MXPA98000465A - Modifier of impact for polyamidas containing a elastomer and a copolymer of isoolefina han - Google Patents

Abstract

The invention relates to impact modifiers for polyamide compositions that improve the impact resistance of polyamides without adversely affecting the flexural moduli of the composition. Impact modifiers comprise physical blends of general purpose rubbers and a halogenated copolymer of a C4 to C7 isomonoolefin and an alkylstyrene. In addition, the invention is directed to a polyamide composition containing such impact modifiers.

Description

MODIFIER OF IMPACT FOR POLYAMIDAS CONTAINING AN ELASTOMER AND A HALOGENATED ISOPLEFIN COPOLYMER Field of the Invention The present invention relates to a novel class of impact modifiers for polyamides. In addition, the invention is directed to a polyamide composition containing such impact modifiers. The impact modifier of this invention comprises a general purpose rubber and a halogenated copolymer of a C4 to C7 isomonoolefin and an alkyl-styrene. Background of the Invention It is known that polyamides show low Izod impact resistance with notch. Methods for improving the impact resistance of polyamides have been disclosed. For example, U.S. Patent No. 4,174,358 discloses a multistage thermoplastic composition, made more tenacious, consisting of a polyamide matrix resin and a second phase consisting of polymer particles ranging from 0.01 to 10 microns. The second phase - a straight or branched chain polymer - adheres to the polyamide matrix resin. In addition, U.S. Patent No. 4,350,794 discloses a polyamide composition prepared by physical melt blending of a polyamide resin and a halobutyl composition. Non-functionalized elastomers, such as general purpose rubbers, are not able to provide toughness to the polyamides because they are not able to interact properly with the polyamides so as to achieve dispersed phases of optimal size and strong interfacial bond. There is a need to be able to impart toughness to polyamides with elastomers such as general purpose rubbers. More improved, tenacious polyamide compositions have been found which employ a physical mixture comprising non-functionalized elastomers such as general purpose rubbers and a halogenated copolymer of a C4 to C7 isomonoolefin and a para-alkylstyrene as an impact modifier. SUMMARY OF THE INVENTION According to the present invention, a polymeric physical mixture useful as an impact modifier for polyamide compositions is provided, the physical mixture comprising: (a) a halogen-containing copolymer of a C4 to C7 isomo-noolefin and a para-alkylstyrene; and (b) a non-functionalized elastomer such as a general purpose rubber. The physical mixture forms either a dispersed core-shell phase in a polyamide matrix with an internal elastomer core and an outer halogenated copolymer shell, or a phase of (a) and (b) capable of mixing. Detailed Description of the Invention The present invention is directed to a composition suitable for giving toughness to polyamides. The impact modifier of this invention forms dispersed phases in the polyamide matrix. It consists of a core-shell type morphology where the outer sleeve consists of a halogenated copolymer and the inner core consists of a general purpose rubber. The diameter of such impact modifiers is most preferably between about 0.25 to about 2 microns, preferably 0.4 to 0.6 microns. The Elastomer. Such rubbers comprise natural rubber and synthetic rubbers. Suitable synthetic oils are homopolymers and copolymers of conjugated dienes including polyisoprene, styrene butadiene rubber, styrene-isoprene rubber, neoprene or polychloroprene, butyl rubber, nitrile rubber and polybutadiene, and mixtures thereof. The Mooney viscosity at 100 ° C (ML 1 + 4) of such rubbers is generally between about 20 and about 150. (The Mooney viscosity, as referred to herein, is measured according to the ASTM D method. 1646.) The natural rubber for use in the present invention preferably has a Mooney viscosity at 100 ° C (ML 1 + 4) of about 30 to about 120, more preferably about 30 to about 65. The thickness of commercially available natural rubber consists of cis-1, 4-polyisoprene. Generally, between 93 and 95% by weight of the natural rubber is cis-1,4-poly-soprene. Included in the natural rubber group are Malaysian rubbers such as SMR CV, SMR 5, SMR 10, SMR 20 and SMR 50, and their mixtures. The natural rubber spread with oil can be used additionally to varying degrees. The raw rubber portion may be a latex or a re-ground rubber type. Aromatic or non-staining cycloparaffinic oils are typically used at 10, 25 and 30% by weight. Polyisoprene rubber, which is essentially identical in structure to natural rubber, can also be used. The polyisoprene, like the natural rubber, can be all composed of cis-polyisoprene with the 1,4-addition structure. It can also differ from natural rubber in 1,4-and 1,3-addition structure amounts. In addition to poly (cis-1,4-isoprene), other forms of polyisoprene, trans-1,4 and trans-3,4 of high purity can be used, as well as the poly-1,2 structure, such as those obtained in conjunction with the other three structures. Polybutadiene can also be used as the general purpose rubber. Polybutadiene, an addition polymerization product, can be a 1,4-addition product and can be a cis-1,4 or trans-1,4 structure. The participation of a single double bond results in a vinyl or 1.2 -adition. The two 1,4 structures contain unsaturation of the spine, while the two 1,2-polybutadienes contain pendant unsaturation. The Mooney viscosity of the polybutadiene rubber, as measured at 100 ° C (ML 1 + 4) preferably ranges from about 40 to about 70, more preferably from about 45 to about 65, and most preferably around 50 to around 60. Additionally useful as a general purpose rubber is neoprene, also known as chloroprene. This rubber, composed of 2-chloro-l, 3-butadiene units, typically consists of a linear sequence of predominantly trans1.4 structure with small amounts of cis-1, 4, 1,2 and 3,4 polymerization. Trans-1,4 and cis-1,4 structures have spinal unsaturation. Structures 1,2 and 3,4 often also have pendant unsaturation. Such polymers are generally prepared by emulsion polymerization of free radicals. In addition, nitrile rubbers, which are random emulsion polymers of butadiene and acrylonitrile, can be employed.

Such polymers are well known in the art and typically vary in acrylonitrile ratios of from about 15 to about 60% by weight. In addition, the styrene-butadiene rubber can also be used as a general purpose rubber. Such copolymers are well known in the art and consist of styrene units as well as any of the three forms of butadiene (cis-1,4, trans-1,4 and 1,2 or vinyl). Such styrene-butadiene copolymers can be randomly dispersed mixtures of the two block monomers or copolymers. Typically, the styrene-butadiene copolymers contain from about 10 to about 90, preferably from about 30 to about 70,% by weight of conjugated diene. The butyl rubber useful in this invention relates to a vulcanizable rubbery copolymer containing, by weight, about 85 to 99.5% of combined isoolefins having from 4 to 8 carbon atoms. Such copolymers and their preparation are well known in the art. Preferably, the butyl rubber has an isobutylene content of about 95 to 99.5% by weight. The preferred Mooney viscosity of the butyl rubber useful in the invention, as measured at 125 ° C (ML 1 + 4) ranges from about 20 to about 80, more preferably from about 25 to about 55, with the greatest preferably from about 30 to about 50. The conjugated diene is preferably butadiene or isoprene. Such butyl rubber may be further halogenated by means known in the art. The halogenated copolymer should preferably contain at least about 0.5% by weight of combined halogens but not more than about one chlorine atom or three bromine atoms per double bond present in the original copolymer. Preferably, it contains from about 0.5 to about 2% by weight of chlorine or from about 0.5 to about 5% by weight of bromine. Most preferably, it contains from about 100 to about 1.5% by weight of chlorine or from about 1.0 to about 2.5% by weight of bromine. The halogenated isobutylene-isoprene copolymer rubber may also contain more than one halogen in its structure, for example chlorine and bromine. When two general purpose rubbers are employed in the present invention, a suitable weight ratio of about 100 to 1 to 1 to 100 is acceptable. It is possible to use more than two such general purpose rubbers. The Halogenated Copolymer. The cap of the impact modifier of this invention comprises a halogenated copolymer of a C4 to C7 isomonoolefin and an alkylstyrene. Halogen-containing copolymers of a C4 to C7 isomonoolefin and alkylstyrene are useful in the physical blends of this invention. Suitable halogenated copolymers comprise between about 0.5 and about 20% by weight, preferably from about 1 to about 20% by weight, more preferably 2.0 to about 20% by weight alkylstyrene units. The halogen content of the copolymer can vary from more than zero to about 7.5% by weight, preferably from about 0.1 to about 7.5% by weight. The Mooney viscosity at 125 ° C (ML 1 + 8) of such halogenated copolymers is typically between about 20 and about 55, preferably from about 25 to 45, most preferably from about 30 to about 35. .

Such halogenated copolymers, as determined by gel permeation chromatography (GPC), have narrow distributions of molecular weights and substantially homogeneous composition distributions or compositional uniformity. Such copolymers include the alkylstyrene fraction represented by the formula: wherein each R is independently selected from the group consisting of hydrogen, alkyl having preferably 1 to 5 carbon atoms, primary haloalkyl having 1 to 5 carbon atoms, secondary haloalkyl preferably having 1 to 5 carbon atoms , and their mixtures, and X is selected from the group consisting of bromine, chlorine and mixtures thereof. The preparation of these polymers is well known, as disclosed in U.S. Patent No. 5,162,445. Preferably, the isomonoolefin is isobutylene and the alkylstyrene is methyl-styrene-non-halogenated, where the halogen is bromine. Particular preference is given to the para isomer.

The halogenated copolymer for use in this invention is produced by halogenating an isobutylene-alkylstyrene copolymer using bromine in solution in normal alkane (for example, hexane or heptane) using a bis azo initiator, for example AIBN or VAZO 52 (2, 2, 1 -azobis (2,4-dimethylpentane nitrile)), at about 55 to 80 ° C for a period of time ranging from about 4.5 to about 30 minutes, followed by a sudden caustic cooling. The recovered polymer is then washed with basic water washes and water / isopropanol washes, recovered, stabilized and dried. At least about 95% by weight of the resulting halogenated copolymer for use in this invention has a halogenated alkylstyrene content within about 10% by weight, and preferably within about 7% by weight, of the average alkylstyrene content for the overall composition, and preferably at least 97% by weight of the copolymer product has an alkylstyrene content within about 10% by weight and preferably about 7% by weight, of the average alkylstyrene content for the overall composition. Replacement of the Non-functionalized Elastomer Portion. The non-functionalized elastomer used in this invention can be partially replaced with an inorganic filler which is capable of minimizing the reduction in the modulus and the thermal distortion temperature of the polyamide matrix. Such fillers include carbon black, carbon fibers, glass fibers, amorphous silica, asbestos, calcium silicate, aluminum silicate, magnesium carbonate, calcium carbonate, kaolin, chalk, talc, quartz, mica, gypsum, etc. Impact modifiers of the invention may comprise between 85 and 32.5% by weight of halogenated copolymer and 15 and 65.5% by weight of general purpose rubber, preferably about 75 to 40% by weight of halogenated copolymer and 25 to 60% by weight of general purpose rubber, most preferably 65 to 30% by weight of copolymer and 35 to 70% by weight of elastomer. (Where the optional polyolefin is employed, the relative amount of the combination of general purpose rubber and halogenated copolymer follows the limitations mentioned for general purpose rubber.) The impact modifiers of the invention can be prepared by physical blending of the halogenated copolymer. with the general purpose rubber (and optional polyolefin) in a high shear mixer such as a two-roll mill, a Banbury mixer or a twin screw extruder to form a master filler. Typically, where a blender is used, the halogenated copolymer is first chewed. The general purpose rubber (and the optional polyolefin) is then added and the components are mixed for approximately five to ten minutes until the mixture is discharged. Where polyolefin is present with the general purpose rubber, the mixing is carried out in the most desirable way above the melting point of the polyolefin. After the discharge materials are cooled, they are ground into pearls. Where a twin screw extruder is used, the halogenated copolymer is first ground into beads. The halogenated copolymer is then physically dry blended with the general purpose rubber (and optional polyolefin). The dry mixed beads are then fed into the feed throat of the pre-heated twin screw extruder. The extruded filaments are then cooled in a water bath and reduced to the desired bead size. The masterbatch is preferably dried to remove the surface moisture before carrying out the combination with the polyamide. The morphological analysis of the impact modifier of this invention demonstrates a general-purpose rubber core-shell dispersed phase (with optional polyolefin) forming the core of the impact modifier. The halogenated copolymer encapsulates the inner core and thereby forms the outer sleeve of the modifier. The morphology of the impact modifier of this invention is formed in situ. Such modifiers provide more sturdy polyamides with high resistance to Izod impact with notch. further, the interaction of the halogenated copolymer outer shell with the polyamide prevents the impact modifier from being exuded to the surface of the polyamide. Suitable polyamides for use in this invention comprise crystalline or high molecular weight resinous solid polymers, including copolymers and terpolymers having recurring polyamide units within the polymer chain. Preferably, the polyamide used in the invention is a semi-crystalline or amorphous resin having a molecular weight of at least 5,000 and commonly referred to as nylons. Both fiber-forming and molding-grade nylons are suitable. Examples of such polyamides are polycaprolactam (nylon 6), polylaurylactam (nylon 12), polyhexamethyleneadipamide (nylon 6,6), polyhexamethylene azelamide (nylon 6,9), polyhexamethylene-bacamide (nylon 6,10), polyhexamethylene-isophthalamide (nylon) 6, IP) and the condensation product of 11-aminoundecanoic acid (nylon 11); partially aromatic polyamide made by the poly-condensation of meta xylene diamine and adipic acid, such as polyamides having the structural formula: The polyamide for use in this invention can be further prepared by the copolymerization of two of the above polymers or terpolymerization of the above polymers or their components, for example a copolymer of adipic acid, isophthalic hexamethylene diamine. Additional examples of polyamides are described in Kirk-Othmer, Encyclopedia of Chemical Technology, vol. 10, p. 919, and in the Encyclopedia of Polymer Science and Technology, vol. 10, pp. 392-414. Commercially available thermoplastic polyamides are advantageously used in the practice of this invention, especially those having a softening point or melting point between 160 and 275 ° C. Typically, the weight ratio of the impact modifier to polyamide in the polyamide compositions is less than 40:60, preferably less than 30:70, and most preferably less than or equal to 20:80. The impact modifier can be physically mixed in the molten state with the polyamide. Preferably, the polyamide is in the form of beads and dried before mixing with the impact modifier. In a particularly preferred embodiment, the polyamide and the impact modifier are physically mixed in a molten state in a twin screw extruder. The extruder filaments are cooled and then reduced in a bead former. The polyamide compositions of the invention can be further modified by means of one or more conventional additives such as stabilizers and inhibitors of oxidative, thermal and ultraviolet degradation; lubricants and mold release agents, colorants, including dyes and pigments, fibrous and particulate fillers and reinforcements, nucleating agents, plasticizers, processing aids, etc. The stabilizers can be incorporated into the composition at any stage in the preparation of the polyamide composition. Preferably, the stabilizers are included early to prevent the onset of degradation before it can be protected. Such stabilizers must be compatible with the composition. The oxidative and thermal stabilizers useful in the materials of the present invention include those used in general addition polymers. They include, for example, up to 1% by weight, based on the weight of the metal halide polyamide composition of group I, for example sodium, potassium, lithium, with cuprous halides, for example chloride, bromide, iodide, phenols impaired, hydroquinones and varieties of substituted members of those groups and their combinations. The ultraviolet light stabilizers, for example in an amount up to 2.0% based on the weight of the polyamide composition, can also be those generally used in addition polymers. Examples of ultraviolet light stabilizers include various substituted resorcinols, salicylates, benzotriazoles, benzophenones, and the like. Suitable lubricants and mold release agents, for example in an amount of up to 1.0% based on the weight of the polyamide composition, are stearic acid, stearic alcohol, stearamides; organic tinctures such as nigrosine, etc., pigments, for example titanium dioxide, cadmium sulfide, cadmium sulfide selenide, phthalocyanines, ultramarine blue, carbon black, etc .; in an amount of up to 50% based on the weight of the composition, of fibrous and particulate fillers and reinforcements, for example carbon fibers, glass fibers, amorphous silica, asbestos, calcium silicate, aluminum silicate, carbonate magnesium, calcium carbonate, kaolin, chalk, talc, powdered quartz, mica, gypsum, etc .; nucleating agents, for example talc, calcium fluoride, sodium phenyl phosphinate, alumina, and finely divided polytetrafluoroethylene, etc .; plasticizers, in an amount up to about 20% based on the weight of the composition, for example dioctyl phthalate, dibenzyl phthalate, butyl benzyl phthalate, hydrocarbon oils, butyl benzene sulfonamide N-normal, ortho and for toluene ethyl sulfonamide , etc. The dyes (dyes and pigments) may be present in an amount of up to about 5.0% by weight, based on the weight of the polyamide composition. The following non-limiting examples and comparative data highlight the salient aspects of the invention. All parts are given in terms of units of weight, unless otherwise indicated. The properties and test performance data noted below were measured as follows: The Mooney viscosity of the designated copolymers was measured according to the method ASTM D1646, ML (1 + 8), 125 ° C.

Izod Impact Test - The prepared samples were stored in metal cans before they were tested. The notched Izod impact test (NI) was conducted according to the ASTM D256 method at room temperature (20 ° C), 0 ° C and -20 ° C. The instrument used was a Wiedemann pendulum impact test apparatus. The average values of at least five samples were reported. For the tests at 0 and -20 ° C, the samples were immersed in a mixture of isopropanol / dry ice pre-adjusted to the desired temperature. Temperature equilibrium was assumed after 10 minutes of immersion. The samples were loaded into the test apparatus and tested immediately. The entire process took less than 10 seconds, so the temperature drop was negligible. The components used in the examples and demonstration examples are: Exxpro A is a halogenated copolymer of para-methylstyrene and isobutylene comprising 4.7% by weight of para-methylstyrene and 95.3% by weight of isobutylene, and which also contains 0.35% by weight of bromine (as measured by X-ray fluorescence). The copolymer exhibits a Mooney viscosity of 30. Exxpro B is a halogenated copolymer of para-methylstyrene and isobutylene comprising 5.0 wt% of para-methylstyrene and 95.0 wt% of isobutylene and further containing 1.2 wt% of bromine (as measured by X-ray fluorescence). The copolymer exhibits a Mooney viscosity of 35 and is commercially available from Exxon Chemical Company as EMDS 89-1. NR SMR L is a natural rubber, a product commercially available from The Natural Rubber Association of Malaysia. PA-6 is a polyamide-6 in the form of beads, commercially available as Capron 8209F from Allied Signal, Inc. Irganox B-215 Antioxidant, commercially available from Ciba-Geigy. ZnO is commercially available as Protox 169, a product of The Zinc Corp. of America. EXAMPLES Examples of the present invention, including controls, are given in Table 1. Demonstration A is unmodified polyamide-6 (PA-6), which has a low Izod impact resistance with notch at the three temperatures at which the tests were done. Demonstration A is a control. Demonstration B is a binary physical mixture of PA-6 and poly (isobutylene-co-p-methylsitrene) (XP-50). ElXP-50, without the functional benzyl bromide group, leads to a small increase in Izod impact strength with PA-6 notch. Demonstration B is also a control, and is not a composition of the present invention. Similar to XP-50, the general purpose rubbers used in this invention, if used alone, do not increase the Izod notched impact strength of PA-6. Demonstrations C and D are PA-6 modified with Exxpro A and B, respectively. They are controls, and are not a composition of the present invention. They show that both Exxpro A and Exxpro B is an agent that imparts extremely effective tenacity for PA-6. The demonstrations E to L are the compositions of the present invention. Demonstrations E and F are PA-6 modified by the pre-mix of Exxpro and XP-50 at the ratios indicated in Table 1. Although XP-50 is not effective in giving toughness to PA-6, the pre-mix of Exxpro B with XP-50 at 50/50 and 70/30 is an effective tenacity imparting agent for PA-6, as indicated in Table 1. This illustrates the key point of this invention. The Exxpro can be combined with a polymer that is not effective to give tenacity to PA-6 without losing its effectiveness to give tenacity to PA-6. The G demonstration is a PA-6 modified by the Exxpro A premix and natural rubber. Again, the pre-mix is effective to give tenacity to PA-6, although it is not the natural rubber by itself. Morphology studies, using transmission electron microscopy, showed that the Exxpro pre-mix and natural rubber form a core-shell morphology in the PA-6 matrix, with Exxpro in the cap surrounding a natural rubber core. The average particle size of the premix is approximately the same as that of the dispersed phase Exxpro in PA-6. The core-shell structure formed in situ explains the effectiveness of the Exxpro / natural rubber pre-mix to give toughness to PA-6. Demonstration H is PA-6 modified by the pre-mix of Exxpro B and polybutadiene rubber. Similar to demonstration G, the pre-mix of Exxpro B and polybutadiene rubber is effective to give toughness to PA-6, although the rubber of polybutadiene is not. Demonstrations 1, J and K are PA-6 modified by Exxpro pre-mix with styrene-butadiene rubber (SBR), butyl rubber and polyisobutylene. The three pre-mixtures are effective to give toughness to PA-6, although SBR, butyl rubber and polyisobutylene are not effective in giving toughness to PA-6 by themselves. The demonstration L is a PA-6 modified by the premix of Exxpro, isoprene rubber and talc. Again, the pre-mix is effective to give toughness to PA-6, although isoprene rubber alone is not. The addition of talc in this composition leads to greater stiffness (modulus), although Izod notched impact strength is adversely affected.

PA6 / Exxpro / GPR All Dex fifteen 0 5 XP-50 is po so ut eno-co-1, 4-methes reno), not brominated.

Claims (8)

1. CLAIMS 1. An impact modifier for polyamide compositions, comprising a physical mixture of: a. a halogenated copolymer of a C4 to C7 isomonoolefin and an alkylstyrene, b. a rubber for general purposes, and c. a polyolefin selected from the group consisting of an elastomeric polyolefin, a crystalline polyolefin or a mixture thereof, wherein the weight ratio of polyolefin to general purpose rubber is less than or equal to 50:50.
2. 2. A polyamide composition having improved impact resistance, comprising: a. a polyamide, b. a halogenated copolymer of a C4 to C7 isomonoolefin and an alkylstyrene, and c. an oilcloth of general purposes.
3. 3. The polyamide composition of claim 2, wherein the general purpose rubber of said impact modifier is natural rubber or a synthetic resin.
4. The polyamide composition of claim 2, wherein the polyamide is selected from the group comprising nylon 6 and nylon 6,6.
5. The polyamide composition of claim 2, wherein the isomonoolefin of the halogenated copolymer is isobutylene and the haloalkylstyrene is para-halomethylstyrene.
6. 6. The polyamide composition of claim 2, wherein the impact modifier further comprises a polyolefin selected from the group consisting of an elastomeric polyolefin, a crystalline polyolefin or a mixture thereof, wherein the weight ratio of polyolefin to rubber of general purposes is less than or equal to 50:50.
7. The polyamide composition of claim 3, wherein the synthetic rubber is selected from the group consisting of polybutadiene, polyisoprene, a copolymer of styrene and conjugated diene, a nitrile rubber, butyl rubber and polychloroprene.
8. 8. A process for preparing modified polyamide on impact, said process comprising mixing together a polyamide and the impact modifier of claim 1.