The present invention relates to methods and apparatus of molding composite parts by liquid resin infusion. The invention involves the creation of temporary resin distribution channels on the surface of a preform to aid in the distribution of resin during infiltration. In general, these methods are improvements over the art because the molds are cheaper to make, the parts produced are of higher quality, minimal waste is produced and the time to infiltrate the preform is reduced.

There are many processes available for the purpose of impregnating a preform with liquid resin in order to make a composite. These processes may be broadly characterized into two categories. One category includes wet lay-up methods while the other category features some form of resin infusion such as resin transfer molding (RTM).
Wet lay-up processes tend to have lower average quality than resin infused parts. They are labor intensive to manufacture because each layer of preform material must be individually coated with resin and carefully positioned by hand. One frequent problem with wet lay-up methods is air bubble entrapment inside the composite while the resin is being applied to the preform. A second difficulty is achieving a uniform part thickness and fiber volume fraction which ultimately influence the material properties. Another problem with wet lay-up processes is the excessive amount of fumes given off by the exposed resin before and during cure.
Resin infusion methods are carried out in a closed system which eliminates most of the fumes. Resin infusion processes can also infuse resin into a preform with a vacuum thus avoiding air bubble entrapment. Resin infusion methods allow for better control over part dimensions and fiber volume fraction. Thus, resin infusion methods overcome many of the limitations of wet lay-up processes. Unfortunately, until recently resin infusion processes tended be more expensive than wet lay-up because of the more expensive molding apparatus required. In the past, a rigid closed mold was required. Even though closed mold methods are improvements over wet lay-up methods, there are problems with closed mold methods beyond that of cost. When infiltrating high volume fraction preforms, standard closed mold methods require high resin injection pressures and long infiltration times because the low permeability of high volume fraction preforms.
More recently, several novel vacuum infusion techniques were introduced which do not require an expensive closed mold. Instead, they incorporate a single rigid mold surface upon which the preform rests. The preform is covered by a impermeable sheet and is sealed at its periphery forming a preform cavity which can be evacuated using a vacuum pump. Atmospheric pressure provides both the compaction force on the preform and also the driving force for resin infusion from an external supply into the lower pressure preform cavity. Despite the simplicity of this approach there were still problems with the infusion process because many high viscosity resins could not adequately infiltrate low permeability preforms.
The resistance to resin infiltration increases with the distance the resin must flow through the preform. In vacuum assisted resin infusion, the injection pressure cannot exceed the ambient atmospheric pressure without pressing the outer sheet away from the preform. Thus, infiltration is often slow and incomplete. Often, regions of the preform are not infiltrated with resin, while excess resin collects in undesired locations.
One clever way to overcome the problem of a low permeability preform was to artificially increase the permeability at certain locations within the preform cavity. There have been several embodiments of this fundamental concept in the art These include but are not limited to: placement of tubular arteries between adjacent preform layers, drilling an array of holes in a rigid plate which rests on the preform, and the use of a distribution medium on top of the preform. All these methods have their own limitations. Of the methods, the processes incorporating a distribution medium are the most useful. They are also the most closely related methods to those disclosed in the present patent and therefore will be described in greater detail.
In the distribution medium process, a preform is placed on a tool surface and covered with a permeable sheet. A distribution medium is placed on top of the permeable sheet and is covered with a continuous non-permeable sheet sealed at its periphery. A vacuum is drawn on the entire assembly of preform, permeable sheet, and distribution medium. Resin is introduced to the distribution medium which provides high permeability pathways for the resin to distribute itself over the entire top surface of the preform. The injection pressure, which must be less than atmospheric pressure, forces most of the resin through the permeable membrane and into the preform. Satisfactory resin impregnation is usually achieved since there is a relatively small resistance to infiltration of the preform in the thickness direction in comparison with the in-plane direction. The lower resistance to infiltration also results in shorter infusion times.
Despite the benefits of this improved resin infusion method, it still has some disadvantages which make it unattractive for many applications. When resin comes into contact with the distribution medium it remains trapped in the distribution medium and is subsequently cured. After the resin has cured, the permeable membrane, the clogged distribution medium, and the impermeable outer membrane must be separated from the composite part and discarded as waste. While the process is quite useful for proto-typing and low volume production, the amount of waste produced is incompatible with the required efficiencies of mass production.
These and other problems remain in the field of infusion molding of composite structures. In this patent we describe novel means of overcoming the aforementioned difficulties.
The molding methods and apparatus of the present invention have many different uses, and the apparatus can take on different forms. An example is provided of infiltrating an advanced composite preform, which is an assemblage of reinforcing fibers, with a liquid plastic resin. What in general could be any low permeability material will in the following disclosure be called the preform. The infiltrating fluid could be one of many different fluids, such as gases, liquids, and liquids containing suspended solid particles, which in the description are collectively referred to hereafter as resin.
The preform can be can be made from a variety of reinforcing fibers including fiberglass, Kevlar (aramid) fibers, and carbon fibers. There are many types and configurations of fibers and yams made from fibers. The yarns may be formed into many different types of assemblages including weaves, braids, and knits as well as short and long fiber mats. Different types of fibers may be combined in an assemblage to form a hybrid preform. All these and other variations are known by those skilled in the art. The preform may also include inserts of various types such as foam cores, honeycomb cores, balsa wood, metal inserts and reinforcements. Additionally, the preform may contain sensors or other devices. All of these components are known in the prior art.
The resin is any of a variety of curable liquid resins such as polyester, vinyl ester, and epoxy. The resins may be catalyzed for high temperature cure or room temperature cure and for various cures times as is compatible with the needs of the molding process. The resin should be properly catalyzed and degassed prior to injection into the preform cavity. The wide variety of useful resins and the methods of preparing the resin are all widely known in the art.
In each of the embodiments of the invention, it is desirable that a vacuum be drawn on the cavity containing the preform prior to beginning the flow of resin. In this way, the problem of entrapping an air bubble in the resin is avoided. A source of vacuum may continue to be applied to the preform cavity during the infiltration of resin and until the resin has cured or it may be removed at some point during the infiltration. Even if the source of vacuum is removed (by closing a valve for example) the space inside the preform cavity should remain substantially a vacuum during resin infiltration if the preform cavity is properly sealed. In some embodiments of the invention, it is possible to infiltrate the preform with resin without initially drawing a vacuum on the preform cavity. However, since this method introduces the possibility of trapping an air bubble in the preform and it is easy to draw a vacuum on the preform cavity, this method is not recommended.
The number and position of the sources of vacuum and resin depend on the specific application. Each resin and vacuum source is able to be controlled individually using a valve or other means of stopping the flow of material through the source. The flow of resin should be stopped when sufficient resin has entered the mold. This may be controlled by properly controlling the cure time and/or measuring the amount of resin that has entered the mold and stopping the flow of resin when sufficient resin has entered the mold.
Temporary Resin Distribution Channels
As is discussed in the Background to the Invention, the prior art contains various means of aiding the distribution of resin over the surface of a preform for the infiltration of a preform with resin. However, none of these methods provides a means of creating temporary resin distribution pathways on the surface of the preform. The advantage of temporary resin distribution channels over the use of a distribution medium is a major reduction in the amount of waste material produced. When producing composites in large quantities, this large amount of waste is costly and a source of pollution and therefore should be eliminated.
Though there are many features and embodiments of the present invention, the essence of the invention is a method and the related apparatus for molding a composite by infusing resin into a permeable preform, comprising the creation of temporary resin channels on the surface of the preform, flowing resin along the channels and from the channels into the preform, stopping the flow of resin, removing the temporary channels if desired, curing the resin in the preform and forming a composite. The methods disclosed in this patent are able to produce a composite if the temporary resin distribution channels are not removed before curing the resin. In this case, cured resin channels remain on the surface of the preform. This is not desirable in most applications and therefore, in the preferred embodiments of the invention, the resin flow channels are removed prior to curing the resin so that there are no cured resin flow channels on the surface of the composite.
There are several means of creating temporary resin distribution channels. One method comprises activating movable portions of the mold surface to create a network of resin distribution channels on the surface of the preform and deactivating them to remove the channels. These movable portions of the mold surface can be constructed in various ways. In a rigid mold, sections of the mold can be made so they are retractable. These portions can be retracted to create the resin flow channels and extended to remove the channels after sufficient resin has entered the preform cavity. The retractable sections of the rigid mold should be constructed in such a way that they do not leak resin.
Constructing retractable sections on the internal surface of the mold makes the mold more expensive than the usual mold used in RTM. However, the speed of infiltration allowed by having high permeability pathways over the surface of the preform is worth the extra cost. This method retains the advantages of closed mold RTM such as good dimensional accuracy and high fiber volume fraction while overcoming difficulties such as high injection pressures and slow infiltration of resin when infiltrating high volume fraction preforms. Also, the problem of determining the proper resin inlet and outlet positions is eliminated.
Under the present art, much effort is put into determining the time evolution of the resin flow front in order to properly place resin inlets and outlets and to determine the time required to inject resin so that the preform is fully impregnated. The use of temporary resin distribution channels essentially eliminates this problem since the time to infiltrate the preform is reduced and the progression of the flow front is easily controlled by the resin distribution network pattern. The methods used to calculate resin flow front evolution are computationally difficult and still a topic of active research.
It is desirable to avoid the problem of resin source and outlet placement entirely by using the resin distribution channels to control the flow front progression. Optimization of the inlet and outlet positions requires repeated calculations and/or experimental trial and error. Both of these tasks are expensive. The network of resin distribution channels provides rapid resin infusion without complicated calculations or expensive trial and error experimentation. In the case of high volume production, the increased speed of resin infusion, the shorter mold development times, and the lower risk of making an unsatisfactory mold are all worth the extra cost of the moveable mold channels.
Another method of creating temporary resin distribution channels is to have mechanically movable portions of the mold surface which are made of a stiff elastomeric material. A means of deforming the stiff elastomeric material into resin distribution channels is provided in the body of the mold. This embodiment of the invention provides a simple, cost effective means of creating temporary resin distribution channels in the surface of the mold. After resin has infiltrated the preform, the stiff elastomeric portions of the mold are pushed into a position flush with the surface of the preform. At this point, curing of the resin may begin.
Instead of deforming or moving portions of rigid molds, a thin flexible membrane can be placed over the preform and portions of the membrane can be caused to deform into resin distribution channels by various means. The various embodiments of this general class of molding apparatus have advantages over the previous embodiments in terms of the cost and ease of making and preparing the mold.
One of the means of deforming the flexible impermeable membrane involves applying mechanically or electro-mechanically induced forces at distributed points along the surface of the flexible membrane. These forces cause the membrane to move away from the surface of the preform temporarily to allow the resin to flow over the surface of the preform.
There are various embodiments of the invention which use an impermeable flexible membrane which is temporarily deformed into resin distribution channels on the surface of a preform. One set of these embodiments relies on a differential pressure between the preform side of the flexible membrane and the other side of the membrane. By properly applying a higher pressure on the preform side of the membrane than the other side of the membrane, the flexible membrane will deform into temporary resin distribution channels. When the proper amount of resin has infiltrated the preform, a source of fluid (usually air) at the proper pressure is applied to the channels in the mold surface. The applied pressure should be greater than the pressure of the resin under the flexible membrane. In this way the resin distribution channels on the surface of the preform are collapsed and the flexible membrane presses down evenly and smoothly over the preform. In fact, the pressure of the resin plus the pressure compressing the preform is equal to the pressure on the other side of the flexible membrane. Thus, by adjusting the amount of resin in the preform and the applied external pressure, the amount of preform compression can be controlled within certain limits.
One method of applying a differential pressure between the two sides of the flexible membrane is to cover the flexible membrane with a mold which contains a network of channels in its surface. Resin is then introduced to the preform side of the flexible membrane at a pressure higher than the pressure on the other side of the membrane. This causes the membrane to be forced out and away from the preform and the membrane then takes on the shape of the internal surface of the containing mold. Since this containing mold has a network of channels in its surface, the flexible membrane now has created a network of resin distribution channels on the surface of the preform.
In one embodiment of the invention which uses a flexible impermeable membrane covered by a mold with internal surface channels, the mold is made from a rigid sheet material with channels impressed upon its surface. The rigid sheet material may be sheet metal or other suitable rigid sheet materials which can be formed into the proper shape. As with the majority of the embodiments of the invention described in this disclosure, it is desirable to maintain a vacuum in the cavity containing the preform. Additionally, it is desirable in this embodiment to maintain a vacuum in the channels in the surface of the rigid sheet above the flexible membrane. Thus, before resin is introduced, there is a vacuum on both sides of the flexible membrane and therefore, the flexible membrane does not deform. Additionally, the ambient atmospheric pressure presses down upon the rigid sheet which in turn presses down on the flexible membrane in regions where there is not a channel. These regions of the flexible membrane in turn press down upon the preform compacting it to a high fiber volume fraction. When liquid resin is introduced under the flexible membrane, the resin presses the flexible membrane into the channels in the surface of the rigid sheet thereby creating temporary resin distribution channels on the surface of the preform. These high permeability channels allow the resin to easily and quickly spread out over the preform and infiltrate the preform quickly and completely. Since all points in the preform are only relatively short distances from a channel in a properly design channel network, the resin has no difficulty reaching all points in the preform. After resin has impregnated the preform, the vacuum in the channels is removed and atmospheric pressure is applied to the channels forcing the flexible membrane against the preform.
In another embodiment of the flexible impermeable membrane covered by a mold with internal surface channels, the mold is made from thick rigid material with a network of channels formed in its surface. The rigid material may be a strong material such as steel. This embodiment provides greater dimensional accuracy for the composite. Also, the compacting pressure is not limited to atmospheric pressure. Higher resin injection pressures are possible since the thick and rigid material can support the flexible membrane. Thick and rigid molds are more expensive and difficult to make than rigid sheets with channels. This is especially true for very large parts. Thus, both embodiments are useful and the specific application will determine which embodiment is most appropriate.
Each of the previous two embodiments of the invention require that the pressure on the preform side of the flexible membrane exceed the pressure on the other side of the membrane. The preferred method of creating this situation is to apply a source of vacuum to the channels in the internal surface of the mold. It is possible to include a layer of porous material known in the art as breather material between the mold surface and the flexible membrane to aid in quickly and evenly evacuating the channels.
An alternate method of causing the flexible membrane to deform into temporary resin distribution channels which still relies on a differential pressure between the preform side of the flexible membrane and the other side of the membrane but does not use a mold with a network of channels in its surface is to use a spacer system. A spacer system is a system of sturdy shapes inter-connected in such a way that they provide a network of gaps into which the flexible membrane can deform to create temporary resin distribution channels when the pressure on the preform side of the flexible membrane exceeds the pressure on the other side of the membrane where the spacer systems is located.
There are many appropriate forms of the spacer system. One form, called a link mat, is a geometric array of spacer blocks connected to each other with link rods. The blocks and link rods can be made of plastic or other suitably sturdy material. The link mat is placed on top of the flexible impermeable membrane which is in contact with the preform and then covered with an additional flexible impermeable membrane which is able to be sealed against the first membrane. The purpose of the second membrane is to allow a reduced pressure to be applied to the cavity containing the spacer system.
Another form of spacer system is similar to a woven mat which is also covered with an impermeable outer cover. The mat consists of large flexible rods in the weft direction held together with thin yams in the warp direction. This arrangement produces a series of channels between the larger rods. The flexible membrane deforms into these channels during resin infusion and the resin distribution channels formed under the membrane and on the surface of the preform aid in flowing resin over the surface of the preform. When higher pressure fluid such as air is introduced to the cavity containing the fabric mat, the impermeable membrane between the preform and the fabric mat is pushed smoothly and evenly against the preform.
Yet another form of the spacer system is a bubble mat or inflatable bubble mat. A bubble mat is a flexible sheet with an array of bubbles on its surface. An inflatable bubble mat has a series of small inter-connections which allow the bubbles to be inflated or deflated. In both cases, the gaps between the bubbles provide a network of channels for the flexible membrane in contact with the preform to deform into when the pressure on the preform side of the flexible membrane is higher than the pressure on the bubble mat side.
The spacer systems discussed above may also contain a layer of breather material to aid in quickly and evenly adjusting the pressure in the spacer system cavity.
In one embodiment, the flexible membrane and the spacer system is combined into one unit. An inflatable bubble mat is placed on a preform which is resting on a tool surface. The bubble mat is sealed at its periphery on the tool surface so that a vacuum can be drawn on the preform cavity. The bubbles in the bubble mat are then inflated which causes the bubble mat to lift away from the preform and thereby create a system of resin distribution channels on the surface of the preform. Resin is injected under the bubble mat and flows through the channels and from the channels into the preform. When sufficient resin has entered the preform cavity, the source of resin is stopped and the bubbles are deflated allowing the bubble mat to press down smoothly and evenly over the surface of the preform.
In the embodiments of the invention disclosed so far, the temporary resin distribution channels have been created by either mechanically moving sections of the mold surface or deforming a flexible impermeable membrane by some means. In another set of embodiments of the invention, the temporary channels on the surface of the preform comprise a flexible mold material containing interior channels below the surface. A resin pressure on the preform side of the flexible mold greater than the pressure in the channels below the surface of the flexible mold causes the flexible mold material between the channels and the preform to deform into the interior channels and thereby create resin distribution channels on the surface of the preform. It is preferable in this embodiment of the invention that a vacuum be drawn on the cavity containing the preform and that a vacuum also be drawn on the channels below the surface of the flexible mold material during resin infusion. After a sufficient amount of resin has entered the preform, the source of resin and vacuum are stopped and a pressure higher than the pressure of the resin in the preform cavity is applied to the channels. This causes the material between the preform and the channels to move toward the preform and become flush with the surface of the preform. Curing the resin after the channels have been removed provides a composite with a smooth surface.


A piezoelectric element having a crystal structure that enables a piezoelectric film to be formed in an unstressed state is provided. The piezoelectric film contains an a-axis oriented crystal and a c-axis oriented crystal, where a difference in lattice constant between the a-axis oriented crystal and the c-axis oriented crystal is not more than 0.06 Å. The present inventors have newly found that a stress accumulated in the piezoelectric film can be reduced while maintaining favorable piezoelectric properties when a condition that the difference in lattice constant between the a-axis oriented crystal and the c-axis oriented crystal is not more than 0.06 Å is satisfied. When the condition is satisfied, the c-axis oriented crystal and the a-axis oriented crystal are properly balanced and as a result crystal particles of the piezoelectric film are closest-packed on its base in an ideal state, which contributes to a reduced stress.

1. Field of the Invention
The present invention relates to a piezoelectric element having an unstressed piezoelectric film, and a gyroscope that uses the piezoelectric element.
2. Description of the Related Art
It is known that properties of a piezoelectric film such as a permittivity, a Curie temperature, a coercive electric field, and a residual polarization vary according to an internal stress of the piezoelectric film. A piezoelectric film formed by a thin film process tends to have a two-dimensional stress that occurs in a film surface during film formation. Accordingly, to obtain a piezoelectric element exhibiting excellent piezoelectric properties, development of a piezoelectric film having a crystal structure with a reduced internal stress is desired. As a piezoelectric element having a crystal structure for reducing an internal stress, for example, Japanese Patent Application Laid-Open No. 2008-28285 proposes a piezoelectric element that has a laminate structure formed by stacking first, second, and third piezoelectric films from one electrode toward another electrode, where a piezoelectric constant of the first and third piezoelectric films is smaller than a piezoelectric constant of the second piezoelectric film. Such a device structure allows for a reduction in internal stress that occurs in an interface between an electrode and a piezoelectric film.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-28285
However, in the device structure disclosed in Japanese Patent Application Laid-Open No. 2008-28285, a difference in physical property such as a lattice constant, a thermal expansion coefficient, and the like between the piezoelectric film and its base may cause a compressive stress or a tensile stress to occur in the piezoelectric film during a process of cooling the piezoelectric film after high-temperature film formation. This makes it difficult to achieve a sufficient stress reduction.


The invention provides an aqueous soil treatment composition comprising water and,

This invention relates to compositions for soil treatment which can provide soil stabilisation benefits whilst being easy to handle using conventional equipment, and their use in irrigation methods.
It is well known to use high molecular weight polyacrylamides as additives within irrigation streams. These products are known to reduce soil movement therefore reducing erosion, increase water infiltration, and decrease the movement of soilborne pesticides and nutrients.
Solid grade products are commonly used in flood irrigation systems. These products are difficult to apply and are either added using complex applicators, which would usually be unavailable on a farm, or are hand applied by the patch method, in which case dose control is difficult.
Liquid products can be injected into the irrigation stream. Emulsions have been applied this way in overhead irrigation systems, as described in the granted patent U.S. Pat. No. 6,000,625. These products are viscous and require specialist pumps which are also not usually available on a farm. The polyacrylamide can also be applied as a solution in fertiliser, as described in the U.S. patent application Ser. No. 09/361,816. These fertiliser/polyacrylamide solutions have low viscosity""s and can be injected into irrigation streams using standard equipment of the type commonly used to apply fertiliser solutions into irrigation streams. U.S. patent application Ser. No. 09/361,816 describes a method of applying polyacrylamides within nutrient solutions, however the polymers described are only suitable for formulation within essentially mono-valent based fertiliser solutions. These fertilisers act as carriers for the polyacrylamide and are not soil stabilisers themselves.
It is also well known that calcium compounds can be used as soil stabilisers, which also show effective water infiltration. Gypsum, calcium chloride and calcium nitrate are widely used for this application. It is also known that calcium plays an important role in the binding of polyacrylamide to soils, due to the calcium depositing on the aggregate surface and maintaining soil structure while facilitating bridging of the polyacrylamide between aggregates. Several trials have shown the synergy of polyacrylamide with calcium products when the two types of products are added separately, but used together.
It is possible to produce a dry blend of polyacrylamide and a calcium based formulation, however these formulations can not be easily applied with conventional farm based application equipment.
It would be desirable to apply a combined polyacrylamide and calcium formulation that displays a high activity due to synergy between the two components, through fertiliser injection systems as described in U.S. patent application Ser. 09/361,816. Such a formulation would need to be a solution or a stable dispersion that would cause no problems, such as clogging, through standard fertiliser systems.
According to the invention we provide an aqueous soil treatment composition comprising water and,
(a) a calcium compound,
(b) a water-soluble anionic polymer which has intrinsic viscosity of less than 30 dl/g and is formed from water-soluble monomer or monomer blend of which less than 40% by weight is anionic monomer.
Preferably, the invention provides an aqueous composition in which the polymer (b) is dissolved. That is, the polymer is taken into the solution such that substantially no visible solid material remains. For some combinations of polymer and calcium compound, some solid lumps or other material visible to the naked eye may remain. These may be filtered out before use. For some combinations of polymer and calcium compound, the composition may be a dispersion that would cause no problems, such as clogging, through standard fertiliser systems.
The composition ideally comprises low salt content water, which gives the maximum synergy between the calcium and the polymer, however this does not limit the scope of the invention.
The polymer must be water-soluble and in particular is soluble in an aqueous solution of calcium compound having the same concentration of calcium compound as the final aqueous composition which is desired to be produced. Generally the polymer is substantially linear and is not cross-linked.
The polymer preferably has intrinsic viscosity (IV) of from 8 to 16 dl/g. In this specification intrinsic viscosity is measured by suspended level viscometer at 20xc2x0 C. in 1 M sodium chloride buffered to pH 7. That is, it is of sufficiently high molecular weight to give a soil stabilisation effect and is not a low molecular weight material which would act as a dispersant.
Preferably IV is at least 8 dl/g, more preferably at least 9 dl/g. It may be up to for instance 30 dl/g but generally we find that the optimum combination of low viscosity of the composition and soil stabilisation performance is given by polymers having IV not more than about 20 dl/g. Particularly preferred IV ranges are from 8 to 16 dl/g, especially 10 to 14 dl/g.
The polymer is formed from water-soluble monomer or monomer blend, usually watersoluble ethylenically unsaturated monomer. The anionic content, i.e. the proportion of anionic monomer in the monomer blend used to form the polymer, is at not more than 40% by weight, preferably not more than 35 or 30% by weight. Particularly preferred polymers have anionic content in the range 2 to 30% by weight.
The monomer blend used to form the polymer preferably comprises at least 2% by weight anionic monomer. This may be any suitable anionic ethylenically unsaturated monomer. It is generally preferred that the anionic monomer is an ethylenically unsaturated carboxylic monomer, in particular acrylic or methacrylic monomer. Salts of acrylic acid are preferred, for instance ammonium or alkali metal, in particular sodium salts.
The polymer may contain small amounts of cationic monomer, for instance up to 20% by weight or 10% by weight but usually the content of cationic monomer is substantially zero.
Generally the anionic monomer is copolymerised with non-ionic monomer, usually ethylenically unsaturated water-soluble non-ionic monomer such as acrylamide or methacrylamide, preferably acrylamide. The monomer blend used to form the polymer comprises at least 65% by weight non-ionic monomer. Particularly preferred polymers have non-ionic content in the range 98 to 65% by weight.
Particularly preferred polymers are copolymers of acrylamide with sodium acrylate.
The calcium compound may be any of those which can be used as soil stabilsers. Water insoluble or partially water soluble calcium compounds which can be used as soil stabilsers include calcium sulphates, calcium oxides, calcium carbonates, calcium phosphate and calcium cyanamide. CaSO42H2O, otherwise known as gypsum, is a calcium sulfate commonly used as a soil stabiliser. CaO in its hydrated form of Ca(OH)2, otherwise known as lime, is a commonly used soil stabiliser. Water soluble calcium compounds which can be used as soil stabilsers include calcium chloride, calcium nitrate, a blend of calcium nitrate with ammonium nitrate and chelated forms of calcium
Preferred calcium compounds are water soluble. Preferred water soluble calcium compounds are calcium chloride, calcium nitrate and calcium ammonium nitrate. A particularly preferred water soluble calcium compound is calcium chloride. The calcium compounds may be used alone or in a mixture.
The polymer is included in the composition in an amount such that when the composition is diluted for irrigation, it provides adequate polymer concentration on the soil to give acceptable soil stabilisation performance. Polymer concentration in the aqueous soil treatment composition of the invention is generally from 0.1 to 10% by weight, in particular at least 0.2 or at least 0.5% by weight. Preferably it is at least 0.7% by weight. Often it is not more than 7% by weight, and particularly preferred compositions contain from 0.1 to 2% by weight polymer.
The calcium compound is present in a concentration which provides calcium in a concentration of at least 0.5% by weight based on the total weight of the composition, for instance at least 2% by weight. Preferably it is at least 3% by weight. It can be as high as 13 or 15% by weight but is usually not more than 12% by weight. Preferred concentration range is 4 to 8% by weight, for instance around 6% by weight.
The aqueous composition of the invention can be made in any convenient manner. For instance polymer may be added to water followed by calcium compound or the two may be added simultaneously. Alternatively, calcium compound may be added to a preformed solution of polymer. However, generally it is preferred that the polymer is added to a preformed solution of the calcium compound. In particular it is preferred that the polymer is added in solid form, i.e. powder or bead. It is possible to add it in other forms, such as reverse phase dispersion, but solid is preferred. Essentially any particle size polymer can be used as long as gel blocking during polymer dissolution is avoided. Preferred solids are smaller than 1400 microns and are made in standard manner, for instance by gel or bead polymerisation followed by comminution and if necessary drying.
The polymer, if added as powder, can be added using known systems such as those described in U.S. Pat. No. 4,086,663 and WO94/19095.
Thus in the invention we provide a process for the production of an aqueous composition of the invention comprising providing a preformed aqueous solution of the calcium compound (a) and mixing into it polymer (b) in powder form. The compositions can be prepared at ambient temperature, however the speed of dissolution is increased at higher temperatures. A suitable temperature range for mixing is between 35 and 65 degrees Celsius.
The thus formed composition should have viscosity which renders the composition easy to handle. It should in particular be easy to handle (i.e. preferably pumpable, pourable or sprayable) in the equipment which is presently used for addition of soil stabilisers to irrigation water and for application of concentrated soil stabiliser solution alone to soil. Preferably viscosity is below 4,000 cPs, more preferably not more than 3,000 cPs. In particular it is not more than 2,000 and especially not more than 1,000 cPs. Particularly preferably it is not more than 600 cPs. Particularly preferred compositions have final viscosity of from 50 to 500 cPs. In this specification viscosity is measured using a Brookfield LVT viscometer at 12 rpm using spindle 2.
Thus aqueous composition of the invention may be applied directly to soil as a soil stabiliser composition. However, the composition of the invention is intended particularly as a concentrate for use in irrigation, in which processes it will be diluted and applied to soil areas. Thus it may contain any materials known for inclusion in such compositions. It generally does not contain additional materials such as oxidising agents, reducing agents, soil materials or seed materials.
The invention also provides a soil treatment process comprising irrigating an area of soil with water to which has been added an aqueous soil treatment composition of the invention.
Suitable irrigation processes include drip irrigation, furrow irrigation and spray irrigation. Spray irrigation processes include commonly known processes such as sprinkler irrigation and micro sprinkler irrigation. Sprinkler irrigation includes processes which use overhead, pivot, solid set, hand line and wheel line irrigation systems. Micro sprinkler irrigation includes processes using small individual spray heads placed at the crop site.
In particular the composition is suitable for use in processes of spray irrigation where irrigation water is pumped to a spray manifold and sprayed over a very large crop area, for instance at least one hectare (ha), and even up to 100 ha. Such methods comprise pumping water through feed ducting and a mixing zone to a spray manifold supplying one or more spraying devices by which the water is sprayed onto the crop area to be irrigated, and the aqueous composition of the invention is metered into the water at or before the mixing zone. Processes of this general type are described in our unpublished PCT Application No. PCT/GB98/01763. In that application it is essential to supply polymer in the form of a dispersion of water-soluble polymer particles in a liquid. In the present case the polymer is of course included in the solution of fertiliser which is metered in the standard manner and thus this system is not necessary in the present case. However, other features of the system described in that application can however be applied herein.
The compositions of the invention may also be applied to lawns and soils generally associated with home and amenity gardening, such as flower beds, grass lawns, vegetable patches etc. The compositions are suitable for use in the processes of irrigation which use garden hoses, spray devices, lawn sprinklers, watering cans, drip and trickle systems (which involve applying water on a slow steady basis to the plant""s root zones to replace water which is lost by evaporation from the soil and transpiration by the plant) and other apparatus commonly used in this area of gardening.

Soil treatment compositions and their use

Abstract: (a) a calcium compound,

Ciba Specialty Chemicals Water Treatments Limited


The description is given of the use of particulate water-insoluble polymer preparations comprising at least one polymer P that is essentially made up of hydrophilic polymer segments and hydrophobic polymer segments as filter aids for filtering aqueous liquids.

The present invention relates to the use of particulate water-insoluble polymer preparations as filter aids for filtering aqueous liquids, and to a process for filtering aqueous liquids using these filter aids.
Separating solid-liquid mixtures by filtration is an important process step in many industrial production processes. In particular when aqueous liquids are filtered, filter aids are frequently used. Filter aids are particulate, for example granulated, pulverulent or fibrous substances which, depending on the type and amount of solids present in the liquid to be filtered, make it possible for a filter cake to build up or are intended to loosen this.
The action of the filter aid is based on developing capillaries in the filter cake which, firstly, are small enough to retain solids, but secondly are numerous enough in order to facilitate the outflow of the liquid phase. For this purpose the filter aid can be added to the suspension to be filtered (pulp) and/or the filter aid can be applied before the filtration as an auxilliary layer on the filter surface (filter cloth). In precoat filtration, for example before the start of filtration, a filter aid precoat is applied to a support surface (filter cloth). The filter aid is then added to the pulp, preferably continuously. During the filtration a loose filter cake of filter aid thus forms, which retains the pulp solids, so that the liquid dispersion medium can flow off as clear filtrate (see also xe2x80x9cRoempp Chemielexikonxe2x80x9d [Roempp""s chemistry lexikon], 9th edition, Georg Thiemer Verlag Stuttgart, pp. 1357 ff. for the terms filter aid and filtration).
Obviously, the filter aids should be chemically inert and insoluble in the pulp to be filtered. In addition, under the action of pressure, they should not deform, so that the pores in the filter cake do not collapse. Furthermore, it is desirable that the filter aids can be regenerated.
The most customary filter aids, in addition to organic substances such as cellulose, wood charcoal and wood powder, comprise inorganic materials, in particular of silicate nature, such as kieselguhr, pearlites, diatomaceous earths and bentonites. However, these materials have the disadvantage that they cannot be regenerated and therefore must be disposed of.
In the drinks industry especially, there is a great requirement for filter aids for aqueous liquids, since fruit juice drinks and fermented beverages such as beer are frequently subjected to filtration. A filter aid frequently used in the drinks industry is kieselguhr. In the production of beer, for example, from 150 to 200 g of filter aid, in particular kieselguhr, are required per hl of beer. Since the filtering action of these filter aids decreases after a certain time, they must be removed and, in the case of the non-regenerable filter aids, disposed of, which obviously is associated with high costs. In addition, a carcinogenic action of the kieselguhr used in the drinks industry is currently a subject of discussion.
There has therefore been no lack of attempts to provide synthetic filter aids. U.S. Pat. No. 4,344,846, for example, describes the use of expanded polystyrene in precoat filtration.
WO 96/35497 and EP 48309 describe filter aids for precoat filtration which are based on spherical, incompressible polymers, for example polyvinylpyrrolidone or Nylon 11, which form a filter cake having a porosity in the range from 0.3 to 0.5.
EP-A 879629 describes filter aids which consist of a particulate or fibrous support and a hydrophobic coating applied thereon.
EP-A 177812 and EP-A 351363 disclose highly crosslinked, scarcely swellable, pulverulent polymers based on N-vinylpyrrolidone which can be used as filter aids.
DE-A 19920944 describes insoluble, scarcely swellable popcorn polymers based on styrene and N-vinyllactams. The use of these popcorn polymers as filter aids is proposed.
The synthetic filter aids based on polymers have an improved regenerability. However, their filtering action sometimes leaves something to be desired. Some of the synthetic filter aids are again less suitable for precoat filtration of aqueous liquids, since they do not sediment in water, or only sediment poorly.
It is an object of the present invention to provide filter aids for filtering aqueous liquids, which filter aids have a good filtering action and are suitable for precoat filtration. In addition, good regenerability of the filter aids is desired.
We have found that this object is achieved, surprisingly, by particulate polymer preparations that comprise a polymer P that is made up of hydrophilic and hydrophobic polymer segements.
The present invention therefore relates to the use of particulate water-insoluble polymer preparations comprising at least one polymer P that is essentially made up of hydrophilic polymer segments and hydrophobic polymer segments, as filter aids for filtering aqueous liquids, in particular for precoat filtration. The invention also relates to a process for filtering aqueous liquids using such polymer preparations, in particular a process which is carried out by the method of precoat filtration.
In the polymers P used according to the invention, the polymer particles essentially consist of hydrophilic polymer segments and hydrophobic polymer segments. Polymer segments are understood by those skilled in the art to be polymer chains or polymer substructures that are made up of a plurality, generally at least 10, preferably at least 20, preferred according to the invention at least 30, identical repeat units. Hydrophobic polymer segments are accordingly polymer substructures or polymer chains that are made up of a plurality of hydrophobic monomer building blocks that are linked to one another. Correspondingly, hydrophilic polymer segments are polymer chains or polymer substructures that are made up of a plurality of hydrophilic monomer building blocks as repeat units. The hydrophilic and hydrophobic polymer segments can be bound to one another by chemical bonds in the manner of a block polymer or grafted polymer. They can also be present as an intimate physical mixture in the polymer P used according to the invention. It is important solely that the individual polymer particles of the polymer P are made up both of hydrophilic and of hydrophobic polymer segments.
For the inventive water insolubility it is advantageous if the proportion by weight of hydrophilic polymer segments does not exceed that of the hydrophobic polymer segments. Generally, therefore, the weight ratio of hydrophilic polymer segments to hydrophobic polymer segments in the polymer P is in the range from 1:1 to 1:100, preferably in the range from 1:2 to 1:50, and particularly preferably in the range from 1:3 to 1:20.
Furthermore, it has proved to be expedient if the hydrophilic polymer segments are of nonionic nature, that is to say have less than 0.1 mol/kg of ionic or ionogenic groups such as carboxylate, sulfonate or amino groups. Particularly preferably, the hydrophilic polymer segments have no ionic or ionogenic groups.
Examples of nonionic hydrophilic polymer segments are those that are made up of ethylenically unsaturated monomers having a water solubility above 50 g/l (at 25xc2x0 C., 1 bar), further polyvinylalcohol structures, and polyether chains. Examples of monomers having a water solubility above 50 g/l are methyl acrylate, acrylamide, methacrylamide, hydroxyalkyl acrylates and hydroxyalkyl methacrylates such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, N-vinylpyrrolidone, N-vinylcaprolactam, methyl vinyl ether and comparable monomers.
Preferred hydrophilic polymer segments have a polyether structure, in particular a poly-C2-C4-alkylene ether structure. Particularly preferably, the hydrophilic polymer segments are derived from polyethylene oxides, polypropylene oxides and/or polyethylene/polypropylene oxide block copolymers, for example block copolymers having a central polypropylene oxide segment and terminal polyethylene oxide segments.
It has further proved to be advantageous if the hydrophilic polymer segments, considered alone, have only limited water solubility. This is achieved, for example, via high molecular weights, for example greater than 10 000, preferably 50 000 daltons, and in particular 100 000 daltons, or by using hydrophilic segments of block-type structure that have oligomeric blocks of limited water solubility, for example polyethylene oxide/polypropylene oxide segments, the polypropylene block causing a reduction of the water solubility of the hydrophilic segment. Here, molecular weights in the range from 1 000 to 20 000 daltons are sufficient. Obviously, both measures can be combined with one another.
In a preferred embodiment of the invention, particulate polymers are used whose hydrophilic segments are selected from polyethylene oxide-polypropylene oxide block copolymers (EO/PO block copolymers), and in particular from triblock copolymers having a central polypropylene oxide block. The proportion of the polypropylene oxide block makes up preferably from 10 to 90% by weight, and in particular from 30 to 80% by weight, of the EO/PO block copolymer.
Preference is given to those particulate polymers in which the hydrophilic polymer segments are selected from the abovementioned polyalkylene oxides, in particular from polyethylene oxide/polypropylene oxide block copolymers, and the hydrophobic polymer segments are essentially formed from vinylaromatic monomers A.
The hydrophobic polymer segments are generally made up of ethylenically unsaturated hydrophobic monomers A. The hydrophobic nature of the monomer A is expressed in their low water solubility that generally does not exceed 10 g/l, and in particular does not exceed 1 g/l at 25xc2x0 C. Examples of hydrophobic monomers A are vinylaromatic monomers, esters of ethylenically unsaturated carboxylic acids such as acrylic acid or methacrylic acid with alcohols that have at least 2, preferably at least 4 carbon atoms, for example from 2 to 10 carbon atoms. Further examples of hydrophobic monomers A are olefins such as ethene and propene and diolefins such as butadiene. Preferred monomers A are the vinylaromatic monomers, in particular styrene, xcex1-methylstyrene and styrene derivatives having alkyl groups on the benzene ring, such as vinyl toluenes and 4-tert-butylstyrene. A particularly preferred vinylaromatic monomer A is styrene. Generally, the hydrophobic polymer segments contain less than 20% by weight, preferably less than 10% by weight, and in particular none, of copolymerized comonomers B that are different from the monomers A. Preferably, at least 80% by weight, in particular at least 90% by weight, and in particular all, monomers A are selected from vinylaromatic monomers. Any comonomers B which come into consideration are the abovementioned hydrophilic monomers, and other customary monomers that are copolymerizable with styrene, for example ethylenically unsaturated nitriles such as acrylonitrile, ethyl acrylate, methyl methacrylate or vinyl acetate.
In addition, it has proved to be advantageous if the hydrophobic polymer segments have a glass transition temperature above 50xc2x0 C., in particular above 70xc2x0 C., and particularly preferably above 80xc2x0 C. The glass transition temperature here is the mid-point temperature determined by DSC (see ASTM-D3418-82). A high glass transition temperature is advantageous, in particular, with regard to a desired low compressibility of the polymer P.
In addition, it has proved to be expedient if the particulate polymer preparations have particle sizes less than 1 mm, preferably in the range from 1 xcexcm to 700 xcexcm, in particular from 2 xcexcm to 500 xcexcm, and particularly preferably from 5 to 200 xcexcm. The values specified here are to be taken to mean that 90% by weight of the particles of the polymer preparation have a diameter in the specified range. The particle sizes can be determined in a conventional manner, for example by light scattering or by sieve methods.
The preparation of the polymer preparations to be used inventively is known in principle and is performed, depending on the desired particle size, by granulation, shredding and/or grinding polymers P and/or compounded materials that comprise further filter aids, or by drying, that is to say by removing the volatile constituents from a solution or suspension of the polymers P, which may comprise further filter aids. Preferably, aqueous dispersions/suspensions of the polymer P or of a mixture of the polymer P are used for drying.
The dispersions/suspensions to be dried can be not only aqueous primary dispersions but also secondary dispersions. Primary dispersions are prepared, as is known, by polymerizing hydrophobic monomer building blocks in an aqueous dispersion medium, preferably in the presence of hydrophilic polymers as surface-active substances. Secondary dispersions are obtained, for example, by dispersing polymers A prepared in a different manner, for example by solution polymerization or solvent-free polymerization, in the aqueous dispersion medium. Secondary dispersions can also be prepared by emulsifying a solution of the polymer P in an organic solvent in an aqueous emulsifying medium. These solutions are then converted into an aqueous dispersion or suspension by a known method. For this purpose a sufficient amount of water, for example, can be added to the polymer solutions and then the organic solvent can be removed, for example can be distilled off, preferably with a vacuum being applied. Suitable organic solvents for preparing the secondary dispersion are those that are able to dissolve the polymer containing hydrophilic and hydrophobic segments and which can be removed by distillation. The type of the respective solvent obviously depends on the type of hydrophilic and hydrophobic segments, and can be determined by a person skilled in the art by means of simple routine experiments.
Examples of suitable organic solvents are C1-C10 alkyl esters of aliphatic carboxylic acids, such as acetic acid or propionic acid, for example ethyl acetate, n-butyl acetate, tert-butyl acetate, aromatic hydrocarbons, such as toulene or tert-butylbenzene, ethers, such as tetrahydrofuran, dioxane or tert-butyl methyl ether, ketones such as acetone or methyl ethyl ketone, and the like.
The particulate polymers are then produced by removing the volatile components from the resultant aqueous dispersions by customary methods of powder production, for example by freeze-drying or by spray-drying, or, in the case of coarse suspensions, by filtration.
Polymers P containing hydrophilic segments and hydrophobic segments for preparing the particulate polymer prepararations to be used according to the invention are known from the prior art or can be prepared by customary methods.
For the inventive use, it has been found to be particularly advantageous if, for preparing the particulate polymer P, those polymers are used which have been prepared by one of the preparation methods described below:
i) polymerizing the hydrophobic monomer building blocks in the presence of at least one hydrophilic polymer, or
ii) polymerizing the hydrophilic monomer building blocks in the presence of at least one hydrophobic polymer.
Polymerization by method i), and also the polymerization by method ii) can be performed by the customary polymerization processes, for example by a polyaddition, polycondensation or a free-radical polymerization process, with the latter procedure generally being preferred.
Usually, to prepare the polymer P, those polymerization conditions are selected in which linkage occurs, that is to say development of chemical bonds between the polymer segments. In the case of polyaddition processes, therefore, preferably those polymers are used as a grafting base that have functional groups which can react with the monomer building blocks. In the case of free-radical polymerization processes, preferably a procedure is followed in such a manner that the grafting base used is a polymer which has graft-active carbon atoms and the polymerization conditions are chosen so that active grafting of the monomers to be polymerized to the introduced polymer occurs. Processes for this are known from the prior art.
Frequently, a polymer P is used which is obtainable by free-radical polymerization of ethylenically unsaturated hydrophobic monomers A, in the presence or absence of copolymers B which are different therefrom, in the presence of a hydrophilic polymer. This then forms in the polymer P the hydrophilic segments, whereas the hydrophobic segments are formed by the polymerized monomers A. In this procedure the abovementioned hydrophobic monomers A are reacted in the presence of a suitable hydrophilic polymer that preferably has the abovementioned characteristics.
Examples of hydrophilic polymers are therefore polyvinyl alcohols, homopolymers and copolymers which are predominantly made up of vinyllactams such as N-vinylpyrrolidone, polyvinyl methyl ethers and polyalkylene oxides, with the last-mentioned being preferred. Particular preference is given to the abovementioned polyethylene oxide/polypropylene oxide block copolymers and polyethylene oxides having molecular weights  greater than 10 000 daltons. Polymers of this type are, under free-radical polymerization conditions, sufficiently graft-active in order to ensure at least partial linkage of the hydrophilic polymer chains to the forming hydrophobic polymer chains.
The free-radical polymerization of the hydrophobic monomers in the presence of at least one hydrophilic polymer is preferably performed as solution polymerization in an organic solvent that is able to dissolve both components, or as solvent-free polymerization.
Generally, the free-radical polymerization is carried out in the presence of polymerization initiators which are customary for this that decompose on heating with the formation of free-radical polymerization centers. Examples of such compounds are organic peroxides, for example peresters of carboxylic acids, such as tert-amyl perpivalate, tert-butyl perpivalate, tert-butyl perneohexanoate, tert-butyl perisobutyrate, tert-butyl per-2-ethylhexanoate, tert-butyl perisononanoate, tert-butyl permaleate, tert-butyl perbenzoate, percarbonates, such as di-(2-ethylhexyl) peroxodicarbonate, dicyclohexyl peroxodicarbonate, di-(4-tert-butylcyclohexyl) peroxodicarbonate, in addition ketone peroxides, such as acetylacetoneperoxide, methyl ethyl ketone peroxide, hydroperoxides such as tert-butyl hydroperoxide and cumene hydroperoxide, in addition azo initiators such as 2-2xe2x80x2-azobis(amidinopropane) dihydrochloride, 2,2xe2x80x2-azobis(N,Nxe2x80x2-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutyronitrile, 2,2-azobisisobutyronitrile, or 4,4xe2x80x2-azobis(4-cyanovaleric acid). Initiators of this type are generally used in an amount of from 0.01 to 5% by weight, and preferably in an amount of from 0.05 to 2.0% by weight, based on the amount of monomers to be polymerized. The polymerization temperature required depends, in a known manner, on the type of monomers to be polymerized and is usually in the range from 20xc2x0 C. to 200xc2x0 C., in particular in the range from 50 to 180xc2x0 C. Depending on the type of solvent used and on the type of monomers, pressure vessels are employed to reach the polymerization temperature. However, frequently, operation at atmospheric pressure is also possible.
If the free-radical polymerization is carried out as solution polymerization, the customary solvents come into consideration for this, preferably the abovementioned solvents, such as diesters of aliphatic carboxylic acids, for example diesters of acetic acid and/or diesters of propionic acid, aromatic hydrocarbons or ketones such as acetone or methyl ethyl ketone. Solution polymerization in addition has the advantage that the resultant polymer solutions can be converted directly into aqueous dispersions of the resultant polymers, which themselves are preferred for preparing the polymer powders.
The starting materials depend on the respective polymerization process, obviously in accordance with the desired composition, that is to say the type and amount of hydrophobic monomer building blocks correspond to the type and proportion by weight of the hydrophobic polymer segments, and the type and amount of the hydrophilic polymers correspond to the type and amount of the hydrophilic polymer segments in the polymer P.
The particulate polymers P to be used according to the invention are distinguished by good filtration action and, in contrast to the customary filter aids, can be more easily regenerated. In addition, they have improved sedimentation in water, so that they are suitable in particular as filter aids for precoat filtration of aqueous liquids.
The polymer preparations to be used according to the invention can consist solely of the polymer P. However, they can also comprise other conventional filter aids. The content of these conventional filter aids will generally not exceed 80% by weight, preferably 50% by weight of the total amount of polymer P and conventional filter aid.
Conventional filter aids are selected from the abovementioned silicate filter aids and the polymeric filter aids. Preference is given to polymeric filter aids such as crosslinked polyvinylpyrrolidone, polystyrenes or polyamides. In a preferred embodiment, the polymer preparations to be used comprise:
a. from 10 to 95% by weight, in particular from 15 to 80% by weight, particularly preferably from 25 to 70% by weight, of at least one polymer P, and
b. from 90 to 5% by weight, in particular from 85 to 20% by weight, particularly preferably from 30 to 75% by weight, of at least one further conventional filter aid.
Preferred conventional filter aids for these uses are selected from synthetic filter aids based on organic polymers, in particular based on styrene polymers and/or polyamides.
The term xe2x80x9cstyrene polymerxe2x80x9d is to be taken to mean the entire group of xe2x80x9cstyrene homopolymers and copolymersxe2x80x9d, as described in A. Aechte; Handbuch der technischen Polymerchemie [Handbook of Industrial Polymer Chemistry], VCH Weinheim 1993. This definition includes both homopolystyrene and copolymers of styrene, in particular with acrylonitrile, maleic anhydride, with acrylate and similar comonomers, and their rubber-modified or toughened derivatives. Suitable polyamides include, in particular, Nylon 12.
The present invention also relates to a process for filtering aqueous liquids, in particular to a process which is carried out by the method of precoat filtration. Owing to their chemical inertness, the polymer powders to be used according to the invention are suitable in particular for use in the food industry, for example for filtering fruit juice drinks and fermented beverages. Owing to their good filtration action, the polymer powders to be used according to the invention are particularly suitable for filtering beer.
The filtration processes can be carried out in a similar manner to the filtration methods of the prior art described at the outset using the above-described polymer powders as filter aids.
In the case of precoat filtration, generally, before the start of filtration, a precoat of the polymer powders to be used according to the invention are applied to a support surface (filter cloth). The liquid to be filtered is then passed through the filter layer by applying a pressure difference, with further polymer powder to be used according to the invention preferably being added as filter aid to the liquid to be filtered during the filtration operation.

Use of particulate polymers as filter aids for aqueous liquids


A method for making supported single-site catalysts useful for olefin polymerization is disclosed. An organometallic complex that contains a nitrogen-functional heterocyclic ligand is first prepared and reacted with an alumoxane. This product is then combined, preferably with high-intensity mixing, with a slurry of inorganic support, followed by solvent removal to give a supported catalyst. By introducing the alumoxane at the right time during preparation, and by judicious selection and chemical treatment of the inorganic support, one can make catalysts with high activity and good aging properties. The supported catalysts give olefin polymers with a favorable balance of physical properties, including low density, narrow molecular weight distribution, good melt-flow properties, and high bulk density.

The invention relates to catalysts useful for olefin polymerization. In particular, the invention relates to an improved method for preparing supported xe2x80x9csingle-sitexe2x80x9d catalysts based on heterocyclic ligands such as carbazolyl and quinolinoxy ligands.
While Ziegler-Natta catalysts are a mainstay for polyolefin manufacture, single-site (metallocene and non-metallocene) catalysts represent the industry""s future. These catalysts are often more reactive than Ziegler-Natta catalysts, and they produce polymers with improved physical properties. The improved properties include narrow molecular weight distribution, reduced low molecular weight extractables, enhanced incorporation of xcex1-olefin comonomers, lower polymer density, controlled content and distribution of long-chain branching, and modified melt rheology and relaxation characteristics.
Metallocenes commonly include one or more cyclopentadienyl groups, but many other ligands have been used. Putting substituents on the cyclopentadienyl ring, for example, changes the geometry and electronic character of the active site. Thus, a catalyst structure can be fine-tuned to give polymers with desirable properties. xe2x80x9cConstrained geometryxe2x80x9d or xe2x80x9copen architecturexe2x80x9d catalysts have been described (see, e.g., U.S. Pat. No. 5,624,878). Bridging ligands in these catalysts lock in a single, well-defined active site for olefin complexation and chain growth.
Other known single-site catalysts replace cyclopentadienyl groups with one or more heteroatomic ring ligands that are pi-electron donors, such as boraaryl (see, e.g., U.S. Pat. No. 5,554,775 or azaborolinyl groups (U.S. Pat. No. 5,902,866).
U.S. Pat. No. 5,539,124 (hereinafter xe2x80x9cthe ""124 patentxe2x80x9d) and U.S. Pat. No. 5,637,660 teach the use of anionic, nitrogen-functional heterocyclic groups such as indolyl, carbazolyl, 2-pyridinoxy or 8-quinolinoxy as ligands for single-site catalysts. These ligands, which are produced by simple deprotonation of inexpensive and readily available precursors, are easily incorporated into a wide variety of transition metal complexes. When used with common activators such as alumoxanes, these catalysts polymerize olefins to give products with narrow molecular weight distributions that are characteristic of single-site catalysis.
One drawback of the catalysts described above is their relatively low activity. Normally, a large proportion of an alumoxane activator must be used to give even a low-activity catalyst system. For example, in the ""124 patent, Example 16, a bis(carbazolyl)zirconium complex is used in combination with methylalumoxane at an aluminum:zirconium mole ratio [Al:Zr] of 8890 to 1 to give a catalyst having a marginally satisfactory activity of 134 kg polymer produced per gram Zr per hour. The activator is expensive, and when it is used at such high levels, it represents a large proportion of the cost of the catalyst system. Ideally, much less activator would be needed to give a catalyst system with better activity. Recently, I developed an improved way to make organometallic complexes based on heterocyclic ligands and useful for olefin polymerization (see copending application Ser. No. 09/716,954, filed Nov. 21, 2000).
An unresolved challenge relates to maintaining high activity, long catalyst lifetime, and favorable polyolefin properties when the complex is used with a support. Often, combining a complex with silica, alumina, or other common supports results in a dramatic loss of catalyst activity or lifetime. These issues are not addressed in the ""124 patent, which talks only in generalities about catalyst supports and provides no actual example in which a supported catalyst is used. Moreover, while application Ser. No. 09/716,954 indicates that supports can be used, the application provides no examples of how to make supported catalysts that maintain a high level of performance.
In sum, there is a continuing need for single-site catalysts that can be prepared inexpensively and in short order from easy-to-handle starting materials and reagents. In particular, there is a need for ways to make supported catalysts that have high activities and good aging properties even at low activator levels. Ideally, the supported catalysts would produce polyolefins with desirable physical properties such as low density, narrow molecular weight distribution, favorable melt-flow characteristics, and high bulk density.
The invention is a five-step method for making supported single-site catalysts useful for olefin polymerization. First, a nitrogen-functional heterocycle is deprotonated to produce an anionic ligand precursor. The heterocycle is an indole, carbazole, 8-quinolinol, 2-pyridinol, or a mixture thereof. In the second step, the anionic ligand precursor reacts with about 0.5 equivalents of a Group 4 transition metal compound in a hydrocarbon solvent to give a mixture that contains the desired organometallic complex. Third, the mixture is reacted with an alumoxane activator, preferably using high-intensity mixing. Fourth, the product from step three is combined with a hydrocarbon slurry of an inorganic support. Finally, the solvents are removed to give a solid, supported catalyst.
The invention includes supported catalysts made by this method as well as olefin polymerization processes that use the catalysts. The supported catalysts actively polymerize olefins, even when used with an exceptionally low level of an activator.
I surprisingly found that introducing the alumoxane at the right time during preparation is crucial for making highly active, supported catalysts with good aging characteristics. Moreover, by judicious selection and chemical treatment of the inorganic support, one can further improve the catalysts. The supported catalysts give olefin polymers with a favorable balance of physical properties, including low density, narrow molecular weight distribution, good melt-flow properties, and high bulk density.
Although they defy easy characterization by common analytical techniques, supported catalysts prepared by the method of the invention are considered to be xe2x80x9csingle sitexe2x80x9d in nature, i.e., they incorporate distinct chemical species rather than mixtures of different species. They qualify as single-site catalysts because they typically give polyolefins with characteristically narrow molecular weight distributions (Mw/Mn less than 3) and good, uniform comonomer incorporation.
The supported catalysts include a complex that contains a Group 4 transition metal, M, i.e., titanium, zirconium, or hafnium. Preferred complexes include titanium or zirconium. The catalysts often include some unreacted starting materials and by-products, e.g., alkali metal or alkaline earth metal salts derived from the deprotonating agent.
In one aspect, the invention is a five-step method for preparing a supported catalyst. In the first step, a nitrogen-functional heterocycle is deprotonated. Suitable nitrogen-functional heterocycles are indoles, carbazoles, 8-quinolinols, and 2-pyridinols. These compounds can have substituents that do not interfere with deprotonation or the subsequent reaction with the transition metal compound. Many of these compounds are commercially available or are easily synthesized. For example, indole, carbazole, 8-quinolinol, and 2-pyridinol are all inexpensive and commercially available, and many indoles are easily made from arylhydrazones of aldehydes or ketones and a Lewis acid using the well-known Fischer indole synthesis (see J. March, Advanced Organic Chemistry, 2d ed. (1977), pp. 1054-1055, and references cited therein). Additional examples of suitable nitrogen-functional heterocycles are described in U.S. Pat. Nos. 5,637,660 and 5,539,124, the teachings of which are incorporated herein by reference.
Any suitable base can be used to deprotonate the nitrogen-functional heterocycle. Examples are alkyllithium compounds (e.g., methyllithium or n-butyllithium), alkali metals (e.g., sodium metal), alkali metal hydrides (e.g., potassium hydride), and Grignard reagents (e.g., methyl magnesium chloride or phenyl magnesium bromide). Alkyllithium compounds are preferred. These can be made by reacting lithium with an alkyl halide, but more often they are purchased as solutions in a hydrocarbon (e.g., toluene or hexanes) or ether (e.g., diethyl ether or tetrahydrofuran) solvent. Preferred alkyllithium compounds are C1-C8 alkyllithiums such as methyllithium, isopropyllithium, n-butyllithium, or t-butyllithium. n-Butyllithium is particularly preferred because it is readily available, relatively easy to handle, and effective.
Usually, equimolar amounts of the deprotonating agent and the nitrogen-functional heterocycle are used to produce the anionic precursor. Deprotonation can be performed at any suitable temperature, preferably at or below room temperature. While the deprotonation reaction can be performed at temperatures as low as xe2x88x9278xc2x0 C. or below, it is preferred to perform this step at room temperature. Vigorous mixing is often essential because alkali metal or alkaline earth metal salts of the anionic ligand tend to precipitate and form a thick slurry. The reaction is usually complete within an hour or two. The resulting anionic ligand precursor includes a carbazolyl, indolyl, 8-quinolinoxy, or 2-pyridinoxy anion and an alkali metal or alkaline earth metal cation.
In Step 2, the anionic ligand precursor reacts with a Group 4 transition metal compound, preferably a tetrahalide. Suitable Group 4 transition metal compounds include zirconium, titanium, or hafnium, and four anionic ligands, which may the the same or different. The anionic ligand is preferably halide, hydride, or C1-C20 alkoxy, siloxy, dialkyamido, hydrocarbyl, or the like. Tetrahalides, such as zirconium tetrachloride or titanium tetrabromide, are especially preferred.
Reaction of about 0.5 equivalents of the Group 4 transition metal compound with one equivalent of the anionic ligand precursor gives an organometallic complex-containing mixture that includes the desired bis(carbazolyl), bis(indolyl), bis(2-pyridinoxy) or bis(8-quinolinoxy) complex. Complexes with mixed nitrogen-functional ligands (e.g., carbazolyl(8-quinolinoxy)zirconium dichloride) are conveniently made either by stepwise reaction of the Group 4 transition metal compound with two different anionic ligand precursors, or by deprotonating a mixture of the ligand precursors and reacting the mixture of anions with the Group 4 transition metal compound.
Preferred organometallic complexes have the general structure LLxe2x80x2MX2, wherein M is zirconium or titanium, X is halide, hydride, or C1-C20 alkoxy, siloxy, dialkyamido, hydrocarbyl, and each of L and Lxe2x80x2, which may be the same or different, is selected from the group consisting of indolyl, carbazolyl, 8-quinolinoxy, and 2-pyridinoxy. More preferably, X is a halide such as Cl or Br.
In another method of the invention, the anionic ligand precursor is reacted with about one equivalent of a xe2x80x9cCp-likexe2x80x9d (e.g., cyclopentadienyl, indenyl, or fluorenyl) Group 4 transition metal compound, preferably a trihalide. The Group 4 transition metal compound is conveniently made according to well-known methods, such as by reacting a cyclopentadienyl, indenyl, or fluorenyl anion with a Group 4 transition metal tetrahalide. The finished organometallic complex includes a Cp-like ligand, a nitrogen-functional ligand, and two other anionic ligands. Examples 22-28 below illustrate this method.
In any event, the complex-forming reaction is preferably performed at temperature greater than about 10xc2x0 C., which is not only convenient, but gives the best results. More preferably, the reaction occurs at a temperature within the range of about 15xc2x0 C. to about 60xc2x0 C.; most preferably, the reaction is simply performed at room temperature. The reaction is usually complete within a few hours, but it is often convenient and desirable to allow the reaction to proceed overnight (about 16-18 hours) at room temperature.
The preparation of the organometallic complex-containing mixture is performed in the presence of a first hydrocarbon solvent. Preferred hydrocarbons are aromatic, aliphatic, and cycloaliphatic hydrocarbons having from 4 to 30 carbons, preferably 4 to 12 carbons, because these are conveniently removed from the mixture. Examples include pentanes, hexanes, cyclohexane, octanes, toluene, xylenes, and the like, and mixtures thereof. Toluene is particularly preferred.
When the reaction is complete, the mixture can be concentrated (although this is not preferred) by solvent removal under a stream of nitrogen or with vacuum stripping to give a solid residue that contains the desired organometallic complex in addition to some unreacted starting materials and some by-products. This residue commonly contains as much as 50 wt. % of recovered starting material (e.g., carbazole). Nonetheless, as shown in copending application Ser. No. 09/716,954, the residue can be used without purification in a subsequent olefin polymerization. For many olefin polymerization processes, however, it is desirable to use a supported catalyst. When, as here, a supported catalyst is the target, the solvent is preferably not removed at this stage of the process, and the solution or slurry is used xe2x80x9cas isxe2x80x9d in the next step.
In Step 3, the organometallic complex-containing mixture reacts with an alumoxane activator. Suitable alumoxanes are well known in the art. Examples include methyl alumoxane (MAO or PMAO), modified methyl alumoxane (MMAO), ethyl alumoxane, diisobutyl alumoxane, and the like, and mixtures thereof. Methyl alumoxane and modified methyl alumoxane are preferred.
The amount of alumoxane activator needed relative to the amount of organometallic complex depends on many factors, including the nature of the complex and activator, the desired reaction rate, the kind of polyolefin product, the reaction conditions, and other factors. Generally, however, the amount used will be within the range of about 0.01 to about 500 moles, preferably from about 0.1 to about 300 moles, of aluminum per mole of Group 4 metal, M. When MAO is used, it is preferably used at a [Al:M] molar ratio of less than about 500, more preferably less than about 300.
The ability to use low levels of an activator is a key advantage of the invention. As the examples below illustrate, MAO can be used at much lower levels than previously employed. While MAO is commonly used at [Al:M] molar ratios in the thousands (see U.S. Pat. No. 5,539,124 at Examples 16 and 22), I have now found that molar ratios as low as [Al:M]=200 or below can give catalysts with excellent activity when the supported complex is prepared as described herein. This is a valuable discovery because the activator is a major contributor to overall catalyst cost, and ways to reduce its use have long been sought by the industry.
An important aspect of the invention is the timing of the reaction of the complex with the alumoxane (see Table 1, below). I surprisingly found that the alumoxane needs to be combined and reacted with the organometallic complex before either component is combined with the support (xe2x80x9cMethod Axe2x80x9d). If the alumoxane is combined with the support first, and the alumoxane-treated support is then reacted with the organometallic complex (xe2x80x9cMethod Bxe2x80x9d), a less active catalyst results, and polymers made from the catalyst have lower melt indices and lower bulk density. Moreover, if the alumoxane is added directly to the reactor (xe2x80x9cMethod Cxe2x80x9d) rather than first combining it with the organometallic complex, a similar penalty results.
After the complex-containing mixture is reacted with an alumoxane, the product is combined with a slurry of an inorganic support in a second hydrocarbon solvent (Step 4). The second hydrocarbon, which may be the same as or different from the first hydrocarbon, is one or more hydrocarbons selected from the solvents described earlier. Thus, the second hydrocarbon is preferably an aromatic, aliphatic, or cycloaliphatic hydrocarbon having from 4 to 30 carbons.
Suitable inorganic supports include silicas, aluminas, silica-aluminas, magnesias, titanias, magnesium halides, and the like. A variety of different inorganic supports can be used with the method of the invention, but silicas are preferred because many varieties are inexpensive and readily available. Particularly preferred silicas have surface areas greater than about 500 m2/g and pore volumes greater than about 2.9 mL/g. An example is MS 3050 silica, a product of PQ Corporation. As Example 1 (Table 1) below demonstrates, the most active catalysts are made with high-surface-area silica. Also suitable, although less preferred, are silicas that have somewhat lower surface areas (e.g., within the range of 280 to 350 m2/g) and somewhat lower pore volumes (e.g., within the range of 1.5 to 2.0 mL/g) such as Davison 948 silica (see Examples 4 and 7, Table 1).
The loading of complex on the support varies depending upon a number of factors, including the identities of the complex and the support, the type of olefin polymerization process used, the reaction conditions, and other concerns. Usually, the amount of complex used is within the range of about 0.01 to about 10 wt. % of Group 4 transition metal based on the amount of supported catalyst. A more preferred range is from about 0.1 to about 4 wt. %.
The support is preferably treated thermally, chemically, or both prior to use to reduce the concentration of surface hydroxyl groups. Thermal treatment consists of heating (or xe2x80x9ccalciningxe2x80x9d) the support in a dry atmosphere at elevated temperature, preferably greater than about 100xc2x0 C., and more preferably from about 150 to about 600xc2x0 C., prior to use. A variety of different chemical treatments can be used, including reaction with organo-aluminum, -magnesium, -silicon, or -boron compounds. See, for example, the techniques described in application Ser. No. 09/318,008, filed May 25, 1999, now allowed, the teachings of which are incorporated herein by reference.
In a preferred method, a high-surface-area silica support is first calcined at a temperature less than about 200xc2x0 C., and is then slurried in a hydrocarbon solvent and treated with a dialkylmagnesium compound such as di-n-butylmagnesium or butylethylmagnesium. The treated slurry is then combined with the reaction product of the alumoxane and organometallic complex, followed by solvent removal, to produce the supported catalyst. As shown in Table 2 below, treatment of the silica support with a dialkylmagnesium compound can improve catalyst activity dramatically (compare Examples 1 and 10 or Examples 4 and 11). The degree of activity improvement, however, depends somewhat on the choice of support (see Examples 7 and 14). Table 2 below shows examples of various support treatment reagents that can be used.
Heat treatment during Step 4 sometimes helps activity (see Table 4, Examples 7 and 21) and sometimes hinders it (see Examples 1 and 19 or Examples 4 and 20). The results depend on how the support is thermally and/or chemically modified prior to exposure to heat.
Mixing intensity is also important. I found that high-intensity mixing is needed during Step 4 to produce catalysts with the highest activities (see Table 3). Mechanical stirring at high rates (i.e., greater than about 300 revolutions per minute (RPM)) is preferred. Other high-intensity mixing methods such as homogenization (see, e.g., U.S. Pat. No. 5,470,813, the teachings of which are incorporated herein by reference) or impingement mixing can also be used.
In Step 5 of the method of the invention, solvents are removed from the slurry to give a solid, supported catalyst that is useful for olefin polymerization. Any desired method can be used for solvent removal. Common techniques include simple distillation, vacuum distillation, rotary evaporation, thin-film evaporation, or the like. Heating under a flow of inert gas (e.g., dry nitrogen or argon) with or without vacuum is an effective way to convert the liquid slurry to a free-flowing powder.
Storage stability is another advantage of catalyst systems prepared by the method of the invention. As the results in Table 6 below confirm, aging has a dramatic negative effect on the activity of supported catalysts made using the complexes described in U.S. Pat. No. 5,539,124. In contrast, supported catalysts made by the method of the invention retain excellent activity, even after 90 days of storage.
As Table 7 shows, the catalyst preparation method of the invention is versatile. Excellent results are obtained with a variety of organometallic complexes that incorporate nitrogen-functional heterocyclic and Cp-like ligands such as cyclopentadienyl or indenyl.
Catalysts made by the method of the invention are particularly valuable for polymerizing olefins. Preferred olefins are ethylene and C3-C20 xcex1-olefins such as propylene, 1-butene, 1-hexene, 1-octene, and the like. Mixtures of olefins can be used. Ethylene and mixtures of ethylene with C3-C10 xcex1-olefins are especially preferred.
Many types of olefin polymerization processes can be used. Preferably, the process is practiced in the liquid phase, which can include slurry, solution, suspension, or bulk processes, or a combination of these. High-pressure fluid phase or gas phase techniques can also be used. The process of the invention is particularly valuable for solution and slurry processes.
The olefin polymerizations can be performed over a wide temperature range, such as about xe2x88x9230xc2x0 C. to about 280xc2x0 C. A more preferred range is from about 30xc2x0 C. to about 180xc2x0 C.; most preferred is the range from about 60xc2x0 C. to about 100xc2x0 C. Olefin partial pressures normally range from about 15 psig to about 50,000 psig. More preferred is the range from about 15 psig to about 1000 psig.
The following examples merely illustrate the invention. Those skilled in the art will recognize many variations that are within the spirit of the invention and scope of the claims.
Complex Preparation (Steps 1 and 2). Carbazole (5.0 g, 30 mmol) is stirred in a flask under an atmosphere of nitrogen in a dry box for 15 min. Toluene (120 mL) is added, and the mixture is stirred for 30 min. n-Butyllithium (12 mL of 2.5 M solution in hexane, 30 mmol) is added by syringe over 5 min. to the stirred carbazole solution. The mixture is stirred at room temperature for 2 h. The mixture turns light pink, and the slurry becomes thick, requiring vigorous stirring. Zirconium tetrachloride (3.50 g, 15 mmol) and more toluene (25 mL) are added to the flask, and the mixture turns brown. Stirring is continued at room temperature for another 18 h, after which the mixture is black-brown-green. Solvents are removed under a flow of nitrogen, and the residue is vacuum dried for 3 h. A yellow solid (9.25 g) that contains 81 wt. % of the desired bis(carbazolyl) complex (15.1 wt. % Zr) is isolated.
Supporting the Complex.
A round-bottom flask is charged with MS 3050 silica (5.0 g, product of PQ Corporation) that has been calcined at 150xc2x0 C. for 2 h prior to use (designated xe2x80x9cS3xe2x80x9d herein), and the silica is stirred under a flow of nitrogen at 100 RPM at room temperature for 15 min. Heptane (35 mL) is added, and the slurry is stirred at 200 RPM under nitrogen for 0.5 h. Di-n-butylmagnesium (5.0 mL of 10 wt. % solution in heptane, product of Akzo-Nobel) is added to the silica slurry, and the mixture is stirred at 250 RPM under nitrogen, still at room temperature, for 0.5 h.
In a separate flask, the organometallic complex-containing mixture prepared above (0.107 g, contains 0.0867 g of bis(carbazolyl)zirconium dichloride, 0.175 mmol) and toluene (10 mL) are stirred at 250 RPM under nitrogen at room temperature for 10 min. Methyl alumoxane (8.0 mL of 4.38 M solution in toluene, 35 mmol, [Al:Zr=200]) is added, and the mixture is stirred at 250 RPM for 20 min (Step 3). The complex/MAO mixture is transferred into a syringe in a dry box.
The complex/MAO mixture is added slowly to the treated silica slurry over 10 min. with rapid (350 RPM) agitation (Step 4); stirring at 350 RPM at room temperature continues for 1 h. The stirring rate is reduced to 250 RPM, and stirring continues for 15 h. The solvents are removed (Step 5) under a flow of nitrogen with stirring at 150 RPM, and the resulting powder is further dried under vacuum for 20 min. The supported catalyst is a light-yellow solid (yield: 9.50 g).
The bis(carbazolyl)zirconium dichloride complex is prepared as described in Method A.
The procedure for supporting the complex is modified as follows: Immediately following di-n-butylmagnesium treatment of the silica, the MAO (8.0 mL of 4.38 M solution in toluene, 35 mmol) is added to the treated silica, and the mixture is stirred at 250 RPM under nitrogen for 20 min.
The organometallic complex/toluene mixture (without any MAO), is added slowly by syringe to the MAO/di-n-butylmagnesium-treated silica over 10 min. at 350 RPM.
The rest of the procedure described earlier is followed to isolate a solid, supported catalyst (9.5 g; light yellow).
The bis(carbazolyl)zirconium dichloride complex is prepared as described in Method A.
The procedure for supporting the complex is modified as follows: No MAO is used in making the supported catalyst. Otherwise, the procedure is identical to that described in Method A.
The procedure of Method A is modified by including a heating step as follows: After adding the MAO/organometallic complex mixture to the n-butylmagnesium-treated silica slurry, and after the one-hour stir period, the reaction mixture is heated at 50xc2x0 C. for 1 h while stirring at 300 RPM. The mixture is then stirred for 15 h at room temperature, and the solid, supported catalyst is isolated as described earlier.
Ethylene, isobutane, and nitrogen are dried prior to use with 13xc3x97 molecular sieves. A 2-L stainless-steel reactor is preconditioned by heating it to 120xc2x0 C. and maintaining that temperature for 20 min. under a flow of nitrogen. 1-Hexene (100 mL) is then added to the reactor.
Triisobutylaluminum (0.5 mL or 3.0 mL of a 0.9 M solution in heptane, 0.45 or 2.7 mmol; the amount used depends upon the moisture level of the feedstock and the reactor system) is charged to one side of a two-side injector. The other side of the injector is charged with the supported catalyst (50-100 mg) and toluene (1.0-2.0 mL).
The triisobutylaluminum solution is flushed into the reactor with isobutane (750 mL). The agitator is started, and the temperature controller is set to maintain a constant reactor temperature of 75xc2x0 C.
The reactor is pressurized with ethylene to 400 psig. The supported catalyst is then flushed into the reactor along with more isobutane (50 mL) to initiate the polymerization. Ethylene is fed on demand using a Brooks mass flow meter to maintain a pressure of 400 psig in the reactor. The concentration of ethylene in the isobutane is about 13 mole %. The polymerization continues at 75xc2x0 C for 0.5 to 1 hour, and is then terminated by closing the ethylene feed valve and venting the reactor. The resulting polyethylene is collected and dried under vacuum at 50xc2x0 C.
The procedure described in the preceding paragraphs is followed except that the methyl alumoxane, rather than being a component of the supported catalyst, is introduced directly into the reactor at the start of the polymerization. Thus, the reactor is charged with comonomer (1-butene or 1-hexene), and then the triisobutylaluminum solution is flushed into the reactor from one side of a two-sided injector with isobutane (750 mL). After the reactor is pressurized with ethylene, a mixture of MAO (less than 0.1 mL of 4.38 M solution in toluene; the amount is based on [Al:Zr=200]), and the supported catalyst suspended in toluene is charged immediately into the reactor from the other side of the injector along with more isobutane (50 mL), and the polymerization begins. The polyethylene product is isolated as described above.

Supported single-site catalysts useful for olefin polymerization