ThreeBond Technical News
Published on January 1, 2009

72

UV-Cured-In-Place Gasket
Introduction ________________________________________________
ThreeBond, founded with the mission to prevent leakage in industrial operation, has put liquidgaskets first on the Japanese market in 1955.
At present, FIPG (Formed-In-Place Gasket) method has been widely adopted with the use of
automatic coating equipment in a wide range of markets of transportation, and electrical and electronicindustries.
CIPG (Cured-In-Place Gasket) method, which is also used for liquid gaskets to be assembled andsealed after coating and curing, has both features of solid gaskets and FIPG method.
In this issue, we introduce outline of CIPG method and our products which have been developed forhigh performance.

Contents
Introduction .......................................................1
1 Background ..................................................22 Sealing Mechanism ......................................23 Process Comparison between Methods .......3
4 CIPG Evaluation...........................................4
4-1 Pressure Resistance ............................4
4-2 Compression Set ..................................4

5 Material Properties ....................................... 45-1 Curing Properties ................................. 45-2 Sealing Properties ................................ 55-3 Durability .............................................. 56 Precautions for Flange Design ..................... 76-1 Flange Design ...................................... 76-2 Example of Flange Design ................... 77 Applications.................................................. 7Conclusion........................................................ 811Background

2In JIS (Japanese Industrial Standard), a gasket isdefined as “any of such objects that is used toprevent leakage from joint parts by inserting itbetween contact surfaces of pipes or equipment
devices or by bolting or bolting or tightening it byother methods”, and it is used as shown in Figure 1.

Sealing Mechanism

Sealing mechanism of gaskets can be broadlyclassified into compression seal and adhesive seal.
As shown in Figure 2, CIPG and solid gaskets
prevent leakage with its own compressed reaction
force which is generated by being tighten up.

Sealed medium
pressure

Sealed medium
pressure

GasketFigure 1. Basic sealing mechanism of gaskets
Gaskets are used in various markets like
automobile, electric and electronic components, etc.
and mediums to be sealed also vary from lubricant
oil, working oil to water, dust, etc. Gaskets arebroadly classified into two types by theirproperties: solid gaskets and liquid gaskets.
Conventionally, solid gaskets have been widelyadopted to seal flange surfaces, but recently, liquidgaskets (FIPG method) have come to be usedwidely as the alternative sealing method to solid
gaskets because of its ease of use. However, there
remains the problem that it requires a large amountof time for complete curing when generalmoisture-curing FIPG materials are used.
In order to get stable sealing in a shorter time,
CIPG method has been invented which coats liquidgaskets on flange surfaces and assemble it aftercuring.
Early CIPG materials were heat-curing type andrequired curing in a heating furnance. That meant alarge size workpiece required longer time for curing
process and heat resistant material accordingly,
which prevented CIPG from practical use.
Then, we focused on UV curing and developed
UV-curing CIPG materials (UV-CIPG) which can
be cured in short time and don’t give negative effecton heat sensitive components.
In this issue, we introduce UV-CIPG sealing
method and material properties.

2

Compressed
reaction force

Tightening force

Figure 2. Sealing mechanism of CIPG
and solid gaskets
On the other hand, FIPG is effective to fill unevenspots on contact surfaces as it is liquid. Also, asshown in Figure 3, it adheres to contact surfaces
and prevents leakage with its own cohesive force
which is generated after being cured.

Sealed medium
pressureContact force
Adhesion force
Viscoelasticity
Cohesive force
Contact force
Adhesion force

Figure 3. Sealing mechanism of FIPG

3

Process Comparison between
Methods

Table 1. Comparison of each gasket method

Process comparison between methods is shownbelow.
Each method takes different processes according
to its features.
In CIPG, the liquid sealant coated to flange
surfaces is generally hardened by heating andassembled. UV-CIPG which we introduce now is
UV-curing type and can be hardened by ultraviolet
irradiation for several seconds or several tens ofseconds. Figure 4 shows processes where UV-curing or heat-curing materials are used.
In FIPG, a workpiece is assembled before theliquid sealant coated to flange surfaces hardens.
Curing time is necessary for hardening afterassembly.
Solid gasket uses each pre-molded workpiece toinsert and assemble.
Energy(heat, UV rays, etc.)

Coating

Liquid gaskets
MethodSolid gaskets

CIPGFIPG

UV-curing

Moisture-curing

Molding

Compressed seal Both side seal Compressed sealSealing
Process
Curing speed
Speed
LineAutomation
Configuration Administration

DesignFlexibility

ShapechangeRemovability

Each item evaluated based on UV-CIPG performance as standard:: Excellent : Equal : Fair

Advantages of UV-CIPG over solid gaskets are:
⋅ Labor cost can be saved by automation⋅ Flexibly to handle workpiece shape change⋅ No inventory required for each workpiece
Advantages over FIPG are:
⋅ Shorter curing time by UV⋅ Easy to remove (workpiece can be reused)

Compressed
sealFigure 5 illustrates processes from material
procurement to assembly completion of each gasket
method. This indicates that UV-CIPG process is theshortest. This results from easy material
procurement and short working site processes.
Figure 4. Image of CIPG processes
As described above, each method/process has
advantages and disadvantages. Shown in Table 1 iscomparison of other methods with UV-CIPG which
we introduce this time.

Shape

Material procurement

Working site(arrangement)

Coat Cure Assemble

Workpiece
shape ACIPG

Shape A-C

FIPG

Shape A-C

Inspect
Complete

Reassemble

CoatWorkpiece
shape B

Assemble

Inspect

Cure/Post-curing
Complete

Set

Assemble

Inspect
Complete

Shape A
Reassemble

Workpiece
shape CSolidgaskets

Shape B

Set

Assemble

Inspect
Complete

Reassemble
Set

Assemble

InspectShape C
Note:

Complete

Reassemble
indicates that a workpiece can be reassembled when it was rejected by inspection.

Figure 5. Process time for each gasket method

34

CIPG Evaluation

5

How to evaluate CIPG is described below.

4-1

Pressure ResistancePressure resistance is checked using model flange
shown in Figure 6.
Compression rate was controlled by a spacer andmaximum pressure was set to 0.4MPa.
Other conditions are as follows.
Model flange:
Flange outside diameter: 70mm
Flange inside diameter: 56mm
Flange width: 7mm
Pressure media: Air
Pressure rising condition: Pressure increased by
0.01MPa/15sec

Material Properties

ThreeBond3081J (hereinafter TB3081J) isdescribed below, which was developed forUV-CIPG. Also, characteristics required for
UV-CIPG are described.

5-1Curing Properties

Reaction mechanisms for CIPG materials areUV-curing, heat-curing, room temperature-curing,etc., and UV-curing is appropriate for fast-curing.
For complete curing, moisture-curing takes
several days, heat-curing takes several tens ofminutes, but UV-curing takes only several seconds
or several tens of seconds. UV-curing is faster thanothers.
Reaction mechanism of ultraviolet-curing isshown in Figure 8.

Figure 6. Flange for pressure resistance test
4-2 Compression Set
Compression set is to evaluate distortion ofgasket after durability test. The larger the value, thelarger the distortion of gasket, and it means keeping
sealing performance becomes difficult.
To evaluate, set a test piece in a test jig as shownin Figure 7, and tighten up using a spacer to keep
stable compression rate, then perform durability test
under a given condition. Compression set iscalculated from the thickness of the test piece
before and after durability test using following
equation.
Compress

Figure 9 and 10 show evaluation results regarding
requisite energy (integrated light intensity) for
curing TB3081J.

After compression
released

Figure 7. Evaluation method ofcompression set
Cs= (t0 – t1) / (t0 – t2)×100
Cs: Compression Set [%],
t0: Original thickness of test piece [mm]t1: Thickness of test piece after compression
test [mm]t2: Thickness of spacer [mm](JIS K6262 compliant)4

By irradiating UV, active radical is generated andradical polymerization is initiated.

Hardness (Durometer A)

Test piece

Figure 8. Reaction mechanism of radicalpolymerization

504030201001530456075

Integrated light intensity (kJ/m2)

Figure 9. Relationship between integrated
light intensity and hardness

90

1080
8Compression set (%)

Deep curing properties (mm)differs depending on workpiece shapes or otherconditions.

6420153060

4575

9060
4020010Integrated light intensity (kJ/m2)

As shown in Figure 9 and 10, stablecharacteristics can be seen when integrated lightintensity is approximately 45kJ/m2 or more, anddeep curing properties enough for CIPG usage areretained.

0.4
0.3
0.2

0.1

203040304050

5-3 Durability
It is important that UV-CIPG materials should notshow any significant changes (heat resistance,moisture resistance, cold resistance) in theenvironment used.
Followings are durability evaluation results inassumed usage environment.
[Test contents](1) Compression set (25% compression)(2) Rubber properties (hardness, elongation,tensile strength)[Curing condition]
Integrated light intensity: 45kJ/m2[Durability test condition](1) High temperature (120°C)(2) High temperature and humidity(85°C×85%Rh)(3) Heat cycle test(-40°C×30min ⇔ 120°C×30min)

50Compression rate (%)

Figure 11. Relationship between compression
rate and pressure resistance
Since pressure resistance of TB3081J rises inproportion to compression rate (as shown in Figure11), compression rate can be set within a range
where necessary pressure resistance is obtained forthe product.
However, as you can see that pressure resistancedeclines at 50% compression rate, it is important touse within a range where TB3081J gets no crack
nor significant creep.
As shown in Figure 12, compression range ofTB3081J can be set by the evaluation ofcompression set for each compression rate.
Compression set is good when compression rate
is within 20 - 40% range, and it is recommended touse TB3081J in this range.
Note: However, appropriate compression range

TB3081J has excellent durability in compressionset (Figure 13) and rubber properties (Figure14~16) required for UV-CIPG materials under thetest condition of high temperature, high temperatureand high humidity, and heat cycle, showing no bigchanges.
80
Compression set (%)

Pressure resistance (MPa)

5-2 Sealing Properties
TB3081J provides requisite sealing performancewith its compressed reaction force generated bytightening.

20

Figure 12. Relationship between
compression rate and compression set
120°C × 72h

Figure 10. Relationship between integrated
light intensity and deep curing properties

010

Recommended
compression range

60
40
200100200

High temp. test

300
Time (h)High temp. andhigh humidity test

400500Heat cycle test

Figure 13. Durability of TB3081J- Compression set Compression rate: 25%5Figure 14. Durability of TB3081J - Hardness
Figure 16. Durability of TB3081J- Tensile strength
Table 2 shows other characteristic values ofTB3081J. Low glass transition point indicates thatthe product provides flexible rubber elasticity in awide range of temperature.
These results prove that TB3081J has requisitecharacteristics as UV-CIPG: curing properties,
sealing properties, durability, etc.

Figure 15. Durability of TB3081J – Elongation

Table 2. Other physical properties of TB3081J

66Precautions for Flange Design

For optimum usage of UV-CIPG which has
characteristics previously described, flange design
must be also taken into consideration.
6-1 Flange Design
Optimum flange shape for CIPG method is shownin Table 3.
In consideration of sealing properties anddurability, one-sided wall shaped flange isrecommended.
Table 3. CIPG applicability of flange shape

For designing flange width, it is necessary to set agap between CIPG bead and wall to prevent CIPG
from touching wall when compressed.
Considering expansion of CIPG bead to sideways
when compressed 30%, approximately 0.4mm gap
for each side (Figure 17) is necessary, resulting asfollows.
∴ Flange width = 3.0 + (0.4×2) = 3.8mm orlarger
It is also necessary to consider size tolerance(such as bead/workpiece accuracy) to actuallydesign wall height and flange width.

Bead height
2.0mm

Wall height
1.4mm

Bead width 3.0mm

0.4mm

Flange width 3.8mm

Figure 17. Example of flange dimensions
This structure can obtain stable compression ratesince it contacts companion flange surface at thewall part, also it functions to protect CIPG beadfrom water, oil, dust, etc. Groove shape has
potential to get CIPG bead cracking as it can’t
absorb inner stress.

7Applications⋅ Case seals of electrical components for vehicles⋅ Waterproof/dustproof seals for various
electric/electronic parts

6-2 Example of Flange Design
An example of flange design is introduced below
describing a model how to set wall height andflange width using Figure 17.
CIPG bead height/width : 2mm/3mm
Note: Syringe coating (using a nozzle)
As shown below, wall height is designed within arange where good durability and compression setare obtained (in this example, calculated with 30%compression rate).
Wall height= Height of 30% compressed CIPG bead height= 70% of CIPG bead height is wall height∴ = 2.0×70% = 1.4mm7Conclusion
CIPG method has both features of solid gaskets and FIPG method.
UV-CIPG technology introduced herein has process benefit of fast curing and provides excellent material
characteristics in wide temperature range, and it can be applied to various applications.
We expect further CIPG technology innovation by utilizing our sealing/coating expertise which has beenaccumulated through our long years’ experience with FIPG, and we are sure to contribute to the development ofindustrial world as an attractive “partner” for customers.
<References>
JIS B 0116
JIS K 6262
JIS K 6824
“ThreeBond Technical News No.42” 1994 ThreeBond“ThreeBond Technical News No.44” 1995 ThreeBond“ThreeBond Technical News No.60” 2003 ThreeBond“ThreeBond Technical News No.69” 2007 ThreeBond
Kuniyuki Watanabe
Masayuki Tanaka
Transportation Market Department
Product Development Division
R&D Group
ThreeBond Co., Ltd.

1456 Hazama-cho, Hachioji-shi, Tokyo 193-8533, Japan
Tel: 81-426-61-1333

8