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Modern Waterborne Adhesives

Driving forces and market trendsOriginally, all furniture and matrasses adhesives were applied by brush, but with the need to im- prove production efficiency and cost, the indus-try has tended towards spray-applied adhesives for some applications, such as mattresses and furniture which were predominantly based on solventborne SBR/SBS*.

Solventborne adhesives have been traditionally used worldwide. But EPA regulations have forced the industry to reduce air pollution in mattress production, prohibiting in 2008 the use of adhe-

sives containing methylene chloride (MeCl), as MeCl poses health risks to anyone breathing air containing this compound. This is one of the reasons why the use of waterborne adhesives in developed markets like Western Europe has become significantly more important in mattress

and upholstery production during the past decade. Furthermore, waterborne contact adhesives are an important factor in meeting the requirements of various eco labels, e.g. Blauer Engel or Öko-Tex Standard 100. However, emer-ging markets are still predominantly working with synthetic rubber-based adhesives (SBR, SBS and SBI)*.

The forces currently driving the upholstery and mattress markets are similar:

• A growing consumer demand for more com-fortable and relaxing mattress and furniture materials

• Increasing sustainability requirements from key players such as IKEA

• The need to reduce production costs as a result of increasing price pressure

• More stringent workplace and consumer safety requirements to ensure compliance with REACH, VOC regulations and eco labels.

Waterborne contact adhesives do indeed play a key contributory role in the production of com-fortable mattresses and upholstery furniture by addressing industry needs such as production efficiency and environmental requirements. Wa-terborne adhesive technology is a key factor in supports the increasing demand for mattresses.

* SBR = Styrene Butadiene Rubber SBS = Styrene Butadiene Styrene SBI = Dihydroxy tetramethyl spiro diindac

Inventing Modern Waterborne Adhesives For YouAlthough solventborne adhesives are still widely used in the production of mattresses and fur-niture, there is a growing demand for waterborne solutions due to changing legal requirements, workplace hygiene considerations, and safety issues. As a result, adhesive, mattress and furniture manufacturers are increasingly looking for alternatives to the conventional solventborne formula-tions. The advances achieved in waterborne, polychloroprene-based contact adhesives in recent years make them an attractive alternative.

02 Modern Waterborne Adhesives

It is not just for environmental reasons that waterborne 1K or 2K contact adhesives based on polychloroprene (CR) dispersions are replacing the traditional solventborne solutions. Even if the radically reduced volatile organic compound (VOC) content of the waterborne products is an

increasingly important argument in their favor, waterborne solutions also offer outstanding performance qualities: at least similar initial bond strength combined with clear advantages in heat resistance, while requiring no specific safety precautions.

Foam Bonding

50,531

17.4 % 20.6 % 21.0 % 18.3 %

37.6 % 33.8 % 34.9 % 38.0 %

31.2 % 29.5 %34.3 % 34.3 %

13.7 % 16.1 %9.9 % 9.4 %

52,729 52,539 52,56654,600

56,275 [1000 units]

2010 2011 2012 2013 2014 2015

Others

Spring

Foam

Latex

17.1 %16.1 %

39.2 % 40.0 %

35.3 % 34.5 %

8.3 % 9.3 %

Benefits of waterborne CR adhesives

• Wet bonding possible on a variety of substrates and excellent early wet strength

• Significant improvement in initial and final bond strength as well as heat resistance by formulating with nano silica sol dispersions

• CO2 activation technology for 1K waterborne spray adhesives enables easy application for bonding foam to various substrates, including wood and several plastics.

Figure 1. Development of mattresses produced in EU27 in 1000sSource: Covestro analysis based on CSIL/EuroStat data

03 Modern Waterborne Adhesives

Clear trend from 2K to 1K Waterborne CR-based adhesives can be used as 2K systems in a spray-mix process with a coagulant, or as 1K systems either as the tradi-tional pH-reduced (destabilized) formulations or as CO2-activated formulations. More and more furniture and mattress manufacturers are turning to waterborne 1K adhesives not just because of environmental pressures and safety issues but because they are much easier to handle. 1K foam adhesives combine the full wet adhesion poten-tial of CR dispersions with the easy and reliable handling qualities of 1K formulations. Research is being undertaken to further improve the benefits delivered by waterborne 1K CR adhesives, e.g. by improving their wet tack properties for spray applications on a variety of substrates. Never-theless, 2K systems still perform best in some applications.

Sprayable CR contact adhesivesSprayable CR contact adhesives are of particular importance for foam-to-foam applications in the mattress and furniture industries.

Covestro’s Dispercoll® C toolbox offers a number of waterborne adhesive raw materials based on CR dispersions. These products display similar properties to solventborne materials, but have very low residual monomer content. The com-monly used 2K spray mix technology has two components: the adhesive, a Dispercoll® C-based formulation, and the coagulant. The two com-ponents are mixed during spraying and the film of coagulated adhesives guarantees high initial bond strength, even in the wet state, to ensure immediate foam-foam, foam-wood and foam-pla-stic bonding.

1K sprayable adhesives are also used for foam-to-foam applications and have the additional ad-vantage of easy handling. This technology is used less often for foam-to-wood applications due to the lower tack between the substrates.

CO2-activation technology improves sprayable 1K adhesives’ performanceTraditionally, 1K spray solutions were pH-reduced (destabilized) formulations, but CO2-activated formulations based on a patent application filed by Covestro are now providing an advantageous alternative. The CO2 activation method is based on the very soft and homogeneous neutralization of the anionic emulsifier. CO2-activated dispersi-ons display very high wet tack properties directly after application and are stable to coagulation in spite of a low pH (≈8.0). The 1K adhesive perfor-mance is similar to 2K waterborne spray-mixing and solventborne systems. In other words, CO2 activation is a very efficient, simple and cheap way of producing highly active spray adhesives that offer users the advantage of easy handling.

04 Modern Waterborne Adhesives

Polychloroprene rubber A traditional and well-established raw material for contact adhesives is polychloroprene (CR) rubber. CR-based,  solvent- or waterborne adhesives offer good initial adhesion on a wide variety of substrates. They are typically applied onto both substrates. During the adhesive’s open time the

substrates are connected under application of the highest possible pressure, which triggers the crystallization process through linearization of the polymer chains. Heat activation is not neces-sary, but does improve contactability and final bond strength. Cross-linkers can also be used to improve heat resistance and final bond strength.

Contact Adhesives

Solventbornephr*

CR solid 100ZnO 2MgO 4Resin 30MEK 170Ethylacetate 170Petrol (65/95) 170Cross-linker 0/7

Solids content 20 %Mixing time 8 h

Waterbornephr*

CR dispersion 100Antioxydant dispersion 2ZnO dispersion 0.5Silica sol dispersion 10-30Resin dispersion -

Cross-linker dispersion 0/7

Solids content > 50 %Mixing time 1 h

05 Modern Waterborne Adhesives

* parts per hundred rubber

CR-based adhesives – typical formulations

Improved initial wet strength though cross-linking If a waterborne CR adhesive is formulated by cross-linking the polychloroprene polymer (Dispercoll® C) with a nano-particulate silica sol dispersion (Dispercoll® S), the network formed between the polymer and silicone particles deli-vers several key benefits:

• Excellent wet bonding on leather and textiles with outstanding early wet strength

• Dramatically improved drying speed (up to 50 % faster dry-to-touch)

• Much improved heat resistance (better than solventborne adhesives)

• 20-50 % increase in bonding strength

Starting Formulations based on Dispercoll® C are available on request.

Winfried Jeske Field Technical Service Adhesives Covestro Deutschland AG winfried.jeske@covestro.com

Dr. Berta Vega Sánchez Marketing Manager Furniture Coatings & Adhesives, Covestro Deutschland AGberta.vegasanchez@covestro.com

For further information please contact:

Solvent- and waterborne CR adhesives have a similar final bonding strength, but the differences in their drying behavior and open time must be taken into account.

109876543210

Peel

str

engt

h [N

/mm

]

0 60 120 180

Time after adhesive application [min.]

240 300

CR solventborne CR waterborne

06 Modern Waterborne Adhesives

Conclusion With waterborne adhesives based on Dispercoll® C (74/84/2694 XP/2325, 2372/1) you can offer en-vironmentally friendly and efficient solutions for foam-to-foam (e.g. mattresses) and foam-to-wood bonding (e.g. upholstery furniture) – that provide the necessary heat-resistant adhesion and combine high bond strength with immediate and good wet tack properties, very fast bond formation and a soft bonding seam in 1K or 2K spray applications.