Customer Solutions

Launch of the BLISTANCETM
blister resistant material series
1. Introduction

mechanism, and introduce our new product line,"BLISTANCETM" series, which is resistant to blisters.

O-rings and other elastomer seal materials（hereinafterreferred to as "seal materials"）are considered to haveexisted since the second half of the 19th century to the

2. Blisters2）
This section describes the mechanism leading to theoccurrence of blisters, a type of degradation in seal

mankind over the past 100 years by preventing liquids

materials.

and gases from leaking from joints and other

Blisters occur under certain conditions, when sealconnections of pipes used in a wide range of industries

material such as O-rings in equipment and devices are

such as automobile, aircraft, chemical and steel.

exposed to sudden pressure fluctuations while in

The development of the aforementioned industries has

contact with gases and fluids such as volatile liquids

been extremely rapid, and the environments to which

under high temperature and high pressure.

seal materials are exposed are also becoming moreFirstly, from a microscopic point of view, elastomers

severe and complex in the process.

are composed of intertwined molecular chains and are

When the elements of environmental complexification

relatively porous materials. Therefore, in high-that was previously mentioned are broken down, theytemperature and high-pressure environments, gases

can be broken down into two, energetic factors andand volatile liquids can easily penetrate the interior of1）

environmental factors . Energetic factors include heat,

the seal material through the gaps in the molecularstress, light, and radiation, while environmental factors

chains, and some of which remain inside.

include air, water, acids, alkalis, oils, and fluids such as

Furthermore, when the pressure is rapidly reduced

organic solvents.

from the state where the fluid is retained inside theWhen seals are used in an environment where suchseal material, the gas or volatile liquid expands infactors are intertwined, their characteristics gradually

volume inside the seal material and tries to escapechange and their mechanical strength and chemicaloutside from the surface of the seal material.

properties deteriorate compared to the initial state, orWhen the above phenomenon occurs or reoccurs

there is a change in appearance. Such phenomena are

multiple times, the force of the fluid trying to escape

generally referred to as degradation, and as degradation

overcomes the mechanical strength of the seal material,

progresses, seals no longer prevent fluids from leaking

causing foaming and cracking inside and on the surface

and eventually reach the end of their service life.

（Figure1）.

As mentioned above, degradation is caused by a

In industries dealing with elastomers, this type of

combination of various factors, and there are many types

degradation, where fluids trapped inside physicallyof degradation. In this paper, we will focus on a type ofdamage the seal material upon depressurization, isdegradation called blisters, explain its formation

called "blister"（Figure2）.
6

Summer 2021

first half of the 20th century. They are one of thecomponents that have supported the development of

No.41

Launch of the BLISTANCETM blister resistant material series② Select a seal material that has low compatibility
with fluids.
③ Decrease the cross-sectional diameter of the sealmaterial to reduce the amount of fluid retention
inside.
Figure1

Schematic diagram of blister formation mechanism

In addition, adjustments to the operating environment,such as lowering the operating temperature andslowing down the decompression rate, are considered
to be effective in preventing blister formation.

3. P
 roduct overview of the"BLISTANCETM" series

Summer 2021
No.41

Figure2 Example of an O-ring where blisters have occurred

Using ① and ② in the previous section 2 as criteria, weWhen blisters occur, the corresponding area may"BLISTANCE TM", including both newly developed

become a leak path, or fracture due to pressure applied

products as well as previously available blister-resistantto the fissure, making the seal material unable toseals, to make it easier for customers concerned about or

have launched a new series of products called

perform its function of preventing fluid leakage.

troubled by blisters forming in high-pressure hydrogen

For instance, high-pressure hydrogen gas environments

gas, high-temperature steam, refrigerant + refrigerant oil,are an area where damage can be caused due toand other environments, to select seal materials.

blisters. If a leak occurs due to blister generation of the

In this section, we will introduce the features of each ofseal material, the static electricity generated in thethe following four products:

surroundings may cause an explosion, which may leadto a severe accident involving human lives.
Moreover, a prime example of volatile fluids are
refrigerants（CFC or CFC substitutes）, which are also akind of fluid where the occurrence of blisters issometimes seen. In recent years, R134a and other CFC
a l t e r na t i v e s h a v e bec o m e t h e m o s t c o m m o nrefrigerants, and unlike the specified CFCs used in the

1．"BLISTANCETM- H Series", suitable for use in hydrogengas environments.
2．"BLISTANCETM- St Series", suitable for use in hightemperature steam environments.
3．"BLISTANCETM- Rf Series", for use in refrigerant +refrigerant oil environments.
4．"BLISTANCETM- Mu Series", for use in a wide range ofother environments.

past, they do not deplete the ozone layer. However,their global warming potential is not significantly

3-1）BLISTANCETM-H series

different, and their impact on global warming is

The BLISTANCETM-H series is a seal material suitableconsidered to be significant in case of leakage.

for use in hydrogen gas environments. Currently,

In order to prevent the leakage caused by these

BLISTANCETM-HST for low pressure（under 2MPa）,

blisters, it is important to select the most suitable seal

BLISTANCE TM-HMP for medium pressure（undermaterial for that environment. Some of the criteria are

35MPa）, and BLISTANCE TM-HLT series for highdescribed below:

pressure（under 95MPa）are available, all three of
which are made of EPDM seal material.

① Select a seal material with high hardness andmechanical strength.
7

The maximum pressure of hydrogen gas used atcurrent hydrogen stations is 82MPa, and its mechanism

Customer Solutions

is as follows: from a container called a "curdle," throughtest was conducted at the Hydrogen Energy Products

a compressor and a pressure accumulator, cooled by a

Research and Testing Center（HyTReC））.

pre-cooler, and then filled into a vehicle through a

We have run a similar test on general-purpose seals

dispenser. Since the filling of hydrogen gas from theand the difference in appearance after the test isdispenser into the vehicle is done by using differential

apparent（Figure4）.

pressure, the compression by the compressor affects
the filling speed. The higher the pressure to increase
the filling speed, the greater the heat generated byadiabatic compression during filling.
Therefore, when hydrogen gas is filled at room
temperature, there is a risk of exceeding the heat
resistance temperature of the hydrogen tank inside the

Figure4

 urface condition of O-ring after high-pressureShydrogen cycle test

vehicle（said to be 85℃ for Type IV hydrogen tanks
made of CFRP）, so it is necessary to cool the hydrogen

BLISTANCETM-HLT also has excellent low-temperature

gas to -40℃ using a pre-cooler（Figure3）.

properties. The following is a comparison of lowtemperature properties between BLISTANCETM-HLT
and a general-purpose seal material also made of
EPDM. The low-temperature properties were evaluatedFigure3 Mechanism of a hydrogen station, schematic diagram

In this case, the situation where blisters are most likely（hereinafter referred to as TR test）in accordance withJIS K6261- 4. The results are shown below（Figure5,
Table1）.

to form is when a sudden decompression from 82 MPa

Summer 2021

by conducting a low temperature elastic recovery test

to atmospheric pressure occurs while the temperature
has risen to around 85℃ and the chances are

No.41

particularly high with general-purpose seal materials. In
addition, the same seal material must be able to seal ata pressure of 82 MPa and temperature of -40℃.
Also, hydrogen gas is handled at pressures of 35 MPain small hydrogen stations and 2 MPa in hydrogen gas
detection sensors, and since these facilities are notequipped with pre-coolers, the presence or absence of
low temperature characteristics is not questioned here.
In introducing the BLISTANCETM-H series, we will first
introduce the features of BLISTANCETM-HLT, which is

Figure5 easurement results of BLISTANCETM-HLT TR test
M
（Comparison: General-purpose EPDM）

Table1 Comparison of BLISTANCETM-HLT and H0970 TR values
BLISTANCETM–HLT

Conventianal EPDM
H0970

TR10（℃）-51-43

TR30（℃）-47-30

depressurization of hydrogen gas at a pressure of 90

TR50（℃）-44-21

MPa at 90℃, no leakage of hydrogen gas was detected

TR70（℃）-39-13

Shrinkageat minus 40℃
（%）

67.4

12.8

most suitable for seals used in areas exposed to highpressure and low temperature3）.
The most remarkable feature of BLISTANCETM-HLT isthat even after 11,250 cycles of rapid pressurization andduring the cycle test and no trace of blisters was foundon the seal material after the test.（The pressure cycle8Launch of the BLISTANCETM blister resistant material series

The above graph shows that the temperature moves

depressurization, resulting in blister formation.

toward room temperature as the horizontal axis moves

Seal materials that are used in food and beverageto the right, and the seal material regains its elasticity

manufacturing facilities are actually exposed to suchas the vertical axis moves downward. From this result,conditions, and blister formation can become a problem.

it can be confirmed that general-purpose EPDM

The product that we would like to recommend forregains 10% of its elasticity at around -43℃, whereas

customers who are facing the above problems is

TM

BLISTANCE -HLT regains the same level of elasticity

BLISTANCE TM-StHT 4）. This product is based on

at around -51℃, showing that it has excellent low-tetrafluoroethylene-propylene rubber（FEPM）, and has

temperature properties.

a different molecular structure from conventional

The fact that no leakage of hydrogen gas was detectedbinary FKMs consisting of vinylidene fluoride（VDF）

after 1,000 cycles of 90 MPa pressurization at -40℃ andand hexafluoropropylene（HFP）（Table2）.

another 20 cycles of 90 MPa pressurization at -50℃ at
HyTReC, indicates that BLISTANCETM-HLT is suitable
as a seal material for use in low-temperature and highpressure hydrogen gas environments.
As mentioned above, BLISTANCETM-HLT is a product

Table2

Molecular structures of FEPM and binary FKM

Type

Molecular Structures

FEPM

that displays its performance in a high-pressurehydrogen gas environment that can be exposed to low

Summer 2021

temperatures, but it is over-specified for use in a
medium-pressure hydrogen gas environment where thetemperature is not as low and the pressure is less thanThe most significant feature of BLISTANCETM-StHT,

35 MPa or in a low-pressure hydrogen gas environment

which wa s developed wit h our compounding

where the pressure is less than 2 MPa. For thesetechnology using FEPM as base material, is that the

TM

No.41

FKM
（Bipolymer）

applications, we recommend BLISTANCE -HMP for

value of the compression set rate is lower than that of

medium-pressure hydrogen gas or BLISTANCETM-HST

the conventional FEPM-based seal materials even in afor low-pressure hydrogen gas.

steam environment of 230℃, and that blisters do not

Finally, please refer to VALQUA Technology News
No.39（2020）for the details of BLISTANCE

TM

-HLT

characteristics and tests.

occur during decompression due to its improved
mechanical strength.
Although EPDM and HNBR-based seal materials havebeen widely used in the past in steam environments of3-2）BLISTANCE -St series

less than 150℃, BLISTANCETM-StHT seals demonstrate

BLISTANCE TM-St series is a blister-resistant seal

significantly higher capabilities than conventionalTMmaterial for high-temperature and high-pressure steam

materials at temperatures above 150℃, where sealing

environments, and there is only one type of BLISTANCETM-

used to be difficult.

StHT in the current range.

The following is a photograph of a compression set test

In general, seal materials made of binary fluororubber

specimen that was actually exposed to a steam（FKM）are used in high temperature environments

environment at 230℃ for 72 hours in a compressed

under air, but it is known that when the environment

state and then rapidly decompressed, as well as the

becomes steam, hydrolysis occurs and the mechanicalmeasured compression set strain rate after exposure tostrength decreases.

a steam environment at 200℃ for 72 hours（Figure6,

In addition, there have been cases where, when used

Table3）.

under high pressure, steam penetrated and stayed
inside the seal material, which expanded upon9

Customer Solutions

from liquid to gas and vice versa. Hence, the occurrenceof blisters is also seen regarding seal materials inapplications where refrigerants are used.
The most important condition for selecting a sealmaterial in a refrigerant environment is that it should
Figure6 C ross-section of test specimen after 72h ofcompression in 230℃ steam

have high mechanical strength to withstand blister

Table3 C omparison of compression set rate between
BLISTANCETM-StHT and conventional FEPM

important that it has low affinity for refrigerants andcompression set rate（％）
200℃×72h
Under steam

formation caused by pressure changes, but it is also

BLISTANCETM–StHT

conventional FEPM

1836

refrigerant oils used as lubricants, in order to reduce
the amount of fluid penetration into the seal material.
BLISTANCETM-RfST, introduced in this section, is a
HNBR-based seal material with high mechanicalstrength and low affinity for refrigerants andTM

refrigerant oils（mineral and synthetic oils）.

StHT does not show blister formation even in

The following photographs show samples removed

environments where it has occurred in conventionalfrom a pressure vessel after depressurization when

FEPM, and furthermore, the compression set rate in

our conventional HNBR and BLISTANCETM-RfST weresteam environment is small and thus favorable.

placed into a pressure vessel filled with refrigerant

In addition, as shown in the beginning of this section,and refrigerant oil, and kept at elevated temperature

FEPM has good acid and alkali resistance. Therefore,

and internal pressure for 72h.（Figure7）.

BLISTANCETM-StHT can be expected to have a longservice life not only in steam but also in acidic andalkaline vapor environments. Thus, customers who

Summer 2021

From the above results, it can be seen that BLISTANCE -have concerns or difficulties about blisters in steam
environments or leakage of acidic and alkaline fluids inhigh-temperature environments are recommended toNo.41

consider using BLISTANCETM-StHT.

Figure7 C omparison of test specimen surfaces
after refrigerant immersion test3-3）BLISTANCETM-Rf series

Blisters occurred on our conventional HNBR, but were

BLISTANCE TM-Rf series is a blister-resistant seal

not observed on BLISTANCETM-RfST exposed to amaterial for use in environments where a refrigerant isrefrigerant environment under the same conditions.

mixed with refrigerant oil, and there is only one

From this example, it can be said that BLISTANCETM-

produce, BLISTANCETMRfST, in the current series.

RfST is suitable for use in a refrigerant environment.

In general, refrigerants（fluorocarbons including CFC

In case the main component of the refrigerant oil is aalternatives）are used as fluids in areas where heat

synthetic oil such as polyalkylene glycol, we would

exchange takes place. Heat exchange is achieved

also like to recommend the BLISTANCETM-H series, inthrough the process of removing heat from theparticular, BLISTANCETM-HMP, as described in 3-1）.

surrounding environment by vaporization heat as wellas its release during liquefaction. The refrigerant3-4）BLISTANCETM-Mu Serieschanges to a liquid when pressurized, and becomes a

BLISTANCETM-Mu series is not a blister-resistant sealgas when the pressure is lowered. Therefore, during

material for specific environments such as high-pressure

heat exchange, the pressure is frequently changed,hydrogen gas, high-temperature steam, and refrigerant

requiring the refrigerant to change its state each timeenvironments introduced so far, but all possess high10

Launch of the BLISTANCETM blister resistant material seriesmechanical strength, and therefore, if there is no

product with hardness 95, and BLISTANCETM-MuHT,

compatibility problem with the used fluid, they can bea FKM-based product with hardness 90.

considered as products that prevent blister formation.

In order to use the most suitable seal material in any

Currently, we offer three types of products:

given environment, when blister formation is a

BLISTANCETM-MuST, a HNBR-based product withhardness 70, BLISTANCETM-MuHP, a HNBR-based

concern, please consider the BLISTANCETM-H, St, andRf series as well.

4. ‌Environmental compatibility and basic physical properties of the
BLISTANCETM series
As a summary, Table4 and 5 show the environmental compatibility and basic physical properties of the BLISTANCETM
series introduced in this paper.
Table4 List of BLISTANCE™ Series Environmental Compatibility
Main Applications

High-pressure hydrogen gas environment

High-pressure
steam
environment

Refrigerant
environment

Series name

BLISTANCETM H Series

BLISTANCETM
St Series

BLISTANCETM
Rf Series

Product name

BLISTANCETM Mu Series

BLISTANCE -HST BLISTANCE -HMP BLISTANCE -HLT BLISTANCE -StHT BLISTANCE -RfST BLISTANCE -MuST BLISTANCETM-MuHP BLISTANCETM-MuHT
TM

TM

TM

TM

TM

TM

EPDM

EPDM

EPDM

FEPM

HNBR

HNBR

HNBR

FKM

70

80

90

90

80/85

70

95

90

Service temperature（℃）*Highest and lowest℃）

Refrigerant※hydrogenMaterial
Nominal Hardness（HA）

Application Suitability

Summer 2021
No.41

Other Environments-40 ～ 120

-40 ～ 130

-50 ～ 100

0 ～ 200-20 ～ 120

-20 ～ 120

-15 ～ 120

-30 ～ 200

High pressure（〜 95MPa）

×

×

◎

×

×

×

×

×

Medium pressure（〜 35MPa）

〇

◎

◎

◎

〇

〇

◎

◎

Low pressure（〜 2MPa）

◎

◎

◎

◎

〇

◎

◎

◎

Steam

〇

◎

△

◎

〇

〇

〇

△

Natural gas

×

×

×

〇

◎

〇

◎

◎

Mineral oil as
refrigeration machine oil

×

×

×

×

◎

〇

◎

×

Synthetic oil as
refrigeration machine oil

◎

◎

◎

×

〇

△

〇

×

※ R134a, R245fa, R32, R400 series, R1234 series and other refrigerants are applicable

Table5 List of BLISTANCE™ Series Basic Physical Properties
Main Applications

High-pressure hydrogen gas environment
BLISTANCETM H Series

Series nameProduct name

Refrigerant
environment

Other Environments

BLISTANCE
Rf Series

BLISTANCETM Mu Series

TM

BLISTANCETM-HST BLISTANCETM-HMP BLISTANCETM-HLT BLISTANCETM-StHT BLISTANCETM-RfST BLISTANCETM-MuST BLISTANCETM-MuHP BLISTANCETM-MuHT

Material
Hardness

High-pressure
steam
environment
BLISTANCETM
St SeriesーNormalTensile MPa
physicalproperties strength
JIS K6251 Elongation ％（JIS No.3
dumbbell） 100% Tensile MPa
StressHardnessーHeat aging test change
JIS K 6257 Tensile strength ％（JIS No.3
changedumbbell） Elongation％
changeCompression set test
JIS K 6262 Compression ％（φ29.5 × 12.5t） Set Rate

EPDM

EPDM

EPDM

FEPM

HNBR

HNBR

HNBR

75

80

93

90

80

73

94

FKM
92

17.1

22.4

14.3

26.9

21.9

30.6

28.8

22.7

200

180

110

120

185

240

90

110

6.4

9.4

10.4

23.0

10.1

7.9

ー

20.0

±0 ※ 4＋1 ※ 4＋2 ※ 4±0 ※ 6＋3 ※ 5＋3 ※ 5＋1 ※ 5±0 ※ 4＋5 ※ 4-4 ※ 4＋4 ※ 4-1 ※ 6＋8 ※ 5＋8 ※ 5＋4 ※ 5-3 ※ 4＋15 ※ 4-4 ※ 4-9 ※ 4±0 ※ 6-4 ※ 5-11 ※ 5-14 ※ 5-3 ※ 412 ※ 57※516 ※ 420 ※ 614 ※-13 ※ 519 ※ 59※4※ Both environmental compatibility and basic physical properties are for reference only and are not guaranteed data.

11

Customer Solutions

5. Acknowledgments

7. References

We would like to express our sincere gratitude to the1）‌H. Nakauchi, Concept of Degradation and Lifetime ofpeople at the Development Office of Ihara Science

Elastomers, Material Life 6［3］, 113-124,（1994）

Corporation for their cooperation since the very

2）‌H. Zushi, Causes and Solutions of Blister Trouble

beginning in the development and evaluation of

Caused by High Pressure Gas and High Volatile

BLISTANCETM-HLT, in particular, among the

BLISTANCETM series.

Liquid, VALQUA Technology News No.31, 17-21,（2016）
3）‌R. Nishihara, Seal Material for High Pressure

6. Conclusion
In this article, we have introduced the BLISTANCETM
series as blister-resistant seal materials, and there is a

Hydrogen Gas, VALQUA Technology News No.39,
16-20,（2020）4）‌H. Zushi, Long Life FEPM TOUGHUORO, VALQUA
Technology News No.36, 25-28,（2019）

background that they were seal material with highmechanical strength. Therefore, we hope that the
BLISTANCE

TM

series will be widely used even in※ ‌"BLISTANCE" is a trademark of VALQUA, LTD.
※“TOUGHUORO" is a trademark of VALQUA, LTD.

environments where blister formation is not expected.
In addition to the expansion of the BLISTANCETM

Summer 2021

series, we will continue to work hard on thedevelopment of new elastomer materials and theimprovement of existing materials so that we canquickly respond to the needs of our customers.

No.41
Ryohei Nishihara
Elastomer Team,
Product Development Div.,R&D Headquarters

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