Basic knowledge of common die-cutting materials (Part 2)

During the cutting process, different materials are chosen for different cutting products. In the previous article "Common Cutting Materials Basics (Part 1)," we introduced the classification and characteristics of eight common cutting materials. In this article, we will further discuss the application, characteristics, and corresponding processes of release materials, adhesives, and conductive shielding materials.

Release Materials

Release materials mainly include PE coated silicone release paper, ordinary kraft paper/silicone release paper, PET silicone release/fluorosilicone release film, PE release film, PP release film, etc.

Production of Coated Paper

Adhesive Materials

Adhesive materials include various types of double-sided tape from 3M, NITTO, SONY, TESA, SEKISUI, and JISUI, as well as various types of single-sided tape.

Single-sided tape vs. Double-sided tape

Similarities: Both have a layer of adhesive on one side, forming a bond between their own molecules and the molecules of the object they adhere to, firmly sticking them together.

Differences: Single-sided tape is generally used for surface protection, insulation, or waste material removal in the cutting process. Double-sided tape is used in various industries to adhere two similar or dissimilar products together.

Structure of Double-sided Tape

The base material of double-sided tape has the following characteristics:

Polymer film type base material (PET, PP, PVC): dimensionally stable, high tear resistance, suitable for cutting and automated processing. Additionally, it has low elasticity (PET), good temperature resistance (PET), good insulation properties, and can act as a plasticizer.

Non-woven fabric type base material: semi-transparent, good conformity, tearable, and good temperature resistance.

Foam type base material (PUR, PE): good cushioning, able to balance tension, meet dimensional requirements, and fill uneven surfaces.

Fabric type base material: resilient, tear-resistant, good conformity, and can improve tape strength.

Transfer (baseless): transparent, with a resilient, highly adherent and non-lifting adhesive layer. Low cost.

Pressure-sensitive Adhesives

They have natural viscoelastic properties, rapid and long-lasting adhesion, good initial tack, do not require water, and can obtain adhesion through solvent or heat reactions. They have significant holding power, cohesion, and elasticity.

Advantages: No need for pre-treatment steps like coating or mixing, even adhesive application, convenient and quick to use, can be cut into various shapes, have long-lasting viscoelasticity to avoid brittleness and breakage. They are odorless, tasteless, and solvent-free.

Factors Affecting Adhesives: Temperature, time, pressure, surface cleanliness, and condition.

Soft Adhesives vs. Hard Adhesives

Hard adhesives have less immediate contact, lower initial bond strength, and require longer dwelling time. Soft adhesives have good immediate contact, higher initial bond strength, and seldom require dwelling time, or even none.

In general, we can make the adhesive flow for a certain period by controlling the temperature and increasing the viscosity, accelerating the adhesive flow and increasing surface wetting. By adjusting the pressure, we can accelerate adhesive flow, increase surface wetting, and remove air bubbles.

Initial tack refers to the initial contact force between the glue and the adhered object, the bonding strength under the condition of minimal pressure and shortest contact time, and is independent of the bonding strength under pressure.

Peel strength refers to the force required to peel off the tape from a standard test panel at a specified rate and at a 180° or 90° angle.

In general, factors such as load, surface properties of the test panel, and temperature affect the static peel adhesion.

Shear strength refers to the relative displacement phenomenon of the material's cross-section along the direction of the external transverse forces of a pair of close, equal-sized, and oppositely-directed forces. Shear strength is also adhesive force and refers to the ability of the tape's free end to resist relative sliding when loaded, while the other end is adhered to a specified surface. In general, soft adhesive - low shear force, hard adhesive - high shear force, thick adhesive - low shear force, thin adhesive - high shear force.

Cohesion is the internal strength of the adhesive, namely the holding power (shear strength) of the tape in use. It is equivalent to the stress parallel to the adhered surface and has high cohesion, generally featuring high temperature resistance, low initial peel strength, high final peel strength, low flowability, and low initial tack.

Factors Leading to Adhesive Failure:

Incompatible adhesive and adhered surface.

Excessively rough surface.

Surface contamination by mold release agents or dust particles.

Plasticizer migration.

Air entrapment.

When encountering difficult-to-bond surfaces, we can first clean the surface, use mold release agents, surface grinding, apply corona treatment/structuring, and use polarization/oxidation to convert the surface into a high-energy surface primer.

Hot melt adhesive

Hot melt adhesive bonding is the use of a hot melt adhesive machine to melt the hot melt adhesive through heat, and the melted glue becomes a liquid. It is then delivered to the surface of the substrate through hot melt adhesive tubes and guns. The bonding is completed after the hot melt adhesive cools down. It was originally mainly used for bookbinding, but with the development of modern technology, it is now widely used in the production of shoes, hats, mobile phones, and other products.

Hot melt adhesive films are mainly divided into two categories: thermoplastic and thermosetting. They are mainly used for bonding electronic product nameplates, plastics, hardware, collecting window frames, and front covers.

Factors that affect the selection of hot melt adhesive include:

1. Color: If the bonded object does not have specific color requirements, yellow hot melt adhesive generally has better stickiness than white.

2. Surface treatment of the substrate: The surface treatment of the substrate for hot melt adhesives is not as strict as other adhesives, but it is still necessary to remove dust and oil stains for better bonding.

3. Operation time: Generally around 15 seconds. With the widespread use of assembly line production, the operation time requirement for hot melt adhesive is becoming shorter.

4. Temperature resistance: Hot melt adhesive is sensitive to temperature. When the temperature is below a certain threshold, the hot melt adhesive may become brittle. Therefore, the temperature changes in the product's environment must be considered when selecting a hot melt adhesive.

5. Adhesion: The early and final adhesive strengths must be consistent to ensure stable bonding between the hot melt adhesive and the substrate. The production process of hot melt adhesive should guarantee its oxidation resistance, halogen resistance, acid-alkali resistance, and plasticizing properties. The adhesive strength of hot melt adhesive may vary depending on the material of the substrate.

Conductive shielding materials

Conductive shielding materials mainly include conductive foam, conductive fabric, conductive double-sided tape, copper foil, aluminum foil, and absorbing materials.

Conductive foam is divided into ordinary conductive foam and omni-directional conductive foam.

Conductive fabric is divided into grid fabric conductive fabric and knitted conductive fabric. Grid fabric has good conductivity, shielding effect, and processability, making it suitable as the preferred material for various regular and irregular conductive foam wrapping. It is mainly used for ultra-thin shielding, conductive fabric foam, conductive fabric tape, conductive fabric pads, etc., with good friction resistance. Knitted conductive fabric has good friction resistance and can be easily stamped after wrapping. It is a low-cost and easily wrapped material, making it the preferred material for I/O pads.

Copper foil/aluminum foil is mainly used in the electronics industry for functions such as conductive, thermal conduction, heat dissipation, magnetic shielding, and anti-static. The material is not very hard, usually below 0.2mm, making it very convenient for processing but easily deformable.

Absorbing materials are mainly classified into ferrite absorbing materials, metal powder absorbing materials, nano-absorbing materials, and optically transparent absorbing materials. They were initially used in military stealth technology and have been increasingly used in various fields.

The main function of absorbing materials is to absorb the electromagnetic wave energy projected onto their surface and convert the electromagnetic wave energy into heat or other forms of energy through the dielectric loss of the material. They are mainly used for interference prevention, electromagnetic wave absorption, radiation suppression, and shielding. However, during die-cutting processing, they are prone to delamination, dust, indentation, extrusion, and scratching.

Applications of conductive shielding materials:

1. Reduce cross-talk between Wi-WAN antennas and LCD screens by applying AB series materials between LCD control modules and antenna modules.

2. Reduce noise levels between antennas and substrates by applying AB series materials between antenna modules and substrates.

3. Reduce noise on camera module signal lines by wrapping them with AB series materials.

4. Reduce coupling effects between LCD modules and surrounding components by covering FPCB and driver IC with AB series products.

5. Minimize secondary antenna effects caused by heat dissipation from CPUs by applying absorbing materials between CPUs and heat sinks.

6. Reduce radiation coupling noise from FPCBs by wrapping them with AB series materials.

7. Reduce electromagnetic noise in data acquisition areas by applying AB series materials in DVD/hard disk signal areas.

8. Reduce radiation noise from high-speed devices such as CPUs/MPUs/memory by applying AB series materials to the corresponding noise sources.

9. Reduce noise radiation from SD/PCMCIA card connectors by applying absorbing materials at the connection points.

10. Improve the performance of shielding enclosures by applying AB series materials inside the enclosures to reduce cavity resonances.

11. Reduce radiation coupling noise from FPCBs by wrapping them with AB series materials.

12. Reduce resonances and standing wave noise on motherboards by applying AB series materials at highly noisy positions.

13. Reduce electromagnetic radiation noise from high-speed USB ports by applying AB series materials at the port locations.

14. Reduce radiation and self-inductance coefficients of internal data lines by wrapping them with AB series materials.

15. Suppress interference from speaker magnetic cores to Hall ICs by applying 1380 or 1380KR materials between speakers and Hall ICs.

16. Shield LCDs from noise interference in capacitive touch screens by embedding 3M 8880 transparent optical electromagnetic shielding materials and conductive pads between LCDs and touch screens.

17. Ground improperly connected metal parts by elastic compression grounding of conductive foam after bonding.

In summary, we have introduced the applications, characteristics, and processes of representative products in the three major categories of release materials, adhesive materials, and conductive shielding materials from various aspects such as product types, applications, and influencing factors. In the next update, we will continue to share the applications, characteristics, and processes of representative products in the five categories of surface protection materials, sealing/cushioning materials, insulating and flame-retardant materials, waterproof/dustproof materials, and backlight module materials. Stay tuned, and we hope our sharing can be helpful to you.