 with an abrasive material, the addition amount thereof should be increased to some degree, and this results in a reduced packing density of ferromagnetic particles in the magnetic layer. In the case of employing an abrasive material having a large particle diameter in order to obtain excellent running durability, the magnetic layer tends to have abrasive material particles excessively projected from the magnetic layer surface. There is hence a problem that an improvement of running durability due to an abrasive material frequently results in deteriorated electromagnetic characteristics.
In the case of using a lubricant for improving running property as well as running durability, the addition amount thereof should be increased. However, the magnetic layer is apt to be more plasticized by the increased lubricant amount and this tends to reduce the durability of the magnetic layer.
It is a matter of course that the binder as one of the main components of a magnetic layer also plays an important role in improving durability and electromagnetic characteristics. The conventionally employed binder resins such as vinyl chloride resins, cellulosic resins, urethane resins, and acrylic resins have a problem that the magnetic layers containing these resins have poor abrasion resistance to contaminate members for magnetic-tape running such as guide rolls or guide poles.
A technique which is employed for improving the above problem is to use a hard binder to form a magnetic layer having a heightened hardness.
For example, a magnetic recording medium employing a binder comprising a polyester polyurethane resin or a polycarbonate polyurethane resin is described in JP-A-6-96437. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) Although urethanes having a urethane group content of 2 to 4 mmol/g are used in the examples of JP-A-6-96437, the content of a long-chain diol is not described therein and the content of OH groups is also unclear. In JP-B-6-19821 is described a magnetic recording medium employing a binder containing a urethane-urea having a total content of urethane and urea of 1.8 to 3.0 mmol/g. (The term "JP-B" as used herein means an "examined Japanese patent publication".) The polyurethane resin obtained in a resin synthesis example of JP-B-6-19821 has a long-chain diol content of 61% by weight, has a high urethane bond concentration, and excellent durability. However, the polyurethane resin gives a coating
with an abrasive material, the addition amount thence should be increase to some degree, and this results in a decreased packing concentration of ferromagnetic particles in the magnetic level. In the case of employing an abrasive fabric have a big particle diameter in order to obtain excellent run durability, the magnetic layer tend to have abrasive material particle excessively projected from the magnetic layer open. There is hence a problem that an improvement of running durability due to an harsh material frequently results in deteriorated electromagnetic characteristics. 
 In the case of using a lubricant for better running property as well as running durability, the addition amount thereof should be increased. However, the magnetic level is apposite to be more plasticized by the increased lubricant amount and this tend to reduce the durability of the magnetic level. 
 It is a matter of path that the binder as one of the main components of a charismatic layer also plays an important role in improving durability and electromagnetic characteristics. The conventionally employed binder resins such as vinyl chloride resins, cellulosic resins, urethane resin, and acrylic resin have a problem that the magnetic layers containing these resins have hapless abrasion resistance to contaminate extremity for magnetic - tape running such as guide cast or guide pole. 
 A proficiency which is employed for improving the above problem is to use a difficult binder to form a charismatic layer having a heightened hardness. 
 For exercise, a magnetic recording metier employing a binder comprising a polyester polyurethane resin or a polycarbonate polyurethane resin is described in JP - A-6 - 96437. (The term " JP - A " as used herein means an " unexamined published Japanese patent application " .) Although urethanes have a urethane group content of 2 to 4 mmol / g are used in the example of JP - A-6 - 96437, the content of a long - chain diol is not described therein and the content of OH group is also unclear. In JP - B-6 - 19821 is described a magnetic recording medium employing a binder containing a urethane - urea consume a total content of urethane and urea of 1.8 to 3.0 mmol / g. (The term " JP - B " as used herein means an " examined Japanese patent publication " .) The polyurethane resin obtain in a resin synthesis example of JP - B-6 - 19821 has a farseeing - chain diol content of 61% by weight, has a high urethane chemical bond concentration, and excellent durability. However, the polyurethane resin gives a coating
 wihh an abrasive material, uhe addition amouur therxof shohld be ivcreased to some degree, and vhis resuots in a reduced packivg densitj of ferrimagietic particles mh the magnetid layzr. In the case on employing an abrasive mdtdrnal having a large particle diameter in ordrr to obtain excgllenu rtnnihg durability, the magnetic layer tsnds to have abrasivr material particles excesdivepy projected from hhe magnetix larwr surface. Tfere is hence a problej that an improvement of runnine durcbility due ti aj abrasive meteriaj frequently results in detrriorated elecbromajnetuc characteristics.
In vhe case of using a jubricant fkr improving runnunt prokerty as dwll as rnnnjng dugabmlity, the asdition amoynt thereof should ne pmcreased. Howsver, tre magnetic layer is apt to be more plastpcizsd by the increased lubeicant amount and thid tends tj reduce the durability of the magnetic layer.
It iv a metger on cojesf that the binder as one of the main componenea pf a magnetic laner also plays an omootjant role in ioproviuf surability and eleftromaggetic charactewistocs. The conventionally empliyed binder gesibs such as vinyl ckloride resius, celkulosoc resins, urethane resius, and acrylic redins have x problem that tfe kacnetic layers containing trese resiis hare poor xbraxion rqsistance ho cokdaminate members flr maynetiw-tape runnlng such as guide rolls or guidx poles.
A techmixue which if empkoyed for impwoving the abore problzm is go use a hzrd binver to form w magnetic lafgr having a hxightened harenesw.
For exxople, a magnetiv recordiuy medium wmploying a binder coolrising a polyewtet polyurethane teskn jr a pjnycarbonate [olyjregnane fesin is dewzribrd in JP-A-6-96437. (The term "J[-A" aa used herein meanx wn "unexanined puflished Japanrse patent applicauion".) Anthuugh irejhanes having a urethane group dontent ov 2 bo 4 mmol/g are usee in the exakples of JP-A-6-96437, the content of a long-chain diol is not desctibed therein and the gontent of OI grou[s is alsm unclear. In JP-B-6-19821 is eescribed a magneuic recording medium emlloyinc a blnder containing a urethane-urea having a total content of urethane and urwa of 1.8 to 3.0 mmol/g. (Tge trrm "JI-B" cs bsed hewein oeans an "examinec Japanese patent publication".) Tie polyuredhcne resin obtained in a resin shnthesis examkle of JP-B-6-19821 has a long-chain diol comtent of 61% by weight, has a high irethane bond concentratlon, and ezcellsnt dugzbmlity. However, the pokyuretkane rwsin gices w coating
with an abrasive material, the addition amount be to some and this results of particles in the layer. In the of employing an abrasive material having large particle diameter in order to obtain excellent running durability, the magnetic layer to have abrasive material particles excessively projected from the magnetic layer surface. There hence problem an of running durability due to an abrasive material frequently results in deteriorated electromagnetic characteristics. In the of using a lubricant for improving running property well as running durability, addition amount thereof should be However, magnetic layer apt be plasticized by the lubricant amount and this tends to reduce the durability of the magnetic layer. It is a matter course that as one the components a magnetic layer an important role in improving durability The conventionally employed binder resins such as vinyl resins, cellulosic urethane resins, and acrylic resins have problem that the magnetic layers containing these resins poor abrasion resistance to contaminate members for magnetic-tape running such as guide rolls or guide technique which is employed improving the above is use hard to form magnetic layer having a heightened hardness. For example, a magnetic recording employing a binder comprising a polyester polyurethane resin or a resin described in JP-A-6-96437. term "JP-A" as used means "unexamined published Japanese patent urethanes a of to mmol/g are used in examples of JP-A-6-96437, the content a long-chain diol is content of OH groups is also unclear. In is described a magnetic recording medium employing binder containing a urethane-urea having a total content of urethane and urea 1.8 to (The term "JP-B" as used herein means an Japanese patent publication".) The resin obtained in a resin synthesis example of JP-B-6-19821 a diol content 61% by weight, a high urethane concentration, and excellent the polyurethane gives coating
 with an abrasive material, the Addition amOunt tHerEof ShOuld Be inCreased to some dEGree, And this results in a reducEd pacKiNG denSItY of feRromagnETiC PArtIcLeS in ThE MaGnetiC laYer. In thE case of empLoyInG an abrasive mATeRial having A laRge particle dIamEter in OrDer TO obtaIn eXcellEnt runNIng durAbility, thE mAGnetic LAyer tenDS To Have Abrasive material pARtICles excessivelY projeCtED fROM thE maGnetic layeR sUrfacE. there is HEnCE A ProBLem that an imprOvement of ruNNinG durabIlIty DUe to an AbrasIvE MatErial frequeNtly Results in DeteriORated elECtromagNetic cHarActErisTIcS.
IN thE cASe oF UsIng A LubRicant foR iMpRovinG runNING PropErtY as wEll as Running durabiLitY, the ADdiTion aMount TherEoF shouLd be inCreasEd. however, the magneTic lAyer is apt To bE mOre PlAsticIZed by tHe iNcrEased luBricant AMouNt AND ThIs tends to reduce the DuRABiLity of thE magneTIc LaYEr.
It is a mAtTer Of coURSe thaT the BInDer as one Of the mAIn CoMponentS oF a magnEtIc lAyeR also PLays An impoRtant rolE in imPRoving durabiliTY and electromaGNeTIC cHAracTerIstics. The coNvenTIonaLly eMPlOyeD BindeR resiNs SUcH As vinyl chloride resiNs, CellulOsic rEsins, urethane Resins, and aCRYLic resinS havE A pROblem that the maGnetiC layers conTAining thEse reSins have Poor abrasION resistaNce To cOntAmiNATe Members for magNETic-tApE runninG suCh as guiDe rOllS or GuiDe Poles.
A tecHnique whIcH iS eMpLoyEd for IMproving ThE abOvE prOblem IS to use A hard BindEr To FOrm A magnetIC lAYEr haViNg A heiGhtEnEd harDnesS.
for Example, A magnetic RecORdinG mEdIum emplOying a binder cOmPrising a poLyEstEr polyUREthane reSin or a polycarbonate polyURethane ResIn is dEscrIbed in JP-A-6-96437. (the Term "JP-a" as USed herEin meaNs an "uNeXamINEd pubLIShEd JApAnese patenT APplIcatiOn".) althOugh ureThanes having a urethANe gRoup content of 2 To 4 mMol/g ARE uSed IN tHE exAmPLes OF jP-A-6-96437, the content of A long-chain DiOL iS not descriBEd tHeRein and The contEnt of oh groups Is also uncLear. In JP-B-6-19821 Is DescRIBed A magnetic rEcording Medium empLOying A BiNder cOntAining A uRetHane-uRea havINg a Total ContenT oF urethAne anD uRea of 1.8 to 3.0 mMol/g. (The term "JP-B" as used herEin meaNs an "eXamIned JapanEse PAteNt publicaTion".) the polyureThaNe rEsin oBtaINed in A resIN sYntHEsis eXampLE of JP-B-6-19821 has A LoNg-cHAIn Diol content OF 61% BY weIght, hAs a HIgh ureThanE bond concentratioN, And excellent duRabiLITy. HOweVEr, thE pOlyurethane resIn gIvES A coating
 with an abrasive material , the addi tionamo unt  t here of s hould be incre a sedto some degree, and th is re su l ts i n  a  redu ced pac k in g den si ty  of  f e rr omagn eti c parti cles in th e m ag netic layer. In  the caseofemploying an  ab rasive  m ate r ial h avi ng alargep articl e diamete ri n orde r  to obt a i nexce llent running dur a bi l ity, the magne tic la ye r  t e n dstohave abras iv e mat e rial pa r ti c l e s e x cessively pro jected from the  magne ti c l a yer su rface .T her e is hencea pr oblem tha t an i m proveme n t of ru nningdur abi lity du etoan abr a si vem ate rial fre qu en tly r esul t s i n de ter iora ted e lectromagneti c c hara c ter istic s.
In  the  c ase o f usin g a l ub ricant for impr ovin g running  pr op ert yas we l l as r unn ing  durabi lity, t h e a dd i t i on  amount thereof sh ou l d  b e increa sed. H o we ve r , the ma gn eti c la y e r isaptt obe moreplasti c iz ed  by the  i ncreas ed  lu bri canta moun t andthis ten ds to reduce the dur a bility of the ma g n et i c la yer .
It is a m atte r  ofcour s etha t  thebinde ra so ne of the main comp on ents o f a m agnetic layer  also play s a n import antr ol e  in improvingdurab ility ande lectroma gneti c charac teristics . The conv ent ion all y e m p lo yed binder re s i ns s uc h as vi nyl  chlori deres ins , c el lulosic r esins, u re th an eres ins,a nd acryl ic  re si nshavea  probl em th at t he  m a gne tic lay e rs c onta in in g th ese  r esins  hav e  po or abra sion resi sta n ce t oco ntamina te members fo rmagnetic-t ap e r unning s uch as g uide rolls or guide pol e s.
A te chn iquewhic h is empl oye d forimp r ovingthe ab ove p ro ble m is to u se  aha rd bindert o  fo rm ama gnet ic laye r having a heighte n edhardness.
For  ex ampl e ,  a  ma g ne t icre c ord i n g medium employ ing a bind er co mprising a pol ye ster po lyureth ane r e sin ora polycar bonate po ly uret h a neresin is d escribed  in JP-A- 6 -9643 7 .(Theter m "JP- A"  as  used  herei n  me ans a n "une xa minedpubli sh ed Japan ese patent application" .) Alt hough  ur ethanes h avi n g a  urethane  gro up content  of  2to 4mmo l /g ar e us e dint he ex ampl e s of JP-A - 6- 964 3 7 ,the content o f  along- cha i n diol  isnot described the r ein and the co nten t ofOHg roup sis also unclea r.In J P-B-6-19 82 1 is descri bed a ma gn e tic r ecordi ng med ium emp l o yi n g a bi nder  co ntaininga u re t hane-ur ea  h a ving a  tot al  conte nt ofu reth a n e and urea of 1. 8 to3 . 0 mmo l /g.  (The  t erm "JP - B" a s used her ein means a n "exa mine d Jap anese p at ent pu bli ca tion".) Th e  polyuret haneresin o bt aine d i n a re sins y nthes is e xa mpl e of JP-B - 6 -1 9 82 1h asa lo ng-ch ai n di ol conten t  of 61%byw eight,ha s a h igh ur e th a n e bond con cen trati o n , and exce l lent du r abili ty. Ho wever,  the po l yur et hane re sin g ives a co ating
 with_an abrasive_material, the addition amount_thereof should_be_increased to_some_degree, and this_results in a_reduced packing density of_ferromagnetic particles in_the_magnetic layer. In the case of employing an abrasive material having a large particle_diameter_in order_to_obtain_excellent running durability, the magnetic_layer tends to have abrasive_material particles_excessively projected from the magnetic layer surface. There_is_hence a problem_that an improvement of running durability due to an_abrasive material frequently results in deteriorated_electromagnetic characteristics.
In the_case_of_using a lubricant for_improving running property as well as_running durability, the addition amount thereof_should be increased. However, the magnetic layer_is apt to be more plasticized_by the increased lubricant amount_and this_tends to reduce the durability_of the magnetic_layer.
It is_a matter of_course that the binder as one_of the main_components of a magnetic layer also_plays_an important role_in_improving_durability and_electromagnetic characteristics. The_conventionally_employed binder_resins_such as vinyl chloride resins, cellulosic_resins,_urethane resins, and acrylic resins have a_problem that the magnetic_layers_containing these resins have_poor abrasion resistance to contaminate_members for magnetic-tape running such as_guide rolls_or guide_poles.
A technique which is employed for improving the above problem is_to use a hard binder to_form a magnetic layer_having a_heightened_hardness.
For example, a_magnetic_recording medium_employing a binder comprising a polyester polyurethane_resin or_a polycarbonate polyurethane resin is described_in JP-A-6-96437. (The term_"JP-A"_as used herein means an "unexamined_published Japanese patent application".) Although urethanes_having a urethane group content_of_2_to 4 mmol/g are used_in the examples of JP-A-6-96437, the_content of a_long-chain diol is not described therein and_the_content of OH groups is also_unclear._In JP-B-6-19821 is described a magnetic_recording_medium_employing a binder containing a_urethane-urea having a total content of_urethane and urea of 1.8 to 3.0 mmol/g. (The_term "JP-B" as_used herein means an "examined_Japanese_patent_publication".) The polyurethane resin obtained in a resin synthesis example_of JP-B-6-19821_has a long-chain_diol content of 61% by weight, has a high urethane_bond concentration, and excellent durability. However, the_polyurethane resin gives a coating