Heat-sensitive recording medium

Abstract

The purpose of the present invention is to provide a heat-sensitive recording medium which hardly causes safety concerns such as endocrine disrupting chemicals, and is excellent in chromogenic properties and light resistance, and also excellent in heat resistance. A heat-sensitive recording medium (1) has a configuration in which a heat-sensitive recording layer (3) is layered on a substrate (2). The heat-sensitive recording layer (3) comprises a color former, a non-phenol-based developer, and a non-phenol-based antioxidant. The non-phenol-based antioxidant comprises a phosphorus-based antioxidant. Preferably, the non-phenol-based developer comprises a compound represented by the following formula (1) and / or a compound represented by the following formula (2). [Formula 1] (see formula 1) [Formula 2] (see formula 2) (The symbols in the formulae (1) and (2) are as defined in the specification.)

Description

- 1 - Description Title of Invention: HEAT-SENSITIVE RECORDING BODY Technical Field [0001) The present invention relates to a heat-sensitive recording medium, and more particularly to a heatsensitive recording medium which hardly causes safety concerns, and is excellent in chromogenic properties, light resistance and heat resistance. Background Art [0002) Heat-sensitive recording media develop a color through a chemical reaction upon heating of a thermal head or the like to obtain a recording image, and are used in a wide range of applications such as not only recording media for facsimiles, automatic ticket vending machines and scientific measurement machines but also heat-sensitive recording labels for POP systems and receipt paper in retail shops. [0003) As described above, heat-sensitive recording media are widely used. Therefore, heat-sensitive recording media are required to have various kinds of performance. For example, chromogenic properties are required which CA 3265824 Date reçue / Received date 2025-02-19 ensure that ·wlYen a ba·rcode is read with· a 'barcode reader,, the ·reading ·with the barcode reader is performed. with good ac.curacy·. ;In additi•Dn; a characte:ri:st:lc is required ·which :ens.ures that a, heatrsensitive· :recording medium is ·1.mlikel.y to turn yellow· when the heat-sensitive: :recording medium. is exposed f.or a long time to intense light in.eluding an u1traviolet raY" i(light ·resistanae) . Further., excel1ent heat res,istance is, xequired which ensu·res· that .even in heating· in a miorowave oven or the. like, a non-pcint portion is unlike1y to• develDP a color while: the chromogenic :prupe:rties ·of a print portion are, nqt deteriorated, [·000.4] l>,:s• such .a· 'heat-sensiti.ve re·co:rding medium, for example:; a heat~.sensitive recurding medi·um has :been proposed in Which a heat·-sensiti:ve recording layer containing a colu·rl.ess· or 1ightrco·lored electron-donating leuco· :dye and an el.ectron-accepting deve·loper is provided on .a support, wherein the· h.eat-.s.ensi:tive• recording layer comprises•, ,as a deve.l·oper, a phenol-based deve·loper such as 2., 4' -dihydroxydiphen,ylsulfone, and compri,ses., as an antioxidantf a :phenol-'ba:sed ,antioxidant 'having a pheno1in hydroxyl gr,oup,i' ·such as 1,11 3~tris•(2~methyl•~4~hydroxy-5- tert~butylphenyl)'buta:ne ·(see, for example,, .Patent Li,terature :1) , G.ita.tion L.ist CA 3265824 Date reçue / Received date 2025-02-19 Batent Literature, ['0005] Patent Literature: 1,:, ,Japanese Patent Laid~open 'No .. 20,:2:G~ 15'1948 Summary ,of 'Inventi,on TechnicaL Problem [000:6] Compounds having a phenolic hY,droxY,l group (phenoL-' based :compounds} r such a·s pheno·l.~based. developers and :pheno·l'-'ba·sed antioxidants used ::tn Patent Literature 1 above, :caμse sa'fety conc(;l:rns. as enq,ocrine, disrupting ch.emicals. Therefo·r,e,. ,in recent years,. heat-sensi.tiv.e: re·cording :media with. add:i ti.ves •Such as a developeT and an: antioxidant, which havi·ng no p'heno'l ,s,keleton,. :are required ·from the viet-lpo:int ,.o:f :environmental, compatibility,

[0007] The pre.sent ,fnvent:Lon has been made: in view of thes.e circumstances, and an obje:ct of the pre.sent :inventi·on is to· .provide. ,a hea:t-sBnsitive: recording medium ·which hardly causes safety· :concerna such a:s endocrine, 'disrupting chemicals,,• .and is: ·excellent in :chromagenic, properties and light :resistance, ,and, also excell·ent in heat resistance,. Solution ta Problem roodaJ CA 3265824 Date reçue / Received date 2025-02-19 The invent.ors of the. pre·sent application have conducted intensive studies. for achieving the above~ described ob:l.ect, and resultantly .found that when .a de;v:e.loper. 'having no pheno,l s·ke.leton (non~phenol-based deve"loper") and a specific antioxidant having no: phenol s·keleton .(non-phenol-based. antioxidant) are blended. in a heat-sensitiv.e recording l·ayer,, it i·s, possible to provide a heat-sensitive re.cording ,medium which hardly causes safety· ,concerns .such as endocrine diB-rupting chemicals; and is excellent in chromogen'ic ;properties, and light resistance:, and also· excel'lent in heat resistance. 'The present inv(;!nt;i.on h<;ls :bes!n c9m~leted Qn the bs:i:s-is of the f.inding_s. [·0009] That is,, an aspect of the, pr,esent invention provides a heat~sensitive recording medium in which a 'heatsens-: l.t:t;v:e recording layer is 1ayered on a substrate, In the heat-sens:l'.t:l.ve recording medium of the. present. invention, the heat-sens-:l.t:l.;v:e recording layer comprises a colo·r ,forme-r, a non~phenol-ibased developer, and -a• nonphen- ol-ibase.d -antiox:idant.

[0010] Conventi•onal heat..,sensj:ti:ve r.eco:rding media typi·cally comprise phenol-based, compounds as a deve'loper and an antioxidant. However, the phenol·-based compounds cause• ,safety. ·c.oncerns as endocrine disrupting chemicals. CA 3265824 Date reçue / Received date 2025-02-19 In contrast,. in the 'heat-sensitive reco:rding medium of: the ·pr.es:ent: invention! the dev.eloper. and the· antioxidant contained in the heat--sensitive re.cording layer are non-phenol-bas.ed coll!pounds. Therefore, the above-described .concerns do· not arise. In :addition,. the heat-sensitive recording_ medium. of the pres.ent invention is :excellent in chromo.g.enic properties,. light resistance and heat resistance· even though the above-described non~ pherrol·,based compounds• are used.

[0011] In the heat-sensitive recording medium of the, pre1;?ent :i.n;verrd.on, 1:he non--;J:>h"8nol-l;)ased !intioxid<J.nt comprises a phosphorus-based antioxidant.. By this, l·ight re-sistance 1can be· particularly improved.

[0012] In an embodiment of the heat-sensitive recording· .medium. of. the present invention,. the non-pheno·1-·based deve1oper preferabl.y :comprises .a -compound represented b.y the followi-ng formu·Ia ( l') and / or a compound represented by the following formu:l·a· (21 . [Formula 1] CA 3265824 Date reçue / Received date 2025-02-19 - 6 - each independently :repr,esent a h,ydrogen atom, :or a subs.tituent. R6· .and R12 each independently :represent a substituent, .m :represents: an Integer :o,f O to 4,. When m is· 2 or more, a plurality o-f R6 may be the, .same, o:r different. n repres.ents· an integer of 0 to 4. When n is 2 or more,, .a p·1ural:ity ,of R12 may be the same or different.') ['Formula 2] R1~ RF 1 1 R23 V N, _,,.N R22 0 C (2) R16 M.,,.o £ II R21 '14, ·' 1s O' (R18)o 1{20 and R2~ each independently .represent a ·hydr,ogen atom,· or a subs ti tuent. R18 represents a substi tuent. o repr.esents an integ.er of O to 4, When o is 2 or ·more,. a plurality of: R1 B' may· 'be the same or different,) [0.013] In ,an embodiment of: the heat-·sensitive recording med:Lum, of the pres·ent invention,: the non-ph-enol.~based developer preferably :comprises a compound, represented. b.y the following· formula (:la) and / :or a ·compound reipres.ented by, the following fcormula (2a,), , ['.Formula 3] CA 3265824 Date reçue / Received date 2025-02-19 (fa} {The symbols in formula: .{la) are the same a:s in formula fll .J. [Formula ·4] (2a) (The symbols, in xormula !(2a) are· the same as in formula (2:) .) L00i.4J This: configur:ation enables the: provisi,on of a heat~ sens{,t:Lve re-carding :med:Lum, t'hat is• further ·exce·;ll.ent :Ln chromogemi.c :properties ,and heat resi·st:a'nce. ['0.015) In anothe.r ·emb.odirnent of:, the heat..;:sensitive recording medium. of, the pr.e:sent invention,:• the content o·f the non~phenol;..,bas·ed 'deve,lc,per is prefe:rabl:y not less than 1,(} mass! / ; and 'not more than 50 mass% with respect to the entirety. ,of· the 'heat-sensitive recording layer, This configuration .enable.s the, provision i!>r a, fieat-sensitlve, CA 3265824 Date reçue / Received date 2025-02-19 reco-rding medium. that is excellent in chromogenic properti:es, and ·exce,llent :in heat res,istance .. [:001.6) In. another embod:i:ment of· the heat-sensitive recording ·med:Lum of the pres.ant invention, the content o.f' the non-phenol-:b.ased antioxidant is preferably not less than 5 ·ma:ss·%: and. not more, than '10 mass% wi.th r.espect to the entirety ·of the heat~sens:itive recording layer. This conf:igurati·on .ena.bl.es the provi•si:on of a heat~.sensit:iverecording ·medium that is excellent in •chromogenic :properties and h.eat resi-stance: and excellent in light resistam;:e, ·even thc;,ughr i:l. nc;,n-ph'enc;,1-based. antioxl:d,mt is used. Advantageou,s, E•f'fect 0£- Inirent:ion [001 7] l\.ccoxding t:o: the :present invention,. it is :p_oss:ible to: provide· a :h.eat~s.ensitive recording medium ·whirch hardly causes safety ,concerns· such ,as ·endocrin:e dis.rupting chemicals', -and is• ·exce'll.ent i:n chromo.genic: proper.ti.es and light :res:istance, -and exce'llent in heat resistance .. ,Bri'ef :des:cr:i;ption of Dr-awing

[0018] ['Fi:gure l:] 'F;Lgure i is a' s.chemat:i:c sectional view showing an embodiment of a heat~sensitive recording medium :of the: present inventlo,rt. CA 3265824 Date reçue / Received date 2025-02-19 Description of :Embodiments [:0019] A heat-sensitive recordin!:J ·medium of the. present imz.ention has a layer.ed structure in. which a .he·atsensitiv. e rec0rding lay.er .is layered, on a substrate. In the heat-sensitive recording medium 0f the: pre·sent invention; the h·eat-sensd.tive recording layer .compr:iseB a c0lor ,farmer, a non~:pnenol"'iba·sed :devel·oper, and a non..,. ·pheno·l..;based ,antiox'idant.. The non-phenol>-'based antloxidant coll]prises a phosphorus--,based antioxidant, [Q02(i] HeTe:inafter, an ·embodiment of the heat-sensitive re:cordi:ng :medium of. the present invention ·wi:11 .be described in :detail w.ith reference: to: the drawings-, :but the present invention is no.t limited bo the ·folJ;owing embodiments·•

[0021] Figure i is a schemat1c sectional ,dew showing an embodiment •of the h.ea:t.-s:ensitive· .r.ecording medium of the ·present in.vent'ian.

[0022] .A heat-sens.itive recording .medium l accord'i•ng to the present ·embodiment has: ,a• la',"ered structure: in which an underc0at Lay.er 61 1, a heat.~.sensitive• recording laye·r 3, .an intermed:f.ate· layer 4 ,and a topcoat layer 5 are layered in CA 3265824 Date reçue / Received date 2025-02-19 - 1(); - the stated order on a sheet~shaped substrat·e 2 as shown in .Figure 1 . [:00231 In ·the ·present embodiment, the substrate 2 functions. as· a support f·or the. heat-.sensitive, :recording medium 1. As· the substrate 2,. for examp1e, pa,pers such a·s, highqua1ity paper, .. art paper,. ,c:oated paper, craft paper, ,and laminated ·paper ·obtained :by laminating a thermoplastic resin such, .as po.lyethylene to a substrate from any of the· foregoing ·pa,pe-rs, synthetic pa,pe,r, and. porous materials such as. nonwoven fabrics can be used, In addition, t:r,ansJ?arent synthet·ic rei,in f.ilms,- for <:,xample, polypropylene fi.lms~ polyethylene te,rephthalate f.ilms, po:lystyr.ene fi.lms -and :polycarbonate .films can be used .. The thickness of t'he substrate 2 is not limited, and' the substrate 2 with a thickness of about 1.0 μm to about. 100 μm ts prepared, the substrate 2 exce'll·ent in coatl:ng properties ls obtalned. In addltion,· th·e substrate 2 ex.ce'.Llent in transparency is obtained. [•0024] In the present embodiment, the. undercoat .layer '6 ha-s, functions such as heat insulating properties f.or preventing :diffusi·on of heat given from a thermal .head, and. cushionin·g prope,rti·e-s. The ·undercoat l·ayer ·6: is formed. :by,- f.or. examp1e•, adding hollow parti·cles, as :a flller to a binder. [0025) CA 3265824 Date reçue / Received date 2025-02-19 - 11 - By providing the heat-sensitive recording :medium 1 with the undercoat layer 6 having heat resistance ·as. described above•, the, sensitivity ,of print is. improv.ed; Therefore,• ,an increase: in :a,ppili.e.d vo.ltage of the th.ermal head can be suppressed, and as ·a .result,. attachment to the thermal he·ad. by burning can be suppress.ed.

[0026] The average _partLcle diameter of the ho:llow· particles added as a .filler to the undercoat layer •6 is preferably 1 μm to 16'0: μm, When average particle. diame.ter of the. hol'low particles- is in this range, the heat;· in1;3μL;i:ting propert::i:ElS of the underqoat li!,yer 6 arEl, improved.. Here, the average ·particle diameter. is. a ·weigh average: particle diameter measured .by laser diffractometry. .Measurement of the average ,particle diame.te·r by 1-a·ser diffractometry can .be· _performed ·us-ing,, for example,• "MT.330:dEx-r:r" .(brand name), manufactured by Mi.crotracBEL Corporation,

[0027] The hoLlow :rat·io of the hollow parti•cl•es is pref.erabl')I' 3:0% to 99%. When the hol3.ow ra,t·io o'f the hollow :particLes is in this, .range, the heat insulating properti·es .of the undercoat lay.er 6 are improved.. The larger the, hoLlow .ratio of the, hollow particles-., the 'higher the heat insulation effect. .Thereforer the color former can e·ffectively, devel·op a ·color with a •small amount of heat.. That i-s:, ;i.ncreasing th.e ho'llo.w -ratio CA 3265824 Date reçue / Received date 2025-02-19 - 1.2 - improves the print quality of. the heat~sensitive reco·rding medium. 1.

[0028] Here, the ·hollow ratio ,of the hollow particle is calculated by· the following .equation. Hollow ratio "" { {v,o]:ume of 'Voids) / {volume of ho.llow _particles)·'), x 100 [0029:] The content ratio: .of hol.low particles, in the undercoat layer 6- :Ls preferably 40. :parts by mass to 90. parts by mass per 100 :parts, by mass of the, undercoat layer, [•0030] The material for forming the ho1.low particl•es .is, for examp1e 1 a thermoplastic resin. .Examples of the thermoplastic res•irr include, polystyrene-base resins,. polyvinyl ch'luride·-based resins, polyvinyliderre, chloridebased -resins, polyvinyl acetate,-based resins, polyacrylic acid ester-based. resins,, po:lyacrylonitrile.~based resins., and po.lybutadiene-based. resins.

[0031] As, the fi11er for ·the undercoat layer 6'; a filler other than hoLlow particles. may be use·d .. Examples thereof; include, f.ired. kaol·in, aluminum oxide,· aluminum silicate, 'heavy calc'ium carbonate, light :calcium carbonate,· titanium oxide,, barium sulfate, silica: gel,. activated white, earth, talc, ciay, kaolinite, CA 3265824 Date reçue / Received date 2025-02-19 -· 13; - diatomaceous 'earth, white, :carbon; magnesium carbonate, magnesium oxide, :magnesium hydroxide,. zinc, oxide, polystyrene resin particles., urea-.fo:rma1in .resin _particles., .and _)?Ol_y.olefin :res;in :part·icles. Thes.e.: fil:le.r.s can be used, alone, or in combination of two or more thereof ..

[0032] :Examples of the, binder contained in the. undercoat· layer 6' include .acryl·-styrene copo'lymers, styrene~ butadiene c.opo'lymers, acryl-butadiene-styrene. copo·lymers, viny·1 acetate resins, vinyl. acetate.-acrylic acid copoly. ' mers., st'yrl:!n,;,-acryl:l.c a·oid ester -c:opolymers, ' ,, ' acryli'c sa-ci·d ester-based resins, and :polyurethane-.based [ 0033) As, the :binde·r, water~soluble po'lymers, such ,as ·polyvinyl alcohol, starch and derivatives thereof, cellul:ose d.erf.vatives such as methoxyce·11u1ose, hydroxyethy:lce'l l ul·ose, carboxymethylce11u'los e, methylcellulose. ·and ethy1ce1lul·ose, sodium polyacrylate,, polyvinylp.yrrolidone, acrylamide-acrylic: •acid ester copo.lymers, acrylamide~.acrylic. acid .ester~methacryl·ic acid terpolymers, styrene.~mal.eic anhydride· copolymer alkali salts;1 isobutylene.~male.ic anhydride, co_polymer alkali salts', poly.acry-lam:i..de, sodium alg:i..nate, gelatin, and casein may be used. CA 3265824 Date reçue / Received date 2025-02-19 The applicati,on. amount [:dry weight'.) of the. undercoat layer 6' is preferab'.Ly 1 g / m~ to 10 ;g / m1;, [,0035] The thi.cknes.s o,f the undercoat '.La_yer :6 :Ls preferabl_y 1 μm to. 20 μm .. [•00361 Wherr the under.coa't layer 6 is prepared such that its application amount and ·thi;ckrres-s, are in the abo.v.e~ described ranges, "the undercoat layer 6 appropriately exh:Lblts a heat insulating function,

[0037] In th<;! pre:;,ent embo.dim(;!nt, the. hea.t.-~en:sit::i..ve recording layer '3, is a layer which develops a color. through a chemical reaction upon heating .of a. thermal head or the like to form a re·cording image; .on the heatsensitive recording :medium 1. ,In the. present embodiment;· the hea.t:-sensit.ive recording 'layer 3 comprises a color f.ormer,, ,a rron-ph.endl-b,ased. developer(' .and, a non-phenol' based and.oxidant. Regarding the col.or f.ormer, the color former wh•i,ch. de!ITe1ops a ·color upon heating is ,a component which de!ITelops a :color through a chemi.cal :react·i.on upon :heating of: a therma.l. .head .or the l·ike to form a recording image, on the heat:-sens1.t:i..v.e •• recording .medium i :of the. present embodiment., 'As the •color former which develops :a •colo.r up.cm heating, a. commo.rtl:y ·used kn.own 'leuco..;ba·se dye, can 'he, CA 3265824 Date reçue / Received date 2025-02-19 ·used .. Exampl·es of the Ieuco-'based dye include 3-·(Nisobutyl~ N,..•ethyl) amino,. 6-methyl,.·7-anil inof·l uoran, 3-: (Nisopentyl- N,--ethyl) amino-.6-methyl-7-o.., chloroanil in.of.lL uoran-, 3i-,.(N,methyl--Ni-p,.tol uidino) ·-6- methyl-7-anilinof.1 uoran, 3- (N-ethyl-N-p-toluidino) -6- methyl-.,7-anilinofl uoran, 3- (N-ethyl-N-isopentyi.) amino-6- methyl-7-anil inof.1 uoran,. 3-{N-ethoxypropyl-N-ethyl) .amino- 6·,methyl,i-7-anilinofl uoran; 3i-:(N-cyclohexyl-N,. .methyl)• amino-6,..methyl:-7-·anil inof·l uoran, 3- '(.N-methyl·-N-n,.. propyl )amino.-6·-methyl-:7-an:il inofl uoran, 3-dibutylamino-i:h methyl--7-an:il inofl uoran, 3-diethylamino-ll-methyl-7-pt9lμid: in9fl u9ran, ~'-d:i~th:r:laminq-6-.met;hyl-7- anilinof l uoran, 3.-diethylamino-6-methyl-8-metnylf-luoran, 3-diethylamino-7- (m-trif.luoromethylanilino.) fluoran, 3- diethyiamino:-7- (o:-chloPoanilino) fluoran, 3-.diethylamino- 7•-ch·lorofluoran., 3-dibutylamino~6-methy'l,..T,.bromofluoran., 3--dibutylamino-1.-,(0-chl·oroanilino) fluoran,. 3- dipentylamino- 6-methyl.-7-ani Lin of luoran, :3-dimethylamino,. 5-methyl·-7-methyif luoran, .3-pyrrolidino- 6-methyl-7- anilinof luoran, and crysta'l violet lactone:. These J.eucobased .dyes :can be used •alone, or in combination -of two or more thereof:. [00 39] The particle ·diameter: of the color former is prefer.ably •O .1 to L .0 μm. Since the col-or .former melts and reacts,, the• .larger the ·particle .diameter,- the slower the reaction and the, ,lower the, sensitivity CA 3265824 Date reçue / Received date 2025-02-19 characteristic., •On the o:ther hand; the smaller the particle diamete·r, the highe.r. the ri,sk. that heat us.ed. to dry' th~ pa:Lnt c.ause·s color development at an unexpe:c,ted t'empe:ratur.e, rn the p:resent emb:odiment,, the particle diame·,ter of the, uoLor f,ormer is s.et. ,within the abo:1Te·described range,, and thu's,, the 'sensitivity .characteristi·o and the ,col:or develqpment. tempe·rature' ,o:f the co1:ar former can be appropriately adjusted. Here; the particle diameJ;er is an average• partic:Ie diameter at '50.'% in measur.ement with a M:Lcrotrac :Lase.r Di£fractl.:on arrd s,catter:Lm;r :Particle slze .. Analyzer, [()'040] In ·the :present embo:diment., th'e aolor, former is prefe.;rably :ccmtai.:ned ,in ·an amcmnt of about 10 to 20' ,ma'ss%' w.i.th r.espect to the entirety of the. heat--:sensitive. re·co:rding layer 3! f.or obtaini.ng exc.ell·en.t chromogen:Lc :properties, The Later-,descr.:l.bed Gievelqpe.r is prceferably cont·a.:l.ned in .an ,amount ·o,f .i to· 3, parts per ·one p_a:rt of 1:h.e .eolbr f:ormer on a dry weight basis, [•0.0,41] In the pres:ent embodiment, tbe, heat-sensitive, recording layer 3 comprises, ,a non~phenol~based developer as. :opposed to a pl:renoI~bas·ed. develo;p.er that has, been commonl,y· used. heretof,ore.. The non~henol.""bas·ed dev.elope.r.r which is among: various .electron~accepting substances that :react with the, :abo.'lle:-described 1-eu.co,,,. 'based dy:e to. make the ieuco~hased. dy:e de'lleiop a. ,color-, is CA 3265824 Date reçue / Received date 2025-02-19 ,_ 17 - a compound hav.ing n·o phenolic ·hydroxyl grnup... The cnnf.iguratinn in. -which t:h.e heat,-·sens:itive r,e:co·rding iayer 3 comprises a non~phenol...:.based :devel:oper :is rephrased as "a phenol'"'hased devel~J?er· which :max threaten s·a:Eety as: an endocrine. disrupting ·chemi•cal is• not used. wtth ,purpos:en. rn the ,pr.e.sent embodiment, the, hea-t.-.sensitive re.cording lay.er 3' comprises: a nori-plreno'l-based. developer as opposed t·o· a ;phenol,..based developer, and thus,1_ a. 1.euca'.'-fbased dye can b:e .made to dev.eJ.ap a co:l•o·r :with. e:Ef:ic:iena.y. The heat-s.ensitive r,eco:rdlng l•aye:r 3, may :inev,itably •compr1'se,: as ,an. 1mp,ur1ty or the like,. ,a :phenol,..;ba·sed ·compound. in an i;fmount $nl{lcl.J.. J,moμ\)'h n'Qt to 9i;l'.use: s,;1:Eet:l conqe.rns ?S enctour..tne dis.r,upting 1ehemi1eals. The ·he.at-s.ensiti-r.e . recording lay:er 31, with such a minute ·amount o.f a phenol,based oompoundr .is within the scope. :o:E the: present inv.en.ti.on. As. the no.n .... ,phenol.,.,based developer, known. .develqpers having no :p:henolk hy,droxy"L group can be· used without 1.imitat:Lon., and examples: the.r.e.of include. '2,2'-',bis [ :(4- methyl....:.3-phenoxycarbanyiJ.ami naphen:yl'Yure·a] .diphenylsul:f,onei, 4,.-11 ·• '-'bis (p,-trisulfony lami μo.ca)'.'bon ylamino) :diphen,,.:·lmethane r 2' .,.. p~phenyl:.ure::i:do):benzenesul:fonanili.de:,. and N'-,(p- .to:l ue.rresul f:ony:l) •:..'N" ~ p·-p~t:o.l ue.rresul :E:o.ny•l oxyphe!liyl') ·urea• ..

[0043] Hei:;e: 1, as the; :deveJ,oper, the: :above-des,crlbe.d non~ phenol-iba,sed developers :can als.0 he: used. H:owe;v:.e~, ·t·n.e CA 3265824 Date reçue / Received date 2025-02-19 present inventors. have found. that compounds ·represented by the fo·11.owing formula (.1) and the following formula (:2) are. preferred from the viewpoint of further improving the heat re.sis.tance o.f the heat-sensl:tive recording medium. 1.

[0044] [.Formula '5] each independently repre·sent a hydrogen atom,. or a substituent. R6. and RI2 each independently represent a substituent. :m represents an integer of 0 to 4.. When m is 2 or more, a p:lurality of R6 .may· be the '6ame: or different, n represents· an integer of 0 to 4. When n is 2 or more, a plurality ·of R•~• may 'be· the same or di ff.eren t. )' ['0045) [Formula 6] . R22 (2) CA 3265824 Date reçue / Received date 2025-02-19 - 19: - (!n. formula (:2:), R~e,, Rr~.; Rilil Ri61 R1~'., Rt;!l,. Rio:, Rii1 .Rf:! and R23 each independently .represent a ·hydrogen atom, or a substi tu.ent, Rf~ .represent a a subst:l. tuent, o· represents an integer of (l to L 'When o is 2 or .more, a ;pl.urality of, Ria may· be the same or differ.ent.) [004,6] ,As, ·the "substi tuent'",. organic groups other than a hydr.ogen a.tom c:an be used .without limitation, .and example·s thereof inelude· a halogen atom, a nitro group; an ,amino .gr:o.up1 ·an alkyl group, an a'lkoxy· gr.oup, an aryl group, an aryloxy g:roup1 an a:lkylc:arbonyloxy group, an i!,lkylcarbqnJlamino grqup, an aryl9arJ;,ony1amino group;, an alkylsulfonylamino group, an arylsul£onylamino group, a .monoal'.kylamino group:, a di•al'.kylamino gxoup,, and an a:rylaminQ group.

[0041] :Examples of the: '''ha,logen atom" :lncl·ude a fl·uo,ri.ne atom, ,a ehl:or:Lne atom,. .a :bromine. atom1 and a iodine atom,, coo '18] 'Elxample'S o,f the "alkyl, (group)" 'include: linear or branched aLkyl groups having' 1 to 12 ca'rbon atoms, ·such a·s· a methyl group; an ethyl, group, a norma1 pr,qpyl :group;: an isopropyl. :group, a normal butyl group, an isobutyl group; a secondary butyl group,, a tertiary butyl gr.oup,· a normal penty;l group,. ,an isopen,tyl group, .a tertiary pe'ntyl group, a neopentyl group, a 2,3·-d:l.methylpropyl group, a 1-.ethylptopy,:i. group, a 1-methyl'butyl group, .. a 2- CA 3265824 Date reçue / Received date 2025-02-19 mathylbuty'.l. group( a normal 'hex,yl gr:oupt ·an isnhexyl g=up, a zu.hexyl group; a .. B:-+hex,yl gr,oup1 a .2:-methylpentyl gr.oup, a }!,.methyJ:pentyl qraup,• ,a normal heptyl gr.ouP,, a. normal octyl g.ro'L\_p, a na.rmal nony'l <:Jroup, a normal .decxl group,, a normal undecyl group and. a :normal. dode:cyl gr,o..up. ['004'.9'] .Examples of th·e, "alkoxy grnup'" :include linear .or :branched. al:k,oxy :g,r.oup.s, ha:v,ing- 1 t.a 8 ca:rbon atoms,; •s,uch as, ,a :methox,Y, ;group, an :ethoxy group-,. a narma:J. pr.epoxy group, an :Lsoprop.oxy .groμp1, ,a normal '.butOX¥' group, a s.econdary ·butoxy· gr.oup, a tertiary :butoxy· gr.oup, a normal ;p"ent):'1:QX,¥ (il:r'OUP, ,,;n isQpentyloxy groμJJ,· ,;r t;e:rt'ia,rq,y pentylaxy group, a neapentyloxy group:, a. ,2, 3'dimet1Iy, 1p-ropyloxy :group, a l-ethylpr0pylaxy· group,. :a 1- :methylbutyloxif group:-, a normal hexyloxy group, an i,s•o:hexyloxy· gr.cup; a :normal, hepty,loxy :groμp and a normal octylox.y gro:Up. l 00 5.d:J ~xamples of ;the '"arY,1 ~,group)," inc::lude ar.omat:Lc hydrocarbon groups having ·6, ·to, :10 carbon a toms" such •a'S a phenY,1 g.!11'.oup, a ;:t-naphthyl group •and a 2-.naphthyl group:. ['005;:LJ In, the ":dia•Leylami·no, group'",, the· two alkyl :groups may· be the, ,same; :or different. D00511 The compound .representea by f:ormula :{1): is p;r:efei!'.ab1y c11 :opmp.ouna represented by· the, £.o11owi•ng CA 3265824 Date reçue / Received date 2025-02-19 - 21. - formula (:la) from the viewpoint of being able, to impart exce'll'ent chromogenic ·properties, and. heat re.si·stance to the h.eat-.sensitive recording medium l, Specific examples ther,eof in.c.lude N.,N'-.di•-[3--(ptoluenesulf. onyloxy)phenyl] urea ·represented by the f.ollowing_ formula (lb),. N,.N'-di-[3-fpxylenesulfonyloxy) phenyllurea,. N, N '·-di- [3- (p. mes±ty.lenesulfonyLoxy)•phenyl]urea1 .N,N' ~di~ [3- (o"' toluenesulforryloxy):phenyl]urea,. N1N 1·-d±- [3·- ('mtoluenesulf. on_yloxyiphenyl].urea1 and N., N'-di- [ 3-, (benzenesulfonyloxy)phenyl]ur.ea. [00 53] [Formula 7] c1a) (The symbol.s· in formula .(ia) are. t:he same as in formula (,1) .. ) ['Formula '8] (1~) CA 3265824 Date reçue / Received date 2025-02-19 - 2,2 - The coll)pound represented by formula (2) is. pref.erably a compound represented. by the, following formula C.2a) from the vlewpoint that excellent chromo9..enlc :J?r.o.perties: and heat resis,tanc.e, ·can ,be imparted to the, heat-.sensitive, recording· medium 1 .. Specific examples·, thereof include [ 3-{3- phenylureidoc) phenyl.] -4,-methylbenz.ene sulfonate represented ;by the following formu'la '(-2b) . [0'055] [Formula 9] R22 ,R21 (2a) (The symbols :Ln formula .(2.a) are; the same as in formula (2) . ) [Formula 10] (2b)

[0056] CA 3265824 Date reçue / Received date 2025-02-19 In the ;present embodiment; the. heat-sensitive. recording layer 3· may comprise. a single non-phenol~based. developer.,. or two or more, non-phenol--;ba·sed dev.elopers. [{)057] When as the non-phenol-based developer, at least one, or both .of .a compound. represented by· the, f•ormula :(1) and a compound repres.ented, by the formula '('2:) ar.e used for the• heat-sensit-ive· recording layer 3,. it is, possible to· improve the heat resistance and chromogenic prope·rties, of the heat-sensltl.ve recording ·medium 1,

[0058] In the pn:!sent embodiment,. th·e. c;:ontent of the l'lonphenol-, based developer is pre•ferably not less than 10 mass% and not more than 50 .rna'Ss%- with respect to the entirety of the 'heat-1Sensitive recording layer 3. .The: configuration in which· the content of· the non-phenolbased developer is 1.0 ·mass% or more, is preferable from the viewpoi-nt of 'being abl·e. to prevent a decline ·in chromogenic :Properties (,a decrease in optical density), due to defi:cienqy of the develope.r.. The configuration ±n ·which the content .o'f the non-phenol-based developer is· 50 mass% .or less is :pre.ferable f,rom the viewpoint of, preventing ,a :decline, in chromog.enic: properties (·,a decrease in optical density.) due to excess, of the developer (that, .isr deficiency ,of the· ·dye) , [·0059] CA 3265824 Date reçue / Received date 2025-02-19 - 24 - In the _present embodiment., as described above; a _phenol<'-'based <developer is not used with p.urpos.e, as a developer. for the. heat-sensitive . .recording lay.er 3, ,but a minute amount of a phenol-·bas.ed com_po,und ma;y be . inevitably contained as an impurity from the :non-phenolbased ·deve,l:oper ,. or the like. E·xamp'les, .of the impurity incLude compounds· formed 'by hydrolysis of all or a part. of· sulfonic acid esters :(-SO2.-0-) and alkoxy groups, aryloxy :groups; alkylcarbonyloxy groups and the like cont·a:Lned as s.ubstituents, in non-pheno'l-based deve'lope.rs represented. :by the formulae, (1} and / or .(2) , Such a ~h·enQ,1-'ba''ied ,9qmpo1.md. 99ntained. as .,;n 1111J?urity can function as a developer .. ['0060] In the present embodiment, the. phenol~based compound that can be inev.itab:l.Y contained as :an :i:mpur.ity in the heat-sensitive recording la.yer j can be contained in, for example, an instrumental'ly· detectable, amount of· ppm order (for example, about idO ppm or less with respect to the entirety o.f the. heat-sensitive creco,rding layer 3), but it is• considered. that such a minute ·amount does not lead to safety concerns ,such as endocrine di•srupting chemicals,,. and derives substantially no ·function as a dev.e•lopeT. [00 61 l In the ;present embodiment., the heat-sensitive recording Layer 3: •comprises, a: non-phenol-based anti.oxidant as opposed to a phenoi-'based antioxidant that CA 3265824 Date reçue / Received date 2025-02-19 has be:en :commonly used heretofore,. .The non~phenol'"'based antioxidant,, which :Ls a substanc.e that pr.e:v,ent•s, :oxidation by ·capturing :or :decompos:ing a hydroperoxide, i& ,a compound having no phenolic, h,;:-drox,;:-1 gr.oup, T.h.e conf,iguration in which' the he·at-s.ensitive r.ecmrding l.ayer 3 compr'.i.ses a non-phenol-bas,ed antioxidant i:s -rephrased as· "·a phenol.-based develo,per which ·may· threaten. safety a·s, arr :endocxirre :disrupting· .chemical is not used with purpose". .In the present embodiment; the· heat~sensitiv.e recording layer ,3 compri,ses· ,a non-phenol~based. antioxidant as opposed to• a phenol,.;based ant"loxidarrt, and thui;,, the 1:t9ht ·resistance am:! th"' heat res:Lstance of the heat-s.ensitive re·cordirrg, :medium 1 can be improved. T.he ·he·at-sens,it.ive recording la.yer :3, •accordirrg· to, the present embodiment1 wi.th a phenoJ.~based antioxidant in an amourrt so: small that ·safety 'Concerns as, endo:cr.ine :disrupting c·hemicals do: not ad.se• ,and, chromo·genic pro_perties, 'light resl.starrce: and heat· resl.starrce •are not aff·ected, is also ·with'in the: .scope of the present :i:nvention, [•006'2] 1\:s, .the non-pheno'L-based. antioxidant, known antioxidants having no. phenoLic hydr.oxyl gro.up can be used without Limitation. Examples, thereof •include phosphorus~based, antioxidants.,. ,aromatic amine:'"based. antioxfdants•, sulfur-based antioxidants,• adip:Lc: ac:Ld,. and vi:tam:Ln Q, The inventors of the: present application have :cound that phosp'ho:tus-iba:sed antioxidants are p:tefer:.red CA 3265824 Date reçue / Received date 2025-02-19 from the viewpoint of furthe.r improving the light resistance, and the heat resistance of ·t:he heat-·sensitive r:e.cording medi.um i , The phosphorus--'based antioxidant is a .compound 'Which has ·a trivalent phosphorus atom in the molecul:e·, is oxidized to pentavalent phosphorus· :by ,reacting with a hydrqperoxide1 and decomposes the hydroperoxide1 to perform an antioxidant function.

[0064] .As, ·the phosphorus~b.ased, antioxidant, compounds havlnc:i a 1':rfv,;tlent ph'Qsphoru;r ;,:t9m in the mole·qule ·qan he, used without limitation, and examples, thereof :include phosphorus acid .ester compo.unds represented, by the fo:llow~ng formula (3a} 1 and pho~phorus acid ester compounds r.epresented, :by the ·fol.lowing :formu'la '('3b,) : ['Formula 1 i ] (Tn formula pa) 1 R24 , R2:• and Rt~, ·each independently rep.resent a substituted, or unsubstitut·ed hydrocarbon group, R24, ,and :R2.'\ ·may be bonded, through a linking g,roup,) [Formula i2J CA 3265824 Date reçue / Received date 2025-02-19 (3b) {'In formu'la {3b) , R'i1 and, R2,B each independently represent a substituted or unsubstituted hydrocarbon ,group.)

[0065] Example's of the, ·substi,tuted :or unsubstituted hydrocarbon gr.oups R4 4 1 R~-5 and R4s in the, formu'la ,(3a) include a'lkyl groups [for .example, a ·methyl group, an ethyl grcmJ?, a: ;propY,l group, i?- butil group, a pen1:yl. group, a hexyl group and a 2-ethyiehxyl group], cycloalkyl g.r,oups• [for ,example, a cyclopr,opyl ,group,, a cyclobuty'l •gro.up1 ,a cyclopentyl group, a cyclohexyl group and a, ,cyclododec,yl group],, ar,yl gr,oups (for examp'le, a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a 2, 6'~di-t~buty1-~,4-methyl,-i-,pheny,l group ,and a 2, 4-d:l:-t-butyL-i:-phenyl group], cyc·loal'ky:L-a,'lkyl groups [,for exampl'e•, a 'Cyclohex-ylmeth,yl ·group and ,a· methyl,,cyclohexyl group], aralkyl groups [for example, a benzyl group ,and, a phenethyl group],; halogenated, hydrocarbon groups obtained by replacing ,one or more hydrog,en atoms, with a halogen atom [·for, exampl,e•, 'halogenated, alkyl, -groups such as, a chl'oromethy'L gro_up, ,a 3-chloropropyl group ,and a 3 r 3,,:3~trif-luoropropyl group'],, arid groups obtained 'by 1:ep'laclng one or more of hydrogen CA 3265824 Date reçue / Received date 2025-02-19 atoms bonded to ,a carbon atom of any of: the foregoing groups 'with a functional group ,such as a hydroxyl group, a carboxy group; a n:i.tro group, a substituted p:r unsubstituted amino group :o:r a mercaptD group .. [,0066] Specific examp'les- .of the li.nking group through whiofi ,R~4 and. Ri:; are bonded include' a single bond, .. alkylene groups [f.or example, al·kyhme groups having :1 to 6 :carbon atoms (carbon atums forming ·the alky:lene group) :r such as a methylene group, .an ethylene: groμp and a tr:i..methylene group] , ,_G,,_ r -co-:1 and g:roqps in which tw,o o.r more: ·of the, fQr<s,golng grqμps a:ri:a- .li'nkec:l ·toge,t;he,r ,. ['0 0 67 l In parti.cular , . .R24, R2'S and .R~6 are ·each imiependently,· preferably ,a subs.tituted or unsubstituted alkyl group, :or a s.1.ibstituted or unsubstituted aryl group, and more: preferably· a substituted or unsubstituted al.k;,rl :groμp having 8 to 2.0 carbon atoms (.carbon atoms formin.g; the al:kyl groqp): (for example, a :z,,-ethylhexyl group. :or a stearyl group')., an aryl ,group ( for example, a phen::,:l group), , oor_ -an al'kyl-substituted aryl group (.for. exampl·e, a 2 1 6-di,~t-butyl-4,-me,thyl-l'~phenyl group or a 2 1 4-di~t~butyl.-l~p'henyl group') .

[0068] .Examples of the substituted or ,unsubstituted 'hydrocarbon g.roups Rg'l and R~~ :En the formula. C3b) :i.nc·lude ·subi3titute.cl ot: unsubstituted. hydroca-ibon. groupi3 i3iinilar CA 3265824 Date reçue / Received date 2025-02-19 - 29 - to those exemplified as R24, .R25 and R2•. In part·icu1ar, :R2J and. R2·e are the same or diff.erent, and are ea•ch preferably a s.ubstituted or unsubs.tituted alky.l group, or a subst:Ltuted or unsubstituted :aryl .grou;P, ,and ,more preferably a substituted or unsubstituted. alkyl. .group having 8 to 20 carbon atoms, (carbon atoms f,orming the alkyl .gr.01.1p) (for .example,, a 2-:ethylhexyl group .or a stearyl group); ,an aryl group (..for example:, a. phenyl group') , or an alkyl-substituted aryl g.roup (.for example, a 2 1 6-.cti,-t-butyl.,-4,-methyl-1-phenyl group :or a 2, 4-di-t' butyl-1-phenyl group)'. (0.069] More specific exampleSa of the phosphorus-based antioxidant inc•lude 9, 10-dihydro·-9-oxa-10- phospbaphenanthrene·-lO-oxide, bis (2-;·6'~.cti-t-butyl-4- :methylpheny:J.,) pentaerythritol diphosph'ite, bis (2, 4.-d:t~tbutylpbenyl) pentaerythritol. di;phosphite,. tris (2, 4-di.-tbutylphenyl) pho.sphite, tris (mono, dinony'lphenyl): phosphite, tris (2:-ethylhexyl) pbosphi.te, trisphenyl ·phosphite, tris (monononylphenyl) pho~ph:ite, and trisisodecyl phosphite. [0070J The phosphorus-based antioxidants can be. used al·one, or used in :combination o:f two or more: thereof. 'As the phosphorus~based ant:Loxidantr commercial products such as "JP-.3fr0•" and "JP-30.SEJ" .as brand. names, (manufactured .. by Johoku Chemical ·co., Ltd.,), 0 ·rRGAFOS.i6s·,; as a brand name CA 3265824 Date reçue / Received date 2025-02-19 - 30 - (manufactured, by BASF SE:), "'8'an'ko Epoclean" as a brand name (manufactured by SANKO Inc.), "ABK STAB 3010" and "ADK STAB PEP-.36" as brand names (manufactured.by ABEKA CORPORATION)o, and "{lSl68'0" as. a ,brand name, (manufactured by Song,w.on 'Industrial) ,can also be 'use·d. In the ;pr.esent erribo:diment., the· content o:E the nonphenol-: based antioxidant 'With respect to the entirety of the heat-Bensitive re·cording· layer 3 is not limited, but is preferably not less than 5' :mass! / ; and not more than 10 mass%, The configuration in ·which the content of the non,-phen9l-lYslsed anti'Qx:i.d,,mt is 5 m!lss%, or more, :Ls prefer.red from the viewpoint of ,being able to impart excellent l.ight :res:istance to the heat-sensitive recording :medium 1 according to the present embodiment. Th·e configuration in which the content of the non-phenol·- ) based ,antioxidant is 'i.6 mass% or less :Ls preferred ·from the viewpoint of 'being• able. to impart exce:llent chromogenic Fropert'ies to· the heat-sensitive recording medium 1 accor.ding· to the. present embodiment. [0.072] In the ·present embodiment,, the. content of the non~ phenol~ba·sed ,antioxidant with respect to the total amo.unt of: antioxidants contained in the. heat~sensitive· ,recording layer 3: :Ls not limited, but is preferably 9b mass% .or more, more preferably 9.5 mass% Qr more, and further .more preferably 99 mass% or more, :from the, viewpoint of CA 3265824 Date reçue / Received date 2025-02-19 - 31 - improving light resistarrce and heat resistarrce ·while reducing' safety :concerns such as. :endocrine, :disrupting· chemicals ..

[0073] In the ;present embodiment, the, content of th·e phosphorus-based.antioxidant with respect to the total amount of. antioxidants• ,contained in the heat-sensitive recording lay.e·r 3: is not limited, but is preferably 90, mass% ·or more,- more preferably ·95 mass%. or more·, and further more preferably .99 :mass%· or more;, from the: viewpoint of improving light resistance and heat resistance, while red1,19:i.ng §afety 9qnc;erns suc;h a$ endo·crine disrupting :chemicals. [•0074 l The heat-sensitive recording· layer 3 :may appropriately com,Pris.e additives. s.uch -as :a binder;- a sensiti.zer, a slipping agent,, a fillerl a storage stability improver and _a :pigment as nec.essary. [007 5] Examples o-f the binder contained in the heatsenSoit± v.e recording 1-ayer .3, include polyvinyl alcohol, modi:fi•ed. poLyvinyl al·oohol,. starch,- ·case,in, gelatin,. po.lyamidei' polyacrylami:de,; rno:di•fi·ed pol.yaorylami•de., hydroxyethyl.ceilulose1 me,thylcel1ulose, carboxymethylceO..lulose, hy:droxypropylcellulose, polyvi.ny1 acetate, pol::facryl:f.c ,ac:f.d esters,,, styrene,.,maleic arihydr.ide copolymers, isobutylene-rnaleit: anhydride, CA 3265824 Date reçue / Received date 2025-02-19 copo'lyme.rs, diis:dbutylene~maleic: ,anhydr.ide: copolymers, vin,yl acetate~maleic. ,anhydride :copolymers; methylvinyl~ maleic anhydride copolymers,, isopr,opylene-,maleic anhydride c.OJ?olymers 1 styre.ne-butadiene c9polymers,, ·po.lyvinyl chl.oride,., polyvinylidene chloride, vinyl chloride-vinyl ae:et·ate ,copa·lymers, :po:lyurethane·, polystyr.ene, polyvinylpyrro:lidone, aoryli•c, acid :esters, aor;ylo.nitrile., and methyl vinyl ether. These binders can. :be used aJ.arre,- o.r in, combination ,of two or more· thereof .. C0076J Example,s o,f the, •sensitiz:er inc'lude thos.e, that are SQll.d at: ro·om temperi:!ture, i;!nd pr,;,:ferably have a melting point of 70 9 t: or higher, such as stearie •acid, stea:ric a•oid amide,, stearanilide., methylolstearic acid amide, :me:thylenebi,ss.teario acid amide1, ethylerrebisstearic:, :a.cid amide,, 1:-benzyloxyrraphthalene·, 2~benzyloxynaphthalene,· 2, '6-d:U.soprop:ylnaphthal,ene" 1, 2.~diphenoxyethane,, 1 1 2- diphenoxymethylben zene, 1.,·2-bis (3 1,4- dimeth:ylpherryl'l ethane,, i, 2-'bis (3'-me:t:hylphenoxy) ethane,, 1, 2-bis• (4-,meth•Jtlphenoxy} ethane, di :(p-chlo:roberrzyl) oxalate, di fp-methylbenzyl) ,oxalate, diberrz.yl ·oxa:late, pbenzylbipherrylt m~terphenyl1 diph·enylsul,phone,, benzyl p~ benzyloxyberrzoat,,,1 diberrzyl, te,rE\phthalate and p~ toluenesu'lf,on-ami·de. Thes-e· s.ensitizers can be .us.ed alone,· or in .combination ·of two or more· thereof, [·0077] CA 3265824 Date reçue / Received date 2025-02-19 - 33 - Examples of the. slipping agent include paraffin wax,• fatty acids such as oiei:c. acid, ·po·ly.olefin waxes su:oh as :polyethylene, wax, metallic soaps. s.uch as zinc .stearate, es,ter waxes such as. carnauba wax, od.ls such as sil:Lcone oil and whale oil. These slipping agents can be used. alone•,, or in •Combination of' two or .more thereof·. [ 00 78] Examples of the, :filler include, al·uminum hydroxide, magnes.ium hydroxide; aluminum oxide, .magnesium oxide·., aluminum silicate, .calcium carbonate, magnesium carbonate, titanium oxide:, 'barium sulfate, silica ·g.e:l, activiit<;ld whi·te, ea,rt-h, t·9-l'q, t;lay, kiiOlin, fired k,,rqlin, diatomaceous, .earth, white carbon., zinc oxide,. s.ilicon oxide, colloi.dal sili•ca, :polystyrene r.esin particles., urea-formalin res•in .particles;· and polyolefin resin particles. These. J:illers can be used :al,.one,: ,or in combination of two or :more thereof,

[0079] Examples of the: storage stability improver include sodium-2, :2 '•-methylenebis:( 4, 6-di-t-butylphenyl)' ;phosphi te,. 4, '4-butylidenebis·(3~methyl-6-t-butylphenol}, 1, 1, 3- tris (2-meth;r.1•-4-hydroxy-s-t~butylphenyl) butane,. 1,,1 ,,3- tris ( 2-methyl'-4'-hydroxy-5 ~.cyclohexylphenyl.) butane,, tris: ( 2 1 .6-dimethyl~4~t-bu tyl~3.-hydroxybenzyl ): isocyanurate, 4- (2·-methylg.l.ycyloxy) -.4 •·benzyloxydi. phenylsulfone, ·2, 2''-methyleneb±s (4-methyl,-6·-tbutylpheno, 1 j, 21 2 •-methylerieb:Ls ( 4-ethy1-6-t-buty1phenol) , CA 3265824 Date reçue / Received date 2025-02-19 - 34, - diethylthiourea, zinc dibutyldithiocarbamate; 4,4'~ thiobis (6-t~but,yl~m-cresolh an:d ,a urea-u'rethane .compound represented .by the £011,owing· £ormu1a (4) . (i008Q] [Formula 13] (4)

[0081] Thes.e storage stability impro.vers .can be, used alone, or in ,cqmbinat·ion q·f two or mor~ ·thereof, Th,;:, storage. stability improver may comprise a known surfactant. [·0082] Fresh foods such as meat and fish are sold in. the fo:rm o.f -a _pack wrapped in a plastic warp, on which :a labe'l indicating a price and the. like: :L-s attached, The packs are typic·ally laid out in a stack, and -there,fore, a l.abel may come i·nto contact with a plastic wrap in which an.othe-r pack is wrapped.. The plastic: wrap. c.omprises a plasti•.cizer for ,imparting plasticity. If ·packs are left to, stand in a stack for a long time,, the, plasticize-r may transfer to the, label; and, af,fect the print. Therefore, the heat-sensitive reco,rding me:dium is preferably ·excellent in -characteristic: that the print :l.s unlikely to disappear even if the plasticizer transfers, that i:s, "p1a:stici:Zer re.sistance•.-" ✓ CA 3265824 Date reçue / Received date 2025-02-19 [·0083] In the ,present embodiment, the, heati-sensitive· recording layer 3; preferably compris.es a storage stabilLty illJJ?r.over ,. and paTticuJ.ar1y :pref.eraul:y ·comprises. a urea-urethane• compound represented, by the formula {4:), from the viewpoint of ,print storage, ,stability,, in particular, _plasticiz:er resistanc.e. It is con·si:dered. that -when the heat~sensitive re·cording layer 3' compri:t,es, a stora.ge stability improver, in particcular, a ur.ea~urethane, ;compound r.~pr.es.ented :by formula {:4)', the ef:fi·ciency of reaction 'between a l.eucotransfer GOIT)plex is easi.ly· foTme.d, and a revers.e reaction is· unl.ikely· to occur, s.o that the heat-sensitive recording ;medium has ;excellent chr.omogenic properties,· is, unlikel.y· to undergo a decrease. in color. optical density,· and. ls excellent i·n :print ,storage stab'i:l•ity·1, in part:1' .cu·lar,, plast:i.I c'lf .zer res,i stance.

[0084] The urea-urethane ,compound. repr.e·sented. b¥ f.ormula (,4) incl'udes specifically three t,ypes, o:f compounds repre.sented. 'by the ·following· formulae, (4a) to ·( 4c'l,, ·which can. be used. alone>, or in ,mixtur.e; .of two or mor.e, the-reof .. [008'5] ['.Formula 14 l CA 3265824 Date reçue / Received date 2025-02-19 [.Forinula 151 [Formula 16]

[0086] In the present ernb,odiment1. ·when th·e. heat~sensitive, reccrrd:tng layer ,3' comprises., .a storage: stability improver,. the .content of the storage stabil1.ty improver is preferably :not less than i mass% .and not more: than ·2() mass% with respe·ot to the entirety of the heat-sens.itive recording !,ayer 3:. 'The configuration :in wh·ich the. content o,f the storage stability improver is 1 ·mass%· or mo.re is preferable from the: vie"lpoint .o.f being able to suppress a :decreas·e in the co·lor :optical density· by a plast:l:cizer or the l:l:ke, and, improving print storage stability, in partfoular, p:lastiofzer resistance., ,The configuration in which ·the content of· the stotilge CA 3265824 Date reçue / Received date 2025-02-19 - 3,7 - stability improver is 20 mass'% .or less is ·preferable from the vi•ewpoint of •pr.eventing a• decline in :chr.omogenic, properties (a decrease. in optical density) ; [•008'. / J In the ;present embodiment, 'When the heat-sensitive recording layer .3' ,comprises, a storage stability improver, the content ratio: .of the storage· stability improver to the non-phenol-based :developer (storage stability impr.over / non-phenol'-'based .developer) is preferably 1 / 20 to 1 / 1, The; :configuration in which the, content ratio is 1 / 1 or less is :preferable; ·from the ·viewpoint of being ab·le to prevent a :decl:l:ne, in qhromogenic;: properties (.a cte·crease in opti•cal density) . The configuration in which the content rati.o is 1 / 20 or more is ;preferabl.e from the v.iewpoint 0£ being abl.e to suppress a :decrease in the co:lor qptical density .by a ,plasticizer or the like, and improving ;print ,storage stability,, in particular, plasti:cizer resi.stance. [008.8] I'n the ,present embodiment, the heat-sensitive reco·rding l•ayer 3; comprises, ·a urea-urethane compound represented, by formula (4.) ,, the content of the ureaurethane compo.und ,represented by formula •( 4) is· preferabl.y not 1·ess. than 1 ma·ss%· and. not more. than 20 mass% with respect to the• entirety of· the heat-sensitive recordfng layer :L The configurati'on in which the content of the ·urea-urethane compound is 1 mass% or .more CA 3265824 Date reçue / Received date 2025-02-19 is preferable fr,om the viewpoint of being abie to .suppress a. :decrease in the co·lor ·opt·ical density by a plasticizer or the like, and improving· print storage. stability,. in particular.,• plasd.ci'zer resistance. The configuration in which the content of' the urea-urethane compound. is 20 mass% ;or less is ,preferabl·e· from the viewpoint of. preventing a decline in chromo.genic properties {a decrease· in optical density) . (0089] In the present embodiment, the, heat-sensitive. recording layer .3 comprises·. a urea-urethane .COIT)pound repres·ent;·ed by t:ormula (4), t;he content; ratio, of the. urea-urethane compound represented by formula. (4): to the non-phenol-based developer turea-urethane compound / .nonphenoI ·--;based developer). is ;preferably 1 / 20 to 1 / 1. The configuration in which the content ratio is 1 / 1 •or less :Ls: prefercibl.e ·fr.om the vd.ewpoint of being ab'le to prevent a decline in chromogenic properties {a decrease, in optical, density) . The: ,configuration in which the. content ratio- .is 1 / 20 or ;mo·re is ·pref.erabl.e :from the viewpo·int of being ·cible to suppress· ·a: dec1,ease in the color optical density· by a plasticizer. or the like,, ,and, improving ;print storage stability, in ;particular, plasticizer resistance. (00 90 J In the ;present embodiment.,. the: content of the ,urea~ urethane compound represented by f.ormula ·(4} with respect ·to. the total .amount' o_f the sto,rage stability improver CA 3265824 Date reçue / Received date 2025-02-19 - 39 - c.ontained in th.e heat~sensitive re:cording layer 3 is, not limite:d; but is preferably 90 mass'% or more,, more prefeceably g.5 mass% o:r mor,e:, and f.urther mor.e: .pre:ferably 99 mass.% or ,more,. from th.e 'viewpoint of being •able to suppress a decreas.e in the c.<flor ,<fptical density by· a ,plasth:cize,r or the :lD::e,. and. impr.oving pri.nt storage• stability,. in particmlar,. plastici:zer ,resi.stance. [0'091] In the present' embo:diment, the, heat~sensitive, recording medLum 1 excellent in water resistan·ce, chemical resistance, plasticizer .r.esist·ance and the like can l:Je Qbti!inet:i by provl:dinlJ' ;;in intermediate layer 4 on the heat-•sensitive reco.r.ding layer, 3. ['0092] ,Examples of :the, mate:id.al fqr forming the. intermediate· la,y.er 4 include water-'based reS:ins, :of polyvinyl alcohol, modl:f:ied polyvinyl .a'lcohdl;· starch,, mod'Lfied . .starch, ca,sein,, gelatin, glue 1, gum ara:biG, po:1yamidet polyacrylamide,, modified polyacrylamide:, hydroxyeth.ylcellul.ose, methyl:celluloBe, carboxymethy:lcellul.ose:, hydroXcypropylceJ.luLoser polyv.iny.1 acetate1 pol,y:acrylic:· ·acid :ester's·, styrene~ma'leic anhydride copolymers,; iscbu1:y,1ene-maleic anhydride, copo.lymers,1 diisdbutylene,~mal.ei:c anhydride: copolymers, -vin;yl ,acetate~maleic ,anhydride: copolymers, methylv.:lnylmaleic' anhy.dr:lde copol.ymers, isopropylene,-,male:lc arthyd:rd'.de copd'lymers, styr.ene-butadiene cdpolymei:,s, CA 3265824 Date reçue / Received date 2025-02-19 - 40 - maleic acid copo.Iymers, po'lyvinyl ch'l.oride, polyvinyliderre chlori:de, vinyl :chloride-vinyl acetate copolymers•, :palyurethaner p.olystyrene.,, :Polxvin,y·lpyrroli.done:, acrylic acid es,ters, acryl•onitrilse, methyl vinyl ether polyvi.nyl ,alcoho'l snd the 'like. Th:e term ":wate,r-based ,resin"· :means ,a. ,resin component in which any o·f these .,compounds• is :d'ispe·rse:d in water o·r dissolve'd in water. These :materials can be used al.one·.; or in combinati.on of two .or ,more thereof .. [CJ0 93] 'By using., as the abo,ve~:described .resin1 a resin havin9 a water-s:q,lμl:;>1'¢ m9,:l_,et,Y, .f¢r ex'iJ.mple,, a pQlyvinyl alcohol (EV:A) res•in wh'ioh :is a :resin having a hydroxy group: as a h,ydrophili:c structural unit, or ·a resin of core·~shel'l ,structur.e .in which 'hydrophobic cone ,particles are c.oated with a wate'r-so.lub'le sheTl polymeT:; for example, a :core,-.she'll·-type acry1ic resin., trans:parency can be imprca.ved, [0094'] hs, the core-shell.-t•ype .resin,. for example, ,a coreshell- type ,acr,ylic resin that ics. sold under the name ,O'f "Bil'.RRIERS.T:A:R" ,(manufactured by Mit·sui, Chemicals,, Tnc,. ): can be used,. [00 95 J The application amount (dr,y weightJ of the: intermediate· layer 4 Is preferably O, 3 g(m~ to 1'0 'g / m~. too9'.6] CA 3265824 Date reçue / Received date 2025-02-19 - 41. - The topcoat layer 5 ill)proves thermal head compatibi.lity of the heat~.sensitive, recording medium 1 with a thermal headr so that the, heat-s.ensi ti ve: recording -lay:er 3: succes;sfully :devel~ps: a color. S.pe.cific.ally,, the heat-sensiti:v:e recording l·ayer 3 dev.elops a color in such a manner as to minimize occurrence of• de,fects such as depo-sition :o.f fouling on the thermal head. and distortion of· the surface o.f· the heat--sensitive recording ,medium l by heat. ,[00~7J In the present embodiment, the, topcoat la:yer 5 of the heat-sensltive recor<;l.ing mectiμm 1 pli,.yS a role, of preventing the shortening .of the life of the thermal head by reducing the wear of the thermal head without addition of ·e'la,stic par.ticl·e·s o:r the: like. Thi,s, means what is called impro.vement of thermal 'head compatibility.. For the topco-at layer 5', it is necessary· to improve: sticking resistance, with respect to the thermal head.. Here,, the sticking resistance means that defects caused because a component of the uppe·rmost l·a,yer .of' the heat-senffitiv:e recording :medium is me·lted :by heat from the thermal head, and adheres to. the thermal head. are, unLikely to: o:ccur. More specifi_call:y, defects such as partial, fail,ure, to perform printing on the heat-sensitive recording medium; and di,stortion of the print surface are unlikely.· to occur,

[0098] CA 3265824 Date reçue / Received date 2025-02-19 The topcoat la1,er 5 according to: the :pr.e.sent embodiment has, ,on a. surface thereof,, :evapo.rat·ion :holes resulting from evapo•rat:Lon of• mocl.ature .and 'Cra:cka, as downwardly protruding rec.essed poi::tiona,. Thia r.educes the contact area between the surf,ace of. the topco·at layer 5 and the" thermal. head. [,009'.9:] F,o:r gen,e.rating re'cessed portions,, in ,parti.cular, cracks on the surface of the topcoat layer 5 •acs, ·des,cribe:d above:, a coating liquid. containing hydr;ophobic resin :particles is: used as a, coating' :l.iquid for forming the t9p90,c1t li;l:'{E;ir 5, [,0100 l T.hat i;s,., in t:he. pr,e:sent ·embo·diment,. the topcoat layer .5, comprises,, as a binder,, an emulsion of hydrophobic r.e·sin partic'les,1 for ex,all)ple,i an emulsion obtained. by d'Lspersing :hydrophobic acry'lic: resin ,particles in water. [@101] Thus',. as the' binder of the topcoat layer .5., an emulsi·on o,f hydrqph·obic resin particles i:s used, and •a' water-soluble pol,ymer is• not used. ['()'102] Fo:r the coating liquid containing a water-soluble polymer, agg,regatfon Js unlike•ly to: :o.ccu:r during application and :dr,ying,. and .a flexible coating fil:m is CA 3265824 Date reçue / Received date 2025-02-19 - 43, - f:ormed, so that :cracks. xesuJ:ting f.rom shrinkage: :of the topcoat layer '5 are n:ot generated. [:0103] On the other :hand, :for ·t;he emuls.i·on. of hydrophobic resin particl:es ,. hydrophdbic resin :particles· a·re aggregated by· ev.aporati.on to shrink during application and drying,, s.o that cracks as recessed. portion are generated on the surface of the topcoat. layer S..

[0104] The cracks,, which are formed by aggregation and resu·1tant shrinkage of hydrophobic re.sin particles, thus end at the, t9pcoat 111yer 5, and do not res1ch the intermediate layer 4, [0105 J In the present embodiment, for :forming·, on the surface· ,of the tqpcoat layer '5·, evaporation holes resu'lt:ing from evaporation of· ·moisture as recessed portions" three layers which are the heat~sensitive recording layer .3, the intermediate: 'layer 4 and the topcoat layer 5 •are f·ormed :b,y thre.e-.layer simultaneous application us:ing. ·a· curtain coater ..

[0106] In the curtai·n coater, coating liquids for forming the heat-sensitive recording layer 31: the intermediate layer ,4 .and the· topco.at layer 5, respectively, are discharged,, respectively,· .from :a plurality ·of •slits, and layered, and the layered coating liquid is: ,continuously CA 3265824 Date reçue / Received date 2025-02-19 run. At this .time" the coating l:iqμid. is. applied in .fnee. fall onto the un:dei::.coat layer. 6 formed. on the. ,substrate: 2 in .advance,. ['Eli b '. / J In ·this• thxee-layer, simultaneous appl.icat·ion using a . curtain ,coater,. drying .of the topcoat layer 5 initiates aggregation of hydrophobic r.esin particles: to ·generate cracks as described above.· Water vapor ex:its through the cracks, so that the half~dry in:termediate layer 4 and heat-s.ensitive recording l•ayer :3 dry and .solidify. The ·wate-r vapor of the ·inte.rmed:Late l:ayer 4. and the, heatse. mrit:Lve r~QQrding layer :3, is mo1?tly released th·rough the c,racks, ,but a part ,o:f the wate-r vapo-r is rel·eased with evap.orati.on ho·1es, formed in the topcoat l'ayer 5. There.fo:rey .cracks, and evaporation ho.leg are ·formed near the topcoat la11;er 5:. [0108) In the :p:r:e'Sent embo_diment1 the evaporation holes f.ormed. in the topcoat layer 5 end. at the, intermediat.e l·ayer -11. T.he-ref:or:e, .even :if oil :or the like. •adheres to the surf-ace of the topcoat layer 5 ·which :is an outermost layer, the, :oil or the like does not :reach the, heat~ sens·itiv.e recording, layer ·3,, and disco·loration and the like of: the heat~.s·ensiti,ve recording Layer 3 do. not occur. CA 3265824 Date reçue / Received date 2025-02-19 - 45 - The topcoat layer 5 comprisea ,additives such ,a·s, a slipping agent, a crosslinker, a dispersant, a defoaming ag,ent, a water resistant additive and a filler as. [ 0110] ,Examples of the slipping agent 'include polyethylene, and zinc stearate. Examples of the crosslinker include zirconium carbonate.

[0111] Examples o,f the filler include. aluminum hydroxide, aluminum oxide, aluminum silicate, heavy calcium carbQnat:E;l, li\;lht calcium carbon<'!tE;l,. titanium oxide,, barium sulfate,. silica .gel,. •ac,tivated white earth, talc,, clay, :kaolinite, diatomaceous earth, white carbon,. magnesium carbonate( magnesium oxide,: magnesium hydroxider zinc oxide,. polystyrene resin particles, urea~· ' ' formalin ·resin part·icles ,- and ;polyole.fin resin particles. These: fillers can be used alone, or in combination of two or more thereof. ·The part{c'le diameter of the fi.ller contained in: the topcoat layer 5, is preferably 1. 0 μm or less. ['0112] In the present embodiment, the. heat-sensitive, recording medium 1 is ;produced using,: as a coating li•quid for ·form:i.ng the, topcoat layer 5, a water-dispersible suspensi'On .in which an emulsion obtained by di•spersing hydrophohic acrylic res:i:n par,ticies in water, poiysty±ene, CA 3265824 Date reçue / Received date 2025-02-19 'W.ax as a slipping agent and cal'Oium :carbonate, as a pigment are '.blen:ded at ·a mass ratio of 4 : 3 ·: 3 on a dry basis. [:0 i 13 l The applicati.on. amount ('dl!:y weight') of the topcoat layer 5 is 1.. 'g / m?. "[•0114] In t·his, :embo:diment1 as, :described ,above, cracks and mo·isture evaporation holes as recessed portions, are formed on the surface of the topcoat layer 5 which is an outermost layer ,of the heat-sensid.:v.e. recording medium 1 1 i3,rtd thex<;!fore the $Urfi3,c;:e• 0,f the tq:Pcoat .laye,r 5 is irregular.. This leads to .a decrease in ,contact area. ,betweeru the topcoat layer 5 and the, th·ermal head, so :that we·ar. 0£: the thermal 'head is, .reduced ta improve thermal head compatibility, and sticking' :i:esistance is improved.

[0115] The thickne.ss of the: topcoat :layer, 5 is adjusted to, f.or .example, less: than f. μm, In the ·present embodiment,, the t:hickness :is adjusted to about O .8 μm. This leads t·o a decreas.ed dist-ance between the s-urface. -of the t·opc-oat: layer 5, ,and, the, heat-,sensit:Lve, -recording layer 3,. so. that 'heat from the thermal head, is e·ffi.ciently conducted to. the heat-·sens:Lt:ive recording layer 3. The. decreaS'ed thickness .contributes to cost reducti.on,

[0116] CA 3265824 Date reçue / Received date 2025-02-19 - 41 - Further1 since the cracks on tbe· surface, of tbe· topcoat layer 5 spread inwar,d in the thickness dire·ction1 the cracks provide discontinuity in a dir.ection orthogona'J.ly, •crossin<;r the thicknes:s di:cect:Lon o,f the. topcoat layer ·s,. that is,. a latera'l direction.. B'y this, heat from the thermal head, is inhibited from being· released in the, late-:cal di·rection. '.As a result., heat from tbe thermal he·ad is effici·ently conducted to the unde·rlying heat-sensitive recording layer 3 located in the thickness direction, [•0117] The aver,age:, diamet:e:,-r :9f moisture:, evsi)?oration .h9leB having a substantially circular shape is preferably 2 μm or more· for decreasing, the contact area .between the topcoat laye·r 5 .and the thermal head.

[0118] The average diameteI .of the ev:ap.oration holes -is calculated by observing the: surface, of the, topc.o.at layer 5 with an electron m:i.croscope (SEM)-, and measuring the diameter o,f evapor·ati·on h6les per unit area, f:or .example, 1 mm2.. The number of· evaporat·ion ho·1es, f.or examp·le, evaporation holes: 'having an. avera·ge, .di,amete:c of 5 μm or more, is pre·ferably 30 or mo.re,, and more, preferably 40 ·or -mo.re. ['0119] In the heat-sensitive recording :medium 1 accordi-ng to. the _present embodiment, for example, a surface 'having CA 3265824 Date reçue / Received date 2025-02-19 -· 48 - a large number. of: •evapor.ation holes and a smal'l number of cracks can be "Obtained as the surface· "Of the topcoat layer 5 by adjusting the formulation and the 1-ike of the topcoat lay.er 5. 'Al ternativ;ely,. :a s.urface having nnly a large. number .of evaporation holes without cracks can be obtained. as the, .surface of the, topcoat layer 5. [·0120] In the ;present· embodiment, three: laye·rs· which. are. the heat-sensitive recording layer. 3; the intermediate layer 4 and the; topcoat 'layer 5 are; :formed by multi~•layer , simu·1taneous, application using a curtain coater, but the :Pre1,3ent invent'ion is not l'imxted to m1,1lti-1axer simultaneous application, and the heat-sensitive re·cording layer 3', the intermediate, layer 4 and the topcoat layer '5 may 'be· individually formed in sequence. [0121J In the :present embo.diment, the undercoat. layer 6 and the -intermediate layer 4. are ·formed on the: substrate, 2., ·but as another embodiment. of the, present. invention, at le·ast :one of· the unde·rcoat layer 6 and the intermediat:e. l·ayer 4 may :be omitted. (0122] The heat-sensitive recording medium according to the present. :embodiment, which eomprises a heat~s·ensitiv.e recording layer having_ the above-deseribed ·configuration, thus i,s- exce·llent in .light resi•s.tance, chromog_enic properties and heat resistance,. CA 3265824 Date reçue / Received date 2025-02-19 [·01231 The amount of chan.qe :in wh·itenes.s (%) ,of· the heatsens, itfve recording :medi.um accoTding to the pr,esent embodiment,, ·which: :Ls g,hren ,b.;r the :foll·owing e9uation., is prefer.ably -10% :o.r more,. ,more :preferably -,9% or mor.e·, fu:rther mo·re preferably -8% .or more,, and particularl.y· prefer.ably -7•% or more, .from the viewpoint .of obtaining excellent l,ight resd.stance and ,suppressing a decrease in wh,iteness due to light. irradiation. Amount of· change in whiteness: .(,'1,J = whitenes.s after standing· at an illuminance of 5,:000 Lux fo.r 100 hours - whitene$$ before te$t The whit:eness is determined acco:i:cding to. JIB P 8148. The minus· :(.-~ be·fore the amount of: change i·n wh·itene·ss ('.%0, indicates an amount .of decrease, in wh·iteness;- .and :be·comes: close.r, to: Q as, the decrease in ·whiteness 'becomes smaller :and light .resistance is improved., • [012.4] The absolute: value of llb of· the heat-sensitive re·cording medium according to the present embodiment, which is given 'by the following equati·on,; is: preferably 5 OT less, moTe pref·erably 4 o.r less·,· -and further mor.e, preferably .3 or less',, from the, vi·e.,;point. of obtaining excell·ent l.ight resistance and ,suppressing .a change into yell.ow or. a change into b:lue (bluing) due t·o light irradiation, CA 3265824 Date reçue / Received date 2025-02-19 ·- 50 - t.b: = b value: after standing at a luminance ,o·f .5; 000 Lux for 100 hours -~ b value. be-fc0re test The b value represents a chroma.tici.ty (b value) the Ll"a'<'b* color space :defined :in Jrs, z·97,s1-.4: 2013 The b value i·ndicates a change, ·from blue- to yellow, where, .the col.or becomes clos.er to yellow ·as the b value, increases:,. and the color becomes, closer to: blue: as the b value .decreases. The t.b. indicates- an amount of .change· in b va1ue·, .where the plus indicates a. :change ±n.to: yellow and the minus indicates a chang.e, into blue.. Therefore,, the change: into yellow or the change into 'blue ·becomes smalle·r and. light .resist·anc;:e is impro:v:ed as the absc,l·ute value of t.b ,becomes c1oser to 0, The Lib i:ndi·cates a degl'.'e·e of change into. yellow, whose. value de·creases as the change. into _yellow become'S smaller and light resistance is improved. ,

[0125] The dynamic sensitivity· (OD value) at O .i·6· m::j / dot -of the print portion of the heat-sensitive recording :medium according to· .the :pr.esent embodiment :is preferab:l:y O. 3 o,r more, ·and more :pref.er-ably 'O. 35 or more, from the viewpoint of: obtaining, ·exce·llent chr.omogenic properties .. The dynamic sensitivity ,(OD value) at 0:.20 mj / dot of the print portion ·of .the ·heat-sensitiv_e recording medium according to· .the present embodiment :is preferably 0.. 9 or more, ,and more preferably :1. ·or more,, from the viewpoint. o.£ obtaining excellent ·chromogenic properties .. CA 3265824 Date reçue / Received date 2025-02-19 The dynamic sensitivity .(OD value) -at 0. 40 mj' / dot .of the print ·portion of the heat-sensitive reco·rding medium according to the ·present embodiment :ls preferably l.i or more, .. and more ,preferably 1 ,.:2. or mor.e, £rom t'he vie"'.point of .. obtaining .excellent chromogenic properties .. The dynamic sensitivity (OD value) is measured i'n Examples ·shown .bel.ow, and incre·as.es ·as cihromogenic properties are improved .. [ 0126] The OD value of the non-print portion of the heatsensitive recording medium according to the pr.esent embodiment, in Example§• Cevaluati,m of heiclt .resist·ance) shown below is preferably :o .2 or less., more preferably 0 .18 or less•, and further more preferably O . .15 or. less,. from the viewpoint of obtaining excell.ent he·at resistance, so. t:hat the print portion can .be clearly identified even after cooking in a microwave oven or the Like, Examples In ·each :0£ Exampl.es and Comparative. Exarnpl.es bel·ow, a heat-'S'ensi.tLve recording ·medium comp.rising, ,a non- I phenol-based developer ,and, a non~phenol.-based antioxidant in .a 'heat-sensitive recording l:ay,er was prepared, .and its, chrornogenic properties.,. light resist·ance,, and heat CA 3265824 Date reçue / Received date 2025-02-19 - 5.2 - resistance, we:ce ·eva·luated. Note that the present invention is not limite·d to these Examples,.

[0128] (Eixamp.les 1 to .6 and ·comparativ.e. Exal'J\ples 1 to 2), :(Preparation .of heat-.sensitive, record1.ng· medium} <Undercoat layer> A co:ating l·iquid f.or an undercoat layer, which had been obtained by,m:ixing and stirring a composition comprising '70 parts :by mass, of holJ.ow particles, ('solid content concentration 26 ;,5%·, ROPAQUE HP-1055': Rohm And Haas Japan K,K.J,. 10 parts 'by mass of modified styr.ene buta:cti·ene 1,;tt;ex (59lici ,content ·concentrati(;m 4~%) ,;t·nd 20 parts by· mass of water was appl'ie:d onto high-quality paper (thickness: 80 μrn): ·having a weight per, unit area of 70 gf:m2, and serving, as ·a substrate,, and :dried to form ther.eon a 5 μm-thick undercoat .layer in an application amount of 3,·0 g / m2 on a dry basis. [0i29] <Heat-.sensitive recording laye,r> Coat,ing liquids :for forming· ,a heat-sens·i t'.Lve recording l•ayer., ·wh·ich ·are shown in Table 1, were prepared. The·. prepared, coating liquid. for •forming a heat-sensitive recording layer was· applied onto. the undercoat la'S,(er •such ·that the appl.ication amount ,was, 4,. 0 g / m2 ·on ,a :dry weight basis, :and drying ·was then perfO.rmed to· form .a 3,5 μm,-thick heat~sensitive' recording layer on CA 3265824 Date reçue / Received date 2025-02-19 the underc.oat laye.r.. In T.a.b'le 1., values for the materials blended indicate 'Weight ratios on a dry basis. ['0i30J As the 'materials bl.ended, :3-di.butxlamino.-6-.methyl~?-, anilinofluofJ.uorane having a particle: diameter of O .. 6 to 0 . 7 μm, was used .as a leuco d,ye,, [3- (3'- phenyl ur.eido,) pheny'l] -4,-methy·Lbenzene sulfonate represented :b;y the formula '(.2b:) was used as a. developer 1,. and N,,N'r-df~ [.3 .. (p:,.toluenesul.fonyloxy}phenyl] urea repr.esented 'by the fm:mtl'la (1b), was used ·as a dev.elqper 2 .. As the antioxidant i, tris ,C,2•,4-.di-tert-butylphenyl) pho1>phl.te (manufactured J:?.::r 9ongwon Ind1.1l,tria.1J '.bi;llong:tn! / to· •a phospborus type was used. ['0131] In addition; 1 1 2...:bis :C3~methylphenoxy) ethane ,(,fn the form of, a dispers•ion ·obt·ained b,Y disper.si:on in an: aqueous B'\l'A .solution to .a solid. content concentration of 20%:) was used as a sensiti.zer, a styrene acrylic copo'lymer emulsi:on wa,s: used as a binder, calcium .carbonate (in the form of· •a: dispersion ·.obtained .by, ·dispe.:n:si:on in a 5% aqueous• s·oiuti.on o'f sodium hexametaphosphate to· ·a· solid content concentration of· 30%): was used as a pigment,, ,and a zinc stearate. 'emulsion ·was used. as a sl'i;pping ,agent. [0132J <Intermediate layer> An acryl:Lc emulsion '.(s.olid content concentration 30.%). t:Lquia. wa.s a.pp'lHid onto. the. hea.t-sensitlv.e, rec6rding CA 3265824 Date reçue / Received date 2025-02-19 -· 54, - layer,, and :dried. to form the:ceon .a 1. 5 μm;-;thicik intermediate layer in an application amount of L 6 .g.,!m~ on .. a dry;· basis:,, [0L3::lJ <Topcioat layer> A. liquid. obtained by mi•xing and stirring· 40 parts: by mass oE ,.an .aoryli_c emulsion (sOlid content ,co•noentration 20%) 1 .5• pa:i::ts by ,mass of calcium carbonate,, 15 parbs, by .mass· o.f· polyethylene wax (.solid content concentration 4()%): and 46 ;parta by mass of water ·was a;ppll.ed onto the intermedl.at.e layer; and. dried to f.orm thereon a 0:.9 μmth: iok topcioat: li:lxer in an a,Pplioad.on amount of LO g / m~ on a dry· bas-is.

[0134] :By the above me.thods, heat·~s.ensitive· r-eeording :medi.a of Bxall)ples l to 6 and Compar,ative .Exampl.es 1 to 2 wer.e ·prepared,

[0135] [Table l] CA 3265824 Date reçue / Received date 2025-02-19 'O p; Q. CD l,J 0 (l"able 1) ti ::, ,:: I-' rt en Ill w I-'· I-'- I-' 0 rt S' p ~"' ::, '<: P> -~ rt (D I-'· 0 <1 0 P> tJ P>. ::, g. <1 r 0 P> P> Hj pl I-' rt ::, p I-'· I-' IQ CD 0 H· CD ::, IQ d 0 ::r )-,- Hj rt ;=:. t-h 'O I-' ti 0 ti CD t-':'O I-'" cn '<: ::, IQ I-'· ~- rt ::r en rt rt 1 Leticodye 17 Deyeioper 1 36, Qev~lgp_e_r 2 - Heaf-sensitive Antioxidanf1 p rec~ing f~Yl;!J Se_l)sitizel'.' 12. Binder· ·13· _Pigm_ent 1.S: Slipping,agen! 2 I-' 'O ti P> ·0.:' 0 g ti CD rt en (D I-'· I-'- '<: 0 en CD ::, lJ >-"' ..,__ I-'' 0 ::, 0 q 0 .: CD I-'· <1 ::, P> ii> (Q' I-' p ::, CD p,· 6 ::, 0 'O p;, Hi rt I-'· P> ::, 0 0 P> 0 ::, I-' ::r' I ll> 'O ::, ti IQ P"" _CD ::, rt _El(ample arative_E~ 2 !l 1 16.3 15,7 18.:i 34,7 332 38,8 - - - . 7,f, 10 - t1.5 11-1 12.9 13 13 13 15, 15 15 2 ,2 2 Example 4 5, 17 16.3 - - 3,6 34-;? ,5 r:s 12 11,5 13 13 15 15• ,2 2 6 15.7 - 33,2 10 1t1 13 1_5 2' ·GP.r.np_~r.;t_ti'v'.e E~~mpJe 2 18.3 - 38:8 - 12.9 13 15- 2 01 JJl_ CA 3265824 Date reçue / Received date 2025-02-19 in whiteness, were each measured for the :print portions and non~print portions of the heat·-sensiti'Ve recording ·media of Examples and Comparative Examp!l.es.. Hereinafter,, the procedure of evaluation ,o·f ,light resistance; will be described.

[0137] Pri·nting· was performed ,on the prepared heatsensitive re·cording medium under a condition of a printing energy of 0 ,,40 mJ: / dot using a heat-sensitive ·paper printing test apparatus (manufactured by Okura Engineering Co, Ltd. 1 'brand name,: Pu'lse Simulator TH~ Ml2 / PP) , whe·re the printing- r<;lj:.e 'WGIS :set: to s·o mm / seqi, thEl applied voltage was set to 17 .. 0 V, the head resistance value was set to 870 Q and the pulse •width was set to 0. 48'8 to 1 .3:94 ms,.

[0138] Using an illuminometer, a. distance: from a fluorescent lamp was ,so as to ensure 5,006 Lux, At the corresponding 'location, the: heat-sensi-ti'Ve recording medium :pr.inted as• de.s.cribed ·above ,is l·eft to stand :for, 1·0.0 hours. [0139) The optical densit;y of ·each •of the pri·nt po.rtion and the non~print portion (:OD value of ,print portion / OD 'Value. of. non-print portion) in a samp'le of the· heat.~,sensitive recording medium before the test and after the standing CA 3265824 Date reçue / Received date 2025-02-19 was measured using a spectrophotometer (manufactured by Videoj·et x~Rite, 'K. K. , '.brand name: exact) . [Oi4.6 J The whiteness (%) .and the hue (L, a., 'b) in a samp}e of, the heat-sensitive recording medium before, the test and the standing w.ere measured. The whiteness was measured according to JIS l' S:148 using a Photovolt type, re-flection. .densitometer .(manufactured by TokyoDenshoku. co,.,- Ltd .. ; brand name: T.c~6DS / A).

[0141] The hue· (L,, a, b) was measured using a color differenoe meter (m.;inufaqturi;,d b.y Vid1,9jet. x-.Rite .K.K., brand name,: SpectroEye) . [·0142] Table, 2 show the results of meas,urement in the test. In the ·measur.ement results in Table. Z, the· optical density (0D va'lue) in the: print portion and :the non--:print po.rtion :Lnd:t.cates higher col·or deve·lqpment (,the, colored state becomes _c·lo.ser to black) in the. case. of a large value (that is, •a low light r.eflectance), and insuff,icient col·or development ,in the· case· ,of a sma·11 value, (that is,- a high- light refl·ectance.) . The, whitenes"s ('%:} irrdicates that the color becomes closer to wh'ite as the 'ITalue increases.. Amorrg the indi·ces. of the hue (L,. a,. b), •(L} :f.nd:Ecates• a change from .blac"k to white, _and the col·or becomes closer to white as, the "value. ·of ·(L), iricr.e.ases ., (a) inc'fi·cates a change. from green to red, and CA 3265824 Date reçue / Received date 2025-02-19 the :colo,r l:recomes c1os.e:r: t:a· .re.d as the va'lue of (a). increases.. [b') in:dica.tes. a. !change from b'l:ue, to yel'.low, and the: ·co,l·or b:e:comes clos.e.r to. y,e1Lo:w as the: value of: Cb:,) increases, E:r:om these changes.. l:n col.o,:r:, the light resf,stance, :O',f ea·ch heat-sensitive recording medium ,was evaluated .. (Evai·uati,on of dynami·c sensiti:v:ity) In the dynamic sens·iti:vity test,, p:rinting 'Was :perf.ormed on t·he heat~,sens1tl'.ve recordl'.ng :medfa of .Examples an<!! ·Comparatf:ve :Exam,:,.l.es while the printing ' ' . en·e:i;:q;ir ·was 9h~n';)'ed, !;1:m;i the Qp,t;:i.o<:tl <;lens :i:t;ir (OD' valus) of print poi:;tion) at each printing erre;r;gy was, mea•s,ured. F:rom th(;) results of the measurement,, the, dynamic .. sens:id:f:vity of the heab--.·sensitive reooi:;ding medium in each of' ExaTI)Ples and :C.omparative, Exatl)ples was :e,;a'luate·d .. Here:l.nafter,, the p,rocedure of the dynam:l.c sensi,tivity· tes,t will .be desc:d'.bed. [014,4] Printing .was pe:r:f'ormed ,on. the prepared heat-. sensitf;v;e reco'rding medium under ,conditions o:f :pcinting energies of 0.1.6 ·mcT / do,tr ,0:.20 mJ / dot and 0.4'0 mJ / dot using a '.heatrs:ensitive, paper printing· test apparatus. (manuf.actured. by Okura '.Engin:ee,r.in:g Go,. Lt:d. r b:rand name,: Pulse 'Simul,at,or TH~M2 / RP:!:, whe.r,e· the ·printing· :rate was set to 50 ,mm / sec1 the app'l.led voltage was set to 17,,0 Vr the head. re&is:taoce value, .was: se,t to. 870 a .and t'he, pulse CA 3265824 Date reçue / Received date 2025-02-19 - 59 - width was set to 0.488: to 1.394 ms. The optical density (OD value) under the :relevant printing ener,gy 'condition was measured using a spectrophotometer ,(manufactured by Videoj,et x,-.Rite X,K.·, .brand name:: eXactJ. [014'5] Table, -2 show, the results or measurement in the test. Simi:larly to the light ,resistance test,. the me·asurement. re·sults, in. Table 2 show that higher ;color deve'lopment occurs in the case where the value of the optical density (OD value) ls 'large, and color deve,lo,pment is insufficient. in the case where, the value, is small. For exampl·e., a siimpl·e in whi-c:h th~, printing energv is small, ,but the: value of the o,ptical density (OD -value) is large is ·evaluated -a's having, "good, ch·romogenic' properties·" . On the other hand;· a sample in which the: printing energy is large.;, .but the. value of the optical density (OD. value). is, small is evaluated as having ":poor chromogenic :properties", In other wo.rds,. the dynamic sensitivity test i.s· evaluati:o.n of chromogenic properties, [014 6 J (Evaluation of heat resistance) In the heat resis,tance test,1 heat was, ,appli'ed to the print po.rtion and the non"'print ,portion of the heat-· s-ensi tive recording, medium, in ,each of :Examples and Comparative Exampl·es,, and the op.ti.cal density .of the print. port.ion and the non . ..,print 'Portion (OD value of· print portion). was measured. From the results of· the CA 3265824 Date reçue / Received date 2025-02-19 - 60 - measurement,. the heat resi-stance, of the heat-s·ensitiv.e recording medium, in each of Examples and Comparative· Examples was evaluated. Hereinafter, the procedure o.f the heat resistance te.st will be .described, Pri·nting· was performed ,on the prepared heatsensitive rec.ording medi.urn. under ,a condition -of• a· ,printing energy ·o·f O ..40 mJ: / dot using a heat-"Sensitive paper printing test apparatus (manufactured by Okura :Engineering Go. Ltd •. , :brand name,: Pu'lse S1:muTator. THM2 / PPJ,. where the printing rate was set to 50 mm / sec, the, applied vol tai::,e, wa1e set: to i 7, O v, the hestd resi@tance value, was set to 870 n ,and the pulse ·width was set to 0 .48.8 to .1 .3'94, :ms;.

[0148] A. contai·ne.r {,diameter: 12 cm, internal volume: 220 I l· • " • • I ' ; cc) conta .. ning 1'00 .g :of water 1,s covered ,with a p1astic wrap made of: vinyl chloride, (.thickness.: i·O μm)', and a samp1e of the heat-sensitive recording medium (3 cm in length and .IJ cm .in width) printed. as described above was attached onto the wrap.

[0149] :Next, 10 through-holes. were formed in the plastic wrap w.i.th a safety: pin so that water v.apor exited during heating_. The through-·ho·les were formed in •such a manner that the sample por:tion was. avoided, and the distances ·betwe.eri the through-holes were, equal. CA 3265824 Date reçue / Received date 2025-02-19 - 61 - [·0150 l :Next.r the container. was heated in a. microwave oven. (1,566 'W) for i minute.; and the optical dens:it-y ,of .each cf th.e ;pr.int port:l:on .and the non-print portion (OD value of. pri·nt portion / cm :value, of non-print portion) in the sample of the heat-sensitive recording medium ,was then measured using a spectrophotometer .(manufactured by V.ideojet X-R!ite K.K., .brand name: exact). [ 0151] Table, 1 show the results: cf measur.ement in the test. In the evaluation of heat resistance, when the va·iue, of the o;iti9al density (QD vg;lue) is sm;,.11 in t;he non-print po·rtion and large in the print por.tion, the reaction of the heat-sensitive recording medium to heat is low. That i·S•; the· :degree 0£ color development of the: print portion or the non-print ,portion when the heat-sensitive recording :medium. is heated. in a microwave oven and heat from v,apor :Ls -a,pplied. to the heat·-sensitive recording medium. is presented, F,o.r this reason, the· non-:print portion prefer.abl.y develops. ·a color as littl.e .. as poss·ible, and thus can be evaluated as "having good heat resistance," in the case ,where the ¥alue of the opti·cal density (GD value.) is smal'L On the other hand,, for the print portion, it is ·confi'rmed that the colored portion is not erased by heat from vapor. Specifically, the print portion, where• the v.alue• :of the optical density ·(OD. value;) is iarge, hardly· reacts to he.at. CA 3265824 Date reçue / Received date 2025-02-19 A ~ <l 6 CD ._:..:.. ti .Ul P·· w !"tt ~ p, 0 p,· (Tatile_2) Example para~e~ Example Compaf<l~VS ~-n:ip!e i :2 '3 1 4. 5 6 2 oo·va1ue• 1:55 / 0.0S: '1.51 / 0.05 1.'19 / 0.05 1.61 / 0.05 1.2010.03 12110.03 1.23 / 0.03 -120 / 0.03 -Wh!~~ (%) 84.S 85.0 85,~ 84.9 87,8 88.0 ,87~7 87:3 ,.., ~ 6 P> 1--' ,t_r, "U1' CD "' ~ rt P· 'B~fore fest L .!)5£13: ,96.12 9!;.03 96.-20 ,ril.Ti 91.ss 97.63, .97.fill Q. a -0.53 -0.55 -0.62 -0.57 ·-028 -025 -0:31 -0.26 ::, b 1.26 1.39 1,16 1,59 1.36 121 r:ar 1_,42• ti CD Liglil OD value~ {507o.06i ·1.4sio.oo 1;4810.06 1:s2.I0.07 1.1610,03 1.21 / 0.03 1.16io.03 '1.22ffi.03 [ / ). ~ ,-.. ct [ / ) resistance Whiteness·(%) 76.7 .7f1.T 79.3 TT.4 87.9 88.0 ·88.3 87.9 .SOOOLux'. L :95.1 95.3"( 9523 ~.?3 97.80 97.TIJ 97,89. 97.63 afier100 hr -- a o:os: 0.02. 0,07 02 ·-0.16 .:0.15 -0:15· -0.10 y b 4:52' 422 4.27 uo 121 1;45 1.34 1.44 Co.!Qr of change in. 'Whiter_ ,8.20 -5._30 ,a· .. 10. ,1.®. 0.10 il.oo 0.60 ·a.so· difference / lb 326, 283. 3.11 3.31 -0.15 024 0.03 0.02: 0:.1_6_r:r:ij / d_ot ·0.63 0.5"(' O.~ 0.64 0.36 0.42 D.?5 MO Dynamic sensitivity 6.20mj / dot 1:16: 1.oir 1.07 123 0.94 0.91 :b.91'.' 6.97 {OD. value)• 0.40mj / dot 1.52' 1.55 1.53 -1.58 1.16 4.15 U7 1:20- ·~ Heat resj;sianc,t t.51_ / p.1"2 ·1.4810.11 _J,48 / d.11 1.~21i)j3 u_s10,12 _1.2310.12 1.1810.10 12410.12 •: (OD va_~ue of ~rint_porti~)l(OD value of nonJrinl PQrtiori). CA 3265824 Date reçue / Received date 2025-02-19 - 63 - The fol.lowing was confirmed f·rom the results: shown, in Table 2, ['Examples, 1 to 3 and ·comparative. Example :i] .Example:s 1 to 3 and Compar.ative ExamJ?le 1 with the same dev.e·lope.r 1 will be discussed. [0154) (1), In the light resi'Stance test, the amount o·f change in whiteness is• sma·11er and the whitenes.s after the test is higher in Examples '2 and 3 than in Comparative Example 1, This ·may be because of the incorporation of the: antioxidant 1 (non-phenol-'ba·sed ilhtioxidant). in ExamJ?lei:i 2 and 3.. .On the other hand, the, amount of change in whiteness in Example l with the antioxidant 1 blended in an ·amount of 5 mass'%, which is smaller than that in E'xamples 2 and .3. (7 ,,5, mass% and 10 mass%,; respectiv.e'l:y),; wa'S :-8. 2·, and higher than that in Comparative Example i, with .a s·light difference. of O. 70. Therefore, it can be ,said that Examp'le l is comparable in level :of whiteness to Comparative Example 1. .The absolute value of· .L\.b .in Examples• 1 to. 3 ·was lower than that in: Comparative Example 1,, and ther.e was .no significant dif:ference in qptical density (OD value) of the non~pri;nt portion after the test between 'Exampl.es l to. 3 and C'orl)parative, Example 1. From these: ·facts, ·the heat~sensitive recording ·media o:f Examples 1 to 3 with a non-pheno'l--,based antioxidant CA 3265824 Date reçue / Received date 2025-02-19 wel'.)e conf.irmed to be, superior in light ·resistance to Comparative Example 1 without an antioxidant.

[0155] (2) In the dynamic sensitiv:i:ty test •(chromogeni.c prope-rties), the optical density (OD val'ue) in Examples 1 to. 3 was 1. 52 to 1. '55 and the optical. density (OD value•) in Comparativ.e .Exampl·e 1 was 1 . .58 when the printing energy· was ,set to: 0 .. 40' mJ / dot, the opti.caI :dens-ity (OD yalue) in 'Examples 1 to 3 .was 1. 07' to 1. 1,6: and the optical density (OD value;} in Comparative Example 1 was 1.23 when the printing energy was set to 0,.20 mJ / dot, and the qpt:L9al dens:i.t,:> (QD vi;(lue) in Examples: 1 to ~- wa:;; 0. 57 to: 0 .. 63! ·and the optical density (;OD value) in Comparative Example 1 'was ·o. 64 when the printing energy was set to 0.16 mJ / dot. T.he optical density (OD value.) tended. to be:. Lowi'!r in Examples l to 3 than in Comparative. Example i, However, in Examples i to· :j, there was Just a 2 to i.3% decrease, and chromogeni•c properties enabling successfu'l use as· .a heat-sensitive recording medium. were exhibited. From these facts, the heat-s:ensi.tive recording media of. 'Exall)ples 1 to 3 with a non-phenol-'ba·sed anti.oxidant were confirmed to. be. ·comparable and never inferior ·in chromog,enic ;pro_perties to Comparative: Exall)ple. 'l without an antioxidant, [·0156] CA 3265824 Date reçue / Received date 2025-02-19 - 65. - (3.) In the, heat res·istarrce te·st, the optical density (OD value:) nf the print portion and the optica'l. dens,ity (OD value) of t'he. non-,pr.int porti•on, ::Ln Examples. 1 to, 3 we.re 1, 4 8. to L.51 and O, i 1 to O. i2, ·respectively·, The optical density (OD value,) of. the print portion and. the, optical density (OD value:) of the non-print portion in Comparative Exampl.e 1 were 1. 52 and .0 .13, r.espective:ly. Irr particular,. in the non-print portion; an increase in optical .dens•ity (OD value) tended to :be lowe·r in Examp'les 1 to 3 than :Ln Comparative Example 1. From thes.e: .facts,. the heat~·sens:Lt:Lve record:Lng .media of: Examples 1 to 3 with a non-;phenol-'based antioxidant were confirmed to· have improved heat resi,stance a,s compared. to Comparative Example 1 without any antioxidant. [ 0157] [Examples 4 to :5 and Gomparat:i.'Ve, .Example: 2] Examples 4 to 6 and Comparative Examp'le· 2 ·with the same developer 2 will 'be discussed, ['0.158 J (4.) In the. li·ght re·sistance test, there was no decrease in ·whiteness either in Exampl·es 4 to 6: where the amount of. change in whiteness was O to :0 .·6·, or in Comparati'ITe Exampl·e 2 wher.e· the amount of change in wh•:Lteness was .Cl, 6'. In addition,- the degrees, ·of whiteness ·after the test •were .the same, CA 3265824 Date reçue / Received date 2025-02-19 From these, ·facts,, Exall)ples 4 to :6 with non-phenolbased antioxidant were confirmed to be never. inferior in light res:istanc.e to Comparative Example 2 ·without an antioxidant, [015'.9] (5), In the dynamic sensitivity test, the qptical density (OD value) in Exampl.es 4 to •6' was 1.15 to 1.17• and the optical .density .{'OD value): in Comparative Exampl·e· 2 was :1. 20 when the printing energy .was set to O. 40 mJ / dot,, the optical density (OD value.) in Examples 4 to 6' ·was 0,91 to 0,.94 and the opt:i.ca:1 . .dens-ity (OD ·:value.) in Comparat;ive Ex<;1m;pl<;l 2 ·waE, 0. ~7 wh(;ln the I?ri:nt:i.n9 en~rgx was set to •0 .. 20 mJ / dot, and the optical density (OD value) in Examples 4 to 6 was O .35 to O. 42 and the optical. :dens,ity (OD value.} in Comparative Example 2 was 0.40 when the printing, energy was set. to 0.16 mJ / dot. The optical density (OD va'lue'J, tended to be lower in .Examples 4 to 6 than in Comparative· Examp·le 2. However 1 in Exampl.es 4 to 6,, there: was just a 13% :decrease, .and chromog_enic :pr.operties• enabling successful use as .a heatsens: it.±ve recording medium·were exhibited. From these. ,facts, the he·at-sensitive recording :media of; Examples 4 to 6 with a non-phenol-'ba·sed antioxidant were conf:irme:d to, be, :compa·rable and never infesrior in chromog_enic ·properties to· Comparative Example• 2 without. an .antioxidant, t.0'160l CA 3265824 Date reçue / Received date 2025-02-19 ·- 67 - (6) In the. heat. resistance test; Examples 4 to :6 and Comparative Example 3 were comparable· in .optical density _ (013 value,) of the. print portion and optical densi t.y (013 value) of: the non-print portion. From this fact, Examples 4 to 6 ·were confirmed to: be never inferior in heat .resistance to Comparati-ve Example 2 without an antioxidant even though a non-phenol-'bas.ed antioxidant was contained. [0161 l ['Conc·lus ions] F·rom the measurement. ·res.ults described above, heatsemiitive recording. medii;i c:ont<;lining a non-phenQl-cba$ed developer and. a non-phenol-,ba'Sed antioxidant were not conf.irmed to: be .infer.ior. in light res.istance, chromogenic propertie·s .and 'heat re'Sistance. to heat-sensitive recording .media without an antioxidant. .It was found that ·when the heat-sensitive recording medium contained a non-phenol-based. anti:ox:Ldant,, an ·e·ffect of· improving· light. resistance while ma:Lntad.ning good heat resistance: of· the heat-sensitive recording .medium was. ,exhibited', and it. was :possible to suppr.ess a· deer.ease .in ·wh·iteness and a change into yellow. Further, the non-pheno:l'-bas.ed developer and the non~. phenol~base·d antioxidant .were s1.1perior in sa·fety to pheno'l:-;based c.ounterparts, Therefore,, the• use of• a .non~ pheno·l:-'based deve'l·oper and a non~phenol-based :ant:Lox:L·dant CA 3265824 Date reçue / Received date 2025-02-19 was very effective from the viewpoint of envir.onmental compatibility. Hereinafter, the variaticrn,s o·f the present invention will be appended .. [Appended item 1 J A heat-sensitive recording :medium in ·which a heatsensitive · recording layer .is layered on a substrate, the heat~sensitive recording layer compri·sing a color former, a non,.._phenol-'based dev.eloper and a nonphenol--' based antioxidant, the noTI-phenol-basi,,d antioxidant comprisin(3' a phosphorus-based antioxidant. [Appended item 21 The hea.t-sensitive recording· medium according to appended item ·1-, wherein the non~phenol--'based develqper compr:Lses a compo.und represented by the fo-llowing formula • (1) and / or a :compound. represented by- the, ·f·ollowing· formula (.2): ['Formula l 7 J. wherein FJ; J,;i .. , R'.31. Ri,. R$ 1 R7,- :R8,, R~, Rl.0 and R'°l each i·ndeperident1y represent a. hydrogen atom, or a (1) CA 3265824 Date reçue / Received date 2025-02-19 - 69 - substituent; R6 and R12 :each independently r,epresent a substituent; m repres'ents an integer of O to 4; when m i•s, 2 or. more,. ,a pl:ural:ity, .:of R• is. the same or d:L'ff.erent; n represents an integer of . .0 to 4; .and ·when n .is 2 p:r: ,more, a plurality· of .R12 is: the s.ame or di.fferent,. [Formula 18] {2) each independentl.y represent a hydrogen atom, .. or a substituent; Riil . .represents a .substituent; o represents an integer o:f O to 4; and .when o: is 2 or more; a plurality of RJ.~· is the same or different. [Appended item 3] The heat-sensitive ·recording medium :according to appended ·item 1 o.r 2, wherein the non~phenol-'based developer. comprises a comp.ound repre·sented by the follow.ing formul·a ('la) ·and / or a compound repre"Sented by the following formula {'2aJ : [Formula 19] CA 3265824 Date reçue / Received date 2025-02-19 - 70 - where-in the symbols are the· s·ame• ,as in ·formula '( 1:) , [Formula 20] * R16 R17 1H H o I I ·R22 R1& M_..,ovN...___c,,.N II I -~ R14; ·R130 • ,,.,p R1s R21 (R1e)o R20 wherein the symbo'ls are the same ,a'S •in :fo.rmula (:2.) .. [Appended item 4] (fa), (2a) The heat-sensitive recording medi·um accordi:ng to any one of appended items 1 to 31 wherein a content ·of the non-pheno1.-based. developer is no.t ·1ess than 10 ·mass% and no.t more than 50 ·mass%: with .respect to an entirety of the. heat-senSoit±.v.e recording medi.um. ['Appended i tern 5 I The heat-sensitive recording medi:um accordi:ng to any one of appended i,tems 1 to 4, wherein a content ·o:f the non-phenol~bas.ed. antioxidant is not less than 5: mass% and not more than 10 mass%: with respect to the entirety of the heat·-sensiti ve recording layer. CA 3265824 Date reçue / Received date 2025-02-19 Industrial ,l\:pp'li·cability [0'163] - 71. - As :described above,, the present invent:L.on is particularly., useful for heat-,sensitive recordin<J· media . . printed with· a 'barcode .or the li.ke . . Referenc.e Signs List [ 0164] 1 Heat-sens,itive re.cord:i'.ng .medium 2 Substrate 3 Heat-sensitive recording layer 4 Intermed:Latl;l layl;lr 5 Topcoat layer 6 Undercoat layer

Claims

- 72 - We Claim:

1. A heat-sensitive recording medium in which a heatsensitive recording layer is layered on a substrate, the heat-sensitive recording layer comprising a color former, a non-phenol-based developer and a non-phenol-based antioxidant, wherein the non-phenol-based developer comprises a compound represented by the following formula (1) and / or a compound represented by the following formula (2), the non-phenol-based antioxidant comprising a phosphorus-based antioxidant: wherein R1 , R2 , R3 , R4 , R5 , R7 , R8 , R9 , R10 and R11 each independently represent a hydrogen atom, or a substituent; R6 and R12 each independently represent a substituent; m represents an integer of Oto 4; when mis 2 or more, a plurality of R6 is the same or different; n represents an integer of Oto 4; and when n is 2 or more, a plurality of R12 is the same or diffe' rent, CA 3265824 Date reçue / Received date 2025-10-31 - 73 - R1e R14 H H R17 I I 0 -(rN'-c,,,-N 11,,...,o II S 0 II 1s R1aO. (R lo R23 R22 R21 Formula (2) R20 wherein R13, R14, R1s, R16, R17, R19, R20, R21, R22 and R23 each independently represent a hydrogen atom, or a substituent; R18 represents a substituent; o represents an integer of Oto 4; and when o is 2 or more, a plurality of R1B is the same or different.

2. The heat-sensitive recording medium according to claim 1, wherein the non-phenol-based developer comprises a compound represented by the following formula (3) and / or a compound represented by the following formula (4): Formula (3) wherein the symbols are the same as in formula (1), CA 3265824 Date reçue / Received date 2025-10-31 ' . - 74 - R1e R11 H H R23 o I I R22 j ~.,-,o'ON"c.,,,N II I II Formula (4) R14 R130 ~ 0 R19 R21 (R1a)o Rzo wherein the symbols are the same as in formula ( 2) .

3. The heat-sensitive recording medium according to claim 1 or 2, wherein a content of the non-phenol-based developer is not less than 10 mass% and not more than 50 mass% with respect to an entirety of the heat-sensitive recording medium.

4. The heat-sensitive recording medium according to claim 1 or 2, wherein a content of the non-phenol-based antioxidant is not less than 5 mass% and not more than 10 mass% with respect to the entirety of the heat-sensitive recording layer.

5. The heat-sensitive recording medium according to claim 3, wherein a content of the non-phenol-based antioxidant is not less than 5 mass% and not more than 10 mass% with respect to the entirety of the heat-sensitive recording layer.

6. The heat-sensitive recording medium according to claim 1 or 2, wherein the color former is a leuco-base dye and the non-phenol-based antioxidant is a compound having a trivalent phosphorus atom in the molecule.