Патент USA US3022282код для вставки
United States r. atent 1 l€€ c _ 3,022,272 Patented Feb. 20, 1962 2 lysts, according to the processes as described in the co. 3,022,272 pending US. patent applications Ser. Nos. 461,938, 557, Hermann Schnell, Krefeld-Uerdinger, and Gerhard Fritz, 256, 572,793, 572,802, 583,382 and 596,398, so far as those applications refer to inter-esteri?cation processes, PROCESS FOR THE PRODUCTION OF HIGH MOLECULAR POLYCARBONATES Krefeld-Bockum, Germany, assignors to Farhenfahri ken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany N0 Drawing. Filed Oct. 8, 1956, Ser. No. 614,340 Claims priority, application Germany Dec. 21, 1955 , 14} Claims. (Cl. 260-47) For the production of polyesters from dicarboxylic can ‘be overcome if these basic catalysts are neutralised towards the end of the inter-esteri?cation by adding base binding materials to the melt. The process according to the invention can be used with advantage for the production of polycarbonates from e.g. aliphatic dihydroxy compounds such as diethylene glycol, triethylene glycol, polyethylene glycol, thiodigly acids and dihydroxy compounds, the free acids can be col and the di- or poiy-glycols produced from propylene esteri?ed with dihydroxy compounds with separation of oxide-l,2,butanediol-l,4, hexanediol-1,6, octanediol-l,8, decanediol-1,10, m-, p-xylylene glycol; from cycloali High molecular ?lm and ?bre-forming products are only obtainable accord 15 phatic dihydroxy compounds such as cyclohexane diol-l, 4, 2,2-di-(p-hydroxycyclohexyl)propane and 2,6-dihy ing‘to this process with di?iculty. For the production of roxy-decahydronaphthalene; from aromatic dihydroxy high molecular polyesters it has therefore been preferred compounds such as hydroquinone, resorcinol, 4,4'-dihy to inter-esterify dihydroxy compounds with dicarboxylic water at elevated temperatures. ' droxydiphenyl, l,4-dihydroxynaphthalene, 1,6-dihydroxy naphthalene, 2,6-dihydroxynaphthaiene, 1,5-dihydroxyan general necessary in inter-esteri?cation to use basic cata monohydroxyarylene-alkanes, like di-(p-hydroxyphenyl carbonates of volatile aliphatic or aromatic compounds, no high molecular ?lm or ?bre products are formed in droxyphenylene) -pentane, acid esters of volatile hydroxy compounds with separa u-n>~sxg ji tion of the volatile compound. ' 20 thracene and m-, p-hydroxybenzyl alcohol or mixtures of Although the esteri?cation can normally be carried out even without catalysts with considerable speed it is in 1 ,such dihydroxy compounds, but especially such as di ene)-methane, 2,2-di-(p~hydroxyphenylcne)-propane, 1,1_ lysts. According to the conventional inter-esteri?cation process the added catalysts remain in the end product. 25 di- (p-hydroxyphenylene ) -cyclohexane, 1,1-di- (p-hydroxy m-methylphenylene)-cyclohexane, 3,4~di-(p-hydroxyphen If alkali catalysts are added in the inter-esteri?cation ylene ) hexane, 1,1-di-(p-hydroxyphenylene)-1-phenyl-eth of aliphatic or aromatic dihydroxy compounds with di ane, 2,2-di-(p-hydroxyphenylene)-butane, 2,2-di-(p-hy 3,3-di-(p-hydroxyphenylene) - general because these catalysts decompose high molecu 30 pentane, 2,2-di-(p-hydroxyphenylene)~3-methyl-butane, 2, 2 - di - (p - hydroxyphenylene) - hexane, 2,2 - di - (p lar polycarbonates. hydroxyphenylene ) -4-methyl-pentane, 2,2-di- (p-hydroxy~ Processes have therefore hitherto been operated by 'phenylene)-heptane, 4,4'di-(p-hydroxyphenylene)-heptane beginning the reaction of aliphatic dihydroxy compounds and 2,2-(p-hydroxyphenylene)-tridecane. I with the carbonates of mono-hydroxy compounds in the As suitable dicarbonates for inter-esteri?cation with presence of non-volatile, only slightly water soluble, car 35 the dihydroxy compounds there are mentioned aliphatic boxylic acids and a more than equivalent amount of an ‘_ alkali metal, dissolving the low molecular product ?rst' ‘ diesters such as diethyl-, dipropyl-, dibutyl-, diamyl-, di~ octyl—, methylethyl-, ethylpropyl- and ethylbutyl-carbon formed in a solvent, removing the alkali metal by extrac ates; cycloaliphatic diesters such as dicyclohexyl~ and tion with dilute acid, e.g. aqueous hydrochloric acid, with out removing the carboxylic acid and then after distilling 40 dicyclopentyl-carbonate, preferably however, diarylesters, such as‘ diphenyl- and ditolylcarbonate; furthermore off the solvent, completing the reaction to form a high mixed esters such as methylcyclohexyl-, ethylcycloh'exyll, :molecular ?lm- and ?bre-forming product. methylphenyl-, ethylphenyl- and cyclohexylphenyl-car This process is unduly involved. The added non-vola bonate. tile carboxylic acid which is not water soluble remains If desired, one also can start from compounds such in the high molecular polyester.- Acid and basic com 45 as dialkyl-, dicycloalkyl-, diaryl- or mixed dicarbonates ponents alike tend during the Working up, especially of high melting high molecular polycarbonates from the of aromatic dihydroxy compounds which inter-esterify when heated by themselves with separation of the cor melt, to spoil the structure with the formation of gaseous responding dicarbonates or when heated with dihydroxy carbonic acid. This gas blowing makes the production of good shaped bodies such as ?lms, ?bres and bristles 50 compounds with separation of the mono-hydroxy com from the melt practically impossible. Mou'dings from pounds, e.g. according to the process described in the polycarbonates made in this way are seriously lacking in copending US. patent application Ser. No. 596,398. ' As basic catalysts there can be added: alkali metals, fastness to water especially at high temperatures. such as lithium, sodium, potassium; alkaline earth met Aromatic dihydroxy compounds however, can indeed be converted during the complete inter-esteri?cation pe 55 als, such as magnesium, calcium, barium; alcoholates of the alkali- or alkaline earth metals, such as sodium riod in the presence of suitable basic catalysts into the methylate and calciumethylate; phenolates, such as so high molecular ?lm- and ?bre-forming state. But the catalysts remaining in the end product spoil the structure dium phenolate; sodium salts of dimonohydroxyarylene pounds, in the presence of basic inter-esteri?cation cata- ' 'benzoyl chloride, and toluene sulphochloride, organic alkanes; hydrides of the alkali- and alkaline earth met during working up in this case also with formation of carbonic acid. Blown melts are thus obtained which 60 als such as lithium hydride and calcium hydride, oxides --of the alkali- and alkaline earth metals such as lithium make working up di?’icult or impossible. Mouldings pro oxide and sodium oxide, amides of the alkali and alkaline duced from these melts show a reduced stability to ele earth metals, such as sodium amide and calcium amide, vated temperatures and to water, ‘especially to hot water. basic reacting salts of the alkali- and alkaline earth met It has now been found that this drawback, in the inter als with organic or inorganic acids such as sodium acetate, esteri?cation of aliphatic, cycloaliphatic or aromatic di 65 sodium benzoate and sodium carbonate. hydroxy compounds with dicarbonates of ' aliphatic or In order to neutralise these basic catalysts a large va aromatic mono-hydroxy compounds or in the polycon riety of base-binding organic or inorganic substances can densation of diary1-, dialkyl- or dicycloalkyl-dicarbonates be added in accordance with the invention e.g. aromatic of aromatic dihydroxy ‘compounds of thcmselveslor with 70 sulphonic acids such as p-tolyl sulphonic acid, organic aliphatic, cycloa'liphatic or aromatic dihydroxy com acid halides such as stearyl chloride, butyryl chloride, 3,022,272 4 or into extendable ?bres and ?lms. lies about 60° C. chlorocarbonates such as phenyl chloroformate, p-hy~ droxydiphenyl chloroformate, and bischloroformates of The softening point Example 2 di-monohydroxy arylene alkanes, dialkylsulphates such as dimethyl sulphate and bibutyl sulphate, organic chlorine compounds such as benzoyl chloride and w-chlo~ A mixture of 45.6 parts of 2,2-di-(p-hydroxyphenylene)-propane 47.1 parts of diphenylcarbonate, and 0.008 part of lithium hydride roacetophenone as well as acid salts of polycondensa tion inorganic acids such as ammonium hydrogen sul phate. Base-binding substances which are volatile under greatly reduced pressure at esteri?cation temperatures are especially suitable since an incidental excess over that required to neutralise the basic catalysts can be easily are melted together under a nitrogen atmosphere with stirring at 110~l50° C. The phenol which separates is distilled off by further heating to 210° C. under a pres The pressure is then reduced to 0.2 mm. mercury gauge and the temperature chloroformate and benzoyl chloride are examples of sub— raised for one hour to 250° C., and for two further stances of this group. 15 hours to 280° C. At the end of the condensation the removed from the melt. sure of 20 mm. mercury gauge. Dimethyl sulphate, phenyl In order to operate the process the inter-esteri?cation is brought about between the dihydroxy compounds and catalyst is neutralised by stirring 0.05 part of dimethyl sulphate into the melt. The excess of neutralising agent is ?nally removed by further heating under reduced pres the di-carbonates of mono-hydroxy compounds, or the polycondensation of the bis’phenyl-alkyl- or cycloalkyl sure. A viscous melt is obtained which solidi?es to a carbonates of the aromatic dihydroxy compounds is 20 thermoplastic material melting at 240° C. which is suit brought about with the' aforementioned basic catalysts able, e.g. for the production from the melt or from in a customary manner, preferably at temperatures of solutions, for example in methylene chloride, of injection from 50 to 330° (3., especially between 100—300‘’ C. and mouldings and bristles, ?lms and ?bres which can be orientated by stretching. The K-value measured in or the neutral carbonate of the mono-hydroxy com 25 m-cresol is 51. Mouldings of the material are stable pounds, at elevated temperature, preferably in vacuo, and at working temperatures up to more than 300° C. with~ with introduction of nitrogen, until the desired degree out decomposition or evolution of carbonic acid. Moulded of condensation is completely or nearly attained. bodies produced from the melt withstand elevated tem According to the present invention the base-binding peratures, even in the presence of water, for long periods. continued by distilling off the volatile hydroxy compounds substances are now introduced into the viscous melt. 30 This can be done by stirring into the viscous melt the Example 3 A mixture of 550 parts of the bis-(phenylcarbonate) exactly calculated quantity for neutralising the basic of 2,2-di-(p-hydroxyphenylene)~propane, 228 parts of catalysts or by introducing, optionally together with an 2,2-di-(p-hydroxyphenylene)-propane and 0.015 part of indifferent gaseous carrier such as nitrogen, a volatile baseébinding substance in vapour form. When volatile 35 the sodium salt of 2,2-di-(pshydroxyphenylene)-propane are melted together with stirring under nitrogen. At base-binding substances are used an excess over the quan tity used to neutralise the basic catalyst can be removed later by evacuation. After the neutralisation of the catalysts, the inter temperature between 120~200=° C. the phenol which sep arates is distilled off at 20 mm. mercury gauge. Finally by further three hours’ heating at 280° C. under a pres esteri?cation can if necessary be further continued to a 40 sure of 0.5 mm. mercury gauge a highly viscous melt is limited extent for the attainment of a desired molecular weight. obtained. The alkali remaining in the catalyst is then neutralised by the addition of 0.3 part of dimethylsul phate to the melt and the excess of neutralising agent re After the end of the poly-condensation the polycar moved in vacuum. A highly colourless melt is obtained bonate melt formed is converted by conventional meth ods into granular form or directly into moulded bodies, 45 which solidi?es to a material with a K-value measured in m-cresol of 53 and possessing the properties described ?lms, ?bres or bristles or the like. The polycarbonates in Example 1. obtained may be worked up from the melt without in Example 4 volving the destructive in?uence of carbonic acid blow ing, since even with prolonged heating over their melt A mixture of 550 parts of 2,2-di-(p-hydroxyphen ing points, they develop no carbonic acid. Shaped bodies 50 ylene)-butane, 650 parts of diphenyl carbonate and 0.025 produced from the melt display an especially good sta part of the potassium salt of 2,2-di-(p-hydroxyphen bility to elevated temperatures even in the presence of ylene)-propane are melted together with stirring at 120° water. C. under nitrogen. The phenol which separates in the The following examples are given for the purpose of inter-esteri?cation distils oil‘ almost completely at the 55 temperatrue (of the melt) of 120-180” C. in the course illustrating the invention, the parts being by weight. . Example 1 A mixture of 40 parts of hexanediol-l,6 42 parts of diethylcarbonate, and 0.003 part of sodium ethylate are heated for half an hour to IOU-130° C. under re of 30 minutes at 20 mm. mercury gauge. After further stirring and heating to 280° C. at 0.5 mm. mercury gauge the polycondensation is completed. The alkali contained in the catalyst is then neutralised by introduc 60 ing 0.8 part of dimethylsulphate vapour with nitrogen as a carrier. Finally the melt is stirred for a further half an hour at 0.5 mm. mercury gauge at 280° C. where by the excess of dimethylsulphate is distilled off. The polycarbonate is obtained with a K-value of 48 measured ethyl alcohol separated by esteri?cation is distilled otf. 65 in m-cresol which melts at 210° C. and which can be After a further 3 hours’ stirring at 200° C. under a pres Worked up Without evolution of carbonic acid at tem sure of 30 mm. mercury gauge the sodium ethylate used peratures up to over 300° C. into injection moulds, ex ?ux with stirring and with introduction of nitrogen. The as catalyst is neutralised by stirring 0.1 part of phenyl pendable ?bres, ?lms and the like. The shaped bodies chloroformate into the melt. Finally, the condensation produced from the polycarbonate display an unusual sta~ is completed within 3 hours by heating to 250° C. under 70 bility to elevated temperatures, even in the presence of a pressure of 0.5 mm. mercury gauge. The excess of moisture. neutralising agent is then distilled off. A viscous melt Example 5 is obtained which solidi?es to a colourless high-polymeric A mixture of 45 parts of 2,2-di-(p~hydroxyphenylene)body, which possesses the K-value of 65.4 measured in m-cresol and which may be worked up from the melt 75 propane, 50 parts of di-o-cresylcarbonate,v 0.007 part of 3,022,272 calciumhydride and 0.01 part of sodium benzoate are melted together with stirring under nitrogen. The greater part of the phenol which separates distills oft at tempira 'tures of 140-200° C. at 20 mm. mercury gauge. A ter a further 3 hours heating at 280° C. at 0.5 mm. mercury gauge, 0.1 part of ammonium hydrogen sulphate are stirred into the highly viscous melt obtained. The melt is then stirred for a further half an hour at 280° C. and 0.5 mm. mercury gauge whereby the excess ammonium hydrogen sulphate is removed. A highly viscous melt is obtained of a polycarbonate with the K-value of 49 measured in m-cresol and with the properties described in Example 2. , the melt a base-neutralizing compound selected from the group consisting of phenylchloroformate, aromatic sul fonic acid halide, w-chloroacetophenone, dialkyl sulphate Example 6 A mixture of 46.8 parts of bis-phenylcarbonate of 2,2 -di-(p-hydroxyphenylene)-propane, 0.008 part of calcium 6 group consisting of aliphatic, cycloaliphatic and aromatic dihydroxy compounds, (b) bis-carbonates selected from the group consisting of bis-alkyl, bis-cycloalkyl and bis aryl carbonates of aromatic dihydroxy compounds and said organic dihydroxy compounds, and (c) said bis-car bonates of aromatic dihydroxy compounds with them selves, at temperatures from about 50 to about 330° C. in ‘the presence of a basic interesteri?cation catalyst until highly polymeric polycarbonates are obtained, the im provement which comprises neutralizing the basic catalyst 10 ‘at the end of the interesteri?cation reaction by adding to and ammonium hydrogen sulphate in an amount at least 15 equivalent to the amount of the basic catalyst employed in said interesteri?cation reaction. 2. In the process of producing highly polymeric ?ber and ?lm-forming polycarbonates by interesterifying reac hydride and 0.008 part of sodium benzoate is melted 'to gether under nitrogen and with stirring. The diphenyl carbonate split o?" is distilled off at 200° C. under a tion mixtures selected from the group consisting of (a) pressure of 2 mm. mercury gauge. After further heat 20 dicarbon'ates selected from the group consisting of ali ing to 280° C. at a pressureof 0.2 mm. mercury gauge phatic, cycloaliphatic and aromatic diesters of carbonic the alkali catalyst is neutralised by stirring in 0.05 part of dimethyl sulphate. The mixture is then stirred for a acid and organic dihydroxy compounds selected from the group consisting of aliphatic, cycloaliphatic and aromatic further half an hour at 280° C. at 0.2 mm. mercury dihydroxy compounds, (b) bis-carbonates selected from gauge pressure, whereby the excess of dimethyl sulphate 25 the group consisting of bis-alkyl, bis-cyclo'alkyl and bis is removed and a colourless high molecular weight ther aryl carbonates of aromatic dihydroxy compounds and moplastic polycarbonate is obtained which softens at - said organic dihydroxy compounds, and (c) said bis-car about 230° C., possesses a K-value of 52 measured in ~bonates of aromatic dihydroxy compounds with them m-cresol and can be worked up from solutions, e.g. in methylene chloride or from the melt, into stretchable ?le ments or ?bres and injection mouldings. 30 Example 7 A mixture of 38 parts of the bis-phenylcarbonate of selves, at temperatures from about 50 to about 330° C. in the presence of a basic interesteri?cation catalyst and con densing until highly polymeric polycarbonates are ob tained, the improvement which comprises neutralizing the basic catalyst after the liberation of substantially all of the theoretically obtainable monohydroxy component of 2,2-di-(phydroxyphenylene)propane and 0.8 part of the 35 the carbonate by adding to the melt a base-neutralizing compound selected from the group consisting of phenyl pane and 0.001 part of the sodium salt of 2,2-di-(p-hy chloroformate, aromatic sulfonic acid halide, w-ChlOl'O droxyphenylene)-propane is melted together under a ni acetophenone, dialkyl sulphate and ammonium hydrogen trogen atmosphere with stirring. The neutral carbonate sulphate, in an amount at least equivalent to the amount bis-ethylcarbonate of 2,2 - di-(p-hydroxyphenylene)-pro formed is distilled o?’ at 200° .C. under a pressure of 5 mm. mercury gauge. By further heating to 260-280° C. under a pressure of 0.2 mm. mercury gauge, a highly vis cous melt is obtained into which 0.05 partpof phenyl of the basic catalyst employed in said interesteri?cation reaction, and continuing the condensation until the desired molecular weight of the polycarbonates is obtained. 3. The process of claim 2 wherein the base-neutraliz chlorocarbon'ate are stirred to neutralise the alkali. The ing compound is volatile at a temperature below the de excess of phenylchlorocarbonate is then removed by half 45 composition temperature of the resulting polycarbonate, an hour’s stirring at 280° C. and at 0.2 mm. mercury and excess base-neutralizing compound is removed by gauge pressure. The colourless high molecular Weight distillation. , resin so produced with a softening point of about 230° C. 4. In the process of producing highly polymeric ?ber and the K-value of 51 measured in m-cresol shows the and ?lm-forming polycarbonates by interesterifying reac same properties as the product described in Example 1. 50 tion mixtures selected from the group consisting of (a) di Example 8 carbonates selected from the group consisting of aliphatic, 15 parts of the bis-(phenyl carbonate) of the resorcinol (melting point 124-125° C.) and 0.01 part of the sodium cycloaliphatic and aromatic diesters of carbonic acid and ' melted together under nitrogen and with stirring. hydroxy compounds, (b) bis-carbonates selected from the group consisting of bis-alkyl, bis-cycloalkyl and bis-aryl carbonates of aromatic dihydroxy compounds and said organic dihydroxy compounds, and (c) said bis-car bonates of aromatic dihydroxy compounds with them organic dihydroxy compounds selected from the group salt of the 2,2-(4,4’-dihydroxy-diphenylene)-propane are 55 consisting of aliphatic, cycloaliphatic and aromatic di At 200° C. and under a pressure of 12 mm. mercury gauge the splitting o?f of the diphenyl carbonate begins. After half an hour the pressure is reduced to 12 mm. mercury ‘gauge and the melt is stirred for 2 hours at 220° C. The 60 selves, at temperatures from about 50 to about 330° C. in melt slowly becomes high viscous and is heated for fur the presence of a basic 'interesteri?cation catalyst and ther 2 hours at 250° C. and ?nally for a further hour at condensing until highly polymeric polycarbonates are ob 270° C. under 0.5 mm. mercury gauge. Then 0.05 part tained, the improvement which comprises neutralizing the of phenylchlorocarbonate is mixed in and the excess of this compound is distilled off in vacuo. A yellowish ther 65 basic catalyst after the liberation of substantially all of the theoretically obtainable monohydroxy component of moplastic polycarbonate is obtained which melts at about 210° C. It may be worked up from solutions of from the melt into mouldings. We claim: 1. In the process of producing highly polymeric ?bre 70 and ?lm forming polycarbonates by interesterifying reac tion mixtures selected frcm the group consisting of (a) dicarbonates selected from the, group consisting of ali the carbonate by adding to the melt a base-neutralizing compound selected from the group consisting of phenyl chloroformate, aromatic sulfonic acid halide, w~chloro~ acetophenone, dialkyl sulphate and ammonium hydrogen sulphate in an amount at least equivalent to the amount of the basic catalyst employed in said interesteri?cation reaction. ' 5. The process of claim 4 wherein the base-neutraliz phatic, cycloaliphatic and aromatic diesters of carbonic acid and organic dihydroxy compounds selected from the 75 ing compound is volatile at a temperature belowthe de~ 3,023,272 8 7 composition temperature of the resulting polycarbonate, and excess base-neutralizing compound is removed by distillation. 6. The process for the production of a high molecular ?bre- and ?lm-forming polycarbonate which comprises heating a mixture of hexanediol-1,6,diethylcarbonate and a catalytic amount of sodium ethylate at temperatures of from about 50 up to 250° C. under stirring and under re duced pressure, adding phenylchloroformate in excess of 9. The process for the production. of: ‘a high molecular ?bre- and ?lm-forming polycarbonate whichscomprises heating a mixture of bis-(phenylcarbonate) of, 2,2-di-(p hydroxyphenylene)propane and a catalytic amount of calcium hydride and sodium benzoate under stirring’ to temperatures of from about 50 up to 280° C. and under reduced pressure, adding (ii-methyl sulphate in excess of that required for neutralizing said catalyst to. the melt, and removing excess. neutralizing agent under‘ reduced. pres» that required for sodium ethylate- neutralization to the 10 sure. melt before the polycouclensation. is completed, and, dis 10. The process for the production of a high molecu tilling off excess phenylchloroformate under reduced iar ?hre- and ?lm-forming polycarbonate, which com 7. The process for the production of a high molecular prises heating a mixture of the bis-(phenylcarbonate) of resorcinol and a catalytic "amount of the sodium salt of ‘fibre and ?lm-forming polycarbonate which comprises 2,2-di-(p-hydroxyphenylene)-propane under stirring at heating a mixture of bis-(phenylcarbonate) of 2,2-di-(p— temperatures of from about 50 upv to 270° C., adding phenylchlorocarbonate in excess of that required for neu tralizing said sodium saltto the melt at the end of the polycondensation reaction and removing excess neutral pressure. a hydroxyphenylene)~propane, 2,2 — di - (p-hydroxyphenyl ene)-propane and a catalytic amount of the sodium salt of 2,2-di-(p-hydroxyphenylene)-propane under stirring at temperatures of from about 50 up to 280° C.- and under 20 izing agent under‘ reduced pressure. ' reduced pressure, adding di-methyl sulphate in excess of that required for neutralizing said sodium salt to the melt atv the end of the "polycondensation reaction and remov ing excess di-methyl sulphate under reduced pressure. 8. The process for the production of a high molecular ?bre- and ?lm-forming polycarbonate, which comprises heating a mixture of 2,2-di-(p-hydroxyphenylene)—pro pane, di-o-cresylcarbonate and a catalytic amount’ of cal-v cium hydride and sodium benzoate under stirring to tem peratures of from about 50 up to 280° C. and under re 30 References Cited in the tile of this patent UNITED STATES PATENTS 1,995,291 2,210,817 2,739,957 2,789,968 2,808,390 Renolds et a1. ________ __ Apr. 23, 1957 Caldwell ______________ __ Oct. 1, 19,57 FOREIGN PATENTS duced pressure, adding ammonium hydrogen sulphate in excess of that required for neutralizing said catalyst to the melt and removing excess neutralizing agent under re duced pressure. Carothers ____________ _.. Mar. 26, 1935 Peterson _______________ __ Aug. 6, 1940 Billica et al. _________ __ Mar. 27, 1956 650,002 546,377 Great Britain __________ __ Feb. 7, 1951 Belgium _____________ __ Mar. 23, 1956 L.