ETHYLENE COPOLYMERS REACTED WITH METAL OXIDES

Abstract: Melt-reacted blends of ethylene copolymer containing olefinically-unsaturated carboxylic acids with metal oxides are improved by first incorporating the metal oxide into an ethylene copolymer of LDPE, HDPE, or LLDPE to form a concentrate or masterbatch, then melt-blending a minor amount of the concentrate into the ethylene/carboxylic acid copolymer thereby obtaining a uniform, homogeneous reaction of the metal oxide with the carboxylic acid groups. These melt-reacted blends provide tough molding resins. Especially preferred are melt-reacted blends of EAA with minor amounts of MgO/LLDPE concentrates.

Description: This pertains to ethylene copolymers having pendant carboxyl groups which are reacted with metal oxides. It is known that ethylene copolymers having pendant carboxylic acid groups are reactive with metal oxides, metal hydroxides, and metal hydrates to form metal salts of at least some of the carboxylic acid groups. The carboxylic acid groups are usually those provided by acrylic acid or methacrylic acid, or other such olefin acids, when copolymerized or interpolymerized with ethylene. The ethylene/carboxylic acid-containing copolymers preferred in the present invention are commercially available, especially those of the type known as "interpolymer", but may also be of the type known as "graft copolymers" and "block copolymers". These expressions are known to practitioners of the art. Interpolymers are made by polymerizing a mixture of the monomers; graft copolymers are made by grafting olefin acid groups onto a polyethylene chain; block copolymers are those wherein long polymer chains comprise chain segments of a polymerized plurality of ethylene units and segments of a polymerized plurality of the carboxylcontaining monomer units. As used herein the expression "olefin acids" refers to olefinically-unsaturated carboxylic acids which are copolymerizable with ethylene, especially acrylic acid, methacrylic acid, crotonic acid, and 1-buteneoic acid, most especially acrylic acid and methacrylic acid. Patents which disclose interpolymerizations of ethylene and unsaturated carboxylic acids in a steady state reaction at high temperature and high pressure in a stirred reactor in the presence of a free-radical initiator are, e.g., Canadian Patent 655,298 (and its U.S. counterpart No. 4,351,931); U.S. 3,239,270; U.S. 3,520,861; U.S. 3,658,741; U.S. 3,884,857; U.S. 3,988,509; U.S. 4,248,990; and U.S. 4,252,924. Also included as a part of the present invention are polyethylenes and, preferably, certain ethylene interpolymers of the linear low density variety, known by the acronym LLDPE. These LLDPE resins are distinguishable from the non-linear (branched) low density polyethylene (LDPE) made by homopolymerizing ethylene using free-radical initiators; the LDPE resins contain branched chains of polymerized monomer units pendant from the main polymer "backbone" and generally have densities in the range of 0.910 to 0.935 gm/cm³. The LLDPE resins are also distinguishable from the linear high density polyethylene (HDPE) resins by the fact that these LLDPE resins are prepared by interpolymerizing ethylene with enough of a higher alpha-olefin to yield a linear ethylene copolymer which has a density, generally, in the same range of the LDPE. Linear HDPE generally has a density in the range of 0.941 to 0.965 gm/cm³ Both HDPE and LLDPE are linear polymers, prepared using a coordination catalyst, e.g., the well-known Ziegler catalyst, or modifications thereof such as the Natta catalyst. As used in this disclosure, the expression "ethylene polymers" refers to the homopolymers (LDPE and HDPE) and the ethylene/olefin interpolymers (LLDPE). Some teachings about the differences in LDPE, HDPE, and LLDPE resins are found, e.g., in U.S. 4,327,009. A method of making various LLDPE resins is disclosed, e.g., in U.S. 4,076,698. The addition of metal oxides to molten carboxylic acid-containing ethylene polymers, e.g., ethylene/acrylic acid (EAA) or ethylene/methacrylic acid (EMAA) is usually done by carrying the metal compounds, as a hydroxide or hydrate, in an aqueous carrier, employing, in some cases, an acid aqueous carrier to solubilize the metal. This causes bubbling of the water (as steam) and often has deleterious effects on the product sought to be made. See, e.g., U.S. 4,440,893 which proposes the use of an acetylene peroxy compound to alleviate bubble formation. Directly blending dry anhydrous metal oxides (e.g. MgO, CaO, BaO, ZnO) into molten EAA or EMAA can be performed to avoid the use of aqueous carriers for the metal oxide, but because of the reactivity of the carboxylic acid groups with the metal oxides, non-homogeneous blending often occurs. U.S. 4,420,580 discloses that inorganic metal fillers, e.g. polyvalent metal oxides, are made more compatible with a polyolefin resin, e.g., linear low density ethylene copolymers, by incorporating an ethylene/acrylic acid copolymer into a molten mixture of the polyolefin/metal oxide. In these blends, the polyolefin is present in significantly greater concentration than is the ethylene/acrylic acid copolymer. Patents pertaining to ionomers are, e.g., U.S. 3,249,570; U.S. 3,264,272; U.S. 3,322,734; U.S. 3,379,702; U.S. 3,404,134; U.S. 3,649,578; U.S. 3,789,035; U.S. 3,969,434; and U.S. 3,970,626. The present invention provides a means for blending metal oxides into molten ethylene copolymers having pendant carboxylic acid groups which avoids the use of aqueous carriers. According to the present invention dry metal oxides are conveniently blended into molten ethylene copolymers having pendant carboxylic acid groups, whereby excessive reaction of the metal oxide with the said acid groups is substantially minimized, thereby permitting a more uniform dispersion of the metal oxide to be made. A curable or cross-linkable composite comprising an ethylene copolymer, having pendant carboxylic acid groups, and having substantially uniformly dispersed therein at least one metal oxide is also suitably preferred in accordance with the present invention. The present invention is a process for preparing uniformly reacted blend comprising a major amount of an ethylene copolymer containing olefinically-unsaturated carboxylic acid groups and a minor amount of a metal oxide characterized in that a masterbatch blend of metal oxide in an ethylene polymer, wherein said ethylene polymer is selected from the group consisting of LDPE, HDPE, and LLDPE is blended with mixing into said ethylene copolymer containing the olefinically-unsaturated carboxylic acid groups under molten conditions at which the metal oxide reacts with the carboxylic acid groups. In another aspect, the present invention is a substantially homogeneous, uniformly reacted blend comprising a major amount of an ethylene copolymer containing olefinically-unsaturated carboxylic acid groups and a minor amount of a masterbatch blend of a metal oxide in an ethylene polymer, said ethylene polymer being at least one of the group consisting of LDPE, HDPE, and LLDPE which blend is prepared by blending, with mixing a masterbatch blend of metal oxide in an ethylene polymer, wherein said ethylene polymer is selected from the group consisting of LDPE, HDPE, and LLDPE, into an ethylene copolymer containing olefinically-unsaturated carboxylic acid groups under conditions at which the metal oxide reacts with the carboxylic acid groups. Still in another aspect, the present invention is an article comprising a substrate having compression or injection molded onto its surface foregoing melt-reacted blends of an ethylene copolymer containing olefinically-unsaturated carboxylic acid groups and a masterbatch blend of metal oxide in an ethylene polymer. The carboxylic acid-containing ethylene copolymer is one wherein the carboxylic acid-containing moiety comprises 1 percent to 40 percent by weight of the ethylene copolymer. The carboxylic acid-containing moiety may be any of the olefinic acids or olefinic acid anhydrides having 3 to 12 carbon atoms, such as, acrylic acid (AA), methacrylic acid (MAA), 1-buteneoic acid, crotonic acid, maleic acid or maleic anhydride, especially acrylic acid and/or methacrylic acid. These copolymers generally have melt flow values (MFV) in the range of 1 g/10 min. to 3000 g/10 min. as measured by ASTM D-1238 (Condition E) and, for these type of copolymers, are considered to be of intermediate to high molecular weight. The preferred range for the MFV is 10 g/10 min. to 500 g/10 min. and the preferred range for the amount of the carboxyl-containing moiety is 1 percent to 25 percent by weight. The LLDPE resin preferably used is one wherein the alpha-olefin comonomer comprises 0.2 percent to 35 percent by weight of the interpolymer, the alpha-olefin having from 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms. Preferably the comonomer comprises 1 percent to 20 percent by weight of the interpolymer. Octene-1 is an especially preferred comonomer. A mixture of the comonomers may be used in preparing the ethylene interpolymers, such as butene-1/octene-1 or hexene-1/octene-1. These LLDPE interpolymers are generally of intermediate to very high molecular weight, having MFV's in the range of 1 g/10 min. to 200 g/10 min. as measured by ASTM D-1238(E), preferably 10 g/10 min. to 70 g/10 min. The LDPE and HDPE resins which may be used are normally solid homopolymers having melt indexes (MFV's) in the range of 1 g/10 min. to 200 g/10 min. as measured by ASTM D-1238(E). Further preferred ethylene copolymers and LLDPE resins are subject-matter of the sub-claims. Whereas there are many metal oxides which can be substantially uniformly dispersed in a carboxylic acid-containing ethylene copolymer by being carried in LLDPE in accordance with the method of the present invention, it is preferred that the metal oxide be at least one of the group comprising CaO, MgO, BaO, and ZnO, all of which are divalent. These divalent metals are readily available, are inexpensive, and provide beneficial crosslinking or curing of the carboxyl-containing ethylene copolymers without untoward discoloration. The masterbatch of metal oxide in LLDPE, LDPE or HDPE is conveniently prepared by mixing at a temperature at which the ethylene polymer is molten or by any other methods which allow the metal oxide to be dispersed in the polymer, such as dispersing the metal oxide in a polymer solution and then removing the solvent. These ethylene polymers have little or no tendency to react with the metal oxide, thus the reactivity of the metal oxide is preserved for subsequent reaction with the carboxylic acid-containing ethylene copolymer. The ratio of metal oxide/ethylene polymer may be virtually any practical ratio which provides for efficient loading of the metal oxide into the carboxylic acid-containing ethylene copolymer without unduly overloading with ethylene polymer. A metal oxide/ethylene polymer ratio in the range of, e.g., 4/1 to 1/20 is particularly operable, though a ratio in the range of 2/1 to 1/5 is generally preferred; a ratio in the range of 2/1 to 1/2 is especially preferred. The blending of the masterbatch into the carboxyl-containing ethylene copolymer is done at melt temperatures to provide uniform blending. The amount of masterbatch per 100 parts of the copolymer is dependent on the amount of crosslinking one wishes to achieve. For example, 6 parts by weight of an ethylene polymer/MgO masterbatch of 1/1 wt. ratio, mixed into 94 parts by weight of an ethylene/acrylic acid copolymer (20 percent AA by weight; MFV of 300 dg/10 min) crosslinks to a strong tough composite wherein the AA groups are 50 percent, ±3 percent, crosslinked. The 3 percent ethylene polymer in the composite contributes to the overall strength, toughness, and abrasion-resistance of the final product, as well as serving to improve the dispersion of the MgO in the EAA copolymer. A convenient blending technique comprises the addition of masterbatch pellets to molten copolymer; the pellets become substantially uniformly distributed during the mixing and the distributed pellets disintegrate upon melting. The preferred LLDPE has a different morphology from the branched-chain LDPE and the linear HDPE. The LLDPE is essentially a linear polymer having side-groups (not side-chains) along the polymer backbone due to the pendent alkyl moiety of the alpha-olefin comonomer which is interpolymerized with the ethylene. For example, the pendent alkyl moiety of 1-butene is -CH₂CH₃ and the pendant alkyl moiety of 1-octene is (CH₂)₅CH₃. The weight ratio of masterbatch/carboxyl-containing ethylene copolymer is variable over a wide range, depending on the amount of metal oxide in the masterbatch, and is preferably a ratio which will provide a final composition containing 0.5-100 parts of LLDPE and 0.5-10 parts of metal oxide per 100 parts of the acid copolymer. Because of the compatibilizing effect of the ethylene polymer in the masterbatch, the metal oxide is more readily and evenly distributed in the carboxyl-containing ethylene copolymer, thus the reaction between the metal oxide and the carboxyl groups creates a substantially homogeneous final product which is substantially transparent or transluscent. As a result of this uniform chemical reaction the metal values become ionic groups on the copolymer chain and do not function as discrete particles or fillers. Fillers are known to form heterogeneous, substantially opaque blends with polymers by way of being inert, with respect to the polymers, or else by being non-uniformly or irregularly reacted if there is, in fact, a tendency to react. The examples which follow are to illustrate particular embodiments, but the invention is not limited to the embodiments illustrated. Unless noted otherwise, the polymer properties are measured as follows: Example 1 (comparative example) Fine-particle MgO (3 parts) was blended with 100 parts of an ethylene/acrylic acid copolymer (EAA) (20 percent AA, 300 MFV) by being tumble-blended at ambient temperature for one hour, then the mixture was hand-fed into the hopper of a Werner-Pfleiderer twin-screw extruder. The extruder (a ZSK-53L extruder) was operated under the following conditions: The extruded resin was found to contain high levels of unreacted MgO, observed as large white specks and was extremely difficult to process due to the variations in the degree of crosslinking. See Table I below for comparison data. Example 2 (EAA plus MgO/ethylene polymer masterbatch) Using the ZSK-53L extruder but with extrusion conditions given below, the same EAA copolymer of Example 1 was blended with a masterbatch. The masterbatch was a 50/50 mixture of 700 parts of fine particle MgO and 700 parts of an ethylene/1-octene copolymer (MFV: 25g/10 min, density: 0.921 g/cm³, 7 percent 1-octene) prepared in a Banbury mixer with the mixing blades operated at 150 rpm for 5 minutes until the polymer melts. Once blended the masterbatch was cooled and ground into particles. The masterbatch was fed (6 parts/hr.) through a feeder into the twin-screw extruder and the EAA copolymer was fed (50 parts/hr) simultaneously through a separate feeder. The extruded resin was clear and contained no visible levels of unreacted MgO. Because of the increased dispersability the extruder was operated effectively using a shorter L/D ratio which appreciably conserves energy. See Table I below for comparison data. Example 3 A masterbatch (concentrate) of MgO/LLDPE, 1/1 ratio, was blended with EAA copolymer (20 percent AA, 300 M.I.) using the extruder conditions of Example 2 above. The feed rate to the extruder for the EAA copolymer was 75 parts/hour while the feed rate of the MgO/LLDPE concentrate was varied from 2.51 parts/hour to 3.85 parts/hour thus obtaining different levels of neutralization of the acid groups. Table II following shows the bulk physical properties of these blends. In general, as the concentration of the MgO in the EAA was increased, an improvement in physical properties was observed. This behaviour apparently results from the decreased mobility of the resin molecules. There also appears to be a limiting point where additional amounts of MgO do not cause additional property improvements. Example 4 (Comparative Data) Using the same EAA as in Example 3 above, 52 percent of the acid groups were neutralized with neat MgO and compared with another portion of the EAA which had 52 percent of the acid groups neutralized with a 50/50 concentrate of MgO/LLDPE. The EAA/MgO blend was prepared in a Banbury mixer where the temperature reached 204°C. The EAA/concentrate blend was prepared in an extruder as in Example 2 above. The physical properies in Table III show improved properties using the concentrate; these improvements appear to be caused by the compatibility effect of the LLDPE. Example 5 In similar manner to the foregoing examples and comparisons, it was found that LDPE and HDPE, when mixed with MgO as a masterbatch concentrate, also improve the dispersivity of the MgO in the EAA copolymer, but LLDPE is preferred for such concentrates. Example 6 Blends of ethylene/carboxylic acid copolymers with minor amounts of metal oxide/ethylene polymers prepared in accordance with the present invention provide useful molding compositions and coating compositions. For example, the following melt-reacted blend was found to be useful, when compounded with fillers, colorants and the like, as injection molded or compression molded coverings for articles where toughness and scuff-resistance are needed, such as golf balls. 94 percent of EAA (20 percent AA, 300 M.I.) 6 percent of masterbatch of 1/1 ratio of MgO/LLDPE, here MgO was finely divided and LLDPE contains about 7% 1-octene interpolymerized with ethylene and has a density of 0.92 gm/cm³ and M.I. of 25. The above ingredients were melt-blended in an extruder where the LLDPE causes the MgO to be uniformly distributed throughout the EAA and a homogeneous reacted ionomer was formed.

Claims: A process for preparing uniformly reacted blend comprising a major amount of an ethylene copolymer containing olefinically-unsaturated carboxylic acid groups and a minor amount of a metal oxide, characterized in that a masterbatch blend of metal oxide in an ethylene polymer, wherein said ethylene polymer is selected from the group consisting of LDPE, HDPE, and LLDPE is blended with mixing, into said ethylene copolymer containing the olefinically-unsaturated carboxylic acid groups under molten conditions at which the metal oxide reacts with the carboxylic acid groups. The process of Claim 1 wherein the ratio of metal oxide/ethylene polymer in the masterbatch blend is in the range of 4/1 to 1/100. The process of Claim 1 wherein the metal oxide is at least one of the group comprising CaO, MgO, BaO, and ZnO. The process of Claim 1 wherein said ethylene copolymer containing olefinically-unsaturated carboxylic acid groups is copolymer of ethylene and acrylic acid or methacrylic acid. The process of Claim 1 wherein said ethylene copolymer containing olefinically-unsaturated carboxylic acid groups is copolymer of ethylene and acrylic acid containing 1 percent to 40 percent by weight of the acrylic acid moiety, having a melt flow value in the range of 10 g/10 min. to 3000 g/10 min., and said ethylene polymer is LLDPE having 0.2 percent to 35 percent by weight of the ethylene moiety, the remainder being a higher olefin moiety having from 3 to 12 carbon atoms, having a melt flow value in the range of 1 g/10 min. to 200 g/10 min., and having a density in the range of 0.89 to 0.935 g/cm³. A substantially homogeneous, uniformly reacted blend comprising a major amount of an ethylene copolymer containing olefinically-unsaturated carboxylic acid groups and a minor amount of a masterbatch blend of a metal oxide in an ethylene polymer, said ethylene polymer being at least one of the group consisting of LDPE, HDPE, and LLDPE prepared according to the process of Claim 1. The blend of Claim 6 wherein said ethylene copolymer containing olefinically-unsaturated carboxylic acid groups comprises at least one where the carboxylic acid is acrylic acid, methacrylic acid, 1-buteneoic acid, crotonic acid, maleic acid, or maleic anhydride. The blend of Claim 7 wherein the carboxylic acid is acrylic acid or methacrylic acid. The Blend of Claim 6 wherein the metal oxide is at least one selected from the group consisting of CaO, MgO, BaO, and ZnO. An article comprising a substrate having compression or injection molded onto its surface a melt-reacted blend of Claim 6. The article of Claim 10 wherein the melt-reacted blend is that of Claim 8. The article of Claim 10 wherein the melt-reacted blend is that of Claim 9. The article of Claim 12 wherein the article is a golf ball.

Inventors: BRYCE, KENNETH L., LANCASTER, GERALD M., NEILL, PAUL L.
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1985
Main classification: C08F8
IPC codes: C08L33, C08L23, A63B37, C08F8, C08J3, C08L51, C08L101, C08L77, C08K3