BACKGROUND OF THE TNVENTTON

1 . Field of the Invention

The present invention generally relates to resin compositions and to products made therefrom. More specifically, the present invention is directed to an improved high density polyethylene (HDPE) resin, preferably containing recycled high density polyethylene (recycled HDPE or RHDPE) and an additive to improve the environmental stress crack resistance (ESCR) and impact resistance of products made therefrom. The most preferred resin comprises virgin HDPE, recycled HDPE and an additive selected from the group consisting of linear low density polyethylene (LLDPfi) and thermoplastic elastomers, especially polyisobutylene (PIB).

2. Description of th Background

Among the many uses of HDPE is the production of bottles for consumer liquids. Millions of HDPE bottles are produced annually. Exemplary products include miDc bottles, distilled, spring and drinking water bottles, oil bottles and the like. Because these containers are typically one way containers, they result in large quantities of waste.

The desire to recycle plastics has increased in recent times. Recycling offers benefits by conserving the raw materials from which the plastics are produced and by minimizing the requirements for limited trash disposal facilities. In fact, the need to conserve has heea perceived by some to be so severe that legislation has been proposed which would severely limit, if not eliminate, disposable plastic packaging. In view of this trend, rapid development of recycling systems for plastics is necessary to preserve the viability of the industry in the face of legislation against single use disposable packaging.

Because the blow molding industry is especially vulnerable to these legislative initiatives, it has mobilized to implement recycling programs. Perhaps most critical to the development of effective recycling programs is development of collection, sorting and reprocessing systems needed to supply the large quantities of clean, recycled material necessary for meaningful recycling volumes. The ability to supply recycled plastic materials of known resins is crucial. The Plastic Bottle Institute of the Society of Plastics Industries has proposed a container coding system which will help facilitate the sorting of bottles produced from different resins. Most major bottle producers now have programs in place to investigate the feasibility of both monolayer and coextruded containers using various

concentrations of recycled resin.

A typical, one-way, plastic consumer product produced in high volume is one quart oil containers. In response to recycling concerns, Exxon USA and Exxon Chemical Co. began a study of the use of recycled HDPE for consumer oil bottles. Continued ability to produce its familiar red bottles was a constraint on this program. Both monolayer and coextruded multi-layer containers employing recycled HDPE were considered. Although coextrυded multi-layer containers would permit the use of colored, recycled resins by permitting the resin containing the colored, recycled material to be buried between layeπ of virgin material of the desired color or to be hidden in an inside layer of the container, higher capital costs and more complex manufacturing procedures make coextrusion the less favored system. The more preferred system would produce a monolayer container including the recycled material in a single layer. Accordingly, preferred recycled materials would have to be clear so as not to interfere with the desired color of the final product. An ideal, clear recycled material is dairy RHDPE. Because of the large quantities of dairy RHDPE available from plastic milk bottles, dairy RHDPE was selected for this study for use in manufacturing oil bottles using recycled HDPE.

Bottles produced using RHDPE provide unacceptable resistance to impact and to environmental stress cracking. Accordingly, RHDPE cannot be used alone for producing plastic bottles. Others have attempted to circumvent the poor properties of RHDPE by ming blends of recycled HDPE together with virgin HDPE. However, bottles produced using these blended resins still lack acceptable resistance to impact and to environmental stress cracking. Accordingly, these blended resins and products produced therefrom were also unsatisfactory. The blow molding industry continues to seek a resin having improved resistance to environmental stress cracking and to impact and which employs recycled HDPB.

SUMMARY OF TOE INVENTION

The present invention provides a new and improved resin composition useful for blow molding. This improved resin comprises recycled HDPE and optionally virgin HDPE, together with an additive selected from the group consisting of LLDPE, thermoplastic elastomers, mixtures of those elastomers and mixtures of LLDPE and at least one of those elastomers. These improved resin compositions broadly comprise from about 0.1 to about 40 weight percent recycled HDPE and from about 0.1 to about 50 weight percent additive with the balance comprising virgin HDPE. Preferably, the additive is selected from the group consisting of LLDPE, PIB and mixtures thereof. More preferably the recycled HDPE and additive each comprise not more than about 25 weight percent of the resin and are present in about equal weight percents. More preferably the improved resin compositions contain from about 15 to about 25 weight percent recycled HDPE and from about 15 to about 25 weight percent additive.

The methods of the present invention provide methods for producing blow molded products having improved ESCR and/or impact resistance by employing an improved resin comprising HDPE, preferably a blend of virgin and recycled HDPE, with an additive selected from the group consisting of LLDPE, thermoplastic elastomers and mixtures thereof. The improved resins of the present invention which employ the described additives together with HDPE, preferably including recycled HDPE, produce blow molded products having improved environmental stress crack resistance (ESCR) and improved drop impact resistance. Broadly, an effective amount of additive increases these properties over those exhibited for products made from similar resins but without the claimed additive. In a more preferred embodiment, an effective amount of additive provides dramatic increases in these properties to produce products having resistance to environmental stress cracking and drop impact greater than that for similar products of virgin HDPE.

The present invention provides methods for improving the resistance to environmental stress cracking and drop impact of a blow molded product These methods broadly comprise producing a modified resin comprising HDPE and an additive selected from the group consisting of LLDPE, thermoplastic elastomers, mixtures of those elastomers and mixtures of LLDPE and at least one of those elastomers and blow molding a product from that resin, wherein the additive is added in an amount sufficient to increase the ESCR and/or impact resistance of the product so that the ratio of the ESCR and/or impact resistance of the product

to the ESCR and/or impact resistance of a similar product comprised of the same resin but not including the additive is greater than 1. In a more preferred embodiment, these methods comprise adding an effective amount of the additive to increase the ESCR and/or the impact resistance of the product so that the ratio of the ESCR and/or impact resistance of the product to the ESCR and/or impact resistance of a similar product of virgin HDPE is greater than 1. HDPE useful in this method is selected from the group consisting of virgin HDPE, recycled HDPE and mixtures of virgin and recycled HDPE. Preferably the HDPE comprises a blend of virgin and recycled HDPE Most preferably the recycled HDPE is present in an amount up to about 25 weight percent of the composition. The resin compositions, blow molded products and methods of improving the ESCR and impact resistance of blow molded products of the present invention provide improved properties to HDPE products, especially HDPE products containing recycled HDPE. The present invention offers a method for improving the ESCR and/or impact resistance of blow molded HDPE products and is particularly useful in permitting the use of recycled HDPE to produce products having improved properties. These and other meritorious features and advantages of the present invention will be more fully appreciated from the following detailed description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and intended advantages of the present invention will be more readily apparent by the references to the following detailed description in connection with the accompanying drawings, wherein: Fig. 1 is a bar graph illustrating the measured environmental stress crack resistance

(ESCR) for identical bottles produced from varying resin formulations and illustrating the dramatic improvement in ESCR for bottles produced using resin compositions in accord with the present invention;

Fig. 2 is a bar graph illustrating the measured resistance to top load for identical bottles produced from varying resin formulations, including bottles produced using resin compositions in accord with the present invention;

Fig. 3 is a bar graph illustrating the drop impact resistance for identical bottles produced from varying resin formulations and iUustrating the improvement in impact resistance for bottles produced using resin compositions in accord with the present invention; and

Fig. 4 is a bar graph illustrating the information in preceding Figs. 1-3 wherein the measured values have been converted to percentages relative to virgin resin B to illustrate more clearly the changes and improvements in properties achieved by using resin compositions in accord with the present invention. While the invention will be described in connection with the presently preferred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included in the spirit of the invention as defined in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to improved resin compositions useful for blow molding products, particularly bottles. The improved resin compositions comprise HDPE and an additive selected from the group consisting of LLDPE, thermoplastic elastomers and mixtures thereof. The present invention provides methods for improving the environmental stress cracking and the resistance to drop impact for products, particularly bottles, manufactured from the improved resin compositions. Most preferably, the improved resin compositions comprise a blend of recycled HDPE together with virgin HDPE and an effective amount of the above additive sufficient to improve the ESCR and/or impact resistance to the desired level.

As the need to employ recycled plastics has increased, bottle producers have examined both monolayer and cocxtnided multi-layer products. Monolayer construction offers the advantage of simple processing and fast project start-up. However, many recycled polymers contain unwanted dyes which will adversely effect the color of the final product in a monolayer project. Colored recycled material is easier to accommodate in coextrυded multi¬ layer products. Multi-layer products permit the use of recycled polymers of mixed colon in an inner or hidden layer while using virgin polymers with the appropriate dye for the desired color for the exterior surface. However, coextnided multi-layer products are more difficult and expensive to produce. The capital cost for coextrasion equipment for multi-layer applications is higher. Accordingly, monolayer products are presently preferred.

Because the physical properties of recycled polymers are often poorer than virgin polymers, it has been desirable to explore the use of blends of virgin and recycled polymers. Exxon USA and Exxon Chemical Co. have studied the use of recycled high density polyethylene (recycled HDPE or RHDPE) for the manufacture of oil bottles, particularly ooe- quart consumer oil bottles. Dairy RHDPE was chosen for this study. Dairy RHDPE is a plentiful recycled polymer particularly appropriate for this use because it generally does not include any colored dyes. Although exhibiting poorer physical properties than virgin HDPE, dairy RHDPE may be blended with virgin HDPE to produce a recycled blend which would permit manufacture of the bright and familiar red color of Exxon oil bottles. Because of the lower cost and ready availability, studies employing dairy grade recycled HDPE were begun. Because mixed recycled and virgin HDPE resins exhibit better roughness properties than those of RHDPE alone, it was decided to employ blends of virgin and recycled HDPE It became

readily apparent that the toughness properties of recycled HDPE and of blends thereof required improvement. The present invention is directed to improving those properties in HDPE products, particularly where the resin composition includes RHDPE

Consumer oil bottles are subjected to significant abuse and, accordingly, must be of high integrity. These oil containers must exhibit adequate top load force resistance to withstand crushing when palletized and stacked, must exhibit acceptable resistance to drop impact and must exhibit sufficient resistance to environmental stress cracking (ESCR) for storage while loaded. The integrity of these containers must not be compromised by the inclusion of recycled materials. In order to develop a database which encompassed these elements, three samples of commercial oil containers produced by different companies using different resins were tested. These one-quart commercial oil bottles have been identified as being produced from resins A, B and C. Physical properties, including weight, resin density, resin melt index, and resistance to top load, to drop impact and to environmental stress cracking were determined for each of these bottles. The tests were chosen based on the perceived criticality of properties for consumer oil containers. The results are listed in Table I.

TABLE I

'ASTM D-2659, filled with tap water, platen speed 1.8 in./min.

'ASTM D-2463, procedure C. 'ASTM D-2561, procedure C, 1/3 filled with 10% Igepal* al 140 ^β F and

4.7 psi internal pressure.

Conventional testing methods were employed. Resistance to top load was measured according to the procedure set forth in ASTM D-2659 using a moving platen device with a load cell. The containers were filled with room temperature tap water and capped. The speed of the moving platen was set at 1.8 inches per minute. The load values were measured at both one-quarter inch deflection and at yield. The results are listed in Table I.

Resistance to drop impact was measured using the drop test procedure set forth in cumulative method C of ASTM D-2463. Containers were filled with water, capped and dropped, initially from ten feet. Each subsequent drop was increased one foot in height until failure. The average cumulative drop height was then calculated as shown in ASTM D-2463.

The results are listed in Table I.

Environmental stress crack resistance (ESCR) was measured using the method set forth in ASTM D-2561. The test was performed at a temperature of 140'F and a constant internal pressure of 4.7 psi. The containers were one-third filled with a ten percent solution of

Igepal* in water. IgepaT* is the registered trademark for a nonyl-phenoxy poly (ethyleneoxy) ethanol sold by GAF Corp. The results are listed in Table I.

The following conclusions were reached:

(1) Top load is the most immediately critical property in terms of stacking strength.

(2) ESCR is important in terms of longevity of containers in stacked warehouse storage. (3) Drop impact resistance is assigned the lowest importance since all containers tested passed at least a ten foot drop.

Bottle weight, together with the density and melt index of the resins, were also measured and are listed in Table I. See also Table II listing these properties for virgin resins

A, B and C together with the same properties for another virgin resin D, and some exemplary additives useful in accord with the present invention.

TABLE π PROPERTIES OF RESBXS

Resins Melt Index (g. lO min HLMI ( JlO min

Resin A (virgin HDPE) 0.36 Resin B (virgin HDPE) 0.27

Resin C (virgin HDPE) 0.44

Resin D (virgin HDPE) 0.38

Recycled HDPE 0.66

LLDPE 1.00 65% PIB, 35% virgin 0.25 HDPE

The virgin resins comprise HDPE prepared using both the Phillips and Ziegler catalyst systems. The virgin resin properties illustrated in Tables I and π define the general property ranges found in commercial oil bottles. While all have from 80 to 90 pounds loafing maximum, the loading rates at one-quarter inch deflection reflect the varying effects of the

bottle design. The average drop heights of at least 14 feet show that oil containers have a large cushion of safety in this area, since the containers withstand at least four drops of greater than 10 feet. The ESCR data shows that eight hours is probably an adequate acceptance criteria in this testing procedure for containers produced with recycled HDPE In order to investigate the tendency of standard motor oil to initiate stress cracking, tests were performed in accord with the procedure set forth in ASTM D-1693 using two different standard resin grades and two different liquids. In these comparative tests, the testing liquid comprised a ten percent solution of IgepaT* in water in a first series compared with 10W-40 oil in a second series. From these tests a rough estimate may be made that the ESCR potential of oil as compared to a ten percent Igepal* solution is on the order of 20 to

700 or 1 to 35. That is, a ten percent Igepal* solution is 35 times more effective at initiating environmental stress cracking than is oil. The results of these tests are listed in Table m.

TABLE ffl ESCR USING DIFFERENT FLUIDS ESCR' at F-SQ fhrc.)

Testing Liquid Resin B RCSJn D

10% Igepal* 20 120

10W-40 Oil 700 > 1000*

'ASTM D-1693. *No failure.

Having determined properties for a variety of virgin resins, it was now desired to produce and test bottles containing recycled material, particularly dairy grade recycled HDPE

Identical bottles were produced by a commercial bottle manufacturer and by Exxon Chemical

Company at its Baytown Polymer Center (BP . Bottles produced at BPC were manufactured in a Battenfeld Fischer VK-1 continuous-type machine. The bottles produced by the

commercial manufacturer were of a design similar to a commercial container while the bottles produced at the BPC facility were similar to a Boston Round with 32 ounce volume. Both types of bottles were produced using a standard blow molding resin B comprising virgin HDPE and using the standard resin B to which had been previously added 20 percent dairy- grade RHDPE obtained from Partek, Inc. These bottles were tested for resistance to top load, drop impact and environmental stress cracking in accord with the procedures described above. The results of these tests are listed in Table IV.

TABLE IV

'ASTM D-2659, filled with tap water, platen speed 1.8 in.Λnin. 'ASTM D-2463, procedure C.

'ASTM D-2561, procedure C, 1/3 filled with 10% Igepal* at 140 ^β F and 4.7 psi internal pressure.

*No failure.

These tests illustrate that the inclusion of 20 percent recycled HDPE results in little change in the top load performance of bottles produced therefrom. While the drop impact resistance of these bottles is negatively effected, the change is not dramatic. However, ESCR is reduced by about 30 percent with the addition of 20 percent recycled HDPE. This dramatic reduction in ESCR would result in an unacceptable resin. In summary, the addition of recycled HDPE to virgin HDPE lowers both the drop impact resistance and the ESCR of the produced bottles. More particularly, the drastic reduction in ESCR would result in unacceptable products. Accordingly, a method for improving both the ESCR and the drop impact resistance of resins containing recycled HDPE is required. The present invention provides a method for improving these properties and, in fact, for improving these properties to levels meeting or exceeding those exhibited by the virgin HDPE in resin blends comprising virgin HDPE and recycled HDPE

In the method of the present invention the ESCR and/or drop impact resistance of a blow molded product is improved by the addition to the resin HDPE of an effective amount of an additive selected from the group consisting of LLDPE thermoplastic elastomers, mixtures of those elastomers and mixtures of LLDPE and al least one of those elastomers. The HDPE is selected from the group consisting of virgin HDPE, recycled HDPE and mixtures of virgin and recycled HDPE. Preferably the HDPE comprises a blend of virgin and recycled HDPE Preferably, the recycled HDPE is present in the resin in an amount between about 0.1 and about 40 weight percent of the resin, more preferably up to about 25 weight percent and most preferably between about 15 and about 25 weight percent In a more preferred embodiment an effective amount of the additive is added to increase the ESCR and/or drop impact resistance of the product to equal or exceed the ESCR and/or drop impact resistance of a similar product comprised of the virgin HDPE. In this most preferred embodiment the modified HDPE resin includes recycled HDPE virgin HDPE and the additive and produces products having ESCR and/or drop impact resistance better than achieved with virgin HDPE. Accordingly, the methods and resin compositions of the present invention not only permit use of recycled HDPE but also produce products having properties matching or exceeding those of products produced with virgin HDPE. In summary, the present invention both permits advantageous use of recycled HDPE and produces products having improved ESCR and/or drop impact resistance.

The resin compositions of the present invention may also be described as comprising

recycled HDPE, optionally virgin HDPE and an additive selected from the group consisting of LLDPE, thermoplastic elastomers, mixtures of those elastomers and mixtures of LLDPE and at least one of those elastomers. The preferred resin compositions comprise from about 0.1 to about 40 weight percent recycled HDPE, from about 0.1 to about 50 weight percent additive with the balance being virgin HDPE. Preferably the recycled HDPE and additive comprise about equal weight percents. Preferably the recycled HDPE and additive are present in amounts less than about 25 weight percent, more preferably between about 15 and about 25 weight percent and most preferably about 20 weight percent. The most preferred additives comprise LLDPE, PIB and mixtures thereof. The present invention further comprises blow molded products produced from the improved resin compositions described above. These products preferably contain an effective amount of the additive to increase the ESCR and/or drop impact resistance of the product above that of a similar product comprised of the same resin but not including the additive. More preferably these products contain an effective amount of the additive to increase the ESCR and/or drop impact resistance of the product to a level greater than that exhibited by a similar product of the virgin HDPE in the blend.

The improvements achieved by the present invention are illustrated in the following examples. Five resin blends were prepared. All blends used Resin B as the virgin HDPE and dairy grade recycled HDPE as the recycled material. LLDPE and PIB were employed as the additive. The blend ratios and melt indices of Resin B and those blends are listed in Table V.

TABLE V BLEND FORMULATIONS AND PROPERTIES

BLEND COMPONENT

Virjia

3.25

6.5

20

Standard test bottles were prepared at the Baytown Polymer Center as previously described. Those test bottles were then tested for resistance to top load, drop impact and environmental stress cracking using the standard ASTM methods previously described. The results of those tests are listed in Table VI.

TABLE VI

'ASTM D-2561, procedure C, 1 3 filled with 10% Igepal* at 140 ^β F and

4.7 psi internal pressure.

'ASTM D-2659, filled with tap water, platen speed 1.8 in./ in.

'ASTM D-2463, procedure C.

These test results are illustrated in Figs. 1-4. Figs. 1-3 illustrate with bar graphs the effect of recycled HDPE and additive on, respectively, ESCR, top load and drop impact

These measured values have been converted to percentages based upon the respective values of virgin resin B and the percentages illustrated with bar graphs in Fig. 4.

Figs. 1 and 4 illustrate that ESCR is the property most effected by addition of recycled HDPE to virgin HDPE and also most improved by the additive of the present invention. In summary, the ESCR of bottles including 10 to 20 percent recycled HDPE is about 30 percent less than that for bottles of virgin HDPE ESCR is improved by the addition of 3.25 weight percent PIB and, in fact, is about 20 percent better than that for virgin resin with the addition of only about 6.5 weight percent PIB. Addition of 20 weight percent LLDPE improves the ESCR by almost 500 percent

Figs. 2 and 4 illustrate that resistance to top load is relatively uneffected by the addition of recycled HDPE to virgin HDPE. However, addition of the additives of the present invention causes some of loss resistance to top load, thus limiting the desirability of adding higher percentages of additive. Figs. 3 and 4 illustrate that drop impact resistance decreases with the addition of recycled HDPE to virgin HDPE. Resistance to drop impact shows improvement with the addition of PIB and, in fact, is 10 percent better than that for virgin HDPE with the addition of 20 weight percent LLDPE.

In summary, both ESCR and drop impact resistance appear to progressively improve with the addition of more additive. However, because resistance to top load appears to be adversely effected, a compromise must be reached in order to maximize the benefits of improved ESCR and drop impact resistance while minimizing loss of top load resistance.

The foregoing description of the invention has been directed in primary part to a particular preferred embodiment in accordance with the requirements of the patent statutes and for purposes of explanation and illustration. It will be apparent, however, to those skilled in the art that many modifications and changes in the specifically described resin compositions, blow molded products thereof and methods for improving the resistance to drop impact and environmental stress cracking of blow molded products may be made without departing from the true scope or spirit of the invention. Therefore, the invention is not restricted to the preferred embodiments described but covers all modifications which may fall within the scope of the following claims.