“What is the best type of adhesive to use to join two threaded components that are reusable and generally sterilized by steam chambers at temperatures up to 275°F?”
For devices that require repeated cycles of steam sterilization, I would suggest a two-part or heat-curable epoxy. Masterbond and Epoxy Technology offer such products in medical grade versions.
“Do you have a list or can you point me to a list of adhesives and epoxies that are compatible with mineral oil? These would be ones that do not break down or release their adhesiveness when mineral oil passes over the adhesive/epoxy. Along those lines, which materials are better/best for tubing carrying mineral oil?”
The table below was provided courtesy of Cole Parmer. There may be other chemical compatibility charts available. You can rank various adhesives into different chemical categories, such as urethane, epoxy, or silicone, and should follow the basic trends listed below. For Example: DYMAX 1187-M light-curable adhesive is classified as a Urethane Acrylate adhesive family of chemicals. Evaluation of specific adhesives for a given set of substrates should be evaluated fully.
| Material | Compatibility |
|---|---|
| 304 stainless steel | A-Excellent |
| 316 stainless steel | A-Excellent |
| ABS plastic | D-Severe Effect |
| Acetal (Delrinr) | A-Excellent |
| Aluminum | A-Excellent |
| Brass | N/A |
| Bronze | A-Excellent |
| Buna N (Nitrile) | A-Excellent |
| Carbon graphite | A-Excellent |
| Carbon Steel | A-Excellent |
| Carpenter 20 | C-Fair |
| Cast iron | B-Good |
| Ceramic Al203 | N/A |
| Ceramic magnet | N/A |
| ChemRaz (FFKM) | N/A |
| Copper | N/A |
| CPVC | A-Excellent |
| EPDM | D-Severe Effect |
| Epoxy | A-Excellent |
| Fluorocarbon (FKM) | A-Excellent |
| Hastelloy-Cr | B-Good |
| Hypalonr | C-Fair |
| Hytrelr | N/A |
| Kalrez | N/A |
| Kel-Fr | A-Excellent |
| LDPE | B-Good |
| Natural Rubber | D-Severe Effect |
| Neoprene | C-Fair |
| NORYLr | A-Excellent |
| Nylon | A-Excellent |
| Polycarbonate | C-Fair |
| Polyetherether Ketone (PEEK) | N/A |
| Polyurethane | B-Good |
| PPS (Ryton®) | A-Excellent |
| PTFE | A-Excellent |
| PVC | A-Excellent |
| PVDF (Kynarsup>®) | N/A |
| Silicone | D-Severe Effect |
| Titanium | B-Good |
| Tygonr | B-Good |
| Vitonr | A-Excellent |
“I need a medical-grade adhesive to bond Ultem material to stainless steel (SS). This product will be a reusable medical product that will be autoclaved for 30 minutes @ 250° F”
To bond materials like Ultem and stainless steel, for a reusable device that will see autoclave conditions, the right choice in adhesives is important. As a general category, acrylates, urethanes, and cyanoacrylates will survive only limited autoclaving. Epoxies and silicones will have better success. Ultem is a difficult material, but with proper evaluation you might find a successful candidate. Silicone materials are available from companies like Dow Corning, Momentive, NuSil, and Wacker. Epoxy materials can be obtained from Epoxy Technology, Henkel/Loctite, and numerous others. Silicones will be softer and flex with the thermal stresses, while epoxies will be more rigid. It will ultimately depend on the part design and the number of autoclaving cycles the part will see.
“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.
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.
DYMAX recently had a webinar informing people how to save 30% on their assembly bonding process. We talked about real-life ways to optimize assembly processes with cure-on-demand UV/Visible light-curable adhesives. This archived webinar is now available for viewing.
A lot of questions were asked during the webinar session. I decided to post a few below. Some of you may have the same questions in mind.
| Question | Answer |
|---|---|
| Can UV lights be added onto an XYZ robotic arm? Are they compatible with the software systems? | Light sources can be mounted and used with many XYZ systems and integrated seamlessly into the software controls. Some systems offer the ability to dispense a bead or gasket and then follow the bead or gasket with the end of a lightguide from a high-intensity spot lamp system. |
| What thicknesses can the light-curable materials be used to? | Typically, applications with a thickness of <0.25 inches are common. Best bond line thicknesses are usually 0.002-0.006 inches (0.05-0.15 mm), conformal coatings are typically 0.001-0.003 inches, and some special deep-section potting can be over 0.25 inches. |
| How heat resistant are the light-cure materials? | This varies by product, but most will be in the 200-400°F temperature range. |
| Most processes are validated/established processes. How much costs have you seen associated with an initial implementation of a UV-curing system? | This depends on the lamp type and application. Some starter R&D and low-production lamps start in the $2,500 range while other lamps with conveyors or XYZ tables can be much more. DYMAX offers a Trial Rental/Lease lamp program with 2 weeks free for trials and evaluations. |
| Can you explain See-Cure technology again? What are other methods to check cure quality? | See-Cure Technology utilizes a dye that loses its color with the light energy (intensity and time exposure). The color goes from blue to clear upon cure. Once the material is clear, it will remain clear, and be aesthetically pleasing to the eye. Other methods to check the state of cure is by either mechanical testing (such as tensile strength, durometer, and pull to destruction), or by chemical analytical testing (such as gas chromatograph on an extract sample, or FTIR of the cured material) |
| You mentioned “potting”. Can you please expand on? What is the maximum depth of the potting? Can you cover moisture cure technology? | Potting is typically filling a small well or dam with adhesive to protect components, circuits, or seal a housing/port. The viscosity of the adhesive/coating is low so that it self levels, and fills the cavity. Typical maximum depth of potting applications are <0.25 inches, but some special 2-part light-curable adhesives can be mixed to get a chemical reaction at deeper sections, while still allowing the benefit of a light-curable adhesive to lock in and seal the top surface. Moisture cure technology allows areas that can’t see UV/visible light to be cured with atmospheric moisture in the air, and takes a few hours to complete the cure. |
| What kinds of eye protection do you need when implementing UV-curable materials? | DYMAX recommends that lights be fixtured to point away from the operators to avoid direct exposure. We provide tinted goggles that meet current ANSI standards, and some customers create custom shielding using brown PVC shielding or smoked/tinted polycarbonate sheet. We also provide training to operators as needed. |
| Will any of your adhesives continue to cure after the UV light has been removed? | Some types of hybrid systems with moisture cure technology may continue to cure after the UV light has been removed. Some UV light-curable epoxies continue to harden slightly if they have achieved 90% of full cure, but extra care must be taken when working with these materials. |
| Are any of the light-curable materials RF & microwave frequency “friendly”? | Yes. Certain formulations are compatible with RF and microwave frequencies, and are transparent to these wavelengths. |
| Is there any concern, other than cosmetic appearance, when yellowing of the cured media occurs? In other words, is there cure quality issues if yellowing occurs? | Usually yellowing is a cosmetic phenomenon, with little impact on physical properties. Some optical applications do have a problem with yellowing as it would change the optical transmission of light through the adhesive. Therefore, an optically clear adhesive designed to be non-yellowing may be a good choice in this situation. |
| Can you overcure? Does the adhesive break-down? | It is more difficult to overcure these acrylic-based light-cure adhesives. They are very forgiving, and it would have to be an extreme case of overcuring. However, I have seen a few cases where engineers put an adhesive under a static light source and went to lunch. Upon return, the adhesive had too much UV light at high intensity with too much resultant heat, and started to break down. |
| Do you recommend specific fillers that will not hinder the cure process? | There are a number of fillers available on the market which do not hinder the cure process. Selecting the proper filler that yields a clear or translucent adhesive is a trick that the chemists use as they formulate. |
| Can you affect durometer with level of cure? | If you plot durometer versus cure time with a constant intensity, you would actually see the durometer level off and plateau. Over-exposing the adhesive to 2x, 3x, 4x cure times do not usually have a negative effect. |
| What, if any, surface preparation is required to optimize the effectiveness of these adhesives? | On some difficult to bond to substrates like PE and PP, surface preparation can improve the adhesion. Chemical primers, corona treatment, or plasma treatment (preferably with oxygen gas) are very commonly explored, as well as UV pretreatment of the surface. |
| How do you clean up “bleed out” or excess material? | Removal of uncured adhesive after application can be done with a foam wipe, cloth, or cotton swab, followed with an alcohol wipe (isopropanol, methanol, or other organic solvent). We do have a technical bulletin available with suggestions on how to clean up both cured and uncured adhesive residue. |
| I have heard that pre-exposing the substrate to UV light has a similar effect to surface treatment. Can you comment on this? | Pre-exposing a low-surface-energy plastic or substrate with high energy, short wavelength UV light is one effective way to increase adhesion, similar to other surface treatment options. |
| What is the pot life of adhesive once dispensed? | As long as the adhesive is kept away from light and dust, it is okay for a long time. We generally recommend short work times since manufacturing environments typically have a little bit of visible light that could start to polymerize the material. Also dust contamination should be avoided. |
| Does the fluorescence of the adhesive change from pre-cure to post-cure? | The fluorescence of the adhesive does not change from pre-cure to post-cure in most cases. |
| What packaging is available? | We offer a number of different package sizes, from 3, 10, 30 mL syringes, 170, 300, 600 mL cartridges, L or kg bottles, 15 L pails, 55 gallon drums, and totes. |