High-volume users who always used material in one designated location might have been served reasonably well with expensive meter-mix equipment, which is still a viable option for large-scale dispensing applications, such as automated assembly lines. However, for most users of two-component adhesives at remote job sites, or in small volumes not suitable for meter-mix systems, the only available options are pails, cans, tubs and tubes that require manual pouring, squeezing, weighing, and mixing (Figure 1). While many use these manual systems today, most people have found two-component cartridges to be significantly more convenient and economical after considering the following factors:
- Labor involved in manually pouring, squeezing, weighing, mixing and cleanup
- Reliability from one mix to another (accurate and consistent control of each amount and avoidance of under- or over-mixing)
- Waste and disposal of unused material
- Health risks from direct contact with material
- Exact placement of material
Coaxial SystemsThe most mature cartridge design contains one component surrounded by the other (e.g., two cylinders, one within the other). These are typically available in volumes ranging from 75 mL to 380 mL, and in ratios of 1:1, 2:1, 4:1 and 10:1. They require a dispensing gun made specifically for this style of cartridge, although some of the smaller 75 and 150 mL versions can be dispensed using a screw adapter or a caulking gun and another adapter. Contents are mixed on demand using a static mix nozzle; if material is left over, the user can simply throw away the static mixer and reseal the cartridge for future use.
Side-by-SideCurrently the most widely used design, these systems consist of two side-by-side cylinders (Figure 2) that are either snapped together or molded into one piece. This cartridge offers a much greater range of volumes and ratios, and is available in unit dose or small syringe configurations ranging from 1 mL to 30 mL. These dual syringes are usually dispensed with a hand-held plunger. The larger sizes range from 50 mL to 1500 mL. Many ratios are available, with 1:1, 2:1, 4:1 and 10:1 being the most popular.
Barrier- or Injection-Style KitsThese are fairly specialized cartridges, and the oldest technology of the group. They are ideal for non-standard ratios that are not readily available in other cartridge systems, such as 7:1, 1:3:1, etc. Due to the design of these kits, the ratio options are almost limitless, and volumes range from 30 mL to 600 mL.
The barrier style is typically used with ratios between 1:1 and 10:1, and the injection style with ratios greater than 10:1. Similar to coaxial and side-by-side cartridges, these kits require a special dispensing gun with a cartridge retainer to fit the particular size and ratio cartridge. However, those same dispensers can also be used with many single-component materials that are available in many of these same-sized cartridges.
Unlike the coaxial or side-by-side cartridges, these systems are not mixed as they are dispensed - no static mixer is used. The user must manually break the barrier or inject the second component, then pump back and forth several times for 30-60 seconds to properly mix the materials (this can be done manually, semi-automatically or automatically). The inherent disadvantages of this system are that it’s very easy to under- or over-mix the components. In addition, all of the contents of the cartridge must be used within the gel time of the material or the material is wasted.
Universal Cartridge SystemThis is a fairly new technology that has been revolutionized by the u-TAHTMUniversal Cartridge (Figure 4) from TAH Industries. It involves dispensing a two-component material in a cartridge that fits into standard, professional-grade 1/10th gal (310 mL) caulking guns.
Choosing the Right Cartridge OptionWith all of these options, it can sometimes be difficult for an adhesive manufacturer to decide which is best for his or her application, market and customers. Consider the following factors when choosing a cartridge system:
- Volume required in the cartridge
- Ratio of the materials
- Whether it is a brand new, mature or recently introduced market for cartridge systems
- Application(s) (knowing how and where the product is being applied)
~ Will the application use the entire cartridge at once with only one static mixer, or will multiple uses require several static mixers?
~ Is accurate placement of a thin bead required, or will the user be simply filling a hole or spreading a generous amount out in a wide area that might be masked off?
~ End user (e.g., plant maintenance, construction contractor or DIYer)
~ Knowing your user will point you in the direction of whether they will have certain dispensers, or not want to use a dispenser at all
The following scenarios illustrate the thinking that should go into the decision-making process.
Small Packages for the Retail Market
For the retail market, manual dual-syringe options from 1-30 mL should be considered, as the DIY customer base will not want to buy a special dispenser. Another factor to consider is whether a static mixer will be used, as there are several products in home stores today that are available in the 30-mL size without a static mixer. Most of the other smaller sizes from 1-14 mL are used with a static mixer.
Non-Standard Ratio Material
Here, there may not be a viable option in the coaxial, side-by-side or universal configurations, leaving the barrier/injection style package as the only choice. As mentioned, the ratios are almost limitless.
Large Volume Required
If the application requires a lot of material to be dispensed, side-by-side cartridges are available in volumes up to 1500 mL, with a number of options and ratios between 600 mL and 1500 mL. Other cartridge systems are currently limited to less than 600 mL.
Markets that Already Use Cartridge Systems
In many cases, this decision has already been made, because competitors are supplying products in a particular cartridge system - whether it’s a 50-mL side-by-side in dental, a 200/300-mL side-by-side in automotive aftermarket, a 380-mL coaxial in marine, a 600-mL side-by-side in construction anchoring, or a 1500-mL side-by-side in sprayed-on truck bed liners.
Since customers are used to using these particular sizes and already have specific dispensers for them, suppliers will likely keep the same “cartridge footprint.” However, this does not mean that you can’t be unique and introduce another size/style cartridge system like the universal style, which provides the freedom to break away from “special” dispenser requirements entirely.
Entering a New Market for Cartridge Systems
In this scenario, customers may be using two-component adhesives supplied from bulk dispensers (e.g., meter-mix equipment) or smaller bulk containers (pails, tins, tubs or tubes).
Historically, penetrating new markets with cartridge systems that require users to have dedicated dispensers has been a slow process, as end users were reluctant to start buying special dispensers that could only be used with a specific cartridge. This barrier has largely been eliminated with the invention of the universal cartridge system, which allows end users to use the same standard caulking guns they are already using for single-component jobs.
However, since the universal cartridge system requires a static mixer that creates additional backpressure, a professional caulking gun with a mechanical advantage of 12:1 or greater will often be required. The good news is that home centers sell these 12:1 guns inexpensively, and 18:1 and 26:1 guns are available from industrial dispenser manufacturers as well. If a contractor or plant worker is doing a lot of dispensing with single-component caulking tubes, they probably already have higher-quality caulking guns.
Dispenser OptionsAnother factor in the cartridge system decision-making process is which dispenser options the end user has or wants. Traditionally, cartridge systems have been dispensed from either a manual or pneumatic gun, but battery-powered electric guns have entered the market in recent years.
These are expensive, but because they can be used with both two-component universal-style cartridges and single-component caulking tubes, their cost can be quickly justified.
ConclusionIt’s important to research and evaluate all options before making a final decision on a cartridge system. There are only a few cartridge manufacturers worldwide, and because some manufacture more than one of these options, they can be a good source of information to help make an educated decision.
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