Properties and applications of polyamide hot melt adhesives

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For information on the properties and applications of polyamide hot-melt adhesives, please call 0595-8816-7918 to get more updates from Qingyi Chemical. Polyamide resins were originally invented by the American company DuPont, and it has been over 60 years since then. Polyamide resins have a complex structure, but due to their regular and symmetrical structure, low steric hindrance, and the polarity of the amide groups, they exhibit properties such as easy crystallization, high melting points, and poor solubility; as a result, they are difficult to use as hot-melt adhesives. With the development of polymer chemistry, people have gained a deeper understanding and research into the structure of polyamides, and high-performance polyamide hot-melt adhesives have been developed through modification. Its main advantage is a narrow range of softening points; it solidifies immediately at temperatures slightly below its melting point, and it has good oil and chemical resistance ； Furthermore, due to the presence of polar groups such as amino, carboxyl, and amide groups in the molecule, it exhibits good adhesion properties to many polar materials. Therefore, it is widely used in industries such as footwear, apparel, electronics and telecommunications, home appliances, automobiles, and machinery. 1. Types and characteristics of polyamide hot-melt adhesives. Polyamides can generally be divided into two major categories based on their synthesis methods. One category is formed by the polycondensation of diacids and diamines. Another category is obtained by the polycondensation of ∞-amino acids or by the ring-opening polymerization of caprolactam. Due to its extremely high melting point, polyamide is generally converted into a copolyamide when used as an hot melt adhesive, thereby giving it a lower melting point and a longer curing time. Its strong polarity allows for significant intermolecular forces, resulting in excellent adhesion properties. Polyamide hot melt adhesive is solid at room temperature and liquid above its melting point. It possesses fluidity and wetting capacity, and upon curing and cooling, it forms a highly strong bond. Polyamide hot-melt adhesives can be formulated into products with different softening and crystallization points to meet the requirements of various operating temperatures. Polyamide hot melt adhesives are mainly divided into 3 categories: (1) diacid type, namely the polycondensation product of diacids and aliphatic diamines ； (2) Nylon type, namely copolymers of nylon 6, 6/12, 6/66/10, etc. (3) Binary or ternary copolymers of aromatic dicarboxylic acids with aliphatic diamines, or aliphatic dicarboxylic acids with aromatic diamines. The first two types are commonly used; the third type improves flexibility and viscosity by introducing aromatic groups and other side chains, as well as copolymers, into the molecule. However, due to the use of a solution polymerization method, the post-treatment of solvent separation inevitably leads to environmental pollution. 2. Main performance characteristics of polyamide hot melt adhesives: (1) Wash resistance of polyamide hot melt adhesives. The wash resistance of these adhesives is primarily related to the hygroscopicity of the polyamide; the higher the ratio of methylene groups to amide groups in the molecular chain, the lower the hygroscopicity and the better the wash resistance. The wash resistance of various nylons is as follows: PA1212 > PA12 > PA11 > PA1010 > PA612 > PA610 > PA66 > PA6. At present, high-quality polyamide hot-melt adhesives used abroad are all based on PA6/PA66/PA12 terpolymers, with the proportion of PA12 being over 40% (acting as the main component). Li Zaiseng and others from Ningbo Huadong Hot Melt Adhesive Co., Ltd. prepared PA6/66/1010 terpolyamides with different melting points by using various mixing ratios; these polymers exhibited low melting points and good flexibility. To improve its wash resistance as well as its adhesion strength and flexibility, foreign countries have also used branched 2,2,4-trimethylhexamethylenediamine and 2,2,4-trimethylhexamethylenedioic acid to produce nylon salts for the synthesis of polyamide hot-melt adhesives; this approach has led to a significant improvement in wash resistance. However, the availability of these raw materials is limited and their prices are high ； Additionally, dimers of fatty acids and linear Cs–C are also used abroad. dicarboxylic acids of s and linear C. Polyamide hot-melt adhesives are synthesized using diamines as raw materials; these adhesives exhibit good resistance to washing. However, due to the overly long alkyl chains of the dimeric fatty acids, as well as the presence of a certain amount of monofatty acids in those dimeric fatty acids, their resistance to dry cleaning is poor. In recent years, the application market for long-chain nylons has developed rapidly; the fields of use for PA11 and PA12 continue to expand, and more manufacturers are using PA12 to produce high-quality hot melt adhesives. Organizations such as Zibo Mining Bureau have utilized the technology provided by the Chinese Academy of Sciences and Zhengzhou University to synthesize long-chain nylons such as PA1111 and PA1212 by using biological fermentation to break down petroleum-derived dicarboxylic acids; industrial production of these materials has been achieved, and they hold the potential to replace nylon 11 and nylon 12. (2) Thermal oxidability and thermal stability of polyamide hot melt adhesives: Polyamide hot melt adhesives need to remain in a molten state for extended periods during heat processing and use, which makes them prone to thermal oxidative degradation reactions. During thermal oxidation, polyamides undergo chain scission and cross-linking, resulting in changes in their molecular weight and mechanical properties. Since most polyamide hot-melt adhesives are prone to thermal oxidative degradation, it is essential to improve their resistance to thermal oxidation. 3. Applications of polyamide hot melt adhesives (1) Applications in textiles: Textiles that use hot melt adhesives include clothing, carpets, and fabric flocking. The traditional clothing industry relies heavily on manual sewing, which is not only time-consuming but also requires experience and skill ； Using hot melt adhesive to bond trims, lace, and decorations not only allows for permanent bonding with clothing fabrics, thereby making the garments more durable, structured, and smooth in appearance, but it also helps reduce costs and **improve work efficiency**. The biggest obstacle in the application of hot melt adhesives for fabric bonding is fabric cleaning, namely dry and wet wash resistance as well as the fine texture that resists washing. Due to its excellent wash and dry clean resistance, polyamide hot melt adhesive has become the mainstream product for hot melt adhesives in the apparel industry. (2) Applications in the electrical industry: Due to its excellent flexibility, oil resistance, dielectric properties, and strong adhesive strength toward various materials, polyamide hot melt adhesive is also widely used in industries such as electrical equipment. (3) Applications in the shoe industry: Adhesives used in shoes are commonly employed for bonding parts such as the upper, outsole, main sole component, toe cap, heel, eyelet, and insoles. The materials used for the upper are typically natural leather, synthetic leather, and fabrics, while the materials for the soles are usually rubber and plastics. Due to the irregular shape of the upper during bonding, gluing can only be done at certain areas of the shoe upper; it is necessary to bond it to the outsole without leaving any glue on the outside of the upper, which could affect its appearance, thus increasing the difficulty of the bonding process ； Polyamide hot melt adhesives possess excellent flexibility, making them very suitable for bonding in shoe lasts, such as at the toe part, heel cup, and heel wrap. Polyamide hot melt adhesives for shoes generally use polyamides with a low relative molecular mass; however, by thermally mixing polyamides with a small amount of epoxy resin and plasticizers, the adhesive strength and toughness of the hot melt adhesive strips used in shoes can be significantly improved. (4) Other applications: Polyamide hot melt adhesives can also be used for bonding metals. The hot-melt adhesive strip, made by thermal mixing of polyesteramide and polystyrene, exhibits good adhesion to metals and high bonding strength, maintaining ideal adhesion even under aging conditions and at high temperatures. Polyester amide is produced by a two-step copolymerization reaction using polyester prepolymer (50%–80%) and polyamide prepolymer (20%–80%); the polyester acts as a crystalline segment, which confers to the adhesive a higher melting point and bonding strength ； Polyamide, as an amorphous block, imparts wetting properties, elasticity, and rubber-like characteristics to the adhesive ； Polystyrene enhances the bonding strength of adhesives, reduces melt viscosity, and provides anti-aging properties. Introducing polyethylene or polypropylene-based copolymers into PAll and PAl2 series polyamides can **improve the adhesion strength of the polyamides. The preparation method can employ a two-step approach: first, a polyamide resin is formed in a reactor, and then polyester is added to produce polyesteramide IV. Thanks to its excellent adhesion to metals and non-polar plastics, as well as its ability to bond at high speeds, polyamide hot melt adhesive can be widely used for laminating metals such as lightweight steel sheets and stainless steel sheets, as well as for laminating metals and plastics such as PET/steel sheets and PVC/steel sheets. Hot melt adhesives formulated using low softening-point polyamide resins, ultra-low softening-point polyamide resins, polyethylene, dibutyl phthalate, bisphenol A epoxy resin, and rosin resin are cold-resistant hot melt adhesives. Using polyamide resins with a low softening point (105–115°C) and an ultra-low softening point (43°C) as the matrix, it exhibits good flexibility and toughness at low temperatures. It also has excellent adhesion properties to plastics that are difficult to bond, such as polyethylene and polypropylene; therefore, it can be used for bonding car roofs as well as for reinforcing the roof arch beams. Qingyi (Fujian) Heat Transfer Printing Technology Co., Ltd. was founded in 1996; we have been dedicated to the research and development, testing, production, and advancement of chemical products for heat transfer printing ； The company’s headquarters is located in the Jinjiang Economic Development Zone (Wuliyuan), Fujian Province. It owns more than 20,000 square meters of land and over 30,000 square meters of production facilities. By adopting advanced international production and testing equipment, the company has achieved a high level of technical expertise and distinct product qualities, which have won it widespread recognition from both the market and its customers. Currently, our products and solutions have been applied in over 10** countries and regions, serving numerous top-quality heat transfer printing manufacturers. They help these clients improve efficiency, reduce costs, and develop new products, thereby gaining a competitive edge and generating more profits, and making heat transfer printing even more impressive. As a leading chemical supplier of heat transfer coating solutions in China, we offer competitive solutions for the production of heat transfer printing products! From manual to semi-automatic to fully automatic, continuous technological upgrades and improvements in product applications are implemented to create the greatest value for customers, paving the way for a bright future for heat transfer printing. Main products or services: Heat transfer coating chemicals ； Heat transfer heat transfer ink ； Heat transfer printing paste ； Screen printing hot melt adhesive ； Heat transfer release agent. 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