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SikaMelt-678, Polyurethane Hot Melt Adhesive for Assembly Operations, Interior

SikaMelt-678, Polyurethane Hot Melt Adhesive for Assembly Operations, Interior

Adhesives & Sealants
SIKA

Sika is a global leader in specialty chemicals for the construction and industrial sectors. The company develops and supplies innovative products and systems for bonding, sealing, damping, reinforcing, and protecting structures. With a strong focus on sustainability and performance, Sika serves a wide range of applications including concrete production, waterproofing, roofing, flooring, and structural strengthening.

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General Specifications
Packaging 2 kg
Usage High-Temp Bonding In Automotive Interiors
Usage Area Interior
Color White – beige
Chemical Base Polyurethane
Storage Conditions +5 °C to +30 °C - Store in original, unopened, undamaged packaging in dry conditions. Always refer to packaging.
Density 1.2 kg/L
Service Temperature N/A
Application Time 60 min.
Curing Time 10 hours
Application Thickness ≤100 mm
Application Method Gun
UV Resistant No
Moisture Resistant Yes
Mold Resistant N/A
Paintable No
Sealant No
Flexible Yes

Polyurethane Hot Melt for assembly operations

SikaMelt-678 is a reactive polyurethane hot melt adhesive. It cures on exposure to atmospheric humidity. Due to its long open time SikaMelt-678 is in particular suitable for assembly application.  

  • Long open time for assembly (bead application)
  • Very high green strength also under warm conditions
  • Good adhesion on metals and polar plastics
PRODUCT BENEFITS
  • Long open time for assembly (bead application)
  • Very high green strength also under warm conditions
  • Good adhesion on metals and polar plastics
 
Usage
SikaMelt-678 is suitable for permanent bonding of polar plastics as well as for wood, foam, textiles, painted and primed steel. Non polar plastics like PP and PE can be bonded after proper physical pretreatment.
SikaMelt-678 can be used for Automotive interior assembly applications, where a high initial temperature resistance is required because of elevated temperature in the working environment. This product is suitable for experienced professional users only. Tests with actual substrates and conditions have to be performed ensuring adhesion and material compatibility.  
Packaging
Bag2 kg

Pail

20 kg

Bag (cardboard)22 kg
Typical Product Data
Chemical base

Polyurethane

Colour (CQP001-1)

White – beige, opaque

Cure mechanism

Moisture curing

Density (uncured)

1.2 kg/l

Viscosity (by Brookfield)at 130 °C

9 000 mPa·s

Softening temperature (CQP538-5)

72 °C

Application temperatureShort term max. 1h

110 – 140 °C

150 °C A

Open time (CQP559-1)

Medium

Curing time (CQP558-1)

10 h

Green strength (CQP557-1)

1.2 MPa

Shore D hardness (CQP023-1 / ISO 48-4)

40

Shelf life

9 months

CQP = Corporate Quality ProcedureA)Only valid for nozzle
Technical Information
CURE MECHANISM

SikaMelt-678 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. In such cases project related tests with original substrates and conditions are mandatory.

en_PNG_01-en-SikaMelt-678_v_20_05_08_FINAL

Diagram 1: Curing time for 500 µm film

CHEMICAL RESISTANCE

SikaMelt-678 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 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-678 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-678 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 be swelled with SikaMelt-001 and needs to be removed mechanically (see also cleaning instruction).
Uncured SikaMelt-678 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 Sika Cleaner-350H or a suitable industrial hand cleaner and water.

Do not use solvents on skin.
STORAGE CONDITIONS

SikaMelt-678 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.