EP0385976A4

EP0385976A4 - Vinylidene chloride interpolymer possessing improved extrudability

Info

Publication number: EP0385976A4
Application number: EP19870907874
Authority: EP
Inventors: Mark J. Hall
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1987-10-23
Filing date: 1987-10-23
Publication date: 1991-03-20
Also published as: JPH03500662A; WO1989003858A1; EP0385976A1; KR890701690A

Abstract

A process for improving the extrudability of a vinylidene chloride interpolymer particles wherein the vinylidene chloride interpolymer particles are melt blended with at least one extrusion aid having a calculated hydrophile/lipophile balance of less than about 2.0. Melt extruded products prepared therefrom have reduced carbon speck contamination, and, when in pellet form have improved extrudability for reextrusion into melt shaped articles.

Description

VINYLIDENE CHLORIDE INTERPOLYMER POSSESSING IMPROVED EXTRUDABILITY

The present invention relates generally to vinylidene chloride interpolymers. More specifically, the present invention relates to certain vinylidene chloride interpolymer pellets possessing improved extrudability and a reduced level of carbon contamination; and their manner of preparation by incorporation of an extrusion aid having a hydrophile/lipophile balance of less than 2.0.

Vinylidene chloride interpolymers are wellknown in the prior art. In the past, vinylidene chloride interpolymers have been produced by an emulsion or suspension polymerization process. Both the emulsion and suspension polymerization processes produce an aqueous dispersion of polymer particles having a relatively small particle diameter. The polymer particles are recovered from the aqueous dispersion by drying or other means for removing a majority of the aqueous phase. In the past, the practice has been to extrude the vinylidene chloride interpolymer directly from the particle form in which it is recovered.

In some instances, it is desirable to form the vinylidene chloride interpolymer particles into pellets prior to final extrusion. Unfortunately, melt extrusion-pelletization of the vinylidene chloride interpolymers leads to an undesirable level of carbon contamination in said pellets. Additionally, it has been found that such pellets are not easily extrudable. Attempts to extrude vinylidene chloride interpolymer pellets on conventional extrusion equipment have proven unsatisfactory due to variations in extrusion rate, variations in torque within the extruder, and variations in pressure within the extruder.

There is a need to produce vinylidene chloride interpolymer particles and pellets which are capable of being extruded without producing an unacceptable level of carbon contamination in the resultant extrudate without exhibiting excessive variations in extrusion rate, torque within the extruder, and pressure within the extruder.

In a first aspect, the present invention is a process for improving the extrudability of particles of a vinylidene chloride interpolymer of the type prepared from a major molar amount of vinylidene chloride and a minor molar amount of at least one second monomer selected from vinyl chloride and methyl acrylate: wherein the particles of vinylidene chloride interpolymer are blended with at least one extrusion aid having both a hydrophile portion and a lipophile portion and a calculated hydrophile/lipophile balance of less than 2.0; and wherein said extrusion aid is present in an amount in the range of from 0.01 to 1 part by weight per 100 parts by weight of vinylidene chloride interpolymer.

In a second aspect, the present invention is the product pellets formed by the first aspect of the invention, wherein the pellets have a lower carbon speck count and better extrudability than comparative pellets prepared without use of the extrusion aid having a calculated hydrophile/lipophile balance of less than 2.0.

Additionally, the present invention concerns a composition comprising a blended mixture of vinylidene chloride interpolymer particles and at least one extrusion aid having a hydrophile/lipophile balance of less than 2.0, and pellets formed therefrom.

Vinylidene chloride interpolymers suitable for use in the present invention are those vinylidene chloride interpolymers formed from vinylidene chloride and an amount of one or more monoethylenically unsaturated monomer copolymerizable with vinylidene chloride.

The vinylidene chloride interpolymers have polymerized therein vinylidene chloride in an amount of from about 40 to about 98 weight percent, beneficially from about 50 to about 96 weight percent, and desirably from about 60 to about 94 weight percent, based on total weight of the vinylidene chloride interpolymer.

The vinylidene chloride interpolymer comprises one or more monoethylenically unsaturated monomer copolymerizable with vinylidene chloride. The amount of monoethylenically unsaturated monomer is suitably from about 60 to about 2 weight percent, beneficially from about 50 to about 4 weight percent, and desirably from about 40 to about 6 weight percent, based on total weight of the vinylidene chloride interpolymer.

Monoethylenically unsaturated monomers suitable for use in the present invention include vinyl chloride, alkyl acrylates, alkyl methacrylates, acrylic acid, methacrylic acid, itaconic acid, acrylonitrile, and methacrylonitrile. The ethylenically unsaturated monomers are desirably selected from the group consisting of vinyl chloride, alkyl acrylates, and alkyl methacrylates, the alkyl acrylates and alkyl methacrylates having from about 1 to about 8 carbon atoms per alkyl group. The alkyl acrylates and alkyl methacrylates preferably have from about 1 to about 4 carbon atoms per alkyl group. The alkyl acrylates and alkyl methacrylates are most preferably selected from the group consisting of methylacrylates, ethylacrylates, and methyl methacrylates.

Methods of forming the vinylidene chloride interpolymers suitable for use in the present invention are well-known in the prior art. The vinylidene chloride interpolymer is generally formed through an emulsion or suspension polymerization process. Exemplary of such processes are U.S. Patents 2,558,728; 3,007,903; 3,642,743; and 3,879,359; and the methods described by R. A. Wessling, in Polyvinylidene

Chloride, Gordon and Breach Science Publishers, New York, 1977, Chapter 3. Typically, the monomeric materials are emulsified or suspended in an aqueous phase. The aqueous phase contains a polymerization initiator and a surface active agent capable of emulsifying or suspending the monomeric materials in the aqueous phase. The polymerization of the monomeric materials is usually carried out with heating and agitation. After polymerization is complete, the resulting suspension or emulsion of vinylidene chloride interpolymer has a majority of the aqueous phase removed.

In a preferred embodiment, the present invention concerns a process for improving the extrudability of the above described vinylidene chloride interpolymer. The process comprises melt blending the vinylidene chloride interpolymer with at least one defined extrusion aid. Extrusion aids suitable for use in the present invention have a "calculated hydrophile/lipophile balance" of less than 2.0, and preferably of less than 1.5.

The hydrophile/lipophile balance (HLB) refers to surfactant-type molecules which, by definition, contain a hydrophilic portion and a lipophilic portion. In effect, HLB is an expression of the relative simultaneous attraction of an emulsifier for water and for oil. For the purposes of this invention, the hydrophile/lipophile balance of many common substances are calculated by using a hydrophile/lipophile equation known to skilled artisans, and from knowing the chemical formula of the extrusion aid. The equation is set forth at page 244 of Surfactants and Interfacial Phenomena by Milton J. Rosen, J. Wiley and Sons

Interscience (1978). In particular, the formula used to calculate HLB's for nonionics is set forth as follows: 20 X [M_H/(M_H + M_L)], wherein M_H is the formula weight of the hydrophilic portion of the molecule and ML is the formula weight of the lipophilic (hydrophobic) portion of the molecule.

Hydrophile/lipophile balance values are set forth in McCutcheon's Emulsifiers & Detergents, McCutcheon Division, M. C. Publishing Co., Glen Rock, N.J. (North American Edition, 1983). For compounds not appearing in the listed reference, the HLB may be determined by blending the compound of unknown HLB with a compound of a known HLB. The two compounds are blended in varying ratios. The various blends of compounds are used to emulsify an oil of known required HLB. The best performing blend is assumed to have an HLB approximately equal to the known required HLB of the oil. From this, the HLB value of the compound of unknown HLB can be determined. This procedure is set forth in more detail in Kirk-Othmer Encyclopedia of Chemical Technology, (Third Edition), Volume 8, pages 910-916.

Extrusion aids suitable for use in the present invention are selected from the group consisting of oxidized polyethylene; oxidized polypropylenes; montan ester waxes, having 28 to 32 carbon atoms per molecule; long chain acids, having 18 or more carbon atoms per molecule, and the salt, ester, and amide derivatives thereof; naturally derived waxes; and mixtures thereof. Beneficially, the extrusion aid is selected from the group consisting of oxidized polyethylene; oxidized polypropylene; montan ester waxes having 28 to 32 carbon atoms per molecule; and mixtures thereof.

Preferably, the extrusion aid is oxidized polyethylene; oxidized polypropylene; or mixtures thereof. Oxidized polyethylene and oxidized polypropylene are well-known in the prior art. Oxidized polyethylene and oxidized polypropylene are generally prepared by forming the ethylene or propylene polymer through methods well-known in the art, and subsequently exposing said polymer to oxygen at an elevated temperature and for a time sufficient to achieve the desired degree of oxidation. Preferably, oxidized polyethylene is employed as the primary extrudion aid. Suitably, Allied 629A oxidized polyethylene, commercially available from Allied Corp., is the oxidized polyethylene.

The extrusion aids suitable for use in the present invention are typically melt blended with the vinylidene chloride interpolymer in an amount of from 0.01 part of extrusion aid per 100 parts vinylidene chloride interpolymer to 1 part of extrusion aid per 100 parts of vinylidene chloride interpolymer. Preferably the extrusion aid is melt blended with the vinylidene chloride interpolymer in an amount of from 0.01 part of extrusion aid per 100 parts of vinylidene chloride interpolymer to 0.3 part of extrusion aid per 100 parts of vinylidene chloride interpolymer. Most preferably the extrusion aid is melt blended with the vinylidene chloride interpolymer in an amount of from 0.015 part of extrusion aid per 100 parts of vinylidene chloride interpolymer to 0.2 part of extrusion aid per 100 parts of vinylidene chloride interpolymer. Most most preferably, the extrusion aid is melt blended with the vinylidene chloride interpolymer in an amount of from 0.03 part of extrusion aid per 100 parts vinylidene chloride interpolymer to 0.08 part of extrusion aid per 100 parts vinylidene chloride interpolymer.

When the extrusion aid is selected from the group consisting of oxidized polyethylene, oxidized polypropylene, or mixtures thereof, it is desirable that the extrusion aid comprise from 2 to 10 weight percent oxygen based on total weight of extrusion aid.

In one preferred embodiment of the present invention, wherein the extrusion aid is oxidized polyethylene comprising about 5 weight percent oxygen, the extrusion aid is melt blended with the vinylidene chloride interpolymer in an amount of from 0.03 part of extrusion aid per 100 parts vinylidene chloride interpolymer to 0.08 part of extrusion aid per 100 parts vinylidene chloride interpolymer.

The mixture of vinylidene chloride interpolymer and extrusion aid may contain a number of additives well-known to those skilled in the art. Exemplary of additives which may be incorporated in the mixture are plasticizers such as the epoxidized oils and resins, heat stabilizers such as inorganic bases, light stabilizers such as hindered phenol derivatives, pigments such as titanium dioxide, processing aids such as high molecular weight polymeric additives, lubricants such as low molecular weight wax-type additives, and the like. Each of these additives is known and several types of each are commercially available.

The inventor has found that a particular combination of specific additives yields pellets formed from vinylidene chloride interpolymer with superior extrudability. Specifically, the preferred formulation comprises the following additives.

An ethylene-vinyl acetate copolymer is employed as an additional extrusion aid; suitably, EVA 3180 ethylene-vinyl acetate copolymer which contains about 28 percent vinyl acetate and is commercially available from E. I. DuPont de Nemours Co. The EVA 3180 or an equivalent ethylene-vinyl acetate copolymer is incorporated into the vinylidene chloride interpolymer in the useful range of from 0.01 percent to 10 percent, most preferably in the range of from 1.2 percent to 2.1 percent.

A tetrasodium pyrophosphate is employed as an

HCl scavenger and stabilizer. For example, a modified tetrasodium pyrophosphate, commercially available from Monsanto, may be incorporated into the vinylidene chloride interpolymer. The tetrasodium pyrophosphate is micronized to between about 1-40 microns. The tetrasodium pyrophosphate is employed in the range of from 0.1 percent to 3 percent, most preferably in the range of from 1.2 percent to 2.1 percent.

Epoxidized oils and resins are suitably employed as plasticizers and stabilizers; suitably,

Vikoflex 7177 epoxidized soybean oil which contains oxirane groups and is commercially available from Viking Chemical Co. The Vikoflex 7177 epoxidized soybean oil or an equivalent epoxidized soybean oil is incorporated into the vinylidene chloride interpolymer in the range of from 0.1 percent to 3 percent, most suitably, in the range of from 0.7 percent to 1.1 percent. Further, when the vinylidene chloride is copolymerized with vinyl chloride, minor amounts of an antioxidant can be added to the film for stabilization. Suitable antioxidants include ional, citric acid, vitamin E. IRGANOX^® 1076 antioxidant, commercially available from CIBA-GEIGY Corp., is the most preferred anitoxidant. The antioxidant may be incorporated into the vinylidene chloride interpolymer in an amount in the range of from 50 to 2000 parts per million, most preferably in the range of from 200 to 800 parts per million.

Blending of the vinylidene chloride interpolymer and any additives can be accomplished by using conventional melt processing, as well as dry blending techniques.

Melt blending of the vinylidene chloride interpolymer, the extrusion aid, and any additives can be accomplished by using conventional melt processing techniques provided two conditions are met. First, melt processing must be accomplished at a temperature below that at which decomposition of the vinylidene chloride interpolymer becomes significant. Second, sufficient shear must be generated during melt processing to provide a homogenous extrudate within a reasonable mixing time.

Conventional melt processing equipment which may be used includes heated two-roll compounding mills, Brabender mixers, Banbury mixers, single screw extruders, twin screw extruders, and the like. Desirable results are obtained when an extruder, either single screw or twin screw, is used for melt blending the vinylidene chloride interpolymer and the extrusion aid.

When dry blending, the components should form a visually uniform admixture. Suitable dry blending equipment includes Hobart mixers, Welex mixers, Henschel High Intensity mixers, and the like.

The vinylidene chloride interpolymer and extrusion aid mixture is then extruded. In one embodiment, the additives and interpolymer are physically blended and melt processed into any suitable final product.

In a preferred embodiment of the present invention, the mixture of vinylidene chloride interpolymer and extrusion aid is pelletized. Methods of forming the mixture into pellets are well-known to those skilled in the art. Any method capable of forming the mixture into pellets is suitable for use in the present invention. For the purposes of this application, the terms "pellet" or "pellets" refer to "particles" having a minimum cross-sectional dimension of at least 1/32 inch, beneficially of at least 1/16 inch, and preferably of at least 1/8 inch, said pellets suitably have a maximum cross-sectional dimension of at least 1/2 inch, beneficially of at least 3/8 inch, and preferably of at least 1/4 inch. Exemplary of a method suitable for use in forming the pellets of the mixture are extrusion through a strand die and pelletization by chopping the extruded strand into pellets.

Applicant has discovered that the process and composition according to the present invention improves the extrudability of the vinylidene chloride interpolymer and allows for the satisfactory extrusion of vinylidene chloride interpolymer pellets formed therefrom. The vinylidene chloride interpolymer is considered to possess improved extrudability when the mixture of vinylidene chloride interpolymer and extrusion aid can be formed into a pellet which possesses less carbon contamination than a pellet formed from the vinylidene chloride interpolymer alone. Pellets formed from the mixture of vinylidene chloride interpolymer and extrusion aid are considered to be satisfactorily extrudable when the pellets exhibit a relatively constant rate of extrusion, torque within the extruder, and pressure within the extruder.

The process of the present invention can be used to form a variety of films or other articles. As is well known in the art, the films and articles are fabricated with conventional coextrusion, e.g, feedblock coextrusion, multimanifold die coextrusion, or combinations of the two; injection molding; extrusion molding; and lamination techniques. Articles formed therefrom include blown and cast, mono and multilayer, films; rigid and foam sheet; tubes; pipes; rods; fibers; and various profiles. Lamination techniques are particularly suited to produce multi-ply sheets. As is known in the art, specific laminatng techniques include fusion, i.e., whereby selfsustaining lamina are bonded together by applications of heat and pressure; wet combining, i.e., whereby two or more plies are laminated using a tie coat adhesive, which is applied wet, the liquid driven off, and combining by subsequent pressure laminating in one continuous process; or by heat reactivation, i.e., combining a precoated film with another film by heating and reactivating the precoat adhesive so that it becomes receptive to bonding after subsequent pressure laminating.

Exemplary articles include relatively rigid containers used for the preservation of food, drink, medicine and other perishables. Such containers should have good mechanical properties, as well as low gas permeabilities to, for example, oxygen, carbon dioxide, water vapor, odor bodies or flavor bodies, hydrocarbons or agricultural chemicals. Most organic polymers such as the polyolefins, styrene polymers and the like, by themselves, do not possess sufficent resistance to transmission of atmospheric gases and vapors. Consequently, multilayer sheet structures employed in packaging materials have organic polymer skin layers laminated on each side of a vinylidene chloride interpolymer barrier layer, generally with glue layers used to promote adhesion between the barrier layer and dissimilar material layers. As is well known in the art, such laminated structures are fabricated with conventional injection molding, extrusion molding, coextrusion or conventional lamination processes, or similar techniques.

The present invention is illustrated in further detail by the following examples. The examples are for the purposes of illustration only, and are not to be construed as limiting the scope of the present invention. All parts and percentages are by weight unless otherwise specifically noted. Examples

Example 1

A vinylidene chloride interpolymer is formed through a suspension polymerization process. The vinylidene chloride interpolymer is formed from a monomer mixture comprising about 80 weight percent vinylidene chloride and about 20 weight percent vinyl chloride, based on total monomer mixture weight. The vinylidene chloride contained 1.5 percent EVA 3180 ethylene-vinyl acetate copolymer which contains about 28 percent vinyl acetate and is commercially available from E. I. DuPont de Nemours Co.

The vinylidene chloride interpolymer described above is blended with 1 percent epoxidized soybean oil commercially available from the Viking Chemical Co. under the trade designation Vikoflex 7177; and 2 percent tetrasodium pyrophosphate commercially available from Monsanto, which has been micronized. The mixture of vinylidene chloride interpolymer and additives is pelletized by extrusion through a strand die and subsequently chopping the strand into pellets. The pellets have an average length of about 0.130 inch and an average diameter of about 0.145 inch. The presence of the additives was found to render the vinylidene chloride interpolymer pellets satisfactorily extrudable and possessed of a low level of carbon contamination.

Extrudablity is determined by "melt adhesion", "melt rheology", and "friction". For the "melt rheology" tests, a 3/4 inch diameter, 24:1 L/D single screw extruder is used to provide a polymer melt continuously to the attached slit die. The polymer melt is subjected to a minimum heat history, i.e., whereby the polymer will not degrade, of about 175°C. The melt is generally free of air/gas bubbles. Several slit dies can be used to provide wider shear rate range. Three pressure transducers are mounted along the extruder die wall at equal distances. The first transducer is located at L/h = 10 for h = 0.05" to assure that the steady-state flow is generally established. A slit die having a height (gap) of 0.05" and a width of 1" wide is employed.

Melt rheology is determined by calculating the true shear rate γ and the true shear stress τ at the wall for the Slit Die Rheometer according to the procedure set forth by David J. Williams, in Polymer Science and Engineering, Prentice-Hall , Inc. Englewood, New Jersey, 1971, Chapter 12. Specifically, melt rheology is calculated by the following equations: where n = (d lnτ)/(d In γ_app)

(2) τ = (-ΔP/ ΔZ) h/2,

where (-ΔP/ ΔZ) denotes the pressure gradient; h the thickness of the slit; and Y_app the apparent shear rate is defined by: with G being the mass flow rate, w the slit die width, and ρ, the melt density, which is obtained by weighing the extrudates displaced by the precision volume change in a Sieglaff-McKelvey Rheometer. The melt adhesion comprises the use of a tworoll mill test consisting of two steam heated rolls approximately three inches in diameter and six inches in length that rotate in opposite directions. There is an adjustable gap between the two rolls which are rotating at different speeds. The rolls moving at different speeds cause a shearing effect on the material being tested.

The general sample testing procedure for vinylidene chloride interpolymer is the following:

1) Steam pressure is adjusted to acheive the desired roll temperature, generally 340° to 350°F.

2) A two hundred gram sample is weighed.

3) The rolls are started and closed to provide a gap of about zero.

4) Begin monitoring the time as the sample is poured on the rolls.

5) Slowly open the gap between the rolls as the material melts and adheres to the rolls.

6) When the material is fully melted, i.e., no visible solids are present, record the time elapsed since the start of step 4).

7) Adjust the gap between the rolls so that a small roll of material about one-half inch in diameter is between them.

The "roll adhesion" is the relative adhesion of the main mass of the material to the roll surface and is determined by how easily the material can be scraped from the roll.

Data regarding the adhesion of the compositions to the roll is generated by the test. The adhesion rating is characterized by a rating on a scale of 1 to 5.

0 - The main mass will lift from the roll without leaving any material in a sheet.

1- The polymer will lift from the roll but will leave a spotty thin coating.

2 - The polymer will not lift from the roll in a sheet. It is necessary to scrape the material off the roll, but it is possible to get the roll fairly clean.

3 - The material will not lift from the roll at all. A path will be scraped. A thin soft layer will remain at the boundary between the roll and melt.

4 - The material must be scraped to the end of the roll. A fairly heavy layer will remain on the roll and melt.

5 - It is very hard to scrape through to the roll. There is a hard layer of material at the boundary and melt.

"Friction" is determined by measuring the change in pressure associated with moving a sample through a cylinder. The sample is loaded into a cylinder; the sample is indexed through the cylinder with a piston. The differential of the pressure applied by the piston at the proximate end of the cylinder and the pressure applied by the piston at the distal end of the cylinder is measured. Friction, the cause of the differential piston pressure, is calculated by the following equations:

(4) Δp (πd²/4) = k μ_sP . πdΔh

Δp is the pressure drop across the cylinder; πd²/4 is the cross-sectional area of the sample subject to the pressure drop, with d being the diameter of the sample; k μ_sP is the friction force at the sample-cylinder wall Interface, with k being the radial pressure loss factor ranging from about 0.25 to about 1.0, μ_s being a friction coefficient, and P being pressure; and πdΔh is the surface area of the sample which contacts the cylinder wall, with Δh being the height of an infinitely thin disc-shaped element of the sample.

Integrating equation (4) provides the following relationship:

(5) P_b = P_t e^-[(4kμ _S ^L)/d]

where P_b is the pressure at the bottom of the sample; P_t is the pressure at the top of the sample; L is the height of the sample; and d is the diameter of the sample.

By rearranging equation (5), the following equation is obtained:

(6) 4kμ_s = d/L ln(P_t/P_b) with 4kμ_s defined as storage friction, the pressure drop from top to bottom in a confined space due to friction at the cylinder wall.

Results of Example 1 are set forth in Table 1.

Example 2

Example 1 is repeated with the exception that the vinylidene chloride interpolymer produced as described above is not melt blended with an ethylenevinyl acetate copolymer, but is additionally melt blended with 0.03 parts per hundred parts interpolymer of an oxidized polyethylene commercially available from the Allied Chemical Company under the trade designation Allied 629A. The oxidized polyethylene has a calculated hydrophile/lipophile balance of about 1.3. The presence of the oxidized polyethylene in additon to the other additives was found to render the vinylidene chloride interpolymer pellets satisfactorily extrudable and possessed of a low level of carbon contamination.

Results of Example 2 are set forth in Table 1.

Example 3

Example 2 is repeated with the exception that the formulation contained 0.06 parts of Allied 629A oxidized polyethylene per hundred parts interpolymer, and addtionally contained 1.5 percent EVA 3180 ethylene-vinyl acetate copolymer. The presence of the EVA 3180 ethylene-vinyl acetate copolymer in addition to the other additives was found to render the vinylidene chloride interpolymer pellets satisfactorily extrudable and possessed of a low level of carbon contamination.

Results of Example 3 are set forth in Table 1.

Example 4

Example 3 is repeated with the exception that the formulation contained 0.3 parts of Allied 629A oxidized polyethylene in additon to the other additives per hundred parts interpolymer. The presence of the relatively large quantity of Allied 629A oxidized polyethylene was found to render the vinylidene chloride interpolymer pellets satisfactorily extrudable and possessed of a low level of carbon contamination.

Results of Example 4 are set forth in Table 1.

Example 5

Example 2 is repeated with the exception that

0.5 parts per hundred parts interpolymer of a montan ester wax, commercially available from Hoechst AG under the trade designation Wax E, is substituted for the oxidized polyethylene.

All examples were found to produce vinylidene chloride interpolymer pellets which are satisfactorily extrudable and possessed of a low level of carbon contamination.

Results of Example 5 are set forth in Table 1. TABLE I

Montan

OP¹ ester wax² TSPP³ ESO⁴ EVA⁵ melt melt

Example (%) (%) (%) (%) (% ) adhesion⁶ rheology⁷ friction⁸

1 0 0 2 1 1.5 3 9000 0.25

2 0.03 0 2 1 0 * * *

3 0.06 0 2 1 1.5 3 9000 0.31

4 0.3 0 2 1 1.5 1.5 8500 0.23

5 0 0.5 2 1 0 1 9200 *

* Not measured. 1 OP = an oxidized polyethylene commercially available from the Allied Chemical Company under the trade designation Allied 629A.

2 Montan Ester Wax = commercially available from Hoechst AG under the trade designation Wax E.

3 TSPP = tetrasodium pyrophosphate commercially available from Monsanto, which has been micronized.

4 ESO = Vikoflex 7177 epoxidized soybean oil commercially available from the Viking Chemical Co.

5 EVA = EVA 3180 ethylene-vinyl acetate copolymer which contains about 28 percent vinyl acetate and is commercially available from E. I. DuPont de Nemours Co.

6 Melt Adhesion = melt adhesion according to two roll mill test procedure.

7 Melt Rheology = melt rheology at 175°C in poise § 100 sec^-1.

8 Friction = friction in torque @ 25°C, 1000 psi.

As can be seen from the above table, the compositions of the present invention possess an excellent extrudability. In one embodiment, the unique combination of tetrasodium pyrophosphate, epoxidized soybean oil, and an ethylene-vinyl acetate copolymer which contains about 28 percent vinyl acetate added to the vinylidene chloride interpolymer provides a composition having superior melt adhesion. In another embodiment, the further addition of an oxidized polyethylene provides a composition having improved melt adhesion.

Examples 6-11

A vinylidene chloride interpolymer is formed through a suspension polymerization process. The vinylidene chloride interpolymer is formed from a monomer mixture comprising about 80 weight percent vinylidene chloride and about 20 weight percent vinyl chloride, based on total monomer mixture weight.

The vinylidene chloride interpolymer described above is blended with 1 percent epoxidized soybean oil commercially available from the Viking Chemical Co. commercially available under the trade designation Vikoflex 7177; and 2 percent tetrasodium pyrophosphate commercially available from Monsanto, which has been micronized.

The vinylidene chloride interpolymer is melt blended with several extrusion aids having a variety of calculated HLB's. Each extrusion aid is added in an mount of about 0.5 weight percent. The extrusion aids are all commercially available and are described in more detail in the footnotes of Table II. Extrudablity of the various compositions is determined by melt adhesion, melt rheology, and friction as described in Example 1.

Results are reported in Table II.

TABLE II

Calculated

Extrusion HLB Melt Melt

Example Aid Value¹ Adhesion² Rheology³ Friction⁴

6* ** ** 4 10 X 10³ **

7* Glycerol 2 9.8 X 10³ 2

Mono- 6.0^(a) stearate⁶

8* Stearic 1 8.8 X 10³ 1 Acid² 3.0^(b)

9* 2 9.4 X 10³ 2

Stearate³ 2.0^(c)

10 Oxidized 1 6.2 X 10³ 1

Poly- 1.3^(d) ethylene⁴

11* n,n' 2 9.9 X 10³ 2

Ethylene 3.2^(e)

Diamine bisstearamide⁵

*Comparative example. Not an example of the present invention.

** Not measured.

¹ HLB values determined by the following equation:

20 X [M_H/(M_H + M_L)], wherein M_H is the formula weight of the hydrophilic portion of the molecule and ML is the formula weight of the lipophilic (hydrophobic) portion of the molecule.

The extrusion aids tested have the following values for M_H and M_L:

(a) Glycerol monostearate commercially available from Henkel Corp. under the trade designation, Loxiol 7131, having a M_H of 107 and a M_L of 251.

(b) Stearic acid commercially available from Harwick Chemical Corp., having a M_H of 45 and a M_L of 253.

(c) Magnesium stearate commercially available from Mallinckrodt, Inc, under the trade designation Magnesium Stearate RSN 1-1, having a M_H of 56 and a M_L of 502. (d) Oxidized polyethylene commercially available from Allied Chemical Company under the trade designation Allied 629A, having a M_H of 45 and a M_L of 631.

(e) N,N'-Ethylene diamine bis-stearamide commercially available from Glyco, Inc., under the trade designation Acrawax C, having a M_H of 114 and a M_L of 593.

Melt Adhesion = melt adhesion according to two roll mill test procedure. 3 Melt Rheology = melt rheology at 175°C in poise @

100 sec^-1. 4 Friction = friction in torque @ 25°C, 1000 psi. As can be seen from the above table, the compositions of the present invention possess an excellent extrudability. Applicant has unexpectedly discovered that the claimed extrusion aids having calculated HLB values of less than about 2.0 provide unexpectedly better properties to vinylidene chloride interpolymers than extrusion aids having calculated HLB values of about 2.0 or greater.

Claims

1. A process for improving the extrudability of particles of a vinylidene chloride interpolymer of the type prepared from a major molar amount of vinylidene chloride and a minor molar amount of at least one second monomer selected from vinyl chloride and methyl acrylate: wherein the particles of vinylidene chloride interpolymer are blended with at least one extrusion aid having both a hydrophile portion and a lipophile portion and a calculated hydrophile/lipophile balance of less than 2.0; and wherein said extrusion aid is present in an amount in the range of from 0.01 to 1 part by weight per 100 parts by weight of vinylidene chloride interpolymer.

2. The process of Claim 1 wherein the extrusion aid has a calculated hydrophile/lipophile balance of less than 1.5.

3. The process of Claim 1, wherein the extrusion aid is selected from the group consisting of oxidized polyethylene, oxidized polypropylene; montan ester waxes, having 28-32 carbon atoms per molecule; long chain acids, having 18 or more carbon atoms per molecule, and the salt, ester and amide derivatives thereof; naturally derived waxes; and mixtures thereof,

4. The process of Claim 1, wherein the extrusion aid is oxidized polyethylene.

5. The process of Claim 1, wherein said at least one second monomer is vinyl chloride and the vinyl chloride is present in an amount of from 10 to 30 mole percent based upon the interpolymer.

6. The process of Claim 1, wherein said at least one second monomer is methyl acrylate and the methyl acrylate is present in an amount of from 2 to 20 mole percent based upon the interpolymer.

7. The process of Claim 1, which comprises blending with the particles of vinylidene chloride interpolymer (a) an ethylene-vinyl acetate copolymer, as an additional extrusion aid, in an amount of from 0.01 to 10 weight percent; (b) tetrasodium pyrophosphate, as an HCC scavenger and stabilizer in an amount of from 0.1 to 3 weight percent; and (c) an epoxidized oil or resin, as a plasticizer, stabilizer or lubricant, in an amount of from 0.1 to 3 weight percent; all based on the weight of the interpolymer.

8. The process of Claim 7, wherein the interpolymer contains a minor amount of vinyl chloride and the process comprises blending an antioxidant with the particles of vinylidene chloride interpolymer in an amount in the range of from 50 to 2000 parts per million, based on the weight of the particles of interpolymer.

9. The process of Claim 1 which includes the steps of:

(1) blending solid particles of vinylidene chloride interpolymer with the extrusion aid having a calculated hydrophile/lipophile balance of less than 2.0 to form a blended mixture;

(2) melt extruding the blended mixture to form a melt extrudate; and (3) cooling and pelletizing the melt extrudate to form pellets.

10. The product pellets of Claim 9, wherein the pellets have a lower carbon speck count and better extrudability than comparative pellets prepared without use of the extrusion aid having a calculated hydrophile/lipophile balance of less than 2.0.