U.S. patent application number 15/141679 was filed with the patent office on 2016-08-25 for marking paper products.
The applicant listed for this patent is XYLECO, INC.. Invention is credited to Marshall Medoff.
Application Number | 20160247004 15/141679 |
Document ID | / |
Family ID | 43876491 |
Filed Date | 2016-08-25 |
United States Patent
Application |
20160247004 |
Kind Code |
A1 |
Medoff; Marshall |
August 25, 2016 |
MARKING PAPER PRODUCTS
Abstract
Methods of marking paper products and marked paper products are
provided. Some methods include irradiating the paper product to
alter the functionalization of the paper.
Inventors: |
Medoff; Marshall;
(Brookline, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
XYLECO, INC. |
Wakefield |
MA |
US |
|
|
Family ID: |
43876491 |
Appl. No.: |
15/141679 |
Filed: |
April 28, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14308190 |
Jun 18, 2014 |
9342715 |
|
|
15141679 |
|
|
|
|
13440141 |
Apr 5, 2012 |
8986967 |
|
|
14308190 |
|
|
|
|
PCT/US2010/052388 |
Oct 12, 2010 |
|
|
|
13440141 |
|
|
|
|
61251633 |
Oct 14, 2009 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 33/346 20130101;
H01J 3/02 20130101; G01N 2223/102 20130101; G03C 11/02 20130101;
C08B 15/00 20130101; G06K 5/00 20130101; H01J 3/04 20130101; B32B
29/002 20130101; B32B 2262/0276 20130101; B32B 2554/00 20130101;
G06K 5/02 20130101; G21K 5/00 20130101; C08J 7/123 20130101; D21H
25/04 20130101; C12M 45/06 20130101; C12P 19/00 20130101; G01N
2223/1013 20130101; D21H 21/48 20130101; C12M 45/00 20130101 |
International
Class: |
G06K 5/02 20060101
G06K005/02; B32B 29/00 20060101 B32B029/00; D21H 21/48 20060101
D21H021/48 |
Claims
1. A marked paper product comprising: a sheet comprising a
cellulosic or lignocellulosic fibrous paper material comprising
fibers derived from a non-wood fiber source, wherein the cellulosic
or lignocellulosic fibrous material of an irradiated discrete,
predefined portion of the sheet contains functional groups or a
number thereof not present in the sheet prior to irradiation or in
a non-irradiated portion of the cellulosic or lignocellulosic
fibrous material.
2. The marked paper product of claim 1 wherein the discrete portion
of the sheet comprises a number of carboxylic acid groups that is
greater than is present in the sheet prior to irradiation or in the
non-irradiated portion of the cellulosic or lignocellulosic fibrous
material.
3. The marked paper product of claim 1 wherein the functional
groups are selected from the group consisting of aldehyde groups,
nitroso groups, nitrile groups, nitro groups, ketone groups, amino
groups, alkyl amino groups, alkyl groups, chloroalkyl groups,
chlorofluoroalkyl groups, and enol groups.
4. The marked paper product of claim 1 wherein the cellulosic or
lignocellulosic material is selected from the group consisting of
cotton, hemp, linen, rice, sugarcane, bagasse, straw, bamboo,
kenaf, jute, flax, and mixtures thereof.
5. The marked paper product of claim 1 wherein the paper further
includes synthetic fibers.
6. The marked paper of claim 6 wherein the synthetic fibers include
polyethylene and/or polypropylene.
7. The marked paper of claim 1 wherein the paper comprises a
multi-layer laminate.
8. The marked paper product of claim 1 wherein the marked paper
product comprises a note.
9. The marked paper product of claim 8 wherein the marked paper
product is a paper comprising currency.
10. The marked paper product of claim 9 wherein the currency is
paper money.
11. The marked paper product of claim 1 wherein the predefined
portion is in the form of a symbol.
12. The marked paper product of claim 10 wherein the predefined
portion is in the form of a watermark.
Description
RELATED APPLICATIONS
[0001] This application is a continuation application of U.S. Ser.
No. 14/308,190, filed Jun. 18, 2014, which is a continuation
application of U.S. Ser. No. 13/440,141, filed Apr. 5, 2012, now
U.S. Pat. No. 8,986,967, granted on Mar. 24, 2015, which is a
continuation of International Serial No. PCT/US2010/052388, filed
Oct. 12, 2010, which claims priority of U.S. Provisional
Application Ser. No. 61/251,633, filed on Oct. 14, 2009. The
entirety of each of these applications is incorporated herein by
reference.
TECHNICAL FIELD
[0002] This invention relates to methods and systems for marking
paper products, such as currency, and products produced by such
methods and systems.
BACKGROUND
[0003] Paper, as that term is used herein, refers to the wide
variety of cellulose-based sheet materials used for writing,
printing, packaging, and other applications. Paper may be used, for
example, but without limitation, in the following applications: as
paper money, bank notes, stock and bond certificates, checks,
postage stamps, and the like; in books, magazines, newspapers, and
art; for packaging, e.g., paper board, corrugated cardboard, paper
bags, envelopes, wrapping tissue, boxes; in household products such
as toilet paper, tissues, paper towels and paper napkins; paper
honeycomb, used as a core material in composite materials; building
materials; construction paper; disposable clothing; and in various
industrial uses including emery paper, sandpaper, blotting paper,
litmus paper, universal indicator paper, paper chromatography,
battery separators, and capacitor dielectrics.
[0004] In some applications, for example when paper is used as
currency and in other financial applications, it is often desirable
to be able to "mark" or "tag" the paper with a special marking that
is not visible to the naked eye, and/or cannot easily be produced
by counterfeiters. Marking can be used, for example, to prevent or
detect counterfeiting of currency, art and other valuable
documents. Marking can also be used on currency to allow the
currency to be traced and/or identified, e.g., if it is stolen or
used in a criminal transaction.
SUMMARY
[0005] The invention is based, in part, on the discovery that by
irradiating paper at appropriate levels, the functionalization of
the irradiated paper can be altered, thereby making the paper
distinguishable, e.g., by infrared spectrometry (IR) or other
techniques, from paper that has not been irradiated. In some cases,
the paper is also distinguishable from paper that has been
irradiated, but under other process conditions. As a result, paper
products such as currency can be "marked" by the methods described
herein. In some implementations, the marking is invisible to the
naked eye, e.g., it is detected by the use of instruments. In other
implementations, the marking is visible to the naked eye.
Generally, the marking is difficult to replicate without relatively
sophisticated equipment, thereby making counterfeiting more
difficult.
[0006] By "functionalization," we mean the functional groups that
are present on or within the paper.
[0007] In one aspect, the invention features methods of making a
marked paper product. Some methods include irradiating a paper
product under conditions selected to alter the functionalization of
at least an area of the paper product.
[0008] Some implementations include one or more of the following
features. The paper can be irradiated with ionizing radiation. The
dose of ionizing radiation can be at least, for example, 0.10 MRad,
e.g., at least 0.25 MRad. The dose of ionizing radiation can be
controlled to a level of about 0.25 to about 5 MRad. Irradiating
can include irradiating with gamma radiation, and/or with electron
beam radiation or other particles. Electrons in the electron beam
can have an energy of at least 0.25 MeV, e.g., from about 0.25 MeV
to about 7.5 MeV.
[0009] The methods can further include quenching the irradiated
paper product. For example, quenching can be performed in the
presence of a gas selected to react with radicals present in the
irradiated paper product.
[0010] In some cases, only a portion of the paper product is
irradiated. In some cases, only a portion of the irradiated area,
or only a portion of the paper product as a whole, is quenched. For
example, an area that is to remain unmarked and/or unquenched can
be masked.
[0011] Irradiation can occur during formation of the paper product.
Formation can include amalgamating the pulp material into a wet
paper web. Irradiating can be performed on the wet paper web or
prior to formation of the wet paper web. Formation can further
include drying the wet paper web, and irradiating can occur after
drying. In some implementations, powders, granulates, chemical
solutions, dyes, inks, or gases can be applied, singularly or in
combination, before, during, or after formation of the paper.
[0012] In another aspect, the invention features marked paper
products that include a cellulosic or lignocellulosic fibrous
material containing functional groups not present in a naturally
occurring cellulosic or lignocellulosic fibrous material from which
the marked paper product was obtained.
[0013] The cellulosic or lignocellulosic material in the paper
product can be selected, for example, from the group consisting of
fiber derived from wood and recycled paper, vegetable fiber
materials, such as cotton, hemp, linen, rice, sugarcane, bagasse,
straw, bamboo, kenaf, jute, and flax, and mixtures thereof. In some
embodiments metal or inorganic fibers can also be included with the
cellulosic or lignocellulosic material or included in a portion of
the paper product being irradiated.
[0014] In a further aspect, the invention features a method of
identifying whether a paper product is marked. The method includes
comparing the functionalization of a sample paper product to the
functionalization of a marked paper product.
[0015] In some cases, the method includes determining the
functionalization of the sample paper product using infrared
spectrometry (IR). The method may include comparing the number of
carboxylic acid groups present in the sample paper product with the
number of carboxylic acid groups present in the marked paper
product.
[0016] In some cases, the functionalization is determined using
atomic force microscopy (AFM), chemical force microscopy (CFM), or
electron spin resonance (ESR).
[0017] The paper product may be, for example, currency or a work of
art.
[0018] In any of the methods disclosed herein, functionalization
can include increasing the number of carboxylic acid groups present
in the paper. The number of carboxylic acid groups is determined by
titration.
[0019] The irradiated material can also include functional groups
selected from the group consisting of aldehyde groups, nitroso
groups, nitrile groups, nitro groups, ketone groups, amino groups,
alkyl amino groups, alkyl groups, chloroalkyl groups,
chlorofluoroalkyl groups, and enol groups.
[0020] In some implementations, the irradiated material may include
a plurality of saccharide units arranged in a molecular chain, and
from about 1 out of every 5 to about 1 out of every 1500 saccharide
units comprises a nitroso, nitro, or nitrile group, e.g., from
about 1 out of every 10 to about 1 out of every 1000 saccharide
units of each chain comprises a nitroso, nitro, or nitrile group,
or from about 1 out of every 35 to about 1 out of every 750
saccharide units of each chain comprises a nitroso, nitro, or
nitrile group. In some cases the irradiated material comprises a
mixture of nitrile groups and carboxylic acid groups.
[0021] In some embodiments, the saccharide units can include
substantially only a single type of group, such as a carboxylic
acid group, a nitrile group, a nitroso group or a nitro group.
[0022] The term "paper," as used herein, is intended to include
cellulose-containing sheet materials and composite sheet materials
containing cellulose. For example, the paper may include cellulose
in a plastic matrix, or cellulose combined with additives or
binders.
[0023] In any of the methods disclosed herein, radiation may be
applied from a device that is in a vault.
[0024] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
methods and materials similar or equivalent to those described
herein can be used in the practice or testing of the present
invention, suitable methods and materials are described below. All
mentioned publications, patent applications, patents, and other
references are incorporated herein by reference in their entirety.
In case of conflict, the present specification, including
definitions, will control. In addition, the materials, methods and
examples are illustrative only and not intended to be limiting.
[0025] Other features and advantages of the invention will be
apparent from the following detailed description, and from the
claims.
DESCRIPTION OF DRAWINGS
[0026] FIG. 1 is a diagrammatic view of a paper making system.
[0027] FIG. 2 is a diagram that illustrates changing a molecular
and/or a supramolecular structure of a fibrous material.
[0028] FIG. 3 is a perspective, cut-away view of a gamma irradiator
housed in a concrete vault.
[0029] FIG. 4 is an enlarged perspective view of region R of FIG.
3.
[0030] FIG. 5 is a schematic diagram of a DC accelerator.
DETAILED DESCRIPTION
[0031] As discussed above, the invention is based, in part, on the
discovery that by irradiating fibrous materials, i.e., cellulosic
and lignocellulosic materials, at appropriate levels, the molecular
structure of at least a cellulosic portion of the fibrous material
can be changed, changing the functionalization of the fibrous
material. In addition to marking the paper, changing the
functionalization can also favorably affect the surface properties
of a paper product, e.g., the receptivity of the surface to
coatings, inks and dyes.
[0032] Moreover, the change in molecular structure can include a
change in any one or more of an average molecular weight, average
crystallinity, surface area, polymerization, porosity, branching,
grafting, and domain size of the cellulosic portion. These changes
in molecular structure can in turn result in favorable alterations
of the physical characteristics exhibited by the fibrous materials.
Such changes are discussed in detail in U.S. Ser. No. 12/417,707,
filed Apr. 3, 2009, the full disclosure of which is incorporated
herein by reference.
[0033] Radiation can be applied at one or more selected stages of
the papermaking process. In some cases, irradiation will improve
the strength and tear resistance of the paper, by increasing the
strength of the cellulosic fibers of which the paper is made. In
addition, treating the cellulosic material with radiation can
sterilize the material, which may reduce the tendency of the paper
to promote the growth of mold, mildew of the like. Irradiation is
generally performed in a controlled and predetermined manner to
provide optimal properties for a particular application, by
selecting the type or types of radiation employed and/or dose or
doses of radiation applied.
[0034] A low dose of ionizing radiation can be applied, for
example, after pulping and before amalgamation of the pulped fibers
into a web; to the wet fiber web; to the paper web during or after
drying; or to the dried paper web, e.g., before, during, or after
subsequent processing steps such as sizing, coating, and
calendering. It is generally preferred that radiation be applied to
the web when it has a relatively low moisture content. In the
example shown in FIG. 1, irradiation can be performed during drying
and finishing, e.g., between sizing, drying, pressing and
calendaring operations, or during post-processing, e.g., to the
finished paper in roll, slit roll or sheet form.
[0035] As noted above, in some embodiments radiation is applied at
more than one point during the manufacturing process. For example,
ionizing radiation can be used at a relatively high dose to form or
to help form the pulp, and then later at a relatively lower dose to
alter the functionalization of the paper. If desired, high dose
radiation can be applied to the finished paper at selected areas of
the paper web to create locally weakened areas, e.g., to provide
tear zones.
[0036] As a practical matter, using existing technology, it is
generally most desirable to integrate the irradiation step into the
papermaking process either after pulping and prior to introduction
of the pulp to the papermaking machine, after the web has exited
the papermaking machine, typically after drying and sizing, or
during or after processing of the web into a final product. In some
cases, a finished or existing paper product, such as currency, art
or documents, can be irradiated to mark the product. However, as
noted above, irradiation may be performed at any desired stage in
the process.
Irradiating to Affect Material Functional Groups
[0037] After treatment with one or more ionizing radiations, such
as photonic radiation (e.g., X-rays or gamma-rays), e-beam
radiation or irradiation with particles heavier than electrons that
are positively or negatively charged (e.g., protons or carbon
ions), the paper becomes ionized; that is, the paper includes
radicals at levels that are detectable, for example, with an
electron spin resonance spectrometer. After ionization, the paper
can be quenched to reduce the level of radicals in the ionized
material, e.g., such that the radicals are no longer detectable
with the electron spin resonance spectrometer. For example, the
radicals can be quenched by the application of sufficient pressure
to the ionized material and/or by contacting the ionized material
with a fluid, such as a gas or liquid, that reacts with (quenches)
the radicals. Various gases, for example nitrogen or oxygen, or
liquids, can be used to at least aid in the quenching of the
radicals and to functionalize the ionized material with desired
functional groups. Thus, irradiation followed by quenching can be
used to provide pulp or paper with desired functional groups,
including, for example, one or more of the following: aldehyde
groups, enol groups, nitroso groups, nitrile groups, nitro groups,
ketone groups, amino groups, alkyl amino groups, alkyl groups,
chloroalkyl groups, chlorofluoroalkyl groups, and/or carboxylic
acid groups. These groups increase the hydrophilicity of the region
of the material where they are present. In some implementations,
the paper web is irradiated and quenched, before or after
processing steps such as coating and calendering, to affect the
functionality within and/or at the surface of the paper and thereby
affect the ink receptivity and other properties of the paper.
[0038] FIG. 2 illustrates changing a molecular and/or a
supramolecular structure of fibrous material, such as paper
feedstock, paper precursor (e.g., a wet paper web), or paper, by
pretreating the fibrous material with ionizing radiation, such as
with electrons or ions of sufficient energy to ionize the material,
to provide a first level of radicals. As shown in FIG. 2, if the
ionized material remains in the atmosphere, it will be oxidized,
e.g., to an extent that carboxylic acid groups are generated by
reaction with the atmospheric oxygen. Since the radicals can "live"
for some time after irradiation, e.g., longer than 1 day, 5 days,
30 days, 3 months, 6 months, or even longer than 1 year, material
properties can continue to change over time, which in some
instances can be undesirable.
[0039] Detecting radicals in irradiated samples by electron spin
resonance spectroscopy and radical lifetimes in such samples is
discussed in Bartolotta et al., Physics in Medicine and Biology, 46
(2001), 461-471 and in Bartolotta et al., Radiation Protection
Dosimetry, Vol. 84, Nos. 1-4, pp. 293-296 (1999). As shown in FIG.
2, the ionized material can be quenched to functionalize and/or to
stabilize the ionized material.
[0040] In some embodiments, quenching includes application of
pressure to the ionized material, such as by mechanically deforming
the material, e.g., directly mechanically compressing the material
in one, two, or three dimensions, or applying pressure to fluid in
which the material is immersed, e.g., isostatic pressing. Pressure
may be applied, e.g., by passing the paper through a nip. In such
instances, the deformation of the material itself brings radicals,
which are often trapped in crystalline domains, into proximity
close enough for the radicals to recombine, or react with another
group. In some instances, pressure is applied together with
application of heat, e.g. a quantity of heat sufficient to elevate
the temperature of the material to above a melting point or
softening point of a component of the ionized material, such as
lignin, cellulose or hemicellulose. Heat can improve molecular
mobility in the material, which can aid in quenching of radicals.
When pressure is utilized to quench, the pressure can be greater
than about 1000 psi, such as greater than about 1250 psi, 1450 psi,
3625 psi, 5075 psi, 7250 psi, 10000 psi, or even greater than 15000
psi.
[0041] In some embodiments, quenching includes contacting the
ionized material with fluid, such as liquid or gas, e.g., a gas
capable of reacting with the radicals, such as acetylene or a
mixture of acetylene in nitrogen, ethylene, chlorinated ethylenes
or chlorofluoroethylenes, propylene or mixtures of these gases. In
other particular embodiments, quenching includes contacting the
ionized material with liquid, e.g., a liquid soluble in, or at
least capable of penetrating into, the ionized material and
reacting with the radicals, such as a diene, such as
1,5-cyclooctadiene. In some specific embodiments, the quenching
includes contacting the ionized material with an antioxidant, such
as Vitamin E. If desired, the material can include an antioxidant
dispersed therein, and quenching can come from contacting the
antioxidant dispersed in the material with the radicals.
[0042] Other methods for quenching are possible. For example, any
method for quenching radicals in polymeric materials described in
Muratoglu et al., U.S. Patent Publication No. 2008/0067724 and
Muratoglu et al., U.S. Pat. No. 7,166,650, the disclosures of which
are incorporated herein by reference in their entireties, can be
utilized for quenching any ionized material described herein.
Furthermore, any quenching agent (described as a "sensitizing
agent" in the above-noted Muratoglu disclosures) and/or any
antioxidant described in either Muratoglu reference, can be
utilized to quench any ionized material.
[0043] Functionalization can be enhanced by utilizing heavy charged
ions. For example, if it is desired to enhance oxidation, charged
oxygen ions can be utilized for the irradiation. If nitrogen
functional groups are desired, nitrogen ions or any ion that
includes nitrogen can be utilized. Likewise, if sulfur or
phosphorus groups are desired, sulfur or phosphorus ions can be
used in the irradiation.
[0044] In some embodiments, after quenching, the quenched material
can treated with one or more further doses of radiation, such as
ionizing or non-ionizing radiation, and/or can be oxidized for
additional molecular and/or supramolecular structure change.
[0045] In some embodiments, the fibrous material is irradiated
under a blanket of inert gas, e.g., helium or argon, prior to
quenching.
[0046] The location of the functional groups can be controlled,
e.g., by selecting a particular type and dose of ionizing
particles. For example, gamma radiation tends to affect the
functionality of molecules within paper, while electron beam
radiation tends to preferentially affect the functionality of
molecules at the surface.
[0047] In some cases, functionalization of the material can occur
simultaneously with irradiation, rather than as a result of a
separate quenching step. In this case, the type of functional
groups and degree of oxidation can be affected in various ways, for
example by controlling the gas blanketing the material to be
irradiated, through which the irradiating beam passes. Suitable
gases include nitrogen, oxygen, air, ozone, nitrogen dioxide,
sulfur dioxide and chlorine.
[0048] In some embodiments, functionalization results in formation
of enol groups in the fibrous material. When the fibrous material
is paper, this can enhance receptivity of the paper to inks,
adhesives, coatings, and the like, and can provide grafting sites.
Enol groups can help break down molecular weight, especially in the
presence of added base or acid. Thus, the presence of such groups
can assist with pulping. In the finished paper product, generally
the pH is close enough to neutral that these groups will not cause
a deleterious decrease in molecular weight.
Masking
[0049] In some cases it may be desirable to irradiate and/or quench
only a small area of a paper product, e.g., to create a "watermark"
or to irradiate a particular symbol printed on the paper, e.g., an
"E" on currency. In such cases, the remainder of the paper product,
which is to remain unmarked, can be masked.
[0050] If only a small portion is to be irradiated, the remainder
is masked with a radioopaque material, e.g., lead or other heavy
metal. The mask should be of sufficient thickness to prevent
radiation from passing through, or to reduce the radiation that
passes through sufficiently to prevent marking. If it is desired to
mark a particular symbol, such as the E on currency, the paper
product should be in registration with the mask such that the
symbol to be marked is lined up with an opening in the mask.
Techniques for such masking are well known, e.g., in the
semiconductor industry.
[0051] If only a small portion is to be quenched, the remainder of
the paper product can be masked during quenching, e.g., with a
material that inhibits contact of the paper product with the liquid
or gas used in quenching.
Particle Beam Exposure in Fluids
[0052] In some cases, the paper, or its cellulosic or
lignocellulosic starting materials, can be exposed to a particle
beam in the presence of one or more additional fluids (e.g., gases
and/or liquids). Exposure of a material to a particle beam in the
presence of one or more additional fluids can increase the
efficiency of the treatment.
[0053] In some embodiments, the material is exposed to a particle
beam in the presence of a fluid such as air. For example, particles
accelerated in an accelerator can be coupled out of the accelerator
via an output port (e.g., a thin membrane such as a metal foil),
pass through a volume of space occupied by the fluid, and then be
incident on the material. In addition to directly treating the
material, some of the particles generate additional chemical
species by interacting with fluid particles (e.g., ions and/or
radicals generated from various constituents of air, such as ozone
and oxides of nitrogen). These generated chemical species can also
interact with the material. For example, any oxidant produced can
oxidize the material.
[0054] In certain embodiments, additional fluids can be selectively
introduced into the path of a particle beam before the beam is
incident on the material. As discussed above, reactions between the
particles of the beam and the particles of the introduced fluids
can generate additional chemical species, which react with the
material and can assist in functionalizing the material, and/or
otherwise selectively altering certain properties of the material.
The one or more additional fluids can be directed into the path of
the beam from a supply tube, for example. The direction and flow
rate of the fluid(s) that is/are introduced can be selected
according to a desired exposure rate and/or direction to control
the efficiency of the overall treatment, including effects that
result from both particle-based treatment and effects that are due
to the interaction of dynamically generated species from the
introduced fluid with the material. In addition to air, exemplary
fluids that can be introduced into the ion beam include oxygen,
nitrogen, one or more noble gases, one or more halogens, and
hydrogen.
Cooling Irradiated Materials
[0055] During treatment of the materials discussed above with
ionizing radiation, especially at high dose rates, such as at rates
greater then 0.15 Mrad per second, e.g., 0.25 Mrad/s, 0.35 Mrad/s,
0.5 Mrad/s, 0.75 Mrad/s or even greater than 1 Mrad/sec, the
materials can retain significant quantities of heat so that the
temperature of the material becomes elevated. While higher
temperatures can, in some embodiments, be advantageous, e.g., when
a faster reaction rate is desired, it is advantageous to control
the heating to retain control over the chemical reactions initiated
by the ionizing radiation, such as crosslinking and/or
grafting.
[0056] For example, in one method, the material is irradiated at a
first temperature with ionizing radiation, such as photons,
electrons or ions (e.g., singularly or multiply charged cations or
anions), for a sufficient time and/or a sufficient dose to elevate
the material to a second temperature higher than the first
temperature. The irradiated material is then cooled to a third
temperature below the second temperature. If desired, the cooled
material can be treated one or more times with radiation, e.g.,
with ionizing radiation. If desired, cooling can be applied to the
material after and/or during each radiation treatment.
[0057] Cooling can in some cases include contacting the material
with a fluid, such as a gas, at a temperature below the first or
second temperature, such as gaseous nitrogen at or about 77 K. Even
water, such as water at a temperature below nominal room
temperature (e.g., 25 degrees Celsius) can be utilized in some
implementations.
Types of Radiation
[0058] The radiation can be provided, e.g., by: 1) heavy charged
particles, such as alpha particles; 2) electrons, produced, for
example, in beta decay or electron beam accelerators; or 3)
electromagnetic radiation, e.g., gamma rays, x-rays or ultraviolet
rays. Different forms of radiation ionize the cellulosic or
lignocellulosic material via particular interactions, as determined
by the energy of the radiation.
[0059] Heavy charged particles include alpha particles, which are
identical to the nucleus of a helium atom and are produced by alpha
decay of various radioactive nuclei, such as isotopes of bismuth,
polonium, astatine, radon, francium, radium, several actinides,
such as actinium, thorium, uranium, neptunium, curium, californium,
americium and plutonium.
[0060] Electrons interact via Coulomb scattering and bremsstrahlung
radiation produced by changes in the velocity of electrons.
Electrons can be produced by radioactive nuclei that undergo beta
decay, such as isotopes of iodine, cesium, technetium and iridium.
Alternatively, an electron gun can be used as an electron source
via thermionic emission.
[0061] Electromagnetic radiation interacts via three processes:
photoelectric absorption, Compton scattering and pair production.
The dominating interaction is determined by the energy of incident
radiation and the atomic number of the material. The summation of
interactions contributing to the absorbed radiation in cellulosic
material can be expressed by the mass absorption coefficient.
[0062] Electromagnetic radiation is subclassified as gamma rays,
x-rays, ultraviolet rays, infrared rays, microwaves or radio waves,
depending on its wavelength.
[0063] Referring to FIGS. 3 and 4 (an enlarged view of region R),
gamma radiation can be provided by a gamma irradiator 10 that
includes gamma radiation sources 408, e.g., .sup.60Co pellets, a
working table 14 for holding the materials to be irradiated, and
storage 16, e.g., made of a plurality iron plates. All of these
components are housed in a concrete containment chamber (vault) 20
that includes a maze entranceway 22 beyond a lead-lined door 26.
Storage 16 defines a plurality of channels 30, e.g., sixteen or
more channels, allowing the gamma radiation sources to pass through
storage on their way proximate the working table.
[0064] In operation, the sample to be irradiated is placed on a
working table. The irradiator is configured to deliver the desired
dose rate and monitoring equipment is connected to an experimental
block 31. The operator then leaves the containment chamber, passing
through the maze entranceway and through the lead-lined door. The
operator mans a control panel 32, instructing a computer 33 to lift
the radiation sources 12 into working position using cylinder 36
attached to hydraulic pump 40.
[0065] Gamma radiation has the advantage of significant penetration
depth. Sources of gamma rays include radioactive nuclei, such as
isotopes of cobalt, calcium, technicium, chromium, gallium, indium,
iodine, iron, krypton, samarium, selenium, sodium, thalium and
xenon.
[0066] Sources of x-rays include electron beam collision with metal
targets, such as tungsten or molybdenum or alloys, or compact light
sources, such as those produced commercially by Lyncean
Technologies, Inc., of Palo Alto, Calif.
[0067] Sources for ultraviolet radiation include deuterium or
cadmium lamps.
[0068] Sources for infrared radiation include sapphire, zinc or
selenide window ceramic lamps.
[0069] Sources for microwaves include klystrons, Slevin type RF
sources or atom beam sources that employ hydrogen, oxygen or
nitrogen gases.
[0070] In some embodiments, a beam of electrons is used as the
radiation source. A beam of electrons has the advantages of high
dose rates (e.g., 1, 5, or even 10 MRad per second), high
throughput, less containment and less confinement equipment.
Electrons can also be more efficient at causing chain scission. In
addition, electrons having energies of 4-10 MeV can have
penetration depths of 5 to 30 mm or more, such as 40 mm.
[0071] Electron beams can be generated, e.g., by electrostatic
generators, cascade generators, transformer generators, low energy
accelerators with a scanning system, low energy accelerators with a
linear cathode, linear accelerators, and pulsed accelerators.
Electrons as an ionizing radiation source can be useful, e.g., for
relatively thin materials, e.g., less than 0.5 inch, e.g., less
than 0.4 inch, 0.3 inch, 0.2 inch, or less than 0.1 inch. In some
embodiments, the energy of each electron of the electron beam is
from about 0.25 MeV to about 7.5 MeV (million electron volts),
e.g., from about 0.5 MeV to about 5.0 MeV, or from about 0.7 MeV to
about 2.0 MeV. Electron beam irradiation devices may be procured
commercially from Ion Beam Applications, Louvain-la-Neuve, Belgium
or from Titan Corporation, San Diego, Calif. Typical electron
energies can be 1, 2, 4.5, 7.5, or 10 MeV. Typical electron beam
irradiation device power can be 1, 5, 10, 20, 50, 100, 250, or 500
kW. Typical doses may take values of 1, 5, 10, 20, 50, 100, or 200
kGy.
[0072] Tradeoffs in considering electron beam irradiation device
power specifications include operating costs, capital costs,
depreciation and device footprint. Tradeoffs in considering
exposure dose levels of electron beam irradiation would be energy
costs and environment, safety, and health (ESH) concerns.
Generators are typically housed in a vault, e.g., of lead or
concrete.
[0073] The electron beam irradiation device can produce either a
fixed beam or a scanning beam. A scanning beam may be advantageous
with large scan sweep length and high scan speeds, as this would
effectively replace a large, fixed beam width. Further, available
sweep widths of 0.5 m, 1 m, 2 m or more are available.
[0074] In embodiments in which the irradiating is performed with
electromagnetic radiation, the electromagnetic radiation can have
an energy per photon (in electron volts) of, e.g., greater than
10.sup.2 eV, e.g., greater than 10.sup.3, 10.sup.4, 10.sup.5,
10.sup.6 or even greater than 10.sup.7 eV. In some embodiments, the
electromagnetic radiation has energy per photon of between 10.sup.4
and 10.sup.7, e.g., between 10.sup.5 and 10.sup.6 eV. The
electromagnetic radiation can have a frequency of, e.g., greater
than 10.sup.16 hz, greater than 10.sup.17 hz, 10.sup.18, 10.sup.19,
10.sup.20 or even greater than 10.sup.21 hz. In some embodiments,
the electromagnetic radiation has a frequency of between 10.sup.18
and 10.sup.22 hz, e.g., between 10.sup.19 to 10.sup.21 hz.
[0075] One type of accelerator that can be used to accelerate ions
produced using the sources discussed above is a Dynamitron.RTM.
(available, for example, from Radiation Dynamics Inc., now a unit
of IBA, Louvain-la-Neuve, Belgium). A schematic diagram of a
Dynamitron.RTM. accelerator 1500 is shown in FIG. 5. Accelerator
1500 includes an injector 1510 (which includes an ion source) and
an accelerating column 1520 that includes a plurality of annular
electrodes 1530. Injector 1510 and column 1520 are housed within an
enclosure 1540 that is evacuated by a vacuum pump 1600.
[0076] Injector 1510 produces a beam of ions 1580, and introduces
beam 1580 into accelerating column 1520. The annular electrodes
1530 are maintained at different electric potentials, so that ions
are accelerated as they pass through gaps between the electrodes
(e.g., the ions are accelerated in the gaps, but not within the
electrodes, where the electric potentials are uniform). As the ions
travel from the top of column 1520 toward the bottom in FIG. 5, the
average speed of the ions increases. The spacing between subsequent
annular electrodes 1530 typically increases, therefore, to
accommodate the higher average ion speed.
[0077] After the accelerated ions have traversed the length of
column 1520, the accelerated ion beam 1590 is coupled out of
enclosure 1540 through delivery tube 1555. The length of delivery
tube 1555 is selected to permit adequate shielding (e.g., concrete
shielding) to be positioned adjacent to column 1520, isolating the
column. After passing through tube 1555, ion beam 1590 passes
through scan magnet 1550. Scan magnet 1550, which is controlled by
an external logic unit (not shown), can sweep accelerated ion beam
1590 in controlled fashion across a two-dimensional plane oriented
perpendicular to a central axis of column 1520. As shown in FIG. 5,
ion beam 1590 passes through window 1560 (e.g., a metal foil window
or screen) and then is directed to impinge on selected regions of a
sample 1570 by scan magnet 1550.
[0078] In some embodiments, the electric potentials applied to
electrodes 1530 are static potentials, generated, e.g., by DC
potential sources. In certain embodiments, some or all of the
electric potentials applied to electrodes 1530 are variable
potentials generated by variable potential sources. Suitable
variable sources of large electric potentials include amplified
field sources, e.g. such as klystrons. Accordingly, depending upon
the nature of the potentials applied to electrodes 1530,
accelerator 1500 can operate in either pulsed or continuous
mode.
[0079] To achieve a selected accelerated ion energy at the output
end of column 1520, the length of column 1520 and the potentials
applied to electrodes 1530 are chosen based on considerations
well-known in the art. However, it is notable that to reduce the
length of column 1520, multiply-charged ions can be used in place
of singly-charged ions. That is, the accelerating effect of a
selected electric potential difference between two electrodes is
greater for an ion bearing a charge of magnitude 2 or more than for
an ion bearing a charge of magnitude 1. Thus, an arbitrary ion
X.sup.2+ can be accelerated to final energy E over a shorter length
than a corresponding arbitrary ion X. Triply- and quadruply-charged
ions (e.g., X.sup.3+ and X.sup.4+) can be accelerated to final
energy E over even shorter distances. Therefore, the length of
column 1520 can be significantly reduced when ion beam 1580
includes primarily multiply-charged ion species.
[0080] To accelerate positively-charged ions, the potential
differences between electrodes 1530 of column 1520 are selected so
that the direction of increasing field strength in FIG. 5 is
downward (e.g., toward the bottom of column 1520). Conversely, when
accelerator 1500 is used to accelerate negatively-charged ions, the
electric potential differences between electrodes 1530 are reversed
in column 1520, and the direction of increasing field strength in
FIG. 5 is upward (e.g., toward the top of column 1520).
Reconfiguring the electric potentials applied to electrodes 1530 is
a straightforward procedure, so that accelerator 1500 can be
converted relatively rapidly from accelerating positive ions to
accelerating negative ions, or vice versa. Similarly, accelerator
1500 can be converted rapidly from accelerating singly-charged ions
to accelerating multiply-charged ions, and vice versa.
[0081] Various methods may be used for the generation of ions
suitable for ion beams which may be used in treating the paper or
the starting cellulosic or lignocellulosic materials. After the
ions have been generated, they are typically accelerated in one or
more of various types of accelerators, and then directed to impinge
on the material to be treated. Various types of accelerators and
ion beam generating equipment are described in U.S. Ser. No.
12/417,707, incorporated by reference hereinabove.
Doses
[0082] In some embodiments, irradiating (with any radiation source
or a combination of sources) is performed until the material
receives a dose of at least 0.05 MRad, e.g., at least 0.1, 0.25,
1.0, 2.5, or 5.0 MRad. In some embodiments, irradiating is
performed until the material receives a dose of between 0.1 and 2.5
MRad. Other suitable ranges include between 0.25 MRad and 4.0 MRad,
between 0.5 MRad and 3.0 MRad, and between 1.0 MRad and 2.5
MRad.
[0083] The degree of functionalization achieved is generally higher
the higher the dose.
In some embodiments, the irradiating is performed at a dose rate of
between 5.0 and 1500.0 kilorads/hour, e.g., between 10.0 and 750.0
kilorads/hour or between 50.0 and 350.0 kilorads/hours. When high
throughput is desired, e.g., in a high speed papermaking process,
radiation can be applied at, e.g., 0.5 to 3.0 MRad/sec, or even
faster, using cooling to avoid overheating the irradiated
material.
[0084] In some embodiments in which coated paper is irradiated, the
paper coating includes resin that is cross-linkable, e.g.,
diacrylate or polyethylene. In some cases, the resin crosslinks as
the paper is irradiated, which can provide a synergistic effect to
optimize the scuff resistance and other surface properties of the
paper. In these embodiments, the dose of radiation is selected to
be sufficiently high so as to achieve the desired functionalization
of the paper, i.e., at least about 0.25 to about 2.5 MRad,
depending on the material, while being sufficiently low so as to
avoid deleteriously affecting the paper coating. The upper limit on
the dose will vary depending on the composition of the coating, but
in some embodiments the preferred dose is less than about 5
MRad.
[0085] In some embodiments, two or more radiation sources are used,
such as two or more ionizing radiations. For example, samples can
be treated, in any order, with a beam of electrons, followed by
gamma radiation and/or UV light having wavelengths from about 100
nm to about 280 nm. In some embodiments, samples are treated with
three ionizing radiation sources, such as a beam of electrons,
gamma radiation, and energetic UV light.
Identifying Marked Paper Products
[0086] Paper products that have been marked using the methods
described herein are distinguishable from similar looking unmarked
paper products by determining the functionality of the paper. This
can be accomplished, for example, by preparing an IR scan of the
paper in question, using an infrared spectrometer, and comparing
the scan to a "control" IR scan of a marked paper. For example, if
the marked paper has been by functionalized so as to increase the
number of carboxylic acid groups in the paper, the IR scan of a
paper being tested to see whether it has been similarly marked
should have a carboxyl peak that is substantially the same height
as the carboxyl peak in the control IR scan.
[0087] Alternative methods of testing whether a paper has been
marked or not include AFM, CFM, and ESR.
Paper Additives
[0088] Any of the many additives and coatings used in the
papermaking industry can be added to or applied to the fibrous
materials, papers, or any other materials and products described
herein. Additives include fillers such as calcium carbonate,
plastic pigments, graphite, wollastonite, mica, glass, fiber glass,
silica, and talc; inorganic flame retardants such as alumina
trihydrate or magnesium hydroxide; organic flame retardants such as
chlorinated or brominated organic compounds; carbon fibers; and
metal fibers or powders (e.g., aluminum, stainless steel). These
additives can reinforce, extend, or change electrical or mechanical
properties, compatibility properties, or other properties. Other
additives include starch, lignin, fragrances, coupling agents,
antioxidants, opacifiers, heat stabilizers, colorants such as dyes
and pigments, polymers, e.g., degradable polymers,
photostabilizers, and biocides. Representative degradable polymers
include polyhydroxy acids, e.g., polylactides, polyglycolides and
copolymers of lactic acid and glycolic acid, poly(hydroxybutyric
acid), poly(hydroxyvaleric acid),
poly[lactide-co-(e-caprolactone)],
poly[glycolide-co-(e-caprolactone)], polycarbonates, poly(amino
acids), poly(hydroxyalkanoate)s, polyanhydrides, polyorthoesters
and blends of these polymers.
[0089] If desired, various cross-linking additives can be added.
Such additives include materials that are cross-linkable themselves
and materials that will assist with cross-linking of the cellulosic
or lignocellulosic material in the paper. Cross-linking additives
include, but are not limited to, lignin, starch, diacrylates,
divinyl compounds, and polyethylene. In some implementations, such
additives are included in concentrations of about 0.25% to about
2.5%, e.g., about 0.5% to about 1.0%.
[0090] When additives are included, they can be present in amounts,
calculated on a dry weight basis, of from below about 1 percent to
as high as about 80 percent, based on total weight of the fibrous
material. More typically, amounts range from between about 0.5
percent to about 50 percent by weight, e.g., from about 0.5 percent
to about 5 percent, 10 percent, 20 percent, 30, percent or more,
e.g., 40 percent.
[0091] Any additives described herein can be encapsulated, e.g.,
spray dried or microencapsulated, e.g., to protect the additives
from heat or moisture during handling.
[0092] Suitable coatings include any of the many coatings used in
the paper industry to provide specific surface characteristics,
including performance characteristics required for particular
printing applications.
[0093] As mentioned above, various fillers can be included in the
paper. For example, inorganic fillers such as calcium carbonate
(e.g., precipitated calcium carbonate or natural calcium
carbonate), aragonite clay, orthorhombic clays, calcite clay,
rhombohedral clays, kaolin clay, bentonite clay, dicalcium
phosphate, tricalcium phosphate, calcium pyrophosphate, insoluble
sodium metaphosphate, precipitated calcium carbonate, magnesium
orthophosphate, trimagnesium phosphate, hydroxyapatites, synthetic
apatites, alumina, silica xerogel, metal aluminosilicate complexes,
sodium aluminum silicates, zirconium silicate, silicon dioxide or
combinations of the inorganic additives may be used. The fillers
can have, e.g., a particle size of greater than 1 micron, e.g.,
greater than 2, 5, 10, or 25 microns or even greater than 35
microns.
[0094] Nanometer scale fillers can also be used alone, or in
combination with fibrous materials of any size and/or shape. The
fillers can be in the form of, e.g., particles, plates or fibers.
For example, nanometer sized clays, silicon and carbon nanotubes,
and silicon and carbon nanowires can be used. The fillers can have
a transverse dimension less than 1000 nm, e.g., less than 900, 800,
750, 600, 500, 350, 300, 250, 200, or 100 nm, or even less than 50
nm.
[0095] In some embodiments, the nano-clay is a montmorillonite.
Such clays are available from Nanocor, Inc. and Southern Clay
products, and have been described in U.S. Pat. Nos. 6,849,680 and
6,737,464. The clays can be surface treated before mixing into,
e.g., a resin or a fibrous material. For example, the clay can be
surface treated so that its surface is ionic in nature, e.g.,
cationic or anionic.
[0096] Aggregated or agglomerated nanometer scale fillers, or
nanometer scale fillers that are assembled into supramolecular
structures, e.g., self-assembled supramolecular structures can also
be used. The aggregated or supramolecular fillers can be open or
closed in structure, and can have a variety of shapes, e.g., cage,
tube or spherical.
[0097] Lignin Content
[0098] The paper products discussed herein can contain lignin, for
example up to 1, 2, 3, 4, 5, 7.5, 10, 15, 20, or even 25% by weight
of lignin. This lignin content can be the result of the lignin
present in the lignocellulosic material(s) used to manufacture the
paper. Alternatively, or in addition, lignin can be added to the
paper as an additive, as mentioned above. In this case, the lignin
can be added as a solid, e.g., as a powder or other particulate
material, or can be dissolved or dispersed and added in liquid
form. In the latter case, the lignin can be dissolved in solvent or
a solvent system. The solvent or solvent system can be in the form
of a single phase or two or more phases. Solvent systems for
cellulosic and lignocellulosic materials include DMSO-salt systems.
Such systems include, for example, DMSO in combination with a
lithium, magnesium, potassium, sodium or zinc salt. Lithium salts
include LiCl, LiBr, LiI, lithium perchlorate and lithium nitrate.
Magnesium salts include magnesium nitrate and magnesium chloride.
Potassium salts include potassium iodide and nitrate. Examples of
sodium salts include sodium iodide and nitrate. Examples of zinc
salts include zinc chloride and nitrate. Any salt can be anhydrous
or hydrated. Typical loadings of the salt in the DMSO are between
about 1 and about 50 percent, e.g., between about 2 and 25, between
about 3 and 15 or between about 4 and 12.5 percent by weight.
[0099] In some cases, lignin will cross-link in the paper during
irradiation, further enhancing the physical properties of the
paper.
Paper Types
[0100] Paper is often characterized by weight. The weight assigned
to a paper is the weight of a ream, 500 sheets, of varying "basic
sizes," before the paper is cut into the size as sold to end
customers. For example, a ream of 20 lb, 81/2.times.11'' paper
weighs 5 pounds, because it has been cut from a larger sheet into
four pieces. In the United States, printing paper is generally 20
lb, 24 lb, or 32 lb at most. Cover stock is generally 68 lb, and
110 lb or more.
[0101] In Europe the weight is expressed in grams per square meter
(gsm or just g). Printing paper is generally between 60 g and 120
g. Anything heavier than 160 g is considered card stock. The weight
of a ream therefore depends on the dimensions of the paper, e.g.,
one ream of A4 (210 mm.times.297 mm) size (approx
8.27''.times.11.7'') weighs 2.5 kilograms (approx 5.5 pounds).
[0102] The density of paper ranges from 250 kg/m.sup.3 (16
lb/ft.sup.3) for tissue paper to 1500 kg/m3 (94 lb/ft.sup.3) for
some specialty paper. In some cases the density of printing paper
is about 800 kg/m.sup.3 (50 lb/ft.sup.3).
[0103] The processes described herein are suitable for use with all
of these grades of paper, as well as other types of paper such as
corrugated cardboard, paper board, and other paper products. The
processes described herein may be used to treat paper that is used,
for example, in any of the following applications: as postage
stamps; as paper money, bank notes, securities, checks, and the
like; in books, magazines, newspapers, and art; and for packaging,
e.g., paper board, corrugated cardboard, paper bags, envelopes, and
boxes. The paper may be single-layer or multi-layer paper, or may
form part of a laminate. The marking can be used in commerce to
indicate purchase, use, or other events. For example, marking can
be used to "cancel" postage, or to indicate where and/or when an
item was purchased.
[0104] The paper may be made of any desired type of fiber,
including fiber derived from wood and recycled paper, as well as
fiber derived from other sources. Vegetable fiber materials, such
as cotton, hemp, linen, and rice, can be used alone or in
combination with each other or with wood-derived fibers. Other
non-wood fiber sources include, but are not limited to, sugarcane,
bagasse, straw, bamboo, kenaf, jute, flax, and cotton. A wide
variety of synthetic fibers, such as polypropylene and
polyethylene, as well as other ingredients such as inorganic
fillers, may be incorporated into paper as a means for imparting
desirable physical properties. It may be desirable to include these
non-wood fibers in paper used in special application such as for
paper money, fine stationary, art paper and other applications
requiring particular strength or aesthetic characteristics.
[0105] The paper may be irradiated before or after printing.
Process Water
[0106] In the processes disclosed herein, whenever water is used in
any process, it may be grey water, e.g., municipal grey water, or
black water. In some embodiments, the grey or black water is
sterilized prior to use. Sterilization may be accomplished by any
desired technique, for example by irradiation, steam, or chemical
sterilization.
Other Embodiments
[0107] It is to be understood that while the invention has been
described in conjunction with the detailed description thereof, the
foregoing description is intended to illustrate and not limit the
scope of the invention, which is defined by the scope of the
appended claims. Other aspects, advantages, and modifications are
within the scope of the following claims.
* * * * *