1 What is... PUR Hot melt adhesive

PUR Yes Polyurethane Reactive The abbreviation , Belongs to the polyurethane system , By chemical properties , Polyurethane hot-melt adhesives can be divided into two categories. , One type is thermoplastic polyurethane hot-melt adhesive. , The other type is reactive polyurethane hot-melt adhesive. The former hardens upon cooling after being heated, forming a bond. , The latter, after being heated, crosslinks and cures upon reaction with moisture through cooling. , Produces adhesion. Thermoplastic polyurethane hot melt adhesive is also known as hot melt polyurethane hot melt adhesive. (TPU) And reactive polyurethane hot-melt adhesive (PUR) It can also be divided into moisture-curing polyurethane hot-melt adhesives and blocked polyurethane hot-melt adhesives. What we often refer to as... PUR It is a moisture-curing, reactive polyurethane hot melt adhesive. PUR It boasts excellent bonding strength. , Temperature resistance , Chemical corrosion resistance and aging resistance , It is now widely used in national economic sectors such as packaging, wood processing, automotive, textiles, electromechanical engineering, and aerospace.

2、 PUR What are the characteristics of hot melt adhesive?

PUR The adhesive contains urethane groups with polarity and chemical reactivity in its molecular structure. ( ← NHC ○○ -) or isocyanate group

(-NCO), With materials containing active hydrogen , It exhibits excellent adhesion to both porous materials such as wood, leather, fabrics, paper, and ceramics, as well as smooth-surfaced materials like plastics, metals, glass, and rubber. In terms of gluing processes... ,PUR Hot melt adhesive is applied under conditions that inhibit chemical reactions. , Heat and melt into a fluid. , So that after the two adherends are bonded and cooled, the adhesive layer will coalesce and exert its bonding effect. ; Subsequently, it reacts with and extends the chain by utilizing the moisture present in the air as well as the moisture adhering to the surface of the bonded material. , Generate highly cohesive polymer polymers. , Significantly improves adhesion, heat resistance, and low-temperature resistance. Due to its extremely high reactivity, , Therefore, it exhibits excellent adhesion to a wide variety of materials. Polyurethane hot-melt adhesives also have other classification criteria. , By shape , It can be divided into adhesive films, adhesive tapes, and powders. 3 Type of adhesive. After the solution evaporates from the surface of the material to be bonded, it forms a hot-melt adhesive film. The tape has a reinforcing material or carrier as its backing. , The adhesive film, meanwhile, is supported by the adhesive itself.

3 — The differences and connections between it and ordinary hot melt adhesives

In the past, most hot melt adhesives were made using ethylene-vinyl acetate. (EVA Made from thermoplastic resins such as polyester and polyamide.

Due to And E ∨ A It has poorer strength and elasticity compared to polyester hot melt adhesive. , Cannot withstand excessive external force. ; Also, due to the thermoplastic polyamide adhesive...

High melting point and hardness , Therefore, its use is subject to certain limitations. Meanwhile, polyurethane has long been regarded as less suitable for use as a hot melt adhesive.

Merit , Because its carbamate bond is unstable at the application temperature. , Therefore, there are few varieties of polyurethane hot-melt adhesives. , The application field is also relatively narrow.

In recent years, research on polyurethane hot-melt adhesives has once again become active in various countries. , This has led to new developments in hot melt adhesives in terms of both variety and performance.

With EVA Hot melt adhesive , Water-based /) Compared to solvent-based adhesives ,PUR Has the following advantages :

1) Solvent-free , —Liquid type. Unlike solvent-based adhesives, it doesn’t require a drying process. , No environmental pollution due to the presence of solvents.

And the issue of poisoning , Meets environmental protection requirements. The bonding process is simple. , Applying methods such as roller coating or spray coating can be used.

2) Good operability. The two bonded objects can be securely fixed in a short period of time. , Therefore, the assembly components can be quickly transferred to the next processing stage.

Preface , Improve efficiency.

3) Excellent performance in heat resistance, cold resistance, steam resistance, chemical resistance, and solvent resistance. Compared to conventional hot melt adhesives, it... , Due to the opposition

The crosslinked structure of thermoplastic hot melt adhesives significantly enhances the listed properties as well as the bonding strength.

4. PUR Solidification treatment

1)           Moisture-curing polyurethane hot melt adhesive

Moisture-curing polyurethane hot melt adhesive is end- -NCO The base prepolymer serves as the base material. , Combined with a thermoplastic that does not react with isocyanate groups.

Made from additives such as thermosetting resins, tackifying resins, antioxidants, catalysts, and fillers. The adhesive is heated and melted into a fluid state. , Coating

On the surface of the adhered substrate , To put 2 The adhered object is bonded. , Bonds upon cooling. , Thereafter, moisture in the air or trace amounts of water and other compounds containing active hydrogen in the adhered substrate are utilized to react with... NCO The group undergoes a reaction and chain extension. , Polymer with a cross-linked network structure and high cohesion , To further enhance adhesion. In isocyanates, NCO The group readily reacts with compounds containing active hydrogen.

2) Closed-type polyurethane hot melt adhesive

The end of the polyurethane prepolymer -NCO The group is capped with a capping agent under certain conditions. , Form a closed-type prepolymer.

body. In fact, it’s about freeing the free-standing -NCO Protect the group. , Make it non-reactive at room temperature. , Improved storage stability of the adhesive. : When heated to a certain temperature, the sealant undergoes dissociation. , Active -NCO Group regeneration , It can undergo chemical reactions with active hydrides such as polyols, amines, and water, leading to crosslinking. Commonly used blocking agents include oximes, phenols, sodium bisulfite, pyrrolidone, and others.

5. PUR Applications of hot melt adhesive

Since the dissociation temperature of sealants is mostly at 100 ° C The above , It often causes bubbles to form in the adhesive layer. , So, closed-cell polyurethane.

Hot-melt adhesives are used only for maintenance applications, etc. Although moisture-curing reactive hot-melt adhesives boast excellent performance, , But due to its manufacturing, storage, and transportation...

Moisture must be strictly isolated during sizing. , This has placed certain limitations on its promotion. In recent years, , Due to breakthroughs in technology and equipment,

The exhibition gradually addressed these issues. , The applications are gradually increasing.

PUR Hot melt adhesive can bond not only porous materials. , Such as foam plastics, ceramics, wood, fabrics, and so on. , Moreover, it can bond materials with smooth surfaces. , Such as steel, aluminum, stainless steel, metal foil, glass, plastics, leather, and rubber. It also exhibits remarkably high cohesive strength. , The ratio of ingredients can be adjusted as needed. , To obtain a series of adhesives ranging from flexible to rigid. The key characteristic of reactive polyurethane hot-melt adhesives is that they can cure under ambient conditions. , It has a lower application temperature than traditional hot melt adhesives. In short, , This is a hot melt adhesive with relatively good overall performance. , and is applied in the following industries :

(1) Automotive Structure and Components , Such as windshield sealing and lighting fixture assembly

(2) Textile and footwear industries , Such as fabric seam bonding and sole bonding , It boasts advantages such as water resistance as well as softness and comfort.

(3) Wireless bookbinding , Due to the flexibility of the adhesive layer , Ensures high flatness when books are opened. , And prevent the formation of grooves at the binding or the book from suddenly closing shut while reading. , than EVA Binding is more superior. ;

(4) Food packaging industry , Can withstand high- and low-temperature sterilization treatments as required by food hygiene regulations. I

(5) Woodworking and Furniture Industry , The adhesive layer exhibits excellent water resistance and aging resistance. , And it does not contaminate or corrode wood. :

(6) Electronics and Electrical Appliances Industry , Rapid curing of the adhesive layer , No need to mix adhesive. , Low shrinkage upon curing , Particularly suitable for bonding precision components in the electronics industry.

6、 PUR the development of

Although reactive polyurethane hot-melt adhesives have exceptionally outstanding performance characteristics, , However, there are still some technical issues that need to be addressed. ,

As : Reduce the melting temperature and melt viscosity. ; Improve initial adhesion , Shorten the positioning time ; Enhance the product’s flexibility, heat resistance, and flame retardancy, among other properties. Additionally... , The preparation processes and equipment, as well as gluing equipment, currently still lack sufficient development and are imperfect. , The cost is also relatively high. Reactive polyurethane hot-melt adhesives represent a new generation of high-performance adhesives. , It has a wide range of applications and promising development prospects, based on current research findings. , The next step should focus on research aimed at enhancing its overall performance, improving the creep resistance of hot-melt adhesives, increasing flexibility, reducing melt viscosity, and boosting heat resistance and flame retardancy. At the same time, ... , The preparation process and gluing equipment should be improved. This high-performance, environmentally friendly green adhesive not only offers significant economic benefits but also holds great social value. , Moreover, it holds positive significance for promoting green consumption among the entire population.