"Can you cure DYMAX Ultra Light-Weld^® 1161-M adhesive with just heat or does the adhesive need to be exposed to UV/Visible light?"

Unfortunately, products like Ultra Light-Weld^® 1161-M are designed to cure with UV and visible wavelengths of light only, and heat will not cause this material to cure. There are families of DYMAX products that are considered Multi-Cure^®, which have both UV/Visible light-curing capability as well as thermal-cure capability. I would recommend calling a DYMAX Applications Engineer to discuss the specifics of your application, so that we can recommend the right Multi-Cure^® adhesive for your application.

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"Hello, I am using DYMAX 140-M to bond ABS to stainless steel. The product will be sold sterile in a Tyvek and LDPE/PET laminate pouch. Is there any data that shows the adhesive will not interact with the packaging in a way that could compromise the sterile barrier as the product sits on the shelf?"

Unfortunately we do not have data as specific as this. With so many applications around the world, and with so many substrates and packaging options being used, we have not attempted to determine the effects of cured adhesive in contact with the device packaging. The medical adhesives are usually tested for contact with blood, skin, muscular implant, etc., per ISO 10993/USP Class VI procedures, all with good results. If the material is cured properly, then after cure it is considered a solid plastic (urethane/acrylic type). We do not use any type of plasticizers or migrating materials that could compromise the integrity of the sterile barrier.

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"We use a lot of RTV adhesives. Every lot is tested by QA. Last week we found out that in one of our components the adhesive did not cure at all. The RTV is one component and it adheres metal to ceramic. It has holes for air to penetrate. Even after opening the bond and exposing it for one week it still did not cure. What could be the reason for not curing?"

RTV silicone adhesives rely on moisture and humidity in the air to cure properly. Generally the conditions have to be 40-60% RH, but can extend down to 20%, and up to 70% in certain cases. The moisture in the air reacts with the stabilizer in the RTV, and once the stabilizer is removed, the adhesive can cure fully. In a very high-humidity environment, the humidity in the air can saturate the surface of the RTV, and effectively seal it off, limiting the penetration of the humidity to deeper levels. If you have a thick bond line or cross section of material, it may take longer than one week to cure fully. The silicone manufacturers generally set a 5-7 day cure schedule for RTV’s before they can test the physical properties in a thick slab of material, and that’s with the condition of 40-60%. If you have a 70% RH condition during the summer time, it may take longer, or disrupt the cure enough to appear gummy or semi-cured. Acidic surfaces may also cause problems with the cure mechanism.

Another avenue to explore: Was this failure linked to just one lot of material? And was it 100% failure for this lot, or 1% failure of one tube within the lot? These answers can lead the manufacture of the RTV to help determine the root cause of the failure.

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"I have a lead wire containing a polyimide jacket. I need to bond the polyimide jacket to a titanium housing. The bond needs to provide a strain relief, and more importantly a fluid-tight seal. The adhesive needs to be rated for long-term implant use. Can you make an adhesive recommendation for this application?"

There are relatively few long-term implant adhesives on the market. NuSil Technology offers MED-2000, which is a one-component silicone RTV adhesive, and MED1-4213 is a two-component addition-cure silicone adhesive. Applied Silicone also offers long-term implant adhesives, such as P/N 40064. Since both companies offer other alternatives besides these, I would recommend contacting their respective sales/technical departments to discuss further.

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"I need inert and non-water absorbent adhesive film, with good sealing properties, to cover a surface (ceramic) already covered with a suspension of bacteria (dried). This set will be placed in a stomacher bag that contains culture media and the bacteria should be able to pass from the adhesive film to the media. It must be sterile or be able to be sterilized."

There are a few different options, depending on whether you want it to be sticky or non-sticky, or somewhere in between. Various silicone manufacturers or converters may offer cured silicone sheet in various durometers that would be inert and non-water absorbant. The lower the durometer (A-5 to A30), the better it will seal, but will be soft and “grabby” to the touch. Higher durometer silicone will be slightly easier to handle, but will not be as sticky or grabby as the lower durometer materials. You can go with an even lower durometer with silicone gels for better adhesion, but these need to be on a backing (similar to the tacky gel woundcare dressings or ouchless bandaids). Thin film PTFE or PTFE tape may also be an option. Many of these options will be sterilizable.

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"We have a segment of uncured adhesive inside a tube encapsulated with the adhesive DYMAX 204-CTH-F-VLV due to UV-opacity of the said tube’s segment. Does contact with uncured adhesive deteriorate properties of cured adhesive?"

Unfortunately, yes. Uncured adhesive will attack the bond line and the cured adhesive. The extent of deterioration is dependent on the area and volumes in contact with each other, and the duration of how long they are in contact. We would recommend sealing the tube, or removing the uncured adhesive if possible.

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"Is there a UV-curable adhesive that when cured conforms to USP Class VI and passes ISO 10993 requirements for permanent implant?"

Unfortunately, not that I am aware of. Technically, most light-curable adhesives are acrylated urethanes or epoxy-based systems, and would not survive permanent implantation. There are other hybrid light-curable technologies, but as far as I know none have been released technically for long-term implantation. In addition, the legal liability is too high for most applications. Perhaps something from the dental cement industry might be a suitable option.

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"I have an application where the cuff is glued to the tube and I require a smooth, tapered transition between the cuff edge and the tube.
Writing will take place over this area; that is why I need the smooth, tapered glue connection."

It is very common to use an adhesive to make a nice, smooth, tapered transition between cuff edges and the tube, or marker bands, or transitions where there is a jump from one size tube to another. A low-viscosity adhesive in the 200-600 cP range, which cures rapidly to a smooth tack-free finish, is ideal. DYMAX light-curable materials like 1120-M-UR or 204-CTH-F are often used in these types of applications. Techniques include applying the adhesive in either a vertical or horizontal position, or even at a slight upward angle to achieve the taper. If it is a horizontal or tilted orientation, rotating the shaft during application and curing with a spot system for 1-8 seconds (typical), will allow the material to cure in the proper profile without risk of the adhesive slumping or running. Typically these transitions have a max height of 2-5 mils or less. Lower viscosities will have a sharper taper, and higher viscosities will have a shallower taper. Selecting the right needle dispense tip will help control adhesive quantity and position on the catheter shaft.

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"I am trying to determine the proper cure time for the Loctite 3106 using a Dymax PC-5 Light Welder. Can you help?"

To determine the proper cure time of any light-curable adhesive when exposed to light from any light source, there are a couple of different approaches that can help. The greatest tool is a radiometer, which will tell you how much intensity you have at the bond line. The PC-5 is an older model flood lamp, with an intensity of 50-150 mW/cm² over a 5" x 5" area. The different approaches depend on how you are using the adhesive. If you are using the adhesive between two substrates in a bond-line thickness of 0.002-0.006 inches, then measuring the fixture time should be sufficient. Per the Loctite TDS, fixture time at this intensity should be <5 seconds. If you are potting a deeper section, then depth of cure is important, and you can reach a depth of 2 mm in approx 12 seconds. The Loctite TDS plots the depth of cure at an intensity of 50 mW/cm². If the adhesive bond line has some squeeze out, or has a surface exposed to air, then a tack-free surface cure may be important. Tack-free time is the point when the adhesive is sufficiently cured that you will not get smearing or residue transfer onto a gloved finger.

With any of the three described situations, measuring this yourself is the best way to figure out the proper cure time, whether looking at fixture time, depth of cure, or tack free time. Set the bond line up at the lowest intensity you can use – say 50 mW/cm². Do this by increasing the distance away from the lamp until the radiometer measures 50 mW/cm². (You will want to manufacture your parts at a higher intensity to start, and within a window of intensity and time. This will control your process.) After setting a constant intensity, cure the adhesive for different times. You will see the tensile strength, burst pressure, tack-free time, depth of cure, durometer, or other datapoint climb to a max value and then plateau. Once you have identified the start of the plateau, add a safety margin, and you have the foundation for your process. You can also set the time constant, vary the intensity, and record the same datapoints. You want to define your process by knowing the minimum and maximum intensity and time needed to cure the adhesive.

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"I need a recommendation of a medical grade non-cytotoxic UV adhesive for bonding together clear polystyrene moldings. What adhesive would you recommend? What is a simple but effective method to monitor if the curing reaction has gone to completion? Is there any dosimeter available to accurately measure the UV exposure? Would a post bake after UV curing help? Does anything "outgas" from the UV medical-grade acrylates during curing?"

Two options come to mind when looking for a medical-grade light-curable adhesive for polystyrene – 1201-M-SC and 1120-M-UR from DYMAX Corporation. These materials exhibit excellent adhesion to polystyrene, and are both ISO10993/USP Class VI tested. Product data sheets are available at www.dymax.com. One simple but effective method to monitor if the curing has gone to completion is incorporated into the 1201-M-SC product. This material uses a technology called "See-Cure", where the material starts off with a brilliant blue color, and as it cures changes to clear. This is an excellent visual indicator that complete cure has been achieved in all parts of the bond line. Other methods to determine state of cure include destructive testing of the components to measure tensile force, or a drop of adhesive at the bond-line surface and using this droplet to measure for tack/semi-cure (a go/no-go measurement observed by the presence or absence of adhesive transfer onto a gloved finger). More complex methods include microscope FTIR analysis of the adhesive to identify the presence of the double-bonds peak (on the spectrum) before cure, and the removal of the double-bond peak after cure.

Dosimeters are necessary to accurately measure light exposure, and there are different versions, with different sensors, that measure different parts of the UV and visible light spectrum. While most light-curable adhesives cure with a combination of UV-A, UV-B, UV-C, and visible light, it is often convenient to reference the UV-A light spectrum coming from the light source. UV-A is commonly referred to as 365 nm, but actually covers a range of approximately 320-395 nm. This can be measured with an ACCU-CAL™ 50. If the polystyrene is UV blocking, then you would have to rely on the visible light spectrum of the lamp. The ACCU-CAL™ 50V measures 395-465 nm. Both units can give you average intensity (mW/cm²), peak intensity, and total energy (Joules/cm²). Other options are available like the ACCU-CAL™ 50 LED, which was developed for special lamps (such as LED lights which only emit a single wavelength at either 385 nm or 405 nm) to integrate around the center of the lamp spectrum.

A post bake is not necessary on most adhesives, but there are a few adhesives with a peroxide thermal initiator, which can use heat to cure areas not able to see light.

In regard to the question on outgassing of UV light-curable adhesives during cure, it is sometimes observed that a small amount of smoke comes up from the adhesive surface during the cure step. This is typical, as the adhesive may emit trace amounts of some of the ingredients (or fractions of the ingredients) contained in the formulation while light is shining on the adhesive and cure is taking place. Sometimes this can be overcome by varying the intensity and duration of cure, as well as adhesive choice and light source. This does not happen when the adhesive is used between two surfaces. Proper ventilation can help remove this smoke. If the smoke deposits onto a spot or flood lamp, then periodic cleaning of the end of the lightguide or lamp housing should be done to remove the film that may form there, as this thin film can reduce the intensity at the bond line.

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