CA1103453A - Heat-sensitive coating composition with 4-aromatic and hydroxy substituted piper-idine derivative and cyclic polyketo compound - Google Patents

Abstract

HEAT-SENSITIVE COATING COMPOSITION WITH

DERIVATIVE AND CYCLIC POLYKETO COMPOUND

ABSTRACT OF THE DISCLOSURE

A heat-sensitive coating composition acquiring a stable color contrasting with the background color in selected regions that are heated to an elevated tempera-ture. The coating composition comprises (1) a piperi-dine derivative substituted in the 4 position with an aromatic group and a hydroxyl group, (2) a cyclic poly-keto compound reactive with the piperidine derivative to form a dye, and (3) polymeric binder means for binding the reactants to a substrate.

Description

~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 ~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, r,,~' ~' ~?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 ~< :
` .

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~

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.

~ 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.

.
, .~ .

.
.~
. .

. : ~
.

::

_g_ 453 ~

~1 0 0 1 1 ~ R S ~ R ) I O O
a) ~ ~ ~ .4 R a) ) ~: Q Q O ~: Q R
o o 3 ~ ~ ~ 3 ~ ~ ~1 3 ~ ~ o s~ h O ~ ~ ~1 0 S~
h O S~ rd ~1 a~ C
E~ C) Q ~ R ~ Q ~ ~ ~ R ~ h 5 ; .
4~
a) u7 ~3 ~1 ~ r) CO ~ 00 0 ~D ~1 ~ O N ~ ~r ~1 O ~ ; >

~ Q
m ~
:

O ~ ~ \ \ \ N t~

.
U~ . .0 ~ ~0 X V U O Q O N
~1 0 (1~ al O rl tl~
O N O U U
~ ~ J 0 ~1 H ~ ~ o ~ O
~ O O O h IN
~ cn o b P. N N

O .~
lQ 5~ ~ S~ .
h V ~C h o aJ
,~
~\ ~
~1 X
O
~n h : : = : : : : ~ : : ~ : - :
R~ ~

~r ~.$~3~;3 O S~
~ a) a ''0 ~1 ~ X X
O O u O t.~ ~ 3 ~ a) 3 a) 3 r-l ~ 1 r~ O ~1 ~> O ~a O r-l r-l r t tlJ S~ 1 0 0 1-~ ~u 0 s~
.) ~ ) ,~ O tJ) ~J r~ R S I rJ Q S-.

; ~' .
~C
. . rl .~ ~0 t~ r-l r~

m r~

. . . ~ .
O r1rl rl ~I r-l rl .:rt~l ~r tN ~1 ~ ~ (N t~ ~ N ~ t~l 0 ~ ~ ~ ~ \
P~ r~ 1 r I r I,_1 r I ~--1 r-l r I r-l r~

. ~ rl rl rl O O O
:~ ~ ~ 0 0 :' 11) 0 N U
rl -rl~ 1 rl ~1 r~l ~ I t rl r-lr-l r I r-l ~: ~? O ~1 0 ,,OJ
.`~ ` ~ I ~ ~ ~
u~ ~ a~
:: .
;'~
` :' :;

.,1 ,1 1~1 ~
O ,1 0 ~1 0 U~
~ ~: ~rl ~ ~rl ~ rl X rl ~ rl X
C) ,~ ~ O ~) O ~) O
O ~ 0 ,~ ~ r~l ~1 rl ~ r~
~ ~ 1 0 O ,~ ~

X O ~ 0 ~ ~ Or~ O ~ ~ O ~ ~ O
R a~ ~ 0 ~5 1: C) ~1 a) C) o u~ Q. ~ ~ ,C Q

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. 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-hydroxy-piperidine, 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.

2. The coating composition of claim 1, containing an activator enhancing thermal sensitivity of said coating, said activator being selected from the group consisting of:
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-toluic acid p-toluic acid thioacetanilide thiobenzanilide phenoxazine phenyl-3-thiocarbazide N-cyclohexyl-2-benzothiazolesulfenamide 2-(2,6-dimethyl-4-morpholinothio benzothiazole) N-tert-butyl-2-benzothiazolesulfenamide sulfanilamide 4,4-dithiodimorpholine 1,1,3,3-tetramethyl-2-thiourea 2,4-thiazolidenedione thiazolidenethione N-methylbenzothiazole-2-thiourea p-hydroxy-acetophenone 1,3-indanedione butylziram 2,2-dithiobis (benzothiazole) chloroacetophenone 3,5-dibromosalicylaldehyde 3,4-dihydroxybenzoic acid biphenyl acetoneoxime.

3. The coating composition of claim 1, containing a stabilizer enhancing permanency of color formed in said preselected region after heating, said stabilizer being selected from the group consisting of substituted ureas and thioureas, gallic acid, o-toluic acid, m-toluic acid, p-toluic acid, 2-mercapobenzothiazole, and 2,2-dithiobis (benzothiazole).

4. The coating composition of claim 1, wherein said 4-hydroxy substituted piperidine derivative is 4-hydroxy-4-phenylpiperidine and said coating composition further contains a compound selected from the group consisting of acetoacet-o-toluidide, ethyl urea, and gallic acid.

5. The coating composition of claim 1, wherein said polymeric binder means is selected from the group con-sisting of acrylic polymers and copolymers, methacrylic polymers and copolymers, vinyl ester polymers and co-polymers, and polyvinyl butyral.