Understanding IPA and IPA substitutes, part I

Isopropanol (IPA) is a highly effective, general use cleaning solvent that is used to clean a variety of substrates and remove a variety of soils. IPA helps increase the viscosity of the fount; enhance the cooling effect; affects surface tension and affects the ink.

Which of these is the most important? The simple answer is, all of them. IPA is kind of ‘cure for all ills’ to the press. Most issues originating out of non-proper press-setting disappear upon the addition of IPA. Reducing IPA is likely to bring this back to the foreground. Also, close monitoring by press-minders is critical.

IPA has following properties:

1 Reduce surface tension

2 Pure water has a surface tension of 72-dynes/cm. In dampening solution, an alcohol concentration of 10-25% reduces the surface tension to 35-45-dynes/cm

3 Increase fountain solution viscosity

4 Act as coolant to different surfaces due to evaporation

5 Act as a mild disinfectant the fountain solution circulation system

6 Measurably reduce the dampening solution conductivity

IPA reduces the ‘interfacial’ tension between the dampening water and ink, and, the dampening water and rollers.

This means thinner and continuous water film; greater adhesion between dampening water and ink and greater adhesion between dampening water and rollers.

IPA & the Ink-Water Emulsion

IPA aids a stable and consistent emulsion of ink-water. A multifunctional material that assists the printer in producing clean, consistent results, IPA promotes a thin and even water film at the plate; stabilises the ink/water balance and increases the latitude in ink and water settings. it also increases the latitude in dosing and temperature of damping water.

But it introduces problems of its own. It adds to global warming and pollutes the atmosphere. It is flammable. It is expensive. It reduces gloss; dot definition and print density.

Possible solutions include

1 IPA reduction - fount + IPA 4-7%

2 IPA elimination - fount + IPA substitute

3 Go with single step fount (with zero or < 4% IPA)

Many printers use too much IPA (better than too little!). Modern, well-maintained machines running modern inks should have no trouble running 8-10% IPA – if it requires more.

 The press is set to work with IPA once following is done:

1 Press settings need adjustment

2 Dampening rollers to be adapted for optimal use

3 Pressure settings to be decreased (to enhance water release)

Maintenance, therefore, is an issue since the process of IPA reduction is time consuming and support from both the management and the printers is required to do the alcohol reduction.

Press latitude

Because IPA-free offset printing requires more precise adjustments of the press settings, keep the following parameters under control:

1 Ink and dampening roller quality

2 Ink and dampening roller adjustments

3 Special hydrophilic dampening rollers

4 Lighter adjustment of the dampening metering roller

5 No bombastic shape of the dampening rollers

6 Higher temperature of the fountain solution: 15 degrees Celsius

7 Pressure: Ink and dampening rollers

8 Pressure: Ink and dampening rollers

9 Rollers to be adjusted to the supplier’s recommendation

10 Is the rubber hardness according to the specifications also needs to be ensured

IPA-free offset printing: machine settings

1 Pressure: Roller adjustment; this means the rubber hardness as per machine specifications

2 Stripe or nip: Follow supplier’s recommendation, which normally is as below:

• Ink forme rollers: ± 30° Shore A

• Dampening form rollers: ± 26° Shore A

• Dampening metering roller: 18-22° Shore A (IPA- free)

3 Smaller stripes

4 Lighter adjustment of the metering roller

Remember, unlike alcohol, the alcohol substitutes do not increase the viscosity of the water. Therefore, we need to enable more transport of fountain solution to the plate by a smaller nip between the metering roller and the oscillator roller! Therefore, the dampening settings of the press are higher than with alcohol, as the amount of water on the plate will be the same. Dampening levels will go up upon using less IPA.

Some printers fear the plates will be too wet, because of the higher settings, However, this is not true. Less water is coming to the plate to wet the plate fully. Therefore, dampening levels need to go up. Alternatively adjust the dampening nip roller settings. Due this misconception, often the journey of going IPA-free is left in between.

The point to remember is that higher water feed level at operating consol does not necessarily mean more water on the plate.