POLYMERIC PLASTICIZERS FOR POLYVINYL CHLORIDE

Abstract: Blends of polyvinyl chloride with E/X/Y terpolymers, in which X is a C1-C10 n-alkyl acrylate and Y is CO or SO2, the terpolymers having a swelling ratio of no more than 2.14, can be calendered into smooth sheets, which are suitable for use in such applications as instrument panel skins, pond liners, roofing membranes, etc.

Description: TITLE POLYMERIC PLASTICIZERS FOR POLYVINYL CHLORIDE BACKGROUND OF THE INVENTION This invention relates to certain polyvinyl chloride compositions having improved properties and processability consisting essentially of blends of polyvinyl chloride with plasticizers which are members of a class of defined terpolymers. It is known in the art to add plasticizers to polyvinyl chloride (PVC) to improve its flexibility. Although various plasticizers have been used in such applications, certain ethylene terpolymers of the general formula E/X/CO, where E is ethylene, and X is a "softening" monomer such as, for example, vinyl acetate or an acrylic ester, have been found to be particularly suitable for this purpose. Such terpolymers and their use as plasticizers for PVC are described in U.S. Patent 3,780,140 to Hammer. Because of their polymeric nature, these materials do not have the tendency, exhibited by conventional aromatic ester type plasticizers, of exuding or evaporating with time from PVC, which would make PVC brittle and unsuitable for many applications. These polymeric plasticizers have the additional advantage that they are completely compatible with PVC within rather broad composition ranges. Terpolymers having the same general structure, but with the SO2 group replacing the CO group, have been disclosed in U.S. Patent 3,684,778 to Hammer and are suitable for the same purpose. Nevertheless, calendered sheets made of PVC plasticized with acrylic ester-containing terpolymers described in the above two patents generally are rough, rather than smooth. This means that those blends have "high nerve". It would be desirable, therefore, to be able to plasticize PVC in a manner which would permit the plasticized polymer to be calendered into smooth sheets. SUMMARY OF THE INVENTION According to this invention, it has now been unexpectedly discovered that there is a correlation between roughness of calendered sheets of a blend of PVC with an E/X/Y terpolymer, where Y is CO or SO 2 , and terpolymer's swelling ratio, which is defined as the ratio of the maximum diameter of terpolymer extruded from a standard melt indexer to that of the indexer's orifice under standardized conditions, so that the smaller that ratio, the lower is the "nerve" of sheets calendered from such blends. In particular, there is provided a blend of PVC with a terpolymer represented by the general formula E/X/Y, wherein E is ethylene; X is a Ci-Cio n-alkyl acrylate; and Y is CO or SO 2 , the respective weight proportions of the comonomers other than ethylene in this terpolymer being 5-60/3-20%, ethylene constituting the balance (100% -X -Y) , said terpolymer having a swelling ratio of at most 2.14, and the amount of the terpolymer in the blend being about 20-400 parts by weight per 100 parts by weight of PVC. Further, there is provided a smooth sheet calendered of such a blend. DETAILED DESCRIPTION OF THE INVENTION The goal of the invention is to provide a blend of PVC with a defined E/X/Y terpolymer having a maximum swelling ratio of 2.14. Swelling ratio is discussed in the article entitled "A Computerized System for Measurement of Transient and Equilibrium Extrudate Swell" by M. R. Ka al et al. in Advances in Polymer Technology, vol. 8, No. 4, pp. 367-381 (1988), John Wiley and Sons, Inc. It is believed that there is a correlation between the swelling ratio of a terpolymer and terpolymer branching, although the exact nature of this correlation has not been rigorously established. Generally, one skilled in art of homopolymerization and copolymerization of ethylene will know how the process conditions must be modified to make a terpolymer having the desired swelling ratio. For example, it is generally assumed that, when the feed temperature is kept constant, a decrease of the reactor temperature will produce a polymer which will have less branching or less long chain branching, or will be less affected by branching; under these conditions, the swelling ratio will tend to decrease. However, decreasing the reactor temperature has its drawbacks, since it reduces the polymer yield and increases reactor fouling, especially in the presence of highly reactive co onomers. This problem can be overcome by maintaining or increasing the reactor temperature but then increasing the feed temperature, so that the temperature differential, ΔT, is decreased. The lower ΔT, the smaller will be the swelling ratio. It is preferred to operate the polymerization process at a reactor temperature of about 140-195"C, especially at 160-170°C, and at a ΔT of about 80-150°C, especially at about 100-120°C. Further, it is preferred that the terpolymer used as the plasticizer be manufactured by a continuous process, below the maximum conversion attainable for a given type of terpolymer. For an E/X/Y terpolymer in which Y is CO, the maximum attainable conversion (determined on the basis of the weight of terpolymer produced, relative to the weight of monomers introduced into the reactor during a given time interval) may be as high as 14-15%, while the preferred maximum conversion is about 11.5 + 1. The basic operation of the process is the same as described, e.cr. , in U.S. 3,780,140, which is incorporated herein by reference. It is a free-radical intitiated, preferably high pressure process. Howevex, contrary to the conventional wisdom regarding free-radical polymerizations, the process of this invention is not run to maximum conversion. Conventionally, it is considered advantageous to operate a polymerization process at maximum conversion because this reduces the number of passes and the amount of monomer feed that must be recycled. The limiting conditions usually are the monomer recycle rate, or, in the case of E/X/Y terpolymers used in this invention, the CO or SO 2 feed rate, or the amount of heat generated by the polymerization reaction. However, according to the present invention, the terpolymer used in blends with PVC is produced at a conversion which does not exceed about 80% of the maximum attainable value. The low conversion reduces the production rate and thus increases the production cost, but it results in significantly improved properties of calendered sheets made from PVC plasticized with these terpolymers. It is not certain why terpolymers produced under these conditions impart those improved properties to the blends, but it is believed that such conditions decrease branching and particularly long chain branching, as compared with copolymerization run at full conversion and at a higher temperature or at a higher ΔT. Since the type and amount of branching itself cannot be directly determined, it is necessary to resort to the determination of the above-defined maximum swelling ratio for comparing the terpolymers made under different conditions and selecting those that perform satisfactorily in blends with PVC. The maximum swelling ratio value of 2.14 has thus been established empirically. One skilled in the art will be able to adjust the conversion and the reactor temperature or ΔT so as to produce a terpolymer having a swelling ratio of 2.14 or less. One would need to run only a very limited number of trial experiments to determine the optimum polymerization conditions for providing at a satisfactory conversion a terpolymer having an acceptable swelling ratio. Since there is a trade off between the polymer properties and the production rate, one would naturally wish to operate at as high a conversion as possible. Similarly, because of reactor fouling at lower temperatures and/or at lower ΔT's, one would wish to operate at as high a reactor temperature as possible. Another factor which influences the swelling ratio is the " amount of CO or SO2 in the terpolymer. The preferred amount of CO in the terpolymer is 15% by weight or less, especially about 10%. At higher CO or SO2 levels, the thermal stability of the E/X/Y terpolymer tends to deteriorate to an unacceptable degree. These copolymerizations always are run in the presence of a chain transfer agent (telogen) , which may be any one of a number of known compounds normally used in such reactions, for example, propane, methanol, or acetone. A polar telogen, especially acetone, is preferred because it also acts as a solvent for the terpolymer and thus reduces reactor fouling. A significant amount of telogen, for example, 12-20 weight percent of the reactor contents can be used. Generally, the copolymerization conditions are in many respects similar to those used for the preparation of low density polyethylenes and would be well understood by a polymer chemist or a chemical engineer, who would be able to modify them as required to suit his or her particular needs. PVC plasticized with terpolymers whose swelling ratio does not exceed about 2.14 can be calendered into smooth sheets, which can be used in such applications as, e.g. , instrument panel skins, pond liners, and roofing membranes. While it would be generally expected that terpolymers of the type contemplated by the present invention, and frequently other copolymers as well, would tend to have lower swelling ratios when made at lower conversions and at lower reactor temperatures or at lower T's, the present inventor has surprisingly recognized the effect of branching on the "nerviness" of blends of these terpolymers with PVC. An additional benefit of at least some of the blends of this invention is that they also have very good low temperature properties, but all have improved thermal stability, especially when compared with blends of PVC with certain E/VA/CO terpolymers, where VA stands for vinyl acetate. PVC blends with E/VA/CO are now well established commercially as popular plasticized PVC compositions for general use. Particularly good low temperature properties are exhibited by blends of PVC with E/nBA/CO terpolymer, where nBA stands for n-butyl acrylate. The lowest member of this class of terpolymers, where the acrylic ester is methyl acrylate, does not impart to PVC blends improved low temperature properties; yet, it still offers improved thermal stability and the ability of the blends to be calendered into smooth sheets. Typical n-alkyl acrylates suitable in this invention include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, and octyl acrylate. Branched alkyl acrylates give terpolymers which form blends with PVC that have high nerve properties and cannot.be calendered into smooth sheets. Although the amount of terpolymer plasticizers in blends with PVC may vary over broad ranges, the preferred range is about 20-150 parts of terpolymer per 100 parts of PVC. The properties of the articles made from PVC blends of the present invention will also to some extent depend on the respective monomer ratios of the terpolymer plasticizers. For example, for limp compositions, the respective monomer weight ratios other than ethylene in the E/X/Y terpolymer will be about 10-60/10-20, while for rigid or semirigid articles, they will be about 5-25/3-7. This invention is now illustrated by the following examples of certain preferred embodiments thereof, where all parts, proportions, and percentages are by weight, unless otherwise indicated. The terpolymers were prepared according to the general process and in the equipment described in U.S. 3,780,140 and 3,684,778. Commercial ethylene, carbon monoxide, and pure n-alkyl acrylate were fed in a continuous manner to a stirred pressure vessel. Free-radical initiator was fed by a separate line. The flow of monomers was adjusted to give constant molar ratios, and the feed rate was the same as the rate of discharge of polymer and of unchanged monomers from the reactor. Allowance was made for the different rates of polymerization of the various comonomers, so that none of them was depleted. The polymerization initiator was a commercial peroxide. A small amount of a telogen (chain transfer agent) also was introduced into the reactor with the feed monomers to control the molecular weight. The components and the experimental conditions are shown in the following Table I, where Examples 1-11 are within the scope of the present invention, while C1-C19 are comparative examples, either based on the conventional techniques of polymerization to high conversion or on the use of a branched acrylate or of vinyl acetate. The following abbreviations are used in Table I: E = ethylene nBA = n-butyl acrylate EA = ethyl acrylate VAc = vinyl acetate MA = methyl acrylate IBA = isobutyl acrylate All acrylic esters as well as vinyl acetate contained polymerization inhibitors and were used as received, without purification. Commercial polymerization initiators used in the experiments are designated as follows: A = di(sec-butyl) peroxydicarbonate solution in an 80/20 mixture of t-butyl alcohol/methanol. B = t-butyl peroctoate solution in an 80/2Q mixture of t-butyl alcohol/methanol. Table II provides the compositions, melt indices, and swelling ratios of the resulting terpolymers, while Table III gives the appearance of calendered sheets made from blends of 100 parts of PVC with 80 parts of terpolymers, as well as (for most terpolymers) torsional modulus values at five temperatures. In all the Tables, results originally obtained in units other than SI have been converted to the SI units. The swelling ratios were determined according to a method developed in the laboratories of the assignee of the present invention. A standard melt indexer constructed and operated according to the requirements of ASTM D-1238 is used. The diameter of the melt indexer's orifice is 0.0825 inch (2.096 mm). The temperature is adjusted to 115°C and maintained within ± 2°C. A 6.5-7 g sample of polymer blend is charged into the indexer in less than 60 seconds. The sample is preheated for 6 minutes without applying external force. The sample extruded during that period is cut off and discarded. Material is allowed to extrude through the orifice until about 2.5-3.8 cm of extrudate has been obtained. This extrudate is cut off and allowed to cool for at least 10 minutes. The average diameter of the forward end (about 9-10 mm) is measured with a micrometer. The swelling ratio is calculated as the ratio of the average diameter to the diameter of the orifice. TABLE I TERPOLYMER SYNTHESIS Initiator Feed Rates (kα/hr) 'or Relative Rates(r) Example Polymer Telogen Comp. Concn (ppm) Monomers Telogen Init. so 1 E/nBACO Methanol A 1885 5.67 0.33 0.19 1.20 0.12 2 E/nBA/CO Acetone B 394 5.67 0.32 0.17 0.30 0.073 3 E/MA/CO Methanol A 471 5.67 0.32 0.15 0.73 0.21 4 E/EA/CO Mόthanol A 471 5.67 0.23 0.12 0.89 0.29 5 E/nBA/CO Acet/Meth B 394 5.67 0.34 0.15 0.32 0.068 (90/10) 6 E/EA/CO Methanol A 471 5.67 0.35 0.17 0.37 0.30 7 E/nBA/CO Propane A 942 5.68 0.26 0.13 0.91 0.14 8 E/nBA/CO Acet/Meth A 942 5.68 0.25 0.12 0.35 0.050 (90/10) 9 E/nBA/CO Acet/Meth A 471 5.68 0.26 0.11 0.30 0.10 (90/10) 10 E/nBA/CO Acet/Meth A 471 5.68 0.24 0.10 0.43 0.091 (90/10) 11 E/nBA/CO Acetone A 942 6.26 0.29 0.11 0.40 0.091 Cl E/nBA/CO Methanol A 1885 5.67 0.32 0.17 1.16 0.29 C2 E/nBA/CO Acet/Meth B 197 5.67 0.41 0.22 0.42 0.17 C3 E/nBA/CO Propane [12.77 0.96 0.38(r)] [0.99(r)] TABLE I - Continued TERPOLYMER SYNTHESIS Initiator Feed Rates (kg/hr) or Relative Rates(r) Example ! Polymer Telogen Comp . ( _.oncn Monomers Telogen Init. so C4 E/VAc/CO Propane [11.77 4.95 0.35(r)] [0.395(r)] C5 E/MA/CO Methanol A 942 6.35 0.53 0.29 0.52 0.54 C6 E/MA/CO Methanol A 1649 6.35 0.97 0.27 0.53 0.37 C7 E/EA/CO Methanol A 1649 6.35 1.06 0.27 0.50 0.30 C8 E/EA/CO Methanol A 1649 6.35 0.91 0.27 0.51 0.33 C9 E/VAC/CO - B 1972 6.35 3.18 0.20 None 0.03 C10 E/VAc/CO - B 1972 6.35 3.22 0.19 None 0.03 Cll E/VAC/CO - B 1972 6.35 3.26 0.23 None 0.16 C12 E/VAC/CO - B 1972 6.35 3.48 0.19 None 0.22 C13 E/IBA/CO - B 592 4.54 0.49 0.14 None 0.05 C14 E/IBA/CO Cyclohexane B 592 4.54 0.45 0.17 0.045 0.08 C15 E/IBA/CO Cyclohexane B 592 4.54 0.40 0.22 0.17 0.11 C16 E/IBA/CO Cyclohexane B 592 4.54 0.66 0.20 0.20 0.07 C17 E/IBA/CO Cyclohexane B 592 4.54 0.51 0.18 0.31 0.02 TABLE I - Continued TERPOLYMER SYNTHESIS Initiator Feed Rates (kg/hr) or Relative Rates(r) Example Polymer Telogen Comp. Concn (ppm) Monomers Telogen Init. so C18 E/IBA/CO Cyclohexane 4.54 0.50 0.15 0.19 0.02 C19 E/nBA/CO Acet/Meth A 942 5.68 0.19 0.19 0.30 0.09 (90/10) TABLE I - Continued TERPOLYMER SYNTHESIS Press. Agitat. Monomer Reactor Example MPa) rpm Inlet Temp Temp (°C) ΔT Conver. ( 2 ) 1 172.3 2400 34 161 127 11.1 2 172.3 2400 60 192 132 9.1 3 172.3 2400 59 162 103 6.2 4 172.3 2400 60 160 , 100 6.9 5 172.3 2400 60 190 130 8.0 6 172.3 2400 32 189 157 11.7 7 186.2 2330 30 160 130 7.7 8 186.2 2420 30 160 130 6.5 9 186.2 2430 50 160 110 5.7 10 186.2 2345 50 160 110 5.8 11 186.2 2320 30 160 130 7.4 Cl 172.3 2400 13 159 146 13.2 C2 172.3 2400 25 190 165 10.5 C3 186.2 — 50 190 140 — C4 165.5 __ 55 190 135 —— TERPOLYMER SYNTHESIS AND PROPERTIES Press . Agitat. fMPal Monomer rom Reactor Inlet Temp TemD (°c) ΛT Conver. C 1 ) 172. 3 2400 20 189 169 17.2 172.3 2400 10 191 181 16.8 172. 3 2400 17 190 173 16.4 172.3 2400 10 190 180 17.3 172.3 1880 50 191 141 8.7 172.3 1840 31 190 159 10.1 172.3 1885 10 189 179 11.8 172.3 1888 2 190 188 12.5 172 .3 2335 32 186 154 13.0 172 . 3 2370 31 186 155 12.8 172 .3 2340 29 187 158 11.0 186.2, 2340 60 185 125 9.3 186.2 2340 60 185 125 6.9 186.2 2340 63 188 125 6.3 C19 186.2 2200 ( 1 ) - Approximate +1. 0% 30 160 130 5.8 TABLE II POLYMER PROPERTIES E/X/Y Swelling Example Composition MI Ratio 1 54.8/32.3/13 19.1 1.98 2 60.4/30.1/9.5 21.1 2.05 3 54.8/31.5/10.1 6.3 1.88 4 42.2/39.6/18.2 19.7 1.88 5 55.8/33.2/11 13.6 2.13 6 47.8/37.5/14.7 21.2 2.12 7 57.3/32.2/10.5 4.6 2.01 8 55.1/33.1/11.8 6.3 1.91 9 53.5/35.0/11.5 5.3 1.86 10 56.9/32.1/11.0 17.8 1.84 11 58.6/32.8/8.6 8.3 1.89 Cl 53.8/29.6/16.6 19.8 2.18 C2 48/39.8/12.2 26.1 2.38 C3 60/30.6/9.6 8.3 2.38 C4 62.5/28.5/9.0 37.2 1.97 C5 59.5/29.1/11.4 24.2 2.37 C6 61.2/27.2/11.6 19.3 2.29 C7 56.3/32.1/11.6 27.4 2.34 C8 58.2/30.1/11.7 40.4 2.24 C9 60.2/28.9/10.9 17.5 1.92 CIO 60.8/29.6/9.6 23.3 1.94 Cll 58.5/30.9/10.6 20.5 2.01 C12 60.5/29.6/9.9 22.6 2.07 C13 60.5/29.6/9.9 3.5 2.38 C14 60.5/29.6/9.9 3.5 2.34 C15 60.5/29.6/9.9 0.4 2.43 C16 48.8/39.3/11.9 3.2 2.42 C17 49.7/38.2/12.1 3.3 2.41 C18 54.2/35.8/10.0 9.5 2.20 C19 52.1/32.3/15.6 15.7 2.18 TABLE III BLEND PROPERTIES Appearance Torsion Modulus, (MPa) Example Milled Sheet 25°C 10°C 0°C -10°C -20°C 1 Smooth 2.63 6.50 34.7 162.5 327.5 2 Smooth 5.92 19.94 63.9 188.7 354.6 3 Smooth 3.93 16.71 124.3 354.6 491.4 4 Smooth 3.91 12.63 100.6 269.5 449.3 5 SI. Rough 3.14 6.97 30.7 132.9 323.4 6 Si. Rough 3.91 10.90 56.3 232.8 430.2 7 Smooth 8 Smooth 9 Smooth 10 V. Smooth 11 Smooth Cl Si. Rough 5. 01 18.76 75.2 239.1 371. 3 C2 Rough 2 . 82 8.28 42.1 171.4 330 .5 C3 Rough 3 . 18 8.62 40.0 170.4 345. 5 C4 Smooth 7 . 26 26.66 115.2 291.5 TABLE III - Continued BLEND PROPERTIES Appearance Torsion Modulus, (MPa) Example Milled Sheet 25°C 10°C 0°C -10°C -20°C C5 Rough 3.87 14.76 104.9 330.0 493.8 C6 Rough 4.67 17.72 99.7 343.8 517.7 C7 Rough 4.68 8,28 49.4 200.2 414.9 C8 Rough 4.60. 11.52 61.8 227.4 421.6 C9 Smooth 3.63 14.9 101.4 300.9 467.8 CIO Smooth 4.66 17.1 112.7 315.5 478.15 Cll V. SI. Rough 3.66 18.76 118.5 333.7 510.3 C12 V. SI. Rough 5.15 17.10 106.6 333.5 503.3 C13 Rough C14 Rough C15 Rough C16 Rough C17 Rough C18 Rough C19 Rough

Claims: WE CLAIM: 1. A composition consisting essentially of a low nerve blend of polyvinyl chloride with a terpolymer having the general formula E/X/Y, wherein E is ethylene; Y is CO or SO 2 ; and X is a C =Cιo n-alkyl acrylate, said terpolymer having been produced by a free-radical initiated continuous copolymerization of its E, X, and Y comonomers at a less than maximum attainable conversion for the given X comonomer under the polymerization conditions and having a maximum die swell ratio of about 2.14; the respective weight proportions of these comonomers other than ethylene being 5-60/3-20 percent, ethylene constituting the balance, 100% -X -Y; said blend comprising about 20-400 parts by weight of the E/X/Y terpolymer per 100 parts by weight of polyvinyl chloride. 2. A composition of Claim 1 wherein the terpolymer E/X/Y has been produced at a temperature differential between the feed temperature and the terpolymer discharge temperature of about 80-150°C, preferably 100-120 β C. 3. A composition of Claim 2 wherein the terpolymer X/Y/Z has been produced at a conversion not over about 80% of the maximum attainable conversion for the particular terpolymer composition. 4. A composition of Claim 4 wherein Y is CO and the terpolymer has been produced at a conversion of about 11.5 ± 1%. 5. A composition of Claim 2 wherein the reactor temperature is about 140-195°C, preferably 160-170°C. 6. A composition of Claim 1 wherein X is methyl acrylate, ethyl acrylate, or butyl acrylate, and Y is CO. 7. A calendered sheet made from a low nerve blend of polyvinyl chloride with a terpolymer having the general formula E/X/Y, wherein E is ethylene; Y is CO or SO2; and X is a Cτ_-Cιo n-alkyl acrylate, said terpolymer having been produced by a free-radical initiated continuous copolymerization of its E, X, and Y comonomers at a less than maximum attainable conversion for the given X comonomer under the polymerization conditions and having a maximum die swell ratio of about 2.14; the respective weight proportions of the comonomers other than ethylene being 5-60/3-20 percent, ethylene constituting the balance, 100% -X -Y; said blend comprising about 20-400 parts by weight of the E/X/Y terpolymer per 100 parts by weight of polyvinyl chloride. 8. A calendered sheet of Claim 7 wherein the E/X/Y terpolymer has been made at a temperature differential between the feed inlet temperature and the polymer discharge temperature of at most about 80-150°C, preferably 100-120°C. 9. A calendered sheet of Claim 8 wherein Y in the E/X/Y terpolymer is CO and the terpolymer has been made at a conversion no higher than about 11.5 + 1%, determined from the weight of the terpolymer produced relative to the weight of monomers introduced into the reactor during a given time interval. 10. A calendered sheet of Claim 7 wherein the E/X/Y terpolymer has been made at a reactor temperature of about 140-195°C, preferably 160-170°c 11. A calendered sheet of Claim 7 wherein the comonomer X in the E/X/Y terpolymer is methyl acrylate, ethyl acrylate, or n-butyl acrylate, and Y is CO.

Inventors: CASE ROBERT BURTON, STATZ ROBERT JOSEPH, CASE, ROBERT, BURTON, STATZ, ROBERT, JOSEPH
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1990
Main classification: C08L81
IPC codes: C08J5, C08L23, C08L27, C08L31, C08L33, C08L73, C08L81