Products
Solvent-Based Gravure Inks
Polyurethane gravure inks for reverse-printed flexible packaging, where the ink is not on the pack but inside it.
Products
The ink is a layer in the laminate
A laminated pouch is printed in reverse. The image is mirrored and printed on the inner face of the outer web — PET, BOPP or nylon — so it is read through the film, and the gloss belongs to the film rather than to the ink. The printed web is then coated with a polyurethane laminating adhesive and married to the sealant web: cast polypropylene, polyethylene, metallised film or foil. The ink film is now buried. It sits between the outer film and the adhesive, and every force that acts on the pack acts through it.
That changes what the ink has to do. It is no longer a decoration on a surface; it is a structural interlayer, and the laminate bond has to pass through it. Four properties decide whether the pack survives. First, bond strength through the ink: the laminate must not separate where the ink film is heaviest, which is almost always the solid white or a double-hit dark. Second, resistance to the adhesive and its carrier solvent — the dry ink is wetted with ethyl acetate and isocyanate at the laminator, and must neither redissolve nor swell. Third, heat resistance through the sealing jaws, where the outer film is thin and the jaw face typically runs at 130 – 190 °C. Fourth, resistance to the packed product. In Indian flexible packaging that means chilli and turmeric oleoresins, edible and mustard oils, masala blends, detergent surfactants and hot-fill, all of which reach the ink from the inside through a sealant that is not a barrier to them.
Polyurethane is chosen as the binder for reasons that map onto those four duties. Its polar urethane and urea groups anchor to corona-treated PET and BOPP and to the amide surface of nylon, which is where a nitrocellulose or polyamide surface-print binder gives up. The segmented structure — soft polyol blocks with hard, hydrogen-bonded urethane blocks — gives a film that is tough but elongates, so the print survives web tension, forming, creasing and the flexing of a filled pouch without micro-cracking. Residual hydroxyl functionality in the binder reacts with the isocyanate of a two-component polyurethane laminating adhesive, so the adhesive does not merely lie on the ink but couples to it chemically. And because the ink and the adhesive are the same family of chemistry, the two are compatible in a way a nitrocellulose ink is not: the same hydrogen bonding that holds the ink together holds it to the adhesive.
Food packaging adds a separate discipline. Reverse print puts the outer film between the ink and the outside world, but nothing except the sealant stands between the ink and the food, and a polyolefin sealant is not a functional barrier to low-molecular-weight substances. Migration is therefore controlled where it can be controlled — in raw-material selection against the EuPIA Charter, in heavy-metal-free pigments, in toluene-free and, for food-contact work, ketone-free solvent blends, and in retained solvent after drying. Typical industry targets are below 5 mg/m² total retained solvent, with tighter limits on named solvents where a brand owner specifies them. Formulation references Regulation (EC) 1935/2004 and Regulation (EU) 10/2011 for its substance lists, the Swiss Ordinance and its Annex 10 positive list, the BfR recommendations, and, where a customer asks for it, the Nestlé Guidance. Every grade carries a Technical Data Sheet, a Safety Data Sheet and a Regulatory Summary.
Grades in this series
The grades share the same polyurethane chemistry and differ in where they sit in the structure and in what the filled pack has to survive.
UniGrav-410PU
Lamination, polyurethane. The core reverse-print grade for adhesive lamination on treated PET, BOPP and nylon, formulated so the laminate bond passes through the ink film without an ink-side failure plane. Through a process solid, typically 300–500 g/15 mm on the PET/adhesive/CPP structure stated on this page, ASTM F904, reported with its failure mode and confirmed on the customer’s structure.
UniGrav-415PW
Lamination white. High-opacity titanium dioxide laid down at the heaviest deposit in the structure, usually as the last down colour. 48–58 % w/w solids, 1.25–1.38 kg/l, print viscosity 18–22 s DIN 4 at 25 °C. Bond through this film is the number that decides the pack: typically 250–400 g/15 mm on the stated structure, measured at the heaviest deposit and confirmed on the customer’s own laminate.
UniGrav-430RT
Two-component retort, supplied with UniGrav-439HD added at the press. On the stated PET / foil / CPP structure with a retort-grade adhesive, typically 500–800 g/15 mm and ΔE00 ≤ 2.0 after 121 °C for 30 min against a 450 g/15 mm design floor, on shades built from retort-stable pigments. Ester-only solvent system; pot life 6–8 h at 30 °C. Qualified on the customer’s structure and filled product.
UniGrav-439HD
Aliphatic polyisocyanate hardener for the 430RT series, 3–5 % w/w on ink. 1 kg and 5 kg packs, 6 months sealed, moisture sensitive.
UniGrav-450SP
Surface print, polyurethane-nitrocellulose, for printed film that is not laminated. Gloss, slip and scuff resistance rather than lamination bond. Jaw resistance to 160 °C bare, 180–200 °C with the matched varnish.
UniGrav-460MF
Metallised film and foil, for metallised BOPP and PET and for aluminium foil structures. Adhesion to the metal layer without lifting or attacking it; bond after lamination typically 150–300 g/15 mm, limited by the metal-to-polymer anchorage rather than by the ink. Establish the metallised film’s own unprinted bond before attributing a low figure to the ink.
UniGrav-470PB
Paper and board gravure, for paper, metallised paper and board wrappers. Fast solvent release into an absorbent substrate with holdout tuned to keep colour on the surface. Paper structures fail by fibre tear, so bond is reported as fibre tear.
UniGrav-480LM
Low-migration food-contact series. Raw materials selected against the EuPIA Charter and the applicable positive lists, heavy-metal-free, toluene free and ketone free, for direct food packs where the sealant is the only layer between the ink and the product.
UniGrav-490OV
Overprint varnish for surface print, gloss and matt, carrying the slip and the jaw resistance the ink film is not asked to provide on its own.
UniGrav-495RD
Reducer, matched to each series’ solvent blend; ester-only version for the 430RT series.
UniGrav-496SL
Slow blend for deep cells and hot press halls, n-propyl acetate rich.
Product data
| Process | Rotogravure. Reverse print for lamination, surface print where the film is not laminated. Electromechanical engraving, 70–110 l/cm for tone and 50–70 l/cm at 35–45 µm cell depth for solids. |
|---|---|
| Solvent system — house position on ketones | Toluene free and aromatic free across the range. Ketone free is the standard on every grade, not only the food-contact series: no MEK, MIBK, acetone or cyclohexanone. Where a non-food surface print on treated PET or nylon has historically been run on an MEK blend, the answer here is the 450SP binder and a hotter tunnel, not a ketone. This is the same wording as the flexo range carries, and it applies to the whole solvent business. |
| Solvent system — UniGrav-410PU and 415PW, lamination | Ethyl acetate 55–65 %, n-propyl acetate 15–25 %, ethanol 15–25 %, w/w as supplied. Press reducer UniGrav-495RD is the same blend; UniGrav-496SL raises n-propyl acetate for deep cells and hot halls. |
| Solvent system — UniGrav-430RT, two-component retort | Ester only: ethyl acetate 75–85 %, n-propyl acetate 15–25 %, w/w. Alcohol is excluded from the ink and the reducer once hardener is in, because hydroxyl consumes the isocyanate that the retort performance depends on. |
| Solvent system — UniGrav-450SP, surface print | Ethyl acetate 45–55 %, ethanol 30–40 %, n-propyl acetate 10–15 %, w/w. The nitrocellulose in the polyurethane-nitrocellulose binder needs the ester; the alcohol sets release. |
| Solvent system — UniGrav-470PB, paper and board | Ethanol 50–60 % with ethyl acetate 40–50 %, w/w, and little or no slow solvent, so the film sets on the surface of an absorbent stock before it can be drawn into the fibre. |
| Supply viscosity | Colours 45 ± 10 s. Lamination white 75 ± 15 s. Two-component base before hardener 40 ± 10 s. Overprint varnish 30 ± 5 s. DIN 4 mm to ISO 2431 at 25 °C. |
| Print viscosity | Process and tone work on 70–110 l/cm engraving: 15–18 s. Solids and lamination white on 50–70 l/cm at 35–45 µm cell depth: 18–22 s. Surface-print line work: 16–20 s. Paper and board gravure: 18–22 s. DIN 4 mm to ISO 2431 at 25 °C, set to cylinder engraving and running speed. Letdown from supply is typically 25–40 % w/w. |
| Viscosity — method note | Quote the cup. A DIN 4 second is not a Ford B4 second. Sample and cup at 25 ± 1 °C. On a long run, viscosity held by an automatic solvent-addition unit reading every 30–60 s does more for colour consistency across a reel than any correction made at the mixer afterwards. |
| Solids and density, as supplied | Transparent and process shades 28–38 % w/w solids, 0.95–1.05 kg/l. Lamination white 48–58 % w/w, 1.25–1.38 kg/l, titanium dioxide being the heaviest thing in the structure. Overprint varnishes 28–35 % w/w. Solids by ISO 3251, 1 g for 1 h at 105 °C. |
| Two-component addition and pot life | UniGrav-439HD aliphatic polyisocyanate adduct at 3–5 % w/w on ink, added at the press. Pot life 6–8 h at 30 °C and 4–5 h at 35 °C, taken as a 5 s rise on DIN 4. Hardened ink is not returned to stock. Full crosslink development 5–7 days at 25 °C, so a retort trial run on day one is testing an unfinished film. |
| Bond strength through the ink — method | T-peel on a 15 mm strip to ASTM F904, crosshead 300 mm/min, 23 °C and 50 % RH, after the laminating adhesive has fully cured — typically 48 h at 45 °C for a general two-component polyurethane and 5–7 days at 45–50 °C for a retort adhesive. Report the mean plateau load in g/15 mm and the failure mode with it: adhesive-to-ink, ink-to-film, cohesive split within the ink, or film stretch. A lower load ending in film stretch is a better result than a higher one that splits the ink film, and a number quoted without its failure mode is not a result. |
| Bond strength — general lamination | Typical on the stated structure — PET 12 µm / two-component polyurethane adhesive at 2.5–3.5 g/m² dry / CPP 30–50 µm, adhesive fully cured: unprinted margin 400–700 g/15 mm; through a single process solid 300–500 g/15 mm; through the solid white or a double-hit dark 250–400 g/15 mm. 200 g/15 mm is the floor the grades are designed to, and the heaviest deposit is where it is measured, because that is where the pack fails. Bond is a property of the finished structure — film, treatment, adhesive, coat weight, cure and sealant — so the figure that goes into a specification is the one measured on the customer’s own structure, reported with its failure mode. |
| Bond strength — metallised structures | Metallised BOPP and metallised PET with UniGrav-460MF: 150–300 g/15 mm, limited by the metal-to-polymer anchorage rather than by the ink, with metal transfer to the sealant web as the normal failure mode. Establish the metallised film’s own unprinted bond before attributing a low figure to the ink. |
| Bond strength — paper and foil structures | Paper-based laminates fail by fibre tear under the ink, so the result is reported as fibre tear rather than as a load. Foil structures on 7–9 µm aluminium: 350–600 g/15 mm, failure typically at the foil-to-adhesive interface. |
| Bond strength — retort structures | Typical on the stated structure — PET 12 / aluminium foil 7–9 / CPP 60–80, printed with UniGrav-430RT and laminated with a named two-component retort-grade adhesive at its own cured coat weight: before processing 700–1100 g/15 mm; after 121 °C for 30 min typically 500–800 g/15 mm against a design floor of 450 g/15 mm, with no tunnelling, ink lift, blistering or delamination observed at the seal. Retort behaviour belongs to the whole structure and to the retort schedule and the filled product, none of which the ink maker controls, so it is confirmed on the customer’s own structure with their own adhesive and product before any specification is fixed. |
| Heat-seal resistance — surface print | UniGrav-450SP with the jaw on the printed face: flat Teflon-faced jaw, one side heated, 1 s dwell at 0.2 N/mm² (2 bar), tape pull after cooling. Typically no pick-off, transfer or gloss change to 160 °C bare, and to 180–200 °C with the matched overprint varnish. Where the job’s jaw range runs to 190 °C, the varnish is part of the specification and not an option. Confirmed on the customer’s film, varnish and jaw settings. |
| Heat-seal resistance — reverse print in a laminate | In a reverse-printed laminate the jaw contacts the outer film, not the ink, so what the ink is asked for is bond retention inside the seal. After sealing at 180 °C, 1 s, 0.2 N/mm², there is no delamination in the seal area and the bond measured through the ink inside the seal is within 15 % of the bond measured outside it. |
| Retort, boil and pasteurisation schedule | Typical retained bond on the structures stated above, measured after processing with the adhesive fully cured: pasteurisation 85 °C for 30 min, ≥ 350 g/15 mm; boil-in-bag 100 °C for 30 min, ≥ 300 g/15 mm; retort 121 °C for 30 min, ≥ 450 g/15 mm with 500–800 typical. High-temperature retort at 135 °C for 30 min is assessed on the actual pack, with the filled product in it, and is not quoted from a laminate trial. Each figure is a design target confirmed on the customer’s structure and product, not a guarantee for a structure we have not seen. |
| Colour stability through retort | Typical for shades built on the named retort-stable pigments — phthalocyanine, quinacridone, benzimidazolone and carbon black: ΔE00 not more than 2.0 after 121 °C for 30 min, measured to ISO 13655 M1, D50, 2°, on the laminate against the pre-retort print. The result is shade- and structure-dependent: diarylide yellows and rubine reds shift or bleed into the sealant, so retort shades are built without them and a customer’s existing shade may need rebuilding before it can be retorted. Confirm shade by shade on the structure that will be run. |
| Blocking in the printed reel | No blocking after 24 h at 50 °C under 10 kPa for the lamination grades, and at 40 °C for the surface-print grades carrying slip. Reel stores in North India routinely pass 40 °C in summer, so reels are not stacked more than three high on a hot day and a reel coming out of a hot store is allowed to equilibrate before it is unwound. |
| Retained solvent | Below 5 mg/m² total on the printed web is achievable on a compliant tunnel at the stated web speed with the solvent blends given above, by static headspace GC-FID on a 100 cm² sample equilibrated 30 min at 80 °C, calibrated against the solvents actually in use; named-solvent limits of 1 mg/m² where a brand owner specifies them. This is a drying and line-speed result rather than an ink specification: the ink makes the figure reachable, and the tunnel, the air balance, the engraving and the web speed decide whether it is reached, so it is verified on the running job. |
| Handling — classification and flash point | Flammable liquid, GHS Category 2, H225. Transport UN 1210, Printing ink, flammable, Class 3, Packing Group II. Class A petroleum under the Petroleum Rules 2002. Flash point −4 to +8 °C for the 410PU, 415PW, 450SP and 470PB grades and −4 to 0 °C for the ester-only 430RT, Abel closed cup to ISO 13736; the Safety Data Sheet figure for the individual product governs area classification. |
| Storage | 5–35 °C, below 30 °C where possible, containers closed and upright, out of direct sun, in a licensed flammable-liquids store away from ignition sources and oxidising agents, earthed and bonded during every transfer. UniGrav-439HD hardener is moisture sensitive: keep it sealed, buy the smallest pack that covers a shift, and do not return hardened ink to stock. |
| Pack sizes | 5 kg and 20 kg lacquered pails for colours and varnishes. 200 kg mild-steel drums for lamination white and for long runs. 1 kg and 5 kg tins for match shades and press-side corrections. UniGrav-439HD hardener in 1 kg and 5 kg. Reducers, slow blends and wash solvent in 20 l tins and 200 l drums. All packaging UN-approved for Class 3, Packing Group II. |
| Shelf life | 12 months from manufacture in the unopened original container at 5–35 °C for one-component inks and varnishes. 6 months for UniGrav-439HD hardener. |
| Migration and food contact | Raw materials selected under the EuPIA Charter, heavy-metal-free pigments, toluene free and ketone free. Raw-material selection is referenced to the EuPIA Suitability List, to the substance lists of the Swiss Ordinance Annex 10, to the BfR recommendations and, on request, to Nestlé Guidance; Regulation (EU) 10/2011 governs plastic food-contact materials rather than printing inks and is used as a substance reference only. Naming these documents describes how raw materials are chosen and is not a declaration of compliance for any pack, and none of them is a brand-owner approval. Conformity of a finished pack under Regulation (EC) 1935/2004 rests on an assessment of that pack; migration and food-contact conformity are assessed on the pack, on request, and no migration figure is published against an ink on its own. |
| Documentation | Technical Data Sheet, Safety Data Sheet and Regulatory Summary with every grade. |
Compliance and standards
- Raw materials selected to the EuPIA Charter
- Toluene-free
- Aromatic-solvent-free
- Ketone-free grades for food-related work
- Heavy-metal-free pigments
- Raw materials screened against Swiss Ordinance Annex 10 and the BfR recommendations
- Migration assessed on the finished pack, on request
White paper
Bond strength through the ink: where a reverse-printed laminate fails
In an unprinted laminate the bond is a single interface problem: adhesive to film on each side. In a reverse-printed laminate the adhesive never touches the outer film where there is ink. The load path runs film, ink, adhesive, sealant, and the weakest plane in that stack is the bond of the pack. This is why a laminate can peel cleanly in the unprinted margin at a perfectly acceptable figure and still delaminate in the middle of the solid white.
Three failure planes are worth separating when a peel is examined. Ink to film means the ink never anchored — usually treatment that has decayed below roughly 38 mN/m, a slip additive that has bloomed to the surface, or a film qualified for a different binder. Adhesive to ink means the adhesive wetted the ink film but did not couple to it; the ink face comes away clean and glossy. Cohesive failure within the ink means the ink film itself split, which points to over-pigmentation, to too much ink laid down in one pass, or to a colour built on a binder that was never intended to carry a structural load. The peel test gives a number, but the number is only useful with the failure mode written next to it, so a T-peel through the heaviest coverage and a note on where the split ran are worth more than a figure from the clear edge of the web.
Retained solvent is the quiet contributor. Solvent left in the ink film at the laminator plasticises the ink, keeps it soft under the adhesive and, in a solventless line, evolves later as gas that shows up as bubbles and tunnels in a reel that measured well on day one. Gravure deposit is set by cell volume, not by ink, so the usual root cause is a heavy engraving combined with a dryer that is moving air too slowly rather than too coolly. Indicative dryer air for film work is 45 – 70 °C with enough velocity and exhaust to keep the vapour concentration low; raising temperature to compensate for poor airflow softens the film and does not remove the solvent from underneath a heavy white.
The chemistry helps if it is allowed to. A two-component polyurethane adhesive carries free isocyanate, and a polyurethane ink binder carries residual hydroxyl. Those groups react across the interface during cure, which turns an adhesive contact into a covalent one, and it is the main reason a polyurethane ink outperforms a nitrocellulose ink under the same adhesive. The reaction needs time and moisture: bond through ink is measured after full cure, typically several days at ambient, not on the reel as it leaves the laminator. Primary aromatic amines, where they are a concern, come from the aromatic isocyanate in the adhesive and not from the ink, and the control for them is the same cure time.
White paper
Retort, hot-fill and the packed product
Retort is a different duty, not a harder version of the same one. In a retort cycle — commonly 121 °C for 30 minutes, with boil-in-bag at 100 °C for 30 minutes as the lighter case — the laminate is held above the boiling point of water while saturated steam is on both faces of the pack and hot product is on the inside. A thermoplastic polyurethane ink film softens at that temperature and, with water present, can blush: water swells the film, light scatters at the interface, and the print goes milky. Bond figures measured hot, during the cycle, are the ones that decide whether a pouch survives it.
The answer is crosslinking. A two-component ink takes a polyisocyanate hardener at the press, which reacts with hydroxyl functionality in the binder to build a network rather than a linear film. The network does not soften at retort temperature and does not redissolve, and it resists the hot water that a linear film absorbs. The cost is pot life: once the hardener is in, the ink has a working window, viscosity climbs, and what is left at the end of the shift cannot be returned to stock. Cylinders and the press must be washed before the ink sets in the cells. Structures for this duty are normally PET or nylon outside, an adhesive rated for retort, and a CPP sealant, and the ink has to be qualified in the specific structure rather than in isolation.
Product resistance is the failure mode that arrives later and is more common in practice. Chilli and turmeric oleoresins, cardamom and clove essential oils, mustard and groundnut oil, and the surfactants in detergent powders all diffuse into and through a polyolefin sealant. They arrive at the adhesive and at the ink face over weeks, and they act as plasticisers. The pack that passed every test on the day of lamination loses bond in the printed areas after a month in a warehouse at 40 °C. Hot-fill shortens that timescale by driving the first dose of product into the sealant while it is soft. A crosslinked ink film resists this for the same reason it resists retort: there is less free volume for a small molecule to occupy, and no soluble fraction for an oil to take away.
Qualification should follow the failure mode rather than the calendar. Fill the actual laminate with the actual product, seal it, store it at 40 – 50 °C, and peel it at intervals against a control stored cold — peeling through the heaviest ink coverage each time and recording where the split ran. A laminate that holds through a retort cycle and through accelerated storage with the real product is qualified; one that has only been peeled fresh has been measured, not qualified.
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