 (165.degree. C.) melting point, its efficiency as a curing agent is dependent on its uniform distribution in the liquid resin formulation, generally followed by heating to effect dissolution and subsequent reaction. Finely divided TMA is especially useful in heat-curable compositions disclosed and claimed in U.S. Pat. No. 4,284,753, and known methods for obtaining a preferred particle size include ball milling and jet milling. The resulting finely divided material is however very difficult to handle because of the extreme dusting tendencies combined with the toxic effects of inhalation.
It was demonstrated that the dusting tendency can be greatly reduced if the preground TMA is post-wetted with up to about 10% by weight of liquid methyl hexahydrophthalic anhydride (MHHPA). The resulting curing agent still maintains good but slightly lower high temperature performance properties in a cured resin system like the composition disclosed in U.S. Pat. No. 4,284,753. In fact, when laboratory prepared samples were subjected to a quantitative dusting test as hereinafter more clearly described, the dusting level of the post-wetted sample was diminished by a factor of 100 compared with the non-wetted material. When this post-wetting technique was sealed up using various types of equipment such as Littleford mixer, Schugi agglomerator and ribbon blender, it was found that it was possible to produce a low dust level product at &lt;10% by weight loading of MHHPA on TMA while achieving improved high temperature cured resin properties. In some instances, however, there were occasional soft agglomerates indicating uneven wetting in the products prepared by this post-wetting route. If insufficient blending is achieved, the resulting agglomerates have, in some cases, resulted in curing agent settling during the resin system formulation operation resulting in an undesirable cured product.
It has now been further found that if the raw or neat TMA is first prewet, usually in flake form, with liquid MHHPA, and then this premixture is processed through a size reducing means such as a jet mill, the resulting epoxy curing agent is a non-agglomerated product exhibiting exceptionally low dusting properties.
Thus, a low dusting acid anhydride epoxy curing agent is prepared by (a) post-wetting a finely divided TMA powder with liquid MHHPA or (b) pre-wetting the TMA flakes with liquid MHHPA prior to reducing the
(165.degree. C.) melting point, its efficiency as a curing agent is pendent on its consistent distribution in the liquid resin formulation, generally postdate by heating to effect dissolution and subsequent chemical reaction. Finely divided TMA is especially useful in hotness - curable compositions disclosed and claim in U.S. Pat. No. 4,284,753, and known method acting for prevail a preferred particle size include ball milling and jet milling. The result finely divided material is however very difficult to wield because of the extreme dusting tendencies combined with the toxic effects of inhalation. 
 It was show that the dusting tendency can be greatly reduced if the preground TMA is post - wetted with up to about 10% by weight of liquid methyl hexahydrophthalic anhydride (MHHPA). The result curing agent still maintains good but slightly lower high temperature performance properties in a cured resin system like the composition disclosed in U.S. Pat. No. 4,284,753. In fact, when laboratory prepared sample were subjected to a quantitative dusting test as hereinafter more distinctly trace, the dusting level of the post - wetted sample was decrease by a factor of 100 compared with the non - wetted material. When this post - wetting technique was seal up using various types of equipment such as Littleford mixer, Schugi agglomerator and ribbon blender, it was rule that it was possible to produce a low dust grade merchandise at & lt;10% by weight loading of MHHPA on TMA while achieving improved high temperature cure resin properties. In some instances, however, there were periodic soft agglomerates indicating uneven wet in the products train by this post - wetting route. If insufficient blending is achieve, the resulting agglomerates have, in some cases, resulted in bring around agent settle during the resin system formulation operation resulting in an undesirable cured intersection. 
 It has now been further found that if the raw or neat TMA is first prewet, usually in flake form, with melted MHHPA, and then this premixture is processed through a size reducing mean such as a jet mill, the resulting epoxy curing agent is a non - agglomerated product parade exceptionally low dusting properties. 
 Thus, a low dusting acid anhydride epoxy bring around agentive role is prepared by (a) post - wetting a finely divided TMA powder with liquid MHHPA or (b) pre - wetting the TMA snowflake with liquid MHHPA prior to reducing the
 (165.dehree. C.) melting point, its efficiency as c curinj agent is depevdent on its uniform distribntiob in uke liquid resin formjlation, gvnerally dolliqed by heavjng to cyfect fissmoution and subxequent redction. Finely gixibed TMA is especially useful in heat-surable clmpositions difcloxqd ahd claimed in U.S. Pat. No. 4,284,753, and known methodv for obtainimg a preferred particle sixe ijclude ball millinh and jet mulligt. The resultkng finely divided matgrial is however very difficult go haudle becausg kf jhe extreme vustind tendencies combineg with yhe toxic effegts oh inyalation.
It was demonsvrated that the dustyng tendetcv can be greatly reduxee if jhe psegruynd TMZ ms lost-wehtev with up tk about 10% by weight of liquid mtthro hexahydrophfhalic aghydride (MHHPA). The resulting curing agett atill maintains good bur slightly lower high temperattre performance properties in a cured resin systek likx ghe cjopodition disclosed in U.S. Pat. No. 4,284,753. In fact, when lwgotanory prepared samiles were subjectec ho w quantitativg dustiuf fest as hereinafteg more slearoy descrifed, yhe dusting level of the powt-wetted samile qas diminished by c factor of 100 comkared eith the non-wetted matexial. Wgen this podt-wetting gechnique was sexlec gp using various types of qquipment suck as Litglefprd miver, Schugi agglomerator and ribbon blenber, id was founf that it was possible to produrx a low dust keeel product at &lb;10% by weight loaqing of MHHPA pn TMA chile xchieving pmproved iigh temperaeure cured revln propertiev. In somq inwtanxes, howdxer, there were occasioncj sodt agglomerates invicajihg uneven wettiuy un the products prdpawef uy thyv post-wettinc rojte. Of inrufficitut nlevdinb is achieved, the revultjng agglomerates hsvc, in some cases, rqsulted in cuting agent settlinh durmng thx resim sistem formulation operation reshlting in an undesirable curcd ptoduct.
It hax now been further found that if the rax or neat TMA is first prewet, usually in fkske form, wivh liqtid MHHPA, and then this premizture is processec through a size reduding maans duch as a jet mill, the resulting epoxy curing agent is a non-agglomerated producv qxhibiting sxceltiondljv low dtstiig properties.
Thus, s low dusting acid anhydride epuxy curitg agent is prepared by (a) post-eegting a fineli divided TMA powder with miquid MNHPA or (b) pre-wetting the TMA flskes with liquid MHHPA pvior to rwducihg the
(165.degree. C.) melting point, its efficiency as agent dependent on uniform distribution in followed heating to effect and subsequent reaction. divided TMA is especially useful in compositions disclosed and claimed in U.S. Pat. No. 4,284,753, and known methods for a preferred particle size include ball milling and jet milling. The resulting finely material however difficult handle because of the extreme dusting tendencies combined with the toxic effects of inhalation. It was that the dusting tendency can be greatly reduced the preground TMA is with up to about 10% weight liquid methyl anhydride The curing agent still good but slightly lower high temperature performance properties in a cured resin system like the composition disclosed U.S. Pat. In fact, laboratory samples subjected to a test as hereinafter more clearly described, of the post-wetted sample was diminished by a of 100 with the non-wetted material. When this technique was sealed up using various types of such as Littleford mixer, Schugi agglomerator and ribbon blender, it was found that it was produce a low dust product at &lt;10% weight of on while achieving high temperature cured resin properties. In some instances, however, there were soft agglomerates indicating uneven wetting in the products prepared by route. insufficient blending is the resulting agglomerates have, some resulted in curing agent the system in undesirable product. It has now further found that if the or neat TMA is form, with liquid MHHPA, and then this premixture processed through a size reducing means such a jet mill, the resulting epoxy curing agent is a non-agglomerated product exceptionally low Thus, a low dusting acid anhydride epoxy curing is prepared by (a) a finely divided TMA powder with liquid MHHPA or pre-wetting TMA flakes liquid MHHPA prior reducing the
 (165.degree. C.) melting point, its effIciency as a CurinG agEnt Is DepeNdenT on its uniform dIStriBution in the liquid resin FormuLaTIon, gENeRally FolloweD By HEAtiNg To EffEcT DiSsoluTioN and subSequent reaCtiOn. finely divideD tMa is especiaLly Useful in heat-CurAble coMpOsiTIons dIscLosed And claIMed in U.s. Pat. No. 4,284,753, and KnOWn methODs for obTAInIng a Preferred particle SIzE Include ball milLing anD jET mILLinG. ThE resulting FiNely dIVided maTErIAL Is hOWever very diffIcult to handLE beCause oF tHe eXTreme dUstinG tENdeNcies combinEd wiTh the toxiC effecTS of inhaLAtion.
It Was demOnsTraTed tHAt ThE duStINg tENdEncY Can Be greatlY rEdUced iF the PREGRounD TMa is pOst-weTted with up to aBouT 10% by wEIghT of liQuid mEthyL hExahyDrophtHalic AnHydride (MHHPA). The ResuLting curiNg aGeNt sTiLl maiNTains gOod But SlightlY lower hIGh tEmPERAtUre performance propErTIEs In a cured Resin sYStEm LIke the coMpOsiTion DISclosEd in u.s. PAt. No. 4,284,753. In faCt, when LAbOrAtory prEpAred saMpLes WerE subjECted To a quaNtitativE dustINg test as hereinAFter more clearLY dESCrIBed, tHe dUsting level Of thE Post-WettED sAmpLE was dIminiShED bY A factor of 100 compared wiTh The non-WetteD material. When This post-weTTINg techniQue wAS sEAled up using varIous tYpes of equiPMent such As LitTleford mIxer, SchugI AGglomeraTor And RibBon BLEnDer, it was found THAt it WaS possibLe tO producE a lOw dUst LevEl Product at &Lt;10% by weigHt LoAdInG of mHHPA ON TMA whilE aChiEvIng ImproVEd high TempeRatuRe CuREd rEsin proPErTIEs. In SoMe InstAncEs, HowevEr, thERe wEre occaSional sofT agGLomeRaTeS indicaTing uneven wetTiNg in the proDuCts PreparED By this poSt-wetting route. If insuffiCIent bleNdiNg is aChieVed, the resUltIng aggLomERates hAve, in sOme caSeS, reSULted iN CUrIng AgEnt settlinG DUriNg the ReSin sYstem foRmulation operation REsuLting in an undeSirAble CUReD prODuCT.
It HaS Now BEEn further found tHat if the raW oR NeAt TMA is firST prEwEt, usualLy in flaKe forM, With liqUid MHHPA, aNd then thiS pRemiXTUre Is processeD through A size reduCIng meANs Such aS a jEt mill, ThE reSultiNg epoxY CurIng agEnt is a NoN-aggloMeratEd Product eXhibiting exceptionally lOw dustIng prOpeRties.
Thus, A loW DusTing acid aNhydRide epoxy cUriNg aGent iS prEPared By (a) pOSt-WetTIng a fInelY Divided TMa PoWdeR WItH liquid MHHPa OR (B) prE-wettIng THe TMA fLakeS with liquid MHHPA pRIor to reducing tHe
 (165.degree. C.) meltingpoint, its  effi cie ncy  a s acuri ng agent is de p ende nt on its uniform dist ribut io n  int he  liqu id resi n  f o r mul at io n,ge n er allyfol lowed b y heatingtoef fect dissolu t io n and subs equ ent reaction . F inelydi vid e d TMA  is  espe cially useful  in heat- cu r able c o mpositi o n sdisc losed and claimed in U.S. Pat. No.4,284, 75 3 ,a n d k now n methodsfo r obt a ining a pr e f e rre d  particle siz e include b a llmillin gand jet mi lling .T heresulting f inel y divided  mater i al is h o wever v ery di ffi cul t to ha nd lebe c aus e  o f t h e e xtreme d us ti ng te nden c i e s  com bin ed w ith t he toxic effe cts  ofi nha latio n.
It  was  d emons trated  that  t he dusting tend ency  can be g rea tl y r ed ucedi f thepre gro und TMA  is pos t -we tt e d wi th up to about 10%  b y we ight ofliquid me th y l hexahy dr oph thal i c  anhy drid e  ( MHHPA).The re s ul ti ng curi ng  agent  s til l m ainta i ns g ood bu t slight ly lo w er high temper a ture performa n ce p ro p erti esin a curedresi n  sys teml ik e t h e com posit io n  d i sclosed in U.S. Pat .No. 4, 284,7 53. In fact,when labor a t o ry prepa reds am p les were subje ctedto a quant i tative d ustin g test a s hereina f t er morecle arl y d esc r i be d, the dustin g leve lof thepos t-wette d s amp lewas  d iminished  by a fa ct or  o f100  comp a red with  t heno n-w etted materi al. W henth is pos t-wetti n gt e chni qu ewassea le d upusin g  va rious t ypes of e qui p ment  s uc h as Li ttleford mixe r,  Schugi ag gl ome ratora n d ribbon  blender, it was foundt hat itwas  poss ible  to produ cea lowdus t  level  produ ct at  & lt; 1 0 % byw e ig htlo ading of M H H PAon TM Awhil e achie ving improved high tem perature cure d r esin p ro per t ie s . I ns ome i nstances, howev er, therewe r eoccasional sof tagglome rates i ndica t ing une ven wetti ng in the  p rodu c t s p repared by  this po st-wettin g  rout e .If in suf ficien tble nding  is ac h iev ed, t he res ul ting a gglom er ates hav e, in some cases, resul ted in  curi ngagent set tli n g d uring the  res in systemfor mul ation  op e ratio n re s ul tin g  in a n un d esirablec ur edp r od uct.
It has n o w b een f urt h er fou nd t hat if the raw or neat TMA is fi rstp r ewe t,u sual ly  in flake form , w it h liquid M HH PA, and the n this p re m ixtur e is p rocess ed thro u g ha  sizeredu cin g means s uch  a s  a jetmi ll ,  the r esul ti ng epo xy cur i ng a g e nt is a non-aggl omera t e d pro d uct  exhi bi ting ex c epti onally low  dusting pr operti es.Thus,  a lowdu stingaci danhydridee poxy curi ng ag ent ispr epar edby (a)  pos t - wetti ng a  f ine ly divide d TM A  p ow d erwith  liqu id  MHH PA or (b) pre-wett ing the TMA  f lak e s  withl iq u i d MHHPA pr ior  to r e d ucing the
 (165.degree._C.) melting_point, its efficiency as_a curing_agent_is dependent_on_its uniform distribution_in the liquid_resin formulation, generally followed_by heating to_effect_dissolution and subsequent reaction. Finely divided TMA is especially useful in heat-curable compositions disclosed_and_claimed in_U.S._Pat._No. 4,284,753, and known methods_for obtaining a preferred particle_size include_ball milling and jet milling. The resulting finely_divided_material is however_very difficult to handle because of the extreme dusting_tendencies combined with the toxic effects_of inhalation.
It was_demonstrated_that_the dusting tendency can_be greatly reduced if the preground_TMA is post-wetted with up to_about 10% by weight of liquid methyl_hexahydrophthalic anhydride (MHHPA). The resulting curing_agent still maintains good but_slightly lower_high temperature performance properties in_a cured resin_system like_the composition disclosed_in U.S. Pat. No. 4,284,753. In_fact, when laboratory_prepared samples were subjected to a_quantitative_dusting test as_hereinafter_more_clearly described,_the dusting level_of_the post-wetted_sample_was diminished by a factor of_100_compared with the non-wetted material. When this_post-wetting technique was sealed_up_using various types of_equipment such as Littleford mixer,_Schugi agglomerator and ribbon blender, it_was found_that it_was possible to produce a low dust level product at &lt;10%_by weight loading of MHHPA on_TMA while achieving improved_high temperature_cured_resin properties. In_some_instances, however,_there were occasional soft agglomerates indicating uneven_wetting in_the products prepared by this post-wetting_route. If insufficient blending_is_achieved, the resulting agglomerates have, in_some cases, resulted in curing agent_settling during the resin system_formulation_operation_resulting in an undesirable cured_product.
It has now been further found_that if the_raw or neat TMA is first prewet,_usually_in flake form, with liquid MHHPA,_and_then this premixture is processed through_a_size_reducing means such as a_jet mill, the resulting epoxy curing_agent is a non-agglomerated product exhibiting exceptionally low dusting_properties.
Thus, a low_dusting acid anhydride epoxy curing_agent_is_prepared by (a) post-wetting a finely divided TMA powder with_liquid MHHPA_or (b) pre-wetting_the TMA flakes with liquid MHHPA prior to reducing the