Thin Film Analyser
TFA

• Applications
• Introduction
• How does the Thin Film Analyser work?
• Features
• Simulation of the cure cycles of various paints
• Specifications
• View .PDF file on-line
• Download .PDF file
• Download latest software

Applications

The Thin Film Analyser is able to continually measure rheology of a PAINT or POLYMER film as it CURES or DRIES! For a FILM which is drying or curing under REAL conditions it is possible to measure VISCOSITY with time (using a big probe with low load) and RELATIVE CURE (using a sharp probe with high load to monitor scratch resistance). The technique can be applied to almost any film forming material and over a wide range of film weights. It is the ONLY instrument available which is able to determine on real films ALL the following information:

· Viscosity during solvent loss
· Build up of scratch resistance
· Extent of cure with time
· Levelling of paints
· Gelation and vitrification
· Water resistance of cured coatings
· Cure rates and behaviour at different temperatures (simultaneously)
· Time-Temperature-Transformation (TTT) diagrams in a single experiment

The TFA is able to test any material which can be drawn into a film.

Introduction

The Thin Film Analyser (TFA) evolved from a concept originally conceived at ICI Paints to fill a gap in tests for characterising drying films. Low cost methods such as the travelling needle or sand dry tests are highly subjective and at best are only semi-quantitative.

Expensive instruments such as Dynamic Mechanical Analysers (DMA) provide graphical output but require complex sample preparation and do not mimic real-life conditions. The Thin Film Analyser overcomes all these problems and offers:

· EASY sample preparation using a sliding block applicator
· REAL LIFE drying conditions rather than impregnated braid or coated shim
· QUANTITIVE output of drying against time
· UNIQUE ABILITY to measure drying at more than one temperature simultaneously
· Unique ability to measure viscosity build up in a FILM LOSING SOLVENT (conventional rheometers prevent solvent evaporation as the sample is sandwiched between two plates)

The computer periodically instructs the TFA to draw a probe, in this case a needle, through the film recording the force required each time.

How does the Thin Film Analyser work?

Liquid samples are applied to a test panel at the desired film weight using a block applicator and placed on the instrument platen. The temperature of the platen is preset by the user and is electronically controlled. The computer controlled test then begins.

A test probe consisting of a needle with an imposed lateral restoring force is moved through the sample in short strokes periodically throughout the experiment. The magnitude of deflection of the probe during each stroke provides a measure of the level of film formation, and is automatically logged and saved. The speed, pressure and periodicity of the probe movements may be changed by the user to suit the wide range of characteristics exhibited by such materials as emulsion and automotive paints.

Film weights of typically 200 micrometers are used for paints, but any film weight may be used. Depending on the type of experiment, the instrument may be operated in one of two modes. The platen may be isothermal, or have an imposed temperature gradient.

During an experiment the user can check the temperature gradient of the instrument easily from the LCD display. Temperature is controlled from the PC software and is continually recorded.

Features

The Thin Film Analyser is a sophisticated instrument, but is designed to be easy to use, and can be put to work almost immediately by a laboratory technician. Features include:

· Complete PC control and data logging with Windows™ software
· Testing under real conditions of solvent evaporation
· Simultaneous testing at multiple temperatures
· Electronic temperature control, including sub-ambient temperatures
· Choice of substrate (glass or metal)
· Self-cleaning probe
· A LCD which gives the user continual information on the instrument temperature and operational status.
· Once an experiment is set running, the instrument is completely operator free. Experiments may be left to run for a few minutes, as in the case of VOC based paints, or for many hours, as in the case of one component polyurethanes.

The TFA is opperated from a PC through a Windows™ software package which gives complete control of experimental parameters, real-time data collection and display and exports to other data management programs

Simulation of the cure cycles of various paints

	Figure 1 : Thermally cured paint - simulation of the cure cycle of a paint which is sprayed on to a surface at ambient temperature, where some cure takes place and then stoved at a higher temperature to cross-link.
	Figure 2 : Water based paint - after about only five minutes the deflection begins to rise sharply, showing the rapid viscosity build up characteristic of emulsions.
	Figure 3 : Solvent based enamel - once the film is cast the sample takes about 30 minutes before a rapid build up in viscosity begins to occur, characteristic of the cure in these systems.
	Figure 4 : One component poly(urethane) - initially the film is a liquid and the deflection begins to increase after about three hours as cross-linking occurs. After about six hours a plateau is reached but further reaction is still occurring and after eight hours the film becomes so hard that the needle no longer penetrates and starts to skate over the surface.

Specifications

Isothermal temperature range: (0 - 60 °C)

The user may set the isothermal temperature of the TFA platen to be anywhere in the 0 - 60 °C range in 1 °C increments. (As with laboratory Hot Stage.)

Temperature gradient: Spread of up to 80 °C in the range -5 to +110 °C)

The user may set any imposed temperature gradient on the TFA platen, within certain physical constraints, shown in the table below.

For each of the cold end temperatures listed, the MAXIMUM temperature at which the hot end may be simultaneously maintained is shown underneath. It may, therefore, be set to less than this value if required. For example it is possible to impose a narrow gradient, such as 0 - 10 °C, or a much wider one, such as 50 - 85 °C. The real-time gradient is always displayed in the instrument LCD.

Minimum temperature of -5 Degrees C only achievable with coolant temperature below 18 Degrees C.