Advances in Reactive Adhesive Application Technologies

June 1, 2009
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In order to achieve the sophisticated designs that consumers demand, manufacturers are asking their suppliers for more efficient and productive ways to make use of the powerful bonds of reactive adhesives.

Automation can be facilitated by visual detection systems for integrated inspection, compensation and feedback.


The pace of progress is increasing. As you read this, technology is getting smaller, faster and less expensive. For most of the world, that’s good news. For manufacturers, this new production paradigm represents an unprecedented opportunity that brings with it increasing design and production challenges.

As such, manufacturers need to find the technology to effectively achieve the sophisticated designs that consumers demand while maintaining a cost/productivity position that allows for competitive retail pricing. To accomplish this, they've turned to their suppliers with a wish list. Among their requests is a more efficient and productive way to make use of the powerful, durable bonds of reactive adhesives - bonding materials that offer significant production and functional benefits for a range of applications. Today, the industry has answered with a number of technologies that satisfy the demands of both manufacturers and consumers.  

Accurate, consistent dispensing of thin bond lines is critical for miniaturized consumer electronics.

Technology Drivers

The demand for increasingly high-tech devices is one of many factors driving manufacturers’ focus on reactive materials. A number of other dynamics have manufacturers looking for new solutions to enhance efficiency and reduce waste, including the following.

Automation
Especially in a down economy, manufacturers must cut costs and/or increase production rates; automation allows them to do both. New reactive adhesive application technologies are meeting the need for total automation, offering self-actuating and adjusting technologies that can specifically handle the unique characteristics of reactive adhesives.

The Smart-Phone Revolution
Even in this weak economy, the consumer electronics market - including mobile phones, mp3 players and computers - is showing strength. The market’s growth intensified with the appearance of smart phones, particularly the iPhone introduced in 2008. Offering an ever-increasing display size and growing functionality on a hand-held device, as well as a sleek design that grows thinner with every new model, smart phones continue to set new standards for electronics design, raising consumers’ expectations from mobile-phone manufacturers.

Today, the smart phone market is projected to grow more than 3% despite decreases in nearly every other market. Other mobile phone manufacturers are staying competitive by continually introducing new phones. In 2008, more than 1.2 billion phones were made and sold; more than 11% were smart phones.

The “smart-phone revolution” has escalated competition across consumer electronics, altering the public’s design expectations for all electronic and hand-held devices - from phones to blood-glucose meters. Consumers are looking for minimized size with maximum functional areas and multiple features.

This intense production competition means manufacturers typically run only six months from design to the store shelves, and even new models are quickly outdated. Retail stock is always changing to newer, better and smaller models.

Why Reactives?

There are several types of reactive adhesives, but the category generally includes any adhesive that undergoes a reaction in order to cure and form a bond. In some cases, the adhesive reacts with air, water or light; in others, two components, kept separate until the moment of application, react when combined to form a bond.

Two types of reactive adhesives dominate many of the current applications. Single-component polyurethane (PUR) hot melts are frequently used because of their significant durability as well as their good initial green strength. Products adhered with PURs can stay together without clamping, requiring minimal work-in-progress space in a facility.

Two component (2K) adhesives offer another powerful option for manufacturers - they can cure in the absence of air or moisture. As a result, they are often used to form structural bonds between a variety of substrates, including metal, wood and plastic. 2Ks deliver an exceptionally fast cure, with their ultimate physical properties developing in minutes instead of hours.

The reactive adhesives market was one of the few North American adhesive segments to increase in both volume and dollars in 2007. One reason for this is that reactive adhesives provide tremendous, lasting bond strength in the face of strenuous use and powerful elements, such as moisture and intense temperature changes. As such, they make the ideal bonding agent for products that are exposed to a variety of environmental conditions and are constantly handled, such as cell phones, computers, and blood-glucose meters.

In addition, standard reactive adhesives can be modified to exhibit various unique properties. Examples include: multiple degrees of conductivity, thereby offering exceptional thermal or electrical management; differing cure profiles; and unique optical properties.

Because of their intense bond strength, reactive adhesives, applied accurately and in the proper volumes, can be used in very thin bond lines. As such, reactive adhesives can replace the conventional screws and clips that once held together many electronic products like mobile phones, mp3 players, and hand-held medical devices, making them smaller and more durable than ever. These qualities mean that reactive adhesives are key to enabling manufacturers to meet the demanding design needs of their markets.

Realizing the Potential of Reactives

Until recently, manufacturers haven’t been able to harness the full potential of reactives in their processes because of the adhesive’s unique characteristics and the advanced technology needed to handle and dispense it. Because reactive adhesives begin curing as soon as they are exposed, they must be properly contained and dispensed to prevent and/or account for premature curing. Without this proper containment and subsequent accurate dispensing, adhesive - a costly resource - is wasted and products are not bonded correctly.

Given the early-curing quandary, a conventional 5- or 55-gal drum could be too much adhesive for a given application. Material suppliers have addressed this by offering smaller container sizes (such as cartridges and syringes) - a move that has made using reactive adhesives more economically viable in a wider range of applications. However, the smaller packaging sizes have created another challenge: finding application technologies that can handle such containers. Often, in order to take advantage of the new, smaller sizes, manufacturers have had to make a choice: sacrifice performance by using a simple time/pressure system or expend a large amount of capital on gear-metered equipment to ensure accurate dispensing. What’s more, these systems are not scalable, so manufacturers often have to purchase new dispensing platforms to transition between different sizes of adhesive containers to match their production needs.

Reactive Adhesive Application Systems in Action

Cell Phones
Cell phones are not just getting larger screens and thinner bodies; they’re also being made of new materials, such as steel or magnesium backings with polycarbonate housings. Manufacturers typically use PURs to adhere these dissimilar materials, requiring accurate dispensing equipment to achieve profit-requisite, high-speed production.

Thin bond lines are also critical for new mobile phone designs. One example is the ability to consistently put down a 1 mm thick bead on a 3 mm landing area over extended run times. Accuracy is crucial to adhere the elements properly without excess, as well as for minimizing adhesive use and eliminating the need for metal fasteners.

In addition, cell-phone manufacturers face an extraordinarily short time-to-market window, due to the pressure to churn out new designs multiple times a year. Retooling a production line every six months to accommodate new product designs (as conventional reactive adhesive technologies might require) would be impossible; therefore, the dispensing technology must be flexible and adaptable to changing projects.

New reactive application technologies address these challenges.
  • Premature cure prevention. Closed systems and disposable needles protect the adhesive and prevent waste.
  • Viscosity monitoring. Dispensing systems are pressure-based; natural viscosity changes can adversely affect the amount of adhesive dispensed. Until now, there have been two ways to deal with this: an employee manually adjusts the pressure or an expensive gear-metered system is used. New visual systems, however, overcome this challenge by continuously taking photographs of each bead, measuring the bead size against specifications and automatically adjusting the pressure to maintain ideal bead size.
  • Production efficiency. Decreasing the cost of labor and increasing the speed of assembly are key to achieving profitability. Traditional reactive adhesive dispensing technologies struggled with programs that required multiple starts and stops during the adhesive dispensing cycle. New systems use pneumatic valves to quickly and efficiently start and stop the flow of adhesive automatically to ensure accurate placement while preventing dripping.
  • Scalability. New technologies use the same controller, robot and feedback loop independent of the syringe or cartridge size of adhesive. If a manufacturer’s production volume suddenly varies, only the dispensing head needs to be changed, thereby reducing wasted material and equipment costs.
Computers
According to market research, computers are undergoing the same size revolution as hand-held electronics. Increasingly slim and tiny laptops, called “netbooks,” represent 17.2% of personal-computer sales, showing 160% quarter-to-quarter growth in 2008. New technologies for use with 2K adhesives, offering similar benefits to those described above, present new design and production options for computer manufacturers as well.

Medical Devices
Reactive adhesive application advances are also improving the form and function of many medical technologies, including personal medical devices such as glucose meters, as well as professional medical technologies.

Putting Reactives to Work

Reactive adhesives have been around for years. However, until recently, manufacturers have been limited in fully realizing their benefits. Now, the technologies described above are available and are ready to use in a range of applications. In addition to being extremely effective in technology production, reactive adhesives also offer exceptional results in other durable products, including windows, HVAC systems, books and appliances.

Every industry is facing greater competition, particularly in these difficult economic times. By advancing product design and executing those designs with the highest possible efficiency and accuracy, manufacturers can rise above the competition and make the most of a difficult economy.

For more information on dispensing reactive adhesives, visit www.nordson.com.

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