CA1131021A - Color-developing sheet for pressure-sensitive recording sheets - Google Patents

Abstract

Title of the Invention COLOR-DEVELOPING SHEET FOR PRESSURE-SENSITIVE RECORDING SHEETS

Abstract of the Disclosure A color-developing sheet for pressure-sensitive recording sheets, said sheet comprising as a color-developing agent at least one 2,2'-bisphenolsulfone zinc salt selected from compounds of the general formula

Description

~ ~ 3 BACKGROUND OF ~ ION
~ his invention relates to pressure~sensi-tive recording sheets, and more specifically~ to a color developing sheet for pressure-sensitive recording sheets which contains a novel color developing agent~
Pressure sensitive recording sheets are also known as carbonless copying paperO ~hey produce a color upon the application of a mechanical or impact pressure by writing or by pounding a typewriter, thus permitting duplication of several copies simultaneously. ~he color is based on a color forming reaction between an electron-donating colorless dye and an electron-accepting color developer.
~he structure of a pressure-sensitive recording sheet and the mechanism of color formation are illustrated generall~ with reference to the accompanying drawing.
~he back surface o~ each of a top (CB: Coated Back) sheet and a middle ~CFB: Coated Front and Back) shee-t 2 is coated with m~crocapsules 4 having a diameter of several microns to ten and several microns and composed of a shell of a polymeric film such as gelatin and a solution of a colorless color-forming pressure-sensitive dye in an in volatile oil enclosed therein~ ~he sur~ace o~ each of the middle (CFB) sheet 2 and the bottom (C1;': Coated Front) sheet 3 is coated with a layer 5 containing a color deve-loping agerlt having the property of reacting with the colorless dye upon contact therewith and, thus producing a colorO A sheet coated with a coating composition conta.in-~ ~'3~

-- 3 --ing a color developer, such as the CFB shee~t and the CF
sheet, is called a color-developing sheet~ ~en a local-ized pressure is applied by a writing instrument 6 (or a typewriter or the like) to a pressur~-senti-tive recording sheet composed of a multiply structure of -the C~ sheet 1, CFB sheet 2 and CF sheet 3 so that the microcapsule-coated surface ~aces the surface coated with the color developer_containing layer 5, the microcaps~les 4 under the applied pressure break and the solution of the color-less dye moves to the color developer-containing layer 50 ~hus, the dye reacts with the color developer to form a colored image 7 in the desired pattern of recording~ In the pressure-sensitive recording sheet illustrated in the drawing7 only one CFB sheet is interpose~ between the CB
sheet 1 and the CF sheet 3, but :if desired, two or more C~B sheets may be interposed~
Conventionally known e:lectron~accepting color developing agents include (1) inorganic solid acids such as acid clay (Fuller's earth) or attapul~,ite, (2) sub~
stituted phenols and diphenols, ~3) p-substituted phenol formaldehyde polymers, and (4) metal sal-ts of aromatic carboxylic acidsO ~hese color-de~eloping agents, howe~er, are not entirely satisfactory. For example, the inorganic solid acids adsorb gases or moisture in tb.e air and cause yellowing of the sheet or are deteriora~ed in color-form-ing property~ Wi-th the substituted phenols and diphenols, the ultimate density of color is insufficient~ ~he p-substituted phenol formaldehyde polymers (for example, p-phenyl phenol novolak resin) have superior color~forming properties, but have the defect that the coated ~heet undergoes yellowing upon exposure to sunlight9 ~he aroma-tic carboxlic acid metal salts are superior in color-forming abili~y, light fastness of the colored irnage andresistance to yellowing under light, but -their water resis-tance a~d plasticizer resist~nce are n~t- entirely satisfac-toryO
SUMM~RY OF ~HE INV~N~ION
It is a first object of this invention to pro-vide a color-developing sheet which exllibits an equivalent or higher color-developing ability to or than developing sheets containing conventional inorganic scllid acids or . p-ph~nylphenol novolak resin as ~ color developing agen-t, and which give colors having superior wa.-ter resistance and plasticizer resistance.
A second object o~ this invention is to provide a color developing sheet which gives a colored image having superior light ~astness and undergoing little decrease in density with time, and whose ~endency to yellowing under sun~light or the like is dras-tically reducedO
A third object of thi.s invention is to provide a color-developing sheet which lends itself to very advantageous handling and-storage~
~ ccording to this invention7 thexe is provided a color-developing sheet for pressure-sensitive recarding sheets, said sheet comprising as a color~developing agent ~3~

at least one 2,2'-bisphenolsulfone zinc salt selected from the group consistin.g of compounds of -the formula Zn 0 ' (I) ~ -S02- ~

Rl R2 wherein Rl and R2 are identical or differellt, and re-prese.nt a nydrogen atom, a halogen atom, an all~yl group containing 1 to 10 carbon atoms, a cycloalkyl group con-talning 3 to 10 carbon atoms, an aralkyl group containing 7 to 11 carbon a-toms, or a phenyl group.
In a preferred embodiment, -the present in~ention provides a color-developing sheet for pressure~sensitive recording sheets, said color-developing sheet comprising both the aforesaid 2,2'-bisphenolsulfone zinc salt and at least one polyvalent metal compound selec-ted ~rom the group consisting of oxides, hydroxides al~d carbonates of zinc, magnesium, aluminum, ~ead, titani.u~, calcium, cobalt, nickel, manganese and bc~rium~
The 2,2'-bisphenolsul~one zinc salts o~ formula (I) are known compounds~ However, it has not been known that these compounds form a color upon con-tcct with a colorless pressure-sensitive dye to form a colored image having superior fastness characteris-tics, and are -thus suitable as a color--developing a~ent for pressure-sensitive recordln~ sheetsa In addition, it has been diffi~ult to ~ L3~2 anticipate -the suitability of the 2,2'-bisphenolsulfone zinc salts as a color-developing agent4 Free bisphenol~sulfone, a precursor for the zinc salts of formula (I), has been founcl-to have lit-tle or I10 color-forming abili-ty when used as a color-develop-ing agent for pressure-sensitive recordin~ sheets.
~ he color-developing sheet of this invention containing the zinc salt of formula (I) has an equivalent or greater color-forming ability -to or thall color-develop-ing sheets containing inorganic solid acicls or p-phen~l phenol novolak resin as a color-developing agent, and the formed image has good resistance to fading u~lder the action of water, plasticizers, light, etcJ ~he color-developing sheet of this invention also has much improved resistance to yellowing under exposure of sunlight or the like, and lends itself to very adval1tageous handling and storage.
DE~AILED DE~CRIP~ION OF PR~FERRED E~5~0DI~ S
~he subaect matter of this invention is a color-developing sheet for pressure-sensitive recording sheets, said color-developing sheet comprising as a color-developing agent at least one 2~2'-bisphenolsulfone zinc salt selected from the group consisting of compounds of the gerleral formula ~ ~ 3 Zn ~ -~2 ~ ~ (I) wherein Rl and R2 are identical or different~ and represent a hydrogen a-tom, a halogen atom, an alkyl group containing 1 to lO carbon atoms, a cycloalkyl group containing 3 to : 5 10 carbon atoms, an aralkyl group containing 7 to ll ` carbon atoms, or a phenyl group.
2g2'-b1sphenolsulfone~used to produce the z-nc : salt o~ formula (I) is produced, for ex~mp1e, by (i) oxidizing w1th hydr~ogen peroxide a 2,2l-bisphenol sulfide co~pound obtained by the reaction of a p-substituted phenol wi-th sulfur dichloride, or (ii) oxidizing with :~`
: hydrogen peroxide a 2~2'~bisphen.ol sulfoxide compound obtained ~ the reaction o~ a p-substitu~ed phenol with th1onyl chloride~ Examples o~ the p substitu-ted phenol that can be used in the above reaction include p-halo-phenols such as p-chlorophenol and p-bromophenol;:p-alkyl-phenols such as p-cresol~ p~a~ylphenol, p-octylphenol~
p-tertiary butylphenol ana p-nonylphenol; p-cycloalkyl~
pheno1s such as p-cyclohexylphenol; p-(a~-dlmethylbenzyl) phenol; and p-phenylphenolO Among theseS p~oc-~ylphenol, p~nonylphenol, p~cyclohexylphenol~ and p (~ dimethyl-benzyl)phenol are preferred~ ~hese p-substituted phenols may be used alone or in combimation with one another~ -When two or more p-substituted phenols are used7 there $~

can be obtained a mixture composed of -two or more 2,2'-bisphenolsulfones having the formula OH OH

2 -R

in which two R groups are different from each other.
Some known methods can be applied -to the produc-tion of the zinc salt of formula (I) from -the resulting 2,2'-bisphenolsulfone or i-ts mixture.
One method comprises reacting ~L alkali metal salt of the 2,2'-bisphenolsulfone with a wa-ter-soluble zinc salt in a solvent capable of dissol~in~ both~ Ac-cording to this method, the 2,2'-bisphenolsulfone is first :reacted with an alkali metal hydroxide or alkoxide to form the alkali metal salt of 2,2'-bisphenolsulfone or its solu-tion in water, an alcohol or in a mixture of water and an alcoholO ~hen, the produc-t is reacted with the water-soluble zinc salt.
Speci~ical~y, when ~the 2,2'-bisphenolsulfone zinc salt of formula (I) is to be produceclg at least 2 moles of the alkali me-tal hydroxide or alkoxide and at least one mole of the water-soluble zinc s~lt are used per mole of the 2,2'-bisphenolsulfone. Examples of the watar-soluble zinc salt that can be usecl are inorganic acid salts such as zinc chloride, zinc sulfate and zinc nitrate and organic acid salts such as zl,^nc oxalate and ~3 _ 9 zinc acetate.
~ he zinc salt of forr,1ula (I) can also be pro-duced by reacting 2,2' bisphenolsulfone wi-th an organic acid salt such as zinc oxalate, or zinc acetate in an organic solvent at an elevated temperatureO Useful organic solvents for this reaction include methanol, ethanolg butanol~ acetone, benzene 7 tOlUelle 9 and methylene chloride. It is especially effective to dis-solve the 2,2'-bisphenolsulfone compound in such a solvent"
The zinc salts of genera~ forrnula (I) are used as color-developing agents either alone or in combination with each other according to the purpose of use~
~ he color~developing agent in accordance with this i~ention can be used jointl~ with ~Ol~n color-developing agents, such as inor~anic solid acids (eOg.
~CtiVc~ted acid clay~ org~lic polymers (e.g., phenol-formaldehyde resin~, and aromatic carboxJlic acid metal salts, wqthout any deletcriOU~ effect~
In one pre~erred embodiment of this invention, O~Ol to lO parts by weight, preferably 0~2 to 5 parts by weight, por part by weight of` the color-developing agent of at least one polyvalent metallic compound selected from the group consisting of oxides, hydroxides and carbonates of zinc~ magnesium, aluminum, lead, titanium, calcium, cobalt, nickel and me~lgQnese is coated together with the color-developing agent o~ formula (I) on a sheet. Examples of the polyvalent metal compounds ~3~
_ 10 -are zinc oxide, magnesium oxide, alumin~m oxide1 calcium oxide, lead oxide, titanium oxide, manga~ese oxide, m~gnesium hydroxide, alumim ~ hydroxide, calcium hydro xide~ zinc hydroxide1 and calcium carbonate. I~en these polyvalent metal compounds are used, the resulting color-developing sheet has improved resistance to yellowing under light, and the rate of color development becomes faster and the color density increases. Moreover, the light fastness, plasticizer resistance an~ storage stability of the formed image are improved at -the same timeO Among the aforesaid polyvalent metal compounds, zinc oxide is most practical.
~ he color developing sheet of tllis invention can be prepared by various methods. A ~ypical method comprises coating a sheet such as paper with a water-base coating color containing the color-developing agent suspended therein. ~he coating color is conditioned to have a suitable viscosity and suitable coa-tin~ charac teristics by incorporating a kaolin clay~ calcium car-bonate, starch, etc. n a synthetic or na-tural latex, and desirabably contains 10 to 70% by weight of the color-developing agent based on the total solids con~ent.
When the content of the color-developing agent is less than 10% by weight, the color~developing agent ca~not ex-hibit sufficies color-~3rming properties~ When it ex-ceeds 70% by weight, the characteristics of the surface o~ the resulting color~developing sheet are deterior~~tedO
~he amount of the coating color to be coated on the base , sheet is at least 005 g/m2, preferabl~ 1 to 10 g/m2, as solids content~ In other words, at least 0~05 g/m2, preferably 0~1 to 7 g/m2, of the color~developing agen-t is applied to the sheetO
~he color-developing sheet o~ -this invention cal also be produced by an alternative metllod which com~
prises dissolving or suspending the color-developing agent in an organic solvent such as alcohols, hyclrocarbons or ketones, optionally incorpora-ting a kaolin cla~ calcium carbonate, etc~, and coating the resulting solution or suspension on a sheet such as paper. ~he s~ount of the coating solution or suspension is at le~s.st 0905 g/m2, preferably Ool to 7 g/m , as the color-developing agent.
Still another method for producing the color-developing sheet of this inveIltion comprises incorporatingthe color-developi~g agent into a sheet-forming stock, and subjecting the mi~ture -to a sheet-~orming process.
The amount of the color-developing agent can be reduc2d in the present invention, and the conce~tr~tion, viscosi-ty, etc. of the coat mg composi-tion can be varied over relati~ely wide rangesr Accordingly, both on-~achine coating and off-machine coating are possible, and great advan-tages can be obtained not only in the properties of the color-d2veloping sheet, but also in -the process steps of sheet production~
~ 'he following Examples specifically illustrate the present lnvention.
S~nthesis Exam~le 1 ~ ~ 3 In a mixture of carbon tetrach:Loride and n-hexane, p-tert-~octyl phenol was reactecl wlth sulfur di chloricle to form 2,2'-bis(p~tert-octylphenol)sulfide Th0 sulfide was oxidized with hydrogen peroxide in glacial acetic acid to form 2,2'-bis(p-ter-t-octylpheno:l)sulf'one.
Recrystallization from carbon tetrachloride/n-hexane afforded a purified pr0duct having a melt-ing point of 142 to 144G.
Then, 9.48 ~ (0.02 mole) of the resul-ting 2,2'-bisphenolsulfone was added -to a solution of 1~6 g (0~04 mole) of sodium hydroxide in 100 ml of e-thyl alcoholr The solution was stirred for 1 hour under reflux, and then cooled to 30C~ A solution of 2.73 g (0302 mole) of zinc chloride in 50 ml of ethyl alcohol was added, and the mixture was refluxed for 1 hourO The reac-tion mixture was poured into 500 ml of ice water~ The precipitated white crystals were collected by filtra-tioll, a.nd dried to afford 10~6 g of 2,2'-bis(p-tert-octylphenol)sulfone zinc salt (to be referred to as compound ~To~ 1) corresponding to general formula (I)o ~Le~
Pale yellow 2,2'-bis(p-tert-bu-tylphenol)sulfone was prepared in the same way as in Synthesls Example 1 using p-tert-butylphenolO
To a solu-tion of lo 38 g (0.06 r.. lole) of metallic sodium in 180 ml of ethyl alcohol wa.s addecl 1402 g (0~03 mole) of the aforesaid 2,2'-bisphenolsulfonen The mixture was s-tirred for 1 hour under reflux, al~ t-lhen cooled to 30C. The reaction mixture was added -to a solution of 4.09 g of zinc chloride in 100 ml of e-tll~l alcoholO
~he mixture was stirred for 4 hours at 30Cv '~he preci-pitated crystals were separated by filtra-tion, and ethyl alcohol was distilled off under reduced pressure from the filtrate to afford 13.6 g of pale yellow crystals of 2,2'-bis~p-tert-butylphenol)sulfone zinc salt (to be referred to as compound No~ 2) corresponding to general formula ~I).

In dichloroethane, 2 moles of p-cyclohexylphenol was reacted with 1 mole of thionyl chloride to form 2,2'~
bis(p-cyclohexylphenol)sulfoxideD ~he product was then oxidized with hydrogen peroxide in glacial acetic acid to form 2$2'-bis(p-cyclohexylphenol)sulfone~ Recrystalliza-tion from carbon tetrachloride afforded wl1ite crystals having a melting point of 176 to 178C. IJsing this pro-duct, 292'~bis(p-cyclohexylphenol~sulfone zinc salt (to be referred to as compound l~oO ~) corre.sponding to ge~eral formula (I) was prepared in the same wa~ as in ~ynthesis Example 1.
r~
Using p-phenylphenol, 2,2'~bis(p~phenylphenol) sulfone zinc salt (to be referred to as colapound NoO 4) was prepared in the same way as in SyntJhesis Example 1.
_ r]os I to ( Using each of compounds Nos. 1 to 4 in Synthesis Examples 1 to 12 as a color-developing agent, a suspension of the followirLg formulation was prepared by means of a '~ ' ' .

2'~

sand grinding mill.
Par~
Color-de~eloping agent240 5 Sodium ligninsulfonate~0 Water ~2.5 A coating composition of the following formulation was prepared by using the above suspension~
Parts~ E~
Suspension Kaolin 100 Styrene/butadiene latex (concentration 5~/0) 15 Oxidized s-tarch 15 Water 180 ~he ¢oating composition was coated on a sheet of fine paper and dried so that the amoun-t of the coating composition applied was 6 g/m2 upon drying~ ~hus, a color-developing sheet was obtained.
Comparat e ~ e~
A suspension and a coating composition were prepared in accordance with the same formulations as in Example 1 using 2,2'-bis(p tert-octylphenol~sul~one which is a precursor of the 2,2'-bis(p-tert-octy3phenol)sulfone zinc salt (compound No. 1) obtained in S~n-thesis Example 1. The coating composition was coated on a sheet of fine paper and dried so that the amount of the coating composi-tion was 6 g/m2 upon drying. ~hus, a color-developing sheet was obtainedO

. ~ : : . :. :
.... .

3 ~

Co~parative Example 2 A color-developing sheet was prepared in the same way as in Co~parative Example 1 using 2~2'-bistp-(a7a-dimethylbenzyl)phenol~sulfone~
9g~5 ~3t~ 5aC~el:~
~ glass reactor was charged wi-th 170 g of p-phe~ylphenol, 2205 g of 80,~ para-formaldehyde, 2~0 g of p-toluenesulfonic acid and 200 g of benzene~ and wi-th stirring~ -the contents were heatedO ~hile wa-ter generated as a result of the reaction was distille~. off out of the reactor as an azeotrope with benzene, the~ were reacted at 70 to 80C for 2 hours. ~hen, 320 g of a l~' aqueous solution of sodium hydroxide was added, and benzene was distilled off by steam distillationO Dilute sulfuric acid was added dropwise, a~d the precipitated p-phenylphenol/
formaldehyde polymer was collected by filtration, washed with water~ and dried to a~ford 176 g of a whi-te powderO
A color-developing ~heet was produced in the same way as in Comparative Example 1 using -the resul-ting p-phenyl-phenol~ormaldehyde polymer~

A color-developing sheet was prepared in the same way as in Comparative Example l except using zinc 3_t4'~ ,a_dimethylbenzyl)phenyl~-5-(a7~-dimethylbenzyl) salicylate~
~est Examples ~ he properties of the color-developing sheets produced in Examples 1 to 4 and Comparative Examples 1 to

4 were tested by the following methods~ r~he results are tabulated belowO
(1) Color-developing rates of the color-developing sheet A cornmercially avail~ble CB shse-t (N~50~, a product of Jujo Paper Co., Ltd.) contailling crystal viole-t lactone as a main pressure-sensitive d~e and a sample color-developing sheet are laid so that the coa-ted surfaces of the sheets contacted each o-ther~ A pressure is applied to the multiply sheet by an electric typewriter to forrn a cobalt blue color~ The reflectance Io Of the sheet befoxe color formation, the reflectence Il of the sheet two minutes after color developmen-t~ and -the reflec-tance I2 of the sheet 24 hours after color development are measured by using a Hunter Reflectmeter (using an amber filter). ~he initial color-developi.ng ra-te (Jl) and the ultimate color-developing rate (J2) are calculated in accordance with the following equations~

I - I

Jz = ~ x 100 (%) Higher initial ~nd ul-tirna-te color-developing rates are preferred~
(2) Retention of color intensity (Li~ht-~de resis-tance) ~he color developing sheet havi~g a color formed by the method described in (1~ is exposed -to a fade-o-.-.. .. . .

meter for 2 hours and 6 hours~ respec-tively~ '~he color-developing ra-tes of the sheets are calculated in the same way as in ~1) above as J3 and J4O ~he retention of color is calculated in accordance with the following equations~

Color retention J
after 2 hour ~xposure = ~ x 100 (~,) ~olor re-tention J4 after 6 hour exposure = ~ x 100 (~) Higher color retention values are preferredO
(~) Retention of whiteness (Resistance ''GO yellowing) ~he color-developing sheet before color forma-tion is exposed to a fade-o-meter for 6 boursO ~he re-flec-t?~ce Kl of the sheet before the exposure7 and its reflectance K2 after the exposure are measured by using a Hunter Reflectmet~r (using a blue fil-ter)~ ~he retention of white~ess (H) is calculated in accordance with the following equation.
K

H = ~ x 100 (%) Higher whiteness reten-tion values show less yellowing of -the sheet under light~
(4) Plasticizer resistance of a coloxed :lmage A small amount of dioctyl phth.~la-te (a plas-ticier for vinyl chloride resins) is coa-ted on the colored surface of the color-developing sheet af'GeX color forma-tion by the method described in (1) above. A change in ~3~2 density of the color was observed wit'n u~aided eyes immediately after coating and two weeks af-ter coatingO

(5) Water resistance of colored image ~he color-developing shee-t after color forma tion by the me-thod described in (1) is dipped in waterO
A change in the density of the color was observed with unaided eyes two 1 hours after dipping.

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It can be seen from the table t~a-t the color-developing sheets of this invention ha~e a marked improve-ment in color forming properties than the color-developing sheets of Comparative ~xamples 1 and 2 (prepared in the same way as in Example 1 using free sul:orles which are precursors of the color-developing agents of the present invention). In other words, while the free sulfones have no color-forming proper-ties, the zinc salts -thereof have very good color-forming properties~ ~urthermore, the color~developing sheets of this invention have equivalent or slightly better color forming proper-ties (the color-developîng rate) and water resistance to or than the color-developing sheets of Comparative E~aples 3 and 4 (color-developing sheets containing known color developing-agents), but have much better light f~ding resistance(color retention), resistance to yello~ling under light (whiteness retention) and plasticizer relsi.stance tha~ the latterO
Since the color produced by -the color-developing sheet of this in~ention is s-table to light and plasticizers or the like and scarcely undergoes a decrease in density, it can be used in ~pplications for whicll co.nventional color-developing sheets are unsuitable because of -the need for long-term s-torage stability. Hence~ -the color-develop-ing sheet of this invention has a very great practical significance.

, . . '-- :

" ..
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:

Claims (3)

WHAT WE CLAIM IS:

1. A color-developing sheet for pressure-sensitive recording sheets, said color-developing sheet comprising as a color-developing agent at least one 2,2'-bisphenol-sulfone zinc salt selected from the group consisting of compounds of the following general formula (I) wherein R1 and R2 are identical or different, and re-present a hydrogen atom, a halogen atom, an alkyl group containing 1 to 10 carbon atoms, a cycloalkyl group containing 3 to 10 carbon atoms, an aralkyl group contain-ing 7 to 11 carbon atoms, or a phenyl group.

2. The color-developing sheet of claim 1 wherein the 2,2'-bisphenolsulfone zinc salt is a product from at least one p-substituted phenol selected from the group consisting of p-halophenols, p-alkylphenols, p-cycloalkyl-phenols, p-(.alpha.,.alpha.-dimethylbenzyl)phenol and p-phenylphenol.

3. The color-developing sheet of claim 1 which further comprises at least one polyvalent metal compound selected from the group consisting of oxides, hydroxides and carbonates of zinc, magnesium, aluminum, lead, titanium, calcium, cobalt, nickel and manganese.