FAQs on thickness measurement

Why is Film Thickness Important?

Plastic films are often used to encapsulate, protect and preserve products that are sold to consumers or industry. The film is used as a two-way barrier to stop product leaking out and also external contaminants from migrating in.

Variable Force Precision Thickness Gauge (FT3-V)

The effectiveness of the film as a barrier is related to its chemical composition and also its thickness.

Films which are below a specified thickness may fail physically- bursting, splitting or leaking, they will also be less effective at stopping the migration of oxygen and contaminants that can lead to product spoilage.

Who Measures Film Thickness?

Packaging developers and product manufacturers measure and specify the thickness of the film to ensure the robustness of the packaging and the functionality of the barrier.

Various test methods are used in this specification including burst testing, tear testing and various film migration tests. These tests, including thickness measurement, are repeated as part of Quality Assurance inspection throughout the manufacture of a product.

Using A Film Thickness Gauge

In contrast to this, film manufacturers need to ensure that a film, whilst conforming to a customers specification is also manufactured in the most cost-effective manner possible. By measuring and manufacturing within tight tolerances the amount of raw materials used can be significantly reduced, leading to improvements in productivity.

The Hanatek Precision Thickness Gauge (FT3) can also measure the thickness of paper, metallic foils, carton board, corrugated board, tissue, textile and any other packaging substrate.

Precision Thickness Measurement

Thickness is a key parameter for many manufacturers as it affects the functionality, quality and cost of finished products.

Functionality- Raw material thickness directly influences the physical properties of a product. Important examples include;

Tensile strength of textiles, plastic films, paper and tissue.
Rigidity of plastic film, and cardboard packaging.
Barrier properties of plastic films.
Puncture resistance of plastic microwaveable containers.
Opacity of inks, coatings, plastic film and paper.

Quality- Thickness should be controlled to ensure batch consistency and ensure products have the correct tactile “feel”.

High-quality goods are packaged in robust high gauge materials.
Quality toilet tissue, baby wipes, and kitchen paper are supplied thicker and stronger.
Thicker, heavier paper is used for certificates, brochures and art supplies.

Cost-Using a low accuracy gauge inevitably leads to the supply of goods that are above or below thickness tolerance.

Out of tolerance material can be rejected by customers leading to huge re-working costs and loss of credibility.
A few microns saving in reduced thickness can equate to tens of thousands of Dollars/Pounds/Euros of raw material savings in a relatively short period.

The FT3 thickness gauge allows product to be manufactured within tight tolerances targeted right in the middle of a customer’s specification.

The high accuracy and resolution give absolute confidence that material is always supplied within customer requirements.
A high confidence in results often allows tighter manufacture control and a reduction in raw material use. Raw material savings can pay for the gauge in a matter of weeks or months.
Securely date and time-stamped result labels can be attached to retained samples or job sheets giving absolute confidence that a product has been tested throughout its production run.

How does the FT3 achieve high precision?

Sensor

The FT3 is uses a precision LVDT displacement sensor with highly stable electronics to produce a very sensitive transducer system.

Measurement Parameters-The key to repeatability and accuracy is to tightly control all the parameters that can lead to measurement uncertainty.
The parameters that affect thickness measurement are;

Measurement pressure.
Presser foot profile and size.
Measurement velocity.
Parallelism of presser foot to measurement plate.
Dwell time.

To allow manufacturers in the same industry sector to measure using the same conditions, these key measurement parameters are often specified by international standards (ASTM/ISO etc.).

External Factors

External effects such as temperature change and vibration will affect the measurement, the FT3 instrument is designed to reduce the impact of these.

Calibration

The FT3 has a multi-point calibration routine to reduce/eliminate the effect of non-linearity in the LVDT sensor.

Electronic Drift

The 0.01micron resolution instrument includes routines to reduce the effects of short term thermo-electronic drift of <0.1 microns.

Why do different applications have different measurement parameters?

Measurement Pressure

Many materials including plastic film, plastics, and rubber may crush or deform dependent on the pressure applied during testing and the momentum of the presser foot.

Textiles require high pressures during testing to remove wrinkles and airgaps.

Tissue thickness testing demands a light measurement pressure and slow presser foot speed so the paper fibres are measured without being crushed and flattened.

It is clear that different industries have adopted measurement parameters that give meaningful results for their own application.

FT3 measurement forces are applied using fixed masses; each instrument is supplied ready to apply the exact force specified in the relevant international standard.

The FT3-V variable pressure thickness gauge can be useful if a sample needs to be tested to more than one standard, it can also be used to determine the compressibility of samples under different conditions.

Measurement foot size and profile

The measurement head size and profile is usually determined by the ISO Standard for the material.

Domed measurement head- Small areas can be measured with high resolution- Plastic films and coatings.
Small diameter flat measurement heads- used to apply a large pressure in a small area- Paper and board applications.
A large diameter flat foot – Measures the average thickness of fibrous material over a large area with light pressure – Tissue Paper. Opacity of inks, coatings, plastic film and paper.

Measurement velocity

The speed of the measurement head can also have an effect on thickness measurement. A fast-moving head will impact a sample with more energy and may deform or dent the material.

The measurement velocity of the FT3 head can be set by the user from 1 to 5mm/sec. This speed is sometimes specified in international standards.

The most significant source of measurement error in any system is often introduced by the human operator.

The FT3 family of instruments have a number of features that reduce the impact of a human operator.

Fully automated operation

the main parameters are fully controlled by the instrument; measurement pressure, speed and dwell time.

Onboard statistical calculation

Mistakes are often made in transcribing results and calculating statistics, these functions are performed automatically by the instrument.

Results can also be output via RS232 to SPC programs, lab networks or MS Excel.

QA labels record results throughout the batch

Securely time and date stamped labels with statistical results can be produced throughout a batch run and attached to job cards or retained samples. This traceable control gives the customer confidence that the whole batch of product is within specification and allows manufacturers to issue certificates of conformance.