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High-Adhesion Aluminum Sheeting: KO Process Sheets

1.

INTRODUCTION

Surface treatment of aluminum makes it possible to further upgrade film adhesion, adhesive strength and corrosion resistance, and for this reason a variety of chemicaltreatments, including chromate-phosphate and anodic
oxide treatment (alumite processing) have been used. In
recent years, however, there have been demands forincreases in adhesive strength and calls for materials thatare more environment-friendly, raising the hope that new
surface treatment materials will be brought forward.

2.

FEATURES OF KO PROCESS FILM

(1) Is “earth-friendly”, with no constituents that are harmful to man or the environment:
Table 1 compares the constituents of KO process film
against others. Since electrolysis is carried out using anelectrolyte of degreasing property that includes no chromium or other heavy metals, the aluminum oxide film thatis formed contains no heavy metals and is low in surface
contamination.
(2) Exhibits a high degree of adhesion:
Figure 1 shows a TEM image of the cross section of aKO process film. By forming an aluminum oxide film having a branching structure it is possible to achieve extremely good adhesion between the adhesive agent and thecoating, plus it is relatively free from the effects of heating
and processing.
Table 1

Chemical constituents of selected coating materials.

(3) Performance is retained over long periods:
An alkaline electrolyte is used and rinsing is done using
deionized water, so that there is no residue in the film of
acidic constituents that could promote corrosion and thelevel of impurities such as chlorine is extremely low. Thus
virtually no change in performance occurs over time.
(4) High heat dissipation:
KO process film is so thin--less than 250 nm--that thehigh thermal conductivity of aluminum is not compromised.

3. PRODUCT SPECIFICATIONS
Table 2 shows the specifications of KO process sheets.
For processing outside this range, please make specificinquiries.
Figure 2 diagrams the KO process. It uses an alkaline
electrolyte containing a surfactant, and is characterizedby carrying out degreasing and AC electrolysis simultaneously.
Table 2Specifications of KO process sheets.
1000 series (A1100P-H24 and the like)

Aluminum materials

3000 series (A3003-H18 and the like)
5000 series (A5052P-H34 and the like)

4.

Outline dimensions

1050 mm square (max.)Thicknesses

0.5 - 5.0 mm

PERFORMANCE

Film composition (mol %)
AlO

Other

KO process film

40.7

58.2

1.1

Sulfuric acid anodic oxide film

32.0

64.0

4.0

Al2O3 (theoretical value)

40.0

60.0

0.0

Branching structure layer

Figure 1Barrier layer

TEM image of KO process film.

100 nm

4.1 Adhesion
Figure 3 shows the 90° peeling strength using polyestertape with acrylic adhesive. It can be seen that the highest
peeling strengths are provided by the oxide film surface
treatment agents, led by KO process sheets.
High secondary adhesion is yet another feature of theKO process. Figure 4 shows the T-peel strength with ahot-melt type epoxy bond. Compared to the KO process
sheets, which suffer only a minor drop in strength due toretort processing (121°C), the drops for sulfuric acid andphosphoric acid anodic oxide treatment agents wereenormous.
From this it can be seen that compared to pretreatment
methods used in the past to prepare surfaces for adhesives, the KO process delivers high adhesion that is stableeven under the most extreme conditions.

Furukawa Review, No. 29

200633

2.0
1.5
1.00.5

KOprocCarbon electrodes

Workpiece

Electrolyte (alkali + surfactant)

4. Rinsing

5. Drying

Deionized water
Air bubbling

KO process.

121086
4
20

Result of filiform corrosion tests on selected surface
treatments.

ical treatment agents for corrosion resistance, and exhibit
an outstanding level of corrosion resistance.
4.3 Durability
Figure 6 shows the change in 90° peeling strength using
polyester tape with acrylic adhesive for KO process sheetsthat have been exposed to a humid atmosphere for up tosix months.
If ordinary treatment agents are exposed without adhesives or coatings, moisture absorption and surface contamination result in changes in properties, causing a precipitous drop in adhesion strength. KO process material,on the other hand, is mainly composed of aluminumoxide, which is low in impurities, and therefore undergoes
virtually no drop in performance.
It is therefore highly suitable for use in components inwhich degradation in performance is unacceptable andthe highest reliability is required.

90° peeling strength for selected surface treatmentswith acrylic adhesive.

30
Normal temperature
After 16 hr in retort
After 32 hr in retort

252015121086420Figure 61001530
Days exposed (d)90180

Change in 90° peeling strength for KO process
sheets with exposure to humid atmosphere.

5proc

Sulfu

KOri cox i a c i dde anotrea dictm e
Phos pnthoric aox i c i dde anotrea dic
tm e
Chntrom
at e-phostrea phatetm eAlkalinnt
eetc hin gac i +d tr nit
eat ric
ment
De
greasingtrea
tm ent0e ss

T-peel strength (N/cm2)

Figure 3

90° peeling strength (N/cm2 )KOprocessSulfu
ricac
ox
i de i d at r e no d
Ph
atm ic
os
en
pht
ori
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ate-phostre phaatm te
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FP
Lt
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tm
ent
De
greasing
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atm
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90° peeling strength (N/cm2)

Figure 2

Figure 5Galvanizinp ho + z gsph incat i ng

0.0ess

3. KO processing

2.5p ho Z
sph inc
at i ng

2. Cutting

Chrotrea matet ment

1. Rolling

Filiform corrosion length (cm)High-Adhesion Aluminum Sheeting: KO Process Sheets

Figure 4T-peel strength for selected surface treatments withepoxy bond.

4.2 Corrosion Resistance
Figure 5 shows the result of filiform corrosion tests after
cathodic electrodeposition coating. The KO process
sheets showed shorter filiform corrosion than other chem-

5.

APPLICATIONS

By reason of their high heat dissipation and high adhesion, KO process sheets have been highly acclaimed foruse as aluminum printed circuit boards. In addition theiroutstanding adhesion properties recommend them foruse as construction materials, coated sheeting and compound sheeting that offer excellent visual appeal.
Fore more information, please contact:
Fourth Sales Dept., Sales Div., Furukawa-Sky Aluminum
Corp.
TEL: +81-3-5611-2410
FAX: +81-3-5611-2412

Furukawa Review, No. 29200634