Depending on the solvents used, adhesives are classified in one of the following ways:
- Water-based adhesives: Water-based adhesives use water as a carrier for the adhesive. They are generally non-hazardous and environmentally friendly, containing no VOCs. These adhesives also have a high solid content, providing stable bonding. They are non-flammable and dry more slowly than solvent-based adhesives.
- Solvent-based adhesives: Solvent-based adhesives use solvents as a carrier for the adhesive. They are suitable for long-term applications and are ideal in industries where application and production speed are required. Solvent-based adhesives are more chemically resistant than water-based adhesives, withstand a wide range of temperatures, and provide high bond strength.
What are solvents?
Solvents are diluents used in the adhesive industry to provide beneficial properties necessary for the effective functioning of adhesives, especially when it comes to maintaining spreadability. The chemical industry worldwide, particularly in coatings production, consumes excessive amounts of solvents. To achieve a smooth and uniform coating with paint or adhesive, appropriate solvents are required.
What types of solvents are used in the adhesive industry?
Toluene
Toluene, an aromatic hydrocarbon consisting of a benzene ring linked to a methyl group, is a very effective solvent. Unlike water, toluene can dissolve several organic compounds, and due to its low toxin content, it is used as an alternative to benzene.
Isopropyl alcohol
Isopropyl alcohol, such as isopropyl alcohol, is the best choice of solvent for plastic materials. Isopropyl alcohol dissolves a wide range of nonpolar compounds, evaporates quickly, leaves little oily residue compared to ethanol, and is relatively non-toxic compared to alternative solvents.
Methyl ethyl ketone (MEK)
Methyl ethyl ketone, also known as butanone, is an organic solvent that serves as an excellent degreaser for heavy industrial oils and lubricating materials. It can also be used for cleaning certain adhesives, varnishes, and latex paints. It has a high evaporation rate, though not as fast as acetone.
Xylene
Xylene is a colorless mixture of chemically related hydrocarbons that is often used as a solvent for paints, adhesives, and latex paints. It is highly effective in dissolving compounds that are poorly soluble in water.
Ethanol
Ethanol easily mixes with water and other organic compounds, making it an effective solvent for use in paint coatings.
Due to the numerous advantageous properties of solvents, many industries, especially the chemical industry, require large quantities of solvents for their production. This has a direct impact on the environment, and in recent years, there have been many discussions and studies on the adverse effects of solvents on the environment. The main conclusion of these discussions is that the use of solvents needs to be reduced.
These studies prompted the R&D team at Adhesive Specialities to conduct research comparing adhesives containing different solvents. They tested rubber adhesives with varying toluene solvent content and obtained the following results:
| 55% Toluene in Solvent | 80% Toluene in Solvent | |
| Shear Test | 4 hours | 2 hours |
| Production Speed | 8 | 6 |
| External Characteristics | Clarity of the coating immediately after application | Formation of bubbles during coating application |
The results clearly showed that by reducing the amount of toluene, they could improve the product quality and make it more cost-effective.
There are other benefits discovered during the research, and they include:
- The production speed will increase by 25%, as with less solvent, it evaporates faster, and the drying speed of the adhesive is also reduced.
- Shear strength, or the setting time of the rubber adhesive, has increased by 2 hours, clearly indicating that reducing the amount of toluene in the solvent has improved the adhesive’s strength.
- Reducing the amount of solvents in the adhesive also reduces the amount of emissions into the environment. This helps to mitigate the negative impact on the environment.
- The tape with less solvent content has almost no residual content, thereby creating a better and shorter curing cycle.
- By reducing the toluene content, the rubber could be more efficiently crushed and mixed with all additives and resins in the recipe.
- The overall aesthetic value of the tape is better when there are fewer solvents.
Without a doubt, it can be concluded that with a lower content of toluene, the properties of rubber adhesives improve. Reducing the amount of solvent makes the product more efficient, economical, ensures faster production, aesthetics, and most importantly, supports environmental cleanliness.
Thus, fewer solvents mean more benefits.
