US3074616A - Article of blend of a copolymer of ethylene and 1-butene and polyisobutylene - Google Patents

Description

United States Patent poration of Delaware N0 Drawing. Filed July 13, 1959, Ser. No. 826,424 4 Claims. (Cl. 229--53) This invention relates to an improved plastic film. In one aspect the invention relates to bags fabricated from such film.

It is known in the prior art to package inorganic synthetic fertilizers such as ammonium nitrate in polyethylene bags for shipment. The polyethylene which has been used for this purpose is that polyethylene which is made by the polymerization of ethylene at high pressures of the order of 500 atmospheres and higher and in the presence of small amounts of oxygen or peroxide. Such polyethylenes have densities of the order of 0.92 gram per cc. In order to prepare satisfactory bag containers of this material it has been necessary in the past to prepare these bags from film having a thickness of at least mils. These bags are fairly expensive and are still subject to a relatively high degree of breakage during shipment. Such breakage often occurs at the seal.

In order to test the suitability of a thermoplastic film bag as a container for inorganic fertilizer materials, a test has been developed which comprises filling a bag with about 50 pounds of the fertilizer, sealing the bag, dropping the same from increasing heights to the floor, and determining the maximum height from which the filled bag can be dropped without bursting.

It is desirable that fertilizer bags be able to withstand a drop from a height of at least four feet without breakage. This is a requirement particularly for those bags which ar destined for shipment in interstate commerce.

An object of this invention is to produce an improved film. A further object of the invention is to provide a bag made of improved film. Another object of the invention is to provide a bag having a capacity of the order of 50 pounds and suitable for the shipment of synthetic inorganic fertilizers such as ammonium nitrate, ammonium sulfate and phosphates such as triple superphosphate. An additional object is to provide a bag which has improved resistance to bursting during shipment. Further objects and advantages of this invention will become apparent to those skilled in the art from a reading of this disclosure.

According to this invention there is provided a film of blended thermoplastic consisting essentially of from 65 to 75 weight percent of a copolymer of ethylene and l-butene, said copolymer having a density in the range 0.946 to 0.954, preferably 0.948 to 0.952, and from 35 to 25 weight percent, respectively, of a polyisobutylene having a Staudinger molecular weight in the range 80,000 to 200,000, preferably 120,000 to 160,000. In one modification of the invention, there is provided a fertilizer bag which is heat-scalable, Which has a capacity of the order of 50 pounds of synthetic inorganic fertilizer of the type hereinbefore described, and which is prepared from the film hereinbefore defined.

In a preferred embodiment, the invention comprises a bag made of film prepared from a blend of from 68 to 72 weight percent of the ethylene-l-butene copolymer having a density in the range 0.948 to 0.952 and from 32 to 28 weight percent, respectively, of the described polyisobutylene of molecular weight 120,000 to 160,000. In a further preferred emodiment, the invention resides in a bag prepared from a film of a blend of about 70 weight percent of the last-mentioned ethylene-l-butene copolymer and about 30 weight percent of the last-mentioned polyisobutylene.

The preferred ethylene-l-butene copolymer utilized in accordance with this invention has a density (hereinafter defined) of from 0.948 to 0.952; this represents an incorporation of from 1.5 to 1.0 weight percent, respectively, based on total monomers, of the l-butene comonomer into the copolymer molecule. Preferably, the density of the copolymer is approximately 0.950 to 0.951 and the melt index is approximately 0.3. Copolymers of this type are preferably prepared by the copolymerization of a major amount of ethylene and a minor amount of l-butene in the presence of a catalyst consisting essentially of chromium oxide supported on a silica-alumina composite, the catalyst containing at least 0.1 weight percent chromium in the hexavalent state. The total chro mium content of the catalyst is generally, though not necessarily, within the range 1 to 10 weight percent of the total catalyst. The copolymerization is frequently carried out at a temperature within the range of from about 230 to about 300 F. Ordinarily, the copolymerization is conducted in the presence of a hydrocarbon diluent which i liquid and inert under the reaction conditions. Generally, this diluent is a naphthene or a paraffin hydrocarbon having from 3 to 12 carbon atoms per molecule. Examples of such hydrocarbons are normal pentane, normal hexane, 2,2,4-trimethylpentane, cyclohexane and methylcyclopentane. The catalyst is preferably used as a granular suspension thereof in the diluent. Further details of this process can be obtained by a reading of United States Patent 2,825,721 which was issued March 4, 1958, to J. P. Hogan and R. L. Banks. Other suitable copolymers, though less preferred than those already described herein, can be obtained by the copolymerization of ethylene and l-butene at approximately the temperatures already described herein, in the presence of a catalyst prepared from or containing organometal compounds. Examples of such catalysts are those obtained by mixing, for example, triethylaluminum with titanium tetrachloride, a mixture of diethylaluminum monochloride and monoethylaluminum dichloride with titanium tetrachloride, a mixture obtained by admixing metallic aluminum with titanium tetrachloride, a mixture of ethylaluminum chloride with titanium tetrabutoxide, and similar catalysts, discussed in more detail in U.S. Patent 2,846,427, issued August 5, 1958, to R. A. Findlay, and U.S. Patent 2,827,- 447, issued March 18, 1958, to Gene Nowlin and H. D. Lyons.

The preferred polyisobutylene utilized in accordance with this invention is a normally solid polymer of isobutylene having a Staudinger molecular weight in the range 120,000 to 160,000. Examples of this type of material and the preparation thereof are discussed in U.S. Patent 2,240,582.

The blends from which the thermoplastic bags in accordance with our invention are prepared can be obtained by placing the desired quantities and proportions of the copolymer and of the polyisobutylene in a Banbury mixer (without prior heating) and mixing the materials in said mixer for a period of 5 to 7 minutes, for example, the temperature of the polymer mixture rising during this time to about 320 F. The mixture so obtained can then be sheeted on a roll mill.

An alternative method for preparing the blends consists in milling the polyisobutylene in the Banbury mixer for one minute and then adding the ethylene-l-butene copolymer and continuing the milling operation for 5 to 7 mmutes.

Still another method of preparing the blends according to this invention comprises chopping the polyisobutylene into small particles (e.g. to 4 inch maximum dimension), dry-blending the chopped polyisobutylene with the rd ethylene-l-butene copolymer in the form of pellets (e.g. x A; inch cylinders) in a kneader or extruder, extruding the blend through dies, and cutting the extrudate into cylindrical pellets.

ithe presence of a catalyst comprising approximately 2.5 weight percent chromium as oxide supported on a silicaalumina carrier and containing at least 0.1 weight percent hexavalent chromium. In the product polymer, approxi- The thermoplastic blend can be fabricated in the form mately 1.0 to 1.5 percent of the monomer units in the of film by any method known in the prior art for making polymer are butene-l-units. thermoplastic film. One method which we have found The ethylene homopolymer referred to in Test No. 4 satisfactory is to extrude the polymer blend, e.g. at 315 is produced by polymerizing ethylene in the presence of to 350 F., in the form of a hollow tube. The end of a chromium oxide catalyst of the type hereinbefore spethis tube is then closed, and the tube is inflated to from cified at a temperature of approximately 285 F. 1 /2 to 3 times its extruded diameter. The film is prefer- The polyisobutylene referred to in the subsequent tabuably produced in thicknesses of from 4 to 9 mils, preferlation is a commercial, normally solid polyisobutylene ably 5 to 7 mils. Other methods of producing film known sold under the trade name Vistanex. in the art are also satisfactory for use in accordance with The following tabulation illustrates 3 specific embodithe present invention. ments of our invention (Tests 5-7) and shows a compari- Tne extended film is often obtained in the form of a son of the bags in accordance with our invention with tube which can be closed by sealing one end to form an other and related materials. open bag. After the bag has been filled, the open end The blends described in the following tabulation were can also be sealed. The sealing can be effected by purely prepared by blending /s x /s inch cylindrical. pellets of thermal methods such as the use of a hot bar sealer, the the ethylene homopolymer or copolymer with a block use of an impulse type sealer, or by the use of adhesives (about 0.5 cu. ft.) of the polyisobutylene of desired weight or a pressure-sensitive tape. in an initially unheated Banbury mixer for about 5 min- Stabilizers or other additives can be incorporated into utes. The resulting blends were extruded at about 330 the blend from which the films are formed in accordance F. to form tubes which were then inflated with air to with this invention in order to stabilize the polymers about double their extruded diameter.

D,gm. Thick- Drop Test Nature of Film per cc. ness, Test, Other Observations M Mils Feet 1 High-pressure homopolymer ofethylenc 0.02 10 12 15-30 percent breakage during shipment. 2 Same as Test1 0.92 10 Could not be handled manually with- 1 out fingers punching through. 3 Ethylene-l-butene copolymer a; 0.948 10 4 4 Blen 70 wt. percent ethylene homopolymer 0.944 5 4 Extensive breakage at creases.

(density, 0.960; melt index 0.2)+ wt. percent polyisobutylene (mol. wt. 120,000). 5 Blend 75 wt. percent copolymer. of ethylene and 1- 5-7 14 Bag stretched at 140 F.

butane (density, 0,951 ;.n1elt index O.3)+25 wt. percent polyisobutylene (mol. wt. 120,000). g 6 Blend of 70 wt, percent ethylene-l-butene copolymcr 0.938 5-7 14 Substantially no stretching at, 140 F.

(density, 0.951; melt index 0.3)+30 wt. percent 4.5 percent breakage during shippclyisobutylene (120,000 mol. wt.). ment. 7 Same asflest 6, except polyisobutylene mol. wt. 7 32 Filled with lb. polyethylene (denbetween 140,000 and 160,000. (dgopped 3113131 8.960), cylindrical M; x inch wice pc e s.

against the deteriorative action of heat, ultraviolet light and other degradative action. Furthermore, pigments or fillers can be added to these blends if desired. A

Several specific embodiments of our invention are described hereinafter. In the described tests, various testing procedures were applied to bags made from films of dilferent thermoplastic polymer compositions. These bags were filled with prilled ammonium nitrate fertilizer and tested as described herein. I

The drop tests is that test, previously referred to herein, which consists in filling the bag to be tested with 50 pounds of prilled ammonium nitrate, sealing; and dropping the sealed and filled bag from measured increasing heights until the bag bursts upon dropping. The maximum height from which the bag can be dropped twice without bursting is reported as the drop test. I This height is given in feet. In the breakage tests during shipment referred to hereinafter, large lots of the prilled ammonium nitrate were bagged in 50 pound units and were shipped, in freight cars from Cactus,Texas, to Argo, Minnesota. The percentage breakage figure is the percentage of the total number of shipped bags which broke in transit.

In the following description, ,the high-pressure homopolymer of ethylene described in the subsequent tabulation is one which is marketed for the purposes of. forming bags and is produced by high-pressure (ie 500 atmospheres or higher) polymerization of ethylene in the presence of small amounts of oxygen or a peroxide. I

The ethylene-l-butene copolymers described in the subsequent tabulation were obtained by copolyrnerizing an ethylene-l-butene mixturecontaining approximately 2 to 10 mol percent of l-butene at about 250 to 275 F. in

The foregoing data clearly demonstrate that the bags in accordance with our invention are far superior, as regards breakage resistance, to the high-pressure homopolymers of ethylene which were tested in accordance with Tests 1 and 2. Not only was the breakage resistance of the bags in accordance with our invention superior, but the bags in accordance with our invention can safely be produced and used in thicknesses far less than are utilizable with the high pressure homopolymers. This results in a decrease in the weight and in the volume of the material to be shipped and resultant savings to the shipper;

The data further show that the blends in accordance with our invention are far superior in burst strength to the ethylene-l-butene copolymer alone, which was tested in accordance with Test 3.

The data further show that the bags in accordance with our invention are far superior, as regards breakage, to bags fabricated from a film of ethylene homopolymer produced in a manner similar to the copolymer in accordance with our invention blended with the same amount of polyisobutylene, as shown in Test No. 4.

The data also illustrate the preferred nature of the bags in accordance with our invention which contain 70 percent of the copolymer and 30 percent of the polyis'obutylene (Test 6). A comparison of Test 6 with Test 5 shows that, whereas the 75/25 blend produced bags which had a highly satisfactory drop test, the bags exhibited some stretching when subjected to temperatures of approximately F. These bags, although satisfactory, were not so good as those illustrated in Test 6.

In connection with Test 6, all of the bags which broke during shipment broke along the seal, and it appeared that these breaks were due to the fact that solid matter from the bag contents was not properly removed from the sealed surfaces prior to sealing, in those bags which broke.

The density referred to herein, is determined by ASTM Method D 1505-57T which defines the density of plastics as the weight per unit volume of material at 23 C. Ethanol and water were used as the suspending liquids. The samples used for density determination are prepared by compression-molding molten pellets of the ethylene polymer to form a slab about 6 inches square and to /2 inch thick. The slabs are molded at 20,000 psi. and 330 F. The heat is then turned or'f. Tap water is circulated through the mold cooling system. The slab is cooled to 200 F. at the rate of 25 F. per minute, and then to 150 F. as rapidly as possible by increasing the flow rate of the cooling water. The slab is then removed from the mold and allowed to stand for 24 hours at room temperature. Small pieces of the slab, e.g. about /4 inch squares, are cut ofi for the density determination. These pieces are examined to be sure that they have no surface pits or other features which might occlude or entrap air when immersed in liquid.

The molecular weight of polyisobutylene, as referred to herein, is based on viscosity determination and is determined in accordance with the Staudinger method described by P. I. Flory, J. Am. Chem. Soc. 65, 372-382 (1943).

The melt index, as referred to herein, is determined in accordance with ASTM Method D 1238-52T.

While numerous examples, process steps, and compositions have been specifically described herein for purposes of illustration, it will be clear to those skilled in the art that the invention is not limited thereto.

We claim:

1. A film of blended thermoplastic consisting essentially of from 68 to 72 weight percent of a copolymer of ethylene and l-butene, said copolymer having a density in the range 0.948 to 0.952 at 23 C., and from 32 to u 28 weight percent, respectively, of a polyisobutylene having a molecular weight in the range 80,000 to 200,000 based on viscosity determination.

2. A bag having a wall thickness in the range 4 to 9 mils and fabricated from a film of blended thermoplastic consisting essentially of from 68 to 72 Weight percent of a copolymer of ethylene and l-butene, said copolymer having a density in the range 0.948 to 0.952 at 23 and from 32 to 28 weight percent, respectively, of a polyisobutylene having a molecular weight in the range of 80,000 to 200,000 based on viscosity determination.

3. A bag having a wall thickness in the range 5 to 7 mils and fabricated from a film of blended thermoplastic consisting essentially of 70 weight percent of a copolymer of ethylene and l-butene, said copolymer having a density in the range 0.948 to 0.952 at 23 C., and about 30 weight percent of a polyisobutylene having a molecular weight in the range 80,000 to 200,000 based on viscosity determination.

4. A bag having a wall thickness in the range 5 to 7 mils and fabricated from a film of blended thermoplastic consisting essentially of 70 weight percent of a copolymer of ethylene and l-butene, said copolymer having a density of from 0.950 to 0.951 at 23 C., a melt index of 0.3, and 30 weight percent of a polyisobutylene having a molecular weight in the range 120,000 to 160,000 based on viscosity determination, said bag having a capacity of approximately pounds of granular ammonium nitrate.

References Cited in the file of this patent UNITED STATES PATENTS 2,369,471 Latham Feb. 13, 1945 2,414,300 Hamilton Jan. 14, 1947 2,727,024 Field et a1. Dec. 13, 1955 2,788,340 Dannels Apr. 9, 1957 2,825,721 Hogan et al Mar. 4, 1958 2,854,435 Briggs et a1. Sept. 30, 1958

Claims (1)

1. A FILM OF BLENDED THERMOPLASTIC CONSISTING ESSENTIALLY OF FROM 68 TO 72 WEIGHT PERCENT OF A COPOLYMER OF ETHYLENE AND 1- BUTENE, SAID COPOLYMER HAVING A DENSITY IN THE RANGE 0.948 TO 0.952 AT 23* C., AND FROM 32 TO 28 WEIGHT PERCENT, RESPECTIVELY, OF A POLYISOBUTYLENE HAVING A MOLECULAR WEIGHT IN THE RANGE 80,000 TO 200,000 BASED ON VISCOSITY DETERMINATION.