Laser Processing of 3M™ VHB™ Tape 4926

Introduction

3M™ VHB™ Tape 4926 is part of a product line of foam core double-sided adhesives including 4919F, 4936(F), 4941(F), 4974F, 4956(F), 4991, and 4991B. The 3M VHB Tape 4926 product is a three layer material consisting of a core layer of closed cell acrylic foam that is placed between two layers of densified kraft paper release liner. The acrylic foam core of the 3M VHB Tape 4926 is 381µm thick, and each kraft paper release liner is 76µm thick. A diagram depicting the 3M VHB Tape 4926 material is shown in Figure 1.

Figure 1. 3M VHB Tape 4926 diagram showing the 76µm densified kraft paper release liners on the top and bottom of the 381µm thick acrylic foam adhesive.

3M VHB Tapes are viscoelastic adhesives, having both elastic and viscous characteristics, along with being resistant to both chemicals and moisture. The viscoelasticity, along with the tacky nature of this material, makes it challenging to process using conventional mechanical methods. The non-contact nature of laser processing overcomes this difficulty and enables the processing of applications with fine geometry and intricate detail. 3M VHB materials are only suitable for laser cutting, which produces smooth laser-processed edges and minimal heat-affected zones without degrading the physical properties of the materials. Other laser processes are not suggested as they are not conducive to the intended use of these materials. Universal Laser Systems makes it simple to consistently and repeatedly process these materials to a high degree of dimensional accuracy because the non-contact nature of laser processing eliminates material deformation during processing.

Laser Processing Notes

3M VHB Tape 4926 was tested to assess laser processing compatibility and to determine the best configuration of laser peak power and wavelength. The three layers of the 3M VHB Tape 4926 absorb 9.3µm energy more efficiently than other wavelengths, meaning less peak power was necessary to produce good results with minimal heat affects. Laser processing of 3M VHB Tape 4926 produces a small amount of debris that adheres to the processed edge, requiring some cleaning by wiping the processed edge with a solvent such as isopropyl alcohol. Microscopy images taken at 300x magnification of the processed edge of the 4926 after post-processing with the liners in place and the liners removed are shown in Figures 2 and 3, respectively. These images show that the kraft paper release liners contain most of the heat affects and discoloration, leaving the acrylic foam layer relatively free of adverse heat effects.

Figure 2. Microscopy image (300x) of the laser-processed edge of 3M VHB Tape 4926 with the kraft paper release liners in place. The heat-affected zone measures 135µm.

Figure 3. Microscopy image (300x) of the laser- processed edge of 3M VHB Tape 4926 with the kraft paper release liners removed from the material. The heat affected zone measures 65µm.

Further analysis of the laser-processed material shows that the kraft paper release liner and acrylic adhesive layer are cleanly processed along the processed path, the best configuration being a 75 watt 9.3µm CO2 laser source. Figures 4 and 5 depict 3D-rendered microscopy images of the processed surfaces shown in Figures 2 and 3. Figure 4 shows how the kraft paper release liner layer reacts to the laser energy by forming a consistent edge along the processed path (red area). In Figure 5, the kraft paper release liners are removed from the material, showing the smooth flat surface and laser-processed edge of the acrylic foam adhesive layer, free of adverse heat effects.

Figure 4. 3D-rendered microscopy image (300x) of the laser-processed edge of the 3M VHB Tape 4926 with the kraft paper liners in place.

Figure 5. 3D-rendered microscopy image (300x) of the laser-processed edge of the 3M VHB Tape 4926 with the kraft paper liners removed.

3M VHB Tape 4926 was also tested with an alternate system configuration of 10.6µm laser energy at equivalent laser power level for comparison and determination of the effectiveness of each system configuration. The results of these tests were compared by analyzing the heat effects, quality of the processed edge, and post-processing requirements. The results of the comparison of these system configurations are listed in tabular form in Table 1 and shown photographically in Figure 6. Both system configurations appear viable with some reduction in quality of the results for the 10.6µm configuration as stated in the comparison.

Table 1 System Configuration Comparison

System ConfigurationHeat-Affected ZoneProcess CharacteristicsPost-Processing Requirements
9.3µm (Recommended)Minimal heat-affected zone of approximately 135µm The 9.3µm laser energy has the advantage of better absorption by the material, resulting in a consistent edge along the processed path, with a reduced heat-affected zone Processing of the 3M VHB Tape 4926 with either the 9.3µm or the 10.6µm configuration produces a nominal amount of surface debris along the laser cutting path that can be removed with light abrasion and a solvent such as isopropyl alcohol
10.6µmIncreased heat-affected zone compared to 9.3µm wavelength, approximately 180µmThis configuration results in an increased heat-affected zone in the kraft paper release liner and produces a rougher edge and heat effects along the laser cutting path in the adhesive layer when compared to the 9.3µm configuration

Figure 6. Comparison microscopy images (300x) of the processed edge resulting from 9.3µm processing (left), and 10.6µm processing (right). Heat-affected zones measure 104µm for the 9.3µm process and 156µm for the 10.6µm process.The kraft paper release liner is in place on both of the images shown above.

Processing Example

3M VHB Tape 4926 applications requiring fine geometry and intricate detail without degrading the physical properties of the material can be accomplished with Universal Laser Systems technology. An example demonstrating the results of laser processing of 3M VHB Tape 4926 material is shown in Figure 4.

Figure 4. Example of the geometry possible with laser processing 3M VHB Tape 4926.

Conclusion

3M VHB Tape 4926 is suitable for laser processing and was extensively tested to determine the most efficient processing configuration. Through this testing it was determined that laser cutting is viable, and a 75 watt 9.3µm CO2 laser source is the best configuration of wavelength and power for laser cutting this material. The kraft paper release liner and acrylic adhesive layer efficiently absorb the 9.3µm wavelength laser energy, and, coupled with the peak power of the 75 watt laser source, produce a smooth clean edge that has a minimal heat-affected zone and discoloration. Other materials in this VHB product line are expected to process similarly.