HK1076830B - An ionomer/high density polyethylene blend and a method of reducing the viscosity thereof - Google Patents

Description

Ionomer/high density polyethylene blends and methods for reducing the viscosity of the blends

Technical Field

The present invention relates to ionomer/high density polyethylene blends having improved flow and a process for making the same. More particularly, but not by way of limitation, the present invention relates to the addition of low molecular weight ethylene/acrylic acid (methacrylic acid) copolymers to ionomer/high density polyethylene blends to reduce the viscosity and improve the flow of the blend without significantly reducing the physical properties such as impact resistance, tensile strength.

Background

As is generally known in the art: thermoplastic blends based on blends of ionomers and high density polyethylene are used for exterior automotive color molded instrument panels, bumper facings, side moldings and other decorative finishes in injection molding processes. Blends of these polymers are disclosed, for example, in U.S. patent 4,387,177 and are available from E.I. du Pont de Nemours and company under the trademark E.I. DuIt comprises a copolymer of an alpha-olefin, usually ethylene, copolymerized with an alpha, beta-ethylenically unsaturated carboxylic acid, usually acrylic acid, methacrylic acid or mixtures thereof, wherein preferably 5 to 80% of the acid groups in the acid copolymer are neutralized with a metal ion such as zinc, sodium or the like. Such ionomersCommercially available from E.I.du Pont de Nemours and Company under the trade nameIn the 1188 patent, a partially neutralized acid copolymer is mixed with a linear polymer of alpha-olefin and glass fiber to make an injection molded resin. One difficulty with such blends is achieving and maintaining optimum rheology without sacrificing physical properties, such as impact resistance and tensile strength.

Disclosure of Invention

In view of the above, it has now been found that the addition or incorporation of low molecular weight copolymers of ethylene with acrylic acid, methacrylic acid and mixtures thereof can improve the flow of the resulting blends without significantly reducing the physical properties such as impact resistance, tensile strength. It was further found that the incorporation of maleic anhydride grafted high density polyethylene (MAN-g-HDPE) into such ionomer/high density polyethylene blends with improved flow properties did not significantly impair the flow improvement in order to improve impact resistance.

Thus, the present invention provides an ionomer/high density polyethylene blend having improved flow properties comprising, per 100 parts by weight of the ionomer/high density polyethylene blend, from 1 to about 20 parts by weight of a low molecular weight copolymer of ethylene and at least one other comonomer selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof, wherein said low molecular weight copolymer has a melt index (ASTM D1238) as low as 350, and more typically greater than 900dg/min, and the combined comonomer content of acrylic acid and methacrylic acid is at least 5 weight percent.

The present invention further provides a method of reducing the viscosity of an ionomer/high density polyethylene blend without significantly reducing impact resistance and tensile strength comprising the step of mixing a low molecular weight copolymer comprising cumulatively from 1 to about 20 parts by weight of ethylene and at least one other comonomer selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof in a final mixture for every 100 parts by weight of ionomer/high density polyethylene, wherein said low molecular weight copolymer has a melt index (ASTM D1238) as low as 350 and more typically greater than 900dg/min and the combined acrylic and methacrylic comonomer content is at least 5 weight percent.

Preferably, the low molecular weight copolymer has a melt index of at least 5000dg/min and the combined acrylic and methacrylic comonomer content is at least 9% by weight. For the flow improved ionomer/high density polyethylene blend, 1 to about 20 parts by weight of polyethylene modified with 0.2 to 5.0 weight percent maleic anhydride comonomer may also be included per 100 parts by weight of ionomer/high density polyethylene blend.

Brief Description of Drawings

FIG. 1 is a schematic view ofMelt index profile of additive AC580 as a function of weight percent of AC580 in the/HDPE blend.

FIG. 2 is a schematic view ofMelt index profile of three different AC resin additives as a function of the weight percent of the corresponding AC resin in the/HDPE blend.

Detailed Description

The present invention relates to the addition of low molecular weight ethylene/acrylic acid copolymers to ionomer/high density polyethylene blends in order to reduce the viscosity of the mixture and improve its flowability without significantly reducing the physical properties such as impact resistance, tensile strength. Unless otherwise specified, in the present description and claims, the term "copolymer" means a polymer obtained by polymerization of two or more different monomers, which serve as alternative reactants in the polymerization. Thus, the term is meant to include "terpolymers" as well as polymers produced from three or more comonomers, and may also include "copolymers". The term "blend" means a composition, mixture, and/or plurality of polymers with or without additives that work together or produce a thermoplastic matrix or polymer alloy that may exhibit dispersed, continuous, and/or discontinuous phases even when analyzed in microanalysis. While the term "consisting essentially of means that the recited components are essential, minor amounts of other components may also be present in amounts that do not detract from the operability of the invention. Rather, the term "comprising" is intended to recognize the presence of larger amounts of other components, provided that the benefits and advantages of the present invention are still achieved (e.g., improved flow or flow characteristics, etc.).

Useful ionomer/high density polyethylene blends according to the present invention broadly include any thermoplastic blend plastic based on combining or mixing neutralized or partially neutralized ethylene/α, β -unsaturated carboxylic acid copolymers (acid copolymers) with thermoplastic linear polyethylenes. Such mixtures may and typically are reinforced with various fibers. Such polymer blends with reinforcing fibers are disclosed, for example, in U.S. Pat. No. 4,387,188, the acid copolymer content of the blend is typically from 38 to 90 weight percent of the mixture, in accordance with the teachings of this reference; but now more preferably 20-80 wt% of the acid copolymer is considered. Such acid copolymers for obtaining ionomers are further disclosed in U.S. patents 3,520,861, 4,026,967, 4,252,924, and 4,248,990. Neutralized or partially neutralized ionic copolymers (ionomers) are disclosed in U.S. Pat. No. 3,264,272.

The high density polyethylene of the ionomer/HDPE blend of the present invention can be any thermoplastic linear polyolefin commonly known in the art. The polyethylene has a density of about 0.91 to 0.97, preferably 0.935 to about 0.970, most preferably 0.95 to about 0.97.HDPE is generally characterized by a melt index of generally 0.1 to 100, preferably about 1.0 to about 10, most preferably about 2 to about 6. Thus, it is known in the art that HDPE is a higher molecular weight polymer composed primarily of ethylene, with or without minor amounts of other copolymerized α -olefins, resulting in a linear characteristic characterized by about 8 or fewer branch points per 1000 carbon atoms. For the purposes of the present invention, the HDPE content of the mixture is generally from 20 to 80% by weight, preferably from 50 to 75% by weight, most preferably from 60 to 70% by weight, of the mixture.

The low molecular weight ethylene/acrylic acid copolymer used as the polymer viscosity modifying additive for the ionomer/high density polyethylene blend is a high melt index copolymer of ethylene and an unsaturated carboxylic acid selected from the group consisting of acrylic acid (E/AA copolymer) and methacrylic acid (E/MAA copolymer), as described in U.S. patent 5,118,746. The improved viscosity polymer preferably has a melt index greater than 900dg/min, preferably at least about 5000dg/min, and most preferably at least about 10,000dg/min (as determined according to ASTM 1238, condition E). For the purposes of the present invention, however, the viscosity modifying polymers may advantageously have a melt index as low as 350 and still exhibit the beneficial effects of the present invention. However, to produce the same superior results, a greater amount of low melt index polymer may be required than for the more preferred melt flow polymers. The viscosity modifying polymer preferably also contains a total of at least 5 wt.%, more preferably 9 wt.% of carboxylic acid monomers. And the ethylene/acrylic acid copolymer used is preferably selected to have a similar carboxylic acid comonomer content as the ionomer used. A small amount of the third comonomer may be present provided that a suitable MI level is maintained. The third comonomer may be selected from C₃-C₇C of alpha, beta-unsaturated carboxylic acids₁-C₁₀Alkyl esters, vinyl ethers, acrylonitrile, methacrylonitrile, carbon monoxide, sulfur dioxide, and the like.

In general, the relative amounts of viscosity modifying polymers used are selected according to the desired MI to be obtained. Mathematically, the log MI of the resulting viscosity-improved ionomer/HDPE blend is directly proportional to the weight percent of ethylene/acrylic acid copolymer used up to about 20 weight percent E/AA. It should be understood, however, that for the purposes of this invention, the effects of this invention can be partially achieved at viscosity modifying polymer loadings greater than 20 weight percent, and a comparable amount should be considered for the purposes of this invention. Even at higher loading levels, the physical properties of the resulting mixture may begin to degrade.

The high melt index, viscosity modifying copolymers described above are available from Honeywell Performance Polymers and Chemicals under the trade name HONEYWELL PERFORMANCE POLYMERS AND CHEMICALSCopolymers (E/AA copolymers). These copolymers may also be prepared according to the general disclosure in us patent 3264272.

In practice, the viscosity-improving mixture of the invention will advantageously contain minor amounts, generally up to several percent, of other additives such as pigments, colorants, carbon black, ultraviolet light stabilizers, antioxidants, processing aids, glass fibers, mineral fillers, anti-slip agents, plasticizers, nucleating agents, and the like. The various additives described above and their respective uses are well known in the art and are used commercially in conjunction with the application of ionomer/HDPE blends. The combination is particularly preferably used, and is specifically described in examples.

It has further been found that the viscosity modifying blends of the present invention may contain up to about 20 weight percent Maleic Anhydride (MAN) modified high density polyethylene (i.e., copolymerized with 0.2 to 5.0 weight percent maleic anhydride) incorporated as an impact resistance additive into an ethylene acid copolymer/ionomer/high density polyethylene blend without significantly compromising the flow improvement thereof. More specifically, in melts 2 and 4 of example 6, the following description describes the addition of an ethylene/acrylic acid copolymer flow additive and a commercial product available from DuPont, Canada under the trademark "DuPontA MAN grafted polyethylene (Sclair 2907HDPE) impact additive of MB-100D (MAN-g-HDPE; -1% MAN, MI ═ 2). The combination is present in the mixture at the same time. For the purposes of this invention, the maleic anhydride grafted HDPE polymer is preferably any polyethylene having a density greater than about 0.91 or greater. However, it is known that polyethylenes having a density as low as 0.82 can be grafted with maleic anhydrideExhibit some degree of beneficial impact improvement and are therefore considered equivalent to the claimed MAN-g-HDPE.

The preparation of the blends of the present invention can be carried out by using standard mixing means well known in the art. It is preferred to use an industrial mixer, such as an internal mixer, or a commercially available thermoplastic extruder, especially a twin screw extruder, or the like, to achieve thorough mixing of the components and to achieve uniform dispersion of the components. Or the final uniform dispersion can be accomplished during the final plastic injection molding of the article made starting from the individual components, intermediates, component precursors, or combinations thereof. The mixing can also be staged, depending on the choice of starting components and availability. Thus, a commercially available ionomer/HDPE blend can be coextruded directly with the ethylene/acrylic acid copolymer flow improver or the ionomer, HDPE, and ethylene/acrylic acid copolymer can be coextruded simultaneously to give the desired blend. The degree of neutralization of the ionomer can be further purposefully increased by adding metal hydroxides, metal oxides, etc. in the mixing stage. It is further contemplated that the high melt index copolymer of ethylene and the unsaturated carboxylic acid (E/AA or E/MAA) copolymer precursor of the ionomer may be neutralized with a metal component during the coextrusion stage, thus producing the ionomer in situ during the mixing stage.

The following examples serve to more fully illustrate the invention and to further illustrate various aspects and features of the invention. Thus, these statements are intended to illustrate the differences and advantages of the present invention, and not to unduly limit the present invention. In the following examples, all mixtures are generally extrusion compounded on a ZSK-30 co-rotating twin screw extruder using the following temperature profiles, unless otherwise specified.

Feeding: cold

Section 1: 150 ℃ C

Section 2: 225 deg.C

Section 3: 225 deg.C

Section 4: 225 deg.C

Die (single strand, 1/4 inch diameter): 230 deg.C

Screw rate: 200rpm

The discharging rate is as follows: 5-20lb/hr

Melting temperature: generally 245 ℃ and 260 DEG C

Test bars (Test bars) (5 inches × 1/2 inches × 1/8 inches), plaques (3 inches × 5 inches × 1/8 inches), and trays (3 inches × 1/8 inches) for physical testing were molded using a single screw injection molding machine under the following temperature characteristics and conditions:

rear part: 220 deg.C

Center: 225 deg.C

Front end: 230 deg.C

A nozzle: 230 deg.C

Die opening: 25 deg.C

The stamping rate is as follows: fast-acting toy

Screw rate: 60rpm

Injection time: 35 seconds

Residence time: 25 seconds

Back pressure: 50psig

Different test conditions were used to determine the physical properties. Melt Index (MI) was measured at 190 ℃ under a load of 2160 grams according to ASTM D1238, condition E. Melt viscosity was measured at 240 ℃ using a capillary 30 mm long and 1 mm in diameter. Tensile Properties test bars die cut from die cut plaques (3 inches by 5 inches by 1/8 inches) according to ASTM D1708And (4) determining. The test was conducted at a crosshead speed of 2 inches/minuteOn a tensile strength tester (Instron). Flexural modulus was measured according to ASTM D790 using test bars with a distance between bars of 2 inches (5 inches by 1/2 inches by 1/8 inches). Notched cantilever beam impact strength was performed according to ASTM D256 using bars (21/2 inches x 1/2 inches x 1/8 inches) with 0.1 inch grooves machined on the face of the bar. The bars were cut in two parts (i.e., one near the gate end and the other at the tip end) from a single 5 inch by 1/2 inch by 1/8 inch molded bar. Pneumatic ram impact strength measurements were made according to ASTM D3763 at 1/2 inch ram and 5mph drop rate on a 3 inch x 1/8 inch disk in a vertical fashion (i.e., 98.2lb load and 10 inch drop height).

The raw materials, their characteristics and their respective commercial sources are summarized below:

AC 540-95/5: E/AA copolymer wax, acid number (mg KOH/gm) 40, density 0.93gm/cc, MI > 15,000, Mettler drop point 105 ℃ (Allied-Signal).

AC 580-90/10: E/AA copolymer wax (4.15 mol% AA), acid number (mg KOH/gm) 75, density 0.94gm/cc, MI > 15,000, Mettler drop point 95 ℃ (Allied-Signal).

AC 5120-85/15: E/AA copolymer wax, acid number (mg KOH/gm) 120, density 0.94gm/cc, MI > 15,000, Mettler drop point 92 ℃ (Allied-Signal).

6060-HDPE, MI 6.0 (specification range 5.4-6.6) (LyondellPetrochemical).

7030-HDPE, MI 2.8 (specification range 2.4-3.2) (Lyondell petrochemical).

944 FD-hindered amine light stabilizer (Ciba-Geigy Co.).

EMB-100D-MAN-modified Sclair 2907 HDPE; about 1% MAN, MI ═ 2 (modified polymer, DuPont of Canada).

1010-tetramethylene (3, 5-di-tert-butyl-4-hydroxycinnamate) (Ciba-GeIGy).

B215 ═ 1: 21010 and Irgafos 168 blend, Irgafos 168 ═ tris (2, 4-di-tert-butylbenzene) phosphate (Ciba-Geigy).

·HPU E/MAA-B10：30＝E/MAA(9.6％MAA，983MI)

·HPU E/MAA-E14：30＝E/MAA(17.7％MAA，1023MI)

PPG 3540 ═ glass fiber (PPG company)

9520-90/10: an E/MAA copolymer neutralized 68-71% with zinc, base resin MI 33; ionomer MI 1.1

9650-89/11: E/MAA copolymer (3.87 mol% MAA) neutralized 57% with zinc, base resin MI ═ 100; ionomer MI-5

770DF ═ UV stabilizer (Ciba-Geigy Co., Ltd.)

Example 1

A series of 8 different blends of high density polyethylene and ionomer were prepared and tested, generally in accordance with the procedure described above. Four batches in the melt were related to a lower molecular weight HDPE having a melt index of 6.06060) And higher melt index ionomers9650). In the other four batches of melt, the mixture contained lower melt index ionomers (b9520) And a lower melt index HDPE7030). Each of the four batches of melt contained three different low molecular weight ethylene copolymers (i.e., ethylene copolymerized with acrylic or methacrylic acid) as flow additives and no additive in the control. The detailed composition and resulting data are shown in table 1.

As shown in table 1, the ethylene/methacrylic acid copolymer flow modifier was more effective than the ethylene/acrylic acid copolymer, both resulting in a reduced viscosity relative to the control. Also, the tensile properties at room temperature were not substantially changed and the flexural modulus was only slightly reduced.

Example 2

To further illustrate the enhanced flow characteristics of the flow modified blends of the present invention, the ionomer/HDPE blend of melt 1 in example 1 was modified with an ethylene/acrylic acid copolymer (AC 580; 90/10E/AA) at four different additive concentrations between 3.0 and 9.0 wt%. The melt index of the resulting blend was measured and plotted as a function of the weight percent of ethylene/acrylic acid copolymer in the blend, with the results shown in figure 1. When C580 was increased from 3.0% to 9.0%, the melt index almost doubled compared to the control, the melt viscosity decreased by 40-50%, and the flexural modulus, low temperature notch cantilever impact strength, and melt strength were not substantially affected.

Example 3

Additional 10 batches of melt containing high density polyethylene and ionomer blends were prepared and tested. These melts contained higher molecular weight HDPE having a melt index of 2.8Melt and higher melt index (MI-5) ionomersWhich (HDPE-) The blend was mixed at a weight ratio of 1.65 and the resulting mixture had a melt index of 3.2 prior to the addition of the flow modifier. Three different ethylene/acrylic acid copolymers (AC540, 5% AA; AC580, 10% AA; AC5120, 15% AA) with different acrylic acid comonomer contents were added to each mixture at different fluid modifier concentrations (3.0, 6.0 and 9.0 wt%). The data obtained are shown in Table 2. As shown by these data, mixing is reduced by increasing the AC resin contentThe melt viscosity of the compound and increases the melt index. The tensile properties are not substantially affected, while the deflection coefficient is only slightly reduced. As AC540 and AC5120 increased, the low temperature notched cantilever impact strength decreased. In contrast, the impact strength was unchanged using AC580 low temperature notched cantilever beam. Also, as the amount of AC580 was increased, there was no change in low temperature notched cantilever impact strength. The melt index of the resulting blend is plotted as a function of the weight percent of ethylene/acrylic acid copolymer in the blend, and the results are shown in FIG. 2.

Example 4

An additional set of lot number blends containing ionomers with a relatively high melt index were prepared and tested9650) Relatively low molecular weight HDPE(s) blended and otherwise combined with three different amounts of glass fiber additives6060). Each blend was modified by adding two different ethylene/acid copolymers (HPU E/MAA, 9.6% MAA and AC580E/AA, 10% AA) in nearly the same amount. The data obtained are shown in Table 3. The data show that: the flow was improved when ethylene/methacrylic acid copolymer or ethylene/acrylic acid copolymer was added to ionomer/HDPE blends reinforced with 10% glass fibers.

The melt viscosity is reduced by 50-60%.

Example 5

Additional 5 batches of melt containing high density polyethylene and ionomer blends were prepared and tested. Run No. 1 relates to ionomer blended with relatively low melt index/viscosity ((II))9520) A relatively high molecular weight HDPE having a melt index of 2.87030). In subsequent batches, by replacing the higher melt index ionomers respectively ((II))9650) (ii) a Replacing ionomer with higher melt index grade replacing HDPE: (6060) The main portion of (1); and replacing only the major portion of the HDPE, reducing the viscosity of the mixture. Run No. 5 contained the ionomer/HDPE blend of run No. 1, which contained 9.1% ethylene/acrylic acid copolymer (AC580) as a flow modifier. The data obtained are shown in table 4. As shown in the table, at each recorded shear rate, the composition of run No. 5 had properties comparable to other compositions with much lower melt viscosities. In other words, the addition of the ethylene/acrylic acid copolymer to the ionomer/high density polyethylene blend improves flow characteristics without significantly degrading physical properties.

Example 6

To illustrate the effect of adding a cantilever impact additive to a flow modified ionomer/high density polyethylene blend, another set of four batches of a co-batch was prepared and testedAnd (3) mixing. 1.0 wt.% of glass fiber reinforcement was added to each batch. No additional flow or impact additives were added to batch 1. Batch 3 had an ethylene/acrylic acid copolymer (AC580) as the flow modifier. The other two batches contained both a flow modifier (AC580) and a Maleic Anhydride (MAN) modified high density polyethylene (Sclair 2907HDPE) available from DuPontof Canada under the trade name of CanadaE MB-100D (MAN-g-HDPE; -1% MAN, MI ═ 2). The data obtained are shown in Table 5. As shown, the compositions in batches 2 and 4 had properties comparable to melt 3, wherein the beneficial effect of the ethylene/acrylic acid copolymer flow modifier was not compromised by the additional presence of MAN modified polyethylene impact additive.

Industrial applicability

As described above, the addition or incorporation of a low molecular weight ethylene/acrylic acid (methacrylic acid) copolymer to an ionomer/high density polyethylene blend can reduce the viscosity and improve the flowability of the resulting blend without significantly reducing physical properties such as impact resistance, tensile strength. The blends obtained according to the invention exhibit reduced viscosity and improved flow and are particularly useful for the manufacture of automotive parts, instrument panels and the like having class a surfaces.

Claims (8)

1. An ionomer/high density polyethylene blend comprising 80 to 20 parts by weight high density polyethylene per 20 to 80 parts by weight ionomer and having improved flow properties, comprising 1 to 20 parts by weight of a low molecular weight copolymer of ethylene and at least one other comonomer selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof, for each 100 parts by weight ionomer/high density polyethylene blend, wherein the low molecular weight copolymer has a melt index greater than 350dg/min as determined according to ASTM D1238 and the acrylic and methacrylic acid mixed comonomer content is at least 5% by weight.

2. The ionomer/high density polyethylene blend of claim 1 wherein said low molecular weight copolymer of ethylene and at least one other comonomer has a melt index of at least 900 dg/min.

3. The ionomer/high density polyethylene blend of claim 1 wherein said low molecular weight copolymer of ethylene and at least one other comonomer has an acrylic acid and methacrylic acid mixed comonomer content of at least 9 weight percent.

4. The ionomer/high density polyethylene blend of claim 1 further comprising 1 to 20 weight percent of a polyethylene modified with 0.2 to 5.0 weight percent of a maleic anhydride comonomer per 100 parts by weight of the ionomer/high density polyethylene blend.

5. A method of reducing the viscosity of an ionomer/high density polyethylene blend comprising 80-20 parts by weight high density polyethylene per 20-80 parts by weight ionomer, comprising the step of mixing 1 to 20 parts by weight of a low molecular weight copolymer of ethylene and at least one other comonomer selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof, wherein said low molecular weight copolymer has a melt index greater than 350dg/min as determined according to ASTM D1238 and the acrylic and methacrylic acid mixed comonomer content is at least 5% by weight, per 100 parts by weight ionomer/high density polyethylene.

6. The process of claim 5 wherein the low molecular weight copolymer of ethylene and at least one other comonomer has a melt index of at least 900 dg/min.

7. The process of claim 5 wherein said low molecular weight copolymer of ethylene and at least one other comonomer has an acrylic acid and methacrylic acid mixed comonomer content of at least 9 weight percent.

8. The method of claim 5 further comprising the step of blending into each 100 parts by weight of the ionomer/high density polyethylene blend from 1 to 20 weight percent of polyethylene modified with 0.2 to 5.0 weight percent of a maleic anhydride comonomer.