What is reactive polyurethane (PUR) hot melt adhesive?

What is PUR hot melt adhesive?

PUR (Polyurethane Reactive), also known as moisture-curing reactive polyurethane hot melt adhesive in Chinese, is primarily composed of an isocyanate-terminated polyurethane prepolymer. It is a single-component, 100% solids adhesive. PUR hot melt adhesive cures through both physical cooling and chemical reaction, resulting in excellent bonding performance and durability. It is widely used in furniture edge banding, bookbinding, packaging, electronics, and automotive applications.

Reaction principle of PUR hot melt adhesive

1. Physical curing stage (cooling and shaping)

PUR hot melt adhesive is a molten liquid when heated and has good fluidity and initial adhesion.

As the temperature drops, the molten adhesive cools and solidifies, quickly forming initial bonding strength (a few seconds to tens of seconds), making it easier to position and process.

2. Chemical reaction curing stage (moisture reaction)

PUR molecules contain isocyanate groups (–NCO).

Under the influence of air humidity or substrate moisture, –NCO reacts with water molecules to form urea groups (–NH–CO–NH–) and release carbon dioxide (CO₂).

Some –NCO groups will also react with hydroxyl groups (–OH) in polyols to form polyurethane bonds (–NH–CO–O–).

The adhesive layer gradually forms a cross-linked structure, ultimately achieving a bonding effect that is high-strength, resistant to high and low temperatures, resistant to chemicals, and resistant to aging.

The main characteristics of PUR adhesive

1. Single component, 100% solid content, solvent-free, green and environmentally friendly;

2. Strong initial adhesion, quick positioning and high production efficiency;

3. Excellent bonding effect on various substrates such as wood, plastic, metal, paper, textiles, etc.

4. After curing, the adhesive layer is tough and elastic, resistant to vibration and impact, and moisture and water;

5. Excellent high temperature resistance, no softening or sagging for a long time;

6. Highly compatible with automated production, suitable for high-speed gluing, edge banding machines, book binding machines and other equipment.

The difference between PUR and EVA hot melt adhesive

1. The ingredients are different. PUR belongs to polyurethane, and EVA uses ethylene vinyl acetate.

2. The reaction mechanisms are different. PUR cures with moisture and is irreversible after the reaction is complete. EVA is a physical adhesive that cures upon cooling and can be remelted after heating, making the operation reversible.

3. PUR is irreversible after curing, and has higher strength and high and low temperature resistance, and excellent resistance to heat, cold, water vapor, chemicals and solvents.

PUR hot melt adhesive instructions

Precautions for using PUR

PUR adhesive is highly sensitive to moisture and should be used as soon as possible after opening to avoid prolonged exposure to air.

The glue pot can be kept clean for 48 hours (in a sealed state). If the time is exceeded, the glue pot may absorb moisture and solidify, so the solidified material should be cleaned in time.

During a short shutdown, the temperature of the hose, pressure plate, and gluing shaft should be reduced to 80-100°C for insulation, or the heating system should be turned off.

Do not maintain high temperature of 140~145℃ for a long time when there is no operation, otherwise it will easily cause aging of the colloid and equipment.

It is recommended to clean the hose every three months. If conditions are limited, clean it at least once every six months.

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