Mastering Hot Melt Extrusion with Twin Screw Extruder

In the ever-evolving landscape of manufacturing, efficiency and precision are the cornerstones of success. One remarkable technology that epitomizes these principles is the twin screw extruder. In this article, we’ll explore how this amazing machine transforms solid hot melt materials into a variety of useful forms.

From the fundamentals of hot melt adhesives to the intricacies of the extrusion process and the undeniable advantages it brings, we will embark on a journey through the world of “Twin Screw Extruder for Hot Melt.”

What is hot melt adhesive?

Hot melt adhesive, often referred to as hot glue, exemplifies a typical hot melt material. This plastic adhesive exhibits a unique trait of altering its physical state within a specific temperature range while retaining its chemical characteristics. Notably, it is non-toxic, odorless, and qualifies as an eco-friendly chemical product.

It is widely used for bonding a variety of materials because it can be easily applied in a molten state and then solidifies as it cools. The product itself is solid, easy to package, transport, and store, solvent-free, pollution-free, and non-toxic. Furthermore, it offers the benefits of a straightforward manufacturing process, elevated value addition, strong bonding capabilities, and rapid performance, which makes it a preferred choice in related industries.

Main types and applications of hot melt adhesive

PA hot melt adhesive

Its outstanding features are a narrow softening point range, solidification immediately when the temperature is slightly lower than the melting point, and good oil resistance and drug resistance; and because the molecule contains polar groups such as amino, hydroxyl, and amide groups, it is resistant to many polar materials. Has better bonding properties.

Therefore, it is widely used in footwear, clothing, electronics, telecommunications, home appliances, automobiles and machinery industries.

PU hot melt adhesive

Polyurethane has the characteristics of wear resistance, chemical resistance, low temperature resistance, flexibility and high bonding strength. It has been widely used in the fields of elastomers, foam plastics, coatings and adhesives.

Since the 1960s, solvent-based polyurethane adhesives have been used in shoemaking, luggage, ink and other industries. However, the volatilization of a large amount of organic solvents not only pollutes the environment but also increases costs, thus limiting its further development. With people’s increasing awareness of environmental protection and energy, solvent-free adhesives have developed rapidly.

EVA hot melt adhesive

Ethylene/vinyl acetate (EVA) hot melt adhesive is the most widely used and used hot melt adhesive. It has excellent adhesive properties and can bond to almost all materials. It is commonly known as universal glue. It has low melt viscosity, convenient glue application, good compatibility with compounding agents, and a wide range of compounding agents. Hot melt adhesives with reasonable performance/price can be formulated according to usage requirements.

EVA hot melt adhesive is widely used in wireless book binding, wood laminate production, panel furniture edge sealing, non-woven fabric production, etc.

Now that we’ve explored the versatile world of hot melt adhesives, it’s crucial to understand how these materials are efficiently processed and shaped for various applications.

Hot melt extrusion process

One of the key methods for working with hot melt adhesives is through a specialized manufacturing process known as hot melt extrusion.

Hot Melt Extrusion is accomplished through the use of an extruder, a device equipped with one or two rotating screws enclosed within a barrel. These screws work to transport materials along the length of the device. An extruder is made up of four main components:

• Feed Section: Here, materials are introduced through an opening into the feed barrel, which can feature either a hopper filled with the material to be extruded or can be continuously supplied in a controlled manner by one or more external feeders.
• Conveying (Processing) Section: This section, comprising the barrel and screws, serves the purpose of conveying and, where necessary, mixing materials.
• Die, Nozzle, or Mould: This component shapes the material as it exits the extruder.
• Downstream Auxiliary Equipment: Responsible for cooling, cutting, and/or collecting the final product, these components play a crucial role in the extrusion process.

The process for achieving hot melt extrusion using an extruder involves the following steps:

1. Material feeding: Hot melt materials, such as polymers and additives, are loaded into the feed hopper. This is the starting point of the extrusion process.
2. Material Conveyance: The material is gravity-fed or aided by external feeders into the conveying section of the extruder. In a twin screw extruder, this section consists of the interlocking screws within a barrel.
3. Melting and Mixing: The screws exert strong shearing and mixing forces, facilitating the symmetrical exchange and penetration of multiphase materials. Eventually, these materials transition into a single-phase state and achieve a high level of uniform dispersion.
4. Devolatilize: This operation effectively removes moisture or other solvents from the material, ensuring the desired purity and consistency.
5. Extrusion: The material is conveyed and pressurized by the screws while undergoing further mixing. It is then smoothly extruded through the die. Depending on the specific requirements, the extrudate’s shape can be altered as needed via the die.
6. Cooling and Solidification: Upon exiting the die, the hot melt material undergoes rapid cooling and solidification. This occurs either through exposure to ambient conditions or with the assistance of cooling systems integrated within the extruder.
7. Collection or Further Processing: The final product is either collected directly or proceeds for additional downstream processes, depending on the specific application.

Common hot melt extruder machine

Enter the instrumental players of this hot melt extrusion process – the “hot melt extrusion machines”. These sophisticated devices are the driving force behind the transformation of hot melt materials.

In the realm of hot melt extrusion equipment, two primary types stand out: plunger and screw extruders. Plunger extruders, owing to their limited mixing abilities, are gradually falling out of favor. Meanwhile, screw extruders come in variations such as single-screw, twin-screw, and multi-screw models. Presently, single-screw and twin-screw extruders reign supreme in the field of material preparation.

Single-screw extruder

The single-screw extruder features an integrated design, comprising distinct sections including a cooling hopper area, a solid conveying area, a melting area, and a melt conveying area. It is predominantly employed for the purpose of melting and conveying polymers, shaping them into continuous forms.

Twin screw extruder

In contrast, twin screw extruders find their primary utility in melt-mixing polymers alongside supplementary materials, such as pigments, fillers, reinforcers, and APIs. Additionally, twin screw extruders serve the role of devolatilization in specific industrial processes. This particular extruder boasts a consolidated structure, consisting of five key sections: solid conveying area, melting area, mixing area, exhaust area, and melt conveying area.

Advantages of using twin screw extruder for hot melt

Now, let’s delve deeper into the core of our discussion – the application of twin-screw extruders in the hot melt extrusion process. This method offers a multitude of advantages, which we will thoroughly explore to comprehend its crucial role in the manufacturing landscape.

1. Superior Mixing and Homogenization: Twin screw extruders provide excellent mixing capabilities due to the intermeshing screws. This results in homogeneous and consistent distribution of additives, such as pigments or APIs, within the hot melt material. This is crucial for industries like pharmaceuticals and plastics, where uniformity is paramount.
2. Precise Temperature Control: Twin screw extruders offer precise temperature control within the barrel. This ensures that the hot melt material is processed at the optimal temperature for its specific requirements, avoiding thermal degradation while maintaining efficient melting and mixing.

3. Versatility and Customization: These extruders are highly versatile and can be customized with different screw designs and configurations to meet specific production needs. This adaptability makes them suitable for a wide range of applications, from pharmaceuticals to plastics and food processing.
4. Increased Throughput: Twin screw extruders often have higher throughput rates compared to other extrusion methods. This leads to increased productivity and efficiency in manufacturing process.
5. Enhanced Dispersion of Additives: The intense shearing and mixing capabilities of twin screw extruders result in superior dispersion of additives in the hot melt material. This is particularly beneficial in industries like adhesives and pharmaceuticals, where the properties of the end product depend on the uniform distribution of components.
6. Improved Product Quality: The consistent and controlled processing in twin screw extruders leads to better product quality and fewer defects. This is essential in industries like food production, where product consistency is critical.

As we conclude our journey through the realm of “Twin Screw Extruder for Hot Melt,” one thing becomes abundantly clear: this technology represents the future of efficient and versatile material processing. It empowers industries to achieve consistency, quality, and customizability on a scale previously unattainable.

From comprehending the nature of hot melt adhesives and the meticulous hot melt extrusion process to the machinery that brings it all to life, we’ve ventured deep into the heart of this transformative technology. The advantages it offers are undeniable, making it an invaluable asset in fields as diverse as pharmaceuticals, plastics, and food production. As industries continue to innovate and evolve, the role of twin screw extruders will undoubtedly grow, shaping our future in ways yet unimagined.