Sikaflex®-645
Adhesive sealant with superior compatibility and primerless adhesion to certain thermoplastics
Sikaflex®-645 is an adhesive sealant with primerless adhesion to plastics such as PC and PVC blends. It has superior compatibility with thermoplastics, with minimized impact on Environmental Stress Cracking of the bonded materials.
- Superior compatibility with thermoplastics
- Primerless adhesion on PC and PVC blends
- Multi-purpose adhesive sealant
Overview
PRODUCT BENEFITS
- Superior compatibility with thermoplastics
- Primerless adhesion on PC and PVC blends
- Multi-purpose adhesive sealant
Areas of Application
Sikaflex®-645 is suitable for assembly bonding and sealing applications in industrial manufacturing. Its superior compatibility to sensitive thermoplastics make Sikaflex®-645 the ideal adhesive sealant for elastic bonding of such materials. It is formulated for primerless adhesion to various blends of PC and PVC and can be used for interior and exterior sealing applications. 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
| Unipack | 600 ml |
| Pail | 23 l |
Product Details
| Chemical base | 1-component polyurethane (Purform®) | |
| Color (CQP001-1) | White, Black | |
| Cure mechanism | Moisture-curing | |
| Density (uncured) | 1.42 kg/l | |
| Non-sag properties | Good | |
| Application temperature | ambient | 10 ─ 30 °C |
| Skin time (CQP019-1) | 30 minutes A | |
| Open time (CQP526-1) | 25 minutes A | |
| Curing speed (CQP049-1) | See diagram 1 | |
| Shore A hardness (CQP023-1 / ISO 48-4) | 40 | |
| Tensile strength (CQP036-1 / ISO 527) | 4 MPa | |
| Elongation at break (CQP036-1 / ISO 527) | 750 % | |
| Tear propagation resistance (CQP045-1 / ISO 34) | 9 N/mm | |
| Tensile lap-shear strength (CQP046-1 / ISO 4587) | 2 MPa | |
| Service temperature (CQP509-1 / CQP513-1) | -50 ─ 80 °C | |
| Shelf life (CQP016-1) | 6 months B |
| CQP = Corporate Quality Procedure | A) 23 °C / 50 % r. h. | B) stored below 25 °C |
CURE MECHANISM
Sikaflex®-645 cures by reaction with atmospheric moisture. At low temperatures the water content of the air is generally lower and the curing reaction proceeds somewhat slower (see diagram 1).
Diagram 1: Curing speed Sikaflex®-645
CHEMICAL RESISTANCE
Sikaflex®-645 is generally resistant to fresh water, seawater, diluted acids and diluted caustic solutions; temporarily resistant to fuels, mineral oils, vegetable and animal fats and oils; not resistant to organic acids, glycolic alcohol, concentrated mineral acids and caustic solutions or solvents.
Application
Surface preparation
Surfaces must be clean, dry and free from grease, oil, dust and contaminants.
Surface treatment depends on the specific nature of the substrates and is crucial for a long lasting bond. Sikaflex®-645 may bond without use of chemical surface preparation to PC, ABS and PVC blends.
Suggestions for surface preparation may be found on the current edition of the appropriate Sika® Pre-treatment Chart. Consider that these suggestions are based on experience and have in any case to be verified by tests on original substrates.
Application
Sikaflex®-645 can be processed between 10 °C and 30 °C (climate and product) but changes in reactivity and application properties have to be considered. The optimum temperature for substrate and sealant is between 15 °C and 25 °C.
Consider that the viscosity will increase at low temperature. For easy application, condition the adhesive at ambient temperature prior to use.
To ensure a uniform thickness of the bondline it is recommended to apply the adhesive in form of a triangular bead (see figure 1).
Figure 1: Recommended bead configuration
Sikaflex®-645 can be best processed with electric driven piston guns as well as pump equipment.
The open time is significantly shorter in hot and humid climate. The parts must always be installed within the open time. Never join bonding parts if the adhesive has built a skin.
For advice on selecting and setting up a suitable pump system, contact the System Engineering Department of Sika Industry.
Tooling and finishing
Tooling and finishing must be carried out within the skin time of the product. It is recommended using Sika® Tooling Agent N. Other finishing agents must be tested for suitability and compatibility prior the use.
Removal
Uncured Sikaflex®-645 may be removed from tools and equipment with Sika® Remover-208 or another suitable solvent. Once cured, the material can only be removed mechanically.
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.
Overpainting
Sikaflex®-645 can be painted after formation of a skin. If the paint requires a baking process, best performance is achieved by allowing the sealant to fully cure first. 1C-PUR and 2C-acrylic based paints are usually suitable. All paints have to be tested by carrying preliminary trials under manufacturing conditions.
The elasticity of paints is usually lower than that of sealants. This could lead to cracking of the paint in the joint area.