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SikaMelt®-679

SikaMelt®-679

Polyurethane hot melt for assembly applications with long open time

SikaMelt®-679 is a reactive polyurethane hot melt adhesive which cures on exposure to atmospheric humidity. It combines long open time with high initial strength and has a broad and durable adhesion range.  

  • Very high tack
  • Long open time
  • Outstanding green strength
  • High final strength and flexibility over a broad temperature range
  • Very good ageing and heat resistance
  • Broad adhesion spectrum
 
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PRODUCT BENEFITS

  • Very high tack
  • Long open time
  • Outstanding green strength
  • High final strength and flexibility over a broad temperature range
  • Very good ageing and heat resistance
  • Broad adhesion spectrum
 

Areas of Application

SikaMelt®-679 is suitable for permanent bonding of polar plastics as well as for foam, textiles, painted, aluminium, primed steel and coated glass. Non polar plastics like PP and PE can be bonded after proper physical pre-treatment. Typical area of application is assembly bonding in home appliances.
This product is suitable for experienced professional users only. Tests with actual substrates and conditions have to be performed ensuring adhesion and material compatibility.  

Product Details

Typical Product Data
Chemical base

Polyurethane

Color (CQP001-1)

White

Cure mechanism

Moisture curing

Density (uncured)

1.14 kg/l

Viscosity (by Brookfield)

at 130 °C

10 000 mPa·s

Softening temperature (CQP538-5)

60 °C

Application temperature

 

short term max. 1h

120 - 140 °C

150 °C A

Open time (CQP559-1)

Long

Curing time (CQP558-1)

26 h

Green strength (CQP557-1)

after 30 min

0.7 MPa

Shelf life

9 months

CQP = Corporate Quality Procedure

A) only valid for nozzle

Technical Information

CURE MECHANISM

SikaMelt®-679 cures by reaction with atmospheric moisture. At low temperatures the water content in the air is lower, which will result in a lower curing speed (see diagram 1). When bonding hydrophobic (e.g. PP) and/or moisture impermeable substrates a significantly longer curing time has to be taken into account. This applies especially on assembly applications with an adhesive thickness > 100 µm.
For lamination applications of hydrophobic and/or moisture impermeable substrates the adhesive layer shall not exceed 100 µm.

en_PNG_01-diagram-sikamelt-679

Diagram 1: Curing time for 500 μm film


 

CHEMICAL RESISTANCE

SikaMelt®-679 is resistant to aqueous surfactant, weak alkaline/acids solutions and temporarily resistant to fuels, solvents and mineral oils.
The chemical resistance is influenced by several factors such as chemical composition, concentration, period of exposure and temperature. Therefore a project related testing in case of chemical or thermal exposure is required.

Application

Application Information

Surface preparation

Surfaces must be clean, dry and free from grease, oil and dust.
Based on the surface and type of material, a physical or chemical pre-treatment might be required. Type of pre-treatment must be determined by preliminary tests.
For metals best results are achieved, if substrates are heated up between 40 °C and 60 °C prior the assembly process.

 

Application

With adequate processing equipment SikaMelt®-679 can be applied as film, dot, bead or spray application. For automated applications a suitable filter system is required.
To meet the required application properties the adhesive viscosity can be adjusted by adapting the application temperature (see table Typical Product Data).
During breaks SikaMelt®-679 is to be processed as follows:
For breaks ≥ 1 h the heating needs to be lowered to 80 °C and for breaks ≥ 4 h the heating needs to be switched off.
To ensure a constant quality during the whole production process it is mandatory to protect the adhesive in the melting tank with nitrogen, carbon dioxide or dried air (to avoid possible reaction of the product with humidity). At breaks or shut downs dip nozzle in dried oil in order to prevent curing of the adhesive (avoid blockage).
For advice on selecting and setting up suitable processing equipment contact the System Engineering Department of Sika Industry.

Removal

Equipment and application tools can be cleaned with SikaMelt®-009. Cured material can for cleaning purposes be swelled with SikaMelt®-001 and needs to be removed mechanically (see also cleaning instruction). SikaMelt®-679 may be removed from tools and equipment with Sika® Remover-208 or another suitable solvent.
Hands and exposed skin have to be washed immediately using hand wipes such as Sika® Cleaner-350H or a suitable industrial hand cleaner and water.

Do not use solvents on skin.

STORAGE CONDITIONS

SikaMelt®-679 has to be stored at temperature below 30 °C in a dry place.
For transportation purposes, the storage temperature can be exceeded for a period of max. 2 weeks up to 60 °C.