CA1117240A - Heat-sensitive recording composition - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A heat reactive recording composition capable of acquiring a stable color in selected re contrasting with the background color of the sheet upon exposing these regions to an elevated temperature and comprising a paper or polymeric film substrate a coating comprising (1) an N-substituted condensation product of a heterocyclic diimino compound and an aromatic aldehyde and (2) a cyclic polyketo compound reactive with amines and amides at elevated temperature to form a color.

Description

BACKGROUND OF T~IE INVENTION

This invantion relates to recording members con-taining heat reactive components and, mvre particularly, to recoxding members capable of use in thermographic copying, thermal printing, event recording, and as transparencies for overhead projection.

~ eat sensitive sheets containing the cyclic polyketQ
compounds of this invention, useful for copying and recording and characteri~ed by the ability to form a mark of contrasting color when heated to an activation temperature of 50C are `
known in the art. They are used in thermographic processes wherein a recording member is positioned on a graphic original and exposed to infrared radiation to cause selective heating of the dark areas of the original sufficient to form a copy thereof on the heat sensitive member. The thermally responsive members have also been used to record the heated portions of a thermal print-head and also to record a colored trace when contacted by the hot stylus of a thermal recorder.
the ninhydrinamine rea,ction wherein ninhydrin reacts with amino acids, primary amines, and certain derivatives of morpholine, pipexidine, and pyrrolidine to give the dye commonly referred to as Ruhrman's purple, is well known. , Isatin reacts with these same amines to give isatin blue.~' Alloxan reacts with ~he amines to give a red dye~ These reactions have been used in numerous inventions for thermally responsive copy and recording papers and films. ~awton, US 3,736,166 used ninhydrin with various morpholine and piperidine derivatives to prepare transparencies for o~er-head projection. Law~on, US 3,293,061 comhined ninhydrin or ~7~

hydridantin with isatin-amine condensates to provide thermographic copy sheets. Bauman and Lawton reacted ninhydrin or hydrindantin with complexes of amines and flavans or phenolic compounds to make thermographic copy sheets, see US 3,149,991 and US 3,149,992. Huffman, US 3,664,858 combined ninhydrin with the adducts of morpholine or piperidine and organic acids in thermal recording members. 5us, US 3,024,362 combined hydrindantin with amino acids or salts of primary amines with organic carboxylic and sulfonic 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 3,573,958 combined an amine with a halide or organometallic halide of germanium, silicone, lead, and tin with hydrindantin to provide a heat sensitive recording sheet. In each case the normal dye formations of Ruhrman's purple with ninhydrin, red dye with alloxan and isatin blue were obtained.
It is often desirable and an objective of this invention to obtain colored records which have colors dif~
fering from those normally obtained with the above cyclic polyketo compounds.
Undesirable odors and fumes are obtained by the heat dissociation or decomposition of the complexes, salts, or adducts during the imaging process. There is a problem of image bleaching during excessive heating, or aging, or prolonged exposure to ultraviolet containing lightO
Attempts to use heterocyclic diimino compounds such as the piperazine derivatives result in colarless or very pale images, genexal dPterioration of coatings, and a coating layer unacceptable due to the very hygroscopic nature of the piperazines and the;r unpleasant odor.
I have found that the above objectionable problems can be minimized or eliminated by the combination o~ an N-substituted condensation product of a piperazine and an aromatic aldehyde, and a cyclic polyketo color precursor.
Thus the invent;on provides a heat-sensitive, non-volatile, non-hygroscopic, and odor-free recording composition adapted to acquire a color contrasting visibly with a background color of the composition upon heating a selected re~ion thereof an elevated temperature, comprising an N-substituted condensation product of a heterocyclic diimino compound and an aromatic aldehyde, said heterocyclic diimino compound being selected from the group consisting of pip-erazine, homopiperazine, 2-alkylpiperazine, and 2,5-dialkylpip-erazine; and a cyclic polyketo compound reactive with amines and amides at elevated temperature to form a color.
The heterocyclic diimino-aldehyde condensate and the color precursor react at temperature between 50C and 200C to form a number of different highly colored dyes. The volatility, odor, and hygroscopic characteristics of the original piperazine derivatives are eliminated. The materials for preparing the piperazine condensates are generally less expensive than those used for the adducts and complexes described in the prior art and the product yield is high which leads to a less costly record member.
Preparation of the Substituted ~leterocyclic Diimine Compound One gram mole of the cyclic diimino compound such as piperazine or substituted piperazine or homopiperazine or its derivative is condensed with one gram mole of an aromatic !
aldehyde hy refluxing in methanol or ethanol for 4 to 8 hours.

Upon cooling, the condensate precipitates, the precipitate is filtered off, washed with alcohol and dried. If a precipitate does not readily form, precipitat;on may be induced ~y adding water to the reaction mixture.

~4a-:

f~

Preparation of Transparencies The cyclic polyketo compound and the piperazine condensate are dissolved in a binder contained in an organic solvent. The binder acts only as a vehicle to carry the color reacting products. Any transparent binder such as acrylic and methacrylic copolymers, cellulose esters, nitrocellulose, polyvinyl acetates, butyrals, styrene polymers and copolymers, etc., can be used. The solvents convenient for us with this system include ketones such as methylethylketone, alcohols such as methanol, esters such as ethyl acetate, and aromatics such as toluene. It is normal to include stabilizers in the transparency formulations. Commonly used stabilizers are those described in US Patent No. 3,736,166 and include sub-stituted ureEs and thioureas such as ethylurea, n-propyl urea, allylurea, N-methyl thiourea, and allyl thiourea, gallic acid; o-,m- and p-toluic acids; 2-mercaptobenzothiazole;
and 2,2'-dithiobis (b~nzothiazole).
Activators can be used to increase the sensitivity or thermal response of the transparencies as well as the recording papers of this invention. A simple procedure for selecting useful activators is as fol_ows:
A grind of a selected heterocyclic condensate and a cyclic polyketo compound is obtained by ball-milling these materials as a dispersion in an aqueous solution of polyvinyl alcohol. The dispPrsion is coated onto a base paper and heated on a hot plate. If the color develops more rapidly in the area where the additive powder has been applied, the material will increase the sensitivity of the system when compounded with the heterocyclic condensate and cyclic polyketo compound of this inventionr Some of the more suitable activators include the following:
TABLE I

2-mercaptobenzoxazole 2-mexcaptobenzothiazole 2,2'-dithiobis(benzothiazole) 2-benzoxazolethiol 2-benzothiazolol 2-morpholinothiobenzothiazole 2,4-dichloro-1-naphthol 2-chloroacetamide o-,m~ and p-toluic acids thioacetanilide thiobenzanilide phenoxazine phenyl-3-thiocarbazide N-cyclohexyl-2-benzothiazolesulfenamide N-tert-butyl-2-benthiazolesulfenamide sulfanilamide 4,4'-dithiodimorphollne 1, 1, 3, 3-tetramethyl-2-thiourea 2,4-thiazolidenQdione thiazolidenethione N-methylbenzothiazole-2-thiourea p-hydroxyacetophenone -1,3-indanedione butyl ziram 2,2-dithiobis(benzothiazole) chloroacetophenone

3,5-dibromosalicylaldehyde 3,4-dihydroxybenzoic acid biphenyl - acetone oxime Suitable transparent films which may be used as the substrate for the transparencies include terephthalate polyester film, polycarbonates, polyamides, polyst~rene and cellulose acetate-butyrate copolymers.
The coatings may be applied by any of the normal coating procedures such as Meyer rod, reverse roll, kiss-coat, etc. The coating ~eights of the thermosensitive layers can be ~aried from 2 to over 10 lb/300Q sq ft.
Example A, which follows, shows typical combinations useful as transparencies for overhead projection.
Example A: Preparation of transparencies for overhead projection.
A resin solution of the following composition was prepared:
Parts methanol 134`
methylethylketone 386 nitrocellulose 39 polymethylmethacrylate 90 The following mixes were then prepared:

"A" Mix Parts resin solution 100 ~`~
stabilizer 1.0 lactic acid 0.7 piperazine-aldehyde condensate 4.0 "B" Mix Parts resin solution 142 cyclic polyketone 4 The coating composition obtained from 13 parts "B" and 10 parts "A" was coated onto 3 mil terephthalate polyester film with a No. 24 wire wound Meyer rod and dried ' .

to give a transparent film. The dried coated transparency was placed in contact with an infrared absorbing original and passed thxough thermal copier in the normal manner.
Imaged transparencies suitable for overhead projection were obtained with images projected in a variety of colors.
The following are examples of combinations used to prepare the transparencies.

7~

TABLE II -- TRANSPARENCY EXAMPLES
Condensate cyclic Diimino polyketo ~ image Compound aldeh~de compound color 1. piperazine benzaldehyde ninhydrin :~rown 2 1I salicylaldehyde " brown 3. " 5-nitrosalicyl-aldehyde " brown

4. " o-chlorobenzalde-hyde " brown

5. " p-chlorobenzalde-hyde " brown

6. " bromosalicylalde-hyde " bro~n

7. " 3,5-dibromosalicyl-aldehyde " brown

8. " 2,4-dimethoxyben-zaldehyde " brown

9. " 2-hydroxy-3-methoxy-benzaldehyde " brown

10. " o-vanillin " brown-black

11. " 3r4,5-trimethoxy-benzaldehyde " brown-black

12. " cinnamaldehyde " brown

13. " ~ -methoxy cinna-maldehyde " brown

14. " p-hydroxybenzalde-hyde " brown-black

15. " 5-hydroxy-2-nitro-benzaldehyde " brown-black

16. " m-nitrobenzaldehyde " brown-black

17. " o-nitrobenzaldehyde " blue-black 13. piperazine 9-anthraldehyde ninhydrin brown-black 19. " 2-hydroxy-1-naph- .
thaldehyde " brown 20. " p-isopropyl-benzaldehyde " brown 21. " p-c~anobenzal-dehyde " brown 22. " l-n~phthaldehyde " brown 23. " o-methox~benzaldehyde " brown 24. " o-ethoxybenzaldehyde " brown-black 25. " 6-nitroveratral-dehyde " brown 26. " 3-ethoxy-4-hydroxy-benzaldehyde " brown~
black 27. " 2,4-dinitrobenzal-dehyde " brown-black 28. " o-phthalic dicarboxaldehyde " dark blue 29. " terphthal-dicarboxaldehyde " brown ' 30. " p-N,N-dimethylamino cinnamaldehyde " brown-black 31. homopipera- p-chloxobenzal~ehyde " dark :
zine brown 32, " m-nitrobenzaldehyde " dark ::
brown 33. " cinnamaldehyde " brown ~4. 2,5-dimethyl l-naphthaldehyde " brown piperazine 35. " m-nitrobenzaldehyde " brown ~ .
36. " o-phthalic dicarboxaldehyde " dark brown 37. 2-methyl- 2-naphthaldehyde " dark piperazine brown ' ~ ~
, 38. 2-methyl- o-phthalic nin~ydrin dark piperazine dicarboxaldehyde brown 39. homopiper- p-chlorobenzal- Isatin brown azine deh~de 40. " " 5-bromoisatin brown 41. " " 5,7-di-chloro-isatin brown 42. " " 5-nitroisatin brown 43- " alloxan red 44. " " alloxazine red-brown 45. 2-methyl- o-phthalic 5-nitroisatin piperazine dioax~oxaldehyde 46. 2 methyl- " alloxan "
pipera~ine 47. 2,5-dimethyl- " alloxan "
pîperazine In Examples 37, 38, 45 and 46 above the preferred heterocyclic diimino compound is 2~methylpiperazine. Persons skilled in th~ art will understand that equi~alent alkyl-substituted piperazines such as 2-ethylpiperazine give sub stantially the same results. Similarly, other 2,5-dia~kyl substituted piperazines such as 2,5-dipropyl piperazine may be used in Examples 34, 35, 36 and 47 above.
Example B: Preparation of coated papers for thermocopy, thermal printer, and thermal stylus chart recording applications.
Separate grinds were made o the piperazine compounds, the cyclic polyketone derivatives, and any additives used as accelexators or stabilizers. The following examples list ~he combinations, ratios, coating weights and image colors obtained when on a thermal copier, a matrix thermal printer and a thermal chart recorder. The mixes were prepared by ball-milling the components in a 5 percent 7~

aqueous polyvinyl alcohol solution at a 15 percent con-centration of the dry components. The mixes were combined in the indicated ratios and coated with a No. 16 wire wound Meyer rod onto a 25 lb/3000 sq ft sulfite paper base stock.

v ~ o ~ ~
R h olX ~3 ~ R ,Y ~ I ~ O
r~~ 0 ~ d O h ~1 )~ O
O~1 ~Ih ~IQ) ~1 ~ 1~ h ~ h V ~ RR 5~ h R R ~1:] R :~ ~ ,4 ., ~o .C O ~
3--1 ~ ~i NN ~ ~ N ~i _i ~i ~I N

O N N N N N ~1 ., N _I N ~ el' ~I r-l ~1 ~1 ~1 ~1 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ `~
h ~I N

U~
~ .
a~ .
1~ ~ ~
- a ~a s~ - = - ~ -P~
.. , .~ X rl h ~ O
~1 p~O ~ U~
~ ~ ,5 .

C~
~ ,, H U '.
H ,.
~ ';
E~ ~ $ = = - -~1 d ,~
~ U~

h o ~ a3 rl O h P~O ~ :

. . --~1 N ~

- 1 3~

:

O O O O O
S~ h )~
5~ ~ Q
~: .Y 3 .Y ~ ~ 3 ~ 3 3 ~ 3 h h O h ~1 Li O ~1 0 0 0 0 I~J td S I 11]nl (1S h::~ h S~ h h rQ ~ R ~ Q .4 _ ., .,~ I
,~ d O Q) X '1 --I ~ ~
O O ~ ~ O O I~1 ~
N01 a~ IN
R O~I N O-rl O ~ ~1 .~:1 QO w O ~ U
O O ~ Nrlrl ~ O U 1~1 S rl ~ ~_I Or~l (a 5: X ~O N,~: ~1 0 ~) n~.1 ~ o o~ ~:u o s, ,~
U U~1 0 N NQ. ~Jrl S O
hI N 1~ R~ ~1 ~1 ~1 o oI .c~ o - = c ~3--I --I ~ a) ~ ~
I O I O ~ Q I I I ~
N ~ N (`I-- tN` ~ ~ ~N ~: CN
~' ., ~ ~
S S
a, ~1 U--l O
Srq S~
~4 U
I ~1 0~
.. . . .

~ x ~ ~ ~ o o ~ ~ o ~o 3 td 3 h ~ 3 3 h ~
_i ~1 0 ~1 0~:1 ~ O O R O

3 ~ 3 3 ,y 3 ,~ ~-1 ,~ 3 3 O C) O O ~ O ~ O O
h h h .
,.,~,1 ~ ,~ o ~ ~ ~ N N ~`I t`~ ~1 ~ ~1 ~I N ~r N N N N N N N N N N N N
N ~ ~`1 N ~1 ~ N ~ CD r~ t`l ~ oo c~

1:
.,1 ,1 ~ rl .,1 ;.

u u u u u u u u u o o = = = o = - - o = = = o o ~ ~ ~ ~ ~

a) :

~ a) N
U
O S~ ~ O
~4 U
I ~-~ I I I I :
O ~ ~
~9 t~ co a~ o x ~ ~ u u~u ~ u~ u ~13 ~ 3 ~1~10 .-1 ~ Q.4 0 Q .4~1 ~ I I I h ,!t ,Y X~: X ~ X
ie 3,~: 3 U U OU UQ~ U U
O Oh O t~

o _I o(~ D CO O
.

S
.,1 .,1 ~t A ~,1 ~rl U C) U
U O U t) V

O =O - - O =_ = O = = _O -- .

a N

N al ~1 0 ~I ~1 C E~ ~ h O
d ~rl ` N
' aJ
~ --I O --I R ~I
.

u O ~1 ~. I
R ~
X 3 ,~ o h ~I h R R R

o N
,1 ,~ ~ ,1 :,,' R
.,1 `, .,.1 .,.1 ~ : , h = h ~
~ ~ ,1 .,,~ ,i a ~ ~ :

~a ~
Id ~d .,, ."., ~1 _I~1 o = o o I
~ ~ ~ .

I ~ bQ)oa) O ~~ R 1~:
h ~0 ~ 0 N ~ N
~: ~h,~:: h ~
~0 ~0 I N
a) I O I c Ln ~D

Claims (8)

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

1. A heat-sensitive, non-volatile, non-hygroscopic, and odor-free recording composition adapted to acquire a color contrasting visibly with a background color of the composition upon heating a selected region thereof to an elevated temperature, comprising an N-substituted condensation product of a heterocyclic diimino compound and an aromatic aldehyde, said heterocyclic diimino compound being selected from the group consisting of piperazine, homopiperazine, 2-alkylpiperazine, and 2,5-dialkylpiperazine; and a cyclic polyketo compound reactive with amines and amides at elevated temperatures to form a color.

2. The composition of claim 1, wherein said 2-alkylpiper-azine comprises 2-methyl piperazine.

3. The composition of claim 1, wherein said 2,5-dialkylpiperazine comprises 2,5-dimethyl piperazine.

4. The composition of claim 1, wherein said cyclic polyketo compound is selected from the group consisting of ninhydrin, isatin, 5-bromoisatin, 5,7-dichloroisatin, alloxan, alloxazine and hydrindantin.

5. The composition of claim 1, wherein said aromatic aldehyde is an aldehyde selected from Table II of the specifica-tion.

6. The composition of claim 1, and further comprising a stabilizer selected from the group consisting of substituted ureas and thioureas; gallic acid; o-toluic acid; m-toluic acid;
p-toluic acid; 2-mercaptobenzothiazole; and 2,2' dithiobis (benzothiazole).

7. The composition of claim 1, and further comprising an activator selected from Table I of the specification.

8. The composition of claim 1, and further comprising binder means adapted to bind said composition to a substrate.