TESTING WATER BALANCE WITH THE LITHOTRONIC

• new printability tester, operated and controlled by conventional personal computer
• direct torque measurements at controlled speed
• calibrated liquid dispension system
• integrated sample temperature control
• flexible test programs can be adapted to individual requirements
• rugged and compact design
• easy handling and cleaning
• typical test duration of 12 minutes
• digital indicator shows measured and calculated values: speed, torque, delta torque, emulsification capacity, temperature, time and status
• automatic storage of results
• modern MS Windows software permits easy comparison of different curves

Background of printing ink applications

A good ink-water balance is important for high quality printing on lithographic offset printing presses. In order to be able to predict the performance on the press, the water absorbency of lithographic inks must be tested. The LITHOTRONIC is a state-of-the-art measuring device for accurate and reproducible determination of the amount and rate of water absorption of a lithographic ink. A typical and characteristic test pattern is showing three parameters:

• quick changes in torque reflecting to the hydrophobic (= water repellent) nature of an ink,

• the torque profile reflecting to the rheological changes during the emulsification process and

• the sudden drop in torque at the point where the emulsion is saturated with water.
  

The emulsification capacity is the weight ratio of the ink or varnish to the total water titration. The rheological behavior of emulsions is depending on the theology of all ingredients. In order to optimize the performance of lithographic offset inks, the effect of

• resins, varnishes or other binders,

• pigments or carbon black,

• additives,

• fountain solutions

on the emulsification properties must be investigated. Additional tests with various standard emulsions at increasing or decreasing rotation speeds can be performed.

Test method

The test method is based on rheometric principles.

The sample is poured into a mixing bowl and continuously stirred by a motor driven spindle. The water or fountain solution is slowly dispensed into the mixing bowl during continuous torque monitoring. The test conditions can be changed by intelligent computer software.

Novel design features

Novel design features are providing an easy access to the stirrer and to the mixing bowl clamping arrangement. The mixing bowl itself is made out of aluminum and is very simple to clean. The torque of the rotating stainless steel mixing spindle that is inserted into the bowl is continuously monitored. A low inertia precision DC-motor is driving the stirrer at a controlled speed. Speed and torque can be displayed on a digital display during the test. As the water absorbency of lithographic inks is temperature dependent, automatic sample temperature control has been integrated in the LITHOTRONIC.

Continuous liquid dispension system with a precision, maintenance-free miniature pump is integrated in the instrument. The liquid flow is digitally controlled by the integrated microprocessor system providing a calibrated flow characteristic. This simplifies measurements with different kinds of fountain water, saves time and improves measurement reproducibility. The compact and rugged design of the LITHOTRONIC guarantees a long-term performance.

The High Speed-LITHOTRONIC 

The High Speed LITHOTRONIC has been developed in order to become more close to the conditions on modern high speed presses. In modern high speed presses the trend towards speed of 20 m/s or more for heat set and 20000 prints/hour for sheet fed. Furthermore the ink industry towards the use of higher structured materials. These trends are forcing higher demands on the physical properties of inks and their capability of high speed water pickup and release. The high speed LITHOTRONIC were adapted to these demands and performs emulsification test at high stear rates up to 6000 per sec.

The maximal speed of 2800 rpm relates closely to the typical shear rates of high speed presses. As a faster fountain solution transfer may shows better the water uptake limits of the ink under test, the capability to pick up and release water fast at high shear rates with a stable and known emulsion behavior is crucial for the quality of modern lithographic inks.

A higher shear rate creates higher thermal energy into the emulsion under test. In order to control the adjusted temperature an improved temperature system has been implemented, which supports an active cooling of the sample. The innovative Peltier based system is featuring stable temperatures under this high shear rate conditions.

Flexible test programs

Beside standard programs with parameters which are recommended by EUROCOMMIT the free control of all test parameters is possible by use of the Free Run option. Within up to twelve program steps all essential parameters, like temperature, rotation speed, dispension speed and time, are free definable. Special tests (shock and recovery tests) can be defined easily.

Rheology and flow properties are important to any kind of liquid and these properties are not easy to test as the viscosity of liquids depends on many parameters and conditions. To test these properties of a mixture of two non-compatible liquids is even more complicated. The LITHOTRONIC instrument has been developed for these tests and offers a lot of important features, such as automatics temperature control, shear rate control and dispension rate control. The automatic dispension is a special feature which enables the user continues titration of a liquid into the sample during operation. The liquid that is added can be water, solvent, oil or anything else. By mixing these two liquids under controlled conditions, emulsification can be tested in a reproducible and standardized way.

Typical applications:

• natural and synthetic varnishes
• offset inks and flushes
• rheology modifiers and additives
• fountain solutions

Technical specification