PUR (Polyurethane Reactive), whose full name is Moisture-Curing Reactive Polyurethane Hot Melt Adhesive, is primarily composed of a polyurethane prepolymer with terminal isocyanate groups. PUR adhesives offer adjustable bonding properties and toughness (elasticity), along with excellent bonding strength, temperature resistance, chemical corrosion resistance, and aging resistance. It has become a significant category within the adhesive industry and is now widely applied across various sectors of the national economy, including packaging, wood processing, automotive, textiles, electromechanical, aerospace, etc.

PUR adhesives contain polar and chemically reactive urethane groups (-NHCOO-) or isocyanate groups (-NCO) in their molecular structure. They exhibit superior bonding strength with materials containing active hydrogen atoms, such as porous materials like wood, leather, fabric, paper, and ceramics, as well as smooth-surface materials like plastics, metals, glass, and rubber.

This article first introduces the characteristics and working principle of PUR hot melt applicators. It then elaborates on the installation safety precautions for PUR hot melt laminating machines, daily operational procedures, and safety considerations for PUR applicators. Finally, it details the precautions for changing PUR adhesive drums. For specific details, please follow the comprehensive explanation below.

Characteristics and Working Principle of PUR Hot Melt Applicators

Due to the unique properties of PUR hot melt applicators, PUR hot melt adhesive is also known as Moisture-Curing Reactive Polyurethane Hot Melt Adhesive or Moisture-Induced Hardening Reactive Polyurethane Hot Melt Adhesive, abbreviated as PUR hot melt adhesive. During hot melt application, it reacts and cures upon contact with moisture in the air. Therefore, the melting and application process using a PUR hot melt applicator must be completely isolated from air. PUR hot melt applicators are specifically designed for the application of polyurethane hot melt adhesives.

Installation Precautions for PUR Hot Melt Laminating Machines

When installing the hot melt applicator, a proper and effective grounding wire must be connected. Any equipment using high voltage requires a grounding wire. Without it, even components protected by insulation on the applicator could become conductive, posing an electric shock hazard.

Based on the load requirements of the hot melt applicator and its peripheral equipment, verify that the power cords used and the insulation protection comply with regulations. The wire load capacity must be higher than the applicator's rated power.

Ensure the voltage supplied externally to the hot melt applicator matches the applicator's specifications. For example, a single-phase 220V standard applicator will be damaged if supplied with 380V power. Conversely, supplying below 220V to such an applicator will prevent it from reaching its designed performance and may also cause damage. When wiring, ensure the power cord is correctly connected to the external circuit breaker.

Operate the hot melt applicator at the specified voltage. Using a voltage different from the specified one may cause the applicator to burn out.

PUR Hot Melt Adhesive Usage Method

Storage Conditions: Store PUR hot melt adhesive at 8~22°C (46~72°F) in a dark, dry place. Avoid excessive air humidity. Do not use products with damaged packaging.

Pre-Use Preparation:

Before use, check that the vacuum packaging is intact. Do not use if leaking.

Allow the adhesive to return to room temperature before use.

Pre-Heating: Preheat the adhesive without removing the aluminum foil seal (typically 5~15 minutes). Alternatively, preheat the intact package in an oven, recommended temperature: 100°C (212°F).

After preheating, remove the hardened adhesive skin from the top and bottom ends of the PUR adhesive cartridge before use.

Clean the bonding surfaces to remove oil, dust, paint, release agents, oxidation layers, or any other substances that might affect adhesion. Ensure the workpiece surfaces are dry.

Dispensing:

Dispensing temperature and air pressure vary depending on the project; consult KY technical personnel for specifics.

Use stainless steel dispensing needles whenever possible. The inner diameter of the needle tip depends on the specific project.

Before installing the needle tip, dispense a small amount of adhesive to ensure the PUR hot melt flows correctly.

The length of the needle tip exposed beyond the heater should not exceed 3mm.

Tip: It is generally recommended not to heat continuously for more than 4 hours, and not to reheat the same cartridge more than three times. Prolonged heating can cause skinning at the rear of the cartridge; piercing this skin layer can reduce dispensing pressure.

Assembly and Pressing: Apply PUR01 to the bonding surface at the application temperature. After positioning the parts, press them together firmly within the open time to achieve initial bonding.

Curing: Store the initially bonded components under suitable conditions for complete curing (full cure time varies depending on adhesive application amount, ambient temperature, and humidity; contact support staff if assistance is needed).

Daily Operational Safety Precautions for PUR Hot Melt Applicators

Avoid using PUR hot melt applicators near volatile, explosive materials, or gases. Do not store flammable or explosive items near the applicator.

Do not operate the hot melt applicator without appropriate protective devices, adequate insulation, or well-secured protective panels.

Only personnel professionally trained in maintenance should disassemble and repair the PUR applicator.

Do not operate the PUR hot melt applicator if the ambient temperature is below -20°C (-4°F) or above 80°C (176°F).

Ensure the operating area has no fast-flowing air. Rapidly flowing air cooling the PUR adhesive drum and melting platen will affect adhesive flow rate and waste energy.

When replenishing PUR adhesive, inspect the drum for deformation. Severely deformed PUR adhesive drums should be discarded to avoid damaging the applicator's platen.

Whenever disassembling the PUR applicator's hoses or dispensing guns, immediately seal any exposed PUR adhesive with silicone oil to prevent moisture-induced curing.

During prolonged applicator inactivity, seal the circumference of the applicator's heating platen with silicone oil to protect the performance of the PUR adhesive within the drum.

Precautions for Changing PUR Adhesive Drums

Before cleaning the PUR hot melt applicator, first disengage the heating platen from the PUR adhesive drum. After disengagement, maintain pressure in the lifting cylinder, then cut all power.

When detaching the drum, gradually increase the applied air pressure from low to high. Never use high-pressure gas directly to detach the drum to prevent accidents.

After the heating platen separates from the drum, and before cleaning residual adhesive, close the passage between the platen and the pump body using the special mechanism on the platen to prevent curing.

Personnel cleaning the heating platen must wear specialized high-temperature protective clothing and gloves. Avoid skin contact with the hot adhesive drum, molten PUR adhesive, heating platen, or other high-temperature parts to prevent burns.

The optimal method for drum detachment is to inject dried nitrogen gas into the 5-gallon (approx. 19-liter) adhesive drum. Avoid using undried compressed air directly. If compressed air must be used, ensure it is thoroughly dried. Regularly check the condition of the desiccant.

After detaching the drum, immediately and thoroughly clean residual PUR adhesive from the heating platen. Do not use any hard tools during cleaning to avoid scratching the platen's Teflon (non-stick) coating.

For platens with special constructions that cannot be cleaned thoroughly quickly, clean residual PUR adhesive under a protective atmosphere of dry nitrogen. Cleaning time must not exceed 10 minutes. Do not use any hard tools.

Immediately after cleaning the platen, press it into a new PUR adhesive drum to avoid prolonged exposure to air. When pressing the platen into the drum, gradually increase the lifting cylinder pressure from low to high. Do not use high pressure directly. Ensure operator safety.

When pressing the platen into the drum, apply a small amount of silicone oil to the platen's sealing ring for lubrication and protection.

After pressing the heating platen into the new drum, open the overflow valve to completely expel residual air from the drum. Purge adhesive containing air bubbles to prevent air-entrained adhesive from entering the pump body and hoses.

After expelling air, close the overflow valve. Then, appropriately increase the pressure in the stroke cylinder for smoother operation.

After changing the adhesive drum, wait at least 20 minutes for the PUR applicator to heat up before starting the gear pump and motor. Starting immediately can damage the polyurethane gear pump and reduce the applicator's lifespan.