Custom Polymer Blending and Formulation Guidelines
North Star Elastomers (NSE) is a custom polymers producer. We will do all we can to satisfy your requirements for quality assurance and product development. If you should find that our existing products do not exactly fit your needs, we are happy to work to develop a product for you. All of these products have proven useful both as base polymers and as modifiers for coatings, sealants and adhesives.
With all these rubbers, it is easiest to examine them when they are blended with a C-5 tackifying resin. We like Wingtack 95 from Goodyear or the Escorez 5300 series, but others such as Hercules resins will work as well. The rubbers will be compatible with any of the aliphatics, but there may be problems with resins that contain aromatics.
A simple 50/50 blend (rubber to resin) is a good place to start. Different grades of NSE polymers can be blended together to create unique properties for your formulas.
With optimum blending and formulation, your products can demonstrate dramatic and profitable enhancements. These partially depolymerized elastomers add significant gains in critical adhesion properties at rather low levels and cost.
EVAs and Block Copolymers
Some of our customers have used our rubbers to modify more traditional hot melt polymers. In modifying EVAs, NSE polymers act as a co-agent with the tackifying resin. Make a blend of rubber and resin first, then add this blend to the EVA. The compatibility of our rubbers with the EVAs must be addressed on a case-by-case basis. As a general rule, our products are compatible with EVAs. However, we can encounter problems when blended with EVAs with a high vinyl acetate content. The only way to know for certain is to try a blend with the EVA in question keeping in mind the mixing order specified above.
NSE’s Norst® Polymers can also be used to modify SBS or SIS block copolymers. There are limitations however. We have found that the percentage of NSE polymers in the formulation must be over 75% or under 25% to achieve good results. Blending NSE polymers and SIS or SBS in approximately equal amounts generally does not work well.
Most coal tars and alpha-methyl-styrene resins are highly incompatible with NSE polymers due to their aromaticity. There are a few coal tars which are non-aromatic, although they may not be advertised as such. For this reason, it may be worth trying these if you really want to use them.
Gel development is almost unheard of. However, if it should take place, Ethyl 330 from Ethyl, Wingstay L from Goodyear, and Irgonox 1010 from Ciba-Geigy have been found to be effective stabilizers at 350°F.
Tufflo Oils from Calumet Specialty Products – some are water white and may be useful in adhesive formulations.
Avoid polar solvents. Polar polymers such as urethanes, acrylics, polyesters and polyamides are also generally incompatible
Blending Norst® Polymers
Each of our polymers offers distinct advantages, so depending on the type of adhesive you are trying to formulate, you may want to consider one polymer alone or a blend of two or three polymers to achieve the desired balance of properties in your formulations.
As a means of initial evaluation, you may blend one or two or three polymers with an equal part of resin.
1 part PB 800
1 part PB 600 or PB 500 or PB 400
2 parts Wingtack 95
This will allow you to get an idea of the nature of the rubbers, for use as a guide to make your desired formulations for testing.
Following are notes on each of these polymers as potential blends with the others:
PB 400 – We know of no approximate equal in the industry. This blend of EPDM and butyl rubbers provides a softening point much higher than that which is typically found in these hot melts. The crystalline nature of the PB 400 provides a softening point in excess of 350°F. This necessitates that it be processed at higher temperatures in order to completely remove the crystallinity. The PB 400 does have good adhesive properties by itself, but you may want to consider blending it with a tackifying resin and the PB 800 or the PB 402-24 to improve its elasticity and/or tack.
PB 500 – This product offers the high softening point and tack of the PB 400 with the elastic strength and tack of the PB 800. This “single package” approach may be more convenient if it provides the desired balance. If it does not have the exact balance of desired properties, simply add PB400 to raise the softening point, or PB 800 to increase the elastic strength, or PB 402-24 to increase aggressive tack.
PB 600 – Also adds a higher softening point and tack of PB 500 and PB 400. Desired balances may be achieved by adding PB 800 or PB 402-24.
PB 800 – This will stop the cold flow of the PB 402-24. It is most often used for the strength and elasticity it provides to a hot melt formulation. It is a rubber with a lot of general “guts” and will build strength in a hot melt without affecting the softening point. The PB 800 has strength approaching that of the Kratons, and is often considered as a low cost replacement for Kraton.
Some customers use PB 800 for pressure sensitive adhesives all by itself; others blend it with PB 402-24 for higher tack; others may use it alone or in combination with the PB 400 as a conventional hot melt.
PB 402-24 – A very soft, very elastic and very tacky rubber widely used for pressure sensitive adhesives; this is particularly outstanding for its tack and adhesion. It is a polyisobutylene product that may be likened to the LM type Vistanex from Exxon, but we believe that it offers better elasticity, tack and adhesion at a lower cost
It is especially suitable for low temperature applications, since it retains its tack and adhesion even at low temperatures. The PB 402-24 does have cold flow, but the cold flow can easily be overcome by blending it with PB 400, 500 or 800. PB 402-24 is suitable for high temperature applications up to 450°F.
PB 402-24 can be provided at 100% solids or 70% solids in mineral spirits.
PB 403-34 – Similar to PB 402-24, except can withstand high temperatures up to 650°F.
PB 404-44 – Similar to PB 402-24, except can withstand high temperatures up to 800°F. PB 404-44 was initially developed for use with autoclaves.
PB 4015 – A very tacky, pressure sensitive, butyl rubber compound with low viscosity – about 40,000 cps at 350°F and no cold flow. PB 4015 performs very nicely as a hot melt adhesive when blended with a C5 tackifying resin such as Wingtack 95 or Escorez 5300.
Typical formula for bright white caulks, not using soy oil.
112 parts PB 4015 – 100% solids 1 part TiO2
250 parts Drikalite 1 part ESS5 Mini Fiber
20 parts Escorez 5300 Mineral Spirits
Add all the above items at once to the mixer – the solid resin will dissolve quite readily. Usually, the thixotrope (ESS5 mini fiber) is added at the end of the mix, and the final amount of solvents added to adjust the extrusion rate or gunning ease. The thixotrope and the solvent concentration are balanced according to your requirements with the objective of maintaining the highest possible solids concentration. The suggested solids level is at least 85%. Usually 87-88% solids can be obtained.
Other calcium carbonates can be utilized, with a preference for the largest particle sizes. Another such possibility would be Marble Dust. VM & P can be used in place of mineral spirits and will aid sag control.
An interesting alternative to the PB-4015, if you wish to make a non-drying, or permanently tacky sealant, is the use of our PB402-24.