Authors
Dr. Volker Kraft
JMP
Dr. Simon Stelzig
Lohmann GmbH & Co. KG
Muralidhara A
JMP
Objective
Application of statistical methods to understand the process and enhance its performance through Design of Experiments and regression techniques.
Background
Lohmann is a manufacturer of adhesive tape systems and adhesive solutions for industrial applications. The company was founded in Frankfurt am Main by Julius Lüscher in 1851. The adhesive business of the company includes a wide choice of services ranging from formula development to customized adhesive solutions. Lohmann has been serving her customers in the home appliances, electronics, transportation, graphics, building, renewables, textile, paper, hygiene, and medical markets for 170 years. The company’s claim "The Bonding Engineers" is lived out by the employees in the 29 subsidiaries and distribution partners in more than 50 countries daily. The adhesive tape group is headquartered in Neuwied, Germany.
The company’s focus is to develop cutting-edge and innovative products. Always bearing the customer benefit in mind, Lohmann works every day on making processes even more effective and efficient by means of adhesive solutions. The Research & Development team deals with the question of how innovative ideas can be "translated" into new applications and how existing products can be improved.
Lohmann’s Research and Development experts focus on three areas that will shape the company in the future also concerning market potential and environmental issues. These are: Faster solutions for market and customer, data driven product and process development and leveraging new technologies.
Pressure Sensitive Adhesives
One of the key products of the company are Pressure-Sensitive Adhesives (PSA). It is a non-reactive type of adhesive which forms a bond when pressure is applied with a surface. No solvent, water, or heat is needed to activate the adhesion. Besides pressure, the viscoelastic behavior of the adhesive plays a major role in the degree of bonding.
Pressure-sensitive polymer compositions have been used for over 50 years and many types of polymers can be made pressure sensitive via various formulation methods. Thus, polymers represent a vital ingredient in pressure sensitive adhesives.
For a solvent-based PSA, one class of polymers is based on the polymerization of acrylates. The basic polymer is normally formulated with further ingredients, like (optionally) resins or cross-linkers to further 3 tune the properties of the adhesive. The performance of a PSA can be improved by tuning the properties of the basic polymer, which is applied in the adhesive formulation.
Fine-tuning of the polymer can be achieved by changing the composition of the monomers, changing the molecular weight and distribution of the molecular weight, changing the structure of the polymer and finally the type of polymerization.
Molecular Weight Distribution (MWD) or Molar Mass Distribution is a key item of information in tailoring polymer structures for different end uses. It is basically the amounts of component polymers that make up a polymer. A polymer’s molecular weight (MW) is related to that of the monomer, and the number of monomers forming the polymer molecule(repeating units). Therefore, measuring MW requires measuring the MW of individual chains and the number of chains of any specific weight.
See Exhibit 1 (PDF) for Moments related to Molecular Weight Distribution.
The Task
On one hand, the R&D team has to enhance the process and product performance by understanding the relationship between the input and output variables. On the other hand, they also want to identify those key variables influencing the molecular weight distribution.
Therefore, one task is to identify the key factors influencing the molecular weight distribution. There were multiple process variables influencing the molar mass. An internal discussion with subject matter experts 4 resulted in three continuous process variables (X1, X2 and X3) and a categorical parameter called type of the ingredient (X4). The goal is to understand the effect of these variables on the moments of molecular weight.