How to measure and analyse the texture of food, cosmetics, pharmaceuticals and adhesives.

Tuesday, 18 March 2014

Sticky standards for your adhesive tape testing



Application of heavy duty silver tapeAdhesiveness / Tackiness / Stickiness are key to perceived product quality, performance and effectiveness of such products as sealing tapes, adhesive plasters and labels used in the pharmaceutical, food, medical and packaging sectors.

These properties can be influenced by many factors, including temperature, liner material, moisture level and repeated use. By matching adhesive performance to functional and consumer requirements, manufacturers can identify the ideal adhesive composition.

However, a measurement principle needs to be adopted so that these properties can be monitored either during the development stage or at the point of quality control.


Measurements allow the viewing of subtle differences between different formulas, materials, chemical ingredients, and manufacturing processes.  For QC/QA production, verification of batch conformity to an existing standard can be checked and a comparison of consistency between batches, shifts and different manufacturing facilities can be made.

The traditional standard approach - What’s the testing solution?
Standard test methods according to adhesive tape associations (FINAT, AFERA, PSTC, ASTM) that specify a tensile testing machine are built into the software for automatic testing and analysis.

Tack, the most important determinant of the success of an adhesive bond, is assessed with a loop tack test or a probe tack test, using a stainless steel ball probe. In these tack tests, the “debonding strength” of the adhesive is determined by the force required to pull away the adhesive and the length of time this takes.

The most common standard is approach is to perform a 90 degree peel.  Peel adhesion is defined as the force required to remove pressure sensitive coated material, which has been applied to a standard test plate under specified conditions from the plate at a specified speed and approximate angle of 90°. 

video video Probe tack test
Above, left to right: Loop Tack Test; 90 Degree Peel Test; Probe Tack Test

Standard test methods according to adhesive tape associations (FINAT, AFERA, PSTC, ASTM) that specify a tensile testing machine are built into the software for automatic testing and analysis.

Tack, the most important determinant of the success of an adhesive bond, is assessed with a loop tack test or a probe tack test, using a stainless steel ball probe. In these tack tests, the “debonding strength” of the adhesive is determined by the force required to pull away the adhesive and the length of time this takes.

The most common standard is approach is to perform a 90 degree peel.  Peel adhesion is defined as the force required to remove pressure sensitive coated material, which has been applied to a standard test plate under specified conditions from the plate at a specified speed and approximate angle of 90°. 

Standard Methods that are applicable to 90 degree peel testing using the Texture Analyser are:

 
FIAT 2 – Peel adhesion (90º) at 300mm per minute
This test method differs from FINAT 1 in that it can allow the end user to compare the repositionability of different laminates.  Adhesion is measured 20 minutes and 24 hours after application, the latter being considered as the ultimate adhesion.   Measuring peel adhesion at 90º normally gives a lower value than at 180 and allows values to be measured for materials normally giving paper tear.  Peel adhesion (90) is expressed as the average results for the strips tested in Newtons per 25mm for either 20 minutes or 24 hours application time.
Note: FINAT 2 can also be performed under the conditions of FINAT 5 (at elevated temperatures) and FINAT 6 (under ultra violet light)

AFERA 4015 – Quick stick
This test method is designed to measure the ability of adhesive tape to adhere to a surface, with the application of a very light pressure.
For each test specimen, force measurements are taken at 5 intervals in ascending order and the central value is taken. Similarly, these 5 central values are arranged in ascending order and their central value taken.  The results are expressed in Newtons per centimetre widths of tape.

AFERA 5001 – Test Method F – Single-coated Tapes – Measurement of peel adhesion from stainless steel or from its own backing

Test Method F can show the relative bond strength of a given tape to one or more surfaces (material and texture) as compared to the standard stainless steel panel.  Substitution of representative samples of materials in question for the standard steel panel would suffice to do this.


Test Method F cannot be used to compare two pressure-sensitive tapes of the same type but of different manufacture for their ability to adhere to a surface.  This is because the measured peel force is not normalised for a fixed area of stress.  The area under stress varies with backing stiffness and adhesive rheology (firmness).  Two different tapes seldom agree in these properties.

When you don’t need to ‘stick’ to the standard approach
A number of common and established adhesive tests can be carried out using Stable Micro Systems’ Texture Analyser. A 180 degree peel test, usually used for packaging applications, can be performed using the Peel Strength Test Rig. Other fixtures can be attached to the Texture Analyser to carry out tensile strength, “T” peel and drum peel tests. An adhesive indexing system is also available to allow multiple testing of one sample, highlighting variations within it, and giving an indication of its likely performance.

video video Tensile test using roller grips  

Above, left to right: Adhesive Indexing System; Drum Peel Test; Tensile strength/elongation measurement

However, many parameters that can be quantified with the Stable Micro Systems texture analyser range and its software are not otherwise quantifiable with alternative instruments.   Data captured during the tests is presented as real-time graphs and allows detailed analysis of the compressive and tensile stress-strain behaviour of the adhesive.

The TA.XTplus and TA.HDplus texture analysers have been used to assess the following typical adhesive products:

Adhesives/Glues; Bandages; Paints, inks etc.; Hot Melt products; Packaging; Labels; Gums; Caulkings; Resins; Coatings; Sealants; Waxes; Creams/lotions; Solder paste; Transdermal patches; Gels: silicon, medical, cosmetic; Adhesive tapes: double-sided, duct, electrical, foam-backed, masking, office, packaging. 

 
Objective and repeatable measurement can be used to highlight the molecular structure and performance of the adhesive, and helps manufacturers achieve critical but awkward textural properties for their products. 


For more information, visit our page detailing Adhesive Applications.










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