NBSIR 85-3180

Relationships Between Mechanical

Properties and Performance of

Inks As the Basis for Quality

Control Techniques: Part III

Donald L. Hunston and George W. Bullman

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Polymers Division

Gaithersburg, MD 20899

January 1985

©c

IP 0

Prepared for U.S. Department of Treasury

Bureau of Engraving and Printing

partment of Research and Technical Services

•shington, DC 20226

NBSIR 85-3180

RELATIONSHIPS BETWEEN MECHANICAL

PROPERTIES AND PERFORMANCE OF

INKS AS THE BASIS FOR QUALITY

CONTROL TECHNIQUES: PART III

Donald L Hunston and George W. Bullman

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Polymers Division

Gaithersburg, MD 20899

January 1985

Prepared for U.S. Department of Treasury

Bureau of Engraving and Printing

Department of Research and Technical Services

Washington, DC 20226

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director
,
SU MM AR Y

This report summarizes the results obtained during 1994 in

the joint program between the National Bureau of Standards (NES

)

and the Bureau of Engraving and Printing (BEP) to study the

mechanical properties of printing inks as the basis for

developing quality control tests and procedures. Eight specific

research topics will be covered: rubber mill cure experiments,

ultrasonic tests, poker-chip experiments, squeeze flow tests, a review of black ink test results, recent data obtained for green

inks, ink uniformity tests, and results of laboratory ink

e x p e r i men t s

.

The results from experiments using the rubber mill to study

cure suggest that it is the early phases of cure that are most

important in performance of the ink on the press. In addition,

although the amount of data is very limited, the cure kinetics

measured in the rubber mill experiments appear to be the same

over the range of film thicknesses and temperatures that were

examined. These test conditions include both these where the

cure rates are relatively slow and those designed to more nearly

simulate the conditions actually present on the press. This is

useful because in the latter case the cure rates are too rapid to

permit convenient study.

Construction of the BEP ultrasonic cure monitoring apparatus

is complete by the addition of the items needed to make the

system self sufficient. Experiments show that this test is

sensitive to the effects of temperature and film thickness in

cure rate and, to at least some degree, can follow surface and

subsurface drying. Both cure rates and induction times were

found to change with curing parameters, and since no simple

relationship between these two properties was found, it was

concluded that both must be measured to characterize cure

Without agitation, subsurface drying was found to proceed for

days even in thin films.

The poker-chip test results show that the film splitting

behavior of the inks is highly rate dependent. Like viscosity

measurements, however, when the film splitting test is used for

cure monitoring, similar results are obtained over a wide range

of low and intermediate rates. A comparison of the poker-chip

test and viscosity measurements as cure monitoring me'thods

reveals that although the former may be more sensitive to

initiation, in general, the latter is the preferred method and by

itself provides a reasonable characterization of relative cure

rata.

Results for the squeeze flow test suggest that as a cure

monitoring method, it gives data similar to the viscosity tests
Consequently, the squeeze flow experiment provides a simple

alternative to viscosity measurements for characterizing cure.

The report reviews the data obtained previously for 8 black

ink samples with known performance on the press. These results

indicated that inks with short cure times generally gave poor

performances while inks with long cure times usually performed

well Inks with intermediate cure times gave a wide variety of

performances, and it was concluded that in these cases ether

factors, such as the set-up of the press, influenced performance

The inks tested also exhibited a wide variation in cure times.

This variation was not anticipated and is suspected to be a major

contributing factor to the spoilage obtained for these inks.

Spoilage is defined as the percentage of printed sheets that are

unacceptable due to ink related problems.

To examine this hypothesis, 17 batches of green ink were

obtained. These inks were examined for cure behavior and the

results showed that there were large batch-to-batch variations

even when consecutive batches were compared. In general, the

cure times were found to be somewhat slower than those typical of

the black inks, and since longer cure times generally mean a better chance for good press performance, this result may explain

wh y spoilage has been less of a problem with the green inks.

Nevertheless, the batch-to-batch variations are very large and

must therefore be viewed as a problem and probably a major

contributing factor to spoilage. As a result, it was concluded

that the need to identify and control the sources of this

variation is crucial to reducing ink spoilage levels for both the

green and black inks.

To further study these variations, three production inks

were examined by taking samples from the top and bottom of each

batch and measuring the drying behavior. The results show that

variations within a batch contribute significantly to those

differences found between batches. For the three inks examined

no consistent trend was found for the variation in drying

properties with position in the batch. Although still

preliminary, these data suggest that the differences result from

a random variable such as poor mixing rather than a factor such

as a systematic segregation of ingredients induced by processing.

Variables of this second type might be expected to introduce

position dependent variations in properties within a batch.

To determine if controlled and reproducible inks could be

fabricated, three ink samples were carefully prepared in the

laboratory at BEP. When tested at NBS, these three inks showed

very little difference in behavior relative to the variations

observed in production batches. Th is result is encouraging since

it suggests that systematic studies can be performed with

laboratory inks to analyze the effects of variations in

formulation and processing on the drying properties. This offers

the best hope for identifying the sources of the variations in

ink properties and from this identification developing methods

and procedures to minimize this unwanted variability.

3
RE LATI 04 SH IP S 3 ETVE EN ME CH AN IC AL PR QP ER TI E3 AND P ER FO RM AN C E OF INKS AS THE BASIS FOR QUALITY CO NT RO L TECHNIQUES

In cooperation with the Bureau of Engraving and Printing

(3EP), NBS is studying the rheological properties of printing

inks, particularly properties associated with drying behavior, in

an effort to develop a better basic understanding of the factors

that control ink performance. The goals in this work are to use

the information developed to generate - test methods and guidelines

for improved ink quality control. In addition the results will

be valuable in formulating improved inks. This report describes

the work performed during 1984. It covers progress in eight

research areas: (1) the use of a rubber mill as an ink cure

device, (2) the further development of the ultrasonics test

device, (3) the evaluation of the poker-chip test as a method to

monitor ink curing, (4) the continued development of the squeeze

flow experiments as a method to study ink curing, (5) a rav.ew

and evaluation of results previously obtained for black inks with

known performance, (6) an analysis of results obtained for 17 new

samples of green ink, (7) an examination of ink batch uniformity

with production lots, and (8) an evaluation of reproducibility

for ink samples prepared in the laboratory. Each of these topics

will be discussed in detail below.

RU BB ER -M ILL E XP ER IN EN T5 As discussed in the previous

Annual Report (1), the rubber mill provides an excellent and

4
versatile device for curing inks under circumstances that

simulate some of the conditions present on the printing press.

The advantages of the rubber mili as compared to other roller

devices are that both rolls are heated for more uniform

temperature control and the film thickness can be varied in a controlled manner.

By using the rubber mill, there are two important questions

related to the study of ink curing behavior that can be

addressed: (1) what part of the cure is most important in ink

performance on the press, and (2) are the kinetics measured in

the mili studies the same as those operating on the press?

Although complete and definitive answers to these questions would

require a long and detailed study of kinetics, the tests

performed here provide some valuable insight into these

quest ions

.

A series of experiments was conducted on a sample of black

ink using different cure temperatures and film thicknesses. The

times required for solidification were measured and the results

are listed in Table I. Solidification was defined as the point

where the ink was completely dry and no flow could be obtained.

Tin i s point could easily be estimated by noting that all of the

ink transferred to the back roll on the mill when dry Eased on

the data from these tests, an estimate could be made for the

corresponding time to solidification under press conditions,

i e., preheated ink, < 100 pm thickness, and 80 C. Such an

estimate indicates the ink-would completely harden in

significantly less than 1 minute. The actual residence time of

the ink on the press rollers is much less that 1 minute. This

5
suggests that it is the early stages of the drying that are most

important for proper press performance. Of course, the later

phases of cure may be of concern for other aspects of spoilage,

such as the smearing and sticking together of printed sheets.

Nevertheless, in light of the apparent importance of the early

phases of cure on press performance, future work will focus cn

this aspect.

A second interesting and important result was also obtained

from these cure data. When the logarithm of the time to

solidification was plotted agai.nst reciprocal temperature, the

points were found to fall roughly along parallel straight lines

for each thickness (Figure 1). Obviously, the data are limited

and the uncertainties in the time to solidification measurement

are significant so only a first impressions can be obtained.

Nevertheless, within these limits, there is no indication of a major change in kinetics over the range of conditions studied

More experiments are planned but, for the moment at least, it

appears that the standard test conditions used in this work ( o 0 and 0.3 mm film thickness) should provide a good indication of

the relative reaction rates on the press

UL TR AS CN I C E X PE RI ME NT S : Th e details of the ultrasonic tes

apparatus being developed for BEP (see Fi

described previously (1,2). Since last y several additional components have been a apparatus a stand-alone system: an oscill

an attenuator. A prototype temperature control chamber has been

see Figure 2

)

have been

last year's Annual Report

been added to make the

o s c i lloscope, a r e c order

6
completed and tests to evaluate this preliminary design are now

underway. The results of the first experiments, which evaluated

temperature and film thickness effects, will be reported here.

Figure 3 shows the drying curves obtained by measuring the

increase in attenuation as a function of time in the ultrasonic

apparatus as different film thickness samples of the same ink

cure at 60 C. These curves indicate that both the cure rate and

the induction time changed as the film thickness was decreased

although the major change was in the cure rate. A five fold

reduction in the thickness in creased the drying rate by roughly

25 fold while decreasing the induction time by only about 20%.

The effects of increasing temperature at a fixed film

thickness (0.007 cm) showed similar trends, Figure 4. The

differences in rates observed here, however, were less than those

seen in Figure 3. Nevertheless, an increase in cure temperature

of 20 C still produced roughly a 3 fold increase in rate The

induction period also seemed to decrease as the temperature was

increased although the particular curve shown here for 40.7 C

dees net show this trend.

Many of the curves obtained in these experiments exhibited a distinct h ump (see Figure 4). Th is h ump is believed to be an

indication that there were two drying processes: surface drying

and subsurface drying. The general observation was that when the

hump was reached, the surface was dry but the ink below the

surface was not (even in thin films). Thus, the ultrasonic

technique shows promise as a measurement tool for both surface

and subsurface drying, and the - latter is difficult to monitor by

other techniques. The measurements indicated that the subsurface

7
drying is very slow and continued for days. This could be an

important problem if the ink thickness in printing w,p re ;o be too

large.

The results shown in Figures 3 and 4 also clearly

demonstrate that both the induction times and cure rates changed

significantly as a function of temperature and film thickness

No simple correlation between the two properties was observed in

these tests, however, and thus a major result of this study is

that both must be measured to characterize the ink curing. If

only one is measured, the reliability of the test as a quality

control tool will be severely limited. The Figures also suggest

that without agitation the drying rates are very low. Conditions

which produced complete drying on the rubber mill in 40 min. gave

measurable changes associated with drying in the ultrasonic

apparatus for days. Additional experiments to investigate this

difference are planned.

PQ KE R- CH I P TE ST : Th e poker-chip test (Figure 5) has also

been described in the previous Annua I Reports (1,2). With the

completion of the computerization of the MBS tensile test

ma chi ne , i t wa s possible to examine the poker-chip test over a very wi de range of film splitting rates ( c ross-head s p e e d s ) as shown in Figure 6 As pointed out in the previously (1,2), the

results show that , like viscosi ty, the f a i lure loads for film

splitting are a 5 trong function of rate Th is is an important

result and raises quest ions with regard t c wh at rate should be

used in cure monitoring tests. To study this question, a

3
particular ink sample (batch 9 prepared on 1/16/82 in the BEP

quality control program) was cured on the rubber mill, and

\ periodically during the cure, samples were removed and

characterized with the poker-chip test. Th e MB 5 test device made

it possible to examine the partially cured inks over a wide range

of rates. The results, which were first presented in last years

Annual Report (1), are shown in Figure 6. When these results are

compared to cure data curves obtained previously (1,2) for other

inks using viscosity experiments (Figure 7), two important

similarities (in addition to the high rate dependence) are

observed. First, over most of the range of rates examined,

curing produces a roughly vertical shift in the curves ootained

with both techniques. Second in both measurements there is a

tendency- for the curves to come together at high rates This

means that in using either test to monitor cure, there are a variety of intermediate or low rates where the choice of a testing rate will have little effect on the results.

Since both the poker-chip and viscosity tests have new been

developed into potential cure monitoring tools, it is of interest

to compare them. The first such comparison was presented -in last

year's report (1). Since then a number of additional experiments

of this type have been conducted. In these experiments samples

of various inks were cured to various degrees on the rubber mill

and characterized with the two tests. The viscosities were

- l measured at a shear rate of 5 sec , and the poker-chip tests

were conducted at a cross-head speed of 0.0008 cm/sec. The

resulting data were then compared, and a typical plot is shown in

Figure 8. The vertical scale in this Figure represents the

9
viscosity in mPa sec divided by 10 or the shear flew tests and

the failure load in kg for film splitting tests. .Such plots

reveal a clear similarity between the two experiments. The

poker-chip results are perhaps more sensitive to the onset of

cure Once cure is we 11 underway, however, the poker-chip test

loses accuracy in that it shows a good deal of scatter and, on

average , little change with curing In this range the fi 1 m tends

to split rather cleanly and exhibi ts a grainy structure. The

viscosi ty test on t he other hand gives a clear indication o f

curing over most of the drying range. This indicates that the

viscosity test is a more complete, overall cure measuring

procedure

.

Data such as that shown in Figure 8 are now available for a number of different ink samples and the trends are quite

consistent. Based on this data base, it is now felt that

although the poker-chip test provides some additional insight

into curing, this information is not sufficiently valuable from a quality control point of v i ew to make it wo r t hwh ile to utilise

both a viscosity type test and the poker- chip test when

characterizing the curing of an ink. To state this another way,

the results show that for the ink formulations tested here a viscosity test wiil probably detect any ink cure problems that

show up in the poker-chip test. Consequently, future experiments

will focus on the viscosity test or a suitable substitute

evaluation procedure.

SQ UE EZ E F LQ V T ZS T : As mentioned previously Cl.', the squeeze

1 0
flow test is being considered as a quick and easy experiment that

can be used in place of the more complex and time consuming

viscosity measurement method to follow cure This test is

conducted by placing an ink sample between two places and

applying a c omp ressive load to the top plate (Figure 9). Th e

plate separation then decreases as a func-tion of time with the

major change occurring in less than 30 seconds. As a result a relatively reproducible measurement can be obtained after 60

seconds. Although this experiment is much simpler to perform

than a careful shear viscosity test, the flow involved is more

complex. On the other hand, shear viscosity plays an important

role in the squeeze flow test, and the technique has the

advantage that it can be performed quickly and easily with

inexpensive, off-the-shelf equipment. For the experiments

performed here, a simple hardness tester was used, and thus the

results are expressed in terms of hardness numbers; higher

hardness numbers mean a larger plate separation at 60 seconds or

a higher viscosity.

Since the flew pattern in the squeeze flow test is not well

defined for a complex, nonlinear viscoelastic fluid such as the

inks, it is useful to conduct a detailed comparison between the

results of this test and those for a well defined shear flow

viscosity test. This will help determine if the results for the

squeeze flow tests can be interpreted in a manner equivalent to

the results of the viscosity tests. 3uch experiments are now

underway. Meanwhile, a series of tests was performed using the

squeeze flow experiments to follow the cure behavior of a wide

range of black and green inks. The results of these tests will
be reported in detail below, but it is worth noting here that the

data from these experiments clearly demonstrate the ability of

this test to easily monitor cure behavior in inks. Moreover, the

general shape of the cure curves obtained by squeeze flow

measurements is remarkably similar to that for the curves

obtained by viscosity tests. Consequently, the results are very

encouraging with regard to the possibility of substituting

squeeze flow measurements for viscosity tests.

RE VI EU _0F_ RE SU LT 3 FOR. JE_PU Q_Q I NK S : Before discussing the

new results for tests conducted with the 17 batches of green

inks, it is useful to review one set of experiments presented and

discussed in last year's Annual Report (1). These experiments

involved the evaluation of a specially selected set of black

inks. During a period of 4 weeks in early 1982, samples were

taken from every batch of black ink formulated at BEF and these

samples were stored in freezers. For all of these inks detailed

spoilage figures were obtained at BEP by tracking the printing

performance of each batch. Based on these figures, eight inks

we re selected for further study: four with very low spoilage

(less than 1.7%) and four with very high spoilage (greater than

9.3%) The stored samples of these selected inks were then

retrieved and subjected to detailed characterization experiments

Although variations in a number of properties were found, the

only parameter that correlated with spoilage was the cure

behavior. The drying curves for the eight inks were measured by

curing on the rubber mill and monitoring changes in properties
with the squeeze flow test. The results are shown in Figure 10.

Solid curves are drawn through the points for the low spoilage

inks while dashed lines are used for the high spoilage inks.

Each ink curve is designated by a letter, and Table II lists the

batch numbers and fabrication dates (in 1982) for these inks

Table II also lists the spoilage figures and the cure rates

determination (Fast or Slow) made in tests at BE? using IR

e s p e r i men t s

.

Based on an examination of these results, last years Annual

Report (1) concluded that the cure rates could be divided into

three regions: fast, intermediate, and slow. The inks vith fast

cure rates inevitably gave poor performance, those with slow cure

rates almost always gave good performance, and those with

i n t e rmed iate cure rates could have a wide range of performance

levels. The evidence suggests that in this third case, the

performance depended on other factors in addition to the ink

quality, for example, the set-up of the press. One simple way to

compare cure rates is to determine the time required for the

squeeze flow test results -to reach a hardness number of 30.

Unlike the previously used t i me - t o - s o 1 i d i f i c a t i on measurement,

this procedure has the advantage that the time can be determined

quite accurately since both the times to lower hardness and the

times to higher hardness can be used for interpolation.

Moreover, like the previous method, this technique includes the

influence of both the induction time and the cure rate. For

these reasons, it was concluded in the previous Annual Report (1)

that this evaluation method represents a good choice for

characterizing the inks when only a single parameter is to be
used.

Table II lists the values of this parameter for the eight

inks tested. By using these results, the previous work (1)

suggested that inks with time to 30 hardness values less than 32

min. had a cure rate that was too fast and hence these inks gave

poor press performances; inks with values greater than 33 had

sufficiently slow cure rates to give good performances; and inks

which had intermediate values of this parameter involved the risk

of unsatisfactory performance. Although these conditions

included all of the test results obtained, it is reasonable to

assume that there must also be a lower limit to the acceptable

range of cure rates, i.e., cure ti me s that are beyond some

limiting value will indicate cure rates too slow to give adequate

performance on the press. The results to date in this program,

however, suggest that this end of the scale is generally not the

ma j or probl em

.

Since these results were reported in last year's Annual

Report (1), one new observation has been made; i.e., the degree

of batch-to-batch variation that was found in these tests was

surprisingly large. The cure times (time to 30 hardness) var; ;d

by almost a factor of 2. This seems disturbingly high and is

clearly undesirable although it must be admitted that these inks

represent extremes over a 4 week period. Th e inks undoubtedly

involve different lots of starting materials, different people

performing the formulation, and possibly variations in storage

times and histo-ries. As a result, it is difficult to determine

how typical these variations are. In the new experiments

1 4
conducted recently with the green inks, these potential

complications were considered in designing the test plan.

R ES UL T5 FQ R N EW IN K S AM PL ES : The recent studies employed a

series of 17 batches of green ink. All of the samples were taken

in a 4 day period artd in many cases involved samples from

consecutive batches made by the same people with the same

starting materials. The samples were stored in a freezer for

only a minimal time period before testing. The tests involved

characterizing the cure rate using the rubber mill-squeeze flow

procedure. The results are shown in Figures 11 to 14 where each

Figure contains data for batches formulated on a given day.

Table III lists the formulation date ( in 1983), batch number, and

corresponding symbol used to represent the results in the

Figures

.

Despite the fact that most of the uncertainties involved in

the tests on the black inks were controlled in these recent

experiments, the b a t ch - t o - b a t ch variations in the green inks

continued to be very large. Here again, the cure times differed

by a 1 mo s t a factor of 2 , and in some cases , these large

di f ferences we re seen i n consecutive batches ma d e o f the same

day. Moreover, these v a r i a t ions we r e not isolated t o a single

day but were typical of the results obtained ail 4 days. This

same trend can be seen in Table III which lists the time to 30

hardness values for the 17 batches of green ink.

Although the spoilage figure for these inks were not

available, it is instructive to compare their characteristic

times to cure with those obtained previously for the black inks.
This is done in Figure 15 with dashed lines separating the fast,

intermediate, and slow cure regimes. Interestingly enough, all

but one of the green inks fell into the slow cure region where

good press performance was normally obtained for the black inks

The single green ink batch falling outside this' range had an

intermediate cure rate which could well give good performance if

other factors are properly controlled. The data here is

obviously limited but they do suggest that the green ink

formulation shows large batch-to-batch variations just as was

found for the black inks. For the green inks, however, the cure

rates were, on average, significantly slower that those for the

black inks and this may explain why the spoilage figure for the

green inks have generally been lower than those for the black

inks.

The final and most important conclusion from the test

conducted here concerns the possible consequences of the batchto-batch variations. Previous work has concluded that the press

and other factors can -be adjusted to compensate for a wide range

of ink parameters so long as the variations in these parameters

occur slowly over a time period of months or years. Rapid and

unpredictable variations such as those seen in Figures 10-14,

however, represent a serious problem that can clearly lead to

spoilage if not properly controlled. At the present time, there

is no explanation for these variations, nor any reason to suspe:

that they must be present. As a result, there is a need to

develop an understanding of the factors that are responsible for

these batch-to-batch differences.
UN IF OR MITT OF PRODUCTION INKS: In view of the above

results, there are two important questions that must be

addressed. First, to what extent are the apparent b a t c h - t oh a t c

h

variations really reflections of non-uni f ormi ty within each

batch. The degree to which this is true will have a great

influence on what must be done to minimize such variations. The

second question concerns the ability to prepare laboratory ink

batches with minimal variations both within and between batches.

Only if we I I - c o n t r o I I e d , reproducible laboratory samples can be

fabricated will it be possible to study the origins of the

variations in properties for production ink batches in a simple

and systematic way. In an effort to address both of these

questions, ink samples were obtained from SEP and tested at NBS

.

To judge the homogeneity of ink batches, tests were

conducted with samples from three different production batches.

In each case two samples were obtained: one from the top of the

batch and the other from the bottom. The drying behavior of each

sample was then measured using the rubber mill-squeeze flow test.

The results are shown in Figure 16. A different symbol is used

to designate each batch with the open symbols indicating the

samples from the top of each batch and the filled symbols for the

samples from the bottom.

The results in this Figure represent only three batches and

thus the conclusions must be taken as tentative; nevertheless,

three important observations can be made. First, very

significant variations in cure behavior were found to occur

within two of the three batches. To compare these within batch
differences with the variations measured previously between

batches, the curing behavior of these samples was characterized

by determining the time to 30 hardness values. These results

were then plotted in Figure 17 together with the results from

Figure 15. Clearly the within-batch heterogeneity represents a significant factor contributing to the b a t c h - t o - b a t c h variations

Consequently, correlations between the spoilage figures for

various batches of ink and their performances can only be

established when the differences are large enough to overcome the

influence of the within-batch variations.

The second observation that can be made from the data in

Figure 16 concerns the shape of the drying curves. Here again

the limited number of results must be noted but for these cases

at least it appears that samples from the same ink batch give

drying curves with similar shapes but different induction times.

This is in contrast to curves for samples from different batches

where both the shape and induction times can be different. This

would suggest that the b a t c h - t o - b a t ch variations -may in some

cases be qualitatively different than the within batch

he ter ogene i t y .

A third important observation can also be made from the

drying curves. It is of interest to see if the inhomogeneity

within a batch exhibits any systematic trends. The existence or absence of such trends provides an important clue as to the

source of the variations An examination of the results in

Figure 16 clearly shows that, for these samples at least, no consistent trends are present; i.e., in one case the sample from
the top of the batch gave a shorter cure time while in another

case the reverse was true It might be speculated, therefore,

that the variations within a batch are random inhomogeneities

attributable to factors such as inadequate mining rather than

some type of segregation of ingredients produced by the

processing itself. The latter circumstance might be expected to

produce the same effect each time thus leading to a consistent

trend and property variations that depend on location in the

batch. Additional studies are needed to test this speculation,

but these results provide a very useful indication with regard t what future experiments should be conducted.

VA HI AB IL IT Y T ES T5 CM LA BO RA TO RY IN KS : In view of the large

variations in ink properties, it is important to determine if

laboratory samples can be produced with controlled and

reproducible properties. To examine this question, three ink

batches were fabricated in the laboratory at BEF using starting

materials from the same lots and taking care to minimize

variations in the processing. These samples were tested at N5S

for drying behavior again using the rubber mill-squeeze flow

technique. The drying curves are shown in Figure 18. These

results can be compared with the data for production inks shown

in Figure 16. From this comparison it is clear that the

laboratory samples were very similar relative to the production

inks.

This same observation can be made in another way by again

using the time to 30 hardness values as characterization

parameters for cure These times were determined and the result
plotted together with the data from Figure 17 in Figure 19. Th i s

graph shows that controlled and reproducible inks can be made xn

the laboratory.

Although these experiments involved only one set of

laboratory inks, the results are very .encouraging because they

suggest that systematic studies can be performed with laboratory

inks to analyze the effects of variations in formulations and

processing on the drying properties. This offers the best hope

for identifying the sources of the variations in ink properties

and, from this identification, developing methods and processes

to minimize the variability.

2 0
RE FE RE NC ES

1. Donald L. Hunston and George W. Bullman, "Relationship

Between Mechanical Proper .ties and Performance of Inks as

Basis for Quality Control Techniques: Part II," NBSIR 84

2901, November 1984.

2. Donald L. Hunston, "Relationships Between Mechanical

Properties and Performance of Inks as a Basis for Gualit

Control Techniques," NBSIR 83-2691, May 1983.

2 1

the
TA BL S I : CURING OF INKS OF RUBBER MILL

TEMPERATURE FILM THICKNESS TIME TO

( C ) ( mm) SOLIDIFICATION

(min)

4 0 0 . 3 65

40 ^0 . 1 2 6

50 0 . 3 3 1 50 *-0.1 1 5

60 0 . 3 2 1 60 w 0 . 1 9

70 0 . 3 1 2 70 ~ 0 . 1 5

80 0 . 3 8

2
TABLE II: COMPARISON CF INK CURE RESULTS

INK

BATCH

DATE DESIGNATION SPOILAGE

(%)

TIME TO 30

HARDNESS

(min)

EEP

CURE RATE

9 1-16-32 A 2 2.3 37 S = £ L 0V

1 0 1-22-82 B 11.2 3 1 F=F AST

3 1-26-82 C 9 . 9 29 F

1 7 1-28-82 D 13.5 2 7 F

7 1- 12-82 E 0.74 33 c

5 1-25-82 F 16 4 4 2 s

1 3 1-27-82 G 1.19 4 1 s

9 2- 2-82 H 0.95 52 s

2 3
TAB L E III: CURE DATA FOR GREEN INKS

BATCH

NUMBER

SYMBOL T IM E TO 3 0 HA RD NE SS ( mi n) F OR INKS FABRICATED ON

1 1 -14-33 11-15-83 11-17-83 11-18-83

1 4 9 6 2 4 4

n + 5 4 — 3 3 5 4

3 A 55 — 58 3 5

4 0 6 0 -- 5 5 5 4

ew X 52 _ — _ __ _ _

6 50 -- -- --

1 4 U _ _ . _ 5 o

1 5 — 45 — —

1 6 • — 5 1 —

2 4
F IG UR E C AP TI CM 3

F i gu r e _1 :

F i qu r e _2 :

F i gu r e 3 :

F i gu r e jj

F i qu r e 3 :

Fi gu r a _6 :

F i qu r e 7 :

F i qu r e _8 :

F i_gu_re_ _9 :

Arrhenius type plot of time to solidification data at

two different film thicknesses: Q = 0.3 mm , =

"0.1 mm. The lines correspond to activation energies

of about 12 k cal /mol.

Diagram of the ultrasonic test apparatus with typical

oscilloscope display (test frequency is 3 or 5 MHz).

Drying curves from ultrasonic apparatus at three film

thicknesses . 5 , 13, and 25 x 10

J cm. Drying curves from ultrasonic apparatus for film of

- 3 thickness 7 x 10 cm at three temperatures: 40.7,

50.3, and----— 60.4 C.

Diagram of poker-chip test and sample of data output.

Film splitting force measured at various rates for

samples of ink batch 9 (1/16/32) cured on mill for

times of: 0 min. ^ , 7 min. fl , 15 min. -t- , 25 min. &

32 min. X , 3 7 min o - and 43 min. Q

Viscosity as a function o f shea r rate for samp 1 e s

ink BK- 60 cured o n mi 1 1 for 0 m i n . X , 1 0 min. ^

20 min. , and 3 0 min. *r Comparison of poker-chip, , and viscosity, ^ , cure

data on same ink: batch 17 (1/23/82). Vertical bars

on poker-chip data represent scatter range found with

8 tests.

Diagram of squeeze flow test and schematic of data to

unc u r ed and partially cured “ink.
F i qu r e 1

Q

Squae:e flow results for 3 specially selected, black

inks cured on the rubber-mill. Dashed curves

correspond to inks with high spoilage while solid

curves are for low spoilage inks. Letters designati ng part icular ink samples are defined in Table I i .

F i qu re 11 : Squeeze f 1 ow results for green inks fab ricitad on

11/14/33 and cured on the rubber-mill. The symfao 1 s

used in this graph designate the batch numb e r and a r

d e f i ne d in Table III.

F i qu re 12 : Squeeze f I ow results for green inks fab ricated on

11/15/83 and cured on the rubber-mill. The symbo 1 s used in this graph designate the batch number and a r

d e f i ne

d

i n Tab I e III.

F i qu re 13 : Squeeze f 1 ow results for green inks fab ricated on

11/17/83 and cured on the rubber-mill. Th e s ymb o 1

s

used in this graph designate the batch numb e r and a r

d a f i ne d in Table III.

F i au re 14 : Squeeze f 1 ow results for green inks fab ricated on

11/13/83 and cured on the rubber-mill. The symbols

used in this graph designate the batch numb e r and a r

’ defined in Table III.

_Fi_au_re_ 15 : Comparison of ink cure times for ink samples

including data from Figures 10 to 14,

^ . Data tor

the Black inks, Q , comes from Table II, and based

the black ink results, vertical dashed lines are

drawn to separate the data into

according to press behavior.

performance regions
F i qu r e 1 6 : Drying curves for production samples of EK-62-RCA

Mod. 3A inks made on 7/9/34: Sample number 5

, 9 -A- 10-A, 11 -0' and 12 - Open

indicate samples from the top of the batch;

symbols from the bottom.

F i qu re 1 7 : Time to 30 hardness v a 1 u e s for a variety o

£

green i nk s Data from Figure 16 is plotted

top of the graph using the same s y mb o 1 s as i

16. The other points are taken from Figure

F i qu r e 1

3

: Drying curves for laboratory samples of 3K-6

inks fabricated on 6/30/84: Sample number 1 ^ , and 3 - ^>

.

F i qu r e 19 : Data for laboratory inks added to Figure 17;

symbols as Figure 16.

2 7

- m, 6 -

s ymb o 1

s

filled

black and

at the

n Figure

1 5 .

2 - RCA

- , 2 -

same
Figure 1

o o o

h-*-»z:lu h- O COO

802

0.083

0.001

1/TEMPERATURE

<K>
Figure 2
EFFECT

OF

FILM

THICKNESS

OH

CURE

5,

13,

AND

25

X

10t-3

cm

Figure 3

OZ<XZ<Jlll <Zt-H-LU TJ GQ

100

200

300

400

5

00

CURE

TIME

<

n

i

n
FECT

OF

TEMPERATURE

OH

CURE

0.7

C,

50.8

C,

AND

60.4

C

Figure 4

UJ

UKTZUUJ *-« 2: <x*-»— ljz: sen

ICO

200

300

400

'^O

CURE

TIME

<nin>
LOAD

Figure 5

POKER-CHIP TEST

TIME (sec)
POKER-CHIP

CURING

TEST:

INK

9/1-16

Figure 6

Ls_ <X •—« \Z3Q£UJ JOCQ Cl

CROSS-HEAD

SPEED

cn/nin
CURING

STUDY

:

BK

- G0

Figure 7

O

<D

V>

V

O

L

O

<D

00

CD

O

( O Q S D JW) |

I S O O S !
INK

CURE

TEST:

INK

17/1-28

Figure 8

© 00 KO Tt 04 ©

Q.CKOQ.LLI ££(->- ZT LU <Z C/) 3 111 Z= UJ 2= hCURE

TIME

(Min)
Figure 9

SQIIFF7F FLOW TEST

TIME
100

Figure 10

CD O Q CD CD co ko cvi

<r oc Ot zl uj co co DZfflUitt

TIME

<nin>
CURE

DATA

FOR

BATCHES

MADE

OH

11-14-83

Figure 11

X <r O' C2» X Ui CD (f) ZCQ LUQi

CURE

TIME

(nin)
CURE

DATA

FOR

BATCHES

HADE

OH

11-15-83

Figure 12

r-o o ® CD <9 Q (9 CD CD

in rf ro cm ^

X<ZQCOZUiO>CO muac

CURE

TIME

<

n

i

tO
CURE

DATA

FOR

BATCHES

MADE

OH

11-17-83

Figure 13

<X C> 21 tU CD (ft ZDZianiicz

CURE

TIME

(fiin)
CURE

DATA

FOR

BATCHES

HADE

OH

11-18-83

Figure 14

<X O' Oi ZUi CO CO z mujtt:

CURE

TIME

<nin>
Figure 15

O

Q

rw

©

KD

©

in

©

©

ro

©

Csl

LU

©

(_> O

LU

CD

39\ni0dS
Figure 16

QQ 00 00 05

m ^ n cvi

<x a: c» ziu co co zsEaiutt

CURE

TIME

<nii*>
COMPARISONS

OF

INKS

Figure 17

TIME

TO

CURE

<nin>
LABORATORY

INKS

OF

BK-62-RCA

Figure 18

O Q Q 0

to m* ro cm

<X QC Z LU CO CO ZGQIUOC

CURE

TIME

<MiiO
COMPARISONS

OF

INKS

Figure 19

©

©

©

in

©

©

PO

©

CM

TIME

TO

CURE

<nin>
NSS-I14A irev. 2 -ao) U.S. OEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO.

SHEET (See instructions)

4. TITLE AND SUBTITLE

Relationships Between Mechanical Properties and Performance of Inks as the Basis for Quality Control Techniques: Part III

5. AUTHOR(S)

Donald L. Hunston and George W. Bullman

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, O.C. 20234

7. Contract/Grant No. W-0840-00

S. Type of Report & Period Covered

Annual Report 1984

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADORESS (Street. City. State. ZIP)

U.S. Department of Treasury

Bureau of Engraving and Printing

Department of Research and Technical Service

Washington, D.C. 20226

10.

SUPPLEMENTARY NOTES

| [ Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here

)

This report reviews the progress of a joint program with the Bureau of Engraving and

Printing (BEP) designed to study the mechanical properties of ink both before and

during curing. The objectives are to develop quality control tests and guidelines

for improved ink formulations. This report covers progress in a number of

specific research areas. First, the development of a variety of test methods

is discussed. These methods include shear viscosity measurements, squeeze flow

experiments, and the poker-chip test. Second, the correlation that was developed

previously between ink drying behavior and press performance is examined further

.

Large batch-to-batch variations in drying behavior were found for production inks,

and this is concluded to be a major contributor to poor ink performance since

the press can not be adjusted to compensate for these rapid and unpredictable

variations. Third, the variations in properties within an ink batch were studied

and found to be a significant fraction of the between batch variations. Finally,

Laboratory inks were prepared and studied. These inks exhibited relatively little

variation either within or between batches . Consequently , the results indicate

that model inks can be prepared in the Laboratory for systematic studies of

property-performance relationships

.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) curing; drying; intaglio ink; printing; quality control; rheology? viscoelasticity;

viscosity

13. AVAILABILITY

| ^Unlimited

| | For Official Distribution. Do Not Release to NTIS

I | Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

1 xQrder From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

15. Price

i

°i. cis

-

U SCOMM-DC G043-P80