Surface Finishing Technologies of Aluminum Building Materials in Japan

ttffitta-n- By T. Sa to and K. Kaminaga 2737 7 ~

Abs t rac t

We report surface finishing techniques used

for the production of aluminum building

materials in Japan and, in particular:

(1) Status of the aluminum surface finishing industry,

(2) St:itistics relating to the production of

surface finished aluminum,

(3) Development of the vertical racking

system, electrolytic coloring, electrodeposition

coating (ED) and other coating techniques,

and

(4) Organizations for supporting the technical

development.

1. Introduction

One day in 1950s a Japanese businessman

crossed the Pacific, and made a tour in an

American aluminum extrusion plant. He

perceived a promising future with aluminum

building materials and, back in Japan,he

founded an "aluminum sash" production

company, first ever in the country. The

Japanese often call window frames "sashes",

so :I business dealing them "aluminum sash

kaisha (company or firm)".

Current Japanese annual production of

aluminum building materials amounts 600,000

tons and, including civil engineering and like

materials, 800,000 tons. They are produced

for the most part by five major firms. They

are somewhat different from American or

European competitors in way of operation,

including production, sales and surface

finishing. For example, the Japanese have

been using vertical racking systems for

carrying the work of extruded profiles as well

as electrodeposition coating (ED) from more

than 20 years, while they rarely employ the

electrolytic coloring with tin sulfate bath, :is

well as powder coating. We describe those

topics along with some statistic data for

surface finished aluminum used for building

materials in Japan.

2. Past and present of aluminum surface

finishing industry

There a re remarkable differences in

business circumstances of the surface finished

aluminum industry between Japan and

America or European countries. Recent

technical development, illustrated in Fig. 1,

may be accountable for the difference.

In the days when the commercial

production of aluminum window frames

started in Japan, "aluminum sash" companies

235

19-55

Fig.1 Changes of companies by new

technologies

were just surfiice finishing extruded profiles of

duminum which they got from aluminum

refineries. Around 1965 some "sash"

manufacturers for the first time installed

extrusion machines and began the successive

processes of extrusion and surface finishing

themselves. They further worked surface

finished profiles and packaged for shipment.

A lot of persons were employed to sell the

products. TV commercials were aired for

their aluminum sashes. Then developed were

such techniques as electrolytic coloring,

electrodeposition coating (ED) and vertical

racking system. Confronted with those novel

techniques, some manufacturers could, while

the other could not afford for adopting them.

As a result, the surface finishing industry

became divided into the classes of il few

major firms whose business extended to

other steps of the production, and lesser, or

middle and small, enterprises specializing

in the surface finishing. Their difference in

capital size affected the scope of adopted

techniques, productivity, and coverage of

the distribution network, as well as the

production capacity.

Middle-scale manufacturers some how

could sustain their business around 1975; then

the thin economical benefit they could earn

from their modest capacity of production and

poor distribution network forced them to

withdraw from the sector of standardized resi-

dential window frames; they a r e now

specializing in made-to-order materials for

office (and other non-residential) building

window frames. Some enterprises were

purchased in by i1 larger one, or even went

bankrupt. Currently in Japan there exist five

major aluminum firms who supply, in total,

100% of residential window frames and 70 to

80% of non-residential window frames as well

as curtain walls for office buildings.

In contrast to America and European

countries where window frames a re surface

finished, worked and sold "separately and

individually" at and by separate enterprises,

such jobs are done "integrally" by a single one

in Japan. Most of them have also established

their operations in Asian countries outside

Japan to produce and sell the materials.

Here we are not boasting those Japanese

236

Japanese entrepreneurs achievements: instead

we would like to suggest that the advent of

some advanced techniques may not always

bring about favorable results equally to all the

surface finishers around.

We would like to point out another basic

difference between Japanese and AmericadEuropean industries, which is observed in the association of chemical

suppliers and finishers. In both America and

European countries a finisher purchases II

ready composition for the treatment and, in

case of troubles, can get technical assistance

from the supplier. In contrast, Japanese

finishers often purchase necessary chemicals

separately and compose themselves their

electrolytic coloring solution, if not

pretreatment or sealing agent. Their staff

work out solutions to technically problems.

The major companies manage their R&D

centers for the materials and file several

patent applications in relation with surface

finishing each year.

Such different situations essentially affect

the process openness of the corresponding

surface finishing businesses in Japan and

American o r European countries, as

figuratively illustrated in Fig. 2. While

finishers abroad can be "liberal" to disclose

their processes, the Japanese take a "secretive" attitude because they consider

them as "highly confidential". That is, the

former use electrolytic coloring solutions on

the market, so they may not need to be

n

I

Fig.2 "OPEN" and "SECRET"

secretive (Fig. 2 (A); the Japanese, on the

other hand, prepare their solutions themselves

and hold the coloring a s "top secret" (Fig. 2

(W. AmericadEuropean chemical suppliers do

not disclose the composition of surface

finishing solutions. In this sense their finishing

processes a re not completely accessible. Yet

their show-if-you-want principle (Fig. 2 (A))

about the process may help to secure

customers in Asian countries outside Ji1p:ln.

3. Statistics for production of surface finished

aluminum in Japan

We are showing in this section some

statistic data for suggesting the trend in

demands and technical development relating

to surface finished aluminum building

237

materials. Fig. 3 shows the world

consumption of extruded aluminum profiles in

1990111. The production of aluminum

materials is not small in Japan where more

than 90% of the residential windows are made

of aluminum.

Fig.3 Consumption of extruded profiles of

aluminum in the eastern world in 1990 (in ton

x 1000)

Statistics about the volume of finished

aluminum building materials are compiled

and published by the Aluminum Products

Association of Japan (APAJ)[2]. Fig. 4 shows

the transition of their annual production (for

both residential and non-residential

combined)in Japan from 1955 to date. The

production of aluminum sashes became

regular late in 1950s, and soon increased a

substantially. It decreased by 20% in 1974 at

oil crisis, then turned upwards; it kept

increasing until 1977, when a plateau of about

600,000 tons was reached.

In Japan several coatings fire employed for

the surface finishing, as shown in Table 1131.

The annual production for different coatings

1985 1995 1955 1965 1975

Fig.4 Production amount of surface finished

aluminum for houses and buildings in Japan

Table 1 Surface finishing methods of

aluminum building materials

1. Anodizing, Sealing

2. Anodizing, Coloring, Sealing

3. Anodizing, ED coating

( Clear, Bright )

4. Anodizing, ED coating

( Clear, Matte )

5. Anodizing, ED coating

( Wight piggment )

6. Anodizing, Coloring, ED

( Clear, Bright )

7. Anodizing, Coloring, ED ( Clear, Matte )

18. Solvent-type painting

are shown in Fig.5. Anodized and

electrodeposition (ED) coated liyers a re

238

formed on the surface of 95% of the aluminunt

produced during this period.

Fig.5 Anodized-sealed alumimum, Anodized-

ED coated aluminum, and painted aluminum

Fig. 6 shows the production of iinodized

aluminum without (non-colored) and with

electrolytic coloring alone (colored), The rittio

non-colored remains iilmost constant iIt about

1 to 1 recently.

% l . O O O h

T-

1987 1988 1989 1990 1991 1 Fig.6 Anodized-sealed aluminum, and

anodized-colored-sealed aluminum

Fig. 7 shows the production statistics for the

double-layered coating by anodizing and ED, which is for the most part formed by

electrolytic coloring and clear ED.

I

7ig.7 Anodized-ED ( clear ) coated aluminum,

Anodized-colored-ED ( clear ) coated

aluminum and anodized-ED ( white piggment )

coated alumium

Fig. 8 shows the corresponding data for

other painting techniques than ED coating.

Although acrylic acid resin painting is

1) red o m in ;in t , poly mer s a re

increasingly employed recently 11s :I ting

miiterial.

flu 0 roc i t r bo n

7659 % I,OOOtbn

Fig.8 Solvent type painting on aluminum

Fig. 9 shows the market shares of residential

window frames and doors for 1993[4]. Almost

100% of the former were supplied by the five

major firms.

239

Fig.9 Market share of aluminum window

frames for houses

4.

racking system

Past and present of vertical suspension

In Japan a technical innovation was

realized in the aluminum surface finishing

industry and a substancial increase in the

production of aluminum window frames was

achieved, as shown in Fig. 4, by the

introduction of a novel work carrying system

whereby extruded aluminum profiles a re

anodized as carried on a rack in vertical posi-

tion, the technique apparently not employed

widely outside Japan.

In the early days of aluminum sash

production, short aluminum extruded bars

for window frames were anodized on a manually operated rack which carried the

work in horizontal position, until around 1965

when line automation started. Then around

1970 the vertical suspension racking system

was for the first time adopted and operated in

it finishing line[S]. This riicking however did

not attract much attention of researchers

or technicians, many of whom were rather

skeptical about the performance and

considered as "impractical", for the 6 meter-

long work would swing inevitably during the

transfer from one bath to another (Fig. lo),

and, if put in it cell while swinging, may

eventually come in contact with the electrode

to ci1uSe a disaster by short circuit.

EX JRU PED Pp o F I L E

- . . . . . .

.*

. . . . . : . I .. .. ..- _ . : .. ~ . .. . . . .

Fig.10 Swing of extruded profile in vertical

raching

Afterwitrds the system was accomplished with

both improvement in crane operation and

development of mounting jigs. Recent versions

permit less down time for the work transfer

and a substantial decrease in crane travel over

the finishing cells, which had a smaller width

than earlier models. Decrease in cell width is

useful for improving both surface layer

240

product quality a s well :is power efficiency.

Full or semi-automatic racking and unracking

(mounting t o and dismounting from the rack)

are now available. A n automatic racking

(mounting) system using laser welding is also

coming to commercial application.

Photo 1 shows ;i surface finishing line of

monthly output of 2,000 tons with a state of

art vertical suspension racking system. 300 to

360 extruded aluminum profiles are processed

a s hanging from three racldng frames in :i

single run , each frame with 100 to 120 pieces,

as illustrated in Fig. 11. I

I I Photo.1 Vertical racking(1)

Photo 2 shows a number of aluminum

profiles which a re in transition to the vertical

position after mounted automatically to the

rack in the horizontal. The surface finishing

plants with such vertical suspension racking

has a rather large monthly capacity of 1,000

to 3,000 tons, and their supplementary

equipments are accordingly large as shown

in Photos 3 to 6.

Fig.1 I Vertical racking by three carriage bars

in a single run

L

Photo.2 Vertical rucking(2)

Photo.3 Exhaust equipment on the clane

24 1

I I

1

Photo.4 Electrolyte liquid cooling equipment

There are four arrangemcnts of cells

currently used: straight line (type l ) , curved

lines with a single turn (type U and C) o r ;I

double turn (type A) in Fig.12. Racking and

unracking (Rack mounting and dismounting)

are done at the opposite ends of the line of type

I, while a full o r semi-automatic operation can

be done in type U and C plants hy less workers

as the both ends are located in a proximity. A

type U plant of 1,000 ton monthly output

me:isures 35 to 40 by 80 to 100 by 20 mctcrs.

k

L! V

__t

Photo5 D. I. Water supply equipment

Fig.12 Arrangements of electrolyzing tanks

Photo.6 Exhust equipment

Type A plants, the latest model of the four, are

ver- satile with the shorter and longer

stretches and can be i1ditI)ted to various

techniques of surface finishing. A large

storage house or room is often anncxctl to ;I

high capacity production line with the

vertical suspension racking system.

Five major Japanese "aluminum sash

to 45 vertical kaishas", in total, have 40

suspension racking lines, and 10 to 15

horizontal. It can be estimated that there are

10 to 15 vertical suspension racking lines

outside Japan.

These can be listed as merits to the above

described vertical suspension racking system:

(1) High area-efficient process which can be

effectively applied to a mass production

surface finishing plant (monthly output of tons),

as compared with the upper limit of 1,000 tons

for the horizontal conveying system;

(2) Full or semi-automated racking and

unracking (mounting and dis-mounting);

(3) Least loss by dragging of chemicals or

mediums from the finishing cell, and ready

removal of water after washing;

(4) Least labor and cost necessary for the maintenance o r repair of the racking

(mounting) jigs, as they do not pass in the

bath:

(5) High quality coating regularly produced in

a computer-controlled automated process.

The demerits include:

(1) Higher capital investment: the

construction cost is higher for this system

than for the horizontal system of

corresponding production capacity and as

much as 1.8 times for a monthly output of

1,000 tons, for example.

(2) Difficult adaptation to the processing of curved o r bent works:

(3) Film thickness varying lengthwise from the

top to lower end of the work.

(4) finishing cell which sometimes may have a

depth of 7 meters.

5. Past and present of electrolytic coloring

In the early days of commercial production

aluminum window frames, they were simply

anodized without coloring. Later coloring

started by processing with ferric oxalate

ammonium o r "Kalcolor bath for integral

coloring, and in 1960s, Dr. Tahei Asada's

patented coloring, AC electrolytic coloring in

a nickel sulfate solution bath, was applied to

the commercial production in Japan, for the

first time in the world. An 'electrolytic

coloring had been developed by Mr. Caboni of

Italy, but not applied on a commercial scale.

Asada coloring was licensed only to 12

Japanese aluminum sash enterprises; the

others thus had to use another coating such as

integrril coloring or DC electrolytic coloring

for the production of colored window frames.

In 1980s when the patent expired, almost all

the rest started the A C electrolysis on their

plants.

First nickel sulfate solution was the bath

used for the electrolytic coloring; the finished

products often suffered from spalling

troubles or inconsistency in color development,

and the solution was replaced by a tin

sulfatebased one which, after a short time of

use,got little employed as unpopular with the

greenish brown color the coating developed.

At present, nickel sulfate solutions are

predominant again, although some middle to

small finishers employ nickel/tin sulfate

243

solutions. Anyway the bath compositions are

held concealed as the top secret. Table 2

summarizes the advantages and disadvan-

tages of the both nickel and tin sulfate

solutions.

Table 2 Nickel bath and tin bath

Advantages

0 Easy coloring I Sn bath

color

oxide film

Disadvantages

0 Yellowish brown color Damage of oxide film Special chemicals to privent the reaction,Sn 2 G n 4

0 I f operations are not careful,

( 1 ) poor uniformity of color

(2) 'spalling' 0 longer coloring time

for black coloring

The sine AC wave was the pattern used first

for the electrolysis.Lnter various wave

patterns were developed and appeared in

Japanese patent bulletins. At present

combined AC/DC and pulse tensions are more

widely employed than simple AC.

For multicolor finishing, five or six

companies employ the interference coloring

coating on a small scale, with an intermediate

treatment in phosphate bath. This coating was

presented by a researcher from one of the

users of this technique at the May, 1994

conference of the Light Metals Association o f

Japan, 8s summarized in Fig. 13[6].

Anodized aluminum NiS0.4. 6H;P 50g/l 10Fm MgS0.i. 7 H 8 8Og/l + [ %Bo3 30gA

lOoL!/l H304+ Tartaric Acid 1 Og/l AC 1OV Pulse, 30°C

Fig.13 Interference coloring method

There are two problems to be solved before

t in sulfate-based multicoloring electrolytes

from American or European suppliers can be

widely adopted by Japanese industry: first

fresh blue or green has been traditionally not

very popular to many Japanese, and

second,most of the solutions used for

electrolytic coloring in Japan are nickel

sulfate-based, which makes switching to a tin

sulfate-based solution difficult.

6. Past and present of electrodeposition

coating

The electrodeposition coating (ED) was a

coating developed in America for finishing of

automobile bodies. Its application to the

anodized surface of aluminum was began in

Japan on a commercial basis in 1965. The

earliest version of the coating, called "rinsing-

type", needed rinsing to wash away excessive deposited pigment from the work surface. In

1974 the "non-rinsing type" was developed

and such rinsing was no more necessary.

Then a paint recycling by RO was developed

in 1975. Matt surface also became available in

244

1980, in addition to the earlier bright surfaces.

White ED coating became available in 1984, in

the place of conventional clear surfaces by

either bright or matte coating. This coating

may interest finishers from Europe where

white surface finishing is preferred.It is noted

that the bath has to be continuously circulated

in the cell, in order to prevent precipitation

of the white pigment.

A few years ago another ED coating

technique was developed for forming a more

corrosion-resistant surface layer of

fluorocarbon polymer, and confirmation

experiments are under way in some enter-

prises ;is ;I prep;ir:ition for practical

application. It is estimated that this coating

can exhibit a life of 30 years, now that acrylic

coatings have already performed a life of 10

years or more. Fig. 14 compares the coating

life for different ED processesj71.

Fig.14 UV light test against acrylic and

fluoroc;irbon ED film

The following has been reported as the

advantages of electrodeposition coatings[8]:

(1) Consistent coating thickness: A uniform

coating can be formed on a work of

complicated design with sharp edges, like

extruded aluminum profiles. On the other

hand any excessive coating is not necessary

which was deposited for securing the thickness.

(2) Ready control of coating thickness: The

thickness can be readily and precisely

controlled as it grows proportionally to the

current supplied:

(3) Excellent appearance and protection: The

coating is little susceptible to such defects

trouble as sags, craters, pinholes, lack of

hiding, and dewetting which a re common with

conventionul painting techniques, but whose

elimination is essential to practice of a single

pass finishing.

(4) Full automation feasible: With the coating

thickness being clectric;illy controllablc, tlic

sequence of pretreatment, anodizing,

electrodeposition coating (ED) and baking can

be stream-lined and automated a s ;I

continuous process. Quality control can be

thereby facilitated and at the same time

reduction in power consumption can be

achieved.

( 5 ) High productivity: 2 to 3 minutes of

power supply is sufficient for the finishing,

with no need of correction.

(6) Chemical saving achievable: Economic as

little chemical is dragged out from the bath,

due to the use of low content (8 to 10%) and

low viscosity.

(7) Fire-free from fire and explosion as using

245

aq uco us so I u t i o n.

(8) Environment-friendly: This coating

causes little working o r environmental

problem with an emission hazardous or

harmful to human health, as it uses aqueous

solution of paint which contains no highly

volatile organic solvent. Thinner or any other

organic medium is not necessary.

The probelm is that a very careful process

control is necessary.For example, works as

anodized have to be rinsed with both hot water

and deionized water before the electrophoresis.

Cases of defective finishing are compiled in a

book by the Light Metals products

Association[lO].It gives (1) photo image, (2)

definition, (3) phenomenon, (4) cause and ( 5 )

solution for each defect, just as Dr. Brace's

publication: "Anodic coating defects"[ 11 1. A

few examples are shown in Photos 7 to 12. It

appears to be the only reference book of

immedinte importance for engineers who

intend to practice the coating.

Another major problem is that this technic

~~~~ -

Photo.7 Defective finish

---Short circuit

cannot yield ;I uniform coating o n an

aluminum plate and thus is not suitable, to

curtainwalls.

Photo.8 Defective finish

--- Cratering

Photo.9 Defective finish

--- paint slobbery

Photo.10 Defective finish

--- Adhesion of gel paint

246

Photo.] 1 Defective finish

--- Dust stain

I I

L I

Photo.12 Defective finish

--- Water spot

7. Past and present of other coatings

Acrylic acid resins were commonly coated

by spraying or electrostatically until the

development of the electrodepositing (ED)

coating. The latter has been since the only

coating technique for aluminum extruded

profiles. However as it can yield only clear

and white coating, paint spraying and some

other coatings are back for color coating

n o n- res i den t i a I b u i Id i n g mat e r i 111s. 1 n Japan

the ED coating is commonly differentiated

from others which are often called as "color

coatings". The paints iivailiible include

thermosetting acrylic ;icitl resins,

polyureth:inc ilnd fluorocarbon polymers.

Anyway the total volume of color coated

aluminum works is not much, a s it accounts

for only irbout 10% of the total production of

aluminum building mittcri:lls ;IS shown i n Figs.

5 itnd 8.

I n Europe powder coating is widely

usedl 121 for aluminum building m;tterials,

while it r:trely is in Japiin beciiuse the

electrodeposition (ED) coating has been fully

employed, and the powder coating yields ;I

rough surf;ice which is not lovcd mucli in

Jail an. oc c u r rcn c c' o f ti I i fo rm

corrosion, whose mcchanism is illustri1tcd in

Fig. 16, ;tlso hinders the wide use(l21.

F r cquc n t

C H D N L G O B I E F i

counlrlea

Fig.15 Replacement of anodizing by powder

coating in 1991

Fig. 16 Di;igriim of lileform corrosion process

247

8. Institutions for the surface finishing o f

aluminum building materials

Academic societies include:

(1) Surface Finishing Society of japan

(members: 4,000 persons)

(2) Light Metals Association of Japan (2,000

persons)

Industrial societies include:

(1) Association for Light Metal Products (192

corporations)

(2) Jal);in Sash Association (138 corporations)

(3) Curtain Wall Industry of Japan (15

corporirtions)

Aluminum surfilce finishing is studied in 5

o r 6 universities, but most of the subjects are

anodized films (barrier films) for electrolytic

capacitors, and two universities alone are

studyiny! surface finishing of aluminum

building materials. This particular subject is

also investigated, idthough principally at basic

levels, in prefectural and municipal technical

research centers.

Of all, the efforts of the Association for

Light Metal Products are most useful for the

advancement of technology of the building

material surface finishing. Their technical

committee, which consists of surface finishing

engineers from more than 10 enterprises

works i n cooperation, issues publications like

the Handbook for Practical Surface Finishing

of Aluniinum Materials, ;IS well as various

reports. The case o f defective surface finishing

present above a r e from their publication.

They have been engaged with making drafts of

JIS stilnards reliltive to the surf;icc finishing of

aluminum. They dispiltch delegates to the

corresponding IS0 subcommittee. Enquiry in

English may be accepted by director Mr.

Kikuchi, who has studied in Germany for two

J'eiirS.

9. Remarks

Much has been studied by Japanese

researchers and engineers from literature

written in English rcgitrding the surface

finishing. A lot of Jap;inese works have been

also published or disclosed i n various forms

such iis patent bulletins, mi1giuines and

reports, although in Japanese, which most of

the readers outside Japan may not understand,

to the authors' regret. We hope that this

report can help you underst;ind the technical

situation of aluminum surfitce finishing in

J:ip:i n .

References

1) M. Conserva; Proceedings of "Aluminium

2000", vol.1, pS (1993).

2) Japan Aluminum Products Associiltion ed.;

"Statistics of Aluminum Products", (book), in

Jiil)ilnesc.

3) N. S;lto; Proceedings of the 40th Japan

Corrosion Confercncc, 1,633 (1993) in

Ji1l):tnesc.

1) NIKKEI INDUSTRY NEWS PAPER, July,

8th (19%).

5) K. Suzuki; "Handbook of Aluminum

Surface Finishing Technologies", (book)

240

Kallos Publishing Co., Tokyo, Japan, p1270

(1980) ill Japanese.

6) Japan Aluminum Products Association ed.;

"Theories and Practises of Aluminum Surface

Treatmcnts", (book), in Japanese.

7) A. Wakatsuki, M. Ohtsubo; Proceedings of

the 86th Japan Light Metals Conference, 11169

(1994) in Japanese.

8) S. Shirai; "Textbook of Seminar on

Aluminum Surface Finishing", (book),

Technicid Center of Tokyo Metropolitan

Goverment, 111 (1992) in Japanese.

9) S. Titkao; "Handook of Aluminum Surface

Finishing Technologies", p1302 (1980) in

Japanese.

10) Japan Aluminum Products Association

ed.; "ED Coating Defects on Anodized

Aluminum", (book) in Japanese.

11) A. W. Brace; "Anodic Coating Defects --- Their Causes and Cure", (book), Technicopy

Books, Stonehouse, Glas., UK (1992).

12) D. M. Heath; Proceedings of "Aluminum

2000", \fo1.3, p143 (1993).

13) I. D. Miguel, E. Gomez; Proceedings of "Aluminium 2000", vo1.3, p175 (1993).

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