adh e s i v e s a n d s e a l a n ts

Performance comparison of adhesives

What are the differences? Anyone who wants to find the perfect adhesive to suit their application from the multitude of high-performance adhesives available on the market not only needs to know the different performance profiles but must also consider the practical conditions involved. What are the differences between the four common adhesive groups, silicones, MS-based hybrids or silane-terminated polymers, acrylic dispersions and polyurethanes?

Volker Weidmann

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igh-performance adhesives, which are increasingly replacing mechanical joining methods and are used in the manufacturing and construction industries, must have a performance profile that is matched to the assembly job concerned, Figure 1.

Figure 1: High-performance adhesives that are increasingly being used to replace mechanical joining methods in industry and construction must have a performance profile that corresponds to the assembly job involved.

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adhesion ADHESIVES & SEALANTS 1/2011

Anyone who wants to make the perfect choice for a specific job from the extensive and constantly increasing range of adhesives available not only needs to know the different performance profiles but must also consider how the adhesive behaves under practical conditions, for example with regard to moisture, temperature fluctuations or UV radiation.

It is important, therefore, to consider the differences between the properties of silicones, MS-based hybrids or silaneterminated polymers, acrylic dispersions and polyurethanes (PU), Figure 2. In this context, particular attention should be paid to PU adhesives, as these, as a result of stricter labelling requirements, fall under the regulations of the

Figure 2: Comparison of the properties of the most important adhesives groups for high-performance applications.

adhesives and seal ants

New general legal conditions for PU adhesives

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European Union

Chemicals Prohibition Ordinance in Germany with effect from 1 December 2010, including, for example, a ban on self-service sales, Figure 3.

Silicone adhesives: flexible and highly resistant

General

Sales to private persons

As of 01. 12. 2010 At an MDI share > 1 %

As of 27. 12. 2010 At an MDI share > 0.1 %

Additional hazardous substance markings as “R 40” and “R 48/20”

Additional labelling on packaging

ADAPTATIOn • Packaging labelling • Safety data sheets • Hazard assessment • Product accreditations

Obligation to provide protective gloves

In addition to the EU regulations in individual states additional restrictions may apply to putting PU products on the market. They must be adhered to.

Figure 3: the eU-wide classification “limited evidence of carcinogenic effect”, which came into force on 1 december 2010, is based on animal tests with a high exposure to Mdi in aerosol form. 9999754 Klebstoffe perfekt auswählen GB 02.08.2010.indd 11 09.08.2010 14:58:46

Silicone adhesives not only have high elasticity, they are also insensitive to water and humidity, sunlight, the effects of temperature and temperature fluctuations, chemical influences and ageing. As a result, they are ideally suited for applications in environments in which other adhesives fail, Figure 4: on glass building facades outdoors, in sanitary facilities and even under water or when exposed to high temperatures, for example in ovens. Their high resilience also means that they are the adhesive of choice whenever the adhesive bond is subject to movement. They have sufficient properties to ensure that the bond is not damaged even under shear or compressive stresses and to ensure that it returns to its initial position when the load has been removed, Figure 5. That is ideal, for example, for glass and window construction, where the parts to be joined together are subjected to different rates of expansion due to temperature fluctuations. However, their maximum adhesive force is relatively low compared to other adhesives.

Hybrid adhesives: between two worlds

Figure 4: silicone adhesives are ideally suited, for example, for outdoor applications — such as for producing the floor shown here, which consists of individual glass elements.

In areas in which silicone is not to be used, hybrid adhesives are an elastic alternative with similar stress-compensating properties, even though they have a lower performance overall and do not withstand high temperatures as well as silicone. Hybrid adhesives are also very notch-resistant and have a high tear resistance. Due to their good adhesion spectrum even under water loads and their good UV and weathering resistance, they are suitable for adhesive bonds both indoors and outdoors and can be painted over. adhesion adhesives & sealants 1/2011

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Figure 5: In many cases, the adhesive is required to have compensating properties to ensure that the bond is not damaged even under shear and compressive stresses and to ensure that it returns to its initial position when the load is removed.

DOI: 10.1365/s35784-011-0005-5

Images: Otto-Chemie

Figure 6: One-component PU adhesives foam slightly during application, thus filling small cavities on uneven and rough surfaces to ensure optimum conditions for reliable adhesion even in the sandwich components shown here.

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PU-based adhesives are considered to be unbeatable by trade and industry professionals. However, they require a substance that is suspected of being hazardous to health: diphenylmethane diisocyanate (MDI).

No compromises at the expense of health MDI can cause allergies after repeated skin contact or can represent a health risk if concentrated vapours (“aerosols”) are inhaled. Aerosols are produced above all during spraying (e.g. in paintshops) or when PU products are heated during processing. The EU-wide classi­ fication “Limited evidence of carcinogenic effect”, which came into force on 1 December 2010, is based exclusively on animal tests with a high exposure to MDI in aerosol form. The risk for humans was determined in a scientific study (which can be found on the homepage of the Federal Institute for Occupational Safety and Health in Dortmund, www.baua.de) on the basis of epidemiological investigations. The experts reached the following conclusion: “The available extensive epidemiological data

Acrylic dispersion adhesives: the low-cost alternative

PU adhesives: unbeatable with regard to adhesion

PU adhesives without a labelling requirement

Acrylic dispersion adhesives are paintable and also have good adhesive strength. However, their UV resistance is relatively low and their temperature and weather resistance is even lower, as are their stress-compensating properties. As acrylic adhesives are water-based, they are sensitive to frost while in their uncured state. Furthermore, there range of application is further restricted by the fact that the parts being joined have to be porous. Nevertheless, the group of acrylic adhesives is a low-cost alternative to other adhesives preferably for interior application.

Structural PU adhesives are the preferred adhesive group whenever a forcefit adhesive bond with very high strength is required. One-component PU adhesives foam slightly during application, thus filling small cavities on uneven or rough surfaces to provide optimum conditions for reliable adhesion, Figure 6. After curing, they can easily be sanded and painted over. Due to their low UV and temperature resistance and their limited weathering resistance, they should however be used only for interior applications and for water-protected exterior applications. As far as their adhesive strength is concerned,

In many trades, the use of PU adhesives is seen as indispensable. For professional tradesmen who do not want to make any compromises regarding quality, a PU adhesive is now available that neither requires labelling with R40 nor is subject to the Chemicals Prohibition Ordinance. This allows users from industry and trades to work safely and legally with regard to sales of the adhesive to both industrial customers and private persons. For further information, please contact: [email protected]

adhesion ADHESIVES & SEALANTS 1/2011

adhesives and seal ants

Guidebook “Finding the perfect adhesive” The different performance profiles of adhesives are the subject of the recently published professional guidebook “Finding the perfect adhesive”. The brochure describes the specific properties of the four common adhesive groups, silicones, MS-based hybrids or silane-terminated polymers, acrylic dispersions and polyurethanes (PU) — with special attention being paid to PU adhesives. The brochure can be ordered free of charge from [email protected]

do not provide conclusive evidence of a carcinogenic effect of MDI aerosols on humans.” In order to nevertheless indicate the theoretically possible risk, EU legislation has ruled that polyurethane adhesives with an MDI content greater than 1 % have to be labelled with R 40 or R 48/20 from 1 December 2010. Adhesives containing PU and labelled with R40 are automatically subject to the Chemicals Prohibition Ordinance in Germany, i.e. they may be sold to industrial users only by trained persons and may be sold to the general public only after instruction by trained experts (self-service ban). With these measures,

the legislator aims to ensure the correct handling of products containing MDI. ¢

The Author Dr. Volker Weidmann (Phone: + 49 (0) 86 84 / 908 0, [email protected]) is Managing Director at Otto-Chemie, Fridolfing, Germany

Graco expands its bulk supply systems lineup with smaller ram systems

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raco has introduced a line of small ram bulk supply systems designed to transfer sealants and adhesives from 5, 7 and 16-gallon (20, 30 and 60-liter) containers.

These systems are used in a wide variety of applications. Manufacturers use them to seal and bond parts and products such as meters, auto parts and electronics, while contractors use these systems to fill and repair expansion joints and cracks in floors, sidewalks and roadways, as well as build pre-fabricated houses. Like the larger Graco Supply Systems, the new smaller rams provide many of the same technologies and features that minimize maintenance and streamline everyday operations. Graco is pleased to announce the launch of the new 20L – 60L Supply Systems for dispensing and transfer of medium to high viscosity materials. The Supply Systems are the platform for the next generation of Graco offerings and provide significant advancements, including: ✔ DataTrak electronic pump monitoring with pump runaway control, material totalizers, and more ✔ Redesigned modular platens that provide versatility and easy wiper replacement ✔ New air controls with one-touch blow-off that eases pail removal ✔ New 60cc lower that provides five new ratio options; 5:1,11:1, 20:1, 38:1 & 61:1 ✔ Improved packings, and optional Maxlife pump that provides 2-3x longer life

GRACO N.V.

adhesion ADHESIVES & SEALANTS 1/2011

Slakweidestraat 31 • B-3630 Maasmechelen • Tel: +32 89 770 700 • Fax: +32 89 770 777 • [email protected] •

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www.graco.be