Rubber/resin materials

Rubber materials

Nitrile rubber (NBR)

Nitrile rubber is widely used as a sealing material for various products including automobiles, and has the best balance of performance, workability and price. This is the result of its polymer structure that allows the heat resistance and oil resistance to be improved when the acrylonitrile group is increased, and the cold resistance to be improved when the butadiene group is increased. Thus, the heat resistance, cold resistance and oil resistance can be varied widely by changing this copolymerization ratio.

In terms of material properties, it has excellent mechanical strength and compression set resistance, but it is slightly less resistant to ozone and heat than other materials.

Hydrogenated nitrile rubber (HNBR)

Hydrogenated nitrile rubber (HNBR) is a material in which the double bond of butadiene, which had been a drawback of NBR, is highly hydrogenated in response to the recent demands for use under higher temperatures and a longer service life. It is superior to NBR in terms of heat resistance, oil resistance, mechanical strength, and compression set resistance; however, it has the disadvantages of lower cold resistance and higher cost.

More applications are expected in the future, and recently, an HNBR copolymerized with a third component, giving improved low temperature performance, has been developed.

Acrylic rubber (ACM)

Since the main component is composed of acrylic acid esters and has a side chain of highly polar ester groups on the main chain of ethylene, ACM has superior oil resistance, heat resistance and ozone resistance compared to general-purpose diene rubber. It is widely used as a sealing material for lubricants.

On the other hand, water and ester-based synthetic oils cause softening with significant swelling. In addition, its mechanical strength is inferior to that of NBR and HNBR. Improvement in the molecular structure of the polymer has improved its cold resistance, and enabled the material to be applied to -40 ° C, and its applications are expected to expand. In addition, the resistance to compression set has been improved by the development of a new vulcanization system, and the possibility of applying it to O rings and gaskets has emerged.

Silicone rubber (VMQ)

A general-purpose silicone rubber with a methyl group bonded to a polysiloxane structure, VMQ has excellent heat and cold resistance as well as lubricant and water (LLC) resistance. In addition, it is easy to color because it is possible to design materials with low hardness.

On the other hand, the disadvantages are that the mechanical strength of the material is low and that the polymer structure is susceptible to hydrolysis by acids and alkalis that are added, for example, to lubricating oil, which can cause unexpected deterioration even within the applicable temperature range. Conventionally, VMQ has been widely used as a sealing material for engines, but because of this hydrolytic degradation, the material is increasingly being replaced by FKM.

Fluorosilicone rubber (FVMQ)

Fluorosilicone rubber (FVMQ) is a material that has a fluoroalkyl group introduced into VMQ, which is a general-purpose silicone rubber. Therefore, FVMQ has excellent fuel oil resistance in addition to the properties of VMQ.

On the other hand, in addition to the disadvantages of general-purpose VMQs, there are issues in terms of adhesion to metal and cost. As with VMQ, it should be noted that it is susceptible to the additives in fuel oil.

Fluororubber (FKM)

Fluororubber (FKM) has the highest heat, oil, and fuel oil resistance of all rubber materials, but it has disadvantages in terms of low temperature performance and cost. The material includes binary polymers consisting of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), and ternary polymers consisting of VDF and HFP with tetrafluoroethylene (TFE) as an oil/fuel oil resistance improver. The fluorine content is approximately 66 to 70 weight percent. In general, the higher the fluorine content, the better the heat and oil resistance, but the worse the cold resistance.

ACMs and VMQs have traditionally been used to seal engines and drivetrains, but the use of FKMs has gradually expanded because of the demand for higher performance and longer life. On the other hand, it has been an issue to improve the additive resistance to amine additives contained in engine oil and fuel oil (cracking when bent), but we have improved the structure by copolymerizing VDF, TFE and perfluoromethyl vinyl ether (PMVE), and it has already been used in O rings for injectors in direct-injection engines.

In addition, special fluoroelastomers, such as TFE with propylene copolymerization, TFE with ethylene and PMVE ternary copolymerization, and perfluoroelastomers (FFKM) with PMVE copolymerization of TFE with heat resistance up to 300°C, have also been produced, but cost reduction has been an issue.

Ethylene propylene rubber (EPDM)

Ethylene propylene rubber (EPDM) has a structure in which a small amount of unsaturated group having a double bond of the third component is introduced as a cross-linking site into a copolymer of ethylene and propylene, and since the material does not have a double bond in the polymer molecular chain, it has excellent ozone and heat resistance. In addition, it shows excellent resistance to water vapor, cold, and polar solutions including LLC.

The disadvantage is that because of its polymer structure, EPDM is not resistant to ordinary mineral oil-based lubricants.

Chloroprene rubber (CR)

All kinds of CR are characterized by the inclusion of chlorine (Cl), a polar group, in their structures. The microcrystalline ethylene chains provide excellent mechanical strength and flexural fatigue resistance, but their tendency to crystallize can be a problem.

In the synthetic process, CR is made by emulsification polymerization of chloroprene, whereas CSM is made by introducing chlorine and sulfurous gas. Since this CSM does not have a double bond in its main chain, it has superior ozone resistance and heat aging resistance compared to CR, but its low temperature resistance is slightly inferior.

Chlorosulfonated polyethylene (CSM)

As with CR, all kinds of CSM are characterized by the inclusion of chlorine (Cl), a polar group, in their structures. The microcrystalline ethylene chains provide excellent mechanical strength and flexural fatigue resistance, but their tendency to crystallize can be a problem.

In the synthetic process, CR is made by emulsification polymerization of chloroprene, whereas CSM is made by introducing chlorine and sulfurous gas. Since this CSM does not have a double bond in its main chain, it has superior ozone resistance and heat aging resistance compared to CR, but its low temperature resistance is slightly inferior. It has been used as a post-CR material for constant velocity joint boots.

Styrene-butadiene rubber (SBR)

A typical type of general-purpose rubber, SBR, is made by emulsification of styrene and butadiene. High styrene SBR is a resinous material with excellent wear resistance and a good balance of processability, physical properties and cost.

The material can be used for polar solutions such as brake fluids, but not for general industrial hydraulic fluids. In addition, the use of EPDM has been increasing in recent years due to SBR’s inferior heat resistance.

Butyl rubber (IIR)

Butyl rubber (IIR) is a chemically stable rubber made by copolymerizing isobutylene and a small amount of isoprene. The material is a chemically stable rubber made from the copolymerization of isobutylene and a small amount of isoprene. It has the lowest gas permeability among various rubbers and has excellent mechanical strength, shock absorption, weather resistance, heat aging resistance, and ozone resistance.

It is unsuitable as a fluid sealing material because of its inferior workability, adhesiveness, and oil resistance to general industrial oils; however, it is used in accumulator bladders and other applications that take advantage of its gas shielding properties.

Urethane rubber (AU)

Urethane rubber (AU) is an elastic material that has a urethane group in its structure and falls in the area between rubbers and plastics. In addition to its high mechanical strength, abrasion resistance, ozone resistance and low temperature resistance, it has a particularly wide range of hardness adjustment, from sponge to hard thermoplastic.

One disadvantage of this product is that it lacks heat and water resistance, and therefore, use under high loads that generate frictional heat may result in abnormal wear due to heat, even within the applicable range.

Resin materials

Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE) is a crystalline polymer with a linear structure consisting of a simple repetition of "−CF2−" as the basic structural unit, which is linearly connected. The material can be used in a wide range of temperatures, which is not possible for rubber, and has excellent abrasion, weather, moisture, chemical, and flame resistance as well as electrical insulation properties. In addition, it has a low coefficient of friction, which allows for low starting and sliding resistance.

As a disadvantage, it is difficult to form, which limits its application to products with complex shapes. In addition, it may be used in combination with an O ring to regulate the amount of leakage, but in this case, the operating conditions such as the operating temperature range depend on the rubber.

When used under high load and high-speed conditions, wear and creep are high, and therefore it is used as a composite material reinforced with fillers (such as glass fiber, carbon fiber, bronze, graphite, and molybdenum disulfide).