Another question that came in recently:

“I am investigating insert molding potential of PC/ABS or PC over PEEK tubing. With the significant melt temperature differential I am uncertain that I can achieve a secure bond. Can you suggest an adhesive that can be applied to the PEEK outer diameter prior to molding that will act as a bond layer?”

Answer:

I would recommend investigating a silane primer, sometimes called an adhesion promoter. These thin materials can be applied to the outer surface of the PEEK tubing, allowing it to dry (most contain some type of solvent), and then overmold as normal. The silane groups usually have two different reactive chemistries attached to them - one that will be attractive to the PEEK, and one that will be attractive to the PC. There are a number of different primers available from different companies. You might have to try a few different ones to determine which primer will work best for your combination. The primers can be applied with a brush, foam wipe, spray, or even a simple dip application (only coat the outside, not the inside). Apply the primer just short of the length of the overmold, and this will hide the primer under the PC.

Structural PEEK, Plastic Bonding, Plastics, Primer

An inquiry that came through:

“We have an application that requires a hermetic seal between dissimilar materials.  The bonds must be able to withstand the conditions of autoclaving and sustain immersion in a fluid for approximately 30 days.  One bond is between ceramic and silicon, and the other is ceramic and SS.

Please advise on materials and other recommendations for surface prep, bond line, etc.”

Response:

There are a few materials that may be candidates for evaluation to bond dissimilar materials. To withstand one autoclaving cycle, followed be immersion in a fluid (I am going to assume a water/aqueous liquid), and give good adhesion to ceramic and silicon, and ceramic and stainless steel, I would recommend either an epoxy or an acrylic-based adhesive.  Two-part epoxies will generally withstand these conditions, come in a wide variety of hardnesses, and give good adhesion.  One-part thermal-cure acrylates will survive the autoclaving (1 cycle) with a protected bond line.  A protected bond line can be best described as large mating surface areas between the two substrates, with only the edge of the adhesive being exposed to the steam or fluid.  I would recommend a bond line thickness of 0.002-0.004 inches for this type of application.  If it’s too thin you might have voids.  If it’s too thick you might have too much surface area of the adhesive being exposed to these conditions.  In this case, smaller bond line thicknesses are better. Products with a viscosity of 200-1000 cP would be ideal for this bond line thickness. Another adhesive option to improve efficiency in your manufacturing is to look at products classified as Multi-Cure^®.  Products of these types cure in different ways, including the ability to cure with heat or light.  The ability to cure with light would allow these parts to be assembled and tacked in place in seconds, and then exposed to heat to cure the remaining shadowed area.

To verify one point:  We always double check if the substarte is silicon or silicone.  While made up of the same elements, silicone is a flexible, rubbery material.  Silicon, as in silicon wafers, are generally metallic, hard, rock-like surfaces.  We work with both materials, but there has been enough confusion over the years that we like to double check.  That little “e” at the end can make a big difference in selecting the proper adhesive.  If you are looking at bonding ceramic to silicone, then I would recommend a silicone one- or two-part adhesive. 

Regarding surface preparation:  A rough surface will (generally)  give better adhesion than an electropolished surface. A rough-surface topography often has microscopic mountains, valleys, and pores that the adhesive can fill, which provides additional surface area, as well as a mechanical interlock.  A smooth-surface topography only gives one value of surface area, and no mechanical interlock.  If the surfaces can be roughened by abrasion, shot preening, scoring, or a chemical primer - these methods will improve the overall bond strength.  Making sure that the bonding surface is free of contaminants, oils, release agents, cutting lubricants, or even finger oils can help yield a repeatable bond strength.

Structural Adhesives, Dissimilar Substrates, Epoxies, Structural

Help needed:

“We are trying to glue a stack of coin cells to a .003 inch polyester substrate that has been printed with silver ink.  The bond must be electrically conductive. We’ve tried Loctite 401, 3M CA4, and 3M CA8.  Our problem is that the glue does not adhere consistently to the stainless steel can of the battery even when fixtured for 50 seconds. Roughing the surface of the battery has not helped.”

Recommendation:

A chemical primer on the surface of the stainless steel might help with the consistency. Cyanoacrylates generally cure with moisture in the air and on the surface. Controlling the environment goes a long way towards making a consistent process and getting consistent bond strength. Now we have to look at the level of moisture sitting on the surface of the stainless steel battery surface. Putting a primer onto the surface helps by putting a uniform concentration of -OH hydroxy groups on the surface. Be careful of how the operator is impacting your bonding process. Amazingly, an operator’s breath can apply a thin layer of moisture and help or hinder cure and adhesion. Plasma treatment systems can also be helpful in making a uniform bond line as it make a homogenous uniform surface each time. Cyanoacrylates are susceptible to these kinds of variations in the environment. If another alternative is required, two-part epoxies or one-part light curable acrylated urethanes or two-part acrylated urethanes (light and/or activator) are usually more consistent as they do not rely on environmental conditions for cure.

Structural Adhesives, CA's, Cyanoacrylates, Primer

A question that came through:

“What is the best adhesive for bonding a polyethylene terephthalate (PET) balloon to a polyether block amide (Pebax) substrate? What is the recommended surface preparation? Are other catheter-shaft substrate materials more suitable than Pebax for bonding to a PET balloon?”

Answer:

You should select a medium-flexibility light-curing adhesive with the viscosity to achieve the level of wetting and gap filling appropriate to your design. For example, DYMAX’s 204-CTH-F and 208-CTH adhesives have viscosities ranging from 155 to 500 cP. Such adhesives bond well to both PET and Pebax. In addition, it is important to choose an adhesive that fluoresces under a black light, enabling operators to detect and fix voids or air bubbles before the assembly is cured. This feature results in a better-quality bond and greater yields during production.

You can perform a surface treatment using plasma together with oxygen gas. While a plasma treatment with air gas—which has a lower O₂ content than oxygen—is also effective, it is not as advantageous as using an oxygen plasma treatment. The oxygen deposits onto the surface of the material and increases the number of bond sites to which the adhesive can stick.

You ask whether other catheter-shaft substrate materials are more suitable than Pebax for bonding to a PET balloon. Pebax is commonly used for manufacturing catheter shafts because adhesives bond well to it. A polyether/nylon copolymer, the material can be mixed with higher proportions of nylon (polyamide) to create higher-durometer materials (72D), or it can be mixed with lower proportions of nylon to create lower-durometer materials (35D). The greater the amount of nylon in the Pebax, the farther apart are the bond sites and the more difficult it is to bond. For example, bonding PET to 35D Pebax is easier than bonding it to 72D Pebax. If you can incorporate a small layer of 35D Pebax at the bond location while retaining 72D Pebax underneath to achieve greater material stiffness, the bonding application will be improved. 

Catheter Bonding Adhesives, Catheter-Bonding, Medical-Grade, Pebax, Surface Treatment

A question that came through:

“We currently use one of your medical-grade adhesives with a viscosity of 500 cP. We are looking for a higher-viscosity adhesive and do not want to have to redo biocompatibility testing. Can you tell me if you have an adhesive that is made of the same materials as the one we now use but with a higher viscosity?”

Answer:

DYMAX offers adhesives with several viscosity variations. An adhesive might have a standard base viscosity of 500 cP but also be available in a T (thick) grade with a viscosity of approximately 5,000 cP, a VT (very thick) grade with a viscosity of approximately 12,500 cP, and a gel grade with a viscosity of approximately 25,000 cP. These thixotropic versions all use a nonreactive biocompatible thickener and exhibit the same biocompatibility test results as the standard product. The thixotropic adhesives with gel viscosity allow the material to have a little slump, a minor slump, or no slump at all, enabling them to be dispensed along a ridge or in a groove.

View our Viscosity Comparison Chart.

Adhesives, Medical Adhesives, Medical-Grade, Viscosity

A recent question came in about a recommended plastic-bonding adhesive:

“We’re looking for the best clear adhesive that will work with polyethylene terephthalate (PET) material. The adhesives we have tried in the past often react with PET and turn a translucent white color. Can you recommend an adhesive that will not have this reaction with PET and remain clear upon application?”

Answer:

A large number of clear adhesives work with PET material. The material you select will depend on whether the part in question is a molded PET part or a thin film. It will also depend on whether you are looking for a medical, industrial, or packaging-grade adhesive. There is even an adhesive for use with PET material that changes color when it is cured, indicating that it has received enough ultraviolet light. Choosing the proper light source is also important and will depend on whether the application requires the curing of a 3-D part or whether it involves a web coating or lamination. All of these materials are designed to provide a crystal-clear bond line without stressing the PET material, which causes the translucent white effect you refer to.

Adhesives Bond PET, Plastic Bonding, Plastics

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