radiation. With other words: the short wave UV light has greater energy than the long-wave light. NewV flex_direction for use 06/2017 Page 3/9

4 Hindrance of reaction The short wave UV radiation energy absorption of pigments and fillers is high, but the penetration depth of the UV rays into ink films is low. Generally pigments can take up to 30% of the overall ink composition, the pigments in the opaque whites may take even bigger part. One of the characteristics of the pigments is, that they absorb those short wave rays which are necessary for the reaction. Therefore they extract activation energy from the reactive components of the ink - from the photoinitiators and the vehicle. The absorption property of dark pigments and opaque white inks is high and it grows with the pigment concentration and with the ink film thickness. The high energy, short wavelength UV radiation is consumed at the surface of ink film. This means that in case of a thick ink layer the crosslinking of the vehicle is hindered down to the lower layers of the print. Therefore in case of wet-on-wet printing the highest UV absorption ink has to be printed first. Technical requirements Printing plates for flexo printing NewV flex and NewV lac can be used for rubber and photopolymer plates as well. For printing with UV flexo inks, plates with approximately 70 Shore hardness are recommended. Please consider that the performance of the UV flexo inks can be affected by dot deformation, by the hardness of the plate. In case the plate is too hard the colour intensity is reduced. If it is too soft, the heavy deformation of the dot will result high dot gain. Mounting tape The previously mentioned dot deformation can also be the result of the not carefully chosen mounting tape. To achieve the required print quality the right mounting tape is essential. However they may seem to have the only function to stick the plate to the printing cylinder, the wrong choice will show its effect on the print. Medium density tape is recommended when you print fine dots and solids from the same plate (four-color-process). Use soft, low density tape for printing only halftone, fine dot area and use hard, high density tape for solid tone coverage. Anilox rollers The number of cells affects the print quality. The higher is their number (the more cups you have), the better ink distribution, the more stable solids areas and the better curing you will get. Compared to the water/solvent based flexo inks, UV flexo inks have a higher viscosity and this is why they need less deep cups. It is important that only the 25-30% of the pick-up volume is transferred. Example: 4 cm³/m² * transfers ~ g of ink. The most frequently used screen roller type is the ceramic roller with 60 angle. These rollers have approximately 15% more cells than rollers with 40 angle, and this gives a better ink transfer. UV inks have no volatile compound. By this reason, thinner ink layer gives the same intensity than in case of water/solvent based flexographic inks. *cm³/m² = theoretical volume, total volume of the cells for 1 m² surface Blade NewV flex and NewV lac can be used with positive, negative and chambered doctor blade systems as well. By the reason of the higher viscosity we recommend to use negative doctor blade angle or chambered system. Washup solution Use only wash-up solutions that were developed for UV inks and varnishes. The wash-up solutions for solvent or water based flexo inks are not suitable for UV products. For details about our wash-up solutions please find the related Technical Information sheet of the NewV sup auxiliaries on our webpage. NewV flex_direction for use 06/2017 Page 4/9

5 UV lamps Most commonly standard mercury UV lamps are used for curing the UV inks. For specific applications amongst others, nitrogen-neutralised, gallium-doped, iron-doped mercury lamps are also preferred by the market, and for the even less environmental impact and electrical efficiency LED lamps are also popular. To provide the right drying of the inks and varnishes, the condition of the lamps (eg. operation time, damage, cleanness) and the reflectors (dirty, distorted) must be checked regularly. For more information about the proper curing results of lamps please contact your UV lamp manufacturer. Please consider that not only the lamp, but many further parameters of the printing process have effect on the curing: room temperature, humidity, printing speed, substrate, etc. Cooling Since a big part of the energy used in the lamp is not transformed into UV radiation, but into visible light and infrared radiation (eg. heat), cooling of the system is essential. Extraction The interaction of short-wavelength UV light with oxygen generates ozone. Extraction is necessary for removing this and also for removing the heat. It also helps cooling the lamps. Shutter Shutters are recommended for safety reasons to prevent the operator exposure to UV and visible light. In case of an immediate stop, automatic shutters are closing and the lamp power is reduced, to avoid the risk of the ignition of the substrate. Using UV-curing inks UV curing inks has to be mixed with UV curing inks and their auxiliaries. But never mix radical inks and varnishes with cationic curing products. Handling UV-curing inks, varnishes and wash-up solutions UV-curing inks and vanishes irritate and wash-up solutions degrease the skin. The effect on the skin depends on the intensity and the duration time of the contact, as well as the sensitivity of the user s skin. To avoid this, special handling and safety instructions must be observed. For further information please read the EuPIA "Guideline for Printers on the Safe Use of Energy Curing Printing Inks and Varnishes", ask the International Paint and Printing Ink Council ( or your ink and varnish supplier. Please also keep the following instructions: Avoid skin contact. Wear suitable protective gloves. In case of skin contact, wash the contaminations down immediately with water and ph neutral soap. Never use solvent or detergent. If there is a risk of ink, varnish, additive or wash-up solution splashing into your eyes, wear protective goggles. In case it goes into the eyes, rinse them thoroughly with water and consult a doctor. Use skin care product. Protective creams can be applied on clear skin, but never use cream on contaminated skin. Contaminated clothes have to be changed and washed immediately. Eating, drinking and smoking are strictly prohibited in the area where UV curing inks and varnishes are handled and stored. If you spill ink, varnish or wash-up solution, clean it up immediately. Store used cleaning materials in separate containers. Further details can be found in the safety data sheet of the products. NewV flex_direction for use 06/2017 Page 5/9

6 Disposing of inks and varnishes The waste of UV products must be handled as hazardous waste (including cleaning material, substrate with non-cured UV inks and varnishes, wash-up solution residue and also non-returnable containers). Please find further information about the handling of wastes in the safety data sheets. Recycling of UV prints While the printing materials represent only a small proportion of the waste substrate, they do not affect the recyclability of the end product. Prints with dried UV inks and varnishes can be recycled together with the standard flexo print scrap. Recommended application parameters Parameters Process Inks PANTONE Area Anilox (lines / cm) Anilox (lines / inch) Pick-up volume (cm 3 /m 2 ) Angle Application rate g/m The higher viscosity -that stays stabile in the production run-, as well as the higher tack of UV inks ensure uniform, thin ink transfer and considerably lower dot gain. As a result, it offers possibility to use very fine halftone sleeves, which provide constant print quality during the entire production run. Substrates Standard UV flexo inks are suitable for printing on the following substrates 1 : Coated and uncoated papers and card stocks Top-coated grades of board Metal coated papers Thermal papers Pretreated (corona or gas flame) or pre-primed, non-absorbent substrates such as PE, PET, PVC, PS, PP, BOPP, etc Other substrates, but only after technical evaluation Generally, previous test are always recommended to see the result in real life conditions. Adhesion on films, foils, metals and cast-coated substrates Treated metals, films, foils and cast-coated substrates can have a negative effect on the adhesion of inks and varnishes. Their lubricant and plasticizer components have a tendency to migrate to the surface of the substrate and step into chemical reaction with the substances of the ink/varnish layer. UV inks and varnishes needs to have a good tape (Scotch) resistance in order to ensure trouble-free further processing. But the good result tape test does not consequently mean good scratch resistance (nail test) as well. Overcoating the ink layer with UV varnish that contains lubricants can improve scratch resistance. However, the adhesion to a substrate cannot be improved this way, it can be the result. The adhesion of the ink can be improved by adding hardener. But please consider that the hardener decreases the shelf life. Using UV-curing inks and varnishes on thermal papers UV-curing inks and varnishes can be printed on thermographic paper. But a number of thermal papers react to UV vehicles. Depending on the paper quality, the paper may be stained (discoloured) and/or 1 Non-absorbent substrates must have a surface tension of at least 38 mn/m in order to ensure optimum ink adhesion. In view of the large number of substrate suppliers and different substrates and substrate grades available, we recommend to carry out an adhesion test before beginning the commercial print run. NewV flex_direction for use 06/2017 Page 6/9

7 the cured UV ink and varnish film can have poor adhesion. To avoid such problems in and after the real print run, we recommend conducting a prior test. UV flexo inks are often not or only conditionally suitable for printing on economy thermal papers* due to the fact that they darken the thermal layer. This is not the case for some new, special paper types. (*Economy thermal paper: Economy quality, white thermal paper without protective surface coat layer.) Printing on solvent based ink surface In case the evaporation process of the solvent based inks is not fully finished, the dry ink layer can still contain solvent residues that dissolve the pigments out from the UV ink film. The dissolved pigments separate from the ink layer and cause bleeding problem. To prevent this, we recommend previous print tests before the commercial production run, to make sure that the solvent composition and the UV ink do not step into chemical reaction with each other. UV varnishing of UV ink surface Wet-on-wet coating of UV-curing inks with UV-curing varnishes generally does not present any problems. In case of poor efficiency of the curing unit, the curing of the ink film may be affected as the varnish film absorbs the UV radiation. The result is insufficient adhesion of the different layers (cured ink and varnish films) and also reduced gloss of the print. Inks containing poor fastness property pigments as well as mixtures from these colours may change shade after UV varnishing. Therefore we recommend making print test before the commercial production. Further information about the fastness properties of inks and varnishes, please find in our product related Technical information sheets. Cracking of cured UV ink and varnish films Cracking is caused by the tension difference among the applied layers and the substrate, the change in the temperature (thermal strain) and/or by mechanical stress, especially if there is insufficient bond between the different layers. In extreme cases, layers can flake off. Set-off in the reel Similar to plastics, UV inks and varnishes has also thermoplastic behaviour. Due to the pressure and the temperature especially on non-absorbent materials (films, foils), inks and varnishes can soften which can lead to adhesion problems. In worst case the ink/varnish sticks to the reverse side of the reel. For a better result cool the web after UV drying and keep it in the possible coolest conditions (< 30 C). Suitability for gluing Only suitable water-based glues can be used for UV-coated prints. And only UV varnishes are recommended for this application which are stampable and do not include lubricants. Please contact glue suppliers for product recommendation. For the good result we recommend to leave blank or roughen the area which needs to be glued. Based on the wide range of products and technologies on the market, preliminary tests are necessary. Heat-seal resistance The heat-seal resistance of UV-printed and/or coated substrates depend on the substrate itself. For details about the suitability of our inks and varnishes, please read the Technical information sheet of NewV flex and NewV lac products. Hot-foil stamping Only stampable UV varnishes that were developed for this reason are recommended to this application. They do not contain lubricants which presence leads to adhesion problems. The stamping NewV flex_direction for use 06/2017 Page 7/9

8 pressure and the temperature need to be adjusted to achieve the required result. For the suitable varnishes please see our Technical information sheets about NewV lac varnishes. Greying of the cardboard surface The UV varnish penetrates into the upper layer of the board, makes it transparent, therefore the colour of the supporting layers shows through. It also can be caused by the light reflection in the varnish layer. Contact the cardboard supplier to choose the whitest possible cardboard. Water and weather resistance of UV-curing inks and varnishes UV-cured ink and varnish layers do not act as a barrier against moisture or water. They show changeable resistance to the influences of moisture depending on their adhesion on non-absorbent substrates (eg. plastic film and metal surfaces). The lower is the adhesion strength, the less favourable conditions are obtained under the influence of moisture. The water gets under the cured UV layer and lifts that up. In case of mechanical force this film layer separates from the surface. Once the ink and varnish have dried completely, their adhesion properties can considerably improve again. Pre-treatments, such as corona treatment or a base layer with screen-printing ink or covering the ink layer with NewV lac products can improve the resistance against moisture. In case the UV print needs to be weather resistant, suitability tests should be conducted under the customer required conditions. Thermal transfer, laser printing on UV-cured ink and varnish films The good adhesion of the printed image depends on the ink ribbon, the surface smoothness of the substrate and also on the thermal transfer printing process, not only on the varnish or on the ink. By these reasons we recommend you to conduct real life tests before the commercial production run. If the thermal transfer print is applied directly on the ink surface, the problem may appear that the TTR ink has the required adhesion at some parts of the surface, and poor on other parts. This is based on the difference in the densities and the colour shades of the ink. In this case we recommend to apply an overprint varnish to create an even, consistent surface for the TTR ink. In case the fusing temperature of the toner is too high, there is a possibility of deposits building up in the hot-laser printer on the fusing roller or on the fusing plate. The thicker the ink/varnish layer, the larger amount of deposits you can find, due to thermoplastic properties of the cured ink/varnish films. The producers of laser printers demand that inks and varnishes that are used in their equipment neither soften after drying, nor contain any volatile components. Softening of the inks within the fixing station leads to blocking and build-up on fixing and press rollers and may lead finally to their destruction. Volatile components such as mineral oil evaporate within the fixing station and lead to unwanted smoke formation Any fumes that are developed during the hot-laser marking are not caused by UV inks and varnishes. They contain no solvents. Pigments with poor heat resistance properties can sublimate during the fusing process. In this case these products must be substituted by similar colour shade inks that are formulated from heat-resistant pigments. In order to avoid such problems, please choose stampable varnishes from our NewV lac portfolio. Please find the detailed information on our webpage about the properties of inks and varnishes in the product related Technical information sheets. Shrink foil applications Radical-curing UV flexo inks are only conditionally suitable for shrink wrap applications on OPS, OPP, PVC and PET. If high shrinkage is required (up to 70%), specially formulated UV flexo inks needed. Fittings and bearings for varnish and ink pumps Avoid using fittings and pipe systems which contain copper. Contact between them and the UV-curing inks and varnishes may start the hardening process ( dark reaction ). NewV flex_direction for use 06/2017 Page 8/9

9 UV-curing inks and varnishes do not have any self-lubricating properties. This fact needs to be considered when selecting materials for bearings and ink pumps! Teflon is suitable for bearings. Auxiliaries For information please read our technical information 50.A.003 NewV sup Auxiliaries for UV printing_flexo and 50.A.002 NewV sup Auxiliaries for UV varnishes. UV curing inks has to be mixed with UV curing products and their auxiliaries. But never mix radical inks and varnishes with cationic curing products. Note for application: to avoid problems, always mix the auxiliaries well into the inks and varnishes. Food and confectionery packaging Our NewV MGA product family is recommended for printing primary food packaging or secondary packaging where the primary layer is not a barrier against migration of substances from the printed layer to the packed product. These products are recommended also for further applications where the migration of substances needs to be avoided: eg. cosmetics and pharmaceutical products More information on the subject of packaging for food, cosmetics, pharmaceutical products, tobacco can be found in the information sheet 50.G.002 NewV for food packaging. Please also find information on the webpage of the European Printing Ink Association: In case you are interested in UV varnishes for the applications mentioned above, please contact us for recommendations. Classification Safety data sheet is available on request. Shelf life Keep the ink/varnish containers closed. Protect from direct sunlight and frost. Store them in cool, dry place, between 5-25 C. Lower temperatures increase the shelf life of UV inks and varnishes. The packaging has to be closed right after the usage. Note: UV inks always begin to harden at the bottom of the container ( dark reaction ). Their consistency changes from rubber-like till hard. Skin does not form on UV inks. Do not use hardened UV inks and varnishes. Please find the shelf of life information in the product related Technical information sheets. Contact addresses for advice and further information can be found under This Technical information sheet reflects the current state of our knowledge. It is designed to inform and advise. We assume no liability for correctness. Modifications may be made in the interest of technical improvement. NewV flex_direction for use 06/2017 Page 9/9