Not Yet Over The Edge

Despite the availability of other alternatives in the market, edge gluing continues to dominate the market. The latest developments in adhesive technologies have diversified application, offering even greater application potential. By Daniel Fernandez, Rayt Adhesives

 

Edge bonding technology, edgebanding, emerges with the evolution of materials used in the manufacture of furniture. In the mid-20th century, the industry began to replace the solid wood with synthetic materials. High-pressure laminates (HPL) and fibreboards or chipboards were imposed.

The first gluing solutions were completely manual, using synthetic aqueous dispersion adhesives for natural veneer or solid wood edges, or contact adhesives based on synthetic rubber that also allowed the bonding of synthetic materials such as HPL.

However, the contact adhesives require the application of the glue on both sides, board and covering materials, and a waiting time for the complete drying of the adhesive before gluing. In addition, they were adhesives with a moderate heat resistance and a limited service life.

Development Of Edgebanding Machines

The need to automate the process of covering the edges led to the emergence of the first machines for edgebanding in the 1960s that worked with adhesives in aqueous dispersion, applied separately on both sides, board and covering materials. Adhesives were dried using heat lamps. 

Immediately after both sides were put in contact and a new heat source reactivated the glue, creating an instant and high quality bonding. This process allowed operations to run continuously to speeds of approximately 25 metres per minute, but was not suitable for non-absorbent synthetic materials because aqueous dispersion adhesives do not have penetration on that kind of substrates.

These kinds of machines were very similar to the current edgebanders, and it was only necessary to develop an adhesive suitable for non-absorbent synthetic materials such as HPL, PVC and ABS, and an adequate system of application. 

These demands gave rise to the development of heat applied adhesives called ‘hot-melts’, which over the past 40 years have dominated the application of edgebanding.

Along with direct application, edgebanding material productes also developed another application of hot-melt glue known as ‘glue precoated edges’. The application has endured to present day and is the basisfor some of the most innovative technologies.

The generalisation of the use of the hot-melt adhesives in the edgebanding application has developed a very large market of manufacturers of gluing machines and competition among manufacturers to provide improvements in the processes.

Currently, the vast majority of edgebanding machines apply the adhesive through a vertical roll and usually directly onto the board. The other two most implanted systems are application by injection and more recently,application by slot nozzle which requires an autonomous system to be incorporated into the machine that is manufactured by a specialised company.

New Demands From Producers

As the industry evolves, so have the requirements of furniture manufacturers. There are currently five major trends.

Productivity

The need to increase productivity in the furniture manufacturing has led to the emergence of increasingly faster machines. There are currently glue edging machines in the market with feed rates from five up to 100 metres per minute. The hot-melt adhesives have to adapt to these working speed.

Another important trend is the need for manufacturing flexibility. Automated production of different furniture models in small batch sizes is required while keeping production costs low. On the other hand, when making an investment in new edgebanding machinery, users should consider which adhesive application system is required. 

In this regard, certain manufacturers of machinery are developing machines compatible with the use of different types of adhesives so that investment in dedicated application systems is not necessary.

Improved Heat/Cold Resistance

With the raise of international trade and increasing quality requirements from the consumer, manufacturers need to pay more attention to the final resistance of furniture. This requirement must be considered in relation to the end use of the furniture and conditions that can be reasonably expected during its lifetime. 

As a heat applied adhesive, hot-melt adhesives are sensitive to temperature. However, a good quality hot-melt adhesive, even on EVA base, can overcome the conditions demanded by the quality regulations.

New Materials

Furniture manufacturing is closely related to interior design. Originally, the main obsession of the manufacturers was to imitate natural materials such as wood. 

Later on, the trend was to create new varieties that look natural, but are clearly artificial. Currently, synthetic products have become more important, with designs such as ‘high gloss’, the use of aluminium or metalised surfaces. Hot-melt adhesives have been able to adapt to these new trends successfully.

Sustainability &Social Responsibility

Users are increasingly aware that their actions have an impact on the environment. Strategies such as the 'carbon footprint' and the use of renewable or organic materials are being implemented. There is also a greater control over the chemicals, such as the European initiative ‘REACH’, and consumers are concerned about the emission of formaldehyde from furniture, asking for panels of low or zero emission.

The use of PVC is also being monitored, and there exist alternatives since a long time ago.In that sense, conventional hot-melt adhesives (EVA based) do not pose any concern, since they can be made even with raw materials suitable for contact with food. By contrast, reactive adhesives (PUR hot-melt) generate harmful emissions during their use.

Invisible Glue Line

The goal of emulating nature and improving appearance is leading to the search of virtually invisible glue lines. This quest has intensified with the new synthetic materials, and to some extent the use of new gluing systems responds to this need. 

PUR hot-melt adhesives also allow working with few application quantities, but they pose a significant additional cost and are more difficult to apply. The use of transparent EVA hot-melt adhesives, with an adequate system of application, offers an excellent balance between final appearance, cost, ease of use and capacity to fill the materials.

Emergence Of New Edgebanding Technologies

In the last decade, new gluing systems have been developed which, on the same machine structure, propose improvements on the line of the requirements of the customers, promising less visible joints and better resistance. 

They are systems incorrectly called ‘glue less’ since the hot air or laser systems require that the edging material is previously pre-glued with a functional layer.

Choosing The Best Adhesive System

A vast majority of furniture manufacturers are stillusing hot-melt adhesives for gluing edges and this situation will continue, since the producers of machinery still sell more machines that work with HM adhesives rather than those who may work with the technologies of laser, plasma or air. 

These furniture producers find today far more adhesives systems available than before, and must choose the most appropriate one for their production lines. On the other hand, the choice of the adhesive may have implications when making investment in machinery for edgebanding. What to do then?

First, the user must be clear about the use of its furniture. For example, if they are intended for consumption in the domestic market or for export. The resistance required for office furniture could hardly be the same (to heat or moisture) than the one for a dining table or a kitchen cabinet.

In this sense, manufacturers must bear in mind that regulations for resistance of gluing give them orientation regarding maximum resistances which are required or expected in normal conditions. These standards require the test to be carried out on the finished furniture, and not just on the glue itself. 

Some adhesives manufacturers have developed rules that are dubious and not comparable to the recognised regulations issued by known institutes. We must not confuse the softening point of the adhesive with its heat resistance, which used to be less.

On the other hand, the inner resistance of materials to be glued must not be forgotten. For example, the plastic edges have softening points ranging between 72deg C (PVC) to 94deg C (ABS), so using adhesives with more resistance has questionable economic sense.

The minimum resistances required by different methods (between 60 and 85 deg C) are far below the resistance of up to 150 degC offered by certain adhesives, so each user must assess to what extent is it worthwhile (in terms of economy, ease of use, maintenance, or safety of the user) to go beyond the limits that the standards considered realistic. 

Finally, it is interesting to summarise the comparative advantages of the different types of adhesives on the market, to assist in the selection of the most suitable adhesive for every furniture manufacturer.

There are different edgebanding alternatives available in the market that can address certain demands of the users. However, none of the new technologies has yet reached a level of maturity to threaten the widespread use of hot-melt adhesive in the last decade.

The latest developments in the market of adhesives enrich the good properties of existing EVA based hot-melts, offering solutions to the most demanding user such as polyolefin hot-melts (APAO) without the need to radically change their production lines.

 

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