When the liquid gradually evaporates from the material in the case of conventional paints and varnishes, these mixtures harden and acquire their physical and operational properties. But for some resins, such a process is not possible without additional intervention. Curing in this case is a consequence of a chemical reaction. During this, the mixture polymerizes and acquires the final structure.
What are hardeners for?
Hardeners of epoxy resins act as a catalyst for the reaction and participate fully in the process. They combine with the resin; as a result, it is possible to obtain the properties of the products according to the type of uniformity, hardness, durability and transparency. These characteristics are determined by how accurately the proportions were chosen when the resin and hardener were combined.
During self-mixing of ingredients, the correct dosage must be observed. Various substances act as hardeners, it can be anhydrides, carboxylic acids, diamines. In a mixture with the aforementioned hardeners, the resins form thermosetting compounds that have the following characteristics:
- high adhesion;
- good water resistance;
- excellent dielectric properties;
- mechanical strength;
- a small percentage of shrinkage.
Composition of different hardeners
Epoxy hardeners can be acidic or amine. The first include dicarboxylic acids and anhydrides. The curing of the resin using these mixtures occurs at elevated temperatures up to 200 ° C. These hardeners are hot cured.
Hardeners of epoxy resins are amine. This group includes different amines. This is the simplest and most common hardener. Under the influence of these substances, the resin hardens at normal temperature. There is a plus here, consisting in ease of use. There is no need to use special equipment. Such hardeners are popular, but more effective results can be achieved using acidic compounds.
When hot cured, the resin gains improved physicochemical characteristics. Among the hardeners of epoxy resins that belong to the acid group, dicarboxylic acid anhydrides should be distinguished, namely:
- methyltetrahydrophthalic;
- maleic;
- methylendic;
- phthalic;
- hexahydrophthalic.
These compounds have good dielectric properties, are resistant to temperature influences and contact with moisture. They are often used for electrical insulation and as a bonding element for reinforced plastic. Among the substances of the amine group, it is worth highlighting:
- triethylenetetramine (THETA);
- polyethylene polyamine (PEPA);
- aminoacrylates;
- polyamines.
Application and proportions of some hardeners
In order to get acquainted with the hardener, you should know its characteristics. For example, diethylenetriamine, which is also indicated by the following abbreviation - DETA, is liquid transparent, has no shade. Shelf life is 2 years at temperatures ranging from - 5 to + 40 ° C. The substance has an ammonia odor. The recommended curing mode is in a day at a temperature of + 25 ° C. If this limit is increased to plus + 70 ° C, then curing will occur in 5 hours. The material is exothermic, which means that the curing process will be accompanied by an increase in temperature. It cannot be used for filling volumetric parts.
Before starting work, you may wonder how much hardener for epoxy is required. In the case of the described substance, the volume can vary from 8 to 12%. This is true when combined with ED-20 resin. The analogue of PEPA is Telalit 0210. It is a viscous transparent hardener with a pungent odor. You can’t leave it open. There are no extraneous additives in it, so it is not so thermostable. Before use, you need to carry out a test batch.
RC-19
If you are wondering which epoxy hardener to use, you might consider RC-19, which has proven to be a substance that works well in high humidity and low temperatures. Consumption is 500 g per kilogram of resin. Gelatinization period - in half an hour. Suitable composition for casting large parts. Convenient for installation of bulk floors.
Epilox H 10-40
If you saw the marking Epilox H 10-40, then in front of you is a reactive hardener, which can be used as an accelerator for amine hardeners. It works at low temperature, which allows it to be used to create volumetric fillings. The viscosity of this material is medium. The recommended dose is 50 parts per 100 parts of resin.
DIY hardener
You can even prepare a hardener for epoxy with your own hands, but its quality will be doubtful. This need arises quite often, because hardeners are sold complete with resin, but the first component is not always enough. It is quite difficult to maintain the exact dosage, so the hardener is consumed faster.
In the construction market or in a store, it is quite difficult to find a hardener. Before home craftsmen, quite often the question arises of replacing or self-manufacturing a component. At home, it is almost impossible to replace the hardener. The improvised means are completely unsuitable, it is necessary to purchase the appropriate chemicals - hardeners, which are little known. Among them, the Etal-45M should be highlighted. The method of use of such a substance may differ from the use of conventional polyethylene polyamine. You will have to select the most suitable ratio of hardener and resin in a test method.
Self cooking
However, several options for making a hardener at home still exist, but the effectiveness remains dubious. One option is to add dry alcohol to the resin. Urotropin tablets should be crushed into powder and mixed with resin. It is necessary to use a ratio of 1 to 10. In this case, some masters recommend leaving the prepared mixture for up to 10 hours. After it acquires viscosity, you can use the substance for its intended purpose.
Features of the application. How to breed
If you observe the technology of mixing the hardener with the resin, then you can achieve a positive final result. All components of the mixture are measured according to the instructions. For work it is necessary to prepare:
- a wooden stick;
- mixing container;
- two syringes.
A stick is needed for mixing. Before diluting an epoxy resin with a hardener, it is important to remind yourself that the reaction is irreversible. It is better to practice on test samples, use a small amount of material for this. This will allow you to determine the proportions and understand how much the resin will dry. It is heated above room temperature before mixing. The substance should become less viscous. If the resin has crystallized, it is returned to its original state, heated to a temperature of + 40 ° C. In this case, stir the mixture constantly. Warming up is best done in a water bath.
It is important to avoid overheating of the resin, since after boiling it will become covered with foam, being unusable. In the syringe, dial the resin and place it in a glass. You must calculate the dosage in advance. The required amount of hardener should be typed by adding it to the container with resin. The composition mixes well to a homogeneous consistency, and you cannot use electric tools.
After the transparent epoxy resin with the hardener is mixed, it can be considered that the mixture is ready for use. It is applied to the desired area, where the composition gradually hardens. The mass must be worked out quickly enough, because within a few minutes after mixing, the polymerization will begin. The structure of the substance will change, which will adversely affect the characteristics of the hardened epoxy.
Some modern compositions
On sale today you can find modified hardeners, which are devoid of some of the disadvantages of traditional mixtures, but their cost is slightly higher. Finished products gain high strength characteristics, the resin polymerizes more fully. These agents play the role of plasticizers, and in some cases are able to plasticize and dilute epoxy.
Among others, hardener M-4, which is an amine and has a high viscosity, should be highlighted. Its color is reddish brown. Mixing is carried out in a volume of 20 to 25% of the base material. The substance cures epoxy at a temperature of + 2 ° C, as a result it is possible to obtain a product with increased strength.
The tool is a fast-curing substance and is made on the basis of PEPA. In addition to cold curing, you can make hot polymerization. The plasticization and gelatinization time will be 30 minutes at room temperature. If the temperature is lower, then the time may increase up to 50 minutes.
If you want to combine a transparent epoxy non-shrink resin with a hardener, you can consider substance 921, which is sold in several varieties. The tool is low viscosity, allows you to get unique epoxy compositions. They are resistant to ultraviolet and damage.