How Much Do You Know about Hot Melt Adhesive

1、 Composition of hot melt adhesive

(1) Polymer: Provides strength, toughness, bonding strength, and weather resistance.

(2) Thickener: improves adhesion, improves wettability, and reduces viscosity.

(3) Diluent: Reduce viscosity, improve operational performance, adjust curing speed and opening time.

(4) Antioxidant: slows down the aging and deterioration of hot melt adhesives.

2、 Characteristics of hot melt adhesive

1. Advantages

(1) 100% solid, solvent-free and pollution-free

(2) Fast curing speed, suitable for high-speed automatic production lines

(3) Low energy consumption, no need for drying equipment

(4) Convenient transportation and long storage period

(5) Thermoplasticity, which can be melted and reused.

2. Disadvantages

(1) Narrow usage temperature, poor high temperature and cold resistance

(2) Limited adhesive strength

(3) Require specialized coating equipment

 

3、 Types and applications of hot melt adhesives

1. PUR hot melt adhesive (Polyurethane Reactive) is a moisture cured reactive polyurethane hot melt adhesive in Chinese. The adhesion and toughness (elasticity) of PUR can be adjusted, providing excellent adhesion strength, temperature resistance, chemical corrosion resistance, and aging resistance.

PUR adhesive is a molecular structure containing polar and chemically active amino ester groups (- NHCOO -) or isocyanate groups (- NCO -), which have excellent adhesion with materials containing active hydrogen, such as porous materials such as wood, leather, fabrics, paper, ceramics, and surface finishing materials such as plastic, metal, glass, rubber.

2. EVA hot melt adhesive (Ethylene Viny Acetate) is a plastic material composed of ethylene (E) and vinyl acetate (VA). The general VA content is between 5% and 40%. It is widely used in the fields of foam shoe materials, functional greenhouse films, packaging films, and wires and cables.

 

4、 Main testing indicators of hot melt adhesive

Viscosity: Brinell viscometer

Thermal stability: 200ml beaker 100g, 175 ° C for 72 hours

Heat resistance: Simulated practical applications, SAFT (shear failure temperature), PAFT (peel failure temperature)

Opening hours

Curing speed

Initial adhesion force: rolling ball method, ring method

Peel strength: 180 °, 90 °

Aging resistance

 

5、 The main factors affecting the adhesion of hot melt adhesive

Three major factors: adhesive, substrate, equipment and process

(1) Adhesive: Its year, softening point, opening time, affinity, cohesion, high temperature resistance, and aging resistance can all affect the bonding effect.

(2) Substrate: The polarity, density, surface tension and temperature, moisture, surface treatment agents and contamination, surface morphology, adsorption and transfer properties of the substrate can all affect the bonding effect.

(3) Equipment and process: The speed of the production line, glue temperature, opening distance, pressure, glue amount, and glue application mode also affect the bonding effect.

 

6、 Correct usage of hot melt adhesive

(1) Choose different types of hot melt adhesives correctly based on application requirements and equipment process conditions. Process parameters such as set temperature, pressure, and glue usage need to be adjusted appropriately. The temperature setting should not exceed 200 ° C to slow down the carbonization of hot melt adhesive and equipment damage.

(2) The amount of glue used should be suitable.

(3) When replacing materials with different properties, it is necessary to retest the adhesive's adhesion performance and aging rate.

(4) Keep the glue box clean and regularly check the position of the glue in the box.

(5) If the production line is temporarily shut down for more than 2 hours, the working temperature of the hot melt adhesive machine should be lowered by 20-30 ° C, and then the temperature should be adjusted back to the set value during operation.

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