| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | April 4, 2000 |
| PATENT TITLE |
Maleated high acid number high molecular weight polypropylene of low color |
| PATENT ABSTRACT |
A novel, continuous process for the manufacture of novel higher molecular weight and higher acid numbered maleated polypropylenes with lower color at higher efficiencies involving specified ratios of polypropylene, maleic anhydride, and free radical initiator is described. The novel maleated polypropylenes have an acid number greater than 4.5, a yellowness index color of no greater than 76, and a number average molecular weight of at least 20,000. The process entails continuously forming an intimate mixture of molten polypropylene and molten maleic anhydride at one end of a reactor, continuously introducing a free radical initiator, and continuously removing high acid number high molecular weight maleated polypropylene of low color from the opposite end of the reactor. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | February 24, 1999 |
| PATENT REFERENCES CITED |
Database WPI, Week 9351, Derwent Publications Ltd., London, GB; AN 93-410862 & JP,A,05 310 817 (Toyobo KK), Nov. 22, 1993 (see abstract). Material Safety Data Sheet (MSDS), MSDS No. P579015, Issued Oct. 15, 1993, Tradename: POLYBOND 3150, Chemical Name: Polypropylene, modified. Journal of Applied Polymer Science, Effect of Compatibilization on the Properties of Polypropylene/Polyamide-66 (75/25 Wt/Wt) Blends, Apr. 11, 1994, pp. 195-206. Uniroyal Product Information, POLYBOND Modified Polyolefin, Effective Date: Mar. 15, 1995. Reactive Extrusion, Plastics Formulating and Compounding, May/Jun. 1996, pp. 33, 35, 36. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A process for the production of maleated polypropylene comprising: (a) continuously forming an intimate mixture of molten polypropylene and molten maleic anhydride at one end of a reactor, (b) continuously introducing a free radical initiator into said intimate mixture of molten polypropylene and molten maleic anhydride to initiate the grafting of the maleic anhydride onto the molten polypropylene to produce a maleated polypropylene, and (c) continuously removing the maleated polypropylene product from the opposite end of said reactor, wherein the weight ratio of polypropylene to maleic anhydride is about 10 to 200, the molar ratio of polypropylene to free radical initiator is about 200 to 4,000, and the molar ratio of maleic anhydride to free radical initiator is about 1 to 70. 2. The process according to claim 1 wherein the weight ratio of polypropylene to maleic anhydride is about 25 to 60. 3. The process according to claim 1 wherein the molar ratio of polypropylene to free radical initiator is about 270 to 2,100. 4. The process according to claim 1 wherein the molar ratio of maleic anhydride to free radical initiator is about 3.5 to 15. 5. The process according to claim 1 wherein the melt flow rate of said polypropylene in (a) is about 0.1 to 50 at 230.degree. C. 6. The process according to claim 5 wherein the melt flow rate of the polypropylene is about 0.1 to 20 at 230.degree. C. 7. The process according to claim 1 wherein said reactor is a screw extruder. 8. The process according to claim 1 wherein said free radical initiator is a peroxide having a half life greater than 3 seconds at 180.degree. C. 9. The process according to claim 8 wherein said peroxide is selected from the group consisting of ditertiary butyl peroxide, tertiary butyl hydroperoxide, cumene hydroperoxide, p-menthane peroxide, p-menthane hydroperoxide and 2,5-dimethyl-2,5-bis-(t-butylperoxy)hexane. 10. The process according to claim 1 wherein step (b) is conducted at a temperature between 190 and 205.degree. C. 11. The process according to claim 1 wherein the reaction proceeds at an efficiency rate of greater than 35 percent maleic anhydride incorporation into polypropylene. 12. The process according to claim 1 wherein the efficiency rate is at least 49 percent maleic anhydride incorporation into polypropylene. 13. The process according to claim 7 wherein said screw extruder is a twin screw extruder run at an RMP of 50 to 400 and the residence time of said molten polypropylene in said reactor is about 0.45 to 2.5 minutes. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION This invention relates to novel lower color, maleated polypropylenes with higher acid numbers and higher molecular weights. This invention also relates to a novel polypropylene maleation process utilizing low flow rate polypropylenes involving specified ratios of polypropylene, maleic anhydride, and free radical initiator. BACKGROUND OF THE INVENTION Grafting of monomers onto polyolefins is well known (see `Polymer Chemistry` by M. P. Stevens, (Addison-Wesley), 1975, pp. 196-202). Maleation is a type of grafting wherein maleic anhydride is grafted onto the backbone chain of a polymer. Maleation of polyolefins falls into at least three subgroups: maleation of polyethylene, maleation of polypropylene, and maleation of copolymers of propylene and ethylene or other monomers. Maleation of polyethylene provides higher molecular weight products with a noticeable decrease in melt index due to cross-linking, unless special provisions are made, (see for example `Journal of Applied Polymer Science`, 44, 1941, N. G. Gaylord et al (1992); and U.S. Pat. Nos. 4,026,967; 4,028,436; 4,031,062; 4,071,494; 4,218,263; 4,315,863; 4,347,341; 4,358,564; 4,376,855; 4,506,056; 4,632,962; 4,780,228; 4,987,190; and 5,021,510). Maleation of polypropylene follows an opposite trend and yields lower molecular weight products with a sharp increase in flow rate due to fragmentation during the maleation process (see for example U.S. Pat. Nos. 3,414,551; 3,480,580; 3,481,910; 3,642,722; 3,862,265; 3,932,368; 4,003,874; 4,548,993; and 4,613,679). Some references in the literature fail to note the difference between maleation of polyethylene and polypropylene, and claim maleation of polyolefins with conditions which are useful only for either polyethylene or polypropylene, respectively. In general, conditions which maleate polypropylene are not ideal for maleation of polyethylene due to the opposite nature of the respective maleation chemistries: fragmentation to lower molecular weights for polypropylene and cross-linking to higher molecular weights for polyethylene. This is shown in U.S. Pat. No. 4,404,312. Maleation of copolymers of propylene and ethylene or other monomers follow the pattern of the majority component. Maleations of polypropylene can also be further subdivided into batch or continuous processes. In batch processes all of the reactants and products are maintained in the reaction for the entire batch preparation time. In general, batch maleation processes cannot be used competitively in commerce due to high cost. Batch processes are inherently more expensive due to startup and cleanup costs. The maleated polypropylene's that are reported in the previous literature can also be divided into two product types as a function of whether or not solvent is involved, either as a solvent during reaction or in workup of the maleated products. In U.S. Pat. Nos. 3,414,551; 4,506,056; and 5,001,197 the workup of the product involved dissolving the maleated polypropylene product in a solvent followed by precipitation, or washing with a solvent. This treatment removes soluble components and thus varies both the `apparent` molecular weight and the acid number. Processes using an extruder produce a product in which solvent soluble components remain. In addition, extruder processes often incorporate a vacuum system during the latter stages of the process to remove volatile lower molecular weight components. Thus different compositions are necessarily present in products produced in an extruder in contrast to those products from solvent processes or those which use a solvent in product workup. Another subdivision of maleation of polyolefins concerns the state of the reaction process. Solvent processes, or processes where solvent is added to swell the polypropylene (see U.S. Pat. No. 4,370,450), are often carried out at lower temperatures than molten polyolefin (solvent free) processes. Such processes involve surface maleation only, with substantial amounts of polypropylene below the surface being maleation free. Processes using molten polypropylene involve random maleation of all of the polypropylene. Solvent processes are also more expensive in that solvent recovery/purification is necessary. Solvent purification is even more expensive if the process inherently produces volatile by-products, as in maleation. Note that if water is the `solvent`, polypropylene is not soluble and reaction must occur only on the surface of the polypropylene solid phase. Further, in aqueous processes maleic anhydride reacts with the water to become maleic acid. In these two ways processes containing water are necessarily different from non-aqueous processes. In a molten process no solvent or water remains at the end of the process to be purified or re-used. Thus a molten process would be environmentally `greener` and less expensive. Present commercial maleation of low flow rate (high molecular weight) polypropylene by continuous processes, such as in an extruder, produce products with acid numbers well below 4. These products are used in adhesives, sealants, and coatings and as couplers and compatibilizers in polymer blends. However, due to the low acid numbers, the adhesion and coupling properties of these maleated polypropylenes are limited. As noted above, attempts to produce higher acid number polypropylene in continuous processes yield higher colored products with much lower molecular weight with maleic anhydride conversion efficiencies of 20-30% or lower (see for example U.S. Pat. No. 5,001,197). Attempts to produce higher acid number polyethylene in continuous processes yield cross-linking, higher color, and gels (see for example U.S. Pat. Nos. 4,612,155; 4,639,495; 4,751,270; 4,762,890; 4,857,600; and 4,927,888). The patent literature does describe continuous maleation of high flow rate (low molecular weight) polypropylene waxes to higher acid numbers. However, as noted above the molecular weights of the maleated waxes so produced are even lower than that of the starting material due to fragmentations during maleation. In light of the above, it would be very desirable to maleate lower flow rate polypropylenes in a continuous process to higher molecular weights and higher acid numbers with lower colors than have been known before. It would also be very desirable to maleate these polypropylenes at higher efficiencies. SUMMARY OF THE INVENTION The composition according to the present invention comprises a maleated polypropylene having an acid number greater than 4.5, a yellowness index color of no greater than 76, and a number average molecular weight of at least 20,000. The process for the production of high acid number high molecular weight maleated polypropylene of low color comprises continuously forming an intimate mixture of molten polypropylene and molten maleic anhydride at one end of a reactor, continuously introducing a free radical initiator into said intimate mixture of molten polypropylene and molten maleic anhydride, and continuously removing high acid number high molecular weight maleated polypropylene of low color from the opposite end of said reactor, wherein the weight ratio of polypropylene to maleic anhydride is about 10 to 200, the molar ratio of polypropylene to free radical initiator is about 200 to 4,000, and the molar ratio of maleic anhydride to peroxide is about 1 to 70, and wherein the melt flow rate of said molten polypropylene is preferably about 0.1 to 50 at 230.degree. C. DETAILED DESCRIPTION OF THE INVENTION The applicants have unexpectedly discovered a novel continuous process to maleate low flow rate polypropylenes. The compositions so formed are novel in that the color is lower, the acid number is higher, and the molecular weight is higher than previously known. The process is also unique in that the efficient use of maleic anhydride is generally much higher than expected. The composition according to the present invention has an acid number greater than about 4.5 (the method of determining acid number is illustrated in the examples). The maleated polypropylene composition according to the present invention preferably has an acid number greater than 5, more preferably between 6 and 70, with an acid number between 9 and 60 being most preferred. Generally, at the higher acid numbers the resulting maleated polypropylene exhibits higher adhesiveness to polar substrates and thus is more useful in combination with materials used in adhesives and sealants. Additionally, at the higher acid numbers the maleated polypropylene is useful as a compatibilizing agent or coupler when used in blends of dissimilar materials, including polymer blends such as a nylon and polypropylene blend. At higher acid numbers lower amounts of maleated polypropylene is needed for any of these purposes. However, due to practicality acid numbers generally above 70 are difficult to produce economically. Thus, practical preferred limits on acid numbers of the maleated polypropylene are below 70. The composition according to the present invention has a yellowness index color no greater than 76 or about 75. The yellowness index color analysis is illustrated in the examples. At a yellowness index color less than about 75, the resulting maleated polypropylene has a desirable color in that when blended with other materials it imparts less of an undesirable yellow tint or brown tint to the final product. Thus, yellowness index colors well below 75 are more preferred. The maleated polypropylene composition according to the present invention preferably has a yellowness index color less than about 65 or 60, more preferably less than 50 with a yellowness index color less than 40 being most preferred. The composition according to the present invention has a number average molecular weight of at least 20,000 which corresponds to a Brookfield Thermosel Melt Viscosity of at least about 16,000 cP at 190.degree. C. This number average molecular weight is preferably as high as possible. At higher number average molecular weights the resulting maleated polypropylene is more durable and flexible which is desired in many applications. Thus, the maleated polypropylene preferably has a number average molecular weight greater than 25,000 and even greater than 30,000. However, the maleated polypropylene generally has a number average molecular weight less than 100,000 due to fragmentation that occurs during the process of maleating the molten polypropylene. Therefore, the maleated polypropylene generally has a number average molecular weight for the more preferred compositions between 25,000 and 80,000 with a number average molecular weight between 30,000 and 70,000 being most preferred. The composition according to the present invention is made from polypropylene that contains less than 20 weight percent of a comonomer and is preferably a homopolypropylene containing less than 5 weight percent of a comonomer, more preferably less than 2 weight percent of a comonomer. At amounts of comonomer higher than 20 weight percent, and sometimes higher than 5 weight percent, the crystallinity of the maleated polypropylene is significantly reduced, and in the case of ethylene as comomomer crosslinking can occur. The composition according to the present invention can be blended with many other materials to serve as a compatibilizer, such as in blends with nylon and polypropylene. This type of blend preferably contains about 10 to 90 weight percent nylon, about 10 to 90 weight percent polypropylene, and about 0.1 to 10 weight percent maleated polypropylene, more preferably about 25 to 75 weight percent nylon, about 25 to 75 weight percent polypropylene, and about 0.1 to 10 weight percent maleated polypropylene. Additionally, the maleated polypropylene composition of the present invention can be extended with many components such as wood flour, glass fibers, talc, and mica. The use of these components extend the material reducing the final cost. The process according to the present invention for producing the high acid number high molecular weight maleated polypropylene of low color comprises (a) continuously forming an intimate mixture of molten polypropylene and molten maleic anhydride at one end of a reactor, wherein the melt flow rate of said polypropylene is preferably about 0.1 to 50 at 230.degree. C., (b) continuously introducing a free radical initiator into said intimate mixture of molten polypropylene and molten maleic anhydride to produce a maleated polypropylene, and (c) continuously removing the maleated polypropylene product from the opposite end of said reactor, wherein the weight ratio of polypropylene to maleic anhydride is about 10 to 200, the molar ratio of polypropylene to free radical initiator is about 200 to 4,000, and the molar ratio of maleic anhydride to free radical initiator is about 1 to 70. The process according to the present invention maleates a molten polypropylene that preferably has a melt flow rate of about 0.1 to 50 at 230.degree. C. For all practical purposes, a polypropylene with a melt flow rate below 0.1 is difficult to produce and requires significant torque in a twin screw extruder to be able to process. Whereas, a polypropylene with a melt flow rate greater than 50 at 230.degree. C. yields a maleated polypropylene product with a molecular weight that is lower than is generally useful according to the present invention. The melt flow rate of the polypropylene used to produce a maleated polypropylene of the present invention is more preferably about 0.1 to 40 @ 230.degree. C., with a melt flow rate of about 0.1 to 20 @ 230.degree. C. being most preferred. The process according to the present invention uses a free radical initiator to initiate the grafting of the maleic anhydride onto the molten polypropylene. Any free radical source could be useful in the process of the present invention. However, peroxides are generally more preferred due to availability and cost. Peroxides with short half lives i.e. less than 3 seconds at 180.degree. C. are less desirable, since a significantly higher amount of peroxide is needed and results in a maleated polypropylene product of poor color and higher cost. The preferred peroxides are alkyl peroxides, more preferably dialkyl peroxides. Examples of suitable peroxides useful in the process of the present invention include ditertiary butyl peroxide, tertiary butyl hydroperoxide, cumene hydroperoxide, p-menthane peroxide, p-menthane hydroperoxide and 2,5-dimethyl-2,5-bis-(t-butylperoxy)hexane with ditertiary butyl peroxide and 2,5-bis-(t-butylperoxy)hexane being most preferred. The process according to the present invention is conducted in a continuous process. Any continuous process can be used in the practice of the present invention. However, stirred pot reactors with powerful stirring mechanisms or screw extruders are favored, with screw extruders generally being more preferred due to the ease in operation and acceptability in manufacturing processes. Twin-screw extruders are the most preferred screw extruders due to their ease of use and efficient mixing action. Screw extruders are also more preferred in that the polypropylene is maleated continuously with a shorter residence time in the reaction zones. The use of a screw extruder in the process of the present invention aids in the production of maleated polypropylenes of improved color and higher molecular weight due in part to less fragmentation of the polypropylene. The process according to the present invention is preferably conducted at a weight ratio of polypropylene to maleic anhydride between 10 and 200, more preferably between 15 and 120, even more preferably between 20 and 100, with a weight ratio of polypropylene to maleic anhydride of about 25 to 60 being most preferred. At amounts of polypropylene/maleic anhydride below the ratio of 10 too much maleic anhydride is present and the efficiencies are dramatically reduced. Whereas, at ratios above 200 the amount of maleation in the final maleated polypropylene is significantly lower. Such ratios simply increases the need for longer residence time or recycle of low acid number maleated polypropylene. The residence time of the polypropylene in the continuous reactor depends upon the pumping rate of the polypropylene and the size (volume) of the reactor. This time is generally longer than three times the half life of the free radical initiator so that a second pass through the rector is not needed to obtain sufficient maleation of the polypropylene. In a stirred reactor the residence time generally varies from about 5 minutes to 1 hr, more preferably about 10 minutes to 30 minutes. In a screw extruder this time generally varies from about 1 to 3 minutes at RPMs of 50 to 400 for a single screw and about 0.45 to 2.5 minutes with twin screws, more preferably about 1 to 2 minutes at RPMs of 150 to 300 with twin screws. As shown in the examples, at certain set amounts of reactants (within the general ratios of reactants required in the present invention) a polypropylene of lower than desired acid number is produced. In this instance the RPM in a screw extruder can be reduced or the residence time increased such that the acid number is increased to be within the more desired acid number limits. The molar ratio of polypropylene to free radical initiator used in the maleation process according to the present invention is preferably about 200 to 4,000, more preferably about 210 to 3,500, with a molar ratio of polypropylene to free radical initiator of about 270 to 2,100 being most preferred. At amounts below the molar ratio of 200 the presence of high amounts of free radical initiator produces excess fragmentation of the polypropylene resulting in a lower molecular weight polypropylene. At amounts above the molar ratio of 4,000 the free radical initiator is at such a low concentration that efficient maleation is not obtainable. The process according to the present invention is preferably conducted at a molar ratio of maleic anhydride to free radical initiator between about 1 and 70, more preferably between about 2 and 60, even more preferably between about 3 and 50, with a molar ratio of maleic anhydride to free radical initiator of about 3.5 to 15 being most preferred. At molar ratios below 1 the amount of free radical initiator is significantly higher than required for the particular amount of maleation on the polypropylene, and thus increases fragmentation while not significantly increasing the acid number of the maleated polypropylene. For amounts such that the molar ratio of maleic anhydride to free radical initiator is above 70, the efficiencies of the grafting of maleic anhydride onto the polypropylene is dramatically reduced and the color of the resulting product is inferior. The maleic anhydride useful for the present process is any commercial grade of maleic anhydride. Those with maleic anhydride contents of 95-100% are preferred in that fewer volatile by-products must be handled by the vacuum system. Molten maleic anhydride with a purity over 99% is most preferred for the same reason, fewer volatiles are produced to be handled by the vacuum system. The process according to the present invention is generally conducted at a temperature above the melting point of the polypropylene. This temperature is preferably between 160 and 220.degree. C., more preferably between 180 and 210.degree. C., with a temperature between 190 and 205.degree. C. being most preferred. At temperatures much below 160 the viscosity of the molten polypropylene is too high to be efficiently pumped through the screw extruder. At temperatures much above 220.degree. C. the fragmentation of the molten polypropylene dramatically increases and molecular weight decreases. The process according to the present invention is generally conducted such that a vacuum is used at or after step (c) to remove volatiles from the maleated polypropylene product. The process according to the present invention is generally efficient, grafting onto polypropylene a high percent of the maleic anhydride present during the reaction, thus producing a maleated polypropylene with grafted maleic anhydride at a preferred efficiency percent above 35. This percent maleic anhydride incorporated into polypropylene can be up to or near 100 percent. However, this efficiency rate is generally over about 40 and up to 93 percent, more preferably at least 49 percent. At efficiency rates below 35 percent, maleic anhydride recovery is increased and cost per unit maleation onto the polypropylene is also increased. However, efficiencies at or below 85 percent are generally acceptable. |
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| PATENT PHOTOCOPY | available on request |
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