Offset Inks

Important innovations have been made in the formulation of Offset or “paste” inks over the last few years, keeping pace with the evolutions that have marked the Graphic Industry :

• The appearance of high technology printing equipment with faster and faster printing speeds, requiring inks with excellent printing stability.

• A diversification in the range of printed substrates (recycled paper, more varied synthetic substrates, etc.) requiring more and more versatile inks.

• An evolution in environmental legislation (VOC emissions, recycling of packaging, etc.).

To get to know these inks better, we propose to cover the following points:

● formulation

● drying

● different types of ink

● ink profiles

● troubleshooting

Formulation

Offset ink formulations are based on the following constituents:

Component	Content	Principal functions
Siccative vegetable oils (soya, linseed, wood, rape)	20 – 40%	Vegetable oils are used for solubilising the resins, wetting and coating the pigment and influence the drying.
Petroleum (aliphatic, paraffinic, etc.) or vegetable based diluents	3 – 40%	Diluents are firstly used for solubilising the resins and then to obtain the rheological properties of the final ink.
Modified rosin or oil based resins	30 – 35%	Essential constituents of varnishes (resins + oils) that determine the required rheological, setting, tack, etc. properties of the ink.
Organic or mineral pigments	10 – 20%	Colouring materials chosen as a function of the required applications and fastnesses.
Additives: fillers, waxes, drying agents, etc	1 – 8%	These products determine or influence specific properties such as rheology, abrasion resistance, drying, etc.

Typical offset ink formulation

Vegetable oil based inks

The varnishes and diluents used in the formulation of these inks are exclusively vegetable based and renewable. However, the fillers, pigments and drying agents are mineral based. For this reason, no ink is 100% vegetable.

These inks provide numerous advantages for the printer:

• Better transfer, giving more intense, glossier colours and reduced ink consumption.

• Better ink / water stability, enabling high speed printing (up to 18000 sheets/hour) and reduced waste.

• Better environmental management: reduction of VOCs (Volatile Organic Compounds), easier recycling of printed materials, etc.

However, they have a strong odour and cannot be used for printing foodstuff packaging because they can have an adverse effect on the organoleptic pro- perties of the packaged goods.

Drying

The drying of the ink is a combination of a physical phenomenon “penetration into the substrate” and a chemical phenomenon “air oxidation”.

Penetration into the substrate

During printing, as soon as the ink is deposited on the substrate, certain ingredients of the ink penetrate into the substrate. These are liquid ink components, i.e. mineral or vegetable diluents. Mineral diluents, which are more fluid, have a tendency to penetrate more quickly than vegetable diluents.

This penetration is very dependent on the type of substrate printed.

On paper and cardboard, the rapidity and ease with which they penetrate depends on the quality, surface condition and porosity of the substrate. The more porous the substrate, the faster the penetration.

Conventional offset ink drying

In the case of non-absorbent subs- trates such as tracing paper or synthetic substrates, no penetration occurs. Drying is entirely through air oxidation.

Air oxidation

This chemical phenomenon begins as soon as the print leaves the press. Air oxidation corresponds to the hardening of the varnishes in the ink through a chemical process that occurs on contact with oxygen in the air. In the first stage, the reaction begins on the surface of the ink film and then spreads throughout the body of the film.

This air oxidation mechanism can be accelerated on the press itself by adding drying agents, such as Triple Drying Agent, to the ink.

The balance between penetration/ air oxidation

The drying of the ink, whatever its for- mulation, involves the two above men- tioned phenomena. By adjusting the siccativity of the ink, the balance can be switched towards penetration or air oxidation.

Different types of ink

It is on the basis of this balance, which determines the drying mode, that 3 types of inks can be distinguished: overnight inks, semi-overnight inks and siccative inks.

Overnight inks

● These inks are only slightly siccative: there is practically no air oxidation. Thanks to improvements in raw materials (resins, etc.), their setting and drying, formerly quite moderate, have been considerably enhanced.
With this type of ink, the ink tin can be left open for several days, and the ink left in the duct for more than 24 hours, without the formation of a dried skin on the surface.

● Precautions

Since overnight inks dry mainly through penetration, they may cause set-off problems on some substrates, such as non-absorbent coated or matt coated papers.

● Semi-overnight inks

Semi-overnight inks are moderately siccative. They therefore dry more quickly, allowing the prints to be handled several hours after printing. The printing conditions, the type and the quality of the substrate are criteria that have a considerable influence on the drying and therefore how soon prints can be cut and folded.

● Precautions

Air oxidation of the ink leads to the formation of a dry skin on the surface of the ink in tins that have been left open or in ink ducts after around twelve hours. To slow down this phenomenon, we recommend covering the surface of the tins with cello- phane and spraying an antioxidant (Anti Drying A11) onto the ink ducts and rollers for stoppages longer than this time.

● Siccative inks

These inks contain high contents of drying agent. Their rate of surface and in-depth drying is very rapid, around 2 to 3 hours. For this reason they are recommended for printing matt coated paper, non absorbent substrates and synthetics.

● Precautions

Drying begins as soon as the ink comes into contact with the air. Care should be taken to assure the absence of any surface skin in the tin so as to avoid introducing particles of dry ink into the ink duct (risk of hickies). If the press is stopped for longer than 30 minutes, an antioxidant (Anti Drying A11) should be sprayed over the ink duct and rollers.

Despite this classification, recent advances in chemistry have made it possible to develop inks that are more and more versatile in terms of their behaviour and performance characteristics.

For this reason, we have developed an “Ink Profile” for each of our Process Colour ranges, enabling the most suitable ink to be recommended as a function of the substrate and quality of the print.

Ink profiles

The performance of Process Colour ranges are described according to 6 criteria graphically represented by the Ink Profile.

Each criterion is assigned a simple rating between 1 and 6:

Example : LOGO 18000 Process Colours

1 = average to low performance.

6 = excellent performance. By visualising the technical profile of a Process Colour range, the printer can predict the behaviour of the ink on the press as well as the qualitative results of the print, providing a suitable substrate has been chosen.

Definitions of ink performance criteria:

Duct freshness: Ability of the ink not to dry, either on the press or in open tins.

Setting: Ability of the printed ink not to remain sticky when touched (touch dry state). It provides an indication of the speed at which the ink penetrates into the substrate: if the setting is rapid (in other words, touch dry within one minute of printing), the risk of set-off is considerably reduced.

Colour strength: Ability of an ink to give maximum optical density with a minimum inking.

Gloss: Light intensity reflected by the dry ink film (very dependent on the surface condition of the substrate).

Rub resistance: Ability of the dry ink film to resist rubbing and abrasion.

Drying speed: Time required to obtain complete hardening of the ink film through air oxidation.

We have analysed all of the different types of substrate used in offset prin- ting according to the criteria of absorption, surface condition and abrasiveness as defined hereafter. This analysis has enabled recommendation tables to be established for different ink series.

Non coated	**
Matt coated	**
Gloss coated	***
Lightweight paper	**
Cardboard	***
Non absorbent substrates (1)	*
Synthetic substrates (2)	♦

*** Perfectly suitable ** Suitable * Test necessary ♦ Not suitable

Example : Recommendation for the LOGO 18000 Process Colours range as a function of the substrate type.

Definitions of substrate performance criteria:

Absorption: Ability of the substrate to absorb part of the components of the printed ink.

Surface condition: Characterises the surface relief of the substrate (flat or irregular). Abrasiveness: Ability of a substrate to deteriorate a dry ink film by rubbing.

Troubleshooting

Incidents

1. Picking

2. Deformation in the stack

3. Double print
Abnormal pressure force and dots blurred.

4. Binding of the plate
Deterioration of the printing areas and/or graining areas (non- printing areas).

5. Scumming Blocking

6. Out of register prints

7. Set-off

8. Incorrect drying

9. Hickies

10. Creasing
Deformation of the substrate, mainly at the tail end.

11. Powdering
The ink solids remain on the surface.

12. Poor trapping
Ability of one ink to be accepted by another when it is not yet dry (this phenomenon only applies to wet-on-wet printing).

13. Curling
Excessive deformation of the printed material in the stack (excessive curling beyond 4cm/m).

14. Mottling
Irregular appearance (mainly on solid print areas).

15. Linting
Loose paper accumulated on the blanket.

16. Piling / Buildup
Ink build up on image areas of the blanket

17. Guttering

Phantom effect
Reappearance of the previous print run or the print run underway but out of shift.

Probable causes and remedies

1. Picking (back to incidents)

Cause	Paper too fragile (poor coating or poor structure).
Remedie	Change the paper, dilute the ink or use a more suitable ink (less tack). AddAnti Tack Compound (3 % max.) or Arctic Thinner 501 (3% max.).
Cause	Restarting after a prolonged press stoppage.
Remedie	Spray Rototack start-up aerosol over the rollers. Apply a little thinner (Artic Thinner 501) onto the rollers. Clean the rollers. Clean the blankets.
Cause	Print shop temperature too low.
Remedie	Dilute the ink before restarting printing. .
Cause	Excessive dampening.
Remedie	Reduce the dampening.
Cause	Excessive blanket / paper pressure.
Remedie	Check the blanket / cylinder pressure, the counter pressure and the cylinder coverings.
Cause	Blanket has too much “affinity” for the ink.
Remedie	Apply talc on the blankets.

2. Deformation in the stack (back to incidents)

Cause	Substrate stored incorrectly.
Remedie	Before printing: store in the original packaging at a temperature of around 20°C and a relative humidity of 60 %, for a period determined by the temperature in relation to the volume of the stack. During printing: between runs, do not hesitate to cover pallets to avoid deformation phenomena.
Cause	Excess or irregular use of anti set-off powder.
Remedie	Adapt the quantity of anti set-off powder and its particle size to the job in hand. Clean the powder spray nozzles.
Cause	Excess water, principally on the paper edges.
Remedie	Reduce or adjust the uniformity of the dampening.

3. Double print, abnormal pressure force and dots blurred.
(back to incidents)

Cause	Substrate deformed before printing.
Remedie	Change the substrate. Avoid important relative humidity and temperature variations between the storage and printing areas. Place the paper in the print shop several hours before printing.
Cause	Blanket not tight enough.
Remedie	Retighten the blanket.
Cause	Excess pressure.
Remedie	Check the cylinder coverings.
Cause	Slack impression cylinder or transfer cylinder clips.
Remedie	Adjust the clips (wear on the heels of the clips).
Cause	Tack of the ink too high.
Remedie	Add Anti Tack Compound (3% max.) or Arctic Thinner 501 (3% max.) to the ink.

4. Binding of the plate, deterioration of the printing areas and/or graining areas (non- printing areas).

(back to incidents)

Cause	Abrasive particles from the paper coating deposited on the blankets.
Remedie	Pre-lacquer the substrate. If possible, place the first group under pressure only with the dampening.
Cause	Pre-sensitised plate exposed too long to light.
Remedie	Rework the plate. Protect the plate during print runs and apply gum during press stoppages.
Cause	Quality of the plate unsuited to the length of the print run.
Remedie	Properly oven treat the plates.
Cause	Form rollers incorrectly adjusted (pressure too high).
Remedie	Adjust the roller settings.
Cause	Excess plate cylinder / blanket cylinder pressure.
Remedie	Adjust the pressures. Check the cylinder coverings.
Cause	Excessive hardness of rollers.
Remedie	Deglaze the rollers with Roline Arctic Deglazer or change them.
Cause	Abnormal movement of form rollers (with certain presses, equipped with form roller movement, it is recommended to use special high quality or oven treated plates).
Remedie	Change the bushes or rollers.
Cause	Abusive use of hicky removal systems (delta effect).
Remedie	Use the system sparingly (less than 1 minute).
Cause	Water too acid.
Remedie	Adjust the pH to obtain a fount solution within the norms.
Cause	Water too hard.
Remedie	Check the water hardness.

5. Scumming, blocking (back to incidents)

Cause	Paper surfacing or coating fragile. Incorrect ratio between surface tension of fount solution / surface energy of plate (ST < SE).
Remedie	Improve the transfer of the fount solution by checking its dosage and, if necessary, add a transfer improving agent. Rework the plate.
Cause	Paper too alkaline.
Remedie	Readjust the water / ink balance.
Cause	Oxidation of the plate due to insufficient or incorrect gumming.
Remedie	Clean the plate with a de-oxidising solution followed by light gumming.
Cause	Dampeners clogged up.
Remedie	Check/ clean the dampening rollers and the dosing units.
Cause	Partial swelling of the blanket due to excessive use of deglazer.
Remedie	Change the blanket.
Cause	Temperature too high in the inking rollers (ink becomesmore fluid).
Remedie	Reduce the temperature and the print speed, change the ink and restart the print run.
Cause	Excessive inking.
Remedie	Reduce inking. Use an ink with higher colour strength.
Cause	Tack of the ink too low.
Remedie	Use a more tacky ink.
Cause	Ink too diluted.
Remedie	Open a new tin of ink.
Cause	Ink too siccative.
Remedie	Use a less siccative ink.

6. Out of register prints (back to incidents)

Cause	Poor dimensional stability of the paper (paper fibre in wrong direction) and excess water.
Remedie	Always print the substrate with the paper fibres parallel to the cylinders.
Cause	Blanket tension incorrect.
Remedie	Retighten.
Cause	Unsuitable cylinder coverings.
Remedie	Adapt the cylinder coverings to rectify them if possible.
Cause	Clips loose due to incorrect adjustment and / or tacky ink.
Remedie	Adjust the clips.
Cause	Paper deformed after several print runs and / or high inking level.
Remedie	Reduce inking.

7. Set-off (back to incidents)

Cause	Optical Density too high, out of standard.
Remedie	Print using the Brunner standard, for example, or print using two printing units. Reduce inking.
Cause	Poor ink distribution.
Remedie	Adjust the form rollers of the printing unit.
Cause	Incorrect Dampening.
Remedie	Adjust the fount solution.
Cause	Excess water.
Remedie	Adjust the water / ink balance.
Cause	Deformation of the stack due to heavy loads. Stack toohigh.
Remedie	Adapt the height of the stack according to the inking level and paper weight. Do not stack up pallets.
Cause	Not enough anti set-off powder.
Remedie	Adjust the amount of anti set-off powder.
Cause	Particle size of the anti set-off powder not adapted tothe substrate.
Remedie	Adapt the particle size to the weight of the paper / cardboard. Use Arctic Vanesse or Arctic Vanesse 15μm anti set-off powders. Take account of post printing operations (varnishing, laminating).
Cause	IR lamps at incorrect temperature.
Remedie	Adjust the temperature of the IR lamps as a function of the prin- ting speed, substrate grammage and whether printing on both sides. Recommended temperatures: Top side: maximum 35°C Reverse side: maximum 30°C.
Cause	Magnetisation of the paper.
Remedie	Use a suitable anti-static system. Properly earth the press. Humidify the print shop.
Cause	Handling of the stack after printing.
Remède	Descend the loader slowly. Handle the stacks carefully.
Cause	Unsuitable ink.
Remedie	Change the ink / substrate. Consult the supplier.
Cause	Ink too emulsified.
Remedie	Wash the printing unit and re-start with minimum dampening.

8. Incorrect drying (back to incidents)

Cause	Substrate too acid (destabilisation of the water / ink balance).
Remedie	Check the pH of the fount solution. Change the substrate.
Cause	Fount solution too acid.
Remedie	Check and adjust the fount solution
Cause	Excessive inking.
Remedie	Reduce the amount of inking.
Cause	Excessive dampening.
Remedie	Reduce the amount of dampening. If necessary, clean the inking train so as to completely eliminate the emulsion and restart with less dampening. Check the pressure of the dampening rollers.
Cause	Wrapping or film covering too rapid (air oxidation ofthe ink film insufficient).
Remedie	Allow inks to dry completely before wrapping or covering in film.
Cause	Ink too emulsified.
Remedie	Find the correct ink / water balance.
Cause	Ink does not dry correctly.
Remedie	Add Triple Drying Agent (1 % max. since too much drying agent can inhibit drying).
Cause	Ink not adapted to the substrate
Remedie	Consult the supplier.

9. Hickies (back to incidents)

Cause	Poor quality paper (linting, coating lift off).
Remedie	Change the paper or reduce the tack of the ink with Anti Tack Compound(3% max.). Carry out a run without inking.
Cause	Accumulation of ink on the dampeners and / or thedampener form rollers.
Remedie	Wash the dampening rollers. Prevention: replace the first form roller with an anti-hicky roller. If re-guillotining the paper, square it up well, and avoid making a reject cut.
Cause	Ink used from opened or incorrectly protectedcontainers.
Remedie	Protect opened tins correctly with cellophane or by spraying Anti-drying A11 and remove the surface skin.
Cause	Skin on the ink when container opened.
Remedie	Change the container of ink.

10. Creasing, deformation of the substrate, mainly at the tail end.

(back to incidents)

Cause	Paper wrapped before printing.Excess paper hygrometry.
Remedie	Check the storage of the paper. Store the paper in the print shop before printing.
Cause	Deformation of the paper on first print run due to toomuch inking or an ink with too high tack.
Remedie	Reduce the tack of the ink during the second print run. Use Anti Tack Compound or Arctic Thinner 501.
Cause	Clips incorrectly adjusted on the margin or wheelsincorrectly adjusted (pressure too high).
Remedie	Adjust the clip settings to regular pressures. Reduce the wheel pressure settings.
Cause	Blanket not sufficiently tight.
Remedie	Retighten the blanket.

11. Powdering, the ink solids remain on the surface.

(back to incidents)

Cause	Paper too porous, causing the ink binder to separatefrom the pigment.
Remedie	Apply a primer coat.
Cause	Ink viscosity too low.
Remedie	Use a higher viscosity ink.
Cause	Drying of ink too slow.
Remedie	Use a more siccative ink. Consult the supplier.
Cause	Dampening water too acid, leading to longer dryingtimes.
Remedie	Adjust the fount solution. To mask the phenomenon, apply an overprint varnish.

12. Poor trapping, ability of one ink to be accepted by another when it is not yet dry (this phenomenon only applies to wet-on-wet printing).
(back to incidents)

Cause	Unsuitable colour sequence.
Remedie	Adjust the colour sequence: Print low colour deposits before high colour deposits (e.g. Violet = 75 % Red and 100 % Blue ⇒ Print the Red first). In the case of poor trapping, dilute the second colour (e.g. Violet = 100 % Red and 100 % Blue ⇒ Dilute the Blue with a suitable thinner).

13. Curling, excessive deformation of the printed material in the stack (excessive curling beyond 4cm/m).

(back to incidents)

Cause	Problem with the paper.Curling of the sheet parallel or perpendicular to thedirection of the press (central region of the parent roll,foudrinier table, dryer).
Remedie	Change the paper.
Cause	Hygrometry too high or important change in the hygrometry.
Remedie	Check the storage conditions.
Cause	Unsuitable blanket hardness.
Remedie	Use a blanket with a harder surface.
Cause	Excessive dampening.
Remedie	Reduce the dampening.
Cause	Ink too tacky.
Remedie	Reduce the tack with Anti Tack Compound (3 % max.). When printing large solid areas, print a light screen first (base print), which then allows the thickness of the ink film to be reduced on a second print run.

14. Mottling, irregular appearance (mainly on solid print areas).

(back to incidents)

Cause	Paper has irregular smoothness.
Remedie	Change the paper. Change the ink.
Cause	Excess dampening, which has the effect of reducingthe tack.
Remedie	Adjust the dampening to the minimum.
Cause	Ink too emulsified.
Remedie	Change the ink.
Cause	Lack of pressure (piling).
Remedie	Adjust the pressure settings.
Cause	Ink from previous prints deposited on the blanket.
Remedie	Dilute the ink of the previous printing units that are being trans- ferred.

15. Linting, loose paper accumulated on the blanket. (back to incidents)

Cause	Binding or surfacing of the sheet of paper insufficient.
Remedie	Print a solid print area with transparent white ink without dam- pening. Carry out a run without inking. Change the paper.
Cause	New or badly washed blanket that is too adherent.
Remedie	Wash the blanket correctly and apply talc.
Cause	Excessive pressure between the blanket cylinder andthe counter pressure cylinder.
Remedie	Adjust the pressure settings.
Cause	Ink too tacky.
Remedie	Reduce the tack with Anti Tack Compound (3 % max.).
Cause	Non uniform water supply to blanket.
Remedie	Adjust the water meteringspeed settings.

16. Piling / buildup, ink build up on image areas of the blanket.
(back to incidents)

Cause	Spalling of the paper coating by the fount solution.
Remedie	Change the paper. Slightly increase the dampening.
Cause	pH of the fount solution too acid.
Remedie	Adjust the pH of the fount solution
Cause	Irregular dampening.
Remedie	Increase the speed of the dampening tank roller.
Cause	Incorrect water / ink balance.
Remedie	Check the water / ink balance. Slightly reduce the alcohol level.
Cause	Ink too sticky.
Remedie	Soften the ink with Arctic Thinner 501 (3 % max.).

17. Guttering (back to incidents)

Cause	Irregular ink deposition.
Remedie	Incorrect imposition. Check the form roller movement. Adjust the pressure settings.

18. Phantom effect, reappearance of the previous print run or the print run underway but out of shift.

(back to incidents)

Cause	Worn blanket.
Remedie	Change the blanket. Even if the blanket seems to be clean, its compressible layer may be altered and the phantom image may appear later.
Cause	Form rollers incorrectly adjusted on inking rollers.
Remedie	Adjust the pressure settings of the form rollers on the inking rol- lers.