Knowledge of common die cutting materials -- Introduction to foam knowledge
Foam classification
According to the pore structure, it can be divided into open cell foaming, semi open cell (independent) foaming, closed cell foaming (independent foaming) and microporous foaming.
According to the material, it can be divided into: silicone foam, PU foam, EPDM sound-absorbing cotton, EPE pearl cotton, PVC foam, PE foam, PP foam, Cr foam, EVA foam, XPE foam, IXPE foam, acrylic foam, etc.
Material type
Classification by material
Polyethylene foam: PE foam (chemical crosslinking, electronic crosslinking), EVA foam.
Polyester foam: polyether foam (chemical foaming, physical foaming), polyurethane foam.
Rubber foam: Cr foam (neoprene), NR foam (nitrile rubber), SBR foam (styrene butadiene rubber), EPDM foam (EPDM).
Classification by foaming structure
Perforated foam: soft texture, high water absorption and high compression rate. It is suitable for sound absorption and sealing applications, such as compressed sponge of earphone, air conditioning sealing strip, etc.
Closed cell foam: independent foaming, low compression residue rate, low water absorption, good heat insulation and cushioning performance, good dust prevention, suitable for sealing, dust prevention, waterproof and shock absorption of electronic products.
Mobile phone industry
Closed cell foam is widely used in the electronic industry, and polyethylene and polyurethane are mostly used. At present, the products of the following companies are mostly used in the market:
Rogers (USA) mainly produces PU foam, brand PORON, BISCO
INOAC (Japan) mainly produces PU foam, brand PORON, nanex
Nitto (Japan) mainly produces Po & PP foam, brand SCF
S & K (Korea) mainly produces PU foam, and its brand is nanocell
Sk (Korea) mainly produces PU foam, brand esobra
Sekisui (Japan) mainly produces PE foam, with brands of volara and alveolit
NHK (Japan) mainly produces PU foam, brand nippalay
Saint Gobain (France) mainly produces PU foam, brand KoreL
Electronic industry
Shock absorbing foam: component loss prevention and shock absorption, motor shock absorption
Dustproof foam: dustproof between lens, LCD and camera
Sound insulation and absorption: covered with screen for speaker
Conductive foam: used to fill conductive shielding
Footrest and padding: shock absorption, anti-skid and padding
Development history of polyurethane foam
Microporous polyurethane foam, commonly known as PORON foam in the market, was first used in mobile phones and other handheld devices by Rogers company. With the rapid popularization of mobile phones, microporous polyurethane foam has been widely used. (PORON) was originally just a registered trademark of microporous polyurethane foam produced by Rogers company. Now it has become an alias of microporous polyurethane foam and is widely used in the industry.
Microporous polyurethane foam has a history of more than 40 years since its invention. The source of its technology is the microporous foaming technology of polyurethane foam invented by United carbon chemical company of the United States in the 1970s. The (PORON) foam developed by Rogers company on the basis of this technology has always led the development trend of technology in the industry. Rogers company has successfully cut into the supply circle of Japanese brands that have always been relatively exclusive through the establishment of (r IC company) in Japan and Inoue company. Therefore, there are American regulations and Japanese Regulations for (P o r o n) foam.
With the rapid rise of Korean mobile phone brands, Korean microporous polyurethane foam also occupies a very considerable market share. Korean SK company's microporous polyurethane foam is the main supplier of Korean Samsung, LG and other brands. With the expansion of the mobile phone market of Samsung and LG, it has become an important supplier of microporous polyurethane foam comparable to Rogers, forming a tripartite confrontation with PORON foam American regulations and Japanese regulations. The technical source of SK company's microporous polyurethane foam has not been known to the outside world. After SK company, many manufacturers of similar products soon appeared in Korea, For example, S & K (product brand is PSR), DRC (product brand is SRF), DSR, etc. the addition of these manufacturers has rapidly reduced the market price of microporous polyurethane foam. However, because its performance and quality are difficult to meet the application requirements of the high-end market, only a large number of them are applied to the low-end market, especially the Shanzhai mobile phone market.
A few years ago, Rogers company acquired the microporous polyurethane foam business unit of SK company. The microporous polyurethane foam market once again formed the dominant pattern of Rogers company, and several other Korean manufacturers died miserably in the low-end market (including domestic brand mobile phone market and Shanzhai mobile phone market).
Saint Gobain's microporous polyurethane foam also re entered the market at this time. (Saint Gobain supplied the product to the market more than 10 years ago, but it seemed to withdraw from the market 7 - 8 years ago). It is said that the technical source of Saint Gobain's microporous polyurethane foam is the same as that of Rogers. This time, it is a high-end and low-end take all.
Saint Gobain's low-end products have been widely used in domestic mobile phones, and high-end products have been used in large European and American manufacturers led by n okia. At the same time, the products did not blindly follow Rogers company, but developed some product lines that Rogers did not have, which were used by large factories in Europe and America.
How to evaluate and characterize microporous polyurethane foam from a technical point of view? We usually use the following four parameters:
1. Density, 2 Resilience, 3 Elasticity loss, 4 Compression ratio.
Density is an important standard to measure microporous polyurethane foam. Generally, the smaller the density, the smaller the resilience and the larger the compression. It is more suitable for the growing trend of mobile screen saver.
According to the above definition, Resilience (also known as CFD) is the force that the foam responds to the applied object after compressing a certain proportion and reaching mechanical equilibrium. For the same foam, the greater the compression proportion, the greater the rebound force. During the actual use of the foam, the foam has always been in the compression state of a certain proportion. The greater the compression proportion, the greater the rebound force, the better the sealing and protection effect, but it is too large The compression force may affect the display effect of LCD screen and the fixation of housing.
Therefore, the structural design related to foam is to keep the foam in a proper compression state, and the elastic loss is a parameter to measure the aging resistance of foam.
The following table shows the test results of some common foams for reference only:
It can be seen from the above table that there is a great difference in aging resistance between high-end microporous polyurethane foam and low-end microporous polyurethane foam. The compression ratio is the ratio of the compressed part of the foam to the original thickness. The maximum compression ratio refers to the ratio of the maximum compression thickness of foam to the original thickness on the premise of ensuring normal use.
The compression curve of polyurethane foam is as follows:
Polyurethane foam - features and benefits:
Features and advantages:
• excellent compression deformation resistance
• excellent resilience
• stress dispersion
• chemical, moisture, UV resistance
• flexibility retention in harsh environments
• easy to form various complex die-cutting parts
• pet face with glue (optional), which reduces the glue coating process and has more cost advantages
• pet backing is conducive to the dimensional stability of die cutting
Typical applications include:
• mobile phones and other handheld devices, GPS, MP4
• LCD TV module
• electronics enclosure liner
• vibration damping
• shock absorber
• sound cavity diversion
• industrial instrument panel gasket
• gap filling
Polyurethane foam - compression selection for sealing
The tightness of foam is a very important index in design.
1. Sealing of dust and water droplets: 5% compression.
2. Water sealing (10cm): 30% compression
Sealing performance can be improved by:
·Increase compression: the higher the compression, the better the sealing performance.
·Skinned foam surface: products with skin reduce the probability of contact surface leakage
·Tape: double sided tape can reduce the probability of contact surface leakage, even if the compression is small.
·Consistent resilience: it can ensure that all contact surfaces have the function of resilience
·Increase foam area: increase the path of leakage.
Application site
Advantages and disadvantages of foam of various brands
Selection criteria
Function → final thickness → compression load → compression ratio → final selection
A: After assembly, a sealed cavity is formed to effectively prevent the pollution of dust and dirt
B: · suitable for assembly in lens factory
·Reduce lens contamination during assembly in the assembly plant
·Specially designed strong and weak glue composite membrane to reduce lens pollution
·The process is suitable for foam assembly of mobile phone front case
·Suitable for hand stick assembly
·It is assembled with positioning holes, and the accuracy can reach 0.15mm
·Lowest material cost