water - soluble resinous materials useful for the invention may preferably obtained by copolymerizing at least one of ethylenic monomers and conjugated diolefinic monomers with at least one unsaturated carboxylic acid . among the useful ethylenic monomers , there are included monomers having 2 to 25 carbon atoms such as linear or branched olefins , e . g ., ethylene , propylene , butylene , etc . ; aromatic vinyl compounds , e . g ., styrene , vinyl toluene , halogen - substituted styrene , etc . ; vinyl cyanide compounds , e . g ., acrylonitrile , methacrylonitrile , etc . ; alkyl acrylates and methacrylates , e . g ., methylacrylate , butyl acrylate , methyl methacrylate , etc . ; vinyl ethers , e . g ., isopropyl vinyl ether , methyl vinyl eter , etc . ; vinyl halides , e . g ., vinyl chloride , vinylidene chloride , etc . ; and vinyl acetate . there are preferably used linear or branched olefins , aromatic vinyl compounds , alkyl acrylates and methacrylates . particularly ethylene , styrene , methylacrylate , butyl acrylate and methyl methacrylate are most preferably used . among the conjugated diolefinic monomers , there are included monomers having 4 to 10 carbon atoms such as butadiene , isoprene , chloroprene , piperylene etc . butadiene is most preferably used . among the useful unsaturated carboxylic acids , there are included acrylic acid , methacrylic acid , crotonic acid , itaconic acid , maleic acid , fumaric acid etc . acrylic acid , methacrylic acid and maleic acid are preferably used . when the amount of the unsaturated carboxylic acid copolymerized is less than 30 % by weight on the basis of that of the copolymer , the coating film of the copolymer is soft and sticky . on the other hand , when the amount of the unsaturated carboxylic acid is more than 70 % by weight , the coating film becomes very hard to produce a roughened color developing layer and to degrade the quality of the resultant heat - sensitive record material . accordingly , the copolymer comprising 30 % to 70 % by weight of the unsaturated carboxylic acid unit is preferably used . as described above , according to the invention , water soluble resinous materials having carboxyl radicals are used . in order to achieve the advantages aimed by the invention , it is essential that the carboxyl radicals of the water - soluble resinous material are wholely or partly by at least 35 % of its total amount , neutralized by alkaline materials . the salt produced by neutralization must be a magnesium salt with and at least one another salt which is a member selected from the group consisting of sodium salt , potassium salt , ammonium salt and amine salt . the preferred another salt is sodium salt or potassium salt . the carboxyl radicals existing in the form of magnesium salt must be within the range of 30 to 80 %, preferably 40 to 70 % of the total carboxyl radicals and the carboxyl radicals existing in the form of another salt must be within the range of 5 to 70 % of the total carboxyl radicals . if the carboxyl radicals of the water - soluble resinous material are neutralized by more than 90 %, preferably , more than 95 % of its total amount , the so - called &# 34 ; fogging &# 34 ; or undesired incidental color developing can be prevented in addition to the above mentioned improvement in the water resistance and the continuous recordability . it is known to use as a binder sodium salts or ammonium salts of copolymers having carboxylic radicals . however , it has never been proposed to use a copolymer in which the carboxyl radicals are neutralized in the above specified manner to improve the water resistance and the continuous recordability of the resultant record material . the above specified water - soluble resinous material may be added in the color developing layer in an amount of 10 to 40 % preferably 15 to 30 % by weight on dry basis of the total amount of the solid components of the color developing layer . the other usual binders such as polyvinyl alcohol , methylcellulose , hydroxyethylcellulose , styrene - butadiene latex and the like may also be added , if required and in an amount within such the range as not sacrificing the advantages obtained according to the invention . there is no limitation about the amount of the other binders used but usually it will be within the range of two parts by weight or less , preferably one part by weight or less per part by weight of the specified water - soluble resinous material . among examples for the combination of color former and acceptor included in the color developing layer according to the invention , there are included the combination of basic colorless chromogenic material with inorganic or organic acidic material and the combination of metal salt of long chain fatty acid , e . g ., ferric stearate , ferric myristate and the like with phenol , e . g ., tannic acid , gallic acid and the like . the former combination is preferred for obtaining stable record images . any of various known colorless chromogenic materials may be used for the present invention . among them there are included , by way of examples , 3 , 3 - bis ( p - dimethylaminophenyl )- 6 - dimethylaminophthalide ( cvl ), 3 , 3 - bis ( p - dimethylaminophenyl ) phthalide , 3 -( p - dimethylaminophenyl )- 3 -( 1 , 2 - dimethylindole - 3 - yl ) phthalide , 3 -( p - dimethylaminophenyl )- 3 -( 2 - methylindole - 3 - yl ) phthalide , 3 , 3 - bis ( 1 , 2 - dimethylindole - 3 - yl )- 5 - dimethylaminophthalide , 3 , 3 - bis ( 1 , 2 - dimethylindole - 3 - yl )- 6 - dimethylaminophthalide , 3 , 3 - bis -( 9 - ethylcarbazole - 3 - yl )- 5 - dimethylaminophthalide , 3 , 3 - bis -( 2 - phenylindole - 3 - yl )- 5 - dimethylaminophthalide , 3 - p - dimethylaminophenyl - 3 -( 1 - methylpyrrole - 2 - yl )- 6 - dimethylaminophthalide , 4 , 4 &# 39 ;- bis - dimethylaminobenzhydrinebenzylether , n - halophenyl - leucoauramine , n - 2 , 4 , 5 - trichlorophenyl - leucoauramine , rhodamine - b - anilinolactam , rhodamine -( p - nitroanilino ) lactam , rhodamine -( p - chloroanilino ) lactam , 7 - dimethylamino - 2 - methoxyfluoran , 7 - diethylamino - 2 - methoxyfluoran , 7 - diethylamino - 3 - methoxyfluoran , 7 - diethylamino - 3 - chlorofluoran , 7 - diethylamino - 3 - chloro - 2 - methylfluoran , 7 - diethylamino - 2 , 3 - dimethylfluoran , 7 - diethylamino -( 3 - acetylmethylamino ) fluoran , 7 - diethylamino -( 3 - methylamino ) fluoran , 3 , 7 - diethylaminofluoran , 7 - diethylamino - 3 -( dibenzylamino ) fluoran , 7 - diethylamino - 3 -( methylbenzylamino ) fluoran , 7 - diethylamino - 3 -( chloroethylmethylamino ) fluoran , 7 - diethylamino - 3 -( diethylamino ) fluoran , 2 - phenylamino - 3 - methyl - 6 -( n - ethyl - n - p - toluyl ) amino - fluoran , benzoylleucomethylene blue , p - nitrobenzyl - leucomethylene blue , 3 - methyl - spirodinaphtopyrane , 3 - ethyl - spiro - dinaphthopyrane , 3 , 3 &# 39 ;- dichloro - spirodinaphthopyrane , 3 - benzylspiro - dinaphthopyrane , 3 - methyl - naphtho -( 3 - methoxy - benzo )- spiropyrane and 3 - propyl - spiro - dibenzopyrane . the above colorless chromogenic materials may be used either solely or in combination . the acidic material as acceptor may be either or organic or inorganic . among organic acidic materials as acceptor there are included phenolic compounds , aromatic carboxylic acids and their polyvalent metal salt . typical phenolic compounds which can be used as acceptor are : 4 - tert - butylphenol , 4 - hydroxydiphenoxide , α - naphthol , β - naphthol , 4 - hydroxyacetophenol , 4 - tert - octylcatechol , 2 , 2 &# 39 ;- dihydroxydiphenol , 2 , 2 &# 39 ;- methylene - bis ( 4 - methyl - 6 - tert - isobutylphenol ), 4 , 4 &# 39 ;- isopropylidene - bis -( 2 - tert - butylphenol ), 4 , 4 &# 39 ;- sec - butylidenediphenol , 4 - phenylphenol , 4 , 4 &# 39 ;- isopropylidenediphenol ( bisphenol a ), 2 , 2 &# 39 ;- methylene - bis ( 4 - chlorophenol ), hydroquinone , 4 , 4 &# 39 ;- cyclohexylidenediphenol , novolak phenol resin and other phenol polymers . typical aromatic carboxylic acids which can be used as acceptor are : aromatic carboxylic acids , for example , benzoic acid , o - toluylic acid , m - toluylic acid , p - toluylic acid , p - tert - butylbenzoic acid , o - chlorobenzoic acid , p - chlorobenzoic acid , dichlorobenzoic acid , trichlorobenzoic acid , phthalic acid , isophthalic acid , terephthalic acid , 2 - carboxybiphenyl , 3 - carboxybiphenyl , m - hydroxybenzoic acid , p - hydroxybenzoic acid , anisic acid , p - ethoxybenzoic acid , p - propoxybenzoic acid , p - benzyloxy benzoic acid , p - phenoxybenzoic acid , gallic acid , anthranilic acid , m - aminobenzoic acid , p - aminobenzoic acid , phthalic acid monoamide , phthalic acid monoanilide , 3 - isopropyl - 4 - hydroxybenzoic acid , 3 - sec - butyl - 4 - hydroxybenzoic acid , 3 - cyclohexyl - 4 - hydroxybenzoic acid , 3 - phenyl - 4 - hydroxybenzoic acid , 3 - benzyl - 4 - hydroxybenzoic acid , 3 , 5 - dimethyl - 4 - hydroxybenzoic acid , 3 , 5 - dichloro - 4 - hydroxybenzoic acid , trimellitic acid , pyromellitic acid , α - naphthoic acid , β - naphthoic acid , tetrachlorophthalic acid , 2 , 2 &# 39 ;- dicarboxydiphenyl , salicylic acid , o - cresotinic acid , m - cresotinic acid , p - cresotinic acid , 3 - ethylsalicylic acid , 4 - ethylsalicylic acid , 3 - isopropyl - salicylic acid , 3 - sec - butylsalicylic acid , 5 - sec - butyl - salicylic acid , 3 - tert - butylsalicylic acid , 3 - cyclohexyl - salicylic acid , 5 - cyclohexylsalicylic acid , 3 - phenyl - salicylic acid , 5 - phenylsalicylic acid , 3 - benzylsalicylic acid , 5 - benzylsalicylic acid , 5 - tert - octylsalicylic acid , 3 -( α - methylbenzyl ) salicylic acid , 5 -( α - methylbenzyl )- salicylic acid , 3 - nonylsalicylic acid , 5 - nonylsalicylic acid , 5 -( α , α - dimethylbenzyl )- salicylic acid , 3 - chlorosalicylic acid , 5 - chlorosalicylic acid , 3 - hydroxy - salicylic acid , 4 - hydroxysalicylic acid , 5 - hydroxy - salicylic acid , 6 - hydroxy salicylic acid , 3 - methoxysalicylic acid , 3 - ethoxysalicylic acid , 4 - methoxysalicylic acid , 5 - methoxysalicylic acid , 5 - benzyloxysalicylic acid , 5 - octoxysalicylic acid , 3 , 5 - dichlorosalicylic acid , 3 - chloro - 5 - methylsalicylic acid , 3 - chloro - 5 - ethylsalicylic acid , 3 - chloro - 5 - isopropylsalicylic acid 3 - chloro - 5 - tert - butylsalicylic acid , 3 - chloro - 5 - cyclohexylsalicylic acid , 3 - chloro - 5 - phenylsalicylic acid , 3 - chloro - 5 -( α - methyl - benzyl ) salicylic acid , 3 - chloro - 5 -( α , α - dimethylbenzyl )- salicylic acid , 3 - chloro - 5 - chlorosalicylic acid , 3 , 5 - dimethylsalicylic acid , 3 - methyl - 5 - tert - butylsalicylic acid , 3 - isopropyl - 5 - tert - butylsalicyclic acid , 3 - isopropyl - 5 - cyclohexylsalicylic acid , 3 - isopropyl - 5 -( α - methylbenzyl )- salicylic acid , 3 - isopropyl - 5 -( α , α - dimethylbenzyl )- salicylic acid , 3 - sec - butyl - 5 - tert - butylsalicylic acid , 3 - tert - butyl - 5 - cyclohexylsalicylic acid , 3 - tert - butyl - 5 -( 4 - tert - butylphenyl ) salicylic acid , 3 -( 4 &# 39 ;- tert - octyl - phenyl )- 5 - tert - octylsalicylic acid , 3 -{ 4 &# 39 ;-( α , α - dimethyl - benzyl ) phenyl }- 5 -( α , α - dimethylbenzyl ) salicylic acid , 3 , 5 - di - α - methylbenzylsalicylic acid , 3 , 5 - di - α , α - dimethylvenzylsalicylic acid , 3 - phenyl - 5 - α , α - dimethylbenzylsalicylic acid , 3 - hydroxysalicylic acid , 1 - hydroxy - 2 - carboxynaphthalene , 1 - hydroxy - 2 - carboxy - 4 - isopropylnaphthalene , 1 - hydroxy - 2 - carboxyl - 7 - cyclohexylnaphthalene , 5 -( 4 &# 39 ;- hydroxybenzyl ) salicylic acid , 5 -( 3 &# 39 ;- carboxyl - 4 &# 39 ;- hydroxybenzyl ) salicylic acid and 3 -( α , α - dimethylbenzyl )- 5 -{ 3 &# 39 ;- carboxyl - 4 &# 39 ;- hydroxy - 5 -( α ,. alpha .- dimethylbenzyl ) benzyl } salicylic acid . polymers of the above mentioned aromatic carboxylic acids with aldehydes or acetylene are also useful . in addition , various polyvalent metal salts of the above mentioned phenolic compounds and aromatic carboxylic acids ( including their polymers with aldehydes or acetylene ) are also useful as acceptor . among the polyvalent metals which can form such metallic salts like this there are included magnesium , aluminum , calcium , titanium , chromium , manganese , iron , cobalt , nickel , copper , zinc , silver , cadmium , tin and barium . preferred metals are zinc , magnesium , aluminum and calcium . among useful inorganic acidic materials as acceptor there may be included activated clay , acid clay , attapulgite , bentonite , colloidal silica , aluminum silicate , magnesium silicate , zinc silicate , tin silicate , calcined kaolin and talc . the above enumerated acceptors may be used either solely or in combination . there is no special limitation about the composition ratio of the color former and the acceptor . in case where the combination of a basic colorless chromogenic material with an acidic material is used , the amount of the acceptor is usually within the range of 1 to 50 parts by weight , preferably 4 to 10 parts by weight , per one part by weight of colorless chromogenic material . the color developing layer of a heat sensitive record material according to the invention may be formed by any conventional method . typically it may be formed by preparing an admixture of color former and acceptor , pulverizing the admixture into finely divided particles utilizing attritor , sand mill , ball mill or any other pulverizer , preparing a coating composition in which color former particles and acceptor particles are dispersed , adding to the coating composition the above mentioned specified binder and by coating a suitable base sheet with the thus prepared coating composition . after the coating the sheet may be subjected to a calendering step for smoothening the coated surface of the sheet . in the coating composition various additives may also be added . among the additives , for example , there are included pigments having a good oil - absorbability in order to prevent the heat - sensitive record material from being stuck in contact with stylus of recording head ; surfactants such as sodium dioctylsulfosuccinate and sodium dodecylbenzenesulfonate ; ultraviolet ray absorbing agents such as benzophenone derivatives and triazol derivatives ; sensitivity moderators such as stearic acid amide , palmitic acid amide and 2 , 6 - diisopropylnaphthalene ; releasing agents such as zinc stearate and aluminum stearate ; fluorescent dyes and coloring dyes . as for the base sheet , paper , plastic film , synthetic paper , and metal film may be used , but paper is used most preferably from the economical viewpoint and the coating receptivity . the amount of coating composition applied to form a color developing layer , though not particularly limited , usually is 2 - 15 g / m 2 , preferably 3 - 12 g / m 2 on dry basis . the following examples serve to illustrate the invention in more detail although the invention is not limited to the examples . unless otherwise indicated , parts and % signify parts by weight and % by weight , respectively . ______________________________________2 - phenylamino - 3 - methyl - 6 -( n - ethyl - n - p - tolyl ) 25 partsaminofluoranstearic acid amide 10 parts5 % aqueous solution of methylcellulose 35 partswater 105 parts______________________________________ pulverization was continued until an average particle size of 3 microns . ______________________________________4 , 4 &# 39 ; isopropylidene - diphenol ( bisphenol a ) 100 partsstearic acid amide 40 parts5 % aqueous solution of methylcellulose 140 partswater 420 parts______________________________________ pulverization was continued until an average particle size of 3 microns . a dispersion was obtained by mixing and agitating the following components : ______________________________________a liquid 175 partsb liquid 700 partssilicon oxide (&# 34 ; syloid no . 74 &# 34 ; manufactured by 100 partsfuji - davidson chemical ) styrene - butadiene copolymer latex 70 parts (&# 34 ; dow latex 1571 &# 34 ; manufactured by dow chemicalcompany , solid content : 50 %) water 550 parts______________________________________ 500 parts of 20 % aqueous solution of a water - soluble resin which was made from the monomers as shown in table 1 and neutralized in the neutralization ratio as shown in table 1 was added to the above dispersion to prepare a coating composition . the coating composition was coated on a base sheet of 50 g / m 2 in the weight of an amount of 8 . 0 g / m 2 on dry basis to obtain a heat - sensitive record material . ______________________________________crystal violet lactone ( cvl ) 25 parts10 % aqueous solution of polyvinyl alcohol 25 partswater 75 parts______________________________________ pulverization was continued until an average particle size of 3 microns . ______________________________________4 , 4 &# 39 ;- cyclohexylidene - diphenol 80 parts4 , 4 &# 39 ;- methylidene - diphenol 20 parts10 % aqueous solution of polyvinyl alcohol 100 partswater 300 parts______________________________________ pulverization was continued until an average particle size of 3 microns . a dispersion was obtained by mixing and agitating the following components : ______________________________________a liquid 125 partsb liquid 500 partspolyethylene (&# 34 ; hi - wax &# 34 ; manufactured by mitsui 250 partspetrochemical industries , ltd . solid content : 20 %) kaolin (&# 34 ; ultra white 90 &# 34 ; manufactured by engelhard 500 partsminerals & amp ; chemicals corporation ) ______________________________________ to the dispersion there was added 800 parts of 20 % aqueous solution of a water - soluble resin obtained by copolymerizing the monomers as shown in table 2 and neutralizing the carboxyl radicals of the resultant copolymer to 70 % of magnesium salt and 30 % of sodium salt to prepare a coating composition . the coating composition was coated on a base sheet of 50 g / m 2 in the weight of an amount of 5 g / m 2 on dry basis to obtain a heat - sensitive record material . the properties of the fourteen heat - sensitive record materials obtained by the above examples and controls were examined with the following methods . all - mark image was recorded on the heat - sensitive record materials with the use of practical heat - sensitive facsimile kb - 600 ( manufactured by tokyo shibaura electric co ., ltd .) for one minute . the applied voltage was 19 v , dot density of thermal head was 5 dots / mm and line density was 4 lines / mm . the resultant sticking on the surface was checked . the color density of the obtained images was measured by macbeth densitometer model no . rd - 100r ( manufactured by macbeth corporation ). as to water resistance , the images were rubbed with the finger wetted with water five times in the same condition and the color density of the rubbed images was measured . additionally , the brightness of the color developing layer was measured by hunter multipurpose deflect meter ( according to jis p 8123 ) to determine the fogging . these results are shown in table 3 . as shown in table 3 , the heat - sensitive record materials obtained in examples according to the invention are superior in both of water resistance and continuous recordability and substantially are not fogged . table 1__________________________________________________________________________ neutralization ratio of carboxylmonomers (%) radicals (%) methyl methacrylic maleic magne - styrene acrylate acid acid sium sodium potassium ammonium__________________________________________________________________________control 1 30 10 60 100control 2 30 10 60 10 80example 1 30 10 60 40 60example 2 30 10 60 70 30example 3 50 10 40 70 25control 3 50 10 40 40 25example 4 40 60 50 30 10example 5 50 50 80 20__________________________________________________________________________ table 2______________________________________monomers (%) butyl methyl - metha - sty - ethy - acry - metha - but - acrylic cyrlicrene lene late crylate adiene acid acid______________________________________con - trol 4 30 10 40 20ex - ample 6 40 10 10 40ex - ample 7 30 10 60ex - ample 8 40 60ex - ample 9 30 10 60ex - ample 10 30 10 60______________________________________ table 3______________________________________ color watersticking density resistance brightness (%) ______________________________________control 1 o 0 . 80 0 . 11 73control 2 δ 0 . 80 0 . 13 70example 1 o 0 . 80 0 . 75 73example 2 o 0 . 81 0 . 79 78example 3 o 0 . 80 0 . 77 72control 3 × 0 . 81 0 . 70 58example 4 o 0 . 80 0 . 78 73example 5 o 0 . 81 0 . 80 70control 4 ×× 0 . 80 0 . 77 70example 6 o 0 . 80 0 . 77 72example 7 o 0 . 80 0 . 75 72example 8 o 0 . 81 0 . 76 70example 9 o 0 . 80 0 . 75 71example 10 o 0 . 80 0 . 75 70______________________________________ ( note )- 1 . sticking : o sticking was never found . δ the sound of sticking wa recognized but the color images were stable . × the loud sound of sticking was heard and the change of the color images was recognized . ×× sticking was very hard . the continuous recording was stopped early , lest the recording head should be damaged . 2 . color density : the larger the number , the higher or more preferable th density . 3 . water resistance : the larger the number , the fewer the peeling of the color developing layer and the more preferable the water resistance . 4 . brightness : the larger the number , the more superior the brightness an the fewer the fogging .