U.S. patent number 3,790,389 [Application Number 05/115,727] was granted by the patent office on 1974-02-05 for photoxidizable compositions.
This patent grant is currently assigned to Monsanto Company. Invention is credited to Robert A. Heimsch, Eric T. Reaville.
United States Patent |
3,790,389 |
Heimsch , et al. |
February 5, 1974 |
PHOTOXIDIZABLE COMPOSITIONS
Abstract
This invention relates to light sensitive compositions
comprising a photosensitizer and a substrate useful in preparing
photographic images.
Inventors: |
Heimsch; Robert A. (St. Louis,
MO), Reaville; Eric T. (Webster Groves, MO) |
Assignee: |
Monsanto Company (St. Louis,
MO)
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Family
ID: |
22363071 |
Appl.
No.: |
05/115,727 |
Filed: |
February 16, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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644121 |
Jun 7, 1967 |
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Current U.S.
Class: |
430/286.1;
430/374; 430/920; 522/63; 522/129; 522/166; 522/182 |
Current CPC
Class: |
G03C
1/73 (20130101); G03F 7/0045 (20130101); Y10S
430/121 (20130101) |
Current International
Class: |
G03C
1/73 (20060101); G03F 7/004 (20060101); G03c
001/68 () |
Field of
Search: |
;96/98,87,115,36
;260/314 ;204/159.23 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Torchin; Norman G.
Assistant Examiner: Kimlin; Edward C.
Attorney, Agent or Firm: Kennedy; Joseph D. Upham; John D.
Willis; Neal E.
Parent Case Text
This application is a continuation-in-part of an earlier copending
U.S. Pat. application Ser. No. 644,121, filed June 7, 1967.
This invention relates to photosensitive surfaces useful in
photography and photo-copy reproduction processes. More
particularly, this invention provides new photosensitive
compositions suitable for coating surfaces to impart thereto the
ability to receive a photographic latent or visual image, and also
provides new photosensitized surfaces useful directly for replica
or image reproduction and copy work. The invention also includes
processes for copying by developing the latent images which are
produced on surfaces of photosensitive articles of this invention,
using the compositions of this invention.
In the graphic arts industry represented by photography,
photoengraving, photolithography, collotype, etc. silver halides
and diazo compounds have been used as photosensitive materials to
absorb energy from the light spectrum in processes for making
photographic images and in reprography. Such photosensitive agents
have usually required close control of chemicals used, time and
amount of treatment to develop the images of objects replicated on
the surface by exposure of the object of the photosensitive surface
in the light spectrum. Such processes are both expensive and
impractical, however, when it is desired to prepare numerous copies
or replicas of an object or image on an inexpensive surface such as
a cellulosic web for example cellulosic films, paper sheets and
boards, and closely woven cellulosic textiles. In addition, the
chemicals often used to develop and fix the silver halide or diazo
photosensitized surfaces often need close temperature and
concentration control, or the use of water solutions to effect
acceptable reproduction on the photosensitized surface.
It is therefore desirable to find photosensitive materials and
substrates which can be placed on smooth surfaces to effect simple,
inexpensive photoreproduction of images exposed thereon without the
need for special facilities such as dark rooms, and for extensive
controls on time of exposure to light, developer type, or
concentration.
In addition, it is well known that silver used in most photographic
and reproduction processes is in short supply, thereby making it
desirable to develop a commercial inexpensive non-silver halide
process.
An object of this invention is to provide new, simple and
inexpensive photosensitive elements useful for receiving latent or
visual images as in photographic print or photocopy reproduction
processes.
A further object of this invention is to provide new and useful
methods for effecting photoreproduction of image forming objects
using a minimum of liquid reagents.
A more specific object of this invention is to provide new types of
photosensitized surfaces which are inexpensive and easily used in
photo-reproduction work to effect simple photocopy operations with
a minimum of chemical treatment.
Other and different objects, features and advantages of this
invention will become apparent to those skilled in the art upon
consideration of the following detailed description thereof and the
examples attendent thereto.
We have discovered that photosensitized oxidation, of a type
previously known, may be used to produce a latent image in a
suitable substrate by imagewise exposure of the substrate to light
in the presence of light and proper photosensitizers. The latent
image is in terms of non-migrating hydroperoxide groups
differentially distributed in a film of a suitable matrix or binder
of constraining properties. The hydroperoxide groups can be
produced in direct proportion to the light intensity on each
differential area. The latent image can be rendered visible by
various development techniques dependent on the difference in
properties between exposed and non-exposed regions.
In accordance with this invention, a base member is treated on at
least one surface thereof with (1) a photochemically oxidizable
substrate and (2) an organic photo-oxidizing sensitizer, which can
absorb radiant energy from that portion of the electromagnetic
spectrum between and including the near infrared and the
ultraviolet to effect a transfer of oxygen from the surroundings to
form a chemical bond between the oxygen and the substrate, said
radiant energy being hereinafter referred to as "light" or "light
energy". The resulting treated surface of this invention upon
exposure to light applied through an image forming object generates
a latent or visible image which can be fixed or developed by
treating the light exposed treated surface with a suitable dye
solution. For the purpose of this invention in preferred aspects,
the photochemically oxidizable substrate (1) is defined as a
coatable chemical substance containing or to which is added a
photochemically oxidizable double bond system, said substrate being
sufficiently stable under the conditions of use herein that it can
be retained on a base support in the presence of air. Furthermore,
upon exposure of the treated surface to light, said substrate can
be chemically attacked by the excited state oxygen generated by the
sensitizer (2) to effect chemical change in the substrate (1)
sufficient to change the affinity or attraction of the substrate
for the dye solution in the areas of chemical attack or which may
be amplified or developed by organic solvents or other chemical
reagents.
The photooxidizable substrate (1) may be any natural or synthetic
material containing suitable carbon-to-carbon unsaturation, which
material is spreadable on a suitable base support such as a glass
or metal plate, a plastic solid or sheet, or a paper sheet or board
surface, etc., and is sufficiently non-volatile at the temperature
used. For use of this invention at ordinary room temperature the
substrate material should have a molecular weight above about 140
so that it will not be removed from the surface or from the
reaction site by migration in the oxidized form or by evaporation
from the treated surface. The photooxidizable substrate may contain
the suitable carbon-to-carbon unsaturation as part of its structure
or molecules containing suitable carbon-to-carbon unsaturation may
be added thereto. Higher molecular weight polymers or other
materials may be used as a binder for low molecular weight
materials containing the unsaturation to provide a suitably stable
layer or film for imaging.
Natural materials which may be used include rosin and the double
bond containing components thereof, terpenes such as abietic acid,
neoabietic acid, maleopimaric acid, levopimaric acid,
.alpha.-pinene, camphene, 3-carene, citronellol, aldehyde modified
rosin materials such as formaldehyde modified rosins, and fortified
rosin materials such as those obtained by reacting the rosin with
alpha, beta-olefinically unsaturated polycarboxylic acids and
anhydrides thereof, and partial and complete esters of such acids
as maleic acid, fumaric acid, itaconic acid, aconitic acid,
citraconic acid, etc., both saponified or unsaponified with an
alkaline material. Other examples include the use of unsaturated
fatty oils either in the glyceride ester form or in the free acid
form. A few examples of such oils include olive, peanut, almond,
neat's foot, pecan nut, lard, tung, safflower, cottonseed and
soybean oils. Non-glyceride source unsaturated oils such as tall
oil may also be used.
Unsaturated hydrocarbons of natural and synthetic origin, may also
be used. Examples of such materials include the aliphatic
olefinically unsaturated hydrocarbons having an average of at least
about 10 carbon atoms, e.g., 1-dodecene, 1-tridecene,
1-tetradecene, 1-pentadecene, 1-hexadecene, 1-docosene,
1-pentacosene and the internally unsaturated olefins such as
7-heptadecene, 7,10heptadecadiene, etc., the aromatic olefinically
unsaturated hydrocarbons in the unpolymerized form such as
isopropenyl toluene, phenylisobutene, phenylhexadiene and
isopropenyl naphthalene.
Natural and synthetic polymeric materials containing unreacted
carbon-to-carbon double bonds therein may also be used as the
photooxidizable substrate material in practicing this invention.
The carbon-to-carbon unsaturation may be intralinear, e.g.,
--CH.sub.2 --CH=CH--CH.sub.2 --, a vinylene linkage, terminal,
e.g., --CH.sub.2 --CH=CH.sub.2 vinyl, ##SPC1##
vinylidene and the like. Attached groups to the aforedescribed
entities may be linear or branched. In general, the polymeric
backbone will be hydrocarbon in structure with any halide, ester,
ether, hydroxyl, nitrile, phenyl or other group present in the
polymer molecule appended to the polymeric backbone.
It will be understood that the vinyl compounds are a species of
vinylidene compounds since they contain the characteristic CH.sub.2
=CH-- group, the indicated free carbon valence being satisfied by
another atom in the polymer molecule. The term "vinylidene" is used
herein to include both vinylidene and vinyl unsaturation.
Illustrative examples of these olefinically unsaturated polymers
include natural rubbers, homopolymers, copolymers and polymers from
three or more monomers prepared from diolefins such as butadiene,
isoprene, 2,3-dimethyl-1,3-butadiene, piperylene, chloroprene,
bromoprene, 2-acetoxy-butadiene-1, 3, 2-methyl-pentadiene,
2-ethylhexadiene; and polymers prepared from diolefins such as
those aforementioned and compounds containing a vinyl or a
vinylidene group such as:
a. Vinyl ethers, e.g. vinyl alkyl ethers such as vinyl ethyl ether,
vinyl butyl ether, vinyl octyl ether, vinyl dodecyl ether, vinyl
tetradecyl ether, vinyl hexadecyl ether, vinyl octadecyl ether and
vinyl alkenyl ethers, e.g., vinyl ether, vinyl octenyl ether, vinyl
tetradecenyl ether, vinyl octadecenyl ether;
b. vinyl esters, e.g. vinyl acetate, vinyl butyrate, vinyl
caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl
palmitate, vinyl stearate;
c. vinyl halides, e.g. vinyl chloride, vinyl bromide;
d. vinyl ketones, e.g. vinyl methyl ketone;
e. vinyl sulfides, sulfoxides and sulfones, e.g. vinyl ethyl
sulfide; vinyl propyl sulfoxide, vinyl tert-butyl sulfone;
f. vinylidene compounds, e.g. vinylidene chloride;
g. acrylic, methacrylic acids or crotonic acids and their
derivatives, e.g. acrylic acid, acrylonitrile, methacrylamide,
crotonamide;
h. acrylic, methacrylic esters or crotonic esters, e.g. methyl
methacrylate, ethyl acrylate, propyl acrylate, amyl acrylate,
heptyl acrylate, octyl methacrylate, nonyl acrylate, undecyl
acrylate, tetradecyl acrylate, hexadecyl acrylate, octadecyl
acrylate, ethenyl acrylate, hexenyl methacrylate, dodecenyl
acrylate, octadecenyl arcylate, ethyl crotonate;
i. allyl esters, e.g. allyl acetate, allyl butyrate, allyl
caprylate, allyl caprate, allyl laurate, allyl myristate, allyl
palmitate, allyl stearate;
j. allyl alkyl ethers, e.g. allyl ethyl ether, allyl octyl ether,
allyl dodecyl ether, allyl tetradecyl ether, allyl hexadecyl ether,
allyl octadecyl ether, and vinyl alkenyl ethers, e.g. allyl ethenyl
ether, allyl octenyl ether, allyl tetradecenyl ether, allyl
octadecenyl ethers;
k. cycloaliphatic vinyl compounds, e.g, vinyl cyclohexane;
l. aryl vinyl compounds, e.g. styrene, vinyltoluene, vinylbiphenyl,
vinyl naphthalene and the ar-chloro substituted styrenes;
m. heterocyclic vinyl compounds, e.g. vinyl pyridine and vinyl
dihydropyrane;
n. alpha-olefins, e.g. ethylene, propylene, butene-1, octene-1,
dodecene-1, tetradecene-1, hexadecene-1 and heptadecene-1,
dichloroethylenes, tetrafluoroethylene; and
o. branched olefins, e.g. isobutylene, isoamylene, 2, 3,
3-trimethyl-1-butene.
It is to be understood that the unsaturated polymers which are used
in the practice of this invention can also be prepared by
copolymerization of two or more different diolefins, e.g. from a
mixture of butadiene and piperylene, either in the presence or
absence of one or more non-dienic copolymerizable monomers.
The preferred vinyl or vinylidene monomers are those having at
least one valence attached to an electronegative group such as a
double or triply bonded carbon, e.g. vinyl, propynyl, or other
groups such as phenyl, nitrile, carboxy and the like. The preferred
vinylidene co-monomers are represented, e.g. by the classes of
monomers listed hereinbefore in (a), (b), (c), (d), (g), (h), (k),
(l), (m) and (o). The hydrocarbon vinyl monomers represented by
monomers listed by monomer classes (l) and (o) are particularly
preferred. The amount of copolymerized diolefin monomer in a
copolymer of diolefin monomer and vinyl monomer is generally from
about 0.1 to 99 percent by weight. However, when polymers of
copolymerized diolefin monomer and vinyl monomer are used it is
preferred that they contain at least about 1 percent by weight of
copolymerized diolefin monomer.
The physical characteristics of the olefinically unsaturated
polymers which can be photooxidized in accordance with the present
invention may vary from low molecular weight polymer oils
containing relatively few olefinic bonds to high molecular weight
rubbers and resins such as those resulting from the polymerization
or copolymerization of diolefins in the presence or absence of one
or more non-dienic copolymerizable monomers.
The sensitizers or photosensitizers as they are sometimes called
herein, which may be used as component (2) in practicing this
invention in general undergo no permanent chemical change. The
sensitizer may be any organic compound or mixture of compounds
which become excited by photon absorption and enter into a sequence
of chemical reactions with atmospheric oxygen causing a
photochemical oxidation reaction to occur in which the substrate
(1) becomes oxidized and the sensitizer is generally regenerated at
the end of the cycle.
Prefered photosensitizers used herein are referred to generally as
being of the porphyrin type. The porphyrin type of photosensitizer
may be described as any compound having the porphin structure,
i.e., four pyrrole rings connected by single carbon or nitrogen
atoms, which includes related compounds such as the prophyrazines,
phthalocyanines or chlorophylls.
Particular photosensitizers useful in practicing the present
invention are the aromatic group meso-substituted porphin
compounds. Among such aromatic substituted prophins are the
ms-tetraarylporphins (ms-meso). These compounds are those porphins
in which aryl groups having from six to 24 carbon atoms are
substituted on the bridging carbon atoms of the porphin ring
structure which contains four pyrrol nuclei linked together in a
circular pattern by four bridging carbon atoms to form a great
ring. Examples of aryl groups which may be substituted in the
meso-position of these compounds are phenyl, chlorophenyl,
dichlorophenyl, methylphenyl, N,N-dimethyl-aminophenyl,
hydroxyphenyl, naphthyl, biphenyl, anthracyl, phenanthryl, etc. In
addition to the substituents in the aryl group substituents noted
above, the aryl groups can also have any or a combination of such
substituents, e.g., as alkyloxy (one to 20 carbon atoms)
substituents such as methoxy, ethoxy, isopropoxy, butoxy, hexyloxy,
etc., as well as any other substituents which do not change the
fundamental aromatic character of the groups. These porphin
sensitizers including the above exemplified arylporphins, can have
various other substituents, particularly at the beta and beta'
positions of the pyrrole rings, e.g., such substituents as lower
alkyl (one to 20 carbon atoms) such as vinyl or allyl or alkanoic
acid groups such as methylcarboxy or ethylcarboxy.
Examples of porphin compounds which are useful as photochemical
sensitizers in practicing this invention are the arylporphins such
as the tetraphenyltetrazoporphins and the complexes thereof, such
as diamagnetic complexes, e.g., magnesium
tetraphenyltetrazoporphin, tetraphenyl tetrazoporphin acetate,
tetraphenyltetrazoporphin sulfate, zinc tetraphenyltetrazoporphin,
and the meso-aryl porphins including alpha, beta, gamma,
delta-naphthylporphin and the diamagnetic metal chelates thereof,
e.g.,
tetraphenylporphin
tetrakis(2,4-dichlorophenyl)porphin
tetrakis(2-furyl)porphin
tetrakis(4-methoxyphenyl)porphin
tetrakis(4-methylphenyl)porphin
tetrakis(2-thienyl)porphin
tetraphenylporphin zinc complex
tetrakis(4-nitrophenyl)porphin
tetrakis(4-dimethylaminophenyl)porphin zinc complex;
the tetrabenzomonoazo- and tetrabenzodiazo porphins, the
1,2,3,4,5,6,7,8-octaphenylporphins and azoporphins such as
octaphenylporphyrazine, the tetrabenzoporphins, e.g.,
tetrabenzoporphin and the zinc complex of tetrabenzoporphin.
Other useful porphin types of photosensitizing materials which may
be used include chlorophyll, such as chlorophyll a and chlorophyll
b, hemin, the tetrazoporphins, chlorophyllin salt derivatives such
as the reaction product of an alkaline metal chlorophyllin salt and
sodium bisulfite, hematoporphin, mercury proto- and
hemato-porphins, vitamin B.sub.12 and its derivatives and tetrakis
(1-naphthyl) porphin.
Related porphin type materials which may be used include the
phthalocyanines including the metal-free phthalocyanine and metal
complexes of phthalocyanine such as the zinc and magnesium
complexes of phthalocycanine, as well as phthalocyanine derivatives
such as the barium or calcium salts of the phthalocyanine sulfonic
acid, acetylated phthalocyanine, alkoxy- and
aryloxy-benzosubstituted phthalocyanines,
5,5',5",5'"-tetraamino-metalphthalocyanine-4,4',4",4'"-tetrasulfonic
acid, magnesium tetra(4)methylthiophthalocyanine, arylthioethers of
phthalocyanines, vinyl group containing tetraazoporphins and
polymers therof, mercaptoamino phthalocyanine derivatives and
phthalocyanine.
Other useful photosensitizers which can be used include fluorescein
type dyes and light absorber materials based on a triarylmethane
nucleus. Such compounds are well known and include Crystal Violet,
Malachite green, Eosin, Rose Bengal and the like.
Another group of photosensitizers particularly useful in the
ultraviolet region include the aromatic compounds such as
acetophenone, benzophenone, benzoin, benzil and triphenylene.
Light necessary in the practice of this invention can vary
considerably in wave lengths, depending on the sensitizer in this
system. The light can be monochromatic or polychromatic. Light of
wave lengths in the range of 3,600 to 8,000 Angstroms has been
found very suitable.
The present invention is concerned with the use of a photochemical
oxidation of organic carbon-to-carbon double bonds in the substrate
in a manner which makes this phenomenon useful for
photo-reproduction purposes. The photooxidizable substrate (1) and
the photo-sensitizer (2) are put together on a suitable surface,
light is brought to bear on the treated surface in an amount in
controlled areas to effect photooxidations of discernible
intensities and then the photochemical reaction is stopped by
removal of intense light. The extent of oxidation which is allowed
to occur may vary widely depending upon the substrate (1) and the
sensitizer (2), and the dye receptivity characteristics of the
oxidized substrate. For example, a substrate (1) such as a
polyisoprene polymer coated on a desired surface will require more
oxidation to make a bright image than will a substrate consisting
of a polymer of 60 parts of styrene and 40 parts of butadiene
because of the difference in the dye receptivity characteristics of
the two substrates. With substrates such as styrene-butadiene
containing polymers containing about 60 parts of styrene and about
40 parts of butadiene, and optionally containing small amounts of
other functional monomers such as itaconic acid or anhydride,
oxidation sufficient to provide for the uptake of about
10.sup.-.sup.9 to about 10.sup.-.sup.7 moles of oxygen per square
centimeter of coated surface is generally quite suitable for
producing an intense image upon treating the surface with a dye.
Generally, developable images can be obtained when oxidation has
occured to an extent sufficient to provide for the uptake of about
10.sup.-.sup.2 to about 10.sup.-.sup.10 moles of oxygen per square
centimeter of substrate surface. The depth of the oxidation into
the substrate is not known. However, as an example, with the above
referred to styrene-butadiene polymer substrate, oxidation to the
extent of 10.sup.-.sup.8 to 10.sup.-.sup.9 moles of oxygen/per
square centimeter uptake by the polymer corresponds to a minimum
coating depth of about 250 to 500 Angstroms if all of the double
bonds in the polymer were oxidized. It will be recognized that in
this application of the photooxidation reaction to the weight
concentration of the photosensitizer (2) relative to the weight
concentration of the organic carbon-to-carbon unsaturated
photooxidizable substrate (1) need only be quite small for the
desired purpose. It is not necessary to effect oxidation of all of
the available unsaturation in the substrate, that is, it is not
necessary to oxidize all of the carbon-to-carbon double bonds in
the substrate. It is sufficient that enough of such oxidation takes
place to permit the formation of developable latent images which
can be made visible by treating the oxidized surface with a dye, or
by other methods.
The photosensitizer (2) and the photooxidizable substrate (1) may
be applied to the desired surface separately, or as a single
composition by conventional methods such as incorporation in a
suitable diluent emulsion technique. They may also be applied with
suitable pigments wherein the photooxidizable material (2) acts not
only as the photooxidizable substrate but also as a component of a
pigment binder or adhesive. A typical example of a useful polymeric
composition used for this purpose is a 48 percent solids
styrene/butadiene aqueous latex emulsion used either alone or in
combination with starch or casein type materials as pigment binders
in the coating of paper surfaces to make high quality printing
papers. Within the scope of this invention a coating composition is
prepared so as to contain a small amount of the photosensitizer,
e.g., tetraphenylporphin, a pigment or mixture of pigments,
typically a kaolin clay and titanium dioxide and a binder or
adhesive, e.g. an aqueous latex of styrene/butadiene copolymer, the
total solids content in such composition ranging from about 10
percent to 70 percent by weight. The coating composition may be
applied to a suitable paper sheet or board, or to a metal, plastic
or glass article of manufacture may be used immediately or stored,
and packaged for future use for effecting photocopying according to
this invention.
It will be appreciated by those skilled in the art that the
selection of the diluent or other means used with the
photosensitive compositions will depend upon the nature of the
substrate being treated and the photosensitizer being applied in
order to obtain a complete surface coverage.
Exemplary of the diluents which may be used alone or in combination
with the photosensitizer compositions of this invention are
chlorinated hydrocarbons such as ethyl chloride, methylene
chloride, chloroform, carbon tetrachloride, trichloropropane,
monochlorobenzene, trichloroethylene, perchloroethylene,
difluorodichloro-methane, ortho-chlorobenzene, chlorinated
polyphenyls, chlorinated paraffins and the like; hydrocarbons such
as heptane, hexane, cyclohexane, eiscosane, octadecene, benzene,
xylene, toluene and the like; polyethylene glycols, butyl
cellosolve; esters such as methyl acetate, ethyl acetate, carbitol
acetate, di-2-ethylhexyl phthalate, dimethyl phthalate, dimethyl
cellosolve phthalate, ditetrahydrofurfuryl phthalate and the like;
acetone, methylethyl ketone, cyclohexanone, undecanone, etc.;
dibutyl stearate dimethyl sulfoxide and the like.
When the photooxidation reaction has progressed to the desired
extent for photo-reproduction purposes of this invention, the
reaction may be essentially stopped by removal of the
photo-reproductive element, i.e., the element containing the
combination of photooxidation sensitizer (2) and the
photooxidizable substrate (1) from intense light. Usually from
about 10 seconds, say up to about 60 seconds exposure to the
equivalent of the light energy absorbed from a 1,000 watt white
light, 12 inches away from the photo-reproduction element is
sufficient to induce a photochemical reaction suitable for making a
clear print of the object to be copied.
The dyes used in this invention to fix or develop the images
produced in the photo-oxidation step of this invention may be any
dye which has varying affinities for oxidized and non-oxidized
sites on the light exposed treated surface. Dyes generally found
useful in this invention are the organic soluble or oil soluble
dyes such as the alcohol soluble dyes or kerosene soluble dyes,
e.g., the triphenylmethane type, azo dyes and disperse dyes. We
have found that dyes dissolved in a solvent such as deodorized or
highly refined kerosene are directed generally to the non-oxidized
portion of the exposed treated surface and that dyes dissolved in
an alcohol such as 2-ethylhexanol are directed chiefly to the
oxidized portions of the exposed treated surface. The particular
site at which the dye locates itself appears to depend on the
selective swelling characterisitcs of the solvent used, the effect
of the dye on the solubility parameter of the solvent, and on the
polarity of the dye. Although these factors appear to control the
direction of the dye, the actual chemical or physical mechanism of
the direction and image application brought by the dye is not fully
understood.
The solvents or dispersants which are used for the dye may be any
organic material which will (1) dissolve or disperse the dye and
which will aid in selectively directing the dye to the oxidized or
non-oxidized regions of the exposed treated surface so that the
differences in photooxidation in the various areas of the surface
can be readily made apparent thereby. Suitable solvent or diluents
for the dyes which can be used include low melting molten waxes,
liquid alkanes, cycloalkanes, alkanes mixed with aromatic compounds
such as benzene, toluene, xylene, chlorobenzene, etc., aliphatic
fatty acids having from six to 24 carbon atoms, molten unsaturated
fatty acids such as palmitic acid, higher liquid aliphatic alcohols
having from six to about 20 carbon atoms, and such higher alcohols
mixed with up to about 50 percent of lower alcohols, aliphatic
esters which are liquid or low melting (below 100.degree.C) solids
at room temperatures such as triacetin, ethyl hexanoate, methyl
oleate. The dyes may be used in any desired concentration in the
solvent or diluent but a solution containing about 0.1 to about 6
percent of dye by weight in the selected solvent is generally
sufficient for most fixing or developing purposes of this
invention. The dyes may also be applied as a solid.
Examples of dyes found in the Colour Index which are useful for
amplifying or developing latent images produced with a positive
image forming object, e.g., a typewritten opaque white sheet,
include Sudan Brown, Sudan Red, or Calco Oil Red dissolved in
deodorized kerosene. Examples of dyes useful for amplifying or
developing latent images produced with a negative image forming
object, e.g., a photographic negative film, include Crystal Violet,
Malachite Green, Victoria Blue or Nigrosine B dissolved in
2-ethylhexanol.
The site to which the dye is directed depends both on the dye and
the solvent. For example, Sudan Brown dissolved in kerosene goes
preferentially to the non-oxidized site. A strongly basic dye like
Crystal Violet goes preferentially to the oxidized sites except at
sites where higher amounts of oxidation have occurred. In those
areas of higher oxidation inversion appears to occur with the dye
being rejected at too highly oxidized sites.
The dyes may be simply wiped on the exposed photooxidized element
as with a rag, brush, or sprayed on or applied by other
conventional methods, and then dried as by wiping the dye treated
surface with a dry cloth or tissue. The result is a clear, useful
print or copy of the object to be copied or reproduced.
Chelates, graphite, metal oxides as solids and the like may also be
used on the exposed photooxidized surfaces to prepare the desired
products and are picked up because of differential tack produced by
photooxidation.
The photosensitizers (2) used in practicing this invention may be
used alone or in combination to make more effective use of the
incident light spectrum radiation, so long as the combined
sensitizers do not quench or neutralize the light absorbing ability
of each other. For example, Rose Bengal and Methylene Blue may be
used as sensitizers in combination with the preferred porphin type
of sensitizers such as tetraphenylporphin. Suitable base or support
materials include metals, e.g., steel, aluminum plates, zinc,
copper, magnesium, sheets and foils, glass, wood, paper,
composition board, cloth, cellulose esters, e.g., cellulose
acetate, cellulose propionate, cellulose butyrate, etc., the films
or plates composed of various film-forming synthetic resins or high
polymers, such as the addition polymers, including those mentioned
in both monomeric and polymeric form for use in the photooxidizable
layer and in particular the vinylidene polymers, e.g., the vinyl
chloride copolymers with vinyl chloride, vinyl acetate, styrene,
isobutylene and acrylonitrile; the linear condensation polymers
such as the polyesters, e.g., polyethylene terephthalate; the
polyamides, e.g., polyhexamethylene sebacamide, polyester amides;
e.g., polyhexamethylene adipamide/adipate, etc. Fillers or
reinforcing agents can be present in the synthetic resin or polymer
bases such as the various fibers (synthetic, modified or natural)
e.g., cellulosic fibers, for instance, cotton, cellulose acetate,
viscose rayon, paper; glass, wood; nylon and the like. These
reinforced bases may be used in laminated form.
The imagery process of this invention which makes use of visible
light, a photosensitizer composition and a substrate such as
styrene-butadiene is capable of producing a latent image by using
reflex, reflective and transmittive systems. The latent image so
prepared is made visible by suitable dye systems to produce high
quality continuous tone pictures.
The latent image may also be used to selectively deposit finely
divided solids, metals and/or metal oxides and chelates. If
graphite is used, it may be used as a conducting base for
electroplating metals. If natural rubber is used as the substrate,
the unexposed area may be selectively dissolved to produce a relief
image. Multicolor images are also contemplated by the practice of
this invention.
The compositions of this invention have a wide utility and are
generally useful in the graphic arts, wherein a reproduction of a
drawing, design, plan, etc., is desired. Thus, in the manufacture
of templates for use in preparing parts of airplanes, automobiles,
boats, radio and electrical equipment, etc., the materials to be
used, such as steel, aluminum, etc., are coated with the
light-sensitive compositions of this invention, dried, exposed
through the master drawing and developed. The finished print is an
exact reproduction of the original and adheres firmly to the metal
or other material. Stencils or lettered transparencies may also be
used to reproduce directions, identification numbers, etc., on
parts of finished articles of manufacture. The photosensitive film
elements of the present invention may also be used as print stock
in the production of black and white prints.
The photosensitized layer is exposed to light, generally through a
process transparency, e.g., a process negative or positive (an
image-bearing transparency consisting solely of substantially
opaque and substantially transparent areas where the opaque areas
are substantially of the same optical density), the so-called line
or halftone negative or positive.
It is possible to expose the photosensitized layer through paper or
other light transmitting materials. A stronger light source or
longer exposure times must be used, however. Reflex exposure can
also be used, e.g., in copying from paper or translucent films.
Light sources suitable for use in the practice of this invention
include carbon arcs, tungsten and mercury-vapor arcs, fluorescent
lamps, argon glow lamps, electronic flash units, photographic flood
lamps and sunlight.
The present invention is particularly concerned with imaging
procedures utilizing photosensitized oxygen transfer reactions in
which light in the presence of a sensitizer causes the oxygen to
oxidize the carbon-to-carbon unsaturated substrate by being added
to one carbon atom of a double bond with shift of the double bond
to the allyl position and movement of the allylic hydrogen atom to
the oxygen atom of the oxygen molecule which is not attached to the
carbon atom. The reaction can be postulated: ##SPC2##
The aforesaid oxygen transfer reaction does not include
autooxidations, proceeding by a free radical mechanism in which
irradiation with light serves to initiate free radicals and cause
the formation of free radical sites in the substrate by hydrogen
abstraction. The true photosensitized oxidation or oxygen transfer
reactions used herein are characterized by the fact that they can
proceed using wavelengths of light which may be ineffective for
autooxidation and by the fact that in general ordinary oxidation
inhibitors do not retard the reaction.
The photosensitized oxygen utilized herein involves what is
referred to by Gollnick and Schenck (K. Gollnick and G. O. Schenck,
Pure and Applied Chemistry, Vol. 9, 507 [1964]) as a Type 2
reaction, or "photosensitized oxygen transfer". The reaction
involves some excited oxygen species, whether pictured as an oxygen
molecule itself in an excited singlet state, or an excited
sensitizer-oxygen adduct. Irradiation with light appears to
transform the sensitizer to an excited state, such as a triplet
state: ##SPC3##
The sensitizer then transfers its energy to oxygen. This can be
postulated as ##SPC4##
and the excited singlet delta oxygen can then add to the double
bond as pictured above. It should be understood that if the triplet
energy of the sensitizer is above 37 kcal., singlet sigma oxygen
may also be produced. It may react directly or decay to the lower
energy delta species. The reaction involves light energy to excite
the sensitizer and produce an excited state oxygen which reacts
with the substrate to cause addition of oxygen to one of the
doubly-bonded carbons thereof. The reaction ordinarily does not
include any chain propagation, but only one oxygen addition per
photo absorbed at quantum yield of unity. The photosensitized
reaction can proceed using wave lengths of light other than
ultraviolet, and ordinary oxidation inhibitors do not inhibit the
reaction. A sensitizer-oxygen adduct is presumably formed but is
apparently short-lived; however it should be understood that the
oxidation is effective regardless of what the mechanism and exact
contribution of the adduct to the oxidation of the olefin may
be.
In another aspect, the present invention can utilize an oxidation
reaction in which a hydrogen atom is abstracted to give a radical
and oxygen is then added. For example the Type 1 reaction in the
foregoing Gollnick and Schenck article involves a reaction in which
the allylic hydrogen atom at C-3 is abstracted to give a mesomeric
mono-radical ##SPC5##
and oxygen is then attached at either of radical sites C.sub.1 or
C.sub.3, and the peroxyradicals thus formed extract hydrogen from
the C-3 position of the olefin to give hydroperoxides and a new
mesomeric radical, thus permitting chain propagation. Sensitizers
which are voracious hydrogen abstractors when excited by light
energy are suitable for use in such reaction. One group in such a
class is the carbonyl compounds, as for example, benzophenone,
acetophenone, etc. Aside from olefins containing allyl hydrogen,
other types of materials containing labile hydrogen can undergo
reactions similar to that of Type 1 to produce materials containing
hydroperoxy groups, and such materials can be used for photoimaging
in accordance with this aspect of the invention, for example, such
materials as ditetrahydrofurfuryl phthalate, di-2-ethylhexyl
phthalate, compounds containing tertiary hydrogen, etc. If such
materals are liquid they will generally be used in conjunction with
a polymer or some other high molecular weight binder to provide a
suitable matrix. In oxidations involving abstraction of labile
hydrogen to generate free radicals, other reactions such as
cross-linking can also occur and may interfere with the desired
photoimaging reaction, and such oxidations, while part of the
present invention and useful to some extent, are not in accord with
the preferred aspects of the present invention.
Sensitizers which can function in both Type 1 and Type 2 reactions
include benzophenone, acetophenone, benzil, benzoin, etc. These
carbonyl type sensitizers require ultraviolet light of suitable
wave length for excitation. Sensitizers which also function in both
Type 1 and Type 2 reactions, but are active in the visible region
as well as the ultraviolet region of the spectrum include eosin,
fluorescein, rose bengal, etc. Sensitizers which are not hydrogen
abstracters and which function largely or wholly by energy
interchange as in Type 2 reactions, include the various porphyrin
type photosensitizers. In general photosensitizers capable of Type
2 sensitization are much preferred, and ordinarily the better ones
of this Type are not very effective as Type 1 photosensitizers.
Moreover, the absence of Type 1 activity minimizes side reactions.
There will be variations in the effectiveness of sensitizers with
the physical type of phase involved and more generally its
environment and it will be understood that the sensitizers utilized
herein will be those effective under the conditions of use. The
sensitizers described above are known to function in liquid phase.
In the practice of this invention some systems have involved the
post-application of a sensitizer-solvent system to an already
pre-formed film. The resulting system can be called a quasi-solid
phase as it consists of a solid polymer lightly swollen with a
swelling solvent system. In such a quasi-solid phase, the
sensitizers listed above and similar photosensitizers are found to
effect photochemical addition of oxygen, although with great
variation in effectiveness. In the practice of the invention it is
also feasible to use solid phase systems in which the sensitizer
has been incorporated into a polymeric film composition which has
not been swollen by solvent. In the solid phase such sensitizers as
rose bengal, fluorescein, eosin, methylene blue, etc. did not
exhibit significant photoimaging capability in reasonable exposure
times. Benzophenone, acetophenone, benzil, etc., were found to
require high level of application, circa 10 percent, and prolonged
exposure, circa 30 minutes at ultraviolet flux of 7 .times.
10.sup.5 ergs/cm.sup.2 /sec. in order to show substantial
photoimaging capability. In contrast to this, porphyrins, such as
tetraphenyl porphin are very active at levels as low as 0.1 percent
at a flux of 2.5 .times. 10.sup.5 ergs/cm.sup.2 /sec. for 1 to 2
minutes. Triphenylene in the solid phase seems to function largely
by cross-linking, making it of little value for continuous tone
image production.
The photosensitizers can be placed in solid phase by incorporation
into a coating solution, emulsion, melt, or suspension etc. and
application to a support. After evaporation, drying, or other means
of removing volatile solvents or other liquid medium, the
photosensitizer remains in the residual coating composition
dispersed in solid form in the solid composition. Even if the
photosensitizer is incorporated by post-application with a solvent,
it can be converted to the solid state by permitting the solvent to
evaporate. For ease of handling and reproducibility, it is
preferred that the photosensitive compositions be dry at the time
of photoimaging. It will be recognized that in referring to the
photosensitizer as being in a solid medium, it is not meant to
exclude such resilience, elasticity or other properties as may be
desirable in photosensitive films for various purposes, and that
plasticizers or low molecular weight materials may be present for
such purposes. Thus the solid state contrasts with the quasi solid
state in which liquid is present to swell the polymer structure as
in a plastisol or organosol and to provide a liquid medium in which
the photosensitizer can be present, aside from how much of the
photosensitizer is actually present in such medium.
The photosensitizer as employed will generally be of a type
suitable for producing a desired amount of oxygen addition in the
particular photosensitive composition upon degrees of light
exposure within ranges of practicality for some photoimaging
applications. For most applications it will be desirable that a
required energy absorption be no greater than 10.sup.7
ergs/cm.sup.2, or possibly 10.sup.8 ergs/cm.sup.2 in some
applications, and preferred that such absorption be sufficient with
a concentration of photosensitizer no greater than 1 percent by
weight of the photosensitive composition, for example with a flux
sufficient to obtain such absorption over a 2-minute exposure
period. The energy required for imaging will generally lie in the
range of 1 to 10 .times. 10.sup.6 ergs/cm.sup.2. Absorptions with
usual imaging procedures are frequently of the order of 2.5 .times.
10.sup.4 ergs/sec./cm.sup.2. The foregoing energy ranges are those
generally employed with the concentrations of photosensitizer
generally used, but increasing the concentration makes it possible
to use shorter exposure time for the photoimaging as the imaging
requirements are approximately in inverse proportion to the
photosensitizer concentration. The use of various amplifying means
also makes it possible to lower the energy requirements. In order
to have practical value in a photoimaging system, a photosensitizer
as used should produce an oxygen uptake of at least about
10.sup.-.sup.9 moles/cm.sup.2 with an absorbed energy of 10.sup.7
ergs. A styrene-butadiene polymer (40 wt. parts styrene/60 wt.
parts butadiene) film can suitably be used for determining oxygen
uptake at particular energy absorptions.
Only a portion of the applied light flux will be absorbed by the
sensitizer, with that portion varying with the absorption
characteristics of such sensitizer, as well as with the wave length
of the light. Absorptions may, for example, be less than 10
percent, or of the order of 7 percent in some cases. Visible light
can effectively be used in the present invention, and this is a
definite advantage as it avoids the cost and loss in efficiency
which results from having to produce light in particular ranges,
such as the ultra violet range. In the present invention it is not
necessary to utilize the ultra violet range, and in fact, the range
of 4,000 to 4,500 angstroms appears most efficient. If desired,
light in ranges above 4,000 angstroms can be used to avoid possible
ultra violet catalysis of competing reactions, although this is not
ordinarily necessary. While visible light is effective, the present
materials can generally be handled in ordinary daylight, such as by
removing the photosensitive material from the intense light used
for exposure, and carrying out development or other steps without
special precaution to avoid further exposure to ordinary ambient
light.
The preferred sensitizers for use herein belong to the class of
porphyrins which are compounds with pyrrol rings linked together by
carbon atoms to form a conjugated double bond structure, and in
which one or more of the carbon atoms, i.e. methine groups, can be
replaced by a nitrogen atom, and which class also includes the
phthalocyanines and benzoporphyrins, as well as the
meso-arylporphyrins, or other compounds having various substituents
on the basic porphyrin structure. The tetraaryl porphyrins,
particularly tetraphenyl porphyrin, are characterized by the
capability to utilize energy from three of the main areas of the
visible light spectrum, i.e., the blue, green and red areas and
therefore to make efficient use of light energy. Such sensitizers
can be termed panchromatic photooxidation sensitizers and are
particularly valuable. Some other sensitizers are active only in
limited areas of the spectrum, for example chlorophyll absorbs
mainly in the red region. Aside from efficiency, the panchromatic
sensitizers are advantageous for multi-color work in that it makes
it possible to use a single sensitizer for exposures to reproduce
different colors from an original, rather than having to change
sensitizers for each of the main segments of the color spectrum.
Tetraphenyl porphyrin absorbs most strongly in the violet, and less
in the green and least in the red, which is advantageous in that
visible light is the reverse, being strong in the red, etc., and
therefore the sensitizer compensates for the variation in
light-intensity and tends to equalize the effect of different
intensities. Utilizing the panchromatic sensitizers, the present
invention produces images from multi-color transparencies. If
polychromatic light is used with a single exposure, the resultant
image will not ordinarily exhibit appreciable differentiation
between the colors, but the image produced will have parts
corresponding to the various colors. The image can be developed by
applying a single dye to give a monochromatic image, e.g., red and
white, or by using a solvent to dissolve areas either corresponding
to the colored regions or the non-colored regions. The present
invention also works for the production of multi-color images. For
example color separations can be used to provide separate exposures
for the different colors, and the exposures can then have colors
applied to correspond to the original, coloring either the oxidized
or the non-oxidized areas. The exposures can then be assembled in
register to provide a multi-color image corresponding to an
original. A laminate of appreciable thickness is thus provided
having portions which have been hydroperoxidized by image-wise
exposure to light, and with coloring materials present in either
hydroperoxide portions or non-hydroperoxide portions to present an
image to the viewer. In this particular embodiment the
hydroperoxide areas corresponding to different colors are present
at different levels in the laminate. Other expedients may be
employed to provide oxidized or non-oxidized areas in an image with
colors of proper correspondence to an original.
For the production of images of practical value, an uptake of about
10.sup.-.sup.9 moles oxygen per cm.sup.2 is ordinarily required and
usually is in a range from 10.sup.-9 to 10.sup.-.sup.6 moles
oxygen/cm.sup.2. The oxygen is incorporated into the molecules of
the coating as chemically-bonded oxygen. The bonded oxygen is more
concentrated on the surface with generally decreasing concentration
with depth into the film, e.g., the concentration per cm.sup.3
measured at a 5 micron depth may be about double that measured at a
10 micron depth, although the relationship is generally a
non-linear curve. If the 10.sup.-.sup.9 moles is considered as
distributed in a 10 micron thickness, the average concentration is
10.sup.-.sup.6 moles/cm.sup.3, or about 10.sup.-.sup.6 moles
O.sub.2 /gram of film, assuming the film has a density near one. An
exemplary styrene-butadiene polymer substrate can have about 2
butadiene moieties for each styrene moiety, and the gram molecular
weight of this --B--S--B-- unit is 212. Thus there is about
0.000212 moles per polymer unit, and the uptake of 10.sup.-.sup.9
to 10.sup.-.sup.6 moles O.sub.2 per cm.sup.2 represents 0.000212 to
0.212 moles oxygen, or hydroperoxy groups, per --B--S--B-- unit in
the polymer. This can also be expressed as a range from about 1
hydroperoxy group for every 50,000 carbon atoms in the polymer up
to about one hydroperoxy group for every 50 carbon atoms in the
polymer. While there will be variances in the degree of desired
oxidation with different polymers, the foregoing is largely a
matter of the concentration of hydroperoxy groups (or moles of
oxygen combined) in the quantity of material (in the 10 micron
film), and will be generally valid regardless of the particular
polymer. If the film contains non-photooxidizable polymers or other
materials, as well as the photooxidizable polymer, the above ratios
of hydroperoxy groups can be considered on the basis of the carbon
atoms in the total composition, so as to have about 10.sup.-.sup.6
to 10.sup.-.sup.3 moles O.sub.2 per gram of film. While the amount
of oxidation will generally be within the foregoing ranges, it is
to be understood that higher degrees of oxidation can be employed,
up to 100 percent of that theoretically possible for oxidation of
all photooxidizable unsaturated groups, but the use of degrees of
oxidation higher than the foregoing does not ordinarily result in
advantageous changes in the property attributes significant for
photoimaging. The desired degree of oxidation will depend to some
extent on the type of develoment contemplated, e.g., solvent
dissolution development may require more oxidation.
It is known that various kinds of reactions can be catalyzed by
light and that various kinds of reagents influence the cause of
such ractions. Thus such reactions as photopolymerization, or photo
cross-linking have been used for photoimaging purposes. Under some
conditions some of the sensitizers and oxidizable materials
employed herein are capable of undergoing such reactions. However,
under the conditions and with the components utilized herein such
competing processes are minimized or eliminated and the predominant
reaction utilized herein is that involving addition of oxygen with
chemical bonding to an organic substrate. Thus the materials
employed herein will generally not involve any materials with
readily polymerizable monomers, at least not with sensitizers apt
to cause polymerization thereof, and an ample supply of ambient
oxygen will be present to permit the desired photooxidation, and
also to some extent to serve to inhibit polymerization or
cross-linking in the case of some components prone to such
reactions. Any cross-linking or polymerization which accompanies
the predominant oxidation reaction will desirably be very minor in
nature and not result in appreciable changes in properties of the
composition, as for example, not causing any substantial change in
solution viscosity of such polymer. Such reactions as chain
scission, cross-linking, and carbonyl formation are possible side
reactions which are ordinarily minor in nature, and may not even
involve the sensitizers employed herein, but simply be possible
side reactions which can occur upon exposure of some kinds of
substrates to light. It is to be recognized that addition of oxygen
in accordance herewith will generally produce hydroperoxy groups as
taught herein.
The photoimaging procedure of the present invention causes a
gradual change in properties with the intensity of the light
exposure and is well suited for the production of continuous tone
images, e.g., for producing prints of ordinary pictures, as well as
for half-tones or stencils. The degree of hydroperoxidation
increases directly with the light exposure and a graph of image
density vs. light exposure shows a gradual curve over a
considerable range, rather than a steep slope. In this respect the
present process contrasts with many processes involving solvent
development of a latent image produced by cross-linking or
polymerization, in which the polymeric material is usually either
soluble or insoluble, without much gradation therebetween. Aside
from the chemical bonding with oxygen, and allylic shift of the
double bond, the molecular structure of the substrate is
essentially unchanged by the imaging procedure, i.e., the polymeric
chains are ordinarily substantially the same length and
configuration as in the substrate prior to imaging. There may be
some minor cross-linking isomerization, or scission, and some minor
loss in unsaturation, but not in quantities sufficient to change
significantly such polymer attributes as molecular weight, etc.
Characteristically, most of the polymers employed are soluble in
toluene, benzene, etc., both before and after exposure. There are,
of course, some solubility changes due to the presence of the polar
hydroperoxy group, but the toluene solubility is as stated. To have
particular coating properties, it may at times be desirable to
utilize a polymer substrate having some cross linking in its
structure, but the post-imaging structure will in such case still
be substantially the same as the pre-imaging structure. For most
applications it will be desirable to utilize essentially linear
structures, or those having only a moderate or light amount of
cross-linking. When development by solvent dissolution is
contemplated, the polymer structure and solubility should be
matched with the proposed developing solvents. Even when dye
development is contemplated, the structure has some significance,
as cross-linking has some influence on the degree to which
dye-containing solvents are absorbed by the polymer. For some
applications it is preferred to utilize essentially linear
polymers, and to produce by the imaging procedure essentially
linear polymers containing hydroperoxy groups. While the
photoimaging procedure does not cause cross-linking, it is possible
by other or further treatments to bring about cross-linking. For
example, thermal treatments can be employed to cause reactions of
the hydroperoxy groups with cross linking.
In the photooxidation of the present invention the oxygen becomes
bonded to one of the carbons of the polymer substrate, but the
double bond is retained in the polymer. There may be some loss of
residual unsaturation in the polymer, but it should be minor
compared to the oxidation, and the major proportion of such
unsaturation will ordinarily still be present after the exposure.
In common photopolymerization or photo cross-linking procedures,
double bonds are utilized in a polymerization or cross-linking
procedure, and are to some extent used up in such reactions, so
that the residual unsaturation is much less after imaging than
before imaging. In the preferred aspect of the invention the
hydroperoxy group is formed on one of the carbons of the original
double bond, with an allylic shift, so that in final conformation
the hydroperoxy group is in the allyl position with respect to the
double bond. The latent photoimages produced in the present
invention are formed of hydroperoxy groupings, particularly allylic
hydroperoxy groupings, which can be developed in various ways as
taught herein. Developability is generally based upon the
hydroperoxy group, so the image can still be developed if the
allylic group should become saturated.
Dyes, pigments, or other coloring materials can be used for
developing images in accordance with the present invention, and the
colorents or coloring materials can be chromatic or achromatic and
include the various colors of the spectrum.
The photoimaging in the present invention depends upon the change
in properties caused by addition of oxygen to molecular structures
of the photosensitive substrate, and appears to a considerable
extent to be due to the polarity of hydropoeroxy groups in such
molecules. The photooxidation makes possible differentially
profound point-by-point property changes in a film due to
differential distribution of non-migrating hydroperoxy groups in
such film. The differential distribution of hydroperoxide
accurately reproduces the intensity of light to which each
differential area was exposed and the difference in chemical and
physical properties of the hydroperoxidized regions compared to the
non-exposed regions results in a latent image which can be rendered
visible by difference in dye sorption, solubility, surface tack or
other properties. For the differences caused by the photooxidation
to be most evident, it is desirable that the original
photosensitive composition not have groups with properties similar
to hydroperoxides, although some such groups can be tolerated, even
though contributing to an objectionable background in some
photoimaging procedures. Such polar groups as carboxy, hydroxyl,
nitrile, etc. may mask the photoimaging effect of hydroperoxy
groups to some extent. For this reason some of the preferred
polymers for use herein are hydrocarbon polymers with residual
unsaturation, e.g., styrene/butadiene copolymers, etc. However, for
the effect upon the original solvent solubility, or upon mechanical
film properties it may at times be desirable to use polymers having
various substituents, such as halogen, nitrile, carboxyalkyl, etc.
and polymers containing such substituents can be used if some loss
in photoimaging sensitivity can be tolerated in the particular
application in view. In general it will be preferred that polar
monomers not constitute more than three-fourths of the monomer
content of a copolymer used as the photooxidizable substrate in the
present invention.
To be effective for photoimaging, the hydroperoxy groups formed
should not migrate appreciably from the relative position in which
they were formed. In general this does not constitute any problem
with the polymeric systems generally employed herein. However, it
can be appreciated that an oxidizable material dissolved as a
free-flowing solution would have little value as such as a
photooxidizable substrate. Ordinarily any film forming materials
can be used in the photosensitive compositions of the present
invention to provide a stable matrix to prevent migration of the
oxygen-containing substituents. Polymers of the various types
disclosed herein as substrates can be used, as can various other
film forming materials. Even relatively low molecular weight
non-volatile materials containing carbon-to-carbon double bonds can
be used as the photooxidizable component in conjunction with other
suitable binder materials sufficient to provide a stable layer or
stratum for photoimaging. In general coating compositions with
sufficient binder materials to provide a stable coating or film
will have a suitable matrix to prevent undue migration of
oxidizable materials in such compositions. Of course, some of the
materials disclosed herein have both the needed oxidizable groups
and the properties suitable for forming stable films or coatings,
e.g., high molecular weight polymers containing residual
unsaturation, such as styrene/butadiene copolymers. Thus in general
there will be no need for using separate binder materials, but the
use of such are fully consonant with the present invention. Even
though a particular polymer in itself has all the properties
necessary to serve as a photooxidizable substrate, it may
nevertheless also be used in conjunction with other polymeric
binder materials which do not have photooxidizable groups; or in
conjunction with other materials which do have such photooxidizable
groups.
Aside from characteristics of the photosensitive compositions for
forming latent photoimages in accordance herewith, various other
mechanical or other properties of the polymers will have
significance with respect to ease of coating application,
durability and handling properties of the film, but in general
those skilled in the art will be able to select appropriate
materials for particular applications, particularly in view of the
present disclosure.
One class of polymers suitable for use herein are solid,
substantially linear materials having a weight average molecular
weight of at least 50,000 and having at least one carbon-to-carbon
double bond with an allylic hydrogen adjacent thereto for about
every fifty carbon atoms. A more limited class of such polymers are
hydrocarbon in structure to avoid possible adverse effects of polar
or other substituents.
It may be noted that the light absorptions in the present process
are often several orders of magnitude higher than those utilized in
some other photoimaging processes, e.g., say 1 to 10 .times.
10.sup.6 ergs/cm.sup.2 compared to 10 to 100 ergs/cm.sup.2 for some
processes utilizing a photopolymerization reaction. This is to a
considerable extent a reflection of the fact that the present
procedure is not a chain propagation reaction, while
photopolymerization processes generally are.
Claims
1. A method of obtaining an image which comprises exposing a coated
surface to light in the presence of oxygen with a replica of an
image interposed between the light source and the coated surface,
to oxidize the surface forming a chemical bond between oxygen and
the coating composition to an extent sufficient to give the
oxidized portions as selective affinity by polarity for alcohol
soluble dyes, the coating composition comprising a photochemically
oxidizable substrate having aliphatic carbon-to-carbon unsaturation
and an oxidation photosensitizer capable of absorbing radiant
energy in that portion of the electromagnetic spectrum from the
near infrared through the ultraviolet to effect a transfer of
oxygen from the surroundings to form a chemical bond between oxygen
and the coating
2. The method of claim 1 in which the photosensitizer is an aryl
porphyrin.
3. The method of claim 1 in which the photosensitizer is
4. A method of obtaining an image which comprises selectively
photooxidizing a coated surface by contact with oxygen and exposure
to light with a replica of an image interposed between the light
source and the coated surface to an extent for an uptake of at
least about 10.sup..sup.-9 moles of oxygen per square centimeter of
coated surface, the coated surface comprising a photochemically
oxidizable substrate having aliphatic carbon-to-carbon
unsaturation, and an oxidation
5. A method as described in claim 4 in which a visible image is
formed by
6. The method of claim 4 in which a visible image is formed by
absorbtion
7. The method of claim 4 in which a relief image is formed by
dissolving a
8. The method of claim 4 in which portions of the image which have
not been
9. The method of claim 4 in which the photosensitizer is
substantially
10. A method of obtaining an image which comprises exposing
imagewise to light in the presence of oxygen a layer comprising a
photosensitizer and a photochemically oxidizable polymer having
aliphatic carbon-to-carbon unsaturation, causing addition of oxygen
to said polymer forming chemical bonds therewith in exposed areas
while otherwise substantially retaining the structure of such
polymer, thereby forming a latent image in said
11. The method of claim 5 in which a continuous tone transparency
is used
12. The process of developing a latent image which comprises
providing a layer containing a polymer having carbon-to-carbon
double bonds with a latent image composed of allylic hydroperoxy
groupings in some areas while other areas lack such groupings, and
developing such image by treatment with a coloring material which
has selective affinity for one of such
13. The process of developing a latent image which comprises
providing a layer containing a polymer having aliphatic
carbon-to-carbon double bonds with a latent image composed of
allylic hydroperoxy groupings in some areas while other areas
differ therefrom essentially only in lacking such groupings, and
developing such image by selectively dissolving one of such
14. The process of claim 13 in which the portion lacking such
groupings is
15. The process of obtaining an image which comprises exposing to
light imagewise through a multi-color transparency in the presence
of oxygen a layer comprising a solid polymer with aliphatic
carbon-to-carbon double bond unsaturation and a panchromatic
photooxidation photosensitizer, thereby causing oxidation to
chemically bond oxygen to areas of the layer struck by light passed
through various colors of the transparency to provide a latent
image in said layer corresponding to the image of said
transparency, and developing said image.
Description
The invention will be more fully understood by reference to the
following examples. These examples, however, are given for the
purpose of illustration only and are not to be construed as
limiting the scope of the present invention in any way.
Photosensitive compositions suitable for coating paper and other
suitable base supports are prepared to contain (A) a solvent or
carrier (B) a photoxidation sensitizer and (C) a substrate which is
photooxidized when the composition is exposed to light. Such
compositions are illustrated in Example 1 below wherein the
compositions A through T are applied to a styrene-butadiene coated
paper. All parts are parts by weight unless otherwise
specified.
______________________________________ Example 1 -Compositions A
through T: Composition Component A B C D
______________________________________ Chloroform 300 300 300 300
Di-2-ethylhexyl phthalate 300 300 300 300 Tetraphenylporphin 2 2 2
2 Tall oil Rosin (Acid No. 170-180) 100 -- -- -- Formaldehyde
Modified Rosin (Acid No. 18 to 20) -- 100 -- -- Fortified Rosin
Adduct (Acid No. about 200) -- -- 100 -- Maleopimaric Acid -- -- --
100 ______________________________________
Composition Component E F G H
______________________________________ Chloroform 300 300 300 300
Di-2-ethylhexyl phthalate 300 300 300 300 Zinc chelate of
tetraphenylporphin 2 -- -- -- 2, 4-Dichlorotetraphenyl-porphin -- 2
-- -- 3, 4-Dichlorotetraphenyl-porphin -- -- 2 -- Rose Bengal -- --
-- 5 Gum Rosin (Acid No. 160-170) 100 100 100 -- Maleopimaric Acid
-- -- -- 50 ______________________________________
Composition Component I J K L
______________________________________ Chloroform 300 300 100 100
Ditetrahydrofurfuryl phthalate 300 300 100 100 Chlorophyll 3 -- --
-- Eosin A -- 5 -- -- Tetraphenylporphin -- -- 2 2 Maleopimaric
Acid 100 -- -- -- Tung Oil -- 10 -- -- Gum Rosin (Acid No. 160-170)
-- -- 100 -- Pinene -- -- -- 100
______________________________________
Composition Component M N O P
______________________________________ Chloroform 15 1.0 4.4 40.0
Ditetrahydrofurfuryl phthalate 25 -- 3.5 50.0 Octadecene -- 12 --
25.0 Chlorinated paraffin -- 2 -- 25.0 Undecanone -- -- 0.1 --
Tributyltin Stearate -- -- 3.5 -- Dimethylfuran -- -- 0.1 --
Tetraphenylporphin 0.1 -- 0.1 1 2,4-Dichlorotetraphenyl-porphin 0.1
-- -- -- Naphthyltetraphenyl-porphin -- 0.3 -- -- Maleopimaric Acid
2 -- -- 5.0 Gum Rosin (Acid No. 160-170) -- 0.5 0.6 5.0
______________________________________
Composition Component Q R S T
______________________________________ Chloroform 300 300 700 600
Di-2-ethylhexyl phthalate 300 300 700 800 Tetraphenylporphin 2 3 6
6 Chlorinated Paraffin -- -- 200 -- Maleopimaric Acid 100 100 100
50 Tung oil rosin -- -- -- 150 Pinene -- -- -- 100
______________________________________
The aforedescribed compositions A through T are used on coated
paperboard. Exact positives of the positive transparencies used to
mask the substrate are produced when the photosensitive
compositions are exposed to light through the transparencies and
further developed with a kerosene solution of DuPont Brown N
dye.
Example 2
A solution containing 9 parts of ditetrahydrofurfuryl phthalate and
1 part of acetophenone is applied to a paperboard previously coated
with a styrene-butadiene latex. A suitable positive transparency is
placed over the coated board. The board is then exposed for a
period of 15 minutes to an 85 watt ultraviolet light. The exposed
board is wiped with an odorless kerosene solution containing 0.4
percent DuPont Brown N dye. A clear image of the transparency is
obtained on the board.
Similar results are obtained as in Example 2 when the acetophenone
is replaced with benzophenone, benzoin, benzil or triphenylene.
Example 3
A paperboard previously coated with styrene-butadiene latex is
coated with Composition A of Example 1. A lantern slide
transparency is placed on the coated board. A fluorescent light is
used to expose the board for about 10 minutes. The image is
developed with a kerosene solution of DuPont Brown N dye.
Example 4
Example 3 is repeated with a 300 watt incandescent flood lamp being
used as the light source.
Example 5
An opaque paper sheet coated with a styrene-butadiene latex is
treated with a solution having the following composition:
Levopimaric-formaldehyde adduct 100 parts Chloroform 400 parts
Chlorinated paraffin (Chlorowax 50) 250 parts Ditetrahydrofurfuryl
phthalate 600 parts Tetraphenylporphin 3 parts
The resulting coated sheet is useful for accepting an image of an
object to be copied such as a typewritten letter on light bond
paper upon directing a 1000 watt light source at a distance of 14
inches on the paper sheet for about 30 seconds with the object
interposed between the light source and the treated paper. The
image is developed with a 0.4 percent solution of Calco Oil Violet
V in dodecane.
Example 6
Following the procedure of Example 5, similar results are obtained
when levopimaric acid or dihydroabietic acid is substituted for the
levopimaric acid-formaldehyde adduct.
Example 7
The following solution is prepared.
______________________________________ Composition U Parts
______________________________________ Chloroform 600 Chlorinated
paraffin (Chlorowax 50) 500 Ditetrahydrofurfuryl phthalate 1200
Levopimaric acid-formaldehyde adduct 50 Gum Rosin 100 Maleopimaric
Acid 50 ______________________________________
A variety of photosensitizer solutions are prepared by adding 5
parts of the sensitizers listed below to 1,000 parts of solution U.
Each resulting photosensitizer solution is applied to a board
coated with styrene-butadiene latex. The board is then covered with
a transparency and exposed to a 300 watt light at 10 inches for
four minutes. A kerosene solution of DuPont Brown N dye, Calco Oil
Violet, Violet BN or Nigrosin B is used to produce a photographic
image on the board.
The results obtained are noted below.
______________________________________ Interpretation of Resulting
Sensitizer Developed Image ______________________________________
Tetraphenylporphin Good picture Methoxytetraphenylporphin Faint
picture Zinc tetraphenylporphin Faint picture
Hydroxytetraphenylporphin Dark background
Naphthyltetraphenylporphin Good picture
3,4-Dichlorotetraphenylporphin Good background and definition
2,4-Dichlorotetraphenylporphin Good background and definition
Chlorophyll Good picture - fair definition Eosin Y Faint picture
Eosin B Faint picture Rose Bengal Good picture
______________________________________
Example 8
A mixture containing 3 parts of 2,4-dichlorotetraphenylporphin, 400
parts of chloroform and 1,600 parts of eicosane is heated to a
temperature of about 40 to 50.degree.C and applied to a paperboard
coated with a styrene-butadiene latex. An excellent image is
produced when the board is covered with a transparency, exposed to
a 300 watt lamp and developed with a DuPont Brown N dye
solution.
Example 9 through 13
Following the procedure of Example 8, sensitizer solutions
described below are substituted for the sensitizer solution of
Example 8 to obtain excellent reproduced images.
__________________________________________________________________________
Example Number Parts by Weight Component 9 10 11 12 13
__________________________________________________________________________
2,4-Dichlorotetraphenyl-porphin 3 -- 3.5 5 3.6 -Polyethyleneglycol
(Carbowax 1000) 1100 150 -- -- -- Polyethylene glycol (Carbowax
4000) 900 50 -- -- -- Rose Bengal -- 2 -- -- -- Chlorinated
polyphenyl (54% chlorine) Aroclor 5442 -- -- 400 -- -- Eicosane --
-- 1600 -- 1000 Chlorinated polyphenyl (12% chlorine) Aroclor 1254
-- -- -- 1400 -- Paraffin Wax (m.p. 65.degree.C) -- -- -- 700 --
Chloroform -- -- -- -- 250 Butylated hydroxy toluene -- -- -- --
4.6
__________________________________________________________________________
Examples 14 through 20
These examples illustrate the incorporation of both the
photosensitizer and oxidizable substrate in the surface coating on
a cellulosic web. A standard coating is prepared as follows: 1.25
grams of tetrasodiumpolyphosphate is dissolved in 300 grams of
water and added to a Waring blendor. While this mixture is being
stirred, 450 grams of clay and 50 grams of titanium dioxide are
added. The resulting mixture is stirred for 10 minutes. One hundred
twenty nine grams of a 60/40 styrene-butadiene polymeric latex
containing 48 percent solids and 11 grams of water are added to 200
grams of the standard coating and the mixture is stirred gently for
15 minutes. Aliquots of this coating solution are mixed with the
photosensitizer solution as indicated in each example below and
applied to a sulfite paperboard. The results of the evaluation of
each treated board as photographic substrates after exposure
through transparency for 1 to 2 minutes using a 1,000 watt lamp and
subsequent developing with dye are given below.
__________________________________________________________________________
Parts of Exam. Standard Parts of Sensitizer Image No. Coating
Sensitizer Composition Results
__________________________________________________________________________
1% 2,4-dichlorotetra- Fair picture phenylporphin in yellow 14 7 3
dimethyl sulfoxide background Fair picture Same as yellow 15 7 1.5
Example 14 background 2% dichlorotetra- phenylporphin in -16 8 2
chloroform Fair picture 1%2,4-dichlorotetra- phenylporphin in 17 8
2 carbitol acetate Good picture Fair picture 2% Rose Bengal in pink
18 9 1 carbitol acetate background Same as 19 9 1 Example 17 Good
picture 0.5% 2,4-dichloro- tetraphenylporphin 20 30 2 in butyl
cellosolve Fair picture
__________________________________________________________________________
Example 21
The styrene-butadiene latex coating material is replaced with a
natural rubber latex. The sensitizer solution of Example 8 is added
to the rubber latex. The resulting solution is applied to a sulfite
paperboard. The resulting surface is found to produce an image when
covered with a transparency, exposed to a 1,000 watt lamp for 1 to
2 minutes and developed with a suitable dye.
Example 22
A standard paperboard is double coated by the air knife method with
a styrene-butadiene latex containing a 90:10 clay/titanium dioxide
pigment in a ratio of two parts of pigment to one part of
styrene-butadiene copolymer. A sensitizer solution containing 83.8
mg. of tetraphenyl porphin, 6.5 g. of chlorinated polyphenyl, 13.5
g. mineral oil and 8 g. of chloroform is wiped on the coated board.
A negative transparency is placed on the board and exposed to a
1,000 watt lamp for about 1 minute. The board is dusted with
activated carbon and the excess is brushed away. An image is
produced on the board. The carbon is found to adhere to the
unexposed area.
Example 23
A standard paperboard is coated with a pigmented styrene-butadiene
copolymer latex. A sensitizer solution of Example 22 is applied to
the coating. The coated board is exposed to light through a
photographic negative transparency. The image on the board is
developed with the use of a solid dye solution of crystal violet in
a petroleum wax having a melting point of 117.degree.F.
Example 24
A standard paperboard coated with a pigmented styrene-butadiene
copolymer latex (2:1 pigment ot binder) is sensitized with a
solution of 320 mg of tetraphenylporphin, 50 g. of chloroform, 90
g. of a 1:1 mixture C.sub.18 hydrocarbon and chlorinated
polyphenyl. Particular areas of two sets of the above-treated
boards are exposed to light. The first board is wiped with
graphite. The nonexposed areas become darker than the exposed area.
The resistance obtained for each area is shown below. The second
board is first wiped with kerosene, followed by a kerosene solution
of Calco oil red BMC and then a 2-ethylhexanol solution of Victoria
Blue R. The surface is finally wiped with dry graphite. The
resistance obtained for each area is shown below.
______________________________________ Board No. 1 Board No. 2
______________________________________ Nonexposed Area 300,000
ohm/cm 40,000-50,000 ohm/cm Exposed Area .infin. .infin.
______________________________________
A surface which is differentially conductive is obtained on each
board.
Example 25
A standard board coated and sensitized as in Example 24 is exposed
to light through a negative. The image is first developed with a
kerosene solution of Sudan Brown dye and then the surface is
polished with a kerosene solution of Victoria Blue R to obtain a
bronzed image.
Example 26
A standard board coated and sensitized as in Example 24 is exposed
to light with a strip of aluminum foil laid on the board. After a 5
to 10 minute exposure the coated surface is wiped with kerosene and
graphite. The graphite is selectively deposited on the nonoxidized
area. The board is then copper plated using 1.5 volt dry cells and
a copper sulfite sulfuric acid bath. The copper is deposited on the
graphited areas.
A piece of brass shim stock similarly treated as the above paper
board is copper plated by the same procedure. The copper is
deposited on the graphited area.
Example 27
The sensitizer solution of Example 24 is applied to a paperboard
coated with a natural rubber latex. The coated board is exposed
through a transparency. The surface is then wiped with kerosene to
obtain a relief image.
Similar results are obtained when Rose Bengal is substituted for
the tetraphenylporphin in the sensitizer solution.
Example 28
A sulfite bleached carton stock is coated with a 4 to 5 mil
thickness of coating color containing 2 parts of pigment (90:10
clay-titanium dioxide) and 1 part of vinyl acetate latex of 50-60
percent solids. The board is sensitized with a solution containing
tung oil, tetraphenylporphin, chloroform and octadecane. After
exposure through a transparency the image is developed with a 0.5
percent solution of DuPont Brown N dye in kerosene.
Example 29
Similar results are obtained as in Example 28 when an
ethylene/vinyl chloride latex of 50-60 percent solids is used in
place of the vinyl acetate latex.
Example 30
The procedure of Example 28 is repeated wherein a butyl acrylate
latex containing 50-60 percent solids is used in place of the vinyl
acetate latex. An excellent image is obtained.
Example 31
Example 28 is repeated using polyethylene terephthalate as the base
support in place of the carton stock.
Example 32
Following the procedure of Example 28 a polyvinyl chloride latex is
substituted for the vinyl acetate latex, further demonstrating
successful results with unsaturation in a component (tung oil)
other than the polymer.
Example 33
A sheet of tracing paper is coated with a styrene-butadiene latex
containing finely divided polyvinyl chloride. A sensitizer solution
consisting of 2 parts of tetraphenylporphin, 100 parts of
maleopimaric acid, 300 parts of chloroform and 300 parts of
di-2-ethylhexyl phthalate is applied to the coated surface of the
paper. The treated paper is placed coated side down over a printed
sheet of paper the printing of which can be seen through the coated
paper. A light source of 300 watts is placed 10 inches over the
coated paper and printed paper for 15 seconds to obtain a latent
image of the printing on the translucent paper. The latent image is
developed with a solution of 0.4 percent Sudan Brown dye in
kerosene. A reproduction of the printing of the printed sheet is
obtained on the translucent paper.
Example 34
In this example a board is coated with the sensitizer solution of
Example 33. The light from a 500 watt lamp is reflected off a black
image on a white background and passed through a convex lens. The
rays of the light are focused for a period of about 30 minutes on
the sensitized board placed about 42 inches from the image. The
resultant latent image is developed with a solution of 0.5 percent
Brown N dye in kerosene.
Example 35
A standard paperboard coated with a styrene-butadiene latex is
treated with a sensitizer solution of Example 24, and exposed
through a negative transparency. The image is developed with an
octanol solution of 8-hydroxquinoline and a ferric nitrate
dissolved in water. A black positive image is obtained.
Example 36
Following the procedure of Example 35 the developed image is
further treated with a solution of potassium hydroxide in ethanol
to form iron oxide on the oxidized portion of the substrate.
Example 37
Following the procedure of Example 35 the exposed substrate is
developed with a solution of silver nitrate in a mixture of
ethanol, isopropanol and octanol. The treated area is then exposed
to hydrogen chloride vapors and light to obtain a brown image.
Example 38
Following the procedure of Example 35 the exposed area is developed
by applying in sequence the following solutions.
1. Potassium hydroxide in ethanol and octanol,
2. Hydroquinone in octanol,
3. Silver nitrate in water and mixture of ethanol and methanol.
An image is obtained wherein the metal is selectively deposited on
the oxidized areas.
Example 39
Following the procedure of Example 35 ferric sulfate is substituted
for ferric nitrate to produce a yellow positive image.
Example 40
The procedure of Example 35 is repeated except copper sulfate is
substituted for the ferric nitrate. A positive image is
produced.
Example 41
A pigmented styrene/butadiene copolymer latex coated paperboard
treated with a sensitizer solution of Example 24 is covered with
vinylidene copolymer film which tightly adheres to the surface in
some areas and leaves wrinkles in other areas. The board assembly
is exposed to light and the surface is then developed with a
solution of Crystal Violet in 2-ethylhexanol. The areas under the
wrinkles selectively absorb the dye. The areas to which the film
tightly adheres show a lack of dye receptivity.
Example 42
Following the procedure of Example 41, drops of water are
substituted on the coating for the plastic film. After exposure to
light and developing with a solution of Victoria Blue R in
2-ethylhexanol, the area under the drops of water are most
discernible as light areas in a dark background. The Victoria Blue
R dye solution is selectively absorbed by the oxidized areas.
Example 43
The procedure of Example 42 is repeated, except that a solution of
Sudan Brown in kerosene is used to develop the exposed surface. The
areas under the drops of water appear as dark areas in a light
background. The Sudan Brown dye solution is selectively absorbed by
the non-oxidized areas.
From the foregoing general discussion and detailed specific
examples, it will be evident that this invention provides novel
photosensitizer compositions which are useful for a variety of
copying, printing, decorative and manufacturing applications. The
advantage lies in the inexpensive, quick and simple procedures
involved in the general application of the compositions of this
invention.
The photoimaging procedure employed herein is suitable for
production of continuous gradient three dimensional images. Such
images can be produced by using solvents to selectively remove
portions of the image with the amount removed depending upon the
intensity of the light exposure on the portions. In general the
solvents used herein for such purpose will be relatively poor
solvents for the polymer substrate involved, as a selective removal
is desired. For selective removal of non-exposed areas, solvents
will be selected which are effective to soften or dissolve the
non-exposed areas, but which are not sufficiently effective to
remove the exposed areas in which hydroperoxy groups are present.
Solubility parameters present a suitable guide for choosing
appropriate solvents, although there will be some variance with
individual members for such classes. Such parameters based on
cohesive energy density, are described in Solubility Parameters by
Harry Burrell, Parts I and II, Interchemical Review, Vol. 14, No.
1, pages 3-16, and Vol. 14, No. 2, pages 31-46 (1955). As the
hydroperoxy groups increase the solubility parameter, the solvent
will generally be selected to have a parameter slightly less than
that of the polymer employed. Thus with a diene rubber having a
solubility parameter around 8.5, a suitable solvent would probably
have a solubility parameter less than 8, such as methylcyclohexane
with a parameter of 7.8. Many of the hydrocarbon diene polymers
suitable for use herein have solubility parameters in the range of
8 to 9.5, and accordingly the developing solvents usually will have
solubility parameters below 8, although higher parameters may be
suitable. Depending upon the polymer, e.g., cyclohexane with a
parameter of 8.2 can be used with styrene-butadiene copolymers of
high styrene content. Most of the solvents suitable for use herein
for removal of non-exposed areas will have solubility parameters in
the range of 7 to 8 or 8.2. Poorer solvents when used sometimes
require longer development times, but this may not be objectionable
in some applications. Aliphatic hydrocarbons, including
cycloaliphatics, provide a number of suitable solvents for use with
particular polymer systems, e.g., kerosene, VM and P naphthas,
methylcyclohexane, octane etc. Some aliphatic, i.e. non-benzenoid,
unsaturation may be present in such solvents, but aromatic solvents
generally have too high a solubility parameter for use with the
preferred polymer systems herein. Solvents such as benzene,
toluene, etc. will ordinarily dissolve both the exposed and
non-exposed areas. Thus it is not desirable to use really good
solvents for the polymer for the development purposes, but to
select solvents of lower solubility parameter than the polymer,
e.g. 0.2 to 0.5 or more units lower. If the starting polymer is
readily soluble in toluene or benzene, as is usually the case
herein, the exposed areas after imaging are still readily soluble
as the imaging does not cross-link or otherwise change such polymer
so as to render it insoluble in such solvents. It will be
recognized that the suitability of particular development solvents
will vary with such factors as the molecular weight of polymers in
the film substrate, characteristics of other additives or
components in the film, desired speed of development, film
thickness and strength, etc. The hydroperoxy groups are strongly
polar, and therefore to avoid dissolution of the exposed areas,
solvents lacking strong polar groups are ordinarily employed.
Hydroxy, keto, etc. groups tend to increase the solubility
parameter, and are therefore not generally used unless with a high
solubility parameter polymer system, or if such groups are present
in such proportions in the solvent as not to unduly affect the
parameter. Similarly strongly halogenated solvents tend to have
higher solubility parameters, and are not ordinarily employed as
development solvents herein.
For the development of images by dissolution of the exposed areas,
solvents of higher solubility parameter, such as polar solvents,
are employed. In broad terms, solvents will dissolve polymers if
the solubility parameters match. Thus if a high solubility
parameter solvent is used, it can dissolve the hydroperoxidized
region having a similar solubility parameter, but has too high a
parameter to dissolve the non-exposed regions of the polymer. The
precise relationship between the number of hydroperoxy groups and
the solubility parameter is not known, but the solvents chosen
should have a solubility parameter above that of the original
polymer so as not to dissolve non-exposed areas. Polar solvents,
such as hydroxyl containing compounds, e.g., various alcohols,
glycols, cellosolves, etc. can be used. Solvents will be selected
so as to give the desired degree of solubility without unduly
affecting the non-exposed area, and may at times have solubility
parameters considerably above that of the original polymer
substrate. It is to be recognized that the solvents herein can
include mixtures of various solvents, and that descriptions herein
are mainly concerned with the overall characteristics of solvents,
rather than with characteristics of individual components thereof.
For example, a particular naphtha may be considered as a low
solubility parameter aliphatic hydrocarbon solvent even though it
has some aromatics content. With some of the solvents for the
hydroperoxidized areas it may be desirable to use small amounts of
bases, for example, alkalies such as sodium hydroxide, or chemical
reagents to aid in the dissolution.
Example 44
A sheet of release paper was coated with a solution of polymer and
sensitizer. The polymer was a styrene/butadiene copolymer with a 15
percent butadiene content (Pliolite S-5A brand of Goodyear Co.).
The solution was obtained by dissolving 50 mg. of tetraphenyl
porphin in 20 grams of chloroform, and adding thereto 100 grams of
a 20 percent solution of the polymer dissolved in toluene. The
coated sheet was exposed imagewise in the presence of air through a
high contrast negative using a 1,000 watt tungsten halogen lamp at
18 inches for 5 minutes. The sheet was then immersed in cyclohexane
for a few minutes with gentle agitation. The exposed area had
turned green under the light, and the non-exposed area was
dissolved away revealing the white surface therebeneath. The
contrast and detail were sharp, as in a circuit board photoresist.
The procedure is suitable for use in making photoresists for use
e.g. in making printed circuit boards or other applications
involving etching, chemical milling, plating or other deposition of
materials etc. For example, if the photoresist is formed on a
copper surface, areas where the coating was removed can be etched
with ferric chloride solution, removing all the copper in such
areas. If desired, the remnants of the photosensitive coating can
then be removed with a solvent such as toluene.
Example 45
A coated release paper was utilized and coated with a polymer
containing a sensitizer. The polymer was a styrene/butadiene
copolymer having equal contents of the monomeric components
(XPRD-C-309, available from Polymer Corporation). The coating
solution was prepared by dissolving 200 mg tetraphenylporphin in
100 grams of chloroform, and adding thereto a 100 grams of a 20
percent solution of the polymer in benzene. The solution was coated
on the paper with a No. 8 wire wound rod, and allowed to dry. The
sheet was imaged as in Example 44. The sheet was then immersed in
methylcyclohexane for a short time, dissolving away the non-exposed
area. A red dye (2 percent solution) was added to make the image
formed by exposed areas stand out from the white areas where the
polymer had been removed. The solubility parameter of the polymer
system here was apparently lower than in Example 44 because of the
higher butadiene content of the polymer.
Example 46
The styrene/butadiene polymer solution of Example 44 was coated on
a 3 mil clear sheet of cellulose acetate using a No. 30 wire wound
rod. The coated sheet was exposed to a light as in Example 44 for 5
minutes, through a continuous tone negative picture of a woman,
with the negative next to the non-coated side of the sheet. The
sheet was immersed in methylcyclohexane for about 15 seconds,
quickly removed and rinsed with hexane. Non-exposed areas were
selectively dissolved away inversely with the intensity of light
exposure to give a three dimensional continuous tone image. In some
areas the polymer was completely removed, with progressively more
polymer in areas with a gradient dependent on light intensity.
Holding the sheet up to light made the facial features of the woman
readily apparent.
Example 47
The polymer solution of Example 45 was coated on a 7.5 mil
cellulose acetate sheet, which was then exposed imagewise to a
continuous tone negative as in Example 46. The sheet was then dyed
with a red dye to make the latent image visible. The sheet was then
immersed briefly for 10 to 15 seconds in a solution of 50 ml
cyclohexane and 80 ml hexane, followed by immediate rinsing with
n-hexane. The non-exposed areas were differentially dissolved away,
leaving a continuous tone three dimensional image. The facial
features and other details of the negative were produced.
Example 48
A 20 percent solution of styrene/butadiene polymer (Solprene 303
brand of Phillips Petroleum Co.) composed of about equal weight
quantities of its monomeric components, in cyclohexane was prepared
and to 50 grams of the solution was added 20 grams of chloroform
containing 20 mg. of dissolved tetraphenylporphin. A piece of
release paper was coated with the solution using a No. 8 wire wound
rod. After drying, the sheet was exposed either through a high
contrast negative as in Example 44, then immsered for 15 minutes in
a solution of ethyl cellosolve containing a small amount of sodium
hydroxide. The sheet was then rinsed with methanol and allowed to
dry. The exposed areas were dissolved away, leaving glossy
non-exposed areas. This procedure can be used to make positive
prints from positive transparencies. It can suitably be employed
with various other polymer systems, including those employed herein
in procedures in which the non-exposed area was dissolved. Thus the
present invention provides sensitized compositions which can be
used for either positive or negative working systems.
Example 49
A piece of copper was whirl coated with a solution of 20 grams of
the styrene/butadiene copolymer of Example 48, 200 mg.
tetraphenylporphin, 80 grams chloroform, 80 grams toluene and 940
grams xylene. It was exposed through a half-tone variable dot
negative for 10 minutes with a 1,000 watt lamp. The plate was
immersed for 13 minutes in a solution of 90 ml. 2.5N NaOH and 10 ml
acetone. It was then washed with water, dried and immersed in
40.degree. Baume FeCl.sub.3 for 7 minutes. The plate was cleaned
with chloroform and microscopic examination showed etched cells had
formed in the exposed areas. The procedure can be used for
preparing photoresists for various etching, chemical milling and
plating procedures, in the same manner as where the coating is
removed in non-exposed areas.
Example 50
A copper square was whirl coated with a solution of trans
polyisoprene (Trans-pip brand of Polymer Corporation). The coating
solution contained 50 mg. tetraphenylporphin, 20 grams chloroform,
45 grams toluene, 5 grams of the polyisoprene and 140 grams of
tetrhydrofuran. The square was exposed imagewise to light through a
transparency, employing a 1,000 watt tungsten lamp for 1 minute.
The plate was immersed in 2-ethoxyethanol for 90 seconds, and the
exposed areas of the coating were removed. A repeat of the
procedure, but employing 2-butoxyethanol for development similarly
removed the polymer in exposed areas.
Example 51
Photooxidizable coating compositions were prepared containing a
styrene/butadiene copolymer, tetraphenylporphin senstiizer and
cyclohexane solvent. The amounts of the photosensitizer in three
compositions were 0.1 percent, 0.3 percent and 0.6 percent by
weight, based on the copolymer. Boards were coated with the
compositions, and portions thereof used for photoimaging in the
presence of oxygen with subsequent dye development to produce good
images. The procedure was repeated with other portions of the
boards after fifteen days storage in the dark, with no perceptible
loss in image quality. Similarly storage for an additional fourteen
days did not cause loss of image quality upon repetition of the
procedure with other portions of the boards.
Example 52
A surface was coated with a composition having a styrene-butadiene
copolymer, 0.1 weight tetraphenylporphin, and 0.5 percent by weight
CoBr.sub.2. The copolymer (Kraton 101) contained about 40 parts by
weight styrene to 60 parts by weight butadiene. The coating was
exposed imagewise for 5 seconds, heated for 2 minutes at
110.degree.C and then treated with dye solution. A strong image was
obtained. The image was comparable to that of a control coating
without the cobalt salt after exposure for 300 seconds. A similar
procedure was conducted in which the cobalt was applied to the
coating surface as a solution of cobalt naphthenate (in isooctanol)
and wiped off, with similarly good results comparable to that of a
control exposed for 300 seconds. The amplification effect can be
obtained using dyes which go preferentially to the non-oxidized
site, such as Sudan Brown in kerosene, or dyes which go
preferentially to oxidized sites, such as Crystal Violet in
2-ethylhexanol. Cobalt compounds, e.g. cobalt salts or cobalt
chelates have the facility of causing cleavage of hydroperoxy
groups, and this in the present process apparently causes a free
radical chain reaction with incorporation of more oxygen into the
polymer, thus amplifying effects of light exposure. Heating the
materials accelerates the effect of the cobalt compounds, although
heating is not necessary. The use of cobalt salts will be
advantageous in some amplifications where amplification is desired.
However, the use of cobalt introduces a type of reaction providing
some control problems particularly with strong exposures, so its
use is not always indicated.
Example 53
Coatings applied as 10 percent solutions in cyclohexane, or 1:1
mixtures of toluene and kerosene were employed for photoimaging and
development with dyes. Employing a styrene/butadiene block
copolymer, good quality images were obtained with very little
background. Similarly good results were obtained when a
polybutadiene polymer was mixed with the styrene/butadiene
copolymer in the coating solution or when an ethylene/vinyl acetate
polymer was mixed with the copolymer. In some procedures it was
observed that use of solution rather than latex coatings aided in
obtaining light backgrounds.
Example 54
An untreated cellulosic bristol board was coated with a thin film
of styrene/butadiene copolymer from a 10 percent solution thereof
in cyclohexane. The coating was sensitized with a
tetraphenylporphin solution, and then exposed imagewise to light.
The image was developed with a polar dye, Basacryl Red GL, in a 3:1
mixture of 2-ethylhexanol and ethanol. Upon rubbing off the
coating, it was seen that the dye had penetrated to the board and
formed an image thereon. Similar results were obtained with films
of around 2, 5 and 9 microns thickness, although the image from the
9 micron film was of only fair quality with the allotted
photoimaging time. The coating and imaging procedures were
repeated, but employing a 15 percent polymer solution, so that a
slightly heavier coating, about 15 microns, was obtained with No.
40 wire wound rod previously used to obtain the approximately 9
micron coating. The dye had not penetrated through this heavier
coating with a 5 minute exposure time. Similar results to the above
were obtained when the coating was on a sub-surface which had
previously been coated with a pigmented styrene/butadiene latex
(Gardner board), or with ethylene/vinyl chloride latex. Thus it is
demonstrated that films or coatings can be made differentially
permeable to fluids by differential light exposure, and fluids can
be passed through a film or coating in imagewise fashion, for
dying, deposition or other purposes on a substrate beneath the
film. The exposure time or other imaging variables can be adjusted
in conjunction with the coating thickness to obtain the desired
degree of photooxidation penetrating to the opposite coating
surface to define the image and to permit selective passage of
fluids through the coating in imagewise manner. In general, fluid
permeability can be used herein in the manner taught herein with
respect to dye development, those carriers and dyes suitable for
development being suitable for selective passage through the
photoimaged film. However some dyes can be selectively passed
through the film in a suitable carrier to form an image on a
support surface, even though the areas of the film itself do not
absorb the dye. For example polar and similar fluids, such as
alcohols, can be caused to selectively penetrate the photooxidized
areas of a film. Similarly, non-polar and similar type fluids can
be utilized to penetrate the areas which have not been
photooxidized. The solubility parameters as discussed herein can be
used as a general guide, with fluids which are capable of
dissolving areas being suitable for passage therethrough. Complete
disintegration of the film can be avoided by using only moderate
amounts of solvent at a time to achieve penetration and by avoiding
mechanical stress, for example by just wiping a small amount of
solvent and dye on the film. Moreover, complete solubility of the
polymer is not required, but generally only that the polymer in the
desired areas sufficiently absorb or be swelled by the fluid to
permit penetration therethrough, so the solvents for this purpose
may at times be poorer solvents than would be used for development
of an image by selective removal of coating areas. The fluids will
be selected to give the desired permeability through selected areas
in the desired time while not passing through other areas in such
time. The differentiation above was sharp enough that the
penetration time was not significant, i.e., there was prompt
penetration in photooxidized areas and none in other areas. Time
will be a useful control in less selective systems.
In carrying out the present invention there are advantages in
utilizing polymer systems which given uniform homogeneous coatings.
In particular, solution coatings systems give homogeneous coatings,
whereas emulsion or other dispersion systems give coatings in which
the coating film is composed of fairly large particles, possibly
formed by agglomeration together of polymer molecules. While
emulsion coatings can be usefully employed, the solution coatings
are definitely preferred. Also it is advantageous to have the
photosensitizer well-dispersed in the polymer coating, at least on
a horizontal basis to the depth in the film to which photoimaging
is desired. This can advantageously be accomplished by
incorporating the sensitizer in a good solvent therefor, e.g.,
chloroform or other solvents for tetraphenylporphin, which is
compatible with the solvents used for applying the polymer
coating.
While this invention has been described with respect to certain
embodiments it is not so limited and it is to be understood that
variations and modifications thereof may be made which are obvious
to those skilled in the art without departing from the spirit or
scope of this invention.
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