Improved blow molding process and compositions

Abstract: This invention relates to an improved process of blow molding, and to improved compositions useful for blow molding, wherein articles are blow molded from compositions formed from thermoplastic polymeric material, a fluorinated olefinic polymer or copolymer and, optionally, an elastomeric impact modifier. The presence of the fluorinated olefinic polymer or copolymer in the blow molding composition increases the melt strength of the thermoplastic polymeric material. This makes the thermoplastic polymeric material more useful for blow molding because a parison of greater size and weight can be formed from the polymeric material because of its increased melt strength.

Description: This invention relates to an improved process for blow molding thermoplastic compositions, more particularly relates to a process for modifying thermoplastic polymeric materials or resins to make them more useful for blow molding purposes, and relates also to such modified compositions and articles blow molded therefrom. Although many thermoplastic resins have been found to be injection moldable over a broad range of conditions, only certain thermoplastic resins are suitable for blow molding. This is due to the unique demand placed on a thermoplastic material by the blow molding operation. In one aspect of the conventional blow molding operation, a cylindrically shaped parison of a heat softened thermoplastic material is extruded vertically downward until the parison has attained a pre-selected length. A split cavity mold is then closed around the parison, pinching its walls together at least at one end, and optionally at intermediate locations and at the other end as well. Compressed gas is injected into the parison, either from one of the ends or through one or more blow pins inserted in its side, to inflate the parison against the sides of the mold in a fashion similar to the expansion of a balloon. Contact of the thermoplastic material with the mold causes it to cool and harden in the shape of the mold. Because a parison is formed as a single, integral piece of thermoplastic material, and the inflating medium acts from its interior to shape it with outward pressure, blow molding makes possible the fabrication of "hollow" articles, wherein two or more walls define or contain a completely enclosed space, or a series of such spaces. The shape of a blow molded article may range from something as simple as a bottle to a complex piece such as an extensively contoured automotive instrument panel containing multiple interior channels for the location of wiring or ventilating ducts. However, the successful use of a particular thermoplastic resin to blow mold the great variety of articles for which molds of different sizes and shapes can be designed is dependent to a great extent on certain physical characteristics of the heat softened polymeric resin or material. For example, a low level of melt strength in the material from which a parison is extruded can limit the length and diameter of the parison, and thus the size and wall thickness of the object being molded. US-A- 3, 723, 373 discloses a composition comprising (1) polyethylene terephthalate (PET) having incorporated therein small amounts (from about 0.1% to about 2.0% by weight) of a polytetrafluoroethylene emulsion, said emulsion having a solids content of from about 30% to about 80%. This composition can be blow molded: see example 6 where the composition is blow molded into a bottle, however without mentioning its weight or size. Further, example 2 of this patent demonstrates that the mixing of a PTFE emulsion with PET is required. The use of fibril-forming polytetrafluoroethylene ("PTFE") to increase the melt viscosity and elasticity of high molecular weight organic polymers for use in melt extrusion and thermoforming is set forth in Busse, U.S. Patent No. 3,005,795. However, no mention is made therein of the blow molding process, or of the use of non-fibril-forming PTFE or other fluorine-containing olefin polymers or copolymers for the purpose of improving the melt properties of an organic polymer. Nor is any suggestion present therein as to the use of a fluorine-containing olefin polymer or copolymer in conjunction with a blend of two or more organic polymers. It would accordingly be desirable to have methods and compositions wherein a variety of fluorinated olefinic polymers or copolymers may be used to increase the melt strength of a variety of thermoplastic polymeric materials or resins in a blow molding operation, thereby improving the quality of articles blow molded from said compositions. In one aspect, this invention is a method of blow molding a contoured article, comprising (a) providing a composition by dry blending (i) 75 parts to 99.999 parts by weight thermoplastic polymeric material which contains less than 40 percent rubber and excludes fluorinated olefinic polymers, and (ii) a fluorinated olefinic polymer or copolymer which is 0.001 parts to 5 parts of said composition by weight, which composition does not contain a polyethylene having a viscosity average molecular weight higher than 200,000 or a copolymer containing epoxy or ionic groups; (b) optionally melt mixing such dry-blended composition in an extruder; (c) melt processing said composition into a hollow parison which weighs more than 5 kilograms; and (d) blow molding said article from said parison. In a further aspect, this invention is a parison for use in blow molding comprising, in admixture, thermoplastic polymeric material and a fluorinated olefinic polymer or copolymer as defined hereinbefore, said parison being characterized by the ability to support its own weight when suspended from a die bushing. The methods and compositions of this invention are useful, for example, in the production of molded or shaped articles of virtually all varieties, especially bottles and other containers, and components for use in the transportation and appliance industries. In the methods of this invention as defined hereinbefore, a fluorinated olefinic polymer or copolymer and, optionally, an elastomeric impact modifier, is admixed (by dry blending) with thermoplastic polymeric material (or more than one such material) for the purpose of increasing the melt strength of the polymeric material in a blow molding operation, thereby improving the blowability of the polymeric material and the surface quality and the tack seam strength of the article molded. The compositions of this invention are those as defined hereinbefore in which a fluorinated olefinic polymer or copolymer is admixed (by dry blending) with thermoplastic polymeric material for the purpose of increasing the melt strength of the thermoplastic polymeric material. An elastomeric impact modifier can optionally be incorporated into the compositions of this invention as well. Suitable ranges of content for the compositions of this invention, in parts by weight of the total composition, are as follows: 75 parts to 99.999 parts thermoplastic polymeric material, 0.001 parts to 5 parts fluorinated olefinic polymer or copolymer, and optionally up to 20 parts elastomeric impact modifier. Preferred ranges of content for the compositions of this invention, in parts by weight of the total composition, are as follows: 81 parts to 99.99 parts thermoplastic polymeric material, 0.01 parts to 3 parts fluorinated olefinic polymer or copolymer, and optionally up to 16 parts elastomeric impact modifier. A fluorinated olefinic polymer or copolymer is used in this invention in an amount of 0.001 parts to 5 parts by weight of the total thermoplastic composition which is being blow molded. Enough fluorinated olefinic polymer or copolymer, i.e. 0.001 parts by weight ("pbw") or more, must be used to achieve the desired increase in melt strength. However, it is found that use of a fluorinated olefinic polymer or copolymer in an amount greater than 5 pbw in a thermoplastic composition to be blow molded ( a ) yields a molded article which has a tendency to suffer from surface pitting, a condition similar to that resulting in a blow molded article when a fluorinated olefinic polymer or copolymer is poorly dispersed in a thermoplastic polymeric composition, and ( b ) significantly increases the likelihood that the molded article will experience brittle rather than ductile failure when impacted at subambient temperature. Preparation of the compositions of this invention can be accomplished by any suitable means known in the art which result in a thorough, homogeneous distribution in the thermoplastic polymeric material or resin of the substances to be admixed therewith. In the admixing process, the materials are dry blended and agitated in particulate form. The dry blended formulation can later, if desired, be melt mixed in an extruder as a separate step. Alternatively, the dry blend is supplied directly to be melt processed into a hollow parison. Thermoplastic Polymeric Material . Virtually any thermoplastic polymeric material or resin which can be melted, heat softened or dissolved in a solvent is appropriate for use in the methods and compositions of this invention. Thermoplastic resins such as polymers, copolymers and alloys and blends of two or more thereof, including but not limited to non-carbonate polymers or copolymers, but excluding fluorinated olefinic polymers and copolymers, are suitable for use as the thermoplastic polymeric material of this invention. Non-carbonate polymers or copolymers are those which do not contain an -[-O-R-O-C(O)-]- repeating unit, where R is an organic ( e.g. , C 1 -C 20 , S, S 2 , SO 2 , SO, O or CO) radical. The following are exemplary of polymers suitable for use as the thermoplastic polymeric material herein, but this listing is not intended to be exhaustive or to limit the scope of this invention: polyacetal, including that which is formed by the bond opening and'polymerization of the carbonyl group of an aldehyde to give a -(-CH 2 -O-)- repeating unit, as well as the reaction products of polyols and aldehydes; polyacrylate; polyamide, including that which is prepared by the reaction of a diamine and diacid or the self polymerization of a cyclic lactam; polycarbonate, including that which is prepared by the reaction of a dihydroxy compound with a carbonate precursor such as a carbonyl halide, a diarylcarbonate or a bishaloformate, and copolymers thereof; polyester, including that which is prepared by the condensation reaction of a diacid and a diol or the self esterification of a hydrocarboxylic acid, and copolymers thereof; poly(ethylene oxide); polymethacrylate; polyolefin, including copolymers thereof; poly(phenylene ether), including that which is prepared by the oxidative coupling polymerization of a phenol to give a -(- p Ar-O-)- repeating unit; polystyrene, including copolymers thereof; polyurethane, including that which is prepared by the reaction of a diisocyanate and a polyol; and vinyl polymers, including poly(vinyl acetate), poly(vinyl alcohol), poly(vinyl amide), poly(vinyl chloride), and poly(vinyl ether), including copolymers of each; where Ar in the foregoing list of polymers is an aromatic organic ( e.g ., C 6 -C 10 ) radical. Copolymers formed from two or more monomers or co-monomers can also be used as the thermoplastic polymeric material in this invention, such copolymers including but not being limited to the following: acrylonitrile/butadiene/styrene copolymer, acrylonitrile/EPDM/styrene copolymer where EPDM is ethylene/propylene/diene rubber, acrylonitrile/styrene/alkyl acrylate copolymer, co-polyester/carbonate, ethylene/carbon monoxide copolymer, ethylene/vinyl acetate copolymer, methyl methacrylate/butadiene/styrene/acrylonitrile copolymer, phenyl maleimide/acrylonitrile/butadiene/styrene copolymer, polycarbonate formed from more than one dihydroxy compound, polyester formed from more than one diol and/or more than one diacid, styrene/acrylonitrile copolymer, and styrene/maleic anhydride copolymer. Blends and alloys of two or more thermoplastic polymers and/or copolymers are also suitable for use as the polymeric material in this invention. Representative examples of such blends are those prepared from the polymers and copolymers mentioned above, and the following: acrylonitrile/butadiene/styrene copolymer blended with polycarbonate, polyamide, polyester, or polyurethane; polyacetal blended with polyurethane; polycarbonate blended with polyamide, polyester, or styrene/acrylonitrile copolymer; and poly(phenylene ether) blended with (i) polyamide and a vinyl aromatic/conjugated diene di- or tri-block copolymer; (ii) polyester; or (iii) polystyrene to which can be grafted a vinyl aromatic/conjugated diene di- or tri-block copolymer. Mixtures of thermoplastic polymers and/or copolymers and/or blends of two or more thermoplastic polymers and/or copolymers are also suitable for use as the polymeric material in forming the compositions of this invention. Thermoplastic polymers, copolymers, and blends of two or more thermoplastic polymers and/or copolymers, can, if desired, be used to form the compositions of this invention in a rubber-modified form. Rubber modification of a polymer, copolymer or blend typically results from grafting a rubbery domain to the thermoplastic material, which serves as the matrix. The thermoplastic polymeric material in this form, and thus the total composition, contain less than 40 percent rubber by weight. This is to be distinguished from the optional addition of an elastomeric impact modifier as a separate component to the compositions of this invention, which results in a composition containing more than 40 percent rubber by weight. Fluorinated Polyolefin. The fluorinated olefinic polymers or copolymers useful in this invention are those wherein fluorine atoms or fluorinated organic ( e.g. C 1 -C 12 ) side chains have been substituted for the hydrogen atoms on an ethylenic polymeric backbone, and include as examples: PTFE; fluorinated ethylene/propylene copolymers ("FEP"), such as tetrafluoroethylene/hexafluoropropylene copolymer; perfluoroalkoxy fluorocarbons ("PFA"), such as tetrafluoroethyl/perfluoro propyl vinyl ether copolymer; and ethylene/tetrafluoroethylene copolymers ("ETFE"). Of these fluorinated olefinic polymers or copolymers, PTFE, either fibril-forming or non-fibril-forming, is preferred, and fibril-forming PTFE is most preferred. PTFE can be made by the granular polymerization process wherein tetrafluoroethylene ("TFE") is pressured into an agitated aqueous solution of free radical initiator at pressures of 5 to 80 kg/cm 2 and at temperatures of 50 to 150°C. Initiators can be redox systems, azo initiators, peroxides or inorganic persulfates. The polymer particles coagulate as they are formed. Fine-powder PTFE can be made by a process similar to the foregoing except that sufficient dispersing agent is used to maintain a stable dispersion throughout polymerization and avoid premature coagulation. The dispersing agent is anionic and substantially non-telogenic, such as a fluorinated carboxylate containing 7 to 20 carbons. TFE is prepared by reacting hydrogen fluoride and chloroform to give chlorodifluoromethane, which is then pyrolyzed in a noncatalytic gas-phase reaction at atmospheric or reduced pressure, usually at about 590 to 900°C, to obtain tetrafluoroethylene. The processes for making PTFE described above are discussed in greater detail in U.S. Patents 2,393,967, 3,855,191 and 4,186,121. Although it is preferred to employ fibril-forming PTFE in this invention, non-fibril-forming PTFE is also useful herein. Fibril-forming PTFE is typically considered to be that which has a structure wherein PTFE particles having an average size of 0.1 to 0.2 micrometer are held together by fibrils having diameters from a fourth to a tenth or less of the diameters of the particles. PTFE which loses or does not form such structure, as a result of mechanical shearing, is typically considered to be non-fibril-forming. For example, PTFE which has been sintered by heating above 330°C, or has been given 10 6 rep. or more of 2 mev. electron radiation, loses or has greatly reduced capacity to form fibrils upon mechanical shearing. Hexafluoropropylene ("HFP") can be produced by thermally cracking TFE at reduced pressure at 700 to 800°C or by fluorinating 3-chloropentafluoro-1-propene at 200°C over activated carbon catalyst. These methods of producing HFP are discussed in greater detail, respectively, in U.S. Patent No. 3,758,138 and U.S. Patent No. 3,047,640. HFP and TFE form a random copolymer and can be copolymerized to form FEP by irradiation, or by using trichloroacetyl peroxide as the catalyst at low temperature, or by aqueous or nonaqueous dispersion. These methods of making FEP are discussed in greater detail, respectively, in U.S. Patent No. 2,598,283 and U.S. Patent No. 3,132,124. PFA are copolymers which contain a fluorocarbon backbone in the main chain and randomly distributed perfluorinated ether side chains, and can be generally represented by a repeating unit such as -[-CF 2 -CF 2 -C(O-CF 2 -R)F-CF 2 -]-, where R is a fluorinated organic ( e.g. C 1 -C 11 ) radical. A PFA is prepared by polymerizing a perfluorovinyl ether. A perfluorovinyl ether can be prepared by oxidizing HFP to the epoxide, reacting the epoxide with a perfluorinated acyl fluoride to obtain an alkoxyacyl fluoride, which is then converted to a perfluorovinyl ether by treatment with base at about 300°C, a method which is discussed in greater detail in U.S. Patent No. 3,291,843. Ethylene and TFE can be polymerized to form ETFE by suspension or emulsion methods, usually below 100°C and at about 5 MPa. The reaction conditions should favor the homopolymerization of PTFE but not ethylene. Initiators can include peroxides, redox systems, free-radical sources, and ionizing radiation. Such methods for forming ETFE are discussed in greater detail in U.S. Patent No. 3,401,155. The fluorinated olefinic polymer or copolymer of this invention increases the melt strength of thermoplastic polymeric material with which it is admixed. The desirability for such increase can be described with reference, for example, to extrusion blow molding. In extrusion blow molding, molten polymeric material or resin passes from an extruder into an accumulator head, from which it is discharged to flow about a torpedo-shaped mandrel which is surrounded by a die. The die and mandrel make up an annulus through which the resin melt stream forms a parison as it flows out from, and becomes suspended from, the die bushing. The shearing forces of the extruder screw, and the forced flow from the accumulator head through the die, mechanically induce molecular elongation and orientation in the resin. However, as the parison is extruded and descends from the die bushing, those shearing forces are relieved, and the resin is free to undergo elastic recovery. The fluorinated olefinic polymer or copolymer assists in this process because it appears to possess a high degree of elastic memory and is believed to experience strain relaxation much as a stretched coil spring would upon release from a stretching tension. However, the elastic recovery of the fluorinated olefinic polymer or copolymer which results when it is freed from the shearing, mechanical stress of the extruder and accumulator head is to be distinguished from similar behavior which PTFE may display when contained in an extruded sheet which is heated for use in thermoforming. In an extruded sheet, PTFE has by cooling been locked into a stretched, elongated position and orientation within the molded extrudate from which the sheet is formed. When the sheet is softened in preparation for thermoforming, the PTFE molecules are allowed to move into a more stable configuration because of the application of heat rather than because of the removal of shearing forces. The recoil action of a fluorinated olefinic polymer or copolymer at low shear increases the melt strength of thermoplastic polymeric material with which it is admixed, which is of particular importance when that polymeric material or resin is being used to blow mold large articles, which frequently weigh more than three kg. The blow molding of such large articles requires parisons which often weigh more than five kg, and exceed twenty centimeters in diameter and two meters in length. Melt strength in this context refers to the ability of the molten polymeric material to support its own weight, when suspended from the die bushing, under the tensile stress imposed by gravitational pull. High melt strength is needed in the thermoplastic polymeric material from which a large parison is formed to prevent the parison from experiencing drawdown, which is a continual thinning of the parison wall occurring simultaneously as the parison is being extruded. The initial effect of drawdown is that the resin forming the parison, after being forced from the die bushing by a piston in the accumulator head, continues thereafter to flow downward under the force of gravity and distort the shape of the parison. When such vertical displacement of polymeric material or resin continues during and after expulsion from the accumulator head, the parison tends to assume an hourglass shape, and too great a quantity of resin accumulates in its lower portion. If the polymeric material forming the parison wall in the area immediately adjacent to the die bushing becomes thin enough that the melt strength of the resin is insufficient to support the weight of the parison, the entire parison can tear away from the die bushing. This is clearly the most undesirable result of drawdown because the parison is then completely useless for any molding activity. Although the tearing away of a parison from a die bushing is a qualitative indication that the parison is unable to support its own weight because the resin from which it is formed has insufficient melt strength to allow it so do so, an example of a quantitative melt strength test useful in the blow molding context is the ratio of the times of extrusion of the first and second halves of a polymer strand. For example, where a 15.2 cm (six inch) strand is extruded from a melt index apparatus with a constant drive piston, the ratio (T 1 /T 2 ) of the time required to extrude the first half of the strand compared to the time required to extrude the second half of the strand indicates the melt strength of the polymer. The extreme requirement which the need for parison support places on the melt strength of blow molding material can be illustrated by contrasting that requirement with the conditions applicable to a sheet of polymeric material to be thermoformed. Consider, for example, a 60 in x 24 in x 1/8 in (152.4 cm x 60.96 cm x 0.3175 cm) sheet weighing 400 grams which is supported for thermoforming purposes 1 / 2 in (1.27 cm) on all four sides. Almost all of the gravitational pull, which causes the sheet to drop as it is softened, impacts the unsupported portion of the sheet, which weighs approximately 377 grams. The weight of the unsupported portion of the sheet subject to deformation during the heating process is therefore spread over the 1 / 2 in (1.27 cm) rails to the extent of an average of approximately 4.54 g/in 2 (0.7 g/cm 2 ). If the same sheet were to be extruded as a parison, the entire weight of the parison, 400 grams, is not only unsupported by rails or any other mechanical means, but is supported solely by the melt strength of the molding material which is present in the 1/8 in (0.3175 cm) thickness of the portion of the parison immediately adjacent to the die bushing. That portion of the parison, using the dimensions of the sheet set forth above, has an area of 2.95 in 2 (19 cm 2 ), meaning that the weight of the whole parison is supported by the melt strength of the molding material alone to the extent of an average of approximately 135.6 g/in 2 (21 g/cm 2 ), approximately thirty times more than the value calculated for thermoforming. Further, the melt strength of a blow molding material must resist not only the gravitational pull on the weight of the parison, but the momentum which the parison experiences because of its downward motion as it is extruded from the die. High melt strength is therefore a critical aspect of any resin to be blow molded, and the need for high melt strength in a blow molding resin can often be many times greater than the need for it in a thermoforming material. When not accompanied by high melt strength, high viscosity alone in the molten extrudate is believed to typically not be sufficient to give the degree of tenacity needed to allow a parison to resist the effects of drawdown and support its own weight during extrusion and during the interval between completion of extrusion and the closing of the mold around it. In fact, if a blow molding resin is too viscous, its usefulness for blow molding purposes may be reduced. For example, a parison formed therefrom may swell upon extrusion to the extent that its walls are undesirably thickened, the pressure of the inflating medium may not be sufficient to properly inflate such a parison within a mold, or sufficient pressure may not exist in the accumulator head to extrude the resin and form a parison in the first place. It is very difficult, if not impossible, to blow mold an article of acceptable quality from a parison which has experienced drawdown. Acceptable quality in this context denotes a blow molded article which does not suffer from the reduction of quality in appearance and physical properties which can be caused by the adverse effects of parison drawdown. Among the adverse effects of parison drawdown, the primary example is improper vertical distribution of the polymeric material used for molding. If the molding material simply thins out, the walls of the parison, and thus the molded article, will almost certainly be too thin in the upper and/or middle portions and too thick in the lower portion. Where walls are too thin, they are subject to rupture by forces ordinarily encountered in the service environment in which the article is to be used. If curtaining occurs, where waves or rivulets of the molding material dribble down the parison wall, detailed features of the article, such as ribbing, a bottle handle, lip and threads at bottle mouth for screw or snap-on closure, or undercuts to form body panels for bottle labeling, will likely be ruined. The methods of this invention reduce the adverse effects of parison drawdown to the extent necessary, and the compositions of this invention are characterized by forming a parison sufficiently free of drawdown, to obtain therefrom a blow molded article of acceptable quality. As the thermoplastic polymeric compositions of this invention contain a fluorinated olefinic polymer or copolymer and are thus characterized by increased melt strength, they can be compounded in an extruder and formed into a parison at a higher temperature, without experiencing drawdown, than a molding material which does not contain a fluorinated olefinic polymer or copolymer and therefore does not have increased melt strength. The ability to blow mold the compositions of this invention at such a higher temperature without experiencing parison drawdown is one of the desirable features of this invention, and is a distinct advantage in forming a strong, durable tack seam. A tack seam is formed at any point where the structure of the mold causes the walls of the parison to be pinched together. At least one tack seam is formed at an end of the cylindrical parison opposite from the end at which an inflating medium is injected, but tack seams can also be formed at both ends and at numerous intermediate points according to the design of the article being molded and the location of the blow pins. The hotter the material forming the parison, the more readily the walls of the parison adhere and tack to one another when pinched together, thereby enhancing formation of a strong tack seam. Good tack seam strength is realized in the methods and compositions of this invention when a composition, containing thermoplastic polymeric material and a fluorinated olefinic polymer or copolymer, is blow molded at a temperature which is higher than the temperature at which a parison, formed from said thermoplastic polymeric material not admixed with a fluorinated olefinic polymer or copolymer, experiences the adverse effects of drawdown. An article which is constructed with multiple walls formed from strong tack seams is surprisingly rigid and has a high strength to weight ratio as compared to a solid article of identical size and shape formed from the same material, for example, by injection molding or conventional thermoforming. Additional advantages are obtained when the blow molding compositions of this invention are extruded at higher temperature to form a parison because higher temperature will cause the parison to be less viscous, and the inflating medium will consequently press the walls of the parison tighter against the mold. The surface of a molded article will more faithfully reproduce the condition of the mold because of this more intimate contact between the heat softened resin of which the parison is formed and the mold surface. If the mold is smooth, the surface of an article will be smoother and have a higher gloss when molded from a hot resin, and when the mold is textured, an article will show that texture with greater definition when molded from a parison brought to a high temperature. Good surface quality cannot be as easily obtained from blow molding materials which do not have the higher melt strength of the compositions of this invention because such materials will experience drawdown before they can be brought to a high enough temperature to obtain the desired improvement in surface quality. The use of a fluorinated olefinic polymer or copolymer to increase the melt strength of a thermoplastic polymeric material therefore enables extruding a parison at a higher temperature and furnishes a method of blow molding an article having a tack seam of increased strength with a surface which more faithfully reproduces the condition of the mold. It is preferred, but not necessary, that the thermoplastic polymeric compositions of this invention be melt processed, in preparation for blow molding, at a temperature below the melting point of the fluorinated olefinic polymer or copolymer contained therein. The melt processing temperature of a composition of this invention is the temperature at which the components thereof flow and are workable sufficiently to enable homogeneous dispersion in the thermoplastic polymeric material of a fluorinated olefinic polymer or copolymer (and other components, if any). However, some of the polymeric materials useful herein, known as "high heat" materials, cannot be softened to the extent necessary to be compounded with a fluorinated olefinic polymer or copolymer (i.e. cannot be melt processed) at a temperature below the melting point of such fluorinated olefinic polymer or copolymer. It may nevertheless be desirable to prepare a composition of this invention, containing at least one of such high heat polymeric materials, at a temperature below the melting point of a fluorinated olefinic polymer or copolymer. In such case, it is found to be particularly helpful in accomplishing that objective by incorporating the high heat material into a blend of two or more thermoplastic polymers and/or copolymers. The melt processing temperature of a polymeric blend used in this invention is lower than the highest processing temperature of any of its respective components. High heat polymeric materials, which could not by themselves be melt processed at a temperature below the melting point of a fluorinated olefinic polymer or copolymer, can consequently be compounded in preparation for blow molding below such melting point by being incorporated into a polymeric blend which does have a processing temperature below such melting point. When a thermoplastic polymeric blend is used as described above to lower the melt processing temperature of a composition below the melting point of a fluorinated olefinic polymer or copolymer, a greater variety of polymeric materials can be advantageously compounded with a fluorinated olefinic polymer or copolymer to form said composition than is true when blends are not used. Melt processing high heat materials as a part of a blend at a temperature below the melting point of a fluorinated olefinic polymer or copolymer creates an opportunity to advantageously use many high heat polymeric materials for blow molding purposes in the methods and compositions of this invention which would otherwise have to be processed at higher than desired temperatures. Elastomeric Impact Modifier. The elastomeric impact modifiers which can be optionally used in this invention are core-shell or thermoplastic rubbers having a glass transition temperature (T g ) less than 0°C and typically containing greater than 40 percent by weight of rubber. When used, these elastomeric impact modifiers are added as separate components during preparation of the compositions of this invention as distinguished from the grafting of a rubbery phase onto the thermoplastic matrix of a thermoplastic polymer or copolymer used in a composition of this invention. Representative examples of elastomeric impact modifiers useful in this invention are a core-shell methacrylate/butadiene/styrene copolymer (MBS rubber) or a selectively hydrogenated vinyl aromatic/conjugated diene di- or tri-block copolymer. An MBS rubber contains a substrate latex, or core, which is made by polymerizing a conjugated diene, or by copolymerizing a conjugated diene with a monoolefin or polar vinyl compound, such as styrene, acrylonitrile or methyl methacrylate. The substrate latex is typically made up of about 45 to 75 percent conjugated diene and about 25 to 55 percent of the monoolefin or polar vinyl compound. A mixture of monomers is graft polymerized to the substrate latex. A variety of monomers may be used for this grafting purpose, of which the following are exemplary: vinyl compounds such as vinyl toluene, alpha-methyl styrene, halogenated styrene, naphthalene, acrylonitrile, methacrylonitrile or alpha-halogenated acrylonitrile, or a C 1 - C 8 alkyl acrylate such as methacrylate, ethylacrylate or hexyl acrylate, a C 1 - C 8 alkyl methacrylate such as methyl methacrylate, ethyl methacrylate or hexyl methacrylate, an acrylic or methacrylic acid, or a mixture of two or more of the foregoing. The grafting monomers may be added to the reaction mixture simultaneously or in sequence, and, when added in sequence, layers, shells or wart-like appendages can be built up around the substrate latex, or core. The monomers can be added in various ratios to each other although, when just two are used, they are frequently utilized in equal amounts. A typical weight ratio for an MBS rubber is about 60 to 80 parts by weight substrate latex, about 10 to 20 parts by weight first monomer and about 10 to 20 parts by weight second monomer. A preferred formulation of an MBS rubber is one having a core built up from about 71 parts of butadiene, about 3 parts of styrene, about 4 parts of methyl methacrylate and about 1 part of divinyl benzene; a second phase of about 11 parts of styrene; and a shell phase of about 11 parts of methyl methacrylate and about 0.1 part of 1,3-butylene glycol dimethacrylate, where the parts are by weight of the total composition. A product having substantially such content is available commercially from Rohm and Haas Company as Paraloid™ EXL 3607 core-shell polymer. The MBS rubber and methods for making same, as described above, are discussed in greater detail in Saito, U.S. Patent No. 3,287,443 (Kanegafuchi), Curfman, U.S. Patent No. 3,657,391 (Borg-Warner) and Fromuth, U.S. Patent No. 4,180,494 (Rohm and Haas). The hydrogenated block copolymer utilized in this invention can be either linear or branched, and can be either a di-block copolymer having a -[-A-B-]- repeating unit or a tri-block copolymer having a -[-A-B-A-]- repeating unit. The "A" portions are made by polymerizing a mono-alkenyl aromatic hydrocarbon and has an average molecular weight of about 4,000 to about 115,000, and a weight preferably of about 8,000 to about 60,000. The "B" portion of the block copolymer results from polymerizing a conjugated diene and has a molecular weight of about 20,000 to about 450,000, and a weight preferably of about 50,000 to about 300,000. The "A" groups typically constitute about 2 weight percent to about 55 weight percent of the whole block copolymer, and preferably are between 5 weight percent and 30 weight percent of the whole block copolymer. Monomers from which the "A" blocks of the block copolymer can be formed are, for example, styrene and substituted derivatives thereof such as α-methyl styrene, vinyl xylene, vinyl naphthalene and mixtures of two or more thereof. The polymerization is initiated by lithium metal, or alkyl- or aryl lithium compounds such as butyl lithium or isoamyl lithium. Polymerization is normally conducted at temperatures ranging from about -20°C to about 100°C. A hydrocarbon inert to the polymerization reaction, for example an alkane such as hexane, is used as solvent for the reaction. Polymerization is typically carried out under a nitrogen blanket. The "B" group of the hydrogenated block copolymer can be formed simply by injecting suitable monomer into the reaction vessel and displacing the lithium radical from the just-polymerized "A" block, which acts as an initiator because it is still charged. The "B" block is formed predominantly from C 4 -C 10 conjugated dienes, such as butadiene or isoprene. The "B" block will be characterized by elastomeric properties which allow it to absorb and dissipate an applied stress and then regain its shape. To reduce oxidative and thermal instability, the block copolymers used herein are also desirably hydrogenated to reduce the degree of unsaturation on the polymer chain and on the pendant aromatic rings. Typical hydrogenation catalysts utilized are Raney nickel, molybdenum sulfide, finely divided palladium and platinum oxide. The hydrogenation reaction is typically run at 24 to 232°C (75 to 450°F) and at 0.79 to 7.00 MPa (100 to 1,000 psig) for 10 to 25 hours. The hydrogenated block copolymers used herein can also contain reactive groups, such as an anhydride group, which are capable of reacting with and bonding to the thermoplastic polymeric material of this invention. The most preferred -[-A-B-A-]- block copolymers are those having a styrene-butadiene-styrene or a styrene-isoprene-styrene configuration. Kraton™ G-1651, available from Shell Chemical Company, is an -[-A-B-A-]- block copolymer which has been found particularly useful in this invention. The -[-A-B-]- and -[-A-B-A-]- block copolymers described above are discussed in greater detail in Haefele, U.S. Patent No. 3,333,024 (Shell) and Wald, U.S. Patent No. 3,595,942 (Shell). The elastomeric impact modifiers useful in this invention also include, but are not limited to, alkyl acrylate rubbers, ethylene/propylene and ethylene/propylene/diene rubbers, neoprene, nitrile rubbers, polyether rubbers, polyisoprene, and silicone rubbers. The processes and compositions of this invention are applicable in operations which include, but are not limited to, extrusion blow molding and injection blow molding, including both stretch extrusion blow molding and stretch injection blow molding, profile blow molding, and rotational blow molding. The compositions of this invention can further contain conventional thermoplastic polymer additives which include, but are not limited to, fillers, thermal stabilizers, dyes, flame retarding agents, reinforcing agents, softeners, mold-release agents, seed-forming agents, pigments, plasticizers, antistatic agents, UV absorbers, lubricants and compatibilizers in conventional amounts generally not exceeding 25 percent by weight of the total composition. To illustrate the practice of this invention, examples of several preferred embodiments are set forth below. It is not intended, however, that these examples (Examples 1-17) should in any manner restrict the scope of this invention. Some of the particularly desirable features of this invention may be seen by contrasting the characteristics of Examples 1-17 with those of various controlled formulations (Controls A-K) which do not possess the features of, and are not therefore embodiments of, this invention. Examples 1-17 and Controls A-K, shown below as the compositions set forth in Tables I-VII, are dry blended and agitated in a Lightning Blender for 30 seconds. The dry blended formulations are then melt mixed in a vented 30 mm Werner-Pfleiderer co-rotating, twin screw extruder at 250 rpm using a set temperature sufficient to fully soften and obtain good processability of the material, depending on the contents of a particular formulation. The set temperatures utilized to obtain good processability in the formulations of Examples 1-17 and Controls A-K range from about 130°C to about 280°C. Each extruded composition is passed through a water bath, chopped into granules and collected for molding. To counteract moisture absorption, all samples except the olefins are thoroughly dried in a circulated air oven at 115°F (46.1°C) for a minimum of 4 hours prior to molding. ASTM Type I tensile bars (see ASTM Designation D 638-87b) are prepared by injection molding on a 75 ton Arburg molding machine. Mold temperatures in the range of 100°F to 175°F (38°C to 80°C), are used in molding the tensile bars from the various compositions. The content of Examples 1-17 and Controls A-K is set forth below in parts by weight of the total composition in Tables I-VII. Composition (by weight) of Examples 1-2 and Controls A-B Control A Example 1 Control B Example 2 PC 300-10 65.5 65.8 31.4 31.5 Branched PC 0 0 31.4 31.5 ABS Y23 34.0 34.0 30.9 31.0 Paraloid™ 3607 0 0 5.8 5.8 Irganox™ 1076 0.2 0.2 0.2 0.2 Teflon™ 6C 0 0.3 0 0.3 where PC 300-10 is Calibre™ linear polycarbonate from The Dow Chemical Company having a 10 melt flow rate ("MFR"), as measured in g/10 min. by ASTM Designation D 1238-86 (Condition 300/1.2). Branched PC is 3 MFR branched polycarbonate. ABS Y23 is acrylontrile/butadiene/styrene copolymer ("ABS") resin having, by weight, 23 percent acrylonitrile, 20 percent butadiene, and 57 percent styrene. Paraloid™ 3607 is methacrylate/butadiene/styrene copolymer ("MBS") rubber from Rohm & Haas Company. Irganox™ 1076 is phenolic antioxidant from Ciba-Geigy Corp. Teflon™ 6C is fibril-forming PTFE from DuPont. Composition (by weight) of Example 3 and Control C Control C Example 3 Kodar™ PETG 100 99.7 Teflon™ 6C 0 0.3 where Kodar™ PETG is polyester from Eastman Kodak Co. Teflon™ 6C is fibril-forming PTFE from DuPont. Composition (by weight) of Examples 4-7 and Control D Control D Example 4 Example 5 Example 6 Example 7 X16 100 99.7 99 99 99 Teflon™ FEP 0 0 0 1 0 Teflon™ PFA 0 0 1 0 0 Tefzel™ 0 0 0 0 1 Teflon™ 6C 0 0.3 0 0 0 where X16 is ABS resin having, by weight, 16 percent acrylonitrile, 7 percent rubber and 77 percent styrene. Teflon™ FEP is powdered fluorinated ethylene/propylene copolymer from DuPont. Teflon™ PFA is powdered perfluoralkoxy copolymer from DuPont. Tefzel™ is powdered ethylene/tetrafluorethylene copolymer from DuPont. Teflon™ 6C is fibril-forming PTFE from DuPont. Composition (by weight) of Examples 8-10 and Control E Control E Example 8 Example 9 Example 10 PC 300-10 100 99 99 99.7 Teflon™ PFA 0 1 0 0 Tefzel™ 0 0 1 0 Teflon™ 6C 0 0 0 0.3 where PC 300-10 is 10 MFR Calibre™ polycarbonate from The Dow Chemical Company. Teflon™ PFA is powdered perfluoralkoxy copolymer from DuPont. Tefzel™ is powdered ethylene/tetrafluorethylene copolymer from Dupont. Teflon™ 6C is fibril-forming PTFE from DuPont. Composition (by weight) of Examples 11-13 and Control F Control F Example 11 Example 12 Example 13 PC 300-3 0 0 99.5 0 PC 300-6 0 0 0 99.5 PC 300-10 100 99.7 0 0 Teflon™ 9B 0 0.3 0 0 Teflon™ 6C 0 0 0.5 0.5 where PC 300-3 is 3 MFR Calibre™ polycarbonate from The Dow Chemical Company. PC 300-6 is 6 MFR Calibre™ polycarbonate from The Dow Chemical Company. PC 300-10 is 10 MFR Calibre™ polycarbonate from The Dow Chemical Company. Teflon™ 9B is pre-sintered, non-fibril-forming PTFE from DuPont. Teflon™ 6C is fibril-forming PTFE from DuPont. Composition (by weight) of Examples 14-15 and Controls G-H Control G Example 14 Control H Example 15 Noryl™ N300 100 99.7 0 0 PC 300-10 0 0 73.8 73.5 Tratuf™ 9506 0 0 20.0 20.0 Metablen™ PA2130 0 0 6.2 6.2 Teflon™ 6C 0 0.3 0 0.3 where Noryl™ N300 is polyphenylene oxide/polystyrene alloy from General Electric. PC 300-10 is 10 MFR Calibre™ polycarbonate from The Dow Chemical Company. Tratuf™ 9506 is 0.95 intrinsic viscosity polyester from Goodyear Tire and Rubber Co. Metablen™ PA2130 is MBS rubber from M&T Chemicals. Teflon™ 6C is fibril-forming PTFE from DuPont. Composition (by weight) of Examples 16-17 and Controls J-K Control J Example 16 Control K Example 17 ECO 100 99.7 0 0 PUR 0 0 100 99.7 Teflon™ 6C 0 0.3 0 0.3 where ECO is ethylene/carbon monoxide copolymer, 10 percent by weight of which is derived from carbon monoxide. PUR is Isoplast™ 201 rubber-modified, high hard segment polyurethane from The Dow Chemical Company. Teflon™ 6C is fibril-forming PTFE from DuPont. Various amounts of weight are attached to the end of each of the predried tensile bars, prepared as above, and the bars are hung vertically in a forced air oven for 5 minutes at temperatures which are comparable to those at which the compositions from which the tensile bars prepared would be blow molded. The weight reported in Table VIII for each tensile bar is the amount of weight which had to be attached to the bar before it showed any visually detectable elongation by reason of being heated with weight attached. The dramatic increase in the amount of weight which a tensile bar can support without elongation at temperatures representative of blow molding conditions, resulting from the presence of a fluorinated olefinic polymer or copolymer in the composition from which the bar is fabricated, is readily evident from the above data. For instance, when a fluorinated olefinic polymer or copolymer is added to Control A, a tensile bar formed from the resulting composition (Example 1) supports more than 9 times the weight, and Example 2 supports more than 7 times as much weight as Control B. Controls C and J support no weight, but the addition of a fluorinated olefinic polymer or copolymer to the compositions from which they are formed (Examples 3 and 16, respectively) enables a tensile bar to support a significant amount of weight without elongation. Similarly improved results are seen for each of other thermoplastic polymeric materials tested. Examples 5-9 show that the addition of fluorinated olefinic polymers and copolymers other than PTFE to thermoplastic polymeric material is effective to increase the amount of weight supportable without elongation by a tensile bar, and Example 11 shows that pre-sintered, non-fibril-forming PTFE is also effective for this purpose. The increase in the amount of weight supportable without elongation by the tensile bars in the above examples indicates that the melt strength of the thermoplastic polymeric material from which the bars are made is increased by the presence of a fluorinated olefinic polymer or copolymer therein. Correspondingly, the melt strength of blow moldable thermoplastic polymeric material is increased in similar fashion by the presence of a fluorinated olefinic polymer or copolymer therein. As a further demonstration of increased melt strength, the composition of Example 2 is blow molded using a 50 (22.5 kg) pound Kautex accumulator head which has an 18 inch (45.72 cm) tooling diameter and a tooling angle of 30°. The head employs a 3.5 inch (8.89 cm) extruder, with a length to diameter ratio of 24:1, utilizing a barrier screw running at 18 rpm and having set temperatures at 350°F (176.7°C) to 365°F (185°C) for each zone. Melt temperatures are measured at approximately 425°F (218.3°C), and mold temperatures are set at 150°F (65.5°C). A parison 85 inches (2.16 m) in length is extruded weighing 40 pounds (18 kg) and having a layflat of 26 inches (966.04 cm) at both the top and bottom. Pinch bars to support the parison are not required because of its high melt strength; and, because of reduced drawdown, pre-blow of the parison is not required. An excellent quality blow molded part with uniform wall thickness, excellent tack strength and good surface quality is obtained. Testing on this blow molded part obtained the physical properties shown in Table IX. 264 psi (1.82 MPa) deflection temperature under load (ASTM D 648-82) 215°F (101.67°C) Flexural modulus (ASTM D 790-84a) 317,000 psi (2,185.64 MPa) Tensile strength (ASTM D 638-84) 7,000 psi (48.3 MPa) Elongation (ASTM D 638-84) 78 percent 10 mil notched Izod impact (ASTM D 256-84) 73°F (9°C) 11.5 ft-lbs (15.6J) -20°F (-9°C) 8.6 ft-lbs (11.7J) It is within the skill in the art to practice this invention in numerous modifications and variations in light of the above teachings. It is, therefore, to be understood that the various embodiments of this invention described herein may be altered without departing from the spirit and scope of this invention as defined by the appended claims.

Claims: A method of blow molding a contoured article, comprising (a) providing a composition by dry blending (i) 75 parts to 99.999 parts by weight thermoplastic polymeric material which contains less than 40 percent rubber and excludes fluorinated olefinic polymers, and (ii) a fluorinated olefinic polymer or copolymer which is 0.001 parts to 5 parts of said composition by weight, which composition does not contain a polyethylene having a viscosity average molecular weight higher than 200,000 or a copolymer containing epoxy or ionic groups; (b) optionally melt mixing such dry-blended composition in an extruder; (c) melt processing said composition into a hollow parison which weighs more than 5 kilograms; and (d) blow molding said article from said parison. The method of Claim 1 wherein the thermoplastic polymeric material is one or more of (a) polyamide; (b) polycarbonate; (c) polyester; (d) poly(methyl methacrylate); (e) polyacetal; (f) poly(phenylene ether); (g) polystyrene; (h) polyurethane; (i) acrylonitrile/butadiene/styrene copolymer; (j) acrylonitrile/EPDM/styrene copolymer where EPDM is ethylene/propylene/diene rubber; (k) acrylonitrile/styrene/alkyl acrylate copolymer; (l) ethylene/carbon monoxide copolymer; (m) ethylene/vinyl acetate copolymer; (n) methacrylate/butadiene/styrene copolymer; (o) styrene/acrylonitrile copolymer; (p) polyolefin homopolymer having a viscosity average molecular weight less than 200,000; (q) a blend of (I) poly(phenylene ether), and (II) polystyrene to which has been grafted a vinyl aromatic conjugated diene di- or tri-block copolymer; (r) a blend of (I) poly(phenylene ether), (II) polystyrene, and (III) a vinyl aromatic/conjugated diene di- or tri-block copolymer; (s) polyacrylate; (t) poly(ester/carbonate) copolymer; (u) poly(ethylene oxide); and (v) poly(vinyl chloride). The method of Claim 1 wherein the thermoplastic polymeric material is one or more of (a) polycarbonate; (b) polyester; (c) poly(phenylene ether); (d) poly(vinyl chloride); (e) polyurethane; (f) acrylonitrile/butadiene/styrene copolymer; (g) polyolefin homopolymer having a viscosity average molecular weight less than 200,000; (h) poly(ester/carbonate) copolymer; (i) ethylene/vinyl acetate copolymer; (j) methacrylate/butadiene/styrene copolymer; (k) styrene/acrylonitrile copolymer; (I) a blend of (I) poly(phenylene ether), and (II) polystyrene to which has been grafted a vinyl aromatic/conjugated diene di- or tri-block copolymer; (m) a blend of (I) poly(phenylene ether), (II) polystyrene, and (III) a vinyl aromatic/conjugated diene di- or tri-block copolymer. The method of Claim 1 wherein the thermoplastic polymeric material is polycarbonate, a blend of polycarbonate and polyester, or a blend of polycarbonate and acrylonitrile/butadiene/styrene copolymer. The method of any one of Claims 1-4 wherein said composition further comprises one or more elastomeric impact modifiers which contain more than 40 percent rubber by weight. The method of any one of Claims 1-5 wherein said composition further comprises one or more additives selected from fillers, thermal stabilizers, dyes, flame retarding agents, reinforcing agents, softeners, mold-release agents, seed-forming agents, pigments, plasticizers, antistatic agents, UV absorbers, lubricants, and compatibilizers. The method of any one of Claims 1-6 wherein said fluorinated olefinic polymer or copolymer comprises non-fibril-forming polytetrafluoroethylene. The method of any one of the preceding claims wherein said hollow parison exceeds 20 centimeters in diameter and 2 meters in length. The method of any one of the preceding claims wherein the contoured article weighs more than 3 kilograms. The method of any one of the preceding claims wherein said contoured article is an automotive component. The method of any one of the preceding claims wherein said contoured article is an automotive instrument panel. An article or parison obtainable according to the method of any one of Claims 1-11. The article of Claim 12 which is free of the adverse effects of parison drawdown.

Inventors: LAUGHNER MICHAEL K, LAUGHNER, MICHAEL K.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1990
Main classification: C08L101
IPC codes: C08L101, B29C49, B29L22, B29K27