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MNL17-EB/Jun
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Price 1

THE CONTAINERINDUSTRY IS A MAJOR USER of p a i n t s a n d coatings
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The m a j o r i t y of these are coated
individually, m o s t with different coatings on each side
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The processes r e q u i r e d for the efficient a n d e c o n o m i c a l l y
acceptable m a n u f a c t u r e of two- a n d three-piece cans a n d can
ends involve c o m p l e x engineering
...
A m a j o r i t y of the tests currently in use to ensure
t h a t all the r e q u i r e m e n t s are m e t are discussed
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D E S C R I P T I O N OF T H E CAN I N D U S T R Y

The Can Coating Industry
The v o l u m e of coatings c o n s u m e d by coating cans for food
a n d beverage in the United States places the c o n t a i n e r industry a m o n g the highest users of finishes for all industries
...
Over 40 million gallons of coating were used
with an e s t i m a t e d sales value of 350 million dollars
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Europe, w h i c h currently uses a b o u t 21 billion cans,
is expected to double its usage d u r i n g the 1990s as this f o r m
of p a c k a g i n g b e c o m e s m o r e acceptable as a r e p l a c e m e n t for
glass containers
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The type a n d quality of p r o d u c t s
identified with this i n d u s t r y are largely influenced by the
unique characteristics of the can m a n u f a c t u r i n g processes
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Coatings
b a s e d on epoxies are often chosen for p r i m e r s a n d for can
ends, poly(vinyl chloride) for can ends, oleoresinous a n d phenolics for can interiors, acrylic, polyester a n d alkyd resins for
~Consultant, Consolidated Research, Inc
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, 2205 Stannye Drive, Louisville, KY 40222
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Copyright9 1995 by ASTM International

TABLE l--United States production of beer and beverage cans
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08
0
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08

52 955
2 855
55 810

49 235
4 090
53 325

7
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2
4
...
9
27
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3

decorative exteriors
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W a t e r - b a s e d spray coatings (often epoxy-acrylic based) are c o m m o n l y u s e d as inter i o r coatings for two-piece can bodies
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A significant level of p r o d u c t d e v e l o p m e n t effort
continues in this field to define new a n d i m p r o v e d products
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A d e s c r i p t i o n of can p r o d u c t i o n processes for
these two m a j o r can types will be presented
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I)

About 70% of the total U
...
p r o d u c t i o n or 95 billion cans
u s e d in the b e e r a n d beverage p o r t i o n of the c a n n i n g i n d u s t r y
are c o n s t r u c t e d with a l u m i n u m a n d c o m p r i s e w h a t are comm o n l y called two-piece cans
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The cups are t h e n forced t h r o u g h a series of rings to
iron out a n d form a full-length can a n d to form the b o t t o m
dome
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The lid, secured a n d sealed after filling, is the second
piece
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astm
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1-Two-piece can production process
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I n c r e a s e d m a n u f a c t u r i n g
speed a n d s m o o t h m o v e m e n t on the p r o d u c t i o n lines requires the p r o p e r lubricity in the coating
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Cans r u b b i n g against each
o t h e r during m o v e m e n t in any of m a n y p r o d u c t i o n process
steps a n d shipping can cause scratches
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It is interesting to note
that cans are frequently so thin t h a t sealing after filling w i t h a
c a r b o n a t e d beverage is r e q u i r e d to give the c o n t a i n e r adequate rigidity
...

Coatings are usually a p p l i e d to the i n t e r i o r of these cans b y
spray techniques
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This procedure is used with m o s t food a n d d r i n k containers
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Thus a coating m u s t be
a p p l i e d w h i c h presents an a d e q u a t e b a r r i e r to this erosion
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W h e n a protective
coating is used, it c a n n o t alter the taste of the p a c k a g e d
product
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Coatings suitable for c o n t a i n e r use (a) m u s t b e FDA compliant, (b) m u s t pass subjective taste tests to ensure no contrib u t i o n to the flavor of the product, a n d (c) m u s t also m e e t
d e m a n d i n g flexibility requirements
...
F o r a m a j o r i t y of cases, after the
can is p a c k e d a n d sealed, it is subjected to a t h e r m a l treatm e n t to c o m p l e t e the processing of the contents
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5 ~ to 82
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Coatings on the
c r i m p e d edges of the can that m a y have survived the actual
c r i m p i n g p r o c e d u r e m u s t retain adhesion, clarity, color, a n d
a b r a s i o n resistance after these t h e r m a l treatments
...
2)
I n a typical m a n u f a c t u r i n g process for the three-piece can,
a large m e t a l coil is s h e a r e d into sheets
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2-Three-piece can production process
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When exterior coating is required, the
"exterior" of the can is coated with the decoration defined by
the customer
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On lowrust potential metal, when paper is the chosen labeling technique defined by the customer, or when ultraviolet-cured
coatings are employed, this second stoving operation may not
be required
...
) The coated sheets that are stacked and shipped to the
fabricating plant must easily slide over one another during
subsequent processing steps
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In the fabricating plant, the coated body sheets are slit into
individual body blanks; usually about 35 body blanks are
obtained from each sheet
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A coating is required to cover this seam since the initially applied coating is
usually destroyed or deformed during the seaming process
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This coating must have all the requirements

of the main coating, including FDA compliance, and cause no
detectable alteration to the taste of the contained product
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With
some metals the side destined to become the exterior will also
require the application of a coating to impart corrosion resistance
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As with the two-piece can, the
coating including the crimped sections must maintain integrity through the elevated temperature food processing steps
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This process has several distinct
advantages over more traditional oven-bake systems
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At this writing, industrial production using ultraviolet cure mainly involves
external clear coatings
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The
coating is hardened virtually instantaneously
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The
extremely fast cure permits the process to proceed rapidly to
the next stage in the can production process which may be
application of a water-dilutable or solvent-based interior
coating
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Only one oven pass
is required
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Sheets, often printed with an
ultraviolet-curable ink, are oven coated with an ultraviolet
light-curable overprint coating
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A coating which will eventually
be the "inside" coating of the can is then applied and the
entire sheet is cured by a standard oven process
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Again the economic advantage of
only one oven pass is realized
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Ultraviolet coatings have been developed which meet the
requirements of adhesion, flexibility, slip, gloss, abrasion resistance, and food process stability for exterior use
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Testing of Can Coatings
Tests Conducted on Liquid Paint
Viscosity--As discussed in the previous section, speed of
production is a critical aspect of an economically successful
can production plant
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To ensure complete coverage with the standard thin layer of paint, outstanding flow
must be assured
...

Alternate means of determining viscosity include the use of
the Ford Cup or the Zahn Cup, ASTM Test Method for Viscosity of Paints, Varnishes, and Lacquers by Ford Viscosity Cup
(D 1200) and ASTM Test Methods for Measurement of Wet
Film Thickness of Organic Coatings (D 212), respectively
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The Ford technique is generally
considered more accurate, though less convenient than the
Zahn
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8~
for an extended time period
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The change in viscosity can be evaluated every seven
days using the technique employed to rate initial viscosity
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Density--Density can be measured by using a Gardner
"Weight per Gallon" cup [ASTM Test Methods for Indentation Hardness of Organic Coatings (D 1474)]
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The cap is pressed onto the cup and the overflow
carefully wiped from the outside of the cup
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1
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The specimen is
placed in an aluminum dish and after dilution with solvent is
baked for 60 min and the percent weight loss of the sample
determined
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The volatile organic compound content (VOC) is determined according to Federal Reference Method 24, using the
weight % volatile content, the density of the liquid coating,
and the weight percent water content, using the equations
shown in ASTM Practice for Volatile Organic Compound
(VOC) Content of Paints and Related Coatings (D 3960)
...
A Hegman Grind Gauge with a double-wedge steel
scraper placed on a flat, nonskid surface is used (ASTM
D 1260)
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The scraper is then drawn down over the entire length
of the gauge with sufficient pressure to clean the sides of the
gauge
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The reading consists of a visual observation made by viewing
the side of the gauge perpendicularly to the drawn coating:
the point where the sample shows a definite speckled pattern
is read from the numbers on the side of the gauge
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Flash Point--The flash point of a coating is the minimum
temperature at which vapor given off by the coating will
ignite when exposed to a spark or flame
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A method to determine what is referred to as a closed-cup rating flash point
uses a Seta Flash apparatus [ASTM Test Methods for Flash
Point of Liquids by Setaflash-Closed-Cup Apparatus
(D 3278)]
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In both methods the substance under test is
heated at a controlled rate (for example, 2~
and a flame
is passed over the surface
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Cure Speed--A variety of methods have been devised for the
determination of this difficult to determine and even difficult
TM

CHAPTER 62--CAN COATINGS
to define characteristic of a thermoset coating
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The customer and the coating supplier frequently
agree on an empirical test to satisfy cure speed requirements
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Nonadherence of fine fiber wads to a surface is often rated as
adequate cure because it relates to the ability to permit the
continuation of production
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Rubbing a cured surface with a cloth moistened with a strong solvent is a method frequently employed
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Tests Conducted on Cured Surfaces
Hardness--The hardness of a coated panel can be determined with the use of a series of pencils that have lead of
various, known hardness, that is, lead with the following
increasing hardness: 5B, 4B, 3B, 2B, B, HB, 2H, 3H, 4H, and
5H
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01
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The device is calibrated with standard sheets of known film
thickness placed on an uncoated surface of a similar substrate test section
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The film surface is often measured at

721

several locations on the surface of the specimen
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A StrandGauge TM is often employed in the metal decorator
industry because of the ease of determining the thickness of
very thin coatings characteristic of this industry
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, Castro
Valley, California
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Can corrosion and contamination of the can contents at these voids could cause taste or
color degradation
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3)
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Electrical contact is made
on a cleaned area of the can exterior
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The current flow will
be impeded by the protective coating on the can interior
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The customers and suppliers usually agree on a
maximum acceptable value
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In this test a sheet
of coated metal is immersed in a solution of acidified copper
sulfate for 2 to 4 min
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The
presence of flaws in the coating is an unacceptable condition
for most commercial products
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3 - W A C O TM Enamel Rater test device for film voids
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4)
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The coefficient of friction is d e t e r m i n e d a n d is indicated directly on an electronic analog meter
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Cans are sealed a n d the entire can is processed at an elevated t e m p e r a t u r e for the p e r i o d r e q u i r e d to
c o m p l e t e the food processing
...
D e t e r m i n a t i o n of the
ability of a coating to w i t h s t a n d this t r e a t m e n t is often m a d e
by careful e x a m i n a t i o n of a section of coated substrate w h i c h
has been m a n d r e l b e n t (ASTM D'1737)
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7~
for 16 to 24 h
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A less severe test is available for the p a s t e u r i z a t i o n process
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The t e m p e r a t u r e for this process is 150 to 180~ (65
...
2~ for 3 h, S i m i l a r visual e x a m i n a t i o n of the surface of
the coated steel o r a l u m i n u m s u b s t r a t e is c o n d u c t e d for disc o l o r a t i o n o r blushing, a d h e s i o n loss, or film failure
...
As m e n t i o n e d
earlier in the Can P r o d u c t i o n p o r t i o n of this discussion, occasionally a b r a s i o n resulting from cans r u b b i n g against each
o t h e r especially d u r i n g s h i p m e n t can be severe e n o u g h to
actually cause r u p t u r e of the metal
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A simple technique involves r u b b i n g the
coated surface with a s t a n d a r d pencil eraser, counting the
n u m b e r of rubs or d o u b l e r u b s r e q u i r e d to r e m o v e the coating a n d reveal the u n c o a t e d surface
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4-Altek TM Mobility/Lubricity Tester,

resistance
...
The value is often r e p o r t e d
as weight loss in milligrams/cycle x 1000
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5)
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The device vibrates the cans or coated strips at a rate
a n d d u r a t i o n w h i c h can be controlled, e m u l a t i n g the a b r a sion received d u r i n g t r a n s p o r t a t i o n
...

Pack Testing--A r e q u i r e m e n t for p a c k a g i n g of m a n y food
p r o d u c t s is that no u n d e s i r a b l e effects on the a p p e a r a n c e of
the c o n t a i n e r or to the taste or color of the contents occur
w h e n the p r o d u c t is stored on a shelf for three years or more
...

The can is sealed a n d exposed to the food processing conditions previously described, after w h i c h the p r o d u c t is aged at
an elevated t e m p e r a t u r e for an extended p e r i o d of time
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8~ with a generally a c c e p t e d
estimate that one m o n t h exposure at this t e m p e r a t u r e relates
to one y e a r of r o o m t e m p e r a t u r e exposure
...
This test is useful for new p r o d u c t evaluation
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At the
end of the test period, evaluations include can a p p e a r a n c e ,
food taste, a n d v a c u u m testing
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This gauge d e t e r m i n e s the p r e s s u r e before c a n
opening
...

Adhesion Test--This test is similar to one used t h r o u g h o u t
the coatings industry
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The surface of the
coated substrate is often scored with a r a z o r in an X p a t t e r n
o r a cross h a t c h p a t t e r n before the tape is a p p l i e d [ASTM Test
Methods for Measuring Adhesion by Tape Test (D 3359-83)]
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The test
evaluates the flexibility characteristics of a p a i n t on a substrate by d e f o r m a t i o n of the substrate a n d s u b s e q u e n t evaluation of the a d h e r e d coating
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The b e n d
e x a m i n a t i o n can be visual, microscopic, or it can use Scotch
B r a n d TM t a p e o r copper-sulfate exposure
...

A second 180 ~ b e n d a r o u n d the b e n d a l r e a d y m a d e represents a lesser level of flexure
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A third b e n d represents 2-T, etc
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5-Gavarti TM abrasion test unit
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In this test flexibility
is evaluated by dropping a large bullet-shaped weight from a
measured height down a cylindrical guide tube onto the
uncoated surface of a test sheet
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Microscopic examination of the impacted area is employed for evidence of cracking in the coating
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A test more specific to the can industry involves use of the
Erichsen Lacquer Testing Instrument
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J
...
, 1340 Home Ave, Akron, Ohio
or A
...
Erichsen, GMBH 587 Hemer, Sundwig, Germany)
...
The Food and Drug Administration has established a series of limits and has defined
certain liquids to be used for testing based on the planned
contents of the container
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21, Section 175
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An
extraction technique is also described in detail in this government publication
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The meter should be equilibrated
and calibrated against standard panels
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Care must be taken to control film thickness as

deviations in gloss level will be observed at varying thicknesses
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Spectrophotometric analyses using L A B ranges are reported [ASTM Test Method for
Calculation of Color Differences from Instrumentally Measured Color Coordinates (D 2244)1
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Such storage can often occur after an oven
operation, which means that the sheets are stacked at an
elevated temperature
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Efficient and rapid movement of these sheets individually for
subsequent processing is essential to achieve an economical
container production rate
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In one such test a series of coated sheets or panels are
stacked face to back
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The stack which can be stored at
controlled temperature for defined periods of time is examined after cooling for ease of separation
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724

PAINT AND COATING TESTING MANUAL

REFERENCES
[1] Lamboune, R
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523
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5, March 1992, p
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[3] Chemical Week, 5 Aug
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22-26
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, "Cans Try New Coats," Industrial Finishing, November
1982
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21, Section 175
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S
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[6] The Canmaker, Vol
...
28
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5, December 1991, p
...

[8] "Guide to Tinplate," International Tin Research Institute Publication 622, Lamport Gilbert Printers, Reading, England, 1981

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