Note: Descriptions are shown in the official language in which they were submitted.
~a6334~3
BACKGROUND OF THE I~VENTION
Thls invention relates o recording members con-
taining heat-reactlve components and, more part~cularly9 to
recording members capable of us in thermographic eopying,
~hermal printing, event recording, andas transparencies for
overhead projection.
Heat sensiti~e sheets containing the cyclic polyketo
compound~ of this invention, useful for copylng and recording
and characterlzed by the ability to form a mark of eontrasting
color when heated to an ac~ivation tempera~ure of 50 C are
known in th~ ar~, They are used in thermographic processes
wherein a recording member is positioned on a graphic or1ginal
and exposed to infrared radlation to cause selective heating
of the dark areas of the original suficient to orm a copy
thereof on the heat sen5iti~e memberO The thermally re~ponsive
members have also been used to record the heated portions o
a thermal print head and also to record a colored trace when
~ contaeted by the hot stylus of a thermal recorder. The
'A ninhy~rinamine-reaction wherPin ninhydrin reacts with amino
acids, primary amines, and certain derlvatives of morpholine,
piperidine, and pyrrolidine to give the dye commonly referred
to as Ruhrman's purple is well known. Isatin reacts with these
same amlnes to ~ive lsatin blue. Alloxan reacts with the amines
to give a red dye. These reactions have been used in numerous
inventions for thermally responsive copy and recording papers
and films. Lawton, US 3,736,166 used ninhydrin wi~h various
~ 5 3
morpholine and piperidine derivatives to prepare transparencies
for overhead projection. Lawton, US 3, 293,061 combined
ninhydrin or hydrindantin with isatin-amine condensates to
provide thermographlc copy sheets. Bauman ~nd Lawton reacted
ninhydrin or hydrindantin with complexes of amines and flavans or
phenolic compounds to make thermographic copy sheets, seP
US 37149,991 and US 3 jl4~,992. Huf~man, US 3, 664,858 comblned
ninhydrin with the adducts of morpholine or piperidine and
organic acids in thermal recording members~ Sus, US 3,024,362
combined hydrindantin with amino ;acidg or salts of primary
amin~3 with organic carboxylic and sul~Eonic acids to make a
thermocopy paper. Allen, US 2,967,785 used the adducts of
morpholine or piperidine with Isatin or ninhydrin as`the
color forming material in thermocopy papers. Small, US 3,573,9S8
combined an amine with a halide or organometalli~ halide or
garmanium, silicon 9 lead, and tin wlth hydrindantin to
provide a heat-sensitive recording shleet. In each case the
normal dye forma~ionsof Ruhrman's purpIe with ninhydrin, red
dye with alloxan, and isatin blue were obtained.
The above thermally reacting color forming systems
containing ninhydrin, isatin, alloxan, and thcir derivat~ves
have a number o~ limitationsO The most accep$ed comrnercial
products use ninhydrin or hydrindantin as the color former.
The i~nage Is purple, and has a tendency to fade with exposure
~o light and with time. It is desirable ~o have more acceptable
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~3453
image co]ors such as blacks, dark browns, and the like and improved resistance
to image fading by light exposure or aging.
I have found that thermal images with more desirable colors and
greater stability to light and aging can be obtained by using as the heat
- reacting material a cyclic polyketo color precursor and piperidine derivatives
substituted at the 4 position with an aromatic group and a hydroxyl group or
hydrogen atom. The substituents at the 4 position cause a color shift from
the purple normally obtained when piperidine and other amines are reacted
with ninhydrin or hydrindantin to give dark shades of brown, black, blue-
- 10 black, blue, etc. Similar color shifts are found when isatin derivatives
were used to replace the ninhydrin.
This invention relates ~o a heat-sensitive coating composition
~- acquiring in a region thereof a stable color contrasting visibly with a
background color of said coating composition upon heating said region to an
elevated temperature, containing polymeric binder means for binding said
coating composition to a substrate, a 4-hydroxy substituted piperidine
derivative selected from the group consisting of 4-benzyl-4-hydroxypiperidine,
4-hydroxy-4-phenylpiperidine and 4-~p-chlorophenyl)-4-hydroxypiperidine, and
a cyclic polyketo compound reactive with said piperidine derivative at an
elevated temperature to form a color contrasting visibly with a background
color of said coating composition, said cyclic polyketo compound being
selected from the group consisting of ninhydrin, hydrindantin, isatin and
- alloxan.
DETAILED DESCRIPTION OF THE INVENTION
Preparation of Transparencies
The cyclic polyketo compound and the 4-substituted piperidine
derivative are dissolved in a solution of a polymeric binder in an organic
solvent. The binder acts only as a vehicle which holds the color reactants
on the substrate. Any transparent binder such as acrylic and methacrylic
polymers or copolymers, vinyl ester polymers and copolymers, cellulose esters,
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r,,~'
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~?Q39~S3
` nitrocellulose, styrene polymers and copolymersg polyvinyl butyral, etc.,
can be used. The solvents convenient for use with this system include
ketones such as methylethylketone7 alcohols such as methanol, esters such
ethyl acetate, and aromatics such as toluene. It is normal to include
stabilizers
'~ ,
.
., .
- 4a -
~ 3~3
in the transparency formulations. Commonly used stabilizers
are those described in US 3,736,166 and include substituted
ureas and thioureas such as ethylurea, n-propylurea, allyl-
urea, N-methylthiourea, and allylthiourea; and gallic acid,
o-, m-, and p-toluic acids, 2-mercaptobenzothiazole and
2,2'-dithiobis (benzothiazole). Activators can be used to
increase the sensitivity or thermal response of the trans-
parencies as well as the recording papers of this inven-
tion. Some of the useful activators include the following:
TABLE I -- ACTIVATORS
2-mercaptobenzothiazole
~ 2-mercaptobenzoxazole
- 2,2'-dithiobis (benzothiazole)
2-benzoxazolethiol
2-benzothiazolol
.~ 2-morpholinothiobenzothiazole .
2,4-dichloro-1 naphthol
2-chloroacetamide
o-toluic acid
m-tolulc acid
p-toluic acid
thioacetanilide
thiobenzanilide
phenoxazine
phenyl-3-thiocarbazide
N-cyclohexyl-2-benzothiazolesulfenamide
(Santocure powder)
2-(2,6-dimethyl-4-morpholinothio benzothiazole)
(Santocure 26)
N-tert-butyl-2-benzothiazolesulfenamide
(Santocure NS)
~ 3~ 3
sulfanilamide
4 ,4~dithiodimorphollne (Sulasan R)*
1~ 1, 3, 3~cetramethyl-Z-thiourea
- 2 94-thiazolidenedione
thiazolidenethione
;~ N methylbenzothiazole-2-thiourea
.. . .
- p-hydroxy-~cetophenone
.~ 1,3-indanedione -
. .
bu~ylzLram
2,2-di hiobis (benzothiazole~
chlo~oacetophenone
3,5~dibromosallcylaldehyde
, .. . . . .
, ~ 3 ,4-dihydroxybenzoic acid
.- ~
biphenyl
. ~ ace~oneoxim~e
.. :
,
Suitable transparen~ film~.which~may be used for 3
the substrate for~the~transparencies include Mylar~brand~
terephthalate polyester film manufactured ~y duPont, poly-
carbonate~, polyamides, polystyrene~ and cellulose ace~ate-
butyrate copolymers.
The coatings may be:applied by any o~ the normal
coatLng procedure9 such as Meyer rod, reverse roll, k~ss-~coat~
etc. The coating weights o the thermosensitive layer9 can
be varied from 2 to over 10 lb/3000 sq ft.
~k T ~ ~ P ~ R ~< :
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3L~L5P3~L~3
Exarnple A, which follows, shows typical c:ombinations
useEul as transparencies for overhead proj ection . The ratlos
of amine ~o ninhydrin have been vari2d from 2/1 ~o 1¦10.
- Acceptable thermal images have beea obtained with all coatings.
A typical transparency is prepared in the following manner.
~ .~ ' .Parts
134 methanol
386 m~thylethylketone
nitrocellulose RS 5-6 sec. (Hercules)
45- Elvac~ te~2044 polybu~ylmethacrylate (duPont)
. . ~' .
. Parts
. .
resin solutior
1. 6 piperidine derival~ive
. 8 acetoacet-o-tolu:ldide st~bllizer
1. 5 p-toluic acid
,~, ' ,, :
"B" MIX
Parts
142 resin solution
4 ninhydrin
The formula consisting of 10 parts "A" wi~h 14 parts
"B" is coated on 3 mil Mylar with a No. 24 Meyer wire wound
rod. After coatlng and drying, the resulting transparent ~heet
is imaged on a Thermofax~m~chine in the normal manner to g~Ye
high density imaged transparencles suitable for overhead
TR~DE ~R~
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3~ 3
projection. The coated sheets showed excellent stability at
ambient condltion5, in a 100 percent relative humidity chamber,
and at 55 C. The color of image~ from typical 4~aronatic
. substltuted piperidines in the above formula are as follows:
4 benzyl-4-hydroxypiperidine-dark green
4- hydroxy-4-phenylpiperidine-b lack
i 4- ~p-chlorophenyl) -4-hydroxypiperidine - black
In additlon to the functionality of the 4-subQtituents
as a determinant of image color, the color can also be controlled
. ~ by the selection of a stabilizer. As examples of this) 4-hydr~y-
4~phenylpiperidine w~th acetoacet-o-toluidide gives a black image, .
with ethyl urea a blue image, and with gallic acid a black image
::,
is ob~ained. Obv~ously~ the use of stabilizer additives increaqes
the range of imaging colors. : . .
Other positions on the 4-substituted piperidlne ring
may be substituted so long as one of~the positions adjacent to the
nitrogen atom i9 un~ubstituted,-
Example B: Preparation of coated papers fcr thermocopy, thermal
printer, and thermal stylus chart recording applications,
Separate ball mill grinds were made o~ the piperidine
co~pounds, the cyclic polyketo deriv~tives, and any addltives
used as accelerators or stabilizers~ The following exampIes:
list the com~i~ations, ratiss, coating weights, and image colors
obtained when imaged on a 3M Co. thermal copier sold under the
trademark Thermofax Secretary, Texas Instrumen~Silent 700
matrix thermal printer, and a Sanborn~Viso Cardiette thermal
chart recorderO
TR~ E ~ ~RK.
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~ 3~S3
The coatin~ mixes were prepared by ball-milling the components
in a S percen~ aqueous polyvinyl alcohol solution at a 15
percen~ concentration oE the dry components. The mixes were
combined i~ the indicated ra~ios and coated with a No.l~ wlre
wound Meyer rod onto a 25 lb/3000 sq ft sulfite paper base
stock.
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