Colored light-curable acrylated urethane adhesives are usually custom-made and therefore hard to find. In order to find a product that will meet your specific needs (colored, medical grade, adhesion to specific substrates), you should contact the adhesive supplier of your choice.

In general, it is possible to add dyes to acrylated urethanes and to achieve ISO/FDA approval. Typically, each formulation is tested to ensure full compliance. The cured properties are usually not impacted; the only area of concern is the ability to achieve a full cure, since some colors can inhibit the light-curing process.

There are 4 types of cyanoacrylates. Two of them can be used for closing wounds and are available from different suppliers:

1. Butyl cyanoacrylate is used to bond skin and close wounds. Available from Henkel (Indermil), Advanced Medical Solutions Group (LiquiBand), and B. Braun (Histoacryl), all versions are FDA approved.

2. Octyl cyanoacrylate is a newer-generation glue for bonding skin and closing wounds. It is supposed to provide higher breaking strength and be less irritating to skin than the butyl-type adhesive. Available from Adhezion Biomedical (SurgiSeal), Ethicon (Dermabond), and Chemens Medical Products (derma+flex QS), all products are FDA approved.

3. Ethyl cyanoacrylate is the most commonly used adhesive for assembly purposes.

4. Methyl cyanoacrylate is used for assembly purposes.

Fully cured UV adhesives such as 1-20323-W are cross-linked thermoset resins, which do not melt and may be difficult to remove from a substrate, especially if they stick very well to it. For your removal purposes, I would recommend heat or chemical exposure to weaken and then remove the adhesive bonds or coatings. It may be very difficult since PVC and the cured adhesive have similar limitations in terms of temperature and chemical resistance.

I first suggest placing a part in an oven at 60°C for 10 minutes and immediately applying a peel or cleavage force to the bond or coating. Next, you can try to increase the temperature up to the point at which the part will not be adversely affected.

Several chemicals will dissolve or swell 1-20323-W, such as dichloromethane, MEK, and acetone. However, these chemicals will also damage the PVC and may not be suitable for your specific needs. Using isopropyl alcohol may be the only option in this particular case. A long soak in warm IPA with the help of an ultrasonic cleaner could be the last option if the previously mentioned options do not provide the desired results.

Latex rubbers can usually be bonded with cyanoacrylates, typically referred to as super glues. They have excellent adhesion to brass in most cases. Various types of rubber are used to manufacture latex-free rubbers, from synthetic rubber, butyl rubbers, isoprene, or even silicone. Thus, the type of adhesive to recommend depends on the specific rubber. Cyanoacrylates would be a good starting place. They are available with different viscosities (low-water-like viscosities of 20 or 50 cP, higher-viscosity materials such as 500 or 1000 cP, and all the way up to GEL viscosity). They also come in different grades, such as low odor, low bloom, surface insensitive, or rubber-toughened for better impact resistance. Dymax 222/100, which is a low-odor/low-bloom cyanoacrylate, might be a good starting point.

I would have the component tested at a biotesting company such as NAMSA. In the past, I have run evaluations using the C0020 USP physicochemical test, which is a leachables and extractables test in water. This method picks up and identifies the value in parts per million of residuals on the substrate. NAMSA also offers a C0046 glutaraldehyde analysis in aqueous samples, which can be collected by rinsing the part in water, capturing the water, and sending it in for analysis. I expect that this C0046 test method has defined limits of what is allowable for patient contact, but a call to NAMSA would define the test further.

The right choice depends on what needs to be accomplished with the initial bond. To adhere two substrates together and later be able to take them apart easily, you can try Master Bond MB600, a single-component adhesive for glass, metal, and many plastics that cures at room temperature as well as via exposure to heat.

For temporary coating or masking of a surface, I suggest looking at Dymax 713-Gel, which is a light-curable temporary maskant.

Both products dissolve easily in hot water.

The following table 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 you should follow the basic trends listed below. For Example: Dymax 1187-M light-curable adhesives are classified in the urethane acrylate adhesive family of chemicals. Evaluation of specific adhesives for a given set of substrates should be evaluated fully.

Ratings—Chemical effect
A = Excellent
B = Good—Minor effect, slight corrosion or discoloration
C = Fair—Moderate effect, not recommended for continuous use. Softening, loss of strength, swelling may occur
D = Severe effect, not recommended for any use
N/A = Information not available

Dow Corning offers Silastic MDX4-4210, a two-component silicone adhesive that has a tensile strength of 5 MPa. NuSil offers MED-1000 one-part silicone adhesive and MED2-4013 two-part silicone adhesive, which have similar strength characteristics. Momentive Performance Materials, Rhodia, and Wacker offer alternatives as well. These adhesives are listed as tensile-strength materials. Their operating data are acquired by molding a dog-bone tensile bar and pulling it 180° apart until it breaks. The breaking point determines the tensile strength. Bonding two pieces of a substrate is tensile shear strength, but adhesion depends on the substrate itself as well as the surface area. Most vendors cannot test all combinations and substrates, so evaluation of these candidate adhesives determines if they will reach 4–5 MPa, as you require.

I recommended these materials based on their tensile strength. If a material has a lower tensile strength, it might tear cohesively in the application, leaving silicone adhesive on both substrates. By selecting a high-tensile-strength material, the cohesive strength of the adhesive will be above your minimum value, so that you can focus on the actual adhesion of the silicone adhesive to the substrate.

I would initially start looking at either Epoxy Technology’s Epo-Tek 730 or Henkel’s Hysol M-21 HP epoxy adhesives for medical device applications. This is a good place to start, but there are other products on the market as well. Pebax is a copolymer of nylon and urethane-type polymers. The 55D is a mid-range polymer, while the 72D is more nylonlike and 32D is more urethanelike.

There are a number of clear adhesives that are suitable for bonding glass to plastic and that remain clear and colorless. Dymax 429 or 4-20418 are candidates that cure with UV light in seconds to form a strong bond between multiple substrates. Epotek 353ND is a clear two-part epoxy that would also work well. These few options might get you started looking in the right direction.

A key criterion for selecting the right material for your application is to identify how many parts you will make per day, per month, and per year and what type of process you can envision. Is high-speed UV curing the best option, or should you perhaps consider using the benefits of light-curing materials, which cure “on-demand”? Such adhesives allow you to align the parts, and once they are aligned, you shine light on them for a few seconds, locking them in place. Or are you more comfortable using a two-part material that needs to be mixed and degassed prior to use to avoid air bubbles? Some epoxies are available in 1:1 mix-ratio cartridges, allowing you to dispense through a static mixer system and easing the formation of air bubbles. Dymax ER1196/CT1196 is an 8000 cP two-component epoxy available in a 1:1 mix.

Another factor in selecting the right material is to determine what viscosity will work best for your part or application. To put this in perspective, water = 1 cP, honey = 10,000 cP, Dymax 429 = 2,500 cP, and Dymax 4-20418 = 450 cP.