Adhesives come in a variety of chemistries and forms, and each has unique features that are formulated to solve a particular problem or need. Science has allowed for engineering very specific adhesives, and they tend to come in polar opposites: solvent or acrylic, clear or pigmented, removable or permanent.
From epoxy adhesives to threadlockers, and everything in between, choosing the correct adhesive for your project comes down to the application it will be used for and the environment in which it will be applied.
To get the best results, ask yourself the following questions before selecting your adhesive:
What surface, container or product will the adhesive be applied to?
Adhesives attach to the surfaces of two substrates, unlike a process that fuses substrates into a unified whole such as welding metal or solvent activation of plastics. In selecting a GlueGun.com adhesive, surface condition must be considered: roughness, smoothness, porosity, coated, uncoated, cleanliness, flexibility, and size of the part. Check out our Surface Preparation Tips and Tricks for adhesive bonding.
Not every adhesive will work on every surface. For example, polyurethane adhesives are an excellent choice for finish carpentry and other woodworking projects, as they provide durability, impact resistance and flexibility in open times.
Pressure sensitive adhesives (PSAs) adhere to most surfaces, and contact adhesives are particularly well-suited in applications where clamping is difficult.
Some adhesives, like epoxies, require thorough surface preparation (cleaning, roughening) in order to adhere properly. MMA's would be better for metal bonding in general because they require little or no surface preparation.
Hot melt glue sticks and bulk hot melt excel at bonding porous materials such as paper, cardboard, wood, as well as some plastics.
Shop Hot Melt Glue Sticks Shop Bulk Hot Melts
Power Adhesives Tecbond F Bulk Hot Melt
$50.00
Infinity SuperTAC 11 Product Assembly Bulk Hot Melt
$150.00
What temperature will the adhesive endure or be exposed to during use, distribution and storage?
Many environmental conditions affect how adhesives cure and perform over long periods of time. One of the most significant environmental factors is temperature. Minor changes in temperature can have major changes in cure speed and storage life of adhesives. Most organic adhesives have maximum continuous operating temperatures and if exposed to higher temperatures for long periods of time their performance drops significantly.
Thermosetting adhesives such as melamine, phenolic and formaldehyde resins form strong bonds and have good resistance to higher temperatures. Silicone adhesives have a high degree of flexibility as well as a very high temperature resistance, making them excellent choices for marine or plumbing applications. As a rule, curing will be slower at lower temperatures and faster at higher temperatures.
Shop Silicone Adhesives & Sealants
ASI 600 High Temperature Red Gasket Maker Silicone
$80.00
ASI 335 Neutral Cure Window Silicone Sealant
$102.00
Will the adhesive need to be one that forms a strong, permanent bond, or one that allows the joined surfaces to be removed or re-positioned as needed?
Adhesive strength is the interfacial strength between adhesive and substrate, and usually the most important consideration when designing a strong adhesive bonded assembly. However, adhesive strength is not the only factor critical to creating an effective bond. Even when using the world's toughest adhesive, a bond will fail if the adhesive does not bond to the surface of the substrate.
Water-based adhesives are commonly used for laminating, they're also a lower cost alternative to resins. Hot melt adhesives can be melted or softened repeatedly by heat, or set by cooling, which allows for re-positioning during assembly. Often, removable adhesives are used as positioning aids during product build.
Polyurethane hot melt, more commonly known as PUR, is an adhesive that shares many characteristics of traditional glue sticks and bulk hot melt. That said, PUR hot melt is not dispensed in a traditional glue gun and can offer some additional bonding attributes that may fit applications that require a stronger bond or higher endurance to the elements.
Shop PUR Hot Melt Adhesives
Infinity PUR WW30
$12.00
Infinity Bond PUR Cartridge Gun
$90.00
Infinity PUR WW60
$12.00
For more information, please visit BGP.
Will the adhesive be exposed to high humidity during end use, application or distribution?
Excessive humidity can cause adhesives to become more foamy in appearance or softer in quality. It can also result in film formation in certain curing agents. Some adhesives may not be affected by humidity within a certain range, but if condensation forms on top of a substrate, you can be assured that the bond strength will be negatively impacted.
Moisture and humidity will both have an effect on adhesion performance. Acrylic adhesives have excellent environmental resistance but because they are water-based, they are more susceptible to moisture which affects their application and durability aspects. When it comes to humidity, when it's low, drying is accelerated; when high, drying is slower.
Shop Structural Adhesives
3M DP460 Super High Performance Epoxy
$257.00
ASI MP General Purpose MMA Adhesive
$14.98
Even after all of these questions are answered, there's no guarantee a particular adhesive will perform exactly as you need it to. Adhesive testing is strongly recommended prior to production or purchase. When testing, some factors affecting bond strength you'll want to consider include:
At GlueGun.com we offer quality products and deliver great customer service in equal measure; our experienced professionals guarantee it.
PUR adhesives come in many different formulations, each of which spread, bond and perform in slightly different ways. These characteristics have implications for assembly process economics and the type of equipment used, so it's important to consider them when selecting a specific adhesive.
One of the widest ranges of PUR adhesives is made by 3M. (They may also be the best-known adhesive manufacturer.) Here's a look at how to go about choosing one of their PUR adhesives, and remember that these same points apply to PURs from other reputable manufacturers.
Before delving into the differences between various formulations, here's a reminder of when PUR adhesives are a good choice and why.
Single part adhesive ' no mixing
No solvent vapors or VOCs
Quickly forms strong bonds to porous materials (like wood) and high surface energy plastics, and gains more strength as it cures
The main criteria to consider are:
Open time
Set time
Viscosity
Open time refers to the time available to make a bond after the adhesive has been applied. In a small volume, manual assembly process a long period might be desirable to allow time for positioning. Conversely, a short open time might be better in an automated process.
Set time refers to how long it takes to build strength at the bond. Again, the type of process in which the adhesive is being used will determine how much time is needed or available.
Viscosity indicates how the adhesive will spread after application. One with low viscosity will tend to flow out, covering a larger area with a thin layer. A high viscosity adhesive will go down as a bead. This may be advantageous if the product design calls for a minimum thickness or adhesive to only be in a specific location.
3M produces one range of PUR adhesives for bonding wood and another for plastics. Open times for the wood PURs range from 1 ' 4 minutes while for plastic PURs the times are 2 ' 10 minutes. Set times are 15 ' 120 seconds (wood) and 30 ' 150 seconds (plastics). (3M defines set time as 'time to handling strength'.)
Viscosity for both wood and plastic PUR adhesives ranges from around 3,000 ' 16,000 cP. (For comparison, water has a viscosity of 1.0 cP while maple syrup is around 3,200 cP.)
These values vary with temperature. Set and open times and viscosity will all increase in cold conditions and fall in high ambient temperatures.
In some applications other factors affect the choice of adhesive. Again with reference to the wide range of 3M PUR adhesives, these may include some or even all of the following:
Elongation and hardness ' high values indicate a stiffer, more rigid bond, low values the opposite. Measured on the Shore D hardness scale (also used for rubber,) 3Ms PURs for plastics range from 35 - 50 while those for wood are more rigid at 60 ' 65. (For comparison, a golf ball has a Shore D hardness of 60.)
Color ' 3Ms wood bond PUR adhesives come only in off-white. The plastic PURs are available in off-white, gray and black.
UV tracer dye ' when an adhesive has this it's possible to check for presence by making it fluoresce with a black light. This can be a valuable Quality Control aid where inspection is needed to verify adhesive presence. (Medical devices are one such application.) When manufacturing wood products an absence of tracer shows that a surface has no glue and so can be stained or painted.
Pack format and application method ' 3M packages their PUR adhesives in several formats. Almost all come in the 0.1 gallon tube that works with their PUR Easy 250 Applicator. Many are also available in 5 gallon pails and 55 gallon drums. The larger formats are intended for extrusion, spray and roll coating processes.
As PUR adhesives are relatively new, potential users might want to learn more about them before committing to their use. Our guide to PUR adhesives is a good place to start.