PROCESS FOR PRODUCING IONOMERS OF LOW MOLECULAR WEIGHT ACID COPOLYMERS

Abstract: High viscosity ionomer compounds are produced from low molecular weight organic copolymers having an acid moiety. The compounds of the invention are high viscosity ionomer salts which are the reaction product of a metal base and the low molecular weight acid copolymer. The ionomers are produced at a reduced cycle time and lower reaction temperature by an intensive mixing of the viscous products by a high shear mixer. The process uses lower temperatures and cycle times to produce high viscosity ionomers which also have a reduced number of polymer gels and base particles.

Description: PROCESS FOR PRODUCING IONOMERS OF LOW MOLECULAR WEIGHT ACID COPOLYMERS BACKGROUND OF THE INVENTION Field of the Invention The invention relates to ionomers and to a method of producing such ionomers. More particularly, the invention pertains to high viscosity ionomers which are produced from low molecular weight copolymers having a acid moiety. In the preferred embodiment the ionomers of the invention are high viscosity ionomer salts which are the reaction product of a metal base and a low molecular weight copolymer of an alpha-olefin and an acid. The ionomers are produced at a reduced cycle time and lower reaction temperature by an intensive mixing of the viscous products with a high shear intensive mixer. Description of the Prior Art Ionomers are formed from organic polymers which are copolymerized with a minor proportion of an acid to provide a copolymer having an acidic moiety. These are then neutralized with a metal or quaternary ammonium base to incorporate metal or ammonium ions into the polymer. Ionomers are known in the art to be useful as lubricants for plastics and as carriers for plastic additives and colorants. U.S. patent 5,130,372 discloses certain low molecular weight ionomers which contain an amide group. U.S. patent 4,412,040 discloses other ionomers which are useful as lubricants for plastic processing. These patents are incorporated herein by reference. Due to the relatively low viscosity of prior art ionomers, it has been necessary to produce them by use of a stirring process. Paradoxically, the very use of stirring reactors has limited the production of ionomers to those having low viscosities. The incorporation of metal ions into the copolymer invariably causes an increase in viscosity, however, since stirring reactors can only process materials having a relatively low viscosity, diluents and plasticizers have been used to reduce ionomer viscosity. It would be desirable to produce ionomers which are substantially higher in viscosity than those which are currently known in the art. Although it would be desirable to produce high viscosity ionomers, preparing them has been considered a problem since stirring reactors are unsuitable for high viscosity compositions. As an example, the ionomers of U.S. patent 4,412,040 have a viscosity which is about an order of magnitude below those of this invention. Producing high viscosity ionomers had been considered difficult since, while the initial viscosity of the ionomers is low, the final viscosity is much higher and hence not processable in a simple stirring reactor. While the aforesaid diluents and plasticizers have been used to reduce ionomer viscosity, the resulting lower viscosity ionomers have limited compatibility with other polymers with which blending would be desirable. It is known that the amount of lubricant required for processing polymers is important. Too much lubricant causes polymer slippage through the barrel of an extruder which results in processing inefficiencies. The ionomers produced by the improved process of this invention have an enhanced viscosity range and hence better compatibility with a wider assortment of polymers such as styrenics, polyamides, polyesters and olefins. They are viscous enough to be used in plastics equipment alone or in combination with other plastics without the slippage problems that over-lubrication can cause. The ionomers of this invention are compounds to which plastic additives and/or colorants can be added during the final stages of manufacture to produce concentrates of the additive or colorant. The concentrate has the necessary properties which allow it to be extruded and formed to a specific shape, or to be let-down at high concentration into a variety of plastics for extrusion and shaping. The ionomers can be produced at reduced temperatures without increasing preparation time. Unwanted gel and color formation has also been a problem with prior art ionomers. Some commercially produced ionomers have gels that render the product unfilterable and hence unusable in some fiber applications. These gels are believed to be created from copolymer crosslinking by the high temperature and long cycle time of current manufacturing methods in stirred reactors. It would be desirable to produce high viscosity, low molecular weight ionomers by a process which uses lower temperatures and cycle times than the prior art and which ionomers also have a reduced number of polymer gels. SUMMARY OF THE INVENTION The invention provides a method of producing ionomers which comprises forming a blend of a melt of a copolymer or terpolymer having an acid moiety with a metal or quaternary ammonium containing base in an amount sufficient to neutralize the acid moiety and subjecting the blend to a high shear mixing to provide a mixing work to the blend of from about 5.9 x 10 5 Joules/Kg to about 2.1 x 10 7 Joules/Kg over a period of from about 60 minutes to about 480 minutes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The ionomers of this invention are formed from organic polymers which are copolymerized to have a minor proportion of an acid moiety, and which are neutralized with a metal or quaternary ammonium containing base. The resulting ionomer, formed from an acid containing copolymer or terpolymer, has an attached metallic or ammonium ion. The ionomers have groups which enhance their compati¬ bility with other polymers, particularly other polymers having a higher viscosity than the ionomers. Organic polymers useful for this invention non- exclusively include homopolymers and copolymers of rosins, modified rosins, olefins, polyethers, polyesters, acrylics, polyurethanes, polybutadienes, vinyls, polystyrenes and polycarbonates, and blends thereof, among others. The preferred polymers are alpha-olefins, preferably C2-C 8 olefins and more preferably polyethylene and polypropylene and most preferably polyethylene. The copolymers include an acid moiety which in the preferred embodiment is a carboxylic acid, preferably an unsaturated carboxylic acid. Useful carboxylic acids include monocarboxylic and polycarboxylic acids and deriva¬ tives thereof, including esters and anhydrides, which are capable of reacting with the bases recited below. Useful carboxylic acids or derivatives thereof include unsaturated monocarboxylic acid containing from 3 to 6 carbon atoms and dicarboxylic acids containing from 4 to 8 carbon atoms. Examples of acids copolymerizable with the organic polymer include acrylic acid, methacrylic acid, ethacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, sulfonic acids and phosphonic acids. Also useful are acid halides, amides and esters including acrylyl chloride and acrylamide. Esters which can be used include methyl acrylate, methyl methacrylate, ethyl acrylate and dimethyla inoethyl methacrylate. Also useful are monoesters of dicarboxylic acids, such as methyl hydrogen maleate, methyl hydrogen fumarate, ethyl hydrogen fumarate, and maleic anhydride. Particularly preferred compounds in- elude alpha,beta-ethylenically unsaturated acids and derivatives thereof. A preferred copolymer acid is a copolymer of ethylene and an alpha,beta- ethylenically unsaturated monocarboxylic acid having 3 to 6 carbon atoms. A most preferred alph ,beta-ethylenically unsaturated monocarboxylic acid is acrylic acid. The most preferred copolymer is ethylene-acrylic acid copolymer. In general the copolymer has an acid number in the range from about 1 to about 250, with an acid number from about 40 to 160 being preferred, and an acid number from about 40 to 120 being most preferred. The acid number is determined by the number of milligrams of potassium hydroxide needed to neutralize one gram of polymer. In accordance with the invention, the organic polymer portion desirably is of low molecular weight and has a number average molecular weight of from about 500 to about 6,000, and preferably from about 1,000 to about 3,500. It constitutes at least about 50, preferably from about 50 to about 99.5, more preferably, about 65 to about 99.2, and most preferably from about 80 to about 98 mol percent of the copolymer. The balance is the acid moiety. The formed copolymers are also of low molecular weight and have a number average molecular weight of from about 500 to about 6,000, and preferably from about 1,000 to about 3,500. Multifunctional polymers with two or moles of acid per polymer molecule are of particular use. The copolymers desirably have a Brookfield viscosity of from about 2 to about 20 grams/cm-sec (200 to about 2,000 centipoises) at 140 °C., preferably from about 5 to about 10 grams/cm-sec. (500 to about 1,000 centipoises) at 140 °C. Preferred are copolymers of ethylene and acrylic or methacrylic acid containing from about 1% to about 20% by weight acrylic acid or methacrylic acid in the copolymer, preferably about 3.5% to about 12%, and further characterized by a number average molecular weight of from about 1500 to about 3500, an acid number of from about 10 to about 200, preferably about 20 to about 130, and hardness (0.1 mm penetration) of from about 0.5 to about 30, preferably from about l to about 10 when tested at room temperature, about 25 °C, according to ASTM D-5 using a needle with a load of 100 grams for 5 seconds. The low molecular weight copolymer acids include the copolymers of ethylene disclosed in U.S. Patent 3,658,741 which is hereby incorporated by reference. The most preferred copolymer is a 15% acrylic acid/85% ethylene copolymer. Useful copolymer acids are available from AlliedSignal Inc. as AC R 540; AC R 580, AC R 5120, AC R 5180 and AC R 5200. The copolymer is then neutralized by a suitable metal or ammonium base which can be reacted directly with the copolymer by addition. The base is preferably added in the form of an aqueous slurry and/or solution to enhance dispersion in the copolymer. The neutralization reaction is preferably conducted at a temperature above the melt temperature of the copolymer reaction product. The reaction is preferably conducted at about 1 atmosphere. The reaction can be conducted continuously or in batches. The reaction is conducted until a desired degree of neutralization is attained. Bases having valences of 1 to 3 can be used to neutralize the copolymer acid. Preferably, the bases have metallic cations derived from a group of metals which can be chosen from Groups I, II, III and the transition elements for use in this process. Metal cations which are preferred are sodium, potassium, magnesium, calcium, barium, zinc and aluminum cations, with sodium, zinc, calcium and magnesium cations being most preferred. Suitable bases can be metal salts including oxides, hydroxides, acetates, methoxides, oxylates, nitrates, carbonates and bicarbonates. Preferred metallic salt containing materials include calcium oxide, calcium hydroxide, calcium acetate, magnesium oxide and zinc acetate. The copolymer acid can be neutralized up to 100 percent. It is preferred to neutralize the copolymer reaction product to from l to 100 percent, more preferably from 25 to 100 percent. Most preferably 40 to 100 percent of the total acid groups in the reaction product are neutralized with the base. Reaction additives to help facilitate the reaction can also be added. A particularly preferred additive is an acid such as acetic acid, preferably glacial acetic acid which is added to help speed the reaction and make a more uniform ionomer. Other acids include organic acids such as formic acid and propionic acid as well as inorganic or mineral acids such as HCl and H 2 S0 4 . The organic or inorganic acid, when it is used is present in an amount sufficient to protonate the base. Suitable amounts of the additive range from about 0.1 to 1.0, preferably from about .2% to about .5% based on the weight of the copolymer. The acid converts the base, such as the metal oxides, or hydroxides to more soluble forms. This helps to speed the reaction and reduce agglomerates of the metal compound. It has been found that the addition of water significantly assists in driving the reaction. In the preferred embodiment, water is added to the blend in an amount of from about 0.1% to about 50%, preferably from about 0.1% to about 25% and most preferably from about 0.1% to about 10% based on the total reaction mass. In a most preferred embodiment an aqueous slurry of the cation containing compound is combined with the reaction additive, i.e., acetic acid, and this slurry added to a reactor containing molten polymer. The preferred method of preparing the ionomer of the invention comprises heating the copolymer to above the melting point of the copolymer, preferably from about 100 °C. to about 250 °C, more preferably about 125 °C. to about 250 °C, and most preferably about 140 °C. to about 175 °C. A sufficient amount of at least one metal or quaternary ammonium containing base is added to neutralize the acid moiety of the copolymer as soon as the polymer or polymer mixture is molten, preferably at a rate that prevents surface accumulation of the base or slurry. An ionomer is formed by the reaction of residual acid groups on the acid containing copolymer with a cation from the base. Preferably, the ionomers formed from this invention have a number average molecular weight that ranges from about 1,000 to about 100,000, preferably from about 3,000 to about 10,000. However, the molecular weight can be several orders of magnitude higher where polymer networks are formed by neutralizing multifunctional polymers. For certain applications including, but not limited to color and polymer additive concentrates, the formation of such networks is beneficial to the processing and dispersion of the color or additive. As an important feature of the invention, the ionomers are produced using a high shear intensive mixer such as a kneading mixer, Banbury mixer, roll mill, conical mixer, extruder and the like. The preferred mixer is a double arm kneading mixer commercially available from Baker Perkins, Inc. Such equipment imparts a mixing work to the composition of from about 5.9 x 10 5 Joules/Kg to about 2.1 x 10 7 Joules/Kg, preferably from about 8.9 x 10 5 Joules/Kg to about 2.1 x 10 7 Joules/Kg, and more preferably from about 1.6 x 10 6 Joules/Kg to about 2.4 x 10 6 Joules/Kg. The work is based on the solids of the mixture since the water present quickly evaporates. The composition has a residence time in the mixer of from about 60 minutes to about 480 minutes, preferably from about 60 minutes to about 360 minutes, and more preferably from about 60 minutes to about 120 minutes. During this time the composition is heated to at least the melt temperature of the copolymer. The ionomers have a viscosity at 190° C of from about 500 to about 50,000 grams/cm-sec (about 50,000 to about 5,000,000 centipoise) , preferably from about 750 to about 20,000 grams/cm-sec. (about 75,000 to about 2,000,000 centipoise) and most preferably from about 1,000 to about 10,000 grams/cm-sec. (about 100,000 to about 1,000,000 centipoise) . Microscopic observation of the resulting composition reveals a substantial reduction or absence of base and gel particles normally associated with similar the products produced with standard stirring mixers. Preferably the ionomers have a gel content and gel size that is less than the amount required to clog an extruder screen pack of 3.18 cm (1.25 inch) in diameter and 325 mesh size such that a pressure drop across the screen pack does not exceed 35.15 Kg/sq.cm (500 psi) when 3,600 g of a blend of 5% ionomer and 95 % of a polymer, such as polypropylene, polyethylene, polyacrylate, polystyrene, polycarbonate, etc, is extruded within a 30 minute time period. The following non-limiting examples serve to illustrate the invention. EXAMPLE 1 The steam pressure on a kneading mixer jacket is set to 50 psi. 3.182 Kg (7 lbs.) of AC R 5120 are charged to the mixer and the rotors are started. When the polymer becomes molten a water slurry composed of 0.1336 Kg (0.294 lbs.) of CaO and 0.636 Kg (1.4 lbs.) of water is added over a 15 minute period. After the addition of CaO slurry is completed, the batch is monitored by viscosity and IR tests. In the following table the T=0 sample is taken and tested as soon as the slurry addition is completed. The viscosity is measured on a Brookfield Thermocel Viscometer with a #28 spindle a 190°C. An FTIR is used to determine the ratio of COOH to salt formed. These peaks occur at 1700 and 1565 reciprocal seconds. TABLE 1 Sample Reaction FTIR Viscosity Notes Time, sec. Ratio cps 1 0 7.16 2,000 50 psi(100°C) 2 30 1.70 11,000 52 psi(100°C) 3 60 0.82 90,000 52 psi(120°C) 4 120 0.58 90,000 52 psi(140°C) 5 150 - 90,000 End Run EXAMPLE 2 Example 1 is duplicated except with the addition of 2 g of acetic acid to the slurry. The acid hydrates the oxide to its more reactive hydroxide. The following results are noted. TABLE 2 Sample Reaction FTIR Viscosity Notes Time, sec. Ratio cps 1 0 2.376 20,000 50 psi(100°C) 2 30 0.499 100,000 50 psi(114°C) 3 60 0.384 400,000 50 psi(134°C) 4 120 0.260 500,000 End Run EXAMPLE 3 The procedure of Example 2 is followed except a lower acid containing polymer (AC R -580) , 2 g of acetic acid and 0.1177 kg (0.259 lbs) of CaO are used to increase the percentage of acid groups neutralized. The increased amount of base increases the viscosity. TABLE 3 Sample Reaction FTIR Ratio Viscosity Notes Time,sec. cps 1 0 .353 25,000 50 psi(100°C) 2 30 0.078 200,000 50 psi(124°C) 3 60 0.065 500,000 50 psi(148°C) 4 120 0.012 800,000 End Run EXAMPLE 4 Using the amount of ionomer resulting from Example 3, a slurry containing approximately 18% carbon black and about 82% water is added in three equal additions to the batch. The steam pressure on the jacket is maintained at 50 psi. The carbon black migrates to the ionomer phase leaving clear water behind. The water is decanted from the mixture by tilting the reactor on a horizontal axis. (This process is known in the industry as flushing) . This process is continued until the mixture contains about 50% ionomer and 50% carbon black. The mixture is then cooled with dry ice and granulated in the mixer. The black granules are then mixed with polybutylene terephthalate at a 1:1 ratio. The resultant mixture is fed into a 3.18 cm (1.25 inch) di_.rn.eter single screw extruder which is preheated to a temperature of about 270°C and strand pelletized. The resultant pellets are further reduced in polyethylene terephthalate 20:1 and melt spun into fibers and collected as yarn using conventional fiber spinning equipment. KYAMPT. 5 (Comparative) In this example a batch is made in a stirred reactor and compared to Example 2 and a commercially prepared product (Actone R 2010) in a performance test that determines the feasibility of use of the product in fiber spinning applications. The test determines the presence, amount, and size of gel particles by relating gel size and amount to pressure build-up as a certain amount of the ionomer is filtered through screens of known mesh size. Excessive gel content interferes with fiber spinning by developing excess pressure in fiber extrudes. In this test a pressure build-up of over 500 psi is unacceptable. (a) Stirred Reactor Batch 6000g of AC R 5120 is charged to a paddle agitated flask equipped with a 0.5 HP stirrer powered by 115 V DC current. The polymer is melted and a slurry of 244g CaO, l,380g water, and 3.6g acetic acid is added to the melt over a 30 minute time period. The batch temperature is between 100°C and 105°C. After the addition of slurry, the batch temperature is raised to about 225°C and held for 180 minutes. The final viscosity of the batch is 340,000 cps at 190°C. (b) Commercial Batch (stir reactedi The batch is made by the same procedure as (a) but because of increased scale the run time is considerably longer (40-60 hrs.). On occasion, due to limitations of power to the stirrer, the temperature must be raised to 250-260°C to reduce viscosity so batch stirring can be maintained. During these occasions, batch movement in the reactor is slow which hampers completion of the batch as well as increasing exposure to temperatures in excess of 275°C (at the wall of the reactor) . The slow movement past hot surfaces is believed to increase both gel content and discoloration. (c) Performance Test 3600g of a blend composed of 95% polyethylene terephthalate and 5% ionomer is passed through a 5 inch diameter extruder heated to about 270°C at a rate so that all of the blend is extruded in about 30-40 minutes. A screen pack consisting of 5 screens with mesh sizes of 60, 100, 325, 60, and 20 is placed at the exit of the extruder so the blend would flow through the screens starting at the 60 end. A pressure transducer is placed in the extruder in front of the screen pack to record pressure build-up that would occur as gel particles clogged the screen. The results are recorded below. TABLE 4 Composition Example 2 Example 5a Example 5b 10 Min. Pressure 40 psi 100 psi 1000 psi Test stopped 20 Min. Pressure 100 psi 350 psi 30 Min. Pressure 200 psi 600 psi EXAMPLE 6 This example shows that ionomer components can be blended to give specific compatibility with various resins. (a) 787g AC-5120 are melted in a steam heated (50 psi) Baker-Perkins mixer. When melting is complete 203g of Polypale R polymerized rosin, known to be compatible with styrenic resins, and available commercially from Hercules is added to the melt. After a brief mixing period a slurry of 40.6g CaO, 230.3g of water and 0.63g of acetic acid is added to the batch over a 15 minute period. The temperature in the mixer is allowed to rise to 148°C and mixing is continued for a period of 2 hours. The batch is cooled with liquid nitrogen and ground to about 0.125 particle size. (b) The ionomer from Example 2 is compared with the ionomer from Example 6(a) by blending each ionomer with medium impact polystyrene at a 70:30 weight ratio. (70% styrene, 30% ionomer) . Each blend is then strand pelletized utilizing a 3.18 cm (1.25 inch) diameter 24:1 extruder, water bath and Conair R pelletizer. The ionomer blend of Example 2 extrudes well, but close examination of individual pellets reveals fibrous whiskers on each end of the pellets where the pelletizer knife cut them. This is known in the art as delamination and is an indication of reduced compatibility with the matrix resin (i.e., polystyrene). The ionomer blend of Example 6(a) cut cleanly and demonstrates increased transparency indicating superior compatibility with the polystyrene resin matrix. EXAMPLE 7 1000 g of AC R -5120, a 15% acrylic acid copolymer of ethylene, is charged to a model #54077 Baker- Perkins kneading mixer. The mixer is started and heated by steam to 3.515 Kg/sq.cm (50 psig) . When the copolymer is melted and reaches a temperature of approximately 105 °C, a slurry of 300 g of water, 42 g of CaO, and 2g of acetic acid is added to the mixing copolymer over about 30 minutes. After the addition of the slurry, mixing continues and the batch temperature rises to about 140 °C over a 2 hour period. The viscosity increases by several orders of magnitude during the mixing period. 2.52 x 10 6 Joules/Kg of polymer are applied for the duration of the 2 1/2 hour period. This is noted visually and by the increase of amperage on the mixer's motor. An IR scan is run on the batch 20 minutes after the slurry addition is completed. The scan shows a low ratio of COOH/carboxylate salt indicating that the copolymer acid groups are neutralized by calcium in this short period of mixing. After a 2 hour mixing period the batch is cooled and granulated in the mixer. The viscosity of the batch is measured at 190 °C on a Brookfield Viscometer and determined to be approximately 3,000 grams/cm-sec. (300,000 cps). This viscosity is equivalent to batches produced in a stirring reactor which take as long as 40 hours to complete. The batch is examined microscopically for polymer gels and unreacted CaO. Some gels are present but no CaO is found. EXAMPLE 8 The method of Example 7 is duplicated except a water slurry of the CaO is not used. Rather, the CaO is added to the mixer by sifting into the melt. In this example, reaction fails to occur until small amounts of water (1-2 g) are added to the melt. The final viscosity is only about 30% as high as Example 1 indicating that the addition of the CaO in a water/acid slurry is preferred. However, the viscosity build-up is still much more rapid than the prior art batch process that uses a water slurry and a stirred reactor.

Claims: What is claimed is: 1. A method of producing ionomers which comprises forming a blend of a melt of a copolymer or terpolymer having an acid moiety with a metal or quaternary ammonium containing base in an amount sufficient to neutralize the acid moiety and subjecting the blend to a high shear mixing to provide a mixing work to the blend of from about 5.9 x 1 ( P Joules/Kg to about 2.1 x 10 7 Joules/Kg over a period of from about 60 minutes to about 480 minutes. 2. The method of claim 1 wherein the copolymer comprises one or more monomers selected from the group consisting of olefins, rosins, modified rosins, ethers, esters, acrylics, urethanes, butadienes, vinyls, styrenes, carbonates and blends thereof. 3. The method of claim 1 wherein the copolymer is a polyethylene containing copolymer. 4. The method of claim 1 wherein the copolymer is a carboxylic acid containing copolymer. 5. The method of claim 1 wherein the copolymer comprises one or more components selected from the group consisting of acrylic acid, methacrylic acid, ethacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, sulfonic acids and phosphonic acids, acid halides, amides and esters. 6. The method of claim 1 wherein the copolymer is an ethylene-acrylic acid copolymer. 7. The method of claim 1 wherein the copolymer is neutralized by at least one base selected from the group consisting of Groups I, π, HI and transition element oxides, hydroxides, acetates, methoxides, oxylates, nitrates, carbonates and bicarbonates. 8. The method of claim 1 further comprising adding sufficient water to the melt blend to accelerate the reaction between the copolymer or terpolymer and the base. 9. The method of claim 1 wherein the neutralization is conducted by a pre-formed aqueous slurry of a base and a protonating acid. 10. The ionomers produced by the method of claim 1.

Inventors: DOERRIES ROBERT ALAN, DOERRIES, ROBERT, ALAN
Applicants: ALLIED SIGNAL INC, ALLIEDSIGNAL INC.
Application year: 1996
Main classification: C08F8
IPC codes: C08C19, C08F8, C08G85