Processing Modifier for High-Density Polyethylene

This invention relates to a processing modifier for high-density polyethylene. More particularly, this invention relates to the use of a polyvinyloctadecyl ether as an additive in the extrusion of high-density polyethylene resins.

In the absence of a processing modifier, the surface of most extruded polyethylene resins is undesirably rough and non-uniform. Moreover, such extruded resins may exhibit a reduction in physical properties such as tensile strength at break, percentage elongation at break, tearing resistance, and impact resistance. Addition of process modifiers to extruded resin compositions is therefore beneficial in regard to physical strength properties and surface appearance. However, such additives may result in the reducing of other properties of the extrudates such as gloss, heat-sealability, blocking, transparency and moisture resistance. Therefore, it is advisable to avoid an excess of such additives.

In general, the present invention provides a process for extruding high-density polyethylene resins, comprising the steps of (a) heating above its melting point a mixture of about one hundred parts by weight of high-density polyethylene, and between about 0.03 and about 0.5 parts by weight of a polyvinyloctadecyl ether; and (b) extruding the melt formed in step (a), thereby forming an extrudate.

It is an object of this invention to provide a processing modifier for high-density polyethylene. It is a further object of this invention to provide an improved process for extruding high-density polyethylene resins. It is a further object of this invention to provide a process for extruding high-density polyethylene resins whereby the extrudates are characterized by a smooth and uniform surface. It is a still further object of the invention to provide a process for the extrusion of high-density polyethylene resins whereby the extrudates exhibit an improved tensile strength at break, percentage elongation at break, tearing resistance, and impact resistance. These and other objects of the invention will be apparent to those skilled in the art from the more detailed description which follows.

The following terms used herein are defined as follows:

Yield Strength--expressed in pounds per square inch, as defined in ASTM Standard No. D 882, is the ratio of the yield load to the original minimum cross-sectional area of the specimen.

Tensile Strength at Break--expressed in pounds per square inch, as defined in ASTM Standard No. D 882, is the ratio of the load at break to the original cross-sectional area of the specimen.

Percentage Elongation at Break--expressed in percent, as defined in ASTM Standard No. D 882, is the ratio of the elongation at the moment of rupture of the specimen to the initial gage length of the specimen times one-hundred.

Tearing Resistance--expressed in grams per millimeter, as defined in ASTM Standard No. D 1922, is calculated by the following formula: ##EQU1## The Elmendorf Tear-Resistance Meter is described in ASTM Standard No. D 1922.

Impact Resistance--expressed in pounds per square inch, defined as work done per volume acted on, is calculated by the following formula: ##EQU2##

The following description illustrates the manner in which the principles of the present invention are applied, but is not to be construed as in any sense limiting the scope of the invention.

In the preferred method of practicing this invention, about one hundred parts by weight of high-density polyethylene resin is blended with between about 0.1 and about 0.3 parts by weight of a polyvinyloctadecyl ether. The mixture of polyethylene and polyether is heated to a temperature between about 140.degree. C. and about 350.degree. C. in an extruder, thereby forming a melt adapted for extrusion. The melt is then extended into a fused extrudate of any desired form or shape.

More preferably, the mixture is heated to a temperature between about 200.degree. C. and about 300.degree. C. in the extruder. The polyvinyloctadecyl ether used in the present invention as a process modifier is characterized as having a number-average molecular weight of between about 1,000 and about 10,000, and more preferably between about 3,000 and about 5,000. A polyvinyloctadecyl ether suitable for practicing this invention is manufactured and sold by the American Hoechst Corporation, Mountainside, New Jersey, under the tradename "Wax V."

The present invention will now be further illustrated by means of the following examples, which are not to be interpreted as in any sense limiting the scope of the invention.

A sample of high-density polyethylene resin was multiply-extruded into pellets on a three-quarter-inch 24:1 screw ratio thermoplastic extruder with a temperature profile for Zones 1 through 4 of 170.degree., 185.degree., 190.degree., and 190.degree. C. respectively, at fifty revolutions per minute (RPM). The pellets obtained thereby were then blown into film on a one-inch laboratory extruder with a one-inch annular die and a die gap of 0.025 inches, at a screw speed of sixty RPM, and a temperature profile for Zones 1 and 2, and Gate and Die Zones 1 and 2 of 193.degree., 196.degree., 198.degree., and 198.degree. C., respectively. Conventional high-density polyethylene film and rheological tests were made to characterize the extruded film.

In Example 1, no processing modifier was added to the polyethylene. In Example 2, 0.2 weight percent zinc stearate, a known processing modifier, was added. In Examples 3 and 4, 0.2 weight percent of a polyvinyloctadecyl ether was added, said ether characterized as having a number-average molecular weight of about 4,000. The test results obtained are listed in Table I, below.

The data displayed in Table I above clearly show the results of adding a polyvinyloctadecyl ether to high-density polyethylene as a processing modifier during extrusion. With the exception of yield strength, the properties listed therein were significantly improved by the use of the polyether modifier according to the present invention. By way of comparison, the use of zinc stearate in Example 2 led to values of these properties which were intermediate between the resin extruded with no processing modifier added, in Example 1, and the resins extruded with the addition of 0.2 percent polyvinyloctadecyl ether, in Examples 3 and 4.

In addition, the surfaces of the films blown in Examples 3 and 4 were considerably smoother than the surface of the film blown in Example 1, and substantially smoother than the surface of the film blown in Example 2.

While certain representative embodiments and details have been shown for the purpose of illustrating the present invention, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention.