A prosthetic facet joint having compression springs interposed between articulating surfaces for providing gradual resistance to extreme movements.

One of the most common surgical interventions in spine today is arthrodesis, or spine fusion, in which two or more adjacent vertebral bodies are fused together in order to alleviate pain associated with the disc(s) located between those vertebral bodies. Approximately 300,000 such procedures are performed annually in the United States alone. Clinical success varies considerably, depending upon technique and indications, and consideration must be given to the concomitant risks and complications.
While spine fusion generally helps to eliminate certain types of pain, it has also been shown to decrease function by limiting the range of motion for patients in flexion, extension, rotation and lateral bending. Furthermore, it is believed that spine fusion creates increased stresses on (and, therefore, accelerated degeneration of) adjacent non-fused motion segments. Additionally, pseudoarthrosis, resulting from an incomplete or ineffective fusion, may reduce or even totally eliminate the desired pain relief for the patient. Also, the fusion device(s) used to effect fusion, whether artificial or biological, may migrate out of the fusion site, thereby creating significant new problems for the patient. Lastly, the recuperation time after a fusion procedure can be lengthy.
Recently, several attempts have been made to recreate the natural biomechanics of the spine through the use of an artificial disc. Artificial discs are intended to restore articulation between vertebral bodies so as to recreate the full range of motion normally allowed by the elastic properties of the natural disc, which directly connects two opposed vertebral bodies. However, the artificial discs developed to date do not fully address the mechanics of motion of the spinal column.
In addition to the foregoing, posterior elements called the facet (or zygapophyseal) joints help to support axial, torsional and shear loads that act on the spinal column. Furthermore, the facet joints are diarthroidal joints that provide both sliding articulation and load transmission features. The facet's articular surfaces contact in extension, limiting extension and increasing compressive load. The articular surfaces also contact on one side of the spine in lateral bending and axial rotation, also limiting rotation and transferring load.
However, the facet joints can also be a significant source of spinal disorders and, in many cases, debilitating pain. The articular cartilaginous surfaces can degenerate due to mechanical or biological factors and cause pain as with other joint osteoarthritis, or enlarge and produce stenosis. For example, a patient may suffer from arthritic facet joints, severe facet joint tropism or otherwise deformed facet joints, facet joint injuries, etc. There is currently a lack of suitable intervention procedures for facet joint disorders. Facetectomy, or the removal of the facet joints, may provide some relief, but is also believed to significantly decrease the stiffness of the spinal column (i.e., hypermobility) in all planes of motion: flexion and extension, lateral bending, and rotation. Furthermore, problems with the facet joints can also complicate treatments associated with other portions of the spine. By way of example, contraindications for artificial discs include arthritic facet joints, absent facet joints, severe facet joint tropism or otherwise deformed facet joints. Accordingly, there is a need for a facet joint replacement that addresses these concerns.
U.S. Pat. No. Re. 36,758 (Fitz I) discloses an artificial facet joint where the inferior facet, the mating superior facet, or both, are simply covered with a cap. Because placement of the cap requires no preparation of the bone or articular surfaces; it covers and, therefore, preserves the bony and articular structures.
However, simple capping of the facet has several potential disadvantages. If the facet joint is osteoarthritic, a cap will not remove the source of the pain. Additionally, at least in the case of surface replacements for osteoarthritic femoral heads, the capping of articular bone ends has proven to lead to clinical failure due to mechanical loosening. This clinical failure is hypothesized to be a consequence of disrupting the periosteum and ligamentum teres femoris, both of which play a role in delivering nutrition to the femoral head, thereby leading to avascular necrosis of the bony support structure for the surface replacement. It is possible that corresponding problems could develop from capping the facet. Another potential disadvantage of facet capping is that in order to accommodate the wide variability in anatomical morphology of the facets, not only between individuals but also between levels within the spinal column, as well as due to associated hypertrophic and degenerative changes, a very wide range of cap sizes and shapes is required, or significant reshaping.
U.S. Pat. No. 6,132,464 ("Martin") describes a replacement of the articular surfaces and means for supporting and fixing these replacements to the posterior processes. The articulating surface itself is described as having "the shape, position, and orientation of a natural articular facet". It discloses a spinal facet joint prosthesis that is supported on the lamina (which is sometimes also referred to as the posterior arch). Extending from this support structure are inferior and/or superior blades that replace the cartilage at the facet joint. The prosthesis of U.S. Pat. No. 6,132,464 generally preserves existing bony structures and therefore does not address pathologies which affect the bone of the facets in addition to affecting the associated cartilage. Furthermore, the prosthesis of U.S. Pat. No. 6,132,464 requires a secure mating between the prosthesis and the lamina. However, the lamina is a very complex and highly variable anatomical surface. As a result, in practice, it is very difficult to design a prosthesis that provides reproducible positioning against the lamina so as to correctly locate the cartilage-replacing blades for the facet joints.
The U.S. Pat. No. 6,132,464 patent describes articular surfaces and means of attachment, but does not describe a capsular replacement.
U.S. Pat. No. 5,571,191 ("Fitz II") describes a facet prosthesis comprising superior and inferior components, pyramidal or conical in shape, fitting over the facet processes, and having low friction mating surfaces. Although this patent describes articular surfaces and means of attachment, it does not describe a capsular replacement.
Gardner et al. Eur. Spine J (2002) (Supp 2): S157-163, discloses Graf ligamentoplasty as a means of stabilizing and reducing mobility of one or more severely symptomatic motion segments associated with degenerative disc disease. FIG. 1 shows Polyester bands wrapped around a pair of pedicle screws extending from adjacent vertebral bodies. This ligament also appears to be disclosed in U.S. Pat. No. 5,092,866 ("Breard"). According to Gardner, appropriate Graf bands immobilizes the motion segment in lordosis with the facet joints in a position of full extension, in which position they are very stable. See page S159. Accordingly, Graf ligamentoplasty essentially immobilizes the facet joint. Gardner does not disclose a mobile ligament that traverses a facet joint.
Senegas et al., Eur. Spine J. (2002) 11 (Supp 2): S164-9 discloses a Wallis implant system comprising a titanium interspinous blocker and a Dacron ligament, wherein the blocker is placed between two spinous processes and the Dacron ligament wraps around spinous processes. See p. S165. Accordingly, Senegas does not disclose a ligament that traverses a facet joint.
WIPO PCT Published Patent Application No. WO 00/53126 ("Ogun") discloses a memory metal implant for fixing an articulated joint, including a facet joint.
The Dynesys system is generally used as a replacement for the natural posterior longitudinal ligament. The system includes a cable housed inside a plastic sheath, and is attached to superior and inferior pedicles. The ligament of the Dynesys system does not traverse a facet joint.
US Published Patent Application No. 2003/0004572 ("Goble") discloses a prosthesis comprising an intervertebral disc prosthesis and a fact joint prosthesis. Goble does not disclose a facet joint ligament. FIG. 12 of Goble discloses a facet joint replacement system wherein each of the superior and inferior components are fixed respectively to the upper and lower pedicles. However, the superior component of the Goble system has no adjustability (i.e., the screw-articulation surface distance is fixed). Second, the articulation surface appears to be set higher than the pedicle screw securing the inferior component. In such a case, long term bearing may cause twirling of the inferior component about the lower pedicle screw axis.
As demonstrated above, it is the goal of an artificial facet joint to recreate the physiological biomechanics of a normal spine to the extent possible. These physiological mechanics include a non-linear relationship between force and displacement. During the initial motion of the facet joint, termed the "neutral zone", the stiffness of the joint is low. As motion progresses, and the joint enters the "elastic zone", the stiffness of the joint increases. The ligamentous and fibrous structures around the spine create this behaviour, as more fibers become taught as motion increases.
It has been found that the non-linear force-displacement behaviour found in a physiologic facet joint is difficult to reproduce using artifical ligaments, as large strain (5 -30%) is required in the face of large forces. In general, artificial ligaments do nor possess both high ultimate strength and high ultimate strain. Therefore, most artificial ligaments have difficulty replicating large natural movements.
Accordingly, there is a need to provide the natural non-linear force displacement relationship of a facet joint without the need of ligamentous prosthetic components.

Artificial facet joint device having a compression spring


An irrigating technique that can be used to increase the flow of fluid through the trabecular meshwork. Pulses of relatively high pressure irrigating are directed at the trabecular meshwork. These pulses can be focused, thereby perforating the trabecular meshwork, or applied over a larger area so as to stimulate the trabecular meshwork for improved fluid transport. In addition, the pulses of the irrigating balance salt solution can be used to clean away material, such as iris pigment, that may be blocking or clogging the trabecular meshwork. Such a technique may be practiced using the herein disclosed tip with commercially available surgical handpieces.

This invention relates generally to the field of eye surgery and more particularly to a method for glaucoma surgery.
Glaucoma affects approximately 2% of the population under 65 years of age and 11% over 65, and it is exceedingly difficult to diagnose and define. The eye is a hollow structure that contains a clear fluid called "aqueous humor." Aqueous humor is formed in the posterior chamber of the eye by the ciliary body at a rate of about 2.5 microliters per minute. The fluid, which is made at a fairly constant rate, then passes around the lens, through the pupillary opening in the iris and into the anterior chamber of the eye. Once in the anterior chamber, the fluid drains out of the eye through three different routes. Fluid can be absorbed by the iris, which normally accounts for less than 1% of drainage. In the "uveoscleral" route, fluid percolates between muscle fibers of the ciliary body. This route accounts for less than ten percent of the aqueous outflow in humans. The primary pathway for aqueous outflow in humans is through the "canalicular" route that involves the trabecular meshwork and Schlemm's canal.
The trabecular meshwork and Schlemm's canal are located at the junction between the cornea and the sclera. This is anterior to the insertion of the iris into the scleral. The junction or corner of the iris insertion and the cornea is called "the angle." The trabecular meshwork is a wedge-shaped structure that runs around the circumference of the eye. It is composed of collagen beams arranged in a three-dimensional sieve-like structure. The beams are lined with a monolayer of endothelial cells called trabecular cells. The spaces between the collagen beams are filled with an extracellular substance that is produced by the trabecular cells. These cells also produce enzymes that degrade the extracellular material. Schlemm's canal is adjacent to the trabecular meshwork. The outer wall of the trabecular meshwork coincides with the inner wall of Schlemm's canal. Schlemm's canal is a tube-like structure that runs around the circumference of the cornea. In human adults, Schlemm's Canal is believed to be divided by septa into a series of autonomous, dead-end canals.
The aqueous fluid travels through the spaces between the trabecular beams, across the inner wall of Schlemm's canal into the canal, through a series of collecting channels that drain from Schlemm's canal and into the episcleral venous system. In a normal situation, aqueous production is equal to aqueous outflow and intraocular pressure remains fairly constant with a mean of approximately 16 mm Hg. In glaucoma, the resistance through the canalicular outflow system is abnormally high, creating a higher intraocular pressure.
In primary open angle glaucoma, the most common form of glaucoma in the United States, the abnormal resistance is believed to be along the outer aspect of trabecular meshwork and the inner wall of Schlemm's canal. In normals, this accounts for approximately 50% of resistance. In glaucoma patients, this accounts for all of the additional resistance. It is believed that an abnormal metabolism of the trabecular cells might lead to an excessive build up of extracellular materials or a build up of abnormally "stiff" materials in this area. Histopathology of glaucoma eyes also demonstrates a collapse of Schlemm's canal. Primary open angle glaucoma accounts for approximately eighty-five percent of all glaucoma in the Americas and Europe. Other forms of glaucoma (such as angle closure glaucoma and secondary glaucomas) also involve decreased outflow through the canalicular pathway but the increased resistance is from other causes such as mechanical blockage, inflammatory debris, cellular blockage, etc.
With the increased resistance, the aqueous fluid builds up because it cannot exit fast enough. As the fluid accumulates, the intraocular pressure (IOP) within the eye increases. The increased IOP compresses the axons in the optic nerve and also may compromise the vascular supply to the optic nerve. The optic nerve carries vision from the eye to the brain. Some optic nerves seem more susceptible to a specific level of IOP than other eyes. While research is investigating ways to protect the nerve from an elevated pressure, the only therapeutic approach currently available in glaucoma that is proven either to prevent or retard the progression of nerve loss and resultant visual disability leading to blindness is to reduce the intraocular pressure.
The clinical treatment of glaucoma is commonly approached in a step-wise fashion. Medication often is the first treatment option. Usually administered either topically, these medications work to either reduce aqueous production or they act to increase outflow. Currently available medications have many serious systemic side effects including: congestive heart failure, respiratory distress, systemic hypotension, depression, sedation, renal stones, aplastic anemia, sexual dysfunction and death. As an asymptomatic disease, compliance with medical therapy is a major problem, with estimates that over half of glaucoma patients do not follow their correct dosing schedules. This lack of adherence to prescribed medical therapy may account for the fact that more than 20% of patients go blind bilaterally within a 20 year period.
When medication fails to adequately reduce the pressure, laser trabeculoplasty often is performed. In laser trabeculoplasty, energy from a laser is applied to a number of noncontiguous spots in the trabecular meshwork. It is believed that the laser energy stimulates the metabolism of the trabecular cells in some way, and changes the extracellular material in the trabecular meshwork. In approximately eighty percent of patients, aqueous outflow is enhanced and IOP decreases. However, the effect often is either not sufficient or not long lasting and at least fifty percent of patients develop an elevated IOP within five years. In many cases, the laser surgery is not usually repeatable. In addition, laser trabeculoplasty is not an effective treatment for primary open angle glaucoma in patients less than fifty years of age, nor is it effective for angle closure glaucoma and many secondary glaucomas.
If laser trabeculoplasty does not adequately reduce the IOP, then filtering surgery is performed. With filtering surgery, a hole is made in the sclera near the angle. This hole allows the aqueous fluid to leave the eye through an alternate route. The most commonly performed filtering procedure is a trabeculectomy. In a trabeculectomy, a conjunctiva incision is made, the conjunctiva being the transparent tissue that covers the sclera. The conjunctiva is moved aside, exposing the sclera at the limbus. A partial thickness scleral flap is made and dissected half-thickness into the cornea. The anterior chamber is entered beneath the scleral flap and a section of deep sclera and/or trabecular meshwork is excised. The scleral flap is loosely sewn back into place. The conjunctival incision is tightly closed. Post-operatively, the aqueous fluid passes through the hole, beneath the scleral flap which offers some resistance and collects in an elevated space beneath the conjunctiva called a bleb. The fluid then is either absorbed through blood vessels in the conjunctiva or traverses across the conjunctiva into the tear film.
Trabeculectomy and filtration surgery are both associated with many problems. Fibroblasts that are present in the episclera proliferate and migrate, and can scar down the scleral flap. Failure from scarring may occur, particularly in children, young adults, those with active inflammation or eyes with prior intraocular surgery. Of eyes that have an initially successful trabeculectomy, up to eighty percent will fail from scarring within three to five years after surgery. To minimize this scarring, surgeons now are applying antifibrotic agents such as mitomycin C (MMC) and 5-fluorouracil (5-FU) to the scleral flap at the time of surgery or giving injections of 5-FU daily for up to 14 days postoperatively. The use of these agents has increased the success rate of trabeculectomy but also has increased the prevalence of multiple complications which are sight-threatening and potentially blinding. The most serious complication is cataract which can occur in up to 20% of eyes. Bleb infections can occur in all eyes for the rest of the patient's life following surgery. Hypotony is a problem that develops when aqueous flows exits the eye faster than aqueous humor is made. The eye pressure drops too low (usually less than 6.0 mmHg); the structure of the eye collapses and vision decreases as the choroids and macula become swollen and folded.
Trabeculectomy also creates a pathway for aqueous fluid to escape to the surface of the eye. At the same time, it creates a pathway for bacteria that normally live on the surface of the eye and eyelids to get into the eye. If this happens, an internal eye infection can occur called endophthalmitis. Endophthalmitis often leads to permanent and profound visual loss. Endophthalmitis can occur anytime after trabeculectomy. The risk increases with the thin blebs that develop after MMC and 5-FU and is cumulative at about 0.4% per year. Another factor that contributes to infection is the placement of a bleb. Eyes that have trabeculectomy performed inferiorly have about eight times the risk of eye infection than eyes that have a superior bleb. Therefore, initial trabeculectomy is performed superiorly under the eyelid, in either the nasal or temporal quadrant.
In addition to scarring, hypotony and infection, there are other complications of trabeculectomy. The bleb can tear and lead to profound hypotony. The bleb can be irritating and can disrupt the normal tear film, leading to blurred vision. Approximately 67% of patients experience continuous persistent discomfort which can last for years. Patients with blebs generally cannot wear contact lenses. All of the complications from trabeculectomy stem from the fact that fluid is being diverted from inside the eye to the external surface of the eye.
Therefore, a need continues to exist for a surgical method for increasing the outflow of aqueous from the eye to help reduce IOP in glaucoma patients.


A nail polish removal system (310) broadly comprises a hollow applicator handle (316) having an applicator end (318) with an absorbent material (320) attached thereto. The handle (316) has an opening (326) at the applicator end (318). The handle (316) contains a breakable capsule (328). Adjacent to the breakable capsule (328) and opposite to the opening (326), the handle (316) has a seal (330). The breakable capsule (328) is filled with up to one ounce of the nail polish removal solution. The breakable capsule (328) is broken releasing the nail polish removal solution. The released nail polish removal solution saturates the absorbent material (320) by flowing through the opening (326). The nail polish removal solution is prevented from escaping the handle (316), other than through the opening (326), by the seal (330). The nail polish removal system (310) is used and discarded.

1. Field of the Invention
The present invention relates to methods and systems for removing cosmetic nail polish from fingernails and toenails. More particularly, the invention relates to a nail polish removal system and method including a conveniently packaged disposable single-use nail polish removal tool comprising an applicator handle and an absorbent material pre-saturated or saturateable with a nail polish removal solution, wherein a plurality of the disposable single-use nail polish removal tools may be provided in a resealable package.
2. Description of the Prior Art
It is often desirable to quickly remove cosmetic nail polish from fingernails and toenails, such as, for example, prior to applying a new cosmetic finish. Currently there exist two general categories of removal means, bottle-based systems and dipping jar-based systems. Bottle-based nail polish removal systems typically include a multiple-use bottle containing a relatively large quantity of a nail polish removal solution sufficient for numerous applications. The bottle opens at one end and must be properly secured with a cap to prevent the solution from spilling. In use, the solution must be controllably poured from the bottle onto a suitable material, such as a cotton ball or a cloth rag. Once the material is saturated with the nail polish removal solution, the user uses his or her fingers to apply the material to a polished nail in order to remove the nail polish therefrom, thereby undesirably simultaneously exposing other nails to the solution. Bottle-based systems are relatively cumbersome and inconvenient to carry in a pocket or purse; are prone to potential leakage which may damage property or expose users to hazardous or flammable fumes or solutions; and are messy to apply.
The problems identified above are greatly compounded for a nail are professional who performs the process of removing nail polish many times each day and is therefore exposed to the hazardous nail polish removal solution on a substantially continuous basis. Although wearing gloves may reduce such exposure, manual dexterity is undesirably inhibited.
An improvement on the bottle-based method involves dipping a conventional swab into the bottle, thereby saturating an absorbent end portion of the swab with the nail polish removal solution. Unfortunately, commonly available swabs are typically not as long as commonly available bottles are deep. Where the swab is unable to reach the bottom of the bottle, the bottle must either be discarded, thereby wasting a portion of the solution, or the solution must be controllably poured from the bottle onto the swab, thereby risking spillage which may damage property or expose users to hazardous or flammable fumes or solutions.
Dipping jar-based systems typically include a multiple-use dipping jar containing a sponge saturated with a relatively large quantity of the nail polish removal solution sufficient for numerous applications. In use, the nail and its associated finger are both inserted into the dipping jar and the polished nail is rubbed against the sponge until all nail polish is removed. Thus, the finger is undesirably soaked in a potentially hazardous and unhealthy combination of the nail polish removal solution and dissolved nail polish.
The dipping jar-based system requires a relatively high level of manual dexterity, which can be a concern for some people, particularly when removing toenail polish. For example, the user is required to either lower the dipping jar to the level of the toe or elevate the toe to the level of the dipping jar. Both methods require that the jar be securely held, in some manner, to prevent spillage, while the toenail is rubbed against the sponge. Lowering the dipping jar to the level of the user""s toe necessitates that the user either inconveniently bend over, in order to hold the jar, or place the jar into a holding apparatus. Raising the toe to the dipping jar is equally cumbersome and may not be possible for some users, particularly the elderly or disabled.
Accordingly, there is a need for an improved nail polish removal system that overcomes the limitations of the prior art.
The nail polish removal system of the present invention overcomes the problems and disadvantages identified above and provides a distinct advance in the art of nail polish removal systems and methods. Specifically, the present invention provides a disposable single-use nail polish removal tool comprising an applicator handle and an absorbent material pre-saturated or saturateable with a nail polish removal solution and packaged in such a manner as to allow use of the tool without spilling or inadvertently contacting the polish removal solution.
In a preferred embodiment, the nail polish removal system comprises a disposable single-use nail polish removal tool and a non-resealable package. The single-use nail polish removal tool includes an applicator handle having an applicator end and an absorbent material attached thereto. The absorbent material is saturated with the nail polish removal solution. At least the absorbent material is sealed in the non-resealable package to contain and retain the polish removal solution. The tool is conveniently stored and transported in quantities of one or more.
In use, a user removes and discards the non-resealable package. The user then rubs the absorbent material, saturated with the nail polish removal solution, against the nail polish to be removed. Once the nail polish has been removed, the user discards the single-use nail polish removal tool. Thus, cumbersome bottles are eliminated; spilled polish removal solution is avoided; and the user avoids undesirable contact with the potentially hazardous polish removal solution.
In another preferred embodiment, the applicator handle is hollow and releasably contains the nail polish removal solution by means of either a breakable capsule or a breakable seal. Thus, the packaging, in this embodiment, is not relied upon to contain or retain the polish removal solution. The hollow applicator handle also includes a substantially nonbreakable seal opposite the applicator end.
In use, a user breaks the breakable capsule or the breakable seal to release the nail polish removal solution from the handle""s applicator end. Pieces of the broken capsule or broken seal are prevented from escaping the handle by the absorbent material. Once released, the polish removal solution saturates the absorbent material. The user then removes the nail polish as described above and thereafter discards the nail polish removal system.
These and other important features of the present invention are more fully described in the section titled DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT, below.


A process is provided for preparing W/O emulsions having crosslinked water-swollen polymers dispersed therein, by aftertreatment with a redox initiator system to reduce the residual monomer content.

The invention relates to a process for preparing W/O emulsions comprising crosslinked water-swellable addition polymers dispersed therein, by aftertreatment with a specific redox initiator system to reduce the amount of residual monomers.
Crosslinked acrylic acid polymers are used as thickeners in textile printing and also in cosmetic and pharmaceutical formulations. These polymers can be prepared by free-radical polymerization or copolymerization in W/O emulsions. On incorporation into aqueous formulations, emulsions of this kind invert and cause thickening of the formulations.
EP 383 057 describes a crosslinked copolymer of acrylic acid and nitrile comonomers prepared in a water/paraffin emulsion. The emulsions described are used in textile printing.
DE 35 22 419 describes the inverted emulsion polymerization of acrylamide with acrylic acid in one process step.
A process for preparing water-soluble or water-swellable polymers in a W/O emulsion is claimed by EP 126 528, and comprises polymerizing the water-soluble monomers in the presence of emulsifiers with the addition of a specific dispersing system comprising alkanols.
Crosslinked acrylic acid polymers in a W/O emulsion are also described in EP 297 184 for use as water absorbents.
Following their preparation by free-radical polymerization or copolymerization, W/O emulsion polymers include an unwanted fraction of unpolymerized free monomers (residual monomers) in addition to a polymer solids fraction of from 15 to 50% by weight. The reason for this is the incomplete polymerization of the monomers employed in the free-radical main polymerization, which is normally conducted up to a monomer conversion of 95% and, preferably, from 98 to 99.8% by weight. For reasons primarily of toxicology, the market demands polymers combining a low residual monomer content with unimpaired processing and performance properties.
Methods of lowering residual monomers in aqueous polymer dispersions are well known. In addition to nonchemical methods, such as stripping with inert gas or steam, a wide variety of chemical methods is available, as described, for example, in EP-B 028 348, EP-B 563 726, EP-A 764 699, and US-A 4 529 753, to lower residual monomer contents in aqueous polymer dispersions.
In accordance with WO 95/33775, aqueous polymer dispersions can be aftertreated using redox systems whose reducing agent comprises an adduct of hydrogen sulfite anion and a ketone of 3 to 8 carbon atoms, and/or the conjugate acid of said adduct. The aftertreatment is performed in the presence of metal compounds which are soluble in the aqueous medium.
For the reduction of residual monomer contents, EP-A 767 180 recommends a redox initiator system comprising organic hydroperoxides which are soluble only very sparingly if at all in water, and, inter alia, adducts of bisulfites with aldehydes having a carbon chain of 4 to 6 carbon atoms.
The patent application DE 19840586 describes the use of oxidizing agents in combination with a redox system comprising an aldehyde for depleting residual monomers in aqueous polymer dispersions.
In accordance with DE 19741187, a system comprising an oxidizing agent and an organic xcex1-hydroxy carboxylic acid is used for chemical removal of residual monomers.
All processes relate to the treatment of aqueous polymer dispersions. No process has to date been described for lowering residual monomers in W/O emulsions of W/O emulsion polymers comprising acrylic acid. Within these W/O emulsions, the polymers are located within isolated water droplets emulsified in the oil phase. This prevents the formation, as observable in a system with a continuous aqueous phase, of a gel phase which is difficult to process.
It is an object of the present invention to provide a novel, effective process for reducing the amount of residual monomers in W/O emulsions comprising crosslinked water-swellable polymers. In such a process the performance properties of the W/O emulsion, especially the thickener effect, should remain unaffected. Furthermore, the reduction in the amount of residual monomers should be easy to utilize industrially.
We have found that the subject is achieved and that the amount of residual monomers in W/O emulsions comprising crosslinked polymers swollen in water can be effectively reduced if the W/O emulsion comprising the residualmonomers is aftertreated with the addition of a redox initiator system.
A preferred process comprises conducting the aftertreatment with a redox initiator system comprising essentially
a) from 0.001 to 5% by weight, based on the total monomer amount used to prepare the polymer,
a1) of an oxidizing agent:
R1OOH,
xe2x80x83where R1 is hydrogen, a C1- to C8-alkyl or C6- to C12 aryl group, and/or
a2) of a compound which in aqueous medium releases hydrogen peroxide, and
b) from 0.005 to 5% by weight, based on the total monomer amount used to prepare the polymer,
b1) of an xcex1-hydroxy carbonyl compound:
xe2x80x83where, independently at each occurrence,
R2 is hydrogen or a C1-C12-alkyl group which if desired contains functional groups and/or can be olefinically unsaturated,
R3 is hydrogen, OH, a C1-C12-alkyl group which if desired contains functional groups and/or can be olefinically unsaturated,
and R2 and R3 can form a ring structure which can include a heteroatom and/or functional groups and/or can be olefinically unsaturated, and/or
b2) a compound which in aqueous medium releases such an xcex1-hydroxy carbonyl compound, and
c) catalytic amounts of a polyvalent metal ion which is able to exist in a plurality of valence states.
The oxidizing agent of the redox initiator system should be in a position to form free radicals. Oxidizing agents employed in the redox system are preferably hydrogen peroxide but also include inorganic compounds such as potassium peroxide, sodium peroxide, sodium perborate, and other precursors which in aqueous medium form hydrogen peroxide. It is also possible, for example, to employ ammonium, potassium or sodium persulfate, peroxodisulfuric acid and its salts, ammonium, potassium or sodium perphosphate or diperphosphate, potassium permanganate, and other salts of per acids. Also suitable in principle are organic hydroperoxides, such as tert-butyl hydroperoxide and cumene hydroperoxide. It is, however, also possible to employ mixtures of different oxidizing agents.
The amount of added oxidizing agent is usually within the range from 0.001 to 5, preferably from 0.002 to 3, with particular preference from 0.003 to 2, with very particular preference from 0.01 to 1 and, most preferably, from 0.02 to 0.8% by weight, based on the total monomer amount.
The reducing agent used in the redox initiator system can be any of the agents which are usually susceptible to use.
Particularly suitable reducing agents are aliphatic xcex1-hydroxy carboxylic acids and also precursors which in aqueous solution release these xcex1-hydroxy carboxylic acids. Examples that may be mentioned of xcex1-hydroxy carboxylic acids are aliphatic hydroxy carboxylic acids of preferably 2 to 8 carbon atoms, such as glycolic acid (hydroxyacetic acid), glycoxylic acid hydrate (dihydroxyacetic acid), lactic acid (2-hydroxypropionic acid), glyceric acid (2,3-dihydroxypropionic acid), malic acid (2-hydroxysuccinic acid) or tartronic acid (2-hydroxymalonic acid). The use of tartaric acid is preferred.
Also suitable as reducing agents, however, are aliphatic xcex1-hydroxy carbonyl compounds, such as aliphatic xcex1-hydroxy aldehydes and/or aliphatic xcex1-hydroxy ketones, their isomers, and/or functional group substituted and/or olefinically unsaturated compounds and mixtures thereof, and also precursors which in aqueous solution release these xcex1-hydroxy carbonyl compounds. Examples that may be mentioned of xcex1-hydroxy carbonyl compounds are glycol aldehyde and/or its dimer, 2,5-dihydroxy-1,4-dioxane, phenylglycol aldehyde, 2-hydroxy-3-phenylpropionaldehyde, glyceraldehyde and its higher homologous compounds, such as aldotetroses, aldopentoses and aldohexoses, and also xcex1-hydroxyacetone, xcex1,xcex1xe2x80x2-dihydroxyacetone, 1-hydroxy-2-butanone, 1-hydroxy-2-pentanone, 1-hydroxy-2-hexanone, 2-hydroxy-2-methyl-3-butanone (acetoin), 4-hydroxyhept-2-en-5-one, 2-hydroxy-3-pentanone, 3-hydroxy-2-pentanone, 3-hydroxy-4-heptanone, 4-hydroxy-3-heptanone, 4-hydroxy-2,2-dimethyl-3-pentanone, 3-hydroxy-2,2-dimethyl-4-pentanone, 2-hydroxy-1-phenyl-1-propanone, 1-hydroxy-1-phenyl-2-propanone, 1-hydroxy-1-phenyl-2-butanone, 2-hydroxy-1-phenyl-1-butanone, 2-hydroxy-1,2-diphenylethanone (benzoin), 2-hydroxy-1-phenyl-1,4-pentanedione, 1-hydroxy-1-phenyl-2,4-pentanedione, and cyclic xcex1-hydroxy ketones, such as 2-hydroxycyclohexanone and 2-hydroxycyclopentanone. Preference is given to the use of xcex1-hydroxyacetone, xcex1,xcex1xe2x80x2-dihydroxyacetone, 1-hydroxy-2-butanone, 1-hydroxy-2-pentanone, glutaroin, adipoin and/or 2-hydroxy-2-methyl-3-butanone (acetoin), but particular preference to xcex1-hydroxyacetone and/or xcex1,xcex1xe2x80x2-dihydroxyacetone.
The amount of added reducing agent is customarily within the range from 0.005 to 5, preferably from 0.01 to 3, with particular preference from 0.03 to 2, with very particular preference from 0.05 to 1 and, most preferably, from 0.02 to 0.8% by weight, based on the total monomer amount. Higher amounts of reducing agent, although possible, are not generally sensible from the economic standpoint.
The metal compounds advantageous for the aftertreatment are, customarily, completely soluble in the aqueous medium of the W/O emulsion and their metallic component, moreover, is capable of existing in a plurality of valence states. The dissolved metal ions have a catalytic effect and assist the electron transfer reactions between the actually active oxidizing and reducing agents. Suitable dissolved metal ions are principally iron, copper, manganese, vanadium, nickel, cobalt, titanium, cerium or chromium ions. It is of course also possible to use mixtures of different, mutually compatible metal atoms, such as the system Fe2/3+/VSO431. Preferably, iron ions are used.
The dissolved metal ions are used in catalytic amounts, usually in the range from 1 to 1000, preferably from 5 to 500 and, with particular preference, from 10 to 100 ppm, based on the total monomer mass.
For the aftertreatment of the W/O emulsion polymer, which is heated at from about 30 to 130, preferably from 40 to 90 and, with particular preference, from 40 to 80xc2x0 C., the components of the initiator system used in accordance with the invention are judiciously metered in gradually with stirring, preferably under atmospheric pressure or, alternatively, under a pressure of greater than or less than 1 bar (absolute), metered addition taking place simultaneously or in succession, in the latter case preferably with addition of the oxidizing agent first. A particularly favorable procedure is the simultaneous metered addition of oxidizing agent and reducing agent by way of two separate feed streams. In this case the initiator components, for example, can be added from above, from below, or through the side of the reactor. Preferably, however, the initiator system is metered in from below. Since the optimum duration of initiator metering is dependent on the monomer composition, on the size of the reaction mixture, and on the reactor geometry, it is judicious to determine said duration in preliminary experiments. Depending on the task at hand, the duration of addition of initiator can extend from a few seconds to several hours. It is particularly favorable for the metal compound, which is employed in catalytic amounts, to be added to the W/O emulsion polymer prior to the addition of the oxidizing and reducing agent. In order to ensure sufficient concentrations of metal ions during the aftertreatment, it is therefore particularly advantageous to add complexing agents, such as, for example, ethylene diamine tetraacetic acid, nitriloacetic acid and diethylenetriamine pentaacetic acid, and/or their respective sodium salts, and/or to use stable metal ion complexes, such as, for example, iron(III)/sodium ethylenediaminetetraacetate.
The pH of the emulsion during the aftertreatment is preferably xe2x89xa69.
The invention also relates to the W/O emulsions prepared by the process of the invention, especially those W/O emulsions whose residual monomer content is less than 300 ppm, preferably less than 200 ppm, based on the total W/O emulsion.
The W/O emulsion polymers preferably used in the present invention consist of
a) from 35 to 100% by weight of ionic monomers,
b) from 0 to 65% by weight of nonionic monomers, and
c) from 0.3 to 1 mol %, based on a) and b), of at least one at least bifunctional monomer.
The reduction process of the invention is particularly suitable for reducing the amount of residual monomers in polymers comprising acrylic acid and prepared by free-radical polymerization in W/O emulsion.
The preferred end use of the W/O emulsions is in cosmetic formulations for the skin or hair.
The W/O polymer emulsion described in the present invention is prepared by inverse emulsion polymerization. In the first step, an aqueous monomer solution is emulsified in an oil phase with W/O emulsifiers typical of these systems. The polymerization is started by free-radical initiators. Since the polymers are intended to function as thickeners, they must be in chemically crosslinked form. The crosslinker is preferably added to the monomer solution.
The monomers used are preferably unsaturated C3-C5-carboxylic acids, such as, for example, acrylic acid, methacrylic acid, maleic acid (anhydride), fumaric acid (anhydride), itaconic acid or mixtures thereof. They can be homopolymerized or copolymerized with nonionic monomers. Suitable such monomers are unsaturated compounds which can be dissolved in water in addition to the ionic monomers; examples are acrylamide, methacrylamide, vinylpyrrolidone, vinylimidazole, vinylcaprolactam, hydroxyalkyl esters of carboxylic acids such as, for example, hydroxyethylacrylic acid. The fraction of ionic monomers in the overall monomer mixture is from 35 to 100%, preferably from 50 to 100%. Particular preference is given to an acrylic acid fraction of  greater than 90%.
The ionic monomers are neutralized to the extent of from 5 to 80%, preferably from 10 to 50%. Neutralization can in principle be carried out using all bases that can be attuned to cosmetic requirements. It is preferred to use, for example, triethanolamine, NaOH or tetrahydroxypropylethylenediamine. Mixtures of bases are also suitable.
The concentration of the monomers in the aqueous solution prior to the polymerization is from 10 to 60%.
The polymer is crosslinked by copolymerization of the monomers with at least doubly unsaturated water- or oil-soluble compounds. Suitable such compounds are methylenebisacrylamide, divinylpyrrolidone, allyl (meth)acrylate, triallylamine, ethyleneglycol diacrylates (up to 50 EO), (meth)acrylic esters with dihydric or higher polyhydric alcohols, such as trimethylolpropane triacrylate or pentaerythritol tetraacrylate; in this case the alcohol functions can carry up to 50 EO groups and can each have different degrees of ethoxylation. These crosslinkers are present in proportions of from 0.3 to 1 mol % individually or as a mixture. Water-soluble crosslinkers are preferred.
Oil components which can be used are all oils liquid at room temperature, such as, for example, fatty alcohols such as oleyl alcohol, fatty acid esters, natural oils such as sunflower oil, olive oil, avocado oil or coconut oil, wax esters such as jojoba oil, lanolin derivatives, silicone oils and aliphatic hydrocarbons having 6 or more carbon atoms, such as liquid paraffins or cyclohexane, for example.
The oil phase consists preferably of liquid paraffins or of one or more fatty acid esters. These latter components have a beneficial effect on the cosmetic formulation (appearance, sensation on the skin). Examples of such components are fatty acid isopropyl esters such as isopropyl palmitate, isopropyl myristate or polyglycerides of fatty acids, especially fatty acid mixtures containing at least 50% caprylic and/or capric acid (Miglyol 812 from Hxc3xcls). Preference is given to polyglycerol fatty acid esters based on a polyglycerol mixture containing essentially mono-, di-, tri- and tetraglycerol, especially diglycerol and triglycerol. It is of course also possible to employ mixtures of said oil components.
The fraction of the oil phase as a proportion of the total emulsion is from 15 to 70%, preferably from 20 to 35%.
In order to disperse the aqueous phase in the organic phase use is made of W/O emulsifiers known for the purpose. The HLB of the emulsifiers used is between 4 and 8 [HLB=hydrophilic/lipophilic balance, cf. W. C. Giffin, J. Soc. Cosmet. Chem. 1, 311 (1950)]. Examples of such emulsifiers are sorbitan monooleate, sorbitan monostearate, glyceryl monostearate, block copolymers of hydroxy fatty acids-polyesters and polyoxyethylene. They can be used alone or in combination in total concentrations of from 0.25 to 10%, preferably from 0.5 to 5% with respect to the total emulsions.
In addition, emulsifiers having an HLB of more than 8 can added to the emulsion in concentrations of from 0.25 to 7% with respect to the total emulsion. Examples of such emulsifiers are ethoxylated C6-C12 nonylphenols or C12-C18 fatty alcohols; the degree of ethoxylation is from 5 to 20 mol %.
The emulsification of the aqueous phase in the oil phase does not require any special equipment; instead, the aqueous monomer phase can be emulsified in a standard polymerization vessel by stirring using, for example, an anchor stirrer. The rotary speed is between 30 and 400 rpm depending on the geometry of the vessel.
Initiators which can be employed are water- and/or oil-soluble free-radical initiators such as, for example, alkali metal or ammonium peroxodisulfates, hydrogen peroxide, organic peroxides, with or without redox partners, and azo initiators. It is also possible to use initiators having different decomposition temperatures in unison or in succession. Based on the monomer mixture, the amount of initiator used is from 0.05 to 0.5%, preferably from 0.05 to 0.3%.
The temperature at which polymerization takes place lies between 20 and 150xc2x0 C.; it can be kept constant or altered in a discontinuous manner (for example, in order to increase the degree of conversion by an increase in temperature). Following the polymerization, water-in-oil emulsions are obtained which have a solids content of from 10 to 40%, preferably from 15 to 35%. In order to raise the solids content, the emulsions can be partly or fully dewatered by distillation.
The W/O emulsions of crosslinked polymers according to the invention are used as thickeners preferably in cosmetic or pharmaceutical applications. The polymers are not used in isolation but instead directly in the form of the W/O emulsion. Typical use concentrations are from 0.1 to 0.8%, preferably from 0.2 to 0.5% of active substance (polymer). The thickening action of the W/O emulsion ensues directly following the mixing of the W/O emulsion with the cosmetic O/W emulsion; the addition of an inverter is unnecessary for achieving the optimum effect. Even purely aqueous systems can be thickened. The results is a gel cream.
The aftertreatment of the W/O emulsion polymer to reduce the residual monomer amount, in accordance with the invention, takes place in particular after at least 95 and preferably at least 98, with particular preference up to at least 99.9, % by weight of the total monomer amount has undergone reaction in the free-radical solution polymerization. The conditions during the main polymerization and during the aftertreatment are generally different. In the case of the aftertreatment, the concentration of initiating system is markedly increased relative to the main polymerization, in general, for the purpose of residual monomer depletion. Further deployment of the initiating system of the main polymerization leads to a drastic impairment of the thickener effect. Furthermore, completion, in the sense of the space-time conversion, with the initiating system from the main polymerization is ineffective and uneconomic. For the preparation of W/O emulsion polymers, therefore, different initiator systems are usually required for the main polymerization and for the aftertreatment.
As with processes of free-radical addition polymerization in general, the process of the invention also generally takes place under an inert gas (e.g. N2, Ar).
It is of course possible to pass on the aftertreated W/O emulsion polymers for stripping with inert gas and/or steam.
The free-radical redox initiator systems to be used in accordance with the invention enable an effective reduction in residual monomer amount to be obtained within a relatively short time. A further point of significance is that the reducing agent claimed in accordance with the invention is, advantageously, unable to reduce the microbicides which are generally added as preservatives to W/O emulsion polymers, and so the application thereof in excess does not reduce the quality of the W/O emulsion polymer in this respect.