Патент USA US2405977код для вставки
Aug. 20, 1946. F. T. PETERS ' 2,405,977 FILM MANUFACTURE ' Filed Sept. 2, 1943 r I Jolui‘l'onof 0/5”: Poll/met: wens ‘ A’ fllJ'ZOnHOffef B Jpray of Cooling liquid 2;; Jiream of ' Removable ZZ'QZ win 070W \5 rm Air H02“ Ill/Qatar f'z'Zm. casiz'nq surface ‘Film of fiiz'l/lene Poll/mew J'oZuZzon 3mm EaT-Lkhn Travi'is F ETEPE Mow“, - ‘Patented u'g. "2G, is... ' . 2,405,977 rnM Franklin Traviss Peters, Wilmington, Dei, assign or to E. ii. du Font de Nemonrs & @ompany, Wilmington, Del, a corporation of Delaware i Application September 2, 1942, Serial No. 500,989 2 Claims. (on. 18-57) 2 This invention relates to ?lm manufacture, and and the necessity for heating the ?lm above the more particularly to improvements in the pro melting point before quenching. duction of ?lms from normally solid polymers of The above objects are accomplished‘ by a ethylene. method more particularly described hereinafter The polymers of ethylene with which this in 5 which comprises casting a ?lm on a support from vention is concerned are solid polymers obtained a solution of the polymer of ethylene, the solu by known procedures through the polymeriza tion being at a temperature above the melting tion with heat and pressure of ethylene alone or point of the polymer and the support being at of mixtures consisting of ethylene and another a temperature below the melting point of the compound containing at least one polymer form 10 polymer but not lower than 15° C. below the melt ing unsaturated linkage. These polymers can ing point, evaporating the solvent, and, just prior be obtained, for example, by heating ethylene or ‘ to the time at which crystallization and haze the mentioned mixture thereof under a pressure formation wouldoccur, bringing the ?lm and its above 500 atmospheres and preferably above 1000 support in contact with a non-solvent cooling atmospheres at temperatures of from 100° to 400° 15 liquid, and then stripping the ?lm from the cast C.. and preferably from 150° to 250° C. as de ing surface. scribed in United States Patents 2,153,553, The invention will be better understood in 2,188,465, and 2,200,429. Another method of connection with the accompanying drawing in making these ethylene polymers consists in heat which: ing the ethylene alone or in admixture with an 20 Fig. 1 is a view in elevation of one form of ap other polymerizable compound in contact with paratus suitable for carrying out the invention, water and a per-compound catalyst at tempera Fig. 2 is a similar view of a modi?ed appa tures in the range of 40° to 350° C. and at super ratus, and » atmospheric pressures in excess of 3 atmos Fig. 3 is an elevational view of a further modi pheres. The polymers of ethylene alone are nor 25 ?ed apparatus. mally solid, correspond in composition substan In Figs. 1 and 2 the numeral l indicates a con? tially to (CH2)¢, show a crystalline pattern by X-ray diffraction analysis, and in general melt in the range of about 100° to about 120° C. The ventional extrusion hopper having an extrusion lip 72 past which the ?lm 3 of polymer solution ?ows through a slot, not shown, to the casting physical properties of the polymers of ethylene 30 drum 6. A conduit 5 passes to the interior of the with other polymerizable organic compounds drum in known manner at its axis of rotation to vary depending upon the composition of the provide means for introducing heating ?uid, polymer and the nature of the organic compound preferably a mixture of hot water and steam, to polymerized with the ethylene: the interior of the drum. A similar conduit, not Films of the normally solid polymers of ethyl 35 shown, is provided at the other side of the drum ene referred to above are crystalline and trans for removal of the heating ?uid. As the ?lm is lucent unless they are heated above the melting stripped from the drum in Fig. 1 at the point C point of the polymer and then shock cooled, that it passes over a roll 6 to a drying apparatus, not is, cooled very rapidly below the melting point. shown, which can consist of a heated cabinet This cooling can be effected by casting a ?lm of 40 or a series of warm rollers, etc., and is then wound the molten polymer on a cold support, or by quenching the molten ?lm with a cooling liquid. The requirement that the ?lm be heated above the melting point of the polymer before it is up in a roll. A nozzle 1 is placed to direct a spray of cold water against the ?lm at the point B within the required period of time before crys tallization and haze formation would occur. The quenched prevents the use of a heated conven 45 point A indicates the point on the drum where tional casting drum as a support for the molten haze formation would occur had not the ?lm been ?lm during quenching since a greater di?‘erential rapidly chilled at the proper time before that point is reached. The position of the point A is required than can be maintained between two on the drum, and hence that of point B where points on the periphery of the drum. 50 the cooling liquid is applied will depend on par This invention has as an object to provide a ticular conditions of operation, as will be further new and improved method for obtaining clear referred to later. ethylene polymer ?lms. A further object is a In Fig. 2 the spray of water is replaced with method for casting these ethylene polymer ?lms a stream of water which ?ows through a shallow which avoids the disadvantages of melt casting 55 tank 8 and against a small area of the underside between the casting and quenching temperatures 2,405,977 3 of the drum. The point D on the drum corre sponds to the point A in Fig. 1 and the water likewise contacts the ?lm within the required polymer melting at 105° C. and one part of alumi num palmitate are dissolved in 399 parts of hot xylene. This solution is heated to a temperature time before haze formation would occur. The ' in the range from 110° ‘to 120° C. and ?owed ?lm, after being stripped from the drum by pass from an extrusion hopper or suitable spreader ing over a roller 9 mounted in the tank 8, is led blade on a rotating hollow casting drum such as under a second roller l0 and then to suitable that shown in Fig. 1 of the drawing. The drum wind up mechanism not shown. is maintained at 94° to 98° C. by circulating In Fig. 3 the ?lm of ethylene polymer solution through its interior a mixture of hot water and is ?owed on a ?lm casting surface or ?at plate 10 steam. The rate of solvent evaporation from the II by a spreader blade or other means to obtain liquid ?lm is controlled by circulation of heated the desired ?lm thickness. This ?lm casting air above the ?lm surface. The rate of evapo surface is the upper side of a hollow steel box I2 ration is thus regulated and the speed of the and is heated by means of a stream of hot water rotation of the drum is also regulated so that entering the box at i3 and leaving by the outlet the ?lm becomes substantially solvent-free, solid, M. This steel box I2 is enclosed in a larger box and crystalline when it reaches point A in Fig. 1. IS on the bottom of which the steel box 12 rests However, as soon as these adjustments have been on supports l6. Box I5 is provided with a. re-' made so that crystallization occurs at the point movable lid I‘! having a window l8 to observe the A, a spray of cold water is directed against the condition of the ?lm. Warm air is passed 20 ?lm at point B on the drum’s periphery,. thus through the box from an inlet l9 to an outlet 20 causing it to solidify without crystallization and to control the evaporation rate of the solvent haze formation. The ?lm is stripped from the from the ?lm. The ?lm is quenched at the proper drum back to the point C, where it leaves the time by removing the lid and applying water to water spray. As the drum rotates and casting the ?lm. continues, the ?lm is drawn off the drum at The time at which crystallization and haze this point as described in connection with Fig. 1. The evaporated xylene can be recovered for re formation would occur and therefore the time just prior to this condition when the shock cool use by passing the vapors through a conventional ing isapplied, is determined empirically for the solvent recovery system. particular casting equipment and evaporation 30 Although the spray of cold water tends to re conditions used. This interval which exists be duce the drum temperature, the desired range tween the ?rst moment at which the non-solid of 94° to 98° C., as measured at the point of cast ?lm can be quenched to a clear solid ?lm and ing, can be maintained by increasing the tem the moment it will crystallize and become trans perature and rate of flow of the inlet water and lucent if not quenched may be referred to as the 35 steam used to heat the drum. The water cling ing to the drum’s surface above the point of critical time interval, which varies somewhat in magnitude with a number of other variables. If quenching and stripping is removed, as by blow quenching is carried out before this interval the ing it off with a blast of hot air, before the point of casting is reached on the next cycle. The rate liquid ?lm will be converted to a weak, opaque, white film‘. Quenching is, of course, useless after 40 of solvent evaporation and rotation of the, drum can also be adjusted so that if no shock cooling this time. is carried out the crystallization takes place just By operating at a temperature below the melt beyond the lowest point on the drum’s periphery, ing point of the polymer (de?ned herein as the as at the point D in Fig. 2 where the water spray temperature at which the haze disappears from a crystalline solid ?lm as it is subjected to grad 45 is replaced by a stream of water ?owing against a small area of the under side of the drum. ually increasing temperature, for example, at The invention is further illustrated by the the rate of 1° C. per minute), but not more than following examples in which the parts are by 15° C. below, it is possible to maintain a time weight. ~ interval de?ned above within which the quench Example I .ing can be applied to'yield clear ?lms and the 50 method conducted as a continuous process. The most favorable operating conditions with regard to temperature are from 7° C. to 15° C. below the melting point of the polymer. Within the above mentioned temperatures the critical time interval does not vary signi?cantly with the tempera ture except as temperature a?ects evaporation To 1500 parts of an ethylene polymer having a melting point of 105° C. is added 15 parts of aluminum palmitateand the mixture is dissolved in 6000 parts of xylene by heating and stirring together under re?ux at about 120° C. This solution at 120° C. is extruded, by means of an extrusion head having a slot ori?ce with a clear ance of 0.010" between the lips, on the surface of a rotating hollow stainless steel casting drum rate of the solvent. The rate of solvent evapora tion from the liquid ?lm ?owed out from the polymer solution, however, has a marked effect 60 (6 feet in diameter) at the highest point of the on the critical time interval, which decreases drum’s periphery. The drum is rotated at a as the rate of solvent evaporation is increased. peripheral speed of 20 feet per minute and is Solvent evaporation so rapid that this interval heated to 94° to 98° C. by circulating a mixture is too short for the quenching process to be con of water and steam through its interior. After trolled is therefore avoided. At a given tem 65 the liquid ?lm is formed the xylene is evaporated. perature the rate of solvent evaporation can be At a point about 1 foot beyond the lowest point controlled by regulating the rate of air flow used of the drum’s periphery, that is, at point B in to remove solvent vapor above the ?lm. Fig. 1, the drum is sprayed with water at 10° C., A valuable embodiment of this invention re whereupon a self-supporting ?lm is formed. sides in the increased critical time interval which 70 The ?lm is stripped at the point (C in Fig. 1) at can be obtained by incorporating with the poly which it leaves the water spray. As the process mer solution aluminum soaps and related ma continues the ?lm is led away over rollers and terials which are referred to in more detail here wound up on a roll. The temperature at the inafter. surface of the drum, at the point of casting, is In a typical procedure 100 parts of an ethylene 75 maintained at 94° to 98° C. by adjusting the 5 ‘2,405,077 ?ow of steam and water through its‘ interior. The ?lm'obtained by this process is transparent, of a plus b is equal to the valence of X. In this de?nition the ammonium ion and alkyl substi~ tough, and ?exible. It has a tensile strength of 1800 lbs./s‘q. in. and an elongation at the break tuted ammonium ions are regarded as metals. Comparative critical time intervals for ethyl one polymer ?lms containing various modifyingv agents of the kind referred to above are shown in the following table: ing point of 250%. Example II To 1500 parts of an ethylene polymer having a melting point of 110° C. is added 15 parts of Critical time interval in seconds Composition magnesium stearate and the mixture dissolved in 6000 parts of toluene by heatingand stirring together under re?ux at 120° C. This solution is ?owed out with a spreader blade having a clearance of 0.012" on the ?lm casting surface or ?at plate H shown in Fig. 3 which is heated to 100° C. by hot water ?owing through the steel box [2, as previously described. A current Unmodi?ed ethylene polymer. . 1% aluminum palmitate _ . . _ . _ _ _ l5 _ . _ . . . __ 120 1 _ 180 magnesium stearate..__ 1 a titanium tetrastearate__ 90 60 1% sodium oleate ________ __ 17 ammonium stearate ____ __ __- 1% potassium naphthenate ________________________ __ of warm air passing from the inlet 19 through 2/40 . 10% titanium tetrastearate. the outlet 20 circulates through the chamber formed by the box l5 containing the casting 20 surface and removes the toluene vapor formed _ 1% aluminum stearate _____ ._ 1% Zinc tomato _________ __ 1% palmitic acid 30 30 30 45 30 The per cent of each modi?er indicated in the above table is calculated on the weight of ethylene polymer used. All solutions used for casting the the ?lm has dried for about 3 minutes, cold ?lms were in xylene and contained 10% of an water (about 20° C.) is poured onto a portion 25 ethylene polymer having a melting point at 105° of the ?lm. Heating of the plate is continued C. The ?lms were all cast at 100° C. under a by circulating a stream of water at 100° C. spreader blade having a clearance of 0.0127. through the interior of the steel box. After about The evaporation conditions were the same'for all another 3 minutes the portion of the ?lm which the ?lms and were such that the unmodi?ed ?lm has not been wet with water becomes hazy and 30 was substantially solvent-free and crystallized 4 crystalline. The portion that is wet with water minutes after casting. More rapid evaporation remains clear and non-crystalline. The steel . will shorten the critical time interval for each of casting box is cooled to about 80° C. and the the compositions indicated in the table. Con ?lm is stripped. The portion of the ?lm which versely, slower evaporation will lengthen the crit has been Wet with water remains transparent 35 as the ?lm dries. The condition of the ?lm can be observed through a window in the lid. After ical time intervals. However, the ratio between and non-crystalline; the part that has not been wet with water remains hazy and crystalline. The clear ?lm has substantially the same tensile strength and elongation as that described in Ex ample I. the critical time intervals of two different com positions is substantially independent of the evap oration rate. Thus, it will be seen that the proc 40 ess is more easy to control if ‘a modifying agent The following experiment, which is illustrative of the value of the classof modifying agents used for increasing the critical time interval, compares the results obtained from ?lms made from two solutions of the polymer each of which is com 45 of the kind pointed out above is used. The pre ferred modifying agent is aluminum palmitate. Aluminum salts of other long chain aliphatic acids and magnesium salts of these acids also are very effective modifying agents. Similar salts of alkaline earth metals, alkali metals, ammonia . posed of 1500 parts of the polymer (melting point and amines, as well as the, long chain acids them 105° C.) dissolved in 6000 parts of xylene, but selves, also are operable, but do not increase the only one of which contains aluminum stearate critical time intervals as markedly as the alumi (15 parts). A ?lm from each solution was flowed num salts. Effective concentrations of these out at 100° C. These ?lms were flowed, simul 50 modifying agents, based on the ethylene polymer, taneously and under opposite sides of the same are from about 0.1% to about 10%. spreader blade having a clearance of 0.012," on The critical time interval will vary appreciably the casting plate I I described in connection with with the solvent used. Aliphatic hydrocarbons Fig. 3, and the behavior of the two ?lms was having boiling points above about 100° C. also observed through the window l8. Pouring cold 55 are suitable. Chlorinated hydrocarbons having water on the ?lm not containing the aluminum boiling points above about 100° C. are also oper soap within the time interval of from about 4 able but have substantially smaller critical time to, 4.25 minutes after casting sets the ?lm to a intervals. , clear solid ?lm. This ?lm or that containing the The quenching liquid is preferably water hav aluminum soap cannot be quenched before about 60 ing a temperature of from 0° to 10° C. _ The 4 minutes without becoming opaque, white and temperature of the water can, however, be con weak, but the ?lm containing the aluminum soap siderably higher, and temperatures as high as 70° can be quenched to a clear non-crystalline ?lm C. can be used if the water is kept ?owing rapidly. at any time during the much longer period of The higher temperatures are less desirable be from 4 to 8 minutes after casting. cause of greater tendency toward partial crystal The modifying agents used to increase the crit lization and slight haze formation. The water ' ical time interval are of the formula X(R)a(Y)b, should ?ow against and then away from the ?lm in which X is a member of the class consisting so that it does not become stagnant and heated of hydrogen and metals, R is a member of the at the point where it contacts the ?lm. In place class consisting of carboxylic and sulfonic acid 70 of water various other quenching liquids, such radicals containing from 6 to 30 carbon atoms as alcohols, esters and ethers, which are non--’ and preferably from 10 to 30 carbon atoms, Y is an hydroxyl group, a is an integer ranging from 1 solvents for the polymer can be used. The temperature of the ethylene polymer solu tion from which the ?lm is formed is not particu . to the valence of X, b is an integer ranging from 0 to one less than the valence of X, and the sum 75 larly important, except that as in any solution 2,405,977 7 8 casting process it should be below the boiling point but somewhat higher than the temperature of the casting support in order to prevent the I claim: 1. A process for preparing transparent ?lms from a normally solid polymer of ethylene which melts at a temperature of from 100° C. to 120° C., formation of vapor bubbles in the ?lm, The con centration of the ethylene polymer in the solu tion is preferably about 25% by weight,but can range from 5% to‘ 40%. Although the present process is most ad vantageously carried out on a drum as the casting said process comprising casting a ?lm on a cast ing support from a liquid composition, the tem perature of said liquid composition being above the melting point of said polymer, and the tem— perature of said support being below the melting support, other types of casting supports, such as 10 point of said polymer but not more than 15° C. an endless belt, can be used. This invention is below the melting point of said polymer, said also applicable to coating of various substrates, liquid composition comprising a modifying agent including paper, cloth, and the like. and a solution of said polymer, maintaining the The transparent ?lms prepared by the process film in contact with said support until substan of this invention are characterized by high ?exi 15 tially all of the solvent is evaporated from the bility, high resistance to tearing, retention of ?lm, quenching the ?lm by contacting it with a toughness at very low temperatures, and excel non-solvent cooling liquid at a temperature of lent waterproofness and moisture impermeability. from 0° C. to 70° C. just prior to crystallization Because of these properties they are well adapted and haze formation in the ?lm, and then strip~ as protective wrappings for food, tobacco, medic ping from the casting support the'transparent inal products, clothing and the like. They are ?lm thus obtained, said modifying agent being also useful as protective coatings for paper, card present in amount of from 0.1% to 10% of the board, fabrics. and other ?exible materials, to weight of the ethylene polymer in said solution which they may be laminated by heat or pressure or with an adhesive. The unsupported ?lms or - laminated articles are particularly useful as elec trical insulating materials. ' As many apparently widely di?‘erent embodi ments of this invention may be made without de parting from the spirit and scope thereof, it is to be understood that I do not limit myself to the speci?c embodiments thereof except as de?ned in the appended claims. and consisting of a substance selected from the group consisting of fatty acids containing from 6 to 30 carbon atoms, and salts of said acids. 2. The process set forth in claim 1 in which said small amount of substance contained in said solution of ethylene polymer is aluminum palmi tate. FRANKLIN TRAVISS PETERS.