Polyurethane adhesives are a proven choice for industrial bonding and adhesive requirements. From furniture, and automotive manufacturers to aerospace, construction, and electronics brands – polyurethane adhesives are used by some of the largest businesses across a countless range of industries and sectors.
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Whether referred to as PU adhesives, polyurethane glues, or polyurethane sealants, polyurethane adhesives offer unrivalled levels of versatility, and can be formulated to accommodate for any number of your adhesive requirements.
This aside, when sourcing polyurethane adhesives, or any industrial/large-scale adhesive supply for that matter, there are many questions that you need answering before you can begin your order. If you’re wondering “what are polyurethane adhesives?” or “what adhesive formulation is best for my application?” – you are in the right place.
In this pu adhesive guide – we cover everything you need to know about polyurethane adhesives. For more information and advice, including order quotes and custom formulations, speak to our friendly experts today.
Quick Guide:
Polyurethane adhesives (PU adhesives) are polymer-based glues generally used in high strength bonding applications. Polyurethane systems used for adhesives can be separated into two main classifications, 1K (one-part) and 2K (two-part) systems, which share many similarities. All polyurethane adhesives use the same fundamental chemical reaction, this being a reaction between a diisocyanate and a polyol.
This chemical reaction is known as polymerisation: a process where monomers (such as the diisocyanates and polyols) join to form long polymer chains. The polymerisation of polyurethane glues lends to its trademark adhesive properties, making it an ideal choice for any bonding, joining or adhesion application where strong bonds are required.
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Polyurethane adhesives can be used to bond a wide variety of substrates. Offering a high resistance to water, PU adhesives are ideal for manufacturing parts and components that are intended for use in outdoor or exterior applications.
Suitable substrates:
Common uses for businesses:
Polyurethane adhesive systems are an ideal choice for a range of business needs. At Chemique, we can provide everything you need to get started, overhaul or improve your adhesive usage, including custom PU adhesives and application equipment. We can build and install manual and automatic application systems for rolling, spraying or beading to maximise your potential.
Need polyurethane adhesives or industrial adhesives for your business? Whether you opt for one of our existing brands (such as Solfre, Turftak or Axil) or a custom manufactured solution, we provide the adhesives you need that fit your business. Speak to us today to discover how we can help.
Two-part polyurethane systems are manufactured and supplied as separate components. For the polymerisation and crosslinking (curing) reaction to take place, the two primary components (diisocyanate and the polyol) must be mixed just prior to use. The components must be combined in the correct ratio to ensure the polyurethane glues/adhesives have the correct physical properties as required.
What this means for you: Two-part PU systems (2K PU systems) offer fast curing times, excellent control over final properties, and strong, durable bonds that you expect when selecting an industrial-scale adhesive. As they are supplied and stored in separate components, 2K systems generally have a long shelf life (even when opened) with the advantage of not curing unless mixed – this allows you to reduce waste by only using the quantities you require.
One-part PU systems (1K PU systems) require water to be present to crosslink/cure, which can be derived from moisture in the atmosphere. Depending on the exact type of 1K system used, a water mist may be required to crosslink the adhesive prior to the second substrate being bonded.
What this means for you:
As the diisocyanates and polyols are pre-mixed, one-part PU systems can reduce the time and labour required for preparing the adhesives for use, simplifying the process. This can also offer certainty that the adhesives are prepared to the correct ratios, maintaining consistency in your use. As one-part PU systems are moisture or water activated, the adhesives must be correctly stored once opened and used within the correct time frame to prevent premature curing in the container/bottle. Depending on the size and scale of your adhesive use, however, this may not be as large of a concern.
Most substrates that bond with a one-part system will also adhere with a two-part system and vice versa. Consequently, the choice you make between one-part or a two-part adhesive can depend on your use requirements, and what will benefit your business most.
Two-part systems are guaranteed to achieve full through-cure in a specified time, but the two components will need to be properly mixed in the correct ratio. In contrast, a one-part system may be easier to apply and require no mixing; but could require water-misting. It is important to remember that the cure time will be more affected by ambient conditions. Therefore, the desired application method of the adhesive along with any time constraints will influence which system to use.
At Chemique, we regularly help businesses in their decision between one-part and two-part polyurethane adhesives. Sometimes a business may need a blend of the two systems to suit different areas and uses for adhesive applications.
If you’re stuck deciding between the two polyurethane adhesive systems, we are on hand to help you. From discussing your operations and adhesive requirements, and custom formulation options, to the impacts on efficiency, product quality, and more, get in touch with our friendly experts to find your solution, today.
There are many advantages to using polyurethane adhesives in your business operations. These include:
The polymerisation/chemical reaction of the diisocyanate and the polyol in polyurethane adhesives has a significant influence over the physical properties for bonding and adhesion.
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Polymerisation greatly increases the molecular weight of the adhesive, with the long polymer chains creating strong intermolecular forces (e.g. van der Waals forces) and strong internal bonds within the adhesive itself. As a result, polyurethane adhesives have high cohesion properties which are crucial for forming durable, strong and long-lasting bonds.
Polyurethane adhesives are often crosslinked, meaning the polymer chains are bonded to each other at numerous points. This produces a strong and rigid network of bonds once cured which greatly increases the adhesive’s strength, durability, and resistance to heat and chemicals.
Additives can also be included in the manufacture of polyurethane adhesives to tailor their specific properties for various applications. From catalysts, plasticisers, and stabilisers to thixotropic agents, colourants, and flame retardants, additives can control and tailor a number of properties, including: curing time; bond flexibility; protection against heat, light, and moisture; viscosity/thickness; colour; fire resistance.
At Chemique, we have over 35 years of experience as pioneers in polyurethane adhesive systems. We manufacture a complete range of adhesive solutions to supply leading businesses worldwide with high-quality, dependable, and cost-effective products.
From our Solfre panel lamination range to our Turftak artificial turf adhesives, we cater to a complete range of business needs, supplying one-off or repeat orders for any volume you require.
We also offer a Total Service Package offering for businesses which includes: tailor-made/custom adhesive solutions (including custom polyurethane adhesives); full engineering and technical support; comprehensive training; product demos and samples; after sales support and advice, and more.
The molecular chain of waterborne polyurethane resin is generally linear or branched, and the strength of the film without crosslinking is lower. In order to improve the water resistance, chemical resistance, high temperature resistance and mechanical properties of the cured film, it is necessary to appropriately increase the degree of crosslinking during the synthesis of the resin, or insert some crosslinkable groups, or add some crosslinking. It can produce enough cross-linking during curing to form a film to form an interpenetrating network system or a polymerized cross-linking system to meet various requirements.
The cross-linking modification of waterborne polyurethane can be divided into internal cross-linking and external cross-linking. It is a method of cross-linking linear molecular chains into a network structure through a chemical cross-linking modification method to improve the water resistance of the material.
Internal crosslinking modification usually selects a trifunctional or higher alcohol instead of diol, or selects a trifunctional or higher isocyanate to replace part of the diisocyanate as raw materials to produce a certain degree of crosslinking and branching waterborne polyurethane.
The external cross-linking method is equivalent to a two-component system, that is, adding the cross-linking agent component to the water-based polyurethane main agent before use. During the film formation or heating after the formation, a chemical reaction occurs to form a cross-linked film.
Compared with the internal cross-linking method, the obtained emulsion through external method has good performance. Besides, the performance of the film can be adjusted according to the variety and dosage of different cross-linking agents. The disadvantage is that it needs to be configured before use and has a limited pot life.
There are two types of isocyanate crosslinkers used in waterborne polyurethanes, hydrophobic and hydrophilic.
Hydrophobic isocyanates such as HDI trimers, IDI trimers, and IPDI trimers are added to waterborne polyurethane and must be dispersed under high shear.
The hydrophilic modified aliphatic polyisocyanate is easier to disperse in water, and the polyisocyanate can be more uniformly dispersed by mechanical mixing. This water-dispersible polyisocyanate has become the main crosslinking agent of waterborne polyurethane and is used as the room temperature crosslinking component of two-component waterborne polyurethane coatings and adhesives.
Dispersible polyisocyanate crosslinking agent products are mainly aliphatic, because aliphatic polyisocyanates react very slowly with water, leaving active NCO to react with the hydroxyl groups in the film during the film formation process. These polyisocyanate crosslinkers are generally 100% non-volatile liquid polyisocyanate products, and a few are organic solutions of polyisocyanates, with solvents such as butyl acetate and dipropylene glycol dimethyl ether.
The general addition amount is 1%-5%, and the pot life is 4-6 hours. Adding too much will cause the film to be harder, and it needs to be sealed and stored.
The aziridine (aziridine) can react with carboxyl and hydroxyl groups at room temperature. Compounds with multiple aziridine rings are suitable as carboxylic acid type waterborne polyurethane crosslinkers, mainly to improve water resistance.
There are such products at home and abroad. It is added to waterborne polyurethane and mainly reacts with carboxyl groups. Generally, it should be used up within 24 hours. It can also self-polymerize under acidic conditions. The general dosage is 1%-4%.
However, aziridine compounds are toxic, have ammonia odor, and are expensive. It is relatively stable under alkaline conditions. Some people believe that adding aziridine to alkaline emulsions to form an internal cross-linking system can be cross-linked by controlling the pH of the emulsion.
Polycarbodiimide crosslinking agent is a light yellow transparent liquid, which can improve the adhesion to special substrates. Polycarbodiimide can be used as room temperature crosslinking of carboxylic acid type waterborne polyurethane, etc., and can exist stably in PU emulsion, and its crosslinking reaction is carried out by acid catalysis.
Due to the volatilization of water and neutralizer during the drying process of the coating film, the pH value in the film will decrease, which provides conditions for the occurrence of cross-linking reaction. The dosage is generally 5%-10%, and some are even less, and the pot life is about 12 hours.
Compared with aziridine cross-linking agent, polycarbodiimide does not affect the yellowing property. Common carbodiimide crosslinking agents are difficult to disperse in water, and can be modified with PEG to make them easy to disperse.
In addition, there are crosslinking agents such as epoxy compounds, epoxy silanes, N-methylol compounds, and polyamines.