How to choose the right hot melt material to improve sealing

How to choose the right hot melt material to improve sealing

In many industrial applications and daily production and life, hot melts are playing an increasingly important role, and the quality of their sealing often directly affects the quality and performance of the product. For international wholesale buyers, choosing the right hot melt material to improve sealing is the key. This article will explore this topic in depth and provide you with comprehensive and practical guidance when choosing hot melt materials.

1. The relationship between hot melt material characteristics and sealing
Hot melts are usually low-melting point fibers produced by composite spinning of polyester and modified polyester, with characteristics such as low melting point, thermoplasticity and self-adhesion. When heated to a certain temperature, it softens and melts into a viscous fluid with a certain fluidity, and then solidifies again after cooling to become a solid. This characteristic enables it to be closely bonded to other materials, thereby achieving a sealing effect.
Crystallinity: Hot melt materials with higher crystallinity have better fluidity after melting, and can be more evenly filled in the microscopic gaps on the connection surface to form a continuous and dense bonding layer, thereby improving sealing. For example, polyester hot melt wires generally have a crystallinity between 30% and 50%. The crystalline region and the amorphous region can cooperate with each other. When heated and melted, the amorphous region provides good fluidity, while the crystalline region guarantees the strength and stability of the material to a certain extent, so that the molten material can better adapt to the shape of the connection surface and achieve a tight fit.
Viscosity: Appropriate viscosity helps the hot melt wire to quickly wet the surface of the adherend in a molten state, and effectively fill the gap under pressure to achieve a good seal. If the viscosity is too high, the hot melt wire will have difficulty flowing and it will be difficult to fully fill the gap; if the viscosity is too low, it may cause insufficient bonding between the material and the adherend after curing, affecting the sealing effect. Generally speaking, the viscosity range of the hot melt wire is more suitable between 1000-10000 Pa・s, and it needs to be adjusted according to the actual application and equipment conditions.
Elasticity and recovery rate: Hot melt wire materials with high elasticity and good recovery rate can quickly return to their original state and maintain the integrity of the seal after a slight deformation of the sealing interface caused by external force. For example, some specially modified polyamide hot melt wires have a high elastic modulus. After the external forces such as compression and stretching are eliminated, they can effectively restore the sealing contact pressure and prevent the sealing failure caused by the permanent deformation of the material.

2. The influence of application requirements and working environment on material selection
Temperature conditions: Different application scenarios have different requirements for temperature tolerance. In some high-temperature environments, such as the sealing of parts in the engine compartment of an automobile, the sealing of industrial baking equipment, etc., it is necessary to select hot melt wire materials with high softening temperature and thermal stability, such as high-temperature hot melt wires in polyamide or polyolefin. This type of material can still maintain good bonding and sealing properties at higher temperatures, and will not lose the sealing effect due to softening or decomposition; in low-temperature environments, such as refrigeration equipment, mechanical seals for outdoor low-temperature operations, etc., hot melt wires with excellent low-temperature performance should be selected, such as some modified polyester hot melt wires, which have a low glass transition temperature and still have certain flexibility and viscosity at low temperatures, which can ensure the reliability of the seal.
Chemical environment: If the hot melt is used in a chemically corrosive environment, such as chemical pipeline sealing, battery electrolyte contact parts sealing, etc., then the chemical corrosion resistance of the material is particularly important. Polyamide hot melts usually have good oil resistance and chemical resistance, can resist the erosion of a variety of chemicals, and maintain the stability of sealing performance; while polyolefin hot melts have good tolerance to chemicals such as acids and alkalis, but may swell or degrade in certain specific solvents. Therefore, when selecting, it is necessary to determine the appropriate material according to the specific chemical medium type.
Mechanical stress and vibration: For some occasions that need to withstand large mechanical stress and frequent vibration, such as the sealing of automotive suspension system components and the sealing of industrial machinery transmission devices, the hot melt material must have sufficient strength and toughness to resist the effects of mechanical forces such as stretching, compression, and shearing, and prevent the sealing from failing due to material breakage or deformation. Reinforced hot melts, such as adding reinforcing materials such as glass fiber to polyester hot melts, can significantly improve their mechanical properties, so that they can maintain good sealing effects in complex mechanical environments.

3. Common hot melt materials and their sealing performance characteristics
Polyamide (PA) hot melt: Polyamide hot melt has good heat resistance, chemical resistance and mechanical properties. Its softening temperature is generally between 150℃-250℃, and it can adapt to a wide temperature range. It has good adhesion with a variety of materials such as metals, plastics, rubber, etc., and is widely used in automobiles, electronics, machinery and other fields. In terms of sealing, polyamide hot melt can form a tough bonding layer, which has a good effect on preventing liquid leakage and gas penetration, and is especially suitable for some sealing applications that require oil resistance and chemical resistance.
Polyester (PET) hot melt: Polyester hot melt is known for its excellent dimensional stability and weather resistance. Its crystallinity and orientation can be adjusted in a wide range, so as to meet the needs of different sealing applications. The softening temperature of ordinary polyester hot melt is around 120℃-200℃, and its heat resistance and bonding performance can be further improved by modification. It works well as a bonding and sealing material in the textile, clothing, packaging and other industries. It can effectively prevent fiber displacement and air infiltration, and maintain the appearance and performance of the product. However, the long-term stability of polyester hot melt wire in strong acid and alkali and high temperature and high humidity environments is relatively poor, and material selection and modification need to be carried out according to specific circumstances.
Polyolefin (PO) hot melt wire: Polyolefin hot melt wire mainly includes polyethylene (PE) and polypropylene (PP), etc. These materials have good flexibility, low temperature resistance and electrical insulation, and their softening temperature is relatively low, generally between 80℃-140℃. In the fields of food packaging, agricultural greenhouse film, light industrial products, etc., polyolefin hot melt wire is widely used as a sealing material. It can ensure the freshness of the packaging contents and prevent the entry of external pollutants. At the same time, it has good processing performance and is easy to achieve rapid sealing through hot melt processing. However, the heat resistance and oil resistance of polyolefin hot melt wire are relatively poor, and it is limited in some sealing applications at high temperature or in contact with oil.

4. Supplier selection and quality control
Supplier reputation and experience: Selecting a hot-melt supplier with good reputation and rich experience is an important prerequisite for ensuring material quality. Suppliers with a good reputation usually have strict standards and specifications in raw material procurement, production process control, product quality testing, etc., and can provide stable and reliable hot-melt products. At the same time, they often have a long development history and successful application cases, which can provide a strong reference for your purchasing decision. For example, the hot-melt products produced by some well-known chemical companies enjoy a high reputation in the market, and their quality and technical services have been recognized by many customers.
Quality certification and testing standards: The hot-melt materials provided by the supplier should comply with relevant quality certification and testing standards, such as ISO 9001 quality management system certification, ISO 14001 environmental management system certification, etc. These certifications indicate that the supplier pays attention to quality and environmental sustainability in the production and management process. In addition, hot-melt materials also need to meet specific industry standards and application requirements. For example, in the field of food packaging, the materials need to comply with the requirements of relevant food safety regulations such as the FDA (U.S. Food and Drug Administration) to ensure that the safety and sealing of the products meet the strict standards of the food industry. When purchasing, ask the supplier to provide detailed quality inspection reports and certification certificates, and review and evaluate the various performance indicators of the product to ensure that the purchased hot melt material meets the expected quality and sealing performance requirements.
Sample testing and evaluation: Before determining the supplier and purchasing batch products, sample testing and evaluation are essential steps. By requesting samples from suppliers, a series of laboratory tests and simulation experiments are conducted on the sealing performance, temperature resistance, chemical resistance, mechanical properties, etc. of the hot melt material according to the actual application conditions and test standards, so as to intuitively understand the performance of the material and determine whether it meets your specific application requirements. For example, when testing the sealing performance of the hot melt, a gas permeation tester or a liquid leakage tester can be used to pressurize and maintain the test piece sealed with the sample material, observe the gas or liquid leakage within a certain period of time, and thus evaluate its sealing effect. If the sample test results are not ideal, even if the supplier’s quotation is low and the delivery cycle is short, you should carefully consider whether to choose the supplier’s products to avoid product quality problems and economic losses due to poor material sealing performance in actual applications.

5. Cost-effectiveness analysis and material optimization
Cost factor: When selecting hot melt materials, cost is one of the important considerations. There are large differences in the prices of hot melts of different materials. For example, polyamide hot melts are usually more expensive, but their sealing effect and service life in high-performance applications are longer, which can provide better cost-effectiveness; while polyolefin hot melts are relatively cheap, and are an economical choice in some cost-sensitive sealing applications where performance requirements are not particularly high. In addition, factors such as the purchase volume, transportation costs, and processing technology requirements of materials will also affect the final cost-effectiveness, and comprehensive considerations are needed to select the most cost-competitive hot melt materials.
Performance optimization and customization: In order to reduce costs while meeting sealing performance requirements, you can work with suppliers to optimize the performance and customize the development of materials. By adjusting the formula, fiber structure, additives, etc. of the hot melt, you can get materials with specific performance characteristics, which can not only meet your application needs, but also avoid unnecessary performance excess, thereby achieving effective cost control. For example, in some applications that have certain requirements for chemical resistance but do not require extremely high heat resistance, the chemical resistance of polyester hot melt wire can be improved by adding an appropriate amount of chemical resistant additives to it, without choosing the more expensive polyamide hot melt wire.

6. Practical application case analysis
Sealing application cases in the automotive industry
In automobile manufacturing, hot melt wires are widely used in the bonding and sealing of body parts, such as the assembly of car seats, the connection between the dashboard and the body, and the sealing of car doors. A certain automobile manufacturer uses specially modified polyamide hot melt wire in the bonding and sealing of the seat back and the sponge layer. This hot melt wire not only has good heat resistance and chemical resistance, and can withstand the high temperature environment inside the car and the erosion of various detergents and lubricants, but also its high elasticity and bonding strength ensure the sealing and comfort of the seat during long-term use. After actual application tests, the seats using the hot melt wire can still maintain good sealing effects after multiple seat adjustments, collision tests, and long-term weather resistance tests, without problems such as air leakage, water ingress, or material aging and cracking, which effectively improves the quality and reliability of car seats, and also reduces the after-sales maintenance costs caused by poor sealing for car manufacturers.
Sealing application cases in the electronic and electrical industry
In the field of electronic and electrical appliances, electronic products such as mobile phones, tablets, and laptops usually use hot melt wires to seal the shell seams and button parts in order to prevent dust and moisture from entering the internal circuit board area. An electronic equipment manufacturer selected polyester hot melt wire as the sealing material for the shell in the design of a new tablet computer. The polyester hot melt wire has been modified to have a low softening temperature and good fluidity, and can achieve fast and uniform hot melt processing on the production line. At the same time, its sealing performance after curing is excellent, which can effectively block the intrusion of tiny particles and water vapor. In the reliability test of the product, after rigorous drop test, humidity test and temperature cycle test, the tablet computer shell sealed with this hot melt did not fail to seal, ensuring the normal operation of the internal electronic components and improving the overall quality and market competitiveness of the product.

7. Future development trends and prospects for innovative materials
With the continuous advancement of science and technology and the increasing diversification of market demand, the application of hot melt materials in the field of sealing will continue to expand and deepen. In the future, the research and development of hot melt materials with higher performance, more environmental protection and more intelligent will become an important development direction.
High-performance composite hot melt: By compounding a variety of polymer materials, such as blending or copolymerizing polyamide with polyester, polyolefin with elastomer, etc., the advantages of each material can be combined to develop a composite hot melt material with higher heat resistance, chemical resistance, mechanical properties and sealing. For example, the developed polyamide/polyester composite hot melt has both the good heat resistance and chemical resistance of polyamide and the excellent dimensional stability and cost advantage of polyester. It has broad application prospects in aerospace, high-end electronic equipment and other fields with extremely high requirements for sealing performance.
Environmentally friendly hot melt wire: In the context of increasingly stringent environmental protection policies, the development of degradable, non-toxic and harmless environmentally friendly hot melt wire materials has become an inevitable trend. Bio-based hot melt wires, such as hot melt wires made from biodegradable polymers such as polylactic acid (PLA) and polyhydroxyalkanoates (PHA), have good biodegradability and environmental friendliness. They can effectively reduce environmental pollution in sealing applications in packaging, agriculture, disposable products and other fields, and meet the requirements of sustainable development.
Intelligent hot melt wire materials: Combining intelligent material technology, the development of intelligent hot melt wire materials with sensing, response and self-healing functions will bring revolutionary changes to the sealing field. For example, adding nanosensors or shape memory materials to hot melt wires enables them to monitor the sealing status in real time. When a small leak or damage is detected in the sealing part, the self-healing mechanism of the material can be automatically triggered to restore the sealing performance, thereby greatly improving the reliability and service life of the product and reducing maintenance costs.

In short, choosing the right hot melt wire material is crucial to improving sealing. International wholesale buyers should consider multiple factors such as material properties, application requirements, working environment, supplier reputation, quality control and cost-effectiveness when selecting materials. At the same time, they should pay attention to the future development trend of the industry and the application of innovative materials to ensure that the purchased thermal fuse products can meet the ever-changing market and the high-quality requirements of customers, stand out in the fierce market competition and achieve sustainable business success.