ADHESIVES & SEALANTS OVERVIEW

The constantly increasing requirements being put on new consumer products is the driving force for technological progress: Nowadays, each new product that is developed must – as in the past – not only be better and more favorably priced than its predecessor, but must also meet the requirement of sustainability. The consideration of environ­mental aspects means that the development of new products is becoming ever more demanding and that manufacturers must take into consideration more complex requirements for their new products. The increasing requirements put on products has since time immemorial been the key driving force for the development of advanced and new materials.

In addition to the classic metals, these materials include special alloys, plastics and also ceramics and glass. So-called composite materials, pro­duced by combining different materials, have played a major role in this development.

Reinforced concrete is a well-known composite material that has been around a long time. Newer composite materials are glass-fiber reinforced plastics and carbon fiber reinforced plastics which are used, for example, for constructing speed boats and yachts and increasingly also for car, rail vehicle and aircraft manufacture.

Another good example of the development and use of new materials is the wheel and tires.

Materials and Technology Development – The Wheel

Spoked wheels made of wood met the require­ments of the ancient Egyptians. Today, the manufacture of tires for modern means of transport can no longer be achieved using even natural rubber. The high speeds we now expect of a car can only be achieved using composites of different materials – and a car tire is nothing more than that.

A car tire today utilizes Rubber, Synthetic Fiber, Steel Cord, Fabric, Aluminum, etc.

More than 100 different Chemical Compounds 

ADHESIVE SELECTION: Adhesive selection involves the following considerations:

• Substrates: What are you trying to bond?  Are the surfaces the same or dissimilar, porous or smooth?  Are you covering a large area? Do you have heat or solvent sensitive surfaces?

• Application restrictions: How do you intend to apply the adhesive- examples: spray, roll, heat gun, cartridge, squeeze bottle?

• Use Requirements: How does the bonded piece get used? How much strength is required? For example, bonding wood requires much more strength than decorative paper crafts do. What kind of environments might it see?  Will it experience temperature extremes or water/steam?

ADHESIVE TECHNOLOGIES:

Adhesives and sealants have been used for centuries, with the earliest adhesives and sealants being made of natural materials, such as tree sap, beeswax and tar. Later, processed natural products were used such as animal protein, resin, natural latex.

With the emergence of the chemical industry and synthetic polymers, the range of adhesive and sealant formulations exploded. Today’s adhesives and sealants may be classified in many different ways, such as by cure (bonding) mechanism, chemistry type, and even application (e.g. structural vs. non-structural).

PHYSICALLY HARDENING

Physically hardening adhesives are adhesives which, on application, are already present in their final chemical state. Only polymers that can be liquefied can be used for this category of adhesive, namely thermoplastics that can be melted, soluble thermoplastics or elastomers, or polymer dispersions. Although poorly crosslinked elastomers with good swelling properties are strictly speaking insoluble, they can still be used in certain cases to produce adhesives if they swell enough for the substrates to be wetted. Physically hardening adhesives provide a wide range of adhesive properties, generally good bond flexibility, and are used in a variety of applications.

Four physically hardening adhesives are:

• Hot Melts
• Organic Solvent Adhesives
• Plastisols
• Water-Based Adhesives

CHEMICALLY CURING

Chemically curing adhesives are reactive materials that require chemical reaction to convert them from liquid (or thermoplastic) to solid. Once cured, these adhesives generally provide high strength, flexible to rigid bond lines that resist temperature, humidity, and many chemicals. They may be classified into two groups:

1.- SINGLE COMPONENT (1-C)

• Anaerobic
• Cyanoacrylates
• Heat Cure
• Moisture Cure
• Radiation Cure
• Silicones

2.- TWO COMPONENT (2-C)

• Epoxies
• Methyl Methacrylates (MMA)
• Silicone Adhesives
• Urethanes

SEALANT TECHNOLOGIES 

The main difference between adhesives and sealants is that sealants typically have lower strength and higher elongation than do adhesives. Since the main objective of a sealant is to seal assemblies and joints, sealants need to have sufficient adhesion to the substrates and resistance to environmental conditions to remain bonded over the required life of the assembly. When sealants are used between substrates having different thermal coefficients of expansion or differing elongation under stress, they need to have adequate flexibility and elongation. Sealants generally contain inert filler material and are usually formulated with an elastomer to give the required flexibility and elongation. They usually have a paste consistency to allow filling of gaps between substrates. Low shrinkage after application is often required. Many adhesive technologies can be formulated into sealants.

BENEFITS OF ADHESIVES & SEALANTS 

The development of new materials with diverse applications puts additional challenges on proces­sing technology. This is particularly so when differ­ent materials have to be joined to make compo­nents which retain their individual beneficial prop­erties in the composite product. This raises the question: which joining technique is able to join these different materials in such a way that their specific properties are retained? Traditional join­ing techniques have well-known disadvantages. With thermal techniques such as welding, the spe­cific properties of the material alter within the heat-affected zone. Mechanical techniques such as riv­eting or the use of screws in their turn only allow force transfer at points; in addition, it is necessary to drill holes in the work pieces that are being joined and this “damages” and hence weakens the ma­terials. In contrast, it is anticipated that bonding technology will assume an ever more important role in industry and the handicraft sector in the future.

There are four key reasons for this:

• Material: With specialist application, bonding technology can be used to bond virtually any desired com­bination of materials with each other, creating long-lasting bonds.

Processing: 

Assembly Line

The use of bonding technology in production processes in general allows the material prop­erties of the substrates to be retained. Compared to welding and soldering/brazing, the bonding process requires relatively little heat input. No damage occurs, unlike when rivets or screws are used.

• Joining: In product manufacture, the two aforementioned considerations enable the specific material prop­erties of substrates to be optimally utilized in components. This allows new construction methods to be employed.

• Design: It is also possible to use bonding technology to introduce customized additional properties into the component via the actual joining. In addition, the use of bonding technology in industrial production can lead to time savings, can accelerate the production process and hence give rise to specific economic benefits. In shipbuilding, for example, the inside decks can nowadays be bonded into the primary structure, so eliminating time-consuming straightening work that would be required if the inside decks were attached by welding. 

THE SIX KEY REASONS YOU SHOULD CONSIDER ADHESIVES AND SEALANTS IN YOUR NEXT DESIGN ARE: 

1. Improved Product Durability and Reliability
2. Increased Product Performance
3. Increased Design Flexibility
4. Increased Product Quality
5. Enhanced Product Aesthetics
6. Improved Process Productivity and Reduced Manufacturing Costs

Please let us know if there is anything we can help you with. Jet Chemical, as well as its manufacturer’s technical staffs, will be happy to assist you. It would be our pleasure to assist you with any persistent concerns that may have arisen while visiting our website, or answering any question, even if you think it’s silly.

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