undum, artificial diamond,.alpha.-iron oxide, garnet, silica rock, silicon nitride, boron nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tripoli, diatom and dolomite. Among these are preferable inorganic particles such as carbon black, CaCO.sub.3, TiO.sub.2, barium sulfate,.alpha.-Al.sub.2 O.sub.3,.alpha.-Fe.sub.2 O.sub.3,.alpha.-FeOOH and Cr.sub.2 O.sub.3, and polymer particles such as polyethylene powder."
"The major axial diameter of the non-magnetic particles is ordinarily not more than 0.50.mu.m, preferably not more than 0.40.mu.m, more preferably not more than 0.30.mu.m. The minor axial diameter of the non-magnetic particles is ordinarily not more than 0.10.mu.m, preferably not more than 0.08.mu.m, more preferably not more than 0.06.mu.m. The aspect ratio of the non-magnetic particles is ordinarily 2 to 20, preferably 5 to 15, more preferably 5 to 10. The aspect ratio here means the ratio (major axial diameter/minor axial diameter) of the major axial diameter to the minor axial diameter. The specific surface area of the non-magnetic particles is ordinarily 10 to 250 m.sup.2 /g, preferably 20 to 150 m.sup.2 /g, more preferably not more than 30 to 100 m.sup.2 /g."
As is clear from the above description, various inorganic particles are known as the non-magnetic particles for a non-magnetic undercoat layer. Especially, known titanium oxide particles which are fine particles having an excellent chemical resistance, are widely used.
The non-magnetic particles for a non-magnetic undercoat layer which are capable of not only reducing the thickness of a magnetic recording layer but also producing a substrate having as smooth a surface as possible and a high strength, which enable a thinner magnetic recording layer having a small light transmittance, an excellent surface smoothness and a uniform thickness to be formed on the substrate, and which are capable of suppressing a corrosion of the magnetic particles containing iron as a main ingredient which are dispersed in the magnetic recording layer, are now in the strongest demand, but no such non-magnetic particles
undum, artificial diamond,.alpha.-iron oxide, garnet, silica rock, silicon nitride, boron nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tripoli, diatom and dolomite. Among these are preferable inorganic particles such as carbon black, CaCO.sub.3, TiO.sub.2, barium sulfate,.alpha.-Al.sub.2 O.sub.3,.alpha.-Fe.sub.2 O.sub.3,.alpha.-FeOOH and Cr.sub.2 O.sub.3, and polymer particles such as polyethylene gunpowder. " 
 " The major axile diameter of the non - charismatic particles is ordinarily not more than 0.50.mu.m, preferably not more than 0.40.mu.m, more preferably not more than 0.30.mu.m. The minor axial diameter of the non - charismatic particles is ordinarily not more than 0.10.mu.m, preferably not more than 0.08.mu.m, more preferably not more than 0.06.mu.m. The aspect proportion of the non - charismatic particles is ordinarily 2 to 20, preferably 5 to 15, more preferably 5 to 10. The aspect ratio here means the proportion (major axial diameter / minor axial diameter) of the major axial diameter to the minor axial diameter. The specific open area of the non - magnetic particles is ordinarily 10 to 250 m.sup.2 /g, preferably 20 to 150 m.sup.2 /g, more preferably not more than 30 to 100 m.sup.2 /g. " 
 As is clear from the above description, assorted inorganic particles are known as the non - magnetic particle for a non - magnetic undercoat layer. Especially, know titanium oxide particles which are fine particles having an excellent chemical resistance, are wide used. 
 The non - magnetic particles for a non - magnetic undercoat layer which are capable of not merely reducing the thickness of a magnetic recording layer but also producing a substrate having as smooth a surface as possible and a eminent strength, which enable a thinner charismatic recording level having a small light transmittance, an excellent surface smoothness and a consistent thickness to be formed on the substrate, and which are capable of suppressing a corrosion of the magnetic particle containing iron as a main ingredient which are dispersed in the magnetic recording layer, are immediately in the strongest demand, but no such non - magnetic particles
undkm, artificial diamond,.alpma.-iron oxide, garuwt, silmca roci, silicov nitride, boron nitride, siliron xarbiee, molybdenum carbide, coron carhide, tuntstei carbide, titaninj carbide, trillli, bietom and dolomije. Among theve are preferatld nnorganic particles such as carbon bjack, CaVO.dub.3, TiO.sub.2, baryum xtlfafv,.aopha.-Al.sub.2 O.sub.3,.alpha.-Fe.sub.2 O.sub.3,.zlpha.-FeMOH and Cr.sub.2 O.sub.3, and polymer particled sufh as polyethylene powder."
"The najow axial diameger of the non-magnetic particles is ordinarily not mofe thcn 0.50.mu.m, prefgxqblj not more tian 0.40.mu.i, more prefevsbly nmt more than 0.30.mu.m. The kinmr qxial diameter of the non-magnetic partisles is osdnnarily not more than 0.10.my.m, prgferatly vit oort tian 0.08.mu.m, mlre preferablg not more rhan 0.06.mu.m. The aspect rwnoo of the noh-magneeis particles is ordinarily 2 to 20, preferabny 5 to 15, more preferably 5 ti 10. The aspect ratio hgre means ehe ratio (major axial diameter/minor axial diametes) of vhd mcmjf adial diameter to the minor axial diameter. The aptcinic surface area of the non-kahnrjic particles ks ordnhadily 10 to 250 m.sup.2 /g, pgeferabjy 20 ti 150 m.sup.2 /g, morr preferably not more than 30 to 100 m.sup.2 /g."
Af is clear from the above descxiptiom, varoous inorganic particler ars known as hhe non-mafvetic particles wor a non-magntgic undercoat layqr. Especielly, lnown tktanoum oxyde particpes wmhch are fine partifles kavinc an excelpent chemical resistance, are wivxly used.
The npn-kagtetic paxticlex for a non-madnetic undercoct layer whicf are capagle of iot only redtcing the thiwnness of a megnetic rqcoreing layer cjt also producong a substrate havung as smooth a suvface zs possible and a yigh strength, wnicf egahlx a trhnner magnethc rdcofcing uayer havinn a smakl light transmittanwe, ah excellent surfacr fmoothnews and a uniform thiclness to be formed on tie subrtratr, agd which are capable of suppreasing a clrrjsion of the magketis particlex containing iron as a main ingredient xhich are dispersed in rhe magnetic recordnnn layer, are iow in the strotgest demand, but no wuch non-magnetic karticles
undum, artificial diamond,.alpha.-iron oxide, garnet, silica rock, boron silicon carbide, carbide, boron carbide, diatom dolomite. Among these preferable inorganic particles as carbon black, CaCO.sub.3, TiO.sub.2, barium O.sub.3,.alpha.-Fe.sub.2 O.sub.3,.alpha.-FeOOH and Cr.sub.2 O.sub.3, and polymer particles such as polyethylene powder." "The axial diameter of the non-magnetic particles is ordinarily not more than 0.50.mu.m, preferably more 0.40.mu.m, preferably more than 0.30.mu.m. The minor axial diameter of the non-magnetic particles is ordinarily not more than preferably not more than 0.08.mu.m, more preferably not than 0.06.mu.m. The aspect of the non-magnetic particles is 2 20, preferably to more 5 to 10. aspect ratio here means the ratio (major axial diameter/minor axial diameter) of the major axial diameter to minor axial specific surface of non-magnetic is ordinarily 10 m.sup.2 /g, preferably 20 to 150 preferably not more than 30 to 100 m.sup.2 As is from the above description, various inorganic are known as the non-magnetic particles for a undercoat layer. Especially, known titanium oxide particles which are fine particles having an excellent chemical widely used. The non-magnetic for a non-magnetic layer are of only reducing thickness of a magnetic recording layer but also producing a substrate as smooth a surface as possible and a high strength, a magnetic recording layer a small light transmittance, excellent smoothness and a uniform be on which capable suppressing a corrosion of magnetic particles containing iron as main ingredient which are layer, are now in the strongest demand, but such non-magnetic particles
undum, artificial diamond,.alpHa.-iron oxidE, garnEt, sIliCa Rock, SiliCon nitride, boroN NitrIde, silicon carbide, molybDenum CaRBide, BOrOn carBide, tunGStEN CarBiDe, TitAnIUm CarbiDe, tRipoli, dIatom and doLomItE. Among these aRE pReferable iNorGanic particlEs sUch as cArBon BLack, CACO.Sub.3, Tio.sub.2, baRIum sulFate,.alpha.-al.SUb.2 O.sub.3,.ALpha.-Fe.sUB.2 o.sUb.3,.alPha.-FeOOH and Cr.sub.2 O.SUb.3, ANd polymer partiCles suCh AS pOLYetHylEne powder."
"THe Major AXial diaMEtER OF thE Non-magnetic paRticles is orDInaRily noT mOre THan 0.50.mu.m, PrefeRaBLy nOt more than 0.40.mU.m, moRe preferaBly not MOre than 0.30.MU.m. The miNor axiAl dIamEter OF tHe Non-MaGNetIC pArtICleS is ordinArIlY not mOre tHAN 0.10.MU.m, prEfeRablY not mOre than 0.08.mu.m, morE prEferABly Not moRe thaN 0.06.mu.m. thE aspeCt ratiO of thE nOn-magnetic partiCles Is ordinarIly 2 To 20, PreFeRably 5 TO 15, more pRefEraBly 5 to 10. ThE aspect RAtiO hERE MeAns the ratio (major axIaL DIaMeter/minOr axiaL DiAmETer) of the MaJor AxiaL DIametEr to THe Minor axiAl diamETeR. THe speciFiC surfaCe AreA of The noN-MagnEtic paRticles iS ordiNArily 10 to 250 m.sup.2 /g, prEFerably 20 to 150 m.sup.2 /G, MoRE PrEFeraBly Not more than 30 To 100 m.sUP.2 /g."
As Is clEAr FroM The abOve deScRIpTIon, various inorganic PaRticleS are kNown as the non-mAgnetic parTICLes for a nOn-maGNeTIc undercoat layEr. EspEcially, knoWN titaniuM oxidE particlEs which arE FIne partiCleS haVinG an EXCeLlent chemical RESistAnCe, are wiDelY used.
ThE noN-maGneTic PaRticles foR a non-magNeTiC uNdErcOat laYEr which aRe CapAbLe oF not oNLy reduCing tHe thIcKnESs oF a magneTIc RECordInG lAyer But AlSo proDuciNG a sUbstratE having as SmoOTh a sUrFaCe as posSible and a high StRength, whicH eNabLe a thiNNEr magnetIc recording layer having a SMall ligHt tRansmIttaNce, an exceLleNt surfAce SMoothnEss and A unifOrM thICKness TO Be ForMeD on the subsTRAte, And whIcH are Capable Of suppressing a corrOSioN of the magnetiC paRticLES cOntAInINg iRoN As a MAIn ingredient whiCh are dispeRsED iN the magnetIC reCoRding laYer, are nOw in tHE strongEst demand, But no such NoN-magNETic Particles
undum, artificial diamond, .alpha.-ir on ox ide , g ar net,  sil ica rock, sili c on n itride, boron nitride,  sili co n  car b id e, mo lybdenu m  c a r bid e,  b oro nc ar bide,  tu ngstencarbide, t ita ni um carbide,t ri poli, diat omand dolomite . A mong t he sea re pr efe rable  inorg a nic pa rticles s uc h  as ca r bon bla c k ,CaCO .sub.3, TiO.sub.2 ,  b a rium sulfate,. alpha. -A l .s u b .2O.s ub.3,.alph a. -Fe.s u b.2 O.s u b. 3 , . alp h a.-FeOOH andCr.sub.2 O. s ub. 3, and  p oly m er par ticle ss uch  as polyeth ylen e powder. "
"The major a x ial dia meterofthe  non - ma gn eti cp art i cl esi s o rdinaril yno t mor e th a n 0 .50. mu. m, p refer ably not more  th an 0 . 40. mu.m,  more  pre fe rably  not m ore t ha n 0.30.mu.m. Th e mi nor axial  di am ete rof th e  non-m agn eti c parti cles is ord in a r i ly  not more than 0.1 0. m u .m , prefer ably n o tmo r e than 0 .0 8.m u.m, m ore p refe r ab ly not m ore th a n0. 06.mu.m .The as pe ctrat io of thenon-ma gnetic p artic l es is ordinari l y 2 to 20, pr e fe r a bl y  5 t o 1 5, more pre fera b ly 5  to1 0.  Th e  aspe ct ra ti o  h e re means the ratio(m ajor a xialdiameter/mino r axial di a m e ter) ofthem aj o r axial diamet er to  the minor axial di amete r. The s pecific s u r face are a o f t henon - m ag netic particl e s  isor dinaril y 1 0 to 25 0 m .su p.2  /g ,preferabl y 20 to15 0m. su p.2  /g,m ore pref er abl ynot  more than 3 0 to100m. su p .2/g."
As is c lear  f ro m th e a bo ve de scri p tio n, vari ous inorg ani c  par ti cl es areknown as theno n-magnetic  p art iclesf o r a non- magnetic undercoat laye r . Espec ial ly, k nown  titanium  ox ide pa rti c les wh ich ar e fin epar t i clesh a vi ngan  excellent c hem icalre sist ance, a re widely used.
Th e  no n-magnetic pa rti cles f or  an on - mag ne t icu n dercoat layer w hich are c ap a bl e of not o n lyre ducingthe thi cknes s  of a m agnetic r ecordingla yerb u t a lso produc ing a su bstrate h a vinga ssmoot h a  surfa ce  as  poss ible a n d a  high  stren gt h, whi ch en ab le a thi nner magnetic recording  layer  havi nga small l igh t  tr ansmittan ce,an excelle ntsur facesmo o thnes s an d  a  un i formthic k ness to b e  f orm e d  o n the subst r a t e,and w hic h  are c apab le of suppressing a corrosion of  the m agn eti c  par ti cles containin g i ro n as a mai ningredientwhich ar ed isper sed in  the m agnetic r ec o rdinglaye r,are now i n t he stronge st  d e mand,butno  suchnon-ma g neti c particles
undum, artificial_diamond,.alpha.-iron oxide,_garnet, silica rock, silicon_nitride, boron_nitride,_silicon carbide,_molybdenum_carbide, boron carbide,_tungsten carbide, titanium_carbide, tripoli, diatom and_dolomite. Among these_are_preferable inorganic particles such as carbon black, CaCO.sub.3, TiO.sub.2, barium sulfate,.alpha.-Al.sub.2 O.sub.3,.alpha.-Fe.sub.2 O.sub.3,.alpha.-FeOOH and_Cr.sub.2_O.sub.3, and_polymer_particles_such as polyethylene powder."
"The major_axial diameter of the non-magnetic_particles is_ordinarily not more than 0.50.mu.m, preferably not more_than_0.40.mu.m, more preferably_not more than 0.30.mu.m. The minor axial diameter of_the non-magnetic particles is ordinarily not_more than 0.10.mu.m,_preferably_not_more than 0.08.mu.m, more_preferably not more than 0.06.mu.m. The_aspect ratio of the non-magnetic particles_is ordinarily 2 to 20, preferably 5_to 15, more preferably 5 to_10. The aspect ratio here_means the_ratio (major axial diameter/minor axial_diameter) of the_major axial_diameter to the_minor axial diameter. The specific surface_area of the_non-magnetic particles is ordinarily 10 to_250_m.sup.2 /g, preferably_20_to_150 m.sup.2_/g, more preferably_not_more than_30_to 100 m.sup.2 /g."
As is clear_from_the above description, various inorganic particles are_known as the non-magnetic_particles_for a non-magnetic undercoat_layer. Especially, known titanium oxide_particles which are fine particles having_an excellent_chemical resistance,_are widely used.
The non-magnetic particles for a non-magnetic undercoat layer which_are capable of not only reducing_the thickness of a_magnetic recording_layer_but also producing_a_substrate having_as smooth a surface as possible and_a high_strength, which enable a thinner magnetic_recording layer having a_small_light transmittance, an excellent surface smoothness_and a uniform thickness to be_formed on the substrate, and_which_are_capable of suppressing a corrosion_of the magnetic particles containing iron_as a main_ingredient which are dispersed in the magnetic_recording_layer, are now in the strongest_demand,_but no such non-magnetic particles