Stabilizer

Stabilizer for thermoplastic paste formulations

The following description of the stabilizer agents is applicable for thermoplastic paste formulations. Thermoplastic paste formulations are used to transfer  hotmelt adhesive powders via rotary screen printing machines for various applications.

A thermoplastic paste formulation contains essentially the following components:

The ROWAFLEX stabilizers for thermoplastic paste formulations are a mixture of acrylamide / acrylate and a high molecular weight polyethylene oxide.
The product is anionic and compatible with the additives of the thermoplastic paste formulations.


Adding stabilizer agents in thermoplastic paste formulation induces following properties:

   


The above properties have the following effect on the coating.

The pseudo-plastic viscosity determines the viscosity variation due to high shear forces, such as the following graph is showing:



Stabilizer agents for thermoplastic paste formulations are highly water soluble and can be customized with suitable agitation systems to be applied very quickly.  High visco-elastic properties of the stabilizer agent tend during mixing to “climb” along the shaft of the agitator.
In practice this property is called "stringing".

The following figure shows a tooth-stirring disc suitable for mixing in stabilizer agents:




Without the addition of stabilizer agents and their property of water retention, the paste would run dry during coating. Agglomerates would arise in the printing template which sit in front of the wiper and lead to stiffness on the substrate.

The surface of the template would be quickly contaminated with dry paste blocking the apertures. Adding stabilizer agents allows the paste to be applied with high production speeds  in the range of 20 - 80 m / min with all common process printing screens.




The good lubricity prevents high friction forces on the machine parts, thus creating a gentle coating. The exiting of the paste from the printing screen is supported by an optimal "stringing" of the paste due to the pseudo-elastic viscosity property which gives sharp contours of the paste dot and enhanced adhesive grip.

To ensure an effective protection against temperature variations during storage and transport time, an antimicrobial additive was incorporated into the formulation.  It prevents a decreasing in viscosity.

The emission values of stabilizers for the thermoplastic paste formulation and the product is far below national limits.  Toxicological studies have shown that due to the high molecular weight of the stabilizer an absorption in the intestine and skin irritation causes cannot be determined.

A high salt content of water is not a problem due to appropriate stabilizers being resistant to water ions.

The influence of stabilizers on the quality of the finished coating shall:

     
Figure: coated substrate   Figure: Continuous press


Under economic aspects the stabilizer should not be visible in the cost structure.


The following table shows the quantitative composition of a thermoplastic paste formulation. In our case, the proportion of the stabilizer is 10.00 kg.

 Standard paste formulation    kg
 Water    55,00
 Defoamer, eg. ROWAFLEX DF 2       0,20
 Emulsifier/Plasticizer, eg. ROWAFLEX X 500    4,50
 Thermoplastic fine powder    30,00
 Thickener, eg. ROWAFLEX TH 3    0,50
 STABILIZER, eg. ROWAFLEX X 100    10,00

   
Table: Percentage of components based in kg


Figure: In terms of costs the proportion of the stabilizer is about 10.00% in the finished thermoplastic paste formulation.



Competence

Please direct any further questions on this topic to our experienced technical staff.

Yours ROWAK AG