United States Control Technology EPA-450/3-89-024
Environmental Protection Center June 1989
Agency Research Triangle Park NC 27711
SEPA
Ultrasonic Cleaning of
Rotogravure Cylinders
control gj technology center
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DCN: 89-203-080-34-11
EPA-450/3-89-024
June 1989
ULTRASONIC CLEANING
OF ROTOGRAVURE CYLINDERS
by
Keith W. Barnett
Claire E. Most
Radian Corporation
P.O. Box 13000
Research Triangle Park, North Carolina 27709
EPA Contract No. 68-02-4392
Project Officer
Robert J. Blaszczak
Chemicals and Petroleum Branch
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Prepared for:
Control Technology Center
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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ACKNOWLEDGEMENT
This report was prepared for EPA's Control Technology Center (CTC) by
K. W. Barnett and C. E. Most of Radian Corporation. The project officer was
Robert Blaszczak of EPA's Office of Air Quality Planning and Standards
(OAQPS). Also on the project team was Dr. Dean Smith of the Air and Energy
Engineering Research Laboratory.
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PREFACE
This project was funded by EPA's Control Technology Center (CTC). The
CTC was established by EPA's Office of Research and Development (ORD) and
Office of Air Quality Planning and standards (OAQPS) to provide technical
assistance to State and local air pollution control agencies. Three levels
of assistance can be accessed through the CTC. First, a CTC Hotline has
been established to provide telephone assistance on matters relating to air
pollution control technology. Second, more in-depth engineering assistance
can be provided when appropriate. Third, the CTC can provide technical
guidance through publication of technical guidance documents, development of
personal computer software, and presentation of workshops on control
technology matters.
The technical guidance projects, such as this one, focus on topics of
national or regional interest that are identified through contact with State
and local agencies. In this case, the CTC became interested in a
rotogravure printing facility which had reduced their use of organic
solvents in cylinder cleaning by the application of ultrasonic cleaning
combined with an aqueous cleaning solution. This document discusses the
general applicability of aqueous ultrasonic cleaning to the rotogravure
printing process and other graphic arts process. It also identifies
benefits and costs of ultrasonic cleaning.
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EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental Protection
Agency and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policy of the Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendations for use.
This document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161.
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TABLE OF CONTENTS
Section Page
1.0 INTRODUCTION 1-1
2.0 DESCRIPTION OF ULTRASONIC CLEANING 2-1
2.1 Introduction 2-1
2.2 Process Description 2-1
2.3 Factors Affecting Performance 2-3
2.4 References 2-8
3.0 ROTOGRAVURE PRINTING AND AQUEOUS ULTRASONIC CLEANING 3-1
3.1 Rotogravure Printing Process 3-1
3.2 Conventional Cleaning Methods 3-4
3.3 Aqueous Ultrasonic Cleaning of Rotogravure
Printing Cylinders 3-5
3.3.1 Process Description 3-5
3.3.2 Benefits 3-6
3.3.3 Costs 3-6
3.4 Hypothetical Cases Demonstrating Impacts of Applying
Aqueous Ultrasonic Cleaning 3-9
3.4.1 Example 1 3-9
3.4.2 Example 2 3-12
3.5 References 3-14
4.0 ULTRASONIC CLEANING APPLIED TO OTHER
GRAPHIC ARTS PROCESSES 4-1
4.1 Introduction 4-1
4.2 Applicabil ity of Ultrasonic Cleaning 4-1
4.3 References 4-3
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LIST OF TABLES
Table Page
2-1 Potential Applications for Selected Cleaning Solutions 2-6
3-1 Potential Benefits and Disadvantages of Aqueous Ultrasonic
Cleaning of Rotogravure Printing Cylinders 3-7
3-2 Hypothetical Rotogravure Floor Covering Facility Before and
After the Installation of an Aqueous Ultrasonic System
for Cleaning Printing Cylinders 3-10
3-3 Hypothetical Rotogravure Flexible Packaging Facility Before
and After the Installation of an Aqueous Ultrasonic System
for Cleaning Printing Cylinders 3-11
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LIST OF FIGURES
Figures Page
2-1 Simplified Ultrasonic Cleaning System 2-2
3-1 Six color rotogravure printing press 3-2
3-2 Diagram of rotogravure printing unit 3-3
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1.0 INTRODUCTION
This report evaluates the potential application of a new method for
cleaning cylinders used in rotogravure printing. This method, ultrasonic
cleaning, has the potential to reduce organic solvent use, volatile organic
compound emissions, and solvent waste generation.
The ultrasonic cleaning method is based on the scrubbing action created
by the passage of ultrasonic waves through a liquid cleaning medium. This
method is now used in other industries to clean a wide variety of parts,
assemblies, and finished goods. Among the benefits of ultrasonic cleaning
are the speed of cleaning and the high level of cleanliness achieved. In
addition, when an aqueous rather than solvent-based cleaning liquid is used,
emissions of volatile organic compounds (VOC) from cylinder cleaning are
eliminated and hazardous waste handling problems are reduced.
The rotogravure printing process is typically used only for printing
where high quality is required because rotogravure cylinders are very
expensive to produce. Due to their high cost, cylinders are frequently
reused as long as possible. However, cylinders must be thoroughly cleaned
between runs or prior to storage in order to maintain high print quality.
In a typical rotogravure process, the printing cylinders are manually
or mechanically cleaned using an organic solvent. However, at least one
facility is now using aqueous ultrasonics to clean rotogravure printing
cylinders. Aqueous ultrasonic cleaning may be applicable to all rotogravure
printing operations which reuse cylinders such as the flexible packaging
industry, vinyl printing, wallpaper printing and other decorative printing
operations. It may also be applicable to other types of printing operations
as well. The benefits of the increased application of ultrasonic cleaning
would be a reduction in solvent use and VOC emissions from graphic arts
processes.
cml.105 1-1
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This report presents findings of a study on the aqueous ultrasonic
cleaning of rotogravure printing cylinders. Section 2.0 presents a short
review of ultrasonic cleaning. Section 3.0 describes the rotogravure
printing process and the potential application of aqueous ultrasonic
cleaning for cylinder cleanup. Section 4.0 discusses the potential
application of ultrasonic cleaning to other graphic arts processes.
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2.0 DESCRIPTION OF ULTRASONIC CLEANING
2.1 INTRODUCTION
Ultrasonic cleaning can be used to clean parts, assemblies, and finished
goods. It is primarily used to meet precision cleaning requirements during
product manufacture or equipment maintenance. Industries which have
successfully applied ultrasonics include the medical, optics, electronics,
electroplating, graphic arts, transportation, textile, plastics, glass,
instrument, communications, automotive, aircraft, jewelry, paper, sporting
goods, and metal cleaning industries. Ultrasonic cleaning is used on parts as
small as rings and switch contacts to as large as 21 foot printing rolls, and
jet engine and other aircraft parts. Ultrasonic cleaning equipment is
available from industrial equipment manufactures and vendors of cleaning
solutions.
2.2 PROCESS DESCRIPTION
The ultrasonic cleaning method is based on the use of ultrasonic waves
(sound waves whose frequency is over 18 kHz) in a liquid medium. During
ultrasonic cleaning, alternating zones of high and low pressure are generated
when ultrasonic waves pass through the cleaning solution. In areas of low
pressure, microscopic bubbles of vapor form because the pressure has dropped
below the vapor pressure of the liquid. These areas of low pressure become
high pressure areas a half-cycle later. Under high pressure, the vapor
bubbles implode, generating a localized, but highly intense shock wave. This
process of alternating high and low pressure formation is called cavitation.
It is the cavitation that produces the scrubbing action in an ultrasonic
cleaning system.
A simplified ultrasonic cleaning system is shown in Figure 2-1. All
ultrasonic cleaning systems contain three basic elements: a generator, a
transducer, and a tank containing the cleaning liquid. The generator
produces high frequency electrical current. The electric current is
cml.105 2-1
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Transducers
Generators
Cleaning Solution
Tank
Figure 2-1. Simplified ultrasonic cleaning system
a
10
2-2
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converted into mechanical vibrations by the transducer. Transducers are
usually placed on the bottom or sides of the tank. They can be bonded to the
tank exterior or sealed in an immersible stainless steel container and
attached to the tank interior. Figure 2-1 shows the immersible type of
transducer.
There are two basic types of transducers used for ultrasonic cleaning:
magnetostrictive and piezoelectric. The selection of transducer type is based
on vendor preference. For industrial cleaning purposes, transducers generally
operate at ultrasonic frequencies of less than 60 kHz (60,000 cycles per
second). Frequencies of about 20 to 40 kHz are common.
In its simplest form, an ultrasonic cleaning system includes a single
ultrasonic tank (Figure 2-1). More complex systems incorporate other stages
of cleaning as well. For example, conveyorized systems are available that
automatically move parts through various cleaning stages such as rinsing,
2
cleaning, and drying. Another type of system, called a carousel, moves parts
through multiple cleaning stages in rotating baskets. The parts are placed in
baskets suspended from arms extending from a central column. As the arms
rotate around the central column, the baskets move from one cleaning stage to
2
another. Systems are also available to clean continuous strip materials. In
these systems, the material to be cleaned runs from a feed spool to a take up
spool. It passes through a tank with opposed transducers at different
frequencies that are approximately 1/2 to 3 inches apart. The opposed
transducers create an intense ultrasonic field which allows the part to be
cleaned during the short time period that the part is actually submerged in
the tank.
2.3 FACTORS AFFECTING PERFORMANCE
Numerous factors affect the successful application of an ultrasonic
system. One important factor is the ultrasonic power. At any specific
frequency, it requires a certain power input to the transducer(s) in order to
reach point at which cavitation begins. The power input beyond that required
o
to initiate cavitation is the power available for cleaning.
cml.105 2-3
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The greater the power input, the shorter the cleaning time. However, too
much power may damage the parts to be cleaned. Determination of the optimum
power levels is typically done by the equipment or cleaning solution vendors
based on testing using specimens of the actual parts which will be cleaned.
When delicate parts are being cleaned, variacs should be designed into the
system to allow for the appropriate power level to be set. It is always
advisable to conduct actual tests on the items to be cleaned prior to
purchasing equipment.
A second factor is the ultrasonic frequency. At a constant power level,
the cavitation intensity decreases as the ultrasonic frequency increases.
Higher frequencies can provide less intense cavitation and, therefore, gentler
and more penetrating cleaning. To achieve the same cavitation intensity when
A
the frequency is increased, more power must be supplied. The optimum
frequency may also be affected by the cleaning solution because different
cleaning solutions have different cavitation thresholds.
A third factor is temperature. In general, cleaning solutions are more
effective as the temperature increases. However, as temperature increases the
vapor pressure of the cleaning solution increases, causing the bubbles to have
a higher vapor concentration. Vapor present in the bubbles reduces cavitation
intensity. Therefore, increasing the temperature of the cleaning solution
reduces cavitation. In practice there is a temperature where the combination
of cleaning solution effectiveness and cavitation intensity are optimized.
This is usually no higher than 30°F below the boiling point of the cleaning
solution.
The presence of dissolved gas in the cleaning solution will reduce the
performance of ultrasonic cleaning. For this reason, the solution should be
degassed prior to its first use. This can be accomplished by heating the
solution, operating the ultrasonic system to drive off the gas, or adding a
degassing agent.
Other factors influencing the performance of an ultrasonic system
include: the design and composition of baskets, the placement and design of
parts to be cleaned, the position of transducers, the duration of part
exposure, and the modulation of the sonic field. For example, parts with
blind holes must be rotated to remove all air from the holes, otherwise the
cml.105 2-4
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cleaning solution will not contact the entire surface and any portion of the
part not contacted by the cleaning solution will not be cleaned. Ultrasonic
sound will not pass from liquid into or through gas. However, as long as all
the part surface contacts the solution, ultrasonic cleaning is especially
effective compared to hand scrubbing for parts that have intricate designs,
engraving, or small nooks and crannies.
As shown in Table 2-1, ultrasonic cleaning is applicable to a wide
variety of soils and types of parts. The materials which can be cleaned
include metals, plastics, and rubber. However, plastic and rubber tend to
attenuate sound which may reduce the effectiveness of ultrasonic cleaning.
As previously discussed, testing of the actual materials to be cleaned should
always be performed prior to applying ultrasonic cleaning. The soils which
are removable include oils, dust, various particulates, buffing and polishing
compounds, and mold release agents.
The selection of the proper cleaning solution is of primary importance
for the successful application of ultrasonic cleaning. The cleaning solution
must be able to remove the soil of concern and must not react with the surface
to be cleaned. In addition, the solution must be easily removable from the
cleaning surface. As shown in Table 2-1, both aqueous- and solvent-based
solutions are used for ultrasonic cleaning. For some applications, only
aqueous solutions clean effectively, whereas for some other applications, only
solvent systems clean effectively. In many cases, however, both aqueous and
solvent systems are available for use. For example, Table 2-1 shows that
atmospheric soils can be removed from plastic parts using either the solvent
trichlorotrifluoroethane or an aqueous solution of mild alkaline detergent.
The selection of solvent-based solutions is less desirable because of
the potential for emissions of volatile organic compounds and the adverse
environmental impacts of solvent disposal. Also, use of some organic solvents
may be banned due to the Montreal accords. However, even if a solvent
solution is required for a particular application, using ultrasonics allows
the cleaning vessel to remain closed and offers an alternative to the labor
intensive methods such as hand scrubbing.
Once the proper cleaning solution is selected, other properties of the
cleaning solution must be considered in selecting the design parameters of the
ultrasonic system. These properties of importance include the solution
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TABLE 2-1. POTENTIAL APPLICATIONS FOR SELECTED CLEANING SOLUTIONS
Cleaning assignment
Soils
Cleaning method
Solvent/solution
Brass parts
Atmospheric Ultrasonic immersion; immersion
soils rinse; dry
Vapor rinse; ultrasonic
immersion; solvent spray rinse;
vapor rinse
Mild acidic detergent; tap water
Methylene chloride
Aluminum parts Grease, oils, Vapor rinse; ultrasonic immersion;
particulate solvent spray rinse; vapor rinse
Stabilized blend of trichloro-
trifluoroethane and methanol
Nickel parts
Forming and
cutt ing
lubricants
participates
Vapor rinse, ultrasonic immersion;
solvent spray rinse; vapor rinse
Ultrasonic immersion; immersion
rinse; dry
Perchloroethylene, methylene
chloride or 1,1,1-
trichloroethane
Strong, chelated alkaline
detergent; tap water
Steel, mild
Grease, oils, Vapor rinse; ultrasonic immersion;
particulates solvent spray rinse; vapor rinse
Methylene chloride, azeotrope
of trichlorotrifluoroethane
and methylene chloride or
1,1,1-trichloroethane
Steel, stainless
Buffing and Ultrasonic immersion; immersion
polishing rinse; dry
compounds
Soap-free alkaline cleaner;
tap water
Ultrasonic immersion; solvent
spray rinse; vapor rinse
1,1,1-trichloroethane, or
stabilized blend of trichloro-
trifluoroethane and methanol
Titanium
Machining
oils,
particulates
Ultrasonic immersion; immersion
rinse; dry
Alkaline cleaner; chloride-free
rinse water
Plastic parts,
miscellaneous
Atmospheric
soils
Ultrasonic immersion; rinse; dry
Vapor rinse; ultrasonic immersion;
solvent spray rinse; vapor rinse
Mild alkaline detergent;
tap water
Trichlorotrifluoroethane
Polypropylene
Mold release
agents
Vapor rinse; ultrasonic immersion;
solvent spray rinse; vapor rinse
Trichlorotrifluoroethane
Rubber, neoprene
Mold release
agents
Vapor rinse; ultrasonic immersion;
solvent spray rinse; vapor rinse
Stabilized blend of trichloro-
trifluoroethane and methanol
Rubber molds
Carbonized
rubber
residues,
release
agents
Presoak; ultrasonic immersion;
spray rinse; dry
Strong alkaline detergent and
tap water; or specialized
strippers
Bearings
Oil, dust, Ultrasonic immersion; boiling
lint immersion; ultrasonic immersion;
solvent spray-rinse; vapor rinse
Blend of trichloro-
trifluoroethane and
surfactant/water emulsion;
trichlorotrifluoroethane
Source: Reference 1.
Note that some of the organic solvents shown in this table may soon be banned due to the
Montreal Accords.
2-6
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surface tension, viscosity, vapor pressure, density, and dissolved gas
content. Determination of the optimum system frequency, power levels,
temperature and other parameters depends on the cleaning solution properties
and is usually based on actual testing performed by the vendors.
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2.4 REFERENCES
1. Calhoun, T. Ultrasonic Cleaning Boosts Your Scour Power. Production
Engineering, 28(10):58-62, 1981.
2. Crawford, A.M. Large Scale Ultrasonic Cleaning. Ultrasonics,
6(4):211-16, 1968.
3. Letter from Streeton, R., Intex Chemical, Inc., to K. Barnett, Radian
Corporation. May 11, 1989. 5 pp.
4. Fuchs, F. J. Ultrasonic Cleaning Metal Finishing, 82(1):15-18, 1984.
5. Telecon. Barnett, K., Radian Corporation with Streeton, R. Intex
Chemicals, Inc. May 1989. Conversation concerning ultrasonic cleaning,
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3.0 ROTOGRAVURE PRINTING AND AQUEOUS ULTRASONIC CLEANING
3.1 ROTOGRAVURE PRINTING PROCESS
Gravure is distinguished from other printing methods by the nature of
the image surface. The method is often referred to as the "intaglio"
process. The surface of the gravure printing cylinder is etched or engraved
with many tiny recesses (cells). The depth of each cell determines the
amount of ink that will be applied to the substrate at that point.
Rotogravure is the most widely used gravure printing process. A six
color (unit) rotogravure printing press is illustrated in Figure 3-1. In
rotogravure, or web-fed gravure, a continuous web of paper is fed from a roll
and passed over the image surface of a revolving printing cylinder. A web-fed
2
rotogravure printing press typically consists of 5 to 8 printing units. All
units of a press must be of the same size and width. In addition, all the
units must simultaneously operate at the same press speed. Each unit handles
an individual color of ink and prints on only one side of the web.
An expanded diagram showing an end view of an individual printing unit is
presented in Figure 3-2. The web is woven through a series of rollers which
precisely adjust its path through the press. The rollers also help regulate
the paper tension and maintain constant speed. The web is guided between the
revolving gravure printing cylinder and a rubber roller. The substrate is
pressed against the image surface of the gravure cylinder by the rubber
roller, which serves as a backing. Pressure is applied to the rubber roller
by a pressure cylinder. The point of contact between the web and the gravure
cylinder is called the "nip" area.
Each printing unit has its own ink handling system. In a mixing tank
(ink reservoir), the raw ink is diluted with additional solvent or extender to
achieve the desired viscosity. The mixture is then continuously circulated
through the ink fountain and back to the mixing tank. This circulation
prevents the ink pigments from settling out of the mixture. Solvent is
periodically added to the ink fountain to replace fugitive losses.
cml.105 3-1
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The gravure cylinder, on which the image surface has been etched, is
about one-fourth submerged in a trough of ink called the ink fountain. Before
a portion of the gravure cylinder contacts the substrate, it picks up ink from
the ink fountain and is then scraped by a flexible "doctor blade". This blade
removes ink from the smooth non-image surface, but leaves ink in the cells.
These ink laden cells contact the substrate to form the image.
After ink has been transferred to the substrate, the substrate travels up
through an enclosed dryer where jets of heated air evaporate the volatile
solvent. The web exits the top of the dryer and is guided along rollers to the
next printing unit. In a typically controlled facility, the exhaust from all
the dryers are gathered in a header, and directed to a carbon adsorption
system or an incinerator. In an uncontrolled plant, the dryer exhaust is
vented to the atmosphere.
3.2 CONVENTIONAL CLEANING METHODS
After a job has been completed (or at least when the ink color is
changed), all parts that come in contact with the ink must be thoroughly
cleaned. These parts include the ink pans, ink reservoirs, pumps, doctor
blades, and printing cylinders. Depending on the facility, parts may be
left on the press or removed from the press for cleaning. At facilities
leaving parts on the press for cleanup, rollers, pumps and ink pans are
generally washed down with solvent. In addition, the printing cylinder may
be manually scrubbed with a brush. At facilities removing parts from the
press for cleanup, parts are generally placed in a tank, immersed in
solvent, and soaked or manually scrubbed. Cylinders frequently require
scrubbing with a brush. Some facilities do a combination of on-press and
off-press cleaning. For example, the printing cylinder may be cleaned off
the press and all other parts may be cleaned on the press; or, the cylinder
may be wiped first while still on the press and then removed from the press
for additional cleaning. Alternate cleaning methods, such as aqueous
detergent solutions, agitated caustic baths, and solvent degreasers are also
used at some rotogravure printing facilities. The prevalence of these methods
within the rotogravure industry is unknown.
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3.3 AQUEOUS ULTRASONIC CLEANING OF ROTOGRAVURE PRINTING CYLINDERS
3.3.1 Process Description
Ultrasonic cleaning with an aqueous solution is one potential
alternative to conventional solvent-based cleaning methods used for
rotogravure printing cylinders. In this method, the dirty
cylinder is removed from the press and placed in a tank containing an
aqueous detergent solution. The solution is then sonicated for a brief
period (usually a few minutes). For more difficult cleaning jobs, the
sonication period may be extended or repeated. Because the cylinder must be
cleaned over its entire surface, the cylinder must be rotated during
cleaning. The simplest and cheapest tanks allow the cylinder to be manually
rotated on its support. More sophisticated tanks are equipped with an
automatic mechanism to slowly rotate the cylinder. After cleaning, the
cylinder is moved to a rinsing tank, where it is rinsed with clean water.
After rinsing, the cylinder is dried using air drying or some other method
such as compressed air or hand drying with towels. The cylinders are
usually hot when they come out of the cleaning bath; when rinsed with hot
water (and sometimes with cold water), they tend to dry quickly.
The optimum frequency, power levels, cleaning time and other parameters
of the ultrasonic system are usually based on actual testing performed by the
vendors on the parts to be cleaned. An ultrasonic system must be properly
designed to prevent damage to the cylinder being cleaned. If power levels are
too high, for example, the cylinder surface may be damaged due to cavitational
erosion. Well designed systems will include a variac to allow a reduction
from full power when delicate parts are being cleaned. Rotogravure
cylinders engraved using photoresist acid etch tend to be more delicate than
mechanically engraved cylinders.
The general applicability of an aqueous system for rotogravure
cylinders must also be considered. Two factors are of primary concern: (1)
whether rotogravure cylinders are damaged by water immersion, and (2)
whether the cylinders are difficult to dry (i.e., would require thorough
drying at high cost). Neither of these factors appears to be a problem for
rotogravure cylinders.
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3.3.2 Benefits
Conversion to aqueous ultrasonics offers many benefits (Table 3-1).
For example, potential environmental hazards associated with the use of
solvents are avoided. Use of the aqueous solution reduces solvent emissions
from the plant and worker exposure to solvent. Lack of solvent reduces fire
hazards in the cleanup area. In addition, many detergent solutions are
available that are biodegradable and nonhazardous. Use of these solutions
not only ensures worker safety, but minimizes waste disposal problems. When
the printing inks used do not contain metals or other hazardous ingredients,
these solutions can generally be flushed directly to the sewer. In
contrast, spent solvent used for cleanup always produces a hazardous waste.
Another major benefit is that cylinder cleanup is faster and less labor
3 4
intensive. ' This not only reduces time and labor spent on cleanup after a
job has been completed, but can reduce downtime during a printing run. For
example, if a problem occurs at the beginning or during a run due to a dirty
cylinder, the cylinder can be quickly cleaned and the press returned to
service in minimal time.
Improved product quality can also result from the more effective
cleaning achieved by the ultrasonic system. For example, ultrasonic systems
effectively remove waterborne inks, which are characteristically difficult
to clean. Because cleaning is more uniform and thorough, problems of poor
print quality due to ink buildup can be reduced. In addition, cylinder
cleaning performed on the press can be less thorough or even eliminated.
The rotogravure facility mentioned in the introduction switched to
ultrasonic cleaning mainly to improve product quality.
3.3.3 Costs
The disadvantage of an ultrasonic system is its capital cost relative
to using simple tanks. Based on discussions with equipment vendors, an
ultrasonic system could cost from roughly $10,000 to $150,000, depending
largely on the tank size required as well as on other design features of the
system. In some cases, it may be beneficial to lease the equipment.
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TABLE 3-1. POTENTIAL BENEFITS AND DISADVANTAGES OF AQUEOUS ULTRASONIC
CLEANING OF ROTOGRAVURE PRINTING CYLINDERS
Benefits Disadvantages
Reduces solvent use High capital cost relative to other
cleaning methods
Reduces solvent emissions
Reduces worker exposure to solvent Waste disposal costs per gallon of
waste may increase if ink residues
Minimizes solvent waste disposal or detergent produce a hazardous
problems waste.
Detergent solutions that are
biodegradable and non-hazardous
and inks that do not contain
metals or other hazardous
ingredients can be directly
sewered.
Reduces time and labor spent on
cylinder cleanup
Reduces downtime during printing
run
Cleans more effectively
Reduces problem of poor print
quality due to ink buildup on
cylinders
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Because the cost of purchasing an ultrasonic system is potentially high, the
use of ultrasonics would be less beneficial at facilities where cylinders
are not reused or are cleaned infrequently due to long printing runs. In
rotogravure publishing, for example, installation of an ultrasonic system
would be less beneficial because printing cylinders are rarely reused.
The primary operating cost of an aqueous ultrasonic system is the cost
of chemicals purchased for the cleaning solution. This cost is influenced
by the volume of parts to be cleaned and by how often the solution needs to
be changed. Because the dirt cleaned from each part remains in the tank,
each part cleaned enters a dirtier tank than the part cleaned previously.
Consequently, one factor influencing the frequency of cleaning solution
changes is the amount of dirt on each part and how clean the parts need to
be. In addition, the tank may need to be cleaned periodically due to a
buildup of ink solids on the transducers if they are on the bottom of the
tank. Locating the transducers on the sides of the tank will reduce solids
buildup on transducer surfaces.
After the installation of an aqueous ultrasonic system, operating costs
for cylinder cleanup would be expected to decrease. A facility would no
longer need to purchase solvent for cylinder cleanup. Instead, the facility
would purchase aqueous detergent solution. The detergent solution would
probably cost much less annually than the solvent previously purchased. Thus,
the operating costs would be expected to decrease. The magnitude of the cost
reduction, however, would be facility-specific.
The effect of an aqueous ultrasonic system on the costs of waste disposal
also varies from plant to plant. The cost for disposal of the spent aqueous
solution depends on the type of waste treatment required. It is important
to note that both the nature of the cleaning solution and the soil being
removed must be considered. A solution that contains biodegradable
detergent, no hazardous ink residues, and is nearly neutral in pH, generally
requires no treatment and can be flushed directly to the sewer. A solution
that contains non-biodegradable detergent or hazardous ink residues (such as
certain metallic pigments) must be sent to an appropriate treatment
facility. Solvent wastes, in contrast, must always be treated as hazardous
wastes.
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After installation of aqueous ultrasonics, waste disposal costs would be
expected to decrease for facilities using biodegradable detergents and inks
with nonhazardous ingredients. At facilities where the spent aqueous solution
would require treatment, the change in waste disposal costs would depend on
the relative amount of waste generated and the relative costs of waste
disposal before and after the application of ultrasonics. Based on one
facility now using aqueous ultrasonics, the volume of aqueous waste
generated is expected to be less than the volume of solvent waste. However,
the disposal of hazardous aqueous wastes can be more expensive per gallon
than solvent wastes. Therefore, the cost of waste disposal may increase at
some facilities.
3.4 HYPOTHETICAL CASES DEMONSTRATING IMPACTS OF APPLYING AQUEOUS
ULTRASONIC CLEANING
Two examples were developed to illustrate the potential effect of
aqueous ultrasonics on hypothetical rotogravure facilities. In Example 1,
the presses have a 16 foot printing width. Production is characterized by
short (less than 8 hours) production runs. In Example 2, the press print
width is approximately 2 feet. Production runs are much longer than in
Example 1, but because the facility has more presses, the same number of
cylinders are cleaned each day.
Tables 3-2 and 3-3 present estimates of solvent emissions, waste
generation, and costs for cylinder cleanup before and after the installation
of an aqueous ultrasonic system for Examples 1 and 2, respectively. The
parameters for Example 1 and Example 2 are based on phone conversations and
two site visits. Neither example, however, is intended to represent any
particular facility. Each example is described in more detail below.
3.4.1 Example 1
Example 1 has 2 rotogravure presses. Run lengths are generally less
than 8 hours. The printing cylinders have a 16 foot etched surface and a
total length of about 20 feet. The facility cleans about 48 of these
cylinders/day.
cml.105 3-9
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The capital cost of the aqueous ultrasonic system for this facility is
estimated to be about $80,000. This is an order of magnitude cost estimate
only, and is based on the average of cost estimates received from equipment
vendors. The capital cost of an ultrasonic system for any particular
facility would depend on that facility's specific needs.
When this facility installs aqueous ultrasonics, atmospheric emissions of
solvent from cylinder cleanup are reduced by an estimated 130,000 Ib/yr. This
assumes total cleanup solvent use for cylinder cleaning is reduced by
100 percent, and that half of the solvent originally used for tank cleanup
evaporated. In addition, the hazardous solvent waste generated by the
facility is reduced by about 20,000 gal/yr. The spent aqueous waste
generated by the facility is assumed to require no treatment and is dumped
directly to the sewer.
The facility previously spent about $110,000/yr to purchase cleaning
solvent and about $6,000/yr to dispose of waste solvent. The facility now
spends about $5,600/yr to purchase cleaning solution and a negligible amount
for solution disposal. Thus, the facility now saves about $110,000/yr in
cleaning chemical purchasing and disposal costs. Because ultrasonic cleaning
is more effective than the previous method, the problem of poor print quality
resulting from ink buildup on the cylinder has been eliminated. Thus, the
facility also saves $12,000/yr in cylinder dechroming/rechroming costs.
3.4.2 Example 2
Example 2 has 4 rotogravure presses. Run lengths are about 12 hours
long. The total length of the printing cylinders is about 3 feet. The
facility cleans about 48 of these cylinders/day. The capital cost of the
aqueous ultrasonic system for this facility is estimated to be about
$30,000. This is an order of magnitude estimate only and is based on the
average of cost estimates received from equipment vendors. The capital cost
of an ultrasonic system for any particular facility would depend on that
facility's specific needs.
After installation of the aqueous ultrasonic system, atmospheric
emissions of solvent from cylinder cleanup at the facility are reduced by an
estimated 27,000 Ib/yr. Solvent waste generated at the facility is reduced by
cml.105 3-12
-------
about 27,000 Ib/yr, but aqueous waste is increased by 1,100 gal/yr. This
facility is assumed to produce a hazardous aqueous waste that must be sent
off-site for treatment and disposal.
The facility previously spent about $22,000/yr to purchase cleaning
solvent and about $l,200/yr to dispose of waste cleaning solvent. The
facility now spends about $l,100/yr to purchase the aqueous detergent and
about $l,300/yr to dispose of the hazardous aqueous waste. Thus, the
facility saves roughly $21,000/yr in cleaning chemical purchasing costs and
spends roughly $100/yr more for waste disposal. This facility is assumed to
not have a problem of poor print quality due to ink buildup, and thus, does
not save any costs for cylinder dechroming/rechroming.
cml.105 3-13
-------
3.5 REFERENCES
1. U.S. Environmental Protection Agency. Publication Rotogravure Printing
Background Information for Proposed Standards. Research Triangle Park,
North Carolina. Publication No. EPA-450/3-80-031a. October 1980.
pp. 3-7 to 3-13.
2. Howie, R.H., S.A. Shareef, M.A. Baviello, Radian Corporation. Source
Category Survey Report for Paper, Film and Foil Converting Industry.
Prepared for U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina. November 1984.
3. Memorandum from Keith Barnett, Radian Corporation, to Rotogravure
Cylinder Cleaning Project File. January 23, 1989. Trip Report -
Congoleum Corporation.
4. Telecon. Keith Barnett, Radian Corporation, with Lofton, Deatwyler
Company. January 24, 1989.
5. Telecon. Barnett, K., Radian Corporation with Streeton, R., Intex
Chemicals, Inc., May 1989.
6. Letter from Streeton, R., Intex Chemicals, Inc., to K. Barnett, Radian
Corporation. May 11, 1989. 5 pp.
cml.105 3-14
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4.0 ULTRASONIC CLEANING APPLIED TO OTHER GRAPHIC ARTS PROCESSES
4.1 INTRODUCTION
Aqueous ultrasonics may potentially be used in graphic art processes
besides rotogravure depending on the nature of the process and the
particular facility. This section discusses the potential application of
aqueous ultrasonics in letterpress, lithography, flexography, and screen
printing. Because of the limited data available, however, detailed examples
were not developed.
4.2 APPLICABILITY OF AQUEOUS ULTRASONIC CLEANING
There are two questions which must be answered to determine whether
aqueous ultrasonic cleaning is applicable to other graphic arts processes
and what the benefits of ultrasonic cleaning would be. They are:
1) Are aqueous solutions combined with ultrasonic cleaning capable of
removing the inks used without damaging the underlying materials?
2) Does the particular printing process being evaluated use a
significant amount of solvent for cleanup and are the parts being
cleaned removable from the press?
As long as sufficient care is taken to select an appropriate cleaning
solution, it can be generally stated that aqueous ultrasonics should be able
to remove inks used in all graphic arts processes. The exception to this
may be a few specially formulated inks, such as caustic resistant inks used
on kitchen wallpapers or detergent containers. To determine if a specific
facility can use ultrasonic cleaning, tests should be performed using that
facility's specific inks and cylinder or part materials. Because aqueous
ultrasonic cleaning should be capable of removing most inks, the
applicability and benefits of ultrasonic cleaning appear to be most
dependent on the cleaning process itself.
In flexography, printing plates are generally not reused. However,
other press parts are frequently cleaned and can be removed for cleaning.
cml.105 4-1
-------
Except for the rubber-faced fountain roll, aqueous ultrasonics could be used
to clean these other press parts. For example, aqueous ultrasonics may be
especially useful for the cleaning of engraved ink metering (or anilox)
rolls. The major benefit of ultrasonics would be a reduction in cleanup
time. The actual benefits realized would be facility-specific; the more
cleanups required at a given facility (i.e., the shorter the run lengths),
the more benefits from aqueous ultrasonics.
In addition, flexography is one sector of graphic arts which is moving
fastest to replace solvent based inks. Because ultrasonic cleaning appears
to be ideally suited for waterborne inks, this factor would also tend to
favor the use of ultrasonic cleaning in this sector of graphic arts.
Ultrasonic cleaning does not appear to be applicable to offset
1 2
-lithography. In this process, plates are generally not reused. ' Other
press parts are not dissembled for cleaning.
Detailed information on cleanup procedures for letterpress and screen
printing was not obtained due to the fact that these processes make up a very
small part of the total industry. Ultrasonic cleaning would appear to be
applicable to letterpress since individual type letters are removed from the
press and reused. Screens could also be cleaned using ultrasonics. However,
the number of times screens are typically reused is likely to vary
significantly from one facility to another.
cml.105 4-2
-------
4.3 REFERENCES
1. Telecon from Keith Barnett, Raidan Corporation, to Jim Lofton,
Deatwyler Company. January 24, 1989.
2. Telecon from Rich Pandullo, Radian Corporation, to Patrick Doyle, Abbey
Press. January 27, 1989.
cml.105 4-3
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA-450/3-89-024
4. TITLE AND SUBTITLE
Ultrasonic Cleaning of Rotogravure Cylinders
7. AUTHOR(S)
Keith Barnett, Radian Corporation
Research Triangle Park, NC 27711
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Control Technology Center (MD-13)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Air and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, NC 27711
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
July 1Q«Q
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT
N
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO
68-02-4392
13. TYPE OF REPORT AND PERIOD COV6REI
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Project Officer is Bob Blaszczak, MD-13, (919) 541-0800. The Control Technology
Center i-s a joint effort with the Office of Research and Development.
16. ABSTRACT
This report summarizes available information on
(in an aqueous solution) for cleaning cylinders used
Ultrasonic cleaning has the potential
compound emissions, and solvent waste
the use of ultrasonic techniques
in rotogravure printing processes
to reduce organic solvent use, volatile organic
, , , generation. The report briefly reviews the
ultrasonic cleaning process, describes the rotogravure printing process and the
potential application of aqueous ultrasonic cleanings for cylinders, reviews potential
benefits and costs, and discusses the potential for application to other graphic arts
processes.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
18. DISTRIBUTION STATEMENT
Unlimited Distribution
b.lDENTIFIERS/OPEN ENDED TERMS
Air Pollution Control
Hazardous Air Pollutants
Volatile Organic Compound
Flexographic Printing
Ultrasonic Cleaning
Rotogravure Printing
Metal Cleaning
Aqueous Cleaning
19. SECURITY CLASS (This Report)
Unclassified
20 SECURITY CLASS 1 This page)
Unclassified
c. COSATi Field/Group
21. NO. OP PAGES
22. PRICE
EPA Form 2220-1 (Rev. 4-77)
PREVIOUS EDI TION IS OBSOLETE
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