Tackiness or stickiness may be noticed on the surface of some ultraviolet (UV) light curable adhesives and coatings. This phenomenon, known as oxygen inhibition, is the result of atmospheric oxygen inhibiting the cure on the surface layer of the polymerizing material. This condition is present anytime free radical polymerization occurs. However, the ability of a UV resin to be cured "tack-free or to a slick, dry finish" is dependent on the composition of the adhesive or coating formulation and the intensity and wavelength of the UV light.

Overcoming the effects of oxygen inhibition and producing a tack-free surface cure is dependent upon several factors:

• Heat generated by the UV curing system
• Intensity generated over the entire UV spectrum (200-390 nm)
• Exposure time
• Specific formulation of the adhesive or coating

Typically, short and medium wavelength (220-320 nm) UV light generated by mercury vapor lamps achieve more efficient surface cures. Short and medium wavelength curing systems, however, do have depth of cure and safety issues associated with them making them an undesirable option for many UV curing applications. Longer wavelength (320-390 nm) systems, which usually emit a small fraction of UV light in the lower wavelengths, will provide fast, tack-free curing while achieving better depth of cure.

Time to cure “tack free” should not be confused with full cure time. It is only an indication of the material’s ability to overcome oxygen inhibition, at the surface of the curing material, when the material is exposed to a given level of light intensity for a specific period of time. It has been demonstrated that the higher the intensity of the UV light the lower the total energy level needed to achieve a "tack free" surface. For example, to produce a tack-free surface cure of a DYMAX conformal coating (984-LVUF) using a 200 mW/cm² light source, the coating should be exposed for 20-30 seconds. This equals approximately 7 J/cm² of energy. This same coating cures in 1-2 seconds when exposed to 2500 mW/cm² equaling 2.5 J/cm² of energy.

Even though removing oxygen from the surface will also work at achieving a tack-free surface, this tends to be the least desirable method since it can be logistically challenging to implement.

Adhesives, Coatings, Conformal Coatings, Dome Coatings, Electronic Adhesives, Conformal Coatings, Dome Coatings, Oxygen Inhibition, Tack-Free

The answer is a little more complex than most people realize. In the world of adhesive bonding, most failures can be categorized into three distinct groups. They are:

• Substrate Failure: Substrate fails before the adhesive.
• Cohesive Failure: Adhesive fails down the middle, adhesive remains on both substrates.
• Adhesive Failure: Adhesive fails from one substrate. Usually a customer would say, "The adhesive failed from the cold rolled steel but remained on the glass."

  In many cases, however, customers experience a combination of all three types of failure.

  When asked what would be the preferable mode of failure, most customers will answer substrate failure. Is this an accurate answer?

   

  My response to this question is that while the mode of failure is important, what should drive the adhesive manufacturer and the customer’s selection is choosing the adhesive that will meet the customer’s specific requirements. For example, if a company wants their assembly to withstand rigorous environmental testing while being subjected to 2500 psi of pressure, then the adhesive also needs to meet this requirement. Whether the customer experiences cohesive, adhesive, or substrate failure, for the most part, is irrelevant if the adhesive does not meet their requirements.

   

  Is there any situation when the mode of failure is important? Yes, when everything is equal during the qualification process, it may be helpful to review the failure modes to narrow the field of adhesive candidates down. Also, in the case of failure analysis, the mode of failure is important to help determine the root cause. This information can be used to determine why a particular adhesive is or is not bonding to one or more of the substrates.

   

  Ultimately, identifying the mode of failure is only important once the customer’s requirements have been met. And even then, does it really matter that the adhesive failed from one of the substrates if the customer’s requirements have been exceeded?

  
  

  

  Adhesives adhesive failure, Adhesives, bond failure, Cohesive Failure, substrate failure

“Should we install ventilation for our ultraviolet (UV) light-curing process?”

Well it depends… We’ve addressed this question from an overall chemical-usage perspective since our answer looks at the “bigger picture”, not just the UV light-curing process.

When determining the ventilation requirements for a specific chemical or process, you must consider the following:

1. The size of the room. (In a larger room, you may be able to incorporate normal room ventilation to dilute chemical fumes or vapors below permissible exposure limits)
2. The volume of chemical being used. (Larger volumes of chemicals may pose greater health and safety concerns)
3. The physical and health hazards of the specific chemical. (More hazardous chemicals such as corrosives, solvents or flammable liquids may require venting. Always consult the material safety data sheet for information and special instructions)
4. The chemical state, vapor pressure, and vapor density (i.e. gas, liquid or solid) will help determine whether ventilation is needed, will work, and where to install it if it is needed.
5. Monitoring chemical levels in the workplace. (If levels are below permissible exposure limits, there may be no need to vent or exhaust) Additionally, if a ventilation system is put into place you must re-evaluate exposure levels to chemical fumes or vapors within the work area. This will determine if additional protection is required.
6. Atomization of the airborne chemical. (It is always recommended to vent or exhaust a chemical if you are spraying it)
7. How often the chemical is being used? (When combined with other factors, this could help drive a company’s decision whether to vent or not)
8. Cost. (this is always an important factor)

In the case of a UV light-curing process the answer also depends on the amount of heat generated by the UV light-curing system and the impact it has on the performance of the HVAC system in the area.

Ultimately, the decision to install a ventilation system is up to the user of the chemical after a thorough hazard/risk analysis (including workplace monitoring) is completed.

Curing Equipment, Safety Curing Equipment, Safety, Ventilation

Another question that came through recently:

“I’m looking for assistance bonding a Teflon^® wire jacket to a PEEK housing. Do you have an adhesive recommendation?”

Response:

Teflon^® or polytetrafluoroethylene (PTFE) is a low-surface energy plastic used in a variety of different industries from non-stick cookware to wire jacketing. Its accidental development led to the unique characteristics we have come to associate with Teflon, such as its use as a low-friction coating or non-stick surface. Because of these unique properties, Teflon presents many challenges to adhesive manufacturers whose customers wish to bond to it.

PEEK or PolyEtherEtherKetone is a high-performance polymer ideal for high heat-resistant applications where dimensional stability is needed. Its excellent chemical resistance makes it an ideal choice for many automotive, medical, and food processing applications. PEEK also presents many adhesive-bonding challenges.

While the question asked seems pretty straightforward, it is far from it. Before any adhesive manufacturer can answer a question like this, additional information is needed to identify a solution.

• The adhesive manufacturer needs to know what industry or market the finished part will be used in. For example, if it will be used in the medical industry, the customer may require a USP Class VI or ISO 10993 approved adhesive.
• Information on how the adhesive will be qualified, such as any temperature, chemical, or strength testing, will help an adhesive manufacturer narrow down their potential list of suitable products.
• Also, understanding the environment in which the final product will operate will provide additional information needed for the adhesive manufacturer to make a qualified adhesive recommendation.

While both substrates are difficult to bond, Teflon is considered to be the more challenging of the two. In this question, bonding the Teflon wire to PEEK may not be feasible. It may make more sense to encapsulate over the Teflon wire to the PEEK using a UV light-curable adhesive instead of bonding the two substrates together. In this case, you would bond to the PEEK by encapsulating the Teflon jacketed wire in place. Provided there are minimal external forces or stresses on the wire, this solution could pass a manufacturer’s qualification testing. In many cases, adhesion to PEEK can be improved by surface treating (i.e. corona, plasma, etc) the plastic before bonding. This will improve the overall performance of the adhesive bond and the quality of the finished assembly.

Any recommendation made by an adhesive manufacturer should be treated as such. The adhesive company will provide a manufacturer with their best candidate for the application based on the information provided to them during discussions with the company’s technical staff. Every company is responsible for determining the success of the adhesive recommendation by testing the performance of the assembly to see if it meets their established test criteria.

Adhesives, Medical PEEK, Teflon

Cold-bonding aerobic structural adhesives, those that cure “on demand” without heat, allow manufacturers to assemble parts when they want to without being limited by two-component mixing, additional heating and cool downtimes or oxygen presence within the bond area. Cold-bonding aerobic adhesives provide companies with the ability to bond dissimilar substrates within the production line without having to worry about long fixture times. Because the adhesives experience rapid bond strength development, the parts can continue through the production line without increasing work in process (WIP) times. This means companies who switch to cold-bonding adhesives will improve production efficiencies within their process while experiencing decreased energy costs. All of these are extremely important to companies in today’s current economic conditions. Companies need to explore different methods to become more efficient without sacrificing quality. Cold-bonding aerobic adhesives are one method to help companies.

It reminds me of a story of a company who was using an induction heat-curing epoxy to bond magnets into a cold-rolled-steel motor housing. Not only were they experiencing a number of in-line quality issues but the cool down time to handle the parts added significant WIP and expense to their process. By switching to an aerobic structural adhesive they were able to improve their quality and eliminate any non-valued added steps in their process. This allowed the company to produce a quality assembly quickly while improving their profits.

These adhesives cannot, however, be used in all applications and are only recommended when alternative bonding methods such as ultraviolet light-curing adhesives cannot be used. Aerobic adhesives have been successfully used in DC and brushless DC motor, speaker hardware, and opaque metal and glass bonding applications, in some cases exceeding the strength of one of the substrates.

How do they cure? Aerobic structural adhesives are two-component but in a non-traditional manner. Cold bonding technology incorporates a liquid activator and (usually) a gelled adhesive. As shown in the picture to the left, adhesive is applied to parts of a motor, in this case the magnets. Unlike a two-part epoxy where the components are statically mixed together, the activator for the aerobic adhesive is applied to the opposite part, in this case to the motor housing. Once the parts are ready to assemble, the magnets are pressed into the motor housing. The adhesive spreads through the activator, filling any gaps that exist between mating parts. As the adhesive spreads through the bond area and activator, this mixing action starts the curing within seconds and eventually finishes it. Again, there is no need to batch or rack curing parts since the buildup of strength is immediate and ongoing, allowing manufacturers to keep the assembly within the production flow.

Aerobic adhesives do not work in all applications, but should be selected as an alternative to cyanoacrylates, second-generation acrylics, induction heat-curing and two-part epoxies, and anaerobic adhesives. Each application should be reviewed with the technical staff of the manufacturers’ products that you are considering using. Changing to a new adhesive should only be considered after you have thoroughly tested the performance of the assembly to see if it meets your established test criteria.

Structural Adhesives, Cold Bonding, Dissimilar Substrates, Structural

REACH, BPA, DEHP, WEEE??? This is not your mother’s alphabet soup but acronyms for new environmental compliance directives, regulations, and initiatives…

As the world shrinks and companies continue to span many continents, we are seeing an increase in global environmental and safety regulations.  Many of these are being initiated in Europe and are spreading throughout Asia and within our own country.  Directives like REACH, WEEE, RoHS, and GHS are driving many companies crazy as they try to understand how the directives affect them.  Initiatives to identify and eliminate DEHP and BPA use in plastics and adhesives are also plaguing many manufacturers.  Very few international companies are immune from these new directives and initiatives.

It’s important to understand each one and how it affects your specific business before investing resources.  In today’s economy companies must invest their resources wisely in order to stay competitive.  It is important to understand the impact of these new regulations and initiatives both financially and from the safety and compliance perspective before moving forward. 

What are they?

REACH, a new European Community Regulation on chemicals and their safe use, entered into law on June 1^st 2007.  The legislation addresses the Registration, Evaluation, Authorization and restriction of Chemical substances.  The main objective of REACH is to improve the protection of human health and the environment from the risks that can be posed by chemicals used in an industry.

REACH makes industries responsible for assessing and managing the risks posed by these chemicals and provides the appropriate safety information to their users.  The criterion is based on volume (equal or greater than 1 metric tonne) imported into the European Union (EU) or if it is a Substance of Very High Concern (SVHC).  Registration of the substances occurs in phases based on the previously mentioned criteria, with the last occurring in 2018.  Learn more. 

WEEE or Waste Electrical and Electronic Equipment is another directive (Directives 2002/95/EC & 2002/96/EC) from the EU which restricts the use of hazardous substances (see RoHS) in electrical and electronic equipment while promoting the collection and recycling thereof.  The recycling program is aimed at re-using electronic waste and encourages consumers to return outdated, broken electronic equipment to the manufacturers at no cost to the consumers.  This eliminates the used electrical and electronic equipment from ever reaching a landfill where it would contaminate the environment with harmful substances that could potentially leech out.  WEEE goes hand-in-hand with RoHS.  Learn more.

RoHS or the Restriction of Hazardous Substances (directive 2002/95/EC) works closely with WEEE and is designed to shift manufacturers away from restricted chemicals to safer alternatives.  The EU identified the following substances under RoHS as hazardous with a significant impact to the environment.  They are: 

• Cadmium (Cd)
• Lead (Pb)
• Hexavalent Chromium (CrVI)
• Mercury (Hg)
• Polybrominated biphenyls (PBB)
• Polybrominated diphenyl ether (PBDE )

Additionally, the EU restricted three other flame retardants under 2003/11/EC for their negative impact on human health and the environment.

• Pentabromodiphenyl ether (PentaBDE)
• Octabromodiphenyl ether (OctaBDE)
• Decabromodiphenyl ether (DecaBDE)

Please click here for more information. 

GHS or Globally Harmonized System of classifying and labeling of chemicals is a regulation that was created in collaboration with the members of the United Nations (UN). Essentially, this regulation looks at unifying and standardizing all classification and labeling of chemicals so they are globally harmonized.  This means whether you are in Russia, France, Mexico, or the United States the safety information would be communicated in an identical manner through pictograms, hazard warnings, signal words, etc.  Read more from the OSHA website. Each specific country’s adoption of this new standard will vary.  Click here to learn more about your specific country’s adoption schedule for GHS.

DEHP and other phthalates

Di(2-ethylhexyl)phthalate (DEHP) is a plasticizer added to polyvinyl chloride (PVC) to make the normally rigid plastic more flexible.  Many companies, especially those in the medical device industry, are requiring suppliers to inform them of DEHP or other phthalate use.  The FDA issued a health warning¹ advising the public that DEHP could leech out of PVC and pose a health risk in certain high risk groups.  Specifically, there are concerns pertaining to the effects on the development of the male reproductive system.  More information is available from the FDA website.   

BPA

Bisphenol A² is a key ingredient in the manufacturing of polycarbonate and a constituent within many epoxies.  “In recent years, a hypothesis has been advanced claiming that exposure to extremely low doses of certain substances could cause adverse health effects in humans, including disruption of normal hormonal functions.”² There have been many conflicting studies completed showing that in some cases there is concern to human health but in other studies demonstrating no harmful effects.  Based on some initial tests through the National Toxicology Program (NTP) it appears as though there is “some concern” especially in small children and infants.  To alleviate some of the discrepancies in testing, NTP is requesting additional information from the scientific community pertaining to the health effects of BPA.³  It may be years before we really know whether there is truly a concern with BPA.  It will probably be too late for industry however, who regardless of the outcomes, will have made the switch to BPA alternatives because of these initial concerns.   More information on BPA can be found here.

Is there any good from these regulations and initiatives?

While many of these regulations and initiatives may be seen as cumbersome and confusing, some of them really are.  They make sense when you look at the overall picture and what is trying to be accomplished.  Many of the regulations are needed to reduce the impact and bioaccumulation of harmful chemicals in the environment, while minimizing or eliminating any risk to the safety and health of the greater population.

DYMAX ECO Benefits Everyone

DYMAX understands that safe ecologically friendly products benefit our customers, the environment, and us. We have created materials with attributes that lower products costs, life-cycle costs, and ecological impact. Learn more…DYMAX Eco underlines the DYMAX commitment to the environment.

¹ Retrieved from the FDA website http://www.fda.gov/MedicalDevices/Safety/AlertsandNotices/PublicHealthNotifications/ucm062182.htm

² Retrieved from the website http://www.bisphenol-a.org/

³ Retrieved from the website
http://www.ehponline.org/docs/2009/117-3/EHP117pa96PDF.PDF 

Safety BPA, DEHP, GHS, REACH, RoHS, Safety, WEEE

Exposure to chemicals in the workplace is one of the leading causes of skin diseases in the United States. According to the bureau of labor and statistics, skin diseases are more prevalent in the workplace than respiratory illnesses, outpacing them better than 2:1 based on 2006 figures.¹

Why should you be concerned? Many chemicals are easily absorbed through the skin. In most cases the resulting skin disease, such as contact dermatitis, is caused by direct contact with the chemical. But in some cases, just breathing in the vapors can cause a more serious systemic reaction to the chemical. The resulting effect could show up as a rash or something far worse. The economic impact of occupational skin diseases “may range from $222 million to $1 billion” according to C.G. Toby Mathias’s, MD editorial The Cost of Occupational Skin Disease.² These costs, however, do not include the effect it has on the quality of life for the individual.

While there are many different effects from dermal exposure to chemicals, this post only describes two of the more common types, contact dermatitis and sensitization. “Contact dermatitis: A skin condition caused by contact between skin and some substance. Includes irritant contact dermatitis (a rash brought on purely by repeated irritation from a substance such as water causing “dish pan hands”) and allergic contact dermatitis (involving a specific sensitivity or allergy to a specific substance such as poison ivy).”³

“Chemical sensitization is caused by an allergic reaction the body can develop to many chemicals. This allergy may exist already or may develop following a few days, weeks or even years of exposure. Once a person becomes sensitized, even very small amounts of chemicals can bring out an allergic reaction.”⁴

While dermal exposure to chemicals is a problem for many employers, there is good news.
It’s preventable!

How is it preventable? Many options exist to protect employees from chemical exposure such as employing a variety of engineering and administrative controls, or through the use personal protective equipment (PPE). Substituting the problem chemical with a non-hazardous alternative will remove the potentially harmful effect. When substitution is not possible or feasible, installing protective controls to minimize or eliminate contact with the chemicals is the next best option. Lastly, personal protective equipment, which may or may not be used in conjunction with other types of safety controls, will protect or cover any exposed skin. PPE like gloves, disposables sleeves, coveralls, chemical suits, goggles, and face shields, etc., will not eliminate the hazard but will provide personal protection from them. One key component to minimizing or eliminating dermal exposure to chemicals is training. Training should include information on the hazards, effects, and how to protect employees (from PPE use and selection to the use of engineering controls).

What happens if I get a chemical onto my skin? The immediate solution is to wash your hands with soap and water. You should never wash your hands with an organic solvent for this could exacerbate a skin condition and be absorbed quickly into your circulatory system, potentially causing other harm.

Before you work with any new chemical you should consult the material safety data sheet (msds) before using. This document will provide information on the hazardous effects, routes of entry, PPE or other controls to protect you from the chemical. It will also provide information on how to treat an exposure to the chemical correctly and safely.

As defined within OSHA’s (Occupational Safety and Health Administration) Hazard Communication Standard 29 CFR 1910.1200, it is your legal “right to know” about the hazardous chemicals you may be exposed to at your place of employment.

Each individual or cumulative effect has the potential to adversely affect a company and their employees. Only through a proactive effort to prevent contact with hazardous chemicals through the proper use of engineering and administrative controls, and personal protective equipment will a company minimize or eliminate dermal exposure to chemicals. This will ensure the safety and health of their most valuable asset, their employees.

¹ Retrieved from the website http://www.osha.gov/SLTC/dermalexposure/index.html
² C. G. Toby Mathias, MD Arch Dermatol. 1985;121(3):332-334.
³ Retrieved from the website http://www.medterms.com/script/main/art.asp?articlekey=20442
⁴ Retrieved from the website http://www.bacweb.org/safety_training/sh_tips.htm

Safety Chemical Exposure, Safety

True or False? - The adhesive smells so it must be harmful. 

For the most part… False.

The majority of people have a sense of smell that is acute and sensitive enough to detect odors in the parts per million (ppm). Ozone, for example, can be detected at concentrations as low as 0.01 ppm.  However, it is not dangerous until the 8-hour time-weighted average (TWA) for the permissible exposure limit (PEL) of 0.1 ppm is exceeded.

On the other hand, isocyanates, which are used in many single and two-part polyurethanes have poor olfactory warning properties.  This means that if a person detects its odor he has already exceeded the OSHA¹ or ACGIH² exposure limits.  For example, one form of isocyanate, TDI’s (toluene 2, 4-diisocyanate) has a PEL of 0.02 ppm over an 8-hour TWA, and due to the chemical’s poor warning properties a person’s exposure would exceed this limit if an odor is detected. 

In some situations when using a solvent-based adhesive, such as one that contains methylene chloride, employers should establish safe use procedures that incorporate engineering controls and the use of personal protective equipment to minimize exposure. Even better would be to replace the solvent-based product with a solvent-free adhesive.  In the case of most solvent-containing materials, the nose will provide ample warning to an employee that an odor/exposure is detected,  but it will not tell them if it’s harmful or if exposure limits have been exceeded.

The best way to learn more about a particular chemical or adhesive is to consult the material safety data sheet (MSDS).  The nose should never be used to determine if a product is harmful.

Why does this new adhesive smell so much more than our current product? 

The short answer is that a person’s sense of smell, through prolonged exposure, becomes desensitized to the current odor.  When a different odor is detected your nose smells only the new odor. 

Additionally, people develop olfactory fatigue which is a temporary inability to detect a particular odor. For example, when you enter a restaurant and smell freshly cooked garlic, this odor is only noticed for a short period of time.  When a new odor is introduced, lets say, freshly baked cookies, your olfactory senses detect the new aroma but not the garlic smelled earlier.

After a prolonged exposure to a new adhesive, an employee will also become desensitized to this material and if you were to switch back to the old adhesive this one would smell a lot worse.

Does the new adhesive smell worse?  Maybe, but it is more likely that it’s just different and your nose has yet to become accustomed to it.

Photo courtesy of  http://www.freeimages.co.uk/index.htm

¹ Occupational Safety and Health Administration

² American Conference of Governmental Industrial Hygienists

Safety Odor, Safety

 A standard question that many manufacturers ask our Technical staff is:

“How do your adhesives stand up to certain chemicals?”

Seems simple, right? Based on the chemical used, there should be a standard answer to follow. Well it turns out this question is far more complex than people think.

There are many factors that determine chemical resistance.  Once you understand these factors, a manufacturer can work closely with their customers to determine the best adhesive to recommend.  Factors to consider are:

1.   The chemical resistance must be tested in the actual bond configuration where the adhesive will be used.  Example:  Interfacial bonds will be more resistant than an adhesive exposed directly to the chemicals.

2.   The temperature of the chemicals.  Example:  A bath of sulfuric acid at 80°C is more aggressive than one at 25°C. 

3.   The concentration of the chemical solution.  Example:  A higher concentration of sulfuric acid is more aggressive than a lower one.

4.   The type and length of exposure.  Example:  A splash or wipe is less aggressive than a soak.  The length of exposure to the chemical will also yield different results.

5.   The adhesion of the specific adhesive to the substrates.  Example:  If you were to test the resistance of an adhesive to a specific chemical when bonded to polycarbonate it may pass.  If you take the same adhesive, same chemical and a different substrate, such as polyethylene, it may fail miserably in this example.

6.   The chemicals the adhesive will be exposed to.  Example:  A product may do better withstanding ammonia and water, than potassium hydroxide and water.

7.   The polarity of the chemicals.  Example:  Acrylated urethanes withstand non-polar materials better than polar materials.

In general, it is difficult to predict the outcome of an adhesive’s chemical resistance without specifically testing the adhesive on the customer’s parts, through their process, using their curing equipment.  However, by understanding the factors that may affect the adhesive’s resistance, can ultimately lead to a better adhesive recommendation for the customer.

Adhesives Chemical Resistance