Get documents about "AnRp95 Quick Response Printing
Document Sample
G95-1 1
TITLE: Quick Response Printing
Project Number: G95 1 (xG92-5)
Investigators: W. W. Carr (leader), W. C. Tincher, P. Desai, and F. L. Cook,
Georgia Institute of Technology
P. H. Pfromm, Institute of Paper Science & Technology
Research Scientist: Deverakonda Sarma, Georgia Institute of Technology
Project Goal: To develop new technologies of textile printing
(electrophotography and ink-jet) that will meet the requirements of
time-driven, demand activated manufacturing.
ABSTRACT
Textile printing systems are needed that will meet the requirements of time-driven, demand
activated manufacturing. Electrophotography and ink-jet printing are technologies that have the
potential of meeting these requirements. Textile-specific, electrophotographic and ink-jet printing
toners/inks must be developed if these technologies are to gain acceptance in the textile industry.
The development of such toners/inks are the main goal of the current research effort. Computer
simulation is employed as an important tool for predicting the properties of resin binder systems
and to assist in the selection of promising candidates for both ink-jet and electrophotographic
printing.
INTRODUCTION
Current textile printing technologies are deficient in meeting today’s time-driven, demand
activated manufacturing strategies necessary for future success of the fiber/textiles/fabricated
products (FIFP) complex. Archaic technologies, e.g., storage of information on wire screens for
current printing processes, must be replaced with dry, computer-driven systems if the U.S. FTFP
complex is to remain globally competitive [1,2].
National Textile Center Annual Report: August 1995 161
G95-1 2
The goal of this project is to develop new technologies of textile printing (electrophotography
and ink-jet) that will meet the requirements of time-driven, demand activated manufacturing while
eliminating effluents associated with current printing technologies. The main barriers are the lack of
textile-specific, electrophotograhpic and ink-jet printing processes and toners/inks in the market
place today.
Numerous materials and process problems must be resolved before either electrophotography
or ink-jet printing technologies become viable methods of commercial textile printing. This project
will examine electrophotographic processes (xerography, ion deposition and direct electrostatic
imaging) which have the potential for high speed textile printing. Fundamental research leading to
a toner satisfying both textile and electrophotograhic requirements will be conducted. Research
leading to the development of ultraviolet (UV) curable resin systems for ink-jet resin-pigment
printing of textiles will be conducted. Ink-jet systems based on dye printing will also be explored.
This report describes the research conducted in three areas: electrophotographic printing, ink-
jet printing and molecular modeling.
ELECTROPHOTOGRAPHY
Electrophotography involves the formation of a latent image and transforming it into a visible
record or a print. Xerography is the most important and highly developed form of
electrophotography and is explored here for textile printing. It involves forming an electrostatic
image by charging a photoconductive surface and exposing the surface to a light pattern. The latent
image is developed using an electrostatic powder developer system. The developer system consists
of a toner and a carrier. The developed image is transferred to the substrate and fused to it.
Xerography has been extremely successful in printing of paper; however, the lack of textile-
specific, xerographic processes and toners in the marketplace today prevent xerography from being
used commercially to print fabric. One of the goals of this project is to conduct fundamental
research leading to a toner satisfying both textile and electrophotographic requirements.
Polymers used in toners for xerographic printing on paper are typically thermoplastic,
primarily due to the manner in which the toner is fixed to the paper. Space limitations in office
copiers necessitate fixing the toner in a very short time (milliseconds), precluding the use
thermosets. High pressure and elevated temperature are used to fix the toner to the paper. This
technique works well with paper, but is not effective on textile fabric. The crockfastness is
162 National Textile Center Annual Report: August 1995
G95-1 3
extremely poor when typical paper toners such as poly(styrene-co-acrylic acid) are used to print on
textile fabrics. Longer fixation times can be used for textile printing, making it possible to consider
thermoset polymers as potential candidate binders for textile toners. The thermoset polymers can
be low molecular weight polymers that flow well at relatively low temperatures and cure at
temperatures compatible with textile fibers. In previous research [3,4], a thermoset epoxy toner
was used to xerographically print on fabrics. Dry crockfastness properties of the prints made
using the thermoset epoxy toner were much better than those for the paper toners and comparable
to those for rotary screen prints. However, the wet crockfastness properties were less than
desired, and the epoxy-based toner prints were stiffer than rotary screen prints. The stiffness may
have been related to the degree of crosslinking.
Toners based on thermoset polymers such as epoxies, polyesters and hybrids (copolymer of
polyester and epoxies) are being produced and evaluated as potential textile-specific toners. Toner
is produced by melt blending the components (mainly polymer, pigment, and charge control
agent), cooling to solidify the material, and grinding to produce a fine powder, usually in the size
range of S-20 microns.
The major components of the toner (polymer, pigment, and charge control agent) have been
obtained from commercial suppliers. Shell, Ruco and Dow Chemicals have provided candidate
polymers with the potential for producing toners having high flexibility and good fastness
properties. The pigments, obtained from BASF and Hoechst-Celanese, were selected for good
light fastness. The charge control agents were supplied by Hodogaya Chemical (USA), Inc.
Carriers for producing positive charge on the toners were supplied by Steward Manufacturing
Company, Limited.
Thermoset toners being studied have been compounded by industrial affiliates such as
International Communication Materials, Inc. (ICMI) and H. B. Fuller. Capabilities for
compounding toners using the facilities at Georgia Tech are being developed so that the
composition of the toners can be varied and better controlled. Thermoplastic polyester-base toners
used for color printing on paper are also being investigated.
A Colorocs (Model # CP 4007) printer is being used in our research to xerograpically print
fabric with the test toners. This printer is a commercial color paper printer that uses four polyester-
based primary toners and has a resolution of 300 X 300 dots per inch. The test toners are mixed
with carriers to make developer systems that can be used in the xerographic machine. The
electrostatic charge on the toner and carrier particles (characterized by the triboelectric number)
National Textile Center Annual Report: August 1995 163
G95-1 4
must be compatible with the Colorocs printer. Thus, the carrier used for the developer system
must be carefully selected. Some adjustment of the triboelectric number can be made by adding
charge controlling agents.
The relationships between the physical properties of xerographic toners and the textile print
properties are being studied. The results will be used to optimize the toner properties. Toner
properties being studied include thermal and mechanical properties, flow properties such as
viscosity and surface tension, and adhesion. Using these toners, prints will be made on various
fabric samples such as 100% cotton (unfinished and finished), 100% polyester (PET), 50150
PET/cotton (unfinished and finished), and 100% nylon.
The surface interactions between toner and fabric is a subject of this investigation. The
interaction of fiber with the toner is very difficult to study directly due to geometry of the fabric.
Films simulating the surface of the fabric will be used in these studies. The films will be produced
from common fabric materials (cellulose, PET, nylon) and from experimental toners. Some of
these films will be treated with chemicals typically used in the textile finishing process. These
films will simulate fabrics finished prior to printing. Film coated with selected toners will be
produced so that the surface properties of the toners can also be evaluated. Measurements of
contact angles, surface energies, adhesion, etc., will be made to characterize the surfaces. The
surface morphologies of printed and unprinted fabric will be investigated using scanning electron
microscopy and optical microscopy. The results of the studies will be used to the explain the
interaction of toner with fabric. Screen printed and xerographic printed fabrics will be evaluated
and compared.
INK- JET PRINTING ON TEXTILES
Print engines based on the ink-jet principle have developed very rapidly over the past five
years. Manufacturers are now in third or fourth generation systems with speed and print quality
improving with each successive model. The low cost and small size of ink-jet printers have made
them competitive for computer systems, particularly for color printing.
Ink-jet printers are generally one of two major types: drop on demand or continuous jet
printers. Drop on demand printers have dominated the computer printer market due to the
simplicity of this technology and the ability to build very small printers. However, drop on
demand units suffer from inherent limitations on print speed. Continuous jet systems have been
164 National Textile Center Annual Report: August 1995
G95-1 5
the technology of choice for the few cases in which ink-jet printing has been used for textile
applications (Millitron, Stork).
Because of its importance in printing on paper, pattern design, computer image manipulation,
color transforms and physical transport systems have all been well worked out for ink-jet printing.
The hydrodynamics of ink flow and the fundamental principles of drop formation have all been
elucidated and are available in the literature. Thus, a solid base for development and application of
ink-jet printing on textile substrates is already available.
Although the hardware systems that have been developed for printing on paper can be readily
adapted for textile printing, the materials used in current paper printing systems are unacceptable
for textile applications. Existing ink formulations show poor wet fastness, poor light fastness and
low abrasion resistance. In some cases extensive pretreatment and/or post treatment of textile
substrates is required for acceptable print quality. It is clear that new material systems must be
developed for ink-jet printing to gain acceptance in the textile industry. Such systems are the goal
of the current research effort.
To function in an ink-jet system, a liquid must have low viscosity and high surface tension.
After application to the textile substrate the colorant must adhere tenaciously to the substrate and
must not alter the desirable “hand” properties of the substrate. This combination of properties
required for the ink delivery system and the properties demanded by the end use requirements is
very difficult to achieve simultaneously.
The current research is directed at both dye based and resin-pigment based printing systems. A
very strong experience base already exists for resin-pigment systems both in textile printing and in
printing on paper. This knowledge base should assist the progress in understanding and
developing resin-pigment systems for ink-jet printing on textiles. Directions for research on dye
based systems is much less clear, particularly systems that do not require extensive fabric treatment
either before or after printing.
Research on resin-pigment ink-jet printing has two major thrusts. The first thrust is directed
toward investigation of ultraviolet (UV) curable systems for resin binders. Low viscosity mixtures
of monomers, crosslinking agents and reactive diluents (either 100% active or in aqueous systems)
can be formulated that are deliverable by ink-jet systems. After application on the fabric, the
components can be polymerized using UV light and a suitable initiator to give the necessary
properties required for a good pigment binder.
National Textile Center Annual Report: August 1995 165
G95-1 6
Selection of the complex mixture that can satisfy all of the requirement for a UV curable binder
system cannot be easily accomplished by trial and error. Computer simulation is being employed
to predict properties of resin binder systems and to assist in selection of promising candidates. A
number of polymer samples have been synthesized and tested to assess the ability of the computer
simulation software to accurately predict polymer properties of interest for both ink-jet and
xerographic printing. This work will be the subject of a master’s thesis later this year.
A laboratory has been equipped to characterize candidate resin binder systems. Instruments for
measurement of viscosity, surface tension, particle size and conductivity are available to ensure that
the properties of selected systems will satisfy the electrical and hydrodynamic constraints for
ink-jet printing. An ink-jet print engine of advanced design manufactured by Imaje has been
obtained and installed to further characterize the resin binder systems and to produce test pieces for
characterization of printed fabric properties. The Kawabata Evaluation System at Georgia Tech
will be utilized to assess printed fabric “hand”
properties.
Work on colorants for ink-jet printing of textiles is also underway. It became obvious early in
the investigation of new printing technologies that the colorants developed for these new printing
systems had severe limitations in textile applications. More stable pigments and systems that could
be used to dye the resin binder are under investigation.
Work has recently been initiated on dye-based systems for ink-jet printing. These systems
have the potential to avoid the problems inherent with the reactive dyes that have been the basis for
all ink-jet work on dye based printing. This work is in an very early stage.
Addition of a multiple nozzle ink-jet printer to the laboratory to permit printing of large areas is
planned this year. This new unit will permit generation of samples for more extensive testing and
samples for studies of color gamuts that can be achieved with candidate colorants.
MOLECULAR MODELING
Computer simulation is an important tool for predicting the properties of resin binder systems
and to assist in selection of promising candidates for both ink-jet and xerographic printing. The
modeling work has a two-prong approach. The first is to predict polymer properties given a
proposed polymer structure. The second attempts to model changes in properties, especially
166 National Textile Center Annual Report: August 1995
G95-1 7
optical properties, as a function of deformation of a polymer in the context of a chain extension
methodology.
Prediction of Polymer Properties
Molecular modeling has been used to determine the relationship between molecular structure
and performance properties of polymers. The software used is Insight II, developed by Biosym
Corp., on a Silicon Graphics Indigo XS24 - 4000 workstation.
Two methods have been used to determine the relationship between molecular structure and
performance properties. These methods can be used to provide guidelines for the synthesis of
polymers having desired properties. These methods, however, have certain severe limitations, and
can only be used as very broad guidelines. A variety of polymers have been generated and their
properties predicted. On the basis of the predictions candidate polymers have been synthesized and
characterized.
QSPR (Quantitative Structure Propertv Relationships): This method uses the group contribution
method [4]. A monomer unit is considered to be made up of some permutation of the 68 groups
defined. These 68 groups can be used to build most of the polymers currently available. QSPR
can be used to predict several thermodynamic, mechanical and transport properties for amorphous
and semi-crystalline polymers and statistical copolymers.
Svnthia:
This method uses a connectivity based methodology [S], and has been optimized for
novelty polymers and statistical copolymers. A wide range of thermodynamic, mechanical and
transport properties can be predicted for the amorphous phase for polymers consisting of the nine
elements: carbon, hydrogen, nitrogen, oxygen, silicon, sulfur, fluorine, chlorine, and bromine.
No group contribution-type database need be maintained for this method.
Chain Extension Methodology
The classical rubber elasticity theory considers extension of a polymer chain to be essentially
entropic in nature caused by the disentanglement of the molecules. The theory fails to consider the
uncoiling that occurs along with extension, i.e., due to the rotation of the main-chain carbon-
carbon bonds. Each rotational state has an energy associated with it, giving rise to a different
energy level for different end-to-end lengths.
National Textile Center Annual Report: August 1995 167
G95-1 8
This study considers polyethylene as a model system, and uses Flory‘s Rotational Isomeric
State model [6] to identify the rotational states of a C-C bond. The three states are trans, gauche+
and gauche-. The idea of paired bond interactions is used; i.e., the energy of the rotational state of
the ith bond depends on the rotational state of the (i- 1) th bond. Further, the correlation segment is
determined, such that the N bond chain can be said to be a random flight chain of N/n correlation
segments. The probability distribution function of the end-to-end length for the segment can be
accurately determined computationally. This can then be used to refine the rubber elasticity theory
in terms of the entropic deformation of a chain of correlation segments. Additionally, the estimation
of the partition function as a function of the end-to-end length will also give an excellent handle on
the thermodynamics during chain deformation.
A result of this methodology is the determination of structure property relationships. The
structure parameter of interest is the end-to-end length (or the deformation) and polymer property
of interest is the polarizability tensor. The approach consists of tensorially adding the C-C and the
C-H bond polarizability tensors of the entire chain by performing appropriate coordinate
transformations. This method of estimating polarizability in the amorphous phase has a great
potential, because optical properties, flow properties, mechanical properties and dielectric
properties are related to the polarizability. As an example, we are computing how the refractive
index of the polymer changes as well as how the optical anisotropy (i.e. birefringence) changes
with chain extension. These properties are of obvious interest in designing new polymeric binder
systems to be applied to textile substrates.
REFERENCES:
1. Cook, F. L., “Textile Printing Enters The Technology Revolution,” Textile World , 145(3),
Pages 73-79 (1995).
2. Dewitt, J. W., “Freeing The Bottleneck,” Apparel Industry Magazine, 56(3), Pages QR3-QR8
(1995).
3. Carr, W. W., Cook, F.L., Lanigan, W.R., Sikorski, M.E. and Tincher, W.C., “Printing
Textile Fabrics with Xerography,” Textile Chemists and Colorists, 23(5), pages 33-41,
(1991).
168 National Textile Center Annual Report: August 1995
G95-1 9
4. van Krevelen, D. W., “Properties of Polymers: Their Estimation and Correlation with
Chemical Structure; Their Numerical Estimation and Prediction from Group Additive
Contributions,” 3rd edition, Elsevier: Amsterdam (1990).
5. Bicerano, J., “Predictions of the Properties of Polymers from their Structures,” Marcel
Dekker, Inc.: New York (1993).
6. Flory, P. J., “Statistical Mechanics of Chain Molecules,” Hanser (1989).
[Other Contributors: Graduate Students: Xiaodong Hu, Tian Lan, Xiaofel Li, Hemant Nanavati,
Songhua Shi, Sukasem Tejatanalert, Lejun Wang]
[Industrial Interactions: H. B. Fuller, International Communications Materials, Inc., Spartan
Mills, Springs Industries, Inc., Toner Research Services, Toxot Science & Applications]
National Ilkxtile Center Annual Report: August 1995 169
