CA2081223A1 - Microfine melt flow rate polymer powders and process for their preparation - Google Patents
Microfine melt flow rate polymer powders and process for their preparationInfo
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- CA2081223A1 CA2081223A1 CA002081223A CA2081223A CA2081223A1 CA 2081223 A1 CA2081223 A1 CA 2081223A1 CA 002081223 A CA002081223 A CA 002081223A CA 2081223 A CA2081223 A CA 2081223A CA 2081223 A1 CA2081223 A1 CA 2081223A1
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Abstract
ABSTRACT The present invention relates to crosslinkable microfine ethylene copolymer powder which are substantially spherical in shape and range in size from about 10 up to about 500 microns and to the process of crosslinking the powders to reduce their melt flow rate. The powders are crosslinked by contacting with water in the presence of a silanol condensation catalyst at temperatures from ambient up to about 110°C. The reduction in melt flow rate is accomplished without substantially changing the powder characteristics, i.e., particle size and particle size distribution.
Description
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ICROFINE MELT FLOW RATE POLY~ER P0~1DERS AND
PROCESS FOR THEIR PREP.~RATION
The present invention relates to microfine 5 ethylene copolymer powders which are crosslinkable and wherein the powder particles are spherical or substantially spherically in shape. The invention also relates to a process for producing and crosslinking the polymer powder.
The use of thermoplastic resin powders is well documented in the prior art. For example, powdered thermoplastic resins in dry form have been used to coat articles by dip coating in either a static or fluidized bed and by powder coating. Powders can also be applied 15 in dispersed form, by roller coating, spray coating, slush coating, and dip coating substrates such as metal, paper, paperboard, and the like. Powders are also widely employed for conventional powder lining and powder molding processes, e.g., rotational molding.
20 Still other applications for powders include use as paper pulp additives; mold release agents; additives to waxes, paints, caulks, and polishes; binders for non-woven fabrics; etc.
Besides the physical properties of the powder~
which are dictated by the resin being used, the size and shape of the particles are the other major properties which influence the selection of a powder for various applications. These latter properties are primarily a function of the process by which the powders are prepared, which can include mechanical grinding, solution processes and dispersion processes. Particle size is determined using U.S. Standard Sieves or light ;.
'. ': ' --2- 2 ~ 2~ J ~ 33 1 scattering techniques and, depending on the method used, will be reported in mesh size or microns. The inverse relationship between the sieve size (mesh number) and particle size (in microns) is well documented and 5 conversion tables are available. The shape of the particles is ascertained from photoimicrographs of the powders. Particle shape has a marked influence on the bulk density of the powder and its handling properties.
~or most effective fluidization and dry 10 spraying, it is generally considered advantageous to use powders which have a fairly narrow particle size distribution and wherein the particles are spherical in shape. Powders produced by mechanical grinding or pulverization, which are typically irregular in shape 15 and generally have quite broad particle size distributions, are not well suited for fluidization and dry spraying. While the particles of powders produced by solution processes are less irregular than those obtained by mechanical means, they are still not 20 spherical.
Powders obtained using dispersion techniques, such as those described in U.S. Patent Nos. 3,422,049 and 3,746,681, wherein the particles produced are spherical in shape and fall within a relatively narrow 25 size range are most advantageously employed for ~luidization and dry spraying. These processes involve dispersing a molten synthetic organic polymeric thermoplastic resin in about 0.8 to 9 parts by weight of water per part of resin in the presence of from about 2 30 to 25 parts by weight per 100 parts of resin of a water-soluble bloc~ copolymer of ethylene oxide and propylene oxide having a molecular weight above about 3500 and : : ~ :
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1 containing at least about 50~ by weight of ethylene oxide and in the absence of an organic solvent for the polymer. The fine dispersion which is produced is then cooled to below the softening temperature of the resin 5 to obtain the powder.
A continuous process for the preparation of finely divided polvmer particles is disclosed in U.S.
Patent No. 3,432,483. The process comprises the sequential steps of feeding to the polymer, water and a 10 water-soluble block copolymer of ethylene oxide and propylene oxide surfactant into a dispersion zone;
vigorously agitating the mixture under elevated temperature and pressure to form a dispersion of the molten polymer; withdrawing a portion of the dispersion 15 and coolin~ to a temperature below the melting point of said polymer to form solid, finely divided polymer particles in the dispersion; reducing the pressure of said cooled dispersion to atmospheric pressure;
separating the solid polymer particles from the surfactant solution phase and washing; drying the washed polymer particles; and recovering dry, finely divided powder.
While it is possible to produce a wide range of fine powders using such procedures, the method is not adaptable for use with all resins. As the melt index of a resin approaches 1, it becomes increasingly difficult to achieve the type of dispersions necessary to form fine powders. Dispersion having droplets of the size necessary for the production of fine powders cannot be formed with ractional melt flow rate resins, i.e., resins having a melt index less than 1. This is believed to be duer in part, to the high molecular ' :
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l weights of such resins. The relationship of melt flow rate to molecular weight and the inability to form dispersions suitable for the production of fine powders with low melt flow rate resins is discussed in U.S.
5 Patent No. 3,746,681.
It would be advantageous if fine powders o~
low melt flow rate resin powders could be produced utilizing a dispersion process, particularly if the particles had a relatively narrow particle size lO distribution and were spherical in shape. Coatings obtained using such powders would be expected to have improved thermal stability, improved creep resistance, improved chemical resistance and other desirable properties.
Ethylene/vinylalkoxysilane copolymers are known. They are disclosed in U.S. Patent Nos. 3,225,018 and 3,392,156. In U.S. Patent No. ~,392,156 it is also disclosed that the ethylene/vinyltrialkoxysilane copolymers can be used in finely divided form where the 20 copolymer has an average size of less than about 1~ mesh and preferably in the range of about 150 to 2000 microns. While the reference states that the finely divided material may be prepared by mechanical grinding, solution or dispersion technigues or other methods, no 25 details are provided. Furthermore, it is a requirement of the process that the products be mechanically worked to obtain a reduction of melt index and an increase in stress cracking resistance. Melt indexes obtained after mechanical workiny range from 7.95 to zero.
It would be advantageous to have a process whereby the melt flow rate of polymer powders could be reduced independent of the powder forming operation.
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_5_ 1 This would e~able proCessQrs to "customize" the melt flow rate of the powders to their specific application.
It could also provide better control of the crosslinking. By having the crosslinking take place 5 outside the powder-forming reactor, fouling or corrosion of the primary reactor caused by the presence of crosslinking catalysts could be avoided. It would be particularly useful if the melt flow reduction could be performed on the powders without substantially changing 10 the particle size or particle size distribution.
Accordingly, the present invention relates to a microfine olefin copolymer powder comprised of particles which are spherical or substantially spherical in shape and wherein 80 percent or more of the particles 15 range in size from 10 microns to 500 microns, said olefin copolymer comprised of an a-olefin having from 2 to 8 carbon atoms and an unsaturated alkoxysilane of the formula R-Si(R-)~(Y)3_~
20 where X is an eth~lenically unsaturated hydrocarbon radical having from 2 to 6 carbon atoms, R~ is a hydrocarbon radical having from 1 to 10 carbon atoms, Y
is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from 0 to 2. More particularly, the 25 present invention relates to the foregoing defined microfine olefin copolymer wherein the powder is capable of being crosslinked and having a melt flow rate greater than 1. -Also, the present invention relates to a microine copolymer powder being chemically crosslinked 30 and having melt flow rate less than about 1 comprised of particles which are spherical or substantially spherical in shape and wherein 80 percent or more of the particles ' - ' :. ' ' . :- , ~ , - ' .
2 ~ 3 1 range in size from 10 microns to 200 microns, said olefin comprised of an a-olefin having from 2 to 8 carbon atoms and an unsaturated al~;oxysilane of the formula R-Si(R )~(Y)3_rl where R is an ethylenically unsaturated hydrocarbon radical having from 1 to 10 atoms, Y is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from 0 to 2.
The particles of these fractional melt flow rate powders are substantially spherical in shape and fall within a relatively narrow particle distribution range. For the process of the invention, a dispersion is first formed using an olefin copolymer resin which 15 has a melt flow rate such that acceptable dispersions can be produced, i.e., dispersions wherein a droplet size necessary to produce fine powders can be formed.
More particularly, the present invention provides for a process for producing substantially 20 spherical microfine polymer powders comprising to the steps of: combining an olefin copolymer having a melt index greater than 1 with 4 to 50 percent, based on the weight of the olefin copolymer, of a nonionic surfactant which is a block copolymer of ethylene oxide and 25 propylene oxide, and a polar liquid medium which is not a solvent for the olefin copolymer and which does not react with any of the foregoing ingredients under the conditions employed, the weight ratio of the polar liquid medium to the olefin copolymex ranging from 0.8:1 30 to 9:1; heating the mixture to a temperature above the melting point of the olefin copolymer; dispersing the mixture to form droplets of the desired size; cooling . . . . . , - , . .. .
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2~ J2 1 the dispersion to below the melting point of the olefin copolymer; and recovering the olefin copolymer powder.
In accordance with said process, microfine ethylene copolymer powders are produced which are 5 crosslinkable. The particles of these crosslinkable powders are spherical or substantially spherical in shape, typically with 80 percent or more of the particles ranging in size from about 10 up to about 500 microns. The ability to crosslink the powders provides 10 a convenient means ~or reducing the melt ~low rate of the powder and in those cases where it is desired, makes it possible to produce fractional melt flow rate powders.
This necessarily requires that the olefin 15 copolymer used has a melt flow rate greater than 1 since it is not possible to adequately disperse resins having melt flow rates lower than 1 and to produce acceptable powders. While forming the powder having the desired shape and size or subsequent to forming the powder, the 20 formed powder is contacted with moisture and a silanol condensation catalyst to reduce the melt flow rate to the desired level. The silanol condensation catalyst is a catalyst selected from the group consisting of organic bases, mineral or carboxylic acids, organic titanates 25 and complexes or carboxylates of lead, cobalt, iron, nickel and tin and is usually present in an amount from about 0.001 to 10 percent, based on the weight of the olefin copolymer. In a particularly useful embodiment of the invention, the crosslinking and melt flow 30 reduction are accomplished by suspending the powder in an a~ueous medium containing the catalyst and contacting at an elevated temperature below the melt point of the .
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l polymer for a period of time sufficient to effect the desired degree of crosslinking and melt flow reduction.
The olefin copolymer powder is then recovered by conventional procedures.
For the process of this invention, powders of olefin copolymer resins which are readily dispersible using conventional dispersion techniques, i.e., which have melt flow rates greater than 1, are first produced.
These powders are produced using known procedures such lO as those of U.S. Patent Nos. 3,422,049, 3,432,483 and 3,746,681, details of which are incorporated herein by reference thereto. Olefin copolymers having an unsaturated alkoxysilane incorporated therein by copolymerization or grarting are employed for this 15 invention.
For the powder-forming process, the ole~in copolymer is charged to the reactor with a polar liguid medium, a nonionic sur~actant, and optionally a silanol condensation catalyst and a dispersion is formed in 20 accordance with conventional dispersing procedures ~nown to the art. The dispersing apparatus may be any device capable of delivering su~ficient shearing action to the mixture at elevated temperature and pressure.
Conventional propeller stirrers designed to impart h~gh 25 shear commercially available for this purpose can be used. The reactor may also be equipped with baffles to assist in dispersion. The particle size and distribution of particles are dependent on the shearing action which, in turn, is related to the stirrer design and rate of stirring. ~gitation rates can vary over wide limits but the speed of the stirrer will usually be controlled so that the tip speed is between about 500 ' - :
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~ higher tip speed is generally required for batch operation, usually 2500-3000 ft/min. Tip speeds for continuous procedures will most generally be between 750 5 and 2500 ftlmin~
The dispersion process is typically conducted in an autoclave since this permits the process to be conducted at elevated temperature and pressure. In the usual batch conduct of the process, all of the ingredients are charged to the 10 autocla~e and the mixture is heated to a temperature above the melting point of the olefin copolymer. While the temperature will vary depending on the specific copolymer used, it will typically range from about 90C to 250C. Since the ~luidity of polymers is temperature related, it may be desirable to 15 carry ou~ the process at temperatures substantially above the melting point of the olefin copolymer to facilitate dispersion formation. Stirring is commenced after the desired temperature is reached. Stirring is continued until a dispersion of the deslred droplet size is produced. This will vary depending on the copolymer being used, the temperature and amount and type of surfactant, and other process variables but generally will range from about 5 minutes to about 2 hours. Most generally, the stirring is maintained for a period from 10 to 30 minutes.
A polar liquid medium which is not a solvent ~or the olefin copolymer is employed to form the dispersions~ These polar mediums are hydroxylic compounds and can include water, alcohols, polyols and mixtures thereof. The weigbt ratio o~
the polar liquid medium to olefin copolymer ranges from about 3o 0.8:1 to about 9:1 and, more preferably, from 1:1 to 5:1. It is particularly advantageous to use water as the dispersing medium or to use a liquid medium where water is the major component. The pressure o~ the process is not critical so long as a liquid phase is maintained and can range from about 1 up -. ~ .
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l to about 217 atmospheres. The process can be conducted at autogenous pressure or the pressure can be adjusted to exceed the vapor pressure of the liquid medium at the operating temperature. Most generally, with aqueous dispersions the pressure will range from about S to 120 atmospheres.
To obtain suitable dispersions with the olefin copolymers, one or more dispersing agents are employed for the process. Useful dispersing agents are nonionic surfactants which are b~ock copolymers of ethylene oxide and propylene oxide. Preferably, these nonionic surfactants are water-soluble block copolymers of ethylene oxide and propylene oxide and have molecular weights greater than about 3500. Most will contain a major portion by weight of ethylsne oxide and are obtained by polymerizing ethylene oxide onto preformed polyoxypropylene segments. The amount of nonionic surfactant employed can range from about 4 to 50 percent, based on the weight of the olefin copolymer. Most preferably, the nonionic ~urfactant ie present from about 7 to 45 percent, based on the weight of the polymer.
Useful nonionic surface active agents of the above type are manu~actured and sold ~y BASF Corporation, Chemicals Division under the trademark Pluronic. These products are obtained by polymerizing ethylene oxide on the ends of a preformed polymeric base o~ polyoxypropylene. Both the molecular weight of the polyoxypropylene base and the polyoxyethylene segm~nts can be varied to yield a wide variety of products. one such compound found to be suitable for the practice of the process of this invention is the product designated as F-98 wherein a polyoxypropylene of average molecular weight of 2,700 is polymerized with ethylene oxide to give a product of molecular weight averaging about 13,500. This product contains 20 weight percent propylene oxide and 80 weight percent ethylene oxide. Other effective Pluronic~
surfactants include F-88 (M.W. 11,250, 20S propylene oxide, 80%
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l ethylene oxide), F-108 (M.W. 16,250, 20~ propylene oxide, 80 ethylene oxide), and P-85 (M.W. 4,500, 50% propylene oxide, 50 ethylene oxide). These compounds, all containing at least a~out 50 weight percent ethylene oxide and having molecular weights of at least 4,500, are highly effective as dispersing agents for the aforementioned oleEin copolymers.
It is also possible to employ products sold under the trademark T~tronic which are prepared by huilding propylene oxide block copolymer chains onto an ethylenediamine nucleus and then polymerizing with ethylene oxi~e. Tetronic~ 707 and Tetronic~ 908 are most effective for the present purposes.
Tetronic~ 707 has a 30 weight percent polyoxypropylene portion, of 2,700 molecular weight, polymerized with a 70 weight percent oxyethylene portion to give an overall molecular weight of 12,000. Tetronic~ 908, on the other hand, has a 20 weight percent polyoxypropylene portion, of 2,gO0 molecular weight, polymerized with an 80 weight percent oxyethylene portion to give an overall molecular weight of 27,000. In general, useful Tetronic0 surfactants have molecular weights above 10,000 and contain a major portion by weight o ethylene oxide.
- ~ The powder-forming p~ocess may also be conducted ln a continuous manner. If continuous operation is desired, the lngredients are continuously introduced to the system while removing the dispersion from another part of the system. The ingredients may be separately charged or may be combined,for introduction to the autoclave.
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Olefin copolymers containing randomly copolymerized or grafted unsaturated alkoxysila~e is necessarily employed to obtain the crosslinkable powders of the invention. More specifically, the olefin copolymers are comprised of ~-olefins having from 2 to 8 carbon atoms and unsaturated alkoxysilanes of the formula R -si (R*)o(Y)3o where R is an ethylenically unsaturated hydrocarbon radical havlng from 2 to 6 carbon atoms, R* is a hydrocarbon radical having from 1 to lO carbon atoms, Y is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from Q to 2. The olefin copolymers must be readily dispersible in the liquid medium employed for the process. The olefin copolymers will therefore have melt flow rates greater than 1, and more typically g~eater than about 3. While the melt index may range as high as 500, it generally does not exceed about 300 and, more preferably, will ba less than 100.
Random copolymers of ethylene and unsaturated 20 al~oxysilanes, such as vinyltrialkoxysilanes, are known. Such copolymers can be obtained in accordance with any of the recognized procedures such as those described in U.S. Patent .. _ ....... . . . . . .
Nos. 3,225,018 and 3,3~2,15~. Generally, these copolymeriza-tions are carried out at high pressure and temperature in the 25 presence of a free radical initiator. Copolymers wherein an unsaturated alkoxysilane is grafted onto an olefin polymer backbone are also known and can ~e prepared in accordance with conventional procedures. Free radical initiators, such as peroxides, are generally used to facilitate grafting alkoxy-3 silanes onto the polyolefins.
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The unsaturated alkoxysilane will constitute from about 0.25 to 20 percent ~y weigllt and, more preferably, from about 0.5 to lo percent by weight of the ole~in copolymer. In a highly useful embodiment of th:is invention, the unsaturated alkoxysilane is a vinyltrialkoxysilane, i.e., where R is a vinyl group and n is o. It is especiaily advantageous to utilize vinyltrimethoxysilane or vinyltriethoxysilane, i.e., where R is a vinyl group, n=o and Y is methoxy or ethoxy, respectively. Olefin copolymers derived from C23 ~-olefins are especially useful. Minor amounts of higher olefins may be present, particularly if the unsaturated alkoxysilane is grafted. ~hile polyethylene is-most commonly grafted, copolymers of ethylene with propylene, butene-1 and hexene-l are also suitable. When the ~-olefin and unsaturated alkoxy-silane are copolymerized, ethylene is preferably e~ployed particularly when the alXoxysilane is vinyltrimethaxysilane or vinyltriethoxysilane. When the olefin copolymer is comprised of an ~-ole~in and unsaturated alkoxysilane only, the ~-olefin will constitute from 80 to 99.7S weight percent and, more preferably, 90 to 99.5 weiqht percent of the polymer.
one or more other monomers may be included with ~-olefin and unsaturated alkoxysilane. Such comonomers include vinyl esters of C2~ aliphatic carboxylic acids, C~ alkyl acrylates, and Cl~ alkyl methacrylates. The comonomers can be copolymerized with the unsaturated alkoxysilane and ~-olefin or the unsa~urated alkoxysilane can be grafted onto a copolymer form by copolymerizing an ~-ole~in and the comonomer. When comonomers are present, the olefin copolymer will comprise 55 30 to 99.5 percent ~-olefin, 0.25 to 20 percent unsaturated alkoxysilane and 0.25-to 4s percent comonomer(s~. More commonly, the copolymers will contain 55 to 99 percent ~ olefin, O.S to 40 percent unsaturated alkoxysilane and 0.5 to . .
-14- 2~2~,3 1 40 percent comonomer. Preferred vinyl esters of c~ aliphatic carboxylic acids include vinyl acetate and vinyl butyrate.
Ethyl acrylate and n-butyl acrylate are particularly useful C~b alkyl acrylate comonomers. Ethyl methacryla~e is a 5 particularly useful cl~ alkyl methacrylate comonomer.
The microfine olefin copolymer powders obtained Wi have 80 percent or more of the particies ranging in size from 1~ microns to 500 microns. In an especially useful embodiment, the particle size will range from 20 to 300 microns. To produce powders of the desired particle size, a dispersion having droplets of the desired size must be formed. This requires proper selection of the operating conditions, such as, temperature and agitation, as well as proper selection of the dispersing agent (surfactant) to coat the droplets. The temperature of the dispersion is then lowered to oelow the melting temperature of the olefin copolymer and the polymer is separated from the liquid phase by filtration, centrifugation, decantation' evaporation, or the like. In a highly useful . . ...
embodiment of the invention, the temperature of the dispersion is lowered to below the boiling point of the water or other liquid medium and the finely di~ided polymer is recovered by atmospheric or vacuum-assisted filtration. The cooling may be accomplished by removing the heating source and allowiny the mixture to cool or the hot dispersion may be rapidly quenched by mixing with cold liquid which is not a solvent for the polymer. This liquid may be the same or different than that employed as the dispersing medium. ~ater is preferably used for this purpose.
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: ; : - , -15~ ?J3 1 The polym~r powder may be washed and/or dried before being subjected to the crosslinking operation; however, this is not necessary. The powder may be crosslinked as it i5 obtained from the powder-forming process. For example, if the powder is recovered using the quenchin~ procedure, it may be advantageously crosslinked while suspended in all or a portion of the quenching medium.
To crosslink the result:ing olefin copolymer powders and effect reduction of the melt flow rates, the powders are contacted with water in the presence of a silanol condensation catalyst. If the powders are dried after the powder-forming operation, they are suspended in an aqueous medium containing the condensation catalyst. If, however, the powder is used directly as it is obtained from the quenching step, the catalyst may simply be added to this mixture and additional water added if desired.
The amount of water required for crosslinking can be varied over wide limlts. Small amounts of water may be used since, in theory, each molecule of water can produce one crosslink site. on the other hand, large excesses on the order of 100 or mdre parts water per part olefin copolymer can be used. Such large volumes of water are not necessary, however, and can present handling and disposal problems. Generally, the weight ratio water to olefin copolymer powder will range from 25 0.001:1 to 20:1 and, more preferably, from 0.01:1 to S:1. One or more other organic liquids may be included with the water.
~ These organic liquids should be miscible with water and cannot ; be a solvent for the polymer. Such iiquids include alcohols, polyols, ketones, aldehydes, carboxylic acids, carboxylic acid 3lesters and the like. If a carboxylic acid is employed with water as the suspending medium, it can also serve as the crosslinking catalyst. The organic liquids should not , :
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1 excessively swell or soften the powders as this will cause the powder particles to agglomerate. As a practical matter, the organic liquid will also generally have a boiling point above the operating temperature used for the crosslinking. If an organic liquid is present with the water, the ratio of water to organic liquid can range from about 99:1 to about 1:99.
While the olefin copolymer powders can be crosslinked under ambient conditions it is more customary to carry out the crosslinking at an elevated temperature. The temperature can range up to just below the melt point of the olefin copolymer;
however, if the temperature is above the boiling point of water or other liquids present, use o~ a con~enser or pressure vessel is necessary. Generally, the crosslinking and melt flow reduction will be carried out at a temperature fro~ ambient up to about 110C and, more preferably, from 50C to 100C.
While it is not necessary to employ a surlact~nt in the crosslinking step, surfactants or dispersants may be included in the aqueous medium if desired. If a surfac~ant is used it may be the same or different than the surfactant used in tha powder-forming operation. Residual surfactant resulting from the powder-forming operation can be utilized for this purpose or dther surfactants may be employed. In continuous processes, the first wash of the powder produced in the powder-2, forming step which will contain the bulk of the surfactant maybe recycled and the powder and any residual surfactant can be fed to a downstream vessel where the crosslinking reaction will be carried out. After crosslinking, the powder can be washed to then remove final traces of surfactant and catalyst 3~ residues.
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` -17- 2~ 23 l A silanol condensation catalyst is necessarily employed to crosslink the powders. These catalysts generally include organic bases, mineral ac:ids, c~22 carboxylic acids or anhydrides, organic titanates and complexes or carboxylates of lead, cobalt, iron, nic~el, zinc and tin. Lauryl amine, acetic acid, azelaic acid, lauric acid, palmitic acid, stearic acid, maleic acid, maleic anhydride, dibutyltin dilaurate, dibutyltin maleate, dibutyltin diacetate, dibutyltin dioctoate, stannous acetate, stannous octoate, lead naphthenate, zinc caprylate, and cobalt naphthenate are illustrative of the catalysts which can be used. Dialkyl tin carboxylates, especially dibutyltin dilaurate and dibutyltin maleate, and Ct~l aliphatic monocarboxylic acids, especially acetic acid and stearic acid, are highly effective crosslinking catalysts for this invention.
The amount of catalyst used can vary over wide limits depending on the catalyst and ole~in copolymer used and ~ince, in some instances, the catalyst can also serve as the suspending medium. Where the catalyst also functions as the suspending medium, such as in the case of certain carboxylic acids, it can constitute up to as high as 90 percent of the total suspension mixture. In most instances where the catalyst is not part of the suspending medium, the catalyst will typically constitute from 0.01 percent up to about 5 percent of the total mixture. More commonly, the silanol condensation catalysts comprise from about 0.1 to 1 percent of the suspenslon.
The following examples illustrate the process of the invention and the crosslinkable powders obtained therefrom more 3 fully. As will be apparent to those skilled in the art, numerous variations are possible and are within the scope of the invention. In the examples all parts and percentages are given on a weight basis unless otherwise indicated.
' ` -18- ~ 3 l The powders produced in khese examples were analyzed using laser light scattering to determine average particle size and particle size distribution. ~ Model 2600C Malvern Particle Size Analyzer with the proper lens configuration for the expected particle size to be measured and equipped to automatically calculate the distribution curve and average particle size was used. For the analysis, water is charged to the water bath and circulated th;roug~ the sample measuring chamber. After obtaining the baseline measurement, the agitator and sonic vibrator are turned on and powder is added to the water bath until the obscuration reading is 0.3. Mixing and circulation are controlled to obtain acceptable dispersion without excessive foaming. A drop of liquid detergent is added to facilitate dispersion. After eight minutes a~itation, - measurements are taken over a period of time and the distribution curve and average particle size are calculated.
Duplicate runs are made for each powder sample. The particle size reported in the examples is the number average particle size D(v, 0.5). The range reported for the particle size distribution in the examples is for 80 percent of the distribution curve, i.e., 10 percent of the powder particles will ~all below the lower limit of the recited distribution and 10 percent will be larger than the upper recited particle size distribution limit.
Melt flow rates provided in the examples were measured in accordance with ASTM D1238-89 at 190C with a ~inius Olsen Extrusion Plastometer. Melt flow rates are expressed in grams per 10 minutes.
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E~:HPI.~B I
To demonstrate the improved process of the invention whereby fractional melt flow rate microfine powders are produced, 340 parts random copolymer of ethylene and vinyltri-ethoxysilane having a melt flow rate of 4.8 and containing 4.0%
vinyltriethoxysilane was charged to a reactor with 810 parts deionized water, 97.2 parts nonionic.surfactant (Pluronic~ F-98 - a block copolymer of ethylene oxide and propylene oxide of molecular weight 13500 and containing 20~ propylene oxide3, and 7 parts polyethylene grafted with 2% maleic anhydride ~MFR 10).
Based on the weight of the copolymer, the amount of surfactant and catalyst used was 28% and 2~, respectively. The reactor was sealed and the mixture heated for 52 minutes at 216C ~nder 400 psi pressure. Agitation was commenced and maintained for 15 minutes. The stirrer speed was maintained at 3000-3300 rpm (tOp speed 2350 to 2590 ft/min) during the 15 minute interval.
The contents of the reactor were then emptied into a stainle~s steel tank containing approximately 5 liters cold water to precipitate the copolymer. The resulting ethylene-vinyltriethoxysilane copolymer powder was recovered by filtration and dried. The powder had a melt flow rate of 0.14, number average particle size of 62 um and the particle size distribution ranged from 28 to 161 um. Micro-~copic examination f the powder particles showed them to be spherically shaped.
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Example I was repeated except that a dif f erent catalyst was used to brinq about the melt flow reduction. The amount o~ copolymer, water and sur.Eactant used was identical to Example I. Five parts acetic acid (1.44~ based on the copolymer) was used as the catalyst. The resulting powder had a melt flow rate of 0.11, an average particle size of 56 um and particle size distrib~tion ranging from 25 to 145 um.
, -21- ~ ?~3 1 E~A~P~B III
Following the procedure of Example I an experiment was conducted using stearic acid as the catalyst. The amount of copolymer, water and surfacta:nt used was the same as in that example except that 0.2 parts stearic acid (0.06~ based on the weight of the copolymer) was useld. The resulting microfine powder particles were spherically shaped, had a melt flow rate of 0.01, an average size of 76 um and size distribution of 37-148 um.
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-22- 2~8~223 CO~SPAR~TIVE Ea~lPL}: A
To demonstrate the need to use a catalyst for the process of the invention, Example I was repeated except that the polyethylene grafted with mal~eic anhydrids was omittad from the reaction. The reactant chargle and reaction condi~ions wer~
otherwise identical, While a fine powder was produced (average particle sizs 55 um and particle ~size distribution 27-108 um), the melt flow rate of the resultin~ ethylene-vinyltriethoxy-silane powder was 4.6.
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-23- 2~122~
COHPAR~TIyE E~.H2~E E3 To demonstrate the ina~ility to disperse fractional melt flow rate polymers, 347 parts polyethylene having a melt index of o. 17 was charged to the reactor with 49 parts surfactant (Pluronic~ F-98) and and.810 parts water. The mixture was heated for 52 minutes at 216C under 400 psi pressure and then agitated for 15 minutes at the same rate as used for Example I. When the reactor contents were discharged, essentially all of the polymer re~ained in the reactor.
Dlsassembly and inspection of the reactor revealed that the polymer was agglomerated on the agitator blades. Increasing the surfactant ~oncentration, up to as high as equal parts surfactant based on the resin, still did not produce acceptable dispersions capable of yielding f ine powders.
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.
, -24- 2~ 2~
1 E~AHP~E IV
To demonstrate the ability to use other ethylene-vinyltriethoxysilane copolymers, in the process of the invention, the following experiment was carried out. For the reaction, 350 parts ethylene-~inyltriethoxysilane copolymer having a melt index of 5 and containing 1.9 weight percent copolymerized vinyltriethoxysilane was charged to a reactor with 810 parts water. Twenty-eicJht percent surfactant (Pluronic~ F-98), based on the we.ight of the copolymer, and o.06~ stearic acid, based on the weight of the copolymer, were also charged to the reactor. The materials were then dispersed and the copolymer recovered in accordance with the procedure of Example I. The resulting powder comprised of spherical particles had a melt flow rate of 0.17. The average partlcle size of the powder was 53 um and the particle size distribution was 27-96 um.
When the above procedure was repeated, except that the amount of stearic acid used was doubled, comparable fractional melt flow ra~e microfine powders were produced. The powders had no measurable flow rate, an average particle size of 77 um and particle size distribution ranging from 47 to 140 um.
3o - -: : . , , ~ ' ~ :
.
-~5-2~3~w23 E~A~PLE V
Example IV was repeated using ethylene-vinyltri-Pthoxysilane copolymer having 0.8 weight percent vinyltri-ethoxysilane copolymerized. The copolymer had a melt index of 6. When 0.12% stearic acid based on the amount of the copolymer was employed, the resu:Lting spherical powder had a melt index of 0.44, an average particle size of 42 and particle size distribution of 21-72 um. Xncreasing the catalyst (stearic acid) level to 0.23~, based on the weight of the copolymer, yielded a powder of melt index 0.25, average particle size of 51 um and particle size distribution ran~ing from 25-125 um.
.. . ..
. -26-2 ~
1 E~AMPIE VI
The versatility of the present process is further illustrated by the following example wherein a fractional melt flow rate powder of an ethylene-vinyl acetate copolymer grafted wlth vinyltriathoxysilane is produced. The EVA resin contained 9~ vinyl acetate and was gra~ted with 0.9~ vinyltriethoxy-silane. The graft copolymer had a melt flow rate of 23. For this example, 350 parts gr~ft copolymer, 810 parts water, 10 parts acetic acid and 97.2 parts surfactant (Tetronic~ 908) were used. After sealing the reactor, the mixture was heated for 50 minutes at 210C at 350 psi pressure and then agitated for 15 minutes. The stirrer speed was maintained at 3500 rpm (tip speed 2750 ft~min). The reactor contents were then discharged into water and the resulting powder recovered by filtration and dried overnight in a hood. The melt flow rate of the polymer was reduced to O.OS as a result of the treatment. The powder consisted of spherically shaped particles having an average particle size of 69 um and particle size distribution ranginy from 25 to 135 um.
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. -27~ 2~
E~HPLE VII
The procedure of Exa~ple V.L was repeated except that lauryl amine was used as the catalyst in place of the acetic acid and Pluronic~ F-98 was substituted for Tetronic~ 908. The melt flow rate of the polymer powcler produced was O.OS. The number average particle size of the powder was 43 um and particle size distribution was 18--95 ym.
2 ~ 2 ~
1 E2AXPL~ VIII
Example VI was repeated except that a different graft copolymer was employed. For this reaction, an EvA copolymer (9% VA) grafted with 0.3% ~inyltrimethoxysilane was used. The EVA resin had a melt flow rate of 20. one part acetic acid and 97.2 parts Pluronic0 F-98 surfactant were used for this reaction. The powder produced had a melt flow rate of 0.3~, average particle size of 9S um and particle size distribution lO from 65 to 142 um.
..
. -29- 2~22,~
1 ! EXnHP~E IX
Preparation of ethylen~v~nyltriethoxy~llane copolym~r powder: A crosslinkable microfine powder was produced in accordance with the dispersion procedure descri~ed in U.S. Patent No. 784,862. To produce the powder, an electrically heated two-liter Paar reactor equipped with a thermowell and thermocouple connected to a digital display was used. The reactor was equipped with an agitator haYing three six-bladed impellers driven by a drill press equipped with a 2 HP DC varia~le speed motor. Three hundred and forty seven parts of a random copolymer of ethylene and vinyltriethoxy-silane having a melt flow rate of 4.1 and containing 4.1%
vinyltrieth~xysilane was charged to ~he autoclave with ~lO
parts deionized water and 97.Z parts nonionic surfactant. The nonionic surfactant employed was Pluronic~ F-9~ - a block copolymer of ethylene oxide and prop~^lene oxide of molPcular weight 1350 and containing 20~ propylene oxide. The autoclave was sealed and heated over a period of 45 minutes up to 222C
wh~ch resulted in a pressure of 340 psi. Agitation was commenced and maintained for 15 minutes at 3300 rpm (tip speed 2750 ft/min). The contents of the reactor were then rapidly discharged thraugh a Strahman valve into a stainless steel ~an~
containing 5 liters of cold water to precipitate the polymer.
The resulting,,e,thylene-vinyltriethoxysilane copolymer powder was washed several times with water, collected by filtration and drled. 'The powder had a melt flow rate of 3.0fi and number average particle size of 141 microns. The particle size distribution ranged from 83 to 258 microns. Microscopic examination of the powder showed the powder particles to be spherically shaped.
-30- ~ 3 1 E~HPhEiX_ To demonstrate the ability to crosslink the olefin copolymer powders of the invention to reduce the melt flow ra~e, lOo parts of the dry powder o ethylene-vinyltriethoXy silane copolymer powder produced in.ExampleIX was combined wlth 300 parts deionized water and ~5 parts glacial acetic acid.
The powder was suspended in the liquid medium by stirring with a magnetic stirrer while heating the mixture at 70c for 1-1/2 hours. After this period, the polymer was recovered by filtra~ion, washed several times with water and dried. The melt flow rate of the dried powder was reduced from 3.06 to ~.66 as a result of this treatment.
, . .
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~ 31- 2~ 2~
1 E~HPLE_XI
To further illustrate the ability to crosslin~ the olefin copolymer powders and the ability to produce fractional melt flow rate polymer powders, 25 parts of the ethylene-vinyltriethoxysilane copolymer po~wder of ExampleIX was suspended in 200 parts glacial acetic acid. The mixture wa~
stirred for 1-l/2 hours while maintaining the temperature at 70-B0C. The resulting crosslinked powder had no measurable melt flow, i.e., melt flow rate of zero. Furthermore, this siqnificant reduction in melt index was accomplished without significantly alterin~ the powder characteristics. The averaqe particle size of the crosslink powder was 153 microns and particle size distribution ranged from 88 to 261 microns, essentially comparable to the starting specifications of the powder. The powder particles retained their spherical sha~e after the melt flow reduction.
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- E~HP~R XII
To demonstrate the ability to crosslink the polymer powders using other catalysts, 50 parts of the olefin copolymer powder of Example IX and 2.5 parts stearic acid were combined with 300 part~ deionized water. The.mixture was stirred for 1-1/2 hours at a temperature o~ 70-80C. The resulting powder, after washing with ethanol and drying, had an average particle size of 148 microns and particle size distribution from 83 to 254 microns. Whereas the original powder had a melt 1OW rate of 3.06, the powder after the above treatment had no measurable flow.
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2 ~ 3 1 E~AMP~E XII~
The versatility of the process is further demonstrated by the following experiment wherein the conditions were varied. For the reaction, 40 grams dry ethylene-~inyltrlethoxysilane copolymer powder (melt index 1.7, 4.1%
VTEOS) was charged to an 800 ml resin fiask containing 50 grams acetone and 150 grams deionized water. The resin flask was equipped with a reflux condenser, thermometer and agitator driven by an electric motor (Gerald ~eller GT-21 with controller). The stirred suspension was heated to about 50C
and 0.8 gram dibutyltinlaurate dissolved in 100 grams acetone added. After stirring the mixture at 50-521C ~or 1-1/2 hour~, the suspension was cooled and the crosslinked powder was recovered by filtration. The powder was washed three times by resuspending in acetone, agitating and refiltering. The dried powder had no measurable melt flow rate. Average particle ~ize of the powder was 141 microns and particle size distrib-ltion was 80-~40 microns.
.
.
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2~,2~
E~H IJE XIY
In a manner similar to that of Examplex~ o grams of EVTEOS copolymer was suspended in ~olution of 188 grams ethylene glycol and 2 grams deionized water. The mixture was heated to 80C wlth agitation and a solution of 2 grams laurylamine in 10 grams ethylene glycol added. The mixture was then stirred at 80-85C for 1-1/2 hours. Cold deionized water was added and the mixture was filtered to recover the powder The product was washed by resuspending in water (2x) and acetone t2x). The dried powder had ~ melt index of 0.012, an average particle size of 127 micron~ and part~cle size distri~ution of 60-Z21 microns.
..
.
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865~ I,SS
, c~SPEC\8654 . LSS
ICROFINE MELT FLOW RATE POLY~ER P0~1DERS AND
PROCESS FOR THEIR PREP.~RATION
The present invention relates to microfine 5 ethylene copolymer powders which are crosslinkable and wherein the powder particles are spherical or substantially spherically in shape. The invention also relates to a process for producing and crosslinking the polymer powder.
The use of thermoplastic resin powders is well documented in the prior art. For example, powdered thermoplastic resins in dry form have been used to coat articles by dip coating in either a static or fluidized bed and by powder coating. Powders can also be applied 15 in dispersed form, by roller coating, spray coating, slush coating, and dip coating substrates such as metal, paper, paperboard, and the like. Powders are also widely employed for conventional powder lining and powder molding processes, e.g., rotational molding.
20 Still other applications for powders include use as paper pulp additives; mold release agents; additives to waxes, paints, caulks, and polishes; binders for non-woven fabrics; etc.
Besides the physical properties of the powder~
which are dictated by the resin being used, the size and shape of the particles are the other major properties which influence the selection of a powder for various applications. These latter properties are primarily a function of the process by which the powders are prepared, which can include mechanical grinding, solution processes and dispersion processes. Particle size is determined using U.S. Standard Sieves or light ;.
'. ': ' --2- 2 ~ 2~ J ~ 33 1 scattering techniques and, depending on the method used, will be reported in mesh size or microns. The inverse relationship between the sieve size (mesh number) and particle size (in microns) is well documented and 5 conversion tables are available. The shape of the particles is ascertained from photoimicrographs of the powders. Particle shape has a marked influence on the bulk density of the powder and its handling properties.
~or most effective fluidization and dry 10 spraying, it is generally considered advantageous to use powders which have a fairly narrow particle size distribution and wherein the particles are spherical in shape. Powders produced by mechanical grinding or pulverization, which are typically irregular in shape 15 and generally have quite broad particle size distributions, are not well suited for fluidization and dry spraying. While the particles of powders produced by solution processes are less irregular than those obtained by mechanical means, they are still not 20 spherical.
Powders obtained using dispersion techniques, such as those described in U.S. Patent Nos. 3,422,049 and 3,746,681, wherein the particles produced are spherical in shape and fall within a relatively narrow 25 size range are most advantageously employed for ~luidization and dry spraying. These processes involve dispersing a molten synthetic organic polymeric thermoplastic resin in about 0.8 to 9 parts by weight of water per part of resin in the presence of from about 2 30 to 25 parts by weight per 100 parts of resin of a water-soluble bloc~ copolymer of ethylene oxide and propylene oxide having a molecular weight above about 3500 and : : ~ :
~ ~ $ ~ ~ 2 ~
1 containing at least about 50~ by weight of ethylene oxide and in the absence of an organic solvent for the polymer. The fine dispersion which is produced is then cooled to below the softening temperature of the resin 5 to obtain the powder.
A continuous process for the preparation of finely divided polvmer particles is disclosed in U.S.
Patent No. 3,432,483. The process comprises the sequential steps of feeding to the polymer, water and a 10 water-soluble block copolymer of ethylene oxide and propylene oxide surfactant into a dispersion zone;
vigorously agitating the mixture under elevated temperature and pressure to form a dispersion of the molten polymer; withdrawing a portion of the dispersion 15 and coolin~ to a temperature below the melting point of said polymer to form solid, finely divided polymer particles in the dispersion; reducing the pressure of said cooled dispersion to atmospheric pressure;
separating the solid polymer particles from the surfactant solution phase and washing; drying the washed polymer particles; and recovering dry, finely divided powder.
While it is possible to produce a wide range of fine powders using such procedures, the method is not adaptable for use with all resins. As the melt index of a resin approaches 1, it becomes increasingly difficult to achieve the type of dispersions necessary to form fine powders. Dispersion having droplets of the size necessary for the production of fine powders cannot be formed with ractional melt flow rate resins, i.e., resins having a melt index less than 1. This is believed to be duer in part, to the high molecular ' :
: , . .~ , ~ - :
2~$~
l weights of such resins. The relationship of melt flow rate to molecular weight and the inability to form dispersions suitable for the production of fine powders with low melt flow rate resins is discussed in U.S.
5 Patent No. 3,746,681.
It would be advantageous if fine powders o~
low melt flow rate resin powders could be produced utilizing a dispersion process, particularly if the particles had a relatively narrow particle size lO distribution and were spherical in shape. Coatings obtained using such powders would be expected to have improved thermal stability, improved creep resistance, improved chemical resistance and other desirable properties.
Ethylene/vinylalkoxysilane copolymers are known. They are disclosed in U.S. Patent Nos. 3,225,018 and 3,392,156. In U.S. Patent No. ~,392,156 it is also disclosed that the ethylene/vinyltrialkoxysilane copolymers can be used in finely divided form where the 20 copolymer has an average size of less than about 1~ mesh and preferably in the range of about 150 to 2000 microns. While the reference states that the finely divided material may be prepared by mechanical grinding, solution or dispersion technigues or other methods, no 25 details are provided. Furthermore, it is a requirement of the process that the products be mechanically worked to obtain a reduction of melt index and an increase in stress cracking resistance. Melt indexes obtained after mechanical workiny range from 7.95 to zero.
It would be advantageous to have a process whereby the melt flow rate of polymer powders could be reduced independent of the powder forming operation.
.
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_5_ 1 This would e~able proCessQrs to "customize" the melt flow rate of the powders to their specific application.
It could also provide better control of the crosslinking. By having the crosslinking take place 5 outside the powder-forming reactor, fouling or corrosion of the primary reactor caused by the presence of crosslinking catalysts could be avoided. It would be particularly useful if the melt flow reduction could be performed on the powders without substantially changing 10 the particle size or particle size distribution.
Accordingly, the present invention relates to a microfine olefin copolymer powder comprised of particles which are spherical or substantially spherical in shape and wherein 80 percent or more of the particles 15 range in size from 10 microns to 500 microns, said olefin copolymer comprised of an a-olefin having from 2 to 8 carbon atoms and an unsaturated alkoxysilane of the formula R-Si(R-)~(Y)3_~
20 where X is an eth~lenically unsaturated hydrocarbon radical having from 2 to 6 carbon atoms, R~ is a hydrocarbon radical having from 1 to 10 carbon atoms, Y
is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from 0 to 2. More particularly, the 25 present invention relates to the foregoing defined microfine olefin copolymer wherein the powder is capable of being crosslinked and having a melt flow rate greater than 1. -Also, the present invention relates to a microine copolymer powder being chemically crosslinked 30 and having melt flow rate less than about 1 comprised of particles which are spherical or substantially spherical in shape and wherein 80 percent or more of the particles ' - ' :. ' ' . :- , ~ , - ' .
2 ~ 3 1 range in size from 10 microns to 200 microns, said olefin comprised of an a-olefin having from 2 to 8 carbon atoms and an unsaturated al~;oxysilane of the formula R-Si(R )~(Y)3_rl where R is an ethylenically unsaturated hydrocarbon radical having from 1 to 10 atoms, Y is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from 0 to 2.
The particles of these fractional melt flow rate powders are substantially spherical in shape and fall within a relatively narrow particle distribution range. For the process of the invention, a dispersion is first formed using an olefin copolymer resin which 15 has a melt flow rate such that acceptable dispersions can be produced, i.e., dispersions wherein a droplet size necessary to produce fine powders can be formed.
More particularly, the present invention provides for a process for producing substantially 20 spherical microfine polymer powders comprising to the steps of: combining an olefin copolymer having a melt index greater than 1 with 4 to 50 percent, based on the weight of the olefin copolymer, of a nonionic surfactant which is a block copolymer of ethylene oxide and 25 propylene oxide, and a polar liquid medium which is not a solvent for the olefin copolymer and which does not react with any of the foregoing ingredients under the conditions employed, the weight ratio of the polar liquid medium to the olefin copolymex ranging from 0.8:1 30 to 9:1; heating the mixture to a temperature above the melting point of the olefin copolymer; dispersing the mixture to form droplets of the desired size; cooling . . . . . , - , . .. .
,. . . . ~, .
2~ J2 1 the dispersion to below the melting point of the olefin copolymer; and recovering the olefin copolymer powder.
In accordance with said process, microfine ethylene copolymer powders are produced which are 5 crosslinkable. The particles of these crosslinkable powders are spherical or substantially spherical in shape, typically with 80 percent or more of the particles ranging in size from about 10 up to about 500 microns. The ability to crosslink the powders provides 10 a convenient means ~or reducing the melt ~low rate of the powder and in those cases where it is desired, makes it possible to produce fractional melt flow rate powders.
This necessarily requires that the olefin 15 copolymer used has a melt flow rate greater than 1 since it is not possible to adequately disperse resins having melt flow rates lower than 1 and to produce acceptable powders. While forming the powder having the desired shape and size or subsequent to forming the powder, the 20 formed powder is contacted with moisture and a silanol condensation catalyst to reduce the melt flow rate to the desired level. The silanol condensation catalyst is a catalyst selected from the group consisting of organic bases, mineral or carboxylic acids, organic titanates 25 and complexes or carboxylates of lead, cobalt, iron, nickel and tin and is usually present in an amount from about 0.001 to 10 percent, based on the weight of the olefin copolymer. In a particularly useful embodiment of the invention, the crosslinking and melt flow 30 reduction are accomplished by suspending the powder in an a~ueous medium containing the catalyst and contacting at an elevated temperature below the melt point of the .
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.
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l polymer for a period of time sufficient to effect the desired degree of crosslinking and melt flow reduction.
The olefin copolymer powder is then recovered by conventional procedures.
For the process of this invention, powders of olefin copolymer resins which are readily dispersible using conventional dispersion techniques, i.e., which have melt flow rates greater than 1, are first produced.
These powders are produced using known procedures such lO as those of U.S. Patent Nos. 3,422,049, 3,432,483 and 3,746,681, details of which are incorporated herein by reference thereto. Olefin copolymers having an unsaturated alkoxysilane incorporated therein by copolymerization or grarting are employed for this 15 invention.
For the powder-forming process, the ole~in copolymer is charged to the reactor with a polar liguid medium, a nonionic sur~actant, and optionally a silanol condensation catalyst and a dispersion is formed in 20 accordance with conventional dispersing procedures ~nown to the art. The dispersing apparatus may be any device capable of delivering su~ficient shearing action to the mixture at elevated temperature and pressure.
Conventional propeller stirrers designed to impart h~gh 25 shear commercially available for this purpose can be used. The reactor may also be equipped with baffles to assist in dispersion. The particle size and distribution of particles are dependent on the shearing action which, in turn, is related to the stirrer design and rate of stirring. ~gitation rates can vary over wide limits but the speed of the stirrer will usually be controlled so that the tip speed is between about 500 ' - :
- .
,~ ' ' " ' . - : , , ~, , 2 ~ ,rS~ ?, ~3 1 and 3500 ftjmin and, more commonly, 750 and 3000 ft/min.
~ higher tip speed is generally required for batch operation, usually 2500-3000 ft/min. Tip speeds for continuous procedures will most generally be between 750 5 and 2500 ftlmin~
The dispersion process is typically conducted in an autoclave since this permits the process to be conducted at elevated temperature and pressure. In the usual batch conduct of the process, all of the ingredients are charged to the 10 autocla~e and the mixture is heated to a temperature above the melting point of the olefin copolymer. While the temperature will vary depending on the specific copolymer used, it will typically range from about 90C to 250C. Since the ~luidity of polymers is temperature related, it may be desirable to 15 carry ou~ the process at temperatures substantially above the melting point of the olefin copolymer to facilitate dispersion formation. Stirring is commenced after the desired temperature is reached. Stirring is continued until a dispersion of the deslred droplet size is produced. This will vary depending on the copolymer being used, the temperature and amount and type of surfactant, and other process variables but generally will range from about 5 minutes to about 2 hours. Most generally, the stirring is maintained for a period from 10 to 30 minutes.
A polar liquid medium which is not a solvent ~or the olefin copolymer is employed to form the dispersions~ These polar mediums are hydroxylic compounds and can include water, alcohols, polyols and mixtures thereof. The weigbt ratio o~
the polar liquid medium to olefin copolymer ranges from about 3o 0.8:1 to about 9:1 and, more preferably, from 1:1 to 5:1. It is particularly advantageous to use water as the dispersing medium or to use a liquid medium where water is the major component. The pressure o~ the process is not critical so long as a liquid phase is maintained and can range from about 1 up -. ~ .
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~.
2 ~:~3 ~ ~?~ ~ ~
l to about 217 atmospheres. The process can be conducted at autogenous pressure or the pressure can be adjusted to exceed the vapor pressure of the liquid medium at the operating temperature. Most generally, with aqueous dispersions the pressure will range from about S to 120 atmospheres.
To obtain suitable dispersions with the olefin copolymers, one or more dispersing agents are employed for the process. Useful dispersing agents are nonionic surfactants which are b~ock copolymers of ethylene oxide and propylene oxide. Preferably, these nonionic surfactants are water-soluble block copolymers of ethylene oxide and propylene oxide and have molecular weights greater than about 3500. Most will contain a major portion by weight of ethylsne oxide and are obtained by polymerizing ethylene oxide onto preformed polyoxypropylene segments. The amount of nonionic surfactant employed can range from about 4 to 50 percent, based on the weight of the olefin copolymer. Most preferably, the nonionic ~urfactant ie present from about 7 to 45 percent, based on the weight of the polymer.
Useful nonionic surface active agents of the above type are manu~actured and sold ~y BASF Corporation, Chemicals Division under the trademark Pluronic. These products are obtained by polymerizing ethylene oxide on the ends of a preformed polymeric base o~ polyoxypropylene. Both the molecular weight of the polyoxypropylene base and the polyoxyethylene segm~nts can be varied to yield a wide variety of products. one such compound found to be suitable for the practice of the process of this invention is the product designated as F-98 wherein a polyoxypropylene of average molecular weight of 2,700 is polymerized with ethylene oxide to give a product of molecular weight averaging about 13,500. This product contains 20 weight percent propylene oxide and 80 weight percent ethylene oxide. Other effective Pluronic~
surfactants include F-88 (M.W. 11,250, 20S propylene oxide, 80%
- - , ..
- : , : -' .
l ethylene oxide), F-108 (M.W. 16,250, 20~ propylene oxide, 80 ethylene oxide), and P-85 (M.W. 4,500, 50% propylene oxide, 50 ethylene oxide). These compounds, all containing at least a~out 50 weight percent ethylene oxide and having molecular weights of at least 4,500, are highly effective as dispersing agents for the aforementioned oleEin copolymers.
It is also possible to employ products sold under the trademark T~tronic which are prepared by huilding propylene oxide block copolymer chains onto an ethylenediamine nucleus and then polymerizing with ethylene oxi~e. Tetronic~ 707 and Tetronic~ 908 are most effective for the present purposes.
Tetronic~ 707 has a 30 weight percent polyoxypropylene portion, of 2,700 molecular weight, polymerized with a 70 weight percent oxyethylene portion to give an overall molecular weight of 12,000. Tetronic~ 908, on the other hand, has a 20 weight percent polyoxypropylene portion, of 2,gO0 molecular weight, polymerized with an 80 weight percent oxyethylene portion to give an overall molecular weight of 27,000. In general, useful Tetronic0 surfactants have molecular weights above 10,000 and contain a major portion by weight o ethylene oxide.
- ~ The powder-forming p~ocess may also be conducted ln a continuous manner. If continuous operation is desired, the lngredients are continuously introduced to the system while removing the dispersion from another part of the system. The ingredients may be separately charged or may be combined,for introduction to the autoclave.
.
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-12- 2~ J~
Olefin copolymers containing randomly copolymerized or grafted unsaturated alkoxysila~e is necessarily employed to obtain the crosslinkable powders of the invention. More specifically, the olefin copolymers are comprised of ~-olefins having from 2 to 8 carbon atoms and unsaturated alkoxysilanes of the formula R -si (R*)o(Y)3o where R is an ethylenically unsaturated hydrocarbon radical havlng from 2 to 6 carbon atoms, R* is a hydrocarbon radical having from 1 to lO carbon atoms, Y is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from Q to 2. The olefin copolymers must be readily dispersible in the liquid medium employed for the process. The olefin copolymers will therefore have melt flow rates greater than 1, and more typically g~eater than about 3. While the melt index may range as high as 500, it generally does not exceed about 300 and, more preferably, will ba less than 100.
Random copolymers of ethylene and unsaturated 20 al~oxysilanes, such as vinyltrialkoxysilanes, are known. Such copolymers can be obtained in accordance with any of the recognized procedures such as those described in U.S. Patent .. _ ....... . . . . . .
Nos. 3,225,018 and 3,3~2,15~. Generally, these copolymeriza-tions are carried out at high pressure and temperature in the 25 presence of a free radical initiator. Copolymers wherein an unsaturated alkoxysilane is grafted onto an olefin polymer backbone are also known and can ~e prepared in accordance with conventional procedures. Free radical initiators, such as peroxides, are generally used to facilitate grafting alkoxy-3 silanes onto the polyolefins.
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The unsaturated alkoxysilane will constitute from about 0.25 to 20 percent ~y weigllt and, more preferably, from about 0.5 to lo percent by weight of the ole~in copolymer. In a highly useful embodiment of th:is invention, the unsaturated alkoxysilane is a vinyltrialkoxysilane, i.e., where R is a vinyl group and n is o. It is especiaily advantageous to utilize vinyltrimethoxysilane or vinyltriethoxysilane, i.e., where R is a vinyl group, n=o and Y is methoxy or ethoxy, respectively. Olefin copolymers derived from C23 ~-olefins are especially useful. Minor amounts of higher olefins may be present, particularly if the unsaturated alkoxysilane is grafted. ~hile polyethylene is-most commonly grafted, copolymers of ethylene with propylene, butene-1 and hexene-l are also suitable. When the ~-olefin and unsaturated alkoxy-silane are copolymerized, ethylene is preferably e~ployed particularly when the alXoxysilane is vinyltrimethaxysilane or vinyltriethoxysilane. When the olefin copolymer is comprised of an ~-ole~in and unsaturated alkoxysilane only, the ~-olefin will constitute from 80 to 99.7S weight percent and, more preferably, 90 to 99.5 weiqht percent of the polymer.
one or more other monomers may be included with ~-olefin and unsaturated alkoxysilane. Such comonomers include vinyl esters of C2~ aliphatic carboxylic acids, C~ alkyl acrylates, and Cl~ alkyl methacrylates. The comonomers can be copolymerized with the unsaturated alkoxysilane and ~-olefin or the unsa~urated alkoxysilane can be grafted onto a copolymer form by copolymerizing an ~-ole~in and the comonomer. When comonomers are present, the olefin copolymer will comprise 55 30 to 99.5 percent ~-olefin, 0.25 to 20 percent unsaturated alkoxysilane and 0.25-to 4s percent comonomer(s~. More commonly, the copolymers will contain 55 to 99 percent ~ olefin, O.S to 40 percent unsaturated alkoxysilane and 0.5 to . .
-14- 2~2~,3 1 40 percent comonomer. Preferred vinyl esters of c~ aliphatic carboxylic acids include vinyl acetate and vinyl butyrate.
Ethyl acrylate and n-butyl acrylate are particularly useful C~b alkyl acrylate comonomers. Ethyl methacryla~e is a 5 particularly useful cl~ alkyl methacrylate comonomer.
The microfine olefin copolymer powders obtained Wi have 80 percent or more of the particies ranging in size from 1~ microns to 500 microns. In an especially useful embodiment, the particle size will range from 20 to 300 microns. To produce powders of the desired particle size, a dispersion having droplets of the desired size must be formed. This requires proper selection of the operating conditions, such as, temperature and agitation, as well as proper selection of the dispersing agent (surfactant) to coat the droplets. The temperature of the dispersion is then lowered to oelow the melting temperature of the olefin copolymer and the polymer is separated from the liquid phase by filtration, centrifugation, decantation' evaporation, or the like. In a highly useful . . ...
embodiment of the invention, the temperature of the dispersion is lowered to below the boiling point of the water or other liquid medium and the finely di~ided polymer is recovered by atmospheric or vacuum-assisted filtration. The cooling may be accomplished by removing the heating source and allowiny the mixture to cool or the hot dispersion may be rapidly quenched by mixing with cold liquid which is not a solvent for the polymer. This liquid may be the same or different than that employed as the dispersing medium. ~ater is preferably used for this purpose.
.
: ; : - , -15~ ?J3 1 The polym~r powder may be washed and/or dried before being subjected to the crosslinking operation; however, this is not necessary. The powder may be crosslinked as it i5 obtained from the powder-forming process. For example, if the powder is recovered using the quenchin~ procedure, it may be advantageously crosslinked while suspended in all or a portion of the quenching medium.
To crosslink the result:ing olefin copolymer powders and effect reduction of the melt flow rates, the powders are contacted with water in the presence of a silanol condensation catalyst. If the powders are dried after the powder-forming operation, they are suspended in an aqueous medium containing the condensation catalyst. If, however, the powder is used directly as it is obtained from the quenching step, the catalyst may simply be added to this mixture and additional water added if desired.
The amount of water required for crosslinking can be varied over wide limlts. Small amounts of water may be used since, in theory, each molecule of water can produce one crosslink site. on the other hand, large excesses on the order of 100 or mdre parts water per part olefin copolymer can be used. Such large volumes of water are not necessary, however, and can present handling and disposal problems. Generally, the weight ratio water to olefin copolymer powder will range from 25 0.001:1 to 20:1 and, more preferably, from 0.01:1 to S:1. One or more other organic liquids may be included with the water.
~ These organic liquids should be miscible with water and cannot ; be a solvent for the polymer. Such iiquids include alcohols, polyols, ketones, aldehydes, carboxylic acids, carboxylic acid 3lesters and the like. If a carboxylic acid is employed with water as the suspending medium, it can also serve as the crosslinking catalyst. The organic liquids should not , :
- . . ~ : :
2~2~'~
1 excessively swell or soften the powders as this will cause the powder particles to agglomerate. As a practical matter, the organic liquid will also generally have a boiling point above the operating temperature used for the crosslinking. If an organic liquid is present with the water, the ratio of water to organic liquid can range from about 99:1 to about 1:99.
While the olefin copolymer powders can be crosslinked under ambient conditions it is more customary to carry out the crosslinking at an elevated temperature. The temperature can range up to just below the melt point of the olefin copolymer;
however, if the temperature is above the boiling point of water or other liquids present, use o~ a con~enser or pressure vessel is necessary. Generally, the crosslinking and melt flow reduction will be carried out at a temperature fro~ ambient up to about 110C and, more preferably, from 50C to 100C.
While it is not necessary to employ a surlact~nt in the crosslinking step, surfactants or dispersants may be included in the aqueous medium if desired. If a surfac~ant is used it may be the same or different than the surfactant used in tha powder-forming operation. Residual surfactant resulting from the powder-forming operation can be utilized for this purpose or dther surfactants may be employed. In continuous processes, the first wash of the powder produced in the powder-2, forming step which will contain the bulk of the surfactant maybe recycled and the powder and any residual surfactant can be fed to a downstream vessel where the crosslinking reaction will be carried out. After crosslinking, the powder can be washed to then remove final traces of surfactant and catalyst 3~ residues.
-, :
': ' ' '. : ' - - ' :
. ..
, .. .. , :
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:
` -17- 2~ 23 l A silanol condensation catalyst is necessarily employed to crosslink the powders. These catalysts generally include organic bases, mineral ac:ids, c~22 carboxylic acids or anhydrides, organic titanates and complexes or carboxylates of lead, cobalt, iron, nic~el, zinc and tin. Lauryl amine, acetic acid, azelaic acid, lauric acid, palmitic acid, stearic acid, maleic acid, maleic anhydride, dibutyltin dilaurate, dibutyltin maleate, dibutyltin diacetate, dibutyltin dioctoate, stannous acetate, stannous octoate, lead naphthenate, zinc caprylate, and cobalt naphthenate are illustrative of the catalysts which can be used. Dialkyl tin carboxylates, especially dibutyltin dilaurate and dibutyltin maleate, and Ct~l aliphatic monocarboxylic acids, especially acetic acid and stearic acid, are highly effective crosslinking catalysts for this invention.
The amount of catalyst used can vary over wide limits depending on the catalyst and ole~in copolymer used and ~ince, in some instances, the catalyst can also serve as the suspending medium. Where the catalyst also functions as the suspending medium, such as in the case of certain carboxylic acids, it can constitute up to as high as 90 percent of the total suspension mixture. In most instances where the catalyst is not part of the suspending medium, the catalyst will typically constitute from 0.01 percent up to about 5 percent of the total mixture. More commonly, the silanol condensation catalysts comprise from about 0.1 to 1 percent of the suspenslon.
The following examples illustrate the process of the invention and the crosslinkable powders obtained therefrom more 3 fully. As will be apparent to those skilled in the art, numerous variations are possible and are within the scope of the invention. In the examples all parts and percentages are given on a weight basis unless otherwise indicated.
' ` -18- ~ 3 l The powders produced in khese examples were analyzed using laser light scattering to determine average particle size and particle size distribution. ~ Model 2600C Malvern Particle Size Analyzer with the proper lens configuration for the expected particle size to be measured and equipped to automatically calculate the distribution curve and average particle size was used. For the analysis, water is charged to the water bath and circulated th;roug~ the sample measuring chamber. After obtaining the baseline measurement, the agitator and sonic vibrator are turned on and powder is added to the water bath until the obscuration reading is 0.3. Mixing and circulation are controlled to obtain acceptable dispersion without excessive foaming. A drop of liquid detergent is added to facilitate dispersion. After eight minutes a~itation, - measurements are taken over a period of time and the distribution curve and average particle size are calculated.
Duplicate runs are made for each powder sample. The particle size reported in the examples is the number average particle size D(v, 0.5). The range reported for the particle size distribution in the examples is for 80 percent of the distribution curve, i.e., 10 percent of the powder particles will ~all below the lower limit of the recited distribution and 10 percent will be larger than the upper recited particle size distribution limit.
Melt flow rates provided in the examples were measured in accordance with ASTM D1238-89 at 190C with a ~inius Olsen Extrusion Plastometer. Melt flow rates are expressed in grams per 10 minutes.
3o . .. . .
.
2~$~?J2~
E~:HPI.~B I
To demonstrate the improved process of the invention whereby fractional melt flow rate microfine powders are produced, 340 parts random copolymer of ethylene and vinyltri-ethoxysilane having a melt flow rate of 4.8 and containing 4.0%
vinyltriethoxysilane was charged to a reactor with 810 parts deionized water, 97.2 parts nonionic.surfactant (Pluronic~ F-98 - a block copolymer of ethylene oxide and propylene oxide of molecular weight 13500 and containing 20~ propylene oxide3, and 7 parts polyethylene grafted with 2% maleic anhydride ~MFR 10).
Based on the weight of the copolymer, the amount of surfactant and catalyst used was 28% and 2~, respectively. The reactor was sealed and the mixture heated for 52 minutes at 216C ~nder 400 psi pressure. Agitation was commenced and maintained for 15 minutes. The stirrer speed was maintained at 3000-3300 rpm (tOp speed 2350 to 2590 ft/min) during the 15 minute interval.
The contents of the reactor were then emptied into a stainle~s steel tank containing approximately 5 liters cold water to precipitate the copolymer. The resulting ethylene-vinyltriethoxysilane copolymer powder was recovered by filtration and dried. The powder had a melt flow rate of 0.14, number average particle size of 62 um and the particle size distribution ranged from 28 to 161 um. Micro-~copic examination f the powder particles showed them to be spherically shaped.
-. . ' . .. ` :
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` -20 1 EgAHPL~
Example I was repeated except that a dif f erent catalyst was used to brinq about the melt flow reduction. The amount o~ copolymer, water and sur.Eactant used was identical to Example I. Five parts acetic acid (1.44~ based on the copolymer) was used as the catalyst. The resulting powder had a melt flow rate of 0.11, an average particle size of 56 um and particle size distrib~tion ranging from 25 to 145 um.
, -21- ~ ?~3 1 E~A~P~B III
Following the procedure of Example I an experiment was conducted using stearic acid as the catalyst. The amount of copolymer, water and surfacta:nt used was the same as in that example except that 0.2 parts stearic acid (0.06~ based on the weight of the copolymer) was useld. The resulting microfine powder particles were spherically shaped, had a melt flow rate of 0.01, an average size of 76 um and size distribution of 37-148 um.
.
. .. - . .
::
-22- 2~8~223 CO~SPAR~TIVE Ea~lPL}: A
To demonstrate the need to use a catalyst for the process of the invention, Example I was repeated except that the polyethylene grafted with mal~eic anhydrids was omittad from the reaction. The reactant chargle and reaction condi~ions wer~
otherwise identical, While a fine powder was produced (average particle sizs 55 um and particle ~size distribution 27-108 um), the melt flow rate of the resultin~ ethylene-vinyltriethoxy-silane powder was 4.6.
-.
~:
, . . - ,.. : , . : .` : .
-23- 2~122~
COHPAR~TIyE E~.H2~E E3 To demonstrate the ina~ility to disperse fractional melt flow rate polymers, 347 parts polyethylene having a melt index of o. 17 was charged to the reactor with 49 parts surfactant (Pluronic~ F-98) and and.810 parts water. The mixture was heated for 52 minutes at 216C under 400 psi pressure and then agitated for 15 minutes at the same rate as used for Example I. When the reactor contents were discharged, essentially all of the polymer re~ained in the reactor.
Dlsassembly and inspection of the reactor revealed that the polymer was agglomerated on the agitator blades. Increasing the surfactant ~oncentration, up to as high as equal parts surfactant based on the resin, still did not produce acceptable dispersions capable of yielding f ine powders.
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, -24- 2~ 2~
1 E~AHP~E IV
To demonstrate the ability to use other ethylene-vinyltriethoxysilane copolymers, in the process of the invention, the following experiment was carried out. For the reaction, 350 parts ethylene-~inyltriethoxysilane copolymer having a melt index of 5 and containing 1.9 weight percent copolymerized vinyltriethoxysilane was charged to a reactor with 810 parts water. Twenty-eicJht percent surfactant (Pluronic~ F-98), based on the we.ight of the copolymer, and o.06~ stearic acid, based on the weight of the copolymer, were also charged to the reactor. The materials were then dispersed and the copolymer recovered in accordance with the procedure of Example I. The resulting powder comprised of spherical particles had a melt flow rate of 0.17. The average partlcle size of the powder was 53 um and the particle size distribution was 27-96 um.
When the above procedure was repeated, except that the amount of stearic acid used was doubled, comparable fractional melt flow ra~e microfine powders were produced. The powders had no measurable flow rate, an average particle size of 77 um and particle size distribution ranging from 47 to 140 um.
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.
-~5-2~3~w23 E~A~PLE V
Example IV was repeated using ethylene-vinyltri-Pthoxysilane copolymer having 0.8 weight percent vinyltri-ethoxysilane copolymerized. The copolymer had a melt index of 6. When 0.12% stearic acid based on the amount of the copolymer was employed, the resu:Lting spherical powder had a melt index of 0.44, an average particle size of 42 and particle size distribution of 21-72 um. Xncreasing the catalyst (stearic acid) level to 0.23~, based on the weight of the copolymer, yielded a powder of melt index 0.25, average particle size of 51 um and particle size distribution ran~ing from 25-125 um.
.. . ..
. -26-2 ~
1 E~AMPIE VI
The versatility of the present process is further illustrated by the following example wherein a fractional melt flow rate powder of an ethylene-vinyl acetate copolymer grafted wlth vinyltriathoxysilane is produced. The EVA resin contained 9~ vinyl acetate and was gra~ted with 0.9~ vinyltriethoxy-silane. The graft copolymer had a melt flow rate of 23. For this example, 350 parts gr~ft copolymer, 810 parts water, 10 parts acetic acid and 97.2 parts surfactant (Tetronic~ 908) were used. After sealing the reactor, the mixture was heated for 50 minutes at 210C at 350 psi pressure and then agitated for 15 minutes. The stirrer speed was maintained at 3500 rpm (tip speed 2750 ft~min). The reactor contents were then discharged into water and the resulting powder recovered by filtration and dried overnight in a hood. The melt flow rate of the polymer was reduced to O.OS as a result of the treatment. The powder consisted of spherically shaped particles having an average particle size of 69 um and particle size distribution ranginy from 25 to 135 um.
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. -27~ 2~
E~HPLE VII
The procedure of Exa~ple V.L was repeated except that lauryl amine was used as the catalyst in place of the acetic acid and Pluronic~ F-98 was substituted for Tetronic~ 908. The melt flow rate of the polymer powcler produced was O.OS. The number average particle size of the powder was 43 um and particle size distribution was 18--95 ym.
2 ~ 2 ~
1 E2AXPL~ VIII
Example VI was repeated except that a different graft copolymer was employed. For this reaction, an EvA copolymer (9% VA) grafted with 0.3% ~inyltrimethoxysilane was used. The EVA resin had a melt flow rate of 20. one part acetic acid and 97.2 parts Pluronic0 F-98 surfactant were used for this reaction. The powder produced had a melt flow rate of 0.3~, average particle size of 9S um and particle size distribution lO from 65 to 142 um.
..
. -29- 2~22,~
1 ! EXnHP~E IX
Preparation of ethylen~v~nyltriethoxy~llane copolym~r powder: A crosslinkable microfine powder was produced in accordance with the dispersion procedure descri~ed in U.S. Patent No. 784,862. To produce the powder, an electrically heated two-liter Paar reactor equipped with a thermowell and thermocouple connected to a digital display was used. The reactor was equipped with an agitator haYing three six-bladed impellers driven by a drill press equipped with a 2 HP DC varia~le speed motor. Three hundred and forty seven parts of a random copolymer of ethylene and vinyltriethoxy-silane having a melt flow rate of 4.1 and containing 4.1%
vinyltrieth~xysilane was charged to ~he autoclave with ~lO
parts deionized water and 97.Z parts nonionic surfactant. The nonionic surfactant employed was Pluronic~ F-9~ - a block copolymer of ethylene oxide and prop~^lene oxide of molPcular weight 1350 and containing 20~ propylene oxide. The autoclave was sealed and heated over a period of 45 minutes up to 222C
wh~ch resulted in a pressure of 340 psi. Agitation was commenced and maintained for 15 minutes at 3300 rpm (tip speed 2750 ft/min). The contents of the reactor were then rapidly discharged thraugh a Strahman valve into a stainless steel ~an~
containing 5 liters of cold water to precipitate the polymer.
The resulting,,e,thylene-vinyltriethoxysilane copolymer powder was washed several times with water, collected by filtration and drled. 'The powder had a melt flow rate of 3.0fi and number average particle size of 141 microns. The particle size distribution ranged from 83 to 258 microns. Microscopic examination of the powder showed the powder particles to be spherically shaped.
-30- ~ 3 1 E~HPhEiX_ To demonstrate the ability to crosslink the olefin copolymer powders of the invention to reduce the melt flow ra~e, lOo parts of the dry powder o ethylene-vinyltriethoXy silane copolymer powder produced in.ExampleIX was combined wlth 300 parts deionized water and ~5 parts glacial acetic acid.
The powder was suspended in the liquid medium by stirring with a magnetic stirrer while heating the mixture at 70c for 1-1/2 hours. After this period, the polymer was recovered by filtra~ion, washed several times with water and dried. The melt flow rate of the dried powder was reduced from 3.06 to ~.66 as a result of this treatment.
, . .
. : : ., . ., - .
~ 31- 2~ 2~
1 E~HPLE_XI
To further illustrate the ability to crosslin~ the olefin copolymer powders and the ability to produce fractional melt flow rate polymer powders, 25 parts of the ethylene-vinyltriethoxysilane copolymer po~wder of ExampleIX was suspended in 200 parts glacial acetic acid. The mixture wa~
stirred for 1-l/2 hours while maintaining the temperature at 70-B0C. The resulting crosslinked powder had no measurable melt flow, i.e., melt flow rate of zero. Furthermore, this siqnificant reduction in melt index was accomplished without significantly alterin~ the powder characteristics. The averaqe particle size of the crosslink powder was 153 microns and particle size distribution ranged from 88 to 261 microns, essentially comparable to the starting specifications of the powder. The powder particles retained their spherical sha~e after the melt flow reduction.
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: , , . :
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- E~HP~R XII
To demonstrate the ability to crosslink the polymer powders using other catalysts, 50 parts of the olefin copolymer powder of Example IX and 2.5 parts stearic acid were combined with 300 part~ deionized water. The.mixture was stirred for 1-1/2 hours at a temperature o~ 70-80C. The resulting powder, after washing with ethanol and drying, had an average particle size of 148 microns and particle size distribution from 83 to 254 microns. Whereas the original powder had a melt 1OW rate of 3.06, the powder after the above treatment had no measurable flow.
' ..
~, .
..
2 ~ 3 1 E~AMP~E XII~
The versatility of the process is further demonstrated by the following experiment wherein the conditions were varied. For the reaction, 40 grams dry ethylene-~inyltrlethoxysilane copolymer powder (melt index 1.7, 4.1%
VTEOS) was charged to an 800 ml resin fiask containing 50 grams acetone and 150 grams deionized water. The resin flask was equipped with a reflux condenser, thermometer and agitator driven by an electric motor (Gerald ~eller GT-21 with controller). The stirred suspension was heated to about 50C
and 0.8 gram dibutyltinlaurate dissolved in 100 grams acetone added. After stirring the mixture at 50-521C ~or 1-1/2 hour~, the suspension was cooled and the crosslinked powder was recovered by filtration. The powder was washed three times by resuspending in acetone, agitating and refiltering. The dried powder had no measurable melt flow rate. Average particle ~ize of the powder was 141 microns and particle size distrib-ltion was 80-~40 microns.
.
.
- : . ~ ' :
... ..
2~,2~
E~H IJE XIY
In a manner similar to that of Examplex~ o grams of EVTEOS copolymer was suspended in ~olution of 188 grams ethylene glycol and 2 grams deionized water. The mixture was heated to 80C wlth agitation and a solution of 2 grams laurylamine in 10 grams ethylene glycol added. The mixture was then stirred at 80-85C for 1-1/2 hours. Cold deionized water was added and the mixture was filtered to recover the powder The product was washed by resuspending in water (2x) and acetone t2x). The dried powder had ~ melt index of 0.012, an average particle size of 127 micron~ and part~cle size distri~ution of 60-Z21 microns.
..
.
.: :
Claims (22)
1. A microfine olefin copolymer powder comprised of particles which are spherical or substantially spherical in shape and wherein 80 percent or more of the particles range in size from 10 microns to 500 microns, said olefin copolymer comprised of an .alpha.-olefin having from 2 to 8 carbon atoms and an unsaturated alkoxysilane of the for.mula R-Si(R*)n(Y) 3 - n where R is an ethylenically unsaturated hydrocarbon radical having from 2 to 6 carbon atoms, R* is a hydrocarbon radical having from 1 to 10 carbon atoms, Y
is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from 0 to 2.
is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from 0 to 2.
2. A microfine olefin copolymer powder according to Claim 1 wherein the particles are capable of being crosslinked and have a melt flow greater than about 1.
3. A microfine olefin copolymer powder according to Claim 1 wherein the particles are chemically crosslinked and have a melt flow rate less than about 1 said particle being spherical or substantially spherical in shape and 80 percent or more of the particles range in size from 10 microns up to 200 microns.
4. The olefin copolymer powder of any one of Claims 1-3 wherein the olefin copolymer is comprised of 80 to 99.75 weight percent C2-3 a-olefin and 0.25 to 20 weight percent unsaturated alkoxysilane.
5. The olefin copolymer powder of any one of Claims 1-4 wherein the unsaturated alkoxysilane is a vinyltrialkoxysilane wherein R is vinyl, n is zero and Y
is an alkoxy group having from 1 to 4 carbon atoms.
is an alkoxy group having from 1 to 4 carbon atoms.
6. The polymer powder of Claim 5 wherein the vinyltrialkoxysilane is vinyltrimethoxysilane or vinyltriethoxysilane.
7. The olefin copolymer powder of any one of Claims 1-6 which is a random copolymer of ethylene and vinyltriethoxysilane or vinyltrimethoxysilane, or a grafted copolymer of vinyltriethoxysilane or vinyltrimethoxysilane onto an ethylene polymer.
8. A process for producing substantially spherical microfine polymer powders comprising:
(1) combining (a) an olefin copolymer having a melt index greater than 1 comprised of (i) an a-olefin having from 2 to 8 carbon atoms (ii) an unsaturated alkoxysilane of the formula R-Si(R*)n(Y) 3 - n where R is an ethylenically unsaturated hydrocarbon radical having from 2 to 6 carbon atoms, R*
is a hydrocarbon radical having from 1 to 10 carbon atoms, Y is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from O to 2; and, (iii) optionally, a comonomer selected from the group consisting of vinyl esters of C2-6 aliphatic carboxylic acids, C1-6 alkyl acrylates and C1-6 alkyl methacrylates;
(b) 4 to 50 percent, based on the weight of the olefin copolymer, of a nonionic surfactant which is a block copolymer of ethylene oxide and propylene oxide;
(c) a polar liquid medium which is not a solvent for the olefin copolymer and which does not react with (a) or (b) under the conditions employed, the weight ratio of the polar liquid medium to the olefin copolymer ranging from 0.8:1 to 9:1;
(2) heating the mixture to a temperature above the melting point of the olefin polymer;
(3) dispersing the mixture to form droplets of the desired size;
(4) cooling the dispersion to below the melting point of the olefin copolymer;
and (5) recovering the olefin copolymer powder.
(1) combining (a) an olefin copolymer having a melt index greater than 1 comprised of (i) an a-olefin having from 2 to 8 carbon atoms (ii) an unsaturated alkoxysilane of the formula R-Si(R*)n(Y) 3 - n where R is an ethylenically unsaturated hydrocarbon radical having from 2 to 6 carbon atoms, R*
is a hydrocarbon radical having from 1 to 10 carbon atoms, Y is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from O to 2; and, (iii) optionally, a comonomer selected from the group consisting of vinyl esters of C2-6 aliphatic carboxylic acids, C1-6 alkyl acrylates and C1-6 alkyl methacrylates;
(b) 4 to 50 percent, based on the weight of the olefin copolymer, of a nonionic surfactant which is a block copolymer of ethylene oxide and propylene oxide;
(c) a polar liquid medium which is not a solvent for the olefin copolymer and which does not react with (a) or (b) under the conditions employed, the weight ratio of the polar liquid medium to the olefin copolymer ranging from 0.8:1 to 9:1;
(2) heating the mixture to a temperature above the melting point of the olefin polymer;
(3) dispersing the mixture to form droplets of the desired size;
(4) cooling the dispersion to below the melting point of the olefin copolymer;
and (5) recovering the olefin copolymer powder.
9. The process according to Claim 8 for producing substantially spherical microfine powders having reduced melt flow rate comprising the addition of 0.001 to 10 percent, based on the weight of the olefin copolymer, of a silanol condensation catalyst selected from the group consisting of organic bases, mineral acids, C2-22 carboxylic acids, adducts of unsaturated carboxylic acids or carboxylic acid anhydrides, organic titanates and complexes or carboxylates of lead, cobalt, iron, nickel, zinc and tin; and maintaining the dispersion of said mixture for a period of time sufficient to reduce the melt index of the olefin copolymer.
10. The process of Claim 9 wherein the catalyst is present in an amount from 0.01 to 4 percent based on the weight of the copolymer selected from the group consisting of dialkyl tine carboxylates and C2-18 aliphatic monocarboxylic acids.
11. The process of Claim 9 or 10 wherein the recovered olefin copolymer powder has a melt flow rate less than 1 and 80 percent or more of the particles range in size from 10 microns up to 200 microns.
12. The process according to Claim 8 wherein the polymer powders are spherical or substantially spherical in shape and wherein 80 percent or more of the particles range in size from 10 to 500 microns.
13. The process of any one of Claims 8-12 wherein the nonionic surfactant is a water soluble block copolymer of ethylene oxide and propylene oxide having a molecular weight greater than 3500 and the polar liquid medium is selected from the group consisting of water, alcohols, polyols and mixtures thereof.
14. The process of any one of Claims 8-12 wherein the nonionic surfactant is present in amount from 7 to 45 percent, based on the weight of the olefin copolymer and is obtained by polymerizing ethylene oxide on the ends of a preformed polymeric base of polyoxypropylene or by polymerizing ethylene oxide onto an ethylene diamine nucleus containing propylene oxide block polymer chains.
15. The process of any one of Claims 8-14 wherein the polar liquid medium is water and the weight ratio of the polar liquid medium to olefin copolymer is 1:1 to 5:1.
16. The process of any one of Claims 8-15 wherein the olefin copolymer is comprised of 55 to 99.5 weight percent C2-3 a-olefin, 0.25 to 20 weight percent unsaturated alkoxysilane and 0 to 45 weight percent comonomer selected from the group consisting of vinyl acetate, methyl acrylate, ethyl acrylate or butyl acrylate.
17. The process of Claim 16 wherein the unsaturated alkoxysilane is a vinyltrialkoxysilane wherein R is vinyl, n is zero and Y is an alkoxy group having from 1 to 4 carbon atoms.
18. A process for crosslinking microfine olefin copolymer powders comprised of particles which are spherical or substantially spherical in shape and wherein 80 percent or more of the particles range in size from 10 microns to 500 microns which comprises contacting the olefin copolymer powder with water at a temperature below the melt point of the olefin copolymer and in the presence of a crosslinking amount of a silanol condensation catalyst selected from the group consisting of organic bases, mineral acids, C2-22 carboxylic acids or carboxylic acid anhydrides, organic titanates and complexes or carboxylates of lead, cobalt, iron, nickel, zinc and tin; said olefin copolymer having a melt flow rate greater than 1 and derived from an a-olefin having from 2 to 8 carbon atoms and an unsaturated alkoxysilane of the formula R-Si(R*)n(Y)3-n where R is an ethylenically unsaturated hydrocarbon radical having from 2 to 6 carbon atoms, R is a hydrocarbon radical having from 1 to 10 carbon atoms, Y
is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from 0 to 2.
is an alkoxy group having from 1 to 4 carbon atoms and n is an integer from 0 to 2.
19. The process of Claim 18 wherein the olefin copolymer powder is suspended in an aqueous medium containing the silanol condensation catalyst and the weight ratio of water to olefin copolymer is from 0.001:1 to 20:1.
20. The process of Claim 18 or 19 wherein the aqueous medium contains an organic liquid selected from the group consisting of alcohols, polyols, ketones, carboxylic acids and carboxylic acid esters.
21. The process of any one of Claims 18-20 wherein the silanol condensation catalyst is selected from the group consisting of dialkyl tin carboxylates and C2-18 aliphatic monocarboxylic acids.
22. The process of any of Claims 18-20 wherein the olefin copolymer contains 90 to 99.5 weight percent C2-3 .alpha.-olefin and 0.5 to 10 weight percent vinyltrimethoxysilane or vinyltriethoxysilane.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/784,826 US5213769A (en) | 1991-10-30 | 1991-10-30 | Mixture forming method and apparatus |
| US784,862 | 1991-10-30 | ||
| US07/797,834 US5209977A (en) | 1991-11-26 | 1991-11-26 | Crosslinkable ethylene copolymer powders and processes |
| US797,834 | 1991-11-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2081223A1 true CA2081223A1 (en) | 1993-05-01 |
Family
ID=27120332
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002081223A Abandoned CA2081223A1 (en) | 1991-10-30 | 1992-10-23 | Microfine melt flow rate polymer powders and process for their preparation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2081223A1 (en) |
-
1992
- 1992-10-23 CA CA002081223A patent/CA2081223A1/en not_active Abandoned
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| Date | Code | Title | Description |
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Effective date: 20040329 |