Three Bond Technical News
Issued July 1, 2001

Introduction

57

Development of Sealants andAdhesives for HDDs________________________________________________

Hard-disk drives (HDDs) have played an essential role in recent progress in information technology
and digitalization. More than 200 million hard disks are produced each year as storage devices forboth personal and mainframe computers. These hard disks offer high capacity, high-speed access, andcost-effective performance. Three Bond develops anaerobic sealants, epoxy resins, ultraviolet-curingresins, and conductive resins that have low-outgas characteristics, and they are used as sealants andadhesives in current HDDs. This issue introduces technologies to produce low-outgas sealant andadhesive, their capabilities, and methods to measure outgas.
HDD is a sealed storage device. Therefore, if any corrosive, volatile gases are generated inside thedevice, it may impact device performances. HDDs are magnetic storage devices that incorporate
magnetic heads to record signals to a recording film (or medium) deposited upon on smooth aluminumor glass disks rotating at some 5,000 to 10,000 revolutions per minute. Clearance between the head
and the surface of the medium is on the order of several tens of nanometers. Therefore, any foreign
objects adhere between the head and the disk may cause a major damage. For this reason, major
imperatives in HDD development are to protect the devices from penetration of small dust andhumidity, and reduce the generation of volatile gasses from parts and adhesives used to assemble thedevices. These adhesives used for this purpose have numerous requirements other than low outgas
levels, including special functionality on workability, productivity, quality control and supply
management of the products. All Three Bond groups in domestic and overseas development, sales, andmanufacturing plants work in concert to ensure timely product development and stable product supply
that fulfills these requirements.
In the rest of this document, Three Bond is abbreviated TB.
Contents
Introduction ............................................................... 1
1. Sealants and adhesives used in hard disks ........ 2
1-1. Various types of sealants and adhesives............ 2
1-2. Understanding outgas that sealants
and adhesives generate ............................. 3
1-3. Outgas components ................................... 3
2. Methods of measuring outgas ............................. 3
2-1. Qualitative and quantitative determination ... 3
2-2. Measurement of thermal mass reduction using
TGA .............................................................. 3
2-3. Qualitative and quantitative determination using GC-MS ..... 4
2-4. Evaluation of measurements ...................... 4

3. Anaerobic sealants and ultraviolet-curing resins....4
3-1. Anaerobic sealants and ultraviolet-curingresins for HDDs .............................................4
3-2. A new anaerobic sealant: TB1360D..............5
3-3. Ultraviolet-curing resin TB3061H ..................5
4. Epoxy resins .........................................................6
4-1. Two-part epoxy resins TB2087F and TB2087G ...64-2. One-part epoxy resin TB2270C ...................6
5. Conductive resins .................................................7
5-1. Two-part non-solvent conductive resin TB3380B .7
5-2. TB3305B ultraviolet-curing conductive resin........7
6.
Summary .....................................................81

1.

Sealants and adhesives used in hard
disks

Figure 1 shows an exploded view of a HDD and
the Three Bond sealants and adhesives used in a
HDD. Three Bond offers a variety of sealants andadhesives for hard disks.
1-1. Various sealants and adhesives for hard
disks
Many Three Bond products are used in hard disks.
Ultraviolet-curing sealants are used for the top
cover of the hard disk; anaerobic resins and epoxy

resins are used in the spindle motor to fix the
bearing and shaft and to keep the magnet in place.
Ultraviolet-curing resins and conductive resins areused in the magnetic head and suspension. Epoxy
resins are used in the voice coil motor (VCM) to fix
the coil and the magnet.
Three Bond develops and offers various sealants
and adhesives specifically matched to each regionof HDD assemblies, aiming to minimize total
outgas generated from sealants and adhesives.

Hard disk spindle motor
Adhesion ofmagnets

Cap sealant
Cover sealantAdhesion of shaft
to caseAdhesion of
the shaft andbearing

Connector seal

Actuator

Securing of
the wire

VCM magnet

Securing of
the head

Securing of the pivot
Adhesion of the
VCM magnet

Adhesion of coil toaluminum block

Figure 1: Exploded view of HDD and sealants and adhesives used2

TG/DTA
Data name: TB3057H
Date: 1/5/15 2:31
Sample: TB3057H

20.6165 mg
Reference:
0 mg

Temperature program:[C] [C/min] [min] [sec]1* 20-  500 1 
0 20

0.000

Comments:
Operator
TB3057H
20 mg 3000 mj/cm2
1 /min.
25
500

354.3C-3.526%

Outgas

-10.000

TG %-20.000
Thermaldecomposition-30.000-40.000
410.1C-51.487%-50.000
100.0

200.0
300.0
Temp

400.0

500.1C-53.924%

500.0

Figure 2: Thermally-induced mass change rateduring heating of TB3057H
1-3. Outgas components
The volume and components of outgas differ
from adhesive to adhesive. Major outgas
components include the moisture, reduction objectsof curing agents, polymerization inhibitors,
un-reacted monomers, organic metal catalysts,
organic acids, and impurities in raw materials suchas organic solvents that are contained in sealants
and adhesives. The outgas components that poseserious failures to HDDs are those with strong
adhesive and corrosive properties.

2.

Methods of measuring outgas

Chemical analyzers such as GC-MS (gaschromatograph-mass spectrometer) and TGA(thermo-gravimetric analyzer) are used to measure
the outgas generated from cured adhesives. In
particular, GC-MS, which combines gas
chromatography and mass spectroscopy, is used inmany industries as standard equipment for
qualitative and quantitative outgas analysis. GC-MS
has recently begun to be used to analyze clean-room
contaminants and to detect endocrine disruptors.
2-1. Qualitative and quantitative determination
The outgas components generated by sealants andadhesives are measured to determine the volume ofgas generated (quantitative determination) and to
identify the components (qualitative determination).
It is required to know the volume of generated gas
and its components from sealants and adhesives.
The gas components must also be scrutinizedwhether they are corrosive, or not.
2-2.

Measurement of thermal mass reduction
using TGATGA is used to measure changes in the mass ofsealants and adhesives during application of heat.
TGA equipment can measure the absolute volumeof the moisture, and inorganic and organic gas
generated from sealants and adhesives under
specific heating conditions. This measurement
clarifies the relationship between changes in massand time or temperatures. However, it cannot
identify the components of the generated gas or the
proportions of each component in the gas generated.
Figure 3 shows the thermal mass changes on
TB3057H caused by continuous application of heatof 80°C and 120°C. Outgas evaluation is typically
performed with continuous measurement at an
optional temperature between 80°C and 150°C. Thechange in thermal mass at the temperature ismeasured and the volume of outgas is determined.
TG/DTA
Data name: TB3057H
Date: 0/2/26 23:28
Sample: TB3057H

20.6608 mg
Reference: NONE

0 mg

Temperature program:
C C/min min sec
1 20  80 10 240 1

Comments:
Operator
TB3057H

Dot 20 mg
80
120

2h
2h

0.000

0.000
80
120

0.200
0.400

0.200

0.39

0.600

0.400
0.600

0.800

TG

Understanding outgas that sealants andadhesives generate 1)
Outgas generated from sealants and adhesives arevolatile organic or inorganic gases of low molecularweights up to around 300, generated during curing
time or from cured objects after curing completed.
Reducing outgas from sealants and adhesives is
specifically required inside HDDs.
Figure 2 shows the thermal mass change when acured mass of TB3057H ultraviolet-curing resin isheated to 500°C. Increasing the temperature
gradually decreases mass. Thermal decompositionof the cured object starts at approximately 300°C.
The temperature inside HDDs goes up to
approximately 100°C. Specifically the thermal massdecreased before starting thermal decomposition
equals to the outgas.

TG

1-2.

0.800
0.93

1.000
ThreeBond Co.,Ltd.

20.0

40.0

60.0
Time min

80.0

100.0

120.0

1.000

Figure 3: Thermal mass change rate during continuous
application of heat of 80°C and 120°C on
TB3057H3

2-3.

Qualitative and quantitative
determination using GC-MS 2)
GC-MS can perform quantitative and qualitative
determination of organic gases with molecularweights approximately ranging from 30 to 500. Thisequipment also provides various methods for
extracting outgas, including the head space method
and the dynamic head space (DHS) method. Since
the DHS method uses a constant flow of inert gas in
the sample chamber and adsorbs the generated
outgas to an adsorbent, it enables analysis with highsensitivity. Figure 4 is a schematic diagram of the
GC-MS used by Three Bond. Table 1 shows resultsof GC-MS measurement on TB3061H.

2-4. Evaluation of measurements
Quantitative values and qualitative components
measured are varied with measurement equipment,
curing conditions, shape and surface area of thecured object. Also, measurements of the adhesive
itself are different with ones of the adhesive used in
actual assembly. These factors must be consideredwhen evaluating measurement results. Also,
diversified measurements ensure certain evaluation.

Table 1:
Instrument of Outgassing test
GC-MS
Doubleshot
pyrolyzer(DSP)

DHS

TGA
Headspace
DSP

outgass
Headspaceof
DHS

GC-MS measurement results for
TB3061H

library

GC-MS

Figure 4: Schematic diagram of outgas
measurement equipment

3.

Anaerobic sealants and ultraviolet-curing resins

3-1.

Anaerobic sealants and ultraviolet-curingresins for HDDs 3)
Anaerobic sealants are one-part non-solvent
adhesives that react at room temperature in small
gaps between metals. Therefore, this characteristic
is particularly well suited to surface adhesion andfitting adhesion applications such as fixing the shaft
and bearing. Other one-part non-solvent adhesives
include ultraviolet-curing resins, which cure rapidly
when irradiated with ultraviolet light.

These sealants and adhesives are ideal for fixing
parts and for sealing against oil and dust. Sealants
and adhesives are primarily classified as acrylic- or
epoxy-based resins. Both anaerobic sealants andultraviolet-curing resins start the curing reaction by
resolving curing catalysts in curing time. Part of theresolution material volatilizes from the cured object
and forms the outgas. Table 2 lists the anaerobic
sealants and ultraviolet-curing resins used in HDDs.

Table 2: Anaerobic sealants and ultraviolet-curing resins for hard disks
Product nameThreeBond 1360D
Anaerobic sealantColor and appearance
Viscosity
Specific gravity
Hardness
Compressed Iron
shearing
Stainless steel
strength
Aluminum
Shearing
Glass/glass
adhesive strength Acrylic/acrylic
Glass transition point (DMA tan δ)Rate of thermal mass change
Linear expansion coefficient
Applications*1

4

Pa•s (cP)MPa {kgf/cm2}
MPa {kgf/cm2}
MPa {kgf/cm2}
MPa {kgf/cm2}
MPa {kgf/cm2}°C％
×10-6 / °C

Uncured resin at 80°C after 16 hours

0.90 (900)37.1 (371)
20.7 (207)28.1 (281)
165
-3*1
81.9
Fixing of spindle
motor shafts
Primer TB1390K*2

ThreeBond 1372D
Anaerobic sealant
UV curing added
Green
0.11 (110)33 (336)
31 (305)
27 (275)
147
-35*1
80.5
Fixing of spindle
motor shafts
Primer TB1390E, F

Cured resin at 120°C after 2 hours

ThreeBond 3057H
Ultraviolet-curing resin
UV and heat curingBlue
12 (12000)
1.14
D 85
20.5 (205)SUS/SUS *3
5.2(52) SUS/Acrylic
85.8-0.6 *2
46.8
Sealant for spindle motor
caps
Homogeneous sealant*3

ThreeBond 3059D
Ultraviolet-curing resin
UV curing only
Creamy white
76 (76000)
1.18
D 88
8.0 (80)
3.0 (30)82-0.6 *2
Fixing wires
High viscosity

Curing conditions: 100°C × 0.5 hours

ThreeBond 3061H
Ultraviolet-curing resin
UV and anaerobic curing
Dark Blue8 (8000)
1.14
D 65
8.8 (88)
7.0 (70)35-0.9 *2
210
Sealant for spindle motor
caps
Heterogeneous sealantA new anaerobic sealant: TB1360D

The TB1360D anaerobic sealant was developed
for fitting adhesion of the shaft and the bearing of
the spindle motor. This material offers a high glasstransition temperature of 165°C and low volatile
content in the uncured object (liquid). For shaft
adhesion of the spindle motor, provisions against
heat are particularly important while the disk isspinning; if the shaft shifts even slightly (on theorder of sub-microns), the disk on the shaft(particularly at outer perimeter) will inevitably shift
significantly (on the order of microns). The resin
used here must be heat-resistant; in other words, theresin must have a high glass transition temperature.
Figure 5 shows the heated strength of TB1360D.
Figure 6 shows the thermal degradation of strength
on TB1360D and TB1373B. TB1373B is an older
product. TB1360D clearly offers superior
performance. Here, excess anaerobic sealant in thefitting adhesion does not cure with oxygen andreleases significant volumes of outgas. TB1360D
significantly reduces outgas emitted from excesssealant, compared to older sealants. Due to theirpotential causes to harm HDD components,
TB1360D also uses no organic sulfur compounds,
however, used in combination with a special
TB1390K primer, it is achieving anaerobic curing
properties comparable to older products.

TB1360D
TB1373B

TB1360D
TB1373B

Comparative strength (%)

3-2.

120

x number of days

Figure 6: Comparison of thermal degradation
between TB1360D and TB1373B
3-3. Ultraviolet-curing resin TB3061H
Ultraviolet-curing resin TB3061H is a one-partnon-solvent acrylic-based adhesive with anaerobic
curing properties. Developed as a cap sealant for thespindle motor, TB3061H offers excellent
ultraviolet-curing
properties
andadhesion
capabilities with metals and plastics. Similar to
TB1360D, it contains no organic sulfur or organic
tin compounds. Figure 7 compares the reaction
ratios of TB3061H and an old product. The acrylylgroup reaction ratio is measured by real-time FT-IR(Fourier transform infrared spectroscopy). The
figure clearly shows that TB3061H completes thereaction rapidly.

TB3061H
Old type

Irradiation time (sec)Figure 5: Comparison of hot strength between
TB1360D and TB1373B

Figure 7: Ultraviolet irradiation time andreaction ratios of TB3061H and an
older product5

4.

Epoxy resins

Epoxy resins for hard disks are classified as
one-part and two-part resins. Epoxy resins generateless outgas than anaerobic sealants andultraviolet-curing resins. This is due to the curing
mechanism of epoxy resins, which does not

generate resolution objects. The cured objects of
epoxy resins are also hard (due to the three
dimensional mesh structure), and have thecapability to suppress the volatilization of gas
components with low molecular weights containedin them. Table 3 lists the epoxy resins for HDDs.

Table 3: List of epoxy resins for hard disks
Product nameThreeBond 2202

ThreeBond 2270C

ThreeBond 2087F
Primary agent

ThreeBond 2087G

Curing agent

Primary agent

Product under development

Curing agent

Primary agent

Red

Transparent
yellow

Color
Viscosity
Specific gravity
Standard curingcondition
Working time
Shearing adhesivestrength
Peeling adhesivestrength
Glass transition point
Thermal masschange rate
Linear expansion
coefficient

ApplicationsPa•s (cP)

Black

Black

Pink

Blue

13 (130)
1.14

70 (700)
1.95
100°C × 40 minutes
120°C × 30 minutes
150°C × 20 minutes

13 (130)
1.17

4.4 (44)1.10

80°C × 20
minutesminutes22.5 (25)
1.19

25-30
(when mixing 100 g)

80 (when mixing 100 g)

240 (when mixing 100 g)

11.8 (120)

12.9(131)

60°C × 3 hours
80°C × 1 hours

10.0 (102)21.6 (220)28.4 (290)N/m {kgf/25mm}

160 (0.4)2100 (5.4)

589 (1.5)

°C

105

140

-6

×10 / °C

74
Bonding spindle
motor rotor magnets
Bonding general
hard disk parts

41
Bonding VCM(Coil and arm)

4-1.

Two-part epoxy resins TB2087F and
TB2087G
A two-part epoxy resin consists of a main agent
and a curing agent. These components are mixed in
the appropriate ratios and heated to cure. TB2087F
and TB2087G are designed for use to fix themagnet in the spindle motor.
Offering lesser changes in viscosity than older
adhesives, (longer working time) after mixing atroom temperature, TB2087F and TB2087G are alsoable to cure at lower temperatures. Figure 8 shows
appearance in the curing of TB2087G measured byRheometer. TB2087G shows small viscosity changearound room temperature, but after application ofheat, it starts curing reaction in a short time.
In addition to the products above, we areconsidering to market products of two-partoil-resistant epoxy resin designed to seal oil within
fluid dynamic bearing (FDB) motors. Compounding
and mixing are crucial for two-part epoxy resins,
since errors in the area may leave uncured portionof the resin. To prevent this, Three Bond's epoxy
resins use different colors for the primary agent andthe curing agent, enabling easily visualize themixing state.
4-2. One-part epoxy resin TB2270C
One-part epoxy resins are one-part non-solvent
resins that contain powdered curing agents
dispersed in the main agent. They do not have aworking time as defined for two-part resins.
TB2270C is used to bond the coil and the arm of the
VCM. TB2270C offers high thermal conductivity

6

13 (130)
5 (50)
1.20
1.25
60°C × 30 minutes
70°C × 20 minutes
80°C × 10 minutes

MPa {kgf/cm }%Pale blue

Curing agent

Transparent
deep bluegreen
3 (30)
1.00

90°C × 1 hour

85

145

130

At or below 0.001

At or below 0.001

At or below 0.001

72

60

Bonding spindle motor
rotor magnets
Bonding general harddisk parts

Bonding spindle motor
rotor magnets
Bonding general harddisk parts

60
For FDB oil sealing

and excellent adhesive strength with metals. The
cured objects are hard and strong and do not affect
VCM operations. Table 4 shows the results of theadhesive strength test after the PCT. Since one-partepoxy resins use powdered curing agents, they are
unsuitable for fitting adhesion applications such as
fixing the shaft and bearing. Since the curing agent
would partially penetrate into the fitting area as
inserting the shaft, which would leave uncured
resin.

Figure 8: Viscosity changes in TB2087G by time at various
temperatures, as measured by a Rheometer
Table 4:

Adhesive strength of TB2270B after
PCT

Items
Curingconditions
Blank

ThreeBond 2270C
120°C
120°C
× 40min× 40min
41 MPa39 MPa120°C
× 20min
44 MPaAfter PCT

21 MPa23 MPa21 MPa*PCT conditions: 121°C, 2 atm, after 12 hours

Competing product
130°C × 50min+155°C × 120min
40 MPaPeeled directly after
PCT

5.

Conductive resin

A conductive resin consists of a binder such as an
epoxy resin and a conductive powder (conductive
filler) such as silver powder. The conductive filler,
constituting 80 to 90% of total weight is dispersed
throughout the binder. Conductivity emerges as the
conductive filler objects become closer whenvolume shrinks during binder curing. The highvelocity rotations of hard disk generate static
electricity, which may cause significant damage on
the magnetic heads and medium. Conductive resins
are used to remove this static electricity. Figure 5
illustrates the properties of conductive resins for
HDDs.

Table 5: List of conductive resins for hard disks
Product name
Color and appearance
Viscosity
Specific gravity
Standard curing condition
Working time
Shearing adhesive strength
Peeling adhesive strength
Glass transition point
Thermal mass change rate
Linear expansion coefficientPa•s (P)Minutes2MPa {kgf/cm }N/m {kgf/25mm}°C%-6×10 /°C

Applications

ThreeBond 3380E
Primary agent
Curing agent
SilverGray
31 (310)2.9 (29)3.7
3.2
60°C × 3 hours
240 (*1)
19.5 (198) (*2)
0.09 (*3)
Cap seal

ThreeBond 3305B
Burnt umber
22 (220)1.8
120°C × 30 minutes
16.9 (172) (*2)
2.7 (6.7)
17
0.10 (*4)
For assembling hard disk magnetic
read/write heads*1: Time after mixing required for viscosity to double*2: 2 φ ceramic chip/glass adhesive strength*3: Aging at 120°C for 1 hour
*4: Aging at 120°C for 2 hours

5-1.

Two-part non-solvent conductive resin
TB3380B
TB3380B conductive resin uses a two-part epoxy
resin (non-solvent) as binder. Both the primaryagent and the curing agent contain dispersed silver
powder conductive filler. TB3380B is used to seal
the spindle motor and drain static electricity.
TB3380B forms flexible cured objects that
accommodate heat cycles with stable volume
resistance values.
5-2.

TB3305B ultraviolet-curing conductive
resin
The TB3305B ultraviolet-curing conductive resin
uses a one-part ultraviolet-curing resin as binderand silver powder (spherical powder of 10 microns)
as conductive filler. TB3305B is used to bond theslider and suspension and to remove static
electricity from these parts. To date, two types ofresins have been used to meet this requirement: anultraviolet curing resin for adhesion and a
conductive resin to remove static electricity.
TB3305B simplifies the process by serving bothroles. TB3305B provides temporary binding whenirradiated with ultraviolet light, complete curing of
shadow areas with heat and enables verticalconductivity (removal of static electricity) oversmall vertical gaps of 10 microns or less. The cured
objects are flexible, create minimal stress whencuring, and do not increase strain on the magnetic
heads. Figure 9 illustrates an application sample of
TB3305B.
Processes incorporating
TB3305B
Suspension
SliderDisk

Conventional processes
Ultraviolet-curing
Conductive
resin

Figure 9: Illustrated example of TB3305B
application

7

6.

Summary

The low outgas sealant and adhesive technologies discussed in this article have become essential for electronic
devices other than HDDs. Low outgas requirements will continue to increase for sealants used in liquid crystals
and EL display boards, used as conductive resins for securely positioning quartz oscillators, or used as adhesives
around optical pickup lenses. We remain dedicated to advancing the state of the art in resin functionality andoutgas characteristics.
Three Bond Co., Ltd. Research Laboratory
Development Department Electric Development Division
Yoshihide Arai
Manabu Inoue
Aki Kusuyama
Hironori Suzuki
Katsunori Ito
References
1) Storage Device Terminology, Nikkei BP
2) Tatsuo Nonaka, et al., Sumika Chemical Analysis Service, Ltd., Outgas analysis of materials, including clean
room components, Clean Technology, Vol. 9, No. 2, Japan Industrial Publishing Co., Ltd.
3) Aki Kusuyama, Three Bond Co., Ltd., Anaerobic sealants in electric applications, Industrial Materials, Vol. 49,
No. 51456 Hazama-cho, Hachioji-shi, Tokyo 193-8533, Japan
Tel: 81-426-61-1333

8