How to Choose The Right Foam
Topic: die cutting material topic (www.flyingmancuttingmachine.com)
Classification of foam:
According to the hole structure: open foaming, half open foaming (independent), closed foaming (independent foaming), microcellular foaming.
According to the material, it can be divided into silicone foam, PU foam, EPDM soundabsorbing cotton, EPE pearl foam, PVC foam, PE foam, PPP foam, CCR foam, EVA foam, XPE foam, IXPE foam, acrylic foam, etc.
Classification by material:
- Polyethylene foam: PE foam (chemical crosslinking, electronic crosslinking), EVA foam.
- Polyester foam: polyether foam (chemical foam, physical foam), polyurethane foam.
- Rubber foam: CR foam (neoprene), NR foam (nitrile rubber), SBR foam (styrene-butadiene rubber), EPDM foam (EPDM).
Classified by foaming structure:
- Open hole foam: soft texture, high water absorption, high compression rate, suitable for sound absorption and sealing applications, such as compressed sponge for headphones, air conditioning seal strip, etc.
- Closed cell foam: independent foaming, low compression residual rate, low water absorption, good heat insulation and buffering performance, good dustproof, suitable for electronic products sealing dustproof, waterproof shock absorption, etc.
Closed-cell foam is widely used in the mobile phone industry, and the materials are mostly polyethylene and polyurethane. At present, the products of the following companies are mostly used in the market:
Rogers(USA): The main production of PU foam, brand Poron, Bisco
Inoac(Japan) : The main production of PU foam, brand Poron,Nanex
Nitto(Japan): The main production of PO&PP foam, brand SCF
S&K(Korea) : The main production of PU foam, brand Nanocell
SK(Korea): The main production of PU foam, brand Esobra
Sekisui(Japan): The main production of PE foam, brand Volara,Alveolit
NHK(Japan): The main production of PU foam, brand Nippalay
Saintgobain(France): The main production of PU foam, brand Korel
Application Scenarios
- Shock absorbing foam: anti-loss shock absorbing components, motor shock absorbing.
- Dustproof foam: dustproof between lens and LCD and Camera.
- Sound insulation and sound absorption: overlapped with screen mesh for Speaker.
- Conductive foam: Used to fill conductive shielding
- Foot pad and filling: shock absorption, anti-slip, filler.
How to evaluate and characterize microporous polyurethane foam from a technical point of view.
Typically we use the following four parameters:
1. Density 2. Resilience 3. Elastic loss 4. Compression ratio.
Density is an important standard to measure the microporous polyurethane foam. In general, the smaller the density of foam, the smaller the resilience and the larger the compression. It fits the trend of bigger screens on mobile phones.
The rebound force (also called C F D) is the force that responds to the applied material when the foam is compressed in a certain proportion and reaches a mechanical equilibrium. The same foam, if the greater the compression ratio, the greater the resilience. In the actual use of foam, foam is always in a certain proportion of the compression state. The higher the compression ratio, the greater the resilience, the better the sealing and protection effect, but too large compression force may affect the LCD display effect and the fixing of the case.
Therefore, the structural design related to foam is to keep the foam in a suitable compression state, and the elastic loss is a parameter to measure the aging resistance of foam.
There are very big differences between high-end and low-end microporous polyurethane foam in aging resistance. Compression ratio is the ratio of the compressed part of the foam to the original thickness. Maximum compression ratio refers to the ratio of the maximum compression thickness of foam to the original thickness under the premise of ensuring normal use.
The characteristics and advantages of polyurethane foam:
- Excellent compression and deformation resistance
- Excellent resilience
- The stress dispersion
- Resistance to chemicals, moisture and UV
- Flexibility and retention in demanding environments
- Easy to form a variety of complex die cutting parts
- PET surface adhesive (optional), reduce the coating process, more cost advantage
- PET backing has stable size for die-cutting
Typical applications include
- Mobile phones and other handheld devices, GPS navigation devices
- LCD TV module
- Wall liner for electronic products
- Absorption of vibration
- Shock absorbing cushion
- Sound cavity diversion
- Panel liners for industrial instruments
- Gap filling
Compression selection of polyurethane foam seals
The tightness of foam is a very important index in design
1. Sealing of dust and water droplets: 5% compression
2. Water seal (10cm) : 30% compression
The sealing performance can be improved in the following ways:
· Increase the amount of compression: the more high pressure shrinkage, you can have better sealing
· Crusted foam surface: products with skin reduce the chance of contact surface leakage
· Adhesive tape: Double-sided adhesive tape can reduce the chance of leakage of contact surface, even if the compression is small
· Consistent resilience: to ensure that all contact surfaces have the role of resilience
· Increase foam area: increase the leakage path to pass through
Foam selection criteria:
Function → Final thickness → compression load → compression ratio → final selection.
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