Using polyurethane adhesives instead of traditional resins for bonding purposes is increasingly on the rise in the industrial world, both due to their composition and their benefits.
This article will guide you through the world of polyurethane adhesives to understand their advantages, chemical composition, reaction times, technical features and usefulness.
To start with, let’s explain the term ‘polyurethane resin’. This is a reactive substance that perfectly adheres to a number of substrates. It is versatile and provides top performance levels, including flexibility and the ability to create a strong, long-lasting joint.
They are structural adhesives, which means that they do not simply bond two materials together, but become one with them, an integral part.
Plus, they are also renowned for their ability to withstand high mechanical stress and in some cases they can indeed replace traditional joining systems such as welds and screws.
SINGLE OR DUAL-COMPONENT?
Expanding polyurethane resin consists of two macro categories: single-component and dual-component ones.
These are glues whose main component, a prepolymer (NCO), is integrated with other chemicals (additives, solvents, etc.). After being applied, it reacts with the moisture content of the substrate and air, and forms covalent bonds with the material’s surface.
Dual-component polyurethane has an entirely different chemical formula.
It consists of a polyol blend (component A) and a hardener (component B) which, when mixed, react to produce a polymer of urethane bonds by polyaddition.
Other chemicals can be integrated to adjust chemical and physical properties for the dual-component adhesive as well.
WHAT’S THE RIGHT GLUE FOR MY INDUSTRY?
At this point, you might wonder when you should use a single component adhesive rather than a dual-component one.
Here are the main factors to consider when choosing the adhesive:
- Environmental conditions.
Temperature and humidity are the two main environmental factors to take into account as they affect the reaction of the glue.
Indeed, if using a single-component glue you need to consider that the higher the environmental humidity and temperature, the higher the reaction speed of the adhesive.
- The type of surface.
Depending on the moisture in the substrate, you may use a 1K adhesive rather than a 2K one. As a general rule, singe-component adhesives are used in materials containing moisture (such as wood) as the latter allows for a strong bond.
A dual-component glue is instead applied on surfaces that do not contain moisture, for example PVC.
- Surface thickness.
Thickness may indicate which kind of glue can ensure the best result. Most of the time a dual-component is used for thin materials to be glued to avoid undulations caused by the release of carbon dioxide.
- Item size.
In the case of large dimensions, you need to take into account that due to single-component glues might cause an unsuitable reaction due to environmental humidity and the material’s moisture content. The issue can be solved by wetting the surface or using a dual-component glue to obtain an even reaction.
- The technology.
Some prefer single-component glue just because it is easy to apply as it does not require complex tools to distribute it on the surface.
Dual-component glue instead requires a dispensing and dosing machine that mixes the two components before applying it.
- Adhesive reaction times.
The reaction times of the compound need to be compared with your production times in order to identify an adhesive that is roughly in line with them.
Here are the three main ones you need to know.
Il Pot Life: the interval during which the product can be used after being mixed.
This mainly concerns dual-component glues, as due to their nature they need to be mixed before applying them.
Open time:the available time to glue the two parts after applying the glue.
Press time: his is the time required to compress a product, a mandatory step for single-component adhesives, and ensure the adhesive reaches a polymerisation stage allowing for extraction and initial handling.
The press time may vary according to the reactivity of the glue: the higher the reactivity, the shorter the press time.
Please bear in mind that the reaction times of single-component glues may vary, again due to humidity, while dual-component glues have a constant process regardless of environmental humidity and moisture content of the substrate.
A dual-component adhesive may be the glue of choice also for those seeking a constant and well-defined process.
THE ROLE OF ADDITIVES
After explaining the two macro categories characterising the world of adhesives, the surfaces and times, let’s take a closer look at the chemical composition.
As mentioned, both glues are integrated with other compounds to modify the features of the adhesive according to its use.
Indeed, almost all adhesives, both 1K and 2K, contain substances that improve their performance, such as anti-foaming agents to reduce emulsion, charge dischargers to improve mixing for fillers and substances that increase adhesion in case of critical surfaces, e.g. glass, which is considered a hostile surface.
Moreover, fillers (or loads) are used to reduce shrinkage during drying or polymerisation, decrease the exothermic temperature during polymerisation, improve cohesive properties, abrasion resistance, flame and smoke suppression, moisture resistance, chemical agents and corrosion and obtain specific rheological properties.
Solvents, which are also present in small amounts, ensure greater regularity for some chemical properties of resin.
They improve viscosity and therefore process operability, wettability, adhesion on plastic substrates and add plasticity to the adhesive.
This begs the question: are there solvent-free adhesives?
Yes, although they are not easy to find on the market. Solvent-free glues are also called adhesives without VOC (Volatile Organic Compounds) that improve their toxicological properties.
Polyurethane adhesives generally have a natural colour ranging from cream to beige.
This should not hold back those who want a glue with a different colour, as pigments can be used to obtain the desired shade.
WHAT’S THE DIFFERENCE BETWEEN EPOXY RESINS AND POLYURETHANE RESINS?
Epoxy resin, particularly renowned in the flooring field, also falls within the category of thermosetting polymers.
They both have a good chemical resistance and set quickly, though some of their properties differ.
The first difference is related to the operating temperature, an essential factor to consider when talking about fixing systems to prevent the compound from losing its quality.
As an indication, epoxy adhesives work at a higher operating temperature – approximately 150°C – than polyurethane glues, which reach a maximum of about -100°/+80°C.
Main analyses – Differences between epoxy and polyurethane adhesive
First of all, to understand whether it is better to use an epoxy glue or a polyurethane one, once again we need to examine the bonding material. Secondly, we need to look at the working environment and the reaction times of the adhesive.
A damp environment or with sudden changes in temperature can lead to choosing one kind of glue over another one.
If for instance the workplace is exposed to UV rays, epoxy glue is not suitable due to its poor resistance to said rays.
We can say that one of the most obvious differences is related to the type of bonding.
Indeed, polyurethane adhesive ensures very flexible bonding, which means it is more versatile due to its mechanical properties, given the option of creating a compound with varying elasticity.
Epoxy adhesives are known for their lack of flexibility and elasticity and are usually referred to as ‘glassy’ glues.
This is precisely why they are frequently used in the construction sector, especially for floors, to ensure a sound and rigid result.
When looking at the bonding material, epoxy glue is usually the adhesive of choice when the surfaces are the same, while with two different materials (such as a panel made of polyurethane and PVC), polyurethane glue ensures a stronger bond.
Lastly, if we consider the economic component – which may be more or less influential – polyurethane systems are more cost-effective.
Suprafix is the range of industrial polyurethane resins that Europoliuretani manufactures in its laboratories.
Suprafix is a casting polyurethane resin and thanks to the extensive knowledge and experience of our chemists in the sector, we formulate it and produce it according to our customers’ needs.
In other words, we are able to design a specific chemical formula of the adhesive for your bonding by examining all the factors involved.
Features of the Suprafix polyurethane adhesive
Suprafix is available in a single or dual-component version, with or without solvents, and above all, it does not contain formaldehyde or heavy metals.
Suprafix exceeds the main features required on market: it is resistant to high temperatures and provides unparalleled weatherproofing, as well as being water repellent.
Bio- based Suprafix
We have a strong environmental focus and we believe it is vital to make a significant contribution to safeguarding the planet.
We have replaced composites in our polyurethane systems, thereby creating a plant-based system, such as castor oil, and a natural one.
Nowadays, R&D is used to seek technologies to improve adhesives while preserving ecosystems as much as possible.
Experimenting with new, less harmful additives with fewer emissions and less aggressive solvents, is one of our missions.
Because of its quality, Suprafix complies with the following certifications: the RINA (rules for the certification of marine equipment)certification, which is particularly required in the naval sector.
The EN204-205 – class D4 standard, a classification that certifies the excellent use of the adhesive on wood thanks to its water resistance.
EN14257, a certification that confirms Suprafix’s resistance for wood against heat and high temperatures.
Our experts are at your service to identify the type of adhesive, carefully examine your sector, bonding materials and carry out sampling tests to find out which glue guarantees the best result.
A poor choice involves a number of risks, including first of all damaging the appearance of the surface, causing the material to shrink, air bubbles, and non-lasting bonding.
Moreover, experts are at your side not only to find the right adhesive, but also to help you store the glue so that it does not lose its properties.
We are happy to assist you and produce the right industrial polyurethane adhesive for you.