Polyurethane adhesives — properties, types and applications

What are polyurethane adhesives?

Polyurethane adhesives are a type of adhesives characterized by exceptional adhesion and elasticity, which are the result of polymerization of components containing isocyanates and polyols. These products form bonds with high resistance to weather conditions, temperature, water  and various chemicals.

Importantly, they are more  resistant  to the action  of water,  solvents, oils and other chemicals  compared  to traditional adhesives, and also exhibit  high resistance to weather conditions and UV radiation. Therefore, their application is particularly valued in sectors requiring shear and tensile strength, i.e. construction, automotive or furniture production.

Key properties of polyurethane adhesives

• Adhesion. High adhesion capacity to many types of surfaces, e.g. metals, wood, plastics, ceramics and concrete. Their molecular structure allows for the

creation of strong  bonds with various substrates, which is crucial in ensuring the durability of joints.

• Flexibility. This property is particularly valued in applications where materials are subjected to dynamic loads, thermal expansion or other mechanical deformations.
• Chemical and  weather resistance.   This includes  hydrolysis,  ozone, UV radiation and  many  chemicals,  making  them  ideal  for  outdoor use.
• Thermal durability. This allows  them  to  be used in both very low  and high  temperatures.

Structure and production of sandwich panels

The production of PWS panels is one of the latest technologies. These sandwich panels consist of skin and a structural-insulating  core. In the production cycle, the core and the skin are connected using polyurethane adhesive. More and more often, the connection of several insulating sheets is performed by milling. The core of the panel is made of materials such as polyurethane foam (spray insulation), mineral wool, expanded and extruded polystyrene and others. Below is the structure of an example sandwich panel. Regardless of its purpose, properties or manufacturer, such a panel with a steel skin should consist of:

• two steel sheets, with any profile, which constitute the outer skin. They determine the appearance of the board and are responsible for functionality, especially under in terms of design;
• thermal insulation layer, which is located inside and provides adequate thermal and acoustic insulation parameters, and is also responsible for maintaining the appropriate distance between the skin, adequate the forces acting in the system.

The standard PN-EN 14509:2013-12 “Self-supporting double skin metal faced insulating sandwich panels – Factory made products. Intended uses. Specifications.” states that a product with such design can be a self-supporting structural element.

Read: https://www.products.pcc.eu/en/blog/installation-of-sandwich-panels-step-by-step-to-a-durable-structure/

Fig. 1 Example of a sandwich panel structure: 1 – steel core of the sheet, 2 – zinc coating, 3 – passivation layer, 4 – protective varnish, 5 – adhesive, 6 – prime coat, 7 – decorative surface layer, 8 – thermal insulation material core. http://www.inzynierbudownictwa.pl/technika,materialy_i_technologie,artykul,lekkie_pokrycia_z_plyt_warstwowych,9890

Types of polyurethane adhesives

Polyurethane adhesives are available in two main types: one-component and two- component.  Their division mainly affects the method  of application, and consequently the scope of use in individual industries.

One-component adhesives

One-component polyurethane adhesives are formulated so that  they contain  all the necessary components in one mixture. Their curing process begins after the adhesive is applied to the surface and exposed to air.

One-component polyurethane adhesives are used in many fields, including construction, automotive and furniture production, offering good adhesion properties and resistance to weather conditions and chemicals. In addition, they are appreciated for their ease of application.

Two-component adhesives

Two-component polyurethane adhesives consist of two separate components which must be mixed  just before  use. The first  component is polyol, and the second is isocyanate. Mixing  these two components initiates  a chemical reaction  that leads to the curing of the adhesive.

This category of adhesives offers higher strength and better resistance to extreme conditions, which is why they are used where special mechanical strength and chemical durability is required (for example, in the construction industry, when assembling heavy elements).

Example: https://www.products.pcc.eu/en/id/638728/sil-pur-80-3/

Use of polyurethane adhesives in industry

Polyurethane adhesives have a wide range of applications in various industries due to their exceptional properties, i.e., high mechanical strength, flexibility and resistance to various weather conditions and chemicals. The following sectors deserve special mention as they use adhesives most frequently: construction, industry, and automotive.

Construction

Polyurethane  adhesives  in  construction  are  used  due  to  their   durability, elasticity and  resistance  to  weather  conditions. They are  considered  ideal  for joining   structural elements,  such  as wall  panels,  roof  or  floor   insulation, as well as for installing windows  and doors.

Wood and furniture industry

In the wood and furniture industry polyurethane adhesives are valued  for  their strong  bonds and resistance to moisture — so important in the production of furniture and other  wooden  products.  Additionally, they are used to join  various  components, from wooden frames to laminated surfaces.

Automotive

Used, among others, in the assembly of windows, body elements and in the components of vehicle interiors. Their use enables the achievement of light,  but  durable  vehicles, which translates  into better  performance and greater  fuel efficiency.

Packaging industry

In the packaging industry, polyurethane adhesives are used for the production of multi- layer packaging  that requires  strong  and durable  bonds. Their resistance to water and oils makes them  ideal for food, cosmetics or chemical products packaging,  where  the integrity of the  packaging  and the  protection of the  contents  are a priority. These adhesives are used in both  flexible  and rigid  packaging,  ensuring safety and durability during  transport and storage of products.

Advantages of polyurethane adhesives

#1. High resistance to weather conditions

Polyurethane adhesives are particularly resistant to weather conditions (e.g. moisture, temperature and UV radiation), which is why they are perfect for external applications, where other types of adhesives could quickly degrade.

#2.Elasticity

Polyurethanes are characterized by natural elasticity, which allows adhesives to maintain durability and integrity even in the case of dynamic loads, vibrations or changes of temperature. This elasticity is key in applications that require the ability to stretch and twist without cracking or breaking.

#3. Strong bonds

Polyurethane adhesives create exceptionally strong bonds between various materials, including metals, wood, plastics and concrete. The strength of these bonds results from the deep penetration of the adhesive into the micropores of the materials, which increases the force of adhesion. This makes them an excellent choice for furniture production, structural assembly and any applications requiring impressive durability.

#4. Fast curing

Many polyurethane adhesives are characterized by a relatively short curing time, which is important in rapidly changing, dynamic production environments. Additionally, fast curing allows for the acceleration of assembly and production processes, increasing efficiency and reducing downtime.

How to properly apply polyurethane adhesives? Practical tips

1. Surface preparation

Before applying a polyurethane adhesive, make sure that the surfaces to be bonded are clean, dry and free of grease and other contaminants. Thorough cleaning of the surfaces may involve degreasing with a solvent and light matting.

2. Thorough mixing (for two-component adhesives)

If you are using a two-component adhesive, thorough mixing of components A (polyol) and B (isocyanate) is crucial for achieving optimal bond strength. Follow the recommended proportions provided by the manufacturer and mix the components thoroughly to ensure a uniform chemical bond.

3. Applying the right amount of adhesive

More is not always better. Using too much polyurethane adhesive can lead to overflow that, when it leaks out of the joint, becomes unsightly and difficult to remove. Too little adhesive, on the other hand, may not provide sufficient bonding strength.

4. Control of environmental conditions

Polyurethane adhesives react with moisture, so it is important to control environmental conditions during application. Too high humidity can accelerate the curing process, shortening the working time, while too low humidity can delay it. Optimal conditions for most polyurethane adhesives are room temperature and moderate humidity.

Manufacturers’ offering

The PCC Group, as a producer of specialty chemicals, in its portfolio also offers two-component and one-component polyurethane adhesives. One example of a two-component  adhesive is Ekoprodur 1331B2. It stands out as an adhesive for PWS polystyrene foam panels, but also for panels with a core of mineral wool or polyurethane. It is worth emphasizing that it is characterized by a reduced emission of volatile organic compounds (VOC), thanks to the fact that it does not contain foaming agents that cause depletion of the ozone layer. Another proposal for a two- component adhesive is RokaPur PR2K 105 K and Ekoprodur KW1.

Among the products, we can also find Ekoprodur KW-A2 (which is a polyol component) and EKOPROMER G20, which are components of two-component polyurethane adhesive. EKOPROMER G20 can also be used in construction alone as a one-component adhesive. Its characteristic feature is the durable bonding of building materials together and excellent adhesion.

Among the available adhesives for EPS or fiberboards, which can be joined with sheet metal, an example of a single-component product will be EKOPRODUR RB-2. It is a pre-polymer based on diphenylmethane diisocyanate (MDI). It is characterized by its versatility, is also easy to use and can be applied manually, e.g. with a spatula, but also mechanically. It is characterized by a high temperature tolerance during application, as well as excellent adhesion to substrates made of various materials. Other single-component adhesives that

you can find in the offering this RokaPur PR1K_15 (one-component primer for sandwich panels).

We offer a wide range of polyurethane adhesives, which differ in unique properties suitable for various applications. However, their key role is in the production of sandwich panels and this is a future direction in the construction industry.