Hot melt adhesive (hot glue) is a thermoplastic bonding agent, which is solid at room temperature and melted for use. As the hot melt adhesive cools and solidifies, it binds materials together and can be used to attach multiple types of materials, including paper, ceramics, and wood. It also works on plastics and rubbers, as well as on metals and glass.
A hot glue gun from a hardware store works well to melt solid glue sticks for small-scale application. However, in industrial settings, more powerful hot glue guns are used, along with sophisticated and specialized application machines.
Hot melt adhesive has three main components, each contributing to its different properties:
- Polymers give it its strength and flexibility.
- Resins control how well it wets and adheres to the substrate.
- Its viscosity and ease of application come from plasticizers.
Hot glue is versatile, easy to use, and has a long shelf-life. The absence of water and solvents in its formulation eliminates the need for drying and curing, thus speeding up production. In addition, hot melt adhesive contains very few, if any, potentially harmful volatile organic compounds (VOCs). These properties contribute to its far-reaching use in industrial settings.
Key Chemical Properties of Hot Melt Adhesive
Some of the properties of hot melt adhesive change depending on the material on which it’s applied. Some vary with the temperature of the surroundings. Here are four of its main chemical properties.
Melt viscosity
Melt viscosity is a temperature-dependent property that affects how well the adhesive spreads and its wetting ability. It is lower at higher temperatures.
Melt flow index
Melt flow index (MFI) is a measure of how well the glue flows as it is extruded. The MFI increases as both the molecular weight and viscosity of the hot melt adhesive decrease and vice versa. An adhesive with greater MFI flows easily, but its strength, flexibility, and other mechanical properties are lowered.
Pot life stability
Pot life stability indicates how long the hot melt adhesive can be kept in a molten state without degrading. It goes by several other names, including aging performance, heat stability, and thermal stability.
Bond-formation temperature
The temperature below which the adhesive does not sufficiently wet the substrate is the bond-formation temperature. It is essential because good wetting of the substrate helps to produce high-quality bonds.
Industrial Uses of Hot Melt Adhesive
Hot melt adhesive binds many kinds of materials and is the perfect choice for porous and permeable substrates, accounting for its widespread use in product assembly, including:
- Sealing flaps on food packaging and packaging for other consumer items.
- Assembling furniture and other woodwork products.
- Affixing automotive components, such as trim and paneling.
- Mattress assembly.
- Bookbinding — attaching pages to the spine of a book.
- Attaching and securing components in electronic devices.
Constructing diapers, carpeting, and other products made of non-woven fabrics.
Read one of our recent blogs, Industrial Hot Melt Adhesive Applications, for more examples of hot glue applications.
Benefits of Hot Melt Adhesive
Hot melt adhesive has several other advantages apart from its ability to bind a variety of materials.
It streamlines supply chain processes.
Hot melt adhesive is quick-drying, does not contribute to delays, and improves efficiency when used in conjunction with a first-rate, hot-melt delivery system.
It speeds up on-demand manufacturing.
Speed is a critical feature in on-demand manufacturing. Waiting a day or two for the glue to dry before moving on to the next production stage is counterproductive. Hot melt adhesive dries in seconds, helping you to produce items in a timely fashion.
You can use it repeatedly.
Hot melt adhesive is melted when needed, then allowed to cool and solidified for use again at another time, reducing waste and lowering production costs.
It is an environmentally friendly option.
Solvent-based adhesives often contain volatile organic compounds (VOCs). Some VOCs have demonstrated ill effects on the health of persons exposed to them. They also harm the environment. Hot melt adhesive either does not contain VOCs or is made with significantly reduced amounts, making it a safer choice.
Hot Melt Adhesive Application Equipment
There are important points to consider when deciding which hot melt adhesive application equipment to use. The final choice impacts the speed of the manufacturing process, quality of the finished product, and, eventually, the company’s profitability.
Let’s take a look at some of the options.
Supply Units
The supply unit is the storage tank or reservoir that heats and holds the hot melt adhesive before application. It has digital controls for regulating both the adhesive’s output flow and the high temperatures needed to melt it. Supply units vary according to storage capacity and the number of hose and applicator attachments they accommodate.
Applicators
When using hot melt adhesive, one of the first decisions to make is whether to use a manual or automatic applicator or a combination of both. Here are a few factors to consider when choosing.
Manual vs. Automatic
- Company size: Smaller companies with a few workers generally opt for manual applicators. In large companies, however, automatic systems help reduce the number of workers and associated labor costs.
- Budget: Manual applicators tend to be less expensive than automatic ones in upfront costs and long-term expenses.
- Product design: Complex designs are often best handled by automatic systems. Some offer the convenience of multiple modules controlled by inline technology.
- Precision and accuracy: Automatic applicators maintain precision and accuracy while working quickly on large quantities of products. Manual applicators are the better choice for hand-crafted items ad similar products. They give a greater sense of control over the amount of adhesive used and how and where it is placed.
- Level of demand: It is difficult for workers and manual applicators to keep up with a high productivity demand. Under these circumstances, the obvious choice is using automated applicators instead.
Application Type
Hot melt adhesive can be applied using several methods. It is possible to use just one approach if it is suitable for all your production needs. There are, however, application systems that allow you to switch from one method to another.
- Extrusion: Extrusion typically involves placing small dots of adhesive on the substrate, whether singly or in a pattern. Extrusion applicators are either manual or automatic.
- Slot coating: Automatic systems are best suited to this application method. That’s because it calls for greater precision in the placement of the adhesive. These applicators can deliver adhesive in complex patterns.
- Spray: Spray applicators may not have the precision of slot coaters, but they are best for applying large quantities of adhesive over a wide area. This type of application can use both manual and automatic systems.
Hoses
Hoses come in a range of lengths and with temperature control options. They take the hot, molten glue from the supply unit to the applicator. These hoses must be sufficiently insulated and have appropriate thickness and diameter to facilitate the glue’s pressure and flow.
Other Accessories
Other pieces of equipment may be needed depending on your operation’s size, the applicators you use, and the products you make.
For instance, operator panel lockouts allow a supervisor to set the application temperatures then block the operator from changing them. Flow valve heaters increase the temperature or melt rate of the adhesive. Some other accessories to consider are:
- Glue pressure gauge assembly.
- Flow adjustment lockout.
- Motors.
- Foot pedals.
- Bracketry for mounting and hanging hoses.
About Sure Tack Systems
Sure Tack Systems is a division of Crist Company, Inc. We are a leading manufacturer of hot melt adhesive application equipment. Besides producing top-quality machines, we also provide one-on-one or team training in how to operate the application equipment.
Sure Tack System applies our “Keep It Simple” philosophy to the engineering of our products. Our offerings include hot melt adhesive supply units, automatic applicators, and manual applicators. Our product range also contains a wide selection of hoses and accessories.
Customers benefit from ongoing technical support, which is available 24/7. What’s more, Sure Tack Systems conducts refresher courses for current staff and assists with training new staff.
These reasons (and more) are why you should make Sure Tack Systems your chosen supplier of hot melt adhesive equipment.