Polyester casting resin R&G, crystal clear

Unsaturated polyester resins (UP resins) belong to the plastic family of duroplasts. They cannot be reformed once they have hardened, are insoluble, cannot be melted or welded and will char at high temperatures. Cured polyester resins are highly transparent but are only UV resistant when – like the ones we have on offer – they include the suitable additives. Polyester casting resins can be coloured very well using DYES FOR SYNTHETIC RESINS

Cold curing of the UP resins requires the addition of peroxide hardeners (benzoyl peroxide or ketone peroxide: e.g. MEKP) and small amounts of an accelerator in order to start the chemical reaction going. The resins that we have on offer come pre-accelerated with a cobalt accelerator from the factory.

Not only for casting seahorses in synthetic blocks but for model making as well: the so-called unsaturated polyester resins (UP) are the right choice anytime transparent bodies need to be created. The disadvantages include having to take into account a great deal of shrinkage (approximately 7 to 10%). UP resins´ main use is in the production of glass fibre reinforced plastic. For this use – lamination – we are readying as fast as possible a comprehensive product line for you.

Storage and Shelf Life: Polyester resins must be kept closed, cool and protected from light. In the closed original packaging they can be stored between 3 and 6 months at room temperature (preferably colder).

Safety at the Workplace: Polyester casting resin is inflammable and hazardous to your health because of the styrol that it contains. The MEKP hardeners work as fire accelerators and are caustic. There must be good ventilation at the work station and contact with skin and eyes should be avoided at all costs by means of, for instance, wearing chemical resistant GLOVES and protective glasses. A barrier cream is recommended for the cleaning and care of your skin. Beyond that, polyester casting resin is hazardous to water and must not be allowed to enter into the plumbing, bodies of water or the soil.

Please take note of the dangers and the safety information on the package and the information titled “Safety at the Workplace” found under “Casting Resins”. We will be glad to send you safety data sheets upon request.

Treatment: In the case of polyester resins, the mixing ratio is dependent on the amount being used. The most accurate way to add the extremely small amount of hardener required as a percentage of volume is to use a pipette or a DISPOSABLE SYRINGE. The working time and the de-moulding time is also determined by the amount of hardener used. The relevant data can be found at the individual products. If the resin is worked with in low temperatures (but not less that 16 °C!), the amount of hardener can be slightly increased. All in all, it is more practical not to try and force the curing process through the addition of large amounts of hardener because that can lead to stresses or even cracks in the material and to a yellowing of the material to boot. Amounts of hardener larger than 5% will make the resin soft.

Metallic, inorganic or organic objects can be used for the purposes of embedding as long as they are completely dry. Moisture – or older MEKP hardener as well – will cause striations to form in the material. Casting moulds can be made from materials that have smooth, polished surfaces (glass, metal, plastic). Transparent moulds allow one to check on the casting process with regards to the development of bubbles. Moulds that are made from non-releasing materials must definitely be treated with a release agent beforehand. Silicone moulds and PP or PE moulds release themselves from the moulded piece. But it should be noted that even with these moulds some adhesive residue can occur. The following can help in these instances:

• Use a RELEASE AGENT,
• Heat the mould before the pour,
• Add a bit more hardener,
• Pour the mixture into the mould shortly before it begins to gel.

Large volumes of polyester casting resin can be used at one time but does have the disadvantage as compared to PUR casting resin that is has much more shrinkage when hardened (7 to 10%!). Large blocks should not be poured all at once because the resulting heat from the reaction can create a high degree of tension in the material and thereby cause cracks. It is much better to do the work in many stages of 2 cm thick layers.

Embedding of objects is done in the following manner: first a layer of resin should be poured on the bottom of the mould to form a base and be allowed to begin curing – the resin begins to gel. The dry object should them be placed upon this layer whereby it will no longer sink into it. In order to be able to better monitor and remove any bubble inclusions, 10 to 20 mm thick layers should then be poured one after the other. Each layer should be added after the heat from the reaction occurring in the previous layer has subsided. As it hardens, the moulded piece usually separates itself from the wall of the mould by virtue of the shrinkage that is typical for polyester. Thereby it is possible that, especially in the case of smaller objects, a small amount of sticky residue may remain on the surface. This is caused by the contact with oxygen in the air. This smudgy, incompletely hardened film-like layer can be removed by means of WET SANDPAPER with a grit of 500 to 700 or by washing it away with ACETONE.

For the same reason, when a mirror smooth surface is the goal, the poured resin must be covered up at the area where it can come in contact with the air before it begins to gel but after all the air bubbles have risen to the top. For this purpose, glossy POLYPROPYLENE or hostaphan film will serve you well. If the moulded piece is not covered, the surface can display a certain glueyness which can be removed as described above.

During the hardening process of UP resins, it can be that, as a result of the action of exhaust gases which have concentrated themselves in air spaces like bubbles or simply under the covering film, the hardening process can be negatively effected. Polyester resins should therefore be poured as free of bubbles as possible and de-moulded or, alternatively, have the covering film removed as fast as possible after the cessation of the reaction heat.

In order to attain a high grade of hardening, objects that were produced at room temperature can be further hardened by exposing them to 80 °C heat (post curing). Both hardened UP resin and casting putty have similar mechanical workability. They can be sawn, drilled, sanded and polished with POLISH using both wood or metal working tools.

GTS and R&G polyester casting resins are medium reactive unsaturated polyester resins that are pre-accelerated with cobalt. Their most distinguishing features are their transparency and their UV resistance. These polyester resins are crystal clear when cured but can also be coloured (DYES FOR SYNTHETIC RESINS) quite nicely - which accounts for the fact that they are so often used in model making as well in the decoration sector (e.g. for moulding objects).

As is the case with all polyester resins, the mixing ratios between resin and hardener are dependent on the amount being employed. The most accurate way to add the extremely small amount of hardener required as a percentage of volume is to use a pipette or a DISPOSABLE SYRINGE. Please take note of the following data when working with these resins:

Mixing ratios for polyester casting resin R&G:

Please note that when more that 2.5% hardener is added to GTS casting resin it will become yellowish. Too much hardener will also lead to very high temperatures which, in turn, will lead to cracking in the material. Amounts of hardener larger than 5% will make the resin soft.

The working time and the de-moulding time are also determined by the amount of hardener used. The following data are based on room temperature.

Data for polyester casting resin R&G (1 kg mixture):

We only offer the polyester casting resin R&G in large quantities because it is so much less expensive in bulk than the GTS resin. On top of that, the R&G casting resin can be used to make as large as a 5 litre block in a single pour without the risk of cracks developing in the material. If the heat that is thereby produced bothers you, layers of between 2 and 3 cm thickness can be poured one after the other as soon as the reaction heat has subsided for each segment. These casting resins should never be worked with in temperatures under 18 °C.