IL9922A - novel drawn polymers and process for the production thereof - Google Patents

Description

CASE 6023 This invention relates to drawn or extended polymers. In one aspect it relates to a process for producing drawn or extended polymers. In another aspect it relates to an improved polymer film. In another aspect it relates to an improved polymer filament or fiber.

It is known in the art to produce films and fibers, filaments or threads from polymers of various types. The extrusion of polymers through slits or dies of small width or diameter is well known.

The present invention provides an improved process for producing a film or a filament or other form of drawn polymer from an olefin polymer. It also provides films and fiber of improved strength, resistance to shrinkage, and transparency. The filaments, threads or fibers produced according to this invention can be fabricated to produce improved textiles, e.g. for use in filter cloths, automobile upholstery, curtains, rugs, furniture covers, and similar applications. The filaments can be used as fishing lines, fishing leaders, fish nets, rope strands, sutures, or strings for musical instruments. The films produced according to the invention can be used as wrappers for foods, tobacco and other items or can be fabricated to produce transparent windows in various containers such as boxes, envelopes, and similar articles.

An object of the invention is to produce a polyethylene film of increased strength and transparency. Still another object is to produce a polyethylene filament having a high tensile strength, even at, elevated temperature s„ Another object is to produce a polyethylene filament which is trans-parent or translucent. Still another object of the invention is to produce a polymeric filament having a high resistance to shrinkage,, According to the present invention there is provided a drawn polymer, comprising a cold-dravn and preshrunk olefinic polymer having a drawn thickness within the range of 0,1 to 100 mils, said polymer exhibiting substantially no shrinkage at temperatures up to 2$0°Fo and having a tensile strength of at least 30,000 psi at a temperature within the range of 65° to 100°Po There is also provided a process for the production of drawn polymers comprising a process for drawing polymers so as to produce an improved polymer comprising extending an olefin polymer having a density of at least 0„9lj. and a crystallinity of at least 70 per cent, cold drawing said extended polymer at a temperature between substantially room temperature and its softening point, heating the cold-drawn polymer at a temperature below its softening point and recovering an improved drswn polymer „ The filaments produced according to this invention have an outside diameter in the range 0„01 to 100 or more mils, usually 0„1 to 50 mils. This dimension is, of course, thickness in the case of a film0 Filaments according to this invention have a tensile strength of at least 30,000 psi„ Many of the filaments according to the invention have tensile strengths of the order of 90,000 to 100,000 and the tensile strength may range as high as 150,000 to 250,000 psi. These tensile strengths are measured at atmospheric temperature, e„go, 65 to 100°F. A further outstanding characteristic of polymers according to this invention is that they have tensile strengths, measured at 212°F., of 10,000 psi or higher. When it is considered that polyethylene of the type hitherto available on the market undergo virtually complete deformation when subjected to steam or boiling water, the fact that polyethylene filaments according to the present invention have tensile strengths of 10,000 psi or higher at 212°F. is highly unexpected. A further characteristic of the filaments, especially polyethylene filaments, according to this invention, is that they undergo substantially no shrinkage when immersed in water at temperatures up. o 265°F0 Thus textiles prepared from filaments according to this invention can be washed, dry cleaned or steam pressed substantially without damage. Films in accordance with the invention have similarly desirable properties, including translucence or transparency.

The starting materials for the process of this invention can be characterized as polymers of olefins which polymers have a density of at least 0.¾ and a crystallinity of at least 70 per cent. Preferably the density is at least 0.95 and the crystallinity is at least 80 per cent. More preferably, the density is at least about 0.96 and the crystallinity 90 per cent or higher. Polyethylenes having the foregoing densities and crystallinities are p eferred starting materials for the process. However polymers (including copolymers) of other olefins can be used provided the foregoing density and crystallinity limitations are satisfied.

A highly satisfactory, and often preferred, starting material for use in the present invention can be obtained by the process set forth in -Belgian Pfltonl ΖΐΒ,θΰϊΙ grantod July 22, 19 ir. Polymers according to that patent are produced by polymerizing an 1-olefin having a maximum chain length of 8 carbon atoms and no branching nearer the double bond than the I .-position by contacting with a solid catalyst containing, as an essential catalytic ingredient, chromium oxide associated with at least one porous oxide selected from the group consisting of silica, alumina, zirconia and thoria. Suitable olefins are ethylene, propylene, 1-butene , l-pentene and l-hexene. Copolymers or interpolymers of two or more such olefins can be preparedβ For the purpose of obtaining a starting material for the purposes of the present invention, ethylene is ordinarily the preferred olefin. A highly satisfactory starting material for the present invention can be obtained by polymerizing ethylene in admixture with a liquid inert hydrocarbon such as cyclohexane in which is suspended a comminuted catalyst of the type described in the above-mentioned Bolglaa patent 0 It is preferred that the chromium content of the catalyst be within the range 0.5 to 10 weight per cent and it is highly preferable that an appreciable proportion of the chromium be in the hexavalent state. The catalyst can be maintained in suspension in the reaction mixture by any suitable agitation means „ The reaction temperature is preferably in the range 2$0 to 375°P0, although temperatures outside this range can be used0 A pressure sufficient to maintain the cyclohexane or other solvent substantially in the liquid phase is satisfactory. The reactor effluent is ordinarily heated to obtain maximum solution of polymer in solvent and the catalyst is removed by filtration. The product polymer can be recovered from the resulting solution by vaporization of the solvent and/or cooling to precipitate the polymer from the solvent, and subsequent separation of the precipitated polymer. A polymer produced by the process just outlined will ordinarily have a molecular weight in the range 359000 to 100, 000 a density in the range 0.95 to 0.97 » e.g. approximately 0.96 , and a crystallinity in the range 90 to 95 per cent. The tensile strength of the polymer, as produced, will ordinarily be of the order of lj.,000 to 5» 000 psi, but can be higher or lower.

The polymer ordinarily has a melting point of approximately 250 to 255°P. and a softening point of about 265°F. or higher. The difference between the melting point and the softening point is due to the different methods by which these values are obtained. Polymers produced by this process have unsaturatlon which is preponderantly of the terminal vinyl and/or trans-internal structure. So-called "branched vinyl" unsaturatlon is substantially absent.

Another suitable starting material for the process of the present invention can be produced by the polymerization of an olefin such as ethylene, propylene, or l-butene, preferably ethylene, by contacting with a catalyst such as a mixture of a compound represented by the formula AI ^, wherein R is a saturated aliphatic, cycloaliphatic or aromatic hydrocarbon radical or hydrogen; and a second component which is ordinarily a halogen compound of a metal such as titanium, zirconium, chromium or molybden m. An example of such a catalyst is a mixture of triethyl aluminum and titanium tetrachloride.

A similar suitable catalyst comprises a mixture of a compound represented by the formula Rm.lXn wherein R is a hydrocarbon radical of the type previously described, X is a halogen and m + n = 3 , i.e., the valence of aluminum. In connection with this type of catalyst metal compounds such as titanium dioxide and the tetraalloxides of titanium as well as tetravalent titanium salts of organic ca boxylic acids can be utilized. An example of such a catalyst is a mixture of diethyl aluminum chloride, ethyl aluminum dichloride, and titanium tetrachloride. A similar type of catalyst mixture comprises a halide of a Group IV metal, e„ g o , titanium tetrachloride and a free metal, such as metallic sodium or metallic magnesium,, The polymerization reaction is ordinarily conducted at a temperature which can range from room temperature up to approximately 300°C. The reaction is preferably conducted with the olefin in admixture with a hydrocarbon such as isooctane, cyclohexane or toluene which is inert and non-deleterious to the catalyst under the reaction conditions. The pressure is ordinarily sufficient to maintain the inert hydrocarbon substantially in the liquid phase. The reactor effluent is ordinarily treated with a compound such as methanol, acetone, acetic acid, or water, which decomposes the remaining catalyst, and the polymer is recovered by vaporization of the hydrocarbon solvent or by precipitation of the polymer by cooling. Polymers produced by this general type of process have molecular weights which can range from ,000 to 200,000 or higher. They generally have crystallinities of 80 to 8 per cent and densities of about 0.95» Although these polymers are suitable for use in our process, polymers produced by the process disclosed in the above-men oned Bolgian patent are preferred because filaments produced from the latter-mentioned polymers (density 0.96 or higher crystallin-ity 90-95 er cent) have from l to 6 times the resistance to degradation under ultraviolet light than is exhibited by filaments produced from the other type of polymer just de- scribed o Furthermore filaments produced from polyethylenes of the former type are significantly more resistant to deformation or distortion at elevated temperatures , It will be noted that the foregoing speci ications as to density and crystallinity are not satisfied by most of the polyethylenes which have hitherto been available on the market. Most such polyethylenes have been produced by polymerization at extremely high pressures, e.g. of the order of 10 ,000 psi or higher, usually in the presence of a peroxide type catalyst or without any added catalyst „ These materials ordinarily have densities of the order of 0.91 or 0.92 and crystallinlties of 60 per cent or lowere They ordinarily have molecular weights within the general range 5, 00 to , 000 and tensile strengths of the order of 1 ,500 to 2 , 000 psie The unsaturation in such polymers is preponderantly of the branched vinyl type0 The first step according to the process of the present invention is to extrude or otherwise extend the polymer to form a filament or a film„ This step ordinarily comprises forcing the polymer, usually in the molten state, through a small opening or die.

It is ordinarily preferred that the extruded filament or ilm be quenched before further treatment „ This can be done by exposure to air, nitrogen, or other fluid at, for example, atmospheric temperature, but is preferably done by immersion in an inert fluid such as water „ Highly satisfactory results are produced by cooling the water to subatraospheric temperatures, e.g. 32°F.

The quenched filament is treated in a second step which is ordinarily described as "cold drawing". This term generally signifies that the material is stretched, drawn or elongated at a temperature below its softening point and at a rate such that the filament does not break. The temperature of cold drawing can range from room temperature, e.g. 65 or 70°Fo. up to temperatures slightly below the softening point of the polymer, e.g. 260°P. The temperature is generally in the range 70 to 260°P., preferably from 100 to 260°F. Filaments produced according to this invention by cold drawing below 150°F. are translucent, whereas those produced by cold drawing at 150°F, or above are transparent. Excellent results are obtained when the cold drawing is conducted at temperatures of 212°F. or higher, preferably from 225 to 250 or 260°F o It will be understood that the upper limit of temperature will be dictated by the softening temperature of the polymer itself and should be a few degrees below the softening temperature. It is noteworthy that polyethylenes previously available on the market could not be cold drawn at temperatures of 225°F. or higher since they would be liquid at this temperature. As previously indicated, the oold drawing is conducted at a rate which is insufficient to effect breakage of the filament. Ordinarily the cold drawing is conducted at a rate just short of the rate necessary to break the filament. This maximum rate will vary, depending upon the temperature of the filament. At relatively low temperatures the rate will be relatively low. The rate can be much higher at higher temperatures within t he range discussed. The maximum or optimum rate of cold drawing is readily determinable by mere routine test in any given set of circumstances by one skilled in the art. The extent of cold drawing will also depend upon the temperature. The filament is ordinarily drawn to a length which is from 5 to 10 times the length of the undrawn filament. Of course, the upper limit of cold-drawn length will be dictated by the break point, and the filament is always drawn to a length which is less than that at which the filament breaks. The break point is readily determinable by routine test in any given set of circumstances „ The third main step of the process according to this invention is a preshrinking step. The cold-drawn filament is preferably immersed in a fluid, usually water, at an elevated temperature, preferably in the range 160 to 260°F, but below the softening point of the polymer, A satisfactory method is to immerse the filament for a period of time in the range f? to 30 minutes in boiling water. Although water is ordinarily preferred, other fluids, such as glycerol or other polyhydric alcohols which are inert toward the polyethylene filament can be used. Thus the film can be passed through a nitrogen (or, less preferably, air) atmosphere maintained at a temperature in the range previously described. An advantageous characteristic of the polyethylenes utilized according to this invention is that they undergo a much smaller degree of shrinkage in the shrinking step than do polyethylenes previously available on the market. Thus th losses sustained in the preshrinking step are reduced according t this invention. The fiber or filament recovered from the preshrinking step undergoes substantially no further shrinkage during washing or dry cleaning.

The accompanying drawing is a schematic flow sheet of a process according to this invention. A polyethylene of the type previously described, and ordinarily in a comminuted state, is passed from storage means 2 through a star valve 3 to melting zone wherein it is melted by heat supplied, for example, by a steam coil $0 The molten polyethylene passes through valve 6 and propulsion means 7» which can be any suitable form of pump or other means for effecting the pressuring and flow of fluids,, the molten polyethylene is then forced under pressure through valve 8 into extrusion zone 9o When propulsion means 7 is a piston type pump, as indicated diagramraatically in the drawing, valve 6 can be a check valve which opens only upon the suction stroke of the piston, allowing polymer to flow into propulsion means 7o Under these circumstances, valve 8 can also be a check valve which opens only on the compression stroke of the piston of propulsion means 7. With such an arrangement, polymer flows into propulsion means 7 on the suction stroke of the piston and out of propulsion means 7 to extrusion zone 9 on the compression stroke „ Prom extrusion zone 9, the molten polymer is forced through a small opening or die 10 to form a filament 11. The filament passes into a quench zone 12 which can be a tank containing a liquid 13 such as water which is cooled to around freezing temperature by means of a coolant or refrigerant supplied through cooling coil Hj.0 The filament passes around a rotating roller or spool l$f then out of quench zone 12 to roller 16 „ The filament then passes into drawing zone 17, which can be in the form of a tank containing a suitable chemically inert fluid 18 which is heated by means of heating coil 19. Suitable fluids are nitrogen, air, or a polyhydric alcohol such as ethylene glycol, propylene glycol, diethylene glycol, or glycerol. The filament passes around rollers 20, 21 and 22 to roller 23. The filament is preferably wound around rollers 20, 21 and 22 several times so that a tension is produced „ Roller 21 is caused to rotate at a higher speed than roller 20 , e„g„, twice the speed of roller 20, Roller 22, in turn, is caused to rotate at a higher speed than roller 21, for example, twice the speed of roller 21„ Drawing zone 1? s preferably maintained at an elevated temperature below the softening temperature of the polymer, as previously discussed. Under the conditions in zone 17, a drawing of the filament is produced between rollers 20 and 21 and is completed between rollers 21 and 22e The drawing is ordinarily conducted at such a rate that a maximum speed of elongation is produced but the break point of the filament is never reached „ The dra/n filament passes over roller 23 and into preshrinkage zone 21+, which can be a tank filled with a fluid 25, such as water, which can be maintained at or near its boiling point by means of a, heating coil 26. The filament passes over or around rollers 27 and 28 and is wound upon a spool or roller 9» The finished filament ca be unwound from roller 29 for use.

The melting and propulsion zones can be combined into a single zone if desired, e„g„, by use of a screw conveyor with a heating jacket 0 It will be understood by those skilled in the art that the filament can be wound any desired number of times around any of rollers l£, 16, 20, 21, 22, 23, 27, 28 and 29. A suitable source of power for producing the rotation of the rollers can readily be supplied by those skilled in the art but is not shown in the drawing.

While the process illustrated in the drawing is described with particular reference to filaments, it will be clear to those skilled in the art that the process is also applicable to film production,, EXAMPLE I utilizing a reactor provided with a stirrer. The catalyst used was prepared by Impregnating a macroporous, steam-aged, co-precipitated, silica-alumina gel containing 90 weight per cent silica and 10 weight per cent alumina with an aqueous solution of chromium trioxide, drying the impregnated material and heating in a stream of substantially anhydrous air for about 5 hours at about 9$O0 „ The final catalyst contained approximately 2 , 5 weight per cent chromium in the form of chromium oxide.

The hexavalent chromium content of the catalyst was approximately 2 weight per cente The catalyst, having a particle size in the range 20 to 8 0 mesh, was suspended in cyclohexane in the reactor and a mixture of ethylene and cyclohexane was passed into the reactor o The reactor was maintained at a temperature of about 300 °P o and a pressure of about £00 psi0 After a reaction or residence time of approximately 30 minutes, the reactor effluent was withdrawn, heated to about 350°F„ and filtered to remove the catalyst „ The polymer was recovered from the resulting clarified solution by cooling and filtration,. The product polyethylene had a molecular weight of 33 * 000 , Samples of the polyethylene were cold drawn at room temperature (about 75°Fo) at the rate of 2 inches per minute. The tensile strength of the drawn materials was then determined. The cold-drawn filaments were then immersed in hot water for a period of 10 minutes and the percentage shrinkage was measured.

Two commercially available polyethylenes prepared by high-pressure polymerization (not In the presence of a chromium oxide catalyst) were treated In a manner similar to that above described. One of these materials, designated as B In the following table, had a molecular weight of approximately 30 , 000 , The second material, designated as C in the following table, had a molecular weight of approxima ely 21,000, Each of these commercial materials had a tensile strength of about 2,000 psi prior to cold drawing.

The polyethylene produced by the described chromium oxide-catalyzed polymerization is designated as A in the following table. Prior to the cold drawing, it had a tensile strength of approxima ely £,000 psi.

The comparative data are shown in Table I, TABLE I Cold Drawn Length of 5-Inch Per to (Per Cent Oriented Strip After ImmerCent Original Tensile , sion in Hot Water, Shrin-e- si In. agj „_ Ethylene Polymer A 800-900 40,000 .75 (1) 5 B 455 11,480 2,75(2) 45 C £ 0 10,750 2,50 (2) 50 (1) Immersed in boiling water for 10 minutes (2) Immersed in water at 200°F, for 5 minutes * Original length 2 in,, cross section 0,25 x 0,070 in.

The above data clearly indicate the superiority of the filament produced from polymer A according to this invention. This filament had a much higher tensile strength than those produced from the commercially available polyethylene. Furthermore, the difference in tensile strength is far 4» higher than ^ is evident from the differences in tensile strengths of the two types of polymers before cold drawing. Thus, before cold drawing, the polymer produced by chromium oxide catalysts had a tensile strength of about 2,5 times that of the other polyethylene s, whereas the filament produced from the polyethylene produced by chromium oxide-catalysed polymerization had a tensile strength of about four times that of the filaments produced from the other polymers,, In addition, the shrinkage produced upon immersion in hot water was much less in the case of the polyethylene produced according to this invention. Polyethylenes B and C utilized in this example had densities of from 0,91 to 0o92 and crystallinities of approximately h$ per cent. Poly-ethylene A showed greater extensibility than B or C.

EXAMPLE II The following table shows properties of other filaments produced in substan ially the same manner as described in Example I from polymers produced by polymerization of ethylene in the presence of a chromium oxide catalyst in a process similar to that described in Example I.

TABLE II Diameter 20 mil 8 mil 6 mil Denier (gm/9 km) I809o902 305«100 U¾.o600 Linear density (gm/cm) 0.00201 O.OOOl+O 0.00019 Moisture regain {%) 0.22l| 0.501 0.519 Tensile (psi) lj.7,700 lj.9,067 58,250 Tensile (gm denier)* 3oll- 3«50 k-k^ Elongation { ) 30 18.7 10.5 Knot Break Strength (gms) k,5&k 1,121 7*1-5 # 12w min., 10" gage, room temperature The foregoing data show the very desirable properties of filaments obtained according to this inven ionβ EXAMPLE III Table III below shows the desirable high-temperature properties of filaments produced according to this invention.

These filaments were produced in substantially the same manner as described in Example I, utilizing chromium oxide-catalyzed polymerization of ethylene as a source of starting material.

Fiber Diameter (mils) 20 8 6 Tensile (psi at 158°FJ 17,700 28,900 .. ,800 Tensile (psi at 212°Fe) 10,000 12,600 26,200 Elongation {% at l58eF„) II4.7 133 35 Elongation { at 212°F0) 176 2^7 190 The foregoing data show that even at temperatures as high as 212°F„, filaments produced according to this invention have tensile strengths of 10,000 psi or higher β This is believed to be an. unexpected characteristic, which was never attained by polyethylene filaments previously produced, EXAMPLE IV The data in Table IV below show data obtained upon dry cleaning and pressing of 1-meter lengths of 6~mil filaments produced in a manner similar to that described in Example I, utilizing chromium oxide-catalyzed polymerization. The filaments were Inserted in wool flannel pockets and submitted to commercial dry cleaning conditions „ TABLE IV Tensile ShrinkStrength Elonga¬ Treatment age tion ( ) Control 58,250 11 Cleaned and dried 1 cycle by Method A 1,5 68,380 38 Cleaned and dried 50 cycles by Method A 5 70,650 1+3 Cleaned, dried, and pressed 1 cycle by Method A 5 67,510 lj.8 Cleaned, dried, and pressed 50 cycles by Method A 6 66,525 33 Cleaned and dried 1 cycle by Method B 205 70,050 33 Cleaned and dried 50 cycles by Method B 6 70,233 21 Cleaned, dried and pressed 1 cycle by Method B 5 72,310 ij.2 Gleaned, dried and pressed 0 -cycles by Method B 9 67,700 18 the filaments with perchlor©ethylene at 80°F. and drying at about li|.0oF„ The pressing was conducted with steam at a filament temperature of about 212°Pe Method B consisted in cleaning at 8o°F. with a low boiling petroleum liquid containing small amounts of a detergent, water, and an oil similar to the natural oils in wool, and drying at 160°F_. The pressing was conducted with steam at a filament temperature of from 220 to 230°F„ These methods are representative of dry cleaning processes in current commercial use.

The foregoing data show that filaments according to this invention can be satisfactorily cleaned and pressed by ordinary methods. It should be noted that the foregoing data were obtained with fibers prepared according to the process of this invention but without preshrinkage . Preshrinkage, as previously described, substantially eliminates the shrinkage obtained upon dry cleaning and pressing,, EXAMPLE V The data in Table V below indicate the effect of cold-drawing temperature upon the tensile strength and elongation at break of fibers produced from polyethylene obtained by chromium oxide -catalyzed polymerization according to this invention (similar to method described in Example I). The shrinkage values set forth in Table V were those which the cold-drawn fibers sustained in the pre shrinking step according to this invention, i.e. shrinkage in boiling water.

TABLE V Cold-Drawing Shrinkage, Tensile, pel Elongation. % Temperature _°F. ( ) Treated* Control*-* Treated* Control** 10G°Fe 8 .8 50,696 53 ,390 27 30 150?F. 3 .8 6i ,560 56, 030 28 ∑¾. 200°F. 2,5 50 70 53 ,090 20 30 * Immersed in boiling water for 30 minutes. No tension.

· EXAMPLE VI The following tables show data obtained at various extrusion temperatures and cold-drawing temperatures, and with various temperatures and materials used for quenching immediately following the extrusion step0 The filaments tested were produced from polyethylene obtained by a process very similar to that described in Example I, utilizing a chromium oxide-silica-alumina catalyst 0 An 18-or fice 0e023-inch orifice diameter spinneret was used to produce the filaments. The length of the fibers before cold drawing was 2 inc hes „ ffi eneh Bath Temperature' 32°F» (Water) Drawing Speed ϋΐο/πψΐβ 1 Drawing Temperature °F. WO 100 150 212 100 Preshrinlsage (HgO) Temp. °F.

Tensile 75°F» 62,833 67,110 1*9,770 56,670 65,1*57 55,670 6 Strength, l50<>Fe 52,720 ·» 1*9,980 67,660 56,920 ,9,310 l*9,5io 1* (psi) 212°F. 1ίΟ,756 i β» - ,93,113 55,697 53,953 60,670 1*1*,193 1* Elongation, 7 ^· 15 20 30 25 % 1 0OF, 35 10 . - 50 30 25 /to 212°F. 15 15 55 21* 20 20 Elongation, 75°F- 10 5 10 10 10 15 IS 10 Ί5 10 20 2120F. 10 5 20 10 5 15 (jueneh Bath Temperature l50°Fe (Water) Drawing Speed in»/mine i - 5 Drawing Temperature °F. Ϊ00 150 212 100 150 212 100 Presfarinfcage ¾20) Temp. °F.

Tensile 75°F« 1*9,697 81*,900 1+6,110 1*6,620 63,976 51,930 7 Strength l50°F. 1*9,790 66,630 50,690 58,920 51*, 690 1* (psi) 212°F. 50,563 es 73,756 56,0lj0 1*2,367 53,990 53,290 5 Elongation, 75°F<» 15 C9 10 20 25 25 30 % 150OF. 1*5 25 . 35 30 20 50 2120F. 25 15 'I4D 20 15 30 ffiueneh Bath Temperature 375°F<> 32°F. (Water) Drawing Speed in»/mine 1 Drawing Temperature "F» 300 150 212 100 150 21 Pre shrinkage (H20)~Teinpo °Fo - Tensile , 75°F , $$922 Strength l50°Fo 52,010 (psi) 212°F. $Oa6$6 Elongation 75°F« 15 30 18 '25 % 150°F. 2$ D 30 65 212°F. 20 1+0 1+5 15 duench Bath Temperature 37 °F» 75°Fo (Air) Drawing Speed ine/mine 1 5 Drawing Temperature °F, loo 150 2i2 Ιόό 150 2l -preshrinkage (HgO) "Tempo °F<> - Tensile 75°F<> 52*136 "55,730 36,606 ,220 1+7, Strength T^O^F, 52,070 1+5,700 1+9,080 58,57© 1+5, (psi) 212°Fo 1+3, 906 50,333 38*196 1+8,110 1+6, Elongation T5°F« 10 20 15 IS 20 % l5o°F. 20 15 35 1+5 212°F. ID 20 ID 25 15 Drawing Temperature QFA IPO 150 212 300 150 21 Preshrinkage (H20) Tem 0 °F0 Tensile 75°F* 1*6*876 53*663 7$ ,730 1*1* 60 - 7li Strength 150°FC 50*1*) 55*070 65 980 58*980 5l*2ljO 1*0* (psi) 2120F0 50,956 52*056 69*61* 51*133 52*3 6 66 Quench Bath Temperature 1*25?F«> 75°F<> (Air) Drawing Speed in./min9 1 5 Drawing Temperature OFT*"" "~ lOQ 150 2l2 100 150 21 Preshriiikage (H O) "Temp. °F.

Three different polyethylene s were formed into filaments by extrusion through different orifices in the molten state at l.B2°F „ and 23 psi„ In each case, the length of the land of the orifice was three times the diameter β Polyethylenes I and II were produced by chromium oxide-catalyzed polymerization substantially as in Example I and had a molecular weight of about -4.0,000s a density of about 0„96, and a crystallinity of about 93 ©r cent. Polyethylene III was produced by use of a polymerization catalyst comprising an organo-aluminum compound and had a density of about 0o95 and a crystallinity of about 80-85 per cen 0 The data are shown in Table I β TABLE IX* Undrawn Drawn Filament Filament Extrusion Diarric Diarn, , Rate., ίη,,/min. mils mil.

Po 1 Smooth Smooth Polyethylene II 12-rail orifice 10 7o0 Slightly rough surface 6-mil orifice 3 11 3.5 Slightly rough surface Polyethylene III 12-mil orifice 28=314- 8 6-mil orifice 15 Plugged Rough surface orifice The foregoing data show the superiority of polyethylenes produced by chromium oxide=eatalyzed polymeriza on in producing a smooth filament,, Polymer molecular weight as used herein, is determined, unless otherwise specified, on the basis of the equation # No pre shrinka e wherein is the inherent viscosity as determined with a solution of 0.2 gram of the polymer in 50 cc of tetralin at 130*C. This general type of molecular weight determination is described by Kemp and Peters, Ind. Eng. Chem. 35 . 1108 (1¾3), and by Dienes and Klemm, J. Applied Phys. 2.» k5& (June 191+-6) β The tensile strengths of undrawn polymers referred to herein are determined by ASTM Methods D-638-52T and The melting points referred to herein were determined by melting a polymer sample, cooling slowly while plotting temperature against time, and determining the temperature corresponding to a plateau in the cooling curve.

Softening point is determined by use of the method of Karrer, Davies, and Dieterich, Ind. Eng. Chem. , Anal.

Ed., 2, 96-99 (1930). The point on the so tnessrtemperature curve at which the slope is 60° is determined, and the corresponding point on the temperature axis (usually abscissa) is the softening temperature.

The tensile strengths of the filaments reported herein were determined by ASTM Method D-2£8-£2T, Test No. 12-Θ-3. The moisture regain values were determined by the same Method, Test No. 8. The knot break strengths were determined by the same Method, Test No. H\.„ Prom the foregoing disclosure, it will be seen that we have produced an improved filament or film by treatment of a polymer having specified properties. Although certain process steps, structures, and examples have been disclosed for purposes of illustration, it is clear that the invention is not limited thereto. Thus the cold drawing of films can be effected both longitudinally and transversely at the same time or in all directions simultaneously, i„ee polyaxial orientation,, Film blowing or inflation techniques can be used o

Claims (13)

v · Having now particularly described and ascertained the nature of our said invention and in what manner the same Is to be performed, we declare that what we claim Iss

1. A drawn polymer, comprising a cold -drawn and pre-shrunk oleflnic polymer having a drawn thickness within the range of 0.1 to 100 mils, said polymer exhibiting substantially no shrinkage at temperatures up to 250°F„ and having a tensile strength of at least 30,000 psi at a temperature within the range of 6$° to 100°F.

2. A polymer according to claim 1, wherein said drawn polymer is in the form of a translucent to transparent filament exhibiting substantially no shrinkage when Immersed In water at a temperature up to 265°F., said filament having a tensile strength from 30,000 to 2j?0,000 psi at a temperature within the range of 65° to 100°F.

3. A polymer according to claim 1 or 2, wherein the filament diameter is within the range of 0.1 to £0 mils, said filament having a tensile strength of at least 10,000 psi at substantially 212°F0

4. I4.. A polymer according to claim 1, wherein said drawn polymer is in the form of a transparent film having a thickness in the range of 0.1 to $0 mils, said film exhibiting substantially no shrinkage when immersed in water at a temperature up to 265°P.

5. A process for drawing polymers so as to produce an Improved polymer according to any one of the preceding claims, comprising extending an olefin polymer having a density of at least 0.9i and a crystallinity of at least 70 per cent , cold drawing said extended polymer at a temperature between substantially room temperature and its softening point, heating the cold-drawn polymer at a temperature below its softening point and recovering an improved drawn polymer.

6. A process according to claim 5» wherein said cold drawing is conducted at a temperature within the range of 100° to 260eF.

7. » A process according to claim 5 or 6, wherein the extended polymer is quenched prior to being cold drawn, said quenching being carried out in a quench medium having a temperature from substantially 32° to substantially 150°F.

8. A process according, to any one of claims 5-7, wherein the cold-drawn polymer is heated at a temperature abo¾e substantially 160°F, and preferably within the range of 160° to 260°F.

9. A process according to any one of claims 5-8, wherein the extended polymer is cold drawn while being immersed in an inert fluid at a temperature above 212°F, and preferably within the range of 22 ° to 260°F.

10. A process according to any one of claims 5-9, wherein the cold drawn polymer is heated in boiling water for a period of from to 30 minutes.

11. A process according to any one of claims 5-10, wherein the extended polymer is cold drawn at a rate just below the breaking rate, said polymer being cold drawn to 5 to 10 times its undrawn length.

12. A process according to any one of claims 5-H, wherein the olefin polymer comprises polyethylene.

13. A drawn polymer substantially as hereinbefore described with reference to the Examples.