Thickener

Thickener for thermoplastic paste formulations

Within this glossary, we exclusively treat information about thickeners in thermoplastic paste formulations / thermoplastic adhesive pastes (eg. copolyamide, copolyester, HDPE/LDPE or TPU fine powder). They are primarily applied by pastedot coating. The standard recipe consists of the following components:

The thickener used in thermoplastic paste fomulations is commonly liquid polymer dispersion. Polymerisation is already been executed in emulsion phase. This enables a constant polymer structure and a high polymer concentration. Thickeners for thermoplastic paste formulations are mostly based on polyacrylic acid derivatives.

Polyacrylic acid is a brittlle, colourless substance that is well soluble in water but less in unpolar substances.



For the manufacturing of polyacrylic acid preferably solution polymerisation in water, precipitation- or emulsion polymerisation, and/or hydrolysis of acrylic acid derivatives (ester, nitrile, amide) is been choosen.

A particularly broad variety of properties can be achived through copolymerisation of other comonomers. Polyacrylic acid is a polyelectrolyte that is able to chip a protone as each component unit contains a carboxyl-group.

Thickener for thermoplastic paste formulations are usually anionic and must fulfil following criteria.

Production of thermoplastic pastes

The used thickener should be able to adjust the viscosity of the paste to a level making the paste able to easily pass the screen holes of the print screen. The viscosity should be resisitant to high shear forces.

Anionic thickeners may not interefere with other paste components.



They should be self-thickening. Addition of eg. ammonia to adjust pH-value and thus final viscosity is not neccessary.

As only small quantities (max. 0.8%) are added to reach the final viscosity, an optimal emulsifying property of the thermoplastic paste formulation is a prerequisite.

The product composition tend to VOC-emission. Therefore, tolerance values must be considered when composing the paste formulation. In thermoplastic paste formulations, the detection limit (due to its small quantites in the exhaust duct of the dryer) must be within legal regulations.

After the paste has been produced a storage stability of a couple days is neccessary to bridge production interruptions. At reutilization, its rheologic behaviour must be maintained. A quick stirring of the paste is recommended. The product has only limited resistance against ionic concentration. Therefore the past should be ideally prepared with softened water.

Processing

To guarantee a proper coating, thickeners must be compatible with all components used in the paste formulation.

Procedural, thickeners may have no influence to


In combination with pseudoplastic additives the screen surface is kept clean and high production speeds can be achieved.

Ready coated substrate

In summary

Following criteria of the thickener should be fulfilled to provide the needed coating quality:

The thickener shall provide a sharp contour building of the printed dot. This advances a positive influence of the bond strength due to an increased mechanical anchoring of the melted plastic and increaes adhesion.


Following diagram reflects the quantitative composition of a thermoplastic paste formulation. In this recipe, a ratio of 0.5 kg thickener is underlying.

    kg

 Water

   55.00
 Defoamer  

                 0.20

 Emulsifyer/Plasticizer    4.50
 Thermoplastic finepowder    30.00
 THICKENER    0.50
 Stabilizer    10.00



Figure 1: Ratio of components by kg

The cost ratio of the thickener is at 1.2 % of the ready thermoplastic paste formulation in relation to other components.

Figure 2.: Ratio of components by costs (% , average product prices)

Competence


Please address your questions or inquiry for this topic at our experienced technicians.

ROWAK AG