“I need to bond PE to both metal and Pebax^®. If possible, a light-cure product is preferable. Would the surface treatment be the same for PEBAX to PE? Do both materials need to be treated?”

There are a few light-curable adhesives that come to mind that will bond to both metals and plastics, and have good adhesion to both PEBA and PE. Treatment of the PE is a good idea, and methods include corona treatment of the PE, or plasma treatment with an oxygen-gas attachment. Regarding adhesion to PEBA, (as a block copolymer) this material can have different levels of a nylon characteristic. Usually, the higher the durometer, the more like nylon it will behave, which is a little more difficult to bond to. A lower durometer PEBA is typically easier to stick to. If you are bonding PEBA to PE, you would generally only need to treat the PE. If you are using a high durometer PEBA it would be a wise test to treat the PEBA and see if better bond results are found.

If you are looking for a recommendation from DYMAX, I suggest evaluating either 1161-M or 1168-M. Other competitive companies offer some very good adhesives for these substrates, and I am sure their technical support groups can help make a proper recommendation. There is a new technology available which can actually let you see the blue colored adhesive as it is dispensed, and upon cure will become clear. The See-Cure technology, as found in a product like 1202-M-SC, can bond to metal, PEBA, and PE (with treatment), as well as provide a safety feature by allowing the operator to see where the adhesive is dispensed, and when it has reached full cure.

Adhesives, Medical Pebax, See-Cure

“I am looking for an adhesive that can be used to bond an injection-molded PET part to a stretch blow-molded PET container. Ideally, this adhesive should be compatible with the PET recycling stream. Any recommendations?”

There are a few options available to bond PET to PET, whether injection molded or stretch-blow molded.  One available option is light-curable adhesives. These adhesives are available from Partner Pak, and a few other players in the market that work closely with the container/packaging industry.  While DYMAX has not tested each material for the recycle-ability of our adhesives, David Cornell, the Technical Director from APR (Association of Postconsumer Plastic Recyclers, www.plasticsrecycling.org) offered these comments regarding PET clamshells

Does the presence of the adhesive:

1. Cause the PET to yellow when re-melted?
2. Cause the IV of the PET to fall excessively when melted?
3. Cause haze in melted PET?
4. Cause films to crystallize too quickly?
5. Cause black specks in melted PET?

Generally, one should find out by testing a control of un-bonded components and a test sample of bonded components.  Make new components by grinding up bonded and un-bonded structures separately and processing as regrind after the hot water wash.  If you find no difference in appearance and performance at 25% and 50% regrind levels, the adhesive is probably not going to be an issue if the clamshells are recycled.

Clamshells generally are not pursued as sources of recycled PET, but PET clamshells do occasionally end up in bales, asked for or not. As such, the real world experience would have the adhesive present at much less than 25% of the recyclate.  But if you can show no problems at 25%, concerns will be allayed.  The cured adhesive should not affect solid stating performance, but should be tested fully.

My thought is that there is no problem with recycling PET sealed with a DYMAX light-curable adhesive since our adhesive is a clear thermoset (when cured) that constitutes a small % of the total assembled package.

Adhesives Bond PET, Packaging

“We have to manufacture a component which is comprised of two individual parts molded from acrylic (PMMA) that have slightly different additives. The parts have concave and convex surfaces which fit onto each other. We want optical coupling between these two surfaces. Can we place one piece as an insert and mold the other over it? Is there some other, better method to achieve the same effect?”

One common technique to bond couplets together as described is to mold both acrylic lenses separately and then bond them together with an optically-clear adhesive. There are optical grades of adhesives that have excellent adhesion to acrylic, are designed to be transparent to most visible wavelengths, possess low shrinkage, stress, and viscosity for easy dispensing and alignment, and then cure uniformly and evenly under the proper light source. The real benefit is that you can optically align the lenses together while the adhesive is wet, and then cure on-demand. Suppliers of optically-clear adhesives include Fiber Optic Center (carries DYMAX optical-grade materials and curing equipment) and Edmunds Optics (carries DYMAX, Norland, and Summers optical-grade adhesives).

Adhesives Optical Bonding

“I’m looking for a UV adhesive that will bond a PET or Acrylic lens to a photo print such as those you get from a professional photo lab.”

DYMAX light-curable dome coatings have crystal-clear coating/adhesive properties, and stick well to plastic lens, thin films, and professional photo printing paper, without wrinkling or distorting the image.  I recommend a soft, flexible A-70 durometer material with a viscosity of 1,500 cP that it is easy to apply and roll onto the printing paper surface, so the entrapment of bubbles is eliminated.  It’s important to use a low-medium intensity light to reduce stress during cure. Other coatings are available that provide a glossy, scratch-resistant coating over the photograph, usually in applications without a covering of PET or acrylic lens.

Adhesives, Coatings Acrylic, Adhesives, Bond PET, Dome Coatings, Photo

A recent question that came through:

“Can you recommend an adhesive that will adhere to inorganic salts?  I have used UV-curable adhesives in the past, including some of your products, and had good results in bonding poly-blend substrates.  But I’m not sure if that type of adhesive would work with the salts.”

Response:

Our experience has been that adhesives that bond to other inorganic materials like glass and metal will bond to inorganic salts.  We have seen applications where inorganic salt plates/crystals were bonded together with very good results.  We have also had success with salt-like crystals that are deposited onto a thin film of adhesive, imbed themselves into the coating, and then are cured in place.  It comes down to selecting an adhesive with the right properties important to your application, such as durometer/hardness and viscosity.

Structural

“Our application requires a watertight seal between FEP tubing (0.8 mm OD, 0.2 mm ID) and a borosilicate glass capillary (0.17 mm OD, 0.10 mm ID) with an overlap of 1-3 mm. This is part of a one-time use, disposable cartridge. We are currently using a 5 minute epoxy because the zero shrinkage is advantageous. The cure time, however, is not. We have tried UV-cure epoxy in the past for this joint but found that the epoxy did not cure inside the FEP tubing. Any suggestions?”

UV light-curable epoxies typically cure with the UV spectrum from 300-390 nm and do not make use of visible light to cure. With the semi-hidden bond described in the application above, switching to a visible-light-curable, acrylated-urethane adhesive would be worth trying. A visible-light-curable adhesive will allow more of the available light to hit the adhesive and cure deep within the FEP tubing.

An important issue with this application is that the borosilicate glass capillary will act like a light fiber.  It will take the light, carry it like a fiber-optic cable, not allow it to get to the adhesive (as it is bouncing the light internally within the glass), and move it past the bond area. The visible-light-curable adhesive should be exposed with high-intensity light. The adhesive should allow the light to penetrate into the gap.

One alternative to a visible-light-curable adhesive is a cyanoacrylate adhesive that could cure deep within the FEP tubing without light.  Due to the deep overlap area in this application, only the top surface would be exposed to water and could provide enough protection to create a water-tight seal.  Another alternative is a new product, DYMAX 9440 A/B, which is a light-curable silicone adhesive.  This material is unique in that you can expose the adhesive to light during dispensing and assembly and still have enough time to assemble the part before the material starts to set up.  DYMAX Applications Engineers can work with you one-on-one to discuss exact options and materials.

Medical, Structural Adhesives, CA's, Cyanoacrylates, Epoxies, FEP Tubing

A recent question that came through:

“Do you have an adhesive recommendation for gluing polycarbonate to acrylic? We are currently using 3M Marine Adhesive/Sealant 5200.The adhesive holds initially but starts to “weaken” after some time. The adhesive seems to be sticking well to the acrylic (Plexiglas) but not to the polycarbonate. We tried sanding the polycarbonate surface before gluing, but the adhesive still did not hold. Any suggestions?”

Response:

Typically, bonding to polycarbonate and acrylic is a very feasible application for many adhesives. If you want to try a light-curable, acrylated-urethane adhesive, DYMAX 3099 or 3025 adhesive might be a good option.

The comment about the adhesive weakening after achieving good results the first time is concerning. I recommend that you speak to your polycarbonate supplier/molder to discuss why this might be happening. For instance, the raw resin supplier may be adding a mold release to improve molding with polycarbonate and allow the polycarbonate to release from the metal mold easier. If a monomeric mold release is used, it can sometimes migrate to the surface and push the adhesive away from the bond line, causing interference with adhesion over time. If they are using a polymeric mold release, it cannot migrate as easily and should not have a negative effect on adhesion. Or, maybe the polycarbonate molder is spraying a Teflon^® mold release every 200^th shot to help the part release from the mold.

I also suggest asking the polycarbonate supplier/molder about the levels of stabilizers being used. Most stabilizers in the plastic are at acceptable levels and do not interfere with bonding. On occasion, however, the supplier/molder adds additional stabilizers to give light or heat resistance and stability to the plastic. These stabilizers can also migrate to the surface over time and destroy a bond line. To be sure, you can submit samples of the polycarbonate before and after heat aging to an analytical laboratory to run a solvent extraction on the surface of the plastic, to see if there is a contaminant at the surface, and to identify the contaminant. I have even seen contaminants like finger oil at the surface of the plastic migrate along the bond line and eventually degrade the bond strength.

Structural Acrylic, Plastic Bonding, Plastics, Polycarbonate

A recent question that came through:

“Are there FDA required or recommended adhesives for constructing non-DEHP or
non-phthalate PVC medical devices?”

Response:

That’s a good question and one we are seeing a lot these days. The good news from an adhesive manufacturing standpoint is that many of the adhesives used in medical-device assembly don’t need a plasticizer like DEHP or phthalate-based materials. Most light-curable acrylated urethanes, cyanoacrylates, epoxies, silicones, and polyurethanes do not contain these materials. These adhesive products bond readily to the polymers that are replacing DEHP plasticized PVC, even if they are alternative grades of PVC, extruded silicone, latex, urethane, or other polymer families. Most companies, DYMAX included, are usually asked to provide a letter at the beginning of a project stating that these adhesives do not contain DEHP or BPA.

On a related note, letters similar to the DEHP and BPA letters are available to certify if a product contains material of bovine origin. When Mad Cow Disease came to the forefront a few years ago, the polymers derived from bovine materials became an issue and companies required similar statements from their adhesive and plastic suppliers.

Read more on DEHP and BPA.

Adhesives, Medical BPA, DEHP