Reactive PUR adhesive has the advantages of solvent-free, high bond strength, fast fixation, water washing resistance, aging resistance, and less VOC emission. This paper mainly describes the application and development trend of reactive hot melt polyurethane PUR in different industries, such as more and more widely used in industrial and civil industries, including building materials, woodworking, automobile, textile, electronics, household appliances and so on. According to the design and analysis of the bonding principle of reactive hot melt polyurethane, the market pain points and research directions are universal function, double curing, packaging diversification and so on.

Firstly, the reactive hot melt polyurethane (PUR) is introduced. PUR adhesive can be regarded as the prepolymer of polyurethane, and isocyanate-based end polymers of different molecular weights can be obtained by reacting different isocyanates (different types, different functional degrees, different branched chains, etc.) with different polyols (polyester type, polyether type, mixed type). These polymers contain reactive aminoester or isocyanate groups, which have strong activity and polarity, and can bond well with materials containing active hydrogen, such as textiles, paper, wood, ceramics, leather, rubber, glass, as well as smooth surface materials such as plastics and metals. Hydrogen bond is formed between polyurethane macromolecular chains or between the adhesive, which enhances molecular cohesion, higher bond strength, better wear resistance and solvent resistance. Polyurethane with ether bond is easy to rotate and has good flexibility, so it shows good low temperature performance and hydrolysis resistance. This paper introduces the specific application and research direction of reactive hot melt polyurethane PUR according to its adaptability to the substrate.

Bonding principle of reactive hot melt polyurethane PUR

The curing process of PUR hot melt adhesive is divided into two stages: cooling condensation and moisture curing. In the first stage, PUR hot melt adhesive is the same as ordinary thermoplastic hot melt adhesive. The adhesive is heated and fused. After sizing on the base material, the initial adhesive strength is generated by cooling and condensation. In the wet curing stage, PUR hot melt adhesive reacts with the moisture in the air to form a rigid structure of polyurethane molecular chain, so that it has high bonding strength, good chemical resistance, heat resistance, hydrolysis resistance, and can be bonded to a variety of types, such as paint surface treated with good compatibility.

Typical applications of reactive hot melt polyurethane PUR

1. Building materials industry

With more and more personalized requirements for home decoration, on-site decoration needs more manpower and material resources, and more construction waste is generated. Therefore, customized home decoration building materials are becoming more and more popular, mainly reflected in integrated wallboard and ceiling, which is also the main application point of PUR in building materials. Building materials industry is arguably and woodworking industries have a bigger relevance and application scenario is similar, different colors, patterns of the PVC skin nicely on the wood plastic board for various types of plate, wall panel manufacturer again according to the requirements of different individuals semifinished product and good size cutting plate, can be installed in the semifinished product directly put the plank, Instead of wall scraping, painting, woodworking, wallpaper, etc. Lower cost, faster decoration speed, more diverse choices, integrated wallboard and ceiling is a new trend in the building materials industry, so there are a lot of wallboard manufacturers, also means the opportunity of PUR adhesive. This kind of material application, there are still a considerable number of manufacturers using solvent-based products, but the characteristics of PUR without solvent, high bond strength, low comprehensive cost will gradually completely replace solvent glue, manufacturers in the industry are actively exploring this market, in the next few years, the amount of PUR in this market may have explosive growth.

2. Woodworking industry

Woodworking industry is one of the most main industry at present domestic PUR application, consumption is expected to more than 15000 tons in 2020, but also the most concentrated PUR manufacturers at home and abroad the most competitive industry, woodworking industry, the main points including furniture, bedding face of appressed stick a skin, coated, aluminum alloy window frames, furniture edge banding, such as different application materials, process flow, Different requirements are put forward for PUR, which is mainly divided into flat adhesive and coating adhesive. The former has a low requirement for initial strength, while the latter has a high requirement for initial strength. There is a 10%~20% difference in price between the two. Carpentry industry PUR users are more dispersed, there are great river north and south, equipment differences, climate differences, material differences, production rate differences and so on, PUR requirements are different and the threshold of entry is relatively low, after a few years of carpentry industry is still the focus of PUR.

3. The automobile industry

The application of PUR in the automotive industry is mainly the assembly or fitting of parts, including headlight shell assembly, roof skylight frame bonding, spare tire cover plate composite, interior parts vacuum composite, door panel structural parts bonding, etc.

Headlamps shell assembly is PUR a great applications in the automotive industry, due to air tightness test online, so to PUR adhesive glue with high initial strength requirements, PC chimney to prevent mist processing at the same time, also to PUR adhesive glue on the bonding performance request, and lights in the external environment for a long time, weather resistance for PUR adhesive glue can also request. Based on the requirements of basic adhesion and long-term weather resistance, the choice of adhesive for headlight manufacturers is conservative.

Due to the high strength and good heat resistance of PUR adhesive, it can meet the load-bearing and heat resistance needs of roof skylight frame. Therefore, more and more domestic manufacturers of roof use PUR to replace non-reactive hot melt adhesive such as EVA or PO and solvent chloroprene adhesive. Another major application of PUR in the automotive industry is the composite of interior parts, such as door panels, seat backs, and upholster panels. These parts at present domestic many USES is solvent-based glue, even if some vendors also gradually adopted a more environmentally friendly water-based glue, but the basic process is very similar, first the spray adhesive, dry again, then laminating or vacuum forming, need a lot of human labor, production efficiency is not high also, and PUR composite used for interior trim parts, only need to put the volume on the device of automatic forming, Such a production line requires only one worker.

4. Home appliance industry

With the intensification of competition in the home appliance industry, home appliance manufacturers are becoming more and more concentrated. Many small manufacturers have gone out of business, and large manufacturers have reduced the manpower input in the production line and increased their efforts in automatic production due to cost considerations. The traditional adhesive tape or other fixed methods require a lot of manpower, and the appearance of PUR meets the requirements of electrical appliance manufacturers for automation. The base material of home appliance bonding is mainly glass panel and ABS frame bonding, so the application point of PUR includes air conditioning panel, washing machine cover glass, drinking machine glass panel, range hood control panel and so on. For example, domestic air conditioning, wall hanging panel, air conditioning, water dispenser, range hood and so on almost all use PUR bond. Home appliance uses PUR product is not only the replacement of adhesive, it is the progress of production technology, can expect home appliance to use PUR will be more and more extensive.

5. Textile industry

The textile industry is also one of the earlier industries in which PUR is applied. As early as the end of last century, many textile enterprises have used PUR for fabric fitting, including water-splashing fabric fitting of charging clothes, breathable film fitting of different fabrics, female underwear fabric fitting, diving suit fabric fitting and so on. Although the application of PUR in the textile industry has been relatively early, due to the variety of textile enterprises, small yield dispersion and other reasons, solvent glue PUR has always been coexisting, until now there are still a considerable number of enterprises using solvent glue.

6. Electronics industry

With the development of handheld electronic devices, especially smart phones in recent years, people put forward more and more requirements for large screen, material diversification and so on, so the application of PUR is becoming more and more widespread. Due to its fast fixation and high bond strength, PUR has gradually replaced tape in specific applications such as frame bonding and screen bonding in mobile phones. Bluetooth earbuds and portable audio devices are also assembled using PUR.

Research direction of reactive polyurethane

According to the above analysis of the application of reactive polyurethane PUR in multiple fields, according to the pain points and demands of each market, the research direction of PUR is also deepening with the continuous improvement of performance requirements, environmental protection requirements, and replacement requirements for other solvent-based glues, the function is constantly universal, and the application is also constantly expanding. Mainly for the following aspects.

1. Universal function

PUR though is a new type of adhesive glue, but in different industries, due to the different factors influence different skin surface tension to a variety of PUR products to adapt to, and so on, various and a little is a sore point PUR industry at present, developing a or a few good commonality/substrate wide adaptability of PUR products is currently a research direction.

The initial strength of PUR product is obtained by cooling physical cross-linking, and the subsequent wet curing forms other bond cross-linking methods to obtain the final strength. However, the initial cooling physical bond strength is not high enough to meet the requirements, and the subsequent slow wet curing will also affect the production efficiency. According to the pain points and difficulties of different industries, PUR manufacturers have researched and developed dual curing PUR products, such as UV curing + moisture curing. After construction, UV radiation can instantly accelerate the curing of PUR and achieve a certain operating strength. Have adopted react when heated to melt at the same time, in addition to moisture curing help after cooling, also instantly at bond strength, this is a hot type of single-component PUR glue, is stable at room temperature, heating internal reaction and curing, no by-products, bond strength is high, stable performance is good, have a two phase system, Masking active hydrogen and masking isocyanate three types.

With the comprehensive well-being of China, a happy and healthy life has become the standard people increasingly pursue. Social development should not be at the expense of the environment. The country and society attach great importance to environmental protection and safety, desolvation and VOC emissions, especially driven by the European and American markets, non-solvent adhesives have achieved great development. Reactive hot melt polyurethane PUR as a new adhesive, will be in more industries and fields to be promoted and applied.